Introduction
From the very ancient time to till now plants have been the basis of many traditional medicine systems throughout the world and continued to furnish mankind with new remedies. A great variety of medicinal plants, their purified constituents and natural products from the medicinal plants provide unlimited opportunities for new drugs development because of the unparalleled accessibility of diverse chemical compounds [
1] and also have been shown to have beneficial therapeutic potential. When our body cells use oxygen, they naturally produce free radicals which can cause damage to cell. Free radicals contribute to more than one hundred disorders in humans, including atherosclerosis, arthritis, ischemia and repercussion injury of many tissues, central nervous system injury, gastritis, and cancer [
2]. Recent research has confirmed that antioxidants are the most effective tools to eliminate free radicals which cause oxidative stress and are possible protective agents that protect the cells from reactive oxygen spices and retard the progress of many diseases as well as lipid peroxidation [
3‐
5]. Additionally, they also possess anti-inflammatory, anti-viral and anti-cancer properties [
6]. The medicinal value of plant is related to their phytochemical component content and secondary metabolites, including: phenolic compounds, flavonoids, alkaloids, tannins, and other stress gene response products [
7]. Recently, pathogenic microorganisms of human have exhibited multifarious drug resistance for frequent use of potent anti-microbial drugs in infectious diseases. In this situation, researchers are trying to seek of new anti-microbial lead compounds from medicinal plants, a good source of novel antimicrobial drugs [
8]. The side effects of synthetic anti-inflammatory drugs including gastric injury, ulceration, bronchospasm, inhibition of platelet aggregation, liver and kidney toxicity have limited their use [
9]. Therefore, it is requisite to investigate for new anti-inflammatory drugs with fewer side effects and plants may be our potential solution to combat this [
10].
Colocasia affinis Schott (Family: Araceae), a perennial herb, height 46–91 cm. It is found all over in Bangladesh and locally known as Kochu (bengali). English name is Dwarf elephant’s ear. Traditionally leaves are cooked as vegetables and are reported to be effective to treat cataract. The leaves are often boiled with coconut milk to make a soup which is rich in iron. To the best of our knowledge no attempts were taken before to evaluate in vitro antioxidant, anti-microbial, brine shrimp lethality bioassay, anti-inflammatory and antidiarrheal properties of methanol extract of leaf part of C. affinis Schott. So in this study we have investigated antioxidant, antimicrobial and brine shrimp lethality bioassay anti-nociceptive, anti-inflammatory and antidiarrheal activities of leaf methanolic extract of C. affinis Schott.
Materials and methods
Plant material
Leaves of Colocasia affinis Schott were collected from the campus of Jahangirnagar University, Savar, Dhaka, Bangladesh and identified by the taxonomist of the National Herbarium of Bangladesh, Mirpur, Dhaka. The voucher specimen of the plant had been deposited in the herbarium for further reference.
Leaves of the plant were sun dried and then crushed through grinding machine. Then 100 g of dried leaf powder was taken in a separate container. To this 250 ml of methanol was added and kept for 24 h at room temperature with periodic shaking. Then filtered with Whatman No. 1 filter paper and the filtrate were collected. The procedure was repeated three times with fresh volume of methanol. The filtrates were pooled to ensure maximum extraction. Then the extract was dried and weighed. Yield was 41.50 g.
Phytochemical screening
The freshly prepared crude extract was qualitatively tested to reveal the presence of phytochemical constituents such as alkaloid, carbohydrate, flavonoid, glycoside, tannin, steroid and saponin. These were identified by characteristic color changes using standard procedures [
11].
Tests for antioxidant activity
Determination of total antioxidant capacity
By the phosphomolybdenum method, the total antioxidant activity of the extract was evaluated according to Prieto et al, 1999 [
12]. 0.3 ml extract solution was combined with 3 ml of reagent solution (0.6 M sulfuric acid, 28 mM sodium phosphate and 4 mM ammonium molybdate). The tubes containing the reaction solution were kept for incubation at 95 °C for 90 min. Then absorbance of the solution was evaluated at 695 nm using a spectrophotometer (UV visible spectrophotometer, Shimadzu, 1601) against blank after cooling at room temperature. Methanol (0.3 ml) is used as the blank. The antioxidant activity is expressed as the number of ascorbic acid equivalents.
Determination of total phenolic contents
To determine the total phenolic contents of LMCA, Folin–Ciocalteu reagent was used [
13]. Plant extract solution (100 μl) was mixed with 500 μl of the Folin–Ciocalteu reagent and 1.5 ml of 20% sodium carbonate. The mixture was shaken thoroughly and added distilled water up to 10 ml. The whole mixture was allowed to stand for 2 h. Then the absorbance was taken at 765 nm. These data were used to estimate total phenolic contents using a standard curve obtained from various concentration of standard Gallic acid.
Determination of total flavonoids content
The content of total flavonoids in the extract was determined by the method by Chang et al., 2002 [
14]. 1 ml of sample (LMCA) solution was mixed with methanol (3 ml), aluminum chloride (0.2 ml, 10%), potassium acetate (0.2 ml, 1 M) and distilled water (5.6 ml) and incubated the mixture for 30 min at room temperature. Then the absorbance was determined at 415 nm against blank. Methanol (1 ml) in the place of sample solution was used as the blank and Quercetin was used as the standard solution. The amount of flavonoids in plant extracts in Quercetin equivalents (QE) was calculated by the following formula: X = (A × m
0)/ (A
0 × m), where X is the total flavonoid content, mg/mg plant extract in QE, A is the absorption of plant extract solution, A
0 is the absorption of standard quercetin solution, m is the weight of plant extract in mg and m
0 is the weight of quercetin in the solution in mg.
Cupric reducing antioxidant capacity (CUPRAC)
Cupric reducing antioxidant capacity of LMCA was determined according to Resat et al., 2004 [
15]. Different concentrations of extract (5–200 μg) in 0.5 ml of distilled water were mixed with cupric chloride (1 ml, 0.01 M), ammonium acetate buffer (1 ml, pH 7.0), neocuproine (1 ml, 0.0075 M) and at last distilled water (0.6 ml). The mixture was incubated for 1 h at room temperature. Then the absorbance was measured at 450 nm against blank. Distilled water (0.5 ml) is used as the blank. From the slope of the calibration line concerned, the molar absorptivity of the CUPRAC method for each antioxidant was found. Ascorbic acid was used as the standard.
Ferric reducing antioxidant power (FRAP)
According to the method by Oyaizu, 1986 the ferric reducing antioxidant power was assessed [
16]. In this method, the reduction of Fe
3+ to Fe
2+ is assessed by measuring the absorbance of Perl’s Prussian blue complex. Different concentrations of extract solution (LMCA) (5–200 μg) in 1 ml of distilled water were mixed with phosphate buffer (2.5 ml, 0.2 M, pH 6.6) and potassium ferricyanide [K
3Fe (CN)
6] (2.5 ml, 1%). The mixture was incubated at 50 °C and waited for 20 min. 2.5 ml of trichloroacetic acid (10%) was added to the mixture and centrifuged at 3000 rpm for 10 min. The supernatant (2.5 ml) was mixed with distilled water (2.5 ml) as well as FeCl
3 (0.5 ml, 0.1%) and the absorbance was measured at 700 nm. Ascorbic acid was used as the reference standard.
DPPH free radical scavenging activity
DPPH scavenging activity of the extract was determined by the method described by Braca et al., 2001 [
17]. Extract solution (0.1 ml) of each concentrations were added to 3 ml of a 0.004% ethanol solution of DPPH. Absorbance at 517 nm was fixed to determined after 30 min and the percentage inhibition activity was estimated from [(A
o-A
1)/A
o] × 100, where A
o is the absorbance of the control (DPPH solution) and A
1 is the absorbance of the extract/standard. The DPPH free radical scavenging activity curves were prepared and IC
50 values were calculated.
Cytotoxicity test
Brine shrimp lethality bioassay method was applied to predict possible cytotoxic action [
18,
19]. The eggs of brine shrimp (
Artemia salina leach) were collected and hatched in a glass tank at a temperature around 37 °C with oxygen supply. Two days later the mature naupliies were allowed to assess for cytotoxic test. Stock solution of sample extract was prepared by dissolving required amount of extract in specific volume of dimethyl sulfoxide (DMSO). Ten alive nauplii were taken to each of the vial that contains different concentrations of test sample with Pasteur pipette. Then sample were transferred from the stock solution to the vials to get final sample concentration. In the control vials same volumes of DMSO (as in the sample vials) were taken. For the positive control, Vincristine sulphate was used. After 24 h the vials were observed and the number of nauplii was counted that were survived in each vial. From this, the percentage of mortality of brine shrimp nauplii was calculated for each concentration of the sample extract.
Antimicrobial activity by disc diffusion method
The antimicrobial activity of the plant extract was figured out by disc diffusion method described by Bauer-Kirby [
20,
21]. With the help of a sterile swab, the inoculums of microorganisms were spread over nutrient agar plates. One hundred milligram of the test sample was dissolved in 1 ml of methanol to obtain the concentration 100 μg/μl in an aseptic condition. Sterilized metrical filter paper discs (Whatman No. 1, 6 mm diameter) were soaked with different concentrations (30 μg/μl, 20 μg/μl and 10 μg/μl) of the test sample. Then the soaked discs were placed on the marked agar plate and dried. The extract was tested in triplicate and the plates were inoculated at 37 °C for 24 h. Amoxicillin was used as a positive control. Inhibition zones (diameters) were measured.
In-vivo pharmacological activity evaluation
Acute toxicity study
Acute oral toxicity study for the test extract of the plant was carried out as per the guidelines set by Organization for Economic Cooperation and Development (OECD). Overnight-fasted Swiss albino mice (30–45 g) and Wister rat (120–130 g) of either sex were used for the study. The animals were divided into seven groups of five animals each. Groups A to F received orally 250, 500, 1000, 2000, 3000, 4000 mg/kg of the extract respectively, while the control (group G), received distilled water (3 ml/kg) by the same route. General symptoms of toxicity and mortality in each group were observed within 24 h. Animals that survived after 24 h were observed for any signs of delayed toxicity for 2 weeks.
Analgesic activity evaluation
Acetic acid induced writhing test
The method described by Koster et al., 1959 was employed for this test [
22]. Four groups of five mice each were pretreated with extracts (500 and 1000 mg/kg), diclofenac (10 mg/kg) and distilled water (3 ml/kg). After forty five minutes, 0.7% acetic acid at a dose of 10 ml/kg body weight was injected intraperitoneally in each mouse. The number of writhing responses was recorded for each animal during a subsequent 5 min period after 15 min of i.p. administration of acetic acid and the mean abdominal writhing for each group was obtained. The percentage inhibition of writhing was calculated by comparison with the control mice.
For formalin induced analgesic activity evaluation the method described by Hunskaar S et al. [
23] was used. The control group received normal saline (0.1 ml/10 g) and standard group Aspirin (100 mg/kg). Extract solutions (500 mg/kg & 1000 mg/kg) were orally administered and after 30 min of treatment, 20 μl of 1% Formalin solution was injected subcutaneously in the right hind paw of the mice. The time spent in licking and biting of the affected paw was noted. The total paw licking response was measured as early phase (0–5 min) and late phase (15–20 min) after formalin injection [
24,
25]. The percentage of pain inhibition was expressed by the given formula: Percentage inhibition = [(Control mean-Treated mean)/Control mean] × 100.
Anti-inflammatory activity evaluation
Xylene induced ear edema method
Mice were divided into four groups of five animals each. Group A & B were treated orally with the LMCA solution 500 and 1000 mg/kg respectively while group C received diclofenac 10 mg/kg and group D was treated with distilled water with Tween 80 (10 ml/kg). Thirty minutes afterwards, edema was induced in each mouse group by applying a drop of xylene to the inner surface of the right ear. Fifteen minutes later, the animals were sacrificed under ether anesthesia and both ears cut off, sized and weighed. The anti-inflammatory activity was manifested as the percentage inhibition of edema in the treated mice in comparison with the control mice [
26].
Carrageenan induced rat paw edema method
The anti-inflammatory activity of LMCA was investigated by carrageenan induced inflammation in rat paw by following the method of Winter et al. [
27] with minor modifications. Rats were randomly divided into four groups, each consisting of five animals, of which group I was kept as control giving only distilled water. Group II was given indomethacin (5 mg/kg) as standard drug. Group III and group IV were given the test sample at the dose of 500 mg/kg and 1000 mg/kg body weight respectively. Half an hour after the oral administration of the test materials, 1% carrageenan in saline was injected to the left hind paw of each rat. The volume of paw edema was measured at 1,2,3,4 and 6 h using water plethysmometer after administration of carrageenan. The right hind paw served as a reference of non-inflamed paw for comparison.
The average percent increase in paw volume with time was calculated and compared against the control group. Percent inhibition was calculated using the formula-.
% Inhibition of paw edema = [(Vc – Vt) / Vc] × 100.
Where Vc and Vt represent average paw volume of control and treated animal respectively.
Antidiarrheal activity evaluation
Castor oil-induced diarrhea test
The antidiarrheal activity of LMCA was studied according to the method described by Jebunnessa et al., 2009 [
28]. Mice fasted for 24 h were divided into control (Group I), positive control (Group II: Loperamide) and test groups (Group III, IV) containing five animal in each group. Control group received distilled water at the dose of 10 ml/kg p.o. Positive control group was given Loperamide at the dose of 5 mg/kg p.o. Test groups III & IV were given LMCA at doses of 500, 1000 mg/kg respectively. After 1 h each group were treated with 0.5 ml of castor oil orally. Then each animal was placed in a separate cage with blotting paper lined floor. The blotting papers were changed every hour. The animals were observed for the next 4 h to record the time of onset of diarrhea, the total number of fecal output (frequency of defecation) and weight of feces excreted by the animals were recorded. The percent (%) inhibition of defecation was calculated using the formula: % Inhibition of defecation = [(A-B)/A] × 100 here, A = Mean number of defecation caused by castor oil and B = Mean number of defecation caused by drug or extract.
Magnesium sulfate induced enteropooling
To appraise the antidiarrheal activity through magnesium sulfate induced enteropooling method Wistar rats were fasted for 18 h and divided into four groups of five animals per group. Group I animals which received normal saline (2 ml, p.o.) served as the control group. Group II animals received loperamide (3 mg/kg, p.o.) and served as standard. Group III and IV received LMCA 500 mg/kg and 500 mg/kg respectively, p.o. Immediately after the treatment magnesium sulfate (10%
w/
v) was administered. After 30 min following administration of magnesium sulfate the rats were sacrificed, the small intestine was removed after tying the ends with threads and weighed. The intestinal content was collected into a graduated cylinder and their volume was measured. The intestine was reweighed and the difference between the full and empty was calculated [
29,
30].
Statistical analysis
The results were expressed as mean ± standard deviation (SD) from triplicate experiments and evaluated with the analysis of student’s t-test. Differences were considered significant at a level of P < 0.05. IC50 was calculated using Sigma Plot 11.0 software.
Discussion
The findings of the preliminary phytochemical screening laid the foundation for further works as it showed positive result for alkaloid, tannin, flavonoid, carbohydrate etc.
On the basis of several reports, it has been vested that phenolic content is closely related with antioxidative activity of the fruits and vegetables. It is also evident that in various diseases like cardiovascular disease, aging and cancer, Phenolic compounds (natural antioxidants) exhibit their therapeutic activity [
32]. In addition, phenolic compounds exhibit their antioxidant activity for their redox properties [
33]. It has been also revealed that flavonoids posses antioxidant activities. Due to having the ability of scavenging of free radicals, chelation of metal ions, such as iron and copper, and inhibition of enzymes responsible for free radical generation, flavonoids show the antioxidative properties [
34]. The reactive hydroxyl groups of polyphenolics, oligomeric flavonoids are oxidized to the corresponding quinines with CUPRAC reagent [
15,
35]. The presence of phenolic compound in the extract purports it to be a potential antioxidant. In reducing power assays, the presence of antioxidants can reduce the oxidized form of iron (Fe
3+) to its reduced form (Fe
2+) by donating an electron. Thus, it might be assumed that the presence of reductants (i.e. antioxidants) in LMCA causes the reduction of the Fe
3+/ferricyanide complex to the ferrous form which reveals the antioxidative nature of the extract [
36]. The DPPH antioxidant assay was done on the basis of the ability of 1, 1-diphenyl-2-picryl-hydrazyl (DPPH), a stable free radical, which is decolorized in the presence of antioxidants [
37]. The findings of DPPH scavenging test impose a status that the plant might have active principles which showed antioxidant activity due to their redox properties, play a vital role in absorbing and neutralizing free radicals.
There is a correlation between the brine shrimp assay and in vitro growth inhibition of human solid tumor cell lines demonstrated by the National Cancer Institute (NCI, USA). The significant toxicity of plants is principally contributed by the presence of alkaloids, glycosides, steroids, tannins and flavonoids which were showed in preliminary phytochemical screening [
38]. Our findings supported that the extract might have active constituents which is responsible for anti-tumor potential of the extract.
In anti microbial assay by disc diffusion assay the extract showed dose dependent inhibition. It is evident that alkaloids have potentials to show antimicrobial activity [
39]. In phytochemical screening we found alkaloid in the extract which may be correlated in this context. Presence of tannin in LMCA may also be responsible for antimicrobial activity [
40].
For evaluation of analgesic activity two established method were employed. Acetic acid induced writhing
test is a chemical method used to induce pain of peripheral origin by injection. Such pain stimulus leads to the release of free arachidonic acid from tissue phospholipids [
41]. It is a sensitive procedure used for the evaluation of peripherally acting analgesics. Peritoneal mast cells, acid sensing ion channels and the prostaglandin are responsible for mediating the response [
42,
43]. In this test the extract produced significant inhibition of pain which indicates the analgesic potential of the extract.
Research found that the early phase pain sensation (immediately after injection) might be caused by C-fiber activation as a result of peripheral stimulus where as the late phase (starting approximately 15 min after formalin injection) appears to be dependent on the integration of an inflammatory reflection, NMDA exhilaration and non-NMDA receptors and NO cascade in the peripheral tissue and the functional changes in the dorsal horn of the spinal cord. The result of the test suggests that LMCA causes partial inactivation of NMDA and non-NMDA [
44,
45].
Xylene produces severe vasodilation, edematous changes of skin and of inflammatory cellular infiltration when applied topically [
46]. As the extract reduced inflammatory symptoms it would be the reflective sign of the anti inflammatory potential of LMCA. The findings of the most classical acute anti-inflammatory activity evaluation method, carrageenan induced paw edema test [
47] suggest that LMCA might have potential which is responsible for potent anti-inflammatory action possibly due to the inhibition the mediators of inflammation, principally prostaglandin [
48].
Research has been made to show the anti-diarrheal activity may be due to the presence of tannins, saponin and terpenoids [
49,
50]. It is withal evident that flavonoids and polyphenols were exposed to have anti-diarrheal activities [
51]. As in case of castor oil-induced diarrhea test and magnesium induced enteropooling test the extract produced marked reduction in defecation and intestinal fluid secretion respectively, it might be concluded that the extract posses denoting antidiarrheal activity.
Conclusion
In the current investigation, LMCA was evaluated for in vitro antioxidant, brine shrimp lethality, antimicrobial activity and in vivo analgesic activity, anti-inflammatory activity, antidiarrheal activity. The outcomes of this evaluation have exhibited that methanolic leaf extract is rich in antioxidant properties and has significant cytotoxic potentials also. Both Gram positive and Gram negative bacterial strains growth were controlled effectively by the extract. This study also showed that the LMCA have significant analgesic and anti-inflammatory effects at different doses. At different doses the plant extract showed significant dose dependent delayed onset of diarrhea induced by castor oil and magnesium when compared with the control. Different types of phytochemical constituents like alkaloids, flavonoids, glycosides, saponins and tannins present in the plant, which may be responsible for the observed activities. However well-structured in vitro and in vivo evaluations would be required to identify the bioactive compounds responsible for these activities as well as to examine the underlying mechanism action to find out novel lead molecules.
Acknowledgements
The authors would like to express their gratitude to Department of Pharmacy, Jahangirnagar University, Savar, Dhaka, Bangladesh for instantaneous support during the period of the study.