Surujdeen Persad

COMPARISON OF THE EFFECTS OF UV‐VISIBLE IRRADIATION OF MELANINS and MELANIN‐HEMATOPORPHYRIN COMPLEXES FROM HUMAN BLACK and RED HAIR

Clinical evidence indicates that people with light skin and red hair have a higher incidence of UV radiation‐induced diseases including cancer. It is not known whether this is because of the lower protection due to the smaller amounts of eumelanin present in the skin of these people or whether the presence of pheomelanin in their skin is responsible for the higher susceptibility to carcinogenesis. Irradiation of melanoproteins from red hair with UV‐visible light has been reported to produce superoxide. Comparative studies on the formation of superoxide during the irradiation of the melanins isolated from human black and red hair (BHM and RHM, respectively) are reported in this paper. These showed that no superoxide formation could be detected in the case of the BHM. whereas the formation of superoxide during the irradiation of RHM could be definitely demonstrated. Irradiation of the RHM with NADH resulted in the oxidation of more NADH than the irradiation of NADH with BHM. The observation that RHM is an active photosensitizer indicates that this property of pheomelanin present in light skin may at least partly be responsible for the harmful effect of radiation on people with light skin and/or red hair. Administration of hematoporphyrin followed by visible irradiation is a currently used mode of therapy for cancer. The present studies have shown that hematoporphyrin is bound to both BHM and RHM. The binding of hematoporphyrin to the melanins increased the formation of superoxide by RHM and the oxidation of NADH by both the melanins. The binding of porphyrins to melanins may have an influence upon the photosensitivity in diseases such as porphyrias and may also affect the therapeutic efficacy of hematoporphyrin.

Bovine retinal pigment epithelial cells cultured in vitro: Growth characteristics, morphology, chromosomes, phagocytosis ability, tyrosinase activity and effect of freezing

We compared the bovine melanotic and amelanotic retinal pigment epithelial (RPE) cells cultivated in vitro using a number of parameters. Both cell types could be readily harvested from the eye by dissection or by enzyme treatment of the RPE. Both types of cells grew equally well in the primary culture, and in serial subcultures for over 600 days, and also after being stored frozen for over two months. The two types of cells were similar in their growth patterns, morphology, chromosome characteristics and phagocytic activity but they differed in their tyrosinase activity. Although in long-term cultures cells showed chromosome loss, a high proportion of the cells retained their normal diploid chromosome number (2n = 60) with apparently normal karyotype.

Phototoxicity of chlorpromazine on retinal pigment epithelial cells

As it is known that chlorpromazine (CPZ) can bind to melanins as well as cause ocular phototoxicity, we investigated the cytotoxic effects of UV-visible irradiation of melanotic and amelanotic retinal pigment epithelial (RPE) cells in the presence of CPZ. At low concentrations (5 micrograms/ml) of CPZ a photosensitization reaction took place which lysed the cells as measured by the release of 51Cr from cells labelled with chromium. At concentrations of CPZ less than 5 micrograms/ml, no significant cell lysis occurred when the cells were incubated at 37 degrees C in the dark. As the concentration of CPZ was increased to 25 micrograms/ml or more, high percentages of cells were lysed. When the melanotic RPE cells were exposed to different concentrations of CPZ and grown in culture, the cell growth (multiplication) diminished drastically with low concentrations (less than 2 micrograms/ml CPZ). Vitamin E decreased the cell lysis both in the dark and upon irradiation. Oxygen radical scavengers such as glutathione, B-carotene, mannitol, D-penicillamine as well as superoxide dismutase and catalase did not decrease cell lysis. The phototoxic effects of CPZ was found not to be due to stable photoproducts formed during irradiation of CPZ.

A qualitative study of the melanins from blue and brown human eyes.

Abstract This investigation compares the physical and chemical properties of melanins isolated from the human Eye Bank eyes which were divided into two groups viz. blue and brown on the basis of the colour of the iris. The uveal tissues in each group were pooled and homogenized with water. The supernatants after removal of debris were mixed with equal volumes of 12 n -HCl. The mixture was refluxed for 48 hr. The protein-free melanin was washed with water and dried. The melanin from blue eyes had a bluish tinge and that from brown eyes was brown. There was no significant difference between the U.V.-vis spectra of the two melanins. The i.r. spectra showed a characteristic major band in the region of 1000/cm which was absent in dopa melanin. Both blue and brown eye melanins showed similar composition of C,H,N and S. Protoporphyrin, chlorpromazine and paraquat formed complexes with these melanins. Both melanins catalyzed a few oxidation-reduction reactions. No significant difference in their catalytic activity in the coupled oxidation of NADH and reduction of ferricyanide was observed. However, the brown melanin-protoporphyrin complex showed decreased activity in the oxidation-reduction reaction as compared with blue melanin complex. Our studies show that although they are similar in most respects there are some differences in the physical and chemical properties of melanins from the blue and brown eyes.

Binding of Imipramine, 8-Methoxypsoralen, and Epinephrine to Human Blue and Brown Eye Melanins

AbstractPrevious studies have shown that although human blue and brown eye melanins are similar in several respects they differ in some physical, chemical, and biological properties. This paper reports a comparison of the binding of three drugs—imipramine, 8-methoxypsoralen, and epinephrine—to the melanins isolated from human blue and brown eyes. It was found that these three drugs are bound to both of these melanins. There were differences between the binding sites and the association constants for their binding to blue and brown eye melanins. The binding of 8-methoxypsoralen to blue eye melanin showed two types of binding sites. It is suggested that the binding of drugs to eye melanins could decrease their immediate concentration in the eyes but could also result in higher concentrations for prolonged periods of time in the eyes compared to concentrations in nonmelanotic tissues. The differences between the blue and brown eye melanins in the binding of certain drugs may result in differences in the acti...

Role of Melanins and Drugs in Cutaneous Photosensitivity

Melanins present in the hair, skin and eye are considered to be two chemically different but biogenetically interrelated types of pigments: eumelanin and pheomelanin. Melanins are stable free radicals. The free radical contents of the melanins are enhanced by UV-visible irradiation. This effect was influenced by the presence of pho to sensitizers during the irradiation e.g. hematoporphyrin, rose bengal. Melanins undergo reversible oxidation-reduction reactions; these reactions are accelerated by irradiation of the melanin and by the presence of photosensitizers during the irradiation. Eumelanins and pheomelanins often behave differently with respect to the above properties.