Podocyte-specific overexpression of human angiotensin-converting enzyme 2 attenuates diabetic nephropathy in mice.

Angiotensin-converting enzyme 2 (ACE2) degrades angiotensin II to angiotensin-(1-7) and is expressed in podocytes. Here we overexpressed ACE2 in podocytes in experimental diabetic nephropathy using transgenic methods where a nephrin promoter drove the expression of human ACE2. Glomeruli from these mice had significantly increased mRNA, protein, and activity of ACE2 compared to wild-type mice. Male mice were treated with streptozotocin to induce diabetes. After 16 weeks, there was no significant difference in plasma glucose levels between wild-type and transgenic diabetic mice. Urinary albumin was significantly increased in wild-type diabetic mice at 4 weeks, whereas albuminuria in transgenic diabetic mice did not differ from wild-type nondiabetic mice. However, this effect was transient and by 16 weeks both transgenic and nontransgenic diabetic mice had similar rates of proteinuria. Compared to wild-type diabetic mice, transgenic diabetic mice had an attenuated increase in mesangial area, decreased glomerular area, and a blunted decrease in nephrin expression. Podocyte numbers decreased in wild-type diabetic mice at 16 weeks, but were unaffected in transgenic diabetic mice. At 8 weeks, kidney cortical expression of transforming growth factor-ß1 was significantly inhibited in transgenic diabetic mice as compared to wild-type diabetic mice. Thus, the podocyte-specific overexpression of human ACE2 transiently attenuates the development of diabetic nephropathy.

Development of a beta-trace protein based formula for estimation of glomerular filtration rate.

Beta-trace protein (BTP) is a novel marker of glomerular filtration rate (GFR). To date, no pediatric formula for calculating GFR based on BTP has been developed. We measured GFR, serum creatinine and BTP in 387 children who underwent 474 (99m)Tc-diethylene triamine pentaacetic acid renal scans. A BTP-based formula for estimating GFR was derived using stepwise linear regression analysis. A separate control group of 116 measurements in 99 children was used to validate the novel formula. A formula was also developed for each gender. The novel formula is: [formula: see text]. The Spearman rank correlation coefficient between the BTP-derived GFR estimate and the measured GFR was 0.80 [95% confidence interval (CI) 0.76-0.83], which is substantially better than that derived with the Schwartz formula (r = 0.70, 95% CI 0.65-0.74). The Bland-Altman analysis revealed a mean bias of 1.21% [standard deviation (SD) 28%] in the formula development dataset, which was virtually identical to the 1.03% mean bias (29.5% SD) in the validation group and no different from the Schwartz formula bias. The percentage of values within 10% (33.0 vs. 28.3%) and 30% deviation (76.8 vs. 72.6%) were better for BTP-based formula than for the Schwartz formula. Separate formulas according to gender did not perform better than that for the pediatric population. This BTP-based formula was found to estimate GFR with reasonable precision and provided improved accuracy over the Schwartz GFR formula.

Body mass does not have a clinically relevant effect on cystatin C eGFR in children.

BACKGROUND: Unlike creatinine, Cystatin C (CysC) is believed to be independent of body composition in both adults and children. Recent findings in adults, suggesting an improved performance of CysC-based estimated glomerular filtration rate (CysC eGFR) by accounting for body mass, necessitated a careful re-evaluation of this issue in children. METHODS: We studied 240 children (median age 11.7 years, range 2-17.9 years, 107 girls), with various kidney diseases, for any change in the relationship between (99)Tc DTPA GFR and CysC eGFR after accounting for body mass. For body mass assessment, body mass index (BMI) z-score was calculated using height-adjusted age, to account for growth retardation secondary to chronic kidney disease. RESULTS: CysC eGFR did not have a significant correlation with BMI z-score (correlation coefficient = 0.06; P = 0.34). Accounting for BMI z-score did not add to the 65% variance in nuclear GFR explained by CysC eGFR. Moreover, it did not change the regression coefficient of 0.85 between CysC eGFR and nuclear GFR either. On Bland & Altman analysis, the bias of 0.05 and standard deviation of 20.39 also did not improve after accounting for BMI z-score in the revised CysC eGFR formula. CONCLUSIONS: In children, body mass exerts a minimal effect on the performance of CysC eGFR estimation.

Pharmacokinetics of pyridostigmine in a child with postural tachycardia syndrome.

Pyridostigmine has been proposed for the treatment of postural orthostatic tachycardia syndrome in adults at a dose of 60 mg twice daily, but no dosing recommendation exists for children. With the approval of our local ethics board, we tested the pharmacokinetics of pyridostigmine in 6 children with myasthenia and a pediatric index patient with severe postural orthostatic tachycardia syndrome whose condition failed all conventional therapy and who had developed significant postural hypertension. Pyridostigmine was quantified by using a validated, semiautomated, and specific high-performance liquid chromatography/tandem mass spectrometry assay in combination with online column-switching extraction and turbo electrospray ionization. The patient with postural orthostatic tachycardia syndrome showed a dose-dependent favorable response to oral pyridostigmine. Pharmacokinetic evaluation revealed a short half-life of 2.29 hours, similar to the 2.0 +/- 0.63 hours in the patients with myasthenia. The patient with postural orthostatic tachycardia syndrome has subsequently been treated at a dose of 45 mg in the morning, 30 mg at lunchtime, and 15 mg at bedtime; after 9 months, there has been persistent positive effect and without additional blood pressure medication. No major adverse effects occurred. Pyridostigmine has been a safe and effective treatment modality for this child with postural orthostatic tachycardia syndrome. The short half-life suggests that dosing 3 times per day is preferable.