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Biomedical subjects

S Persad

Publications and source records attributed to S Persad.

27 records · Page 2Linked to original sources
PubMed1985

Role of superoxide and hydrogen peroxide in cell lysis during irradiation in vitro of Ehrlich ascitic carcinoma cells in the presence of melanin.

The reactive species involved in the cell lysis during ultraviolet irradiation of Ehrlich ascitic carcinoma cells in the presence of red hair melanin (RHM) were investigated by determining 51Cr release from labeled cells. Cysteine at 1 mM in the presence of RHM increased the cell lysis during the incubation in the dark as well as during irradiation; this lysis was enhanced by superoxide dismutase (SOD). Catalase abolished the dark reaction and inhibited the cysteine-induced increase of cell lysis during irradiation. The cell lysis by the superoxide-generating xanthine oxidase system was not significantly increased by SOD, but was significantly decreased by nitroblue tetrazolium and completely abolished by catalase. The cell lysis induced by the supernatants obtained from the suspensions of RHM either irradiated alone or with cysteine was abolished by catalase. Sediments of irradiated RHM when incubated in the dark with the cells did not release 51Cr. Irradiation of the cells in the presence of the same sediments produced lysis which was not inhibited by catalase. These studies suggest that superoxide per se is not toxic to the cells, but the H2O2 formed by dismutation of superoxide produces cell lysis either directly or by generating OH through Fenton-type reactions. A large part of the cell lysis seen during irradiation of cells in the presence of RHM is not due to H2O2, but may possibly be due to the melanin free radicals formed during irradiation.

Animals↗
PubMed1983

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.

Animals↗
PubMed1983

Effects of ultraviolet-visible irradiation in the presence of melanin isolated from human black or red hair upon Ehrlich ascites carcinoma cells.

The present study is an attempt to investigate the possibility that ultraviolet irradiation in the presence of pheomelanin may be more harmful to cells than the irradiation in the presence of eumelanin. The effects of UV-visible irradiation upon Ehrlich ascites carcinoma cells in the presence of the melanin isolated from human black hair (eumelanin) or from red hair (pheomelanin) were investigated. Irradiation of these cells was found to produce cell lysis, as observed by leakage of 51Cr from labeled cells and intracellular lactic dehydrogenase from the cells and decrease in cell viability demonstrated by the trypan blue exclusion test. The three parameters were quantitatively parallel to one another under various experimental conditions, namely different periods of irradiation and irradiation in the presence of different concentrations of melanin. The above effects were more pronounced when the irradiation was carried out in the presence of melanin from red hair than in the presence of black-hair melanin. In the absence of either melanin, the irradiation did not produce any significant effect in cell viability or cell lysis. Irradiation of the cells in the presence of red-hair melanin also decreased the transplantability of these cells. These observations clearly show that irradiation of cells in the presence of pheomelanin could produce cytotoxic effects. The present experimental design may have application in the development of in vitro models for the study of UV radiation-induced cutaneous carcinogenesis. The reactions of pheomelanin may be related to the susceptibility of "Celtic" skin to UV radiation-induced skin damage and carcinogenesis.

Animals↗
PubMed1982

Novel free radicals in synthetic and natural pheomelanins: distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy.

Synthetic pheomelanins from enzymic oxidation of the 3,4-dihydroxyphenylalanine (dopa) derivative 5-S-cysteinyldopa have been examined by ESR spectroscopy. These alkalisoluble polymers contain a novel kind of free radical that is spectroscopically distinct from that found in eumelanins. Delocalization of the unpaired electron onto a nitrogen atom and the ability of the radical to chelate complexing metal ions strongly suggest an o-semiquinonimine structure. The synthetic pheomelanin was compared with natural red pigments extracted from human red hair and from red chicken feathers. Spectroscopically, the chicken feather pheomelanin is almost identical to synthetic cysteinyldopa pheomelanin. In contrast, the pigment from red hair has a major spectral component very similar to that found in dopa melanin, with a smaller component corresponding to that found in cysteinyldopa melanin.

Cysteinyldopa↗
PubMed1981

Binding of protoporphyrin to melanin and oxidation-reduction properties of melanin-protoporphyrin complex.

The binding of protoporphyrin to melanin and the effect of the binding of protoporphyrin to melanin on the oxidation-reduction properties of melanin were studied. Various concentrations of protoporphyrin were incubated with melanin suspensions. The amounts of protoporphyrin remaining in the supernatant after sedimentation of the melanin were determined. The amount of bound protoporphyrin was determined by extraction with 3 M HCl. The results showed that when the initial concentration of protoporphyrin was varied, the amounts of protoporphyrin bound were in accordance with Langmuir's isotherm. From these results it was calculated that at infinite concentration of protoporphyrin 7.62 +/- 0.38 microgram protoporphyrin would be bound to 1 mg melanin. The activity to catalyze the coupled oxidation of NADH and reduction of ferricyanide was less in the case of the melanin-protoporphyrin complex than the free melanin. It is suggested that the binding of a naturally occurring photosensitizer such as protoporphyrin to melanin may have significant biological effects viz (i) photosensitivity due to protoporphyrin, (ii) the chemical reactivity of melanin in internal organs, and (iii) protective action of melanin in skin against ultraviolet radiation.

Ferricyanides↗
PubMedDate not supplied

Modification of beta-adrenoceptors and adenylyl cyclase in hearts perfused with hypochlorous acid.

It is now well known that the signal transduction pathway involving beta-adrenoceptors and adenylyl cyclase is altered in ischemic heart disease. Since leukocytes accumulate in the ischemic heart and produce hypochlorous acid (HOCl), we investigated the effects of HOCl upon beta-adrenoceptors and adenylyl cyclase activities by perfusing rat hearts with 0.1 mM HOCl for 10 min and isolating cardiac membranes. Marked depressions in both the density and affinity of beta1-adrenoceptors were observed, whereas no significant change in the affinity or density of beta2-adrenoceptors was seen in hearts perfused with HOCl. After treatment of hearts with HOCl, competition curves using isoproterenol, a beta-adrenoceptor agonist, revealed a decrease in the proportion of high affinity binding sites. The adenylyl cyclase activities in the absence and presence of forskolin, NaF, Gpp(NH)p, or isoproterenol were depressed in hearts perfused with HOCl; however, the stimulatory effects of these agents on adenylyl cyclase were either unaltered or augmented. The presence of methionine in the perfusion medium prevented the HOCl-induced changes in beta1-adrenoceptors and adenylyl cyclase activity. These results suggest that HOCl may produce a defect in the beta-adrenoceptor linked signal transduction mechanism by affecting both beta1-adrenoceptors and adenylyl cyclase enzyme in the myocardium.

Adenylyl Cyclases↗