Nopal Cactus (Opuntia ficus-indica) as a Source of Bioactive Compounds for Nutrition, Health and Disease

Opuntia ficus-indica, commonly referred to as prickly pear or nopal cactus, is a dicotyledonous angiosperm plant. It belongs to the Cactaceae family and is characterized by its remarkable adaptation to arid and semi-arid climates in tropical and subtropical regions of the globe. In the last decade, compelling evidence for the nutritional and health benefit potential of this cactus has been provided by academic scientists and private companies. Notably, its rich composition in polyphenols, vitamins, polyunsaturated fatty acids and amino acids has been highlighted through the use of a large panel of extraction methods. The identified natural cactus compounds and derivatives were shown to be endowed with biologically relevant activities including anti-inflammatory, antioxidant, hypoglycemic, antimicrobial and neuroprotective properties. The present review is aimed at stressing the major classes of cactus components and their medical interest through emphasis on some of their biological effects, particularly those having the most promising expected health benefit and therapeutic impacts.


Individual Classes of Cactus Compounds and Related Biological Activities
Regarding its composition in polyphenols, vitamins and other specific compounds, the cactus pear appears to be an excellent candidate for nutritional diet recommendations and therapeutic indications. The spectrum of biological and medical effects reported for each class of cactus compounds is presented thereafter.

Phenolic Compounds
Polyphenols represent a family of organic molecules widely distributed in the plant kingdom. As suggested by their name, their chemical structures are characterized by the presence of several phenolic groups, which may be associated with more or less complex groups of chemicals, generally of high molecular weight. These compounds are usually byproducts of plant metabolism. The growing interest in polyphenols results from their antioxidant potential, which is involved in health benefits such as the prevention of inflammation [24], cardiovascular dysregulation and neurodegenerative diseases. Polyphenols have also proven anticancer activity.
All parts of the cactus plant are rich in members of the polyphenol family such as various flavonoids and phenolic acids (Table 1). In the flower, gallic acid and 6-isorhamnetin 3-O-robinobioside are the major compounds, amounting to 4900 and 4269 mg/100 g of dry matter, respectively [20,[25][26][27]. Other phenolic molecules are present in small quantities not exceeding 10 mg/g ( Table 2). In the fruit pulp, total phenol content is 218.8 mg/100 g [28], along with a high content of isorhamnetin glycosides (50.6 mg/100 g) compared to other flavonoids [14,[29][30][31][32]. Fruit seeds contain high amounts of phenolic compounds ranging from 48 to 89 mg/100 g and including feruloyl derivatives, tannins and sinapoyl diglucoside [33] (Table 1). Interestingly, fruit peel has a very high phenol content of 45.7 g/100 g. Several of these phenols are bioactive molecules, notably flavonoid derivatives such as kaempherol and quercetin, the contents of which are 0.22 and 4.32 mg/100 g, respectively [5,30,34]. Cactus flowers appear to be the most important source of polyphenols and flavonoids.
Interestingly, some polyphenols are produced only by cladodes of some varieties of cactus such as the snowshoeing cactus. This plant presents high amounts of unusual flavonoid-like compounds such as nicotiflorin (146.5 mg/100 g) and narcissin (137.1 mg/100 g) (Table 1) along with high content  values found for isoquercetin and ferulic acid: 39.67 and 34.77 mg/100 g, respectively [4,29,[35][36][37]. Cladode age, environment, soil type and climate could explain these variations in cactus polyphenol contents. Health beneficial effects of cactus polyphenols might be conditioned by their antioxidant and radical scavenging activities. For instance, gallic acid, largely found in cactus flowers, exhibits high antioxidant activity responsible for its ability to reduce DNA damage [39] and to buffer free radicals [40]. At a concentration of 4.17 mM, it may neutralize 44% of 2,2-diphenyl-1-picrylhydrazyl radical and 60% of hydrogen peroxide in given experimental conditions. Gallic acid also exerts a cytotoxic activity against tumoral cells from leukemia, lung and prostate cancer origins [41].
Opuntia ficus-indica cladodes are rich in nicotiflorin which, through antiinflammatory and neuroprotective mechanims, was shown to reduce brain infarct size, to attenuate neurological deficits induced by ischemia, and to up-regulate endothelial nitric oxide synthase in cultured rat brain vascular endothelial cells [42]. Nicotiflorin is neuroprotective against hypoxia-, glutamate-or oxidative stress-induced retinal ganglion cell death at nanomolar concentrations [43]. In a murine multi-infarct dementia model, nicotiflorin preserved spatial memory performances measured in Morris water maze tests. Besides this protective effect on memory dysfunction, nicotiflorin also protects against energy metabolism failure and oxidative stress. In ischemic brains, these beneficial effects were associated with attenuation of rises in lactic acid and malondialdehyde (MDA) and with prevention of drops in lactate dehydrogenase (LDH), Na + K + ATPase, Ca 2+ Mg 2+ ATPase and superoxide dismutase (SOD) activities [44].
As mentioned above, the fruit peel contains large amounts of isorhamnetin. Isorhamnetin (3'-methoxy-3,4',5,7-tetrahydroxyflavone) exerts anticancer action by inhibition of epidermal growth factor (EGF)-induced neoplastic cell transformation through a direct lowering of MAP (mitogen-activated protein)/ERK (extracellular signal regulated kinase) kinase 1 and phosphoinositol 3-kinase signaling pathways [45]. Isorhamnetin exhibits cardioprotective effects by improving viability of neonatal rat ventricular myocytes under in vitro ischemia/reperfusion (I/R) via inhibition of lactate dehydrogenase (LDH) activity and prevention of apoptosis [46]. Isorhamnetin improves skin barrier function through activation of Peroxisome Proliferator-Activated Receptor (PPAR)-α and suppression of inflammatory cytokines production [47]. It also inhibits adipocyte differentiation of murine 3T3 fibroblasts via a decrease of adiponectine expression and secretion, and downregulation of mRNAs of PPAR-γ and C/EBP-α, the major adipogenic nuclear receptors [48]. In contrast, isorhamnetin significantly increases the expression of PPAR-γ in tumor tissues obtained from xenograft model of gastric cancer cells and, in combination with chemotherapeutic drugs, causes strong antiproliferative effects and cytotoxicity [49]. These different effects of a same PPAR ligand are explained by the fact that a ligand-activated nuclear receptor can exert different biological activities through the recruitment of their coregulator partners in a way specific to the cell type context.

Fatty Acids
Chromatographic analyses of total lipids extracted from cactus cladodes ( Table 2) [50] show that palmitic acid (C16:0), oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3) contribute 13.87, 11.16, 34.87 and 32.83% of the total fatty acid content, respectively (Table 1). These four fatty acids thus represent over 90% of total fatty acids with linoleic and linolenic acids, the major polyunsaturated fatty acids, amounting to 67.7%. The linoleic acid content in cactus cladode (34.87%) is thus close to the percentage (29% to 40.41%) found in argan oil [51]. It is however lower than in extracts from barely (51.26%) and soybean (53.0%), respectively (Table 2) [50]. Several studies have indicated that cactus particularly; fruits, pulp, seed and pickely pear peel were rich in linolenic, oleic and palmitic acids [21,52,53,60]. High level of omega-6 linoleic acid was reported in cactus seed oil (53.5% to 70.29%) ( Table 1), and this level is higher than in sunflower oil [59], grape seed oil or sesame oil. As a precursor of arachidonic acid, linoleic acid has long been accepted as having a hypocholesterolemic effect and inhibitory properties against colon cancer metastatic cells [61]. Omega-3 linolenic acid is known to be beneficial for health, cardiovascular diseases, inflammatory conditions, autoimmune disorder and diabetes.

Vitamins
The Opuntia ficus indica develops a fruit known as cactus pear, a fleshy bay (pulp) containing seeds and enveloped by a prickly peel (skin). The fruit, particularly its skin, is enriched in vitamin E at amounts up to 17.6 g/kg of α-tocopherol (Table 3). In contrast, the oil extracted from the fruit's seeds has a low content in vitamin E: 0.403 g/kg, mostly γ-tocopherol (0.330 g/kg) [21,52,60]. Such an amount is very low compared to argan oil content (7.6 to 8.6 g/kg) [62,63]. The essential oil extracted from the fruit's pulp is rich in σ-tocopherol with 4.220 g/kg (Table 3). Cactus pear contains 180 to 300 mg/kg of vitamin C. This content is higher than that found in other common fruits like apple, banana, or grape [64]. Vitamin K1 is present in all parts of the fruit, ranging from 0.5 to 1 g/kg [52,60]. Vitamin B is present only in the cladodem in which it is found in trace amounts [65]. To our knowledge, the precise vitamin contents in flowers of Opuntia ficus indica still remains to be elucidated.

Sterols
Ramadan and Morsel [52,60], have documented β-sitosterol as the major sterol extracted from different parts of the fruit oils: pulp, skin and seeds, with a content ranging from 6.75 to 21.1 g/kg [52,60]. Campesterol is present in the pulp, seed and skin, in an amount of 1.66 to 8.76 g/kg (Table 4). Similar contents of campesterol are found in some other food oils such as argan oil (4 g/kg) [67], whereas higher contents have been measured in soybean oil (between 19 and 23 g/kg) [67]. Other sterols are found in small quantities notably stigmasterol, lanosterol, avenasterol Δ 5 ,Δ 7 -avenasterol, Δ 7 -avenasterol and ergosterol, So far, sterol composition of the essential oil of cladode and flowers remains to be determined. In comparison with cactus, in argan oil, for instance, sterols such as spinasterol and schottenol have been identified [67].

Amino Acids
In cactus cladodes, the major amino acid detected is glutamine, followed by leucine, lysine, valine, arginine, phenylalanine and isoleucine. By contrast, in cactus seed the major amino acid is glutamic acid at a percentage varying from 15.73% to 20.27%, followed by arginine, (4.81% to 14.62%) ( Table 6) [75,76]. Interestingly, in the cactus fruit, the two predominant amino acids are proline and taurine, which represent 46% and 15.78% of the total amino acid content, respectively. Total proteins in fruit seeds (13.62%) are higher than in cladodes (4%-10%) ( Table 6) [75,76]. Thus, fruit seeds and pulp can be considered as very good sources of amino acids and proteins [75][76][77].

Cactus in Nutrition and Prevention of Disease
The nutritional value of cactus pear fruit mainly rests on its content in ascorbic acid, vitamin E, carotenoids, fibers, amino acids, and on large amounts of glucose and fructose. Prickly pears are also rich in phenols, flavonoids, betaxanthins and betacyanins ( Figure 1 and Table 7), which favor a healthy status through hypoglycaemic and hypolipidemic actions, and antioxidant properties [4,[8][9][10]. Remarkably, among existing natural pigments betalains are present at high amount in cactus. Regarding consumers' increasing aversion for synthetic colorants, natural colorants, such as the red betacynins and the yellow betaxanthins, represent a good natural alternative to meet the growing demand of the food industry. The antioxidant properties of these betalain pigments represent an additional argument in favor of the development of their use in nutrition and health [78][79][80].

Cactus in Health and Disease
Diverse benefits of cactus extracts and cactus compounds have been suggested by the traditional medicine uses (see below). Meanwhile, these benefits have progressively received a scientific basis thanks to numerous experimental models dedicated to the evaluation of cactus compounds to treat different diseases. Therapeutic potential has been suggested for metabolic syndrome (including diabetes type 2 and obesity), non-alcoholic fatty liver disease (NAFLD), rheumatism, cerebral ischemia, cancers, and virological and bacterial infections [83][84][85][86]. Interestingly, cactus preparations might exert preventive and therapeutic effects against alcoholism and alcohol addiction [87].
On the basis of our current knowledge of redox biology of normal and diseased cells, including cancer ones, the concept of "antioxidant" activity of phytochemicals has to be carefully evaluated. It should be recalled that action mechanisms of phytochemicals might be different according to the context. Indeed, although ROS can promote cell damage, inflammation and cancer, the so-called antioxidants, including the dietary "antioxidants" may fail to protect, and may even be dangerous for healthy cells under certain conditions. It should also be kept in mind that ROS are necessary to cells, where they play important roles, and serve the essential function to maintain the peroxide or nucleophilic tone governing all cell functions. Redox-active phytochemicals (or products from their transformation after absorption) are possibly used by cells to cause adaptive responses allowing induction of molecular defenses or block of dangerous processes, which may be different from cell to cell and from healthy to malignant cells.

Cactus Use in Traditional Medicine
In traditional medicine, Opuntia ficus indica has been used for the treatment of burns, wounds, edema, hyperlipidemia, obesity and catarrhal gastritis. Alcoholic extracts are indicated for anti-inflammatory, hypoglycemic, and antiviral purposes [84].

Experimental Models and Randomized Trials
Experiments on animal and cell models have highlighted therapeutic potentialities of cactus extracts or compounds through their impacts on key parameters involved in diseases previously targeted by traditional herbal medicines. These scientific studies and bodies of experimental proofs have strengthened the attraction of the pharmacological industry for exploring cactus as a tool to identify new natural bioactive leads and to develop new nutritional supplementations or formulations.

Pharmacological Potentials of Antioxidant and Antiinflammatory Effects of Cactus
In vitro and in vivo studies are convergent to conclude that Opuntia ficus indica extracts exhibit antioxidant and anti-inflammatory properties. The models and conditions, in which these cactus compound properties are highlighted, obviously support that they may be subject to further pharmacological exploration and development.

In Vitro Studies (on Intact Cells)
Oxidative stress and inflammation are involved in numerous diseases. Many studies support the fact that many dietary redox active/antioxidant and anti-inflammatory phytochemicals are promising compounds to prevent oxidative and inflammatory mechanisms taking place in many pathological states. In human intestinal epithelial cancer cells (Caco-2) stimulated by IL-1β, co-treatment with indicaxanthin (a pigment from the edible fruit of Opuntia ficus-indica) prevents activations of NOX-1 and NF-kB and attenuates the rise in inducible NO synthase [88]. These data suggest that cactus dietary pigments may directly influence intestinal inflammatory mechanisms [88]. In human chondrocyte cultures stimulated with IL-1β, lyophilized extracts of Opuntia ficus-indica cladodes reduce the production of key molecules usually released upon chronic inflammation such as nitric oxide (NO), glycosaminoglycans, prostaglandin-E2 (PGE-2) and reactive oxygen species [89]. For this reason, lyophilized extracts of Opuntia ficus indica cladodes might have a pharmacological interest in preventing cartilage alterations and in treating joint disease. On human umbilical vein endothelial cells (HUVECs), non-cytotoxic micromolar concentrations of betalain (a pigment of Opuntia ficus-indica purified from fresh pulp of cactus pear) decrease the expression of cell adhesion molecules such as ICAM-1 [90]. Because it has also radical scavenging/antioxidant properties [90], betalain exhibits an interesting pharmacological profile for degenerative disorders affecting endothelial function such as atherosclerosis, atherothrombosis, low limb ischemia, and stroke. On the murine microglial cell line (BV-2), a butanol fraction (obtained from 50% ethanol extracts of Opuntia ficus indica and hydrolysis products) inhibits the production of NO in LPS-activated BV-2 cells via suppression of iNOS protein and mRNA expressions, inhibits the degradation of IκB-α, and displays peroxynitrite scavenging activity [91]. Moreover, in cultured mouse cortical cells, the butanol fraction of Opuntia ficus indica significantly reduces N-methyl-D-aspartate-, kainate-, and oxygen-glucose deprivation-induced delayed neurotoxicity [92]. These results support that Opuntia ficus indica might alleviate neuronal damages resulting or not from microglial activation.

In Vivo Studies (on the Whole Animals)
In a rat model of acute inflammation (pleurisy), the oral administration of indicaxanthin (mentioned above) reduces exudate size and leukocytes recruitment in the pleural cavity, as well as the protein and/or mRNA expressions of PGE-2, NO, IL-1β, iNOS, and cyclooxygenase-2 (COX2) in the recruited leukocytes [93]. In gerbils, protective effects of methanol extracts of Opuntia ficus indica given per os were also observed against neuronal damages caused by global ischemia in the hippocampal region [92].

Pharmacological Potentialities of Cactus Effects on Non-Alcoholic Fatty Liver Disease
Non-alcoholic fatty liver disease is a complex pathology involving oxidative stress, inflammation, and cell death. Noteworthy, when obese Zucker (fa/fa) rats are fed with a diet containing 4% Opuntia ficus indica for 7 weeks, the rats have around 50% lower hepatic triglycerides than the control group along with a reduction of hepatomegaly and biomarkers of hepatocyte injury (alanine and aspartate aminotransferases). A higher concentration of adiponectin and a greater abundance of genes involved in lipid peroxidation, lipids export and production of carnitine palmitoyltransferase-1 and microsomal triglyceride transfer proteins are observed in livers from cactus-treated animals. Furthermore, rats fed with cactus have a lower postprandial serum insulin concentration and a greater phosphorylated protein kinase B (pAkt):Akt ratio in the postprandial state [94]. Altogether, data obtained in obese Zucker (fa/fa) rats fed with Opuntia ficus indica support that cactus consumption attenuates hepatic steatosis, a pathology currently under the radar screen of the pharmacological industry.

Pharmacological Potentials of Antimicrobial Activities of Cactus
Campylobacter is one of the most common agent causative of food-borne bacterial gastroenteritis in the humans. Epidemiological studies reveal that consumption of poultry products represents an important risk factor of this disease. Noteworthy, the extracts of Opuntia ficus indica have marked bactericidal effects on the growth of Campylobacter jejuni and Campylobacter coli. Moreover, adherence of Campylobacter to Vero cells is strongly reduced [95].
Antimicrobial activities of methanolic, ethanolic, or aqueous extracts of Opuntia ficus indica have also been studied on Vibrio cholerae, indicating that the methanolic extract was the most efficient [96]. This extract causes membrane disruption, leading to increased membrane permeability and consequent marked decreases in pH and ATP.
Altogether, these data obviously support a pharmacological interest of Opuntia ficus indica preventing food contamination by Campylobacter and Vibrio cholerae and in treating gut tract disorders associated with these microorganisms.

Pharmacological Potentials in Targeting Alcoholism with Cactus Extracts
Several studies have evaluated the benefits of Opuntia ficus indica against symptoms of alcohol hangover in humans. The cause of severity of the alcohol hangover can be, at least in part, inflammation and disruption of lipid metabolism homeostasis. In the rat, the effect of mucilage obtained from cladodes on the healing of ethanol-induced gastritis seems correlated with a (re)stabilization of plasma membranes in damaged gastric mucosa. Molecular interactions between mucilage monosaccharides and membrane phospholipids (mainly phosphatidylcholine and phosphatidylethanolamine) may represent the molecular basis for changes in the functions of membrane-attached proteins observed during the healing process consecutive to chronic gastric mucosal damages [97]. Moreover, in humans, an extract of the Opuntia ficus indica plant has been reported to reduce the symptoms of alcohol hangover like nausea, dry mouth, and anorexia [98].

Side Effects Caused by Cactus Compounds
Little information is currently available on cactus side effects. To date, a low colonic obstruction has been attributed to the consumption of Opuntia ficus indica seeds [99].

Conclusions
During the last decade, growing interest in cactus has resulted in a large number of scientific papers describing the composition and/or the bioactivity of a whole extract or a specific purified cactus compounds. Beside the compound contents of Optunia ficus-indica, this review has also devoted a special effort to account for the biological activities of the different parts of the cactus plant (summarized in Table 8). Interestingly, data from several human trials or rodent experiments show that cladodes and fruits extracts are the cactus preparations the most widely tested for their biological activities. Accordingly, as potential metabolic regulators, cactus extracts reveal beneficial effects on the metabolisms of both lipid and glucose, which bode well for the treatment of human metabolic disorders including diabetes and obesity. On the other hand, antioxidant and anti-inflammatory properties of cactus pear and cladodes need to be explored in depth to better understand biological activities and preventive potentials exhibited against several age-linked diseases by polyphenols and flavonoids abundant in cactus pear. At the nutritional level, cactus may be used as an alternative source of natural colors and nutriments, via supply in betalains, aminoacids, sugars, proteins and vitamins. The latter compounds offer a high nutritional value to the food industry for which the development of a real cactus-sourcing branch is awaited. Cladodes (Glycoproteine) Mice [100] Seeds powder and seeds oil Rats [53] Anti-diabetic Capsule: cladode and fruit skin extract Human [101] Cactus powder in capsule Human (Man and women) [102] Aqueous extract of the cladode and fruit and mixture Rats [103] Cladode and fruit skin extract capsule Man [104] Hypoglycemic Polysaccharide extract from the cladode Rats [105] Extract powder racket after drying Rats [106] Anti-Inflammatory   [110] Aqueous and alcoholic extracts of cladode Bacteria: Proteus mirabilis [111] Acknowledgments This work was supported by the Action Intégrée of the Comité Mixte Inter-universitaire Franco-Marocain (CMIFM, AIMA/14/310, Campus France) from the PHC Volubilis/Toubkal program, Ministère des Affaires Etrangères, the Conseil Régional de Bourgogne, the Ministère de l'enseignement et de la Recherche and The Projet Sectoriel CNRST.

Author Contributions
KE, YE and AB: collected data from the literature and prepared tables and figure. PA: involved in writing the manuscript and formatting the references. JV was deeply involved in the manuscript correction and revision. JV and MSE: involved in general supervision of the review. NL and GL: Involved in writing several paragraphs and revision. BN and MC-M: Designed the review, revised the manuscript and supervised the collected data by KE, YE and AB. All authors have read and approved the manuscript.

Conflicts of Interest
The authors declare no conflict of interest.