Claude Senault

Relation between membrane phospholipid composition, fluidity and function in mitochondria of rat brown adipose tissue. Effect of thermal adaptation and essential fatty acid deficiency.

Male weanling rats were maintained either at 28 degrees C (thermoneutrality) or at 5 degrees C (cold adaptation). During 9 weeks they were fed either a 2% hydrogenated coconut oil diet deficient in essential fatty acids or a diet containing 2% sunflower oil. The respective incidences of cold adaptation and of EFA deficiency on lipid composition of mitochondrial membranes from brown adipose tissue (BAT) were investigated. Using 1,6 diphenylhexatriene (DPH) as a probe, the parameters of membrane fluidity were estimated by steady-state fluorescence polarization measurements (rs) and by time-resolved fluorescence anisotropy decay (order parameter S). Cold acclimation induced a decrease of phosphatidylcholine to phosphatidylethanolamine (PC/PE ratio), an increase of the total fatty acid unsaturation index (T.U.). EFA deficiency had the same effect as cold on the PC/PE ratio, but decreased T.U. Cold adaptation induced a larger decrease of S than of rs, whereas EFA deficiency only increased rs and did not modify S. In liposomes prepared from mitochondrial lipids, rs values were smaller than in whole mitochondria. Both in cold-adapted and in EFA-deficient rats the variations of rs were correlated with lipid unsaturation. Comparison between BAT thermogenic activity, assessed by GDP binding and proportions of PE and PC showed a high correlation suggesting a change in the membrane occurring with the increase of mitochondrial activity that could be related to phospholipid composition rather than to membrane fluidity.

Oleic acid-rich increase increase the capacity of postprandial serum to promote cholesterol efflux from Fu5AH cells

Abstract Cell cholesterol efflux to serum is stimulated after an oral fat load. The impact of meal fatty acid composition was explored by measure of serum promoted cholesterol efflux from Fu5AH cells after ingestion of 4 different fats: sunflower (Sf), oleic-sunflower (Ol), a mixed oil (Mx), and beef tallow (Bt). High density lipoprotein (HDL)2 and HDL3 were isolated and analyzed. Cholesterol efflux increased regularly after Ol (P

The lipid composition of plasma membrane and mitochondrial fractions from epididymal adipocytes of cold-acclimated rats

1. The effects of cold acclimation (5 degrees C) on the lipid composition of plasma membrane and mitochondrial fractions from epididymal adipocytes of rats were studied. 2. The adipocyte plasma membrane fraction of the cold-acclimated rats had lower lipid, phospholipid and cholesterol to protein weight ratios, a lower cholesterol to sphingomyelin molar ratio, and a higher linoleic acid content in the phospholipids than controls. 3. The mitochondrial fraction of the cold-acclimated rat adipocyte had lower ratios of cholesterol to protein (weight), to phospholipid and to cardiolipin (molar), and less sphingomyelin content than did controls. 4. These data, discussed in terms of alterations in physical and biochemical properties, indicate cold-induced changes at the membrane level in rat epididymal adipocytes.

Non-shivering thermogenesis and brown adipose tissue activity in essential fatty acid deficient rats.

The effects of essential fatty acid (EFA) deficiency on energetic metabolism and interscapular brown adipose tissue (BAT) activity were examined in the cold acclimated rat. Weanling male Long-Evans rats were fed on a low fat semipurified diet (control diet, 2% sunflower oil; EFA deficient diet, 2% hydrogenated coconut oil) for 9 weeks. They were exposed at 5 degrees C for the last 5 weeks. In EFA deficient rats, compared to controls, growth retardation reached 22% at sacrifice. Caloric intake being the same in the two groups, it follows that food efficiency was decreased by 40%. Resting metabolism in relation to body surface area was 25% increased. Calorigenic effect of norepinephrine (NE) in vivo (test of non-shivering thermogenesis) underwent a marked decrease of 34%. BAT weight was 21% decreased but total and mitochondrial protein content showed no variation. A 26% increase in purine nucleotide binding per BAT (taken as an index of thermogenic activity) was observed, suggesting that the enhancement in resting metabolism observed was mainly due to increased BAT thermogenesis. However, BAT mitochondria respiratory studies which are more direct functional tests showed a marked impairment of maximal O2 consumption of about 30% with palmitoyl-carnitine or acetyl-carnitine (both in presence of malate) or with alpha-glycerophosphate as substrate. It is likely that this impaired maximal BAT oxidative capacity may explain the impaired NE calorigenic effect in vivo. A possible increase in mitochondrial basal permeability is also discussed.

Cold-induced changes in fatty acid composition of rat brown fat during the perinatal period

Cold exposure of the newborn rat has little effect on the fatty acid composition of triglycerides and phospholipids up to the 14th day. During the 3rd week, cold exposure inhibits the involution of brown fat observed in the warm-exposed rat.

Cellularity and composition of epididymal adipose tissue from cold-acclimatized rats

Cold acclimatization induces morphological and compositional modifications of rat epididymal adipose tissue: a decrease in fat cell size, an increase of fat cell number per g of tissue, but no significant increase in total fat cell number in the tissue; finally, an increase in protein content and a decrease in triglyceride content.

Prostaglandins E2 and Fα levels in white and brown adipose tissues of cold acclimated rats as measured by a new micromethod

A new micro-method was used to determine the effects of cold acclimation of rats on the levels of prostaglandin E2 and F alpha in both white and brown adipose tissues. Whereas PGF alpha levels were significantly higher than PGE2 levels in white fat, no difference between the amounts of the two prostaglandins was observed in brown fat. In both tissues, cold acclimation did not induce any change in prostaglandin levels.

Beta-adrenergic receptors in white fat cells of cold-acclimated rats

Beta-adrenergic receptors were studied in membranes prepared from isolated fat cells obtained from both control and cold-acclimated rats. Beta-adrenergic receptors were identified using beta-adrenergic antagonist, (-) - [3H] dihydroalprenolol. Scatchard plots of specific binding suggest the existence of two binding sites for (-) - [3H] dihydroalprenolol with different affinities. Beta-adrenergic agonists competed for specific binding sites with typical beta 1-adrenergic specificity. There appears to be approximately 5,000 sites of high affinity per fat cell. Cold-acclimation (4 weeks at 4 degrees C) reduced adipocyte size; it did not appear to alter either the maximal number of binding sites of high and low affinity, or their affinity for beta-antagonists or agonists; however the density of binding sites in the fat cell was increased in cold-acclimated rats. It is concluded that the cold-adaptative process which induces in vivo the enhancement of calorigenic effect of norepinephrine is not found at the level of beta-receptors in white fat cells. The increased lipolytic response to norepinephrine observed in vitro in epididymal fat may be explained by cold-induced modifications in cell size and number.