Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hyperglycemia is the major causal factor in the development of diabetic vascular complications and can mediate their adverse effects through multiple pathways. One of those mechanisms is the activation of protein kinase C (PKC) by hyperglycemia-induced increases in diacylglycerol (DAG) level, partly due to de novo synthesis. The activation of PKC regulates various vascular functions by modulating enzymatic activities such as cytosolic phospholipase A2 and Na+,K+-ATPase, and gene expressions including extracellular matrix components and contractile proteins. Some of the resulting vascular abnormalities include changes in retinal and renal blood flow, contractility, permeability, proliferation, and basement membrane. Among the various isoforms of PKC predominantly the beta isoforms are activated in cultured vascular cells exposed to high glucose and vascular tissues isolated from animal models of diabetes mellitus. Administration of vitamin E, which decreases DAG level possibly through the activation of DAG kinase, prevents hemodynamic changes in retina and renal glomeruli of diabetic rats. In addition, the inhibition of PKC beta isoforms by a specific inhibitor (LY333531) can normalize the changes in gene expression of cytokines, caldesmon, and hemodynamics. These results provide supportive evidence that the activation of PKC, especially the beta isoforms, is involved in the development of diabetic vascular complications, and that PKCbeta inhibitors can be used in the treatment of diabetic vascular complications.
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PMID:Protein kinase C activation and its role in the development of vascular complications in diabetes mellitus. 946 65

In the retinas of diabetic animals, protein kinase C (PKC) activity is elevated, and Na+-K+-ATPase and calcium ATPase activities are subnormal. These abnormalities are also present in another model of diabetic retinopathy, experimental galactosemia. We have investigated the relationship between hyperglycemia-induced abnormalities of PKC and ATPases using a selective inhibitor of beta isoform of PKC (LY333531). Diabetes or experimental galactosemia of 2 months' duration resulted in > 50% elevation of PKC activity in the retina, and administration of LY333531 prevented the elevation. In retinas of the same rats, the LY333531 prevented hyperglycemia-induced decreases of both Na+-K+-ATPase and calcium ATPase activities. Retinal microvessels, the main site of lesions in diabetic retinopathy, likewise showed elevated activity of PKC and inhibition of ATPases in diabetes and in experimental galactosemia, and administration of LY333531 to diabetic animals prevented these abnormalities. PKC activity in sciatic nerves, in contrast, became subnormal in diabetes and experimental galactosemia, and LY333531 had no effect on PKC activity in the sciatic nerve. PKC activity in the cerebral cortex was not affected by diabetes or experimental galactosemia. The results suggest that diabetes-induced reductions in Na+-K+-ATPase and calcium ATPase in the retina are mediated in large part by PKC-beta. The availability of an agent that can normalize the hyperglycemia-induced increase in PKC activity in the retina should facilitate investigation of the role of PKC in the development of diabetic retinopathy.
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PMID:Abnormalities of retinal metabolism in diabetes or experimental galactosemia: V. Relationship between protein kinase C and ATPases. 951 55

In the lateral hypothalamic area (LHA) of rat brain, approximately 30% of cells showed sensitivity to small changes in local concentrations of glucose. These "glucose-sensitive" neurons demonstrated four types of behavior, three of which probably represent segments of a continuous spectrum of recruitment in response to ever more severe changes in blood sugar. Type I cells showed maximum activity </=5.6 mM blood glucose but became completely silent at hyperglycemia of 10-12 mM (normoglycemia 7.6 +/- 0.3 mM; mean +/- SD). Type II and III neurons exhibited a wider range of response. Type IV cells (5-7% of glucose-sensitive neurons) paralleled the behavior of sugar-sensitive cells in ventromedial hypothalamic nucleus (VMH). In VMH, approximately 40% of cells responded to changes in blood glucose over a range of concentrations from 3.6 to 17 mM, by increasing their firing rate as sugar level rose and vice versa. Ionic shifts during increases in blood (brain) glucose levels were similar in LHA types I-III but fastest in I and slowest in III. [Na+]i fell by 5-9 mM, [K+]i rose by 6-8 mM, and plasma membrane hyperpolarized by 5 mV. [Ca2+]i declined by 15-20 nM in line with membrane hyperpolarization. In VMH and type IV LHA cells, [K+]i fell 3-8 mM and plasma membrane depolarized -3 to -5 mV as blood/brain glucose concentration increased from 7.6/2.4 to 17.6/4.2 mM, whereas [Ca2+]i increased from 125 to 180 nM as a consequence of falling membrane potential. During falls in blood/brain sugar concentration the effects in both VMH and LHA cells were reversed. The findings are consistent with the ionic shifts in types I-III LHA cells being dependent on alterations in Na/K-ATPase activity, whereas those in VMH and type IV LHA cells could be caused by modulation of ATP-dependent K+ channels. A possible mechanism for linking the effects of small changes in glucose to ATP generation, which could bring about the above phenomena, is the interposition of a "glucokinase-type" enzyme in a role similar to that which it has in glucose-sensing pancreatic beta-cells.
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PMID:Glucose-induced intracellular ion changes in sugar-sensitive hypothalamic neurons. 953 43

Recent studies have identified that the activation of protein kinase C (PKC) and increased diacylglycerol (DAG) levels initiated by hyperglycemia are associated with many vascular abnormalities in retinal, renal, and cardiovascular tissues. Among the various PKC isoforms, the beta- and delta-isoforms appear to be activated preferentially in the vasculatures of diabetic animals, although other PKC isoforms are also increased in the renal glomeruli and retina. The glucose-induced activation of PKC has been shown to increase the production of extracellular matrix and cytokines; to enhance contractility, permeability, and vascular cell proliferation; to induce the activation of cytosolic phospholipase A2; and to inhibit Na+-K+-ATPase. The synthesis and characterization of a specific inhibitor for PKC-beta isoforms have confirmed the role of PKC activation in mediating hyperglycemic effects on vascular cells, as described above, and provide in vivo evidence that PKC activation could be responsible for abnormal retinal and renal hemodynamics in diabetic animals. Transgenic mice overexpressing PKC-beta isoform in the myocardium developed cardiac hypertrophy and failure, further supporting the hypothesis that PKC-beta isoform activation can cause vascular dysfunctions. Interestingly, hyperglycemia-induced oxidative stress may also mediate the adverse effects of PKC-beta isoforms by the activation of the DAG-PKC pathway, since treatment with D-alpha-tocopherol was able to prevent many glucose-induced vascular dysfunctions and inhibit DAG-PKC activation. Clinical studies are now in progress to determine whether PKC-beta inhibition can prevent diabetic complications.
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PMID:Protein kinase C activation and the development of diabetic complications. 960 60

Motor and sensory nerve conduction velocities (MNCV and SNCV) were reduced in the sciatic nerve of rats after 4 weeks of untreated streptozotocin-induced diabetes, and declined further during the following 4 weeks. Treating diabetic rats with the novel peptide HP228 had no effect on the decline of MNCV after the first 4 weeks of diabetes but attenuated the decline in SNCV. HP228 treatment also prevented any further decline in MNCV or SNCV between weeks 4 and 8 of diabetes. Consequently, at the conclusion of the study, the nerve conduction velocities (NCVs) in treated rats were significantly (both P < .001) higher than in untreated diabetic rats. Reduced nerve homogenate Na+,K+-adenosine triphosphatase (ATPase) activity in diabetic rats was significantly (P < .05) increased by HP228 but remained significantly (P < .05) lower than in untreated controls. HP228 treatment also reduced nerve Na+,K+-ATPase activity of control rats compared with untreated controls (P < .05). There was no effect of HP228 on the hyperglycemia, nerve polyol accumulation, myo-inositol depletion, reduced nerve laser Doppler blood flow, thermal hypoalgesia, or reduced mean axonal caliber in diabetic rats or on any of these parameters in control rats. These data demonstrate that a novel peptide may protect against the slowing of nerve conduction in prolonged diabetes and that the mechanism of action is unrelated to aldose reductase inhibition, prevention of nerve ischemia, or axonal atrophy. HP228 may prove a potential therapeutic agent for the treatment of prolonged diabetic neuropathy.
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PMID:Effects of the peptide HP228 on nerve disorders in diabetic rats. 962 61

This study was done to elucidate the mechanism of hypoglycorrhachia and elevated lactate concentrations leading to neuronal dysfunction in neonatal meningitis, and to determine the effects of induced hyperglycemia on these disturbances. Thirty-eight newborn piglets were divided into three groups: 12 in the control group (CG), 12 in the normoglycemic meningitis group (NG), and 14 in the hyperglycemic meningitis group (HG). Meningitis was induced by intracisternal injection of 108 cfu of Escherichia coli. Hyperglycemia (blood glucose 300-400 mg dl-1) was induced and maintained for 60 min before induction of meningitis and throughout the experiment using modified glucose clamp technique. CSF-to-blood glucose ratio decreased significantly in NG. In HG, baseline CSF-to-blood glucose ratio was lower than two other groups, but increased at 1 h after induction of meningitis. CSF lactate concentration was increased progressively in both meningitis groups, and positively correlated with CSF leukocyte numbers (r=0.41, p<0.001) and TNF-alpha level (r=0.43, p<0.001). Brain glucose concentration was significantly increased in HG and showed inverse correlation with CSF leukocyte numbers (r=-0.59, p<0.01). Brain lactate concentration was not significantly different among three groups and positively correlated with the CSF TNF-alpha level (r=0.51, p<0.05). Lipid peroxidation products were increased in NG. Na+,K+-ATPase activity, ATP/PCr concentrations were not different among three groups. Increased intracranial pressure, CSF pleocytosis (214+/-59 vs. 437+/-214/mm3, p<0.02) and increased lipid peroxidation products observed in NG were reduced in HG. These results suggest that hypoglycorrhachia and elevated lactate concentration in the CSF during meningitis originates primarily from the increased anaerobic glycolysis in the subarachnoid space, induced by TNF-alpha and leukocytes. Induced hyperglycemia attenuates the inflammatory responses of meningitis and might be beneficial by providing an increased glucose delivery to meet its increased demand in meningitis.
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PMID:Effect of induced hyperglycemia on brain cell membrane function and energy metabolism during the early phase of experimental meningitis in newborn piglets. 966 26

The purpose of this study was to test the hypothesis that hyperglycemia ameliorates changes in brain cell membrane function and preserves cerebral high energy phosphates during hypoxia-ischemia in newborn piglets. A total of 42 ventilated piglets were divided into 4 groups, normoglycemic/normoxic(group 1, n=9), hyperglycemic/normoxic(group 2, n=8), normoglycemic/hypoxic-ischemic(group 3, n=13) and hyperglycemic/hypoxic-ischemic(group 4, n=12) group. Cerebral hypoxia-ischemia was induced by occlusion of bilateral common carotid arteries and simultaneous breathing with 8% oxygen for 30 min. Hyperglycemia (blood glucose 350-400 mg/dl) was maintained for 90 min before and throughout hypoxia-ischemia using modified glucose clamp technique. Changes in cytochrome aa3 were continuously monitored using near infrared spectroscopy. Blood and CSF glucose and lactate were monitored. Na+, K+-ATPase activity, lipid peroxidation products (conjugated dienes), tissue high energy phosphates (ATP and phosphocreatine) levels and brain glucose and lactate levels were determined biochemically in the cerebral cortex. During hypoxia-ischemia, glucose levels in blood and CSF were significantly elevated in hyperglycemic/hypoxic-ischemic group compared with normoglycemic/hypoxic-ischemic group, but lactate levels in blood and CSF were not different between two groups. At the end of hypoxia-ischemia of group 3 and 4, triangle up Cyt aa3, Na+, K+-ATPase activity, ATP and phosphocreatine values in brain were significantly decreased compared with normoxic groups 1 and 2, but were not different between groups 3 and 4. Levels of conjugated dienes and brain lactate were significantly increased in groups 3 and 4 compared with groups 1 and 2, and were significantly elevated in group 4 than in group 3 (0.30+/-0.11 vs. 0.09+/-0.02 micromol g-1 protein, 26.4+/-7.6 vs. 13.1+/-2.6 mmol kg-1, p<0.05). These findings suggest that hyperglycemia does not reduce the changes in brain cell membrane function and does not preserve cerebral high energy phosphates during hypoxia-ischemia in newborn piglets. We speculate that hyperglycemia may be harmful during hypoxia-ischemia due to increased levels of lipid peroxidation in newborn piglet.
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PMID:Effect of hyperglycemia on brain cell membrane function and energy metabolism during hypoxia-ischemia in newborn piglets. 966 46

Metabolic abnormalities observed in retina and in cerebral cortex were compared in diabetic rats and experimentally galactosemic rats. Diabetes or experimental galactosemia of 2 months duration significantly increased oxidative stress in retina, as shown by elevation of retinal thiobarbituric acid reactive substances (TBARS) and subnormal activities of antioxidant defense enzymes, but had no such effect in the cerebral cortex. Activities of sodium potassium adenosine triphosphatase [(Na,K)-ATPase] and calcium ATPase became subnormal in retina as well as in cerebral cortex. In contrast, protein kinase C (PKC) activity was elevated in retina but not in cerebral cortex in the same hyperglycemic rats. Dietary supplementation with an antioxidant mixture (containing ascorbic acid, Trolox, alpha-tocopherol acetate, N-acetyl cysteine, beta-carotene, and selenium) prevented the diabetes-induced and galactosemia-induced elevation of retinal oxidative stress, the elevation of retinal PKC activity and the decrease of retinal ATPases. In cerebral cortex, administration of the antioxidant diet also prevented the diabetes-induced decreases in (Na,K)-ATPase and calcium ATPases, but had no effect on TBARS and activities of PKC and antioxidant-defense enzymes. The results indicate that retina and cerebral cortex differ distinctly in their response to elevation of tissue hexose, and that cerebral cortex is more resistant than retina to diabetes-induced oxidative stress. The greater resistance to oxidative stress in cerebral cortex, as compared to retina, is consistent with the resistance of cerebral cortex to microvascular disease in diabetes, and with a hypothesis that oxidative stress contributes to microvascular disease in diabetes. Dietary supplementation with these antioxidants offers a means to inhibit multiple hyperglycemia-induced retinal metabolic abnormalities.
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PMID:Abnormalities of retinal metabolism in diabetes or experimental galactosemia. VI. Comparison of retinal and cerebral cortex metabolism, and effects of antioxidant therapy. 989 29

The pathogenesis of diabetic neuropathy remains unclear, although several factors have been implicated in its pathogenesis. We have examined possible roles of decreased production of nitric oxide, ion channel dysfunction and decreased capacity of nerve regeneration. STZ-induced diabetic rats showed decreases in nociceptive threshold and NADPH-diaphorase positive neurons, nNOS level and cGMP content of DRG at 12 weeks after induction of diabetes. The rats injected by L-NAME, potent nNOS inhibitor, showed decreased nociceptive threshold, although D-NAME, inactive in nNOS inhibition, did not. These results suggest that decreased NO production might be involved in hyperalgesia in diabetic rats. Both hyperglycemia and decreased Na/K-ATPase activity are thought to be characteristic features of diabetic neuropathy. To investigate the presence of ion channel abnormality in diabetic nerves, a Vaseline-gap voltage clamp technique was applied for a single myelinated fibers under 30 mM high glucose plus 0.1 mM ouabain. Since K current was increased, a Ca activated K channel blocker was applied and this increase was shown to be suppressed. Furthermore, Ca channel blockers all suppressed increased K currents, suggesting that the condition induced an increase of Ca influx, thereby increasing Ca activated K currents through K channels. The data are important in that diabetic condition may induce both Ca influx, leading to nerve degeneration, and increased K current, resulting in decreased nerve conduction. Nerve regeneration has been known to be disturbed in diabetic condition. We have shown a decrease in nerve elongation rate in diabetic rats after crush of sciatic nerve, although this decrease was not ameliorated by ARI. Furthermore, Wallerian degeneration was shown to be delayed in diabetic nerves, leading to delayed nerve regeneration. Hyperphosphorylation of both medium and high molecular weight neurofilaments that might be induced by protein kinases including CDK 5 may be involved in the mechanism.
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PMID:[New trend in pathogenesis of diabetic neuropathy]. 1037 17

Many vascular diseases in diabetes are known to be associated with the activation of the diacylglycerol (DAG)-protein kinase C (PKC) pathway. The major source of DAG that is elevated in diabetes is de novo synthesis from glycolytic intermediates. Among the various PKC isoforms, the beta-isoform has been shown to be persistently activated in diabetic animals. Multiple lines of evidence have shown that many vascular alterations in diabetes--such as a decrease in the activity of Na+-K+-adenosine triphosphatase (Na+-K+-ATPase), and increases in extracellular matrix, cytokines, permeability, contractility, and cell proliferation--are caused by activation of PKC. Inhibition of PKC by two different kinds of PKC inhibitors, LY333531, a selective PKC-beta-isoform inhibitor, and d-alpha-tocopherol, were able to prevent or reverse the various vascular dysfunctions in diabetic rats. These results have also provided in vivo evidence that DAG-PKC activation could be responsible for the hyperglycemia-induced vascular dysfunctions in diabetes. Clinical studies are now being performed to clarify the pathogenic roles of the DAG-PKC pathway in developing vascular complications in diabetic patients.
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PMID:The role of protein kinase C activation in the pathogenesis of diabetic vascular complications. 1040 23


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