Effect of cholesterol feeding on circadian rhythm of hepatic and intestinal cholesterol biosynthesis in hamsters.

Forty-eight adult hamsters were divided equally into two groups fed a control diet and a 2% cholesterol diet, respectively, under a rigid lighting (6 PM-6 AM) and feeding (6 PM-8 AM) schedule for three weeks. The cholesterol synthetic activity of the liver, stomach, small intestine, cecum, colon and kidney was measured by in vivo conversion of acetate-1-14C to cholesterol in four animals each time at 4 hour intervals. A remarkable circadian rhythm with the peak at midnight and the nadir at noon was found in the liver of the control hamsters, but was completely abolished in the cholesterol-fed animals since the activity was nearly totally suppressed at all times. The small intestine exhibited a similar rhythm with the peak at midnight but maintained a high baseline activity from 8 AM to 6 PM. Cholesterol feeding did not alter the baseline activity but reduced 17% of the peak activity. Other organs failed to show such a circadian rhythm.     

Atherogenic hyperlipoproteinemia induced by cholesterol feeding the Patas monkey.

Patas monkeys were studied for 2 years on three dietary regimes: (1) commercial chow (control diet); (2) semipurified diet plus lard (fat-fed); and (3) semipurified diet plus lard and cholesterol (cholesterol-fed). The control and fat-fed animals had similar lipoproteins which were equivalent to the human very low density, low density (LDL), and high density lipoproteins. An additional lipoprotein referred to as LDL-II appeared to be equivalent to the human Lp(a). The cholesterol-fed animals developed accelerated atherosclerosis associated with a hypercholesterolemia which was characterized by (1) the appearance of beta-migrating lipoproteins (B=VLDL) in the d less than 1.006, (2) an increase in the intermediate lipoproteins and LDL, and (3) the appearance of LDL-II which contained a prominence of the arginine-rich apoprotein. The arginine-rich apoprotein was also a prominent component of the B-VLDL and intermediate lipoproteins. Characterization of this apoprotein revealed that it contained 11.5 mol % arginine, had a molecular weight of approximately 34 000, and coelectrophoresed with the arginine-rich apoprotein of man, dog, swine, rat, and rabbit.     

Metabonomic characterization of early atherosclerosis in hamsters with induced cholesterol

Atherosclerosis is a complicated and multifactorial disease, induced not only by genotype, but also, even more importantly, by environmental factors. Study on the metabolic perturbation of endogenous compounds may offer deeper insight into development of atherosclerosis. Gas chromatography/mass spectrometry (GC/MS)-based metabonomics was used to profile a metabolic fingerprint of serum obtained from hamsters with induced cholesterol. The deconvoluted GC/MS data were processed by multivariate statistical analysis tools, such as principal component analysis (PCA) and partial least squares projection to latent structure and discriminant analysis (PLS-DA). For the first time we showed a time-dependent development of the model animal from normal to hypercholesterolaemia, and further to early atherosclerosis. Twenty-one compounds were identified as markers involved in the development to atherosclerosis. Identification of the compounds suggests that amino acid metabolism and fatty acid oxidation are significantly perturbed following cholesterol overloading. The data provide novel information to approach the pathophysiological processes of the hypercholesterolaemia and atherosclerosis disease continuum.     

Swine lipoproteins and atherosclerosis. Changes in the plasma lipoproteins and apoproteins induced by cholesterol feeding.

Cholesterol feeding in miniature swine resulted in a hypercholesterolemia with a distinctive hyperlipoproteinemia and the subsequent development of atherosclerosis. Alterations in the type and distribution of plasma lipoproteins induced by cholesterol feeding were as follows: (a) the occurrence of beta-migrating lipoproteins (B-VLDL) as well as very low density lipoproteins in the d less than 1.006 ultracentrifugal fraction; (b) an increased prominence of the intermediate lipoproteins (d = 1.006-1.02); (c) an increased prominence of low density lipoproteins; and (d) the occurrence of a distinctive lipoprotein with alpha mobility which was referred to as HDLc (cholesterol induced). Characterization of the various plasma lipoproteins included chemical composition, size by electron microscopy, and apoprotein content. The B-VLDL resembled the beta-migrating lipoproteins of human Type III hyperlipoproteinemia and contained a prominent protein equivalent to the arginine-rich apoprotein in addition to the B apoprotein, apo-A-I, and the fast-migrating apoproteins (apo-C). The HDLc were rich in cholesterol, ranged in size from 100 to 240 A in diameter, and contained the arginine-rich apoprotein and apo-A0I but lacked the B apoprotein. The arginine-rich apoproteins isolated from B-VLDL and HDLc by gel chromatography were similar in amino acid analyses, with glutamic acid as their amino-terminal residue. The occurrence of a spectrum of cholesterol-rich lipoproteins which contained the arginine-rich apoprotein with the occurrence of accelerated atherosclerosis suggested an interesting, although speculative, association.     

Splenic hypertrophy and extramedullary hematopoiesis induced in male Syrian hamsters by short photoperiod or melatonin injections and reversed by melatonin pellets or pinealectomy

Adult male Syrian hamsters either placed in a short photoperiod alone or kept in a long photoperiod and given daily afternoon injections of the pineal indole melatonin (25 micrograms) exhibited splenic hypertrophy and extramedullary hematopoiesis in addition to a marked regression in testicular weight. The testicular regression as well as the changes in spleen weight and histology could be prevented if the animals in short photoperiod were either pinealectomized or implanted subcutaneously with a pellet containing 1 mg melatonin. Female Syrian hamsters given afternoon injections of melatonin for 7 or 12 weeks had ovaries devoid of corpora lutea; additionally, these animals had reduced relative spleen weights compared to the control animals. In conclusion, it is apparent that spleen weight varies with the functional status of the gonads. Splenic hypertrophy accompanied by pineal-induced testicular regression in males may be related to splenic extramedullary hematopoiesis.     

Liver nucleotides in acute experimental liver injury induced by dimethylnitrosamine and by thioacetamide

1. The concentrations of the nicotinamide-adenine dinucleotides in rat liver have been determined at intervals during the period 1-24hr. after feeding adult female rats with dimethylnitrosamine or thioacetamide. 2. The administration of dimethylnitrosamine resulted in a rapid decrease in the sum of NAD+NADH(2). This sum was decreased by 40% 3hr. after dosing. 3. Dimethylnitrosamine administration also produced an overall decrease in the NADP+NADPH(2) but this decrease was not so early nor as marked as that found for NAD+NADH(2). 4. The changes produced by thioacetamide were quite different from those obtained with dimethylnitrosamine. Thioacetamide produced a temporary rise in the NAD+NADH(2) followed by a small fall. The NADP+NADPH(2) was little changed in the early hours after dosing with thioacetamide but had decreased by approx. 15% 18hr. after administration. 5. These changes are discussed in terms of the known hepatotoxic actions of dimethylnitrosamine and thioacetamide, and are compared with previously reported changes found after the administration of carbon tetrachloride.     

Development of lipidic composition of neonatal chick liver and intestine microsomes: changes induced by cholesterol feeding

Changes in cholesterol and phospholipid content of chick liver and intestine microsomes were studied throughout the two first weeks of life. Differences observed throughout postnatal development were mainly due to the free cholesterol. Cholesterol feeding resulted in a clear increase of the amounts of both free and esterified cholesterol. Phospholipid content of chick liver and intestine microsomes did not change significantly after hatching. Phosphatidylcholine and phosphatidylethanolamine were found to be the major phospholipids. Although the amount of each phospholipid could be affected by cholesterol feeding, its relative percentage did not change by this treatment.     

Influence of resveratrol on liver fibrosis induced by dimethylnitrosamine in male rats

Liver fibrosis is a significant health problem which represents the liver’s scarring process and response to injury through deposition of collagen and extracellular matrix, and ultimately leads to cirrhosis. Resveratrol is a naturally occurring phytoalexin found predominantly in grapes. This study aimed to investigate the antifibrotic role of resveratrol on dimethylnitrosamine (DMN)-induced liver fibrosis in rats. Rats were divided into four groups and treated for three weeks; control, resveratrol administered orally (20 mg/kg daily), DMN intraperitoneally injected (10 mg/kg 3 days/week), and the last group was pre-treated daily with resveratrol then injected with DMN, 3 days/week. DMN administration induced severe liver pathological alterations. However, oral administration of resveratrol before DMN significantly prevented the induced loss in body weight, as well as the increase in liver weight which arise from DMN administration. Resveratrol has also inhibited the elevation of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and bilirubin levels. Furthermore, resveratrol significantly increased hepatic reduced glutathione (GSH) levels and reduced the levels of malondialdehyde (MDA) due to its antioxidants effect as well as increased serum protein levels. In addition, DMN induced elevation in hydroxyproline content. On the other hand, hydroxyproline level was significantly reduced in the resveratrol pretreated rats. Resveratrol has also remarkably maintained the normal liver lobular architecture. Moreover, resveratrol had displayed potent potentials to prevent collagen deposition, lymphocytic infiltration, necrosis, steatosis, vascular damage, blood hypertention, cholangiocyte proliferation. It can be concluded that resveratrol has a marked protective role on DMN-induced liver fibrosis in rats, and can be considered as antiproliferative, antihypertensive, as well as antifibrotic agent and may be used to block the development of liver fibrosis.     

蜂胶对二甲基亚硝胺诱导的大鼠肝纤维化的作用

目的:观察蜂胶抗二甲基亚硝胺(DMN)所致大鼠肝纤维化作用.方法:50只大鼠随机分为5组:正常对照组、模型组及高、中、低剂量蜂胶乙醇提取物(EEP)给药组,模型组及各EEP组腹腔注射DMN10mg/kg,每周2次,持续6周,各EEP组自造模之日开始给予不同剂量EEP,1次/d.结果:给予EEP组肝功能指标均有不同程度的改善,AST、ALT含量较模型组明显降低(P＜0.05);血清HA、LN、PCⅢ的含量较模型组显著降低(P＜0.05);病理组织学检查结果表明,EEP对肝细胞坏死及肝纤维化有一定的抑制作用.结论:蜂胶具有一定的改善肝功能、减轻肝纤维化的作用.     

Effect of 1,10-phenanthroline on acute liver injury induced by dimethylnitrosamine in the rat

Acute liver damage was induced in rats by intragastric doses of dimethylnitrosamine (DMN, 3 mg/100 g body weight) and measured 24 hours later by morphological and biochemical methods. 1, 10-Phenanthroline (1, 10-P, 2 mg/100 g) administered simultaneously with DMN prevented the development of the characteristic morphological picture of liver injury. At the same time, the amount and synthesis of total liver proteins, the activity and distribution of liver β-glucuronidase, and the level of seromucoid and isocitric dehydrogenase (ICDH) activity in the serum, significantly changed by DMN, was within the range of control values when 1, 10-P was simultaneously administered. The protective effect of 1, 10-P against acute DMN hepatotoxicity paralleled the inhibition of some liver microsomal drug-metabolizing enzymes (aniline hydroxylase, morphine demethylase, content of cytochrome P-450). At higher doses of DMN (6 mg and 10 mg/100 g), the administration of 1, 10-P was no longer protective, although the content of cytochrome P-450 was only 20% of the value for normal liver microsomes. Therefore, in acute administration within a certain range of concentration of DMN, 1, 10-P might inhibit the microsomal drug-oxidizing enzymes, thus inhibiting the metabolism of the drug to a more toxic product.     

Anacetrapib promotes reverse cholesterol transport and bulk cholesterol excretion in Syrian golden hamsters

Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester (CE) and triglyceride between HDL and apoB-containing lipoproteins. Anacetrapib (ANA), a reversible inhibitor of CETP, raises HDL cholesterol (HDL-C) and lowers LDL cholesterol in dyslipidemic patients; however, the effects of ANA on cholesterol/lipoprotein metabolism in a dyslipidemic hamster model have not been demonstrated. To test whether ANA (60 mg/kg/day, 2 weeks) promoted reverse cholesterol transport (RCT), 3H-cholesterol-loaded macrophages were injected and (3)H-tracer levels were measured in HDL, liver, and feces. Compared to controls, ANA inhibited CETP (94%) and increased HDL-C (47%). 3H-tracer in HDL increased by 69% in hamsters treated with ANA, suggesting increased cholesterol efflux from macrophages to HDL. 3H-tracer in fecal cholesterol and bile acids increased by 90% and 57%, respectively, indicating increased macrophage-to-feces RCT. Mass spectrometry analysis of HDL from ANA-treated hamsters revealed an increase in free unlabeled cholesterol and CE. Furthermore, bulk cholesterol and cholic acid were increased in feces from ANA-treated hamsters. Using two independent approaches to assess cholesterol metabolism, the current study demonstrates that CETP inhibition with ANA promotes macrophage-to-feces RCT and results in increased fecal cholesterol/bile acid excretion, further supporting its development as a novel lipid therapy for the treatment of dyslipidemia and atherosclerotic vascular disease.     

Depression of hepatic dolichol levels by cholesterol feeding

A study was conducted to determine whether repression of 3-hydroxy-3-methylglutaryl CoA reductase by a chronic high-cholesterol diet would deplete hepatic dolichol levels. Four-week-old male C57BL/6J mice were maintained on a control diet or a diet supplemented with 5% cholesterol. Animals from both groups were killed at various times and reductase activity and levels of free dolichol, dolichyl acyl ester, dolichyl phosphate, and ubiquinone were measured. The reductase activity was reduced by 90% within 1 week and remained depressed through 56 days. Initially, the levels of the free dolichol, acyl ester, phosphoryl ester, and ubiquinone were 7, 16, 5, and 80 micrograms/g liver, respectively. Early increases in the concentration of dolichyl phosphate and free dolichol were similar in both the cholesterol-fed and control groups. However, in the cholesterol-fed group the concentration of dolichyl acyl esters was only 50% of that in the control group by 7 days and it remained lower throughout the experiment. Total dolichol levels were lower by about 30%. Ubiquinone levels were transiently depressed at 7 days by 33% but returned to control levels by 4 weeks. After 56 days, the control values of dolichol and dolichyl phosphate remained constant whereas the dolichyl acyl ester levels continuously increased to a value of 133 micrograms/g of liver by 156 days. Subcellular fractionation of livers from 4-week-old mice indicated a lysosomal distribution of dolichol and dolichyl acyl ester and a lysosomal and microsomal distribution of dolichyl phosphate.     

Morphology and proliferation kinetics of early tumor stages induced by dimethylnitrosamine in rat kidneys

A total of 49 dimethylnitrosamine (DMN)induced rat renal cell tumors were analyzed and classified cytomorphologically at an early stage of development. Of these, 17 were basophilictubular tumors, two of which showed a direct transition to proximal tubules of the P₃segment; 21 lesions were vacuolated and contained glycogen; these were defined cytomorphologically as a separate tumor type the histogenetic derivation of which from the collecting duct system was established by documentation of a direct transition. Morphological similarities point to the lipidstoring variant of the basophilic tumor, but a carcinoma of the ducts of Bellini is another possible human equivalent of this tumor type. Another seven lesions were clear and granular cell tumors. In two of these a direct transition from the collecting duct system was found, thus confirming that this only recently established origin of experimentally induced rat renal clear cell tumors also applies to lesions induced by DMN. The proliferation kinetics of DMNinduced lesions were studied in autoradiograms after pulselabeling with tritiated thymidine. The basal proliferation of these early tumor stages displayed a marked proliferative advantage over the normal parenchyma. The lesions were still subject to physiological growth stimulation as determined by³HTdRcontinuouslabeling with osmotic minipumps following unilateral nephrectomy. However, compared with normal kidney parenchyma, the³HTdRlabeling index of the lesions was even higher indicating a response modification during early neoplasia.     

Regulation of gallbladder cholesterol concentration in the hamster. Role of hepatic cholesterol level

The goal of this investigation was to determine how alterations in hepatic cholesterol metabolism influence the cholesterol content of gallbladder bile in hamsters. Although the rate of hepatic cholesterol synthesis was varied over 600-fold, there was no direct relationship between the rate of cholesterol synthesis and the cholesterol content of gallbladder bile. However, expansion of the hepatic cholesterol pool by 42-fold resulted in an 11-fold increase in gallbladder bile cholesterol. Examination of four subfractions of the hepatic cholesterol pool revealed that the cholesterol content of gallbladder bile was most consistently correlated with the free cholesterol level in both hepatic tissue and hepatic microsomes from all experimental groups. In most groups of animals in which gallbladder bile cholesterol was increased, plasma lipoprotein cholesterol levels were also increased. It was concluded that in hamsters, under these experimental conditions, changes in the cholesterol content of gallbladder bile were directly related to alterations in cholesterol content of the liver and most closely related to alterations in the free cholesterol content of that tissue.