Kwok-Pui Fung

Morin hydrate is a plant-derived and antioxidant-based hepatoprotector.

Morin hydrate, or simply morin, is shown here to be an effective hepatoprotector in vitro and in vivo. Between 0.25-2.0 mM, morin prolongs survival of rat hepatocytes against free radical damage triggered by xanthine oxidase-hypoxanthine, and substantially better than equimolar concentrations of Trolox (a vitamin E analogue), mannitol, and ascorbate. In a rat model of 80 min ischemia-24 h reperfusion in the liver, infusion of morin at 2.5, 5.0 and 10 mumol/Kg body weight before reperfusion reduces liver necrosis in the placebo control by 51.48 +/- 9.94%, 66.55 +/- 2.18%, and 79.37 +/- 11.03%, respectively, for n = 6 per group. Mechanistically, morin acts in a two-pronged manner: as a preventive antioxidant by partially inhibiting xanthine oxidase and partly as a curative antioxidant by scavenging oxyradicals. The role of morin as an effective free radical scavenger is further evidenced by its ability to protect human red cell membrane from peroxidative attack better than ascorbate, Trolox, and mannitol. Collectively, our data demonstrate that morin is an effective hepatoprotector, both in cultured cells and in hepatic ischemia-reperfusion.

Molecular properties and myocardial salvage effects of morin hydrate

Morin hydrate is a bioactive pigment found in yellow Brazil wood. Recently, we reported that morin hydrate prolongs the survival of three types of cells from the human circulatory system against oxyradicals generated in vitro. The protection excels that given by equimolar concentrations of ascorbate, mannitol, and Trolox. Here, we demonstrate that, in vivo, morin hydrate at 5 mumol/kg actually reduced by > 50% the tissue necrosis in post-ischemic and reperfused rabbit hearts. Mechanistically, morin hydrate not only scavenges oxyradicals, but also moderately inhibits xanthine oxidase, a free-radical generating enzyme from the ischemic endothelium. Among other possibilities, morin hydrate appears to chelate some metal ions (e.g. Fe2+) in oxyradical formation, although this needs to be examined further. Nuclear magnetic resonance (at 500 mHz) and electron-impact mass spectrometry also supported a molecular formula of C15H10O7 for morin hydrate. Only by X-ray crystallography was it clearly revealed that there are two water molecules attached by intermolecular hydrogen bonds to a morin molecule. Also, the three rings of morin hydrate approach coplanarity. This conformation favours a delocalization of electrons after oxyradical reduction, making morin an effective antioxidant. Thus, we have documented some of the molecular properties and myocardial salvage effects of morin hydrate.

Morin hydrate protects cultured rat glomerular mesangial cells against oxyradical damage

Cultured rat glomerular mesangial cells were damaged when exposed to oxyradicals generated either from xanthine oxidase plus hypoxanthine, or by superoxide radicals formed from menadione. Morin hydrate is an antioxidant extracted from yellow Brazil wood. When morin hydrate was added to cultured rat glomerular mesangial cells which were attacked by oxyradicals generated by xanthine oxidase plus hypoxanthine, the survival time of the cells was doubled. However, this protective effect of morin hydrate was less marked when the cells were attacked by menadione. Note that the protective effects of Trolox which is a polar analogue of vitamin E were miniscule relative to those of morin hydrate with both oxidants.

Antioxidation of human low density lipoprotein by horin hydrate

Oxidative modification of low density lipoprotein (LDL) has been suggested to be a risk factor for the development of atherosclerosis. Agents which can protect LDL from oxidation may be useful in preventing atherogenesis. Here, we found that morin hydrate, at 100 microM concentration, effectively inhibits Cu(2+)-induced oxidation of LDL. The oxidation of LDL was assessed by agarose gel electrophoresis. This was further studied by measuring the increased values of the malondialdehyde equivalents and the decreased numbers of reactive amino groups on oxidized LDL. Trolox, at equimolar concentrations, exhibit similar effects in preventing oxidation of LDL.

Molecular structure and antioxidant specificity of purpurogallin in three types of human cardiovascular cells.

Purpurogallin (PPG) in an active cytoprotector found in certain oak barks. We have shown that PPG prolongs the survival of cultured cardiocytes from rats and rabbits against different oxidants better than do antioxidants such as Trolox (a hydrophilic analogue of vitamin E) in a morphometric assay system. First, we verified by X-ray crystallography that PPG is a bicyclic molecule comprising a phenolic ring fused with a seven-membered ring in a highly planar conformation. In analogues of PPG wherein the two double bonds in the seven membered ring of the parent molecule are saturated or where the four OH groups of the parent compound are substituted by four OCH3 groups, the derivatives are less planar and less protective of the human cells than native PPG. Second, PPG in a concentration-dependent manner protected myocytes and endothelial cells of humans against oxyradicals generated with any one of the following oxyradical generators: (a) xanthine oxidase plus hypoxanthine, (b) menadione, or (c) paraquat. In each case, PPG was more cytoprotective than comparative antioxidants. Also, PPG protected erythrocytes against peroxyl radicals better than the two PPG derivatives mentioned. Third, the cytoprotective action of PPG detected in vitro was accompanied by declines of malondialdehyde. Finally, we observed that PPG chelated ferrous ions and, therefore, can suppress the formation of radicals in the Fenton reaction. Thus, PPG with its molecular architecture and presumably its affinity for ferrous ions protects multiple types of cardiovascular cells against oxyradicals.

Radiochemical quantitation of conjugated dienes in rat hepatocytes exposed to oxyradicals

Conjugated dienes are fingerprint signatures of oxidant damage in cells. We used a radiochemical method based on the Diels-Alder reaction of 14C-labeled tetracyanoethylene with conjugated dienes to delineate the changes of its levels in ischemia-reperfusion in the rat liver. To more directly illustrate the kinetics of diene appearance in hepatocytes, we have applied the same radiochemical assay to rat hepatocytes exposed to xanthine oxidase and hypoxanthine. We observed that the conjugated dienes rose to a maximum under our condition at approximately 10 min, while Trolox--an antioxidant derived from vitamin E found previously to protect rat hepatocytes from oxyradical damage (2)--markedly reduced the formation of conjugated dienes.

Chemical syntheses of Trolox conjugates which protect human ventricular myocytes against in situ-generated oxyradicals.

Synthetic conjugates of the antioxidant Trolox (6-hydroxy-2,5,7,8-tetramethyl chroman-2-carboxylic acid) have been prepared by coupling it with 1-ethyl-3-(3-dimethyl-amino-propyl) carbodiimide hydrochloride either to p-aminophenyl-beta-D-lactopyranoside, or to higher molecular weight ligands such as dextran and polylysine. Compared to Trolox and on a mole to mole basis, dextran-Trolox is almost equally active, while lactosylphenyl- and polylysine-Trolox conjugates are distinctly more active in preventing the damage on human ventricular myocytes by oxyradicals generated from xanthine oxidase-hypoxanthine. Listed in order of decreasing cytoprotective activity, they are: lactosylphenyl-Trolox >> polylysine-Trolox > Trolox > dextran-Trolox. Thus, Trolox can be chemically modified by coupling it to one of a number of ligands and, in some cases, with resultant increases in its ability to protect human ventricular myocytes from oxyradical damage.