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Little is known about the regulatory effects of steroid hormones on the intestinal H(+)/oligopeptide transporter PEPT1. In the present study, we investigated the effects of progesterone and its related compounds on the uptake of cephalexin, a typical PEPT1 substrate, using the human intestinal cell line Caco-2. Caco-2 cell monolayers were cultured on plastic cell culture plates coated with rat tail collagen type I. The determination of cephalexin uptake was performed with HPLC. To investigate the effect of progesterone treatment on cephalexin uptake, the monolayers were incubated with cephalexin after progesterone treatment. Progesterone decreased cephalexin uptake in a concentration-dependent manner, and the IC(50) value was calculated to be 2.3 microM. A significant decrease in cephalexin uptake was observed after progesterone treatment for 12 h, and the decrease was maximal when the monolayers were treated for 24-72 h. Cephalexin uptake was significantly inhibited by treatments with 17alpha-hydroxyprogesterone, norethisterone, and chlormadinone. By contrast, treatment with dehydroepiandrosterone, pregnenolone, estradiol, testosterone, hydrocortisone, and dexamethasone did not affect cephalexin uptake. The effects of progesterone and norethisterone treatment on the kinetic parameters of cephalexin uptake were investigated. The saturable component of cephalexin uptake was markedly inhibited by progesterone and norethisterone treatments. The J(max) of cephalexin uptake with progesterone and norethisterone treatments was significantly decreased compared with the control, whereas K(m) and K(d) values were not affected. Therefore the quantitative decrease in PEPT1 density is considered to be one cause of the decrease in cephalexin uptake with progesterone and norethisterone treatments.

The aim of this study was to investigate whether the concomitant administration of the substrates or inhibitors of PEPT1, OCTN1, OCTN2, and P-glycoprotein affects the intestinal absorption of sulpiride in rats. The absorption of sulpiride from rat intestine was decreased by the substrates or inhibitors of PEPT1, OCTN1, and OCTN2. On the other hand, the absorption was increased by the substrates of P-glycoprotein. The effects of these concomitantly administered drugs on the pharmacokinetic behavior of sulpiride after oral administration in rats were investigated. Peak concentration (C(max)) and area under the plasma concentration-time curve (AUC(0-8 h)) of sulpiride were decreased by the concomitant administration of the substrates or inhibitors of PEPT1, OCTN1, and OCTN2. However, the same parameters were significantly increased by the concomitant administration of the substrates of P-glycoprotein. The present results suggest the possibility of drug-drug interaction during the absorption process in the small intestine due to the coadministration of sulpiride and these agents. These findings provide important information for preventing adverse effects and for ensuring the effectiveness of sulpiride and concomitantly administered drugs.

KV-2920 is a novel acyl-CoA: cholesterol acyltransferase (ACAT) inhibitor. To confirm the efficacy of KV-2920-low density lipoprotein (LDL) complex (KV-LDL complex) as a drug-carrier complex on experimental atherosclerosis, we examined its inhibitory effects in vitro and in vivo. LDL was isolated from human plasma and the KV-LDL complex was prepared by incubation in the presence of Celite 545. The complex contained about 800 mol KV-2920 in 1 mol LDL. The cholesterol levels in the serum and aorta of atherogenic mice after 14 weeks of feeding were significantly higher than those of nonatherogenic mice. With the intravenous injection of KV-LDL complex, although the cholesterol levels in the serum were not influenced, the level of cholesterol ester in the aorta of atherogenic mice was significantly reduced. The concentration of cholesterol ester in the macrophages derived from ICR mice was predominantly increased by incubation with LDL for 48 h, this increase was significantly inhibited by incubation with KV-LDL complex. Moreover, the complex also inhibited the increase of cholesterol ester in macrophages following incubation with oxidized LDL. These findings suggest that KV-LDL complex inhibits the foam cell formation of macrophages though action of KV-2920 as an ACAT inhibitor, and prevents the accumulation of cholesterol ester in the aorta of atherogenic mice. Therefore, KV-LDL complex may be useful as a drug-carrier complex in antiatherosclerotic therapy.

We investigated whether the uptake of a specific antipsychotic agent, sulpiride, in Caco-2 cells is mediated by a carrier-mediated system. Caco-2 cell monolayers were cultured in plastic culture dishes and uptake and efflux studies were conducted. The determination of sulpiride was performed by HPLC. At 37 degrees C, sulpiride uptake in pH 6.0 was twice as much as in pH 7.4. At 4 degrees C, however, no significant difference was observed between pH 6.0 and 7.4. The uptake at 4 degrees C was markedly lower than that obtained at 37 degrees C. The subtraction of the uptake at 4 degrees C from the uptake at 37 degrees C indicated a saturable process, and the result of the Eadie-Hofstee plot analysis indicated that the uptake consists of two or more saturable components. The uptake was significantly inhibited by uncoupler, protonophore, amino acid modifying agent and proteinase. Sulpiride efflux was temperature-dependent and was significantly inhibited by uncoupler and amino acid modifying agent. These findings indicate that sulpiride uptake and efflux in Caco-2 cells are carrier-mediated. Furthermore, the uptake was significantly decreased by some substrates and inhibitors of peptide transporter, PEPT1, and organic cation transporters, OCTN1 and OCTN2, and was significantly increased by preloading with them. The uptake was also significantly increased by a typical substrate of P-glycoprotein. From these findings, we presumed that peptide transporter PEPT1 and organic cation transporters OCTN1 and OCTN2 are involved with this uptake. P-glycoprotein may also contribute to the efflux of sulpiride.

Effect of acetazolamide (AZA) on the anticonvulsant potency of several antiepileptics was investigated in mice by maximal electroshock seizure test. By the coadministration of AZA, a remarkable increase in the anticonvulsant activity was brought about not only for the barbiturates including barbital (BA), mephobarbital (MB) and metharbital (MET), but also for the other antiepileptics such as phenytoin (PHT), valproic acid (VPA) and trimethadione (TMO). This potentiating effect of AZA, however, was relatively weak for PHT, MET and TMO (about 2.5 fold) in contrast to those for phenobarbital (PHB), BA, MB and VPA (4-5 fold). The brain-serum concentration ratio (B/S) of PHB was elevated by the coadministration of AZA, while the B/S of PHT was not changed. Thus it was inferred that the difference in the potentiating effect of AZA on the activity of the antiepileptics was due to the difference in its effect on the brain levels of the antiepileptic drugs. However, the potentiating effect of AZA was still observed for PHT, VPA and MET, as well as PHB, in reserpinized mice. Therefore, some pharmacodynamic effect of AZA other than its increasing effect on the brain levels of the antiepileptic drugs may partly contribute to the potentiation of the activity of the antiepileptic drugs.

When the mice were treated with acetazolamide (AZA) 30 min before the administration of pentobarbital, the sleeping time was prolonged. At the moment of awakening from sleep, no change in the brain level of pentobarbital was observed by the AZA pretreatment, which suggests the constant brain sensitivity to the barbiturate. At that time, the plasma level was lowered by the AZA pretreatment. Pentobarbital had no effect on a carbonic anhydrase activity in brain inhibited by AZA. The results similar to those were obtained also in thiopental and norhexobarbital. Thus it was inferred that the prolongation of barbiturate sleep in mice pretreated with AZA is due to a decrease in the rate of removal of the barbiturate from the brain, through brain carbonic anhydrase inhibition followed by the lowering of cerebrospinal fluid flow. Hexobarbital sleeping time was shortened by the AZA pretreatment. At awakening, the brain hexobarbital level was somewhat, but not significantly, increased and the plasma level was significantly raised by the AZA pretreatment. Brain carbonic anhydrase inhibited by AZA was restored to control level with hexobarbital dosing. There seemed to be some particular interaction between AZA and hexobarbital in brain, which may be related to difference in barbiturate structures including N-methyl group.

In the previous paper, acetazolamide (AZA) was reported to shorten the hexobaribital sleeping time, while prolonging the norhexobarbital (NHB) sleeping time in mice. Since AZA was found to prolong the sleeping time induced with metharbital (MET) and mephobarbital (MB) as well as barbital (BA) and phenobarbital (PHB) in this study, N-methylation of barbiturates does not appear to be a critical factor in the action of AZA. The induction times of the five barbiturates, including NHB, were shortened by AZA pretreatment. At the moment of awakening from sleep, the brain level of BA was the same as that without the AZA pretreatment, which suggests unchanged brain sensitivity to the barbiturate. At that time, however, the plasma level was reduced in the case of AZA pretreatment. Similar results were obtained with PHB, MET, and MB. Thus, the prolongation of barbiturate sleep and shortening of the induction time are probably due to a decrease in the rate of removal of the barbiturates from the brain due to the reduction of cerebrospinal fluid flow and/or the inhibition of a system for acid transport out of the brain.