Effect of eicosapentaenoic acid on glucose-induced diacylglycerol synthesis in cultured bovine aortic endothelial cells

Evaluating the effectiveness of melatonin in reducing the risk of foot ulcers in diabetic patients

Objectives

Diabetes and its complications, as a major health concern, are associated with morbidity and mortality around the world. One of these complications is diabetic foot ulcer. Factors such as hyperglycemia, neuropathy, vascular damage and impaired immune system can cause foot ulcers. The present review aims to study the potential effects of melatonin, the main product of pineal glands, on diabetic foot ulcers.

Methods

A narrative review was performed using present literature in an attempt to identify the different aspects of melatonin's impact on diabetic foot ulcers by searching related keywords in electronic databases without any restriction.

Results

This review shows that, melatonin has anti-diabetic effects. It is effective in reducing the risk of hyperglycemia, neuropathy, vascular damage and immune system impairment in diabetic patients. By reducing these complications with melatonin, correspondingly, the incidence of diabetic foot ulcers may also decrease in these patients.

Conclusions

The results of this study indicate promising properties of melatonin while dealing with diabetic foot ulcers and their common underlying conditions, but still, it needs to be investigated more in future studies.

8-oxoguanine DNA glycosylase (OGG1) deficiency elicits coordinated changes in lipid and mitochondrial metabolism in muscle

Oxidative stress resulting from endogenous and exogenous sources causes damage to cellular components, including genomic and mitochondrial DNA. Oxidative DNA damage is primarily repaired via the base excision repair pathway that is initiated by DNA glycosylases. 8-oxoguanine DNA glycosylase (OGG1) recognizes and cleaves oxidized and ring-fragmented purines, including 8-oxoguanine, the most commonly formed oxidative DNA lesion. Mice lacking the OGG1 gene product are prone to multiple features of the metabolic syndrome, including high-fat diet-induced obesity, hepatic steatosis, and insulin resistance. Here, we report that OGG1-deficient mice also display skeletal muscle pathologies, including increased muscle lipid deposition and alterations in genes regulating lipid uptake and mitochondrial fission in skeletal muscle. In addition, expression of genes of the TCA cycle and of carbohydrate and lipid metabolism are also significantly altered in muscle of OGG1-deficient mice. These tissue changes are accompanied by marked reductions in markers of muscle function in OGG1-deficient animals, including decreased grip strength and treadmill endurance. Collectively, these data indicate a role for skeletal muscle OGG1 in the maintenance of optimal tissue function.

Erythrocyte phospholipid and polyunsaturated fatty acid composition in diabetic retinopathy

Background

Long chain polyunsaturated fatty acids (LCPUFAs) including docosahexaenoic acid and arachidonic acid are suspected to play a key role in the pathogenesis of diabetes. LCPUFAs are known to be preferentially concentrated in specific phospholipids termed as plasmalogens. This study was aimed to highlight potential changes in the metabolism of phospholipids, and particularly plasmalogens, and LCPUFAs at various stages of diabetic retinopathy in humans.

Methodology and Principal Findings

We performed lipidomic analyses on red blood cell membranes from controls and mainly type 2 diabetes mellitus patients with or without retinopathy. The fatty acid composition of erythrocytes was determined by gas chromatography and the phospholipid structure was determined by liquid chromatography equipped with an electrospray ionisation source and coupled with a tandem mass spectrometer (LC-ESI-MS/MS). A significant decrease in levels of docosahexaenoic acid and arachidonic acid in erythrocytes of diabetic patients with or without retinopathy was observed. The origin of this decrease was a loss of phosphatidyl-ethanolamine phospholipids esterified with these LCPUFAs. In diabetic patients without retinopathy, this change was balanced by an increase in the levels of several phosphatidyl-choline species. No influence of diabetes nor of diabetic retinopathy was observed on the concentrations of plasmalogen-type phospholipids.

Conclusions and Significance

Diabetes and diabetic retinopathy were associated with a reduction of erythrocyte LCPUFAs in phosphatidyl-ethanolamines. The increase of the amounts of phosphatidyl-choline species in erythrocytes of diabetic patients without diabetic retinopathy might be a compensatory mechanism for the loss of LC-PUFA-rich phosphatidyl-ethanolamines.

Molecular mechanisms of diabetic vascular complications

Diabetic complications are the major causes of morbidity and mortality in patients with diabetes. Microvascular complications include retinopathy, nephropathy and neuropathy, which are leading causes of blindness, end‐stage renal disease and various painful neuropathies; whereas macrovascular complications involve atherosclerosis related diseases, such as coronary artery disease, peripheral vascular disease and stroke. Diabetic complications are the result of interactions among systemic metabolic changes, such as hyperglycemia, local tissue responses to toxic metabolites from glucose metabolism, and genetic and epigenetic modulators. Chronic hyperglycemia is recognized as a major initiator of diabetic complications. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on vascular tissues. These include increased polyol pathway, activation of the diacylglycerol/protein kinase C pathway, increased oxidative stress, overproduction and action of advanced glycation end products, and increased hexosamine pathway. In addition, the alterations of signal transduction pathways induced by hyperglycemia or toxic metabolites can also lead to cellular dysfunctions and damage vascular tissues by altering gene expression and protein function. Less studied than the toxic mechanisms, hyperglycemia might also inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, platelet‐derived growth factor and activated protein C, which play important roles in maintaining vascular homeostasis. Thus, effective therapies for diabetic complications need to inhibit mechanisms induced by hyperglycemia’s toxic effects and also enhance the endogenous protective factors. The present review summarizes these multiple biochemical pathways activated by hyperglycemia and the potential therapeutic interventions that might prevent diabetic complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00018.x, 2010)

Reduced expression of adipose triglyceride lipase enhances tumor necrosis factor alpha-induced intercellular adhesion molecule-1 expression in human aortic endothelial cells via protein kinase C-dependent activation of nuclear factor-kappaB

We examined the effects of adipose triglyceride lipase (ATGL) on the initiation of atherosclerosis. ATGL was recently identified as a rate-limiting triglyceride (TG) lipase. Mutations in the human ATGL gene are associated with neutral lipid storage disease with myopathy, a rare genetic disease characterized by excessive accumulation of TG in multiple tissues. The cardiac phenotype, known as triglyceride deposit cardiomyovasculopathy, shows massive TG accumulation in both coronary atherosclerotic lesions and the myocardium. Recent reports show that myocardial triglyceride content is significantly higher in patients with prediabetes or diabetes and that ATGL expression is decreased in the obese insulin-resistant state. Therefore, we investigated the effect of decreased ATGL activity on the development of atherosclerosis using human aortic endothelial cells. We found that ATGL knockdown enhanced monocyte adhesion via increased expression of TNFα-induced intercellular adhesion molecule-1 (ICAM-1). Next, we determined the pathways (MAPK, PKC, or NFκB) involved in ICAM-1 up-regulation induced by ATGL knockdown. Both phosphorylation of PKC and degradation of IκBα were increased in ATGL knockdown human aortic endothelial cells. In addition, intracellular diacylglycerol levels and free fatty acid uptake via CD36 were significantly increased in these cells. Inhibition of the PKC pathway using calphostin C and GF109203X suppressed TNFα-induced ICAM-1 expression. In conclusion, we showed that ATGL knockdown increased monocyte adhesion to the endothelium through enhanced TNFα-induced ICAM-1 expression via activation of NFκB and PKC. These results suggest that reduced ATGL expression may influence the atherogenic process in neutral lipid storage diseases and in the insulin-resistant state.

Metformin reduces angiotensin-mediated intracellular production of reactive oxygen species in endothelial cells through the inhibition of protein kinase C

Oxidative stress plays a major role in the pathogenesis and in the onset of macrovascular complications of diabetes. We previously reported that the antihyperglycaemic drug metformin was able to decrease significantly intracellular reactive oxygen species (ROS) production of bovine aortic endothelial cells (BAEC) activated by high levels of glucose and angiotensin II (ANG). The aim of the present study was to investigate whether the antioxidant effect of metformin on BAEC could be mediated through a modulation of protein kinase C (PKC) activity, which plays a key role in the pathophysiology of diabetes. The effects of metformin on intracellular ROS production, PKC translocation and activity were studied on endothelial cells stimulated by PMA (a direct PKC activator), ANG or high levels of glucose as pathophysiological stimuli of endothelial dysfunction in diabetes. We showed that metformin decreased ROS production on PMA-, ANG- and glucose-stimulated BAEC in a similar manner to that obtained by PKC specific inhibitors (calphostin C, chelerythrine) alone. On the other hand, metformin reduced both PKC membrane translocation and kinase activity in ANG-stimulated cells. In PMA-activated cells, metformin reduced membrane PKC activity but we did not observe any alteration of PKC membrane translocation. Finally, in vitro incubation with purified PKC indicated that metformin had no direct effect on PKC activity. Taken together, our results suggest that metformin exerted intracellular antioxidant properties by decreasing ROS production through the inhibition of PKC activity.

Statin attenuates high glucose-induced and diabetes-induced oxidative stress in vitro and in vivo evaluated by electron spin resonance measurement

An increased oxidative stress may contribute to the accelerated atherosclerosis in diabetic patients. Here we show that 3-hydroxy-3-methylglutaryl CoA reductase inhibitor (statin) attenuates a high glucose-induced and a diabetes-induced oxidative stress through inhibition of vascular NAD(P)H oxidase. Exposure of cultured aortic endothelial cells and smooth muscle cells to a high glucose level (450 mg/dl) for 3 days significantly increased oxidative stress compared with a normal glucose level (100 mg/dl), as evaluated by the staining with 2',7'-dichlorofluorescein diacetate and electron spin resonance (ESR) measurement. This increase was completely blocked by the treatment with pitavastatin (5 x 10(-7)M) as well as a NAD(P)H oxidase inhibitor (diphenylene iodonium) or a PKC inhibitor (calphostin C) in parallel with the change of small GTPase Rac-1 activity, a cytosolic regulatory component of NAD(P)H oxidase. Next, using streptozotocin-induced diabetic rats, the effect of pitavastatin on oxidative stress was evaluated by in vivo ESR measurements, which is a sensitive, noninvasive method. Administration of pitavastatin (5 mg/kg/day) for 4 days attenuated the increased oxidative stress in diabetic rats to control levels. In conclusion, pitavastatin attenuated a high glucose-induced and a diabetes-induced oxidative stress in vitro and in vivo. Thus, our data may provide a new insight into antioxidative therapy in diabetes.

The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina

In this work we advance the hypothesis that omega-3 (omega-3) long-chain polyunsaturated fatty acids (LCPUFAs) exhibit cytoprotective and cytotherapeutic actions contributing to a number of anti-angiogenic and neuroprotective mechanisms within the retina. omega-3 LCPUFAs may modulate metabolic processes and attenuate effects of environmental exposures that activate molecules implicated in pathogenesis of vasoproliferative and neurodegenerative retinal diseases. These processes and exposures include ischemia, chronic light exposure, oxidative stress, inflammation, cellular signaling mechanisms, and aging. A number of bioactive molecules within the retina affect, and are effected by such conditions. These molecules operate within complex systems and include compounds classified as eicosanoids, angiogenic factors, matrix metalloproteinases, reactive oxygen species, cyclic nucleotides, neurotransmitters and neuromodulators, pro-inflammatory and immunoregulatory cytokines, and inflammatory phospholipids. We discuss the relationship of LCPUFAs with these bioactivators and bioactive compounds in the context of three blinding retinal diseases of public health significance that exhibit both vascular and neural pathology. How is omega-3 LCPUFA status related to retinal structure and function? Docosahexaenoic acid (DHA), a major dietary omega-3 LCPUFA, is also a major structural lipid of retinal photoreceptor outer segment membranes. Biophysical and biochemical properties of DHA may affect photoreceptor membrane function by altering permeability, fluidity, thickness, and lipid phase properties. Tissue DHA status affects retinal cell signaling mechanisms involved in phototransduction. DHA may operate in signaling cascades to enhance activation of membrane-bound retinal proteins and may also be involved in rhodopsin regeneration. Tissue DHA insufficiency is associated with alterations in retinal function. Visual processing deficits have been ameliorated with DHA supplementation in some cases. What evidence exists to suggest that LCPUFAs modulate factors and processes implicated in diseases of the vascular and neural retina? Tissue status of LCPUFAs is modifiable by and dependent upon dietary intake. Certain LCPUFAs are selectively accreted and efficiently conserved within the neural retina. On the most basic level, omega-3 LCPUFAs influence retinal cell gene expression, cellular differentiation, and cellular survival. DHA activates a number of nuclear hormone receptors that operate as transcription factors for molecules that modulate reduction-oxidation-sensitive and proinflammatory genes; these include the peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and the retinoid X receptor. In the case of PPAR-alpha, this action is thought to prevent endothelial cell dysfunction and vascular remodeling through inhibition of: vascular smooth muscle cell proliferation, inducible nitric oxide synthase production, interleukin-1 induced cyclooxygenase (COX)-2 production, and thrombin-induced endothelin 1 production. Research on model systems demonstrates that omega-3 LCPUFAs also have the capacity to affect production and activation of angiogenic growth factors, arachidonic acid (AA)-based vasoregulatory eicosanoids, and MMPs. Eicosapentaenoic acid (EPA), a substrate for DHA, is the parent fatty acid for a family of eicosanoids that have the potential to affect AA-derived eicosanoids implicated in abnormal retinal neovascularization, vascular permeability, and inflammation. EPA depresses vascular endothelial growth factor (VEGF)-specific tyrosine kinase receptor activation and expression. VEGF plays an essential role in induction of: endothelial cell migration and proliferation, microvascular permeability, endothelial cell release of metalloproteinases and interstitial collagenases, and endothelial cell tube formation. The mechanism of VEGF receptor down-regulation is believed to occur at the tyrosine kinase nuclear factor-kappa B (NFkappaB). NFkappaB is a nuclear transcription factor that up-regulates COX-2 expression, intracellular adhesion molecule, thrombin, and nitric oxide synthase. All four factors are associated with vascular instability. COX-2 drives conversion of AA to a number angiogenic and proinflammatory eicosanoids. Our general conclusion is that there is consistent evidence to suggest that omega-3 LCPUFAs may act in a protective role against ischemia-, light-, oxygen-, inflammatory-, and age-associated pathology of the vascular and neural retina.

Evidence for contribution of vascular NAD(P)H oxidase to increased oxidative stress in animal models of diabetes and obesity

It is well established that oxidative stress is enhanced in diabetes. However, the major in vivo source of oxidative stress is not clear. Here we show that vascular NAD(P)H oxidase may be a major source of oxidative stress in diabetic and obese models. In vivo electron spin resonance (ESR)/spin probe was used to evaluate systemic oxidative stress in vivo. The signal decay rate of the spin probe (spin clearance rate; SpCR) significantly increased in streptozotocin-induced diabetic rats 2 weeks after the onset of diabetes. This increase was completely normalized by treatment with the antioxidants alpha-tocopherol (40 mg/kg) and superoxide dismutase (5000 units/kg), and was significantly inhibited by treatment with a PKC-specific inhibitor, CGP41251 (50 mg/kg), and a NAD(P)H oxidase inhibitor, apocynin (5 mg/kg). Both obese ob/ob mice (10 weeks old) with mild hyperglycemia and Zucker fatty rats (11 weeks old) with normoglycemia exhibited significantly increased SpCR as compared with controls. Again, this increase was inhibited by treatment with both CGP41251 and apocynin. Oral administration of insulin sensitizer, pioglitazone (10 mg/kg), for 7 days also completely normalized SpCR values. These results suggest that vascular NAD(P)H oxidase may be a major source of increased oxidative stress in diabetes and obesity.

Diacylglycerols Containing Omega 3 and Omega 6 Fatty Acids Bind to RasGRP and Modulate MAP Kinase Activation

We elucidated the effects of different diacylglycerols (DAGs), i.e. 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG), 1-stearoyl-2-docosahexaenoyl-sn-glycerol (SDG), and 1-stearoyl-2-eicosapentaenoyl-sn-glycerol (SEG), on [3H]PDBu binding to RasGRP. The competition studies with these DAGs on [3H]PDBu binding to RasGRP revealed different Ki values for these DAG molecular species. Furthermore, we transfected human Jurkat T cells by a plasmid containing RasGRP and assessed the implication of endogenous DAGs on activation of MAP kinases ERK1/ERK2, induced by phorbol-12-myristate-13-acetate (PMA). In control cells, GF109203X, a protein kinase C inhibitor, inhibited ERK1/ERK2 activation. However, this agent curtailed but failed to completely diminish ERK1/ERK2 phosphorylation in RasGRP-overexpressing cells, though calphostin C, a DAG binding inhibitor, suppressed the phosphorylation of MAP kinases in these cells. In cells incubated with arachidonic acid (AA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), PMA induced the production of endogenous DAGs containing these fatty acids, respectively: DAG-AA, DAG-DHA, and DAG-EPA. The inhibition of production of DAG-AA and DAG-DHA significantly inhibited MAP kinase activation in RasGRP overexpressing, but not in control, cells. Our study demonstrates that three DAG molecular species bind to RasGRP, but only DAG-AA and DAG-DHA participate in the modulation of RasGRP-mediated activation of MAP kinases in Jurkat T cells.

Protein kinase C-dependent increase in reactive oxygen species (ROS) production in vascular tissues of diabetes: role of vascular NAD(P)H oxidase

Hyperglycemia seems to be an important causative factor in the development of micro- and macrovascular complications in patients with diabetes. Several hypotheses have been proposed to explain the adverse effects of hyperglycemia on vascular cells. Both protein kinase C (PKC) activation and oxidative stress theories have increasingly received attention in recent years. This article shows a PKC-dependent increase in oxidative stress in diabetic vascular tissues. High glucose level stimulated reactive oxygen species (ROS) production via a PKC-dependent activation of NAD(P)H oxidase in cultured aortic endothelial cells, smooth muscle cells, and renal mesangial cells. In addition, expression of NAD(P)H oxidase components were shown to be upregulated in vascular tissues and kidney from animal models of diabetes. Furthermore, several agents that were expected to block the mechanism of a PKC-dependent activation of NAD(P)H oxidase clearly inhibited the increased oxidative stress in diabetic animals, as assessed by in vivo electron spin resonance method. Taken together, these findings strongly suggest that the PKC-dependent activation of NAD(P)H oxidase may be an essential mechanism responsible for increased oxidative stress in diabetes.

Insulin's stimulation of endothelial superoxide generation may reflect up-regulation of isoprenyl transferase activity that promotes rac translocation

Recent research demonstrates that statin drugs exert a number of favorable effects on endothelial function, independent of lipid modulation, that appear to be mediated by a partial inhibition of prenylation reactions. Statin-induced suppression of PKC-evoked superoxide production may be attributable to an inhibition of rac prenylation and thus translocation that impedes activation of the membrane-bound NAD(P)H oxidase. Conversely, it is now known that hyperinsulinemia up-regulates prenylation reactions by boosting the activities of isoprenyl transferases. In light of new evidence that hyperinsulinemia stimulates endothelial superoxide production via NAD(P)H oxidase, it is tempting to conclude that up-regulation of rac prenylation is at least partially responsible for this phenomenon. In patients afflicted with insulin resistance syndrome, this adverse impact of hyperinsulinemia may be exacerbated by an excessive free fatty acid flux that activates endothelial PKC - another stimulant of the NAD(P)H oxidase - while impeding insulin-mediated activation of nitric oxide synthase. The resulting imbalance of endothelial nitric oxide and superoxide production may be responsible for much of the excess vascular risk associated with this syndrome.

High glucose down-regulates angiotensin II binding via the PKC-MAPK-cPLA2 signal cascade in renal proximal tubule cells

BACKGROUND

It has been reported that renal renin-angiotensin system contributes to the development of diabetic nephropathy. However, the mechanism of angiotensin II receptor regulation in diabetic condition has not been elucidated.

METHODS

The effects of high glucose on [(3)H]-arachidonic acid (AA) release and angiotensin II (Ang II) binding and its related signal pathway were examined in primary cultured rabbit renal proximal tubule cells (PTCs).

RESULTS

High glucose down-regulated (125)I-Ang II binding from 12 hours and this response was sustained over 48 hours. Thus, the treatment of 25 mmol/L glucose for 48 hours was used for this study. High glucose-induced down-regulation of (125)I-Ang II binding was reversed by the removal of extracellular glucose, suggesting a role for glucose specificity. The high glucose-induced down-regulation of (125)I-Ang II binding was blocked by mepacrine, AACOCF3, phospholipase A2 inhibitors, indomethacin, ibuprofen, and cyclooxygenase inhibitors. Indeed, high glucose significantly increased prostaglandin E2 synthesis. In addition, the high glucose-induced AA release was blocked by PD 98059, a p44/42 mitogen-activated protein kinase (MAPK) inhibitor. PD 98059 also prevented the down-regulation of (125)I-Ang II binding by high glucose, suggesting a role for p44/42 MAPK. Indeed, high glucose significantly increased p44/42 MAPK activity after the 15-minute time point. Protein kinase C (PKC) inhibitor blocked high glucose-induced activation of p44/42 MAPK, increase of the [(3)H]-AA release, and down-regulation of 125I-Ang II binding. W-7 and KN-62 also blocked the high glucose-induced increase of [(3)H]-AA release and down-regulation of (125)I-Ang II binding. However, phospholipase A2 inhibitor did not block high glucose-induced activation of p44/42 MAPK.

CONCLUSION

High glucose down-regulates (125)I-Ang II binding via the PKC-MAPK-cPLA2 signal pathway.

Implication of acyl chain of diacylglycerols in activation of different isoforms of protein kinase C

We synthesized diacylglycerols (DAGs) containing omega-6 or omega-3 polyunsaturated fatty acids [i.e., 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG), 1-stearoyl-2-docosahexaenoyl-sn-glycerol (SDG), and 1-stearoyl-2-eicosapentaenoyl-sn-glycerol (SEG)] and assessed their efficiency on activation of conventional (alpha, beta I, gamma) and novel (epsilon, delta) protein kinase C (PKC). SAG exerted significantly higher stimulatory effects than SDG and SEG on activation of PKC alpha and PKC delta. Activation of PKC beta I by SEG and SDG was higher than that by SAG. Activation of PKC gamma did not differ significantly among DAG molecular species. Addition of SAG to assays containing SEG and SDG exerted additive effects on activation of alpha and epsilon, but not on beta I and gamma, isoforms of PKC. SDG- and SEG-induced activation of PKC delta was significantly curtailed by the addition of SAG. Three DAG species significantly curtailed the PMA-induced activation of beta Iota, gamma, and delta, but not of alpha and epsilon, isoforms of PKC. Our study demonstrates for the first time that in vitro activation of different PKC isoenzymes vary in response to different DAG species, and one can envisage that this differential regulation may be responsible for their in vivo effects on target organs.

New gene targets related to schizophrenia and other psychiatric disorders: enzymes, binding proteins and transport proteins involved in phospholipid and fatty acid metabolism

Phospholipids make up about 60% of the brain's dry weight. In spite of this, phospholipid metabolism has received relatively little attention from those seeking genetic factors involved in psychiatric and neurological disorders. However, there is now increasing evidence from many quarters that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. To date the possible specific proteins and genes involved have been relatively ill-defined. This paper reviews the main pathways of phospholipid metabolism, emphasizing the roles of phospholipases of the A2 and C series in signal transduction processes. It identifies some likely protein candidates for involvement in psychiatric and neurological disorders. It also reviews the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.