Nicotinamide in Friedreich's ataxia: useful or not?

Friedreich’s ataxia is an autosomal recessive neurodegenerative disorder caused by mutations in the frataxin gene (FXN), leading to progressive ataxia, cardiomyopathy, scoliosis, and various other clinical features. Most patients have GAA repeat expansions in intron 1 of FXN, leading to decreased concentrations of frataxin protein and downstream mitochondrial dysfunction. The GAA repeats lead to gene silencing through heterochromatin formation, and decreased transcription of FXN mRNA. The coding region of the mRNA and the aminoacid sequence of the protein are normal, but the amount of protein produced is reduced; as a result, reversal of the epigenetic changes (such as histone deacetylation) represents a potential therapeutic strategy in Friedreich’s ataxia. Inhibitors of histone deacetylase (HDAC) have been reported to increase frataxin concentrations in cell culture and in animal models of Friedreich’s ataxia. In an open-label, dose-escalation study reported in The Lancet, Vincenzo Libri and colleagues note an increase in FXN mRNA expression and frataxin protein concentration in peripheral blood mononuclear cells in patients given nicotinamide, a drug that has HDAC inhibitor activity when given at high concentrations. Ten adult patients with Friedreich’s ataxia from the UK were given single doses (phase 1) and repeated daily doses of 2–8 g oral nicotinamide for 5 days (phase 2) and 8 weeks (phase 3). In phase 1, a single dose of up to 8 g (about 200 times higher than the typical recommended daily allowance for nicotinamide as a vitamin [B3]) led to an increase in frataxin concentration in peripheral blood mononuclear cells, and this eff ect increased with increasing dose (p=0·0004). In phases 2 and 3, repeated daily dosing at 3·5–6 g resulted in a sustained and signifi cant (p<0·0001) upregulation of frataxin expression, which was associated with changes in chromatin structure (a signifi cant reduction methylation at aminoacid position 9 of the histone H3 tail and a non-signifi cant increase in H3 acetylation at the FXN locus). The investigators did not report any signifi cant improvements in neurological measures, as assessed by the scale for the assessment and rating of ataxia and the spinocerebellar ataxia functional index. These results are of interest for several reasons. First, although nicotinamide has several potential Emmanuel Futier Departement Anesthesie et Reanimation, Hopital Estaing, CHU de Clermont-Ferrand, 63003 Clermont-Ferrand, France efutier@chu-clermontferrand.fr