The mechanisms impairing muscle quality and leading to myofibrosis (MF) and myosteatosis (MS), are incompletely known. In biopsies of paraspinous muscle (PM) of 16 healthy elderly men undergoing elective vertebral surgery, we histologically determined the area of MF and MS expressed as muscle quality index (MQI), in order to investigate the relation between them, as well as the main predictors of muscle quality. Total PM muscle area and intermuscular adipose tissue (IMAT) were evaluated by MRI and body composition by DXA. Circulating fasting glucose, insulin, hs-CRP, leptin, adiponectin and IL-6 were measured and HOMA index calculated. Quantification of gene expression in PM and in subcutaneous adipose tissue (SAT) overlying the muscle was performed by real time-PCR. The degree of MS and MF were significantly and positively related to each other and positively associated with BMI, waist circumference, FM and FM% as well as with the amount of IMAT. Leptin levels were positively associated with MF and MS, whereas hs-CRP was significantly related only to MF. In backward regression analyses, larger waist circumference and smaller PM muscle area explained 90% of MF variance, whereas leptin predicted about 80% of MS variance. IL-6 expression in SAT was significantly higher in participants with higher MQI values. In PM biopsies we found significantly higher expression of SOCS-3 and a trend toward higher expression of myostatin with greater degrees of MQI. MS and MF are related phenomena that concur to alter muscle quality with aging and both should be considered in the evolution of sarcopenia.

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In recent years, evidence has emerged indicating that insulin resistance and diabetes mellitus type 2 are associated with inflammation of adipose tissue (AT). Interest has been focused on epicardial AT (EAT) because of its possible involvement with atherosclerosis and cardiovascular diseases. The aim of this study was to characterize adipocyte size and inflammatory profile in subcutaneous (SAT) and EAT among subjects with or without diabetes. Biopsies were collected from SAT and EAT in 34 men undergoing elective cardiac surgery. Weight, height, body mass index, waist circumference, as well as serum levels of glucose, insulin, lipids, adiponectin, and leptin were determined in all subjects. Adiponectin, MCP-1, and CD68 mRNA levels present within cells from AT biopsies were determined by real-time polymerase chain reaction. Adipocyte size was determined by optic microscopy and morphometry. Regarding the experimental group as a whole, gene-expression levels within EAT were significantly lower for adiponectin and higher, albeit not significantly, for MCP-1, when compared with that of SAT. In addition, adipocytes in EAT were significantly smaller than those in SAT. Subjects with diabetes showed lower adiponectin gene-expression levels in both SAT and EAT when compared with subjects without diabetes. By contrast, MCP-1 and CD68 gene-expression levels were higher in both tissue types of diabetic subjects. Adipocyte size in EAT was significantly larger in diabetic subjects than in nondiabetic subjects. Our data revealed a predominantly inflammatory profile in both SAT and EAT in subjects with diabetes in comparison with those without diabetes.

Deposition of fat between skeletal muscle bundles and beneath the muscle fascia, recently called intermuscular adipose tissue (IMAT), is gaining attention as potential contributor to insulin resistance, metabolic syndrome, muscle function impairment and disability. The aim of this study was to compare IMAT as measured at the erector spinae level by MRI, a well-recognized gold standard method to evaluate fat content inside muscles, and histology estimates. In 18 healthy elderly men and women with a wide range of BMI (25.05–35.58 Kg/m2), undergoing elective vertebral surgery, IMAT within the erector spinae muscle was evaluated by MRI, by body composition using dual energy x-ray absorptiometry and histological evaluation of intraoperative biopsy sample. The concordance between IMAT/TA ratio evaluated by MRI and histological examination was analyzed employing Lin’s concordance correlation coefficient and the procedure proposed by Bland and Altman. Two threshold to distinguish between muscle and IMAT calculated respectively by 20% and 10% reduction of the gray level intensity evaluated by MRI from surrounding subcutaneous adipose tissue were used. With a 20% reduction, calculated IMAT/TA as evaluated by MRI on average exceeds histological evaluation by 21.79%, whereas by reducing the threshold by 10% agreement between MRI and histology improved with a 12.42% difference. Our data shows a good degree of concordance between IMAT assessment by magnetic resonance and histology and seems to show that agreement between the two methods could be improved by using a more restrictive threshold between muscle and fat.