4.6. Four-Day Suppressive Test

The anti-malarial activity of quercetin was assessed in male ICR mice according to the four-day suppressive test [66,67]. Mice were randomly divided into eight groups (n = 7) for P. berghei NK65 infection. Each mouse was inoculated i.p. with 0.2 mL of 2×10⁷ of pRBC (parasitised red blood cells) containing P. berghei NK65. The animals infected with NK65 strain were administered i.p. with 2.5, 5, 10, 25, and 50 mg/kg BW/day quercetin. In a separate experiment, animals were randomly divided into six groups (n = 7) for P. berghei ANKA infection. Each mouse was inoculated i.p. with 0.2 mL of 2×10⁷ of pRBC containing P. berghei ANKA. The animals infected with ANKA strain were then administered i.p. with 15, 25, and 50 mg/kg BW/day quercetin. For both infections, CQ at 10 mg/kg BW/day was used as anti-malarial reference drug (positive control), LiCl at 100 mg/kg BW/day as GSK3 inhibitor reference drug, and an injection of 0.2 mL of 0.85% (w/v) NaCl to the infected animals as non-treated controls (negative control). Mice were administered with test compounds for four consecutive days, starting at one hour after parasite inoculation on day 0 (D0). Thin blood smears were prepared at day 4 (D4) from tail blood of infected mice. The percentage of chemo-suppression (PC) (%) was then determined by using the following formula:

where A represents the percentage of parasitaemia (%) of non-treated negative control and B represents the percentage of parasitaemia (%) in test groups.