Dose dependency of aflatoxin B1 binding on human high molecular weight DNA in the activation of proto-oncogene.

Abstract

The binding of aflatoxin B1, AFB1, a potent hepatocarcinogen, to various high molecular weight (HMW) DNAs from human normal liver and two liver cancer cell lines, Alexander primary liver carcinoma (PLC) and Mahlavu hepatocellular carcinoma (hHC) and from NIH/3T3 cell have been investigated. The kinetics of AFB1 binding to these DNAs showed similar initial rates but the extents of binding to the PLC and hHC DNAs seemed to be slightly higher. Preferential AFB1 bindings were identified in both PLC and hHC DNAs compared to normal liver DNA when analyzed by restriction endonuclease digestions and agarose gel electrophoresis. A critical AFB1 binding dosage, ranging 100 to 460 fmole/,Lg DNA, was found to activate the carcinogenic effect of the Mahlavu hHC HMW DNA, but not normal liver HMW DNA, rendering it capable of inducing focal transformation in NIH/3T3 cell. Excessive AFB1 binding on the hHC and PLC HMW DNAs resulted in an "over-kill" of both cell transformation capability and templating activity of the DNA.

Free and DNA Adducted Aflatoxins in Chronic Liver Diseases that Predispose Patients to Hepatocellular Carcinoma in Mexico

“…AFs covalently bind to albumin, forming AFB 1 -albumin adducts, and to DNA, forming aflatoxin-DNA adducts, which primarily exist as 8,9-dihydroxy-8-(N 7 ) guanyl-9-hydroxy AFB 1 adducts (AFB 1 -N 7 -Gua) [30]. These adducts are converted to two secondary lesions: an apurinic site and the AFB 1 -formamido pyrimidine (AFB 1 -FAPY) adduct, which is primarily responsible for the genotoxic, mutagenic and carcinogenic properties of AFB 1 [31]. These adducts are valuable biomarkers for hepatic diseases, such as hepatitis B [32], hepatitis C [13], and HCC [33].…”