EFFECTS OF β-HYDROXY-β-METHYLBUTYRATE SUPPLEMENTATION ON MUSCLE MASS AND STRENGTH IN ONABOTULINUMTOXIN TYPE-A-INJECTED AND CONTRALATERAL QUADRICEPS FEMORIS IN RABBITS

Rafael Fortuna, PhD1, Andrew Sawatsky, MSc1, John C. Fuller, Jr , PhD2 and Walter Herzog, PhD1

From the 1Human Performance Laboratory, University of Calgary, Calgary, Alberta, Canada and 2Metabolic Technologies, LLC, Missoula, MT, USA

abstract

Objective: To determine the effects of the leucine metabolite β-hydroxy-β-methylbutyrate (HMB) on strength, muscle mass, and contractile material in muscle wasting induced by onabotulinumtoxin type-A (BoNT-A) injection into the quadriceps femoris muscles of New Zealand white rabbits.

Methods: A total of 21, female rabbits were divided into 3 groups (n = 7, each). Group 1 (Control) received intramuscular injection of saline. Groups 2 and 3 received intramuscular injection of BoNT-A (3.5 units/kg), with group 3 receiving supplementation with HMB (120 mg/kg-BW/day). Muscle morphology, mass, and strength were assessed 8 weeks later in both injected and non-injected contralateral limbs.

Results: Injected muscle strength of group 2 (BoNT-A) and group 3 (BoNT-A+HMB) was reduced by 63% and 60%, respectively, compared with Controls (p < 0.0001). Strength in contralateral muscles of group 2 was reduced by 23% vs Controls (p <0.002), while in group 3, strength was similar to Controls. Muscle mass in the injected muscles of the BoNT-A and BoNT-A+HMB groups was significantly reduced, by 46% and 48%, respectively.

Conclusion: While HMB did not prevent loss of muscle strength and mass in the BoNT-A-injected musculature, it prevented significant loss of contractile material in the injected musculature and strength loss in the contralateral non-injected musculature.

Key words: botulinum toxin; Botox®; β-hydroxy-β-methylbutyrate supplementation; muscle strength; muscle mass; skeletal muscle.

Accepted Jul 23, 2021; Epub ahead of print Aug 25, 2021

J Rehabil Med 2021; 53: jrm00229

Correspondence address: John C. Fuller, Jr, Metabolic Technologies LLC 135 West Main St. Suite B Missoula, MT 59802, USA. E-mail: Fuller@mti-hmb.com

lay abstract

Onabotulinum toxin A (BoNT-A) is currently approved for cosmetic procedures and for the treatment of many conditions, such as migraine headaches and neuromuscular conditions associated with spasticity, such as cerebral palsy or post-stroke in USA. Once injected into the muscle BoNT-A causes muscle paralysis, which is reversible. The current study examined the local and distant detrimental effects of BoNT-A on decreasing muscle wasting and muscle function in a rabbit model, and the effects of dietary use of HMB (β-hydroxy-β-methylbutyrate), a leucine metabolite, on these detrimental effects. BoNT-A was injected into 1 leg of a rabbit model and muscle mass and strength measured in both the injected and non-injected legs. BoNT-A caused a loss of muscle mass in the injected legs. It also caused a loss of strength in the injected legs and a somewhat reduced loss of strength in the non-injected legs. This suggests that BoNT-A injections can cause a decrease in function in distant, non-target muscles. HMB partially reversed some of the detrimental side-effects of BoNT-A, being shown to be effective in maintaining muscle strength in the non-injected leg.

introduction

Muscle mass is maintained by a balance between protein synthesis and degradation. However, when this balance is disturbed by either an increase in protein breakdown or a reduction in protein synthesis, muscle wasting occurs. Muscle wasting has significant clinical consequences, including muscle weakness, fatigue, morbidity, and it is an important contributing factor for reduced quality of life (QoL). Treatment modalities to prevent muscle wasting include exercise, inhibitors of inflammatory cytokines, and anti-inflammatory cytokines (1). Recently, there has been an increase in dietary supplement use aimed at increasing muscle mass, or preventing muscle atrophy in healthy, active, and sedentary people, in high-performance athletes, and in patients exposed to prolonged bed rest (2–5). However, the efficacy of dietary supplements in preventing strength loss and atrophy is a matter of debate (3).

Onabotulinumtoxin type-A (BoNT-A) is a potent neurotoxins (6, 7). Once injected into the target muscle, BoNT-A binds with high affinity to the neuromuscular junction, preventing acetylcholine release, and thereby inducing dose-dependent muscle paralysis (8, 9). Due to its extreme potency and specificity, BoNT-A has been used for both therapeutic and scientific interventions (10–12).

Localized BoNT-A injections are used clinically in an increasing number of neuromuscular disorders, with the primary aim of relaxing the hyperexcitability of peripheral nerve terminals; for example, in patients with cerebral palsy or following a stroke (11, 13). In experimental settings BoNT-A has been used to induce muscle weakness in an attempt to mimic muscle atrophy following injury, denervation, in elderly patients (14–16), or to determine the effects of muscle weakness on bone and joint health (17, 18). BoNT-A-induced muscle weakness can also be used to investigate strategies for the prevention of, or the reverting of, strength loss and muscle atrophy (19).

β-Hydroxy-β-methylbutyrate (HMB) is naturally produced from the amino acid leucine (20). As a dietary supplement, HMB has been used to improve strength and gain lean body mass, reduce muscle protein degradation, and improve recovery following exercise in trained, untrained, and elderly people (5, 21–24). Supplemental HMB has also been shown to increase lean body mass in elderly subjects without exercise (2) and to retain lean body mass during bed rest (4). Other studies have shown HMB can improve protein turnover in muscle atrophy conditions, such as AIDS (25), trauma (26) and cancer (27), and in endotoxin-induced septic rats (28).

Despite the increasing use of HMB as a dietary supplement, there have been no definitive studies showing the efficacy of HMB to prevent muscle weakness under conditions known to produce muscle paralysis and consequent atrophy.

The objective of the current study was to evaluate the effects of supplemental HMB on strength, muscle mass, and contractile material following BoNT-A-induced weakness in the quadriceps femoris of New Zealand white (NZW) rabbits. It was hypothesized that HMB supplementation would reduce the loss of strength and atrophy in both BoNT-A-injected target muscles and non-injected, non-target muscles.

METHODS

Experimental design

A total of 21 female NZW rabbits (43 weeks old) (Covance Research Products, Inc., Greenfield, IN, USA) were used in this study. All procedures were approved by the Animal Care Committee of the University of Calgary. Rabbits were allowed normal activity in a 65 × 45 × 30 cm cage and had ad libitum access to food and water.

The rabbits were divided into 3 groups: