A Comprehensive Review on Chemical constituents, Pharmacological activity and Medicinal uses of Plectranthus amboinicus (Lour.) Spreng

Abstract

Plectranthus amboinicus (Lour.) Spreng, popularly known as Indian borage and country borage, is a multifaceted herb widely used in ethnomedicine. In this review, the focus is given on its phytochemistry, pharmacology, plant morphology and traditional medicinal uses. P. amboinicus contains numerous active components including the putative bioactive compounds flavonoids, phenolic acids, terpenes, and its essential oils carvacrol and thymol and has a broad range of biological activities such as antioxidant, antimicrobial, anti-in?ammatory, analgesic, anti-convulsant, anxiolytic and anticancer activities. It is used traditionally for a variety of health issues including those related to the respiratory, digestive, cutaneous, and cardiovascular system. The role of the plant in medicine is further underscored by the activity of its essential oil and extracts against pathogenic microbes and inflammatory diseases, which makes it a candidate for natural drug development. In addition, the herbal plant’s value as a nutrition source, ease of cultivation, and function as a novel food will foment its appreciation in the pharmaceutical and nutraceutical industries. While promising in terms of therapeutics, more work is needed to discover new bioactive materials, examine the drug-like toxicity, and prepare the necessary biodata for clinical safety. This review highlights the need for looking at P. amboinicus as a cheap sustainable medicine.

Keywords

Introduction

Currently, several plant-based medicines are used in public health practices around the world due to their efffectiveness, safety, and cost efficiency in dealing with diseases and promoting good health. Herbal medicine is practiced widely in folk medicine, Ayurveda, Sidda, Unani, and other traditions. The World Health Organization claims that 80% of people in the world continue relying on traditional herbal medicine because it is cost-friendly, easy to obtain, and arguably does not harm as much as modern allopathic medicine[1]. Plectranthus amboinicus (Loureiro) A herbaceous plant up to one meter long. Sprengel is known as malvariço in some regions and as Indian borage in others. It has brittle stem, oval leaves with thick apex, sharply toothed margins, and a stout petiole tipped with a pointed extremity[2]. It can be eaten fresh. However, the plant has been poorly appreciated and rather unpopular by the natives. Reports suggest it has long been used for the treatment of several common disorders, including skin infections, headaches, stomachaches, and coughs[3]. The most profound ones include phenolic acids such as rosmarinic acid, chlorogenic acid, caffeic acid, Hydroxycinnamic acid, and P-coumaric acid, flavonoids like quercetin, luteolin, apigenin and genquanine, as well as carotenoids, steroidal glycosides, alkaloids, saponins, tannins, and phytosterols among many other compounds exceeding one-hundred with these health benefits[4]. As indicated by the growing number of articles related to the bioactivities of P. amboinicustract, scientists have begun to pay close attention to this species over the past decade. The plant extract was found to be active against reproductive tract infections caused by Candida albicans, Proteus vulgaris, and Klebsiella pnumoniae and had antibacterial activity against methicillin-resistant Staphylococcus aureus using a mouse model[5]. Apart from phytocompounds such as flavonoids, cinnamic derivatives, and terpenes with anti-inflammatory, antioxidant, and anticancer activities, leaves of the plant contain essential oil with high concentrations of bioactive compounds such as carvacrol, thymol, β-caryophyllene, α-humulene, γ-terpinene, p-cymene, α-terpineol, and β-selinene[6]. Due to its tropical nature, P. amboinicus vegetatively reproduces in Indonesia, interfering with the physiological process of plants and inhibiting seed formation. Through the cutting of the stem, P. amboinicus is extremely easy to propagate naturally. Plant tissue cultures are also known as in vitro vegetative propagation[7]. Indian borage, country borge, French thyme, Indian mint, Mexican mint, Cuban oregano, soup mint, and Spanish thyme are some of the popular English names for P. amboinicus. A compound resembling forskolin and applied in hair coloring is derived from the leaf extract. It also inhibits passive cutaneous anaphylaxis to yield an important oil with anti-allergic properties. Reports say that Plectranthus species can be used to treat cancer due to their cytotoxic and anti tumor properties[8]. Since the leaves of the plant contain high levels of calcium, potassium, and iron—nutrients required for healthy bones, heart, and kidneys—and since they aid in transporting oxygen by red blood cells all over the body, they are often eaten raw or as tea and juice[5].

Figure. Plectranthus amboinicus

The taxonomical position of Plectranthus amboinicus [9]

Vernacular name:[10]

Geographical distribution

The widest geographical distribution of Plectranthus amboinicus is in the Americas, beyond the African and Asian continents [11]. It has been cultivated and spread ever since across the tropics. The species is referred to as Amboinicus because its type material was discovered in Amboina, Moluccas [1]. The geographical origin of P. ambonicus has yet to be proven, though certain botanists assume it was from the Indian subcontinent [12].

Pharmacognostical features

The fleshy herb Plectranthus amboinicus is a creeping or climbing habit. In the wild, its width and height may be more than one metre. Pale purplish flowers are in close whorls at far-apart intervals in a long, narrow raceme on a short, short-pedical stem. Flowers have a bell-shaped calyx, and the throat is smooth internally with two lips. The lower lip contains four narrow teeth, and the upper lip is thin and elliptical [13]. Soft, fleshy, simple, thick, broad, hairy, and oval, the base of the lowest leaves are loaded with numerous. It is 2.5–4 cm long, has a conspicuous petiole, acute apex, and pleasant, aromatic taste and smell. Petiole conspicuous, serrated margin. The dorsal side of the leaf is light green, and the ventral side is dark green[9].

Chemical constituents

GC-MS was utilized to find out the chemical composition of the essential oil of P. amboinicus. These are the primary ingredients which are non-polar molecules [14]. Among all the extracts that were tested, methanolic extract of P. amboinicus contained highest amounts of total flavonoids and polyphenols. HPLC analysis revealed rosmarinic acid, naringin, catechol, syringic acid, ellagic acid, and myricetin as significant phenolic compounds in the P. amboinicus extract, while GC-MS analysis found carvacrol as the primary component [15,16]. The essential oil obtained by hydrodistillation of P. amboinicus stem and leaves was found to contain 53% monoterpene hydrocarbons and a further 45% of the oxygenated monoterpenes, sesquiterpenes, and oxygenated sesquiterpenes,1–3. These constituents were carvacrol, b-caryophyllene, q-cymene, c-terpinene, a-bergamotene, a-caryophyllene, eudesma-4,11-diene, 4-terpineol, a-cubebene, and caryophyllene oxide [17]. Chlorogenic acid, vanillic acid, caffeineic acid, p-coumaric acid, ferulic acid, salicylic acid, and quercitin are some of the compounds which are examined by HPLC in methanolic extracts of Plectranthus amboinicus [15].

Pharmacological activity of P. amboinicus

Anticonvulsant activity

Phytochemical analysis and comparative anticonvulsant activity of Plectranthus amboinicus leaves, stem, and root showed the existence of carotenoids in the leaf and stem extracts and alkaloids, flavonoids, tannins, triterpenoids, and saponins in all the extracts. In MES as well as in PTZ model, the highest anticonvulsant activity was shown by the leaf extract, followed by stem and root extracts. The paper also puts forward a possibility that the activity can be due to the flavonoids, alkaloids, and saponins present in the extracts[18].

Anxiolytic activity

Based on the present research, the ethyl acetate fraction (EAF) and methanolic fraction (MF) containing alkaloids and saponins from Plectranthus amboinicus methanol extract possess anxiolytic activity[19].

Analgesic activity

Two different animal models were employed to evaluate PA's analgesic effect. Intraperitoneal injection of acetic acid causes an increase in prostaglandins such as PGE2 and PGF2α, serotonin, and histamine. The model was used extensively to screen the peripheral analgesics [20].

Antimicrobial activity

Both gram-positive and gram-negative bacteria were effectively inhibited by Bangun-bangun essential oil, or BEO. The growth of S. aureus and E. coli is prevented by the essential oil of P. amboinicus. Strong antibacterial activities were exhibited by Plectranthus amboinicus essential oil. It is very likely that the two dominant monoterpenoid compounds, camphor and carvacrol, are the reason for the antibacterial effect[21].

Respiratory disorders

In the Caribbean Islands and India, P. amboinicus is traditionally employed in the treatment of bronchitis, asthma, chronic coughs, and sore throats. Consistent with this, on guinea pigs, P. amboinicus leaves have shown positive bronchodilator activity. In Eastern Cuba, asthma is treated with essential oil from P. amboinicus aerial parts. For the treatment of asthma, decoction or juice derived from leaves and other herbs is also administered orally. Also, this decoction is employed to cure catarrhal infections, which are caused by an overabundance of mucus or thick phlegm in a body cavity or airway. The high levels of carvacrol and thymol in the plant's essential oil could be responsible for this. Great expectorants, carvacrol and thymol are employed to cure a range of respiratory ailments. Administration of a drink or bath of P. amboinicus decoction or juice is suggested as an effective remedy for bronchitis, cough, influenza, and throat infections [1].

Anticancer activity

Since each and every one of the flavonoid components in Plectranthus amboinicus (Lour.) Spreng leaves are effective antioxidants as well as anti-cancer substances, the ethanolic extract of Plectranthus amboinicus (Lour.) Strong antioxidant activity is identified in sporang leaves [22, 23].

Digestive conditions

Plectranthus amboinicus is used in treating numerous various digestive problems. Plectranthus amboinicus is commonly employed in India and Africa as a carminative and to treat indigestion, diarrhoea, and dyspepsia [11].

Medicinal uses:

This herb is useful in the management of cardiovascular, respiratory, skin, oral, urinary and digestive illnesses. The significant therapeutic activity of P. amboinicus attests to the feasibility of its employment in more cost-effective and safer herbal drug preparations compared to allopathic medicines. Nevertheless, future research may focus on the isolation and characterization of new bioactive molecules from P. amboinicus and evaluate their efficacy in the treatment of other human ailments. Additional studies are also necessary on the toxicity of the isolated compounds and human safety in the use of this plant. Therapeutic uses of P. amboinicus can also advance its functional use as a nutraceutical food[24].

CONCLUSION:       

The Plectranthus amboinicus plant has a lot of potential in modern herbal medicine due to its ethnobotanical history and impressive pharmacological profile. It is scientifically established that the plant can treat infections, respiratory problems, inflammation, and even some cancer disorders, which is beyond its traditional uses. For future drug development, the abundance of essential oils, flavonoids, and phenolic acid available in the plant serve as strong candidates. The plant's ease of cultivation and nutritional benefits further enhance its applicability in both medicinal and dietary domains. Despite its current uses, further research on the plant's bioactive components, standardiztion, formulations, along with safety assessments in clinical trials need to be conducted. Advancements in those areas will aid in making P. amboinicus further evolve from being a traditional medicine to a scientifically proven alternative herbal medicine which can greatly aid the complexesion of integrative healthcare systems and nutraceutical innovations.

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