AUTHOR=Seika Philippa , Janikova Monika , Asokan Sahana , Janovicova Lubica , Csizmadia Eva , O’Connell Mckenzie , Robson Simon C. , Glickman Jonathan , Wegiel Barbara 

TITLE=Free heme exacerbates colonic injury induced by anti-cancer therapy

JOURNAL=Frontiers in Immunology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.1184105

DOI=10.3389/fimmu.2023.1184105

ISSN=1664-3224

ABSTRACT=<p>Gastrointestinal inflammation and bleeding are commonly induced by cancer radiotherapy and chemotherapy but mechanisms are unclear. We demonstrated an increased number of infiltrating heme oxygenase-1 positive (HO-1+) macrophages (Mø, CD68+) and the levels of hemopexin (Hx) in human colonic biopsies from patients treated with radiation or chemoradiation versus non-irradiated controls or in the ischemic intestine compared to matched normal tissues. The presence of rectal bleeding in these patients was also correlated with higher HO-1+ cell infiltration. To functionally assess the role of free heme released in the gut, we employed myeloid-specific HO-1 knockout (<italic>LysM-Cre : Hmox1<sup>flfl</sup></italic>), hemopexin knockout (<italic>Hx<sup>-/-</sup></italic>) and control mice. Using <italic>LysM-Cre : Hmox1<sup>flfl</sup></italic> conditional knockout (KO) mice, we showed that a deficiency of HO-1 in myeloid cells led to high levels of DNA damage and proliferation in colonic epithelial cells in response to phenylhydrazine (PHZ)-induced hemolysis. We found higher levels of free heme in plasma, epithelial DNA damage, inflammation, and low epithelial cell proliferation in <italic>Hx<sup>-/-</sup></italic> mice after PHZ treatment compared to wild-type mice. Colonic damage was partially attenuated by recombinant Hx administration. Deficiency in <italic>Hx</italic> or <italic>Hmox1</italic> did not alter the response to doxorubicin. Interestingly, the lack of Hx augmented abdominal radiation-mediated hemolysis and DNA damage in the colon. Mechanistically, we found an altered growth of human colonic epithelial cells (HCoEpiC) treated with heme, corresponding to an increase in <italic>Hmox1</italic> mRNA levels and heme:G-quadruplex complexes-regulated genes such as <italic>c-MYC, CCNF</italic>, and <italic>HDAC6.</italic> Heme-treated HCoEpiC cells exhibited growth advantage in the absence or presence of doxorubicin, in contrast to poor survival of heme-stimulated RAW247.6 Mø. In summary, our data indicate that accumulation of heme in the colon following hemolysis and/or exposure to genotoxic stress amplifies DNA damage, abnormal proliferation of epithelial cells, and inflammation as a potential etiology for gastrointestinal syndrome (GIS).</p>