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The o-naphthoquinone derivative, CGS 8515 (I), is a potent inhibitor (IC50, 0.1 µM) of 5-lipoxygenase, but its therapeutic potential is compromised by a short plasma half-life (22 min) and extremely poor oral bioavailability (<2%). Poor biopharmaceutical properties of CGS 8515 were attributed to poor aqueous solubility and rapid in vivo hydrolysis of its methyl ester function to an inactive metabolite (IC50, 100 µM). An active amide analogue (II) was synthesized to prevent rapid hydrolysis. While analogue II appeared to be stable in vivo, its plasma half-life was also short (10 min), possibly because of rapid tissue distribution rather than metabolic elimination. Therefore, three potent analogues with increased aqueous solubilities were synthesized and compared with respect to their pharmacokinetic properties. The analogue with the highest aqueous solubility (V) demonstrated a plasma concentration vs time profile with the largest area under the curve (AUC) and the smallest distribution (a) phase of all the analogues studied. The percentage AUC of the terminal phase (ß) for three analogs paralleled their aqueous solubilities. The oral bioavailability of V was improved to 27%, compared to 2% for the parent compound, CGS 8515.

The optimal conditions for performing the caffeine CO2breath test (CBT) were investigated in smokers and nonsmokers. Caffeine labeled with13C or 14C in all three (1, 3, and 7) methyl groups or specifically in the 1-, 3-, or 7-methyl groups were orally administered to healthy adults and the expiration of labeled CO2was measured for 8 or 24 hr. The absolute rate of labeled CO2excretion from trilabeled caffeine was proportional to the dose up to 3 mg/kg in all subjects. In smokers, the rate of labeled CO2excretion averaged twice that in nonsmokers at all doses. A correlation was observed between the 2-hr cumulative CO2excretion from trilabeled caffeine and the apparent oral metabolic clearance rate (MCR) of caffeine (r = 0.90). Monolabeled CBTs in smokers and nonsmokers demonstrated that 80% ± 4% of labeled CO2expired in the breath during the first 2 hr of a trilabeled CBT was derived from the 3 position; at 6 to 8 hr equal amounts were derived from the 3 and 7 positions. Little N-demethylation was observed from the 1 position at any time during the 8-hr test. The results indicate that the 2-hr cumulative excretion of labeled CO2could be used to accurately predict the metabolic clearance rate of caffeine and is the best CBT parameter for detecting the effect of smoking on caffeine N-demethylation. The data suggest that the primary routes of caffeine metabolism are 3-N-demethylation and ring hydroxylation and confirm that caffeine metabolites are N-demethylated primarily in the 3 and 7 positions.Clinical Pharmacology and Therapeutics (1982) 32, 261–269; doi:10.1038/clpt.1982.157

The effects of low- and high-protein diets on theophylline kinetics and the time course of changes in 13C-labeled caffeine and aminopyrine CO2breath tests were examined in six young men. With a low-protein diet, mean theophylline clearance fell 21% (P < 0.04) and the t1/2rose from 8.0 to 10.6 hours (P < 0.02). With a high-protein diet, mean theophylline clearance rose 26% (P < 0.004) and the t1/2shortened to 7.4 hours (P < 0.03). Theophylline volume of distribution and protein binding did not change. Renal clearance of theophylline was lowered during the low-protein diet. Theophylline clearance correlated with caffeine breath test values during the low- (r = 0.73) and high- (r = 0.70) protein diets. Theophylline clearance correlated less well with the aminopyrine breath test values during the low- (r = 0.47) and high- (r = 0.55) protein diets. Thus dietary protein significantly influenced theophylline clearance, but the caffeine and aminopyrine breath tests showed a differential response to this important environmental factor.

Cytochrome P-450 mediated mixed function monooxygenases (P-450) are a group of enzymes which metabolize many substrates including steroids, environmental chemicals and drugs. P-450 in animals has been shown to be important in certain chemical induced birth defects, cancer, mutations and organ damage. Select P-450 isozymes can be induced by exposure to certain chemicals. We and others have shown that P markedly decreases maternal hepatic P-450 function. To further investigate the effect of P on P-450 we used an HPLC method (PNAS 77:6473 1980) to analyze tlhe profile of P-450 during P. Solubilized hepatic microsomes from non-pregnant female and pregnant C57BL/6 mice were compared. Comparison of elution profiles of P-450 from nonpregnant and pregnant mice show a marked increase during P in a specific peak (P-450-P) as shown. P-450-P did not co-chromatograph with the classical P-450 isozyme peaks induced by phenobarbital, 3 methylcholanthrene, or pregnenolone-16 ∝ carbonitrile. P-450-P is detectable by day 6 of gestation and remains elevated at least through post partum day 3. In summary, P induces in mice a new major P-450 isozyme peak, P-450-P, which does not co-chromatograph with the classical forms of P-450.

Maternal E consumption in P poses a known risk to the mother and fetus. The purpose of this study was to determine the effects of P on in vivo metabolism of E. The in vivo rate of E metabolism can be monitored by the EBT by measuring the rate of CO2derived from the metabolism of radiolabeled E (Toxicol Appl Pharmacol, 61:177, 1981). The EBT was conducted in 7 pregnant (Pg) and 5 nonpregnant (Npg) C57/B6J mice of similar ages. Day 0 was when vaginal plugs were found or when Npg mice were entered into the protocol. The EBT was conducted on days 6,8,10,14, and 16. [14C] E (5×105dpm) and unlabeled E (50 mg/kg) were administered i.p. The mice were immediately placed in air collection chambers, 14CO2was collected by bubbling exhaled air through an alcohol trapping solution and then a CO2trapping solution of ethanolamine methanol, and the rate of 14CO2exhaled was determined. The elimination rate constant (Kel) of labeled CO2was calculated and used as the measurement parameter of E clearance. The Kel did not change for Npg mice. In the Pg mice, the Kel did not differ from that of Npg mice on day 6 or 10 of gestation, but was increased on day 8 (Npg Kel=0.0592±0.002, Pg Day 8 Kel=0.0698±0.003; p<.001) and was decreased on days 14 and 16 (0.0525±0.002 and 0.0501±0.002, respectively; p<.001 vs. Npg). In summary, the rate of E metabolism in P changes biphasically. The rate of E metabolism as determined by the EBT increased significantly during organogenesis but decreased in late P.

Many xenobiotics and endogenous substrates are metabolized by P450, an enzyme system induced by certain substrates. We and others have shown that P decreases P450 in animals fed lab chow; however, little is known of how P alters the interaction of xenobiotics, diet, and P450. Pregnant (Pg) and nonpregnant (Npg) female C57BL/6J mice were maintained on lab chow and H2O ad lib before the study began. They were fed a diet containing 25% ethanol-derived calories (EDC). Controls were pair-fed a similar diet with 25% sucrose-derived calories (SDC). Day 6 of gestation was day 0 of the diet for Pg mice. The aminopyrine breath test (ABT) was done on diet days 0,2,4,8, and 10 by our previously described methods (Pediatr Res 17:150, 1983). The elimination rate constant was the ABT parameter used for comparison.The change from lab chow to SDC caused a general decrease in P450 and prevented the decrease in P450, which we have previously shown to occur in pregnancy. Exposure of Npg mice to ethanol increased P450 activity, which was not seen in the Pg animals.