Caffeine: a model compound for measuring liver function

Effects of aging on respiration, ATP levels and calcium transport in rat liver mitochondria. Response to theophylline

The concept that aging results in an impairment of mitochondrial biochemistry has been tested on organelles isolated from the liver of 3-4-month-old and 24-month-old rats of the Wistar strain. Our data suggest that aging results in significant decreases in succinate-supported respiration, ATP levels and calcium uptake. When theophylline was added to the incubation mixture, both respiration and calcium uptake were depressed in approximately the same proportion in the mitochondria from old rats, although the mitochondrial ATP of young animals was significantly decreased by this substance.

The effects of ageing on aminopyrine and caffeine breath tests in the rat

The influence of ageing on demethylation of 14C-aminopyrine (AP) and 14C-caffeine (Caf) in Wistar littermate rats was studied serially using the 14CO2-breath test. In both sexes, the elimination half-life (t1/2) of 14C-AP fell from a mean of approximately 75 min when weaned at 17 days to 45 min at maturity (49 days); thereafter t1/2 became prolonged, being most prolonged (82 min) in elderly male rats (210 days). Similarly, t1/2 of 14C-Caf was also prolonged with ageing. These studies using in vivo and longitudinal techniques indicate the importance of ageing on hepatic demethylation.

Factors influencing the caffeine test for cytochrome P 448-dependent liver function

Liver functions in patients with liver disease can be estimated by caffeine clearance. Our data, however, demonstrate the additional influence of factors other than liver disease on the caffeine test. Smoking enhances caffeine clearance in both healthy volunteers and patients with severe hepatic disorders, whereas co-medication with mexiletine strongly inhibits caffeine elimination.

Overnight salivary caffeine clearance: a liver function test suitable for routine use

The feasibility of measuring caffeine clearance from saliva (SCl) was assessed in ambulatory patients with liver disease and in a control group, and the results were compared with quantitative liver function tests. For this purpose, the subjects were given 280 mg caffeine p.o. in decaffeinated coffee powder between noon and 4 p.m., and caffeine concentrations were measured in saliva (using an enzyme immunoassay) before bedtime and upon arising. In the cirrhotics (n = 29), SCl was 0.58 +/- S.D. 0.45 ml per min X kg, thus being reduced to approximately one-third of drug-free, nonsmoking controls (1.53 +/- 0.46, n = 18); although patients with noncirrhotic liver disease showed intermediate values (0.95 +/- 0.47), their reduction in SCl was significant (p less than 0.001). SCl was correlated with indocyanine green fractional clearance, galactose elimination capacity and aminopyrine breath test; however, the closest relationship (Rs = 0.80) was observed with the aminopyrine breath test. It is suggested that the measurement of SCl represents a noninvasive and innocuous procedure for quantifying hepatic microsomal function, and is suitable for routine use. Since a.m. saliva concentrations of caffeine are highly correlated (Rs = -0.94) with SCl, further simplification of the test to a single-point measurement appears possible.

Rapid high-performance liquid chromatography assay for salivary and serum caffeine following an oral load. An indicator of liver function

A rapid isocratic reversed-phase high-performance liquid chromatography (HPLC) system for the quantitative measurement of serum and salivary caffeine is described. The best separation of caffeine from other methylxanthines was achieved by chromatography on an ODS-Hypersil column using a solvent system of 0.1 M ammonium acetate pH 4.6-acetonitrile (85:15, v/v). The effluent was monitored at 280 nm. Caffeine was extracted from diluted serum and saliva samples (10-500 microliter) by adsorption on a small Bond-Elut C18 cartridge and recovered by elution with methanol. Thermospray HPLC-mass spectrometry conditions were optimized to afford a means of directly identifying caffeine in samples. The positive-ion mass spectrum was characterized by an intense protonated molecular ion, MH+, at m/z 195 and negligible fragmentation. When the mass spectrometer was operated in selected ion monitoring mode, caffeine could be detected in less than 1 microliter of serum and saliva at a concentration of 1 microgram/ml. Caffeine (3.5 mg/kg body wt.) was administered orally to healthy adults, children, and newborn infants, and to patients with liver disease. The clearance rate and half-life were determined as a test of liver function. A prolongation in the elimination of caffeine was observed in patients with liver disease and, although there was some overlap in the values obtained for patients with noncirrhotic liver disease and healthy persons, the oral caffeine load test may usefully serve as a dynamic assessment of liver function in the serial follow-up of patients with liver disease.

Influence of mexiletine on caffeine elimination

In an acute experiment in healthy volunteers and in patients under long-term treatment for cardiac arrhythmias, mexiletine inhibits caffeine elimination by about 50%. The clearance of mexiletine is not influenced by caffeine. Some side effects of mexiletine may possibly at least partially be attributable to a retention of caffeine.

Influence of alcohol and caffeine consumption on caffeine elimination

Ten healthy male volunteers were each studied on four separate occasions to assess the role of regular caffeine and alcohol intake on caffeine elimination. Antipyrine disappearance was also studied as an established quantitative test of hepatic microsomal function. Regular caffeine intake in high doses for 1 week failed to alter either antipyrine or caffeine pharmacokinetics. In contrast, alcohol intake of 50 g/day significantly prolonged caffeine half-life by 72% (P less than 0.005) and diminished caffeine clearance by 36% (P less than 0.0005). However, antipyrine kinetics were unaltered. These results demonstrate that alcohol, in amounts commonly consumed, is a strong inhibitor of caffeine metabolism.

Prognostic value of the aminopyrine breath test in cirrhotic patients

The aminopyrine breath test has been proposed as a quantitative test of hepatic function, but its long-term prognostic value in patients with cirrhosis has not been determined. The aim of this study was to examine the usefulness of the aminopyrine breath test in assessing prognosis and to compare it with traditional methods of evaluating liver function. One-hundred eighty-seven patients with histologically confirmed cirrhosis were studied prospectively. An aminopyrine breath test was obtained at the time of inclusion in the study and results were expressed as per cent of the dose excreted in 2 hr. At inclusion, the severity of liver disease was also assessed according to the Pugh modification of the Child-Turcotte classification based on ascites, neurological status, serum albumin, serum bilirubin and prothrombin time. Mean follow-up was 844 days. During that period, 59 of 187 patients died of their liver disease. Two-year survival decreased with increasing Child-Turcotte classification score: survival was 98% in Child Class A patients (n = 62), 66% in Child Class B (n = 76) and 36% in Child Class C (n = 49) (chi 2 = 65.6, p less than 0.001). Two-year survival also decreased significantly with increasing degree of aminopyrine breath test abnormalities: survival was 90% in patients with aminopyrine breath test greater than 4% (n = 56); 78% in patients with aminopyrine breath test = 2 to 4% (n = 66), and 43% in patients with aminopyrine breath test less than 2% (n = 65) (chi 2 = 36.9, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative pharmacokinetics of caffeine and its primary demethylated metabolites paraxanthine, theobromine and theophylline in man

The pharmacokinetics of caffeine (CA), paraxanthine (PX), theobromine (TB) and theophylline (TP) were studied in six healthy male volunteers after oral administration of each compound on separate occasions. The total plasma clearances of CA and PX were similar in value (2.07 and 2.20 ml min-1 kg-1, respectively) as were those for TP and TB (0.93 and 1.20 ml min-1 kg-1, respectively). The unbound plasma clearances of CA and PX were also similar in magnitude (3.11 and 4.14 ml min-1 kg-1, respectively) as were those of TP and TB (1.61 and 1.39 ml min-1 kg-1, respectively). The half-lives of TP and TB (6.2 and 7.2 h, respectively) were significantly longer than those of CA and PX (4.1 and 3.1 h, respectively). The volume of distribution at steady state of TP (0.44 l kg-1) was lower than that of the other methylxanthines (0.63-0.72 l kg-1). The unbound volume of distribution of TP (0.77 l kg-1) was however the same as that of TB (0.79 l kg-1) whereas the unbound volume of distribution of PX (1.18 l kg-1) was similar to that of CA (1.06 l kg-1).

Drug pharmacokinetics and the carbon dioxide breath test

The interrelationship of the pharmacokinetics of a drug and the expiration of carbon dioxide formed as a metabolite have been studied. The pharmacokinetic characteristics of the drug that affect the usefulness of the carbon dioxide excretion as a measure of liver function were examined by means of computer simulations. The parent drug extraction ratio, fraction demethylated, volume of distribution, and absorption rate of an oral dosage form all contribute to the carbon dioxide breath test result. A drug that would be a useful substrate when the carbon dioxide breath test is used as a probe for changes in liver function should be at least 50% metabolized by demethylation, have a hepatic extraction ratio of 0.2-0.5, and be administered in a form that is rapidly absorbed.

Chronic verapamil administration lowers portal pressure and improves hepatic function in rats with liver cirrhosis

The effects of verapamil on portal pressure, microsomal liver function and extravascular albumin space were investigated in rats rendered cirrhotic by chronic exposure to phenobarbital and carbon tetrachloride. Verapamil significantly decreased splenic pulp pressure by 28% (P less than 0.05). In cirrhotic animals it improved liver function, measured by the aminopyrine and caffeine breath tests, by 36% (P less than 0.025) and 53% (P less than 0.05), respectively. The extravascular albumin space, an important determinant of drug clearance, was measured by a multiple indicator dilution technique. It was significantly larger in verapamil treated than in untreated cirrhotics (4.41 +/- 1.06 vs 2.73 +/- 0.79 ml/g; P less than 0.01). We conclude that verapamil has significant potential as a portal antihypertensive agent and its value in treating cirrhosis in man should be explored by controlled studies.

Quantitative liver function in the elderly assessed by galactose elimination capacity, aminopyrine demethylation and caffeine clearance

Hepatic function was assessed in 13 healthy elderly subjects, 71-88 years of age, with three quantitative tests of liver function. The galactose elimination capacity was significantly (P less than 0.05) lower in the elderly (6.08 +/- 1.30 mg X min-1 X kg-1, mean +/- SD) than in a group of 70 subjects under 40 (7.48 +/- 0.94 mg X min-1 X kg-1) and 11 subjects between the age of 40 and 70 (7.08 +/- 0.68 mg X min-1 X kg-1). The demethylation of aminopyrine as assessed by the aminopyrine breath test, and the systemic clearance of caffeine, two measures of microsomal function, demonstrated a comparable decrease but showed much more interindividual variation. Caffeine clearance decreased from 1.49 +/- 0.44 ml X min-1 X kg-1 in young adults to 0.97 +/- 0.39 ml X min-1 X kg-1 (P less than 0.01) in the elderly, and the demethylation of aminopyrine decreased from 0.79 +/- 0.15 to 0.62 +/- 0.20% dose X kg X mmol-1 (P less than 0.05). Our data indicate that aging is associated with a loss of the functioning mass of hepatocytes. The decrease in drug metabolism parallels the loss of functional mass but shows more interindividual variation probably reflecting the many genetic and environmental factors influencing these tests of microsomal function.

Caffeine elimination: a test of liver function

Fasting plasma caffeine concentration and various parameters of caffeine elimination from plasma obtained after a standardized oral dose of 140 mg caffeine have been compared in nine patients with liver cirrhosis, eight patients with non-cirrhotic liver disease and ten healthy volunteers with regard to their ability to discriminate between the different groups. Fasting plasma caffeine concentrations were significantly higher in cirrhotics (11.1 +/- 10.5 mumol/l) than in healthy volunteers (1.5 +/- 0.8 mumol/l). The respective values measured in patients with non-cirrhotic liver disease (3.1 +/- 3.1 mumol/l) did not differ significantly from the controls. Plasma disappearance rate and clearance of caffeine were significantly decreased in cirrhotics (0.11 +/- 0.02 h-1; 1.0 +/- 0.3 ml/min per kg) and in patients with non-cirrhotic liver disease (0.18 +/- 0.04 h-1; 2.2 +/- 0.7 ml/min per kg) as compared to healthy volunteers (0.23 +/- 0.04 h-1; 3.1 +/- 0.9 ml/min per kg). Plasma caffeine concentration determined 12 h after administration of the test dosage discriminated best between patients with cirrhosis (5.4 +/- 1.6 mumol/l), patients with non-cirrhotic liver disease (2.0 +/- 1.4 mumol/l) and healthy volunteers (0.8 +/- 0.2 mumol/l). These results, the safety of the test compound and the simplicity of a single caffeine determination in plasma 12 h after a standardized dose of caffeine make this test attractive for evaluation of liver function.

Fasting plasma caffeine concentration. A guide to the severity of chronic liver disease

Fasting plasma caffeine concentrations (FPCC) were measured in 86 outpatients being examined for suspected or known liver disease. Seven patients (8%) who avoided caffeine consumption had nonmeasurable FPCC; they were dropped from further consideration. The remaining 79 subjects were divided into 4 diagnostic groups: surgical shunt (n = 11); alcoholic, posthepatitic, or primary biliary cirrhosis (n = 29); miscellaneous liver disease (n = 23); and normal liver (n = 16). FPCC was highest (mean, 17.8 mumol/l) in the shunt group, followed by the cirrhosis (12.3), miscellaneous liver diseases (4.6), and normal liver (2.1) groups. FPCC seemed to reflect severity of functional impairment, further supported by highly significant correlations with quantitative liver function tests, such as aminopyrine breath test (Rs = -0.89; n = 66), indocyanine green disappearance (Rs = -0.85; n = 65), and galactose elimination capacity (Rs = -0.70; n = 75). A careful dietary history showed no significant difference in caffeine consumption among the groups. It is suggested that in regular coffee drinkers FPCC might serve as a simple and convenient guide to the severity of functional impairment in chronic liver disease.

High-performance liquid chromatographic determination of dimethylxanthine metabolites of caffeine in human plasma

A normal-phase high-performance liquid chromatographic assay of caffeine and its metabolites, theophylline, theobromine and paraxanthine, in human plasma is described. The two internal standards ethyltheophylline and 1,3,7-trimethyluric acid are used simultaneously and cover the range of different polarities from caffeine to the three dimethylxanthines. Plasma (0.5 ml) in the presence of ammonium sulphate is extracted with chloroform--isopropanol (1:1, v/v). The extract is chromatographed with a LiChrosorb Si 60 5-micron column and a mobile phase of dichloromethane containing 2.5% of a formate buffer in methanol. Calibration is performed with six different calibration mixtures which take into account the large plasma concentration differences between caffeine and its metabolites in man. The method is suitable for the simultaneous determination of caffeine and its dimethylxanthine metabolites in plasma of healthy and diseased persons.

Fasting serum bile acid level in cirrhosis. A semi-quantitative index of hepatic function

We examined the roles of the factors which influence bile acid levels in order to define to what extent fasting serum total bile acid (FSTBA) level might reflect hepatic function and/or anatomy of the portal circulation in patients with cirrhosis. In a first group of 13 patients having mild to moderately advanced cirrhosis we determined the apparent oral clearance (CLo) of chenodeoxycholic acid (764 mumol) and their FSTBA levels. In a second group of 15 similar patients we measured FSTBA levels and by hepatic vein catheterization the intrinsic clearance (CLi) of ICG as well as total hepatic blood flow (Q). We found a significant inverse log-log relationship (r = 0.752, P less than 0.01) between the FSTBA and the CLo on the one hand and significant inverse log-log relationship (r = 0.707, P less than 0.01) between the FSTBA and CLi on the other hand. Q was not found to bear any significant relation to FSTBA (r = 0.120, P greater than 0.1). To conclude, in view of the observed relationship between CLi and CLo vs FSTBA, the latter might serve as a simple non-invasive semiquantitative index of hepatic function and/or anatomy of portal circulation in cirrhosis.