David Longino

Changes in contractile properties of muscles receiving repeat injections of botulinum toxin (Botox)

Botulinum toxin type A (BTX-A) is a frequently used therapeutic tool to denervate muscles in the treatment of neuromuscular disorders. Although considered safe by the US Food and Drug Administration, BTX-A can produce adverse effects in target and non-target muscles. With an increased use of BTX-A for neuromuscular disorders, the effects of repeat injections of BTX-A on strength, muscle mass and structure need to be known. Therefore, the purpose of this study was to investigate the changes in strength, muscle mass and contractile material in New Zealand White (NZW) rabbits. Twenty NZW rabbits were divided into 4 groups: control and 1, 3 and 6 months of unilateral, repeat injections of BTX-A into the quadriceps femoris. Outcome measures included knee extensor torque, muscle mass and the percentage of contractile material in the quadriceps muscles of the target and non-injected contralateral hindlimbs. Strength in the injected muscles was reduced by 88%, 89% and 95% in the 1, 3 and 6 months BTX-A injected hindlimbs compared to controls. Muscle mass was reduced by 50%, 42% and 31% for the vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM), respectively, at 1 month, by 68%, 51% and 50% at 3 months and by 76%, 44% and 13% at 6 months. The percentage of contractile material was reduced for the 3 and 6 months animals to 80-64%, respectively, and was replaced primarily by fat. Similar, but less pronounced results were also observed for the quadriceps muscles of the contralateral hindlimbs, suggesting that repeat BTX-A injections cause muscle atrophy and loss of contractile tissue in target muscles and also in non-target muscles that are far removed from the injection site.

Muscle weakness causes joint degeneration in rabbits.

OBJECTIVE The objective of this study was to investigate the effects of botulinum toxin type-A (BTX-A) induced quadriceps weakness on micro-structural changes in knee cartilage of New Zealand White (NZW) rabbits. DESIGN Fifteen rabbits were divided randomly into an experimental and a sham control group. Each group received a unilateral single quadriceps muscle injection either with saline (sham control; n=4) or BTX-A (experimental; n=11). RESULTS BTX-A injection produced significant quadriceps muscle weakness (P<0.05) and loss of quadriceps muscle mass (P<0.05). Degenerative changes of the knee cartilage, assessed with the Mankin grading system, were the same for the injected and non-injected hind limbs of the experimental group animals. Sham injection had no effect on joint degeneration but all control animals showed some degenerative changes in the knee. Degenerative changes of the retro-patellar cartilage were more severe in the experimental compared to sham control group rabbits (P<0.05). The distal region of the retro-patellar cartilage was more degenerated than the proximal part in the experimental and control group rabbits (P<0.05). The Mankin grades for the tibiofemoral region were not significantly different between experimental and control group rabbits (P>0.05). CONCLUSION Quadriceps muscle weakness caused increased degeneration in the retro-patellar cartilage of NZW rabbits, providing evidence that muscle weakness might be a risk factor for the onset and progression of osteoarthritis (OA). Future work needs to delineate whether muscle weakness directly affects joint degeneration, or if changes in function and movement execution associated with muscle weakness are responsible for the increased rate of OA onset and progression observed here.

Altered cell metabolism in tissues of the knee joint in a rabbit model of Botulinum toxin A‐induced quadriceps muscle weakness

Quadriceps muscle weakness is frequently associated with knee injuries in sports. The influence of quadriceps weakness on knee joint homeostasis remains undefined. We hypothesized that quadriceps weakness will lead to tissue‐specific alterations in the cell metabolism of tissues of the knee. Quadriceps weakness was induced with repetitive injections of Botulinum toxin A in six 1‐year‐old New Zealand White rabbits for 6 months. Five additional animals served as controls with injections of saline/dextrose. Muscle weakness was assessed by muscle wet mass, isometric knee extensor torque, and histological morphology analysis. Cell metabolism was assessed for patellar tendon, medial and lateral collateral ligament, and medial and lateral meniscus by measuring the total RNA levels and specific mRNA levels for collagen I, collagen III, MMP‐1, MMP‐3, MMP‐13, TGF‐β, biglycan, IL‐1, and bFGF by reverse transcription and polymerase chain reaction. While the total RNA levels did not change, tissue‐specific mRNA levels were lower for relevant anabolic and catabolic molecules, indicating potential changes in tissue mechanical set points. Quadriceps weakness may lead to adaptations in knee joint tissue cell metabolism by altering a subset of anabolic and catabolic mRNA levels corresponding to a new functional and metabolic set point for the knee that may contribute to the high injury rate of athletes with muscle weakness.

Altered molecular metabolism of knee joint tissues in a botox induced quadriceps muscle weakness model in the rabbit

Background Muscle weakness due to joint injuries (eg, anterior cruciate ligament rupture) or muscle injuries (eg, muscle strain) are very frequent in sports. Objective To analyze changes to knee joint ligaments and menisci induced by quadriceps muscle weakness by measuring molecular metabolism. Design Prospective randomised controlled trial. Setting Laboratory study. Interventions Chronic quadriceps muscle weakness was induced in six 1-year old New Zealand White rabbits through monthly injections of Botox (botulinum toxin A) for six months. Five age- and sex-matched rabbits served as controls. Main outcome measurements Muscle weakness was assessed by measuring muscle weight, isometric quadriceps force, and histologic muscle degeneration. Molecular metabolism was measured in the patellar tendon, medial and lateral collateral ligaments, and medial and lateral menisci by measuring total RNA yields, and nine tissue specific RNA yields (eg, Collagen I, MMP-III). Results Muscle weights were decreased by 46.6%, muscle forces by 58.6 to 61.3% depending on the knee flexion angle, and cross sectional areas of the contractile apparatus by 54.7% (all results p<0.001) for the test—compared to the control group animals. Molecular analysis showed significantly decreased overall turnover (MMP-I), and significantly decreased metabolism for anabolic factors (Collagen I, MMP-III, MMP-XIII, TGFâ) and reduced injury response (Collagen III, MMP-XIII). Discussion Quadriceps muscle weakness leads to adaptive changes in knee joint structures by adjusting specific RNA activities while overall cell metabolism remains unchanged. In the concept of the joint as an organ, this may reflect a new functional steady-state. Muscular unloading of the knee might impair the biomechanical function of the knee joint and its component structures. This could describe an underlying pathomechanism of the fact, that injured athletes are more susceptible to additional overuse injuries than healthy athletes. Therefore, we suggest that weaknesses of muscles and component joint structures being considered in injury treatment and rehabilitation.