Paeonia × suffruticosa (Moutan Peony)—A Review of the Chemical Composition, Traditional and Professional Use in Medicine, Position in Cosmetics Industries, and Biotechnological Studies

The aim of this review is to perform a systematic review of scientific papers and an in-depth analysis of the latest research related to Paeonia × suffruticosa Andrews as a valuable plant species, important in pharmacy and cosmetology. P. × suffruticosa bark root-Moutan cortex is a medicinal raw material formerly known from traditional Chinese medicine (TCM) but less common in official European medicine. It was introduced for the first time in the European Pharmacopoeia Supplement 9.4 in 2018. In this work, the numerous possible applications of this raw material were depicted based on modern professional pharmacological studies documenting its very valuable medicinal values, including antioxidant, cytoprotective, anti-cancer, anti-inflammatory, cardioprotective, anti-atherosclerotic, anti-diabetic and hepatoprotective activities. The scientific studies indicated that the profile of raw material activity is mainly due to paeonol, paeoniflorin and 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose. Moreover, the significance of this plant (its different organs) in the production of cosmetics was underlined. P. × suffruticosa finds increasing application in cosmetology due to research on its chronic dermatitis, anti-aging and brightening effects. Furthermore, some biotechnological research has been described aimed at developing effective in vitro micropropagation protocols for P. × suffruticosa.


Paeonia Genus and Paeonia lactiflora and Paeonia veitchii as Known Medicinal Plants-General Characteristic
The classification of the genus Paeonia (Paeoniaceae) is complex from a taxonomic point of view. The species are divided according to three sections: Moutan DC., Paeon DC. and Onaepia Lindley [1,2]. The section on Moutan DC. contains the evolutionarily older shrub peonies. The Moutan section has two subsections: subsect. Vagintae and subsect. Delavayanae including peony species, such as P. cathayana, P. decomposita, P. jishanensis, P. ostii, P. qiui, P. rockii, P. rotundiloba, P. delavayi, P. ludlowii and P. suffruticosa [1,3]. Paeon DC. is an extensive section consisting of 26 varieties of herbaceous plants with fleshy leaves with deep indentations. Characteristic species here include P. lactiflora and P. veitchii [1]. In the section Onaepia Lindley, there are several species of peonies with grassy leaves, including P. brownii and P. californica [1].
The Latin name of the genus, 'Paeonia', is derived from Greek legend about Paeon and Pluto. Paeon was a disciple of Aesculapius, the Greek god of medicine. According to the legend, Paeon used a peony concoction to heal Pluto, who had been wounded in the

Antioxidant Effect
Phenolic compounds found in Moutan cortex are mainly responsible for the antioxidant activity of the raw material.
Ethanolic extract of Moutan cortex at a concentration of 1 mg/mL reduces the production of reactive oxygen species (ROS) and oxidative stress-induced cytotoxicity in PC12 cells (rat adrenal pheochromocytoma cells) by enhancing the expression of genes for, among others, catechol-O-methyltransferase and hemoxygenase, which are involved in the regulation of cell cycle and free radical production [45].
The antioxidant effect was also confirmed in studies on mice exposed to cigarette smoke for 4 weeks, which caused inflammatory infiltration of the lungs, increased permeability of pulmonary vessels and increased levels of chemokines, cytokines and 4hydroxynonenal (a biomarker of oxidative stress) in the lungs. Chronic treatment with peonol suppressed the aforementioned symptoms. In addition, extended studies on human bronchial epithelial cells showed that paeonol treatment reduced extracellular and intracellular ROS levels, inhibited mitogen-activated kinase (MAPK/NF-κB) signaling and reduced interleukin-8 (IL-8) levels induced by cigarette smoke extract [56].
In another study, a beneficial combined effect of paeonol (at a dose of 80 mg/kg) and 3-(3,4-dihydroxyphenyl)-2-hydroxypropionic acid (danshensu, the main component of Salviae milthiorrhizae radix at a dose of 160 mg/kg) was demonstrated in cases of isoproterenolinduced rat myocardial infarction (85 mg/kg). The authors of the study concluded that the mechanism of this effect may be related to the enhancement of antioxidant activity through activation of Nrf2 transcription factor signaling that controls the expression of genes encoding enzymes and cytoprotective proteins [64] (Table 3).

Cytoprotective Effect
Scientific studies prove the cytoprotective effect of paeoniflorin isolated from the Moutan cortex. Paeoniflorin (50-200 µg/mL) protected thymocytes ("pre-T lymphocytes") from 60 Co radiation-induced oxidative damage [38]. Another study showed that peoniflorin protected human cell lines (EA.hy926) from gamma radiation-induced oxidative damage through the Nrf2/HO transcription factor pathway [39]. In addition, some studies also suggest that paeoniflorin protects retinal pigment epithelial cells from oxidative stress by reducing ROS production and inhibiting activation of the caspase-3 pathway [40].

Anti-Inflammatory Effect
Studies conducted both in vitro and in vivo on the anti-inflammatory activity of Moutan cortex indicated that two compounds-paeonol and paeoniflorin-are mainly responsible for this effect.
Studies conducted with Moutan cortex extracts at concentrations of 0.1 and 0.3 mg/mL on regulatory mechanisms of cytokine and nitric oxide production, involved in immune activity of mouse macrophage/monocyte RAW264.7 cells, showed inhibition of nitric oxide synthase (iNOS) and inducible cyclooxygenase (COX-2) expression by suppressing phosphorylation of the inhibitory protein (I-κBα) transcription factor NF-κB [20].
Another study focused on gene expression changes in cultures of human gingival fibroblasts stimulated by lipopolysaccharides (LPS). The results suggested that a crude extract containing paeonol and paeoniflorin blocked the induction of inflammation by comprehensively inhibiting the activation of multiple genes associated with the formation of inflammation [65].
Treatment with paeonol significantly improved the survival rate and mean arterial pressure (MAP) and attenuated the pathological damage to the lung tissue in acute lung injury rats. Western blotting revealed that paeonol also inhibited the total expression of HMGB1, NF-κB P65 and TNF-α in the lung tissue of acute lung injury rats. Moreover, paeonol increased the expression of HMGB1 in the nucleus, inhibited the production of HMGB1 in the cytoplasm and decreased the expression of P65 both in the nucleus and cytoplasm of lung tissue cells in LPS-induced acute lung injury rats. These findings indicate that paeonol may be a potential treatment for acute lung injury through its repression of the HMGB1-NF-κB P65 signaling pathway [35].
Examination of paeoniflorin on the activity of M1 pro-inflammatory and M2 antiinflammatory macrophages showed that the compound can suppress the activity of M1 cells while increasing the function of M2 cells. This action can be used to treat autoimmune and autoinflammatory diseases [36].

Anticancer Effect
Many experiments on the anticancer properties of the raw material have been based on studies of the isolated compounds, paeonol and paeoniflorin. It was demonstrated that paeonol reduces paclitaxel resistance in human breast cancer cells by regulating the expression of transgelin 2 [42] and also exerts an anti-cancer effect on colon cancer cells by suppressing prostaglandin (PGE-2) synthesis and COX-2 expression. In addition, paeonol inhibits metastasis of melanoma [43] and chondrosarcoma [44] and, at doses of 150 and 300 mg/kg, induces apoptosis of EMT6 breast cancer cells [46] at concentrations (7.81-250 mg/L) of human HepG2 liver cancer cells [47] and at doses of 100, 200 or 400 mg/kg/day of HepA cells in a mouse model [48].
In studies on mouse forestomach carcinoma (MFC) cell lines and on SGC-7901 human gastric cancer cells, paeonol was shown to cause dose-dependent inhibition of cell proliferation and induction of apoptosis. Cell cycle analysis showed reduced cell proliferation in G/G1 phase, with arrest in S phase. In MFC and SGC-790 cells, paeonol significantly decreased the expression of proteins that regulate the release of cytochrome c from mitochondria (Bcl-2) and increased the expression of apoptosis-accelerating protein (Bax) in a concentration-dependent manner. Administration of paeonol to mice with an MFC tumor significantly reduced tumor growth and caused its regression [49].
Studies demonstrated that paeoniflorin inhibits the proliferation and invasion of breast cancer cells by suppressing the signaling pathway for the gene encoding the Notch-1 single-pass trans-membrane receptor [109] and inhibits the macrophage-dependent metastasis of lung cancer [50]. In addition, paeoniflorin at concentrations of 10 and 20 µM inhibits proliferation and induces apoptosis of human glioma cells through up-regulation of microRNA-16 and down-regulation of metalloproteinase-9 [51].
Scientific studies further showed that Moutan cortex extracts show greater selectivity in inhibiting growth against bladder cancer cells than mitomycin C, doxorubicin or cisplatin. The raw material also reduced the expression of angiogenesis-stimulating factors, including vascular endothelial growth factor (VEGF) [53].
Aqueous extracts of P. × suffruticosa were tested for action on pancreatic cancer cell line PANC1 and in vivo in mouse xenograft tumors. The extracts induced stress on endoplasmic reticulum (ER)-related proteostasis and affected mitochondrial membrane potential to increase autophagosome numbers and block their degradation, followed by autophagy induction and, finally, cell apoptosis. Nevertheless, oral administration of P. × suffruticosa aqueous extracts, alone or in combination with gemcitabine in mice, delayed tumor growth in a xenograft model without affecting body weight [54].
Another study demonstrated that paeonol can exert antitumor effects on hepatocellular carcinoma (HCC) cells by targeting survival via the COX-2/PGE2 signaling pathway. Peonol significantly inhibited the proliferation of human liver cancer cell line (HepG2) and human hepatocarcinoma cell line (SMMC-7721) and induced apoptosis, concomitant with the down-regulation of survival. The levels of COX-2 and PGE2 were also reduced by paeonol [55] (Table 3).

Cardioprotective and Anti-Atherosclerotic Effects
Scientific studies of isolated compounds present in both Paeoniae alba radix and Moutan cortex for their anti-aggregation and anti-coagulation properties showed that paeonol, paeoniflorin, benzoylpaeoniflorin and benzoyloxypaeoniflorin are the main compounds that together can contribute to improving blood circulation. These compounds had an inhibitory effect on thrombocyte aggregation and blood coagulation. In addition, it is possible that other compounds in the raw materials, i.e., methyl gallate, (+)-catechin, paeoniflorigenone, galloylpaeoniflorin and daucosterol may also be involved in improving circulation [21].
Another study showed that Moutan cortex extract administered at a dose of 1.98 g/kg for 14 days exerts a protective effect in a rat model of ischemia and reperfusion [78].
Studies of paeoniflorin administered at doses of 5, 10 and 20 mg/kg confirmed its ability to alleviate acute myocardial infarction in rats by inhibiting inflammatory processes and nitric oxide synthase (iNOS) signaling pathways [79]. It was also demonstrated that paeoniflorin reduces vascular damage and the expression of E-selectin and the intercellular adhesion molecule (ICAM-1) in a mouse model of cutaneous Arthus reaction [80]. Paeonol and paeoniflorin enhance thrombus recanalization by inducing endothelial growth factor-165 [81] and up-regulating urokinase-type plasminogen activator, respectively [82]. In both cases, the mechanism of action was related to the mitogen-activated kinase (MAPK) signaling pathway.
It was also confirmed that paeonol prevents the development of atherosclerosis by inhibiting monocyte adhesion, induced by the oxidized form of low-density lipoprotein (LDL), to the vascular endothelium through inhibition of the mitogen-activated kinase (MAPK) signaling pathway [83].
Studies have shown that the paeoniflorin bioactive compound from P. × suffruticosa prevented arterial thrombosis in vivo from the dose of 10 mg/kg without prolonging bleeding time or blood clotting time in rats [84] (Table 3).

Antidiabetic Effect
In in vitro studies conducted on four models (intestinal brush border epithelial cells-BBMV, cells of the H4IIE (rat hepatoma) line, human fibroblast cells-Hs68 and mouse adipocytes 3T3-L1), it was shown that Moutan cortex extract and its main component, paeonol, have antidiabetic effects by inhibiting glucose uptake by intestinal brush border membrane vesicles (BBMV) and increasing glucose uptake in human skin fibroblast cells (Hs68) and mouse adipocytes (3T3-L1). Paeonol (at doses of 200 and 400 mg/kg) was also shown to improve glucose tolerance in an in vivo model [85].
In a study of encephalopathy in rats with streptozocin-induced diabetes, a significant decrease in receptor expression for glycation products and NF-κB was noted in the hippocampus and brain cortical neurons after treatment with paeonol (at doses of 50 and 100 mg/kg). In addition, peonol significantly increased glutathione content and noticeably decreased nitric oxide synthase (iNOS) activity in hippocampal tissue [70]. In another study conducted on rats with streptozocin-induced diabetes, paeoniflorin (at doses of 5, 10 or 20 mg/kg) was shown to have a preventive effect against the onset of nephropathy [71].
Subsequent studies in rats with streptozocin-induced diabetes and Freud's complete adjuvant showed that polysaccharide-2b present in Moutan cortex could significantly delay the onset and alleviate the degree of lens opacification in diabetic cataracts. Compared to the model group, the groups treated with polysaccharide-2b had reduced levels of malonylaldehyde (MDA), and, in the groups treated with its medium and high doses, reduced levels of glutathione peroxidase, superoxide dismutase and catalase were observed, as well as increased Na+/K+ ATP-ase activity. These results indicate a positive relationship between the dose of polysaccharide-2b and its effect [34].
Palbinone and certain triterpenoids isolated from Moutan cortex stimulated glucose uptake and glycogen synthesis via the AMPK pathway in a dose-dependent manner in human insulin-resistant HepG2 cells. These compounds may have significant potential in alleviating metabolic disorders associated with diabetic complaints [72] (Table 3).
In studies conducted on nerve cell cultures, paeonol at concentrations of 12.5, 25 and 50 µmol/L was shown to protect rat neurons from oxygen and glucose deficiency-induced damage. As a result, it reduces morphological damage to cells and prolongs their life span. This effect may be related to inhibition of N-methyl-D-aspartate (NMDA) receptor binding capacity and reduction in intracellular calcium ion concentration [58]. Paeonol was also confirmed to suppress LPS-induced neuroinflammatory responses through suppression of the NF-κB pathway and mitogen-activated kinase (MAPK) [59]. In studies conducted on microglia cells, paeonol significantly inhibited the release of nitric oxide (NO) and the expression of iNOS and COX-2. Paeonol treatment also reduced ROS production and inhibited excessive ATP-induced cell migration. The anti-neuroinflammatory effect of paeonol was also found to be regulated by AMPK-α kinase and glycogen synthase kinase 3 α/β (GSK 3α/β) [60].
In addition, the protective properties of paeoniflorin at doses of 5 mg/kg administered twice daily for 14 days against ischemic brain injury in rats were confirmed by inhibiting the MAPKs/NF-κB-dependent inflammatory response [61]. It was also demonstrated that 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose can protect neuronal cells from oxidative stress by inducing the expression of the hemooxygenase-1 gene [62].
Additionally, resveratrol oligomers: resveratrol trimers-suffruticosol A, suffruticosol B, suffruticosol C, trans-suffruticosol D, trans-gnetin H and resveratrol dimer-trans-ε-viniferin, found in the seed coat extracts of P. × suffruticosa, had an effect on cholinesterase and the reduction in cytotoxicity induced by oxygen and glucose reoxygenation/reoxygenation (OGD/R) in PC12 cells (cell line that was derived from a transplantable rat pheochromocytoma) and on scopolamine-induced cognitive deficits in mice. The seed coat extracts of P. × suffruticosa display good inhibition of acetylcholinesterase and butyrylcholinesterase activities and significantly increase the viability of normal and OGD/R-injured PC12 cells. The seed coat extracts of P. × suffruticosa improve the cognitive performance of scopolaminetreated mice in behavioral tests. Furthermore, the seed coat extracts of P. × suffruticosa increase acetylcholinesterase, choline acetyltransferase, superoxide dismutase (SOD) and catalase (CAT) activities and acetylcholine, glutathione GSH and iterleukin-4 (IL-4) levels and decreases interleukin-1β (IL-1β), interleukin-6 (IL-6) and TNF-α levels in the model animals [63] (Table 3).

Effects in Neurodegenerative Diseases
Studies demonstrated that paeonol treatment can protect against many of the biochemical, morphological and behavioral changes resulting from amyloid-β administration in a rat model of Alzheimer's disease. The results suggest that paeonol is a potential therapeutic agent in slowing down the pathogenic processes associated with the disease [22]. A study conducted on ICR mice (albino mice) in a D-galactose assay injected subcutaneously for 60 days at a dose of 50 mg/kg/day showed that paeonol at 50 and 100 mg/kg, together with D-galactose, increased acetylcholine and glutathione levels, restored superoxide dismutase activity and Na + /K + -ATPase levels, and decreased MDA levels and cholinesterase activity. In addition, paeonol alleviated neuronal damage in both the hippocampus and temporal cortex [110]. It was also confirmed that 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose inhibits the formation and destabilizes the pre-formation of amyloid-β fibrils in in vitro and in vivo models [111] (Table 3).

Hepatoprotective Effect
In in vivo studies, Moutan cortex extract was proven to have a protective effect against liver damage from paracetamol. The extract reduced glutathione deficiency and cytochrome P450 2E1 activity and protected against the destruction of hepatic DNA [73].
In another experiment, the effect of paeonol on model alcoholic liver damage in mice was studied. Paeonol treatment significantly reduced serum aminotransferase levels, liver cell damage, steatosis and inflammatory cell infiltration. In addition, paeonol significantly reduced hepatic mRNA expression of lipogenic genes and serum and tissue levels of inflammatory cytokines, tissue lipid peroxidation and neutrophil infiltration and inhibited hepatocyte apoptosis [74]. In addition, paeonol was shown to attenuate epirubicin-induced hepatotoxicity by inhibiting the PI3K/Akt/NF-κB pathway [75].
Paeoniflorin (at a dose of 50 mg/kg) injected into the tail vein in a mouse model protected against concanavalin A-induced liver inflammation by inhibiting certain proinflammatory cytokines, i.e., TNF-α, IL-6 and IFN-γ and down-regulating the NF-κB pathway [76]. Another study showed that paeoniflorin attenuated liver fibrosis by inhibiting hypoxia-inducible factor-1α, in part through the m-TOR-dependent pathway [77] ( Table 3).

Anti-Allergic Effect
The anti-allergic effect of the ethanol extract of Moutan cortex was evaluated in some animal models. The raw material extract (at 30 and 100 mg/kg, i.p.) dose-dependently inhibited systemic anaphylactic shock induced by compound 48/80 (a polymer that increases histamine release) in mice. It also dose-dependently inhibited the scratching reflex induced by compound 48/80 or histamine at a dose of 100 mg/kg b.w. Increased vascular permeability induced by compound 48/80 or histamine was also inhibited by Moutan cortex extract. In addition, in vitro, the raw material reduced histamine release from rat peritoneal cell mast cells. Aiming to test the active component of the crude extract, it was suspended in water and extracted with ethyl acetate. Fractions insoluble in acetone extract (A) and soluble in it (B) were obtained. The effect of extract (B) was stronger than that of extract (A) in inhibiting histamine release. This study indicates that the raw material may be useful in alleviating symptoms of atopic dermatitis and other allergy-related diseases [112].
In vitro and in vivo studies showed that the ethanolic extract of Moutan cortex does not cause cytotoxicity in human mast cells. The ethanolic extract of the raw material (200 mg/kg) significantly inhibited the passive cutaneous anaphylactic reaction in vivo and inhibited the histamine release induced by compound 48/80 from rat peritoneal mast cells [113] (Table 3).

Antibacterial and Antifungal Effects
P. × suffruticosa buds extract showed the most efficient antibacterial effect against Staphylococcus aureus and E. coli, for which the minimum inhibition concentration (MIC) and minimum bactericide concentration (MBC) both were 1.56 mg/mL and 6.25 mg/mL, respectively [32,115].
Studies have shown that Moutan cortex has antifungal activity against Candida glabrata. The compound responsible for the above activity may be 1,2,3,4,6-penta-O-galloyl-β-Dglucopyranose, due to its cell wall degradation inducing activity [116] (Table 3). Table 3. Directions and general mechanisms confirmed by scientific research of biological activity of Paeonia × suffruticosa.

Anticancer activity
Reduction resistance to paclitaxel in human breast cancer cells by regulating the expression of transgelin 2 (paeonol) [42] Induction of an anti-tumor effect on colon cancer cells by suppressing prostaglandin synthesis (PGE-2) and expression of COX-2 (paeonol) [43] Inhibition of the metastasis of melanoma and chondrosarcoma (paeonol) [44] Induction of apoptosis of EMT6 breast cancer cells, HepG2 human liver cancer cells and HepA cells in a mouse model (paeonol) [46,48] Inhibition of cell proliferation and induction of apoptosis on mouse gastric cancer cell lines (MFC) and on human gastric tumor cells SGC-7901 (paeonol) [49] Decreases the expression of proteins regulating the release of cytochrome c from mitochondria (Bcl-2) and increased the expression of the apoptosis accelerating protein (Bax) in MFC and SGC-7901 (paeonol) [49] Cells' suppression of the signaling pathway for the gene encoding the single-pass Notch-1 transmembrane receptor in breast cancer cells (paeoniflorin) [50] Inhibition of macrophage-dependent metastasis of lung cancer (paeoniflorin) [50] Inhibition of proliferation and induction of apoptosis of human glioblastoma cells by up-regulation of microRNA-16 and down-regulation of metalloproteinase-9 (paeoniflorin) [51] Reduction in proliferation on human SK-HEP-1 hepatocellular carcinoma cells (1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose) [52] Inhibition of the growth of bladder cancer cells (extract of Moutan cortex) [53] Induction stress on endoplasmic reticulum (ER)-related proteostasis and affected mitochondrial membrane potential to increase autophagosome numbers and block their degradation (aqueous extracts of Moutan cortex) [54] Inhibition of the proliferation of human liver cancer cell line (HepG2) and human hepatocarcinoma cell line (SMMC-7721) and induction apoptosis, concomitant with the down-regulation of survivin (paeonol) [55] Cardioprotective and anti-atherosclerotic activity Inhibition of thrombocyte aggregation and blood coagulation (paeonol, paeoniflorin, benzoylpaeoniflorin and benzoyloxypaeoniflorin) [21] Protective effect in the rat model of ischemia and reperfusion (extract of Moutan cortex) [78] Inhibition of inflammatory processes and signaling pathways of iNOS (paeoniflorin) [79] Reduction in vascular damage and the expression of E-selectin and intercellular adhesion molecule (ICAM-1) in a mouse model of the skin Arthus reaction (paeoniflorin) [80] Increases thrombus recanalization by inducing endothelial growth factor-165 and up-regulating urokinase plasminogen activator (paeonol and paeoniflorin) [81,82] Inhibition of the adhesion of monocytes, induced by the oxidized form of LDL, to the vascular endothelium by inhibiting the mitogen-activated kinase (MAPK) signaling pathway (paeonol) [83] Prevention arterial thrombosis (paeoniflorin) [84] Antidiabetic activity Inhibition of glucose uptake by intestinal brush border membrane vesicles (BBMV) and increased glucose uptake in human skin fibroblasts (Hs68) and Mouse adipocytes (3T3-L1) (extract of Moutan cortex) [85] improved glucose tolerance (paeonol) [85] Decrease in receptor expression for glycation products and NF-κB in the hippocampus and cortical neurons of the brain (paeonol) [70] Increases the content of glutathione and noticeably reduces the activity of iNOS in the tissue of the hippocampus (paeonol) [71] Delays the onset and alleviates the degree of lens opacities in diabetic cataracts (polysaccharide-2b present Moutan cortex) [34] Stimulation of human insulin-resistant HepG2 cells glucose uptake and glycogen synthesis via the AMPK pathway (palbinon and some triterpenoids isolated from Moutan cortex) [72]

Applications in Cosmetology
Moutan cortex extract also has scientifically proven cosmetic effects, such as antioxidant, anti-aging and skin brightening effects [86,87]. In studies on B16 cells used to study skin can-cer, the extracts were shown to inhibit tyrosinase activity and 3,4-dihydroxyphenylalanine (DOPA), which contributes to the reduction in melanin content in cells [86]. Additionally, kinetic analyses revealed that the ethanol Moutan cortex extract and paeonol are noncompetitive tyrosinase inhibitors. The cellular melanin content and L-DOPA oxidation assays demonstrated that the ethanol Moutan cortex extract was an appropriate alternative whitening agent to paeonol and arbutin in ultraviolet-induced A2058 human melanoma cells. The ethanol Moutan cortex extract was also confirmed as a promising ingredient in sun protection and skin whitening cosmetics [87]. In vitro, P. × suffruticosa root extract and paeonol significantly inhibited UVB-induced phosphorylation of mitogen-activated protein kinase and activator protein 1 in keratinocytes, which consequently led to degradation of procollagen type I. In vivo, topical application of P. × suffruticosa root extract and paeonol attenuated UVB-induced matrix metalloproteinase-1 production and promoted procollagen type I in hairless mice [117]. Recent reports revealed paeonol from P. × suffruticosa exhibited good effects on chronic dermatitis, such as atopic dermatitis (AD) and psoriasis. One study analyzed the effects of paeonol on a mouse model of dry skin treated with acetone-etherwater (AEW). The results showed impressive activities in reducing scratching behavior and skin inflammation. The studies indicated that paeonol can ameliorate AEW-induced inflammatory response and itching behavior and reduce the expression of spinal astrocyte activity-dependent genes induced by AEW, reducing the expression of spinal astrocyte activity-dependent genes induced by AEW [88].
According to the CosIng (Cosmetic Ingredient Database) [118], in addition to extracts from the root and bark of P. × suffruticosa, it is also possible to use extracts from stems, leaves, flowers, from the whole plant, as well as from the biomass of callus cultures in the production of cosmetics in the countries of the European Union (Table 4) [118]. In cosmetics, hydrolates from flowers, roots and seed oil have also found application. These raw materials can be found mainly in facial skin care cosmetics with anti-aging, antioxidant, brightening and nourishing properties. In addition to the above-mentioned properties, hydrolats also give cosmetics a pleasant fragrance. Additionally, the P. × suffruticosa root is found in the filtrates of products obtained from the fermentation of the roots of various plant species by bacteria: Acetobacter, Lactobacillus and Leuconostoc and by fungi: Aspergillus, Monascus and Saccharomyces (Table 4). Paeonia suffruticosa root extract is most commonly used in cosmetic products. It is found in Korean (e.g., A'pieu, Holika Holika), French (e.g., L'Oreal, Yves Saint Laurent, Lancôme), Polish (e.g., Dermofuture) and American (e.g., Estée Lauder) cosmetics.  The filtrate of the product obtained by the fermentation of the bark of Cudrania tricuspidata, and Paeonia × suffruticosa; the fruits of Lycium chinense; the kernels of Prunus armeniaca (apricot); the leaves of Artemisia capillaris; the roots of Angelica dahurica, and Scutellaria baicalensis; the seeds of Glycine soja (soybean); the whole plants, Houttuynia cordata, and Viscum album (mistletoe); and the fungus, Poria cocos, by the microorganism Lactobacillus.

Skin Conditioning
Monascus/Paeonia × suffruticosa flower/rice bran ferment filtrate The filtrate of the product obtained by the fermentation of the flowers of Paeonia × suffruticosa and the bran of Oryza sativa (rice) by the microorganism, Monascus.

Skin conditioning
Saccharomyces/Camellia japonica flower/Castanea crenata shell/Diospyros kaki leaf/Paeonia × suffruticosa root/Rhus javanica/Sanguisorba officinalis root extract ferment filtrate The filtrate of the product obtained by the fermentation of Camellia japonica flower extract, Castanea crenata shell extract, Diospyros kaki leaf extract, Paeonia × suffruticosa root extract, Rhus javanica extract and Sanguisorba officinalis root extract by the microorganism, Saccharomyces.

Skin conditioning
Saccharomyces/Cyperus rotundus root/Magnolia obovata bark/Paeonia × suffruticosa root/Peach kernel ferment extract filtrate The filtrate of the extract of the product obtained by the fermentation of the roots of Cyperus rotundus and Paeonia × suffruticosa, the bark of Magnolia obovata, and the kernel of Prunus persica (peach) by the microorganism, Saccharomyces.

Paeonia × suffruticosa-Toxicity
Moutan cortex is a safe raw material. There are no studies confirming its toxic effect. Benzoic acid present in the extracts is considered a harmful component, but in this species, it is present at low levels [119]. Attention should be paid to the ease of contamination of the raw material with heavy metals familiar to soil, irrigation waters, atmospheric dust, car and industrial exhaust fumes, as well as pesticides and fertilizers [120]. Moutan cortex can become contaminated with exogenous substances such as heavy metals, pesticide residues or excessive sulfur content from sulfur fumigation. Therefore, the determination of trace elements in Moutan cortex is essential to ensure the high quality of the raw material. Due to these reasons, the places where this species is grown are important [121][122][123].

Paeonia × suffruticosa-Pant Biotechnological Studies
Increasingly, the species P. × suffruticosa is becoming the subject of biotechnology research due to breeding problems such as severe browning, difficulty in differentiation and rooting, and low regeneration efficiency. Establishing an efficient regeneration system is considered to be an important goal among peony researchers.
The first research on P. × suffruticosa in vitro cultures was carried out in 1977 by Gildow and Mitchell [124]. Tissue cultures of P. × suffruticosa were established using explants of etiolated stems. Callus formation was induced on agar-solidified Schenk and Hildebrandt medium (SH) containing the plant growth regulators 2,4-dichlorophenoxyacetic acid (2,4-D)-0.2 mg/L and kinetin (KIN)-0.1 mg/L. Growth was tested on a range of liquid media: SH/2, SH, SH × 2 and SH-M, containing 1250, 2500, 5000 and 2500 mg/L potassium nitrate. The SH-M medium, additionally, contained 1650 mg/L ammonium nitrate. Growth measured as increased fresh weight was best on the SH/2, SH and SH-M media and was curtailed on the SH × 2 medium [124].
Zhu et al. recently described the callus induction, shoot organogenesis and plant regeneration using young P. × suffruticosa leaves as explants. Various media containing diverse plant growth regulators were assessed for their potency in propagation. After exposure of dark-adapted leaf discs to 30 µmol/m 2 s of light, inoculation in a Murashige and Skoog (MS) medium containing 0.2 mg/L 2,4-D, 0.2 mg/L 1-naphthaleneacetic acid (NAA) and 3.0 mg/L thidiazuron (TDZ) resulted in the highest callus induction rate, with values reaching up to 87.8%. The studies also documented MS with 0.2 mg/L NAA, 2.0 mg/L, 6-benzyladenine (6-BA) and 2.0 mg/L KIN to be the optimal medium for further callus proliferation under light. Inoculation on MS containing 2.0 mg/L 6-BA, 0.2 mg/L NAA and 0.3 mg/L TDZ medium allowed callus cultures to differentiate into adventitious shoots, whereas a similar rate of root formation was detected when 1/2 MS containing 0.1 mg/L NAA, 0.05 mg/L 3-indolebutyric acid (IBA) and 30 g/L sucrose medium was used [125].
Protocol for high-frequency callus induction and establishment of P. × suffruticosa was described by Chen et al. [126]. Cultures were started from flower petals as explants. MS medium supplemented with 2.0 mg/L 2,4-D, 1.5 mg/L 6-BA and 0.3 mg/L NAA was identified as the best medium for callus induction, achieving an induction rate of up to 98.52%. The highest P. × suffruticosa proliferation rate (234%) was achieved on MS medium supplemented with 0.2 mg/L NAA and 3.0 mg/L 6-BA. The highest callus differentiation rate (34.81%) was achieved on MS supplemented with 2.0 mg/L 6-BA and 0.5 mg/L zeatin (Zea). The highest rooting rate was 23.33% when using 1/2 MS supplemented with 0.1 mg/L NAA and 0.05 mg/L IBA [126].

Conclusions
Paeonia × suffruticosa root bark, under the name of Moutan cortex, was introduced for official medicinal use in European Union countries by Supplement 9.4 to the European Pharmacopoeia in 2018 [23]. This plant has long been known and used in TCM. According to the indications of TCM, the raw material has an antipyretic effect, regulates hormonal cycles in women, improves blood circulation, reduces swelling and accelerates the treatment of ulcers. Contemporary professional pharmacological research of this raw material has proven numerous valuable directions of its activity, e.g., antioxidant, cytoprotective, anti-cancer, immunomodulating, anti-inflammatory, cardioprotective, anti-atherosclerotic, anti-diabetic, hepatoprotective as well as antimicrobial properties. Moreover, the raw material shows neuroprotective activity and can be used in neurodegenerative diseases. Mainly two compounds present in the raw material have been indicated as responsible for this wide range of activity directions-paeonol (phenolic compound) and paeoniflorin (monoterpenoid glycoside), and, partly, also 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose. The roots, bark of the roots and other organs of P. × suffruticosa, hydrolates and seed oil, as well as callus cultures, can be used in accordance with the CosIng base in the European Union countries in the production of cosmetics.
There has been some biotechnological research aimed at developing effective in vitro micropropagation protocols of P. × suffruticosa.