Daniel Gripois

Lipid atherogenic risk markers can be more favourably influenced by the cis-9,trans-11-octadecadienoate isomer than a conjugated linoleic acid mixture or fish oil in hamsters.

The aim of our present study was to compare the efficiency of conjugated linoleic acids (CLA) and fish oil in modulating atherogenic risk markers. Adult male hamsters were given a cholesterol-rich diet (0.6 g/kg) for 8 weeks; the diet was supplemented with 5 g cis-9,trans-11-CLA isomer/kg, 12 g CLA mixture (CLA-mix)/kg, 12 g fish oil/kg or 12 g fish oil+12 g CLA-mix/kg. The plasma cholesterol status was improved only with the cis-9,trans-11-CLA (HDL-cholesterol and HDL-cholesterol:LDL-cholesterol ratio, P<0.05), but was of borderline significance for CLA-mix (HDL-cholesterol:LDL-cholesterol ratio, P=0.06), with an increase (33-40 %) in the liver lipoprotein receptors (scavenger receptor-type I and LDL ApoB/E receptor) and HDL-binding protein 2 (P<0.05). A 100 % pigment gallstones incidence and a slight insulin resistance (homeostatic model assessment index) were observed in the CLA-mix-fed hamsters (P=-0.031). In comparison, fish-oil feeding alone improved merely the scavenger receptor-type I and HDL-binding protein 2 liver status and faeces sterol output. For most of our present observations, the concomitant intake of fish oil and CLA-mix gave dominant effects that were exclusive and specific to one or the other oil. In conclusion, part of the beneficial effects of CLA in the present study can be ascribed to the cis-9,trans-11-isomer, and these did not generally overlap with those of fish oil. In addition, the CLA-mix effects are clearly affected by the marine (n-3) fatty acids.

1H NMR metabonomics can differentiate the early atherogenic effect of dairy products in hyperlipidemic hamsters

Diet is an important environmental factor modulating the onset of atherosclerosis. The aim of this study was to evaluate the effects of different dairy-based food products on early atherogenesis using both conventional and metabonomic approaches in hyperlipidemic hamsters. The hamsters received up to 200 g/kg of fat as anhydrous butter or cheese made from various milk fats or canola-based oil (CV), in addition to a non-atherogenic low-fat diet. Aortic cholesteryl ester loading was considered to be an early atherogenic point, and metabolic changes linked to atherogenesis were measured using plasma (1)H NMR-based metabonomics. The lowest atherogenicity was obtained with the plant-oil cheese diet, followed by the dairy fat cheese diet, while the greatest atherogenicity was observed with the butter diet (P<0.05). Disease outcome was correlated with conventional plasma biomarkers (total cholesterol, triglycerides, LDL cholesterol, R(2)=0.42-0.60). NMR plasma metabonomics selectively captured part of the diet-induced metabotypes correlated with aortic cholesteryl esters (R(2)=0.63). In these metabotypes, VLDL lipids, cholesterol, and N-acetylglycoproteins (R(2) range: 0.45-0.51) were the most positively correlated metabolites, whereas a multimetabolite response at 3.75 ppm, albumin lysyl residues, and trimethylamine-N-oxide were the most negatively correlated metabolites (R(2) range: 0.43-0.63) of the aortic cholesteryl esters. Collectively, these metabolites predicted 89% of atherogenic variability compared to the 60% predicted by total plasma cholesterol alone. In conclusion, we show that the food environment can modulate the atherogenic effect of dairy fat. This proof-of-principle study demonstrates the first use of plasma metabonomics for improving the prognosis of diet-induced atherogenesis, revealing novel potential disease biomarkers.

Insulin injections enhance cholesterol gallstone incidence by changing the biliary cholesterol saturation index and apo A-I concentration in hamsters fed a lithogenic diet

BACKGROUND/AIMS A link between insulin and cholesterol gallstone disease has often been suspected but never demonstrated. The aim was to evaluate the direct implication of insulin in the gallbladder cholesterol gallstone formation process. METHODS Hamsters fed with a soft-inducing lithogenic diet, enriched with sucrose, were injected daily, for 1 week, either with long-acting insulin or saline (controls). RESULTS Insulin injections doubled the cholesterol gallstone incidence. The cholesterol saturation index (CSI) of bile significantly increased (+19%) and biliary apolipoprotein A-I (apo A-I) decreased, both in concentration (-71%) and the proportion relative to the total biliary proteins (-25%). No modifications in the biliary bile acid composition were noticed. Hepatic HMGCoA reductase activity was higher (+341%), CYP7A1 activity was lower (-52%), whereas CYP27A1 and CYP7B1 were not affected. The hepatic low-density liprotein (LDL)-receptor and SR-BI masses did not vary. The hepatic total cholesterol content increased (+42%). Fasting plasma phospholipid and triglyceride concentrations significantly decreased (-15 and -60%, respectively), but the cholesterol concentration remained constant. CONCLUSIONS These results suggest that insulin injections enhance cholesterol gallstone incidence by increasing the CSI of bile and decreasing the concentration and proportion of a biliary anti-nucleating protein, apo A-I. Insulin modulates the major enzymes of cholesterol and bile acid metabolisms in vivo.

Postprandial variations in the cholesteryl ester transfer protein activity, phospholipid transfer protein activity and plasma cholesterol efflux capacity in normolipidemic men.

BACKGROUND AND AIM Plasma cholesterol efflux capacity is stimulated during postprandial (PP) hypertriglycerdemia. Plasma cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are the key proteins in lipoprotein metabolism and remodelling, but their role during the PP cholesterol efflux process remains indeterminate. The aim of this study was to determine the effect of a fatty meal intake on plasma CETP and PLTP activities, and the capacity of plasma to promote cholesterol efflux, as well as to evaluate the relationship between these three key mechanisms of the reverse cholesterol transport process. METHODS AND RESULTS CETP and PLTP activities and the cholesterol efflux capacity of plasma were measured over eight hours following a fatty meal (1000 kcal, 62% fat) in 13 normolipidemic men. CETP activity and the cholesterol efflux capacity of plasma from Fu5AH cells increased after the meal, reaching a maximum after eight hours (respectively 32%, p = 0.06, and 6.5%, p = 0.045), whereas PLTP activity remained unchanged. CETP and PLTP activities did not correlate with plasma cholesterol efflux capacity in the fasting or PP state. Plasma CETP activity in the fasting state positively correlated with the plasma non-esterified fatty acid (NEFA) levels, but no correlation was found with any lipid or apolipoprotein postprandially. The cholesterol efflux capacity of plasma correlated positively with high-density lipoprotein (HDL) components, the best correlation being with the HDL phospholipid fraction in both the fasting and PP states. CONCLUSIONS These findings suggest that plasma CETP and PLTP activities in healthy normolipidemic subjects are differently regulated in the PP state, and are not correlated with the increased cholesterol efflux capacity of PP plasma. HDL-phospholipid remains the key factor in the regulation of the capacity of plasma to promote Fu5AH cell cholesterol efflux.

Fat-depleted CLA-treated mice enter torpor after a short period of fasting

Resting energy expenditure (Resting-EE), EE with treadmill exercise, and post-prandial thermogenesis were continuously monitored by indirect calorimetry during a 24 h recording session in control (CT) and CLA-treated (CLA) (1% CLA in the food, by weight) C57Bl/6 male mice. After 15 days of CLA treatment, the fat content of CLA mice had fallen to 20% of that in CT mice. CLA mice were able to face the energy challenge of exercise but used less lipid than CT mice. Resting-EE values fell during the post-exercise period. The thermogenic response to a calibrated test meal given 5 h after the run abolished the differences in EE and substrate oxidation between CT and CLA mice. However, 2.5 h after ingestion of the test meal onward, CT mice gradually increased their lipid oxidation to sustain resting-EE levels. In contrast, CLA mice did not increase their lipid oxidation and their resting-EE levels fell significantly until they entered into torpor. Blood leptin was low but similar in CT and CLA-treated mice suggesting that leptin is not critical to induce torpor. We suggest that the durable inhibition of lipid oxidation in fasting CLA mice was an adaptive behaviour devoted at sparing the residual adipose deposits.

Effects of insulin deficiency on lipoproteins and their hepatic receptors in Rico rats.

The present study was designed to examine the effect of streptozotocin (STZ)-induced diabetes on the plasma lipoprotein profile and hepatic expression of the LDL receptor and HDL binding protein (HB2) in hypercholesterolemic Rico rats. The plasma level of HDL1 (density range 1.040-1.063), which is particularly high in this rat strain, decreased (-25%) 28 d after STZ administration (50 mg/kg). In contrast, the treatment increased (+54%) the plasma concentration of HDL2 (density range 1.063-1.210). These variations in the lipoprotein concentrations were associated with inverse changes in the hepatic protein levels of the LDL receptor (+118%) and HB2 (-46%). These results suggest that the hepatic expression of HB2, a putative HDL receptor, can influence the plasma level of apo Al-rich HDL as has already been shown for the LDL receptor for apo B/E containing lipoproteins.

Diet-dependent effects of insulin infusion on the hepatic lipoprotein receptors and the key enzymes of bile acid synthesis in the hamster.

The effects of an induced hyperinsulinemia on both the cholesterol and bile acid metabolisms were analyzed in the hamster. The role of dietary sucrose as modulator of these effects was evaluated by feeding the animals with two semi-synthetic diets containing a low (SD, 20%) and a high (LD, 62.5%) sucrose proportion. Hamsters fed under basal nutritional conditions (chow diet, CD) were also used. LD enabled the consequences of an insulin infusion on cholesterol gallstone formation to be evaluated. Subcutaneous osmotic pumps were implanted in all the animals and delivered either 3 IU/day of insulin (insulin groups: CDI, SDI, LDI) or saline (control groups: CDC, SDC, LDC). Several parameters bound to lipid metabolism were measured. The plasma cholesterol concentration remained constant in all the insulin treated groups compared to the controls. Phospholipid and triglyceride concentrations decreased in both the plasma and liver in the CDI and SDI groups. A lower SR-BI mass (around 50%) was found in the liver of CDI and SDI hamsters with concomitant higher hydroxy-methyl-glutaryl coenzyme A reductase activity. The LDL-receptor mass and cholesterol 7alpha-hydroxylase activity in the LDI group were both decreased (-47%, -71% respectively). No variations in the cholesterol gallstone incidence were observed. In conclusion, chronic insulin infusion in growing hamsters induced similar effects on cholesterol metabolism in the CD and SD groups but different ones, between diets containing a low (SD) and a high (LD) sucrose proportion. The distribution of triglycerides and phospholipids in the plasma, liver and bile was also affected by the insulin infusion.

Effects of insulin on brain serotonin in the young rat: Influence of thyroid status

Thyroid status has been shown to modify the adrenal catecholaminergic response to insulin. The influence of thyroid status on the brain serotonergic response to insulin is the subject of the present report. Newborn rats were divided into three groups: euthyroid, hypothyroid (propylthiouracil given to the suckling mother), and hypothyroid-treated with triiodothyronine (T3) as replacement therapy. At 14 days of age, the animals in each group received either insulin (10 IU/kg SC) or saline. Levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were determined in several brain regions. Hypothyroidism induced increases in hypothalamic 5-HT and 5-HIAA and in cortical 5-HIAA levels. The elevations in 5-HIAA levels were reversed by T3. Insulin treatment-induced increases in 5-HIAA levels in all brain regions of both the hypothyroid and the T3-replaced rats. Thyroid status thus influences the serotonergic response to insulin in the young rat, but contrary to what occurred in adrenals for catecholamines, hypothyroidism enhances the central serotonergic response to insulin.