EVALUATING BIOFLAVONOID INDUCED DNA DOUBLE-STRAND BREAKS AND CHROMOSOMAL TRANSLOCATIONS
Analytics
37 views ◎14 downloads ⇓
Abstract
Dietary bioflavonoids are a class of chemical compounds found in soy, fruits, vegetables, tea, coffee, wine, and dietary supplements. They are separated into 12 different sub-classes based upon their structure, however only six are dietarily relevant: flavanols, flavonols, flavones, isoflavones, flavanones, and anthocyanidins. Similar to the chemotherapeutic etoposide, bioflavonoids are characterized by multiple phenolic rings. Etoposide is a chemotherapeutic drug that causes extensive DNA double-strand breaks (DSBs) through the poisoning of the enzyme topoisomerase II (Top2). The Top2 enzyme’s normal function is to relax supercoiled DNA and to do this the enzyme catalyzes a transient DSB. However, Top2 poisons, such as etoposide, interrupt Top2 a prevent the enzyme from religating the normally transient DSB. These DSBs must be legitimately repaired by the cells, otherwise chromosomal translocations may occur. Etoposide treatment is associated with the development of therapy-related leukemia due to chromosomal translocations involving the MLL gene. These translocations have been linked to etoposide’s Top2 poisoning capabilities. Infant leukemia, which is characterized by aggressive symptoms and a low survival rate, are characterized by MLL translocations which may be linked to maternal ingestion of bioflavonoids while pregnant. The purpose of my dissertation research was to investigate the mechanisms by which bioflavonoids may cause DNA DSBs and chromosomal translocations involving the MLL gene. I hypothesized that bioflavonoids would cause DNA DSBs similarly to etoposide and that bioflavonoids of the same sub-class would resolve these breaks with similar kinetics. I also hypothesized that combination treatments of bioflavonoids would show similar resolution kinetics to the individual bioflavonoid treatments. Next, I hypothesized that bioflavonoids would cause DNA DSBs and chromosomal translocations through poisoning of Top2. Finally, I hypothesized that chronic, low dose treatments of bioflavonoids would cause sustained chromosomal translocations. Utilizing -H2AX, a marker of DNA DSBs, and a chromosomal translocation reporter cell line I tested these hypotheses with a panel of bioflavonoids. I determined that while bioflavonoids do cause DNA DSBs similar to etoposide, the mechanism by which these DSBs are resolved is not dependent on their sub-class, but instead is dependent upon their classification as a traditional or covalent Top2 poison. Additionally, I determined that while bioflavonoids do utilize Top2 to cause DNA damage and translocations, bioflavonoids also cause damage and translocation through Top2-independent mechanisms, that may be more mutagenic for specific bioflavonoids. Finally, I determined that chronic, low dose bioflavonoids do appear to cause small populations containing translocation events, but further research is needed to verify these observations.