Nephropathy and hypertension in diabetes

Akt and RhoA activation in response to high glucose require caveolin-1 phosphorylation in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic renal disease. Serine/threonine kinase PKC-β1 mediates glucose-induced Akt S473 phosphorylation, RhoA activation, and transforming growth factor (TGF)-β1 upregulation and finally leads to matrix upregulation in mesangial cells (MCs). It has been reported that glucose-induced PKC-β1 activation is dependent on caveolin-1 and the presence of intact caveolae in MCs; however, whether activated PKC-β1 regulates caveolin-1 expression and phosphorylation are unknown. Here, we showed that, although the caveolin-1 protein level had no significant change, the PKC-β-specific inhibitor LY-333531 blocked caveolin-1 Y14 phosphorylation in high glucose (HG)-treated MCs and in the renal cortex of diabetic rats. The Src-specific inhibitor SU-6656 prevented the HG-induced association between PKC-β1 and caveolin-1 and PKC-β1 membrane translocation, whereas PKC-β1 small interfering RNA failed to block Src activation, indicating that Src kinase is upstream of PKC-β1 activation. Although LY-333531 blocked PKC-β1 membrane translocation, it had no effect on the PKC-β1/caveolin-1 association, suggesting that PKC-β1 activation requires the interaction of caveolin-1 and PKC-β1. PKC-β1-mediated Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation in response to HG were prevented by SU-6656 and nonphosphorylatable mutant caveolin-1 Y14A. In conclusion, Src activation by HG mediates the PKC-β1/caveolin-1 association and PKC-β1 activation, which assists in caveolin-1 Y14 phosphorylation by Src kinase. The downstream effects, including Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation, require caveolin-1 Y14 phosphorylation. Caveolin-1 is thus an important mediator of the profibrogenic process in diabetic renal disease.

Fenofibrate attenuated glucose-induced mesangial cells proliferation and extracellular matrix synthesis via PI3K/AKT and ERK1/2

Excess mesangial extracellular matrix (ECM) and mesangial cell proliferation is the major pathologic feature of diabetic nephropathy (DN). Fenofibrate, a PPARα agonist, has been shown to attenuate extracellular matrix formation in diabetic nephropathy. However, the mechanisms underlying this effect remain to be elucidated. In this study, the effect of fenofibrate on high-glucose induced cell proliferation and extracellular matrix exertion and its mechanisms were investigated in cultured rat mesangial cells by the methylthiazoletetrazolium (MTT) assay, flow cytometry and western blot. The results showed that treatment of mesangial cells (MCs) with fenofibrate repressed high-glucose induced up-regulation of extracellular matrix Collagen-IV, and inhibited entry of cell cycle into the S phase. This G1 arrest and ECM inhibition was caused by the reduction of phosphorylation and activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and AKT. On the contrary, PPARα siRNA accelerated high glucose-induced cell cycle progression by ERK1/2 and AKT activation. Taken together, fenofibrate ameliorated glucose-induced mesangial cell proliferation and matrix production via its inhibition of PI3K/AKT and ERK1/2 signaling pathways. Such mechanisms may contribute to the favorable effects of treatment using fenofibrate in diabetic nephropathy.

Gene polymorphism of transforming growth factor-β1 in Egyptian patients with type 2 diabetes and diabetic nephropathy

Role of the transforming growth factor-β1 (TGF-β1) gene polymorphisms located at codons 10 and 25 in the genetic predisposition to type 2 diabetes (T2D) and in diabetic nephropathy (DN) in Egyptian patients was investigated. A case control study was done for 99 unrelated Egyptian patients with T2D (50 DN(-) and 49 DN(+)) and 98 age- and sex-matched healthy controls. TGF-β1 T869C (codon 10) and G915C (codon 25) polymorphism detection was done by amplification refractory mutation system method. DN(+) patients were younger, with higher body mass index, serum triglycerides, serum creatinine, and lower serum albumin than those in DN(-) patients. Moderate and bad grades of diabetic control were associated with DN (P < 0.001). The TGF-β1 (T869C) C allele, TC and TC + CC genotypes were significantly higher in patients; the T allele and TT genotype were significantly higher in controls (Pc < 0.001). The TGF-β1 TC genotype was associated with DN (Pc < 0.05). Non-significant differences were detected between T2D patients and controls in the frequencies of TGF-β1 (G915C) alleles and genotypes. In conclusion, these preliminary data showed that the TGF-β1 codon 10 C allele, and C allele-containing genotypes may be susceptible, and T allele/TT genotype may be protective factors for T2D and DN(+) complications.

SREBP-1 activation by glucose mediates TGF-β upregulation in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. Recent studies showed that overexpression of the transcription factor sterol-responsive element-binding protein (SREBP)-1 induces pathology reminiscent of diabetic nephropathy, and SREBP-1 upregulation was observed in diabetic kidneys. We thus studied whether SREBP-1 is activated by high glucose (HG) and mediates its profibrogenic responses. In primary rat mesangial cells, HG activated SREBP-1 by 30 min, seen by the appearance of its cleaved nuclear form (nSREBP-1), EMSA, and by activation of an SREBP-1 response element (SRE)-driven green fluorescent protein construct. Activation was dose dependent and not induced by an osmotic control. Site 1 protease was required, since its inhibition by AEBSF prevented SREBP-1 activation. SCAP, the ER-associated chaperone for SREBP-1, was also necessary since its inhibitor fatostatin also blocked SREBP-1 activation. Signaling through the EGFR/phosphatidylinositol 3-kinase (PI3K) pathway, which we previously showed mediates HG-induced TGF-β1 upregulation, and through RhoA, were upstream of SREBP-1 activation (Wu D, Peng F, Zhang B, Ingram AJ, Gao B, Krepinsky JC. Diabetologia 50: 2008–2018, 2007; Wu D, Peng F, Zhang B, Ingram AJ, Kelly DJ, Gilbert RE, Gao B, Krepinsky JC. J Am Soc Nephrol 20: 554–566, 2009). Fatostatin and AEBSF prevented HG-induced TGF-β1 upregulation by Northern blot analysis, and HG-induced TGF-β1 promoter activation was inhibited by both fatostatin and dominant negative SREBP-1a. Chromatin immunoprecipitation analysis confirmed that HG led to SREBP-1 binding to the TGF-β1 promoter in a region containing a putative SREBP-1 binding site (SRE). Thus HG-induced SREBP-1 activation requires EGFR/PI3K/RhoA signaling and SCAP-mediated transport to the Golgi for its proteolytic cleavage. Activated SREBP-1 binds to the TGF-β promoter, resulting in TGF-β1 upregulation in response to HG. SREBP-1 thus provides a potential novel therapeutic target for the treatment of diabetic nephropathy.

High glucose-induced RhoA activation requires caveolae and PKCβ1-mediated ROS generation

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. We previously showed that RhoA activation by high glucose in mesangial cells (MC) leads to matrix upregulation (Peng F, Wu D, Gao B, Ingram AJ, Zhang B, Chorneyko K, McKenzie R, Krepinsky JC. Diabetes 57: 1683-1692, 2008). Here, we study the mechanism whereby RhoA is activated. In primary rat MC, RhoA activation required glucose entry and metabolism. Broad PKC inhibitors (PMA, bisindolylmaleimide, Gö6976), as well as specific PKCβ blockade with an inhibitor and small interfering RNA (siRNA), prevented RhoA activation by glucose. PKCβ inhibition also abrogated reactive oxygen species (ROS) generation by glucose. The ROS scavenger N-acetylcysteine (NAC) or NADPH oxidase inhibitors apocynin and DPI prevented glucose-induced RhoA activation. RhoA and some PKC isoforms localize to caveolae. Chemical disruption of these microdomains prevented RhoA and PKCβ1 activation by glucose. In caveolin-1 knockout cells, glucose did not induce RhoA and PKCβ1 activation; these responses were rescued by caveolin-1 reexpression. Furthermore, glucose-induced ROS generation was significantly attenuated by chemical disruption of caveolae and in knockout cells. Downstream of RhoA signaling, activator protein-1 (AP-1) activation was also inhibited by disrupting caveolae, was absent in caveolin-1 knockout MC and rescued by caveolin-1 reexpression. Finally, transforming growth factor (TGF)-β1 upregulation, mediated by AP-1, was prevented by RhoA signaling inhibition and by disruption or absence of caveolae. In conclusion, RhoA activation by glucose is dependent on PKCβ1-induced ROS generation, most likely through NADPH oxidase. The activation of PKCβ1 and its downstream effects, including upregulation of TGF-β1, requires caveolae. These microdomains are thus important mediators of the profibrogenic process associated with diabetic nephropathy.

HB-EGF release mediates glucose-induced activation of the epidermal growth factor receptor in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. We showed that transactivation of the epidermal growth factor receptor (EGFR) is an important mediator of matrix upregulation in mesangial cells (MC) in response to high glucose (HG). Here, we study the mechanism of EGFR transactivation. In primary MC, EGFR transactivation by 1 h of HG (30 mM) was unaffected by inhibitors of protein kinase C, reactive oxygen species, or the angiotensin II AT1 receptor. However, general metalloprotease inhibition, as well as specific inhibitors of heparin-binding EGF-like growth factor (HB-EGF), prevented both EGFR and downstream Akt activation. HB-EGF was released into the medium by 30 min of HG, and this depended on metalloprotease activity. One of the metalloproteases shown to cleave proHB-EGF is ADAM17 (TACE). HG, but not an osmotic control, activated ADAM17, and its inhibition prevented EGFR and Akt activation and HB-EGF release into the medium. siRNA to either ADAM17 or HB-EGF prevented HG-induced EGFR transactivation. We previously showed that EGFR/Akt signaling increases transforming growth factor (TGF)-β1 transcription through the transcription factor activator protein (AP)-1. HG-induced AP-1 activation, as assessed by EMSA, was abrogated by inhibitors of metalloproteases, HB-EGF and ADAM17. HB-EGF and ADAM17 siRNA also prevented AP-1 activation. Finally, these inhibitors and siRNA prevented TGF-β1 upregulation by HG. Thus, HG-induced EGFR transactivation in MC is mediated by the release of HB-EGF, which requires activity of the metalloprotease ADAM17. The mechanism of ADAM17 activation awaits identification. Targeting upstream mediators of EGFR transactivation including HB-EGF or ADAM17 provides novel therapeutic targets for the treatment of diabetic nephropathy.

Expression-based network biology identifies alteration in key regulatory pathways of type 2 diabetes and associated risk/complications

Type 2 diabetes mellitus (T2D) is a multifactorial and genetically heterogeneous disease which leads to impaired glucose homeostasis and insulin resistance. The advanced form of disease causes acute cardiovascular, renal, neurological and microvascular complications. Thus there is a constant need to discover new and efficient treatment against the disease by seeking to uncover various novel alternate signalling mechanisms that can lead to diabetes and its associated complications. The present study allows detection of molecular targets by unravelling their role in altered biological pathways during diabetes and its associated risk factors and complications. We have used an integrated functional networks concept by merging co-expression network and interaction network to detect the transcriptionally altered pathways and regulations involved in the disease. Our analysis reports four novel significant networks which could lead to the development of diabetes and other associated dysfunctions. (a) The first network illustrates the up regulation of TGFBRII facilitating oxidative stress and causing the expression of early transcription genes via MAPK pathway leading to cardiovascular and kidney related complications. (b) The second network demonstrates novel interactions between GAPDH and inflammatory and proliferation candidate genes i.e., SUMO4 and EGFR indicating a new link between obesity and diabetes. (c) The third network portrays unique interactions PTPN1 with EGFR and CAV1 which could lead to an impaired vascular function in diabetic nephropathy condition. (d) Lastly, from our fourth network we have inferred that the interaction of β-catenin with CDH5 and TGFBR1 through Smad molecules could contribute to endothelial dysfunction. A probability of emergence of kidney complication might be suggested in T2D condition. An experimental investigation on this aspect may further provide more decisive observation in drug target identification and better understanding of the pathophysiology of T2D and its complications.

Collagen I induction by high glucose levels is mediated by epidermal growth factor receptor and phosphoinositide 3-kinase/Akt signalling in mesangial cells

AIMS/HYPOTHESIS

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. Recent data have linked the serine/threonine kinase protein kinase B (Akt) to matrix modulation. Here, we studied its role in high glucose-induced collagen elaboration by mesangial cells.

METHODS

Primary rat mesangial cells were treated with high glucose levels (30 mmol/l) or mannitol as osmotic control. Western blots, northern blots, ELISA and immunohistochemistry were used for assessment. Diabetes was induced in rats by streptozotocin.

RESULTS

Phosphorylated Akt at S473 (pAktS473), corresponding to Akt activation, was seen in diabetic glomeruli. In mesangial cells, high glucose levels induced pAktS473 by 20 min. This was sustained to 72 h, while mannitol had no effect. Akt activation by kinase assay and phosphorylation on threonine 308 was also observed. Phosphoinositide 3-kinase (PI3K) inhibitors LY294002 (20 micromol/l) and wortmannin (100 nmol/l) prevented pAktS473. Collagen IA1 transcript and collagen I protein upregulation by high glucose levels were inhibited by PI3K blockade, as was collagen I secretion into the medium (ELISA). Dominant-negative Akt overexpression also inhibited high glucose-induced collagen IA1 transcript and collagen I protein production. Since signalling through the epidermal growth factor receptor (EGFR) can activate PI3K-Akt, we studied its activation by high glucose levels. EGFR was correspondingly activated by 10 min; mannitol had no effect. EGFR activation was also seen in glomeruli from diabetic rats and co-localised with collagen IA1 in diabetic glomeruli. Specific EGFR inhibition (AG1478, 5 micromol/l or dominant-negative EGFR) blocked high glucose-induced pAktS473, phosphorylation on threonine 308 and activation of the EGFR downstream target p44 extracellular signal-regulated kinase (Erk) mitogen-activated protein kinase. Finally, EGFR inhibition also blocked high glucose-induced collagen I upregulation at transcriptional and protein levels.

CONCLUSIONS/INTERPRETATION

We conclude that EGFR-PI3K-Akt signalling mediates high glucose-induced collagen I upregulation in mesangial cells and that this pathway is activated in diabetic glomeruli. Targeting its components may provide a new therapeutic approach to diabetic kidney disease.

TGF-β1 and TSC-22 Gene Polymorphisms and Susceptibility to Microvascular Complications in Type 2 Diabetes

BACKGROUND/AIM

There is a strong evidence for the involvement of genetic factors in diabetic microvascular complications. The aim of our study was to investigate the role of molecular variants of the TGF-beta1 (transforming growth factor beta 1) and the TSC-22 (transforming growth factor beta stimulated clone 22) genes in diabetic nephropathy and diabetic retinopathy in type 2 diabetes.

METHODS

A case-control study was conducted in 503 patients and 400 healthy subjects. DNA samples were genotyped by polymerase chain reaction and restriction fragment length polymorphism methods.

RESULTS

Among the patients, 245 had diabetic nephropathy, 195 had retinopathy, and 168 were free from complications. All subjects were genotyped for T869C and C -509T polymorphisms of the TGF-beta1 gene and for -396 polymorphism of the TSC-22 gene. A significantly increased frequency of the CC genotype of the T869C polymorphism was observed in patients with nephropathy and retinopathy (33 and 48%, respectively, vs. 19 and 15%, respectively, in controls and patients free from complications). The frequency of the C allele was also higher (0.58 for nephropathy and 0.64 for retinopathy vs. 0.42 in controls). The G allele of the TSC-22 polymorphism was associated with an increased risk of diabetic nephropathy (frequency 0.15 vs. 0.07 and 0.06, respectively, in patients free from complications and controls). An interaction was observed between the G allele of the TSC-22 polymorphism and the C-allele of the TGF-beta polymorphism.

CONCLUSIONS

Our data suggest the association of TGF-beta T869C gene polymorphism with an increased risk of nephropathy and retinopathy in type 2 diabetes patients. It interacts with the TSC-22 gene involved in the TGF-beta signaling pathway, promoting the development of diabetic nephropathy.

The TGF-beta 1 gene codon 10 polymorphism contributes to the genetic predisposition to nephropathy in Type 1 diabetes

AIMS

We hypothesize that transforming growth factor-beta (TGF-beta), a multifunctional growth factor which plays a key role in the development of tissue fibrosis, may be involved in the pathophysiology of diabetic nephropathy. Our aim was to examine three polymorphisms within the TGF-beta 1 gene, in codons 10, 25 and 263, for association with nephropathy in Type 1 diabetes.

METHODS

We conducted a large case-control study using cases with Type 1 diabetes and clinical nephropathy. Controls were Type 1 diabetic subjects who have been injecting insulin for at least 50 years and have extremely low risk of nephropathy. Genotyping was by polymerase chain reaction with sequence-specific primers.

RESULTS

There was a significant difference in the frequency of the TGF-beta 1 codon 10 genotypes in the diabetic nephropathy group (n = 420) when compared with the controls (n = 410, P = 0.007). There were no significant differences when the frequencies of the TGF-beta1 codons 25 and 263 genotypes in the diabetic nephropathy group were compared with the control group.

CONCLUSIONS

In our study the TGF-beta 1 codon 10 polymorphism is associated with nephropathy in Type 1 diabetes and variation in this gene may contribute to the genetic predisposition to this complication in Type 1 diabetes.

The Impact of Vitamins and/or Mineral Supplementation on Blood Pressure in Type 2 Diabetes

OBJECTIVE

The present study designed to assess the effect of Mg+Zn, vitamin C+E, and combination of these micronutrients on blood pressure in type 2 diabetic patients.

MATERIALS AND METHODS

In a randomized, double-blind, placebo controlled clinical trial, 69 type 2 diabetic patients were randomly divided into four groups, each group receiving one of the following daily supplement for three months; group M: 200 mg Mg and 30 mg Zn (n = 16), group V: 200 mg vitamin C and 150 mg vitamin E (n = 18), group MV: minerals plus vitamins (n = 17), group P: placebo (n = 18). Blood pressure was measured at the beginning and at the end of the trial. Treatment effects were analyzed by general linear modeling.

RESULTS

Results indicate that after three months of supplementation levels of systolic, diastolic and mean blood pressure decreased significantly in the MV group by 8 mmHg (122 +/- 16 vs. 130 +/- 19 mmHg), 6 mmHg (77 +/- 9 vs. 83 +/- 11 mmHg), and 7 mmHg (92 +/- 9 vs. 99 +/- 13 mmHg), respectively (p < 0.05). Also combination of vitamin and mineral supplementation had significantly effects in increasing serum potassium (p < 0.05) and in decreasing serum malondialdehyde (p < 0.05). There was no significant change in the levels of these parameters in the other three groups.

CONCLUSION

The results of the present study indicated that in type 2 diabetic patients a combination of vitamins and minerals, rather than vitamin C and E or Mg and Zn, might decrease blood pressure.

Long-term caffeine consumption exacerbates renal failure in obese, diabetic, ZSF1 (fa-fa(cp)) rats

BACKGROUND

Our preliminary studies indicate that chronic caffeine consumption has adverse renal effects in nephropathy associated with high blood pressure and insulin resistance. The purpose of this study was to investigate the effects of early (beginning at 8 weeks of age) and long-term (30 weeks) caffeine treatment (0.1% solution) on renal function and structure in obese, diabetic ZSF1 rats.

METHODS

Metabolic and renal function measurements were performed at six-week intervals and in a subset of animals (N = 6 per group) heart rate (HR) and mean arterial blood pressure (MABP) were monitored by a radiotelemetric technique. At the end of the study acute, measurements of renal hemodynamics and excretory function were conducted in anesthetized animals.

RESULTS

Caffeine produced a very mild increase (4 to 5%) of MABP and HR, but greatly augmented proteinuria (P < 0.001), reduced creatinine clearance (P < 0.05) and had a mixed effect on metabolic status in obese ZSF1 rats. Caffeine significantly reduced body weight, glycosuria, fasting glucose and insulin levels and improved glucose tolerance, had no effect on elevated plasma triglycerides levels and significantly increased plasma cholesterol level (P < 0.001). Acute measurements of renal function revealed increased renal vascular resistance (95.1 +/- 11 vs. 50.7 +/- 2.4 mm Hg/mL/min/g kidney, P < 0.01) and decreased inulin clearance (0.37 +/- 0.11 vs. 0.97 +/- 0.13 mL/min/g kidney, P < 0.002) in caffeine-treated versus control animals, respectively. Caffeine potentiated the development of more severe tubulointerstitial changes (P < 0.05) and increased focal glomerulosclerosis (14.7 +/- 1.7 vs. 6.5 +/- 0.9%, caffeine vs. control, P < 0.002).

CONCLUSION

The present study provides the first evidence that caffeine (despite improving insulin sensitivity) exacerbates renal failure in obese, diabetic ZSF1 rats. Further mechanistic studies of adverse renal effects of caffeine in chronic renal failure associated with metabolic syndrome are warranted.

Microvascular complications. Retinopathy and nephropathy

Diabetic retinopathy and diabetic nephropathy extract an enormous toll on patients with diabetes and an enormous burden on the health care system. With aggressive control of glycemia and blood pressure, coupled with aggressive use of laser photocoagulation and treatment of microalbuminuria, these problems can largely be eliminated. In the future, specific interventions may emerge that will allow interdiction of the pathophysiologic processes that lead to initiation and progression of these microvascular complications. The challenge for the primary care physician and diabetologist is to attain excellent glycemic control and aggressive control of blood pressure, while assuring that every patient has appropriate dilated fundus examinations at least annually, preferably by an ophthalmologist or retinal specialist, and regular screening for microalbuminuria. With such medical management, appropriate intervention can occur to reduce the risk of blindness and renal failure and to lessen the burden from diabetic retinopathy and nephropathy.

Pathogenesis of diabetic nephropathy: focus on transforming growth factor-beta and connective tissue growth factor

Although considerable improvement in the prognosis of diabetic nephropathy has been achieved in recent years due to intensive insulin and angiotensin-converting enzyme inhibitor treatment, these approaches do not provide complete protection against progression of diabetic nephropathy. An urgent need for additional novel therapies to prevent or further slow the progression of diabetic nephropathy motivated us to provide an up-to-date review with particular emphasis on the potential role of two growth factors--transforming growth factor-beta and connective tissue growth factor--in the pathogenesis of diabetic nephropathy. The most intensively studied to date, transforming growth factor-beta appears to play a central role in the pathogenesis of diabetic nephropathy. Recently, attention has focused on connective tissue growth factor, which mimics the biological activity of transforming growth factor-beta in profibrotic tissue formation. Thus, acting as a downstream mediator of the profibrotic activity of transforming growth factor-beta, connective tissue growth factor may constitute a more specific target for future antifibrotic therapies.

Renal and metabolic effects of caffeine in obese (fa/fa(cp)), diabetic, hypertensive ZSF1 rats

In Western society, the triad of hypertension, metabolic syndrome and obesity (which caries a high risk for renal disease) is increasing, as is the intake of caffeine. However, no information is available regarding the metabolic or renal consequences of caffeine consumption in this complex disease entity. The purpose of this study was to investigate the effects of chronic caffeine consumption on renal function and metabolic status in obese ZSF1 rats, an animal model of obesity, hypertension and the metabolic syndrome. Fifteen, 18-week-old male, obese ZSF1 rats were randomized to drink tap water (Cont, n = 8) or 0.1% solution of caffeine (Caff, n = 7) for 8 weeks. Metabolic and renal function measurements were performed at baseline and after 4 and 8 weeks of treatment. Caffeine treatment significantly (p < 0.05) reduced body weight, food, and fluid consumption and improved insulin sensitivity (fasting insulin 129.6+/-8.1 vs 97.5+/-3.6 microIU/mL; fed insulin 146.3+/-8.5 vs 110.6+/-3.4 microIU/mL; fasting glucose 138.7+/-13.4 vs 145+/-8.0 mg/dL; fed glucose 373+/-19.4 vs 283.3+/-19.6 mg/dL, Cont vs Caff, respectively). After 8 weeks of caffeine treatment, animals were less glycosuric as compared with control group. Area under glucose curves (AUC-glucose) in oral glucose tolerance test did not differ between the two groups (AUC- glucose: 592.5+/-42.7 vs 589.5+/-20.5 mg/dL x h, Cont vs Caff), whereas caffeine treatment significantly decreased AUC of insulin (AUC-insulin: 257.77+/-12.9 vs 198.0+/-5.9 microIU/mL x h, Cont vs. Caff, p<0.05). No differences were found with regard to plasma triglycerides and glycerol levels; however, caffeine significantly increased cholesterol levels after 4 and 8 weeks (2F-Anova, p<0.001). Moreover, caffeine significantly decreased creatinine clearance after 4 and 8 weeks (CrCl, Cont: 3.5+/-0.4, Caff: 2.2+/-0.2 L/kg/day, p<0.05) and increased protein/CrCl ratio (Cont: 323+/-30, Caff: 527+/-33 mg/L/day). Caffeine treatment for 8 weeks tended to increase plasma norepinephrine levels (p<0.06), but the two groups did not differ with regard to plasma renin activity, blood pressure, renal blood flow or and renal vascular resistance. The study indicates that caffeine improves insulin sensitivity but increases plasma cholesterol levels and impairs renal function in obesity with the metabolic syndrome and hypertension. Our results imply that the health consequences of chronic caffeine consumption may depend heavily on underlying pathophysiology process.

Renal function and structure in diabetic, hypertensive, obese ZDFxSHHF-hybrid rats

The obese ZDFxSHHF-fa/fa(cp) model was developed by crossing lean female Zucker Diabetic Fatty (ZDF +/fa) and lean male Spontaneously Hypertensive Heart Failure (SHHF/Mcc-fa(cp), +/fa) rats. The purpose of the present study was to determine renal function and morphology, hemodynamics, and metabolic status in ZDFxSHHF rats. Two sets of experiments were conducted. First, we evaluated heart and kidney function and metabolic status in aged (46 weeks old) male obese ZDFxSHHF and age matched obese SHHF rats, lean Spontaneously Hypertensive (SHR) and lean normotensive Wistar Kyoto (WKY) rats. In the second set of experiments, renal function and structure as well as metabolic and lipid status were determined in lean (LN) and obese (OB) adult (29-weeks of age) ZDFxSHHF rats. At 46 weeks of age ZDFxSHHF rats are hypertensive expressing marked cardiac hypertrophy associated with diastolic dysfunction and preserved contractile function. Fasted hyperglycemia and hyperinsulinemia are accompanied by moderate hypercholesterolemia and hypertriglyceridemia. Obese aged ZDFxSHHF have marked renal hypertrophy, a 3-8 fold decrease in creatinine clearance (compared with SHHF, SHR and WKY), a high percent of segmental + global glomerulosclerosis (59.8%+/-10.8), and severe tubulointerstitial and vascular changes. Obese ZDFxSHHF rats die at an early age (approximately 12 months) from end-stage renal failure. Studies conducted in 29-week animals showed that, although both LN and OB 29-week old animals are hypertensive, OB animals have more severely compromised renal function and structure as compared with lean litter-mates (kidney weight: 2.56+/-0.16 vs. 1.61+/-0.12 g; creatinine clearance: 0.42+/-0.04 vs. 1.24+/-0.13 L/g kid/day; renal vascular resistance 12.39+/-1.4 vs. 6.14+/-0.42 mmHg/mL/min/g kid; protein excretion: 556+/-16 vs. 159+/-9mg/day/g kid, p < 0.05, OB vs. LN, respectively). Obesity is also associated with hyperglycemia (424+/-37 vs. 115+/-11 mg/dL), hyperinsulinemia (117.2+/-8.8 vs. 42.3+/-3.5 microU/mL), hypertriglyceridemia (5200+/-702 vs. 194+/-23 mg/dL), hypercholesterolemia (632+/-39 vs. 109+/-4mg/dL), and presence of segmental + global glomerulosclerosis (20.1+/-3.2% vs. 0.1+/-0.1%) with prominent tubular and interstitial changes (p < 0.05, OB vs. LN, respectively). In summary, the present study indicates that the crossing of rat strains of nephropathy produces hybrids that carry a high risk for severe renal dysfunction. The ZDFxSHHF rats express insulin resistance, hypertension, dislipidemia and obesity and develop severe renal dysfunction. In addition, the hybrids do not develop some of the complications (hydronephrosis or congestive heart failure) common for the parental strains that may compromise studies of renal function and structure. Therefore, the ZDFxSHHF rat may be a useful model fore valuating risk factors and pharmacological interventions in chronic renal failure.

A practical approach to the management of patients with chronic renal failure

The number of patients with significant chronic renal failure is expanding rapidly in the United States. All physicians and medical-care providers will have an increasingly important role in the detection and management of renal failure in patients who are not undergoing dialysis. Patients with diabetes or hypertension should be carefully monitored for the development of renal insufficiency by using screening tools such as blood pressure measurement, determination of serum creatinine, urinalysis, and determination of 24-hour urinary microalbuminuria. In order to slow the progression of renal disease, attenuate uremic complications, and prepare patients with renal failure for renal replacement therapy, all medical-care providers should "take care of the BEANS." Blood pressure should be maintained in a target range lower than 130/85 mm Hg, and in many patients, angiotensin-converting enzyme inhibitors may be beneficial. Erythropoietin should be used to maintain the hemoglobin level at 10 to 12 g/dL. Access for long-term dialysis should be created when the serum creatinine value increases above 4.0 mg/dL or the glomerular filtration rate declines below 20 mL/min. Nutritional status must be closely monitored in order to avoid protein malnutrition and to initiate dialysis before the patient's nutritional status has deteriorated. Nutritional care also involves correction of acidosis, prevention and treatment of hyperphosphatemia, and administration of vitamin supplements to provide folic acid. Specialty referral to nephrology should occur when the creatinine level increases above 3.0 mg/dL or when the involvement of a nephrologist would be beneficial for ongoing management of the patient.