---Pro-inflammatory cytokines inhibit thiamin uptake by human and mouse pancreatic acinar cells: Involvement of transcriptional mechanism(s).

Thiamin (vitamin B1) plays critical roles in normal metabolism and function of all mammalian cells. Pancreatic acinar cells (PACs) import thiamin from circulation via specific carrier-mediated uptake that involves thiamin transporters-1 & -2 (THTR-1 & -2; products of SLC19A2 and SLC19A3, respectively). Our aim in this study was to investigate the effect(s) of pro-inflammatory cytokines on thiamin uptake by PACs. We used human primary (h)PACs, PAC 266-6 cells, and mice in vivo as models in the investigations. First, we examined the level of expression of THTR-1 & -2 mRNA in pancreatic tissues of patients with chronic pancreatitis and observed severe reduction in their expression compared to normal control subjects. Exposing hPACs and PAC 266-6 to pro-inflammatory cytokines (hyper IL-6, TNF-α, and IL-1β) was found to lead to a significant inhibition in thiamin uptake. Focusing on hyper-IL-6 (which also inhibited thiamin uptake by primary mouse PACs), the inhibition in thiamin uptake was found to be associated with significant reduction in THTR-1 & -2 proteins and mRNAs expression as well as in activity of the SLC19A2 and SLC19A3 promoters; it was also associated with reduction in level of expression of the transcription factor Sp1 (which is required for activity of these promoters). Finally, blocking the intracellular Stat3 signaling pathway was found to lead to a significant reversal in the inhibitory effect of hyper IL-6 on thiamin uptake by PAC 266-6. These results show that exposure of PACs to pro-inflammatory cytokines negatively impacts thiamin uptake via (at least in part) transcriptional mechanism(s).