Hepatobiliary excretion and brain distribution of caffeine in rats using microdialysis

Genome-wide association study of caffeine metabolites provides new insights to caffeine metabolism and dietary caffeine-consumption behavior

Caffeine is the most widely consumed psychoactive substance in the world and presents with wide interindividual variation in metabolism. This variation may modify potential adverse or beneficial effects of caffeine on health. We conducted a genome-wide association study (GWAS) of plasma caffeine, paraxanthine, theophylline, theobromine and paraxanthine/caffeine ratio among up to 9,876 individuals of European ancestry from six population-based studies. A single SNP at 6p23 (near CD83) and several SNPs at 7p21 (near AHR), 15q24 (near CYP1A2) and 19q13.2 (near CYP2A6) met GW-significance (P < 5 × 10-8) and were associated with one or more metabolites. Variants at 7p21 and 15q24 associated with higher plasma caffeine and lower plasma paraxanthine/caffeine (slow caffeine metabolism) were previously associated with lower coffee and caffeine consumption behavior in GWAS. Variants at 19q13.2 associated with higher plasma paraxanthine/caffeine (slow paraxanthine metabolism) were also associated with lower coffee consumption in the UK Biobank (n = 94 343, P < 1.0 × 10-6). Variants at 2p24 (in GCKR), 4q22 (in ABCG2) and 7q11.23 (near POR) that were previously associated with coffee consumption in GWAS were nominally associated with plasma caffeine or its metabolites. Taken together, we have identified genetic factors contributing to variation in caffeine metabolism and confirm an important modulating role of systemic caffeine levels in dietary caffeine consumption behavior. Moreover, candidate genes identified encode proteins with important clinical functions that extend beyond caffeine metabolism.

Disposition kinetics of caffeine and paraxanthine in Nile tilapia (Oreochromis niloticus): characterization of the main metabolites

The reproductive and developmental toxicities of caffeine (CA) reported in mammals have been linked with the characteristics of its kinetic disposition. Because undesirable reproductive effects in fish have also been reported, and considering that CA has been found worldwide at relatively high concentrations in most bodies of waters, this study evaluated the disposition kinetics of CA and its main metabolite paraxanthine (1,7-dimethylxanthine; PX) in Nile tilapia after a single intraperitoneal administration (4 mg/kg). CA showed rapid absorption, first-order elimination with biexponential decay, rapid intercompartmental transfer, wide distribution in almost the entire body water (apparent volume of distribution [Vd(ss)] 0.45 l/kg), terminal elimination half-life (t(1/2) (β)) 4.08 h, and systemic clearance (Cl) 0.75 ml/min/kg; there were no important differences between parameters determined in plasma or in other organs (liver and gills). PX was rapidly formed in liver, showing saturable-kinetic properties in this organ, with V(max) 8.11 μg/g h and K(m) 12.58 μg/g. The terminal elimination linear process was similar between matrices, with a half-life (t(1/2 el)) 2.12 h, Vd(ss) 0.35 l/kg, and Cl 1.24 ml/min/kg. CA in tilapia was extensively metabolized to 1-methyl-uric acid and 1-methyl-xanthine in all of the organs studied. Metabolic and kinetic patterns were comparable with those reported for mammals. The observation of a concentration-dependent kinetic of PX is an important finding. Thus, toxicities of CA in fish would appear to be similar to those in mammals and should be considered in the risk assessments for this species, especially during the early stages of development.

Effects of the aqueous extract from Salvia miltiorrhiza Bunge on caffeine pharmacokinetics and liver microsomal CYP1A2 activity in humans and rats

Objectives

The effects of the aqueous extract of Salvia miltiorrhiza Bunge (Danshen) on metabolism/pharmacokinetics of caffeine and on liver microsomal CYP1A2 activity in humans and rats have been investigated.

Methods

The effects of Danshen aqueous extract on CYP1A2 activity were determined by metabolism of model substrates in the rat in vivo and in humans and rats in vitro. HPLC was used to determine model substrates and metabolites.

Key findings

In the rat, single dose Danshen aqueous extract treatment (100 or 200 mg/kg, i.p.) decreased metabolism of caffeine to paraxanthine, with overall decrease in caffeine clearance (6–20%), increase in area under the curve (AUC; 7–24%) and plasma half-life (t½ 14–16%). Fourteen-day Danshen aqueous extract treatment (100 mg/kg/day, i.p. or 200 mg/kg/day, p.o.) decreased caffeine clearance (16–26%), increased AUC (18–31%) and prolonged plasma t½ (8–10%). Aqueous extract of Danshen (125–2000 µg/ml) competitively inhibited human and rat liver microsomal CYP1A2 activity with inhibition constant (Ki) values at 190 and 360 µg/ml, respectively.

Conclusions

These studies demonstrated that Danshen aqueous extract affected the metabolism of CYP1A2 substrates through competitive inhibition and altered their clearance.