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Query: UMLS:C0011849 (diabetes)
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The data for an independent association between triglyceride concentrations and risk for coronary artery disease (CAD) are equivocal, unlike the data for low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol, which show strong, consistent, and opposing correlations with CAD risk. There is some evidence for triglyceride as an independent risk factor in certain subgroups, for example, women 50-69 years of age (Framingham Heart Study) and in patients with noninsulin-dependent diabetes. However, the evidence is stronger for triglyceride as a synergistic CAD risk factor. For example, patients with the "lipid triad" of high LDL cholesterol, low HDL cholesterol, and high triglyceride accounted for most of the event reduction with lipid-lowering therapy in the Helsinki Heart Study. An important confounder of the correlation between triglyceride and CAD risk is the heterogeneity of triglyceride-rich lipoproteins: the larger triglyceride-rich particles are thought not to be associated with CAD risk, whereas the smaller (and denser) particles are believed to be atherogenic. At present, measurement of fasting triglyceride levels and triglyceride assessment in conjunction with LDL cholesterol and HDL cholesterol concentrations are the most practical methods of evaluating hypertriglyceridemia in CAD risk, although postprandial lipemia may prove a better indicator of atherogenicity. Management of hypertriglyceridemia should initially focus on nonpharmacologic therapy (i.e., diet, exercise, weight control, and alcohol reduction). In diabetic patients, meticulous glycemic control is also important. However, if this approach proves inadequate, there are several pharmacologic options. Fibrates may be effective in decreasing triglyceride and increasing HDL cholesterol. Nicotinic acid (niacin) has been shown to decrease triglyceride, increase HDL cholesterol, lower LDL cholesterol, and decrease lipoprotein(a); it also decreases fibrinogen. The statins appear to be effective in decreasing triglyceride and LDL cholesterol in hypertriglyceridemia; however, they do not normalize metabolism of apolipoprotein B, and HDL cholesterol may remain low. Therefore, combination with a fibrate or niacin may be appropriate. Attention to hypertriglyceridemia with respect to increased CAD risk represents an important step in assessing global risk for CAD development.
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PMID:Triglyceride as a risk factor for coronary artery disease. 981

There is increasing evidence that high-density lipoprotein (HDL) and its subfractions are protective against atherosclerotic cardiovascular disease. Physical exercise, weight reduction, smoking cessation, diabetes mellitus control, and specific drugs, including niacin, fibrates, and estrogens, are effective methods to increase HDL levels. Niacin is the oldest and most powerful clinical agent for raising HDL levels. Niaspan, an extended-release niacin formulation, is as potent as immediate-release niacin in increasing levels of HDL cholesterol; subfractions HDL2 and HDL3; apolipoprotein A-I, the major protein of HDL, and its cardioprotective subfraction lipoprotein A-I. Recent research from our laboratory suggests a novel mechanism by which niacin inhibits hepatic removal of HDL-apoprotein A-I without interfering with the removal of cholesterol carried by HDL, thus augmenting reverse cholesterol transport. Other mechanistic studies indicate that fibrates and estrogens stimulate the synthesis and production of HDL-apoprotein A-I. Because niacin decreases HDL-apoprotein A-I removal, and fibrates and estrogens increase HDL-apoprotein A-I production, combinations of niacin with these agents may raise HDL levels more than fibrates or estrogens alone.
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PMID:Mechanistic studies of high-density lipoproteins. 991 62

Usual risk factors for coronary artery disease account for only 25-50% of increased atherosclerotic risk in diabetes mellitus. Other obvious risk factors are hyperglycemia and dyslipidemia. However, hyperglycemia is a very late stage in the sequence of events from insulin resistance to frank diabetes, whereas lipoprotein abnormalities are manifested during the largely asymptomatic diabetic prodrome and contribute substantially to the increased risk of macrovascular disease. The insulin-resistant diabetes course affects virtually all lipids and lipoproteins. Chylomicron and very-low-density lipoprotein (VLDL) remnants accumulate, and triglycerides enrich high-density lipoprotein (HDL) and low-density lipoprotein (LDL), leading to high levels of potentially atherogenic particles and low levels of HDL cholesterol. Hyperglycemia eventually impairs removal of triglyceride-rich lipoproteins, the accumulation of which accentuates hypertriglyceridemia. As triglycerides increase-still within the so-called normal range-abnormalities in HDL and LDL became more apparent. Thus, when triglycerides are >200 mg/dL, LDL particles are small and dense (when they are <90 mg/dL, the particles are of the large, buoyant variety). The atherogenicity of small, dense LDL particles is attributed to their increased susceptibility to oxidation, but in many patients they may be a marker for insulin resistance or the presence of atherogenic VLDL. Hypertriglyceridemia is associated with atherosclerosis because (1) it is a marker for insulin resistance and atherogenic metabolic abnormalities; and (2) the small size of triglyceride-enriched lipoproteins enables them to infiltrate the blood vessel wall where they are oxidized, bind to receptors on macrophages, and ingested, leading to the development of the atherosclerotic lesion. Various studies (primary prevention with gemfibrozil: Helsinki Heart Study; secondary prevention with simvastatin and pravastatin: Scandinavian Simvastatin Survival Study [4S] and Cholesterol and Recurrent Events [CARE], respectively) have demonstrated that lipid-lowering therapy in type 2 diabetes is effective in decreasing the number of cardiac events. Risk reduction was 22% to 50% (statins) and approximately 65% (fibrate) relative to placebo. It was also noted (in 4S and CARE) that the risk of major coronary events in untreated diabetic patients was 1.5-1.7-fold greater than in untreated nondiabetic patients. Although gemfibrozil (fibric acid derivative) is more effective in decreasing triglycerides and increasing HDL cholesterol in diabetic patients than the statins, it does not change and may even increase LDL-cholesterol levels (fenofibrate may be an exception, decreasing LDL cholesterol by 20-25% in some studies). However, gemfibrozil does increase LDL particle size. Nevertheless, the statins are the current lipid-lowering drugs of choice because the change in LDL-cholesterol-to-HDL-cholesterol ratio is better than with gemfibrozil. Moreover, the diabetic patient may be more likely to benefit from statin therapy than the nondiabetic patient. It should be noted that, in theory, nicotinic acid can correct or improve all lipid or lipoprotein abnormalities in patients with type 2 diabetes. Unfortunately, it is relatively contraindicated because it causes insulin resistance and may precipitate or aggravate hyperglycemia (in addition to its other well-known side effects such as flushing, gastric irritation, development of hepatotoxicity, and hyperuricemia). It is unknown at present whether newer formulations such as once-daily Niaspan may be better tolerated in diabetes. In any case, most patients with type 2 diabetes have risk factors for coronary artery disease and qualify for aggressive LDL cholesterol-lowering therapy. At the same time, it is presently unknown whether improved glycemic control decreases coronary artery disease risk in such patients.
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PMID:Diabetic dyslipidemia. 991 65

The objective of this study was to assess the role of free fatty acids (FFAs) as insulin secretagogues in patients with type 2 diabetes. To this end, basal insulin secretion rates (ISR) in response to acute increases in plasma FFAs were evaluated in patients with type 2 diabetes and in age- and weight-matched nondiabetic control subjects during 1) intravenous infusion of lipid plus heparin (L/H), which stimulated intravascular lipolysis, and 2) the FFA rebound, which followed lowering of plasma FFAs with nicotinic acid (NA) and was a consequence of increased lipolysis from the subject's own adipose tissue. At comparable euglycemia, diabetic patients had similar ISR but higher plasma beta-hydroxybutyrate (beta-OHB) levels during L/H infusion and higher plasma FFA and beta-OHB levels during the FFA rebound than nondiabetic control subjects. Correlating ISR with plasma FFA plus beta-OHB levels showed that in response to the same changes in FFA plus beta-OHB levels, diabetic patients secreted approximately 30% less insulin than nondiabetic control subjects. In addition, twice as much insulin was secreted during L/H infusion as during the FFA rebound in response to the same FFA/beta-OHB stimulation by both diabetic patients and control subjects. Glycerol, which was present in the infused lipid (272 mmol/l) did not affect ISR. We concluded that 1) assessment of FFA effects on ISR requires consideration of effects on ISR by ketone bodies; 2) ISR responses to FFA/beta-OHB were defective in patients with type 2 diabetes (partial beta-cell lipid blindness), but this defect was compensated by elevated plasma levels of FFAs and ketone bodies; and 3) approximately two times more insulin was released per unit change in plasma FFA plus beta-OHB during L/H infusion than during the FFA rebound after NA. The reason for this remains to be explored.
Diabetes 1999 Mar
PMID:Effects of fatty acids and ketone bodies on basal insulin secretion in type 2 diabetes. 1007 59

To obtain optimal image quality in myocardial viability studies, it is recommended that 18F-fluordeoxyglucose (18F-FDG) studies be performed with hyperinsulinaemic glucose clamping. 18F-FDG imaging after oral administration of acipimox, a nicotinic acid derivative, results in comparable image quality to clamping. Twenty consecutive patients (7 with diabetes mellitus) with angiographically confirmed coronary artery disease and similar demographic/clinical profiles were randomly allocated to gated cardiac 18F-FDG-PET with a standard euglycaemic hyperinsulinaemic clamp protocol or using a combination of oral administration of acipimox and the insulin clamp technique. The image quality, expressed as the myocardial-to-blood pool activity ratio, was superior in the combined protocol compared with the insulin clamping technique alone (3.37 +/- 1.46 vs 2.27 +/- 0.62, P = 0.037). Although there were no significant differences in plasma insulin and free fatty acids concentrations between the two protocols, plasma glucose concentrations obtained with the standard protocol were elevated compared with the combined protocol (11.1 +/- 3.7 vs 6.3 +/- 3.0 mM during clamping; 10.2 +/- 3.3 vs 5.5 +/- 3.0 mM during acquisition). We conclude that gated 18F-FDG-PET imaging after oral administration of acipimox plus insulin clamping yields image quality superior to that obtained with clamping alone.
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PMID:Combined hyperinsulinaemic glucose clamp and oral acipimox for optimizing metabolic conditions during 18F-fluorodeoxyglucose gated PET cardiac imaging: comparative results. 1058 93

The 'metabolic syndrome' is a special clinical entity characterized by upper body segment obesity (android obesity), together with one or more of a constellation of metabolic disorders that includes glucose intolerance, which may amount to frank diabetes mellitus, hypertension, cardiovascular lesions, hyperuricemia, and dyslipidemias (hypercholesterolemia, hypertriglyceridemia and reduced serum HDL). Recently, lipoprotein (Lp) (a) proved to be a new member in this syndrome. Lp(a) has the distinctive feature of containing apolipoprotein (a), which is a glycoprotein linked to apo B100, and has a similarity to plasminogen; it is also structurally related to LDL. Lp(a) is a macromolecular complex which is genetically determined, and has been identified as an independent risk factor for premature coronary artery disease (CAD). It is elevated in diabetic and non-diabetic android obese subjects, and aggravates the atherogenic effect of diabetes mellitus. Lp(a) is poorly influenced either by dietary measures or by hypolipidemic drugs. Unfortunately, few pharmacologic agents, such as niacin, nicotinic acid, sex hormones (estrogen and testosterone), alcohol and neomycin, affect Lp(a).
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PMID:Lipoprotein (a) in android obesity and NIDDM: a new member in 'the metabolic syndrome'. 1066 39

Nicotinamide adenine dinucleotide (NAD) and its derivatives NADH, NADP and NADPH have regulatory functions in the generation of triose phosphates and pyruvate from glucose. In many studies of the influence of the diabetic state on relationships between pyridine nucleotide and glucose metabolism, the focus has been on the sorbitol pathway. Less attention has been paid to other aspects of the role of pyridine nucleotides in pyruvate formation from glucose, in particular the effects of the NAD precursors nicotinamide and nicotinic acid on glucose metabolism. This paper reviews current knowledge of the involvement of pyridine nucleotides and their precursors in glucose catabolism in the normal and diabetic state. Reference is also made to the following three current hypotheses for mechanisms underlying diabetic microangiopathy: 1. Chronic glucose overutilization, caused by hyperglycemia, in tissues which lack insulin receptors and therefore are freely permeable to glucose. 2. Enhancement of sorbitol pathway activity with an ensuing decrease in the ratio of NAD/NADH. 3. Enhanced utilization of both glucose and pyridine nucleotides in formation of triose phosphates and pyruvate. Therapy with NAD precursors like nicotinamide might have corrective effects on these proposed biochemical aberrations, thereby retarding progression of microangiopathy.
Diabetes Metab Res Rev
PMID:Pyridine nucleotides in glucose metabolism and diabetes: a review. 1070 37

In clinical trials, all lipid-lowering agents have been associated with mild, asymptomatic elevations of alanine aminotransferase (ALT) and asparate aminotransferase enzymes. This, along with the fact that 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors are hepatotoxic in some animals, led the US Food and Drug Administration (FDA) to recommend monitoring of liver enzymes for all lipid-lowering agents, except the bile acid sequestrants. Because the drugs act by different mechanisms, ALT elevations may be a pharmacodynamic effect related to lipid lowering, rather than a direct effect of the drug. Animal studies support this assumption. ALT elevations of 3 times the upper limit of normal occur in <3% of patients in clinical trials of lipid-lowering drugs. The elevations are transient and often dose-related, and they usually revert to normal while continuing therapy and have never been associated with hepatotoxicity. Confounding factors include alcohol, acetaminophen, and pre-existing liver disease, such as chronic hepatitis C and type II diabetes with fatty liver, which are both associated with mild, intermittent elevations of ALT. The more important issue is whether or not lipid-lowering agents are hepatotoxic. There are case reports of hepatotoxicity (cholestasis, jaundice, hepatitis, chronic active hepatitis, fatty liver, cirrhosis and acute liver failure) with all of the drugs, except cholestyramine. To date there are just 5 cases of documented liver failure linked to lovastatin. There is no evidence that monitoring reduces the rate of hepatotoxicity. Mild elevations of ALT that occur with many drugs, including HMG-CoA reductase inhibitors, do not predict hepatotoxicity. Liver enzyme elevations appear to be a class characteristic of lipid-lowering agents. Hepatotoxicity is a rare idiosyncratic reaction, occurring only with sustained released nicotinic acid.
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PMID:Defining patient risks from expanded preventive therapies. 1085 89

The hypertriglyceridemia attends the physiopathology of the atherosclerosis by various mechanisms: association of low levels of high density lipoprotein-cholesterol (HDL-c), modification of quality of low density lipoprotein-cholesterol (LDL-c), influence on hemostatic processes, association with other hazard's factors (obesity, hypertension, etc.). The hypertriglyceridemia distinguishes in primary and secondary. In primary forms the origin is essentially genetic, while the secondary ones are metabolic consequence of various pathologies (renal, thyroid, diabetes mellitus etc.). The hypertriglyceridemia's treatment is founded on a correct feeding and/or on eventual use of drugs. Apart from the secondary forms, in which is obligatory to treat at first the basal disease, the pharmacological therapy of the hypertriglyceridemia is suggested only in resistant cases to alone dietetic therapy and overall in presence of other factors of atherothrombotic hazard. The most utilized drugs are: omega-3 fatty acids, the nicotinic acid and its derivatives, the fibrates and the statins. The stronghold of alpha-glucosidases inhibitors is the acarbose. It reduces the biosynthesis of very low density lipoproteins (VLDL) by the reduction of substrata with an improvement of glucidic metabolism. Atorvastatin and cerivastatin develop a greater action to reduce serum levels of triglycerides as to the foregoing ones because of the better selectivity of receptor binding, the greater halflife and inhibition of the apolipoprotein's B100 synthesis.
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PMID:[Treatment of hypertriglyceridemia. Current aspects]. 1093 25

Nicotinamide, the amide derivative of nicotinic acid, has over the past forty years been given at high doses for a variety of therapeutic applications. It is currently in trial as a potential means of preventing the onset of Type I (insulin-dependent) diabetes mellitus in high-risk, first-degree relatives. Nicotinamide is for regulatory purposes classed as a food additive rather than a drug and has not therefore required the formal safety evaluation normally expected of a new therapy. Because the safety of treatment with megadoses of vitamins cannot be assumed, a full literature review has been undertaken. The therapeutic index of nicotinamide is wide but at very high doses reversible hepatotoxicity has been reported in animals and humans. Minor abnormalities of liver enzymes can infrequently occur at the doses used for diabetes prevention. There is no evidence of teratogenicity from animal studies and nicotinamide is not in itself oncogenic; at very high doses it does however potentiate islet tumour formation in rats treated with streptozotocin or alloxan. There is no evidence of oncogenicity in man. Growth inhibition can occur in rats but growth in children is unaffected. Studies of its effects on glucose kinetics and insulin sensitivity are inconsistent but minor degrees of insulin resistance have been reported. The drug is well tolerated, especially in recent studies which have used relatively pure preparations of the vitamin. Experience to date therefore suggests that the ratio of risk to benefit of long-term nicotinamide treatment would be highly favourable, should the drug prove efficacious in diabetes prevention. High-dose nicotinamide should still, however, be considered as a drug with toxic potential at adult doses in excess of 3 gm/day and unsupervised use should be discouraged.
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PMID:Safety of high-dose nicotinamide: a review. 1112


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