Association of Ceramide Accumulation with Photodynamic Treatment-Induced Cell Death

Abstract

Ceramide, a stress-induced second messenger, has been associated with apoptosis in several malignant and non-malignant cell lines. We have shown that photodynamic treatment (PDT), using the phthalocyanine photosensitizer Pc 4 (HOSiPcOSi[CH3]2[CH2]3N[CH3]2), causes increased ceramide generation and subsequent induction of apoptosis in L5178Y-R (LY-R) mouse lymphoma cells. To test further if ceramide generation accompanies photocytotoxicity, we treated various cell lines with a PDT dose producing a 99-99.9% loss of clonogenicity. Like LY-R cells, human leukemia (U937) cells underwent rapid DNA fragmentation initiating within 1 h after PDT. Similarly, Chinese hamster ovary (CHO) cells showed rapid DNA laddering, beginning 1 h following the treatment. In contrast, mouse radiation-induced fibrosarcoma (RIF-1) cells showed no apoptosis within 24 h post-PDT, as judged by the absence of 50 kbp and oligonucleosome size DNA fragments, as well as no annexin V binding to cells with preserved membrane integrity. Using the same doses of PDT, we observed a time-dependent ceramide accumulation in all three cell lines. While a significant increase in ceramide levels was reached within 1 and 10 min in U937 and CHO cells, respectively, elevated ceramide production was measured only after 30 min in RIF-1 cells. In addition, exogenous N-acetyl-sphingosine was able to mimic PDT-induced apoptosis in U937 and CHO cells. We suggest that ceramide accumulation is associated with PDT-induced apoptosis and photocytotoxicity.

Therapeutic applications of bioactive sphingolipids in hematological malignancies

“…26,[98][99][100][101][102] In addition to their roles in chemotherapeutic cell death, ceramides were also shown to be associated with the photodynamic therapy-induced and gamma radiationinduced apoptosis in different leukemia cell lines. 103,104 As supportive to those observations, suppression of sphingomyelin synthase converting ceramide into SM was shown to potentiate the effects of photodynamic therapy. 105 However, according to the cell type used in the experiment, observations for roles of ceramides may differ.…”

Mechanisms in photodynamic therapy: part two—cellular signaling, cell metabolism and modes of cell death

“…The sphingolipid ceramide has proven to be a powerful second-signal effector molecule that regulates diverse cellular processes including apoptosis, cell senescence, the cell cycle, and cellular differentiation. Ceramide has been shown to activate a number of enzymes involved in stress signaling cascades including both protein kinases and protein phosphatases [34]. Dolgachev et al [35] showed that the oxidative stress induced by phthalocyanine (Pc4)-PDT in Jurkat human T lymphoma and CHO cells was accompanied by increases in ceramide with a concomitant decrease in sphingomyelin.…”

Direct tumor damage mechanisms of photodynamic therapy.

“…Ceramidedependent induction of apoptosis was observed in Photodynamic therapy different PDT models (Separovic et al, 1997;1998;. Interestingly, in RIF-1 cells an increase in ceramide production following PDT did not augment cell death, suggesting a dual role of these substances in the tumor cell metabolism (Separovic et al, 1998). Niemann-Pick (N-P) human lymphoblasts that lack SMases exposed to Pc4-mediated PDT showed an increased survival rate.…”