Glomerular basement membrane metabolism in the diabetic rat. In vivo studies

The complex pathology of diabetic nephropathy in humans

This review summarizes the pathomorphological sequences of nephron loss in human diabetic nephropathy (DN). The relevant changes may be derived from two major derangements. First, a failure in the turnover of the glomerular basement membrane (GBM) based on an increased production of GBM components by podocytes and endothelial cells leading to the thickening of the GBM and accumulation of worn-out GBM in the mesangium. This failure may account for the direct pathway to glomerular compaction and sclerosis based on the continuous deposition of undegraded GBM material in the mesangium. Second, an increased leakiness together with an increased propensity of glomerular capillaries to proliferate leads to widespread plasma exudations. Detrimental are those that produce giant insudative spaces within Bowman's capsule, spreading around the entire glomerular circumference and along the glomerulo-tubular junction onto the tubule resulting in tubular obstruction and retroactively to glomerulosclerosis. Tubular atrophy and interstitial fibrosis develop secondarily by transfer of the glomerular damage onto the tubule. Interstitial fibrosis is locally initiated and apparently stimulated by degenerating tubular epithelia. This leads to a focal distribution of interstitial fibrosis and tubular atrophy accompanied by a varying interstitial mononuclear cell infiltration. Spreading of fibrotic areas between intact nephrons, much less to the glomerulus, has not been encountered.

Peritoneal Vascular Changes in Continuous Ambulatory Peritoneal Dialysis (CAPD): An in Vivo Model for the Study of Diabetic Microangiopathy

Replication of the basement membrane of the peritoneal capillaries and the mesothelium is observed in all uremic patients after a period of continuous ambulatory peritoneal dialysis (CAPD). Biopsy specimens of the parietal peritoneum were taken in diabetic and non-diabetic patients on insertion or repositioning of the CAPD catheter. The basement membrane of the capillaries and mesothelium was normal in non-diabetics on insertion of the catheter, but after 2 to 66 months of CAPD, multiple replication was found. In nearly all the diabetics there was already replication of the basement membrane of the peritoneal capillaries before CAPD was begun but the basement membrane of the mesothelium was intact. After several months of CAPD thickening of the basement membrane of the capillaries was found in 36% of diabetics, sometimes to the point of occlusion. After CAPD, replication of the basement membrane of the mesothelium has been observed in both diabetics and nondiabetics although it is initially perfectly normal in both. CAPD is proposed as an experimental model for diabetic microangiopathy in man.

Rethinking glomerular basement membrane thickening in diabetic nephropathy: adaptive or pathogenic?

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease in the United States and is a major cause of cardiovascular disease and death. DN develops insidiously over a span of years before clinical manifestations, including microalbuminuria and declining glomerular filtration rate (GFR), are evident. During the clinically silent period, structural lesions develop, including glomerular basement membrane (GBM) thickening, mesangial expansion, and glomerulosclerosis. Once microalbuminuria is clinically apparent, structural lesions are often considerably advanced, and GFR decline may then proceed rapidly toward end-stage kidney disease. Given the current lack of sensitive biomarkers for detecting early DN, a shift in focus toward examining the cellular and molecular basis for the earliest structural change in DN, i.e., GBM thickening, may be warranted. Observed within one to two years following the onset of diabetes, GBM thickening precedes clinically evident albuminuria. In the mature glomerulus, the podocyte is likely key in modifying the GBM, synthesizing and assembling matrix components, both in physiological and pathological states. Podocytes also secrete matrix metalloproteinases, crucial mediators in extracellular matrix turnover. Studies have shown that the critical podocyte-GBM interface is disrupted in the diabetic milieu. Just as healthy podocytes are essential for maintaining the normal GBM structure and function, injured podocytes likely have a fundamental role in upsetting the balance between the GBM's synthetic and degradative pathways. This article will explore the biological significance of GBM thickening in DN by reviewing what is known about the GBM's formation, its maintenance during health, and its disruption in DN.

Thiamine and benfotiamine prevent apoptosis induced by high glucose-conditioned extracellular matrix in human retinal pericytes

BACKGROUND

Early and selective loss of pericytes and thickening of the basement membrane are hallmarks of diabetic retinopathy. We reported reduced adhesion, but no changes in apoptosis, of bovine retinal pericytes cultured on extracellular matrix (ECM) produced by endothelial cells in high glucose (HG). Since human and bovine pericytes may behave differently in conditions mimicking the diabetic milieu, we verified the behaviour of human retinal pericytes cultured on HG-conditioned ECM.

METHODS

Pericytes were cultured in physiological/HG on ECM produced by human umbilical vein endothelial cells in physiological/HG, alone or in the presence of thiamine and benfotiamine. Adhesion, proliferation, apoptosis, p53 and Bcl-2/Bax ratio (mRNA levels and protein concentrations) were measured in wild-type and immortalized human pericytes.

RESULTS

Both types of pericytes adhered less to HG-conditioned ECM and plastic than to physiological glucose-conditioned ECM. DNA synthesis was impaired in pericytes cultured in HG on the three different surfaces but there were no differences in proliferation. DNA fragmentation and Bcl-2/Bax ratio were greatly enhanced by HG-conditioned ECM in pericytes kept in both physiological and HG. Addition of thiamine and benfotiamine to HG during ECM production completely prevented these damaging effects.

CONCLUSIONS

Apoptosis is strongly increased in pericytes cultured on ECM produced by endothelium in HG, probably due to impairment of the Bcl-2/Bax ratio. Thiamine and benfotiamine completely revert this effect. This behaviour is therefore completely different from that of bovine pericytes, underlining the importance of establishing species-specific cell models to study the mechanisms of diabetic retinopathy.

The number of podocyte and slit diaphragm is decreased in experimental diabetic nephropathy

PURPOSE

To determine the number of podocyte, slit diaphragms, slit diaphragm extensions and GBM thickness in diabetic nephropathy.

METHODS

Sixty "Rattus Wistar"of both sexes weighing 200-300 g were divided in two experimental groups: normal group 10 animals, and alloxan diabetic rats--50 animals. Alloxan was administered in a single IV dose of 42 mg/kg body weight. Body weight, water and food intake, diuresis, and blood and urine glucose were determined in both groups before alloxan injection and two weeks, six and twelve months after alloxan injection. Proteinuria was measured at 12 months in both groups. After 12 months animals were sacrificed, and the right kidney processed for electron microscopy.

RESULTS

Clear clinical and laboratory signs of severe diabetes were seen, in all alloxan-diabetic rats at all follow-up times. Glomerular basement membrane (GBM) thickening, podocyte number, and slit diaphragm number and extension were determined. GBM of all diabetic rats was significantly thicker (median=0.29 microm; semi-interquartile range=0.065 microm) than in the normal rats (0.23 microm; 0.035 microm). Diabetic rat podocyte number (8; 1), slit diaphragm number (4; 1), and slit diaphragm extension (0.021 microm; 0.00435 microm) were significantly lower than in normal rats (11; 1) and (7; 1.5), and (0.031 microm; 0.0058 microm). Diabetic rat proteinuria (0.060 mg/24 h; 0.037 mg/24 h) was higher than in normal rats (0.00185 mg/24 h; 0.00055 mg/24 h).

CONCLUSION

Experimental diabetes is associated with significant (p<0.05) changes in podocyte foot process, slit number, slit diaphragm extension, and GBM thickness.

Glucosepane Is a Major Protein Cross-link of the Senescent Human Extracellular Matrix

The extracellular matrix in most tissues is characterized by progressive age-related stiffening and loss of proteolytic digestibility that are accelerated in diabetes and can be duplicated by the nonenzymatic reaction of reducing sugars and extracellular matrix proteins. However, most cross-links of the Maillard reaction described so far are present in quantities too low to account for these changes. Here we have determined in human skin and glomerular basement membrane (GBM) collagen the levels of the recently discovered lysine-arginine cross-links derived from glucose, methylglyoxal, glyoxal, and 3-deoxyglucosone, i.e. glucosepane, MODIC, GODIC, and DOGDIC, respectively. Insoluble preparations of skin collagen (n = 110) and glomerular basement membrane (GBM, n = 28) were enzymatically digested, and levels were measured by isotope dilution technique using liquid chromatography/mass spectrometry. In skin, all cross-links increased with age (p < 0.0001) except DOGDIC (p = 0.34). In nondiabetic controls, levels at 90 years were 2000, 30, and 15 pmol/mg for glucosepane, MODIC, and GODIC, respectively. Diabetes, but not renal failure, increased glucosepane to 5000 pmol/mg (p < 0.0001), and for all others, increased it to <60 pmol/mg (p < 0.01). In GBMs, glucosepane reached up to 500 pmol/mg of collagen and was increased in diabetes (p < 0.0001) but not old age. In conclusion, glucosepane is the single major cross-link of the senescent extracellular matrix discovered so far, accounting for up to >120 mole% of triple helical collagen modification in diabetes. Its presence in high quantities may contribute to a number of structural and cell matrix dysfunctions observed in aging and diabetes.

Hyperglycemia-induced TGFbeta and fibronectin expression in embryonic mouse heart

Cardiovascular defects are common in diabetic offspring, but their etiology and pathogenesis are poorly understood. Extracellular matrix accumulates in adult tissues in response to hyperglycemia, and transforming growth factor-beta1 (TGF beta1) likely mediates this effect. The objective of this study was to characterize TGF beta expression in the organogenesis-stage mouse heart and to evaluate TGF beta and fibronectin expression in embryonic mouse heart exposed to hyperglycemia. Prominent TGF beta1, and minimal TGF beta2 or TGF beta 3, protein expression was demonstrated in embryonic day (E) 9.5-E13.5 hearts. Hyperglycemia for 24 hr produced significantly increased fibronectin, slightly increased TGF beta1, and unchanged TGF beta2 or TGF beta 3, by immunohistochemistry. Increased TGF beta1 was demonstrated by enzyme-linked immunosorbent assay in embryonic fluid and isolated hearts after hyperglycemia for 24 hr, but not 48 hr. Hyperglycemia increased fibronectin protein and mRNA expression in embryonic hearts after 24 hr, and pericardial injection of TGF beta1 also increased fibronectin mRNA in the embryonic heart. It is proposed that TGF beta1 and fibronectin may play a role in diabetes-induced cardiac dysmorphogenesis.

A study of capillary pericyte viability on extracellular matrix produced by endothelial cells in high glucose

AIMS/HYPOTHESIS

Thickening of the basement membrane and selective loss of pericytes occur early in diabetic retinopathy. As we showed previously that pericyte adhesion is impaired on extracellular matrix produced by endothelial cells in high hexose concentrations, we aimed to verify if altered adhesion could influence pericyte viability and replication.

METHODS

Conditioned extracellular matrices were obtained by growing human umbilical vein endothelial cells in media containing 28 mmol/l D-glucose, with or without the inhibitors of protein glycation thiamine or aminoguanidine, and D-galactose or L-glucose up to 28 mmol/l. Having removed the endothelium, bovine retinal pericytes were grown on these matrices and, in separate experiments, on laminin, fibronectin or type IV collagen. Pericyte viability and replication were measured by cell counts and DNA synthesis after 7 days, cell cycle traversal after 2 days and apoptosis after 18 h, 2 days and 7 days.

RESULTS

Pericyte counts and DNA synthesis were reduced on matrices produced in high D-glucose and D-galactose, whilst matrix obtained in L-glucose reduced DNA synthesis but not counts. Both thiamine and aminoguanidine corrected reduced pericyte viability when added to high D-glucose. Cell cycle and apoptosis were not affected by growing pericytes on different conditioned matrices. Laminin, fibronectin and type IV collagen did not modify pericyte replication.

CONCLUSIONS/INTERPRETATIONS

Reduced pericyte counts could depend on impaired initial adhesion to the extracellular matrix produced by endothelium in high hexose concentrations, rather than impaired replication or viability. Altered cell-matrix interactions might facilitate pericyte dropout in diabetic retinopathy, independently of the effects of high glucose on pericyte replication.

A quantitative analysis of perineurial cell basement membrane collagen IV, laminin and fibronectin in diabetic and non-diabetic human sural nerve

The thickness of the perineurial cell basement membrane was examined in diabetic and non-diabetic human sural nerve. A significant increase in thickness was found in the diabetic group. The nature of this thickening was investigated using immunohistochemistry and image analysis in order to semi-quantify three of the major intrinsic components of the perineurial cell basement membrane: collagen IV, laminin and fibronectin. Amounts of all three components were shown to be increased in the diabetic group, but not significantly so. However, significant linear correlations between fascicle size and perineurial collagen IV, laminin and fibronectin were identified in both diabetic and non-diabetic nerve.

Diabetic retinopathy: morphometric analysis of basement membrane thickening of capillaries in different retinal layers within arterial and venous environments

AIMS

To assess quantitatively variations in the extent of capillary basement membrane (BM) thickening between different retinal layers and within arterial and venous environments during diabetes.

METHODS

One year after induction of experimental (streptozotocin) diabetes in rats, six diabetic animals together with six age-matched control animals were sacrificed and the retinas fixed for transmission electron microscopy (TEM). Blocks of retina straddling the major arteries and veins in the central retinal were dissected out, embedded in resin, and sectioned. Capillaries in close proximity to arteries or veins were designated as residing in either an arterial (AE) or a venous (VE) environment respectively, and the retinal layer in which each capillary was located was also noted. The thickness of the BM was then measured on an image analyser based two dimensional morphometric analysis system.

RESULTS

In both diabetics and controls the AE capillaries had consistently thicker BMs than the VE capillaries. The BMs of both AE and VE capillaries from diabetics were thicker than those of capillaries in the corresponding retinal layer from the normal rats (p < or = 0.005). Also, in normal AE and VE capillaries and diabetic AE capillaries the BM in the nerve fibre layer (NFL) was thicker than that in either the inner (IPL) or outer (OPL) plexiform layers (p < or = 0.001). However, in diabetic VE capillaries the BMs of capillaries in the NFL were thicker than those of capillaries in the IPL (p < or = 0.05) which, in turn, had thicker BMs than capillaries in the OPL (p < or = 0.005).

CONCLUSIONS

The variation in the extent of capillary BM thickening between different retinal layers within AE and VE environments may be related to differences in levels of oxygen tension and oxidative stress in the retina around arteries compared with that around veins.

Treatment with a glycosaminoglycan formulation ameliorates experimental diabetic nephropathy

Previous studies have indicated that administration of glycosaminoglycans can prevent some of the morphological and physiological alterations which occur in experimental diabetic nephropathy. The aims of this study were to further elucidate the effect of these drugs on glomerular basement membrane permeability by dextran clearance studies, to test the ability of glycosaminoglycans to revert established diabetic nephropathy and to examine the effect of glycosaminoglycans on renal extracellular matrix synthesis. Five groups of Sprague-Dawley rats were studied for 12 months: two control groups (treated or untreated non-diabetic), three streptozotocin diabetic animal groups, two of which received a glycosaminoglycan formulation, one from the induction of diabetes and the other after the fifth month of diabetes. At five months the 35S-sulfate glomerular incorporation, albuminuria, glomerular basement membrane thickness and anionic charge density were determined. At 12 months albuminuria, renal collagen IV and perlecan mRNA levels, anionic and neutral dextran clearances, glomerular basement membrane morphometry, and mesangial cell proliferation were evaluated. We demonstrate that long-term administration of glycosaminoglycans prevents renal morphological and functional alterations in diabetic rats and appears to revert established diabetic renal lesions. Glycosaminoglycan administration modified renal matrix composition by the normalization of collagen gene expression and increasing glomerular 35S-sulfate incorporation.

Improvement of blood glucose control in IDDM patients retards the progression of morphological changes in early diabetic nephropathy

We investigated in a randomized, prospective study the influence of improved blood glucose control during 2-3 years in young insulin-dependent diabetic (IDDM) patients with microalbuminuria, which is indicative of early nephropathy. Patients were randomized either to intensive treatment by continuous subcutaneous insulin infusion (CSII) (n = 9) or CT (n = 9). Kidney biopsies were taken at baseline and after 26-34 months. End points were structural changes in the glomeruli. Sensitive, quantitative, morphometric methods were used. The blood glucose control improved significantly (p = 0.01) during the study in the CSII-group as glycated haemoglobin (HbA1c) fell from 10.1% ([95% CI] 8.9-11.3) to 8.6% (7.9-9.2), but not in the CT-group, 10.1% (8.3-11.9) vs 9.7% (8.7-10.8). Mean HbA1c during the study period was significantly lower in the CSII-group than in the CT-group, 8.7% (8.1-9.3) vs 9.9% (8.5-11.3), p = 0.04. Basement membrane thickness (BMT) increased in both groups, most (CT vs CSII, p = 0.03) in the CT-group: 140 nm (50-230) vs CSII: 56 nm (27-86). In the CT-group only an increase was seen in matrix/mesangial volume fraction (p = 0.006) and matrix star volume (p = 0.04). Furthermore, a positive correlation between mean HbA1c during the study and change from baseline in BMT (r = 0.70, p = 0.001) and matrix/glomerular volume fraction (r = 0.33, p = 0.09, NS) was demonstrated. Albumin excretion rate correlated significantly to BMT and most of the matrix parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetic retinopathy: quantitative variation in capillary basement membrane thickening in arterial or venous environments

Diabetes mellitus was induced in male beagles by a single injection of an alloxan and streptozotocin cocktail and fasting blood sugar levels maintained between 15 and 20 mmol/l. Five years after induction of diabetes, three diabetic animals were sacrificed, together with sex and age-matched controls, and the retinas fixed for either transmission electron microscopy (TEM) or trypsin digestion. In TEM specimens, capillaries in close proximity to the major vessels were designated as either AE (arterial environment) or VE (venous environment) and the thickness of their basement membranes (BMs) measured using an image analyser based two dimensional morphometric analysis system. Results show that the BMs of retinal capillaries from the diabetic dogs were significantly thicker than those from control dogs. Furthermore, within the diabetic group the AE capillaries had thicker BMs than VE capillaries (p < or = 0.05). The controls, however, showed no significant difference in BM thickness between AE and VE capillaries. Although many of the capillaries designated as AE or VE would actually have been derived from the opposite side of the circulation, with respect to BM thickness, they conformed to values of their specific group. The conclusion is that diabetic capillaries are more vulnerable to BM thickening in an arterial environment than in a venous environment.

Increased expression of basement membrane collagen in human diabetic retinopathy

Basement membrane thickening is the most prominent and characteristic feature of early diabetic microangiopathy. Unknown is not only the causative process but also whether the thickening reflects increased synthesis of specific components. Because collagen type IV is uniquely present in basement membranes and represents their predominant structural element, we studied its expression in retinas obtained postmortem from five patients with 8 +/- 3 yr of diabetes and six nondiabetic controls. The collagen IV transcript proved to be rare in adult human retina and undetectable by Northern analysis. We thus identified a set of primers and conditions to detect the transcript by the reverse transcriptase polymerase chain reaction and to measure its level relative to an endogenous internal standard (beta-actin mRNA). In the diabetic patients the levels of collagen IV mRNA were increased twofold over levels in controls, whereas the actin mRNA levels were similar in the two groups. Hence, the collagen IV/actin ratio was 0.53 +/- 0.15 in diabetic samples and 0.24 +/- 0.09 in control samples (P = 0.004). These results indicate that diabetes induces a twofold increase in the expression of collagen IV by the cells that synthesize basement membranes in the adult retina (vascular cells). Insofar as high ambient glucose in vitro elicits the same effect, it may be proposed that basement membrane thickening in diabetes results from enhanced synthesis of specialized component molecules sustained by hyperglycemia.

A comparison of perineurial and vascular basal laminal changes in diabetic neuropathy

Measurements were made of the thickness of the basal lamina of perineurial cells in the sural nerve in a series of patients with diabetic neuropathy and compared with a group of patients with type I hereditary motor and sensory neuropathy (HMSN) and with organ donor control cases. The thickness was significantly greater in the diabetic patients as compared both with the HMSN cases and the organ donor controls. This was most obvious for the intermediate layers of the perineurium. Perineurial basal laminal thickness was only slightly greater in the HMSN cases than in the organ donor controls and the difference was not statistically significant. The thickening of the perineurial cell basal laminae was compared with the thickening of the basal laminal zone around the endoneurial microvessels. No significant correlation was found either for the diabetic neuropathy or HMSN cases or for the organ donor controls. As had been observed previously, the basal laminal zone around the endoneurial capillaries was of increased thickness both in the diabetic neuropathy and the HMSN cases and, although it was greater for the diabetic neuropathy patients, the difference was not statistically significant. Taken together, these findings indicate that the thickening of the basal lamina of the perineurial cells is a more characteristic feature of diabetic neuropathy than is thickening of the basal laminal zone around the endoneurial capillaries. The results suggest that the causative mechanisms are likely to differ, a conclusion supported by the morphological appearances: the basal laminal thickening around the perineurial cells is uniform, whereas that around the capillaries consists of basal laminal reduplication.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum and urinary concentrations of type IV collagen and laminin as a marker of microangiopathy in diabetes

Serum and urinary concentrations of type IV collagen and laminin were measured by enzyme-linked immunosorbent assay (ELISA) in diabetic patients and compared with normal control subjects. In diabetic patients with proteinuria or with renal insufficiency, serum and urinary concentrations of type IV collagen were higher than those of control subjects (p less than 0.005). Furthermore urinary concentrations of type IV collagen and laminin were significantly higher in diabetes, even in the absence of nephropathy, than in normal controls (p less than 0.05). Urinary concentrations of type IV collagen in patients with diabetes and microalbuminuria (0.73 +/- 0.11 mg mmol-1) were significantly higher than in diabetic patients without nephropathy (0.40 +/- 0.060 mg mmol-1) (p less than 0.025). Urinary concentrations of type IV collagen may have a role as an indicator of early diabetic nephropathy. Serum concentrations of type IV collagen in diabetic patients with retinopathy were significantly higher than in normal controls (p less than 0.025). However, urinary concentrations of type IV collagen (p less than 0.05) and serum concentrations of laminin (p less than 0.025) were significantly higher in diabetic patients than normal controls and the difference between patients with and without retinopathy was not significant.

Early increased renal procollagen alpha 1(IV) mRNA levels in streptozotocin induced diabetes

Changes in renal procollagen mRNA levels were measured shortly after the induction of streptozotocin induced diabetes in the rat. "Medullary" procollagen alpha 1(IV) levels seven days after diabetes induction was significantly higher in untreated diabetic rats (DM, N = 12; 244 +/- 57% of the mean control value), than in diabetic rats receiving small doses of insulin insufficient to achieve euglycemia (NPH, N = 10; 87 +/- 12%) and in diluent injected nondiabetic control rats (C, N = 15; 100 +/- 12%; P less than 0.01, DM vs. C and DM vs. NPH). "Medullary" procollagen alpha 1(I) mRNA levels were numerically increased in DM to a lesser degree (141 +/- 5%, ANOVA not significant) compared to C (100 +/- 13%), and this small increment was further normalized by insulin treatment (NPH, 120 +/- 11%). A trend for increased beta-actin mRNA levels in DM did not reach significance (P greater than 0.05). Increases in "medullary" procollagen mRNA levels did not correlate with kidney weight, glomerular tuft volume, creatinine clearance, food intake, or body weight gain, and occurred when renal morphology was normal by light microscopy. Statistically significant but weak correlations were noted between the serum glucose levels and "medullary" procollagen alpha 1(IV) mRNA levels (r = 0.43, P less than 0.05). In addition, weak correlations were noted between glycosuria and "medullary" procollagen alpha 1(I) levels (r = 0.38, P less than 0.05). In situ hybridization studies localized the increased procollagen alpha 1(IV) mRNA levels predominantly in the DM group primarily in the deep cortex and medullary outer stripe of proximal tubules. Glomerular procollagen alpha 1(IV), alpha 1(I), alpha 1(III) and beta-actin mRNA levels were not increased in untreated diabetic rats 7 or 28 days after diabetes induction. Thus, tubular procollagen alpha 1(IV) mRNA levels increased prior to any measurable change in glomerular levels and were ameliorated by insulin administration.

Immunogold studies of monomeric elements from the globular domain (NC1) of type IV collagen in renal basement membranes during experimental diabetes in the rat

The protein A-gold immunocytochemical technique was applied to reveal the monomeric elements M1, M2* and M3 from the non-collagenous globular domain (NC1) of type IV collagen over various renal basement membranes from control and long-term streptozotocin-induced diabetic rats. This study includes the basement membranes of the proximal tubule, the Bowman's capsule and the glomerulus as well as the extracellular matrix of the mesangium. The labellings obtained were confined to basement membrane material. The quantitative analysis demonstrated changes in labelling intensities and distribution between tissues from normal and diabetic animals. Increased labelling intensities were observed for M1 and M2* monomers in all the basement membranes studied except for the mesangial matrix which remained unchanged. In addition, the labelling for M1 monomers, present on the endothelial side of the glomerular basement membrane of control animals, was found to be distributed throughout the entire thickness of the basement membrane of diabetic animals. In contrast, neither the intensity of the labelling, nor the distribution of M3 monomers were altered in diabetic animals. Since M1 monomers are markers of the alpha 1(IV) and alpha 2(IV) chains of type IV collagen while M2* and M3 mark alpha 3(IV) and alpha 4(IV) chains respectively, the present results demonstrate changes in the nature of the collagenous elements of basement membranes during diabetes. Furthermore, the results indicate that the alpha 3(IV) and the alpha 4(IV) chains are not necessarily present in the same molecule. The modifications of the collagenous elements of the basement membranes during diabetes must alter the structural characteristics of these matrices which in turn might influence their functional properties.

Sorbinil does not prevent galactose-induced glomerular capillary basement membrane thickening in the rat

We investigated the role of the polyol pathway in the pathogenesis of glomerular basement membrane thickening in galactosaemic rats, an animal model that develops basement membrane lesions comparable to those of human diabetic subjects. Normotensive Wistar-Kyoto rats fed a 30% galactose diet for nine months developed significant glomerular basement membrane thickening by comparison with rats on a control test diet (p = 0.008). However, addition of an aldose reductase inhibitor, sorbinil (250 mg/kg diet), to the galactose diet did not prevent the increase in glomerular basement membrane thickness. Furthermore, by using a quantitative electron microscopic immunogold technique, we examined biochemical alterations in the composition of glomerular basement membranes in this animal model. The labelling density (comparable to relative concentration) of collagen type IV in thickened glomerular basement membranes of galactosaemic animals was significantly increased by comparison to those of control rats (p = 0.015). However, there was no significant difference in labelling densities of laminin and heparan sulfate proteoglycan core protein of these animals. Thus, our results indicate that an increase in glomerular basement membrane thickness accompanied by an increase in the labelling density of collagen type IV occurs in the galactosaemic rats, but this thickening is not prevented by sorbinil at the dose used in this experiment. Our study raises the strong possibility that glomerular basement membrane thickening in galactosaemic rats may not be due to excessive polyol pathway activity.

Effects of long-term diabetes and galactosaemia upon lens and retinal mRNA levels in the rat

The levels of mRNAs encoding the alpha 1 chain of collagen IV and the B1 chain of laminin were assayed in the lenses and retinas of long-term (28-week) diabetic and galactosaemic rats in order to gain some insight into the effects on basement membrane (BM) synthesis in these tissues. mRNAs coding for beta-actin, glucose transporter protein and the alpha 2 catalytic subunit of Na+,K(+)-ATPase were also assayed to determine whether any effects on BM-coding mRNA levels were specific. Long-term diabetes had no significant effect on the levels of alpha 1 (IV) collagen mRNA but caused a significant reduction in the laminin B1 message in the lens. In the same samples, the level of the glucose transporter protein mRNA was found to be elevated significantly in the diabetic tissue, whereas the mRNAsen coding beta-actin and alpha 2 Na+,K(+)-ATPase were unaffected in comparison with age-matched controls. Long-term galactosaemia resulted in significant increases in the levels of all mRNAs assayed when expressed per micrograms total RNA used for each analysis. However, this effect appeared to be due to a specific loss of ribosomal RNA from these severely cataractous lenses. When related to the beta-actin mRNA internal control, the levels of mRNA in the galactosaemic lenses were very similar to that found in the diabetics. Laminin B1 mRNA levels were decreased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased expression of basement membrane components in human endothelial cells cultured in high glucose

Although the degree of hyperglycemia is a powerful and independent risk factor for diabetic microvascular disease, it has not been established if and how high glucose per se can induce the typical lesions of microangiopathy. We have investigated in human vascular endothelial cells the expression of messenger RNA (mRNA) for collagen type IV and fibronectin, the two glycoproteins characteristically increased in diabetic basement membranes. In 12 confluent primary cultures exposed for 11 +/- 1 d (mean +/- SD) to 30 mM glucose and exhibiting cell number and thymidine incorporation similar to control cultures, the levels of collagen IV and fibronectin mRNA were, respectively, 238 +/- 140 and 221 +/- 231 percent of control (P less than 0.01). The effects of high glucose were selective (the levels of collagen I and c-myc mRNA remained unchanged), independent of the proliferative activity of the cultures and of the plating substratum, and maintained throughout multiple passages. However, several days of exposure to high glucose were required before their appearance. These observations establish that high glucose is a perturbation sufficient to mimic the effects of diabetes on the regulation of basement membrane components and propose that modifications in gene expression may pertain to the chain of events leading to diabetic angiopathy.

Serum from diabetic patients enhances synthesis of arterial basement membrane-like material in cultured smooth muscle cells

The effect of serum from both type I and type II diabetic subjects on the metabolism of arterial basement membrane (BM)-like material was studied in cultures of rabbit aortic smooth muscle cells. The basement membrane-like material was isolated from the cell-layer by a combined sonication and centrifugation technique. Serum from type I diabetic persons added to the incubation medium increased statistically significantly the incorporation of L-[4,5]-3H-leucine into the basement membrane-like material as compared to serum from non-diabetic subjects (2P less than 0.05). The same effect was seen with serum from type II diabetic patients as compared to serum from nondiabetic subjects (2P less than 0.05). No effect of serum from type I diabetic persons was seen in degradation experiments. Incubation medium supplemented with normal serum and extra glucose neither changed the production of basement membrane-like material nor the disappearance rate of radioactive leucine from the basement membrane-like material in degradation experiments. The present study indicates that serum from diabetic subjects enhances the production of arterial basement membrane-like material from arterial smooth muscle cells in culture. The obtained data may be relevant for the understanding of the development of macroangiopathy among diabetic patients.

Degradation of glomerular basement membrane in diabetes. II. Proteolytic activity of diabetic and nondiabetic glomeruli

The proteolytic effects of isolated glomeruli of diabetic rats on glomerular basement membrane of nondiabetic rats was investigated at various times after streptozotocin injection. One week after induction of diabetes, proteolytic activity remained unchanged as compared with nondiabetic controls. However, 4 and 10 weeks after streptozotocin injection, glomerular degradation of collagenous (but not noncollagenous) peptides of basement membranes increased (+24% as compared with control experiments). Using diabetic basement membrane as substrate, degradation of collagenous and noncollagenous peptides caused by diabetic glomeruli was 2.6-fold and 1.7-fold higher than in control experiments with nondiabetic glomeruli. The results indicate that the disturbed degradation of glomerular basement membrane in diabetes is not due to a decreased activity of glomerular proteolytic enzymes. In contrast, it can be concluded that the increased resistance of diabetic basement membrane to proteolytic degradation could be partially compensated by quantitative and qualitative changes of the proteolytic potential of diabetic glomeruli.

Degradation of glomerular basement membrane in diabetes. I. Susceptibility of diabetic and nondiabetic basement membrane to proteolytic degradation of isolated glomeruli

Degradation of glomerular basement membrane in diabetic and nondiabetic rats was measured by incubating isolated basement membrane with a homogenate of glomeruli obtained from metabolically healthy rats. When diabetic basement membrane was used, there was a marked decrease in the amount of collagen-typical (hydroxyproline, hydroxylysine, glycine) and noncollagen-typical amino acids (proline, lysine, leucine) released in the supernatant of the incubation assay. A negative correlation was found between the amount of collagen-typical amino acids released by diabetic basement membrane and the duration of diabetes. The results indicate that the collagenous and noncollagenous peptides of diabetic basement membrane are less susceptible to proteolytic degradation than those of nondiabetic controls. This may be due to increased nonenzymatic glycosylation of diabetic basement membrane.

Sulfate metabolism in the alloxan-diabetic rat: relationship of altered sulfate pools to proteoglycan sulfation in heart and other tissues

The incorporation of [35S]sulfate into heart proteoglycans has been studied in normal and alloxan-diabetic rats by perfusion and in vivo administration of the isotope; in the latter situation, comparison was also made of radiolabeled sulfate utilization by several other tissues (kidney, liver, lung, muscle, testes and skin). The radiolabeled products were characterized by sodium dodecylsulfate polyacrylamide gel electrophoresis and anion exchange chromatography, as well as by sizing of the glycosaminoglycan chains by gel filtration both before and after nitrous acid treatment. The most prominent band observed in the heart guanidine extract by electrophoresis had a molecular weight of 85,000 and minor components (Mr = 360,000 and 170,000) were also detected; approximately 20% of the proteoglycan associated [35S]sulfate was present in heparan sulfate chains. After perfusion the pattern, as well as the amount of radioactivity recovered from the diabetic heart, was similar to the normal heart. In contrast, after intraperitoneal injection of the [35S]sulfate, a substantial reduction in incorporation was found not only in heart but in several other tissues studied, although no qualitative differences were noted in the macromolecules formed by the two groups of animals. Measurement of the serum sulfate concentration indicated that the level in the alloxan-diabetic rat (1.23 mmol/l) was significantly less (p less than 0.01) than that of the normal rat (1.67 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased glucose increases glomerular basement membrane in metanephric culture

A model of in vitro renal development has been used to examine the effect of glucose on the glomerular basement membrane. Glomerular differentiation in this system progresses to an arborizing tuft of podocytes overlying well-formed basal lamina. The proportional amount of lamina densa and dense fibrillary matrix was increased in blastemas grown in an increased amount of glucose during the last 4 of 7 days in culture. These observations indicate that glucose itself can stimulate an accumulation of basement membrane, an excess of which is characteristic of diabetic microangiopathy.

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.

Type IV collagen antigens in serum of diabetic rats: a marker for basement membrane collagen biosynthesis

The nature of type IV collagen antigens in the serum of streptozotocin diabetic rats was studied using radioimmunoassays for the N-terminal (7S-collagen) and C-terminal domain of type IV collagen. Type IV collagen antigen crossreacting with antibodies to the C-terminal domain was elevated from 32.0 +/- 5.36 ng/ml (n = 10) in serum of normal rats to 94.9 +/- 24.5 ng/ml (n = 10, P less than 0.0001) in serum of streptozotocin diabetic rats and could be normalized to 40.1 +/- 8.30 ng/ml (n = 18) by insulin treatment. Molecular sieve chromatography of serum demonstrated a high molecular weight fraction containing the C-terminal and N-terminal domains and smaller material containing only the N-terminal domain. Degradation of the high molecular weight material by collagenase indicates that it consists of intact collagen type IV. Its relative proportion increased from 42% to 54% 4 weeks after diabetes induction. Together with unaltered clearance rates of 7S collagen in normal and diabetic rats, the data suggest that the increase of collagen type IV antigens in diabetic states reflects increased synthesis of collagen type IV.

Increased concentrations of basement membrane collagen fragment in urine of diabetic mice

Levels of a urinary component of basement membrane collagen (type IV) were compared in diabetic (db/db) and normal (db/+) C57BL/Ks inbred mice. A modification of the enzyme-linked immunosorbent assay (ELISA) technique was used with antigen and antibody preparations previously defined to be specific for a fragment from human basement membrane collagen. Significantly elevated levels of basement membrane collagen were found in the urine of homozygous diabetic (db/db) mice as soon as the fourth week after birth. These levels were consistently higher than those found in age-matched normal (db/+) mice throughout the 28 weeks in which measurements were made. Results described here support previous evidence that increased basement membrane collagen synthesis occurs in the db/db model of diabetic nephropathy.

Effects of mesangial localization of polyvinyl alcohols on glomerular basement membrane thickness

We studied the effects of mesangial localization of polyvinyl alcohols (PVA) on glomerular basement membrane (GBM) thickness in inbred Lewis rats. To avoid possible influences of PVA redistribution after localization in liver, lung, and other organs, the kidneys of rats given PVA were transplanted into uninephrectomized normal rats. Normal kidneys transplanted into normal rats served as a control. GBM thickness at the time of transplantation was the same in PVA kidneys as in normal kidneys. However, by 18 weeks post-transplant GBM thickness was greater in PVA kidneys, and this increase was sustained at 30 weeks. Within the glomeruli of PVA kidneys, lobules with marked mesangial PVA accumulation had more marked GBM thickening than lobules with little or no PVA accumulation. It is concluded that changes within the mesangium can influence GBM thickness. Whether this represents a direct effect of mesangial architectural distortion, a consequence of local phlogistic activities such as the influx of macrophages into the mesangium of glomeruli with PVA localization, or the result of intraglomerular hemodynamic perturbations is unclear.

In vitro insulin action on different ATPases of erythrocyte membranes in normal and diabetic rats

The in vitro effect of porcine insulin on Na+ + K+, Ca2+- and Mg2+-ATPases of the rat erythrocyte membrane of normal and alloxan-induced diabetic rats was investigated. Na+ + K+- and Ca2+-stimulated enzyme activities were significantly decreased in diabetic rats in comparison to normal animals. The specific activities of both these ATPases in the latter group were markedly reduced on pre-incubating the ghosts with insulin. Similar treatment of the erythrocyte membranes of diabetic animals, however, resulted in a significant increase of these activities. These qualitatively different effects of the hormone in the two groups increased progressively with hormone concentration and duration of pre-incubation. Mg2+-stimulated ATPase activity was not significantly affected in diabetes or by insulin.

Basement membrane of hypothalamus and cortex capillaries from normotensive and spontaneously hypertensive rats with streptozotocin-induced diabetes

Basement membrane (BM) thickness of hypothalamic arcuate nucleus capillaries was measured in normotensive (WKY) and hypertensive (SHR) rats 4 and 8 months after streptozotocin or saline injection. Three groups were studied: controls (C), diabetics (D), and animals with impaired glucose tolerance (L). For comparison, BM thickness of cortical capillaries of an occipital and a frontal area was measured in three different layers starting from the pial surface. Independently from strain, hypothalamic capillary BM was thicker in older than in younger animals. At both 4 and 8 months, BM thickness was lowest in C, highest in D, and intermediate (between C and D) in L. Hypertension combined with diabetes did not further increase BM thickness. In both C and D no difference was found between the two cortical areas. The BM thickness of C increased from the superficial to the deep layer. In C hypertension induced BM thickening in the superficial frontal and the deep occipital layer. In the intermediate and the deep layer of the frontal area BM was thicker in WKY-D than in WKY-C. In every layer BM was thicker in SHR-D than in corresponding controls. Hypertension combined with diabetes enhanced BM thickening in the intermediate and the deep layer of the frontal and in the intermediate layer of the occipital area. Degenerative changes occurred in hypothalamic and cortical pericytes. These changes were more frequent in hypertensive than in normotensive animals. In conclusion, a microangiopathy characterized by BM thickening and pericytic degeneration occurs in the brain of diabetic animals. Its intensity and enhancement by a concomitant hypertension vary from hypothalamus to cortex.

Inhibition of collagen fibril formation in vitro and subsequent cross-linking by glucose

Glucose inhibits collagen fibril formation in vitro. A linear dose response was observed, with half-maximum inhibition of fibril formation occurring at 50 mM glucose. Nonfibrillar collagen cannot be cross-linked by lysyl oxidase, an enzyme that catalyzes the initial cross-linking reaction. The degree of decreased fibril formation correlated with the loss of ability of the collagen to serve as a substrate for lysyl oxidase. Collagen that is not cross-linked is unstable and more susceptible to collagenolytic attack. Interference with collagen cross-linking and more rapid degradation may explain the decreased amounts of interstitial collagen and the poor healing of wounds associated with diabetes mellitus.

Effect of diabetes on the sugar nucleotides in several tissues of the rat

Studies have been carried out to determine the effect of diabetes on the concentrations of sugar nucleotides in several tissues of the rat. This represents one aspect of an investigation aimed at evaluating the role which alterations in the metabolism of glycoproteins or other glycoconjugates may play in the development of the long-term complications of this disease. Measurements were made of the nucleotides of hexoses, N-acetylhexosamines, hexuronic acids, and sialic acid in liver, kidney, skeletal muscle, testis and heart of alloxan-diabetic rats and age-matched controls. Of the intermediates studied, only UDP-glucose and UDP-galactose showed significant alterations in diabetes. The direction of the changes depended on the tissue, with the levels in liver and skeletal muscle being decreased, those in kidney and testis increased and the concentrations in heart being unchanged. In the diabetic liver, the concentrations of UDP-glucose was reduced to 0.75 that of normal, while in skeletal muscle both UDP-glucose and UDP-galactose were significantly decreased (diabetic to normal ratios of 0.67 and 0.64, respectively). Kidney and testis, on the other hand, showed elevations of both UDP-glucose and UDP-galactose, with the diabetic levels being 1.2 to 1.3 those of normal levels. The direction of change in UDP-glucose in a tissue appeared to reflect its known ability to synthesize glycogen in diabetes. The finding of elevated UDP-glucose and UDP-galactose concentrations in diabetic kidney is considered to be potentially of great importance to the increased synthesis of basement membrane collagen by this tissue.

In vivo studies on basement membrane synthesis in diabetic and nondiabetic rats

In rats with chronic diabetes, the synthesis of glomerular basement membrane was investigated in vivo by injection of 3H-proline. Compared to the nondiabetic controls, the basement membrane synthesis was markedly raised. The formation of hydroxyproline as parameter for the synthesis of the collagen portion of the basement membrane increased to a somewhat greater extent than the incorporation of 3H-proline. Hydroxyproline formation and proline incorporation showed a close correlation with the blood sugar level in the diabetic rats.

In vivo crevicular leukocyte response to a chemotactic challenge: inhibition by experimental diabetes

Diabetes in rats inhibits the migration of neutrophils into the healing gingival crevice, an effect associated with impaired in vitro neutrophil chemotactic activity. We recently described the in vivo response of human and rat crevicular neutrophils to a chemotactic challenge and used this assay in the present study on streptozotocin-induced diabetic rats. Optimal concentrations of two chemotactic agents, casein (0.2 mul, 2 mg/ml) or N-formylmethionylleucylphenylalanine (0.2 mul, 10(-4) M), were placed into the gingival crevices of control and diabetic rats (time zero) after the resting neutrophil count was measured. After a 15-min delay, the neutrophil counts and gingival crevicular fluid flow were assessed every 5 min for another 0.5 h. The control rats (n = 14) showed an increase in neutrophil counts which reached maximum levels 30 min after the N-formylmethionylleucylphenylalanine challenge ("peak" neutrophil response) and decreased dramatically 5 min later. Diabetes of 4 days (n = 4), 14 days (n = 8), and 20 days (n = 5) duration reduced the peak neutrophil response 45, 66, and 71%, respectively. Casein produced the same response as N-formylmethionylleucylphenylalanine in control rats. Uncontrolled diabetes of 20 days duration reduced the peak neutrophil response to casein by 83%; diabetics administered insulin on a daily basis showed a reduction of only 34%. The pattern of change in gingival crevicular fluid flow in response to chemoattractants paralleled the neutrophil response. The chemotactic activity of peritoneal neutrophils was assessed in vitro with the agarose gel technique and was found to be correlated (r = 0.84; P < 0.01) with the in vivo chemotactic response in the same rats. If the same in vivo defect is observed in humans with diabetes (or with other systemic diseases associated with leukocyte dysfunction), this test could be useful diagnostically to rapidly assess neutrophil chemotaxis in lieu of in vitro assays and to identify patients who are unusually susceptible to aggressive periodontal disease.

Effects of early diabetes on uridine diphosphosugar synthesis in the rat renal cortex

To assess the effects of streptozotocin-induced diabetes on the substrates utilized in the formation of glycoproteins, the pools of uridine 5'-diphosphoglucose (UDPG), uridine 5'-diphosphogalactose (UDP-GAL), uridine 5'-diphosphoglucuronic acid (UDPGA), and uridine 5'-diphospho N-acetyl galactosamine (UDPA-GAL) were measured in the renal cortex of control and over a 48-hr period in diabetic rats. In control rats these pools measured: UDPG, 256 +/- 23; UDP-GAL, 75 +/- 14; UDPGA, 147 +/- 16; UDPAG, 367 +/- 23; UDPG-GAL, 131 +/- 13 nmoles/mg DNA. In diabetic rats, except for UDP-GAL, all pools were increased 41 to 68%. The incorporation of radiolabeled orotate was increased in all pools, except UDP-GAL, in diabetic rats by 41 to 77% compared to control rats. The incorporation into UDPG and UDPAG was increased even after correction for the specific radioactivity of their immediate precursor, uridine 5'-triphosphate (UTP). Expansion of the UTP pool after orotate infusion was associated with an increase in the size of the UDPG and UDPAG pools in both control and diabetic rats. Depletion of the UTP pool after adenine infusion in controls was associated with a decrease in all pools. This study demonstrates that after the induction of diabetes there is a rapid increase in the bioavailability of substrates utilized in the synthesis of glycoproteins and glycosaminoglycans. It is theorized that this increase is necessary for the augmented synthesis of basement membrane-like material in the diabetic kidney.

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.