Pharmacological Properties of Chalcones: A Review of Preclinical Including Molecular Mechanisms and Clinical Evidence

Chalcones are among the leading bioactive flavonoids with a therapeutic potential implicated to an array of bioactivities investigated by a series of preclinical and clinical studies. In this article, different scientific databases were searched to retrieve studies depicting the biological activities of chalcones and their derivatives. This review comprehensively describes preclinical studies on chalcones and their derivatives describing their immense significance as antidiabetic, anticancer, anti-inflammatory, antimicrobial, antioxidant, antiparasitic, psychoactive, and neuroprotective agents. Besides, clinical trials revealed their use in the treatment of chronic venous insufficiency, skin conditions, and cancer. Bioavailability studies on chalcones and derivatives indicate possible hindrance and improvement in relation to its nutraceutical and pharmaceutical applications. Multifaceted and complex underlying mechanisms of chalcone actions demonstrated their ability to modulate a number of cancer cell lines, to inhibit a number of pathological microorganisms and parasites, and to control a number of signaling molecules and cascades related to disease modification. Clinical studies on chalcones revealed general absence of adverse effects besides reducing the clinical signs and symptoms with decent bioavailability. Further studies are needed to elucidate their structure activity, toxicity concerns, cellular basis of mode of action, and interactions with other molecules.

Chalcones are among the leading bioactive flavonoids with a therapeutic potential implicated to an array of bioactivities investigated by a series of preclinical and clinical studies. In this article, different scientific databases were searched to retrieve studies depicting the biological activities of chalcones and their derivatives. This review comprehensively describes preclinical studies on chalcones and their derivatives describing their immense significance as antidiabetic, anticancer, anti-inflammatory, antimicrobial, antioxidant, antiparasitic, psychoactive, and neuroprotective agents. Besides, clinical trials revealed their use in the treatment of chronic venous insufficiency, skin conditions, and cancer. Bioavailability studies on chalcones and derivatives indicate possible hindrance and improvement in relation to its nutraceutical and pharmaceutical applications. Multifaceted and complex underlying mechanisms of chalcone actions demonstrated their ability to modulate a number of cancer cell lines, to inhibit a number of pathological microorganisms and parasites, and to control a number of signaling molecules and cascades related to disease modification. Clinical studies on chalcones revealed general absence of adverse effects besides reducing the clinical signs and symptoms with decent bioavailability. Further studies are needed to elucidate their

INTRODUCTION
Chalcones are among the leading categories of flavonoids across the entire kingdom of plant (Hideo and Tatsurou, 1997;Abbas et al., 2014). The term chalcone is originated from the Greek name chalcos which means bronze. Chalcones were initially manufactured in the research lab in late 1800s (Shimokoriyama, 1962). The chalcone chemistry has created thorough scientific research all the way through the globe (Hideo and Tatsurou, 1997).
Naturally existing chalcones were not separated till the year 1910 (Shimokoriyama, 1962). Chalcones that derived from nature exist mostly as colors of petal and furthermore have been established in the heartwood, leaf, bark, fruit, and root of a range of plants and botanicals (Schroder, 1999).
Chalcones are also recognized as benzyl acetophenone. Chalcones are alpha, beta unsaturated ketones holding two fragrant rings (rings A and B) having different arrangement of substituents. In chalcones, two fragrant rings are connected by an aliphatic three carbon series (Rojas et al., 2002) (Figure 1).
Plants containing chalcones, for instance, the Glycyrrhiza, Piper, Angelica, and Ruscus genus, have long been utilized as therapeutic remedies in Balkan countries (Schroder, 1999;Chatzopoulou et al., 2013;Maccari and Ottana, 2015). Numerous unadulterated chalcones were accepted for clinical applications or experimented in humans. Licochalcones segregated from the plant of licorice has been stated to have a range of biological activities, for instance, antispasmodic, chemopreventive, antimalarial, antitumour, anti-inflammatory, antifungal, antioxidant, and antibacterial activities (Real, 1967;Takahashi et al., 1998). Both apples and sour fruits are loaded nutritional sources of dihydrochalcones and chalcones. Moreover, these complexes could even compose a better contribution to the overall daily consumption of unrefined or organic polyphenolics compounds than other considerably researched flavonoids (Tomás- Barberán and Clifford, 2000).
The purpose of this review is to summarize the most important pharmacological activities highlighting the cellular and molecular mechanisms of action of natural and synthetic chalcones, to better understand their therapeutic potential in the future.

Inclusion Criteria
The inclusion criteria included research studies or reviews that reported the pharmacological actions of chalcones were included; articles published in English, book chapters that also included phytochemical data, and preclinical studies on cell cultures or animal model with evidence of cellular and molecular mechanisms of action; studies that included chalcones and their derivatives from plants whose nomenclature is included in the Plant List (http://www.theplantlist.org/).

Exclusion Criteria
The exclusion criteria included abstracts, case reports, and conference proceedings that did not meet the inclusion criteria, as well as studies that included homeopathic preparations.

Data Collection
Selected pharmacological studies included data on chalcones and their derivatives analyzed, experimental model (in vivo or in vitro), dose, concentration, and results of pharmacological activities with molecular mechanisms included. All information obtained and analyzed in this comprehensive and updated review were summarized in tables and figures.
A study evaluated the antidiabetic activity of sulfonamide chalcone derivatives in silico using methods like homology modeled structure, molecular docking, and MD simulation. This study indicated that these derivatives can bind to residues of the active site as the same way as drugs such as acarbose and voglibose (Bharatham et al., 2008).

In Vivo Antidiabetic Activity
Several authors have evaluated the antihyperglycemic activity of synthetic chalcones in streptozotocin-induced diabetic rats (Satyanarayana et al., 2004;Shukla et al., 2007;Najafian et al., 2010;Rawat et al., 2011;Mahapatra et al., 2017a;Sengupta et al., 2017;Shukla et al., 2017;Tajammal et al., 2017;Acharjee et al., 2018;Naidu, 2018;Raju et al., 2018). It was found that these compounds have a moderate to potential ability to reduce blood sugar. The same effect was noted in starch-loaded rats, using Frontiers in Pharmacology | www.frontiersin.org January 2021 | Volume 11 | Article 592654 chalcone derivative 8c (Rawat et al., 2011). Moreover, serum glucose levels were measured in hyperglycemic rats treated with chalcone analogs, which showed a significant antihyperglycemic effect (Alberton et al., 2008). In a study conducted by Damazio et al., it was evaluated the antihyperglycemic activity of nitrochalcones (Damazio et al., 2009) and naphthylchalcones (Damazio et al., 2010) in diabetic rats by determining blood glucose levels, insulin secretion, and 14C-glucose uptake into the soleus muscle of the animal. This indicates that the effect of chalcones on lowering blood glucose in the hyperglycemic rat can be attributed mainly to insulin secretion with potency similar to that of glipizide. In addition, the glycogen levels in the liver, brain, and spinal cord of rats were estimated following 25 mg/kg dose of chalcone administration for 7 days to discover that these chalcones were able to reduce the glycogen content in the liver, and therefore exerted a strong antidiabetic activity (Jamal et al., 2009). Furthermore, when 2-hydroxychalcone was administered to male rats, they rendered insulin resistance by a high fructose diet. This chalcone was found to have significant hypoglycemic activity by increasing insulin secretion and glycosylated hemoglobin (Jayanthi et al., 2012).
Chalcone derivatives (13a-h) and (19a-h) instreptozotocininduced diabetic mice, compounds13e, 13g, and 19f reduced TG, TC, and Glu levels, respectively (Zhu et al., 2018). Diabetic mice were treated with trihydroxychalcone derivatives, and therefore, chalcone 13 stimulated activation of AMP-activated protein kinase (AMPK), increased muscle FAO, improved tolerance to glucose, and decreased fat accumulation in the liver and skeletal muscles (Shin et al., 2018). Hypoglycemic activity of sulfonylurea chalcones 1-3 was also exhibited in normoglycemic rabbits to show that all these chalcones have activity comparable to that of gliclazide (Rao et al., 2014).
Chalcones exhibited promising activity against NO and PGE2 ( Table 2). The effect of dimethylamino-chalcones on the generation of NO and PGE2 mediators was studied in LPSstimulated RAW 264.7 macrophage cells. The results showed that chalcones suppressed NO production in a dose-depending manner (Rojas et al., 2002). In another study, in order to evaluate the inhibitory effects of trimethoxychalcone derivatives on NO production, the results showed a suppression of NO and PGE2 in LPS-activated RAW 264.7 macrophage cells by 2,4,6-trimethoxy-20-trifluoromethylchalcone. This suggestion was supported by the data which showed an inhibition of nitrite and PGE2 levels (Rojas et al., 2003a;Rojas et al., 2003b).
Natural chalcones have also shown the ability to inhibit NO and PGE2 production. Mallotophilippen chalcones isolated from Mallotus philippinensis fruit extracts, exhibited suppression of NO synthesis in a murine macrophage-like cell line (Daikonya et al., 2004). Xanthohumol and dihydroxanthohumol isolated from Humulus lupulus L. are other natural chalcones, which considerably inhibited NO production by suppressing iNOS induced by LPS and INF-γ in a murine macrophage-like cell line (Zhao et al., 2003).
Frontiers in Pharmacology | www.frontiersin.org January 2021 | Volume 11 | Article 592654 fungi probably by inhibiting the biosynthesis of one or both polymers of the fungal cell wall (Lopez et al., 2001). A large series of chalcones were synthesized and studied for antifungal activity against Candida albicans; the chalcones (60-64) exhibited promising anti-candidal activities (Batovska et al., 2007).
Chalcone derivatives administrated intraperitoneally to the Plasmodium yoelii-infected mice model showed significant inhibition of these strains (Tomar et al., 2010). Table 4 summarizes the principal studies carried out on the antimalarial effect of natural and synthetic chalcones.

Cytotoxic and Antiproliferative Activity
Chalcones (natural and derivatives) displayed potent antiproliferative consequences in both initial as well as developed ovarian cell carcinoma (De et al., 1995) and also in stomach carcinoma HGC-27 cell (Shibata, 1994) (Table 5).
Chalcones with piperazine moiety were created, and their in vitro anti-carcinoma-producing activity was observed (Rahaman et al., 2010). New fragrant chalcones with in vitro anti-carcinoma-producing property have also been recorded (Viveka et al., 2014). In addition, Jurkat cell line of human T-lymphocyte blood cancer along with HL-60 human blood cancer cell lines is also targeted by diaryl chalcones. The in vitro study was performed for ascertaining compound activity in opposition to two breast carcinoma cell lines MCF-7 (Chauhan et al., 2014) and T47D (Jeon et al., 2016). Table 6 The result specified that all the compounds were dynamic but not analogous with doxorubicin. However, it displayed some effects against two breast carcinoma cell lines (Ugwu et al., 2015). In another study, 25 chalcone-derived compounds were reported to exhibit anticarcinogenic properties (Syam et al., 2012). Recent research conducted on 46 different chalcones to measure exact antiproliferative activities against the human tumor necrosis factor-associated programmed cell death-inducing ligand (TRAIL) against cervical (HeLa), liver (HepG2), breast (MCF-7, MDA-MB-231), ovarian (Caov-3), nasopharyngeal (CNE-1), erythromyeloblastoid (K-562), lung (A549), colorectal (HT-29), T-lymphoblastoid carcinoma cells (CEM-SS), and common human embryonic kidney (HEK-293) cells.
Chalcone derivatives with enone and thiophene rings also possess activity against tubulin assembly and colchicines; they bind to tubulin of K562 cells (chronic myeloid leukemia; CML) and inhibit their growth on G 2 /M stage of the cell cycle (Romagnoli, 2008). In addition, those thiophene chalcone derivatives inhibit human T-lymphocyte (Molt 4 and CEM) and human cervix cancer (HeLa) cells. This research was conducted on murine blood carcinoma (L1210), murine mammary cancer (FM3A), human HeLa, Molt 4, and CEM cells by taking 0.3-0.5 million cells/mL of culture medium. After incubating the cells with testing compounds at 37°C for 2 days, cell number was counted by means of a Coulter counter.

Anticancer Potential of Chalcones
Cancer is one of the most feared diseases of the 21st century-according to the 2012 Globocan report, 14 million people are diagnosed with cancer each year and more than 8 million deaths are reported each year (Ferlay et al., 2013). Because radiotherapy or chemotherapy has multiple adverse effects, new molecular therapies are being tested for use in the HSP90 inhibitory effect (Jeong et al., 2014;Oh and Seo, 2017) Frontiers in Pharmacology | www.frontiersin.org January 2021 | Volume 11 | Article 592654 10 Salehi et al.

Tested cells lines
MDA-MB231 basal resembling (more invasive) human triple negative breast adenocarcinoma cell line. MDA-MB468 human triple negative breast adenocarcinoma cell line originated from metastatic spot T47D human breast ductal cancer cell line

Neuroprotective Activity
A research has been conducted on 10 different chalcones, out of which two have nearly similar activity as of diazepam: isoliquiritigenin (ISL, 2',4',4-trihydroxychalcone) and butein (BUT,2',4',3,4,tetrahydroxychalcone). This research based on outcomes of chalcones on different replacements, investigated in animal models for instance open field experiment, equine protozoal myeloencephalitis test, rotarod performance, and grip analysis. These experiments are typical models for screening CNS actions giving information regarding tranquilizing or sleep inducing, psychomotor performance, anxiety, and musclerelaxant effects . The kinetic study of ISL to monoamine oxidase-A indicated that it merged to variable positions of the enzyme, independent of the pre-binding of serotonin (Tan et al., 2000). In the wideranging perception, reasonably lipophilic medicines traverse the blood-brain barrier (BBB) by submissive diffusion (Salehi et al., 2020c;Sharifi-Rad et al., 2020d). Opposing molecules are usually poor central nervous system agents, except they pass through dynamic transport across the central nervous system (Pajouhesh and Lenz, 2005;Salehi et al., 2020a). Hence, it can be approximated that they are able to traverse the BBB and attain their target (Di et al., 2003;Calina et al., 2020;Sharifi-Rad et al., 2020e). Chalcones one, nine, fourteen, fifteen, and sixteen with fine affinity for the BZD binding positions of the GABA category A receptors, chalcones one and five with attraction for the 5hydroxytryptamine 1A receptor, and compounds six and twelve for the µ-opioid receptor were preferred to be experimented as antidepressants, anti-anxiety agents, and against the sensation and perception of pain in extensively applied pharmacological experiments in rats (Salehi et al., 2019c). During the tail suspension experiment, chalcone one demonstrated antidepressant-like activity in rodents, while compound six demonstrated action against sensations and perceptions of pain in an acute chemical stimulated nociception assessment.
The new fifty-methyl-twenty-hydroxy-thirty-nitrochalcone exhibited marginal and central activities against perceptions and sensations of pain either in acute thermal or chemical nociception experiments. According to the consequences recapitulated, plain chalcone derived compounds are favorable compounds for the discovery and growth of new central nervous system medicines and contain an encouraging scaffold in medical chemistry for the evolution of medicines and for the management of pain, depression, and anxiety (Dominguez et al., 2009).

Chalcones in Treatment of Chronic Venous Insufficiency
Chronic venous insufficiency (CVI) is a clinical syndrome that results from chronic disorders of venous circulation from the lower limb level. The main symptoms in moderate stages are heavy legs, tension in the lower limbs, varicose veins dilated, followed in severe stages by swelling of the lower limbs, skin changes, and the appearance of venous ulcer (Lichota et al., 2019). A therapeutic option is represented by laser therapy, sclerotherapy, and venoactive drugs (Ianosi et al., 2019). These venoactive drugs are a heterogeneous group of substances from plant or synthetic origin that modulate the venous tone, attenuates the blood rheology, improves micro-and macrocirculation, regulates capillary permeability, have antiinflammatory effects by inhibiting leukocyte-endothelial interaction, and reduces the oxidative stress (Salehi et al., 2020b).
Recent clinical trials have shown the main role of two chalcones hesperidin methylchalcone and hesperidin trimethylchalcone in the treatment of chronic venous disorders (Boyle et al., 2003) and varices of the trunk of the internal saphenous vein, respectively (Weindorf and Schultz-Ehrenburg, 1987). In a randomized open-label study, the therapeutic effect of a mixture of hesperidin methyl chalcone, Ruscus aculeatus with vitamin C compared to rutozide in patients diagnosed with chronic venous insufficiency was investigated (Beltramino et al., 2000). This clinical trial was conducted for three months and included eighty patients divided into two groups: the first group received the combination with hesperidin methyl chalcone, and the second received only rutoside. The signs and symptoms of chronic venous insufficiency were evaluated initially and then monthly. From the clinical point of view, a significant and lasting reduction of the symptoms was obtained in the patients from the first group treated with the mixture of chalcone and vitamin C compared to the second group, treated only with rutozide (Beltramino et al., 1999).
The mechanism of the venotonic effect of Ruscus and hesperidin methylchalcone extract is exerted by a two-way adrenergic mechanism: 1) direct effect as agonist of the postjunctional alpha-adrenergic receptors of the smooth cell in the vascular wall and 2) indirect effect expressed by increasing the release of noradrenaline from the presynaptic vesicles (Beltramino et al., 1999;Peralta et al., 2007;Gomes et al., 2017). The dose-effect relationship in the single dose and the respective role of each constituent of this combination with hesperidin methylchalcone (150 mg), Ruscus aculeatus plant (150 mg per capsule), and ascorbic acid (100 mg) on the venous tone were also demonstrated in a clinical study that included 37 women with superficial venous insufficiency. It has been shown that the effect of a capsule administered twice daily is similar to the administration of two capsules daily in the morning, and no adverse digestive effects have been reported. Clinical efficiency consisted in improving the permeability of the vascular walls, increasing the vascular tone, reducing the edema and normalizing the blood circulation in the blood vessels (Boccalon et al., 1998). Similar beneficial effect of hesperidin methylchalcone (HMC) on lymphatic venous insufficiency in a recent meta-analysis of some clinical trials has also been demonstrated. The good tolerability and the reduced adverse effects of the combination of HMC, Ruscus extract, and vitamin C have led the specialists to propose their inclusion in the new treatment guidelines for chronic venous insufficiency (Kakkos et al., 2018).
In a randomized double-blind study, the pharmacological effect of trimethyl hesperidine chalcone associated with Ruscus extract and vitamin C was demonstrated in patients diagnosed with femoral trunk varicose (Weindorf and Schultz-Ehrenburg, 1987). The study included fifty patients, divided into two groups: one orally treated 14 days with this combination and the other with placebo. In both the groups, the venous tone was evaluated by plethysmography, both in motion and at rest. In the group treated with trimethyl hesperidine chalcone associated with Ruscus extract and vitamin C, the clinical signs were significantly reduced (Weindorf and Schultz-Ehrenburg, 1987).

Chalcones in Treatment of Skin Conditions
Skin diseases are leading causes of morbidity with high prevalence and incidence, affecting the patients'quality of life and being associated with very important social, economic, and healthcare costs (Ianosi et al., 2018;Scheau et al., 2020). This is why the search for new treatment options in dermatology is one of the most important research areas in both fundamental and clinical science (Ianoşi et al., 2016;Sifaki et al., 2020).
Various clinical trials have evaluated the role of chalcones in inflammatory skin conditions and one of the most investigated substances was licochalcone A. An interesting study including sixty-two women with persistent mild to moderate facial redness (Weber et al., 2006) has evaluated skin compatibility and effect of a skin care regimen containing licochalcone A with duration of 8 weeks. The topical products were very well tolerated, and the results of the study showed significant improvements of erythema and in quality of life of the patients. A subsequent study on 33 rosacea patients showed that the skin care products with licochalcone A are compatible with the standard topical treatment of the disease.
Another research has assessed the effects on sensitive skin of licochalcone A in combination with 4-t-butylcyclohexanol (Sulzberger et al., 2016). The authors have conducted a singleblind, randomized study in order to evaluate subjective and objective symptoms of skin sensitivity. The formulation containing licochalcone A-rich licorice extract combined with 4-t-butylcyclohexanol showed a significant reduction of shavinginduced erythema. It was suggested that the anti-inflammatory effect of licochalcone A is induced by a significant reduction of NFκB signaling and prostaglandin E2 (PGE2) secretion.
A recent randomized, prospective, investigator-blinded study (Boonchai et al., 2018) has evaluated the effects of a moisturizer containing 4-t-butylcyclohexanol and licochalcone A on eighty patients with mild to moderate facial dermatitis. The chalcone containing topical treatment has induced significant improvements of clinical aspect, hydration of cutaneous tissue, and transepidermal water loss as well as the patients' subjective evaluation. The results of facial moisturizer were compared with those induced by 0.02% triamcinolone acetonide cream and even if the topical corticoid treatment was associated with faster improvement of patients' symptoms, the chalcone containing moisturizer showed better effects on skin hydration and inflammation control.
A complex research including two clinical studies and several in vitro experiments was conducted in order to evaluate the antiirritative effect of cosmetic formulations containing licochalcone A . The prospective randomized vehiclecontrolled clinical trials enrolled a total of 57 healthy subjects, 45 of them being included in study using a post-shaving skin irritation model and 12 volunteers taking part in a UV-induced erythema test. Even if in one model inflammation was induced by impairment of skin barrier and in the second by UV-penetration damage, in both studies, the topically applied licochalcone A-rich licorice extract showed a highly anti-irritative effect, significantly reducing erythema. The additional in vitro data emphasized possible cellular and molecular mechanisms showing a strong inhibitory effect of licochalcone A on pro-inflammatory responses of different cell types such as granulocytes, keratinocytes, dermal fibroblasts, and monocyte-derived dendritic cells.
Moreover, licochalcone A has proved to be effective in scalp disorders. The effect of a tonic solution containing licochalcone A, among other active components, has been investigated in 30 subjects with dry and itchy scalp conditions and showed a significant reduction of scalp dryness, itching, and microinflammation (Schweiger et al., 2013). The role of chalcones in the treatment of inflammatory skin conditions in children is another important area of research. A randomized, double-blind, split-side comparison study on 75 infants between the age of 2 weeks and 1 year showed that a moisturizer containing 0.025% licochalcone is equally effective as topical 1% hydrocortisone for the treatment of infantile seborrhoeic dermatitis (Wananukul et al., 2013). The same research group, in a multicenter randomized, prospective, split-side, double-blind study, has evaluated the effect of a moisturizer containing licochalcone A compared to 1% hydrocortisone topical therapy in the treatment of childhood atopic dermatitis (Wananukul et al., 2013). The study included 55 children with mild to moderate lesions and showed that the moisturizer containing licochalcone A significantly reduces the clinical severity of the lesions and the transepidermal water loss, being equally effective as topical corticosteroid treatment. Moreover, continuing the treatment with licochalcone A moisturizer was able to stabilize the clinical improvement and the skin barrier recovery. These results are in accordance with data from a previous randomized, controlled, investigator-blinded study (Udompataikul and Srisatwaja, 2011).
Chalcones are also evaluated as potential treatment options in acne patients. A double-blinded, prospective, randomized, vehicle-controlled clinical trial has investigated the tolerability and effect of a moisturizer containing licochalcone A, L-carnitine, and 1,2-decanediol as adjuvant treatment in topical therapy with retinoids (Chularojanamontri et al., 2016). The study included 120 subjects with mild to moderate acne and showed a significant reduction of total lesions in patients treated with the moisturizer containing active substances. Moreover, they had less inflammatory lesions and skin irritations.
Anti-aging medicine is another important area of research in which chalcones are investigated (Sharifi-Rad et al., 2020b). A double-blind, placebo-controlled trial including ninety-two subjects showed that oral intake of Boesenbergia pandurata extract containing panduratin A as bioactive compound for 12 weeks significantly increases skin hydration and gloss and decreases wrinkling without any adverse symptoms, suggesting a possible use of Boesenbergia pandurata extract as a nutraceutical or nutricosmetic product (Kim et al., 2017).

BIOAVAILABILITY OF CHALCONES
Research on the bioaccessibility of chalcones from sources of food are bounded, but experimented artificial chalcones have accounted to contain broad ranges of biological activities (Won et al., 2005). Although chalcones have an essential position in the bio-production of flavonoids (Shirley, 1996) and are familiar in a number of foods and drinks, like rooibos tea or apples, there are unavailability of data on their bioaccessibility in human beings.
The prenylated chalcone xanthohumol is the amplest chalcone produced in hop cones. Throughout beer preparation, a huge fraction of xanthohumol is changed to the related isomeric prenylflavanone isoxanthohumol. Following administration of xanthohumol to rodents by force feeding at extremely elevated dosage (1 g/kg of body weight), linked metabolites were identified in plasma. The most important metabolite, xanthohumol-49-Oglucuronide, attained its topmost concentration of 3.1 lmol/L 4 h after administration. The maximum concentration of unmetabolized xanthohumol was 10 times lower with the similar Tmax of 4 h (Gerhäuser, 2005). One more rodent study discovered only conjugates in plasma following oral administration of xanthohumol however unsuccessful to distinguish unmetabolized xanthohumol (Avula et al., 2004).
Conversely, these studies demonstrate that prenylated chalcones are bioavailable, although their bioaccessibility appears to be commonly low.
Another study explored the prospective accessibility of flavanones in diversely processed Citrus sinensis (L.) Osbeck juices by imitating stomach and small intestinal in vitro digestion (Gil-Izquierdo et al., 2001).
In addition to showing the power of pasteurization and storage on the substance of dissolvable flavanones, these researchers detected that in vitro pancreatin intake of Citrus sinensis (L.) Osbeck juice in a mild alkaline medium, imitating absorption in the small intestine, converted fifty to sixty% of the dissolved flavanones (primarily hesperidin) to chalcones (principally hesperidin chalcone) (Cermak et al., 2009). Particularly the poor dissolvability of a large number of chalcone compounds, the bioequivalence effectiveness has not achieved the anticipated intensities in preclinical assessments.
Therefore, the maximization of the physicochemical activities will be one of the principal study routes of chalcone-dependent compounds. For the objects of chalcone compounds, a number of anticipated targets must be confirmed. Activity-dependent protein outlining is a potent approach for recognition of target that must be decided by considering each case individually because of the properties of chalcone molecules (Zhuang et al., 2017).

DISCUSSION
The results of our study confirmed the therapeutic potential of chalcones. The limitations of this research result from the fact that many meta-analyzes were included and not individual studies. But this can be considered as a strong point because recent meta-analyzes have summarized the most important pharmacological effects in vitro and especially in vivo. Another strength of this review is that the latest studies and clinical trials on patients have been described, thus confirming the clinical importance and positive prospects in medical therapy.
Natural and synthetic chalcones and their derivatives presented antidiabetic effects, and the effect can be attributed mainly to lowering of insulin secretion with potency similar to that of hypoglycemic agents (ig Glipizide) (Jamal et al., 2009). Numerous studies have reported the anti-inflammatory effects of chalcones on several targets such as enzymes implication in promoting inflammation process: cyclo-oxygenase, interleukins, nitric oxide synthase, cell adhesion molecules (CAM), lipooxygenase (LOX), and prostaglandins (PGs) (Salehi et al., 2020c;Mititelu et al., 2020). The suppression and/or inhibition of cyclooxygenase enzyme is a promising therapeutic way in the treatment of inflammatory diseases (Salehi et al., 2019d;Sharifi-Rad et al., 2020c). Many bioactive compounds, both natural and synthetic, have been isolated and synthetized to develop anti-cyclooxygenase activity (Salehi et al., 2019b;Padureanu et al., 2019;Sharifi-Rad et al., 2020a). PGE2 and NO are among the inflammatory mediators that promote inflammation in several diseases (Salehi et al., 2019c;Salehi et al., 2020b). Consequently, the inhibition of these mediators is strongly suggested as remedy for numerous inflammatory diseases. (Mocan et al., 2014;Toiu et al., 2019). Chalcones also have proved their ability to inhibit NF-κB (nuclear factor kappa) which regulates the most important factors involved in inflammatory process such as cytokines, chemokines, and adhesion molecules (Salehi et al., 2019d;Salehi et al., 2019a). Several studies have suggested the use of chalcones and their derivatives target specifically NF-κB as an antiinflammatory therapeutic strategy (Chu and Guo, 2016).
Chalcones are natural products, produced by plants as a natural defense mechanism against pathogens as fungi and bacteria. Synthesized β-chlorovinyl chalcones exhibited antifungal activity (Bandgar and Gawande, 2010). In general, the natural chalcones (synthesized or modified) are being increasingly documented because of their interesting antimicrobial activities and can be represented as promising agents in the perspective of new antibiotic drugs discovery. Some of the chalcones have been implicated in inhibition of exoenzymes responsible for fungal invasion mechanisms, also inhibiting biofilm and germ tube formation as in C. albicans. They may affect the cellular cytoplasmic membrane and induce cell apoptosis as it was noted in case of carvacrol (Zuzarte et al., 2012). In addition, it was also reported that flavonoid compounds as chalcones inhibit the growth of bacteria by acting on the membrane potential which might affect the overall bacterial metabolic activity, resulting in some biosynthetic pathway inhibition, as demonstrated by the strong inhibition of DNA, RNA, and protein synthesis (Dzoyem et al., 2013;Ungureanu et al., 2017). Chalcones also showed to be a promising anticancer potential because it induces selective cell death in carcinoma cells with not upsetting regular cells (Syam et al., 2012) and psychoactive and neuroprotective activities. (Brady et al., 2012).

OVERALL CONCLUSIONS AND FUTURE PERSPECTIVES
The curiosity and attraction toward natural compounds are increasing gradually because of the recognized favorable consequences on numerous prevalent and general diseases like carcinoma, allergic reactions, cardiovascular disease, infectious diseases, parasitic diseases, type 2 diabetes mellitus, or diseases of central nervous system. Starting from the ethnopharmacological uses of chalcones, in this study, the most important in vitro and in vivo biological activities such as antibacterial, antioxidant, antineoplastic, cytotoxic, antiulcer, antidepressant, anxiolytic, and anti-inflammatory were highlighted. Chalcones derivatives have shown anticancer activity against a variety of cancer cell lines, antibacterial activity against Gram-negative and Grampositive germs, and anti protozoal activity. Although conducted in a small number, clinical studies of chalcones have shown a lack of adverse effects in patients with chronic venous insufficiency, the reduction of clinical signs and symptoms, and good plasma concentrations. However, further clinical studies are needed to fully understand the mechanisms of action at the cellular level and to establish correlations between their structure and pharmacological actions, especially anticancer activity.
Although they showed many interesting biological effects and many preclinical experiments could be performed, their mechanism of action is not entirely known. Being compounds that could be synthesized relatively easily, in the future, it is necessary to develop new synthesis methods that allow the research of new biological properties, a deeper knowledge of the molecular mechanisms of action, and especially the identification of the target of the action. And so, this successful story of the promising therapeutic effects of chalcones to be applicable in the discovery of new drugs, pharmaceutical forms, using modern strategies, especially new nano-formulations in order to increase their bioavailability, prolonged effect, or transport to the target of the action. Further research and clinical trials can explore its pharmacological actions, their interactions with other compounds or medicines, and the level of toxicity it can cause.