Angiostatin production increases in response to decreased nitric oxide in aging rat kidney.

The development of interstitial fibrosis occurs with aging. Impaired angiogenesis, associated with progressive loss of the renal microvasculature, is thought to be a cause of age-related nephropathy. However, the mechanism of capillary loss in aging kidney has not been fully elucidated. Angiostatin is a kringle-containing fragment of plasminogen and is a potent inhibitor of angiogenesis in vivo. Whether angiostatin generation is increased in the aging kidney has not been investigated. We examined 4, 10, 16, and 24-month-old Sprague-Dawley rats for angiostatin production and found that angiostatin generation was increased in aged rats. The protein expression and the activity of cathepsin D-the enzyme for angiostatin production--were increased in aged rats. In the aging kidney, nitric oxide (NO) availability is decreased. To investigate the role of NO in angiostatin production, human umbilical vein endothelial cells were treated with L-NG-nitroarginine methyl ester (L-NAME). L-NAME-treated cells showed increased cathepsin D activity and angiostatin production. For in vivo experiments, 16- to 18-month-old rats were treated with L-NAME or molsidomine for 3 months. Angiostatin production was increased in L-NAME-treated kidney, accompanied by increased cathepsin D activity. In contrast, angiostatin production was decreased in molsidomine-treated kidney, accompanied by decreased cathepsin D activity. In conclusion, angiostatin generation by cathepsin D was increased in the aging rat kidney. Decreased NO production activated cathepsin D activity. Increased angiostatin production may be related to capillary loss and interstitial damage in the aging rat kidney.

Mitochondrial damage-induced impairment of angiogenesis in the aging rat kidney.

Decreased expression of vascular endothelial growth factor (VEGF) in the renal tubules is thought to cause progressive loss of the renal microvasculature with age. Mitochondrial dysfunction may be a principal phenomenon underlying the process of aging. The relation between VEGF expression and mitochondrial dysfunction in aging is not fully understood. We hypothesized that mitochondrial dysfunction blocks VEGF expression and contributes to impaired angiogenesis in the aging kidney. The aim of this study was to assess the role of mitochondria in VEGF expression in the aging rat kidney. We evaluated the accumulation of 8-hydroxy-2'-deoxyguanosine in mitochondrial DNA, as well as mitochondrial dysfunction, as assessed by electron microscopy of mitochondrial structure and histochemical staining for respiratory chain complex IV, in aging rat kidney. An increase in hypoxic area and a decrease in peritubular capillaries were detected in the cortex of aging rat kidneys; however, upregulation of VEGF expression was not observed. The expression of VEGF in proximal tubular epithelial cells in response to hypoxia was suppressed by the mitochondrial electron transfer inhibitor myxothiazol. Mitochondrial DNA-deficient cells also failed to upregulate VEGF expression under hypoxic conditions. These results indicate that impairment of VEGF upregulation, possibly as a result of mitochondrial dysfunction, contributes to impaired angiogenesis, which in turn leads to renal injury in the aging rat kidney.

Reactive oxygen species mediate compensatory glomerular hypertrophy in rat uninephrectomized kidney.

Hyperfiltration in glomeruli is the most common pathway to progressive renal dysfunction. Moreover, reduction of renal mass by unilateral nephrectomy results in an immediate increase in glomerular flow to the remnant kidney, followed by compensatory glomerular hypertrophy. Reactive oxygen species (ROS) are involved in renal hypertrophic responses; however, the role of ROS in compensatory glomerular hypertrophy remains unclear. Therefore, this role was investigated in the present study. Wistar rats were randomly placed into two groups: uninephrectomized rats (Nx) and uninephrectomized rats treated with tempol (Nx + TP). The glomerular volume increased in the Nx 1 week after surgery, but was significantly suppressed in the Nx + TP. Levels of phospho-Akt and phospho-ribosomal protein S6, which are critical for cell growth and hypertrophy, were markedly increased in the glomeruli of the Nx, while tempol treatment almost abolished the activation of these proteins. These results suggest that ROS have important roles in compensatory hypertrophy in glomeruli.

[Case of uremic platelet dysfunction].

The present case was a 59-year-old woman who underwent a right nephrectomy at 30 years of age, and in whom renal dysfunction occurred at 51 years of age. In November 199X, when her creatinine level reached 7 mg/dl, renal replacement therapy was recommended. She refused this therapy and began her own diet therapy, which consisted of taking only supplement beverage, but no food. Afterwards she became unable to do daily work, and entered our hospital in July of the next year. On admission, her bleeding time was over 10 minutes, but coagulation function tests showed normal values. Platelet function tests showed that coagulation with the addition of ADP was mildly decreased and that coagulation with the addition of aggregation was severely decreased. These data and her bleeding tendency improved with hemodialysis. Therefore, a diagnosis of aggregation non-responsive uremic platelet dysfunction was made. On admission, we were not able to insert a catheter for hemodialysis because of her severe bleeding tendency. A platelet transfusion was made so that we could insert the catheter without severe bleeding. However, this hemostatic effect lapsed after about five to six hours. Six hours after insertion of the catheter, oozing from the orifice of the catheter was seen and a red blood transfusion was necessary. Three days after beginning hemodialysis, the bleeding tendency was no longer seen. Her platelet function and coagulation test results also improved. We can make two conclusions regarding this case. The first is when the physician's medical strategy cannot be carried out due to uremic platelet dysfunction, a platelet transfusion can temporarily eliminate the bleeding tendency. The second is that the pathophysiology of uremic platelet dysfunction involves suppression of the primary step of platelet aggregation with collagen. Experience with the present case revealed the appropriate therapeutic strategy for the pathophysiology of uremic platelet dysfunction.