A Butyrate Derivative Attenuates the Bruton's Tyrosine Kinase Phosphorylation-Dependent Activation of Calcium Phosphate

Abstract N-[2-(2-Butyrylamino-ethoxy)-ethyl]-butyramide (BA-NH-NH-BA), a derivative of butyrate in fermentation metabolites of skin bacteria, can suppress the calcium phosphate (CaP)-induced itching, interleukin-6 (IL-6) production in skin and activation of phosphorylated Bruton's tyrosine kinase (p-BTK) in dorsal root ganglion (DRG). By using IL-6 knockout (KO) mice, we verified that IL-6 was essential for CaP-induced activation of p-BTK in DRG. Data in western blotting showed that both butyrate and BA-NH-NH-BA at 4 mM could effectively attenuate CaP-induced activation of p-BTK. Flow cytometry analysis revealed that the topical application of BA-NH-NH-BA at lower doses (< 4 mM) on mouse skin was sufficient to induce the acetylation on lysine 9 of histone H3 (AcH3K9) in keratinocytes. By knock-downing free fatty acid receptor 2 (Ffar2) in mouse skin, we demonstrated that, unlike butyrate, BA-NH-NH-BA down-regulated the CaP-induced activation of p-BTK via a Ffar2 independent pathway. Exploring the biological mechanism underlying AcH3K9 and/or Ffar2 may expedite the development of BA-NH-NH-BA as a therapeutic for the treatment of uremic pruritus in patients of chronic kidney disease (CKD).