Short-term effects of tolvaptan on renal function and volume in patients with autosomal dominant polycystic kidney disease
2011; Elsevier BV; Volume: 80; Issue: 3 Linguagem: Inglês
10.1038/ki.2011.119
ISSN1523-1755
AutoresMaría V. Irazabal, Vicente E. Torres, Marie C. Hogan, James F. Glockner, Bernard F. King, Troy G. Ofstie, Holly B. Krasa, John Ouyang, Frank S. Czerwiec,
Tópico(s)Birth, Development, and Health
ResumoTolvaptan and related V2-specific vasopressin receptor antagonists have been shown to delay disease progression in animal models of polycystic kidney disease. Slight elevations in serum creatinine, rapidly reversible after drug cessation, have been found in clinical trials involving tolvaptan. Here, we sought to clarify the potential renal mechanisms to see whether the antagonist effects were dependent on underlying renal function in 20 patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD) before and after 1 week of daily split-dose treatment. Tolvaptan induced aquaresis (excretion of solute-free water) and a significant reduction in glomerular filtration rate (GFR). The serum uric acid increased because of a decreased uric acid clearance, and the serum potassium fell, but there was no significant change in renal blood flow as measured by para-aminohippurate clearance or magnetic resonance imaging (MRI). No correlation was found between baseline GFR, measured by iothalmate clearance, and percent change in GFR induced by tolvaptan. Blinded post hoc analysis of renal MRIs showed that tolvaptan significantly reduced total kidney volume by 3.1% and individual cyst volume by 1.6%. Preliminary analysis of this small cohort suggested that these effects were more noticeable in patients with preserved renal function and with larger cysts. No correlation was found between changes of total kidney volume and body weight or estimated body water. Thus, functional and structural effects of tolvaptan on patients with ADPKD are likely due to inhibition of V2-driven adenosine cyclic 3′,5′-monophosphate generation and its aquaretic, hemodynamic, and anti-secretory actions. Tolvaptan and related V2-specific vasopressin receptor antagonists have been shown to delay disease progression in animal models of polycystic kidney disease. Slight elevations in serum creatinine, rapidly reversible after drug cessation, have been found in clinical trials involving tolvaptan. Here, we sought to clarify the potential renal mechanisms to see whether the antagonist effects were dependent on underlying renal function in 20 patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD) before and after 1 week of daily split-dose treatment. Tolvaptan induced aquaresis (excretion of solute-free water) and a significant reduction in glomerular filtration rate (GFR). The serum uric acid increased because of a decreased uric acid clearance, and the serum potassium fell, but there was no significant change in renal blood flow as measured by para-aminohippurate clearance or magnetic resonance imaging (MRI). No correlation was found between baseline GFR, measured by iothalmate clearance, and percent change in GFR induced by tolvaptan. Blinded post hoc analysis of renal MRIs showed that tolvaptan significantly reduced total kidney volume by 3.1% and individual cyst volume by 1.6%. Preliminary analysis of this small cohort suggested that these effects were more noticeable in patients with preserved renal function and with larger cysts. No correlation was found between changes of total kidney volume and body weight or estimated body water. Thus, functional and structural effects of tolvaptan on patients with ADPKD are likely due to inhibition of V2-driven adenosine cyclic 3′,5′-monophosphate generation and its aquaretic, hemodynamic, and anti-secretory actions. Tolvaptan is an orally effective, non-peptide arginine vasopressin (AVP) V2 receptor antagonist currently approved in the United States and EU for the treatment of hyponatremia associated in euvolemic and hypervolemic states and SIADH, respectively, and in Japan for the treatment of cardiac edema resistant to diuretics. Tolvaptan is also being studied as an adjunct therapy for volume overload in patients with heart failure and as a primary therapy to delay progression of Autosomal Dominant Polycystic Kidney Disease (ADPKD). Both tolvaptan and a related V2-specific AVP receptor antagonist have been shown to delay disease progression in animal models of human polycystic kidney disease.1.Gattone V.H. Wang X. Harris P.C. et al.Inhibition of renal cystic disease development and progression by a vasopressin V2 receptor antagonist.Nat Med. 2003; 9: 1323-1326Crossref PubMed Scopus (491) Google Scholar, 2.Torres V.E. Wang X. Qian Q. et al.Effective treatment of an orthologous model of autosomal dominant polycystic kidney disease.Nat Med. 2004; 10: 363-364Crossref PubMed Scopus (377) Google Scholar, 3.Wang X. Gattone II, V. Harris P.C. et al.Effectiveness of vasopressin V2 receptor antagonists OPC-31260 and OPC-41061 on polycystic kidney disease development in the PCK rat.J Am Soc Nephrol. 2005; 16: 846-851Crossref PubMed Scopus (241) Google Scholar The mechanism of these effects is proposed to involve inhibition of the AVP V2 receptor and the subsequent decrease in adenosine cyclic 3′,5′-monophosphate concentrations in the kidney. Elevated adenosine cyclic 3′,5′-monophosphate in the kidney is thought to promote cyst fluid accumulation and the epithelial cell growth, thereby displacing normal kidney and accelerating renal failure.4.Belibi F.A. Reif G. Wallace D.P. et al.Cyclic AMP promotes growth and secretion in human polycystic kidney epithelial cells.Kidney Int. 2004; 66: 964-973Abstract Full Text Full Text PDF PubMed Scopus (206) Google Scholar, 5.Yamaguchi T. Pelling J. Ramaswamy N. et al.cAMP stimulates the in vitro proliferation of renal cyst epithelial cells by activating the extracellular signal-regulated kinase pathway.Kidney Int. 2000; 57: 1460-1471Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar Transient decreases in blood urea nitrogen and increases in serum creatinine and uric acid have been observed during tolvaptan's evaluation for indications involving patients with hyponatremia and heart failure.6.Konstam M.A. Gheorghiade M. Burnett Jr, J.C. et al.Effects of oral tolvaptan in patients hospitalized for worsening heart failure: the EVEREST Outcome Trial.JAMA. 2007; 297: 1319-1331Crossref PubMed Scopus (1209) Google Scholar, 7.Schrier R.W. Gross P. Gheorghiade M. et al.Tolvaptan, a selective oral vasopressin V2-receptor antagonist, for hyponatremia.N Engl J Med. 2006; 355: 2099-2112Crossref PubMed Scopus (932) Google Scholar In these studies, the incidence of adverse events related to acute or chronic renal failure have been similar, but consistently numerically lower in those treated with tolvaptan than with placebo. Similar changes have been seen in ADPKD patients who have been given twice-daily tolvaptan (to consistently inhibit AVP action at the kidney's AVP V2 receptors) over the last 4 years in an open-label study.8.Torres V.E. Winklhofer F. Chapman A.B. et al.Phase 2 open-label study to determine long-term safety, tolerability and efficiacy of split-dose Tolvaptan in ADPKD.J Am Soc Nephrol. 2009; 20: 746ACrossref Scopus (6) Google Scholar Because renal function is critically important to those diagnosed with ADPKD, we sought to clarify the possible mechanisms of these changes in serum creatinine by studying renal hemodynamics and function in ADPKD patients given daily, split-dose tolvaptan administration over 1 week. We also sought to determine whether the level of residual renal function impacts the effect of tolvaptan on glomerular filtration rate (GFR) and creatinine clearance. Analysis of renal structure, along with correlations to hemodynamics and function were added post hoc. The baseline (day 0) clinical and laboratory parameters are shown in Table 1. Baseline total kidney volume (TKV) was inversely correlated with baseline para-aminohippurate (PAH)-renal blood flow (RBF) (and, not shown, magnetic resonance (MR)-RBF) and GFR, and directly correlated with urine albumin excretion (Figure 1a–c). PAH- and MR-RBFs were highly correlated (r=0.958, P<0.001), but the ratio of PAH-RBF to MR-RBF was lower in the patients with a GFR <60 ml/min per 1.73 m2 possibly because the 90% renal extraction of PAH used to estimate RBF-PAH is too high when renal function is low (results not shown).Table 1Short-term effects of tolvaptan on clinical and laboratory parameters and on TKVsAll study participantsPrePost%ΔP-valueAge (years)47.8±8.7Weight (kg)84.0±22.082.7±21.7−1.6±1.3<0.001MAP (mm Hg)92.0±10.190.0±10.8−1.7±10.10.390RKV (ml)1236±15381211±1533−4.0±4.1<0.001LKV (ml)1081±12111064±1201−2.5±2.90.003TKV (ml)2316±27152274±2700−3.1±3.0<0.001Hb (g/dl)13.0±1.113.0±1.00.1±5.40.925Protein (g/dl)7.0±0.67.1±0.42.8±7.80.153Albumin (mg/l)4.4±0.24.4±0.30.9±4.10.323GFR (ml/min per 1.73 m2)69.3±34.862.4±28.7−8.6±13.90.018PAH (ml/min per 1.73 m2)345.7±184.4320.5±156.7−5.7±13.10.071RBF-PAH (ml/min per 1.73 m2)619±338570±286−5.9±15.60.109RBF-MRI (ml/min per 1.73 m2)536±266514±2211.0±18.90.459SCr (mg/dl)1.4±0.81.5±0.88.9±10.50.004Cystatin C (mg/l)1.2±0.61.3±0.68.9±10.40.011BUN (mg/dl)21.7±10.721.1±10.0−1.3±16.40.564Uric acid (mg/dl)5.6±2.16.2±2.213.0±14.10.002Sodium (mmol/l)137.9±2.3139.5±2.71.1±1.2<0.001Potassium (mmol/l)4.6±0.54.4±0.6−4.8±5.50.001Urine flow (ml/min)7.3±3.28.5±3.123.8±43.90.012CH2O (ml/min)4.1±2.76.0±2.891.7±160.7<0.001(CH2O/GFR) × 1005.6±2.79.1±2.2107±131<0.001Cosm (ml/min)3.3±0.82.7±0.8−16.0±16.90.001(Cosm/GFR) × 1005.1±2.24.8±2.2−6.6±16.70.121Curi (ml/min)9.6±4.96.8±3.0−26.8±14.8<0.001(Curi/GFR) × 10012.8±3.610.6±4.5−18.7±17.2<0.001Abbreviations: BUN, blood urea nitrogen; CH2O, free water clearance; Cosm, osmolar clearance; Curi, uric acid clearance; GFR, glomerular filtration rate determined by iothalamate clearance; Hb, serum hemoglobin; LKV, left kidney volume; MAP, mean arterial pressure; PAH, para-aminohippurate clearance; RKV, right kidney volume; RBF-PAH, renal blood flow determined by para-aminohippurate clearance; RBF-MRI, renal blood flow determined by magnetic resonance imaging; SCr, serum creatinine; TKV, total kidney volume.Bold denotes statistical significance. Open table in a new tab Abbreviations: BUN, blood urea nitrogen; CH2O, free water clearance; Cosm, osmolar clearance; Curi, uric acid clearance; GFR, glomerular filtration rate determined by iothalamate clearance; Hb, serum hemoglobin; LKV, left kidney volume; MAP, mean arterial pressure; PAH, para-aminohippurate clearance; RKV, right kidney volume; RBF-PAH, renal blood flow determined by para-aminohippurate clearance; RBF-MRI, renal blood flow determined by magnetic resonance imaging; SCr, serum creatinine; TKV, total kidney volume. Bold denotes statistical significance. As expected the administration of tolvaptan induced aquaresis, which was accompanied by reductions in body weight of 1.6% and increases in plasma sodium concentration of 1.1% (Table 1). Estimated total body water decreased by 1.1% (not shown). No significant changes were observed in blood pressure, hematocrit or serum protein, and albumin concentrations (Table 1). Serum creatinine, cystatin C, and uric acid increased by 8.9, 8.9, and 13.0% (Table 1), respectively. The percent increase in serum uric acid was numerically greater than creatinine or cystatin C but not significantly so (P=0.16 and 0.30). Serum blood urea nitrogen and plasma renin activity and aldosterone did not change significantly (not shown). The administration of tolvaptan increased urine flow and free water clearance, and induced an 8.6% reduction in GFR, without a consistent or significant change in RBF-PAH or RBF-magnetic resonance imaging (MRI; Table 1). There was no correlation between percent changes in GFR and GFR values at baseline (P=0.398). Consistent with its effect on GFR, tolvaptan significantly reduced the osmolar and uric acid clearances, but only the reduction in uric acid clearance remained significant when these clearances were adjusted for the reduction in GFR (Table 1). Moreover, the percent reduction in uric acid clearance was significantly larger than the reduction in GFR, indicating that a change in the rates of uric acid reabsorption and/or secretion contributes to the reduction in uric acid clearance in addition to the reduction in GFR. Changes in TKV were not an initial focus for this study, as it had been believed that it would take months to detect the effects due to inhibition of cell proliferation or fluid secretion. Unexpectedly, however, a post hoc-blinded analysis of the renal MRI obtained for measurement of renal blood flow and to document disease progression showed a 3.1% reduction in TKV from baseline after 1 week of tolvaptan therapy (P<0.001; Table 1, Figure 2). The percent change in right and left kidney volumes were significantly correlated (r=0.526, P=0.017). No significant correlation was detected between the changes in TKV and body weight (r=0.054, NS) or estimated body water (r=0.184, NS; not shown). The percent reduction in TKV was higher in patients with a GFR ≥60 ml/min per 1.73 m2 than in those with a GFR <60 ml/min per 1.73 m2, without reaching statistical significance (P=0.057). To determine whether the reduction in kidney volume was due to changes in cyst volume, we measured individual cyst volumes in nine patients (six with a GFR ≥60 ml/min per 1.73 m2 and three with a GFR <60 ml/min per 1.73 m2). A total of 11–20 cysts per patient were measured before and after the administration of tolvaptan. To protect against bias the two MRIs for each patient were de-identified and dates of examinations removed, so that the examiner was blinded to the dates and patient data. The two MRI studies for each patient, however, were examined at the same time. Excellent image quality in both studies was used as the criterion to otherwise randomly select 11–20 cysts from each patient between 10 and 100 mm in diameter to measure individual cyst volumes. In eight of the nine patients, the mean cyst volume was lower following the administration of tolvaptan and in three of them the change was statistically significant. The overall percent reduction in individual cyst volume was 1.64% (P=0.0004). The percent reduction of individual cyst volumes was more marked in patients with a GFR ≥60 ml/min per 1.73 m2 than in those with a GFR <60 ml/min per 1.73 m2 (Figure 3a). The percent reduction in cyst volume associated with the administration of tolvaptan was significant in cysts ≥10 ml, but not in those <10 ml (Figure 3a). Percent changes in individual cyst volumes were correlated with natural log transformed cyst volumes at baseline (P=0.002; Figure 3b). The administration of tolvaptan was well tolerated and all the patients completed the study without discontinuation of the medication. Common adverse events included polyuria (100%), polydipsia (100%), nocturia (85%), and dry mouth (45%). There were no serious adverse events. The main observations of this study are that the administration of tolvaptan over 1 week reduces GFR and significantly reduces kidney and cyst volume to a greater extent than it reduces body weight and body water. The reduction in GFR induced by tolvaptan occurred without a significant change in RBF measured indirectly by the PAH clearance or directly using MRI. Nevertheless, reductions in PAH clearance and PAH-RBF approached statistical significance, and an effect of tolvaptan on PAH clearance and RBF cannot be excluded because of the small sample size. We cannot exclude either that a reduction in filtered PAH or an interference of tolvaptan or one of its metabolites with the tubular secretion of PAH could account for these trends. The MR results suggest that the administration of tolvaptan does not have an effect on RBF or that this effect is small and not likely to explain the reduction in GFR. As previously observed in patients with ADPKD, administration of this drug acutely results in a small increase in serum creatinine concentration, which is paralleled by a similar reduction in GFR. The percent reduction in GFR is similar in patients with chronic kidney disease stage 1 or 2 and in those with chronic kidney disease stage 3. It is unlikely that the observed 1.1% reduction in total body water accounts for the 8.9% increase in serum creatinine. Moreover, an increase in serum creatinine by this mechanism should be self-limiting, as it would result in an increase in filtered creatinine and creatinine clearance. It is also unlikely that relative contraction of plasma volume accounts for the 8.6% reduction in GFR, as no significant change in blood hemoglobin or serum protein or albumin concentration was detected and GFR is usually maintained in the presence of moderate volume contraction by efferent arteriolar constriction and an increase in glomerular pressure.9.Schor N. Ichikawa I. Brenner B.M. Glomerular adaptations to chronic dietary salt restriction or excess.Am J Physiol. 1980; 238: F428-F436PubMed Google Scholar As the administration of tolvaptan results in an increase in vasopressin release, the possibility that a higher level of circulating vasopressin accounts for the reduction in GFR has to be considered.10.Grantham J.J. Chapman A.B. Torres V.E. et al.Acute and chronic osmostasis after vassopressin V2 receptor inhibiton with Tolvaptan in ADPKD.J Am Soc Nephrol. 2005; 16: 361AGoogle Scholar Direct hemodynamic effects of vasopressin on V1a receptors in the renal vasculature are not likely to account for the observed change. Under physiological conditions, elevations of circulating vasopressin within the physiological range induced by water restriction or exogenous administration have no effect on RBF or GFR.11.Gellai M. Silverstein J.H. Hwang J.C. et al.Influence of vasopressin on renal hemodynamics in conscious Brattleboro rats.Am J Physiol. 1984; 246: F819-F827PubMed Google Scholar, 12.Harrison-Bernard L.M. Brizzee B.L. Clifton G.G. et al.Renal versus hindquarter hemodynamic responses to vasopressin in conscious rats.J Cardiovasc Pharmacol. 1990; 16: 719-726Crossref PubMed Scopus (8) Google Scholar, 13.Liard J.F. Deriaz O. Schelling P. et al.Cardiac output distribution during vasopressin infusion or dehydration in conscious dogs.Am J Physiol. 1982; 243: H663-H669PubMed Google Scholar A renal vasoconstrictor response to vasopressin is observed only with very high concentrations of vasopressin.14.Roald A.B. Tenstad O. Aukland K. The effect of AVP-V1 receptor stimulation on local GFR in the rat kidney.Acta Physiol Scand. 2004; 182: 197-204Crossref PubMed Scopus (9) Google Scholar Increased levels of circulating vasopressin are more likely to have an effect on the efferent arterioles and medullary circulation,15.Cowley Jr, A.W. Control of the renal medullary circulation by vasopressin V1 and V2 eceptors in the rat.Exp Physiol. 2000; 85 Spec No: 223S-231SCrossref PubMed Google Scholar, 16.Davis J.M. Schnermann J. The effect of antidiuretic hormone on the distribution of nephron filtration rates in rats with hereditary diabetes insipidus.Pflugers Arch. 1971; 330: 323-334Crossref PubMed Scopus (38) , 17.Edwards R.M. Trizna W. Kinter L.B. Renal microvascular effects of vasopressin and vasopressin antagonists.Am J Physiol. 1989; 256: F274-F278PubMed Google Scholar, 18.Fisher R.D. Grunfeld J.P. Barger A.C. Intrarenal distribution of blood flow in diabetes insipidus: role of ADH.Am J Physiol. 1970; 219: 1348-1358PubMed Google Scholar, 19.Yamada K. Nakano H. Nishimura M. et al.Effect of AVP.V1-receptor antagonist on urinary albumin excretion and renal hemodynamics in NIDDM nephropathy: role of AVP.V1-receptor.J Diabetes Complications. 1995; 9: 326-329Abstract Full Text PDF PubMed Scopus (11) Google Scholar, 20.Zimmerhackl B. Robertson C.R. Jamison R.L. Effect of arginine vasopressin on renal medullary blood flow. A videomicroscopic study in the rat.J Clin Invest. 1985; 76: 770-778Crossref PubMed Google Scholar but this would increase rather than decrease GFR. Although direct effects of vasopressin on the renal vasculature are unlikely explanations for the observed changes, a direct effect of circulating vasopressin on glomerular function may contribute to the reduction in GFR. Administration of vasopressin to rats undergoing water diuresis induces a marked decline in hydraulic pressure within the Bowman's space, but GFR remains unchanged because the increase in pressure gradient is offset by a reduction in the glomerular ultrafiltration coefficient, possibly due to a direct effect on mesangial V1a receptors and mesangial cell contraction.21.Jard S. Lombard C. Marie J. et al.Vasopressin receptors from cultured mesangial cells resemble V1a type.Am J Physiol. 1987; 253: F41-F49PubMed Google Scholar, 22.Schor N. Ichikawa I. Brenner B.M. Mechanisms of action of various hormones and vasoactive substances on glomerular ultrafiltration in the rat.Kidney Int. 1981; 20: 442-451Abstract Full Text PDF PubMed Scopus (175) Google Scholar Tolvaptan may also lower GFR by inhibiting the vasopressin V2-mediated urine concentrating activity and indirectly affecting renal hemodynamics.23.Bankir L. Antidiuretic action of vasopressin: quantitative aspects and interaction between V1a and V2 receptor-mediated effects.Cardiovasc Res. 2001; 51: 372-390Crossref PubMed Scopus (230) Google Scholar, 24.Bouby N. Ahloulay M. Nsegbe E. et al.Vasopressin increases glomerular filtration rate in conscious rats through its antidiuretic action.J Am Soc Nephrol. 1996; 7: 842-851PubMed Google Scholar Urine osmolality and GFR were found to be directly correlated in conscious rats when urine concentrating activity was increased by a constant infusion of 1-deamino-8-D-arginine vasopressin or reduced by increasing water intake. Reducing AVP V2R activity may reduce GFR through reduction of urea recycling and/or sodium chloride reabsorption in the thick ascending Henle's limb, lowering the sodium concentration at the macula densa and suppressing tubuloglomerular feedback. Urine concentrating activity and GFR are also correlated in healthy human volunteers during low and high hydration.25.Anastasio P. Cirillo M. Spitali L. et al.Level of hydration and renal function in healthy humans.Kidney Int. 2001; 60: 748-756Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar AVP administration to water loaded healthy volunteers induces parallel increases in creatinine clearance and urine osmolality.26.Andersen L.J. Andersen J.L. Schutten H.J. et al.Antidiuretic effect of subnormal levels of arginine vasopressin in normal humans.Am J Physiol. 1990; 259: R53-R60PubMed Google Scholar Conversely, administration of V2R antagonists after dehydration induces a fall in creatinine clearance. The other main observation of this study is that administration of tolvaptan for 1 week is sufficient to induce a significant reduction in TKV and volume of individual cysts. It seems unlikely that the 1.1% reduction in total body water entirely accounts for the 3.1% reduction in TKV. The lack of correlation between the percent changes in total body water (or body weight) and in total kidney weight supports this interpretation. A plausible explanation for the tolvaptan induced reduction in kidney and cyst volumes in this study is consistent with its proposed mechanism of action in polycystic kidneys, that is, inhibition of adenosine cyclic 3′,5′-monophosphate production and chloride-driven fluid secretion.1.Gattone V.H. Wang X. Harris P.C. et al.Inhibition of renal cystic disease development and progression by a vasopressin V2 receptor antagonist.Nat Med. 2003; 9: 1323-1326Crossref PubMed Scopus (491) Google Scholar, 2.Torres V.E. Wang X. Qian Q. et al.Effective treatment of an orthologous model of autosomal dominant polycystic kidney disease.Nat Med. 2004; 10: 363-364Crossref PubMed Scopus (377) Google Scholar, 3.Wang X. Gattone II, V. Harris P.C. et al.Effectiveness of vasopressin V2 receptor antagonists OPC-31260 and OPC-41061 on polycystic kidney disease development in the PCK rat.J Am Soc Nephrol. 2005; 16: 846-851Crossref PubMed Scopus (241) Google Scholar, 4.Belibi F.A. Reif G. Wallace D.P. et al.Cyclic AMP promotes growth and secretion in human polycystic kidney epithelial cells.Kidney Int. 2004; 66: 964-973Abstract Full Text Full Text PDF PubMed Scopus (206) Google Scholar, 5.Yamaguchi T. Pelling J. Ramaswamy N. et al.cAMP stimulates the in vitro proliferation of renal cyst epithelial cells by activating the extracellular signal-regulated kinase pathway.Kidney Int. 2000; 57: 1460-1471Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar Indeed, renal cysts excised from patients with ADPKD secrete as well as absorb fluid in vitro and the rate of net fluid secretion is augmented by forskolin, which activates adenylate cyclase.27.Ye M. Grantham J. The secretion of fluid by renal cysts from patients with autosomal dominant polycystic kidney disease.New Eng J Med. 1993; 329: 310-313Crossref PubMed Scopus (96) Google Scholar Moreover, tolvaptan inhibits AVP-induced chloride currents in ADPKD cell polarized monolayers and AVP-induced growth of ADPKD cell-derived microcysts in collagen gels.28.Reif G.A. Nivens E. Pinto C.S. et al.Tolvaptan inhibits AVP-induced Cl-secretion and in vitro cyst growth of human ADPKD cyst epithelial cells.J Am Soc Nephrol. 2008; 19: 365ACrossref PubMed Scopus (108) Google Scholar Therefore, inhibition of fluid secretion by tolvaptan may alter the balance between secretion and absorption, and induce net fluid reabsorption and reduction in cyst volume. The greater effects of tolvaptan on kidney and cyst volumes in patients with a GFR ≥60 ml/min per 1.73 m2 suggest that tolvaptan may be more effective in early than in late stages of the disease. Given the small sample size, however, these comparisons should be regarded as exploratory and hypothesis generating. Confirmation of these specific hypotheses will necessitate a replicate study in which the proposed hypothesis is stated as primary or secondary with appropriate adjustment to exclude type I error. A few other observations merit comment. Administration of tolvaptan resulted in a reduction in uric acid clearance and an increase in serum uric acid levels that were more marked than changes in GFR and levels of serum creatinine and cystatin C. An elevation in serum uric acid is a characteristic of both central and nephrogenic diabetes insipidus.29.Decaux G. Prospert F. Namias B. et al.Hyperuricemia as a clue for central diabetes insipidus (lack of V1 effect) in the differential diagnosis of polydipsia.Am J Med. 1997; 103: 376-382Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar, 30.Gorden P. Robertson G.L. Seegmiller J.E. Hyperuricemia, a concomitant of congenital vasopressin-resistant diabetes insipidus in the adult.N Engl J Med. 1971; 284: 1057-1060Crossref PubMed Scopus (17) Google Scholar It has been suggested that the degree of the elevation may be more marked in central than in nephrogenic diabetes insipidus because stimulation of V1a receptors may have a uricosuric effect.29.Decaux G. Prospert F. Namias B. et al.Hyperuricemia as a clue for central diabetes insipidus (lack of V1 effect) in the differential diagnosis of polydipsia.Am J Med. 1997; 103: 376-382Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar Changes in uric acid clearance often closely correlate with changes in RBF. In our study, however, the reduction in uric acid clearance occurred in the absence of a significant change in RBF, particularly when we consider the RBF-MRI, which likely is more reliable than RBF-PAH in patients with impaired renal function. The reduced renal clearance of uric acid associated with the administration of tolvaptan may be linked to increased proximal reabsorption of sodium to compensate for reduced V2 receptor-mediated sodium reabsorption in the distal nephron and collecting duct.31.Bankir L. Fernandes S. Bardoux P. et al.Vasopressin-V2 receptor stimulation reduces sodium excretion in healthy humans.J Am Soc Nephrol. 2005; 16: 1920-1928Crossref PubMed Scopus (96) Google Scholar, 32.Perucca J. Bichet D.G. Bardoux P. et al.Sodium excretion in response to vasopressin and selective vasopressin receptor antagonists.J Am Soc Nephrol. 2008; 19: 1721-1731Crossref PubMed Scopus (74) Google Scholar, 33.Sauter D. Fernandes S. Goncalves-Mendes N. et al.Long-term effects of vasopressin on the subcellular localization of ENaC in the renal collecting system.Kidney Int. 2006; 69: 1024-1032Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar, 34.Mutig K. Saritas T. Uchida S. et al.Short-term stimulation of the thiazide-sensitive Na+-Cl- cotransporter by vasopressin involves phosphorylation and membrane translocation.Am J Physiol Renal Physiol. 2010; 298: F502-F509Crossref PubMed Scopus (70) Google Scholar An additional finding associated with the administration of tolvaptan is a small but significant reduction in the level of serum potassium. This may be due to the increased rate of sodium and fluid delivery to the cortical collecting duct.35.Muto S. Potassium transport in the mammalian collecting duct.Physiol Rev. 2001; 81: 85-116PubMed Google Scholar In summary, the results of this study suggest that, very early after initiation of treatment with tolvaptan, there is an increase in serum creatinine because of a reduction in GFR likely due to its effects on tubuloglomerular feedback and/or glomerular ultrafiltration, a reduction in TKV and cyst volume accounted at least in part by its effects on fluid secretion, and a serum uric acid increase and potassium decrease likely explained by its effects on sodium reabsorption in the distal nephron and collecting duct. Study participants were previously diagnosed ADPKD patients based on Ravine's criteria,36.Ravine D. Gibson R.N. Walker R.G. et al.Evaluation of ultrasonographic diagnostic criteria for autosomal dominant polycystic kidney disease 1.Lancet. 1994; 343: 824-827Abstract PubMed Scopus (466) Google Scholar, 37.Pei Y. Obaji J. Dupuis A. et al.Unified criteria for ultrasonographic diagnosis of ADPKD.J Am Soc Nephrol. 2009; 20: 205-212Crossref PubMed Scopus (436) Google Scholar 18–60 years of age, and selected to represent a wide range of disease severity with estimated creatinine clearances by the Cockcroft–Gault equation ≥30 ml/min. A total of 20 participants (10 caucasian males and 10 caucasian females) were enrolled in the study, in which 12 had eCrCl ≥60 ml/min (6 without hypertension and 6 hypertensive) and 8 had eCrCl 30–59 ml/min (all hypertensive). Exclusion criteria included concurrent diseases that could interfere with the conduct of the study or the interpretation of the results (for example, diabetes mellitus), uncontrolled hypertension, use of diuretics, administration of an investigative drug or donation of blood within 30 days before dosing, allergy to iodine or benzazepines, and contraindications to MR studies. The antihypertensive regimen for the study participants with hypertension included an angiotensin I converting enzyme inhibitor or an angiotensin II receptor blocker. The protocol was approved by the Mayo Institutional Review Board. Written informed consent was obtained from all patients. This is a single center, sequential, multiple-dose study of the effect of a split-dose regimen of tolvaptan tablets on renal function in patients with ADPKD. Subjects checked into the outpatient clinic on day -1 and underwent physical examination and measurements of serum chemistry and hematology parameters, urinalysis, and if applicable exclusion of pregnancy. On study day 0, all subjects underwent baseline renal function testing. Subjects were given enough study medication for 7 days and were instructed to administer tolvaptan in a split-dose regimen, 45 mg (3 × 15 mg, oral tablets) on awakening followed by 15 mg (1 × 15 mg, oral tablet) 8 h later on study days 1–6. On day 7, subjects administered tolvaptan 45 mg (3 × 15 mg) on awaking at home and the 15 mg dose was administered in the study facility ∼8 h after the morning dose. On study day 8, subjects were given the 45 mg dose at 0700 hours in the study facility and underwent measurements of renal clearances, followed by measurements of RBF by MRI, and chemistry and hematology parameters. On days 0 and 8, subjects were instructed to wake up at 0600 hours, remain upright for 2 h. They reported to the Renal Function Laboratory at 0645 hours at which time height and weight were obtained and an intravenous needle for blood collection was placed in the dominant arm. At 0700 hours, they drank 240 ml of water (day 0) or took 45 mg of tolvaptan with 240 ml of water (day 8). Between 0700 and 0800 hours they drank 720–1200 ml of water. At 0800 hours, blood and urine samples were collected for plasma aldosterone, serum cystatin C, standing plasma renin activity, and predose iothalamate and PAH. An intravenous catheter was inserted into the non-dominant arm to administer the priming and sustaining solutions of iothalamate and PAH. Blood and urine samples were collected within 5 min of each other every 30 min between 0900 and 1030 hours for measurements of iothalamate, PAH, urea, creatinine, uric acid, osmolality, urinary protein, and albumin. Bladder emptying was monitored by ultrasound. GFR and renal plasma flow (RPF) were determined by iothalamate and PAH clearances, respectively. Clearances were calculated as Ui × V/Pi and UPAH × V/PPAH × 1.1 and the average of the three collection intervals were considered the final value of the renal function test. RBF was estimated from RPF values obtained from clearance of PAH using the measured hematocrit values as RBF=RPF/(1-hematocrit). Race- and sex-specific total body water (TBW) prediction equations38.Chumlea W.C. Guo S.S. Zeller C.M. et al.Total body water reference values and prediction equations for adults.Kidney Int. 2001; 59: 2250-2258Abstract Full Text Full Text PDF PubMed Google Scholar were used to estimate TBW at baseline. TBW on day 8 was estimated as the baseline TBW minus free water deficit, calculated as baseline TBW ((Na post/Na pre)-1). MR images were obtained on 1.5-T scanners (Signa; GE Medical Systems, Milwaukee, WI) at 1100 hours on study day 0 and 8. After an initial scout to localize the kidneys, coronal T2-weighted images (single-shot fast spin-echo/fast imaging employing steady-state acquisition) with 3 and 9 mm fixed slice thickness and three-dimensional volume-interpolated spoiled-gradient echo coronal T1-weighted images were obtained (5-mm slice thickness). For kidney volume measurements, image data were transferred digitally to a workstation. The two MRIs for each patient were examined at the same time, but they were de-identified and the examiner was blinded to the dates and patient data. Coronal T2-weighted images were used to outline both kidneys and TKV was calculated using the ANALYZE bioimaging software system (Mayo Foundation, Biomedical Imaging Resource, Rochester, MN). On five arbitrarily selected patients, measurements were carried out on two separate occasions for later assessment of intraobserver variability. The interval between the consecutive sets of measurements was at least 30 days. The average intraobserver variability (or percentage measurement error) was 0.70%. For measurements of individual cyst volumes, 11–20 cysts measuring 16–97 mm in diameter, with good quality images on both, pre- and post-tolvaptan studies were selected. Coronal T2-weighted images (3 mm sections) were used to outline each cyst and cyst volumes were calculated using the ANALYZE bioimaging software system. As for TKV, all measurements were blinded to study dates. For RBF measurements, thick-section, oblique-axial, two-dimensional, phase-contrast, breath-hold MR angiograms were obtained along the course of each renal artery and acted as reference images. The MR flow measurements were obtained perpendicular to the oblique-axial, two-dimensional reference images of the renal arteries using a cardiac-gated, two-dimensional, fast gradient-echo, phase-contrast pulse sequence. MR blood flow pulse sequence parameters were repetition time=8–10 ms, echo time=3–5 ms, field of view=14–20 cm, flip angle=20°, 5-mm slice thickness, 224–256 phase encodings, one excitation. The velocity encoding value was 100 cm/s, and flow acquisition was obtained in the slice direction. Flow analysis was performed using FLOW software version 4 (Medis, Leiden, The Netherlands). Semiautomated or manual techniques were used for definition of the vessel borders in the flow images depending on image quality. Vessel area estimations were made in images at all phases of the cardiac cycle. All RBF measurements were performed by the same radiologist (JG). Validation of the technique used in regards to accuracy and reproducibility have been reported.39.Torres V.E. King B.F. Chapman A.B. et al.Magnetic resonance measurements of renal blood flow and disease progression in autosomal dominant polycystic kidney disease.Clin J Am Soc Nephrol. 2007; 2: 112-120Crossref PubMed Scopus (116) Google Scholar, 40.King B.F. Torres V.E. Brummer M.E. et al.Magnetic resonance measurements of renal blood flow as a marker of disease severity in autosomal-dominant polycystic kidney disease.Kidney Int. 2003; 64: 2214-2221Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 41.Dambreville S. Chapman A.B. Torres V.E. et al.Renal arterial blood flow measurement by breath-held MRI: accuracy in phantom scans and reproducibility in healthy subjects.Magn Reson Med. 2010; 63: 940-950Crossref PubMed Scopus (16) Google Scholar No formal sample size calculation was performed. The number of subjects tested was based on experience from other previous clinical studies. Only key exploratory analyses are reported in this paper, pharmacokinetic analyses will be reported elsewhere. The primary outcome variables were the changes in GFR and RBF determined by PAH and MR from study day 0 to 8. Secondary outcomes were changes in urine volume, uric acid, osmolar and free water clearances, urine protein/creatinine ratio, urine albumin/creatinine ratio, serum cystatin C concentrations, plasma renin activity, plasma aldosterone concentrations, and the assessment of the safety of tolvaptan determined by the presence of adverse event, vital signs, laboratory tests, and electrocardiograms. Exploratory assessments included markers of volume status, for example, serum sodium, serum protein, blood hemoglobin, fluid intake, and thirst ratings. Changes in TKV and individual cyst volume were assessed post hoc by raters blinded to image sequence. The changes in the primary and secondary renal hemodynamic parameters at study day 8 were tested against study day 0 using paired t-test. Comparisons between patients with GFR ≥60 ml/min per 1.73 m2 and <60 ml/min per 1.73 m2 were performed using unpaired t-test. All tests were two-sided with alpha level 0.05. Pearson's correlations were performed to determine linear correlation. Measurement error was calculated as the absolute value of the difference between the measured volumes of the same patient at the two readings. Intraobserver variability, as the percentage measurement error, was determined by dividing the measurement error by the average of the two measurements for each MR study. An adverse event was defined as any new medical problem, or exacerbation of an existing problem, experienced by a subject while enrolled in the study, whether or not it was considered drug related by the investigator. Data are presented as means (±s.d.) or medians (range) when appropriated. All statistics were performed at Mayo using JMP software, version 8.0 (SAS Institute, Cary, NC). We thank the patients for taking part in the study. Funding for this study was provided by Otsuka Pharmaceutical Development & Commercialization, Inc.
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