Loss of lysosomal integrity caused by the decrease of proton translocation in methylene blue-mediated...

Area of Science:

• Biochemistry
• Cell Biology
• Cancer Therapy

Background:

• Lysosomal integrity is vital for cancer cell death in photodynamic therapy (PDT).
• The precise mechanisms of photodamage leading to lysosomal disintegration remain incompletely understood.

Purpose of the Study:

• To investigate the role of impaired lysosomal proton translocation in the loss of lysosomal integrity following photosensitization.
• To elucidate the mechanism by which photosensitized lysosomes disintegrate.

Main Methods:

• Isolated rat liver lysosomes were exposed to light with Methylene blue.
• Lysosomal delta pH and membrane potential were monitored using Acridine orange and 3,3'-dipropylthiadicarbocyanine iodide, respectively.
• Lysosomal enzyme latency (beta-galactosidase, beta-hexosaminidase) was assessed under various conditions, including the presence of Mg-ATP and n-ethylmaleimide.

Main Results:

• Photosensitization of lysosomes led to a loss of Mg-ATP dependent proton translocation and decreased proton pump electrogenicity.
• Lysosomal latency decreased significantly after photosensitization, indicating loss of integrity.
• Mg-ATP partially protected lysosomal latency, an effect abolished by n-ethylmaleimide, highlighting the role of proton translocation via H(+)-ATPase.
• Photosensitization did not impair lysosomal latency in the absence of Mg-ATP, suggesting proton translocation is the primary photodamage pathway studied.

Conclusions:

• Loss of lysosomal proton translocation is a key mechanism driving lysosomal disintegration after photosensitization.
• Targeting lysosomal proton translocation may represent a strategy to enhance PDT efficacy in cancer treatment.