Inhibition of the mutagenicity of bay-region diol epoxides of polycyclic aromatic hydrocarbons by naturally occurring plant phenols: exceptional activity of ellagic acid

Ferulic, caffeic, chlorogenic, and ellagic acids, four naturally occurring plant phenols, inhibit the mutagenicity and cytotoxicity of (+/-)-7beta,8alpha-dihydroxy-9alpha, 10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (B[a]P 7,8-diol-9,10-epoxide-2), the only known ultimate carcinogenic metabolite of benzo[a]pyrene. The mutagenicity of 0.05 nmol of B[a]P 7,8-diol-9,10-epoxide-2 in strain TA100 of Salmonella typhimurium is inhibited 50% by incubation of the bacteria and the diol epoxide with 150 nmol of ferulic acid, 75 nmol of caffeic acid, 50 nmol of chlorogenic acid or, most strikingly, 1 nmol of ellagic acid in the 0.5-ml incubation mixture. A 3-nmol dose of ellagic acid inhibits mutation induction by 90%. Ellagic acid is also a potent antagonist of B[a]P 7,8-diol-9,10-epoxide-2 in Chinese hamster V79 cells. Mutations to 8-azaguanine resistance induced by 0.2 muM diol epoxide are reduced by 50% when tissue culture media also contains 2 muM ellagic acid. Similar to results obtained with the bacteria, ferulic, caffeic, and chlorogenic acids are approximately two orders of magnitude less active than ellagic acid in the mammalian cell assay. The antimutagenic effects of the plant phenols result from their direct interaction with B[a]P 7,8-diol-9,10-epoxide-2, because a concentration-dependent increase in the rate of diol epoxide disappearance in cell-free solutions of 1:9 dioxane/water, pH 7.0, is observed with all four phenols. In parallel with the mutagenicity studies, ellagic acid is 80-300 times more effective than the other phenols in accelerating the disappearance of B[a]P 7,8-diol-9,10-epoxide-2. Ellagic acid at 10 muM increases the disappearance of B[a]P 7,8-diol-9,10-epoxide-2 by approximately 20-fold relative to the spontaneous and hydronium ion-catalyzed hydrolysis of the diol epoxide at pH 7.0. Ellagic acid is a highly potent inhibitor of the mutagenic activity of bay-region diol epoxides of benzo[a]pyrene, dibenzo[a,h]pyrene, and dibenzo[a,i]pyrene, but higher concentrations of ellagic acid are needed to inhibit the mutagenic activity of the chemically less reactive bay-region diol epoxides of benz[a]anthracene, chrysene, and benzo[c]phenanthrene. These studies demonstrate that ellagic acid is a potent antagonist of the adverse biological effects of the ultimate carcinogenic metabolites of several polycyclic aromatic hydrocarbons and suggest that this naturally occurring plant phenol, normally ingested by humans, may inhibit the carcinogenicity of polycyclic aromatic hydrocarbons.

Mouse skin tumor-initiating activity of 5-, 7-, and 12-methyl- and fluorine-substituted benz[a]anthracenes

As an approach for elucidation of structure activity relationships that underlie the exceptionally large difference in carcinogenic activity between benz[a]anthracene and 7,12-dimethylbenz[a]anthracene (7,12-DMBA), 11 methyl- and/or fluorine-substituted benz[a]anthracenes were evaluated for tumor-initiating activity on mouse skin. Outbred CD-1 and outbred Sencar mice received a single topical application of the hydrocarbons followed by twice weekly applications of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate for 16-26 weeks. 7,12-DMBA was almost two orders of magnitude more active as a tumor-initiator than 7- and 12-methylbenz[a]anthracene. Methyl substitution at the 7- and 7,12-positions of benz[a]anthracene was significantly more effective in the enhancement of tumorigenic activity than fluorine substitution at these positions. Although 7-fluorobenz[a]anthracene, 12-fluorobenz[a]anthracene, and 7,12-difluorobenz[a]anthracene had only 0.15, 0.26, and less than 0.005 times the tumor-initiating activity of their respective methyl-substituted derivatives, they were severalfold more active than benz[a]anthracene. 7-Fluorobenz[a]anthracene was slightly less active than 12-fluorobenz[a]anthracene, whereas 7-methylbenz[a]anthracene was about twofold more than 12-methylbenz[a]anthracene. For 7,12-di-substituted benz[a]anthracenes, 7-methyl-12-fluorobenz[a]anthracene was more than twice as tumorigenic as 7-fluoro-12-methylbenz[a]anthracene, but each was individually more active than 7-methylbenz[a]anthracene and 12-methylbenz[a]anthracene, respectively. Both fluorinated compounds were much less active than 7,12-DMBA. Substitution of fluorine or methyl at the 5-position of 7-methylbenz[a]anthracene and substitution of fluorine at the 5-position of 12-methylbenz[a]anthracene dramatically reduced their tumorigenic activity.

Mutagenicity of the optical isomers of the diastereomeric bay-region chrysene 1,3-diol-3,4-epoxides in bacterial and mammalian cells

The mutagenic activities of the four optically pure (+)- and (-)-enantiomers of the two diastereomeric bay-region chrysene 1,2-diol-3,4-epoxides were evaluated in histidine-dependent strains of Salmonella typhimurium and in cultured Chinese hamster V79 cells. In strain TA98 of S. typhimurium, (-)-1 alpha, 2 beta-dihydroxy-3 beta, 4 beta-epoxy-1,2,3,4-tetrahydrochrysene was 5 to 10 times more active than the other three optical isomers. However, in strain TA100 of S. typhimurium and in Chinese hamster V79 cells, (+)-1 beta, 2 alpha-dihydroxy-3 alpha, 4 alpha-epoxy-1,2,3,4-tetrahydrochrysene was the most mutagenic diol-epoxide and was from 5 to 40 times more active than the other three optical isomers. The bay-region (+)- and (-)-3,4-epoxy-1,2,3,4-tetrahydrochrysene isomers has identical mutagenic activities in all three systems. These studies indicate that the presence and orientation of the hydroxyl groups play an important role in modulating the mutagenic activity of bay-region epoxides of chrysene in both bacterial and mammalian cells.

Absence of seasonal variation in antipyrine metabolism

The induced activity of aryl hydrocarbon hydroxylase (AHH), measured by the metabolism of benzo[a]pyrene to fluorescent products in cultured human lymphocytes, shows a strong seasonal variation. The in vivo metabolism of antipyrine, which is also catalyzed by microsomal cytochrome P-450-dependent monooxygenases, has been reported to be correlated with AHH inducibility in human lymphocytes. To determine whether antipyrine metabolism also showed seasonal changes, we measured antipyrine half-life (t 1/2) in 10 nonsmokers and eight smokers at the two times of the year that correspond to the high and low peaks of inducible AHH activity as measured in lymphocytes. The mean antipyrine t 1/2 determined in all 18 subjects in summer was almost identical to that found in winter (mean +/- SEM = 10.90 +/- 0.65 and 10.96 +/- 0.78 hr). AHH activity in cultured human lymphocytes from the nonsmoking subjects was determined in control and 3-methylcholanthrene-induced cells to obtained inducibility ratios of 4.2 +/- 0.56 (SEM) in the summer and 1.4 +/- 0.14 (SEM) in winter. These results indicate that the seasonal variation in AHH inducibility in human lymphocytes is not reflected by a corresponding seasonal variation in antipyrine metabolism in vivo.

Highly tumorigenic bay-region diol epoxides from the weak carcinogen benzo[c]phenanthrene

In the four years since its inception, the bay-region theory has proved highly successful in predicting which diol epoxide of a polycyclic aromatic hydrocarbon would have the highest tumorigenic activity. The present studies on benzo[c]phenanthrene have shown this hydrocarbon to be unique. It is the first hydrocarbon for which the bay-region diol epoxide that has its benzylic hydroxyl group and epoxide oxygen cis (isomer-1 series) has significant tumorigenic activity. Additionally, its bay-region diol epoxides are the most tumorigenic diol epoxides yet tested on mouse skin despite their expected and observed very low chemical reactivity. Perhaps some unique feature of the shape of benzo[c]phenanthrene can account for the remarkable biological activity of its bay-region diol epoxides. The high degree of crowding in the bay-region of benzo[c]phenanthrene may be such a contributing factor. It is know, for example, that methyl-substitution in the bay-region but not on the critical benzo-ring enhances the tumorigenic activity of 7,12-dimethylbenzo[a]anthracene relative to 7-methylbenzo[a]anthracene (Newman, 1976), of 5-methylchrysene relative to chrysene (Hecht et al., 1974), and of 11-methylbenzo[a]pyrene relative to benzo[a]pyrene (Iyer et al., 1980). Steric crowding in the bay-region of benzo[c]phenanthrene (Hirshfeld, 1963) and 7,12-dimethylbenzo[a]anthracene has been shown by x-ray crystallography to cause out-of-plane deformation of their aromatic ring systems.

Mutagenicity of the bay-region diol-epoxides and other benzo-ring derivatives of dibenzo(a,h)pyrene and dibenzo(a,i)pyrene

The mutagenic activities of dibenzo(a,h)(pyrene, dibenzo(a,i)pyrene, and a total of 11 of their benzo-ring derivatives were evaluated in bacterial and mammalian cells in the absence or presence of a mammalian metabolic activation system. trans-1,2-Dihydroxy-1,2-dihydrodibenzo(a,h)pyrene and trans-3,4-dihydroxy-3,4-dihydrodibenzo(a,i)pyrene, the expected dihydrodiol precursors of bay-region diol-epoxides, were metabolized to products which were more mutagenic to strains TA98 and TA100 of Salmonella typhimurium than were the metabolic products formed from their respective parent hydrocarbons. For each dihydrodiol, replacement of the benzo-ring double bond adjacent to the diol moiety with a single bond resulted in tetrahydrodiol derivatives which could not be metabolically activated, suggesting that one or both diastereomeric bay-region diol-epoxides were the bioactivated metabolites. The authentic bay-region diol-epoxide diastereomers of dibenzo(a,h)pyrene and dibenzo(a,i)pyrene in which the benzylic hydroxyl group and the epoxide oxygen are trans (diol-epoxide 2 series) were highly mutagenic in strains TA98 and TA100 of S. typhimurium and in cultured Chinese hamster V79 cells. Neither diol-epoxide was significantly, if at all, metabolized by epoxide hydrolase. The bay-region diol-epoxide of dibenzo(a,i)pyrene was from 1.5 to 5 times more active as a mutagen than the diol-epoxide of dibenzo(a,h)pyrene, and in strain TA98 of S. typhimurium as well as Chinese hamster V79 cells, it had activity comparable to that of the highly carcinogenic bay-region diol-epoxide of benzo(a)pyrene.

Tumorigenicity of the diastereomeric bay-region benzo(e)pyrene 9,10-diol-11,12-epoxides in newborn mice

The tumorigenic activities of benzo(e)pyrene, 9,10-dihydrobenzo(e)pyrene, 9,10-epoxy-9,10,11,12-tetrahydrobenzo(e)-pyrene, the diastereomeric bay-region 9,10-dihydroxy-11,12-epoxy-9,10,11,12-tetrahydrobenzo(e)pyrenes, and the K-region benzo(e)pyrene 4,5-oxide were assessed in newborn mice, Swiss-Webster mice received a total dose of 0.7 mumol of compound divided into three i.p. injections of 0.1, 0.2, and 0.4 mumol on the first, eighth, and 15th days of life, respectively. 9,10-Epoxy-9,10,11,12-tetrahydrobenzo(e)pyrene was highly toxic to the newborn mice, and the first injection of 0.1 mumol of this benzo(e)pyrene derivative killed all the mice within two weeks. The total dose of 9,10-epoxy-9,10,11,12-tetrahydrobenzo(e)pyrene was therefore reduced to 0.07 mumol in divided doses of 0.01, 0.02, and 0.04 mumol. When the animals were killed at 39 to 43 weeks of age, one of the diastereomeric bay-region diol-epoxides, (+/-)-9 beta, 10 alpha-dihydroxy-11 beta, 12 beta-epoxy-9,10,11,12-tetrahydrobenzo(e)pyrene, produced a small but significant increase in pulmonary tumors in male mice but had no significant hepatotumorigenic activity. The diastereomerically related diol-epoxide. (+/-)-9 beta, 10 alpha-dihydroxy-11 alpha, 12 alpha-epoxy-9,10,11,12-tetrahydrobenzo(e)pyrene, produced a significant incidence of hepatic tumors but had no effect on the formation of pulmonary tumors. Benzo(e)pyrene and the other benzo(e)pyrene derivatives were all nontumorigenic at the doses tested.

Activation and inhibition of benzo(a)pyrene and aflatoxin B1 metabolism in human liver microsomes by naturally occurring flavonoids

The effects of several naturally occurring and synthetic flavonoids on the metabolism of benzo(a)pyrene and aflatoxin B1 were evaluated. Addition of apigenin, chrysin, fisetin, flavonone, galangin, hesperitin, kaempferol, morin, myricetin, haringenin, or quercetin to human liver microsomes inhibited the hydroxylation of benzo(a)pyrene. In contrast to these results, the addition of flavone, nobiletin, tangeretin, or 7,8-benzoflavone to human liver microsomes caused a many-fold stimulation in the hydroxylation of benzo(a)pyrene, the metabolism of aflatoxin B1 to 2,3-dihydro-2,3-dihydroxyaflatoxin B1, and the metabolic activation of aflatoxin B1 to mutagenic products. Quercetin, morin, and kaempferol inhibited cytochrome c (P-450) reductase in human liver microsomes whereas flavone and 7,8-benzoflavone had no effect. These results suggest that the inhibitory effects of quercetin, morin, and kaempferol on monooxygenase activity may be caused at least in part by an inhibition in the reduction of cytochrome P-450. An examination of the structural features required for the inhibition and stimulation of benzo(a)pyrene hydroxylation indicated that all of the 12 flavonoid inhibitors that were studied possessed hydroxyl groups whereas the flavonoid activators were less polar molecules that lacked hydroxyl groups.

An enantiomeric interaction in the metabolism and tumorigenicity of (+)- and (-)-benzo[a]pyrene 7,8-oxide

The (+)- and (-)-enantiomers of benzo[a]pyrene 7,8-oxide are hydrated stereospecifically at C-8 to (-)- and (+)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, respectively, by rat hepatic epoxide hydrolase. The (-)-enantiomer of benzo[a]pyrene 7,8-oxide is metabolized by microsomal epoxide hydrolase at a rate 3- to 4-fold greater than the (+)-enantiomer. At low conversion of racemic substrate, however, benzo[a]pyrene 7,8-oxide is metabolized to the dihydrodiol at a rate equal to that of the (+)-enantiomer. An analysis of the enantiomeric composition of the dihydrodiol formed from the racemic substrate revealed preferential formation of (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo-[a]pyrene. At low substrate conversion (< 20% metabolism), the enantiomeric purity of the dihydrodiol was much higher than at high substrate conversion (> 50% metabolism). Similar results were obtained with microsomes from hamster, rabbit, guinea pig, mouse, and human liver. These results indicate that epoxide hydrolase has a higher affinity for (+)-benzo[a]pyrene 7,8-oxide than for the (-)-enantiomer. The kinetics of hydration of (+)- and (-)-benzo[a]pyrene 7,8-oxide by purified epoxide hydrolase in detergent solution showed the (+)- and (-)-enantiomers to have apparent Km values of 1.7 and greater than or equal to 20 microM, respectively. Tumorigenicity studies with benzo[a]pyrene 7,8-oxide on mouse skin and in newborn mice revealed that (+)-benzo[a]pyrene 7,8-oxide, the metabolic precursor of the more tumorigenic (-)-7,8-dihydrodiol, is significantly more tumorigenic than the (-)-enantiomer. However, racemic benzo[a]pyrene 7,8-oxide was more tumorigenic than either enantiomer alone, indicating an enantiomeric synergism in the carcinogenicity of benzo[a]pyrene 7,8-oxide. The data are discussed in relation to the complete sequence of metabolic pathways leading to an ultimate carcinogen from benzo[a]pyrene.

Mutagenicity and tumor-initiating activity of cyclopenta(c,d)pyrene and structurally related compounds

The biological activities of benzo(a)pyrene, cyclopenta(c,d)pyrene, and 12 other structurally related compounds were assessed by mutagenicity studies with bacterial and mammalian cells and/or skin tumorigenicity studies with mice. The ability of the parent hydrocarbons to be metabolically activated to mutagenic products was examined in strains TA98 and TA100 of Salmonella typhimurium, using 3 experimental protocols. In each case, cyclopenta(c,d)pyrene was metabolically activated to products mutagenic to the bacteria to a greater extent than was benzo(a)pyrene. However, 7,8-dihydrobenzo(a)pyrene and 0,10-dihydrobenzo(e)pyrene were the best substrates for metabolic activation to bacterial mutagens. Highly purified epoxide hydrase added to a purified and reconstituted monooxygenase system readily abolished the mutagenic activity observed in strain TA100 of S. typhimurium when cyclopenta(c,d)pyrene was the substrate, but not when benzo(a)pyrene was the substrate. Inherent mutagenicity of several epoxides of the hydrocarbons generally paralleled the ability of their potential metabolic precursors to be activated to mutagens. 1-Pyrenyloxirane and 10,11-dihydrocycloheptapyrene 8,9-oxide were highly mutagenic in strains TA98 and TA100 of S. typhimurium, and in the former strain these activities were comparable to that observed with 9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene, 4-Pyrenyloxirane was significantly less mutagenic than was 1-pyrenyloxirane in both strains of bacteria and in mammalian cells. Benzo(a)pyrene was over 20 times more tumorigenic than was cyclopenta-(c,d)pyrene, and it was the most potent of the 11 compounds tested for tumor-initiating activity in 2-stage initiation-promotion experiments on the skin of mice. Cyclopenta(c,d)pyrene had tumor-initiating activity comparable to that of benzo-(a)anthracene, but it was significantly less active than chrysene. Thus, contrary to inferences made from its high mutagenic activity, cyclopenta(c,d)pyrene is a weak tumor initiator on mouse skin.

Tumorigenic activity of benzo(e)pyrene derivatives on mouse skin and in newborn mice

The tumorigenic activities of benzo(e)pyrene and several of its derivatives were determined in two mouse tumor models. Newborn Swiss-Webster mice were given i.p. injections of 0.4, 0.8, and 1.6 mumol of compound on the first, eighth, and 15th day of life, respectively. When the mice were 62 to 66 weeks old, the experiment was terminated by killing the animals. Benzo(e)pyrene, trans-4,5-dihydroxy-4,5-dihydrobenzo(e)pyrene, and trans-9,10-dihydroxy-9,10-dihydrobenzo(e)pyrene had little or no tumorigenic activity in lung tissue, although trans-9,10-dihydroxy-9,10-dihydrobenzo(e) pyrene did induce a significant number of hepatic tumors. The tumor-initiating activities of benzo(e)pyrene and several of its derivatives were determined on the skin of female CD-1 mice. A single topical application of 1.0 to 6.0 mumol of the test compound was followed 7 days later by twice-weekly applications of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate for 35 weeks. Control mice and mice treated with 6.0 mumol of benzo(e)pyrene, trans-4,5-dihydroxy-4,5-dihydrobenzo(e)pyrene, trans 9,10-dihydroxy-9,10-dihydrobenzo(e)pyrene, and trans-9,10-dihydroxy-9,10,11,12-tetrahydrobenzo(e)pyrene had a tumor incidence of less than 20% and had less than or equal to 0.25 papillomas/mouse. 9,10-Dihydrobenzo(e)pyrene was the only derivative tested that had significant tumor-initiating activity on mouse skin; an initiating dose of 2.5 mumol gave a 67% tumor incidence and 1.43 papillomas/mouse.

An assessment of the potential use of anionic dextrans as a plasma substitute

Several problems exist when dextrans are used as plasma substitutes. High molecular weight dextrans can cause red cell aggregation and increased blood viscosity. Low molecular weight dextrans, although shown to improve circulation and promote flow, are removed rather rapidly from the circulation due to high premeation rates across capillary walls. In the present study, a small anionic charge is introduced onto the dextran to make it electrostatically negative. Since capillary walls have been shown to retain negatively charged solutes in preference to neutral solutes, the anionic dextran should retain its effectiveness for longer periods of time compared to similar sized neutral dextran. Studies were done on eight unanaesthetized dogs to compare the relative disappearance rates of dextran and anionic dextran (carboxymethyl dextran) from the circulation. It was shown that anionic dextrans do remain in the circulation over a longer period of time compared to neutral dextrans.

Differences in mutagenicity and cytotoxicity of (+)- and (-)-benzo[a]pyrene 4,5-oxide: a synergistic interaction of enantiomers

In order to study the biological effects of (+)- and (-)-benzo[a]pyrene 4,5-oxide, a synthesis of these molecules has been developed based on the resolution of (+/-)-cis-4,5-dihydroxy-4,5-dihydrobenzo[a]pyrene. The (-) enantiomer of benzo[a]pyrene 4,5-oxide was 1.5- to 5.5-fold more mutagenic than the (+) enantiomer in strains TA 98, TA 100, TA 1537, and TA 1538 of Salmonella typhimurium and in Chinese hamster V79 cells. In studies with V79 Cells, the (-) enantiomer of benzo[a]pyrene 4,5-oxide was also more cytotoxic than the (+) enantiomer. When mixtures of the enantiomers were studied in V79 cells, synergistic cytotoxic and mutagenic responses were observed. The greatest cytotoxic and mutagenic effects occurred with a 3:1 mixture of the (-) and (+) enantiomers of benzo[a]pyrene 4,5-oxide, respectively.

Carcinogenicity of 2-hydroxybenzo(a)pyrene and 6-hydroxybenzo(a)pyrene in newborn mice

Benzo(a)pyrene (BP), 2-hydroxybenzo(a)pyrene (2-HOBP), and 6-hydroxybenzo(a)pyrene (6-HOBP) were tested for tumorigenicity by i.p. injection into newborn mice. The mice were treated sequentially with 200, 400, and 800 nmol of compound on the first, eighth and fifteenth day of life, and the animals were killed at 24 weeks of age. Treatment with 2-HOBP caused about 4-fold more pulmonary tumors than BP, while 6-HOBP had little or no tumorigenic activity. Newborn mice treated with 2-HOBP, BP, and 6-HOBP had a 98, 81, and 11% incidence of pulmonary adenomas with an average of 24, 6.4, and 0.11 adenomas per mouse, respectively. In the control group, 7.5% of the animals had pulmonary adenomas with an average of 0.08 adenoma per mouse. When 25, 50, or 100 nmol of BP or 2-HOBP was applied to mouse skin once every 2 weeks for 60 weeks, both compounds had about the same carcinogenic activity. These results demonstrate the importance of evaluating the carcinogenic potential of chemicals in more than one tumor system. BP and 2-HOBP were tested for mutagenicity towards two strains of Salmonella typhimurium and towards Chinese hamster V79 cells in the presence of hepatic microsomes from rats pretreated with Aroclor 1254. The products formed during the metabolism of 2-HOBP or BP by liver microsomes had significant mutagenic activity.

Formation of a thiomethyl metabolite of phenacetin and acetaminophen in dogs and man

Conjugates of 3-methylthio-4-hydroxyactanilide were found in the urine of dogs and humans treated with phenacetin (4-ethoxyacetanilide) or acetaminophen (4-hydroxyacetanilide). About 1% to 3% of the administered dose was excreted as this thiomethyl metabolite after administration of phenacetin or acetaminophen to dogs. An average of 0.39% of the dose was excreted in the urine as 3-methylthio-4-hydroxyacetanilide conjugates after administration of phenacetin to several subjects, and an average of 0.66% of the dose was excreted as this metabolite in the urine after administration of acetaminophen to humans. The possibility that the thiomethyl metabolite is derived from a mercapturic acid conjugate or an N-hydroxy derivative of phenacetin or acetaminophen is discussed.

Evidence for bay region activation of chrysene 1,2-dihydrodiol to an ultimate carcinogen

The tumor-initiating activities of chrysene and the three metabolically possible trans-dihydrodiols at the 1,2-, 3,4-, and 5,6-positions of chyrsene were determined on the skin of female CD-1 mice. A single topical application of 0.4, 1.25, or 4.0 mumol of each compound was followed 7 days later by twice-weekly applications of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate for 25 weeks. The most potent tumor initiator was chrysene 1,2-dihydrodiol, which had approximately twice the tumorigenic activity of the parent hydrocarbon chrysene at all doses tested. Chrysene 3,4-dihydrodiol and chrysene 5,6-dihydrodiol had no significant tumorigenic activity. 1,2-Dihydroxy-1,2,3,4-tetrahydrochrysene, a compound related to chrysene 1,2-dihydrodiol but with the conjugated nonaromatic double bond removed from the 3,4-position of the molecule, had less than 25% of the tumorigenic activity of chrysene 1,2-dihydrodiol. These results indicate that chrysene 1,2-dihydrodiol is a proximate carcinogenic metabolite of chrysene and that a chrysene 1,2-diol-3,4-epoxide, in which the epoxide group forms part of the bay region in the molecule, is a likely candidate as an ultimate carcinogenic metabolite of chrysene.

Marked differences in the tumor-initiating activity of optically pure (+)- and (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene on mouse skin

The ability of optically pure (+)- and (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene to initiate skin tumors in mice was determined with a two-stage tumorigenesis system. A single application of 50 to 200 nmoles of (+)- or (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene to the backs of CD-1 mice followed by twice-weekly applications of 12-O-tetradecanoyl-phorbol-13-acetate revealed that the (-)-enantiomer was 5- to 10-fold more potent than was the (+)-enantiomer as a tumor initiator at the three dosage levels tested. When the tumor-initiating activities of the (+)0 and (-)-enantiomers of trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene were compared to the activity of benzo(a)pyrene at an equimolar dose, the (-)-enantiomer was more active while the (+)-enantiomer was considerably less active. This is the first report of differences in the carcinogenic activity between optical enantiomers.

Tumorigenicity of five dihydrodiols of benz(a)anthracene on mouse skin: exceptional activity of benz(a)anthracene 3,4-dihydrodiol

Benz[a]anthracene and the five metabolically possible vicinal trans dihydrodiols of benz[a]anthracene were tested for ability to initiate skin tumors in CD-1 female mice. A single topical application of 0.4-2.0 mumol of hydrocarbon was followed 18 days later by twice weekly applications of the skin promoter 12-O-tetradecanoylphorbol-13-acetate. Comparisons of latency period, percent of mice with tumors, and number of papillomas observed per mouse indicated that benz[a]anthracene 1,2-, 5,6-, 8,9-, and 10, 11-dihydrodiols were all less active tumor initiators than was benz[a]anthracene. The high tumorigenicity of benz[a]anthracene 3,4-dihydrodiol, presumably the result of metabolism to either or both of the diastereomeric benz[a]anthracene 3,4-diol-1,2-epoxides, supports the bay region theory of polycyclic hydrocarbon carcinogenicity and provides the first example of a proximate carcinogenic metabolite that is much more active than the parent hydrocarbon on mouse skin.

Mutagenicity and cytotoxicity of benz[alpha]anthracene diol epoxides and tetrahydro-epoxides: exceptional activity of the bay region 1,2-epoxides

Three diastereomeric pairs of diol epoxides, two tetrahydro-epoxides, and the K-region oxide of the polycyclic aromatic hydrocarbon benz[a]anthracene were evaluated for mutagenic activity in strain TA 100 of Salmonella typhimurium and in line V79-6 of Chinese hamster lung cells. The two diastereomeric 1,2-epoxides of the trans-3,4-dihydrodiol of benz[a]anthracene are 15 to 35 times more mutagenic to the bacteria and 65 to 125 times more mutagenic to the mammalian cells than are the diastereomeric pairs of benz[a]anthracene-8,9-diol-10,11-epoxides or benz[a]anthracene-10,11-diol-8,9-epoxides. 1,2-Epoxy-1,2,3,4-tetrahydrobenz[a]anthracene is the most mutagenic and cytotoxic of the nine derivatives and is 5 and 25 times more mutagenic than 3,4-epoxy-1,2,3,4-tetrahydrobenz[a]anthracene in bacterial and mammalian cells, respectively. In either test system, benz[a]anthracene 5,6-oxide (K-region oxide) has less than 10% of the activity of any of the 1,2-epoxides derived from benz[a]anthracene. The relative stabilities of the derivatives in aqueous solution do not account for the differences in mutagenic activity because the more mutagenic derivatives tend to be less stable. The benz[a]anthracene diol epoxides, like the benzo[a]pyrene diol epoxides, are refractory to the action of epoxide hydrase. The exceptional mutagenic activity of the 1,2-epoxide derivatives of benz[a]anthracene is consistent with and supportive of the hypothesis that bay region epoxides on saturated, angular benzo-rings of unsubstituted polycyclic aromatic hydrocarbons are ultimate carcinogens.

Mutagenicity and cytotoxicity of benzo(a)pyrene benzo-ring epoxides

Four benzo-ring epoxides of the environmental carcinogen benzo(a)pyrene (BP) were tested for mutagenic and cytotoxic activity in 3 strains of Salmonella typhimurium (TA1538, TA98, and TA100) and in Chinese hamster V79 cells. Although very unstable in aqueous solution, 7beta,8alpha-dihydroxy-0beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (diol epoxide 1), with the 7-hydroxyl group on the same face of the molecule as the epoxide oxygen, was 1.5 to 4 times as mutagenic in the bacterial strains as was its more stable stereoisomer 7beta,8alpha-dihydroxy-9alpha,10beta-epoxy-7,8,9.10-tetrahydrobenzo(a)pyrene (diol epoxide 2). In V79 cells, diol epoxide 1 had one-third the mutagenic activity of diol epoxide 2 but was at least 10 times more labile than diol epoxide 2 in the tissue culture medium. The half-life of diol epoxide 1 in tissue culture medium was about 30 sec, whereas the half-life of diol epoxide 2 was between 6 and 12 min. 9,10-Epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene, which is saturated in the benzo ring, is also very unstable and has mutagenic activity equal to or greater than diol epoxide 1 in the bacterial and mammalian cells. 7,8-Epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene was more stable in aqueous solution than any of the 9,10-epoxides of BP but was much less mutagenic in both the bacterial and mammalian cells. In v79 cells, diol epoxides 1 and 2 and 9,10-opoxy-7,8,9,10-tetrahydrobenzo(a)pyrene were more than 40 times more cytotoxic than 7,8-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene. The mutagenicity of the 2 tetrahydro epoxides toward strain TA98 of S. typhimurium was readily abolished by purified epoxide hydrase, whereas the mutagenic activity of the 2 diol epoxides was relatively unaffected by coincubation with the enzyme.

Mutagenicity and cytotoxicity of benzo(a)pyrene arene oxides, phenols, quinones, and dihydrodiols in bacterial and mammalian cells

Twenty-nine benzo(a)pyrene derivatives were tested for mutagenic acitivity without metabolic activation in Salmonella typhimurium strains TA98, TA100, and TA1538 and in Chinese hamster V79 cells. The compounds studied included 4 arene oxides, all 12 isomeric phenols, 5 quinones, and 8 dihydrodiols. Benzo(a)pyrene 4,5-oxide was the most mutagenic of the compounds tested in both the bacterial and mammalian systems. The other arene oxides [benzo(a)pyrene 7,8-, 9,10-, and 11,12-oxides] were only weakly mutagenic in the S. typhimurium strains. However, in Chinese hamster V79 cells benzo(a)pyrene 11,12-oxide. Among the phenols, 6-hydroxybenzo(a)pyrene and 12-hydroxybenzo(a)pyrene were moderately mutagenic in strain TA98 of S. typhimurium, and 6-hydroxybenzo(a)pyrene was moderately mutagenic in V79 cells. The other 10 phenols, 5 quinones [benzo(a)pyrene 1,6-, 3,6-, 4,5-, 6, 12-, and 11,12-quinones] and 8 dihydrodiols [benzo(a)pyrene cis-4,5,trans-4,5-, cis-7,8-, trans-7,8-, cis-9,10-, trans-9,10-, cis-11,12-, and trans-11, 12-dihydrodiols] were eitherinactive or only weekly mutagenic. 1-Hydroxybenzo(a)pyrene and 3-hydroxybenzo(a)pyrene were weakly mutagenic in strain TA98 of S. typhimurium, and benzo(a)pyrene 7,8-dihydrodiol was weakly mutagenic in V79 cells. Benzo(a)pyrene 11,12-quinone was extremely cytotoxic to the V79 cells but had no observable toxicity in the bacterial strains.

Antipyrine: radioimmunoassay in plasma and saliva following administration of a high dose and a low dose

A simple and senstitive radioimmunoassay has been developed for the determination of antipyrine levels in plasma and saliva of man. Antiserum to antipyrine was obtained from rabbits immunized with an immunogen prepared by covalently coupling N-(4-antipyrinyl)-succinamic acid to bovine serum albumin (BSA). The radioimmunoassay can detect antipyrine levels as low as 10 ng/ml of plasma or saliva, using a 0.1-ml sample. This contrasts with the sensitivity of a commonly used spectrophotometric method that can measure about 4,000 ng/ml using a 2-ml plasma sample. Agreement between the radioimmunoassay and spectrophotometric assay of antipyrine was excellent for plasma (r = 0.98) and salvia (r =0.97) when samples were analyzed from 6 subjects receiving 18 mg/kg of antipyrine. The correlation between plasma and saliva antipyrine half-lives using the radioimmunoassay and an 18 mg/kg dose of antipyrine was r = 0.90 (p less than 0.005). After a dose of 1.8 mg/kg of antipyrine, the drug disappeared monoexponentially from plasma and saliva for at least 51 hr, and the correlation between plasma half-life and saliva half-life was r = 0.97 (p less than 0.001) in the 6 subjects. Excellent agreement was also observed between half-lives after the high and low doses of antipyrine (r = 0.99, p less than 0.001 for plasma and r = 0.98, p less than 0.001 for saliva).

Permselectivity of the glomerular capillary wall. Studies of experimental glomerulonephritis in the rat using dextran sulfate

To determine whether the increased filtration of serum proteins after glomerular injury is the consequence of altered electrostatic properties of the glomerular capillary wall, we measured fractional clearances of the anionic polymer, dextran sulfate, in nine Munich-Wistar rats in the early autologous phase of nephrotoxic serum nephritis (NSN). In agreement with previous studied from this laboratory, whole kidney and single nephron glomerular filtration rates were normal in NSN rats despite histological evidence of glomerular injury, and despite a marked reduction in the glomerular capillary ultrafiltration coefficient to approximately one-third of normal. In the companion study (9), it was shown that in NSN rats the mean fractional clearances of neutral dextrans over the range of effective molecular radii from 18 to 42 A were reduced, compared to normla. In contrast, in the present study the mean fractional clearances for dextran sulfate over the same range of molecular radii were significantly greater than those found previously for normal Munich-Wistar rats. The fractional clearance of dextran sulfate molecules of the same molecular radius as serum albumin (approximately 36 A) was increased markedly, from 0.015 +/- 0.005 (SEM) in nonnephritic controls to 0.24 +/- 0.03 in NSN (P less than 0.001). The sialoprotein content of glomeruli, estimated by the colloidal iron reaction, was reduced in NSN rats as compared to normal controls. It is concluded that the abnormal filtration of anionic serum proteins, such as albumin, seen in glomerulopathies is, at least in part, the consequence of loss of fixed negative charges from the glomerular capillary wall.

Permselectivity of of the glomerular capillary wall. Studies of experimental glomerulonephritis in the rat using neutral dextran

Polydisperse [3h] dextran was infused into eight Munich-Wistar rats in the early autologous phase of nephrotoxic serum nephritis (NSN), thereby permitting direct measurements of pressures and flows in surface glomeruli and fractional clearances for dextrans [(U/P) dextran/(U/P) inulin] ranging in radius from 18 to 42 A. Despite glomerular injury, evidenced morphologically and by a marked reduction in the glomerular capillary ultrafiltration coefficient, the glomerular filtration rate remained normal because of a compensating increase in the mean net ultrafiltration pressure. In NSN rats, as in normal controls, inulin was found to permeate the glomerular capillary wall without measurable restriction, and dextrans were shown to be neither secreted nor reabsorbed. For dextran radii of 18, 22, 26, 30, 34, 38, and 42 A, (U/P) dextran/(U/P) inulin in NSN and control rats, respectively, averaged 0.90 vs. 0.99, 0.81 vs. 0.97, 0.63 vs. 0.83, 0.38 vs 0.55, 0.20 vs. 0.30, 0.08 vs. 0.11, and 0.02 vs. 0.03. Using a theory based on macromolecular transport through pores, the results indicate that in NSN rats, effective pore radius is the same as in controls, approximately 50 A. In NSN, however, the ratio of total pore surface area to pore length, a measure of the number of pores, is reduced to approximately 1/3 that of control, probably due to a reduction in capillary surface area. These results suggest that proteinuria in glomerular disease is not due simply to increases in effective pore radius or number of pores, as previously believed. Using a second theoretical approach, based on the Kedem-Katchalsky flux equations, dextran permeability across glomerular capillaries was found to be slightly lower, and reflection coefficient slightly higher in NSN than in control rats.

Correlation of 14C-griseofulvin metabolism in rat liver microsomes, isolated perfused rat livers, and in rats with bile duct cannulas

The metabolism of 14C-griseofulvin has been compared in rat liver microsomes, isolated perfused rat livers, and rats with bile duct cannulas. In all three preparations, 4-desmethylgriseofulvin and 6-desmethylgriseofulvin were the major metabolites. The ratio of total 4-desmethylgriseofulvin to 6-desmethylgriseofulvin formed was 1.20, 0.89, and 1.01 in liver microsomes, isolated perfused livers, and rats with bile duct cannulas, respectively. After a 7-min incubation with liver microsomes, most (96%) of the griseofulvin remained unchanged. Only small amounts of 4-desmethylgriseofulvin (1.26%) of dose) and 6-desmethylgriseofulvin (1.05% of dose) were formed. In isolated perfused liver, most of the drug (59% of dose) was excreted into bile within 4 hr, primarily as 4-desmethylgriseofulvin (24% of dose) and 6-methylgriseofulvin (24% of dose). In animals with bile duct cannulas, 65% of the dose was excreted into bile and 18% of the dose into urine within 4 hours. In bile, 32% of the dose was excreted as 4-desmethylgriseofulvin and 20% of the dose as 6-desmethylgriseofulvin, whereas in urine the drug was excreated predominantly as 6-desmethylgriseofulvin (13% of dose) with only a small amount of 4-desmethylgriseofulvin (1% of dose), during the first 4 hr. These results show that there is good correlation in the metabolic fate of 14C-griseofulvin in the liver microsomes, isolated perfused liver, and rats with bile duct cannulas. In addition to the similar ratio of 4-desmethylgriseofulvin to 6-desmethylgriseofulvin, there is also an agreement in the extent of metabolism and biliary excretion in isolated perfused liver and in rats with bile duct cannulas, which suggests that the isolated perfused liver is an important technique for studying drug metabolism in animals.

Permselectivity of the glomerular capillary wall: III. Restricted transport of polyanions

The clearance of albumin relative to that of inulin is greatly exceeded by that of uncharged dextrans of the same effective molecular radius (approximately 36A), less than 0.01 vs. 0.20 in normal hydropenic rats. This marked difference in fractional clearances of albumin and neutral dextran suggests that some factor in addition to molecular size retards the transglomerular passage of albumin. Since albumin is a polyanion in physiological solution, we tested the effect of charge on macromolecular permeability by infusing the anionic polymer, dextran sulfate (approximately 2.3 sulfate groups per glycosyl residue), into seven normal hypropenic Munich-Wistar rats. For dextran sulfate with an effective radius of approximately 36A, the fractional clearance was reduced essentially to that found for albumin (approximately 0.01). This enhanced restriction of dextran sulfate, relative to neutral dextran, was also noted for smaller and larger dextran sulfate molecules. These differences in the transport of dextran sulfate vs. dextran suggest electrostatic repulsion of charged macromolecules by some component of the glomerular capillary wall, perhaps the negatively charged sialoprotein which coats glomerular epithelial cells. Loss of this polyanionic coat, as has been reported to occur in proteinuric disorders, might thereby account for the enhanced transmural passage of albumin.

Permselectivity of the glomerular capillary wall to macromolecules. II. Experimental studies in rats using neutral dextran

To determine the permselectivity characteristics of the glomerular capillary wall, known molecular size fractions of [3H]dextran, prepared by gel chromatography, were infused into normally hydrated Wistar rats, thus permitting simultaneous measurement of Bowman's space/plasma water (BS/P) and urine/plasma water (U/P) concentration ratios, along with glomerular pressures and flows. Since (BS/P)inulin = 1.01 +/- 0.01 SE(n = 34, radius = approximately 14 A) and since (BS/P)dextran/(BS/P)inulin equaled (U/P)dextran/(U/P)inulin for dextrans ranging in molecular radius from 21 to 35 A, these findings validate that dextrans are neither secreted nor reabsorbed. For dextran radii of 20, 24, 28, 32, 36, 40, and 44 A, (U/P)dextran/(U/P)inulin averaged 0.99, 0.92, 0.69, 0.42, 0.19, 0.06, and 0.01, respectively. In accord with theoretical predictions that these fractional dextran clearances should vary appreciably with changes in glomerular transcapillary pressures and flows, an increase in glomerular plasma flow rate, induced in these same rats by plasma volume expansion, resulted in a highly significant lowering of fractional clearance of all but the smallest and largest dextrans studied. These findings emphasize that fractional solute clearances alone are inadequate to describe the permselective properties of the glomerular capillary wall unless glomerular pressures and flows are also known. This sensitivity of fractional dextran clearance to changes in plasma flow indicates that dextrans are transported across the capillary not only by bulk flow but also to an important extent by diffusion.

Mutagenic and cytotoxic activity of benzol[a]pyrene 4,5-, 7,8-, and 9,10-oxides and the six corresponding phenols

The benzo[a]pyrene 4,5-, 7,8-, and 9,10-oxides and the six corresponding phenols (4-, 5-, 7-, 8-, 9-, and 10-hydroxybenzo[a]pyrene) have been tested for mutagenic and cytotoxic activity in bacteria and in a mammalian cell culture system. Benzo[a]pyrene 4,5-oxide (K-region) was highly mutagenic in two histidine-dependent strains (TA1537 and TA1538) of Salmonella typhimurium which detect frameshift mutagens. In contrast, benzo[a]pyrene 7,8- and 9,10-oxides were less than 1% as mutagenic as the 4,5-oxide. Benzo[a]pyrene 7,8- and 9,10-oxides were unstable in aqueous media, whereas the 4,5-oxide was stable for several hours. This difference in stability could not account for the different mutagenic activities of the three arene oxides. The benzo[a]pyrene oxides were inactive in a strain (TA1535) that is reverted by base pair mutagens such as N-methyl-N'-nitro-N-nitrosoguanidine or in a strain (TA1536) that detects framshift mutagens similar to the acridine half-mustard ICR-191. Benzo-[a]-pyrene and the six phenols were all stable in aqueous media, but they had little or no mutagenic activity in any of the four Salmonella strains. Conversion of 8-azaguanine-sensitive Chinese hamster V79 cells to 8-azaguanine-resistant variants was increased by benzo[a]pyrene 4,5-oxide, whereas the 9,10-oxide was considerably less active. Benzo[a]pyrene and the other derivatives had little or no effect. Benzo[a]yrene 4,5-oxide was more cytotoxic to the Chinese hamster V79 cells than the 7,8- and 9,10-oxides, while 8-hydroxybenzo[a]pyrene was the most cytotoxic of the six phenols.