Effect of cholesterol oxidation products on cholesterol metabolism in the laying hen

Oxidised cholesterol is more hypercholesterolaemic and atherogenic than non-oxidised cholesterol in hamsters

The present study was to test the relative hypercholesterolaemic and atherogenic potency of oxidised cholesterol (OxC) and non-oxidised cholesterol in hamsters. An OxC mixture, prepared by heating pure cholesterol (100 g) at 160 degrees C in air for 72 h, contained 78 % cholesterol and 22 % OxC. Fifty Golden Syrian hamsters were randomly divided into five groups of ten animals and fed the control diet, a 0.05 % cholesterol diet (C-0.05), a 0.10 % cholesterol diet (C-0.1), a 0.05 % OxC mixture diet (OxC-0.05) or a 0.10 % OxC mixture diet (OxC-0.1), respectively. The OxC-0.05 and OxC-0.1 groups were more hypercholesterolaemic and had serum total cholesterol 22 and 12 % higher than the corresponding C-0.05 and C-0.1 hamsters (P < 0.05). The OxC-0.1 group demonstrated greater deposition of cholesterol and had a larger area of atherosclerotic plaque in the aorta than the corresponding C-0.1 hamsters (P < 0.05). Similarly, the aorta in the OxC-0.1 group showed greater inhibition on acetylcholine-induced relaxation compared with that in the C-0.1 hamsters. It was concluded that OxC was much more hypercholesterolaemic and atherogenic than cholesterol.

Changes in mRNA expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol 7 alpha-hydroxylase in chickens

3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and cholesterol 7 alpha-hydroxylase (CYP7A1), essential enzymes of cholesterol synthesis and excretion, respectively, were isolated from a chicken liver cDNA library. When their recombinant proteins were overexpressed in HNK293 cells, corresponding enzyme activities were observed. The complete open reading frames of MHGR and CYP7A1 contained (i) 2625 base pairs (bp), predicting a protein of 875 amino acids, and (ii) 1539 bp, predicting a protein of 513 amino acids, respectively. By Northern blot analysis, chicken HMGR mRNA expression was detected in most tissues examined, however, the highest levels were found in liver, brain and ileum. CYP7A1 mRNA was detected only in the liver. Changes in chicken HMGR and CYP7A1 mRNA expression with nutritional state were examined and were shown to respond to certain nutritional treatments, i.e. fast refeeding and cholesterol supplementation. HMGR and CYP7A1 mRNA levels were significantly increased with maturation (i.e. egg producing), when compared to immature chickens. However, these stimulations were not associated with estrogen, although this does enhance triacylglycerol and very low density lipoprotein secretion by the chicken liver. The present study is the first to report the molecular characterization of HMGR and CYP7A1, key enzymes of cholesterol metabolism in avian species.

Dietary soybean protein moderates the deleterious disturbance of lipid metabolism caused by exogenous oxidized cholesterol in rats

Effects of dietary protein on oxidized cholesterol-induced disturbance of lipid metabolism were examined in 4 week old male Sprague-Dawley rats, using casein and soybean protein as dietary protein source. The rats were given one of the two proteins in 0. 078% cholesterol (control), 0.25% cholesterol or 0.25% oxidized cholesterol mixture (containing 0.078% cholesterol) diets. Dietary oxidized cholesterol, compared to cholesterol, tended to inhibit hepatic sterol biosynthesis in casein-fed rats, whereas this inhibitory action was slightly moderated by intake of soybean protein. As a result, the hepatic 3-hydroxy-3-methylglutaryl-CoA reductase activity was rather higher in the rats fed oxidized cholesterol than in those fed cholesterol in the soybean protein-fed group. The hepatic cholesterol 7alpha-hydroxylase activity tended to be higher in the rats fed oxidized cholesterol than in those fed control diet in the soybean protein-fed group, despite the fact that oxidized cholesterol lowered the hydroxylase activity in the casein-fed group. On the other hand, dietary oxidized cholesterol tended to slightly enhance the hepatic Delta6 desaturase activity in the casein-fed group; however, this observation was not shown in the soybean protein-fed group. Moreover, dietary soybean protein facilitated fecal oxidized cholesterol excretion and simultaneously inhibited the accumulation of oxidized cholesterol in serum and liver. In conclusion, dietary soybean protein alleviated the deleterious actions of exogenous oxidized cholesterol on hepatic cholesterol and linoleic acid metabolism, although these efficacies were not necessarily significant. A great part of these moderations may be exerted by the specific hypocholesterolemic function of soybean protein, such as the stimulation of fecal oxidized cholesterol excretion, the change of hormonal release and modulation of lipoprotein catabolism.

Effect of dietary 7-ketocholesterol, pure, or oxidized cholesterol on hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity, energy balance, egg cholesterol concentration, and 14C-acetate incorporation into yolk lipids of laying hens

Experiments were conducted to study the effect of 7-ketocholesterol (7-k) in the presence or absence of pure cholesterol (PCH) or oxidized cholesterol (OCH) in diets of laying hens on reproductive performance and several parameters of cholesterol metabolism. In the first experiment, cholesterol synthesis and transport was examined by the in ovo incorporation of 14C-acetate into yolk triglycerides and cholesterol. Energy balances were also conducted. In the second experiment, hepatic 3 hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity was measured in vitro to evaluate potential cholesterol synthesis. In both experiments, reproductive performance and egg yolk cholesterol concentration were measured. Dietary PCH or OCH (.5%) significantly reduced relative acetate incorporation into yolk cholesterol, while 7-k (.025%) had no effect on carbon flow from acetate into egg cholesterol. While 7-k alone did not alter total yolk cholesterol concentration, it moderated the effect of PCH or OCH on increasing yolk cholesterol concentration. No consistent effects of dietary sterols on reproductive performance or energy balance were observed. Hepatic HMG CoA reductase activity was dramatically suppressed by feeding PCH or OCH and moderately suppressed by 7-k. In combination with PCH or OCH, 7-k did not further depress enzyme activity. The observations that 7-k alone depressed hepatic HMG-CoA reductase activity, without changing relative acetate incorporation into yolk cholesterol while limiting cholesterol deposition in egg yolk from PCH or OCH, is interpreted to mean that 7-k may stimulate sterol transport and excretion while limiting cholesterol synthesis.

The effect of dried and fresh eggs on plasma cholesterol and atherosclerosis in chickens

Oxidation products of cholesterol, which have been observed to be formed in powdered eggs and other dehydrated cholesterol-containing foods, have been suspected as the probable primary cause of atherosclerotic lesions. The feeding of powdered vs. fresh egg yolks to young male chickens up to 30 and 43 weeks of age, respectively, produced approximately the same increase in plasma cholesterol, liver fat, and liver cholesterol when compared to the feeding of a soybean-based cholesterol-free diet. Aortic atherosclerosis, however, was found to be more severe in a group of birds fed fresh egg yolks than in those fed powdered egg or the cholesterol-free diet. A previously demonstrated, enhanced feedback inhibition of cholesterol synthesis by oxidized cholesterol derivatives may at least partly explain these results.