The subcellular localization sites of
TPPS4 and TPPS1 and the subsequent cellular site damage during
photodynamic therapy were investigated in CT-26 colon
carcinoma cells using spectroscopic and electron microscopy techniques. The association of both
porphyrins with the mitochondria was investigated and the implications of this association on cellular functions were determined. Spectrofluorescence measurements showed that
TPPS4 favors an aqueous environment, while TPPS1 interacts with lipophilic complexes. The subcellular localization sites of each sensitizer were determined using spectral imaging. Mitochondrial-CFP transfected cells treated with
porphyrins revealed localization of TPPS1 in the peri-nuclear region, while
TPPS4 localized in the mitochondria, inducing structural damage and swelling upon irradiation, as shown by transmission electron microscopy.
TPPS4 fluorescence was detected in isolated mitochondria following irradiation. The photodamage induced a 38% reduction in mitochondrial activity, a 30% decrease in cellular
ATP and a reduction in Na(+)/K(+)-
ATPase activity. As a result, cytosolic concentrations of Na(+) and Ca(2+) increased, and the level of K(+) decreased. In contrast, the lipophilic TPPS1 did not affect mitochondrial structure or function and
ATP content remained unchanged. We conclude that
TPPS4 induces mitochondrial structural and functional photodamage resulting in an altered cytoplasmic ion concentration, while TPPS1 has no effect on the mitochondria.