In the normal kidney glomerular filtration rate (GFR) is accompanied by parallel changes in Na reabsorption (TNa). Since TNa constitutes the major obligation for kidney oxygen utilization (QO2) (>80%) QO2 changes more or less in parallel with TNa. The remnant kidney or 5/6th nephrectomy (A/I) model has been used as a valid experimental example of progressive chronic kidney disease (CKD). Blockade of angiotensin II activity greatly prevents or ameliorates progressive loss of kidney function and glomerulosclerosis. We have examined the metabolic and molecular changes in the early phases of the A/I kidney one week after creation. QO2 factored by TNa or QO2/TNa is increased markedly leading to low oxygen tension in the A/I at this earlier stage. Combined AII blockade with ACE inhibitor (CAP) and AT-1 receptor blocker (LOS) (A/I + T1) totally normalizes the QO2/TNa. These findings were not the result of either the reduction of blood pressure since triple therapy (A/I + T2) did not normalize QO2/TNa nor did the increase in GFR that accompanies AII blockade by administration of lysine (A/I + T3) Several molecules and enzymes were overexpressed in the untreated A/I kidney including NADPH oxidase, heme-oxygenase-1 (HO-1),, and ERK 1/2 phosphorylation and functional nitric oxide activity was decreased. All of these findings were normalized by AII blockade but not by changes in blood pressure and GFR. Several factors activated by hypoxia inducible factor-1 alpha (HIF-1 alpha) e.g., VEGF, GLUT-1 and HO-1 were expressed in the untreated 5/6th nephrectomy kidney.
In Specific Aim #1 we will examine in all groups the effects of several treatments to define the 'pars value' of contributions to the ~60% increase in QO2/TNa corrected by AII blockade; sham control, A/I untreated, A/I + T1, A/I + T2 and A/I + T3. These include 1) reduced NO functional activity, 2) role of AII induced insulin resistance in the kidney (we have shown that acute insulin infusion ameliorates approximately 40-50% of the increase in QO2/TNa), 3) increased kidney gluconeogenesis, 4) kidney cell proliferation due to growth stimuli using DFMO, inhibitor of ornithine decarboxylase, 5) NADPH oxidase and ROS, 6) decreased efficiency of Na reabsorption using micropuncture and microinjection techniques. We will examine further the effects of maneuvers that reduce oxygen consumption on disease progression at 4 weeks after subtotal nephrectomy.
In Specific Aim #2 we will focus upon the systems biology of the molecular algorithm of activation in the A/I kidney with the hypothesis that NADPH oxidase and HIF-1 alpha constitute the major critical hubs leading to activation of other molecules, enzymes and cyclins/CKI important to cell proliferation and potential kidney fibrosis. We will examine the effects of NADPH oxidase inhibition with apocycnin. We will both inhibit (echinomycin and YC-1) and induce HIF-1 alpha (CoCl2 and DMOG) to determine complex net effects on downstream molecular events. We will also examine the effects of manipulation of NADPH oxidase and HIF-1 alpha on progression of disease at 4 weeks.
Project Narrative There are 20-40 million Americans with chronic kidney disease (CKD) and the impact of this disease on the Veterans population is very significant. CKD is not only progressive, in many cases to end stage kidney disease requiring artificial kidney treatments or kidney transplantation, but also contributes greatly to the very high incidence of heart and circulatory disease. Blockade of the renin-angiotensin system with drugs that also lower blood pressure has been shown of benefit in that they slow the rate of progressive loss of kidney function. Combined treatment with two agents that decrease angiotensin effects in the kidney normalizes oxygen consumption factored by NaCl reabsorption in a model of CKD. We will determine the multiple contributing factors leading to increased oxygen consumption and the reasons why blockade of angiotensin restores oxygen consumption to normal and define the molecules and enzymes that are involved in this process.