Effect of three lipophilic methotrexate derivatives upon mediator release by lipopolysaccharide-stimulated rat peritoneal macrophages

A novel MyD-1 (SIRP-1alpha) signaling pathway that inhibits LPS-induced TNFalpha production by monocytes

MyD-1 (CD172) is a member of the family of signal regulatory phosphatase (SIRP) binding proteins, which is expressed on human CD14+ monocytes and dendritic cells. We now show a novel role for MyD-1 in the regulation of the innate immune system by pathogen products such as lipopolysaccharide (LPS), purified protein derivative (PPD), and Zymosan. Specifically, we demonstrate that ligation of MyD-1 on peripheral blood mononuclear cells (PBMCs) inhibits tumor necrosis factor alpha (TNFalpha) secretion but has no effect on other cytokines induced in response to each of these products. In an attempt to understand the molecular mechanisms underlying this surprisingly selective effect we investigated signal transduction pathways coupled to MyD-1. Ligation of the SIRP was found to recruit the tyrosine phosphatase SHP-2 and promote sequential activation of phosphatidylinositol (PI) 3-kinase, phospholipase D, and sphingosine kinase. Inhibition of LPS-induced TNFalpha secretion by MyD-1 appears to be mediated by this pathway, as the PI 3-kinase inhibitor wortmannin restores normal LPS-driven TNFalpha secretion. MyD-1-coupling to this PI 3-kinase-dependent signaling pathway may therefore present a novel target for the development of therapeutic strategies for combating TNFalpha production and consequent inflammatory disease.

Tris lipidation: a chemically flexible technology for modifying the delivery of drugs and genes

1. One of the major challenges in the development of pharmaceuticals is their formulation with other materials to give them the desired bioavailability profile when administered into the body. 2. We have developed a flexible platform technology (Tris lipidation) to simply and effectively alter the lipophilicity of drugs. As implied by the name, the technology uses the common buffer Tris as a linker between the drugs of interest and a domain of variable hydrophobicity. 3. We demonstrate, using a mouse melanoma model, that Tris-lipidated conjugates of the widely used cytotoxic and anti-inflammatory drug methotrexate (MTX) display enhanced potency in the local treatment of tumours and reduced systemic toxicity when compared with the unconjugated drug. 4. With genes now being predicted to be the pharmaceuticals of the future, we show that Tris-lipidated cationic peptides can efficiently deliver DNA into (transfect) cells in culture. Furthermore, by comparing the abilities of variants of these Tris-based cationic lipids to transfect cultured cells, we demonstrate that modifications made to variable regions of Tris-lipidated compounds can dramatically alter their delivery profiles.

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

1. Liposomes with conventional and long-circulation times were employed as carriers 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 non-toxic dose, both MTX-EPC and MTX-PEG inhibited the lipopolysaccharide (LPS) induced release of IL-1beta from activated rat peritoneal macrophages (rPMPhi) 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 microg) and MTX-EPC inhibited the LPS induced rise in plasma IL-1beta levels observed in MTX-PEG and saline treated rats. 3. When used to treat established CIA, MTX-EPC resulted in significantly lower clinical score (CS) (1.0+/-0.42 (P<0.001)) and hind paw diameter (HPD) (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 lower 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 controls (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 the health and well being of the animals was compromised and the experiment terminated at this time-point. 4. Our results clearly demonstrate that both MTX-EPC and MTX-PEG liposomes have potential for development into therapeutic modalities for the treatment of inflammatory joint disease in man.

Methotrexate and leflunomide: biochemical basis for combination therapy in the treatment of rheumatoid arthritis

OBJECTIVES

Methotrexate is currently one of the most widely prescribed disease-modifying antirheumatic drugs (DMARDs) for the treatment of rheumatoid arthritis (RA). Combination therapy of methotrexate with other DMARDs increases the clinical success of low-dose methotrexate treatment. Leflunomide is a new DMARD that may have a high potential for success in combination therapy with methotrexate. This review compares the mode of action of methotrexate and leflunomide and speculates on how this contributes to therapeutic efficacy in RA when these agents are used singly or in combination.

METHODS

A literature review of the biochemical mechanisms considered to be the basis for the therapeutic efficacy of methotrexate and leflunomide in treating RA is presented.

RESULTS

Low-dose methotrexate inhibits cytokine production, purine biosynthesis, and, in an animal model, causes the release of adenosine, a potent antiinflammatory agent. Leflunomide, through inhibition of de novo pyrimidine biosynthesis, can regulate lymphocyte proliferation.

CONCLUSIONS

The biochemical mechanisms underlying the therapeutic efficacy of low-dose methotrexate and leflunomide in the treatment of RA are quite different. The potentially complementary mechanisms of action of these two effective DMARDs should provide a rationale for their use in combination therapy for patients whose condition no longer responds to methotrexate alone.

The mechanism of action of methotrexate

Because of methotrexate's well-documented efficacy in the treatment of rheumatoid arthritis, it is important that we understand the mechanism of action of this drug. There are two biochemical mechanisms by which methotrexate may modulate inflammation: (1) promotion of adenosine release and (2) inhibition of transmethylation reactions. Evidence is reviewed that favors the notion that the endogenous anti-inflammatory autocoid adenosine mediates the anti-inflammatory effects of methotrexate. This insight should aid in the design of new agents for the treatment of rheumatoid arthritis and other inflammatory diseases.

Biocompatibility of bicarbonate buffered peritoneal dialysis fluids: influence on mesothelial cell and neutrophil function

The present study compares the effects of lactate and bicarbonate buffered PDF on human neutrophil (PMN) and human peritoneal mesothelial cell (HPMC) viability and function. Acute exposure of PMN to lactate buffered PDF at pH 5.5 (CAPD 2, 1.5% and CAPD 3, 4.25% glucose) resulted in significant reductions in cellular ATP levels, the phagocytosis of serum treated zymosan (STZ) and respiratory burst activation (CL). Exposure of PMN to bicarbonate buffered PDF (BIC 20, 1.5% glucose and BIC 30, 4.25% glucose both at pH 7.2) had no significant effect on cell viability or the CL response. Phagocytosis was, however, depressed significantly more following exposure to BIC 30 than BIC 20. PMN cellular ATP levels and phagocytosis were significantly better in cells exposed to BIC 30 than to CAPD 3 at pH 7.4 (P = 0.043 for both). Pre-exposure of HPMC to CAPD 2, CAPD 3 or BIC 30 for 30 minutes resulted in a significant reduction in cellular ATP content compared to control medium. Pre-exposure to BIC 20 did not result in a reduction in HPMC ATP levels. HPMC synthesis of IL-6 was unaffected by 15 or 30 minutes pre-exposure to BIC 20 or BIC 30, in contrast pre-exposure to CAPD 2 or CAPD 3 for 15 or 30 minutes resulted in a significant reduction in stimulated IL-6 synthesis (24.5 +/- 3.01 and 32.3 +/- 5.0 vs. 43.9 +/- 10 pg/microgram cell protein in M199, N = 6; P = 0.02). Neutralization of the pH of CAPD 2 and CAPD 3 resulted in normalization of HPMC IL-6 secretion. Analysis of IL-6 mRNA expression in control, BIC 20 and 30 pre-treated HPMC subsequently stimulated with IL-1 beta revealed no differences in the expression of the IL-6 specific 465 base pair transcripts. The improved cellular function in bicarbonate buffered PDF indicates potentially improved host defence status and preservation of the peritoneal membrane in CAPD patients.

Prostaglandin and tumor necrosis factor secretion by peritoneal macrophages isolated from normal and arthritic rats treated with liposomal methotrexate

The effect of a novel liposomal preparation containing a phospholipid conjugate of methotrexate (MTX-LIPO) upon macrophage mediator release was investigated in normal and arthritic rats ex vivo. Peritoneal macrophages isolated from MTX-LIPO-treated arthritic rats and stimulated with lipopolysaccharide produced significantly less tumor necrosis factor (TNF) and prostaglandin (PGE2) than did macrophages isolated from saline-treated controls. In the same experimental system, free methotrexate only inhibited prostaglandin release, but it was more potent than MTX-LIPO in this respect. Additional studies are presently underway to investigate the effect of MTX-LIPO and MTX treatment upon the lipopolysaccharide-induced rise in plasma levels of various proinflammatory mediators in vivo. Haematopoietic toxicity was demonstrated in blood isolated from rats treated with free MTX, and this was as characterized by a significant reduction in reticulocyte count compared with MTX-LIPO and saline-treated rats.