Search

Microalgae are an excellent source of valuable compounds for nutraceutical and cosmeceutical applications. These photosynthesizing microorganisms are amenable for large-scale production, thus overcoming the bottleneck of biomass supply for chemical and activity characterization of bioactive compounds. This characteristic has recently also prompted the screening of microalgae for potential pharmaceutical applications. Here, we show that monoacylglycerides (MAGs) purified from the marine diatom Skeletonema marinoi have selective cytotoxic activity against the haematological cancer cell line U-937 and colon cancer cell line HCT-116 compared to normal MePR-2B cells. LC-MS analysis of the raw extract revealed that in their natural form, MAGs occur as 2-monoacyl derivatives and include mainly C16 and C20 analogues, but they are converted into the corresponding 1-isomers during purification processes. Pure compounds along with the synthetic 1-monoarachidonoylglycerol tested on HCT-116 and U-937 tumor cell lines induced cell death via apoptosis. The mechanism of action was investigated, and we show that it involves the induction of apoptosis through caspase 3/7 activation. These findings pave the way for the possible use of these molecules as potential anticancer agents or as precursors for the generation of new and more potent and selective compounds against tumor cells.

Pregnane-X-receptor (PXR) is a member of nuclear receptors superfamily that activates gene transcription by binding to responsive elements in the promoter of target genes. PXR is a master gene orchestrating the expression/activity of genes involved in the metabolism of endobiotics including bilirubin, bile acids, glucose and lipid. In addition PXR oversights the metabolism of the large majority of xenobiotics including a large amount of prescribing drugs. Thus, developing PXR ligands represents a great opportunity for a therapeutic intervention on human diseases including diabetes, obesity, dyslipidemias and liver disorders. To this end, natural compounds represent an arsenal of new chemical scaffolds useful for the identification of novel PXR ligands. Here, we report a series of 4-methylenesteroid derivatives isolated from Theonella marine sponges as novel PXR modulators. In addition, combining medicinal chemistry, pharmacological experiments and computational studies, we have investigated the effects of different modifications on ring A and on the side chain of 4-methylenesteroid derivatives toward PXR modulation. This study provides the molecular bases of ligand/PXR interaction useful for designing novel PXR modulators., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

Using theonellasterol as a novel FXR antagonist hit, we prepared a series of semi-synthetic derivatives in order to gain insight into the structural requirements for exhibiting antagonistic activity. These derivatives are characterized by modification at the exocyclic carbon-carbon double bond at C-4 and at the hydroxyl group at C-3 and were prepared from theonellasterol using simple reactions. Pharmacological investigation showed that the introduction of a hydroxyl group at C-4 as well as the oxidation at C-3 with or without concomitant modification at the exomethylene functionality preserve the ability of theonellasterol to inhibit FXR transactivation caused by CDCA. Docking analysis showed that the placement of these molecules in the FXR-LBD is well stabilized when on ring A functional groups, able to form hydrogen bonds and π interactions, are present.

Seven synthetic analogues of the PXR (pregnane-X-receptor) potent natural agonist solomonsterol A were prepared by total synthesis. Their activity toward PXR was assessed by transactivation and RT-PCR assays. The study discloses cholestan disulfate (8) as a new, simplified agonist of PXR. By in vitro studies on hepatic cells we have demonstrated that this compound is a potent PXR agonist and functional characterization in human macrophages and hepatic stellate cells provided evidence that cholestan disulfate (8) has the ability to modulate the immune response triggered by bacterial endotoxin as well as to counter-activate hepatic stellate cell activation induced by thrombin. Because inhibition of immune-driven circuits might have relevance in the treatment of inflammation and liver fibrosis, the present data support the development of cholestan disulfate (8) in preclinical models of inflammatory diseases.

We report the isolation and the structural elucidation of a family of polyhydroxylated steroids from the marine sponge Theonella swinhoei. Decodification of interactions of these family with nuclear receptors shows that these steroids are potent agonists of human pregnane-X-receptor (PXR) and antagonists of human farnesoid-X-receptor (FXR) with the putative binding mode to nuclear receptors (NRs) obtained through docking experiments. By using monocytes isolated from transgenic mice harboring hPXR, we demonstrated that swinhosterol B counter-regulates induction of pro-inflammatory cytokines in a PXR-dependent manner. Exposure of CD4(+) T cells to swinhosterol B upregulates the expression of IL-10 causing a shift toward a T cells regulatory phenotype in a PXR dependent manner. These results pave the way to development of a dual PXR agonist/FXR antagonist with a robust immunomodulatory activity and endowed with the ability to modulate the expression of bile acid-regulated genes in the liver., (Copyright © 2012 Elsevier Inc. All rights reserved.)

We report the isolation and pharmacological characterization of conicasterol E isolated from the marine sponge Theonella swinhoei. Pharmacological characterization of this steroid in comparison to CDCA, a natural FXR ligand, and 6-ECDCA, a synthetic FXR agonist generated by an improved synthetic strategy, and rifaximin, a potent PXR agonist, demonstrated that conicasterol E is an FXR modulator endowed with PXR agonistic activity. Conicasterol E induces the expression of genes involved in bile acids detoxification without effect on the expression of small heterodimer partner (SHP), thus sparing the expression of genes involved in bile acids biosynthesis. The relative positioning in the ligand binding domain of FXR, explored through docking calculations, demonstrated a different spatial arrangement for conicasterol E and pointed to the presence of simultaneous and efficient interactions with the receptor. In summary, conicasterol E represents a FXR modulator and PXR agonist that might hold utility in treatment of liver disorders.

Recently, we reported the identification of a novel class of pregnane-X-receptor (PXR) agonists, solomonsterols A and B, isolated from the marine sponge Theonella swinhoei. Preliminary pharmacological studies demonstrated that these natural compounds are potential leads for the treatment of human disorders characterized by dysregulation of innate immunity. In this article, we describe the first total synthesis of solomonsterol A and its in vivo characterization in animal models of colitis. Using transgenic mice expressing the human PXR, we found that administration of synthetic solomonsterol A effectively protects against development of clinical signs and symptoms of colitis and reduced the generation of TNFα, a signature cytokine for this disorder. In addition, we have provided the first evidence that solomonsterol A might act by triggering the expression of TGFβ and IL-10, potent counter-regulatory cytokines in inflammatory bowel diseases (IBD). Finally, we have shown that solomonsterol A inhibits NF-κB activation by a PXR dependent mechanism. In summary, solomonsterol A is a marine PXR agonist that holds promise in the treatment of inflammation-driven immune dysfunction in clinical settings.

Silica gel column chromatography, followed by HPLC purification on the apolar fraction of the methanol extract of marine sponge Theonella swinhoei, resulted in the isolation of a library of 10 polyhydroxylated steroids which we named theonellasterols B-H (1-7) and conicasterols B-D (8-10). The structures were determined on the basis of extensive spectroscopic data (MS, (1)H and (13)C NMR, COSY, HSQC, HMBC, and ROESY) analysis, and the putative binding mode to nuclear receptors (NRs) has been obtained through docking calculations. Pharmacological and structure-activity relationship analysis demonstrate that these natural polyhydroxylated steroids are potent ligands of human nuclear pregnane receptor (PXR) and modulator of farnesoid-X-receptor (FXR). In addition, the molecular characterization of theonellasterol G allowed the identification of the first FXR modulator and PXR ligand so far identified. Exposure of liver cells to this agent resulted in potent induction of PXR-regulated genes and modulation of FXR-regulated genes, highlighting its pharmacological potential in the treatment of liver disorders.