Absorption of methotrexate and hepatotoxicity

Toward a systems level understanding of organic anion and other multispecific drug transporters: a remote sensing and signaling hypothesis

Organic anion transporters (Oats) are located in the barrier epithelia of diverse organs, where they mediate the absorption and excretion of a wide range of metabolites, signaling molecules, and xenobiotics. Although their interactions with a broad group of substrates have been extensively studied and described, the primary physiological role of Oats remains elusive. The presence of overlapping substrate specificities among the different Oat isoforms, together with recent metabolomic data from the Oat1, Oat3, and renal-specific transporter (RST/URAT1) knockout mice, suggests a possible role in remote signaling wherein substrates excreted through one Oat isoform in one organ are taken up by another Oat isoform located in a different organ, thereby mediating communication between different organ systems, or even between different organisms. Here we further develop this "remote sensing and signaling hypothesis" and suggest how the regulation of SLC22 subfamily members (including those of the organic cation, organic carnitine, and unknown substrate transporter subfamilies) can be better understood by considering the organism's broader need to communicate between epithelial and other tissues by simultaneous regulation of transport of metabolites, signaling molecules, drugs, and toxins. This systems biology perspective of remote signaling (sensing) could help reconcile an enormous array of tissue-specific data for various SLC22 family genes and, possibly, other multispecific transporters, such as those of the organic anion transporting polypeptide (OATP, SLC21) and multidrug resistance-associated protein (MRP) families.

Liver damage in children with acute leukaemia and non-Hodgkin's lymphoma on oral maintenance chemotherapy

Eight of 36 children receiving maintenance chemotherapy for acute lymphoblastic leukaemia or non-Hodgkin's lymphoma had liver biopsies on the basis of clinical abnormalities and/or elevated serum enzyme levels. Six biopsies were abnormal, including one in a boy with spider naevi who showed micronudular cirrhosis; he appeared to retain methotrexate in the blood for a prolonged period and his SGOT level did not return to normal for 19 months after maintenance chemotherapy was discontinued. The five other abnormal biopsies showed minor changes in the portal tracts. The six children with abnormal liver histology showed a wide variation in their early handling of an oral methotrexate dose. There was a statistically significant rise in mean SGOT and alkaline phosphatase during treatment, but the wide scatter in values precluded their use as accurate indicators of liver damage in these children.