Intermuscular and perimuscular fat expansion in obesity correlates with skeletal muscle T cell and macrophage infiltration and insulin resistance

Inter-tissue expression patterns of the key metabolic biomarker PGC-1α in severely obese individuals: Implication in obesity-induced disease

OBJECTIVE

PGC-1α is already known as a significant regulator of mitochondrial biogenesis, oxidative phosphorylation and fatty acid metabolism. Our study focuses on the role of PGC1α in morbid obesity, in five different tissues, collected from 50 severely obese patients during planned bariatric surgery.

METHODS

The investigated tissues included subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT), skeletal muscle (SM), extramyocellular adipose tissue (EMAT) and liver. PGC1α expression was investigated with immunohistochemistry and evaluated with microscopy.

RESULTS

Our findings highlighted significant positive inter-tissue correlations regarding PGC-1α expression between several tissue pairs (VAT-SAT, VAT-SM, VAT-EMAT, SAT-SM, SAT-EMAT, SM-EMAT). Moreover, we found significant negative correlations between PGC1α expression in VAT with CD68 expression in skeletal muscle and EMAT, implying a possible protective role of PGC1α against obesity-induced inflammation.

CONCLUSION

Unmasking the inter-tissue communication networks regarding PGC-1α expression in morbid obesity, will give more insight into its significant role in obesity-induced diseases. PGC1α could potentially represent a future preventive and therapeutic target against obesity-induced disease, probably through enhancing mitochondrial biogenesis and metabolism.

Associations of pre-existing co-morbidities with skeletal muscle mass and radiodensity in patients with non-metastatic colorectal cancer

BACKGROUND AND AIM

Co-morbidities and computerized tomography-measured muscle abnormalities are both common in cancer patients and independently adversely influence clinical outcomes. Muscle abnormalities are also evident in other diseases, such as diabetes and obesity. This study examined for the first time the association between co-morbidities and muscle abnormalities in patients diagnosed with colorectal cancer (CRC).

METHODS

This cross-sectional study included 3051 non-metastatic patients with Stages I-III CRC. Muscle abnormalities, measured at diagnosis, were defined as low skeletal muscle mass index (SMI) or low skeletal muscle radiodensity (SMD) quantified using computerized tomography images using optimal stratification. Co-morbidities included in the Charlson index were ascertained. χ2 tests were used to compare the prevalence of co-morbidities by the presence or absence of each muscle abnormality. Logistic regressions were performed to evaluate which co-morbidities predicted muscle abnormalities adjusting for age, sex, body mass index, weight change, cancer stage, cancer site, race/ethnicity, and smoking.

RESULTS

Mean age was 63 years; 50% of patients were male. The prevalence of low SMI and low SMD were 43.1% and 30.2%, respectively. Co-morbidities examined were more prevalent in patients with low SMD than in those with normal SMD, and most remained independent predictors of low SMD after adjustment for covariates. Co-morbidities associated with higher odds of low SMD included myocardial infarction [odds ratio (OR) = 1.77, P = 0.023], congestive heart failure (OR = 3.27, P < 0.001), peripheral vascular disease (OR = 2.15, P = 0.002), diabetes with or without complications (OR = 1.61, P = 0.008; OR = 1.46, P = 0.003, respectively), and renal disease (OR = 2.21, P < 0.001). By contrast, only diabetes with complications was associated with lower odds of low SMI (OR = 0.64, P = 0.007).

CONCLUSIONS

Prevalence of muscle abnormalities was high in patients with non-metastatic CRC. Pre-existing co-morbidities were associated with low SMD, suggestive of a potential shared mechanism between fat infiltration into muscle and each of these co-morbidities.

Cysteine- and glycine-rich protein 3 regulates glucose homeostasis in skeletal muscle

Skeletal muscle is the major site of postprandial peripheral glucose uptake, but in obesity-induced insulin-resistant states insulin-stimulated glucose disposal is markedly impaired. Despite the importance of skeletal muscle in regulating glucose homeostasis, the specific transcriptional changes associated with insulin-sensitive vs. -resistant states in muscle remain to be fully elucidated. Herein, using an RNA-seq approach we identified 20 genes differentially expressed in an insulin-resistant state in skeletal muscle, including cysteine- and glycine-rich protein 3 ( Csrp3), which was highly expressed in insulin-sensitive conditions but significantly reduced in the insulin-resistant state. CSRP3 has diverse functional roles including transcriptional regulation, signal transduction, and cytoskeletal organization, but its role in glucose homeostasis has yet to be explored. Thus, we investigated the role of CSRP3 in the development of obesity-induced insulin resistance in vivo. High-fat diet-fed CSRP3 knockout (KO) mice developed impaired glucose tolerance and insulin resistance as well as increased inflammation in skeletal muscle compared with wild-type (WT) mice. CSRP3-KO mice had significantly impaired insulin signaling, decreased GLUT4 translocation to the plasma membrane, and enhanced levels of phospho-PKCα in muscle, which all contributed to reduced insulin-stimulated glucose disposal in muscle in HFD-fed KO mice compared with WT mice. CSRP3 is a highly inducible protein and its expression is acutely increased after fasting. After 24h fasting, glucose tolerance was significantly improved in WT mice, but this effect was blunted in CSRP3-KO mice. In summary, we identify a novel role for Csrp3 expression in skeletal muscle in the development of obesity-induced insulin resistance.

Peripheral Lymphocytes, Obesity, and Metabolic Syndrome in Young Adults: An Immunometabolism Study

BACKGROUND

Obesity is characterized by a low-intensity chronic inflammatory process in which immune system cells interact in a complex network, which affects systemic metabolic processes. This raises interest in analyzing possible changes in the proportions of immune system cells in individuals with obesity with and without metabolic syndrome (MS), in relation to their body composition.

METHODS

Circulating cells were analyzed with flow cytometry in young adults: monocytes, granulocytes, lymphocytes (T, B, and natural killer [NK]), TCD4⁺CD62^-, TCD8⁺CD28^-, and naive and memory cells of TCD3⁺ and TCD4⁺. Body composition was obtained by bioelectrical impedance analysis and dual-energy X-ray absorptiometry, and metabolic parameters.

RESULTS

A total of 169 persons were evaluated: 20% presented normal body mass index (BMI); 49% was overweight, and 31% had obesity; 28% had MS. It was observed that with an increase in BMI and visceral adipose tissue increase (VATI), body composition and biochemical variables were negatively altered. With regard to cell subpopulations, total lymphocytes increased and granulocytes and NK lymphocytes decreased in patients with MS and VATI. Memory cells increased with BMI and VATI. In individuals with MS, monocytes, and NK lymphocytes comprised a negative association with VAT, fat mass, and skeletal muscle mass (SMM). In individuals with MS and VATI, a negative correlation was observed between monocytes and SMM.

CONCLUSIONS

Significant changes were detected in the subpopulations of lymphocytes, suggesting that weight gain, SMM, and VAT accumulation gave rise to immunological changes at the peripheral level, and the presence of increased memory cells could be related to low-intensity chronic inflammation.

The Role of T Lymphocytes in Skeletal Muscle Repair From Traumatic and Contraction-Induced Injury

Skeletal muscle is prone to damage from a range of stimuli, and initiates a robust repair process that requires the participation of immune cells. Among the more well characterized immune cells involved in muscle repair are those of the myeloid lineage, including neutrophils, macrophages, monocytes, and eosinophils. More recently, studies have begun to elucidate the role of the lymphoid-derived immune cells, most notably T lymphocytes (T-cells), in the complex processes of muscle repair. Though T-cells have been traditionally been associated with pathological degeneration of skeletal muscle in disease, recent studies show that T-cells are instrumental in the repair/regeneration process following severe muscle damage in mice. Furthermore, a few studies using basic immunohistochemical assays have shown that T-cells accumulate in human skeletal muscle in the days following contraction-induced muscle damage. The functional significance of T-cells in the repair and adaptation process following contraction-induce muscle damage remains uncertain, and is an active area of intense investigation. This mini-review summarizes recent findings on the involvement of T-cells in skeletal muscle repair.

Curcumin ameliorates palmitate-induced inflammation in skeletal muscle cells by regulating JNK/NF-kB pathway and ROS production

Curcumin, a natural polyphenol compound, has the beneficial effects on several diseases such as metabolic syndrome, cancer, and diabetes. The anti-inflammatory property of curcumin has been demonstrated in different cells; however, its role in prevention of palmitate-induced inflammation in skeletal muscle C2C12 cells is not known. In this study, we examined the effect of curcumin on the inflammatory responses stimulated by palmitate in C2C2 cells. The results showed that palmitate upregulated the mRNA expression and protein release of IL-6 and TNF-α cytokines in C2C12 cells, while pretreatment with curcumin was able to attenuate the effect of palmitate on inflammatory cytokines. The anti-inflammatory effect of curcumin was associated with the repression of phosphorylation of IKKα-IKKβ, and JNK. Palmitate also caused an increase in reactive oxygen species (ROS) level that curcumin abrogated it. Collectively, these findings suggest that curcumin may represent a promising therapy for prevention of inflammation in skeletal muscle cells.

Obesity, Metabolic Syndrome, and Musculoskeletal Disease: Common Inflammatory Pathways Suggest a Central Role for Loss of Muscle Integrity

Inflammation can arise in response to a variety of stimuli, including infectious agents, tissue injury, autoimmune diseases, and obesity. Some of these responses are acute and resolve, while others become chronic and exert a sustained impact on the host, systemically, or locally. Obesity is now recognized as a chronic low-grade, systemic inflammatory state that predisposes to other chronic conditions including metabolic syndrome (MetS). Although obesity has received considerable attention regarding its pathophysiological link to chronic cardiovascular conditions and type 2 diabetes, the musculoskeletal (MSK) complications (i.e., muscle, bone, tendon, and joints) that result from obesity-associated metabolic disturbances are less frequently interrogated. As musculoskeletal diseases can lead to the worsening of MetS, this underscores the imminent need to understand the cause and effect relations between the two, and the convergence between inflammatory pathways that contribute to MSK damage. Muscle mass is a key predictor of longevity in older adults, and obesity-induced sarcopenia is a significant risk factor for adverse health outcomes. Muscle is highly plastic, undergoes regular remodeling, and is responsible for the majority of total body glucose utilization, which when impaired leads to insulin resistance. Furthermore, impaired muscle integrity, defined as persistent muscle loss, intramuscular lipid accumulation, or connective tissue deposition, is a hallmark of metabolic dysfunction. In fact, many common inflammatory pathways have been implicated in the pathogenesis of the interrelated tissues of the musculoskeletal system (e.g., tendinopathy, osteoporosis, and osteoarthritis). Despite these similarities, these diseases are rarely evaluated in a comprehensive manner. The aim of this review is to summarize the common pathways that lead to musculoskeletal damage and disease that result from and contribute to MetS. We propose the overarching hypothesis that there is a central role for muscle damage with chronic exposure to an obesity-inducing diet. The inflammatory consequence of diet and muscle dysregulation can result in dysregulated tissue repair and an imbalance toward negative adaptation, resulting in regulatory failure and other musculoskeletal tissue damage. The commonalities support the conclusion that musculoskeletal pathology with MetS should be evaluated in a comprehensive and integrated manner to understand risk for other MSK-related conditions. Implications for conservative management strategies to regulate MetS are discussed, as are future research opportunities.

An Integrated View of Immunometabolism

The worldwide obesity epidemic has emerged as a major cause of insulin resistance and Type 2 diabetes. Chronic tissue inflammation is a well-recognized feature of obesity, and the field of immunometabolism has witnessed many advances in recent years. Here, we review the major features of our current understanding with respect to chronic obesity-related inflammation in metabolic tissues and focus on how these inflammatory changes affect insulin sensitivity, insulin secretion, food intake, and glucose homeostasis. There is a growing appreciation of the varied and sometimes integrated crosstalk between cells within a tissue (intraorgan) and tissues within an organism (interorgan) that supports inflammation in the context of metabolic dysregulation. Understanding these pathways and modes of communication has implications for translational studies. We also briefly summarize the state of this field with respect to potential current and developing therapeutics.

Interactions Between the Neuroendocrine System and T Lymphocytes in Diabetes

It is well established that there is a fine-tuned bidirectional communication between the immune and neuroendocrine tissues in maintaining homeostasis. Several types of immune cells, hormones, and neurotransmitters of different chemical nature are involved as communicators between organs. Apart of being key players of the adaptive arm of the immune system, it has been recently described that T lymphocytes are involved in the modulation of metabolism of several tissues in health and disease. Diabetes may result mainly from lack of insulin production (type 1 diabetes) or insufficient insulin and insulin resistance (type 2 diabetes), both influenced by genetic and environmental components. Herein, we discuss accumulating data regarding the role of the adaptive arm of the immune system in the pathogenesis of diabetes; including the action of several hormones and neurotransmitters influencing on central and peripheral T lymphocytes development and maturation, particularly under the metabolic burden triggered by diabetes. In addition, we comment on the role of T-effector lymphocytes in adipose and liver tissues during diabetes, which together enhances pancreatic β-cell stress aggravating the disease.

Expression of macrophage genes within skeletal muscle correlates inversely with adiposity and insulin resistance in humans

Local inflammation in obese adipose tissue has been shown to contribute to insulin resistance; however, the role of macrophage infiltration within skeletal muscle is still debatable. This study aimed to evaluate the association of skeletal muscle macrophage gene expression with adiposity levels and insulin sensitivity in obese patients. Twenty-two nondiabetic obese patients and 23 healthy lean controls were included. Obese patients underwent a 3-month weight loss intervention. Macrophage gene expression in skeletal muscle (quantitative real-time polymerase chain reaction), body composition (dual-energy X-ray absorptiometry), and insulin sensitivity (homeostatic model assessment (HOMA) and oral glucose tolerance test) were compared between groups and their associations were analyzed. To validate skeletal muscle findings, we repeated the analyses with macrophage gene expression in adipose tissue. Expression levels of macrophage genes (CD68, CD11b, CD206, CD16, CD40, and CD163) were lower in skeletal muscle tissue of obese versus lean participants. Macrophage gene expression was also found to be inversely associated with adiposity, fasting insulin, and HOMA (r = -0.4 ∼ -0.6, p < 0.05), as well as positively associated with insulin sensitivity (r = 0.4 ∼ 0.8, p < 0.05). On the other hand, adipose tissue macrophage gene expression showed higher levels in obese versus lean participants, presenting a positive association with adiposity levels. Macrophage gene expression, in both skeletal and adipose tissue samples, was only minimally affected by the weight loss intervention. In contrast with the established positive relationship between adiposity and macrophage gene expression, an unexpected inverse correlation between these 2 variables was observed in skeletal muscle tissue. Additionally, muscle macrophage gene expression was inversely correlated with insulin resistance.

The Spleen: A Hub Connecting Nervous and Immune Systems in Cardiovascular and Metabolic Diseases

Metabolic disorders have been identified as major health problems affecting a large portion of the world population. In addition, obesity and insulin resistance are principal risk factors for the development of cardiovascular diseases. Altered immune responses are common features of both hypertension and obesity and, moreover, the involvement of the nervous system in the modulation of immune system is gaining even more attention in both pathophysiological contexts. For these reasons, during the last decades, researches focused their efforts on the comprehension of the molecular mechanisms connecting immune system to cardiovascular and metabolic diseases. On the other hand, it has been reported that in these pathological conditions, central neural pathways modulate the activity of the peripheral nervous system, which is strongly involved in onset and progression of the disease. It is interesting to notice that neural reflex can also participate in the modulation of immune functions. In this scenario, the spleen becomes the crucial hub allowing the interaction of different systems differently involved in metabolic and cardiovascular diseases. Here, we summarize the major findings that dissect the role of the immune system in disorders related to metabolic and cardiovascular dysfunctions, and how this could also be influenced by neural reflexes.

Deconstructing metabolic inflammation using cellular systems

Over the past years, we have embarked in a systematic analysis of the effect of obesity or fatty acids on circulating monocytes, microvascular endothelial cells, macrophages, and skeletal muscle cells. With the use of cell culture strategies, we have deconstructed complex physiological systems and then reconstructed "partial equations" to better understand cell-to-cell communication. Through these approaches, we identified that in high saturated fat environments, cell-autonomous proinflammatory pathways are activated in monocytes and endothelial cells, promoting monocyte adhesion and transmigration. We think of this as a paradigm of the conditions promoting immune cell infiltration into tissues during obesity. In concert, it is possible that muscle and adipose tissue secrete immune cell chemoattractants, and indeed, our tissue culture reconstructions reveal that myotubes treated with the saturated fatty acid palmitate, but not the unsaturated fatty acid palmitoleate, release nucleotides that attract monocytes and other compounds that promote proinflammatory classically activated "(M1)-like" polarization in macrophages. In addition, palmitate directly triggers an M1-like macrophage phenotype, and secretions from these activated macrophages confer insulin resistance to target muscle cells. Together, these studies suggest that in pathophysiological conditions of excess fat, the muscle, endothelial and immune cells engage in a synergistic crosstalk that exacerbates tissue inflammation, leukocyte infiltration, polarization, and consequent insulin resistance.

Skeletal muscle inflammation and insulin resistance in obesity

Obesity is associated with chronic inflammation, which contributes to insulin resistance and type 2 diabetes mellitus. Under normal conditions, skeletal muscle is responsible for the majority of insulin-stimulated whole-body glucose disposal; thus, dysregulation of skeletal muscle metabolism can strongly influence whole-body glucose homeostasis and insulin sensitivity. Increasing evidence suggests that inflammation occurs in skeletal muscle in obesity and is mainly manifested by increased immune cell infiltration and proinflammatory activation in intermyocellular and perimuscular adipose tissue. By secreting proinflammatory molecules, immune cells may induce myocyte inflammation, adversely regulate myocyte metabolism, and contribute to insulin resistance via paracrine effects. Increased influx of fatty acids and inflammatory molecules from other tissues, particularly visceral adipose tissue, can also induce muscle inflammation and negatively regulate myocyte metabolism, leading to insulin resistance.

Systemic Regulators of Skeletal Muscle Regeneration in Obesity

Skeletal muscle maintenance is a dynamic process and undergoes constant repair and regeneration. However, skeletal muscle regenerative capacity declines in obesity. In this review, we focus on obesity-associated changes in inflammation, metabolism, and impaired insulin signaling, which are pathologically dysregulated and ultimately result in a loss of muscle mass and function. In addition, we examine the relationships between skeletal muscle, liver, and visceral adipose tissue in an obese state.

Skeletal muscle quality as assessed by CT-derived skeletal muscle density is associated with 6-month mortality in mechanically ventilated critically ill patients

Background

Muscle quantity at intensive care unit (ICU) admission has been independently associated with mortality. In addition to quantity, muscle quality may be important for survival. Muscle quality is influenced by fatty infiltration or myosteatosis, which can be assessed on computed tomography (CT) scans by analysing skeletal muscle density (SMD) and the amount of intermuscular adipose tissue (IMAT). We investigated whether CT-derived low skeletal muscle quality at ICU admission is independently associated with 6-month mortality and other clinical outcomes.

Methods

This retrospective study included 491 mechanically ventilated critically ill adult patients with a CT scan of the abdomen made 1 day before to 4 days after ICU admission. Cox regression analysis was used to determine the association between SMD or IMAT and 6-month mortality, with adjustments for Acute Physiological, Age, and Chronic Health Evaluation (APACHE) II score, body mass index (BMI), and skeletal muscle area. Logistic and linear regression analyses were used for other clinical outcomes.

Results

Mean APACHE II score was 24 ± 8 and 6-month mortality was 35.6%. Non-survivors had a lower SMD (25.1 vs. 31.4 Hounsfield Units (HU); p < 0.001), and more IMAT (17.1 vs. 13.3 cm²; p = 0.004). Higher SMD was associated with a lower 6-month mortality (hazard ratio (HR) per 10 HU, 0.640; 95% confidence interval (CI), 0.552–0.742; p < 0.001), and also after correction for APACHE II score, BMI, and skeletal muscle area (HR, 0.774; 95% CI, 0.643–0.931; p = 0.006). Higher IMAT was not significantly associated with higher 6-month mortality after adjustment for confounders. A 10 HU increase in SMD was associated with a 14% shorter hospital length of stay.

Conclusions

Low skeletal muscle quality at ICU admission, as assessed by CT-derived skeletal muscle density, is independently associated with higher 6-month mortality in mechanically ventilated patients. Thus, muscle quality as well as muscle quantity are prognostic factors in the ICU.

Trial registration

Retrospectively registered (initial release on 06/23/2016) at ClinicalTrials.gov: NCT02817646.

Using RNA-Seq SNP data to reveal potential causal mutations related to pig production traits and RNA editing

RNA-Seq technology is widely used in quantitative gene expression studies and identification of non-annotated transcripts. However this technology also can be used for polymorphism detection and RNA editing in transcribed regions in an efficient and cost-effective way. This study used SNP data from an RNA-Seq assay to identify genes and mutations underlying production trait variations in an experimental pig population. The hypothalamic and hepatic transcriptomes of nine extreme animals for growth and fatness from an (Iberian × Landrace) × Landrace backcross were analyzed by RNA-Seq methodology, and SNP calling was conducted. More than 125 000 single nucleotide variants (SNVs) were identified in each tissue, and 78% were considered to be potential SNPs, those SNVs segregating in the context of this study. Potential informative SNPs were detected by considering those showing a homozygous or heterozygous genotype in one extreme group and the alternative genotype in the other group. In this way, 4396 and 1862 informative SNPs were detected in hypothalamus and liver respectively. Out of the 32 SNPs selected for validation, 25 (80%) were confirmed as actual SNPs. Association analyses for growth, fatness and premium cut yields with 19 selected SNPs were carried out, and four potential causal genes (RETSAT, COPA, RNMT and PALMD) were identified. Interestingly, new RNA editing modifications were detected and validated for the NR3C1:g.102797 (ss1985401074) and ACSM2B:g.13374 (ss1985401075) positions and for the COG3:g3.4525 (ss1985401087) modification previously identified across vertebrates, which could lead to phenotypic variation and should be further investigated.

Suppressor of Cytokine Signaling-1 Peptidomimetic Limits Progression of Diabetic Nephropathy

Diabetes is the main cause of CKD and ESRD worldwide. Chronic activation of Janus kinase and signal transducer and activator of transcription (STAT) signaling contributes to diabetic nephropathy by inducing genes involved in leukocyte infiltration, cell proliferation, and extracellular matrix accumulation. This study examined whether a cell-permeable peptide mimicking the kinase-inhibitory region of suppressor of cytokine signaling-1 (SOCS1) regulatory protein protects against nephropathy by suppressing STAT-mediated cell responses to diabetic conditions. In a mouse model combining hyperglycemia and hypercholesterolemia (streptozotocin diabetic, apoE-deficient mice), renal STAT activation status correlated with the severity of nephropathy. Notably, compared with administration of vehicle or mutant inactive peptide, administration of the SOCS1 peptidomimetic at either early or advanced stages of diabetes ameliorated STAT activity and resulted in reduced serum creatinine level, albuminuria, and renal histologic changes (mesangial expansion, tubular injury, and fibrosis) over time. Mice treated with the SOCS1 peptidomimetic also exhibited reduced kidney leukocyte recruitment (T lymphocytes and classic M1 proinflammatory macrophages) and decreased expression levels of proinflammatory and profibrotic markers that were independent of glycemic and lipid changes. In vitro, internalized peptide suppressed STAT activation and target gene expression induced by inflammatory and hyperglycemic conditions, reduced migration and proliferation in mesangial and tubuloepithelial cells, and altered the expression of cytokine-induced macrophage polarization markers. In conclusion, our study identifies SOCS1 mimicking as a feasible therapeutic strategy to halt the onset and progression of renal inflammation and fibrosis in diabetic kidney disease.

Altered Myokine Secretion Is an Intrinsic Property of Skeletal Muscle in Type 2 Diabetes

Skeletal muscle secretes factors, termed myokines. We employed differentiated human skeletal muscle cells (hSMC) cultured from Type 2 diabetic (T2D) and non-diabetic (ND) subjects to investigate the impact of T2D on myokine secretion. Following 24 hours of culture concentrations of selected myokines were determined to range over 4 orders of magnitude. T2D hSMC released increased amounts of IL6, IL8, IL15, TNFa, Growth Related Oncogene (GRO)a, monocyte chemotactic protein (MCP)-1, and follistatin compared to ND myotubes. T2D and ND hSMC secreted similar levels of IL1ß and vascular endothelial growth factor (VEGF). Treatment with the inflammatory agents lipopolysaccharide (LPS) or palmitate augmented the secretion of many myokines including: GROa, IL6, IL8, IL15, and TNFa, but did not consistently alter the protein content and/or phosphorylation of IkBa, p44/42 MAPK, p38 MAPK, c-Jun N-terminal kinase (JNK) and NF-kB, nor lead to consistent changes in basal and insulin-stimulated glucose uptake or free fatty acid oxidation. Conversely, treatment with pioglitazone or oleate resulted in modest reductions in the secretion of several myokines. Our results demonstrate that altered secretion of a number of myokines is an intrinsic property of skeletal muscle in T2D, suggesting a putative role of myokines in the response of skeletal muscle to T2D.

Targeting inflammation in diabetic kidney disease: early clinical trials

INTRODUCTION

The age-standardized death rate from diabetic kidney disease increased by 106% from 1990 to 2013, indicating that novel therapeutic approaches are needed, in addition to the renin-angiotensin system (RAS) blockers currently in use. Clinical trial results of anti-fibrotic therapy have been disappointing. However, promising anti-inflammatory drugs are currently on phase 1 and 2 randomized controlled trials.

AREAS COVERED

The authors review the preclinical, phase 1 and 2 clinical trial information of drugs tested for diabetic kidney disease that directly target inflammation as a main or key mode of action. Agents mainly targeting other pathways, such as endothelin receptor or mineralocorticoid receptor blockers and vitamin D receptor activators are not discussed.

EXPERT OPINION

Agents targeting inflammation have shown promising results in the treatment of diabetic kidney disease when added on top of RAS blockade. The success of pentoxifylline in open label trials supports the concept of targeting inflammation. In early clinical trials, the pentoxifylline derivative CTP-499, the CCR2 inhibitor CCX140-B, the CCL2 inhibitor emapticap pegol and the JAK1/JAK2 inhibitor baricitinib were the most promising drugs for diabetic kidney disease. The termination of trials testing the anti-IL-1β antibody gevokizumab in 2015 will postpone the evaluation of therapies targeting inflammatory cytokines.

Macrophages Play a Key Role in the Obesity-Induced Periodontal Innate Immune Dysfunction via Nucleotide-Binding Oligomerization Domain-Like Receptor Protein 3 Pathway

BACKGROUND

Obesity is associated with infiltration of macrophages into adipose tissue. However, effects of obesity on macrophage infiltration and activation in periodontal tissues with periodontitis are still to be elucidated.

METHODS

A diet-induced obesity 16-week mouse model was constructed, and periodontitis was induced by periodontal ligation for 10 days. The model consisted of periodontitis (P) and control (C) groups, with high fat (HF) and normal (N) diet conditions. Bone loss (BL) was analyzed by microcomputed tomography. In periodontal tissues, immunohistochemical staining and quantitative polymerase chain reaction (qPCR) detected expressions of: 1) nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) pathway; 2) macrophage-specific marker (F4/80); and 3) macrophage chemotactic protein 1 (MCP1). Bone marrow-derived macrophages (BMDMs) from the mouse model were stimulated by Porphyromonas gingivalis lipopolysaccharide (LPS) in vitro (NC/NC + LPS: BMDMs from NC group without/with LPS stimulation; HFC/HFC + LPS: BMDMs from HFC group without/with LPS stimulation). Expressions of NLRP3 pathway in BMDMs were detected by immunocytochemical staining and qPCR.

RESULTS

BL increased significantly with periodontitis (NC versus NP; HFC versus HFP) and obesity (NP versus HFP). Expressions of NLRP3 pathway were significantly elevated in gingival tissues with periodontitis (NC versus NP; HFC versus HFP), but not with obesity (NC versus HFC; NP versus HFP). F4/80 and MCP1 expressions were significantly upregulated in gingival tissues with periodontitis (NC versus NP; HFC versus HFP) but significantly downregulated in the context of obesity (NP versus HFP). In vitro, NLRP3 pathway expressions were significantly upregulated in BMDMs after LPS stimulation (NC + LPS versus NC; HFC + LPS versus HFC), but significantly downregulated in HFC groups (HFC versus NC; HFC + LPS versus NC + LPS).

CONCLUSION

Obesity may paralyze innate immune response of periodontium via attenuating infiltration and activation of macrophages and further aggravate periodontal disease.

Predicting appendicular lean and fat mass with bioelectrical impedance analysis in older adults with physical function decline - The PROVIDE study

BACKGROUND & AIMS

No generalizable formulas exist that are derived from bioelectrical impedance analysis (BIA) for predicting appendicular lean mass (ALM) and fat mass (AFM) in sarcopenic older adults. Since precision of regional body composition (BC) data in multicentre trials is essential, this study aimed to: 1) develop and cross-validate soft tissue BIA equations with GE Lunar and Hologic DXA systems as their reference 2) to compare our new ALM equation to two previously published models and 3) to assess the agreement between BIA- and DXA-derived soft tissue ratios as indicators of limb tissue quality.

METHODS

Two-hundred and ninety-one participants with functional limitations (SPPB-score 4-9; sarcopenia class I or II, measured by BIA) were recruited from 18 study centres in six European countries. BIA equations, using DXA-derived ALM and AFM as the dependent variable, and age, gender, weight, impedance index and reactance as independent variables, were developed using a stepwise multiple linear regression approach.

RESULTS

Cross-validation gave rise to 4 equations using the whole sample: ALM_LUNAR (kg) = 1.821 + (0.168*height²/resistance) + (0.132*weight) + (0.017*reactance) - (1.931*sex) [R² = 0.86 and SEE = 1.37 kg] AFM_LUNAR (kg) = -6.553 - (0.093* height²/resistance) + (0.272*weight) + (4.295*sex) [R² = 0.70 and SEE = 1.53 kg] ALM_HOLOGIC (kg) = 4.957 + (0.196* height²/resistance) + (0.060*weight) - (2.554*sex) [R² = 0.90 and SEE = 1.28 kg] AFM_HOLOGIC (kg) = -4.716 - (0.142* height²/resistance) + (0.316*weight) + (4.453*sex) - (0.040*reactance) [R² = 0.73 and SEE = 1.54 kg] Both previously published models significantly overestimated ALM in our sample with biases of -0.36 kg to -1.05 kg. For the ratio of ALM to AFM, a strong correlation (r = 0.82, P < 0.0001) was found between the mean estimate from BIA and the DXA models without significant difference (estimated bias of 0.02 and 95% LOA -0.62, 0.65).

CONCLUSION

We propose new BIA equations allowing the estimation of appendicular lean and fat mass. Our equations allow to accurately estimate the appendicular lean/fat ratio which might provide information regarding limb tissue quality, in clinical settings. Furthermore, these BIA equations can be applied to characterize sarcopenia with Hologic and Lunar reference values for BC. Previously published BIA-based models tend to overestimate ALM in sarcopenic older adults. Users of both GE Lunar and Hologic may now benefit from these equations in field research.

Metabolic Inflammation-Differential Modulation by Dietary Constituents

Obesity arises from a sustained positive energy balance which triggers a pro-inflammatory response, a key contributor to metabolic diseases such as T2D. Recent studies, focused on the emerging area of metabolic-inflammation, highlight that specific metabolites can modulate the functional nature and inflammatory phenotype of immune cells. In obesity, expanding adipose tissue attracts immune cells, creating an inflammatory environment within this fatty acid storage organ. Resident immune cells undergo both a pro-inflammatory and metabolic switch in their function. Inflammatory mediators, such as TNF-α and IL-1β, are induced by saturated fatty acids and disrupt insulin signaling. Conversely, monounsaturated and polyunsaturated fatty acids do not interrupt metabolism and inflammation to the same extent. AMPK links inflammation, metabolism and T2D, with roles to play in all and is influenced negatively by obesity. Lipid spillover results in hepatic lipotoxicity and steatosis. Also in skeletal muscle, excessive FFA can impede insulin's action and promote inflammation. Ectopic fat can also affect pancreatic β-cell function, thereby contributing to insulin resistance. Therapeutics, lifestyle changes, supplements and dietary manipulation are all possible avenues to combat metabolic inflammation and the subsequent insulin resistant state which will be explored in the current review.

Skeletal Muscle Inflammation Following Repeated Bouts of Lengthening Contractions in Humans

Skeletal muscle responds to exercise-induced damage by orchestrating an adaptive process that protects the muscle from damage by subsequent bouts of exercise, a phenomenon called the repeated bout effect (RBE). The mechanisms underlying the RBE are not understood. We hypothesized that an attenuated inflammation response following a repeated bout of lengthening contractions (LC) would be coincidental with a RBE, suggesting a potential relationship. Fourteen men (n = 7) and women (n = 7) completed two bouts of lengthening contractions (LC) separated by 28 days. Muscle biopsies were taken before the first bout (B1) from the non-exercised leg, and from the exercised leg 2- and 27-d post-B1 and 2-d following the second bout (B2). A 29-plex cytokine array identified alterations in inflammatory cytokines. Immunohistochemistry quantified inflammatory cell infiltration and major histocompatibility complex class 1 (MHC-1). Muscle soreness was attenuated in the days following B2 relative to B1, indicating a RBE. Intramuscular monocyte chemoattractant protein (MCP1) and interferon gamma-induced protein 10 (IP10) increased following B2 relative to the pre-exercise sample (7–52 and 11–36 pg/ml, respectively p < 0.05). Interleukin 4 (IL4) decreased (26–13 pg/ml, p < 0.05) following B2 relative to the pre-exercise sample. Infiltration of CD68⁺ macrophages and CD8⁺ T-cells were evident following B2, but not B1. Moreover, CD8⁺ T-cells were observed infiltrating apparently necrotic muscle fibers. No changes in MHC-1 were found. We conclude that inflammation is not attenuated following a repeated bout of LC and that CD8⁺ T-cells may play a role in muscle adaptation following LC. Moreover, it appears that the muscle or the immune system becomes sensitized to an initial bout of damaging exercise such that inflammatory cell infiltration into the muscle is enhanced upon a repeated bout of damaging exercise.

Mitochondrial regulation of macrophage cholesterol homeostasis

This review explores the relationship between mitochondrial structure and function in the regulation of macrophage cholesterol metabolism and proposes that mitochondrial dysfunction contributes to loss of the elegant homeostatic mechanisms which normally maintain cellular sterol levels within defined limits. Mitochondrial sterol 27-hydroxylase (CYP27A1) can generate oxysterol activators of liver X receptors which heterodimerise with retinoid X receptors, enhancing the transcription of ATP binding cassette transporters (ABCA1, ABCG1, and ABCG4), that can remove excess cholesterol via efflux to apolipoproteins A-1, E, and high density lipoprotein, and inhibit inflammation. The activity of CYP27A1 is regulated by the rate of supply of cholesterol substrate to the inner mitochondrial membrane, mediated by a complex of proteins. The precise identity of this dynamic complex remains controversial, even in steroidogenic tissues, but may include steroidogenic acute regulatory protein and the 18 kDa translocator protein, together with voltage-dependent anion channels, ATPase AAA domain containing protein 3A, and optic atrophy type 1 proteins. Certainly, overexpression of StAR and TSPO proteins can enhance macrophage cholesterol efflux to apoA-I and/or HDL, while perturbations in mitochondrial function, or changes in the expression of mitochondrial fusion proteins, alter the efficiency of cholesterol efflux. Molecules which can sustain or improve mitochondrial function or increase the activity of the protein complex involved in cholesterol transfer may have utility in resolving the problem of dysregulated macrophage cholesterol homeostasis, a condition which may contribute to inflammation, atherosclerosis, nonalcoholic steatohepatitis, osteoblastic bone resorption, and some disorders of the central nervous system.