Cholesterol-induced inflammation and macrophage accumulation in adipose tissue is reduced by a low carbohydrate diet in guinea pigs.

BACKGROUND/OBJECTIVES: The main objective of this study was to evaluate the effects of a high cholesterol (HC) dietary challenge on cholesterol tissue accumulation, inflammation, adipocyte differentiation, and macrophage infiltration in guinea pigs. A second objective was to assess whether macronutrient manipulation would reverse these metabolic alterations. MATERIALS/METHODS: Male Hartley guinea pigs (10/group) were assigned to either low cholesterol (LC) (0.04g/100g) or high cholesterol (HC) (0.25g/100g) diets for six weeks. For the second experiment, 20 guinea pigs were fed the HC diet for six weeks and then assigned to either a low carbohydrate (CHO) diet (L-CHO) (10% energy from CHO) or a high CHO diet (H-CHO) (54% CHO) for an additional six weeks. RESULTS: Higher concentrations of total (P < 0.005) and free (P < 0.05) cholesterol were observed in both adipose tissue and aortas of guinea pigs fed the HC compared to those in the LC group. In addition, higher concentrations of pro-inflammatory cytokines in the adipose tissue (P < 0.005) and lower concentrations of anti-inflammatory interleukin (IL)-10 were observed in the HC group (P < 0.05) compared to the LC group. Of particular interest, adipocytes in the HC group were smaller in size (P < 0.05) and showed increased macrophage infiltration compared to the LC group. When compared to the H-CHO group, lower concentrations of cholesterol in both adipose and aortas as well as lower concentrations of inflammatory cytokines in adipose tissue were observed in the L-CHO group (P < 0.05). In addition, guinea pigs fed the L-CHO exhibited larger adipose cells and lower macrophage infiltration compared to the H-CHO group. CONCLUSIONS: The results of this study strongly suggest that HC induces metabolic dysregulation associated with inflammation in adipose tissue and that L-CHO is more effective than H-CHO in attenuating these detrimental effects.

Effects of increased dietary cholesterol with carbohydrate restriction on hepatic lipid metabolism in Guinea pigs.

Excessive lipid accumulation within hepatocytes, or hepatic steatosis, is the pathognominic feature of nonalcoholic fatty liver disease (NAFLD), a disease associated with insulin resistance and obesity. Low-carbohydrate diets (LCD) improve these conditions and were implemented in this study to potentially attenuate hepatic steatosis in hypercholesterolemic guinea pigs. Male guinea pigs (n = 10 per group) were randomly assigned to consume high cholesterol (0.25 g/100 g) in either a LCD or a high-carbohydrate diet (HCD) for 12 wk. As compared with HCD, plasma LDL cholesterol was lower and plasma triglycerides were higher in animals fed the LCD diet, with no differences in plasma free fatty acids or glucose. The most prominent finding was a 40% increase in liver weight in guinea pigs fed the LCD diet despite no differences in hepatic cholesterol or triglycerides between the LCD and the HCD groups. Regardless of diet, all livers had severe hepatic steatosis on histologic examination. Regression analysis suggested that liver weight was independent of body weight and liver mass was independent of hepatic lipid content. LCD livers had more proliferating hepatocytes than did HCD livers, suggesting that in the context of cholesterol-induced hepatic steatosis, dietary carbohydrate restriction enhances liver cell proliferation.

A lutein-enriched diet prevents cholesterol accumulation and decreases oxidized LDL and inflammatory cytokines in the aorta of guinea pigs.

Lutein has been shown to be protective against age-related macular degeneration; however, the antiinflammatory and antioxidant effects of this carotenoid in aortas are less known. Guinea pigs were fed a hypercholesterolemic diet (0.25 g cholesterol/100 g) and randomly allocated to a control group (n = 9) or a lutein group (n = 10) (0.01 g/100 g lutein) [corrected] and fed the experimental diets for 12 wk. Plasma LDL cholesterol and TG did not differ between groups; however, the lutein group had lower concentrations of medium size LDL (P < 0.05). As expected, guinea pigs from the lutein group had higher concentrations of plasma and liver lutein than those from the control group (P < 0.0001). Aortic cholesterol and malondialdehyde concentrations were lower in the lutein group (9.6 ± 2.8 mmol/g and 1.69 ± 1.35 nmol/mg protein) compared to the control group (15.5 ± 2.3 mmol/g and 2.98 ± 1.45 nmol/mg protein) (P < 0.05). Hematoxilin and eosin staining indicated that aortas from the control group presented focal intimal thickening, whereas either less thickness or no visible thickness was present in aortas from the lutein group. Oxidized LDL (oxLDL) was lower both in plasma and aorta in the lutein group compared to the control group (P < 0.001). Aortic cytokines were also lower in the lutein group (P < 0.05). Plasma lutein and oxLDL (r = -0.79; P < 0.0001) and plasma lutein and aortic oxLDL (r = -0.64; P < 0.0001) were negatively correlated. These data suggest that lutein exerts potent antioxidant and antiinflammatory effects in aortic tissue that may protect against development of atherosclerosis in guinea pigs.

Low-carbohydrate diets reduce lipid accumulation and arterial inflammation in guinea pigs fed a high-cholesterol diet.

INTRODUCTION: Low-carbohydrate diets (LCD) efficiently induce weight loss and favorably affect plasma lipids, however, the effect of LCD on atherosclerosis is still argued. OBJECTIVE: To evaluate the effect of LCD on the prevention of atherosclerosis. METHODS: Twenty guinea pigs were fed either a LCD or a low-fat diet (LFD) in combination with high-cholesterol (0.25g/100g) for 12 weeks. The percentage energy of macronutrient distribution was 10:65:25 for carbohydrate:fat:protein for the LCD, and 55:20:25 for the LFD. Plasma lipids were measured using colorimetric assays. Plasma and aortic oxidized (oxLDL) were quantified using ELISA methods. Inflammatory cytokines were measured in aortic homogenates using an immunoassay. H&E stained sections of aortic sinus and Schultz stained sections of carotid arteries were examined. RESULTS: LDL cholesterol was lower in the LCD compared to the LFD group (71.9+/-34.8 vs. 81.7+/-26.9mg/dL; p=0.039). Aortic cholesterol was also lower in the LCD (4.98+/-1.3mg/g) compared to the LFD group (6.68+/-2.0mg/g); p<0.05. The Schultz staining method confirmed less aortic cholesterol accumulation in the LCD group. Plasma oxLDL did not differ between groups, however, aortic oxLDL was 61% lower in the LCD compared to the LFD group (p=0.045). There was a positive correlation (r=0.63, p=0.03) between oxLDL and cholesterol concentration in the aorta of LFD group, which was not observed in LCD group (r=-0.05, p=0.96). Inflammatory markers were reduced in guinea pigs from the LCD group (p<0.05) and they were correlated with the decreases in oxLDL in aorta. CONCLUSION: These results suggest that LCD not only decreases lipid deposition, but also prevents the accumulation of oxLDL and reduces inflammatory cytokines within the arterial wall and may prevent atherosclerosis.

Low-carbohydrate diet disrupts the association between insulin resistance and weight gain.

The cornerstone to treat metabolic syndrome and insulin resistance is dietary intervention. Both low-carbohydrate diet (LCD) and low-fat diet (LFD) have been reported to induce weight loss and improve these conditions. One of the factors associated with a subject's adherence to the diet is satiety. The aim of this study was to evaluate the effects of LCD and LFD on body weight, appetite hormones, and insulin resistance. Twenty guinea pigs were randomly assigned to LCD or LFD (60%:10%:30% or 20%:55%:25% of energy from fat/carbohydrate/protein, respectively) for 12 weeks. Weight and food intake were recorded every week. After this period, animals were killed and plasma was obtained to measure plasma glucose and insulin, appetite hormones, and ketone bodies. Guinea pigs fed LCD gained more weight than those fed LFD. The daily amount of food intake in grams was not different between groups, suggesting that food density and gastric distension played a role in satiety. There was no difference in leptin levels, which excludes the hypothesis of leptin resistance in the LCD group. However, plasma glucagon-like peptide-1 was 47.1% lower in animals fed LCD (P < .05). Plasma glucose, plasma insulin, and insulin sensitivity were not different between groups. However, the heavier animals that were fed LFD had impairment in insulin sensitivity, which was not observed in those fed LCD. These findings suggest that satiety was dependent on the amount of food ingested. The weight gain in animals fed LCD may be related to their greater caloric intake, lower levels of glucagon-like peptide-1, and higher protein consumption. The adoption of LCD promotes a unique metabolic state that prevents insulin resistance, even in guinea pigs that gained more weight. The association between weight gain and insulin resistance seems to be dependent on high carbohydrate intake.