Carlos A. Velasco

Drug-Induced Reversal of Early Diabetic Microangiopathy

We performed three oral glucose-tolerance tests and three muscle biopsies over a period of approximately three years in 41 asymptomatic patients with chemical diabetes. At base line, 13 (32 per cent) had an increased capillary basement-membrane width in muscle. Twenty-three patients received glipizide, a new oral hypoglycemic compound, and 18 received placebo. In the patients receiving placebo the mean width of the muscle capillary basement membrane increased from 135.9 +/- 9.0 nm (S.E.M.) to 169.3 +/- 9.5 nm (P = 0.01), but in those receiving glipizide the value decreased to a level no different from that in subjects without diabetes: from 152.9 +/- 2.9 to 127.5 +/- 5.1 nm (P = 0.01). These findings suggest that microangiopathy, as indicated by an increased capillary basement-membrane width in muscle, may be present in a considerable number of patients with asymptomatic diabetes and that the changes can be reversed by early drug treatment.

Diabetic microangiopathy in KK mice. II. Suppression of Glomerulosclerosis by pyridinolcarbamate.

Abstract KK mice with genetic diabetic glomerulosclerosis were treated with 250 mg/kg of pyridinolcarbamate (PDC), an antibradykinin agent, by 20 days of age and the kidney glucosyltransferase activity was measured. This enzyme facilitates the attachment of glucose to hydroxylysine-galactose unit of the basement membrane, which is glycoprotein in nature. No effect of PDC on the glucosyltransferase activity was observed up to 50 days of treatment. However, after 80 days of treatment, the enzyme activity was significantly increased. This finding was associated with a similar increase in total protein synthesis by the renal cortex of the treated KK mice. Amelioration of severity to only mild glomerulosclerosis was observed after 50 days of PDC administration. However, after 80 days of drug treatment, no severe type of glomerulosclerosis was present. PDC had no effect on either the fasting blood sugars or serum immunoreactive insulin levels. However, the oral glucose tolerance appeared to be improved in mice treated for 80 days. Glycogen synthesis by diaphragm muscle and total lipid synthesis by epididymal fat pad were significantly increased after 80 days of drug treatment, indicating increased tissue sensitivity to endogenous insulin. The observation that glucosyltransferase activity responded to PDC treatment with concomitant prevention of diabetic glomerulosclerosis suggests a relationship between this enzyme activity and glycoprotein synthesis in the kidney. It is suggested that PDC is a potential drug for the treatment of diabetic glomerulosclerosis.

Diabetic microangiopathy in KK mice. VI. Effect of glycemic control on renal glycoprotein metabolism and established glomerulosclerosis.

Twenty-three nonobese KK mice with abnormal tolerance to glucose, hyperinsulinemia with insulin resistance and human diabetic-like nephropathy were treated with either saline (12 mice) or glipizide, an oral hypoglycemic compound, 1 mg/kg, (11 mice) from 120 to 360 days of age. These mice develop significant increases in mesangial volume and matrix by 40 days of age. Oral glucose tolerance (OGTT), glucosyltransferase and N-acetyl-beta-glucosaminidase (enzymes involved in synthesis and degradation of kidney glycoproteins, respectively) in the kidney and serum, 24-hr proteinuria, and light microscopy studies of the kidney were performed. Glipizide-treated mice improved their OGTT. There was no difference in body weight; however, a 16% decrease (P less than 0.05) in kidney weight was observed in glipizide-treated mice. Both enzymes were significantly increased in the kidneys of mice treated with glipizide. No difference in serum enzymes was found between the two groups of mice. About 58% of the saline-treated mice had moderate glomerulosclerosis. By contrast, only 27% of glipizide-treated mice had moderate glomerulosclerosis. Also, a significant decrease in proteinuria was found in glipizide-treated mice. These data suggest that glipizide improves glucose metabolism, decreases kidney size, prevents kidney glycoprotein and mesangial matrix accumulation, and reduces proteinuria in type II diabetic KK mice. This indicates that good glycemic control prevents further progression of established diabetic nephropathy in animals.

Elevated kidney glucosyltransferase activity in genetic prediabetic mice

Glucosyltransferase activity in the renal cortex of genetic diabetic KK mice was significantly increased at 40 days of age when compared to that of Swiss albino and F1 hybrid mice. This increase in enzyme activity in the absence of glucose intolerance can be regarded as an earlier genetic marker for the diagnosis of diabetic microangiopathy.

Enzyme activities as a predictor of diabetic vasculopathy

Forty-one patients with chemical diabetes had three oral glucose tolerance tests and underwent muscle biopsy three times over a period of three years. Twenty-three received glipizide and 18 placebo. Those taking placebo had an increase in the mean muscle capillary basement membrane width (p = 0.01), but those taking glipizide showed a decrease (p = 0.01) to values no different from those of nondiabetic subjects. Determinations of enzyme activities involved in the synthesis and degradation of glycoproteins revealed a three-year decrease (not significant) in muscle glucosyltransferase activity in the glipizide-treated patients, but a statistically significant difference (p less than 0.01) comparing the adjusted means of the two treatment groups. N-acetyl-beta-glucosaminidase activity was significantly increased in muscle from baseline values (p less than 0.01), with adjusted means also significantly different (p less than 0.01). The data suggest that changes in basement membrane and enzyme activities are correlated, and the latter may be a predictor to follow the development, progression, or regression of diabetic vasculopathy.

Sulfonylurea-induced decrease of muscle capillary basement membrane thickness in diabetes

Three muscle biopsies were performed in 53 overt type 2 diabetics over a period of approximately 2 years. At baseline, 21 (40%) had an increased capillary basement membrane width in muscle. Thirty-five patients received glipizide and 18 received placebo. In the patients receiving placebo, the mean of the muscle capillary basement membrane width increased from 158.7 +/- 11.5 nm (SEM) to 170.9 +/- 14.7 nm (P = NS), but in those receiving glipizide the value decreased from 192.9 +/- 13.2 nm to 161.0 +/- 10.2 nm (P = 0.02). Plasma glucose and glycosylated hemoglobin A1 decreased significantly (P less than 0.001) after 2 years in patients receiving glipizide. In 15, mean glycosylated hemoglobin A1 reached a normal range, and mean basement membrane width decreased to a level close to that found in subjects without diabetes (P = NS). These findings are consistent with the hypothesis that effective response to oral medication can decrease the basement membrane thickening, suggesting that diabetic microangiopathy is not necessarily progressive.

Diabetic microangiopathy in KK mice: V. Effect of early glyburide treatment on kidney glucosyltransferase activity

Abstract KK mice with spontaneous hereditary diabetes were treated with 0.5 mg/kg of glyburide once a day by intubation for 5 days a week from 20 days of age. A representative number of KK mice received 0.9% saline (0.1 ml/10 g) and served as controls for glyburide treated mice. The SA mice were not treated with saline. After an 18 hr fast, both saline and glyburide-treated mice were sacrificed at 40, 50, 70, and 100 days of age. Glyburide-treated mice showed a decreased trend in blood sugar levels, and this was significant in 50- and 70-day-old mice. The serum IRI levels increased significantly in the 70-day-old glyburide-treated mice. Glyburide caused a significant decrease in glucosyltransferase activity in the renal cortex of the KK mice at 40, 50, and 70 days of age. Early glyburide treatment is effective not only in preventing the progression of glomerulosclerosis but also in normalizing biochemical changes contributory to genetic diabetic glomerulosclerosis in KK mice.

Genetic Transmission of Vasculopathy in KK Mice

Publisher Summary This chapter describes the genetic transmission of vasculopathy in KK mice. The existence of diabetic like glomerular lesions and genetically impaired tolerance to glucose makes the KK mouse a suitable animal for studies of diabetic genetic mechanisms. The nonoccurrence of significant glomerulopathy in various strains of mice with advanced metabolic disorders including intolerance to glucose allows the conclusion that a specific genetic component is necessary for the development of diabetic-like vasculopathy. Genetic influence is definitely necessary, in addition to various environmental factors, to produce advanced diabetic-like glomerulopathy in these mice. Certain environmental factors such as age, duration of the disease, and hyperglycemia and hyperinsulinism enhance the development and increase the severity of vasculopathy. The chapter presents a study in which transmission of significant glomerulosclerosis from the KK mice to healthy recipients was demonstrated by special mating procedures.

Delay of progression of diabetic microangiopathy

Three muscle biopsies were performed in 53 overt type II diabetics over a period of approximately 2 years. At baseline, 21 (40%) had an abnormally increased capillary basement membrane width in muscle. Thirty-five subjects received glipizide and 18, placebo. At baseline, no statistically significant difference was found in the muscle capillary basement membrane width between the two groups (P = NS). In the subjects receiving placebo, the mean width of the muscle capillary basement membrane increased (P = NS), but in those receiving glipizide, the mean decreased from 193 +/- 13 nm (SEM) to 161 +/- 10 nm (P = .02). Fasting plasma glucose and glycosylated hemoglobin A1 significantly decreased (P less than .001) after two years in those receiving glipizide. In 15 subjects, mean glycosylated hemoglobin A1 reached the normal range, and mean muscle capillary basement membrane width decreased to a level close to that found in subjects without diabetes (P = NS). Determinations of enzyme activities involved in the synthesis and degradation of glycoproteins revealed a 2-year significant decrease of muscle glucosyltransferase (synthesis) activity (P less than .01) in the glipizide-treated subjects as opposed to a significant increase (P less than .001) in those receiving placebo. Muscle N-acetyl-beta-glucosaminidase activity (degradation) was statistically increased (P less than .001) in those subjects taking glipizide, but decreased in those taking placebo (P less than .001).

Progression of Early Diabetes

The hereditary nature of diabetes has been amply established. Even though the nature of the genetic change is unknown, diabetes is a molecular disease; that is, a disease in which important cellular components are seriously impaired. Eventually, the activities or the products arising from the impairment find expression in various ways, finally culminating in the abnormalities of diabets. Insulin deficiency, one of the landmarks of overt, symptomatic diabetes, was investigated by us in patients at different stages of the disease, in an attempt to elucidate the pathophysiology of the progression of the disease.