In sickness and in health: Corneal epithelial stem cell biology, pathology and therapy.

Our window to the world is provided by the cornea on the front surface of the eye. The integrity and functionality of the outermost corneal epithelium is essential for vision. A population of limbal epithelial stem cells (LESCs) are responsible for maintaining the epithelium throughout life by providing a constant supply of daughter cells that replenish those constantly lost from the ocular surface during normal wear and tear and following injury. LESC deficiency leads to corneal opacification, inflammation, vascularization and discomfort (Daniels et al., 2001, 2007). Cultured LESC delivery is one of several examples of successful adult stem cell therapy in patients. The clinical precedence for use of stem cell therapy and the accessibility of the transparent stem cell niche make the cornea a unique model for the study of adult stem cells in physiological conditions as well as in disease.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. 5. 6-(Fluoren-9-yl)- and 6-(fluoren-9-ylidenyl)-3,5-dihydroxyhexanoic acids and their lactone derivatives.

A limited study was conducted to determine the biological consequences of rendering the phenyl rings of the previously reported 7-(3,5-disubstituted [1,1'-biphenyl]-2-yl)-3,5-dihydroxy-6-heptenoic acids coplanar. Such constraint substantially diminished intrinsic HMG-CoA reductase inhibitory activity.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. 8. Side chain ether analogues of lovastatin.

A general route for preparing side chain ether analogues of lovastatin is presented. These analogues proved to be weaker inhibitors of HMG-CoA reductase than the corresponding side chain ester analogues. Interestingly, inhibitory potency was enhanced markedly when the 4-fluoro group was incorporated in the aromatic moiety of the side chain benzyl group of 2d.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. 1. Structural modification of 5-substituted 3,5-dihydroxypentanoic acids and their lactone derivatives.

A series of 5-substituted 3,5-dihydroxypentanoic acids and their derivatives have been prepared and tested for inhibition of HMG-CoA reductase in vitro. In general, unless a carboxylate anion can be formed and the hydroxy groups remain unsubstituted in an erythro relationship, inhibitory activity is greatly reduced. Furthermore, only one enantiomer of the ring-opened form of lactone 6a(+/-) possesses the activity displayed by the racemate. Insertion of a bridging unit other than ethyl or (E)-ethenyl between the 5-carbinol moiety and an appropriate lipophilic moiety (e.g., 2,4-dichlorophenyl) attenuates activity.

3-Hydroxy-3-methylglutaryl-coenzyme a reductase inhibitors. 7. Modification of the hexahydronaphthalene moiety of simvastatin: 5-oxygenated and 5-oxa derivatives.

Modification of the hexahydronaphthalene ring 5-position in simvastatin 2a via oxygenation and oxa replacement afforded two series of derivatives which were evaluated in vitro for inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and acutely in vivo for oral effectiveness as inhibitors of cholesterogenesis in the rat. Of the compounds selected for further biological evaluation, the 6 beta-methyl-5-oxa 10 and 5 alpha-hydroxy 16 derivatives of 3,4,4a,5-tetrahydro 2a, as well as, the 6 beta-epimer 14 of 16 proved orally active as hypocholesterolemic agents in cholestyramine-primed dogs. Subsequent acute oral metabolism studies in dogs demonstrated that compounds 14 and 16 evoke lower peak plasma drug activity and area-under-the-curve values than does compound 10 and led to the selection of 14 and 16 for toxicological evaluation.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. 2. Structural modification of 7-(substituted aryl)-3,5-dihydroxy-6-heptenoic acids and their lactone derivatives.

A series of 7-(substituted aryl)-3,5-dihydroxy-6-heptenoic (heptanoic) acids and their lactone derivatives have been prepared and tested for inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase in vitro. A systematic exploration of the structure-activity relationships in this series led to the synthesis of (+)-trans-(E)-6-[2-[2,4-dichloro-6-[(4-fluorophenyl) methoxyl]phenyl]ethyl]-3,4,5,6-tetrahydro-4-hydroxy-2H-pyran-2-one (66(+)), which has one-half of the inhibitory activity of compactin.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. 3. 7-(3,5-Disubstituted [1,1'-biphenyl]-2-yl)-3,5-dihydroxy-6-heptenoic acids and their lactone derivatives.

The syntheses of a series of 7-(3,5-disubstituted [1,1'-bephenyl]-2-yl)-3,5-dihydroxy-6-heptenoic acids and their lactones are reported. Intrinsic 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitory activity is enhanced markedly when the biphenyl moiety is substituted by chloro or methyl groups at positions 3 and 5 and a fluoro group at position 4'. These substitutions, followed by resolution, provided compounds 100(+) and 110(+) with 2.8 times the intrinsic inhibitory activity of compactin. Compound 100(+) was shown to possess the same chirality in the lactone ring as compactin by single-crystal X-ray crystallography.

Studies on cholesterol esterification in human tissues.

In vitro cholesteryl synthesis from oleic acid [1-14C] was studied with enzyme preparations from human thoracic aorta and liver. Results from studies on the properties of the esterifying system provide good evidence that the mechanism involves fatty acyl-CoA-cholesterol acyl transferase. In studies on human thoracic aorta with varying degrees of atherosclerotic disease, and pairs of normal and diseased aorta from the same subject, there was no obvious relationship between aortic cholesteryl esterifying activity and severity of atheroma. Normal aorta from two young males, presumably free of atherosclerosis, had relatively very low esterifying activity. In the six liver samples tested, there was negligible esterifying activity, in contrast to the high activity seen in the case of rat liver. For the thin layer chromatographic isolation of the labeled cholesteryl oleate a solvent system of isooctane:diethyl ether (100:6) was found to give a better separation of the ester than the petroleum ether: diethylether:acetic acid system generally used.

Effect of three bile acid binding polymers on the biosynthesis of 14C-cholesterol from 14C-sodium acetate in the rat.

The relative activity of three bile acid binding polymers in increasing cholesterol biosynthesis in the rat from 14C-acetate was determined by measuring blood levels of 14C-cholesterol after intraperitoneally administered 14C-acetate. CAT-FLOC and 3,3-ionene were 4-5 times more active than cholestyramine in this study which correlated well with the results of hypocholesteremic testing in dogs.

A new platelet aggregation inhibitor which possesses hypolipemic and uricosuric properties, 2-[3-(2-thiazolylthio)phenyl]propionic acid (TPA).

In vitro, 2-[3-(2-thiazolylthio)phenyl]propionic acid (TPA) at plasma concentrations ranging from 0.02 to 1.0 microgram/ml prevents aggregation of human platelets induced by various aggregating agents. Oral administration of TPA to guinea pigs inhibits platelet aggregation; the estimated dose to reduce aggregation by 50% is 0.3 mg/kg. TPA protects rabbits against arachidonate-induced thromboembolic death (50% protection at 0.79 mg/kg i.p.). TPA is a potent hypotriglyceridemic agent in rats when present in the diet in concentrations as low as 0.003%. In chimpanzees, TPA is uricosuric at oral doses of 0.625 and 2.5 mg/kg. This rare combination of pharmacological properties suggests that TPA is a potentially useful antithrombotic agent.