Apurv Khanna

Amelioration of metabolic acidosis in patients with low GFR reduced kidney endothelin production and kidney injury, and better preserved GFR

Metabolic acidosis often accompanies low glomerular filtration rate and induces secretion of endothelin, which in turn might mediate kidney injury. Here we tested whether treatment of metabolic acidosis in patients with low glomerular filtration rate reduced the progression of kidney disease. Fifty-nine patients with hypertensive nephropathy and metabolic acidosis had their blood pressure reduced with regimens that included angiotensin-converting enzyme inhibition. Thirty patients were then prescribed sodium citrate, and the remaining 29, unable or unwilling to take sodium citrate, served as controls. All were followed for 24 months with maintenance of their blood pressure reduction. Urine endothelin-1 excretion, a surrogate of kidney endothelin production, and N-acetyl-beta-D-glucosaminidase, a marker of kidney tubulointerstitial injury, were each significantly lower, while the rate of estimated glomerular filtration rate decline was significantly slower. The estimated glomerular filtration rate was statistically higher after 24 months of sodium citrate treatment compared to the control group. Hence it appears that sodium citrate is an effective kidney-protective adjunct to blood pressure reduction and angiotensin-converting enzyme inhibition.

Cigarette smoking exacerbates and its cessation ameliorates renal injury in type 2 diabetes.

Background: Patients with type 2 diabetes and macroalbuminuria generally experience progressive glomerular filtration rate (GFR) decline despite angiotensin‐converting enzyme inhibition (ACEI) and blood pressure (BP) control but this therapy generally stabilizes GFR in those without macroalbuminuria. Cigarette smoking exacerbates GFR decline in patients with type 2 diabetes and macroalbuminuria despite ACEI and BP control; whether this therapy prevents nephropathy progression in nonmacroalbuminuric type 2 diabetic smokers is unknown. Methods: We determined the course of urine excretion of indices of renal injury that distinguished patients with type 2 diabetes with and without macroalbuminuria but with normal plasma creatinine who were prospectively followed 6 months while receiving ACEI and BP control. We compared this course in nonsmokers and smokers with normo‐, micro‐, and macroalbuminuria (n = 157) and in response to smoking cessation in a separate cohort (n = 80) with microalbuminuria. Results: Urine excretion of transforming growth factor &bgr;‐1 (UTGF&bgr;V) increased in macroalbuminuric but not in nonmacroalbuminuric nonsmokers and UTGF&bgr;V rate was higher in smokers than nonsmokers within each albuminuria group. In the separate microalbuminuric cohort, the rate of UTGF&bgr;V change for quitting smokers was not different from nonsmokers (0.093 versus −0.123 ng/g of creatine/week, P = not significant) but that for nonquitting smokers (0.970) was higher than nonsmokers (P = 0.017). Conclusions: Patients with type 2 diabetes who are at high risk compared with low risk for nephropathy progression have progressive renal injury as measured by increasing UTGF&bgr;V. Cigarette smoking exacerbates renal injury in type 2 diabetes despite BP control and ACEI, but its cessation in those with microalbuminuria ameliorates the progressive renal injury caused by continued smoking.

Increased Endothelin Activity Mediates Augmented Distal Nephron Acidification Induced by Dietary Protein

We tested the hypothesis that increased dietary protein augments distal nephron acidification through an endothelin-dependent mechanism. Munich-Wistar rats ate minimum electrolyte diets of 50% (HiPro) and 20% (CON) casein-provided protein, the latter comparable to standard chow. HiPro vs. CON had higher distal nephron H+ secretion (41.3 +/- 4.0 vs. 23.0 +/- 2.1 pmol/mm.min, p < 0.002) mediated by augmented Na+/H+ exchange and H(+)-ATPase activity. Renal cortex of HiPro vs. CON had higher ET-1 addition to microdialysate and higher ET-1 mRNA, consistent with increased renal ET-1 production. Bosentan, an endothelin A/B receptor antagonist, decreased HiPro distal nephron H+ secretion (28.4 +/- 2.4 vs. 41.3 +/- 4.0 pmol/mm.min, p < 0.016) through decreased Na+/H+ exchange and decreased H(+)-ATPase activity. Increased dietary protein augments distal nephron acidification through an endothelin-sensitive increase in Na+/H+ exchange and H(+)-ATPase activity, supporting an endothelin role in the distal nephron response to this common challenge to acid-base status.

Role of free hemoglobin in 8-iso prostaglandin F2-alpha synthesis in chronic renal failure and its impact on CD163-Hb scavenger receptor and on coronary artery endothelium.

Free hemoglobin (Hb) during autoxidation increases 8-iso-prostaglandin-F2-alpha (8-isoprostane) formation in vitro. Because 8-isoprostane and plasma Hb are elevated in chronic renal failure (CRF), we evaluated the role of Hb in this isoprostane synthesis in vivo. By monitoring correlations between Hb, haptoglobin (Hp), CD163-Hb-scavenger receptor, and 8-isoprostane that is known to induce CD163 shedding, we examined whether 8-isoprostane blocks Hb catabolism in CRF. Additionally, by studying the effect of 8-isoprostane on human coronary artery endothelium (HCAEC) in vitro and its impact on intercellular adhesion molecule-1 (ICAM-1) in vivo, we tested its role in promotion of cardiovascular events in CRF. Twenty-two never-dialyzed CRF patients and 18 control patients were screened for renal function, plasma and urine 8-isoprostane, and plasma Hb, Hp, thiobarbituric-acid-reactants (TBARS), C-reactive-protein (CRP), and soluble (s) ICAM-1 and sCD163. HCAEC exposed to 8-isoprostane were tested for ICAM-1 and apoptosis. In CRF, urine 8-isoprostane was significantly elevated and correlated with free-Hb and TBARS. The increased free-Hb, Hp, and sCD163 in CRF suggested 8-isoprostane–mediated suppression of Hb catabolism through CD163 receptor shedding. 8-Isoprostane enhanced ICAM-1 expression and apoptosis in HCAEC. CRF patients showed elevated sICAM-1. In conclusion, free-Hb, via 8-isoprostane, paradoxically blocks its own catabolism. Free-Hb and/or 8-isoprostane may intensify cardiovascular events in CRF.

330 ORAL ALKALI IMPROVES INDICES OF INCREASED CARDIOVASCULAR RISK IN CHRONIC KIDNEY DISEASE ASSOCIATED WITH PRIMARY HYPERTENSION

Subjects with compared to those without chronic kidney disease (CKD) have increased risk for cardiovascular disease (CVD). We tested the hypothesis that oral alkali as Na+ citrate improves indices of CVD risk in primary hypertensives with CKD. Nonsmoking hypertensives with CKD (HTN-CKD, calculated GFR = 35 ± 3 mL/min, n = 15) and without CKD (HTN, calculated GFR = 89 ± 3 mL/min, n = 21) had systolic blood pressure (BP) reduced to similar levels (132 ± 2 and 135 ± 1 mm Hg, respectively) over six months with regimens that included angiotensin-converting enzyme inhibitors. After BP reduction, HTN-CKD had higher serum C-reactive protein (CRP) (13.7 ± 1.9 vs. 8.4 ± 0.9 mg/L, p < .01) and higher urine albumin excretion measured by (mg) albumin-to-(g) creatinine (alb/cr) ratio (71.4 ± 20.7 vs. 9.9 ± 1.5, p < .002) in an a.m. specimen. HTN-CKD subjects with serum total CO2 < 22 mM (n = 9) were prescribed Na+ citrate (1 meq HCO3 equivalent/kg/day) as per current recommendations but the remaining HTN-CKD subjects (n = 6) received no alkali therapy. Systolic BP control was unchanged throughout the additional six months of follow-up for alkali-treated and not-treated HTN-CKD subjects. After six months, serum total CO2 increased in the alkali-treated HTN-CKD subjects (20.2 ± 0.4 to 24.4 ± 0.4 mM, p < .001) but decreased in the untreated HTN-CKD subjects (24.0 ± 0.5 vs. 23.3 ± 0.4 mM, p < .02). Serum CRP (13.0 ± 1.3 to 10.2 ± 0.8 mg/L, p < .02, paired t) and urine alb/cr (91.9 ± 29.8 to 67.4 ± 23.7, p < .007, paired t) decreased in the alkali-treated HTN-CKD subjects but neither CRP (14.7 ± 4.6 to 15.7 ± 4.1 mg/L, p = .14, paired t) nor urine alb/cr (40.8 ± 23.4 to 44.2 ± 20.4, p = .35, paired t) changed in the untreated HTN-CKD subjects. These data show that alkali therapy following BP reduction in primary hypertensives with CKD reduces serum CRP and urine albumin excretion, two indices of increased CVD risk. The data suggest that alkali amelioration of metabolic acidosis in subjects with CKD reduces their increased CVD risk.

328 INCREASED DIETARY PROTEIN AS CASEIN BUT NOT SOY AUGMENTS RENAL ENDOTHELIN PRODUCTION

Increased dietary protein provided as purified casein augments renal endothelin production (JASN 2004;15:2266) by mechanisms that have not been fully elucidated. We tested the hypothesis that augmented renal endothelin production induced by dietary protein as casein is mediated by the acid challenge to systemic acid-base status induced by metabolism of this protein source. Munich-Wistar rats ate minimum electrolyte diets with protein provided as either casein (CAS) that yields net acid or soy that yields net base when metabolized. After 3 weeks of diet we measured blood and urine acid-base data, urine endothelin-1 (ET-1) excretion as a surrogate of renal ET-1 production, and renal cortical endothelin-1 mRNA with real-time PCR and light cycler technology. Within groups eating the two protein types, those eating diets with higher protein content (50%) were compared to those eating 20% protein, the latter % being comparable to standard rat chow. Animals eating 50% compared to 20% CAS had lower serum total CO2 (23.3 ± 0.5 vs. 25.2 ± 0.6 mM, p < .03), higher urine net acid excretion (NAE) (7067 ± 937 vs. 4460 ± 639 μM/d, p < .04), and higher urine ET-1 excretion (70 ± 14 vs. 22 ± 3 pg/day, p < .005). By contrast, total CO2 (27.3 ± 0.6 vs. 26.6 ± 0.7 mM, p = .78), urine NAE (1698 ± 247 vs. 1803 ± 332 μM/d, p = .80), and urine ET-1 excretion (42 ± 10 vs. 37 ± 3 pg/day, p = .64) were not higher in animals eating 50% compared to 20% soy. ET-1 mRNA was higher in 50% vs. 20% CAS but was similar in 50% vs. 20% soy. 50% CAS animals given oral bosentan, an endothelin A/B receptor antagonist, had higher serum total CO2 (24.8 ± 0.5 vs. 23.3 ± 0.4 mM, p < .04, paired t) and lower urine NAE (7067 ± 937 to 5704 ± 594 μM/d, p < .05, paired t) than 50% CAS animals not given bosentan. Serum total CO2 and urine NAE were not different in the bosentan-ingesting vs. non-ingesting 20% CAS or in either soy group. The data show that increasing dietary protein with the acid-producing casein diet but not with the base-producing soy diet increases renal endothelin production and induces endothelin-mediated augmentation of renal acidification. The data support the hypothesis that augmented renal endothelin production induced by increased dietary protein as casein is medicated through the acid challenge to systemic acid-base status provided by the casein diet.