Z-Ile-Glu(O-t-butyl)-Ala-Leucinal

We examined whether the proteasome could regulate endothelin (ET)-1 production in vascular endothelial cells (ECs). A proteasome inhibitor N-benzyloxycarbonyl-Ile-Glu (O-t-Bu)-Ala-leucinal (PSI) significantly decreased ET-1 release from ECs by about 25% of the basal release. PSI also suppressed tumor necrosis factor (TNF)-alpha-induced ET-1 release from ECs in a dose-dependent manner. Similar inhibitory effects were observed using another proteasome inhibitor lactacystin, whereas a calpain inhibitor calpeptin had no apparent effect on ET-1 release. Furthermore, PSI significantly attenuated prepro ET-1 mRNA expression under basal and TNF-alpha-stimulated conditions. Electrophoretic mobility shift assay showed that proteasome inhibitors diminished TNF-alpha-stimulated nuclear factor-kappa B (NF-kappaB) activation in ECs. Pretreatment with antioxidants, pyrrolidine dithiocarbamate and alpha-lipoic acid, both of which are known to be suppressors of NF-kappaB activation, effectively attenuated basal and TNF-alpha-induced ET-1 release. Thus, a proteasome-dependent proteolytic pathway is at least partly involved in ET-1 production under basal conditions, and this proteolytic pathway seems to have a crucial role in ET-1 production enhanced by TNF-alpha.

Acute renal failure was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function parameters such as blood urea nitrogen, plasma creatinine, creatinine clearance, urine flow and urinary osmolality were measured to test the effectiveness of drugs. Renal function in untreated acute renal failure rats markedly decreased at 24 h after reperfusion. The administration of PSI, N-benzyloxycarbonyl-Ile-Glu(O-t-Bu)-Ala-leucinal, a proteasome inhibitor, at a dose of 1 mg/kg before the occlusion abolished the decreases in the renal function of acute renal failure rats. Calpeptin (1 mg/kg), a calpain inhibitor, attenuated the deterioration of renal function to the same extent as 0.1 mg/kg PSI, but no significant difference was observed between the untreated and calpeptin-treated acute renal failure groups. Histopathological examination of the kidney of untreated acute renal failure rats revealed severe lesions, such as tubular necrosis, proteinaceous casts in tubuli and medullary congestion, all of which were significantly suppressed by PSI (1 mg/kg) treatment. In contrast, calpeptin, at the same dose, was ineffective against the development of renal lesions.

1. In the present study, we investigated the potential of the proteasome inhibitor N-benzyloxycarbonyl-Ile-Glu(O-t-Bu)-Ala-leucinal (PSI) to prevent vascular hypertrophy induced by deoxycorticosterone acetate (DOCA) and salt in rats. 2. Vehicle (35% ethanol, 35% polyethylene glycol and 30% saline solution)-treated DOCA-salt rats developed marked hypertension at 4 weeks. Morphological studies on the rats given vehicle showed aortic hypertrophy, with a significant increase in wall thickness, wall area and wall-to-lumen ratio. A significant decrease in vascular wall hypertrophy was observed in PSI (3 mg/kg)-treated DOCA-salt rats. In addition, a marked increase in aortic endothelin (ET)-1 content was evident in vehicle-treated DOCA-salt rats compared with findings in sham-operated rats. A significant attenuation of this increase occurred in PSI-treated DOCA-salt rats. 3. These results indicate that PSI can prevent the vascular hypertrophy in DOCA-salt hypertensive rats and the effect is accompanied by suppression of ET-1 production in the aorta. We suggest that a proteasome-dependent proteolytic system has an important role in the development of vascular hypertrophy in cases of DOCA-salt-induced hypertension, possibly through the enhancement of ET-1 production in vascular tissues.