Effects of ultraviolet radiation on 3,4-benzpyrene and other polycyclic aromatic hydrocarbons; carcinogenic activity of aqueous extracts from irradiated 3,4-benzpyrene.
It was shown in preceding papers (2, 3) that when 3,4-benzpyrene dissolved in benzene was irradiated with monochromatic radiation of wave length 2,537 A. in the presence of oxygen, at least two water-soluble substances were included in the products and that these could be recognized, and some of their properties deduced, by spectrophotometric methods. The first, substance A, was characterized at pH 8 by an absorption band whose maximum intensity was at 3,600 A. It was labile, readily taking up atmospheric oxygen irreversibly when its aqueous solutions were allowed to stand at room temperature; but it could be stabilized by cooling them to 0 ~ C. and storing them in an atmosphere of nitrogen. The second substance, B, absorbed at 2,760 A. and was more stable to oxygen, but it was destroyed by strong alkali. It reacted readily with glutathione and with other compounds containing sulfhydryl groups. Water-soluble oxidation products of 3,4-benzpyrene are of course well known. A monohydroxy derivative is excreted as a metabolite when the hydrocarbon is fed to rats (8, 13); and a photoderivative has been described that has the power to inhibit respiratory enzymes (6, 7). None of them, however, has been reported to have any carcinogenic activity. Rideal and Schulman have shown (12) that materials very similar to, if not identical with, substances ,4 and B are readily adsorbed onto protein monolayers, and so might be expected to pass more readily than the unadsorbed hydrocarbon through cell membranes. By analogy with hemolytic substances, which they showed to possess this property to a high degree, substances ,4 and B might thus be expected to be biologically active. Other observations recorded in the literature, which were summarized in the introduction to Part I, seem to support this view. Since the absorption bands of ,4 and B do not accord with those of any derivative
Metabolism of 3,4-Benzpyrene in Mice
IF 3,4-benzpyrene is introduced into a mouse, it is eventually excreted as the phenol 8-hydroxy-benzpyrene1,2. It has been established that this transformation proceeds by various steps3,4. Four different benzpyrene derivatives have now been separated from extracts of various fresh tissues; they are provisionally termed X1, X2, F1 and F2, because they are responsible for the ‘BPX’ and ‘BPF’ fluorescences that Peacock5 and Chalmers6 discovered in the liver, bile, intestine and fæces of various animals after application of benzpyrene. The separation of X1, X2, F1 and F2 has been effected by fluorescence chromatography and selective extraction, using alumina and silica as adsorbents and acetone, benzene, xylene, petroleum ether, methyl, ethyl and amyl alcohols and water as solvents. X1 and X2 occur in vivo not only in the liver and digestive system but also in the lung, kidney cortex, subcutaneous tissue, skin (after painting with benzpyrene), and in the mammary glands as evidenced by the milk of mice; F1 and F2 occur in the large intestine and fæces, and occasionally in the lungs. The amount of fresh uncontaminated mouse urine did not suffice for a definite analysis, but there were indications of the presence of the X derivatives. Post mortem, all X-bearing tissues show slowly increasing amounts of the F derivatives unless they are kept in formol. The 3,4-benzpyrene-5,8-quinone that Berenblum and Schoental2 discovered in the fæces never appeared in fresh tissues.
Absorption Spectra of 1,2-Benzanthracene and of Some Methoxy Derivatives
Preliminary observations of the ultraviolet absorption of the methylated metabolite, described in the preceding section, showed that it contained some absorbing impurities. The moving plate method previously described (1) was well suited for the investigation of this product, since the complex absorption band system shown by 1,2-benzanthracene and its derivasten steel electrodes. The plates were matched with a Hilger photoelectric microphotometer. The absorption curve of u cene is plotted in Fig. 2. The position of the absorption bands of the above mentioned compounds was also determined by the moving plate method. +Comparison of band positions obtained by the two methods