Ascorbic acid ameliorates renal injury in a murine model of contrast-induced nephropathy.

BACKGROUND: Contrast induced nephropathy (CIN) is the commonest cause of iatrogenic renal injury and its incidence has increased with the advent of complex endovascular procedures. Evidence suggests that ascorbic acid (AA) has a nephroprotective effect in percutaneous coronary interventions when contrast media are used. A variety of biomarkers (NGAL, NGAL:creatinine, mononuclear cell infiltration, apoptosis and RBP-4) in both the urine and kidney were assayed using a mouse model of CIN in order to determine whether AA can reduce the incidence and/or severity of renal injury. METHODS: Twenty-four BALB/c mice were divided into 4 groups. Three groups were exposed to high doses of contrast media (omnipaque) in a well-established model of CIN, and then treated with low or high dose AA or placebo (saline). CIN severity was determined by measurement of urinary neutrophil gelatinase-associated lipocalin (NGAL):creatinine at specific time intervals. Histological analysis was performed to determine the level of mononuclear inflammatory infiltration as well as immunohistochemistry to determine apoptosis in the glomeruli by staining for activated caspase-3 and DNA nicking (TUNEL assays). Reverse transcriptase PCR (rtPCR) of mRNA transcripts prepared from mRNA extracted from mouse kidneys was also performed for both lipocalin-2 (Lcn2) encoding NGAL and retinol binding protein-6 (RBP4) genes. NGAL protein expression was also confirmed by ELISA analysis of kidney lysates. RESULTS: Urinary NGAL:creatinine ratio was significantly lower at 48 h with a 44% and 62% (204.3µg/mmol versus 533.6µg/mmol, p = 0.049) reduction in the low and high dose AA groups, respectively. The reduced urinary NGAL:creatinine ratio remained low throughout the time period assessed (up to 96 h) in the high dose AA group. In support of the urinary analysis ELISA analysis of NGAL in kidney lysates also showed a 57% reduction (12,576 ng/ml versus 29,393 ng/ml) reduction in the low dose AA group. Immunohistochemistry for apoptosis demonstrated decreased TUNEL and caspase-3 expression in both low and high dose AA groups. CONCLUSIONS: Ascorbic acid reduced the frequency and severity of renal injury in this murine model of CIN. Further work is required to establish whether AA can reduce the incidence of CIN in humans undergoing endovascular procedures.

[Effects of exercise and resveratrol on retinol binding protein 4, blood glucose and insulin sensitivity in aged obese rats].

OBJECTIVE: To explore the effects of exercise and resveratrol on retinol binding protein 4( RBP4) mRNA and protein expression in visceral adipose tissue, plasma RBP4 concentration and blood glucose and insulin sensitivity of aged obese rats. METHODS: To establish elderly obese SD rat model, 6 aged rats of natural growth were selected normal group, 24 obese rats were randomly divided into four groups: obesity control group, exercise group, resveratrol group, exercise combined with resveratrol group. For Resveratrol treatment, each rat was fed 52. 5 mg/( kg d), 5 times/week, continuous intervention for 8 weeks. After intervention, measured blood glucose, insulin sensitivity, visceral adipose tissue RBP4 mRNA expression( qRT-PCR), protein expression( Western blot) and plasma RBP4 concentration( ELISA). RESULTS: After 8week intervention, ( 1) RBP4 mRNA expression: The obesity group( 2. 63 ± 0. 45) was higher than that of the normal group( 2. 10 ± 0. 15)( P < 0. 05). The resveratrol group( 1. 84 ± 0. 33), exercise group( 1. 91 ± 0. 15), and exercise combined with resveratrol group( 2. 131 ± 0. 111) were lower than that of the obesity group( P < 0. 05, P < 0. 01). ( 2) RBP4 protein expression: The obesity group( 1. 346 ± 0. 025) was higher than that of the normal group( 1. 196 ± 0. 017)( P < 0. 01). The exercise group( 1. 025 ± 0. 006)was lower than that of the obesity group( P < 0. 01), The resveratrol group( 0. 735 ±0. 015) and exercise combined with resveratrol group( 0. 701 ± 0. 018) were lower than that of the exercise group( P < 0. 01). The exercise combined with resveratrol group was lower than that of resveratrol group( P < 0. 05). ( 3) Plasma RBP4 concentration: The obesity group [( 16. 00 ± 1. 54) µg/L]was higher than that of the normal group [( 13. 02± 2. 20) µg/L]( P < 0. 01). The exercise group [( 14. 76 ± 1. 56) µg/L] was lower than that of the obesity group, but the difference was not statistically significant. The resveratrol group [( 13. 59 ± 0. 07) µg/L]and exercise combined with resveratrol group[( 12. 98 ± 1. 69) µg/L] were lower than that of the obesity group( P < 0. 05, P <0. 01). ( 4) Blood glucose: The obesity group [( 17. 93 ± 6. 09) mmol/L]was higher than that of the normal group [( 11. 64 ± 3. 57) mmol/L ]( P < 0. 01). The exercise group [( 13. 36 ± 1. 82) mmol/L]was lower than that of the obesity group( P < 0. 05), the resveratrol group [( 15. 24 ± 2. 19) mmol/L] and exercise combined with resveratrol group [( 13. 95 ± 2. 26) mmol/L] were lower than that of the obesity group, but the difference was not statistically significant( P > 0. 05). ( 5) Insulin sensitivity: The obesity group( 0. 37 ± 0. 02) was lower than that of the normal group( 0. 39 ± 0. 02)( P < 0. 05). The resveratrol group( 0. 38 ± 0. 01) and the exercise group( 0. 39 ± 0. 02)were higher than that of the obesity group, but the difference was not statistically significant, the exercise combined with resveratrol group( 0. 39 ± 0. 15) was higher than that of the obesity group( P < 0. 05). Above indexes( except protein expression) were no significant difference between the each intervene groups( P > 0. 05). CONCLUSION: RBP4 mRNA expression and protein expression in the visceral adipose tissue of aged obese rats, plasma RBP4 concentration and blood glucose were increased, and insulin sensitivity was decreased. Exercise and resveratrol could reduce the expression of RBP4 mRNA and protein expression and plasma RBP4 concentration. The simple exercise could significantly reduce the blood glucose and exercise combined with resveratrol could significantlyimprove insulin sensitivity. The decrease in protein expression, plasma RBP4 concentration and improve insulin sensitivity, exercise combined with resveratrol showed synergy.

The effect of acitretin treatment on insulin resistance, retinol-binding protein-4, leptin, and adiponectin in psoriasis vulgaris: a noncontrolled study.

BACKGROUND/AIM: To investigate the effects of acitretin treatment on insulin resistance (IR) and adipokines, particularly retinol-binding protein (RBP)-4. METHODS: Thirty-four patients with chronic plaque psoriasis and a control group of 34 healthy volunteers were recruited in the study. Screening for the parameters was performed before starting and after 3 months of acitretin treatment in the psoriasis group. The control group was only evaluated at the beginning of the study and did not receive placebo. We could not compare our results with a placebo control group because of ethical reasons. RESULTS: Basal adiponectin (p = 0.01), insulin (p < 0.0001) levels and homeostasis model assessment (HOMA) IR (p < 0.0001) were significantly higher in psoriasis patients. After the treatment, insulin (p = 0.014), C peptide (p = 0.011), RBP-4 (p < 0.0001) levels and HOMA-IR (p = 0.008) decreased significantly. Posttreatment leptin (p = 0.036) levels were significantly lower than those of the controls. Posttreatment adiponectin (p = 0.005) and insulin (p = 0.048) levels were higher than those of the controls. CONCLUSIONS: This study showed for the first time that RBP-4 levels and IR are decreased significantly with acitretin treatment. This finding is very important in psoriasis patients because psoriasis may cause insulin resistance and diabetes. Further experimental and clinical studies are needed to clarify the effect of acitretin on adipocyte structure and behavior.

Effects of 1-year orlistat treatment compared to placebo on insulin resistance parameters in patients with type 2 diabetes.

WHAT IS KNOWN AND OBJECTIVE: The behavioural approach is usually slow and not always sufficient to achieve optimal targets in weight and metabolic control in obese diabetic patients, and a pharmacological treatment is often necessary. The aim of this study was to compare the effects of orlistat and placebo on body weight, glycaemic and lipid profile and insulin resistance in patients with type 2 diabetes. METHODS: Two hundred and fifty-four obese, diabetic patients were enrolled in this study and randomized to take orlistat 360mg or placebo for 1year. We evaluated at baseline and after 3, 6, 9 and 12months body weight, waist circumference (WC), body mass index (BMI), glycated haemoglobin (HbA(1c) ), fasting plasma glucose (FPG), post-prandial plasma glucose (PPG), fasting plasma insulin (FPI), homeostasis model assessment insulin resistance index (HOMA-IR), lipid profile, retinol-binding protein-4 (RBP-4), resistin, visfatin and high-sensitivity C-reactive protein (Hs-CRP). RESULTS AND DISCUSSION: We observed a significant reduction in body weight, WC, BMI, lipid profile, RBP-4 and visfatin in the orlistat group but not in control group. Faster improvements in HbA(1c) , PPG, FPI, HOMA-IR, resistin and Hs-CRP were recorded with orlistat than with placebo. A similar decrease in FPG was seen in the two groups. Significant predictors of change in insulin resistance (HOMA-IR) were RBP-4 and resistin concentration in the orlistat group (r=-0·53, P<0·05, and r=-0·59, P<0·01, respectively). WHAT IS NEW AND CONCLUSION: To the best of our knowledge, this is the first study investigating the effect of orlistat on insulin resistance and markers of inflammation. Orlistat improved lipid profile and led to faster glycaemic control and insulin resistance parameters than the control, without any serious adverse event. Orlistat also improved RBP-4 and visfatin, effects not observed with placebo.

Changes in insulin resistance and cardiovascular risk induced by PPARgamma activation have no impact on RBP4 plasma concentrations in nondiabetic patients.

Retinol binding protein 4 (RBP4) has recently been suggested as a good biomarker for insulin resistance and the metabolic syndrome. With this study, we wanted to investigate the effect of pioglitazone (PIO) and simvastatin (SIMVA) on insulin resistance and RBP4 plasma concentrations in nondiabetic patients with metabolic syndrome and increased risk for cardiovascular complications. The prospective, parallel, randomized, double-blind clinical trial was performed with 125 nondiabetic patients with increased cardiovascular risk (78 females, 47 males, age (mean+/-STD): 58.6+/-7.8 years, BMI: 30.8+/-4.2 kg/m (2)). They were randomized to either receive PIO (45 mg)+placebo, SIMVA (40 mg)+placebo, or PIO+SIMVA for 3 months. Key outcome measures were the HOMA (IR)-Score, an oral glucose tolerance test, adiponectin, hsCRP, and RBP4 at baseline and endpoint. No correlation could be detected between the HOMA (IR) values or the impaired fasting glucose tolerance status and RBP-4. Treatment with PIO alone or in combination with SIMVA resulted in a significant improvement of the HOMA (IR)-Score and the adiponectin values, while no change in HOMA (IR) and a decrease in adiponectin (p<0.05) were observed with SIMVA monotherapy. Reductions of hsCRP were seen in all three treatment arms (p<0.001). No changes of the plasma RBP4 concentrations were observed in any of the treatment groups (PIO: 35.6+/-7.2/36.3+/-8.7 ng/ml, PIO+SIMVA: 36.5+/-10.8/36.5+/-8 ng/ml, SIMVA: 36.1+/-8.1/36.6+/-11.1 ng/ml, all n.s. vs. baseline). Despite a partial or comprehensive improvement in insulin resistance and/or cardiovascular risk indicators in all treatment arms, no change in RBP4-levels could be observed. The regulation of RBP4 expression and secretion occurs through biochemical pathways independent from those influenced by pioglitazone or simvastatin.

Retinol-binding protein 4 in polycystic ovary syndrome--association with steroid hormones and response to pioglitazone treatment.

CONTEXT: Polycystic ovary syndrome (PCOS) is frequently associated with insulin resistance. OBJECTIVE: The aim of the study was to investigate a putative role of the adipokines retinol-binding protein 4 (RBP4), adiponectin, and visfatin in a cohort of patients with PCOS and their response to treatment with pioglitazone. DESIGN AND SETTING: We conducted a randomized, controlled, double-blind study at a tertiary referral center. PATIENTS AND INTERVENTIONS: Forty premenopausal women with PCOS were allocated to receive treatment with either pioglitazone (30 mg/d) or a placebo for a period of 3 months. MAIN OUTCOME MEASURES: Serum concentrations of RBP4, adiponectin, and visfatin were determined along with metabolic and hormonal parameters before and after treatment. RESULTS: Serum adiponectin concentrations were higher after treatment with pioglitazone (P = 0.003), whereas RBP4 levels tended to decrease (P = 0.06), and visfatin concentrations remained unchanged. We found RBP4 serum concentrations at baseline to be positively correlated with serum levels of testosterone (R = 0.446; P = 0.005), 17-OH progesterone (R = 0.345, P = 0.037), and dehydroepiandrosterone sulfate (R = 0.347; P = 0.041). However, these correlations were abolished after treatment with pioglitazone. Patients with high RBP4 levels had significantly higher hirsutism scores (P = 0.038 before and P = 0.034 after treatment). In contrast, serum adiponectin concentrations were related to parameters of impaired glucose metabolism, and no significant associations were detected for visfatin. CONCLUSIONS: Our results suggest that RBP4 may contribute to endocrine changes and to the phenotypic manifestation of patients with PCOS because higher RBP4 concentrations are associated with higher androgen levels and higher clinical hirsutism scores independently of pioglitazone treatment. The molecular involvement of RBP4 in human steroid metabolism requires further clarification.

Effects of trans10cis12CLA-induced insulin resistance on retinol-binding protein 4 concentrations in abdominally obese men.

In this randomized, placebo-controlled, double-blind study of 57 abdominally obese middle-aged men, conjugated linoleic acid (CLA) did not induce changes in retinol-binding protein 4 concentrations (RBP4), despite marked induced insulin resistance. Further, there were no associations between CLA-induced insulin resistance and changes in RBP4.

Circulating retinol-binding protein-4 concentration might reflect insulin resistance-associated iron overload.

OBJECTIVES: The mechanisms behind the association between retinol-binding protein-4 (RBP4) and insulin resistance are not well understood. An interaction between iron and vitamin A status, of which RBP4 is a surrogate, has long been recognized. We hypothesized that iron-associated insulin resistance could be behind the impaired insulin action caused by RBP4. RESEARCH DESIGN AND METHODS: Serum ferritin and RBP4 concentration and insulin resistance were evaluated in a sample of middle-aged men (n = 132) and in a replication independent study. Serum RBP4 was also studied before and after iron depletion in patients with type 2 diabetes. Finally, the effect of iron on RBP4 release was evaluated in vitro in adipose tissue. RESULTS: A positive correlation between circulating RBP4 and log serum ferritin (r = 0.35 and r = 0.61, respectively; P < 0.0001) was observed in both independent studies. Serum RBP4 concentration was higher in men than women in parallel to increased ferritin levels. On multiple regression analyses to predict serum RBP4, log serum ferritin contributed significantly to RBP4 variance after controlling for BMI, age, and homeostasis model assessment value. Serum RBP4 concentration decreased after iron depletion in type 2 diabetic patients (percent mean difference -13.7 [95% CI -25.4 to -2.04]; P = 0.024). The iron donor lactoferrin led to increased dose-dependent adipose tissue release of RBP4 (2.4-fold, P = 0.005) and increased RBP4 expression, while apotransferrin and deferoxamine led to decreased RBP4 release. CONCLUSIONS: The relationship between circulating RBP4 and iron stores, both cross-sectional and after iron depletion, and in vitro findings suggest that iron could play a role in the RBP4-insulin resistance relationship.