Euterpe oleracea Mart . ( açai ) : an old known plant with a new perspective

The açai (Euterpe oleracea Mart) fruit pulp is extensively used in Brazil as food among other uses. The health benefits of açai are largely reported by the Amazon inhabitants. Nonetheless, just a few pharmacological and toxicological studies were made to probe the innocuousness and the safety of the use of this product. The aims of this work were to update knowledge about the chemical composition, pharmacological and toxicological studies of the fruits and to identify possible vacuum of knowledge in the use, evaluation, and characterization of E. oleracea Mart (Açai) as a promising Amazon superfruit. It was made a draw out internet revision, especially in databases as NCBI, SCOPUS, PUBMED, SCIELO, and ELSEVIER by using the keywords E. oleracea, açai, nutraceuticals and food supplementations. Also, it was looked for each one of the ethnobotanical uses reported for this plant species combined with the first keywords. A complete record of the chemical composition of this species was achieved. Just two studies in humans were found in the literature using the açai fruit pulp. There is no sufficient systematic evidence to assure that all of the ethnobotanical uses of this species are true. A great emptiness of scientific knowledge related to the real benefits of this plant species exist. There exist neither pharmaceutical forms nor standardized product derived from the açai fruit. Until now, the number of scientific studies that allow the validaton of the ethnopharmacological practices, the innocuousness and the safety of the use of this plant fruit is insufficient.


INTRODUCTION
Euterpe oleracea Mart (EOM), commonly known as acai, has long been used by the inhabitants of the Amazon. This is a plant with many beneficial health effects, which has been used in other countries of Europe, North America and Middle-Eastern (Menezes et al., 2011). The increase of the interest in the international community for the açai was clearly related by Heinrich et al. (2010). They demonstrated by using an overall search for açai from 2004 to 2010, that it was an increase in the searches about this plant all over the world and especially in USA, UK, Australia, New Zealand and Canada.The harvest period of this fruit is between August and December and approximately 1000 jobs are created every year for the local populations in the Northern Brazil. The northern states of Brazil produce 95% of all the country's açai (Heinrich et al., 2010). Just in 2015, 198.9 thousand ton of the acai were produced in Brasil; of it, 54% were produced in Para, 33.6% in Amazonas, 7% in Maranhão, 2% in Acre, and 1.1% in Amapá, Rondônia, and Roraima (0.9%).
The intake of açai fruit pulp with chicken meat, fish, and vegetals as tapioca or maize flour is a traditional practice of the Brazilian population. The açai fruit pulp is also used for the preparation of pies, jellies, creams, ice creams and liqueurs as run and wines (Rogez, 2000).
The interest for the use of this plant is continually increasing over the years (Schauss, 2016). To this regard, it was observed that there are a lot of publications (On the Internet) about the use of this species as nutraceutical and as a cosmetic ingredient. The majority of these publications lack the scientific perspectives with no serious data to support their characteristics.
Several ethnobotanical uses have been linked to the chemical composition of the açai fruits pulp (Portinho et al., 2012). Different parts of this plant have been used by Amazonian populations (Bourdy et al., 2000). Over the years, studies have been made to identify chemical characteristics of the fruits of EOM. The main secondary metabolites present in the fruits of açai are phenolics, principally flavonoids and anthocyanins (Costa et al., 2013). The dissimilar chemical composition of the açai fruit pulp allows their use in nutraceuticals, cosmetic and food industries (Schauss, 2015;Schauss, 2016). However, there are few scientific studies supporting the pharmacological and toxicological properties of the açai fruit pulp.
This paper aims to update knowledge about the chemical composition, pharmacological and toxicological studies related to the açai fruits and to identify possible vacuum of knowledge in the use, evaluation and characterization of E. oleracea Mart (Açai) as a promising Amazon superfruit.

MATERIAL
A draw out revision was made in databases as NCBI, SCOPUS, PUBMED, SCIELO, and ELSEVIER by using the keywords E. oleracea, açai, nutraceuticals and food supplements. Also, it each one of the ethnobotanical uses reported for this plant species (antiinflammatory, anticancer, antioxidant, cardiovascular, dyslipidemic, neuroprotective, renal diseases, cosmetic, food, toxicity test, and pharmacological test) was looked for combined with the first keywords. The review was made from 1980 until 2016.

RESULTS AND DISCUSSION
The increase on the interest in this Amazonian fruit is noticeable. Figure 1 shows the increase of the research to prove the biological, nutraceutical and pharmaceutical activity of this species from 1980 to 2016. From 1980up to 2016 publicatons were made about E. oleracea Mart. Nonetheless, just 2181 (54.75%) of these publications were found in the scientific database. In the last five years, it was an augment of 173% on the publications about this plant. Nonetheless, just 33% of these publications were publicized in scientific database. These are evidence of the increasing interest on this plant but just a few amounts of these are scientifically founded.

Botanical aspects
The açai palm belongs to the Arecaceae family. This family has about 200 genera and about 2600 species distributed in tropical and subtropical areas (Jones, 1995). Of the native species from Brazil, the most important are E. oleracea, Euterpe edulis, and Euterpe precatoria. The first is popularly known as Palmiteira, açai de Pará and açai real. This species was the main source of raw material in the Palmito industry (Palm"s heart pickled) (Choi et al., 1998 (Schauss, 2015(Schauss, , 2016. Figure 2 show the açai palm tree and the collected fruit ready to be commercialized.

Chemical composition
Species E. oleracea Mart has been extensively investigated for their chemical composition. Table 1 present all chemical compounds reported, until now, for the fruit of E. oleracea Mart.
The açai fruit pulp is rich in polyphenols like flavonoids and anthocyanins and content a diversity of fatty acids (Silva and Rogez, 2013). Anthocyanins are glycosidic derived from anthocyanidins. At low pH, they are predominantly present in the form of flavylium cation, giving a reddish color in aqueous solutions. At higher pH, the flavylium cation is converted into other species, some of them being uncolored (Cheminat and Brouillard, 1986).
The lipid fraction of the pulp contains between 68.0 and 71.0% of mono-unsaturated fatty acids and 7.8 and 10.6% of poly-unsaturated fatty acids, including linoleic acid, oleic acid and palmitic acid (Nascimento et al.,2008) in high concentrations. A large number of other minor fatty acids have been reported. Schauss et al. (2006a) reported the presence of nineteen amino acids in the lyophilized powder of açai fruit pulp, corresponding to 7.59% of the lyophilized fruit pulp. Furthermore, three sterols campesterol and stigmasterol were also reported (0.48 mg/g of dry weight) with 0.44 mg/g of dry weight of b-sitosterol.
The açai fruit pulp content is a complete chemical composition that made them an excellent nutraceutical complement of vitamins, mineral, fatty acids and antioxidants compound like anthocyanins, polyphenols, and flavonoids.
These compounds can help to prevent several degenerative diseases. Besides this, the chemical composition of the açai fruit pulp can justify the fact that peoples living on the banks of the rivers having the açai fruit pulp as the basis of their diet as they lack other foods that will enable them to balance their nutrition. They are strong people and healthy from childhood. On the other hand a lot of ancient peoples in this region were observed just for intake of açai fruit pulp as a basis diet, just accomplished by some grains and cereals like maize, wheat, and oats.

Ethnobotanical and pharmacological uses of açai
Açai fruit pulp, the whole fruit, and the root of the açai palm tree have been used by Amazonian tribes as the remedy for treating diarrhea, parasitic infections, bleeding, and ulcer (Schauss, 2015(Schauss, , 2016. The decoction of the açai crushed seed has been used for the treatment of fever, menstrual pain, liver diseases, and malaria. The root mixed with other medicinal plants was used as antimalarial (Vigneron et al., 2005), for the treatment of the prostate cancer (Homma et al., 2006) and for the treatment of leishmaniasis (Odonne et al., 2011). Some of these ethnobotanical uses can be attributed to the presence of metabolites like phenolics, flavonoids, and anthocyanins. Nonetheless, there is a not reported study about these conditions.
Despite the great number of publications on the internet about the uses of EOM, just a few number of them are significantly and scientifically founded. Table 2 presents the most significant studies reported for this species in the scientific database. The fact that just one study in humans was made is interesting (Udani et al., 2011).
Is contradictory that the fact that the açai fruit pulp, probably the most consumed vegetal in the North and Northeast of Brazil, lack off the studies to probe the innocuousness, security and efficacy of their use by the population as food and as an ethnobotanical remedy. Still, more is curious that no work in humans was conducted to evaluate the real benefits of the majority of the popular uses of this product. Consequently, if this plant and especially the fruits have been used for centuries with certain "innocuousness", is mandatory to confirm the ethnopharmacological use in order to validate, scientifically, the efficacy and safety of their use.

Antioxidant activity
Antioxidant activity is the most studied property of the E. oleracea Mart. Data about the açai fruit antioxidant potential are disagreeing. Del Pozo-Insfran et al. (2004) reported that anthocyanins are the predominant factor of the antioxidant capacity of açai pulp. Kang et al. (2010) concluded that the predominant factor in the açai antioxidant activity is the presence of seven flavonoids present on it (orientin, isoorientin, vitexin, luteolin, criseriol, quercetin, and dihydrokaempferol). Our judgment, both authors are on the right because the principal antioxidant effect of the natural extracts is the synergy among all of the compound present in the extracts, which are able to efficiently inactivate reactive nitrogen and oxygen species. Spada et al. (2009) have shown an antioxidant activity of açai frozen fruit pulp in the cerebral cortex, hippocampus, and cerebellum of rats treated with hydrogen peroxide (H 2 O 2 ). Pretreatment of tissues with açai extract decreased the H 2 O 2 -induced damage of both lipids and proteins. The extract of the fruit was also able to reduce the activities of the antioxidant enzymes superoxide dismutase and catalase to basal levels. They observed a negative correlation between the polyphenol content of açai and the levels of lipid (r=0.689; P<0.05) and protein damage (r=0.569; P<0.05), suggesting the participation of polyphenols in the observed antioxidant activity.
Practically, all the compounds presents in açai fruits are recognized antioxidants. The synergistic antioxidant action of fatty acids, vitamins, sterols, flavonoids, anthocyanins and phenolics makes the pulp of this fruit a powerful antioxidant. The antioxidant activity of the majority of this compounds in others vegetal species were reported (Ismail et al., 2010;Lee et al., 2002;Liolios et al., 2009).
Some sickness like diabetes, hepatitis, and some degenerative diseases promote an imbalance in the body antioxidant defense. It could be interesting to test the preventive or regenerative activity of the differents açai fruit extracts as a way for the evaluation of the real benefit of these extracts in differents related pathologies. On the other side, there was no publishing article evaluating the benefits of the açai fruit pulp (or in derived extracts) in humans" model. Thus, a lack of these studies is a real necessity.
The use of this product must be cautiously in patients with diabetes or those using antidiabetic agents as, according to human research, açai may lower glucose and insulin (Udani et al., 2011).

Assays in cardiovascular diseases
The açai fruit pulp contains a large number of fatty acids, including linoleic acid, oleic acid, palmitic acid and other fatty acids (Schauss et al., 2006a). These substances showed a cardioprotective effect in rats improving the lipid profile (Bhattacharya et al., 2006). Another study reported a vasodilator effect on mesenteric vessels of rats related to a lipid profile improved by the açai fruit extract (Mantovani et al., 2003;Xie et al., 2011) reported the atheroprotective effects of açai fruit pulp in apolipoprotein E-deficient in mice, mediated by a reducing lipid peroxidation through boosting antioxidant enzymes and inhibiting pro-inflammatory cytokine production.
One study was conducted in overweight patients who consumed 100 g açai pulp twice daily for 1 month. There was a reduction in glucose levels from 98.0 ± 10.1 to 92.8 ± 10.9 mg/dl. There were also reductions in total da Silva et al. 1001 cholesterol and triglycerides (Udani et al., 2011). Animals" feed with hypercholesterolemic diet, treated with açai pulp extract, showed an improvement in the lipid profile. These results suggest that açai pulp promotes a hypocholesterolemic effect in a rat model of dietaryinduced hypercholesterolemia (De Souza et al., 2010). A diet rich in antioxidants can improve both the lipid metabolism and glucose homeostasis reducing complications in the two types of diabetes and in metabolic syndrome (Dembinska-Kiec et al., 2008).
In this sense, until we know, there is only one study in humans and the report is not enough to confirm the potential utility of the açai fruit to control dyslipidemic disorders and other imbalances of the lipidic profiles. Thus, the richness in chemical compounds of these products could be taken advantage for this kind of treatment, but other studies are needed.

Anti-inflammatory activity
The oily extract of the açai fruit reduced the number of neutrophils migrating in a carrageenan-induced peritonitis model in rats. These results suggested that the oil of açai fruit has anti-inflammatory and antinociceptive activity. It was attributed to the presence of flavonoids and a lot of unsaturated lipid present in the extract (Favacho et al., 2011). On the other side, açai fruit pulp showed potential cyclooxygenases COX-1 and COX-2 inhibitor activity (Schauss et al., 2006b).
The anti-inflammatory effects of the açai extract were screened by the secretion embryonic alkaline phosphatase (SEAP) assay. This assay is designed to measure NF-jB activation. It studied the capacity of activation of NF-jB of the açai extract by the secretion embryonic alkaline phosphatase (SEAP) assay in rats. A dose-dependent SEAP inhibitory activity in RAW-blue cells induced by lipopolysaccharides was observed. It was also observed an inhibition of SEAP induced by oxidized LDL, indicating a potential atheroprotective effect in rats .
Açai extracts inhibited lipopolysaccharide and interferon-gamma-induced nitric oxide (NO) production in a macrophage cell line. Overproduction of NO may lead to activation of NO synthase, leading to the generation of cells mediating inflammatory processes. The mechanism of action was associated with inhibition of NO synthase expression (Matheus et al., 2006).
The anti-inflammatory activity of açai fruit is still no conclusive, the studies made until now are none conclusive, in some of them was used the oily fraction of the açai fruit pulp, in others, they use the açai fruit pulp mixture with other species (Jensen et al., 2008;Schauss, 2016). There is not any report of the evaluation of any formulation made by using and extract or the lyophilized fruit pulp. We do not find ethnopharmacological reports for the use as anti-inflammatory.

Neuroprotective activity
One study examined whether açai fruit extract afforded protection against β-amyloid (Aβ)-mediated loss of cell viability and oxidative stress associated with anti-fibrillar effects. PC12 cells were exposed to either Aβ1-42, Aβ25-35 or tertbutyl hydroperoxide (t-BHP), alone or in the presence of açai extract (0.5 to 50 μg/ml). The study shows that exposure to Aβ1-42, Aβ25-35 or t-BHP decreased PC12 cell viability. Pretreatment with açai extract significantly improved cell viability following Aβ1-42 exposure. Açai extract inhibited the thioflavin T fluorescence and disrupted Aβ1-42 fibril and aggregate morphology. In comparison with other phenolics, açai was most effective at inhibiting Aβ1-42 aggregations. Inhibition of β-amyloid aggregation may underlie a neuroprotective effect of açai (Wong et al., 2013).
The β-amyloid proteins are strongly implicated in Alzheimer"s disease (Murphy and Levine, 2010;Schauss, 2016). A negative correlation was reported between the polyphenol content of açai and the levels of lipids and proteins damage. These data suggested that açai has a positive contribution to the prevention of the development of age-related neurodegenerative diseases. Nonetheless, further investigation is needed to evaluate the role of chemical compounds present in açai in these findings.

Anticancer effect
An anthocyanin-rich extract from açai fruit was used (AEA) to investigate the antioxidant properties and antiproliferative activity against C-6 rat brain glioma cells and MDA-468 human breast cancer cells. AEA remarkably suppresses proliferation of C-6 rat brain glioma cells, but has no effect on the growth of MDA-468 human breast cancer cells. Further experiments demonstrated that the AEA treatment dose-dependently inhibited the growth of C-6 rat glioma cells with an IC 50 of 121 μg/ml. The DNA ladder fragmentation results indicated that AEA-induced apoptosis of C-6 rat brain glioma cells (Hogan et al., 2009).
Açai fractions containing polyphenolic compounds reduced the proliferation of HL-60 leukemia cells through caspase-3 activation in a dose-and time-dependent manner. The mechanism of action is associated with polyphenolic phytochemicals activating caspase-3, leading to cell death or apoptosis (Del Pozo-Insfran et al., 2006).
In another work, the anticancer activity in different human malignant cell lines derived from breast and colorectal adenocarcinomas was evaluated. Cell lines were treated with 10, 20, and 40 μg/mL of bark, seed, and total açai fruit hydroalcoholic extracts for 24 and 48 h. After treatment, cell viability was measured and cell morphological features were observed. The study demonstrated that açai possesses antitumorigenic potential in the MCF-7 cell line. This fact demonstrated the need to identify the compounds responsible for this activity and the molecular target in the cell (Silva et al., 2014). As observes, the real anticancer potential of the açai fruit pulp and the açai fruit extracts are still unexplored and just a few studies have been made to this regard, despite that the ethnopharmacological use in cancer is well reported for the population.

Use of açai extract in renal diseases
The use of açai extract in reduced acute renal failure (ARF) was reported. The study investigated the effect of açai fruit extract on glycerol-induced ARF in rats. Results showed for a different dose a significant decrease in serum urea, serum creatinine, and blood urea nitrogen. Moreover, there was significant amelioration in renal oxidative stress markers and renal histopathological changes. These results suggest that açai fruit extract has a potential effect in ameliorating renal damage involved in ARF (Unis, 2015).
Other study examined the effect of açai seed extract (ASE) on cardiovascular and renal alterations in adult offspring rats, whose mothers were fed with low-protein diet during pregnancy. It was observed that hypertension and the reduced acetylcholine-induced vasodilation in the low-protein group were prevented by ASE. This product improved nitrite levels and the superoxide dismutase and glutathione peroxidase activity in low-protein, with a decrease of malondialdehyde and in the protein carbonyl levels. Kidney volume and glomeruli number were reduced and glomerular volume was increased in lowprotein group. These renal alterations were prevented by ASE (De bem et al., 2014).
A study to investigate the possible mechanisms of renal injury attenuation caused by açai extract in a rat renal (I/R) model was reported. Rats were administered with açai extract at 500 and 1000 mg/kg for 15 days, before bilateral renal I/R induction. Serum and kidneys were isolated and used for subsequent biochemical analysis. The açai extract significantly and dose-dependently attenuated I/R-induced renal damage. It suppressed the levels of blood urea nitrogen (BUN), serum creatinine, and renal tissue content of kidney injury molecule-1 (KIM-1). In addition, the serum lactate dehydrogenase (LDH) activity was inhibited. Moreover, renal contents of malondialdehyde (MDA), myeloperoxidase (MPO), interferon-gamma (IFN-γ), caspase-3, collagen IV, and endothelin-1 were reduced, while renal interleukin-10 (IL-10) content was increased by açai extract administration (El Morsy et al., 2014).
The reported studies assuring the renal protective activity function did not specify the nature of the extract used. Finally, there is no study in humans, for the evaluation of the renal function or renal failure. Thus, this kind of studies is imperative.

Uses of açai in cosmetics
The high content of anthocyanins and phenolic compounds with important antioxidant activity was used in cosmetic preparation for the treatment and prevention of skin damages (Herculano, 2013). Among these products, both the extract and the pulp of açai fruits are used as moisture agents in creams, hair conditioner, and shampoo. The açai fruit pulp has properties of nutrition and capillary brightness. The oil extracted from the pulp is used in shampoos and body lotions (Hogan et al., 2009). The glycolic extract of açai was used to prepare a sunscreen emulsions (o/w). The resulted cream showed a good protection UV-A and UV-B factor (Daher et al., 2014).
In the face of all reports that can be found on the Internet promoting the use of cosmetics with açai fruit pulp or açai extracts as active principle, there are no reports of the studies evaluating the effectiveness and the security of all of these products. Thus, there are a lot of cosmetics and nutraceutical products using some product derived from açai as an active principle without scientific foundation. Nonetheless, this represents an excellent opportunity to do research in this area to justify scientifically the use of these products.

Pharmaceutical forms and foods based on açai
Due to the richness in phytochemical substances present in the açai fruit pulp, it is used in a variety of formulations. The freeze dried açai fruit pulp was used in a formulation for the erectile dysfunction. An increase in the time of shelf life of this product was observed . Tablets and açai capsules can be found in the market. Everything is marketed as the nutritional supplement. In these formulations, the lyophilized açai fruit pulp was used (Empresa Saúdeja, 2015). In a general way, a lot of cosmetic and nutritional preparations containing açai fruit pulp including juices, powders, capsules, liquids, creams, and lotions can be found in the market. However, there is no product registered as a medicament (Medicament: A preparation containing a tested active drug used to diagnose, cure, treat, or da Silva et al. 1003 prevent disease) (United States Pharmacopoeia, 2012). In all cases, there is no scientific evidence supporting the biological activities attributed to these preparations.

Toxicological studies involving açai fruit pulp
The toxicity of a mixture of the açai fruit pulp with a berry functional juice was studied. The mixture was neither cytotoxic nor genotoxic. The LD 50 based on a 14-day acute oral toxicity study was greater than 2000 mg/kg body weight . In another study, the genotoxicity of açai fruit pulp was investigated in Swiss albino mice by using a doxorubicin (DXR)-induced DNA damage model. The protective effect of açai fruit pulp was observed in both acute and subacute treatments when administered prior to DXR. The protective effects were associated with the phytocompound presents in the açai fruit pulp. Despite that the pulp of this fruit, it is used as food in Brazil and other parts of the world, and besides that, it is widely available in a variety of forms, including juices, powders, and capsules, etc., açai is not listed on the U.S. Food and Drug Administration (FDA) Generally Recognized As Safe (GRAS) list (Schauss, 2016). Açai has been very well accepted by the population of big cities, attracted by the nutritional and medicinal properties of the fruit (Rogez, 2000). With the constant increase of açai consumption, a standardization of the quality of this product is required (Bhattacharya et al., 2006;Boghani et al., 2012;Nogueira et al., 2005).
Nonetheless, the evaluation of the safety of any pharmaceutical and food product is an imperious necessity. Thus, there is a lack of studies to demonstrate the safety in the use of the açai. Taking into account that the açai fruit is one of the most consumed vegetal product in the North and Northeast of Brazil, in some Asian country and in North America toxicological studies by means of the international standards are imperative to assure the innocuity of this product. On the other side, there is no published results talking about the safety and efficacy of any of the nutraceutical products that are sold in the market.

Nutritional composition
Each 100 g of the dry açai fruit pulp content has 533.9 calories, 32.5 g of total fats, 8.1 g of saturated fats, 13.5 mg of cholesterol, 52.2 g of carbohydrates, 44.2 g of dietary fiber, 1.3 g of sugar, and 8.1 g of proteins. Also, it contains vitamin A 1002 UI, vitamin C 0.1 mg, calcium260 mg, and sodium 30.4 mg (Costa et al., 2013;Schauss et al., 2006a).
For the diet, the great contribution of açai is their energetic value because of the high content of lipids (70 to 90% of the calories) (Crozier et al., 2011;Rufino et al., 2010). The high fiber content and a considerable amount of anthocyanins present in açai make this fruit a great help to prevent chronic degenerative diseases (Rufino et al., 2010). Açai is also an important source of trace elements such as calcium, phosphorus, sodium, zinc, iron, manganese, copper, boron, chromium, magnesium, potassium, and nickel (Crozier et al., 2011).

Conclusions
Despite the widespread use of açai by populations of Brazil and other countries, there are few scientifically based studies on nutrition and medicinal properties of the fruit pulp of this plant. The antioxidant activity has been the most investigated. No dosage forms using açai as the active ingredient were registered; until now, as a medicine to the health authorities of any country. Just two studies, in humans were found in the literature using the açai fruit pulp. There are no sufficient systematic evidence to assure that all of the ethnobotanical uses of this species could be scientifically founded. A great emptiness of scientific knowledge related to the real benefits of this plant species exists. There exist neither pharmaceutical forms nor standardized product derived from the açai fruit pulp. Until now, the number of scientific studies that allow the validation the ethnopharmacological practices, the innocuousness and the safety of the use of this plant fruit is insufficient.