Synthesis of an insulin analogue embodying a strongly fluorescent moiety, [19-Tryptophan-A]insulin

As part of our aim to study the conformation of insulin in solution by time-resolved fluorescence spectroscopy, we have synthesized the analogue [19-Tryptophan-A]insulin. In this compound, the tyrosine residue at position 19 of the A-chain of insulin, one of the most strongly conserved residues in insulins from various species, is substituted with the strongly fluorescent tryptophan residue. [19-Tryptophan-A]insulin displays 4.1±1.9% of the potency of natural insulin in binding to the insulin receptor from rat liver plasma membranes, 5.0±2.3% in stimulating lipogenesis in rat adipocytes, and 75.7±4% of the potency of insulin in radioimmunoassay. In connection with our previous work, these data indicate that an aromatic side chain at position A¹⁹ of insulin seems necessary but not sufficient for high biological activity. We further conclude that in regard to the immunogenic determinants of insulin, tryptophan in position A¹⁹ is an essentially neutral substitution for tyrosine in that position, in sharp contrast to the situation with regard to biological activity.     

Influence of red pepper and capsaicin on body composition and lipogenesis in rats

Inclusion of red pepper or its active principle ‘capsaicin’ in the diet led to a lowering of total lipids, particularly triglycerides in the liver. The total body fat was lowered in animals fed red pepper or capsaicin but not in animals fed paprika powder which had negligible capsaicin content. Hyperlipogensis and hypertriglyceridemia caused by fructose feeding were significantly were decreased in capsaicin-fed animals. Activities of the key lipogenic enzymes were reduced as reflected by decreased lipogenesis.     

Comparative Effects of Dietary Fat Types on Hepatic Enzyme Activities Related to the Synthesis and Oxidation of Fatty Acid and to Lipogenesis in Rats

The effects of different types of dietary fat on the activities of hepatic enzymes related to fatty acid synthesis {glucose-6-phosphate dehydrogenase (G6PDH) and acetyl-CoA carboxylase ACC)}, oxidation {acyl-CoA synthetase (AST), carnitine palmitoyl transferase (CPT), and peroxisomal β-oxidation (P βOX)}, and lipogenesis {phosphatidate phosphohydrolase (PAP), diacylglycerol acyltransferase (DGAT), and phosphocholine diacylglycerol transferase (PCDGT)}, and plasma and liver lipid levels were investigated in male Wistar rats. The animals were 6 weeks old and about 120 g of body weight, and were fed on test diets containing 20% of a mixture of tripalmitin, tristearin and corn oil (SFA), olive oil (OLI), sunflower oil (SUN), linseed oil (LIS), and sardine oil (SAR) for 2 weeks. The concentrations of plasma total cholesterol (T-CHOL), high-density lipoprotein-cholesterol (HDL-CHOL), triacylglycerol (TG) and phospholipid (PL) were generally higher in the rats fed on SEA and OLI than in those given SUN, LIS and SAR. The rats fed on OLI had a higher level of liver T-CHOL than those fed on the other fats. The liver TG content was nearly higher from the intake of SFA and OLI than from SUN, LIS and SAR, although the liver PL level was not affected by the type of dietary fat. The SFA and OLI groups had the highest activities of hepatic G6PDH and ACC, and the SAR group, the lowest activities. The activities of AST and CPT, and peroxisomal P βOX in the liver were higher in the rats fed on the LIS and SAR diets than in those given the other diets. The hepatic PAP activity was higher from the intake of OLI and SUN, and tended to be higher from SFA than from LIS and SAR. The activity of liver DGAT was higher from SFA and inclined to be higher from OLI, SUN, and LIS than from SAR, while the PCDGT activity in the liver was not effected by the type of dietary fat. The concentrations of plasma and liver TG were generally positively correlated with the activities of liver enzymes related to the synthesis of fatty acids and lipids, and negatively with those involved in fatty acid oxidation. Based on these results, it is suggested that the levels of plasma and liver TG were controlled by different types of dietary fat through changes in the hepatic enzyme activities related to fatty acid synthesis, lipogenesis, and fatty acid oxidation.     

Repression of endometrial tumor growth by targeting SREBP1 and lipogenesis

The aberrantly increased lipogenesis is a universal metabolic feature of proliferating tumor cells. Although most normal cells acquire the bulk of their fatty acids from circulation, tumor cells synthesize more than 90% of required lipids de novo. The sterol regulatory element-binding protein 1 (SREBP1), encoded by SREBF1 gene, is a master regulator of lipogenic gene expression. SREBP1 and its target genes are overexpressed in a variety of cancers; however, the role of SREBP1 in endometrial cancer is largely unknown. We have screened a cohort of endometrial cancer (EC) specimen for their lipogenic gene expression and observed a significant increase of SREBP1 target gene expression in cancer cells compared with normal endometrium. By using immunohistochemical staining, we confirmed SREBP1 protein overexpression and demonstrated increased nuclear distribution of SREBP1 in EC. In addition, we found that knockdown of SREBP1 expression in EC cells suppressed cell growth, reduced colonigenic capacity and slowed tumor growth in vivo. Furthermore, we observed that knockdown of SREBP1 induced significant cell death in cultured EC cells. Taken together, our results show that SREBP1 is essential for EC cell growth both in vitro and in vivo, suggesting that SREBP1 activity may be a novel therapeutic target for endometrial cancers.     

Mitochondrial protein acetylation as a cell-intrinsic,evolutionary driver of fat storage: Chemical and metabolic logic of acetyl-lysine modifications

Abstract

Hormone systems evolved over 500 million years of animal natural history to motivate feeding behavior and convert excess calories to fat. These systems produced vertebrates, including humans, who are famine-resistant but sensitive to obesity in environments of persistent overnutrition. We looked for cell-intrinsic metabolic features, which might have been subject to an evolutionary drive favoring lipogenesis. Mitochondrial protein acetylation appears to be such a system. Because mitochondrial acetyl-coA is the central mediator of fuel oxidation and is saturable, this metabolite is postulated to be the fundamental indicator of energy excess, which imprints a memory of nutritional imbalances by covalent modification. Fungal and invertebrate mitochondria have highly acetylated mitochondrial proteomes without an apparent mitochondrially targeted protein lysine acetyltransferase. Thus, mitochondrial acetylation is hypothesized to have evolved as a nonenzymatic phenomenon. Because the pK_a of a nonperturbed Lys is 10.4 and linkage of a carbonyl carbon to an ? amino group cannot be formed with a protonated Lys, we hypothesize that acetylation occurs on residues with depressed pK_a values, accounting for the propensity of acetylation to hit active sites and suggesting that regulatory Lys residues may have been under selective pressure to avoid or attract acetylation throughout animal evolution. In addition, a shortage of mitochondrial oxaloacetate under ketotic conditions can explain why macronutrient insufficiency also produces mitochondrial hyperacetylation. Reduced mitochondrial activity during times of overnutrition and undernutrition would improve fitness by virtue of resource conservation. Micronutrient insufficiency is predicted to exacerbate mitochondrial hyperacetylation. Nicotinamide riboside and Sirt3 activity are predicted to relieve mitochondrial inhibition.     

Mechanisms Preserving Insulin Action during High Dietary Fat Intake

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RGC-32 Deficiency Protects against Hepatic Steatosis by Reducing Lipogenesis

Hepatic steatosis is associated with insulin resistance and metabolic syndrome because of increased hepatic triglyceride content. We have reported previously that deficiency of response gene to complement 32 (RGC-32) prevents high-fat diet (HFD)-induced obesity and insulin resistance in mice. This study was conducted to determine the role of RGC-32 in the regulation of hepatic steatosis. We observed that hepatic RGC-32 was induced dramatically by both HFD challenge and ethanol administration. RGC-32 knockout (RGC32^−/−) mice were resistant to HFD- and ethanol-induced hepatic steatosis. The hepatic triglyceride content of RGC32^−/− mice was decreased significantly compared with WT controls even under normal chow conditions. Moreover, RGC-32 deficiency decreased the expression of lipogenesis-related genes, sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase, and stearoyl-CoA desaturase 1 (SCD1). RGC-32 deficiency also decreased SCD1 activity, as indicated by decreased desaturase indices of the liver and serum. Mechanistically, insulin and ethanol induced RGC-32 expression through the NF-κB signaling pathway, which, in turn, increased SCD1 expression in a SREBP-1c-dependent manner. RGC-32 also promoted SREBP-1c expression through activating liver X receptor. These results demonstrate that RGC-32 contributes to the development of hepatic steatosis by facilitating de novo lipogenesis through activating liver X receptor, leading to the induction of SREBP-1c and its target genes. Therefore, RGC-32 may be a potential novel drug target for the treatment of hepatic steatosis and its related diseases.     

Estimation of net nutrient oxidation and lipogenesis in growing pigs

Data from previous series of trials were reevaluated in order to quantify the net nutrient oxidation and lipogenesis by combining data from balance experiments and indirect calorimetry measurements. The experiments were carried out with eight castrated males of Danish Landrace measured individually from 30 to 100 kg BW. All pigs were fed alternately on high feeding level, near ad libitum and on low feeding level, near maintenance. Oxidation of carbohydrate (OXCHO) and fat (OXF) was calculated from gas exchange measurements. On high feeding level the contribution from OXCHO and OXF to the total heat production was 55 and 30%, respectively, at 30 kg BW and fairly constant from 60 kg BW with OXCHO around 80% and no net OXF. At low feeding level the contribution from OXCHO and OXF was 28 and 63%, respectively, at 30kg BW, increasing to 52% for OXCHO and decreasing to 37% for OXF at 95 kg BW. The lipogenesis on high feeding level increased from 2.4 to 11.9 MJ/d, while on low feeding level it increased from 2.5 to 3.6 MJ/d at 30 to 95 kg BW. The intake of carbohydrate was too low to cover energy requirement by OXCHO on low feeding level and in the first periods on high feeding level and OXF occurred. In spite of a deficit of carbohydrate for oxidation a part of carbohydrate (2.6 MJ/d, ～ 150 g/d) was used for fat synthesis, indicating an importance of lipogenesis in growing pigs.