Metabolism of individual fatty acids during infusion of a triacylglycerol emulsion

Gluteofemoral adipose tissue plays a major role in production of the lipokine palmitoleate in humans

The expansion of lower-body adipose tissue (AT) is paradoxically associated with reduced cardiovascular disease and diabetes risk. We examined whether the beneficial metabolic properties of lower-body AT are related to the production and release of the insulin-sensitizing lipokine palmitoleate (16:1n-7). Using venoarterial difference sampling, we investigated the relative release of 16:1n-7 from lower-body (gluteofemoral) and upper-body (abdominal subcutaneous) AT depots. Paired gluteofemoral and abdominal subcutaneous AT samples were analyzed for triglyceride fatty acid composition and mRNA expression. Finally, the triglyceride fatty acid composition of isolated human preadipocytes was determined. Relative release of 16:1n-7 was markedly higher from gluteofemoral AT compared with abdominal subcutaneous AT. Stearoyl-CoA desaturase 1 (SCD1), the key enzyme involved in endogenous 16:1n-7 production, was more highly expressed in gluteofemoral AT and was associated with greater enrichment of 16:1n-7. Furthermore, isolated human preadipocytes from gluteofemoral AT displayed a higher content of SCD1-derived fatty acids. We demonstrate that human gluteofemoral AT plays a major role in determining systemic concentrations of the lipokine palmitoleate. Moreover, this appears to be an inherent feature of gluteofemoral AT. We propose that the beneficial metabolic properties of lower-body AT may be partly explained by the intrinsically greater production and release of palmitoleate.

Parenteral and enteral metabolism of anaplerotic triheptanoin in normal rats. II. Effects on lipolysis, glucose production, and liver acyl-CoA profile

The anaplerotic odd-medium-chain triglyceride triheptanoin is used in clinical trials for the chronic dietary treatment of patients with long-chain fatty acid oxidation disorders. We previously showed (Kinman RP, Kasumov T, Jobbins KA, Thomas KR, Adams JE, Brunengraber LN, Kutz G, Brewer WU, Roe CR, Brunengraber H. Am J Physiol Endocrinol Metab 291: E860-E866, 2006) that the intravenous infusion of triheptanoin increases lipolysis traced by the turnover of glycerol. In this study, we tested whether lipolysis induced by triheptanoin infusion is accompanied by the potentially harmful release of long-chain fatty acids. Rats were infused with heptanoate +/- glycerol or triheptanoin. Intravenous infusion of triheptanoin at 40% of caloric requirement markedly increased glycerol endogenous R(a) but not oleate endogenous R(a). Thus, the activation of lipolysis was balanced by fatty acid reesterification in the same cells. The liver acyl-CoA profile showed the accumulation of intermediates of heptanoate beta-oxidation and C(5)-ketogenesis and a decrease in free CoA but no evidence of metabolic perturbation of liver metabolism such as propionyl overload. Our data suggest that triheptanoin, administered either intravenously or intraduodenally, could be used for intensive care and nutritional support of metabolically decompensated long-chain fatty acid oxidation disorders.

Improved insulin sensitivity after weight loss and exercise training is mediated by a reduction in plasma fatty acid mobilization, not enhanced oxidative capacity

Obesity is characterized by excessive rates of plasma fatty acid mobilization and uptake, which play a key role in mediating insulin resistance. While weight loss via diet-only or a diet + exercise program clearly improves insulin sensitivity, the precise mechanisms modulating this improvement are not completely understood. The purpose of the present study was to determine the role of the reduced fatty acid mobilization and uptake after weight loss in obese women who were randomly assigned to lifestyle interventions of either weight loss without exercise (WL) (n = 7) or a weight loss + exercise program (WL + EX) (n = 10). Before and after losing 12% of their body weight, we measured insulin sensitivity (S(I)), systemic fatty acid rate of appearance (Ra) and disappearance (Rd), oxidative capacity, and markers for pro-inflammatory pathways in skeletal muscle. Fatty acid Ra and Rd were reduced by 30% after both interventions (P < 0.05). While oxidative capacity increased 25% in WL + EX (compared with no increase after WL), the improvement in S(I) was identical in both groups (60%; P < 0.05), and skeletal muscle pro-inflammatory pathways were reduced (P < 0.05) similarly in both groups. When we artificially increased fatty acid mobilization after weight loss to pre-weight-loss levels via an overnight lipid infusion, the improvement in S(I) was almost completely reversed. Importantly, WL + EX did not protect against this lipid-induced reversal in S(I) despite a significant increase in resting whole-body fat oxidation and a marked increase in skeletal muscle oxidative capacity. In conclusion, reduced fatty acid mobilization and uptake appears to be a primary mediator of improved insulin sensitivity after weight loss. Moreover, enhancing fatty acid oxidative capacity via exercise training is not sufficient to prevent the insulin resistance caused by high fatty acid mobilization, such as that found in obesity.

Dynamics of blood chylomicron fatty acids in a marine carnivore: implications for lipid metabolism and quantitative estimation of predator diets

Blubber fatty acid(s) (FA) signatures can provide accurate estimates of predator diets using quantitative FA signature analysis, provided that aspects of predator FA metabolism are taken into account. Because the intestinal absorption of dietary FA and their incorporation into chylomicrons (the primary transport lipoproteins for dietary FA in the blood) may influence the relationship between FA composition in the diet and adipose tissue, we investigated the metabolism of individual FA at these early stages of assimilation. We also investigated the capacity of chylomicron signatures to provide quantitative estimates of prey composition of an experimental meal. Six captive juvenile grey seals (Halichoerus grypus) were fed either 2.3 kg (n = 3) or 4.6 kg (n = 3) of Atlantic herring (Clupea harengus). Although chylomicron FA signatures resembled diet signatures at all samplings, absolute differences were smallest at 3-h post-feeding, when chylomicrons were likely largest and had the greatest ratio of triacylglycerol to phospholipid FA. Specific FA that differed significantly between diet and chylomicron signatures reflected either input from endogenous sources or loss through peroxisomal beta-oxidation. When these aspects of metabolism were accounted for, the quantitative predictions of diet composition generated using chylomicron signatures were extremely accurate, even when tested against 28 other prey items.