Portulaca oleracea L.: A Review of Phytochemistry and Pharmacological Effects

Portulaca oleracea L., belonging to the Portulacaceae family, is commonly known as purslane in English and Ma-Chi-Xian in Chinese. It is a warm-climate, herbaceous succulent annual plant with a cosmopolitan distribution. It is eaten extensively as a potherb and added in soups and salads around the Mediterranean and tropical Asian countries and has been used as a folk medicine in many countries. Diverse compounds have been isolated from Portulaca oleracea, such as flavonoids, alkaloids, polysaccharides, fatty acids, terpenoids, sterols, proteins vitamins and minerals. Portulaca oleracea possesses a wide spectrum of pharmacological properties such as neuroprotective, antimicrobial, antidiabetic, antioxidant, anti-inflammatory, antiulcerogenic, and anticancer activities. However, few molecular mechanisms of action are known. This review provides a summary of phytochemistry and pharmacological effects of this plant.


Introduction
Portulaca oleracea L. is a warm-climate, herbaceous succulent annual plant with a cosmopolitan distribution belonging to the Portulacaceae family. It is commonly known as purslane (USA and Australia), rigla (Egypt), pigweed (England), pourpier (France), and Ma-Chi-Xian (China) [1]. It is distributed widely in the tropical and subtropical areas of the world including many parts of the United States and is eaten extensively as a potherb and is added to soups and salads around the Mediterranean and tropical Asian countries [2]. Americans and aborigines of Australia grind the seeds of this plant into flour for use in mush and bread [3]. Portulaca oleracea also provides a source of nutritional benefits owing to its rich omega-3 fatty acids and antioxidant properties [4].
Portulaca oleracea has been used as a folk medicine in many countries, acting as a febrifuge, antiseptic, vermifuge, and so forth [5]. It exhibits a wide range of pharmacological effects, including antibacterial [6], antiulcerogenic [7], antiinflammatory [8], antioxidant [9], and wound-healing [10] properties. It is listed by the World Health Organization as one of the most used medicinal plants, and it has been given the term "Global Panacea" [11]. The Chinese folklore described it as "vegetable for long life" and it has been used for thousands of years in traditional Chinese Medicine [12,13]. It is cold in nature and sour in taste and is used to cool the blood, stanch bleeding, clear heat, and resolve toxins. The dried aerial part of this plant is indicated for the treatment of fever, dysentery, diarrhoea, carbuncle, eczema and hematochezia, with a recommended dose of 9-15 g [14][15][16].
Portulaca oleracea has a high potential to be used as human and animal food and to be utilized as a pharmacological agent in medicine. In this paper, phytochemistry and pharmacological activities of this plant are reviewed and its potential for further investigation, exploitation, and utilization are discussed.

Phytochemistry
Many constituents of Portulaca oleracea have been isolated, including flavonoids, alkaloids, fatty acids, terpenoids, polysaccharides, vitamins, sterols, proteins, and minerals; these are listed in Table 1 and the chemical structures of the main compounds are presented in Figure 1.
One of the most effective constituents present in Chinese Herbal Medicines are flavonoids which are biologically active and possess a wide range of pharmacological properties such as antibacterial, antivirus, anti-inflammation, and antioxidation properties. In the Portulaca oleracea plant, the flavonoids levels vary according to the part of the plant; the highest levels are present in the root followed by stem and the leaf; and seven different flavonoids are present in this plant, including kaempferol, myricetin, luteolin, apigenin, quercetin, genistein, and genistin [17]. However, only kaempferol and apigenin have been found in ethanolic extracts of leaves and stems, with the levels in the former being higher [11]. Portulacanones B-D, three homoisoflavonoids compounds, display selectively cytotoxic activities against three human cancer cell lines (SF-268, NCI-H460, and SGC-7901) [18]. Flavonoids are also widely present in foods such as fruits and vegetables [19].
In addition to flavonoids, another important chemical found in this plant is alkaloids including dopa, dopamine, and noradrenalin. The content of dopamine and noradrenalin is higher in leaves compared to stem and seeds. The amount of dopamine and noradrenalin obtained from leaves varies according to the solvents used in the extraction process, suggesting that the levels of these compounds are dependent on the solvents used during the extraction process [20]. Oleraceins A, B, C, D, and E are cyclodopa alkaloids isolated from this plant [21] and several analytes such as (3R)-3,5bis(3-methoxy-4-hydroxyphenyl)-2,3-dihydro-2(1H)-pyridinone and 1,5-dimethyl-6-phenyl-1,2-dihydro-1,2,4-triazin-3(2H)-one display cytotoxic activities against human cancer cells [22].
Portulaca oleracea is also an excellent source of omega-3 fatty acids, which is usually present in oil and fat of fishes but not normally found in plants. Omega-3 fatty acids play an important role in the enhancement of immune function [23] and prevention and treatment of hypertension, coronary artery disease, cancer, and other inflammatory and autoimmune disorders [24]. It includes -linolenic acid and linoleic acid, which are essential for normal growth, health promotion, and disease prevention in humans. Polysaccharides found in Portulaca oleracea are potential therapeutic agents for the treatment of diabetes mellitus owing to their modulation of blood lipids, metabolism, and decrease of blood glucose. Portulaca oleracea contains monoterpenes such as portulosides A and B, diterpenes such as portulene, andamyrin type triterpenoids [1,25]; in addition, vitamins have also been isolated from the leaves of this plant. It contains the highest content of vitamin A which is a natural antioxidant playing an important role in vision, maintaining healthy mucus membranes and protecting against lung and oral cavity cancers among green leafy vegetables. This plant also contains ascorbic acid, -tocopherol, and B-complex vitamins, for example, niacin, pyridoxine, and riboflavin [26]. Furthermore it is rich in minerals like phosphorus, manganese, icon, calcium selenium [3], and the amino acids isoleucine, proline, leucine, lysine, phenylalanine, methionine, cystine, valine, threonine, and tyrosine [2]. Many other constituents have also been isolated from this plant, such as -carotene, glutathione, melatonin, portulacerebroside A, catechol, and bergapten.

Pharmacology
Over the past decades, numerous researchers have investigated the pharmacological activities of Portulaca oleracea. This review provides a comprehensive summary of the main pharmacological properties which are presented below.

Antioxidant Activity.
The antioxidant property of Portulaca oleracea is attributed to its constituents, such as gallotannins, omega-3 fatty acids, ascorbic acid, -tocopherols, kaempferol, quercetin, and apigenin [8,16,17]. The single cell gel electrophoresis assay (comet assay), which is an simple, rapid, and inexpensive method for measuring DNA strand breaks, confirmed that the aqueous extract significantly alleviated hydrogen peroxide-induced oxidative DNA lesions in human lymphocytes, whereas the ethanolic extract had no effects, which may be associated with the antioxidant constituents contained in the aqueous extract [35]. The aqueous extract decreases high fat diet-elicited oxidative damage by modulating blood and liver antioxidant enzyme activities, elevating leptin/ -actin and liver PPAR a/ -actin and inhibiting the protein expression of p-PERK and the FAS mRNA expression of liver and spleen in mice [9]. In another study, the aqueous extract at a concentration range of 100, 150, 200, and 400 g/mL and the ethanolic extract at a range of 1200 and 1800 g/mL, respectively, exerted cytoprotective effects on 2,2 -azobis hydrochloride-induced hemolytic damages of RBCs in a concentration-dependent manner [36].

3.5.
Antimicrobial. Portulaca oleracea possesses antibacterial, antifungal, and antiviral activities as revealed by its antifungal effect against dermatophytes of the genera Trichophyton [44]. A pectic polysaccharide isolated from the aerial part of this plant displays antiherpes property against simplex virus type 2 which is due to the inhibition of virus penetration and not virus adsorption [45]. A 70% methyl alcohol extract of Portulaca oleracea shows antibacterial activity against the Gramnegative stains: Escherichia coli, Pseudomonas aeruginosa, and Neisseria gonorrhea with inhibition zones of 14, 15, and 15 mm, respectively, and the Gram-positive strains: Staphylococcus aureus, Bacillus subtilis, and Streptococcus faecalis with    3.9. Other Activities. The ethanol extract from Portulaca oleracea at a concentration range of 100, 200, and 400 mg/kg, respectively, displays a dose-dependent effect in prolonging the survival time of mice in hypoxic models, including closed normobaric hypoxia and potassium cyanide or sodium nitrite toxicosis. This extract also enhances the activities of phosphofructokinase, pyruvate kinase, and lactate dehydrogenase in glycolysis and the level of adenosine triphosphate of mouse cortices in hypoxia models [12]. The preliminary wound healing activity of Portulaca oleracea has been appraised in Mus musculus JVI-1 and it has been shown that a fresh crude extract significantly accelerates the wound healing course by the stimulation of wound contraction and downregulation of the surface area of the excision wound [10]. Portulaca oleracea also has the ability to accumulate Se even at the shortest time span of 42 days, and hence it can perform the dual functions of preventing the occurrence of Se deficiency linked diseases such as Keshan and Kashin-Beck diseases [47].

Conclusion
Portulaca oleracea is of considerable importance to the food industry and also possesses a wide spectrum of pharmacological properties such as neuroprotective, antimicrobial, antidiabetic, antioxidant, anti-inflammatory, antiulcerogenic, and anticancer activities, which are associated with its diverse chemical constituents, including flavonoids, alkaloids, polysaccharides, fatty acids, terpenoids, sterols, proteins, vitamins, and minerals. Although bioactivities of extracts or compounds isolated from Portulaca oleracea are substantiated by using in vitro and in vivo studies including animal models and cell culture studies, the mechanisms of action have not been addressed. Hence, more mechanistic studies are required before Portulaca oleracea can be considered for further clinical use. This review concludes that Portulaca oleracea is an edible and a medicinal plant which is important to the food industry and may also have a significant role to play in health care provided that adequate studies are conducted.

Conflict of Interests
The authors have declared that there is no conflict of interests.