Effects of aging and caloric restriction on I-compounds in liver, kidney and white blood cell DNA of male Brown-Norway rats

The evolution of aging: a new approach to an old problem of biology

Most gerontologists believe aging did not evolve, is accidental, and is unrelated to development. The opposite viewpoint is most likely correct. Genetic drift occurs in finite populations and leads to homozygosity in multiple-alleled traits. Episodic selection events will alter random drift towards homozygosity in alleles that increase fitness with respect to the selection event. Aging increases population turnover, which accelerates the benefit of genetic drift. This advantage of aging led to the evolution of aging systems (ASs). Periodic predation was the most prevalent episodic selection pressure in evolution. Effective defenses to predation that allow exceptionally long lifespans to evolve are shells, extreme intelligence, isolation, and flight. Without episodic predation, aging provides no advantage and aging systems will be deactivated to increase reproductive potential in unrestricted environments. The periodic advantage of aging led to the periodic evolution of aging systems. Newer aging systems co-opted and added to prior aging systems. Aging organisms should have one dominant, aging system that co-opts vestiges of earlier-evolved systems as well as vestiges of prior systems. In human evolution, aging systems chronologically emerged as follows: telomere shortening, mitochondrial aging, mutation accumulation, senescent gene expression (AS#4), targeted somatic tissue apoptotic-atrophy (AS#5), and female reproductive tissue apoptotic-atrophy (AS#6). During famine or drought, to avoid extinction, reproduction is curtailed and aging is slowed or somewhat reversed to postpone or reverse reproductive senescence. AS#4-AS#6 are gradual and reversible aging systems. The life-extending/rejuvenating effects of caloric restriction support the idea of aging reversibility. Development and aging are timed by the gradual loss of cytosine methylation in the genome. Methylated cytosines (5mC) inhibit gene transcription, and deoxyribonucleic acid (DNA) cleavage by restriction enzymes. Cleavage inhibition prevents apoptosis, which requires DNA fragmentation. Free radicals catalyze the demethylation of 5mC while antioxidants catalyze the remethylation of cytosine by altering the activity of DNA methyltransferases. Hormones act as either surrogate free radicals by stimulating the cyclic adenosine monophosphate (cAMP) pathway or as surrogate antioxidants through cyclic guanosine monophosphate (cGMP) pathway stimulation. Access to DNA containing 5mC inhibited developmental and aging genes and restriction sites is allowed by DNA helicase strand separation. Tightly wound DNA does not allow this access. The DNA helicase generates free radicals during strand separation; hormones either amplify or counteract this effect. Caloric restriction slows or reverses the aging process by increasing melatonin levels, which suppresses reproductive and free radical hormones, while increasing antioxidant hormone levels. Cell apoptosis during CR leads to somatic wasting and a release of DNA, which increases bioavailable cGMP. The rapid aging diseases of progeria, the three diseases: (xeroderma pigmentosum (XP), Cockayne syndrome(CS), and ataxia telangiectasia (AT)), and Werner's syndrome are related to or caused by defects in three separate DNA helicases. The rapid aging diseases caused by mitochondrial malfunctions mirror those seen in XP, CS, and AT. Comparing these diseases allows for assignment of the different symptoms of aging to their respective aging systems. Follicle-stimulating hormone (FSH) demethylates the genes of AS#4, luteinizing hormone (LH) of AS#5, and estrogen of AS#6 while cortisol may act cooperatively with FSH and LH, and 5-alpha dihydrotestosterone (DHT) with FSH in these role. The Werner's DNA helicase links timing of the age of puberty, menopause, and maximum lifespan in one mechanism. Telomerase is under hormonal control. Most cancers likely result from malfunctions in the programmed apoptosis of AS#5 and AS#6. The Hayflick limit is reached primarily through loss of cytosine methylation of genes that inhibit replication. Men suffer the diseases of AS#4 at a higher rate than women who suffer from AS#5 more often. Adult mammal cloning suggests aging-related cellular demethylation, and thus aging, is reversible. This theory suggests that the protective effect of smoking and ibuprofen for Alzheimer's disease is caused through LH suppression.

Age-dependent increase of indigenous DNA adducts in rat brain is associated with a lipid peroxidation product

Indigenous DNA adducts (I-compounds) are considered to be a biomarker of aging tissues. Thus far, few studies have been conducted to investigate the accumulation patterns of I-compounds in the brain during aging. Particularly, identities of age-dependent I-compounds have largely remained unknown. In the current study, we have determined the amounts of I-compounds in the brains of male Fischer 344 rats at ages 1, 6, 12, 18, and 24 months using a 32P-postlabeling technique. The results indicate that I-compounds increase in the rat brain age dependently from 6 to 24 months of age. Total I-adduct levels (central and upper cutouts) increase 3.5-fold from 6 to 24 months. Contrary to the results of other investigators, brains of 1-month-old rats contain the highest level of I-compounds, which may be due to the hypermetabolic status during the infant period. In an effort to characterize I-compounds, different deoxynucleosides were coincubated with malondialdehyde (MDA). The results show that only deoxyguanosine (dGMP)-MDA adducts overlap with I-compounds of the rat brain DNA adducts map. A total of five dGMP-MDA adducts have been identified as responsible for I-compounds in brain tissues. It is known that brain tissue contains high levels of lipids that are susceptible to oxygen free radicals and that MDA is the most abundant and genotoxic product of lipid peroxidation. The present study provides supporting evidence that lipid peroxidation and its product (MDA) may play an important role in endogenous brain DNA modification, which may partly contribute to cerebral aging and age-related degenerative disorders of the brain. The accumulation of I-compounds with aging may serve as an index of indirect oxidative damage to DNA as evidenced by the presence of MDA-DNA adducts.

Rapid decreases in indigenous covalent DNA modifications (I-compounds) of male Fischer-344 rat liver DNA by diquat treatment

I-compounds are indigenously appearing covalent DNA modifications that can be detected by 32P-postlabeling assay in tissues of normal animals without known exposure to any carcinogens or toxins. Although these compounds have not been structurally identified, indirect evidence from earlier work suggested the possibility of involvement of molecular fragments derived from lipid peroxides. Diquat is a herbicide that stimulates lipid peroxidation and massive intrahepatic oxidant stress through redox cycling-mediated generation of reactive oxygen species. In the present study, we examined the effects of diquat on hepatic I-compounds of male Fischer-344 rats. Two groups of rats, approximately 14 weeks and 8 weeks old, were given a hepatotoxic dose (0.1 mmol/kg) of diquat or equal volumes of saline, i.p. Two and 6 h later plasma alanine aminotransferase (ALT) activities were measured and hepatic DNA I-compound levels were examined by nuclease P1-enhanced 32P-postlabeling. Elevated ALT activities were observed in some animals in both groups, at both time points, but considerable inter-animal variation was seen. A total of 15-16 I-compound fractions were measured in control and in diquat-treated animals, but no extra spots indicative of treatment-induced adducts were detected. Despite the qualitative similarities, the quantities of individual I-compounds were markedly decreased at 2 h in diquat-treated animals of both age groups. In 14 week old rats the hepatic I-compound contents were decreased at 2 h by 22-59%, which was statistically significant (ANOVA, P < 0.05) for all of the 9 polar I-compound fractions and none of the non-polar fractions. Eleven I-spots from this group showed significant negative linear correlations (P < 0.05) with ALT values. In 8 week old rats treated with diquat a 22-43% depletion in I-compound contents was statistically significant for 4 of the 7 nonpolar and 2 of the 8 polar adduct fractions, but there was no significant correlation of I-compound contents with ALT values at the 2 h time point. By 6 h most of the I-spot levels had returned to normal or above normal values in both groups of animals. While most I-spots from 14 week old rats did not correlate with ALT levels at 6 h, two I-spots displayed positive correlations in the 8 week group. Overall, the susceptibility to diquat-associated DNA alterations appeared to differ with age.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of dietary restriction on DNA repair and DNA damage

Dietary restriction is the only experimental manipulation known to extend lifespan and retard aging in mammals. Therefore, it is a powerful tool for identifying cellular processes that are involved in aging and senescence. Recently, several laboratories have begun to examine the effects of dietary restriction on the integrity of the genome and the ability of cells to repair DNA. In most studies, it was found that the repair of DNA damage, as measured by unscheduled DNA synthesis, was significantly higher in cells isolated from rodents fed calorie-restricted diets compared to cells isolated from rodents fed ad libitum. Dietary restriction also was observed to be associated with a reduction of the levels of certain types of DNA damage; however, preliminary experiments suggest that the effect of dietary restriction on the age-related accumulation of DNA damage depends on the type of DNA damage studied.

Biomarkers of aging: correlation of DNA I-compound levels with median lifespan of calorically restricted and ad libitum fed rats and mice

I-compounds are species-, tissue-, genotype-, gender-, and diet-dependent bulky DNA modifications whose levels increase with animal age. While a few of these DNA modifications represent oxidation products, the majority of I-compounds appear to be derived from as yet unidentified endogenous DNA-reactive intermediates other than reactive oxygen species. Circadian rhythms of certain I-compounds in rodent liver imply that levels of these DNA modifications are precisely regulated. Caloric restriction (CR), the currently most effective method available to retard aging and carcinogenesis, has been previously shown to elicit significant elevations of I-compound levels in tissue DNA from Brown-Norway (BN) and F-344 rats as compared to age-matched ad libitum fed (AL) animals. The present investigation has extended this work by examining liver and kidney DNA I-compound levels in three genotypes of rats (F-344, BN, and F-344 x BN) and two genotypes of mice (C57BL/6N and B6D2F1) under identical experimental conditions in order to determine whether correlations exist between I-compound levels, measured in middle-aged animals, and median lifespan. Levels of a number of liver and kidney I-compounds were found to display genotype- and diet-dependent, statistically significant positive linear correlations with median lifespan in both species. In particular, the longer-lived hybrid F-344 x BN rats and B6D2F1 mice tended to exhibit higher I-compound levels than the parent strains. CR enhanced I-compound levels substantially in both rats and mice. Thus, I-compounds, measured at middle age, reflected the functional capability ('health') of the organism at old age, suggesting their predictive value as biomarkers of aging. The positive linear correlations between levels of certain I-compounds (designated as type I) and lifespan suggest that these modifications may be functionally important and thus not represent endogenous DNA lesions (type II), whose levels would be expected to correlate inversely with lifespan.

Effects of polychlorinated dibenzofurans on compounds in hepatic DNA of female Sprague-Dawley rats: structure dependence and mechanistic considerations

Previous work indicated that covalent age-dependent DNA modifications of endogenous origin termed I-compounds may represent useful biomarkers for tumor promotion/carcinogenesis, as various tumor promoters/carcinogens, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and phenobarbital, reduce rat I-compound levels in liver, the target organ. The present study addressed the question as to whether polychlorinated dibenzofurans (PCDFs), which are related to TCDD and its congeners with regard to their toxic and biochemical properties, would also affect hepatic I-compound patterns and levels, and whether such effects would be chemical structure-dependent. Female Sprague-Dawley rats were treated once a week with a single dose (100 micrograms/kg) of 1,2,3,7,8-pentachlorodibenzofuran (1,2,3,7,8-PeCDF), 1,2,4,7,8-PeCDF, 2,3,4,7,8-PeCDF, or 2,3,4,6,7,8-hexachlorodibenzofuran (2,3,4,6,7,8-HeCDF) for 4 weeks and liver DNA was analyzed at the end of the last week by 32P-postlabeling assay. No carcinogen-DNA adducts were detected; however, levels of both non-polar and polar I-compounds were reduced in a structure-dependent manner. Potencies increased in the order, control (100%, 122 modifications in 10(9) DNA nucleotides = 1,2,4,7,8-PeCDF (104%) < 1,2,3,7,8-PeCDF (80%) < 2,3,4,7,8-PeCDF (61%) and 2,3,4,6,7,8-HeCDF (61%). Structure-activity relationships for total I-compounds, therefore, paralleled those reported for Ah receptor agonist activity, i.e., compounds that exhibit high cytosolic Ah receptor binding affinities and are also potent inducers of aryl hydrocarbon hydroxylase activity (1,2,3,7,8-PeCDF, 2,3,4,7,8-PeCDF, and 2,3,4,6,7,8-HeCDF) were active, while 1,2,4,7,8-PeCDF, which is a less potent Ah receptor agonist, was inactive. Polar I-compounds responded to a greater extent than did non-polar ones and, in general, individual I-compounds were affected differentially, thus decreased formation or increased removal of I-compounds played a role in the observed effects of the toxins on DNA. It is proposed that Ah receptor-mediated enzyme induction, particularly of cytochrome P450, is involved in reduced hepatic I-compound formation and that subnormal I-compound levels may contribute to tumor promotion.

Bulky DNA-adduct formation induced by Ni(II) in vitro and in vivo as assayed by 32P-postlabeling

Various small oxidation products (e.g. 8-hydroxydeoxyguanosine) can be induced in DNA by nickel compounds. In this study, the 32P-postlabeling assay was applied to determine whether Ni(II) compounds are able to induce bulky DNA-adduct formation in vitro and in vivo. In vitro studies detected two major and several minor adducts in DNA incubated with NiCl2 and H2O2 at 37 degrees C for 1 h. Formation of the two major adducts increased with incubation time (0-24 h) and NiCl2 concentration (0-800 microM). Adduct levels were greatly reduced by hydroxyl free-radical scavengers, i.e. 0.4 M sodium formate or 0.05 M p-nitrosodimethylaniline, and by a singlet oxygen scavenger, 0.05 M sodium azide. The in vitro effects of NiCl2 on DNA were significantly enhanced by (1) addition of 3 mM ascorbic acid, (2) replacement of H2O with D2O in the reaction, and (3) prior denaturation of DNA. Adduct formation presumably involved a Fenton-type reaction, in which DNA crosslinks may arise by reaction with hydroxyl free radicals and singlet oxygen. For in vivo studies, male 6-8 wk old B6C3F1 mice were used. In untreated mice, several I-compounds (putative indigenous DNA modifications that increase with age) were detected in liver, kidney, and lung. Two of these (spots 1 and 2) were chromatographically identical to the two major spots induced by Ni(II) in vitro. The intensities of spots 1 and 2 in kidney and of some other spots in liver and lung were increased 1 and 2 h after i.p. injection with a single dose of 170 mumols/kg NiAc2. The effects of NiAc2 were reduced or undetectable in the three tissues 24 h after treatment. These observations indicate the capacity of Ni(II) to induce and modulate bulky DNA modifications both in vitro and in vivo.

Enhancement of age-related increases in DNA I-compound levels by calorie restriction: comparison of male B-N and F-344 rats

Caloric restriction (CR), known to extend median and maximum life spans, improve resistance to carcinogenesis, and significantly retard age-associated degenerative diseases in rodents, was previously reported to modulate levels of indigenous, age-dependent DNA modifications, called I-compounds, in male Brown-Norway (B-N) rats. Since profiles of these adduct-like derivatives are species-, strain-, sex-, and tissue-specific, we explored this apparent CR/I-compound relationship in a comparative study between male B-N and male Fischer 344 (F-344) rats, the latter having a shorter life expectancy and high incidence of renal disease. Control animals were fed NIH-31 diet ad libitum (AL), while the caloric intake of CR animals was limited to 60% of AL, starting at 3.5 months. Liver and kidney DNA from 1, 8, 12, 16, 24 (AL, CR), and 30 (CR only) month old rats was analyzed by 32P-postlabeling. Corresponding tissues from the two strains yielded similar DNA profiles. Total liver I-compound levels displayed 2.3-4.6-fold age-dependent increases from 1 to 24 months, and kidney values at 24 months were 5.2-8 times higher than those at 1 month. In both strains, I-compound levels of CR animals were higher, up to 2-fold, than in age-matched AL rats. Regression analyses indicated linear relationships between most CR relative adduct labeling values (both total and individual fractions) and age, whereas many AL values exhibited this type of link with log age. These findings confirm that a correlation exists between CR and I-compound levels, and, given the above physiological benefits of CR, indicate that I-compounds represent biomarkers of aging with potential utility in intervention studies.

Circadian rhythm of covalent modifications in liver DNA

32P-postlabeling analysis recently revealed that in addition to 5-methylcytosine, mammalian DNA contains covalently modified nucleotides of unknown structures and functions termed I-compounds whose levels increase with age. I-compound levels, in addition, depend on species, strain, sex, tissue, and diet and are generally lowered by carcinogen exposure. As shown here, levels of several non-polar I-compounds in liver DNA of untreated male C3H mice were elevated 2 to 8.5 times at 1800 h and 2400 h as compared to 0600 h and 1200 h, while polar I-compounds and persistent carcinogen-DNA adducts induced by safrole were unaffected by time of day. In liver DNA of male F-344 rats 4 non-polar I-compounds and 4 polar I-compounds showed significant circadian rhythm at 2000 h compared to 0800 h. This novel circadian variation of DNA structure implies mechanisms precisely regulating I-compound levels in vivo and may conceivably be linked to diurnal differences of DNA synthesis and gene expression.

Oat lipids-induced covalent DNA modifications (I-compounds) in female Sprague-Dawley rats, as determined by 32P-postlabeling

Previous studies have shown that the presence of oats in the diet contributes to formation of I-compounds (age-dependent covalent DNA modifications detected by 32P-postlabeling assay) in female Sprague-Dawley rat liver DNA. The current study explored the possible ingredients in oats responsible for the observed effects on DNA. Feeding AIN-76A diet containing 5% oat lipids (obtained by methanol extraction and dissolved in trioctanoin) in place of corn oil for 2 months successfully induced the formation of 3 oats-specific (spots 2-4) and 4 natural ingredient diet-specific I-compounds (spots 6-9) in liver DNA. Barley, an oatlike cereal, induced 3 of these spots at very low intensities but not the 3 oats-specific I-spots. Oral administration of oat lipids to weanling rats of both sexes for 7 days elicited trace amounts of the oats-specific spots and spot 9 in liver DNA. However, when oat lipids were given at 6 or 9 weeks of age, the oats-specific spots were detected at high levels in female but not in male rats. These oats-related DNA modifications were also present in 6-week-old female rats which had received oat lipids p.o. for 2 or 3 days or i.p. for 4 days. Rats given trioctanoin or extracts from natural ingredient Wayne diet (lacking oats) did not show any of these spots. On the other hand, rats treated with extracts from an oats-containing Teklad diet displayed a trace amount of one of these I-compounds. Oat lipids did not induce any extra spots in rat kidney DNA. Feeding of AIN diet supplemented with oats to female Syrian hamsters did not elicit any renal or hepatic DNA alterations, as detected by 32P-postlabeling. Rats fed oat lipids-supplemented AIN diet or Purina diet showed the highest levels of I-compounds overall in liver among all dietary groups and these two groups also had significantly higher hepatic DNA synthesis rates. Oat lipids enhanced kidney DNA synthesis also. The total hepatic or renal cytochrome P-450 contents were not significantly affected by different diets. These results demonstrate a novel link between a natural dietary ingredient and covalent DNA modifications and shed light on the origins of certain I-compounds.

Exogenous and endogenous DNA modifications as monitored by 32P-postlabeling: relationships to cancer and aging

32P-postlabeling analysis, a highly sensitive method for the detection and measurement of covalent carcinogen-DNA adducts and other DNA modifications, does not require radioactive test substances and, therefore, can be applied to DNA of mammals, including humans exposed to low doses of environmental or occupational genotoxicants. The basic procedure entails the enzymatic incorporation of 32P-label into hydrolysis products of DNA, followed by chromatographic mapping and autoradiography of the 32P-labeled digestion products and quantitative scintillation spectrometry. Microgram amounts of DNA are analyzed: Thus the assay is suited for limited amounts of cells or tissues. Various versions of the assay afford different sensitivities of adduct detection. A single aromatic or bulky/hydrophobic adduct in 10(8)-10(10) nucleotides can be detected and measured (corresponding to 0.3-30 amol adduct/micrograms DNA or 0.1-10 nmol adduct/mol DNA-P). In animal models, the assay has been successfully applied to a variety of mutagenic (genotoxic) as well as nonmutagenic carcinogens. In humans, DNA specimens from cigarette smokers, iron foundry workers, and coke oven workers whose total aromatic adduct levels ranged from 1 adduct in 10(6)-10(8) DNA nucleotides have been examined by 32P-postlabeling. The assay also detects DNA modifications--Indigenous (I)-compounds--that increase with age in untreated animals. I-compound profiles and levels are highly species-, strain-, sex-, and tissue-specific, and also depend on diet composition. Caloric restriction, a highly efficient method for improving resistance to carcinogenesis and extending life span, increased rather than decreased I-compound levels in various tissues of male rats. Nonmutagenic hepatocarcinogens reduced levels of I-compounds in the target organ. Because of the specificity of this effect, reduction of I-compound levels appears to represent a novel biomarker for the action of nonmutagenic carcinogens. DNA from various hepatomas was found largely devoid of I-compounds. The results support a possible antineoplastic and antiaging role of these DNA modifications.

Modulation of DNA modification (I-compound) levels in rat liver and kidney by dietary carbohydrate, protein, fat, vitamin, and mineral content

I-compounds are DNA modifications detected by 32P-postlabeling that increase with age in rodents without known carcinogen exposure. Diet type (natural ingredient versus purified) greatly influences patterns and levels of I-compounds. To test the hypothesis that I-compound formation is affected, also, by dietary macro- and micronutrients, effects of carbohydrate, protein, fat, vitamin, and mineral content on rat liver and kidney I-compounds were determined. Female Sprague-Dawley rats were fed basic or modified AIN-76A purified diets for 3-6 months. High protein (HP) diet (50%, w/w) increased I-compound levels in liver but not kidney. High carbohydrate (HC) diet (78%) produced a significant increase in the polar as well as total I-compound levels in both tissues. High fat diets (20%) elicited significantly lower levels of liver I-compounds than HC, HP, and basic diets. There were few significant differences between high polyunsaturated (safflower oil) and saturated fat (lard) diet groups. No qualitative differences in I-compound profiles were observed in either tissue. In rats fed basic diet supplemented with vitamins and/or minerals, increased vitamin content reduced the levels of polar I-compounds in liver. No extra diet-induced adducts were observed; all effects were of a quantitative nature. These data provide direct evidence that nutrients significantly influence I-compound levels and support the hypothesis that normal metabolism of nutrients leads to the production of small amounts of DNA-reactive electrophiles. These observations suggest a novel mechanism where nutrient composition of the diet may play a role in development of neoplasia and other adverse health effects.

Sex-specific modulation of hepatic covalent DNA modifications (I-compounds) by the cytochrome P450 inducer, pregnenolone-16 alpha-carbonitrile

I-compounds are recently discovered, age-dependent covalent DNA modifications, which are detectable by 32P-postlabeling assay for DNA adducts. The effects of the catatoxic antiglucocorticoid, pregnenolone-16 alpha-carbonitrile (PCN), on hepatic and renal I-compound levels have been studied in male and female Sprague-Dawley rats together with the levels of microsomal cytochrome P450 and rates of ethylmorphine N-demethylation. PCN (50 mg/kg ip) was dissolved in corn oil and administered to rats once daily for 4 days, and animals were killed at 1 day or 8 days after the last treatment. Hepatic and renal I-compounds were analyzed by 32P-postlabeling in control and PCN-treated animals at both time points. Microsomal cytochrome P450 and ethylmorphine N-demethylase activities were also determined. Total levels of liver nonpolar and polar I-compounds were reduced in female rats by 37 and 51%, respectively, compared to controls, at 1 day. Ten out of sixteen individual I-compounds were also markedly reduced in female rat liver DNA as a result of PCN administration. In contrast to females, total levels of liver I-compounds were not significantly altered in males by PCN at 1 day; however, two individual I-compounds were lowered. I-compound levels recovered 8 days after termination of PCN treatment in both males and females. Total levels of renal I-compounds were not affected by PCN treatment in either males or females. [3H]Methylthymidine incorporation studies showed an increase in mean DNA synthesis rate at 1 day in liver of both males and females, but this was significant in males only. Marked induction of hepatic microsomal cytochrome P450 (2.2-fold) and ethylmorphine N-demethylase (4.0-fold) activity was observed in female rats treated with PCN at 1 day as compared to controls. The extent of induction of these enzymes was much higher in females than males. At 8 days the levels of cytochrome P450 and ethylmorphine N-demethylase activity had returned to uninduced values. The results are consistent with a pivotal role for PCN-inducible cytochrome P450 in the metabolism of I-compounds.

Natural dietary ingredients (oats and alfalfa) induce covalent DNA modifications (I-compounds) in rat liver and kidney

Mammalian tissue DNA has recently been found, via 32P postlabeling, to contain complex profiles of age-dependent bulky carcinogen adductlike covalent modifications, which have been termed I-compounds, referring to their apparent indigenous origin without exposure to exogenous carcinogens. I-compound patterns are highly species, sex, tissue, and diet specific. As shown here, the presence of certain plant ingredients in diet, i.e., ground oats and alfalfa meal, significantly contributed to the formation of these DNA derivatives. Six groups of weanling female Sprague-Dawley rats were fed one of the following diets for three months: a natural ingredient diet containing neither oats nor alfalfa (Wayne MRH 22/5 Rodent Blox), Wayne diet supplemented with oats or alfalfa or both, a purified semisynthetic diet (AIN-76A), and AIN diet supplemented with oats. The natural ingredient diet produced more complex patterns and higher levels of I-compounds than purified diet in both liver and kidney DNA. Supplementation of either diet with oats elicited the formation of four additional oats-specific I-compounds in liver DNA. Oats and alfalfa, individually and in combination, tended to significantly raise nonpolar and diminish polar I-compound levels. To determine whether the oats-related extra spots were derived from mycotoxin contamination, two groups of rats were fed either Wayne diet or Wayne diet containing zearalenone (0.05 mg/kg) for three weeks. Zearalenone significantly increased the uterine weight but did not induce any DNA adduct formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term effects of the tumor promoting polychlorinated biphenyl mixture, Aroclor 1254, on I-compounds in liver, kidney and lung DNA of male Sprague-Dawley rats

The effects of a tumor promoting polychlorinated biphenyl mixture, Aroclor 1254, on I-compounds (tissue, species and sex dependent DNA modifications that increase with age in untreated rodents) were studied by 32P-postlabeling in male Sprague-Dawley rat liver, kidney, and lung DNA. Aroclor 1254 was dissolved in corn oil and intraperitoneally (i.p.) injected (2 x 500 mg/kg, 2 weeks apart) into 3-month-old rats. Control rats were given corn oil. Groups of 3 animals were sacrificed at 2 and 6 weeks after the second injection of corn oil or Aroclor 1254. At both time points Aroclor 1254-treated rats had significantly lower body weights and higher liver weights while kidney and lung weights were unaffected. Thymidine incorporation into liver and lung DNA was significantly increased at both time points, while kidney DNA showed a small decrease at 2 weeks. Treatment resulted in significant reductions (ranging from 29 to 100%) of each of nine liver I-spots at 2 and 6 weeks. In treated rats there was no decrease in kidney I-spots at 2 weeks, while the levels of only two out of ten kidney spots were reduced by 42-91% at 6 weeks. At 2 weeks three out of seven and at 6 weeks four out of seven lung I-spots were lowered by 51-100% in the Aroclor 1254-treated rats. Thus the effects decreased in the order liver greater than lung greater than kidney. Since Aroclor 1254 has been reported to be a tumor promoter in liver and lung but not kidney, these results suggest a correlation between organ specific promotion of carcinogenesis by Aroclor 1254 and the reduction of DNA I-compounds.