Morimasa Amemiya

Circulating endothelial progenitor cells are reduced in hemodialysis patients

SUMMARY Objective: The risk of cardiovascular disease in hemodialysis patients is far greater than in the general population. Endothelial progenitor cells (EPCs) circulating in the peripheral blood contribute to neovascularization in the ischemic tissue. EPCs are considered to be included in CD34 positive (CD34+) or AC133 positive (AC133+) mononuclear cells (MNCs). This studys aim was to determine the number and functional activity of EPCs in hemodialysis patients and age-matched control subjects. Methods: The numbers of CD34+ MNCs and AC133+ MNCs in the peripheral blood were quantified by flow cytometry. The peripheral blood EPCs were also examined by an in vitro culture assay. The levels of serum vascular endothelial growth factor (VEGF) were measured by sandwich enzyme immunoassay. Results: The numbers of CD34+ MNCs and AC133+ MNCs were significantly reduced by 56% and 49%, respectively, in hemodialysis patients (n = 50) compared with control subjects (n = 36). The number of EPCs determined by the culture assay was also significantly reduced by 41% in hemodialysis patients compared with control i subjects. Multivariate analysis revealed that none of the atherosclerotic risk factors were independent predictors of reduced CD34+ MNC counts. The serum VEGF levels in hemodialysis patients were not different from those in control subjects and did not correlate with CD34+ MNC counts. Conclusion: Circulating EPCs are significantly reduced in hemodialysis patients, which might be related to impaired neovascularization and cardiovascular disease in these patients.

Activation of protein kinase A acutely inhibits and phosphorylates Na/H exchanger NHE-3

In the mammalian renal proximal tubule, protein kinase A (PKA) plays an important role in mediating hormonal regulation of apical membrane Na/H exchanger activity. This exchanger is likely encoded by NHE-3. The present studies examined regulation of NHE-3 by PKA. NHE-3 was stably expressed in Na/H exchanger-deficient fibroblasts (AP-1/NHE-3 cells). PKA activation (0.1 mM 8-BrcAMP x 20 min) inhibited NHE-3 activity by 39% (P < 0.01) with no change in NHE-3 protein abundance in the plasma membrane. To define the structural requirements for PKA-mediated inhibition, full-length NHE-3 and a cytoplasmic domain-truncated mutant (NHE-3 delta cyto) were expressed in Xenopus laevis oocytes. 8-BrcAMP inhibited NHE-3 activity by 27% (P < 0.05), an effect that was blocked by 10(-7) M PKA inhibitor peptide. NHE-3 delta cyto had baseline activity similar to that of full-length NHE-3 but its activity was not regulated by 8-BrcAMP. The purified recombinant cytoplasmic domain of NHE-3 was phosphorylated in vitro by the catalytic subunit of PKA on serine residues. In AP-1/NHE-3 cells, NHE-3 was immunoprecipitated as a approximately 87-kD phosphoprotein. Addition of 0.1 mM 8-BrcAMP increased the phosphocontent of NHE-3 by threefold. In summary, acute activation of PKA inhibits NHE-3 activity, an effect that is likely mediated by phosphorylation of its cytoplasmic domain.

Chronic hyperosmolality increases NHE3 activity in OKP cells.

This study investigated the effect of chronic hypertonicity on the OKP cell Na/H antiporter, encoded by Na/H exchanger 3 (NHE3). Chronic (48 h) increases in extracellular glucose, mannitol, or raffinose concentration caused a significant increase in Na/H antiporter activity, while increases in urea concentration were without effect. This effect was seen with changes in osmolality of only 20 mOsm/liter, a magnitude that is observed clinically in poorly controlled diabetes mellitus. Increases in mannitol concentration acutely inhibited and chronically stimulated Na/H antiporter activity. The increase in Na/H antiporter activity induced by hypertonic incubation was resistant to 10(-7) and 5 x 10(-6) M but inhibited by 10(-4) M ethylisopropyl amiloride, consistent with regulation of NHE3. In addition, hypertonicity increased total cellular and plasma membrane NHE3 protein abundance twofold, with only a small increase in NHE3 mRNA abundance. We conclude that chronic pathophysiologically relevant increases in tonicity lead to increases in NHE3 protein abundance and activity. This may be responsible for increased proximal tubule apical membrane Na/H antiporter activity in poorly controlled diabetes mellitus, which could then contribute to hypertension, glomerular hyperfiltration and diabetic nephropathy.

AVP inhibits LPS- and IL-1β-stimulated NO and cGMP via V1 receptor in cultured rat mesangial cells

The present study examined how arginine vasopressin (AVP) affects nitric oxide (NO) metabolism in cultured rat glomerular mesangial cells (GMC). GMC were incubated with test agents and nitrite, and intracellular cGMP content, inducible nitric oxide synthase (iNOS) mRNA, and iNOS protein were analyzed by the Griess method, enzyme immunoassay, and Northern and Western blotting, respectively. AVP inhibited lipopolysaccharide (LPS)- and interleukin-1β (IL-1β)-induced nitrite production in a dose- and time-dependent manner, with concomitant changes in cGMP content, iNOS mRNA, and iNOS protein. This inhibition by AVP was reversed by V1- but not by oxytocin-receptor antagonist. Inhibition by AVP was also reproduced on LPS and interferon-γ (IFN-γ). Protein kinase C (PKC) inhibitors reversed AVP inhibition, whereas PKC activator inhibited nitrite production. Although dexamethasone and pyrrolidinedithiocarbamate (PDTC), inhibitors of nuclear factor-κB, inhibited nitrite production, further inhibition by AVP was not observed. AVP did not show further inhibition of nitrite production with actinomycin D, an inhibitor of transcription, or cycloheximide, an inhibitor of protein synthesis. In conclusion, AVP inhibits LPS- and IL-1β-induced NO production through a V1 receptor. The inhibitory action of AVP involves both the activation of PKC and the transcription of iNOS mRNA in cultured rat GMC.

Incubation of OKP cells in low-K+ media increases NHE3 activity after early decrease in intracellular pH

Chronic hypokalemia increases the activity of proximal tubule apical membrane Na+/H+antiporter NHE3. The present study examined the effect of the incubation of OKP cells (an opossum kidney, clone P cell line) in control medium {K+ concn ([K+]) = 5.4 mM} or low-K+ medium ([K+] = 2.7 mM) on NHE3. The activity of an ethylisopropyl amiloride-resistant Na+/H+antiporter, whose characteristics were consistent with those of NHE3, was increased in low-K+ cells beginning at 8 h. NHE3 mRNA and NHE3 protein abundance were increased 2.2-fold and 62%, respectively, at 24 h but not at 8 h. After incubation in low-K+ medium, intracellular pH (pHi) decreased by 0.27 pH units (maximum at 27 min) and then recovered to the control level. Intracellular acidosis induced by 5 mM sodium propionate increased Na+/H+antiporter activity at 8 and 24 h. Herbimycin A, a tyrosine kinase inhibitor, blocked low-K+- and sodium propionate-induced activation of the Na+/H+antiporter at 8 and 24 h. Our results demonstrate that low-K+ medium causes an early decrease in pHi, which leads to an increase in NHE3 activity via a tyrosine kinase pathway.Chronic hypokalemia increases the activity of proximal tubule apical membrane Na+/H+ antiporter NHE3. The present study examined the effect of the incubation of OKP cells (an opossum kidney, clone P cell line) in control medium (K+ concn ([K+]) = 5.4 mM) or low-K+ medium ([K+] = 2.7 mM) on NHE3. The activity of an ethylisopropyl amiloride-resistant Na+/H+ antiporter, whose characteristics were consistent with those of NHE3, was increased in low-K+ cells beginning at 8 h. NHE3 mRNA and NHE3 protein abundance were increased 2.2-fold and 62%, respectively, at 24 h but not at 8 h. After incubation in low-K+ medium, intracellular pH (pHi) decreased by 0.27 pH units (maximum at 27 min) and then recovered to the control level. Intracellular acidosis induced by 5 mM sodium propionate increased Na+/H+ antiporter activity at 8 and 24 h. Herbimycin A, a tyrosine kinase inhibitor, blocked low-K+- and sodium propionate-induced activation of the Na+/H+ antiporter at 8 and 24 h. Our results demonstrate that low-K+ medium causes an early decrease in pHi, which leads to an increase in NHE3 activity via a tyrosine kinase pathway.

Glucagon Acutely Inhibits but Chronically Activates Na+/H+ Antiporter 3 Activity in OKP Cells

Background: We previously found that the Na+/H+ exchanger 3 (NHE3) is localized in the apical membrane of the rat renal proximal tubule and thick ascending limb of Henle. In the present study, we examined the direct effect of glucagon on the opossum kidney P (OKP) cell Na+/H+ antiporter, encoded by NHE3. Methods: Na+/H+ antiporter activity was measured as the rate of cell pH recovery from an acid load using 2′,7′-bis(carboxyethyl)-5(6)-carboxyfluorescein. Northern blot and Western blot analyses were performed using OKP NHE3 cDNA and anti-OKP-NHE3 antibodies. Results: Glucagon (1 ng/ml) acutely (1 h) inhibited, but chronically (24 h) activated NHE3 activity in OKP cells. These effects were blocked by either KT5720 or RpcAMP [protein kinase A (PKA) inhibitors], and mimicked by 10–4M dibutyryl-cAMP. Both NHE3 mRNA and protein abundance increased with the 24-hour incubation in glucagon or dibutyryl-cAMP. Cycloheximide did not prevent a significant increase in NHE3 activity at 24 h. We therefore examined NHE3 protein abundance in the surface membrane by the biotinylation mehtod. cAMP or glucagon significantly increased NHE3 protein abundance in the surface membrane when incubated with cycloheximide for 24 h. Conclusions: Glucagon acutely inhibits but chronically activates NHE3 activity in OKP cells via a PKA-dependent pathway. Both protein-synthesis-dependent and -independent mechanisms play important roles in the chronic activation of NHE3.

A case of encapsulating peritoneal sclerosis at the clinical early stage with high concentration of matrix metalloproteinase-2 in peritoneal effluent.

In encapsulating peritoneal sclerosis (EPS), matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases are involved in the remodeling of peritoneal tissue. We measured the MMP-2 concentration in the peritoneal effluents of a patient with EPS who discontinued continuous ambulatory peritoneal dialysis (CAPD) therapy because of ultrafiltration failure and/or underdialysis. First, we report a 58-year-old female patient who discontinued CAPD therapy because of underdialysis. Several months after cessation of CAPD, she complained of slightly blood-colored ascites and had an elevated level of C-reactive protein (CRP) in plasma. She was diagnosed as having clinical early-stage EPS. Peritoneal effluents drained from this case, and from 11 patients who discontinued CAPD therapy because of ultrafiltration failure and/or underdialysis, and who underwent peritoneal lavage with 1.5% dextrose peritoneal dialysis fluid for several months, were analyzed by gelatin zymography. MMP-2 concentration was also measured by enzyme-linked immunosorbent assay (ELISA). MMP-2 concentration in peritoneal effluent of this patient was highest compared with that of the other patients. There was some tendency of a positive correlation between MMP-2 concentration per 1 g protein and D/Pcr, and was negative correlation between MMP-2 concentration per 1 g of protein and D/D0 glucose. We concluded that MMP-2 is involved in the peritoneal remodeling of long-term CAPD therapy and the progression of EPS.

Stimulation of NHE3 in OKP Cells by an Autocrine Mechanism

Background/Aims: Chronic hypokalemia increases NHE3 activity in OKP cells. The aim of the present study was to determine whether an autocrine mechanism is involved in this activation. Methods: After incubation of OKP cells in normal-K⁺ and low-K⁺ media for 24 h, the potassium concentration in the low-K⁺ media was adjusted to a normal level. These conditioned media were then used as the normal-K⁺ and low-K⁺ supernatants. Other OKP cells were incubated in these normal-K⁺ and low-K⁺ supernatants and the mechanism of Na⁺/H⁺ antiporter activation was examined. Results: The EIPA-resistant Na⁺/H⁺ antiporter activity of OKP cells increased after 4 h incubation in the low-K⁺ supernatant, and the amount of NHE3 protein increased at 24 h. Since both BQ788 and saralasin blocked this antiporter activation, the supernatant concentration of endothelin I (ET-I) and angiotensin II (Ang-II) were measured. The ET-I concentration was reduced, but the Ang-II concentration remained unchanged. There was a significant association between a reduction in the ET-I concentration and an increase in Na⁺/H⁺ antiporter activity, but only when Ang-II was present in the supernatant. Conclusion: An autocrine mechanism is involved in the activation of NHE3 in OKP cells. Both ET-I and Ang-II play a role in this activation.

The Anti-Platelet Agent, Ticlopidine, Upregulates Interleukin-1-Beta-Stimulated Nitric Oxide Production in Cultured Rat Vascular Smooth Muscle Cells

Background: Hemodialysis patients who had been treated with anti-platelet aggregation drugs, including ticlopidine, sometimes developed hypotension. The mechanism by which ticlopidine lowers the blood pressure in hemodialysis patients is unclear. To elucidate the mechanism of the action of this drug, we investigated cytokine-stimulated nitric oxide (NO) metabolism by ticlopidine in cultured rat vascular smooth muscle cells (VSMC). Methods: Nitrite, a stable metabolite of NO, and intracellular cAMP and cGMP contents were assayed by the Griess method and enzyme immunoassay, respectively. iNOS mRNA and protein expressions were analyzed by Northern blotting and Western blotting. Results: Ticlopidine enhanced interleukin-1β (IL-1β)-induced nitrite production in a dose- and time-dependent manner. The mRNA and protein expressions of inducible NO synthase were upregulated by ticlopidine in a dose- and time-dependent manner. IL-1β alone stimulated both intracellular cAMP and cGMP contents, and the addition of ticlopidine further enhanced their contents. KT 5720, a selective inhibitor of protein kinase A, but not KT 5823, a selective inhibitor of protein kinase G, abolished the enhancement of IL-1β-induced nitrite production by ticlopidine. In addition, a phosphodiesterase inhibitor, isobutylmethylxanthine, enhanced IL-1β and ticlopidine induced nitrite production. Conclusion: We concluded that ticlopidine enhanced the IL-1β-induced NO production via cAMP and subsequent activation of protein kinase A in cultured rat VSMC.

Effectiveness of a fixed combination formula of ombitasvir/paritaprevir/ritonavir for hepatitis C virus infection in patients on maintenance haemodialysis

A fixed‐dose formula that combines Ombitasvir (OBV), Paritaprevir (PTV) and Ritonavir (RTV) has been launched into the field of anti‐HCV therapy in Japan for patients infected with HCV genotypes 1 and 2 in 2015. However, little is yet known as to the efficacy and safety of this novel therapy in patients on maintenance haemodialysis (HD). The present report describes a preliminary experience in 10 patients (five males and five females) who underwent maintenance HD. All of them had HCV genotype 1b, without having the resistance‐associated variants at Y93 or L31 in the nonstructural proteins 5A (NS5A) region. After the treatment, eight patients successfully achieved virus eradication and sustained a virological response at 12 weeks (SVR12). In addition, mac‐2 binding protein glycosylation isomer (M2BPGi), a biomarker for liver fibrosis, was reduced after the therapy. Two patients withdrew from the therapy due to the development of erythema multiforme and a strong drowsiness, respectively. These results suggest that triple therapy combining OBV, PTV and RTV is effective in achieving SVR12 in most of the HCV‐infected patients on HD. In addition, this combination therapy contributed to retard the progression of liver fibrosis. However, we suggest that further trial will be required to establish its clinical efficacy and safety.