Prevention of work-related airway allergies; summary of the advice from the Health Council of the Netherlands.

The Health Council of the Netherlands published a report in which the best procedure and method for recommending health-based occupational exposure limits (OELs) for inhaled allergens were identified by evaluating the scientific state of the art. Many respiratory disorders in the workplace arise from inhalation of substances which can cause allergy. To protect workers against respiratory allergy, various preventive measures are taken, one of them being reduction of exposure by setting legally binding standards. These are based on health-based OELs that specify a level of exposure to an airborne substance, a threshold level, below which it may reasonably be expected that there is no risk of adverse health effects. The Council is of the opinion that an OEL should prevent against allergic sensitization, as sensitization plays a crucial biological role and is a prerequisite for the development of allergy. Furthermore, the Council considers it most likely that the exposure level below which no allergic sensitization develops for most allergens is so low, that OELs are difficult to set with the current knowledge and technical feasibilities. An alternative approach is to accept exposure, which carries a small predefined risk in developing allergic sensitization. In addition, it is worth considering periodic screening of exposed workers on allergic sensitization, because timely intervention can prevent worse. The feasibility of periodic screening and what else is needed to comply with the most important criteria, should however be judged case-by-case.

Time and dose-related ultraviolet B damage in viable pig skin explants held in a newly developed organ culture system.

For facilitating photochemical and toxicological studies an ex vivo skin model was developed in our laboratory using skin from domestic pigs. The model comprised the use of a complete skin piece, including the dermis and stratum corneum, of bigger areas to make future topical applications easier. Fully differentiated skin explants (5 x 50 mm, thickness 5 mm) were irradiated with ultraviolet B (UVB; 1-10 kJ/m2; 6 W/m2). Directly thereafter they were brought in culture (Dulbeccos modified Eagles medium containing hydrocortisone; air/liquid interface) for a maximum of 144 h. In nonirradiated skin explants, signs of tissue degeneration were observed after 48 h in culture (hematoxylin and eosin, light microscope). However, keratinocytes, isolated enzymatically (thermolysin and trypsin) at different time intervals in culture from nonirradiated skin explants showed negligible loss in viability (trypan blue exclusion) and increased apoptosis (terminal deoxynucleotidyl transferase-mediated deoxy uridine triphosphatase nick end labeling assay) for up to 72 h. Explants irradiated with a single dose of UVB showed a clear and reproducible dose- and time-dependent tissue degeneration, loss in keratinocyte viability and increase in apoptosis compared with nonirradiated explants at the same time interval. In conclusion, the presently designed ex vivo pig skin model can be a useful and cheap tool for future investigations of short-term UV-induced effects in combination with phototoxic and photoprotective compounds.

Effects of dietary fat and a vegetable-fruit mixture on the development of intestinal neoplasia in the ApcMin mouse.

The variation in colorectal cancer (CRC) incidence worldwide strongly suggests a role for dietary influences. Based on epidemiological data, protective effects of vegetables and fruit intake on CRC are widely claimed, while other data indicate a possible increased CRC risk from (higher) dietary fat intake. Therefore, we have investigated single and interactive effects of dietary fat and a vegetable-fruit mixture (VFM) in the ApcMin mouse, a mouse model for multiple intestinal neoplasia. In this study, four different diets (A-D) were compared, which were either low in fat (20% energy diets A/B) or high in fat (40% energy diets C/D). In addition, 19.5% (wt/wt) of the carbohydrates in diets B and D were replaced by a freeze-dried VFM. The diets were balanced so that they only differed among each other in fat/carbohydrate content and the presence of specific plant-constituents. Because the initiation of intestinal tumors in ApcMin mice occurs relatively early in life, exposure to the diets was started in utero. Without the addition of VFM, mice maintained at a high-fat diet did not develop significantly higher numbers of small or large intestinal adenomas than mice maintained at a low-fat diet. VFM added to a low-fat diet significantly lowered multiplicity of small intestinal polyps (from 16.2 to 10.2/mouse, 15 animals/group), but not of colon tumors in male ApcMin mice only. Strikingly, addition of VFM to female mice maintained on a low-fat diet and to both sexes maintained on a high-fat diet significantly enhanced intestinal polyp multiplicity (from 16.5 to 26.7 polyps/mouse). In conclusion, our results indicate that neither a lower fat intake nor consumption of VFM included in a high-fat diet decreases the development of polyps in mice genetically predisposed to intestinal tumor development.

Effects of a vegetables-fruit mixture on liver and colonic 1,2-dimethylhydrazine-metabolizing enzyme activities in rats fed low- or high-fat diets.

The effects of a vegetables-fruit mixture (19.5% w/w) were studied on hepatic (h) and colonic (c) 1,2-dimethylhydrazine (DMH)-metabolizing enzyme activities (ethoxy- and pentoxyresorufine-O-deethylation, NDMA-demethylase, glutathione-S-transferase, UDP-glucuronyltransferase) in rats fed low- or high-fat diets (20 or 40 energy%). A vegetables-fruit mixture added to the diets resulted in altered enzyme activities in animals either treated or not treated with DMH. Remarkably, the vegetables-fruit mixture given to DMH-treated rats decreased glutathione-S-transferase (h) and increased NDMA-demethylase activities (c), whereas the mixture given to controls increased glutathione-S-transferase (h) and decreased NDMA-demethylase activities (c). The high-fat diets only modulated enzyme activities in animals not treated with DMH.

Absence of an inhibitory effect of a vegetables-fruit mixture on the initiation and promotion phases of azoxymethane-induced colorectal carcinogenesis in rats fed low- or high-fat diets.

The potential inhibitory effects of a vegetables-fruit mixture on the initiation and promotion phases of azoxymethane-induced colorectal carcinogenesis were examined in rats fed low- or high-fat diets. Rats were fed low-fat diets (20 energy percent, Diets A and B) or high-fat diets (40 energy percent, Diets C and D), supplemented with a vegetables-fruit mixture (19.5% wt/wt, Diets B and D) or unsupplemented (Diets A and C) for 36 weeks. After the animals were maintained on the respective diets for four weeks, they were given three weekly injections of azoxymethane at 15 mg/kg body wt sc. Eight weeks after the start of the study, animals maintained on Diet A were switched to Diet B or C or maintained on the same diet. Animals maintained on Diet B or D were switched to Diet A or C, respectively. Furthermore, animals maintained on Diet C were switched to Diet A or D or maintained on the same diet. Multiplicity of colorectal tumors did not differ between groups fed a vegetables-fruit mixture during the initiation or the promotion phase (Group B-->A vs. Group A-->B; Group D-->C vs. Group C-->D). However, multiplicity was significantly lower in animals fed low-fat diets than in animals fed high-fat diets in combination with a vegetables-fruit mixture (Group A-->B/B--A vs. Group C-->D/D-->C). Furthermore, multiplicity was significantly increased in groups fed a high-fat diet during the promotion phase only in comparison with animals fed a low-fat diet during the whole experiment (Group A-->C vs. Group A-->A). No other differences in multiplicity or tumor incidences were observed among the eight experimental groups.

Effects of vegetables-fruit extracts and indole-3-carbinol on stearic acid-modulated intercellular communication and cytochrome P450-IA activity.

Modulatory effects were investigated of extracts of a vegetables-fruit mixture and indole-3-carbinol (I3C) on stearic acid-modulated gap junctional intercellular communication (GJIC) and cytochrome P450-IA activity (EROD). In V79 cells, pure water and hexane extracts of a vegetables-fruit mixture and 25 µg/ml I3C significantly protected against decreased GJIC caused by 10 µM stearic acid. Furthermore, pure, 10× and 100× diluted vegetables-fruit extracts significantly maintained their capacity to induce EROD activity in Caco-2 cells, but only when these extracts were added to the cells in media already containing 500 µM stearic acid for 48 h. Stearic acid itself did not induce EROD activity. I3C (10, 25, and 50 µg/ml) clearly induced EROD activity in Caco-2 cells, irrespective of the order at which I3C and stearic acid were added to the cells. In conclusion, the present in vitro study showed that vegetables-fruit extracts and I3C modulate effects of stearic acid on intercellular communication and cytochrome P450-IA activity.

Carcinogenicity testing of complete human diets in rats.

So far, in most animal experimental studies isolated food components have been tested. However, as components may interact with each other at different mechanistic levels, testing complex food mixtures more representative for human consumption patterns may better predict the ultimate carcinogenic risk. Studies were performed in Wistar rats using human and rat control diets to assess the effect of relevant food factors such as heat processing and the presence of non-nutrients in vegetables and fruit. The complete human diets, containing meat, bread and eggs, with or without vegetables and fruit, were composed according to mean consumption figures, balanced for macro- and micronutrients. Experiments were performed with spontaneous as well as with chemical-induced tumor models. Heat processing had no effect on tumor induction, while vegetables and fruit only exerted a protective effect on chemically induced tumors in rats fed low-fat animal diets. Data suggest interaction between major food factors in the human diet on colon carcinogenesis.

Interaction of dietary fat with a vegetables-fruit mixture on 1,2-dimethylhydrazine-induced colorectal cancer in rats.

The aim of the present investigation was to study the interaction of dietary fat in combination with a vegetables-fruit mixture on 1,2-dimethylhydrazine (DMH)-induced colorectal carcinogenesis in rats. For this purpose, 120 weanling male. Wistar rats received a semisynthetic diet without (Groups A and C) or with a vegetables-fruit mixture (Groups B and D; vegetables and fruit content 19.5% wt/wt) for 35 weeks. Diets of Groups A and B contained 20 energy percent (20e%) fat, whereas diets of Groups C and D contained 40e% fat. The vegetables and fruit used the amount of fat, and its fatty acid composition were chosen according to the mean consumption values of The Netherlands. After the animals were maintained for four weeks on the respective diets, they were given 10 weekly injections of DMH at 50 mg/kg body wt sc. After sacrifice, their colons were removed and examined macroscopically and microscopically for the presence of tumors. Rats fed high-fat diets developed significantly more tumors than rats fed low-fat diets. Furthermore, although not statistically significant, a lower number of colorectal tumors was observed in rats fed a low- or a high-fat diet containing the vegetables-fruit mixture than in rats fed diets without the vegetables-fruit mixture. No differences were observed in intestinal tumor incidences among all groups. The results suggest that the vegetables-fruit mixture used in this experiment, present in an amount comparable with the mean consumption in The Netherlands, has no significant inhibitory effect on the development of colorectal tumors induced by DMH in rats maintained on diets low or high in fat.

Modulation of dietary fat-enhanced colorectal carcinogenesis in N-methyl-N'-nitro-N-nitrosoguanidine-treated rats by a vegetables-fruit mixture.

The modulation of a vegetables-fruit mixture on N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced colorectal carcinogenesis was studied in rats maintained on a low- or a high-fat diet. For this purpose, 120 rats received a semisynthetic diet without (Groups A and C) or with a vegetables-fruit mixture (19.5% wt/wt, Groups B and D) for 35 weeks. Diets of Group A and B contained 20 (low) energy percent (20e%) fat, whereas diets of Groups C and D contained 40e% (high) fat. Between Weeks 4 and 9 the animals were given weekly intrarectal instillations of 6 mg MNNG/kg body wt. The colorectal adenocarcinoma incidences showed a significant decrease in animals fed high-fat diets with a vegetables-fruit mixture compared with animals fed a high-fat diet alone. Furthermore, without a vegetables-fruit mixture, diets high in fat caused a significant increase in adenocarcinoma incidence compared with diets low in fat. Although not significant, the adenoma incidences tended to be lower in animals fed a vegetables-fruit mixture than in animals maintained on a diet without this mixture. The results demonstrate that a vegetables-fruit mixture has a significant inhibitory potency on the development of colorectal tumors induced by MNNG in rats fed diets high in fat.