Shiro Maeda

Amelioration of accelerated diabetic mesangial expansion by treatment with a PKC β inhibitor in diabetic db/db mice, a rodent model for type 2 diabetes

Activation of protein kinase C (PKC) is implicated as an important mechanism by which diabetes causes vascular complications. We have recently shown that a PKC β inhibitor ameliorates not only early diabetes‐induced glomerular dysfunction such as glomerular hyperfiltration and albuminuria, but also overexpression of glomerular mRNA for transforming growth factor β1 (TGF‐βΙ) and extracellular matrix (ECM) proteins in streptozoto‐cin‐induced diabetic rats, a model for type 1 diabetes. In this study, we examined the long‐term effects of a PKC β inhibitor on glomerular histology as well as on biochemical and functional abnormalities in glomeruli of db/db mice, a model for type 2 diabetes. Administration of a PKC β inhibitor reduced urinary albumin excretion rates and inhibited glo‐merular PKC activation in diabetic db/db mice. Administration of a PKC β inhibitor also prevented the mesangial expansion observed in diabetic db/db mice, possibly through attenuation of glomerular expression of TGF‐β and ECM proteins such as fibronectin and type IV collagen. These findings provide the first in vivo evidence that the long‐term inhibition of PKC activation in the renal glomeruli can ameliorate glomerular pathologies in diabetic state, and thus suggest that a PKC β inhibitor might be an useful therapeutic strategy for the treatment of diabetic nephropathy.—Koya, D., Haneda, M., Nakagawa, H., Isshiki, K., Sato, H., Maeda, S., Sugimoto, T., Yasuda, H., Kashiwagi, A., Ways, D. K., King, G. L., Kikkawa, R. Amelioration of accelerated diabetic mesangial expansion by treatment with A PKC b inhibitor in diabetic db/db mice, a rodent model for type 2 diabetes. FASEB J. 14, 439–447 (2000)

Enhancement of glomerular heme oxygenase-1 expression in diabetic rats.

An increase in oxidative stress in diabetic subjects is implicated to play a pivotal role in diabetic vascular complications. In response to oxidative stress, antioxidant enzymes are considered to be induced and protect cellular functions to keep in vivo homeostasis. However, it remains to be clarified whether antioxidant enzymes are induced against oxidative stress especially in renal glomeruli at an early stage of diabetes. To answer this question, we examined the gene expression of a variety of antioxidant enzymes in glomeruli isolated from streptozotocin-induced diabetic rats. The mRNA expression of antioxidant enzymes such as catalase, glutathione peroxidase, and CuZn-superoxide dismutase, was unaltered in glomeruli of diabetic rats and was comparable to control rats. In contrast, the mRNA expression of heme oxygenase-1 (HO-1) was enhanced in glomeruli of diabetic rats as compared with control rats. A treatment with insulin as well as with vitamin E (40 mg/kg body weight every other day, intra-peritoneal injection) normalized the mRNA expression of HO-1 in the glomeruli of diabetic rats. Immunohistochemical analysis revealed that the up-regulated expression of HO-1 protein was localized in glomerular cells of diabetic rats. In conclusion, these results provide the first evidence that among antioxidant enzymes HO-1 expression is preferentially increased in diabetic glomeruli.

Glucose inhibits myo-inositol uptake and reduces myo-inositol content in cultured rat glomerular mesangial cells

Although activation of polyol pathway has been proposed as one of the etiologic factors of diabetic complications, precise mechanism of the effect of polyol accumulation is still unclear. In order to test the hypothesis that there is an association of polyol pathway with myo-inositol metabolism, we measured myo-inositol content in cultured rat glomerular mesangial cells. By exposing the cells to high concentrations of glucose, intracellular myo-inositol content was reduced from 12.39 +/- 0.64 nmol/mg protein at 0 mmol/L glucose to 6.54 +/- 0.38 nmol/mg protein at 27.5 mmol/L glucose and 4.88 +/- 0.43 nmol/mg protein at 55 mmol/L glucose. This decrease of myo-inositol content was partially prevented by co-incubation with aldose reductase inhibitor, sorbinil. To examine further the mechanism of myo-inositol depletion, myo-inositol uptake by mesangial cells was studied. Major myo-inositol uptake process was sodium-dependent, saturable, and ouabain sensitive with Vmax of 171 pmol/mg protein/20 min and Km of 33 mumol/L. Sodium-dependent myo-inositol uptake was significantly inhibited by glucose in a dose-dependent manner only when glucose was present during uptake experiment, and kinetic analysis revealed the inhibition was competitive. Aldose reductase inhibition failed to prevent inhibitory effect of glucose on myo-inositol uptake. These data suggest that myo-inositol content of glomerular mesangial cells, which is reduced by high concentrations of glucose, is maintained by two processes: a glucose-sensitive but sorbitol-insensitive process, sodium-dependent myo-inositol uptake; and a sorbitol (aldose reductase) sensitive process, myo-Inositol depletion under high glucose condition may induce dysfunction of mesangial cells seen in diabetes.

Do inflammatory cytokine genes confer susceptibility to diabetic nephropathy

Microinflammation has been recognized as an important process for the progression of diabetic nephropathy. Inflammatory cytokines, such as interleukin-6 produced by infiltrating cells or renal cells, play important roles in the pathogenesis of diabetic nephropathy. Although the mechanisms underlying the regulation of these cytokines in the kidneys of patients with diabetes mellitus remain unclear, genetic variations in the genes encoding the inflammatory cytokines might confer susceptibility to the disease by altering their functions or expressions.

A Case of Lipoprotein Glomerulopathy Successfully Treated with Probucol

A 54-year-old woman presented proteinuria and severe hyperlipoproteinemia, She had type III hyperlipoproteinemia with the phenotype E2/2. Renal biopsy specimen revealed lipoprotein thrombi within the glomerular capillary lumina without tubulointerstitial lesion and deposition of IgA in the mesangium and peripheral capillary loops, indicating lipoprotein glomerulopathy with IgA nephropathy. Treatment with probucol resulted in the improvement of both hyperlipoproteinemia and proteinuria with the disappearance of the lipoprotein thrombi in the glomerular capillary without any change in the mesangial IgA deposition. The data suggest that probucol may be effective against the early stage of lipoprotein glomerulopathy with less lipoprotein thrombi and without tubulointerstitial damage.

Reduced activity of renal angiotensin-converting enzyme in streptozotocin-induced diabetic rats

To clarify the possible role of intrarenal renin-angiotensin system (RAS) in the evolution of renal hemodynamic alteration in diabetes, we investigated the change of tissue angiotensin-converting enzyme (ACE) activity, a key enzyme of RAS, in the kidneys obtained from streptozotocin-induced diabetic rats. Tissue ACE activity was significantly reduced in both outer cortex (0.29 +/- 0.04, mean +/- SEM, n = 6) and inner cortex with outer medulla (2.43 +/- 0.28, n = 6) of the kidneys from diabetic rats 2 weeks after induction of diabetes compared with those from control rats (0.47 +/- 0.05, n = 7, in outer cortex; 3.68 +/- 0.32, n = 7, in inner cortex with outer medulla). ACE activities in the lung and aorta of diabetic rats were not different from those of control rats. ACE activities in the serum and urine were significantly elevated in diabetic rats. Treatment of diabetic rats with insulin to achieve near euglycemia completely prevented these alterations in ACE activity, except that, in the urine, the elevation of ACE was partially corrected with insulin. In contrast to ACE activity, activity of N-acetyl-beta-D-glucosaminidase (a lysosomal enzyme of the tubule) and r-glutamyl transpeptidase (a brush border enzyme) in the kidney were not reduced in diabetic rats, whereas in the urine both enzyme activities were significantly elevated in diabetic rats. It is likely, therefore, that the reduction of ACE activity in the kidneys of diabetic rats may reflect the impairment of vascular endothelial cells in the kidney, rather than tubular damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Microalbuminuria associated with a rise in blood pressure in non-insulin-dependent diabetes

The association between microalbuminuria and systemic blood pressure was investigated in 80 nonproteinuric subjects with non-insulin-dependent diabetes. Seventeen of 80 diabetics had urinary albumin excretion rates (AER) over 20 micrograms/min and were defined as microalbuminuric. The microalbuminuric diabetics showed a higher incidence of proliferative retinopathy and neuropathy than the normoalbuminurics. Moreover, the former group had significantly higher values of systolic blood pressure compared to the latter, although the creatinine clearance was not significantly different between the two groups. These results suggest that microalbuminuria is strongly associated with a rise of systemic blood pressure in non-insulin-dependent diabetics.

Glucose-induced overproduction of type IV collagen in cultured glomerular mesangial cells

Type IV collagen production by cultured rat glomerular mesangial cells was evaluated quantitatively by measuring type IV collagen secreted into culture media and associated with the cells using enzyme-linked immunosorbent assay (ELISA). The majority of type IV collagen was secreted into culture media; type IV collagen increased with cell growth in the early log phase and decreased in the late log phase and after cofluency. By exposing the cells to high concentrations of glucose (27.8 mM), both secreted and cell-associated type IV collagens increased significantly compared with the cells cultured under normal glucose concentrations (5.6 mM) or under equivalent concentrations of mannitol, resulting in a significant increase in total type IV collagen accumulation.

Insulin-like growth factor I stimulates glucose uptake and expression of glucose transporter 1 in cultured mesangial cells

AbstractBackground. Glomerular mesangial cells were found to have a considerable number of receptors for insulin-like growth factor I (IGF-I) and to proliferate in response to IGF-I. However, the mechanism of the metabolic actions of IGF-I in mesangial cells has not yet been fully elucidated.nMethods. In order to clarify the effect of IGF-I on glucose metabolism in mesangial cells, we performed a kinetic analysis of 2-deoxyglucose (2-DOG) uptake, the first step of glucose metabolism, and examined the gene and protein expression of glucose transporter 1 (GLUT 1), a major facilitative glucose transporter in mesangial cells.nResults. IGF-I was able to increase 2-DOG uptake significantly after 12 h, and the kinetic analysis of 2-DOG uptake revealed that IGF-I increased maximum velocity (Vmax) without changing Michaelis constant (Km). The expression of GLUT 1 mRNA was increased after the exposure to IGF-I and reached the maximal level at 6 h, followed by an increase in its protein expression.nConclusions. These results suggest that IGF-I plays an important role in glucose metabolism in glomerular mesangial cells by enhancing glucose transport through an increase in the expression of GLUT 1.