Gender differences in the development of hyperlipemia and atherosclerosis in hybrid hamsters

Probiotic Effects of Lactobacillus fermentum ZJUIDS06 and Lactobacillus plantarum ZY08 on Hypercholesteremic Golden Hamsters

Hypercholesteremia or high cholesterol is one of the important factors leading to atherosclerosis and other cardiovascular diseases. The application of probiotics with cholesterol-lowering characteristics has become increasingly popular over the past decade due to their contribution to human health. This study aimed to evaluate the probiotic effects of Lactobacillus fermentum ZJUIDS06 and Lactobacillus plantarum ZY08 on hyperlipidemic golden hamsters. A hyperlipidemic model was established through a high cholesterol diet in golden hamsters, after which lyophilized Lactobacillus fermentum ZJUIDS06 and Lactobacillus plantarum ZY08 were orally administered individually for 8 weeks. The physiological characteristics of golden hamsters and short chain fatty acid (SCFA) in the colon were assessed by automatic Biochemical Analyzer and gas choromatograph, respectively. A MiSeq sequencing-based analysis of the bacterial 16S rRNA gene (V3–V4 region) in the cecum content was performed to analyze the cecum microbiota. Correlations between sets of these variables were also investigated using the R package “corrplot.” Results showed that neither Lactobacillus fermentum ZJUIDS06 nor Lactobacillus plantarum ZY08 inhibited body weight increase. However, supplementation with Lactobacillus fermentum ZJUIDS06 for 8 weeks increased colon SCFA levels (P < 0.05), decreased serum low-density lipoprotein, total cholesterol, and triglycerides levels, and also induced changes in the cecum microbiota of hyperlipidemic golden hamsters. Remarkably, oral administration of Lactobacillus fermentum ZJUIDS06 increased the relative abundance of Parabacteroides in the cecum, which served as a biomarker for colon SCFA production and improvement of serum cholesterol levels. In a word, Lactobacillus fermentum ZJUIDS06 improved hyperlipidemia in golden hamsters, which correlated with an increase in SCFA levels and relative abundance of Parabacteroides, indicating its potential importance in functional foods that can help lower cholesterol.

Small rodent models of atherosclerosis

The ease of breeding, low cost of maintenance, and relatively short period for developing atherosclerosis make rodents ideal for atherosclerosis research. However, none of the current models accurately model human lipoprotein profile or atherosclerosis progression since each has its advantages and disadvantages. The advent of transgenic technologies much supports animal models' establishment. Notably, two classic transgenic mouse models, apoE-/- and Ldlr-/-, constitute the primary platforms for studying underlying mechanisms and development of pharmaceutical approaches. However, there exist crucial differences between mice and humans, such as the unhumanized lipoprotein profile, and the different plaque progression and characteristics. Among rodents, hamsters and guinea pigs might be the more realistic models in atherosclerosis research based on the similarities in lipoprotein metabolism to humans. Studies involving rat models, a rodent with natural resistance to atherosclerosis, have revealed evidence of atherosclerotic plaques under dietary induction and genetic manipulation by novel technologies, notably CRISPR-Cas9. Ldlr-/- hamster models were established in recent years with severe hyperlipidemia and atherosclerotic lesion formation, which could offer an alternative to classic transgenic mouse models. In this review, we provide an overview of classic and innovative small rodent models in atherosclerosis researches, including mice, rats, hamsters, and guinea pigs, focusing on their lipoprotein metabolism and histopathological changes.

ApoF knockdown increases cholesteryl ester transfer to LDL and impairs cholesterol clearance in fat-fed hamsters

Cholesteryl ester transfer protein (CETP) regulates intravascular lipoprotein metabolism. In vitro studies indicate that ApoF alters CETP function by inhibiting its activity with LDL. To explore in vivo the complexities driving ApoF's effects on CETP, we developed a siRNA-based hamster model of ApoF knockdown. In both male and female hamsters on chow- or fat-fed diets, we measured lipoprotein levels and composition, determined CETP-mediated transfer of cholesteryl esters (CEs) between lipoproteins, and quantified reverse cholesterol transport (RCT). We found that apoF knockdown in chow-fed hamsters had no effect on lipoprotein levels or composition, but these ApoF-deficient lipoproteins supported 50-100% higher LDL CETP activity in vitro. ApoF knockdown in fat-fed male hamsters created a phenotype in which endogenous CETP-mediated CE transfer from HDL to LDL increased up to 2-fold, LDL cholesterol increased 40%, HDL declined 25%, LDL and HDL lipid compositions were altered, and hepatic LDLR gene expression was decreased. Diet-induced hypercholesterolemia obscured this phenotype on occasion. In fat-fed female hamsters, ApoF knockdown caused similar but smaller changes in plasma CETP activity and LDL cholesterol. Notably, ApoF knockdown impaired HDL RCT in fat-fed hamsters but increased sterol excretion in chow-fed animals. These in vivo data validate in vitro findings that ApoF regulates lipid transfer to LDL. The consequences of ApoF knockdown on lipoproteins and sterol excretion depend on the underlying lipid status. By minimizing the transfer of HDL-derived CE to LDL, ApoF helps control LDL cholesterol levels when LDL clearance mechanisms are limiting.

Systematic review of the mechanisms and evidence behind the hypocholesterolaemic effects of HPMC, pectin and chitosan in animal trials

Dietary fibres have diverse mechanisms in reducing plasma cholesterol, which could be useful for treating high levels of low-density lipoprotein cholesterol (LDL-C). The objective of this review is to determine the state of the evidence for the cholesterol-lowering effects of three selected fibres and their mechanisms, using the most recent animal trials. Therefore, a systematic review was conducted for hydroxypropyl methylcellulose (HPMC), pectin and chitosan in Pubmed, Embase and the Cochrane Library. All fibres reviewed reduced total cholesterol, very low-density lipoprotein cholesterol (VLDL-C) and LDL-C. Pectin gave a small, and chitosan an impressive rise in high-density lipoprotein cholesterol (HDL-C). A limitation of this study is the variety of animal models, each with distinct cholesterol profiles. Possible publication bias was also detected. In conclusion, chitosan seems to be the most promising of the studied fibres. A dietary fibre could be designed that yields the best cholesterol-lowering effect, using experiences in tailoring physicochemical properties and primarily exploiting the biophysical mechanisms of action.

Serum perfluorooctanoic acid (PFOA) concentrations in normal and hyperlipidemic female hamsters dosed orally with ammonium perfluorooctanoate (APFO) for up to 30 days

In epidemiology studies, the presence of perfluorooctanoate (PFOA) in human blood has been associated with higher serum cholesterol concentrations. A possible explanation for these results is that elevated serum cholesterol might reduce clearance of PFOA. In this study, female hamsters, which transport and regulate cholesterol in a manner similar to humans, were fed normal diet or diet supplemented with 0.05% cholesterol and 10% coconut oil (high-fat diet) resulting in hyperlipidemia throughout the study in supplemented animals. Hamsters on either a normal and high-fat diet were given oral doses of 0.1, 1.0, or 10 mg APFO/kg for 30 days. Serum PFOA concentrations evaluated 24 h after 1, 10, 20, and 30 doses of APFO were not altered in hyperlipidemic hamsters compared to those fed normal diet. For a given dose group, serum concentrations of PFOA were highest following the 10 doses (except for the 10 mg/kg group where concentrations were the highest after the first dose) and were lowest after 20 and 30 doses. Under the condition of this study, higher serum lipids did not affect the absorption and clearance of serum PFOA. Serum PFOA concentrations declined over the course of the study despite continued daily dosing with APFO. This does not support the hypothesis that higher serum lipids might increase the retention of PFOA in the body.

Use of hamster as a model to study diet-induced atherosclerosis

Golden-Syrian hamsters have been used as an animal model to assess diet-induced atherosclerosis since the early 1980s. Advantages appeared to include a low rate of endogenous cholesterol synthesis, receptor-mediated uptake of LDL cholesterol, cholesteryl ester transfer protein activity, hepatic apoB-100 and intestinal apoB-48 secretion, and uptake of the majority of LDL cholesterol via the LDL receptor pathway. Early work suggested hamsters fed high cholesterol and saturated fat diets responded similarly to humans in terms of lipoprotein metabolism and aortic lesion morphology. Recent work has not consistently replicated these findings. Reviewed was the literature related to controlled hamster feeding studies that assessed the effect of strain, background diet (non-purified, semi-purified) and dietary perturbation (cholesterol and/or fat) on plasma lipoprotein profiles and atherosclerotic lesion formation. F1B hamsters fed a non-purified cholesterol/fat-supplemented diet had more atherogenic lipoprotein profiles (nHDL-C > HDL-C) than other hamster strains or hamsters fed cholesterol/fat-supplemented semi-purified diets. However, fat type; saturated (SFA), monounsaturated or n-6 polyunsaturated (PUFA) had less of an effect on plasma lipoprotein concentrations. Cholesterol- and fish oil-supplemented semi-purified diets yielded highly variable results when compared to SFA or n-6 PUFA, which were antithetical to responses observed in humans. Dietary cholesterol and fat resulted in inconsistent effects on aortic lipid accumulation. No hamster strain was reported to consistently develop lesions regardless of background diet, dietary cholesterol or dietary fat type amount. In conclusion, at this time the Golden-Syrian hamster does not appear to be a useful model to determine the mechanism(s) of diet-induced development of atherosclerotic lesions.

Safety evaluation of oligofructose: 13 week rat study and in vitro mutagenicity

Oligofructose (OF), comprised of fructose oligomers with a terminal glucose unit, is a family of oligosaccharides derived from the hydrolysis of inulin. Consumption of OF in animals and humans increases colonic bifidobacteria levels. The present study evaluates the safety of OF in both a 13 week rat feeding study and using in vitro mutagenicity tests. Fecal bifidobacteria levels were also determined by in situ hybridization to assess a biological function of OF. Rats received either a control diet or diets containing one of four doses of OF. Total, HDL, and LDL-cholesterol levels were significantly lower at several time points during the study in groups receiving OF compared to controls with the largest effects occurring in the high dose male animals. Weight gain in the male high dose group was significantly lower at early time points compared to controls but not significantly different at the end of study. As expected, cecal weights increased in a dose-related manner and fecal bifidobacteria levels also demonstrated a dose-related increase. There were no consistent differences in gross pathology or histopathology related to dietary OF. OF did not induce a positive response in the Ames test or chromosomal aberration test with CHO cells. These results demonstrate no adverse effects of OF.

Effects of dietary alpha linolenic acid on cholesterol metabolism in male and female hamsters of the LPN strain

N-3 polyunsaturated fatty acids and estrogens are recognized as protective factors of atherosclerosis, however their interactions on cholesterol metabolism remain unclear. Male and female hamsters were fed for 9 weeks diets containing 12.5% lipids and rich in either alpha-linolenic acid ("linseed" diet) or saturated fatty acids ("butter" diet). Hamsters fed the "linseed" diet exhibited lower plasma concentrations of cholesterol (-29%), total LDL (-35%) and HDL (-17%), glucose (-20%), insulin (-40%) and of the LDL-cholesterol/HDL-cholesterol ratio (-27%) than those fed the "butter" diet. In the liver, cholesterol content was 2.7-fold lower in response to the "linseed" diet, whereas the concentration of HDL receptor (SR-BI) and the activities of HMGCoA reductase and cholesterol 7alpha-hydroxylase were 30 to 50% higher than with the "butter" diet. By contrast, the LDL receptor concentration did not vary with the diet. Females exhibited higher concentration of LDL (+24%), lower concentration of plasma triglycerides (-34%), total VLDL (-46%) and VLDL-cholesterol (-37%) and of biliary phospholipids (-19%). Besides, there was also an interaction between gender and diet: in males fed the "butter" diet, plasma triglycerides and VLDL concentration, were 2 to 4 fold higher than in the other groups. These data suggest that gene and/or metabolic regulations by fatty acids could interact with that of sex hormones and explain why males are more sensitive to dietary fatty acids.

Species-related variations in lipoprotein metabolism: The impact of FERHDL on susceptibility to atherogenesis

Several animal models have been used to investigate the mechanisms of atherogenesis. Each animal species has advantages and disadvantages with regard to similarity with human lipoprotein metabolism. In humans, fractional esterification rate in apolipoprotein B-depleted plasma (FER(HDL)) has been shown to correlate with the quality of high density lipoprotein particles. Increased values of FER(HDL) indicate an atherogenic lipoprotein profile. Such an association has not been defined in animal models. Thus, we have characterized plasma lipoprotein profile and FER(HDL) values in four animal species namely, cats, pigs, guinea pigs and rabbits. These animal species have been used in experimental dyslipidemia and atherosclerosis. Our data indicate a wide rage of variations among various animal species. High-density lipoprotein (HDL) particles contain approximately 40% of total plasma cholesterol concentrations in rabbits, pigs and cats <10% in guinea pigs. A negative association between FER(HDL) values and plasma HDL-cholesterol levels was observed in pigs, rabbits and guinea pigs. On the other hand, FER(HDL) values showed a positive association with plasma triglyceride levels in all animal species tested. These findings are in agreement with data reported in humans. More research is needed to identify the better animal models which closely resemble human lipoprotein metabolism.

Study of diet-induced changes in lipoprotein metabolism in two strains of Golden-Syrian hamsters

The objective of this study was to characterize two strains of Golden-Syrian hamsters for use in the study of diet-induced changes in lipoprotein metabolism. In Experiment 1, the time course and response to dietary saturated fat was investigated for serum lipoprotein profiles and aortic lesion formation in Golden-Syrian hamsters from Charles River Laboratories, Wilmington, MA (CR) and Bio Breeders, Watertown, MA (F(1)B). Hamsters were fed a nonpurified diet containing 10 g/100 g saturated fat and 0.1 g/100 g dietary cholesterol. After 12 wk, CR hamsters had significantly lower serum total and non-HDL cholesterol (TC and nHDL-C) levels, but higher aortic cholesteryl ester (CE) than the F(1)B hamsters (P < 0.05). In Experiment 2, CR hamsters were fed a nonpurified diet containing 10 g/100 g saturated fat and 0.1, 0.5 or 1 g/100 g dietary cholesterol. After 10 wk of dietary intervention, TC and nHDL-C levels were significantly higher in the 0.5 and 1.0 g/100 g cholesterol groups than in the 0.1 g/100 g cholesterol group. These levels declined after 20 wk of dietary intervention in all groups, potentially reflecting the toxic effect of high cholesterol intakes. CR hamsters fed a 10 g/100 g saturated fat containing 0.1 g/100 g dietary cholesterol for 10 wk appear to be a good model for investigating diet-induced change in plasma lipids.

Soy isoflavones prevent ovariectomy-induced atherosclerotic lesions in Golden Syrian hamster model of postmenopausal hyperlipidemia

OBJECTIVE

Soy isoflavones, as dietary supplements, may reduce the formation of atherosclerotic lesions that increase in women after menopause. The objectives of this study were to determine whether (1) ovariectomized (ovx) hamsters will develop atherosclerotic lesions and (2) soy isoflavones can dose-dependently prevent the ovariectomy-induced rise in plasma cholesterol and atherosclerotic lesions in hamsters.

DESIGN

Seventy-two 6-month-old female Golden Syrian hamsters were randomly assigned to six groups: sham-operated; ovx control; ovx + 17beta-estradiol (E(2); 10 microg E(2) per kilogram of body weight); and ovx + 9.5 (low-dose), 19 (medium-dose), or 38 (high-dose) mg isoflavones per kilogram diet. Treatments were initiated immediately after surgery and continued for 120 days. Blood was drawn via abdominal aorta for assessment of circulating lipids, and tissues were collected, including the aortic arch for assessment of atherosclerotic lesions.

RESULTS

All three doses of isoflavones prevented the rise in plasma total cholesterol from ovx; and, as the isoflavone dose increases, the cholesterol-lowering effects of isoflavones become more pronounced (7.8%, 11.8%, and 19.6% reductions in total cholesterol for low-dose, medium-dose, and high-dose, respectively). Ovx hamsters developed atherosclerotic lesions without being on an atherogenic diet. Ninety-two percent of hamsters in the ovx control group had atherosclerotic lesions compared with only 8% in sham, 62% in the E(2) group, 29% in the low-dose group, 38% in the medium-dose group, and 58% in the high-dose group. The aortic fatty streak area was approximately 20 times higher in ovx hamsters compared with the sham animals. All doses of isoflavones were able to significantly reduce fatty streak area to that of the sham group.

CONCLUSIONS

Soy isoflavones, independent of the protein source, prevent hypercholesterolemia and the formation of atherosclerotic lesions induced by ovarian hormone deficiency in hamsters. The antiatherogenic mechanisms of isoflavones need further investigation.

Dietary soy and soy isoflavones have gender-specific effects on plasma lipids and isoflavones in golden Syrian f(1)b hybrid hamsters

The specific components of soy responsible for its beneficial effects on plasma lipids are unknown. Golden Syrian F(1)B Hybrid hamsters (75 male, 74 female) were evaluated for the effect of dietary soy and soy isoflavones on plasma lipids. They were fed the following diets for 16 wk: casein/lactalbumin (C/L), soy protein with isoflavones [Soy(+)], soy protein with isoflavones removed [Soy(-)], Soy(-) plus isoflavone extract (IF), and C/L + IF. At necropsy, plasma total cholesterol, HDL cholesterol (HDLC), LDL + VLDL cholesterol (LDL + VLDLC), isoflavones, and uterine and accessory gland weights were measured. Male hamsters fed the three soy-containing diets had lower LDL + VLDLC concentrations than those fed the two C/L diets (P < 0.01), and those fed Soy(-) + IF did not differ from those fed Soy(+). In females, diet did not affect plasma LDL + VLDLC concentration. Females fed Soy(+) or Soy(-) had higher HDLC (P < 0.05) than those fed C/L. HDLC was not affected by diet in males. Due to higher equol production (P < 0.01), males had greater plasma isoflavone concentrations (P < 0.01) than females. There was a positive association between plasma total isoflavones and LDL + VLDLC (r = 0.65, P < 0.05) in females. These data suggest gender differences in plasma lipid and isoflavone responses to soy- based diets in Syrian F(1)B Hybrid hamsters, which offer an opportunity to explore effects of sex hormones on isoflavone metabolism and the effects of isoflavones on lipid metabolism.

Subcutaneous lipectomy causes a metabolic syndrome in hamsters

The insulin resistance syndrome X is related to excess intra-abdominal adipose tissue. With lipectomy of >50% of subcutaneous adipose tissue (SQAT) in nonhibernating, adult female Syrian hamsters on high-fat (HF; 50 calorie%) diet and measurements of oral glucose tolerance, oral [(14)C]oleic acid disposal, serum triglycerides, serum leptin, liver fat, perirenal (PR) adipose tissue cellularity, and body composition, we studied the role of SQAT. Sham-operated (S) animals on HF or low-fat (LF; 12.5 calorie%) diets served as controls. After 3 mo there was no visible regrowth of SQAT but HF diet led to similar levels of body weight and body fat in lipectomized and sham-operated animals. Lipectomized (L) animals had more intra-abdominal fat as a percentage of total body fat, higher insulinemic index, a strong trend toward increased liver fat content, and markedly elevated serum triglycerides compared with S-HF and S-LF. Liver and PR adipose tissue uptake of fatty acid were similar in L-HF and S-HF but reduced vs. S-LF, and were inversely correlated with liver fat content and insulin sums during the oral glucose tolerance test. In summary, lipectomy of SQAT led to compensatory fat accumulation implying regulation of total body fat mass. In conjunction with HF diet these lipectomized hamsters developed a metabolic syndrome with significant hypertriglyceridemia, relative increase in intra-abdominal fat, and insulin resistance. We propose that SQAT, via disposal and storage of excess ingested energy, acts as a metabolic sink and protects against the metabolic syndrome of obesity.

Differences between men and women in the response of serum cholesterol to dietary changes

BACKGROUND

Hypercholesterolaemia is initially treated by diet. However, most studies of diet and cholesterol response have been carried out in men, and it is not known whether women react to diet to the same extent as men do. We therefore studied sex differences in the response of serum cholesterol and lipoproteins to diet.

MATERIALS AND METHODS

We measured the responses of serum cholesterol to a decrease in dietary saturated fat in seven trials involving 126 men and 147 women, to a decrease in dietary trans fat in two trials (48 men and 57 women) and to a decrease in dietary cholesterol in eight trials (74 men and 70 women). We also measured responses to the coffee diterpene cafestol, which occurs in unfiltered coffee, in nine trials (72 men and 61 women). All subjects were lean and healthy.

RESULTS

The response of total cholesterol (+/- standard deviation) to a decrease in the intake of saturated fat was greater in men (-0.62 +/- 0.39 mmol L-1) than in women (-0.48 +/- 0.39 mmol L-1; 95% confidence interval, 0.04-0.23 mmol L-1). The response of total cholesterol to a decrease in the intake of cafestol was also larger in men (-1.01 +/- 0.49 mmol L-1) than in women (-0.80 +/- 0.49 mmol L-1; 95% confidence interval, 0. 04-0.39 mmol L-1). Responses to trans fat and to dietary cholesterol did not differ between men and women.

CONCLUSION

Men have larger responses of total and low-density lipoprotein cholesterol to saturated fat and cafestol than women do.

Gender differences in response to a hypercholesterolemic diet in hamsters: effects on plasma lipoprotein cholesterol concentrations and early aortic atherosclerosis

Gender is a strong predictor of coronary heart disease (CHD) susceptibility and reports indicate that males are more likely to develop CHD compared to age-matched premenopausal females. To test whether similar gender differences exist in hamsters, 16 male and 16 female F1B Golden Syrian hamsters, aged 10 weeks, were fed a hypercholesterolemic nonpurified diet (HCD) containing 10% coconut oil and 0.05% cholesterol for 12 weeks. Plasma lipid and lipoprotein cholesterol concentrations, LDL oxidative susceptibility, LDL tocopherol concentrations, LDL fatty acid composition, LDL particle size, plasma estradiol and testosterone concentrations, and early aortic atherosclerosis were analyzed. Female hamsters had significantly lower plasma total cholesterol and nonhigh-density lipoprotein cholesterol (nonHDL-C) and greater high-density lipoprotein cholesterol (HDL-C) concentrations compared to male hamsters (-15, -33, and 33%; respectively). Female hamsters had significantly greater LDL particle size (4%), LDL 22:6 (21%) fatty acid, and rate of LDL oxidation (34%) compared to male hamsters. Female hamsters had a significantly higher concentration of plasma estradiol (49%) compared to male hamsters. Female hamsters also had significantly less early aortic atherosclerosis compared to male hamsters (-77%). In female hamsters, aortic fatty streak formation was significantly associated with plasma nonHDL-C (r = 0.76, P<0.0007), LDL particle size (r = -0.66, P<0.005), plasma TC (r = 0.68. P<0.004), and lag phase of LDL oxidation (r = 0.84. P<0.02). In male hamsters, aortic fatty streak formation was significantly associated with plasma nonHDL-C (r = 0.52, P<0.04), plasma TC (r = 0.55, P<0.03), plasma TG (r = 0.79, P<0.0003), and LDL 22:6 (r = -0.78, P<0.03) with no association with any measures of LDL oxidation susceptibility. This study demonstrates that female hamsters have an improved plasma lipoprotein cholesterol profile, larger LDL particle size, and less early aortic atherosclerosis compared to male hamsters fed the same HCD.

Estrogen-induced hepatic toxicity and hepatic cancer: differences between two closely related hamster species

AIMS/BACKGROUND

Estrogen is known to affect hepatobiliary function; however, it is unusual for high serum levels of estrogen to actually result in clinically detectable hyperbilirubinemia. Women affected by cholestatic jaundice during pregnancy share this genetic susceptibility with two Cricetulus hamsters, the Armenian hamster (Cricetulus migratorius) and the Chinese hamster (Cricetulus griseus). Nevertheless, the pathophysiologic process responsible for this estrogen induced icterus may be different in women and hamsters. The present study compares various facets of estrogen-induced icterus in these two closely related hamsters.

METHODS

Hamsters were injected with various estrogens and the acute and chronic effects on liver were monitored by measuring changes in serum constituents and by observing changes in hepatic structure as seen grossly and by light and electron microscopy.

RESULTS

In previous studies, hepatic tumors developed in most Armenian hamsters after chronic estrogen treatment, but in the present study, the livers of Chinese hamsters were remarkably free of neoplastic change under similar conditions. Also, when compared with the responses in the Armenian hamsters, signs of hepatic destruction and regeneration were less prevalent in estrogen-treated Chinese hamsters, and they were less susceptible to the effects of estrogen (because larger doses of estrogen were required to produce icterus and the bilirubin levels were lower and of shorter duration). In contrast to the findings in Armenian hamsters, bile canaliculi were severely affected in livers of estrogen-treated Chinese hamsters, and hepatic microvesicular steatosis, indicative of an unusual lipodystrophy caused by estrogen, was prominent. An additional lesion peculiar to the Chinese hamster was striking sinusoidal dilatation, which may be analogous to the oral contraceptive-induced sinusoidal dilatation in humans.

CONCLUSIONS

Although these two hamster species are genetically similar, the genes activated by the estrogen receptor show remarkable heterogeneity when their respective livers are examined. Comparisons within these species may provide information about the specific gene activation responsible for particular pathologic events.

The effects of diet and lovastatin on regression of fatty streak lesions and on hepatic and intestinal mRNA levels for the LDL receptor and HMG CoA reductase in F1B hamsters

This study examined the effects of lovastatin supplementation (25 mg/kg per day) in conjunction with an atherogenic diet (10% coconut oil (w/w), 0.05% cholesterol) on regression of pre-existing foam cells and on hepatic and intestinal LDL receptor and HMG CoA reductase mRNA levels. F1B hamsters fed the atherogenic diet had significantly greater (p < 0.0002) foam cell accumulation (10078 +/- 1452 (S.E.M.) micron2) compared to those fed a low fat, no cholesterol chow diet (64 +/- 10 micron2) or the atherogenic diet supplemented with lovastatin (1621 +/- 132 micron2). Regression of fatty streak lesions was achieved by feeding either a chow diet or supplementing the atherogenic diet with lovastatin as evidenced by the significant (p < 0.0002) reduction in foam cell accumulation in the chow regression (94 +/- 55 micron2) and lovastatin regression (48 +/- 18 micron2) groups compared to the atherogenic diet group (10078 +/- 1452 micron2). Lovastatin supplementation of the atherogenic diet induced significant upregulation of both LDL receptor and HMG CoA reductase message levels in liver and intestine compared to the chow and atherogenic diet fed groups. These data demonstrate that lovastatin supplementation of an atherogenic diet decreases foam cell accumulation and induces upregulation of hepatic and intestinal LDL receptor and HMG CoA reductase mRNA levels. Furthermore, regression of pre-existing, diet-induced fatty streak lesions can be achieved by lovastatin supplementation of an atherogenic diet or by feeding a low fat, low cholesterol chow diet. The specific effects of lovastatin on foam cell accumulation and regression and messenger RNA levels are secondary to reductions in plasma total cholesterol concentrations and do not demonstrate a direct effect of lovastatin on atherosclerotic lesions.