Mechanisms of elevation of serum and urinary concentrations of soluble thrombomodulin in diabetic patients: possible application as a marker for vascular endothelial injury

Reduced Glomerular Endothelial Thrombomodulin Is Associated with Glomerular Macrophage Infiltration in Diabetic Nephropathy

The endothelial glycoprotein thrombomodulin regulates coagulation, inflammation, and apoptosis. In diabetic mice, reduced thrombomodulin function results in diabetic nephropathy (DN). Furthermore, thrombomodulin treatment reduces renal inflammation and fibrosis. Herein, thrombomodulin expression was examined in human kidney samples to investigate the possibility of targeting thrombomodulin in patients with DN. Glomerular thrombomodulin was analyzed together with the number of glomerular macrophages in 90 autopsied diabetic cases with DN, 55 autopsied diabetic cases without DN, and 37 autopsied cases without diabetes or kidney disease. Thrombomodulin mRNA was measured in glomeruli microdissected from renal biopsies from patients with DN and nondiabetic controls. Finally, glomerular thrombomodulin was measured in diabetic mice following treatment with the selective endothelin A receptor (ET_AR) blocker, atrasentan. In diabetic patients, glomerular thrombomodulin expression was increased at the mRNA level, but decreased at the protein level, compared with nondiabetic controls. Reduced glomerular thrombomodulin was associated with an increased glomerular influx of macrophages. Blocking the ET_AR with atrasentan restored glomerular thrombomodulin protein levels in diabetic mice to normal levels. The reduction in glomerular thrombomodulin in diabetes likely serves as an early proinflammatory step in the pathogenesis of DN. Thrombomodulin protein may be cleaved under diabetic conditions, leading to a compensatory increase in transcription. The nephroprotective effects of ET_AR antagonists in diabetic patients may be attributed to the restoration of glomerular thrombomodulin.

Thrombomodulin as a Physiological Modulator of Intravascular Injury

Thrombomodulin (TM), which is predominantly expressed on the endothelium, plays an important role in maintaining vascular homeostasis by regulating the coagulation system. Intravascular injury and inflammation are complicated physiological processes that are induced by injured endothelium-mediated pro-coagulant signaling, necrotic endothelial- and blood cell-derived damage-associated molecular patterns (DAMPs), and DAMP-mediated inflammation. During the hypercoagulable state after endothelial injury, TM is released into the intravascular space by proteolytic cleavage of the endothelium component. Recombinant TM (rTM) is clinically applied to patients with disseminated intravascular coagulation, resulting in protection from tissue injury. Recent studies have revealed that rTM functions as an inflammatory regulator beyond hemostasis through various molecular mechanisms. More specifically, rTM neutralizes DAMPs, including histones and high mobility group box 1 (HMGB1), suppresses excessive activation of the complement system, physiologically protects the endothelium, and influences both innate and acquired immunity. Neutrophil extracellular traps (NETs) promote immunothrombosis by orchestrating platelets to enclose infectious invaders as part of the innate immune system, but excessive immunothrombosis can cause intravascular injury. However, rTM can directly and indirectly regulate NET formation. Furthermore, rTM interacts with mediators of acquired immunity to resolve vascular inflammation. So far, rTM has shown good efficacy in suppressing inflammation in various experimental models, including thrombotic microangiopathy, sterile inflammatory disorders, autoimmune diseases, and sepsis. Thus, rTM has the potential to become a novel tool to regulate intravascular injury via pleiotropic effects.

Plasma levels of thrombomodulin, plasminogen activator inhibitor-1 and fibrinogen in elderly, diabetic patients with depressive symptoms

Background

Diabetes, depression and aging have been associated with pro-inflammatory and prothrombotic state.

Aim

The aim of the study was to determine the plasma levels of thrombomodulin, plasminogen activator inhibitor-1 (PAI-1) and fibrinogen in elderly diabetic patients with and without depressive symptoms and to examine factors (including thrombomodulin, PAI-1, fibrinogen levels) associated with depressive symptoms in elderly patients with type 2 diabetes (T2DM).

Methods

A total of 276 T2DM elders were evaluated: 82 subjects with depressive symptoms and 194 controls. Data were collected concerning biochemical parameters and biomarkers.

Results

Plasma thrombomodulin, PAI-1 and fibrinogen were elevated in patients with depressive symptoms compared to controls. Thrombomodulin level was correlated with fibrinogen and PAI-1 levels. All parameters were correlated with the Geriatric Depression Scale-30 score. The univariate logistic regression models revealed that variables which increased the likelihood of diagnosis of depressive symptoms in elderly patients with T2DM were: female sex, smoking habit, longer duration of T2DM, hyperlipidemia, neuropathy, increased number of co-morbidities, higher BMI, and higher levels of total and LDL cholesterol, thrombomodulin, PAI-1 and fibrinogen. In addition, the multivariable analysis indicated that female sex, smoking habit, increased number of co-morbidities, higher BMI, and higher levels of LDL cholesterol and thrombomodulin are the predisposing factors for depressive symptoms.

Conclusions

Elderly diabetic patients with depressive symptoms have higher levels of thrombomodulin, PAI-1 and fibrinogen. Further prospective larger studies are needed to provide potential directions for the research, treatment and prevention of co-morbid depression and diabetes.

Molecular mechanisms of diabetic vascular complications

Diabetic complications are the major causes of morbidity and mortality in patients with diabetes. Microvascular complications include retinopathy, nephropathy and neuropathy, which are leading causes of blindness, end‐stage renal disease and various painful neuropathies; whereas macrovascular complications involve atherosclerosis related diseases, such as coronary artery disease, peripheral vascular disease and stroke. Diabetic complications are the result of interactions among systemic metabolic changes, such as hyperglycemia, local tissue responses to toxic metabolites from glucose metabolism, and genetic and epigenetic modulators. Chronic hyperglycemia is recognized as a major initiator of diabetic complications. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on vascular tissues. These include increased polyol pathway, activation of the diacylglycerol/protein kinase C pathway, increased oxidative stress, overproduction and action of advanced glycation end products, and increased hexosamine pathway. In addition, the alterations of signal transduction pathways induced by hyperglycemia or toxic metabolites can also lead to cellular dysfunctions and damage vascular tissues by altering gene expression and protein function. Less studied than the toxic mechanisms, hyperglycemia might also inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, platelet‐derived growth factor and activated protein C, which play important roles in maintaining vascular homeostasis. Thus, effective therapies for diabetic complications need to inhibit mechanisms induced by hyperglycemia’s toxic effects and also enhance the endogenous protective factors. The present review summarizes these multiple biochemical pathways activated by hyperglycemia and the potential therapeutic interventions that might prevent diabetic complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00018.x, 2010)

Association of kidney function with changes in the endothelial surface layer

BACKGROUND AND OBJECTIVES

ESRD is accompanied by endothelial dysfunction. Because the endothelial glycocalyx (endothelial surface layer) governs interactions between flowing blood and the vessel wall, perturbation could influence disease progression. This study used a novel noninvasive sidestream-darkfield imaging method, which measures the accessibility of red blood cells to the endothelial surface layer in the microcirculation (perfused boundary region), to investigate whether renal function is associated with endothelial surface layer dimensions.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Perfused boundary region was measured in control participants (n=10), patients with ESRD (n=23), participants with normal kidney function after successful living donor kidney transplantation (n=12), and patients who developed interstitial fibrosis/tubular atrophy after kidney transplantation (n=10). In addition, the endothelial activation marker angiopoietin-2 and shed endothelial surface layer components syndecan-1 and soluble thrombomodulin were measured using ELISA.

RESULTS

Compared with healthy controls (1.82 ± 0.16 µm), ESRD patients had a larger perfused boundary region (+0.23; 95% confidence interval, 0.46 to <0.01; P<0.05), which signifies loss of endothelial surface layer dimensions. This large perfused boundary region was accompanied by higher circulating levels of syndecan-1 (+57.71; 95% confidence interval, 17.38 to 98.04; P<0.01) and soluble thrombomodulin (+12.88; 95% confidence interval, 0.29 to 25.46; P<0.001). After successful transplantation, the perfused boundary region was indistinguishable from healthy controls (without elevated levels of soluble thrombomodulin or syndecan-1). In contrast, however, patients who developed interstitial fibrosis and tubular atrophy showed a large perfused boundary region (+0.36; 95% confidence interval, 0.09 to 0.63; P<0.01) and higher levels of endothelial activation markers. In addition, a significant correlation between perfused boundary region, angiopoietin-2, and eGFR was observed (perfused boundary region versus GFR: Spearman's ρ=0.31; P<0.05; perfused boundary region versus angiopoietin-2: Spearman's ρ=-0.33; P<0.05).

CONCLUSION

Reduced renal function is strongly associated with low endothelial surface layer dimensions. After successful kidney transplantation, the endothelial surface layer is indistinguishable from control.

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 impact of metabolic syndrome and CRP on vascular phenotype in type 2 diabetes mellitus

BACKGROUND

The burden of cardiovascular disease in diabetes mellitus type 2 (DM2) patients is variable. We hypothesize that metabolic syndrome (MS) and low-grade systemic inflammation modify the extent of atherosclerosis in DM2.

METHODS

Vascular phenotype was determined using the following endothelium-related, hemostatic, and sonographic endpoints in 62 DM2 patients with mild dyslipidemia: sVCAM, sE-selectin, von Willebrand factor (VWF), fibrinogen, s-thrombomodulin (sTM), tPA, PAI-1, flow-mediated dilation (FMD), and intima media thickness (IMT). The impact of MS load (number of criteria present), MS components, and CRP on these parameters was assessed.

RESULTS

Serum sVCAM, sTM, and tPA levels significantly increased with increasing MS load. IMT also significantly increased from 0.602+/-0.034 (one MS criterion) to 0.843+/-0.145 (four MS criteria, p=0.007). LogCRP significantly correlated with fibrinogen, PAI-1, and IMT. In a multiple regression (MR) model with age and gender as covariates, MS load predicted sVCAM and sTM; CRP predicted PAI-1 and fibrinogen; MS load and CRP simultaneously predicted tPA and IMT. For each MS criterion present, IMT significantly increased by 0.04 mm. An increase in CRP from 1 to 3 mg/L resulted in a significant increase of 0.04 mm. Patients with four MS criteria and inflammation (CRP >or=3 mg/L) are predicted to have a 0.21 mm thicker IMT than those without. A second stepwise MR analysis based on gender, traditional risk factors, diabetes-related parameters, renal function, individual MS criteria, and LogCRP as explanatory variables showed a significant effect of systolic and diastolic blood pressure, HDL, and LogCRP on IMT(r(2)=0.36, p<0.001).

CONCLUSION

MS and low-grade chronic inflammation have an independent impact on vascular phenotype including IMT in DM2.

Reduction expression of thrombomodulin and endothelial cell nitric oxide synthase in dermatomyositis

Dermatomyositis (DM) is a systemic microvasculitis predominantly involving the capillaries. We investigated the expression of thrombomodulin (TM) and endothelial cell nitric oxide synthase (eNOS) in microvessels of DM patients. Twelve patients with acute or subacute onset of proximal muscle weakness and erythematous rash over their faces and shoulders were included in this study. Serum creatine phosphokinase was elevated in almost all patients. Electromyograph showed a myopathic pattern in all patients. Muscle biopsies were performed in all patients and 10 non-DM controls and studied with histological, enzyme histochemical and immunohistochemical staining. von Willebrand factor, TM and eNOS antibodies were used as the primary antibodies. Perifascicular degeneration and inflammatory cell infiltration in the perimysium were noted in almost all patients. Non-special esterase staining was markedly positive in capillary and microvascular endothelium. Marked reduction in TM and eNOS staining was noted in DM patients in perimysium microvessels and perifascicular area capillaries. Vascular lesions in DM were not only limited to capillaries. The low expression of TM and eNOS in microvessels suggests the anticoagulation and vasodilation functions of vascular endothelium is reduced. DM is an inflammatory vascular endothelial disease.

Soluble thrombomodulin as a predictor of type 2 diabetes: results from the MONICA/KORA Augsburg case-cohort study, 1984-1998

AIMS/HYPOTHESIS

Previous studies have shown an inverse association between soluble thrombomodulin (sTM) and incident CHD, but there is a lack of data on the association between sTM and type 2 diabetes. Since CHD and type 2 diabetes share many risk factors, the aim of this study was to assess whether elevated sTM levels are associated with a lower incidence of type 2 diabetes.

MATERIALS AND METHODS

A case-cohort study was performed in initially healthy middle-aged men and women based on data from the Monitoring of Trends and Determinants in Cardiovascular Disease/Cooperative Health Research in the Region of Augsburg (MONICA/KORA) studies conducted between 1984 and 1998. Levels of sTM were measured with an ELISA in serum samples from 138 men and 86 women who developed type 2 diabetes during follow-up (cases) and 534 men and 446 women who did not develop type 2 diabetes (non-cases).

RESULTS

An inverse association was found between sTM and type 2 diabetes risk after multivariable adjustment for diabetes risk factors, including several other markers of inflammation and endothelial dysfunction. Markers of inflammation and endothelial dysfunction were particularly strong confounders of the observed association. In the fully adjusted model, a 1 SD increase in sTM was associated with a 27% decrease in the risk of type 2 diabetes (hazard ratio=0.73, 95% CI 0.58-0.91) in the total study population. We did not observe significant risk differences between men and women.

CONCLUSIONS/INTERPRETATION

These data suggest that, in initially healthy middle-aged men and women, levels of sTM are inversely associated with the risk of type 2 diabetes.

Normalization of multiple hemostatic abnormalities in uremic type 1 diabetic patients after kidney-pancreas transplantation

To evaluate the effects of kidney-pancreas transplantation on hemostatic abnormalities in uremic type 1 diabetic patients, we conducted a cross-sectional study involving 12 type 1 diabetic patients, 30 uremic type 1 diabetic patients, 27 uremic type 1 diabetic patients who had a kidney-pancreas transplant, 12 uremic type 1 diabetic patients who had a kidney-alone transplant, and 13 healthy control subjects. We evaluated platelet and clotting system. Platelets in the group of uremic type 1 diabetic patients were significantly larger than platelets in the other groups. Resting calcium levels were significantly higher in the uremic type 1 diabetic patients and uremic type 1 diabetic patients who had a kidney-alone transplant than in the type 1 diabetic patients who had a kidney-pancreas transplant and control subjects. CD41 expression was significantly reduced in platelets from the uremic type 1 diabetic patients compared with the other groups. Levels of hypercoagulability markers in the type 1 diabetic patients who had a kidney-pancreas transplant and, to a lesser extent, the uremic type 1 diabetic patients who had a kidney-alone transplant but not the uremic type 1 diabetic patients were similar to those of the control subjects. A reduction in natural anticoagulants was evident in the uremic type 1 diabetic patients, whereas near-normal values were observed in the type 1 diabetic patients who had a kidney-pancreas transplant and uremic type 1 diabetic patients who had a kidney-alone transplant. Hemostatic abnormalities were not observed in type 1 diabetic patients who had a kidney-pancreas transplant. This finding might explain the lower cardiovascular death rate observed in type 1 diabetic patients who had a kidney-pancreas transplant compared with uremic type 1 diabetic patients who had a kidney-alone transplant or uremic type 1 diabetic patients.

High plasma homocysteine concentrations are associated with plasma concentrations of thrombomodulin in patients with type 2 diabetes and link diabetic nephropathy to macroangiopathy

In type 2 diabetic patients with or without nephropathy, we examined relationships between plasma concentrations of total homocysteine (tHcy) and clinical macroangiopathy, as well as endothelial dysfunction indicated by plasma thrombomodulin (TM) concentrations. We studied 103 type 2 diabetic patients including 26 with macroangiopathy (12 patients with coronary artery disease [CAD], 10 with stroke, and 4 with peripheral vascular disease [PVD]). Plasma tHcy was measured by high-performance liquid chromatography. Plasma TM was determined by enzyme immunoassay. As an index of glomerular filtration rate, creatinine clearance (Ccr) also was determined in a 24-hour urine collection. Considering all diabetic patients, plasma tHcy concentrations were significantly higher in those with macroangiopathy than in those without (10.4 +/- 3.7 v 8.5 +/- 2.8 micromol/L, P=.0077). By univariate and multivariate analyses, plasma tHcy was correlated inversely with Ccr. Plasma tHcy concentrations were significantly higher in the patients with overt albuminuria than in those with normoalbuminuria or microalbuminuria. After exclusion of patients with renal insufficiency (Ccr<60 mL/min), differences in plasma tHcy concentrations between patients with and without macroangiopathy were abolished. By multivariate analysis, total cholesterol, urinary albumin, Ccr, C-peptide, and tHcy retained significant influence on the plasma TM. Even in patients with normal renal function (Ccr > or = 80 mL/min), plasma tHcy was correlated positively with plasma TM. In conclusions, diabetic nephropathy is a main determinant of plasma tHcy elevation in type 2 diabetic patients. Since plasma TM is independently associated with plasma tHcy, in diabetic patients with overt nephropathy, elevation of tHcy reflecting reduced clearance is a likely cause of endothelial dysfunction, resulting in the atherosclerosis underlying development of cardiovascular disease.

Thrombomodulin deficiency in human diabetic nerve microvasculature

Human diabetic neuropathy is multifactorial in etiology, with ischemia as a final common pathology. Although impaired vascular endothelial cell function in diabetic microvascular injury is established, the role of thrombomodulin (TM)-dependent protein C antithrombotic mechanism in the pathogenesis of neuropathy is unclear. This neuropathologic case-control study investigated whether vascular endothelial TM expression is deficient in peripheral nerve microvessels in diabetic neuropathy. Sural nerve biopsies from 7 patients with diabetic neuropathy and 10 with axonal neuropathy without vasculopathy were immunostained with anti-TM and anti-von Willebrand factor (vWF; an endothelial cell marker) antibodies. The proportion of TM-positive microvessels was expressed relative to total vWF-staining vessels, according to vessel caliber and regional distribution within the nerve. In diabetic nerves compared with reference controls, the proportion of TM-positive endoneurial microvessels was 15-fold lower (0.02 vs. 0.30 in diabetic nerves vs. controls, P < 0.004), and the proportion of small-caliber epineurial microvessels was 10-fold lower (0.04 vs. 0.43, P < 0.001). No TM expression was detected at the perineurium in diabetic or control nerves. We demonstrate a substantial reduction of vascular endothelial TM expression throughout human diabetic neuropathy. These findings suggest that an impaired native TM-dependent protein C antithrombotic mechanism may contribute to microvascular ischemia in the pathogenesis of diabetic neuropathy.

Elevation of von Willebrand factor in plasma in diabetic patients with neuropathic foot ulceration

AIMS

The present study examines the relationship between markers of endothelial dysfunction and diabetic neuropathy or consequent neuropathic foot ulceration in patients with Type 2 diabetes mellitus.

METHODS

We studied 65 Type 2 diabetic patients including 25 diabetic patients without neuropathy, 27 with neuropathy but no history of foot ulceration, and 13 with neuropathic ulceration. Plasma concentrations of von Willebrand factor (vWF) and soluble thrombomodulin (TM), measures of endothelial dysfunction, were determined by enzyme immunoassays. We performed various tests quantifying aspects of diabetic neuropathy including vibration perception threshold (VPT; for sensory neuropathy), coefficient of variation of R-R intervals (CVR-R; for cardiac autonomic neuropathy), and cold-induced vasodilation in the great toe for peripheral sympathetic neuropathy.

RESULTS

CVR-R and cold-induced vasodilation were significantly diminished in patients with neuropathic foot ulceration compared with patients with neuropathy but no history of foot ulceration. Plasma vWF concentrations were positively correlated with VPT and cold-induced vasodilation test, and were inversely correlated with CVR-R. Multivariate analysis disclosed that VPT and percentage vasodilation were independent factors for plasma vWF. Plasma vWF was significantly elevated in patients with foot ulceration compared with patients without neuropathy or those with neuropathy but not foot ulceration. However, plasma TM concentrations did not differ between the three groups.

CONCLUSIONS

Diabetic patients with neuropathic foot ulceration had severe impairment of cardiac autonomic and peripheral sympathetic nerves. Elevation of vWF in plasma was associated with neuropathic foot ulceration, linking endothelial dysfunction to foot ulceration.

Relationship between soluble thrombomodulin in plasma and coagulation or fibrinolysis in type 2 diabetes

Serum concentration of soluble thrombomodulin (TM) is thought to be a marker for endothelial damage. Although several studies have reported that serum TM concentrations are increased in patients with diabetes mellitus, there is little information on the physiological function of soluble TM in human plasma. To evaluate the relationship of soluble TM in plasma between coagulation and/or fibrinolysis system in patients with diabetes, we measured plasma soluble TM, protein C activity (a natural anticoagulant induced by thrombin-TM complex), prothrombin F1+2 (a direct marker of thrombin generation), and plasmin-alpha 2-antiplasmin complex (PAP) and D dimer (measures of fibrinolytic activity) in 55 patients with type 2 diabetes mellitus. The plasma concentrations of soluble TM (P<0.01), protein C activity (P<0.01), prothrombin F1+2 (P<0.05), PAP (P<0.001) and D dimer (P<0.001) were significantly higher in the diabetic patients than the 48 age-matched control subjects. The plasma concentrations of TM and PAP were obviously increased in patients with diabetic nephropathy. In the diabetic patients, the plasma concentrations of soluble TM were inversely correlated with the protein C activity (r=-0.43, P<0.005), and were positively correlated with the plasma concentrations of prothrombin F1+2 (r=0.63, P<0.0001) and the plasma PAP concentrations (r=0.30, P<0.05). The present study demonstrated that both coagulation and fibrinolysis are enhanced concomitantly in patients with type 2 diabetes mellitus, and that an increase in plasma concentration of soluble TM is associated not only with hypercoagulability but also with enhanced fibrinolysis in diabetic patients.