The natural history of diabetic nephropathy in type I diabetes and the role of metabolic control in its prevention, reversibility and clinical course

Multimarker Panels in Diabetic Kidney Disease: The Way to Improved Clinical Trial Design and Clinical Practice?

Diabetic kidney disease (DKD) is a complex and multifactorial disorder associated with deregulations in a large number of different biological pathways on the molecular level. Using the 2 established biomarkers, estimated glomerular filtration rate (eGFR) and albuminuria will not allow allocating patients to tailored therapy. Molecular multimarker panels as sensors for the deregulation of the various disease mechanisms combined with a better understanding of how investigational as well as approved drugs interfere with these disease processes forms the basis for platform trials in DKD. In these platform trials, patients with DKD are assigned to the most suitable treatment arm based on their molecular marker profile. Close monitoring of biomarkers after treatment initiation together with assessment of renal function and "off-target" effects will allow identification of therapy responders, with nonresponders shifted to the next-best treatment arm based on their molecular profile. In this viewpoint article, we summarize evidence on the variation of DKD disease progression as well as the response to therapy and outline procedures to model disease pathophysiology supporting biomarker panel construction. Finally, the use of biomarkers in clinical trial setup is discussed.

Regression of glomerular and tubulointerstitial injuries by dietary salt reduction with combination therapy of angiotensin II receptor blocker and calcium channel blocker in Dahl salt-sensitive rats

A growing body of evidence indicates that renal tissue injuries are reversible. We investigated whether dietary salt reduction with the combination therapy of angiotensin II type 1 receptor blocker (ARB) plus calcium channel blocker (CCB) reverses renal tissue injury in Dahl salt-sensitive (DSS) hypertensive rats. DSS rats were fed a high-salt diet (HS; 4% NaCl) for 4 weeks. Then, DSS rats were given one of the following for 10 weeks: HS diet; normal-salt diet (NS; 0.5% NaCl), NS + an ARB (olmesartan, 10 mg/kg/day), NS + a CCB (azelnidipine, 3 mg/kg/day), NS + olmesartan + azelnidipine or NS + hydralazine (50 mg/kg/day). Four weeks of treatment with HS diet induced hypertension, proteinuria, glomerular sclerosis and hypertrophy, glomerular podocyte injury, and tubulointerstitial fibrosis in DSS rats. A continued HS diet progressed hypertension, proteinuria and renal tissue injury, which was associated with inflammatory cell infiltration and increased proinflammatory cytokine mRNA levels, NADPH oxidase activity and NADPH oxidase-dependent superoxide production in the kidney. In contrast, switching to NS halted the progression of hypertension, renal glomerular and tubular injuries. Dietary salt reduction with ARB or with CCB treatment further reduced blood pressure and partially reversed renal tissues injury. Furthermore, dietary salt reduction with the combination of ARB plus CCB elicited a strong recovery from HS-induced renal tissue injury including the attenuation of inflammation and oxidative stress. These data support the hypothesis that dietary salt reduction with combination therapy of an ARB plus CCB restores glomerular and tubulointerstitial injury in DSS rats.

Differences in susceptibility to develop parameters of diabetic nephropathy in four mouse strains with type 1 diabetes

One-third of diabetes mellitus patients develop diabetic nephropathy, and with underlying mechanisms unknown it is imperative that diabetic animal models resemble human disease. The present study investigated the susceptibility to develop diabetic nephropathy in four commonly used and commercially available mouse strains with type 1 diabetes to determine the suitability of each strain. Type 1 diabetes was induced in C57Bl/6, NMRI, BALB/c, and 129Sv mice by alloxan, and conscious glomerular filtration rate, proteinuria, and oxidative stress levels were measured in control and diabetic animals at baseline and after 5 and 10 wk. Histological alterations were analyzed using periodic acid-Schiff staining. Diabetic C57Bl/6 displayed increased glomerular filtration rate, i.e., hyperfiltration, whereas all other parameters remained unchanged. Diabetic NMRI developed the most pronounced hyperfiltration as well as increased oxidative stress and proteinuria but without glomerular damage. Diabetic BALB/c did not develop hyperfiltration but presented with pronounced proteinuria, increased oxidative stress, and glomerular damage. Diabetic 129Sv displayed proteinuria and increased oxidative stress without glomerular hyperfiltration or damage. However, all strains displayed intrastrain correlation between oxidative stress and proteinuria. In conclusion, diabetic C57Bl/6 and NMRI both developed glomerular hyperfiltration but neither presented with histological damage, although NMRI developed low-degree proteinuria. Thus these strains may be suitable when investigating the mechanism causing hyperfiltration. Neither BALB/c nor 129Sv developed hyperfiltration although both developed pronounced proteinuria. However, only BALB/c developed detectable histological damage. Thus BALB/c may be suitable when studying the roles of proteinuria and histological alterations for the progression of diabetic nephropathy.

Sugar, sex, and TGF-β in diabetic nephropathy

TGF-β is well known to play a critical role in diabetic kidney disease, and ongoing clinical studies are testing the potential therapeutic promise of inhibiting TGF-β production and action. An aspect of TGF-β action that has not received much attention is its potential role in explaining sex-related proclivity for kidney disease. In this review, we discuss recent studies linking TGF-β signaling to sex-related effects in diabetic kidney disease and suggest targets for future studies.

Long-term renal changes in the liver-specific glucokinase knockout mouse: implications for renal disease in maturity-onset diabetes of the young 2

To investigate the functional and structural renal changes in a long-term liver-specific glucokinase (gck) knockout mouse, a model was developed of maturity-onset diabetes of the young (MODY2). Hemizygous gck knockout mice, gck(w/-) groups, were compared at 6, 10, and 14 months with their age-matched normal littermates, gck(w/w) groups. To examine changes, we compared body weight, fasting blood glucose, serum insulin, and creatinine levels, as well as 24-h urine samples that were collected for urine volume and protein analysis between the 2 groups. Renal tissues were collected and stained with hemotoxylin-eosin and periodic-acid Schiff for light microscopic observation. The expression of renal transforming growth factor β1 (TGF-β1) was determined by Western blot. Our results show that fasting blood glucose levels were significantly higher in gck(w/-) mice compared with gck(w/w) mice (P < 0.01) for all age groups. Compared with age-matched gck(w/w) mice, 10-month old gck(w/-) mice have significantly elevated body weights (P < 0.01) and protein contents (P < 0.001). A gradual increase in mesangial matrix and a thickening of the glomerular basement membrane was observed in gck(w/-) mice at 10 and 14 months. The levels of renal TGF-β1 expression are increasing in both gck(w/-) and gck(w/w) mice. Our results indicate that renal changes occur in the liver-specific gck knockout mouse model of MODY2 and suggest that TGF-β1 may play a key role in pathogenesis of these renal changes.

Amelioration of established diabetic nephropathy by combined treatment with SMP-534 (antifibrotic agent) and losartan in db/db mice

BACKGROUND/AIMS

Diabetic nephropathy is the main cause of end-stage renal disease. Previously we have demonstrated that SMP-534 (an antifibrotic agent) prevents the development of diabetic nephropathy in db/db mouse and that combined treatment with SMP-534 and losartan (antihypertensive agents) markedly prevents the development of diabetic nephropathy compared with single treatment. SMP-534 or losartan was prophylactically administered to db/db mice before the onset of diabetic nephropathy. In the present study, we evaluated the efficacy of combined treatment when administration was started after the onset of diabetic nephropathy.

METHODS

db/db mice were raised untreated until 17 weeks of age, by which time increase of urinary albumin was noted, and then treated with SMP-534 and/or losartan for another 8 weeks. Biochemical and histological analyses were performed at 25 weeks of age.

RESULTS

Combined treatment with SMP-534 and losartan markedly prevented the increase of urinary albumin and ameliorated the progression of mesangial matrix expansion, even when administration was started long after the increase of urinary albumin.

CONCLUSION

The study results indicate that a combination of SMP-534 and losartan might be a valuable therapeutic approach for the treatment of diabetic nephropathy even when administration is started after the onset of diabetic nephropathy.

Mouse models of diabetic nephropathy

Mice provide an experimental model of unparalleled flexibility for studying mammalian diseases. Inbred strains of mice exhibit substantial differences in their susceptibility to the renal complications of diabetes. Much remains to be established regarding the course of diabetic nephropathy (DN) in mice as well as defining those strains and/or mutants that are most susceptible to renal injury from diabetes. Through the use of the unique genetic reagents available in mice (including knockouts and transgenics), the validation of a mouse model reproducing human DN should significantly facilitate the understanding of the underlying genetic mechanisms that contribute to the development of DN. Establishment of an authentic mouse model of DN will undoubtedly facilitate testing of translational diagnostic and therapeutic interventions in mice before testing in humans.

Prevention and reversal of renal injury by leptin in a new mouse model of diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease, for which effective therapy to prevent the progression at advanced stages remains to be established. There is also a long debate whether diabetic glomerular injury is reversible or not. Lipoatrophic diabetes, a syndrome caused by paucity of adipose tissue, is characterized by severe insulin resistance, dyslipidemia, and fatty liver. Here, we show that a genetic model of lipoatrophic diabetes (A-ZIP/F-1 mice) manifests a typical renal injury observed in human diabetic nephropathy that is associated with glomerular hypertrophy, diffuse and pronounced mesangial widening, accumulation of extracellular matrix proteins, podocyte damage, and overt proteinuria. By crossing A-ZIP/F-1 mice with transgenic mice overexpressing an adipocyte-derived hormone leptin, we also reveal that leptin completely prevents the development of hyperglycemia and nephropathy in A-ZIP/F-1 mice. Furthermore, continuous leptin administration to A-ZIP/F-1 mice by minipump beginning at 40 weeks of age significantly alleviates the glomerular injury and proteinuria. These findings demonstrate the therapeutic usefulness of leptin at least for a certain type of diabetic nephropathy. The model presented here will serve as a novel tool to analyze the molecular mechanism underlying not only the progression but also the regression of diabetic nephropathy.

Reversibility of established diabetic glomerulopathy by anti-TGF-beta antibodies in db/db mice

Treatment with a neutralizing anti-transforming growth factor-beta (TGF-beta) antibody can prevent the development of diabetic nephropathy in the db/db mouse, a model of type 2 diabetes. However, it is unknown whether anti-TGF-beta therapy can reverse the histological lesions of diabetic glomerulopathy once they are established. Diabetic db/db mice and their non-diabetic db/m littermates were allowed to grow until 16 weeks of age, by which time the db/db mice had developed glomerular basement membrane (GBM) thickening and mesangial matrix expansion. The mice were then treated with an irrelevant control IgG or a panselective, neutralizing anti-TGF-beta antibody for eight more weeks. Compared with control db/m mice, the db/db mice treated with IgG had developed increased GBM width (16.64+/-0.80 nm vs. 21.55+/-0.78 nm, P<0.05) and increased mesangial matrix fraction (4.01+/-0.81% of total glomerular area vs. 9.55+/-1.04%, P<0.05). However, the db/db mice treated with anti-TGF-beta antibody showed amelioration of GBM thickening (18.40+/-0.72 nm, P<0.05 vs. db/db-IgG) and mesangial matrix accumulation (6.32+/-1.79%, P<0.05 vs. db/db-IgG). Our results demonstrate that inhibiting renal TGF-beta activity can partially reverse the GBM thickening and mesangial matrix expansion in this mouse model of type 2 diabetes. Anti-TGF-beta regimens would be useful in the treatment of diabetic nephropathy.