May 7, 2014

Valproic Acid as a Treatment for Retinitis Pigmentosa

Clinical trials of valproic acid for the treatment of retinitis pigmentosa began in both the USA and Korea in late 2011. As well, a smaller shorter open-label trial was begun in Japan. Although the two larger trials have not yet reported, results of the small 30-person Japanese trial were presented at ARVO.

The trial did show improvement in average visual acuity (how clear vision is) after three months of taking valproic acid (400 mg daily for 3 months) with an improvement of about 5 letters on a standard eye chart. There was a slightly added improvement (about one more letter on average) after months of treatment. A measurable increase in retinal sensitivity reported was not evident at either time period. The person’s vision returned to baseline fairly quickly after they stopped taking the treatment. In this preliminary report, there was really no detail offered about the variation between individuals receiving the treatments. We don’t know if some individuals did considerably better than others.

These results build on the first small study of valproic acid involved six people with autosomal dominant retinitis pigmentosa, particularly mutations in the RHO gene. However, there is growing evidence that valproic acid may be a useful treatment for some types of retinitis pigmentosa and not for others. Dr. Orson Moritz, a researcher at the University of British Columbia has been exploring this question with funding from Fighting Blindness Canada.

Dr. Moritz tested valproic acid treatment in tadpoles whose vision was damaged by different genetic mutations all within the RHO gene. He found that valproic acid treatment had a powerful beneficial effect on eyes damaged by one type of mutation and a strong negative effect on eyes damaged by another type of mutation. For two other mutation types, the drug had minimal effect.

These results suggest that valproic acid treatment will need to be carefully targeted to certain genetic types of autosomal dominant retinitis pigmentosa.

Source:

Satoshi Iraha, Yasuhiko Hirami, Sachiko Oota, Michiko Mandai, Hidenobu Tanihara, Masayo Takahashi and Yasuo Kurimoto^. The efficacy of valproic acid for retinitis pigmentosa patients. ARVO Abstract #1390 – A0247.

Ruanne Y. Lai, Zusheng Zong, Beatrice M. Tam, Chris May and Orson L. Moritz. Opposing effects of valproic acid treatment in four animal models of retinitis pigmentosa. Abstract #4370 – C0153