142

NEWS AND VIEWS

28 C. S. Foote, Chemical mechanisms of photodynamic action, in C. J. Gomer (ed.), Future Directions and Applications in Photodynamic Therapy, SPIE Institutes for Advanced Optical Technologies, Vol. IS6, SPIE Optical Engineering Press, Bellingham, WA, 1990.

Biological implications of aerobically obtained sensitized photoproducts of tryptophan Eduardo

riboflavin-

Silva

Facultad de Quimica, P. Universidad Catc%ca de Chile, Casilla 306, Santiago (Chile)

Tryptophan (Trp), an essential amino acid, and the riboflavin (Rb) vitamin are natural constituents of living organisms that must be ingested by humans in food. The role of free and protein-bound Trp in the sensitivity of biological systems to light has prompted numerous studies of the photoprocess of this amino acid, either following the direct absorption of light by the indole group or promoted by compounds acting as sensitizers [l]. Among the sensitized photoprocesses, those involving the Rb-Trp system are of particular interest owing to the endogenous nature of the sensitizer. The photo-oxidation of Trp sensitized by Rb is characterized by higher quantum yields than those observed with other sensitizers such as methylene blue or rose bengal which involve a type II photo-oxidation mechanism. This behaviour suggested that Rb may act via different sensitizing mechanism from that accepted for other sensitizers. In this respect it was reported in 1977, that not only did irradiation with visible light of lysozyme in the presence of Rb and molecular oxygen produce photo-oxidation of some amino acid residues of that enzyme but also a binding of this sensitizer to the protein occurred [2]. In subsequent studies, after obtaining peptides from lysozyme, it was found that Trp residues were specifically involved in the binding between Rb and lysozyme [3]. Through the irradiation of this essential amino acid in its free form in the presence of Rb it was possible to isolate and characterize spectrophotometrically at least two types of photoadduct, according to the degree of modification of the flavin [4]. It is noteworthy that a binding has also been obtained between Rb and Trp by the excitation of this vitamin through an energy transfer from an enzymatically generated triplet acetone [5]. Although the precise chemical nature of these bindings has not been elucidated still, it has been recently demonstrated that the interaction of a flavin triplet with indole leads to the formation of the indolyl cation radical and the flavosemiquinone anion radical 163, species which could be responsible for the generation of these adducts [7]. implications [8j Despite the fact that Rb is a vitamin and Trp is an essential amino acid found in nearly all foods containing proteins, the presence of these substances has been related to hepatic dysfunctions produced by parenteral nutrition [9]. Moreover hepatic dysfunctions in neonatal gerbils [lo] and a lethal effect on mammalian cells in culture [ll] are produced by photoproducts of Trp only in the presence of Rb. In all these studies, the photo-oxidation products of Trp were postulated as responsible for these

1. Biological

NEWS AND VIEWS

143

anomalies. Considering that the action of visible light on solutions containing Trp and Rb generates not only photo-oxidation products but also photoadducts indol-flavin and indol-indol [12], it became of interest to study the possible toxicity of these compounds. In this way it was found that rats intraperitoneally injected during 12 days with the products of anaerobic irradiation of a Trp-Rb solution presented a significantly diminished weight gain as well as a remarkable increase in plasma concentration of y-glutamil transpeptidase (y-GT) [13]. This enzyme is usually employed in clinical studies as an indicator of hepatic canalicular membrane function and integrity, and an increase of y-GT at the plasma level is associated with hepatic dysfunctions. When the products of the anaerobic irradiation of a Trp-Rb solution were added to cell culture media seeded with teratocarcinoma F-9 cells it was observed that these products inhibited both cellular adhesion to the substrate and the natural proliferation process [14]. Simultaneously, studies with pre-implanted mouse embryos showed inhibition of the normal development [14]. The irradiation of rat lens-soluble protein fractions in the presence of Rb - an endogenous component of the lens - leads to an increase in the higher molecular weight fraction [12]. In an aging study with rats it was found that the proportion of the higher molecular weight protein fraction drastically increased with increasing age, whereas the proportion of the low molecular weight protein fraction concomitantly diminished [12]. It is postulated that aging produces an increase in the accessibility of the Trp residues of lens proteins, as established from iodide-quenching experiments, which would be more susceptible to the interaction with excited riboflavin, with generation of radical species which could be responsible for the initiation of the aggregation processes. 1 D. Creed, The photophysics and photochemistry of the near-W absorbing amino acids. I. Tryptophan and its simple derivatives, Phorochem. Photobiol., 39 (1984) 537-562. 2 E. Silva and J. Gaule, Light-induced binding of riboflavin to lysozyme, Radiat. Environ. Biophys., 14 (1977) 303-310. 3 I. Ferrer and E. Silva, Study of a photo-induced lysozyme-riboflavin bond, Radiat. Environ. Biophys., 24 (1985) 63-70. 4 M. Salim-Hanna, A. M. Edwards and E. Silva, Obtention of a photo-induced adduct between a vitamin and an essential amino acid. Binding of riboflavin to tryptophan, Znt. J. fitam. Nutr, Res., 57 (1987) 155-159. 5 J. Rojas and E. Silva, Photochemical-like behaviour of riboflavin in the dark promoted by enzyme-generated triplet acetone, Photochem Photobiol., 47 (1988) 467470. 6 A. Yoshimura and T. Ohno, Lumiflavin-sensitized photooxygenation of indole, Photochem Photobiol., 48 (1988) 561-565. 7 E. Silva, V. Riickert, E. Lissi and E. Abuin, Effects of pH and ionic micelles on the riboflavinsensitized photoprocesses of tryptophan in aqueous solution, J. Photochem. PhotobioL 8: BioL, 11 (1991) 57-68. 8 E. Silva, M. Salim-Hanna, A. M. Edwards, M. I. Becker and A. E. De loannes, A lightinduced tryptophan-riboflavin binding: biological implications, in M. Friedman (ed.), Nutritional and Toxicological Consequences of Food Recessing, Plenum, New York, 1991, pp. 33-48. 9 R. A. Vileisis, K. Sorensen, F. Gonz&lez-Crussi and C. E. Hunt, Liver malignancy after parenteral nutrition, J. Pediatr. 100 (1982) 88-90. 10 J. Bhatia and D. K. Rassin, Photosensitized oxidation of tryptophan and hepatic dysfunction in neonatal gerbils, J. Parent. Enter. Nutr., 9 (1985) 491495. 11 B. T. Nixon and R. J. Wang, Formation of photoproducts lethal for human cells in culture by daylight fluorescent light and billirubin light, Photo&em. Photobio&, 26 (1977) 589-593. 12 R. Ugarte, A. M. Edwards, M. S. Diez, A. Valenzuela and E. Silva, Riboflavin photosensitized anaerobic modification of rat lens proteins. A correlation with age-related changes.J. Photochem PhotobioL B: Biol., 13 (1992) 161-168.

144

NEWS AND VIEWS

13 M. N. Donoso, A. Valenzuela and E. Silva, Tryptophan riboflavin photo-induced adduct and hepatic dysfunction in rats, Nutr. Rep. Znt., 37 (1988) 599-606. 14 E. Silva, M. Salim-Hanna, M. I. Becker and A. De loannes, Toxic effect of a photo-induced tryptophaa-riboflavin adduct on F9 teratocarcinoma cells and preimplantation mouse embryos, Znt. J. Ktam. Nutr. Res., 58 (1988) 394-401.

Ultraweak

photons emitted by cells: biophotons

Hugo J. Niggli Cosmital SA (Research Company of Wella AG, Darmstadt), Rte de Ch&alles 21, CH-1723 Marb (Switzerland)

1. Introduction

Photons necessarily participate in all atomic and molecular interactions and changes in the physical universe. At the beginning of this century, Gunvitsch suggested that ultraweak photons transmit information in living systems [l] and several papers were published on this so-called mitogenetic radiation determined by biological detectors (onion roots) in the period from 1923 to 1935. Although some laboratories carried out their measurements by means of counter tubes containing photoelectric metal plates (for review see Quickenden and Que Hee [2]), these physical methods have not produced clear evidence for the existence of mitogenetic radiation. Finally, the results of Gurwitsch were refuted by Hollander and Klaus [3] and interest in this subject declined in the following decades. The presence of biological radiation was reexamined with the development of photomultiplier tubes in the mid-1950s by Facchini and co-workers [4]. In the 1960s most of the work on ultraweak photon emission was performed by Russian scientists [5-71, while in Western countries several pioneers, Quickenden in Australia [8], Popp in Germany [9] and Inaba in Japan [lo], independently developed methods for ultraweak photon measurements in a variety of different cells by the use of an extremely low noise, highly sensitive photon counting system which allows maximal exploitation of the potential capabilities of a photomultiplier tube. In the meantime it is commonly agreed that plant, animal and human cells emit ultraweakphotons often called biophotons [ll-171. From these and additional investigations different origins for this very weak radiation have been proposed which will be discussed shortly.

2. Radical

reactions

as source

of biopbotons

Most of the investigators think that this very weak radiation results from radical reactions such as, for instance, lipid peroxidation. In studies of microsomal lipid peroxidation [18, 191, it has been shown that the amount of malonaldehyde production and the intensity of emitted light are related to each other. On the basis of these studies, Inaba and co-workers proposed in their most recent report [20] that the reason for their finding of oxygen dependent light emission in rat liver nuclei was most probably lipid peroxidation in the nuclear membrane. As discussed in detail by Cadenas

Biological implications of aerobically obtained riboflavin-sensitized photoproducts of tryptophan.

142 NEWS AND VIEWS 28 C. S. Foote, Chemical mechanisms of photodynamic action, in C. J. Gomer (ed.), Future Directions and Applications in Photodyna...
248KB Sizes 0 Downloads 0 Views