Effect of Plasmodium yoelii nigeriensis infection and chloroquine on the hepatic mixed function oxidase system of mice

Malaria-induced Alterations of Drug Kinetics and Metabolism in Rodents and Humans

BACKGROUND

Infections and inflammation lead to a downregulation of drug metabolism and kinetics in experimental animals. These changes in the expression and activities of drug-metabolizing enzymes may affect the effectiveness and safety of pharmacotherapy of infections and inflammatory conditions.

OBJECTIVE

In this review, we addressed the available evidence on the effects of malaria on drug metabolism activity and kinetics in rodents and humans.

RESULTS

An extensive literature review indicated that infection by Plasmodium spp consistently decreased the activity of hepatic Cytochrome P450s and phase-2 enzymes as well as the clearance of a variety of drugs in mice (lethal and non-lethal) and rat models of malaria. Malaria-induced CYP2A5 activity in the mouse liver was an exception. Except for paracetamol, pharmacokinetic trials in patients during acute malaria and in convalescence corroborated rodent findings. Trials showed that, in acute malaria, clearance of quinine, primaquine, caffeine, metoprolol, omeprazole, and antipyrine is slower and that AUCs are greater than in convalescent individuals.

CONCLUSION

Notwithstanding the differences between rodent models and human malaria, studies in P. falciparum and P. vivax patients confirmed rodent data showing that CYP-mediated clearance of antimalarials and other drugs is depressed during the symptomatic disease when rises in levels of acute-phase proteins and inflammatory cytokines occur. Evidence suggests that inflammatory cytokines and the interplay between malaria-activated NF-kB-signaling and cell pathways controlling phase 1/2 enzyme genes transcription mediate drug metabolism changes. The malaria-induced decrease in drug clearance may exacerbate drug-drug interactions, and the occurrence of adverse drug events, particularly when patients are treated with narrow-margin-of-safety medicines.

In silico multiple-targets identification for heme detoxification in the human malaria parasite Plasmodium falciparum

Detoxification of hemoglobin byproducts or free heme is an essential step and considered potential targets for anti-malaria drug development. However, most of anti-malaria drugs are no longer effective due to the emergence and spread of the drug resistant malaria parasites. Therefore, it is an urgent need to identify potential new targets and even for target combinations for effective malaria drug design. In this work, we reconstructed the metabolic networks of Plasmodium falciparum and human red blood cells for the simulation of steady mass and flux flows of the parasite's metabolites under the blood environment by flux balance analysis (FBA). The integrated model, namely iPF-RBC-713, was then adjusted into two stage-specific metabolic models, which first was for the pathological stage metabolic model of the parasite when invaded the red blood cell without any treatment and second was for the treatment stage of the parasite when a drug acted by inhibiting the hemozoin formation and caused high production rate of heme toxicity. The process of identifying target combinations consisted of two main steps. Firstly, the optimal fluxes of reactions in both the pathological and treatment stages were computed and compared to determine the change of fluxes. Corresponding enzymes of the reactions with zero fluxes in the treatment stage but non-zero fluxes in the pathological stage were predicted as a preliminary list of potential targets in inhibiting heme detoxification. Secondly, the combinations of all possible targets listed in the first step were examined to search for the best promising target combinations resulting in more effective inhibition of the detoxification to kill the malaria parasites. Finally, twenty-three enzymes were identified as a preliminary list of candidate targets which mostly were in pyruvate metabolism and citrate cycle. The optimal set of multiple targets for blocking the detoxification was a set of heme ligase, adenosine transporter, myo-inositol 1-phosphate synthase, ferrodoxim reductase-like protein and guanine transporter. In conclusion, the method has shown an effective and efficient way to identify target combinations which are obviously useful in the development of novel antimalarial drug combinations.

Quinine distribution in mice withplasmodium berghei malaria

The disposition of a single 80 mg/kg injection of quinine base was compared in control and Plasmodium berghei-infected mice. Pharmacokinetic parameters were determined on repeated whole blood samples from caudal vein (experiment 1) and quinine distribution was evaluated in tissues and blood fractions from mice sacrificed two hours post dosing (experiment 2). Quinine concentrations were assessed by high performance liquid chromatography with fluorometric detection. Whole blood concentrations and AUC(0 - infinity) of quinine increased in a parasitaemia-dependent manner. Quinine blood clearance and peak blood concentrations of metabolites negatively correlated with the parasitaemia. The apparent distribution volume of quinine only decreased in severely ill mice. Quinine concentrations rise in a parasitaemia-dependent manner in homogenates of spleen, lungs and kidney and in erythrocyte pellets. The negative relationship, observed between the parasitaemia and the tissue-to-whole blood ratio for muscle, heart, liver and brain, contributes to the reduction of the blood distribution volume. Quinine uptake by muscle and heart was dependent on the free fraction of plasma quinine. The liver and brain concentrations of quinine were similar in control and infected mice. The tissue-to-plasma free fraction ratios decrease when the parasitaemia rises suggesting a restrictive uptake of quinine by these tissues. In conclusion. P. berghei malaria decreases both total clearance and apparent volume of distribution with a heterogeneous redistribution of quinine between the tissues.

Increased generation of superoxide in erythrocytes infected with Babesia gibsoni

The present study was conducted to clarify the mechanism underlying the oxidative process in erythrocytes infected with Babesia gibsoni. The parasite B. gibsoni was cultured together with erythrocytes from normal dogs for 7 days. When parasitemia reached 12.0-13.4% at Day 7. the production of superoxide in erythrocytes was significantly higher in the parasitized culture than in the control culture (p<0.005). The concentration of thiobarbituric acid reactive substances (TBARS) in erythrocytes in parasitized culture was also significantly increased compared with the control culture (p<0.005), indicating that lipid peroxidation was greater in infected erythrocytes than in non-infected cells. In addition, the rates of superoxide generation in the blood of B. gibsoni-infected dogs were also significantly higher than in non-infected dogs (p<0.001). These results indicate that superoxide anions are increased in erythrocytes parasitized with B. gibsoni. and suggest that oxidative damage, due to lipid peroxidation, might be caused in host erythrocytes by the parasite.

Studies of the hepatic mitochondrial and microsomal mixed-function oxidase system during Plasmodium yoelii infection and inducer treatment in Swiss albino mice

Plasmodium yoelii infection resulted in depression of hepatic mitochondrial and microsomal mixed-function oxidase system indices, e.g. cytochrome P-450, cytochrome b5 and phase II detoxification enzyme glutathione-S-transferase, while heam and haemozoin registered a marked increase in Swiss albino mice. Phenobarbitone (inducer) treatment showed induced levels of hepatic mitochondrial and microsomal cytochrome P-450 and glutathione-S-transferase in normal as well as in infected mice. The induced cytochrome P-450 and glutathione-S-transferase activities were similar in normal and infected mice. The findings were further supported by the isoenzymic profile and drug-binding properties of the terminal monoxygenase, cytochrome P-450.

Effect of malaria infection and endotoxin-induced fever on phenacetin O-deethylation by rat liver microsomes

We have investigated the effect of malaria infection with the rodent parasite Plasmodium berghei and fever induced by Escherichia coli endotoxin on the metabolism of phenacetin to paracetamol by rat liver microsomes from young (4 weeks old) male Wistar rats (N = 5 in control and fever groups; N = 10 in malaria-infected group). Following determination of % parasitaemia, the malaria-infected group was divided into a low parasitaemia subgroup (N = 5; mean % parasitaemia = 9.87 +/- 2.6) and a high parasitaemia subgroup (N = 5; mean % parasitaemia = 36.6 +/- 8.1). The control group received normal saline. Total microsomal protein was not significantly affected by fever or malaria infection while cytochrome P450 levels were reduced by approximately 50% in the high parasitaemia subgroup, 20% in the low parasitaemia subgroup and 20% in the endotoxin-treated group. Phenacetin-O-deethylation kinetics were biphasic in both control and malaria-infected rats, but monophasic in endotoxin-treated rats. Total apparent intrinsic clearance (CL(int),total; calculated as Vmax/Km; Vmax is maximum velocity, Km is Michaelis constant) of phenacetin was reduced approximately 6-fold in low parasitaemia, 30-fold in high parasitaemia and 35-fold in fever. There was a poor correlation between CL(int),total and % parasitaemia (r = -0.6). However, log CL(int),total correlated inversely with % parasitaemia (r = -0.9), suggesting that Cl(int),total decreased exponentially with an increase in % parasitaemia. Phenacetin O-deethylation is a marker for cytochrome P4501A2 activity and the results of the present study suggest that both malaria infection and fever might specifically reduce P4501A2 activity in the rat.

Aberrations in cerebral vascular functions due to Plasmodium yoelii nigeriensis infection in mice

Plasmodium yoelii nigeriensis infection in mice caused an increase in uptake of 125I-labeled bovine serum albumin, 51Cr-labeled erythrocytes and Evans blue dye from peripheral circulation into the brain. Isolated cerebral microvessels which were characterized in terms of their morphology under scanning electron microscope and enhancement of the specific activities of biochemical markers, viz. alkaline phosphatase, gamma-glutamyl transpeptidase, and monoamine oxidase, showed significant decrease in these activities due to P. yoelii nigeriensis infection. On the other hand, relatively minor (statistically insignificant) changes occurred in the first two enzyme specific activities in the cerebral cortex and monoamine oxidase registered an increase in this tissue due to infection. Histological examination of the cerebral tissue of infected animals by light and electron microscopy showed broken blood vessel walls and leakage of erythrocytes into extravascular space, some of which contained intraerythrocytic malarial parasite in a state of cell division.

Effect of malaria on phenol conjugation pathways in perfused rat liver

The effect of malaria infection (MI) on sulphation and glucuronidation of phenol was investigated in single-pass perfused livers from rats infected with the rodent malaria parasite Plasmodium berghei. At a hepatic inflow (Cin) phenol concentration of 1 microgram/mL in controls, 52% was metabolized to sulphate conjugate and 37% to glucuronide conjugate at steady state. At this Cin, MI had no effect on phenol clearance (CL) (control: 9.63 +/- 0.38 vs MI: 9.65 +/- 0.36 mL/min; P greater than 0.05) or on the formation clearance (CLm) of the glucuronide or sulphate conjugates of phenol. When phenol Cin was increased 10-fold to 10 micrograms/mL, 6% was metabolized to sulphate conjugate and 94% to glucuronide conjugate. At this Cin phenol CL was decreased significantly (control: 9.44 +/- 0.46 vs MI: 7.09 +/- 1.51 mL/min; P less than 0.05) and represented a decrease in intrinsic clearance (sinusoidal perfusion model) of at least 55%. This decrease was accounted for entirely by the decrease in the CLm of the glucuronide conjugate (control: 8.88 +/- 0.96 vs 5.98 +/- 1.87 mL/min; P less than 0.05), whereas the CLm of the sulphate conjugate was unchanged. There was a negative correlation between phenol glucuronide CLm and the severity of the erythrocytic parasitaemia (r2 = 0.75, P less than 0.05). The dose-dependent reduction in phenol glucuronidation in MI may be due to reduced availability of the cosubstrate uridine diphosphoglucuronic acid (UDPGA), because previous studies have shown that UDPGA availability depends on glycogen stores, which are known to be reduced in MI. These data suggest that sulphate conjugation is preserved in MI and that glucuronidation is preserved at low doses of substrate. At high substrate doses, glucuronidation is impaired in MI and the impairment correlates with the severity of the infection.

Malaria infection impairs glucuronidation and biliary excretion by the isolated perfused rat liver

1. The effect of the erythrocyte stage of malaria infection on hepatic glucuronidation, biliary excretion and oxidation processes was investigated using harmol, salbutamol, taurocholate and propranolol. Livers from rats infected with the rodent malaria parasite P. berghei were isolated and perfused in a single-pass (harmol, taurocholate, propranolol) or recirculating (harmol, salbutamol) design. The degree of erythrocytic parasitaemia ranged from 16% to 63%. 2. The hepatic clearance (Cl) of harmol decreased from 7.8 +/- 0.4 ml/min in controls to 5.7 +/- 1.1 ml/min in the malaria-infected group in single-pass studies. This corresponded to a 40-60% reduction in hepatic intrinsic clearance (Clint). Similar changes were observed using the recirculating design when glucuronidation accounted for greater than 90% of harmol metabolism. 3. The Cl of salbutamol, metabolized exclusively by glucuronidation under the conditions used, also decreased significantly from 8.5 +/- 0.8 in controls to 6.6 +/- 1.4 ml/min in the malaria-infected group. This corresponded to a 40-70% reduction in Clint. 4. The Cl of taurocholate, excreted unchanged in bile, decreased slightly but significantly from 9.6 +/- 0.3 ml/min in controls to 8.3 +/- 0.9 ml/min in the malaria-infected group. In the same livers, there was also a slight but significant decrease in propranolol Cl (10.0 +/- 0.1 ml/min and 9.9 +/- 0.1 ml/min, respectively). Both these compounds undergo flow-limited hepatic clearance; the decreases in Clint of taurocholate and propranolol were 87% and 35%, respectively. 5. Cl and Clint of each of the compounds studied were found to correlate significantly with the degree of erythrocytic parasitaemia. This study shows that glucuronidation, biliary excretion and oxidation by liver are impaired in malaria infection in rats, with biliary excretion being the most affected. The data indicate that there is a general decrease in hepatic elimination processes during the erythrocytic phase of malaria infection.

Status of hepatic heme and heme oxygenase during Plasmodium yoelii nigeriensis infection in mice

Plasmodium yoelii nigeriensis infection in albino mice caused a significant increase in hepatic heme level, the increase being concomitant with a rise in parasitemia. This elevated heme was found to be associated with all the subcellular fractions except the cytosol, where its content remained unaltered. Activity of heme oxygenase, the key enzyme responsible for catabolism of heme, also increased progressively with rise in parasitemia. Treatment of normal mice with cobalt chloride [60 mg (kg body wt)-1; subcutaneously] brought about a 150% increase in the level of heme oxygenase; similar treatment of infected mice at low parasitemia could induce the enzyme activity while at high parasitemia the enzymic activity remained unaltered as compared to untreated infected mice. In spite of an increased level of heme oxygenase in the cobalt-treated mice, the level of heme did not show any noticeable change. Oral administration of chloroquine [64 mg (kg body wt)-1 x 4 days] brought about a 56% reduction in the level of heme oxygenase of normal animals but there was no change in infected animals when compared with the corresponding untreated infected mice. However, the amount of chloroquine present in livers of normal and infected animals was not significantly different.

Effect of Plasmodium berghei infection and chloroquine on the hepatic drug metabolizing system of mice

The hepatic microsomal mixed-function oxidase (MFO) system was markedly impaired during Plasmodium berghei infection in mice. Cytochrome P-450 and other mono-oxygenases, viz. aniline hydroxylase, aminopyrine-N-demethylase and benzo(a)pyrene hydroxylase, were significantly decreased while microsomal heme showed a four-fold increase at peak parasitemia (greater than 50%). Oral treatment with chloroquine (16 mg kg-1 body wt for 4 days) of P. berghei-infected mice cleared the parasitemia within 72 h and almost normalized the altered levels of MFO indices, a week after cessation of treatment. The findings were further supported by the isoenzymic profile and drug-binding properties of terminal mono-oxygenase, cytochrome P-450.

The effect of malaria infection on paracetamol disposition in the rat

The effect of Plasmodium berghei infection, a rodent malarial model, on the disposition of paracetamol (50 mg/kg, i.v.) was investigated in rats. Malaria infection (MI) resulted in a significant decrease in clearance (control: 21.6 +/- 5.5 vs test: 11.8 +/- 2.9 mL/min/kg, P less than 0.005) with no change in volume of distribution and a significant prolongation of the elimination half-life (control: 30.7 +/- 6.3 vs 53.3 +/- 12.1 min, P less than 0.005) of paracetamol in malaria infected rats. These changes were not related to the severity of MI. Malaria infection also decreased biliary clearance of paracetamol (64%) but not its glucuronide and sulphate conjugates in the bile compared with controls. In addition, glutathione conjugates were not detected in bile samples of malaria infected rats. These data suggest that important pathways of drug detoxification may be compromised by MI in a relatively selective fashion and the relevance of these findings to the clinical use of drugs eliminated by these pathways merits further study.

The effect of malaria infection on antipyrine metabolite formation in the rat

We have shown that malaria infection can impair selectively the formation of antipyrine metabolites in the rat. During malaria, a significant increased urinary levels of unchanged antipyrine was observed (control: 1.7 +/- 0.4 vs test: 8.1 +/- 1.1% of dose, P less than 0.001). This was associated with significantly decreased excretion of 3-hydroxymethylantipyrine (control: 24.5 +/- 1.2 vs test: 21.4 +/- 0.7%, P less than 0.001) and 4-hydroxyantipyrine (control: 20.1 +/- 0.9 vs test: 15.5 +/- 1.3%, P less than 0.001) but not norantipyrine compared to control. Following treatment of the malaria infection with halofantrine, only the formation of 3-hydroxymethylantipyrine (control: 25.2 +/- 0.9 vs test: 24.1 +/- 0.6%, P less than 0.05) is impaired. The implications of these findings in relation to metabolism of other antimalarial drugs during malaria remains to be elucidated. Further work is needed to determine the changes in the pharmacokinetics of AP and its metabolites before, during and after MI in the rat in order to give a better insight into the effect of MI on hepatic drug metabolism.

Hepatic microsomal cytochrome P450 system during experimental hookworm infection

Experimental infection of golden hamsters with the hookworm, Ancylostoma ceylanicum, caused a profound decline in the hepatic microsomal cytochrome P450 content. Concomitant decrease was also noticed in aminopyrine N-demethylase and benzo[a]pyrene hydroxylase activities. However, aniline hydroxylase activity was only marginally elevated during the infection. Microsomal markers, viz., cytochrome b5, NADH-cytochrome-c reductase, and glucose-6-phosphatase, were not significantly altered. Hepatic tissue exhibited an accumulation of lipids, especially phospholipids, triglycerides, and cholesterol, resulting in fatty necrosis around the central vein region. Isolated hepatic microsomes showed a decrease in phosphatidylcholine content. Impairment in hepatic mixed function oxidase (MFO) activities was further confirmed by prolongation in hexobarbital sleeping time and zoxazolamine-induced paralysis. The hepatic MFO system of A. ceylanicum-infected hamsters responded qualitatively and quantitatively in a manner similar to that of control hamsters, upon stimulation with selective chemical inducers like phenobarbitone and 3-methylcholanthrene. Kinetic and in vitro substrate binding studies revealed that for aminopyrine the substrate affinity and the maximum enzyme activity (Vmax) were decreased, while for aniline the binding affinity was decreased and the binding capacity was enhanced. Results indicate specific/selective impairment of the hepatic microsomal cytochrome P450 system during hookworm infection and may have many practical implications in toxicology and pharmacology.

The effect of malaria infection on the disposition of quinine and quinidine in the rat isolated perfused liver preparation

The effect of malaria on the disposition of quinine and quinidine was studied in livers isolated from young rats infected with merozoites of Plasmodium berghei, a rodent malaria model, and non-infected controls. Following bolus administration of quinine (1 mg) or quinidine (1 mg) to the 100 mL recycling perfusion circuit, perfusate was sampled (0-4 h) and plasma assayed for quinine and quinidine by HPLC. Higher quinine (AUC:6470 +/- 1101 vs 3822 +/- 347 ng h mL-1, P less than 0.001) and quinidine (AUC: 6642 +/- 1304 vs 4808 +/- 872 ng h mL-1, P less than 0.05) concentrations were observed during malaria infection (MI). MI resulted in decreased quinine clearance (CL) (0.33 +/- 0.08 vs 0.64 +/- 0.09 mL min-1 g-1, P less than 0.001) and volume of distribution (Vd) (53.0 +/- 13.3 vs 81.2 +/- 23.7 mL g-1, P less than 0.05) but no significant change in elimination half-life (t1/2) (1.93 +/- 0.6 vs 1.37 +/- 0.25 h, P greater than 0.05). With quinidine, however, MI resulted in decreased CL (0.38 +/- 0.16 vs 0.64 +/- 0.09, P less than 0.05) with no change in Vd and a significant increase in t1/2 (1.62 +/- 0.42 vs 0.88 +/- 0.22, P less than 0.01). In summary, the hepatic disposition of quinine and quinidine is altered in the malaria-infected rat.

Effect of Plasmodium yoelii infection on GABA metabolism of mouse brain

Plasmodium yoelii infection in albino mice decreased the activity of brain glutamic acid decarboxylase (GAD) by about 30 and 48% in crude homogenate and its synaptosomal fraction, respectively. The decrease was evident from 20% parasitemia and remained more or less constant up to 80% parasitemia. The Km values of GAD in normal and infected animals were 1.2 x 10(-2) and 3.3 x 10(-2) mM, respectively, indicating a decrease in enzyme substrate affinity due to infection. The lowered GAD activity rose to slightly above normal by treatment of infected animals with chloroquine. Decrease in GAD activity reflected lower gamma-aminobutyric acid (GABA) levels in the infected brain; however, GABA-transaminase activity was not significantly influenced by infection. It has been proposed that impaired GABA synthesis may be due to hypoxia induced by malarial infection.

Altered drug metabolism in parasitic diseases

While the immune system represents the main line of host defence against parasite infections, mixed function oxidase (MFO) systems (Box 1) offer the main line of defence against drugs and other biologically active substances. But, as this review shows, many parasites can exert a profound effect on the host MFO system by altering the microsomal drug-metabolizing enzymes and electron transport carriers such as cytochrome P-450. This can markedly affect the host's ability to metabolize biologically active compounds, often with adverse physiological, pharmacological and toxicological consequences. In mammals, drug metabolism occurs predominantly in the liver, and to a lesser extent in the spleen, lungs, kidneys, intestine and cerebral tissues. Thus those parasites that occupy sites in these tissues - such as amoebae, Fasciola, schistosomes and malaria - tend to be those with greatest effects on the host's ability to metabolize drugs. The effects can modify the host response to substances unrelated to the infection, and to drugs which may be administered under a chemotherapeutic regime.