Effects of peroxisome proliferator-activated receptor-gamma activation with pioglitazone on plasma adipokines in nondiabetic patients with either hypercholesterolemia or hypertension

Targeting metabolic disorders by natural products

The most prevalent metabolic disorders are diabetes mellitus, obesity, dyslipidemia, osteoporosis and metabolic syndrome, which are developed when normal metabolic processes are disturbed. The most common pathophysiologies of the above disorders are oxidative stress, Nrf2 pathways, epigenetic, and change in miRNA expression. There is a challenge in the prevention and treatment of metabolic disorders due to severe adverse effects of some synthetic drugs, their high cost, lack of safety and poverty in some conditions, and insufficient accessibility for the general population in the world. With increasing interest in shifting from synthetic drugs to phytotherapy as an alternative treatment, there is still a gap in scientific evidences of plant-derived therapeutic benefits. One reason may be slow rate of translation of animal studies' findings into human clinical trials. Since metabolic disorders are multifactorial, it seems that poly-herbal medications, or drug-herbal combination are needed for their treatment. However, further researches to determine the most effective plant-derived metabolites, and their cellular mechanism in order to set priorities for well-designed animal and clinical trials, and also more studies with strong scientific evidences such as systematic review and meta-analysis of controlled studies are needed.

Spirulina improves non-alcoholic steatohepatitis, visceral fat macrophage aggregation, and serum leptin in a mouse model of metabolic syndrome

BACKGROUND

Nutritional approaches are sought to overcome the limits of pioglitazone in metabolic syndrome and non-alcoholic fatty liver disease. Spirulina, a filamentous unicellular alga, reduces serum lipids and blood pressure while exerting antioxidant effects.

AIM

To determine whether Spirulina may impact macrophages infiltrating the visceral fat in obesity characterizing our metabolic syndrome mouse model induced by the subcutaneous injection treatment of monosodium glutamate.

METHODS

Mice were randomized to receive standard food added with 5% Spirulina, 0.02% pioglitazone, or neither. We tested multiple biochemistry and histology (both liver and visceral fat) readouts at 24 weeks of age.

RESULTS

Data demonstrate that both the Spirulina and the pioglitazone groups had significantly lower serum cholesterol and triglyceride levels and liver non-esterified fatty acid compared to untreated mice. Spirulina and pioglitazone were associated with significantly lower leptin and higher levels, respectively, compared to the control group. At liver histology, non-alcoholic fatty liver disease activity score and lipid peroxide were significantly lower in mice treated with Spirulina.

CONCLUSIONS

Spirulina reduces dyslipidaemia in our metabolic syndrome model while ameliorating visceral adipose tissue macrophages. Human studies are needed to determine whether this safe supplement could prove beneficial in patients with metabolic syndrome.

Adipocytokine levels mark endothelial function in normotensive individuals

Background

Endothelial dysfunction is an independent risk factor for cardiovascular events. Inflammatory mediators released by the adipose tissue can lead to local insulin resistance and endothelial dysfunction. This study addressed the relationship of adipocytokines with endothelial function and blood pressure.

Methods

In 92 newly diagnosed, drug-naïve essential hypertensive patients (HT, mean age 49 yrs) without organ damage and 66 normotensive subjects (NT, mean age 47 yrs), by an automated system, we measured endothelium-dependent and -independent vasodilation as brachial artery flow-mediated dilation before and after administration of glyceryl-trinitrate. Retinol binding protein-4 (RBP4) and resistin levels were determined by ELISA and RIA, respectively. Oxidative stress was evaluated by measuring serum malondyaldehyde (MDA).

Results

Flow-mediated dilation was significantly (p = 0.03) lower in HT (5.3 ± 2.6%) than NT (6.1 ± 3.1%), while response to glyceryl-trinitrate (7.5 ± 3.7% vs 7.9 ± 3.4%) was similar. RBP4 (60.6 ± 25.1 vs 61.3 ± 25.9 μg/ml), resistin (18.8 ± 5.3 vs 19.9 ± 6.1 ng/ml) and MDA levels (2.39 ± 1.26 vs 2.08 ± 1.17 nmol/ml) were not different in HT and NT.

RBP4 (r = −0.25; p = 0.04) and resistin levels (r = −0.29; p = 0.03) were related to flow-mediated dilation in NT, but not in HT (r = −0.03 and r = −0.10, respectively). In NT, multivariate analysis including RBP4 and confounders showed that only BMI or waist circumference remained related to flow- mediated dilation. In the multivariate model including resistin and confounders, BMI, age and resistin were significantly related to flow-mediated dilation, while only age significant correlated with this parameter when BMI was replaced by waist circumference.

Conclusions

Adipocytokine levels may be independent predictors of endothelial dysfunction in the peripheral circulation of healthy subjects, providing a pathophysiological link between inflammation from adipose tissue and early vascular alterations.

PPAR-γ as a therapeutic target in cardiovascular disease: evidence and uncertainty

Peroxisome proliferator-activated receptor γ (PPAR-γ) is a key regulator of fatty acid metabolism, promoting its storage in adipose tissue and reducing circulating concentrations of free fatty acids. Activation of PPAR-γ has favorable effects on measures of adipocyte function, insulin sensitivity, lipoprotein metabolism, and vascular structure and function. Despite these effects, clinical trials of thiazolidinedione PPAR-γ activators have not provided conclusive evidence that they reduce cardiovascular morbidity and mortality. The apparent disparity between effects on laboratory measurements and clinical outcomes may be related to limitations of clinical trials, adverse effects of PPAR-γ activation, or off-target effects of thiazolidinedione agents. This review addresses these issues from a clinician's perspective and highlights several ongoing clinical trials that may help to clarify the therapeutic role of PPAR-γ activators in cardiovascular disease.

Novel adiponectin-resistin (AR) and insulin resistance (IRAR) indexes are useful integrated diagnostic biomarkers for insulin resistance, type 2 diabetes and metabolic syndrome: a case control study

Background

Adiponectin and resistin are adipokines which modulate insulin action, energy, glucose and lipid homeostasis. Meta-analyses showed that hypoadiponectinemia and hyperresistinemia are strongly associated with increased risk of insulin resistance, type 2 diabetes (T2DM), metabolic syndrome (MS) and cardiovascular disease. The aim of this study was to propose a novel adiponectin-resistin (AR) index by taking into account both adiponectin and resistin levels to povide a better indicator of the metabolic homeostasis and metabolic disorders. In addition, a novel insulin resistance (IR_AR) index was proposed by integration of the AR index into an existing insulin resistance index to provide an improved diagnostic biomarker of insulin sensitivity.

Methods

In this case control study, anthropometric clinical and metabolic parameters including fasting serum total adiponectin and resistin levels were determined in 809 Malaysian men (208 controls, 174 MS without T2DM, 171 T2DM without MS, 256 T2DM with MS) whose ages ranged between 40-70 years old. Significant differences in continuous variables among subject groups were confirmed by ANCOVA or MANCOVA test using 1,000 stratified bootstrap samples with bias corrected and accelerated (BCa) 95% CI. Spearman's rho rank correlation test was used to test the correlation between two variables.

Results

The AR index was formulated as 1+log₁₀(R₀)-log₁₀(A₀). The AR index was more strongly associated with increased risk of T2DM and MS than hypoadiponectinemia and hyperresistinemia alone. The AR index was more strongly correlated with the insulin resistance indexes and key metabolic endpoints of T2DM and MS than adiponectin and resistin levels alone. The AR index was also correlated with a higher number of MS components than adiponectin and resistin levels alone. The IR_AR index was formulated as log₁₀(I₀G₀)+log₁₀(I₀G₀)log₁₀(R₀/A₀). The normal reference range of the IR_AR index for insulin sensitive individuals was between 3.265 and 3.538. The minimum cut-off values of the IR_AR index for insulin resistance assessment were between 3.538 and 3.955.

Conclusions

The novel AR and IR_AR indexes are cost-effective, precise, reproducible and reliable integrated diagnostic biomarkers of insulin sensitivity for screening subjects with increased risk of future development of T2DM and MS.

Weight gain by hyperalimentation elevates C-reactive protein levels but does not affect circulating levels of adiponectin or resistin in healthy subjects

OBJECTIVE

Increase of resistin and/or reduction of adiponectin have been implicated in the development of insulin resistance following weight gain. We aimed to study this prospectively in humans.

DESIGN

Prospective and interventional with parallel control group.

METHODS

Twelve healthy men and six healthy women (age 26 ± 6.6 years) and an age-matched control group were recruited. Subjects in the intervention group aimed for a bodyweight increase of 5-15% by doubling the baseline caloric intake by eating at least two fast food-based meals a day in combination with adoption of a sedentary lifestyle for 4 weeks.

RESULTS

Bodyweight increased from 67.6 ± 9.1 to 74.0 ± 11 kg, P<0.001, by the intervention. Insulin levels increased (before: 27.4 ± 12 pmol/l, after: 53.0 ± 22 pmol/l, P=0.004), while plasma levels of adiponectin (before: 5038 ± 3736 ng/ml, after: 6739 ± 7949 ng/ml, P=0.18) and resistin (before: 21.8 ± 19 ng/ml, after: 14.4 ± 6.8 ng/ml, P=0.074) remained unchanged by the weight gain and were similar as in controls. On the other hand, leptin levels increased about threefold following the intervention (before: 5.7 ± 7.4, after: 16 ± 20 ng/ml, P=0.008), and also the inflammatory marker C-reactive protein (CRP) increased from 0.34 ± 0.44 to 0.71 ± 0.87 mg/l, P=0.03, when two outliers >10 mg/l were disregarded.

CONCLUSIONS

Hyperalimentation reduces insulin sensitivity when weight gain of 9% was combined with reduction of exercise. However, the levels of resistin and adiponectin were unaffected by the intervention, while CRP levels increased within this short time period suggesting that low-grade inflammation can occur early in the process of developing a metabolic syndrome.

Pioglitazone abrogates cyclosporine-evoked hypertension via rectifying abnormalities in vascular endothelial function

In addition to insulin sensitization, the thiazolidenedione drug pioglitazone exhibits favorable circulatory effects. Here, we hypothesized that pioglitazone protects against the hypertension and related vascular derangements caused by the immunosuppressant drug cyclosporine (CSA). Compared with vehicle (olive oil)-treated rats, chronic treatment with CSA (20mg/kg/day s.c., for 14 days) increased blood pressure (BP), reduced the aortic protein expression of phosphorylated eNOS (p-eNOS), and impaired responsiveness of isolated aortas to endothelium-dependent vasorelaxations induced by carbachol. The effects of CSA on BP, aortic p-eNOS, and carbachol relaxations were abolished upon concurrent administration of pioglitazone (2.5mg/kg/day). Serum levels of adiponectin, an adipose tissue-derived adipokine, were not altered by CSA but showed significant elevations in rats treated with pioglitazone or pioglitazone plus CSA. The possibility that alterations in the antioxidant and/or lipid profile contributed to the CSA-pioglitazone BP interaction was investigated. Pioglitazone abrogated the oxidative (aortic superoxide dismutase), lipid peroxidation (aortic malondialdyde), and dyslipidemic (serum LDL levels and LDL/HDL ratio) effects of CSA. Histologically, CSA caused focal disruption in the endothelial lining of the aorta and this effect disappeared in rats co-treated with pioglitazone. Collectively, pioglitazone abrogates the hypertensive effect of CSA via ameliorating detrimental changes in vascular endothelial NOS/NO pathway and oxidative and lipid profiles caused by CSA.

Association of resistin with urinary albumin excretion in nondiabetic patients with essential hypertension

BACKGROUND

Evidence suggests that resistin, a recently described protein, is associated with subclinical atherosclerosis in different clinical settings. In this study, we investigated the relationship of increased resistin levels with urinary albumin excretion, expressed as the albumin-to-creatinine ratio (ACR), an established index of diffuse vascular damage, in hypertensives.

METHODS

Our population consisted of 132 untreated nondiabetic subjects with stage I-II essential hypertension (49 males, mean age = 54 years, mean office blood pressure (BP) = 159/100 mm Hg). In all patients, ACR was determined as the average of three nonconsecutive morning spot urine samples, and venous blood sampling was performed for estimation of resistin concentrations. The distribution of resistin was split by the median (4.63 ng/ml), and accordingly, subjects were stratified into those with high and low values.

RESULTS

Hypertensive patients with high (n = 66) compared to those with low resistin (n = 66) exhibited higher ACR values (21.8 + or - 15.3 vs. 10.3 + or - 3.8 mg/g, P < 0.01), even after adjustment for confounders. In the total population, resistin was associated with 24-h systolic BP (r = 0.244, P < 0.05), serum creatinine (r = 0.311, P = 0.007), and ACR (r = 0.499, P < 0.01). Multiple regression analysis revealed that age (b = 0.193, P = 0.02), body mass index (b = 0.237, P = 0.02), 24-h systolic BP (b = 0.338, P < 0.0001), 24-h heart rate (b = 0.169, P = 0.04), and resistin (b = 0.77, P < 0.01) were independently associated with ACR (R(2) = 0.471, P < 0.01).

CONCLUSIONS

Hypertensive subjects with augmented resistin levels exhibit higher albuminuria, independently of established risk factors. Moreover, the association of resistin with ACR suggests a link between resistin and microvascular disease in the early stages of essential hypertension.

Pharmacodynamic effects of rosiglitazone in nondiabetic patients with metabolic syndrome

STUDY OBJECTIVES

To determine the effects of the thiazolidinedione rosiglitazone on the adipocyte-derived cytokines adiponectin (an antiinflammatory and insulin-sensitizing cytokine; low levels have been associated with metabolic syndrome) and resistin (an inflammation mediator; high levels have been associated with metabolic syndrome) in nondiabetic patients with metabolic syndrome, and to characterize the effects of rosiglitazone on other components of the metabolic syndrome phenotype in this population.

DESIGN

Prospective, randomized, double-blind, placebo-controlled study.

SETTING

Outpatient general clinical research center.

PATIENTS

Thirty-two nondiabetic men and women with a clinical diagnosis of metabolic syndrome (as defined in the American Heart Association-National Heart, Lung, and Blood Institute scientific statement).

INTERVENTION

Patients were randomly assigned to receive either oral rosiglitazone 4 mg/day or matching placebo for 12 weeks.

MEASUREMENTS AND MAIN RESULTS

The primary end point was change in serum adiponectin concentrations from baseline to week 12. Secondary end points were changes in serum resistin concentrations, insulin resistance, fasting glucose level, fasting insulin level, body weight, lipid levels, systolic and diastolic blood pressure, and waist circumference from baseline to week 12. Also, changes from baseline in adiponectin and resistin concentrations and insulin resistance were assessed over time at weeks 2, 4, 8, and 12. Rosiglitazone was associated with a significant increase in serum adiponectin concentration after 12 weeks compared with placebo (45.8% vs 2.6%, p=0.002). The increase in adiponectin concentration occurred quickly, with a significant difference observed after 2 weeks of therapy. Compared with placebo, rosiglitazone was not associated with significant 12-week changes in serum resistin concentrations, insulin resistance, fasting glucose level, fasting insulin level, body weight, lipid levels, systolic or diastolic blood pressure, or waist circumference.

CONCLUSION

Rosiglitazone had beneficial effects on adiponectin concentrations without significantly affecting other components of the metabolic syndrome phenotype. Additional studies that further elucidate the time course of thiazolidinedione pharmacodynamic effects, along with their effects on cardiovascular end points, are warranted in nondiabetic patients with metabolic syndrome.

Pioglitazone and mechanisms of CV protection

BACKGROUND AND AIM

Pioglitazone has diverse multiple effects on metabolic and inflammatory processes that have the potential to influence cardiovascular disease pathophysiology at various points in the disease process, including atherogenesis, plaque inflammation, plaque rupture, haemostatic disturbances and microangiopathy.

RESULTS

Linking the many direct and indirect effects on the vasculature to the reduction in key macrovascular outcomes reported with pioglitazone in patients with type 2 diabetes presents a considerable challenge. However, recent large-scale clinical cardiovascular imaging studies are beginning to provide some mechanistic insights, including a potentially important role for improvements in high-density lipoprotein cholesterol with pioglitazone. In addition to a role in prevention, animal studies also suggest that pioglitazone may minimize damage and improve recovery during and after ischaemic cardio- and cerebrovascular events.

DESIGN AND METHODS

In this review, we consider potential cardiovascular protective mechanisms of pioglitazone by linking preclinical data and clinical cardiovascular outcomes guided by insights from recent imaging studies.

CONCLUSION

Pioglitazone may influence CVD pathophysiology at multiple points in the disease process, including atherogenesis, plaque inflammation, plaque rupture and haemostatic disturbances (i.e. thrombus/embolism formation), as well as microangiopathy.

Utility of adiponectin as a biomarker predictive of glycemic efficacy is demonstrated by collaborative pooling of data from clinical trials conducted by multiple sponsors

This study, conducted under the Metabolic Disorders Steering Committee of the Biomarkers Consortium (a public-private partnership managed by the Foundation for the National Institutes of Health (FNIH)), analyzed blinded data on 2,688 type 2 diabetes (T2D) patients from randomized clinical trials conducted by four pharmaceutical companies. An increase in the levels of adiponectin was observed after peroxisome proliferator-activated receptor (PPAR)-agonist treatment (P < 0.0001), but not after treatment with non-PPAR drugs. This increase correlated with decreases in levels of glucose, hemoglobin A(1c) (Hb(A1c)), hematocrit, and triglycerides, and increases in levels of blood urea nitrogen, creatinine, and high-density lipoprotein cholesterol (HDL-C). Early (6-8 weeks) increases in levels of adiponectin after treatment with PPAR agonists showed a negative correlation (r = -0.21, P < 0.0001) with subsequent changes in levels of Hb(A1c). Changes in adiponectin level did not appear to be associated with baseline level of Hb(A1c). Logistic regression demonstrated that an increase in the level of adiponectin predicts a decrease in the level of Hb(A1c). These analyses confirm previously demonstrated relationships between adiponectin levels and metabolic parameters and support the robust predictive utility of adiponectin across the spectrum of glucose tolerance. Cross-company precompetitive collaboration is a feasible and powerful approach to biomarker qualification.

Effect of pioglitazone on visfatin expression in 3T3-L1 adipocytes and SD rats

OBJECTIVE

To investigate the effect of pioglitazone on visfatin expression.

METHODS

We studied the effect of pioglitazone on visfatin expression in 3T3-L1 adipocytes and serum concentrations and tissue expression of visfatin in normal Sprague-Dawley rats and rats with insulin resistance induced by high-fat diet (HF). Metabolic and anatomical parameters of the rats were also performed.

RESULTS

In 3T3-L1 adipocytes, visfatin expression increased during the differentiation and it was not regulated by pioglitazone. In the rats, 12 weeks of HF feeding induced obesity and increased fast blood glucose (FBG), serum insulin and circulating visfatin. Pioglitazone treatment ameliorated insulin resistance with concomitant reduction in serum visfatin, free fatty acid, and triglyceride (TG) of the rats fed HF. Compared with subcutaneous adipose tissue and muscle, visfatin protein expression was much higher in visceral adipose tissue on both diets (p < 0.05 for all). Visfatin expression decreased in visceral adipose tissue but not subcutaneous adipose tissue or muscle after pioglitazone treatment in HF-fed rats. Visfatin expression in the rats fed chow diet was not affected by pioglitazone. Additionally, we demonstrated that serum visfatin was positively correlated with visceral adipose tissue weight, visfatin in visceral adipose tissue, TG and FBG (p < 0.05 for all).

CONCLUSION

Visfatin is preferentially produced by visceral fat and peroxisome proliferator-activated receptor-gamma agonist ameliorates the development of insulin resistance in HF-fed rats with a major decrease in visfatin expression, the effect of pioglitazone on visfatin in HF-fed rats is dependent on glucose and lipid metabolism in the animals.