Studies on hepatic oxidative stress and antioxidant defence system during chloroquine/poly ICLC treatment of Plasmodium yoelii nigeriensis infected mice

Malaria inflammation by xanthine oxidase-produced reactive oxygen species

Malaria is a highly inflammatory disease caused by Plasmodium infection of host erythrocytes. However, the parasite does not induce inflammatory cytokine responses in macrophages in vitro and the source of inflammation in patients remains unclear. Here, we identify oxidative stress, which is common in malaria, as an effective trigger of the inflammatory activation of macrophages. We observed that extracellular reactive oxygen species (ROS) produced by xanthine oxidase (XO), an enzyme upregulated during malaria, induce a strong inflammatory cytokine response in primary human monocyte-derived macrophages. In malaria patients, elevated plasma XO activity correlates with high levels of inflammatory cytokines and with the development of cerebral malaria. We found that incubation of macrophages with plasma from these patients can induce a XO-dependent inflammatory cytokine response, identifying a host factor as a trigger for inflammation in malaria. XO-produced ROS also increase the synthesis of pro-IL-1β, while the parasite activates caspase-1, providing the two necessary signals for the activation of the NLRP3 inflammasome. We propose that XO-produced ROS are a key factor for the trigger of inflammation during malaria.

Effect of chloroquine, methylene blue and artemether on red cell and hepatic antioxidant defence system in mice infected with Plasmodium yoelii nigeriensis

Reactive oxygen species are mediators of tissue injury and are involved in malaria infection. In this study, the status of red cell and hepatic oxidative stress and antioxidant defence indices were investigated during Plasmodium yoelii nigeriensis (P. yoelii) infection, and treatment with chloroquine (CQ), methylene blue (MB) or artemether (ART) in mice. P. yoelii infection caused a significant (p < 0.05) increase in oxidative stress as evidenced by the elevated level of malondialdehyde. This was followed by a significant decrease (p < 0.05) in hepatic antioxidant defence indices, viz. reduced glutathione (GSH) and glutathione-S-transferase (GST). Also, the red cell catalase activity was significantly (p < 0.05) lower in malaria infection, while there was no significant difference (p > 0.05) in the superoxide dismutase (SOD) activity of infected mice when compared to untreated normal. Treatment of infected mice with the three antimalarials showed that the drugs suppressed the parasitaemia in the order CQ > ART > MB. CQ, MB and ART treatment of infected mice caused a significant (p < 0.05) increase in the levels of hepatic GSH and GST. Specifically, CQ, MB and ART increased the levels of hepatic GSH by 108, 124 and 98 %, respectively, at day 6. Also, ART treatment of infected mice significantly (p < 0.05) elevated the red cell SOD level by 200 % at day 3. Taken together, the findings suggest that the antimalarial effect of CQ, MB and ART countered the P. yoelii-induced oxidative stress leading to the elevation of enzymatic and non-enzymatic antioxidants in the host system.

Effect of Plasmodium and Salmonella co-infection in a murine model

The present study was designed to evaluate the effect of Plasmodium and Salmonella co-infection in LACA mice. The parasitaemic level, bacterial load, histological alterations and levels of oxidants/antioxidant activity were measured. Co-infected mice had a high parasitaemic level, increased bacterial load, and died earlier than Plasmodium-infected mice. Histologically, co-infected mice had more architectural damage in the liver, spleen, kidney, and brain than the control groups. The level of lipid peroxidation was significantly increased and the activities of antioxidative enzymes (superoxide dismutase and catalase) were decreased in all organs of co-infected mice compared to the control groups, indicating depression of the antioxidant defense system. The present study demonstrates more severe histological and biochemical alterations in co-infected mice, highlighting the importance of early diagnosis for selection of appropriate treatments and reducing the likelihood of further complications.

Broad-spectrum drugs against viral agents

Development of antivirals has focused primarily on vaccines and on treatments for specific viral agents. Although effective, these approaches may be limited in situations where the etiologic agent is unknown or when the target virus has undergone mutation, recombination or reassortment. Augmentation of the innate immune response may be an effective alternative for disease amelioration. Nonspecific, broad-spectrum immune responses can be induced by double-stranded (ds)RNAs such as poly (ICLC), or oligonucleotides (ODNs) containing unmethylated deocycytidyl-deoxyguanosinyl (CpG) motifs. These may offer protection against various bacterial and viral pathogens regardless of their genetic makeup, zoonotic origin or drug resistance.

Changes in rodent-erythrocyte methemoglobin reductase system produced by two malaria parasites, viz. Plasmodium yoelii nigeriensis and Plasmodium berghei

The methemoglobin reductase system plays a vital role in maintaining the equilibrium between hemoglobin and methemoglobin in blood. Exposure of red blood cells to oxidative stress (pathological/physiological) may cause impairment to this equilibrium. We studied the status of erythrocytic methemoglobin and the related reductase system during Plasmodium yoelii nigeriensis infection in mice and P. berghei infection in mastomys. Malaria infection was induced by intraperitoneal inoculation with 10(6) infected erythrocytes. The present investigation revealed a significant decrease in the activity of methemoglobin reductase, with a concomitant rise in methemoglobin content during P. yoelii nigeriensis infection in mice erythrocytes. This was accompanied with a significant increase in reduced glutathione and ascorbate levels. The activity of lactate dehydrogenase, glucose 6-phosphate dehydrogenase and glutathione reductase increased with a progressive rise in parasitemia. However, no methemoglobin or associated reductase activity was detected in normal and P. berghei-infected mastomys. P. berghei infection in mastomys resulted in an increase in the level of reduced glutathione and ascorbate in erythrocytes, and also in the activity of lactate dehydrogenase, glucose 6-phosphate dehydrogenase and glutathione reductase. These results suggest that antioxidants/antioxidant enzymes may prevent or reduce the formation of methemoglobin in the host and thereby protect the host from methemoglobinemia.

Effect of tumor necrosis factor on hepatic oxidative stress and antioxidant defense indices in normal and Plasmodium yeolii nigeriensis infected mice

BACKGROUND

Plasmodium yoelii nigeriensis (P. y. nigeriensis) produces lethal malaria infection in Swiss albino mice. Reactive oxygen species (ROS) such as superoxide anion, hydrogen peroxide along with endogenously produced tumor necrosis factor (TNF) have been implicated in the pathogenesis of malaria.

OBJECTIVE

Study the effect of TNF on hepatic oxidative stress and antioxidant defense indices in normal and P. y. nigeriensis infected mice.

METHODS

Mice were divided into four groups. Normal group, TNF treated group, P. y. nigeriensis infected group, and P. y. nigeriensis infected mice treated with TNF group (250 microg/kg body weight, i.p.).

RESULTS

TNF treatment of normal mice caused a highly significant decrease in hepatic superoxide dismutase (SOD) while changes in other oxidative stress and antioxidant defense indices were nonsignificant. On the other hand, TNF treatment of P. y. nigeriensis infected mice caused a highly significant increase in hepatic xanthine oxidase, lipid peroxidation and a significant decrease in hepatic SOD with respect to infected mice.

CONCLUSION

These results suggest that exogenous TNF acts synergistically with P. y. nigeriensis infection to generate oxidative stress in the host and also causes an impairment of antioxidant defense enzyme such as superoxide dismutase.