Human glomerular basement membrane: chemical alteration in diabetes mellitus

Histological Manifestations of Diabetic Kidney Disease and its Relationship with Insulin Resistance

Histological manifestations of diabetic kidney disease (DKD) include mesangiolysis, mesangial matrix expansion, mesangial cell proliferation, thickening of the glomerular basement membrane, podocyte loss, foot process effacement, and hyalinosis of the glomerular arterioles, interstitial fibrosis, and tubular atrophy. Glomerulomegaly is a typical finding. Histological features of DKD may occur in the absence of clinical manifestations, having been documented in patients with normal urinary albumin excretion and normal glomerular filtration rate. Furthermore, the histological picture progresses over time, while clinical data may remain normal. Conversely, histological lesions of DKD improve with metabolic normalization following effective pancreas transplantation. Insulin resistance has been associated with the clinical manifestations of DKD (nephromegaly, glomerular hyperfiltration, albuminuria, and kidney failure). Likewise, insulin resistance may underlie the histological manifestations of DKD. Morphological changes of DKD are absent in newly diagnosed type 1 diabetes patients (with no insulin resistance) but appear afterward when insulin resistance develops. In contrast, structural lesions of DKD are typically present before the clinical diagnosis of type 2 diabetes. Several heterogeneous conditions that share the occurrence of insulin resistance, such as aging, obesity, acromegaly, lipodystrophy, cystic fibrosis, insulin receptor dysfunction, and Alström syndrome, also share both clinical and structural manifestations of kidney disease, including glomerulomegaly and other features of DKD, focal segmental glomerulosclerosis, and C3 glomerulopathy, which might be ascribed to the reduction in the synthesis of factor H binding sites (such as heparan sulfate) that leads to uncontrolled complement activation. Alström syndrome patients show systemic interstitial fibrosis markedly similar to that present in diabetes.

Biochemical composition of the glomerular extracellular matrix in patients with diabetic kidney disease

In the glomeruli, mesangial cells produce mesangial matrix while podocytes wrap glomerular capillaries with cellular extensions named foot processes and tether the glomerular basement membrane (GBM). The turnover of the mature GBM and the ability of adult podocytes to repair injured GBM are unclear. The actin cytoskeleton is a major cytoplasmic component of podocyte foot processes and links the cell to the GBM. Predominant components of the normal glomerular extracellular matrix (ECM) include glycosaminoglycans, proteoglycans, laminins, fibronectin-1, and several types of collagen. In patients with diabetes, multiorgan composition of extracellular tissues is anomalous, including the kidney, so that the constitution and arrangement of glomerular ECM is profoundly altered. In patients with diabetic kidney disease (DKD), the global quantity of glomerular ECM is increased. The level of sulfated proteoglycans is reduced while hyaluronic acid is augmented, compared to control subjects. The concentration of mesangial fibronectin-1 varies depending on the stage of DKD. Mesangial type III collagen is abundant in patients with DKD, unlike normal kidneys. The amount of type V and type VI collagens is higher in DKD and increases with the progression of the disease. The GBM contains lower amount of type IV collagen in DKD compared to normal tissue. Further, genetic variants in the α3 chain of type IV collagen may modulate susceptibility to DKD and end-stage kidney disease. Human cellular models of glomerular cells, analyses of human glomerular proteome, and improved microscopy procedures have been developed to investigate the molecular composition and organization of the human glomerular ECM.

Collagen IVα345 dysfunction in glomerular basement membrane diseases. I. Discovery of a COL4A3 variant in familial Goodpasture's and Alport diseases

Diseases of the glomerular basement membrane (GBM), such as Goodpasture’s disease (GP) and Alport syndrome (AS), are a major cause of chronic kidney failure and an unmet medical need. Collagen IV^α345 is an important architectural element of the GBM that was discovered in previous research on GP and AS. How this collagen enables GBM to function as a permselective filter and how structural defects cause renal failure remain an enigma. We found a distinctive genetic variant of collagen IV^α345 in both a familial GP case and four AS kindreds that provided insights into these mechanisms. The variant is an 8-residue appendage at the C-terminus of the α3 subunit of the α345 hexamer. A knock-in mouse harboring the variant displayed GBM abnormalities and proteinuria. This pathology phenocopied AS, which pinpointed the α345 hexamer as a focal point in GBM function and dysfunction. Crystallography and assembly studies revealed underlying hexamer mechanisms, as described in Boudko et al. and Pedchenko et al. Bioactive sites on the hexamer surface were identified where pathogenic pathways of GP and AS converge and, potentially, that of diabetic nephropathy (DN). We conclude that the hexamer functions include signaling and organizing macromolecular complexes, which enable GBM assembly and function. Therapeutic modulation or replacement of α345 hexamer could therefore be a potential treatment for GBM diseases, and this knock-in mouse model is suitable for developing gene therapies.

Activation of bone morphogenetic protein 4 signaling leads to glomerulosclerosis that mimics diabetic nephropathy

Diabetic nephropathy (DN) is the most common cause of chronic kidney disease. We have previously reported that Smad1 transcriptionally regulates the expression of extracellular matrix (ECM) proteins in DN. However, little is known about the regulatory mechanisms that induce and activate Smad1. Here, bone morphogenetic protein 4 (Bmp4) was found to up-regulate the expression of Smad1 in mesangial cells and subsequently to phosphorylate Smad1 downstream of the advanced glycation end product-receptor for advanced glycation end product signaling pathway. Moreover, Bmp4 utilized Alk3 and affected the activation of Smad1 and Col4 expressions in mesangial cells. In the diabetic mouse, Bmp4 was remarkably activated in the glomeruli, and the mesangial area was expanded. To elucidate the direct function of Bmp4 action in the kidneys, we generated transgenic mice inducible for the expression of Bmp4. Tamoxifen treatment dramatically induced the expression of Bmp4, especially in the glomeruli of the mice. Notably, in the nondiabetic condition, the mice exhibited not only an expansion of the mesangial area and thickening of the basement membrane but also remarkable albuminuria, which are consistent with the distinct glomerular injuries in DN. ECM protein overexpression and activation of Smad1 in the glomeruli were also observed in the mice. The mesangial expansion in the mice was significantly correlated with albuminuria. Furthermore, the heterozygous Bmp4 knock-out mice inhibited the glomerular injuries compared with wild type mice in diabetic conditions. Here, we show that BMP4 may act as an upstream regulatory molecule for the process of ECM accumulation in DN and thereby reveals a new aspect of the molecular mechanisms involved in DN.

Deletion of the basement membrane heparan sulfate proteoglycan type XVIII collagen causes hypertriglyceridemia in mice and humans

Background

Lipoprotein lipase (Lpl) acts on triglyceride-rich lipoproteins in the peripheral circulation, liberating free fatty acids for energy metabolism or storage. This essential enzyme is synthesized in parenchymal cells of adipose tissue, heart, and skeletal muscle and migrates to the luminal side of the vascular endothelium where it acts upon circulating lipoproteins. Prior studies suggested that Lpl is immobilized by way of heparan sulfate proteoglycans on the endothelium, but genetically altering endothelial cell heparan sulfate had no effect on Lpl localization or lipolysis. The objective of this study was to determine if extracellular matrix proteoglycans affect Lpl distribution and triglyceride metabolism.

Methods and Findings

We examined mutant mice defective in collagen XVIII (Col18), a heparan sulfate proteoglycan present in vascular basement membranes. Loss of Col18 reduces plasma levels of Lpl enzyme and activity, which results in mild fasting hypertriglyceridemia and diet-induced hyperchylomicronemia. Humans with Knobloch Syndrome caused by a null mutation in the vascular form of Col18 also present lower than normal plasma Lpl mass and activity and exhibit fasting hypertriglyceridemia.

Conclusions

This is the first report demonstrating that Lpl presentation on the lumenal side of the endothelium depends on a basement membrane proteoglycan and demonstrates a previously unrecognized phenotype in patients lacking Col18.

Hemoglobin AI in community care

In order to investigate the potential usefulness of knowing the blood concentrations of HbAI in primary care, HbAI was measured in diabetic subjects attending a primary care centre. The values were compared with concentration of HbAI in a reference group on non-diabetics. The reference group had a mean value in HbAI of 7.6+/-0.1% with a tendency to increased values with advancing age. The diabetic subjects had a mean value in HbAI of 10.8+/-0.2%. Diabetics under good control had lower values (10.2+/-0.2%), than patients under poor control (12.0+/-0.2%) (p less than 0.001). There was a correlation (r=0.50, p less than 0.001) between HbAI and fasting blood glucose levels. It is concluded that determination of HbAI can be an aid in the control of diabetics in primary care. However, the method requires good technical management, and the results are most reliable when the same person analyses all samples. The objective in diabetic therapy in this respect should no doubt be to depress the concentrations of HbAI towards normal values.

Plasmalemmal vacuolar H+-ATPase is decreased in microvascular endothelial cells from a diabetic model

Angiogenesis requires invasion of extracellular matrix (ECM) proteins by endothelial cells and occurs in hypoxic and acidic environments that are not conducive for cell growth and survival. We hypothesize that angiogenic cells must exhibit a unique system to regulate their cytosolic pH in order to cope with these harsh conditions. The plasmalemmal vacuolar type H(+)-ATPase (pmV-ATPase) is used by cells exhibiting an invasive phenotype. Because angiogenesis is impaired in diabetes, we hypothesized that pmV-ATPase is decreased in microvascular endothelial cells from diabetic rats. The in vitro angiogenesis assays demonstrated that endothelial cells were unable to form capillary-like structures in diabetes. The proton fluxes were slower in cells from diabetic than normal model, regardless of the presence or absence of Na(+) and HCO(3) (-) and were suppressed by V-H(+)-ATPase inhibitors. Immunocytochemical data revealed that pmV-ATPases were inconspicuous at the plasma membrane of cells from diabetic whereas in normal cells were prominent. The pmV-ATPase activity was lower in cells from diabetic than normal models. Inhibition of V-H(+)-ATPase suppresses invasion/migration of normal cells, but have minor effects in cells from diabetic models. These novel observations suggest that the angiogenic abnormalities in diabetes involve a decrease in pmV-ATPase in microvascular endothelial cells.

Glomerular extracellular matrices in rat diabetic glomerulopathy by scanning electron microscopy

Characteristic pathological changes in the glomeruli in diabetic nephropathy include expansion of the mesangial matrix and thickening of the glomerular basement membrane (GBM). Using an acellular digestion technique combined with scanning electron microscopy, the three-dimensional ultrastructural changes in glomerular extracellular matrices were studied in rats with diabetic glomerulopathy. Diabetes was induced by the intravenous injection of streptozotocin and morphological analyses were performed 3, 6 and 11 months after the injection. Expansion of mesangial area and GBM thickening became evident with time. After treatment with the series of detergents, all cellular components were completely removed leaving the extracellular matrices intact. In normal controls, the mesangial matrix appeared as fenestrated septa with oval or round stomata between the glomerular capillaries. In diabetic glomerulopathy, expansion of mesangial matrix and narrowing of the mesangial fenestrae were observed. These changes in the mesangial matrices seem to play a vital role in the progression of glomerulosclerosis in rat diabetes. A subendothelial thin layer of the GBM was continuous with the mesangial matrix. One cause of GBM thickening in streptozotocin diabetes may be expansion of the mesangial matrix into the peripheral GBM.

Impairment of endothelium-dependent dilatation of the basilar artery during diabetes mellitus

The goal of this study was to determine whether responses of the basilar artery are altered during diabetes mellitus. We measured the diameter of the basilar artery in vivo in non-diabetic and diabetic rats (streptozotocin; 50-60 mg/kg i.p.). Responses of the basilar artery to agonists, which presumably produce dilatation by releasing endothelium-derived relaxing factor (EDRF), were impaired in diabetic rats compared to non-diabetic rats. Acetylcholine (1.0 and 10 microM) dilated the basilar artery by 13 +/- 2 and 26 +/- 4% (means +/- S.E.M.), respectively, in non-diabetic rats, but by only 4 +/- 1 and 9 +/- 2%, respectively, in diabetic rats (P less than 0.05). Bradykinin (1.0 and 10 microM) dilated the basilar artery by 14 +/- 2 and 35 +/- 6% (means +/- S.E.M.), respectively, in non-diabetic rats, but by only 5 +/- 1 and 6 +/- 2%, respectively, in diabetic rats (P less than 0.05). The response to nitroglycerin was similar in non-diabetic and diabetic rats. Thus, impairment of vasodilatation in diabetic rats in response to acetylcholine and bradykinin is not related to non-specific impaired of vasodilatation. Next, we examined the possibility that impaired dilator responses of the basilar artery in response to acetylcholine and bradykinin in diabetic rats may be related to the activation of the thromboxane A2-prostaglandin H2 receptor. SQ 29548 (a specific thromboxane A2-prostaglandin H2 receptor antagonist) did not alter responses of the basilar artery to acetylcholine and bradykinin. These findings suggest that diabetes mellitus impairs endothelium-dependent dilatation of the basilar artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of diabetes mellitus on disruption of the blood-brain barrier during acute hypertension

The goal of this study was to determine whether the susceptibility of the blood-brain barrier to disruption during acute hypertension is altered during diabetes mellitus. Intravital fluorescent microscopy and fluorescein-labelled albumin were used to evaluate disruption of the blood-brain barrier under control conditions and during acute arterial hypertension in non-diabetic and diabetic rats. Permeability of the blood-brain barrier was quantitated by calculating clearance of fluorescent-labelled albumin and by counting the number of microvascular leaky sites under control conditions and during acute hypertension. In non-diabetic rats, when systemic arterial pressure was increased from 109 +/- 5 (mean +/- S.E.) to 185 +/- 8 mmHg, clearance of albumin increased from 0.16 +/- 0.04 to 1.51 +/- 0.34 ml/s x 10(-6). In diabetic rats, when systemic arterial pressure was increased from 117 +/- 3 to 184 +/- 3 mmHg, clearance of albumin increased from 0.22 +/- 0.10 to 1.30 +/- 0.32 ml/s x 10(-6). These findings suggest that the susceptibility of the blood-brain barrier to disruption during acute hypertension is not altered during diabetes mellitus.

Immunoglobulin deposits in diabetic microangiopathy. Observations in autopsy materials

Non-enzymatic glycosylation of vascular wall collagen is considered to be most important in the pathogenesis of diabetic microangiopathy, and glycosylated collagens are reported to bind immunoglobulins in vivo. We investigated the occurrence of IgG or IgM deposits in the microvasculature of certain organs of diabetics using routine autopsy materials. Glomerular capillary basement membrane/endothelium was often positive for IgM in diabetics. Endothelial cells of glomerular capillaries were positive for HLA-DR in 6 of 16 diabetics and in 2 of 11 controls. This was associated with IgM or IgG deposits in 5 cases. In the esophagus and/or tongue of diabetics, IgG was frequently deposited in the microvasculature. In total, IgG deposits were found in 13 of 16 diabetics, either in the esophagus or the tongue, but in only 3 of 16 controls. The difference was significant at p less than 0.005. These observations suggest that deposition of immunoglobulins is a component of diabetic microangiopathy. Differences in expression of HLA-DR in glomeruli between diabetics and non-diabetics remain to be explored.

Ultrastructural distribution of endogenous IgGs in the glomerular wall of control and diabetic rats

Endogenous IgG molecules were revealed with high resolution EM over the glomerular wall in renal tissues sampled from short and longterm control and streptozotocin induced diabetic rats by applying the protein A-gold immunocytochemical approach. In tissues from control animals, IgG antigenic sites were revealed on the subendothelial side of the basement membrane, the epithelial side being only weakly labelled. In contrast, in longterm diabetic animals IgG antigenic sites were present throughout the entire thickness of the basement membrane, and in patches closely associated with the plasma membrane of the epithelial cells. Deposits of basement membrane-like material present in the mesangial area were also highly labelled for IgG. Numerous intensely labelled lysosome-like structures were present in the epithelial cells. Morphometrical evaluation of the distribution of the labelling over the basement membrane confirmed these observations. In control animals a peak of labelling was found at 30 nm from the endothelial cell region corresponding to the subendothelial side of the lamina densa. In longterm diabetic animals the labelling was more uniformly distributed throughout the entire thickness of the basement membrane. These data were correlated to biochemical determinations of proteinuria and IgG excretion in urine samples from the control and the diabetic animals. These results suggest that in normal conditions the lamina densa may represent the main barrier for the restriction of the passage of IgGs through the glomerular wall. Modifications at that level occur during diabetes leading to or participating in the loss of the selective permeability of the basement membrane.

Pathobiochemical aspects of diabetic nephropathy

Diabetic nephropathy develops in many diabetic patients as consequence of glomerulosclerosis. On the basis of a series of recent observations it is suggested that a combination of metabolic and hemodynamic changes is responsible for the pathogenesis of diabetic nephropathy. Since the glomerular filtration unit has been characterized to consist of collagen type IV and minor components like laminin, fibronectin and heparan sulfate proteoglycan, influence of diabetes on basement membrane (BM) components has been studied. Biochemical alterations of glomerular BM consist of an increased nonenzymatic glucosylation of type IV collagen leading to unphysiological crosslinking. This, in turn, may result in alteration of the size selective properties of the glomerular filtration unit. Changes in composition of glomerular BM have recently been described. An increased synthesis of type IV collagen with concomitant decrease of heparan sulfate proteoglycan may lead to alteration of the charge selective barrier and consequently to increased permeability of the glomerular BM. Permanently unbalanced synthesis of BM components finally results in obliteration of the capillary lumen. In late state nephropathy intrinsic basement membrane components are no longer produced. Instead, massive accumulation of PAS positive material occurs.

Distribution of endogenous albumin in the glomerular wall of streptozotocin-induced diabetic rats as revealed by high-resolution immunocytochemistry

Endogenous albumin was revealed with high resolution in the glomerular wall of renal tissue from normoglycaemic and long-term streptozotocin-induced hyperglycaemic rats applying the protein A-gold immunocytochemical approach. In tissues from normal animals, albumin antigenic sites were detected at the level of the endothelial cell basal plasma membrane and in the subendothelial side of the lamina densa of the glomerular basal laminae. The epithelial side of the laminae was weakly labelled, while the urinary space was devoid of labelling. In the podocytes, labelling for albumin was confined to few lysosomal structures. In diabetic animals, concomitant with hyperglycaemy, low insulin levels, significant glycosuria, proteinuria and albuminuria, the glomerular basal laminae displayed the characteristic increase in thickness found in diabetic microangiopathy (404 +/- 45 nm versus 190 +/- 10 nm). Major basal laminae deposits were also found in the mesangial regions. Albumin antigenic sites were detected throughout the entire thickness of the glomerular basal laminae without any preferential accumulation at any particular site. Labelling was also found over flocculent material present in the urinary space. Numerous densely labelled lysosomal structures were present in the podocytes. The basal laminae deposits in the mesangial regions were labelled for albumin. Morphometrical evaluations made on the distribution of the labelling confirmed the qualitative observations. Two sites for albumin retention were revealed in the glomerular wall of the normal animal: the endothelial cell basal membrane (less than 10 nm) and the subendothelial side of the lamina densa (50 nm).(ABSTRACT TRUNCATED AT 250 WORDS)

Pathological changes in streptozotocin induced diabetes mellitus in the rat

The structural changes in kidneys of diabetic rats induced by streptozotocin were compared with those of age-matched control animals. Degenerative changes were found in the distal tubules of diabetic rats as early as 2 weeks following the onset of diabetes and by one month the entire distal tubule was severely affected. Fibrinoid lesions were also found in diabetic rats after 4 weeks of the disease and became more frequent subsequently. IgG, albumin but not C3 were also found in the glomerular basement membrane of diabetic rats. Diabetic glomerulosclerosis was present only after several weeks, affected glomeruli showed diffuse mesangial sclerosis and only occasionally nodular sclerosis. Diabetic animals developed renal cortical adenomas and mesenchymal tumours after several months.

Interstitial compartment pathology and spermatogenic disruption in testes from impotent diabetic men

Studies utilizing animal models of diabetes suggest that diabetic complications of impotence involve structural lesions in the testis as part of an overall defect in the pituitary-testicular axis. In the present study testicular biopsies from ten oligospermic and/or impotent men with diabetes were evaluated by light and electron microscopy. One biopsy was judged normal. The remaining tissue showed variable testicular pathology ranging from minimally to grossly affected. Seminiferous tubules had decreased tubule diameters, hyalinized tubule walls, and occluded lumina owing either to epithelial encroachment or cellular debris and exfoliated round germ cells. Sertoli cells were vacuolated and showed a high degree of apical cell membrane redundancy and degeneration. Although Sertoli-Sertoli cell junctional complexes appeared normal, Sertoli junctional specializations associated with spermatids were structurally abnormal or absent. All tubules were variably depleted of adluminal compartment germ cell types. The interstitial compartment was filled with a collagen-rich extracellular matrix concentrated around small blood vessels and seminiferous tubule walls. Capillaries and lymphatic endothelia appeared structurally abnormal and compromised by the interstitial "matrix expansion." Some Leydig cells contained a variable number of small to large lipid droplets, vacuoles, and secondary lysosomes. Results indicate the presence of tissue pathology in testes of impotent diabetic men. Discrete ultrastructural lesions in apical Sertoli cell cytoplasm are associated with spermatogenic disruption and morphological changes in the interstitial compartment suggest microvascular complications.

Carbohydrate contents, and glycosidase and glycosyl transferase activities in tissues from streptozotocin diabetic mice

The contents of hexoses and hexosamines in brain, liver, and kidney of streptozotocin diabetic mice are significantly increased in comparison to the controls. These differences for hexoses contents in the heart are not significant. N-acetyl-beta-D-glucosaminidase and beta-D-glucosidase activities in brain, liver and kidney of diabetic mice are significantly higher when compared to the controls. However, beta-D-galactosidase activity is significantly lower in brain, liver, spleen and kidney of the diabetic mice, in comparison to the controls and similar in heart. alpha-D-Mannosidase activity of diabetic mice is significantly increased in spleen and heart and significantly decreased in liver and kidney. alpha-L-Fucosidase of diabetic mice shows higher activities, with significant differences, in liver and spleen; however, in heart and kidney the activities are significantly lower. Brain sialyltransferase and galactosyltransferase activities are significantly increased in diabetic mice; but for heart and kidney these differences are not significant. The activity for brain and kidney fucosyltransferase is not significant and that for the other assayed organs is significantly higher in comparison to the controls.

Nonenzymatic glucosylation of lysyl and hydroxylysyl residues in type I and type II collagens

Nonenzymatic glucosylation of type I and type II collagens was examined by incubating collagen substrates with D-glucose in vitro. In one set of experiments, unlabeled collagen was incubated with [14C]-glucose and the incorporation of [14C]-radioactivity into protein was determined by TCA precipitation. The incorporation was dependent on the concentration of glucose and the time of incubation. The glucosylated product was also examined by SDS-polyacrylamide slab gel electrophoresis. The results indicated that both alpha 1(I)- and alpha 2(I)-chains of type I collagen were glucosylated and the glucosylation occurred both with native and denatured collagen as substrate. In further studies [3H]-lysine-labeled collagens were glucosylated, the products reduced by NaBH4, and the [3H]-lysine-derived residues were separated by amino acid analyzer. After a 144 h incubation in vitro, 18.9% of [3H]-lysyl residues and 36.5% of [3H]-hydroxylysyl residues in type I collagen were substituted with glucose. In contrast, 47.9% of [3H]-lysyl residues and 68.1% of [3H]-hydroxylysyl residues in type II collagen were glucosylated after 144 h incubation. Based on quantitative amino acid analyses of the substrates, these values represent 27.6 lysine plus hydroxylysine residues substituted per triple-helical type I collagen molecule and 65.3 residues per triple-helical type II collagen molecule. Thus, type I and type II collagens display differential susceptibilities to nonenzymatic glucosylation. Finally, [3H]-proline-labeled type I collagen was glucosylated to varying extents, and the glucosylated products were used as substrates for human polymorphonuclear leukocyte collagenase. No difference in susceptibility to this collagenase was noted, irrespective of the extent of glucosylation.

Influence of in vitro non-enzymatic glycosylation on the physicochemical parameters of type I collagen

In vitro non-enzymatic condensation of glucose on acid soluble collagen is shown not to affect the molecular structure and stability as evaluated both by circular dichroism and differential spectrometry. Viscometric studies demonstrate a lowering in intermolecular interactions; whereas the hydrodynamic volume remains unaffected by nonenzymatic glycosylation. alpha 2(I) collagen chains exhibit a modified electrophoretic mobility previously found in collagen of diabetic rats; this peculiar behavior is discussed in terms of lowered hydrophobicity due to addition of hydrophilic groups from glucose. The lowered formation of hydrophobic areas, evaluated from the fluorescence emission of diphenylhexatriene, indicates that non-enzymatic glycosylation is able to influence the close packing of collagen fibers.

Nonenzymatic glycosylation of basement membrane collagen in diabetes mellitus

For a better understanding of the processes leading to diabetic microangiopathy, type IV collagen from kidneys of patients with long-term diabetes was compared with the collagen from kidneys of sex- and age-matched controls. Type IV collagen from diabetic kidneys revealed no abnormalities in amino acid composition, hydroxylation of proline and lysine, enzymatic glycosylation of hydroxylysine, and immunological reactivity with several monoclonal and polyclonal, anti-type IV collagen antibodies. However, ketoamine-linked hexose, resulting from the nonenzymatic condensation of glucose with lysyl or hydroxylysyl residues, was 1.7-fold higher in diabetic type IV collagen. The stoichiometry of this modification was estimated to be 1-2 residues of hexose per triple helical molecule (Mr 380,000). This small amount of ketoamine-linked hexose might hardly have an effect on the function and turnover of type IV collagen, unless it is bound to a crucial site along the collagen molecule. The nonenzymatic glycosylation of collagen might therefore be a mere consequence of the metabolic disturbances, rather than the primary cause for the late complications of diabetes mellitus.

The thickness of the glomerular basement membrane in irradiated and unirradiated Wistar rats and C-57 BL mice of different age groups

In both Wistar rats and C-57 BL mice, the thickness of the glomerular basement membrane increases progressively with age. This change, which can be measured in cohorts of manageable size, produces a measurement of biological age--if one accepts the assumption that it correlates with the viability of the organism that exhibit it. Whole-body exposure to x-rays has no observable influence on this age-related change.

Electron microscopic observation of gastric mucosal capillaries in diabetics--relationship between diabetic microangiopathy and complications following gastrectomy

An electron microscopic study was made of the gastric mucosal capillaries (GMC) of diabetic patients. Ultrastructural findings, including diabetic microangiopathy (DMA), and clinical features of these diabetic patients were investigated in relation to anastomotic leakage after gastrectomy. The gastric mucosa of resected stomachs from 12 diabetics and 10 nondiabetics were examined. Ultrastructurally, DMA was demonstrated in the stomachs of diabetics, in which the basement membrane of GMC was thicker. The degree of this DMA in the stomach significantly correlated with the duration of diabetes and the degree of DMA found in the skin, but not with age and fasting plasma glucose (FPG) level. Marked DMA was observed with significant frequency in diabetics with anastomotic leakage after gastrectomy. In our hospital, anastomotic leakage after gastrectomy occurred in 9 out of 53 diabetics. Diabetics with anastomotic leakage had severe FPG, a long duration of diabetes and diabetic retinopathy. It seems reasonable to presume that anastomotic leakage after gastrectomy occurs more frequently in diabetics with ultrastructurally severe DMA, clinically severe FPG and relatively long duration of diabetes.

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.

N-acetyl beta-D-glucosaminidase and alpha-L-fucosidase activities in relation to glycosylated hemoglobin levels and to retinopathy in diabetes

N-Acetyl beta-D-glucosaminidase and alpha-L-fucosidase were determined in human sera from 25 control subjects, in 23 diabetic patients without retinopathy and in 22 diabetic patients with retinopathy. The results show significantly higher N-acetyl beta-D-glucosaminidase activity in diabetic patients independently of the development of retinopathy and also independently of the length of diabetes. No correlation was found between either serum enzymes and serum glucose concentration and glycosylated hemoglobin (HbA1).

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.

Preservation of mesangium and immunohistochemically defined antigens in glomerular basement membrane isolated by detergent extraction

To define the characteristics of isolated glomerular basement membrane (GBM), immunohistochemical and morphometric analyses have been carried out on rat and human tissues. Site-specific arrays of antigens were identified in detergent-isolated GBM in a distribution similar to that observed in intact kidney. In the human, fibronectin, procollagen IV, and collagen V were observed along the internal aspect of GBM continuous with antigenic sites in the mesangium. Another array of antigens was identified in the GBM but not within the mesangium--Goodpasture's antigen, bovine lens capsule type IV collagen, and amyloid P component. In addition, sites reactive with rabbit antiserum to laminin were present on both sides of the lamina densa as well as within the mesangial region. Actomyosin, a presumed mesangial cell antigen persisted in the mesangium of isolated GBM. Mesangial matrix was identified in detergent-isolated GBM in an amount equivalent to that present in intact glomeruli. Sonicated GBM contained the same antigens but it was not possible to quantitate the amount of mesangial material by immunofluorescence or morphometric analysis. The thickness of the lamina densa was greater in sonicated and detergent-treated rat GBM preparations than in native rat kidney. These studies demonstrated that isolated GBM is heterogeneous with respect to its antigenic constituents and in addition contains mesangial matrix, which is morphologically and immunohistochemically distinct from peripheral GBM.

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.

Myocardial composition and function in diabetes. The effects of chronic insulin use

This study was undertaken in an animal model of mild diabetes to determine if provision of chronic insulin replacement during postprandial hyperglycemia may modify the abnormalities of myocardium. Group 1 served as controls with normal glucose tolerance by intravenous testing. Two additional groups were made diabetic with low doses of alloxan. Diabetic animals of Group 2 were untreated (n = 6). Group 3 animals (n = 6) received regular insulin daily to reduce postprandial hyperglycemia. After one year with maintained body weight, the animals were studied in the intact anesthetized state using the indicator dilution technique for left ventricular volume determinations. Basal left ventricular function and contractility were similar to normals in both diabetic groups. During intraventricular infusion of saline, end-diastolic pressure rose to higher levels in untreated diabetes (14.8 +/- 2 mm Hg) than normals (8.8 +/- 0.84), despite similar basal levels. Insulin treatment was associated with higher filling pressures than in group 1 as well as reduced end-diastolic volume response. Collagen concentrations were enhanced an average of 50% in layers from the inner to outer myocardium in both untreated and treated diabetics, associated with sodium and water accumulation. Since hypertrophy was not present, the diminished compliance appeared related to increased collagen levels. On electron microscopy, the subcellular organelles of the cardiac cell appeared normal in both diabetic groups. Thus, collagen accumulation and abnormal myocardial function in this model of diabetes is not affected by control of postprandial hyperglycemia, but a potential role for sustained hormone replacement is not excluded.

Plasma acidic glycohydrolases in insulin-dependent diabetes mellitus

We assayed plasma activities of beta-galactosidase, beta-hexosaminidase, alpha-fucosidase and alpha-galactosidase involved in degradation of the glycoprotein molecule in 110 insulin-dependent diabetics aged 3-1/2 to 19 years and compared them to a group of normal youngsters. We correlated the plasma enzyme activities with the duration, control and sequelae of insulin-dependent diabetes. Insulin-dependent diabetics had a significantly higher plasma activity of beta-hexosaminidase and alpha-mannosidase (p less than 0.01) and a significantly lower plasma activity of alpha-fucosidase and alpha-galactosidase (p less than 0.01). Of the 5 enzymes studied, only plasma beta-hexosaminidase correlated with fasting and postprandial blood sugar (p less than 0.01), cholesterol and triglycerides (p less than 0.05). Additionally, poor control of diabetes was also associated with a significantly higher plasma beta-hexosaminidase activity (p less than 0.01). Proteinuria or an abnormal Addis count suggestive of renal involvement was associated with various changes in plasma acidic hydrolases. These changes may be related to insulin deficiency rather than hyperglycemia and may be genetically determined.

Sugar residues on proteins

Glycoproteins have become increasingly important in the structure and function of many different mammalian systems; for example, membrane glycoproteins and glycoprotein hormones. It is, therefore, important to understand their chemistry, which would include an understanding of both the carbohydrate and protein parts of the molecule. Since the chemical characterization of the protein moiety has been extensively examined and the techniques for its characterization are well worked out, only the carbohydrate portion of glycoproteins will be reviewed in this article. The chemical nature of the carbohydrate moiety of glycoproteins will be examined. First, the types of monosaccharides present in animal systems, especially those in the mammalian systems, will be described. Next, various types of simple and complex carbohydrate chains will be discussed to establish the diversity, size, and number of chains present in the carbohydrate units in different glycoproteins. Then, the type of linkages of the carbohydrate to the protein will be examined to determine if the primary sequence of protein is important in determining the size and type of carbohydrate chains present in glycoproteins. Finally, the current methods of structural elucidation such as monosaccharide sequence, intersugar bonds, and anomeric linkages in the carbohydrate moiety of glycoproteins will be reviewed. These methods include the techniques of periodate oxidation, methylation, partial acid hydrolysis, and specific glycosidase digestion of glycoproteins, as well as the latest techniques using micromethods of carbohydrate quantitation and characterization involving gas chromatography and mass spectrometry. The function of the carbohydrate in glycoproteins will also be considered. First, hormone glycoproteins will be discussed in their relationship to the immunological and biological function of the glycoprotein when the carbohydrate is sequentially removed. Next, the function of the carbohydrate in the turnover of glycoproteins will be discussed. These topics will be considered in order to develop an understanding of a specific function(s) of the carbohydrate in glycoproteins.

The measurement of biological age

One of the objectives of gerontological research is to achieve, reproducibly and at will, a verifiable discrepancy between the chronological and biological age of organisms. To accomplish this, the experimenter must be in a position to measure biological age independently. In theory, this can be done in the three ways: by actuarial analysis of large populations, assessment of overall morbidity, or observation of chronic degenerative changes that can be actually measured or graded according to a scale. Of these three approaches, only the last appears to be promising in experimental research. However, not all progressive degenerative changes represent practically useful parameters of biological age. Criteria for their evaluation are presented, and their theoretical prerequisites as well as concrete applications discussed. In a more general way, one has to be aware that biological age is a statistical entity. It cannot be directly observed but only inferred from quantifiable epiphenomena, and is, as such, not measurable like temperature or weight.

The biochemical properties of basement membrane components in health and disease

Basement membranes are complex macromolecular structures which occupy the extracellular space between cells of different histologic types. Biochemically it is composed of Type IV collagen, several noncollagenous glycoproteins including laminin, fibronectin, GP-2 and PYS glycoprotein, and heparan sulfate. Morphologic changes are commonplace in a number of renal diseases. In diabetic glomerular disease, the basement membrane is markedly thickened but the biochemical basis has not been elucidated. In other disease-associated basement membrane changes, altered glycosylation of glycoprotein components has been described. The most important issue is the effect such alterations have on the interaction of basement membrane components and the function of the basement membrane.

[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.

Comparison of collagen and glycosaminoglycan synthesis in attaching control and diabetic human skin fibroblasts

Cultured fibroblasts derived from normal subjects and juvenile diabetics attach in the absence of serum to plastic culture dishes and secrete macromolecules, including collagenous components, hyaluronic acid, and proteoglycans into the medium and onto the plastic surface where they form a microexudate carpet. Most diabetic fibroblasts examined did not spread as well as normal cells during a 4-hr interval after the initial attachment. There were no significant differences between normal and diabetic cells with respect to proline and lysine incorporation and lysine hydroxylation. The percentage glycosylation of hydroxylysine was marginally higher in the media proteins of diabetic cells, but glycosylation in both normal and diabetic cells was elevated over that typically observed in human skin collagen. Collagenous components were estimated to constitute approximately 15-20% of the microexudate carpet fraction in both normal and diabetic cell strains. Diabetic fibroblasts exhibited a marginally lower ratio of heparan sulfate to chondroitin sulfate in the cell surface to matrix microexudate carpet fraction (trypsinate) than did normal fibroblasts. The hyaluronate and chondroitin sulfate contents of this fraction of diabetic cells were not significantly different from those of normal cells.