Comparison of renal morphology in the Streptozotocin and the SHR/N-cp models of diabetes

The Streptozotocin (STZ) model of diabetes is commonly used for studies of diabetic nephropathy although the histological lesions of the kidney are mild and do not resemble those seen in diabetic patients. The SHR/N-cp rat model of type II diabetes spontaneously develops pronounced abnormalities in renal histology. In the present study, we compared renal morphology in the STZ rat and the diabetic SHR/N-cp rat. Sprague-Dawley rats received STZ, developed diabetes after 2 days and were treated with insulin. In the SHR/N-cp rat, obesity is inherited as an autosomal recessive trait. The progeny are either lean (used as controls) or obese and diabetic. After 6 months of observation, STZ and SHR/N-cp rats were killed. The renal damage was evaluated by assessing damage indices and by using stereological techniques. In addition, immunohistochemistry and electron microscopy were performed. The glomerular and tubulointerstitial changes were much more pronounced in the diabetic SHR/N-cp compared to the STZ model. In parallel glomerular PCNA+cells were significantly more frequent and expression of TGF-beta and PDGF by immunohistochemistry in glomeruli and in the tubulointerstitial space was more pronounced in SHR/N-cp compared to STZ rats. The glomeruli of SHR/N-cp contained less and larger podocytes as well as smaller mesangial cells embedded in more mesangial matrix compared to STZ. Similarly, less, but larger endothelial cells were found in SHR/N-cp than in STZ rats. The mean glomerular volume was similarly increased in the two models. Albumin excretion was only modestly increased in STZ diabetes, but pronounced in the SHR/N-cp rat. Although the STZ model of diabetes exhibits numerous biochemical sequelae of hyperglycemia, the morphological lesions are unimpressive. In contrast, the diabetic SHR/N-cp exhibits marked structural lesions, particularly podocyte damage and mesangial expansion that promise to make it a more suitable model for investigation of diabetic glomerulosclerosis.

ACE-inhibition is superior to endothelin A receptor blockade in preventing abnormal capillary supply and fibrosis of the heart in experimental diabetes

AIMS/HYPOTHESIS

There is little information whether cardiac capillary supply is deranged in diabetes. Hyperglycaemia is a potent stimulus for endothelin-1 (ET-1) production. We therefore hypothesised that increased ET-1 production in Streptozotocin-induced Type 1 diabetes causes abnormalities of cardiac capillaries and the aorta. To this end we compared the effects of an ET receptor A blocker (ETA-RB) with that of an ACE-inhibitor (ACE-i) or their combination in rats with Streptozotocin (STZ) diabetes.

METHODS

Sprague Dawley rats were injected with 65 mg STZ i.v. and subsequently developed diabetes. Rats were left untreated or received daily either the ACE-i Trandolapril, the ETA-RB Darusentan or a combination of both. After 6 months the experiment was terminated and the heart and the aorta were investigated using quantitative morphological techniques.

RESULTS

ACE-i but not ETA-RB lowered blood pressure in STZ Type 1 diabetic rats. Capillary length density was lower in untreated STZ diabetic rats (2932+/-128 mm/mm3) compared to non-diabetic control rats (3410+/-252 mm/mm3). Treatment with ACE-i (3568+/-431 mm/mm3), but not with ETA-RB (2893+/-192 mm/mm3), prevented the decrease in capillary supply. Volume density of the myocardial interstitium was higher in untreated STZ diabetic rats (0.86+/-0.04%) compared to non-diabetic control rats (0.36+/-0.06%). In all three intervention groups the values were lower (ACE-i: 0.53+/-0.05%, ETA-RB: 0.7+/-0.08% and combination: 0.69+/-0.1).

CONCLUSION/INTERPRETATION

Our study identifies a capillary defect of the heart in STZ diabetes, i.e. decreased capillary supply. This abnormality was reversed by ACE-i, but not by ETA-R blockade. A similar trend, although not complete normalisation, was seen in cardiac fibrosis.

ACE-inhibitors but not endothelin receptor blockers prevent podocyte loss in early diabetic nephropathy

AIMS/HYPOTHESIS

It was the aim of our study to investigate the influence of a selective ET-A receptor antagonist LU 135252 alone and in combination with the ACE-inhibitor, trandolapril on podocyte number and morphology in streptozotocin diabetic rats.

METHODS

Male Sprague-Dawley rats were injected with 65 mg streptozotocin i.v. and subsequently developed diabetes. Animals were left untreated or received daily either trandolapril (0.3 mg/kg body weight), LU 135252 (50 mg/kg body weight) or a combination of both. After 6 months the experiment was terminated. Glomerular geometry and cellularity were assessed by stereological techniques. Protein expression of TGF-beta, ET-1, PDGF-AB, fibronectin, desmin and alpha-smooth muscle cell actin was investigated by immunohistochemistry.

RESULTS

The mean number of podocytes per glomerulus was lower (86+/-17 vs. 138+/-25; p<0.05) and mean podocyte volume was higher in untreated diabetic animals than in non-diabetic controls. Only ACE-i alone and in combination, but not ET(A)-RB alone prevented loss of podocytes and podocyte hypertrophy. In diabetic rats, increased numbers of PCNA positive and p27(kip1) positive cells (mainly podocytes) were reduced by all treatments, but only ACE-i decreased numbers of desmin positive podocytes and tubulointerstitial expression of TGF-beta. Albuminuria was increased in untreated diabetes and was prevented only by ACE-i and combination treatment.

CONCLUSION/INTERPRETATION

Podocyte hypertrophy and degeneration is an early event in diabetic nephropathy leading to a loss of podocytes. Treatment with an ACE-i, but not with an ET(A)-RB, prevented the development of albuminuria as well as damage and loss of podocytes. The well known anti-proteinuric effect of ACE-i is presumably due at least in part to conservation of podocyte structure. Increased plasma endothelin-1 (ET-1) concentrations and urine excretion of ET-1 have been documented in patients with diabetes and proteinuria [1]. It has been shown that experimental diabetes mellitus increases renal ET-1 gene transcription [2]. To assess the relevance of the ET-system in the pathogenesis of renal structural changes in the model of the STZ-induced diabetic rat we compared the effect of an ET(A)-receptor specific antagonist with the well known beneficial effect of an ACE-i, especially on podocyte cell number and morphology.

Physiological doses of calcium regulatory hormones do not normalize bone cells in uraemic rats

BACKGROUND

Low bone turnover despite normal parathyroid hormone (PTH) concentrations has been found in many patients with end-stage renal failure. Hyporesponsiveness to the calcaemic action is also a known feature of uraemia. Hyporesponsiveness of bone surface cells involved in bone modelling has not been demonstrated to date. It was the purpose of this study using a rat model of moderate renal failure to investigate whether doses of PTH and calcitriol that reverse the effect of parathyroidectomy on calcaemia also normalize bone surface cell activity.

MATERIALS AND METHODS

Sham-operated pair-fed male Spraque-Dawley rats were compared with subtotally nephrectomized (SNX), parathyroidectomized (PTX) rats that received either solvent or calcitriol (5 pmol kg -1 h-1) + 1,34 rat PTH (100 ng kg -1 h-1) by osmotic mini-pump. Histomorphometric measurements were carried out in the vertebral body (L5).

RESULTS

In SNX/PTX animals, calcitriol + 1,34 rat PTH caused a modest increase in serum calcium (S-Ca) within the normal range. Osteoclast surface per cent was significantly lower in solvent-treated SNX/PTX rats than in sham-operated controls [3.7 +/- 2.8 osteoclast surface/bone surface (OcS/BS%) vs. 6.3 +/- 3.9], and this was not normalized by PTH + calcitriol (3.3 +/- 3). In contrast, osteoblast surface per cent and osteoid surface per cent were increased over values in sham-operated rats; as a result, co-administration of calcitriol and 1,34 rat PTH caused a highly significant increase in fractional bone volume (BV/TV).

CONCLUSIONS

The results show that administration of PTH and calcitriol in doses that raise serum calcium fails to normalize the percentage of osteoclast surface, but was effective in raising osteoblast number and osteoblast volume in experimental renal failure. The results argue for abnormal response of bone cells to calcium-regulating hormones and/or the action of factors other than calcium regulatory hormones in the genesis of skeletal abnormalities of renal failure.