Lipid Metabolism, comparative

Ans. More than twice as much energy is generated per gram of lipid metabolized compared to protein or carbohydrate. A high lipid intake results in excess (unmetabolized) lipid which is then stored in fat adipose) tissue. Weight increase results in a higher load on the heart. 

Saz, H.J. and Lescure, O.L. (1966) Interrelationships between the carbohydrate and lipid metabolism of Ascaris lumbricoides egg and adult stages. Comparative Biochemistry and Physiology 18, 845-857. 

A recent paper clearly highlighted the limitations of in vitro systems in modeling whole-organism responses, which should be considered when developing biomarkers of in vivo toxicity. Dere and colleagues (58) compared the temporal gene expression profiles of Hepalclc mouse hepatoma cells and of the mice liver after treatment with a dioxin. The analysis revealed that Hepalclc cells were able to model the induction of xenobiotic metabolism in vivo. On the other hand, responses associated with cell cycle progression and proliferation were unique to the in vitro system, while lipid metabolism and immune responses were not replicated effectively in the Hepalclc cells. 

Hansen, H.J.M. (1987). Comparative studies on lipid metabolism in various salt-transporting organs of the European eel (Anguilla anguilla). Mono-unsaturated phosphatidyl ethanolamine as a key substance. Comparative Biochemistry and Physiology 88B, 323-332. 

Lewander, K., Dave, G., Johansson, M.-L., Larsson, A. and Lidman, U. (1974). Metabolic and haematological studies on the yellow and silver phases of the European eel, Anguilla anguilla. -1. Carbohydrate, lipid, protein and inorganic ion metabolism. Comparative Biochemistry and Physiology 47B, 571-581. 

Fats and oils have major roles in human nutrition. They are concentrated dietary sources of energy, providing approximately 9 kcal/g when metabolized compared with 4 kcal/g for carbohydrates and proteins, and account for about 36 percent of domestic caloric intake per capita.19 Dietary lipids also can provide essential molecular structures that are synthesized by the body into compounds required for selective functioning of cell membranes and regulation of life processes. 

After comparing the protein profiles of myocardial mitochondria between a chronic restraint stress group and a control group, 11 protein spots were found to change, of which seven were identified. Five of these proteins, carnitine palmitoyltransferase 2, mitochondrial acyl-CoA thioesterase 1, isocitrate dehydrogenase 3 (NAD ) alpha, fumarate hydratase 1, and pyruvate dehydrogenase beta, were foimd to decrease in abimdance following chronic restraint stress with fimctional roles in the Krebs cycle and lipid metabolism in mitochondria. The other two proteins, creatine kinase and prohibitin, increased after chronic restraint stress (liu et ak, 2004). 

The nutritional characteristics of DAG oil (>80%) have been compared with dietary TAG of similar fatty acid composition. In particular, the 1,3-DAG isoform appears to have distinct metabolic characteristics that can impact postprandial lipid metabolism and use of macronutrients for energy compared with TAG. 

We examined the in vivo effects of various extracts from Geranii Herba, and of geraniin, the main component of tannin of this herb, on rat liver injury induced by oral administration of peroxidized oil, and on lipid metabolism. As shown in "Table (6)", the administration of peroxidized oil for 5 days caused hyperlipidaemia with elevations of total cholesterol (TC), lipid peroxide (LPO), free fatty acid (FFA) and triglyceride (TG) as compared to the control values. Serum TC, FFA and LPO levels were found to be reduced in the rats orally given the acetone-water (1 1) extract of the leaf and leaf-stem (1 2), or the water extract of the leaf-stem as compared with the rats treated with peroxidized oil for 5 days "Table (6)". These extracts prevented the liver injury with the elevation of CJOT and GPT induced by peroxidized oil "Table (7)". As shown in "Table (8) and Table (9)", geraniin was also found to reduce the levels of serum TC, GOT and GPT in the peroxidized oil-treated rats. 

Many aroma compounds in fruits and plant materials are derived from lipid metabolism. Fatty acid biosynthesis and degradation and their connections with glycolysis, gluconeogenesis, TCA cycle, glyoxylate cycle and terpene metabolism have been described by Lynen (2) and Stumpf ( ). During fatty acid biosynthesis in the cytoplasm acetyl-CoA is transformed into malonyl-CoA. The de novo synthesis of palmitic acid by palmitoyl-ACP synthetase involves the sequential addition of C2-units by a series of reactions which have been well characterized. Palmitoyl-ACP is transformed into stearoyl-ACP and oleoyl-CoA in chloroplasts and plastides. During B-oxi-dation in mitochondria and microsomes the fatty acids are bound to CoASH. The B-oxidation pathway shows a similar reaction sequence compared to that of de novo synthesis. B-Oxidation and de novo synthesis possess differences in activation, coenzymes, enzymes and the intermediates (SM+)-3-hydroxyacyl-S-CoA (B-oxidation) and (R)-(-)-3-hydroxyacyl-ACP (de novo synthesis). The key enzyme for de novo synthesis (acetyl-CoA carboxylase) is inhibited by palmitoyl-S-CoA and plays an important role in fatty acid metabolism. 

J. A., Delmas, P.D. and Christiansen, C. (2001) Efficacy of levormeloxifene in the prevention of postmenopausal bone loss and on the lipid profile compared to low dose hormone replacement therapy. The Journal of Clinical Endocrinology and Metabolism, 86, 755-760. 

Despite its proven benefit in the control of blood glucose, PPARy agonists have been associated with an increased incidence of myocardial infarction and death from cardiovascular causes [71]. Numerous companies are therefore working actively on specific PPARa modulators, and a number of discovery and preclinical programs have been initiated with the aim of improving potency and selectivity compared to the fibrates. PPARa-selective compounds that are currently under development are shown in Figure 13.9. With the exception of K-lll (for a recent review, see Ref. [72]), which is developed for the treatment of type 2 diabetes mellitus, the development of all known PPARa activators is focused on lipid metabolism. 

Compared to age-matched controls, an increase in total cholesterol, HDL-Ch, and LDL-Ch was observed in women 40-49 years of age and 50-59 years of age (Stanosz et al. 1994b). The women were exposed to carbon disulfide at 5-7 ppm for 0.5 to greater than 20 years. Only HDL cholesterol and LDL cholesterol were increased when the values were examined by duration of carbon disulfide exposure. Rather than being a hepatic effect, the investigators suggest that the effect may be on hormone production by the ovaries resulting in altered lipid metabolism. 

---