Paracetamol Effect on Oxidative Stress and Renal Function in Severe Malaria

Mortality in severe malaria remains ~15% despite the best available parasiticidal antimalarial therapy, intravenous artesunate. Adjunctive therapies in combination with anti-parasitic drugs have the potential to improve outcomes. However, currently there are no proven adjunctive therapies for the treatment of severe malaria, which can improve case-fatality when used in combination with anti-parasitic drugs. This research proposal focuses on exploring if paracetamol prevents renal dysfunction caused by free haemoglobin induced oxidative damage in severe malaria.

Blackwater fever epidemiology As early as the 1800s, blackwater fever complicating severe malaria caused by Plasmodium falciparum was recognized as an important cause of morbidity and mortality, with a 25-30% mean mortality rate. The etiology and pathogenesis is poorly understood but it is characterized by massive intravascular haemolysis and passage of black or red urine, which can lead to renal impairment and death. This manifestation was linked to quinine therapy as its occurrence nearly disappeared during the chloroquine era from 1950 to 1980. Since 1990, the resurgence in the number of cases noted in both malaria-free and malarious areas in non-immune and immune individuals has generated renewed interest into this manifestation of severe malaria. The largest malaria clinical trials report blackwater fever incidences of 7% and 4% in Asian adult patients with severe malaria treated with artesunate and quinine, respectively and 4% in African children treated with either drug. The prevalence of blackwater fever in Chittagong, Bangladesh was recently determined in a pilot study to be 15% with associated renal failure and mortality rates of 42.9% and 14.2% respectively.

Blackwater fever pathogenesis Although the exact mechanism linking falciparum malaria and blackwater fever is uncertain, numerous explanations have been suggested. It has been proposed to occur in 4 specific circumstances: (1) in case patients with G6PD deficiency with or without malaria who take oxidant drugs (primaquine) (2) in case patients with G6PD deficiency and malaria untreated and treated with quinine (3) when patients (normal G6PD) with severe malaria are treated with quinine (4) when people exposed to malaria self-medicate with quinine or related amino-alcohol drugs. However, new circumstances of blackwater fever have emerged, occurring in patients with normal G6PD levels with severe malaria who have received artesunate rather than quinine.

Role of oxidative stress and free haem The fundamental characteristic of blackwater fever is the presence of massive haemolysis of both infected and uninfected erythrocytes and release of free haemoglobin. The free haem is highly cytotoxic, and an important scavenger of nitric oxide, promoting endothelial damage and is proposed to be involved in the pathogenesis of renal injury and cerebral malaria. When the degree of intravascular haemolysis exceeds the capacity of plasma haptoglobin to bind the haemoglobin released from red blood cells, free haemoglobin is then filtered by the glomeruli and enters the renal tubules. In a series of renal biopsies, fine and coarse haemoglobin granules are present in the proximal tubules, while haemoglobin casts and granular casts predominate in the distal and collecting tubules in patients with blackwater fever and intravascular haemolysis. This classic theory of renal damage by tubular precipitation is challenged by recent findings of reversing oxidative properties of free haem can prevent renal damage. The free haemoglobin present is pathogenic as the ferrous haem can be oxidized to the ferric state (FeIII) subsequently conferring peroxidase activity to the haemoglobin. Consequently, the haemoglobin can reduce hydroperoxides, such as hydrogen peroxide (H2O2) and lipid hydroperoxides, which generate the ferryl state (FeIV=O) of haemoglobin and a globin protein radical.

Haem Fe(III) protein + H2O2 --> haem [Fe(IV)=O] protein• + H+ + H2O The ferryl haem 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). Evidence suggests that F2-isoPs generated by the haemoprotein-catalyzed oxidation of lipids are responsible for the oxidative damage and vasoconstriction associated with renal injury in the setting of hemolytic disorders and rhabdomyolysis.

Paracetamol and oxidative stress A novel mechanism of paracetamol was recently demonstrated, showing that paracetamol acts as a potent inhibitor of haemoprotein-catalyzed lipid peroxidation by reducing ferryl haem to its less toxic ferric state and quenching globin radicals. This effect is enhanced 14-fold in an acidic milieu. In a recent proof of concept trial, paracetamol at therapeutic levels was shown to significantly decrease oxidant injury in the kidney, improve renal function and reduce renal damage by inhibiting the haemoprotein-catalyzed lipid peroxidation, mediated by redox cycling of the haem moiety of myoglobin, in a rat model of rhabdomyolysis-induced renal injury.

Rationale Since adults with severe malaria and blackwater fever associated with haemolysis demonstrate increased concentrations of cell-free haemoglobin, severe acidosis and urinary F2-IsoPs, the investigators hypothesize that this novel inhibitory mechanism of paracetamol may provide renal protection in this population by reducing the haemoprotein-induced lipid peroxidation. As there is currently no consensus that exists concerning adequate medical treatment for blackwater fever, the potential application of this safe and extensively used drug would be of great benefit.

Proposed activities The main activity proposed is a randomised open label controlled study of paracetamol in patients with severe falciparum malaria to assess its modulating effect on renal function and oxidative stress.