Phospholipids and the regulation of pyruvate dehydrogenase from rat adipocyte mitochondria

Identification of altered blood metabolic pathways in equines following ethyl pyruvate administration using non-targeted metabolomics

Ethyl pyruvate (EP) has emerged as a promising compound with potential therapeutic benefits attributed to its anti-inflammatory and antioxidant properties. This study aimed to understand the effects of EP on plasma metabolites and immune cells in horses, utilizing advanced liquid chromatography-mass spectrometry (LC-MS)-based metabolomics, quantitative polymerase chain reaction (qPCR), and blood chemistry analyses. Our comprehensive analysis detected 2,366 ions, and 126 metabolites were accurately identified. Remarkably, EP administration induced significant changes in 28 metabolites at 1 h and 11 metabolites at 8 h, highlighting its time-dependent impact on metabolic pathways such as phenylalanine and arginine biosynthesis. Moreover, EP significantly lowered the expression of inflammatory markers interleukin (IL)-6 and heme oxygenase (HO)-1, indicating its potential as an anti-inflammatory agent. Blood chemistry analysis revealed notable reductions in glucose and triglyceride levels. These findings demonstrate that EP is a substance with potential effects on pathways associated with inflammation, oxidative stress, and metabolic processes.

Phosphatidylserine in Diabetes Research

Phospholipids are lipids that constitute the basic structure of cell membranes. In-depth research has shown that in addition to supporting cell structures, phospholipids participate in multiple cellular processes, including promoting cell signal transduction, guiding protein translocation, activating enzymatic activity, and eliminating dysfunctional/redundant organelles/cells. Diabetes is a chronic metabolic disease with a complicated etiology and pathology. Studies have shown that the level of certain phospholipids, for example, the ratio of phosphatidylcholine (PC) to phosphatidylethanolamine (PE) in liver tissue, is negatively associated with insulin sensitivity. In addition, PS is a phospholipid exhibiting extensive cellular functions in diabetes. For this review, we analyzed many PS studies focusing on diabetes and insulin sensitivity in recent years and found that PS participates in controlling insulin secretion, regulating insulin signaling transduction, and participating in the progression of diabetic complications by mediating coagulation disorders in the microvasculature or targeting mitochondria. Moreover, PS supplements in food and PS-containing liposomes have been shown to protect against type 1 and type 2 diabetes (T1D and T2D, respectively) in animal studies. Therefore, by summarizing the regulatory roles played by PS in diabetes and the potential of successfully using PS or PS-containing liposomes for diabetic therapy, we hope to provide new ideas for further research into the mechanisms of diabetes and for drug development for treating diabetes and its complications.

Human sciatic nerve phospholipid profiles from non-diabetes mellitus, non-insulin-dependent diabetes mellitus and insulin-dependent diabetes mellitus individuals. A 31P NMR spectroscopy study

1. Human sciatic nerve phospholipids obtained from non-diabetes mellitus (NDM), non-insulin-dependent diabetes mellitus (NIDDM), and insulin-dependent diabetes mellitus (IDDM) patients, after lower extremity amputation, were studied by 31P NMR spectrometry. 2. Nine phospholipids resonances in NDM and NIDDM groups were identified as followed: Ethanolamine plasmalogen (Eplas, Chemical shift = 0.07 delta); phosphatidylethanolamine (PE, 0.03 delta); phosphatidylserine (PS, -0.05 delta); sphingomyelin (SM, -0.09 delta); lysophosphatidylcholine (LPC, -0.28 delta); phosphatidylinositol (PI, -0.30 delta); alkylacylphosphorylcholine (A1.PC, -0.78 delta); phosphatidylcholine (PC -0.84 delta), and an unknown resonance (U, 0.13 delta). 3. In the IDDM group a resonance of lysophosphatidylinositol (LPI, 0.01 delta) was detected in addition to the nine phospholipids listed above. 4. IDDM showed that PI and A1.PC were elevated and U was lower when compared with NDM; also, Eplas was lower when compared with NIDDM. PC was elevated and PS was lower when compared with both NDM and NIDDM. 5. Indices calculated from this data, showed that the choline ratio and choline/ethanolamine ratio were elevated; while ethanolamine ratio, and myelin ratio were lower in IDDM group, when compared with both NDM and NIDDM groups. 6. Inactivation of the cholineacethyltransferase enzyme (ChAT) and enhancement of the phospholipidmethyltransferase enzyme (PLMT), secondary to an insulin deficiency, are proposed as an interpretation of these findings.

Permissive role of n-6 polyunsaturated fatty acids on carbohydrate oxidation in human infant skin fibroblasts: one possible mechanism of their intervention on coronary heart disease and diabetes

Many publications indicate the beneficial effect of n-6 polyunsaturated fatty acids (n-6 PUFAs) in the control of coronary heart disease and diabetes, although the mechanism is not clear. Some of our previous results suggest that, in contrast to other lipids, n-6 PUFAs could have a permissive effect on carbohydrate oxidation. To check this hypothesis, we determined pyruvate dehydrogenase (PDH, decarboxylase: EC 1.2.4.1) activity in infant skin fibroblasts (ISF) incubated 6 hours in the presence of 0.25 mM linoleic (LI) or arachidonic (AR) acid, compared to oleic acid (OL) and control ISF incubated without addition of fatty acids. The four groups of cells were preincubated 36 hours either in the presence of fetal bovine serum (FBS), or in the presence of lipoprotein-deprived serum (LPDS).

RESULTS

(1) When the ISF were maintained in the medium containing FBS, the two PUFAs had little inhibitory effect on PDH activity, in contrast with the effect of OL. (2) When the ISF were kept in the lipoprotein-deficient medium, PDH activity was low in controls and in the OL cells, but the addition of LI or AR increased the activity. This suggests the role of n-6 PUFAs in enhancing carbohydrate oxidation, under certain conditions.

Adenosine and oxytocin reverse antagonism of cyclic AMP elevating agents to insulin activation of adipocyte pyruvate dehydrogenase

ACTH, isoprenaline, forskolin, and dibutyryl cyclic AMP prevented insulin from stimulating adipocyte pyruvate dehydrogenase in the presence of adenosine deaminase. Antagonism was reversed by N6-phenylisopropyladenosine as well as oxytocin. The stimulatory effects of insulin, adenosine and oxytocin on adipocyte pyruvate dehydrogenase appear to be through (a) mechanism(s) which is (are) similar or related.

The renal mitochondrial metabolism of 25-hydroxyvitamin D-3: a possible role for phospholipids

The effect of exogenous phospholipids on chick kidney mitochondrial 25-hydroxyvitamin D-3 metabolism was examined. Phosphatidylserine, phosphatidylcholine and phosphatidylinositol had no effect on either the 1- or 24-hydroxylation of 25-hydroxyvitamin D-3. Phosphatidylethanolamine and cardiolipin both brought about a dose-dependent decrease in the 1-hydroxylase activity in mitochondria from vitamin D-deficient chicks but not from vitamin D-replete chicks. There were no major differences in the phospholipid composition of mitochondria from vitamin D-deficient and -replete chicks nor in the fatty acid composition of these phospholipids. Preliminary kinetic studies suggest that cardiolipin acts as a noncompetitive inhibitor of the 1-hydroxylase in mitochondria isolated from vitamin D-deficient chicks. It does not appear to exert its effect by virtue of altering the distribution of substrate or products. Investigation of the effect of fatty acid methyl esters on the hydroxylase activities suggests that it may be the fatty acid moiety of the phospholipid, rather than the phosphate moiety in the polar head group, that is involved in the phospholipid effect on the hydroxylation of 25-hydroxyvitamin D-3.

Further characterization of a muscle factor which activates hepatic branched-chain ketoacid dehydrogenase

A skeletal muscle factor which activates hepatic branched-chain keto acid dehydrogenase has been described. Since this factor is labile, the present study was designed to stabilize and characterize this factor. The muscle factor was stabilized by the addition of KCl and the protease inhibitor, antipain. Muscle factor activity was localized to the 100,000 g pellet fraction of muscle homogenate. The muscle factor was inactivated following trypsin or phospholipase A2 digestion.

Effect of adenosine on insulin activation of rat adipocyte pyruvate dehydrogenase

Adenosine and its analogue N6-phenylisopropyladenosine stimulated pyruvate dehydrogenase activity of isolated rat adipocytes. Maximal stimulation was obtained with concentrations between 50 and 100 mu M, with the effect decreasing at higher concentrations. The effects of insulin on this enzyme was modified by adenosine. The concentration of insulin (10 mu units/ml) that produced almost half-maximal stimulation, had little or no effect, when adenosine deaminase was present. Adenosine also enhanced the effect of suboptimal but not optimal concentrations of insulin. Thus, the mechanism of adenosine action on adipocyte pyruvate dehydrogenase could in some way be similar or related to that of insulin.