Correlation of serum lipids with diabetes control in sulfonylurea-treated diabetic patients

Beneficial Effects of Pentanema vestitum Linn. Whole Plant on the Glucose and Other Biochemical Parameters of Alloxan Induced Diabetic Rabbits

The residents of Lower Dir and Malakand agency, Khyber Pakhtunkhwa, Pakistan, use the dry powder of whole plant of Pentanema vestitum for the treatment of asthma and diabetes. No documented reports are available about the therapeutic action of Pentanema vestitum. The present study was aimed to explore the antihyperglycemic effect of 70% methanol extract of Pentanema vestitum whole plant in glucose-induced nondiabetic hyperglycemic and alloxan-induced diabetic rabbits. During this study, the effects of plant extract on the serum lipid profile, GPT, ALP, bilirubin and creatinine of diabetic rabbits were also studied. The extract of Pentanema vestitum whole plant exhibited significant (P < 0.05) antihyperglycemic activity in glucose-induced hyperglycemic rabbits. Treatment of alloxan-induced diabetic rabbits with extract significantly (P < 0.05) reduced the elevated levels of serum glucose, GPT, ALP, bilirubin and creatinine. During the study of lipid profile, the extract proved to be antihyperlipidemic and HDL boosting in diabetic rabbit models. From the finding of the present research, it was concluded that the 70% methanol extract of Pentanema vestitum whole plant has beneficial effects on serum levels of glucose, lipid profile, GPT, ALP, bilirubin, and creatinine of diabetic rabbits.

Studies on the glycemic and lipidemic effect of Murraya koenigii in experimental animals

Diabetes is often accompanied by lipid abnormalities, which contribute significantly to cardiovascular morbidity and mortality in diabetic patients. Previously, we have demonstrated potent hypoglycemic activity of lyophilized aqueous extract of Murraya koenigii leaves in normal and alloxan induced diabetic rabbits for short duration of 6 h. In this study, we examined the effect of 1 month oral administration of Murraya koenigii aqueous leaves extract in normal and STZ induced severe diabetic rats, at the dose of 300 mg/kg bw, on various biochemical parameters, viz., fasting blood glucose (FBG), total cholesterol (TC), HDL-cholesterol (HDL), triglyceride (TG), alkaline phosphatase (ALKP), serum glutamate oxaloacetate and pyruvate transaminases (SGOT and SGPT) and serum creatinine. In case of diabetic animals fasting blood glucose (FBG) levels of treated animals reduced by 48.2% after 30 days treatment with the aqueous leaves extract. A fall of 19.2 and 30.8% in TC and 22.97 and 37.1% in TG levels were also observed in the case of treated normal as well as diabetic rats, respectively. Feeding the extract increased the HDL-cholesterol level by 16 and 29.4% in normal and diabetic rats, respectively, as compared with their initial values. In the normal rats after 1 month of oral administration of the extract SGOT and SGPT levels were decreased by 21.7 and 25.0%. Serum alkaline phosphatase values of the treated normal animals were also reduced by 33% while negligible change was observed in the normal control animals. In the case of diabetic rats, SGOT and SGPT levels were reduced by 36.7 and 32.2%, respectively, whereas ALKP levels decreased by 39.7% after 1 month oral administration of the extract. The serum creatinine levels decrease in normal as well as in the diabetic animals by 17.75 and 18.2%, respectively, as compared to initial values. In the diabetic control animals the urinary sugar remains at +4 level but there was a decrease of 75% in urine sugar in the case of treated diabetic rats. This indicates that the aqueous extract of Murraya koenigii has favorable effect in bringing down the severity of diabetes.

The effects of tolbutamide on lipoproteins, lipoprotein lipase and hormone-sensitive lipase

Type 2 diabetic patients are at increased risk to develop atherosclerotic vascular disease. These patients are often treated with sulphonylurea derivatives, and it has been suggested that this treatment might contribute to the increased atherosclerotic process. The aim of the present study was therefore to investigate whether tolbutamide influences lipid metabolism in such a way that the atherosclerotic process may be promoted. Addition of tolbutamide (5-500 mg/l) to isolated rat fat adipocytes inhibited the lipoprotein lipase (LPL) activity in a dose-dependent manner to levels about 50% of those registered in the absence of tolbutamide. This effect was due to inhibition of the activation of the enzyme in the tissue and not to interference with the interaction of enzyme with its substrate. Addition of tolbutamide (500 mg/l) also inhibited noradrenaline (100 nM) and isoprenaline (40 nM)-induced lipolysis by 48.1 +/- 7.4% (mean +/- S.E.M.) and 47.3 +/- 5.5%, respectively. The decreased lipolysis in tolbutamide preincubated adipocytes was shown to be the result of an inhibition of the phosphorylation of hormone sensitive lipase (HSL). Three months of tolbutamide treatment (0.5 g t.i.d.) in diet treated type 2 diabetic patients did not influence the plasma concentrations of cholesterol, triglycerides, LDL cholesterol, HDL cholesterol as well as HDL triglycerides and HDL phospholipids, and there were no differences compared to placebo treated patients. There was a tendency towards a decrement in the elimination rate of exogenous triglycerides in the tolbutamide group (P = 0.0801). No differences between the groups and no treatment effects were seen on LPL and hepatic lipase activities. In conclusion, our in vitro data show that tolbutamide has dual effects on lipid transport, with impairment of the LPL system, which would tend to decrease plasma lipoproteins by reducing hepatic production of lipoproteins. In vivo, these two effects seem to balance each other and plasma lipoprotein levels remain unaffected.

Antidiabetic and hypolipidemic effects of Momordica cymbalaria Hook. fruit powder in alloxan-diabetic rats

This study was undertaken to investigate the effect of Momordica cymbalaria fruit powder on blood glucose and other biochemical parameters in alloxan-induced diabetic rats. The treatment was given for 15 days. After the treatment, a significant reduction was observed in fasting blood glucose levels in the treated diabetic rats, but no hypoglycaemic activity in the treated normal rats. M. cymbalaria treatment showed considerable lowering of serum cholesterol and triglycerides in the treated diabetic group. There was a significant improvement in hepatic glycogen level in treated diabetic rats close to normal level after the treatment with M. cymbalaria. These results suggest that the M. cymbalaria fruit powder possesses antidiabetic and hypolipidemic effects in alloxan-induced diabetic rats.

Sulphonylurea treatment of NIDDM patients with cardiovascular disease: a mixed blessing?

Non-insulin-dependent diabetic (NIDDM) patients show a high incidence of cardiovascular disease, with greater risk of recurrent myocardial infarction and a less favourable clinical outcome than non-diabetic patients. The majority of NIDDM patients are treated with sulphonylurea (SU) derivatives. In the 1970's the University Group Diabetes Program concluded that tolbutamide treatment caused increased cardiovascular mortality; the study, which led to curtailment of oral antidiabetic treatment in the USA, was received with scepticism in Europe. Later criticism of its methodology reduced the impact of the study; however, the question of the safety of SU in NIDDM patients with cardiovascular disease has been re-opened in the face of new experimental data. The heart and vascular tissues do have prerequisites for SU action, i.e. SU receptors and ATP-dependent K+ (K+ATP) channels. These channels play an important role in the protection of the myocardium against ischaemia-reperfusion damage, and their closure by SU could lead to amplified ischaemic damage. Here we review evidence from animal and human studies for deleterious SU effects on ischaemia-induced myocardial damage, either by direct action or through diminished cardioprotective preconditioning. Closure of K+ATP channels by SU can lead to reduction of post-infarct arrhythmias; the drug has also been claimed to improve various atherosclerosis risk factors. The evidence for these beneficial effects of SU is also reviewed. We look at the major difficulties that hamper transfer of information from experimental studies to clinical decision-making: a) The affinity of SU for heart K+ATP channels is orders of magnitude lower than for beta-cell channels; is it reasonable to expect in vivo cardiac effects with therapeutic 'pancreatic' SU doses? b) Most studies utilized high doses of acutely administered SU; are effects similar in the chronic steady-state of the SU-treated diabetic patient? c) Convincing SU effects have been demonstrated in acutely induced ischaemia by acutely administering the drug; do such effects persist in the clinical situation of gradually progressive ischaemia? d) Ischaemia and modification of K+ATP channel activity induce complex events, some with opposing effects; what is the net result of SU action, and do different SU derivatives lead to different outcomes? e) In the chronic (and hence clinically relevant) situation, how can direct (deleterious or beneficial) SU effects be separated from beneficial effects mediated by the metabolic action of the drug? Only large prospective clinical studies, making use of advanced technology for assessment of cardiovascular function, can answer these questions. Millions of NIDDM patients are treated with SU derivatives; many are in the age group where cardiovascular risks are extremely high. The question of whether SU derivatives are beneficial or deleterious for these patients must finally be settle unequivocally.

Thromboxane production and platelet aggregation in type 2 diabetes mellitus without vascular complications

Diabetic individuals frequently have platelet hyperaggregability and increased thromboxane (TXB2) production. To evaluate whether improvement of metabolic control or changes in fatty acid composition of serum lipids might alter thromboxane (TXB2) formation and platelet function, we followed up 25 newly diagnosed type 2 diabetics without angiopathy for about 6 months. Improvement of metabolic control (HbA1, fell from 12.0 +/- 0.3 to 9.0 +/- 0.3%; p less than 0.01) was associated with significant decrease in total cholesterol, triglycerides, and ratios of total cholesterol/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol. Palmitic acid of phospholipids decreased significantly, whereas eicosapentaenoic acid increased. Regardless of this, the ADP-induced platelet aggregability and sensitivity were not altered. There was no effect whatever on the TXB2 synthesis capacity of clotting whole blood (204.9 +/- 25.0 vs 222.8 +/- 32.0 ng/ml) over 6 months of treatment. Platelet aggregability and TXB2 formation were not correlated to the degree of metabolic control, nor were there any correlations to serum lipids and their fatty acid composition. Thus, we are tempted to speculate that glucose metabolism in diabetes itself does not affect platelet aggregation or TXB2 formation in type 2 diabetes mellitus.

[Anomalies of lipid metabolism in diabetes mellitus]

Atheroma is by far the most common cause of mortality in diabetic patients (66 to 75% of deaths). Several physiopathological mechanisms are suspected to account for the greater frequency and severity of atheroma in diabetes. Among these, lipid abnormalities hold first rank and include not only quantitative but also qualitative abnormalities of lipoproteins altering their kinetics and bindings to membrane receptors. The main quantitative abnormalities are an increase of triglycerides and very low density lipoproteins (VLDL) and a fall in high density lipoproteins (HDL) and their HDL2 subfraction. Qualitative abnormalities include non-enzymatic glucosylation of apoproteins, changes in lipoprotein size and increase in their triglyceride content, and excessive oxidation of low density lipoproteins (LDL). Both quantitative and qualitative abnormalities of lipoproteins are present in non-insulin-dependent diabetes, whereas only qualitative abnormalities are observed, as a rule, in treated insulin-dependent diabetes. The physiopathology of lipid metabolism disorders is complex, possibly multifactorial and still imperfectly known. However, such factors as modification of insulin status, hyperglycaemia and obesity frequently associated with diabetes, are thought to be involved.

Adverse cardiovascular effects of sulphonylurea drugs. Clinical significance

Sulphonylureas are widely used in the treatment of diabetes mellitus. Since the publication of the University Groups Diabetes Program (UGDP) results the discussion on their possible cardiovascular side effects has been lively and sometimes even passionate. The initial UGDP findings about the adverse effects of tolbutamide on the cardiovascular system have been criticised, particularly for shortcomings in the study design. The results of other epidemiological studies of the sulphonylurea effects on cardiovascular morbidity and mortality published this far have been contradictory. This is understandable because the factors involved are very complex. Most of these studies have used tolbutamide only, and the findings cannot necessarily be directly extrapolated to other sulphonylureas. Only properly performed prospective studies may provide further information on this issue. High concentrations of several sulphonylureas may have inotropic effects on heart muscle in in vitro animal models, but human studies performed in vivo do not support the view of clinically significant inotropy for sulphonylureas. High concentrations of tolbutamide or glibenclamide (glyburide) may affect the myocardial metabolism in isolated organs, but the possible clinical significance of these findings remains unknown. Some epidemiological and experimental studies have associated oral antidiabetic treatment with the occurrence of cardiac arrhythmias or increased digitalis toxicity. Only a few results are available, and there may be differences between the sulphonylureas in this respect. Antiaggregatory properties have been postulated for some sulphonylureas. Gliclazide, in particular, has been studied, but some other compounds of this class have also been effective in short term studies. If confirmed, these effects on haemostasis would be noteworthy. The sulphonylurea effects on serum lipids, especially on HDL-cholesterol, have been discussed widely during the last few years. Decreases in HDL-cholesterol concentrations were suggested to be associated with sulphonylurea therapy. However, these findings were not confirmed in recent cross-sectional and longitudinal studies performed with different sulphonylureas. Chlorpropamide, and to a lesser extent tolbutamide, may cause dilutional hyponatraemia and aggravate existing heart failure. Glibenclamide may increase the clearance of water in the kidney.

Chlorpropamide lowers serum and lipoprotein cholesterol in insulin-dependent diabetes

Changes in serum lipids and lipoproteins were examined during eight weeks chlorpropamide therapy in eight C-peptide negative, insulin-dependent diabetic patients (mean age 40 years, mean onset of diabetes 20 years). Chlorpropamide was found to have a generalized cholesterol lowering effect (progressive significant fall in mean total cholesterol, LDL-C, HDL-C, and HDL3-C) with no significant change in the ratio of high-density lipoprotein to low-density lipoprotein cholesterol which was independent of insulin secretion.

Effect of sulfonylurea therapy on plasma lipids and high-density lipoprotein composition in non-insulin-dependent diabetes mellitus

To assess the effects of sulfonylurea therapy on plasma lipids and high-density lipoprotein composition, 11 obese diabetic Pima Indians with type II, or non-insulin-dependent, diabetes mellitus were studied before and after tolazamide therapy for one month. Diet composition and weight were kept constant, and the data were compared with a control group of 18 age-, sex-, and weight-matched non-diabetic subjects. Improvement of glycemic control was accompanied by significant decreases in total and very-low-density lipoprotein triglycerides. Total and low-density lipoprotein cholesterol also declined significantly, and there was an increase in the ratio of high-density lipoprotein to low-density lipoprotein cholesterol. Concentrations of total high-density lipoprotein cholesterol, phospholipid, and apolipoprotein AI were unchanged. An increase in the proportion of the high-density lipoprotein 2 subfraction, however, was suggested by significant increases in the ratios of high-density lipoprotein 2 to high-density lipoprotein 3 cholesterol and apolipoprotein AI. There was also a change in the composition of the high-density lipoprotein 2 particle, as indicated by changes in the molar ratio of cholesterol to apolipoprotein AI. The data suggest that improvement of glycemic control after sulfonylurea therapy, when weight and diet composition remain constant, reverses several of the lipoprotein abnormalities observed in type II diabetic patients. There was no evidence of changes in lipoproteins in directions associated with an increased risk for atherosclerosis.