Disruption of the type 2 dopamine receptor gene causes a sodium-dependent increase in blood pressure in mice.

BACKGROUND: Dopamine D(2) receptors (D(2)Rs) are expressed in the kidney. It has not been determined whether D(2)Rs are involved in the mechanism of sodium handling and blood pressure (BP) control. METHODS: The function of D(2)Rs was investigated in mice disrupted with D(2)R gene (D(2)KO mice). Six-week-old male D(2)KO mice and wild-type (WT) mice were fed high-salt (4% NaCl) or low-salt (0.01% NaCl) diets for 8 weeks. RESULTS: Before starting the metabolic diet, there were no significant differences in body weight, food consumption, and 24-h urine excretions of creatinine, sodium and potassium. The high-salt diet caused a significant elevation in systolic BP in D(2)KO mice but not in WT mice. Calculation of sodium and potassium balances revealed a significantly high level of sodium retention in D(2)KO mice placed on the high-salt diet. Twenty-four-hour urine norepinephrine excretions and heart rates, indicators of sympathetic activity, were not different in D(2)KO and WT mice on the high-salt diet. Administration of nemonapride, a specific D(2)-like receptor antagonist, to WT mice given 0.9% NaCl in drinking water caused suppression of urinary sodium excretion but had no effect in mice without salt loading. CONCLUSIONS: These results suggest that D(2) receptors promote sodium excretion during a period of high salt intake. A defect in this mechanism may result in sodium-dependent BP elevation.

Intravenous vitamin D therapy reduces PTH-(1-84)/large C fragments ratio in chronic hemodialysis patients.

BACKGROUND: Renal osteodystrophy is one of the major complications in patients with chronic renal failure. Large C-PTH fragments are secreted from the parathyroid glands and exert antagonistic actions against PTH-(1-84). The PTH-(1-84)/large C-PTH fragments ratio reflects both biosynthesis and processing of PTH; however the alteration of the ratio under vitamin D therapy has not been investigated. METHODS: Seventeen hemodialysis patients with intact PTH levels of >300 pg/ml were enrolled. Calcitriol or maxacalcitol were administered intravenously for 78 weeks. Intact PTH, PTH-(1-84), and the PTH-(1-84)/large C-PTH fragments ratio were measured at 0, 13, 26, 52 and 78 weeks. RESULTS: Intact PTH and PTH-(1-84) levels, which were 492.0 +/- 115.7 and 303.4 +/- 105.4 pg/ml, respectively, at baseline, significantly decreased at the end of the study to 268.9 +/- 121.9 (p < 0.0001) and 190.7 +/- 106.9 pg/ml (p = 0.0008), respectively. In contrast, large C-PTH fragments, which were 152.7 +/- 53.5 pg/ml at baseline, did not significantly change at 78 weeks (144.5 +/- 72.2 pg/ml, p = 0.7612). Consequently, the PTH-(1-84)/large C-PTH fragments ratio was significantly reduced from 2.25 +/- 1.31 to 1.47 +/- 0.89 (p = 0.0004). CONCLUSION: The PTH-(1-84)/large C-PTH fragments ratio reflects the change of PTH biosynthesis, processing and secretion from the parathyroid glands, and it may be a beneficial marker to evaluate the overall biological PTH action and predict bone turnover status in hemodialysis patients under intravenous vitamin D therapy.

Long-term use of vitamin E-coated polysulfone membrane reduces oxidative stress markers in haemodialysis patients.

BACKGROUND: Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and an independent predictor of overall mortality and cardiovascular outcome in haemodialysis (HD) patients. In the present study, we compared the effects of a vitamin E-coated polysulfone membrane (PSE) and a non-vitamin E-coated polysulfone membrane (PS) on oxidative stress markers such as ADMA. METHODS: Thirty-one HD patients were enrolled to this investigation. They were allocated into two groups: in the PSE group (n = 16), PSE was used for 6 months, followed by PS for an additional 12 months; in the PS group (n = 15), PS was used for the entire observation period. Plasma ADMA, oxidized low density lipoprotein (Ox-LDL) and malondialdehyde LDL (MDA-LDL) levels were measured at baseline, 3, 6, 12 and 18 months. Plasma ADMA in peritoneal dialysis (PD) patients and in healthy individuals was also measured. RESULTS: Predialysis concentrations of ADMA (0.72+/- 0.13 nmol/ml) were significantly higher in the HD group than in both PD patients (0.63+/-0.10 nmol/ml, P<0.01) and healthy individuals (0.44+/-0.01 nmol/ml, P<0.0001). Treatment with PSE for 6 months significantly reduced predialysis levels of ADMA (0.54+/-0.09 nmol/ml) compared with baseline (0.74+/-0.12 nmol/ml; P<0.01). Predialysis levels of Ox-LDL and MDA-LDL after 6 months therapy with PSE were also significantly lower than baseline values. Treatment with PS subsequent to treatment with PSE again increased ADMA, Ox-LDL and MDA-LDL back to baseline levels. In the PS group, ADMA, Ox-LDL and MDA-LDL levels remained unchanged during the entire treatment period of 18 months. CONCLUSIONS: We confirmed that use of PSE reduced ADMA that had accumulated in HD patients. This finding indicates that PSE exerts anti-oxidant activity. A randomized controlled study will be required to determine whether PSE prevents cardiovascular diseases and other dialysis-related complications by reducing oxidative stress.

Elevated serum interleukin-18 levels might reflect the high risk of hospitalization in patients on peritoneal dialysis.

BACKGROUND: Interleukin (IL)-18 is a potent pro-inflammatory cytokine and plays a central role in atherosclerotic plaque rupture and accelerates atherosclerosis. AIM: The aim of this study was to determine serum IL-18 levels in patients on peritoneal dialysis (PD) and to assess their relationship with hospitalization. METHODS: Forty-three PD patients and 20 healthy individuals were enrolled in this study. We investigated the relationship of the serum concentrations of IL-18 and other well-established atherosclerotic markers, such as asymmetric dimethylarginine (ADMA). Hospitalization data from over a 18-month period were prospectively obtained on all 43 PD patients. Classic factors were entered into a Cox regression model to predict first hospitalization. RESULTS: The serum levels of IL-18 in patients on PD were significantly higher than those of healthy individuals (228.5 +/- 140.3 pg/mL vs 154.8 +/- 44.7 pg/mL, P < 0.05, respectively). Furthermore, serum IL-18 levels showed a positive correlation with duration of PD, serum beta2 microglobulin and serum ADMA levels. Mean serum levels of IL-18 were significantly higher among patients who had experienced at least one hospitalization than those who had not (279.9 +/- 164.3 vs 158.5 +/- 43.9 pg/mL, P = 0.0426). Furthermore, the relative risk for first hospitalization for each increase in IL-18 (pg/mL) levels was associated with a 1.182 (95% confidence interval, 1.012-1.364; P = 0.0071) increase in the risk for future hospitalization events. CONCLUSION: The present study suggests the elevated serum IL-18 levels might increase the risk for future hospitalization in patients on PD.

Dopamine D2 receptor modulates sodium handling via local production of dopamine in the kidney.

We have recently demonstrated that a deletion of the dopamine D2 receptor gene caused suppression of urinary sodium excretion and salt-sensitive elevation of blood pressure in mice. In order to understand the mechanisms underlying this impaired sodium excretion, we studied renal dopamine production and dopamine-induced sodium excretion in 20- to 30-week-old male D2-receptor knockout (D2KO) mice and age- and sex-matched wildtype (WT) mice. Renal local dopamine synthesis, examined by 24-h urine free dopamine excretion (UDAV), was significantly (p < 0.05) reduced in D2KO mice compared to that in WT mice (D2KO versus WT: 1.06 +/- 0.2 versus 1.5 +/- 0.3 ng/mg creatinine). Such a difference between D2KO and WT mice was also observed after oral administration of 3,4-dihydroxyphenylalanine (L-DOPA), a precursor of dopamine, at 5 mg/kg per day for 24 h. Furthermore, activity of aromatic 1-amino acid decarboxylase, a dopamine synthetase, was significantly suppressed in D2KO mice. Next, we examined changes in 24-h urine flow (UV) and 24-h sodium excretion (UNaV) during chronic infusion of dopamine at sub-pressor doses (3-4 microg/kg per min, sq.) or a vehicle via an osmotic pump. Urine flow in 24 h and UNaV were significantly (p < 0.05) smaller in D2KO mice infused with vehicle than in WT mice infused with vehicle (UV: 210 +/- 43 versus 650 +/- 163 microl/day; UNaV: 20.6 +/- 13.2 versus 44.4 +/- 21.6 microEq/day). After administration of dopamine, UV and UNaV in D2KO mice were restored to a level similar to that in WT mice. These results indicate that D2-dopamine receptors play a significant role in renal local dopamine synthesis and that a shortage of dopamine was, at least in part, responsible for the suppression of UV and UNaV in D2KO mice. However, we could not conclude from the present study whether renal tubular sodium reabsorption is intact in D2KO mice because the baseline dopamine contents in kidneys of D2KO mice and WT mice may be different.

The critical role of SRC homology domain 2-containing tyrosine phosphatase-1 in recombinant human erythropoietin hyporesponsive anemia in chronic hemodialysis patients.

The molecular mechanism of anemia that is hyporesponsive to recombinant human erythropoietin (rHuEPO) in hemodialysis patients without underlying causative factors has not been investigated fully in hematopoietic stem cell system. Circulating CD34+ cells (1 x 10(4)) were isolated from rHuEPO hyporesponsive hemodialysis patients (EPO-H; n = 9), patients who were responsive to rHuEPO (EPO-R; n = 9), and healthy control subjects (n = 9). The patients with known causes of EPO hyporesponsiveness were eliminated from the current study. The cells were cultured in STEM PRO 34 liquid medium, supplemented with rHuEPO, IL-3, stem cell factor, and granulocyte-macrophage colony stimulating factor for 7 d and then transferred to a semisolid methylcellulose culture medium for performing burst forming unit-erythroid (BFU-E) colony assay. Expression of src homology domain 2 (SH2)-containing tyrosine phosphatase-1 (SHP-1), phosphorylated Janus kinase 2 (p-JAK2), and phosphorylated signal transducer and activator of transcription 5 (p-STAT5) was assessed with Western blot analysis. In EPO-H patients, SHP-1 antisense or scrambled S-oligos were included in the culture medium, and its effects were evaluated. The number of circulating CD34+ cells was not statistically different among the three groups, and their proliferation rates were similar for 7 d in culture. However, BFU-E colonies were significantly decreased in EPO-H patients compared with EPO-R and control groups. The mRNA and protein expression of SHP-1 and p-SHP-1 was significantly increased, whereas that of p-STAT5 was reduced in EPO-H patients. The inclusion of SHP-1 antisense S-oligo in culture suppressed SHP-1 protein expression associated with p-STAT5 upregulation, increase in p-STAT5-regulated genes, and partial recovery of BFU-E colonies. In EPO-H hemodialysis patients, the EPO signaling pathway is attenuated as a result of dephosphorylation of STAT5 via upregulation of SHP-1 phosphatase activity, and SHP-1 may be a novel target molecule to sensitize EPO action in these patients.

Significance of 8-hydroxy-2'-deoxyguanosine levels in patients with chronic renal failure.

The aim of this study was to determine the significance of 8-hydroxy-2'-deoxyguanosine (8-OHdG), which is known as a marker of oxidative stress in vivo, in patients with chronic renal failure (CRF). Fifty-one non-dialysed CRF patients (29 men and 22 women; mean +/- SD age, 57.8 +/- 12.8 years) who were under dietary therapy for at least 6 months were enrolled in the study. Both serum and urinary 8-OHdG levels were measured by using high-sensitive enzyme-linked immunosorbent assay (ELISA) kits. We examined the relationship between 8-OHdG levels and clinical indices in patients with CRF. As a result, the serum 8-OHdG level was strongly correlated with serum levels of urea nitrogen (UN; r = 0.58; P < 0.0001), creatinine (Cr; r = 0.53; P < 0.0001), and beta2-microglobulin (beta2-MG; r = 0.54; P < 0.0001). Furthermore, the serum 8-OHdG level was inversely correlated with creatinine clearance (Ccr; r = -0.54; P < 0.0001). In contrast, urinary 8-OHdG level was not correlated with any of the clinical parameters. This is the first report of 8-OHdG level determination in patients with CRF. It is suggested that serum 8-OHdG level is not sufficient as a marker of oxidative damage in patients with CRF, and it should be corrected according to the residual renal function to estimate the accurate degree of oxidative stress.