Role of complement components in the susceptibility to Plasmodium berghei infection among inbred strains of mice

Xylopic acid-amodiaquine and xylopic acid-artesunate combinations are effective in managing malaria in Plasmodium berghei-infected mice

Background

Evidence of Plasmodium resistance to some of the current anti-malarial agents makes it imperative to search for newer and effective drugs to combat malaria. Therefore, this study evaluated whether the co-administrations of xylopic acid-amodiaquine and xylopic acid-artesunate combinations will produce a synergistic anti-malarial effect.

Methods

Antiplasmodial effect of xylopic acid (XA: 3, 10, 30, 100, 150 mg kg⁻¹), artesunate (ART: 1, 2, 4, 8, 16 mg kg⁻¹), and amodiaquine (AQ: 1.25, 2.5, 5, 10, 20 mg kg⁻¹) were evaluated in Plasmodium berghei (strain ANKA)-infected mice to determine respective ED₅₀s. Artemether/lumefantrine was used as the positive control. XA/ART and XA/AQ were subsequently administered in a fixed-dose combination of their ED₅₀s (1:1) and the combination fractions of their ED₅₀s (1/2, 1/4, 1/8, 1/16, and 1/32) to determine the experimental ED₅₀s (Z_exp). An isobologram was constructed to determine the nature of the interaction between XA/ART, and XA/AQ combinations by comparing Z_exp with the theoretical ED₅₀ (Z_add). Bodyweight and 30-day survival post-treatment were additionally recorded.

Results

ED₅₀s for XA, ART, and AQ were 9.0 ± 3.2, 1.61 ± 0.6, and 3.1 ± 0.8 mg kg⁻¹, respectively. The Z_add, Z_exp, and interaction index for XA/ART co-administration was 5.3 ± 2.61, 1.98 ± 0.25, and 0.37, respectively while that of XA/AQ were 6.05 ± 2.0, 1.69 ± 0.42, and 0.28, respectively. The Z_exp for both combination therapies lay significantly (p < 0.001) below the additive isoboles showing XA acts synergistically with both ART and AQ in clearing the parasites. High doses of XA/ART combination significantly (p < 0.05) increased the survival days of infected mice with a mean hazard ratio of 0.40 while all the XA/AQ combination doses showed a significant (p < 0.05) increase in the survival days of infected mice with a mean hazard ratio of 0.27 similar to AL. Both XA/ART and XA/AQ combined treatments significantly (p < 0.05) reduced weight loss.

Conclusion

Xylopic acid co-administration with either artesunate or amodiaquine produces a synergistic anti-plasmodial effect in mice infected with P. berghei.

Complement factors C1q, C3 and C5 in brain and serum of mice with cerebral malaria

Background

The patho-mechanisms leading to brain damage due to cerebral malaria (CM) are yet not fully understood. Immune-mediated and ischaemic mechanisms have been implicated. The role of complement factors C1q, C3 and C5 for the pathogenesis of CM were investigated in this study.

Methods

C57BL/6J mice were infected with Plasmodium berghei ANKA blood stages. The clinical severity of the disease was assessed by a battery of 40 standardized tests for evaluating neurological functions in mice. Brain homogenates and sera of mice with CM, infected animals without CM and non-infected control animals were analyzed for C1q, C3 and C5 up-regulation by Western blotting.

Results

Densitometric analysis of Western blots of brain homogenates yielded statistically significant differences in the levels of C1q and C5 in the analyzed groups. Correlation analysis showed a statistically significant association of C1q and C5 levels with the clinical severity of the disease. More severely affected animals showed higher levels of C1q and C5. No differences in complement levels were observed between frontal and caudal parts of the brain. Densitometric analysis of Western blot of sera yielded statistically lower levels of C1q in infected animals without CM compared to animals of the control group.

Conclusion

The current study provides direct evidence for up-regulation of complement factors C1q and C5 in the brains of animals with CM. Local complement up-regulation is a possible mechanism for brain damage in experimental cerebral malaria.

Measurement of modulation of mouse complement levels in vivo, utilizing a microtiter hemolytic assay

The complement system, with its protein components, plays a fundamental role in host defense as the major immunological mechanism of innate immunity. Effects of immunotoxic agents on serum complement have not been studied due to the lack of an assay capable of measuring the in vivo effects of compounds in the mouse, the species of choice for immunotoxicological testing. A microtiter hemolytic assay was developed and utilized to measure modulation of serum complement in vivo in B6C3F1 mice. In order to validate this functional assay. Cobra Venom Factor (CVF) was used to produce decomplementation. CVF administered intravenously produced a dose-dependent suppression of complement activity when evaluated 24 hours after a single injection. Administration of 25 or more anticomplementary units (ACU/kg) completely abolished functional hemolytic activity. The duration of the effect was dose dependent with 100 ACU/kg suppressing the response for 48 hours. A decomplemented state could be maintained for up to 6 days, with a second injection. A third injection failed to prolong the decomplementation. Elevated complement levels were obtained following a single injection with Pyran Copolymer. Pyran, a macrophage activator, produce a dose dependent increase in serum complement levels 8 days after administration. The microtiter hemolytic complement assay represents a useful tool capable of evaluating the in vivo effects of agents on serum complement in the mouse.

Serum inhibition of merozoite dispersal from Plasmodium falciparum schizonts: indicator of immune status

Specific immune serum was found to inhibit the dispersal of the merozoites from mature schizonts, thus interfering with their subsequent reinvasion of new host erythrocytes. This phenomenon is viewed as a protective mechanism against malaria which can be measured in vitro and reflects the immune status of the donor.

Trypanosoma musculi infections in normocomplementemic, C5-deficient, and C3-depleted mice

The role of complement in host resistance to infection with Trypanosoma musculi was studied in normal, C5-deficient, and C3-depleted mice. Infections in normocomplementemic strains (CBA and B10.D2/n) were generally similar to those in strains genetically deficient in C5 (A and B10.D2/o). There were no differences in inhibition of reproduction, duration of infection, persistence of parasites in the kidneys, or resistance to reinfection. However, peak parasitemias in B10.D2/o mice were slightly greater than in B10.D2/n mice. In addition, B10.D2/o mice had slightly decreased serum levels of C1 early in the course of infection and of C3 early during the elimination of adult forms. These components were unchanged or increased in infections of B10.D2/n. Depletion of C3 and late-acting components in B10.D2/n mice by treatment with cobra venom factor during the reproductive stage of infection resulted in an increase of reproductive forms before the apparent development of ablastic immunity as well as slightly greater peak parasitemias when compared with those of untreated controls. Cobra venom factor treatment of B10.D2/o mice during the reproductive stage did not alter the course of infection. Cobra venom factor treatment of C3H mice during the adult stage prolonged infections by interfering with parasite elimination. It is concluded that complement-mediated lysis is not involved in control of T. musculi. It is not clear whether a C3-dependent function such as phagocytosis may facilitate elimination of the parasites. The major difference in degree of parasitemias among the various strains of mice studied is due to genetic factors rather than the levels of C3, C5, or late-acting complement components.