GSTZ1 genotypes correlate with dichloroacetate pharmacokinetics and chronic side effects in multiple myeloma patients in a pilot phase 2 clinical trial

Dichloroacetate (DCA) is an investigational drug targeting the glycolytic hallmark of cancer by inhibiting pyruvate dehydrogenase kinases (PDK). It is metabolized by GSTZ1, which has common polymorphisms altering enzyme or promoter activity. GSTZ1 is also irreversibly inactivated by DCA. In the first clinical trial of DCA in a hematological malignancy, DiCAM (DiChloroAcetate in Myeloma), we have examined the relationship between DCA concentrations, GSTZ1 genotype, side effects, and patient response. DiCAM recruited seven myeloma patients in partial remission. DCA was administered orally for 3 months with a loading dose. Pharmacokinetics were performed on day 1 and 8. Trough and peak concentrations of DCA were measured monthly. GSTZ1 genotypes were correlated with drug concentrations, tolerability, and disease outcomes. One patient responded and two patients showed a partial response after one month of DCA treatment, which included the loading dose. The initial half-life of DCA was shorter in two patients, correlating with heterozygosity for GSTZ1*A genotype, a high enzyme activity variant. Over 3 months, one patient maintained DCA trough concentrations approximately threefold higher than other patients, which correlated with a low activity promoter genotype (-1002A, rs7160195) for GSTZ1. This patient displayed the strongest response, but also the strongest neuropathy. Overall, serum concentrations of DCA were sufficient to inhibit the constitutive target PDK2, but unlikely to inhibit targets induced in cancer. Promoter GSTZ1 polymorphisms may be important determinants of DCA concentrations and neuropathy during chronic treatment. Novel dosing regimens may be necessary to achieve effective DCA concentrations in most cancer patients while avoiding neuropathy.

Acidosis and Formaldehyde Secretion as a Possible Pathway of Cancer Pain and Options for Improved Cancer Pain Control

The prevalence of cancer pain in patients with cancer is high. The majority of efforts are spent on research in cancer treatment, but only a small fraction focuses on cancer pain. Pain in cancer patients, viewed predominantly as a secondary issue, is considered to be due to the destruction of tissues, compression of the nerves, inflammation, and secretion of biological mediators from the necrotic tumor mass. As a result, opioid drugs have remained as the primary pharmacological therapy for cancer pain for the past hundred years. This report reviews evidence that cancer pain may be produced by the metabolic effects of two byproducts of cancer-high acidity in the cancer microenvironment and the secretion of formaldehyde and its metabolites. We propose the research and development of therapeutic approaches for preemptive, short- and long-term management of cancer pain using available drugs or nutraceutical agents that can suppress or neutralize lactic acid production in combination with formaldehyde scavengers. We believe this approach may not only improve cancer pain control but may also enhance the quality of life for patients.

Dichloroacetate at therapeutic concentration alters glucose metabolism and induces regulatory T-cell differentiation in alloreactive human lymphocytes

BACKGROUND

Most cancer cells rely on aerobic glycolysis. Dichloroacetate (DCA) inhibits aerobic glycolysis and is a promising relatively nontoxic anticancer compound. However, rapidly proliferating effector T-cells also rely on aerobic glycolysis, whereas regulatory T-cells (Treg) do not. The effect of DCA on glucose metabolism and Treg differentiation was evaluated in alloreactive lymphocytes.

METHODS

Peripheral blood mononuclear cells from healthy volunteers were used in a two-way mixed lymphocyte reaction. Lymphocyte proliferation was assessed by cell counting; DCA cytotoxicity, by lactate dehydrogenase release assay; and glucose uptake and aerobic glycolysis, by measuring in the supernatants the correspondent glucose and lactate concentrations. Interleukin-10 (IL-10) was measured in the supernatants, whereas the Treg signature transcription factor forkhead box P3 (FOXP3) was measured in cell lysates by means of enzyme-linked immunosorbent assay.

RESULTS

DCA had a minor effect on lymphocyte proliferation and cytotoxicity. However, DCA decreased glucose uptake and inhibited aerobic glycolysis. Finally, DCA markedly increased the production of IL-10 and the expression of FOXP3.

CONCLUSIONS

DCA inhibits aerobic glycolysis and induces Treg differentiation in human alloreactive lymphocytes. This could result in decreased immunosurveillance in case of its use as an anticancer drug. However, DCA could play a role as an immunosuppressant in the fields of transplantation and autoimmunity.

Kinetics and effects of dichloroacetic acid in rainbow trout

Halogenated acetic acids (HAAs) produced by chlorine disinfection of municipal drinking water represent a potentially important class of environmental contaminants. Little is known, however, about their potential to adversely impact fish and other aquatic life. In this study we examined the kinetics and effects of dichloroacetic acid (DCA) in rainbow trout. Branchial uptake was measured in fish confined to respirometer-metabolism chambers. Branchial uptake efficiency was <5%, suggesting passive diffusion through aqueous channels in the gill epithelium. DCA concentrations in tissues following prolonged (72, 168, or 336 h) waterborne exposures were expressed as tissue:plasma concentration ratios. Concentration ratios for the kidney and muscle at 168 and 336 h were consistent with the suggestion that DCA distributes primarily to tissue water. Reduced concentration ratios for the liver, particularly at 72 h, indicated that DCA was highly metabolized by this tissue. Routes and rates of elimination were characterized by injecting chambered animals with a high (5.0mg/kg) or low (50 microg/kg) bolus dose. DCA was rapidly cleared by naïve animals resulting in elimination half-lives (t(1/2)) of less than 4h. Waterborne pre-treatment of fish with DCA increased the persistence of a subsequently injected dose. In high dose animals, pre-treatment caused a 4-fold decrease in whole-body clearance (CL(B)) and corresponding increases in the area under the plasma concentration-time curve (extrapolated to infinity; AUC(0-->infinity)) and t(1/2). Qualitatively similar results were obtained in low dose fish, although the magnitude of the pre-treatment effect ( approximately 2.5-fold) was reduced. Renal and branchial clearance contributed little (combined, <3% of CL(B)) to the elimination of DCA. Biliary elimination of DCA was also negligible. The steady-state volume of distribution (V(SS)) did not vary among treatment groups and was consistent with results of the tissue distribution study. DCA had no apparent effects on respiratory physiology or acid-base balance; however, the concentration of blood lactate declined progressively during continuous waterborne exposures. A transient effect on blood lactate was also observed in bolus injection experiments. The results of this study suggest that clearance of DCA is due almost entirely to metabolism. The pathway responsible for this activity exhibits characteristics in common with those of mammalian glutathione S-transferase zeta (GSTzeta), including non-linear kinetics and apparent suicide inactivation by DCA. Observed effects on blood lactate are probably due to the inhibition of pyruvate dehydrogenase kinase in aerobic tissues and may require the participation of a monocarboxylase transport protein to move DCA across cell membranes.

Pharmacokinetic analysis of trichloroethylene metabolism in male B6C3F1 mice: Formation and disposition of trichloroacetic acid, dichloroacetic acid, S-(1,2-dichlorovinyl)glutathione and S-(1,2-dichlorovinyl)-L-cysteine

Trichloroethylene (TCE) is a well-known carcinogen in rodents and concerns exist regarding its potential carcinogenicity in humans. Oxidative metabolites of TCE, such as dichloroacetic acid (DCA) and trichloroacetic acid (TCA), are thought to be hepatotoxic and carcinogenic in mice. The reactive products of glutathione conjugation, such as S-(1,2-dichlorovinyl)-L-cysteine (DCVC), and S-(1,2-dichlorovinyl) glutathione (DCVG), are associated with renal toxicity in rats. Recently, we developed a new analytical method for simultaneous assessment of these TCE metabolites in small-volume biological samples. Since important gaps remain in our understanding of the pharmacokinetics of TCE and its metabolites, we studied a time-course of DCA, TCA, DCVG and DCVG formation and elimination after a single oral dose of 2100 mg/kg TCE in male B6C3F1 mice. Based on systemic concentration-time data, we constructed multi-compartment models to explore the kinetic properties of the formation and disposition of TCE metabolites, as well as the source of DCA formation. We conclude that TCE-oxide is the most likely source of DCA. According to the best-fit model, bioavailability of oral TCE was approximately 74%, and the half-life and clearance of each metabolite in the mouse were as follows: DCA: 0.6 h, 0.081 ml/h; TCA: 12 h, 3.80 ml/h; DCVG: 1.4 h, 16.8 ml/h; DCVC: 1.2 h, 176 ml/h. In B6C3F1 mice, oxidative metabolites are formed in much greater quantities (approximately 3600 fold difference) than glutathione-conjugative metabolites. In addition, DCA is produced to a very limited extent relative to TCA, while most of DCVG is converted into DCVC. These pharmacokinetic studies provide insight into the kinetic properties of four key biomarkers of TCE toxicity in the mouse, representing novel information that can be used in risk assessment.

Human kinetics of orally and intravenously administered low-dose 1,2-(13)C-dichloroacetate

Dichloroacetate (DCA) is a putative environmental hazard, owing to its ubiquitous presence in the biosphere and its association with animal and human toxicity. We sought to determine the kinetics of environmentally relevant concentrations of 1,2-(13)C-DCA administered to healthy adults. Subjects received an oral or intravenous dose of 2.5 microg/kg of 1,2-(13)C-DCA. Plasma and urine concentrations of 1,2-(13)C-DCA were measured by a modified gas chromatography-tandem mass spectrometry method. 1,2-(13)C-DCA kinetics was determined by modeling using WinNonlin 4.1 software. Plasma concentrations of 1,2-(13)C-DCA peaked 10 minutes and 30 minutes after intravenous or oral administration, respectively. Plasma kinetic parameters varied as a function of dose and duration. Very little unchanged 1,2-(13)C-DCA was excreted in urine. Trace amounts of DCA alter its own kinetics after short-term exposure. These findings have important implications for interpreting the impact of this xenobiotic on human health.

Bayesian population analysis of a harmonized physiologically based pharmacokinetic model of trichloroethylene and its metabolites

Bayesian population analysis of a harmonized physiologically based pharmacokinetic (PBPK) model for trichloroethylene (TCE) and its metabolites was performed. In the Bayesian framework, prior information about the PBPK model parameters is updated using experimental kinetic data to obtain posterior parameter estimates. Experimental kinetic data measured in mice, rats, and humans were available for this analysis, and the resulting posterior model predictions were in better agreement with the kinetic data than prior model predictions. Uncertainty in the prediction of the kinetics of TCE, trichloroacetic acid (TCA), and trichloroethanol (TCOH) was reduced, while the kinetics of other key metabolites dichloroacetic acid (DCA), chloral hydrate (CHL), and dichlorovinyl mercaptan (DCVSH) remain relatively uncertain due to sparse kinetic data for use in this analysis. To help focus future research to further reduce uncertainty in model predictions, a sensitivity analysis was conducted to help identify the parameters that have the greatest impact on various internal dose metric predictions. For application to a risk assessment for TCE, the model provides accurate estimates of TCE, TCA, and TCOH kinetics. This analysis provides an important step toward estimating uncertainty of dose-response relationships in noncancer and cancer risk assessment, improving the extrapolation of toxic TCE doses from experimental animals to humans.

Controlled clinical trial of dichloroacetate for treatment of congenital lactic acidosis in children

OBJECTIVE

Open-label studies indicate that oral dichloroacetate (DCA) may be effective in treating patients with congenital lactic acidosis. We tested this hypothesis by conducting the first double-blind, randomized, control trial of DCA in this disease.

METHODS

Forty-three patients who ranged in age from 0.9 to 19 years were enrolled. All patients had persistent or intermittent hyperlactatemia, and most had severe psychomotor delay. Eleven patients had pyruvate dehydrogenase deficiency, 25 patients had 1 or more defects in enzymes of the respiratory chain, and 7 patients had a mutation in mitochondrial DNA. Patients were preconditioned on placebo for 6 months and then were randomly assigned to receive an additional 6 months of placebo or DCA, at a dose of 12.5 mg/kg every 12 hours. The primary outcome results were (1) a Global Assessment of Treatment Efficacy, which incorporated tests of neuromuscular and behavioral function and quality of life; (2) linear growth; (3) blood lactate concentration in the fasted state and after a carbohydrate meal; (4) frequency and severity of intercurrent illnesses and hospitalizations; and (5) safety, including tests of liver and peripheral nerve function.

OUTCOME

There were no significant differences in Global Assessment of Treatment Efficacy scores, linear growth, or the frequency or severity of intercurrent illnesses. DCA significantly decreased the rise in blood lactate caused by carbohydrate feeding. Chronic DCA administration was associated with a fall in plasma clearance of the drug and with a rise in the urinary excretion of the tyrosine catabolite maleylacetone and the heme precursor delta-aminolevulinate.

CONCLUSIONS

In this highly heterogeneous population of children with congenital lactic acidosis, oral DCA for 6 months was well tolerated and blunted the postprandial increase in circulating lactate. However, it did not improve neurologic or other measures of clinical outcome.

Effect of short-term drinking water exposure to dichloroacetate on its pharmacokinetics and oral bioavailability in human volunteers: a stable isotope study

Dichloroacetic acid (DCAA) is a by-product of drinking water disinfection, is a known rodent hepatocarcinogen, and is also used therapeutically to treat a variety of metabolic disorders in humans. We measured DCAA bioavailability in 16 human volunteers (eight men, eight women) after simultaneous administration of oral and iv DCAA doses. Volunteers consumed DCAA-free bottled water for 2 weeks to wash out background effects of DCAA. Subsequently, each subject consumed (12)C-DCAA (2 mg/kg) dissolved in 500 ml water over a period of 3 min. Five minutes after the start of the (12)C-DCAA consumption, (13)C-labeled DCAA (0.3 mg/kg) was administered iv over 20 s and plasma (12)C/(13)C-DCAA concentrations measured at predetermined time points over 4 h. Volunteers subsequently consumed for 14 consecutive days DCAA 0.02 microg/kg/day dissolved in 500 ml water to simulate a low-level chronic DCAA intake. Afterward, the (12)C/(13)C-DCAA administrations were repeated. Study end points were calculation of AUC(0-->infinity), apparent volume of distribution (V(ss)), total body clearance (Cl(b)), plasma elimination half-life (t((1/2),beta)), oral absorption rate (K(a)), and oral bioavailability. Oral bioavailability was estimated from dose-adjusted AUC ratios and by using a compartmental pharmacokinetic model after simultaneous fitting of oral and iv DCAA concentration-time profiles. DCAA bioavailability had large interindividual variation, ranging from 27 to 100%. In the absence of prior DCAA intake, there were no significant differences (p > 0.05) in any pharmacokinetic parameters between male and female volunteers, although there was a trend that women absorbed DCAA more rapidly (increased K(a)), and cleared DCAA more slowly (decreased Cl(b)), than men. Only women were affected by previous 14-day DCAA exposure, which increased the AUC(0-->infinity) for both oral and iv DCAA doses (p < 0.04 and p < 0.014, respectively) with a corresponding decrease in the Cl(b).

A quantitative description of suicide inhibition of dichloroacetic acid in rats and mice

Dichloroacetic acid (DCA), a minor metabolite of trichloroethylene (TCE) and water disinfection byproduct, remains an important risk assessment issue because of its carcinogenic potency. DCA has been shown to inhibit its own metabolism by irreversibly inactivating glutathione transferase zeta (GSTzeta). To better predict internal dosimetry of DCA, a physiologically based pharmacokinetic (PBPK) model of DCA was developed. Suicide inhibition was described dynamically by varying the rate of maximal GSTzeta-mediated metabolism of DCA (Vmax) over time. Resynthesis (zero-order) and degradation (first-order) of metabolic activity were described. Published iv pharmacokinetic studies in naive rats were used to estimate an initial Vmax value, with Km set to an in vitro determined value. Degradation and resynthesis rates were set to estimated values from a published immunoreactive GSTzeta protein time course. The first-order inhibition rate, kd, was estimated to this same time course. A secondary, linear non-GSTzeta-mediated metabolic pathway is proposed to fit DCA time courses following treatment with DCA in drinking water. The PBPK model predictions were validated by comparing predicted DCA concentrations to measured concentrations in published studies of rats pretreated with DCA following iv exposure to 0.05 to 20 mg/kg DCA. The same model structure was parameterized to simulate DCA time courses following iv exposure in naive and pretreated mice. Blood and liver concentrations during and postexposure to DCA in drinking water were predicted. Comparisons of PBPK model predicted to measured values were favorable, lending support for the further development of this model for application to DCA or TCE human health risk assessment.

Chronic treatment of mitochondrial disease patients with dichloroacetate

Clinical features are reported for 37 patients with various mitochondrial disorders, treated with sodium dichloroacetate (DCA) for 3 weeks to 7 years (mean 3.25 years) at 11-50 mg/kg/day (34.6+/-13.1) in an open-label format. DCA pharmacokinetics showed half-times approximately 86 min for the first intravenous dose of 50 mg/kg, 3.2 h for a subsequent intravenous dose 4-6 h later, and 11 h after continued oral dosing of 12.5-25 mg/kg twice daily. Basal blood and CSF lactate (mean values at entry 29.6 and 46.8 mg/dL, respectively) decreased at 3 months (to 18.1 and 34.2, respectively) and 12 months (to 17.7 and 33.1, respectively). There was some attenuation of the blood lactate response to oral fructose but not glucose, although the baseline lactate was lower with DCA. A standardized neurologic inventory showed stabilization or improvement over one year. The subjective impression of overall disease course was worsening in 21.6%, improvement in 48.6%, and no discernable effect in 29.7%. Among 8 patients who had 17 stroke-like events in 0.25-5 years prior to study entry, there were a total of 2 events over 3-6 years of treatment. In two cases institution of DCA resulted in dramatic relief of severe headaches which had been refractory to narcotics. Given variability of symptoms and limited understanding of natural history of mitochondrial disease, it is difficult to determine the efficacy of DCA in this open-label study, but there did appear to be some cases in which there were at least temporary benefits.

Dichloroacetate does not speed phase-II pulmonary V? O 2 kinetics following the onset of heavy intensity cycle exercise

We hypothesised that pharmacological activation of the pyruvate dehydrogenase enzyme complex (PDC) by dichloroacetate (DCA) would speed phase-II pulmonary O2 uptake (VO2) kinetics following the onset of high-intensity, sub-maximal exercise. Eight healthy males (aged 19-33 years) completed two "square-wave" transitions of 6 min duration from unloaded cycling to a work-rate equivalent to approximately 80% of peak VO2 either with or without prior i.v. infusion of DCA (50 mg kg(-1) body mass in 50 ml saline). Pulmonary VO2 was measured breath-by-breath throughout all tests, and VO2 kinetics were determined using non-linear regression techniques from the averaged individual response to each of the conditions. Infusion of DCA resulted in significantly lower blood [lactate] during the baseline cycling period (means+/-SEM: control 0.9+/-0.1, DCA 0.5+/-0.1 mM; P<0.01) consistent with successful activation of PDC. However, DCA had no discernible effect on the rate at which VO2 increased towards the initially anticipated steady state following the onset of exercise as reflected in the time constant of the fundamental VO2 response (control 26.7+/-4.1, DCA 27.7+/-2.8 s). These results indicate that the principal limitation to oxidative metabolism following the onset of high-intensity, sub-maximal cycle exercise lies downstream from PDC and/or that muscle O2 consumption is primarily under "feedback" control via the concentration of one or more of the reactants associated with ATP hydrolysis.

Improvement of thermal hydrolysis rate of dichloroacetic acid using alcohol

Dichloroacetic acid (DCAA) is produced during the oxidation of trichloroethylene. It is also produced in drinking water treatment as a disinfection by-product. DCAA is a problem material, because of its toxicity. The objective of this research is to find the final products and the reaction pathway of the DCAA decomposition by hydrolysis, and to increase the hydrolysis rate. The removal of both chlorine atoms in DCAA structure was achieved with hydrolysis at around 75 degrees C, and the final products were oxalic acid and glycolic acid. The reaction pathway was the production of oxalic acid and glycolic acid from two glyoxylic acid molecules by Cannizzaro reaction after the glyoxylic acid production from dechlorination of DCAA with hydrolysis. The hydrolysis rate of DCAA was increased with the use of 90% ethanol solution as solvent. The activation energy of DCAA was about 80 kJ/mol in it, while it was around 105 kJ/mol in water.

Efficacy of dichloroacetate as a lactate-lowering drug

Dichloroacetate (DCA) decreases blood, cerebral spinal fluid, and intracellular lactate concentrations by activating the mitochondrial pyruvate dehydrogenase enzyme complex. The authors reviewed the efficacy of this investigational drug in the treatment of acquired or congenital forms of lactic acidosis from data in 40 English-language publications. The hypolactatemic effect of DCA occurs over a broad range of pretreatment lactate concentrations and is directly related to the baseline lactate level. The maximum lactate-lowering effect of the drug is dependent on its dose but independent of time following its administration. Recent clinical studies of acquired lactic acidosis suggest that DCA could be rapidly effective in reducing this risk factor of mortality in patients with mild hyperlactatemeia.

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.

Low-dose pharmacokinetics and oral bioavailability of dichloroacetate in naive and GST-zeta-depleted rats

We studied the pharmacokinetics of dichloroacetate (DCA) in naive rats and rats depleted of glutathione S-transferase-zeta (GST-zeta), at doses approaching human daily exposure levels. We also compared in vitro metabolism of DCA by rat and human liver cytosol. Jugular vein-cannulated male Fischer-344 rats received graded doses of DCA ranging from 0.05 to 20 mg/kg (intravenously or by gavage), and we collected time-course blood samples from the cannulas. GST-zeta activity was depleted by exposing rats to 0.2 g/L DCA in drinking water for 7 days before initiation of pharmacokinetic studies. Elimination of DCA by naive rats was so rapid that only 1-20 mg/kg intravenous and 5 and 20 mg/kg gavage doses provided plasma concentrations above the method detection limit of 6 ng/mL. GST-zeta depletion slowed DCA elimination from plasma, allowing kinetic analysis of doses as low as 0.05 mg/kg. DCA elimination was strongly dose dependent in the naive rats, with total body clearance declining with increasing dose. In the GST-zeta-depleted rats, the pharmacokinetics became linear at doses less than or equal to 1 mg/kg. Virtually all of the dose was eliminated through metabolic clearance; the rate of urinary elimination was < 1 mL/hr/kg. At higher oral doses (less than or equal to 5 mg/kg in GST-zeta-depleted and 20 mg/kg in naive rats), secondary peaks in the plasma concentration appeared long after the completion of the initial absorption phase. Oral bioavailability of DCA was 0-13% in naive and 14-75% in GST-zeta- depleted rats. Oral bioavailability of DCA in humans through consumption of drinking water was predicted to be very low and < 1%. The use of the GST-zeta-depleted rat as a model for assessing the kinetics of DCA in humans is supported by the similarity in pharmacokinetic parameter estimates and rate of in vitro metabolism of DCA by human and GST-zeta-depleted rat liver cytosol.

Dichloroacetate toxicokinetics and disruption of tyrosine catabolism in B6C3F1 mice: dose-response relationships and age as a modifying factor

Dichloroacetate (DCA) is a rodent carcinogen commonly found in municipal drinking water supplies. Toxicokinetic studies have established that elimination of DCA is controlled by liver metabolism, which occurs by the cytosolic enzyme glutathione-S-transferase-zeta (GST-zeta). DCA is also a mechanism based inhibitor of GST-zeta, and a loss in GST-zeta enzyme activity occurs following repeated doses or prolonged drinking water exposures. GST-zeta is identical to an enzyme that is part of the tyrosine catabolism pathway known as maleylacetoacetate isomerase (MAAI). In this pathway, GST-zeta plays a critical role in catalyzing the isomerization of maleylacetoacetate to fumarylacetoacetate. Disruption of tyrosine catabolism has been linked to increased cancer risk in humans. We studied the elimination of i.v. doses of DCA to young (10 week) and aged (60 week) mice previously treated with DCA in their drinking water for 2 and 56 weeks, respectively. The diurnal change in blood concentrations of DCA was also monitored in mice exposed to three different drinking water concentrations of DCA (2.0, 0.5 and 0.05 g/l). Additional experiments measured the in vitro metabolism of DCA in liver homogenates prepared from treated mice given various recovery times following treatment. The MAAI activity was also measured in liver cytosol obtained from treated mice. Results indicated young mice were the most sensitive to changes in DCA elimination after drinking water treatment. The in vitro metabolism of DCA was decreased at all treatment rates. Partial restoration ( approximately 65% of controls) of DCA elimination capacity and hepatic GST-zeta activity occurred after 48 h recovery from 14 d 2.0 g/l DCA drinking water treatments. Recovery from treatments could be blocked by interruption of protein synthesis with actinomycin D. MAAI activity was reduced over 80% in liver cytosol from 10-week-old mice. However, MAAI was unaffected in 60-week-old mice. These results indicate that in young mice, inactivation and re-synthesis of GST-zeta is a highly dynamic process and that exogenous factors that deplete or reduce GST-zeta levels will decrease DCA elimination and may increase the carcinogenic potency of DCA. As mice age, the elimination capacity for DCA is less affected by reduced liver metabolism and mice appear to develop some toxicokinetic adaptation(s) to allow elimination of DCA at rates comparable to naive animals. Reduced MAAI activity alone is unlikely to be the carcinogenic mode of action for DCA and may in fact, only be important during the early stages of DCA exposure.

Genetic polymorphisms in assessing interindividual variability in delivered dose

Increasing sophistication in methods used to account for human variability in susceptibility to toxicants has been one of the success stories in the continuing evolution of risk assessment science. Genetic polymorphisms have been suggested as an important contributor to overall human variability. Recently, data on polymorphisms in metabolic enzymes have been integrated with physiologically based pharmacokinetic (PBPK) modeling as an approach to determining the resulting overall variability. We present an analysis of the potential contribution of polymorphisms in enzymes modulating the disposition of four diverse compounds: methylene chloride, warfarin, parathion, and dichloroacetic acid. Through these case studies, we identify key uncertainties likely to be encountered in the use of polymorphism data and highlight potential simplifying assumptions that might be required to test the hypothesis that genetic factors are a substantive source of human variability in susceptibility to environmental toxicants. These uncertainties include (1) the relative contribution of multiple enzyme systems, (2) the extent of induction/inhibition through coexposure, (3) allelic frequencies of major ethnic groups, (4) the absence of chemical-specific data on the kinetic parameters for the different allelic forms of key enzymes, (5) large numbers of low-frequency alleles, and (6) uncertainty regarding differences between in vitro and in vivo kinetic data. Our effort sets the stage for the acquisition of critical data and further integration of polymorphism data with PBPK modeling as a means to quantitate population variability.

Dichloroacetate: population pharmacokinetics with a pharmacodynamic sequential link model

Dichloroacetate (DCA) is a small molecule that reduces ambient concentrations of lactate in man. It was the purpose of this study to develop pharmacokinetic and pharmacodynamic models for determination of a dose for a pivotal Phase III clinical trial of DCA in patients with traumatic brain injury (TBI). Population pharmacokinetic and pharmacodynamic models were developed for DCA using NONMEM software. The pharmacokinetic data were fit to a physiologic two-compartment model, and the pharmacodynamic data were fit to an indirect physiologic response model. Simulations were employed to evaluate various dosing strategies for consideration in a pivotal Phase III clinical trial of DCA. For the pharmacokinetic model, it was discovered that the clearance of DCA decreased on multiple dosing from 4.82 L/h to 1.07 L/h and that the pharmacokinetics and pharmacodynamics in TBI patients could not be predicted from normal volunteers. Population pharmacokinetic modeling and simulation of the expected effects of several dosing strategies were useful procedures for designing a Phase III trial.

Effect of pre-treatment with dichloroacetic or trichloroacetic acid in drinking water on the pharmacokinetics of a subsequent challenge dose in B6C3F1 mice

Dichloroacetate (DCA) and trichloroacetate (TCA) are prominent by-products of chlorination of drinking water. Both chemicals have been shown to be hepatic carcinogens in mice. Prior work has demonstrated that DCA inhibits its own metabolism in rats and humans. This study focuses on the effect of prior administration of DCA or TCA in drinking water on the pharmacokinetics of a subsequent challenge dose of DCA or TCA in male B6C3F1 mice. Mice were provided with DCA or TCA in their drinking water at 2 g/l for 14 days and then challenged with a 100 mg/kg i.v. (non-labeled) or gavage (14C-labeled) dose of DCA or TCA. The challenge dose was administered after 16 h fasting and removal of the haloacetate pre-treatment. The haloacetate blood concentration-time profile and the disposition of 14C were characterized and compared with controls. The effect of pre-treatment on the in vitro metabolism of DCA in hepatic S9 was also evaluated. Pre-treatment with DCA caused a significant increase in the blood concentration-time profiles of the challenge dose of DCA. No effect on the blood concentration-time profile of DCA was observed after pre-treatment with TCA. Pre-treatment with TCA had no effect on subsequent doses of DCA. Pre-treatment with DCA did not have a significant effect on the formation of 14CO2 from radiolabeled DCA. In vitro experiments with liver S9 from DCA-pre-treated mice demonstrated that DCA inhibits it own metabolism. These results indicate that DCA metabolism in mice is also susceptible to inhibition by prior treatment with DCA, however the impact on clearance is less marked in mice than in F344 rats. In contrast, the metabolism and pharmacokinetics of TCA is not affected by pre-treatment with either DCA or TCA.

Pharmacokinetics and pharmacodynamics of dichloroacetate in patients with cirrhosis

OBJECTIVES

We tested the hypotheses that (1) plasma clearance of dichloroacetate is decreased in patients with end-stage cirrhosis, and (2) patients with cirrhosis are vulnerable to dichloroacetate-induced hypoglycemia caused by exaggerated inhibition of hepatic glucose production.

METHODS

Seven subjects with cirrhosis and six healthy volunteers received a 5-hour primed constant infusion of 6,6-2H2-glucose. After a 2-hour basal period, subjects received intravenous dichloroacetate, 35 mg/kg, over 30 minutes. Dichloroacetate pharmacokinetics were compared by the mixed-effects population-based technique. Glucose production was calculated by means of isotope dilution.

RESULTS

The optimal dichloroacetate pharmacokinetic model for both subjects with cirrhosis and control subjects had two compartments, with all parameters weight normalized. Peak plasma dichloroacetate concentration in subjects with cirrhosis did not differ from that in control subjects, but typical dichloroacetate clearance was only 36% of that in control subjects (P < .001). Dichloroacetate decreased plasma lactate concentration by approximately 50% (P < .001), glucose production by 7% to 9% (P < .05), and plasma glucose concentration by 9% to 14% (P < .05) in both subjects with cirrhosis and control subjects. Dichloroacetate-induced decreases in plasma lactate and glucose concentrations and in glucose production in subjects with cirrhosis did not differ from those in control subjects.

CONCLUSIONS

Plasma dichloroacetate clearance is markedly decreased in patients with cirrhosis, likely because of compromised hepatic function. Subjects with cirrhosis exhibit neither exaggerated inhibition of glucose production nor increased risk of hypoglycemia as a result of acute dichloroacetate-induced hypolactatemia.

Inhibition of glutathione S-transferase zeta and tyrosine metabolism by dichloroacetate: a potential unifying mechanism for its altered biotransformation and toxicity

Dichloroacetate (DCA) inhibits its own metabolism and is converted to glyoxylate by glutathione S-transferase zeta (GSTz). GSTz is identical to maleylacetoacetate isomerase, an enzyme of tyrosine catabolism that converts maleylacetoacetate (MAA) to fumarylacetoacetate and maleylacetone (MA) to fumarylacetone. MAA and MA are alkylating agents. Rats treated with DCA for up to five days had markedly decreased hepatic GSTz activity and increased urinary excretion of MA. When dialyzed cytosol obtained from human liver was incubated with DCA, GSTz activity was unaffected. In contrast, DCA incubation inhibited enzyme activity in dialyzed hepatic cytosol from rats. Incubation of either rat or human hepatic cytosol with MA led to a dose dependent inhibition of GSTz. These data indicate that humans or rodents exposed to DCA may accumulate MA and/or MAA which inhibit(s) GSTz and, consequently, DCA biotransformation. Moreover, DCA-induced inhibition of tyrosine catabolism may account for the toxicity of this xenobiotic in humans and other species.

Glutathione transferase zeta-catalyzed biotransformation of deuterated dihaloacetic acids

Glutathione transferase zeta (GSTZ) catalyzes the biotransformation of alpha-haloalkanoic acids. Treatment of rats or humans with dichloroacetic acid prolongs its elimination half-life, and preliminary studies in this laboratory show that fluorine-lacking, but not fluorine-containing dihaloacetic acids inactivate GSTZ. In the present study, the GSTZ-catalyzed biotransformation of unlabeled and deuterated dihaloacetic acids was investigated. With [(2)H]dichloroacetic acid and [(2)H]chlorofluoroacetic acid as substrates, the deuterium present in the [(2)H]dihaloacetic acid was retained in the [(2)H]glyoxylic acid formed. This finding indicates that the enol of the dihaloacetic acid does not serve as the substrate for the enzyme. The data afford an explanation of the failure of fluorine-containing dihaloacetic acids to inactivate GSTZ: dichloroacetic acid is converted to glyoxylic acid and inactivates GSTZ, whereas chlorofluoroacetic acid is biotransformed to glyoxylic acid, but produces negligible inactivation. Mechanisms are presented indicating that this difference may be attributed to the nucleofugicity of the leaving group.

Dichloroacetate (DCA) dosimetry: interpreting DCA-induced liver cancer dose response and the potential for DCA to contribute to trichloroethylene-induced liver cancer

Pharmacokinetic studies with dichloroacetate (DCA) provide insights into the likelihood that trichloroethylene-induced liver cancers arise from formation of DCA as a metabolite and the mode of action by which DCA induces liver cancer. A simple physiologically based pharmacokinetic model was developed to analyze DCA blood concentration data from mice unexposed to or pre-treated with DCA. The large first pass metabolism of DCA in the liver is significantly reduced by DCA pretreatment. Because DCA inhibits its own metabolism, large increases in area under the blood concentration curve occur at lower doses than would be predicted from single-dose pharmacokinetic studies with naive mice. The dose metrics associated with the incidence of liver tumors in contrast to the multiplicity of tumors per animal may be different, suggesting potentially different roles in the cancer process for DCA versus its metabolites. By linking a model for trichloroethylene (TCE) pharmacokinetics with the DCA model, maximum levels of DCA potentially produced from TCE were estimated to be at or below the analytical chemistry detection limits. In addition, the predicted levels of DCA would be too small to produce the observed liver cancers following corn oil gavage exposure of mice to TCE.

Evaluation of biomarkers of environmental exposures: urinary haloacetic acids associated with ingestion of chlorinated drinking water

A study was conducted to determine if DCAA and TCAA urinary excretion rates are valid biomarkers of chronic ingestion exposure to these disinfection by-products of chlorination of drinking water. Entire first morning urine voids, time-of-visit urine samples, and tap water samples were collected from 47 female subjects. In addition, a 48-h recall questionnaire was administered to determine the amounts and types of liquids ingested by each subject as well as other exposures that could lead to DCAA and TCAA urinary excretion. The TCAA excretion rate for the first morning urine samples was significantly correlated with the estimated 48-h TCAA ingestion exposure for 25 subjects whose ingestion exposures primarily occurred at home, while the DCAA excretion rate was not correlated with the DCAA ingestion exposure. Thus, urinary TCAA appears to be a valid biomarker of chronic ingestion exposure to TCAA from chlorinated water, while urinary DCAA is not. It is proposed that the difference in the biological half-lives between these two compounds is the rationale for this finding. The biological half-life of TCAA is longer than successive exposure intervals; thus TCAA accumulates until it reaches a steady state. The half-life of DCAA is shorter than successive exposure intervals; thus DCAA is almost completely metabolized following an exposure and is eliminated from the body. This study suggests that biological half-life, exposure interval, and sample collection interval should be considered in selecting biomarkers and designing studies to validate them.

Pharmacokinetics and metabolism of [14C]dichloroacetate in male Sprague-Dawley rats. Identification of glycine conjugates, including hippurate, as urinary metabolites of dichloroacetate

Pathways of metabolism of dichloroacetate (DCA), an investigational drug for the treatment of lactic acidosis in humans and a rodent hepatocarcinogen, are poorly understood. In this study, rats were given, by gavage, one or two 50 mg/kg doses of NaDCA. DCA labeled with 14C (carboxy carbon) or 13C (both carbons) was used in studies of disposition and pharmacokinetics, respectively. The effect of fasting for 14 hr before dosing was studied. Expired air, urine, feces, and tissues were collected from [14C]DCA-dosed rats. Urine was analyzed by HPLC, GC/MS, and NMR spectroscopy. Plasma samples were analyzed by GC/MS. DCA plasma elimination half-lives were 0.1 +/- 0.02 and 5.4 +/- 0.8 hr in young adult rats (180-265 g, 3-4 months of age) given one or two doses of DCA, respectively, and 9.7 +/- 1 hr in large, 16-month-old rats given two DCA doses. The percentage of the DCA dose excreted as CO2 varied from 17 to 46% and was lower (p < 0.001) in fed rats, compared with rats fasted overnight before dosing. Urine contained DCA and DCA metabolites, including oxalate, glyoxylate, and conjugated glycine (mainly hippurate and phenylacetylglycine). More unchanged DCA was excreted by large rats pretreated with DCA (mean, 20.2% of the dose) than by young adult rats given one dose of DCA (mean, 0.5%). This study confirmed that CO2, glycine, and oxalate are major products of DCA metabolism, it demonstrated that one dose of DCA altered the elimination of a subsequent dose, and it showed that age or body size, as well as access to food, significantly affected DCA metabolism in rats.

Kinetics of trichloroacetic acid and dichloroacetic acid in the isolated perfused rat liver

Trichloroacetic acid (TCA) and dichloroacetic acid (DCA) are environmental contaminants that are suspected human carcinogens. To obtain more detail on the role of the liver in the kinetics of TCA and DCA, experimental studies in the isolated perfused rat liver (IPRL) system were conducted. The IPRL system was dosed with either 5 or 50 micromol of either TCA or DCA (25 or 250 microM initial concentration, respectively). TCA and DCA concentrations were followed in perfusion medium and bile for 2 h. The chemical concentration in liver was determined at the end of exposure. Liver viability was monitored by measuring leakage of lactate dehydrogenase (LDH) into perfusion medium and the rate of bile production. Studies performed with TCA showed that the total TCA concentration in perfusion medium decreased slightly during the first 30 min of exposure and remained constant thereafter. Most TCA, greater than 90% of total, was bound to albumin in the perfusion medium. A low, linear excretion rate of TCA in bile was obtained. The calculated free TCA concentration in the liver intracellular water space was higher than the unbound TCA concentration in the perfusion medium. Parallel studies with DCA showed that the DCA concentration in perfusion medium decreased rapidly. Of the total DCA in the perfusion medium, 60% was bound to albumin. The concentration of DCA in bile decreased over time. There was no DCA detectable in the liver after 2 h of exposure at both DCA concentrations. Enzyme leakage and bile production did not change in the presence of TCA or DCA, indicating that these concentrations were not acutely cytotoxic to the liver.

A physiologically based pharmacokinetic model for trichloroethylene and its metabolites, chloral hydrate, trichloroacetate, dichloroacetate, trichloroethanol, and trichloroethanol glucuronide in B6C3F1 mice

A six-compartment physiologically based pharmacokinetic (PBPK) model for the B6C3F1 mouse was developed for trichloroethylene (TCE) and was linked with five metabolite submodels consisting of four compartments each. The PBPK model for TCE and the metabolite submodels described oral uptake and metabolism of TCE to chloral hydrate (CH). CH was further metabolized to trichloroethanol (TCOH) and trichloroacetic acid (TCA). TCA was excreted in urine and, to a lesser degree, metabolized to dichloroacetic acid (DCA). DCA was further metabolized. The majority of TCOH was glucuronidated (TCOG) and excreted in the urine and feces. TCOH was also excreted in urine or converted back to CH. Partition coefficient (PC) values for TCE were determined by vial equilibrium, and PC values for nonvolatile metabolites were determined by centrifugation. The largest PC values for TCE were the fat/blood (36.4) and the blood/air (15.9) values. Tissue/blood PC values for the water-soluble metabolites were low, with all PC values under 2.0. Mice were given bolus oral doses of 300, 600, 1200, and 2000 mg/kg TCE dissolved in corn oil. At various time points, mice were sacrificed, and blood, liver, lung, fat, and urine were collected and assayed for TCE and metabolites. The 1200 mg/kg dose group was used to calibrate the PBPK model for TCE and its metabolites. Urinary excretion rate constant values were 0. 06/hr/kg for CH, 1.14/hr/kg for TCOH, 32.8/hr/kg for TCOG, and 1. 55/hr/kg for TCA. A fecal excretion rate constant value for TCOG was 4.61/hr/kg. For oral bolus dosing of TCE with 300, 600, and 2000 mg/kg, model predictions of TCE and several metabolites were in general agreement with observations. This PBPK model for TCE and metabolites is the most comprehensive PBPK model constructed for P450-mediated metabolism of TCE in the B6C3F1 mouse.

Pharmacokinetics and metabolism of dichloroacetate in the F344 rat after prior administration in drinking water

The effect of prior administration of dichloroacetate (DCA) in drinking water on the pharmacokinetics of DCA in male F344 rats was studied. Rats were provided with DCA in their drinking water at 0.2 and 2.0 g/liter for 14 days and then challenged with iv bolus iv or gavage doses of [14C1,2]DCA, 16 hr after pretreatment withdrawal. The blood concentration-time profiles of DCA and the disposition of 14C was characterized and compared with controls. The effect of pretreatment on the in vitro metabolism of DCA in hepatic cytosol was also evaluated. Pretreatment caused a significant increase in the blood concentration and AUC0-->infinity of DCA (433.3 versus 2406 microg ml-1 hr). Pharmacokinetic analysis indicated that pretreatment significantly decreased total body clearance (267.4 versus 42.7 ml hr-1 kg-1), which was largely due to decreased metabolism since only modest differences in the urinary clearance of DCA were observed. Pretreatment significantly decreased the formation of 14CO2 after both iv and oral doses of [14C]DCA. The decrease in CO2 formation was also observed after pretreatment with DCA at 0.2 g/liter. Pretreatment also increased the urinary elimination of DCA and several metabolites, particularly glycolate. The in vitro experiments demonstrated that DCA pretreatment inhibited the conversion of DCA to glyoxylate, oxalate, and glycolate in hepatic cytosol. These results indicate that DCA has an auto-inhibitory effect on its metabolism and that pharmacokinetic studies using single doses in naïve rats will underestimate the concentration of DCA at the target tissue during chronic or repeated exposures.

Pharmacokinetics of dichloroacetate in adult patients with lactic acidosis

The pharmacokinetic properties of the lactate-lowering drug dichloroacetate were investigated in 111 adult patients with lactic acidosis who were randomized to receive dichloroacetate as part of a placebo-controlled clinical trial. The clinical symptoms and etiology of lactic acidosis varied markedly among patients. Dichloroacetate, at a dose of 50 mg per kilogram of body weight, was administered in a 30-minute intravenous infusion into a peripheral vein. A second dose, identical to the first, was administered 2 hours after beginning the first infusion. Plasma levels of dichloroacetate were determined from blood samples collected periodically up to 288 hours after administration and the data were subjected to pharmacokinetic modeling. The pharmacokinetic properties of dichloroacetate in these acutely ill patients were complex and differed markedly from those in healthy volunteers, whose data fitted a one-compartment pharmacokinetic model. In contrast, the data from patients fitted one-, two-, or three-compartment pharmacokinetic models or even none of these, depending on the individual. Drug clearance in plasma tended to decrease as the number of compartments required to fit the data increased or as the number of drug treatments increased.

Reduction of serum lactate by sodium dichloroacetate, and human pharmacokinetic-pharmacodynamic relationships

Sodium dichloroacetate (DCA) or placebo, two infusions 30 min in duration and 8 h apart, was administered to healthy subjects under double-blind conditions. The objectives were to characterize accurately the tolerability of DCA, its pharmacokinetics, and the reduction of resting serum lactate concentration by DCA. A hybrid, one-compartment pharmacokinetic model fitted best, with zero-order elimination mean of 27.9 micrograms/ml/h at concentrations above about 80 to 120 micrograms/ml, and with first-order elimination (mean kelim = 0.54) at lower serum concentrations of DCA. Resting serum lactate was dose-independently, maximally reduced within 15 min of the end of all active infusions. The duration of suppression of resting serum lactate was dose-dependent, from 4.5 h (30 mg/kg) to > 8 h (100 mg/kg). Second infusions (15-50 mg/kg) again promptly and maximally reduced resting serum lactate. Hysteresis loops were asymmetrical for all doses but exhibited change in shape that was dose-dependent; no good pharmacokinetic-pharmacodynamic model could be fitted that was consistent between doses. Infusions were well tolerated, 100 mg/kg + 50 mg/kg being the highest doses. Somnolence, the only dose-related adverse event, was reported by 3 of 37 subjects at times corresponding to the highest serum DCA concentrations. This study demonstrates the tolerability of i.v. DCA, proposes a simple pharmacokinetic model for its elimination, characterizes the dose-response relationship in terms of time course of effect, shows the dissociation between elimination of DCA and offset of response and will guide further studies of DCA in patients with head injury or stroke.

Pharmacokinetics of dichloroacetate in patients undergoing liver transplantation

BACKGROUND

Dichloroacetate (DCA) is an effective alternative to bicarbonate to treat lactic acidosis and stabilize acid-base homeostasis during liver transplantation. Although DCA presumably is metabolized by the liver, the impact of end-stage liver disease and liver transplantation on DCA distribution and elimination is unknown. Therefore, the pharmacokinetics of DCA were determined in patients with end-stage liver disease undergoing orthotopic liver transplantation.

METHODS

Thirty-three patients undergoing liver transplantation were given DCA as two 40-mg/kg infusions over 60 min, the first after induction of anesthesia, the second 4 h later. Plasma DCA concentrations were determined by gas chromatography-mass spectroscopy. One- and two-compartment pharmacokinetic models were fitted to DCA concentrations versus time data using a mixed-effects population approach. Various models permitted changes in central compartment volume and/or plasma clearance to account for changes in hepatic mass and function and circulatory status during the paleohepatic, anhepatic, and neohepatic periods.

RESULTS

The optimal model had two compartments. DCA clearance was 0.997, 0.0, and 1.69 ml x kg(-1) x min(-1) during the paleohepatic, anhepatic, and neohepatic periods, respectively (P < 0.05). Interindividual variability in central compartment volume differed during the paleohepatic and neohepatic periods. There was no apparent influence of blood or fluid requirements during surgery on DCA clearance or volume of distribution.

CONCLUSIONS

Absence of DCA clearance during the anhepatic period indicates that DCA is metabolized exclusively by the liver. Differences in interindividual variability in central compartment volume during the paleohepatic and neohepatic periods possibly result from physiologic changes during surgery. Finally, the results indicate that the newly transplanted liver eliminates DCA better than the native liver.

Metabolism of bromodichloroacetate in B6C3F1 mice

Trichloroacetate (TCA), dichloroacetate (DCA), and bromodichloroacetate (BDCA) are byproducts of the chlorination of drinking water. TCA acts primarily as a peroxisome proliferator, but DCA produces tumors at doses less than required for peroxisome proliferation. BDCA does not induce peroxisome proliferation even at high doses. This study attempts to determine whether differences in the metabolism of the trihaloacetates (THAs) may contribute to their differing toxicological properties. Studies were performed in male B6C3F1 mice given [14C1,2]TCA, [14C1]BDCA, and [14C1,2]DCA by gavage. The replacement of a Cl by a Br greatly enhances THA metabolism. Much less radiolabel from BDCA is retained in the carcass after 24 hr than from TCA. Radiolabel from BDCA is largely found in the urine, with oxalate being the major metabolite. TCA is largely eliminated unchanged in the urine. There are dose-related changes in the rate of CO2 production from BDCA. The initial rate of CO2 production is reduced from 4.1 +/- 0.3 hr-1 at 5 and 20 mg/kg to 2.7 +/- 0.6 hr-1 at 100 mg/kg, but the net conversion to CO2 in 24 hr is greater at the highest dose. As would be predicted, substitution Br for Cl on TCA greatly increased its metabolism.

Pharmacokinetics and pharmacodynamics of dichloroacetate in children with lactic acidosis due to severe malaria

Lactic acidosis frequently complicates severe malaria in African children, and is a strong independent predictor of mortality. We tested the hypothesis that sodium dichloroacetate (DCA), an activator of pyruvate dehydrogenase, rapidly reduces hyperlactataemia in this patient population. Eighteen children with severe malaria and capillary plasma lactate > or = 5 mM were randomized to receive either intramuscular quinine plus a single 50 mg/kg intravenous infusion of DCA in saline, or quinine plus intravenous saline alone. Two patients in each treatment group died following randomization. Thirty minutes after treatment, the mean plasma lactate was 28% below pretreatment baseline values in the DCA group, but was unchanged in the placebo group. Throughout the first 4 h after treatment, mean plasma lactate in the DCA-treated patients was significantly less than that in controls (p = 0.003). Thereafter, mean plasma lactate declined in both groups and was < 2 mM 10 h after treatment. DCA was well tolerated and did not alter quinine pharmacokinetics. A single intravenous dose of DCA rapidly improved lactic acidosis in African children with severe malaria, suggesting that DCA may be a useful adjunct in the initial treatment of these patients, and may increase their chance of survival by improving a major complication of their illness.

Dichloroacetate for lactic acidosis in severe malaria: a pharmacokinetic and pharmacodynamic assessment

Lactic acidosis and hypoglycemia are potentially lethal complications of falciparum malaria. We have evaluated the pharmacokinetics and pharmacodynamics of dichloroacetate ([DCA], 46 mg/kg infused over 30 minutes), a stimulant of pyruvate dehydrogenase and a potential treatment for lactic acidosis, in 13 patients with severe malaria and compared the physiological and metabolic responses with those of a control group of patients (n = 32) of equivalent disease severity. The mean +/- SD peak postinfusion level of DCA was 78 +/- 23 mg/L, the total apparent volume of distribution was 0.75 +/- 0.35 L/kg, and systemic clearance was 0.32 +/- 0.16 L/kg/h. Geometric mean (range) venous lactate concentrations in control and DCA recipients before treatment were 4.5 (2.1 to 19.5) and 5.5 (2 to 15.4) mmol/L, respectively (P > .1). A single DCA infusion decreased lactate concentrations from baseline by a mean of 27% after 2 hours, 40% after 4 hours, and 41% after 8 hours, compared with decreases of 5%, 6%, and 16%, respectively, in controls (P = .032). These changes were preceded by rapid and marked decreases in pyruvate concentrations. Arterial pH increased from 7.328 to 7.374 (n = 10, P < .02) 2 hours after the infusion. Hypoglycemia was prevented by infusing glucose at 3 mg/kg/min. There was no clinical, electrocardiographic, or laboratory evidence of toxicity. These results suggest that DCA should be investigated further as an adjunctive therapy for severe malaria.

A rapid microassay for dichloroacetate in serum by gel-permeation chromatography

We have developed a novel, rapid microassay for dichloroacetate in the serum. The serum sample is directly injected into a gel-permeation high-performance liquid chromatography apparatus. The peak of dichloroacetate appears after a giant protein peak. The method requires a very small amount of serum (10 microliters), and the analysis time is short (20 min). Using this micro method, we measured the serum concentrations of dichloroacetate in healthy adult volunteers and paediatric patients with congenital lactic acidosis. Although the effect of dichloroacetate on the neurological manifestations of congenital lactic acidosis has not been proved to be beneficial, the potential usefulness of dichloroacetate in refractory lactic acidosis in cardiac and respiratory failure has been recognized, and human as well as animal studies have been undertaken in many laboratories. To prevent possible side effects of dichloroacetate, it has been recommended that the minimal effective dose be used. Our microassay method is useful for both human and animal experiments, even after administration of minimal doses.

Relative formation of dichloroacetate and trichloroacetate from trichloroethylene in male B6C3F1 mice

The hepatocarcinogenicity of trichloroethylene (TRI) has been attributed to the metabolite trichloroacetate (TCA). However, mice also form dichloroacetate (DCA) and trichloroethanol (TCE) as metabolites of TRI. TCA and DCA have both been shown to induce hepatic tumors in mice. This study was undertaken to measure the kinetics of TCA and DCA formation in the B6C3F1 mouse using doses of TRI ranging from 0.38 to 15 mmol/kg and TCA at doses of 0.03 to 0.61 mmol/kg. The formation and elimination of TCA and DCA have been found to be nonlinear with the dose of TRI. Quantifiable levels of DCA were found in blood with doses above 0.76 mmol/kg TRI. The peak concentration of DCA did not show an appreciable change with an increased dose; however, the area under the curve (AUC) increased linearly with respect to the dose of TRI. Both peak concentration and AUC of TCA and TCE increased in a linear manner to a dose of 3.8 mmol/kg. The kinetics of TCA elimination following doses of TCA were similar to those found for TCA following doses of TRI. A significant dose-dependent partitioning of TCA into blood over liver was found at the higher doses of TRI and TCA investigated. Binding of TCA to plasma constituents accounted for this distributional pattern. Prior work has documented that DCA can be formed from TCA. However, the AUC for DCA following TRI exceeds that predicted from the formation of TCA from TRI. Additional pathways would, therefore, appear to account for the formation of DCA. Results from this investigation suggest that sufficient concentrations of DCA appear to be formed and may contribute to the hepatocarcinogenicity of TRI.

Tissue distribution, excretion, and urinary metabolites of dichloroacetic acid in the male Fischer 344 rat

The disposition of dichloroacetic acid (DCA) was investigated in Fischer 344 rats over the 48 h after oral gavage of 282 mg/kg of 1- or 2-[14C]-DCA (1-DCA or 2-DCA) and 28.2 mg/kg of 2-DCA. DCA was absorbed quickly, and the major route of disposition was through exhalation of carbon dioxide and elimination in the urine. The dispositions of 1- and 2-DCA at 282 mg/kg were similar. With 2-DCA, the disposition differed with dose in that the percentage of the dose expired as carbon dioxide decreased from 34.4% (28.2 mg/kg) to 25.0% (282 mg/kg), while the percentage of the radioactivity excreted in the urine increased from 12.7 to 35.2%. This percentage increase in the urinary excretion was mostly attributable to the presence of unmetabolized DCA, which comprised more than 20% at the higher dose and less than 1% at the lower dose. The major urinary metabolites were glycolic acid, glyoxylic acid, and oxalic acid. DCA and its metabolites accumulated in the tissues and were eliminated slowly. After 48 h, 36.4%, 26.2%, and 20.8% of the dose was retained in the tissues of rats administered 28.2 and 282 mg/kg of 2-DCA and 282 mg/kg of 1-DCA, respectively. Of the organs examined, the liver (4.9-7.9% of dose) and muscle (4.5-9.9%) contained the most radioactivity, followed by skin (3.3-4.5%), blood (1.4-2.6%), and intestines (1.0-1.7%). One metabolite, glyoxylic acid, which is mutagenic, might be responsible for or contribute to the carcinogenicity of DCA.

Adduction of hemoglobin and albumin in vivo by metabolites of trichloroethylene, trichloroacetate, and dichloroacetate in rats and mice

Adducts to macromolecules from trichloroethylene formed by in vivo and in vitro metabolism have been reported by many investigators. We examined the in vivo adduction of the blood proteins hemoglobin (Hb) and albumin in rats and mice dosed orally with [14C]trichloroethylene ([14C]TRI) to explore the development of a protein adduct biomarker of TRI exposure. We also examined the adduction of these two proteins from doses of [14C]trichloroacetate (TCA) and [14C]dichloroacetate (DCA), two metabolites of TRI. Association of label with albumin peaked at 4-8 hr in the rat (2480 nmol eq TRI/mg protein) and 2-4 hr in the mouse (1580 nmol eq TRI/mg protein). The decay was exponential with a half-life consistent with that of rat or mouse albumin (approx 24 hr). The time course of label with Hb was characterized by an early plateau at 8 hr in rat (28 nmol eq TRI/mg protein), 4 hr in mouse (7 nmol eq TRI/mg protein), and followed by a slow steady increase, peaking at 120 hr (54 nmol eq TRI/mg protein, rat; 38 nmol eq TRI/mg protein, mouse). This apparent binding was linear with dose in the rat, but was convex in the mouse albumin (mouse Hb label was below detection at low dose). We also found that a portion of the irreversibly associated label, referred to by previous investigators as "binding," could be accounted for as metabolic incorporation of label into glycine and serine.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism and lipoperoxidative activity of trichloroacetate and dichloroacetate in rats and mice

Trichloroacetate (TCA) and dichloroacetate (DCA) have been shown to be hepatocarcinogenic in mice when administered in drinking water. However, DCA produces pathological effects in the liver that are much more severe than those observed following TCA treatment in both rats and mice. To identify potential mechanisms involved in the liver pathology, the biotransformation of TCA and DCA was investigated in male Fischer 344 rats and B6C3F1 mice. Rodents were administered 5, 20, or 100 mg/kg [14C]TCA or [14C]DCA as a single oral dose in water. Elimination was examined by counting radioactivity in urine, feces, exhaled air, and carcass. Blood concentration over time curves were constructed for both TCA and DCA at the 20 and 100 mg/kg doses. Analysis of the data reveals two significant differences in the systemic clearance of TCA relative to DCA. First, DCA was much more extensively metabolized than TCA. More than 50% of any single dose of TCA was excreted unchanged in the urine of both rats and mice. In contrast, less than 2% of any dose of DCA was recovered in the urine as the parent compound. Second, while the blood concentration over time curves for TCA were similar in rats and mice, the blood concentrations of DCA were markedly greater in rats compared to those in mice, both when DCA was administered and when DCA resulted from metabolism of TCA. DCA was detected in the urine of TCA-treated animals and chloroacetate was found in the urine of DCA-treated animals. These metabolic products would be expected to arise from a free radical-generating, reductive dechlorination pathway. To evaluate the ability of acute doses of TCA and DCA to elicit a lipoperoxidative response, additional groups of mice were administered 0, 100, 300, 1000, and 2000 mg/kg TCA or DCA and thiobarbituric acid-reactive substances (TBARS) measured in liver homogenates. Both TCA and DCA enhanced the formation of TBARS in a dose-dependent manner, thereby providing further evidence of a reductive metabolic pathway. DCA was found to be the more potent of the chlorinated acetates in increasing TBARS formation in the livers of both rats and mice. In view of these data, it appears that the more extensive metabolism and rapid rate of elimination of DCA relative to TCA and the more potent lipoperoxidative activity of DCA may be important factors in the pathological effects associated with DCA treatment.

Disposition and pharmacodynamics of dichloroacetate (DCA) and oxalate following oral DCA doses

Healthy volunteers received intravenous and/or oral doses of sodium dichloroacetate (DCA) in various single and multiple dose regimens. A crossover bioavailability study proved abortive because second and subsequent doses showed significantly longer terminal elimination half-lives (means 3.64 h and 9.9 h, respectively) than was the case for initial doses (1.58 h). A parallel bioavailability comparison failed to show that oral doses were significantly different from 100 per cent bioavailability (AUCoral, 604 micrograms h-1 ml-1; AUCi.v., 489 micrograms h-1 ml-1). The time required to elapse between individual doses, in order to prevent second doses having relatively long half-life values, varied in different individuals from 1 week to greater than 3 months. No cardiac or central nervous system effects were recorded by echocardiography and digit symbol substitution tests, respectively. The mean renal clearance of DCA was 42.9 ml h-1. No differences were observed in DCA kinetics between male and female subjects.

Haemodialysis studies with dichloroacetate

Seven patients undergoing routine thrice weekly haemodialysis for endstage renal failure participated in 12 investigations of dichloroacetate (DCA) pharmacokinetics and pharmacodynamics. DCA doses were 50 mg/kg by i.v. infusion over 30 min. In each investigation single doses were administered to each subject on two consecutive days, one being a day during which the patient was dialyzed. The timing of drug administration, relative to dialysis, was varied to assess the effect of dialysis on the apparent volume of distribution and elimination rate constants of DCA and on its effect on blood glucose and lactate. Dialysis increased the clearance of DCA by approximately 60%, but had no effect on its apparent volume of distribution. Dialysis did not reduce the maximal lactate-lowering effect of DCA, but slightly decreased the duration of this effect. Blood glucose levels were not significantly altered by DCA and no adverse drug effects were observed. We conclude that dialysis increases plasma clearance of DCA, but has little influence on the metabolic effects of the drug when given at 50 mg/kg doses. DCA can safely and effectively be given to hemodialysis patients who may require the drug for treatment of lactic acidosis.

[Sodium dichloroacetate--a substance with manifold therapeutic potential]

The therapeutic potential of sodium dichloroacetate (DCA) formerly called vitamin B 15, has already been under investigation for the past few years. The predominant property of DCA underlying its therapeutic action is activation of pyruvate dehydrogenase. The potential therapeutic use of DCA in the treatment of lactic acidosis and type II diabetes mellitus related directly to its stimulatory effect on this enzyme. Additional favourable effects of DCA on cardiac performance in states such as ischaemia, where glucose becomes a major energy-yielding substrate, have also been demonstrated. Treatment of lipid disorders might become further indications for the implementation of this substance. DCA inhibits hydroxy-methyl-glutaryl CoA reductase, thus lowering cholesterol and triglyceride levels. Earlier suggestions that DCA produced a major degree of acute toxicity were not confirmed in recent studies using DCA of established purity and homogeneity. These findings and recent evidence suggesting a potentially important role of DCA in the treatment of lactic acidosis are the reason and basis for a review of the established actions of this substance.

The pharmacology of dichloroacetate

Dichloroacetate (DCA) exerts multiple effects on pathways of intermediary metabolism. It stimulates peripheral glucose utilization and inhibits gluconeogeneis, thereby reducing hyperglycemia in animals and humans with diabetes mellitus. It inhibits lipogenesis and cholesterolgenesis, thereby decreasing circulating lipid and lipoprotein levels in short-term studies in patients with acquired or hereditary disorders of lipoprotein metabolism. By stimulating the activity of pyruvate dehydrogenase, DCA facilitates oxidation of lactate and decreases morbidity in acquired and congenital forms of lactic acidosis. The drug improves cardiac output and left ventricular mechanical efficiency under conditions of myocardial ischemia or failure, probably by facilitating myocardial metabolism of carbohydrate and lactate as opposed to fat. DCA may also enhance regional lactate removal and restoration of brain function in experimental states of cerebral ischemia. DCA appears to inhibit its own metabolism, which may influence the duration of its pharmacologic actions and lead to toxicity. DCA can cause a reversible peripheral neuropathy that may be related to thiamine deficiency and may be ameliorated or prevented with thiamine supplementation. Other toxic effects of DCA may be species-specific and reflect marked interspecies variation in pharmacokinetics. Despite its potential toxicity and limited clinical experience, DCA and its derivatives may prove to be useful in probing regulatory aspects of intermediary metabolism and in the acute or chronic treatment of several metabolic disorders.

Dichloroacetate derivatives. Metabolic effects and pharmacodynamics in normal rats

Dichloroacetate (DCA) reduces blood glucose, lactate and lipids in diabetes or during fasting. Chronic use of DCA, however, is limited by toxicity, probably due in part to its rapid conversion to oxalate in vivo. In theory, therefore, DCA's efficacy may be retained and its toxicity minimized by controlling its rate of metabolism. We attempted to alter DCA pharmacokinetics and bioavailability by synthesizing various derivatives comprising DCA esters with polyols and DCA ionic complexes. Twenty-four hour fasted, nondiabetic rats received single, orogastric doses of saline (control) sodium DCA (100mg/kg) or the following derivatives (D1-4): the esters D1-D3: potassium tetra (dichloroacetyl) glucuronate (D1), inositol-monophosphate-tetradichloroacetate (D2), inositol-hexadichloroacetate (D3) and inositol-hexa [N-methylnicotinate] hexadichloroacetate salt (D4). Each derivative was administered at a dose that would ultimately provide 100 mg/kg DCA as the anion. All derivatives were orally effective in significantly decreasing blood glucose and lactate. D4 exerted the most potent and long-lasting glucose- and lactate-lowering effects, yet increased plasma DCA concentrations less than an equivalent dose of the sodium salt. When administered to reverse light-cycled rats, D4 markedly inhibited the incorporation of tritiated water into cholesterol and triglycerides. We conclude that derivatives of DCA retain the biological activity of the parent compound, but may exhibit different pharmacokinetics. They may eventually prove useful in the treatment of diabetes mellitus, hyperlipidemia and lactic acidosis in man.