Interleukin-1 beta (IL-1 beta) inhibition: a possible mechanism for the anti-inflammatory potency of liposomally conjugated methotrexate formulationsin arthritis

1 Liposomes with conventional and long-circulation times were employed as c arriers for the methotrexate derivative MTX-gamma-DMPE (MTX-EPC and MTX-PEG respectively), their mechanism of action was investigated in vitro and in vivo and their therapeutic efficacy assessed using the rat collagen-induced arthritis (CIA) model. 2 At nontoxic dose, both MTX-EPC and MTX-PEG inhibited the lipopolysacchari de (LPS) induced release of IL-1 beta from activated rat peritoneal macroph ages (rPM Phi) in a dose and time dependent manner. Free methotrexate (MTX) was not active in this respect. After a single intravenous injection (i.v. ), and at equivalent doses, both free MTX (500 mu g) and MTX-EPC inhibited the LPS induced rise in plasma IL-1 beta levels observed in MTX-PEG and sal ine treated rats. 3 When used to treat established CIA, MTX-EPC resulted in significantly low er clinical score (CS) (1.0 +/- 0.42 (P < 0.001)) and hind paw diameter (HP D) (6.5 +/- 0.34 mm (P < 0.001)) measurements than controls (3.0 +/- 0.26; 7.33 +/- 0.41 mm), after only two i.v. doses, and remained significantly lo wer for the entire experimental period. By day 24 both CS (2 +/- 0.61 (P < 0.001)) and HPD (6.97 +/- 0.25 mm (P < 0.002)) measurements had also become significantly lower in MTX-PEG treated rats than in saline treated control s (3.62 +/- 0.17, 7.92 +/- 0.38 mm) and remained lower until day 30. Joint inflammation in MTX treated rats was completely ameliorated by day 20 but t he health and well being of the animals was compromised and the experiment terminated at this time-point. 4 Om results clearly demonstrate that both MTX-EPC and MTX;PEG liposomes ha ve potential for development into therapeutic modalities for the treatment of inflammatory joint disease in man.