Temporary angiotensin II blockade at the prediabetic stage attenuates the development of renal injury in type 2 diabetic rats

Diabetic nephropathy is associated with gene expression levels of oxidative phosphorylation and related pathways

The in vitro behavior of skin fibroblasts from patients with or without diabetic nephropathy is associated with diabetic nephropathy risk. Here we compared skin fibroblast gene expression profiles from two groups of type 1 diabetic patients: 20 with very fast ("fast-track") versus 20 with very slow ("slow-track") rates of development of diabetic nephropathy lesions. Gene expression profiles of skin fibroblasts grown in 25 mmol/l glucose for 36 h were assessed by Affymetrix HG-U133A GeneChips to determine the proportion of genes in a given biological pathway that were directionally consistent in their group differences. Five pathways reached statistical significance. All had significantly greater proportions of genes with higher expression levels in the fast-track group. These pathways, the first four of which are closely related and have overlapping genes, included oxidative phosphorylation (P<0.001), electron transport system complex III (P=0.017), citrate cycle (P=0.037), propanoate metabolism (P=0.044), and transcription factors (P=0.046). These results support the concept that oxidative phosphorylation and related upstream pathways may be important in the pathogenesis of diabetic nephropathy. Whether these findings reflect inherent genetic cellular characteristics, "cell memory," or both requires further study.

Young Scholars Award Lecture: Intratubular angiotensinogen in hypertension and kidney diseases

Recent findings related to the renin-angiotensin system have provided a more elaborated understanding of the pathophysiology of hypertension and kidney diseases. These findings have led to unique concepts and issues regarding the intrarenal renin-angiotensin system. Angiotensinogen is the only known substrate for renin that is the rate-limiting enzyme of the renin-angiotensin system. Because the level of angiotensinogen in human beings is close to the Michaelis-Menten constant value for renin, changes in angiotensinogen levels can control the activity of the renin-angiotensin system, and its upregulation may lead to elevated angiotensin peptide levels and increases in blood pressure. Enhanced intrarenal angiotensinogen mRNA or protein levels or both have been observed in multiple models of hypertension including angiotensin II-dependent hypertensive rats, Dahl salt-sensitive hypertensive rats, and spontaneously hypertensive rats, as well as in kidney diseases including diabetic nephropathy, immunoglobulin A (IgA) nephropathy, and radiation nephropathy. Renal angiotensinogen is formed primarily in proximal tubular cells and is secreted into the tubular fluid. Urinary angiotensinogen excretion rates show a clear relationship to kidney angiotensin II contents and kidney angiotensinogen levels, suggesting that urinary angiotensinogen may serve as an index of the intrarenal renin-angiotensin system status. Establishment of concise and accurate methods to measure human angiotensinogen may allow clinical studies that would provide important information regarding the roles of intrarenal angiotensinogen in the development and progression of hypertension and kidney diseases.

Heart and kidney: fatal twins?

The importance of renal function as both a marker of and risk factor for cardiovascular disease is increasingly recognized. This link is apparent even in the earliest stages of renal dysfunction, at levels that are conventionally considered "normal." These findings are of considerable importance, given the prevalence of high-normal levels of albuminuria (i.e., 10 to 20 mg/L) in the general population. There is also a close link between the progression of albuminuria and the development of insulin resistance and type 2 diabetes mellitus, such that kidney disease--far from being simply a consequence of the metabolic syndrome--may be considered a component of it. It may be hypothesized that minor derangements of renal function, such as microalbuminuria or reduced glomerular filtration rate, can lead to dysfunction of the endothelium, with the consequence of sensitizing the vasculature to the injurious effects of hypertension, dyslipidemia, and other risk factors. The renin-angiotensin system (RAS) is highly activated in patients with the metabolic syndrome, and this presumably is also true for the intrarenal RAS systems. Both angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers are known to reduce the progression of renal damage. Still to be resolved, however, is the optimal dosage; several recent studies indicate that the dosage required for maximal blood pressure reduction is insufficient to provide maximal renoprotection.

Long-term blockade of angiotensin AT1 receptors increases survival of obese Zucker rats

Despite the well-documented effect of irbesartan, an angiotensin AT1 receptor antagonist, on diabetic nephropathy, its effect on mortality related to multiple metabolic risk factors is unknown. To address this question, obese fa/fa Zucker rats were submitted to a 13-month treatment by irbesartan (30 mg/kg/day p.o.). Vehicle-treated obese fa/fa Zucker rats exhibited an important mortality (72%), which was markedly reduced by irbesartan (22%, P<0.05). Mortality in control lean fa/+ rats attained 12%. Irbesartan diminished the elevation in urinary protein excretion, plasma creatinine and urea nitrogen levels, and reduced the extent of glomerular and tubulo-interstitial lesions together with a reduction of urinary monocyte chemoattractant protein-1 excretion in fa/fa Zucker rats. Irbesartan treatment prevented the rise in plasma total cholesterol, triglycerides and glucose levels, and partially corrected low-density lipoprotein/high-density lipoprotein (LDL/HDL) cholesterol ratio in fa/fa Zucker rats. Therefore, prolonged irbesartan treatment preserves renal function and metabolic profile, and substantially increases survival in obese fa/fa Zucker rats.

Augmentation of Intrarenal Angiotensin II Levels in Uninephrectomized Aldosterone/Salt-Treated Hypertensive Rats; Renoprotective Effects of an Ultrahigh Dose of Olmesartan

Recent studies have suggested that aldosterone plays a role in the pathogenesis of renal injury. In this study, we investigated whether local angiotensin II (Ang II) activity contributes to the progression of renal injury in aldosterone/salt-induced hypertensive rats. Uninephrectomized rats were treated with 1% NaCl in a drinking solution and one of the following combinations for 6 weeks: vehicle (2% ethanol, s.c.; n=9), aldosterone (0.75 mug/h, s.c.; n=8), aldosterone+Ang II type 1 receptor blocker olmesartan (10 mg/kg/day, p.o.; n=8), or aldosterone+olmesartan (100 mg/kg/day, p.o.; n=9). Aldosterone/salt-treated hypertensive rats exhibited severe proteinuria and renal injury characterized by glomerular sclerosis and tubulointerstitial fibrosis. Aldosterone/salt-induced renal injury was associated with augmented expression of angiotensin converting enzyme and Ang II levels in the renal cortex and medullary tissues. Renal cortical and medullary mRNA expression of transforming growth factor-beta (TGF-beta) and connective tissue growth factor (CTGF) as well as the collagen contents were increased in aldosterone/salt-treated hypertensive rats. Treatment with olmesartan (10 or 100 mg/kg/day) had no effect on blood pressure but attenuated proteinuria in a dose-dependent manner. Olmesartan at 10 mg/kg/day tended to decrease renal cortical and medullary Ang II levels, TGF-beta and CTGF expression, and collagen contents; however, these changes were not significant. On the other hand, an ultrahigh dose of olmesartan (100 mg/kg/day) significantly decreased these values and ameliorated renal injury. These data suggest that augmented local Ang II activity contributes, at least partially, to the progression of aldosterone/salt-dependent renal injury.

Urinary excretions of lipocalin-type prostaglandin D2 synthase predict the development of proteinuria and renal injury in OLETF rats

BACKGROUND

Otsuka Long-Evans Tokushima Fatty (OLETF) rats genetically develop diabetes which is associated with hypertension. In preliminary studies, urinary excretions of L-PGDS (lipocaline-type prostaglandin D synthase) increase before diabetic nephropathy obviously develops, and this may predict progression of renal injury following diabetes. In the present study, we attempted to define whether urinary excretions of L-PGDS behave as the predictor of development of diabetic nephropathy in OLETF rats.

METHODS

We investigated alterations of urinary L-PGDS excretions during the establishment of diabetes and assessed the relationship between the L-PGDS excretions and renal function in OLETF rats. Furthermore, we treated OLETF rats with troglitazone and analysed the effects on L-PGDS metabolisms. Urinary L-PGDS was measured by immunoenzyme assay and the occurrence of L-PGDS and its mRNA in the kidney was assessed by immunohistochemistry and a PCR method.

RESULTS

Urinary excretions of L-PGDS were significantly higher in OLETF rats than non-diabetic Long-Evans Tokushima Otsuka (LETO) rats. The excretions age-dependently increased in OLETF and this increase appeared to be due to increased glomerular permeability to L-PGDS. Messenger RNA and antigenicity of L-PGDS were demonstrated in renal tissue; however, the de novo synthesis of L-PGDS mRNA seemingly contributed to urinary L-PGDS excretions much less than glomerular filtration. Multiple regression analysis revealed that urinary L-PGDS was determined by urinary protein excretions, and not by high blood pressure per se. Conversely, urinary proteinuria in the established diabetic nephropathy was predicted by urinary L-PGDS excretions in the early stage of diabetes.

CONCLUSIONS

Urinary excretions of L-PGDS are likely to reflect the underlying increase in glomerular permeability. This property may be useful to predict forthcoming glomerular damage following diabetes in OLETF rats.