AGENTES Y EQUIPOS INTERVINIENTES

In vivo studies in Wistar rats, Syrian hamsters and Chinchilla rabbits demonstrated the

ability of oyster mushrooms (Pleurotus ostreatus) to lower the cholesterol levels. Rats with hereditary enhanced sensitivity to alimentary cholesterol were fed with 4% fruiting bodies in a diet containing 1% cholesterol. Mushroom consumption prevented serum cholesterol increase after 4 weeks and after 7weeks the cholesterolemia was lowered by 40% compared with control animals. This effect was due to a decrease in the concentrations of very low density lipoproteins (VLDL) and LDL [29] and to an induced delay in cholesterol absorption [30, 31]. A 50% increase in the HDL and activation of antioxidative enzymes was also observed [32]. Similar results were observed using Chinchilla rabbits (fed with 10% P.

ostreatus) where a decrease in total serum cholesterol was also detected primarily affected by

the reduction (70%) of the VLDL-cholesterol. An increase by a factor of 3 in the HDL was also observed [33]. However, the hypocholesterolemic effect was dependent on the amount of dietary oyster mushroom administrated, 1% was ineffective while doses of 5% induced a significantly reduction in normal rats [34]. The ethanol extracts obtained from the same mushroom were less efficient with increasing concentrations of ethanol than the whole body or its water extract. The latter and the extracts including 30 and 60% ethanol were also able to

reduce the cholesterol and triacylglycerol levels in hamsters serum and liver (reduction of 34% cholesterol and 48% triacylglycerols). The consumption of the water and 30% ethanol extracts reduced the VLDL fraction [30]. Another extract obtained from its mycelium with dichloromethane and 95% ethanol lowered cholesterol levels in liver of normal rats [35] but, a β-glucan fraction extracted from the fruiting bodies was unable to affect cholesterols levels in both serum and liver [32].

Supplementation of a high-fat-diet given to hyperlipidemic rats with Pleurotus

citrinopileatus fruiting bodies, a hot-water extract and two specific fractions obtained by

eluting from a silica gel column with ethyl acetate and methanol at different doses showed that serum triglycerides and total cholesterol levels were significantly lower and HLD significantly higher in the groups supplemented with the highest dosage of the two eluted fractions as compared with the control groups with no mushroom addition. The major constituents of the eluted fractions were ergosterol in one of them and nicotinic acid in the other [36].

Other species from the same genera such as Pleurotus eryngii reduced the plasma total cholesterol, triglyceride, LDL, total lipid, phospholipids and LDL/HDL ratio by 24, 46.3, 62.5, 24.6, 19.2 and 57.1% respectively and showed no adverse effects when they were added as supplement (5%) to hypercholesterolemic Sprague-Dawley albino rats. Feeding mushrooms increased total lipid and cholesterol excretion in faeces [37]. Its water extracts showed hypolipidemic and hypocholesterolemic effects in fat-loaded mice. The low fat absorption provoked was due to its lipase inhibitory activity. Apparently, the water extract might prevent the interactions between lipid emulsions and pancreatic lipase [38]. The remarkably reduction of lipid levels, total cholesterol, total triglyceride and LDL-cholesterol and increase in HDL-cholesterol was because of its water-soluble polysaccharides [39].

Ganoderma lucidum is considered by the Asiatic culture as a medicinal mushroom

because of its many different beneficial properties. Several of these properties have been confirmed by scientific studies [40, 41] including its hypocholesterolemic effects in hamsters and minipigs [42]. The organic fractions containing oxygenated lanosterol derivatives inhibited cholesterol synthesis in T9A4 hepatocytes. In hamsters, 5% supplementation did not affect LDL but decreased 9.8% total cholesterol, 11.2% HDL and had effects on several faecal neutral sterols and bile acids. It also reduced hepatic microsomal ex-vivo HMGCoA reducase activity but not its gene expression [43]. In minipigs, 2.5% supplementation decreased 20% total cholesterol, 27% LDL and 18% HDL-cholesterol and increased faecal cholestanol and coprostanol and decreased cholate. Results also indicated that G. lucidum reduced LDL cholesterol in vivo through various mechanisms [42].

Similar studies with the white button mushroom (Agaricus bisporus) indicated that they were able to lowers blood glucose and cholesterol levels in diabetic and hypercholesterolemic Sprague-Dawley rats fed with hypercholesterolemic diets for 3 or 4 weeks [44]. Hypercholesterolemic rats significantly decreased their levels of plasma total cholesterol and LDL (22.8 and 33.1% respect.) and their hepatic levels of cholesterol and triglycerides (36.2 and 20.8% respect.) increasing significantly their plasma HDL concentrations. Apparently, these effects might have been induced by the presence of A. bisporus fibres because when rats were fed with these compounds, the serum total cholesterol, VLDL, IDL (intermediate density lipoprotein) and LDL were lower than control rats while the HDL were lower. These observations could be caused by the overexpression of the hepatic LDL receptor since its mRNA level was significantly higher than in the control rats [45].

After these results, the fibre fraction from other edible mushrooms was also investigated. Rats were fed with the fibre fraction from Grifola frondosa (maitake), Lentinula edodes (Shiitake) and Flammulina velutipes (enokitake mushrooms) for 4 weeks and compared with cellulose as control. The total cholesterol in serum was significantly lower in rats fed with G.

frondosa and F. velutipes than in those rats fed with cellulose. The VLDL, IDL and LDL

levels were also lower when the rats ate any of the three mushrooms whereas only the HDL of the F. velutipes group was significantly lower than the others. The LDL receptor mRNA levels were only significantly higher in the F. velutipes group, thus, F. velutipes lowered cholesterol in serum by enhancement of hepatic LDL receptor mRNA while the other mushroom fibres enhanced the faecal cholesterol excretion [46]. Moreover, G. frondosa and two other mushroom species such as P. eryngii, and particularly Hypsizygus marmoreus also showed antiatherosclerotic effects in atherosclerosis-susceptible C57BL/6J, apolipoprotein E– deficient (apoE−/−) mice [47].

Auricularia auricular (tree-ear mushroom) and Tremella fuciformis (white jelly-leaf

mushroom) fruiting bodies were also capable of reducing total cholesterol in serum (5% fed Sprague-Dawley rats) after 4 weeks (17 and 19% reduction respect.) by decreasing the LDL- cholesterol levels but with no significant differences in the HDL levels nor total lipids or cholesterol in liver [48]. However, the hypocholesterolemic properties of the mushrooms were effective when the animals consumed the fruiting bodies in regular basis and for long terms because when the cholesterol levels were determined 3 or 6 h after in taking, although the glycemic levels were decreased no statistical differences were observed in cholesterol levels in Wistar rats administrated with water or methanol extracts obtained from Lentinula

lepideus, Calvatia cyathiformis and Ganoderma applantum [49].