Aldehydes: occurrence, carcinogenic potential, mechanism of action and risk assessment

Interactions of alpha, beta-unsaturated aldehydes and ketones with human glutathione S-transferase P1-1

In the present study the irreversible inhibition of human glutathione S-transferase P1-1 (GSTP1-1) by alpha, beta-unsaturated aldehydes and ketones was studied. When GSTP1-1 was incubated with a 50-fold molar excess of the aldehydes acrolein (ACR) and 4-hydroxy-2-nonenal (HNE) and the ketones curcumin (CUR) and ethacrynic acid (EA) at 22 degrees C, all of them inactivated GSTP1-1. The remaining activity after 4 h of incubation in all cases was lower than 10%. The aldehydes crotonaldehyde (CRA), cinnamaldehyde (CA) and trans-2-hexenal were found to inhibit GSTP1-1 only at a 5000-fold molar excess and even then, for example, for CA a higher remaining activity of 17% was observed. The same inhibition experiments were conducted with 3 mutants of GSTP1-1: the C47S and C101S mutants and the double mutant C47S/C101S. Remaining activity for C47S varied between +/- 40% for CRA, CA, CUR and HEX and +/- 80% for ACR, EA and HNE. For C101S it varied between 0 and 9% and for the double mutant C47S/C101S, activity after 4 h of incubation was variable. Again it varied between +/- 40% for CRA, CA, CUR and HEX and +/- 80% for ACR, EA and HNE. EA is known to react almost exclusively with cysteine 47. When [14C]EA was incubated with the GSTP1-1, modified by the alpha, beta-unsaturated carbonyl compounds, no [14C]EA was incorporated in the enzyme, indicating that in all cases this cysteine residue was one of the major targets. Since Michael addition with these reagents is known to be reversible, the results of incubation of the inactivated enzymes with an excess of glutathione (GSH) were determined. For all compounds, a restoration of the catalytic activity was observed. The results indicate that alpha, beta-unsaturated carbonyl derivatives inhibit GSTP1-1 irreversibly mainly by binding to cysteine residues of GSTP1-1, especially Cys-47, This means that some of these compounds (e.g. CUR) might modify GST activity in vivo when GSH concentrations are low by covalent binding to the enzyme.

Dosimetry, toxicity and carcinogenicity of inspired acetaldehyde in the rat

Acetaldehyde is a ubiquitous air pollutant. It is an important industrial chemical and is also produced during the combustion of wood or tobacco. In smoky indoor atmospheres concentrations of the aldehyde may reach 100 ppb. Acetaldehyde is metabolized to acetate (releasing hydrogen ion) by aldehyde dehydrogenase a process which, in most tissues, represents a detoxification pathway. In vitro, acetaldehyde forms DNA-DNA and DNA-protein crosslinks. It is a clastogen, and inducer of sister chromatid exchanges, and is, perhaps, a weak mutagen. Inhalation exposure to 1000 ppm may induce DNA-protein crosslink formation in nasal tissues in the rat in vivo. Inhalation toxicity studies have shown acetaldehyde vapor causes chronic tissue injury and tumor formation in nasal tissues at exposure concentrations of 750 ppm or higher, with nasal olfactory mucosa being more sensitive than respiratory mucosa. Dosimetric estimates suggest that marked tissue injury and carcinogenicity occurs only at inspired concentrations which are sufficiently high to overwhelm nasal aldehyde dehydrogenase detoxification capacity. The induction of squamous cell carcinomas in the respiratory mucosa by acetaldehyde displays many analogies to the induction of squamous cell carcinomas by formaldehyde. For both vapors, non-linear concentration response relationships are observed for DNA-protein crosslink formation, tissue injury, and carcinogenicity, suggesting these responses are associated. For both vapors it is possible to document an exposure concentration that produces nasal respiratory epithelial injury without increasing tumor incidence, suggesting that for respiratory mucosa-derived tumors, exposure to non-cytotoxic concentrations may pose limited carcinogenic risk. In addition to squamous cell carcinomas of the respiratory epithelium, acetaldehyde exposure also results in nasal olfactory injury and tumors (adenocarcinomas) in the rat. The studies performed to date have not demonstrated a no observable effect level for these responses, therefore, the precise role of cytotoxicity and regenerative cell proliferation in the carcinogenic process in olfactory tissues can not be evaluated. Acetaldehyde metabolism via aldehyde dehydrogenase results in the formation of two hydrogen ions. The olfactory mucosa is quite sensitive to acid and dosimetric estimates suggest that the intracellular acid production rates that may occur in olfactory mucosa during acetaldehyde exposure may be sufficiently high to cause tissue damage. Such acid-induced tissue damage may enhance the genotoxic and tumorigenic potential of acetaldehyde in olfactory mucosa, and may, therefore, represent an important process in the production of tumors in this tissue.

Dairy cattle as a bioindicator of exposure to genotoxic substances in a heavily polluted area in northern Bohemia

The exposure of dairy cattle to genotoxic agents in two districts with different levels of environmental pollution was estimated using cytogenetic analysis of bovine peripheral lymphocytes. The Teplice district represented an industrialized area where the air pollution rate is extremely high mainly in the winter, and the Prachatice district--an agricultural area with a relatively low level of pollution. The Ames test was used to examine feed samples for the content of mutagenic substances. Cows in the Teplice district showed a significantly higher count of aberrant cells (4.83 +/- 2.36) than cows in the Prachatice district (3.63 +/- 2.12). The sum of revertants induced by rinsings or extracts of feeds in both of the two test strains (Salmonella typhimurium TA 98 and TA 100) was significantly higher in the district of Teplice than in the district of Prachatice. The percentages of findings with mutagenic responses were 56.3 and 34.8% for the districts of Teplice and Prachatice, respectively. No mutagenic activity was found in milk samples collected in any of the districts. Apparently, the cows kept in the Teplice district were more exposed to genotoxic substances than the cows in the Prachatice district. The major source of this exposure was probably fresh fodder contaminated by industrial emissions.

A brief review of formaldehyde carcinogenesis in relation to rat nasal pathology and human health risk assessment

The 1980 report that inhaled formaldehyde induced nasal squamous cell carcinomas in rats had a significant societal impact and resulted in extensive research in the fields of rodent nasal pathology and human cancer risk assessment. This article presents an overview of the evolution of these events. It is concluded that the nasal passages of humans and rats are fundamentally identical biological target organs. Nevertheless, in the case of human health risk assessment, minor differences between these species may be critically important. Special attention should be paid to interspecies differences in nasal dosimetry and local metabolism; thus, chemical toxicity data derived from rats require careful interpretation when used for human risk assessments. In the case of formaldehyde, it is recommended that low-concentration (< or = 2 ppm airborne exposure) extrapolation, where no tissue damage is observed, be uncoupled from the responses at high concentrations (> or = 6 ppm), where epithelial degeneration, regenerative cell replication, and inflammation appear to be essential driving forces in formaldehyde carcinogenesis. The presence of treatment-related nasal lesions in rats following exposure to chemicals should always be treated as an indication of a potential human health risk, whether exposure is by the inhalation, oral, or dermal route.

Genotoxic effects of 2-trans-hexenal in human buccal mucosa cells in vivo

In 7 non-smoking healthy volunteers, the number of micronuclei (MN) was determined in exfoliated buccal mucosa cells before and after rinsing the mouth with an aqueous 10 ppm solution of 2-trans-hexenal during 3 consecutive days. All individuals showed at least a doubling of the MN frequency during one of the next 4 days. An increase of the mean group MN frequency was observed on the fourth day, becoming significant between the sixth and the seventh day. During the next 2 days, the MN frequency dropped down to nearly the control level. In a second study, 7 other volunteers were examined before and after eating 3-6 bananas per day over a period of 3 days. The bananas contained about 35 ppm of hexenal. Six of the 7 individuals showed at least a doubling of the MN frequency during one of the next 6 days. An increase in the mean MN counts was also observed, but the difference to the control value become non-significant during the test period. The results show for the first time that the flavoring constituent 2-trans-hexenal, which is present in many human foods exerts genotoxic effects on human buccal mucosa cells in vivo.

Presence of tetrahydro-beta-carboline-3-carboxylic acids in foods by gas chromatography-mass spectrometry as their N-methoxycarbonyl methyl ester derivatives

Various tetrahydro-beta-carboline-3-carboxylic acids (TH beta C-3-COOH) are identified in commercial foods and drinks by GC-MS. Positive identification of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCA) is demonstrated in soy and tabasco sauces, wine, beer, wine vinegar, cider, orange juice, toasted bread, blue cheese and yoghurt. 1,2,3,4-Tetrahydro-beta-carboline-3-carboxylic acid (THCA) occurs in toasted bread, beer, cider, wine vinegar, soy and tabasco sauce, orange juice and blue cheese. MTCA and THCA are reported for the first time in several of these products. MTCA appears as a mixture of two diastereoisomers with the same mass spectra. MTCA is the major TH beta C-3-COOH in foodstuffs except for toasted bread that contains more THCA. GC-MS analysis of N-methoxycarbonyl methyl ester derivatives of TH beta C-3-COOHs was used for chemical identification. Those derivatives were synthesized in a qualitatively using methyl chloroformate or methyl chloroformate and diazomethane reagents. Electron impact mass spectra of N-methoxycarbonyl-TH beta C-3-COOH methyl esters are reported and fragmentation assigned and discussed. These results prove the presence of TH beta C-3-COOHs in commercial foodstuffs suggesting their uptake during the daily consumption of foods.

Effects of reactive oxygen species (ROS) modulators, TEMPOL and catalase, on methoxyacetaldehyde (MALD) -induced chromosome aberrations in Chinese hamster ovary (CHO)-AS52 cells

Methoxyacetaldehyde (MALD), a metabolite of 2-methoxyethanol, has been shown to be clastogenic and mutagenic in CHO-AS52 cells. PCR-based-deletion screening of MALD induced CHO-AS52 mutants indicates that MALD induces large deletion mutation. Since MALD has an aldehyde as its reactive functional group, it can react with aldehyde oxidase to produce superoxide. The generation of these reactive oxygen species (superoxide, hydrogen peroxide and hydroxyl radical) may be the mechanism for genotoxicity of MALD. In the present study, TEMPOL and catalase which are ROS modulators were used to study the effects on MALD-induced chromosome damage in CHO-AS52 cells. The results showed that neither TEMPOL nor catalase can protect cells from MALD-induced chromosome aberrations. Therefore, the generation of reactive oxygen species may not be the primary mechanism of action of MALD.

DNA single and double strand breaks induced by aliphatic and aromatic aldehydes in combination with copper (II)

The aliphatic n-butyr-and n-valeraldehyde as well as the aromatic benz- and anisaldehyde induced DNA strand breaks in PM2 DNA in the presence of CuCl2. Neither aldehydes nor CuCl2 alone showed DNA breakage properties. The maximum of single strand breaks (SSBs) induced by the combination of CuCl2 and aldehydes was dependent on the CuCl2-concentration. The aliphatic aldehydes induced SSBs and double strand breaks (DSBs) at lower concentrations than aromatic aldehydes when optimal CuCl2 concentration were used. Catalase and neocuproine nearly completely inhibited strand break formation induced by aromatic aldehydes/CuCl2. The prevention of strand breaks induced by aliphatic aldehydes/CuCl2 was less effective. While the inhibition by neocuproine was only 25%, catalase was totally ineffective. In all aldehydes/CuCl2 mixtures the formation of Cu(I) was observed. The results point to different DNA damaging species produced during redox reactions of aromatic and aliphatic aldehydes in combination with CuCl2.

Cytogenetic evaluation of medical students exposed to formaldehyde vapor in the gross anatomy dissection laboratory

Formaldehyde (FA) is a potential carcinogen and mutagen. In addition to inducing genotoxic effects in subhuman laboratory tests, FA has been found to be mutagenic to cultured human cells. Evidence regarding the genotoxic potential of FA on exposed individuals at occupational levels is insufficient and conflicting. The authors of this study examined chromosomal aberrations in peripheral blood lymphocytes from a group of 30 medical students exposed to FA for 15 months in a gross anatomy dissection laboratory. The results were compared with similar analyses from 30 off-site, matched, unexposed controls. At average exposures of less than 1 ppm, 72-hour lymphocyte cultures of the study cohort did not reveal any difference in the incidences of chromosomal aberrations among the exposed and the control group by conventional Giemsa staining and G-banding.

Genotoxic effects of the alpha, beta-unsaturated aldehydes 2-trans-butenal, 2-trans-hexenal and 2-trans, 6-cis-nonadienal

The genotoxic effects of the 2-alkenals crotonaldehyde, 2-trans-hexenal and 2-trans-6-cis-nonadienal were studied by cytogenetic methods, analyzing frequencies of sister-chromatid-exchanges, numerical and structural chromosome aberrations and micronucleus induction in human blood lymphocytes and cells of the permanent Namalva line. Crotonaldehyde and hexenal were tested in concentrations of 5 microM to 250 microM and nonadienal from 5 microM to 70 microM. Significant dose-related increases of sister-chromatid-exchanges and micronuclei were found for all three compounds. Structural chromosomal aberrations were significantly increased only by crotonaldehyde, but not by hexenal and nonadienal. In contrast numerical chromosome aberrations were not induced by crotonaldehyde whereas hexenal and nonadienal were potent inducers of aneuploidy. The micronuclei were classified by using a centromere-specific DNA probe in a fluorescence in situ hybridization assay. Hexenal and nonadienal increased the percentage of centromere-positive micronuclei, nonadienal being considerably more potent than hexenal. From these results it was concluded that crotonaldehyde acts more as a clastogen whereas hexenal and nonadienal preferentially show aneugenic effects.

Inhibition of metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by dietary benzaldehydes

As part of a routine screening assay, benzaldehyde was found to inhibit 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism. Consequently, the effects of benzaldehyde and several structurally related compounds on NNK metabolism were examined in murine hepatic and pulmonary microsomes. All test compounds inhibited formation of the metabolites 4-oxo-4-(3-pyridyl)butyric acid (OPBA), 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in hepatic microsomes and inhibited formation of 4-(methylnitrosamino)-1-(3-pyridyl-N-oxide)-1-butanone (NNK N-oxide), HPB, and NNAL in pulmonary microsomes. m-Anisaldehyde was the most potent inhibitor, and p-hydroxybenzaldehyde and syringaldehyde were less potent than benzaldehyde and vanillin in inhibiting the formation of OPBA and HPB, NNK metabolites that reflect metabolic activation (alpha-hydroxylation). Vanillin was essentially as potent as benzaldehyde. The mechanism of inhibition exhibited by these compounds appears to be competitive in nature. The ability of these compounds to inhibit NNK activation suggests that these compounds may be effective blocking agents (anti-initiating agents) for NNK lung tumorigenesis.

Studies of the reaction of acetaldehyde with deoxynucleosides

The reaction of acetaldehyde with deoxynucleosides was studied in buffered solutions at room temperature (22-24 degrees C) and neutral pH. Reaction products were obtained with all deoxynucleosides with the exception of thymidine, as shown by reversed-phase HPLC analysis. The order of reactivity was dGuo > dAdo > dCyd, for which three, two and one reaction products, respectively, were obtained. We report here data on the kinetics of the reactions, the stability of the adducts at physiological pH, product yields, UV-spectroscopic data at different pH values, and describe the synthesis, isolation and structural characterization by FAB/MS and NMR of the stable adducts of acetaldehyde with dGuo. Furthermore, the formation of adducts with dGuo by the cooperative reaction of Aa with ethanol was studied.

Determination of aliphatic aldehydes as their thiazolidine derivatives in foods by gas chromatography with flame photometric detection

A selective and sensitive gas chromatographic method for the determination of saturated and unsaturated aliphatic aldehydes in foods has been developed. After extraction of the sample with acetonitrile, aldehydes were converted into their thiazolidine derivatives by the reaction with cysteamine, and then measured by gas chromatography with flame photometric detection. The calibration curves for aliphatic aldehydes in the range 20-2500 ng were linear and the detection limits at a signal-to-noise ratio of 3 were ca. 4-100 pg injected. Aliphatic aldehydes in foods could be selectively determined by this method without any interference from coexisting substances. Overall recoveries of aldehydes added to food samples were 82-111%. Analytical results for the determination of aliphatic aldehydes in various food samples are presented.

Study on the embryofeto-toxicity of citral in the rat

Citral, 3,7-dimethyl-2,6-octadien-1-al, found in the essential oils of a large variety of useful plants, is used as a scenting agent in household products, as a fragrance in cosmetics, and as a food flavouring additive. This study was undertaken to investigate the embryofeto-toxic potential of citral in the rat. Citral (60; 125; 250; 500 and 1000 mg/kg) in corn oil was given orally to Wistar rats from day 6 to 15 of pregnancy. Caesarean sections were carried out on day 21 of pregnancy, and the number of resorptions and implantation sites were recorded. Fetuses were weighed, examined for external malformations, and fixed for visceral examination, or cleared and stained with Alizarin Red S for skeleton evaluation. A transient decrease in weight gain from days 6 to 11 of gestation at the lowest doses, and a reduction in body weight minus uterine weight at term at the highest doses, indicated that citral was maternally toxic over the dose range tested. A slight but statistically significant increase in the ratio of resorptions per implantations was observed with 60 and 125 mg/kg body weight. Doses higher than 125 mg/kg reduced dose-dependently the ratio of pregnant per mated female. Signs of fetal growth retardation and a higher incidence of minor skeletal abnormalities were found in doses higher than 60 mg/kg. No increase in the frequency of visceral anomalies was found at any dose level, but an increase in fetal spleen weight was observed in doses higher than 125 mg/kg. Therefore, data presented in this paper indicate that the no-observed adverse effect level for embryofeto-toxicity is lower than 60 mg citral/kg body weight p.o.

Cinnamaldehyde-induced micronuclei in rodent liver

Cinnamaldehyde, a widely used flavoring agent, has so far been subjected to a limited range of genotoxicity tests, mainly carried out in vitro, which produced contradictory results. Therefore we have examined cinnamaldehyde using additional in vivo genotoxicity end-points. In Sprague-Dawley rats, a single oral dose equal to 1/2 LD50 did not induce DNA fragmentation in liver and gastric mucosa as evaluated by the alkaline elution technique, increased the frequency of micronucleated hepatocytes but not of bone marrow micronucleated polychromatic erythrocytes, and gave rise to a significantly higher incidence of total nuclear anomalies but not of micronucleated cells in forestomach mucosa. In Swiss mice, the equitoxic dose of cinnamaldehyde caused the same clastogenic effect in the liver, whilst a negative response was observed in both bone marrow and forestomach mucosa. Finally, in rats initiated with N-nitrosodiethylamine the administration of 500 mg/kg/day cinnamaldehyde for 14 successive days produced a modest but statistically significant increase of the average diameter and area of gamma-glutamyltranspeptidase-positive foci that, together with changes observed in other parameters, might be considered indicative of a potential promoting activity. Taken as a whole, these findings confirm that high doses of cinnamaldehyde may induce genetic alterations at the chromosomal level, and suggest that the liver is the preferential target of its undesirable effects.

Cytotoxic and genotoxic effects of five n-alkanals in primary cultures of rat and human hepatocytes

Five n-alkanals were examined for cytotoxicity, as evaluated by the trypan blue exclusion test, and for genotoxicity, as evaluated by the induction of unscheduled DNA synthesis (UDS), in primary cultures of rat and human hepatocytes. After 20 h exposure, cytotoxicity was similar in cells of the two species, and increased with the length of the carbon chain. In rat hepatocytes, propanal (10-100 mM), butanal (10-100 mM), pentanal (3-30 mM) and hexanal (3-30 mM) induced a modest but significant and dose-dependent increase of net nuclear grain counts, while in human hepatocytes this effect was not detected. Nonanal (3-30 mM), which showed the highest cytotoxic effect, failed to induce UDS in both cell types. These results seem to suggest that at the concentrations which are presumably attained after ingestion with food or generated by lipid peroxidation processes the five n-alkanals tested are presumably unable to induce genotoxic effects in the human liver.

Lack of effect of acute acetaldehyde treatment on X chromosome segregation in Drosophila melanogaster females

The effect of acute acetaldehyde treatments on X chromosome segregation was tested in germinal cells of Drosophila melanogaster females. The experiments were carried out using a test system where the nondisjunctional females (XXY) and only 1/4 of the expected regular progeny are viable. 24 h old virgin females were exposed for 60 min to 3, 4 and 5% acetaldehyde solutions by means of soaked tissue paper placed at the bottom of regular culture vials. After mating the females were brooded daily. Two additional experiments were performed with 0-2 h old and 4-5 day old virgin females using a 4% acetaldehyde solution. The results obtained show that acetaldehyde did not affect X chromosomal segregation in oocytes. This lack of effect could result from the highly efficient ADH-ALDH dependent detoxifying mechanism operating in Drosophila melanogaster.

Mutagenicity of chemicals added to foods

Much attention has recently been brought to the fact that many natural components of the diet are mutagenic and/or carcinogenic. Approximately 2700 distinct chemical entities, chemical mixtures, and plant extracts are allowed as direct food additives by the US F.D.A. These include chemicals found in the body, natural components of foods, and synthetic chemicals. In addition to the chemicals among these additives that are mutagenic, there are a number of mutagens that are normally present in the plant products that are consumed as part of the normal diets. The mutagenicity in Salmonella of these food additives was identified using the National Toxicology Program and US E.P.A. Gene-Tox databases. Relatively few of the chemicals deliberately added to foods have been tested for mutagenicity. Among the chemicals tested, approximately 15% were mutagenic in Salmonella. The mutagens include both organic and inorganic substances. Many of the natural plant components, such as flavonoids, hydrazides, and tannins also have been shown to be mutagenic. However, these natural components are not considered as food additives. A large proportion of the mutagenic food additives appear to act through the generation of oxygen- or free radicals. Although the relationships between mutagenicity and carcinogenicity of electrophilic chemicals has been well studied, the potential hazard of low-level increases in free-radical generating substances on tumor incidences is unknown.

Modification of genotoxicity by naturally occurring flavorings and their derivatives

The number of studies in the research field of antimutagenesis is increasing. The aims of many of these studies are preventing genetic hazards from environmental mutagens and elucidating the process of mutagenesis. Some naturally occurring flavorings such as vanillin, cinnamaldehyde, and coumarin have been reported to inhibit mutagenesis induced by mutagens in bacterial and mammalian cells. These flavorings are considered to act as antimutagens by modifying DNA replication and/or DNA repair systems after cellular DNA was damaged by mutagens. A factor that suppresses mutagenicity in a given situation, however, sometimes exerts enhancing effects when the endpoints investigated or the test conditions used are varied. This makes the evaluation of antimutagenic factors complicated. Different modifying effects of the above-mentioned flavorings observed in various test systems for genotoxicity are discussed, based on their proposed mechanisms.

Cytogenetic studies on gas station attendants

Forty-nine gas station attendants employed to pump fuel and 24 controls were studied cytogenetically. This type of worker is occupationally exposed to fuel fumes and to automotive vehicle emissions. Chromosome analysis showed a significantly higher frequency of chromosome deletions among the gas station attendants than a control group. Taking into account the relationship between clastogenicity and increased cancer risk, we may consider these workers to form a risk group.

A prospective study of stomach cancer among a rural Japanese population: a 6-year survey

Stomach cancer mortality was prospectively studied among 9753 Japanese men and women who first responded to a mailed questionnaire in 1985 and were then followed through May 31, 1991. During this follow-up period, 57 stomach cancer deaths were identified. Current smokers had an increased risk of deaths from stomach cancer compared with never smokers (relative risk (RR) = 2.29, 95% confidence interval (CI): 1.15-4.56), but there was no dose-response to amount of cigarettes smoked. Daily alcohol drinkers who consumed 50 ml or more of alcohol per day also had a greater risk than nondrinkers (RR = 3.05, 95% CI: 1.35-6.91). There was no association between stomach cancer mortality and individual food consumption except a positive association with fruit intake. However, frequent use (greater than or equal to 3-4/week) of broiling of meats and traditional style Japanese salad preparation in their cooking procedures were positively associated with stomach cancer mortality. The RR values compared with infrequent use (less than or equal to 1-2/month) were 2.27 (95% CI: 1.06-4.85) and 3.10 (95% CI: 1.40-6.85), respectively. A positive family history of cancer, especially stomach cancer, significantly increased the risk of stomach cancer deaths (RR = 2.01, 95% CI: 1.12-3.63). The effects of these variables remained after adjustment for other variables.

Thromboerythrocytes. In vitro studies of a potential autologous, semi-artificial alternative to platelet transfusions

In an attempt to overcome the limitations and drawbacks of using fresh platelets for transfusion therapy of thrombocytopenic patients, we have performed in vitro experiments on an autologous, semi-artificial alternative to platelet transfusions. Based on our previous studies of the interactions of unactivated and activated platelets with beads coated with peptides of various lengths, all of which contained the arginine-glycine-aspartic acid (RGD) cell recognition sequence, the peptide Ac-CGGRGDF-NH2 was chosen for covalent coupling to erythrocytes. A heterobifunctional crosslinking reagent (N-maleimido-6-aminocaproyl ester of 1-hydroxy-2-nitrobenzene-4-sulfonic acid) was used to crosslink via the peptide's free sulfhydryl group and the erythrocyte's surface amino groups. Approximately 0.5-1.5 x 10(6) peptide molecules bound per erythrocyte after 2 h of incubation, and most of the peptides appeared to crosslink to glycophorin A. The resulting cells, termed thromboerythrocytes, interacted selectively with activated platelets to form mixed aggregates. Studies with fluid phase RGD peptides and monoclonal antibodies indicated that the RGD peptides on the thromboerythrocytes interacted with the GPIIb/IIIa receptors on activated platelets. Thromboerythrocytes could also bind to platelets adherent to collagen. There was minimal erythrocyte hemolysis during the formation of thromboerythrocytes and studies of thromboerythrocyte osmotic fragility and cellular deformability showed no significant changes from control erythrocytes. Whereas there is a 20:1 ratio of erythrocytes to platelets in the circulation of normal individuals, the erythrocytes from as little as 50 ml of blood could be transformed into the equivalent of 2 U of platelets by numbers (equivalent to 18 U of platelets by mass), and reinfused into the same individual within several hours. These data encourage us to proceed to in vivo studies to assess the hemostatic efficacy of thromboerythrocytes in thrombocytopenic animals.

Catalysis by cytochrome P-450 of an oxidative reaction in xenobiotic aldehyde metabolism: deformylation with olefin formation

As we have briefly described elsewhere, cytochrome P-450 catalyzes the oxidative deformylation of cyclohexane carboxaldehyde to yield cyclohexene and formic acid in a reaction believed to involve a peroxyhemiacetal-like adduct formed between the substrate and molecular oxygen-derived hydrogen peroxide. This reaction is a useful model for the demethylation reactions catalyzed by the steroidogenic P-450s, aromatase, and lanosterol demethylase. In the present study, the cytochrome P-450-catalyzed formation of olefinic products from a series of xenobiotic aldehydes has been demonstrated. Isobutyraldehyde and trimethylacetaldehyde, but not propionaldehyde, are converted to the predicted olefinic products, suggesting a requirement for branching at the alpha carbon. In addition, the four C5 aldehydes of similar hydrophobicity were compared for their ability to undergo the reaction. The straight-chain valeraldehyde gave no olefinic products with five different rabbit liver microsomal P-450 isozymes. However, increasing activity was seen with the other isomers in the order of isovaleraldehyde, 2-methylbutyraldehyde, and trimethylacetaldehyde, with all of the P-450 cytochromes. The catalytic rate with trimethylacetaldehyde is highest with antibiotic-inducible P-450 form 3A6, followed by phenobarbital-inducible form 2B4 and ethanol-inducible form 2E1. Citronellal, a beta-branched aldehyde that is found in many essential oils and is widely used as an odorant and a flavorant, was found to undergo the oxidative deformylation reaction to yield 2,6-dimethyl-1,5-heptadiene, but only with P-450 2B4. The oxidative cleavage reaction with olefin formation appears to be widespread, as judged by the variety of aldehydes that serve as substrates and of P-450 cytochromes that serve as catalysts.