Effect of Plasmodium berghei infection on benzoic acid metabolism in mice

Effect of Plasmodium yoelii nigeriensis infection on hepatic and splenic glutathione-S-transferase(s) in Swiss albino and db/+ mice: efficacy of mefloquine and menadione in antimalarial chemotherapy

The present report deals with the status of hepatic and splenic glutathione-S-transferase (GST) activities in mice during experimental infection with Plasmodium yoelii nigeriensis and subsequent treatment of infected mice with mefloquine (Mf) and menadione (Md). The infection caused significant decline in the hepatic and splenic glutathione-S-transferase (GST) activities of albino and db/+ mice. The decline was observed in the levels of both cytosolic and microsomal GST(s) of liver and spleen in both types of mice. Intraperitoneal administration of mefloquine at a dose of 5 mg/kg and menadione at a dose of 100 mg/kg, twice daily from day 1 p.i. (day 0) until day 10, caused restoration in the levels of hepatic as well as splenic GST(s), albeit to varying degrees. Mf was able to suppress parasitaemia by day 5 in the case of albino mice and by day 3 in the case of db/+ mice but was unable to cure both types of mice completely. On the other hand, Md caused a delay in maturation of infection in both cases, but could not cure the mice.

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.

Status of hepatic glutathione-S-transferase(s) during Plasmodium berghei infection and chloroquine treatment in Mastomys natalensis

Plasmodium berghei infection in Mastomys natalensis impaired the hepatic mitochondrial, microsomal and cytosolic glutathione-S-transferase(s) activity with 1-chloro-2,4-dinitrobenzene as substrate. The enzyme activity was concomitantly decreased with rise in parasitaemia. The decreased enzyme activity due to infection was almost normalized with oral treatment of 16 mg (kg body wt)-1 of chloroquine for 4 days.

Effect of malaria infection on the pharmacokinetics of paracetamol in rat

1. Paracetamol (P; 50 and 300 mg/kg i.v.) was administered to the control and malaria-infected (MI) male Wistar rat in order to assess the effect of MI on the metabolism of paracetamol to its glucuronide (PG) and sulphate (PS) conjugates and their excretion in urine. 2. At a dose of 50 mg/kg, neither total clearance (ClT) (controls, 20.3 +/- 0.5; MI, 19.9 +/- 0.9, ml/min/kg; mean +/- SD, p > 0.05) nor the renal clearance of P (ClR) were affected by MI. Although the formation clearance of PG (Clf PG) was decreased by about 40% (controls, 6.6 +/- 1.1; MI, 3.9 +/- 0.9, ml/min/kg, p < 0.05), the formation clearance of PS (Clf PS) was increased by 30% in the MI rat (controls, 8.8 +/- 0.9; MI, 11.2 +/- 1.7, ml/min/kg, p < 0.05), and therefore Clm (controls, 19.7 +/- 0.5; MI, 19.2 +/- 0.8, ml/min/kg, p > 0.05) was unchanged by MI. 3. At a dose of 300 mg/kg, MI produced a significant decrease in the total clearance of P (ClT) (controls, 16.9 +/- 1.0; MI, 11.9 +/- 0.9, ml/min/kg, p < 0.05), metabolic clearance (Clm) (controls, 15.9 +/- 1.4; MI, 11.3 +/- 0.9, ml/min/kg, p < 0.05) and the formation clearance of PG (Clf PG) (controls, 7.9 +/- 1.3; MI, 4.7 +/- 1.5, ml/min/kg, p < 0.05) without affecting Clf PS and ClR of P. 4. These findings indicate that MI impairs the glucuronidation of paracetamol in rat in vivo at both the low and high doses of P. Increased sulphate formation appeared to compensate for decreased glucuronidation at the lower dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of caffeine and theophylline in rats with malaria and endotoxin-induced fever

1. The effects of malaria infection due to Plasmodium berghei and Escherichia coli endotoxin-induced fever on the metabolism of orally-administered caffeine (CA: 10 mg/kg) to its primary metabolites (theobromine (TB), paraxanthine (PX) and theophylline (TH)) were studied in 5-week-old male Wistar rats (n = 5 for each treatment). In separate experiments, the effects of malaria and endotoxin-induced fever on the clearance of i.v.-administered theophylline (TH; 15 mg/kg) were studied in another group of rats. 2. The ratios of CA to the three primary metabolites (TB/CA, PX/CA, PH/CA) determined in a single plasma sample obtained 3 h after CA administration were significantly reduced (p < 0.05) both by malaria and fever compared with control (saline) treatment. The clearance of TH determined from the concentration of TH in a single plasma sample obtained 6 h after TH administration was significantly reduced (p < 0.05) by fever but not malaria (4.0 +/- 0.7 ml/min/kg in controls; 4.2 +/- 0.5 in malaria; 2.4 +/- 0.4 in fever). 3. These results suggest that malaria and fever have different effects on CA and TH metabolism in vivo, probably as a result of different effects on the hepatic isozymes involved.

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.

The effect of malaria infection on 3'-azido-3'-deoxythymidine and paracetamol glucuronidation in rat liver microsomes

The effect of malaria infection on UDP-glucuronosyltransferase (UDPGT) activity was investigated in rat liver microsomes using 3'-azido-3'-deoxythymidine and paracetamol. The Michaelis-Menten parameters, Km and Vmax were calculated and intrinsic clearance values were estimated for normal and infected livers. The results show that malaria infection alters the activity of UDPGT.

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.

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.

Benzoate modulates renal and extrarenal nitrogen flow: metabolic mechanisms

The mechanism by which benzoate enhances total nitrogen excretion was investigated in-situ and in separated rat renal proximal tubules. Orally administered benzoate augmented NH4+, urea and hippurate excretion 2, 1.9 and 76 fold respectively, as compared to baseline for control. Hippurate had similar effects. Benzoate augmented renal blood flow, glutamine extraction and total NH4+ production. Arterio-venous concentration differences of glutamine, glutamate, and NH4+ across the kidney, liver and gut demonstrated an increase in glutamine uptake by the kidney despite reduced release and uptake by the liver and gut, respectively; glutamate release by the kidney and gut was increased; NH4+ handling was unchanged at these three organs. Studies in separated rat renal proximal tubules demonstrated that benzoate stimulated glutamine dependent ammonia-genesis by activation of gamma-glutamyltransferase, via the synthesis of hippurate. The results demonstrate that benzoate can modulate the interorgan partitioning of nitrogen metabolites across several organs, the net effect of which is physiologically expressed as enhanced NH4+ , urea and hippurate excretion.

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

Plasmodium yoelii nigeriensis infection in albino mice significantly altered the hepatic microsomal mixed function oxidase system. Cytochrome P-450 (the terminal monooxygenase) and other monooxygenases, viz. aniline hydroxylase, aminopyrine-N-demethylase and benzo(a)pyrene hydroxylase were significantly lowered while microsomal heme showed 4-fold increase at 80% parasitaemia. Noticeable impairment in the other components like NADH:cytochrome b5 reductase, NADPH:cytochrome c reductase, cytochrome b5 and glucose-6-phosphatase was also observed. Oral treatment of normal and P. y. nigeriensis infected mice with chloroquine (64 mg per kg body weight for 4 days) caused lowering of mixed function oxidase activities which however showed a recovering trend, a week after cessation of treatment.