Uremic toxins alter coagulation and fibrinolysis-related genes expression in human endothelial cells

The in-vitro influence of urea concentration on thromboelastrography in patients with and without end stage renal disease

BACKGROUND

End stage renal disease (ESRD) is associated with platelet dysfunction but also thromboembolic complications. The specific role of increased blood urea nitrogen (BUN) on coagulation is unclear. We aimed to characterize thromboelastography (TEG) parameters from males and females with ESRD and normal kidney function and evaluate if exogenous urea in vitro reproduced those TEG differences.

METHODS

We collected blood samples from 20 living kidney donors and 20 kidney recipients. TEG was performed without and with two increasing urea concentrations in vitro. TEG parameters were compared between recipients and donors.

RESULTS

Blood from kidney recipients showed baseline increased maximum amplitude (MA) and shortened time to maximum amplitude (TMA) compared to donors. These differences were not confirmed in females. In all patients, BUN was inversely correlated with TMA (r = -0.342; p = 0.031). In males, BUN and creatinine concentrations showed a direct correlation with MA (0.583; p = 0.007) and an inverse correlation with TMA (r = -0.520; p = 0.019). Urea in vitro decreased R-time (p = 0.005) and increased LY30 (p = 0.009) in donors but not recipients.

CONCLUSIONS

ESRD is associated with increased MA and decreased TMA on TEG. No change in MA was observed with increasing urea concentrations in vitro. Gender-specific variability in TEG parameters were observed.

Indoxyl sulfate in atherosclerosis

Atherosclerosis (AS), a chronic vascular inflammatory disease, has become a main focus of attention worldwide for its chronic progressing disease course and serious complications in the later period. Nevertheless, explanations for the exact molecular mechanisms of AS initiation and development remain to be an unsolved problem. The classic pathogenesis theories, such as lipid percolation and deposition, endothelium injury, inflammation and immune damage, provide the foundation for discovering the new key molecules or signaling mechanisms. Recently, indoxyl sulfate (IS), one of non-free uremia toxins, has been noticeable for its multiple atherogenic effects. IS exists at high concentration in plasma for its great albumin binding rate. Patients with uremia have markedly elevated serum levels of IS due both to the deterioration of renal function and to the high binding affinity of IS to albumin. Nowadays, elevated incidence of circulatory disease among patients with renal dysfunction indicates correlation of uremic toxins with cardiovascular damage. In this review, the atherogenic effects of IS and the underlying mechanisms are summarized with emphasis on several key pathological events associated with AS developments, such as vascular endothelium dysfunction, arterial medial lesions, vascular oxidative stress, excessive inflammatory responses, calcification, thrombosis and foam cell formation. Although recent studies have proved the great correlation between IS and AS, deciphering cellular and pathophysiological signaling by confirming key factors involved in IS-mediated atherosclerosis development may enable identification of novel therapeutic targets.

Tissue Factor, Thrombosis, and Chronic Kidney Disease

Coagulation abnormalities are common in chronic kidney disease (CKD). Tissue factor (TF, factor III) is a master regulator of the extrinsic coagulation system, activating downstream coagulation proteases, such as factor Xa and thrombin, and promoting fibrin formation. TF and coagulation proteases also activate protease-activated receptors (PARs) and are implicated in various organ injuries. Recent studies have shown the mechanisms by which thrombotic tendency is increased under CKD-specific conditions. Uremic toxins, such as indoxyl sulfate and kynurenine, are accumulated in CKD and activate TF and coagulation; in addition, the TF-coagulation protease-PAR pathway enhances inflammation and fibrosis, thereby exacerbating renal injury. Herein, we review the recent research studies to understand the role of TF in increasing the thrombotic risk and CKD progression.

Myeloid cell-derived coagulation tissue factor is associated with renal tubular damage in mice fed an adenine diet

Patients with chronic kidney disease (CKD) commonly exhibit hypercoagulability. Increased levels of uremic toxins cause thrombogenicity by increasing tissue factor (TF) expression and activating the extrinsic coagulation cascade. TF is induced in monocytes and macrophages under pathological conditions, such as inflammatory diseases. However, the role of monocyte myeloid cell TF in CKD progression remains unclear. We aimed to clarify this issue, and the present study found that patients with CKD had elevated levels of D-dimer, a marker of fibrin degradation, which was associated with decreased estimated glomerular filtration rate and increased serum levels of uremic toxins, such as indoxyl sulfate. In vitro studies showed that several uremic toxins increased cellular TF levels in monocytic THP-1 cells. Mice with TF specifically deleted in myeloid cells were fed an adenine diet to cause uremic kidney injury. Myeloid TF deletion reduced tubular injury and pro-inflammatory gene expression in the kidneys of adenine-induced CKD but did not improve renal function as measured by plasma creatinine or blood urea nitrogen. Collectively, our findings suggest a novel concept of pathogenesis of coagulation-mediated kidney injury, in which elevated TF levels in monocytes under uremic conditions is partly involved in the development of CKD.