In vitro study

The complexity of living organisms can be a barrier to the identifieation of specific biological interactions. However, using in vitro teehniques it is possible to simplify the system in order to examine interactions at the eellular or molecular level, allowing detailed examination of specifie parts of the system of interest in highly controllable experiments. Examples inelude the assessment 

Cowan et al. exposed human lung small airway cell (SAC) cultures to phosgene at 0.4-25.6 mg min m (1 min) and demonstrated dose dependent increases in IL-8 (neutrophil chemotactic factor) at 24 hours at all but the lowest dose. However, higher exposures ( 12.8 mg min m ) decreased IL-8 from maximal levels this is purported to be due to increased cytotoxicity, as measured by trypan blue exclusion, at high exposure dosages. The authors propose the use of IL-8 as a biomarker both for inflammation following phosgene exposure and to assess the efficacy of medical countermeasures in vitro. 

Sugiyama and Kato [63] described a model for the receptor-mediated endocytosis of the polypeptide hormones epidermal growth factor (EGF) and hepatocyte growth factor (HGF) in isolated perfused rat liver and in isolated rat hepatocytes, to estimate the efficiency of dmg targeting using these polypeptide hormones as potential drng carriers. 

Chan and Murphy [64] applied a mathematical model describing the kinetics of cellnlar trafficking of monoclonal antibodies against melanoma cells, and of immnnotoxins targeted by the antibodies. The model allowed the assessment of eqnilibrinm and kinetic constants by fitting it to the data obtained from in vitro cnltnred cell experiments. 

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Investigations are carried out using a variety of biological systems, including observations on exposed whole animals in vivo studies) or on appropriately treated isolated tissues and cells, homogenates of tissues, or cultured lower organisms in vitro studies). 

Types of Studies. Studies may be conducted in five specimens (in vivo) or in test tubes in vitro). Studies may be carried out by single exposure or by repeated exposure over variable periods of time. The design of any one study, including the monitoring procedures, is determined by a large number of factors, including the nature of the test material, route of exposure, known or suspected toxicity, practical use of the material, and the reason for conducting the study. 

The literature contains a number of studies on the susceptibility of the cobalt-based alloys to pitting corrosion. In-vitro studies conducted by Mueller and Greener , involving static conditions, revealed no evidence of pitting having occurred. Syrett and Wing ", utilising cyclic polarisation analyses, observed that neither as-cast nor annealed Co-Cr-Mo alloy demonstrated hysteresis loops in their cyclic polarisation curves. They... 

In vitro studies in human liver fractions indicated that azacitidine may be metabolized by the liver. Azacitidine and its metabolites are known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. 

In the case of dmg interactions involving metabolic inhibition, little increase in the substrate concentration is expected when the inhibition constant (K ) determined in in vitro studies using human liver samples is larger than the inhibitor concentration in vivo. Various approaches have been adopted using mathematical models in attempts to quantitatively predict in vivo dmg interactions from in vitro data [5]. 

Although there has been substantial success using IFN for the treatment of some cancels, until this point, the great majority of tumors are resistant or show an initial moderate response soon followed by disease progression under treatment. One likely reason for resistance is the progredient loss of susceptibility to IFN, which may be caused by downregulation of IFN receptors or perturbation of intracellular DFN-signaling pathways, a phenomenon also known from in vitro studies. 

For in vitro studies there are a number of compounds available to block protein phosphatase activity. Phosphate buffers inactivate all of these enzymes. Several naturally occurring toxins are potent inhibitors of PPPs, e.g., okadaic acid or microcystin, and are frequently used tools. PPM and PTP family members are not affected by these toxins. Vanadate containing solutions are competitive inhibitors of PTPs, pervanadate is an irreversible inhibitor of PTPs. 

In recent years a number of in vitro studies have shown that the presence of Met(O) residues in a wide variety of proteins causes loss of biological activity. Table 2 lists some proteins which have been demonstrated to lose activity when specific Met residues are oxidized in vitro. Two of these proteins, E. coli ribosomal protein LI 2 and mammalian a-1-PI, have been studied extensively and will be discussed in detail. 

One of the questions confronting investigators in the HS field is whether fever or other acute phase reactants can induce HS gene expression. In vitro studies utilize extraordinary temperatures of 42 °C and higher. Core body temperatures may approach 40 °C as a result of fever. In most in vitro systems, this temperature does not lead to the HS response. However, there are reports that fever induces the increased synthesis of hsps in peripheral blood lymphocytes (Ciavarra, 1990). This response was observed in mononuclear cells exposed to febrile temperatures and in cells isolated from a medical intern who developed fever. 

However, very recent studies by Fish and his co-workers (467) with butyltin compounds showed that the primary, metabolic reaction is not Sn-C bond-cleavage but carbon hydroxylation of the n-butyl group. Using [l- C]tetrabutyltin in an in vitro study, the major, primary metabolite was identified as a 2-hydroxybutyltributyltin derivative that underwent a rapid /3-elimination reaction to afford 1-butene and a tri-butyltin compound (467). 

Tricyclohexyltin hydroxide is metabolized in vivo to inorganic tin via di- and monocyclohexyltin derivatives (502), and in vitro studies suggested that the major, metabolic reaction is carbon-hydroxylation of the cyclohexyl group (503). Studies in vivo using either tri-phenyl[ Sn]tin acetate (467) or triphenyl[" Sn]tin chloride (504) in rats showed that these compounds are metabolized to yield substantial amounts of di- and monophenyltin derivatives, although no significant quantities of hydroxylated metabolites have been identified (503) in this case. 

In vitro studies on the absorption of dioctyltin dichloride and dioctyltin EHMA through rat and human epidermis (occluded and unoccluded) were performed by... 

In recent in vitro studies, an aromatase inhibiting effect on human placental microsomal extracts has been demonstrated with both tributyltin chloride and dibutyltin dichloride (Heidrich et al, 2001 Cooke,... 

In vivo and in vitro studies on the differentiation and proliferation of immature rat thymus subsets have shown that dibutyltin dichloride reduces the production of CD4 CD8 and mature single-positive thymocyte proliferation by selectively inhibiting immature CD4 CD8 thymocyte proliferation but without affecting the differentiation capacity of these cells, suggesting that thymocyte proliferation and differentiation are separately regulated processes (Pieters et al., 1993, 1994a,b, 1995). 

Seinen W, Vos JG, van Spanje I, Snoek M, Brands R, Hooykaas H (1977a) Toxicity of organotin compounds. II. Comparative in vivo and in vitro studies with various organotin and organolead compounds in different animal species with special emphasis on lymphocyte cytotoxicity. Toxicology and Applied Pharmacology, 42(1) 197-212. 

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