Predicting myofiber cross-sectional area and triglyceride content with electrical impedance myography: A study in db/db mice.

BACKGROUND: Electrical impedance myography (EIM) provides insight into muscle composition and structure. We sought to evaluate its use in a mouse obesity model characterized by myofiber atrophy. METHODS: We applied a prediction algorithm, ie, the least absolute shrinkage and selection operator (LASSO), to surface, needle array, and ex vivo EIM data from db/db and wild-type mice and assessed myofiber cross-sectional area (CSA) histologically and triglyceride (TG) content biochemically. RESULTS: EIM data from all three modalities provided acceptable predictions of myofiber CSA with average root mean square error (RMSE) of 15% in CSA (ie, ±209 µm2 for a mean CSA of 1439 µm2 ) and TG content with RMSE of 30% in TG content (ie, ±7.3 nmol TG/mg muscle for a mean TG content of 25.4 nmol TG/mg muscle). CONCLUSIONS: EIM combined with a predictive algorithm provides reasonable estimates of myofiber CSA and TG content without the need for biopsy.

Electrical impedance myography for the detection of muscle inflammation induced by λ-carrageenan.

Electrical impedance myography (EIM) is a technique for the assessment of muscle health and composition and has been shown to be sensitive to a variety of muscle pathologies including neurogenic atrophy and connective tissue deposition. However, it has been minimally studied in pure inflammation. In this study, we sought to assess EIM sensitivity to experimental inflammation induced by the localized intramuscular injection of λ-carrageenan. A total of 91 mice underwent 1-1000 kHz EIM measurements of gastrocnemius using a needle array, followed by injection of either 0.3% λ-carrageenan in phosphate-buffered saline (PBS) or PBS alone. Animals were then remeasured with EIM at 4, 24, 48, or 72 hours and euthanized and quantitative assessment of muscle histology was performed. Parallel alterations in both 5 and 50 kHz EIM values were identified at 4 and 24 hours, including reductions in phase, reactance, and resistance. In PBS-treated animals these values normalized by 48 hours, whereas substantial reductions in phase and reactance in 5 kHz EIM values persisted at 48 and 72 hours (i.e., values of phase 72 hours post-injection were 6.51 ± 0.40 degrees for λ-carrageenan versus 8.44 ± 0.35 degrees for PBS p<0.001, n = 11 per group). The degree of basophilic area observed in muscle sections by histology correlated to the degree of phase change at these two time points (Rspearman = -0.51, p = 0.0029). Changes in low frequency EIM parameters are sensitive to the presence of inflammatory infiltrates, and have the potential of serving as a simple means of quantifying the presence and extent of muscle inflammation without the need for biopsy.

A Moderate Daily Dose of Resveratrol Mitigates Muscle Deconditioning in a Martian Gravity Analog.

While there is a relatively good understanding of the effects of microgravity on human physiology based on five decades of experience, the physiological consequences of partial gravity remain far less well understood. Until recently, no model had been able to replicate partial gravity such as that experienced on Mars (0.38 g), which would be critical to help sustain long-term missions and ensure a safe return to Earth. Recent development of two partial weight bearing (PWB) models, one in mice and one in rats, now allows for quadrupedal partial unloading that mimics Martian gravity. Resveratrol (RSV), a polyphenol most commonly found in grapes and blueberries, has been extensively investigated for its health benefits, including its anti-inflammatory, anti-oxidative, and anti-diabetic effects. In the context of mechanical unloading, RSV has also been shown to preserve bone and muscle mass. However, there is a lack of research regarding its effect on the musculoskeletal system in partial gravity. We hypothesized that a moderate daily dose of RSV (150 mg/kg/day) would help mitigate muscle deconditioning in a Mars gravity analog. Indeed, our results demonstrate that RSV treatment during partial unloading significantly preserves muscle function (e.g., the average change in grip force after 14 days of PWB40 was of -6.18, and +10.92% when RSV was administered) and mitigates muscle atrophy (e.g., RSV supplementation led to an increase of 21.6% in soleus weight for the unloaded animals). This work suggests the potential of a nutraceutical approach to reduce musculoskeletal deconditioning on a long-term mission to Mars.