Genetics of serum and muscle lipids in pigs

Pork meat is one of the most important sources of animal protein in the human diet. Its nutritional properties are partly determined by intramuscular fat content and composition, with existing general consensus about the detrimental effects of cholesterol and saturated fat on cardiovascular health in humans. Because of their physiological resemblance, pigs can be also used as a valuable animal model to study the genetics of human diseases such as atherosclerosis, obesity and dyslipidaemias. Heritability estimates and QTL maps of porcine muscle and serum lipid traits evidence that a considerable amount of genetic variance determining these phenotypes exists, but its molecular basis remains mostly unknown. The recent advent of high‐throughput genotyping and sequencing technologies has revolutionised the field of animal genomics. With these powerful tools, finding needles in the genomic haystack has become increasingly feasible. However, these methodological advances should not be deemed as magic bullets. The goal of identifying the many polymorphisms that shape the variability of lipid phenotypes is so challenging that success can be achieved only under the scope of large international consortia.     

Skeletal muscle lipids. II. Changes in phospholipid composition in man from fetal to middle age

Phospholipid compositions were determined in samples of gastrocnemius muscles of individuals from fetal stage to the age of 55 yr. The lipids were separated by thin-layer chromatography. In order to enable characterization of the individual phospholipids, a lipid extract was prepared from pooled samples of gastrocnemius muscles from adult males and separated by ion-exchange chromatography on TEAE-cellulose. The individual phosphoglycerides were purified by thin-layer chromatography and then characterized according to their content of fatty acids, aldehydes, phosphorus, and the identity of the bases. The relative amounts of the major phospholipids, choline and ethanolamine phosphoglycerides, changed little with age, and in adult males they constituted 47% and 24%, respectively. Cardiolipin increased from 3% in the fetal stage to 9% by the end of the first year of life. Sphingomyelin and serine phosphoglyceride decreased with increasing age, while inositol phosphoglyceride increased. In adult males, cardiolipin constituted 10% of total lipid phosphorus, inositol phosphoglyceride constituted 9%, serine phosphoglyceride 3%, and sphingomyelin 7%.     

Yolk lipids.

The mature egg yolk of the domestic hen possesses remarkably constant lipid and lipoprotein composition despite much variation in dietary and environmental conditions. The greatest differences are seen in the fatty acid composition of the triacylglycerols which may show significant alterations in the content of the minor acids including certain polyunsaturated acids. The lipid class composition appears to be minimally affected by dietary influences, including the cholesterol content of the diet. The limited dietary influence on the yolk lipid composition extends to different strains of the hens. Genetic selection has led to some increase in the cholesterol content of the egg, but the desired lowering of the cholesterol content of egg yolk has not been realized. Likewise, production of a polyunsaturated fatty acid egg does not appear to be practical. As a result the egg yolk continues to provide a food product of nearly constant composition, which serves to maintain its chemical and physico-chemical properties for reliable utilization in the baking, cosmetic and pharmaceutical industries. The great uniformity in the composition of the egg yolk phospholipids makes them desirable starting materials for partial chemical resynthesis of glycerophospholipids. Partial hydrogenation of the egg yolk lipids promises to further increase the utility of the product as a desirable material for the manufacture of liposomes and liposome based drug products. In contrast, the constancy of the egg yolk composition and the inability to alter it significantly by dietary or genetic means also renders egg yolk undesirable for unlimited human consumption. Excessive ingestion of egg yolk raises plasma lipid and cholesterol levels which are believed to contribute to the development of heart disease. The physico-chemical and biological properties of egg yolk apoproteins have been less extensively investigated and their function is less well understood. The finding that phosvitin is a effective chelator of metal ions and thus an effective antioxidant demonstrates that egg yolk lipoproteins possess as yet unexplored potential for beneficial nutritional, medical and industrial application.     

Histochemical investigations of the accumulation of lipids in heart papillary muscle

Synopsis The lipid composition and fatty change of the papillary muscle, arterioles and chordae tendineae of the left cardiac ventricle of sixty-two patients who had died of various diseases in hospital were analysed qualitatively by histochemical techniques and thin-layer chromatography.The histochemical techniques revealed considerable differences in the fatty change of the myocardium, arterioles and chordae tendineae. The myocardial change seems to be due solely to accumulation of triglycerides. The fatty change in the chordae tendineae appears to be the result mainly of accumulation of cholesterol esters and, to some extent, of free fatty acids. The arteriolar fatty change arises mainly from accumulation of cholesterol esters and some triglycerides. The myocardial and arteriolar fatty change is greatest at the tip of the papillary muscle.The results of thin-layer chromatography showed that the lipid composition of the papillary muscle was qualitatively highly constant. The triglycerides and free fatty acid content varied.The osmium tetroxide--naphthylamine technique, which indicates phospholipids, stained the cardiac and arteriolar muscle fibres uniformly. No focal staining, suggestive of fatty change, was noted.All three tissue sites studied reacted with Baker's acid Haematein test. Staining was focal and clearly associated with fatty change. The results observed suggested that Baker's acid Haematein test is not specific for phospholipids, but it may stain neutral fats and cholesterol esters whenever large amounts of these are present in a tissue.     

Leptin, skeletal muscle lipids, and lipid-induced insulin resistance

Leptin-induced increases in insulin sensitivity are well established and may be related to the effects of leptin on lipid metabolism. However, the effects of leptin on the levels of lipid metabolites implicated in pathogenesis of insulin resistance and the effects of leptin on lipid-induced insulin resistance are unknown. The current study addressed in rats the effects of hyperleptinemia (HL) on insulin action and markers of skeletal muscle (SkM) lipid metabolism in the absence or presence of acute hyperlipidemia induced by an infusion of a lipid emulsion. Compared with controls (CONT), HL increased insulin sensitivity, as assessed by hyperinsulinemic-euglycemic clamp ( approximately 15%), and increased SkM Akt ( approximately 30%) and glycogen synthase kinase 3 alpha ( approximately 52%) phosphorylation. These improvements in insulin action were associated with decreased SkM triglycerides (TG; approximately 61%), elevated ceramides ( approximately 50%), and similar diacylglycerol (DAG) levels in HL compared with CONT. Acute hyperlipidemia in CONT decreased insulin sensitivity ( approximately 25%) and increased SkM DAG ( approximately 33%) and ceramide ( approximately 60%) levels. However, hyperlipidemia did not induce insulin resistance or SkM DAG and ceramide accumulation in HL. SkM total fatty acid transporter CD36, plasma membrane fatty acid binding protein, acetyl Co-A carboxylase phosphorylation, and fatty acid oxidation were similar in HL compared with CONT. However, HL decreased SkM protein kinase C theta (PKC theta), a kinase implicated in mediating the detrimental effects of lipids on insulin action. We conclude that increases in insulin sensitivity induced by HL are associated with decreased levels of SkM TG and PKC theta and increased SkM insulin signaling, but not with decreases in other lipid metabolites implicated in altering SkM insulin sensitivity (DAG and ceramide). Furthermore, insulin resistance induced by an acute lipid infusion is prevented by HL.     

Influence of dietary lipids on microsomal membranes from chick breast muscle

1. The effect of different dietary fat intake on the lipid composition and fluidity of microsomal membranes as well as in the enzymatic activity of the Ca2+-ATPase from chick breast muscle was investigated. 2. When a standard diet was supplemented with 10% sunflower seed oil, an increase in the relative amounts of unsaturated fatty acids and membrane fluidity and a decrease in the cholesterol content was observed. 3. The presence of 6% cholesterol in the diet does not modify the fatty acid composition and the fluidity of the membrane but increased, in a low extension, the cholesterol content. 4. The provision of the sunflower seed oil-rich diet supplemented with cholesterol just 48 hr before death promoted an increase in the relative amounts of unsaturated fatty acids and cholesterol content whereas the membrane fluidity decreased in a significant extent. 5. Despite that dietary lipids gave rise in some cases to changes in lipid composition and in the physical state of the microsomal membrane, neither the Ca2+ uptake capacity nor the ATPase activity were significantly affected.     

Spiroplasma membrane lipids.

Membranes of six spiroplasma strains belonging to different Spiroplasma species and subgroups were isolated by a combination of osmotic lysis and sonication in the presence of EDTA to block endogenous phospholipase activity. Analysis of membrane lipids showed that in addition to free and esterified cholesterol the spiroplasmas incorporated exogenous phospholipids from the growth medium. Sphingomyelin was preferentially incorporated from phosphatidylcholine-sphingomyelin vesicles or from the serum used to supplement the growth medium. Palmitate was incorporated better than oleate into membrane lipids synthesized by the organisms during growth. The major phospholipid synthesized by the spiroplasmas was phosphatidylglycerol. The positional distribution of the fatty acids in phosphatidylglycerol of Spiroplasma floricola resembled that found in Mycoplasma species, in which the saturated fatty acids prefer position 2 in the glycerol backbone and not position 1 as found in Acholeplasma species and elsewhere in nature. Electron paramagnetic resonance analysis of spin-labeled fatty acids incorporated into S. floricola membranes exhibited homogeneous single-component spectra without immobilized regions. The S. floricola membranes were more rigid than those of Acholeplasma laidlawii and less rigid than those of Mycoplasma gallisepticum.