2002 Global Researcher Conference Proceeding

April 26 - 28, 2002

Line
Conference: 2002 Global Researcher Conference
Title: Decrease in urine volume and increase in urine osmolality after SR49059 administration in five adult male patients with X-linked nephrogenic diabetes insipidus
Authors: Bichet, Daniel G.; Bouvier, Michel; Brouard, Remi; Morello, Jean-Pierre; Bernier, Virginie; Lonergan, Michele; Arthus, Marie-Francoise
Institutions: Hopital du Sacre-Coeur de Montreal, Universite de Montreal, Sanofi-Aventis, University of Montreal
Line
Bichet The natural history of untreated X-linked nephrogenic diabetes insipidus includes hypernatremia, hyperthermia, mental retardation and repeated episodes of dehydration in early infancy (Crawford JD, Bode HH: Disorders of the posterior pituitary in children. In: Endocrine and Genetic Diseases of Childhood and Adolescence, 2nd ed., edited by Gardner LI, Philadelphia, W.B. Saunders. 1975, pp 126-158; van Lieburg AF, Knoers NVAM, Monnens LAH: Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus. J Am Soc Nephrol 10: 1958-1964, 1999). I initially thought that the identification of AVPR2 mutations in all the families with X-linked NDI, which would allow pre- and perinatal testing of at-risk male infants will not only prevent the episodes of dehydration but also permit a close to normal growth and development. A low sodium diet and distal tubule diuretics may achieve a 20-30% decrease in urine output but a normal growth curve is still difficult to reach during the first 2-3 years of the life of these children. It has become clear, however, that the young affected children eat with difficulties, often vomit, and that their growth is suboptimal. There is a need for a safe further reduction in urine output. We recently used pharmacological compounds to rescue misfolded mutant V2 receptors: we demonstrated in vitro that the non-peptide V2 specific antagonists SR121463 and VPA-985 dramatically increased cell surface expression and rescued the function of eight naturally occurring AVPR2 mutations (del62-64, L59P, L83Q, Y128S, S167L, A294P, P322H, R337X) responsible for NDI by promoting their proper folding and maturation (Morello JP, Salahpour A, Laperrière A, Bernier V, Arthus M-F, Lonergan M, Petäjä-Repo U, Angers S, Morin D, Bichet DG, Bouvier M: Pharmacological chaperones rescue cell-surface expression and function of misfolded V2 vasopressin receptor mutants. J Clin Invest 105: 887-895, 2000). We put forward a general mechanism of rescue: we hypothesized that the non-peptide V2, V1a and possibly, non-peptide oxytocin antagonists could accomplish the same rescue function on misfolded mutant V2 receptors. We had access to a clinically tested specific non-peptide V1a antagonist SR49059 manufactured by Sanofi-Synthelabo. We obtained permission from our Ethics Committee and from the Health Protection Branch (Ottawa, Canada) and we gave SR49059 orally to five adult patients with X-linked NDI. These patients had life-long history of polyuria and polydipsia and extensive prior testing demonstrating a lack of urinary osmolality response to AVP or to dDAVP. They bear the following AVPR2 mutations: del62-64, R137H 3 patients, W164S. Patients were hospitalized in a Clinical Research Unit and received a fixed Na, K, osmotic and caloric diet for 3 days. Mean sodium ingestion (mEq) for the 3 days was: 169±3.4 (day 1); 179.4±0.6 (day 2) and 194±4.2 (day 3). Mean potassium ingestion (mEq) for the 3 days was: 101.2±6.8 (day 1); 106.8±4.2 (day 2); and 107±3 (day 3). Water ingestion was not restricted. After control measurements (day 1, no medication), SR49059 was administered orally for the next 2 days. Blood pressure and pulse were measured every 30 minutes from 08h00 to 24h00 for the first 2 patients and every 2 hours for the last 3 patients and no significant change in blood pressure or pulse were encountered throughout the study. SR decreased 24-hour urine volume (11.9±2.3 l to 8.2±2.0 l, p < 0.05) and 24-hour water intake (10.7±1.9 l to 7.2±1.6 l, p < 0.05). Maximal increase in urine osmolality was observed from 14h00 to 20h00 on day 3 (103±8 mOsm/kg to 147±38 mOsm/kg, p=0.05). 24-hour urine osmolar excretion, Na, K and creatinine excretion and plasma Na were constant throughout the study. Two patients, both bearing the R137H mutation received the SR compound during 8 days and similar beneficial effects on water balance were observed. We have demonstrated here that the administration of non-peptide vasopressin antagonist increased urine osmolality by 50% in selected patients with X-linked NDI. These clinical experiments confirmed the beneficial conformational effect observed in vitro. Given that many pathologies stem from intracellular retention of otherwise functional proteins, this mechanism may offer a new therapeutic approach to the treatment of several different diseases resulting from errors in protein kinesis.

Testing males at risk for X-linked NDI both before and immediately after their birth, and treating them appropriately if they do have it, has reduced the severity of NDI symptoms in these males. Yet, there is still a need to further reduce these symptoms. Using laboratory cell cultures, Bichet, et al, demonstrated that certain chemical compounds could help certain vasopressin 2 receptor (V2R) mutants reach the cell surface and function properly. These chemical compounds accomplished this by helping the mutated V2R proteins develop their proper shape and growth cycle.

Bichet, et al., then tested the effectiveness of a specific chemical chaperone, SR49059, on reducing NDI symptoms in five adult NDI patients. The results were encouraging. The patients' four-hour water intake and urine volume decreased. This treatment approach is not only promising for NDI, it might also treat other diseases resulting from improperly moving proteins.