Effects of short-term exercise on adiponectin and adiponectin receptor levels in rats

Adiponectin and Its Mimics on Skeletal Muscle: Insulin Sensitizers, Fat Burners, Exercise Mimickers, Muscling Pills … or Everything Together?

Adiponectin (ApN) is a hormone abundantly secreted by adipocytes and it is known to be tightly linked to the metabolic syndrome. It promotes insulin-sensitizing, fat-burning, and anti-atherosclerotic actions, thereby effectively counteracting several metabolic disorders, including type 2 diabetes, obesity, and cardiovascular diseases. ApN is also known today to possess powerful anti-inflammatory/oxidative and pro-myogenic effects on skeletal muscles exposed to acute or chronic inflammation and injury, mainly through AdipoR1 (ApN specific muscle receptor) and AMP-activated protein kinase (AMPK) pathway, but also via T-cadherin. In this review, we will report all the beneficial and protective properties that ApN can exert, specifically on the skeletal muscle as a target tissue. We will highlight its effects and mechanisms of action, first in healthy skeletal muscle including exercised muscle, and second in diseased muscle from a variety of pathological conditions. In the end, we will go over some of AdipoRs agonists that can be easily produced and administered, and which can greatly mimic ApN. These interesting and newly identified molecules could pave the way towards future therapeutic approaches to potentially prevent or combat not only skeletal muscle disorders but also a plethora of other diseases with sterile inflammation or metabolic dysfunction.

Potential exerkines for physical exercise-elicited pro-cognitive effects: Insight from clinical and animal research

A sedentary lifestyle is now known as a critical risk factor for accelerated aging-related neurodegenerative disorders. In contract, having regular physical exercise has opposite effects. Clinical findings have suggested that physical exercise can promote brain plasticity, particularly the hippocampus and the prefrontal cortex, that are important for learning and memory and mood regulations. However, the underlying mechanisms are still unclear. Animal studies reveal that the effects of physical exercise on promoting neuroplasticity could be mediated by different exerkines derived from the peripheral system and the brain itself. This book chapter summarizes the recent evidence from clinical and pre-clinical studies showing the emerging mediators for exercise-promoted brain health, including myokines secreted from skeletal muscles, adipokines from adipose tissues, and other factors secreted from the bone and liver.

Adiponectin, Leptin and Visfatin in Hypoxia and its Effect for Weight Loss in Obesity

Rationale: Hypoxia induces leptin gene expression in human adipocytes via hypoxia-inducible factors (HIF-α/β). Under ambient moderate hypoxia, leptin in adipocytes is elevated for at least 14 days. Leptin is supposedly involved in the reduced food intake, increased utilization of fatty acids for energy production and possible weight loss observed at high altitudes. Literature on adiponectin and visfatin in high altitude is inconsistent with reports of elevated levels and non-elevated levels. Exercise in hypoxia studies in obese subjects have shown a significant weight loss after up to 3 weeks, but it is unclear if this effect holds up for longer time periods. Therefore, we aimed to investigate 32 obese subjects completing 52 exercise and rest sessions within 8 months at either moderate or sham hypoxia and to analyze leptin, adiponectin, and visfatin mRNA-expression at different time points of exposure. Methods: Abdominal subcutaneous fat biopsies were taken from 32 obese subjects before, after 3 months and after 8 months of intervention. Subjects were randomly divided into two groups and exercised at moderate intensity at two different study sites twice a week. The IG was exposed to normobaric hypoxia (FiO₂: 14.0 ± 0.2%,) at exercise and at rest (FiO₂: 12.0 ± 0.2%) and the CG to sham hypoxia. Quantitative real-time polymerase chain reaction (qPCR) was used in order to determine mRNA-levels of leptin, adiponectin, and visfatin. Results: No differences in leptin levels after 3 and 8 months compared to baseline and between groups were found. There was no significant difference regarding adiponectin or visfatin at any time point compared to baseline in the hypoxia group, but an increase after 3 months was seen in the control group at normoxia compared to the hypoxia group (adiponectin: p = 0.029 and visfatin: p = 0.014). Conclusion: In this first several months' duration randomized sham controlled hypoxia exercise and rest study with obese subjects, we found no time extended leptin mRNA-expression in subjects under hypoxia after 3 and 8 months compared to baseline levels. Moderate exercise in normoxia not in hypoxia leads to elevated adiponectin and visfatin levels after 3 months.

Inflammatory and Adipose Response in Solid Organ Transplant Recipients After a Marathon Cycling Race

BACKGROUND

Organ transplant recipients frequently have chronic inflammation, with a weighty impact on cardiovascular risk. These patients can benefit from exercise, although the role of intense training is unclear. We evaluated the effect of a 130-km cycling race on inflammatory cytokines and adiponectin levels in transplant recipients.

METHODS

Circulating interleukin (IL)-6, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, and adiponectin were assayed in 35 healthy subjects vs 19 transplant recipients (10 kidney, 8 liver, 1 heart), matched for sex, age, body mass index, and preparation workout. The determinations were performed before the race, at the end, and after 18 to 24 hours. Baseline values of 32 sedentary transplant recipients also were evaluated to explore the possible chronic impact of lifestyle.

RESULTS

All cyclists had 6- to 8-fold increased IL-6 levels after the race that decreased, without returning to baseline, the day after. Conversely, serum TNF-α and IFN-γ showed a progressive increase starting during physical performance and enduring for the next 18 to 24 hours in healthy subjects, whereas they were unchanged over time in cyclists with transplants. In transplant recipients who did not perform exercise, all of the analytes were significantly higher in comparison to basal levels of physically active subjects.

CONCLUSIONS

Our data suggest that clinically stable and properly trained transplant recipients can safely perform and progressively benefit from exercise, even at a competitive level. The changes in inflammation parameters were temporary and parallel with those of the healthy subjects. The comparison with sedentary transplant recipients revealed an overall amelioration of inflammatory indexes as a possible effect of regular physical activity on systemic inflammation.

Exercise and Adipose Tissue Macrophages: New Frontiers in Obesity Research?

Obesity is a major public health problem in the twenty-first century. Mutations in genes that regulate substrate metabolism, subsequent dysfunction in their protein products, and other factors, such as increased adipose tissue inflammation, are some underlying etiologies of this disease. Increased inflammation in the adipose tissue microenvironment is partly mediated by the presence of cells from the innate and adaptive immune system. A subset of the innate immune population in adipose tissue include macrophages, termed adipose tissue macrophages (ATMs), which are central players in adipose tissue inflammation. Being extremely plastic, their responses to diverse molecular signals in the microenvironment dictate their identity and functional properties, where they become either pro-inflammatory (M1) or anti-inflammatory (M2). Endurance exercise training exerts global anti-inflammatory responses in multiple organs, including skeletal muscle, liver, and adipose tissue. The purpose of this review is to discuss the different mechanisms that drive ATM-mediated inflammation in obesity and present current evidence of how exercise training, specifically endurance exercise training, modulates the polarization of ATMs from an M1 to an M2 anti-inflammatory phenotype.

Assembly of adiponectin oligomers

Adiponectin is among the most studied adipokines, the collection of molecules secreted from adipose tissue. It is also one of the most architecturally complex adipokines with its various oligomeric states that include trimers, hexamers, nonamers (9mers), dodecamers (12mers), and octadecamers (18mers). The importance of adiponectin in metabolic regulation is underscored by its strong positive associations with improvement in insulin action and also decreased risks for developing type 2 diabetes. Understanding the mechanisms involved in maintaining the steady-state concentrations of adiponectin oligomers in circulation is therefore likely to provide important insight into the development of insulin resistance. This review will discuss the current state of knowledge regarding the biochemical composition of adiponectin oligomers, the commonly used techniques to analyze them, and the known post-translational modifications that affect their assembly. Evidence based on in vitro oligomer assembly reactions in support of a "cystine ratchet" model of adiponectin oligomer formation will be considered along with limitations of the evidence. Secretory pathway proteins that have been shown to affect the distribution of adiponectin oligomers will also be discussed along with hypotheses regarding their potential involvement in the cystine ratchet model of adiponectin oligomerization.

Green tea polyphenols reduced fat deposits in high fat-fed rats via erk1/2-PPARγ-adiponectin pathway

Objective

Hypoadiponectinemia contributes to the development of obesity and related disorders such as diabetes, hyperlipidemia, and cardiovascular diseases. In this study we investigated the effects of green tea polyphenols (GTPs) on adiponectin levels and fat deposits in high fat (HF) fed rats, the mechanism of signaling pathway was explored as well.

Methods and Results

Male Wistar rats were fed with high-fat diet. GTPs (0.8, 1.6, 3.2 g/L) were administered via drinking water. Serum adiponectin and insulin were measured by ELISA, mRNA levels of adiponectin and PPARγ in visceral adipose tissue (VAT) were determined by Real-time PCR, protein levels of PPARγ, phospho (p) - PPARγ, extracellular signal regulated kinase (erk) 1/2 and p-erk1/2 in VAT were determined by western blot. GTPs treatment attenuated the VAT accumulation, hypoadiponectinemia and the decreased mRNA level of adiponectin in VAT induced by HF. Decreased expression and increased phosphorylation of PPARγ (the master regulator of adiponectin), and increased activation of erk1/2 were observed in HF group, and these effects could be alleviated by GTPs treatment. To explore the underlying mechanism, VAT was cultured in DMEM with high glucose to mimic the hyperglycemia condition in vitro. Similar to the results of in vivo study, decreased adiponectin levels, decreased expression and increased phosphorylation of PPARγ, and elevated erk1/2 phosphorylation in cultured VAT were observed. These effects could be ameliorated by co-treatment with GTPs or PD98059 (a selective inhibitor of erk1/2).

Conclusion

GTPs reduced fat deposit, ameliorated hypoadiponectinemia in HF-fed rats, and relieved high glucose-induced adiponectin decrease in VAT in vitro. The signaling pathway analysis indicated that PPARγ regulation mediated via erk1/2 pathway was involved.

Differential effects of acute (extenuating) and chronic (training) exercise on inflammation and oxidative stress status in an animal model of type 2 diabetes mellitus

This study compares the effects of a single bout of exercise (acute extenuating) with those promoted by an exercise training program (chronic), focusing on low-grade chronic inflammation profile and on oxidative stress status, using the obese ZDF rats as a model of type 2 diabetes mellitus (T2DM). Animals were sacrificed after 12 weeks of a swimming training program and after a single bout of acute extenuating exercise. Glycaemic, insulinemic, and lipidic profile (triglycerides, total-cholesterol) were evaluated, as well as inflammatory (serum CRPhs, TNF-α, adiponectin) and oxidative (lipidic peroxidation and uric acid) status. When compared to obese diabetic sedentary rats, the animals submitted to acute exercise presented significantly lower values of glycaemia and insulinaemia, with inflammatory profile and oxidative stress significantly aggravated. The trained animals showed amelioration of glycaemic and lipidic dysmetabolism, accompanied by remarkable reduction of inflammatory and oxidative markers. In conclusion, the results presented herein suggessted that exercise pathogenesis-oriented interventions should not exacerbate underlying inflammatory stress associated with T2DM.

Voluntary exercise ameliorates the progression of atherosclerotic lesion formation via anti-inflammatory effects in apolipoprotein E-deficient mice

AIM

A sedentary lifestyle with insufficient exercise is associated with cardiovascular disease. Previous studies have demonstrated that endurance exercise benefits atherosclerosis and cardiovascular disorders; however, the mechanisms by which physical activity, such as voluntary exercise (Ex), produces these effects are not fully understood.

METHODS AND RESULTS

Eight-week-old male apolipoprotein (ApoE)-deficient mice were fed a standard diet (STD) or high fat diet (HFD) for 10 weeks. The HFD+Ex group mice performed Ex on a running wheel for 10 weeks. No significant differences in lipid profiles were observed between the HFD and HFD+Ex groups. Although changes in body and brown adipose tissue weights were comparable between the HFD and HFD+Ex groups, white adipose tissue weight was significantly lower in the HFD+Ex group than in the HFD group. The areas of atherosclerotic lesions in the aortic sinus and thoracoabdominal aorta were significantly reduced in the HFD+Ex group than in the HFD group (p<0.001). There was a strong negative correlation between atherosclerotic areas and the mean running distance per day in the HFD+Ex group (r=-0.90, p=0.01). Endothelial function was significantly preserved in the HFD+Ex group (p<0.05). Serum interleukin-6 and macrophage chemoattractant protein-1 levels were significantly lower and those of adiponectin were significantly higher in the HFD+Ex group than in the HFD group (p<0.05).

CONCLUSIONS

These results suggest that Ex ameliorates the progression of endothelial dysfunction and atherosclerotic lesion formation through anti-inflammatory effects, despite continued consumption of HFD.

Intricacies of fat

One of the most exciting cell biology fields of study concerns the physiology and pathology of fat. The basic assumptions once held concerning the function of adipose tissue have been shown to be oversimplified or sometimes completely wrong. Fat does more than store excess energy; it is actually the largest endocrine organ in the body, and it may be one of the most active. Adipocytes release hormones and other molecules that act on nearby tissues and travel through the vasculature to distant sites, such as the brain, skeletal muscle, and liver. Under conditions of normal weight, those signals help the body to suppress hunger, utilize glucose, and decrease the risk of cardiovascular disease. However, under conditions of obesity, the hormones (or the proteins that bind the hormones) become abnormal and can result in states of chronic inflammation leading to diabetes and heart disease. In addition, excessive fat can lead to the accumulation of lipid droplets in nonfat cells, including skeletal and cardiac muscle. Although some lipid droplets are used as an immediate source of energy for cells, large numbers of stored droplets can cause cellular damage and cell death. The purposes of this article are to review the normal and deviant signals released by fat cells, to draw a link between those signals and chronic diseases such as diabetes, and to discuss the role of exercise in reversing some of the deviant signaling perpetrated by excess fat.

Impact of body weight, diet and lifestyle on nonalcoholic fatty liver disease

Nonalcoholic steatohepatitis is part of the broader spectrum of nonalcoholic fatty liver disease, strongly associated with insulin resistance, obesity and the metabolic syndrome. Its increasing prevalence appears to be closely related to the increased frequency of overweight or obesity; which is associated with changes in dietary habits, including an increased consumption of hypercaloric food and saturated fat, often concurrent with decreased activity and energy expenditure. Weight loss through dieting and increasing energy expenditure through the practice of regular exercise has been shown to be effective in improving nonalcoholic fatty liver disease/nonalcoholic steatohepatitis, and is considered the mainstay of treatment. The effectiveness of these lifestyle interventions seems to rely chiefly on an improvement in insulin sensitivity. At present, disease management using a multidisciplinary team is probably pivotal for patient-centered quality of care.