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      Increased Urinary TGF-β1 and Cortical Renal GLUT1 and GLUT2 Levels: Additive Effects of Hypertension and Diabetes

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          Background/Aim: Diabetes and mesangial stretch caused by hypertension increase mesangial matrix deposition which is induced by local production of transforming growth factor beta 1 (TGF-β1). Both conditions are associated with cortical GLUT1 overexpression. We evaluated the effect of genetically determined hypertension and its association with diabetes on urinary TGF-β1 and cortical GLUT1 and GLUT2 expression. Methods: We studied Wistar-Kyoto rats (controls, C) and spontaneously hypertensive rats (SHR), weighing ∼210 g, 30 days after the injection of streptozotocin (diabetic, D) or citrate buffer (10 C, 9 SHR, 12 C-D and 15 SHR-D). Twenty-four-hour urine was collected for glucose, albumin, and TGF-β1 determinations. Catheters were implanted into the femoral artery to measure the arterial blood pressure in conscious animals 1 day later. Then GLUT1 and GLUT2 protein levels (Western blotting) in renal cortex and medulla were evaluated. Results: The cortical GLUT1 levels were 5, 2, and 7 times higher in SHR, C-D, and SHR-D groups versus C group (p < 0.05); the GLUT2 contents were 1.5, 1.8, and 2.3 times higher in SHR, C-D and SHR-D groups versus C group (p < 0.05). The urinary TGF-β1 level was elevated by diabetes and diabetes and hypertension, but not by hypertension alone: 1.39 ± 0.2, 2.34 ± 0.6, 18.2 ± 3.2, and 28.8 ± 7.6 ng/24 h, respectively, in C, SHR, C-D, and SHR-D groups (p < 0.05). Conclusions: Diabetes, hypertension, and especially their association increase the renal cortical GLUT1 and GLUT2 levels. The magnitude of GLUT1 overexpression caused by hypertension is higher than that induced by diabetes alone. The impact on urinary TGF-β1 occurs when diabetes and hypertension are associated, suggesting an effect that is triggered in the presence of GLUT1 overexpression and hyperglycemia.

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          Most cited references 28

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          Intensified multifactorial intervention in patients with type 2 diabetes mellitus and microalbuminuria: the Steno type 2 randomised study.

          In type 2 diabetes mellitus the aetiology of long-term complications is multifactorial. We carried out a randomised trial of stepwise intensive treatment or standard treatment of risk factors in patients with microalbuminuria. In this open, parallel trial patients were allocated standard treatment (n=80) or intensive treatment (n=80). Standard treatment followed Danish guidelines. Intensive treatment was a stepwise implementation of behaviour modification, pharmacological therapy targeting hyperglycaemia, hypertension, dyslipidaemia, and microalbuminuria. The primary endpoint was the development of nephropathy (median albumin excretion rate >300 mg per 24 h in at least one of the two-yearly examinations). Secondary endpoints were the incidence or progression of diabetic retinopathy and neuropathy. The mean age was 55.1 years (SD 7.2) and patients were followed up for 3.8 years (0.3). Patients in the intensive group had significantly lower rates of progression to nephropathy (odds ratio 0.27 [95% CI 0-10-0.75]), progression of retinopathy (0.45 [0.21-0.95]), and progression of autonomic neuropathy (0.32 [0.12-0.78]) than those in the standard group. Intensified multifactorial intervention in patients with type 2 diabetes and microalbuminuria slows progression to nephropathy, and progression of retinopathy and autonomic neuropathy. However, further studies are needed to establish the effect of intensified multifactorial treatment on macrovascular complications and mortality.
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            Interaction of metabolic and haemodynamic factors in mediating experimental diabetic nephropathy.

            Diabetic nephropathy seems to occur as a result of an interaction of metabolic and haemodynamic factors. Glucose dependent pathways are activated within the diabetic kidney. These include increased oxidative stress, renal polyol formation and accumulation of advanced glycated end-products. Haemodynamic factors are also implicated in the pathogenesis of diabetic nephropathy and include increased systemic and intraglomerular pressure and activation of various vasoactive hormone pathways including the renin-angiotensin system and endothelin. These haemodynamic pathways, independently and with metabolic pathways, activate intracellular second messengers such as protein kinase C and MAP kinase, nuclear transcription factors such as NF-kappaB and various growth factors such as the prosclerotic cytokine, TGF-beta and the angiogenic, permeability enhancing growth factor, VEGF. These pathways ultimately lead to increased renal albumin permeability and extracellular matrix accumulation which results in increasing proteinuria, glomerulosclerosis and tubulointerstitial fibrosis. Therapeutic strategies involved in the management and prevention of diabetic nephropathy include currently available treatments such as intensified glycaemic control and antihypertensive agents, particularly those which interrupt the renin-angiotensin system. More novel strategies to influence vasoactive hormone action or to inhibit various metabolic pathways such as inhibitors of advanced glycation, specific protein kinase C isoforms and aldose reductase are at present under experimental and clinical investigation. It is predicted that multiple therapies will be required to reduce the progression of diabetic nephropathy.
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              Changes in sodium or glucose filtration rate modulate expression of glucose transporters in renal proximal tubular cells of rat.

              Renal glucose reabsorption is mediated by luminal sodium-glucose cotransporters (SGLTs) and basolateral facilitative glucose transporters (GLUTs). The modulators of these transporters are not known, and their substrates glucose and Na+ are potential candidates. In this study we examined the role of glucose and Na+ filtration rate on gene expression of glucose transporters in renal proximal tubule. SGLT1, SGLT2, GLUT1 and GLUT2 mRNAs were assessed by Northern blotting; and GLUT1 and GLUT2 proteins were assessed by Western blotting. Renal cortex and medulla samples from control rats (C), diabetic rats (D) with glycosuria, and insulin-resistant 15-month old rats (I) without glycosuria; and from normal (NS), low (LS), and high (HS) Na+-diet fed rats were studied. Compared to C and I rats, D rats increased (P < 0.05) gene expression of SGLT2 by approximately 36%, SGLT1 by approximately 20%, and GLUT2 by approximately 100%, and reduced (P < 0.05) gene expression of GLUT1 by more than 50%. Compared to NS rats, HS rats increased (P < 0.05) SGLT2, GLUT2, and GLUT1 expression by approximately 100%, with no change in SGLT1 mRNA expression, and LS rats increased (P < 0.05) GLUT1 gene expression by approximately 150%, with no changes in other transporters. In summary, the results showed that changes in glucose or Na+ filtrated rate modulate the glucose transporters gene expression in epithelial cells of the renal proximal tubule.

                Author and article information

                Nephron Physiol
                Nephron Physiology
                S. Karger AG
                July 2005
                10 June 2005
                : 100
                : 3
                : p43-p50
                aDepartment of Experimental Medicine, Institute of Cardiology of Rio Grande do Sul/University Foundation of Cardiology, Porto Alegre, bHypertension Unit, Heart Institute, University of São Paulo, São Paulo, cFederal University of Rio Grande do Sul, Porto Alegre, dLaboratory for the Study of Chronic Diseases, Research Center of the Hospital de Clínicas de Pôrto Alegre, Porto Alegre, and eDepartment of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
                85413 Nephron Physiol 2005;100:p43–p50
                © 2005 S. Karger AG, Basel

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