Methotrexate (MTX) is a first line
anti-rheumatic drug. This study was designed to investigate the impact of
rheumatoid arthritis (RA) conditions on its oral absorption, and clarify the relevance with changes of MTX absorption-related transporters in rheumatic models. MTX was orally administered to healthy,
collagen-induced arthritis (CIA), and adjuvant-induced
arthritis (AIA) rats. MTX plasma concentrations were determined by a validated liquid chromatography-mass spectrometry method. We found that intestinal MTX absorption was significantly increased in CIA/AIA rats versus healthy controls. This finding was supported by small intestine-based MTX uptake assay in vitro. Meanwhile, intestinal expression of both
reduced folate carrier 1 (RCF1) and
proton-coupled folate transporter (PCFT) remained unchanged. The everted intestinal sac assay confirms RFC1 is the key transporter accounting for intestinal MTX absorption, as its antagonist
salicylazosulfapyridine showed potent capacity in reducing MTX uptake. No correlation between RA-related
cytokines and RCF1 expression was observed in clinical samples. We further revealed that when cultured with AIA rat or RA patient serum,
lactate and
adenosine triphosphate (
ATP) production as well as MTX uptake in MDCKII cells were significantly increased, and this increase was completely abrogated by
ATP production-related metabolic inhibitors. Thanks to its inhibitory effects on MTX bioavailability, the glycolysis inhibitor
shikonin diminished MTX-induced
injuries of kidney and liver in AIA rats. These data demonstrate that glycolysis-driven high energy metabolism increases MTX absorption in rheumatic subjects, leading to the exacerbated toxicity. These findings will have important implications in optimizing MTX regimens for RA treatment with better efficacy and lower toxicity.