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Apomorphine (APO), a potent treatment for Parkinson's disease, is only administered parenterally either as intermittent injections or as an infusion. This is due to extensive hepatic “first pass” metabolism. Prolonged delivery through buccal mucosa may be potential substitute for parenteral infusions. To investigate this concept of buccal mucosal delivery, permeability ex vivo studies were performed through excised porcine buccal mucosa by utilizing Ussing diffusion chamber. Permeability rates were assessed for APO from simulated saliva medium at pH 7.4 as well as with utilization of different permeability modifying methods. Lowering the pH to 5.9 decreased permeability rate six-fold, while addition of ethanol : propylene glycol solution elevated it four-fold. Addition of nano-scale lipospheres to the donor compartment delayed the accumulation of APO at the receiver side, prolongating the lag-time from one to approx. three hours. These findings were strengthened by results obtained with co-administration of permeability markers (standards) atenolol and metoprolol. Simulation of the obtained permeability rates to in vivo setup in human showed therapeutically relevant plasma levels when using the outcomes of the current study. These findings verify the novel concept of APO prolonged release buccal administration as a noninvasive substitute for parenteral infusions in treating Parkinson's disease.

Lipid-based drug delivery systems have been vastly investigated as a pharmaceutical method to enhance oral absorption of lipophilic drugs. However, these vehicles not only affect drug bioavailability but may also have an impact on gastric emptying, drug disposition, lymphatic absorption and be affected by lipid digestion mechanisms. The work presented here compared the pharmacokinetic (PK) behavior of the non-intoxicating cannabinoid cannabidiol (CBD) in sesame oil

Myeloid differentiation primary response 88 (MyD88) is an intracellular adaptor protein central to the signaling of multiple receptors involved in inflammation. Since innate immune inflammation promotes autoimmunity, MyD88 is an attractive target in autoimmune disease. We previously developed c(MyD 4-4), a novel cyclic peptide competitive inhibitor of MyD88 dimerization that is metabolically stable. Parenteral administration of c(MyD 4-4) reduces disease severity in a mouse model of the human autoimmune disease multiple sclerosis. We now show that N-terminal myristoylation of c(MyD 4-4) enhances the competitive inhibition of MyD88 dimerization in living cells, leading to improved inhibition of the Toll-like receptor and IL-1 receptor signaling. Importantly, myristoylation converts c(MyD 4-4) to an orally bioavailable inhibitor of MyD88. Oral administration of c(MyD 4-4) significantly lowered the inflammatory cytokines secreted by peripheral autoimmune T cells in mice immunized with myelin antigens and ameliorated disease severity in the mouse model of multiple sclerosis. Taken together, we show the conversion of a protein active region to a metabolically stable, selective cyclic peptide that is orally bioavailable.

Contrary to human, porcine mucosa of the inner side of the lip is parakeratinized. Thus, although desirable due to its large surface area, it does not closely resemble human buccal mucosa to be considered a suitable model for systemic drug delivery research. Nevertheless, it can be utilized for comparative screening of topical or systemic delivery of bioactive agents, mostly lipophilic such as cannabinoids.

Delivery of drugs through oral mucosa enables bypass of the gastrointestinal tract and “first pass“ metabolism in the liver and the gut. Thus, a higher and less variable bioavailability can be obtained. Mechanisms of this administration route for cannabidiol were investigated in the current research in pigs. Results show that cannabidiol has substantially low permeability rate over 8 h through oral mucosa and accumulates significantly within it. Furthermore, following the removal of the delivery device, residual prolongation of release from the oral mucosa into systemic blood circulation continues for several hours. This method of delivery enabled acquisition of clinically relevant plasma levels of cannabidiol. The absorption profile indicates that cannabidiol, as well as other lipophilic molecules, should be delivered through oral mucosa for systemic absorption from a device that conceals the drug and prevents its washout by the saliva flow and subsequent ingestion into gastrointestinal tract.

Insulin-dependent type-1 diabetes (T1D) is driven by autoimmune β-cell failure, whereas systemic resistance to insulin is considered the hallmark of insulin-independent type-2 diabetes (T2D). In contrast to this canonical dichotomy, insulin resistance appears to precede the overt diabetic stage of T1D and predict its progression, implying that insulin sensitizers may change the course of T1D. However, previous attempts to ameliorate T1D in animal models or patients by insulin sensitizers have largely failed. Sensitization to insulin by MEthyl-substituted long-chain DICArboxylic acid (MEDICA) analogs in T2D animal models surpasses that of current insulin sensitizers, thus prompting our interest in probing MEDICA in the T1D context. MEDICA efficacy in modulating the course of T1D was verified in streptozotocin (STZ) diabetic rats and autoimmune nonobese diabetic (NOD) mice. MEDICA treatment normalizes overt diabetes in STZ diabetic rats when added on to subtherapeutic insulin, and prevents/delays autoimmune T1D in NOD mice. MEDICA treatment does not improve β-cell insulin content or insulitis score, but its efficacy is accounted for by pronounced total body sensitization to insulin. In conclusion, potent insulin sensitizers may counteract genetic predisposition to autoimmune T1D and amplify subtherapeutic insulin into an effective therapeutic measure for the treatment of overt T1D.

The lipophilic phytocannabinoids cannabidiol (CBD) and Δ9-tetrahydrocannabinol (THC) show therapeutic efficacy in various medical conditions. Both molecules are poorly water soluble and subjected to extensive first pass metabolism in the gastrointestinal tract, leading to a limited oral bioavailability of approximately 9%. We have developed an advanced lipid based Self-Emulsifying Drug Delivery System termed Advanced Pro-NanoLiposphere (PNL) pre-concentrate. The PNL is composed of lipid and emulsifying excipients of GRAS status and are known to increase solubility and reduce Phase I metabolism of lipophilic active compounds. Advanced PNLs are PNLs with an incorporated natural absorption enhancers. These molecules are natural alkaloids and phenolic compounds which were reported to inhibit certain phase I and phase II metabolism processes. Here we use piperine, curcumin and resveratrol to formulate the Advanced-PNL formulations. Consequently, we have explored the utility of these Advanced-PNLs on CBD and THC oral bioavailability. Oral administration of CBD-piperine-PNL resulted in 6-fold increase in AUC compared to CBD solution, proving to be the most effective of the screened formulations. The same trend was found in pharmacokinetic experiments of THC-piperine-PNL which resulted in a 9.3-fold increase in AUC as compared to THC solution. Our Piperine-PNL can be used as a platform for synchronized delivery of piperine and CBD or THC to the enterocyte site. This co-localization provides an increase in CBD and THC bioavailability by its effect at the pre-enterocyte and the enterocyte levels of the absorption process. The extra augmentation in the absorption of CBD and THC by incorporating piperine into PNL is attributed to the inhibition of Phase I and phase II metabolism by piperine in addition to the Phase I metabolism and P-gp inhibition by PNL. These novel results pave the way to utilize piperine-PNL delivery system for other poorly soluble, highly metabolized compounds that currently cannot be administered orally.

Piperine is an alkaloid naturally found in black pepper with a myriad of pharmacological attributes. Piperine's most far reaching indication is drug absorption enhancment, with supportive data regarding its ability to inhibit first pass effect mechanisms. However, alongside these findings, the role of piperine as an absorption enhancer is undermined with publications stating an apparent effect of a metabolic inducer. The aim of this work is to investigate the effect of repeated administration of piperine in a lipid-based formulation ,on oral absorption of cannabidiol (CBD), compared to acute piperine dosing. The effect of piperine on CBD absorption was determined pre-clinically in the freely moving rat model. Results of this work demonstrated that there was no significant difference in piperine's effect, when given chronically or in a single dose regimen. Both groups resulted in approximate 2.5-fold increase in oral bioavailability of CBD compared to control group without piperine.

Humanin (HN) is a 24-amino acid mitochondrial-derived peptide, best known for its ability to protect neurons from damage caused by ischemic stroke and neurodegenerative insults and cardiomyocytes from myocardial infarction or doxorubicin (Dox)-induced cardiotoxicity. This study examines the neuroprotective and myoprotective effects of HN novel synthetic analogs HUJInin and c(D-Ser14-HN), prepared by solid-phase peptide synthesis. The cellular models employed were oxygen-glucose-deprivation (OGD) followed by reoxygenation (R)-induced neurotoxicity in PC12 and SH-SY5Y neuronal cell cultures and Dox-induced cardiotoxicity in H9c2 and C2C12 myoblast cell cultures, respectively. Necrotic and apoptotic cell death was measured by LDH release and caspase-3 activity. Erk 1/2 and AKT phosphorylations were examined by western blotting. Mitochondrial calcium and mitochondrial membrane potential were measured using the fluorescent dye tetramethylrhodamine-methyl ester. It was found that HUJInin and c(D-Ser14-HN) conferred significant dose-dependent neuroprotection, a phenomenon related to attenuation of OGD insult-induced Erk 1/2 phosphorylation, stimulation of AKT phosphorylation and improvement of mitochondrial functions. These peptides also conferred myoprotective effect towards Dox-induced apo-necrotic cell death insults. HUJInin and c(D-Ser14-HN) synthetic analogs may provide new lead compounds for the development of a potential candidate drug for stroke treatment and/or Dox-induced cardiotoxicity therapy in cancer patients.

The aim of this research was to investigate the effect of the lipid component in self-emulsifying drug delivery systems on the oral absorption of major cannabinoids Δ9-tetrahydrocannabinol (THC) and Cannabidiol (CBD). The investigated lipids were either long chain triglycerides (LCT) or medium chain triglycerides (MCT) with different composition, fatty acid chain length, degree of saturation and their absorption pathway to the systemic circulation. Formulations were developed with the purpose of creating thermodynamically stable oil-in-water nano emulsions/suspensions with particle size of 50 nm or less which carry the lipophilic drug and increase water solubility. Following a methodic screening of suitable excipients in-vitro, leading formulations based on sesame oil or MIGLYOL® 812N (Type I LCT/MCT SNEDDS) and cocoa butter or tricaprin (Type II LCT/MCT SNEDDS) were investigated in the freely moving rat model. Results in rat model demonstrated that the effect of each type of lipid on bioavailability of cannabinoids is not straightforwardly anticipated. The differences in the effect of LCT and MCT on absorption was not substantial for Type I formulations, however, more prominent for Type II formulations. This unpredictable behavior in-vivo demonstrates the importance of investigating each vehicle pre-clinically, following the in-vitro development.

Hydrophilic peptides constitute most of the active peptides. They mostly permeate via tight junctions (paracellular pathway) in the intestine. This permeability mechanism restricts the magnitude of their oral absorption and bioavailability. We hypothesized that concealing the hydrophilic residues of the peptide using the lipophilic prodrug charge masking approach (LPCM) can improve the bioavailability of hydrophilic peptides. To test this hypothesis, a cyclic N-methylated hexapeptide containing Arg-Gly-Asp (RGD) and its prodrug derivatives, masking the Arg and Asp charged side chains, were synthesized. The library was evaluated for intestinal permeability in vitro using the Caco-2 model. Further investigation of metabolic stability ex vivo models in rat plasma, brush border membrane vesicles (BBMVs), and isolated CYP3A4 microsomes and pharmacokinetic studies was performed on a selected peptide and its prodrug (peptide 12). The parent drug analogues were found to have a low permeability rate in vitro, corresponding to atenolol, a marker for paracellular permeability. Moreover, palmitoyl carnitine increased the P

MyD88 is a cytoplasmic adaptor protein that plays a central role in signaling downstream of the TLRs and the IL1R superfamily. We previously demonstrated that MyD88 plays a critical role in EAE, the murine model of multiple sclerosis, and showed that the MyD88 BB-loop decoy peptide RDVLPGT ameliorates EAE. We now designed and screened a library of backbone cyclized peptides based on the linear BB loop peptide, to identify a metabolically stable inhibitor of MyD88 that retains the binding properties of the linear peptide. We identified a novel cyclic peptide protein mimetic that inhibits inflammatory responses to TLR ligands, and NFκB activation in response to IL-1 activation. The inhibitor, c(MyD 4-4), is metabolically stable in comparison to the linear peptide, blocks MyD88 in a specific manner, and inhibits MyD88 function by preventing MyD88 dimerization. Finally, treatment of mice with c(MyD 4-4) reduced the severity of clinical disease in the murine EAE model of multiple sclerosis. Thus, modulation of MyD88-dependent signaling using c(MyD 4-4) is a potential therapeutic strategy to lower innate immune inflammation in autoimmune CNS disease.

Phase II biotransformation reactions have been gaining more attention due to their acknowledged significance in drug bioavailability, drug development, and drug-drug interactions. However, the predominant role of phase I metabolism has always overshadowed phase II metabolism, resulting in insufficient data regarding its mechanisms. In this paper, we investigate the effect of an advanced lipid based formulation on the phase II metabolism process of glucuronidation, occuring in the enterocytes monolayer. The investigated formulation is a self-emulsifying drug delivery system, termed pro-nano lipospheres, which contains the natural absorption enhancer piperine. To evaluate the effect of this formulation on direct glucuronidation we chose the model molecule raloxifene. First, glucuronidation is the main clearance pathway of this compound without involvement of preceding mechanisms. Second, raloxifene's extensive glucuronidation site is primarily at the intestine. Raloxifene's oral bioavailability was determined in a series of pharmacokinetic experiments using the freely moving rat model. In order to test the effect of the formulation on the relevant UGT enzymes reported in the clinic, we used the in vitro method of UGT-Glo Assay. Coadministration of raloxifene and piperine pro-nano lipospheres to rats resulted in a 2-fold increase in the relative oral bioavailability of raloxifene. However, coadministration of raloxifene with blank pro-nano lipospheres had no effect on its oral bioavailability. In contrast to the difference found in vivo between the two vehicles, both formulations extended an inhibitory effect on UGT enzymes in vitro. Ultimately, these findings prove the ability of the formulation to diminish intestinal direct phase II metabolism which serves as an absorption obstacle for many of today's marketed drugs. Pro-nano lipospheres is a formulation that serves as a platform for the simultaneous delivery of the absorption enhancer and a required drug. The discrepancy found between the in vivo and in vitro models demonstrates that the in vitro method may not be sensitive enough to distinguish the difference between the formulations.

Thirty percent of top marketed drugs in the USA and 70% of all new drug candidates are lipophilic and exhibit poor water solubility. With such physicochemical properties, the oral bioavailability of these compounds lacks dose proportionality, is very limited and extremely erratic. Different lipid-based formulations have been explored in the past few decades to improve the oral delivery of such compounds. In recent years, the most popular approach is their incorporation into self-emulsifying drug delivery systems (SEDDS), with particular emphasis on self-nano-emulsifying drug delivery systems (SNEDDS).This review offers an updated overview of SNEDDS application from the biopharmaceutical point of view. The focus of this review deals with the potential of SNEDDS utilization to overcome absorption barriers following oral administration of lipophilic drugs. This includes a comprehensive description of the primary mechanisms by which lipids and lipophilic excipients, used to formulate SNEDDS, could affect drug absorption, bioavailability and disposition following oral administration.The utilization of SNEDDS to augment the oral bioavailability of poorly water-soluble drugs goes beyond improvement in drug's solubility, as was initially presumed. In fact, SNEDDS have a potential to increase oral bioavailability by multi-concerted mechanisms such as reduced intra-enterocyte metabolism by CYP P450 enzymes, reduced P-glycoprotein (P-gp) efflux activity and hepatic first-pass metabolism bypass via lymphatic absorption. This unique biopharmaceutical point of view, presented in this review, contributes to the understanding of proper drug candidate selection and of the approach in SNEDDS formulation design.

We describe a systematic approach for the development of both orally bioavailable and bioactive cyclic N methylated hexapeptides as high affinity ligands for the integrin αvβ3. The work is based on two concepts: (a) screening of systematically designed libraries with spatial diversity and (b) masking of the peptide charge with lipophilic pro-moiety. The key steps of the method are i) initial design of combinatorial library of N-methylated analogs of the stem peptide cyclo(D Ala Ala5); ii) selection of cyclic peptides with highest intestinal permeability; iii) design of sub-libraries with the bioactive RGD sequence in all possible positions; iv) selection of the best ligands for RGD-recognizing integrin subtypes; v) fine tuning of affinity and selectivity by additional Ala to Xaa substitutions; vi) protection of the charged functional groups according to the pro drug concept to regain intestinal and oral permeability; vii) proof of biological effects in mice after oral administration

Amphotericin B (AMB) arabinogalactan (AG) conjugate was synthesized by the conjugation of AMB to oxidized AG by reductive amination. The conjugate was evaluated for in vitro antifungal activity and in vivo toxicity. Optimization of the conjugation process was investigated using large batches of 100 g, which are 20 times larger than previously reported for AMB-AG conjugation. The efficacy of AMB-AG conjugates was studied as a function of reaction conditions and time, aldehyde/reducing agent mole ratio, and purification procedure. The most potent AMB-AG conjugate having low minimal inhibitory concentration (MIC) and high maximal tolerated dose (MTD) was obtained following reduction with NaBH4 at 1:2 mol ratio (AG units/NaBH4) at 25 °C for 24 h. AMB-AG conjugate prepared under these conditions demonstrated MIC of 0.5 mg/L (equiv of AMB) in Candida albicans, and an MTD of 60 mg/kg (equiv of AMB) in mice, while AMB clinical formulation (Fungizone) demonstrated high toxicity (MTD = 3 mg/kg). These findings confirm the simplicity and reproducibility of the conjugation allowing this method to be applied on larger scale production.

Bipolar-disorder (manic-depressive illness) is a severe chronic illness affecting ∼1% of the adult population. It is treated with mood-stabilizers, the prototypic one being lithium-salts (lithium), but it has life threatening side-effects and a significant number of patients fail to respond. The lithium-inhibitable enzyme inositol-monophosphatase (IMPase) is one of the viable targets for lithium's mechanism of action. Calbindin-D28k (calbindin) up-regulates IMPase activity. The IMPase-calbindincomplex was modeled using the program MolFit. The in-silico model indicated that the 55-66 amino-acid segment of IMPase anchors calbindin via Lys59 and Lys61 with a glutamate in between (Lys-Glu-Lys motif) and that the motif interacts with residues Asp24 and Asp26 of calbindin. We found that differently from wildtype calbindin, IMPase was not activated by mutated calbindin in which Asp24 and Asp26 were replaced by alanine. Calbindin's effect was significantly reduced by a linear peptide with the sequence of amino acids 58-63 of IMPase (peptide 1) and by six amino-acid linear peptides including at least part of the Lys-Glu-Lys motif. The three amino-acid peptide Lys-Glu-Lys or five amino-acid linear peptides containing this motif were ineffective. Mice administered peptide 1 intracerebroventricularly exhibited a significant anti-depressant-like reduced immobility in the forced-swim test. Based on the sequence of peptide 1, and to potentially increase the peptide's stability, cyclic and linear pre-cyclic analog peptides were synthesized. One cyclic peptide and one linear pre-cyclic analog peptide inhibited calbindin-activated brain IMPase activity in-vitro. Our findings may lead to the development of molecules capable of inhibiting IMPase activity at an alternative site than that of lithium.

Superior bioavailability of BCS Class 2 compounds incorporated into SNEDDS was previously reported. This study aims to elucidate the underlying mechanisms accountable for this phenomenon. SNEDDS of amiodarone (AM) and talinolol were developed. Pharmacokinetic parameters were assessed in vivo. Effect on intestinal permeability, P-gp efflux and toxicity was evaluated in vitro (Caco-2) and ex vivo (Ussing). Solubilization was assessed in vitro (Dynamic Lipolysis Model). Effect on intraenterocyte metabolism was evaluated using CYP3A4 microsomes. Oral administration of AM-SNEDDS and talinolol-SNEDDS resulted in higher and less variable AUC and Cmax. In vitro, higher talinolol-SNEDDS Papp indicated Pgp inhibition. Lipolysis of AM-SNEDDS resulted in higher AM concentration in the fraction available for absorption. Incubation of AM-SNEDDS with CYP3A4 indicated CYP inhibition. SNEDDS didn’t alter mannitol Papp and TEER. SNEDDS effect was transient. Multiple mechanisms are accountable for improved bioavailability and reduced variability of Class-2 compounds by SNEDDS: increased solubilization, reduced intraenterocyte metabolism and reduced P-gp efflux. SNEDDS effect is reversible and doesn’t cause intestinal tissue or cell damage. These comprehensive findings can be used for intelligent selection of drugs for which oral bioavailability will improve upon incorporation into SNEDDS, based on recognition of the drug’s absorption barriers and the ability of SNEDDS to overcome them.

During recent years there has been increasing interest in the Lycopodium alkaloid huperzine A as a potential therapeutic agent for neurodegenerative diseases. This study aimed to characterize huperzine A's permeability across the enterocyte barrier along the gastrointestinal tract with an emphasis on the effect of ionization on the drug absorption. Intestinal permeability of huperzine A was evaluated by in vitro Caco-2 and parallel artificial membrane permeation assay models and by the ex vivo Ussing chamber model. The permeability rate was strongly dependent on the degree of ionization and increased with elevation of the donor medium pH in all studied models. The transport of the unionized fraction was similar to the permeability of the markers for passive transcellular diffusion. Addition of the paracellular permeability modulator palmitoylcarnitine in the Caco-2 model led to significant enhancement in the permeability of the ionized huperzine A fraction. No evidence of active transport of huperzine A was detected in this study. The Ussing chamber model experiments showed similar drug permeability along the entire rat intestine. In conclusion, huperzine A permeates the intestinal border mainly by passive transcellular diffusion whereas some fraction, dependent on the degree of huperzine A ionization, is absorbed by the paracellular route. Huperzine A's permeability characteristics pave the way to the development of its oral extended release dosage form. The specific population of the potential users of huperzine A and the high potency of this molecule support the rationale for such a delivery.

Lipospheres are a drug encapsulation system composed of water dispersible solid microparticles of particle size between 0.01 and 100 μm in diameter with a solid hydrophobic lipid core stabilized by a layer of phospholipid molecules embedded in their surface. The bioactive compound is dissolved or dispersed in the solid lipid matrix of the internal core. Since lipospheres were introduced in the beginning of the 1990s, they have been used for the delivery of multiple types of drugs by various routes of administration. Later, a self-assembling pro-nano lipospheres (PNL) encapsulation system was developed for oral drug delivery. Lipospheres have several advantages over other delivery systems, such as better physical stability, low cost of ingredients, ease of preparation and scale-up, high dispersibility in an aqueous medium, high entrapment of hydrophobic drugs, controlled particle size, and extended release of entrapped drug after administration, from a few hours to several days. This review article focuses on updated information on several aspects of lipospheres and PNL, including preparation techniques, physicochemical properties and in vitro evaluation methods. Additionally, it covers lipospheres and PNL utilization for oral, ocular, and parenteral delivery, with special attention to unique considerations and aspects for each route of administration.

We have recently generated lipophilic D-xylose derivatives that increase the rate of glucose uptake in cultured skeletal muscle cells in an AMP-activated protein kinase (AMPK)-dependent manner. The derivative 2,4:3,5-dibenzylidene-D-xylose-diethyl dithioacetal (EH-36) stimulated the rate of glucose transport by increasing the abundance of glucose transporter-4 in the plasma membrane of cultured myotubes. The present study aimed at investigating potential antihyperglycaemic effects of EH-36 in animal models of diabetes. Two animal models were treated subcutaneously with EH-36: streptozotocin-induced diabetes in C57BL/6 mice (a model of insulin-deficient type 1 diabetes), and spontaneously diabetic KKAy mice (Kuo Kondo rats carrying the A(y) yellow obese gene; insulin-resistant type 2 diabetes). The in vivo biodistribution of glucose in control and treated mice was followed with the glucose analogue 2-deoxy-2-[(18) F]-D-glucose; the rate of glucose uptake in excised soleus muscles was measured with [(3) H]-2-deoxy-D-glucose. Pharmacokinetic parameters were determined by non-compartmental analysis of the in vivo data. The effective blood EH-36 concentration in treated animals was 2 μM. It reduced significantly the blood glucose levels in both types of diabetic mice and also corrected the typical compensatory hyperinsulinaemia of KKAy mice. EH-36 markedly increased glucose transport in vivo into skeletal muscle and heart, but not to adipose tissue. This stimulatory effect was mediated by Thr(172) -phosphorylation in AMPK. Biochemical tests in treated animals and acute toxicological examinations showed that EH-36 was well tolerated and not toxic to the mice. These findings indicate that EH-36 is a promising prototype molecule for the development of novel antidiabetic drugs.

Seven 4-phenoxybenzenesulfonamidopolymethylene carbamoylphosphonates (CPOs) bearing two to eight methylene units in the polymethylene chain were synthesized and evaluated as matrix metalloproteinase (MMP) inhibitors. The five lowest homologues [(CH₂)₂-₆] are selective MMP-2 inhibitors, whereas the two with the longest linkers [(CH₂)₇,₈] lack inhibitory activity. The most potent homologues are those with (CH₂)₅,₆; these two were evaluated for antimetastatic activity in a murine melanoma model and showed good potency both by oral and intraperitoneal administration without any toxic--including musculoskeletal--side effects. In contrast to the previously reported cis-ACCP, which was shown to inhibit MMP-2 for ∼30 min, the new compounds inhibit MMP activity for the duration of measurement, lasting several hours. Pharmacokinetic evaluation revealed, on the one hand, low oral bioavailability; on the other hand, a relatively large calculated volume of distribution, consistent with the observed reversible absorption of CPO 5 to hydroxyapatite, as a model for bone.

Recent progress in peptide synthesis simplified the synthesis of multiple N-methylation of peptides. To evaluate how multiple N-methylation affects the bioavailability of peptides, a poly alanine cyclic hexapeptide library (n = 54), varying in the number of N-methyl (N-Me) groups (1-5 groups) and their position, was synthesized. The peptides were evaluated for their intestinal permeability in vitro using the Caco-2 model. Further evaluation of the transport route of chosen analogues was performed using rat excised viable intestinal tissue, a novel colorimetric liposomal model and the parallel artificial membrane permeability assay (PAMPA). While most members were found to have poor permeability (permeability coefficient, P(app)1 x 10⁻⁶ cm/s, lower than mannitol, the marker for paracellular permeability), 10 analogues were found to have high Caco-2 permeability, (P(app)1 x 10⁻⁵ cm/s, similar to testosterone, a marker of transcellular permeability). No correlation was found between the number of N-methylated groups and the enhanced permeability. However, 9/10 permeable peptides in the Caco-2 model included an N-Me placed adjacently to the D-Ala position. While the exact transport route was not fully characterized, the data suggests a facilitated diffusion. It can be concluded that multiple N-methylation of peptides may improve intestinal permeability, and therefore can be utilized in the design of orally available peptide-based therapeutics.

Conjugation of poorly soluble drugs to polysaccharides affects their solubility, pharmacokinetics (PK), and pharmacodynamics. The need for amphotericin B (AmB) analog with improved solubility and reduced toxicity is immense. Conjugation of AmB to arabinogalactan (AG) produced a highly soluble AmB-AG conjugate, with high and low molecular weight (H-M(w) and L-M(w)) fractions. Its similar antifungal activity to AmB poses the question whether AmB-AG is a prodrug of AmB or a novel pharmaceutical entity. We compared the PK of AmB-AG and AmB in rats. Upon AmB-AG administration, no free AmB was released. The half-lives and the volumes of distribution of AmB, H-M(w) and L-M(w) were 10.9, 8.8, and 1.5 h and 1630, 217, and 133 mL/kg, respectively. We conclude that PK of small molecules conjugated to polysaccharides is mainly dictated by the macromolecular moiety and shows molecular weight dependency. Our findings define AmB-AG as a novel pharmaceutical entity with high clinical potential.

A quasi-equilibrium mass transport analysis has been developed to quantitatively explain the solubility-permeability interplay that exists when using cyclodextrins as pharmaceutical solubilizers. The model considers the effects of cyclodextrins on the membrane permeability (P(m)) as well as the unstirred water layer (UWL) permeability (P(aq)), to predict the overall effective permeability (P(eff)) dependence on cyclodextrin concentration (C(CD)). The analysis reveals that: (1) UWL permeability markedly increases with increasing C(CD) since the effective UWL thickness quickly decreases with increasing C(CD); (2) membrane permeability decreases with increasing C(CD), as a result of the decrease in the free fraction of drug; and (3) since P(aq) increases and P(m) decreases with increasing C(CD), the UWL is effectively eliminated and the overall P(eff) tends toward membrane control, that is, P(eff) approximately P(m) above a critical C(CD). Application of this transport model enabled excellent quantitative prediction of progesterone P(eff) as a function of HP beta CD concentrations in PAMPA assay, Caco-2 transepithelial studies, and in situ rat jejunal-perfusion model. This work demonstrates that when using cyclodextrins as pharmaceutical solubilizers, a trade-off exists between solubility increase and permeability decrease that must not be overlooked; the transport model presented here can aid in striking the appropriate solubility-permeability balance in order to achieve optimal overall absorption.

Tetraphenylphosphonium (TPP), a phosphonium cation, is a promising means for tumor imaging. A major contributor to the pharmacokinetics of phosphonium cations is the efflux transporter P-glycoprotein (P-gp). For this application it is important to ascertain the influence of the multidrug resistance system on TPP. Therefore, our aim was to characterize the interaction of TPP with P-gp, in vitro and in in vivo models. P-gp-mediated transport of [3H]-TPP was assessed in Caco-2 cells and ex vivo in rat intestinal wall by the use of a diffusion cell system. The distribution of [3H]-TPP across the blood-brain barrier (BBB) was studied in rats and mice treated with P-gp modulators and in Mdr-1a/b((-/-)) knockout mice. The in vitro permeability coefficient of basolateral-to-apical transfer (PappB-A) of [3H]-TPP was 8-fold greater than apical-to-basolateral (PappA-B) coefficient, indicative of net mucosal secretion. A concentration dependent decrease of this secretion was obtained by the P-gp substrate verapamil, while no effect was evident by the MRP2 inhibitor MK-571 and the BCRP inhibitor FTC. [3H]-TPP transfer across rat jejunum wall was directional and concentration-dependent. 2,4-Dinitrophenol, cyclosporin A (CsA), verapamil and PSC-833 enhanced A-B transport of TPP 3.6-fold, 4-fold, 4.6-fold and 5.3-fold respectively. Likewise, PappA-B of [3H]-TPP was 5-fold greater in P-gp knockout mice than in controls. In vivo, PSC-833, P-gp inhibitor, significantly increased the uptake of [3H]-TPP in the liver, heart, small intestine and the lungs but not the brain. Similar results were obtained in P-gp knockout mice. Our study demonstrates that P-gp mediates TPP efflux in vitro and in vivo; however, the consistently poor BBB permeation of TPP in all in vivo studies including P-gp knockout animals indicates that it is most likely mediated by other mechanisms. These findings are important for optimized clinical application of TPP as an imaging agent in cancer.

Guaifenesin is a very commonly used and prescribed oral expectorant drug. However, its mechanism of action is not completely elucidated and the available information is limited. The purpose was to evaluate whether guaifenesin action on respiratory tract secretion is mediated through a reflex stimulation of the gastric mucosa or by the systemic exposure due to the absorption of the drug to the blood circulation.Guaifenesin was administered to rats by various routes: intravenous bolus, oral gavage, and gastric, jejunal or cecal infusions (through surgically implanted catheters). Phenol red respiratory tract secretion (after intraperitoneal or intravenous injection) was used as a marker for degree of expectorant action. Administration of saline by gavage was used as control.Respiratory secretion following oral bolus was approximately 2-fold higher (p0.05) than that of control. Following IV administration the increase of respiratory secretion did not occur despite the fact that systemic exposure to guaifenesin was 1.5-fold higher than following oral administration. The abdominal surgery was found to eliminate the effect of guaifenesin although it did not change systemic absorption. Guaifenesin was equally absorbed from all parts of the gastrointestinal tract.It was demonstrated that expectorant action of guaifenesin is mediated by stimulation of the gastrointestinal tract and not by the systemic exposure to the drug.

Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction. The complexity of the disease and its treatments make MG patients particularly susceptible to adverse effects of drugs. MG is not a painful condition; however, as pain management armamentarium includes drugs from diverse pharmacological groups and with potential for drug-drug interactions, managing pain in patients with MG can be challenging. The underlying disease and the concomitant medications of each patient must be considered and the analgesic treatment individualized. This review presents an update on the various aspects of pain pharmacotherapy in patients with MG, focusing primarily on medications used to treat chronic pain. Drugs discussed are opioids, nonsteroidal anti-inflammatory drugs, antidepressants, anticonvulsants, muscle relaxants, benzodiazepines, intravenous magnesium, and local anesthetics. Drug interactions with agents used for MG treatment (acethylcholinesterase inhibitors, corticosteroids, immunosuppressants) and plasmapheresis are discussed. The clinical usefulness and limitations of each of the drug classes and agents are described.

Type 2 diabetes mellitus has reached epidemic proportions; therefore, the search for novel antihyperglycemic drugs is intense. We have discovered that D-xylose increases the rate of glucose transport in a non-insulin-dependent manner in rat and human myotubes in vitro. Due to the unfavorable pharmacokinetic properties of D-xylose we aimed at synthesizing active derivatives with improved parameters. Quantitative structure-activity relationship analysis identified critical hydroxyl groups in D-xylose. These data were used to synthesize various hydrophobic derivatives of D-xylose of which compound 19 the was most potent compound in stimulating the rate of hexose transport by increasing the abundance of glucose transporter-4 in the plasma membrane of myotubes. This effect resulted from the activation of AMP-activated protein kinase without recruiting the insulin transduction mechanism. These results show that lipophilic D-xylose derivatives may serve as prototype molecules for the development of novel antihyperglycemic drugs for the treatment of diabetes.

cis-2-Aminocyclohexylcarbamoylphosphonic acid ( cis-ACCP) was evaluated in vitro and in two in vivo cancer metastasis models. It reduced metastasis formation in mice by approximately 90% when administered by a repetitive once daily dosing regimen of 50 mg/kg via oral or intraperitoneal routes and was nontoxic up to 500 mg/kg, following intraperitoneal administration daily for two weeks. Pharmacokinetic investigation of cis-ACCP in rats revealed distribution restricted into the extracellular fluid, which is the site of action for the antimetastatic activity and rapid elimination ( t 1/2 approximately 19 min) from blood. Sustained and prolonged absorption ( t 1/2 approximately 126 min) occurred via paracellular mechanism along the small and large intestine with overall bioavailability of 0.3%. The in vivo concentrations of cis-ACCP in the blood in rats was above the minimal concentration for antimetastatic/MMP-inhibitory activity, thus explaining the prolonged action following once daily administration. Finally, 84% of the intravenously administered cis-ACCP to rats was excreted intact in the urine.

The purpose of this study was to evaluate the impact of general anesthesia on the lymphatic transport of orally administered drugs. Vitamin D 3 (0.5 mg/kg), a model lipophilic molecule with significant lymphatic transport, was administered to anesthetized rats in close proximity to the lymphatic cannulation procedure. The lymphatic and non-lymphatic absorption of the vitamin in this experimental model was compared to lymph-duct cannulated freely moving conscious rats. The amounts of vitamin D 3 transported via the lymph in the anesthetized animals throughout the time frame of this experimental model (8 h) were 25% lower as compared to the conscious animals, but showed similar absorption kinetics. However, the duration of the anesthesia is limited and thus failed to produce the complete picture of the absorption process. The cumulative percent of the vitamin dose that was recovered in the lymph as well as the vitamin plasma AUC values were both 25% lower in the anesthetized animals as compared to the conscious animals. Hence, the anesthesia did not influence the proportion of the vitamin fraction absorbed via the different pathways. The lymph flow rate was significantly decreased by the anesthesia (threefold), however, higher lymph vitamin concentrations in these animals led to lower differences in the vitamin lymphatic transport (25%) between the models. In conclusion, the anesthetized rat model is suitable for approximating the lymphatic transport. However, the conscious rat model is still required in order to have a more precise and complete measurement of lymphatic transport.

To assess the effects of the unabsorbed fraction of an orally administered antimicrobial drug which enters the colon on the emergence of resistance among the natural microflora, a phenomenon largely overlooked so far despite its clinical importance, especially when sustained release formulations are used.Effects of an orally administered model beta-lactam antibiotic (amoxicillin) on emergence of resistant bacteria were assessed using a microbiological assay for qualitative and quantitative determination of resistant bacteria in fecal samples of rats following gastric administration of the drug to rats for 4 consecutive days. Time- and site-controlled administration of a beta-lactamase to the rat colon was assessed as a potential strategy for prevention the emergence of resistant bacteria following oral administration of incompletely absorbed antimicrobials.Emergence of resistant bacteria was demonstrated following oral administration of amoxicillin to rats, whereas de-activation of the beta-lactam prior to entering the colon, by infusion of a beta-lactamase into the lower ileum, was shown to prevent the emergence of resistant colonic bacteria.This study illustrates the need to consider the emergence of antimicrobial resistance as a goal equally important to microbiological and clinical cure, when designing oral sustained-release delivery systems of antimicrobial drugs.

Following a high-fat meal, triglyceride-rich lipoproteins (TRL) are assembled in the gut and absorbed via the lymph into the blood circulation, producing a temporal hyperlipidemia. The purpose of this study is to verify the hypothesis that this transient acute postprandial hyperlipidemia affects the pharmacokinetics of lipophilic drugs on both absorption and disposition levels by the same underlying mechanism, namely the association of active lipophilic compounds with TRL in the plasma (disposition) or within the enterocyte (lymphatic transport). This concept was assessed in rats using two model compounds, DDT with high affinity to chylomicrons and diazepam which does not bind to chylomicrons. Oral administration of peanut oil significantly increased the AUC of plasma DDT concentrations following its IV bolus administration in comparison to a water treated group. On the other hand, the AUC of diazepam following IV bolus administration was the same in oil and water treated rats. While DDT is known to have significant lymphatic bioavailability, diazepam has negligible intestinal lymphatic transport (0.014+/-0.004% of a given dose). In conclusion, lipophilic molecules that bind extensively to TRL will be prone to both intestinal lymphatic transport and to post-absorptive changes in disposition (decrease in clearance and volume of distribution) following a high-fat meal.

The aim of this article was to investigate the role of intestinal lymphatic transport in the oral bioavailability of two structurally similar synthetic lipophilic cannabinoids: dexanabinol and PRS-211,220. For this purpose, the long chain triglyceride (LCT) solubility and affinity to chylomicrons ex vivo of both cannabinoids were evaluated. Their oral bioavailability was assessed in rats following administration in a lipid-free and a LCT-based formulation. The intestinal lymphatic transport of these two molecules was also directly measured in a freely moving rat model. LCT solubility of dexanabinol and PRS-211,220 was 7.9 ± 0.2 and 95.8 ± 5.3 mg/g, respectively. The uptake by chylomicrons was moderate (31.6 ± 5.2%) and high (66.1 ± 2.4%), respectively. The bioavailability of dexanabinol (37%) was not affected by LCT solution, whereas administration of PRS-211,220 in LCT improved the absolute oral bioavailability three-fold (from 13 to 35%) in comparison to the lipid-free formulation. The intestinal lymphatic transport of dexanabinol and PRS-211,220 was 7.5 ± 0.8 and 60.7 ± 6.8% of the absorbed dose, respectively. In conclusion, despite structural similarity and similar lipophilicity, dexanabinol and PRS-211,220 exhibited a very diverse pattern of oral absorption, and the lymphatic system played quite a different role in the oral bioavailability of these molecules. The low lymphatic transport of dexanabinol is likely driven by relatively lower affinity to chylomicrons and lower LCT solubility.

A high-fat meal induces transient hyperlipidemia characterized by elevated triglyceride-rich lipoproteins (TRL) which are composed mainly of chylomicrons. The purpose of this work was to investigate the effect of this transient hyperlipidemia on the pharmacodynamics of lipophilic drugs, using DDT as a model compound since it binds extensively to TRL and has a distinct neurotoxic effect. The postprandial hyperlipidemia in rats was induced by oral administration of peanut oil and was monitored by measurement of plasma triglyceride levels. The control group received water instead of oil. The rats received a continuous intravenous infusion of DDT (10 mg/h) until onset of a predefined pharmacodynamic endpoint (facial muscle tremor). Plasma and brain samples were then obtained and assayed for DDT. Rats with postprandial hyperlipidemia required higher dose of DDT to induce onset of facial muscle tremor. At the pharmacodynamic endpoint, oil treated rats had significantly higher concentrations of DDT in plasma and in the chylomicron fraction, but DDT brain concentrations were the same in both groups. In conclusion, a high-fat meal induces postprandial hyperlipidemia that may significantly alter the pharmacological profile of lipophilic compounds that bind to TRL. This is due to alteration of the distribution characteristics of the lipophilic compound through its association with postprandial lipoproteins. However, this pharmacokinetic phenomenon did not affect the concentration-effect relationship at the site of action in the brain.

Autotaxin is an extracellular, two zinc-centered enzyme that hydrolyzes lysophosphatidyl choline to lysophosphatidic acid, involved in various cancerous processes, e.g. migration, proliferation and tumor progression. We examined the autotaxin inhibitory properties of extended structure carbamoylphosphonates (CPOs) PhOC(6)H(4)SO(2)NH(CH(2))nNHCOPO(3)H(2), with increasing lengths of methylene chains, (CH(2))(n), n = 4-8. Carbamoylphosphonates having n = 6, 7, 8 inhibited autotaxin in vitro with IC(50) ≈ 1.5 µM. Using an imaging probe we demonstrated that compound n = 6 inhibits recombinant autotaxin activity in vitro and in vivo, following oral CPO administration. Additionally, daily oral administration of compound n = 7 inhibited over 90% of lung metastases in a murine melanoma metastasis model. Both the carbamoylphosphonates and the enzymes reside and interact in the extracellular space expecting minimal toxic side effects, and presenting a novel approach for inhibiting tumor proliferation and metastasis dissemination.

Nonsteroidal anti-inflammatory drugs, including indomethacin, have been found in both epidemiological and clinical studies to reduce the prevalence and severity of Alzheimer's disease. However, long-term use of indomethacin is limited by significant gastrointestinal and renal toxicities. An indomethacin prodrug that delivers low and continuous blood levels of the drug showed a superior safety profile and similar efficacy in comparison to an equivalent dose of free indomethacin because of limited systemic exposure and preferred brain uptake. The purpose of the present investigation was to evaluate whether sustained systemic input causes an increased brain influx in comparison to rapid input of the drug. Oral indomethacin, indomethacin prodrug, or intravenous indomethacin infusion was administered to rats. The infusion was designed to mimic the plasma indomethacin levels resulting from the prodrug. The resultant blood levels and brain indomethacin uptake were evaluated. The brain indomethacin concentrations 8 h following indomethacin administration were 0.45, 0.3, and 0.31 microg/g after the oral indomethacin, oral prodrug, and intravenous infusion, respectively. The corresponding plasma concentrations were 14.1, 4.1, and 4 microg/ml. Therefore, brain versus plasma indomethacin level ratios were 2.5-fold higher after slow systemic input of indomethacin in comparison to rapid drug input. In conclusion, indomethacin brain uptake was found to be mode of administration-dependent, and a sustained input function increases the drug brain uptake. Thus, these unique results indicate that an appropriate indomethacin controlled release delivery system may induce the desirable brain-related pharmacodynamic effects, while avoiding the concentration-dependent adverse effects. These findings may contribute to improved therapy in Alzheimer's disease.

To examine the correlation between the in vitro solubilization process of lipophilic compounds from different lipid solutions and the corresponding in vivo oral bioavailability data. In particular, to assess the influence of intra-enterocyte processes (metabolism and lymphatic absorption) on this correlation. The dissolution of progesterone and vitamin D3 in long (LCT), medium (MCT) and short (SCT) chain triglyceride solutions were tested in a dynamic in vitro lipolysis model. The absolute oral bioavailability of the drugs from the tested formulations was investigated in rats. Vitamin D3 bioavailability was also examined following lymphatic transport blockage induced by cycloheximide (3 mg/kg). The dynamic in vitro lipolysis experiments indicated a rank order of MCT > LCT > SCT for both progesterone and vitamin D3. The bioavailability of progesterone correlated with the in vitro data, despite its significant pre-systemic metabolism. For vitamin D3, an in vivo performance rank order of LCT > MCT > SCT was obtained. However, when the lymphatic transport was blocked the bioavailability of vitamin D3 correlated with in vitro data. The in vitro lipolysis model is useful for optimization of oral lipid formulations even in the case of pre-systemic metabolism in the gut. However, when lymphatic transport is a significant route of absorption, the in vitro lipolysis data may not be predictive for actual in vivo absorption.

Indomethacin has been suggested for the treatment of Alzheimer's disease (AD), but its use is limited by gastrointestinal and renal toxicity. To overcome this limitation, D-Pharm Ltd. (Rehovot, Israel) developed DP-155 (mixture of 1-steroyl and 1-palmitoyl-2-{6-[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolyl acetamido] hexanoyl}-Sn-glycero-3-phosophatidyl [corrected] choline), a lecithin derivative of indomethacin. Safety was tested by daily oral administration of DP-155 or indomethacin to rats in a dose range of 0.007 to 0.28 mmol/kg. The prevalence of gastrointestinal ulceration was significantly lower (10-fold) for DP-155 than for indomethacin, and the ulcerations were delayed. Signs of renal toxicity, namely reduced urine output and increased urine N-acetyl glycosaminidase to creatinine ratio, were 5-fold lower for DP-155. Indomethacin, but not an equimolar dose of DP-155, reduced urine bicyclo-prostaglandin E(2). An equimolar oral dose of DP-155 or indomethacin, administered every 4 h for 3 days, was equally efficacious in reducing the levels of Abeta42 in the brains of Tg2576 mice. Indomethacin was the principal metabolite of DP-155 in the serum. After DP-155 oral administration, indomethacin's half-life in the serum and the brain was 22 and 93 h, respectively, compared with 10 and 24 h following indomethacin oral administration. The brain to serum ratio was 3.5 times higher for DP-155 than indomethacin. This finding explains the efficacy of DP-155 in reducing Abeta42 brain levels, despite the low systemic blood concentrations of indomethacin derived from DP-155. In conclusion, compared with indomethacin, DP-155 has significantly lower toxicity in the gut and kidney while maintaining similar efficacy to indomethacin in lowering Abeta42 in the brains of Tg2576 mice. This superior safety profile highlights DP-155's potential as an improved indomethacin-based therapy for AD.

The present study investigates a novel gene therapy approach for atrial arrhythmias, using a clarithromycin-responsive ion channel subunit mutation, hMiRP1-Q9E, cloned into an expression plasmid; wild-type expression plasmids encoding human minK-related protein 1 (hMiRP1) were also used as controls. In a series of pig studies, right atrial myocardium was injected at one site with hMiRP1-Q9E plasmid DNA; a separate site in the same right atrium was injected with wild-type plasmid or was sham injected. Two weeks after transfection intravenous clarithromycin administration resulted in a site-specific, dose-dependent prolongation of the repolarization phase of the right atrial epicardial monophasic action potential (MAP) only at the hMiRPQ9E sites, but not at sham or wild-type sites. MAP recordings before clarithromycin administration did not differ between hMiRP1-Q9E and control sites. These studies show that regional control of atrial myocardial repolarization by site-specific transfection with plasmid DNA encoding an antibiotic-responsive ion channel subunit is feasible and, because hMiRP1-Q9E-transfected sites were affected only if clarithromycin was given, provide proof of concept for a posttranslational, controllable gene therapy strategy for atrial arrhythmias.

Oral administration of sodium N-[8-(2-hydroxybenzoyl)amino]caprylate (SNAC) has been reported to increase the bioavailability of various macromolecules. The present study was aimed to study the effect of SNAC on the intestinal tissue permeability of polar charged molecules, using 6-carboxy-fluorescein (6-CF) as a model. The effects of SNAC on rat intestinal permeability was investigated ex vivo by utilizing voltage clamp experiments in a side-by-side diffusion chamber model in comparison with the effect of EDTA (10mM). The intestinal permeability of 6-CF was increased two-fold in the presence of 33-66 mM SNAC, and by 6.5-fold in the presence of 10mM EDTA. The voltage clamp experiments show that the effect of SNAC was particularly on the transcellular 7-folds increase (that was five times larger than the paracellular transport of the model agent). While EDTA affected predominantly paracellular pathway transport, SNAC 33-66 mM had no effect on [(3)H]-mannitol transport or any toxic effect on tissue integrity measured by TEER values. In conclusion, this study demonstrates that SNAC can facilitate passive transport of polar charged molecules through the membrane of epithelial enterocytes. This is noteworthy in view of the very low tendency of a charged molecule to permeate across the lipophilic inter-phase of the enterocytes membrane.

The purpose of this study was to examine the feasibility of investigating the lymphatic transport of drugs in vivo utilizing known chylomicron flow blocking substances. Vitamin D(3) (0.5 mg/kg), a model lipophilic molecule, was administered to rats with blocked chylomicron flow, induced by either cycloheximide injection (3 mg/kg), colchicine injection (5 mg/kg) or intraduodenal infusion of pluronic L-81 (1 mg/h). The effect of these experimental models on the absorption of Vitamin D(3) was compared to the outcomes of the mesenteric lymph duct cannulated rat model. The oral d-xylose loading test was used to verify that other intestinal absorptive functions were not affected. Colchicine treatment induced severe adverse effects whereas pluronic L-81 and the cycloheximide models did not affect other absorption pathways and did not cause apparent adverse effects. Vitamin D(3) absorption in these two models was in good correlation to the mesenteric lymph duct cannulation model (25% non-lymphatic relative bioavailability) indicating that the incorporation of the lipophilic molecule into the chylomicron is an essential step in the cascade of lymphatic absorption. Moreover, the data suggest that the drug association with the chylomicron occurs at an early stage of its assembly process. The results also specify that lymphatic absorption and portal blood absorption are separate pathways that are not affected by each other. In conclusion, the chemical blockage of chylomicron flow provides a potential approach for lymphatic transport investigation, and may elucidate processes involving in the absorption of lipophilic compounds.

Expandable gastroretentive dosage forms (GRDFs) have been designed for the past 3 decades. They were originally created for possible veterinary use, but later the design was modified for enhanced drug therapy in humans. These GRDFs are easily swallowed and reach a significantly larger size in the stomach due to swelling or unfolding processes that prolong their gastric retention time (GRT). After drug release, their dimensions are minimized with subsequent evacuation from the stomach. Gastroretentivity is enhanced by the combination of substantial dimensions with high rigidity of the dosage form to withstand the peristalsis and mechanical contractility of the stomach. Positive results were obtained in preclinical and clinical studies evaluating GRT of expandable GRDFs. Narrow absorption window drugs compounded in such systems have improved in vivo absorption properties. These findings are an important step towards the implementation of expandable GRDFs in the clinical setting. The current review deals with expandable GRDFs reported in articles and patents, and describes the physiological basis of their design. Using the dog as a preclinical screening model prior to human studies, relevant imaging techniques and pharmacokinetic-pharmacodynamic aspects of such delivery systems are also discussed.

Metformin, a commonly used antidiabetic drug, exerts its glucose-lowering effect due to metabolic activities at several sites of action (biophases), including liver, intestine, muscle cells, and adipocytes. The relative contribution of the individual biophases to the overall glucose-lowering effect is not known. Thus, the aims of this investigation were to study the influence of mode of drug administration on the kinetics of glucose-lowering action of metformin in diabetic rats and identify the contribution of different sites of action to the overall response. Streptozotocin diabetic rats received metformin in crossover fashion via intraduodenal, intravenous, and intraportal routes as bolus dose or infusion regimens designed to yield similar pharmacokinetic profiles. Metformin plasma concentrations and blood glucose levels were measured following each mode of administration. Despite the similarity in the concentration-time profiles obtained for different routes of metformin administration, intraduodenal administration produced larger response than intraportal metformin infusion, and lowest response was observed following intravenous administration. This finding indicates that a significant "first-pass" pharmacodynamic effect, which occurs in the presystemic sites of action (liver and the gastrointestinal wall), contributes to the overall glucose-lowering response of metformin. We applied a combined pharmacokinetic-pharmacodynamic modeling approach to study the nature of the first-pass pharmacodynamic effect. The observed data were successfully described by a novel integrated indirect response pharmacokinetic-pharmacodynamic model that revealed a correlation between the temporal metformin concentrations that transit the portal vein and through the gut wall rather than with drug concentrations that accumulated in the liver and the intestinal wall.

We studied the differences in pharmacokinetics and pharmacodynamics of the same dose of alendronate administered subcutaneously as intermittent bolus injection or continuous infusion in rats. Two rat models of bone disease were applied. Bone cancer was produced by intratibial inoculation of Walker carcinosarcoma cells, and a model of augmented bone resorption was produced by vitamin D(3) treatment of rats that had undergone thyroidparathyroidectomy. Higher amounts of alendronate were found in bones and in internal organs after bolus drug administration as compared with continuous infusion. Drug effects on plasma calcium levels and on urine calcium excretion were similar in both modes of alendronate administration. Results of the study indicate that the pharmacokinetics (disposition) of alendronate is administration-dependent. The total amount found in bone does not directly represent the amount of alendronate that is pharmacologically active at the site of action in the bone and that affects bone remodeling. The findings suggest that there is no pharmacodynamic advantage for continuous infusion of alendronate. It is concluded that the preferred mode of administration should be selected according to secondary clinical criteria (like incidence of adverse effects and convenience of administration).

We examined the pharmacokinetic (PK) and pharmacodynamic (PD) rationales to develop controlled release (CR) formulations of metformin. Unrestrained diabetic rats received the drug as intravenous bolus (i.v.), oral solution (p.o.), intra-duodenal bolus, 4-h infusion, or intra-colonic bolus. In addition, we developed two CR-gastroretentive dosage forms (CR-GRDF) that released the drug over 3 or 6 h (in vitro), and retained in the rats’ stomach for 8–10 h. Metformin exhibited flip-flop PK. The colonic absorption was low but sustained and was associated with highly variable glucose-lowering effects, thus providing a PK rationale to develop CR-GRDF. In addition, the glucose-lowering effect was greater following p.o. vs. i.v. administration, despite equivalent AUC, indicating a first pass PD effect, thus, adding a PD rationale to develop metformin CR-GRDF. When administered to the diabetic rats, CR-GRDFs produced bioavailability and extent of glucose-lowering effects that were similar to those of the duodenal infusion and p.o. metformin administration. These findings are attributed to the adsorption of metformin to the intestine that yields slow and prolonged absorption even following p.o. administration of drug solution. The data indicates that unless the CR formulation could significantly extend the absorption period, it is not likely to improve glucose-lowering efficacy.

This work was aimed at improving the absorption of bisphosphonates by targeting carrier systems in the intestine and the intestinal peptide carrier system (hPEPT1), in particular. (14)C-Labeled pamidronate and alendronate as well as radiolabeled and "cold" peptidyl-bisphosphonates, Pro-[(3)H]Phe-[(14)C]pamidronate, and Pro-[(3)H]Phe-[(14)C]alendronate were synthesized. In situ single-pass perfusion studies revealed competitive inhibition of transport by Pro-Phe, suggesting peptide carrier-mediated transport. Prodrug transport in the Caco-2 cell line was significantly better than that of the parent drugs, and the prodrugs exhibited high affinity to the intestinal tissue. Oral administration of the dipeptidyl prodrugs resulted in a 3-fold increase in drug absorption following oral administration in rats, and the bioavailability of Pro-Phe-alendronate was 3.3 (F(TIBIA)) and 1.9 (F(URINE)) times higher than that of the parent drug. The results indicate that the oral absorption of bisphosphonates can be improved by peptidyl prodrugs via the hPEPT1; however, other transporters may also be involved.

The goal of this investigation was to optimize antilipid therapy by utilizing the combined activity of two lipid-lowering agents, niacin and bezafibrate, and improve their efficacy by targeting them to their presumed presystemic site(s) of action. Thus, continuous duodenal (IGI) administration of the drug combination should augment their efficacy in comparison with intermittent oral treatment. Three hyperlipidemic rat models were studied: Models A and B were based on cholesterol-enriched diets and Model C was based on on acute hyperlipidemia induced by triton injection. Continuous IGI administration of the drug combination [bezafibrate, 30mg/kg/day, and niacin, 40 mg/kg/day for 3 days (Models A and B) or for 18 h (Model C)] produced significantly greater lowering of total cholesterol and triglycerides and elevation of high-density lipoprotein (HDL) cholesterol in comparison with intermittent oral administration of the same doses either given individually or in combination (Models A and B). Similar results were found in Model C for the IGI administration of the drug combination in contrast to oral and also to intravenous infusions. The results indicate that the combination of bezafibrate and niacin produces a significant hypolipidemic response, with major site(s) of action located presystemically. Because a slow-release matrix tablet of the drug combination resulted in a similar magnitude of effect as the IGI administration, the present study provides a pharmacodynamic rationale for the use of a slow-release low-dose niacin-bezafibrate combination.

The effect of different routes and modes of administration of niacin (nicotinic acid) on its hypolipidaemic activity has been evaluated. Our working hypothesis was that the major sites of niacin action are located presystemically (i.e. in the gut wall or the liver, or both) which would make niacin a gastrointestinal drug. For such drugs continuous administration to the gastrointestinal tract is expected to augment their efficacy compared with bolus oral administration or parenteral administration. The hypothesis was examined in two rat models of experimentally induced hyperlipidaemia—Model A, based on a cholesterol-enriched diet, and Model B, in which acute hyperlipidaemia is induced by intraperitoneal administration of triton (225 mg kg−1). Continuous administration of niacin into the duodenum at 1.66 mg h−1 (total dose 40 mg kg−1 day−1) for up to 7 days (Model A) or at 2.22 mg h−1 over 18 h (Model B) had significantly greater lipid-reducing effects both on total cholesterol and on triglyceride levels (15–25%) and elevation of high-density lipoprotein (HDL) cholesterol levels than did bolus oral administration of the same dose. Continuous duodenal infusion of niacin also had an even greater lipid-reducing effect than continuous intravenous infusion of the drug at the same rate and dose. The results indicate that the site(s) of action are located presystemically and that continuous duodenal administration of a low dose of niacin (40 mg kg−1) has a greater lipid-lowering effect than a higher dose (200 mg kg−1) administered by peroral bolus administration. These conclusions were validated by administration of a specially designed niacin sustained-release matrix tablet formulation that was non-invasively administered to hyperlipidaemic rats. The hypolipidaemic activity of the sustained-release tablet was of similar magnitude to that resulting from continuous duodenal administration, thus providing a pharmacodynamic rationale for this mode of administration.

There is recent evidence that deprenyl may have anticonvulsant action in a rat kindling model of epilepsy as well as in a maximal electroshock model. We therefore investigated the effect of deprenyl on the brain sensitivity threshold to pentylenetetrazol (PTZ)-induced maximal seizures in Lewis rats, in a model that provides pharmacodynamic information free of pharmacokinetic interference. The novel finding of this investigation was the anticonvulsant effect of deprenyl following repetitive administration whereas a single deprenyl dose did not affect the PTZ concentrations required to induce maximal seizures. The data suggests that the mechanism of this effect is not associated with the dopaminergic activity of deprenyl since pretreatment with both bromocriptine (a dopamine D2 agonist) and haloperidol (dopamine antagonist) did not affect the seizure threshold, whereas levodopa caused a proconvulsant effect. It was also concluded that the mechanism is not related to changes in acetylcholine levels since prolonged pretreatment with deprenyl did not attenuate the brain sensitivity to pilocarpine-induced seizures. The fact that long term administration of deprenyl was needed to produce its anticonvulsant effect may indicate that the anticonvulsant effect of deprenyl may be due to changes in levels of certain endogenous compounds or down or up-regulation of relevant receptor/effector units.