Carbolines, azaheterocyclic
amines derived from indoleamines, have various
biological activities, such as neurotoxicity of
beta-carbolines and potent mutagenicity of gamma-
carbolines. In this study, structural significance among these
carbolines was investigated in relation to the types of cell death, apoptosis and
necrosis, using human
neuroblastoma SH-SY5Y cells. DNA damage was quantitatively analyzed by a single-cell gel electrophoresis assay. DNA damage was induced by both
beta-carbolines,
harman and
norharman, and gamma-
carbolines, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]
indole (Trp-P-1) and 3-amino-4-methyl-5H-pyrido[4,3-b]
indole (Trp-P-2), in a dose dependent manner. Gamma-
carbolines were more potent to damage
DNA than
beta-carbolines. Alkaline lysis of the cells prevented DNA damage induced by
beta-carboline, and pre-treatment of the cells with
cycloheximide, an inhibitor of
protein synthesis, reduced DNA damage caused by
norharman. Morphological observation showed condensed and fragmented nuclei typical for apoptosis, in the cells treated with
norharman. Thus, DNA damage induced by
norharman was proved to be apoptotic. However,
harman, which had a methyl substitution at the position 1, might induce
necrosis in the cells. On the other hand, gamma-
carbolines,
Trp-P-1 and
Trp-P-2, directly damaged
DNA. Thus, the
nitrogen atom at the gamma-position and/or an amino group in
carboline structure would be required to induce the direct DNA cleavage.