Hans Helge

Time course of PCDD/PCDF/PCB concentrations in breast-feeeding mothers and their infants

PCDD/PCDF/PCB concentrations were measured in samples from four mothers (at delivery and during lactation) and their infants (at birth and the end of first year of life). For two of these mothers it was the second delivery and breast-feeding period, and additional data were available from first lactation period and the first-born infant at the age of 11 to 12 months. Five of the six infants were fully breast-fed for at least 17 weeks. In four of them a distinct PCDD/PCDF/PCB accumulation was observed at the end of the first year of life: concentrations in blood fat were 1.5 to 3.6 times higher than maternal levels measured at the same time. Due to decreasing maternal body burdens during lactation, PCDD/PCDF concentrations at 11 to 12 months of life were only about half as high in the second infant as in the first one at the same age. During second pregnancy, no important change of the concentrations was observed in maternal blood.

Prevalence of Helicobacter pylori infection in Nicaraguan children with persistent diarrhea, diagnosed by the 13C-urea breath test.

BACKGROUND The impairment of gastric acid barrier caused by Helicobacter pylori (H. pylori) at the onset of infection may predispose to small bowel bacterial overgrowth, which could contribute to persistent diarrhea. METHODS Using the 13C-urea breath test, we determined the prevalence of H. pylori infection in 123 Nicaraguan children from Tipitapa, aged 1 to 65 months, from a low socioeconomic background. RESULTS The overall prevalence of H. pylori infection was 77.2% (95/123). The prevalence varied with age and was significantly (p < 0.001) higher in infants < or = 12 months than in children aged 13-65 months, 91% (57/63) as against 63% (38/60). H. pylori infection was present in 44 of 59 (75%) children suffering from persistent diarrhea compared with 51 of 64 (80%) age-matched asymptomatic controls. In the diarrheal group, 20 of 59 (34%) children presented with malnutrition, and 16 (80%) of them showed H. pylori infection. In the control group, 20 of 64 (31%) were malnourished, and 14 (70%) of them showed H. pylori infection. CONCLUSIONS In Nicaragua, H. pylori is acquired in early infancy. The high prevalence among children in the first 12 months of life and the lower infection rate between 1 and 5 years of age suggest a loss or clearance of infection, also an occasional finding in adults. H. pylori infection appears to be not a risk factor for persistent diarrhea or malnutrition in Nicaraguan children.

CROSS-REACTIVITY OF ANTIHUMAN MONOCLONAL ANTIBODIES WITH CELL SURFACE RECEPTORS IN THE COMMON MARMOSET

In this report we demonstrate that a large number of monoclonal antibodies (mAbs) against human epitopes cross-react with surface receptors on white blood cells of Callithrix jacchus, indicating species similarities. However, a variety of other mAbs do not exhibit any cross-reactivity, thus also providing evidence for distinct differences in the structure of these receptors among nonhuman primates. Such differences have to be known and taken into consideration when attempting extrapolations between species. The results presented provide the prerequisite for performing extensive studies on immunological structures and functions in marmosets under normal and pathological conditions. We conclude that the immune system of Callithrix jacchus is a convenient model for studies on immunotoxicity with relevance for man, and for this purpose it is clearly superior to that of any rodent species.

Polyhalogenated dibenzo-p-dioxins and dibenzofurans and the immune system. 2. In vitro effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on lymphocytes of venous blood from man and a non-human primate (Callithrix jacchus).

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on poke weed mitogen-stimulated proliferation and differentiation of peripheral lymphocytes was studied in vitro with cells from a non-human primate (marmoset monkey,Callithrix jacchus) and from man. Monoclonal antibodies and flow cytometry (FACScan) were used for analysis. The extent of the overall mitogenstimulated proliferation of isolated lymphocytes in vitro from marmoset blood was only slightly reduced in the presence of TCDD compared to the solvent control (0.01% DMSO). However, incubation with TCDD in the culture medium together with the mitogen led to a pronounced decrease in the percentage of the lymphocyte subset with the surface marker CD4, and a concomitant increase in the percentage of CD8+ cells. The lowest concentration found to be effective in vitro was 1 × 10−13 M TCDD (25 fg TCDD/ml). When culturing lymphocytes from human blood of different donors under identical conditions in the presence of TCDD and the mitogen, corresponding effects were observed to those seen with marmoset cells. A closer analysis of the T lymphocyte subsets affected revealed the CD4+ CDw29+ (helper-inducer cells) to be the main target for the action of TCDD. A clear-cut change in the percentage of this subpopulation was induced at concentrations as low as 1 × 10−13 M TCDD. The development of the IL-2-marker in culture was only slightly affected by TCDD, and concentrations of 1 × 10−12 M were required to slightly reduce the number of CD2+CD25+ cells. Special B cells, namely CD20+ (i.e. B1) cells, were found to be especially susceptible to the action of TCDD, and clear-cut effects were seen in several experimental series at 1 × 10−14 M TCDD. The formation of B cells with IgG lambda or kappa chains was also depressed in culture in the presence of TCDD. When the cultures were initiated with whole blood instead of with isolated lymphocyte fractions, the effects described were also observed, but the concentration of TCDD needed seemed to be higher (about 1 × 10−12 M). The mixed lymphocyte culture with human cells provides a simple system for studying the effects of TCDD and similar substances in vitro at low concentrations. For the first time a direct effect of TCDD on peripheral lymphocytes of primates was demonstrated. This in vitro effect on special sub-classes of peripheral lymphocytes from non-human primates represents the biological effect demonstrated with the lowest TCDD concentration ever reported in the literature.

Chlorinated dibenzo-p-dioxins and dibenzofurans and the human immune system. 1. Blood cell receptors in volunteers with moderately increased body burdens

Using monoclonal antibodies (mAbs) and flow cytometry, we studied a variety of surface receptors on lymphocyte subpopulations of workers with moderately increased body burdens of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and of other polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF), expressed here as International-Toxicity Equivalencies (I-TE). The hypothesis to be tested was whether or not humans exhibit a similar susceptibility to PCDDs/PCDFs with respect to the surface receptors found previously to respond to small doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in Callithrix jacchus. These are: helper-inducer (memory) T cells (CD4+CD45R0+CD45RA-CD29highCD11a+), CD20+ B cells, and cytotoxic T cells (CD8+CD56+/CD57+). Furthermore, 68 triple-labellings with mAbs were performed on the cells of each volunteer to possibly generate further hypotheses. It was evaluated whether any of the variables might be used as a biomarker of effects for this class of compounds. There were two main goals: (1) to evaluate whether workers with a moderately increased PCDD/PCDF-body burden [25-140 ppt TCDD or 104-522 ppt I-TE in blood fat] exhibit changes in the surface receptors of white blood cells, as observed in previous studies in non-human primates, and (2) to clarify whether persons at the upper range [10-23 ppt TCDD or 30-90 ppt I-TE in blood fat] of the body burden reference values of a not particularly exposed population show detectable deviations in these immunological variables, when compared with persons at the lower and medium range [1-3 ppt TCDD or 9-29 ppt I-TE] of these body burden reference values. Regression analysis of our data revealed slight trends for some of the biomarkers (e.g. CD45R0+). With one exception, these were all increases. None of the alterations observed are of medical relevance. The slight increase in the percentage of CD4+CD45R0+ cells remained significant even after covariant analysis taking age-related changes into account. Altogether, the data do not provide any evidence to support an assumption that moderately increased body burdens of PCDDs/PCDFs in adults induce decreases in the cellular components of the human immune system. Adult humans certainly are less susceptible to this action of PCDDs/PCDFs than adolescent Callithrix jacchus.

Thalidomide and the immune system. 4. Down-regulation of the CD26 receptor, probably involved in the binding of HIV components to T cells in primates

Thalidomide (Thd) is capable of down-regulating the CD26 receptor on CD4+ lymphocytes after treatment of healthy volunteers. Similar effects are observed when marmosets (Callithrix jacchus) are treated with Thd. The Ta1 epitope of the CD26 receptor has recently been shown to bind the HIV-1 Tat trans-activating protein, and CD26 has also been suggested to be a coreceptor for the binding of the V3 loop of the gp120 HIV envelope protein. This might provide a hint for possible therapeutic interventions.

Einige Eigenschaften der RNS-Polymerase-Reaktion in Warmblüter-Mitochondrien

Characteristics and kinetics of RNA-polymerase activity have been investigated in mitochondria isolated from pigeon heart and rat liver.SummaryCharacteristics and kinetics of RNA-polymerase activity have been investigated in mitochondria isolated from pigeon heart and rat liver.After incorporation of 3H- and 14C-labeled nucleotides in vitro the mitochondrial RNA was extracted using phenol or perchloric acid. Data are presented showing the time course of the reaction and the influence exerted by changing enzyme (mitochondrial protein) or substrate concentration. Accelerations of the incorporation rate were observed when pH-values, temperatur and Mg++ concentrations of the incubation mixture were increased.A comparison of nuclear and mitochondrial RNA-polymerase activities reveals similarities of the basic incorporation process. However, distinct differences appear to be present as far as Km-values are concerned. Since the enzyme is characteristically located within the mitochondrial compartment, accessibility is limited by membrane impermeability. This provides additional proof for the conclusion that the incorporation process is a property of the mitochondria per se.

Induction of caffeine-demethylations by 2,3,7,8-TCDD in marmoset monkeys measured with a 14CO2 breath-test

Abstract The inductive potency of 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD) was studied in marmosets ( Callithrix jacchus ) using a CO 2 breath-test with 14 C-caffeine (labelled at the C3- or C7-position). Using the C3-labelled caffeine as a substrate, studies with single subcutaneous injections of various doses of TCDD revealed a significant increase of 14 CO 2 exhalation with a lowest-observed-effect-level (LOEL) of 3 ng TCDD/kg body wt and a no-observed-effect-level (NOEL) at 1 ng/kg body wt. In contrast, for the C7-labelled caffeine a LOEL as high as 167 ng TCDD/kg body wt and a NOEL of 300 ng TCDD/kg body wt were found.

Feasibility of Studying Effects on the Immune System in Non-Human Primates

The assessment of possible xenobiotic-induced alterations of the immune system is among the most challenging problems of modern toxicology. However, up till now, very few systematic studies have been performed nor has there been any agreement on a testing strategy in this field. The main difficulty rests in the fact that numerous changes may be induced by xenobiotics on various facets of the very complex immune system, and the predictive value of experimental findings for health risk in man is still largely unknown. In recent years some of the prerequisites for such testing in laboratory animals have been improved, and suggestions for testing for xenobiotic-induced alterations in the immune system have been made (Dean et al. 1982; Dean 1987; Luster et al. 1988; Van Loveren and Vos 1989; Neubert et al. 1989).

Risk Assessment for Possible Effects of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Related Substances on Components and Functions of the Immune System

Numerous reports have been published on the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on components and functions of the immune system of animal species, almost exclusively of rodents. Many of the data, obtained with very different dosing schedules, are conflicting or have not been confirmed. Since the overwhelming majority of evaluations were performed with rodents, it is not possible to perform a reliable quantitative or even qualitative risk assessment for TCDD in man based on immunological data obtained from these experiments and to extrapolate them to the situation in humans. In addition to the fact that the doses needed to induce measurable effects in the different species studied varies from 1- to 10,000-fold, there are intrinsic and general difficulties for extrapolations to human beings in the field of immunotoxicology due to the influence of different individual risk factors, e.g. smoking and drinking as well as the lack of experience and validation in this new field of toxicology. Some immunological variables were studied in populations highly exposed to dioxins. In comparison to the results obtained from nonhuman primates, no convincing evidence for substance-related effects was revealed, however, information on only a few immunological components and functions in exposed adults could be assessed so far. Except for one group of studied persons all other subjects were generally exposed to cocktails of several chemicals, vastly complicating the interpretation with respect to one isolated component of these mixtures. Results from studies on exposed children are not available yet.