Antitumor and anti-cachectic effects of shark liver oil and fish oil: comparison between independent or associative chronic supplementation in Walker 256 tumor-bearing rats

Iagher et al. Lipids in Health and Disease 2013, 12:146 http://www.lipidworld.com/content/12/1/146 RESEARCH Open Access Antitumor and anti-cachectic effects of shark liver oil and fish oil: comparison between independent or associative chronic supplementation in Walker 256 tumor-bearing rats Fabíola Iagher1*, Sérgio Ricardo de Brito Belo2†, Wanessa Mazanek Souza2†, Juliana Rehlander Nunes2†, Katya Naliwaiko3†, Guilherme Lanzi Sassaki4†, Sandro José Ribeiro Bonatto2†, Heloísa Helena Paro de Oliveira2†, Gleisson Alisson Pereira Brito2†, Carina de Lima2†, Marcelo Kryczyk2†, Carine Ferreira de Souza2†, Jovani Antonio Steffani1†, Everson Araújo Nunes5† and Luiz Cláudio Fernandes2† Abstract Background: Shark liver oil (SLOil) and fish oil (FOil), which are respectively rich in alkylglycerols (AKGs) and n-3 polyunsaturated fatty acids (PUFAs), are able to reduce the growth of some tumors and the burden of cachexia. It is known that FOil is able to reduce proliferation rate and increase apoptotic cells and lipid peroxidation of tumor cells efficiently. However, there are few reports revealing the influence of SLOil on these parameters. In the current study, effects of FOil chronic supplementation on tumor growth and cachexia were taken as reference to compare the results obtained with SLOil supplementation. Also, we evaluated if the association of SLOil and FOil was able to promote additive effects. Methods: Weanling male Wistar rats were divided into 4 groups: fed regular chow (C), supplemented (1 g/kg body weight) with SLOil (CSLO), FOil (CFO) and both (CSLO + FO). After 8 weeks half of each group was inoculated with Walker 256 cells originating new groups (W, WSLO, WFO and WSLO + FO). Biochemical parameters of cachexia, tumor weight, hydroperoxide content, proliferation rate and percentage of apoptotic tumor cells were analysed. Fatty acids and AKG composition of tumor and oils were obtained by high performance liquid chromatography and gas chromatography – mass spectrometry, respectively. Statistical analysis was performed by unpaired t-test and one-way ANOVA followed by a post hoc Tukey test. Results: Fourteen days after inoculation, SLOil was able to restore cachexia parameters to control levels, similarly to FOil. WSLO rats presented significantly lower tumor weight (40%), greater tumor cell apoptosis (~3-fold), decreased tumor cell proliferation (35%), and higher tumor content of lipid hydroperoxides (40%) than observed in W rats, but FOil showed more potent effects. Supplementation with SLOil + FOil did not promote additive effects. Additionally, chromatographic results suggested a potential incorporation competition between the n-3 fatty acids and the AKGs in the tumor cells’ membranes. Conclusions: SLOil is another marine source of lipids with similar FOil anti-cachectic capacity. Furthermore, despite being less potent than FOil, SLOil presented significant in vivo antitumor effects. These results suggest that the chronic supplementation with SLOil may be adjuvant of the anti-cancer therapy. Keywords: Cachexia, Fish oils, Walker 256, Lipid peroxidation, Apoptosis, Cell proliferation, Rats, Wistar * Correspondence: † Equal contributors 1 Area of Biological and Health Sciences, West University of Santa Catarina, Joaçaba, Brazil Full list of author information is available at the end of the article © 2013 Iagher et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Iagher et al. Lipids in Health and Disease 2013, 12:146 http://www.lipidworld.com/content/12/1/146 Background Cancer susceptibility is determined by genetic factors; however, environmental factors seem to influence which subjects genetically susceptible will be affected. In this context, nutrition has been aroused as a main component in such relation [1]. Nutrition has a central role in this feature, because it can be applied as a preventive tool or as a component of the anti-cancer therapy when the disease is already installed. Among several other nutrients, lipids receive a special attention in such line of thinking. Phospholipids and other lipids, incorporated into cell membranes or other compartments, can have their molecular composition altered depending on the lipid nutrition profile of the subject. This fact justifies the importance of studies investigating the repercussions of different lipid nutritional supply on cancer progress. One of the most common manifestations of cancer is the development of cachexia syndrome, a chronic wasting condition responsible for the loss of both adipose and skeletal muscle tissues. At least 20% of the deaths among cancer patients are due to cachexia [2]. This syndrome involves immune-metabolic pathways, and so far, the mechanisms by which it happens remain not fully understood. Western countries have a diet rich in saturated and n-6 polyunsaturated fatty acids (PUFAs). Such a diet is commonly low in n-3 PUFAs and vitamins C and E, which have been associated with the development of some cancers. Fish oil (FOil) is a source of long chain n-3 PUFAs, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These n-3 PUFAs have been shown to decrease the risk for several cancers [3,4], the tumor growth [5-7], and cancer cachexia [8,9] in both animal models [6,10,11] and clinical trials [3,9,12]. The mechanisms by which n-3 PUFAs cause such effects are not fully understood. Noteworthy, the participation of increased lipid peroxidation in tumor tissue [6,7], reduction of proinflammatory cytokines and chemical mediators that induce cell proliferation [7,13,14], and promotion of tumor cell apoptosis [7,11,15,16] have been reported. Another marine compound that contains n-3 PUFAs is shark liver oil (SLOil). Besides the n-3 PUFAs, SLOil also presents alkylglycerols (AKGs) in its composition. These compounds are constituted by glycerol linked to the hydrocarbon tail in the sn-1 position by ether bonds. AKGs can be associated to fatty acids by ester bonds in the sn-2 and sn-3 positions, constituting alkyldiacylglycerol molecules [17]. AKGs represent about 20% of the shark liver oil lipid composition [18]. These ether lipids are found in hematopoietic organs of mammals, especially in the bone marrow and in human breast milk. SLOil seems to be an immune system enhancer [19,20], and this effect is attributed in part to AKGs. The first clinical studies using SLOil supplementation were for the treatment of leukemia and also as a complementary agent administered Page 2 of 9 to uterine cervix cancer patients submitted to X-ray therapy. In such approaches, SLOil supplementation was able to avoid leukopenia and thrombocytopenia usually caused by radiation [21]. There are in vivo studies showing that SLOil [17] as wel (...truncated)