Medicinal Uses, Phytochemistry, and Pharmacological Activities of Quercus Species

Quercus species, also known as oak, represent an important genus of the Fagaceae family. It is widely distributed in temperate forests of the northern hemisphere and tropical climatic areas. Many of its members have been used in traditional medicine to treat and prevent various human disorders such as asthma, hemorrhoid, diarrhea, gastric ulcers, and wound healing. The multiple biological activities including anti-inflammatory, antibacterial, hepatoprotective, antidiabetic, anticancer, gastroprotective, antioxidant, and cytotoxic activities have been ascribed to the presence of bioactive compounds such as triterpenoids, phenolic acids, and flavonoids. This paper aimed to provide available information on the medicinal uses, phytochemicals, and pharmacology of species from Quercus. However, further investigation is needed to fully clarify the mode of action of its bioactive compounds and to evaluate in vivo chronic toxicity, before exploring their potential use as a supplement in functional foods and natural pharmaceutics.


Introduction
Since primitive times, humans have been using plants for their essential requirements such as food and medicine. ese plants have been used in traditional medicine in order to cure and prevent various human disorders. e important advantage for therapeutic uses of the plants includes their safety, effectiveness, economic feasibility, and ease of availability [1]. Recently, the global demand for medicinal plant products has increased from USD 19.6 billion in 1996 to USD 24.2 billion in 2002 and is projected to reach USD 5 trillion by 2050 [2]. Among a number of medicinal plants, species belonging to the genus Quercus are widely used in traditional medicine.
is genus belongs to the family Fagaceae. It comprises 600 species worldwide, which often differ in their flowering and fruiting dynamics and by the maturation index [3]. Species of the Quercus genus are mainly distributed in the basin Mediterranean (Portugal, Spain, Algeria France, Italy, Tunisia, and Morocco), Asia, and North America. e extraordinary species diversity reported in America and Asia together is with the highest diversity at 15-30°N in Mexico and East Asia [4,5]. Europe exhibits lower species richness (up to 30 species), but the genus is nearly as widespread there as it is in North America and East Asia, as a limited number of European species have expanded across the continent [6].
Species of the genus Quercus are important medicinal plants. Over the centuries, these species have been used in folk medicine to treat various diseases Table 1. Indigenous peoples, in many areas of the world, use them as antiseptics and to treat gastrointestinal tract (GIT) disorders such as diarrhea and hemorrhoids. e bark of the oak has much importance and is used extensively in medicine as an antiseptic and hemostatic, used to cure toothache and gastropathies, and also used as pacifying agents in inflammation and as healing agents in burn [34,37,38]. However, the resin of Quercus leucotrichophora A. Camus is used to cure gonorrhea, asthma, hemorrhages, diarrhea, and dysentery [34]. Powder of gallnuts of Q. infectoria is used to restore the elasticity of the uterine wall, as well as to treat aphthous ulcers [31,39]. e fruit (acorn) of the Quercus species is considered as a nutritionally rich source of energy (source of carbohydrates, proteins, and fat), justifying their use as food or ingredient food for thousands of years in the human diet such as in bread production or as an ingredient for making coffee [40][41][42]. e acorns of the various species of oak are widely used in curing diarrhea, laryngopharyngitis diseases, menorrhagia, obesity, and stomach ulcers [8,9].
As an example, Endo et al. [50] investigated the antitoxoplasma effect of the Quercus crispula Blume outer bark. e authors identified three pentacyclic triterpenoids, namely, 29-norlupane-3,20-dione, oleanolic acid acetate, and ursolic acid acetate, and concluded that these compounds exhibited notable activities against the Toxoplasma gondii parasite. Moreover, Lei et al. [45] successfully isolated new triterpenoids, which were identified as ursane, oleanane, and lupinane type and were found to be associated with the antineuroinflammatory activity. Even so, numerous studies describing the bioactivities of acorns are focused on their strong antioxidant activity, which are believed to be useful in treating oxidation-associated diseases such as diabetes, cancer, and cardiovascular and inflammatory diseases [41,[51][52][53]. e purpose of this review is to provide up-to-date information on traditional medicinal uses, phytochemistry, and pharmacological activities of Quercus species in Bark Used as astringent, venotonic, and hemostatic [7] order to explore their therapeutic potential and evaluate future research opportunities.

Quercus Genus
e oak family (Quercus spp.) plays a major ecological role in terms of sheer abundance of standing biomass [54]. e genus Quercus is among the most widespread and speciesrich tree genera in the northern hemisphere [6]. e highest diversity is exhibited in Mexico and East Asia [4,5]. Europe exhibits lower species richness (up to 30 species), but the genus is nearly as widespread there as it is in North America and East Asia, as a limited number of European species have expanded across the continent [6]. Quercus spp. (oak) represent an important genus of the Fagaceae family which consists of 600 species worldwide, which includes monecious, deciduous, evergreen trees, and rarely shrubs. e genus Quercus has long been considered one of the most imperative clades of all woody plants in terms of species diversity, ecological dominance, and economic value. e leaves of many oak species are conspicuously lobed, but some species reveal variations in shape from small to large and pointed. Oaks are considered monecious plants, having separate male and female flowers on a single tree. Generally, the male flowers occur in clusters but sometimes are organized in a form called catkin. e female flowers are borne on solitary spikes in the axils of leaves or bracteoles of the new growth [55]. e flowers mostly ripen in the sepals, which later mature into the fruit. e fruit identified as acorn, which is a nut, is characterized by the absence of an endosperm and the presence of an achlorophyllous embryo.

Medicinal Uses of Some Species from Quercus
Quercus species have long been used as traditional medicine in several countries and tribes. Almost all parts of the plants including fruit, bark, and leaves were documented to display a broad range of medicinal properties (Table 1). Indigenous peoples, in many areas of the world use them as antiseptics and to treat gastrointestinal tract (GIT) disorders such as diarrhea and hemorrhoids (Table 1). It is widely used to treat gonorrhea, gastritis, asthma, pyrexia, Parkinson's disease, and hepatoprotective diseases [56], and also hemorrhoid, varicose veins, diarrhea, gastric ulcers, and superficial injuries [57]. e bark of the oak has much importance and is used extensively in medicine as an antiseptic and an energizer. e decoctions from the barks of Q. robur and Q. petraea were recognized to have anti-inflammatory, antibacterial, and antihemorrhagic activities [58]. Indeed, it has been suggested for the treatment of patients with high levels of blood sugar [59] and treatment of sore throat [24]. e leaves of Q. virginiana have been used as antimicrobial agent. As well as, can be employed for the treatment of gastrointestinal disorders [60,61]. e galls of Q. infectoria are used to restore the elasticity of the uterine wall, as well as to treat many inflammatory disorders [31]. Also, they are used in Malay traditional medicine commonly to treat wound infections after childbirth [32]. In India, they are employed traditionally as dental applications such as that in treatment of toothache and gingivitis. In Asia, it has been widely used for the treatment of infection diseases, skin disorders, and inflammatory ailments [39]. e traditional system of medicine is an integral part of Kumaun and Garhwal regions of Uttarakhand, and others states in India used Quercus leucotrichophora A. Camus for treatment of urinary infection [34], stomach pain [35], gonorrhea, asthma, hemorrhages, diarrhea, dysentery [33], urinary disorder [62], and diuretics [63]. Besides, in Korean medicine folk, they are widely used for their dysentery, antidiarrhea, and antidermatitic proprieties [64]. e fruit (acorn) of oak species is a rich source of energy, containing high amounts of carbohydrates, proteins, amino acids, lipids, and sterols. e earliest evidence of acorns as a foodstuff was dated to the late Mesolithic era and found in Western Europe. In the North American West Coast, acorns made up more than half of the diet of native peoples [65]. e fruit from Quercus humilis Mill are mainly consumed roasted, raw, or as an ingredient for making coffee only in particular areas [40]. In the northeast of the Iberian Peninsula, the fruit of holm oak Q. ilex subsp. locally known as kiskurras were used raw, boiled, roasted, like coffee, or transformed into flour. In addition, its flour was mixed with cereal grain flour to make bread [66]. Similarly, in Serbia, Quercus cerris seeds are widely used for bread production [16]. Also, the oil obtained from the acorn has been consumed by native peoples for hundreds of years. It is a nutritious cooking oil comparable to those obtained from peanut, cotton, olive, and avocado [52,65]
Triterpenoids have also been isolated from the species of Quercus. Recently, Xu et al. [87] have identified 3 new pentacyclic triterpenes which were elucidated to be 3-O-galloyloleanolic acid, 23-acetoxy-3-O-galloyloleanolic acid, and 3acetoxy-23-O-galloyloleanolic acid (Figure 1(a)), along with 22 compounds known from the Q. liaoningensis acorn which showed antidiabetic effect. Lei et al. [45] successfully isolated new triterpenoids which were identified as ursane, oleanane, and lupinane type and were found to be associated with the antineuroinflammatory activity (Figure 1(b)). In another study, ten pentacyclic triterpenes, three of which were novel, were isolated from acorns Quercus serrata var. brevipetiolata [44] (shown in Figure 1(c)).

Pharmacological Activities
Traditional uses of Quercus species have led researchers to investigate their biological activities and to validate the uses of species of the genus as therapeutic remedies. Several pharmacological activities have been reported to be exhibited by extracts as well as single compounds, such as antioxidant, antibacterial, anti-inflammatory, and cytotoxicity activity. Table 3 summarizes the major bioactive compounds of Quercus species and its pharmacological activities.
5.1. Antioxidant Activity. Quercus genus has been reported to possess antioxidant activity [41,42,69,92]. A recent study by Arina and Harisun [93] has evaluated the effect of extraction temperatures on the tannin content and antioxidant activity of Quercus infectoria (Manjakani). According to the result, the extract gives high DPPH scavenging capacity with an IC50 value of 0.064 mg/ml at the extraction temperature of 75°C. Another study showed that the thermotreatment and extraction technique had a determinant role in the antioxidant efficiency of Quercus cerris L. wood [94]. e antioxidant activities of leaves and acorn of Q. suber were investigated using 3 different solvents (hexane, methanol, and water). In this case, the aqueous extracts displayed the highest antioxidant activity, based on DPPH and ABTS assays.
is antioxidant activity might be ascribed to the presence of phytochemical compounds such as phenolic compounds in the acorn extracts [69,92].
Makhlouf et al. [97] performed antioxidant activity analysis of fixed oil from three acorn species grown in Algeria: Quercus ilex L, Quercus suber L, and Quercus coccifera L and observed that oils methanolic extracts had remarkable antioxidant activity, up to 3. 34   antioxidants which can be explored as ingredients for functional food and nutraceutical industry.

Antibacterial
Activity. e antibacterial activity of Quercus has been investigated against Gram-positive and Gram-negative bacteria including multidrug-resistant bacterial pathogens. An aqueous extract of leaves from four species of white oaks (Q resinosa, Q laeta, Q grisea, and Q obtusata) was investigated for antimicrobial activities against a range of bacteria (E. coli, S. epidermidis, K. pneumoniae, P. mirabilis, P. hauseri, P. vulgaris, and E. aerogenes) and yeast (C. albicans). ey further reported that all aqueous extracts of oak tested showed susceptibility to K. pneumoniae (ATCC 13883). ese researchers also reported that Q. resinosa and Q. grisea denoted antimitotic activity against these organisms [46], whereas Bahador and Baserisalehi [98] tested the antibacterial activity against Gram-negative bacteria (E. coli, Salmonella typhimurium, Shigella dysenteriae, and Yersinia enterocolitica) of the fruit of Q. castaneifolia. According to their finding, S. dysenteriae was more sensitive with a zone of inhibition of 18 mm, and he MIC value was 2.5 × 10 −4 . e lowest MIC values were found for extracts for E. coli. In a study carried out by Sarwar et al. [28], the antibacterial activity of the gold nanoparticle synthesized from the leaves of Quercus incana was evaluated against the human pathogens (Pseudomonas  Figure 3: Chemical structures of bioactive compounds of Quercus species.  Increased the survival of pancreatic beta cells by reducing the production of reactive oxygen species and enhancing the activities of superoxide dismutase, catalase, and glutathione in MIN6 cells damaged by H 2 O 2 . e preliminary mechanism by which the compound protects pancreatic beta cells was through the nuclear factor erythroid-2related factor 2 (Nrf 2 )/heme oxygenase-1 HO-1 pathway [87] 8

Roburgenic acid Cytotoxicity
Roburgenic acid was the most active compound (IC50 � 19.7 μM) reaching a comparable value to those of positive controls and IL-1β [80] Evidence-Based Complementary and Alternative Medicine pickettii, Salmonella setubal, Staphylococcus aureus, Bacillus subtilis, Aspergillus flavus, and Aspergillus niger). e results showed enhanced antibacterial activity against all bacterial pathogens. Besides, the ethanolic extracts of Q. persica have been also tested against S. aureus, B. subtilis, E. coli, and K. pneumoniae [99].
Hobby et al. [100] tested the ability to inhibit the Staphylococcus aureus biofilm using the leaf, stem, and fruit from Quercus cerris. e activity was measured using static crystal violet staining methods and confocal laser scanning microscopy. e study revealed that butanol extracts of both the leaf and stem/fruit samples were the most active, at a dose of 200 ug/ml.
In an agar-well diffusion assay, the methanol and acetone extracts of the gall of Q. infectoria showed activity against oral pathogens such as Streptococcus mutans ATCC 25175, Porphyromonas gingivalis ATCC 33277, Streptococcus salivarius ATCC 13419, and Fusobacterium nucleatum ATCC 25586. e MIC ranged from 0.16 to 0.63 mg/mL, and the most susceptible bacterium was S. salivarius, which suggested that the oak extract might be used against dental caries and periodontitis etiological agents [101]. In another study, the extracts of Quercus infectoria were assessed against many microbial species and used for eggshell decontamination. e antimicrobial activity was evidenced against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, and Candida albicans, and the results showed disinfection of eggshell microbial contamination, by immersion in 1% QIE solution, sharply reduced total colony count, yeasts, and molds, and Enterobacteriaceae, E. coli, and S. aureus were completely inhibited after 60 min of immersion in QIE [102]. Another investigation demonstrated that the extract of the Quercus infectoria gall possesses antimicrobial activity against Leptospira interrogans serovar Javanica and Leptospira interrogans serovar Icterohaemorrhagiae with MIC values of 0.125 mg/mL [103].
In another work, Touati et al. [71] tested the antibacterial activity of the cork from Quercus suber L against Staphylococcus aureus ATCC, Listeria innocua, Escherichia coli, and Pseudomonas aeruginosa. e plant was collected from Algeria. e phenolic fraction of the cork was shown to inhibit the growth of S. aureus (12.1 mm) and P. aeruginosa (10.07 mm). erefore, different types of Quercus can be used as an alternative source of potential antimicrobial agents, and more analysis in in vivo and clinical studies is required to substantiate these in vitro findings.

Cytotoxic and Anticancer
Activity. Several studies have confirmed the cytotoxic and anticancer activity of a wide variety of Quercus species extracts, against various cancer cell lines. e MeOH and water extracts of the barks of Quercus cerris var. cerris, Quercus macranthera subsp. syspirensis, and Quercus aucheri were subjected to the evaluation of their cytotoxicity against the Hep-2 human larynx epidermoid carcinoma cell line. e results demonstrated that aqueous and methanolic extracts of Q. macranthera subsp. syspirensis showed the strongest cytotoxicity against the tested cell line, with IC50 values 165.291 ug/ml and 273.771 ug/ml, respectively [104]. In addition, the ethanolic extract of Quercus ilex has been studied for its cytotoxicity by the MTT assay in various concentrations (250, 500, and 1000 mg/mL). e results indicated that the treatment inhibited cell viability in a dose-and time-dependent manner [96].
Perez et al. [90] studied the cytotoxic activity of 17 triterpenoids isolated from oak heartwood of Quercus robur against human prostate cancer (PC3) and human estrogendependent breast adenocarcinoma (MCF-7) cell lines and lymphocytes derived from human peripheral blood. e obtained results demonstrate that breast cancer cells (MCF-7) were the most affected by triterpenoids, with roburgenic acid, being the most active compound (IC50 � 19.7 μM). e authors also reported the selectivity for some triterpenoids against lymphocytes, exhibiting an IC50 > 200 μM, while active against cancer cells. Moreover, the genotoxicity of Q. resinosa leaves extracts was evaluated on HeLa cells by the single-cell electrophoresis assay (comet assay), indicating that phytochemical compounds present in extracts obtained from their decoctions increase the oxidative process and other damage to DNA in transformed human cells [47].
Recently, apoptotic and antimetastatic activities of betulin isolated from Quercus incana leaves were investigated against non-small-cell lung cancer. e results indicted significant dose-dependent induction of apoptosis after the treatment with betulin, followed by increased expression of the caspase family (i.e., caspase-3, -6, and -9), proapoptotic genes (BAX and BAK), and inhibiting antiapoptotic genes (BCL-2L1 and p53). Additionally, betulin was found to be highly and selectively active against the cancer cells at much lower doses (11.55 μM) [29]. Also, it has been reported that the Quercus suber L. cork extracts induce apoptosis in human myeloid leukaemia HL-60 cells. e extracts showed a time-dependent and dose-dependent cytotoxicity in the human promyelocytic leukaemia cells [105].
Yarani et al. [106] determined the effectiveness of antiangiogenic activity of the Quercus infectoria acorn shell. Treatments showed that the extract possessed antiangiogenic potential, which exerts its inhibitory effect mainly through downregulation of essential mediators such as VEGF and MMPs.

Anti-Inflammatory and Neuroprotective Activity.
Inflammation is a common pathological phenomenon respective of various diseases. e effects of Quercus species on anti-inflammation have been widely studied. Moreno-Jimenez et al. [95] evaluated the anti-inflammatory activity in HT-29 cells from the leaves infusion of Q. sideroxyla, Q. durifolia, and Q. eduardii. e results demonstrated that Q. sideroxyla decreased the levels of the inflammatory markers COX-2 and IL-8 by modulating the expression of NF-Κb. Besides, studies in vitro have shown that triterpenes, isolated from acorns of Quercus serrata var. brevipetiolata, inhibit nitric oxide (NO) production and other proinflammatory cytokines [44]. Moreover, lupeol isolated from white oak leaves (Quercus resinosa, Q. grisea, Q. laeta, and Q. obtusata) was evaluated for their ability to inhibit COX-1 and COX-2 enzymes by the in vitro colorimetric COX (ovine) inhibitor assay. In this study, lupeol from Q. obtusata demonstrated a differential effect to inhibit COX-2 without inhibiting COX-1 [46]. Additionally, (−)-epicatechin, procyanidin B3, and procyanidin B4 (7) obtained from the bark of Quercus gilva Blume presented anti-inflammatory and antioxidative potency.
e three compounds showed dose-dependent inhibitory activities on the gene expression of COX-2 and IL-1β [80]. Studies conducted by Vázquez-Cabral et al. [107] indicate that flavonols such as quercetin glucuronide and kaempferol 3-O-glycoside are glucuronidated by the action of the kombucha consortium and that these metabolites are effective antioxidant and anti-inflammatory agents in human macrophages.
Neurodegenerative disorders are diseases that influence the nervous system, such as brain tumors, glioblastoma, epilepsy, Alzheimer's disease, and Parkinson's disease. It was reported that extracts from Quercus suber and Quercus ilex showed neuroprotective effects through inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and protection of the human dopaminergic cell line SH-SY5Y [84]. Indeed, Gezici and Sekeroglu [43] reported that extracts from the shell, cup, and acorn parts of Quercus coccifera had notable AChE and BChE inhibition. Inhibitors of this enzyme are used to alleviate symptoms associated with Alzheimer's disease [84]. In another investigation, Lei et al. [45] showed potent antineuroinflammatory activity of triterpenoids isolated from Chinese acorns (Quercus serrata var. brevipetiolata), which suggested that these triterpenoids might have activities against Alzheimer's disease.

Hepatoprotective.
Xu et al. [108] reported that acorns (Quercus liaotungensis) and their galloyl triterpenes exhibited stronger antiproliferative effects against t-HSC/Cl-6 cells than the reference silymarin, suggesting its potential for being developed into antihepatic fibrosis food or medicine. In the same year, Singh and Bisht [48] investigated in vivo hepatoprotective activity of the root extract of Q. oblongata D. DON and clearly showed the positive effect of the ethanolic extract at the dose of 300 mg/kg in comparison to the reference silymarin. Similarly, it was stated that the administration of 300 mg/kg of the Q. dilatata extract displayed protective effect against bisphenol A-(BPA-) induced hepatotoxicity by restoring hepatic inflammation towards normal [109]. Other studies performed by Toori et al. [110] investigated the hepatoprotective effects of acorn extracts on carbon tetrachloride-induced liver damage in rats. eir analyses showed that the aqueous extract at 250 and 500 mg/ kg displayed excellent hepatoprotective potential, indicating that this solvent is a better alternative, with no toxic effects. In addition, several studies have shown that Quercus spp. exhibited hepatoprotective effects [111].

Antidiabetic Effect.
Diabetes is a chronic disease characterized by high blood glucose levels that result from the body's inability to produce insulin [112]. One promising approach for the management of diabetes is to postpone the absorption of glucose by inhibiting carbohydrate-hydrolyzing enzymes (α-amylase and α-glucosidase) [85].
Custódio et al. [84] studied the inhibitory effect of leaves and acorns from Quercus suber on key enzymes relevant for hyperglycemia (α-amylase and α-glucosidase). eir study showed that the best results were obtained with the water and methanol leaves extracts with values of 97 and 89%, respectively, which could most likely be attributed to their higher phenolic content. Moreover, the extract from the bark of Q. coccifera exhibited stronger α-glucosidase inhibitory activity with an IC50 value of 3.26 ± 0.08 µg/mL than that reported for acarbose IC50: 50.45 ± 0.20 µg/ml [83]. In another work, triterpenoids obtained from acorns of Quercus liaotungensis have been studied for their inhibitory activity against α-glucosidase, α-amylase, and protein-tyrosine phosphatase 1B.
e authors found that all the compounds showed strong inhibitory effects on PTP1B and α-glucosidase, but inhibition of α-amylase was not observed [87]. It was also reported that the polyphenol fraction from acorn leaves (Quercus liaotungensis) inhibited α-glucosidase and PTP1B activity [49]. Similarly, Yin et al. [85] reported that Mongolian oak cups might be a source of ellagic acid (EA), which possess prominent inhibitory activities against α-glucosidase, α-amylase, and formation of AGEs. Other authors reported that the chloroform extract from Quercus dilatata exhibited maximum antidiabetic activity α-amylase inhibition of 21.61 ± 1.53% at 200 μg/ml [22]. In addition, condensed tannin fractions isolated from the leaves of Quercus phillyraeoides presented potent α-glucosidase inhibitory activities with IC50 values in the range of 2.60 to 3.14 µg/ml, respectively [91].
Furthermore, Lin et al. [81] established that hydrolysable tannins are responsible for the lower digestibility of the acorn of Quercus fabrei Hance. ese results further support the potential use of the acorn for preparation of low glycemic index foods. In a particular study, Ahmadi et al. [113] reported that prebiotics from the acorn can ameliorate HFDinduced defects in the glucose metabolism via positive modulation of the gut-microbiome-brain axis.
Overall, Quercus species may serve as an alternative source of potential antidiabetic agents, and more analysis in in vivo and clinical studies is required to validate these in vitro findings.

Skin Disorder.
Melanin is mainly responsible for skin and hair colors. It plays an important role in protecting the skin against the harmful effects of UV radiation. However, an excessive accumulation of melanin creates various skin Evidence-Based Complementary and Alternative Medicine dermatological disorders like irregular skin hyperpigmentation and aesthetic problems [115]. Tyrosinase is a key enzyme in melanin biosynthesis. Inhibition of this enzyme decreases melanin production and deposition [116].
Sari et al. [83] showed that polydatin isolated from the Quercus coccifera bark displayed potent tyrosinase inhibition compared to the positive control kojic acid, with an IC50 value of 4.05 ± 0.30 µg/ml. In addition, Kim et al. [117] analyzed the effect of some polyamine derivatives from the bee pollen extract of Q. mongolica against the tyrosinase enzyme. ey observed that polyamine derivatives with coumaroyl and caffeoyl moieties exhibited higher tyrosinase inhibitory potential than the others isolated with IC50 values of 19.5-85.8 Μm. Lee and coworkers [118] explored the antidermatitis effects of oak wood vinegar (OWV) in the DNCB-induced contact dermatitis mice model and showed that OWV has antiinflammatory and antiproliferative activity in a DNCBinduced contact dermatitis mice model. is activity may be linked to STAT3 inactivation. e extract from Quercus suber leaves showed effectiveness in the prevention of photo-induced oxidative stress in the skin through scavenging multiple ROS and RNS [119]. Moreover, Koseki et al. [120] showed that the extract of Quercus acutissima Cortex inhibited androgen-related pathogenesis of acne, testosterone conversion, and sebum synthesis, partially via 5α-reductase inhibition.
In consequence, it is possible to conclude that the Quercus species can be an important ingredient in the cosmetic product.

Conclusion
For a long time, Quercus species have been used as a traditional medicine in various countries and tribes. e bark, fruit, and leaves of the species from the genus were reported to possess a broad spectrum of biological effects, such as antioxidant, antidiabetic, anticancer, anti-inflammatory, and antibacterial. e current phytochemical studies of the species from the genus Quercus showed that phenolic acids (particularly gallic and ellagic acids and their derivatives), flavonoids (particularly flavan-3-ol), and tannins are somehow ubiquitous in all Quercus species. From these researches, phenolic compounds, triterpenoids, and flavonoids have a positive effect on anti-inflammatory, antidiabetic, and anticancer actions which can be considered as promising candidates for the development of novel pharmaceutical agents. For this, additional research on other Quercus species need much attention from biochemists for studying their detailed chemical profile and health effect, and also more studies are required to evaluate the safety, side effect, and efficacy of extracts.

Conflicts of Interest
e authors declare that there are no conflicts of interest.