3. Bioactivities M. alba Extracts
To date, there are a number of reported bioactivities of M. alba extracts, including tyrosinase inhibition and photoprotective activities, antimicrobial, antidiabetic, anti-inflammatory, and antioxidant activities.
3.1. Tyrosinase Inhibition and Photoprotective Activities
Tyrosinase is an enzyme that catalyzes the production of melanin. Overexpression of tyrosinase can cause various dermatologic disorders including post-inflammatory hyperpigmentation
[8]. This condition is not only aesthetically undesirable, but it may affect patients’ emotions and quality of life
[9]. It has been reported that (−)-N-formylanonaine, a purified compound isolated from
M. alba inhibits in vitro mushroom tyrosinase activity in a dose-dependent manner with an IC
50 value of 74.3 µM
[10]. This inhibition activity is comparable to an established tyrosinase inhibitor, kojic acid with a recorded IC
50 value of 69.4 µM. In addition, a molecular docking study suggests the tyrosinase inhibitory effect of (−)-N-formylanonaine may be due to its ability to chelate two copper ions in the active site of tyrosinase
[10]. In an epidermal melanocytes cell culture study, (−)-N-formylanonaine was found to inhibit human tyrosinase activity at concentration ranges of 10–200 µM. Consequently, melanin content was also found reduced in cells treated with this compound at the same concentrations with an EC
50 value of 90 µM
[10]. On the other hand, a cell culture study showed the potential of α-terpineol as a skin whitening agent. Treatment of α-terpineol (at 100 and 200 µM) was reported to reduce melanin content and tyrosinase activity in B16 cells stimulated with α-melanocyte-stimulating hormone (α-MSH)
[11]. Importantly, α-terpineol at concentrations of 100 and 200 µM did not affect B16 cell viability. In the same cell model, α-terpineol also prevented oxidative stress by reducing cellular malondialdehyde and increased cellular GSH levels. Tyrosinase inhibition activity of phenylethyl alcohol has been reported by
[12] using in vitro mushroom tyrosinase assay. This compound was isolated from
Rosa rugosa Thunb. var. plena Regal tea. Phenylethyl alcohol inhibits mushroom tyrosinase activity in a dose-dependent manner with an IC
50 value of 315 ± 13 μg/mL. However, kojic acid (positive control) showed more potent inhibitory activity with an IC
50 value of 80 ± 17 μg/mL.
Exposure to solar ultraviolet (UV) radiation on the skin leads to photoaging. This condition is characterized by the degradation of extracellular matrix (ECM) proteins which include type 1 collagen, elastin, proteoglycans, and fibronectin. This will then damage the connective tissue and reduce the elasticity of the dermis
[13]. Irradiation of UV promotes the formation of reactive oxygen species, induces the expression of the mitogen-activated (MAP) kinase signaling pathway, and upregulates the expression of matrix metalloproteinase (MMP)-1, MMP-3, and MMP-9
[13].
M. alba extract inhibits the expression of the three matrix metalloproteinases in UVB-induced activation of p-JNK and p-ERK on cultured human fibroblasts cells and consequently restores total collagen synthesis
[13].
3.2. Antimicrobial Activity
Natural products from microorganisms, plants, animals, and algae may serve as a good source of novel antimicrobial compounds
[14]. A number of phytochemical extracts from flowers (including
M. alba) or their essential oils have been reported to have potential antimicrobial activities for treating various diseases
[15][16][17].
3.2.1. Antibacterial and Anti-Fungal Activities
The antimicrobial activity of the Magnolia family may be due to the presence of various bioactive constituents extracted from different parts of the plants.
M. alba is rich in carbohydrates, alkaloids, terpenoids, flavonoids, tannins, steroids, and phenols. It has been used not only in traditional medicine but also as a potential antiseptic for the prevention and treatment of microbial infections
[18].
M. champaca seed and flower extracts were reported to inhibit the microbial growth of
Aeromonas hydrophila,
E. coli,
Edwardsiella tarda,
Flavobacterium spp.,
Klebsiella pneumonia,
Salmonella typhi,
Vibrio alginolyticus,
V. parahaemolyticus,
V. cholerae,
Pseudomonas aeruginosa,
Staphylococcus aureus,
Bacillus subtilis, and
Shigella dysenteriae [17][19][20].
M. alba and
M. champaca exhibited comparable effects on antibacterial inhibition of
S. aureus,
E. coli, and
Psedumonas aeuroginosa (
Table 1). Notably, the antimicrobial activity of leaf oil was found stronger than that of stem oil on growth inhibition of
S. aureus ATCC 13709;
E. coli ATCC 25922;
Candida albican ATCC 10231
[21]. In addition,
[22] reported the
M. alba dichloromethane leaf extract with 76.6% linalool gave a better inhibitory effect on the growth of
Psedumonas aeuroginosa,
C. albican, and
Fusarium oxysporium compared with the n-pentane flower extract (PF) with 63.2% linalool. The dichloromethane leaf extract was an efficient
C. albicans growth inhibitor, while
F. oxysporium was more susceptible to the dichloromethane flower extract
[22].
The methanol extract of
M. alba bark was reported to inhibit the growth of
C. Verruculosa, which causes leaf spot disease on rice
[23]. It was found that the antifungal activity of
M. alba essential oil was strongly correlated with linalool and caryophyllene which are known to inhibit the growth of
Aspergillus flavus [24]. In addition, the antifungal activity of
M. alba oil against the growth of
Aspergillus niger,
Aspergillus flavus,
Penicillium sp.,
Rhizopus sp.,
Fusarium sp., and
Cladosporium sp. was demonstrated through the application of the oil to the surface of bamboo paper packaging boxes
[25].
3.2.2. Antiparasitics
Anti-parasitic agents have various applications including organic or conventional livestock production systems. Domestic animals such as cattle, pigs, dogs, and cats carry harmful parasites such as
Trypanosoma cruzi [26].
T. cruzi can easily infest livestock animals and becomes an endemic that causes a devastating impact on the livestock industry worldwide. The trypanocidal constituents from the ethanol extract of the bark of
M. alba (
Table 2) showed good antiparasitic activity against
T. cruzi [27]. In addition, the pharmacological activities of −anonaine from
M. alba have been reviewed by Li and colleagues
[28] which showed that the compound gives a significant inhibitory effect against
Plasmodium falciparum that causes malaria in humans. The compound also protected red blood cells against
P. falciparum. As the compound shows low cytotoxicity in the Chinese Ovarian cell line, it may be a potential phytochemical compound for the treatment of malaria (The Pharmacological Ac.).
Table 2. Antimicrobial activities screening from different part of Michelia x alba plant.
Plant Part |
Types of Extract |
Types of Antimicrobial Assay and Pathogens Test |
References |
Antibacterial and antifungal |
Flower |
Essential oil |
Well diffusion—A. flavus |
[24][29] |
Leaves and stems |
Essential oil |
Disc diffusion—S. aureus ATCC 13709; E. coli ATCC 25922; Candida albican ATCC 10231 |
[21] |
Bark |
Crude methanol extract |
Well diffusion—Curvularia verruculosa |
[23] |
Leaf |
Essential oil extract in dichloromethane |
Disc diffusion and in vitro assay—Psedumonas aeuroginosa and C. albican; disc diffusion and in vitro assay—F. oxysporium |
[22] |
Flower |
Extract |
- |
Essential oil |
In vitro assay: A. niger, A. flavus, Penicillium sp., Rhizopus sp., Fusarium sp. and Cladosporium sp. |
[25] |
- |
Essential oil |
Agar plate of spore and mycellium of A. flavus WU 1511 |
[24] |
Flower |
Essential oil |
Disc diffusion: S. aureus and E. coli |
[30] |
Antiparasitics |
Bark |
Caryophyllene oxide, costunolide, dihydrocostunolide, parthenolide, dihydroparthenolide, 11,13-dehydrolanuginolide, santamarine, and dehydrolinalool oxide |
Trypanosoma cruzi |
[27] |
- |
Individual compound isolated from M. alba: (−)-anonaine |
Plasmodium falciparum |
[28] |
3.3. Anti-Diabetic Activity
The anti-diabetic potential of
M. alba essential oil was demonstrated through the inhibition of α-amylase, a digestive enzyme found in saliva and pancreatic juice. This enzyme digests complex carbohydrates into oligosaccharides and disaccharides. α-amylase inhibitors delay the hydrolysis of carbohydrates in the intestines
[31]. Therefore, inhibition of α-amylase may serve as a therapeutic target for the prevention and medical treatment of diabetes
[32]. The essential oil from
M. alba inhibits α-amylase activity with an IC
50 value of 0.67 mg/mL. The inhibition activity is lower than the positive control, acarbose, which showed an IC
50 value of 0.06 mg/mL. GC-MS analysis of essential oil indicated the presence of β-linalool (65.03%) as its major compound
[33]. A molecular docking study suggests the β-linalool forms hydrogen bonds with His-299 and Asp-300 residues of α-amylase with a binding energy of − 5.20 kcal/mol
[33]. On the other hand, aldose reductase is an enzyme that converts glucose into sorbitol in the presence of nicotinamide adenine dinucleotide phosphate (NADPH). Accumulation of sorbitol in the cells has been associated with the development of diabetic neuropathy. Aldose reductase inhibitor can be used as a target to reduce the concentration of sorbitol in the cells. Lee et al.
[34] reported that
M. alba flower extract dose-dependently inhibits aldose reductase activity with an IC
50 value of 1.98 µg/mL.
3.4. Anti-Inflammatory Activity
Gout is an inflammatory arthritis characterized by the accumulation of uric acid in the blood and further deposited within visceral tissues and joints. Xanthine oxidase catalyzes the oxidation of hypoxanthine to xanthine and its further conversion to uric acid. A number of plant extracts and their metabolites showed inhibition against xanthine oxidase
[35]. Leaves extract of
M. alba inhibits in vitro xanthine oxidase activity by 22.49% at a concentration of 100 µg/mL. The observed inhibition activity is higher than
Gliricidia sepium which showed 6.94% at the same concentration. However, the inhibition activity of
M. alba extract was found lower than several medicinal plants such as
Antegonon leptopus (59%),
Mimosa pudica (62.36%), and
Vitex negundo (38.4%) at 100 µg/mL
[36].
3.5. Antioxidant Activity
Oxidative stress has been recognized as one of the classical risk factors for human diseases such as cardiovascular diseases, cancers, and neurodegenerative diseases
[37]. In biological systems, macromolecules such as lipids, proteins, and nucleic acids are prone to oxidation upon exposure to free radicals. Excessive production of free radicals and a low antioxidant level collectively contribute to oxidative stress leading to a negative impact on physiological function.
In 2018, Zheng and colleagues reported antioxidant activity and phenolics profile of 65 edible flowers in China
[38]). In the study, the
M. alba flower was extracted using a mixture of acetone/water/acetic acid (70:29.5:0.5,
v/
v/
v). Its 2,2-diphenyl-1-picrylhydrazyl (DPPH) results showed that the extract recorded 58.22 µmol Trolox equivalents (TE)/g sample) on a dry weight basis, higher than several other edible flowers including
Panax pseudoginseng (15.18 µmol TE/g sample),
Prunella vulgaris (21.39 µmol TE/g sample), and
Siraitia grosvenorii (21.03 µmol TE/g sample)
[38]. In the 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) and ferric reducing antioxidant power (FRAP) assays, the extract showed 111.54 µmol TE/g of dry weight sample and 15.51 mmol of Fe2+E/100 g sample, respectively
[38]. In another study, petroleum ether extract of
M. alba flower showed DPPH free radical scavenging activity with an IC
50 value of 0.7155 mg/mL. This inhibition activity is higher than in several other aromatic plants such as
Plumeria alba and
Cananga odorata [39].