The disposition and effects of two doses of dichloroacetate in adults with severe falciparum malaria

Post hospital admission blood lactate measurements are associated with mortality but not neurologic morbidity in children with cerebral malaria

BACKGROUND

In children with cerebral malaria (CM) admission blood lactate has previously guided intravenous fluid therapy and been validated as a prognostic biomarker associated with death. The usefulness of post-admission measurements of blood lactate in children with CM is less clear. The strength of association between blood lactate and neurological sequelae in CM survivors, as well as the optimal duration of post-admission measurements of blood lactate to identify children at higher risk of adverse outcomes is unknown.

METHODS

A retrospective cohort study of 1674 Malawian children with CM hospitalized from 2000 to 2018 who had blood lactate measurements every 6 h for the first 24 h after admission was performed. The strength of association between admission lactate or values measured at any time point in the first 24 h post-admission and outcomes (mortality and neurological morbidity in survivors) was estimated. The duration of time after admission that lactate remained a valid prognostic biomarker was assessed.

RESULTS

When lactate is analysed as a continuous variable, children with CM who have higher values at admission have a 1.05-fold higher odds (95% CI 0.99-1.11) of death compared to those with lower lactate values. Children with higher blood lactate at 6 h have 1.16-fold higher odds (95% CI 1.09-1.23) of death, compared to those with lower values. If lactate levels are dichotomized into hyperlactataemic (lactate > 5.0 mmol/L) or not, the strength of association between admission lactate and mortality increases (OR = 2.49, 95% CI 1.47-4.22). Blood lactate levels obtained after 18 h post-admission are not associated with outcomes. Similarly, the change in lactate concentrations through time during the first 24 h of hospital admission is not associated with outcomes. Blood lactate during hospitalization is not associated with adverse neurologic outcomes in CM survivors.

CONCLUSIONS

In children with CM, blood lactate is associated with death but not neurologic morbidity in survivors. To comprehensively estimate prognosis, blood lactate in children with CM should be assessed at admission and for 18 h afterwards.

Dichloroacetate and Pyruvate Metabolism: Pyruvate Dehydrogenase Kinases as Targets Worth Investigating for Effective Therapy of Toxoplasmosis

Toxoplasmosis, a protozoan infection caused by Toxoplasma gondii, is estimated to affect around 2.5 billion people worldwide. Nevertheless, the side effects of drugs combined with the long period of therapy usually result in discontinuation of the treatment. New therapies should be developed by exploring peculiarities of the parasite's metabolic pathways, similarly to what has been well described in cancer cell metabolism. An example is the switch in the metabolism of cancer that blocks the conversion of pyruvate into acetyl coenzyme A in mitochondria. In this context, dichloroacetate (DCA) is an anticancer drug that reverts the tumor proliferation by inhibiting the enzymes responsible for this switch: the pyruvate dehydrogenase kinases (PDKs). DCA has also been used in the treatment of certain symptoms of malaria; however, there is no evidence of how this drug affects apicomplexan species. In this paper, we studied the metabolism of T. gondii and demonstrate that DCA also inhibits T. gondii's in vitro infection with no toxic effects on host cells. DCA caused an increase in the activity of pyruvate dehydrogenase followed by an unbalanced mitochondrial activity. We also observed morphological alterations frequently in mitochondria and in a few apicoplasts, essential organelles for parasite survival. To date, the kinases that potentially regulate the activity of pyruvate metabolism in both organelles have never been described. Here, we confirmed the presence in the genome of two putative kinases (T. gondii PDK [TgPDK] and T. gondii branched-chain α-keto acid dehydrogenase kinase [TgBCKDK]), verified their cellular localization in the mitochondrion, and provided in silico data suggesting that they are potential targets of DCA.IMPORTANCE Currently, the drugs used for toxoplasmosis have severe toxicity to human cells, and the treatment still lacks effective and safer alternatives. The search for novel drug targets is timely. We report here that the treatment of T. gondii with an anticancer drug, dichloroacetate (DCA), was effective in decreasing in vitro infection without toxicity to human cells. It is known that PDK is the main target of DCA in mammals, and this inactivation increases the conversion of pyruvate into acetyl coenzyme A and reverts the proliferation of tumor cells. Moreover, we verified the mitochondrial localization of two kinases that possibly regulate the activity of pyruvate metabolism in T. gondii, which has never been studied. DCA increased pyruvate dehydrogenase (PDH) activity in T. gondii, followed by an unbalanced mitochondrial activity, in a manner similar to what was previously observed in cancer cells. Thus, we propose the conserved kinases as potential regulators of pyruvate metabolism and interesting targets for new therapies.

Two dichloric compounds inhibit in vivo U87 xenograft tumor growth

Dichloroacetate (DCA) is an inhibitor of pyruvate dehydrogenase kinase (PDK) that has been shown to reverse the Warburg effect and cause tumor cell death. Clinical research into the anti-cancer activity of DCA revealed high dosage requirements and reports of toxicity. While there have been subsequent mechanistic investigations, a search for DCA alternatives could result in a safer and more effective anticancer therapy. This study evaluates eight small compounds with a conserved dichloric terminal and their in vitro and in vivo potential for anticancer activity. Initial viability screening across six cancer cell lines reveals even at 10 mg/mL, compound treatments do not result in complete cell death which suggests minimal compound cytotoxicity. Furthermore, in vivo data demonstrates that cationic dichloric compounds DCAH and DCMAH, which were selected for further testing based on highest in vitro viability impact, inhibit tumor growth in the U87 model of glioblastoma, suggesting their clinical potential as accessible anti-cancer drugs. Immunoblotting signaling data from tumor lysates demonstrates that the mechanism of actions of cationic DCAH and DCMAH are unlikely to be consistent with that of the terminally carboxylic DCA and warrants further independent investigation.

Adjunctive therapy for severe malaria: a review and critical appraisal

BACKGROUND

Despite recent efforts and successes in reducing the malaria burden globally, this infection still accounts for an estimated 212 million clinical cases, 2 million severe malaria cases, and approximately 429,000 deaths annually. Even with the routine use of effective anti-malarial drugs, the case fatality rate for severe malaria remains unacceptably high, with cerebral malaria being one of the most life-threatening complications. Up to one-third of cerebral malaria survivors are left with long-term cognitive and neurological deficits. From a population point of view, the decrease of malaria transmission may jeopardize the development of naturally acquired immunity against the infection, leading to fewer total cases, but potentially an increase in severe cases. The pathophysiology of severe and cerebral malaria is not completely understood, but both parasite and host determinants contribute to its onset and outcomes. Adjunctive therapy, based on modulating the host response to infection, could help to improve the outcomes achieved with specific anti-malarial therapy.

RESULTS AND CONCLUSIONS

In the last decades, several interventions targeting different pathways have been tested. However, none of these strategies have demonstrated clear beneficial effects, and some have shown deleterious outcomes. This review aims to summarize evidence from clinical trials testing different adjunctive therapy for severe and cerebral malaria in humans. It also highlights some preclinical studies which have evaluated novel strategies and other candidate therapeutics that may be evaluated in future clinical trials.

Adjunctive therapy for cerebral malaria and other severe forms of Plasmodium falciparum malaria

Severe malaria due to Plasmodium falciparum causes more than 800,000 deaths every year. Primary therapy with quinine or artesunate is generally effective in controlling P. falciparum parasitemia, but mortality from cerebral malaria and other forms of severe malaria remains unacceptably high. Long-term cognitive impairment is also common in children with cerebral malaria. Of the numerous adjunctive therapies for cerebral malaria and severe malaria studied over the past five decades, only one (albumin) was associated with a reduction in mortality. In this article, we review past and ongoing studies of adjunctive therapy, and examine the evidence of efficacy for newer therapies, including inhibitors of cytoadherence (e.g., levamisole), immune modulators (e.g., rosiglitazone), agents that increase nitric oxide levels (e.g., arginine) and neuroprotective agents (e.g., erythropoietin).

Lactate interferes with ATP release from red blood cells

Upon exposure to low Po(2), the red blood cells of most species, including humans, release increased amounts of ATP that ultimately serves as a regulator of vascular tone matching oxygen supply with demand. In pathological conditions such as malaria and sepsis, a maldistribution of perfusion exists with its severity often correlated with the extent of elevation of serum lactate frequently in the absence of an alteration in pH. We hypothesized that the increased levels of lactate might impair the ability of red blood cells to appropriately respond to conditions of low Po(2), thus preventing its important blood flow regulatory role. Using an in vitro system and rabbit red blood cells, we evaluated the capacity of cells incubated with lactate to release increased amounts of ATP in response to acute exposure to low Po(2). We found that in the presence of lactate, the red blood cells did not release ATP. However, when sodium dichloroacetate, a drug used clinically to lower blood lactate levels, was added, ATP release was restored to levels that were not different from that of control cells (no lactate), even though intracellular levels of ATP were not. These results support the presence of a distinct flow regulatory pool of ATP within the red blood cell that can be independently regulated, and that lactate interferes with the ATP production within this pool, thereby diminishing the amount of ATP available for release on exposure to low Po(2). Therefore, if lactate levels can be reduced, the vascular regulatory capacity of the red blood cell should be restored, thus enabling the appropriate matching of oxygen supply with oxygen demand.

Metabolic complications of severe malaria

Metabolic complications of malaria are increasingly recognized as contributing to severe and fatal malaria. Disorders of carbohydrate metabolism, including hypoglycaemia and lactic acidosis, are amongst the most important markers of disease severity both in adults and children infected with Plasmodium falciparum. Amino acid and lipid metabolism are also altered by malaria. In adults, hypoglycaemia is associated with increased glucose turnover and quinine-induced hyperinsulinaemia, which causes increased peripheral uptake of glucose. Hypoglycaemia in children results from a combination of decreased production and/or increased peripheral uptake of glucose, due to increased anaerobic glycolysis. Patients with severe malaria should be monitored frequently for hypoglycaemia and treated rapidly with intravenous glucose if hypoglycaemia is detected. The most common aetiology of hyperlactataemia in severe malaria is probably increased anaerobic glucose metabolism, caused by generalized microvascular sequestration of parasitized erythrocytes that reduces blood flow to tissues. Several potential treatments for hyperlactataemia have been investigated, but their effect on mortality from severe malaria has not been determined.

Therapy of falciparum malaria in sub-saharan Africa: from molecule to policy

The burden of falciparum malaria remains as great as ever, and, as has probably always been the case, it is carried mainly by tropical Africa. Of the various means available for the control of malaria, the use of effective drugs remains the most important and is likely to remain so for a considerable time to come. Unfortunately, the extensive development of resistance by the parasite threatens the utility of most of the affordable classes of drug: the development of novel antimalarials has never been more urgently needed. Any attempt to understand the vast complexities of falciparum malaria in Africa requires an ability to think "from molecule to policy." In consequence, the review ambitiously tries to examine the current pharmacopeia, the process by which new drugs are developed and the ways in which drugs are actually used, in both the formal and informal health sectors. The informal sector is particularly important in Africa, where around half of all antimalarial treatments are bought from informal outlets and taken at home without supervision by health care professionals: the potential impact of adherence on clinical outcome is discussed. Given that the full costs are carried by the patient in a large proportion of cases, the importance of drug affordability is explored. The review also discusses the splicing of new drugs into national policy. The various parameters that feed into deliberations on changes in drug policy are discussed.

Population kinetics, efficacy, and safety of dichloroacetate for lactic acidosis due to severe malaria in children

The authors conducted a randomized, double-blind, placebo-controlled trial of intravenous dichloroacetate (DCA) for the purpose of treating lactic acidosis in 124 West African children with severe Plasmodium falciparum malaria. Lactic acidosis independently predicts mortality in severe malaria, and DCA stimulates the oxidative removal of lactate in vivo. A single infusion of 50 mg/kg DCA was well tolerated. When administered at the same time as a dose of intravenous quinine, DCA significantly increased the initial rate and magnitude of fall in blood lactate levels and did not interfere with the plasma kinetics of quinine. The authors developed a novel population pharmacokinetic-pharmacodynamic indirect-response model for DCA that incorporated characteristics associated with disease reversal. The model describes the complex relationships among antimalarial treatment procedures, plasma DCA concentrations, and the drug's lactate-lowering effect. DCA significantly reduces the concentration of blood lactate, an independent predictor of mortality in malaria. Its prospective evaluation in affecting mortality in this disorder appears warranted.

Thiamine deficiency and malaria in adults from southeast Asia

BACKGROUND

Thiamine deficiency (beriberi) is common in some parts of southeast Asia. Acute thiamine deficiency can mimic many complications of malaria, such as encephalopathy and lactic acidosis. We examined the incidence of thiamine deficiency in adults admitted to hospital with malaria in Thailand.

METHODS

For this prospective study, we recruited consecutive patients with malaria or other febrile illness who presented to Paholpolpayuhasena Hospital, Kanchanaburi, Thailand, between May and July, 1992. We used the activation coefficient (alpha) for transketolase activity in erythrocytes to measure thiamine deficiency (defined as alpha>1.31) in patients with severe and uncomplicated malaria and in controls (patients' relatives and healthy volunteers). To exclude the possibility of interference in the assays, transketolase activity was also measured in erythrocytes used to culture parasites.

FINDINGS

12 (52%) of 23 patients with severe malaria and ten (19%) of 54 patients with uncomplicated malaria had alpha values above the normal range (p<0.0001 and p=0.0014, respectively, compared with controls), which indicated severe thiamine deficiency. Thiamine deficiency was more severe in patients with cerebral malaria than in those with uncomplicated malaria and the controls (p=0.008).

INTERPRETATION

In adults admitted to hospital in Thailand, thiamine deficiency commonly complicates acute falciparum malaria, particularly in severe infections, and could contribute to dysfunction of the central nervous system.

An overview of chemotherapeutic targets for antimalarial drug discovery

The need for new antimalarials comes from the widespread resistance to those in current use. New antimalarial targets are required to allow the discovery of chemically diverse, effective drugs. The search for such new targets and new drug chemotypes will likely be helped by the advent of functional genomics and structure-based drug design. After validation of the putative targets as those capable of providing effective and safe drugs, targets can be used as the basis for screening compounds in order to identify new leads, which, in turn, will qualify for lead optimization work. The combined use of combinatorial chemistry--to generate large numbers of structurally diverse compounds--and of high throughput screening systems--to speed up the testing of compounds--hopefully will help to optimize the process. Potential chemotherapeutic targets in the malaria parasite can be broadly classified into three categories: those involved in processes occurring in the digestive vacuole, enzymes involved in macromolecular and metabolite synthesis, and those responsible for membrane processes and signalling. The processes occurring in the digestive vacuole include haemoglobin digestion, redox processes and free radical formation, and reactions accompanying haem release followed by its polymerization into haemozoin. Many enzymes in macromolecular and metabolite synthesis are promising potential targets, some of which have been established in other microorganisms, although not yet validated for Plasmodium, with very few exceptions (such as dihydrofolate reductase). Proteins responsible for membrane processes, including trafficking and drug transport and signalling, are potentially important also to identify compounds to be used in combination with antimalarial drugs to combat resistance.