biomedicines Article A Metabolic Change towards Fermentation Drives Cancer Cachexia in Myotubes Michele Mannelli, Tania Gamberi , Francesca Magherini and Tania Fiaschi *   Citation: Mannelli, M.; Gamberi, T.; Magherini, F.; Fiaschi, T. A Metabolic Change towards Fermentation Drives Cancer Cachexia in Myotubes. Biomedicines 2021, 9, 698. https://doi.org/10.3390/ biomedicines9060698 Academic Editor: Kyle S. McCommis Received: 26 May 2021 Accepted: 15 June 2021 Published: 20 June 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Dipartimento di Scienze Biomediche, Sperimentali e Cliniche “M. Serio”, Università degli Studi di Firenze, Viale Morgagni 50, 50134 Firenze, Italy; michele.mannelli@student.unisi.it (M.M.); tania.gamberi@unifi.it (T.G.); francesca.magherini@unifi.it (F.M.) * Correspondence: tania.fiaschi@unifi.it Abstract: Cachexia is a disorder associated with several pathologies, including cancer. In this paper, we describe how cachexia is induced in myotubes by a metabolic shift towards fermentation, and the block of this metabolic modification prevents the onset of the cachectic phenotype. Cachectic myotubes, obtained by the treatment with conditioned medium from murine colon carcinoma cells CT26, show increased glucose uptake, decreased oxygen consumption, altered mitochondria, and increased lactate production. Interestingly, the block of glycolysis by 2-deoxy-glucose or lactate dehydrogenase inhibition by oxamate prevents the induction of cachexia, thus suggesting that this metabolic change is greatly involved in cachexia activation. The treatment with 2-deoxy-glucose or oxamate induces positive effects also in mitochondria, where mitochondrial membrane potential and pyruvate dehydrogenase activity became similar to control myotubes. Moreover, in myotubes treated with interleukin-6, cachectic phenotype is associated with a fermentative metabolism, and the inhibition of lactate dehydrogenase by oxamate prevents cachectic features. The same results have been achieved by treating myotubes with conditioned media from human colon HCT116 and human pancreatic MIAPaCa-2 cancer cell lines, thus showing that what has been observed with murine- conditioned media is a wide phenomenon. These findings demonstrate that cachexia induction in myotubes is linked with a metabolic shift towards fermentation, and inhibition of lactate formation impedes cachexia and highlights lactate dehydrogenase as a possible new tool for counteracting the onset of this pathology. Keywords: cancer; cachexia; metabolism; lactate dehydrogenase 1. Introduction Cachexia is a complex multi-organ syndrome characterized by progressive body weight loss associated with several chronic or end-stage diseases [1,2]. Particularly, can- cer cachexia affects 50–80% of patients and accounts for about 20% of cancer deaths [3]. Cachectic patients show a drastic worsening of both prognosis and quality of life, as well as a reduced tolerance and response to antineoplastic treatments [4]. In skeletal muscle, cachexia induces wasting and atrophy due to several metabolic alterations [3,5,6]. Muscle loss is due to the great increase in protein degradation, not counterbalanced by adequate protein synthesis, in which activation of the ubiquitin-dependent proteasome pathway plays a crucial role [7,8]. Many intracellular signals are involved in protein turnover lead- ing to muscle wasting [9], such as those signaling pathways activated by inflammatory cytokines, such as tumor necrosis factor alpha [10], interleukin-1 (IL-1) [11], and IL-6 [12], secreted by either immune or tumor cells. Among cytokines, IL-6 exerts a prominent role as cachexia inductor. Indeed, IL-6 secreted by tumor cells promotes the activation of the JAK–STAT signaling pathway, leading to suppression of protein synthesis and muscle wasting [12]. In agreement, inhibition of the JAK/STAT3 pathway impedes muscle wasting in the mouse model of colon carcinoma [13]. Biomedicines 2021, 9, 698. https://doi.org/10.3390/biomedicines9060698 https://www.mdpi.com/journal/biomedicines