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The induction of apoptosis by a positively charged methylene blue derivative
1Department of Biochemistry and Molecular Biology, University of Leeds, UK.
Abstract:
Identifying the cellular responses to photodynamic therapy (PDT) is important if the mechanisms of cell death are to be fully understood. PDT with a methylene blue analog DO15 yielded mitochondrial photodamage whilst membrane and lysosomal integrity were maintained. Apoptosis was detected using the DNA stain HO342, by the appearance of 50 kb fragments and by DNA ladder formation. The release of mono- and oligonucleosomes was further quantified using an ELISA protocol. Large DNA fragments were observed immediately following illumination, and nucleosomes were detected at 1-2 h post-treatment. Increasing the dose 4-fold accelerated the apoptotic response to PDT. This is the first report of a thiazine photosensitiser inducing apoptosis and is consistent with recent proposals suggesting that release of mitochondrial components may play an important role in the mechanism of cell death.
Insights
Photodynamic therapy (PDT) using a thiazine photosensitiser induced apoptosis, a programmed cell death. This response involved mitochondrial damage and DNA fragmentation, highlighting a novel cell death pathway.
Area of Science:
- Biochemistry
- Cell Biology
- Photochemistry
Background:
- Understanding cellular responses to photodynamic therapy (PDT) is crucial for elucidating cell death mechanisms.
- Methylene blue analogs are used as photosensitizers in PDT.
Purpose of the Study:
- To investigate the cellular responses to PDT induced by a methylene blue analog (DO15).
- To characterize the mechanism of cell death following PDT with DO15.
Main Methods:
- Photodynamic therapy using DO15 was administered to cells.
- Mitochondrial photodamage was assessed.
- Cellular and lysosomal integrity was monitored.
- Apoptosis was detected using HO342 DNA stain, observing DNA fragmentation (50 kb fragments, DNA laddering).
- Mono- and oligonucleosome release was quantified via ELISA.
Main Results:
- PDT with DO15 caused mitochondrial photodamage but maintained membrane and lysosomal integrity.
- Apoptosis was confirmed by DNA fragmentation and nucleosome release.
- Large DNA fragments appeared immediately post-illumination; nucleosomes were detected 1-2 hours later.
- A 4-fold dose increase accelerated the apoptotic response.
Conclusions:
- This study reports the first instance of a thiazine photosensitiser inducing apoptosis.
- The findings suggest that mitochondrial damage and subsequent release of components play a significant role in PDT-induced cell death.
- PDT with DO15 offers a potential pathway for targeted apoptosis induction.