Melatonin generates singlet oxygen on laser irradiation but acts as a quencher when irradiated by lamp photolysis
- Authors: Maharaj, Deepa S , Molell, H , Antunes, Edith M , Maharaj, Hiren , Maree, D M , Nyokong, Tebello , Glass, Beverley D , Daya, Santy
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/300335 , vital:57917 , xlink:href="https://doi.org/10.1111/j.1600-079X.2004.00185.x"
- Description: Melatonin, a naturally occurring chemical mediator, although assigned a diverse range of functions, has attracted interest in recent years because of its ability to function as a free radical scavenger. Because of the implications of singlet oxygen in neurotoxicity, the objective of the study was to investigate the ability of melatonin to quench singlet oxygen generated using laser irradiation or lamp photolysis. The results show that melatonin produces radicals upon laser irradation while the lamp photolysis studies show that melatonin is able to scavenge singlet oxygen produced by naphthalene. While melatonin is a free radical scavenger under biological conditions, it acts as a generator of singlet oxygen and or radicals (as ΦΔ is 1.41) when irradiated with laser light, implying that it has the potential to be used in photodynamic therapy in the destruction of tumors.
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- Date Issued: 2005
6-Hydroxymelatonin protects against cyanide induced oxidative stress in rat brain homogenates
- Authors: Maharaj, Deepa S , Walker, Roderick B , Glass, Beverley D , Daya, Santylal
- Date: 2003
- Language: English
- Type: Article , text
- Identifier: vital:6405 , http://hdl.handle.net/10962/d1006478
- Description: Both 6-hydroxymelatonin and N-acetyl-N-formyl-5-methoxykynurenamine are photodegradants and enzymatic metabolites of melatonin and are known to retain equipotent activity against potassium cyanide-induced superoxide generation compared to melatonin. It is not clear whether one or both of these metabolites is responsible for this effect. The present study therefore investigates the possible manner in which 6-hydroxymelatonin protects against oxidative stress induced by cyanide in rat brain homogenates. We examined the ability of 6-hydroxymelatonin to scavenge KCN-induced superoxide anion generation as well as lipid peroxidation. In addition, we also examined the effect of this indole on lactate dehydrogenase activity (LDH) as well as mitochondrial electron transport using dichlorophenol–indophenol as an electron acceptor. The results of this study show that 6-hydroxymelatonin significantly reduces KCN-induced superoxide anion generation, which is accompanied by a commensurate reduction in lipid peroxidation. Partial reversal of the KCN-induced reduction in mitochondrial electron transport is accompanied by a similar reversal of mitochondrial LDH activity blunted by KCN. It can thus be proposed that 6-hydroxymelatonin is potentially neuroprotective against KCN-induced neurotoxicity.
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- Date Issued: 2003
The identification of the UV degradants of melatonin and their ability to scavenge free radicals
- Authors: Maharaj, Deepa S , Anoopkumar-Dukie, Shailendra , Glass, Beverley D , Antunes, Edith M , Lack, Barbara A , Walker, Roderick B , Daya, Santylal
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/184303 , vital:44198 , xlink:href="https://doi.org/10.1034/j.1600-079X.2002.01866.x"
- Description: Ultraviolet (UV) light is known to induce the generation of free radicals in biological tissues such as skin. Of these free radicals, the O2–· and particularly the ·OH radical can induce cellular damage including lipid peroxidation. Thus, the use of antioxidants to prevent such damage induced by UV irradiation has received much attention recently. One such antioxidant, which has the potential to be incorporated into sunscreens, is the pineal secretory product melatonin. One of the concerns of using melatonin in sunscreens is its photostability. In the present study, we investigated the photostability of melatonin subjected to UV irradiation. In addition, we used liquid chromatography mass spectrometry (LC-MS) to identify the degradants and we also assessed the ability of the degradants to inhibit O2–· generation as well as lipid peroxidation in rat brain homogenate. The results show that UV irradiation of melatonin (0.1 mg/mL) using a 400-W lamp for 2 hr caused a significant decline of melatonin to 18% of its original concentration after 20 min, with the decline continuing until the melatonin concentration reaches zero at 120 min. The LC-MS results show that the degradants of melatonin are 6-hydroxymelatonin and N1-acetyl-N2-formyl-5-methoxykynurenamine (AFMK). These degradants were able to provide equipotent activity against potassium cyanide (KCN)-induced superoxide generation compared to non-irradiated melatonin. Thus, the study shows that although melatonin is rapidly degraded by UV irradiation, the degradants retain antioxidant activity, making melatonin a likely candidate for inclusion in sunscreens.
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- Date Issued: 2002
The effect of variations in pH and temperature on stability of melatonin in aqueous solution
- Authors: Daya, Santylal , Walker, Roderick B , Glass, Beverley D , Anoopkumar-Dukie, Shailendra
- Date: 2001
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/184314 , vital:44207 , xlink:href="https://doi.org/10.1034/j.1600-079x.2001.310209.x"
- Description: Melatonin (N-acetyl-5-methoxytryptamine) has a diverse range of functions, including the control of neuroendocrine events. A number of studies have shown that melatonin may be of potential benefit for the treatment of insomnia, as well as neurodegenerative disorders. At present, there are numerous dosage forms of melatonin, with the oral route of administration being most popular. Presently, there is little information on the stability of melatonin over a pH range. With the changes in pH in the gastro-intestinal tract, as well as in different experimental conditions, information on the stability of melatonin would be important. We used a high-performance liquid chromatography method to determine the stability of melatonin solutions over a pH range (1.2–12) at room temperature and at 37°C over a period of 21 days. The results show that no melatonin degradation occurred in the first 2 days. From days 3 to 21, there was a gradual decline in melatonin at all pHs, with the decline not exceeding 30%. No decline in melatonin levels occurred in the first 2 days at 37°C. From days 3 to 21, melatonin levels declined gradually, with the decline not exceeding 29%.
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- Date Issued: 2001
Melatonin alters the photodegradation of paracetamol
- Authors: Anoopkumar-Dukie, Shailendra , Glass, Beverley D , Walker, Roderick B , Daya, Santylal
- Date: 2000
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/184357 , vital:44211 , xlink:href="https://doi.org/10.1211/146080800128735755"
- Description: The effects of melatonin, a known free-radical scavenger, on paracetamol in the presence of UV irradiation was studied by use of HPLC. The experiments were performed in air and nitrogen. The results show that the rate of photodegradation of melatonin is faster in air than in nitrogen whereas that of paracetamol is similar in air and nitrogen. When the two drugs were combined, melatonin retarded the degradation of paracetamol for up to 6h in the presence of nitrogen. However, in the presence of air melatonin rapidly enhances the photodegradation of paracetamol. This study shows that a combination of melatonin and paracetamol in the presence of air and UV irradiation can lead to rapid inactivation of both agents, thus raising important concerns about the possible use of melatonin as sunscreen
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- Date Issued: 2000