The effect of porphyrin and radiation on ferrochelatase and 5-aminolevulinic acid synthase in epidermal cells

Quinolone compounds enhance delta-aminolevulinic acid-induced accumulation of protoporphyrin IX and photosensitivity of tumour cells

Exogenous δ-aminolevulinic acid (ALA)-induced photodynamic therapy (PDT) has been used in the treatment of cancer. To obtain a high efficacy of ALA-PDT, we have screened various chemicals affecting ALA-induced accumulation of protoporphyrin in cancerous cells. When HeLa cells were treated with quinolone chemicals including enoxacin, ciprofloxacin or norfloxacin, the ALA-induced photodamage accompanied by the accumulation of protoporphyrin was stronger than that with ALA alone. Thus, quinolone compounds such as enoxacin, ciprofloxacin and norfloxacin enhanced ALA-induced photodamage. The increased ALA-induced photodamage in enoxacin-treated HeLa cells was decreased by haemin or ferric-nitrilotriacetate (Fe-NTA), suggesting that an increase in iron supply cancels the accumulation of protoporphyrin. On the other hand, the treatment of the cells with ALA plus an inhibitor of haem oxygenase, Sn-protoporphyrin, led to an increase in the photodamage and the accumulation of protoporphyrin compared with those upon treatment with ALA alone, indicating that the cessation of recycling of iron from haem augments the accumulation. The use of quinolones plus Sn-protoporphyrin strongly enhances ALA-induced photodamage. To examine the mechanisms involved in the increased accumulation of protoporphyrin, we incubated ferric chloride with an equivalent amount of quinolones. Iron-quinolone complexes with visible colours with a maximum at 450 nm were formed. The levels of iron-metabolizing proteins in enoxacin- or ciprofloxacin-treated cells changed, indicating that quinolones decrease iron utilization for haem biosynthesis. Hence, we now propose that the use of quinolones in combination with ALA may be an extremely effective approach for the treatment modalities for PDT of various tumour tissues in clinical practice.

Effect of sesamol on radiation-induced cytotoxicity in Swiss albino mice

The radio-protective ability of sesamol (SM) at various doses viz., 0, 10, 25, 40, 50, 70 and 100mg/kg bw, administered intraperitoneally 30min prior to 9.5Gy whole-body gamma-irradiation was studied in Swiss albino mice. Radiation toxicity and mortality were observed during a period of 30 days and the percentage mortality was calculated. SM pretreatment with 50mg/kg bw was found to be the most effective dose in maintaining body weight and in reducing the percentage mortality, while 100mg/kg bw was found to be more effective in maintaining the spleen index and in stimulation of endogenous spleen colony-forming units. Pretreatment with SM (50mg/kg bw) in mice irradiated with 15Gy significantly reduced dead, inflammatory, mitotic and goblet cells in irradiated jejunum. SM at 50mg/kg bw also increased crypt cells, maintained villus height, and prevented mucosal erosion. Nuclear enlargement in epithelial cells was found less in SM-treated mice compared with the irradiated control. The radiation-induced decrease in endogenous antioxidant enzymes (GSH, GST, catalase) and the increase in lipid peroxidation were also reduced by pretreatment with SM [50 and 100mg/kg bw] at all monitored post-irradiation intervals. There was no protection at a dose less than 25mg/kg bw.

Protoporphyria Induced by the Orally Active Iron Chelator 1,2-diethyl-3-hydroxypyridin-4-one in C57BL/10ScSn Mice

Administration in the drinking water of the orally-active iron chelator 1,2-diethyl-3-hydroxypyridin-4-one (CP94) to C57BL/10ScSn mice caused the development of hepatic protoporphyria. This was detected after 1 week and continued as long as the chelator was given (15 weeks). The more hydrophilic 1,2-dimethyl- and 1-hydroxyethyl,2-ethyl-analogues (CP20 and CP102) were also tested, but they were both inactive in inducing accumulation of protoporphyrin in the liver. Restriction of in vivo iron supply for ferrochelatase seemed a likely mode of action, but an approximately 30% decrease in activity of this enzyme was also observed when measured in vitro. Extracts of livers from mice given CP20, CP94, and CP102 showed no potential to inhibit mouse ferrochelatase, in contrast to the findings with an extract from mice treated with the known porphyrogenic chemical 4-ethyl - 3 , 5 - diethoxycarbonyl - 2 , 6 - dimethyl - 1 , 4 - dihydropyridine, -indicating that ferrochelatase inhibition did not occur by the formation of an N-ethyl-protoporphyrin derived from metabolism by cytochrome P450. CP20, CP94, CP102, and CP117 (the pivoyl ester of CP102) all caused significant depression of the levels of ferritin-iron and total nonheme iron, but only CP94 caused the significant accumulation of protoporphyrin. Protoporphyria did not occur with iron overloaded C57BL/10ScSn mice or in SWR mice that had elevated basal iron status. Although the protoporphyrin had only a small effect on the total levels of the hemoprotein cytochrome P450 in C57BL/10ScSn mice, the activity of the CYP2B isoforms of cytochrome P450 was actually induced in both strains. The results show that CP94 could cause protoporphyria in individuals of low iron status, perhaps through specifically targeting particular iron pools available to ferrochelatase and by concomitantly stimulating heme synthesis.

The effect of L-cysteine and N-acetylcysteine on porphyrin/heme biosynthetic pathway in cells treated with 5-aminolevulinic acid and exposed to radiation

The effects of L-cysteine (LC) and N-acetylcysteine (NAC) on porphyrin accumulation in a human dermal microvascular endothelial cell line (HMEC-1) and a human epidermoid carcinoma cell line (A431) loaded with 5-aminolevulinic acid (ALA) and exposed to ultraviolet A (UVA) and blue light radiation were determined. Porphyrin accumulation was decreased in the presence of 0.1-7.5 mM LC (24.8%-31.4% suppression in HMEC-1 cell; 35.8%-48.9% suppression in A431 cells), and in the presence of 0.1-10.0 mM NAC (30.9%-58.0% suppression in HMEC-1 cells; 8.5%-45.3% in A431 cells). The suppression occurred in a LC or NAC dose-dependent fashion. The above was associated with partial reversal of suppression of ferrochelatase (FeC) activity in HMEC-1 cells and in A431 cells. As compared to FeC activity in cells treated with ALA and irradiation, enzyme activity was higher (by 31.9%-62.1%) in the presence of LC (1.0 mM or 5.0 mM) and in the presence of NAC (1.0 mM or 5.0 mM). These data indicate that LC and NAC have protective effects on porphyrin- and irradiation-induced diminution of FeC activity in HMEC-1 cells and A341 cells in vitro.