Background
Medicinal plants are always very promising for the development of new drugs. To distinguish any plant possessing medicinal quality, proper scientific screening is essential. Traditionally different plants are known to have different efficacy for treating various types of diseases. If the right plant is known for healing a particular disease, attempts should be made to isolate the bioactive lead molecule(s) from the plant [
1].
Almost 30 tribal communities are living at different parts of Bangladesh. The Garo is one of them and considered as an ethnic group of ‘Tibbeti Borman’, belonging to the Mongolian human race. They are now living in Mymensingh, Tangail, Netrokona, Sylhet and Sunamgonj districts. They have their own curative practices involving many medicinal plants as evident from some ethnobotanical surveys [
2,
3]. These plants can be systematically evaluated to explore their healing abilities. With this view,
Drynaria quercifolia (L.) J. Sm., a medicinal plant used by the Garo tribe, was selected to perceive its medicinal properties through chemical and biological assays.
D. quercifolia (L.) J. Sm. (Bengali name: Bandor shoal, Pankhiraj) belongs to a large family of ferns, Polypodiaceae, having 56 genera and 1200 species distributed throughout the world. It is native to Bangladesh, India, Southeast Asia, Malaysia, Indonesia, Australia, the Philippines, New Guinea, etc. [
4]. This epiphytic or lithophytic fern is available in wet tropical environments and generally grows on wall, tree or rock anchored by rhizome. It has two types of fronds known as fertile foliage fronds and sterile nest fronds. This plant is traditionally used to heal typhoid, hectic fever, cough, dyspepsia, jaundice, diabetes, tuberculosis, throat infection, etc. [
5‐
8]. Besides, it has been reported to have antifertility, analgesic, antiedematous, antibacterial, etc. activities [
6,
9‐
12]. Preliminary phytochemical screening has revealed the presence of alkaloids, glycosides, saponins, amino acids, flavonoids, triterpenes, phytosterols and carbohydrates [
11,
13].
The aim of the present study is to investigate the rhizomes and the fertile foliage fronds of D. quercifolia for their membrane stabilizing, thrombolytic and antioxidant activities comprehensively. This might explore the remedial potential of this plant to a great extent.
Discussion
The Garo is a tribal community of Bangladesh. Their family pattern, norms, foods, festivals, etc. are different from other tribal communities and mainstream Bangladeshi common people [
3]. The healers of this tribe use many medicinal plants for treating their people. Recently some ethnobotanical surveys have been conducted on this [
2,
6], which have revealed the studied fern,
D. quercifolia, as one of the medicinally important plants of the Garo tribe.
Inflammation is a very complex biological state. Chronic inflammation may be associated with aging, cancer, adipogenesis, diabetes, cardiovascular problems, lung disease, etc. [
23‐
25]. Membrane stabilization assay of erythrocytes is a very popular tool to investigate the anitiinflammatory potential of the plant extract. When erythrocytes are exposed to hypotonic medium, heat, methyl salicylate, phenylhydrazine, etc., the lysis of their membrane occurs. It results in the leakage of serum protein and fluids into the tissues instigating inflammation [
26]. So, the compounds capable of membrane stabilization might be very suitable as antiinflammatory agents [
15]. Crude methanol extract of rhizomes demonstrated noticeable membrane stabilizing property (Fig.
2). Moderate membrane protecting activity was displayed by the crude methanol extract of fertile foliage fronds and petroleum ether fractions of both parts of the fern. The antiinflammatory potential of this plant was also partially verified earlier by another preliminary study using only ethanol extract of rhizomes on mice model [
9]. However, active inflammation of the gastroduodenal mucosa is a cause of dyspepsia [
27].
D. quercifolia is well recognized to treat dyspepsia [
7], which might be linked with antiinflammatory potential of this fern. Several flavonoids and triterpenes have been reported earlier to have antiinflammatory activity [
28,
29]. As flavonoids and triterpenes are also present in
D. quercifolia [
13,
30], it might be a reason for its membrane stabilizing antiinflammatory potential.
Thrombus development leads to many vascular complexities including myocardial infarction, stroke, deep vein thrombosis, renal vein thrombosis, portal vein thrombosis, etc. which might result in death. Tissue plasminogen activator, urokinase, streptokinase, etc. are used currently for treating thrombosis but better thrombolytic agents are still a demand of time [
31,
32]. In the current study, higher thrombolytic activity was exhibited by crude methanol extracts and aqueous fractions of both rhizomes and fertile foliage fronds (Fig.
3). This plant was previously reported to have significant hypolipidemic activity on diabetic rats [
33]. The thrombolytic activity of the plant along with lipid lowering ability might contribute to maintain a healthy cardiovascular system [
34]. It has been noticed earlier that flavonoids might have significant potentials of displaying thrombolytic activity [
35]. The abundance of flavonoids in
D. quercifolia might be a reason for its thrombolytic ability [
13].
Free radicals become notorious when produced in excess in vivo and cause oxidative damages. They can destroy immunity system and develop a wide range of diseases such as alzheimer's disease, parkinson's disease, complication in diabetes, rheumatoid arthritis, neuro-degeneration, cardiovascular complications, DNA damage, carcinogenesis, metabolic disorders, aging, etc. [
36,
37]. To counteract the complications generated by free radicals, antioxidants might be very beneficial. Different fractions of
D. quercifolia were subjected to DPPH and hydrogen peroxide free radical scavenging assays, where crude methanol extracts and their aqueous fractions scavenged the free radicals evidently (Figs.
4 and
5). On the other hand, the decolorization in ABTS assay reveals the capacity of an antioxidant species to donate electrons or hydrogen atoms to deactivate the radical species of ABTS [
20]. Aqueous fractions and crude methanol extracts again displayed noticeable ABTS radical scavenging capacity (Fig.
6). However, FRAP assay measures the reducing potential, where a compound exerts its effect by donating hydrogen atom to ferric tripyridyltriazine complex and interferes the radical chain reaction [
21]. In the present study, aqueous fractions and crude methanol extracts were very dominant for exhibiting ferric reducing potentials (Fig.
7).
It is well-known that phenolic compounds are very useful to serve as antioxidants [
38]. So, the total phenolic content of extractives was assessed (Fig.
8). Higher level of phenolic content was seen in the aqueous fractions and crude methanol extracts of the plant. This finding might explain a reason for stronger antioxidant potential of the high polar extractives.
Jaundice might cause accelerated generation of hydroxyl radicals in plasma and liver tissues as evident from an earlier study performed on common bile duct ligated jaundice rats [
39].
D. quercifolia is traditionally used for curing jaundice [
5] which might be related with the antioxidant potential of this fern. A higher level of free radicals and oxidative stress has a vital role in the deterioration of diabetic complications. Therefore, use of antioxidants reduces oxidative stress and helps in diabetes management [
40]. The Garo healers use
D. quercifolia to treat diabetes mellitus [
6], which is very much reasonable in the context of antioxidant potential of this fern. Antioxidant treatment was reported very promising for quick alleviation of respiratory infection and inflammation [
41]. Rhizomes and fronds of
D. quercifolia are also locally used for treating tuberculosis and throat infections [
8], which might be assisted with the antioxidant potential of this plant as evident from the present study along with its antibacterial potential as reported earlier [
13].