The study on methotrexate therapy in collagen induced arthritis rats

Objective To explore the circadian rhythm of interleukin(IL)-6 in collagen induced arthritis(CIA)rats and investigate the effectiveness and safety of methotrexate(MTX)administered according to IL-6 rhythm. Methods Serum IL-6 concentrations of CIA and normal rats at different time points were measured by enzyme-linked immunosorbent assay(ELISA). CIA rats were randomly divided into the experimental group A, experimental group B and control group. MTX(1/7 mg·kg-1 • d-1)was administered once a day when the IL-6 level began to increase or decrease in the experimental group, while MTX(1 mg/kg)administered once a week in the control group. Arthritis scores and leukocyte counts were observed. The production of IL-6 and C reactive protein(CRP)levels in the serum were measured. Moreover, histological changes in the ankle joint were examined. One-way analysis of variance(ANOVA), two independent sample t test were used to evaluate the experimental data. Results The plasma IL-6 levels in CIA rats were different at different time points, which began to increase at 18:00 and decrease at 6:00. Arthritis score in the experimental group A(4.8±0.7)was lower than that in the control group(5.8±1.0, t=2.256, P=0.0406)and experimental group B(5.5±0.5, t=2.393, P=0.031 3). The levels of TNF-α[(185±21)ng/L], IL-6[(99±6)ng/L], IL-1β[(20.1±1.6)ng/L]and CRP[(1 251 ±282)μg/L]in the experimental group A were significantly lower than those in control group[TNF-α:(207±10)ng/L, t=2.726, P=0.016 4; IL-6:(100±6)ng/L, t=2.669, P=0.018 3; IL-1β:(22.0±1.3)ng/L, t=2.814, P=0.013 8; CRP:(1 417 ±278)μg/L, t=2.369, P=0.032 7]. The level of IL-6 in the experimental group A[(93 ±6)ng/L]was lower than that in the experimental group B[(99 ±6)ng/L, t=2.323, P=0.035 8]. Compared with the control group[(9 650 ±1 062)/μl], the counts of leukocyte in the experimental group A[(4 595 ± 603)/μl, t=3.841, P=0.006 4]and experimental group B[(3 833±585)/μl, t=4.442, P=0.003]were significantly lower. Compared with the control group(9.1 ±2.0), histopathology scores in the experimental group A(6.6 ± 1.3, t= 2.606, P=0.015)and experimental group B(7.4±1.3, t=3.857, P=0.000 7)were significantly lower. Conclusion The plasma IL-6 levels in CIA rats have shown evident circadian rhythm. There-fore, once a day administration is better than once a week. The therapeutic effect of RA may be improved by administering MTX at the time points according to the circadian rhythm of IL-6. Key words: Arthritis, rheumatoid; Chronotherapy; Methotrexate