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Biomedical subjects

K J van den Berg

Publications and source records attributed to K J van den Berg.

At least 19 recordsLinked to original sources
PubMed1996

Persistent alterations in regional brain glial fibrillary acidic protein and synaptophysin levels following pre- and postnatal polychlorinated biphenyl exposure.

Pregnant Wistar WU rats were exposed to 0, 5, and 25 mg of the commercial polychlorinated biphenyl (PCB) mixture Aroclor 1254 per kilogram of body weight on Days 10 to 16 of gestation. Pregnant rats were sacrificed on Gestation Day 20 to observe effects on fetal body and brain weights. Male and female offspring were sacrificed on Postnatal Days 21 and 90 (PND21 and PND90, respectively) and examined for treatment-related effects on neurochemical parameters. The concentrations of the neuronal and glial cell markers, synaptophysin and glial fibrillary acidic protein (GFAP), were measured in diverse brain regions from the offspring using immunochemical techniques. The level of calcineurin (a calmodulin-regulated protein phosphatase) activity was measured in cerebellar homogenates. In addition, ethoxyresorufin O-deethylase (EROD) activity was determined in hepatic microsomes as a measure of a well-characterized response to PCB exposure in experimental animals. The major alterations of GFAP levels following maternal PCB treatment were significant increases in the lateral olfactory tract (LOT) and the cerebellum (CB) and significant decreases in the brain stem (BS) of the offspring on PND21 and 90. Synaptophysin levels were significantly decreased relative to controls in the LOT, prefrontal cortex, and striatum of the offspring on PND90. In the BS, synaptophysin levels were significantly decreased relative to controls in male and female weanlings on PND21 and males on PND90; however, significant increases were observed in the BS of females on PND90. No effect of maternal PCB treatment was observed on levels of GFAP and synaptophysin in the dorsal hippocampus on PND21 and 90. Due to analytical restrictions statistical comparisons of GFAP levels were limited to examining the effect of maternal PCB treatment per brain region per sex per time point. Calcineurin activity was decreased in the female CB on PND21, but a significant increase in activity was observed in the female CB on PND90. No effect of maternal PCB treatment was observed on the cerebellar calcineurin activity in male offspring on PND21 and 90. EROD activity was highly induced in maternal microsomes from both PCB treatment groups, but only slightly induced in fetal hepatic microsomes. On PND21 weanling hepatic microsomal EROD activity was highly induced following gestational and lactational PCB exposure; however, on PND90 EROD activity was unaffected by maternal PCB treatment in male offspring and significantly decreased in female offspring. The results of the present study indicate that gestational and lactational exposure to the commercial PCB mixture results in long-term alterations in a neuronal and glial cell markers in specific brain regions of rats. These marker proteins may be useful for determining the structure-activity relationships in PCB-induced developmental neurotoxicity.

Animals↗
PubMed1994

Regional and temporal profiles of calcium accumulation and glial fibrillary acidic protein levels in rat brain after systemic injection of kainic acid.

Cerebral calcium accumulation and increases in the astroglial intermediate filament protein, glial fibrillary acidic protein (GFAP), have been used as markers of neurotoxic and ischemic brain damage. The present study was aimed at quantitatively investigating the regional and temporal relationship of those indices following a neurotoxic insult. For this purpose, regional changes in 45Ca uptake and GFAP levels, using ELISA, were evaluated in rat brains at both early (several hours) and late time points (up to 6 months) after a single systemic injection of kainic acid (12 mg/kg). After 4 h, limbic brain areas were already heavily labelled by 45Ca. In most investigated brain areas 45Ca accumulation peaked at day 4 (maximum 5 fold increase in amygdala) and returned to normal levels within 1 week (cerebellum, pons/medulla, occipital cortex), 2 weeks (striatum, frontal cortex), 2 or 4 months (limbic brain areas), or remained significantly elevated until 6 months (thalamus). In contrast, in all investigated brain areas, except cerebellum and pons/medulla, GFAP was increased from day 2, reaching maximum levels at day 28 in most limbic structures and remained significantly elevated at the same high level (15 fold increase) in amygdala, or somewhat lower levels in other affected regions (2-7 fold), but not in the thalamus. In all brain areas with 45Ca accumulation, GFAP was increased and the peak responses were highly correlated. Thus, both indices are useful quantitative biochemical markers of acute or subchronic neurotoxicity.

Animals↗
PubMed1993

Hexachlorobenzene-induced hypothyroidism. Involvement of different mechanisms by parent compound and metabolite.

Rats received repeated oral treatment with different doses of hexachlorobenzene (HCB) (0-3.5 mmol/kg) for 2 or 4 weeks. Measurements of thyroid hormone status after 2 weeks showed a dose-dependent decrease of total thyroxine (TT4) levels, decreased free thyroxine (FT4) levels and little change of total triiodothyronine (TT3) levels. The effects on thyroid hormone status were more pronounced after 4 weeks and also included increased thyroid stimulating hormone (TSH) levels. These conditions suggest that HCB had induced hypothyroidism in these animals. Indications for occupation of thyroid hormone binding proteins were found in serum of exposed animals. The major metabolite pentachlorophenol (PCP) also caused, by competitive interactions with thyroid hormone binding proteins in serum, a rapid and dose-dependent decrease of TT4 and FT4 levels, but not of TT3 levels in serum. The decrease of serum TT4 levels by repeated dosing with 3.5 mmol HCB/kg for 4 weeks could be attributed to competitive interactions of PCP with hormone serum binding proteins and to increased metabolism induced by HCB to an equal degree. At lower dose levels or with shorter dosing periods, increased metabolism of T4 is the main cause of decreased TT4 serum levels. This is the first indication that a similar effect is caused simultaneously by the parent compound and its metabolite through different and independent mechanisms.

Animals↗
PubMed1993

Increased glucuronidation of thyroid hormone in hexachlorobenzene-treated rats.

Metabolism of thyroid hormones was investigated in WAG/MBL rats that had been exposed to hexachlorobenzene (HCB). Serum thyroxine (T4) levels were lowered by 35.5%, whereas triiodothyronine (T3) levels were not changed. Bile flow, as well as T4 excretion in bile were increased by HCB treatment. Analysis of bile by HPLC revealed a more than 3-fold increase of T4 glucuronide (T4G) and a concomitant reduction of non-conjugated T4. T4 UDP-glucuronyltransferase activity (T4 UDPGT) activity in hepatic microsomes was increased more than 4.5-fold in animals exposed to HCB. p-Nitrophenol (PNP) UDPGT showed a comparable increase by HCB. Both T3 and androsterone UDPGT activities were low in WAG/MBL rats compared with normal Wistar rats. T3 UDPGT activity was increased 2.5-fold by HCB, but androsterone UDPGT activity was unchanged. These results suggest that T4 is a substrate for HCB-inducible PNP UDPGT and T3 for androsterone UDPGT. In the absence of the latter, T3 is also glucuronidated to some extent by PNP UDPGT. Type 1 iodothyronine deiodinase activity was decreased by HCB treatment. It is concluded that decreased T4 levels in serum of animals after exposure to HCB may be due to a combined effect of displacement of T4 from carriers, an increased glucuronidation of T4 and enhanced bile flow.

Androsterone↗
PubMed1993

Glucuronidation of thyroid hormone in rat liver: effects of in vivo treatment with microsomal enzyme inducers and in vitro assay conditions.

We investigated the effects of in vivo treatment with different microsomal enzyme inducers, including clofibrate (CLOF), hexachlorobenzene (HCB), 3-methylcholanthrene (MC), 3,3',4,4'-tetrachlorobiphenyl (TCB), and 2,3,7,8-tetrachloro-p-dioxin, as well as of in vitro addition of the detergent Brij 56 on the glucuronidation of T4, T3, and rT3 by UDP-glucuronyltransferase (UGT) activities of rat liver microsomes. The results were compared with measurements of UGT activities for bilirubin, p-nitrophenol (PNP), and androsterone. In general, glucuronidation rates were 5-fold or more higher with rT3 than with T4 or T3 as substrate. In liver microsomes from untreated rats, T4 UGT activity was stimulated by Brij 56 to a maximum of about 2-fold at 0.025% detergent. Treatment of Wistar rats for 4 days with CLOF (200 mg/kg BW.day) resulted in significant increases in UGT activities for T4 (to 154%), rT3 (to 155%), and bilirubin (to 194%), in particular if assayed in the presence of 0.025% Brij 56, but had little effect on the UGT activities for T3, PNP, and androsterone. The CLOF-induced increases in T4 and rT3 UGT activities were not observed in Gunn rats, which have a complete lack of bilirubin UGT activity and greatly impaired PNP UGT activity. Treatment of Wistar rats with a single injection of MC (50 mg/kg BW), TCB (50 mg/kg BW), or 2,3,7,8-tetrachloro-p-dioxin (6.25 micrograms/kg BW) resulted, after 4 days, in 6.3- to 7.3-fold increases in T4 UGT activity and 15.1- to 16.7-fold increases in rT3 UGT activity if determined in the absence of Brij 56, whereas T4 UGT activity was only increased by 33-68% when assayed in the presence of Brij 56. T3 glucuronidation was not affected (with Brij 56) or was increased by only 33-68% (without Brij 56) after treatment with these MC-type inducers. PNP UGT activity was induced 3.6- to 4.3-fold, whereas bilirubin and androsterone UGT activities were changed little by these treatments. Similar findings regarding T4, rT3, PNP, and bilirubin UGT activities were obtained after chronic treatment of WAG rats with HCB, another MC-type inducer. However, WAG rats lack androsterone UGT and show low T3 UGT activity, which was increased about 2.3-fold by HCB treatment. On the basis of these and previous findings it is concluded that at least three UGT isoenzymes are involved in the glucuronidation of thyroid hormone.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Effects of hexachlorobenzene and its metabolites pentachlorophenol and tetrachlorohydroquinone on serum thyroid hormone levels in rats.

Effects of administration of equimolar doses of hexachlorobenzene (HCB) and its metabolites pentachlorophenol (PCP) and tetrachlorohydroquinone (TCHQ) on serum thyroxine (TT4) and triiodothyronine (TT3) levels in rats were studied. Furthermore, it was investigated whether the observed effects were related to the serum levels of HCB or PCP. Rats received either corn oil (controls) or HCB, PCP or TCHQ in a single equimolar intraperitoneal dose of 0.056 mmol/kg. Results indicated that HCB did not alter serum TT4 and TT3 levels for a period up to 96 h after dosing. In contrast, PCP and TCHQ were both capable of reducing serum TT4 levels with a maximum effect between 6 and 24 h after exposure. TCHQ was more effective in repressing TT3 than TT4 blood levels. Dose-response experiments were carried out in order to obtain insight into the sensitivity of the observed effects. Rats received different doses of PCP or TCHQ intraperitoneally. The reductions of TT4 levels by PCP were inversely related to serum PCP levels in exposed animals, based on the toxicokinetics and dose-response profiles. Furthermore, PCP serum levels after HCB administration appeared too low to cause an effect. The results of this study indicate that not HCB itself, but rather its metabolites PCP and TCHQ may be involved in reduced serum thyroid hormone levels after HCB administration.

Animals↗
PubMed1991

Hexachlorobenzene and its metabolites pentachlorophenol and tetrachlorohydroquinone: interaction with thyroxine binding sites of rat thyroid hormone carriers ex vivo and in vitro.

Previous results have indicated that hexachlorobenzene (HCB)-induced hypothyroidism may be caused by its main metabolite pentachlorophenol (PCP), and by tetrachlorohydroquinone (TCHQ), rather than by the parent compound. In the present experiments it was investigated whether hormone displacement from serum carriers could be a factor in the development of this hypothyroidism. In an in vitro competition assay PCP was an effective competitor for the thyroxine (T4)-binding sites of serum carriers, whereas HCB was ineffective. Ex vivo experimental results demonstrated occupation of T4-binding sites in sera from PCP-exposed animals but not in sera from HCB- or TCHQ-treated animals. Competing ability for T4-binding sites was still present in sera of PCP-exposed animals but was absent in HCB- or TCHQ-exposed animals. The results suggest that thyroid hormone displacement by the major metabolite PCP may play a role in HCB-induced hypothyroidism.

Animals↗
PubMed1990

Interaction of chlorinated phenols with thyroxine binding sites of human transthyretin, albumin and thyroid binding globulin.

Previous results (Brouwer and van den Berg, Toxicol. Appl. Pharmacol., 85 (1986) 301) indicated preferential binding of a hydroxylated metabolite of tetrachlorobiphenyl to transthyretin (TTR) a carrier of thyroxine (T4). In the present study it was investigated whether the T4 binding site of TTR could be occupied specifically by hydroxylated chlorinated aromatic compounds using chlorinated phenol congeners as model compounds in a competition assay with [125I]T4. Chlorinated aromatics such as 2,3-dichlorobenzene and 3,4,3',4'-tetrachlorobiphenyl, and phenols such as 4-hydroxybiphenyl and phenol were inefficient competitors. All chlorinated phenols tested were competitors for the T4 binding site of TTR. The ranking in competition was pentachlorophenol (PCP) greater than trichlorophenols greater than dichlorophenols greater than monochlorophenols. Structures with chlorine in both ortho positions to the hydroxyl group were more efficient competitors. The relative affinity of binding of pentachlorophenol (PCP) to TTR was about twice that of T4. Scatchard analysis showed that PCP mainly decreased the affinity constant K11 while the binding capacity R1 was not altered, indicating a competitive type of inhibition. PCP was also able to compete with T4 sites on albumin with a relative affinity of 0.25. T4 binding to thyroid binding globulin (TBG) was much less affected by interference of PCP (relative affinity 0.001). The results indicate a specific interaction of chlorophenols with the T4 binding site of TTR.

Binding Sites↗
PubMed1988

Chronic toxicity of 3,4,3',4'-tetrachlorobiphenyl in the marmoset monkey (Callithrix jacchus).

Cotton top marmoset monkeys (Callithrix jacchus) were orally dosed with 3, 1, 0.1 or 0 mg 3,4,3',4'-tetrachlorobiphenyl (TCB)/kg body weight twice per week for 18-23 weeks. Severe toxicity occurred in the highest dose group. Clinical signs of toxicity were a rapid decrease in body weight, alopecia, abnormal nail growth, nodular enlargement of the nipple area and scaly skin. Haematological analysis of peripheral blood revealed mild leukocytosis and anemia. Biochemical alterations observed were elevated triglyceride levels and cholesterol levels. Histopathology revealed dose dependent changes in a variety of tissues. Squamous metaplasia was found in skin and adnexa as well as in salivary glands. In the stomach, parietal cells were decreased and mucus producing cells were increased. The duodenal mucosa was hyperplastic. Ovaries showed an absence of corpora lutea. In the thyroid follicular cell hyperplasia and hypertrophy were noted. Toxicity was less severe in marmoset monkeys dosed with 1 mg TCB/kg, while minor toxic effects were observed in the animals dosed with 0.1 mg TCB/kg. The marmoset monkey appears to be less sensitive to the toxic action of TCB than the rhesus monkey. The pattern of histological and biochemical changes induced by TCB in marmoset monkeys is comparable to that described in humans and in other primate species exposed to PCBs. The marmoset monkey model may be valuable for investigations on human-related toxicity of PCBs.

Animals↗
PubMed1988

Effects of 3,4,3',4'-tetrachlorobiphenyl on thyroid function and histology in marmoset monkeys.

Marmoset monkeys were treated with oral doses of 0.1, 1 or 3 mg 3,4,3',4'-tetrachlorobiphenyl (TCB) per kg body weight 2 times a week for 18-23 weeks. Histological examination of the thyroid gland revealed a dose-dependent follicular cell hyperplasia. The morphological changes were associated with various disturbances of thyroid function. The average serum thyroxine (T4) levels during the treatment period were reduced by more than 99% in monkeys receiving 3 mg TCB/kg, by 81% in marmosets on a dose of 1 mg TCB/kg, and by 35% with 0.1 mg TCB/kg. The reduction in serum T4 levels was established from the earliest time point (2 weeks) throughout the whole dosing period (18-23 weeks). The reduction in serum T4 levels was reflected in decreased free thyroxine (FT4) index in the 1 and 3 mg TCB/kg dose groups. Serum triiodothyronine (T3) levels were lowered in the 3 mg/kg dose group already after 2 weeks. Evidence for decreased binding to carrier proteins is suggested by increased T3 resin uptake in the highest dose group. Levels of thyrotropin (TSH) were increased in the highest dose group as a feedback response to the dramatically reduced serum T4 levels.

Animals↗
PubMed1986

Binding of a metabolite of 3,4,3',4'-tetrachlorobiphenyl to transthyretin reduces serum vitamin A transport by inhibiting the formation of the protein complex carrying both retinol and thyroxin.

The mechanism of serum vitamin A reduction by polychlorinated biphenyls was studied at the level of the plasma transport protein system for vitamin A. Analysis of [3H]retinol-labeled serum proteins by polyacrylamide gel electrophoresis (PAGE) showed association of retinol with two proteins that were identified as retinol binding protein (RBP) and the RBP complex with transthyretin (TTR). The amount of [3H]retinol radioactivity in the serum as well as the label associated with the binding proteins was strongly reduced by 3,4,3',4'-tetrachlorobiphenyl (TCB). A possible interaction of TCB with the retinol binding proteins was investigated, using radiolabeled TCB. Analysis of the plasma proteins by PAGE revealed the presence of four peaks of 3H-TCB label, the major ones being associated with lipoproteins and TTR. No 3H-TCB radioactivity was found in the region of the gel where RBP or the RBP-TTR complex was located. HPLC analysis of the radioactive compound associated with TTR showed the presence of a metabolite of TCB, rather than the parent compound. These data indicate a direct interaction of a metabolite of TCB with TTR leading to an inhibition of formation of the serum transport protein complex carrying both retinol and thyroxin. A model is proposed, which may explain certain characteristic toxicopathological lesions observed in species exposed to polychlorinated biphenyls and related compounds (TCDD, PBBs, etc.).

Animals↗
PubMed1986

Direct assay of thymidine kinase bound to ion-exchange paper for dot spotting and enzyme blotting analysis.

The direct assay of thymidine kinase (Tk) bound to ion-exchange paper was investigated as a means to further simplify the analytical procedure. Thymidine kinase bound firmly and quantitatively to ion-exchange paper at near neutral pH. The enzymatic properties of Tk did not change while bound to the ion-exchange paper. The amount of phosphorylated 125IdU or 125IdC formed on ion-exchange paper was proportional to the amount of applied Tk. Enzymatic activity could be determined visually by autoradiography or by gamma counting. This method was relatively independent of the protein concentration or volume of the sample and which allows the assay from dilute solutions. A simplified dot spot method that can be used for the assay of thymidine kinase activity in cell extracts is described. Thymidine kinase could also be visualized after electrophoresis and blotting on ion-exchange paper.

Animals↗
PubMed1986

Sodium azide is less suitable as a positive control of drug-induced lethality for in vitro clonogenic assays.

Sodium azide (6 mg/ml) was used as a positive control for drug-induced lethality in an in vitro clonogenic assay. Petri dishes containing control and sodium azide treated cultures of WiDr cells were placed together in a large Petri dish and incubated at 37 degrees C in an atmosphere of 10% CO2 in air. No growth was observed. Control cells formed colonies only when the dishes were separated from the sodium azide dishes. Using a microtiter plate the toxic effect was inversely related to the distance of the test cultures from the sodium azide treated cultures. These results suggested the formation of a toxic gas or vapour from sodium azide under cell culture conditions, probably an azide. Chemical analysis was based on characteristic reactions, such as the production of a precipitate with silver ions or formation of a red-coloured complex with ferric salts. On a microtiter plate, a gradient of the expected precipitate or red colour was observed, the highest amounts adjacent to the wells containing sodium azide. These results show that sodium azide acts as a positive control of drug-induced lethality for in vitro clonogenic assays. However, the formation of a highly toxic vapour, most likely hydrazaic acid, makes it a less suitable standard.

Azides↗
PubMed1985

Time and dose responses of the reduction in retinoid concentrations in C57BL/Rij and DBA/2 mice induced by 3,4,3',4'-tetrachlorobiphenyl.

A single ip dose of 15 mg 3,4,3',4'-tetrachlorobiphenyl (TCB)/kg induced a 30 to 40% reduction of retinol and retinyl palmitate concentrations in hepatic tissue of C57BL/Rij mice within 2 to 4 days. This level of reduction was maintained for about 14 days. The ED50 was 32 mg TCB/kg for hepatic retinol and 17 mg TCB/kg for hepatic retinyl palmitate. In DBA/2 mice, however, no reduction in hepatic retinoids was observed even at doses up to 729 mg TCB/kg. The duration of the reduction in hepatic retinoids did not correlate with the induced aryl hydrocarbon hydroxylase (AHH) activity in C57BL/Rij mice. These data suggest that AHH and related enzymes are not directly involved in the TCB-induced reduction in retinoids in these mouse strains. No significant differences in the accumulation of TCB in hepatic tissues of C57BL/Rij and DBA/2 mice were observed; however, the estimated elimination rate in C57BL/Rij was two times faster than that in DBA/2 mice. In serum of DBA/2 mice, a rapid 50% decline in the concentration of retinol was observed after only 2 to 6 hr, remaining at the reduced value for about 14 days. The ED50 for serum retinol was 1 to 2 mg TCB/kg. Only a transient reduction in serum retinol, disappearing within 48 hr, was observed in the C57BL/Rij mouse. TCB accumulated to an almost 15-fold higher extent in serum of DBA/2 mice as compared with C57BL/Rij mice. The effect of TCB on retinoids in a few other strains of mice and in the Sprague-Dawley rat showed a reduction in serum retinol rather than in hepatic retinoids.

Animals↗
PubMed1984

Early and differential decrease in natural retinoid levels in C57BL/Rij and DBA/2 mice by 3,4,3',4'-tetrachlorobiphenyl.

3,4,3',4'-Tetrachlorobiphenyl (TCB) administered by weekly ip injections of 1.5 to 100 mg kg-1 for 4 weeks induced a dose dependent decrease in retinoids in female C57BL/Rij and DBA/2 mice (5 to 7 weeks of age). However, the response differed between the two strains of mice. In C57BL/Rij mice, a dose dependent decrease in liver retinol (up to 60%), retinyl palmitate (up to 40%), and serum retinol (up to 80%) occurred, while in DBA/2 mice a decrease in serum retinol (up to 80%) only was observed. The effects of 3,4,3',4'-TCB on retinoid levels were more pronounced than on toxicity (e.g., decrease in thymus and body weight, increase in liver weight, and induction of AHH activity). This finding suggests that reduction in retinoid levels is a very sensitive parameter for the toxicity of polychlorinated biphenyls (PCBs). In addition, in these experiments the induction of aryl hydrocarbon hydroxylase (AHH) did not correlate with the decrease in retinoid levels in C57BL/Rij and DBA/2 mice, suggesting that the mixed function oxidase (MFO) system is not involved.

Animals↗