Biomedical subjects

Henk van Loveren

Publications and source records attributed to Henk van Loveren.

At least 19 recordsLinked to original sources

PubMed2026

Dietary Titanium Dioxide (E171) Alters the Colon Transcriptome-Evidence From a Human Dietary Intervention Study.

Food-grade titanium dioxide (E171) has been removed from the European food market due to concerns about its potential genotoxicity, yet human evidence remains limited. Given its continuous use outside the European Union, clarifying its potential hazard is essential for human risk assessment. In a randomized crossover study, 31 adults consumed 2 mg/kg body weight/day of E171 for 2 weeks, with biospecimens collected after both control and exposure periods. Oral intake resulted in elevated titanium concentrations in feces (CTRL: 6.3 mg/kg; E171: 377 mg/kg). Particle characterization showed a median size of 228 nm, with 9% <100 nm. Systemic oxidative stress increased, evidenced by increased superoxide radical levels in whole blood (p = 0.057). Transcriptomic profiling of colon biopsies revealed activation of 73 pathways linked to oxidative stress, cellular metabolism, and colorectal cancer-associated processes. The observed transcriptional changes were consistent with findings of its proposed mode of action. This human intervention study characterizes the effects of dietary E171 following human gastrointestinal digestion and provides evidence that exposure to dietary E171 induces systemic oxidative stress and transcriptional changes in the colon. These findings strengthen regulatory concerns about E171 as a food additive and its potentially harmful effects on human gastrointestinal health.

Humans↗

PubMed2007

Toxicogenomics in the assessment of immunotoxicity.

Microarray analysis is used for simultaneous measurement of expression of thousands of genes in a given sample and as such extends and deepens our understanding of biological processes. Application of the technique in toxicology is referred to as toxicogenomics. The examples of assessment of immunotoxicity by gene expression profiling presented and discussed here, show that microarray analysis is able to detect known and novel effects of a wide range of immunomodulating agents. Besides the elucidation of mechanisms of action, toxicogenomics is also applied to predict consequences of exposing biological systems to toxic agents. Successful attempts to classify compounds using signature gene expression profiles have been reported. These did, however, not specifically focus on immunotoxicity. Databases containing expression profiles can facilitate the applications of toxicogenomics. Platforms and methodologies for gene expression profiling may vary, however, hampering data compiling across different laboratories. Therefore, attention is paid to standardization of the generation, reporting, and management of microarray data. Obtained gene expression profiles should be anchored to pathological and functional endpoints for correct interpretation of results. These issues are also important when using toxicogenomics in risk assessment. The application of toxicogenomics in evaluation of immunotoxicity is thus not yet without challenges. It already contributes to the understanding of immunotoxic processes and the development of in vitro screening assays, though, and is therefore expected to be of value for mechanistic insight into immunotoxicity and hazard identification of existing and novel compounds.

Animals↗

PubMed2007

The importance of dietary control in the development of a peanut allergy model in Brown Norway rats.

This report describes the further development of a peanut allergy model in Brown Norway (BN) rats and in particular the importance of allergen-free breeding of the laboratory animals for the allergen to be used. For this purpose BN rats were bred for 3 generations on soy- and peanut-free feed since it is known that the legumes peanut and soy are cross-reactive. In addition, the effect of cholera toxin (CT), an oral adjuvant often used to increase the sensitivity of food allergy models, was investigated in the BN rat model. BN rats that were bred on both soy- and peanut-free feed could be sensitized orally to peanut (all exposed rats developed peanut-specific IgE, IgG2a and IgG1) and the adjuvant CT could only enhance this sensitization to a limited extent. We also found different protein recognition patterns against purified peanut allergens (Ara h1, Ara h2 and Ara h3) between intraperitoneally (i.p.) and orally sensitized BN rats. Orally sensitized rats recognized all tested allergens whereas i.p. sensitized rats only recognized Ara h1 and Ara h2. Our conclusion is that a model for food allergy should preferably be (A) oral and (B) if possible without the use of adjuvantia. Our model in BN rats unites these preferred characteristics. In addition, we show the importance of dietary control when conducting oral sensitization studies. Special attention must be paid to unscheduled dietary pre-exposure of the animals to the protein under investigation to obtain optimal oral sensitization.

Adjuvants, Immunologic↗

PubMed2006

Evaluation of immunomodulation by Lactobacillus casei Shirota: immune function, autoimmunity and gene expression.

Lactic acid bacteria are claimed to have immunomodulating effects. Stimulation as well as suppression of T helper (Th)1 mediated immune responses, have been described for various strains. Experiments involving Lactobacillus casei Shirota (LcS) detected mainly enhancement of innate immune responses and promotion of Th1 mediated immune reactivity. To confirm and further investigate modulation of Th1 responses and development of autoimmune disease by LcS, the consequences of oral administration of LcS were assessed in several experiments. The effect of LcS varied between the different models. No modulation was found in the mitogen-induced cell proliferation and cytokine release assays in mesenteric lymph nodes of Wistar rats. LcS inhibited the Th1 mediated immune response in an adapted murine Local Lymph Node Assay (LLNA) in BALB/c mice, whereas experimental autoimmune encephalomyelitis (EAE) in Lewis rats was aggravated. These varying effects on Th1 responses indicate that beneficial as well as harmful effects on immune related disorders could occur after LcS consumption. Since microarray analysis is suggested to be more sensitive and predictive than functional tests, gene expression profiling was included as an alternative endpoint in the testing of immunomodulation. The detected gene expression profiles did not reflect the effects of LcS on the immune system. Microarray analysis may therefore have no more predictive value than immune function assays when investigating immunomodulation by probiotics. To gain further insight into effects of probiotics on immune function, experiments including cytokine assays and gene expression analysis combined with disease models could be useful.

Animals↗

PubMed2006

Immunotoxic effects of chemicals: A matrix for occupational and environmental epidemiological studies.

BACKGROUND: Many biological and chemical agents have the capacity to alter the way the immune system functions in human and animals. This study evaluates the immunotoxicity of 20 substances used widely in work environments. METHODS: A systematic literature search on the immunotoxicity of 20 chemicals was performed. The first step was to review literature on immunotoxicity testing and testing schemes adopted for establishing immunotoxicity in humans. The second step consisted of providing a documentation on immunotoxicity of substances that are widely used in work environment, by building tables for each chemical of interest (benzene, trichloroethylene, PAHs, crystalline silica, diesel exhausts, welding fumes, asbestos, styrene, formaldehyde, toluene, vinyl chloride monomer, tetrachloroethylene, chlorophenols, 1,3-butadiene, mineral oils, P-dichlorobenzene, dichloromethane, xylene, 1,1,1-trichloroethane, ethylene oxide). The third step was the classification of substances; an index (strong, intermediate, weak, nil) was assigned on the basis of the evidence of toxicity and type of immunotoxic effects (immunosuppression, autoimmunity, hypersensitivity) on the basis of the immune responses. Finally substances were assigned a score of immunotoxic power. RESULTS: Tables have been produced that include information for the 20 substances of interest, based on 227 animal studies and 94 human studies. Each substance was assigned an index of immunotoxic evidence, a score of immunotoxic power and type of immunotoxic effect. CONCLUSIONS: This matrix can represent a tool to identify chemicals with similar properties concerning the toxicity for the immune system, and to interpret epidemiological studies on immune-related diseases.

Animals↗

PubMed2006

Probiotics: immunomodulation and evaluation of safety and efficacy.

The intake of probiotics has been associated with beneficial effects on the immune system, such as improved disease resistance and diminished risk of allergies. This review gives an overview of the immunomodulatory effects of probiotics investigated with in vitro assays, experimental animal models, and clinical trials, and explores possible mechanisms underlying the immunomodulatory effects. Immunomodulation, however, is not always beneficial and might induce detrimental effects; therefore, a scheme is proposed for benefit-risk assessment of immunomodulation by probiotics. Within this scheme, expert judgment based on data derived from a panel of in vitro assays, animal models, and clinical trials should lead to conclusions on efficacy and safety aspects of probiotics.

Animals↗

PubMed2005

Repeated doses of UVR cause minor alteration in cytokine serum levels in humans.

The aim of our study was to compare serum concentration of IL-1beta, IL-6, IL-8, IL-10, and TNF-alpha in 105 healthy volunteers before and after exposure to UVR: 25 subjects (10 days of UVB), 55 (10 days of UVB or solar-simulated radiation, followed by acute UVB dose), and 25 (local high dose of UVB). In all the individuals blood samples were analyzed before and after final irradiation by chemiluminescence assay. After 10 days of UVB irradiation a statistically significant increase in serum concentration only in IL-8 (P<.05) and strong tendency in TNF-alpha (P=.05) were observed. The applied schedules of irradiation have minor impact on serum cytokine level and still a threshold dose of UVR causing systemic immune impairment is unknown.

Humans↗

PubMed2005

In vitro assessment of sensitizing activity of low molecular weight compounds.

Predictive tests to identify the sensitizing properties of chemicals are carried out using animals. There is as yet, no accepted in vitro method for the identification of skin sensitizing chemicals. Such in vitro tests should encompass (parts of) the sensitization phase of contact hypersensitivity. Two cell types are predominantly involved in this process, keratinocytes (KC) and Langerhans cells, the latter being a specialized type of skin dendritic cells (DC). Low molecular weight chemicals act as haptens; KC respond to allergen contact by, among others, producing proinflammatory cytokines, while DC take up the haptenized protein, migrate, and present antigen to T-cells. During migration, DC mature, resulting in a loss of antigen uptake capacity, thereby increasing expression of certain surface molecules. Thus, both cytokine production by KC and surface marker expression by DC may be used as in vitro models for the identification of sensitizers. Several reports have shown that intracellular IL-1 alpha is a promising candidate to identify sensitizers using KC. We have recently shown that the potency of sensitizers may be determined by dose-response analysis of intracellular IL-1 alpha and IL-18 using a murine KC cell line. The ranking of potency using this in vitro method was similar to the ranking previously established using the local lymph node assay. Using DC, effects on the expression of various cell surface markers, cytokines, and molecules involved in antigen uptake have been shown to identify sensitizers. One study showed that also the potency of sensitizers may be determined using DC. Additional studies are required to establish whether KC or DC, or combinations thereof, are most suitable for in vitro identification and potency assessment of sensitizers.

Animals↗

PubMed2005

Current status and burning issues in immunotoxicity testing of drugs.

Besides pathology endpoints, additional immune function endpoints have been included in the Note for Guidance on Repeated Dose Toxicity by the European Union (July 2001), which concern the analysis of antibody responses to a T-cell-dependent antigen. Guidance papers of other regulatory authorities are published as well. The main issue is the need for functional immunotoxicity testing to detect unintended immunosuppression. The International Conference on Harmonization (ICH) has surveyed studies from the files of the pharmaceutical industry to find the proportion of compounds that can be detected by additional immunotoxicity testing. Preliminary analysis shows that 10-15% of the compounds in the survey only react positively to the additional tests. More data are requested from the pharmaceutical industry. The Expert Working Group of the ICH has decided to choose a cause-for-concern approach to immunotoxicity rather than a routine-screening approach. The causes for concern are to be defined during ICH negotiations.

Drug Industry↗

PubMed2005

Suppression of contact hypersensitivity after repeated exposures of humans to low doses of solar simulated radiation.

Although it is generally recognised that UV radiation (UVR) can induce suppression of contact hypersensitivity (CHS) in human subjects, most protocols to date have not tested the effect of low daily doses of solar simulated radiation (SSR). In the present study, healthy individuals, divided into four groups each consisting of approximately 34 subjects, were whole-body irradiated with 1.2 standard erythema doses of SSR for 2, 10 or 30 consecutive days, or were unirradiated. They were sensitised with diphenylocyclopropenone (DPCP) on one exposed body site 24 h after the final UVR. The occurrence and severity of the primary allergic response were noted, and both parameters were shown to be significantly lowered in the group irradiated for 30 days compared with the unirradiated group. Elicitation of CHS was undertaken 3 weeks after the sensitisation, using a range of concentrations of DPCP on a UV-protected body site. The extent of the CHS at 48 h was assessed by the clinical score, by an erythema meter and by histological examination of a biopsy taken from the site challenged with one selected concentration of DPCP. Although erythema and pigmentation did not differ between the groups, a significant negative correlation was found between the clinical CHS score and the number of days of UV exposure, at the lowest challenge dose of DPCP. In addition a significant negative correlation was revealed between the intensity of spongiosis (intraepidermal oedema and vesicles, as evaluated by histology) and the number of days of UV exposure. Thus small daily doses of SSR induce suppression of CHS in human subjects and the effect is cumulative, indicating that there is no adaptation to the immunomodulating effects of UVR, at least over the test period of 30 days.

Cyclopropanes↗

PubMed2005

Use of the local lymph node assay in assessment of immune function.

The murine local lymph node assay (LLNA) was originally developed as a predictive test method for the identification of chemicals with sensitizing potential. In this study we demonstrated that an adapted LLNA can also be used as an immune function assay by studying the effects of orally administered immunomodulating compounds on the T-cell-dependent immune response induced by the contact sensitizer 2,4-dinitrochlorobenzene (DNCB). C57Bl/6 mice were treated with the immunotoxic compounds cyclosporin A (CsA), bis(tri-n-butyltin)oxide (TBTO) or benzo[a]pyrene, (B[a]P). Subsequently, cell proliferation and interferon-gamma (IFN-gamma) and interleukin (IL)-4 release were determined in the auricular lymph nodes (LNs) after DNCB application on both ears. Immunosuppression induced by CsA, TBTO and B[a]P was clearly detectable in this application of the LLNA. Cytokine release measurements proved valuable to confirm the results of the cell proliferation assay and to obtain an indication of the effect on Th1/Th2 balance. We believe to have demonstrated the applicability of an adapted LLNA as an immune function assay in the mouse.

Administration, Oral↗

PubMed2005

Detection of immunotoxicity using T-cell based cytokine reporter cell lines ("Cell Chip").

Safety assessment of chemicals and drugs is an important regulatory issue. The evaluation of potential adverse effects of compounds on the immune system depends today on animal experiments. An increasing demand, however, exists for in vitro alternatives. Cytokine measurement is a promising tool to evaluate chemical exposure effects on the immune system. Fortunately, this type of measurement can be performed in conjunction with in vitro exposure models. We have taken these considerations as the starting point to develop an in vitro method to efficiently screen compounds for potential immunotoxicity. The T-cell lymphoma cell line EL-4 was transfected with the regulatory sequences of interleukin (IL)-2, IL-4, IL-10, interferon (IFN)-gamma or actin fused to the gene for enhanced green fluorescent protein (EGFP) in either a stabile or a destabilised form. Consequently, changes in fluorescence intensity represent changes in cytokine expression with one cell line per cytokine. We used this prototype "Cell Chip" to test, by means of flow cytometry, the immunomodulatory potential of 13 substances and were able to detect changes in cytokine expression in 12 cases (successful for cyclosporine, rapamycin, pentamidine, thalidomide, bis(tri-n-butyltin)oxide, house dust mite allergen (Der p I), 1-chloro-2,4-dinitrobenzene, benzocaine, tolylene 2,4-diisocyanate, potassium tetrachloroplatinate, sodium dodecyl sulphate and mercuric chloride; unsuccessful for penicillin G). In conclusion, this approach seems promising for in vitro screening for potential immunotoxicity, especially when additional cell lines besides T-cells are included.

Animals↗

PubMed2005

Immune function testing of human pharmaceuticals: regulatory overshoot?

Suppression of the activity of the immune system can result in decreased resistance to (opportunistic) infection and cancer. Experimental animal studies have identified many immunotoxic agents, but data on unintended immuno-toxicity of human pharmaceuticals are limited. To enhance the sensitivity of the non-clinical screening of human pharmaceuticals, immunotoxicity endpoints in standard toxicity studies, as well as an immune function study, are requested by the EU, incorporating a T-cell-dependent antigen response in the first screening phase. Authorities from other areas in the world follow similar lines for immunotoxicity testing, but differ in whether or not the functional assay is seen as a primary requisite or can be secondary to other factors or observations. Based on a limited survey in the framework of the International Conference on Harmonization, the European position has been reconsidered to negotiate a broad cause-for-concern approach. The relevance of functional testing of the immune system to show effects of human pharmaceuticals is shown in this review. There is certainly a need for more in-depth testing of the integrity of the immune system and a cause-for-concern approach is, therefore, needed. A broad category is the number of compounds that might interact via binding to receptor sites at the broadly taken population of leukocytes (e.g., lymphocytes, macrophages). Criteria to differentiate among compounds in this category have yet to be ascertained.

Biological Assay↗

PubMed2004

Sunlight exposure and (sero)prevalence of epidermodysplasia verruciformis-associated human papillomavirus.

Ultraviolet radiation (UVR) is associated with an increased risk of squamous cell carcinoma (SCC), which is in part due to immunomodulation. In addition, human papilloma virus (HPV), especially the epidermodysplasia verruciformis (EV)-associated types, may be involved. In view of the capacity of UVR to impair host resistance to infections, we investigated the relationship between solar exposure and the prevalence of cutaneous HPV. In a case-control study on skin cancer (320 controls and 156 patients) a lifetime-retrospective questionnaire on sun exposure was administered. The presence of DNA of HPV types 5, 8, 15, 20, 24, and 38 in plucked eyebrow hair and type-specific seroreactivity were assessed and analyzed in relation to estimated exposure. Sunburn episodes in the past, especially at age 13-20 y, appeared to be associated with an enhanced risk of EV-HPV DNA positivity. In contrast, a higher lifetime sun exposure was associated with a lower risk of HPV infection. These results indicate that UVR at erythematogenic doses increases the risk of EV-HPV infection, possibly due to impaired host resistance to HPV and/or a direct effect of UVR on viral replication. The favorable association between lifetime sun exposure and HPV prevalence, however, underscores the enigmatic role of HPV in skin carcinogenesis.

Aged↗

PubMed2003

Influence of the macrophage bacterial resistance gene, Nramp1 (Slc11a1), on the induction of allergic asthma in the mouse.

Based on the hygiene hypothesis that lack of early childhood bacterial infections would favor development of allergic disease, we hypothesize that genes controlling antibacterial resistance may be important as well. We, therefore, studied whether Nramp1 alleles that determine resistance (Nramp1r) or susceptibility (Nramp1s) to intracellular bacteria at the macrophage level affect sensitivity to induction of allergic asthma. Nramp1s and congenic Nramp1r mice were sensitized with ovalbumin/alum on days 0 and 14 and challenged with ovalbumin or saline aerosols on days 42, 45, and 48. On day 49, airway responsiveness was assessed, blood was withdrawn, and lung lavage was performed. We demonstrated that ovalbumin sensitization and challenge of Nramp1s and Nramp1r mice caused comparable airway hyperreactivity and airway eosinophilia and a similar increase in serum levels of ovalbumin-specific IgG1 and IgG2a. Ovalbumin challenge, however, induced significantly lower serum levels of total and ovalbumin-specific IgE and significantly lower mast cell degranulation in Nramp1r mice as compared with Nramp1s mice. In addition, ovalbumin challenge of Nramp1r mice led to significantly less release of Th2 cytokines into the airways. Results show that Nramp1 can affect the development of allergy but not the development of airway hyperresponsiveness in the mouse.

Animals↗

PubMed2003

Effect of prolonged exposure to low antigen concentration for sensitization.

The local lymph node assay (LLNA) is an assay in mice to identify potential allergens. Compounds that do not induce a stimulation index (SI)>or=3 are not considered sensitizers. Of the chemicals that do, the SI of 3 is used as a benchmark, and indicates the sensitizing potency of a chemical. Compared to the exposure duration of the LLNA (3 days), real life exposure often lasts for months or years. We therefore investigated whether prolonged exposure to sensitizers at concentrations that do not induce a SI>or=3 in the LLNA, were able to surpass this threshold. Mice were treated for 2 months at 7-day intervals with a range of concentrations of the known allergens ethyl-p-aminobenzoate (benzocaine, BENZ), 2,4-dinitrochlorobenzene (DNCB), and tetramethyl thiuram disulfide (TMTD). Both proliferative activity and cytokine production were established at day 60. Neither BENZ nor TMTD showed a significant increase in the proliferation rate compared to vehicle controls. Only DNCB at concentrations originally above the EC(3) a significant increase in proliferation was seen after prolonged exposure. No significant effect on IFN-gamma and IL-4 production was observed for all three compounds compared. These findings indicate that for classification of sensitizers the shorter exposure period employed in the standard LLNA is sufficient, and longer periods of exposure have no bearing on this classification.

Allergens↗

PubMed2003

Ultraviolet B radiation induces upregulation of calcitonin gene-related peptide levels in human Finn chamber skin samples.

One of the neuropeptides that plays a role in UVB-induced immunomodulation is calcitonin gene-related peptide (CGRP), as demonstrated in several animal studies. CGRP can be detected in human skin, but effects of UVB exposure on CGRP levels in human skin are not known. We determined CGRP levels in human Finn chamber skin samples of 15 UVB-irradiated and 10 control volunteers. Filter samples were collected prior to and immediately after a UVB exposure protocol (5 consecutive days, with one personally determined minimal erythema dose (MED(jp)) per day). CGRP levels in filter samples were determined using a commercially available radioimmunoassay kit. CGRP could be detected in the filter samples and volunteers showed statistically significantly increased levels after UVB exposure. In addition, the CGRP levels of UVB-exposed volunteers were positively correlated with the dose of UVB in J/m(2) that they received on 5 consecutive days. In other words, higher UVB doses resulted in higher CGRP levels. In summary, CGRP, a mediator in UVB-induced immunomodulation, could be detected in human Finn chamber skin samples, and was significantly increased after UVB exposure. The CGRP level appeared to depend on the amount of UVB the volunteers received.

Calcitonin Gene-Related Peptide↗

PubMed2003

Persistent hematologic and immunologic disturbances in 8-year-old Dutch children associated with perinatal dioxin exposure.

Perinatal exposure to Dutch "background" dioxin levels in 1990 was high, but comparable with that of other industrialized Western European countries. Exposure during the sensitive perinatal period may cause permanent disturbances. Therefore, we assessed the health status and various hematologic and immunologic parameters among our longitudinal cohort. A medical history was taken and venipuncture performed in a longitudinal cohort of 27 healthy 8-year-old children who had documented perinatal dioxin exposure. Linear regression revealed a decrease in allergy in relation to prenatal (p = 0.02) and postnatal (p = 0.03) dioxin exposure. Increases in CD4+ T-helper cells (p = 0.006) and in CD45RA+ cells (p = 0.02) were seen in relation to postnatal exposure. A persistently decreased platelet count (p = 0.04) and increased thrombopoietin concentration (p = 0.03) were seen in relation to postnatal exposure. This follow-up has shown a decrease in allergy, persistently decreased thrombocytes, increased thrombopoietin, and increased CD4+ T-helper and increased CD45RA+ cell counts. This study provides indications of effects at the stem cell level of perinatal dioxin exposure, persisting until minimally 8 years after birth.

Adult↗