The function of small GTPases is fine-tuned by a complex network of regulatory proteins such as G... more The function of small GTPases is fine-tuned by a complex network of regulatory proteins such as GTPase-activating proteins. The C1 gene at Xq28 encodes a protein assumed to function as a Rho GTPase-activating protein (rhoGAP). Characterization of the molecular defect causing X-linked nephrogenic diabetes insipidus (NDI) in a patient revealed a submicroscopic deletion of a 21.5-kb genomic fragment encompassing the entire arginine-vasopressin V2 receptor gene (AVPR2) and most of the C1 gene locus. In the absence of detailed information about the physiological relevance and specific functions of rhoGAP C1, a thorough clinical and laboratory investigation of the patient was performed. Besides clearly defined NDI symptoms caused by deletion of the AVPR2 gene, no major morphological abnormalities as determined by physical examination, radiography, ultrasound, and computed tomographic scan were detected. Extensive analysis of blood chemical, enzyme, and hormone values over a period of 16 years showed no deviations from normal ranges. On the basis of our observations, the rhoGAP C1 protein is not essential for normal development in the human. Because of a predominant expression pattern of the C1 gene in hematopoietic cells, we focused on immunologic and hematologic laboratory parameters of the affected boy and the mother who was found to be heterozygous. Differential white cell counts, including lymphocyte typing, determination of lymphokines, cytokines, and immunoglobulins, as well as numerous leukocyte function tests, showed no pathological findings. Therefore, we postulate that the loss of rhoGAP C1 function is most likely compensated by other members of the GAP family.
Loss-of-function mutations in the V2 vasopressin receptor (AVPR2) gene have been identified as a ... more Loss-of-function mutations in the V2 vasopressin receptor (AVPR2) gene have been identified as a molecular basis for X-linked nephrogenic diabetes insipidus (NDI). Herein, we describe a novel deletion mutation at nucleotide position 102 (delG102) found in a Russian family resulting in a frameshift and a truncated receptor protein. Furthermore, we analyzed the AVPR2 gene of two other unrelated boys with NDI from our patient clientele. These patients showed previously described mutations (R137H, R181C). In-depth characterization of the three mutant AVPR2s by a combination of functional and immunological techniques permitted further insight into molecular mechanisms leading to receptor dysfunction. Premature truncation of the AVPR2 (delG102) led to a drastically reduced receptor protein expression in transfected COS-7 cells and, as expected, precluded specific AVPR2 functions. As indicated by different ELISA and binding studies, the R137H mutant was almost completely retained in the cell interior. In contrast to previous studies, the few mutant receptors in the plasma membrane displayed a low (2.3-fold above basal) but significant ability to stimulate the Gs/adenylyl cyclase system. In contrast to the latter mutation, the R181C mutant is properly delivered to the cell surface but the mutation interferes with high affinity vasopressin binding. Impaired ligand binding is reflected in an about 100-fold shift of the concentration-response curve toward higher vasopressin concentrations with only slightly reduced agonist potency.
Following 10 years of clinical use of mycophenolate mofetil (MMF), a prodrug of mycophenolic acid... more Following 10 years of clinical use of mycophenolate mofetil (MMF), a prodrug of mycophenolic acid, the FDA has approved enteric-coated mycophenolate sodium (EC-MPS). EC-MPS was developed to reduce the upper-gastrointestinal (GI) effects of MMF. Unlike oral MMF, where absorption starts in the stomach, EC-MPS releases MPA in the small intestine. Along with the pharmacology and pharmacokinetics, three randomized, controlled clinical trials in solid-organ transplantation, comparing MMF and EC-MPS, are reviewed. Disappointingly, EC-MPS was similar to MMF in efficacy and safety and did not significantly improve the GI side effects. Moreover, bioequivalence dosing has only been established with concomitant ciclosporin. The pharmacokinetic characteristics must be studied in greater detail. EC-MPS is a safe and effective immunosuppressive agent approved for use in the prevention of acute rejection after renal transplantation. However, the anticipated improvement of GI side effects has not been forthcoming.
Experimental and Clinical Endocrinology & Diabetes, 2000
There is debate about the most suitable test for investigation of glucose tolerance in children w... more There is debate about the most suitable test for investigation of glucose tolerance in children with chronic renal failure. We therefore studied the agreement between the two most commonly used glucose tolerance tests in 33 children with chronic renal failure (mean age 10.9+/-5.3 years, median GFR was 24 ml/min/1.73 m2). All children underwent an oral glucose tolerance test (OGTT) with blood sampling up to 180 minutes and after an oral load of 1.75 g/kg and a standard intravenous glucose tolerance test (IVGTT) using 0.5 g/kg i.v. The two tests were performed at an interval of 23+/-5 days, with 9 patients having the OGTT before and 24 after the IVGTT. In order to account for the differing glucose load, a subgroup of 19 patients also received a glucose infusion test (GIT) using a total of 1.75 g/kg i.v. On IVGTT, 27 patients had a normal and 6 had a pathological glucose decay constant (k-value). On OGTT, 12 patients had an impaired glucose tolerance (IGT) and 3 patients were diabetic according to WHO standard, and only 18 patients had a normal glucose tolerance. While there was good correlation between both glucose and insulin concentrations between IVGTT and OGTT, only when reapplying the WHO criteria of a glucose concentration below 6.7 mmol/l to the concentration measured 180 minutes instead of 120 minutes after oral glucose load, the agreement between the two tests improved. The proportion of normal findings on GIT when compared to OGTT was identical. When using the appropriate definitions for normal and abnormal carbohydrate tolerance, interestingly the insulin (IRI) concentrations on OGTT were not discriminative between the normal and the pathological group, whereas IRI first phase secretion on IVGTT and IRI 0-180 AUC on GIT did discriminate. We conclude that the standard WHO OGTT criteria may have to be reconsidered in children with chronic renal failure and that OGTT should be extended to 180 minutes. The IVGTT, particularly when insulin early phase secretion (at 0, 1, 3 and 5 minutes) is also monitored, provides a reliable test for assessing glucose tolerance in children with chronic renal failure.
The function of small GTPases is fine-tuned by a complex network of regulatory proteins such as G... more The function of small GTPases is fine-tuned by a complex network of regulatory proteins such as GTPase-activating proteins. The C1 gene at Xq28 encodes a protein assumed to function as a Rho GTPase-activating protein (rhoGAP). Characterization of the molecular defect causing X-linked nephrogenic diabetes insipidus (NDI) in a patient revealed a submicroscopic deletion of a 21.5-kb genomic fragment encompassing the entire arginine-vasopressin V2 receptor gene (AVPR2) and most of the C1 gene locus. In the absence of detailed information about the physiological relevance and specific functions of rhoGAP C1, a thorough clinical and laboratory investigation of the patient was performed. Besides clearly defined NDI symptoms caused by deletion of the AVPR2 gene, no major morphological abnormalities as determined by physical examination, radiography, ultrasound, and computed tomographic scan were detected. Extensive analysis of blood chemical, enzyme, and hormone values over a period of 16 years showed no deviations from normal ranges. On the basis of our observations, the rhoGAP C1 protein is not essential for normal development in the human. Because of a predominant expression pattern of the C1 gene in hematopoietic cells, we focused on immunologic and hematologic laboratory parameters of the affected boy and the mother who was found to be heterozygous. Differential white cell counts, including lymphocyte typing, determination of lymphokines, cytokines, and immunoglobulins, as well as numerous leukocyte function tests, showed no pathological findings. Therefore, we postulate that the loss of rhoGAP C1 function is most likely compensated by other members of the GAP family.
Loss-of-function mutations in the V2 vasopressin receptor (AVPR2) gene have been identified as a ... more Loss-of-function mutations in the V2 vasopressin receptor (AVPR2) gene have been identified as a molecular basis for X-linked nephrogenic diabetes insipidus (NDI). Herein, we describe a novel deletion mutation at nucleotide position 102 (delG102) found in a Russian family resulting in a frameshift and a truncated receptor protein. Furthermore, we analyzed the AVPR2 gene of two other unrelated boys with NDI from our patient clientele. These patients showed previously described mutations (R137H, R181C). In-depth characterization of the three mutant AVPR2s by a combination of functional and immunological techniques permitted further insight into molecular mechanisms leading to receptor dysfunction. Premature truncation of the AVPR2 (delG102) led to a drastically reduced receptor protein expression in transfected COS-7 cells and, as expected, precluded specific AVPR2 functions. As indicated by different ELISA and binding studies, the R137H mutant was almost completely retained in the cell interior. In contrast to previous studies, the few mutant receptors in the plasma membrane displayed a low (2.3-fold above basal) but significant ability to stimulate the Gs/adenylyl cyclase system. In contrast to the latter mutation, the R181C mutant is properly delivered to the cell surface but the mutation interferes with high affinity vasopressin binding. Impaired ligand binding is reflected in an about 100-fold shift of the concentration-response curve toward higher vasopressin concentrations with only slightly reduced agonist potency.
Following 10 years of clinical use of mycophenolate mofetil (MMF), a prodrug of mycophenolic acid... more Following 10 years of clinical use of mycophenolate mofetil (MMF), a prodrug of mycophenolic acid, the FDA has approved enteric-coated mycophenolate sodium (EC-MPS). EC-MPS was developed to reduce the upper-gastrointestinal (GI) effects of MMF. Unlike oral MMF, where absorption starts in the stomach, EC-MPS releases MPA in the small intestine. Along with the pharmacology and pharmacokinetics, three randomized, controlled clinical trials in solid-organ transplantation, comparing MMF and EC-MPS, are reviewed. Disappointingly, EC-MPS was similar to MMF in efficacy and safety and did not significantly improve the GI side effects. Moreover, bioequivalence dosing has only been established with concomitant ciclosporin. The pharmacokinetic characteristics must be studied in greater detail. EC-MPS is a safe and effective immunosuppressive agent approved for use in the prevention of acute rejection after renal transplantation. However, the anticipated improvement of GI side effects has not been forthcoming.
Experimental and Clinical Endocrinology & Diabetes, 2000
There is debate about the most suitable test for investigation of glucose tolerance in children w... more There is debate about the most suitable test for investigation of glucose tolerance in children with chronic renal failure. We therefore studied the agreement between the two most commonly used glucose tolerance tests in 33 children with chronic renal failure (mean age 10.9+/-5.3 years, median GFR was 24 ml/min/1.73 m2). All children underwent an oral glucose tolerance test (OGTT) with blood sampling up to 180 minutes and after an oral load of 1.75 g/kg and a standard intravenous glucose tolerance test (IVGTT) using 0.5 g/kg i.v. The two tests were performed at an interval of 23+/-5 days, with 9 patients having the OGTT before and 24 after the IVGTT. In order to account for the differing glucose load, a subgroup of 19 patients also received a glucose infusion test (GIT) using a total of 1.75 g/kg i.v. On IVGTT, 27 patients had a normal and 6 had a pathological glucose decay constant (k-value). On OGTT, 12 patients had an impaired glucose tolerance (IGT) and 3 patients were diabetic according to WHO standard, and only 18 patients had a normal glucose tolerance. While there was good correlation between both glucose and insulin concentrations between IVGTT and OGTT, only when reapplying the WHO criteria of a glucose concentration below 6.7 mmol/l to the concentration measured 180 minutes instead of 120 minutes after oral glucose load, the agreement between the two tests improved. The proportion of normal findings on GIT when compared to OGTT was identical. When using the appropriate definitions for normal and abnormal carbohydrate tolerance, interestingly the insulin (IRI) concentrations on OGTT were not discriminative between the normal and the pathological group, whereas IRI first phase secretion on IVGTT and IRI 0-180 AUC on GIT did discriminate. We conclude that the standard WHO OGTT criteria may have to be reconsidered in children with chronic renal failure and that OGTT should be extended to 180 minutes. The IVGTT, particularly when insulin early phase secretion (at 0, 1, 3 and 5 minutes) is also monitored, provides a reliable test for assessing glucose tolerance in children with chronic renal failure.
Uploads
Papers by Guido Filler