Treatment with an anti-inflammatory drug is detrimental for muscle regeneration at Bothrops jararacussu envenoming: an experimental study.

We evaluated the effects of deflazacort (DFZ) on muscle regeneration following Bothrops jararacussu envenoming. Tibialis anterior muscle from adult mice was injected with 80 microg of venom. Animals received DFZ during 6days. Seven and 60 days after envenoming, DFZ lead to a decrease in the total number of muscle fibers and an increase in interstitial fibrosis. We conclude that DFZ treatment may aggravate the loss of muscle mass after B. jararacussu envenoming.

Pharmacological and local toxicity studies of a liposomal formulation for the novel local anaesthetic ropivacaine.

This study reports an investigation of the pharmacological activity, cytotoxicity and local effects of a liposomal formulation of the novel local anaesthetic ropivacaine (RVC) compared with its plain solution. RVC was encapsulated into large unilamellar vesicles (LUVs) composed of egg phosphatidylcholine, cholesterol and alpha-tocopherol (4:3:0.07, mole %). Particle size, partition coefficient determination and in-vitro release studies were used to characterize the encapsulation process. Cytotoxicity was evaluated by the tetrazolium reduction test using sciatic nerve Schwann cells in culture. Local anaesthetic activity was assessed by mouse sciatic and rat infraorbital nerve blockades. Histological analysis was performed to verify the myotoxic effects evoked by RVC formulations. Plain (RVC(PLAIN)) and liposomal RVC (RVC(LUV)) samples were tested at 0.125%, 0.25% and 0.5% concentrations. Vesicle size distribution showed liposomal populations of 370 and 130 nm (85 and 15%, respectively), without changes after RVC encapsulation. The partition coefficient value was 132 +/- 26 and in-vitro release assays revealed a decrease in RVC release rate (1.5 fold, P < 0.001) from liposomes. RVC(LUV) presented reduced cytotoxicity (P < 0.001) when compared with RVC(PLAIN). Treatment with RVC(LUV) increased the duration (P < 0.001) and intensity of the analgesic effects either on sciatic nerve blockade (1.4-1.6 fold) and infraorbital nerve blockade tests (1.5 fold), in relation to RVC(PLAIN). Regarding histological analysis, no morphological tissue changes were detected in the area of injection and sparse inflammatory cells were observed in only one of the animals treated with RVC(PLAIN) or RVC(luv) at 0.5%. Despite the differences between these preclinical studies and clinical conditions, we suggest RVC(LUV) as a potential new formulation, since RVC is a new and safe local anaesthetic agent.

Intrinsic laryngeal muscles are spared from myonecrosis in the mdx mouse model of Duchenne muscular dystrophy.

Intrinsic laryngeal muscles share many anatomical and physiological properties with extraocular muscles, which are unaffected in both Duchenne muscular dystrophy and mdx mice. We hypothesized that intrinsic laryngeal muscles are spared from myonecrosis in mdx mice and may serve as an additional tool to understand the mechanisms of muscle sparing in dystrophinopathy. Intrinsic laryngeal muscles and tibialis anterior (TA) muscle of adult and aged mdx and control C57Bl/10 mice were investigated. The percentage of central nucleated fibers, as a sign of muscle fibers that had undergone injury and regeneration, and myofiber labeling with Evans blue dye, as a marker of myofiber damage, were studied. Except for the cricothyroid muscle, none of the intrinsic laryngeal muscles from adult and old mdx mice showed signs of myofiber damage or Evans blue dye labeling, and all appeared to be normal. Central nucleation was readily visible in the TA of the same mdx mice. A significant increase in the percentage of central nucleated fibers was observed in adult cricothyroid muscle compared to the other intrinsic laryngeal muscles, which worsened with age. Thus, we have shown that the intrinsic laryngeal muscles are spared from the lack of dystrophin and may serve as a useful model to study the mechanisms of muscle sparing in dystrophinopathy.

L-arginine enhances muscle regeneration after experimental envenomation by B. jararacussu: a future for nitric oxide-based therapy?

We investigated whether muscle fiber regeneration would be rescued by exogenous administration of l-arginine, the precursor of endogenous synthesis of nitric oxide. The right tibialis anterioris muscle of adult mice (n=20) was injected with 80 microg of venom. One group of mice (n=10) received drinking water containing l-arginine (3.75 mg/ml) and another group (n=10) did not receive any pharmacological treatment. Two months later, muscle regeneration was evaluated by counting the total number of muscle fibers. We found that in l-arginine-treated mice, muscle regeneration was significantly higher (p<0.05) than in saline-treated (2.230+/-478 muscle fibers versus 1.005+/-134, respectively) although the level of muscle fiber population of uninjured tibialis anterioris muscle (3.121+/-102) was not attained. These results show that muscle regeneration was significantly facilitated by l-arginine and suggest that pharmacological activators of the NO pathway may be potentially useful for improving muscle regeneration in human envenomation by B. jararacussu.

Insights into the loss of muscle mass following B. jararacussu venom in mice.

Bothrops jararacussu snake venom produces myonecrosis and nerve degeneration. In this work, we investigated whether nerve lesions or impaired muscle regeneration contributed to the permanent loss of muscle mass, a long-term sequela of envenoming. The right soleus muscle of adult male mice was injected with B. jararacussu venom (80 microg) while the left muscle received only saline (control). The mice were killed after 2 and 3 months and the muscles were removed and processed for examination by transmission electron microscopy and light microscopy. The nerve fibers, Schwann cells and neuromuscular junctions had regenerated in venom-treated muscle. The total number of muscle fibers was significantly lower (p<0.05) than in the control (617+/-48 versus 1235+/-97, respectively; mean+/-SEM, n=10). These results show that the loss of muscle mass was most likely related to a decrease in the ability of the muscle to regenerate rather than to nerve lesions.