SFN: Elevated urinary p-cresol in autism spectrum disorder: Human, rodent and cellular studies

 P-cresol (4-methylphenol) does not derive from human metabolism. It can be absorbed through the skin, GI or respiratory tracts, but its main source consists in gut bacteria (especially some clostridia) able to push the fermentation of tyrosine up to p-cresol. We found elevated urinary amounts of p-cresol in autistic children up to 8 years of age (Altieri et al., Biomarkers 16:252-260, 2011). These initial findings were replicated and extended by measuring total urinary p-cresol and its derivatives p-cresylsulphate and p-cresylglucuronate using HPLC-fluorimetric detection in 33 French autistic children and 33 matched controls. Urinary p-cresol and its derivatives were all significantly elevated in French ASD cases compared to controls (p<0.05). This difference was significant in 18 case-control pairs younger than age 8 (P<0.05), but not in 15 pairs of older children (P=0.211), although two 8-yo children displayed very high amounts. No correlation was found with clinical severity. In another sample including 32 Italian ASD children and 16 controls, we assessed in parallel intestinal permeability using the LA/MA test, presence of Clostridial species and toxinA in the feces, stool habits and recent antibiotic use. No case of gut infection with C. difficile was detected and no correlation was found with intestinal permeability, but a trend with intestinal transit time was detected. Acute behavioral effects were assessed in rodents administering p-cresol 1 mg/Kg (N=4), 10 mg/Kg (N=4), or vehicle (N=4) i.v. to 12 male BTBR mice at P60, using open field, elevated plus maze and object recognition test. Acute p-cresol largely increases time spent in the open arms of the plus maze and decreases exploration of novel objects at the object recognition test (both P<0.05), with no effect in the open field. Finally, calcium-imaging experiments using Fluo-4-AM in cultured cortical neurons demonstrate that p-cresol (40.7 mg/L) does not affect resting intracellular calcium concentration, while significantly antagonizing caffeine (20mM)-induced calcium release through ryanodine receptors (-67%; P<0.001). Urinary p-cresol is thus elevated in autistic children prior to and including age 8, possibly reflecting slow intestinal transit time and acutely modulating behaviour.