Skeletal muscle atrophy impairs quality of life and increases the risk of disease, but current methods for assessment of muscle mass have several limitations. We here investigated the urinary concentration of a fragment of the muscle protein titin as a potential biomarker for the early detection of skeletal muscle atrophy. Four mouse models with different atrophy pathways were studied: those of cardiotoxin-induced acute muscle injury, cast-induced muscle immobilization, lipopolysaccharide-induced sepsis, and streptozotocin-induced diabetes. In all four models, urinary titin levels increased early, concurrent with or preceding upregulation of the atrophy-related genes for atrogin-1 and MuRF-1. The increase in the urinary titin concentration was thus associated with initial muscle damage and the onset of proteolysis, rather than with late-stage muscle wasting. Our findings suggest that urinary titin is a promising biomarker for detection of the onset of skeletal muscle catabolism and prediction of the subsequent development of atrophy in different catabolic states. Noninvasive measurement of urinary titin may therefore allow the earlier detection of skeletal muscle proteolysis compared with conventional techniques.

Background/Objectives: Atractylodes lancea (Thunb.) DC. [Asteraceae] (ALR)-derived exosome-like nanoparticles (ALR-ELNs) exhibit anti-neuroinflammatory effects in microglial cells. However, the associated mechanisms and pathways are unknown. We aimed to characterize the effects of ALR-ELNs on inflammatory responses of BV-2 microglial cells to lipopolysaccharide (LPS) using RNA sequencing. Methods: ALR-ELNs were fractionated from ALR. BV-2 microglial murine cells were stimulated with LPS after treatment with ALR-ELNs. RNA sequencing was performed to analyze variations in mRNA levels. Ingenuity pathway analysis (IPA) was performed to investigate the mechanism of action of ALR-ELNs. mRNA expression was assessed using real-time quantitative polymerase chain reaction (qPCR). Results: The expression of 651 genes was downregulated, whereas that of 1204 genes was upregulated in LPS-stimulated BV2 cells pretreated with ALR-ELNs. The IPA showed that the effects of ALR-ELNs on inflammation took place through pathogen-influenced signaling. Network analysis via IPA showed that the Toll-like receptor (TLR) is involved in the suppression of inflammation by ALR-ELNs. The qPCR analysis showed that pretreatment with ALR-ELNs significantly reduced TLR4 mRNA expression. Conclusions: ALR-ELNs suppress the release of inflammatory mediators by downregulating TLR4 expression, which is a novel mechanism by which ALR-ELNs act on microglia. Identifying active ingredients in ALR-ELNs that downregulate TLR4 expression can advance the development of therapeutic drugs for neuroinflammatory diseases.

Perioperative malnutrition is common in patients with gastroenterological cancer and contributes to postoperative skeletal muscle atrophy, which adversely affects their prognosis. Early assessment of skeletal muscle atrophy is crucial for improving postoperative outcomes. This study aimed to evaluate the efficacy of urinary titin as a biomarker for skeletal muscle atrophy. A prospective observational study was conducted, and a total of 34 gastroenterological cancer patients were included. Urinary titin levels were measured using ELISA at admission, postoperative days (POD) 1, 7, and 14, and at 6 months after surgery. Surgical procedure, operative time, cancer stage, postoperative complications, hospital stay, and preoperative and postoperative body composition were evaluated, along with nutritional status and grip strength from admission to 6 months after surgery. Changes in urinary titin levels were measured at the same time points as described above. Preoperatively, the mean urinary titin level was 5.03 pmol/mg Cr, slightly higher than in healthy subjects. Urinary titin peaked at 33.71 (24.30–66.58) pmol/mg/dL Cr on POD1 and was associated with serum free branched-chain amino acid concentrations. Urinary titin on POD1 was significantly correlated with a decrease in skeletal muscle mass (rs −0.361, p = 0.036) and body cell mass (rs −0.361, p = 0.038) at 6 months postoperatively. The grip strength at 6 months postoperatively tended to decrease (rs −0.342, p = 0.052). BMI and serum LDH at admission were associated with urinary titin on POD1 but were not correlated with skeletal muscle loss at 6 months, suggesting that urinary titin on POD1 is an independent biomarker of skeletal muscle atrophy. These data indicate that urinary titin on POD1 can predict long-term skeletal muscle atrophy.