Kidney biopsies from Pima Indians with type II diabetes were analyzed. Subjects were classified clinically as having early diabetes ( n ϭ 10), microalbuminuria ( n ϭ 17), normoalbuminuria, despite a duration of diabetes equal to that of the subjects with microalbuminuria ( n ϭ 12), or clinical nephropathy ( n ϭ 12). Subjects with microalbuminuria exhibited moderate increases in glomerular and mesangial volume when compared with those with early diabetes, but could not be distinguished from subjects who remained normoalbuminuric after an equal duration of diabetes. Subjects with clinical nephropathy exhibited global glomerular sclerosis and more prominent structural abnormalities in nonsclerosed glomeruli. Marked mesangial expansion was accompanied by a further increase in total glomerular volume. Glomerular capillary surface area remained stable, but the glomerular basement membrane thickness was increased and podocyte foot processes were broadened. Broadening of podocyte foot processes was associated with a reduction in the number of podocytes per glomerulus and an increase in the surface area covered by remaining podocytes. These findings suggest that podocyte loss contributes to the progression of diabetic nephropathy. ( J. Clin. Invest. 1997. 99: 342-348.)

Two groups of adult male Munich-Wistar rats and a third group of nondiabetic age-matched and weight-matched normal control rats underwent micropuncture study 1 mo, and morphologic studies 14 mo, after induction of streptozotocin diabetes or sham treatment. All animals were fed standard rat chow. Diabetic rats received daily ultralente insulin to maintain stable moderate hyperglycemia (-350 mg/dl). In addition, one group of diabetic rats was treated with the angiotensin I converting enzyme inhibitor, enalapril, 15 mg/liter of drinking water. Average kidney weight, whole kidney and single-nephron glomerular filtration rate, and glomerular plasma flow rate were elevated to similar values in both groups of diabetic rats, relative to normal control rats. Non-enalapril-treated diabetic rats exhibited significant elevations in mean glomerular capillary hydraulic pressure and transcapillary hydraulic pressure gradient, compared with the other groups studied, and only this group eventually developed marked and progressive albuminuria. Likewise, histological examination of the kidneys at 14 mo disclosed a high incidence of glomerular structural abnormalities only in non-enalapril-treated diabetic rats. These findings indicate that prevention of glomerular capillary hypertension in rats with diabetes mellitus effectively protects against the subsequekit development of glomerular structural injury and proteinuria. This protection is afforded despite pronounced hyperglycemia and elevated levels of glucosylated hemoglobin, further supporting our view that hemodynamic rather than metabolic factors predominate in the pathogenesis of diabetic glomerulopathy.

Micropuncture and morphologic studies were performed in four groups of male Munich-Wistar rats after removal of the right kidney and segmental infarction of two-thirds of the left kidney. Groups 1 and 3 received no specific therapy. Groups 2 and 4 were treated with the angiotensin I converting enzyme inhibitor, enalapril, 50 mg/liter of which was put in their drinking water. All rats were fed standard chow. Groups 1 and 2 underwent micropuncture study 4 wk after renal ablation. Untreated group 1 rats exhibited systemic hypertension and elevation of the single nephron glomerular filtration rate (SNGFR) due to high average values for the mean glomerular transcapillary hydraulic pressure difference and glomerular plasma flow rate. In group 2 rats, treatment with enalapril prevented systemic hypertension and maintained the mean glomerular transcapillary hydraulic pressure gradient at nearnormal levels without significantly compromising SNGFR and the glomerular capillary plasma flow rate, as compared with untreated group 1 rats. Groups 3 and 4 were studied 8 wk after renal ablation. Untreated group 3 rats demonstrated persistent systemic hypertension, progressive proteinuria, and glomerular structural lesions, including mesangial expansion and segmental sclerosis. In group 4 rats, treatment with enalapril maintained systemic blood pressure at normal levels over the 8-wk period and significantly limited the development of proteinuria and glomerular lesions. These studies suggest that control of glomerular hypertension effectively limits glomerular injury in rats with renal ablation, and further support the view that glomerular hemodynamic changes mediate progressive renal injury when nephron number is reduced.

The visceral epithelial cell, or podocyte, forms the filtration slit structure that prevents the escape of plasma proteins from the glomerular circulation. Considerable evidence in experimental animals indicates that disruption of the podocyte contributes to the development of glomerular sclerosis [1]. By implication, the progressive rise in urinary protein excretion that characterizes diabetic nephropathy points to a putative role for the podocyte in the pathogenesis of diabetic renal disease. Consistent with this hypothesis is a cross-sectional study in diabetic Pima Indians which found that subjects with clinical nephropathy had fewer podocytes per glomerulus than those without nephropathy [2]. Since podocytes are thought to be incapable of replication, this observation suggests Diabetologia (1999) Abstract Aims/hypothesis. The predictive value of glomerular structure on progression of renal disease was examined in patients with Type II (non-insulin-dependent) diabetes and microalbuminuria (urinary albumin-tocreatinine ratio = 30±299 mg/g). Methods. Kidney biopsy specimens were obtained from 16 diabetic Pima Indians (6 men, 10 women). Progression of renal disease was assessed by measuring urinary albumin excretion 4 years after the biopsy (UAE 4 years ) and by computing the change in urinary albumin excretion during the study (D UAE).Results. At baseline, the duration of diabetes averaged 13.3 years (range = 4.0±23.8 years) and the mean glomerular filtration rate was 159 ml × min ±1 × 1.73m ±2 (range = 98 ± 239 ml × min ±1 × 1.73m ±2). Median urinary albumin excretion was 67 mg/g (range = 25±136 mg/g) and it increased to 625 mg/g (range = 9±13471 mg/g) after 4 years; 10 subjects (63 %; 4 men, 6 women) developed macroalbuminuria (urinary albumin-to-creatinine ratio ³ 300 mg/g). Neither mean arterial pressure nor HbA 1 c changed substantially during follow-up. Among the glomerular morphologic characteristics, the number of visceral epithelial cells, or podocytes, per glomerulus was the strongest predictor of renal disease progression (UAE 4 years , r = ±0.49, p = 0.05; DUAE, r = ±0.57, p = 0.02), with fewer cells predicting more rapid progression. Glomerular basement membrane thickness did not predict progression (UAE 4 years , r = 0.11, p = 0.67; DUAE, r = 0.09, p = 0.73) and mesangial volume fraction had only a modest effect (UAE 4 years, r = 0.42, p = 0.11; DUAE, r = 0.48, p = 0.06). Conclusion/interpretation. Whether lower epithelial cell number per glomerulus among those that progressed was due to cellular destruction, a reduced complement of epithelial cells, or both is uncertain. Nevertheless, these findings suggest that podocytes play an important part in the development and progression of diabetic renal disease. [Diabetologia (1999

No abstract

Microbes in the colon produce compounds, normally excreted by the kidneys, which are potential uremic toxins. Although p-cresol sulfate and indoxyl sulfate are well studied examples, few other compounds are known. Here, we compared plasma from hemodialysis patients with and without colons to identify and further characterize colon-derived uremic solutes. HPLC confirmed the colonic origin of p-cresol sulfate and indoxyl sulfate, but levels of hippurate, methylamine, and dimethylamine were not significantly lower in patients without colons. High-resolution mass spectrometry detected more than 1000 features in predialysis plasma samples. Hierarchical clustering based on these features clearly separated dialysis patients with and without colons. Compared with patients with colons, we identified more than 30 individual features in patients without colons that were either absent or present in lower concentration. Almost all of these features were more prominent in plasma from dialysis patients than normal subjects, suggesting that they represented uremic solutes. We used a panel of indole and phenyl standards to identify five colon-derived uremic solutes: α-phenylacetyl-l-glutamine, 5-hydroxyindole, indoxyl glucuronide, p-cresol sulfate, and indoxyl sulfate. However, compounds with accurate mass values matching most of the colon-derived solutes could not be found in standard metabolomic databases. These results suggest that colonic microbes may produce an important portion of uremic solutes, most of which remain unidentified.

With the goal of identifying optimal platforms for developing better models of diabetic nephropathy in mice, we compared renal effects of streptozotocin (STZ)-induced diabetes among five common inbred mouse strains (C57BL/6, MRL/Mp, BALB/c, DBA/2, and 129/SvEv). We also evaluated the renal consequences of chemical and genetic diabetes on the same genetic background (C57BL/6). There was a hierarchical response of blood glucose level to the STZ regimen among the strains (DBA/2 > C57BL/6 > MRL/MP > 129/SvEv > BALB/c). In all five strains, males demonstrated much more robust hyperglycemia with STZ than females. STZ-induced diabetes was associated with modest levels of albuminuria in all of the strains but was greatest in the DBA/2 strain, which also had the most marked hyperglycemia. Renal structural changes on light microscopy were limited to the development of mesangial expansion, and, while there were some apparent differences among strains in susceptibility to renal pathological changes, there was a significant positive correlation between blood glucose and the degree of mesangial expansion, suggesting that most of the variability in renal pathological abnormalities was because of differences in hyperglycemia. Although the general character of renal involvement was similar between chemical and genetic diabetes, Akita mice developed more marked hyperglycemia, elevated blood pressures, and less variability in renal structural responses. Thus, among the strains and models tested, the DBA/2 genetic background and the Akita (Ins2(+/C96Y)) model may be the most useful platforms for model development.

Six groups of Munich-Wistar rats underwent micropuncture study 2-10 weeks and morphologic studies 11-13 months after induction of streptozotocin diabetes or after sham treatment. Diabetic rats received diets containing 6% (group D6), 12% (D12), or 50% protein (D50) and were maintained under similar conditions of moderate hyperglycemia by daily injections of ultralente insulin. Age-and weightmatched normal control rats were also given 6% (Group N6), 12% (N12), or 50% protein (N50 (9,10) to result from an augmentation of both glomerular plasma flow rate (QA) and local transcapillary hydraulic pressure difference (AlP). Glomerular morphologic changes resembling those seen in diabetes have been associated with increases in capillary pressures and flows in other experimental forms of renal disease, including ablation ofrenal mass (11-13), high-protein diet (14), and some models of hypertension (15, 16). Furthermore, the extent of glomerular lesions in diabetic rats can be enhanced by maneuvers known to increase glomerular capillary pressures and flows, such as contralateral renal arterial clipping (17), ablation of the contralateral kidney (18), or high-protein feeding (19).Studies to date have not dissociated the effects of glomerular hypertension and hyperperfusion from those of chronic hyperglycemia per se (20)(21)(22). In the present study, glomerular hemodynamic function was deliberately varied in rats with streptozotocin (STZ)-induced diabetes while stable moderate hyperglycemia was maintained by daily exogenous insulin. This approach made it possible to relate the early alterations in glomerular pressures and flows in experimental diabetes to the subsequent development of glomerular injury. METHODSNinety-three adult male Munich-Wistar rats (220-260 g each) were studied. Forty-three rats were made diabetic by a single intravenous injection of STZ (60 mg/kg). Morning blood glucose concentration was determined biweekly. Rats received daily evening injections of ultralente insulin (NOVO Industries, Copenhagen) (23) in doses to maintain blood glucose concentration (BG) between 200 and 400 mg/dl. Diabetic rats were maintained on diets containing 50% (group D50, n = 15), 12% (D12, n = 15), or 6% casein (D6, n = 13). Normal control rats matched for initial body weight received the same diets containing 50% (group N50, n = 18), 12% (N12, n = 16), or 6% casein (N6, n = 16). The composition of the diets was 82% (wt/wt) casein plus carbohydrate, 5% lipid, 1% phosphate, 1% calcium, and 11% other components.Twenty-five diabetic rats and 24 control rats underwent micropuncture study 2-10 weeks (mean 4.2) after STZ injection. Rats were anesthetized with Inactin (100 mg/kg) and prepared for mnicropuncture in standard fashion (24). Euvolemia was maintained by iso-oncotic plasma replacement (25). Inulin (10 g/dl in isotonic saline solution) was also infused at a rate of 1.2 ml/hr. Tubule fluid was collected from superficial proximal tubules for determinations of flow rate and inulin concentration (26). Blood samples fro...