Absorption, distribution, metabolism and excretion of selenium following oral administration of elemental selenium nanoparticles or selenite in rats.

A suspension of nanoparticles of BSA-stabilized red amorphous elemental selenium (Se) or an aqueous solution of sodium selenite was repeatedly administered by oral gavage for 28 days at 0.05 mg kg(-1) bw per day (low dose) or at 0.5 mg kg(-1) bw per day (high dose) as Se to female rats. Prior to administration, the size distribution of the Se nanoparticles was characterized by dynamic light scattering and transmission electron microscopy, which showed that the particles' mean diameter was 19 nm and ranged in size from 10 to 80 nm. Following administration of the high dose of Se nanoparticles or selenite the concentration of Se was determined by ICP-MS in the liver, kidney, urine, feces, stomach, lungs, and plasma at the µg g(-1) level and in brain and muscle tissue at the sub-µg g(-1) level. In order to test if any elemental Se was present in the liver, kidney or feces, an in situ derivatization selective to elemental Se was performed by treatment with sulfite, which resulted in formation of the selenosulfate anion. This Se species was selectively and quantitatively determined by anion exchange HPLC and ICP-MS detection. The results showed that elemental Se was present in the livers, kidneys and feces of animals exposed to low and high doses of elemental Se nanoparticles or to selenite, and was also detected in the same samples from control animals. The fraction of Se present as elemental Se in livers and kidneys from the high dose animals was significantly larger than the similar fraction in samples from the low dose animals or from the controls. This suggested that the natural metabolic pathways of Se were exhausted when given the high dose of elemental Se or selenite resulting in a non-metabolized pool of elemental Se. Both dosage forms of Se were bioavailable as demonstrated by the blood biomarker selenoprotein P, which was equally up-regulated in the high-dose animals for both dosage forms of Se. Finally, the excretion of Se in urine and its occurrence as Se-methylseleno-N-acetyl-galactosamine and the trimethylselenonium-ion demonstrated that both dosage forms were metabolized and excreted. The results of the study showed that both forms of Se were equally absorbed, distributed, metabolized and excreted, but the detailed mechanism of the fate of the administered elemental Se or selenite in the gastro-intestinal tract of rats remains unclear.

Differential toxicological response to positively and negatively charged nanoparticles in the rat brain.

We investigated the potential for systemic and local toxicity after administration of empty nanosized anionic and cationic PEGylated-micelles and non-PEGylated liposomes, without a ligand attached, intended for use in drug-delivery systems. The particles were administered to 5-6-week-old male rats by three intravenous (IV) administrations over a period of one week at a dose of 100 mg/kg bodyweight or after a single intracerebroventricular (ICV) injection at a dose of 50 µg. The particles were stable and well characterised with respect to size and zeta potential. ICV administration of cationic particles was associated with histological changes near the injection site (hippocampus). Here, we detected focal infiltration with phagocytic cells, loss of neurons and apoptotic cell death, which were not observed after administration of the vehicle. No significant difference was found after IV or ICV administration of the anionic micelles with regard to haematology, clinical chemistry parameters or at the pathological examinations, as compared to control animals. Our study suggests that ICV delivery of cationic particles to the brain tissue is associated with toxicity at the injection site.

Distribution of silver in rats following 28 days of repeated oral exposure to silver nanoparticles or silver acetate.

BACKGROUND: The study investigated the distribution of silver after 28 days repeated oral administration of silver nanoparticles (AgNPs) and silver acetate (AgAc) to rats. Oral administration is a relevant route of exposure because of the use of silver nanoparticles in products related to food and food contact materials. RESULTS: AgNPs were synthesized with a size distribution of 14 ± 4 nm in diameter (90% of the nanoparticle volume) and stabilized in aqueous suspension by the polymer polyvinylpyrrolidone (PVP). The AgNPs remained stable throughout the duration of the 28-day oral toxicity study in rats. The organ distribution pattern of silver following administration of AgNPs and AgAc was similar. However the absolute silver concentrations in tissues were lower following oral exposure to AgNPs. This was in agreement with an indication of a higher fecal excretion following administration of AgNPs. Besides the intestinal system, the largest silver concentrations were detected in the liver and kidneys. Silver was also found in the lungs and brain. Autometallographic (AMG) staining revealed a similar cellular localization of silver in ileum, liver, and kidney tissue in rats exposed to AgNPs or AgAc. Using transmission electron microscopy (TEM), nanosized granules were detected in the ileum of animals exposed to AgNPs or AgAc and were mainly located in the basal lamina of the ileal epithelium and in lysosomes of macrophages within the lamina propria. Using energy dispersive x-ray spectroscopy it was shown that the granules in lysosomes consisted of silver, selenium, and sulfur for both AgNP and AgAc exposed rats. The diameter of the deposited granules was in the same size range as that of the administered AgNPs. No silver granules were detected by TEM in the liver. CONCLUSIONS: The results of the present study demonstrate that the organ distribution of silver was similar when AgNPs or AgAc were administered orally to rats. The presence of silver granules containing selenium and sulfur in the intestinal wall of rats exposed to either of the silver forms suggests a common mechanism of their formation. Additional studies however, are needed to gain further insight into the underlying mechanisms of the granule formation, and to clarify whether AgNPs dissolve in the gastrointestinal system and/or become absorbed and translocate as intact nanoparticles to organs and tissues.

Neurotoxic effect of maneb in rats as studied by neurochemical and immunohistochemical parameters.

Epidemiological investigations document that workers in agriculture, horticulture and people living near areas with frequent use of pesticides have increased risk of developing symptoms of Parkinson's disease. This study investigated the neurotoxic effect of the fungicide maneb by morphological, immunohistochemical and neurochemical methods applying young Sprague-Dawley male rat as the model. Intraperitoneal dosing (7.5, 15 or 30mg maneb/kg bodyweight/week for 12 weeks) demonstrated dose-related increased manganese concentration in corpus striatum. The striatal concentration of 5-hydroxytryptamine (5-HT) increased in a dose-related manner, as did the 5-HT concentrations in the rest of the brain indicating early sign of neurotoxicity. Striatal acetylcholinesterase activity was not affected. The concentrations of noradrenaline, dopamine, neurotransmitter amino acids and the levels of the proteins α-synuclein and synaptophysin in corpus striatum and the rest of the brain were not changed. No histological parameter was affected when studied in corpus striatum and substantia nigra.

Atrial fibrillation in rats induced by rapid transesophageal atrial pacing during brief episodes of asphyxia: a new in vivo model.

Non-pharmacological in vivo models of atrial fibrillation (AF) have been developed in large animals only. We aimed to develop and characterize a new small animal non-pharmacological in vivo model of AF. AF was induced by transesophageal atrial burst pacing during 35 seconds periods of asphyxia in anesthetized male Sprague-Dawley rats. AF was reproducibly induced in 81% of the rats. The presence of AF was associated with an increased heart rate, and a decreased blood pressure. Treatment with amiodarone, D,L-sotalol, flecainide, and propranolol all reduced duration of AF, whereas verapamil treatment was associated with a marked profibrillatory effect. Increasing gap junction intracellular communication using the antiarrhythmic peptide analogue AAP10 did not affect AF duration. Basal plasma level of epinephrine and norepinephrine were increased 5- to 20-fold relative to values reported by others, but unchanged following 35 seconds of asphyxia. The results from our study demonstrate that the rat model shares several clinical key characteristics with human AF: (1) hemodynamic response to AF; (2) increased autonomic tone; (3) antiarrhythmic effects of clinically used drugs; (4) profibrillatory effect of verapamil. Relative to existing models of AF in larger animals, this model offers rapid, predictive, and inexpensive testing of antiarrhythmic/profibrillatory effects of new drugs.

Effects of combined prenatal stress and toluene exposure on apoptotic neurodegeneration in cerebellum and hippocampus of rats.

Pregnant Wistar rats were exposed to 1500 ppm toluene 6 hr/day from gestational day 7-20 or to chronical mild stress from gestational day 9-20 as single exposure or in combination. Behavioural, immunohistopathological, molecular biological, and neurochemical methods were applied to investigate the offspring for developmental neurotoxicity and level of apoptosis in the brain. The number of apoptotic cells in cerebellum postnatal day 22, 24, and 27 and in hippocampus (postnatal day 22, 24, and 27) were counted after visualization by the TUNEL staining or measured by DNA-laddering technique. Caspase-3 activity was determined in cerebellum (postnatal day 6, 22, 24, and 27) and in hippocampus (postnatal day 6 and 22). TUNEL staining and DNA-laddering technique showed a marked decrease in number of apoptotic cells from postnatal day 22 to 27 in both cerebellum and hippocampus. Apparently, a peak in the number of TUNEL positive cells was identified in cerebellum at postnatal day 22. There was no statistically significant influence of exposure except that DNA-laddering in cerebellum at postnatal day 27 was increased by toluene exposure. Caspase-3 activity decreased in cerebellum and hippocampus with age. At postnatal day 6 stress and toluene, when singly exposed, increased activity in cerebellum whereas co-exposure to stress and toluene did not. Stress increased caspase-3 activity in hippocampus postnatal day 22. There was overall consistency between the results obtained by the three supplementary methods regarding the influence of exposure and age on apoptotic activity in cerebellum and hippocampus. New methods to quantitate the relative level of apoptosis measured as DNA-laddering and the caspase-3 activity in tissue are presented.

The combined effects of vinclozolin and procymidone do not deviate from expected additivity in vitro and in vivo.

The combination effects of the well-known antiandrogenic fungicides, vinclozolin and procymidone, were tested both in vitro and in vivo. In vitro both vinclozolin and procymidone significantly inhibited the binding of agonist to the androgen receptor with the concentration that resulted in 50% inhibition (IC(50)) values of 0.1 and 0.6 micro M, respectively. By applying the isobole method, the effect of combining the two pesticides in vitro was found to be additive. In castrated testosterone-treated rats the administration of vinclozolin starting at 10 mg/kg led to a decrease in organ weight of all tested reproductive organs. The levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were increased significantly with doses of 100 mg/kg vinclozolin and above. Expression of the androgen-responsive gene, TRPM-2, was increased starting at 100 mg/kg vinclozolin. For procymidone, reproductive organ weights were diminished at 10 mg/kg and LH was increased at a concentration of 25 mg/kg and above, compared to the testosterone-treated controls. FSH was significantly increased only at 25 mg/kg procymidone. The studied gene expressions were changed by 100 mg/kg procymidone. Dosing the animals with a combination of a 1:1 mixture of vinclozolin and procymidone resulted in a weight reduction in the reproductive organs and an increase of serum LH and FSH as early as with 10 mg/kg combined dose. The relative expressions of TRPM-2 and PBP C3 were changed compared to controls at 100 mg/kg. The level of 5-HT in the rat brain was increased after a dose of 10 mg/kg. Using the isobole method, comparisons of the observed and predicted effects assuming additivity on reproductive organ weights, hormone levels, and gene expression showed agreement and thus the combination effects are suggested to be additive in vivo as well as in vitro.

Development and vulnerability of rat brain and testes reflected by parameters for apoptosis and ornithine decarboxylase activity.

BACKGROUND AND PURPOSE: Awareness of effects of chemicals on brain and sex organs during organogenesis is increasing. Balance between apoptosis and ornithine decarboxylase (ODC) activity has an essential role for final structure and function of these organs. It is important to localize stages in development where these processes may be particularly vulnerable to chemicals. We describe reference data on apoptosis and ODC activity in brain and testes. METHODS: Brain and testes specimens were obtained during gestational days (G) 15 to 21 and on postnatal days (P) 1 to 60, and ODC activity and parameters of apoptosis (DNA laddering and Terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling-staining) were investigated. RESULTS: Brain ODC activity reaches maximum at G19 and thereafter rapidly decreases until P7. Apoptotic DNA laddering occurs in the brain from G17 to P7. Significant apoptotic ladders were not detected between P9 and 60. In the testes, apoptotic laddering was weak from G21 to P15, but increased significantly from P15 to 60. Histologic examination and DNA laddering analyses revealed low-level germ cell apoptosis from G15 to P11. At onset of spermatogenesis at P15, the number of apoptotic germ cells increased markedly. CONCLUSIONS: Brain ODC activity and apoptosis from G15 to P7 and at the onset of testes apoptosis at P15 are relevant markers for chemically induced developmental toxicity in these organs.