Cholesterol homeostasis in lean and obese male Zucker rats

Hydroxytyrosol Linoleoyl Ether Ameliorates Metabolic-Associated Fatty Liver Disease Symptoms in Obese Zucker Rats

A main hepatic consequence of obesity is metabolic-associated fatty liver disease (MAFLD), currently treated by improving eating habits and administrating fibrates yet often yielding suboptimal outcomes. Searching for a new therapeutic approach, we aimed to evaluate the efficacy of hydroxytyrosol linoleoyl ether (HTLE), a dual Ppar-α agonist/Cb1 antagonist with inherent antioxidant properties, as an antisteatotic agent. Using lean and obese Zucker rats, they were administrated daily doses of HTLE (3 mg/kg) over a 15-day period, evaluating its safety profile, pharmacokinetics, impact on body weight, hepatic fat content, expression of key enzymes involved in lipogenesis/fatty acid oxidation, and antioxidant capacity. HTLE decreased the body weight and food intake in both rat genotypes. Biochemical analysis demonstrated a favorable safety profile for HTLE along with decreased concentrations of urea, total cholesterol, and aspartate aminotransferase AST transaminases in plasma. Notably, HTLE exhibited potent antisteatotic effects in obese rats, evidenced by a decrease in liver fat content and downregulation of lipogenesis-related enzymes, alongside increased expression of proteins controlling lipid oxidation. Moreover, HTLE successfully counteracted the redox imbalance associated with MAFLD in obese rats, attenuating lipid peroxidation and replenishing both glutathione levels and the overall antioxidant. Our findings highlight the effectiveness of triple-action strategies in managing MAFLD effectively. Based on our results in the Zucker rat model, HTLE emerges as a promising candidate with triple functionality as an anorexigenic, antisteatotic, and antioxidant agent, offering potential relief from MAFLD symptoms associated with obesity while exhibiting minimal side effects. In conclusion, our study positions HTLE as a highly promising compound for therapeutic intervention in MAFLD treatment, warranting further exploration in clinical trials.

Feeding Soy Protein Concentrates with Low and High Isoflavones Alters 9 and 18 Weeks Serum Isoflavones and Inflammatory Protein Levels in Lean and Obese Zucker Rats

Soy's anti-inflammatory properties contribute to the health benefits of soy foods. This study was designed to investigate the bioavailability of soy isoflavones and whether the isoflavone content of soy protein concentrate diet would affect serum inflammatory proteins in an obese (fa/fa) Zucker rat model. Six-week-old male lean (L) and obese (O) Zucker rats were fed a casein control diet (C), soy protein concentrate with low isoflavones (SPC-LIF), or soy protein concentrate with high isoflavones (SPC-HIF) (7 rats/dietary group) before being killed at 9 and 18 weeks. Serum samples were analyzed for isoflavones and inflammatory proteins. At both time points, serum total (aglycone + conjugates) genistein, daidzein, and equol concentrations were significantly higher in L-SPC-HIF and O-SPC-HIF groups compared with L-SPC-LIF and O-SPC-LIF groups, respectively, and were not detectable in either L-C or O-C groups. At week 9, serum C-reactive protein (CRP) concentration was significantly lower in O-SPC-HIF group compared with O-C and O-SPC-LIF group, whereas proteins tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels did not differ between any groups. At week 18, serum CRP levels in both O-SPC-HIF and O-SPC-LIF groups were significantly lower compared with the O-C group. TNF-α level was higher in the O-SPC-LIF group compared with both O-C and O-SPC-HIF groups, whereas IL-6 levels were not different between any groups. Taken together, feeding Zucker rats SPC-LIF and SPC-HIF diets led to different serum isoflavone concentrations in both L and O Zucker rats and altered CRP and TNF-α levels in obese Zucker rats compared with controls.

The effect of liposuction and diet on ghrelin, adiponectin, and leptin levels in obese Zucker rats

BACKGROUND

The fat-regulating hormones, adiponectin, ghrelin, and leptin, have been studied extensively with the hope that some therapeutic modality might be gleaned from their augmentation or blockade. The authors studied levels of ghrelin, adiponectin, and leptin after liposuction in obese male Zucker rats. In addition, they altered the fat and carbohydrate content of the rats' postoperative diets to determine whether diet affects hormonal levels and/or liposuction outcome.

METHODS

Thirty-five male, obese Zucker rats were divided into four experimental groups. Group I (n = 10) was fed a low-fat/low-carbohydrate diet; group II (n = 10) was fed a regular chow diet; and group III (n = 10) was fed a high-fat/high-carbohydrate diet. Five additional rats served as the baseline, unoperated group. The experimental rats underwent subcutaneous liposuction, and for 6 weeks they were then fed their experimental diets starting on day 0. Experimental rats were euthanized on day 42 and blood was sampled for hormonal, triglyceride, and cholesterol levels.

RESULTS

Triglyceride levels were significantly higher in the high-fat/high-carbohydrate group compared with the regular chow and low-fat/low-carbohydrate groups, indicating an effect of diet on systemic circulation after liposuction. Ghrelin levels decreased significantly and leptin levels demonstrated an increasing trend after liposuction. Adiponectin levels did not demonstrate any change with alteration in diet or liposuction.

CONCLUSIONS

Liposuction may prove to offer patients medically therapeutic benefits through hormonal alterations. After liposuction, diet plays an important role in weight gain.

Disturbed regulation of cholesterol synthesis in monocytes of obese patients with hypercholesterolemia

The aim of the present study was to clarify the influence of obesity on the functions of low-density lipoprotein receptors (LDL-R) and 3-hydroxy-3-methylglutarate-coenyzme A (HMG-CoA) reductase both in healthy control subjects and in patients with hypercholesterolemia (HC). Experiments were performed on monocytes of 15 non-obese (C I) and 11 obese (C II) healthy control subjects and on 22 non-obese (HC I) and 26 obese (HC II) patients with HC. [(125)I]LDL was used to determine LDL-R activity by measuring binding and intracellular degradation. The rate of endogenous cholesterol synthesis was measured using [(14)C]acetate incorporation into the cholesterol fraction of monocytes. The binding ability of [(125)I]LDL was identical across all groups. The [(14)C]acetate incorporation in resting monocytes was increased only in obese HC group. The 50-microg/mL LDL protein-induced inhibition of [(14)C]acetate incorporation was significantly diminished (P <.001) in the same group. A strong positive correlation was detected between the [(14)C]acetate incorporation by resting cells and LDL-induced inhibition in all groups except the obese HC group, in which their correlation was negative (P <.001). Furthermore, in the obese HC group, a significant positive correlation was detected between body mass index (BMI) and the basal level of [(14)C]acetate incorporation, whereas a negative correlation was found between BMI and LDL-induced inhibition of [(14)C]acetate incorporation. The present data suggest that in patients with HC the concomitant obesity results in dysregulation of cholesterol homeostasis, which may contribute to the accelerated atherosclerosis.

Long-term AICAR administration reduces metabolic disturbances and lowers blood pressure in rats displaying features of the insulin resistance syndrome

The insulin resistance syndrome is characterized by several risk factors for cardiovascular disease. Chronic chemical activation of AMP-activated protein kinase by the adenosine analog 5-aminoimidazole-4-carboxamide-1-beta -D-ribofuranoside (AICAR) has been shown to augment insulin action, upregulate mitochondrial enzymes in skeletal muscles, and decrease the content of intra-abdominal fat. Furthermore, acute AICAR exposure has been found to reduce sterol and fatty acid synthesis in rat hepatocytes incubated in vitro as well as suppress endogenous glucose production in rats under euglycemic clamp conditions. To investigate whether chronic AICAR administration, in addition to the beneficial effects on insulin sensitivity, is capable of improving other phenotypes associated with the insulin resistance syndrome, obese Zucker (fa/fa) rats (n = 6) exhibiting insulin resistance, hyperlipidemia, and hypertension were subcutaneously injected with AICAR (0.5 mg/g body wt) daily for 7 weeks. Obese control rats were either pair-fed (PF) (n = 6) or ad libitum-fed (AL) (n = 6). Lean Zucker rats (fa/-) (n = 8) served as a reference group. AICAR administration significantly reduced plasma triglyceride levels (P < 0.01 for AICAR vs. AL, and P = 0.05 for AICAR vs. PF) and free fatty acids (P < 0.01 for AICAR vs. AL, and P < 0.05 for AICAR vs. PF) and increased HDL cholesterol levels (P < 0.01 for AICAR vs. AL and PF). AICAR treatment also lowered systolic blood pressure by 14.6 +/- 4.3 mmHg (P < 0.05), and AICAR-treated animals exhibited a tendency toward decreased intra-abdominal fat content. Furthermore, AICAR administration normalized the oral glucose tolerance test and decreased fasting concentrations of glucose and insulin close to the level of the lean animals. Finally, in line with previous findings, AICAR treatment was also found to enhance GLUT4 protein expression and to increase maximally insulin-stimulated glucose transport in primarily white fast-twitch muscles. Our data provide strong evidence that long-term administration of AICAR improves glucose tolerance, improves the lipid profile, and reduces systolic blood pressure in an insulin-resistant animal model. The present study gives additional support to the hypothesis that AMPK activation might be a potential future pharmacological strategy for treating the insulin resistance syndrome.

Impaired biliary lipid secretion in obese Zucker rats: leptin promotes hepatic cholesterol clearance

Human obesity is associated with elevated plasma leptin levels. Obesity is also an important risk factor for cholesterol gallstones, which form as a result of cholesterol hypersecretion into bile. Because leptin levels are correlated with gallstone prevalence, we explored the effects of acute leptin administration on biliary cholesterol secretion using lean (FA/-) and obese (fa/fa) Zucker rats. Zucker (fa/fa) rats become obese and hyperleptinemic due to homozygosity for a missense mutation in the leptin receptor, which diminishes but does not completely eliminate responsiveness to leptin. Rats were infused intravenously for 12 h with saline or pharmacological doses of recombinant murine leptin (5 microg x kg(-1) x min(-1)) sufficient to elevate plasma leptin concentrations to 500 ng/ml compared with basal levels of 3 and 70 ng/ml in lean and obese rats, respectively. Obesity was associated with a marked impairment in biliary cholesterol secretion. In biles of obese compared with lean rats, bile salt hydrophobicity was decreased whereas phosphatidylcholine hydrophobicity was increased. High-dose leptin partially normalized cholesterol secretion in obese rats without altering lipid compositions, implying that both chronic effects of obesity and relative resistance to leptin contributed to impaired biliary cholesterol elimination. In lean rats, acute leptin administration increased biliary cholesterol secretion rates. Without affecting hepatic cholesterol contents, leptin downregulated hepatic activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, upregulated activities of both sterol 27-hydroxylase and cholesterol 7alpha-hydroxylase, and lowered plasma very low-density lipoprotein cholesterol concentrations. Increased biliary cholesterol secretion in the setting of decreased cholesterol biosynthesis and increased catabolism to bile salts suggests that leptin promotes elimination of plasma cholesterol.

A cooperative interaction between soy protein and its isoflavone-enriched fraction lowers hepatic lipids in male obese Zucker rats and reduces blood platelet sensitivity in male Sprague-Dawley rats

Soy protein diets lower plasma cholesterol in hyperlipoproteinemic human subjects, as well as in animal models. We fed 7-wk-old male obese (fa/fa) and lean Zucker rats a modified AIN-76 diet (20 g protein/kg diet) containing casein (C), low isoflavone soy protein (38 mg isoflavones/kg diet; LI), or high isoflavone soy protein (578 mg isoflavones/kg diet; HI) for 70 d. In obese rats, plasma total cholesterol was 21 and 29% lower in the LI and HI groups, respectively, than in the C group (P: </= 0.004). Liver weight and liver triglyceride and cholesteryl ester concentrations were 27, 33 and 46% lower, respectively, in the LI group than in the C group (P: < 0.003). These liver measurements were 23, 24 and 57% lower, respectively, in the HI group than in the LI group (P: < 0.05). In a complementary study, 5-wk-old male Sprague-Dawley rats were fed the same C, LI and HI diets for 42 d. Thrombin-mediated platelet serotonin release in vitro was 13% lower in the HI group than in the C group (P: = 0.003). In a third study, 7-wk-old male Sprague-Dawley rats were fed either a modified AIN-76 control diet or a high fat casein-based atherogenic diet (140 g fat, 12 g cholesterol, and 2 g cholic acid/kg diet) with or without a soy isoflavones extract (983 mg isoflavones/kg diet) for 63 d. Addition of the isoflavones extract to the atherogenic diet lowered the liver triglyceride concentration by 33% relative to the atherogenic diet without isoflavones (P: = 0.0001). Our studies suggest that the hypocholesterolemic mechanism of dietary soy protein involves a cooperative interaction between the protein and isoflavone-enriched fraction that lowers hepatic lipid concentrations. We speculate that modulation of liver and plasma lipid homeostasis can also lower blood platelet sensitivity.

Regulation of bile acid pool size and plasma lipid levels in the SHR/N-corpulent rat: influence of the level of caloric intake

In the obese progeny of the SHR/N-cp strain of the rat the bile acid pool was at least twice as large as that in their lean littermates even when only 6 weeks old. The composition of the pool remained unchanged in the obese females, but in their male counterparts the proportion of cholic acid was significantly increased. Cholestyramine feeding reduced the pool size by 26% in the obese rats, but a similar effect also occurred in the lean animals. The obese rats consumed about 60% more food per day than their lean littermates. When obese females were pair-fed to the intake of their lean controls from 6 to 11 weeks of age, the bile acid pool remained significantly enlarged, although not to the same extent as in the obese rats fed ad lib. Plasma cholesterol levels were reduced but remained significantly higher than the levels in the lean animals. The marked hypertriglyceridemia exhibited by the obese rats fed ad libitum did not develop in their pair-fed counterparts. In contrast, there was a comparatively smaller reduction in plasma cholesterol and triglyceride levels in the obese rats fed cholestyramine. Hepatic steatosis persisted in the pair-fed animals as well as in those given cholestyramine. Restricting caloric intake significantly reduced the body weight gain of the obese rats but had little effect on the extent of their corpulence. These studies show that at least some of the characteristics of this congenic strain, including hypertriglyceridemia and hepatic and intestinal hypertrophy, are due mainly to excess dietary intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of long-term clofibric acid treatment on serum and tissue lipid and cholesterol levels in obese Zucker rats

The long-term effects of clofibric acid (200 mg/kg body weight) injected subcutaneously from 6-36 weeks of age were assessed in obese, hyperlipemic Zucker rats. At 18 and 36 weeks of age, treated rats had significantly lower fasted serum cholesterol levels but triacylglycerol levels were not affected. Rats were killed at 36 weeks of age at which time there were no differences in body and kidney weights between control and clofibric acid-treated rats. Liver, spleen and heart weights were lowered by clofibric acid treatment. In liver there was an elevation of lipid/g due to treatment but there were no effects on cholesterol/g or on either total liver lipid or cholesterol levels. In the epididymal fat pad of clofibric acid-treated rats, there was a 21% elevation of cholesterol level on a per pad basis. In the other organs, there were no effects of treatment on lipid or cholesterol levels except for lowered total cholesterol in kidney. Several liver lipogenic enzymes were lowered by treatment but malic enzyme was two times higher.

Effect of mevinolin on cholesterol metabolism in obese and lean Zucker rats

Mevinolin is a potent competitive inhibitor of HMG-CoA reductase, the enzyme catalyzing the major rate-limiting step in cholesterol synthesis. In this study the drug was administered as an intragastric dose at 2.5 mg/kg/day to 10 to 12-week-old lean and obese Zucker female rats over a 5-day period. Mevinolin showed no effect on plasma cholesterol levels in the lean rat; however, in the obese rat there was a significant decrease in plasma cholesterol (about a 40% decrease from initial levels). Although there was a difference in effect on plasma cholesterol levels in obese and lean rats, hepatocytes isolated from both fed lean and obese rats incubated with various concentrations of mevinolin exhibited similar levels of inhibition of cholesterol synthesis and showed no effects on the other metabolic processes studied. These results indicate that the drug was effective acutely on cholesterol synthesis in hepatocytes isolated from both lean and obese rats, but on a chronic treatment basis the hypocholesterolemic effect was observed only in the obese Zucker rat. This study supports the idea that the naturally occurring hypercholesterolemic obese Zucker rat may be a good model for testing potential new cholesterol lowering agents.