In both humans and pets, skeletal muscle atrophy can occur naturally with age (sarcopenia).1,2 Consequences of skeletal muscle atrophy include impairments in strength, endurance, activity, and overall health, and a decreased quality of life.1,3 By limiting activity, muscle atrophy interferes with exercise and promotes further muscle disuse and a feed-forward process toward more pronounced functional deficits.4 "Despite the broad prevalence and impact of skeletal muscle atrophy, little research has been performed, as if muscle atrophy was considered inevitable. Promoting skeletal muscle integrity/health/strength is currently an enormous unmet need in canine health." Prevalence The prevalence of sarcopenia has not been fully investigated in dogs. Several studies have shown muscle mass decreases with age while fat mass increases or remains stable, and this change in body composition negatively correlates with lifespan in dogs.5,6 A recent study on 1,273 colony-housed dogs and 1,096 colony-housed cats of different ages indicated lean mass increased until the age of 6.3 years in dogs and 4.5 years in cats before gradually decreasing.6 Further, since muscle loss is also often associated with a decrease in food intake, the real prevalence of sarcopenia is hard to estimate. For example, it is estimated 78 percent of hospitalized dogs will lose body weight, of which 61 percent is lean body mass.7 Because muscle loss is natural in aged dogs and very often observed in dogs during muscle disuse, we can reasonably speculate skeletal muscle atrophy will occur at least once during a dog’s life, especially as it gets older. Despite the broad prevalence and impact of skeletal muscle atrophy, little research has been performed, as if muscle atrophy was considered inevitable. Promoting skeletal muscle integrity/health/strength is currently an enormous unmet need in canine health. Mechanisms Skeletal muscle atrophy has multifactorial mechanisms, including decreased energy intake and alterations in metabolism.3,4 Underlying mechanisms to explain muscle loss involve molecular targets of skeletal muscle proteolysis and atrophy and alterations in muscle growth inhibitors.3,4,8-10 The entire collection of mRNAs that increase or decrease in skeletal muscle as it undergoes atrophy is known as an mRNA expression signature of skeletal muscle atrophy.9,11 When searching for candidate small molecule inhibitors of muscle atrophy in humans and mice, researchers found the mRNA expression signatures generated when administering ursolic acid to mice negatively correlated to the mRNA expression signatures of muscle atrophy.9,11 Developing a supplement Ursolic acid is a naturally occurring pentacyclic triterpene acid found in several edible fruits and herbs.9,12 The effect of ursolic acid on muscle mass, muscle quality (specific force), muscle strength, and endurance exercise capacity was then confirmed in mouse models, showing the protection from muscle atrophy during advanced age, fasting, and muscle disuse.9,10 A recent study found ursolic acid’s effect on age-related muscle atrophy in dogs.4 To conduct this study, a palatable soft chew was developed using a proprietary process that improved the oral bioavailability of ursolic acid in dogs and enhanced palatability of the soft chews to ease administration. The chew contained 24 mg of ursolic acid to provide approximately 2 mg/kg/day to 10-15 kg dogs with one chew per day (recommended daily amount). The safety of the chew was first assessed for 28 days in 16 healthy dogs receiving either nothing (control, n=8) or five times the recommended daily amount (i.e. five chews per day, n=8). Throughout the 28-day study, behavior, general health, food consumption, and stool appearance were assessed daily, and complete physical examinations, including rectal temperature and body weight measurements, were performed once a week. At the beginning and conclusion of the study, blood and urine were collected from each animal for standard hematology and biochemistry blood analysis and for urine analysis of pH and specific gravity. The tolerance study showed no product-related clinical signs, and no significant change in blood or urine parameters were reported. The ursolic acid supplement is well tolerated by dogs, even at five times the recommended daily dose. Efficacy assessment To assess the efficacy of this supplement in dogs, 20 kenneled dogs older than seven years with mild to moderate muscle loss based upon the World Small Animal Veterinary Association (WSAVA) muscle condition scoring scale.13 The dogs were otherwise healthy with no serious illness or medications. The dogs were randomly allocated to one of the two groups, with 10 dogs per group, and received either the ursolic acid supplement or a placebo (control group) for 60 days. The study was blinded to all personnel involved in the investigation, apart from the technicians responsible for dietary supplement assignment and administration. One very old female in the ursolic acid group was removed from the study at day 45 due to illness unrelated to the chew administration. A muscle biopsy was performed at the beginning and end of the study to analyze skeletal muscle mRNA expression. In the placebo group, it was found many mRNAs promoting muscle atrophy and weakness exhibited small but significant increases over the course of the study, consistent with the progressive nature of age-related muscle atrophy. In the group receiving the ursolic acid supplement, such an increase was not observed, and some of these mRNAs even decreased at the end of the study. Relative to placebo, ursolic acid significantly reduced or tended to reduce levels of more than 50 mRNAs that encode mediators or biomarkers of muscle atrophy and weakness. Also, as expected, mRNAs, important for the normal structure and function of skeletal muscle, decreased in the placebo group. In the supplemented group, the decrease was not as pronounced, and most of these mRNAs remained stable or increased by the end of the study. Compared to placebo, there was a significant increase in mediators and biomarkers of muscle health and exercise when the ursolic acid supplement was given. Collectively and consistently with findings in other species, these data indicate dietary supplementation with ursolic acid inhibits atrophy-associated mRNA expression in canine skeletal muscle and stimulates changes that protect the normal structure and function of skeletal muscle and promote overall muscle health. Muscle functionality assessment To assess the impact on muscle functionality of such changes in skeletal muscle mRNA expression, two different assessments reflective of muscle health were evaluated in these dogs: their willingness to exercise and their latency to perform a task. To assess their willingness to exercise, they were encouraged to exercise for six minutes (+/-1 min) in a designated outdoor area on a leash or harness for five consecutive days. The exercise was standardized to the extent possible, varying only by individual willingness and functional ability. Exercise participation was quantitated on a scale of 0-3, with 0 representing no participation and 3 representing enthusiastic participation. The results showed that exercise participation significantly improved in the supplemented group but not in the placebo group. Indeed, exercise participation increased considerably in the treated group, with 7/9 dogs getting a higher score by the end of the study. The two remaining dogs already had a score of 3 initially and could not improve further. Therefore, all impaired dogs (with a score < 3 initially) improved. However, only two out of 10 dogs improved for this criteria in the placebo group. Seven dogs had a score <3 initially, of which two improved, and three dogs had a score of 3 initially, of which one had a lower score (worsening) by the end of the study. These data show ursolic acid supplementation can improve the dog’s willingness to exercise. Immediately after the exercise, muscular endurance was assessed with a T-maze test the dogs were previously acclimated to. The animals traversed the maze through a center aisle containing two weave obstacles and returned to the start box through either the right or left arm of the maze, both of which contained a single jump obstacle. Jump height was determined for each individual animal based on physical ability and remained consistent throughout the study. The task was repeated 20 times, and only the last 10 trials were quantified in terms of latency to avoid potential biases of novelty and excitation. While no change in latency was observed in the placebo group, a significant improvement was observed in the supplemented group, showing that the dogs receiving the ursolic acid supplementation could perform the task quicker and that their performance improved. This study is the first to demonstrate the safety and impact of ursolic acid supplementation in skeletal muscle mRNA expression and muscle function in dogs. Céline Nicolas holds a degree in veterinary medicine (2005) and a PhD (2007) from the University of Nantes, France. She worked as a postdoctoral fellow and research assistant at the University of Bristol, UK, and the University of Nice, France for around eight years. Dr. Nicolas joined Virbac as a medical writer in 2016 and is now the global medical manager for all the pet care products. She published more than 20 scientific articles in medical journals. References Freeman, L. M. Cachexia and sarcopenia in companion animals: An under-utilized natural animal model of human disease. JCSM Rapid Communications 1, 1–17. 2018. Frye, C., Carr, B. J., Lenfest, M. & Miller, A. Canine Geriatric Rehabilitation: Considerations and Strategies for Assessment, Functional Scoring, and Follow Up. Front Vet Sci 9, 842458 (2022). Freeman, L. M. Cachexia and sarcopenia: emerging syndromes of importance in dogs and cats. J. Vet. Intern. Med. 26, 3–17 (2012). Ebert, S. M. et al. Ursolic acid induces beneficial changes in skeletal muscle mRNA expression and increases exercise participation and performance in dogs with age-related muscle atrophy. Animals (Basel) 14, (2024). Adams, V. J. et al. Exceptional longevity and potential determinants of successful ageing in a cohort of 39 Labrador retrievers: results of a prospective longitudinal study. Acta Vet. Scand. 58, 29 (2016). McGrath, A. P., Hancock, L., Stiers, C. A., Brejda, J. & Morris, E. M. Retrospective analysis of dual-energy x-ray absorptiometry data demonstrates body composition changes with age in dogs and cats. Am. J. Vet. Res. 85, 1–11 (2024). Leung, Y. B., Cave, N. & Wester, T. J. Loss of body weight and lean mass in long-stay, hospitalized canine patients. J. Anim. Physiol. Anim. Nutr. 2023. Wakshlag, J. J. et al. Effect of dietary protein on lean body wasting in dogs: correlation between loss of lean mass and markers of proteasome-dependent proteolysis. J. Anim. Physiol. Anim. Nutr. 87, 408–420 (2003). Kunkel, S. D. et al. mRNA expression signatures of human skeletal muscle atrophy identify a natural compound that increases muscle mass. Cell Metab. 13, 627–638 (2011). Ebert, S. M. et al. Identification and Small Molecule Inhibition of an Activating Transcription Factor 4 (ATF4)-dependent Pathway to Age-related Skeletal Muscle Weakness and Atrophy. J. Biol. Chem. 290, 25497–25511 (2015). Adams, C. M., Ebert, S. M. & Dyle, M. C. Use of mRNA expression signatures to discover small molecule inhibitors of skeletal muscle atrophy. Curr. Opin. Clin. Nutr. Metab. Care 18, 263–268 (2015). Frighetto, R. T. S., Welendorf, R. M., Nigro, E. N., Frighetto, N. & Siani, A. C. Isolation of ursolic acid from apple peels by high-speed counter-current chromatography. Food Chem. 106, 767–771 (2008). Of, W. Muscle Condition Score. https://wsava.org/wp-content/uploads/2020/01/Muscle-Condition-Score-Chart-for-Dogs.pdf.
