Methotrexate reduces HbA1c concentration but does not produce chronic accumulation of ZMP in patients with rheumatoid or psoriatic arthritis.

OBJECTIVES: The mechanism by which methotrexate (MTX) improves glucose homeostasis in patients with rheumatoid (RA) and psoriatic arthritis (PsA) remains undetermined. Animal studies indicate a role for intracellular accumulation of 5-aminoimidazole-4-carboxamide-1-ß-d-ribofuranosyl 5'-monophosphate (ZMP) but this has not been directly demonstrated in humans. We explored whether accumulation of ZMP is associated with improvements in glucose homeostasis during MTX therapy. METHOD: MTX-naïve, non-diabetic RA (n = 16) and PsA (n = 10) patients received uninterrupted MTX treatment for 6 months. To evaluate whether ZMP accumulated during MTX therapy, we measured the concentration of ZMP in erythrocytes and the concentration of its dephosphorylated derivative 5-aminoimidazole-4-carboxamide-1-ß-d-ribofuranoside (AICAR) in urine using liquid chromatography mass spectrometry (LC-MS/MS). To assess glucose homeostasis, we determined the concentration of glycated haemoglobin (HbA1c) and homeostasis model assessment of insulin resistance [HOMA-IR: fasting glucose (mmol/L) × fasting insulin (µU/mL)/22.5]. RESULTS: Erythrocyte ZMP and urinary AICAR concentrations did not increase during 6 months of MTX therapy. HbA1c concentration was reduced from 5.80 ± 0.29% at baseline to 5.51 ± 0.32% at 6 months (p < 0.001), while HOMA-IR remained unaltered. Reduction in HbA1c concentration was not associated with increased ZMP or AICAR concentrations. CONCLUSIONS: MTX therapy probably does not produce a chronic increase in erythrocyte ZMP or urinary AICAR concentrations. Collectively, our data do not support the hypothesis that MTX improves glucose homeostasis through chronic accumulation of ZMP.

Annexin A5 binding to giant phospholipid vesicles is differentially affected by anti-beta2-glycoprotein I and anti-annexin A5 antibodies.

OBJECTIVES: Anti-phospholipid antibodies have been recognized to play a role in vascular thrombosis and pregnancy morbidity. They were first thought to be directed to phospholipids, but it is now known that the majority of pathogenic antibodies recognizes epitopes on phospholipid-binding plasma proteins such as beta2-glycoprotein I (beta2GPI) or possibly also annexin A5 (ANXA5). The mechanism of their prothrombotic action is still not completely understood. The aim of the present study was to observe the effect of antibodies against ANXA5 (aANXA5) and antibodies against beta2GPI (abeta2GPI) on the binding of ANXA5 to the negatively charged phospholipid membrane. METHODS: Giant phospholipid vesicles (GPVs) were used as a simple model of the membrane surface. GPVs composed of phosphatidylserine and phosphatidylcholine were produced in an aqueous medium. A single GPV was transferred to the solution containing ANXA5 conjugated with Alexa Fluor 488 (FANXA5) and (i) aANXA5 or abeta2GPI and (ii) different concentrations of abeta2GPI together with beta2GPI. The emission of the fluorescent light from the GPV surface, as the result of FANXA5 binding, was measured. RESULTS: Beta2GPI together with abeta2GPI reduced the binding of FANXA5 to GPVs. On the contrary, aANXA5 enhanced the binding of ANXA5 to the GPV surface. CONCLUSIONS: Our results point to the competition between FANXA5 and complexes of beta2GPI-abeta2GPI for the same binding sites and therefore support the hypothesis of the disruption of the ANXA5 protective shield on procoagulant phospholipid surface. The influence of increased cell surface ANXA5 concentration in the presence of aANXA5 on coagulation needs to be further studied.