TAMOXIFEN INCREASES MUSCULAR STRENGTH OF THE MDX DYSTROPHIC MICE

44TH ANNUAL MEETING - THE AMERICAN SOCIETY FOR CELL BIOLOGY - DECEMBER/7, WASHINGTON, USA

TAMOXIFEN INCREASES MUSCULAR STRENGTH OF THE MDX DYSTROPHIC MICE

A. P. Cavalsan*, R. F. Vasquez*, R. C. Y. Lin*, S. B. Zyngier*, F. J. Velloso**, B. H. Santos**, L. L. Fogaca**, M. Vainzof**, D. Feder*

* Pharmacology, ABC Faculty of Medicine, Santo Andre, Brazil; ** Human Genome Research Center - IB USP, Sao Paulo, Brazil. NEPAS-FMABC, FAPESP-CEPID, CNPq, PRONEX.

Abstract

The mdx mice is a well-known model of Xp21 dystrophin-deficient muscular dystrophy. Although a good genetic and biochemical model, the mdx shows no muscle weakness, but under physical exercise, a loss of muscular strength can be detected. Here we have tested the possible therapeutic beneficial effect of Tamoxifen in the degenerative process of the dystrophic muscle, analyzing muscle strength of tamoxifen treated mdx mice, under intensive physical exercise. A total of 22 mices aged 4 weeks were divided into 3 groups: control (n= 8) treated with 0.5 mL saline ip, Tamoxifen 5 mg/Kg body weight ip (n= 8) daily and Tamoxifen 10 mg/Kg ip (n=6) daily. The exercise protocol was done in a wheel revolving at 18 cm/s, for 10 minutes, twice a day, 5 days/week, up to 12 weeks. Whole-body strength was measured weekly using a force transducer coupled to a computer. Mice tails were attached via a non-flexibile nylon cord to the transducer, the animals were electricly stimulated to run, and the force to pull the cord was registered continuously. Results were analyzed by the Kruskal-Wallis test. The mice treated either with 5 mg/Kg (6.26+ 1.44 dynes/g body weight) or 10 mg/Kg (6.46+ 2.52) showed a significant increase of muscular strength (p<0.05) compared to the control group (3.66+ 0.77) starting in the 5^th week, and maintaining significance up to the end of the experiment. Histological and histochemical analysis of the complex of the gastrocnemius muscle are under analysis, but preliminary results suggest a less degree of degeneration in the Tamoxifen treated groups.
Tamoxifen is an anti tumoral drug and act on TGF-beta. Its possible therapeutic effect in the degenerative process of the dystrophic muscle could ameliorates the clinical course of dystrophic patients

Introduction

The mdx mice is a well-known model of Xp21 dystrophin-deficient muscular dystrophy.Tamoxifen is a nosteroidal drug with anti-estrogenic action, used for treatment and prevention of breast cancer. The drug is also used in other forms of cancer, idiopathic retroperitoneal fibrosis, keloids and other fibrotic diseases. TGF beta-1 is related with the appearance of fibrosis and is increased in Duchenne Muscular Dystrophy (DMD). TGF beta-2 is increased in DMD and is related with muscular regeneration.

Material and Methods

A total of 22 mice aged 4 weeks were divided into 3 groups:

Control (n= 8) treated with 0.5 mL saline IP daily
Tamoxifen 5 mg/kg body weight IP (n= 8) daily
Tamoxifen 10 mg/kg body weight IP (n=6) daily

The exercise protocol was done in a wheel revolving at 18 cm/s, for 10 minutes, twice a day, 5 days/week, up to 12 weeks. Whole-body strength was measured weekly using a force transducer coupled to a computer. Results were analyzed by the Kruskal-Wallis test (p<0.05)

Results

p< 0.05 (saline x tested groups)

Histological and histochemical analysis of the complex of the gastrocnemius muscle are under analysis, but preliminary results suggest a less degree of degeneration in the Tamoxifen treated groups

Muscle biopsy examples from one control (not treated mdx mice submitted to exercise), one mdx mice treated with 5mg/kg of tamoxifen and one with 10 mg/kg. In the HE staining, almost all fibers are centronucleated in the 3 groups. However, groups of degenerated fibers are more frequent in the control group, which is confirmed in the acid phosphatase histochemical reaction (see arrows).

Conclusion

The mice treated either with 5 mg/kg (6.26±1.44 dynes/g body weight) or 10 mg/kg (6.46±2.52) showed a significant increase of muscular strength (p<0.05) compared to the th control group (3.66±0.77) starting in the 5 week, and maintaining significance up to the end of the experiment. Tamoxifen is an anti tumoral drug and act on TGFbeta. Its possible therapeutic effect in the degenerative process of the dystrophic muscle could ameliorates the clinical course of dystrophic patients.

References

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