Croton sp.: a review about Popular Uses, Biological Activities and Chemical Composition

The genus Croton, belonging to the Euphorbiaceae family, is a plant with shrubby characteristics, with the ability to regrow in times of rain, develops wildly, especially in deforestation areas, being reported mainly in the Caatinga and Forest region. One of the main characteristics of this genus is that several species are rich in chemical constituents of importance for medicine. In this way, this review of the literature, has an objective that findings regarding the biological activities and chemical composition of Croton species. This study is a literature review, carried out in the following databases: SciELO, BVS, MEDLINE, LILACS, PubMed and ScienceDirect, with a time frame between 1997 and 2020. The articles studied have shown different activities for Croton species, such as anti-inflammatory, antihypertensive, antifungal, antimicrobial, antidiabetic, antioxidant, antinociceptive and anti-tumor. Regarding toxicological aspects, the findings suggest caution in the use of Croton species, as some are toxic. While, regarding the chemical composition, in most species the presence of several secondary metabolites is observed, such as alkaloids, terpenoids, flavonoids and other phenolic compounds. Therefore, the results described in this article suggest that the therapeutic application of Croton species is supported by the literature, however we point out that caution is required in the use of Croton species, some present due to toxicity.


Introduction
Brazil has one of the greatest diversities of fauna and flora in the world and this biodiversity has a high economic value, because natural products can be used for a lot of purposes, since the food industry up to develop new therapeutic approaches . Natural products are considered one of the main sources that contribute to advances in health research, in such a way that obtaining new active principles and elucidating the action mechanism makes it possible for the industry to delineate new products, providing new applications, inputs and alternatives for the treatment of various pathologies.
In the last years, great advances have been observed in the elucidation of compounds in plant species, being an essential premise to produce new therapeutic agents (Khan et al., 2018;Alves et al., 2019).
The Euphorbiaceae family comprising more than 8,000 species in approximately 334 genus, along the extension of the American territory it is possible to find about 2500 species distributed in 92 genus. In Brazil, 72 genus and about 1100 species are widely distributed in the tropical regions. There is a great diversity among species, ranging from shrub to tall tropical forest trees, but they are widespread across all types of vegetation. One of the main characteristics of Euphorbiaceae species is their plurality of applications in folk medicine, that demonstrate their variety of chemical constituents (Webster, 1987;Trindade et al., 2014).
Other's studies report that the phytochemical profile of species that comprise the Euphorbiaceae family comprises alcohols and hydrocarbons, in addition to phenolic compounds, such as flavonoids, lignin, coumarins, tannins, alkaloids, cyanogen glycosides and glucosinolates. It is considered one of the most important families due to the diversity of chemical compounds with biological activity (Seebaluck-Sandoram et al., 2017).
The Croton genus is one of the most diverse genus in the Euphorbiaceae family. In Brazil, there are about 356 species that belong to the genus, it is reported in the areas Caatinga, Atlantic Forest and Amazon Forest . The literature account that in Pernambuco it is possible to find about 35 species, most of which are distributed in the Caatinga . Described in the literature as a bush plant, which can regrow, especially in periods of rain, in way wildly, especially in deforestation areas, generally forming large homogeneous clusters in the Caatinga, that can reacher several (Trindade & Lameira, 2014).

Methodology
A narrative literature review was carried out, according to Rother (2007), in which a scoping review is carried out by research in another way described with the objective of exploring as a review that already exists for a certain area of research, object identifying existing gaps, doing research, selecting, and synthesizing existing knowledge. This study is a literature review, carried out in several databases (SciELO, BVS, MEDLINE, LILACS, PubMed e Science Direct) and included original articles, books, dissertations, and theses. The main aspects related to the biological activities and chemical composition of the species published between 1997 and 2020 were considered. The keywords used were Croton sp; Croton blancheantius; quince; biological activities; chemical composition, toxicology. The flowchart of research and selection of articles are next, according

Popular Use
The main species of the Croton genus found in Brazil and used in folk medicine is Croton cajucara, C. blancheantius, C. celtidifolius Baill., C. palanostigma, C. schiedeanus Schlech., C. zehntneri Pax, C. eluteria Bennett., C. lechleri, C. palanostigma, C. urucurana, C. malambo Karst e C. nepetaefolius Baill. (Pereira et al., 2002;Salatino et al., 2007;Fontenelle et al., 2008;Hort et al., 2012;Nascimento et al., 2017). The diversity of activities reported to the species of the genus are compiled in Table 1, according to the form of use of the plant and the region in which each species can be found in Brazil. Table 1. Relationship between species, geographic location, and applications in folk medicine.

Species
Native Applications in folk medicine Reference

C. blancheantius Baill Brazilian Northeast
The infusion of the leaves is used for gastrointestinal disorders, rheumatism and migraine. Firmino et al. (2019) C. cajucara Benth Amazon forest region The infusion of leaves, bark and stem is used to treat diabetes, control cholesterol and treat gastric and liver disorders.
Nascimento et al.

C. celtidifolius Baill
Atlantic Forest (especially the southern region of Brazil) The bark infusion is used in the treatment of inflammatory diseases, leukemia and rheumatism. Hort et al. (2012) C. eluteria (L.) W.

Wright Northern region of Brazil
Its bark is used in powder form, with applications in the treatment of diarrhea, bronchitis and some people use it to treat fever.
C. lechleri Müll.Arg Amazon forest region Its red colored latex is used in the wound healing process.

Brazilian Northeast
The tea from the leaves and bark is used for a sedative effect.

Antihypertensive activity
A study by Guerrero et al. (2001) reported that the aqueous extract of the leaves of the Croton schiedeanus Schlecht species associated with the drug phenylephrine can promote a synergistic effect, enhancing an antihypertensive activity. In 2004, Guerrero and colleagues evaluated the effectiveness of the aqueous extract of the same species in hypertensive mice and observed the effect of antihypertensive activity and bradycardia in animals, confirming the previous data.
Tests carried out with trans-dehydrocrotonin diterpene isolated from the bark of the stem C. cajucara concluded that the in vivo assay the diterpene promoted hypotensive and bradycardic effect, which were related to effect separate and independent vasorelaxant in the aortic endothelium. The results suggested that the hypotensive activity is not related to muscarinic, β-adrenergic stimulation or even to ganglionic blockade, however it is suggested that it may be related to the release of nitric oxide by the endothelium. With respect to bradycardia, the results indicated negative chronotropic effect resistant atropine (Silva et al., 2005). Hort et al. (2012) in his studies conducted in mice, evaluated the fraction cardioprotective effect of proanthocyanidin of C. celtidifolius bark, the results demonstrated the prevention of LDL oxidation, in addition to reducing oxidative stress in endothelial cells thus improving the cardioprotective role. In the in vivo results, successful in hypercholesterolemia mice, the fraction was able to prevent endothelial dysfunction, but was not able to reduce the extent of atherosclerotic lesion or reduce plasma lipid levels. In addition, they show that the fraction has a variety of effects by different mechanisms of action and working in cardiovascular protection. Tufer et al. (2021) in their work, aimed to evaluate a diuretic activity of aqueous and methanolic extracts of C.
macrostachyus leaves, their findings revealed that both extracts triggered diuresis, albeit at higher doses, however, it was also concluded that the aqueous extract showed better activity, due to having phytoconstituents responsible for the diuretic action that are more soluble in water. On the other hand, the analysis of biological fluids showed that the extracts have several modes of action, thus, it was possible to conclude that the extract of the species has diuretic activity and, consequently, it can be applied in the control of hypertension. Oliveira et al. (2001) carried out tests with essential oil obtained by steam drawing distillation of Croton zehntneri leaves in mice, to evaluate the antinociceptive effect, and their results concluded that the presence of the constituents anethole and β-myrcene are responsible for the activity, and the authors concluded that the oil exhibits an antinociceptive effect at doses well below the LD50 with a value of 2.5 g/kg orally. Oliveira-Tintino et al. (2018) carried out tests with Croton campestris and proved that the presence of β-caryophyllene (15.91%) and 1.8-cineole (16.98%) in the essential oil are important for reducing edema in the evaluated model. The in vivo model assays of acute and chronic inflammation, with essential oil of C. campestris, concluded that the presence of βcaryophyllene demonstrated a significant anti-inflammatory activity, also inferring that the presence of 1,8-cineole was responsible for activity, and suggest that a mechanism of action by inhibition of cytokines occurs, in addition to describe that LD50 for oral administration was 5000 mg/kg.

Anti-inflammatory and antinociceptive activity
The extract of Croton matarensis leaves arises from obtaining extracts with supercritical CO2 (using different conditions, such as temperature and pressure variation) and was evaluated against in vivo anti-inflammatory activity. The extracts showed high levels of total phenolics and total flavonoids, while in the histopathological analysis of ischemic injury in the motor cortex of rats, the extracts showed influence on tissue reconstruction and cell density reduction, the treatment suggests a potential anti-inflammatory effect and neuroprotective, showing reduced injury in animals treated with SC-CO2 extract (Bezerra et al., 2020).
Martins et al. (2017) carried out tests with Croton rhamnifolioides, with the objective of evaluating the antiedematogenic and anti-inflammatory effect of the essential oil of the leaf of C. rhamnifolioides, their results concluded that the major constituent 1,8-cineole was responsible for and regulating the changes and release of inflammatory mediators in rodents, therefore, suggesting that the essential oil has therapeutic potential for use in the development of new agents with antiinflammatory activity. Other tests were carried out with the crude aqueous and alcoholic extracts of the bark and leaves of Croton roxburghii Balak, against enteric pathogens causing urinary tract infections, and the results concluded that the extracts of the leaf bark were not successful against Salmonella typhimurium; however, the results were promising against Staphylococcus aureus and Escherichia coli. And the study also suggests that the alcoholic extract showed better activity when compared to aqueous extract (Panda et al., 2010). Trypanosoma cruzi, with IC50 values between 1-26 μg/mL. Kundu et al. (2020) evaluated the effect of the methanol extract of Croton hookerio leaves in streptozotocin-induced diabetic rats. The results suggested a considerable increase in the blood glucose level of the test animals when compared to the control group, in addition to demonstrating that the glucose levels in animals treated with the extract at a dose of 200 mg/kg and the positive control with metformin a 200 mg/kg, a significantly reduced was observed, thus suggesting that the extract has regulatory activity on blood glucose levels in diabetic rats. These results suggest that the methanol extract showed significant activity in the oxidative inhibition and inflammation, as it was observed that the extract reduced the glucose present in the blood circulation and improve renal histological damage frame and pancreatic having potential for application to treat diabetes.

Antioxidant activity
Tests with the bark of Croton celtidifolius show that the presence of flavonoids in the crude ethanol extract and fractions (butanolic and ethyl acetate) were able to inhibit deoxyribose, albeit at low rates (1 µg/mL). Other trials analyzed promoted phenolic compounds and subfractions and concluded that these in turn also have antioxidant properties, due to their ability to donate electrons and chelate metals. However, the results also showed that the aqueous fraction showed lower ability to inhibit the antioxidant activity, the authors suggest that this is due to the lipid system used in the experiment, which was biphasic, in which one phase is aqueous and the other lipids, with therefore, compounds which possess more hydroxyl end groups exerting greater antioxidant activity in the aqueous phase. These results corroborate the results compared with the lack of activity observed against the aqueous extract on the inhibition of liver homogenate oxidation in vivo (Nardi et al., 2003). Other studies have shown that two of the clerodane-type diterpenoids, which were isolated from the dichloromethane fraction of Croton hypoleucus, crotonpene hypolein, also showed antioxidant activity by the in vitro test with the crude extract.
The results showed that the extract was able to eliminate the DPPH radical and reduce Fe +3 , mechanisms that suggest a reduction in the oxidative effect, in addition to helping to reduce the liver, thus demonstrating the potential of the genus demonstrate that the K562 cells was more sensitive than Raji cells, the authors reported that phytochemicals present in the species are responsible for this antitumor activity (Suresh et al., 2020).

Toxicity
Tests performed in male Wistar rats with volatile oil of Croton zehntneri in order to investigate systemic toxicity, observed some morphological changes in the organs, but there was no induction of structural abnormalities in the organs, and with this, the findings suggest that doses with concentrations below 250 mg/kg offer a low toxicological risk (Oliveira et al., 2001;Sousa et al., 2005). Compagnone et al. (2010) in their studies evaluated the in vitro the cytotoxicity of essential oil from leaves of C. matarensis against three different human cancer cell lines, colon adenocarcinoma, cervical carcinoma and fibroblasts, the results describe that, the CI50 assays obtained the respective values: 36.60, 83.90 and 132.73 μg/mL, these findings suggest regular cytotoxicity. Studies on toxicity with a type of C. urucurana, carried out by Silva et al. (2020) obtained as a result an increase in liver enzyme activity, a decrease in fetal body weight and an increase in proteins and cholesterol in the bloodstream, and a significant increase in heart weight, in addition to contributing to the development of fetal skeletal abnormalities. Freitas et al.
(2020) evaluated the toxicity and genotoxicity of the ethanolic extract of C. blanchetianus, its description, that the extract requires safety for oral use, but triggered some biochemical, hematological, and histological changes when administered intraperitoneally, in the case of genotoxicity, the findings describe that at all doses and times tested, no formation of micronuclei was observed, in this way, suggesting that the extract is not harmful. Cruz et al. (2020) evaluated the toxicological potential of selected essential essentials from the leaves of C.
argyrophyllus and C. tetradenius in mice, the results describe that when associated and administered intraperitoneally, they have a medium degree of toxicity, so caution is necessary, however when administered orally no toxicity was observed, therefore the authors stated that the application for use in mammals is safe, these described corroborate the good results obtained by Carvalho et al. (2016), that in their studies as the essential oil of C. tetradenius, observed that when administered in mice by orally it did not show toxic aspects, but when administered intraperitoneally it triggered clinical signs and even led to the death of animals in studies, what they described as potentially toxic.

Chemical composition
Phytochemical studies with species of the Croton genus demonstrated that in most species, it is possible to observe the presence of several secondary metabolites, such as alkaloids, terpenoids, flavonoids and other phenolic compounds. Among the constituents, terpenoids are the most widespread and most relevant to the genus (Salatino et al., 2007).
By gas chromatography, Peres et al. (1997) evaluated the methanol extract from the leaves of C. urucurana, and observed the presence of acetyl aleuritolic acid, β-sitosterol and sonderianin diterpene, and identified the presence of the steroids stigmasterol, β-sitosterol and campesterol. In phytochemical studies on the species C. macrostachyus performed with the ethanolic extract of roots showed the presence of fatty acids, β-sitosterol, stigmasterol, lupeol, betulin and cyclohexene diepoxide. While the roots were found traquiloban acid ent-19-oic acid and then traquiloban--18-oic acid; and the analysis of the shell was observed the presence of terpenoid, lupeol, betulin and crotepoxide (Kapingu et al., 2000;Tene et al., 2009). Righi et al. (2013) performed gas chromatography tests coupled with mass spectrophotometry with the ethanol extract of leaves from the C. sphaerogynus, and demonstrated that this specie is rich in terpenoids, of which triterpenoids stand out, were from an unknown compound, that has not been elucidated, however in the constituents elucidated, the presence of spathulenol, bicyclogermacrene and eugenol was observed. In this way, the diversity of chemical compounds reported for the species of the genus is shown in Figure 2, according to the species, structure, and part of the plant.  Other studies describe the presence of flavonoids in some species of the genus, the tests carried out by  describe the identification of four O-glycosylated flavonoids found in C. campestris leaves, 3-O-β-D-apiofuranosil-(1→2)-galactopyranosyl quercetin, 3-O-β-D-galactopyranosyl quercetin (hyperin), 3-O-α-L-arabinopiranosil quercetin (guaijaverin) e 3-Oα-L-rhamnopyranosyl quercetin (quercitrin). Coelho et al., (2016) describes that the leaves of the species Croton betulaster have three types of flavonoids, which are, 5,3′-di-hidroxi-3,6,7,4A′-tetramethoxyflavone (casticin), 4′-dihidroxi-3,6,7-trimethoxyflavone (penduletin) e 5-hidroxi-7,4′-dimethoxyflavone (dimethoxyflavone).
The findings of Wagner et al., (1970) describes five C-glycosylated flavonoids for the aerial parts of C. zambezicus species, in special at leaves, which are, vitexin, suponeretin, orientin, isoorientin and cicenin-2. Salatino et al. (2007) describes in their essays that isolated 3-O-α-L-rhamnopyranoside from C. draco leaves (myricitrin), this same flavonoid was described by Kostova et al. (1999) that are present in C. panamensis leaves. Maciel et al. (2000) carried out studies with Cm cashew leaves and in their results, observed the presence of kaempferol-3-4′,7-trimethyl ether (Kaempferide). The latter, in turn, was also described by Guerrero at al. (2002) in your studies with the roots of the species of C. curiosus and C.saltensis, that used the leaves to make EtOH extract, for elucidation of the compounds. González-Vázquez et al. (2006) do some studies with the hexane extract with C. ciliatoglanduliferus leaves, which as a result brought the elucidation of two flavonoids, they are ,5,4′-dihydroxy-3,7,3′-trimethoxyflavone (pachypodol) and 5hydroxy-3,7,3′,4′-tetramethoxyflavone (retusin). Other studies with the shoots of C. schiedeanus, demonstrated that they contain quercetin-3,7-dimethyl ether (Guerrero et al., 2002). In this way, the flavonoids described are shown in the Figure 3, according to the species, structure, and part of the plant.

Conclusion
The data presented in this review on Croton species reflect a compilation of knowledge about their chemical composition and biological properties already elucidated. The Croton genus is widely used by folk medicine, and as information proves some activities, such as anti-inflammatory, anti-hypertensive, antifungal, antimicrobial, antidiabetic, antioxidant, antinociceptive and antitumor. However, the results described in this article suggest that caution is needed in the use of Croton species, as some of them are toxic. In view of this, in-depth studies are needed to correlate biological activities with chemical composition.