Which of the following DMARD acts by increasing adenosine extracellularly?

Ans. (A) Methotrexate(Ref: Katzung 13/e p627)Major mechanism of methotrexate at low doses used in rheumatoid arthritis is inhibition of AICAR (Aminoimidazole carboxamide ribonucleotide) transformylase and thymidylate synthase enzymes. This results in accumulation of AICAR in the cells. AICAR is a competitive inhibitor of AMP deaminase resulting in accumulation of AMP. Later is converted to adenosine which is a powerful anti-inflammatory compound.