RESUMO
Background: Progressive functional decline is a key element of cancer-associated cachexia. No therapies have successfully translated to the clinic due to an inability to measure and improve physical function in cachectic patients. Major barriers to translating pre-clinical therapies to the clinic include lack of cancer models that accurately mimic functional decline and use of non-specific outcome measures of function, like grip strength. New approaches are needed to investigate cachexia-related function at both the basic and clinical science levels. Methods: Survival extension studies were performed by testing multiple cell lines, dilutions, and vehicle-types in orthotopic implantation of K-ras LSL.G12D/+ ; Trp53 R172H/+ ; Pdx-1-Cre (KPC) derived cells. 128 animals in this new model were then assessed for muscle wasting, inflammation, and functional decline using a battery of biochemical, physiologic, and behavioral techniques. In parallel, we analyzed a 156-subject cohort of cancer patients with a range of cachexia severity, and who required rehabilitation, to determine the relationship between gait speed via six-minute walk test (6MWT), grip strength (hGS), and functional independence measures (FIM). Cachectic patients were identified using the Weight Loss Grading Scale (WLGS), Fearon consensus criteria, and the Prognostic Nutritional Index (PNI). Results: Using a 100-cell dose of DT10022 KPC cells, we extended the survival of the KPC orthotopic model to 8-9 weeks post-implantation compared to higher doses used (p<0.001). In this Low-dose Orthotopic (LO) model, both progressive skeletal and cardiac muscle wasting were detected in parallel to systemic inflammation; skeletal muscle atrophy at the fiber level was detected as early as 3 weeks post-implantation compared to controls (p<0.001). Gait speed in LO animals declined as early 2 week post-implantation whereas grip strength change was a late event and related to end of life. Principle component analysis (PCA) revealed distinct cachectic and non-cachectic animal populations, which we leveraged to show that gait speed decline was specific to cachexia (p<0.01) while grip strength decline was not (p=0.19). These data paralleled our observations in cancer patients with cachexia who required rehabilitation. In cachectic patients (identified by WLGS, Fearon criteria, or PNI, change in 6MWT correlated with motor FIM score changes while hGS did not (r 2 =0.18, p<0.001). This relationship between 6MWT and FIM in cachectic patients was further confirmed through multivariate regression (r 2 =0.30, p<0.001) controlling for age and cancer burden. Conclusion: Outcome measures linked to gait are better associated with cachexia related function and preferred for future pre-clinical and clinical cachexia studies.
RESUMO
Understanding passive skeletal muscle mechanics is critical in defining structure-function relationships in skeletal muscle and ultimately understanding pathologically impaired muscle. In this systematic review, we performed an exhaustive literature search using PRISMA guidelines to quantify passive muscle mechanical properties, summarized the methods used to create these data, and make recommendations to standardize future studies. We screened over 7500 papers and found 80 papers that met the inclusion criteria. These papers reported passive muscle mechanics from single muscle fiber to whole muscle across 16 species and 54 distinct muscles. We found a wide range of methodological differences in sample selection, preparation, testing, and analysis. The systematic review revealed that passive muscle mechanics is species and scale dependent-specifically within mammals, the passive mechanics increases non-linearly with scale. However, a detailed understanding of passive mechanics is still unclear because the varied methodologies impede comparisons across studies, scales, species, and muscles. Therefore, we recommend the following: smaller scales may be maintained within storage solution prior to testing, when samples are tested statically use 2-3 min of relaxation time, stress normalization at the whole muscle level be to physiologic cross-sectional area, strain normalization be to sarcomere length when possible, and an exponential equation be used to fit the data. Additional studies using these recommendations will allow exploration of the multiscale relationship of passive force within and across species to provide the fundamental knowledge needed to improve our understanding of passive muscle mechanics.
