SUMMARYThe accumulation of polyols has been previously found in renal glomeruli isolated from streptozocin-induced diabetic (STZ-D) rats, although the intraglomerular polyol pathway has not been exactly localized. Because we have previously observed mesangial cell dysfunction in STZ-D rats, we examined whether the polyol pathway exists in mesangial cells as a possible candidate of the cause of cellular dysfunction. The activities of two polyol pathway enzymes, aldose reductase and sorbitol dehydrogenase, were clearly detected in the crude homogenate of cultured mesangial cells at higher levels than those of whole glomeruli when DL-glyceraldehyde or D-fructose was used as substrate. When cells were incubated in medium containing 55 mM glucose or galactose, a large amount of sorbitol or galactitol was accumulated intracellularly. The accumulation of polyols was effectively blocked by an aldose reductase inhibitor, ICI 128436. These results suggest that the polyol pathway exists in mesangial cells of rat glomeruli and may play a role in the development of mesangial cell dysfunction found in STZ-D rats. Diabetes 36:240-43, 1987 T here has been increasing evidence that the enhanced activity of polyol pathway plays an important role in the development of various diabetic complications such as cataract, neuropathy, and retinopathy (1,2). Furthermore, recent reports by indicate that diabetic nephropathy might also be caused by sorbitol accumulation in glomeruli. Because the activity of aldose reductase, a key enzyme for sorbitol synthesis, was found immunohistochemically in glomerular epithelium (6), sorbitol accumulation in epithelial cells may be pathogenetically linked to the development of diabetic nephropathy.On the other hand, it has been generally believed that the abnormality of mesangial region plays a crucial role in the development and progression of diabetic glomerulosclerosis (7). Mesangial expansion is known to cause the obliteration of glomerular capillary lumen (8) and to correlate well with clinical parameters of renal involvement in diabetic patients (9). Although the precise mechanism of the development of mesangial expansion has not yet been clarified, the derangement of mesangial cells may be one of the etiological factors (10,11). Therefore, it appears pertinent to investigate whether the activity of polyol pathway exists in mesangial cells in connection with mesangial abnormality. MATERIALS AND METHODSGlomerular isolation and culture. Glomeruli were isolated from male Sprague-Dawley rats weighing 50-100 g by sieving with stainless steel and nylon meshes under sterile conditions as previously reported (12). The yield of glomerular isolation by this technique was -4 0 % and the purity was >90% and was comparable to results obtained in human autopsied kidney using similar technique (13,14). Isolated glomeruli were then cultured with RPMI-1640 culture medium (Gibco, Grand Island, NY) with 20% fetal calf serum plus penicillin and streptomycin according to the method of Kreisberg and Karnovsky (15)....

Although the enhanced activity of the polyol pathway has been detected in diabetic glomeruli, the intraglomerular localization of this pathway has not yet been well defined. In this study, we attempted to identify aldose reductase, a key enzyme of the polyol pathway, in cultured rat mesangial cells and to characterize the properties of this enzyme using enzymological and immunological methods. When the aldose reductase (DL-glyceraldehyde-reducing) activity was analyzed in mesangial cell extract, the Lineweaver-Burk plot showed concave downward curvature, and the Michaelis constant was 0.83 mM DL-glyceraldehyde, and this activity was noncompetitively inhibited by an aldose reductase inhibitor, ICI-128,436. The enzyme activity was enhanced by the addition of sulfate ion and partially suppressed by barbital. The enzyme cross-reacted with the antisera against rat lens and testis aldose reductases on Ouchterlony plate, and migrated to the region of molecular weight of about 36,500 Da on Western blotting. The presence of aldose reductase mRNA was also confirmed by Northern analysis using cDNA for rat aldose reductase, 10Q. From these results, it was concluded that the aldose reductase may exist in rat glomerular mesangial cells and may play a role in the development of diabetic glomerulopathy, though the coexistence of aldehyde reductase(s) may not be fully ruled out.

Serum and corpuscular nickel and zinc concentrations in 30 chronic hemodialysis patients were examined. Serum nickel and zinc levels before dialysis were 0.22 ± 0.03 μg/dl (normal value: 0.56 ± 0.08 μg/dl) and 70.0 ± 13.4 μg/dl (normal value: 96 ± 8 μg/dl) low, respectively. However, corpuscular nickel and zinc levels before dialysis were high: 1.25 ± 0.24 μg/dl (normal value: 0.88 ± 0.17 μg/dl) and 1,299 ± 146 μg/dl (normal value: 1,120 ± 80 μg/dl). Serum zinc levels significantly increased after dialysis, but serum nickel concentrations did not significantly increase during dialysis. Corpuscular nickel and zinc concentrations did not significantly change during dialysis.