Cytotoxic action mode of a novel porphyrin derivative isolated from harmful red tide dinoflagellate Heterocapsa circularisquama.
Heterocapsa circularisquama is known to cause lethal effect on bivalves, but toxic effect on fish has not been reported yet. Recently, we have found that H. circularisquama has potent light-dependent hemolytic toxins. Based on the chemical structural analysis, one of the hemolytic toxins named H2-a was found to be a novel porphyrin derivative with similar structure to pyropheophorbide a methyl ester (PME), a well-known photoactive hemolytic agent (Miyazaki et al., Aquatic Toxicol. 2005;73:382--393). To clarify the cytotoxic action mode of H2-a, we examined the effects of H2-a on HeLa cells in comparison with PME. The cytotoxicities of both reagents were strictly light dependent, and no significant cytotoxic effects including cellular morphological changes were induced without light illumination. The dose response curves revealed that H2-a showed stronger cytotoxicity to HeLa cells than PME. Fluorescence microscopic observation suggested that H2-a tends to accumulate in the plasma membrane, whereas PME seems to distribute entire cytoplasm. Although PME induced typical apoptotic nuclear morphological changes and DNA fragmentation in HeLa cells, no such apoptosis-inducing ability of H2-a was observed. Among the radical scavengers, histidine significantly inhibited the cytotoxic activity of H2-a, suggesting the involvement of singlet oxygen in the cytotoxicity. These results suggest that the cytotoxic mechanism of H2-a is necrotic rather than apoptosis differing from PME, even though these are structurally quite similar to each other. The relatively high affinity of H2-a to the plasma membrane might result in the potent and quick cytotoxicity without induction of apoptotic signal transduction.
College of Ocean Science, School of Applied Marine Science (Post-BK 21), Cheju National University, 66 Jejudaehakno, Jeju-si, Jeju Special Self-Governing Province 690-756, Korea.
Daekyung
D
Kim
Yousuke
Y
Miyazaki
Takuji
T
Nakashima
Takashi
T
Iwashita
Tsuyoshi
T
Fujita
Kenichi
K
Yamaguchi
Kwang-Sik
KS
Choi
Tatsuya
T
Oda
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D049872:Bivalvia / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D053938:DNA Fragmentation / Q000187:drug effects; D004141:Dinoflagellida / Q000737:chemistry*; D004347:Drug Interactions; D016166:Free Radical Scavengers / Q000494:pharmacology; D006367:HeLa Cells; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D008387:Marine Toxins / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology* / Q000633:toxicity; D008856:Microscopy, Fluorescence; D015394:Molecular Structure; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology* / Q000633:toxicity; D011166:Porphyrins / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology* / Q000633:toxicity
D016166:Free Radical Scavengers; D008387:Marine Toxins; D017319:Photosensitizing Agents; D011166:Porphyrins