Sodium phenyl butyrate (PBA) is FDA approved as an ammonia scavenger and used primarily as adjuctive therapy in patients with urea cycle disorders. PBAs also work as a histone deacetylase inhibitor, as a chemical chaperone, as a 'glutamine trap' and as a stimulant of fetal hemoglobin to increase oxygen delivery to the brain, point to its potential as a 'multi-target' treatment in ALS. The mechanism of greatest interest for ALS is as an inhibitor of histone deacetylase (HDAC). Histone deacetylase (HDAC) inhibitors such as trichostatin A and suberoylanilide hydroxamic acid (SAHA) have been shown to arrest ongoing and progressive neurodegeneration induced by polyglutamine repeat expansion in two fruit fly models. As an HDAC inhibitor, sodium phenyl butyrate (PBA) interferes with the regulation of gene expression by inhibiting the activity of enzymes known as histone deacetylases. It is proposed that treatments that raise global levels of acetylation may be effective in ameliorating the effects of Huntington's disease and other neurodegenerative processes, even after the onset of symptoms. HDAC inhibitors markedly retard further neuronal degeneration even when administered to animals already displaying neuronal degeneration.

Sodium phenylbutyrate is an extremely expensive drug (Buphenyl) costing $2900 for 250 gm.   apparently a prescription drug (Systemic).  Tributyrate may be something different, but the latter's website isn't working, so I don't know if it is still available.

PBA (4-phenylbutyrate) May Help: NIH and CIT found that PBA may increase longevity while maintaining youthful health. 4-phenylbutyrate or PBA was great success on fruit flies. The next set of experiments is on mice. PBA is already an FDA-approved drug for treating cystic fibrosis and sickle cell anemia. New Scientist magazine, the fruit flies that were given PBA had a maximum lifespan that was 50 percent longer, while the average lifespan was increased by one-third. The drug seemed to make the flies healthier and stronger. Their weight, sexual function, and offspring they produced later in life were all normal. It blocks the activity of enzymes that switch on a number of genes, including one for superoxide dismutase, which is already known to counter the effects of aging. show a global increase in histone acetylation as well as a dramatically altered pattern of gene expression, including induction or repression of numerous genes. Proc Natl Acad Sci U S A 2002 Jan 22;99(2):838-43. The data suggest that, in healthy adults, 1) large doses of oral phenylbutyrate can be used as a "glutamine trap" to create a model of glutamine depletion; 2) a moderate decline in plasma glutamine does not enhance rates of endogenous glutamine production; and 3) a short-term depletion of plasma glutamine decrease estimates of whole body protein synthesis. A double-blind, placebo-controlled trial in 18 deltaF508-homozygous patients with CF was performed with the maximum approved adult dose of 4PBA, 19 grams p.o. divided t.i.d., given for 1 wk. Nasal potential difference (NPD) response patterns and sweat chloride concentrations were determined before and after study drug treatment, and 4PBA and metabolites were assayed in plasma and urine at the end of study drug treatment. Subjects in the 4PBA group demonstrated small, but statistically significant improvements of the NPD response to perfusion of an  isoproterenol/amiloride/chloride-free solution; this measure reflects epithelial CFTR function and is highly discriminatory between patients with and without CF. Subjects who had received 4PBA did not demonstrate significantly reduced sweat chloride concentrations or alterations in the amiloride-sensitive NPD. Side effects due to drug therapy were minimal and comparable in the two groups. These data are consistent with 4PBA therapy inducing CFTR function in the nasal epithelia of deltaF508-homozygous CF patients. Am J Respir Crit Care Med 1998 Feb;157(2):484-90. Side effects of the drug included weight gain and/or edema caused by increase salt load in 2/12, transient epigastric discomfort in 7/12, and abnormal body odor in 3/12 subjects. Patients were treated for up to 460 days at 20 gr per day. Blood 1995 Jan 1;85(1):43-9.