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Vantagens e desvantagens do consumo de antioxidantes no cancro
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Abstract(s)
O cancro é, de acordo com a Organização Mundial de Saúde (OMS), uma das doenças mais mortais em todo o mundo e, por conseguinte, tem despertado um aumento significativo no interesse pela área de investigação científica.
Neste contexto, os antioxidantes desempenham um papel relevante no tratamento desta patologia. Assim, importa conhecer e analisar o comportamento destes compostos sobre moléculas cruciais para a biologia tumoral, tais como as espécies reativas de oxigénio (ROS) e os radicais livres.
As ROS são compostos químicos formados através da redução do oxigénio molecular, o que as torna mais reativas e instáveis, sendo a sua formação inevitável. Os radicais livres são espécies químicas com um eletrão desemparelhado. A sua formação é consequência da utilização do oxigénio em vários processos bioquímicos relacionados com a respiração aeróbia, com o metabolismo celular e com a atividade do sistema imunitário. Algumas ROS fazem parte do grupo dos radicais livres.
Quando há um desequilíbrio entre os radicais livres e os antioxidantes estamos perante um fenómeno de Stress Oxidativo (SO) que está intimamente ligado com a carcinogénese, não só por mecanismos que induzem o dano e mutação do DNA, como através da facilitação da proliferação, angiogénese e metástase.
A presente monografia analisa o interesse e potencial de utilização dos antioxidantes exógenos no tratamento de doentes com cancro. O texto começa por abordar resultados in vivo e in vitro e, posteriormente, ensaios clínicos. Entre os principais grupos de antioxidantes considerados incluem-se as vitaminas e os polifenóis, e ainda como o selénio e a melatonina.
Dos estudos realizados, verifica-se que o objetivo principal é perceber qual a reação do tumor e do organismo à suplementação com antioxidantes. Porém, o tema é de certa forma paradoxal. Por um lado, esta suplementação leva a uma diminuição dos efeitos adversos causados pela quimioterapia, derivados principalmente dos ROS, o que aumenta a tolerância do doente a mais ciclos de tratamento. Por outro lado, pode também levar a uma diminuição da eficácia, pois a maioria dos agentes citotóxicos utilizados têm como mecanismo o aumento de ROS para induzir a apoptose.
A monografia aborda ainda a problemática associada à utilização de antioxidantes em doses muito elevadas, como agentes citotóxicos.
According to the OMS, cancer is one of the most lethal diseases all over the world and therefore has drawn an increasing interest by the scientific community. In this context, antioxidants play an important role in the treatment of this pathology. Hence, we ought to understand and analyse the effect of these compounds over critical molecules for tumour biology, such as reactive oxygen species (ROS) and free radicals. ROS are chemical species created by reducing the molecular oxygen, which makes them more reactive and unstable. The free radicals are chemical molecules with an unpaired electron. Its formation is consequence of using oxygen in various biochemical processes related to aerobic breathing, alongside cellular metabolism activity of the immune system. Some ROS are part of the group of free radicals. When there is imbalance between free radicals and antioxidants, we witness a an Oxidative Stress (SO) event, which is closely related to carcinogenesis, not just by mechanisms that induce damage and DNA mutation, but also by facilitating the proliferation, angiogenesis and metastasis of cancer. This monography analyses the interest and potential use of exogeneous antioxidants to treat patients with cancer. It starts by analysing both in vivo and in vitro results, and then looking at clinical tests. Among the main groups of antioxidants considered are the vitamins and polyphenols, as well as selenium and melatonin. Among the studies carried out, it has been realised that the main goal is to understand the tumour reaction to supplementation with antioxidants. However, this subject is rather paradoxical. On the one hand, supplementation leads to a reduction of adverse effects caused by chemotherapy, mainly due to ROS, which increases patient tolerance to more cycles of treatment. But on the other hand, it can also lead to a reduced efficacy of treatment since the majority of cytotoxic agents that are used work by increasing ROS to induce apoptosis. This monography also focusses on problems related to the use of high doses of antioxidants as cytotoxic agents.
According to the OMS, cancer is one of the most lethal diseases all over the world and therefore has drawn an increasing interest by the scientific community. In this context, antioxidants play an important role in the treatment of this pathology. Hence, we ought to understand and analyse the effect of these compounds over critical molecules for tumour biology, such as reactive oxygen species (ROS) and free radicals. ROS are chemical species created by reducing the molecular oxygen, which makes them more reactive and unstable. The free radicals are chemical molecules with an unpaired electron. Its formation is consequence of using oxygen in various biochemical processes related to aerobic breathing, alongside cellular metabolism activity of the immune system. Some ROS are part of the group of free radicals. When there is imbalance between free radicals and antioxidants, we witness a an Oxidative Stress (SO) event, which is closely related to carcinogenesis, not just by mechanisms that induce damage and DNA mutation, but also by facilitating the proliferation, angiogenesis and metastasis of cancer. This monography analyses the interest and potential use of exogeneous antioxidants to treat patients with cancer. It starts by analysing both in vivo and in vitro results, and then looking at clinical tests. Among the main groups of antioxidants considered are the vitamins and polyphenols, as well as selenium and melatonin. Among the studies carried out, it has been realised that the main goal is to understand the tumour reaction to supplementation with antioxidants. However, this subject is rather paradoxical. On the one hand, supplementation leads to a reduction of adverse effects caused by chemotherapy, mainly due to ROS, which increases patient tolerance to more cycles of treatment. But on the other hand, it can also lead to a reduced efficacy of treatment since the majority of cytotoxic agents that are used work by increasing ROS to induce apoptosis. This monography also focusses on problems related to the use of high doses of antioxidants as cytotoxic agents.
Description
Trabalho Final de Mestrado Integrado, Ciências Farmacêuticas, 2021, Universidade de Lisboa, Faculdade de Farmácia.
Keywords
Cancro ROS Antioxidantes Vitaminas antioxidantes Terapia anti-carcinogénica Mestrado integrado - 2021