Anticancer potential, molecular mechanisms and toxicity of Euterpe oleracea extract (açaí): A systematic review.

The use of natural products as medicines accounts for approximately 30% of the currently available drugs [ 1 ], and in some therapeutic areas, the amount of plant-derived medicines reaches 60% [ 2 , 3 ]. Brazil has the greatest amount of biodiversity in the world and plays an important role in the area of natural bioactive compounds by contributing natural products to design new clinical medicines [ 1 , 4 ]. Thus, there has been growing research aimed at establishing the therapeutic potential of natural products against several diseases. Euterpe oleracea Mart. is a member of the family Arecaceae and is a typical palm of the rainforest in the Amazon region, in the states of the northern region of Brazil, including Guianas, Colombia, Ecuador, and Venezuela [ 5 ]. The fruit, popularly known as “açaí”, weighs approximately 2 g, and the color of the mature fruit is dark purple [ 6 ]. Açaí is a traditional food in many regions of Brazil [ 7 , 8 ], and its consumption has increased significantly over the last several years, not only in Brazil but also in Europe and the USA, where the fruit gained popularity after being promoted as a “super fruit” [ 9 ]. Currently, due to the health benefits and therapeutic potential of açaí, locally grown açaí are increasingly exported around the world as energy drinks [ 6 , 10 ], “functional foods” [ 7 , 8 ], cosmetics and pharmaceutical products [ 9 ]. Açaí pulp is composed of approximately 48% lipids, 13% protein, 8% amino acids, 25% total sugars and minor compounds such as fiber and vitamins (A, B1, B2, B3, C and E) [ 8 , 11 , 12 ]. Moreover, it is rich in several phytochemicals, including lignans, phenolic compounds (anthocyanins, proanthocyanidins and other flavonoids) and resveratrol, in low concentrations [ 8 , 11 , 12 ]. The seeds of açaí possess the highest concentration of polyphenols (28.3%), followed by the whole fruit (25.5%) and the bark (15.7%) [ 13 ]. The pharmacological effects of açaí are associated with its chemical composition, particularly the presence of bioactive substances, such as phenolics, flavonoids and anthocyanins [ 14 – 17 ]. To date, açaí has been shown to have pharmacological properties including antiinflammatory, antioxidant, cardioprotective and anticancer activities [ 1 , 7 – 9 , 18 , 19 ]. Furthermore, açaí was not shown to be genotoxic in vitro and in vivo studies conducted, in cultured human lymphocytes and hepatoma cell lines [ 20 ], in rodents [ 21 ] and in humans [ 22 ]. The aim of this review was to systematically describe the safety and antitumor effects of açaí in preclinical models using rodents, to provide a comprehensive assessment of açaí for therapeutic use. Preclinical studies using rodents were evaluated to investigate whether the current knowledge supports cancer clinical trials with açaí.

A flowchart of the articles that were included in the review is illustrated in Fig 1 . A total of 60 publications were identified in the databases; however, 31 were duplicate articles. Among the 29 articles selected, 20 were excluded based on the titles and abstracts because they did not meet the inclusion criteria: 2 were literature reviews [ 7 , 24 ]; 6 did not study açaí in an animal model of cancer and/or did not perform a toxicological analysis [ 25 – 30 ]; 10 were in vitro studies [ 13 , 20 , 31 – 38 ]; and 2 did not use the order Rodentia [ 21 , 39 ]. After reading the full texts 9 articles were included for their critical evaluations of the safety and effectiveness of açaí in animal experimental models [ 40 – 48 ]. The articles included were analyzed with a critical appraisal tool (QATRS), which allowed for improved quality control of the experimental studies in animal performed independently (see methods ). QATRS scores ranged from 0 to 20, and the quality of the studies ranged from 16 to 20 points ( Table 1 ). Among the 9 studies that were included, 6 evaluated the pharmacological effects of açaí in experimental models of cancer, including esophageal [ 40 ], urothelial [ 41 ], and colon cancer [ 42 , 43 ], and melanoma [ 44 ] and Walker-256 tumors [ 45 ], and 3 performed toxicological analyses of açaí in experimental models [ 46 – 48 ]. For the interventions used in the experimental models, 4 studies used chemically induced cancer models [ 40 , 41 , 43 ], 2 used inoculation of tumor cells [ 44 , 45 ], and 3 used models with DNA damage induced by a chemotherapeutic agent [ 46 – 48 ]. The studies involved 2 species and 6 varieties of rodents: C57BL/6 mice [ 44 ], F344 rats [ 40 ], Wistar rats [ 42 , 45 , 47 , 48 ], Swiss mice [ 41 , 46 ], ICR mice [ 43 ] and Balb/c mice [ 48 ] ( Table 1 ). AOM = azoxymethane; BBN = N-butyl-N-(4-hydroxybutyl)-nitrosamine; B16F10 = melanoma cell lines; DSS = dextran sulfate sodium; DMH = 1,2-dimethylhydrazine; ICR = International Cancer Research; MNU = N-methyl-N-nitrosourea; NMBA = N-nitrosomethylbenzylamine. a A reference can have more than one model of disease. Table 2 shows the basic information about the açaí extract used in the experimental models. The most commonly used açaí fraction was the pulp [ 40 – 43 , 46 ], followed by the juice [ 48 ], oil [ 44 , 47 ] and seeds [ 45 ]. Seven studies mentioned the açaí origin, and all of the açaí extracts were from Brazil [ 40 – 43 , 45 – 47 ]. The main administration route of açaí was oral; 4 studies administered açaí by gavage [ 45 – 48 ], and 4 studies administered açaí as part of the diet [ 40 – 43 ]. The dosage ranged from 30 mg/kg to 40,000 mg/kg in studies that administered açaí by gavage and was administered as a single dose or as 1 daily dose for 90 consecutive days; in the studies that administered açaí as part of the diet 2.5% to 5% açaí supplementation was provided in the diet for 10 to 35 weeks ( Table 2 ). In addition, Schauss and colleagues used oral and intraperitoneal administration of açaí at a dose of 0.1mg/0.15mL (daily dose during 7 consecutive days) to assess the possible genotoxic effects of açaí using BALB/c mice [ 48 ], and Monge-Fuentes and colleagues used 50 mg/mL of açaí administered intratumorally in an experimental model of melanoma [ 44 ]. The results regarding the therapeutic indications, effects and safety of açaí in experimental models are summarized in Table 3 . AIN = American Institute of Nutrition; IP = intraperitoneal; SP = São Paulo; PBS = Phosphate buffered saline. a A reference can have different methods of administration of açaí. b Juice of MonaVie Active® = In addition to açaí, contains lesser amounts of 19 fruits and berries. c A cereal-based commercial diet for mice formulated by the Orient Bio Group (Seongnam, Korea). COX-2 = cyclooxygenase 2; DXR = antitumoral agent doxorubicin; IFNγ = interferon gamma; MNPCE = number of micronucleated peripheral blood polychromatic erythrocytes cells; PCE = peripheral blood polychromatic erythrocytes cells; PCNA = proliferating cell nuclear antigen. The absence of toxicity of açaí was reported in 6 studies after testing açaí in experimental models [ 41 , 42 , 44 , 46 – 48 ], and no significant differences in animal body weight or food consumption were reported in 4 studies [ 40 – 42 , 48 ]. DNA damage induced by antitumor medication was evaluated in 3 studies, and no genotoxic effects were observed after açaí administration by gavage [ 46 – 48 ] ( Table 3 ). Using a micronucleus test and a comet assay, Ribeiro and colleagues reported no differences between the control and açaí groups in bone marrow and peripheral blood cells polychromatic erythrocytes, and in liver and kidney cells, thus demonstrating the absence of genotoxic effects of açaí. In addition, açaí reduced DNA damage induced by doxorubicin (DXR), suggesting a protective role in human health [ 46 ]. In a study done by Schauss and colleagues, açaí did not cause mutagenic effects, as demonstrated by a bacterial reverse mutation assay, a chromosomal aberration assay, a mammalian cell mutation assay and an in vivo micronucleus study [ 48 ]. In the same way, Marques and colleagues evaluated the genotoxic potential of açaí in rat cells. The authors used a comet assay and a micronucleus test and showed that on both cytogenetic tests, no significant genotoxic effects were observed at the three tested dosages of açaí [ 47 ]. The anticarcinogenic and chemopreventive activities of açaí, as evidenced by reductions in the incidence of tumors, tumor cell proliferation, and multiplicity and size of tumors, were observed in all the experimental models of cancer [ 40 – 45 ] ( Table 3 ). Stoner and colleagues reported that açaí was effective at inhibiting the progression of esophageal tumorigenesis, reducing the levels of the serum cytokines (IL-5 and IL-8), and increasing serum antioxidant capacity and interferon-gamma (IFNγ) levels [ 40 ]. By contrast, the esophageal tumor size and serum levels of IL-1β, IL-4, IL-13 and tumor necrosis factor-alpha (TNF-α) were not significantly affected by adding açaí to the diet for 35 weeks [ 40 ]. Fragoso and colleagues reported that açaí was effective at inhibiting urinary bladder carcinogenesis, reducing DNA damage, and reducing the expression of p63 and proliferating cell nuclear antigen (PCNA) [ 41 ]. However, altered cytoplasmatic and nuclear β-catenin were not significantly affected by adding açaí to the diet for 10 weeks [ 41 ]. Two studies reported that açaí was effective at inhibiting colon carcinogenesis induced by 1,2-dimethylhydrazine (DMH) in Wistar rats [ 42 ] and azoxymethane (AOM) with dextran sulfate sodium (DSS) in ICR mice [ 43 ]. Nevertheless, the opposite results were observed with regard to cleaved caspase-3 expression after supplementation with 2.5% and 5% of açaí in the diet for 10 [ 42 ], 14 [ 43 ] or 20 weeks [ 42 ]. Despite the discrepancies between these studies, the quality evaluation of the results of the articles showed good quality QATRS (16/20 and 20/20, respectively) [ 42 , 43 ]. Moreover, Choi and colleagues reported that açaí treatment down-regulated myeloperoxidase (MPO) and proinflammatory cytokines (TNF-α, IL-1β and IL-6), inhibited cyclooxygenase 2 (COX-2), PCNA and Bcl-2, and increased Bad and cleaved caspase-3 expression in an experimental model of cancer colon [ 43 ]. Monge-Fuentes and colleagues reported that açaí was an effective photosensitizer because it reduced melanoma carcinogenesis by increaseing the necrotic tissue per tumor area after 5 applications of intratumoral açaí during a period of 15 days [ 44 ]. Nascimento and colleagues reported an anticarcinogenic effect (tumor diameter and weight) of açaí in anorexia-cachexia syndrome induced by Walker-256 tumors due to the antioxidant activity of açaí after 1 daily dose of açaí over 14 consecutive days [ 45 ]. Finally, based on the results of this review study, we created a schematic representation of the effects of açaí in tumor cells ( Fig 2 ). Açaí showed antitumoral functions due to its antiinflammatory, antiproliferative and proapoptotic properties. Açaí was shown to have antitumoral functions due its antiinflammatory, antiproliferative and proapoptotic properties.

The results of this review suggest that açaí is safe and can be used as a chemoprotective agent against cancer by exhibiting antiinflammatory, antioxidant, antiproliferative, and proapoptotic properties. Further studies on the functional relevance of açaí are necessary to build a database that can be used in future clinical investigations aimed at discovering antitumor agents.

A careful literature search was performed to identify publications that studied the use of E . oleracea extract in experimental animal models of cancer and/or evaluated the safety/toxicity of açaí in animal models. Studies were identified by searching the electronic databases: PubMed, Medline-Bireme, Lilacs and SciELO from their inception date through December 2017 ( S1 Table ). The search terms were as follows: (“ Euterpe oleracea ” AND cancer treatment) OR (“ Euterpe oleracea ” AND cancer animal model) OR (Açaí AND cancer treatment) OR (Açaí AND cancer animal model) AND (“ Euterpe oleracea ” AND toxicity) OR (Açaí AND toxicity). The search was performed without restrictions on the language or year of publication. Two reviewers (KCRB and JA-P) selected the qualified studies independently by browsing the titles, abstracts or full texts based on the eligibility criteria. The duplicates were removed. The eligible articles were separated for analysis of the study methodology and results ( S1 Table ). Any disagreements were resolved by discussion with two additional reviewers (DEM and JAP). Articles were included if the following criteria were met: (1) evaluated the pharmacological effect of açaí in animal models of cancer and/or (2) performed toxicological analyzes after açaí administration in experimental animal models. Articles were excluded if the following criteria were met: (1) were reviews of literature; (2) did not analyze the use of açaí in vivo ; (3) did not use the order Rodentia ; (4) did not evaluate the toxicological effects of açaí administration in vivo ; and (5) used only in vitro experimental models. Three investigators (KCRB, JA-P and JAP) independently conducted the extraction of details from each study including the following: (1) basic information, including the publication year, the first author's name, the type of animals, the sex, the in vivo model and the experimental interventions; (2) basic information about the açaí treatment, including the fraction and origin of E . oleracea , dose, administration route, posology, diluents and treatment groups; and (3) outcome measures used to evaluate E . oleracea extract, therapeutic indications (pharmacodynamic), açaí signaling pathways and safety evaluations. When a single publication included studies with animals, posology or types of interventions that were different, these data were extracted and considered as independent experiments. Any disagreements regarding the extracted data were resolved by discussion with an additional reviewer (DEM). For assessment of quality, two independent reviewers (KCRB and JA-P) used a quality rating scale as an animal/tissue research scale (QATRS). The QATRS is a 20-point scaled evaluation chart that was designed based on randomization, blinding, the similarity of the animal/tissue model to human applications, standardization and the reliability of the measurement techniques, management of study withdrawals, and appropriateness of the statistical methods [ 23 ]. Any disagreements were resolved by discussion with two additional reviewers (DEM and JAP).

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