Using the Lipidyzer platform, we have created a lipidomic profile of plasma of C26 mice in pre-cachexia and cachexia. We have compared this lipidomic profile to that of additional cachexia mouse models, namely the SW480 model, the APCMin/+ and the LLC Lewis Lung Cancer model. As non-cachectic cancer model, we used the NC26 mice, as well as C26 tumor bearing pre-cachectic mice. We have also compared the lipidomic profile of the cachectic animals to that of patients with cachexia or non-cachectic cancer (collaboration Professor Marilia Seelaender, University of São Paolo). We have measured the expression of key enzymes of ceramide metabolism in adipose tissue, tumor, muscle, and liver of cachectic mice and patients, and identified the liver as likely source of the elevated circulating ceramides. Tissue lipidomics additionally identified alterations to liver lipids, specifically modified ceramides, in liver biopsies of cachectic mice and patients. We have measured the effect of ceramides or ceramide inhibition on adipocytes, muscle cells, and hepatocytes in the cell culture. Further, we have measured the effect of different ceramide synthesis inhibitors on cachexia development in vivo in the C26 mouse model of cachexia, and found myriocin to efficiently block ceramide synthesis and improve several cachexia readouts in these mice.
Overall, this set of experiments demonstrated that ceramides can serve as biomarkers for the early detection of cachexia, and stem from dysfunctional liver lipid metabolism. In cachexia, elevated ceramides cause muscle atrophy and alterations to liver mitochondrial metabolism, that can partially be reversed by the treatment with myriocin.
Using 13C glucose tracing and metabolomics, we have performed in vivo substrate tracing in the C26 mouse model of cachexia over the time course of disease development. We have further performed transcriptomics of adipose tissue, muscle, liver, and tumor, and proteomics of muscle and liver, and are currently integrating the data together with Dr. Dominik Lutter (Helmholtz Munich). We have produced preliminary experiments to validate adipocyte-intrinsic wasting cycles in the cell culture. This set of data is still under investigation, but preliminary data indicate that substrate flux in cachectic adipose tissue is disturbed and can partially be restored by targeting PDK4.
To better understand glucose homeostasis in cachexia, we have performed a range of glucose and insulin tolerance tests over various time points of cachexia development in C26 mice, and the control NC26 mice. We found no glucose or insulin intolerance in these mice, irrespective of their state of cachexia. We have further assessed islet hormone secretion and other indices of pancreatic dysfunction, and found that pancreatic inflammation was associated with cachexia, but not the presence of a tumor. Bulk sequencing of pancreatic islets has further confirmed the inflammatory state of the cachectic islets. First experiments to investigate the crosstalk between cancer cells and pancreatic beta-cells as well as macrophages have been performed in the cell culture and will be expanded. Lastly, collaborating with Dr. Olga Prokopchuk (Technical University Munich), we have analysed clinical data of patients with cachexia and found a close association between disturbed glucose homeostasis and cachexia in patients with pancreatic and colorectal cancer, highlighting that glucose metabolism is indeed important for the etiology of cachexia.
