These data suggest that the protective effect of physiological levels of nitric oxide may be by virtue of inhibition of PHD or increased HIF-1α expression, hence, the pathological changes produced following its withdrawal was accompanied by increased PHD or decreased HIF-1α expression. Exacerbation of hypertension and renal injury following PHD inhibition suggests a deleterious effect in the chronic setting and challenges the dogma that inhibition of PHD is useful in cardiovascular diseases.

KKidney disease could result from hypertension and ischemia/hypoxia. Key mediators of cellular adaptation to hypoxia are oxygen-sensitive hypoxia inducible factor (HIF)s which are regulated by prolyl-4-hydroxylase domain (PHD)-containing dioxygenases. However, HIF activation can be protective as in ischemic death or promote renal fibrosis in chronic conditions. This study tested the hypothesis that increased HIF-1α consequent to reduced PHD expression contributes to the attendant hypertension and target organ damage in deoxycorticosterone acetate (DOCA)/salt hypertension and that PHD inhibition ameliorates this effect. In rats made hypertensive by DOCA/salt treatment (DOCA 50 mg/kg s/c; 1% NaCl orally), PHD inhibition with dimethyl oxallyl glycine (DMOG) markedly attenuated hypertension (P<0.05), proteinuria (P<0.05) and attendant tubular interstitial changes and glomerular damage (P<0.05). Accompanying these changes, DMOG blunted the increased expression of kidney injury molecule (KIM)-1 (P<0.05), a marker of tubular injury and reversed the decreased expression of nephrin (P<0.05), a marker of glomerular injury. DMOG also decreased collagen I staining (P<0.05), increased serum nitrite (P<0.05) and decreased serum 8-isopostane (P<0.05). However, the increased HIF-1α expression (P<0.01) and decreased PHD2 expression (P<0.05) in DOCA/salt hypertensive rats was not affected by DMOG. These data suggest that reduced PHD2 expression with consequent increase in HIF-1α expression probably results from hypoxia induced by DOCA/salt treatment with the continued hypoxia and reduced PHD2 expression evoking hypertensive renal injury and collagen deposition at later stages. Moreover, a PHD inhibitor exerted a protective effect in DOCA/salt hypertension by mechanisms involving increased nitric oxide production and reduced production of reactive oxygen species.

In response to reduced oxygen availability, important cellular and molecular adaptive changes occur in living organisms. Hypoxia‐inducible factor (HIF) is a major adaptive mechanism and prolyl hydroxylase‐binding domain proteins (PHD) is its most important negative regulator. However, peroxisome proliferator‐activated receptor (PPARα), a nuclear transcription factor is activated in response to hypoxia/HIF‐1α and regulates many of the downstream target genes. This study tested the hypothesis that inhibition of prolyl hydroxylase domain (PHD) would confer greater protection against ischemia by a mechanism involving PPARα activation. Rats were subjected to ischemia/reperfusion (I/R) for 48 hours with or without L‐mimosine (L), a PHD inhibitor, fenofibrate, a PPARα ligand, MK886, a PPARα inhbitior. Renal blood flow (RBF; laser doppler flowmetry) recovered to 93±8%, 56±7% (p<0.001) and 87±10% (p<0.001) in control, ischemic and L‐treated groups, respectively. Coincident with these changes, serum uric acid decreased by 41±6% (p<0.05) in I/R group versus 26±3% (p<0.05) following L‐ treatment. Compared to controls, serum nitric oxide decreased by 33±3% (p<0.05) in ischemic group while L treatment abolished the effect of ischemia (P<0.05). Similarly, 24hr urine volume increased by 100±13% (p < 0.001) in I/R and this was abolished by L (3%±0). 24‐hour urinary protein excretion increased 5‐fold in I/R group but was attenuated to a 2‐fold increase in L‐treated (p<0.05) group. Fenofibrate protected rats from the effects of I/R while MK886 blunted its effect. These findings suggest that stabilization of HIF‐1α following inhibition of PHD protects against I/R in the rat kidney and that PPARα contributes to these effects.