Adipose tissue fatty acids

Synthesis and degradation of triacylglycerols in adipose tissue. Fatty acids are delivered to adipose tissue. In times of energy excess these are converted to triacylglycerols and stored until needed, at which point the triacylglycerols are converted back to fatty acids. 

Biong, A. S., Veierod, M. B., Ringstad, J., Thelle, D. S., and Pedersen, J. I. (2006). Intake of milk fat, reflected in adipose tissue fatty acids and risk of myocardial infarction A case-control study. Eur. ]. Clin. Nutr. 60, 236-244. 

Figure 30.13. Synthesis and Degradation of Triacylglycerols by Adipose Tissue. Fatty acids are delivered to adipose cells in the form of triacylglycerols contained in very low density lipoproteins (VLDLs).

Conversion of adipose-tissue fatty acids into CO2 6.7 4,000,000... 

Otto Shape had difficulty losing weight because human fuel utilization is too efficient. His adipose tissue fatty acids are being converted to acetyl CoA, which is being oxidized in the TCA cycle, thereby generating NADH and FAD(2H). The energy in these compounds is used for ATP synthesis from oxidative phosphorylation. If his fuel utilization were less efficient and his ATP yield were lower, he would have to oxidize much greater amounts of fat to get the ATP he needs for exercise. 

Adipose tissue is the major energy store in humans. Synthesis and breakdown of triglycerides are constant events in adipose tissue. Fatty acid and glycerol mobilization is stimulated by activation of hormone-sensitive lipase [9]. 

Most cells have alternative pathways by which a compound may either be degraded or synthesized although one direction may be favoured over the other for example, in muscle cells glucose is broken down rather than synthesized and in adipose tissue fatty acids are synthesized rather than broken down. 

In addition, in vivo C MR spectroscopy has been applied to the study of adipose tissue composition in disease. Children with cystic fibrosis were shown to have lower levels of polyunsaturated adipose tissue fatty acids than healthy children, possibly owing to a disorder in essential fatty acid metabolism that may be partly responsible for the development of the disease. Further studies with in vivo MRS in disease have shown a significant increase in saturated adipose tissue fatty acids following transplantation and subsequent weight gain in malnourished patients with liver cirrhosis. It was suggested that this increase in saturated fatty acids may be secondary to a general repletion of membrane polyunsaturated fatty acids or the use of essential fatty acids for biosynthesis of eicosanoids in the postoperative period. 

Numa et al. (1961), Wieland et al. (1963), and Korchak and Masoro (1962) have demonstrated decreased acetyl-CoA carboxylase activity in liver following starvation or alloxan diabetes. Liver and adipose tissue fatty acid synthesis is virtually arrested in these circumstances. Korchak and Masoro (1962) noted that after a 24-hour fast, the rate-limiting enzyme, acetyl-CoA carboxylase, fell to 50% of its control activity while at the same time there was a 99% depression in fatty acid synthesis by the intact liver cell. They interpreted this to mean that the inhibition of lipogenesis cannot be entirely accounted for by... 

Only the free form of the fatty acid precursors of eicosanoids can be utilized by the enzymes for conversion to the biologically active metabolites. However, the amount of precursor free fatty acid in the cytoplasm and circulating is usually low and so too is basal eicosanoid formation. Eurthermore, basal eicosanoid formation may depend on dietary and adipose tissue fatty acid composition. The amount of eicosanoid precursor free fatty acids is controlled to a large extent by incorporation and release from cellular phospholipids. Which eicosanoids are produced during stimulated synthesis may depend on membrane fatty acid composition as well as the cell type involved. Dietary fatty acid composition, therefore, has the potential to effect basal and stimulated synthesis of eicosanoids and influence endothelial function and thrombotic and inflammatory responses. 

---