Early glomerulopathy is present in young, type 1 (insulin-dependent) diabetic patients with microalbuminuria

Podocyte loss and progressive glomerular injury in type II diabetes

Kidney biopsies from Pima Indians with type II diabetes were analyzed. Subjects were classified clinically as having early diabetes (n = 10), microalbuminuria (n = 17), normoalbuminuria, despite a duration of diabetes equal to that of the subjects with microalbuminuria (n = 12), or clinical nephropathy (n = 12). Subjects with microalbuminuria exhibited moderate increases in glomerular and mesangial volume when compared with those with early diabetes, but could not be distinguished from subjects who remained normoalbuminuric after an equal duration of diabetes. Subjects with clinical nephropathy exhibited global glomerular sclerosis and more prominent structural abnormalities in nonsclerosed glomeruli. Marked mesangial expansion was accompanied by a further increase in total glomerular volume. Glomerular capillary surface area remained stable, but the glomerular basement membrane thickness was increased and podocyte foot processes were broadened. Broadening of podocyte foot processes was associated with a reduction in the number of podocytes per glomerulus and an increase in the surface area covered by remaining podocytes. These findings suggest that podocyte loss contributes to the progression of diabetic nephropathy.

A quantitative ultrastructural study of juxtaglomerular arterioles in IDDM patients with micro- and normoalbuminuria

Hyalinization of juxtaglomerular arterioles is prominent in advanced diabetic nephropathy and may have important functional consequences. We studied the early stages of diabetic renal disease using kidney biopsy material from insulin-dependent diabetic patients, 8 with normal albumin excretion rate (< 15 micrograms/min) and 16 with microalbuminuria (15-200 micrograms/min). Ten living non-diabetic kidney donors served as a control group. Median duration of diabetes was 9.5 years (range 5-31) in patients with normoalbuminuria, and 12 years (7-22) in patients with microalbuminuria (p = 0.27). The tissue was sectioned systematically, 1-micron thick sections for light microscopy at 10-micron intervals, and thin sections for electron microscopy taken at 60-micron intervals. The arterioles were identified as afferent or efferent, and total profiles were photographed (magnification 7500x), providing a systematic independent sample for measurements using standard stereological methods. Patients with microalbuminuria had significantly increased arteriole parameters compared with the control group: for afferent and efferent arterioles the volume fraction of matrix/media, means and (co-efficient of variation, CV), was 0.47 (0.16) vs 0.33 (0.19) (p = 0.0009), and 0.62 (0.14) vs 0.45 (0.23) (p = 0.0004) and matrix-T, expressing amount of matrix per unit arteriolar surface, 2.38 (0.38) micron vs 1.44 (0.30) micron (p = 0.004), and 1.62 (0.28) micron vs. 1.03 (0.34) (p = 0.0009). Patients with normoalbuminuria showed no significant differences from the control group, and had lower values than microalbuminuric patients for all parameters except the afferent matrix-T. In the normoalbuminuric group a correlation was found between parameters for afferent arterioles and those for glomerular structure. In conclusion there is arteriolar accumulation of extracellular material in the early phase of diabetic nephropathy, concomitant with early glomerulopathy.

Glomerular epithelial foot processes and filtration slits in IDDM patients

Diabetic 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.

Analyzing renal glomeruli with the new stereology

The highly specialized architecture of the renal glomerulus is altered in a variety of disease states. Morphometric methods, including stereological methods, have been widely used to analyze these changes in both animal and human glomeruli. However, many of the methods available until recently were biased and provided incomplete information. The past few years have witnessed the development of a new generation of unbiased stereological methods. Another advantage of these new methods and strategies is that they are less influenced by technical artifacts than the traditional methods. This chapter describes how these new stereological methods can be used to quantify glomerular morphology. Parameters considered include glomerular number and volume; glomerular cell number and size; and the length, surface area, and number of glomerular capillaries. Methods for obtaining data for average glomeruli as well as individual glomeruli are described. Technical details are included wherever possible.

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)

Urinary albumin excretion rate and puberty in non-diabetic children and adolescents

Slightly elevated urinary albumin excretion rate (microalbuminuria) is a marker of early diabetic nephropathy, but it is unclear if the established definition of microalbuminuria (20-200 micrograms/min) is correct for children and adolescents. We investigated the albumin excretion rate, albumin/creatinine ratio and urinary albumin concentration in 150 healthy schoolchildren and adolescents to (a) obtain a reference value for albumin excretion rate, (b) relate albumin excretion to pubertal stages and (c) evaluate albumin/creatinine ratio and morning albumin concentration as screening methods for elevated albumin excretion rate. Albumin concentration was measured by immunoturbidimetry in timed overnight urine samples. The albumin excretion showed a skewed distribution (geometric mean 3.2 micrograms/min, 95 percentile 15.1 micrograms/min). In girls, a peak in the albumin excretion rate was found at the pubertal stage 4 (Tanner) and in boys at stage 5. Albumin/creatinine ratio of 2.5 mg/mmol as a screening level for elevated albumin excretion (15 micrograms/min) showed a high positive (0.88) and negative (0.99) predictive value.