Rhein, a major bioactive compound of many medicinal herbs and the
prodrug of
diacerein, is often used with low dose of
methotrexate as
drug combination to treat
rheumatoid arthritis. In this study, potential drug-drug interaction between
methotrexate and
rhein was investigated based on
organic anion transporters (OAT). Our study demonstrated that
rhein acyl
glucuronide (RAG), the major metabolite of
rhein in the human blood circulation, significantly inhibited the uptake of
p-aminohippurate in hOAT1 transfected cells with IC50 value of 691 nM and
estrone sulfate uptake in hOAT3 transfected cells with IC50 value of 78.5 nM. As the substrate of both hOAT1 and hOAT3, the
methotrexate transport was significantly inhibited by RAG in hOAT1 transfected cells at 50 μM and hOAT3 transfected cells at 1 μM by 69% and 87%, respectively. Further in vivo study showed that after co-administrated with RAG in rats the AUC0-24 values of
methotrexate increased from 3109 to 5370 ng/mL*hr and the t1/2 was prolonged by 40.5% (from 7.4 to 10.4 h), demonstrating the inhibitory effect of RAG on
methotrexate excretion. In conclusion,
rhein acyl
glucuronide could significantly decrease the transport of
methotrexate by both hOAT1 and hOAT3. The combination use of
rhein,
diacerein or other
rhein-containing herbs with
methotrexate may cause obvious drug-drug interaction and require close monitoring for potential drug interaction in clinical practice.