Chromosomal aberrations induced in human cultured cells by liposome-encapsulated deoxyribonuclease I

Cytogenetic effects of sodium azide encapsulated in liposomes on heteroploid cell cultures

Lipid vesicles (liposomes) have been shown to be a useful vehicle for the delivery of a variety of compounds to cultured cells. Using multilamellar vesicles (MLV) and small unilamellar vesicles (SUV) we were able to deliver the classical mutagen, sodium azide, into human heteroploid HEp-2 cells. With this method sodium azide is not diluted in culture medium, but it is 'focused' into cells, producing chromosomal aberrations and other major genetic damages. Our results indicate that liposomes are suitable vectors for introducing clastogenic substances into cultured human cells.

Induction of chromosomal aberrations by DNase I

Chinese hamster ovary (CHO) cells were treated with bovine pancreatic DNase I using the method of electroporation. The enzyme induced chromosomal aberrations in a S-phase independent manner. The frequencies of polycentric chromosomes induced in the G1 phase of the cell cycle are positively correlated with the dose of DNase I. The distributions of DNase I-induced polycentric chromosomes were overdispersed.

Induction of chromosomal aberrations by restriction endonucleases encapsulated in liposomes

We used liposomes to deliver the restriction endonucleases BamHI and SmaI into human heteroploid HEp-2 cells. With this method very low concentrations of enzymes (2 units/ml) were active in the production of chromosomal aberrations. SmaI, which produces blunt-ended double-strand breaks in the DNA molecule, induces chromosomal aberrations more effectively than BamHI, which produces cohesive ends. Our results indicate that liposomes are suitable vectors for introducing restriction endonucleases into cultured human cells.

Non random distribution of lesions induced by deoxyribonuclease I in human chromosomes

We studied the action of deoxyribonuclease I on human lymphocytes in order to determine the localization of the DNAase induced aberrations. Our results indicate a non-random distribution of the lesions on chromosome regions which may reflect a differential pattern of sensitivity to the enzyme. Furthermore we observed a correspondence between the preferential DNAase induced breaks and fragile sites that are expressed in lymphocytes maintained in medium without folic acid. A possible interpretation of our findings is that the accessibility to DNAase and/or the efficiency of the repair systems depend on the chromatin structure that influences also the expression of some common fragile sites.