Drugs and the liver. Part II. The role of the antipyrine test in drug metabolism studies

The synthesis, crystal structure and enhanced blue fluorescence emission of novel antipyrine derivatives

Four new antipyrine derivatives were synthesized and characterized by elemental analysis, FT-IR, (1)H NMR, (13)C NMR spectroscopy, and a representative compound 1b was confirmed based on the X-ray crystallographic analysis. The antipyrine-phenylboronic acid 1b crystallizes in the monoclinic space group P2(1)/c, and displays an E configuration about the CN double bond. The absorption and fluorescence spectra of these compounds were investigated. Replacement of a six-membered phenyl group with a five-membered thienyl unit in the antipyrine derivatives resulted in a bathochromic shift approximately 21 nm, while the bithienyl system caused a strong bathochromic effect of 53 nm relative to the substituted phenyl groups. The bithienyl-antipyrine hybrid 1c displayed a turn-on fluorescence response to water, acetic acid (HOAc) and sulfuric acid (H(2)SO(4)) in ethanol solution, but no fluorescence response toward alkali. Whereas the free compound was very weakly fluorescent in ethanol, the addition of water, HOAc and H(2)SO(4) leads to an appearance of strong blue fluorescence and a dramatic increase of emission intensity.

Exercise-induced oxidative stress in older adults as a function of habitual activity level

OBJECTIVES

It has been suggested that regular physical activity might maintain and promote the antioxidant defense capacity against oxidative stress. Therefore, we assessed exercise-induced oxidative stress in relation to habitual physical activity level (PAL) in older adults.

DESIGN

The study included a 2-week observation period for the measurement of average daily metabolic rate (ADMR) and PAL. Exercise-induced oxidative stress was measured during a 45-minute cycling test at submaximal intensity.

SETTING

A university medical research center.

PARTICIPANTS

Twenty-six subjects volunteered for the study (n = 26; mean age +/- standard deviation 60 +/- 1; body mass index 27 +/- 1 kg/m2).

MEASUREMENTS

PAL was determined as ADMR combined with a measurement of basal metabolic rate (BMR): PAL = ADMR/BMR. ADMR was measured over 2 weeks with the doubly labeled water method, preceded by a BMR measurement with a ventilated hood. Antipyrine oxidation was used as marker for oxidative stress in vivo. Reaction of antipyrine with hydroxyl radicals results in the formation of para-hydroxyantipyrine (p-APOH) and ortho-hydroxyantipyrine (o-APOH), where o-APOH is not formed through alternative oxygenetic pathways.

RESULTS

PAL was inversely related to the exercise-induced increase in the ratio of o-APOH to native antipyrine (r = 0.49, P = .010). The relationship between PAL and exercise-induced increase in the ratio of p-APOH (r = 0.30, P = .140) or thiobarbituric acid reactive species (r = 0.31, P = .130) did not reach the level of significance.

CONCLUSION

Physically active older adults have a reduced exercise-induced oxidative stress than older adults with a lower level of physical activity. It seems that regular physical activity improves the antioxidant defense capacity.

Antioxidant supplementation and exercise-induced oxidative stress in the 60-year-old as measured by antipyrine hydroxylates

The effects of 12 weeks of antioxidant supplementation on exercise-induced oxidative stress were investigated in older adults (60 (SE 1) years; BMI 26 (SE 1) kg/m(2)). Subjects were randomly divided in two groups: supplementation (n 11) with 100 mg dl-alpha-tocopheryl acetate, 200 mg ascorbic acid, and 2 mg beta-carotene, and placebo (n 9). Before and after the 12 week supplementation period, subjects cycled for 45 min at submaximal intensity (50 % maximal workload capacity). Antipyrine was used as marker for oxidative stress. Antipyrine reacts quickly with hydroxyl radicals to form para- and ortho-hydroxyantipyrine. The latter metabolite is not formed in man through the mono-oxygenase pathway of cytochrome P450. Daily supplementation significantly increased plasma concentrations of alpha-tocopherol and beta-carotene in the supplemented group (Delta 14.4 (SE 3.2) and 0.4 (se 0.1) micromol/l; P<0.001 and P<0.01). No significant differences, within and between groups, were observed in the exercise-induced increase in the ratios para- and ortho-hydroxyantipyrine to antipyrine. In addition, supplementation did not affect the exercise-induced increase in thiobarbituric acid reactive substances in plasma. In conclusion, in 60-year-old subjects antioxidant supplementation had no effect on the exercise-induced increase in oxidative stress as measured by free radical products of antipyrine.

Exercise training and oxidative stress in the elderly as measured by antipyrine hydroxylation products

Effects of 12 wk exercise training on oxidative stress were examined in elderly humans. We measured oxidative stress during a 45 min cycling test by using antipyrine hydroxylation products. Antipyrine breakdown is independent of blood flow to the liver, which is important during exercise. Furthermore, antipyrine reacts quickly with hydroxyl radicals to form para- and ortho-hydroxyantipyrine. Ortho-hydroxyantipyrine is not formed in man through the mono-oxygenase pathway of cytochrome P450. Twenty subjects (9 women; 60 +/- 3 y) participated in the training program. Thirteen subjects (5 women; 64 +/- 7 y) served as inactive controls. Subjects trained, twice a week for 1 h, at a fitness center. After 12 wk, maximal oxygen uptake (p < .005) and workload capacity (p < .001) were only significantly elevated in the training group. After 12 wk, both groups observed no change in the ratios of antipyrine hydroxylates, para- and ortho-hydroxyantipyrine, to native antipyrine. Furthermore, no differences were observed within or between groups in the exercise-induced increase in the plasma level of thiobarbituric acid reactive species. In conclusion, 12-wk training had no effect on exercise-induced oxidative stress in elderly humans as measured by free radical reaction products of antipyrine. Despite the fact that training in elderly humans improves functional capacity, it appears not to compromise antioxidant defense mechanisms.

Antioxidants reduce oxidative stress in claudicants

BACKGROUND

Low-grade ischemia-reperfusion in claudicants leads to damage of local tissues and remote organs. Since this damage is partly caused by oxygen-derived free radicals (ODFR), scavenging these ODFR could reduce the local and remote injury.

METHODS

Using a new method by which a free radical reaction product (ortho-APOH) of the exogenous marker antipyrine is measured to quantify the oxidative stress, 16 stable claudicants performed a standard walking test before and after administration of vitamin E (200 mg) and vitamin C (500 mg) daily for 4 weeks.

FINDINGS

Ortho-APOH was significantly increased during the reperfusion period (P = 0.026) before administration of the vitamins. After 4 weeks of vitamin supplementation no rise was found in the reperfusion period. Malondialdehyde showed no changes in either group.

INTERPRETATION

These findings indicate that administering extra antioxidants to claudicants reduces oxidative stress in these patients. This may also have an effect on the remote ischemia-reperfusion damage and reduce cardiovascular morbidity in this group.

Gabapentin does not affect antipyrine clearance

The effect of gabapentin on antipyrine clearance was assessed in 12 healthy male volunteers, using a known enzyme inducer, phenytoin, as control. Subjects received gabapentin 400 mg or phenytoin 100 mg three times daily for 2 weeks. Antipyrine tests were performed before, during, and after treatment with gabapentin or phenytoin. In contrast to phenytoin, chronic administration of gabapentin did not affect antipyrine clearance. Gabapentin appears to have little potential for drug interactions.

The effect of folic acid on the drug metabolizing liver function in man with viral hepatitis

The investigations were carried out on 31 patients (16 men and 15 women, at the age of 20-50) with viral hepatitis. The all patients were divided at two groups. The first group (12 man) received usual treatment (diet, corsil), the second group (19 man) received in addition to the base treatment folic acid (5 mg per day, 10 days). It was found, that at patients with viral hepatitis was decreased the activity of monooxygenase system of liver. So, period of semielimination (T1/2) of antipyrine (AP) was greater in 1,4 time, area under the pharmacokinetic curve - 1,5 time and clearance was below by 39% than in volunteers (29 man). On day of treatment only by corsil, the rate of elimination of AP and clearance were increased by 34 and 31% (p < 0.05) respectively, T1/2 was decreased by 23% (p < 0.05) and area under the pharmacokinetic curve - 17 %. On 10 day of treatment by corsil with folic acid (5 mg per day), the rate of elimination of AP and clearance was increased by 43% (p < 0.05), area under the pharmacokinetic curve and T 1/2 were decreased by 30 and 33% (p < 0.05) respectively. The positive effect of folic acid in treatment of hepatitis at restoration period may be cause participating its derivatives in de novo nucleotide synthesis.

Pharmacokinetics of antipyrine, warfarin and paracetamol in the brushtail possum

The plasma pharmacokinetics of antipyrine, warfarin and paracetamol have been studied in the Australian brushtail possum (Trichosurus vulpecula). The plasma elimination half-lives (t1/2) were 1.2 h for antipyrine, 11.9 h for warfarin and 5.2-12.9 h for paracetamol. Our data indicate that the clearance of these three xenobiotics in the possum is similar to that reported in eutherian mammals. There was no dose-dependent increase in paracetamol plasma t1/2 over the dose range 100-1000 mg kg(-1), indicating a lack of capacity saturation. This observation may in part explain the unusual resistance of the possum to the hepatotoxic effect of high doses of paracetamol.

Influence of short-term water deprivation on antipyrine disposition in calves

The effect of four days water deprivation on the metabolism of antipyrine was studied in female Holstein-Friesian calves, aged 24 to 25 days, by measuring the antipyrine plasma clearance and the excretion of three major metabolites of antipyrine in urine. Water deprivation was associated with a statistically significant (P < 0.01) increase in the plasma antipyrine elimination half-life from 10.85(1.14) hours to 14.00(1.05) hours. In water deprived calves the systemic clearance of antipyrine was significantly (P < 0.05) decreased from 0.75(0.07) ml min-1 kg-1 to 0.56(0.05) ml min-1 kg-1. The excretion of three major metabolites of antipyrine: 4-hydroxyantipyrine, 3-hydroxymethylantipyrine and norantipyrine in urine was significantly (P < 0.01) decreased after water deprivation. In the control group no significant differences between the pharmacokinetic parameters of antipyrine in 24 to 25 and 28 to 29 day-old calves were observed. Also urinary profiles of antipyrine in calves from the control group did not differ significantly between 24 to 25 and 28 to 29 days of life. Our data indicate that water deprivation inhibits antipyrine elimination in calves.

Assessment of doxylamine influence on mixed function oxidase activity upon multiple dose oral administration to normal volunteers

The primary purpose of this study was to assess the influence of doxylamine and phenobarbital on antipyrine/metabolites pharmacokinetics and 6 beta-hydroxycortisol urinary excretion. This study was conducted in 48 healthy male human volunteers (16 per treatment group) using a parallel study design. Treatment groups consisted of 12.5 mg of doxylamine succinate, placebo, or 30 mg of phenobarbital administered orally every 6 h for 17 days. Results indicate that no statistically significant differences were observed between the doxylamine and placebo groups that are indicative of enzyme induction. For the phenobarbital group, a significant increase for antipyrine total (36 versus 45 mL/h/kg) and nonrenal (35 versus 44 mL/h/kg) clearances and 6 beta-hydroxycortisol excretion (338 versus 529 micrograms) and a significant decrease in the terminal exponential half-life (11 versus 9 h) of antipyrine were observed.

Trimethadione as a probe drug to estimate hepatic oxidizing capacity in humans

Trimethadione (TMO) has the properties required of probe drugs for the evaluation of hepatic drug-oxidizing capacity in humans in vivo. TMO is demethylated to dimethadione (DMO), its only metabolite, in the liver after oral administration. Involvement of two cytochrome P450's--CYP2C9 and 3A4--in TMO metabolism has been seen in humans, but involvement of 1A2 is not clearly established. In humans with various types of liver disease and hepatectomy, the serum DMO/TMO ratios, which were measured on blood samples obtained by a single collection 4 hr after oral administration of TMO, correlated well with the degree of hepatic damage. This finding suggests that TMO may be used as a probe drug in the rapid determination of the functional reserve mass of the liver as well as hepatic drug-oxidizing capacity in humans in vivo.

Effect of spironolactone on antipyrine metabolism in calves

Ten female calves of the Black and White breed aged seven to eight days were studied before and after seven days of treatment with spironolactone at a dose rate of 1 mg kg bodyweight-1 twice a day. The treatment was associated with a statistically significant decrease in the half-life of antipyrine in plasma and an increase in its rate of metabolic clearance. The excretion of 4-hydroxyantipyrine in urine was significantly increased after the treatment with spironolactone, but there were no changes in the rates of excretion of 3-hydroxymethylantipyrine or norantipyrine. These results indicate that spironolactone enhanced the activity of the microsomal drug-metabolising enzyme system and induced cytochrome P-450 in the calves.

Antipyrine as a probe for human oxidative drug metabolism: identification of the cytochrome P450 enzymes catalyzing 4-hydroxyantipyrine, 3-hydroxymethylantipyrine, and norantipyrine formation

BACKGROUND AND OBJECTIVE

Antipyrine has been widely used as a probe drug for human oxidative drug metabolism. To evaluate the role of antipyrine as a model drug, we have identified the cytochrome P450 enzymes involved in 4-hydroxyantipyrine, 3-hydroxymethylantipyrine, and norantipyrine formation.

METHODS

We used the following methods for this study: (1) determination of enzyme kinetics for antipyrine metabolite formation in human liver microsomes, (2) inhibition studies with antibodies and inhibitors, and (3) formation of metabolites by stable expressed human P450 enzymes.

RESULTS

Antipyrine biotransformation could be described by Michaelis-Menten kinetics: norantipyrine: maximum rate of metabolite formation (Vmax), 0.91 +/- 0.04 nmol . mg-1 . min-1; Michaelis-Menten constant (Km), 19.0 +/- 0.8 mmol/L; 4-hydroxyantipyrine: Vmax, 1.54 +/- 0.08 nmol . mg-1 . min-1;Km,39.6 +/- 2.5 mmol/L. Antibodies against CYP3A4 inhibited the formation of 4-hydroxyantipyrine by 25% to 65%. LKM-2 antibodies (anti-CYP2C) caused a 75% to 100% inhibition of norantipyrine and a 58% to 80% inhibition of 3-hydroxymethylantipyrine formation. Sulfaphenazole inhibited the formation of 3-hydroxymethylantipyrine and norantipyrine by about 50%. Furafylline and fluvoxamine inhibited norantipyrine, 4-hydroxyantipyrine, and 3-hydroxymethylantipyrine formation by about 30%, 30%, and 50%, respectively. Ketoconazole reduced formation of norantipyrine, 3-hydroxymethylantipyrine, and 4-hydroxyantipyrine by up to 80%. Formation in stable expressed enzymes indicated involvement of CYP1A2, CYP2B6, CYP2C, and CYP3A4 in metabolite formation.

CONCLUSION

Antipyrine metabolites are formed by at least six hepatic cytochrome P450 enzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C18, and CYP3A4). 4-Hydroxylation is mainly catalyzed by CYP3A4 and, to a lesser extent, by CYP1A2. The CYP2C subfamily contains the predominant enzymes for norantipyrine formation, and CYP1A2 is also involved. Formation of 3-hydroxymethylantipyrine is mediated by CYP1A2 and CYP2C9. Because several cytochrome P450 enzymes are involved in the formation of each metabolite, antipyrine is not well suited as a probe for distinct human cytochrome P450 enzymes.

Effect of age on the pharmacokinetics of antipyrine in calves

Single doses of 15 mg kg-1 antipyrine were given intravenously to 10 female calves of the black and white breed at one, two, four, six, eight and 12 weeks of age, and the concentrations of antipyrine, 4-hydroxyantipyrine (4-OHA), 3-hydroxymethyl-antipyrine (HMA) and norantipyrine (NORA) were measured in plasma and urine by high performance liquid chromatography. The first three months of life were characterised by a steady decrease in the apparent volume of distribution (aVd) and half-life (t0.5) of antipyrine. The systemic clearance (CIs) of antipyrine per unit bodyweight increased significantly between one and 12 weeks of age. Age did not influence the excretion of HMA and NORA in urine, but the excretion of 4-OHA by 12-week-old calves was significantly greater than by one-week-old calves. There was an age-related change in the partial clearances of the antipyrine metabolites when expressed per unit bodyweight.

Effects of atorvastatin, an HMG-CoA reductase inhibitor, on hepatic oxidative metabolism of antipyrine

Possible effects of multiple-dose administration of atorvastatin on the pharmacokinetics of single-dose antipyrine were evaluated in this drug-drug interaction study. Twelve healthy male volunteers received three 200-mg capsules of antipyrine on days 1 and 22, and two 40-mg atorvastatin tablets in the morning on days 8 through 23. Serial blood and urine samples were collected after administration of each antipyrine dose. Plasma was analyzed for antipyrine, and urine samples were analyzed for antipyrine, 4-hydroxyantipyrine, and norantipyrine by validated high-performance liquid chromatography with ultraviolet detection. Overall, antipyrine and atorvastatin doses were well tolerated in healthy volunteers. Mean antipyrine concentrations in plasma after administration of a single, oral dose of antipyrine during coadministration of multiple doses of atorvastatin were nearly superimposible on concentrations after administration of antipyrine alone. Individual and mean parameter values for plasma pharmacokinetics of antipyrine were similar in both treatment periods. Atorvastatin did not significantly alter the fraction of clearance of antipyrine in plasma that occurred by urinary excretion of 4-hydroxyantipyrine and norantipyrine. These results indicate that the recommended highest daily dose of atorvastatin has negligible effects on antipyrine pharmacokinetics and on oxidative pathways responsible for the metabolism of antipyrine.

Highly sensitive and specific gas chromatographic-tandem mass spectrometric method for the determination of trace amounts of antipyrine metabolites in biological material

A highly sensitive and specific gas chromatographic-tandem mass spectrometric method was developed for the determination of the antipyrine (INN: phenazone) metabolites, norantipyrine, 4-hydroxyantipyrine and 3-hydroxy-methylantipyrine, in biological material. Deuterated analogues of the metabolites were used as internal standards. The method has a limit of quantitation of 5 ng per sample for the determination of norantipyrine, 4-hydroxy-antipyrine and 3-hyddroxymethylantipyrine with coefficients of variation of 19.4, 14.6 and 20.7%, respectively. Precision and accuracy are good over the whole range measured (5-500 ng/sample) with a coefficient of variation, respectively error of determination < or = 20%. Due to its high sensitivity the method can be used to study the formation of these metabolites in microsomal preparations containing only 100 micrograms of protein.

The effect of zileuton on antipyrine and indocyanine green disposition

The effects of single and multiple oral doses of zileuton on the pharmacokinetics of antipyrine and indocyanine green were studied in 16 healthy, nonsmoking adult men by means of a double-blind, randomized, parallel placebo-controlled design. Indocyanine green disposition was not significantly altered by zileuton. Plasma antipyrine clearance declined by 20% (p < 0.0005) and 52% (p < 0.0005) after single and multiple dose zileuton exposure, respectively. Total urinary recovery of unchanged antipyrine and metabolites decreased with zileuton exposure. Selective declines from baseline of 16% (p = 0.007) and 20% (p = 0.003) after single-dose zileuton and 30% (p < 0.0005) and 43% (p < 0.0005) after multiple-dose zileuton were detected in recovery of 4-hydroxyantipyrine and 3-hydroxymethylantipyrine, respectively. Urinary recovery of the N-demethylantipyrine metabolite norantipyrine and percent of conjugation of 3-hydroxymethylantipyrine were unchanged by zileuton. In conclusion, zileuton therapy has no detectable effect on indocyanine green disposition but exerts marked effects on antipyrine plasma and urine metabolite disposition.

Assessment of liver metabolic function. Clinical implications

Inter- and intraindividual variability in pharmacokinetics of most drugs is largely determined by variable liver function as described by parameters of hepatic blood flow and metabolic capacity. These parameters may be altered as a result of disease affecting the liver, genetic differences in metabolising enzymes, and various types of drug interactions, including enzyme induction, enzyme inhibition or down-regulation. With the now known large number of drug metabolising enzymes, their differential substrate specificity, and their differential induction or inhibition, each test substance of liver function should be used as a probe for its specific metabolising enzyme. Thus, the concept of model test-substances providing general information about liver function has severe limitations. To test the metabolic activity of several enzymes, either several test substances may be given (cocktail approach) or several metabolites of a single test substance may be analysed (metabolic fingerprint approach). The enzyme-specific analysis of liver function results in a preference for analysis of the metabolites rather than analysis of the clearance of the parent test substance. There are specific methods to quantify the activity of cytochrome P450 enzymes such as CYP1A2, CYP2C9, CYP2C19MEPH, CYP2D6, CYP2E1, and CYP3A, and phase II enzymes, such as glutathione S-transferases, glucuronyl-transferases or N-acetyltransferases, in vivo. Interactions based on competitive or noncompetitive inhibition should be analysed specifically for the cytochrome P450 enzyme involved. At least 5 different types of cytochrome P450 enzyme induction may result in major variability of hepatic function; this may be quantified by biochemical parameters, clearance methods, or highly enzyme-specific methods such as Western blot analysis or molecular biological techniques such as mRNA quantification in blood and tissues. Therapeutic drug monitoring is already implicitly used for quantification of the enzyme activities relevant for a specific drug. Selective impairment of hepatic enzymes due to gene mutations may have an effect on the pharmacokinetics of certain drugs similar to that caused by cirrhosis. Assessment of this heritable source of variability in liver function is possible by in vivo or ex vivo enzymological methods. For genetically polymorphic enzymes and carrier proteins involved in drug disposition, molecular genetic methods using a patient's blood sample may be used for classification of the individual into: (i) the impaired or poor metaboliser (homozygous deficient); (ii) the extensive (homozygous active) metaboliser group; and (iii) the moderately extensive metaboliser (heterozygous) group. For hepatic blood flow determinations, galactose or sorbitol given at relatively low doses may be much better indicators than the indocyanine green.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation and purification of three glucuronides of antipyrine. Proposal for an original analytical method for quantitation of sulpho- and glucuroconjugated metabolites

The determination of the concentrations of antipyrine metabolites in biological fluids is hampered by the difficulty in obtaining pure conjugated compounds to be used as standards. Most authors have proposed determination of total forms by high performance liquid chromatography (HPLC) after deconjugation of these metabolites using chemical or enzymatic hydrolysis. Up to now there is no satisfactory hydrolysis method for the study of all antipyrine metabolites. The situation is further complicated by the fact that the deconjugated metabolites are highly unstable whichever technique is being used. Because of the lack of stability of all these molecules it has been necessary to isolate the glucuroconjugated compounds from urine. We describe a method which allows us to obtain highly purified glucuroconjugated metabolites of antipyrine. Sulphoconjugated compounds have been synthesized previously. We are thus able to propose a chromatographic procedure which allows us to determine simultaneously all stable phase I and phase II metabolites of antipyrine in biological fluids without any step of extraction. This analytical technique allows us to study the activity of the different isoenzymes implicated in the metabolism of antipyrine.

Drugs and the liver. Part III: Ageing of the liver and the metabolism of drugs

The clearance of many drugs by the liver is reduced in the elderly, and this accounts, at least in part, for the greater frequency of adverse drug reactions in this population. Ageing in experimental animals is accompanied by a decline in the activities of certain microsomal monooxygenase enzymes; this has been said to be the reason for decreased drug elimination. However, recent data suggests that this is probably not the case in humans. Reduced size and blood flow are important features of the ageing liver, and probably account for most of the age-related changes in drug metabolism. Major decrements in hepatic function do occur in frail elderly individuals, although the mechanisms underlying this are at present unclear. Future studies of drug metabolism and ageing must carefully define patient groups to allow full interpretation of data.