Heme is the functional group of diverse hemoproteins and crucial for many cellular processes. However,
heme is increasingly recognized as a culprit for a wide variety of pathologies, including
sepsis,
malaria, and
kidney failure. Excess of free
heme can be detrimental to tissues by mediating oxidative and inflammatory injury. Protective mechanisms against free
heme are therefore pivotal for cellular survival. We postulated that overexpression of
Heme Oxygenase-1 (HO-1) and
Breast Cancer Resistance
Protein (BCRP) would protect against
heme-induced cytotoxicity. HO-1 is a
heme-degrading
enzyme generating
carbon monoxide,
iron, and
biliverdin/
bilirubin, while BCRP is a
heme efflux transporter. Human embryonic kidney cells were transduced using a baculovirus system as a novel strategy to efficiently overexpress HO-1 and BCRP. Exposing cells to
heme resulted in a dose-dependent increase in
reactive oxygen species formation, DNA damage and cell death.
Heme-induced cell death was significantly attenuated when cells overexpressed HO-1, BCRP, or both. The protective effects of HO-1 overexpression were most pronounced, while co-treatment with the HO-activity inhibitor
tin mesoporphyrin reversed these protective effects. Also cells treated with the
anti-oxidants N-acetylcysteine or HO-effector molecule
bilirubin showed protection against
heme insults, which may explain the increased protection by HO-1 compared to BCRP. In conclusion, both HO-1 and BCRP protect against
heme-induced toxicity and may thus form novel therapeutic targets for
heme-mediated pathologies.