This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: NSAIDs, Gout and Rheumatoid Ahritis, Subject name: Pharmacology
Extracellular adenosine is increased by which of the following DMARDs? 
Select and explain. 
A. Leflunomide, B. Sulphasalazine, C. Methotrexate, D. Hydroxychloroquine
C: Methotrexate
Answer: C: Methotrexate 
Explanation: Methotrexate: Methotrexate inhibits an enzyme 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) transformylase leading to accumulation of AICAR, which blocks adenosine deaminase. Thus adenosine accumulates and it decreases inflammation by acting on adenosine receptors.