A high-cholesterol, n-3 polyunsaturated fatty acid diet causes different responses in rats and hamsters

A Preliminary Study on Hepatoprotective, Hypolipidemic and Aortic Morphometric Effects of Omega-3-Rich Fish Oil in Hypercholesterolemic Mice

This study aims to evaluate the hepatoprotective, hypolipidemic and aortic morphometric effects of fish oil rich in omega-3 in hypercholesterolemic BALB/c mice. This is an experimental model that included 16 male BALB/c mice (Mus musculus) divided into three groups (G1 (standard commercial chow and 0.9% saline solution), G2 (hypercholesterolemic diet and 0.9% saline solution) and G3 (hypercholesterolemic diet and fish oil)) for 8 weeks. There was no significant difference in the treatment with omega-3-rich fish oil in the lipid profile (p > 0.05). In the histological analysis, group G2 detected the presence of hepatitis and liver tissue necrosis, but this was not observed in group G3. As for the morphometry in the light area of the vessel, the G1 group had a higher score (2.62 ± 0.36 mm2) when compared to G2 (2.10 ± 0.16 mm2) and G3 (2.26 ± 0.25 mm2) (p < 0.05). The vessel wall thickness did not differ between the groups (p > 0.05). It is concluded that supplementation with fish oil rich in omega-3 carried out in this study may have a protective effect on liver tissue, but it has not yet improved the lipid and morphometric profile. Despite this research being preliminary, it is a relevant study with future prospects for improving the doses of EPA and DHA in order to better elucidate the benefits of fish oil in models of dyslipidemia.

Improvement in serum lipids and liver morphology after supplementation of the diet with fish oil is more evident under regular feeding conditions than under high-fat or mixed diets in rats

BACKGROUND

Dietary n- 3 polyunsaturated fatty acids (PUFAs) have a role in preventing cardiovascular and hepatic diseases. However, their effects might differ significantly depending on individual dietary patterns. The aim of the present study was to evaluate the effects of dietary supplementation with ω-3 fatty acids (FA), administered in different schedules, on hepatic and aortic histological structure, lipid profile, and body weight (BW) in male Wistar rats under standard (SD), high-fat diet (HFD) and mixed feeding conditions.

METHODS

PUFA treatment consisted of the administration of 50 mg/kg fish oil (FO) daily by oral gavage. HFD was obtained by adding a suspension of 4% cholesterol, thiouracil and cholic acid to the animals' drinking water. The rats were maintained on the diets for 6 weeks, and different schedules of PUFA administration were used. At 14, 28, and 42 days, the morphology of liver and aortic samples and the levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), and triglycerides (TG) were assessed.

RESULTS

The HFD groups exhibited significant hyperlipidemia and aortic inflammation, with progression to atherogenesis after 6 weeks. Administration of PUFAs slightly attenuated the aortic changes in these groups and reduced the liver's tendency to steatosis. FO-induced metabolic improvement was more evident in SD than in HFD rats. For instance, after the first 2 weeks, SD animals that received PUFAs had significantly increased HDL levels vs. controls (62.375 ± 4.10 vs. 52.625 ± 8.38 mg/dL, P < 0.05), but HFD rats did not, and decreased TG levels were observed exclusively in the SD rats (57.6 ± 4.09 vs. 66 ± 4.69 mg/dL, P < 0.05). After 6 weeks of n- 3 PUFA administration, LDL was significantly lower in the SD rats than in controls (13.67 ± 4.13 vs. 30.83 ± 2.86 mg/dL, P < 0.001), but the decrease in the HFD rats, although significant (49.17 ± 5.85 mg/dL vs. 57.17 ± 4.96 g/dL, P < 0.05), was not as marked. In the mixed-diet groups, administration of 50 mg/kg/day FO for 14 days under SD conditions following 4 weeks of HFD slightly decreased TG (86.625 ± 11.67 vs. 73 ± 4.52 mg/dL, P < 0.05) and increased HDL (45.875 ± 5.28 vs. 56 ± 3.16 mg/dL). However, in these animals, n-3 PUFA administration had no effect on LDL or TC. Administration of half of the above dose failed to improve any biochemical parameters. FO protected against excessive weight gain mainly under SD conditions.

CONCLUSIONS

The results show that FO confers more protection against cardiovascular risk factors (increased LDL and TG, decreased HDL) and liver lipid accumulation when given to rats consuming regular diets than when given to rats consuming a high-fat diet. This argues that priority should be given to consumption of a healthy diet rather than to the use of supplements. The effectiveness of n-3 PUFAs might be reduced in the case of hyperlipidic intake or after consumption of a high-fat diet.

Effects of fish oil and spirulina on oxidative stress and inflammation in hypercholesterolemic hamsters

Background

Altered plasma lipids, oxidative stress, and inflammation have been involved in the pathogenesis of cardiovascular disease. Fish oil has shown inconclusive effects on plasma lipids and oxidative stress. Spirulina has both cholesterol lowering and antioxidant properties. However, the effect of fish oil and spirulina on hypercholesterolemia has not been studied. We investigated the effects of fish oil, spirulina, and their combination on hypercholesterolemia.

Methods

The hamsters were divided into 7 groups: control, high cholesterol (HF), fish oil (post FO), spirulina (post SP), and a combination of fish oil and spirulina (post SF, pre-SF, and HF + SF) groups. The HF and HF + SF groups were given a high cholesterol diet for 8 weeks. The post FO, post SP, and post SF groups were given a high cholesterol diet for 4 weeks and then the treatment for 4 weeks. The pre-SF group was given the combined treatment for 4 weeks and then a high cholesterol diet for 4 weeks.

Results

The HF and HF + SF groups altered plasma lipids, increased oxidative stress, inhibited antioxidants, and increased inflammation. While the post FO group increased plasma lipids and was more atherogenic. The vice versa was observed in spirulina-treated group. Both the post SP and post SF groups inhibited oxidative stress and increased antioxidant status, and post FO and post SP diets regulated pro-inflammatory cytokines to near the control levels.

Conclusions

Both single treatment of fish oil or spirulina inhibit oxidative stress and inflammation. Treatment with a combination of fish oil and spirulina (post SF) may be beneficial for diet-induced hypercholesterolemic hamsters.

Hyperlipidemic guinea pig model: mechanisms of triglyceride metabolism disorder and comparison to rat

Guinea pigs and rats are both common animal models for hyperlipidemia studies. However, many recent studies have suggested that rats do not develop hypertriglyceridemia in response to cholesterol feeding. In the present work, the differences in triglyceride metabolism between guinea pigs and rats were investigated. Feeding a high-fat diet containing 0.1% cholesterol and 10% lard for 4 weeks led to a significant increase in plasma total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG) and free fatty acid (FFA) in guinea pigs but not in rats. By contrast, hepatic TG levels in rats were greatly increased in response to the high-fat diet, while it remained unchanged in guinea pigs. Furthermore, the hepatic acyl CoA:diacylglycerol acyltransferase (DGAT) activity and microsomal triglyceride transfer protein (MTTP) mRNA levels in guinea pigs fed a high-fat diet were significantly higher than those in the control group, which implies an increased very-low-density lipoprotein (VLDL)-TG secretion rate in guinea pigs in response to a high-fat diet. Hepatic carnitine palmitoyltransferase-1 (CPT-1) activity and peroxisome proliferator-activated receptor-α (PPARα) mRNA levels were upregulated in guinea pigs, but not rats, fed a high-fat diet. These findings may explain the differences in plasma and hepatic TG concentrations between guinea pigs and rats. These results suggest that there are differences in triglyceride metabolism between the two species when fed high-fat diets.

n-3 PUFA prevent metabolic disturbances associated with obesity and improve endothelial function in golden Syrian hamsters fed with a high-fat diet

Glucose intolerance and dyslipidaemia are independent risk factors for endothelium dysfunction and CVD. The aim of the present study was to analyse the preventive effect of n-3 PUFA (EPA and DHA) on lipid and carbohydrate disturbances and endothelial dysfunction. Three groups of adult hamsters were studied for 20 weeks: (1) control diet (Control); (2) high-fat diet (HF); (3) high-fat diet enriched with n-3 PUFA (HFn-3) groups. The increase in body weight and fat mass in the HF compared to the Control group (P < 0.05) was not found in the HFn-3 group. Muscle TAG content was similar in the Control and HF groups, but significantly lower in the HFn-3 group (P = 0.008). Glucose tolerance was impaired in the HF compared to the Control group, but this impairment was prevented by n-3 PUFA in the HFn-3 group (P < 0.001). Plasma TAG and cholesterol were higher in the HF group compared to the Control group (P < 0.001), but lower in the HFn-3 group compared to the HF group (P < 0.001). HDL-cholesterol was lower in the HFn-3 group compared to the Control and HF groups (P < 0.0005). Hepatic secretion of TAG was lower in the HFn-3 group compared to the HF group (P < 0.005), but did not differ from the Control group. Hepatic gene expression of sterol regulatory element-binding protein-1c, diacylglycerol O-acyltransferase 2 and stearyl CoA desaturase 1 was lower in the HFn-3 group, whereas carnitine palmitoyl transferase 1 and scavenger receptor class B type 1 expression was higher (P < 0.05). In adipocytes and adipose macrophages, PPARγ and TNFα expression was higher in the HF and HFn-3 groups compared to the Control group. Endothelium relaxation was higher in the HFn-3 (P < 0.001) than in the HF and Control groups, and was correlated with glucose intolerance (P = 0.03) and cholesterol (P = 0.0003). In conclusion, n-3 PUFA prevent some metabolic disturbances induced by high-fat diet and improve endothelial function in hamsters.

Unrefined and refined black raspberry seed oils significantly lower triglycerides and moderately affect cholesterol metabolism in male Syrian hamsters

Unrefined and refined black raspberry seed oils (RSOs) were examined for their lipid-modulating effects in male Syrian hamsters fed high-cholesterol (0.12% g/g), high-fat (9% g/g) diets. Hamsters fed the refined and the unrefined RSO diets had equivalently lower plasma total cholesterol and high-density lipoprotein (HDL) cholesterol in comparison with the atherogenic coconut oil diet. The unrefined RSO treatment group did not differ in liver total and esterified cholesterol from the coconut oil-fed control animals, but the refined RSO resulted in significantly elevated liver total and esterified cholesterol concentrations. The unrefined RSO diets significantly lowered plasma triglycerides (46%; P=.0126) in comparison with the coconut oil diet, whereas the refined RSO only tended to lower plasma triglyceride (29%; P=.1630). Liver triglyceride concentrations were lower in the unrefined (46%; P=.0002) and refined (36%; P=.0005) RSO-fed animals than the coconut oil group, with the unrefined RSO diet eliciting a lower concentration than the soybean oil diet. Both RSOs demonstrated a null or moderate effect on cholesterol metabolism despite enrichment in linoleic acid, significantly lowering HDL cholesterol but not non-HDL cholesterol. Dramatically, both RSOs significantly reduced hypertriglyceridemia, most likely due to enrichment in α-linolenic acid. As a terrestrial source of α-linolenic acid, black RSOs, both refined and unrefined, provide a promising alternative to fish oil supplementation in management of hypertriglyceridemia, as demonstrated in hamsters fed high levels of dietary triglyceride and cholesterol.

Effect of dietary fats on oxidative-antioxidative status of blood in rats

This study was performed to examine the effect of different fat sources, lard, sunflower oil (SO), and fish oil (FO) in high-fat and low-fat diet on reactive oxygen species generation by blood phagocytes, glutathione redox status in erythrocytes, and total plasma antioxidant ability in rats. Whole blood chemiluminescence (CL) did not differ between three low-fat fed groups. However, baseline and phorbol myristate acetate (PMA)-stimulated CL in blood of high-lard fed rats were lower than in low-lard and high-SO fed animals. Phagocyte-stimulated oxidative burst was higher in rats fed high-SO diet than in those fed low-SO and high-FO diets. The highest level of oxidize glutathione (GSSH), the lowest reduce glutathione (GSH)/GSSG ratio in erythrocytes, and the highest plasma activity to reduce ferric ions were observed in rats fed both diets contaning linoleic acid-rich sunflower oil compared to animals fed the corresponding energy from other fats. 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity of plasma was lower in high-lard and high-FO fed rats compared to the corresponding low-fat diets, and the lowest in low-FO fed rats among low-fat fed animals. We presume from our results that linoleic acid may have dual effect, prooxidative in blood cells but maintaining total antioxidant plasma ability.

Signalling mechanisms linking hepatic glucose and lipid metabolism

Fatty liver and hepatic triglyceride accumulation are strongly associated with obesity, insulin resistance and type 2 diabetes, and are subject to nutritional influences. Hepatic regulation of glucose and lipid homeostasis is influenced by a complex system of hormones, hormonally regulated signalling pathways and transcription factors. Recently, considerable progress has been made in elucidating molecular pathways and potential factors that are affected in insulin-resistant states. In this review we discuss some of the key factors that are involved in both the regulation of glucose and lipid metabolism in the liver. Understanding the molecular network that links hepatic lipid accumulation and impaired glucose metabolism may provide targets for dietary or pharmacological interventions.

Effects of dietary herring roe lipids on plasma lipid, glucose, insulin, and adiponectin concentrations in mice

The aim of this study was to evaluate the effects of dietary Kazunoko (salted herring roe) lipids, which contain large amounts of cholesterol, phosphatidylcholine, and n-3 polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), on lipid and glucose metabolism in mice. Male Crlj:CD-1 (ICR) mice were fed one of four experimental diets which contained 6% lard, 1% Kazunoko lipids + 5% lard, 3% Kazunoko lipids + 3% lard, and 6% Kazunoko lipids for 12 weeks. Plasma total cholesterol, triacylglycerol, phospholipid, and glucose concentrations were significantly lower in the 3% and 6% Kazunoko lipid diet groups than in lard and 1% Kazunoko lipid diet groups (p < 0.05). Plasma adiponectin concentrations of mice fed the 6% Kazunoko lipid diet were higher than those of animals fed the lard diet group. These results suggest that EPA and DHA rather than cholesterol in the Kazunoko lipids influence the plasma total cholesterol level. The constituent Kazunoko lipids may not only decrease the levels of plasma lipids but also decrease glucose concentrations by enhancing plasma adiponectin levels in mice.