Interstitial Fibrosis of Unilateral Ureteral Obstruction is Exacerbated in Kidneys of Mice Lacking the Gene for Inducible Nitric Oxide Synthase

Abstract

SUMMARY:Unilateral ureteral obstruction (UUO) is characterized by decreases in renal function and increases in interstitial fibrosis. Previous studies have indicated that pharmacologic manipulations that increase nitric oxide (NO) are beneficial to the obstructed kidneys. NO is produced from arginine by nitric oxide synthase (NOS), an enzyme that exists in both constitutive and inducible (iNOS) forms. To determine the role of the inducible form of NOS in UUO, we used mice with a targeted deletion of iNOS (iNOS -/-mice) and compared them with wild-type (WT) mice. Kidneys were obstructed for 2 weeks in both WT and iNOS -/-mice, and were then removed and bisected. Half of the kidney was embedded in paraffin and tissue sections were examined for interstitial volume or the presence of macrophages. The remainder was flash-frozen and samples were used to measure tissue collagen (hydroxyproline) or transforming growth factor-␤ (TGF-␤). This study demonstrates that both cortex and medulla of obstructed kidneys of iNOS -/-mice exhibit significantly increased interstitial volume and interstitial macrophages as compared with their WT counterparts. Furthermore tissue collagen was increased to 9.2 Ϯ 1.3 g/mg tissue in WT obstructed kidneys, whereas in iNOS -/-kidneys, collagen was increased to 13.2 Ϯ 0.8 g/mg tissue. The profibrotic cytokine TGF-␤ was also significantly increased in obstructed kidneys of iNOS -/-mice, as compared with WT mice. No differences were noted between the unobstructed kidneys of iNOS -/-mice compared with WT mice in any of the parameters examined. These results demonstrate that targeted deletion of the iNOS results in exacerbation of fibrotic events in the obstructed kidney. These results confirm previous pharmacologic studies, and suggest that NO produced via the inducible NOS normally serves a protective function in UUO. (Lab Invest 2000, 80:1721-1728.

Long-term continuous sildenafil treatment ameliorates corporal veno-occlusive dysfunction (CVOD) induced by cavernosal nerve resection in rats

“…Studies on liver and kidney fibrosis in the iNOS knock-out mouse, and our previous work in Peyronie's disease and its animal models, vaginal fibrosis, aging-related arterial media fibrosis, and in corporal fibrosis, suggests that despite iNOS may be initially induced during an early inflammatory process, its main role is as an antifibrotic agent. 12,13,[24][25][26][27][28][29]32,33,37,38,50 This may occur via cGMP produced by the nitric oxide from iNOS, and/or the nitric oxide can directly reduce collagen synthesis, myofibroblast formation in the interstitial connective tissue, and reactive oxygen species. 26,[30][31][32] In contrast to our study with vardenafil in the BCNR rat, the slight stimulation of iNOS induction by sildenafil in the BCNR animals was not significant.…”

“…[14][15][16][17][18][19][20][21][22][23] The expression of iNOS in certain non-immunological tissues is assumed to be a defense mechanism against fibrosis. [24][25][26][27][28][29] The nitric oxide produced by iNOS, besides inhibiting collagen synthesis and the TGFb1 pathway, also quenches reactive oxygen species, and in some cases, the differentiation of fibroblasts to myofibroblasts, the cells that produce collagen in many fibrotic conditions. [30][31][32] In a recent study, we have shown that the PDE5 inhibitor, vardenafil, given for 45 days in the drinking water to rats subjected to bilateral cavernosal nerve resection (BCNR) [33][34][35] prevented the development of CVOD and the underlying SMC loss and fibrosis in the corpora cavernosa.…”

Role of nitric oxide deficiency in the development of hypertension in hydronephrotic animals

“…Oxidative stress is coupled to hypertension in several models and demonstrated in kidneys with ureteral obstruction (28), where it might impair renal NO production. Treatment modalities that increase NO formation (40) or inhibit oxidative stress (54) are beneficial to the progression of cellular and molecular parameters of tubulointerstitial fibrosis caused by obstruction of the ureter, whereas NO deficiency increases renal damage (21).…”

Rationale for phosphodiesterase 5 inhibitor use post-radical prostatectomy: experimental and clinical review

“…First, the fact that general inhibition of the activity of all NOS isoforms, and hence nitric oxide production, by prolonged sustained administration of N(G)-nitro-L-arginine methyl ester to rats, leads to considerable fibrotic degeneration in organs such as the heart, liver and kidney, independent of hemodynamic factors that may contribute to this process. [21][22][23][24][25] Second, specific genetic blockade of iNOS in the iNOS knockout mice leads to exacerbation of experimental fibrosis of the kidney and liver, 26,27 and the chronic inhibition of iNOS activity in rats by N6-(1-iminoethyl)-L-lysine dihydrochloride (L-NIL) intensifies aging-related fibrosis of the arterial wall and of the experimentally induced Peyronie's disease-like fibrotic plaque in the penis. 28,29 Third, administration of iNOS cDNA in the latter model reduces the fibrotic plaque.…”