Translating In Vitro Acrolein-Trapping Capacities of Tea Polyphenol and Soy Genistein to In Vivo Situation is Mediated by the Bioavailability and Biotransformation of Individual Polyphenols

SCOPE

Acrolein (ACR) is a highly toxic unsaturated aldehyde. Humans are both endogenously and exogenously exposed to ACR. Long-term exposure to ACR leads to various chronic diseases. Dietary polyphenols have been reported to be able to attenuate ACR-induced toxicity in vitro via formation of ACR-polyphenol conjugates. However, whether in vitro ACR-trapping abilities of polyphenols can be maintained under in vivo environments is still unknown.

METHODS AND RESULTS

Two most commonly consumed dietary polyphenols, (-)-epigallocatechin-3-gallate (EGCG) from tea and genistein from soy, are evaluated for their anti-Acrolein behaviors both in vitro and in mice. Tea EGCG exerts a much higher capacity to capture ACR than soy genistein in vitro. But translation of in vitro anti-ACR activity into in vivo is mainly mediated by bioavailability and biotransformation of individual polyphenols. It is found that 1) both absorbed EGCG and genistein can trap endogenous ACR by forming mono-ACR adducts and eventually be excreted into mouse urine; 2) both absorbed EGCG and genistein can produce active metabolites, methyl-EGCG (MeEGCG) and orobol, to scavenge endogenous ACR; 3) both MeEGCG and non-absorbed EGCG show ability to trap ACR in the gut; 4) considerable amounts of microbial metabolites of genistein display enhanced anti-ACR capacity both in the body and in the gut, compared to genistein; and 5) biotransformation of genistein is able to boost its in vivo anti-ACR capacity, compared to EGCG.

CONCLUSION

The findings demonstrate that in vivo anti-ACR ability of dietary polyphenols cannot be reflected solely based on their in vitro ability. The bioavailability and biotransformation of individual polyphenols, and especially the gut microbiome, contribute to in vivo anti-ACR ability of dietary polyphenols.

Cinnamaldehyde in a Novel Intravenous Submicrometer Emulsion: Pharmacokinetics, Tissue Distribution, Antitumor Efficacy, and Toxicity

The purpose of our research is to find a new lipid emulsion to deliver a low water-soluble compound, cinnamaldehyde (CA). Its characteristics, pharmacokinetics, antitumor efficacy, and toxicity were evaluated. The mean particle size, zeta potential, and encapsulation efficiency of the submicromemter emulsion of CA (SME-CA) were 130 ± 5.92 nm, -25.7 ± 6.00 mV, and 99.5 ± 0.25%, respectively. The area under the curve from 0 h to termination time (AUC(0-t)) of SME-CA showed a significantly higher value than that of CA (589 ± 59.2 vs 375 ± 83.5 ng h/L, P < 0.01). Tissue distribution study showed various changes; among them, a 27% higher concentration was found in brain tissue when using SME-CA at 15 min after administration. For the efficacy evaluation, SME-CA exhibited 8- and 11-fold antitumor activity in the depression of HeLa and A549 cell lines with the IC50 decreasing to 0.003 and 0.001 mmol/L, respectively. The LD50 values of CA and SME-CA in mice were 74.8 and 125 mg/kg, suggesting increased safety from the new formulation. The new formulation exhibited lower toxicity, higher antitumor activity, and a more satisfactory pharmacokinetic property, which displayed great potential for future pharmacological application.

Quantitation of acrolein-derived (3-hydroxypropyl)mercapturic acid in human urine by liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry: effects of cigarette smoking

Recently published data suggest that acrolein (1), a toxic but weakly carcinogenic constituent of cigarette smoke, may be involved as a causative factor for the mutations frequently observed in the p53 tumor suppressor gene in lung cancer in smokers. Biomarkers are needed to further assess the possible relationship between acrolein uptake and cancer. In this study, we analyzed (3-hydroxypropyl)mercapturic acid (3-HPMA, 2) in human urine. 3-HPMA is a major metabolite of acrolein in laboratory animals. The method employs [13C3]3-HPMA as an internal standard, with analysis and quantitation by LC-APCI-MS/MS-SRM. Clean, readily quantifiable chromatograms were obtained. The method was accurate and precise and required only 0.1 mL of urine. Median levels of 3-HPMA were significantly higher (2900 pmol/mg of creatinine, N=35) in smokers than in nonsmokers (683 pmol/mg of creatinine, N=21) (P=0.0002). The effect of smoking was further assessed by determining the levels of 3-HPMA before and after a 4 week smoking cessation period. There was a significant 78% decrease in median levels of urinary 3-HPMA after cessation (P<0.0001). The relationship between the levels of urinary 3-HPMA and those of acrolein-derived 1,N2-propanodeoxyguanosine (PdG) adducts in lung was investigated in 14 smokers. There was a significant inverse relationship between urinary 3-HPMA and alpha-hydroxy-PdG (3) but not gamma-hydroxy-PdG (4) or total adduct levels. The results of this study clearly demonstrate that acrolein uptake in smokers is significantly higher than in nonsmokers and underline the need for further investigation of the possible relationship of acrolein uptake to lung cancer.

Fragrance material review on cinnamaldehyde

A toxicologic and dermatologic review of cinnamaldehyde when used as a fragrance ingredient is presented.

Protein binding and metabolism influence the relative skin sensitization potential of cinnamic compounds

Skin protein modification (haptenation) is thought to be a key step in the manifestation of sensitization to low molecular mass chemicals (<500 g/mol). For sensitizing chemicals that are not protein reactive, it is hypothesised that metabolic activation can convert such chemicals into protein reactive toxins within the skin. trans-Cinnamaldehyde, alpha-amyl cinnamaldehyde, and trans-cinnamic alcohol are known sensitizers with differing potencies in man, where the former two are protein reactive and the latter is not. Here, we have used immunochemical methods to investigate the extent of protein-cinnamaldehyde binding in rat and human skin homogenates that have been incubated (for either 5, 15, 30, or 60 min) at 37 degrees C with cinnamaldehyde, alpha-amyl cinnamaldehyde (at concentrations of between 1 and 40 mM), and cinnamic alcohol (at higher concentrations of 200 or 400 mM). Cinnamaldehyde specific antiserum was raised specially. A broad range (in terms of molecular mass) of protein-cinnamaldehyde adducts was detected (as formed in a time- and concentration-dependent manner) in skin treated with cinnamaldehyde and cinnamic alcohol but not with alpha-amyl cinnamaldehyde. Mechanistic observations have been related to relative skin sensitization potential, as determined using the local lymph node assay (LLNA) as a biological read-out. The work presented here suggests that there is a common hapten involved in cinnamaldehyde and cinnamic alcohol sensitization and that metabolic activation (to cinnamaldehyde) is involved in the latter. Conversely, there does not appear to be a common hapten for cinnamaldehyde and alpha-amyl cinnamaldehyde. Such mechanistic work on protein modification is important in understanding the early mechanisms of skin sensitization. Such knowledge can then be used in order that effective and appropriate in vitro/in silico tools for predicting sensitization potential, with a high confidence, can be developed.

The FEMA GRAS assessment of cinnamyl derivatives used as flavor ingredients

This publication is the seventh in a series of safety evaluations performed by the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA). In 1993, the Panel initiated a comprehensive program to re-evaluate the safety of more than 1700 GRAS flavoring substances under conditions of intended use. Elements that are fundamental to the safety evaluation of flavor ingredients include exposure, structural analogy, metabolism, pharmacokinetics and toxicology. Flavor ingredients are evaluated individually and in the context of the available scientific information on the group of structurally related substances. Scientific data relevant to the safety evaluation of the use of cinnamyl derivatives as flavoring ingredients is evaluated.

Cinnamic compound metabolism in human skin and the role metabolism may play in determining relative sensitisation potency

BACKGROUND

trans-Cinnamaldehyde and trans-cinnamic alcohol cause allergic contact dermatitis (ACD) in humans; cinnamaldehyde is a more potent sensitiser than cinnamic alcohol. These two chemicals are principal constituents of the European Standard 'Fragrance Mix', as used in patch testing diagnostics of sensitisation to fragrances by clinical dermatologists. As contact sensitisers are usually protein reactive compounds, it is hypothesised that cinnamic alcohol (not protein-reactive) is a 'prohapten' that requires metabolic activation, presumably by cutaneous oxidoreductases, to the protein-reactive cinnamaldehyde (a 'hapten'). It is postulated that cinnamaldehyde can be detoxified by aldehyde dehydrogenase (ALDH) to cinnamic acid and/or by alcohol dehydrogenase (ADH) to cinnamic alcohol. Hence, a variety of metabolic pathways may contribute to the relative exposures and hence sensitising potencies of cinnamic alcohol and cinnamaldehyde.

OBJECTIVE

To evaluate the extent of cinnamaldehyde and cinnamic alcohol metabolism in human skin and provide evidence for the role of cutaneous ADH and ALDH in such metabolism.

METHODS

The extent of cinnamic alcohol and aldehyde metabolism was investigated in human skin homogenates and sub-cellular fractions. A high performance liquid chromatography method was used for analysis of skin sample extracts. Studies were conducted in the presence and absence of the ADH/cytochrome P450 inhibitor 4-methylpyrazole and the cytosolic ALDH inhibitor, disulfiram.

RESULTS

Differential metabolism of cinnamic alcohol and cinnamaldehyde was observed in various subcellular fractions: skin cytosol was seen to be the major site of cinnamic compound metabolism. Significant metabolic inhibition was observed using 4-methylpyrazole and disulfiram in whole skin homogenates and cytosolic fractions only.

CONCLUSIONS

This study has demonstrated that cutaneous ADH and ALDH activities, located within defined subcellular compartments, play important roles in the activation and detoxification of CAlc and CAld in skin. Such findings are important to the development of computational hazard prediction tools for sensitisation (e.g. the DEREK program) and also to dermatologists in understanding observed interindividual differences, cross-reactivities or co-sensitisation to different cinnamic compounds in the clinic.

Bound malondialdehyde in foods: bioavailability of the N-2-propenals of lysine

The lipid peroxidation product malondialdehyde is mostly bound to proteins in foods as an N-2-propenal derivative that is released as N-epsilon-(2-propenal)lysine by digestive enzymes. N-2-Propenals have been identified as the major forms of malondialdehyde in urine. To determine whether available lysine can be released from the N-2-propenals of lysine in vivo, two preparations containing N-epsilon-(2-propenal)lysine and N-alpha-(2-propenal)lysine or N,N'-di-(2-propenal)lysine were synthesized using radioactively labeled lysine and were administered to rats by gastric intubation and intraperitoneal injection. Both preparations were absorbed from the digestive tract, although not as efficiently as free lysine, but most of the radioactivity was excreted in urine. The radioactive label was also readily excreted after intraperitoneal injection. It is concluded that the N-2-propenals of lysine are fairly stable in vivo, so that, although they are absorbed from the gut, most of the absorbed material is not metabolized and is readily excreted as nonavailable lysine.

High-performance liquid chromatography method for the quantification of non-radiolabelled cinnamic compounds in analytes derived from human skin absorption and metabolism experiments

An isocratic high-performance liquid chromatography method has been developed for the quantification of the skin sensitisers trans-cinnamaldehyde and trans-cinnamic alcohol, and their cinnamic metabolites. The relative standard deviations (RSDs) between the gradients of eight sets of standard curves were 2.8, 3.1 and 1.9% for cinnamic alcohol, cinnamaldehyde and cinnamic acid, respectively. Sample analytes were derived from two series of experiments: in vitro full-thickness human skin absorption and metabolism studies and metabolism studies using human skin homogenates, with non-radiolabelled cinnamic compounds. Skin absorption and metabolism experiments were performed in the absence and presence of the alcohol dehydrogenase inhibitor, pyrazole. Samples from full-thickness skin absorption studies were analysed without extraction; cinnamic compounds from within skin were extracted into methanolic solutions using newly developed methods. The intra-assay RSDs ranged from 0.17 to 2.52% for cinnamic alcohol, 0.24 to 9.14% for cinnamaldehyde and 0.26 to 6.43% for cinnamic acid. The inter-assay RSDs for cinnamic alcohol, cinnamaldehyde and cinnamic acid, respectively, as determined from n=20 HPLC runs, were 2.10, 4.16 and 2.26%.

Oxidative stress promotes the development of transformation: involvement of a potent mutagenic lipid peroxidation product, acrolein

The effect of intracellular oxidative stress on the development of cell transformation was studied. Mouse embryo C3H/10T1/2 fibroblasts pre-treated with benzo[a] pyrene, developed transformed foci on exposure to free radical generators, such as 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and 3-morpholinosydnonimine hydrochloride (SIN-1). These compounds generate peroxyl radicals and peroxynitrite, respectively. Neither AAPH nor SIN-1 alone induced transformation. The level of intracellular antioxidants, such as alpha-tocopherol and glutathione (GSH), decreased with time of exposure to the free radical generators, whereas the addition of exogenous alpha-tocopherol, GSH and ebselen showed a reduction in the frequency of transformation. An early event during exposure to AAPH and SIN-1 was the generation of acrolein, a highly mutagenic lipid peroxidation product, which was suppressed by the addition of alpha-tocopherol. Furthermore, it was confirmed that acrolein induced the transformation of cells which were pre-treated with benzo[a]pyrene but not of the untreated cells. These results suggest that acrolein may act as an important mediator of cell transformation under oxidative stress.

Metabolism and distribution of [2,3-(14)C]acrolein in lactating goats

The metabolism and distribution of [2,3-(14)C]acrolein were studied in a lactating goat orally administered 0.82 mg/kg of body weight/day for 5 days. Milk, urine, feces, and expired air were collected. The goat was killed 12 h after the last dose, and edible tissues were collected. The nature of the radioactive residues was determined in milk and tissues. All of the identified metabolites were the result of the incorporation of acrolein into the normal, natural products of intermediary metabolism. There was evidence that the three-carbon unit of acrolein was incorporated intact into glucose, and subsequently lactose, and into glycerol. In the case of other natural products, the incorporation of radioactivity appeared to result from the metabolism of acrolein to smaller molecules followed by incorporation of these metabolites into the normal biosynthetic pathways.

Metabolism and distribution of [2,3-(14)C]acrolein in laying hens

The metabolism and distribution of [2,3-(14)C]-acrolein were studied in 10 laying hens orally administered 1.09 mg/kg of body weight/day for 5 days. Eggs, excreta, and expired air were collected. The hens were killed 12-14 h after the last dose and edible tissues collected. The nature of radioactive residues was determined in tissues and eggs. All of the identified metabolites were the result of the incorporation of acrolein-derived radioactivity into normal natural products of intermediary metabolism in the hen except for 1,3-propanediol, which is a known degradation product of glycerol in bacteria.

Human skin absorption and metabolism of the contact allergens, cinnamic aldehyde, and cinnamic alcohol

trans-Cinnamaldehyde and trans-cinnamic alcohol have been commonly reported to cause allergic contact dermatitis (ACD) in humans. Cinnamaldehyde is a more potent skin sensitizer than cinnamic alcohol. It has been hypothesized that cinnamic alcohol is a "prohapten" that requires metabolic activation, presumably by oxidoreductase enzymes such as alcohol dehydrogenase (ADH) or cytochrome P450 2E1 (CYP2E1), to the protein-reactive cinnamaldehyde (a hapten). In this study, the in vitro percutaneous absorption and metabolism of cinnamaldehyde and cinnamic alcohol (78 micromol dose) has been examined using freshly excised, metabolically viable, full-thickness breast and abdomen skin from six female donors. Penetration rates and total cumulative recoveries of cinnamic compounds that were present in receptor fluid, extracted from within the skin, evaporated from the skin surface, or remained unabsorbed on the skin surface after 24 h were quantified by reversed-phase high-performance liquid chromatography. Biotransformation of cinnamaldehyde to both cinnamic alcohol and cinnamic acid was observed. Topically applied cinnamic alcohol was converted to cinnamaldehyde (found on the skin surface only) and cinnamic acid. To establish whether these biotransformations were enzymatic, experiments were performed in the absence and presence of varying concentrations (80-320 micromol) of the ADH/CYP2E1 inhibitors pyrazole or 4-methylpyrazole. The observation that pyrazole significantly reduced (p < 0.05) the total penetration of cinnamic metabolites into receptor fluid, following either cinnamaldehyde or cinnamic alcohol treatment, but did not significantly affect parent chemical penetration, suggests that we are measuring cutaneous metabolic products of ADH activity. The skin absorption and metabolism of cinnamaldehyde and cinnamic alcohol will play an important role in the manifestation of ACD following topical exposure to these compounds.

Effects of L-2-oxothiazolidine-4-carboxylate on the cytotoxic activity and toxicity of cyclophosphamide in mice bearing B16F10 melanoma liver metastases

Glutathione (GSH) is the major non-protein thiol in cells that plays a critical role against damage from electrophilic agents such as alkylating drugs. Selective therapeutic GSH elevation in normal but not in tumour cells has been suggested as a means of protecting host tissues against more intense doses of chemotherapy. The present study investigated the response of B16 melanoma to treatment with the cysteine pro-drug L-2-oxothiazolidine-4-carboxylate (OTZ), alone and in combination with cyclophosphamide (CY). We found that OTZ decreased the GSH levels and proliferation rate of B16 melanoma cells in vitro, sensitizing them to the cytotoxic action of the activated metabolite of CY, acrolein (AC). In contrast to OTZ, the cysteine deliverer N-acetylcysteine (NAC) enhanced B16 melanoma cell proliferation by increasing GSH levels, and markedly decreased the sensitivity of these tumour cells to AC. In vivo studies showed the antitumoral activity of OTZ in B16 melanoma liver metastasis-induced mice, increasing their life span. We also observed that, whereas with CY treatment the GSH levels in peripheral blood mononuclear cells (PBMCs) were reduced and a dose-dependent leukopenia was produced, OTZ significantly increased PBMC GSH content, reducing toxicity and enhancing the survival of mice bearing established melanoma liver metastases treated with lethal dose CY. These results suggest a critical role for OTZ in protecting against alkylator agent-induced immunosuppression, which may allow the dose escalation of these cytostatic drugs to improve their therapeutic benefit in the treatment of malignant melanoma.

Urinary excretion and pharmacokinetics of acrolein and its parent drug cyclophosphamide in bone marrow transplant patients

The urinary excretion and pharmacokinetics of acrolein (ACRO) and its parent drug cyclophosphamide (CP) were investigated in 16 randomly selected bone marrow transplant (BMT) recipients when CP was used for conditioning. Patients suffering from aplastic anemia (n = 3) received a 4-day course of CP at a dose of 50 mg/kg daily infused intravenously (i.v.) over 1 h. Patients with leukemia (n = 13) were given either a combination of busulphan followed by CP at a dose of 50 mg/kg infused i.v. over 1 h for 4 days, or CP at a dose of 60 mg/kg by i.v. infusion over 1 h daily for 2 days followed by total body irradiation. Serial plasma samples and urine were collected after the start of the first CP dose. CP was analyzed by capillary gas chromatography, whereas ACRO was measured in urine by liquid chromatography. The plasma concentration-time data for CP conformed to the two-compartment model and the mean and s.e.m. values of alpha, beta, Vss, total clearance, and renal clearance observed were 1.29 (0.31) h(-1), 0.17 (0.03) h(-1), 0.67 (0.13) l/kg, 0.14 (0.02) l/h x kg, and 0.0188 (0.0052) l/h x kg, respectively. The mean and s.e.m. values of fraction of CP excreted in the form of ACRO during this interval (fmu) and ratio of the 24-h urinary concentration of ACRO/creatinine (Cmu(n)) were 1.96 (0.35%) and 9.11 (2.19) microg of ACRO/mg of creatinine, respectively. Two patients developed hemorrhagic cystitis (HC). Each of these two patients excreted significantly (P < 0.01) more ACRO in the first and second 4-h urine collection periods. However, there was no significant difference in fmu or Cmu(n) of ACRO between either of these two patients and the rest. This suggests that the rate of appearance of ACRO in urine is more crucial for developing HC than the cumulative amount excreted.

Metabolism and distribution of [2,3-14C]acrolein in Sprague-Dawley rats. II. Identification of urinary and fecal metabolites

The metabolites of [2,3-14C]acrolein in the urine and feces of Sprague-Dawley rats were identified after either intravenous administration in saline at 2.5 mg/kg or oral administration by gavage as an aqueous solution as either single or multiple doses at 2.5 mg/kg or as a single dose of 15 mg/kg. Selected urine and feces samples were pooled by sex and collection interval and profiled by combinations of reverse-phase, anion-exchange, cation-exchange, and ion-exclusion high-performance liquid chromatography (HPLC). Feces were also profiled by size-exclusion chromatography. Metabolites were identified by comparison with well-characterized standards by HPLC and by mass spectrometry. The urinary metabolites were identified as oxalic acid, malonic acid, N-acetyl-S-2-carboxy-2-hydroxyethylcysteine, N-acetyl-S-3-hydroxypropylcysteine, N-acetyl-S-2-carboxyethylcysteine, and 3-hydroxypropionic acid. The fecal radioactivity from the oral dose groups was partitioned into methanol-soluble, water-soluble, and insoluble radioactivity, some of which could be liberated by dilute acid hydrolysis. HPLC analysis of these extracts revealed no discrete metabolites. Size-exclusion chromatography indicated a molecular weight range of 2,000 to 20,000 Da for the radioactivity, which was unaffected by hydrolysis at reflux with 6 M acid or base. This radio-activity was thought to be a homopolymer of acrolein, which was apparently formed in the gastrointestinal tract. The pathways of acrolein metabolism were epoxidation followed by conjugation with glutathione, Michael addition of water followed by oxidative degradation, and glutathione addition to the double bond either following or preceding oxidation or reduction of the aldehyde. The glutathione adducts were further metabolized to the mercapturic acids.

High-performance liquid chromatographic determination of acrolein as a marker for cyclophosphamide bioactivation in human liver microsomes

A high-performance liquid chromatographic method for the quantification of acrolein following incubation of cyclophosphamide (CP) with human liver microsomes was developed. Based on the formation of the fluorescent derivative 7-hydroxyquinoline by condensation of acrolein with 3-aminophenol quantitation was performed without prior extraction or other sample cleanup procedures. The method showed sufficient sensitivity with a limit of detection of 5 ng/ml and a limit of quantification of 10 ng/ml. The suitability of the method is shown for enzyme kinetic studies.

Metabolism and distribution of [2,3-14C]acrolein in Sprague-Dawley rats

The metabolism and disposition of [2,3-14C]acrolein was studied in Sprague-Dawley rats after oral or intravenous dosing. Four groups of ten rats (five male and five female) were dosed with radiolabeled acrolein intravenously at 2.5 mg kg-1 (Group 2), orally by gavage at 2.5 mg kg-1, either as a single dose (Group 3) or after 14 daily doses of unlabeled acrolein (Group 4), or orally by gavage at 15 mg kg-1 (Group 5). Urine, feces, expired air and organic volatiles were collected for 7 days, after which the animals were sacrificed and tissues collected. All samples were analyzed for total radioactivity. After 7 days, the excretory patterns of male and female rats were almost identical. Urinary excretion was highest in the intravenously dosed animals (66-69%) and lowest in the Group 5 animals (36-40%), whereas the reverse was true for feces (< 2% for i.v. Group 2 animals and 28-30% for the Group 5 animals). Carbon dioxide expiration was comparable (26-31%) across all groups. Tissue concentrations of radioactivity were minimal in all groups (< 1.2%), but concentrations of radioactivity were highest in the intravenous Group 2 animals. The time course of excretion for all groups was similar with the exception of the high-dose animal group, which showed a pronounced delay in excretion during the first 12 h.

Biotransformation of acrolein in rat: excretion of mercapturic acids after inhalation and intraperitoneal injection

Biotransformation of acrolein (ACR) was studied in vivo in the rat following inhalation and ip administration. The major and minor urinary metabolites were 3-hydroxypropylmercapturic acid (HPMA) and 2-carboxyethylmercapturic acid (CEMA), respectively. Male Wistar rats were exposed to ACR, 23, 42, 77 and 126 mg/m3, for 1 hr. The sum of mercapturic acids HPMA and CEMA excreted within 24 hr after the exposure amounted to 0.87 +/- 0.12, 1.34 +/- 0.5, 2.81 +/- 1.15, and 7.13 +/- 1.56 mumol/kg, i.e., 10.9 +/- 1.5, 13.3 +/- 5.0, 16.7 +/- 6.9, and 21.5 +/- 4.8% of the estimated absorbed dose, respectively. The dose estimate was based on reported values of minute respiratory volume and respiratory tract retention and was corrected for the ACR-induced changes in minute respiratory volume. In the relevant dose range (8.9 to 35.7 mumol/kg) the portion of mercapturic acids excreted was nearly constant for ip exposed rats. The sum of HPMA and CEMA amounted to 29.1 +/- 6.5% of the dose. These results indicate that the deficiency in rat lung metabolism of ACR to acrylic acid previously observed is not compensated by the other detoxication pathway in vivo, mercapturic acid formation. The health hazard arising from inhalation of ACR is likely to be higher than that from other routes of exposure.

Acrolein-induced smooth muscle hyperresponsiveness and eicosanoid release in excised ferret tracheae

Acrolein is a ubiquitous toxic air pollutant that can have adverse lung effects. To understand the mechanism governing airway reactivity in relation to acrolein uptake, in vitro experiments were conducted in which excised tracheae from ferrets were exposed for 1 hr to a unidirectional constant flow (100 ml/min) of an acrolein-in-air mixture at several concentrations (0-12.5 ppm). During exposure, acrolein uptake into the trachea was determined by a chromatographic analysis of gas samples taken at the entrance and at the exit of the trachea. Smooth muscle contractility in response to carbachol (CCh), acetylcholine (ACh), and potassium chloride (KCl) was measured following exposure, and eicosanoids released in the perfusate baths were assayed. The results indicate that the fractional uptake into an excised ferret trachea was strongly dependent on inlet concentration, implying that diffusion and reaction processes of acrolein in airway tissue are not linear. Only the low concentration of acrolein caused an increase of eicosanoid release from the exposed tracheae in the perfusate bath; it is possible that, at higher exposure concentration, the epithelium was sloughed off and most of the eicosanoids were lost. Although acrolein did not alter smooth muscle response to KCl, it did increase the contractile responses to CCh and ACh, suggesting an alteration in the pharmacomechanical but not the electromechanical coupling of ferret tracheal smooth muscle; therefore, it is more likely that this hyperresponsiveness occurs primarily by a mobilization of intracellular Ca2+ stores rather than by an increased influx of extracellular Ca2+ through voltage-dependent channels.

Genotoxicity of 2-halosubstituted enals and 2-chloroacrylonitrile in the Ames test and the SOS-chromotest

2-Chloroacrolein and 2-bromoacrolein are very potent direct mutagens not requiring metabolic activation in Salmonella typhimurium strains TA 100 and TA 1535. Mutagenic activities decrease with increasing degree of methyl substitution at carbon atom C-3 of the acrolein moiety from 2-chloroacrolein via 2-chlorocrotonaldehyde to 2-chloro-3,3-dimethylacrolein. With 2-chloroacrylonitrile equivocal results are obtained in strain TA 100 without S9-mix and unequivocal with S9-mix. In the SOS-chromotest the 2-chloroenals are also very strong genotoxins and the structure-activity relationships found in the Ames test are clearly confirmed. 2-Chloroacrylonitrile is not positive in the SOS-chromotest. The mutagenic mechanisms are discussed, and indications are provided that genotoxicity/mutagenicity depends on formation of DNA adducts, e.g., 1,N2-cyclic deoxyguanosine adducts.

Studies on trans-cinnamaldehyde. 1. The influence of dose size and sex on its disposition in the rat and mouse

The metabolism of trans-[3-14C]cinnamaldehyde was investigated in male and female Fischer 344 rats and CD1 mice at doses of 2 and 250 mg/kg body weight given by ip injection and in males at 250 mg/kg by oral gavage. Some 94% of the administered dose was recovered in the excreta in 72 hr in both species with most (75-81%) present in the 0-24-hr urine. Less than 2% of the administered dose was found in the carcasses at 72 hr after dosing. Urinary metabolites were identified by their chromatographic characteristics. In both species the major urinary metabolite was hippuric acid accompanied by 3-hydroxy-3-phenylpropionic acid, benzoic acid and benzoyl glucuronide. The glycine conjugate of cinnamic acid was formed to a considerable extent only in the mouse. The oxidative metabolism of cinnamaldehyde essentially follows that of cinnamic acid, by beta-oxidation analogous to that of fatty acids. Apart from the metabolites common to cinnamic acid and cinnamaldehyde, 7% of 0-24-hr urinary 14C was accounted for by two new metabolites in the rat and three in the mouse, which have been shown in other work to arise from a second pathway of cinnamaldehyde metabolism involving conjugation with glutathione. The excretion pattern and metabolic profile of cinnamaldehyde in rats and mice are not systematically affected by sex, dose size and route of administration. The data are discussed in terms of their relevance to the safety evaluation of trans-cinnamaldehyde, particularly the validity or otherwise of extrapolation of toxicity data from high to low dose.

Rapid plasma clearance of albumin-acrolein adduct in rats

Protein adducts are used as markers of chemical exposure. Determination of the clearance rate of these adducts from the blood circulation will provide the time frame for their measurement. Radioactive albumin was prepared biosynthetically by repeated intraperitoneal injections of L-[4,5-3H]lysine to a rat. After an affinity purification, an aliquot of this native [3H-lysine]albumin was adducted with 5 mM acrolein. Both the native albumin (A-treated group) and the albumin-acrolein adduct (AAA-treated group) were intravenously injected to separate groups of rats, and the clearance of radioactivity from the plasma was measured as a function of time. At the end of the experiment (33 h after the injection), radioactivity in the whole plasma, and in homogenates of liver, kidney and spleen and their trichloroacetic acid(TCA)-soluble and -insoluble fractions in both A- and AAA-treated groups, was measured. The results, at the initial 11 h after the injection, showed that the radioactivity was cleared from the circulating plasma more rapidly in the AAA-treated group (32% of the injected radioactivity remained) than the A-treated group (52%). At 33 h after the injection, 22% of the injected radioactivity remained in the plasma in the AAA-treated group as compared to 32% in the A-treated group. The whole homogenates of liver and kidney and their corresponding TCA-soluble fractions showed higher radioactivity in the AAA-treated group as compared to the A-treated group. However, the TCA-insoluble fractions from livers and kidneys of the AAA-treated group showed lower radioactivity as compared to the A-treated group. These results indicated that the albumin-acrolein adduct was removed more rapidly from the circulation than the native albumin, and degraded more rapidly by the liver and kidney. There was no preferential removal or degradation of the adducted albumin by the spleen.

Detoxication of base propenals and other alpha, beta-unsaturated aldehyde products of radical reactions and lipid peroxidation by human glutathione transferases

Radiation and chemical reactions that give rise to free radicals cause the formation of highly cytotoxic base propenals, degradation products of DNA. Human glutathione transferases (GSTs; RX:glutathione R-transferase, EC 2.5.1.18) of classes Alpha, Mu, and Pi were shown to promote the conjugation of glutathione with base propenals and related alkenes. GST P1-1 was particularly active in catalyzing the reactions with the propenal derivatives, and adenine propenal was the substrate giving the highest activity. The catalytic efficiency of GST P1-1 with adenine propenal (kcat/Km = 7.7 x 10(5) M-1.s-1) is the highest so far reported with any substrate for this enzyme. In general, GST A1-1 and GST M1-1, in contrast to GST P1-1, were more active with 4-hydroxyalkenals (products of lipid peroxidation) than with base propenals. The adduct resulting from the Michael addition of glutathione to the alkene function of one of the base propenals (adenine propenal) was identified by mass spectrometry. At the cellular level, GST P1-1 was shown to provide protection against alpha, beta-unsaturated aldehydes. GST P1-1 added to the culture medium of HeLa cells augmented the protective effect of glutathione against the toxicity of adenine propenal and thymine propenal. No protective effect of the enzyme was observed in the presence of the competitive inhibitor S-hexylglutathione. GST P1-1 introduced into Hep G2 cells by electroporation was similarly found to increase their resistance to acrolein. The results show that glutathione transferases may play an important role in cellular detoxication of electrophilic alpha, beta-unsaturated carbonyl compounds produced by radical reactions, lipid peroxidation, ionizing radiation, and drug metabolism.

Tissue distribution and excretion of 14C-labelled cinnamic aldehyde following single and multiple oral administration in male Fischer 344 rats

14C-labelled cinnamic aldehyde (CNMA) was given as a single oral dose, or 24 hr after multiple oral administration of non-radioactive CNMA for 7 days at 24-hr intervals, to male Fischer 344 rats at dose levels of 5, 50 or 500 mg/kg body weight. Residues of radioactive CNMA were measured. After the single dose radioactivity was distributed primarily in the gastro-intestinal tract, the kidneys and the liver of the rats. The radiolabel was excreted mainly in the urine, and at 24 hr 85.1, 84.2 and 81.2% of the administered radiolabel was recovered in the urine at the 5, 50 and 500 mg/kg dose levels, respectively. Faecal excretion of radiolabel at 24 hr for the 5, 50 and 500 mg/kg doses was 5.1, 4.0 and 3.2% of the administered dose, respectively. At all dose levels, a small amount of the dose was distributed to the fat and was easily measured in animals killed 3 days after dosing at the 50 or 500 mg/kg dose levels. Following multiple oral administration, similar tissue distribution and excretion patterns of radiolabel were found at the three dose levels. After 24 hr the administered radiolabel was distributed mainly to the fat, liver and gastro-intestinal tract. At 24 hr, recoveries of the radiolabel in the urine were 80.4, 80.6 and 81.9% of the dose for the 5, 50 and 500 mg/kg dose levels, respectively. Faecal excretion of radiolabel after multiple dosing at 24 hr accounted for 6.3, 6.9 and 4.5% of the administered radioactivity at the 5, 50 and 500 mg/kg dose levels, respectively. The major metabolic pathway of CNMA for all single and the 5 and 50 mg/kg multiple dose levels in this species of rat was found to be degradation to benzoic acid through beta-oxidation and excretion in the urine mainly as hippuric acid, with much smaller amounts of benzoic and cinnamic acids. At the multiple dose level of 500 mg/kg, benzoic acid was the major urinary metabolite, indicating that in the Fischer 344 male rat at this relatively high oral dose level the detoxification of CNMA proceeds differently and an alternative metabolic pathway is proposed.

Application of microencapsulation for toxicology studies. III. Bioavailability of microencapsulated cinnamaldehyde

The bioavailability of microencapsulated cinnamaldehyde (CNMA) was investigated in male F344 rats. Rats were gavaged with CNMA in corn oil using either microencapsulated or the neat chemical at doses of 50, 250, and 500 mg/kg. No differences between the two formulations at any of the doses were found in either CNMA blood concentration profiles or in the rate of urinary hippuric acid excretion. Both formulations showed a low bioavailability (< 20%) at 250 and 500 mg/kg. Regardless of the formulation used, oral gavage of CNMA significantly increased the urinary excretion of hippuric acid. About 75% of the dose of CNMA was metabolized to hippuric acid and recovered in the urine. The total amount of hippuric acid recovered in a 50-hr urinary collection correlated well with the CNMA dose. The data suggest that there was complete release of CNMA from the microcapsules and that microencapsulation of CNMA does not affect its bioavailability or its metabolism. Since CNMA microcapsules are stable in rodent diet, the microencapsulation of CNMA, and perhaps other labile chemicals, will prevent degradation and facilitate the testing of such compounds in toxicology studies.

Toxicokinetics of cinnamaldehyde in F344 rats

The toxicokinetic profile of cinnamaldehyde (CNMA) was investigated in Fischer 344 rats. CNMA was found to be unstable in blood. After iv administration, a large fraction of CNMA was immediately oxidized to cinnamic acid. The biological half-life of CNMA after iv administration was found to be 1.7 hr. After administration by gavage of CNMA at 250 or 500 mg/kg body weight using corn oil as vehicle, the maximum blood concentrations of CNMA were in the order of 1 microgram/ml. These low blood concentrations were maintained over a 24-hr period after a dose of 500 mg/kg, which is relatively long considering the short (1.7 hr) biological half-life of CNMA. The estimated oral bioavailability of CNMA was less than 20% for both the 250 and 500 mg/kg doses. No CNMA was present in blood at any time in rats dosed with 50 mg CNMA/kg body weight. Only a small amount of the administered CNMA was excreted in rat urine as free cinnamic acid or beta-glucuronide-conjugated cinnamic acid. The majority of CNMA administered orally was excreted in urine as hippuric acid within 24 hr. The maximum excretion rate occurred at 8 hr after gavage. Hippuric acid recovered in 50-hr urine samples was found to be directly proportional to the oral dose of CNMA.

Penetration of the fragrance compounds, cinnamaldehyde and cinnamyl alcohol, through human skin in vitro

The delivery of cinnamaldehyde and cinnamyl alcohol in fragrance through human skin has been investigated by in vitro penetration studies using full thickness human skin. Cinnamaldehyde was transformed to cinnamyl alcohol and cinnamic acid in the skin. The transformation took place in model protein solution, bovine serum albumin, as well as in skin homogenates. After conjugation of cinnamaldehyde with the protein, a lag time was observed after which cinnamyl alcohol and cinnamic acid were released. On the other hand, cinnamyl alcohol was not transformed in detectable amounts to either cinnamaldehyde or cinnamic acid during penetration of the skin.