Effect of mild medical hypothermia on in vitro growth of Plasmodium falciparum and the activity of anti-malarial drugs

Abstract

BackgroundCerebral malaria remains a medical emergency with high mortality. Hypo-perfusion due to obstructed blood vessels in the brain is thought to play a key role in the pathophysiology of cerebral malaria leading to neurological impairment, long-term neuro-cognitive sequelae and, potentially, death. Due to the rapid reversibility of vascular obstruction caused by sequestered Plasmodium falciparum, it is hypothesized that mild medical hypothermia—a standard intervention for other medical emergencies—may improve clinical outcome. This preclinical in vitro study was performed to assess the impact of mild hypothermia on parasite growth and the intrinsic activity of anti-malarials drugs.MethodsThree laboratory-adapted clones and two clinical isolates were used for growth assays and standardized drug sensitivity assessments using the standard HRP2 assay. All assays were performed in parallel under normothermic (37 °C), mild hypothermic (32 °C), and hyperthermic (41 °C) conditions.ResultsParasite growth was higher under standard temperature condition than under hypo- or hyperthermia (growth ratio 0.85; IQR 0.25–1.06 and 0.09; IQR 0.05–0.32, respectively). Chloroquine and mefloquine had comparable in vitro activity under mild hypothermic conditions (ratios for IC50 at 37 °C/32 °C: 0.88; 95 % CI 0.25–1.50 and 0.86; 95 % CI 0.36–1.36, respectively) whereas dihydroartemisinin was more active under mild hypothermic conditions (ratio for IC50 at 37 °C/32 °C: 0.27; 95 % CI 0.19–0.27). Hyperthermia led by itself to almost complete growth inhibition and precluded further testing of the activity of anti-malarial drugs.ConclusionThis preclinical evaluation demonstrates that mild medical hypothermia inhibits in vitro growth of P. falciparum and enhances the pharmacodynamic activity of artemisinin derivatives. Based on these preclinical pharmacodynamic data, the further clinical development of mild medical hypothermia as adjunctive treatment to parenteral artesunate for cerebral malaria is warranted.

Transient temperature fluctuations severely decrease P. falciparum susceptibility to artemisinin in vitro

“…), though conditions exceeding 39 °C strongly inhibited parasite proliferation in the absence of drug (Fig. 2B), as previously reported (Rehman et al, 2016; Chen et al, 1987). Ring-stage survival was not estimated for parasites treated with a 41 °C pulse because this killed nearly all mock-treated cells.…”

“…The dependence on environmental temperature of ring-stage susceptibility to artemisinin was examined by transiently exposing pfk13 wild-type 3D7 parasites to a range of temperatures before and during the RSA 4h . Given previous data suggesting hypothermic conditions (32-34 °C) could enhance anti-plasmodial effects of artemisinin in vitro , estimated as EC 50 in a full life-cycle assay (Rehman et al, 2016), we probed a range of low temperatures (17ºC-36 °C) alongside normothermic (37 °C) conditions in parallel. In contrast to these previous results, our data suggest that environmental temperature and ring-stage artemisinin susceptibility in the 3D7 reference parasite line are negatively correlated in vitro (Fig.…”

“…However, these results show that hypothermic conditions, under exploration for the co-treatment of severe malaria patients, moderately attenuate artemisinin ring-stage cytotoxicity in vitro . As this study specifically examined the effects of transient decreases in environmental temperature, it is likely that the anti-plasmodial effects of continuous hypothermia override the brief contribution of these conditions to reducing ring-stage artemisinin susceptibility (Rehman et al, 2016). As reported previously (Rehman et al, 2016; Long et al, 2001), in our hands hyperthermia exerts strong anti-plasmodial effects on ring-stage cultures, even under transient fever conditions.…”

“…A recent case report suggested the use of controlled hypothermia (32-34 °C) improved the resolution of neurological consequences of cerebral oedema and reduced cranial perfusion, as in other vascular medical emergencies like heart attack and stroke (Gad et al, 2018). Additionally, an in vitro model of mild hypothermia suggested that this treatment may also potentiate certain frontline antimalarials including artemisinin (Rehman et al, 2016).…”

Case Report: A Case of Severe Cerebral Malaria Managed with Therapeutic Hypothermia and Other Modalities for Brain Edema

“…A recent in vitro trial suggested that P. falciparum growth was inhibited by medical hypothermia. 10 This was in concordance with other in vitro studies, suggesting FIGURE 2. Computed tomography scan of the head showing severe brain edema at presentation with loss of sulci/gyri differentiation (A) and the complete resolution of brain edema after treatment with restoration of normal radiologic brain anatomy (B).…”