Akira Owada

Immunohistochemical localization of V2 vasopressin receptor along the nephron and functional role of luminal V2 receptor in terminal inner medullary collecting ducts.

We investigated immunohistochemical localization of V2 vasopressin receptor along the nephron using a specific polyclonal antibody. Staining was observed in some of thick ascending limbs and all of principal and inner medullary collecting duct (IMCD) cells. Not only basolateral but also luminal membrane was stained in collecting ducts, especially in terminal IMCD (tIMCD). To learn the functional role of luminal V2 receptor in tIMCD, we studied the luminal effects of arginine vasopressin (AVP) on osmotic water permeability (Pf), urea permeability (Pu), and cAMP accumulation using isolated perfused rat tIMCD. In the absence of bath AVP, luminal AVP caused a small increase in cAMP accumulation, Pf and Pu, confirming the presence of V2 receptor in the lumen of tIMCD. In contrast, luminal AVP inhibited Pf and Pu by 30-65% in the presence of bath AVP by decreasing cAMP accumulation via V1a or oxytocin receptors and by an unknown mechanism via V2 receptors in the luminal membrane of tIMCD. These data show that V2 receptors are localized not only in the basolateral membrane but also in the luminal membrane of the distal nephron. Luminal AVP acts as a negative feedback system upon the basolateral action of AVP in tIMCD.

Endothelin (ET)-3 stimulates cyclic guanosine 3',5'-monophosphate production via ETB receptor by producing nitric oxide in isolated rat glomerulus, and in cultured rat mesangial cells.

We investigated the effects of endothelins on receptor-mediated cyclic nucleotide metabolism in rat glomerulus, inner medullary collecting duct (IMCD), and also in cultured rat glomerular mesangial cells. Endothelin (ET)-3 dose-dependently stimulated cGMP accumulation in glomerulus, which was higher than that of ET-1 or ET-2. ETB receptor agonist IRL 1620 produced cGMP in a dose-dependent manner, mimicking the effect of ET-3. ETA receptor antagonist BQ123-Na did not inhibit ET-3- or IRL 1620-stimulated cGMP generation. NG-monomethyl-L-arginine (L-NMMA) significantly inhibited ET-3- or IRL 1620-induced cGMP production, suggesting that ET-3- or IRL 1620-stimulated cGMP generation was mediated through nitric oxide (NO). Intracellular Ca chelator BAPTA/AM and calmodulin antagonist W-7, but not Ca channel blocker nicardipine, significantly inhibited ET-3- or IRL 1620-induced cGMP generation. In cultured rat mesangial cells, ET-3 stimulated cGMP generation through NO in the presence of fetal calf serum, which was not inhibited by addition of BQ123-Na. In IMCD, ET-3 had no stimulative effect on cGMP generation. We conclude that ET-3 stimulates NO-induced cGMP generation through ETB receptor in glomerulus. This effect seems to be mediated through intracellular Ca/calmodulin, but not through Ca influx via L-type Ca channel. Mesangial cells can be a source of NO coupled to ETB receptor activation in glomerulus. From these results, mesangial ETB receptor may work to counteract the vasoconstrictive effect of endothelin caused via ETA receptor in glomerulus.

Accumulation of indoxyl-β-D-glucuronide in uremic serum : Suppression of its production by oral sorbent and efficient removal by hemodialysis

We identified and quantified indoxyl-beta-D-glucuronide in uremic serum and urine to determine the metabolism of indoles including indoxyl sulfate in uremic patients. Serum levels of indoxyl-beta-D-glucuronide were markedly increased in undialyzed uremic patients, in patients on hemodialysis, and in patients on continuous ambulatory peritoneal dialysis. Urinary excretion of indoxyl-beta-D-glucuronide was also increased in undialyzed uremic patients. Urinary indoxyl-beta-D-glucuronide was significantly correlated with serum indoxyl sulfate, indicating that a high serum level of indoxyl sulfate leads to the enhanced synthesis of indoxyl-beta-D-glucuronide. Oral sorbent (AST-120) administration markedly decreased the serum and urine levels of indoxyl-beta-D-glucuronide as well as indoxyl sulfate in the undialyzed uremic patients. Serum indoxyl-beta-D-glucuronide could be efficiently removed by hemodialysis despite its high protein-binding ratio of about 50%. In conclusion, the serum level of indoxyl-beta-D-glucuronide increases in uremic patients due to renal insufficiency and its increased production. The production of indoxyl-beta-D-glucuronide can be suppressed by oral sorbent treatment, and serum indoxyl-beta-D-glucuronide can be efficiently removed by hemodialysis.

Urinary indoxyl sulfate is a clinical factor that affects the progression of renal failure.

We recently demonstrated that indoxyl sulfate is a stimulating factor for the progression of chronic renal failure (CRF). In this study we determined whether the urine or serum levels of indoxyl sulfate are related to the progression rate of CRF in undialyzed uremic patients. Fifty-five CRF patients with a serum creatinine of >2 mg/dl who had not been treated with an oral sorbent (AST-120) were randomly enrolled in the study. We measured the serum and urine levels of indoxyl sulfate, and estimated the recent progression rate of CRF as the slope of the reciprocal serum creatinine versus time (1/S-Cr-time) plot. The mean urinary amount of indoxyl sulfate in the patients was 60 mg/day. Those with indoxyl sulfate urine levels of >60 mg/day had a significantly faster progression rate of CRF than those with <60 mg/day. Especially, those patients with indoxyl sulfate urine levels of >90 mg/day had the highest CRF progression rate and those with indoxyl sulfate urine levels of <30 mg/day had the slowest CRF progression rate. Urinary indoxyl sulfate had a significantly negative correlation with the slope of the 1/S-Cr-time plot. However, the serum level of indoxyl sulfate or the ratio of serum indoxyl sulfate to creatinine was not significantly correlated with the slope of the 1/S-Cr-time plot. In conclusion, high urine levels of indoxyl sulfate are related with a rapid progression of CRF in undialyzed uremic patients. Thus, urinary indoxyl sulfate is one of the clinical factors that affect CRF progression.

Effect of Long-Term Administration of Prostaglandin I2 in Incipient Diabetic Nephropathy

Background/Aims: Diabetic nephropathy is one of the primary diseases of refractory renal failure and heads the list of patients undergoing dialysis. Therefore, it is very important to get treatment in incipient nephropathy. Methods: Twenty-seven patients in incipient diabetic nephropathy of type 2 diabetes mellitus who showed signs of microalbuminuria were randomly, but not blindly, assigned to two groups, either the beraprost sodium (PGI2) group or the control group, and effects of the preparation on urinary albumin excretion or other parameters were examined for 24 months. Results: Urinary albumin excretion was significantly decreased after 18 months in beraprost sodium group; however, there was no change in the control group. Difference was observed between the two groups after month 12; however, it was not significant (p = 0.0673 at month 24). Three factors that affect urinary albumin excretion, e.g. blood pressure, blood sugar and protein intake, were almost constant during the study period. The level of creatinine clearance was significantly decreased in beraprost sodium group after 24 months as compared with the control group. Conclusion: In this study, we found that the long-term 24-month administration of PGI2 preparation, beraprost sodium, decreased albuminuria in patients of incipient diabetic nephropathy. The possible mechanisms are that the PGI2 may have alleviated constriction effect of angiotensin II on efferent glomerular arteriole and attenuated glomerular hyperfiltration, and inhibited growth of mesangial cells by platelet-derived growth factor as well.

Role of Urinary Arginine Vasopressin in the Sodium Excretion in Patients With Chronic Renal Failure

Patients with chronic renal failure show almost equal levels of sodium excreted in the urine as healthy subjects through an increase of the fractional excretion sodium (FE(Na)). The mechanisms of this adaptation, however, are unknown. Recently, urinary arginine vasopressin (AVP) has been shown to inhibit the antidiuretic action of plasma AVP in the collecting ducts of rabbits and rats. In this article, the roles of plasma and urinary AVP are examined with other hormones in the sodium excretion of 57 patients with chronic renal disease. The fractional excretion of AVP, plasma atrial natriuretic peptide (ANP) and endothelin-1 (ET-1), urinary ET-1, and FE(ET-1) correlated with the decrease of creatinine clearance (Ccr). Multiple and stepwise regression analyses showed that FE(AVP) is the major dependent determinant for FE(Na) (adjusted r2 = 0.78). These results suggest that the increase of AVP excretion per remaining nephron could be a cause of the increase of FE(Na) in patients with renal failure. Although plasma AVP works as an antidiuretic hormone, urinary AVP serves as an intrinsic diuretic, especially in patients with chronic renal failure.

Antiproteinuric effect of niceritrol, a nicotinic acid derivative, in chronic renal disease with hyperlipidemia: a randomized trial

PURPOSE Lipoprotein (a) [Lp(a)] levels increase in patients with renal disease. We administered niceritrol, a nicotinic acid derivative, to patients with chronic renal disease and a high serum Lp(a) level, and studied its effects on lipid metabolism, proteinuria, and renal function. METHODS Thirty-three patients with chronic renal disease whose serum Lp(a) levels were > or = 15 mg/dL were randomly (but not blindly) assigned to treatment with niceritrol (n = 16) or to an untreated control group (n = 17). Parameters of lipid metabolism, excretion of urinary protein, and renal function were examined for 12 months. RESULTS Changes in urinary protein excretion, as well as Lp(a) levels, differed significantly between the two groups. The mean (+/- SD) change from baseline in excretion of urinary protein was 0.77 +/- 1.23 g/d in the control group compared with -1.41 +/- 2.26 g/d in the niceritrol group at 12 months (P =0.003). Mean Lp(a) levels increased by 3 +/- 10 mg/dL in the control group compared with a decrease of 10 +/- 13 mg/dL in the niceritrol group at 12 months (P =0.004). The mean creatinine clearance declined by 10 +/- 12 mL/min in the control group, compared with 1 +/- 13 mL/min in the niceritrol group at 12 months (P =0.06). CONCLUSION Lipid levels improved with niceritrol treatment, whereas the excretion of urinary protein decreased, perhaps slowing the rate of loss of renal function in chronic renal disease.

Full-dose chemotherapy for esophageal cancer patient under hemodialysis

Accessible online at: www.karger.com/journals/nef Dear Sir, Protocol of chemotherapy, especially optimal dose of cisplatin (CDDP), is not yet well established for esophageal cancer patients under hemodialysis. We report here a successful treatment of advanced esophagus cancer with a full-dose chemotherapy and radiation therapy. A 68-year-old man, who was on maintenance hemodialysis for 7 years, complained of dysphagia in November 1999. Endoscopic examination revealed Borrmann 1 type tumor at the middle portion of the esophagus. Pathological examination of the biopsy specimen confirmed squamous cell carcinoma. Computed tomographic scan of the chest showed swelling of the paratracheal lymph nodes suggesting metastasis. Because the patient abhorred our recommendation to have the operation, chemoradiation therapy was initiated. Chemotherapy consisted of short-lasting 1 h infusion of cisplatin 50 mg on the first day and 5-fluorouracil (5-FU) 500 mg/day as continuous intravenous infusion from days 1 to 5. Administration of cisplatin was started just 1 h before hemodialysis. Four cycles of this therapy were performed at 2 week intervals. Synchronizing to the four cycles of chemotherapy, combined radiotherapy of total 64 Gy was consecutively performed on weekdays. During the whole treatment period, hemodialysis sessions were maintained at three times a week without any technical modification. Direct treatment-related toxic effects were minimal. At the endoscopic examination after the four cycles of chemotherapy and radiation therapy, the tumor had completely disappeared. However, biopsy from the scar lesion showed slight cancer cell nests. These results encouraged us to perform an additional two cycles of chemotherapy under almost the same protocol, only increasing the dose of cisplatin from 50 to 80 mg and 5-FU from 500 to 1,000 mg. Again, no grave adverse effects were observed in these two cycles of chemotherapy. Total plasma platinum levels were measured by atomic absorption spectrometer. The mean total platinum levels at the end of an infusion of 50 and 80 mg cisplatin were 2.68 Ig/ml (n = 4) and 3.06 Ig/ml (n = 2), respectively. The peak total platinum level never exceeded 3.16 Ig/ml. Follow-up endoscopic examinations, performed biannually after six cycles of chemotherapy, revealed only scar at the previous tumor lesion of the esophagus. All the biopsy specimens failed to prove any cancer cells. Additionally, computed tomographic scan of the chest and abdomen showed no sign of recurrence, which evidenced complete response of the chemoradiation therapy for advanced cancer of the esophagus. Two years and 8 months after the onset of the symptoms, the patient is asymptomatic and enjoying his social life. The excellent results of our case suggest that full-dose chemotherapy might be available for hemodialyzed cancer patients. It is difficult to speculate the reason why our patient with advanced esophagus cancer under hemodialysis is surviving more than 2 years with no signs of local recurrence and metastasis. Tanabe et al. [1] reported that the clearance of total platin made no difference between HD and non-HD patients, though the clearance of free platin (free-pl) was smaller in the HD patients than in the non-HD patients resulting in a 5-fold increase in free-pl exposure in HD patients. However, no severe bone marrow suppression was observed. Much longer time of contact between free-pl and cancer, in other words, much larger area under curve (AUC) of free-pl, might be contributory to the effectiveness of the chemotherapy. However, there are little basic and clinical data [2, 3], it is necessary to accumulate much more data to build up an established protocol of chemotherapy for the cancerburdened patients under hemodialysis.

Effects of Oral Adsorbent AST-120 Concurrent with a Low-Protein Diet on the Progression of Chronic Renal Failure

This study was designed to examine the effects of oral adsorbent AST-120 on the progression of CRF in patients on strict LPD. Thirteen patients with CRF (serum creatinine: 1.8-8.2 mg/dl) that had been kept on LPD (0.4-0.7 g/kg/day) were enrolled in this study. After LPD alone for 5-24 months, AST-120 (3-6 g/day) was administered concurrently with the LPD for an additional 5-13 months. In 9 of the 13 patients, the slopes of reciprocal creatinine (Cr) vs. time plot linearly declined before AST-120 treatment. After treatment, the slopes of these patients lessened from -0.01 +/- 0.001 to -0.003 +/- 0.001 dl/mg/month (p < 0.01). Because reciprocal Cr did not decline linearly with time before AST-120 treatment in the remaining 4 patients, the slopes of reciprocal Cr could not be compared before and after treatment with AST-120. Seven of the 9 patients had sufficient creatinine clearance (Ccr) data after treatment with AST-120. The decline of Ccr decreased from -0.59 +/- 0.13 to -0.12 +/- 0.12 ml/min/month in these patients. This study has clearly demonstrated that AST-120 compounds the effects of well-controlled LPD on retarding the progression of CRF. AST-120 may remove some uremic metabolite(s) which promote the progression of CRF.

THE EFFECTS OF BISOPROLOLA SELECTIVE β1-BLOCKERON GLUCOSE METABOLISM BY LONG-TERM ADMINISTRATION IN ESSENTIAL HYPERTENSION

Bisoprolola β1-selective β-blockerwas administered to 13 patients with mild to moderate essential hypertension once daily at doses of 5–10 mg for 24 weeksand its long-term effects on blood pressure and glucose metabolism were investigated. The systolicdiastolic and mean blood pressures were significantly reduced. At the end of the treatment periodthe blood glucose level and hemoglobin A1c were not significantly different from those at baseline. In the glucose tolerance test at the end of the treatment periodthe blood glucose and plasma insulin levels after a glucose load of 75 g were not significantly different at any time pointand the sums of each were not significantly different from their baseline levels. Based on these resultsbisoprolol appears to be a β1-selective β-blocker possessing a satisfactory hypotensive effect without any adverse effects on glucose metabolism for long-term useand is therefore a safe and useful drug for the treatment of essential hypertension.