Tuesday, November 23, 2010
Oxidative stress is defined as a type of physiological stress on the body caused by the damage done by free radicals inadequately neutralized by antioxidants. It has long been known that oxidative stress is an essential mechanism by which chemotherapy works to treat cancer. However, the question of whether this is always the case is seldom debated openly. Taking a deeper look into the research literature yields many examples where oxidative stress on cancer cells has been shown to be counterproductive. For example, a study using human Burkitt lymphoma cells found that oxidative stress actually interferes with the ability of the chemotherapy drugs doxorubicin, cisplatin, etoposide, and cytarabine to cause cancer cell death.
When oxidative stress levels are reduced in cancer cells, their growth is more easily controlled through a process called apoptosis. During apoptosis, cells are removed by the immune system before they lose their cell wall, thus avoiding an inflammatory response to the dying cells.
However, when oxidative stress levels go up, cancer cell death happens through a slower, messier, and less effective pathway called pyknosis or necrosis. Additionally, the ability of the body to “clean up” the resulting cellular debris from cancer cell death is also inhibited by oxidative stress. The body’s house-cleaning cells (called monocyte-derived macrophages) cannot function optimally under conditions of oxidative stress (i.e. low oxygen levels).
The authors of the above-mentioned study on Burkitt lymphoma cells and chemotherapy suggest that including antioxidants in the treatment protocol may enhance chemotherapy-induced apoptosis and phagocytosis. (Shacter, Williams et al. 2000) A second study, involving the chemotherapy drugs etoposide and calcimycin, confirms this finding: Human Burkitt’s lymphoma cells were unable to die quickly by apoptosis in the presence of oxidative stress and instead died using the slower and messier method of necrosis. In this study, it was found that oxidative stress inhibited apoptosis by depleting cells of their energy source, which is called adenosine triphosphate (ATP). (Lee and Shacter 1999)
Related to these observations about the relationship between cellular oxidative stress levels is the widely held view in medicine that the use of antioxidant dietary supplements diminishes chemotherapy’s effectiveness. However, when one looks more closely at the existing published science on how antioxidants and chemotherapy combine, the true answer is not so definitive. Many research studies, encompassing cell culture tests in the laboratory and also animal and some human studies, are coming to a conclusion often very different from the conventional perspective that chemotherapy and antioxidants should never be combined.
One example is a human study in which researchers discovered that higher levels of the antioxidant selenium in the blood of patients with aggressive B-cell non-Hodgkin’s lymphoma correlated with increased achievable doses of anthracycline based chemotherapy, better treatment response, achievement of long term remission, and longer overall survival. It is important to note that in this study, however, the level of selenium present in the blood of patients was from their diet; the study was not a test of supplemented selenium. (Last, Cornelius et al. 2003) As seen in this study, higher levels of natural antioxidants can help treatment outcomes.
On the other hand, the decreased levels of antioxidants (or oxidative stress) that are caused by many chemotherapy treatments correlates with increased side effects. In patients with Hodgkin’s lymphoma, chemotherapy with Adriamycin, bleomycin, vincristine, and dexamethasone significantly decreases antioxidant levels. (Kaya, Keskin et al. 2005) In children with acute lymphoblastic leukemia who received high-dose methotrexate, oxidative damage to proteins as well as other factors was related to toxic side effects. (Carmine, Evans et al. 1995)
Using antioxidants during chemotherapy is an important and controversial question among health care providers, patients, and their support teams. In previous issues of Avenues, we have researched this subject thoroughly for prostate, breast, lung, colon, and ovarian cancers. In this article, we turn our focus to lymphoma, conducting a systematic search for published research that would support or discourage the use of antioxidants in combination with chemotherapy. The overwhelming majority of studies find a favorable interaction between antioxidants and chemotherapy, providing evidence that antioxidants can decrease chemotherapy side effects, increase treatment effectiveness, and decrease resistance to chemotherapy.
For this paper, we searched for clinical or laboratory data published in peer-reviewed medical journals, conducted by cancer researchers in universities and medical research facilities around the world. Some of these studies are still in early stages and include only laboratory or animal data while others have advanced to include human volunteers. We organized these data into the major categories of specific chemotherapy drugs. Within each section for a specific drug are found the research on combinations of that drug with various antioxidants, grouped by the name of the antioxidant in alphabetical order. We also point out specifically which studies were conducted in a laboratory (i.e. used cancer cell cultures), used animals, or involved human volunteers. As each antioxidant appears in the paper for the first time, we provide some introduction to the antioxidant including what food sources naturally contain it, other common applications in clinical use, and typical dosages. The dosages given are not necessarily appropriate for all patients and should be individualized with practitioner guidance.
Click here for the rest of the article