Biochemical abnormalities of the human diabetic glomerular basement membrane

Diabetic nephropathy

Diabetic nephropathy occurs in approximately 35% of all diabetic patients, both insulin and non-insulin dependent. It accounts for the largest proportion increase of all diseases as a cause for endstage renal disease in the United States. Certain populations, i.e., Pima Indians and Mexican and black Americans, have a higher propensity for developing diabetic nephropathy. The reasons for this increased incidence, however, are unclear. Pathophysiologically, numerous changes in vascular reactivity and renal physiology occur in early diabetes. These include increased sodium avidity, lower threshold for vasoconstriction secondary to angiotensin II and norepinephrine, a greater than 50% of normal increase in renal vasodilation following a protein meal, and loss of renal autoregulation. These differences are not seen in nondiabetic hypertensive subjects. The therapeutic approach to lower elevated arterial pressure in these patients should take these changes in physiology into account. Specifically, antihypertensive agents are preferred that have natriuretic properties and also blunt the effects of vasoconstrictors on both the vasculature and the cellular level, i.e., inhibit mesangial hypertrophy and matrix expansion, the hallmark of diabetes. Ideal agents, therefore, are angiotensin converting enzyme (ACE) inhibitors in the early stages of the disease, and certain calcium antagonists once renal insufficiency occurs. These choices are largely due to the hemodynamic, natriuretic, and anti-proteinuric effects of these agents. Good blood pressure control is essential for preservation of renal function, regardless of agents used. The ACE inhibitors and calcium antagonists of the verapamil and diltiazem groups have demonstrated superior efficacy for preservation of renal function over conventional therapy.

Aortic collagen alterations in human diabetes mellitus. Changes in basement membrane collagen content and in the susceptibility of total collagen to cyanogen bromide solubilisation

Structural alterations in arterial extracellular matrix components have been suggested to play a role in the development of arterial disease among patients with diabetes mellitus. This study examines the quantity and quality of collagenous components in aortas from diabetic patients. In order to obtain data about the arterial tissue concentration of type IV and V collagen in diabetic and non-diabetic patients, aortas from 21 patients with diabetes (9 with Type 1 (insulin-dependent) diabetes and 12 with Type 2 (non-insulin-dependent) diabetes), were collected at autopsy together with aortas from groups of sex- and age-matched patients. Intima and media samples from normal and fibrous plaque areas from the individual vessels were evaluated. Pulverized, dried and defatted tissue samples were subjected to chemical solubilization with cyanogen bromide and subsequent immuno-chemical quantitation of the dissolved type IV and V collagen in an ELISA. It was found that the concentration of type IV collagen was increased in the tunica media both in plaque and non-plaque areas in the samples from the diabetic patient groups as compared to the non-diabetic groups. No consistent differences in type IV collagen concentrations were found between diabetic and non-diabetic patients in tunica intima. The type V collagen concentrations and the total collagen content were not altered in the diabetic samples. The fraction of the total collagen that was solubilized during cyanogen bromide treatment was determined, and it was found that this fraction was decreased in most tissue areas in the diabetic patient groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucosyl and galactosyl transferase activities of diabetic (db/db) and obese (ob/ob) mice kidneys

1. Glucosyl and galactosyl activities were determined in kidney cortex tissue prepared from two strains of mice, genetically diabetic and obese mice. 2. These activities were measured as a function of ageing between 6 weeks and 13 months. 3. For both strains glucosyl transferase activity was shown to increase with respect to ageing whereas galactosyl transferase activity decreased at the same time. 4. These changes of enzymatic activities would suggest that a smaller increase of hydroxylysine-linked glycans than expected was observed under these pathological conditions.

Studies on the alpha-glucosidase specific for collagen disaccharide units: variations associated with capillary basement membrane thickening in kidney and brain of diabetic and aged rats

The alpha-glucosidase specific for the hydroxylysine-linked disaccharide units of collagens (or 2-0-alpha-D-glucopyranosyl-5-0-beta-D-galactopyranosylhydroxy-L-lysine glucohydrolase) has been measured in kidney cortex and brain cortical tissue of streptozotocin diabetic rats after 19, 23 or 28 weeks of diabetes and of aged rats 22 months old. Increased specific activities of the enzyme have been found repeatedly in the dialyzed homogenates and the 7.2 X 10(6) g.min supernatants of kidney and brain at the various stages of diabetes when compared with age-matched controls; the specific activities returned to a normal level after insulin treatment. Similar increased specific activities were observed in kidney and brain of the aged normoglycemic rats when compared with young adult rats. In diabetic kidney cortex, beta-galactosidase and p-nitrophenyl-alpha-D-glucoside glucosidase specific activities were decreased in contrast to the increase of glucosyl-galactosyl-hydroxy-lysine glucohydrolase. In kidney cortex of the aged rats, beta-galactosidase activity was also decreased, but p-nitrophenyl-alpha-D-glucoside glucosidase was increased. In both diabetic and aged rats, thickening of the kidney glomerular basement membranes was confirmed; thickening of the brain cortical capillary basement membranes was also observed. Thus in the diabetic and aged animals, the increased glucosyl-galactosyl-hydroxylysine glucohydrolase specific activity was associated with basement membrane thickening in the kidney and the brain.

Biochemistry of glomerular basement membrane of the normal and diabetic human

HGBM were isolated from kidneys of 22 diabetic patients and 32 normal control persons. All diabetic kidneys showed severe alterations of glomerulosclerosis. The amount of basement membranes isolated from diabetic kidneys was significantly higher. The HGBM preparations were individually analyzed for phosphorus, DNA, amino acids, and carbohydrates. The cystine concentration was found to be lower in the diabetic than in normal HGBM. Contrary to other reports, there was no increase in the amounts of hydroxylysine, glucose, and galactose, nor was there a decrease in the lysine content. Glucose and mannose were shown to be significantly lower in the diabetic HGBM. The mean value for sialic acid content was lower in diabetic HGBM; the value did not reach statistical significance. This study's data could not confirm the finding of a specific alteration of diabetic HGBM as proposed previously.

Biochemical differences in human glomerular basement membrane related to diabetes and age

Preparations of glomerular basement membrane from diabetic and young and aged normal subjects have been isolated and purified and the component carbohydrates and amino acids quantitatively determined. Diabetic membrane preparations, compared with membranes from young normal subjects, show significant increases in total hexoses, mannose, and galactose and decreases in sialic acid and glucose; the component amino acids show increases in hydroxylysine, proline, and glycine and decreases in lysine, histidine, and leucine. Basement membrane preparations from aged normals show changes in component carbohydrates and amino acids similar to, but not as great as, those seen in the diabetics.

[Diabetic glomerulosclerosis: current status of its morphology and pathogenesis (author's transl)]

The diabetic glomerulosclerosis as a consequence of the abnormal metabolic state is characterized by an uniform thickening of the glomerular basement membrane (GBM) and an augmentation of the mesangial matrix. Both alterations begin already few years after the onset of the diabetes and are observed in all glomeruli to the same extent (=diffuse type). Later on, nodular deposits of glycoproteins are additionally found in the mesangium (=nodular type). Only these nodules are morphologically specific for the diabetic disorder. In association with both the diffuse and the nodular glomerulosclerosis, insudation of plasma can be seen in the afferent and efferent vessels and the glomerular capillary loops. The mechanism of the increase in the amount of GBM-material is not known, since contradictory data have been reported with regards to both the chemical composition and metabolism of the GBM in human and experimental diabetes. Some postulate that the abnormal deposition of GBM-mateiral is due to an excessive synthesis (anabolic disorder), others argue that a further decrease in the normally slow breakdown and disposal (catabolic disorder) might be responsible. This review presents the different pathogenetic concepts of the glomerulosclerosis and attemps to explain the possible causes for the current discrepancies.