Effect of Paracetamol on Renal Function in Plasmodium Knowlesi Malaria

Acute kidney injury is a common complication of severe Plasmodium knowlesi malaria, and an important contributor to mortality.

The exact pathogenic mechanisms of AKI in knowlesi malaria are not known, however it is hypothesised that haemolysis of red blood cells and subsequent release of cell-free haemoglobin leads to oxidative stress and lipid peroxidation in the renal tubules.

A novel mechanism of paracetamol was recently demonstrated, showing that paracetamol acts as a potent inhibitor of hemoprotein-catalyzed lipid peroxidation. In a proof of concept trial, paracetamol at therapeutic levels was shown to significantly decrease oxidative kidney injury and improve renal function by inhibiting the hemoprotein-catalyzed lipid peroxidation in a rat model of rhabdomyolysis-induced renal injury.

The investigators hypothesize that this novel inhibitory mechanism of paracetamol may provide renal protection in adults with knowlesi malaria by reducing the hemoprotein-induced lipid peroxidation that occurs in haemolytic conditions. As there is currently no consensus that exists concerning adequate medical treatment for severe malaria complicated by intravascular haemolysis and AKI, the potential application of paracetamol would be of benefit, especially as it is safe and widely available.

Plasmodium knowlesi is the most common cause of malaria, and malaria deaths, in Sabah, Malaysia. Acute kidney injury (AKI) is a common feature of severe knowlesi malaria; however the mechanisms of AKI in knowlesi malaria are unknown. In falciparum malaria, recent evidence suggests that oxidative stress from haemolysis-related cell-free haemoglobin (CFHb) may contribute to pathogenesis of AKI.

Cell-free haemoglobin and oxidative stress: CFHb is released during intravascular haemolysis, and when exceeding the binding capacity of plasma haptoglobin, is filtered by the glomeruli and enters the renal tubules. CFHb is pathogenic as the ferrous heme can be oxidized to the ferric state, conferring peroxidase activity to the hemoglobin. Consequently, the hemoglobin can reduce hydroperoxides, such as hydrogen peroxide (H2O2) and lipid hydroperoxides, which generate the ferryl state of heme (FeIV=O) and a protein radical. The ferryl heme and protein radical can then generate lipid radicals by oxidation of free and phospholipid-esterified unsaturated fatty acids. The arachidonic side chains of membrane phospholipids are particularly vulnerable to this free radical-mediated damage in the complex cascade of lipid oxidation leading to the generation of F2-isoprostanes (F2-IsoPs) and isofurans (IsoFs). F2-IsoPs and IsFs are increased in severe falciparum malaria, and have been shown to induce vasoconstriction associated with renal injury in other haemolytic conditions including rhabdomyolysis, sepsis and post-operatively.

Paracetamol and oxidative stress: A novel mechanism of paracetamol was recently demonstrated, showing that paracetamol acts as a potent inhibitor of hemoprotein-catalyzed lipid peroxidation by reducing ferryl heme to its less toxic ferric state and quenching globin radicals. In a proof of concept trial, paracetamol at therapeutic levels was shown to significantly decrease oxidative kidney injury and improve renal function by inhibiting the hemoprotein-catalyzed lipid peroxidation in a rat model of rhabdomyolysis-induced renal injury. In a retrospective study of patients with sepsis, receiving paracetamol in the setting of raised CFHb was associated with reduced lipid peroxidation, and reduced risk of death. More recently, in a randomized placebo-controlled trial, paracetamol was associated with a reduction in F2-IsoPs and improved renal function in adults with sepsis and detectable CFHb.

Rationale: The investigators hypothesize that paracetamol may provide renal protection in patients with severe knowlesi malaria by reducing the hemoprotein-induced lipid peroxidation that occurs in haemolytic conditions. As there is currently no consensus that exists concerning adequate medical treatment for severe malaria complicated by intravascular haemolysis and AKI, the potential application of paracetamol would be of great benefit, especially as it is safe and widely available.

Proposed activities: The main activity proposed is a randomised, open label, controlled trial of regularly-dosed paracetamol, versus no paracetamol, in patients with knowlesi malaria, to assess the effect of paracetamol on renal function and oxidative stress.

Eligibility Criteria:
Inclusion Criteria:

1. Patient age ≥ 5 years
2. Presence of P. knowlesi malaria, confirmed by positive blood smear with asexual forms of P. knowlesi.
3. Temperature \>38C on admission or fever during the preceding 48 hours
4. Enrolled within 18 hours of commencing antimalarial treatment
5. Written informed consent from patient or attending relative able to and willing to give informed consent. Consent form and information sheets will be translated into Malay and copies provided to the patient.

Exclusion Criteria:

1. Patient or relatives unable or unwilling to give informed consent
2. Contraindication or allergy to paracetamol or artesunate therapy
3. Known cirrhosis, or \>6 standard alcoholic drinks/day
4. Pregnancy