Carbohydrate restriction and dietary cholesterol distinctly affect plasma lipids and lipoprotein subfractions in adult guinea pigs

Development of a novel Guinea Pig model producing transgenerational endothelial transcriptional changes driven by maternal food restriction and a second metabolic insult of high fat diet

Developmental programming of chronic adverse cardiovascular health outcomes has been studied both using numerous human populations and an array of animal models. However, the mechanisms that produce transgenerational effects have been difficult to study due to a lack of developmentally relevant models. As such, how increased disease risk is carried to the second generation has been poorly studied. We hypothesized that the endothelium which mediates many acute and chronic vascular inflammatory responses is a key player in these effects, and epidemiological studies implicate transgenerational nutritional effects on endothelial health. To study the mutigenerational effects of maternal undernutrition on offspring endothelial health, we developed a model of transgenerational nutritional stress in guinea pigs, a translationally relevant precocial species with a relatively short lifespan. First- and second-generation offspring were subjected to a high fat diet in adolescence to exacerbate negative cardiovascular health. To assess transcriptional changes, we performed bulk RNA-sequencing in carotid artery endothelial cells, with groups stratified as prenatal control or food restricted, and postnatal control or high fat diet. We detected statistically significant gene alterations for each dietary permutation, some of which were unique to treatments and other transcriptional signatures shared by multiple or all conditions. These findings highlight a core group of genes altered by high fat diet that is shared by all cohorts and a divergence of transgenerational effects between the prenatal ad libitum and dietary restriction groups. This study establishes the groundwork for this model to be used to better understand the interplay of prenatal stress and genetic reprogramming.

Compared with Powdered Lutein, a Lutein Nanoemulsion Increases Plasma and Liver Lutein, Protects against Hepatic Steatosis, and Affects Lipoprotein Metabolism in Guinea Pigs

BACKGROUND

It is not clear how oil-in-water nanoemulsions of lutein may affect bioavailability and consequently alter lipoprotein metabolism, oxidative stress, and inflammation.

OBJECTIVE

The bioavailability as well as effects of a powdered lutein (PL) and an oil-in-water lutein nanoemulsion (NANO; particle size: 254.2 nm; polydispersity index: 0.29; and ζ-potential: -65 mV) on metabolic variables in liver, plasma, and adipose tissue in a guinea pig model of hepatic steatosis were evaluated.

METHODS

Twenty-four 2-mo-old male Hartley guinea pigs, weighing 200-300 g (n = 8/group), were fed diets containing 0.25 g cholesterol/100 g to induce liver injury for the duration of the study. They were allocated to control (0 mg lutein), PL (3.5 mg/d), or NANO (3.5 mg/d) groups. After 6 wk, plasma, liver, and adipose tissue were collected for determination of lutein, plasma lipids, tissue cholesterol, and inflammatory cytokines.

RESULTS

The NANO group had 2-fold higher concentrations of lutein in plasma (P < 0.001) and 1.6-fold higher concentrations in liver (P < 0.001) than did the PL group, indicating greater bioavailability of this carotenoid. The NANO group also had 24% lower hepatic steatosis scores (P < 0.05), 31% lower hepatic cholesterol accumulation (P < 0.05), and 64% lower plasma alanine aminotransferase (P < 0.05) than did the control group. Hepatic oxidized LDL was 55% lower in both the PL and NANO groups than in the control group (P < 0.05). In plasma, the NANO group had 2-fold higher concentrations of LDL and HDL cholesterol as well as a 2-fold higher number of VLDL, LDL, and HDL particles than did the other 2 groups as evaluated by nuclear magnetic resonance. Furthermore, the NANO group had 15% higher concentrations of free cholesterol in adipose tissue, resulting in higher concentrations of inflammatory markers, than did the other 2 groups.

CONCLUSIONS

These results indicate that, although this lutein nanoemulsion exerted protective effects against hepatic steatosis, plasma lipoproteins and adipose tissue cholesterol were increased. These data suggest that the metabolic effects of this particular nanoemulsion might not be protective in all tissues in guinea pigs.

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.

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.

Ruminant-produced trans-fatty acids raise plasma total and small HDL particle concentrations in male Hartley guinea pigs

Although trans-fatty acid (tFA) intake has been positively associated with coronary heart disease (CHD), the relative effect of consuming industrially produced (IP)- compared with ruminant-produced (RP)-tFA on CHD risk factors is unclear. This study was designed to examine the effects of feeding partially hydrogenated vegetable oil (PHVO), IP-tFA source, and butter oil (BO), RP-tFA source, on the development of atherosclerosis and risk factors associated with CHD. Forty-eight male Hartley guinea pigs were fed a hypercholesterolemic diet containing (9% by weight) PHVO, BO, coconut oil (CO; positive control), or soybean oil (SO; negative control) for 8 or 12 wk (n = 6/group). Morphological analysis revealed that none of the groups developed atherosclerosis. Plasma and hepatic lipids did not differ between the tFA groups, but total and small HDL particles were significantly higher in the BO group than in the PHVO group and mean HDL particle size was significantly smaller in the BO group than in the PHVO group. Compared with the other treatment groups, the SO treatment resulted in significantly lower total cholesterol (TC) and LDL cholesterol in plasma, whereas hepatic TC was significantly higher in the SO group than in the other treatment groups. Plasma and hepatic cholesterol concentrations did not differ between the tFA and CO treatments. These results demonstrate that when fed at a high dose, IP- and RP-tFA had the same effect on established CHD risk factors in male Hartley guinea pigs. The effects of RP-tFA on HDL particle sizes and concentrations warrant further investigation.

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.