Effect of Antihypertensive Therapy on Renal Artery Structure in Type 2 Diabetic Rats With Hypertension

Abstract —We have previously demonstrated that antihypertensive treatment with doxazosin (DZN), an α-adrenergic blocker, and lisinopril (LIS), an ACE inhibitor, reverse glomerular sclerosis in corpulent spontaneously hypertensive rats with type 2 diabetes. In this study, we examined the effects of the above-mentioned antihypertensive drugs alone and in combination on the structure of interlobular and arcuate arteries in these rats. Both male and female rats aged 6 months were treated with antihypertensive drugs for 16 weeks. Various structural parameters were evaluated by light microscopy, with the use of digital image analysis, in kidney sections stained with periodic acid–Schiff. Systolic blood pressure was significantly lower in treated than in untreated rats. Untreated diabetic rats had a significantly higher media/lumen ratio (smaller luminal diameter) of both arteries compared with the ratio in treated rats (for interlobular artery, 0.72±0.06 [no treatment], 0.49±0.03 [DZN treatment], 0.54±0.06 [LIS treatment], and 0.52±0.04 [combination therapy], P <0.05 to <0.001 for no treatment versus treatment; for arcuate artery, 0.66±0.11 [no treatment], 0.40±0.02 [DZN treatment], 0.39±0.04 [LIS treatment], and 0.40±0.03 [combination therapy], P <0.05 for no treatment versus treatment). Antihypertensive treatment caused significant increases in total arterial cross-sectional area, internal and external diameters, luminal and medial cross-sectional area, and medial thickness in both interlobular and arcuate arteries. The improvement in arterial structure after antihypertensive treatment was due to remodeling and growth of the vessels. Both DZN and LIS were equally efficacious, and combination therapy had no additive or synergistic effect.

Selenium-deficient diet induces renal oxidative stress and injury via TGF-beta1 in normal and diabetic rats

BACKGROUND

Oxidative stress has been implicated in the pathogenesis of diabetic nephropathy. Although glucose itself can initiate oxidative stress, deficiency of essential trace elements such as selenium (Se) may exacerbate this oxidative stress in diabetic rats. The mechanism by which Se deficiency causes oxidative stress and renal injury is not completely understood. This study tested the hypothesis that Se deficiency induces renal oxidative stress and renal injury via transforming growth factor-beta1 (TGF-beta1).

METHODS

Fifty-four male Wistar rats were used. Diabetes was induced in 27 rats by streptozotocin, and the other 27 rats received buffer only. Ten weeks after induction of diabetes, both normal and diabetic rats were killed, their kidneys removed, and glomeruli were isolated. Glomeruli from normal and diabetic rats were incubated in the presence of TGF-beta1 alone or its neutralizing antibody. Antioxidant enzyme (Cu-Zn) superoxide dismutase (Cu-Zn SOD), catalase, and glutathione peroxidase (GSH-Px) activities; total glutathione; and lipid peroxidation were determined. For Se studies, 15 normal and 15 diabetic rats were divided into groups of five each and fed either a regular, Se-deficient, or Se-supplemented diet one week after induction of diabetes. Ten weeks after feeding these diets, rats were killed and glomeruli were isolated. Oxidative stress was examined by determining the mRNA expressions for antioxidant enzymes and also for TGF-beta1. Plasma glucose and albuminuria were determined. Histology of the kidney and interlobular artery was evaluated by light microscopy.

RESULTS

In vitro studies showed that TGF-beta1 significantly reduced glomerular catalase and GSH-Px activities as well as total glutathione levels with an increase in lipid peroxidation in both normal and diabetic rats. Antibody to TGF-beta abrogated these changes. There was no effect of TGF-beta1 on Cu-Zn SOD. Like TGF-beta1, a Se-deficient diet caused a significant decrease in glomerular mRNA expression for Cu-Zn SOD, catalase, and GSH-Px, but a significant increase in TGF-beta1 mRNA expression. Also, a Se-deficient diet caused an increase in albuminuria, glomerular sclerosis, and plasma glucose levels in both normal and diabetic rats. The deficient diet caused a decrease in the lumen size of the interlobular artery. Se supplementation to diabetic rats up-regulated mRNA expression for antioxidant enzymes, and significantly reduced but did not normalize that of TGF-beta1. Glomerular sclerosis was normalized and the interlobular artery lumen size was greatly enlarged in diabetic rats by Se supplementation. Also, the tubulointerstitium was preserved by Se supplementation in diabetic rats.

CONCLUSIONS

The data show that TGF-beta1 is a pro-oxidant and Se deficiency increases oxidative stress via this growth factor. In addition, Se deficiency may simulate hyperglycemic conditions. Se supplementation to diabetic rats prevents not only oxidative stress but renal structural injury, as well.

L-lysine reduces nonenzymatic glycation of glomerular basement membrane collagen and albuminuria in diabetic rats

In this study, we examined the hypothesis whether exogenous administration of L-lysine in drinking water would reduce nonenzymatic glycation of glomerular basement membrane (GBM) collagen and thus albuminuria in streptozotocin-diabetic rats. The rationale is that the administered lysine would combine with the circulating glucose and make it unavailable to react with epsilon-amino groups of lysine of various proteins in these diabetic rats. Lysine (0.1%) was given to diabetic rats 7 days (early treatment) or 90 days (late treatment) after induction of hyperglycemia. The treatment was continued for 60 days. Diabetic rats had significantly higher glucose, glycosylated HbA(1), kidney weight, nonenzymatic glycation of GBM collagen, albuminuria, and systolic blood pressure than normal rats. Early treatment with lysine prevented the rise in glycosylated HbA(1) (normal 6.98 +/- 0.71% vs. diabetic - early treatment - 7.78 +/- 1.50%; p = NS), reduced glycosylation of GBM collagen by 86%, and significantly improved albuminuria. There was no significant effect on plasma glucose and systolic blood pressure. However, late treatment reduced the glycosylation of GBM collagen by 46% with a significant improvement in albuminuria. Plasma creatinine levels were not different between normal and untreated diabetic or lysine-treated diabetic rats; however, the creatinine clearance was significantly higher in all groups of diabetic rats (normal 0.45 +/- 0.09 vs. diabetic 2.02 +/- 0.39 ml/min; p < 0.001). The data suggest that early rather than late treatment is more beneficial in reducing nonenzymatic glycation of collagen, although both treatments significantly reduced albuminuria. There was no nephrotoxicity as assessed by plasma creatinine levels or creatinine clearances. These beneficial effects occurred independent of changes either in blood pressure or plasma insulin concentration.

Effect of antihypertensive therapy on renal injury in type 2 diabetic rats with hypertension

In a previous study, we demonstrated that doxazosin (DZN), an alpha(1)-adrenergic blocker, prevented proteinuria in streptozotocin diabetic rats. In this study, we investigated whether DZN would lower established proteinuria by improving glomerular sclerosis in spontaneously hypertensive corpulent rats with type 2 diabetes mellitus. DZN treatment was compared with treatment with angiotensin-converting enzyme inhibitor, lisinopril (LIS) alone, and DZN in combination with LIS. Combination therapy was used to examine any additive effect of either drug alone in the reduction of proteinuria and glomerular sclerosis. Both male and female rats age 6 months with established proteinuria were used. The rats were allocated randomly to 1 of 4 groups: untreated, DZN treated, LIS treated, or a combination of DZN and LIS treatment. Drug treatment was continued for 16 weeks. The results show that (1) either drug alone or in combination significantly lowered systolic blood pressure; (2) DZN, LIS, or combination therapy reduced albuminuria at 16 weeks of treatment from baseline by 38.61+/-5.77%, 30.70+/-4. 21%, and 42.17+/-4.77% (mean+/-SE), respectively. No difference in albuminuria was observed among the 3 groups of rats; (3) the fractional mesangial area, which was 20.55+/-3.77% in untreated rats, was significantly reduced to 11.18+/-1.32% in DZN-treated rats, with a further reduction to 8.72+/-0.64% in LIS-treated rats and to 3.48+/-0.35% in rats treated with DZN+LIS; and (4) DZN but not LIS significantly improved plasma glucose levels in spontaneously hypertensive corpulent rats (untreated 21.06+/-0.97 mmol/L versus DZN treated 15.81+/-0.93 mmol/L or DZN+LIS treated 17.38+/-1.10 mmol/L; P<0.025 to 0.005). Thus, the data suggest that 16-week treatment with either DZN or LIS improves established proteinuria and glomerular sclerosis, but combination therapy is superior to either DZN or LIS alone in preventing glomerular sclerosis in type 2 diabetic rats with hypertension.

Renal cortical expression of mRNAs for antioxidant enzymes in normal and diabetic rats

Increased oxidative stress has been implicated in the development of vascular complications of diabetes. In this study, we examined the hypothesis whether chronic hyperglycemia induces oxidative stress by lowering renal expression and activity of antioxidant enzymes and a decrease in glutathione, an antioxidant, in streptozotocin diabetic rats. The results show that the expression of mRNAs for Cu/Zn superoxide dismutase and glutathione peroxidase was significantly increased and that of catalase was decreased in diabetic rats. However, the superoxide dismutase activity was significantly lower in diabetic than normal glomeruli, whereas the activities of the other two enzymes correlated with their mRNA expression. Total glutathione content was significantly decreased in diabetic compared to normal glomeruli. The data suggest that hyperglycemia induces oxidative stress by overexpressing rather than lowering certain antioxidant enzyme mRNAs in the kidney of diabetic rats. Enhanced nonenzymatic glycation of enzyme protein seems to be the cause for the observed decrease in glomerular superoxide dismutase activity.

Heparan sulfate proteoglycan synthesis and its expression are decreased in the retina of diabetic rats

PURPOSE

Heparan sulfate proteoglycan (HSPG) is an integral component of all basement membranes and is implicated in the charge-selective properties of these basement membranes. Studies have shown a decrease in the number of HSPG anionic sites in the retinal capillary and glomerular basement membrane of diabetic animals. This study examined whether a decrease in both HSPG synthesis and its expression as perlecan are reduced in the retina of streptozotocin-diabetic rats.

METHODS

Diabetes was induced in male Wistar rats by intraperitoneal injection of streptozotocin and the rats were sacrificed 20 weeks later. Retinas were isolated and HSPG synthesis was assessed by incorporation of 35S-sulfate into heparan sulfate. The expression of mRNA for perlecan was quantified by RNase protection assay.

RESULTS

Both the synthesis of HSPG and mRNA expression for perlecan were decreased in the retina of diabetic compared to normal rats.

CONCLUSIONS

The decrease in HSPG synthesis may account for the reported decrease in retinal basement membrane anionic sites and increased capillary permeability that occurs in diabetes.

Doxazosin prevents proteinuria and glomerular loss of heparan sulfate in diabetic rats

We examined whether blood pressure reduction or good glycemic control equally lower albuminuria by preventing glomerular loss of heparan sulfate and progression of glomerulosclerosis in streptozotocin-induced diabetic rats. We used doxazosin, and alpha 1-adrenergic blocker, to lower systemic blood pressure, and good glycemic control was achieved by insulin treatment. Rats were killed after 20 weeks of treatment. Doxazosin significantly lowered systolic pressure in diabetic rats; however, it had no effect in normal rats. Good glycemic control also lowered systolic pressure. In diabetic rats with good glycemic control, doxazosin had an additive effect on blood pressure. Glomerular heparan sulfate synthesis was significantly lower and urinary albumin excretion higher in diabetic than in normal rats. Both doxazosin treatment and good glycemic control normalized these abnormalities in diabetic rats. Insulin normalized plasma glucose and glycosylated HbA1 concentrations in diabetic rats, as did doxazosin. Significant increases in mesangial area and glomeruloscelerosis were observed in diabetic rats. Only good glycemic control normalized these pathological changes in all diabetic rats. Two-way factorial ANOVA showed an interaction between the effects of doxazosin and insulin on systolic pressure and plasma glucose. The data show that after 20 weeks of doxazosin treatment, albuminuria was reduced by 80%; however, this treatment had no significant effect on mesangial expansion or progression to glomerulosclerosis. Conversely, good glycemic control prevented all three of the preceding sequelae.

Sodium depletion prevents albuminuria in hypertensive rats

The effect of short term (8 weeks) sodium (Na+) depletion and its repletion on glomerular synthesis of heparan sulfate and urinary excretions of albumin, total protein, heparan sulfate, Na+ and potassium (K+) was studied in spontaneous hypertensive rats (SHR) and their control normotensive Wistar-Kyoto rats (WKY). Na+ depletion in SHRs significantly increased the synthesis of glomerular heparan sulfate and decreased urinary excretions of albumin, Na+ and heparan sulfate when compared with the Na+ repleted group. In WKY rats, Na+ depletion did not cause any of the above changes. These data suggest that Na+ depletion prevents the urinary loss of protein through preservation of glomerular heparan sulfate only in SHRs.

Long-term effects of antihypertensive treatment and good glycemic control on plasma lipids in diabetic rats

The long-term effects of angiotensin-converting enzyme inhibitors (captopril and enalapril), calcium-entry blockers (diltiazem and nicardipine), and good glycemic control on plasma lipids and lipoproteins were studied in streptozotocin diabetic rats. Diabetic rats had increased plasma cholesterol, tryiglycerides, very-low-density lipoprotein (VLDL), and low-density lipoprotein (LDL) cholesterol, and decreased levels of high-density lipoprotein (HDL) cholesterol than in normal rats. Compared to other antihypertensives, nicardipine seems to have a less beneficial effect on lipids and lipoproteins. However, it is only the good glycemic control that normalized these plasma lipids and lipoproteins in diabetic rats. This suggests that good glycemic control prevents dyslipidemia in diabetic rats. The observed beneficial effects of antihypertensives were unrelated to either food or water intake.

Effect of insulin-glipizide combination on skeletal muscle capillary basement membrane width in diabetic patients

This study investigated the long-term effect of insulin or the combination of insulin and an oral hypoglycemic compound (glipizide) on the skeletal muscle capillary basement membrane width in insulin-requiring diabetic patients. Seventy diabetic patients were randomized to treatment with either insulin-placebo or insulin-glipizide (5 mg/d) for 3 years. Of these, only 61 patients completed the study; 27 patients received insulin-placebo and 34 patients received insulin-glipizide. Three skeletal muscle (quadriceps femoris) biopsies were performed in all patients over a 3-year period. Glycosylated hemoglobin A1 was determined every 100 +/- 20 days, including plasma glucose levels. Muscle capillary basement membrane width was quantitated by a previously described method. After approximately 16 months, glycosylated hemoglobin A1 decreased significantly in each group from its baseline (P < 0.001 insulin-glipizide group and P < 0.025 insulin-placebo), although no statistically significant difference was seen between the two groups. After 3 years this decrease was statistically significant (P < 0.001) only in the insulin-glipizide group. At baseline, no statistically significant difference was found in the muscle capillary basement membrane width between the two groups. In spite of the significant decrease in glycosylated hemoglobin A1 in both groups after 14 to 16 months, only muscle capillary basement membrane width in the insulin-glipizide group decreased significantly compared with baseline. Patients receiving insulin-placebo showed a gradual increase in the muscle capillary basement membrane width, which after 3 years was significantly higher than baseline (P < 0.02). Although the mechanisms by which the addition of glipizide to insulin treatment reduced the thickening of the muscle capillary basement membrane are not clearly understood, the current findings suggest that diabetic microangiopathy is not necessarily progressive and that prophylaxis may be attained.

Transforming growth factor-beta 1 enhances glomerular collagen synthesis in diabetic rats

In vitro glomerular collagen synthesis and its response to various concentrations of transforming growth factor-beta 1 were studied in normal and diabetic rats. TGF-beta 1 increased collagen synthesis in normal glomeruli in a dose-dependent manner up to 5 ng/ml. Concentrations > 5 ng/ml showed a gradual decline in collagen synthesis. Basal collagen synthesis was increased in diabetic glomeruli, but addition of TGF-beta 1 had no effect. Antibody to TGF-beta 1 prevented this increase in collagen synthesis. Both circulating TGF-beta 1 concentration and its glomerular expression of mRNA were higher in diabetic than in normal rats. Although addition of TGF-beta 1 did not increase synthesis in vitro, the absence of an effect is consistent with downregulation of its receptors attributable to the high circulating levels. This study clearly indicates a regulatory role of TGF-beta 1 in renal glomerular collagen synthesis in the normal rat, and suggests a possible causal role for enhanced collagen synthesis in the diabetic rat.

Aldose reductase inhibition by ponalrestat (statil) does not prevent proteinuria in long-term diabetic rats

The aldose reductase pathway has been implicated in the development of chronic complications of diabetes. In this study, we investigated the effect of an aldose reductase inhibitor, statil, on glomerular synthesis of heparan sulfate and albuminuria in male Wistar rats made diabetic with streptozotocin. Heparan sulfate is the predominant glycosaminoglycan (GAG) proteoglycan in the glomerular basement membrane (GBM). It confers a negative charge on the GBM, and its loss has been related to the presence of albumin in the urine. Diabetic rats synthesized less glomerular heparan sulfate and excreted more albumin than normal rats. Glomerular sorbitol concentration was significantly higher in diabetic than in normal rats. Chronic treatment of diabetic rats with statil did not improve either heparan sulfate synthesis or albuminuria despite normalization of glomerular sorbitol content. The present study does not support the role of excess sorbitol in the development of glomerular abnormalities in this rat model of streptozotocin diabetes.

Effect of diltiazem on glomerular heparan sulfate and albuminuria in diabetic rats

Calcium entry blockers, particularly diltiazem, have been shown to lower not only systemic blood pressure but also improve proteinuria in non-insulin-dependent diabetic patients. The presence of proteinuria is attributed to the loss of glomerular heparan sulfate, which confers a negative charge on the basement membrane. In the present study, we evaluated the efficacy of diltiazem in lowering blood pressure and proteinuria in diabetic rats and also examined the possibility that diltiazem prevents proteinuria through glomerular preservation of heparan sulfate. Diabetes was induced in male Wistar rats by streptozotocin (60 mg/kg). One group of diabetic rats was treated with diltiazem (25 mg/L) in drinking water for 20 weeks. Another group of diabetic rats and a group of nondiabetic rats were given tap water only. Systolic blood pressure was measured at 4, 8, 12, and 20 weeks. Urinary excretion of albumin was done at 4, 8, 12, 16, and 20 weeks. At the end of 20 weeks, all rats were killed, kidneys were removed, and glomeruli were isolated. Total glycosaminoglycan and heparan sulfate synthesis were determined by incubating glomeruli in the presence of [35S]sulfate. Diltiazem lowered blood pressure significantly in diabetic rats at 8, 12, and 20 weeks. Diabetic glomeruli synthesized less total glycosaminoglycan and heparan sulfate than glomeruli from normal rats. Characterization of heparan sulfate by ion-exchange chromatography showed that the fraction eluted with 1 M NaCl was significantly lower and the fraction eluted with 1.25 M NaCl significantly higher in diabetic than in normal rats. Diltiazem therapy returned not only glomerular synthesis but also various fractions of heparan sulfate to normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of galactose regimen on glomerular heparan sulfate synthesis and albumin excretion in diabetic rats

Decreased glomerular heparan sulfate synthesis could account for the increased albuminuria observed in experimental diabetes. A similar albuminuria has been observed in galactose-fed animals. To test whether heparan sulfate synthesis is also decreased in galactosemic animals we measured the heparan sulfate synthesis in isolated renal glomeruli from streptozotocin diabetic and normal rats fed regular diets or 30% galactose diets for 11-12 weeks. Albumin excretion and glomerular heparan sulfate synthesis were determined at the time of sacrifice. As predicted by this hypothesis glomerular heparan sulfate synthesis was significantly lower in the diabetic group than in normals given regular diets (309 +/- 23 vs 487 +/- 56 dpm/mg glomerular wt.; P < 0.01), and albumin excretion greater in these diabetics than in the normals (20 +/- 4.3 vs 2.0 +/- 0.7 mg/24 hr; P < 0.002). Albumin excretion and glomerular heparan sulfate synthesis were also consistent with the hypothesis, but unpredictably reversed, in the galactose-fed diabetic group. Glomerular heparan sulfate synthesis was significantly increased in this group (713 +/- 67 dpm/mg glomerular wt.) and albumin excretion decreased (10.7 +/- 3.6 mg/24 hr) compared to the diabetic on regular diet. Some possible explanations are discussed, but the galactose effect described here remains phenomenological.

Effect of metformin treatment on glucose tolerance and glomerulosclerosis in KK mice

Non-obese KK mice, aged 90-100 days, demonstrating an abnormal tolerance to glucose, hyperinsulinaemia with insulin resistance and glomerulosclerosis were treated with either water (control N = 10) or metformin (N = 15), a biguanide, orally at a concentration of 50 mg/kg twice daily for 16 weeks. Oral glucose tolerance was performed at 7 weeks. Only 10 of 15 metformin-treated mice (responders) improved their oral glucose tolerance. The remaining 5 mice (non-responders) did not improve their tolerance to the oral glucose load. A repeated oral glucose tolerance test at 16 weeks showed similar results. Blood lactate and insulin levels were similar in all 3 groups of mice. At sacrifice, responders had significantly less glomerulosclerosis compared to control mice. No difference in the incidence of glomerulosclerosis was found between control mice and non-responders. The data suggest that chronic metformin treatment improves glucose tolerance in 70% of KK mice without increasing blood lactate or insulin levels. This improvement in glycaemic control is associated with a lesser incidence of glomerulosclerosis in KK mice.

Erythrocyte Ca, Na/K-ATPase in long-term streptozotocin diabetic rats. Effect of good glycemic control and a Ca antagonist

This study evaluated the effect of chronic hyperglycemia on erythrocyte membrane Ca and Na/K-ATPase activities in streptozotocin-induced diabetic rats. The activity of Ca-ATPase was significantly lower in diabetic than in normal rats. Good glycemic control by insulin restored the Ca-ATPase activity to normal. By contrast, diltiazem, a calcium entry blocker, had no effect on the enzyme activity. Calmodulin stimulated Ca-ATPase activity in all groups of rats. Na/K-ATPase activity was not altered in diabetic rats, and no effects of either insulin or diltiazem treatments were observed. The results suggest that erythrocyte Ca-ATPase activity is decreased in diabetic rats and is normalized by good glycemic control.

Effect of cyclosporine treatment on carnitine and myo-inositol in diabetic rats

1. The effect of long-term (20 wk) treatment of cyclosporine A (CyA) was studied in urine, blood, liver, kidney and pancreatic concentrations of acid-soluble carnitine and free myo-inositol in streptozotocin diabetic rats. 2. Diabetic rats excreted significantly higher concentrations of carnitine and myo-inositol; CyA prevented the urinary loss of carnitine but not myo-inositol. 3. Blood carnitine levels were not different between normal and diabetic rats, however, CyA significantly decreased these levels. Conversely, blood myo-inositol concentrations were higher in diabetic than in normal rats; CyA prevented this increase. 4. Hepatic concentrations of both carnitine and myo-inositol were increased in diabetic rats; CyA treatment caused even further increase. 5. Pancreas from diabetic rats contained less carnitine and myo-inositol compared to normal pancreas. CyA treatment did not affect pancreatic carnitine, but it normalized myo-inositol in diabetic rats. 6. The kidney carnitine or myo-inositol levels were not influenced either by diabetes or by CyA treatment. 7. These results suggest that CyA treatment causes changes in carnitine and myo-inositol concentrations in biologic fluids and certain tissues.

Effect of chronic metformin treatment of hepatic and muscle glycogen metabolism in KK mice

Noninsulin-dependent diabetic KK mice, aged 90-100 days, with hyperinsulinemia and insulin resistance were treated with either metformin (N = 13) or water (control, N = 10) orally at a concentration of 50 mg/kg twice daily for 28 weeks. Age-matched nondiabetic Swiss Webster (SW) mice were also similarly treated. Liver and skeletal muscle glycogen synthase and phosphorylase enzymes were determined in all groups of mice. Both enzymes were significantly lower in control KK than in control SW mice. Metformin did not influence either of these enzymes in nondiabetic SW mice. However, it significantly increased the active form of glycogen synthase (a form) in both the liver and muscle of KK mice. Metformin also increased the active form of phosphorylase (a form) in the liver but not in the muscle of these mice. Hepatic glycogen content was similar in both control and metformin-treated KK mice. However, the muscle glycogen content was significantly higher in metformin-treated than in control KK mice. These data suggest that metformin preferentially stimulates glycogen synthesis in skeletal muscle, and this seems to be responsible for the observed improvement in fasting glucose and glucose response to an oral glucose load in KK mice.

Bioavailability of aspirin and salicylamide following oral co-administration in human volunteers

BC powder (I) is a commercially available analgesic containing the active ingredients aspirin and salicylamide. The kinetics of I, BC powder minus aspirin (II), and BC powder minus salicylamide (III) were evaluated in 13 volunteers. Ten minutes after administration of I, aspirin reached a maximum concentration of 12.9 micrograms/mL, while salicylamide concentration reached a peak value of 3.4 micrograms/mL. However, when III was administered, aspirin was not detected at 10 min and only reached a concentration of 0.4 microgram/mL at 2 and 6 h. Furthermore, the area under the plasma concentration versus time curve for aspirin when III was administered was sixfold less compared with treatment with I. The area under the curve for aspirin metabolites was significantly different in I versus III. After treatment with II, a delay in salicylamide peak concentration was observed. Gentisamide was not detected throughout the study. This study demonstrates that salicylamide significantly enhances plasma levels of aspirin with potential therapeutic implications.

Enalapril improves albuminuria by preventing glomerular loss of heparan sulfate in diabetic rats

Angiotensin converting enzyme (ACE) inhibitors, particularly enalapril and captopril, have been shown to decrease proteinuria in diabetic animals and human subjects. Since heparan sulfate proteoglycan confers a negative charge on the glomerular basement membrane, and either decreased synthesis or loss of this charge causes albuminuria in diabetic animals, we examined the possibility that enalapril prevents albuminuria through glomerular preservation of heparan sulfate in long-term diabetic rats. A total of 22 male Wistar rats were used in the study. Diabetes was induced in 15 rats by a single intraperitoneal injection of streptozotocin (60 mg/kg). The remaining 7 rats received buffer. One week following induction of diabetes, 8 diabetic rats were allowed to drink tap water containing enalapril at a concentration of 50 mg/liter; the remaining 7 diabetic and 7 nondiabetic rats were given only tap water. The drug treatment was continued for 20 weeks. Systolic blood pressure and 24-hr urinary excretion of albumin were measured at 2, 8, 16, and 20 weeks. At the end of 20 weeks, all rats were killed, kidneys were removed, and glomeruli were isolated by differential sieving technique. Total glycosaminoglycan and heparan sulfate synthesis was determined by incubating glomeruli in the presence of [35S]sulfate. Characterization of heparan sulfate was performed by ion-exchange chromatography. Systolic blood pressures were significantly lower in enalapril-treated diabetic rats compared to untreated diabetic rats. Diabetic glomeruli synthesized less heparan sulfate than glomeruli from nondiabetic rats. Also, glomerular heparan sulfate content of diabetics was significantly lower than that of nondiabetics. Further characterization of heparan sulfate showed that the fraction eluted with 1 M NaCl was significantly lower and the fraction eluted with 1.25 M NaCl significantly higher in diabetic than in normal rats. Enalapril treatment normalized not only glomerular synthesis and content but also various fractions of heparan sulfate in diabetic rats. Diabetic rats excreted increased quantities of heparan sulfate and albumin than nondiabetic rats. Enalapril therapy prevented both these increases in diabetic rats. These data suggest that enalapril treatment improves albuminuria through preservation of glomerular heparan sulfate and prevention of its urinary loss in diabetic rats.

Potentiation of renal tumorigenicity by cyclosporine A in streptozotocin diabetic rats

Male Wistar rats with streptozotocin induced diabetes were treated every third day with 10 mg/kg (13 rats) of cyclosporine A (CyA) for 20 weeks. At sacrifice, 7 of 13 rats (53.8%) demonstrated renal tumors. By contrast, only 2 of 16 streptozotocin diabetic rats (12.5%) without CyA demonstrated renal tumors. No tumors were noted in 10 non-diabetic control rats. These studies suggest that CyA potentiates renal tumorigenicity in streptozotocin diabetic rats.

Prevention of albuminuria by captopril in diabetic rats

1. Streptozotocin diabetic rats were treated with captopril (50 mg l), an angiotensin converting enzyme-inhibitor, in drinking water for 20 weeks. 2. Systolic blood pressure and 24-hr urinary excretions of heparan sulfate and albumin were done at 2, 8, 16 and 20 weeks. 3. At the end of 20 weeks, all rats were killed, kidneys removed and glomeruli isolated. 4. Total glycosaminoglycan and heparan sulfate synthesis were determined by incubating glomeruli in the presence of 35S-sulfate. 5. Captopril significantly lowered blood pressure in diabetic rats 8 weeks after treatment. 6. Diabetic glomeruli synthesized less total glycosaminoglycan and heparan sulfate than glomeruli from nondiabetic rats. 7. Further characterization of heparan sulfate by ion-exchange chromatography showed that the fraction eluted with 1 M NaCl was significantly lower and the fraction eluted with 1.25 M NaCl significantly higher in diabetic than in normal rats. 8. Therapy with captopril normalized not only glomerular synthesis and content but also various fractions of heparan sulfate in diabetic rats. 9. Excretions of heparan sulfate and albumin were significantly higher in diabetic than in nondiabetic rats. 10. Captopril therapy did significantly lower but not normalize both these excretions in diabetic rats. 11. The data suggest that catopril therapy improves albuminuria through preservation of glomerular heparan sulfate and prevention of its urinary loss in diabetic rats.

Vitamin and micronutrient concentrations in cyclosporine-induced renal tumor from diabetic rats

Concentrations of vitamins, biopterin, free inositol and acid-soluble carnitine were determined in cyclosporine A induced renal adenocarcinoma and uninvaded renal tissue from streptozotocin diabetic rats. Vitamin B6, thiamin, riboflavin, nicotinate, free inositol and acid-soluble carnitine were significantly decreased in tumor than nontumor tissue. Concentrations of folic acid, B12, biotin, pantothenate and biopterin were similar in both tissues. These studies suggest that renal adenocarcinoma affects concentrations of only certain vitamins and micronutrients.

Effect of short- and long-term diabetes on carnitine and myo-inositol in rats

1. The effect of short- (2 wk) and long-term (20 wk) streptozotocin diabetes was studied on urine, blood, liver, heart, brain, skeletal muscle, pancreas and kidney concentrations of acid-soluble carnitine and free myo-inositol. 2. Short-term diabetic rats excreted significantly higher concentrations of carnitine as well as myoinositol than normal rats. Blood carnitine and myo-inositol were not different between normal and diabetic rats. Diabetes caused a decrease in liver, brain and pancreatic carnitine, but not in heart, skeletal muscle and kidney. Myo-inositol concentration was decreased in liver, heart and kidney but not in brain, pancreas and skeletal muscle. 3. Long-term diabetic rats had higher urinary excretions of both carnitine and myo-inositol. Blood carnitine did not change; however, myo-inositol was higher in diabetic than in normal rats. Diabetes caused a significant increase in liver and a decrease in heart, brain, skeletal muscle and pancreatic content of carnitine; no difference in kidney carnitine was noted. Myo-inositol content was elevated only in liver of diabetic rats. 4. We suggest that carnitine and myo-inositol concentrations are influenced both by short- and long-term diabetes through changes in tissue metabolism.

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.

Diabetic nephropathy. An update

Nephropathy is a serious microvascular complication in patients with insulin-dependent diabetes mellitus. In the United States, diabetes accounts for one fourth of new cases of end-stage renal disease each year. Complication rates and costs are much higher for diabetic than for nondiabetic patients with end-stage renal disease. Despite numerous studies, the pathophysiology of diabetic renal disease is not completely understood. We reviewed the current status of the structural, functional, biochemical, pathogenetic, and treatment modalities of diabetic renal disease and examined future therapeutic interventions.

Effect of genetic diabetes and alcohol on tissue carnitine and inositol concentrations in mice

Concentrations of acid-soluble L-carnitine and inositol were determined in heart, kidney, muscle, pancreas, liver, brain and blood of genetically diabetic obese db/db and their nondiabetic control C57BL/6J (CBL) mice. Results were compared to a group of diabetic and CBL mice fed ethanol (ETOH) 4 g/kg daily for 58-64 days. In CBL and db/db mice, heart muscle was found to have the greatest and brain the least content of carnitine. Diabetes caused a significant decrease in hepatic concentration of carnitine but did not affect carnitine concentration of heart, kidney, skeletal muscle, brain and pancreas. ETOH intake had no effect on carnitine content of any of the tissues studied. Free inositol content was highest in brain and lowest in skeletal muscle of CBL and db/db mice; diabetes or ETOH intake did not affect tissue inositol content. Except for liver, neither diabetes nor ETOH intake affects tissue carnitine or inositol concentration.

Collagen metabolism in the myocardium of normal and diabetic rats

Myocardial collagen and total protein synthesis were studied in normal, diabetic, and insulin-treated diabetic rats after a single intraperitoneal injection of L-[2,3-3H]proline as a radioisotopic precursor. The incorporation of tritiated proline into myocardial protein was regarded as a measure of total protein synthesis and the incorporation into hydroxyproline as indicative of myocardial collagen synthesis. Both total protein and collagen synthesis were found to be significantly lower in diabetic rats. This was associated with decreased degradation of both total protein and collagen in diabetic rats, as suggested by prolonged turnover times. Collagen content was also found to be increased in diabetic myocardium. Early insulin therapy with normalization of blood sugars in diabetic rats returned myocardial collagen metabolism to normal. This suggests that maintenance of euglycemia in diabetic rats is necessary to prevent abnormal myocardial collagen metabolism.

Glomerular basement membrane collagen synthesis rates in normal and diabetic rats

Glomerular basement membrane (GBM) protein and collagen synthesis rates were studied in normal and streptozotocin diabetic rats, using L-(2,3,3H)-proline as a radioactive precursor. The incorporation of tritiated proline into GMB proline was regarded as a measure of total protein synthesis and the incorporation into hydroxyproline as indicative of collagen synthesis. Total GBM protein and collagen synthesis rates were calculated from the simultaneous measurements of specific activities in the precursor (tissue-free) and protein-bound (GBM proline and hydroxyproline) pools. The results suggest that diabetic rats synthesized GBM protein and collagen at the rate of 1.90 and 0.61% per h, respectively, compared to 1.07 and 0.38% per h in normal rats. These data are consistent with our previous findings of increased GBM protein and collagen synthesis in streptozotocin diabetic rats.

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).

Hereditary diabetes in the KK mouse: an overview

Table III compares metabolic and morphologic characteristics of different species of control and KK mice. The C57BL/6J demonstrates no significant metabolic, clinical or histologic abnormalities. Our two highly inbred Swiss albino groups I and II also do not show significant glomerular lesions, although we found striking intolerance to glucose, hyperinsulinism, and obesity among them. Thus a genetic predisposition may be necessary in addition to various environmental factors to produce microangiopathy in KK mice. The yellow AY mouse is included in this table, since it is strikingly hyperinsulinemic and obese without concomitant vasculopathy such as the other mentioned control strains have. In conclusion, the KK mice develop chemical diabetes preceded by a stage of prediabetes and also demonstrate renal, retinal and neurologic complications similar to those seen in human diabetes. Of particular interest is the development of mild to moderate glomerulosclerosis in the prediabetic stage; with progression to severe glomerulosclerosis and attendant proteinuria later in life. With proper back-crossing, both hyperglycemia and glomerulosclerosis can be transmitted to normal control mice, suggesting that a specific genetic background is necessary for the development of diabetes and diabetic-like microangiopathy. We therefore suggest that the KK mouse serves as an ideal genetic animal for the study of non-insulin-dependent diabetes mellitus and its complications for rational prevention and therapy.

Metabolism of glomerular basement membrane in short- and long-term streptozotocin diabetic rats

The synthesis of glomerular basement membrane (GBM) total protein and collagen was assessed by two methods in vivo in normal and streptozotocin diabetic rats 4-6 weeks and 42-44 weeks after onset of hyperglycaemia, using L-[2, 3, 3H] proline as a radioactive precursor. The incorporation of tritiated proline into GBM hydroxyproline was used as a measure of collagen synthesis and that into proline as total protein synthesis. The basement membrane fractions from both short- and long-term diabetic rats attained much higher proline and hydroxyproline specific activities compared to normal GBM proline and hydroxyproline specific activities. Early insulin therapy with normalization of blood sugar levels in short-term (4-6 weeks) diabetic rats returned the abnormal increases in GBM total protein and collagen synthesis to normal. By contrast, poor glycaemic control with insulin did not prevent the increases in GBM protein synthesis. The results of the present study suggest that overall enhancement of GBM protein synthesis occurs in both short- and long-term streptozotocin diabetes. Early insulin therapy with normalization of blood sugar levels prevents this increase in GBM protein synthesis. Poor glycaemic control had no effect on abnormal GBM protein synthesis. This may be of potential significance in view of preventing chronic diabetic microvascular complications such as nephropathy.

Riboflavin nutritional status and flavoprotein enzymes in streptozotocin-diabetic rats

Riboflavin nutritional status was assessed on the basis of activity coefficients of glutathione reductase in erythrocyte hemolysates of normal and streptozotocin-diabetic rats. Activity coefficient values higher than 1.3 were regarded as evidence of riboflavin deficiency. All diabetic animals were found to be riboflavin-deficient, with activity coefficient values of 1.47-2.11. Treatment of diabetic rats with either insulin or riboflavin returned their activity coefficients to normal. Rats fed a restricted diet had normal activity coefficient values. The erythrocyte glutathione reductase activity was significantly lower in diabetic rats, and the augmentation of enzyme activity in the presence of flavin-adenine dinucleotide (FAD) was 72% compared to 16% in normal rats. Hepatic activities of glutathione reductase and succinate dehydrogenase, both FAD-containing enzymes, were significantly lower in diabetic than in normal rats. Like activity coefficient values, all enzyme activities were normalized after insulin or riboflavin treatments. These data suggest that insulin and riboflavin enhance the synthesis of erythrocyte and hepatic FAD. The results of the present study suggest that experimental diabetes causes riboflavin deficiency, which in turn decreases erythrocyte and hepatic flavoprotein enzyme activities. These changes can be corrected for by either insulin or riboflavin. The pathogenesis of riboflavin deficiency in diabetes mellitus is not clearly understood. The data of the present study provide evidence in addition to the previous findings of an increased prevalence of riboflavin deficiency in genetically diabetic KK mice.

Metabolism of glomerular basement membrane in normal, hypophysectomized, and growth-hormone-treated diabetic rats

The in vivo synthesis of the renal glomerular basement membrane (GBM) collagen was studied in normal, hypophysectomized (hypox), diabetic, and growth-hormone (GH)-treated diabetic rats, using tritiated proline (L[2,3,3H]proline) as a radioisotopic precursor. After the injection of tritiated proline, all groups of rats were sacrificed at various time intervals and the specific activities of proline and hydroxyproline of GBM were determined, the latter being used as a measure of GBM collagen synthesis. A significant decrease in both proline and hydroxyproline specific activities were observed in GBM of hypox rats at all periods of study. Administration of GH to hypox rats returned the GBM collagen synthesis to normal. Diabetic GBM had higher proline and hydroxyproline specific activities when compared to normal rats. Treatment of diabetic rats with GH for 10 days further increased both proline and hydroxyproline specific activities when compared either to diabetic or normal rats treated with GH. The activity of glucosyltransferase, an enzyme involved in the biosynthesis of the disaccharide unit of GBM collagen was found to be decreased in glomeruli of hypox rats. In contrast, the activity of N-acetyl-beta-glucosaminidase, a glycoprotein-degrading enzyme, was found to be significantly increased in hypox rats. GH treatment restored both enzyme activities to normal. The results of the present study show that GBM collagen synthesis is decreased in hypox rats and increased in diabetic rats. GH treatment not only normalized GBM collagen synthesis in hypox rats but also caused significant increase in diabetic rats. This suggests that the renal GBM metabolism is influenced by GH, and this may be of particular significance in view of GH involvement in diabetic microvascular complications.

Collagen metabolism in the retina of normal and diabetic rats

Glucosyltransferase, an enzyme involved in the synthesis of the carbohydrate portion of basement membranes and collagens, and collagen content were determined in the retina of normal and streptozotocin diabetic rats. No significant difference in glucosyltransferase activity was found at 4 weeks of diabetes. However, the enzyme activity was significantly increased in diabetic rats 12 and 48 weeks following the induction of diabetes. Similarly, a significant increase in collagen content was observed in diabetic retinas after 12 weeks of diabetes. Electron microscopy showed marked thickening of the retinal capillary basement membrane in long-term diabetic (48 weeks) rats. The data suggest that enhanced collagen synthesis and deposition occurs in the retina of diabetic rats, and with duration of diabetes this may result in thickening of the capillary basement membrane. These results are compatible with previously reported increases in kidney glucosyltransferase, collagen synthesis and thickening of the capillary basement membrane in diabetic rats.

Glucosyltransferase activity in kidney fractions of normal and streptozotocin-diabetic rats

Glucosyltransferase (UDPglucose: galactosylhydroxylysine-basement membrane glucosyltransferase), an enzyme specifically involved in collagen synthesis, was measured in various kidney fractions of normal, diabetic and underfed rats, using as basis the incorporation of radioactivity into protein during incubation with UDP[U-14C]glucose and alkali-soluble fetal calf-skin collagen. Three criteria of enzyme activity were compared: A, total radioactivity of the washed protein precipitate; B, this figure minus activity incorporated in the absence of the collagen acceptor; and C, radioactivity incorporated into the mixed amino acid fraction, collected by elution with dilute NH4OH from a Dowex 50 resin column after alkaline hydrolysis of the protein. Method A was found satisfactory using whole medulla or isolated glomeruli, since the average proportions of total protein radioactivity recovered in the NH3 fraction were 0.81 and 0.87, respectively, and the deviations were small. There was a larger and variable proportion of nonspecific incorporation using whole cortex. Incubation of a control set of sample without added collagen was found to be unnecessary (Method B). Per mg protein, medulla and glomeruli had more enzyme than did whole cortex. In diabetes, activity was enhanced in the 10,000 X g supernatant fraction of cortex, as previously reported. However, the increase associated with diabetes was even more consistent in the medulla, averaging 3-fold in the 10,000 X g pellet fraction. No increase was found in isolated glomeruli in diabetes. Also, no increase was seen in the kidneys of non-diabetic rats with body weight similar to that of the diabetics.