Respiratory burst assay was performed as previously described.29 (link) In brief, human promyelocytic NB4 cells were differentiated into neutrophilic cells by treating with all-trans retinoic acid ATRA (1 µM, Sigma-Aldrich) for 5 days. Cells (5 × 104/well in 96 well plates) were incubated in phenol-free medium containing L-012 for 10 min, and phorbol 12-myristate 13-acetate (PMA, 100 nM) was applied in the presence or absence of niacin (50 µM or 300 µM). Luminescence was quantified using a POLARstar luminometer (BMG Labtech).