Increased serum resistin in elite endurance athletes with high insulin sensitivity

A Narrative Review on Adipose Tissue and Overtraining: Shedding Light on the Interplay among Adipokines, Exercise and Overtraining

Lifestyle factors, particularly physical inactivity, are closely linked to the onset of numerous metabolic diseases. Adipose tissue (AT) has been extensively studied for various metabolic diseases such as obesity, type 2 diabetes, and immune system dysregulation due to its role in energy metabolism and regulation of inflammation. Physical activity is increasingly recognized as a powerful non-pharmacological tool for the treatment of various disorders, as it helps to improve metabolic, immune, and inflammatory functions. However, chronic excessive training has been associated with increased inflammatory markers and oxidative stress, so much so that excessive training overload, combined with inadequate recovery, can lead to the development of overtraining syndrome (OTS). OTS negatively impacts an athlete's performance capabilities and significantly affects both physical health and mental well-being. However, diagnosing OTS remains challenging as the contributing factors, signs/symptoms, and underlying maladaptive mechanisms are individualized, sport-specific, and unclear. Therefore, identifying potential biomarkers that could assist in preventing and/or diagnosing OTS is an important objective. In this review, we focus on the possibility that the endocrine functions of AT may have significant implications in the etiopathogenesis of OTS. During physical exercise, AT responds dynamically, undergoing remodeling of endocrine functions that influence the production of adipokines involved in regulating major energy and inflammatory processes. In this scenario, we will discuss exercise about its effects on AT activity and metabolism and its relevance to the prevention and/or development of OTS. Furthermore, we will highlight adipokines as potential markers for diagnosing OTS.

Alterations in Adiponectin, Leptin, Resistin, Testosterone, and Cortisol across Eleven Weeks of Training among Division One Collegiate Throwers: A Preliminary Study

Cytokine and hormone concentrations can be linked to the manipulation of training variables and to subsequent alterations in performance.

SUBJECTS

Nine D-1 collegiate throwers and 4 control subjects participated in this preliminary and exploratory report.

METHODS

Hormone (testosterone (T) and cortisol (C)) and adipokine (adiponectin, leptin, and resistin) measurements were taken at weeks 1, 7, and 11 for the throwers and weeks 1 and 11 for the control group. The throwers participated in an 11-week periodized resistance training and throws program during the fall preparatory period. Volume load was recorded throughout the study.

RESULTS

Hormone values did not exhibit statistically significant changes across time; however, there were notable changes for C, the testosterone to cortisol ratio (T:C), and adiponectin.

CONCLUSIONS

T:C was increased as volume load decreased, and adiponectin increased in concert with decreases in C and increases in the T:C, possibly suggesting a lesser degree of obesity-related inflammation and a higher degree of "fitness" and preparedness.

The Effect of the Ultra-Marathon Run at a Distance of 100 Kilometers on the Concentration of Selected Adipokines in Adult Men

Pro-inflammatory adipokines have a multifunctional role in adipogenesis, angiogenesis, glucose homeostasis, and inflammation. The aim of the present study is to evaluate the effect of running a 100 km ultra-marathon on serum levels of two adipokines: resistin and chemerin. Fifteen male participants complete a medical questionnaire and their body composition is assessed. Serum resistin, chemerin, high sensitivity C-reactive protein (hs-CRP), glucose, and lactate levels are measured at baseline and post-race. During-race data on fluid and food consumption and energy expenditure are calculated. There is a higher (p < 0.001) post-race concentration of resistin and hs-CRP compared with resting values, with no change in chemerin levels. There is an inverse correlation of the change in resistin levels with post-run glucose values (r = 0.742, p < 0.001) and a positive correlation between changes in hs-CRP and energy expenditure (r = 0.782, p < 0.001). The present results show the impact of running an ultra-marathon on serum levels of pro-inflammatory markers released by adipose tissue. It is difficult to establish whether these results may be due to the stress of exercise, high energy expenditure or caloric deficit. However, we suggest that an addition of resistin to traditional pro-inflammatory markers (including CRP) may improve the assessment of inflammation in conditions of high-energy expenditure.

Running wheel access fails to resolve impaired sustainable health in mice feeding a high fat sucrose diet

Diet and physical activity are thought to affect sustainable metabolic health and survival. To improve understanding, we studied survival of mice feeding a low-fat (LF) or high-saturated fat/high sugar (HFS) diet, each with or without free running wheel (RW) access. Additionally several endocrine and metabolic health indices were assessed at 6, 12, 18 and 24 months of age. As expected, HFS feeding left-shifted survival curve of mice compared to LF feeding, and this was associated with increased energy intake and increased (visceral/total) adiposity, liver triglycerides, and increased plasma cholesterol, corticosterone, HOMA-IR, and lowered adiponectin levels. Several of these health parameters improved (transiently) by RW access in HFS and LF fed mice (i.e., HOMA-IR, plasma corticosterone), others however deteriorated (transiently) by RW access only in HFS-fed mice (i.e., body adiposity, plasma resistin, and free cholesterol levels). Apart from these multiple and sometimes diverging health effects of RW access, RW access did not affect survival curves. Important to note, voluntary RW activity declined with age, but this effect was most pronounced in the HFS fed mice. These results thus challenge the hypothesis that voluntary wheel running can counteract HFS-induced deterioration of survival and metabolic health.

Effects of exercise training and detraining on atheromatous matrix metalloproteinase activity in mice

BACKGROUND AND AIMS

Exercise training (ET) helps treat atherosclerosis. However, many patients stop regular ET for various reasons. The effect of detraining on atherosclerosis is not well studied. We examined the effects of ET vs. short-term detraining on atheromatous matrix-metalloproteinase (MMP) activity in preexisting plaque and circulating cytokines/lipids.

METHODS AND RESULTS

Eighteen-week-old apolipoprotein-E^-/- mice (n = 56) on a Western diet underwent: 1) ET for 6-weeks (ET5+1), 2) ET for 5-weeks and detraining for 1-week (ET5+0), 3) ET for the last 1-week (ET0+1), or 4) no treadmill ET at all for 6-weeks (ET0+0). Atheromatous MMP-activity was visualized using molecular imaging with an MMP-2/9-activatable near-infrared-fluorescent probe. Compared with no ET (ET0+0), regular ET (ET5+1) decreased carotid atheromatous MMP activity, but this protective effect was significantly blunted by short-term detraining (ET5+0). Short-term detraining after longer-term ET showed a reduction in MMP-activity similar to short-term ET (ET0+1). Blood levels of lipids and cytokines paralleled the molecular imaging results: exercise caused higher levels of high-density lipoprotein, adiponectin, and interleukin-10 and lower levels of vascular cell adhesion molecule, monocyte chemoattractant protein-1, interleukin-1β, and low-density lipoprotein. However, this beneficial effect was short-lived, with the ET5+0 group being similar to the ET0+0 group, and the ET0+1 group being similar to the ET5+1 group. The effect of exercise can be modeled with an exponential-decay of the protective factor of about 15%/day.

CONCLUSIONS

Even short-term detraining reduces atheroprotective effects, and tips the balance towards atherosclerosis. This suggests that ET, to be effective, needs to be prolonged and regular, and that detraining should be avoided.

Inflammatory markers in children and adolescents with type 2 diabetes mellitus

This review examines the potential relationship between serum inflammation markers and type 2 diabetes mellitus (T2DM). Inflammation markers have been proposed as prognostic markers for the development of T2DM and its complications. Furthermore, modulation of the inflammatory process may offer future treatment strategies for T2DM. This review focuses on children and adolescents because there is usually little, if any, complications associated with other disease processes, use of medications, or active tobacco smoking. Furthermore, β-cell failure in young age cannot be solely explained by aging and exhaustion of β-cells due to insulin resistance. Pediatric studies have demonstrated that pro-inflammatory cytokines TNF-α, IL-6, IL-1β, IFNγ, PEDF, and fetuin A were increased in insulin resistance, while the anti-inflammatory cytokines adiponectin and omentin were decreased. Furthermore, TNF-α, fetuin A, FGF-21 were altered in obese children with T2DM suggesting a direct involvement in β-cell failure. Future studies focusing on children and adolescents may facilitate our understanding of T2DM as an inflammatory disease process.

The Role of Mineral and Trace Element Supplementation in Exercise and Athletic Performance: A Systematic Review

Minerals and trace elements (MTEs) are micronutrients involved in hundreds of biological processes. Deficiency in MTEs can negatively affect athletic performance. Approximately 50% of athletes have reported consuming some form of micronutrient supplement; however, there is limited data confirming their efficacy for improving performance. The aim of this study was to systematically review the role of MTEs in exercise and athletic performance. Six electronic databases and grey literature sources (MEDLINE; EMBASE; CINAHL and SportDISCUS; Web of Science and clinicaltrials.gov) were searched, in accordance with PRISMA guidelines. Results: 17,433 articles were identified and 130 experiments from 128 studies were included. Retrieved articles included Iron (n = 29), Calcium (n = 11), Magnesium, (n = 22), Phosphate (n = 17), Zinc (n = 9), Sodium (n = 15), Boron (n = 4), Selenium (n = 5), Chromium (n = 12) and multi-mineral articles (n = 5). No relevant articles were identified for Copper, Manganese, Iodine, Nickel, Fluoride or Cobalt. Only Iron and Magnesium included articles of sufficient quality to be assigned as 'strong'. Currently, there is little evidence to support the use of MTE supplementation to improve physiological markers of athletic performance, with the possible exception of Iron (in particular, biological situations) and Magnesium as these currently have the strongest quality evidence. Regardless, some MTEs may possess the potential to improve athletic performance, but more high quality research is required before support for these MTEs can be given. PROSPERO preregistered (CRD42018090502).

Inflammation Markers in Type 2 Diabetes and the Metabolic Syndrome in the Pediatric Population

PURPOSE OF REVIEW

Chronic inflammation, adipokines, and hepatokines have been identified as basis of insulin resistance and β cell failure in animal models. We present our current knowledge concerning the potential relationship between these cytokines, inflammation, metabolic syndrome (MetS), and type 2 diabetes mellitus (T2DM) in the pediatric population.

RECENT FINDINGS

Pro-inflammatory cytokines related to insulin resistance and MetS in children are tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, IL-1β, interferon gamma, pigment epithelium-derived factor, chemerin, vaspin, and fetuin A. Anti-inflammatory cytokines associated with insulin resistance and MetS in children are leptin, adiponectin, omentin, fibroblast growth factor (FGF)-21, osteocalcin, and irisin. These anti-inflammatory cytokines are decreased (adiponectin, omentin, and osteocalcin) or increased (leptin, FGF-21, and irisin) in obesity suggesting a resistance state. TNF-α, fetuin A, and FGF-21 are altered in obese children with T2DM suggesting an involvement in β cell failure. These cytokines, adipokines, and hepatokines may be able to predict development of MetS and T2DM and have a potential therapeutic target ameliorating insulin resistance.

Effects of the inspiratory muscle training and aerobic training on respiratory and functional parameters, inflammatory biomarkers, redox status and quality of life in hemodialysis patients: A randomized clinical trial

Objective

Evaluate and compare the isolated and combined effects of Inspiratory Muscle Training (IMT) and Aerobic Training (AT) on respiratory and functional parameters, inflamatory biomarkers, redox status and health-related quality of life (HRQoL) in hemodialysis patients.

Methods

A randomised controlled trial with factorial allocation and intention-to-treat analysis was performed in hemodialysis patients. Volunteers were randomly assigned to performe 8-weeks of IMT at 50% of maximal inspiratory pressure (MIP), low intensity AT or combined training (CT). Before the interventions, all the volunteers went 8-weeks through a control period (without training). Measures are taken at baseline, 8-week (after control period) and 16-week (after the interventions). Primary outcomes were functional capacity (incremental shuttle walk test), MIP and lower limbs strength (Sit-to-Stand test of 30 seconds). Plasma levels of interleukin-6 (IL-6), soluble tumor necrosis factor receptor 1 (sTNFR1) and 2 (sTNFR2), adiponectin, resistin and leptin, redox status parameters and HRQoL (KDQOL-SF questionnaire) were the scondary outcomes. Data analyses were performed by two-way repeated measurements ANOVA.

Results

37 hemodialysis patients aged 48.2 years old (IC95% 43.2–54.7) were randomized. Increase of MIP, functional capacity, lower limbs strength and resistin levels, and reduction of sTNFR2 levels in 16-week, compared to baseline and 8-week, were observed in all the groups (p<0.001). IMT improved functional capacity, MIP and lower limbs strength in 96.7m (IC95% 5.6–189.9), 34.5cmH₂O (IC95% 22.4–46.7) and 2.2repetitions (IC95% 1.1–3.2) respectively. Increase in resistin leves and reduction in sTNFR2 leves after IMT was 0.8ng/dL (IC95% 0.5–1.1) and 0.8ng/dL (IC95% 0.3–1.3), respectively, without between-group differences. Compared to baseline and 8-week, adiponectin levels (p<0.001) and fatigue domain of the HRQoL (p<0.05) increased in 16-week only in CT.

Conclusion

IMT, AT and CT improved functional parameters and modulated inflammatory biomarkers, in addition, IMT provoked a similar response to low intensity AT in hemodialysis patients.

Trial registration

Registro Brasileiro de Ensaios clínicos RBR-4hv9rs.

Type 2 diabetes mellitus risk and exercise: is resistin involved?

Obesity and associated disorders such as type 2 diabetes mellitus (T2DM) pose an increasing risk to the health of both individuals and society. Adipose tissue is an active endocrine organ, secreting many hormones, known as adipokines. Evidence suggests that one suggest adipokine, resistin, may be elevated in the plasma of individuals with T2DM, and early reports indicated that this may contribute to the impaired glucose tolerance and insulin resistance observed in T2DM, hence its name, resistin, however subsequent evidence suggests it may have a proinflammatory role. Performing regular exercise and dietary interventions improve insulin sensitivity and glucose tolerance in the majority of individuals with T2DM, and we hypothesized that plasma resistin levels may drop in individuals following a long term aerobic and/or resistance exercise intervention program. Articles analyzing the effects of exercise on serum resistin levels were therefore analyzed. Articles were selected and analyzed based on a minimum aerobic and/or resistance training program of 2 sessions per week for 12 weeks. Plasma resistin levels decreased following either endurance aerobic exercise and/or resistance training plans in individuals with obesity and/or insulin resistance, although this was not related to BMI change. Exercise intervention programs generally showed potentially beneficial changes in plasma resistin concentrations. It is possible these effects are mediated through exercise-induced decreases in inflammation via anti-inflammatory cytokine release rather than alterations in glucose metabolism and reductions in BMI per se. A possible link between resistin, exercise and T2DM is discussed.

Inverse association of resistin with physical activity in the general population

Aim

Resistin is a cytokine related with inflammation and ischemic heart disease. Physical activity (PA) prevents chronic inflammation and ischemic heart disease. We studied the relationship of serum concentration of resistin with HDL cholesterol, a known biomarker of PA, and with different measures of PA, in a large sample of the general adult population in the Canary Islands.

Methods

Cross-sectional study of 6636 adults recruited randomly. We analyzed the correlation of resistin and HDL cholesterol with PA (as metabolic equivalent level [MET]), and fitted the results with linear and logistic regression models using adjustment for age, alcohol consumption and smoking.

Results

Mean resistin level was higher in women (p<0.001), correlated inversely with age, HDL cholesterol (p<0.001) and alcohol consumption (p<0.001 in men), and correlated directly with smoking (p<0.001). Resistin correlated inversely with the duration of leisure time PA (p<0.001), leisure time MET (p<0.001) and moderate leisure time PA (p<0.001), with some differences between sexes. Men (OR = 0.78 [0.61–0.99; p<0.05]) and women (OR = 0.75 [0.61–0.92; p<0.01]) in the upper quintile of leisure time PA had a lower risk of elevated resistin. In contrast, a high degree of sedentarism was associated with an increased risk elevated resistin in women (OR = 1.24 [1.04–1.47; p<0.05] and in men (OR = 1.40 [1.01–1.82; p<0.05]).

Conclusions

In our sample of the general population, resistin was inversely associated with measures and levels of PA and HDL cholesterol. The association of resistin with PA was stronger than the association of HDL cholesterol with PA, making resistin a potentially useful biomarker of PA.

Bone mass and bone metabolic indices in male master rowers

The purpose of this study was to assess bone mass and bone metabolic indices in master athletes who regularly perform rowing exercises. The study was performed in 29 men: 14 master rowers and 15 non-athletic, body mass index-matched controls. Dual-energy X-ray absorptiometry measurements of the areal bone mineral density (aBMD) were performed for the total body, regional areas (arms, total forearms, trunk, thoracic spine, pelvis, and legs), lumbar spine (L1-L4), left hip (total hip and femoral neck), and forearm (33 % radius of the dominant and nondominant forearm). Serum concentrations of osteocalcin, collagen type I cross-linked C-telopeptide, visfatin, resistin, insulin, and glucose were determined. Comparative analyses showed significantly lower levels of body fat and higher lean body mass values in the rowers compared to the control group. The rowers also had significantly higher values of total and regional (left arm, trunk, thoracic spine, pelvis, and leg) BMD, as well as higher BMD values for the lumbar spine and the left hip. There were significant differences between the groups with respect to insulin, glucose, and the index of homeostasis model assessment insulin resistance. In conclusion, the systematic training of master rowers has beneficial effects on total and regional BMD and may be recommended for preventing osteoporosis.

Adipose Tissue as an Endocrine Organ: An Update on Pro-inflammatory and Anti-inflammatory Microenvironment

Adipose tissue is recognized as an active endocrine organ that produces a number of endocrine substances referred to as "adipokines" including leptin, adiponectin, adipolin, visfatin, omentin, tumour necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), resistin, pigment epithelium-derived factor (PEDF), and progranulin (PGRN) which play an important role in the food intake regulation and significantly influence insulin sensitivity and in some cases directly affect insulin resistance in skeletal muscle, liver, and adipose tissue. The review summarizes current knowledge about adipose tissue-derived hormones and their influence on energy homeostasis regulation. The possible therapeutic potential of these adipokines in the treatment of insulin resistance, endothelial dysfunction, a pro-inflammatory response, obesity, eating disorders, progression of atherosclerosis, type 1 diabetes, and type 2 diabetes is discussed.

Running a marathon induces changes in adipokine levels and in markers of cartilage degradation--novel role for resistin

Running a marathon causes strenuous joint loading and increased energy expenditure. Adipokines regulate energy metabolism, but recent studies have indicated that they also exert a role in cartilage degradation in arthritis. Our aim was to investigate the effects of running a marathon on the levels of adipokines and indices of cartilage metabolism. Blood samples were obtained from 46 male marathoners before and after a marathon run. We measured levels of matrix metalloproteinase-3 (MMP-3), cartilage oligomeric protein (COMP) and chitinase 3-like protein 1 (YKL-40) as biomarkers of cartilage turnover and/or damage and plasma concentrations of adipokines adiponectin, leptin and resistin. Mean marathon time was 3∶30∶46±0∶02∶46 (h:min:sec). The exertion more than doubled MMP-3 levels and this change correlated negatively with the marathon time (r = –0.448, p = 0.002). YKL-40 levels increased by 56% and the effect on COMP release was variable. Running a marathon increased the levels of resistin and adiponectin, while leptin levels remained unchanged. The marathon-induced changes in resistin levels were positively associated with the changes in MMP-3 (r = 0.382, p = 0.009) and YKL-40 (r = 0.588, p<0.001) and the pre-marathon resistin levels correlated positively with the marathon induced change in YKL-40 (r = 0.386, p = 0.008). The present results show the impact of running a marathon, and possible load frequency, on cartilage metabolism: the faster the marathon was run, the greater was the increase in MMP-3 levels. Further, the results introduce pro-inflammatory adipocytokine resistin as a novel factor, which enhances during marathon race and associates with markers of cartilage degradation.

Lack of association of apoE ε4 allele with insulin resistance

ApoE is a polymorphic protein involved in the metabolism of plasma lipoproteins; the ε4 allele was shown to be associated with coronary and aortic atherosclerosis in age-dependent fashion mediated by unknown mechanisms. This study was undertaken to assess whether the apoE isoforms in humans were associated with normal glucose tolerance and with metabolic and inflammatory risk factors of CVD. ApoE genotype was assessed in 365 individuals. Of those, 309 were studied in the postabsorptive conditions and 142 of them also underwent a 3h-OGTT; 56 additional subjects were studied by means of the insulin clamp in combination with [6,6-2H2] glucose infusion. ApoE genotype frequencies were similar to those previously reported and were not influenced by age and BMI. Fasting plasma glucose, insulin, FFA, the lipid profile, surrogate markers (HOMA-IR, OGTT-derived index) as well as the clamp-derived parameters or insulin sensitivity and insulin secretion were not different by apoE genotypes. Serum adipokines concentrations (leptin, adiponectin, resistin) and markers of inflammation (serum fasting hsCRP and MCP1/CCL2) were also not different by apoE genotypes. In the subgroup of young ε4 carriers which underwent the clamp procedure, a higher fasting endogenous glucose production was detected. ApoE genotype was not associated with insulin resistance or altered insulin secretion, and no abnormalities in the typical circulating endocrine, metabolic, and inflammatory features of the insulin resistance syndrome were detected.

Hemodynamics and metabolism at low versus moderate altitudes

Despite the higher prevalence of diabetes and hypertension in populations residing at moderate altitudes, mortality in these populations is lower than in populations residing at low altitudes. To examine whether metabolic and hemodynamic differences can explain this apparent paradox, we performed a cross-sectional study of a general population sample recruited in the Canary Islands, Spain (n=6729). We recorded altitude of residence, age, heart rate, blood pressure, body mass index, social class, physical activity, energy intake, alcohol intake, smoking habit, prevalence of type 2 diabetes mellitus and hypertension. In a subsample (n=903), we recorded serum concentration of cholesterol, triglycerides, glucose, C peptide, leptin, soluble leptin receptor (sObR), C-reactive protein, resistin, soluble CD40 ligand (sCD40L), and paraoxonase activity (PON), and we estimated insulin resistance and free leptin index. We found an inverse association between altitude and heart rate (p<0.001), leptin (p<0.001), free leptin index (p<0.001), resistin (p<0.001), and sCD40L (p<0.05) and a direct association between altitude and hypertension (odds ratio=1.29 for altitude >600 m; 95% confidence interval=1.03-1.62), glycemia (p<0.05), C peptide (p<0.001), insulin resistance (p<0.001), sObR (p<0.05), and PON (p<0.05). When social class was included in the multivariate model, the association with PON was no longer significant. In conclusion, individuals residing at moderate altitudes have a lower heart rate and lower serum concentration of total leptin, free leptin, and sCD40L. These differences may partially explain the lower mortality in these populations.

The impact of one session resistance exercise on plasma adiponectin and RBP4 concentration in trained and untrained healthy young men

We designed this study, to investigate the predicting effect of a single resistance exercise session on serum level of RBP4 and adiponectin in trained and untrained subjects and to evaluate whether regular training may affect the response of these adipokines to exercise. Thirty four healthy young male students including 19 trained and 15 untrained participated in this study; each group was then randomly assigned to intervention and control groups. The exercise session prolonged 120 minutes intensive resistance program at 70%-80% of 1RM. The blood samples were collected just before the start of training program and 4 hours post exercise to evaluate concentration of adiponectin, RBP4 and CRP as well as other metabolic markers. The serum level of adiponectin, RBP4 and CRP was not significantly different between trained and untrained groups at baseline. More over four hours post exercise adipokines concentration and CRP didn't differ between groups. Adjusted regression model showed, basal adiponectin (β=0.59, p=<0.001) and HDL cholesterol (β=0.28, p=0.09) were the main predictors of post exercise adiponectin concentration. In addition, the basic level of RBP4 appeared to be the only predictor of after exercise RBP4 concentration (β=0.46, p=0.02). Neither one session of high intensity resistance exercise nor long term training had predicting effect on post exercise adiponectin and RBP4 concentration in healthy young men. In the other hand, the beneficial effect of acute resistance exercise training may not be reflected by changes in adiponectin, RBP4 and CRP concentration in healthy young individual no matter they trained or untrained.

Adipokine responses to acute resistance exercise in trained and untrained men

INTRODUCTION

Adipose tissue-derived hormones act as key mediators that may link active lifestyles to improved cardiovascular function. This study tested the hypothesis that a single weight training session would beneficially modulate adipokine profile in a way that would exert protection against endothelial dysfunction, in trained but not sedentary subjects.

METHODS

Male subjects (n = 43) were categorized into four separate groups based on exercise history: 1) sedentary, 2) weight trainers, 3) runners, or 4) weight trainer + runners. All subjects underwent a single progressive leg press weight training session (low weight for two sets of 8-12 repetitions each and then near-maximal exertion for three sets of 8-12 repetitions each).

RESULTS

There were no differences between groups for age, body weight, BMI, waist circumference, or percent body fat. Adiponectin increased (P < 0.05) by 30% and 37%, whereas resistin decreased (P < 0.05) by 35% and 34% in the weight trainers and weight trainer + runners, respectively, after training. Flow-mediated dilation (FMD) was impaired (P < 0.05) in sedentary subjects (-1.1 +/- 0.3%) but not in the athletic groups (1.7 +/- 0.4%). Improvements in FMD were associated with increased adiponectin (r = 0.61, P = 0.01), and decreased resistin (r = -0.56, P = 0.01) in weight trainers only. Leptin was not altered by acute resistance training in any group. There were no differences after training for total, LDL, HDL cholesterol, triglycerides, C-reactive protein levels, and systolic or diastolic blood pressure. Increased adiponectin was related to higher levels of HDL cholesterol after intervention (r = 0.71, P = 0.001).

CONCLUSIONS

These findings suggest that habitual resistance training may modulate adipokine profiles in a way that is protective against endothelial dysfunction.

Adipokine signaling in inflammatory bowel disease

While the incidence of inflammatory bowel disease (IBD) is still increasing, the etiology has not finally been dissected. The main hypothesis suggests that the mucosal immune system is hyperresponsive to dietary factors and commensal bacteria in genetically predisposed individuals. Burrill Crohn himself described a local hypertrophy of the mesenteric fat tissue adjacent to the segments of inflamed intestine. In addition, more recent data indicate altered local expression and serum levels of some adipocyte-derived mediators (adipokines) with immune-modulating capacities in IBD. This review focuses on the role of adipose tissue and adipokines in the immune system, with particular focus on the mucosal immune system. The available data will serve to establish a working hypothesis on how the mesenteric fat tissue contributes to the pathogenesis of Crohn's disease.

White adipose tissue as endocrine organ and its role in obesity

Due to the public health problem represented by obesity, the study of adipose tissue, particularly of the adipocyte, is central to the understanding of metabolic abnormalities associated with the development of obesity. The concept of adipocyte as endocrine and functional cell is not totally understood and can be currently defined as the capacity of the adipocyte to sense, manage, and send signals to maintain energy equilibrium in the body. Adipocyte functionality is lost during obesity and has been related to adipocyte hypertrophy, disequilibrium between lipogenesis and lipolysis, impaired transcriptional regulation of the key factors that control adipogenesis, and lack of sensitivity to external signals, as well as a failure in the signal transduction process. Thus, dysfunctional adipocytes contribute to abnormal utilization of fatty acids causing lipotoxicity in non-adipose tissue such as liver, pancreas and heart, among others. To understand the metabolism of the adipocyte it is necessary to have an overview of the developmental process of new adipocytes, regulation of adipogenesis, lipogenesis and lipolysis, endocrine function of adipocytes and metabolic consequences of its dysfunction. Finally, the key role of adipose tissue is shown by studies in transgenic animals or in animal models of diet-induced obesity that indicate the contribution of adipose tissue during the development of metabolic syndrome. Thus, understanding of the molecular process that occurs in the adipocyte will provide new tools for the treatment of metabolic abnormalities during obesity.

Inverse association between serum resistin and insulin resistance in humans

AIM

To determine how serum concentrations of resistin are distributed in humans in relation to insulin resistance, type 2 diabetes, and obesity.

METHODS

Cross-sectional, descriptive study carried out in a random sample (n=713, 43% men, 18-75 years) of general population of inhabitants of the Canary Islands (Spain). Serum resistin concentration, HOMA2-IR, anthropometric parameters, drug consumption and physical activity were recorded.

RESULTS

There were no differences in resistin concentration between participants with and without diabetes (3.1+/-0.2 vs. 3.2+/-0.1ng/mL; p=0.566), or between obese and non-obese participants (3.1+/-0.1 vs. 3.2+/-0.1ng/mL; p=0.803). Individuals with abdominal obesity (waist-hip ratio [WHR] >or=1 in men or >or=0.9 in women) had lower concentrations of resistin (3.0+/-0.13 vs. 3.4+/-0.1ng/mL; p<0.001). The correlations between resistin and HOMA2-IR (r=-0.231; p<0.001) and between resistin and WHR (r=-0.202; p<0.001) were inverse. Multivariate analysis corroborated the inverse association of this cytokine with HOMA2-IR, WHR and, in women, also retained in the model the direct association between resistin and physical activity and the inverse association between resistin and antihypertensive agents.

CONCLUSIONS

In this population resistin is inversely associated with insulin resistance and abdominal obesity.

Adipokines and insulin resistance

Obesity is associated with an array of health problems in adult and pediatric populations. Understanding the pathogenesis of obesity and its metabolic sequelae has advanced rapidly over the past decades. Adipose tissue represents an active endocrine organ that, in addition to regulating fat mass and nutrient homeostasis, releases a large number of bioactive mediators (adipokines) that signal to organs of metabolic importance including brain, liver, skeletal muscle, and the immune system--thereby modulating hemostasis, blood pressure, lipid and glucose metabolism, inflammation, and atherosclerosis. In the present review, we summarize current data on the effect of the adipose tissue-derived hormones adiponectin, chemerin, leptin, omentin, resistin, retinol binding protein 4, tumor necrosis factor-alpha and interleukin-6, vaspin, and visfatin on insulin resistance.

Serum resistin and polymorphisms of androgen receptor GAGn and GGNn and aromatase TTTAn

There is evidence that androgens are regulators of insulin resistance (IR), and may be involved in the regulation of resistin, a cytokine that has been related with IR. Earlier studies found that androgen receptor length polymorphisms CAGn and GGNn and the aromatase polymorphism TTTAn may influence receptor or enzyme activity and serum concentrations of androgens. This study was designed to determine whether polymorphism length was related to serum resistin concentration and to other variables related with IR. In 1,580 persons chosen randomly from the general population of the Canary Islands (Spain), we measured polymorphism length, waist circumference, waist/hip ratio, BMI, and serum glucose concentration. In smaller subgroups, we also measured C-peptide (n = 677), resistin (n = 583), and leptin concentration (n = 754) and estimated IR (homeostasis model assessment-IR (HOMA2-IR)). In men, polymorphism length correlated with resistin concentration (CAGn, r = 0.13, P = 0.031; TTTAn, r = 0.15, P = 0.005; GGNn, r = -0.15, P = 0.026), and the correlations were confirmed in multivariate regression models. The length of CAGn and TTTAn correlated inversely with C-peptide (r = -0.13, P = 0.016 and r = -0.21, P < 0.001, respectively) and with estimated IR (r = -0.12, P = 0.032 and r = -0.19, P = 0.001, respectively). In men, length of the CAGn, GGNn, and TTTAn was associated with serum resistin concentration. These results support the hypothesis that androgens may be involved in the regulation of resistin. Resistin may be a link between IR and androgens.

Serum resistin and hepatic fat content in nondiabetic individuals

CONTEXT

Serum resistin concentration is increased in patients with nonalcoholic fatty liver disease in proportion with the histological severity of the disease, but the relevance of the contribution of fatty liver per se is undetermined.

OBJECTIVE

The objective of the study was to assess the relationship between serum resistin and the degree of ectopic fat accumulation in vivo in humans.

DESIGN AND SETTING

The hepatic fat (IHF) content, measured quantitatively by means of 1H magnetic resonance spectroscopy, serum resistin, and biochemical and hormonal metabolic correlates of fatty liver and insulin resistance were assessed in 28 affected patients, and 47 individuals with comparable anthropometric features served as controls. Insulin sensitivity was estimated using the computer homeostatic model assessment (HOMA)-2. A subset of volunteers (n = 18) also underwent 1H magnetic resonance spectroscopy of the calf muscles to assess the intramyocellular lipid content (IMCL).

RESULTS

In patients with fatty liver, the IHF content (13 +/- 8 vs. 2 +/- 1% wet weight; P < 0.0001) and also the soleus IMCL content (P < 0.05) were increased in comparison with the controls. Patients with fatty liver had lower insulin sensitivity (HOMA2 insulin sensitivity: 59 +/- 24 vs. 72 +/- 29%; P < 0.04), serum resistin (3.4 +/- 0.8 vs. 3.9 +/- 1.0 ng/ml; P < 0.02), and adiponectin (P < 0.01) concentrations. Serum resistin was inversely correlated with the IHF content (r = -0.35; P < 0.003) and the soleus IMCL content (r = -0.51; P < 0.05) but not HOMA2 insulin sensitivity.

CONCLUSION

This study demonstrates that excessive ectopic fat accumulation in the liver and skeletal muscle of insulin-resistant subjects is associated with lower serum resistin concentration and not with hyperresistinemia.