2.1 Collection of Plant Sample
Matured leaves were harvested from stands of J. secunda plants from three different sites in Lusada, Ado Odo Ota Local Government Area (LGA) Ogun State, Nigeria.
2.2 Preparation of Plant Extract
Cold maceration technique was adopted for the extraction by simply soaking five hundred grams (500g) of the powdered leaves in five (5) litres of eighty percent (80%) ethanol for three days, and the bottle containing the mixtures was agitated at intervals. The liquid extract was filtered into a clean container using a piece of chiffon material after 72 hours. The filtrate was poured into an evaporating dish and placed on a water bath to obtain a solid and more concentrated form of the extract [15].
2.3 Evaluation of Phytochemical Constituent of Plant Extract
A standard method [16] was adopted in the phytochemical screening of the extract. The Gas Chromatography-Mass Spectrometry (GC-MS) analysis was conducted using a 7890B GC System (Agilent Technologies, USA) coupled with a 5977A Mass Selective Detector (Agilent Technologies, USA). The leaf extract of J. secunda was diluted in methanol, and 2μL of the mixture was injected into the GC-MS machine using a micro-syringe. The experimental parameters for the GC-MS system were: initial oven temperature: 70oC, Equilibration Time: 1 min, Max Temperature: 325 ̊C, Slow Fan: Disabled, Oven Program: 5°C/min On 250°C for 1 min, #1 then 30°C/min to 300°C for 0 min, Post Run: 50 °C. Cryo: Off, Front SS Inlet He – Mode: Split. Heater: On 250°C, Pressure: On 11.089psi, Total Flow on 19.204mL/min, Septum Purge Flow: On 3 mL/min, Gas Saver: off, Purge flow to Split vent: on 15mL/min at 0.75min. Holdup time: 1.2386min, Flowrate: 1.0mL/minute
2.4 Maintenance of Experimental Animals
Seventy-five (75) male Swiss albino mice with body weight between 20 and 30g were obtained for this study. Chicken grower’s marsh and water was provided at all time for the experimental mice [17]. The overall maintenance of the experimental animals was in accordance with the procedures approved by the ethical committee of the institution where the experiment was conducted.
2.5 Determination of Lethal Dose of Plant Extract
The median lethal dose of the ethanol leaf extract of J. secunda was determined per the Up and Down method described by the Organization for Economic Co-orporation and Development [18].
2.6 Evaluation of Antiplasmodial Activity of Plant Extract
The infected experimental mice were inoculated intraperitoneally with 0.2mL of blood from donor mouse infected with P. berghei NK65 (30% parasitaemia) and normal saline (1:9) containing 105 P. berghei parasitized erythrocytes. The seven-day curative test was evaluated seventy-two (72) hours after inoculation and confirmation of parasitemia in thirty (30) mice, and they were randomly assigned into six (6) groups. The suppressive test was conducted, and the inception was precisely three (3) hours after the infection of mice for a four-day duration using thirty (30) mice. These tests were performed using the method of Onyegeme-Okerentaa et al. [19], with a slight modification. Groups 1–3 were the control groups treated with 1 mL of normal saline (the negative control), 25 mg/kg of chloroquine (the positive control), and the uninfected and untreated groups (the normal control), respectively. Groups 4-6 were given 500 mg/kg, 1000 mg/kg, and 1,500 mg/kg of the crude extract based on the LD50 for the ethanol leaf extract of J. secunda determined in this study. The oral treatment was done once a day.
2.7 Collection of Blood and Liver Samples
The animals were sacrificed after inhaling vapour from ketamine-damped cotton wool at the end of the experiment. The blood of experimental animals was collected in EDTA bottles for haematological and biochemical analysis through cardiac aspiration. A portion of the liver was placed in cold phosphate buffer for antioxidant and MDA analysis. A small portion of liver of mice was preserved in phosphate-buffered formalin.
2.8 Determination of Parasitaemia and Percentage Chemosuppression
The number of parasitized erythrocytes in ten (10) slides prepared with thin blood smears was counted, and the average was computed to give the parasitemia of each mouse [20].
Percentage parasitaemia and chemosuppression was calculated as:
Parasitaemia (%) = (Number of parasitized RBC/Total number of RBC) x 100
A= mean % parasitaemia in negative control
B= mean % parasitaemia in treated group
2.9 Assessment of Haematological Parameters
The Red Blood Cell (RBC), White Blood Cell (WBC), Packed Cell Volume (PCV) and Haemoglobin (HGB) concentration were analyzed using a Biobase Bk6100 haematology analyzer [21] in blood samples collected in Ethylene Diamine Tetracetic Acid (EDTA) bottles.
2.10 Assessment of Plasma and Liver Biochemicals
The liver homogenate was used to evaluate the levels of Malondialdehyde (MDA), Superoxide dismutase (SOD), Catalase (CAT) and reduced Glutathione (GSH) using a Sigma Aldrich Assay kit. Blood in EDTA bottles was used to check the concentrations of Alanine aminotransferase (Randox kit), Interleukin-10 and Tumour Necrosis Factor-α using ELISA kits by FineTest.
2.11 Liver Histopathological Studies
The liver of mice preserved in phosphate-buffered formalin was prepared for histological study using standard histotechnique and viewed with a microscope at 400 × magnification. The photomicrographs were taken using a digital camera [22].
2.12 Data Analyses
One-way Analysis of Variance (ANOVA) was used to determine statistical differences in the antiplasmodial activity, haematological and biochemical parameters in the in vivo suppressive and curative test. Tukey HSD test was used to rank the difference between significant parameters at p<0.05. Data were represented in tables and summarized in form of mean ± standard error. Statistical analyses were done using 'R' statistical package (version 4.1.2) for windows.