Ruth Østerby

Glomerular structure and function in proteinuric Type 2 (non-insulin-dependent) diabetic patients

SummaryGlomerular ultrastructure was examined in a series of 20 Type 2 (non-insulin-dependent) diabetic patients with proteinuria. Reference was made to data previously obtained in non-diabetic kidney donors and in Type 1 (insulindependent) diabetic patients with similar degrees of proteinuria. The Type 2 diabetic patients demonstrated the changes which characterize the diabetic glomerulopathy seen in Type 1 diabetic patients: basement membrane thickening, and increase in the mesangium and mesangial matrix expressed as fraction of the glomerular volume. Among the Type 2 diabetic patients there was more variation then among the Type 1 diabetic patients, as this group included subjects with normal parameters. The group means and coefficients of variation (=SD/mean) of the glomerulopathy parameters combined in the glomerulopathy index=basement membrane thickness/10+Vv(matrix/glom)·100 were 81 (0.30) and 92 (0.15) in the two diabetic groups, clearly different from the non-diabetic index, 42 (0.16). All Type 2 diabetic patients who also had retinopathy had a glomerulopathy index above the normal range. Similar changes in glomerular composition were seen in the two diabetic groups: with increasing glomerulopathy the volume of matrix dominated over the peripheral basement membrane, and a shift in the ratio of interfaces was seen: mesangial surface towards capillary lumen increased relative to the urinary surface, and peripheral capillary surface comprised less of the total capillary surface. Data indicated marked glomerular hypertrophy, which correlated with the mesangial volume fraction, thus encompassing preserved filtration surface per glomerulus. An inverse correlation obtained between the index of glomerulopathy and current glomerular filtration rate, as well as the ensuing rate of decline in glomerular filtration rate, as well as the ensuing rate of decline in glomerular filtration rate: (index (glomerulopathy) vs rate of decline in glomerular filtration rater=0.84,p<0.0001). No correlation was found between glomerular volume and the ensuing rate of decline in glomerular filtration rate.

Glomerular structural changes in type 1 (insulin-dependent) diabetes mellitus: causes, consequences, and prevention.

SummaryDiabetic nephropathy is caused primarily by advanced glomerulopathy, the renal expression of diabetic microangiopathy. With stereological methods a quantitative description of the structural changes is achieved. The glomerulopathy is characterized by an increase in basement membrane material: thickening of the capillary wall and an increase in mesangial volume relative to glomerular volume, comprising increase in matrix. Among groups of patients conformity between renal function stage and structure exists. The parameters measuring glomerulopathy are normal at the onset of diabetes; patients with normoalbuminuria may show slight basement membrane thickening, or normal parameters; the microalbuminuric group shows a measurable, but moderate glomerulopathy; patients with overt nephropathy have advanced lesions; at this stage heterogeneity among glomeruli makes the estimates weaker. Recent data indicate that the changes in peripheral basement membrane and in mesangial matrix develop in concert and both contribute to the early stage of glomerulopathy in patients with microalbuminuria. As to the consequences of the structural changes the mechanism of albuminuria is not clear. It is suggested that the early glomerulopathy entails other structural modifications, including formation of new vessels which may be the site of leakage. The marked deviations in glomerular filtration rate correspond well with estimates of filtration surface area: in the early hyperfunction state it is increased; in advanced nephropathy it is decreased, due to advanced glomerulopathy in conjunction with glomerular occlusion. The diabetic state is the necessary condition for the glomerulopathy. In relating structural changes to presumed contributing causes no supporting evidence of a relationship with glomerular hyperfunction or hypertrophy was observed. The structural parameters may be useful tools in clinical trials aiming at arresting the development of glomerulopathy, and thereby providing a prevention of diabetic nephropathy.

Glomerular Structure and Function in Diabetic Nephropathy: Early to Advanced Stages

Kidney biopsies from 14 insulin-dependent diabetes mellitus patients with persistent albuminuria were studied by light and electron microscopy. In terms of kidney function, the patients spanned stages from early to advanced nephropathy. The clinical parameters were (ranges, with medians in parentheses) urinary albumin excretion (UAE) 158–5494 μg/min (1153 μg/min), glomerular filtration rate (GFR) 30–128 ml · min −1 · 1.73 m−2 (90 mh ml · min−1 · 1.73 m−2) and mean arterial blood pressure () 87–122 mmHg (109 mmHg). The severity of clinical nephropathy (UAE, GFR, and BP together) correlated with an index of the structural lesions (basement membrane [BM] thickness, mesangial expansion, and glomerular occlusion together; r = 0.62, 2P < 0.05). GFR compared with remnant surface of glomerular capillaries (filtration surface; FS) gave values of r = 0.72 and 2P = 0.004, and UAE compared with the percentage of the peripheral BM surface carrying fluffy loose intrinsic fine structure gave r = 0.62 and 2P = 0.02. BP per se did not correlate with structural parameters. The area of FS per open glomerulus did not decrease with increasing mesangial volume fraction, which indicates compensatory changes of the capillaries in early and advanced stages of glomerulopathy. In 7 patients with <10% occluded glomeruli, correlations between glomerular volume and the parameters of diabetic glomerulopathy (i.e., BM thickness and volume fractions of mesangium and mesangial matrix) failed to reach statistical significance. The actual glomerular volume, however, is a product of the individuals original glomerular volume, probably the early diabetic hypertrophy and modifying changes consequent to the development of glomerulopathy. Our study shows a correlation between the parameters of glomerular structural lesions and those of the functional abnormalities in diabetic nephropathy.

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

SummaryWe 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, mor-phometric methods were used. The blood glucose control improved significantly (p = 0.01) during the study in the CSII-group as glycated haemoglobin (HbAlc) 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 HbAlc 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/mesan-gial volume fraction (p = 0.006) and matrix star volume (p = 0.04). Furthermore, a positive correlation between mean HbAlc during the study and change from baseline in BMT (r = 0.70, p = 0.001) and ma-trix/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. The present study shows that during a period of only 2.5 years, a close relationship between the level of mean blood glucose and progression of glomerular morphological changes in early diabetic nephropathy can be demonstrated. [Diabetologia (1994) 37: 483-490]

A strong correlation between glomerular filtration rate and filtration surface in diabetic nephropathy.

SummaryQuantitative structural studies were performed in kidney biopsy specimens from 24 long-term Type 1 (insulin-dependent) diabetic patients with persistent albuminuria due to diabetic glomerulopathy. Ten patients were receiving antihypertensive treatment, and among the remaining patients the mean blood pressure was 142/91 mmHg (SD = 11/9). The urinary albumin excretion rate showed a range from 100 to 5494 μg/min (geometric mean 688 μg/min.) Glomerular filtration rate also showed a wide range, from supranormal to markedly decreased values (128 to 28 ml·min−1· (1.73 m2)−1, mean 75). The filtration surface (interface between capillary and urinary space) per total number of nephrons (open+occluded) was estimated by combined light- and electron microscopy. The percentage occluded glomeruli as well as structural quantities in the open glomeruli were taken into account in this estimate. A highly significant correlation was seen between glomerular filtration rate and filtration surface per nephron (r=0.77, p<10−4). The percentage occluded glomeruli contributed significantly to the variation in glomerular filtration rate (for this relationship tested separately r=-0.78, p<10−5). The volume of open glomeruli was even larger than that seen in early diabetic glomerular hypertrophy and tended to increase with the percentage of glomerular closure, indicating that a compensatory hypertrophy might have taken place. In the open glomeruli the filtration surface constituted a smaller percent of total capillary surface (the remaining part facing the mesangial regions) than in early diabetic patients and control subjects.Our study has demonstrated that reduced glomerular filtration surface is closely associated with reduced glomerular filtration rate in Type 1 diabetic patients with diabetic nephropathy.

Effect of angiotensin converting enzyme inhibitor or beta blocker on glomerular structural changes in young microalbuminuric patients with Type I (insulin-dependent) diabetes mellitus.

Aims/hypothesis. To investigate the influence of angiotensin converting enzyme inhibitors and beta blockers on the progression of early diabetic glomerulopathy. Methods. Thirteen patients with Type I (insulin-dependent) diabetes mellitus (mean age 18.8 years) with microalbuminuria 31 (19–160) μg/min were randomised to treatment with enalapril (group 1, n = 7) or metoprolol (group 2, n = 6). Renal biopsies were taken before and after 38 (36–48) months of treatment. Albumin excretion rate, blood pressure and HbA1 c were measured every third month. A reference group without antihypertensive treatment (group 3, n = 9), with similar age, diabetes duration and degree of microalbuminuria as group 1 and 2, had baseline and follow-up renal biopsies taken previously with an interval of 26–34 months, analysed at the same laboratory. Glomerular structures were measured by stereological methods. Results. Measurements of basement membrane thickness, mesangial and matrix volume fractions were similar among groups at baseline. Structural variables were only increased in group 3 at follow-up. Delta values in basement membrane thickness and diabetic glomerulopathy index per 24 months were lower in group 1 and 2 than in group 3 (p < 0.05). Microalbuminuria returned to normal in group 1 and 2 only. Decreased albumin excretion rate tended to inversely correlate with increased basement membrane thickness (p = 0.08) and diabetic glomerulopathy index (p = 0.05). Mean HbA1 c was similar between groups. Mean diastolic blood pressure was lower in group 1 and 2 than in group 3 (p < 0.01). Mean HbA1 c and mean diastolic blood pressure correlated to changes in basement membrane thickness, mesangial volume fraction and diabetic glomerulopathy index (p < 0.05). Conclusion/interpretation. Contrary to findings in the group without antihypertensive treatment, no progression of glomerulopathy was seen in those treated with enalapril or metoprolol. [Diabetologia (1999) 42: 589–595]

Blood Pressure Elevation Versus Abnormal Albuminuria in the Genesis and Prediction of Renal Disease in Diabetes

A number of risk factors associated with the development of diabetic nephropathy has been described, such as elevated blood pressure, poor metabolic control, hyperlipidemia, and smoking. Abnormal albuminuria also is associated with progression of renal disease, but has until recently been considered principally a marker of disease activity rather than a risk factor. This article discusses the role of elevated blood pressure versus abnormal albuminuria in a genesis and prediction of renal disease in diabetes. Controversy exists regarding parental disposition to hypertension and early blood pressure elevation in the course of diabetes, but all studies agree that elevated blood pressure—in the presence of abnormal albuminuria—constitutes a risk factor. Because abnormal albuminuria is associated with progression disease, it may itself be a risk factor because increased macromolecular traffic over the glomerular membrane may produce glomerulopathy. Problems related to blood pressure measurement are important, and 24-h recordings of blood pressure may be recommended in some situations. Regarding renal structure, preliminary results suggest that structural lesions precede blood pressure elevation. The solid end point for evaluation of renal disease progression is the fall rate of GFR, with abnormal albuminuria as an intermediate end point, also in drug trials. Abnormal albuminuria may constitute a new indication for antihypertensive treatment, being, as it is, a clear indicator of organ damage, whereas elevated blood pressure with normal AER may not increase risk substantially.

Quantitative changes of cerebral neocortical structure in insulin-treated long-term streptozocin-induced diabetes in rats.

The brains of rats with streptozocin-induced diabetes treated with a low-dose insulin regimen (1 IU/day) were studied with morphometric techniques. After 1 yr of diabetes, brain weight decreased slightly (1350 ± 71 vs. 1521 ± 55 mg, 2P < .01) as did the volume of the neocortex (498 ± 36 vs. 567 ± 40 mm3, 2P < .05). A significant loss of neocortical neurons occurred (38 ± 2 × 106 vs. 46 ± 3 × 106, 2P < .01), and the length of the capillary network in the neocortical tissue shortened disproportionately (405 ± 102 vs. 631 ± 47 m, 2P < .01), leading to increased diffusion distance. The mechanisms underlying cerebral loss in this model are unknown, but abnormalities of the vascular supply with prolongation of the route of diffusion might play a role.

Glomerular epithelial foot processes and filtration slits in IDDM patients

SummaryDiabetic nephropathy is associated with functional changes in the glomerular filtration barrier but the structural counterpart remains unknown. Width of glomerular epithelial cell foot processes and of filtration slits were determined by morphometric methods in 11 non-diabetic kidney donors and in 28 diabetic patients with albumin excretion rates ranging from normal to proteinuria. Foot process width was estimated from the ratio of tuft surface density to length density of slits. At high magnification independently sampled, perpendicularly cut slits were classified. Foot process width on peripheral basement membrane was increased in microalbuminuric compared to normoalbuminuric diabetic patients (p<0.05) but showed no significant correlation with the level of albumin excretion when patients with increased barrier permeability were considered. Width of filtration slits in normo- and microalbuminuric diabetic patients exceeded that in non-diabetic control subjects (p<0.05). Filtration slits were narrower in patients with overt proteinuria than in patients with microalbuminuria (p<0.05) and correlated with glomerular filtration rate in all of the diabetic patients (r=0.65, p<0.005). The results show that insulin-dependent diabetic patients with nephropathy present changes of epithelial cells and filtration slits, demonstrable already in the stage of microalbuminuria. The mechanism of albumin leakage is not achieved by these measures. The dimension of filtration slits may play a contributing role in the level of glomerular filtration rate in diabetic patients.

Glomerular Morphology by Light Microscopy in Non-Insulin-Dependent Diabetes Mellitus: Lack of Glomerular Hypertrophy

We quantitated glomerular structure by light microscopy in 19 subjects with non-insulin-dependent diabetes mellitus (NIDDM) and studied the possible connection between morphology and urinary albumin concentration. Autopsy material was collected retrospectively from diabetic subjects in whom urinary albumin concentration had been measured within 1.5 yr. Nineteen consecutive sex- and age-matched nondiabetic subjects were controls. A quantitative study of a random sample of glomeruli was performed blindly on periodic acid–Schiff (PAS)-stained sections. The main parameters obtained were 1) mean volume of open glomeruli, 2) frequency of glomerular occlusion, and 3) volume fraction of red-stained material (PAS-positive substance) in open glomeruli [Vv(R/G)]. There was no increase in glomerular volume in these NIDDM subjects, contrary to the glomerular hypertrophy found early as well as late in insulin-dependent diabetes mellitus. An increase in Vv(R/G) was found in diabetic subjects, demonstrating the presence of glomerulopathy as it is diagnosed by light microscopy. The frequency of glomerular occlusion was not significantly different between the groups. A high urinary albumin concentration did not necessarily reflect more advanced glomerulopathy.