Apolipoprotein E and methylenetetrahydrofolate reductase genetic polymorphisms in relation to other risk factors for cardiovascular disease in UK Caucasians and Black South Africans.

Genetic polymorphisms for apolipoprotein E (apo E) and methylenetetrahydrofolate reductase (MTHFR) are believed to modulate risk of coronary heart disease (CHD) acting through regulation of lipid and homocysteine metabolism, respectively. The distributions of apo E and MTHFR alleles in Black South Africans, a population with a low CHD incidence, and UK Caucasians from the Cambridge area, with a higher CHD incidence, were therefore compared. Clinically healthy volunteers (207), including 107 UK Caucasians from the Cambridge area and 100 Black South Africans, participated in the study. Apo E and MTHFR genotypes were determined in all of them. Analyses for serum total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides and plasma fibrinogen were carried out in 65 UK Caucasians and 60 Black South Africans. The apo E epsilon4 allele, which is associated with elevated CHD risk, was present in 48% of Black South Africans compared to 20.8% of Caucasians (P < 0.0001); however, both total and LDL cholesterol levels in Black South Africans were 18-32% lower than in Caucasians with similar apo E genotypes. Hyperhomocysteinemia-causing MTHFR 677T variant was detected in only 20% of Black South Africans (no homozygotes) versus 56% of Caucasians with 12% homozygotes (P<0.0001). Our findings suggest that the potentially unfavourable pattern of apo E allele distribution in Black South Africans does not result in increased CHD incidence due to protection by dietary and/or other life style related factors. The exceptionally low frequency of MTHFR mutant homozygotes in this population suggests that this polymorphism should not be regarded as an important CHD risk factor among Black South Africans.

Quantitation of DNA from exfoliated colonocytes isolated from human stool surface as a novel noninvasive screening test for colorectal cancer.

The only widely used screening test for early detection of colorectal cancer, the fecal occult blood test, lacks both sensitivity and specificity because it relies upon incidental bleeding rather than the neoplastic process. With the purpose of developing a new noninvasive diagnostic approach, we quantified DNA extracted from cells isolated from the surface of human stools by a novel procedure. Stools collected from 28 healthy individuals, 17 colorectal cancer patients, and 11 colorectal polyp patients were analyzed. A stool DNA index (SDNAI), expressed as DNA amount in nanograms per gram of stool, had a remarkable 4.5-fold difference in mean values between colorectal cancer patients and healthy people of comparable age. SDNAI was 2133 +/- 407 in the cancer group versus 469 +/- 65 in healthy people of the older (> 50 years) age group (P = 0.0005). The difference was independent of tumor location and size. If 700 ng of DNA/g of stool was taken as a cutoff SDNAI value in discrimination between older healthy people and cancer patients, sensitivity and specificity values reached 1.00 and 0.81, respectively. Age dependence of SDNAI was demonstrated by substantially lower SDNAI values (mean, 227 +/- 41) in younger healthy individuals. Polyp patients sometimes displayed elevated SDNAI values, but considerable variation was observed (mean, 1215 +/- 548). These preliminary findings indicate that SDNAI provides a novel, simple, and powerful noninvasive test for colorectal cancer early detection and screening. The fundamental advantage of the SDNAI is that it directly characterizes colonic epithelium involved in carcinogenesis.

Comparison of metabolic effects of vegetables and teas with colorectal proliferation and with tumour development in DMH-treated F344 rats.

The aim of this study was to screen potentially chemopreventive vegetables and teas for their effects as human dietary components for the colorectal epithelium and also to seek biomarkers of preventive efficacy. Groups of F344 rats were adapted to a human basal diet supplemented with vegetables or teas, having known contents of glucosinolates, polyphenols and anti-oxidants. Both inductions and suppressions were found for overall glutathione S-transferase (GST) and quinone reductase activities. The mitotic index (MI) showed a three-fold range between groups, with substantial reductions by black tea, spinach, petit pois and peppers. Changes to PCNA labelling index and proliferation zone were marginal. No correlation was found between colonic and hepatic enzyme activities, nor with glucosinolate intake. Colonic MI was associated with the activity ratio GST(hepatic)/GST(colonic) (r = 0.49, P < 0.002), possibly reflecting a need for direct induction rather than exposure to products of hepatic conjugation.

Effect of meat and resistant starch on fecal excretion of apparent N-nitroso compounds and ammonia from the human large bowel.

N-nitroso compounds are produced in the human large intestine, but little is known about the dietary modulation of their synthesis at this site. The effects of meat and resistant starch on the fecal excretion of N-nitroso compounds, measured as apparent total N-nitroso compounds (ATNC), were therefore investigated in a crossover study involving eight healthy men. Three controlled diets that differed in the amount of meat (40 or 600 g) and resistant starch (37 g added to 600 g meat diet) were fed in random order, and fecal ATNC, as well as fecal ammonia and parameters of bowel function, were measured after 19 days of dietary adaptation. Mean ATNC excretion during the high-meat period was 114 micrograms/day, three times that during the low-meat period of 35 micrograms/day (p = 0.02); ammonia excretion was twice that during the low-meat period: 2.9 vs. 1.4 mmol/day (p = 0.03). The fecal ATNC were dissolved in the fecal water, and 45% had a molecular weight < 3,000. The addition of readily fermentable resistant starch to the high-meat diet significantly increased stool output from 118 to 153 g/day and decreased fecal pH from 7.2 to 6.6 but had no significant effect on fecal ATNC (151 micrograms/day), ammonia (3.7 mmol/day), whole gut transit time, urinary nitrate, or plasma urea. ATNC produced in the large bowel in association with a high-meat intake could represent an important source of DNA-damaging alkylating agents in the human large bowel.

Does increased endogenous formation of N-nitroso compounds in the human colon explain the association between red meat and colon cancer?

High red meat diets have been linked with risk of sporadic colorectal cancer; but their effects on mutations which occur in this cancer are unknown. G-->A transitions in K-ras occur in colorectal cancer and are characteristic of the effects of alkylating agents such as N-nitroso compounds (NOC). We studied th effect of red meat consumption on faecal NOC levels in eight male volunteers who consumed diets low or high in meat (60 or 600 g/day), as beef, lamb or pork, whilst living in a metabolic suite. Increased intake of red meat induced a significant (P<0.024) 3-fold increase from 40 + or - 7 to ab average of 113 + or - 25 microgram/day NOC, a range of exposure in faeces similar to that from tobacco-specific NOC in cigarette smoke. THe diets were isoenergetic and contained equal amounts of fat, but concentrations of heterocyclic amines were low. Faecal excretion of the promotor ammonia was significantly increased to 6.5 + or - 1.08 mmol/day. When the high red meat diets were supplemented with 20 g phytate-free wheat bran in six volunteers there was no reduction in NOC levels (mean 138 + or - 41 microgram/day NOC), but faecal weight increased. Higher starch and non-starch polysaccharide intakes reduced intraluminal cross-linking in microcapsules (r=-0.77) and reduced faecal pH (r=-0.64). In two volunteers there was no effect of 600 g white meat and fish o faecal NOC (mean low white meat diet 68 + or - 10 microgram/day, high white meat 56 + or -6 microgram/day nor on faecal nitrate, nitrite and iron. Faecal nitrite levels increased on changing from a white to red meat diet (mean high white meat diet 46 + or - 7 mg/day, high red meat diet mean 80 + or - 7 mg/day.) Increased endogenous production of NOC and precursors from increased red meat, but not white meat and fish, consumption may be relevant to the aetiology of colorectal cancer.

Magnetic microcapsules as novel biomonitors of cross-linking agents and diet-dependent reactive oxygen species in the human gastrointestinal tract.

Six healthy, scientifically informed human volunteers were given 14C-labeled polyethyleneimine (PEI) microcapsules by mouth. Fecal 14C recovery was inversely related to mean gut transit time (r = -0.66), and the extent of cross-linking between the membrane and core PEI was inversely related to total fecal output (r = -0.81). Cross-linking of PEI microcapsules may be a biomonitor of endogenous cross-linking agents within the human gastrointestinal tract. Extensive loss of [14C]CH3 label occurred from the microcapsules during human transit and in in vitro fermentations with human fecal flora. A mechanism whereby reactive oxygen species could arise in the iron-rich core of these microcapsules, leading to loss of [14C]CH3 label, is proposed.

Conversion of IQ to 7-OHIQ by gut microflora.

The rates of conversion of 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) to its reportedly mutagenic 7-keto derivative (7-OHIQ) by intestinal bacteria from humans, mice, and rats were compared. IQ was metabolized faster by cecal contents from rats or mice than by human fecal samples (113 and 87 mumol 7-OHIQ formed/hr/g cecal contents, respectively, vs. 12.3 mumol/hr/g feces). Cecal contents from germ-free rats colonized with human fecal bacteria [human flora-associated (HFA) rats] converted IQ to 7-OHIQ at rates generally lower than contents from rats colonized with their native flora. Diet had a marked effect on IQ metabolism by HFA rat cecal contents. The rate of IQ conversion to 7-OHIQ was increased in rats fed a diet high in beef dripping compared with that in rats fed a low-fat control diet. A diet high in olive oil, however, did not produce an increase in the IQ conversion rate. Addition of fiber to a purified diet increased the rate of IQ metabolism in the following order: sugar beet fiber > wheat bran > oat bran fiber > fiber-free diet. In a further study, HFA rats were fed human diets altered independently in their fat, fiber (wheat bran), and beef contents. The high-fiber diet produced the greatest increase in IQ conversion rate, followed by the high-fat diet. The diet with a high beef content and the control diet (low levels of all 3 macrocomponents) produced similarly low rates of IQ conversion. Material from incubations of IQ with HFA rat cecal contents, assumed to be 7-OHIQ on the basis of chromatographic behavior, was confirmed to be directly mutagenic, producing approximately 800 His+ revertants per microgram with S. typhimurium TA98.

Effects of risk-associated human dietary macrocomponents on processes related to carcinogenesis in human-flora-associated (HFA) rats.

Dietary fat, protein and fibre have been shown to modulate cancer risk in humans and the present study examined the biological effects in human-flora-associated (HFA) rats of altering intake levels within the normal human range. Two control groups, one HFA and the other germfree (GF), consumed a human diet low in fat, fibre and beef for 4 weeks; three other groups consumed human diets similar except for independent 3-fold increases in fat, beef protein or fibre. After 2 weeks on the diets, magnetically recoverable microcapsules were given orally to the rats and subsequently recovered from the faeces to assess endogenous cross-linking agents. After 4 weeks, measurements were made of gut microfloral enzyme activities, hepatic activation of dietary mutagens and hepatic DNA adducts by 32P-postlabelling. Activation in vitro of the dietary mutagens 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by hepatic S9, formation of endogenous hepatic DNA adducts in vivo and the beta-glucuronidase activity of caecal contents were all increased in the sequence high fat > high fibre > high beef = control. Of the two DNA adducts found in all HFA rats, only one was present in GF controls, indicating that the human gut microflora (subject to human dietary modulation) either releases a DNA-adducting product able to act outside the gastrointestinal tract, or stimulates the generation of such a product by mammalian processes. Caecal nitrate reductase activity was highest in rats fed the high beef diet, whilst entrapment of cross-linking agents was highest in those fed the high fibre diet. These results show that risk-related components of human diets interact with human gut microflora to modulate the production of endogenous DNA-adducting and cross-linking substances.

Detection by 32P-postlabelling of DNA adducts induced by free radicals and unsaturated aldehydes formed during the aerobic decomposition of fecapentaene-12.

Fecapentaene-12 (fec-12), excreted in human faeces, is genotoxic to human cells and a known animal carcinogen. The mechanism of its genotoxicity is unknown but may involve direct alkylation and/or free-radical generation. The formation of reactive species during fec-12 aerobic degradation was thus investigated by electron paramagnetic resonance (EPR) and NMR spectroscopic techniques. Oxy- and alkyl-radicals were detected as the 5,5'-dimethyl-1-pyrroline-N-oxide spin-trap adducts at fec-12 concentrations of between 0.1 and 2.0 mM. Under anaerobic conditions no free-radical generation was observed. NMR spectroscopy indicated that fec-12 degraded at least initially into three unsaturated aldehydes. The co-formation of free-radicals and unsaturated aldehydes suggests that fec-12 decomposed aerobically via a process analogous to lipid peroxidation. As both types of species, thus formed, may subsequently interact with DNA to form adducts, fec-12-induced DNA damage was investigated by 32P-postlabelling techniques. Using procedures that detect alkyl-type adducts, a number of putative adducts were detected in fec-12-treated DNA; two of similar mobility were observed in fec-12-treated 2'-deoxyguanosine-3'-monophosphate. Adducts with similar mobility have been detected in acrolein-treated DNA. One adduct with similar mobility was also observed in DNA obtained from normal human fibroblasts treated with fec-12. Using a C-18 ODS column, these putative adducts were eluted in 60-85% methanol, whereas 8-hydroxydeoxyguanosine-3'-monophosphate (8OHdGp) was eluted with 1% acetonitrile. Also unlike these putative adducts, the detection of 8OHdGp required HPLC fractionation prior to 32P-postlabelling. The formation of adducts, possibly aldehyde-related, and free-radical damage suggests that fec-12 genotoxicity may be the result of several different mechanisms, the relative importance of each is as yet unknown. Hydroxyl radicals were also detected during the aerobic decomposition of deca-2,4,6,8-tetraenal, a possible degradation product of fec-12 and a less potent mutagen, suggesting that free-radical generation may have only a minor role in fec-12-induced genotoxicity.

Dietary fibre, fat and beef modulation of colonic nuclear aberrations and microcapsule-trapped gastrointestinal metabolites of benzo[a]pyrene-treated C57/B6 mice consuming human diets.

Male C57/B6 mice were adapted to human diets of British origin that had 3-fold differences in either dietary fibre, fat or beef protein within the normal human range, and were then treated p.o. with 200 mg/kg benzo[a]pyrene (B[a]P) to induce colonic nuclear aberrations. [14C]B[a]P was included in the dose that followed 2 h after a gavage of magnetic PEI microcapsules. Untreated control groups were fed mouse chow or the baseline human diet which was low in all three dietary components (LLL). After the animals were killed at 24 h, large reductions (P less than 0.05) in colonic nuclear aberrations, and alterations to faecally excreted, microcapsule-trapped B[a]P metabolites were found for elevations of all three human diet components. Compared to untreated LLL control, B[a]P treatment gave an 8-fold increase in total nuclear aberrations, which was decreased 2- to 3-fold by increased fibre or fat. HPLC assay of B[a]P metabolites desorbed from microcapsules showed dietary fibre and beef protein to increase B[a]P diols and phenols but almost abolish B[a]P diones, consistent with a shift to enzymatic metabolism from non-specific oxidation. Increased fat considerably altered B[a]P metabolite disposition and microcapsule trapping, and comparison with microcapsules removed from colon contents indicated an altered enterohepatic circulation. Although it was not possible to attribute nuclear aberrations to individual B[a]P metabolites, a possible role of B[a]P diones seemed indicated, this being in line with previous microcapsule studies. These results show that microcapsules and human diets can be used in monitoring modulations of xenobiotic agents linked to mucosal chromosomal damage, with the eventual aim of human microcapsule biomonitoring.

Copper phthalocyanine labelled magnetic microcapsules: preparation, and binding properties in vitro and in vivo for mutagens having planar molecular structure.

Copper phthalocyanine tetrasulphonic acid (CPTS) functions were introduced into magnetic semi-permeable polyethyleneimine (PEI) microcapsules in order to create a recoverable scavenging system for trapping and biomonitoring, within the gastrointestinal cavity, of mutagens having a planar molecular structure. Stable ionic CPTS and covalent (thionylated CPTS, TCPTS) adducts to the microcapsule PEI were produced and shown to trap benzo[a]pyrene (B[a]P) in vitro in relation to the porphyrin/B[a]P ratio employed. 3-hydroxy B[a]P and B[a]P 3,6-dione from a crude B[a]P metabolite mixture, and a set of planar mutagens from crude opium/morphine pyrolysate mixtures could also be recovered in 7-86% yields after shaking with modified microcapsules followed by methanol/ammonia (50:1) desorption. Tetraols derived from B[a]P 7,8-diol-9,10 epoxide could also be recovered. Modified microcapsules were recovered magnetically from faeces of rats treated with [14C]B[a]P, and 45-51% of trapped radioactivity could be directly desorbed for HPLC assay compared with 30% for unmodified microscapsules. The relative extent of trapping by unmodified or CPTS- or TCPTS-modified microcapsules was different for various substrates, and it appears that the copper phthalocyanine tetrasulphonic acid moiety competes with another unidentified absorption/desorption structure in the microcapsules. These results show that selective and reversible trapping of carcinogens/mutagens having planar molecular structure can be achieved within the gastrointestinal tract.

Presence of endogenous cross-linking/bifunctional agents in gastrointestinal cavity as detected by transit of magnetic PEI microcapsules.

After gastrointestinal (GI) transit through rats, semipermeable bifunctional microcapsules containing polyethyleneimine (PEI) as a DNA-stimulating nucleophilic target showed physiochemical alterations consistent with PEI amine functions being intermolecularly cross-linked as by bifunctional agents. Such cross-linking both within the membrane and inside the microcapsules between core PEI and membrane PEI was simulated in vitro by glutaraldehyde, guanosine dialdehyde, 4-hydroxynonenal and fecapentaene-12, the latter two agents being known to form cyclic adducts or cross-links on DNA. These in vivo effects were demonstrated using both a radiolabel and a colorimetric label, and were attributable to both stomach and caecal sources by microcapsule recovery from the excised GI tract. By acid treatment of recovered microcapsules, cross-links formed in stomach and caecum were found to be respectively acid sensitive and acid resistant. The cross-linking effects observed were equivalent to treatment with 10 mumols glutaraldehyde but this seems a severe underestimate due both to known limited trapping of GI electrophiles by limited quantity of microcapsules and demonstrated low efficiency by glutaraldehyde in forming cross-links versus amine modifications. These results demonstrate that there are substantial concentrations of endogenous, membrane-penetrating, cross-linking/bifunctional agents in the GI tract which have significance due to the potent DNA-damaging and carcinogenic properties of such agents as a class.

Modulating effects in human diets of dietary fibre and beef, and of time and dose on the reactive microcapsule trapping of benzo[a]pyrene metabolites in the rat gastrointestinal tract.

Trapping by magnetic polyethyleneimine (PEI) microcapsules was utilized to investigate the influence in male rats of dose, human dietary composition and time-dependence on reactive metabolites of benzo[a]pyrene (B[a]P) in the gastrointestinal (GI) tract; also, PEI microcapsules modified with copper phthalocyanine tetrasulphonic acid (CPTS) were tested in vivo for trapping of endogenous mutagens having planar molecular structure. In a preliminary experiment the PEI microcapsules were administered by gavage at 0, 24 and 48 h, with [14C]B[a]P at 2 h to chow-fed BDVI rats; microcapsules were recovered from faeces collected at 24, 48 and 72 h, and then subjected to an extraction sequence showing that the trapped B[a]P metabolites were inconsistent with B[a]P diol epoxide trapping (as previously found) and unaltered by elapsed time or 5-fold dose alteration of B[a]P. Then five groups of F344 rats were fed isocalorically either one of four low-fat human diets or rat chow; in order to investigate influences of diet both on B[a]P and endogenous mutagens, half of each group was tested at 2 weeks with this PEI microcapsule/[14C]B[a]P protocol and then at 3 weeks, PEI-CPTS microcapsules (two gavages). So as to provide a cross-over comparison, the other half of each group was first tested with PEI-CPTS microcapsules followed by PEI microcapsules/[14C]B[a]P 1 week later. The human diets were prepared from cooked British foods so as to simulate the adequate intake of all nutrients required by humans; but with 3-fold differences in intake levels of beef and dietary fibre non-starch polysaccharide (NSP), while ensuring the same intake of available energy, protein, fat and calcium. They gave very similar body-weight gains in the four groups but greatly reduced faecal weight, protein and total faecal enzyme activity compared with chow; the extraction pattern of microcapsule-trapped B[a]P metabolite radioactivity was not significantly altered. However, human diet consumption caused a 2- to 6-fold increase in B[a]P metabolite binding to microcapsules and reductions in microcapsule recovery, net 70-h B[a]P excretion, faecal protein and total activities for beta-glucuronidase and beta-galactosidase; these effects were more pronounced after 3 weeks, presumably due to prolonged dietary adaptation. Increased NSP in human diets significantly increased the B[a]P metabolite excretion and marginally reduced the microcapsule binding. The increase in microcapsule binding of B[a]P metabolites, interpreted as reflecting an increased amount of reactive metabolites encountered, was related to the dietary intake weight ratio of beef/NSP.(ABSTRACT TRUNCATED AT 400 WORDS)

Systematic modulation by human diet levels of dietary fibre and beef on metabolism and disposition of benzo[a]pyrene in the gastrointestinal tract of Fischer F344 rats.

Groups of male Fischer F344 rats isocalorically consuming cooked, low-fat human diets were given magnetic polyethyleneimine (PEI) microcapsules and [14C]benzo[a]pyrene (B[a]P) by gavage in order to determine the effects of 3-fold changes in levels of dietary fibre non-starch polysaccharide (NSP) and beef protein during gastrointestinal transit on microcapsule trapping and associated parameters. Total 14C trapped by microcapsules during 70 h was decreased by fibre and increased by beef with significant effects (P = 0.03) for dietary mass ratio beef/fibre and compared to controls eating chow. Total B[a]P excreted in faeces and the ration for faeces/urine were increased by fibre and not by beef; the distribution of B[a]P metabolites between liquid and solids of faeces was increased by both factors but there was a net decrease by fibre when allowing for its influence on faecal mass. The distribution of binding between microcapsules and faecal solids was increased significantly by beef, but fibre had no effect when mass-normalized. B[a]P metabolites were extracted from microcapsules by methanol-ammonia and HPLC assay showed mainly benzo[a]pyrene-3,6-dione (B[a]P 3,6-dione), benzo[a]pyrene-1,6-dione (B[a]P 1,6-dione), an unidentified metabolite and substances consistent with tetraols; the beef (P = 0.02) and beef/fibre ratio (P = 0.01) significantly increased B[a]P-1,6-dione trapped and released. In vitro, B[a]P 3,6-semidione (dione reduced form) was bound by PEI microcapsules; the extent of extraction/hydrolysis was much lower than for B[a]P e,6-dione or B[a]P 7,8-diol 9.10-epoxide. Urinary excretion of B[a]P metabolites was decreased by fibre but not by beef. Nearly all the above parameters were different in a control group consuming rat chow. Taken together, these results are consistent with the following conclusions; (i) dietary fibre NSP overall decreases the availability of B[a]P metabolites to contact microcapsules and intestinal mucosa through static bulking rather than absorption; (ii) beef protein increases binding to microcapsules, and enhances free radical activation of B[a]P to its 6-yl radical form; (iii) a systematic set of concordant relationships for B[a]P disposition were found between faecal solids, faecal liquids, microcapsules and urine; and (iv) rat chow produced effects quite unrepresentative of the range for human diets prepared to be in the norm for human use. Endogenous UV-absorbing substances trapped by microcapsules or excreted in urine were also altered by dietary beef levels and were different from those of chow-consuming animals. It is generally concluded that human diets can and should be used in studying carcinogen metabolism and disposition.

Analytical tools and biomonitoring for carcinogens in complex mixtures.

Two approaches are described for the analysis and biomonitoring of complex mixtures: (a) activity-guided fractionation of pyrolysed opium followed by spectroscopic determination of molecular structure and (b) trapping of possibly genotoxic metabolites by a series of microencapsulated, recoverable, synthetic macromolecular targets within the milieu of the gastrointestinal tract. Opium pyrolysis was shown to produce (principally from morphine) a series of hydroxyphenanthrenes of novel structure having activity not only in the S. typhimurium used as a guide, but also in a variety of in vitro and in vivo test systems. Many analytical tools were used together for separation, structure determination and activity monitoring, and their relative merits and overall strategy are discussed. The microcapsules have been shown to trap carcinogens, nitrosating agents, cross-linking agents and aldehydes. Their trapping of a model carcinogen in vivo is modulated by components of human diets. Development of these microcapsules for detecting endogenous carcinogens and their sources is discussed with reference to the type of target and analytical tools that may be appropriate.

Nucleophilic selectivity and reaction kinetics of chloroethylene oxide assessed by the 4-(p-nitrobenzyl)pyridine assay and proton nuclear magnetic resonance spectroscopy.

The nucleophilic selectivity (Swain-Scott's constant s) of chloroethylene oxide (CEO), an ultimate carcinogenic metabolite of vinyl chloride, was determined to be 0.71 using the 4-(p-nitrobenzyl)pyridine (NBP) assay (Spears method). The molar extinction coefficient of the adduct formed between NBP and CEO was measured; and the second-order rate constants for the reactions of CEO with NBP and with thiosulfate were estimated at three temperatures. The disappearance of CEO and the formation of chloroacetaldehyde (CAA) and glycolaldehyde (GCA) were followed in D2O or a mixture of D2O/hexadeuterated acetone (acetone-d6), using Fourier transform proton nuclear magnetic resonance spectroscopy (1H-FTNMR). Evidence was obtained that CEO reacts with chloride ions to yield CAA at a rate constant of about 17 M-1 h-1 in D2O/acetone-d6 (1 : 1, v/v) at 280 K. Under the same conditions, the first-order rate constant kr for the thermal rearrangement of CEO into CAA was estimated to be approximately 0.41 h-1. These data suggest that the isomerization of CEO may be a minor reaction in physiological saline. These chemical properties of CEO are discussed in relation to the mechanism of vinyl chloride-induced carcinogenesis.

Time-dependent distribution and excretion of radiolabelled, semipermeable, stable magnetic microcapsules.

The time-dependent excretion and potential body retention of magnetic polyethyleneimine (PEI) microcapsules, methylated with [14C]methyl iodide have been investigated after intragastric administration to mice. Gastric emptying was rapid but about 10% of the administered dose was still present in the stomach after 6 h; the number of microcapsules within the small intestine remained approximately constant over 1-6 h. Excretion of microcapsules in the faeces was virtually complete (98.7% excretion within 72 h), with small amounts of radioactivity excreted via the urine or as [14C]CO2. There was no detectable adsorption or retention of microcapsules within the body as measured by either a whole-body autographic study or by direct quantitation of tissue radioactivity.

Recoverable, semipermeable, microencapsulated DNA surrogates for monitoring the colorectal cavity; in-situ effects of fibre and meat in human diets on benzo[a]pyrene and possible endogenous cross-linking agents.

Semipermeable magnetic microcapsules containing polyethyleneimine (PEI) as a DNA surrogate are shown to trap 14C-benzo[a]pyrene and hitherto unknown, endogenous, putative cross-linking agent(s) within the gut of male Fischer rats. Trapping is substantially modulated by complete, cooked human diets fed isocalorically and varied three-fold in either beef, fat or bran fibre nonstarch polysaccharide within the normal human intake levels. Preliminary results indicate that the crosslinking agent(s) are derived from microflora. Using metabolized benzo[a]pyrene as a model DNA damaging agent within the gut, beef and decreased bran fibre were found to increase its availability, paralleling risk alterations found in nutritional epidemiology. These novel microcapsules are capable of intercepting a range of substances relevant to DNA damage.

Membrane formation and characterization of semi-permeable magnetic polyhexamethyleneterephthalamide microcapsules containing polyethyleneimine (PEI) for trapping carcinogens.

The membrane characteristics were studied of semi-permeable magnetic polyhexamethyleneterephthalamide microcapsules containing polyethyleneimine (PEI) in order to optimize their use for trapping carcinogens in vivo. The microcapsules were prepared by interfacial polymerization techniques from an aqueous mixture of hexamethylenediamine, PEI and ferrofluid EMG 705 dispersed in an organic phase containing terephthaloyl chloride and trimesoyl chloride. The resulting microcapsule membranes had a complex structure consisting of a polyamide component (70-84 per cent by weight) with chain-terminating carboxy functions and the remainder were PEI incorporated throughout the membrane having residual amine functions. Substantial variation in preparative conditions had little effect upon membrane incorporation of PEI which cross-linked the polyamide chains. However, both TEM and SEM data indicated structural differences when lower concentrations of hexamethylenediamine were used, there being a more uniform formation to give a distinct outer membrane layer (18-45 nm) visible on cross-section and appearing as a smooth outer surface. Magnetite particles appeared to be present throughout the membrane. During membrane formation, no PEI was present in the organic phase, indicating that the microcapsule membrane had formed inwards contrary to the membranes formation reported previously in other systems. The inward transfer of reactive acid chlorides into the aqueous phase resulted in a core of modified PEI. Microcapsule binding of probe substances [14C]N-methyl-N-nitrosourea and eosin varied with the microcapsule preparative conditions used, and appeared to be critically dependent upon the membrane characteristics, especially the incorporation of PEI into the membrane. Characterization of membrane formation and properties allows the optimization of microcapsule binding properties.