Platelet adhesiveness and aggregation in relation to diabetic retinopathy

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.

Phenotypes and biomarkers of diabetic retinopathy

Diabetic retinopathy (DR) remains a major cause of blindness as the prevalence of diabetes is expected to approximately double globally between 2000 and 2030. DR progresses over time at different rates in different individuals with only a limited number developing significant vision loss due to the two major vision-threatening complications, clinically significant macular edema and proliferative retinopathy. Good metabolic control is important to prevent and delay progression, but whereas some patients escape vision loss even with poor control, others develop vision loss despite good metabolic control. Our research group has been able to identify three different DR phenotypes characterized by different dominant retinal alterations and different risks of progression to vision-threatening complications. Microaneurysm turnover has been validated as a prognostic biomarker of development of clinically significant macular edema, whereas subclinical macular edema identified by OCT and mfERG appear to be also good candidates as organ-specific biomarkers of DR. Hemoglobin A1c remains the only confirmed systemic prognostic biomarker of DR progression. The availability of biomarkers of DR progression and the identification of different phenotypes of DR with different risks for development of vision-threatening complications offers new perspectives for understanding DR and for its personalized management.

Platelet aggregation in diabetes mellitus

Thirty-eight patients with juvenile diabetes mellitus, aged 21-77, were tested for platelet aggregation in vitro. Vascular complications were found in 20 patients with diabetic retinopathy in 16 of these. All patients received their usual dose of insulin in the morning on the day of the examinations, where were carried out shortly before a 2--3 hours after lunch. Ninety normal controls were tested at the same time of day. The aggregation was estimated turbidometrically and defined by the threshold concentration of adenosine diphosphate or adrenaline that produced a secondary aggregation with a light transmission not less than 80% of that given by the platelet-poor plasma. No significant differences could be demonstrated in platelet aggregation between the normal controls and the patients with diabetes mellitus or any subgroup of these. No correlation was found between the threshold concentrations and the plasma levels of glucose or beta-hydroxybutyric acid.

Elevated concentrations of soluble adhesion molecules and large platelets in diabetic patients: are they markers of vascular disease and diabetic nephropathy?

P-selectin, E-selectin, and mean platelet volume are markers associated with platelet reactivity that have been demonstrated to be increased in diabetes. We were particularly interested to see if there was a difference in mean platelet volume and selectins between diabetics and nondiabetics, and in diabetics with and without nephropathy, and whether there was a correlation between mean platelet volume and selectins. One hundred and fourteen diabetic patients and 31 healthy controls were investigated. Plasma levels of P-selectin and E-selectin were higher in the diabetic group than in controls (P = .001 and P = .007, respectively) and in diabetic patients with proteinuria than in patients without proteinuria (P = .002 and P = .004, respectively). Protein excretion was lower in patients with low mean platelet volume values (P = .004). In conclusion, elevated platelet volume and high selectin values may play a role in the development of vasculopathies and complications in diabetes mellitus. Further studies are needed to prove these results.

Mean platelet volume in Type 2 diabetic patients

BACKGROUND

Altered platelet morphology and function have been reported in patients with diabetes mellitus. They are likely to be associated with the pathological processes and increased risk of vascular disease seen in these patients. We aimed to determine the mean platelet volume (MPV) in diabetics compared to nondiabetics, to see if there is a difference in MPV between diabetics with and without macro- and microvascular complications, and to determine the correlation between MPV and fasting blood glucose, glycosylated hemoglobin (HbA(1)c), patient age, and duration of diabetes, respectively.

METHODS

We measured MPV in 145 consecutive Type 2 diabetic patients and 100 nondiabetic control subjects without known coronary artery disease who had complete blood count on venous blood sample taken into tripotassium EDTA, using a Roche Minos cell counter and automatic blood counter (CELL-DYN 3500). The blood glucose level was measured by glucose oxidase method and HbA1c by calorimetrical method in the autoanalyser. Statistical evaluation was performed by SPSS for Windows statistics programme using multivariate logistical regression analysis, Student's t, and Pearson correlation tests.

RESULTS

MPV was significantly higher and the mean platelet counts were significantly lower in diabetics compared to age- and sex-matched nondiabetic healthy controls [10.62+/-1.71 fl vs. 9.15+/-0.86 fl (P=.00), 260.38+/-68.65 x 10(9)/l vs. 292.33+/-79.19 x 10(9)/l (P=.001)], respectively.

CONCLUSIONS

Our results show significantly higher MPV in diabetic patients than in the nondiabetic controls. This suggests that platelets may play a role in the micro- and macrovascular complications of diabetic patients.

Diabetic patients without vascular complications display enhanced basal platelet activation and decreased antioxidant status

Vascular complications are the leading causes of morbidity and mortality in diabetic patients. The contribution of platelets to thromboembolic complications is well documented, but their involvement in the initiation of the atherosclerotic process is of rising interest. Thus, the aim of the present study was to evaluate basal arachidonic acid metabolism in relation to the redox status of platelets in both type 1 and type 2 diabetic patients, in the absence of vascular complications, as compared with respective control subjects. For the first time, we show that basal thromboxane B(2), the stable catabolite of thromboxane A(2), significantly increased in resting platelets from both type 1 and type 2 diabetic patients (58 and 88%, respectively), whereas platelet malondialdehyde level was only higher in platelets from type 2 diabetic subjects (67%). On the other hand, both vitamin E levels and cytosolic glutathione peroxidase activities were significantly lower in platelets from diabetic patients as compared with respective control subjects. We conclude that platelet hyperactivation was detectable in well-controlled diabetic patients without complications. This abnormality was associated with increased oxidative stress and impaired antioxidant defense in particular in type 2 diabetic patients. These alterations contribute to the increased risk for occurrence of vascular diseases in such patients.

Platelets accumulate in the diabetic retinal vasculature following endothelial death and suppress blood-retinal barrier breakdown

Platelet microthrombi are present in the diabetic retinal vasculature of humans and rodents; however, the mechanisms and consequences of their presence have not been defined. The current study demonstrates that platelet containing microthrombi accumulate in the retinal vasculature of the rat within 2 weeks of experimental diabetes, a timepoint at which leukocyte-mediated endothelial cell injury and death are known to occur. Platelet accumulation increased with the duration of diabetes, and crossover experiments revealed that maximal platelet accumulation required both diabetic platelets and a diabetic endothelium. Platelet accumulation also coincided with the expression of Fas and FasL in the diabetic retina. When endothelial cell apoptosis was inhibited with an anti-FasL neutralizing antibody, platelet accumulation was effectively suppressed. When platelets were depleted from the systemic circulation with an anti-platelet antibody, blood-retinal barrier breakdown worsened in the diabetic animals. These findings suggest that platelet accumulation in the diabetic retinal vasculature is secondary to endothelial cell death and serves, in part, to suppress blood-retinal barrier breakdown.

Regulation of taurine transporter expression by NO in cultured human retinal pigment epithelial cells

Taurine is actively transported at the retinal pigment epithelial (RPE) apical membrane in an Na(+)- and Cl(-)-dependent manner. Diabetes may alter the function of the taurine transporter. Because nitric oxide (NO) is a molecule implicated in the pathogenesis of diabetes, we asked whether NO would alter the activity of the taurine transporter in cultured ARPE-19 cells. The activity of the transporter was stimulated in the presence of the NO donor 3-morpholinosydnonimine. The stimulatory effects of 3-morpholinosydnonimine were not observed during the initial 16-h treatment; however, stimulation of taurine uptake was elevated dramatically above control values with 20- and 24-h treatments. Kinetic analysis revealed that the stimulation was associated with an increase in the maximal velocity of the transporter with no significant change in the substrate affinity. The NO-induced increase in taurine uptake was inhibited by actinomycin D and cycloheximide. RT-PCR analysis and nuclear run-on assays provided evidence for upregulation of the transporter gene. This study provides the first evidence of an increase in taurine transporter gene expression in human RPE cells cultured under conditions of elevated levels of NO.

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.

Platelet expression of tumour necrosis factor-alpha (TNF-alpha), TNF receptors and intercellular adhesion molecule-1 (ICAM-1) in patients with proliferative diabetic retinopathy

Microvascular complications of insulin-dependent diabetes mellitus (IDDM) have been strongly associated with platelet abnormalities, whilst TNF-alpha has been implicated in the pathogenesis of this condition. However, at present it is not clear whether human circulating platelets express TNF-alpha or TNF receptors (TNF-R) or whether impaired expression of these molecules and of the TNF-reactive adhesion molecule ICAM-1 may be associated with platelet abnormalities in patients with IDDM. On this basis we investigated the platelet expression of these molecules in patients with IDDM complicated or uncomplicated by proliferative diabetic retinopathy (PDR) and in healthy subjects. We observed that the proportion of platelets staining for TNF-alpha was significantly higher in IDDM patients with active PDR than in patients without microvascular complications (P = 0.0078), quiescent PDR (P = 0.003) or healthy subjects (P = 0.0013). Patients with active PDR also showed a higher proportion of platelets expressing TNF-RI (P = 0. 0052) and TNF-RII (P = 0.015) than healthy controls or patients with quiescent PDR (P = 0.009 and 0.0006, respectively). In addition, the percentage of ICAM-1+ platelets was significantly higher in patients with active PDR than in patients with quiescent PDR (P = 0.0065) or normal subjects (P = 0.013). There was a direct correlation between platelet expression of TNF-alpha and that of TNF-R in PDR patients, indicating that platelet staining for TNF-alpha may be due to binding of this cytokine to its receptors. The results suggest that increased platelet expression of TNF-alpha, TNF-R and ICAM-1 in IDDM patients may constitute important markers of thrombocyte abnormalities during the development of microvascular complications of diabetes mellitus.

Constrictor responses of resistance arterioles during diabetes mellitus

While diabetes mellitus appears to alter nitric oxide synthase-dependent vasodilatation, the effect of diabetes on constrictor responses of resistance arterioles is not clear. Our goal was to examine the effect of diabetes on constrictor responses of cheek pouch arterioles. In vivo diameter of arterioles ( approximately 50 microm) was measured in response to norepinephrine, the thromboxane analogue (U-46619) and endothelin-1 in nondiabetic and diabetic hamsters (4-6 weeks post streptozotocin). Norepinephrine (1.0 and 10 nM) and U-46619 (0.1 and 1.0 nM) produced similar dose-related vasoconstriction in nondiabetic and diabetic hamsters (P > 0.05). In contrast, vasoconstriction to endothelin-1 (0.1 and 1.0 pM) was greater in diabetic than nondiabetic hamsters (P < 0.05). Next, we examined the role of nitric oxide in basal vascular tone and whether enhanced vasoconstriction in diabetic hamsters to endothelin-1 might be related to an alteration in the modulatory role of nitric oxide. N(G)-monomethyl-L-arginine (L-NMMA) (1.0, 10 and 100 microM) produced dose-related vasoconstriction in nondiabetic, but not diabetic hamsters. Further, L-NMMA did not alter vasoconstriction in response to endothelin-1 in nondiabetic and diabetic hamsters. These findings suggest that diabetes alters constriction of cheek pouch resistance arterioles to endothelin-1 which appears to be independent of the synthesis/release of nitric oxide. In addition, based upon findings using L-NMMA, it appears that there is a reduced influence of nitric oxide on basal diameter of resistance arterioles during diabetes.

The role of platelets in essential hypertension

Recent research is helping us understand the complex interactions that occur between platelets and their environment. The several intracellular events that occur during platelet activation are being identified as ar their effects on other platelets, the endothelium and coagulation factors. Heightened platelet activation is seen early in essential hypertension and probably plays an important role in the initiation and progression of atherosclerosis and the disorders associated with it. This review identifies some of the changes in platelet structure and function in essential hypertension and their role in the pathogenesis of hypertensive vascular disease.

The effect of comorbid conditions on hemodialysis access patency

Vascular access complications are a continuing source of hospitalization and morbidity in chronic dialysis patients. Several factors have been identified that are associated with complications in patients with native vein and prosthetic bridge arteriovenous graft fistulas. Early failure of native vein arteriovenous fistulas most consistently are related to small blood vessels. It remains unclear whether other comorbid factors play a role in complications of this fistula type. Prosthetic bridge fistulas are frequently placed in the United States and are associated with frequent complications. Factors most consistently associated with higher complication rates are diabetes mellitus, older age, and black race. Antiphospholipid antibody-associated syndromes and erythropoietin therapy have also been suggested as contributing factors. In addition, elevated lipoprotein(a) and hypoalbuminemia have been found to be associated with an increase of prosthetic graft thrombosis in white and Hispanic dialysis patients. This information strongly suggests that fistula complications are multifactorial. An improved understanding of the mechanisms of these associations may aid in the delineation of the pathogenesis and an improvement in the outcome of this important problem.

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.

The combined effect of diabetes and ionising radiation on the retinal vasculature of the rat

The clinical impression that pre-existing diabetes exacerbates radiation injury to the retinal vasculature was studied in STZ diabetic rats. Half of 2 groups of streptozotocin (STZ)-induced diabetic rats and 1 group of normal animals had their right eyes irradiated with 1000 cGy of 90 KVP x-rays. The prevalence of acellular capillaries in trypsin digests of the retinal vasculature was quantified for each of the 6 groups of animals at 6.5 months post-irradiation. The prevalence of acellular capillaries in both non-irradiated diabetic groups was significantly higher than in controls while the irradiated animals in each of the three main categories showed a statistically significant increase compared to their non-irradiated equivalents. However, the net increase in acellular capillaries following irradiation was much greater in rats with an 8 month term of pre-existing diabetes (180%) than in those which had only been diabetic for 3 months (36%). The results of this study suggest a synergistic relationship between pre-existing diabetes and ionising radiation in the development of retinal vasculopathy, and that the potentiation of the vascular damage is dependent on the duration of diabetes prior to radiation exposure.

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.

Effect of diabetes mellitus on responses of the basilar artery in rats to products released by platelets

BACKGROUND AND PURPOSE

Aggregation and adherence of platelets to vascular endothelium are increased during diabetes mellitus, and thus responses of cerebral arteries to products released by platelets may have important implications for the pathogenesis of stroke during diabetes. The goal of this study was to determine whether responses of the basilar artery to products released by platelets are altered during diabetes.

METHODS

A craniotomy was performed over the ventral medulla to expose the basilar artery. Diameter of the basilar artery was measured using intravital microscopy in nondiabetic and diabetic (50-60 mg/kg i.p. streptozotocin) rats in response to adenosine 5'-diphosphate, serotonin, and the thromboxane analogue U-46619.

RESULTS

Topical application of 10 and 100 microM adenosine 5'-diphosphate produced only minimal changes in diameter of the basilar artery that were similar in nondiabetic and diabetic rats (p greater than 0.05). At 0.01, 0.1, and 1.0 microM serotonin produced dose-related constriction of the basilar artery that was similar in nondiabetic and diabetic rats (p greater than 0.05). At 0.1 and 1.0 microM U-46619 also produced similar dose-related constriction of the basilar artery in nondiabetic and diabetic rats (p greater than 0.05).

CONCLUSIONS

These findings suggest that responses of the basilar artery to products released by platelets are not altered by diabetes mellitus. Thus, it does not appear that alterations in reactivity of the basilar artery to products released by platelets contribute to the pathogenesis of stroke during diabetes.

Platelet aggregation, disc haemorrhage and progressive loss of visual fields in glaucoma. A seven year follow-up study on glaucoma

Platelet aggregation in vitro, deterioration of visual field defects (VFD) and the prevalence of disc haemorrhages (DH) were assessed in 49 patients with primary open angle glaucoma (POAG) and compared with the findings for 67 individuals with suspected glaucoma (GS) in a seven-year follow-up study (range 5.8 to 8.2 years). The percentage patients with spontaneous platelet aggregation (SPA) was higher for POAG patients with visual field deterioration (60%) than both POAG patients without progressive loss of visual fields (12.5%; P less than 0.005) and those with suspected glaucoma (22.4%; P less than 0.005). The occurrence of DH was higher among POAG patients with progressive loss of visual field (28%) compared to the GS group (8.4%; P less than 0.025) and the group of patients consisting of POAG patients without deterioration of VFD and GS (9.9%; P less than 0.05). DH also occurred more often in patients with low tension glaucoma (41.6%) than in the remaining POAG patients (13.5%; P less than 0.05). No relation between the patients with SPA and the patients with DH was observed.

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.

Spontaneous whole blood platelet aggregation, hematological variables and complications in insulin-dependent diabetes mellitus: the Pittsburgh Epidemiology of Diabetes Complications Study

The role of platelet aggregation in the pathogenesis of diabetes complications remains unclear despite a number of reports suggesting associations in univariate analyses. The Pittsburgh Epidemiology of Diabetes Complications Study is a prospective study initiated in 1985 to determine risk factors for the development of complications in insulin-dependent diabetes mellitus (IDDM). This report focuses on the cross-sectional correlation between platelet count and aggregation and IDDM complications, in 563 participants aged 18 years and older seen at baseline. Spontaneous whole blood platelet aggregation (SWBPA) and other hematological variables [hematocrit, total platelet count (TPC), red blood cell count (RBC), fibrinogen and white blood cell count (WBC)] were evaluated as risk factors for IDDM complications (nephropathy, neuropathy, and retinopathy) in the baseline cross-sectional data of the Pittsburgh Epidemiology of Diabetes Complications Study. SWBPA was determined by a method based on the percentage fall in platelet count after shaking a fresh citrated blood sample kept at 37 degrees C. Subjects with chronic aspirin use or on dialysis were excluded from analysis. An increased TPC was observed in subjects with overt nephropathy (291.4 +/- 65.1 versus 261.2 +/- 64.9, p less than 0.001) compared with subjects without nephropathy. Similar results were found for proliferative retinopathy. The association with nephropathy (but not with retinopathy) persisted in multivariate analyses.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet aggregation and fatty acid composition of platelets in type 1 diabetes mellitus

A raised content of arachidonic acid in platelets from diabetic patients with retinopathy was found without differences in platelet aggregation: platelet aggregability was not related to platelet fatty acid composition. In diabetes, platelet aggregation was inversely correlated to non-esterified fatty acids in plasma and may suggest an inhibiting effect. Mean platelet volume was raised in the diabetic patients, but without hyperaggregability. The findings do not exclude a relationship between platelet fatty acids and platelet aggregability, but suggest that variations in levels of non-esterified fatty acids in plasma might interfere with platelet aggregation.

Early Treatment Diabetic Retinopathy Study design and baseline patient characteristics. ETDRS report number 7

The Early Treatment Diabetic Retinopathy Study (ETDRS), a multicenter collaborative clinical trial supported by the National Eye Institute, was designed to assess whether argon laser photocoagulation or aspirin treatment can reduce the risk of visual loss or slow the progression of diabetic retinopathy in patients with mild-to-severe nonproliferative or early proliferative diabetic retinopathy. The 3711 patients enrolled in the ETDRS were assigned randomly to either aspirin (650 mg per day) or placebo. One eye of each patient was assigned randomly to early argon laser photocoagulation and the other to deferral of photocoagulation. Both eyes were to be examined at least every 4 months and photocoagulation was to be initiated in eyes assigned to deferral as soon as high-risk proliferative retinopathy was detected. Examination of a large number of baseline ocular and patient characteristics indicated that there were no important differences between randomized treatment groups at baseline.

The effect of parenteral nutrition with different lipid emulsions on platelets

This study investigated the effect of parenteral nutrition including 500 ml/day of two different lipid emulsions on platelet numbers and platelet aggregation. One lipid contained 20% long chain triglycerides, the other a mixture of 10% medium chain triglycerides and 10% long chain triglycerides. After 7-10 days parenteral feeding, platelet numbers had not changed significantly, platelet morphology appeared normal and the prothrombin time was unaltered. Platelet aggregation in response to varying concentrations of ADP, adrenaline and collagen was not significantly different from pre-feeding and was similar in patients receiving the two different lipids.

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.

Augmented production of platelet-activating factor in human polymorphonuclear leukocytes by ketone bodies

The production of platelet-activating factor (PAF) in A23187-stimulated human polymorphonuclear leukocytes was markedly increased in the presence of 5 mM acetoacetate and beta-hydroxybutyrate. Such an augmentation was observed even at 500 microM but not at 50 microM. The augmented production of PAF by acetoacetate was also observed in the presence of autologous serum and was most prominent in the case of opsonized zymosan-stimulation rather than A23187-stimulation. These observations suggest that increased levels of acetoacetate and beta-hydroxybutyrate in blood may lead to the augmented production of PAF, which would amplify the various PAF-mediated biological reactions.

Effect of treatment with an inhibitor of platelet aggregation on the evolution of background retinopathy: 2 years of follow-up

Ophthalmic evolution was studied for 2 years in 17 patients with insulin-dependent diabetes mellitus and background diabetic retinopathy. Nine patients were treated with triflusal, a new platelet antiaggregant drug, and the eight remaining patients, with similar clinical and biological characteristics, were considered the control group. At the end of the study the ophthalmic evolution was different in the two groups. In the control group the degree of fluorescein leakage and the number of microaneurysms increased, while in the triflusal-treated group both parameters were reduced. There were no differences in visual acuity and computerised perimetry between the groups. Our results suggest that platelet antiaggregant therapy can be useful in the treatment of background diabetic retinopathy.

Diabetic choroidal and iris vasculature scanning electron microscopy findings

Scanning Electron Microscopy (SEM) was used to study vascular casts of twenty-four autopsy eyes taken from patients with long-standing insulin-dependent Diabetes Mellitus. These casts were compared to casts of ten 'normal' autopsy eyes from patients without a history of diabetes or other vascular disease. The SEM findings in the choroidal vessels of the diabetic eyes included: increased tortuosity, focal vascular dilations and narrowings, hypercellularity, vascular loops and microaneurysm formation, 'drop-out' of choriocapillaries, and sinus-like structure formation between choroidal lobules in the equatorial area. In the iris, neovascularization was evident in the vascular casts in cases with clinically recognized rubeosis iridis. These findings indicate that there is significant involvement of the uveal tract in diabetic eyes. The present study strongly supports the Hidayat and Fine light microscopic observation that the diabetic choroid demonstrates significant vascular changes (e.g. narrowed vessels with possible 'drop-out' of capillaries and neovascularization). Changes in the diabetic choroid, especially in the choriocapillaris, may be a contributing factor in diabetic retinopathy, resulting in decreased oxygenation of the outer layer of the retina. Short reviews and updated information of diabetic eye disease provide some additional insights into the vascular problems in the eye.

Healing of necrobiotic ulcers with antiplatelet therapy. Correlation with plasma thromboxane levels

Necrobiosis lipoidica in diabetics has been considered to be a cutaneous manifestation of diabetic microangiopathy. Seven diabetic patients with necrobiotic ulcers of recent onset that healed after administration of acetylsalicylic acid and dipyridamole had elevated thromboxane levels. Healing was associated with depression of the elevated thromboxane levels in all seven patients.

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.

Increased diene conjugates in diabetic subjects with microangiopathy

Free radicals are highly reactive unstable chemical species which have been implicated in the vascular damage associated with several disease states. Diene conjugates, probable products of free radical activity on lipids, were measured spectrophotometrically in 26 diabetic patients with microangiopathy, 36 uncomplicated diabetic patients, and 36 healthy controls. Total diene conjugates and diene conjugate to triglyceride ratios were significantly elevated in diabetic patients with microangiopathy (0.57 +/- 0.08 and 0.31 +/- 0.14 OD units/ml respectively; mean +/- SD) when compared with patients without complications (0.32 +/- 0.10, p less than 0.001, and 0.17 +/- 0.06, OD units/ml, p less than 0.011). There was no difference in total diene conjugation and their ratio to triglycerides between healthy controls and uncomplicated diabetic patients and the results were not influenced by the type of diabetes or level of diabetic control. Diene conjugate ratios repeated in 14 patients on two occasions, 6 weeks apart, with stable metabolic control were consistent. Increased diene conjugation suggesting increased free radical activity is associated with microangiopathy and this may have pathogenetic implications.

Abnormal cerebrovascular carbon dioxide reactivity in people with diabetes

Cerebral blood flow was measured both under conditions of normocapnia and hypercapnia in 22 diabetic patients and 20 normal control subjects, using either the intravenous 133Xe method or the closely comparable 133Xe inhalation method. While 19 out of 20 control subjects responded appropriately to hypercapnia with an increase in flow, eight of the diabetic patients failed to respond normally, this difference being significant (p = 0.03). Those manifesting an abnormal response included young, insulin-dependent patients with a short duration of diabetes and no clinical evidence of complications.

Aspirin and other antiplatelet drugs in the prophylaxis of thrombosis

Aspirin is of proven value as an antithrombotic drug. In unstable angina it reduces the risk of death and myocardial infarction by half. After a myocardial infarction it reduces the risk of death by about 10% and of coronary incidence (coronary death or definite myocardial infarction) by about 25%. These effects appear to be additive with those of beta-blocking drugs. Aspirin also reduces the risk of occlusion of aortocoronary saphenous vein grafts by about half. In transient cerebral ischaemia, aspirin may reduce the risk of stroke and death by 50%. In most clinical trials to date the daily dose of aspirin ranges from 325 mg to 1400 mg. Interest in very low doses of aspirin (less than 60 mg daily) is considerable but has yet to be translated into proven clinical benefit. Dipyridamole has not been shown to be effective as an antithrombotic when used alone. Its antiplatelet action ex vivo may be enhanced by combination with aspirin but clinical trials have shown relatively little advantage of the combination over aspirin alone. Sulphinpyrazone has not become established as a first line antithrombotic drug. Epoprostenol is useful in extracorporeal circulations to prevent platelet consumption and possibly in severe inoperable peripheral vascular disease.

Paradoxical platelet behaviour in diabetic ketoacidosis

Thrombotic events may occur in patients who present with severe uncontrolled diabetes or with diabetic coma. As a possible explanation for this, platelet function was investigated at presentation with diabetic ketoacidosis and during treatment in 10 patients. Concentrations of the platelet-specific proteins, platelet factor 4 (PF4) and beta-thromboglobulin (beta TG) were elevated and fell towards normal with treatment. Despite evidence of increased aggregation in vivo, platelets from subjects with ketoacidosis were insensitive to adenosine 5'-diphosphate (ADP), sensitivity increasing with correction of ketoacidosis. Platelets from ketoacidotic diabetics were initially insensitive to the anti-aggregatory action of prostacyclin (PGI2) and became normal with treatment. Initial blood glucose concentrations correlated with log10 ADP concentrations (r = 0.72, p less than 0.01) and with log10 PGI2 ID50 (the PGI2 concentration required to half-inhibit ADP-induced aggregation) (r = 0.66, p less than 0.025). Glucose concentrations throughout the 2-week study period correlated with all log10 ADP concentrations (r = 0.32, p less than 0.005) and all log10 PGI2 ID50 concentrations (r = 0.51, p less than 0.001). The decrease in ADP sensitivity in ketoacidosis, paradoxical in view of the evidence of increased in vivo platelet aggregation, may result from an acquired platelet storage pool deficiency.

Platelet aggregation and glaucoma

In this study platelet aggregation was determined in 79 patients with primary open angle glaucoma (POAG) and 81 patients suspected of having glaucoma (ocular hypertension). There is a positive association between high age and the presence of vascular diseases (p less than 0.01). An age dependent association between spontaneous platelet aggregation (SPA) and the presence of POAG was also observed (p less than 0.05). This indicates that the incidence of SPA in the elder group of patients with POAG is higher than in the elder glaucoma suspect group and in the group of younger patients. The association between vascular diseases and SPA and between vascular diseases and the presence of POAG were not significant at the 5% level. The incidence of SPA is not influenced by sex distribution, by the presence of diabetes, smoking or the use of timolol maleate topically.

Altered aortic and cremaster muscle prostaglandin synthesis in diabetic rats

Alterations in the synthesis and release of prostaglandins have been reported in humans and animal models of diabetes mellitus. In the present study synthesis and release of prostaglandins by thoracic aorta and cremaster muscle of rats with streptozotocin-induced diabetes of 8 wk duration was compared with age-matched controls. Prostaglandin synthesis was assessed by the measurement of immunoreactive prostaglandin E2 (PGE2) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) release and by quantifying metabolism of exogenous [1-14C]arachidonic acid by thoracic aortic rings and minced cremaster muscle. The cremaster muscles from diabetic rats released significantly greater quantities of PGE2 and 6-keto-PGF1 alpha and PGE2. In contrast, the aortas from diabetic rats released smaller quantities of 6-keto-PGF1 alpha and PGE2 and exhibited reduced 6-[1-14C]keto-PGF1 alpha. These studies indicate that diminished prostacyclin (PGI2) and/or PGE2 production is not a general feature of all diabetic vascular tissues, suggesting that large and small blood vessels may not be similarly affected by diabetes in regard to the metabolism of exogenous arachidonic acid and the synthesis and release of prostaglandins. Furthermore, the vascular changes often observed in conjunction with diabetes, i.e., alterations in vascular reactivity and microangiopathy in small blood vessels and atherosclerosis of large blood vessels may be related in some way to the segmental differences observed in prostaglandin synthesis.

Plasma beta-thromboglobulin is correlated with platelet adhesiveness to bovine endothelium in patients with diabetes mellitus

We measured simultaneous plasma beta-thromboglobulin (BTG) and adhesion of 51Cr-labelled, washed platelets to confluent, bovine aortic endothelial monolayers in 50 insulin-dependent diabetic patients and 30 normal subjects (respective mean ages (+/- SD) = 45.1 +/- 16.4 and 45.8 +/- 17.2 years). Compared to normal subjects without arteriosclerotic complications, diabetic patients had higher plasma BTG (34.8 +/- 1.8 (SEM) vs. 21.3 +/- 1.8 ng/ml) and platelet adhesiveness to endothelium (PAE) (3240 +/- 170 vs. 2430 +/- 120 X 10(3) platelets per well) (p less than 0.0002, respectively). Results in diabetic patients did not correlate with plasma glucose, hemoglobin AIa-c, known duration of disease, or sex; plasma BTG correlated with age (r = +0.36), and PAE correlated with plasma creatinine (r = +0.39). Those with clinically evident vascular disease, who were also older (47.8 +/- 2.6 (SEM) vs. 37.3 +/- 4.5 years, p less than 0.05), showed trends to higher plasma BTG (36.7 +/- 2.2 (SEM) vs. 28.8 +/- 3.4 ng/ml, p = 0.06) and PAE (3400 +/- 200 vs. 2800 +/- 280 X 10(3) platelets per well, p = 0.09). A strong correlation was found between plasma BTG and PAE in diabetic patients (r = +0.62, p less than 0.0001) either with or without vascular disease, which remained strong after statistical correction (partial Pearson correlation) for age and plasma creatinine, but not in normal subjects (r = +0.08, p greater than 0.1). These studies demonstrate that platelets in some diabetic patients are excessively adhesive to vascular endothelium, and that plasma BTG and platelet adhesiveness are intercorrelated.

Arachidonic acid metabolism by retinas of rats with streptozotocin-induced diabetes

Arachidonic acid metabolism via the cyclooxygenase pathway and the effects of aspirin and indomethacin were studied in whole retinas of rats with streptozotocin-induced diabetes. Diabetes was induced by intravenous injection of streptozotocin (60 mg/kg) and the animals were examined 5-6 weeks later. Whole retinas of nondiabetic and diabetic animals were incubated for 1 1/2 hours, and the amounts of prostacyclin and prostaglandin E2 (PGE2) accumulated in the media were measured. The amounts of PGE2 in the media of diabetic retinas was significantly lower than levels in media of nondiabetic group. However, the amounts of prostacyclin accumulated in the media of nondiabetic and diabetic retinas did not differ significantly. Addition of arachidonic acid (A.A.) to the incubation media caused an enhancement in the amounts of PGE2 and prostacyclin in the incubation media of both diabetic and nondiabetic retinas. Addition of indomethacin or aspirin to the incubation media caused a reduction of prostacyclin and PGE2 levels in the media of both groups.