Thromboxane biosynthesis and platelet function in type I diabetes mellitus

Non-Traditional Pathways for Platelet Pathophysiology in Diabetes: Implications for Future Therapeutic Targets

Cardiovascular complications remain the leading cause of morbidity and mortality in individuals with diabetes, driven by interlinked metabolic, inflammatory, and thrombotic changes. Hyperglycaemia, insulin resistance/deficiency, dyslipidaemia, and associated oxidative stress have been linked to abnormal platelet function leading to hyperactivity, and thus increasing vascular thrombotic risk. However, emerging evidence suggests platelets also contribute to low-grade inflammation and additionally possess the ability to interact with circulating immune cells, further driving vascular thrombo-inflammatory pathways. This narrative review highlights the role of platelets in inflammatory and immune processes beyond typical thrombotic effects and the impact these mechanisms have on cardiovascular disease in diabetes. We discuss pathways for platelet-induced inflammation and how platelet reprogramming in diabetes contributes to the high cardiovascular risk that characterises this population. Fully understanding the mechanistic pathways for platelet-induced vascular pathology will allow for the development of more effective management strategies that deal with the causes rather than the consequences of platelet function abnormalities in diabetes.

Understanding the Activation of Platelets in Diabetes and Its Modulation by Allyl Methyl Sulfide, an Active Metabolite of Garlic

BACKGROUND

Diabetes mellitus (DM) is a chronic metabolic disorder associated with higher risk of having cardiovascular disease. Platelets play a promising role in the pathogenesis of cardiovascular complications in diabetes. Since last several decades, garlic and its bioactive components are extensively studied in diabetes and its complications. Our aim was to explore the antiplatelet property of allyl methyl sulfide (AMS) focusing on ameliorating platelet activation in diabetes.

METHOD

We used streptozotocin- (STZ-) induced diabetic rats as model for type 1 diabetes. We have evaluated the effect of allyl methyl sulfide on platelet activation by administrating AMS to diabetic rats for 10 weeks. Flow cytometry-based analysis was used to evaluate the platelet activation, platelet aggregation, platelet macrophage interaction, and endogenous ROS generation in the platelets obtained from control, diabetes, and AMS- and aspirin-treated diabetic rats.

RESULTS

AMS treatment for 10 weeks effectively reduced the blood glucose levels in diabetic rats. Three weeks of AMS (50 mg/kg/day) treatment did not reduce the activation of platelets but a significant (p < 0.05) decrease was observed after 10 weeks of treatment. Oral administration of AMS significantly (p < 0.05) reduced the baseline and also reduced ADP-induced aggregation of platelets after 3 and 10 weeks of treatment. Furthermore, 10 weeks of AMS treatment in diabetic rats attenuated the endogenous ROS content (p < 0.05) of platelets and platelet macrophage interactions. The inhibition of platelet activation in diabetic rats after AMS treatment was comparable with aspirin treatment (30 mg/kg/day).

CONCLUSION

We observed an inhibitory effect of allyl methyl sulfide on platelet aggregation, platelet activation, platelet macrophage interaction, and increased ROS levels in type 1 diabetes. Our data suggests that AMS can be useful to control cardiovascular complication in diabetes via inhibition of platelet activation.

Platelet aggregation is not altered among men with diabetes mellitus

AIMS

Platelets are pivotal in arterial thrombosis, and platelet hyperresponsiveness may contribute to the increased incidence of cardiovascular events in diabetes mellitus. Consequently, we hypothesized that increased in vitro platelet aggregation responses exist in men with diabetes mellitus.

METHODS

The Danish Cardiovascular Screening Trial (DANCAVAS) is a community-based cardiovascular screening trial including men aged 65-74 years. Platelet aggregation was tested using 96-well light transmission aggregometry with thrombin receptor-activating peptide (TRAP), adenosine diphosphate, collagen type 1, arachidonic acid and protease-activated receptor-4 in three concentrations. Further, cardiovascular risk factors and coronary artery calcification (CAC), estimated by CT scans and ankle-brachial index, were obtained.

RESULTS

Included were 720 men aged 65-74 years, 110 with diabetes mellitus. Overall, there was no difference in platelet aggregation among men with versus without diabetes mellitus when adjusting for or excluding platelet inhibitor treatment and men with established cardiovascular disease (CVD). This was true for all agonists, e.g., 10 µM TRAP-induced platelet aggregation of median 69% (IQR 53-75) versus 70% (IQR 60-76) in men with versus without diabetes mellitus. Platelet aggregation did not correlate with HbA_1c or CAC. Men with diabetes mellitus displayed higher CAC, median 257 Agatston units (IQR 74-1141) versus median 111 Agatston units (IQR 6-420) in the remaining individuals, p < 0.0001.

CONCLUSIONS

Among outpatients with diabetes mellitus, but no CVD and no platelet inhibitor treatment, neither are platelets hyperresponsive in diabetes mellitus, nor is platelet aggregation associated with glycemic status or with the degree of coronary atherosclerosis.

TRIAL REGISTRATION

ISRCTN12157806.

Platelet Activation and Platelet-Leukocyte Aggregates in Type I Diabetes Mellitus

Hyperglycemia alone may not explain the increased risk of cardiovascular diseases (CVDs) in patients with type 1 diabetes (T1D) compared with type 2. This study emphases on the evaluation of some platelet activity markers in patients with T1D, with relevance to some metabolic disorders as hyperlipidemia and hyperglycemia. This study was performed on 35 patients with T1D and 20 healthy controls. All participants were subjected to full history taking, clinical examination and assay of glycated hemoglobin (HbA_1c), and lipid profile. The expression of CD62P and CD36 on platelets and the frequency of platelet–monocyte, and platelet–neutrophil aggregates were assessed by flow cytometry. Patients showed significantly higher expression of CD62P and CD36 than the control group. Platelets aggregates with monocytes were also higher among patients than the control group. Levels of CD36⁺ platelets, CD62P⁺ platelets, and platelet–monocyte aggregates revealed significant correlations with the levels of HbA_1c, total cholesterol, low-density lipoprotein, and triglycerides. Hyperlipidemia and hyperglycemia accompanying T1D have a stimulatory effect on platelet activation which probably makes those patients vulnerable to CVD than nondiabetics.

Association of mean platelet volume with incident type 2 diabetes mellitus risk: the Dongfeng-Tongji cohort study

BACKGROUND

Most of prior studies to demonstrate the association between mean platelet volume (MPV) and type 2 diabetes mellitus (T2DM) risk were cross-sectional design with inconsistent results. In the present prospective cohort study, we aimed to explore the relationship between MPV and incident T2DM risk among a middle-aged and older Chinese population.

METHODS

This prospective study included 14,009 individuals derived from the Dongfeng-Tongji cohort which was launched in 2008. A total of 997 incident T2DM patients were diagnosed during the mean 4.51 years of follow-up period. MPV levels were divided into quartiles. The adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) of incident T2DM was estimated by Cox proportional hazard models.

RESULTS

Compared with study participants with MPV < 7.49 fL, the HRs of T2DM incidence were 1.39 (95% CI 1.11-1.75), 1.14 (0.90-1.44), and 1.39 (95% CI 1.07-1.81) in study participants with 7.49 ≤ MPV < 8.43 fL, 8.43 fL ≤ MPV < 9.69 fL and MPV ≥ 9.69 fL, respectively. This positive association was more pronounced after exclusion of the newly diagnosed incident cases during the first 2 years follow-up. Further adjustment for baseline fasting blood glucose level (FBG) did not materially alter the positive association. The positive association was particularly evident among females, non-current smokers and study participants with FBG level less than 5.6 mmol/L at baseline.

CONCLUSION

Higher levels of MPV were independently associated with increased incident risk of T2DM in a middle-aged and older Chinese population.

Thromboxane biosynthesis and metabolism in relation to cardiovascular risk factors

Enhanced platelet biosynthesis of thromboxane A(2) is associated with several cardiovascular risk factors, as a consequence of a direct effect on platelet biochemistry and/or some form of endothelial dysfunction. Moreover, episodic increases in thromboxane biosynthesis occur in acute coronary and cerebral ischemic syndromes. Thromboxane-dependent platelet activation represents an important mechanism that amplifies the consequences of acute vascular lesions as well as those of longstanding metabolic or hemodynamic disturbances, and results in increased risk of vascular occlusive events.

Effects of the fixed-dose combination therapy with indapamide and valsartan on renal function in patients with Type 2 diabetes mellitus and arterial hypertension

Aim. To study the effects of the fixed-dose combination antihypertensive therapy (noliprel A forte, valsaforce, and indapamide) and the renal function dynamics in patients with Type 2 diabetes mellitus (DM-2) and arterial hypertension (AH). Material and methods. In total, 40 patients with DM-2 and AH were randomised into two groups: Group I received noliprel A forte, and Group II received valsaforce and indapamide for two months. The clinical effectiveness of the fixed-dose combination antihypertensive therapy was assessed by 24-hour blood pressure monitoring (BPM), blood biochemistry, and renal function parameters measured at baseline and 8 weeks after the start of the treatment. Results. The treatment was associated with a substantial reduction in BP levels, improved circadian BP profiles, and metabolic neutrality. The therapy with noliprel A forte resulted in markedly improved circadian BP profiles and renal function, as demonstrated by the microalbuminuria dynamics (Rehberg-Tareev test: by 11±0,56 ml/min; Cockgroft-Gault formula: by 12±0,36 ml/min; MDRD formula: by 10±0,16 ml/min/1,73 m2). Conclusion. In patients with DM-2 and AH, the therapy with noliprel A forte significantly improved renal function parameters.

Glucose and collagen regulate human platelet activity through aldose reductase induction of thromboxane

Diabetes mellitus is associated with platelet hyperactivity, which leads to increased morbidity and mortality from cardiovascular disease. This is coupled with enhanced levels of thromboxane (TX), an eicosanoid that facilitates platelet aggregation. Although intensely studied, the mechanism underlying the relationship among hyperglycemia, TX generation, and platelet hyperactivity remains unclear. We sought to identify key signaling components that connect high levels of glucose to TX generation and to examine their clinical relevance. In human platelets, aldose reductase synergistically modulated platelet response to both hyperglycemia and collagen exposure through a pathway involving ROS/PLCγ2/PKC/p38α MAPK. In clinical patients with platelet activation (deep vein thrombosis; saphenous vein graft occlusion after coronary bypass surgery), and particularly those with diabetes, urinary levels of a major enzymatic metabolite of TX (11-dehydro-TXB2 [TX-M]) were substantially increased. Elevated TX-M persisted in diabetic patients taking low-dose aspirin (acetylsalicylic acid, ASA), suggesting that such patients may have underlying endothelial damage, collagen exposure, and thrombovascular disease. Thus, our study has identified multiple potential signaling targets for designing combination chemotherapies that could inhibit the synergistic activation of platelets by hyperglycemia and collagen exposure.

Urinary biomarkers involved in type 2 diabetes: a review

Diabetes mellitus is one of the most challenging health concerns of the 21st century. With at least 30% of the diabetic population remaining undiagnosed, effective and early diagnosis is of critical concern. Development of a diagnostic test, more convenient and reliable than those currently used, would therefore be highly beneficial. Urine as a diagnostic medium allows for non-invasive detection of biomarkers, including some associated with type 2 diabetes and its complications. This review provides a synopsis of those urinary biomarkers that potentially may provide a basis for the development of improved diagnostic tests. Three main pathways for the sourcing of potential makers are identified: kidney damage, oxidative stress and low-grade inflammation including atherosclerosis/vascular damage. This review briefly presents each pathway and some of the most relevant urinary biomarkers that may be used to monitor the development or progression of diabetes and its complications. In particular, biomarkers of renal dysfunction such as transferrin, type IV collagen and N-acetyl-beta-D-glucosaminidase might prove to be more sensitive than urinary albumin, the current gold standard, in the detection of incipient nephropathy and risk assessment of cardiovascular disease. Inflammatory markers including orosomucoid, tumour necrosis factor-alpha, transforming growth factor-beta, vascular endothelial growth factor and monocyte chemoattractant protein-1, as well as oxidative stress markers such as 8-hydroxy-2'deoxyguanosine may also be useful biomarkers for diagnosis or monitoring of diabetic complications, particularly kidney disease. However, the sensitivity of these markers compared with albumin requires further investigation.

The relationship between glycemic control and platelet activity in type 2 diabetes mellitus

AIMS

Platelet activity and aggregation potential, which are essential components of thrombogenesis and atherosclerosis, can be conveniently estimated by measuring mean platelet volume (MPV) as part of whole blood count. It has been shown that MPV was significantly higher in diabetes mellitus (DM); however, the effect of glycemic control on MPV has not been studied. The aim of this study was to investigate the relationship among MPV, glycemic control, and micro- and macrovascular complications in type 2 DM.

METHODS

Seventy patients with type 2 DM and 40 age- and sex-matched healthy individuals were enrolled. Diabetic patients were grouped into those with glycated hemoglobin (HbA1c) levels <or=7% (Group A, n=35 patients) and those with HbA1c >7% (Group B, n=35 patients). Initially, both groups were compared with regard to MPV, HbA1c, serum lipid levels, coronary artery disease, retinopathy, neuropathy, and nephropathy. Thereafter, Group B was called to monthly visits to obtain improved control glycemic control, which was defined as achievement of HbA1c <or=7%. At the end of 3 months of follow-up, Group B was reevaluated.

RESULTS

MPV was significantly higher in patients with DM than in controls (8.7+/-0.8 fl vs. 8.2+/-0.7 fl, P=.002). In diabetic patients, there was a significant positive correlation between MPV and HbA1c levels (r=.39, P=.001) but not diabetic vascular complications. When we compared the two diabetic groups, Group B patients had significantly higher MPV than Group A (9.0+/-0.7 fl vs. 8.4+/-0.8 fl, P=.01). Thirty patients (86%) of Group B achieved improved glycemic control at the end of the 3 months. MPV of the patients with improved glycemic control were significantly decreased compared to baseline MPV (8.4+/-0.8 fl vs. 9.0+/-0.7 fl, P=.003).

CONCLUSIONS

Our results suggested a close relationship between poor glycemic control and increased platelet activity in patients with type 2 DM. Furthermore, platelet activity recovered through improved glycemic control, which may prevent the possible role of platelets in cardiovascular events in these patients.

Pathobiology and cell interactions of platelets in diabetes

Diabetes is a well-recognised risk factor for atherosclerotic cardiovascular disease and in fact most diabetic patients die from vascular complications. The Diabetes Control and Complications Trial (DCCT) and the U.K. Prospective Diabetes Study (UKPDS) indicate a consistent relationship between hyperglycaemia and the incidence of chronic vascular complications in patients with diabetes. Platelets are essential for haemostasis, and abnormalities of platelet function may cause vascular disease in diabetes. Diabetic patients have hyperreactive platelets with exaggerated adhesion, aggregation and thrombin generation. In summary, the entire coagulation cascade is dysfunctional in diabetes. This review provides a comprehensive overview of the physiological role of platelets in maintaining haemostasis and of the pathophysiological processes that contribute to platelet dysfunction in diabetes and associated cardiovascular diseases, with special emphasis on proteomic approaches and leukocyte-platelet cross-talk.

Enhanced P-selectin expression and increased soluble CD40 Ligand in patients with Type 1 diabetes mellitus and microangiopathy: evidence for platelet hyperactivity and chronic inflammation

AIMS/HYPOTHESIS

Platelet activation, endothelial dysfunction and inflammation may be involved in early stages of diabetic microangiopathy. We therefore investigated patients with Type 1 diabetes mellitus, without ( n=19) and with ( n=20) microangiopathy, matched for glycaemic control and duration of disease, and matched with healthy control subjects ( n=27).

METHODS

Platelet activation was measured as platelet P-selectin expression using whole blood flow cytometry and as soluble P-selectin by immunoassay. Von Willebrand factor antigen in plasma, serum soluble E-selectin, CD40 ligand (sCD40L) and C-reactive protein (CRP) served as markers for endothelial function and inflammation.

RESULTS

Thrombin-induced platelet P-selectin expression was enhanced, and soluble P-selectin and sCD40L concentrations were increased in patients with microangiopathy compared with the control subjects ( p<0.01 for both) and with patients without microangiopathy ( p<0.05 for P-selectin expression and sP-selectin), whereas all three parameters were similar in patients without microangiopathy and in the control subjects. CRP and soluble E-selectin were increased in patients with microangiopathy, compared with the control subjects ( p<0.01 and p<0.05), whereas von Willebrand factor did not differ between the groups.

CONCLUSIONS/INTERPRETATION

Microangiopathy in Type 1 diabetes is associated with platelet hyperactivity, endothelial dysfunction and low-grade inflammation, indicating an increased risk for cardiovascular disease.

Enhanced leukocyte-platelet cross-talk in Type 1 diabetes mellitus: relationship to microangiopathy

BACKGROUND

Platelets and leukocytes may influence each others' function, i.e. platelet-leukocyte cross-talk. Diabetes mellitus (DM) is associated with platelet and leukocyte dysfunction.

OBJECTIVE

To evaluate platelet-leukocyte cross-talk, and if this might contribute to platelet and leukocyte dysfunction and microangiopathy in DM patients.

PATIENTS AND METHODS

We evaluated platelet and leukocyte function, and cross-talk between these cells in Type 1 DM patients without (n = 19) and with (n = 20) microangiopathy, and healthy subjects (n = 27), using whole blood flow cytometry. Platelet-leukocyte cross-talk was studied in hirudinized whole blood incubated at 37 degrees C with stirring.

RESULTS

Basal single platelet P-selectin and leukocyte CD11b expression were similar in DM patients and healthy subjects, whilst circulating platelet-leukocyte aggregates and plasma elastase levels were elevated in DM patients. The thromboxane A2 analog U46619 (3 x 10(-7) m) induced more marked increases of platelet P-selectin expression and platelet-leukocyte aggregation in DM patients than in healthy subjects. The leukocyte-specific agonist N-formyl-methionyl-leucyl-phenylalanine (fMLP) (10(-7) m) induced more marked CD11b expression in DM patients with microangiopathy, compared with healthy subjects. Platelet-leukocyte cross-talk induced by U46619 (10(-6) m) showed no difference between DM patients and healthy subjects. fMLP (10(-6) m) evoked marked leukocyte activation, which subsequently caused mild platelet P-selectin expression. This leukocyte-platelet cross-talk was more pronounced in DM patients than in healthy subjects. Furthermore, enhanced leukocyte-platelet cross-talk was correlated to platelet hyperreactivity among DM patients with microangiopathy only.

CONCLUSIONS

Type 1 DM is associated with platelet and leukocyte hyperactivity, and enhanced leukocyte-platelet cross-talk, which may contribute to platelet hyperactivity and the microvascular complications seen in Type 1 DM.

Shear-induced platelet adhesion and aggregation on subendothelium are increased in diabetic patients

Increased platelet aggregation has been suggested to play a role in the accelerated atherosclerosis of diabetics. However the physiological relevance of the aggregation tests has been questioned. The purpose of this study was to determine platelet activation in diabetic patients, using a novel device--the cone and plate(let) analyzer--to measure shear-induced platelet adhesion and aggregation on extracellular matrix (ECM). Whole blood platelet adhesion and aggregation in patients with noninsulin-dependent diabetes mellitus (n=82) and in nondiabetic controls (n=71) were compared. Clinical and laboratory characteristics of the diabetic patients were analyzed for possible correlation with parameters of platelet activity. Patients with diabetes had a significantly increased platelet activation compared to nondiabetic subjects, demonstrated by an increased adhesion to the ECM (surface coverage, 23% [95% confidence interval, 22-25%] vs. 19% [95% confidence interval, 18-20%], respectively) and an increased average size of the ECM-bound aggregates (54 microm2 [95% confidence interval, 51-57 microm2] vs. 47 microm2 [95% confidence interval, 43-51 microm2], respectively). Platelet adhesion in the diabetic group was found to correlate with triglyceride levels (r=0.36) and hematocrit values (r=0.31) and inversely with high-density lipoprotein cholesterol levels (r=0.30). There were no correlation, however, between parameters of platelet reactivity and duration of diabetes, vascular complications and low-density lipoprotein levels. Our data demonstrate an increased platelet adhesion and aggregation in diabetic patients and suggest a modulatory role of diabetic dyslipidemia.

Discordant effects on eicosanoids and fibrin degradation products in two murine models of antiphospholipid antibody

Two murine models of lupus were employed to challenge an hypothesized mechanism by which antiphospholipid antibodies (APLA) might promote thrombosis: altering prostacyclin (PGI2) and thromboxane (TX) production. PGI2 levels in mouse blood and the ex vivo release of PGI2 and TX from mouse kidney were measured. Since APLA have been reported to alter synthesis or activation of several molecules mediating fibrinolysis, murine plasma levels of the fibrin degradation product, D-dimer were also determined. Two murine strains, one prone to spontaneous "lupus-like" illness (MRL-lpr) and related strain (MRL-(+2)), were compared. The assays confirm that MRL-lpr mice have increased anticardiolipin antibody (ACA) and two-fold increased release of TX from renal tissues compared to MRL-(+2) mice. However, these mice have low levels of plasma D-dimer. NIH Swiss mice injected with IgG (containing APLA) from thrombosis-prone lupus patients had high blood ACA titers and D-dimer levels, but both ACA and D-dimer were low or non-detectable in Swiss mice injected with saline or normal IgG. Unlike mice with spontaneous lupus-like illness, healthy mice injected with APLA did not differ from controls with respect to plasma or tissue PGI2 or TX levels. The two murine models of lupus differ, because an altered PGI2-TX ratio is a finding in the chronic murine lupus strain MRL-lpr, but is not seen when APLA are injected into normal mice. It is unlikely that APLA alone has a direct effect on cellular production of eicosanoids in vivo.

Effects of isradipine sustained release on platelet function and fibrinolysis in essential hypertensives with or without other risk factors

The aim of this study was to assess the chronic effects of a highly selective dihydropiridine calcium channel blocker, israpidine, in its sustained release form (I-SRO), on platelet functions and fibrinolytic parameters in subjects with essential hypertension (EH) combined or not with other well-known cardiovascular risk factors, such as cigarette smoking (EH+S) and type II diabetes mellitus (EH+DM). Thirty-six patients with essential hypertension with sitting diastolic blood pressures of 96-104 mmHg without (EH, n = 12) or with other risk factors (EH+S, n = 12, EH+DM, n = 12) were enrolled. After a 4-week, single-blind, placebo run-in period, the subjects received I-SRO 5 mg once daily for 18 weeks. After both placebo and 6 and 18 weeks of I-SRO treatment, the following parameters were measured: sitting blood pressure by mercury sphygmomanometer; platelet aggregation, plasma beta-thromboglobulin (BTG), platelet factor-4 (PF4), and plasminogen activator inhibitor 1 (PAI-1) by means of ELISA methods; and euglobulin lysis time before (ELT) and after standardized (10 min) venous occlusion (ELT-VO). In the group of patients as a whole compared with placebo, I-SRO significantly reduced SBP/DBP platelet aggregation, BTG, PF4, ELT, and ELT-VO. Significant reductions in these parameters were also observed in each group. In addition to the antihypertensive effect, I-SRO chronic treatment may favorably affect the platelet function and fibrinolytic system in essential hypertension with or without other cardiovascular risk factors.

Oxidative stress and platelet activation in diabetes mellitus

The role of oxidative stress and platelet activation in the development and evolution of diabetic vascular complications is unclear. They can both be the consequence of established vascular disease or a contributing factor to the evolution of atherosclerosis. Free radical generation may both lead to or result from platelet activation, suggesting that oxidative stress and platelet activation may be closely interrelated. Controversial results may partly reflect methodological constraints. Novel techniques for the measurement of in vivo indices of oxidant injury have been developed and will be used in conjunction with pharmacological probes to establish whether oxidative stress is enhanced in diabetes and whether this preceeds the onset of micro and macrovascular disease.

Development of an enzyme-linked immunosorbent assay for 2,3-dinor-6-keto-prostaglandin F1 alpha in urine using a monoclonal antibody

OBJECTIVES

To develop and validate an enzyme-linked immunosorbent assay (ELISA) for measurement of urinary 2,3-dinor-6-keto-prostaglandin F1 alpha (2,3D6KPGF1 alpha) using a monoclonal antibody and a horseradish peroxidase-linked antigen.

DESIGN AND METHODS

Assay validation included optimization of the standard curve, antibody cross-reactivity, accuracy and imprecision studies together with preliminary measurement of clinical samples.

RESULTS

Optimal conditions of the standard curve (0.078-10.0 micrograms/L) used 2 mg/L of antibody and 3 micrograms/L of peroxidase conjugate in each well, at pH 7.2. The coefficient of variation of various concentrations of the standard curve averaged 6.8%. Antibody cross-reactivity was < 0.01% for related prostanoids. Recovery of known amounts (0.1-5.0 micrograms/L) of 2,3D6KPGF1 alpha added to an urinary sample was 101.2 +/- 6.3%. Imprecision studies with non-pregnant (0.24 microgram/L) and pregnant (2.5 micrograms/L) samples displayed an intraassay variability of 8.9 and 9.9%, and an interassay variability of 9.6 and 10.0%, respectively. Urinary measurements in the non-pregnant and pregnant states were similar to those previously reported. An apparent decreased concentration was observed early in pregnancy in future preeclampsia.

CONCLUSION

With similar precision and validity, our assay method is time- and cost-saving. Preliminary urinary measurements show that this analyte may be of interest as an early marker for preeclampsia.

Platelet adhesion to collagen under flow conditions in diabetes mellitus

Since vascular complications in diabetes mellitus are attributed in part to blood platelets, our study tested the hypothesis that adhesion of platelets to collagen is enhanced in diabetic subjects. Platelet adhesion kinetics to type I collagen in the presence of plasma were evaluated by a new continuous-flow, micro-adhesion assay combined with resistive-particle counting to detect the loss of single platelets between 0.3 and 2.3 sec. Adhesion was also studied in a magnesium-containing Krebs-Ringer buffer to help assess whether the platelets themselves might be abnormal. We did not observe any differences in adhesion kinetics to collagen between the insulin-dependent (type I), the non-insulin dependent (type II) diabetics and the control subjects for platelets suspended in plasma or in washed platelets (p > 0.05). These findings suggest that platelet adhesiveness to type I collagen is not enhanced in diabetic subjects and is unlikely to contribute to the development of vascular complications.

Platelet volume and urinary prostanoid metabolites in non-insulin-dependent diabetes mellitus

To evaluate platelet activity in patients with non-insulin-dependent diabetes mellitus (NIDDM), we measured the mean platelet volume (MPV) and 24-hour urinary excretion of 11-dehydro-thromboxane B2 (11-dTXB2) and 6-keto-prostaglandin F1 alpha (6-kPGF1 alpha), stable metabolites of thromboxane A2 and prostacyclin, respectively. The MPV of the 103 subjects in the NIDDM group were 10.72 +/- 0.82 fl for males and 10.52 +/- 1.01 fl for females (mean +/- SD), significantly higher than those of normal controls (9.95 +/- 0.75 fl for males and 9.84 +/- 0.72 fl for females). The MPV of patients with NIDDM showed positive correlations with fasting plasma glucose level and HbA1c (r = 0.234, P < 0.05; r = 0.267, P < 0.01, respectively). The urinary excretion of 11-dTXB2 was greater in the NIDDM group (7.58 +/- 4.42 micrograms/day for males and 5.65 +/- 2.38 micrograms/day for females) than in the normal controls (4.61 +/- 2.31 and 3.83 +/- 1.60, respectively), suggesting that the synthesis of thromboxane A2 by platelets may be accelerated in vivo in patients with NIDDM. The urinary 6-kPGF1 alpha was not different between the NIDDM group and normal controls among the males, but was greater in the NIDDM group among the females. As MPV showed a positive correlation (r = 0.364, P < 0.05) with urinary excretion of 11-dTXB2, MPV may be related to platelet activity. These findings suggest that the platelets of patients with NIDDM may be in a hyperactive state.

Systemic hypertension and the renin-angiotensin system in diabetic vascular complications

Antihypertensive treatment in the diabetic patient is a critical issue because hypertension has an impact on all of the vascular complications of diabetes, including nephropathy, retinopathy, atherosclerosis, and left ventricular hypertrophy. These complications are a consequence of altered endothelial-vascular smooth muscle interrelations that ultimately enhance vasoconstriction and alter the remodeling processes in the vascular wall. Several observations suggest that the renin-angiotensin system (RAS) may be an important contributor to these processes in diabetes mellitus. In both animal and human studies, angiotensin-converting enzyme (ACE) inhibitors have been demonstrated to slow the progression of glomerulosclerosis, prevent abnormal remodeling processes in the heart following injury, and slow the progression of atherosclerosis. In particular, ACE inhibitors appear to protect the kidney more than would be expected from simply the lowering of blood pressure and decreasing of intraglomerular pressure, possibly because angiotensin II has both hemodynamic and direct effects on the glomerulus. Paradoxically, however, the activity of the circulating RAS is low in diabetic patients. Part of these seemingly inconsistent observations may be due to (1) potential activity of tissue RASs, (2) increased sensitivity to angiotensin II in diabetes, or (3) an effect of ACE inhibition on other systems in addition to the RAS. Investigation of these mechanisms will be important in determining the therapeutic role of inhibition of the RAS in diabetes mellitus.

Coagulation activation in diabetes mellitus: the role of hyperglycaemia and therapeutic prospects

Numerous studies have shown that coagulation abnormalities occur in the course of diabetes mellitus, resulting in a state of thrombophilia. These observations are supported by epidemiological studies which demonstrate that thromboembolic events are more likely to occur in diabetic patients. The coagulation abnormalities observed in diabetic patients seem to be caused by the hyperglycaemia, which also constitutes the distinguishing feature of this disease. These data are also supported by in vitro studies which demonstrate how glucose can directly determine alterations in the coagulation system. The abnormalities observed involve all stages of coagulation, affecting both thrombus formation and its inhibition, fibrinolysis, platelet and endothelial function. The final result is an imbalance between thrombus formation and dissolution, favouring the former. Hyperglycaemia probably determines the onset of these abnormalities through three mechanisms which are, respectively, non-enzymatic glycation, the development of increased oxidative stress and a decrease in the levels of heparan sulphate. The first seems to affect the functionality of key molecules of coagulation in a negative sense. Oxidative stress constitutes an important pro-thrombotic stimulus, while the decrease in heparan sulphate determines a reduction in antithrombotic defenses. Good metabolic control could play a key role in controlling the coagulation irregularities in diabetes. However, considering the difficulties in achieving such an objective, it is possible that the use of drugs may represent a valid alternative. In fact, several drugs exist which are of potential interest. It is, however, necessary to perform long-term studies which demonstrate unequivocably that by controlling the coagulation abnormalities in diabetic patients, prolongation of life is possible.

Comparison of platelet aggregability in Japanese type 2 diabetic patients with and without microalbuminuria

Microalbuminuria is associated with higher cardiovascular morbidity and mortality in Type 2 (non-insulin-dependent) diabetic patients. This study was designed to assess whether Type 2 diabetic patients with microalbuminuria (urinary albumin excretion rate (AER) 20-200 microgram min-1) is associated with alterations in platelet aggregability as compared with those with normal urinary albumin excretion (AER < 20 microgram min-1). Platelet aggregability was compared between 21 Japanese Type 2 diabetic patients with microalbuminuria and 21 individually pair-matched (for age, sex, body mass index, treatment, and HbA1c level) patients with normoalbuminuria. The in vitro platelet aggregation induced by 1.0 and 3.0 mumol l-1 ADP and 0.5 and 1.0 mg l-1 collagen was measured using platelet-rich plasma. No significant differences were observed between the two groups in the values for maximum percent platelet aggregation, percent aggregation at 3 min, and aggregation velocities after adding ADP or collagen. Microalbuminuric patients had significantly higher mean values for systolic (p < 0.004) and diastolic (p < 0.02) blood pressures and plasma fibrinogen level (p < 0.03) as compared with the respective mean values in normoalbuminuric patients. The results suggest that Japanese microalbuminuric Type 2 diabetic patients do not differ in the degree of platelet aggregability as compared with normoalbuminuric patients, despite an increase in certain other coronary risk factors.

Cerebral circulation during diabetes mellitus

Diabetes mellitus is characterized by hyperglycemia, a decrease in circulating insulin and the development of macro- and microvascular pathology. Hyperglycemia appears to be a primary determinant for the structural, biochemical and functional changes that occur in large and small blood vessels during diabetes mellitus. While much research has focused on the effects of diabetes mellitus on the peripheral circulation, it is clear that diabetes mellitus also has profound effects on the cerebral circulation. Thus, the focus of this review is to discuss morphological and functional alterations in the cerebral circulation during diabetes mellitus.

Increased thromboxane biosynthesis in patients with acute cerebral ischemia

BACKGROUND AND PURPOSE

Clinical and experimental studies suggest that platelets have a major role in the pathogenesis of cerebral ischemia. However, ex vivo both platelet aggregation studies and measurements of platelet-derived products in patients with cerebral ischemia have shown inconsistent results. The present study was designed to resolve this inconsistency.

METHODS

We have measured the urinary excretion of a thromboxane metabolite, 11-dehydro-thromboxane B2, by a previously validated radioimmunoassay technique in 51 patients with acute cerebral ischemia who had experienced either a transient ischemic attack (14 patients) or an ischemic stroke (37 patients) and in 20 control patients with nonvascular neurological disorders. The median time between the onset of symptoms and urine sampling was 24 hours (range, from 2 hours to 8 days).

RESULTS

The excretion rate of immunoreactive 11-dehydro-thromboxane B2 ranged between 39 and 478 pmol/mmol creatinine in patients with a transient ischemic attack and between 23 and 5,916 pmol/mmol creatinine in stroke patients, with 29% (p = 0.18) and 51% (p = 0.004) of the urine samples, respectively, exceeding the upper limit of the control samples (251 pmol/mmol creatinine [mean +/- 2 SD]) (p = 0.01). In stroke patients, metabolite excretion was not related to the type (cortical or "lacunar") or site of cerebral infarction. Low-dose aspirin (50 mg per day for 7 days) reduced the urinary excretion by approximately 85% in 11 consecutive stroke patients.

CONCLUSIONS

We conclude that 1) episodes of enhanced thromboxane biosynthesis are detected infrequently in patients with a transient ischemic attack, 2) aspirin-suppressible episodes of increased thromboxane formation can be detected during the early phase of acute ischemic stroke, and 3) this finding may provide a rationale for testing the efficacy and safety of this drug in this setting.

High-performance liquid chromatographic assay of platelet-produced thromboxane B2

A method for the routine determination of platelet-produced thromboxane B2 (TXB2) from human serum is presented. To induce the secretion of thromboxane A2 from the platelets, blood is kept at 37 degrees C for 30 min before serum is separated. Serum is prepurified through small reversed-phase columns and TXB2 is analysed by reversed-phase high-performance liquid chromatography. A column-switching technique is used to remove the interfering compounds present in serum. The detection limit with standard solution is 30 ng per injection. The method was applied to the measurement of platelet-produced TXB2 serum from 1040 men. The mean TXB2 was 247 +/- 134 ng/ml in the serum of men who had not used prostaglandin inhibitors, and 208 +/- 123 ng/ml in the serum of men who had used a prostaglandin inhibitor during a two-week period before blood sampling.

The role of endothelium in the pathogenesis of diabetic microangiopathy

Damage caused to the vessel wall by diverse mechanisms may lead to diabetic microangiopathy. Consequently, research work is more and more focusing on the pathophysiology of vascular cells, with particular emphasis on endothelium. This paper reviews the present knowledge on the alterations of small vessel endothelium in diabetes. The most important risk factors for diabetic microangiopathy are the duration of disease and the degree of metabolic control maintained throughout the years. However, genetic factors may also contribute. These are examined first, followed by the presumed roles played by increased protein glycation and the production of Advanced Glycosylation End Products, the "polyol pathway" and free radical generation. Endothelium is a widespread, extremely active organ which regulates complex physiologic functions and its structure and function are discussed in the second section of this review. The third part deals with how diabetes can affect endothelium and describes observations on endothelial metabolism in vitro as well as morphologic and functional alterations in the patients. Unfortunately, the mechanisms leading to progressive degeneration of the microcirculation and organ damage in diabetic patients remain largely unaccounted for.

Thromboxane biosynthesis and metabolism in relation to cardiovascular risk factors

Enhanced platelet biosynthesis of thromboxane A2 is associated with several cardiovascular risk factors, as a consequence of a direct effect on platelet biochemistry and/or some form of endothelial dysfunction. Moreover, episodic increases in thromboxane biosynthesis occur in acute coronary and cerebral ischemic syndromes. Thromboxane-dependent platelet activation represents an important mechanism that amplifies the consequences of acute vascular lesions as well as those of long-standing metabolic or hemodynamic disturbances, and results in increased risk of vascular occlusive events.

Contribution of platelet thromboxane production to enhanced urinary excretion and glomerular production of thromboxane and to the pathogenesis of albuminuria in the streptozotocin-diabetic rat

Previous studies have demonstrated that urinary thromboxane B2 (TXB2) excretion (UTXB2) and glomerular production of TXB2 are enhanced in experimental diabetes and that selective inhibitors of TX synthesis prevent or delay the development of albuminuria. The present study was conducted to examine the contribution of platelet TXB2 production to the enhancement of UTXB2 and glomerular TXB2 production and to the pathogenesis of albuminuria in the partially insulin-treated moderately hyperglycemic (blood glucose, 200 to 400 mg/dL) streptozotocin-diabetic rat (SDR). Treatment of control rats or of SDR with diabetes of 5 months' duration with antiplatelet serum for 4 consecutive days reduced circulating platelet counts and serum TXB2 generation, an index of platelet cyclooxygenase activity, by 80% or greater, but reduced UTXB2 excretion by only 30%. UTXB2 and glomerular production of TXB2 of thrombocytopenic SDR remained markedly elevated compared with corresponding values from age-matched thrombocytopenic or platelet-replete, nondiabetic controls. Similarly, treatment of rats for 180 days with a dose of aspirin (ASA), which selectively inhibited platelet versus renal cyclooxygenase activity, reduced UTXB2 of both SDR and controls by 25% to 35%. The absolute reductions in UTXB2 induced by either ASA or thrombocytopenia in SDR were significantly greater than the absolute decrements in corresponding controls, suggesting that increased platelet TXB2 production in SDR may contribute to the enhanced UTXB2. However, as in the thrombocytopenic SDR, UTXB2 and glomerular production of TXB2 of SDR treated with ASA remained clearly above corresponding control values. Moreover, chronic ASA treatment failed to prevent the development of albuminuria in SDR.(ABSTRACT TRUNCATED AT 250 WORDS)

Human prostacyclin platelet receptors in diabetes mellitus

Conflicting data have been reported about the impaired sensitivity to the inhibitory effect of prostacyclin (PGI2) in platelets from patients with diabetes. In the present paper we investigated binding of and sensitivity to PGI2 of platelets from insulin dependent (IDDM) (n = 9), non insulin dependent (NIDDM) (n = 8) diabetics and two groups of ten healthy subjects of equivalent age in relation to platelet lipidic content. Platelet sensitivity to PGI2 (PGI2 IC50) was found not significantly changed in diabetics as compared to controls; similarly, no significant differences of the number of high affinity receptors for PGI2 in platelets from patients with IDDM and NIDDM were observed. Platelet sensitivity to PGI2 and PGI2 receptors were found to be significantly related to platelet cholesterol content (r = 0.89, p less than 0.001 and r = -0.80, p less than 0.001 respectively). In conclusion platelet PGI2 receptor changes are not detectable in diabetics in good metabolic control, but could take place when platelet lipid composition is altered.

Diabetes and arterial disease

Macroangiopathy (or atherosclerosis) is a common and chronic complication in diabetic patients. Unlike other diabetic complications, atherosclerosis is not unique to diabetes, confounding analysis of its relationship with the diabetic condition. Evidence of an independent role for diabetes in the development of atherosclerosis remains equivocal. The main determinant of macrovascular disease may be an interaction between diabetes and the aging process. Similarly the question of a relationship between macrovascular disease and good metabolic control remains unanswered. Macroangiopathy in diabetic populations seems to be related to similar predictors and pathological mechanisms operating in the general population. However, after analysis of these common risk factors for macroangiopathy, a diabetes-specific risk remains. Low-density lipoprotein metabolism is markedly disturbed in poorly controlled diabetic patients. This is manifest as a concert of actions which increase formation of foam cells and fatty streaks. The next step in the atherosclerotic process, the formation of fibrous plaques, may be associated with the platelet hyperactivity seen in diabetes. This may promote overshooting of repair mechanisms at the vessel wall. Release of a specific diabetic serum growth factor from the platelets may be responsible for the later stages of fibrous plaque development and the increased atherosclerotic risk in diabetes.

Platelet aggregation and disaggregation in the streptozotocin induced diabetic rat: the effect of sympathetic inhibition

Alterations in platelet function have been observed in a number of diabetic states. Increased responsiveness to platelet-aggregating agents in diabetes associated with increased catecholamine production and/or turnover suggested that heightened sympathetic activity may contribute to this increased platelet aggregation response. To investigate this possibility, we made male Wistar-Furth rats diabetic with streptozotocin and treated them either with adrenergic inhibitors (clonidine, yohimbine, reserpine) or saline. After 2 weeks, arterial blood samples were collected in 3.8% sodium citrate or acid citrate dextrose (ACD). Platelet-rich plasma (PRP) was prepared, and platelet aggregation studies were conducted directly or conducted on washed platelets prepared from PRP collected with ACD. Platelet aggregation in response to ADP by PRP was reduced while the rate of disaggregation was increased in platelets from diabetic animals when compared to controls. However, platelet aggregation in response to ADP in washed platelets was increased in diabetic animals when compared to controls. Clonidine, reserpine and yohimbine significantly decreased the diabetes-induced increase in maximum aggregation. Thrombin-induced aggregation was not altered by diabetes or any of the treatments. The platelet size was increased in the diabetic animals and was decreased toward controls by clonidine, reserpine and yohimbine treatment. These studies suggest that diabetes increases platelet aggregation response in diabetic rats, and that blockage or suppression of adrenergic activity reverses or attenuates the diabetes-induced hypersensitivity to ADP.

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)

Platelet and plasma vasoactive amines in type 1 (insulin-dependent) diabetes mellitus with and without vascular disease

Platelet and plasma vasoactive amine concentrations were measured in healthy controls and in type 1 (insulin-dependent) diabetic patients with or without vascular disease. Platelet concentrations of serotonin and noradrenaline were similar in all groups and were unrelated to age or gender, or to duration of diabetes, blood pressure, glycaemia or renal function in the diabetic subjects. Plasma concentrations of serotonin in the diabetic groups were comparable (118 +/- 16 (mean +/- SEM) and 127 +/- 21 pmol/mL), and were significantly higher in comparison to the healthy controls (66 +/- 12 pmol/mL, P = 0.002).

Plasma 6-keto-PGF1 alpha, thromboxane B2 and PGE2 during diabetic ketoacidosis

In 10 patients admitted to hospital with diabetic ketoacidosis plasma prostanoids 6-keto-PGF alpha, thromboxane B2 and PGE2 were studied before treatment and following recovery. During ketoacidosis the median plasma 6-keto-PGF1 alpha and PGE2 were significantly increased compared to those of a normal reference group: 5.2 pg/ml and 3.9 pg/ml versus 1.7 pg/ml and 0.4 pg/ml (p less than 0.01 and p less than 0.05). In response to therapy both prostanoids decreased significantly towards a normal level, 6-keto-PGF1 alpha: 0.5 pg/ml p less than 0.01 and PGE2: 0.08 p less than 0.05 respectively. The changes in plasma 6-keto-PGF1 alpha were negatively correlated to changes in pH, rho: -0.7788 p = 0.0135, whereas the changes in PGE2 were positively correlated to serum creatinine at admittance, rho: 0.6976, p = 0.0368 and to the amount of intravenous fluid and insulin used during treatment, rho: 0.7500 p = 0.0126 and rho: 0.8424, p = 0.0023 respectively. Plasma thromboxane B2 concentrations were not elevated and did not change after treatment of the ketoacidosis.