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Quality and reporting of clinical practice guidelines on the management of Parkinson’s Disease
| Resumo: | The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. |
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| Autores principais: | Serra, Beatriz Machado |
| Assunto: | Parkinson’s Disease Clinical practice guidelines (CPGs) Scientific evidence Quality and variability Therapeutic recommendations Inappropriate prescribing Teses de mestrado - 2019 |
| Ano: | 2019 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. The glioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, as many other tumors, present high levels of redox proteins, which is linked to therapy resistance. Therefore, targeting of redox active systems is becoming increasingly more important in chemotherapy, since cancer cells, due to the greater basal levels of reactive oxygen species (ROS), present a higher vulnerability to oxidative stress than non-cancer cells. One of the major redox systems is the thioredoxin system, which comprises thioredoxin (Trx), the selenoenzyme thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). This system regulates important functions for cancer cells such as DNA synthesis, regulation of transcription factors and reduction of ROS. Also it has an important anti-apoptotic role and therefore inhibition of TrxR and Trx may lead to cell death. Among the main inhibitors of the thioredoxin system, mercury compounds were found to be the most effective. Indeed, mercury presents a high affinity for binding to thiols and selenols, leading to a rapid loss of activity of Trx and especially TrxR. Moreover, mercury compounds can effectively cross the blood-brain barrier (BBB) exerting neurotoxicity, which could facilitate their use for GBM treatment. Therefore, this study aims to evaluate the toxicity of two mercury compounds, ethylmercury (EtHg) and thimerosal (TM) in a mouse glioma cell line (GL261), its relation with the inhibition of the thioredoxin system and the occurrence of oxidative stress. Moreover, insight is provided on the possibility of using these compounds to improve the efficacy of the treatment with temozolomide (TMZ). The results showed that GL261 cells are very sensitive to mercury compounds, with an IC50 for both compounds of approximately 2.5 µM after 24 h of exposure. This was related with a strong inhibition of TrxR (IC50 of 0.8 and 0.7 µM for EtHg and TM, respectively), which supports the notion that this enzyme is a preferential target of these compounds. In agreement, a strong oxidation of both Trx isoforms (cytosolic and mitochondrial) was observed. This oxidation was linked to an increase in ROS levels (50% for 5 µM for EtHg and TM) and was reflected in higher dimerization of Prx2 (20-40%), which is an enzyme downstream of Trx. Also, an increase in Caspase-3 like activity up to 20-50% suggests that apoptosis may be involved in the toxicity of these mercury compounds. Most importantly, co-exposure of GL261 cells to TMZ, a compound commonly used in GBM therapy, and mercury compounds resulted in increased cytotoxicity of the former. Overall, these results showed that Hg compounds, namely EtHg and TM, are potential therapeutic agents to be used in GBM therapy since they target the redox capability of cells at very low exposure levels, enhancing the cytotoxicity of other compounds such as TMZ. Also, these results stress the importance of targeting redox active systems to improve efficacy of GBM therapy. |
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