Thromboxane production and platelet aggregation in diabetic subjects with clinical complications

Relationship between Dietary n-6 Fatty Acid Intake and Hypertension: Effect of Glycated Hemoglobin Levels

The relationship between dietary n-6 fatty acids and hypertension is not clear. The metabolic products of n-6 fatty acids include those that control blood pressure, such as prostaglandin and thromboxane, and that differ depending on the extent of glucose tolerance. This cross-sectional study investigated the association of dietary n-6 fatty acid intake on hypertension, and the effects of glycated hemoglobin (HbA1c) value in 633 Japanese subjects aged 40 years and older. Dietary intake was measured using a validated brief self-administered diet history questionnaire. We defined hypertension as the use of antihypertensive medication or a blood pressure of 140/90 mmHg. The prevalence of hypertension was 55.3%. A high n-6 fatty acids intake inversely correlated with hypertension in subjects with HbA1c values less than 6.5% (odds ratio, 0.857; 95% confidence interval, 0.744 to 0.987). On the contrary, in subjects with an HbA1c value of 6.5% or higher, the n-6 fatty acids intake was significantly associated with hypertension (odds ratio, 3.618; 95% confidence interval, 1.019 to 12.84). Regular dietary n-6 fatty acid intake may contribute to the prevention and treatment of hypertension in a healthy general population. By contrast, in subjects with diabetes, regular n-6 fatty acids intake may increase the risk of hypertension.

Network reconstruction of platelet metabolism identifies metabolic signature for aspirin resistance

Recently there has not been a systematic, objective assessment of the metabolic capabilities of the human platelet. A manually curated, functionally tested, and validated biochemical reaction network of platelet metabolism, iAT-PLT-636, was reconstructed using 33 proteomic datasets and 354 literature references. The network contains enzymes mapping to 403 diseases and 231 FDA approved drugs, alluding to an expansive scope of biochemical transformations that may affect or be affected by disease processes in multiple organ systems. The effect of aspirin (ASA) resistance on platelet metabolism was evaluated using constraint-based modeling, which revealed a redirection of glycolytic, fatty acid, and nucleotide metabolism reaction fluxes in order to accommodate eicosanoid synthesis and reactive oxygen species stress. These results were confirmed with independent proteomic data. The construction and availability of iAT-PLT-636 should stimulate further data-driven, systems analysis of platelet metabolism towards the understanding of pathophysiological conditions including, but not strictly limited to, coagulopathies.

Hydrogen peroxide formation in platelets of patients with non-insulin-dependent diabetes mellitus

A group of 29 patients with non-insulin-dependent diabetes mellitus (NIDDM) was compared with a group of 19 patients who had good glycemic control for platelet activity and hydrogen peroxide formation. NIDDM patients showed platelet hyperactivity in response to low ADP concentrations. In addition, stimulated platelets from untreated NIDDM patients produced more hydrogen peroxide than platelets of treated and normal subjects. Hydrogen peroxide accumulation was not related to modification of the enzymatic systems involved in its synthesis and break-down. The specific activities of NAD(P)H cytochrome C reductase, catalase, glutathione peroxidase and glutathione reductase were not different between patients and healthy subjects. It is likely that the platelet intracellular elevation of reactive oxygen free-radicals could play an important role in the vascular complications and thrombotic risk that is often present in NIDDM patients.

Glibenclamide inhibits thromboxane-mediated vasoconstriction by thromboxane receptor blockade

Because sulfonylureas, such as glibenclamide, are used to treat Type 2 diabetes and because this disease is associated with various cardiovascular complications that may be mediated by thromboxane (TX), this study was designed to characterize the role of glibenclamide on TX-mediated contractions in isolated ring segments of bovine coronary arteries and rabbit aortas. A series of TXA(2) analogs [9,11 Dideoxy-9alpha, 11alpha-methanoepoxy prostaglandin F(2alpha) (U46619), [1S-(1alpha, 2beta(5Z),3alpha(1E, 3R*),4alpha)]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo [2.2.1]heptan-2-yl]-5-heptenoic acid (I-BOP), carbocyclic TXA(2) (CTA(2)) and 9,11-dideoxy-9alpha,11alpha-epoxymethano prostaglandin F(2alpha) (U44069)], endothelin and phenylephrine contracted both types of blood vessels. Glibenclamide (10 microM) inhibited the contraction to each of the TX agonists but had no effect on endothelin- or phenylephrine-induced contractions. We hypothesized that this effect was due to a direct effect to block the vascular smooth muscle cell TX receptor. Receptor binding studies were performed in rabbit vascular smooth muscle cells and indicated that glibenclamide (10 microM) inhibited (125)I-BOP binding by more than 80%. The inhibition constants or K(i) for glibenclamide was 0.53 microM. These studies provide the first evidence that the ability of glibenclamide to inhibit TX-mediated contractions occurs independent of the vascular K(ATP) channel and is, instead, mediated by the blockade of the vascular TX receptor.

Increased synthesis of thromboxane A(2) and expression of procoagulant activity by monocytes in response to arachidonic acid in diabetes mellitus

Thromboxane A(2) (TXA(2)) synthesis and expression of procoagulant activity (PCA) were investigated in mononuclear cells and monocytes prepared from a control and a Type 2 diabetic group. Monocytes from the diabetic group produced 2.10+/-0.81 ng of TXB(2)/5 x 10(5) monocytes compared to 1.26+/-0.43 ng/5 x 10(5) monocytes by the control group (P<0.01, n=11) when incubated in autologous plasma containing arachidonic acid (200 microg/ml). When monocytes were incubated in buffer containing arachidonic acid (20 microg/ml), cells from the diabetic group produced 1.65+/-0.68 ng of TXB(2)/5 x 10(5) monocytes compared to 1.07+/-0.31 ng/5 x 10(5) monocytes by the control group (P<0.02, n=12). Expression of PCA was examined in mononuclear cell preparations. Basal and maximally stimulated PCA with lipopolysaccharide (4.2 microg/ml) were not different between control and diabetic groups. However, arachidonic acid induced a four-fold (P<0.001) increase in PCA in the diabetic group. This activity was characterized as tissue factor. Increased synthesis of TXA(2) and expression of PCA may potentiate thrombosis and increase fibrin deposition, events that play primary roles in the development of vascular disease.

Increased plasma endothelin-1 and intraplatelet cyclic guanosine monophosphate in men with disturbed glucose metabolism

Plasma endothelin-1, the nitric oxide (NO) mediator intraplatelet cyclic guanosine monophosphate (cGMP), the prostacyclin mediator cyclic adenosine monophosphate (cAMP) and the macrophage derived inflammatory mediator plasma neopterin were measured in men with Type 2 diabetes mellitus (n=91), impaired glucose tolerance (IGT; n=51), previously abnormal glucose tolerance (PAGT; n=20), and 34 healthy control men. Plasma endothelin-1was higher in men with Type 2 diabetes mellitus than in controls [4.1 (1.0-14.3) vs. 2.1 (0.2-8. 7) ng/l; P<0.001). Intraplatelet cGMP was higher in men with PAGT [0. 84 (0.57-2.76) pmol/10(9) platelets; P<0.05], IGT [0.85 (0.48-3.53); P<0.001] and Type 2 diabetes mellitus [0.90 (0.47-3.86); P<0.001] than in controls [0.70 (0.42-1.70]. No differences existed between groups concerning intraplatelet cAMP or plasma neopterin. Plasma endothelin-1 correlated with fasting plasma glucose (r=0.33; P<0.001) and HbA1(c) (r=0.29; P<0.001). In conclusion, elevated plasma endothelin-1 in Type 2 diabetes mellitus and its relationship to glucose and HbA1(c) suggest a putative role for endothelin-1 in diabetic endothelial cell damage. Increased cGMP indicating enhanced production/activity of NO suggests that factors other than reduced NO activity contribute to enhanced platelet aggregation in diabetes.

Modifications in the TXA(2) and PGI(2) plasma levels and some other biochemical parameters during the initiation and development of non-insulin-dependent diabetes mellitus (NIDDM) syndrome in the rabbit

Having developed a non-insulin-dependent diabetes mellitus (NIDDM) syndrome model in the rabbit using Wirsung duct ligation, it appeared interesting to use it to study the relationship between glycemia and the plasma levels of TXA(2)and PGI(2), and of some other biochemical parameters such as cholesterol, triglycerides, alkaline phosphatase and transaminases. A comparative study was carried out in the sham-operated rabbits (controls, C) and those having their pancreatic duct ligatured (NIDDM, D) at 15, 30, 40, 50 and 60 days post-ligation. On the 40th days, whereas in the controls, glycemia was 1.17 +/- 0.04 g.l(-1), it reached a maximum of 4.62 +/- 0.76 g.l(-1)(25.40 mM) in the NIDDMs. No significant modification was observed either in cholesterolemia or in triglyceridemia in either group. The GOT and GPT were highly increased, from 11.50 +/- 4.00 IU. l(-1)and 27.00 +/- 1.50 IU.l(-1)(C) to 37.50 +/- 5.64 IU.l(-1)(P<0. 001) and 58.50 +/- 7.50 IU.l(-1)(D) (P<0.001) in the NIDDM group, suggesting that hyperglycemia occurred simultaneously with the degeneration of the pancreatic tissue. In parallel, in D rabbits, the plasma levels of TXB(2)and 6 keto PGF(1alpha)were augmented to 68.22 +/- 6.20 pg.ml(-1)versus 22.49 +/- 5.74 pg.ml(-1)(C) (P<0.001), and 127.11 +/- 14.39 pg.ml(-1)versus 48.65 +/- 4.51 pg.ml(-1)(C) (P<0. 001) respectively. Statistical studies showed a significant correlation (P<0.05 and <0.02) between glycemia and the biosynthesis of eicosanoids under study. Moreover, 25 mM was found to be the threshold level of glucose excess essential to increase the TXA(2)and PGI(2)biosynthesis significantly. This supports the results obtained by other authors studying the action of glucose on phospholipase activity and consequent eicosanoid production.

Improved glycemic control and platelet function abnormalities in diabetic patients with microvascular disease

Patients with diabetes mellitus have a variety of platelet and coagulation system dysfunctions. At least theoretically, these can contribute to microvascular complications. Intensive glycemic control has been demonstrated to decrease microvascular complications in type 1 diabetics. We studied 16 patients with type 1 diabetes mellitus (11 men and five women; mean age, 39 years) with albuminuria greater than 0.1 g/d and/or proteinuria greater than 0.3 g/d and a creatinine clearance rate higher than 30 mL/min. They received a regimen including three to four injections of insulin per day with or without a weekly infusion of intravenous insulin, and were evaluated for 6 months. We compared the plasma level of von Willebrand factor, platelet aggregation responses to adenosine diphosphate (ADP), epinephrine, and collagen, and platelet adhesion at the beginning of the study and at follow-up intervals. Glycemic control improved significantly. There were no significant differences in the platelet aggregation responses to ADP (1.59 +/- 0.34 v 1.88 +/- 0.23 mmol/L, P = .3; normal, 4.6 +/- 0.2), epinephrine (0.50 +/- 0.20 v 1.11 +/- 0.31 mmol/L, P = .06; normal, 7.6 +/- 1.5), or collagen (92.4 +/- 6.61 v 82.60 +/- 3.78 seconds, P = .6; normal, 79.1 +/- 3.1) or in platelet adhesion (126.31 +/- 16.95 v 195.08 +/- 30.2 platelets, P = .34; normal, 68.6 +/- 1.4). Baseline von Willebrand factor increased, but not significantly (166.38% +/- 10.6% v 142.72% +/- 14.73%, P = .21; normal, 102.0% +/- 6.0%). In type 1 diabetic patients with established microvascular complications of nephropathy, a statistically significant improvement in glycemic control did not improve the in vitro platelet function abnormalities. Improved glycemic control delays the progression of microvascular disease through mechanisms not measured by tests of platelet function.

Changes in platelet ATP secretion and aggregation during pregnancy and in preeclampsia

BACKGROUND

Platelet secretion plays an important role in the aggregation of platelets. However, the quantitative relationship between platelet aggregation and secretion of ATP during pregnancy and in pre-eclampsia has yet to be clarified. This study is designed to determine whether platelet count, volume, aggregation, and the amount of secreted ATP change in healthy, nonpregnant women, nonpreeclamptic pregnant women, and preeclamptic pregnant women and whether beta-thromboglobulin (BTG) and platelet factor 4 (PF-4) concentrations alter in nonpreeclamptic and pre-eclamptic women.

METHODS

Peripheral blood was collected from 114 women. Nonpreeclamptic pregnant women were divided into four groups (gestational weeks 10, 20, 30, and 35). Platelet aggregation and ATP secretion were investigated with the use of a lumi-aggregometer. BTG and PF-4 concentrations in peripheral blood were determined in 12 pregnant and 11 preeclamptic women.

RESULTS

The amount of secreted ATP upon induction by 5 microM ADP increased significantly (P < 0.05-0.01) with gestational age. On the other hand, the amount of secreted ATP induced by 5 microg/mL collagen reached the maximal value from gestational weeks 20 to 35 in nonpreeclamptic women. Significantly more platelet aggregation was induced by the ADP and collagen in nonpreeclamptic women in gestational weeks 20 and 30 than in the gestational weeks 10 or 35 (P < 0.05-0.005). The amount of secreted ATP and platelet count were significantly lower (P < 0.05) in preeclampsia than in normal pregnancy. The BTG and PF-4 concentrations were significantly higher (P < 0.05) in preeclampsia than in normal pregnancy.

CONCLUSIONS

The sensitivity of platelets for ATP secretion may intensify with progression of pregnancy. In normal pregnancy, around gestational week 35, the platelets may exhibit weaker ability to aggregate but maintain the capacity to secrete ATP. In preeclampsia, secreted ATP decreased because platelets may be stimulated to undergo a partial secretion.

Platelets from patients with diabetes mellitus have impaired ability to mediate vasodilation

OBJECTIVES

The purpose of this study was to examine vasomotor responses mediated by platelets from patients with diabetes mellitus.

BACKGROUND

Diabetes mellitus is associated with increased cardiovascular morbidity and mortality, which in part may be due to a variety of abnormalities reported in diabetic platelets. However, the effects of diabetic platelets on vasomotor tone have not been characterized.

METHODS

We compared platelet-mediated vasodilation elicited by platelets isolated from 30 healthy volunteers and 29 patients with diabetes mellitus as they were perfused through a preconstricted normal rabbit carotid artery.

RESULTS

Platelets from the diabetic patients mediated an impaired dilatory response in comparison with normal platelets: 2.7 +/- 2% versus 15.8 +/- 3.4% (p < 0.001) and 4.1 +/- 2.7% versus 32.7 +/- 3.3% (p < 0.001) (mean +/- SEM) increase in vessel diameter, for 5 X 10(7) and 1 X 10(8) platelets per milliliter perfused, respectively. The degree of impairment was similar for type I (insulin-dependent) and type II (non-insulin-dependent) diabetes mellitus. Normal platelets incubated in high D-glucose concentrations lost their ability to mediate dilation in a concentration-dependent and time-dependent manner. This was not true for incubation of normal platelets in high concentrations of L-glucose or insulin. However, there was not a significant correlation between glucose control in the diabetic patients and the ability of their platelets to mediate vasodilation.

CONCLUSIONS

Platelets from patients with diabetes mellitus have an impaired ability to mediate vasodilation. This impairment appears to be mediated by high glucose concentration. Further work is needed to elucidate the mechanisms for this abnormality in diabetic platelets.

Hemostatic factors as triggers of cardiovascular events

A growing body of evidence supports a role for hemostatic factors in triggering cardiovascular events. Fibrinogen has been identified as an independent cardiovascular risk factor that is as powerful a predictor as cholesterol. Factor VII, fibrinolytic potential, von Willebrand's factor, and platelet reactivity also have been linked to increased incidence of cardiovascular disease. Further characterization of these factors may lead to improved risk assessment and the development of new therapies for prevention.

Unstable angina. A comparison of angioscopic findings between diabetic and nondiabetic patients

BACKGROUND

Patients with diabetes mellitus have a higher prevalence of atherosclerotic heart disease and a higher incidence of myocardial infarction than the general population. Diabetic patients also have several hematologic, rheologic, and metabolic abnormalities not present in their nondiabetic counterparts that may predispose them to atherosclerotic plaque rupture and intraluminal thrombosis and consequently may lead to the formation of morphologically complex plaques and the development of acute coronary syndromes.

METHODS AND RESULTS

Percutaneous coronary angioscopy was performed in 55 consecutive patients with unstable angina. We observed plaque color, texture, and the incidence of intracoronary thrombus associated with the culprit lesions of these patients. The population consisted of 17 (31%) diabetic and 38 (69%) nondiabetic patients. The presence of coronary risk factors was not significantly different between the two populations. Ulcerated plaque was found in 16 of 17 (94%) diabetic patients versus 23 of 38 (60%) nondiabetic patients (P = .01). Intracoronary thrombi were seen in 16 of 17 (94%) diabetic patients versus 21 of 38 (55%) nondiabetic patients (P = .004).

CONCLUSIONS

The results of the angioscopic examination show that diabetic patients with unstable angina have a higher incidence of plaque ulceration and intracoronary thrombus formation than nondiabetic patients. This increased frequency of complex lesion morphology is consistent with the disproportionately higher risk for development of acute coronary syndromes in these patients.

Lipid peroxidation products and changes in phospholipid composition induced by indobufen in diabetic platelets

Indobufen is an antiaggregatory drug which first of all inhibits platelet aggregation by interfering with cyclooxygenase enzymes in platelets. We have investigated the influence of indobufen (200 mg twice daily for 10 days) on platelet lipid peroxidation and phospholipid metabolism in diabetic patients. The production of lipid peroxidation products was significantly lower after drug treatment. Indobufen administration, however, had no influence on the fatty acid composition of platelet phospholipids.

Improvement in blood flow and diabetic neuropathy by thromboxane A2 dual blocker KDI-792

We studied the effect of a thromboxane A2 (TXA2) dual blocker KDI-792 on skin blood flow as well as on the peripheral nerve function of nine diabetics with neuropathy. After administration of KDI-792, there was no change in urinary TXB2; however, urinary 6-keto-prostaglandin (PG) F1 alpha increased significantly. Nerve conduction velocity (NCV) and vibration perception threshold (VT) in the four extremities improved significantly, as did deep skin temperature and skin blood flow. The degree of improvement in sensory NCV in the lower extremities correlated significantly with that of deep skin temperature in the toes and the degree of improvement of VT in the lower extremities correlated well with that of deep skin temperature in the soles and of skin blood flow in the toes. Based on these findings, treatment of diabetic neuropathy with a TXA2 dual blocker appears to increase PGI2 production, improving blood flow, and resulting in improvement of nerve functions.

Altered platelet functions in non-insulin-dependent diabetes mellitus (NIDDM)

We have studied platelet aggregation and membrane fluidity, along with various biochemical parameters, in 19 non-insulin-dependent diabetes mellitus (NIDDM) patients prior to control of blood sugar, 11 patients after control of blood sugar, and 26 normal subjects. Platelet cholesterol: phospholipid ratio and basal levels of)[Ca+] were comparable between normal and uncontrolled NIDDM. Basal levels of malonaldehyde (MDA) and the levels of [Ca++]i, as well as MDA after the addition of arachidonic acid, were 2.5-fold, 5-fold, and 2.5-fold higher, respectively, in the uncontrolled NIDDM group than normals. Platelet aggregation in response to ADP (0.25 microM), epinephrine (1.25 microM), and arachidonic acid (0.25 mM) was significantly higher in uncontrolled NIDDM than in normals (75%, 40% and 52%, respectively). Platelet fluorescence polarization was also higher in NIDDM patients indicating decreased membrane fluidity in such patients as compared to normals. After control of blood sugar in 11 NIDDM patients, agonist-stimulated platelet aggregation and other biochemical parameters were comparable to normals.

Influence of omega-3 fatty acid treatment on cardiac phospholipid composition and coronary flow of streptozocin-diabetic rats

Cardiac effects of omega-3 fatty acid treatment were studied in streptozocin (STZ)-induced (55 mg/kg intravenously [IV]) diabetic male Wistar rats. Nondiabetic control and STZ-diabetic animals were treated with Promega (0.5 mL/kg/d; Warner-Lambert, Morris Plains, NJ) for a period of 4 weeks beginning 2 weeks after either vehicle or STZ injection. Plasma glucose, triglyceride, and cholesterol concentrations were significantly (P < .05) elevated in diabetic animals; omega-3 fatty acid treatment did not significantly affect these parameters. An isolated working heart preparation was used to determine aortic and coronary flow rates in control, diabetic, treated control, and treated diabetic animals. Aortic and coronary flow rates of untreated STZ-diabetic rats were significantly (P < .05) lower than those of controls over a range of left atrial filling pressures (7.5 to 20 cm water). Both aortic and coronary flow rates of omega-3 fatty acid-treated diabetic animals were significantly (P < .05) increased above those of untreated diabetic rats. Aortic and coronary flow rates of treated diabetic rats paralleled those of control animals; omega-3 fatty acid treatment did not affect aortic or coronary flow rates of control animals. Cardiac phosphatidylcholine (PC) and phosphatidylethanolamine (PE) and sarcoplasmic reticulum (SR) total phospholipid were isolated and the acyl composition was determined. Stearic acid and C22:4, n-6 were significantly reduced in cardiac PE of diabetic animals. Relative to PE acyl species of untreated nondiabetic controls, treated diabetic PE had increased eicosapentaenoic acid (EPA) and decosahexaenoic acid (DHA) and reduced C22:4, n-6 levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute myocardial infarction in the diabetic patient: pathophysiology, clinical course and prognosis

Although there have been significant advances in the care of many of the extrapancreatic manifestations of diabetes, acute myocardial infarction continues to be a major cause of morbidity and mortality in diabetic patients. Factors unique to diabetes increase atherosclerotic plaque formation and thrombosis, thereby contributing to myocardial infarction. Autonomic neuropathy may predispose to infarction and result in atypical presenting symptoms in the diabetic patient, making diagnosis difficult and delaying treatment. The clinical course of myocardial infarction is frequently complicated and carries a higher mortality rate in the diabetic than in the nondiabetic patient. Although the course and pathophysiology of myocardial infarction differ to some degree in diabetic patients from those in patients without diabetes, much more remains to be known to formulate more effective treatment strategies in this high risk subgroup.

Hypertension, the endothelial cell, and the vascular complications of diabetes mellitus

Hypertension is a major factor that contributes to the development of the vascular complications of diabetes mellitus, which primarily include atherosclerosis, nephropathy, and retinopathy. The mechanism of the pathophysiological effects of hypertension lies at the cellular level in the blood vessel wall, which intimately involves the function and interaction of the endothelial and vascular smooth muscle cells. Both hypertension and diabetes mellitus alter endothelial cell structure and function. In large and medium size vessels and in the kidney, endothelial dysfunction leads to enhanced growth and vasoconstriction of vascular smooth muscle cells and mesangial cells, respectively. These changes in the cells of smooth muscle lineage play a key role in the development of both atherosclerosis and glomerulosclerosis. In diabetic retinopathy, damage and altered growth of retinal capillary endothelial cells is the major pathophysiological insult leading to proliferative lesions of the retina. Thus, the endothelium emerges as a key target organ of damage in diabetes mellitus; this damage is enhanced in the presence of hypertension. An overall approach to the understanding and treatment of diabetes mellitus and its complications will be to elucidate the mechanisms of vascular disease and endothelial cell dysfunction that occur in the setting of hypertension and diabetes.

Platelet function in male diabetics with and without macrovascular complications

Changes of platelet aggregation in relation to macroangiopathy and to some of its risk factors were observed in microangiopathy-free, well-controlled type 1 diabetic males. Platelet aggregate ratio was generally lower in patients (n = 77) than in age-matched healthy subjects (n = 48). In the absence of cigarette smoking, hypertension, obesity and hypercholesterolemia (n = 25) in vitro platelet hyperaggregation was found induced with epinephrine, collagen or arachidonic acid, and to a lesser degree with ADP. There was no change in the presence of at least one risk factor in addition to diabetes (n = 29), but there was a further significant increase in platelet aggregation when overt coronary, cerebral or peripheral artery disease was present (n = 23).

Aldose reductase inhibitors and diabetic complications

Aldose reductase inhibitors impede flux of glucose through the sorbitol pathway in diabetes mellitus. They therefore reduce the accumulation of the pathway metabolites, sorbitol and fructose, reduce the impact of the flux on the cofactors used by the pathway and reduce other derived phenomena, such as osmotic stress and myo-inositol depletion. As drugs, their targets are the chronic complications of diabetes--neuropathy, retinopathy, nephropathy and vasculopathy. In experimental models there is proof of activity against biochemical, functional and structural defects in all of the involved tissues, but we await full clinical verification of this potential.

A thromboxane A2 synthetase inhibitor retards hypertensive rat diabetic nephropathy

Spontaneously hypertensive rats (SHR) were injected with streptozotocin (STZ-SHR) to induce diabetes. The effect of DP-1904, a thromboxane A2 synthetase inhibitor, on diabetic nephropathy was then studied by administering it for 5 months (1 or 10 mg/kg). DP-1904 did not affect renal 6-keto prostaglandin (PG)F1 alpha production in STZ-SHR, but markedly inhibited renal thromboxane (TX) B2 production, so that the 6-keto PGF1 alpha/TXB2 ratio was significantly increased (P less than 0.05). STZ-SHR showed significant uraemia and proteinuria, plus increases in urinary gamma-glutamyl-transpeptidase and urinary N-acetyl-beta-glucosaminidase. DP-1904 significantly decreased (P less than 0.01) the urinary changes. STZ-SHR also showed an increase in mesangial periodic acid-Schiff-positive substance and in relative renal weight, both of which were significantly inhibited by DP-1904 (P less than 0.05). Thus, DP-1904 inhibited both TXB2 production and the progression of renal damage in STZ-SHR.

Cardiovascular sensitivity changes to eicosanoids in rats with experimentally induced diabetes mellitus

This paper attempts to provide a short review of the evidence for: 1. Increased platelet production of thromboxane A2 and reduced vascular production of prostacyclin in the human and also animal models of diabetes. 2. Reduced depressor responsiveness to arachidonic acid of anaesthetized alloxan- and streptozotocin-induced diabetic rats. 3. Enhanced constrictor responsiveness to arachidonic acid in blood-perfused hindquarters of alloxan-induced diabetic rats. 4. Potentiation by the thromboxane A2-mimetic, U46619, of constrictor responses to 5-hydroxytryptamine in Krebs'-perfused hindquarters and kidneys of both control and alloxan-induced diabetic rats. 5. Alterations during diabetes in production of, and responsiveness to, eicosanoids may contribute to the cardiovascular changes which occur in this disease.

Thromboxane biosynthesis and platelet function in type II diabetes mellitus

It has been suggested that platelet hyperreactivity in patients with diabetes mellitus is associated with increased platelet production of thromboxane. We therefore compared the excretion of a thromboxane metabolite and platelet function in 50 patients with Type II diabetes mellitus who had normal renal function and clinical evidence of macrovascular disease and in 32 healthy controls. The mean (+/- SD) excretion rate of urinary 11-dehydro-thromboxane B2 was significantly higher in the patients than in the controls (5.94 +/- 3.68 vs. 1.50 +/- 0.79 nmol per day; P less than 0.001), irrespective of the type of macrovascular complication. Tight metabolic control achieved with insulin therapy reduced the levels of 11-dehydro-thromboxane B2 by approximately 50 percent. The fractional conversion of exogenous thromboxane B2 (infused at a rate of 4.5, 45.3, or 226.4 fmol per kilogram of body weight per second) to urinary 11-dehydro-thromboxane B2 was assessed in four patients, in whom it averaged 5.4 +/- 0.1 percent; this value did not differ from that measured in healthy subjects. Aspirin in low doses (50 mg per day for seven days) reduced urinary excretion of the metabolite by approximately 80 percent in four patients. The fact that thromboxane biosynthesis recovered over the following 10 days was consistent with a platelet origin of the urinary metabolite.(ABSTRACT TRUNCATED AT 250 WORDS)

Absence of effect of dipyridamole on renal and platelet function in diabetes mellitus

We evaluated the effect of dipyridamole (5 mg/kg/day) for 12 months on renal and platelet function in 53 children with insulin dependent diabetes mellitus (IDDM) in a prospective double blind placebo controlled trial. Urine albumin excretion (expressed as the geometric mean albumin to creatinine concentration ratio (UA/UC) was measured every three months throughout the study. At 12 months, the geometric mean UA/UC was no different in diabetic children receiving dipyridamole, 0.60 mg/mmol, when compared with those receiving placebo, 0.87 mg/mmol. Glomerular filtration rate, urinary excretion of retinol binding protein, and N-acetyl-beta-D-glucosaminidase (NAG), blood pressure, and spontaneous platelet aggregation in response to stirring whole blood did not differ between the two groups at 12 months. Subgroup analysis to include only those children with high UA/UC before entry into the study also failed to show an effect of the drug on UA/UC. Eleven children had either persistently high UA/UC (n = 8: four on dipyridamole, four on placebo) or progression to high UA/UC (n = 3: two on dipyridamole, one on placebo). These children had significantly higher urinary excretion of retinol binding protein and NAG, bigger kidneys, and higher diastolic blood pressure both before and after treatment than the remaining 42 children, whereas there was no difference in spontaneous platelet aggregation between the two groups. These observations on the associations between UA/UC and other parameters of renal function suggest that measurement of 'tubular' proteins and diastolic blood pressure as well as UA/UC may contribute to the identification of those at risk of developing nephropathy.

The role of platelets in progressive glomerulosclerosis: mechanisms for intraglomerular platelet activation and pathogenetic consequences

Purkerson et al. have hypothesized that platelet aggregation and release reactions contribute to the progressive sclerosis of remnant nephrons. The suggested mechanism for platelet activation is disruption of endothelium by the high hydraulic pressures characteristic of remnant nephrons, with platelet exposure to basement membrane collagen. We herein postulate additional mechanisms whereby platelets might be activated in the microcirculation of remnant nephrons: (i) kinetic activation due to high plasma flow rates; (ii) close cell contact due to concentration of blood cells and platelets in the glomerulus; (iii) concentration of protein macromolecules that act as agonists for platelet release; (iv) glomerular release of saturated and monenoic fatty acids that stimulate platelet synthesis of thromboxane A2; (v) glomerular release of membrane-bound pro-coagulant factor, triggering a chain reaction that activates both platelets and the intraglomerular coagulation cascade. Platelet activation could play a pathogenetic role in many of the known derangements of structure and function in remnant nephrons. This paradigm may also be partially applicable to the glomerulosclerosis of diabetes mellitus.

Altered membrane fatty acid composition and increased thromboxane A2 generation in platelets from patients with diabetes

Lipid composition of platelet membranes and thromboxane A2 (TxA2) generation by platelets were investigated in 42 diabetic patients (14 with macroangiopathic complications, 10 with microangiopathy and 18 without vascular complications) and in 42 clinically healthy subjects of similar age. All subjects were on a similar dietary regimen and the adherence to diet was checked by analysis of red blood cell lipids. Platelets from all groups of diabetic patients produced increased amounts of TxA2 than platelets from controls (at least p less than 0.01) and patients with macroangiopathy (p less than 0.01). Platelet cholesterol and total platelet phospholipids were higher in patients with macroangiopathy, while the relative percentage of the different phospholipid fractions in platelet membrane and their saturated and unsaturated fatty acids were similar in the different groups. Arachidonic acid (AA) content in phosphatidylcholine (PC) was found to be significantly higher in diabetic patients than in controls (at least p less than 0.005). Moreover patients with macroangiopathy had higher AA (p less than 0.001) and lower eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) levels in PC (p less than 0.001) than the other groups of patients and controls.

Thromboxane biosynthesis and platelet function in type I diabetes mellitus

It has been speculated that platelet activation may contribute to the evolution of vascular complications in patients with Type I diabetes mellitus. To address this hypothesis, we measured the plasma and urinary metabolites of thromboxane, presumably of platelet origin, and of prostacyclin, derived from endothelial cells, in addition to more conventional indexes of platelet function. Urinary excretion of the metabolites 2,3-dinor-thromboxane B2 and 2,3-dinor-6-keto-prostaglandin F1 alpha did not differ between diabetics with or without retinopathy and nondiabetic controls. Furthermore, measurement of platelet granule constituents, the aggregation responses to ADP or arachidonic acid, and levels of serum thromboxane B2 failed to discriminate between the groups. The institution of tight diabetic control with multiple daily injections of insulin failed to alter either urinary metabolite excretion or plasma levels of 11-dehydro-thromboxane B2. Conversely, insulin-induced hypoglycemia failed to alter the concentrations of plasma or urinary thromboxane metabolites in nondiabetic volunteers, despite a mean 60-fold increase in plasma epinephrine. These studies suggest that platelet activation does not precede the development of microvascular complications in patients with Type I diabetes who lack clinical evidence of macrovascular disease and have normal renal function. Furthermore, it is unlikely that platelet activation due to intermittent hypoglycemia contributes to the reportedly accelerated development of retinopathy in such patients, when they are subject to tight diabetic control.

Alterations of phospholipid asymmetry in the membrane of spontaneously aggregated platelets in diabetes

The changes of asymmetric distribution of anionic phospholipids of human platelets in diabetic patients were studied by fluorescent and freeze fracture cytochemistry, using merocyanine 540 (MC 540) and polymyxin B (PxB) as specific markers. The membrane anionic phospholipids were detected with PxB, a membrane nonpermeant probe, used either in native form for freeze fracture electron microscopy or as dansylated or iodinated derivative for fluorescence microscopy or gamma counting, respectively. MC 540 is a naturally fluorescent probe which reportedly inserts into less packed bilayer domains. Both in platelet rich plasma and in washed platelets obtained from diabetic patients, some small platelet aggregates were observed, their number being generally dependent on the level of hyperglycemia. In contrast with single platelets, the aggregated ones bind PxB as revealed by all assay methods. The fluorescence microscopic studies with dansyl PxB and MC 540 displayed a strong binding of the fluorescent markers to aggregated platelets. The electron microscopic examination of freeze fracture replicas showed the appearance of characteristic PxB-induced deformations in the plasmalemma of aggregated platelets. The gamma counting of 125I-PxB incubated samples indicates significant differences on the platelets of diabetic patients as compared to those obtained from healthy subjects. Our data provide evidence that in diabetic patients, the spontaneous aggregated platelets are a result of the appearance of the anionic phospholipids in the outer half of plasmalemma. These changes may enhance the procoagulant activity and should represent a determinant of activated platelet recognition and their removal from circulation by splenic macrophages.

Platelet synthesis of cyclooxygenase and lipoxygenase products in type I and type II diabetes

In 24 type I and 22 type II diabetic patients without vascular complications and in 25 controls platelet thromboxane A2 (TxA2) and prostaglandin E2 (PGE2) production (by radioimmunoassay-RIA) and 1-14C arachidonic acid (AA) metabolism (by high pressure liquid chromatography-HPLC) after thrombin stimulation were studied. Platelets both from type I and type II diabetics generated larger amounts of TxB2 (p less than 0.001) and PGE2 (p less than 0.005) than controls, independently of the presence of retinopathy. No significant differences in platelet AA uptake or metabolism via the cyclooxygenase (CO) route, after thrombin stimulation (5 NIH U/ml), were observed in diabetic patients: lipoxygenase metabolites were found to be slightly, but significantly decreased. A positive linear relationship (r = 0.64, p less than 0.001) was found between HbA-1c and TxB2 production, but not with fasting plasma glucose. These results indicate that metabolic alterations can affect platelet function independently of vascular complications. The absence of alterations in intraplatelet 1-14C AA metabolism via CO, in the presence of increased TxB2 and PGE2 production from endogenous AA, suggests that the activation of CO is not the only possible mechanism of platelet activation and that probably an increased availability of platelet AA plays an important role in the enhanced platelet aggregation commonly found in diabetics.

Reevaluation of circulating prostacyclin and thromboxane in diabetes

Although several investigators have attempted to measure the plasma levels of prostacyclin (PGI2) and thromboxane A2 (TXA2) in diabetes and normal subjects, their results have been controversial. In this study, we measured plasma PGI2 and TXA2 levels in diabetic patients and normal subjects. The plasma PGI2 and TXA2 were determined by RIA as 6-keto-PGF1 alpha and TXB2, respectively. The plasma levels of 6-keto-PGF1 alpha were significantly reduced in diabetics with microangiopathy (52.5 +/- 18.9 pg/ml, mean +/- SE, p less than 0.05) compared with those of normal subjects. Diabetics as a whole also showed lower levels of 6-keto-PGF1 alpha than normal subjects (57.8 +/- 26.1 vs. 70.2 +/- 20.7 pg/ml), though this was not significant statistically. The plasma 6-keto-PGF1 alpha levels did not significantly correlate with either age of the patients or duration of diabetes in diabetics. Interestingly, however, hemoglobin A1c significantly correlated inversely with 6-keto-PGF1 alpha levels in diabetics without microangiopathy (r = -0.60, p less than 0.05). The plasma levels of TXB2 in diabetics were significantly higher than those of normal subjects (155.2 +/- 69.5 vs. 108.0 +/- 30.0 pg/ml, p less than 0.05). These data suggest that an imbalance of circulating PGI2 and TXA2 may contribute to the development of diabetic microangiopathy.

Effects of a fish oil supplement on platelet function, haemostatic variables and albuminuria in insulin-dependent diabetics

A randomised trial of the effects of 15 gm per day of a fish oil supplement (MaxEPA) on blood lipids, haemostatic variables (including platelet function) and albuminuria was undertaken in 41 insulin dependent diabetics. Compared with the control group there was a significant reduction in thromboxane production by platelets stimulated by collagen in vitro in the group who took the fish oil supplement. The extent of platelet aggregation was not altered but the lag phase before aggregation was prolonged. There were also statistically significant increases in plasma LDL cholesterol, fibrinogen and clotting factor X in the group who took the fish oil supplement. No other significant differences were noted.

Increased platelet thromboxane receptor sensitivity in diabetic patients with proliferative retinopathy

Platelet aggregation to collagen in 12 Type 1 (insulin-dependent) diabetic patients with background retinopathy and 12 Type 1 diabetic patients with proliferative retinopathy was compared with an age- and sex-matched control group. An analogue of prostaglandin H2, 11,9 epoxymethano-prostaglandin H2, which directly stimulates thromboxane receptors, and EP 092, which is a competitive thromboxane A2 receptor antagonist, were used to investigate changes at platelet thromboxane receptor level in these groups. The concentration of collagen (EC50) required to give 50% of maximum aggregation did not differ between the two diabetic groups and the control group. However, platelets from the proliferative retinopathy group were significantly more sensitive to the thromboxane mimetic (11,9 epoxymethano-prostaglandin H2) (p less than 0.005) than the background retinopathy and control groups. This change may be a factor in the development of proliferative retinopathy.

Behavior of intracellular glutathione during platelet thromboxane synthesis in diabetes

The time-dependent relationship between the levels of the reduced form of glutathione (GSH) and thromboxane A2 (TXA2) synthesis, as measured by the accumulation of TXB2, in platelets from human diabetic and control subjects was investigated during aggregation. In platelets from control subjects, the GSH level decreased to 21% of the initial level within 30 sec in response to arachidonic acid (1.65 mM) and rapidly recovered to 91% by 1 min. In platelets from diabetic subjects, the GSH level decreased to 3% of the initial level within 30 sec and recovered to only 41% by 1 min. During collagen (20 ug/ml) aggregation, platelets from control subjects had a 15 sec lag phase which was followed by a decrease in the GSH level to 21% of the initial level within 1 min and a recovery to 74% by 2 min. Platelets from diabetic subjects in response to collagen showed no lag phase and decreased to 10% of the initial level within 1 min which was followed by a recovery to 34% by 2 min. In all aggregations, the initial GSH level was significantly (p less than .001) lower in platelets from diabetic subjects and remained significantly (p less than .01) lower than GSH in platelets from control subjects throughout the aggregation. The amount of TXB2 formed by platelets from control subjects reached a maximum in response to arachidonic acid and collagen by 1 min and 2 min, respectively, whereas, the TXB2 continued to increase up to 4 min when platelets from diabetic subjects were aggregated. These data indicate that TXA2 synthesis occurs during the decrease in GSH and ceases when the GSH level recovers. The continued synthesis of TXA2 by platelets from diabetic subjects coincides with the gradual recovery of the GSH level.