Modification of Neuromuscular Junction Protein Expression by Exercise and Doxorubicin

Age, cancer, and the dual burden of cancer and doxorubicin in skeletal muscle wasting in female rats: which one to blame?

Sarcopenia and cancer cachexia are two life-threatening conditions often misdiagnosed. The skeletal muscle is one of the organs most adversely affected by these conditions, culminating in poor quality of life and premature mortality. In addition, it has been suggested that chemotherapeutic agents exacerbate cancer cachexia, as is the case of doxorubicin. Herein, we sought to investigate markers of inflammation and neuromuscular junction (NMJ) remodeling during aging and in response to cancer or cancer with chemotherapy. To address this, we utilized female rats across three age groups - young, adult, and old - to examine age-related changes, with old rats serving as a sarcopenia model. Additionally, a chemically-induced breast cancer (BCa) model was implemented in female adult rats, both without (adult BCa) or with doxorubicin administration (adult BCaDOX), to study cancer cachexia. The atrophy of the gastrocnemius muscle was observed in old, adult BCa and adult BCaDOX rats compared to adult ones. No signs of inflammation or NMJ impairment were observed in adult BCa or adult BCaDOX rats, except for the low levels of the subunit α1 of the acetylcholine receptor in adult BCaDOX rats compared to adult ones. In contrast, old rats presented high serum levels of interleukin 6, brain-derived neurotrophic factor (BDNF) and calcitonin gene-related peptide compared to young rats. In the gastrocnemius muscle, BDNF levels were decreased in old rats compared to adult rats, suggesting impaired skeletal muscle regeneration upon age-induced damage. The BDNF muscle levels were inversely correlated with its levels in circulation in adult and old rats. Hence, this work highlights BDNF as a specific biomarker of age-induced skeletal muscle atrophy, at least, in the differential diagnosis against cancer- or cancer with chemotherapy-induced muscle wasting.

Neurochemical and Morphological Comparisons of Motor Nerve Organoids and Spinal-Cord Explants

Organoids are multicellular structures formed in vitro from populations of individual cells allowing modeling of structural and functional aspects of organs and tissues in normal and diseased states. They offer unique opportunities to model and treat disease. Using a mouse embryonic stem cell line, we have cultured organoids that express markers of spinal cord motor neurons as well as motor neurons found within the peripheral nervous system. The morphology and select neurotransmitter content of the organoids and spinal cord explants were compared at different developmental time points. We found indications of maturation in the organoids over time, mirrored by similar trends in the spinal cord explants. Although the organoids contained the same neurotransmitters as the spinal cord explants, the developmental changes of these neurotransmitter levels were less marked in organoids. Given these differences, further work is required to optimize organoid growth conditions to better reproduce in vivo models when using organoids to study development.

Long-term effects of the chronic administration of doxorubicin on aged skeletal muscle: An exploratory study in mice

The widely used chemotherapeutic drug doxorubicin (DOX) has been associated with adverse effects on the skeletal muscle, which can persist for years after the end of the treatment. These adverse effects may be exacerbated in older patients, whose skeletal muscle might already be impaired by aging. Nonetheless, the mediators responsible for DOX-induced myotoxicity are still largely unidentified, particularly the ones involved in the long-term effects that negatively affect the quality of life of the patients. Therefore, this study aimed to investigate the long-term effects of the chronic administration of DOX on the soleus muscle of aged mice. For that and to mimic the clinical regimen, a dose of 1.5 mg kg-1 of DOX was administered two times per week for three consecutive weeks in a cumulative dose of 9 mg kg-1 to 19-month-old male mice, which were sacrificed two months after the last administration. Body wasting and the atrophy of the soleus muscle, as measured by a decrease in the cross-sectional area of the soleus muscle fibers, were identified as long-term effects of DOX administration. The atrophy observed was correlated with increased reactive oxygen species production and caspase-3 activity. An impaired skeletal muscle regeneration was also suggested due to the correlation between satellite cells activation and the soleus muscle fibers atrophy. Systemic inflammation, skeletal muscle energy metabolism and neuromuscular junction-related markers do not appear to be involved in the long-term DOX-induced skeletal muscle atrophy. The data provided by this study shed light on the mediators involved in the overlooked long-term DOX-induced myotoxicity, paving the way to the improvement of the quality of life and survival rates of older cancer patients.

Effects of exercise and doxorubicin on acute diaphragm neuromuscular transmission failure

Doxorubicin (DOX) is a highly effective anthracycline antibiotic used to treat a wide variety of cancers including breast cancer, leukemia and lymphoma. Unfortunately, clinical use of DOX is limited due to adverse off-target effects resulting in fatigue, respiratory muscle weakness and dyspnea. The diaphragm is the primary muscle of inspiration and respiratory insufficiency is likely the result of both muscle weakness and neural impairment. However, the contribution of neuropathology to DOX-induced respiratory muscle dysfunction is unclear. We hypothesized that diaphragm weakness following acute DOX exposure is associated with neurotoxicity and that exercise preconditioning is sufficient to improve diaphragm muscle contractility by maintaining neuromuscular integrity. Adult female Sprague-Dawley rats were randomized into four experimental groups: 1) sedentary-saline, 2) sedentary-DOX, 3) exercise-saline or 4) exercise-DOX. Endurance exercise preconditioning consisted of treadmill running for 1 h/day at 30 m/min for 10 days. Twenty-four hours after the last bout of exercise, animals were treated with DOX (20 mg/kg, I.P.) or saline (equal volume). Our results demonstrate that 48-h following DOX administration diaphragm muscle specific force is reduced in sedentary-DOX rats in response to both phrenic nerve and direct diaphragm stimulation. Importantly, endurance exercise preconditioning in DOX-treated rats attenuated the decrease in diaphragm contractile function, reduced neuromuscular transmission failure and altered phrenic nerve morphology. These changes were associated with an exercise-induced reduction in circulating biomarkers of inflammation, nerve injury and reformation. Therefore, the results are consistent with exercise preconditioning as an effective way of reducing respiratory impairment via preservation of phrenic-diaphragm neuromuscular conduction.

Evaluation of skeletal muscle function in male rats with doxorubicin-induced myopathy following various exercise techniques: the significant role of glucose transporter 4

A common anthracycline antibiotic used to treat cancer patients is doxorubicin (DOX). One of the effects of DOX therapy is skeletal muscle fatigue. Our goal in this research was to study the beneficial effect of exercise on DOX-induced damaged muscle fibers and compare the effect of different exercise strategies (prophylactic, post- toxicity and combined) on DOX toxicity. Five groups were created from 40 male rats: group I, control group; group II, DOX was administered intraperitoneally for 2 weeks over 6 equal injections (each 2.5 mg/kg); group III, rats trained for 3 weeks before DOX; group IV, rats trained for 8 weeks after DOX; and group V, rats were trained for 3 weeks before DOX followed by 8 weeks after. Measures of oxidative damage (H2O2, catalase), inflammation (TNF-α), and glucose transporter 4 (GLUT4) expression on skeletal muscle were assessed. Also, Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) was estimated. Skeletal performance was evaluated by contraction time (CT), half relaxation time (1/2 RT), and force-frequency relationship by the end of this research. The current study demonstrated a detrimental effect of DOX on skeletal performance as evidenced by a significant increase in CT and 1/2 RT compared to control; in addition, H2O2, TNF-α, and HOMA-IR were significantly increased with a significant decrease in GLUT4 expression and catalase activity. Combined exercise therapy showed a remarkable improvement in skeletal muscle performance, compared to DOX, CT, and 1/2 RT which were significantly decreased; H2O2 and TNF-α were significantly decreased unlike catalase antioxidant activity that significantly increased; in addition, skeletal muscle glucose metabolism was significantly improved as GLUT4 expression significantly increased and HOMA-IR was significantly decreased. Exercise therapy showed significant improvement in all measured parameters relative to DOX. However, combined exercise therapy showed the best improvement relative to both pre-exercise and post-exercise groups.

Doxorubicin causes cachexia, sarcopenia, and frailty characteristics in mice

While chemotherapy treatment can be lifesaving, it also has adverse effects that negatively impact the quality of life. To investigate the effects of doxorubicin chemotherapy on body weight loss, strength and muscle mass loss, and physical function impairments, all key markers of cachexia, sarcopenia, and frailty. Seventeen C57/BL/6 mice were allocated into groups. 1) Control (n = 7): mice were exposed to intraperitoneal (i.p.) injections of saline solution. 2) Dox (n = 10): mice were exposed to doxorubicin chemotherapy cycles (total dose of 18 mg/kg divided over 15 days). The body weight loss and decreased food intake were monitored to assess cachexia. To assess sarcopenia, we measured muscle strength loss using a traction method and evaluated muscle atrophy through histology of the gastrocnemius muscle. To evaluate physical function impairments and assess frailty, we employed the open field test to measure exploratory capacity. Doxorubicin administration led to the development of cachexia, as evidenced by a significant body weight loss (13%) and a substantial decrease in food intake (34%) over a 15-day period. Furthermore, 90% of the mice treated with doxorubicin exhibited sarcopenia, characterized by a 20% reduction in traction strength (p<0,05), a 10% decrease in muscle mass, and a 33% reduction in locomotor activity. Importantly, all mice subjected to doxorubicin treatment were considered frail based on the evaluation of their overall condition and functional impairments. The proposed model holds significant characteristics of human chemotherapy treatment and can be useful to understand the intricate relationship between chemotherapy, cachexia, sarcopenia, and frailty.

Long-term Musculoskeletal Consequences of Chemotherapy in Pediatric Mice

Thanks to recent progress in cancer research, most children treated for cancer survive into adulthood. Nevertheless, the long-term consequences of anticancer agents are understudied, especially in the pediatric population. We and others have shown that routinely administered chemotherapeutics drive musculoskeletal alterations, which contribute to increased treatment-related toxicity and long-term morbidity. Yet, the nature and scope of these enduring musculoskeletal defects following anticancer treatments and whether they can potentially impact growth and quality of life in young individuals remain to be elucidated. Here, we aimed at investigating the persistent musculoskeletal consequences of chemotherapy in young (pediatric) mice. Four-week-old male mice were administered a combination of 5-FU, leucovorin, irinotecan (a.k.a., Folfiri) or the vehicle for up to 5 wk. At time of sacrifice, skeletal muscle, bones, and other tissues were collected, processed, and stored for further analyses. In another set of experiments, chemotherapy-treated mice were monitored for up to 4 wk after cessation of treatment. Overall, the growth rate was significantly slower in the chemotherapy-treated animals, resulting in diminished lean and fat mass, as well as significantly smaller skeletal muscles. Interestingly, 4 wk after cessation of the treatment, the animals exposed to chemotherapy showed persistent musculoskeletal defects, including muscle innervation deficits and abnormal mitochondrial homeostasis. Altogether, our data support that anticancer treatments may lead to long-lasting musculoskeletal complications in actively growing pediatric mice and support the need for further studies to determine the mechanisms responsible for these complications, so that new therapies to prevent or diminish chemotherapy-related toxicities can be identified.

Targeting Mitochondria and Oxidative Stress in Cancer- and Chemotherapy-Induced Muscle Wasting

Significance: Cancer is frequently associated with the early appearance of cachexia, a multifactorial wasting syndrome. If not present at diagnosis, cachexia develops either as a result of tumor progression or as a side effect of anticancer treatments, especially of standard chemotherapy, eventually representing the direct cause of death in up to one-third of all cancer patients. Cachexia, within its multiorgan affection, is characterized by severe loss of muscle mass and function, representing the most relevant subject of preclinical and clinical investigation. Recent Advances: The pathogenesis of muscle wasting in cancer- and chemotherapy-induced cachexia is complex, and encompasses heightened protein catabolism and reduced anabolism, disrupted mitochondria and energy metabolism, and even neuromuscular junction dismantling. The mechanisms underlying these alterations are still controversial, especially concerning the molecular drivers that could be targeted for anticachexia therapies. Inflammation and mitochondrial oxidative stress are among the principal candidates; the latter being extensively discussed in the present review. Critical Issues: Several approaches have been tested to modulate the redox homeostasis in tumor hosts, and to counteract cancer- and chemotherapy-induced muscle wasting, from exercise training to distinct classes of direct or indirect antioxidants. We herein report the most relevant results obtained from both preclinical and clinical trials. Future Directions: Including the assessment and the treatment of altered redox balance in the clinical management of cancer patients is still a big challenge. The available evidence suggests that fortifying the antioxidant defenses by either pharmacological or nonpharmacological strategies will likely improve cachexia and eventually the outcome of a broad cancer patient population. Antioxid. Redox Signal. 38, 352-370.

Prolonged Endurance Exercise Adaptations Counteract Doxorubicin Chemotherapy-Induced Myotoxicity in Mice

Doxorubicin (DOX) is a potent chemotherapeutic agent widely used for various types of cancer; however, its accumulation causes myotoxicity and muscle atrophy. Endurance exercise (EXE) has emerged as a vaccine against DOX-induced myotoxicity. However, potential molecular mechanisms of EXE-mediated myocyte protection for the unfavorable muscle phenotype remain unelucidated. In addition, most studies have identified the short-term effects of DOX and EXE interventions, but studies on the prolonged EXE effects used as adjuvant therapy for chronic DOX treatment are lacking. Twelve-week-old adult male C57BL/6J mice were assigned to four groups: sedentary treated with saline (SED-SAL, n = 10), endurance exercise treated saline (EXE-SAL, n = 10), sedentary treated with doxorubicin (SED-DOX, n = 10), and endurance exercise treated with doxorubicin (EXE-DOX, n = 10). Mice were intraperitoneally injected with DOX (5 mg/kg) or saline five times biweekly for eight weeks, while a treadmill running exercise was performed. Body composition was assessed and then soleus muscle tissues were excised for histological and biochemical assays. Our data showed that DOX aggravated body composition, absolute soleus muscle mass, and distinct pathological features; also, TOP2B upregulation was linked to DOX-induced myotoxicity. We also demonstrated that EXE-DOX promoted mitochondrial biogenesis (e.g., citrate synthase). However, no alterations in satellite cell activation and myogenesis factors in response to DOX and EXE interventions were observed. Instead, SED-DOX promoted catabolic signaling cascades (AKT-FOXO3α-MuRF-1 axis), whereas EXE-DOX reversed its catabolic phenomenon. Moreover, EXE-DOX stimulated basal autophagy. We showed that the EXE-mediated catabolic paradigm shift is likely to rescue impaired muscle integrity. Thus, our study suggests that EXE can be recommended as an adjuvant therapy to ameliorate DOX-induced myotoxicity.

Chemotherapy-Induced Myopathy: The Dark Side of the Cachexia Sphere

Simple Summary

In addition to cancer-related factors, anti-cancer chemotherapy treatment can drive life-threatening body wasting in a syndrome known as cachexia. Emerging evidence has described the impact of several key chemotherapeutic agents on skeletal muscle in particular, and the mechanisms are gradually being unravelled. Despite this evidence, there remains very little research regarding therapeutic strategies to protect muscle during anti-cancer treatment and current global grand challenges focused on deciphering the cachexia conundrum fail to consider this aspect—chemotherapy-induced myopathy remains very much on the dark side of the cachexia sphere. This review explores the impact and mechanisms of, and current investigative strategies to protect against, chemotherapy-induced myopathy to illuminate this serious issue.

Abstract

Cancer cachexia is a debilitating multi-factorial wasting syndrome characterised by severe skeletal muscle wasting and dysfunction (i.e., myopathy). In the oncology setting, cachexia arises from synergistic insults from both cancer–host interactions and chemotherapy-related toxicity. The majority of studies have surrounded the cancer–host interaction side of cancer cachexia, often overlooking the capability of chemotherapy to induce cachectic myopathy. Accumulating evidence in experimental models of cachexia suggests that some chemotherapeutic agents rapidly induce cachectic myopathy, although the underlying mechanisms responsible vary between agents. Importantly, we highlight the capacity of specific chemotherapeutic agents to induce cachectic myopathy, as not all chemotherapies have been evaluated for cachexia-inducing properties—alone or in clinically compatible regimens. Furthermore, we discuss the experimental evidence surrounding therapeutic strategies that have been evaluated in chemotherapy-induced cachexia models, with particular focus on exercise interventions and adjuvant therapeutic candidates targeted at the mitochondria.

Muscle weakness caused by cancer and chemotherapy is associated with loss of motor unit connectivity

Skeletal muscle wasting and weakness caused by cancer and its treatments (known as "cachexia") drastically impair quality of life and worsen survival outcomes in cancer patients. There are currently no approved treatments for cachexia. Hence, further investigation into the causes of cachexia induced by cancer and chemotherapy is warranted. Here, we sought to investigate skeletal muscle wasting, weakness and loss of motor unit function in mice bearing cancers or administered chemotherapeutics. Mice bearing colorectal cancers, including C26, MC38 and HCT116, and mice receiving the chemotherapeutics folfiri and cisplatin were assessed for in vivo and ex vivo muscle force, and for in vivo electrophysiological indices of motor unit connectivity, including compound muscle action potential and motor unit number estimation (MUNE). In vivo and ex vivo muscle force, as well as MUNE were reduced in C26, MC38, HCT116 hosts, and in mice receiving folfiri and cisplatin compared to their respective experimental controls. In addition, MUNE was correlated with muscle force and muscle mass in all experimental conditions, while assessment of neuromuscular junction (NMJ) protein expression and changes in presynaptic morphology suggested that cancer and chemotherapy significantly alter muscle innervation. The present results demonstrate that the loss of motor unit connectivity may contribute to skeletal muscle wasting and weakness that occur with cancer and chemotherapy.

Consideration of Sex as a Biological Variable in the Development of Doxorubicin Myotoxicity and the Efficacy of Exercise as a Therapeutic Intervention

Doxorubicin (DOX) is an anthracycline antibiotic used to treat a wide variety of hematological and solid tumor cancers. While DOX is highly effective at reducing tumor burden, its clinical use is limited by the development of adverse effects to both cardiac and skeletal muscle. The detrimental effects of DOX to muscle tissue are associated with the increased incidence of heart failure, dyspnea, exercise intolerance, and reduced quality of life, which have been reported in both patients actively receiving chemotherapy and cancer survivors. A variety of factors elevate the probability of DOX-related morbidity in patients; however, the role of sex as a biological variable to calculate patient risk remains unclear. Uncertainty regarding sexual dimorphism in the presentation of DOX myotoxicity stems from inadequate study design to address this issue. Currently, the majority of clinical data on DOX myotoxicity come from studies where the ratio of males to females is unbalanced, one sex is omitted, and/or the patient cohort include a broad age range. Furthermore, lack of consensus on standard outcome measures, difficulties in long-term evaluation of patient outcomes, and other confounding factors (i.e., cancer type, drug combinations, adjuvant therapies, etc.) preclude a definitive answer as to whether differences exist in the incidence of DOX myotoxicity between sexes. This review summarizes the current clinical and preclinical literature relevant to sex differences in the incidence and severity of DOX myotoxicity, the proposed mechanisms for DOX sexual dimorphism, and the potential for exercise training to serve as an effective therapeutic countermeasure to preserve muscle strength and function in males and females.

Exercise Reduces the Resumption of Tumor Growth and Proteolytic Pathways in the Skeletal Muscle of Mice Following Chemotherapy

Simple Summary

Doxorubicin is a chemotherapeutic agent that contributes to muscle wasting. Based on the evidence that many cancer variants are associated with cachexia and that cancer patients are usually treated with chemotherapeutic agents, it is important to determine strategies to mitigate muscle atrophy. Muscle loss is a poor prognosis during cancer treatment, and exercise has emerged as a potential strategy utilized in this context. Once an ongoing regimen of chemotherapeutic treatment is not always possible, our results demonstrated that continuity of endurance exercise is a potential strategy that can be adopted when chemotherapy needs to be interrupted, minimizing the resumption of tumor growth and avoiding muscle loss.

Abstract

The pathogenesis of muscle atrophy plays a central role in cancer cachexia, and chemotherapy contributes to this condition. Therefore, the present study aimed to evaluate the effects of endurance exercise on time-dependent muscle atrophy caused by doxorubicin. For this, C57 BL/6 mice were subcutaneously inoculated with Lewis lung carcinoma cells (LLC group). One week after the tumor establishment, a group of these animals initiated the doxorubicin chemotherapy alone (LLC + DOX group) or combined with endurance exercise (LLC + DOX + EXER group). One group of animals was euthanized after the chemotherapy cycle, whereas the remaining animals were euthanized one week after the last administration of doxorubicin. The practice of exercise combined with chemotherapy showed beneficial effects such as a decrease in tumor growth rate after chemotherapy interruption and amelioration of premature death due to doxorubicin toxicity. Moreover, the protein degradation levels in mice undergoing exercise returned to basal levels after chemotherapy; in contrast, the mice treated with doxorubicin alone experienced an increase in the mRNA expression levels of the proteolytic pathways in gastrocnemius muscle (Trim63, Fbxo32, Myostatin, FoxO). Collectively, our results suggest that endurance exercise could be utilized during and after chemotherapy for mitigating muscle atrophy promoted by doxorubicin and avoid the resumption of tumor growth.

The Impact of Immune Cells on the Skeletal Muscle Microenvironment During Cancer Cachexia

Progressive weight loss combined with skeletal muscle atrophy, termed cachexia, is a common comorbidity associated with cancer that results in adverse consequences for the patient related to decreased chemotherapy responsiveness and increased mortality. Cachexia's complexity has provided a barrier for developing successful therapies to prevent or treat the condition, since a large number of systemic disruptions that can regulate muscle mass are often present. Furthermore, considerable effort has focused on investigating how tumor derived factors and inflammatory mediators directly signal skeletal muscle to disrupt protein turnover regulation. Currently, there is developing appreciation for understanding how cancer alters skeletal muscle's complex microenvironment and the tightly regulated interactions between multiple cell types. Skeletal muscle microenvironment interactions have established functions in muscle response to regeneration from injury, growth, aging, overload-induced hypertrophy, and exercise. This review explores the growing body of evidence for immune cell modulation of the skeletal muscle microenvironment during cancer-induced muscle wasting. Emphasis is placed on the regulatory network that integrates physiological responses between immune cells with other muscle cell types including satellite cells, fibroblast cells, and endothelial cells to regulate myofiber size and plasticity. The overall goal of this review is to provide an understanding of how different cell types that constitute the muscle microenvironment and their signaling mediators contribute to cancer and chemotherapy-induced muscle wasting.

Prevention of Doxorubicin-Induced Autophagy Attenuates Oxidative Stress and Skeletal Muscle Dysfunction

Clinical use of the chemotherapeutic doxorubicin (DOX) promotes skeletal muscle atrophy and weakness, adversely affecting patient mobility and strength. Although the mechanisms responsible for DOX-induced skeletal muscle dysfunction remain unclear, studies implicate the significant production of reactive oxygen species (ROS) in this pathology. Supraphysiological ROS levels can enhance protein degradation via autophagy, and it is established that DOX upregulates autophagic signaling in skeletal muscle. To determine the precise contribution of accelerated autophagy to DOX-induced skeletal muscle dysfunction, we inhibited autophagy in the soleus via transduction of a dominant negative mutation of the autophagy related 5 (ATG5) protein. Targeted inhibition of autophagy prevented soleus muscle atrophy and contractile dysfunction acutely following DOX administration, which was associated with a reduction in mitochondrial ROS and maintenance of mitochondrial respiratory capacity. These beneficial modifications were potentially the result of enhanced transcription of antioxidant response element-related genes and increased antioxidant capacity. Specifically, our results showed significant upregulation of peroxisome proliferator-activated receptor gamma co-activator 1-alpha, nuclear respiratory factor-1, nuclear factor erythroid-2-related factor-2, nicotinamide-adenine dinucleotide phosphate quinone dehydrogenase-1, and catalase in the soleus with DOX treatment when autophagy was inhibited. These findings establish a significant role of autophagy in the development of oxidative stress and skeletal muscle weakness following DOX administration.