Erythropoietin Increases Expression and Function of Transient Receptor Potential Canonical 5 Channels

Hypertension is a common complication in hemodialysis patients during erythropoietin (EPO) treatment. The underlying mechanisms of EPO-induced hypertension still remain to be determined. Increased transient receptor potential canonical (TRPC) channels have been associated with hypertension. Now, TRPC gene expression was investigated using quantitative real-time RT-PCR and immunoblotting in cultured human endothelial cells and in monocytes from hemodialysis patients. EPO dose-dependently increased TRPC5 mRNA in endothelial cells. EPO increased TRPC5 mRNA stability, that is, EPO prolonged the half-life period for TRPC5 mRNA from 16 hours (control) to 24 hours ( P <0.05). The poly(A) tail length was measured by rapid amplification of cDNA ends-poly(A) test. Increased TRPC5 mRNA stability was attributed to longer 3′ poly(A) tail lengths after EPO administration. EPO also significantly increased TRPC5 channel protein abundance by 70% ( P <0.05). Whole-cell patch clamp showed that angiotensin II–induced, TRPC5-mediated currents were dramatically increased in endothelial cells treated with EPO. Fluorescent dye techniques confirmed that increased calcium influx after EPO treatment was abolished after TRPC5 knockdown ( P <0.05). EPO also significantly increased intracellular reactive oxygen species production. Knockdown of TRPC5 alleviated EPO-induced reactive oxygen species generation in endothelial cells ( P <0.05). In vivo, EPO-treated hemodialysis patients showed significantly increased amounts of TRPC5 mRNA in monocytes compared with EPO-free hemodialysis patients (6.0±2.4 [n=12] versus 1.0±0.5 [n=9]; P <0.01). Patients undergoing EPO treatment also showed significantly elevated systolic blood pressure (160±7 versus 139±6 mm Hg; P <0.05). Our findings suggest that upregulated functional TRPC5 gene may be one cause of EPO-induced hypertension in patients with chronic kidney disease.

Calcium-dependent expression of transient receptor potential canonical type 3 channels in patients with chronic kidney disease

It is unknown whether extracellular calcium may regulate the expression of transient receptor potential canonical type 3 (TRPC3) channels in patients with chronic kidney disease. Using quantitative in-cell Western assay we compared the expression of TRPC3 channel protein in monocytes from 20 patients with chronic kidney disease and 19 age- and sex-matched healthy control subjects. TRPC3 channels were identified by immunoblotting using specific antibodies and TRPC3 protein was further confirmed by mass spectrometry. We observed a significant increase of TRPC3 channel protein expression in patients with chronic kidney disease compared to healthy control subjects (normalized expression, 0.42±0.06 vs. 0.19±0.03; p<0.01). Expression of TRPC3 was significantly inversely correlated with estimated glomerular filtration rates (Spearman r=-0.41) or serum calcium concentration (Spearman r=-0.34). During a hemodialysis session serum calcium concentrations significantly increased, whereas the expression of TRPC3 channels and calcium influx significantly decreased. In vitro studies confirmed that higher calcium concentrations but not magnesium, barium nor sodium concentrations significantly decreased TRPC3 expression in human monocytes. This study indicates that reduced extracellular calcium concentrations up-regulate TRPC3 channel protein expression in patients with chronic kidney disease.

Increased rhythmicity in hypertensive arterial smooth muscle is linked to transient receptor potential canonical channels

Vasomotion describes oscillations of arterial vascular tone due to synchronized changes of intracellular calcium concentrations. Since increased calcium influx into vascular smooth muscle cells from spontaneously hypertensive rats (SHR) has been associated with variances of transient receptor potential canonical (TRPC) channels, in the present study we tested the hypothesis that increased vasomotion in hypertension is directly linked to increased TRPC expression. Using a small vessel myograph we observed significantly increased norepinephrine-induced vasomotion in mesenteric arterioles from SHR compared to normotensive Wistar–Kyoto (WKY) rats. Using immunoblottings we obtained significantly increased expression of TRPC1, TRPC3 and TRPC5 in mesenteric arterioles from SHR compared to WKY, whereas TRPC4 and TRPC6 showed no differences. Norepinephrine-induced vasomotion from SHR was significantly reduced in the presence of verapamil, SKF96365, 2-aminoethoxydiphenylborane (2-APB) or gadolinium. Pre-incubation of mesenteric arterioles with anti-TRPC1 and anti-TRPC3 antibodies significantly reduced norepinephrine-induced vasomotion and calcium influx. Control experiments with pre-incubation of TRPC antibodies plus their respective antigenic peptide or in the presence of anti-β-actin antibodies or random immunoglobulins not related to TRPC channels showed no inhibitory effects of norepinephrine-induced vasomotion and calcium influx. Administration of candesartan or telmisartan, but not amlodipine to SHR for 16 weeks significantly reduced either the expression of TRPC1, TRPC3 and TRPC5 as well as norepinephrine-induced vasomotion in mesenteric arterioles. In conclusion we gave experimental evidence that the increased TRPC1, TRPC3 and TRPC5 expression in mesenteric arterioles from SHR causes increased vasomotion in hypertension.

Superoxide dismutase type 1 in monocytes of chronic kidney disease patients

We analyzed proteomic profiles in monocytes of chronic kidney disease (CKD) patients and healthy control subjects. Two-dimensional electrophoresis (2-DE) and silver staining indicated differences in protein pattern. Among the analyzed proteins, superoxide dismutase type 1 (SOD1), which was identified both by MS/MS mass-spectrometry and immunoblotting, was reduced in kidney disease. We characterized SOD1 protein amount, using quantitative in-cell Western assay and immunostaining of 2-DE gel blots, and SOD1 gene expression, using quantitative real-time polymerase chain reaction (PCR), in 98 chronic hemodialysis (HD) and 211 CKD patients, and 34 control subjects. Furthermore, we showed that different SOD1 protein species exist in human monocytes. SOD1 protein amount was significantly lower in HD (normalized SOD1 protein, 27.2 ± 2.8) compared to CKD patients (34.3 ± 2.8), or control subjects (48.0 ± 8.6; mean ± SEM; P < 0.05). Analysis of SOD1 immunostaining showed significantly more SOD1 protein in control subjects compared to patients with CKD or HD (P < 0.0001, analysis of main immunoreactive protein spot). SOD1 gene expression was significantly higher in HD (normalized SOD1 gene expression, 17.8 ± 2.3) compared to CKD patients (9.0 ± 0.7), or control subjects (5.5 ± 1.0; P < 0.0001). An increased SOD1 gene expression may indicate increased protein degradation in patients with CKD and compensatory increase of SOD1 gene expression. Taken together, we show reduced SOD1 protein amount in monocytes of CKD, most pronounced in HD patients, accompanied by increased SOD1 gene expression.

Continuous reduction of plasma paraoxonase activity with increasing dialysis vintage in hemodialysis patients

Plasma paraoxonase (PON) is an enzyme that hydrolyzes organic phosphate and aromatic carboxylic acid esters. Reduced activity is associated with early events of atherogenesis. The relevance of PON phenotypes is not well characterized in hemodialysis patients. In a cross-sectional study we measured PON activity in 377 hemodialysis patients photometrically using the substrates 4-nitrophenylacetate and phenylacetate. The PON ratio was calculated from 4-nitrophenylacetate-derived activity divided by phenylacetate-derived activity. Frequency distribution of the PON ratio showed three different PON phenotypes. 74% of hemodialysis patients showed PON phenotype 1, 21% PON phenotype 2, and 5% PON phenotype 3. Compared to hemodialysis patients with PON 1, patients with PON 2 or 3 showed higher conversion rates for 4-nitrophenylacetate. We observed a significant reduction of PON ratio with increasing dialysis vintage (P<0.001 by ANOVA and post test for linear trend). In patients on hemodialysis treatment for less than 12 months, the PON ratio was 1.16 ± 0.08 (n=64). In patients on hemodialysis treatment for more than 60 months the PON ratio was 1.00 ± 0.04 (n=130; P=0.05). This reduction of PON activity was due to reduced 4-nitrophenylacetate-derived PON activity with increasing dialysis vintage. In conclusion, plasma PON ratio significantly declines with increasing dialysis vintage.

Activation of TRPV1 by dietary capsaicin improves endothelium-dependent vasorelaxation and prevents hypertension

Some plant-based diets lower the cardiometabolic risks and prevalence of hypertension. New evidence implies a role for the transient receptor potential vanilloid 1 (TRPV1) cation channel in the pathogenesis of cardiometabolic diseases. Little is known about impact of chronic TRPV1 activation on the regulation of vascular function and blood pressure. Here we report that chronic TRPV1 activation by dietary capsaicin increases the phosphorylation of protein kinase A (PKA) and eNOS and thus production of nitric oxide (NO) in endothelial cells, which is calcium dependent. TRPV1 activation by capsaicin enhances endothelium-dependent relaxation in wild-type mice, an effect absent in TRPV1-deficient mice. Long-term stimulation of TRPV1 can activate PKA, which contributes to increased eNOS phosphorylation, improves vasorelaxation, and lowers blood pressure in genetically hypertensive rats. We conclude that TRPV1 activation by dietary capsaicin improves endothelial function. TRPV1-mediated increase in NO production may represent a promising target for therapeutic intervention of hypertension.

High glucose-induced oxidative stress increases transient receptor potential channel expression in human monocytes

OBJECTIVE

Transient receptor potential (TRP) channel-induced cation influx activates human monocytes, which play an important role in the pathogenesis of atherosclerosis. In the present study, we investigated the effects of high glucose-induced oxidative stress on TRP channel expression in human monocytes.

RESEARCH DESIGN AND METHODS

Human monocytes were exposed to control conditions (5.6 mmol/l d-glucose), high glucose (30 mmol/l d-glucose or l-glucose), 100 micromol/l peroxynitrite, or high glucose in the presence of the superoxide dismutase mimetic tempol (100 micromol/l). TRP mRNA and TRP protein expression was measured using quantitative real-time RT-PCR and quantitative in-cell Western assay, respectively. Calcium influx and intracellular reactive oxygen species were measured using fluorescent dyes.

RESULTS

Administration of high d-glucose significantly increased reactive oxygen species. High d-glucose or peroxynitrite significantly increased the expression of TRP canonical type 1 (TRPC1), TRPC3, TRPC5, TRPC6, TRP melastatin type 6 (TRPM6), and TRPM7 mRNA and TRPC3 and TRPC6 proteins. High d-glucose plus tempol or high l-glucose did not affect TRP expression. Increased oxidative stress by lipopolysaccharide or tumor necrosis factor-alpha increased TRP mRNA expression, whereas the reduction of superoxide radicals using diphenylene iodonium significantly reduced TRP mRNA expression. Increased TRPC3 and TRPC6 protein expression was accompanied by increased 1-oleoyl-2-acetyl-sn-glycerol-induced calcium influx, which was blocked by the TRPC inhibitor 2-aminoethoxydiphenylborane. TRPC6 mRNA was significantly higher in monocytes from 18 patients with type 2 diabetes compared with 28 control subjects (P < 0.05).

CONCLUSIONS

High d-glucose-induced oxidative stress increases TRP expression and calcium influx in human monocytes, pointing to a novel pathway for increased activation of monocytes and hence atherosclerosis in patients with diabetes.

Telmisartan prevents weight gain and obesity through activation of peroxisome proliferator-activated receptor-delta-dependent pathways

Telmisartan shows antihypertensive and several pleiotropic effects that interact with metabolic pathways. In the present study we tested the hypothesis that telmisartan prevents adipogenesis in vitro and weight gain in vivo through activation of peroxisome proliferator-activated receptor (PPAR)-delta-dependent pathways in several tissues. In vitro, telmisartan significantly upregulated PPAR-delta expression in 3T3-L1 preadipocytes in a time- and dose-dependent manner. Other than enhancing PPAR-delta expression by 68.2+/-17.3% and PPAR-delta activity by 102.0+/-9.0%, telmisartan also upregulated PPAR-gamma expression, whereas neither candesartan nor losartan affected PPAR-delta expression. In vivo, long-term administration of telmisartan significantly reduced visceral fat and prevented high-fat diet-induced obesity in wild-type mice and hypertensive rats but not in PPAR-delta knockout mice. Administration of telmisartan did not influence food intake in mice. Telmisartan influenced several lipolytic and energy uncoupling related proteins (UCPs) and enhanced phosphorylated protein kinase A and hormone sensitive lipase but reduced perilipin expression and finally inhibited adipogenesis in 3T3-L1 preadipocytes. Telmisartan-associated reduction of adipogenesis in preadipocytes was significantly blocked after PPAR-delta gene knockout. Chronic telmisartan treatment upregulated the expressions of protein kinase A, hormone-sensitive lipase, and uncoupling protein 1 but reduced perilipin expression in adipose tissue and increased uncoupling protein 2 and 3 expression in skeletal muscle in wild-type mice but not in PPAR-delta knockout mice. We conclude that telmisartan prevents adipogenesis and weight gain through activation of PPAR-delta-dependent lipolytic pathways and energy uncoupling in several tissues.

Tissue expression of TRPC3 and TRPC6 in hypertensive Munich Wistar Frömter rats showing proteinuria

BACKGROUND

We investigated whether alterations of transient receptor potential canonical (TRPC) channel expression may be observed in tissues from Munich Wistar Frömter (MWF) rats showing proteinuria compared to control Wistar rats.

METHODS

TRPC expression was investigated in tissue from MWF and Wistar rats using quantitative real time PCR, immunoblotting, and immunohistochemistry.

RESULTS

Compared to Wistar rats MWF rats showed significantly increased systolic blood pressure and significantly higher left ventricle weight (each p < 0.01). Quantitative real time PCR revealed that TRPC3 transcripts were significantly higher in kidney cortex from MWF rats compared to Wistar rats (p < 0.01). TRPC3 transcripts were not significantly different in kidney medulla nor in aorta from both groups (p = n.s.). Furthermore, TRPC6 transcripts were significantly lower in kidney cortex from MWF rats compared to Wistar rats (p < 0.001). Immunoblotting showed that TRPC3 channel protein expression was also significantly higher in kidney cortex from MWF rats compared to Wistar rats (p < 0.01). There was a significant correlation of TRPC3 mRNA and a specific marker for endothelium, von Willebrand factor (vWF; Spearman r = 0.564; p < 0.01). We observed a significant correlation between the TRPC3 transcripts to TRPC6 transcripts ratio in kidney cortex and urinary albumin excretion (Spearman r = 0.785, p < 0.001).

CONCLUSION

Altered TRPC expression pattern in kidney cortex is associated with kidney damage in MWF rats showing hypertension and albuminuria.

Low expression of thiosulfate sulfurtransferase (rhodanese) predicts mortality in hemodialysis patients

OBJECTIVES

To test the hypothesis that impaired expression of the thiosulfate sulfurtransferase rhodanese is associated with oxidative stress and may predict mortality in hemodialysis patients.

DESIGN AND METHODS

Sixty-two hemodialysis patients were investigated to determine protein and mRNA expression of rhodanese in monocytes. Whole cell reactive oxygen species and mitochondrial superoxide production were measured by fluorescence spectrophotometry.

RESULTS

Compared to healthy subjects, hemodialysis patients showed significantly lower rhodanese mRNA and protein expression and significantly increased reactive oxygen species. Lower rhodanese protein expression was significantly associated with higher mitochondrial superoxide production. The hazard ratio for mortality in hemodialysis patients with rhodanese mRNA below compared to patients above the median was 2.22. Survival was shorter with rhodanese mRNA below compared to patients above the median.

CONCLUSION

Impaired rhodanese expression is associated with increased whole cell reactive oxygen species as well as higher mitochondrial superoxide production and predicts mortality in hemodialysis patients.

Hemodialysis versus peritoneal dialysis: a case control study of survival in patients with chronic kidney disease stage 5

It is still controversial whether the mode of dialysis or preexisting comorbidities may influence the prognosis of patients with chronic kidney disease stage 5. Therefore, we performed a prospective case control study to evaluate whether the mode of dialysis may influence outcome. We found 25 cases on peritoneal dialysis (PD) treatment and 75 age and sex-matched controls on hemodialysis (HD) treatment for more than 3 months. Analysis was by intention-to-treat. During the follow up of 58 months, 6 out of 25 patients (24%) died in the PD group, whereas in the HD group 26 out of 75 patients (35%) died (relative risk 0.69 [95% CI 0.32 to 1.49]; P = 0.46). Survival was not significantly different between the groups as indicated by Mantel-Cox log-rank test (hazard ratio 0.52 [95% CI 0.25 to 1.10]; P = 0.11). Multiple variable regression showed that age and diabetes mellitus, but not mode of dialysis, predicted death in patients with chronic kidney disease. It is concluded that age and comorbidities but not mode of dialysis are important to predict survival in patients with chronic kidney disease stage 5.

N-acetylcysteine improves arterial vascular reactivity in patients with chronic kidney disease

BACKGROUND

Patients with stage 5 chronic kidney disease show increased cardiovascular morbidity and mortality that are partly related to impaired arterial vascular reactivity. We investigated whether intravenous administration of the antioxidant acetylcysteine improves arterial vascular reactivity in these patients.

METHODS

Arterial vascular reactivity was determined during reactive hyperemia by photoplethysmography of digital pulse waves in a randomized, prospective, placebo-controlled cross-over study of 24 patients with stage 5 chronic kidney disease with and without infusion of acetylcysteine during hemodialysis. Acetylcysteine (5 g in 5% glucose in a final volume of 50 ml) was continuously administered intravenously during one hemodialysis session.

RESULTS

In the absence of acetylcysteine, the reflective index was 38.5 +/- 9.4 (mean +/- SD; n = 24) at baseline and 33.8 +/- 9.9 during reactive hyperemia, immediately after the hemodialysis session; thus there was no significant vasodilatation (p > 0.05), indicating impaired arterial vascular reactivity in these patients. However, when the hemodialysis session in the same patients was performed in the presence of acetylcysteine, the reflective index significantly decreased from 37.9 +/- 8.6 at baseline to 30.2 +/- 10.3 during reactive hyperemia (n = 24; p < 0.01).

CONCLUSION

The present study shows that intravenous administration of acetylcysteine during hemodialysis significantly improves arterial vascular reactivity during reactive hyperemia.

Mortality risk in hemodialysis patients with increased arterial stiffness is reduced by attainment of classical clinical performance measures

BACKGROUND

We determined whether attainment of classical clinical performance measures for hemodialysis care improves survival in hemodialysis patients with increased arterial stiffness.

METHODS

We performed a prospective cohort study of 538 hemodialysis patients with a median follow-up of 19 months (interquartile range 8-30). Arterial stiffness was measured using applanation tonometry. Clinical performance measure targets were hemoglobin value >or=110 g/l, serum albumin value >or=37 g/l and measured single-pool Kt/V urea value >or=1.2.

RESULTS

During follow-up, 217 patients (40%) died. In non-survivors, arterial stiffness of large arteries (S1) was significantly higher compared with survivors (p = 0.0002). An analysis of hemodialysis patients who were alive 18 months after inclusion into the study showed that survival was significantly longer in those patients that met >or=2 clinical performance measure targets compared with patients that met <or=1 target (chi(2) 4.13; p = 0.04). Better attainment of classical clinical performance measures showed a 54% mortality risk reduction.

CONCLUSION

S1 predicted mortality in hemodialysis patients. However, better attainment of classical clinical performance measures significantly improved long-term outcome in hemodialysis patients despite their pronounced increase in arterial stiffness.

Evidence that kidney function but not type 2 diabetes determines retinol-binding protein 4 serum levels

OBJECTIVE

It has been suggested that retinol-binding protein 4 (RBP4) links adiposity, insulin resistance, and type 2 diabetes. However, circulating RBP4 levels are also affected by kidney function. Therefore, the aim of this study was to test whether RBP4 serum levels are primarily associated with kidney function or type 2 diabetes.

RESEARCH DESIGN AND METHODS

RBP4 serum concentration was determined by enzyme-linked immunosorbent assay in 126 nondiabetic and 104 type 2 diabetic subjects. The study population was divided according to estimated glomerular filtration rate (eGFR) into the following groups: eGFR >90 ml/min per 1.73 m(2) (n = 53), 60-90 ml/min per 1.73 m(2) (n = 90), 30-60 ml/min per 1.73 m(2) (n = 38), and <30 ml/min per 1.73 m(2) (n = 49). Each group was subdivided into nondiabetic and type 2 diabetic subjects.

RESULTS

RBP4 serum concentration was elevated (2.65 vs. 2.01 micromol/l; P < 0.001) and eGFR was reduced (56 vs. 74 ml/min per 1.73 m(2); P < 0.001) in type 2 diabetic vs. nondiabetic subjects, respectively. By stratifying for eGFR, no more differences in RBP4 serum concentration were detectable between type 2 diabetic and nondiabetic subjects. A linear regression analysis revealed an influence of eGFR (r = -0.477; P < 0.001) but not A1C (r = 0.093; P = 0.185) on RBP4 serum concentration.

CONCLUSIONS

Existing human data showing elevated RBP4 levels in type 2 diabetic patients may be the result of moderate renal insufficiency rather than support for the suggestion that RBP4 links obesity to type 2 diabetes.

Increased transient receptor potential canonical type 3 channels in vasculature from hypertensive rats

We tested the hypothesis that transient receptor potential canonical type 3 (TRPC3) channels are increased in vascular smooth muscle cells and aortic tissue from spontaneously hypertensive rats (SHR) compared with normotensive Wistar Kyoto rats. Expression of TRPC3 was analyzed by immunohistochemistry and Western blotting. TRPC3 gene knockdown was performed by specific small interfering RNA and TRPC3 overexpression using the pAdEasy-1 system. Cytosolic calcium was measured using fluorescence spectrophotometry and vasoconstriction of aortic rings using a force transducer. In SHR, the expression of TRPC3 channel protein was significantly higher in aortic rings (1.48+/-0.05 versus 1.00+/-0.06; each n=6; P<0.01) and vascular smooth muscle cells (1.28+/-0.08 versus 1.00+/-0.03; each n=6; P<0.05) compared with Wistar Kyoto rats. Knockdown of TRPC3 gene expression by specific small interfering RNA significantly reduced the angiotensin II-induced calcium influx by 30+/-3% (n=6; P<0.01), whereas TRPC3 overexpression significantly increased it by 55+/-3% (n=6; P<0.01). The angiotensin II-induced calcium increase was significantly enhanced in vascular smooth muscle cells from SHR compared with Wistar Kyoto rats, even in the presence of the calcium channel blocker amlodipine. Angiotensin II significantly elevated the TRPC3 channel protein expression in vascular smooth muscle cells from SHR from 1.28+/-0.08 to 1.61+/-0.08 (each n=6; P<0.01). Angiotensin II-induced TRPC3 expression was prevented by telmisartan. Administration of telmisartan to SHR for 4 weeks significantly reduced blood pressure, angiotensin II-induced vasoconstriction, and TRPC3 channel protein expression in aortic tissue. TRPC3 expression was not significantly reduced after reduction of blood pressure in SHR using amlodipine. In conclusion, we give experimental evidence that increased TRPC3 channel protein expression in the vasculature is important for elevated blood pressure.