Proteinuria: a mediator of interstitial fibrosis?

Canine glomerulonephritis: new thoughts on proteinuria and treatment

Glomerular disease in the dog is not only a common form of renal disease but also an important cause of chronic renal failure. The presence of immune complexes in glomerular capillary walls is a major cause of canine glomerular disease and is commonly referred to as glomerulonephritis. Leakage of plasma proteins, principally albumin, across the damaged glomerular capillary walls results in persistent proteinuria--the clinicopathological hallmark of glomerulonephritis. Recent evidence suggests that, in addition to being a marker of disease, persistent proteinuria is associated with progressive glomerular and tubulointerstitial lesions and loss of additional nephrons. Perhaps the best treatment for glomerulonephritis is the identification and correction of any underlying inflammatory, immune-mediated or neoplastic disease that results in the deposition or formation of glomerular immune complexes. In cases of idiopathic glomerulonephritis, angiotensin-converting enzyme inhibitors have been shown to decrease proteinuria and potentially slow disease progression.

Lysosomal enzymes in preeclamptic women in northern Nigeria

BACKGROUND

The incidence of preeclampsia is high in northern Nigeria, as it is in many other developing countries, and preeclampsia is associated with significant maternal and fetal morbidity and mortality. We inquired if proteinuria or hypertension alone could account for the altered concentrations of urinary lysosomal hydrolases that have been reported in preeclamptic women and pregnant women without preeclampsia.

METHODS

The activities of urinary beta-hexosaminidase and beta-galactosidase were determined fluorometrically in pregnant women assigned to one of four groups: Group I: 41 preeclamptic women; Group II: 31 hypertensive aproteinuric women; Group III: 44 normotensive proteinuric women; and Group IV: 52 healthy pregnant women (controls).

RESULTS

The urinary beta-hexosaminidase concentrations were decreased in the preeclamptic women (P<0.005) and proteinuric women (P<0.001) when compared to the healthy pregnant controls. There was no significant difference in beta-hexosaminidase concentrations between the hypertensive women and the healthy pregnant controls. The urinary beta-galactosidase concentrations for preeclamptic, hypertensive, and proteinuric women did not differ significantly versus healthy pregnant controls.

CONCLUSIONS

The reduced urinary excretion of beta-hexosaminidase in preeclamptic women is associated with proteinuria, but not hypertension. Measuring urinary concentrations of lysosomal hydrolases alone or in conjunction with urinary protein concentrations is not likely to be useful in predicting or monitoring the clinical course of preeclampsia; however, it might prove important in gaining a more complete understanding of the pathogenesis of renal tubular epithelial cell injury and proteinuria that occurs in preeclampsia.

Evaluation of a technique of inducing hypertensive renal insufficiency in cats

OBJECTIVE

To compare 2 techniques of inducing combined renal insufficiency and systemic hypertension in cats.

ANIMALS

22 cats 6 to 12 months of age.

PROCEDURES

Cats were randomly assigned to 1 of 3 groups. Control (C) group cats had 2 intact kidneys, remnant kidney (RK) group cats underwent unilateral partial renal infarction and contralateral nephrectomy, and remnant-wrap (W) group cats underwent unilateral partial renal infarction and partial abtation and wrapping of the contralateral kidney. Systemic arterial blood pressure (BP) was measured continuously by use of implanted radiotelemetric devices. Renal function was assessed via determination of glomerular filtration rate, measurement of serum creatinine and BUN concentrations, and determination of urine protein-to-creatinine ratio (UP/C). Serum aldosterone concentration and plasma renin activity were measured on day 75.

RESULTS

Systolic BP was significantly higher in groups RK and W than in group C, and systolic BP was significantly higher in group W than in group RK. Serum aldosterone concentration and plasma renin activity were significantly higher in group W, compared with groups C and RK. Glomerular filtration rate was significantly lower in groups RK and W, compared with group C. Histologic indices of renal injury and UP/C were significantly higher in group W, compared with groups C and RK.

CONCLUSIONS AND CLINICAL RELEVANCE

Hypertensive renal insufficiency in group W was characterized by marked sustained systemic hypertension, decreased renal function, proteinuria, activation of the renin-angiotensin-aldosterone axis, and renal structural injury. Results support the hypothesis that marked systemic hypertension, activation of the renin-angiotensin-aldosterone axis, and proteinuria may damage the kidney of cats with preexisting renal insufficiency.

Sustained plasma fibrinogen elevation in subtotal nephrectomized rats: effect of cilazapril, an angiotensin-converting enzyme inhibitor

The present study was undertaken to examine whether plasma fibrinogen persistently elevates in subtotal nephrectomized rats, an animal model with inflammatory renal changes. Eight weeks after the induction of 5/6 nephrectomy in male Wistar rats, plasma fibrinogen concentration was determined for the next 12 weeks in the animals received vehicle or an angiotensin-converting enzyme inhibitor, cilazapril (1 or 10 mg/kg per day) orally. In the vehicle-treated nephrectomized rats, plasma fibrinogen concentration significantly (P<0.001) increased (from 127.3 +/- 4.6 [S.E.M.] to 182.3 +/- 5.2 mg/dL) compared with that in the control rats (from 118.0 +/- 2.0 to 153.5 +/- 5.4 mg/dL). Cilazapril attenuated the increases in plasma fibrinogen concentration in a dose-dependent manner. Serum concentration of monocyte chemoattractant protein-1, a key macrophage chemoattractant and activator, increased in the vehicle-treated nephrectomized rats, which was also reduced by cilazapril. These results suggest that plasma fibrinogen elevates persistently in the nephrectomized rats. Local inflammation may be involved in the hepatic fibrinogen synthesis in this model.

Phenotypic changes and cell cycle activation in early tubulointerstitial injury of rat adriamycin nephrosis

Tubular response, including phenotypic changes against a variety of injuries, is an initial event that promotes tubulointerstitial injuries. Using the progressive kidney disease model of rat adriamycin (ADR) nephrosis, the present study focused on the cell cycle activation and phenotypic changes that occur in the tubuli in early tubulointerstitial injury in ADR nephrosis. At 12 weeks, experimental animals developed overt nephrosis with tubulointerstitial injury, which correlated well with the degree of proteinuria and incidence of glomerulosclerosis. Initial pathology of the tubuli showed a slight dilatation of tubuli, which tended to occur in individual nephrons. Immunohistochemistry demonstrated that vimentin-positive tubuli and osteopontin (OPN)-positive tubuli were associated mostly with proliferating cell nuclear antigen expression. Protein levels of OPN in the renal cortex were correlated with the level of proteinuria by western blotting. Vimentin- and OPN-expressing tubuli were tightly associated with a peritubular influx of alpha-smooth muscle actin (SMA)-positive cells or ED-1-positive cells. In addition, we found thrombomodulin+/ TUNEL+ (dUTP-biotin nick-end labeling) peritubular endothelial cells and ED-1+/alpha-SMA+ cells at an early stage among interstitial inflammatory cells. These results suggest that cell cycle activation in tubular cells forms the background for the phenotypic tubular changes that are involved in chronic tubulointerstitial injury in ADR nephrosis.

Activation of mitogenic pathways by albumin in kidney proximal tubule epithelial cells: implications for the pathophysiology of proteinuric states

Albumin is filtered into the proximal tubule in large quantities in nephrotic states. It has been proposed that this protein may have a toxic effect on tubular epithelial cells and may be responsible for the initiation of interstitial inflammation and scarring. The mitogenic effect of recombinant human albumin in wild-type opossum kidney cells and in similar cells transfected with a dominant negative p85 subunit (deltap85) of phopshatidylinositide 3-kinase (PI 3-kinase) has been studied. This study demonstrates that recombinant human albumin stimulates proliferation of opossum kidney cells in culture. This effect is mediated via PI 3-kinase, and is inhibited by wortmannin and deltap85 expression. Albumin stimulates PI 3-kinase activity in opossum kidney cells as determined by three different experimental procedures. Recombinant albumin also stimulates pp70(s6) kinase activity in a kinase cascade downstream of PI 3-kinase. Activity of pp70(s6) kinase is essential for albumin-induced proliferation of opossum kidney cells. It is proposed that this mitogenic pathway may have a critical role in proximal tubular homeostasis and pathophysiology of proteinuric states.