Hemoglobin and hemin induce DNA damage in human colon tumor cells HT29 clone 19A and in primary human colonocytes.

Glei M, Klenow S, Sauer J, Wegewitz U, Richter K, Pool-Zobel BL.
Department of Nutritional Toxicology, Institute for Nutrition, Friedrich-Schiller-University, Dornburger Str. 25, D-07743 Jena, Germany.

Epidemiological findings have indicated that red meat increases the likelihood of colorectal cancer. Aim of this study was to investigate whether hemoglobin, or its prosthetic group heme, in red meat, is a genotoxic risk factor for cancer. Human colon tumor cells (HT29 clone 19A) and primary colonocytes were incubated with hemoglobin/hemin and DNA damage was investigated using the comet assay. Cell number, membrane damage, and metabolic activity were measured as parameters of cytotoxicity in both cell types. Effects on cell growth were determined using HT29 clone 19A cells. HT29 clone 19A cells were also used to explore possible pro-oxidative effects of hydrogen peroxide (H2O2) and antigenotoxic effects of the radical scavenger dimethyl sulfoxide (DMSO). Additionally we determined in HT29 clone 19A cells intracellular iron levels after incubation with hemoglobin/hemin. We found that hemoglobin increased DNA damage in primary cells (> or =10 microM) and in HT29 clone 19A cells (> or =250 microM). Hemin was genotoxic in both cell types (500-1000 microM) with concomitant cytotoxicity, detected as membrane damage. In both cell types, hemoglobin and hemin (> or =100 microM) impaired metabolic activity. The growth of HT29 clone 19A cells was reduced by 50 microM hemoglobin and 10 microM hemin, indicating cytotoxicity at genotoxic concentrations. Hemoglobin or hemin did not enhance the genotoxic activity of H2O2 in HT29 clone 19A cells. On the contrary, DMSO reduced the genotoxicity of hemoglobin, which indicated that free radicals were scavenged by DMSO. Intracellular iron increased in hemoglobin/hemin treated HT29 clone 19A cells, reflecting a 40-50% iron uptake for each compound. In conclusion, our studies show that hemoglobin is genotoxic in human colon cells, and that this is associated with free radical mechanisms and with cytotoxicity, especially for hemin. Thus, hemoglobin/hemin, whether available from red meat or from bowel bleeding, may pose genotoxic and cytotoxic risks to human colon cells, both of which contribute to initiation and progression of colorectal carcinogenesis.

PMID: 16226281 [PubMed - indexed for MEDLINE]

Traducción de las conclusiones: nuestros estudios muestran que la hemoglobina es genotóxica (daña genoma celular) de las células del intestino grueso del humano, y esto está asociado a mecanismos en los que intervienen radicales libres, y además con la citotoxicidad (toxicidad de las células), especialmente por la hemina. Por esto, la hemoglobina (y la hemina), si provienen de las carnes rojas o por sangrado interno de los intestinos, pueden generar riesgos de genotoxicidad y citotoxicidad a las celulas del colon en humanos, y ambos procesos contribuyen a la iniciación y progreso del cáncer de colon.