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      Assessment of the genetic risks of a metallic alloy used in medical implants

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          Abstract

          The use of artificial implants provides a palliative or permanent solution for individuals who have lost some bodily function through disease, an accident or natural wear. This functional loss can be compensated for by the use of medical devices produced from special biomaterials. Titanium alloy (Ti-6Al-4V) is a well-established primary metallic biomaterial for orthopedic implants, but the toxicity of the chemical components of this alloy has become an issue of concern. In this work, we used the MTT assay and micronucleus assay to examine the cytotoxicity and genotoxicity, respectively, of an extract obtained from this alloy. The MTT assay indicated that the mitochondrial activity and cell viability of CHO-K1 cells were unaffected by exposure to the extract. However, the micronucleus assay revealed DNA damage and an increase in micronucleus frequency at all of the concentrations tested. These results show that ions released from Ti-6Al-4V alloy can cause DNA and nuclear damage and reinforce the importance of assessing the safety of metallic medical devices constructed from biomaterials.

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          The in vitro micronucleus technique.

          M Fenech (2000)
          The study of DNA damage at the chromosome level is an essential part of genetic toxicology because chromosomal mutation is an important event in carcinogenesis. The micronucleus assays have emerged as one of the preferred methods for assessing chromosome damage because they enable both chromosome loss and chromosome breakage to be measured reliably. Because micronuclei can only be expressed in cells that complete nuclear division a special method was developed that identifies such cells by their binucleate appearance when blocked from performing cytokinesis by cytochalasin-B (Cyt-B), a microfilament-assembly inhibitor. The cytokinesis-block micronucleus (CBMN) assay allows better precision because the data obtained are not confounded by altered cell division kinetics caused by cytotoxicity of agents tested or sub-optimal cell culture conditions. The method is now applied to various cell types for population monitoring of genetic damage, screening of chemicals for genotoxic potential and for specific purposes such as the prediction of the radiosensitivity of tumours and the inter-individual variation in radiosensitivity. In its current basic form the CBMN assay can provide, using simple morphological criteria, the following measures of genotoxicity and cytotoxicity: chromosome breakage, chromosome loss, chromosome rearrangement (nucleoplasmic bridges), cell division inhibition, necrosis and apoptosis. The cytosine-arabinoside modification of the CBMN assay allows for measurement of excision repairable lesions. The use of molecular probes enables chromosome loss to be distinguished from chromosome breakage and importantly non-disjunction in non-micronucleated binucleated cells can be efficiently measured. The in vitro CBMN technique, therefore, provides multiple and complementary measures of genotoxicity and cytotoxicity which can be achieved with relative ease within one system. The basic principles and methods (including detailed scoring criteria for all the genotoxicity and cytotoxicity end-points) of the CBMN assay are described and areas for future development identified.
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            Comparison of metal release from various metallic biomaterials in vitro.

            To investigate the metal release of each base and alloying elements in vitro, SUS316L stainless steel, Co-Cr-Mo casting alloy, commercially pure Ti grade 2, and Ti-6Al-4V, V-free Ti-6Al-7Nb and Ti-15Zr-4Nb-4Ta alloys were immersed in various solutions, namely, alpha-medium, PBS(-), calf serum, 0.9% NaCl, artificial saliva, 1.2 mass% L-cysteine, 1 mass% lactic acid and 0.01 mass% HCl for 7d. The difference in the quantity of Co released from the Co-Cr-Mo casting alloy was relatively small in all the solutions. The quantities of Ti released into alpha-medium, PBS(-), calf serum, 0.9% NaCl and artificial saliva were much lower than those released into 1.2% L-cysteine, 1% lactic acid and 0.01% HCl. The quantity of Fe released from SUS316L stainless steel decreased linearly with increasing pH. On the other hand, the quantity of Ti released from Ti materials increased with decreasing pH, and it markedly attenuated at pHs of approximately 4 and higher. The quantity of Ni released from stainless steel gradually decreased with increasing pH. The quantities of Al released from the Ti-6Al-4V and Ti-6Al-7Nb alloys gradually decreased with increasing pH. A small V release was observed in calf serum, PBS(-), artificial saliva, 1% lactic acid, 1.2% l-cysteine and 0.01% HCl. The quantity of Ti released from the Ti-15Zr-4Nb-4Ta alloy was smaller than those released from the Ti-6Al-4V and Ti-6Al-7Nb alloys in all the solutions. In particular, it was approximately 30% or smaller in 1% lactic acid, 1.2% L-cysteine and 0.01% HCl. The quantity of (Zr + Nb + Ta) released was also considerably lower than that of (Al + Nb) or (Al + V) released. Therefore, the Ti-15Zr-4Nb-4Ta alloy with its low metal release in vitro is considered advantageous for long-term implants. Copyright 2004 Elsevier Ltd.
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              Nanosize Titanium Dioxide Stimulates Reactive Oxygen Species in Brain Microglia and Damages Neurons in Vitro

              Background Titanium dioxide is a widely used nanomaterial whose photo-reactivity suggests that it could damage biological targets (e.g., brain) through oxidative stress (OS). Objectives Brain cultures of immortalized mouse microglia (BV2), rat dopaminergic (DA) neurons (N27), and primary cultures of embryonic rat striatum, were exposed to Degussa P25, a commercially available TiO2 nanomaterial. Physical properties of P25 were measured under conditions that paralleled biological measures. Findings P25 rapidly aggregated in physiological buffer (800–1,900 nm; 25°C) and exposure media (~ 330 nm; 37°C), and maintained a negative zeta potential in both buffer (–12.2 ± 1.6 mV) and media (–9.1 ± 1.2 mV). BV2 microglia exposed to P25 (2.5–120 ppm) responded with an immediate and prolonged release of reactive oxygen species (ROS). Hoechst nuclear stain was reduced after 24-hr (≥100 ppm) and 48-hr (≥2.5 ppm) exposure. Microarray analysis on P25-exposed BV2 microglia indicated up-regulation of inflammatory, apoptotic, and cell cycling pathways and down-regulation of energy metabolism. P25 (2.5–120 ppm) stimulated increases of intracellular ATP and caspase 3/7 activity in isolated N27 neurons (24–48 hr) but did not produce cytotoxicity after 72-hr exposure. Primary cultures of rat striatum exposed to P25 (5 ppm) showed a reduction of immunohistochemically stained neurons and microscopic evidence of neuronal apoptosis after 6-hr exposure. These findings indicate that P25 stimulates ROS in BV2 microglia and is nontoxic to isolated N27 neurons. However, P25 rapidly damages neurons at low concentrations in complex brain cultures, plausibly though microglial generated ROS.
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                Author and article information

                Journal
                Genet Mol Biol
                GMB
                Genetics and Molecular Biology
                Sociedade Brasileira de Genética (Ribeirão Preto, SP, Brazil )
                1415-4757
                1678-4685
                Jan-Mar 2011
                1 March 2011
                : 34
                : 1
                : 116-121
                Affiliations
                [1 ]Instituto de Pesquisa e Desenvolvimento, Universidade do Vale do Paraíba, São José dos Campos, SP, Brazil
                [2 ]Departamento de Engenharia de Biossistemas, Universidade Federal de São João Del Rei, Campus Dom Bosco, São João Del Rei, MG, Brazil
                [3 ]Departamento de Ciências Naturais, Universidade Federal de São João Del Rei, Campus Dom Bosco, São João Del Rei, MG, Brazil
                [4 ]Universidade Federal de São João Del Rei, Campus Centro Oeste Dona Lindu, Divinópolis, MG, Brazil
                Author notes
                Send correspondence to Fabio V. Santos. Universidade Federal de São João Del Rei (UFSJ), Campus Centro Oeste Dona Lindu, Avenida Sebastião Gonçalves Coelho 400, 35501-296 Divinópolis, MG, Brazil. E-mail: santos_fv@ 123456yahoo.com.br .
                Article
                gmb-34-1-116
                10.1590/S1415-47572010005000118
                3085356
                21637553
                f5c533bd-139c-4916-b548-e2b785461e2b
                Copyright © 2011, Sociedade Brasileira de Genética.

                License information: This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 10 March 2010
                : 29 July 2010
                Categories
                Mutagenesis
                Research Article

                Molecular biology
                micronucleus,biomaterial,cytotoxicity,mutagenicity,ti-6al-4v
                Molecular biology
                micronucleus, biomaterial, cytotoxicity, mutagenicity, ti-6al-4v

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