Retinol-binding protein 4 and insulin resistance in polycystic ovary syndrome

Metformin and Combined Oral Contraceptive Pills in the Management of Polycystic Ovary Syndrome: A Systematic Review and Meta-analysis

CONTEXT

Polycystic ovary syndrome (PCOS) affects more than 1 in 10 women.

OBJECTIVE

As part of the 2023 International PCOS Guidelines update, comparisons between combined oral contraceptive pills (COCP), metformin, and combination treatment were evaluated.

DATA SOURCES

Ovid Medline, Embase, PsycINFO, All EBM, and CINAHL were searched.

STUDY SELECTION

Women with PCOS included in randomized controlled trials (RCTs).

DATA EXTRACTION

We calculated mean differences and 95% CIs regarding anthropometrics, metabolic, and hyperandrogenic outcomes. Meta-analyses and quality assessment using GRADE were performed.

DATA SYNTHESIS

The search identified 1660 publications; 36 RCTs were included. For hirsutism, no differences were seen when comparing metformin vs COCP, nor when comparing COCP vs combination treatment with metformin and COCP. Metformin was inferior on free androgen index (FAI) (7.08; 95% CI 4.81, 9.36), sex hormone binding globulin (SHBG) (-118.61 nmol/L; 95% CI -174.46, -62.75) and testosterone (0.48 nmol/L; 95% CI 0.32, 0.64) compared with COCP. COCP was inferior for FAI (0.58; 95% CI 0.36, 0.80) and SHBG (-16.61 nmol/L; 95% CI -28.51, -4.71) compared with combination treatment, whereas testosterone did not differ. Metformin lowered insulin (-27.12 pmol/L; 95% CI -40.65, -13.59) and triglycerides (-0.15 mmol/L; 95% CI -0.29, -0.01) compared with COCP. COCP was inferior for insulin (17.03 pmol/L; 95% CI 7.79, 26.26) and insulin resistance (0.44; 95% CI 0.17, 0.70) compared with combination treatment.

CONCLUSIONS

The choice of metformin or COCP treatment should be based on symptoms, noting some biochemical benefits from combination treatment targeting both major endocrine disturbances seen in PCOS (hyperinsulinemia and hyperandrogenism).

Serum fat-soluble vitamins and the menstrual cycle in women of childbearing age

Evidence suggests that fat-soluble vitamins are involved in reproduction, but their association with the menstrual cycle, the proxy of female fecundity, remains largely unexplored in women of childbearing age. Serum fat-soluble vitamin levels were measured by HPLC-MS/MS and menstrual cycle data were acquired from 3123 women of reproductive age in Nanjing, China, using standard questionnaires. Irregular and long menstrual cycles occurred in 725 (23.2%) and 604 (19.3%) participants, respectively. Participants with higher levels of vitamins A and K had increased odds of irregular menstrual cycles (vitamin A: OR = 1.39 (95% CI: 1.12, 1.74); vitamin K: OR = 1.41 (95% CI: 1.13, 1.76)) and long menstrual cycles (vitamin A: OR = 1.34 (95% CI: 1.06, 1.69); vitamin K: OR = 1.27 (95% CI: 1.00, 1.61)), and the relationship showed a linear dose-response pattern (P-overall < 0.05, P-nonlinearity > 0.05). Vitamin A was positively associated with the average menstrual cycle length (β: 1.83, 95% CI: 0.28, 3.39). Vitamins A and K were interacted in their associations with irregular menstrual cycles and long cycles. In sensitivity analysis with further exclusion of participants with abnormal thyroid function or a history of polycystic ovary syndrome (PCOS), the association of vitamins A and K with the menstrual cycle remained robust. This study indicates that higher serum vitamin A and K levels in women of childbearing age are significantly associated with higher odds of irregular and long menstrual cycles with a linear dose-response curve. Further investigations are warranted to determine the appropriate fat-soluble vitamin levels for women of childbearing age.

Vitamin A homeostasis and cardiometabolic disease in humans: lost in translation?

Vitamin A (retinol) is an essential, fat-soluble vitamin that plays critical roles in embryonic development, vision, immunity, and reproduction. Severe vitamin A deficiency results in profound embryonic dysgenesis, blindness, and infertility. The roles of bioactive vitamin A metabolites in regulating cell proliferation, cellular differentiation, and immune cell function form the basis of their clinical use in the treatment of dermatologic conditions and hematologic malignancies. Increasingly, vitamin A also has been recognized to play important roles in cardiometabolic health, including the regulation of adipogenesis, energy partitioning, and lipoprotein metabolism. While these roles are strongly supported by animal and in vitro studies, they remain poorly understood in human physiology and disease. This review briefly introduces vitamin A biology and presents the key preclinical data that have generated interest in vitamin A as a mediator of cardiometabolic health. The review also summarizes clinical studies performed to date, highlighting the limitations of many of these studies and the ongoing controversies in the field. Finally, additional perspectives are suggested that may help position vitamin A metabolism within a broader biological context and thereby contribute to enhanced understanding of vitamin A's complex roles in clinical cardiometabolic disease.

Retinol-binding protein-4 and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is becoming increasingly common as the global economy grows and living standards improve. Timely and effective preventions and treatments for NAFLD are urgently needed. Retinol-binding protein-4 (RBP4), the protein that transports retinol through the circulation, was found to be positively related to diabetes, obesity, cardiovascular disease, and other metabolic diseases. Observational studies on the association between serum RBP4 level and the prevalence of NAFLD found contradictory results. Some of the underlying mechanisms responsible for this association have been revealed, and the possible clinical implications of treating NAFLD by targeting RBP4 have been demonstrated. Future studies should focus on the predictive value of RBP4 on NAFLD development and its potential as a therapeutic target in NAFLD.

Intestinal Flora is a Key Factor in Insulin Resistance and Contributes to the Development of Polycystic Ovary Syndrome

CONTEXT

The key gut microbial biomarkers for polycystic ovarian syndrome (PCOS) and how dysbiosis causes insulin resistance and PCOS remain unclear.

OBJECTIVE

To assess the characteristics of intestinal flora in PCOS and explore whether abnormal intestinal flora can affect insulin resistance and promote PCOS and whether chenodeoxycholic acid (CDCA) can activate intestinal farnesoid X receptor (FXR), improving glucose metabolism in PCOS.

SETTING AND DESIGN

The intestinal flora of treatment-naïve PCOS patients and hormonally healthy controls was analyzed. Phenotype analysis, intestinal flora analysis, and global metabolomic profiling of caecal contents were performed on a letrozole-induced PCOS mouse model; similar analyses were conducted after 35 days of antibiotic treatment on the PCOS mouse model, and glucose tolerance testing was performed on the PCOS mouse model after a 35-day CDCA treatment. Mice receiving fecal microbiota transplants from PCOS patients or healthy controls were evaluated after 10 weeks.

RESULTS

Bacteroides was significantly enriched in treatment-naïve PCOS patients. The enrichment in Bacteroides was reproduced in the PCOS mouse model. Gut microbiota removal ameliorated the PCOS phenotype and insulin resistance and increased relative FXR mRNA levels in the ileum and serum fibroblast growth factor 15 levels. PCOS stool-transplanted mice exhibited insulin resistance at 10 weeks but not PCOS. Treating the PCOS mouse model with CDCA improved glucose metabolism.

CONCLUSIONS

Bacteroides is a key microbial biomarker in PCOS and shows diagnostic value. Gut dysbiosis can cause insulin resistance. FXR activation might play a beneficial rather than detrimental role in glucose metabolism in PCOS.

The comparative effectiveness of 55 interventions in obese patients with polycystic ovary syndrome: A network meta-analysis of 101 randomized trials

BACKGROUND

Polycystic ovary syndrome (PCOS) affects up to 18% of reproductive-age females. The prevalence of obesity in PCOS patients reaches up to 80%, which is 2-fold higher than the general population.

OBJECTIVE

The present study aimed to compare the effectiveness of 55 pharmacological interventions across 17 different outcomes in overweight/obese PCOS patients with hyperandrogenism manifestations for both short- and long-term follow-ups. A comprehensive literature search was performed on PubMed, Scopus, Embase, Science Direct, Web of Science, and Cochrane CENTRAL for randomized controlled trials comparing any conventional pharmacological intervention as a monotherapy or a combination in overweight/obese patients with polycystic ovary syndrome and hyperandrogenism manifestations. Extracted data included three main parameters; I. Anthropometric parameters (BMI, Waist and Hip circumferences, and Waist/HIP ratio), II. Hormonal parameters (FSH, LH, FSG, SHBG, Estradiol, Total Testosterone, Free testosterone, DHEAS, Androstenedione), and III. Metabolic parameters (Total Cholesterol, LDL-C, HDL-C, Triglycerides, Fasting glucose, Fasting glucose, HOMA-IR). Critical appraisal and risk of bias assessments were performed using the modified Jadad scale, and the overall quality of this network meta-analysis was evaluated according to the CINeMA framework. We performed both a pairwise meta-analysis and a network meta-analysis to evaluate the effect sizes with 95% CI, and we calculated the surface under the cumulative ranking curve (SUCRA) for each intervention.

RESULTS

Our final search on May 15th 2021 retrieved 23,305 unique citations from searching six electronic databases. Eventually, 101 RCTs of 108 reports with a total of 8,765 patients were included in our systematic review and multi-treatments meta-analysis. 55 different interventions were included: 22 monotherapies, and 33 combinations. The two-dimensional cluster ranking of the average SUCRA values for metabolic and hormonal parameters with significant estimates revealed flutamide (77.5%, 70%; respectively) as the highest and rosiglitazone (38.2%, 26.3%; respectively) as the lowest, in terms of the overall efficacy in reducing weight and hyperandrogenism. However, cyproterone-acetate+ethinylestradiol exhibited a higher ranking in improving hormonal parameters (71.1%), but even a lower-ranking regarding metabolic parameters (34.5%).

CONCLUSIONS AND RELEVANCE

Current evidence demonstrated the superiority of flutamide in improving both metabolic and hormonal parameters, and the higher efficacy of cyproterone-acetate+ethinylestradiol only in improving hormonal parameters. Nearly all interventions were comparable in female hormones, FGS, HDL, glucose, and insulin levels improvements.

Effects of oral contraceptives on metabolic parameters in adult premenopausal women: a meta-analysis

OBJECTIVE

To estimate the effect of oral contraceptives (OC) containing different progestins on parameters of lipid and carbohydrate metabolism through a systematic review and meta-analysis.

PATIENTS AND METHODS

Premenopausal women aged 18 or older, who received oral contraceptives containing chlormadinone, cyproterone, drospirenone, levonorgestrel, desogestrel, dienogest, gestodene or norgestimate, for at least 3 months. Outcome variables were changes in plasma lipids, BMI, insulin resistance and plasma glucose. We searched MEDLINE and EMBASE for randomized trials and estimated the pooled within-group change in each outcome variable using a random-effects model. We performed subgroup analyses by study duration (<12 months vs ≥12 months) and polycystic ovary syndrome (PCOS) status.

RESULTS

Eighty-two clinical trials fulfilled the inclusion criteria. All progestins (except dienogest) increased plasma TG, ranging from 12.1 mg/dL for levonorgestrel (P < 0.001) to 35.1 mg/dL for chlormadinone (P < 0.001). Most progestins also increased HDLc, with the largest effect observed for chlormadinone (+9.6 mg/dL, P < 0.001) and drospirenone (+7.4 mg/dL, P < 0.001). Meanwhile, levonorgestrel decreased HDLc by 4.4 mg/dL (P < 0.001). Levonorgestrel (+6.8 mg/dL, P < 0.001) and norgestimate (+11.5 mg/dL, P = 0.003) increased LDLc, while dienogest decreased it (-7.7 mg/dL, P = 0.04). Cyproterone slightly reduced plasma glucose. None of the progestins affected BMI or HOMA-IR. Similar results were observed in subgroups defined by PCOS or study duration.

CONCLUSION

Most progestins increase both TG and HDLc, their effect on LDLc varies widely. OC have minor or no effects on BMI, HOMA-IR and glycemia. The antiandrogen progestins dienogest and cyproterone displayed the most favorable metabolic profile, while levonorgestrel displayed the least favorable.

Metformin versus the combined oral contraceptive pill for hirsutism, acne, and menstrual pattern in polycystic ovary syndrome

BACKGROUND

Metformin has been proposed as possibly a safer and more effective long-term treatment than the oral contraceptive pill (OCP) in women with polycystic ovary syndrome (PCOS). It is important to directly compare the efficacy and safety of metformin versus OCP in the long-term treatment of women with PCOS. This is an update of a Cochrane Review comparing insulin sensitising agents with the OCP and only includes studies on metformin.

OBJECTIVES

To assess the effectiveness and safety of metformin versus the OCP (alone or in combination) in improving clinical, hormonal, and metabolic features of PCOS.

SEARCH METHODS

In August 2019 we searched the Cochrane Gynaecology and Fertility Group Trials Register, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase and CINAHL, the trial registers, handsearched references of the identified articles, and contacted experts in the field to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of the use of metformin versus the OCP (alone or in combination) for women with PCOS.

DATA COLLECTION AND ANALYSIS

We used standard methods recommended by Cochrane. The primary review outcomes were the clinical parameters of hirsutism and adverse events, both severe (requiring stopping of medication), and minor. In the presence of substantial heterogeneity (I² statistic > 50), which could be explained by pre-specified subgroup analyses on the basis of BMI, we reported the subgroups separately.

MAIN RESULTS

This is a substantive update. We identified 38 additional studies. We included 44 RCTs (2253 women), which comprised 39 RCTs on adult women (2047 women) and five RCTs on adolescent women (206 women). Evidence quality ranged from very low to low. The main limitations were risk of bias, imprecision and inconsistency. Metformin versus the OCP In adult women, we are uncertain of the effect of metformin compared to the OCP on hirsutism in subgroup body mass index (BMI) < 25 kg/m² (mean difference (MD) 0.38, 95% confidence interval (CI) -0.44 to 1.19, 3 RCTs, n = 134, I² = 50%, very low-quality evidence) and subgroup BMI > 30 kg/m² (MD -0.38, 95% CI -1.93 to 1.17; 2 RCTs, n = 85, I² = 34%, low-quality evidence). Metformin may be less effective in improving hirsutism compared to the OCP in the subgroup BMI 25 kg/m² to 30 kg/m² (MD 1.92, 95% CI 1.21 to 2.64, 5 RCTs, n = 254, I² = 0%, low-quality evidence). Metformin may increase severe gastro-intestinal adverse events rate compared to the OCP (Peto odds ratio (OR) 6.42, 95% CI 2.98 to 13.84, 11 RCTs, n = 602, I² = 0%, low-quality evidence). Metformin may decrease the incidence of severe other adverse events compared to the OCP (Peto OR 0.20, 95% CI 0.09 to 0.44, 8 RCTs, n = 363, I² = 0%, low-quality evidence). There were no trials reporting on minor adverse events. In adolescents, we are uncertain whether there is a difference between Metformin and the OCP, on hirsutism and adverse events. Metformin versus metformin combined with the OCP In adult women, metformin may be less effective in improving hirsutism compared to Metformin combined with the OCP (MD 1.36, 95% CI 0.62 to 2.11, 3 RCTs, n = 135, I²= 9%, low-quality evidence). We are uncertain if there was a difference between metformin and metformin combined with the OCP for severe gastro-intestinal adverse events (OR 0.74, 95% CI 0.21 to 2.53, 3 RCTs, n = 171, I² = 0%, low-quality evidence), or for severe other adverse events (OR 0.56, 95% CI 0.11 to 2.82, 2 RCTs, n = 109, I² = 44%, low-quality evidence). There were no trials reporting on minor adverse events. In adolescents, there were no trials for this comparison. The OCP versus metformin combined with the OCP In adult women, the OCP may be less effective in improving hirsutism compared to metformin combined with the OCP (MD 0.54, 95% CI 0.20 to 0.89, 6 RCTs, n = 389, I²= 1%, low-quality evidence). The OCP may decrease the incidence of severe gastro-intestinal adverse events compared to metformin combined with the OCP (OR 0.20, 95% CI 0.06 to 0.72, 5 RCTs, n = 228, I² = 0%, low-quality evidence). We are uncertain if there is a difference between the OCP and metformin combined with the OCP for severe other adverse events (OR 1.61, 95% CI 0.49 to 5.37, 4 RCTs, n = 159, I² = 12%, low-quality evidence). The OCP may decrease the incidence of minor (gastro-intestinal) adverse events compared to metformin combined with the OCP (OR 0.06, 95% CI 0.01 to 0.44, 2 RCTs, n = 98, I² = 0%, low-quality evidence). In adolescents, we are uncertain whether there is a difference between the OCP, compared to metformin combined with the OCP, on hirsutism or adverse events.

AUTHORS' CONCLUSIONS

In adult women with PCOS, metformin may be less effective in improving hirsutism compared to the OCP in the subgroup BMI 25 kg/m² to 30 kg/m² but we are uncertain if there was a difference between metformin and the OCP in subgroups BMI < 25 kg/m² and BMI > 30kg/m². Compared to the OCP, metformin may increase the incidence of severe gastro-intestinal adverse events and decrease the incidence of severe other adverse events with no trials reporting on minor adverse events. Either metformin alone or the OCP alone may be less effective in improving hirsutism compared to metformin combined with the OCP. We are uncertain whether there is a difference between the OCP alone and metformin alone compared to metformin combined with the OCP for severe or minor adverse events except for the OCP versus metformin combined with the OCP where the OCP may decrease the incidence of severe and minor gastro-intestinal adverse events. In adolescent women with PCOS, we are uncertain whether there is a difference between any of the comparisons for hirsutism and adverse events due to either no evidence or very low-quality evidence. Further large well-designed RCTs that stratify for BMI are needed to evaluate metformin versus the OCP and combinations in women with PCOS, in particular adolescent women.

Retinol, Retinoic Acid, and Retinol-Binding Protein 4 are Differentially Associated with Cardiovascular Disease, Type 2 Diabetes, and Obesity: An Overview of Human Studies

Vitamin A is a fat-soluble essential nutrient obtained from plant- and animal-based sources that has roles in growth, vision, and metabolism. Vitamin A circulates mainly as retinol bound to retinol-binding protein 4 (RBP4), and is delivered to tissues and converted to retinoic acid, which is a ligand for several nuclear receptors. In recent years, aspects of vitamin A metabolism have been under scrutiny with regards to the development of metabolic and lifestyle diseases including cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), and overweight and obesity in humans. Studies have mainly focused on RBP4 in this context, whereas the major circulating form, retinol, and the major bioactive form, retinoic acid, have been overlooked in this regard until recently. As one of the main roles of RBP4 is to deliver retinol to tissues for biological action, the associations of retinol and retinoic acid with these diseases must also be considered. In this review, we summarize and discuss recent and available evidence from human studies with focus on retinol, retinoic acid, and RBP4 and provide an overview of these crucial components of vitamin A metabolism in CVD, T2DM, and obesity. In summary, retinol was found to be both inversely and positively associated with CVD whereas the associations with T2DM and obesity were less clear. Although only a few studies have been published on retinoic acid, it was inversely associated with CVD. In contrast, serum RBP4 was mostly found to be positively associated with CVD, T2DM, and obesity. At present, it is difficult to ascertain why the reported associations differ depending on the compound under study, but there is a clear imbalance in the literature in disfavor of retinol and retinoic acid, which needs to be considered in future human studies.

Berberine chloride ameliorated PI3K/Akt-p/SIRT-1/PTEN signaling pathway in insulin resistance syndrome induced in rats

The liver is the main organ involved in lipid metabolism process and it helps in drug detoxification. Insulin resistance is considered one of risk reasons which lead to several metabolic diseases. Currently, berberine (BER) occupies a huge challenge against multiple diseases with no toxic effect. The present work was aimed to identify, does BER-chloride has a poisonous influence on the liver? and investigating the outcome of BER-chloride on PI3K/Akt-p/SIRT-1/PTEN pathway during insulin resistance syndrome. The insulin resistance model was achieved in experimental female rats via high-fat diet (HFD). Glucose, insulin, lipid profiles, and hepatic oxidative stress parameters were assessed. PI3K, AKt-p, SIRT-1, and PTEN levels in hepatic tissue were determined at genome and protein levels. Further adiponectin concentration was performed in serum, hepatic, and white adipose tissues. Molecular study of fold alteration in insulin, insulin receptor, and retinol binding protein-4 (RBP4) in liver was done. PRACTICAL APPLICATIONS: Obesity syndrome causes multiple obstacles in modern years. The current results revealed elevation the body weight of rats, plasma glucose, homeostatic model assessment, glycated hemoglobin, insulin, and lipid profiles concentrations in a group of rats, which nourished HFD for 8 weeks and this rise, was diminished after 2 weeks from BER-chloride administration. Further, BER-chloride improved transaminases enzymes, pro-oxidant, and antioxidant defense system, PI3K, AKt-p, SIRT-1, and PTEN in the liver, with downregulation of hepatic RBP4. Hence, these data provide a crucial message that BER-chloride enhanced both hepatic function and insulin signaling pathways that might be of therapeutic importance to insulin resistance with no harmful effect on the liver. BER-chloride is predicted to be a drug of choice for obesity complications cure.

Serum retinol-binding protein 4 levels in polycystic ovary syndrome

OBJECTIVE

Serum levels of retinol-binding protein 4 (RBP4), an adipokine thought to affect systemic insulin sensitivity, were compared between women with polycystic ovary syndrome (PCOS) and non-PCOS controls to evaluate the association of RBP4 with clinical, hormonal and metabolic parameters of PCOS.

SUBJECTS AND METHODS

Serum RBP4 levels were analysed in 278 women with PCOS (age range 18-57 years) and 191 non-PCOS controls (age 20-53 years) by enzyme-linked immunosorbent assay.

RESULTS

Serum levels of RBP4 were increased in women with PCOS compared with control women in the whole population (45.1 ± 24.0 (s.d.) vs 33.5 ± 18.3 mg/L, P < 0.001). Age-stratified analysis showed that serum RBP4 levels were increased in women with PCOS aged ≤30 years compared with controls (47.7 ± 23.5 vs 27.1 ± 10.4 mg/L, P < 0.001), whereas no significant differences were seen in the other age groups. No significant correlations of RBP4 were seen with either steroids or indices of insulin resistance.

CONCLUSIONS

Although serum RBP4 levels were increased in younger women with PCOS compared with age-matched non-PCOS controls, RBP4 does not seem to be a good marker of insulin resistance or other metabolic derangements in women with PCOS.

The effectiveness of metformin, oral contraceptives, and lifestyle modification in improving the metabolism of overweight women with polycystic ovary syndrome: a network meta-analysis

PURPOSE

We designed a network meta-analysis that investigated relatively different interventions that included the effects of metformin, oral contraceptives, and lifestyle modification on the metabolic parameters of patients with polycystic ovary syndrome. In addition, we searched for eligible interventions that improved the metabolism of glucose and lipids.

METHODS

We searched the PubMed, EMBASE, and Cochrane Central databases from inception to May 2018. Publication types that were categorized as randomized controlled trials met our inclusion criteria. The main outcome included the homeostasis model assessment of insulin resistance, total cholesterol, low-density lipoprotein cholesterol, and total triglycerides. We performed both a pairwise meta-analysis and a network meta-analysis to evaluate the mean difference value and 95% credibility intervals, and we calculated the surface cumulative rank curve.

RESULTS

There were a total of 12 kinds of interventions: metformin, 2 mg cyproterone acetate plus 0.05 mg ethinylestradiol (EE/CA), 0.15 mg desogestrel plus 0.03 mg ethinylestradiol (EE/DSG), and 3 mg drospirenone plus 0.03 mg ethinylestradiol (EE/DRSP), lifestyle, exercise, diet, metformin + lifestyle, metformin + diet, EE/CA + lifestyle, metformin + EE/CA, and EE/DRSP + lifestyle from the 20 eligible RCTs that were included in this study. Our meta-analysis results showed that metformin + lifestyle (MD = -2.04, 95% CrI = -3.64 to -0.41), EE/CA + lifestyle (MD = -2.23, 95% CrI = -4.11 to -0.35), and EE/DRSP + lifestyle (MD = -2.59, 95% CrI = -4.66 to -0.50) resulted in lower in the levels of total cholesterol. Women treated with metformin + lifestyle (MD = -1.82, 95% CrI = -2.88 to -0.79), EE/CA + lifestyle (MD = -2.25, 95% CrI = -3.58 to -1.08), or EE/DRSP + lifestyle (MD = -2.29, 95% CrI = -3.69 to -1.07) exhibited significantly lower low-density lipoprotein cholesterol when compared with the placebo group. There was no significant difference between any of the interventions compared with a placebo in the levels of homeostasis model assessment of insulin resistance and total triglycerides. The surface cumulative rank curve revealed that metformin + lifestyle might be the best intervention with respect to the improvement of the homeostasis model of assessment insulin resistance and EE/DRSP + lifestyle appeared to be the best intervention for the reduction of total cholesterol and low-density lipoprotein cholesterol. Moreover, the metformin + diet intervention was more effective in reducing the level of total triglycerides.

CONCLUSIONS

For overweight polycystic ovary syndrome patients, our evidence revealed that EE/CA and EE/SRSP combined with metformin or lifestyle changes can reduce the adverse effects on glucose and lipid metabolism of the use of oral contraceptive agents alone. Conventional PCOS treatments, such as metformin, EE/CA, and EE/DRSP, combined with lifestyle control can be particularly effective in improving the homeostasis model assessment of insulin resistance and lipid metabolism.

The effect of moderate endurance training on gastrocnemius retinol-binding protein 4 and insulin resistance in streptozotocin-induced diabetic rats

Background

Retinol-binding protein 4 (RBP4) is suggested to be involved in the occurrence of insulin resistance. There are contradictory studies about the effects of exercise training on RBP4 levels and insulin resistance. Hence, we designed this study to investigate the impact of moderate endurance training on gastrocnemius RBP4 and insulin resistance in streptozotocin (STZ)-induced diabetic rats.

Method

Forty male albino Wistar rats were randomly divided into four groups: healthy control (HC), diabetic control (DC), healthy training (HT), and diabetic training (DT). Animals in HT and DT groups ran on a treadmill on the basis of overload principle for 6 weeks, three sessions per week. Rats in DC and DT groups are affected by diabetes using STZ (50 mg/kg of body weight). Gastrocnemius RBP4 content was measured using an enzyme-linked immunosorbent assay kit. Data were analyzed by one-way analysis of variance at P < 0.05 level.

Results

Serum blood glucose level (P = 0.001) and insulin resistance (P = 0.001) increased in DC compared with HC group, whereas serum insulin (P = 0.001) and gastrocnemius RBP4 (P = 0.001) reduced. However, there were no significant differences between serum blood glucose level (P = 0.384), insulin resistance (P = 0.999), and RBP4 (P = 0.999) content in DT compared with HT group.

Conclusion

Moderate endurance training reduces blood glucose level and subsequently improves insulin sensitivity by decreasing gastrocnemius RBP4 content independent of insulin.

Combined oral contraceptives and/or antiandrogens versus insulin sensitizers for polycystic ovary syndrome: a systematic review and meta-analysis

BACKGROUND

Androgen excess is a key pathogenetic mechanism in polycystic ovary syndrome (PCOS), although hyperinsulinism also contributes to androgen secretion. Therapeutic approaches for adult patients not seeking fertility include combined oral contraceptives (COC), antiandrogens (AA) and/or insulin sensitizers, although these practices are supported by limited high-quality evidence.

OBJECTIVE AND RATIONALE

We aimed to assess the efficacy and safety of these common treatments for PCOS by conducting a meta-analysis of RCTs with the following review questions: Which is the more appropriate therapeutic approach for hyperandrogenic symptoms, hyperandrogenemia, and ovulatory dysfunction in adult women with PCOS not seeking fertility; What is the impact on classic cardiometabolic risk factors of the more common treatments used in those women; Does the combination of the antiandrogenic therapy plus metformin have any impact on efficacy or cardiometabolic profile?

SEARCH METHODS

We searched PubMed and EMBASE for articles published up to 16 September 2017. After deleting duplicates, the abstracts of 1522 articles were analysed. We subsequently excluded 1446 articles leaving 76 studies for full-text assessment of eligibility. Of them, 43 articles were excluded. Hence, 33 studies and 1521 women were included in the quantitative synthesis and in the meta-analyses. Meta-analyses calculated mean differences (MD), standardized mean differences (SMD), odds ratio (OR) and 95% CIs. Heterogeneity and inconsistency across studies was assessed by χ2 test and Higgins's I2 statistics. Quality and risk of bias of individual studies were assessed according to the Cochrane Handbook for Systematic Reviews of Interventions 5.1.0. We then used the approach recommended by the Grading of Recommendations, Assessments, Development, and Evaluation (GRADE) group to indicate the global quality of evidence for a selection of primary outcomes.

OUTCOMES

Regarding efficacy, the MD in hirsutism score between COC and/or AA and metformin were not significant. The exclusion of one single study including most women with severe hirsutism yielded a significant effect in favour of COC and/or AA. When only those studies including an AA were compared with metformin, there were significant differences favouring antiandrogenic therapy. The combination of COC and/or AA with metformin was similar to COC and/or AA therapy alone in the whole group of patients. Post-intervention OR for the presence of regular menses favoured COC therapy. In terms of cardiometabolic impact, the MD in BMI were in favour of metformin. The negative effect of COC therapy on BMI was blunted by its combination with metformin. The MD in homoeostasis model assessment of insulin resistance (HOMA-IR) were also in favour of metformin therapy compared to COC and/or AA. The combination of COC and/or AA and metformin decreased MD in HOMA with respect to antiandrogenic therapy alone. There were no significant post-intervention SMD in circulating glucose levels between COC and/or AA and metformin. However, adding metformin to COC and/or AA yielded a beneficial effect on fasting glucose levels. Post-intervention OR for abnormal glucose tolerance showed no significant differences between COC and/or AA and metformin, although after excluding studies including an AA as a comparator (without COC) a significant effect in favour of metformin therapy was observed. There were no significant differences among therapies in lipid profile, blood pressure or prevalence of hypertension. The global quality of evidence was very low when addressing the impact of the treatments explored on prevalence of hypertension and lipid profiles, low in the case of hirsutism, BMI and blood pressure values, and high for endometrial protection and glucose tolerance.

WIDER IMPLICATIONS

These data provide further scientific evidence for the choice of treatment of women with PCOS. COC and AA are more effective than metformin for hyperandrogenic symptoms and endometrial protection. Their combination with metformin adds a positive effect on BMI and glucose tolerance.

PROSPERO CRD REGISTRATION NUMBER

CRD42016053457.

Evaluation of insulin-like growth factor (IGF-1) and retinol binding protein (RBP-4) levels in patients with newly diagnosed pancreatic adenocarcinoma (PDAC)

BACKGROUND/OBJECTIVES

The elevation of insulin-like growth factor 1 (IGF-1) and adipokine retinol-binding protein 4 (RBP-4) is known to be associated with the risk of many cancers. The aim of this study was to evaluate the serum concentrations of IGF-1 and RBP-4 in patients with PDAC and chronic pancreatitis (CP).

METHODS

The study included 43 patients with PDAC, 39 patients with CP and 10 controls. The concentrations of IGF-1 and RBP-4 were obtained using the ELISA method (Corgenix UK Ltd R&D Systems). The study protocol was approved by the Bioethics Committee at the Medical University of Lodz.

RESULTS

In PDAC patients the serum IGF-1 level was significantly higher than in patients with CP (107.79 ± 66.40 ng/ml vs 89.91 ± 74.06 ng/ml; P < 0.05). Patients with both CP and diabetes mellitus (DM) were noted to have a significantly lower level of IGF-1 compared with those who only had CP (51.33 ± 24.30 ng/ml vs 108.42 ± 82.39 ng/ml; P = 0.01). The same result was obtained for men with and without DM (58.05 ± 32.44 ng/ml vs 98.79 ± 79.47 ng/ml, P = 0.05). As regards the serum level of RBP-4, the PDAC and CP groups were not significantly different from each other.

CONCLUSIONS

Diabetes accompanying PDAC does not influence the level of IGF-1 as opposed to diabetes in the course of CP. The IGF-1 level can be useful for early diagnosis of PDAC. High concentration of RBP-4 is not specific to pancreatic cancer, so it does not appear to be a useful biomarker for PDAC.

New markers of insulin resistance in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine-metabolic disorder in women of reproductive age. The diagnostic criteria include two out of three features: hyperandrogenism, polycystic ovaries on ultrasound and menstrual irregularities (Rotterdam Criteria 2003). PCOS patients are more vulnerable to develop diabetes, cardiovascular diseases and metabolic syndrome. Insulin resistance (IR) is prevalent in women with PCOS independently of obesity and is critically involved in reproductive and metabolic complications of the syndrome. Several tests have been developed to measure IR, some very reliable but complex like the hyperinsulinemic euglycemic glucose clamp and others less precise but easier and less invasive like HOMA-IR. New markers are needed to reach a more reliable assessment of insulin resistance. To date, several surrogate markers have been proposed in the literature to facilitate and improve the determination of IR. Many new proteins are strongly involved with PCOS physiopathology and IR, such as some adipocytokines (adiponectin, visfatin, vaspin and apelin), copeptin, irisin, PAI-1 and zonulin. Many other proteins have been proposed as potential new markers of IR in PCOS, such as resistin, leptin, RBP4, kisspetin and ghrelin, but their role is still controversial. In this review, we provide a short characterization of these new markers, recently studied as indicators of metabolic state.

Circulating Zinc-α2-glycoprotein levels and Insulin Resistance in Polycystic Ovary Syndrome

The aim of study was to assess the relationship between zinc-α2-glycoprotein (ZAG) and androgen excess with insulin resistance in polycystic ovary syndrome (PCOS) women. 99 PCOS women and 100 healthy controls were recruited. Euglycemic-hyperinsulinemic clamp (EHC) was preformed to assess their insulin sensitivity. Circulating ZAG was determined with an ELISA kit. In healthy subjects, circulating ZAG levels exhibited a characteristic diurnal rhythm in humans, with a major nocturnal rise occurring between midnight and early morning. Circulating ZAG and M-value were much lower in PCOS women than in the controls. In all population, overweight/obese subjects had significantly lower circulating ZAG levels than lean individuals. Multiple linear regression analysis revealed that only M-value and the area under the curve for glucose were independently related factors to circulating ZAG in PCOS women. Multivariate logistic regression analysis showed that circulating ZAG was significantly associated with PCOS even after controlling for anthropometric variables, blood pressure, lipid profile and hormone levels. The PCOS women with high ZAG had fewer MetS, IGT and polycystic ovaries as compared with the low ZAG PCOS women. Taken together, circulating ZAG levels are reduced in women with PCOS and ZAG may be a cytokine associated with insulin resistance in PCOS women.

Smoking accelerates pancreatic cancer progression by promoting differentiation of MDSCs and inducing HB-EGF expression in macrophages

Smoking is an established risk factor for pancreatic cancer (PC), but late diagnosis limits the evaluation of its mechanistic role in the progression of PC. We used a well-established genetically engineered mouse model (LSL-K-ras(G12D)) of PC to elucidate the role of smoking during initiation and development of pancreatic intraepithelial neoplasia (PanIN). The 10-week-old floxed mice (K-ras(G12D); Pdx-1cre) and their control unfloxed (LSL-K-ras(G12D)) littermates were exposed to cigarette smoke (total suspended particles: 150 mg/m(3)) for 20 weeks. Smoke exposure significantly accelerated the development of PanIN lesions in the floxed mice, which correlated with tenfold increase in the expression of cytokeratin19. The systemic accumulation of myeloid-derived suppressor cells (MDSCs) decreased significantly in floxed mice compared with unfloxed controls (P<0.01) after the smoke exposure with the concurrent increase in the macrophage (P<0.05) and dendritic cell (DCs) (P<0.01) population. Further, smoking-induced inflammation (IFN-γ, CXCL2; P<0.05) was accompanied by enhanced activation of pancreatic stellate cells and elevated levels of serum retinoic acid-binding protein 4, indicating increased bioavailability of retinoic acid which contributes to differentiation of MDSCs to tumor-associated macrophages (TAMs) and DCs. TAMs predominantly contribute to the increased expression of heparin-binding epidermal growth factor-like growth factor (EGFR ligand) in pre-neoplastic lesions in smoke-exposed floxed mice that facilitate acinar-to-ductal metaplasia (ADM). Further, smoke exposure also resulted in partial suppression of the immune system early during PC progression. Overall, the present study provides a novel mechanism of smoking-induced increase in ADM in the presence of constitutively active K-ras mutation.

Association between retinol-binding protein 4 and polycystic ovary syndrome: a meta-analysis

Studies have examined the association between retinol-binding protein 4 (RBP4) and polycystic ovary syndrome (PCOS). However, the results have been inconsistent. To investigate the association between RBP4 and PCOS, we performed a meta-analysis. The Cochrane Library, MEDLINE, the ISI Web of Science, and EMBASE were searched to identify all of the studies that examined the relationship between circulating RBP4 levels and PCOS. Standard mean difference (SMD) values and 95% confidence interval (CI) were estimated and pooled using meta-analysis methodology. A total of seven studies were involved in the meta-analysis, which included a total of 636 subjects (260 controls and 376 patients with PCOS). The RBP4 level was higher in PCOS patients than in non-PCOS patients (random effects MD (95% CI)=0.69, [0.20, 1.18], P=0.006). However, the RBP4 level was not higher in nonobese PCOS patients than in nonobese controls (random effects MD (95% CI)=0.38, [-0.21, 0.98], P=0.20). The effect size revealed that the RBP4 level was higher in overweight or obese PCOS patients than weight-matched controls (fixed effects MD (95% CI)=7.95, [5.96, 9.93], P<0.05). In the subgroup analysis by region, the RBP4 level was higher in PCOS patients in Asia than controls (random effects MD (95% CI)=0.85, [0.54, 1.15], P<0.05), but not in European PCOS patients compared with controls (random effects MD (95% CI)=0.34, [-1.12, 1.80], P=0.65). This subgroup analysis also showed that nonobese PCOS patients have higher RBP4 levels than controls in Asia. Our meta-analysis results indicated that RBP4 might be a useful tool for identifying PCOS women.

Plasma retinol-binding protein 4 (RBP4) levels and risk of coronary heart disease: a prospective analysis among women in the nurses' health study

BACKGROUND

Retinol-binding protein 4 (RBP4) may play an important role in the origin of insulin resistance and metabolic syndrome. Few prospective data are available on the relationship between RBP4 and coronary heart disease (CHD). Furthermore, previous studies did not distinguish among full-length and truncated forms of RBP4 that might have various biological activities.

METHODS AND RESULTS

We measured plasma levels of full-length and several C-terminally truncated subfractions of RBP4 among 468 women who developed CHD and 472 matched controls in the Nurses' Health Study cohort during 16 years of follow-up (1990-2006). We observed a temporal variation in the association of full-length RBP4 levels with CHD risk (P=0.04 for testing proportional hazard assumption). In the first 8 years of follow-up, after multivariate adjustment for covariates, the odds ratio of CHD risk comparing extreme quartiles of full-length RBP4 levels was 3.56 (95% confidence interval, 1.21-10.51; Ptrend=0.003), whereas this association was 0.77 (95% confidence interval, 0.38-1.56; Ptrend=0.44) in the follow-up period of 9 to 16 years. Results were similar for total RBP4 levels (summed levels of all RBP4 isoforms). Levels of the primary truncated isoform, RBP4-L, were not associated with CHD risk in any follow-up period; the odds ratios for extreme quartiles were 1.29 (95% confidence interval, 0.50-3.32) and 1.20 (95% confidence interval, 0.64-2.26) in the first and second 8 years of follow-up, respectively.

CONCLUSIONS

In this cohort of women, higher circulating full-length and total RBP4 levels were associated with increased risk of CHD in a time-dependent fashion. Additional data are warranted to confirm the present findings.

Free fatty acid binding protein-4 and retinol binding protein-4 in polycystic ovary syndrome: response to simvastatin and metformin therapies

Free fatty acid binding protein-4 (FABP4) and retinol binding protein-4 (RBP4) contribute to metabolic syndrome. We investigated serum FABP4 and RBP4 responses to insulin sensitizing and lipid lowering therapies in polycystic ovary syndrome (PCOS). Sixty-two healthy, untreated women with PCOS (age 25.1 ± 3.6 years, BMI: 24.0 ± 4.7 kg/m(2)) were randomized to metformin (n = 24), simvastatin (n = 20) or metformin plus simvastatin (n = 18) for 3 months. Anthropometric measures, fasting blood tests and oral glucose tolerance tests (OGTT) were obtained at the baseline and the end. At the baseline serum FABP4 correlated with obesity (BMI: r = 0.63, p < 0.001), insulin resistance (fasting insulin: r = 0.44, p = 0.0002; QUICKI: r = -0.30, p = 0.02; OGTT-insulin sensitivity index: r = -0.27, p = 0.04), dyslipidemia (HDL: r = -0.26, p = 0.03) and hyperandrogenemia (free-testosterone: r = 0.23, p = 0.03; SHBG: r = -0.28, p = 0.03); while RBP4 correlated with total-cholesterol (r = 0.33, p = 0.009). Multiple regression analysis indicated that t best predictors of serum FABP4 and RBP4 were BMI (β = 1.02, p = 0.0003) and total cholesterol (β = 2326, p = 0.01), respectively. Simvastatin, alone or with metformin did not affect serum FABP4 or RBP4. Serum FABP4 related to the obesity, insulin resistance and inflammation while RBP4 related to lipids. Insulin sensitizing and lipid lowering therapies did not affect FABP4 or RBP4 levels in PCOS.

Kisspeptin, leptin, and retinol-binding protein 4 in women with polycystic ovary syndrome

OBJECTIVES

To compare plasma kisspeptin, serum leptin, and serum retinol-binding protein 4 (RBP4) levels in women with and without polycystic ovary syndrome (PCOS) and to correlate these among each other and with clinical, hormonal, and metabolic parameters.

METHODS

Ninety women, including 54 women with PCOS and 36 without PCOS, participated in this study. For all patients, history and physical examinations were performed and blood samples were collected between days 3 and 8 of a spontaneous bleeding episode in the PCOS group and during normal menses of controls. Plasma kisspeptin, serum leptin, and serum RBP4 levels were measured using specific commercial assays.

RESULTS

Kisspeptin, leptin, and RBP4 levels were significantly higher in the PCOS group than in controls. Kisspeptin and RBP4 levels were significantly higher among obese PCOS patients than controls. Leptin levels were higher among obese PCOS patients than non-obese PCOS patients or controls. Kisspeptin and leptin levels of PCOS patients were significantly correlated with RBP4 levels. When only obese PCOS patients were analyzed, kisspeptin levels correlated with only the free androgen index.

CONCLUSIONS

These findings suggest that kisspeptin, leptin, and RBP4 are associated with metabolic disturbances in women with PCOS.

Higher serum retinol binding protein 4 may be a predictor of weak metabolic control in chinese patients with type 2 diabetes mellitus

OBJECTIVE

To investigate relationships between serum levels of retinol binding protein 4 (RBP4) and clinical and metabolic variables in Chinese patients with type 2 diabetes mellitus.

METHODS

A total of 513 patients (286 males/227 females) provided clinical and lifestyle data and blood and urine samples for analysis. Patients were stratified into four quartile groups according to serum RBP4 concentrations.

RESULTS

RBP4 concentration was independently associated with gender, systolic blood pressure, serum triglyceride and creatinine levels, and estimated glomerular filtration rate (eGFR). Hypertension, dyslipidaemia, micro albuminuria and impaired eGFR (<60 ml/min per 1.73 m2) were significantly more prevalent in patients with the highest RBP4 levels than in those with the lowest levels. Increased serum RBP4 was associated with increased risk of hypertension, dyslipidaemia, micro albuminuria and impaired eGFR after adjusting for gender, age, body mass index and duration of diabetes.

CONCLUSION

Serum RBP4 may be a useful marker of overall metabolic control in Chinese patients with type 2 diabetes mellitus.

Study of Omentin1 and Other Adipokines and Hormones in PCOS Patients

OBJECTIVES

Polycystic ovary syndrome (PCOS) is associated with insulin resistance and obesity. Recent studies have shown that plasma omentin-1 levels decrease with obesity. Currently, no data exists on the relative correlation between omentin-1 with other adipokines or the expression and regulation of omentin-1 in the serum of women with PCOS. The objective of this study is to evaluate the role of omentin-1 levels or omentin-1 /adipokines ratio in the serum of women with PCOS compared with matched control subjects.

METHODS

The study involved 60 patients with PCOS and 30 women without PCOS who were used as controls. To examine the relationship between fasting serum omentin-1 and serum interleukin-6 (IL-6), interleukin-8 (IL-8), resistin, ghrelin, leptin RBP-4 and tumor necrosis factor-a (TNF-a) levels in infertile PCOS and non-PCOS subjects. Also, insulin and other hormones were measured in both groups. All these factors were measured by enzyme-linked immunosorbent assays.

RESULTS

From the total of 60 cases, there was a significant increase (p<0.001) in PCOS patients when compared to the control group in fasting serum, serum interleukin-6 (IL-6), interleukin-8 (IL-8), resistin, leptin RBP-4, tumor necrosis factor-a (TNF-a) levels and insulin. A significant decrease in omentin-1 and ghrelin (p<0.001) was observed. The results also showed that 93.33% and 98.30% in PCOS patients had abnormal omentin1: Insulin ratio and omentin1: Resistin ratio respectively according to the cut off values ≤27.42 and ≤31.35. Moreover, 81.67% of PCOS patients had abnormal omentin1:IL-6 ratio according to the cut of value (≤66.09).

CONCLUSION

This is the first time the role of plasma omentin1 has been investigated with respect to its implication in PCOS. Usually, LH/FSH ratio and FAI (ratio of total testosterone to SHBG) are the important factors used for the diagnosis of PCOS in all previous literature, but none of them referred to the parameters discussed in this report. Also, the percentage of sensitivity and the difference between range of these parameters in PCOS patients and the controls may give a different perspective in trying to understand the etiology of PCOS. Therefore, these parameters may be used for future diagnosis of PCOS. This study also suggested that omentin/resistin ratio may play a crucial paracrine or endocrine role in modulating insulin sensitivity.

The impact of intensified exercise training on insulin resistance and fitness in overweight and obese women with and without polycystic ovary syndrome

OBJECTIVE

  To evaluate mechanisms of insulin resistance (IR) in overweight and obese women with and without polycystic ovary syndrome (PCOS) and explore relationships between IR, fitness and body mass index (BMI) at baseline and following exercise intervention.

DESIGN

  Prospective controlled intensified exercise intervention study.

PATIENTS

  A total of 20 overweight (BMI > 25 kg/m(2) ) and obese (>30 kg/m(2) ), reproductive-aged PCOS women and 13 non-PCOS overweight, healthy controls of comparable BMI and age were studied at baseline. Measures were repeated in 13 PCOS and eight control women following three 1-h exercise sessions per week over 12 weeks.

MEASUREMENTS

  Insulin resistance was measured by glucose infusion rate on euglycaemic hyperinsulinaemic clamp, and fitness was assessed by VO(2max) .

RESULTS

  At baseline, PCOS women were 46% more insulin resistant than controls (175·6 vs 257·2 mg/m(2) /min, P < 0·05) with IR independently associated with VO(2max) and BMI in the PCOS group only (P < 0·01). Postexercise IR improved across both groups (P < 0·01). In PCOS women, IR improved by 16% (P < 0·05) but was not restored to the same level as controls (P < 0·05). Improvement in IR and in VO(2max) was related to the PCOS group (r(2)  = 0·85, P < 0·05), yet change in IR and in fitness was not related. No associations were found in controls.

CONCLUSIONS

  While intensified exercise improves IR in PCOS women, a higher IR persisted following exercise in PCOS women, and a clear relationship between improved IR and improved fitness was not found. Therefore, other mechanisms of, and therapies for, IR must be explored in PCOS as IR remains higher than observed in non-PCOS controls.

Metabolic manifestations of polycystic ovary syndrome in nonobese adolescents: retinol-binding protein 4 and ectopic fat deposition

OBJECTIVE

To determine whether nonobese adolescents with polycystic ovary syndrome (PCOS) have higher levels of retinol-binding protein 4 (RBP4) and ectopic fat than controls and whether RBP4 and ectopic fat correlate with comorbidities of metabolic disease.

DESIGN

Cross-sectional case-control study.

SETTING

Pediatric clinical research center based in a quaternary care medical center.

PATIENT(S)

Twenty-four nonobese adolescents between the ages of 13 and 21 years, 13 with PCOS and 11 controls.

INTERVENTION(S)

Measurement of RBP4, insulin resistance, lipids, and body composition.

MAIN OUTCOME MEASURE(S)

Retinol-binding protein 4, reproductive and adrenal hormones, insulin resistance, intrahepatic and intramyocellular lipid levels, and visceral adipose tissue.

RESULT(S)

Adolescents with PCOS had higher intrahepatic lipid content and a statistical trend for higher RBP4 compared with controls. Retinol-binding protein 4 correlated with body fat, triglycerides, insulin resistance, and androgens but not intrahepatic lipid content; however, when adjusted for body fat, the correlation between RBP4 and triglycerides weakened to a statistical trend and was no longer statistically significant for the other measures.

CONCLUSION(S)

This small preliminary study of nonobese adolescent girls suggests that RBP4 may be involved in the dyslipidemia associated with PCOS and that there may be an independent relationship between RBP4 and triglycerides but not between RBP4 and insulin resistance. Although intrahepatic lipid content was higher in PCOS, it did not correlate with RBP4, triglycerides, or insulin resistance.

Retinol-binding protein 4 is not associated with insulin resistance in pregnancy

Retinol-binding protein 4 (RBP4) is an adipokine proposed to be specifically associated with insulin resistance (IR). We examined whether serum levels of RBP4 were associated with IR in pregnancy. One hundred seventy-two women with gestational diabetes mellitus (GDM) and 361 pregnant Thai women who did not have GDM but had a positive 50-g glucose challenge test result (plasma glucose level was ≥7.2 mmol/L after 1 hour) were enrolled. We measured fasting serum levels of RBP4 and assessed IR at a 100-g oral glucose tolerance test. We found a higher degree of IR in the GDM group compared with the non-GDM group, but serum RBP4 levels between the 2 groups were not different. Retinol-binding protein 4 levels were associated with serum triglyceride levels but were not associated with the degree of IR assessed by homeostasis model assessment or quantitative insulin sensitivity check index. Our results suggest that serum RBP4 levels in pregnancy are not associated with IR.

The relationship between retinol-binding protein 4 levels, insulin resistance, androgen hormones and polycystic ovary syndrome

BACKGROUND

Retinol-binding protein 4 (RPB4), a 21-kDa peptide, is a recently identified adipokine that may contribute to the pathogenesis of polycystic ovary syndrome (PCOS). The aim of this study was to explore the association between serum RBP4 levels, androgen hormones and insulin resistance (IR) in women with PCOS.

METHODS

In this case-control study, 75 PCOS patients and 53 age- and body mass index (BMI)-matched control subjects referred to the Zanjan Metabolic Disease Research Center were enrolled. Serum RBP4 was measured using an enzyme-linked immunosorbent assay. BMI, waist circumference (WC), fasting levels of glucose, lipid profiles and insulin were also measured. A homeostatic model assessment of insulin resistance (HOMA-IR) value was used to determine the level of insulin resistance.

RESULTS

PCOS cases had significantly higher serum RBP4 and insulin levels than control subjects (44130 ± 12760 vs. 32980 ± 9560 μg/L, p < 0.001, and 11790 ± 11480 vs. 7890 ± 4300 μU/L, p < 0.05, respectively), in univariable analysis. RBP4 showed a positive correlation with serum testosterone (r = 0.62, p < 0.0001), dehydroepiandrosterone sulfate (r = 0.45, p < 0.0001) and the waist circumference (r = 0.37, p < 0.001) of PCOS patients but not with other measured clinical and biochemical variables. However, no correlation was observed between serum RBP4 levels and HOMA-IR in all studied subjects. A final logistic regression analysis demonstrated that testosterone and dehydroepiandrosterone sulfate are independently associated with PCOS.

CONCLUSION

These findings indicate that RBP4 is not independently associated with PCOS. The elevation of RBP4 levels in PCOS women might be influenced by androgen hormones. Further prospective studies are needed to clarify molecular mechanisms.

Low-dose pioglitazone and low-dose flutamide added to metformin and oestro-progestagens for hyperinsulinaemic women with androgen excess: add-on benefits disclosed by a randomized double-placebo study over 24 months

CONTEXT AND AIM

Metformin plus oestro-progestagen is a combination treatment for non-obese women with hyperinsulinaemic androgen excess. We explored whether low-dose pioglitazone (Pio) and flutamide (Flu) has readily detectable add-on effects.

DESIGN PATIENTS, INTERVENTION

Randomized, double-placebo pilot study over 24 months; 38 women with hyperinsulinaemic androgen excess (mean age 20 years; BMI 23.7 kg/m(2)); all women received metformin and an oestro-progestagen for 24 months, and add-on Flu (62.5 mg/day; 21/28 days) for 18 months. A first randomization was performed at start of the study, for Pio (7.5 mg/day; 21/28 days) vs. Pio-placebo, with a cross-over of Pio subgroups at 18 month. A second randomization was performed at 18 months, for Flu vs. Flu-placebo until 24 months.

MAIN OUTCOMES

Intima media thickness (IMT); body composition by absorptiometry; abdominal fat partitioning by magnetic resonance; circulating glucose, insulin, IGF-I, androgens, LDL : HDL ratio, RBP4, vaspin.

RESULTS

Add-on effects of Pio included a gain of lean mass (mirrored by a loss of fat) and an accelerated lowering of IMT (P <or= 0.001). Add-on effects of flutamide included a further reduction of androgen excess. Between 0 and 18 months, women lost a quarter of their visceral fat (P < 0.001; independently of Pio); beyond 18 months, a rebound of visceral fat occurred in women who had stopped Pio and Flu. Between 0 and 24 months, insulin sensitivity increased, as did circulating RBP-4 and vaspin (all P = 0.001).

CONCLUSION

Low-dose Pio and Flu further improve long-term markers - such as IMT, lean mass and visceral fat - when jointly added to a treatment of metformin plus an oestro-progestagen in non-obese women with hyperinsulinaemic androgen excess.

Retinol-binding protein-4 in women with untreated essential hypertension

BACKGROUND

Retinol-binding protein-4 (RBP4) is a novel adipokine able to modulate the action of insulin in several tissues. A variable degree of insulin resistance characterizes the vast majority of hypertensive (HYP) patients. The aim of this study was to evaluate the relationship between RBP4 and essential hypertension, exploring potential links between RBP4 and other adipokines with some proxies of early vascular damage in female naive HYP patients.

METHODS

Serum RBP4, leptin, adiponectin, and resistin levels were determined in 35 HYP and 35 normotensive lean women with normal glucose tolerance paired by age and body mass index (BMI) served as controls (CTL); carotid intima-media thickness (IMT) was also measured.

RESULTS

A striking difference was observed in RBP4 levels between HYP and CTL with significantly higher levels in the former than in the latter. No relationship was observed between glomerular filtration rate (GFR) and RBP4. Adiponectin levels were slightly but significantly lower in HYP than in CTL, whereas no differences were observed in resistin and leptin concentrations between the two groups of women. In the whole study group, a strong linear relationship was observed between IMT value and both RBP4 (rho = 0.321, P = 0.0076) and resistin (rho = 0.340, P = 0.0048); these two adipocytokines, together with cholesterol, were the only variables independently related to IMT (r(2) = 0.24; P = 0.004) by a stepwise analysis.

CONCLUSIONS

RBP4 levels are increased in naive HYP women and correlated with the degree of IMT suggesting a participation of this adipocytokine in the modulation of the atherosclerotic process exerted by the adipose tissue as endocrine organ.

Adipocyte fatty acid binding protein levels relate to inflammation and fibrosis in nonalcoholic fatty liver disease

Several circulating cytokines are increased with obesity and may combine with the influence of visceral fat to generate insulin resistance, inflammation, and fibrosis in nonalcoholic fatty liver disease (NAFLD). Little information exists in NAFLD about three recently recognized tissue-derived cytokines that are all lipid-binding and involved in inflammation, namely adipocyte fatty acid-binding protein (AFABP), lipocalin-2, and retinol-binding protein 4 (RBP4). We examined the association of these three peptides with hepatic steatosis, inflammation, and fibrosis plus indices of adiposity, insulin resistance, and dyslipidaemia in 100 subjects with NAFLD and 129 matched controls. Levels of AFABP and lipocalin-2, but not RBP4, were significantly elevated in NAFLD versus control (AFABP, 33.5 +/- 14.4 versus 23.1 +/- 12.1 ng/mL [P < 0.001]; lipocalin-2, 63.2 +/- 26 versus 48.6 +/- 20 ng/mL [P < 0.001]) and correlated with indices of adiposity. AFABP correlated with indices of subcutaneous rather than visceral fat. AFABP alone distinguished steatohepatitis from simple steatosis (P= 0.02). Elevated AFABP independently predicted increasing inflammation and fibrosis, even when insulin resistance and visceral fat were considered; this applied to lobular inflammation and ballooning (odds ratio 1.4, confidence interval 1.0-1.8) and fibrosis stage (odds ratio 1.3, confidence interval 1.0-1.7) (P < or = 0.05 for all). None of the cytokines correlated with steatosis grade. AFABP levels correlated with insulin resistance (homeostasis model assessment of insulin resistance) in controls and NAFLD, whereas lipocalin-2 and RBP4 only correlated positively with insulin resistance in controls.

CONCLUSION

Circulating AFABP, produced by adipocytes and macrophages, and lipocalin-2, produced by multiple tissues, are elevated and may contribute to the metabolic syndrome in NAFLD. AFABP levels, which correlate with subcutaneous, but not visceral fat, independently predict inflammation and fibrosis in NAFLD and may have a direct pathogenic link to disease progression.

Retinol-binding protein 4 is associated with impaired glucose tolerance but not with whole body or hepatic insulin resistance in Mexican Americans

Retinol-binding protein-4 (RBP4), a novel protein secreted mainly by adipose tissue, has been associated with insulin resistance in obese subjects and in individuals with type 2 diabetes mellitus (T2DM). We examined the relationship between plasma RBP4 levels, expression of RBP4 in skeletal muscle and adipose tissue, and insulin sensitivity in Mexican Americans with varying degrees of obesity and glucose tolerance. Seventy-two subjects [16 lean normal-glucose-tolerant (NGT), 17 obese NGT, and 39 subjects with impaired fasting glucose/impaired glucose tolerance/T2DM] received an oral glucose tolerance test (OGTT) and euglycemic-hyperinsulinemic clamp. Insulin secretion was measured as insulinogenic index during OGTT. In a subset of subjects, hepatic glucose production was measured by 3-[3H]glucose infusion, biopsies of the vastus lateralis muscle and subcutaneous adipose tissue were obtained under basal conditions, and quantitative RT-PCR was performed to measure the RBP4 mRNA gene expression. Plasma RBP4 was significantly elevated in impaired glucose tolerance/T2DM compared with NGT lean or obese subjects. Plasma RBP4 levels correlated with 2-h glucose, triglycerides, and hemoglobin A1c. There was no association between RBP4 levels and whole body insulin sensitivity measured with either the euglycemic insulin clamp or OGTT, basal hepatic glucose production rates, and the hepatic insulin resistance index. There was no correlation between plasma RBP4 levels and indexes of insulin secretion. RBP4 mRNA expression in skeletal muscle was similar in lean NGT subjects, obese NGT subjects, and T2DM subjects. There was no difference in RBP4 mRNA expression in adipose tissue between lean and obese NGT subjects or between NGT and T2DM individuals. Plasma RBP4 levels are elevated in T2DM and associated with impaired glucose tolerance, but not associated with obesity or insulin resistance or impaired insulin secretion in Mexican Americans.

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.

Fenofibrate reduces serum retinol-binding protein-4 by suppressing its expression in adipose tissue

Fenofibrate is a peroxisome proliferator-activated receptor-alpha (PPARalpha) activator that has been clinically used to treat dyslipidemia and insulin resistance. To better understand the molecular mechanisms underlying fenofibrate action, we investigated whether fenofibrate affects serum levels of retinol-binding protein-4 (RBP4), an adipocytokine that has recently been shown to link obesity and insulin resistance. Fenofibrate treatment significantly decreased serum RBP4 levels of dyslipidemic patients, which correlated with reduced body weight and increased insulin sensitivity. To elucidate the biochemical mechanisms of fenofibrate action, we investigated the effect of fenofibrate on RBP4 expression in obese rats. Fenofibrate greatly decreased RBP4 mRNA levels in adipose tissue but not in the liver, which correlated with decreased serum RBP4 levels and increased insulin sensitivity in obese rats. Consistent with a direct effect on RBP4 expression, fenofibrate treatment significantly reduced the mRNA expression levels of RPB4 in 3T3-L1 adipocytes. Together, our results demonstrate for the first time that fenofibrate inhibits RPB4 expression in dyslipidemic human subjects and suggest that inhibition of RBP4 expression in adipocytes may provide a mechanism by which fenofibrate improves insulin sensitivity in dyslipidemic patients.

RBP4 variants are significantly associated with plasma RBP4 levels and hypertriglyceridemia risk in Chinese Hans

We previously found that plasma RBP4 levels were strongly associated with metabolic syndrome components. This study aimed to determine whether RBP4 variants are associated with the metabolic syndrome components and plasma RBP4 levels, and to investigate whether the associations between plasma RBP4 and the metabolic syndrome components are causal. Five tagSNPs were tested for their associations with plasma RBP4 levels and metabolic syndrome components in a population-based sample of 3,210 Chinese Hans. A possible causal relationship between plasma RBP4 levels and hypertriglyceridemia was explored by Mendelian randomization. Plasma RBP4 levels were significantly associated with rs10882273 (betaz -0.10SD[-0.17, -0.03], P = 0.0050), rs3758538 (betaz -0.13SD[-0.24, -0.02], P = 0.0249) in all participants, and with rs17108993 in Shanghai participants (betaz -0.19SD[-0.32, -0.05], P = 0.0061). The single nucleotide polymorphism (SNP) rs3758538 was significantly associated with hypertriglyceridemia (OR 0.62[0.45-0.85], P = 0.0026) and triglycerides (betaz -0.19SD[-0.30, -0.07], P = 0.001) in all participants. In Mendelian randomization analysis, the observed effect size of association between rs3758538 and hypertriglyceridemia was different from the expected effect size (P = 0.0213). This is the first study to show that the RBP4 variants are significantly associated with plasma RBP4 levels and hypertriglyceridemia risk in Chinese Hans. However, results of Mendelian randomization do not support the hypothesis that RBP4 levels are causally related to hypertriglyceridemia risk.

Serum retinol-binding protein 4 levels in nonobese women with polycystic ovary syndrome

OBJECTIVE

To test whether there was a difference in serum retinol-binding protein 4 (RBP4) levels between subjects with polycystic ovary syndrome (PCOS) and those with a healthy regular menstrual cycle and, in addition, to correlate serum RBP4 levels with a variety of parameters.

DESIGN

Clinical study.

SETTING

University hospital.

PATIENT(S)

A total of 74 nonobese women were evaluated. Thirty-seven had PCOS, whereas the remaining 37 served as control subjects.

INTERVENTION(S)

Serum RBP4 levels were analyzed using ELISA.

MAIN OUTCOME MEASURE(S)

Serum levels of FSH, LH, TSH, E(2), T, insulin, glucose, cholesterol, triglycerides, and RBP4.

RESULT(S)

The women with PCOS had higher levels of serum RBP4, waist-to-hip ratio, LH, T, insulin, homeostatic model assessment of insulin resistance, cholesterol, and triglycerides. Logistic regression analyses revealed a significant association between odds ratio (OR) values of PCOS and both T (OR = 1.125; 95% confidence interval [CI] 1.050-1.205), and cholesterol levels (OR = 1.029; 95% CI 1.004-1.056). Age and triglycerides were significantly correlated to serum RBP4 levels by multiple linear regression analysis.

CONCLUSION(S)

Our study has shown that [1] elevated RBP4 levels might arise from triglyceride metabolism, and that RBP4 levels might not be influenced by PCOS itself. [2] RBP4 might not be a useful marker of insulin resistance in subjects with PCOS.