Intestinal absorption and metabolism of hydrocarbons

Pharmacokinetics of Anthraquinones from Medicinal Plants

Anthraquinones are bioactive natural products, some of which are active components in medicinal medicines, especially Chinese medicines. These compounds exert actions including purgation, anti-inflammation, immunoregulation, antihyperlipidemia, and anticancer effects. This study aimed to review the pharmacokinetics (PKs) of anthraquinones, which are importantly associated with their pharmacological and toxicological effects. Anthraquinones are absorbed mainly in intestines. The absorption rates of free anthraquinones are faster than those of their conjugated glycosides because of the higher liposolubility. A fluctuation in blood concentration and two absorption peaks of anthraquinones may result from the hepato-intestinal circulation, reabsorption, and transformation. Anthraquinones are widely distributed throughout the body, mainly in blood-flow rich organs and tissues, such as blood, intestines, stomach, liver, lung, kidney, and fat. The metabolic pathways of anthraquinones are hydrolysis, glycuronidation, sulfation, methylation/demethylation, hydroxylation/dehydroxylation, oxidation/reduction (hydrogenation), acetylation and esterification by intestinal flora and liver metabolic enzymes, among which hydrolysis, glycuronidation and sulfation are dominant. Of note, anthraquinones can be transformed into each other. The main excretion routes for anthraquinones are the kidney, recta, and gallbladder. Conclusion: Some anthraquinones and their glycosides, such as aloe-emodin, chrysophanol, emodin, physcion, rhein and sennosides, have attracted the most PK research interest due to their more biological activities and/or detectability. Anthraquinones are mainly absorbed in the intestines and are mostly distributed in blood flow-rich tissues and organs. Transformation into another anthraquinone may increase the blood concentration of the latter, leading to an increased pharmacological and/or toxicological effect. Drug-drug interactions influencing PK may provide insights into drug compatibility theory to enhance or reduce pharmacological/toxicological effects in Chinese medicine formulae and deserve deep investigation.

Association of metabolites with obesity based on two gene variants, MC4R rs17782313 and BDNF rs6265

Previous genome-wide association analyses for obesity related genes demonstrated the association of BDNF gene variant rs6265 and MC4R gene variant rs17782313 with body mass index (BMI). However, the associated metabolite pathways are still behind the curtain. The aim of the current study is to investigate the associations of metabolic changes in obesity with MC4R gene variant rs17782313 and BDNF variant rs6265. Gas chromatography-mass spectrometry based untargeted metabolomics approach was used and 42 identified serum metabolites were selected for statistical analyses. Significant association of seven metabolites with MC4R gene variant rs17782313 based on obesity and thirty metabolites with obesity dependent BDNF variant rs6265 using additive model (adjusted p < 0.05) was observed. This study highlights the importance of alteration of fatty acid biosynthesis, probably due to high consumption of fats may cause to develop obesity. But obesity is a complex disorder and the full clarification of this complex machinery is still distant. To understand the obesity in a better way, more studies are required to identify remaining metabolites and also mechanism of these metabolic entities.

Mineral oil in food, cosmetic products, and in products regulated by other legislations

For a few years, mineral oils and their potential adverse health effects have been a constant issue of concern in many regulatory areas such as food, cosmetics, other consumer products, and industrial chemicals. Analytically, two fractions can be distinguished: mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH). This paper aims at assessing the bioaccumulative potential and associated histopathological effects of MOSH as well as the carcinogenic potential of MOAH for consumer-relevant mineral oils. It also covers the absorption, distribution, metabolism, and excretion of MOSH and MOAH upon oral and dermal exposures. The use and occurrence of consumer-relevant, highly refined mineral oils in food, cosmetics and medicinal products are summarized, and estimates for the exposure of consumers are provided. Also addressed are the challenges in characterizing the substance identity of mineral oil products under REACH. Evidence from more recent autopsy and biopsy studies, along with information on decreasing food contamination levels, indicates a low risk for adverse hepatic lesions that may arise from the retention of MOSH in the liver. With respect to MOAH, at present there is no indication of any carcinogenic effects in animals dermally or orally exposed to highly refined mineral oils and waxes. Such products are used not only in cosmetics but also in medicinal products and as additives in food contact materials. The safety of these mineral oil-containing products is thus indirectly documented by their prevalent and long-term use, with a simultaneous lack of clinical and epidemiological evidence for adverse health effects.

Evaluating the risk to humans from mineral oils in foods: Current state of the evidence

Key issues around the evaluation of risks to humans from mineral oils in food and feedstuffs are discussed. MOHs (MOAH and MOSH) occur in food due to intentional use, contamination from environmental sources and during transport/processing, or through migration from food contact materials. Problems in setting and enforcing human health guidelines for MOH include uncertainty around MOH toxicity and the specialist expertise needed for analysis of complex food matrices. Currently, the method of choice for measuring mineral oils is LC-GC-FID, however some complex food matrices also require additional analytical techniques to differentiate between some naturally occurring hydrocarbons and those from other sources, including of petrogenic origin. This requires the skills of an experienced analyst. Significant toxicological gaps for MOHs prevent robust human health risk assessment and the derivation of guidance values. As food-grade mineral oils are virtually MOAH-free, the key issue explored here is the relevance to humans of liver (micro)granulomas observed in F344 rats following oral intake. Available data suggest that despite the ubiquitous nature of MOH in the human diet, the prevalence of liver lipogranulomas in the population is low. These are not associated with inflammation and based on current evidence are not considered of human health significance.

Ecotoxicity evaluation and human risk assessment of an agricultural polluted soil

The present study aims to evaluate the nature and level of chemical pollution as well as the potential toxicity and ecotoxicity of an agricultural soil irrigated by the water of Litani River. Our findings showed that the soil was mainly contaminated by alkanes (hentriacontane, octadecane, hexadecane) and metal trace elements (nickel, vanadium, chromium, and manganese). Soil organic extracts showed high cytotoxicity against human hepatic (HepG2) and bronchial epithelial cells (Beas-2B). Soil ecotoxicity was revealed by seed germination inhibition of several plant species (wheat, clover, alfalfa, tall fescue, and ryegrass) ranging from 7 to 30% on the polluted soil compared to non-polluted one. In addition, significant decreases in telluric microbial biomasses (bacterial and fungal biomasses), quantified by phospholipid fatty acids (PLFA) analysis were observed in polluted soil compared to non-contaminated soils. The density of the arbuscular mycorrhizal fungal (AMF) spores isolated from the polluted soil was about 316 spores/100 g. Three main AMF species were identified as Funelliformis mosseae, Septoglomus constrictum, and Claroideoglomus lamellosum. Moreover, 16 indigenous plant species were inventoried with Silybum marianum L. as the dominant one. Plant biodiversity indices (Shannon, Simpson, Menhinick, and Margaleff) were lower than those found in other contaminated soils. Finally, it was found that all the present plant species on this polluted site were mycorrhized, suggesting a possible protection of these plants against encountered pollutants, and the possibility to use AMF-assisted phytoremediation to clean-up such a site.

Suitability of n-alkanes and chromium (III) oxide as digestibility markers in calves at the end of the milk feeding period supplemented with a prebiotic

Prebiotics reveal positive effects on the growth performance of pigs and poultry, and might influence intestinal microflora. This, in consequence, could alter recovery rates of digestibility markers. In the current study, we evaluated the suitability of chromium (III) oxide (Cr₂O₃) and the synthetic alkanes n-dotriacontane (C32) and n-hexatriacontane (C36) as external markers for digestibility estimation compared with the standard total collection method in calves supplemented with galacto-oligosaccharides. Eight male German Holstein calves (average age ± SD = 57 ± 8 days) were divided into 2 milk replacer feeding groups (group receiving galacto-oligosaccharides [A] and control group [B]). Each of 2 groups of 4 individually fed calves received a distinct milk replacer with added markers for 14 days. They were fed twice daily restrictively with milk replacer, concentrate and hay. After an adaptation period of 10 days, total faeces were collected. Faecal marker recoveries (FMR, means ± SD) for C32 were (72 ± 14)% for A and (80 ± 12)% for B. Faecal marker recoveries for C36 was (82 ± 15)% and (88 ± 13)% for groups A and B, respectively. The FMR for Cr₂O₃ was (102 ± 11)% and (100 ± 1)% for groups A and B, respectively. There were no significant differences between total collection organic matter digestibility and marker based organic matter digestibility when using Cr₂O₃ and C36. But, when utilizing C32 to calculate nutrient digestibilities, results differed from the total collection method for organic matter, crude protein and ether extract. The results indicate that Cr₂O₃ and C36 can be applied in digestibility studies with calves and give accurate estimates for OM and nutrient digestibilities without correction for FMR.

Importance of Dermal Absorption of Polycyclic Aromatic Hydrocarbons Derived from Barbecue Fumes

Despite the ubiquity and carcinogenicity of polycyclic aromatic hydrocarbons (PAHs), their dermal absorption for the general population has not been adequately addressed. Aiming to verify the importance of dermal absorption of PAHs, barbecue (BBQ) in Guangzhou, China was chosen as a case study. Urine samples were collected and analyzed for nine hydroxyl (OH)-PAHs. Air, food, and cotton clothing samples were analyzed for 16 PAHs. Dietary exposure was the dominant exposure route with the greatest amounts of OH-PAH excretion and PAH intake. Dermal intake of low molecular-weight PAHs was greater than inhalation intake from the occurrence of atmospheric PAHs. In addition, the net excreted amounts of OH-naphthalene, OH-fluorene, OH-phenanthrene, and OH-pyrene via dermal absorption were 367, 63, 98, and 28 ng, respectively, upon 2.5-h exposure, comparable to those via combined dermal and inhalation exposure, which were 453, 98, 126, and 38 ng. The ratios of excretion to intake via dermal absorption were 0.11, 0.036, and 0.043 for fluorene, phenanthrene, and pyrene, respectively, lower than the ratios from dietary exposure (0.38, 0.14, and 0.060) but higher than the ratios from inhalation (0.097, 0.016, and 0.025). In the case of BBQ fumes, dermal absorption was a more important pathway for intake of low molecular-weight PAHs than inhalation.

Mineral oil saturated hydrocarbons (MOSH) in female Fischer 344 rats; accumulation of wax components; implications for risk assessment

Female Fischer 344 rats were exposed to three MOSH mixtures: oils largely below and above C₂₅ (S-C25 and L-C25) and a 1:1 mixture of L-C25 with a wax; doses of 400, 1000 and 4000mg/kg feed were administered during 120days. MOSH were determined by on-line HPLC-GC-FID in liver, spleen, adipose tissue and the carcass. The composition of the hydrocarbons accumulated in the tissues was further analyzed by comprehensive two-dimensional GC (GC×GC). MOSH in the mass range of C_26-30 were more strongly accumulated than those between C_20-25, which does not support the present classification of MOSH differentiating at n-C₂₅ for risk assessment. Compared to the total of the MOSH, n-alkanes and n-alkyl monocyclic naphthenes were generally enriched in adipose tissue. In liver and spleen, n-alkanes up to C₂₅ were eliminated, but strongly accumulated at around C₃₀. Based on this profile, poor solubility and the melting points, it is hypothesized that crystallization protects these wax components against metabolism and elimination. In the liver, relative retention of n-alkanes decreased again beyond C₃₀, accentuated at high exposure, suggesting reduced absorption. Compared to the animal data, accumulation of n-alkanes from food sources, such as apples, into human tissues seems low, perhaps because of low absorption due to their presence in crystalline form. A series of dominant isoalkanes, accumulated in all tissues analyzed, was characterized, though without proposing a structure. Implications on present regulation of white mineral oil products are discussed.

The hOGG1 Ser326Cys polymorphism contributes to digestive system cancer susceptibility: evidence from 48 case-control studies

The Ser326Cys polymorphism in the human 8-oxogunaine DNA glycosylase (hOGG1) gene had been implicated in cancer susceptibility. Studies investigating the associations between the Ser326Cys polymorphism and digestion cancer susceptibility showed conflicting results. Therefore, a meta-analysis was performed to derive a more precise estimation of the relationship. We conducted a meta-analysis of 48 studies that included 12,073 cancer cases and 19,557 case-free controls. We assessed the strength of the association using odds ratios (ORs) with 95% confidence intervals (CIs). In our analysis, the hOGG1 Ser326Cys polymorphism was significantly associated with the risk of digestive system cancers (Cys/Cys vs. Ser/Ser: OR = 1.17, 95% CI = 1.00-1.35, P < 0.001; Cys/Cys vs. Cys/Ser + Ser/Ser: OR = 1.14, 95% CI = 1.00-1.29, P < 0.001). In subgroup analyses by cancer types, we found that the hOGG1 Ser326Cys polymorphism may increase hepatocellular cancer and colorectal cancer risks, but decrease the risk of oral cancer. These findings supported that hOGG1 Ser326Cys polymorphism may contribute to the susceptibility of digestive cancers.

Identifying molecular targets of lifestyle modifications in colon cancer prevention

One in four deaths in the United States is cancer-related, and colorectal cancer (CRC) is the second leading cause of cancer-associated deaths. Screening strategies are utilized but have not reduced disease incidence or mortality. In this regard, there is an interest in cancer preventive strategies focusing on lifestyle intervention, where specific etiologic factors involved in cancer initiation, promotion, and progression could be targeted. For example, exposure to dietary carcinogens, such as nitrosamines and polycyclic aromatic hydrocarbons influences colon carcinogenesis. Furthermore, dietary deficiencies could alter sensitivity to genetic damage and influence carcinogen metabolism contributing to CRC. High alcohol consumption increases the risk of mutations including the fact that acetaldehyde, an ethanol metabolite, is classified as a group 1 carcinogen. Tobacco smoke exposure is also a risk factor for cancer development; approximately 20% of CRCs are associated with smoking. Additionally, obese patients have a higher risk of cancer development, which is further supported by the fact that physical activity decreases CRC risk by 55%. Similarly, chronic inflammatory conditions also increase the risk of CRC development. Moreover, the circadian clock alters digestion and regulates other biochemical, physiological, and behavioral processes that could influence CRC. Taken together, colon carcinogenesis involves a number of etiological factors, and therefore, to create effective preventive strategies, molecular targets need to be identified and beleaguered prior to disease progression. With this in mind, the following is a comprehensive review identifying downstream target proteins of the above lifestyle risk factors, which are modulated during colon carcinogenesis and could be targeted for CRC prevention by novel agents including phytochemicals.

Light White Oils Exhibit Low Tissue Accumulation Potential and Minimal Toxicity in F344 Rats

Female F344 rats were fed diets containing 0.02%, 0.2%, or 2.0% white mineral oil for 90 days. There were no gross or microscopic differences in target organs at the 0.02% level. In the higher-dose groups, relative liver and mesenteric lymph node (MLN) weights were increased, and MLN inflammation was observed. At the 2% level, there was very limited evidence of microgranuloma formation in the liver but at a lower incidence and at lesser severity than has been reported in studies of C22 -C25 oils. Analysis of liver extracts from treated rats revealed that C15 -C20 constituents were underrepresented by comparison to their corresponding concentrations in the test oil. These results provide evidence that although hydrocarbons with carbon numbers <C20 are absorbed, they are not preferentially retained and do not contribute to inflammatory processes in liver.

Green tea extract markedly lowers the lymphatic absorption and increases the biliary secretion of 14C-benzo[a]pyrene in rats

Previously, we have shown that green tea extract (GTE) lowers the intestinal absorption of lipids and lipophilic compounds in rats. This study was conducted to investigate whether GTE inhibits the intestinal absorption and biliary secretion of benzo[a]pyrene (BaP), an extremely lipophilic potent carcinogen, present in foods as a contaminant. Male rats with lymph or bile duct cannula were infused at 3.0 ml/h for 8 h via a duodenal catheter with lipid emulsion containing (14)C-BaP with or without GTE in PBS buffer. Lymph and bile were collected hourly for 8 h. The (14)C-radioactivities in lymph, bile and intestine were determined and expressed as % dose infused. Results showed that GTE drastically lowered the lymphatic absorption of (14)C-BaP (7.6±3.2% in GTE-infused vs. 14.4±2.7% dose/8 h in control rats), with a significantly higher amount of (14)C-radioactivity present in the small intestinal lumen and cecum in rats infused with GTE. GTE also markedly increased the hourly rate (3.9±0.1% dose/h in GTE-infused vs. 3.0±0.1% dose/h in control rats) and the total biliary secretion of (14)C-BaP (31.5±0.8% dose/8 h in GTE-infused vs. 24.3±0.4% dose/8 h in control rats). The findings provide first direct evidence that GTE has a profound inhibitory effect on the intestinal absorption of BaP and promotes the excretion of absorbed BaP via the biliary route. Further studies are warranted to investigate whether green tea could be recommended as a dietary means of ameliorating the toxicity and carcinogenic effect of BaP.

The intestinal lymph fistula model--a novel approach to study ghrelin secretion

The orexigenic hormone ghrelin is secreted from the stomach and has been implicated in the regulation of energy and glucose homeostasis. We hypothesized that ghrelin, like other gastrointestinal (GI) hormones, is present in intestinal lymph, and sampling this compartment would provide advantages for studying ghrelin secretion in rodents. Blood and lymph were sampled from catheters in the jugular vein and mesenteric lymph duct before and after intraduodenal (ID) administration of isocaloric Ensure, dextrin, or Liposyn meals or an equal volume of saline in conscious Sprague-Dawley rats. Total ghrelin levels were measured using an established radioimmunoassay. Acyl and des-acyl ghrelin were measured using two-site ELISA. Fasting ghrelin levels in lymph were significantly higher than in plasma (means +/- SE: 3,307.9 +/- 272.9 vs. 2,127.1 +/- 115.0 pg/ml, P = 0.004). Postingestive acyl and des-acyl ghrelin levels were also significantly higher, whereas the ratio of acyl:des-acyl ghrelin was similar in lymph and plasma (0.91 +/- 0.28 vs. 1.20 +/- 0.36, P = 0.76). The principle enzymes responsible for deacylation of ghrelin were lower in lymph than in plasma. Following ID Ensure, maximum ghrelin suppression occurred at 2 h in lymph compared with at 1 h in plasma. The return of suppressed ghrelin levels to baseline was also delayed in lymph. Similarly, dextrin also induced significant suppression of ghrelin (two-way ANOVA: P = 0.02), whereas Liposyn did not (P = 0.32). On the basis of these findings, it appears that intestinal lymph, which includes drainage from the interstitium of the GI mucosa, is enriched in ghrelin. Despite reduced deacylating activity in lymph, there is not a disproportionate amount of acyl ghrelin in this pool. The postprandial dynamics of ghrelin are slower in lymph than plasma, but the magnitude of change is greater. Assessing ghrelin levels in the lymph may be advantageous for studying its secretion and concentrations in the gastric mucosa.

Household chemicals: management of intoxication and antidotes

Exposure to household products is very common, but in industrialized countries severe or fatal poisoning with household products is rare today, due to the legal restriction of sale of hazardous household products. The big challenge for physicians, pharmacologists and toxicologists is to identify the few exceptional life-threatening situations where immediate intervention is needed. Among thousands of innocuous products available for the household only very few are hazardous. Substances found in these products include detergents, corrosives, alcohols, hydrocarbons, and some of the essential oils. The ingestion of batteries and magnets and the exposure to cyanoacrylates (super glue) can cause complications in exceptional situations. Among the most dangerous substances still present in household products are ethylene glycol and methanol. These substances cause major toxicity only through their metabolites. Therefore, initial symptoms may be only mild or absent. Treatment even in asymptomatic patients has to be initiated as early as possible to inhibit production of toxic metabolites. For all substances not only the compound itself but also the route of exposure is relevant for toxicity. Oral ingestion and inhalation generally lead to most pronounced symptoms, while dermal exposure is often limited to mild irritation. However, certain circumstances need special attention. Exposure to hydrofluoric acid may lead to fatal hypocalcemia, depending on the concentration, duration of exposure, and area of the affected skin. Accidents with hydrocarbon pressure injectors and spray guns are very serious events, which may lead to amputation of affected limbs. Button batteries normally pass the gastrointestinal tract without problems even in toddlers; in rare cases, however, they get lodged in the esophagus with the risk of localized tissue damage and esophageal perforation.

Association of MUTYH Gln324His and APEX1 Asp148Glu with colorectal cancer and smoking in a Japanese population

Background

Genetic polymorphisms of DNA repair enzymes may lead to genetic instability and colorectal cancer carcinogenesis. Our objective was to measure the interactions between polymorphisms of repair genes and tobacco smoking in colorectal cancer.

Methods

The case-control study involved sixty-eight colorectal cancer patients and 121 non-cancer controls divided into non-smokers and smokers according to pack-years of smoking. The genetic polymorphisms of DNA repair enzymes,OGG1 Ser326Cys, MUTYH Gln324His, APEX1 Asp148Glu and XRCC1 Arg399Gln, were examined using PCR-RFLP.

Results

The MUTYH Gln324His showed strong significant associations with a risk of colorectal cancer (crude odds ratio [OR] 3.30, 95% confidence interval [95%CI] 1.44–7.60, p = 0.005; adjusted OR3.53, 95%CI 1.44–8.70, p = 0.006). The ORs for the APEX1 Asp148Glu were statistically significant (crude OR 2.69, 95%CI 1.45–4.99, p = 0.002; adjusted OR 2.33, 95%CI 1.21–4.48, p = 0.011). The ORs for the MUTYH Gln324His and the APEX1 Asp148Glu were statistically significant for colon cancer (adjusted OR 3.95, 95%CI 1.28–12.20, p = 0.017 for MUTYH Gln324His ; adjusted OR 3.04, 95%CI 1.38–6.71, p = 0.006 for APEX1 Asp148Glu). The joint effect of tobacco exposure and the MUTYH Gln324His showed a significant association with colorectal cancer risk in non-smokers (adjusted OR 4.08, 95%CI 1.22–13.58, p = 0.022) and the APEX1 Asp148Glu was significantly increased in smokers (adjusted OR 5.02, 95%CI 1.80–13.99, p = 0.002). However, the distributions of OGG1 Ser326Cys and XRCC1 Arg399Gln were not associated with a colorectal cancer risk.

Conclusion

Our findings suggest that the MUTYH Gln324His and the APEX1 Asp148Glu constitutes an increased risk of colorectal cancer, especially colon cancer. The MUTYH Gln324His is strongly associated with colorectal cancer susceptibility in never smoking history, whereas the APEX1 Asp148Glu genotype constitutes an increased risk of colorectal cancer when accompanied by smoking exposure.

GSTM1 and GSTT1 Polymorphisms, Cigarette Smoking, and Risk of Colon Cancer: A Population-based Case-control Study in North Carolina (United States)

Cigarette smoke is a risk factor for colon cancer, but the importance of dose and interaction with genetic susceptibility remain poorly understood. We used data from a population-based case control study, to examine the association between cigarette smoking and colon cancer in African Americans and whites, and colon cancer and polymorphisms in GSTM1 and GSTT1. A total of 554 cases of primary colon cancer and 874 controls were included in this analysis. We found no association between cigarette smoking (ever versus never) and colon cancer in African Americans (odds ratio (OR)=0.93, 95% confidence interval (CI)=0.65-1.33). In contrast, there was an increased risk of cigarette smoking in whites (OR=1.43, CI=1.05-1.94). There was a small increased risk of colon cancer for individuals with GSTM1 null (African Americans, OR=1.43, CI, 0.98-2.09; whites, OR=1.19, CI, 0.90-1.58) and a decreased risk of colon cancer for individuals with GSTT1 null (African Americans, OR=0.59, CI: 0.40-0.86; whites, OR=0.72, CI: 0.53-1.00). There were weak interactions between GSTT1 null and cigarette smoking in whites, and GSTM1 null genotype and cigarette smoking in African Americans. GSTT1 and GSTM1 polymorphisms may be weakly related to colon cancer risk and there may be racial differences in gene-smoking interactions.

Bioavailability and risk assessment of orally ingested polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are a family of toxicants that are ubiquitous in the environment. These contaminants generate considerable interest, because some of them are highly carcinogenic in laboratory animals and have been implicated in breast, lung, and colon cancers in humans. These chemicals commonly enter the human body through inhalation of cigarette smoke or consumption of contaminated food. Of these two pathways, dietary intake of PAHs constitutes a major source of exposure in humans. Although many reviews and books on PAHs have been published, factors affecting the accumulation of PAHs in the diet, their absorption following ingestion, and strategies to assess risk from exposure to these hydrocarbons following ingestion have received much less attention. This review, therefore, focuses on concentrations of PAHs in widely consumed dietary ingredients along with gastrointestinal absorption rates in humans. Metabolism and bioavailability of PAHs in animal models and the processes, which influence the disposition of these chemicals, are discussed. The utilitarian value of structure and metabolism in predicting PAH toxicity and carcinogenesis is also emphasized. Finally, based on intake, disposition, and tumorigenesis data, the exposure risk to PAHs from diet, and contaminated soil is presented. This information is expected to provide a framework for refinements in risk assessment of PAHs from a multimedia exposure perspective.

Comparative pharmacokinetic and disposition studies of [1-14C]1-eicosanylcyclohexane, a surrogate mineral hydrocarbon, in female Fischer-344 and Sprague-Dawley rats

White oils or waxes [mineral hydrocarbons (MHCs)] with substantial levels of saturated hydrocarbons in the range of C18 to C32 have produced hepatic microgranulomas and lymph node microgranulomas (also referred to as histiocytosis) after repeated administration to female Fischer-344 (F-344) rats. Female Sprague-Dawley (S-D) rats are less sensitive to these MHC-induced hepatic and lymph node effects. Studies reported herein characterized the pharmacokinetics and disposition of a representative C-26 MHC, [1-(14)C]1-eicosanylcyclohexane ([(14)C]EICO), in these two rat strains. Female F-344 and S-D rats were administered by oral gavage either a high (1.80 g/kg) or a low (0.18 g/kg) dose of MHC in olive oil (1:4, v/v) containing [(14)C]EICO as a tracer. Blood, urine, feces, liver, and mesenteric lymph nodes (MLNs) were analyzed for [(14)C]EICO and (14)C-metabolites. After the high dose, F-344 rats had a higher blood C(max) of [(14)C]EICO, a longer time to C(max), and a greater area under the systemic blood concentration-time curve from zero to time infinity compared with S-D rats. After the low dose, F-344 rats displayed a unique triphasic blood concentration-time profile, meaning two distinct C(max) values were observed. Fecal excretion was the major route of [(14)C]EICO elimination for both rat strains (70-92% of the dose). S-D rats eliminated the majority of [(14)C]EICO metabolites recovered in the urine by 16 h (8-17% of the dose), whereas F-344 rats did not excrete the same amount until 72 to 96 h. Beyond 24 h, a greater level of [(14)C]EICO was recovered in livers of F-344 rats; at 96 h, 3 and 0.1% of the dose was retained in livers of F-344 and S-D rats, respectively. The major urinary metabolites of EICO in both rat strains were identified as 12-cyclohexyldodecanoic acid and 10-cyclohexyldecanoic acid. Based on the pharmacokinetic parameters and disposition profiles, the data indicate inherent strain differences in the total systemic exposure, rate of metabolism, and hepatic and lymph node retention of [(14)C]EICO, which may be associated with the different strain sensitivities to the formation of liver granulomas and MLN histiocytosis.

Evaluation of fecal mutagenicity and colorectal cancer risk

Colorectal cancer is one of the most common internal malignancies in Western society. The cause of this disease appears to be multifactorial and involves genetic as well as environmental aspects. The human colon is continuously exposed to a complex mixture of compounds, which is either of direct dietary origin or the result of digestive, microbial and excretory processes. In order to establish the mutagenic burden of the colorectal mucosa, analysis of specific compounds in feces is usually preferred. Alternatively, the mutagenic potency of fecal extracts has been determined, but the interpretation of these more integrative measurements is hampered by methodological shortcomings. In this review, we focus on exposure of the large bowel to five different classes of fecal mutagens that have previously been related to colorectal cancer risk. These include heterocyclic aromatic amines (HCA) and polycyclic aromatic hydrocarbons (PAH), two exogenous factors that are predominantly ingested as pyrolysis products present in food and (partially) excreted in the feces. Additionally, we discuss N-nitroso-compounds, fecapentaenes and bile acids, all fecal constituents (mainly) of endogenous origin. The mutagenic and carcinogenic potency of the above mentioned compounds as well as their presence in feces, proposed mode of action and potential role in the initiation and promotion of human colorectal cancer are discussed. The combined results from in vitro and in vivo research unequivocally demonstrate that these classes of compounds comprise potent mutagens that induce many different forms of genetic damage and that particularly bile acids and fecapentaenes may also affect the carcinogenic process by epigenetic mechanisms. Large inter-individual differences in levels of exposures have been reported, including those in a range where considerable genetic damage can be expected based on evidence from animal studies. Particularly, however, exposure profiles of PAH and N-nitroso compounds (NOC) have to be more accurately established to come to a risk evaluation. Moreover, lack of human studies and inconsistency between epidemiological data make it impossible to describe colorectal cancer risk as a result of specific exposures in quantitative terms, or even to indicate the relative importance of the mutagens discussed. Particularly, the polymorphisms of genes involved in the metabolism of heterocyclic amines are important determinants of carcinogenic risk. However, the present knowledge of gene-environment interactions with regard to colorectal cancer risk is rather limited. We expect that the introduction of DNA chip technology in colorectal cancer epidemiology will offer new opportunities to identify combinations of exposures and genetic polymorphisms that relate to increased cancer risk. This knowledge will enable us to improve epidemiological study design and statistical power in future research.

Ninety-day feeding study in Fischer-344 rats of highly refined petroleum-derived food-grade white oils and waxes

Subchronic 90-day feeding studies were conducted in male and female Fischer-344 (F-344) rats on highly refined white mineral oils and waxes representative of those used for food applications. The goal was to help clarify the mixed results found in other toxicity studies with laboratory animals. Seven white oils and 5 waxes were fed at dietary doses of 20,000, 2,000, 200, and 20 ppm and compared with control groups on untreated diet; toxicity was assessed at 90 days and also after a reversal period of 28 days and/or 85 days. Higher molecular-sized hydrocarbons (microcrystalline waxes and the higher viscosity oils) were without biological effects. Paraffin waxes and low- to midviscosity oils produced biological effects that were inversely related to molecular weight, viscosity, and melting point; oil type and processing did not appear to be determinants. Biological effects were more pronounced in females than in males. Effects occurred mainly in the liver and mesenteric lymph nodes and included increased organ weights, microscopic inflammatory changes, and evidence for the presence of saturated mineral hydrocarbons in affected tissues. Inflammation of the cardiac mitral valve was also observed at high doses in rats treated with paraffin waxes. Further studies are required to elucidate the mechanism for the responses observed and the relevance of these inflammatory responses in the F-344 rat to other species, including humans.

Formulation and analysis of food-grade mineral hydrocarbons in toxicology studies

Methods are presented for the formulation and rapid determination of mineral hydrocarbons (MHCs) in animal diet and tissue. Food grade white oils and low melting point waxes are mixed as liquids with powdered diet. Higher melting point waxes are first powdered using a novel atomization technique before dry mixing with diet. MHCs sufficiently soluble in carbon tetrachloride (CCl4) are determined in diet by ultrasonic solvent extraction, adsorption of polar material on Florisil and analysis of the residue by quantitative Fourier Transform Infra Red (FT-IR) spectroscopy. Quantification in tissue is achieved by aqueous saponification, followed by extraction, clean-up and FT-IR analysis as for diet samples. A 10-fold increase in sensitivity over previous methods is achieved, below 0.002% (w/w) in diet and 0.1 mg/g in tissue. Over 80% of the CCl4 used can be recovered and recycled. Control diet seems to contain approximately 0.003% (w/w) background MHC. The method was modified for one powdered wax, only sparingly soluble in CCl4, high concentrations being extracted from diet by flotation in aqueous cetrimide and determined gravimetrically with a limit of detection of 0.1% (w/w) in diet. Application of these methods to 90-day feeding studies is described, and future developments due to the phasing out of CCl4 are discussed.

Chromatographic methods for the determination of toxicants in faeces

Modern chromatographic techniques and their application in the determination of toxic compounds in faeces are reviewed. Faecal analysis may be of importance in toxicokinetic studies of xenobiotics in order to determine factors such as metabolism, body burden and major routes of elimination. Compounds of interest include various food constituents, drugs and occupational or environmental factors. Further, various mutagenic or carcinogenic compounds which are excreted by faeces have been indicated to represent risk factors for colorectal cancer. In this context, the chromatographic determination of the endogenously generated fecapentaenes and bile acids, both postulated etiological factors in colorectal carcinogenesis, is reviewed. For fecapentaene determination, several high-performance liquid chromatographic (HPLC) methods are available; however, the applicability of some of these methods is limited owing to insufficient separation of various isomeric forms or discrimination between fecapentaenes and their precursors. For the determination of bile acids in faeces, many chromatographic procedures have been reported, and the characteristics of the most relevant methods are compared and discussed. It is concluded that separation by gas chromatography (GC) in combination with mass spectrometry provides the highest selectivity and sensitivity. A relatively rapid alternative analysis for the determination of total and aqueous faecal bile acids is proposed. Further, methods for the determination of polycyclic aromatic hydrocarbons (PAHs) are reviewed. Although the use of radiolabelled PAHs in animal studies has many advantages, it cannot be applied for human biological monitoring and HPLC and GC provide sensitive alternatives. An HPLC method for the determination of non-metabolized PAHs in faeces is described.

Cholestane as a digestibility marker in the absorption of polyunsaturated fatty acid ethyl esters in Atlantic salmon

Salmonid fish require long-chain n-3 fatty acids in their diet. The digestibility of different chemical forms of fish oil fatty acids, fed as triacylglycerols, free fatty acids or ethyl esters, was examined in 300 g farmed Atlantic salmon (Salmo salar) using cholestane as an indicator of fat absorption in lieu of the chromium oxide (Cr2O3) which is commonly used as a marker in digestibility studies. It was established that the two digestibility markers gave similar results. Conveniently, cholestane does not require a separate analysis if fatty acids are to be determined by appropriate gas-liquid chromatography. The long-chain polyunsaturated fatty acids were particularly well absorbed, the apparent digestibility being 90-98% when feeding triacylglycerols or free fatty acids. However, the digestibility of monounsaturated fatty acids (75-94%) was lower, and lower still for saturated fatty acids (50-80%). Ethyl esters of fatty acids were significantly less well absorbed (P less than 0.05) than were the corresponding fatty acids in free acid or triacylglycerol form. Irrespective of dietary fat type, only free fatty acids were identified in feces, indicating total hydrolysis of triacylglycerols and ethyl esters.