Recommended Medicinal Plants as Source of Natural Products: A Review

ABSTRACT

Natural product is one of the sources of drugs in pharmaceutical industry, and one of the notable origin of natural product is the medicinal plants. Medicinal plants tend to treat some certain diseases and could be a source for potential drugs. The Department of Health of the Philippines approved 10 medicinal plants namely Allium sativum (Garlic/Bawang), Blumea balsamifera (Nagal camphor/sambong), Cassia alata (Ringworm bush/akapulko), Clinopodium douglasii (Mint/yerba Buena), Ehretia microphylla (Scorpion bush/Tsaang Gubat), Momordica charantia (Bitter Melon/Ampalaya), Peperomia pellucida (Silver bush/ulasimang Bato), Psidium guajava (Guava/Bayabas), Quisqualis indica (Rangoon creeper/niyug-niyogan), and Vitex negundo (Five-leaved Chaste Tree/lagundi). The review was conducted to show that these medicinal plants are capable in treating infections and some diseases. It was found that Allium sativum for the treatmet of wounds, hypertension and tootache; Blumea balsimifera is effective in diuretic treatment for hypertension; Cassia alata for the treatment of scabies, fungal infection, athlete’s foot, tinea flava, ringworm; Clinopodium douglasii for the treatment of muscle pain, arthritis, rheumatism, cough, headache; Ehretia microphylla for the treatment of diarrhea and stomachache; Momordica charantia for the treatment of diabetes mellitus; Peperomia pellucida for the treatment of gout and rheumatism; Psidium guajava for the treatment of wounds and diarrhea; Quisqualis indica for anti-helmintic medicine; and Vitex negundo for the treatment of cough, asthma, and fever. In conclusion, these 10 medicinal plants have natural products that can be used as source for potential drugs. However, there are still many species of ethnobotanical plants that are not yet investigated thoroughly and might be a source for potential drugs. Therefore, more investigations should be done in other species of plant, most especially for the plants with practical used.

1. Introduction

Ancient medical knowledge has been introduced to us since the dawn of historic times, preserved and transmitted in every nook and corner of this civilized world. Almost all the ancient invention in drug discovery, came from the herbal and natural field ^[1].

Many important medicines are natural products or derived from natural products. More than one third (39.1%) of all Food and Drug Administration (FDA) approved drugs are of natural origin, and 48.6% of all cancer drugs registered from the 1940s until today are either natural products or derivatives. Natural products are important sources in the drug discovery process. The presence of more than 200,000 natural metabolites presenting various bioactive properties demonstrates the importance of natural products in new drugs discovery ^[2].

One of the notable sources of natural products are the medicinal plants ^[3]. Since ancient times up to this day, medicinal plants have been used for treatment in most countries ^[4]. The development of the modern medicine is based on the practices of plant-based traditional medicine, a hundred of years of beliefs and observations ^[5].

Plants have developed a complex defense system which comprise of a complicated range of chemicals. It has been long recognized that the presence of antimicrobial compound in plant tissues as an important factor as natural products and may also serve as botanical pesticides, or as bactericidal and fungicidal agents active against pathogens of human diseases ^[6].

Plants, one of the most important sources of novel pharmacologically active compounds that hit the pharmaceutical industry in drug making, have a long history in the treatment of various diseases. As of this day, there are 35,000-70,000 plant species that have been tested for their medicinal use. The plants with ethnopharmacological uses have been the primary sources of medicine for early drug discovery relating to their original ethnopharmacological purposes. Today’s search for drug derive from plants relied on its bioactivity that led for the isolation of important anticancer drugs such as paclitaxel or camptothecin ^[7].

The Department of Health of the Philippines circulated a list of “Ten scientifically validated” Philippine medicinal plants in 1992 (R.A. No. 8423 – Phil. Institute of Traditional and Alternative Health Care), that comprises akapulco, ampalaya, bawang, bayabas, lagundi, niyug-niyogan, sambong, tsaang gubat, ulasimang bato, and yerba buena. These medicinal plants are used by people especially among the Kalinga people as alternative and first aid medicines ^[8].

Allium sativum (Garlic/bawang) was known for treating cuts or wounds ^[9]; Blumea balsamifera (Nagal camphor/sambong) was known for kidney problems ^[10]; Cassia alata (Ringworm bush/akapulko) was known for the treatment of skin diseases ^[11]; Clinopodium douglasii (Mint/yerba Buena), combined with oregano, was known for anti-asthmatic effect ^[12]; Ehretia microphylla (Scorpion Bush/Tsaang-Gubat) for the treatment of allergic rhinitis ^[13]; Momordica charantia (Bitter Melon/Ampalaya) for antidiabetic effects ^[14]; Peperomia pellucida (Silver Bush/Ulasimang Bato) for the treatment of gout and rheumatism ^[15]; Psidium guajava (Guava/Bayabas) for the treatment of wounds ^[16]; Quisqualis indica (Rangoon Creeper/Niyug-niyogan) for anti-helmintic effects ^[17]; and Vitex negundo (Five-leaved Chaste Tree/Lagundi) for the treatment of cough, and asthma ^[18].

As the demand of drugs rises for our growing population and growing number of various diseases, researchers keep on searching for the sources of new and more effective drugs. Medicinal plants are one of the leading priorities for the search of natural products for drug making industry. Thus, this review article tackled on the approved medicinal plants by Department of Health of the Philippines under R.A. No. 8423–Phil. Institute of Traditional and Alternative Health Care, and some untapped potential indigenous medicinal plants that could contribute in breakthrough of pharmaceutical industries.

2. Methods

Electronic literature review method was used in the study. The data were collected from different databases such as Google, Medline, PubMed, Science Direct, and STUARTXCHANGE for the medicinal uses and natural products that can be found in Allium sativum, Blumea balsimifera, Cassia alata, Clinopodium douglasii, Ehretia microphylla, Momordica charantia, Peperomia pellucida, Psidium guajava, Quisqualis indica, and Vitex negundo. The medicinal plants were found to be effective for the treatment of various wounds and diseases.

3. Results and Discussion

3.1. Medicinal Plants As Source Of Natural Products

Plants in general are rich in antioxidants that are crucial for their survival in the environment. These antioxidants are often associated with a reduction of health risks that contribute to conditions such as diabetes. Plant-based traditional medicines are still prevalent because plants are often inexpensive to prepare, are effective and their use for curing common ailments results in minimal complications. Thus, plant extracts have become an invaluable source of candidate compounds for the development of new drugs ^[19].

There are a lot of certain endophytes that are known to occur inside of a living plant. Endophytes are endosymbiotic group of microorganisms, often a bacterium or fungus that colonizes in plants and microbes without causing apparent diseases. Endophytes are ubiquitous and have been found in all species of plants studied up to this date; however, most of the endophyte or plant relationships are not well understood. Some endophytes may improve the plant’s ability to tolerate abiotic stresses like drought, and some can enhance host growth, nutrition acquisition, and resistance to insects, plant pathogens, and herbivores. These endophytes have an important role in the regulation of plant communities and can be also a potential interest for they are source of secondary metabolites. Many kinds of plant species play a very important role in healing practices in local villages and areas. The use of traditional medicine is still prevalent among the areas of the Philippines. Scientists were furnished with novel information because of the different documentations of rich traditional ethno-medicinal knowledge ^[20].

Allium Sativum (Garlic or Bawang)

Allium sativum (Garlic/Bawang) has been used as a spice, food, and medicine for over 5,000 years, and is one of the earliest documented herbs utilized for the maintenance of health and treatment of diseases such as controlling of level of cholesterol and blood regulation of blood pressure ^[21].

Garlic is a low herb, 30 to 60 cm high. True stem is much reduced. Bulbs are broadly ovoid, 2 to 4 cm in diameter, consisting of several, densely crowded, angular and truncated tubers. Leaves are linear and flat. Umbels are globose, many flowered. Sepals are oblong, greenish white, slightly tinged with purple. Stamens are not exerted from the perianth.

Garlic is native to Central Asia and northeastern Iran, and has long been a common seasoning worldwide, with a history of several thousand years of human consumption and use ^[22].

Blumea Balsamifera (Nagal camphor or Sambong)

Various methods of treatment exist, including herbal treatment in the Philippines that uses the medicinal herb Blumea balsamifera^[10].

A very popular Philippine herbal flowering plant used as medicine to treat wounds and cuts, rheumatism, anti-diarrhea, anti-spams, colds and coughs. It is also used for infected wounds, respiratory infections and stomach pains. Sambong is very popular among people with kidney problems because of its diuretic qualities. It can be taken as an early afternoon tea to maintain a healthy urinary tract. It also helps flush uric acid as well. The Philippine National Kidney and Transplant Institute recommends taking sambong for patients with renal problems. Studies noted that it may help to delay dialysis and other kidney problems. Sambong also possesses antibacterial and antifungal properties.

Blumea balsamifera or sambong is a common medicinal plant found throughout the Philippines. It is common in open fields, grasslands, and waste areas, at low and medium altitudes. It also occurs in China, Hainan, Bhutan, Cambodia, Laos, Indonesia, Malaysia, Thailand and Vietnam ^[23].

Cassia Alata (Ringworm Bush or Akapulko)

Cassia alata L. (Akapulko), commonly known as ‘Ringworm Bush or Senna’, is an erect medicinal shrub (or small tree) that is distributed mainly in the tropics and sub-tropics. Almost all parts of the plant have medicinal uses. Decoctions of the leaves, flowers, and bark are used to treat skin diseases such as eczema or pruritis (itching), while a decoction of the wood is useful in cases of constipation. The plant is a source of a wide array of compounds such as alkaloids, lectins, glycosides, isoflavones, and phyto-estrogens, hydroxyanthraquinones, chrysophanic acid, kampferin, and sannoxide A and B.

Leaf extracts from this species have shown several pharmacological, anti-microbial, and anti-fungal properties, anti-bacterial, anti-inflammatory, analgesic effects, and anti-hyperglycemic activities ^[24] Cassia alata Linn.is locally abundant throughout the Philippines in settled areas at low and medium altitudes ^[25].

Clinopodium Douglasii (Mint or Yerba Buena)

Clinopodium douglasii is an aromatic herb of the Lamiaceae family. It is an aromatic, prostrate, glabrous, slightly hairy, branched herb. It is cultivated throughout the Philippines and is propagated by terminal cuttings. It contains 0.8% volatile oil, which consists mainly of pulgenone, pitoeitone, limonene, menthol, menthene and menthenone ^[26].

Clinopodium douglasii can be found in northern Luzon (Cagayan) to Mindanao, in all or most islands and provinces, as a weed in settled areas, occurring in open, waste places, fallowrice paddies, etc. Introduced from Mexico and now also established in the Marianne and Caroline Islands in Taiwan, in Java, and in Amboina ^[27].

Ehretia Microphylla (Scorpion Bush or Tsaang-Gubat)

Ehretia microphylla (Tsaang Gubat) is 1 of the 10 medicinal plants approved by the Republic of the Philippines Department of Health to treat different ailments C^[8]. The leaves are traditionally used for medicinal purposes as an anti-spasmodic, mouthwash and body cleanser, attributed to the effects of different components (phenolic acids, flavonoids, benzoquinones, cyanogenetic glycosides, and fatty acids) ^[28].

Ehretia microphylla, easily found from the Batan Islands and northern Luzon to Palawan and Mindanao, in most or all islands and provinces, in thickets and secondary forests at low and medium altitudes of Philippines. It also occurs in India to southern China, Taiwan, and Malaysia ^[29].

Momordica Charantia (Bitter Melon or Ampalaya)

Unripe fruit, seeds and aerial parts of Momordica charantia Linn. (Cucurbitaceae) have been used in various parts of the world to treat diabetes. Oral administration of the fruit juice or seed powder causes a reduction in fasting blood glucose and improves glucose tolerance in normal and diabetic animals and in humans ^[30].

Momordica charantia is a traditional plant of Asian origin that has been a popular botanical proposed for treatment of diabetes and diabetes-related complications. Specifically, bitter melon fruit contains cucurbitane-type triterpenoids, steroidal saponins called “charantins,” insulinlike peptides, and alkaloids, which are postulated to have effects on carbohydrate metabolism ^[31]. Momordicine, charantin, saponins, glycosides, phenolic constituents, other alkaloids, and 5-hydroxytryptamine are the phytochemical of Momordica charantia and they are responsible for the antibiotic and antitumor activites along with lycopene and lutein ^[32].

The bitter gourds or ampalaya have many health benefits and medicinal properties. These are such as kills bacteria, reduce inflammation, kill viruses, fights free radicals, kills cancer cells, kills leukemia cells, prevents tumors, cleanses blood, reduces blood sugar and balance hormones ^[33].

Beside these stem and leaf of bitter gourd is used in cancer treatment, in vital infections (HIV, herpes, Epstein Barr, hepatitis, influenza, and measles), in bacterial infections (Staphylococcus, Streptococcus, and Salmonella), as a bitter digestive aid (for dyspepsia and sluggish digestion) and in diabetes ^[34].

Synonyms of M. charantia are M. indica L., M. elegans Salisb., M. chinensis Sprengel, and M. thollonii Cogn. M. charantia (several different names in Asia and Africa exist), is an important market vegetable in southern and eastern Asia. In tropical America, local varieties originate from Asia and are cultivated on a small scale only. M. charantia is a common cucurbit and is widely spread throughout most of tropical Africa ^[35].

The native habitat for bitter melon is not known. The plant is cultivated throughout the tropics, especially in China, India, East Africa, Central America, and South America. Bitter melon has many different common names, reflecting its widespread use in numerous cultures. The fruit has a bitter taste (as its name clearly conveys) and, for the most part, its palatability is said to be “an acquired taste.” In southern China, the melon is commonly eaten to cool the body ^[36].

Peperomia Pellucida (Silver Bush or Ulasimang Bato)

Peperomia pellucida L. is an annular herb. The roots are fibrous; stems translucent pale green, erect or ascending, usually 15-45 cm long, internodes usually 3-8 cm long, glabrous and the leaves are medium green on upper surface, lower surface whitish green, thinly fleshy, drying papery, broadly ovate, 1.5-4 (-5) cm long, 1-3.3 cm wide, palmately 3-nerved or 5-nerved, glabrous, apex acuminate, base subcordate to truncate, petioles 0.5-2 (-3) cm long, glabrous. One to several spikes are available, terminal and axillary or leaf-opposed, filiform, ca. 3-6 cm long, the rachis ca. 0.4-0.6 mm in diameter, glabrous, flowers well-spaced, peduncles ca. 0.6-1 cm long, glabrous; ovary ovoid; stigmas terminal and also fruits were subglobose, ca. 0.5 mm long, longitudinally ridged, apex beaked ^[37]. Peperomia pellucida, a pantropic species of American origin.

Psidium Guajava (Guava or Bayabas)

The Psidium guajava (Guava/bayabas) is a phytotherapic plant used in folk medicine that is believed to have active components that help to treat and manage various diseases. The many parts of the plant have been used in traditional medicine to manage conditions like malaria, gastroenteritis, vomiting, diarrhea, dysentery, wounds, ulcers, toothache, coughs, sore throat, or inflamed gums ^[38].

Bayabas is a somewhat hairy plant reaching a height of 8 m. Young branches are 4-angled. Leaves are opposite, oblong to elliptic, and 5 to 1 cm long, the apex being pointed, and the base usually rounded. Peduncles are 1- to 3-flowered. Flowers are white, 3 to 3.5 cm across, with in-curved petals, coming out solitary or two to three in the leaf axils. Numerous stamens form the attractive part of the flower. Inferior ovaries develop into round or obovoid green fruits 4 to 9 cm long, turning yellow on ripening and have edible, aromatic, seedy pulp.

Guava (Psidium guajava L.) is a native to tropical America and presently found distributed in many tropical and subtropical countries. Guava fruit is commercially important from Brazil, Colombia, Cuba, Egypt, Hawaii, India, New Zealand, Philippines, South Africa, Thailand, West Indies, Venezuela, and Vietnam ^[39].

Quisqualis Indica (Rangoon Creeper or Niyug-niyogan)

Quisqualis indica Linn. is a large scandent shrub of the family Combretaceae, or also known as Rangoon creeper or Chinese Honey Suckle. It is grown in Africa, Bangladesh, India, Malaysia, Philippines, Vietnam, and Thailand. Besides unique demand for beautiful flowers among the plant lovers and gardeners, this species is therapeutically important and used as a remedy for human illnesses. The leaf decoction alleviates flatulent distension of abdomen and has free radical scavenging activity. Fruits and seeds combats nephritis, whereas roots are used to treat rheumatism. Flowers and seeds are also eaten as famine food in Southern Asia. The fruits, leaves and seeds contain chemicals like ‘quisqualic acid’ and anthelmintic tannins, which are used to expel round worms and thread worms from the body. Moreover, methanol extract of flowers contains high polyphenol contents that have strong antioxidant activity. The leaves and flowers also contain rutin, pelargonidin-3-glucoside and 25-O-acetyl-23,24-dihydro-cucurbitacin F; the latter one acts as an anticancer agent and has shown significant cytotoxic activity ^[40].

Vitex Negundo (Five-leaved Chaste Tree or Lagundi)

The genus Vitex belongs to the family Verbenaceae and comprises of large shrubs or small trees. Vitex negundo Linn is most commonly distributed on roadsides and the banks of streams and is called Lakki gida in Kannada. It is a large, silvery-tomentose shrub or small tree with bluish purple flowers in terminal panicles with short cymose branches. Leaflets are 3-5 in number, middle one slightly longer petiolulate, entire, lanceolate, acuminate, 12x2cm and membranous. Bark is thin and grey ^[41].

V. negundo is shown to possess a wide array of biological activities such as antimalarial activity ^[42], anthelmintic ^[43], wound healing ^[44], antipyretic ^[45], antioxidant ^[46], antifungal ^[47], and antibacterial ^[48].

Vitex negundo is globally distributed in Indo-Malesia, cultivated in America, Asia, Europe and West Indies. Within India, it is found throughout the greater part of India, ascending to an altitude of 1,500 metres in the outer Himalayas ^[49].

List of Medicinal plants approved by the Department of Health (DOH) in the Philippines and their medicinal use with corresponding bioactive metabolites are presented in Table 1.

Table 1. Benefits of the Approved Medicinal Plants and the Bioactive Metabolites Present

Medicinal Plants	Medicinal Use	Bioactive Metabolites
Allium sativum	Cuts, regulation of blood pressure, anti-inflammatory supplement, and controlling of level of cholesterol	Alkaloids, flavanoids, saponins, protein, and carbohydrates, tannins, cardiac glycosides, and reducing sugars, flavones, and flavonols
Blumea balsamifera	Kidney problems, hypertension, cuts, infected wounds, diarrhea, rheumatism, spasms, colds and coughs, respiratory infection, stomach pain and improve urinary tract	Steroids or 2-deoxysugars, flavonoids, tannins, polyphenyls, and alkaloids
Cassia alata	Skin diseases such as eczema or pruritis, constipation, insect bites and scabs, ringworm, and can be used as an ointment, shampoo, soap and lotion	Alkaloids, lectins, glycosides, and isoflavones
Clinopodium douglasii	Cold, cough, insect bites, headache and stress, body pain and aches due to gout and rheumatism, nausea and fainting	Tannins, carbonyls, and flavonoids
Ehretia microphylla	Skin allergies psoriasis, itchiness, scabies, eczema, stomach ache and abdominal pain, and diarrhea	Microphyllone, baurenol, ursolic acid, dehydromicrophyllone, hydroxymicrophyllone, cyclomicrophyllone, and allomicro-phyllone
Momordica charantia	Coughs, hemorrhoids, scalds and burns, reducing agent in fasting blood sugar, and improvement of tolerance in glucose intake	Saponins, glycosides, phenolic constituents, other alkaloids, and 5-hydroxytryptamine
Peperomia pellucida	Joint pain in arthritis patient, and lowers the uric acid level in blood	Flavonoid compounds, tannins, saponins, steroids, monoterpenes, and sesquiterpene
Psidium guajava	Cleaning wounds, anti-microbial, anti-plasmodial, anti-inflammatory, antioxidant, anti-genotoxic, cough and cleansing of rectum	Phenolic compounds, isoflavonoids, gallic acid, catechin, epicathechin, rutin, naringenin, kaempferol ascorbic acid, carotenoids (lycopene, β-carotene and β-cryptoxanthin), and glycosides
Quisqualis indica	Deworming, fever, painful urination, ulcer, headache, diarrhea, anti-cancer, nephritis and rheumatism	Quisqualic acid, anthelmintic tannins, rutin, pelargonidin-3-glucoside, and 25-O-acetyl-23,24-dihydro-cucurbitacin
Vitex negundo	Cough, asthma, pharyngitis, rheumatism, boils, diarrhea, and dyspepsia	Phlobatannins, carbohydrates, tannins, glycosides, volatile oils, resins, balsams, flavonoids, and saponins

Taxonomic Classification of Approved Medicinal Plants by the Department of Health (DOH) in the Philippines presented in Table 2.

Table 2. Taxonomic Classification of Approved Medicinal Plants

Scientific Name	Division	Class	Order	Family
Allium sativum	Tracheophyta	Magnoliopsida	Asparagales	Amaryllidaceae
Blumea balsimifera	Tracheophyta	Magnoliopsida	Asterales	Asteraceae
Cassia alata	Tracheophyta	Magnoliopsida	Fabales	Fabaceae
Clinopodium dougasii	Tracheophyta	Magnoliopsida	Lamiales	Lamiaceae
Ehretia microphylla	Tracheophyta	Magnoliopsida	Boraginales	Boraginaceae
Momordica charantia	Tracheophyta	Magnoliopsida	Cucurbitales	Cucurbitaceae
Peperomia pellucida	Tracheophyta	Magnoliopsida	Piperales	Piperaceae
Psidium guajava	Tracheophyta	Magnoliopsida	Myrtales	Myrtaceae
Quisqualis indica	Tracheophyta	Magnoliopsida	Myrtales	Combretaceae
Vitex negundo	Tracheophyta	Magnoliopsida	Lamiales	Lamiaceae

3.2. Other Plants

Due to the abundant flora and fauna of the Philippines, there have been many herbal plants that are not yet approve by the DOH that are used in practicing herbal therapy by local herbalists. Knowing the untapped potential of a certain plant can lead to a new discovery in treating certain diseases. An example is the Brucea mollis Wall. Ex Kurz: It is a bitter shrub found in the mountainous sparse forests, roadside shrubs and tickets in China, India, Philippines, Nepal, Thailand, Malaysia, Laos, Cambodia, Myanmar, and Bhutan ^[50]. It’s used for the treatment of cancer and malaria in China and India. This has been affirmed by revealing the phytochemicals that are found in the plant like Yandanziolide, Bruceine, and Bruceine that has antimalarial and anticancer properties. They exhibit cytotoxic, amoebicidal, antigiardial, insecticidal, antiviral, anti-leukemic, pesticidal, and anti-feedant activities ^[51].

3.3. Secondary Metabolites

Secondary metabolites are the source of natural products that are being developed into medicine. The compounds were separated into phenolics including polyphenols, flavonoids, tannins, and quinones that are known for their potency in antioxidation, cytotoxic, and antimicrobial activities. The adaptation of multi-drug resistant bacteria and the rise of contagious diseases led to the reevaluation of the use of antibiotic agents in treatment, and novel solutions as the use of secondary metabolites as resistance agents though it is still a challenge for Science to exploit under-utilized plants ^[52].

The essential oils generally possess a broad spectrum of bioactivity because of the presence of secondary metabolites. These active ingredients work through different modes of action. It plays a vital role in the survival of plants by producing attractants or pollinators and it also acts as a chemical defense against predators and disease ^[53]. Plants protect themselves from the continuous attack of naturally occurring insect pests, pathogens and environmental stresses by producing several secondary metabolite compounds including alkaloids, cyanogenic glycosides, glucosinolates, flavanoids, saponins, steroids, tannins and terpenoids.

Alkaloids, Steroids, Tannins, Terpenoids, Flavonoids, Saponins, Steroids, Cyanogenic Glycoside and Glucosinolates are the most common secondary metabolites present on plants. Secondary Metabolites are specific to an individual species, the use of secondary metabolites mainly as medicines, flavorings and as a recreational drug.

Plant bioactive metabolites can be extracted through conventional and modern method. Conventional method includes decoction, infusion, soxhlet extraction, maceration, and hydrodistillation. Modern method includes ultrasound assisted extraction, microwave-assisted extraction, and supercriticial fluid extraction ^[54].

According to Dr. Alfonso T. Lagaya, the Philippine government is very supportive in various activities related to educational, research, and production of traditional herbal medicines. The government has established The Philippine Institute of Traditional and Alternative Health Care. Local “quack” doctors have used herbal plants to treat certain diseases. Thus, the government had also research about it to prove the effectivity of different plants that are used traditionally. There have been two groups in practicing herbal medicine in the country. A group of licensed modern medicine doctors and approximately 250,000 disorderly traditional herbalists. In China there are 170 medicinal research that has 15,000 professional researchers. They also have 30 universities and local colleges that has approximately 37,000 medical students that studies medicinal plant as part of the mainstream practice. Koreans have also been practicing traditional medicine and has taken part in the history of South Korea that plays significant role in the health care system. They have a specialized guideline for manufacturers and traders of commercially made herbal medicine ^[55]. World Health Organization narrate that about 70% to 80% relies mainly in herbal medicine ^[56].

The mentioned table above has summarized the common secondary metabolites that can be found in herbal plants. These secondary metabolites have an importance in treating certain diseases.

Alkaloids are an important natural product that is found in primarily on plants. It plays an important role in as part of the defense complex against animals and pathogens. An Alkaloid that belongs to beta-carboline group contains anti-parasite, anti-microbial, and anti-HIV properties ^[57]. It has anti-cancer properties ^[58], has an anti-inflammatory activity ^[59]. It inhibits Trypanosoma cruzi the agent of Chagas’ disease that is one of the serious protozoan diseases ^[60].

Steroids are commonly used in treating rheumatoid arthritis, asthma, inflammatory bowel disease, pulmonary disease, systemic lupus erythematosus ^[61]. It has an anti-inflammatory property and treats certain diseases such as rheumatoid diabetes, lupus and gout ^[62].

Tannins are water-soluble polyphenols. It is reported to be anti-carcinogenic and anti-mutagenic potential because of their anti-oxidative property. It has anti-microbial property because tannic acid inhibits foodborne bacteria and aquatic bacteria. The physiological effects have been reported to reduce blood pressure, decreases serum lipid level and regulate immunoresponses ^[63].

Terponoids are commonly used as commercially natural flavoring compounds in the food industry. It is the largest and diverse class of phytochemicals. More than 40,000 individual terpenoid exist and new ones are found each year. It has anti-oxidant properties and potentially treat liver cancer ^[64]. It has been found to have beneficial properties in as an analgesic, anti-microbial, anti-viral, anti-inflammatory, anti-fungal, anti-parasitic ^[65].

Flavonoids possess anti-oxidant, anti-leukemic, and improves blood circulation in Alzheimer’s disease. It has free radical scavenging which are useful for pharmacological activities along with anti-cancer and anti-aging ^[66].

Saponins are mostly found in vegetable, herbs, and beans. It helps lower your cholesterol, reduce the risk of heart disease, improves your immune function and has anti-cancer property ^[67].

Glucosinolates are present in sixteen families of dicotyledonous angiosperms including large number of edible species. They are used as food flavoring that stimulate appetite and digestive process. Their known for their fungicidal, bacteriocidal, nematocidal and allelopathic properties and have recently attracted intense research interest because of their cancer chemoprotective attributes ^[68].

The -thioglucoside-N-hydroxysulfates, precursors of isothiocyanates, are present in sixteen families of dicotyledonous angiosperms including large number of edible species.

Too much intake and wrong dosage of an herbal plant is very dangerous to your health. It can treat your disease but can affect your other organs in the process of doing so. The common secondary metabolites found in herbal plants have risks also. Alkaloids can lead to plant poisoning if not prepared meticulously and in wrong dosage. Steroids has a lot of side effects such as, acne, blurred vision, cataract or glaucoma, easy bruising, insomnia, bad cholesterol, high blood pressure, increase in appetite, etc. ^[69]. Lack of herbal knowledge can lead to a danger to the patient or user ^[70]. One should be responsible enough in intaking herbal medicine. One phytochemical can react another one if not known by the user of its reaction.

4. Conclusion

Natural products are growing body of research for the development of new drugs derived for different eukaryotic and prokaryotic organisms. However, there are still tons of species of plant that might possess a natural product that are still not screened for medicinal use and might be a cause for a breakthrough in science. Therefore, more investigations should be done in other species of plant that isn’t common especially those species with ethnopharmacological and ethnobotanical used.

Herbal plants are very beneficial in finding a remedy or stabilization of various diseases. By knowing their phytochemicals, we can conclude that creating an intensive study discover more of its benefits and uses and finding its toxicity. Utilizing herbal plants which are abundant to the Philippines can help in industrialization and will help in employing locals. Day by day, scientists find that plants can be a potential drug source and can help people in battling different kinds of diseases. However, further study must be made in knowing its harmful effect of a human’s body and know if it could be lethal or not. In summarizing herbal plants with its natural product, the researchers conclude that further research can make a breakthrough in a potential drug that can treat certain diseases and can also bring employment to locals that cultivates various herbal plants.

Acknowledgments

The authors would like to extend their gratitude and appreciation to the following person and university involved: The professors Dr. Zenaida D. Los Baños, Head of Biological Science Department, Dr. Julieta Z. Dungca, Dean of School of Science and Technology, Dr. Alicia I. Yu, Practicum Coordinator who have molded us to be professionally competitive, academically knowledgeable and resourceful individuals. Dr. Tooba Mahboob, Mr Giovanni Milañez and Assoc. Prof. Frederick Masangkay for guidance and giving us suggestive ideas to make the review possible, the Walailak University and Centro Escolar University for providing us the required facilities to achieve the review. Our parents who have provided their support, trust and financial aid in completion of their study. Assoc. Prof. Dr Veeranoot Nissapatorn for accepting and treating us, providing our needs and making sure that our stay in Thailand educational and memorable.

Competing Interests

The authors declare no conflict of interest.

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