Visible light is a better co-inducer of apoptosis for curcumin-treated human melanoma cells than UVA

Curcumin attracts worldwide scientific interest due to its anti-proliferative and apoptosis inducing effects on different tumor cells at concentrations ranging from 10 to 150 µM (3.7–55 µg/ml). Unfortunately, because of a low oral bioavailability, only low and pharmacologically ineffective serum levels are achievable. In this study, an alternative treatment concept consisting of low concentration curcumin (0.2–5 µg/ml) and irradiation with UVA or visible light (VL) has been tested. The experimental results show clearly that this treatment decreases the proliferation and the viability of human melanoma cells while the cell membrane integrity remains intact. We identified the onset of apoptosis characterized by typical markers such as active caspases 8, 9 and 3 as well as DNA fragmentation accompanied by the loss of cell adhesion. The mitochondrial apoptosis signaling pathway is predominant due to an early activation of caspase-9. The present data indicate a higher efficacy of a combination of curcumin and VL than curcumin and UVA. Reduced effects as a result of light absorption by heavily pigmented skin are unlikely if VL is used. These results indicate that a combination of curcumin and light irradiation may be a useful additional therapy in the treatment of malignant disease

Chronological investigation of caspase activation after treatment with curcumin and light: A375 melanoma cells were incubated with 5 µg/ml curcumin and afterwards irradiated with visible light.

<p>Controls remained light-protected. After different periods of time (upper part: 0.5–4 hours; lower part: 1–24 hours) cells were lysed. Detection of inactive (black arrows) and active (white arrows) forms of caspase-8, caspase-9 and caspase-3 was carried out using the Western blot technique. β-actin-bands represent the loading control (dashed arrows).</p

Mitochondrial redox activity in melanoma cells (A375 and G-361) after treatment with curcumin and light: After incubation with curcumin, cells were irradiated with UVA (gray bars), or visible light (black bars), or remained light-protected (white bars).

<p>All values were referred to the untreated control as a 100% reference. Every bar represents an average of 8 simultaneously determined individual values; standard deviations are shown at the top. Highly significant reduction of viability of the treated cells is marked with * (<i>P</i>≦0.001).</p

DNA fragmentation in melanoma cells (A375 and G-361) after treatment with curcumin and light: After incubation with curcumin, cells were irradiated with UVA (gray bars), or visible light (black bars), or were light-protected (white bars).

<p>All values were referred to the untreated control as a 100% reference. Every bar represents the average of 4 simultaneously determined individual values; standard deviations are shown at the top. Significant increase of DNA fragmentation of the treated cells is marked with * (<i>P</i>≦0.05).</p

LDH release in melanoma cells (A375 and G-361) after treatment with curcumin and light: After incubation with curcumin, cells were irradiated with UVA (gray bars), or visible light (black bars), or were light-protected (white bars).

<p>Cells of the positive control were treated with 1% triton-X100 containing medium (dashed bars). All values were referred to the positive control as a 100% reference. Every bar represents the average of 8 simultaneously determined individual values; standard deviations are shown at the top.</p