Disease Tolerance: Linking Sickness Behaviours to Metabolism Helps Mitigate Malaria

Vitamin C co-administration with artemether-lumefantrine abrogates chronic stress exacerbated Plasmodium berghei-induced sickness behaviour, inflammatory and oxidative stress responses in mice

This study evaluated the effects of vitamin C and artemether-lumefantrine (AL) on sickness behaviour and oxido-inflammatory response in chronically stressed mice infected with Plasmodium berghei. Sickness behaviour severity was examined with weight and assessment of mice behaviours. Results showed that stress increased parasitaemia in infected mice. Vitamin C co-administration with AL increased parasite clearance over AL alone, and modulated inflammatory cytokines (TNF-α, IL-1β, IL-10, IL-12) and antioxidant parameters in plasma and brain tissue. Conclusively, stress worsens malaria-induced sickness behaviour and up-regulates the inflammatory and oxidative stress response. Co-administration of vitamin C with AL appears to counteract these detrimental effects.

Ananas comosus (L) Merrill (pineapple) fruit peel extract demonstrates antimalarial, anti-nociceptive and anti-inflammatory activities in experimental models

ETHNOPHARMACOLOGY RELEVANCE

Pineapple (Ananas comosus) peel is a major waste in pineapple canning industry and it is reported to be used in ethnomedicine as a component of herbal remedies for malarial management. This study aimed to evaluate the antimalarial, antinociceptive and anti-inflammatory properties of Ananas comosus peel extract (PEAC).

METHODS

Ananas comosus peel was extracted with 80% methanol. PEAC (100, 200 and 400 mg/kg) was investigated for antimalarial effect using Peter's 4-day suppressive test (4-DST) model in mice. Antinociceptive activity of PEAC was investigated in hot plate, acetic acid-induced writhing and formalin tests in mice. The anti-inflammatory activity was evaluated using the lipopolysaccharides-induced sickness behavior in mice and carrageenan-induced air pouch in rats' models.

RESULTS

PEAC could not significantly (p > 0.05) suppressed parasitemia level at 7-day post-infection in 4-DST. PEAC (400 mg/kg) mildly prolongs survival of infected mice up till day 21. PEAC demonstrated significant (p < 0.05) antinociceptive activity by increasing latency to jump on the hot plate, reduced number of writhings in acetic acid test and reduced paw licking time in 2^nd phase of formalin test. PEAC significantly reduced anxiogenic and depressive-like symptoms of sickness behavior in LPS-injected mice. PEAC demonstrated significant anti-inflammatory activity in carrageenan-induced air pouch experiment by reducing exudates formation, inflammatory cell counts, and nitrite, tumor necrosis factor-alpha and interleukin-6 levels.

CONCLUSION

Ananas comosus peel extract demonstrated mild antimalarial activity but significant anti-nociceptive and anti-inflammatory properties probably mediated via inhibition of pro-inflammatory mediators.

Host-shift as the cause of emerging infectious diseases: Experimental approaches using Drosophila-virus interactions

Host shifts, when a cross-species transmission of a pathogen can lead to successful infections, are the main cause of emerging infectious diseases, such as COVID-19. A complex challenge faced by the scientific community is to address the factors that determine whether the cross-species transmissions will result in spillover or sustained onwards infections. Here we review recent literature and present a perspective on current approaches we are using to understand the mechanisms underlying host shifts. We highlight the usefulness of the interactions between Drosophila species and viruses as an ideal study model. Additionally, we discuss how cross-infection experiments - when pathogens from a natural reservoir are intentionally injected in novel host species- can test the effect cross-species transmissions may have on the fitness of virus and host, and how the host phylogeny may influence this response. We also discuss experiments evaluating how cooccurrence with other viruses or the presence of the endosymbiont bacteria Wolbachia may affect the performance of new viruses in a novel host. Finally, we discuss the need of surveys of virus diversity in natural populations using next-generation sequencing technologies. In the long term, these approaches can contribute to a better understanding of the basic biology of host shifts.

A First Plasmodium vivax Natural Infection Induces Increased Activity of the Interferon Gamma-Driven Tryptophan Catabolism Pathway

The human immune response that controls Plasmodium infection in the liver and blood stages of the parasite life cycle is composed by both pro- and anti-inflammatory programs. Pro-inflammatory responses primarily mediated by IFN-γ controls the infection, but also induce tolerogenic mechanisms to limit host damage, including the tryptophan (TRP) catabolism pathway mediated by the enzyme Indoleamine 2,3-Dioxygenase (IDO1), an enzyme that catalyzes the degradation of TRP to kynurenines (KYN). Here we assessed total serum kynurenines and cytokine dynamics in a cohort of natural Plasmodium vivax human infection and compared them to those of endemic healthy controls and other febrile diseases. In acute malaria, the absolute free kynurenine (KYN) serum levels and the KYN to TRP (KYN/TRP) ratio were significantly elevated in patients compared to healthy controls. Individuals with a diagnosis of a first malaria episode had higher serum KYN levels than individuals with a previous malaria episode. We observed an inverse relationship between the serum levels of IFN-γ and IL-10 in patients with a first malaria episode compared to those of subjects with previous history of malaria. Kynurenine elevation was positively correlated with serum IFN-γ levels in acute infection, whereas, it was negatively correlated with parasite load and P. vivax LDH levels. Overall, the differences observed between infected individuals depended on the number of Plasmodium infections. The decrease in the KYN/TRP ratio in malaria-experienced subjects coincided with the onset of anti-P. vivax IgG. These results suggest that P. vivax infection induces a strong anti-inflammatory program in individuals with first time malaria, which fades with ensuing protective immunity after subsequent episodes. Understanding the tolerance mechanisms involved in the initial exposure would help in defining the balance between protective and pathogenic immune responses necessary to control infection and to improve vaccination strategies.