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Primary Route (primary + route)
Selected AbstractsBenzo[a]pyrene bioavailability from pristine soil and contaminated sediment assessed using two in vitro modelsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2007Luba Vasiluk Abstract A major route of exposure to hydrophobic organic contaminants (HOCs), such as benzo[a]pyrene (BaP), is ingestion. Matrix-bound HOCs may become bioavailable after mobilization by the gastrointestinal fluids followed by sorption to the intestinal epithelium. The purpose of this research was to measure the bioavailability of [14C]-BaP bound to pristine soils or field-contaminated sediment using an in vitro model of gastrointestinal digestion followed by sorption to human enterocytes (Caco-2 cells) or to a surrogate membrane, ethylene vinyl acetate (EVA) thin film. Although Caco-2 cells had a twofold higher lipid-normalized fugacity capacity than EVA, [14C]-BaP uptake by Caco-2 lipids and EVA thin film demonstrated a linear relationship within the range of BaP concentrations tested. These results suggest that EVA thin film is a good membrane surrogate for passive uptake of BaP. The in vitro system provided enough sensitivity to detect matrix effects on bioavailability; after 5 h, significantly lower concentrations of [14C]-BaP were sorbed into Caco-2 cells from soil containing a higher percentage of organic matter compared to soil with a lower percentage of organic matter. The [14C]-BaP desorption rate from Caco-2 lipids consistently was twofold higher than from EVA thin film for all matrices tested. The more rapid kinetics observed with Caco-2 cells probably were due to the greater surface area available for absorption/desorption in the cells. After 5 h, the uptake of BaP into Caco-2 lipid was similar in live and metabolically inert Caco-2 cells, suggesting that the primary route of BaP uptake is by passive diffusion. Moreover, the driving force for uptake is the fugacity gradient that exists between the gastrointestinal fluid and the membrane. [source] Tributyltin uptake and depuration in Hyalella azteca: Implications for experimental designENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2004Adrienne J. Bartlett Abstract The purpose of this study was to address four aspects of the kinetics of tributyltin (TBT) in the freshwater amphipod Hyalella azteca: time to steady state, route of uptake, depuration rates, and effect of gut clearance. The amphipods accumulated TBT rapidly, reaching steady state within 14 d. Body concentrations were similar between caged and sediment-exposed animals, indicating that the primary route of uptake is via dissolved TBT. However, the rate of uptake was significantly higher in sediment-exposed amphipods. During depuration, body concentrations of TBT exhibited a biphasic decline, with a stronger decrease over the first 24 h that is attributed primarily to gut clearance, followed by a more gradual decrease most likely due to excretion from the body. Gut contents contributed significantly to body concentrations of TBT, accounting for 30% of the initial total body burden in sediment-exposed amphipods. Half-lives of TBT in gut-cleared H. azteca were 8 d and 14 d for amphipods exposed to spiked water and spiked sediment, respectively. The results of this study have significant implications in the experimental design and interpretation of studies involving the effects of TBT in H. azteca. [source] Oxidative stress on EAAC1 is involved in MPTP-induced glutathione depletion and motor dysfunctionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2008Koji Aoyama Abstract Excitatory amino acid carrier 1 (EAAC1) is a glutamate transporter expressed on mature neurons in the CNS, and is the primary route for uptake of the neuronal cysteine needed to produce glutathione (GSH). Parkinson's disease (PD) is a neurodegenerative disorder pathogenically related to oxidative stress and shows GSH depletion in the substantia nigra (SN). Herein, we report that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice, an experimental model of PD, showed reduced motor activity, reduced GSH contents, EAAC1 translocation to the membrane and increased levels of nitrated EAAC1. These changes were reversed by pre-administration of n-acetylcysteine (NAC), a membrane-permeable cysteine precursor. Pretreatment with 7-nitroindazole, a specific neuronal nitric oxide synthase inhibitor, also prevented both GSH depletion and nitrotyrosine formation induced by MPTP. Pretreatment with hydrogen peroxide, l -aspartic acid ,-hydroxamate or 1-methyl-4-phenylpyridinium reduced the subsequent cysteine increase in midbrain slice cultures. Studies with chloromethylfluorescein diacetate, a GSH marker, demonstrated dopaminergic neurons in the SN to have increased GSH levels after NAC treatment. These findings suggest that oxidative stress induced by MPTP may reduce neuronal cysteine uptake, via EAAC1 dysfunction, leading to impaired GSH synthesis, and that NAC would exert a protective effect against MPTP neurotoxicity by maintaining GSH levels in dopaminergic neurons. [source] Experimental exposure of zebrafish, Danio rerio (Hamilton), to Mycobacterium marinum and Mycobacterium peregrinum reveals the gastrointestinal tract as the primary route of infection: a potential model for environmental mycobacterial infectionJOURNAL OF FISH DISEASES, Issue 10 2007M J Harriff Abstract The natural route by which fish become infected with mycobacteria is unknown. Danio rerio (Hamilton) were exposed by bath immersion and intubation to Mycobacterium marinum and Mycobacterium peregrinum isolates obtained from diseased zebrafish. Exposed fish were collected over the course of 8 weeks and examined for the presence of mycobacteriosis. Mycobacteria were consistently cultured from the intestines, and often from the livers and spleens of fish exposed by both methods. Mycobacteria were not observed in the gills. Histological analysis revealed that fish infected with M. marinum often developed granulomas accompanied by clinical signs of mycobacteriosis, while infection with M. peregrinum infrequently led to clinical signs of disease. Passage of the bacteria through environmental amoebae (Acanthamoeba castellani) was associated with increased growth of M. peregrinum over the course of 8 weeks, when compared to infection with the bacteria not passed through amoebae. The results provide evidence that zebrafish acquire mycobacteria primarily through the intestinal tract, resulting in mycobacterial dissemination. [source] Exploration of twin-arginine translocation for expression and purification of correctly folded proteins in Escherichia coliMICROBIAL BIOTECHNOLOGY, Issue 5 2008Adam C. Fisher Summary Historically, the general secretory (Sec) pathway of Gram-negative bacteria has served as the primary route by which heterologous proteins are delivered to the periplasm in numerous expression and engineering applications. Here we have systematically examined the twin-arginine translocation (Tat) pathway as an alternative, and possibly advantageous, secretion pathway for heterologous proteins. Overall, we found that: (i) export efficiency and periplasmic yield of a model substrate were affected by the composition of the Tat signal peptide, (ii) Tat substrates were correctly processed at their N-termini upon reaching the periplasm and (iii) proteins fused to maltose-binding protein (MBP) were reliably exported by the Tat system, but only when correctly folded; aberrantly folded MBP fusions were excluded by the Tat pathway's folding quality control feature. We also observed that Tat export yield was comparable to Sec for relatively small, well-folded proteins, higher relative to Sec for proteins that required cytoplasmic folding, and lower relative to Sec for larger, soluble fusion proteins. Interestingly, the specific activity of material purified from the periplasm was higher for certain Tat substrates relative to their Sec counterparts, suggesting that Tat expression can give rise to relatively pure and highly active proteins in one step. [source] | ||||||||||