Mycophenolic Acid Synergizing with Lipopolysaccharide to Induce Interleukin-1ß Release via Activation of Caspase-1.

BACKGROUND: The previous study showed that mycophenolic acid (MPA) synergizing with lipopolysaccharide (LPS) promoted interleukin (IL)-1ß release, but the mechanism is unclear. This study aimed to investigate the mechanism of MPA synergizing with LPS to induce IL-1ß release. METHODS: Undiluted human blood cells, THP-1 human myeloid leukemia mononuclear cells (THP-1) cells, or monocytes were stimulated with LPS and treated with or without MPA, and the supernatant IL-1ß was detected by enzyme-linked immunosorbent assay. The mRNA levels of IL-1ß were detected by real-time quantitative polymerase chain reaction. The intracellular protein levels of nuclear factor kappa B (NF-κB) phospho-p65 (p-p65), precursor interleukin-1ß (pro-IL-1ß), NOD-like receptor pyrin domain containing-3 (NLRP3), and cysteine aspartic acid-specific protease-1 (caspase-1) p20 in THP-1 cell were measured by Western blot. RESULTS: The MPA alone failed to induce IL-1ß, whereas MPA synergized with LPS to increase IL-1ß in a dose-dependent manner (685.00 ± 20.00 pg/ml in LPS + 5 µmol/L MPA group, P = 0.035; 742.00 ± 31.58 pg/ml in LPS + 25 µmol/L MPA group, P = 0.017; 1000.00 ± 65.59 pg/ml in LPS + 75 µmol/L MPA group, P = 0.024; versus 408.00 ± 35.50 pg/ml in LPS group). MPA alone has no effect on the IL-1ß mRNA expression, LPS induced the expression of IL-1ß mRNA 2761 fold, and LPS + MPA increased the IL-1ß expression 3018 fold, which had the same effect with LPS group (P = 0.834). MPA did not affect the intracellular NF-κB p-p65 and pro-IL-1ß protein levels but activated NLRP3 inflammasome. Ac-YVAD-cmk blocked the activation of caspase-1 and subsequently attenuated IL-1ß secretion (181.00 ± 45.24 pg/ml in LPS + MPA + YVAD group vs. 588.00 ± 41.99 pg/ml in LPS + MPA group, P = 0.014). CONCLUSIONS: Taken together, MPA synergized with LPS to induce IL-1ß release via the activation of caspase-1, rather than the enhanced production of pro-IL-1ß. These findings suggested that patients immunosuppressed with mycophenolate mofetil may have overly activated caspase-1 during infection, which might contribute to a more sensitive host defense response to invading germs.