[In vitro observation on effect of nitric oxide on exflagellation of Plasmodium yoelii].

Objective: To observe the effect of nitric oxide (NO) on exflagellation of malaria parasite.

Methods: The level of parasitemia and gametocytaemia in DBA/2 mice infected with Plasmodium yoelii 17XL was measured by scanning Giemsa-stained blood smears, and the NO level in culture supernatant of splenocytes was checked using Griess reaction. The mice were injected with different doses of NO donor (NOC5) on day 4 post-infection, and control mice were injected with NOC5 precursor. On day 6 post-infection, mice were injected with NOS inhibitor (L-NMMA), and control mice were injected with D-NMMA and PBS, respectively. Blood samples were collected from tail vein of mice before injection, 30 and 60 min after being injected with NOC5 and NOC5 precursor, 4 and 8 h after being injected with L-NMMA, D-NMMA, and PBS respectively. Exflagellation number of gametocytes in blood culture was counted under microscope. Results The NO level in culture supernatant of splenocytes from mice on day 4 and 6 post-infection was 16.5 mmol/L and 30.4 mmol/L, and exflagellation number was 11.33 and 0.66, respectively. The number of exflagellation in parasitized erythrocytes, obtained from mice on day 4 post-infection, was 5.33 and 2.66, respectively, 30 and 60 min after injection of 1 mg NO donor (NOC5), significantly lower than that of the control (P<0.01). The number of exflagellation in parasitized erythrocytes derived from mice on day 6 post-infection was 1.83, 8 h after the injection of NOS inhibitor (L-NMMA), which was significantly higher than that of the control (P<0.01).

Conclusion: NO is a major effector molecule resulting in natural transmission-blocking of malaria parasite by directly inhibiting exflagellation of male gametocytes.