Evaluation of hydrophobic/hydrophilic balance of bile acids by comparative molecular field analysis (CoMFA)

Catanionic gels based on cholic acid derivatives

In this paper, the preparation and characterization of an anionic and a cationic surfactant obtained by chemical modifications of a natural bile acid (cholic acid) are reported. The bile acid was modified by introducing a diamine or a dicarboxylic aromatic residue on the lateral chain. The pure cationic surfactant self-assembles in a network of fibers with a cross-section gyration radius of about 15.1 Å, providing hydrogels with a pH-dependent compactness. On the other hand, the anionic molecule gives rise to prolate ellipsoid micelles. Homogeneous catanionic mixtures have also been obtained, with molar fraction of each surfactant ranging from 0.125 to 0.875. At total surfactant concentration of 0.05% (w/v), the mixtures form gels of fibrils partially arranged in secondary twisted superstructures. Comparison of this concentration with the minimum gelation concentration of the pure cationic derivative (0.16% w/v) suggests that, in the mixtures, the presence of the electrostatic component in self-assembly of the molecules allows the formation of gels starting from more dilute samples. In view of these achievements, this work suggests that catanionic mixtures can be exploited to enhance the efficiency of gelators.

Anticancer steroids: linking natural and semi-synthetic compounds

Steroids, a widespread class of natural organic compounds occurring in animals, plants and fungi, have shown great therapeutic value for a broad array of pathologies. The present overview is focused on the anticancer activity of steroids, which is very representative of a rich structural molecular diversity and ability to interact with various biological targets and pathways. This review encompasses the most relevant discoveries on steroid anticancer drugs and leads through the last decade and comprises 668 references.

Bile acid toxicity structure-activity relationships: correlations between cell viability and lipophilicity in a panel of new and known bile acids using an oesophageal cell line (HET-1A)

The molecular mechanisms and interactions underlying bile acid cytotoxicity are important to understand for intestinal and hepatic disease treatment and prevention and the design of bile acid-based therapeutics. Bile acid lipophilicity is believed to be an important cytotoxicity determinant but the relationship is not well characterized. In this study we prepared new azido and other lipophilic BAs and altogether assembled a panel of 37 BAs with good dispersion in lipophilicity as reflected in RPTLC RMw. The MTT cell viability assay was used to assess cytotoxicity over 24 h in the HET-1A cell line (oesophageal). RMw values inversely correlated with cell viability for the whole set (r2=0.6) but this became more significant when non-acid compounds were excluded (r2=0.82, n=29). The association in more homologous subgroups was stronger still (r2>0.96). None of the polar compounds were cytotoxic at 500 microM, however, not all lipophilic BAs were cytotoxic. Notably, apart from the UDCA primary amide, lipophilic neutral derivatives of UDCA were not cytotoxic. Finally, CDCA, DCA and LagoDCA were prominent outliers being more toxic than predicted by RMw. In a hepatic carcinoma line, lipophilicity did not correlate with toxicity except for the common naturally occurring bile acids and their conjugates. There were other significant differences in toxicity between the two cell lines that suggest a possible basis for selective cytotoxicity. The study shows: (i) azido substitution in BAs imparts lipophilicity and toxicity depending on orientation and ionizability; (ii) there is an inverse correlation between RMw and toxicity that has good predictive value in homologous sets; (iii) lipophilicity is a necessary but apparently not sufficient characteristic for BA cytocidal activity to which it appears to be indirectly related.

Bile acids: Chemistry, physiology, and pathophysiology

The family of bile acids includes a group of molecular species of acidic steroids with very peculiar physical-chemical and biological characteristics. They are synthesized by the liver from cholesterol through several complementary pathways that are controlled by mechanisms involving fine-tuning by the levels of certain bile acid species. Although their best-known role is their participation in the digestion and absorption of fat, they also play an important role in several other physiological processes. Thus, genetic abnormalities accounting for alterations in their synthesis, biotransformation and/or transport may result in severe alterations, even leading to lethal situations for which the sole therapeutic option may be liver transplantation. Moreover, the increased levels of bile acids reached during cholestatic liver diseases are known to induce oxidative stress and apoptosis, resulting in damage to the liver parenchyma and, eventually, extrahepatic tissues. When this occurs during pregnancy, the outcome of gestation may be challenged. In contrast, the physical-chemical and biological properties of these compounds have been used as the bases for the development of drugs and as pharmaceutical tools for the delivery of active agents.

Xanthomonas maltophilia CBS 897.97 as a source of new 7beta- and 7alpha-hydroxysteroid dehydrogenases and cholylglycine hydrolase: improved biotransformations of bile acids

The paper reports the partial purification and characterization of the 7beta- and 7alpha-hydroxysteroid dehydrogenases (HSDH) and cholylglycine hydrolase (CGH), isolated from Xanthomonas maltophilia CBS 897.97. The activity of 7beta-HSDH and 7alpha-HSDH in the reduction of the 7-keto bile acids is determined. The affinity of 7beta-HSDH for bile acids is confirmed by the reduction, on analytical scale, to the corresponding 7beta-OH derivatives. A crude mixture of 7alpha- and 7beta-HSDH, in soluble or immobilized form, is employed in the synthesis, on preparative scale, of ursocholic and ursodeoxycholic acids starting from the corresponding 7alpha-derivatives. On the other hand, a partially purified 7beta-HSDH in a double enzyme system, where the couple formate/formate dehydrogenase allows the cofactor recycle, affords 6alpha-fluoro-3alpha, 7beta-dihydroxy-5beta-cholan-24-oic acid (6-FUDCA) by reduction of the corresponding 7-keto derivative. This compound is not obtainable by microbiological route. The efficient and mild hydrolysis of glycinates and taurinates of bile acids with CGH is also reported. Very promising results are also obtained with bile acid containing raw materials.

Three-dimensional, quantitative-structure-property-relationship study of aqueous solubility for phenylsulfonyl carboxylates using comparative-molecular-field analysis and comparative-molecular-similarity-indices analysis

With both the comparative-molecular-field analysis (CoMFA) and the comparative-molecular-similarity-indices analysis (CoMSIA), the paper describes two five-component, three-dimensional, quantitative-structure-property-relationship (3D-QSPR) models for the aqueous solubility logSw (Sw, mol x L(-1)) of 52 phenylsulfonyl carboxylates. Two models yield the leave-one-out cross-validated correlation coefficient q2 values 0.851 and 0.821, and the conventional correlation coefficient r2 values 0.963 and 0.929, respectively. The achievement of high q2 and r2 values of the CoMFA model indicates the significance of correlation of steric and electrostatic fields with the aqueous solubility. The key features in the CoMFA contour maps are critical to trace the important properties and gain insight to the solvation mechanism of tested compounds. The quality of CoMSIA model is slightly lower than that of CoMFA in terms of q2 and r2 values. Not requiring molecular superposition, CoMSIA may be faster than CoMFA in data processing.

7alpha-OH epimerisation of bile acids via oxido-reduction with Xanthomonas maltophilia

The microbial 7alpha-OH epimerisation of cholic, chenodeoxycholic, and 12-ketochenodeoxycholic acids (7alpha-OH bile acids) with Xanthomonas maltophilia CBS 827.97 to corresponding 7beta-OH derivatives with scarcity of oxygen is described. With normal pressure of oxygen the 7-OH oxidation products are obtained. No biotransformations are achieved in anaerobic conditions. The microbial 7alpha-OH epimerisation is achieved by oxidation of 7-OH function and subsequent reduction. Partial purification, in fact, of the enzymatic fraction revealed the presence of two hydroxysteroid dehydrogenases (HSDH) alpha- and beta-stereospecific together with a glycocholate hydrolase. On the basis of these results a further application is the microbial reduction of 6alpha-fluoro and 6beta-fluoro-3alpha-hydroxy-7-oxo-5beta-cholan-24-oic acid methyl esters to the corresponding 7alpha-OH and 7beta-OH derivatives.