Formation of photoproducts and cytotoxicity of bilirubin irradiated with turquoise and blue phototherapy light

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Aim: To compare continuous and intermittent light exposure in the presence of bilirubin with respect to cellular damage. Furthermore, it was of interest to characterize the nature of cellular toxicity of bilirubin in the dark. Method: A murine lymphoma cell line, L5178Y‐R (LY‐R), was exposed to solutions of bilirubin (160 μM) supplemented with human serum albumin (200 μM) and irradiated with phototherapy light (Philips 20W/52) at a constant total dose of approximately 500 kJ/m2. The irradiation was given either as intermittent or continuous treatment with light of variable irradiance. The three lower irradiance levels were clinically relevant. Cells treated with bilirubin were also kept in the dark for various periods of time. Cell toxicity was determined by measuring apoptosis and necrosis. Apoptosis was measured by terminal deoxynucleotide transferase and propidium iodide staining assay, while trypan blue assay was used for detection of necrosis. Results: There was no difference (n=6, p>0.05) between continuous and intermittent irradiation in the induction of early and late apoptotic cell death. Necrosis was more pronounced after intermittent treatment. Bilirubin dark toxicity was observed and classified as both apoptotic and necrotic. Conclusion: Continuous and intermittent light exposure caused the same degree of apoptotic cell death, while the cells underwent more necrotic death after intermittent exposure. Bilirubin was cytotoxic in the dark by both cell death mechanisms.

Section: Discussionmentioning

confidence: 99%

Bilirubin‐induced cell death during continuous and intermittent phototherapy and in the dark

Roll

2005

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“…During irradiation the cell number decreases, but the nature of the loss cannot be determined. Depending on the time elapsed after irradiation and the applied light dose, the cell population will gradually resume cell division and exceed pre-exposure cell number [17]. Therefore, the increase in cell number above preirradiation values, as observed in the group exposed for 18 h, will probably lead to the underestimation of percentage cell death compared to the group exposed to the higher irradiance for 6 h only.…”

Section: Discussionmentioning

confidence: 99%

“…In the case of direct light effects DNA might be affected [27], and in the case of photosensitivity the apoptotic mechanism is most likely to occur through the formation of reactive oxygen species [28]. The toxicity of native BR will decrease with increasing light dose as BR is converted to less toxic photoproducts [17,29]. Figure 2 illustrates how the total cell death, by dark toxicity and phototoxicity, may vary as a function of light dose.…”

Section: Discussionmentioning

confidence: 99%

Bilirubin-induced cell death during continuous and intermittent phototherapy and in the dark

Roll¹

2005

“…Why does phototherapy fail in some patients with hereditary spherocytosis and hemolytic jaundice? In this month's issue, Bruzell Roll et al present three studies that shed some light on these areas 3–5.…”

mentioning

confidence: 99%

“…In this same cell line, the investigators compared both the efficacy and cytotoxicity of green fluorescent phototherapy (wavelength 490 nm) with conventional blue phototherapy (450 nm) 4. They found that both forms of phototherapy were equally effective at generating water‐soluble photoisomers.…”

mentioning

confidence: 99%

Phototherapy: Old questions, new answers

Madan

2005

Despite its popularity and widespread use, there remains much more to be learned about phototherapy. Conclusion: There is continued debate on whether intermittent phototherapy is more effective than continuous phototherapy; if light of a longer wavelength is more effective than blue light phototherapy; and if phototherapy in the presence of bilirubin is toxic to normal or abnormal red blood cells. Three in vitro studies in this issue of the journal provide answers to some of these questions.