An integrated PK-PD model for cortisol and the 17-hydroxyprogesterone and androstenedione biomarkers in children with congenital adrenal hyperplasia.

AIMS: The aim of this study was to characterize the pharmacokinetic/pharmacodynamic relationships of cortisol and the adrenal biomarkers 17-hydroxyprogesterone and androstenedione in children with congenital adrenal hyperplasia (CAH). METHODS: A nonlinear mixed-effect modelling approach was used to analyse cortisol, 17-hydroxyprogesterone and androstenedione concentrations obtained over 6 hours from children with CAH (n = 50). A circadian rhythm was evident and the model leveraged literature information on circadian rhythm in untreated children with CAH. Indirect response models were applied in which cortisol inhibited the production rate of all three compounds using an Imax model. RESULTS: Cortisol was characterized by a one-compartment model with apparent clearance and volume of distribution estimated at 22.9 L/h/70 kg and 41.1 L/70 kg, respectively. The IC50 values of cortisol concentrations for cortisol, 17-hydroxyprogesterone and androstenedione were estimated to be 1.36, 0.45 and 0.75 µg/dL, respectively. The inhibitory effect was found to be more potent on 17OHP than D4A, and the IC50 values were higher in salt-wasting subjects than simple virilizers. Production rates of cortisol, 17-hydroxyprogesterone and androstenedione were higher in simple-virilizer subjects. Half-lives of cortisol, 17-hydroxyprogesterone and androstenedione were 60, 47 and 77 minutes, respectively. CONCLUSION: Rapidly changing biomarker responses to cortisol concentrations highlight that single measurements provide volatile information about a child's disease control. Our model closely captured observed cortisol, 17-hydroxyprogesterone and androstenedione concentrations. It can be used to predict concentrations over 24 hours and allows many novel exposure metrics to be calculated, e.g., AUC, AUC-above-threshold, time-within-range, etc. Our long-range goal is to uncover dose-exposure-outcome relationships that clinicians can use in adjusting hydrocortisone dose and timing.

A comparison of duloxetine plasma levels in postbariatric surgery patients versus matched nonsurgical control subjects.

BACKGROUND: Bariatric surgery such as the Roux-en-Y gastric bypass (RYGB) is currently used as a treatment for severe obesity. Alteration of the gastrointestinal tract by this procedure suggests a potential for clinically significant alterations in the bioavailability of ingested medications including antidepressants. OBJECTIVES: The purpose of this trial was to determine to what extent the RYGB procedure alters the area under the plasma concentration/time curve (AUC(0-infinity)) of the antidepressant, duloxetine. METHODS: Ten subjects who were 1 year post-RYGB where compared with healthy control subjects matched for body mass index, age, and sex. Ultrarapid or poor metabolizers for cytochrome P450 2D6 were excluded from the study. Subjects received a single dose of 60 mg of duloxetine. Nineteen plasma samples were obtained during 72 hours to characterize the plasma level profile. RESULTS: The mean AUC(0-infinity) was significantly smaller for the postbariatric surgery (PBS) group (646.74 ng × h/mL [SD, 79.70; range, 539.57-791.62], P = 0.017) compared to the nonsurgical control group (1119.91 ng × h/mL [SD, 593.40; range, 415.5-2426.56]). The Tmax was also significantly shorter for the PBS group (2.2 hours) compared to the nonsurgical control group (6 hours; P = 0.005). No significant difference in Cmax or half-life was identified. CONCLUSIONS: To our knowledge, this is the first reported study exploring duloxetine pharmacokinetics PBS. This trial found that the bariatric surgery group was exposed to only 57.7% of duloxetine as compared to the nonsurgery group. This finding suggests that clinicians need to monitor patients closely after bariatric surgery and that further exploration of the effects of bariatric surgery on antidepressant pharmacokinetic parameters is warranted.

Phenanthrene metabolism in smokers: use of a two-step diagnostic plot approach to identify subjects with extensive metabolic activation.

Polycyclic aromatic hydrocarbons (PAHs) in cigarette smoke are among the most likely causes of lung cancer. PAHs require metabolic activation to initiate the carcinogenic process. Phenanthrene (Phe), a noncarcinogenic PAH, was used as a surrogate of benzo[α]pyrene and related PAHs to study the metabolic activation of PAHs in smokers. A dose of 10 µg of deuterated Phe ([D10]Phe) was administered to 25 healthy smokers in a crossover design, either as an oral solution or by smoking cigarettes containing [D10]Phe. Phe was deuterated to avoid interference from environmental Phe. Intensive blood and urine sampling was performed to quantitate the formation of deuterated r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene ([D10]PheT), a biomarker of the diol epoxide metabolic activation pathway. In both the oral and smoking arms approximately 6% of the dose was metabolically converted to diol epoxides, with a large intersubject variability in the formation of [D10]PheT observed. Two diagnostic plots were developed to identify subjects with large systemic exposure and significant lung contribution to metabolic activation. The combination of the two plots led to the identification of subjects with substantial local exposure. These subjects produced, in one single pass of [D10]Phe through the lung, a [D10]PheT exposure equivalent to the systemic exposure of a typical subject and may be an indicator of lung cancer susceptibility. Polymorphisms in PAH-metabolizing genes of the 25 subjects were also investigated. The integration of phenotyping and genotyping results indicated that GSTM1-null subjects produced approximately 2-fold more [D10]PheT than did GSTM1-positive subjects.

In vivo-formed versus preformed metabolite kinetics of trans-resveratrol-3-sulfate and trans-resveratrol-3-glucuronide.

Metabolites in safety testing have gained a lot of attention recently. Regulatory agencies have suggested that the kinetics of preformed and in vivo-formed metabolites are comparable. This subject has been a topic of debate. We have compared the kinetics of in vivo-formed with preformed metabolites. trans-3,5,4'-Trihydroxystilbene [trans-resveratrol (RES)] and its two major metabolites, resveratrol-3-sulfate (R3S) and resveratrol-3-glucuronide (R3G) were used as model substrates. The pharmacokinetics (PK) of R3S and R3G were characterized under two situations. First, the pharmacokinetics of R3S and R3G were characterized (in vivo-formed metabolite) after administration of RES. Then, synthetic R3S and R3G were administered (preformed metabolite) and their pharmacokinetics were characterized. PK models were developed to describe the data. A three-compartment model for RES, a two-compartment model for R3S (preformed), and an enterohepatic cycling model for R3G (preformed) was found to describe the data well. These three models were further combined to build a comprehensive PK model, which was used to perform simulations to predict in vivo-formed metabolite kinetics. Comparisons were made between in vivo-formed and preformed metabolite kinetics. Marked differences were observed in the kinetics of preformed and in vivo-formed metabolites.

Metabolism of [D10]phenanthrene to tetraols in smokers for potential lung cancer susceptibility assessment: comparison of oral and inhalation routes of administration.

Polycyclic aromatic hydrocarbons (PAHs) are believed to be among the causative agents for lung cancer in smokers. PAHs require metabolic activation for carcinogenicity. One pathway produces diol epoxides that react with DNA, causing mutations. Because diol epoxides are converted to tetraols, quantitation of tetraols can potentially be used to identify smokers who may be at higher risk for lung cancer. Our approach uses [D(10)]phenanthrene, a labeled version of phenanthrene, a noncarcinogenic PAH structurally analogous to carcinogenic PAH. Although smokers are exposed to PAH by inhalation, oral dosing would be more practical for phenotyping studies. Therefore, we investigated [D(10)]phenanthrene metabolism in smokers after administration by inhalation in cigarette smoke or orally. Sixteen smokers received 10 µg of [D(10)]phenanthrene in a cigarette or orally. Plasma and urine samples were analyzed for [D(10)]r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene ([D(10)]PheT), the major end product of the diol epoxide pathway, by gas chromatography-negative ion chemical ionization-tandem mass spectrometry. The ratios of [D(10)]PheT (oral dosing/inhalation) in 15 smokers were 1.03 ± 0.32 and 1.02 ± 0.35, based on plasma area under the concentration-time curve (0-∞) and total 48-h urinary excretion, respectively. Overall, there was no significant difference in the extent of [D(10)]PheT formation after the two different routes of exposure in smokers. A large interindividual variation in [D(10)]PheT formation was observed. These results demonstrate that the level of [D(10)]PheT in urine after oral dosing of [D(10)]phenanthrene can be used to assess individual capacity of PAH metabolism by the diol epoxide pathway.

Immediate consequences of cigarette smoking: rapid formation of polycyclic aromatic hydrocarbon diol epoxides.

Polycyclic aromatic hydrocarbons (PAH) are among the likely major causative agents for lung cancer in smokers. PAH require metabolic activation to exert their carcinogenic effects, and one important pathway proceeds through a three-step sequence resulting in the formation of diol epoxides, which react with DNA to produce adducts that can cause mutations and initiate the carcinogenic process. However, no previous published studies have examined this critical pathway in humans specifically exposed to PAH by inhalation of cigarette smoke. This study used a unique approach employing a stable isotope derivative of phenanthrene, the simplest PAH with a bay region, a feature closely associated with PAH carcinogenicity. Twelve subjects each smoked a cigarette to which [D(10)]phenanthrene had been added. Plasma was analyzed for [D(10)]r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene ([D(10)]PheT), the major end product of the diol epoxide metabolism pathway of phenanthrene. The analysis was performed by gas chromatography--negative ion chemical ionization--tandem mass spectrometry, using [(13)C(6)]PheT as internal standard. The results demonstrated that the three-step pathway resulting in the formation of diol epoxides, as monitored by [D(10)]PheT, occurred with remarkable rapidity. Levels of [D(10)]PheT in plasma of all subjects were maximal at the earliest time points examined, 15-30 min after smoking the cigarette containing [D(10)]phenanthrene, and decreased thereafter. These results demonstrate that the formation of a PAH diol epoxide occurs rapidly in smokers. Because PAH diol epoxides are mutagenic and carcinogenic, the results clearly demonstrate immediate negative health consequences of smoking, which should serve as a major warning to anyone contemplating initiating tobacco use.

Formation and distribution of NNK metabolites in an isolated perfused rat lung.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a lung-specific tobacco carcinogen. Metabolism is critical to its elimination given its lipophilic nature. Although NNK can be metabolized through detoxification pathways that safely eliminate it from the body, it can also be bioactivated, resulting in the formation of potentially carcinogenic DNA adducts. The isolated perfused rat lung (IPRL) system was used to determine the effect of NNK perfusate concentration (0.1 and 1.2 microM) on the formation and distribution of metabolites, the level of individual DNA adducts, and total covalent binding in the lung. Coadministration of the chemopreventive agent phenethyl isothiocyanate (PEITC; 20 microM) was also examined to determine its effect on NNK metabolism. NNK was readily metabolized in the IPRL system. In the 0.1 muM perfusions approximately 55% of metabolites formed were through detoxification pathways, whereas roughly 30% were the result of bioactivation pathways. An increase in NNK concentration increased the percentage of unmetabolized NNK and decreased the apparent metabolic clearance in the lung, but the metabolite profiles remained similar between concentrations. The addition of PEITC reduced the formation of oxidative metabolites and increased 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) formation and the percentage of unmetabolized NNK. PEITC also significantly decreased the formation of DNA adducts in the lung tissue. The level of O(2)-[4-(3-pyridyl)-4-oxobut-1-yl]thymidine (O(2)-POB-dThd) and O(6)-[4-(3-pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O(6)-POB-dGuo) decreased by 70 to 75%, and that of O(6)-methylguanine (O(6)-methyl-Gua) and 7-[4-(3-pyridyl)-4-oxobut-1-yl]guanine (7-POB-Gua) decreased by 40 to 45%. Pyridylhydroxybutyl-DNA adducts were not detected in any of the treatment groups. Thus, the IPRL system is useful in determining pulmonary metabolism and DNA adduct formation separate from other metabolizing organs.

Transepithelial transport of the group II metabotropic glutamate 2/3 receptor agonist (1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate (LY354740) and its prodrug (1S,2S,5R,6S)-2-[(2'S)-(2'-amino)propionyl]aminobicyclo[3.1.0]hexane-2,6-dicarboxylate (LY544344).

The limited oral bioavailability of the potent and selective group II metabotropic glutamate (mGlu) 2/3 receptor agonist, (1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate (LY354740), was shown to be improved by its peptidyl prodrug, (1S,2S,5R,6S)-2-[(2'S)-(2'-amino)propionyl]aminobicyclo[3.1.0]hexane-2,6-dicarboxylate (LY544344). The purpose of this study was to elucidate the mechanisms of intestinal absorption of LY354740 and its prodrug LY544344. Transepithelial transport and accumulation studies were performed in Caco-2 cell monolayers; the involvement of the peptide transporter 1 (PEPT1) transporter was also examined. In absorptive transport studies, the peptidyl prodrug LY544344 partially hydrolyzed to release LY354740 intracellularly, and both compounds appeared in the basolateral compartment. The absorptive transport rate of LY544344, basolateral appearance rate of LY354740, and their cellular accumulation after incubation with LY544344 were concentration-dependent. PEPT1 inhibition reduced transepithelial transport and cellular accumulation of LY544344 to 22 and 1.1% of control, respectively. LY354740 showed concentration-independent absorptive transport with negligible cellular accumulation. Efflux and trans-stimulation studies revealed predominantly apical efflux and the existence of specific transporters for LY544344 and intracellularly released LY354740 on the apical and basolateral membranes. LY544344 efflux was also trans-stimulated at the apical side by glycyl-glutamate but not by glycyl-sarcosine. Transport of neither compound was affected by P-glycoprotein-mediated efflux, as shown in transport and uptake inhibition studies in Madin-Darby canine kidney multidrug resistance 1-transfected cell line and inverted membrane vesicles. In conclusion, LY354740 is mainly transported by the paracellular pathway, whereas intestinal absorption of LY544344 is mediated by PEPT1. However, the absorptive transport of LY544344 seems to be modulated by an apical efflux transporter and a rate-limiting transport step across the basolateral membrane.

Quantitation of metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone after cessation of smokeless tobacco use.

Two major metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were previously shown to be highly persistent in human urine after cessation of cigarette smoking. We hypothesized that NNK or its metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), was sequestered in the lung. In this study, we further evaluated this hypothesis by quantifying the NNK metabolites, NNAL and its glucuronides (NNAL-Gluc), in urine and plasma after cessation of smokeless tobacco use, in which NNK is administered p.o. rather than by inhalation. Thirteen male nonsmokers, 11 snuff dippers and 2 tobacco chewers, participated in the study. Urine and plasma were obtained at baseline and at intervals 2-126 days after cessation of smokeless tobacco use. The distribution half-lives t(1/2alpha) (days) of NNAL (1.32 +/- 0.85 versus 3.35 +/- 1.86) and NNAL-Gluc (1.53 +/- 1.22 versus 3.89 +/- 2.43) were significantly shorter in smokeless tobacco users than in smokers. There were no significant differences in the terminal half-lives t(1/2beta) (days) of NNAL (26.3 +/- 16.7 versus 45.2 +/- 26.9) and NNAL-Gluc (26.1 +/- 15.1 versus 39.6 +/- 26.0) in smokeless tobacco users and smokers. Baseline levels as well as renal clearance of the NNK metabolites correlated with number of tins or pouches of smokeless tobacco consumed. Ratios of (S)-NNAL:(R)-NNAL and (S)-NNAL-Gluc:(R)-NNAL-Gluc in urine were significantly (3.1-5.7 times) higher 7 days after cessation than at baseline in both smokeless tobacco users and smokers, indicating stereoselective retention of (S)-NNAL. Collectively, the results of this study suggest that there is a receptor in the human body, possibly in the lung, for (S)-NNAL, the more carcinogenic NNAL enantiomer. These data may have considerable implications for understanding mechanisms of tumor induction by NNK.

CK2 targeted RNAi therapeutic delivered via malignant cell-directed tenfibgen nanocapsule: dose and molecular mechanisms of response in xenograft prostate tumors.

CK2, a protein serine/threonine kinase, promotes cell proliferation and suppresses cell death. This essential-for-survival signal demonstrates elevated expression and activity in all cancers examined, and is considered an attractive target for cancer therapy. Here, we present data on the efficacy of a tenfibgen (TBG) coated nanocapsule which delivers its cargo of siRNA (siCK2) or single stranded RNA/DNA oligomers (RNAi-CK2) simultaneously targeting CK2α and α' catalytic subunits. Intravenous administration of TBG-siCK2 or TBG-RNAi-CK2 resulted in significant xenograft tumor reduction at low doses in PC3-LN4 and 22Rv1 models of prostate cancer. Malignant cell uptake and specificity in vivo was verified by FACS analysis and immunofluorescent detection of nanocapsules and PCR detection of released oligomers. Dose response was concordant with CK2αα' RNA transcript levels and the tumors demonstrated changes in CK2 protein and in markers of proliferation and cell death. Therapeutic response corresponded to expression levels for argonaute and GW proteins, which function in oligomer processing and translational repression. No toxicity was detected in non-tumor tissues or by serum chemistry. Tumor specific delivery of anti-CK2 RNAi via the TBG nanoencapsulation technology warrants further consideration of translational potential.

Comparison of cortisol exposures and pharmacodynamic adrenal steroid responses to hydrocortisone suspension vs. commercial tablets.

The Endocrine Society Clinical Practice Guidelines on congenital adrenal hyperplasia (CAH) recommend against using hydrocortisone suspension based on a study that examined a commercial suspension. Our objective was to examine the absorption of an extemporaneously prepared hydrocortisone suspension and compare it to tablets. Secondary objectives were to evaluate the 17-hydroxyprogesterone and androstenedione adrenal steroid responses. Using a parallel design, 34 children diagnosed with CAH received either suspension (n = 9; median age 1.8 years) or tablets (n = 25; median age 7.5 years). Patients were given their usual morning hydrocortisone formulation and dose; 12 serial blood samples were obtained and the area under the curve (AUC) was calculated. The mg/m(2) dose-normalized cortisol AUCs were no different in the suspension and tablet groups (P = ·06), nor was there a significant difference in the C(max) or T(max) (P = .08 and P = .41, respectively). Although there were no differences in the 17-hydroxyprogesterone change-from-baseline AUCs, baseline concentrations, or the nadir concentrations when comparing suspension and tablet formulations, the androstenedione values were significantly lower as expected in the younger aged suspension group. Our results offer compelling evidence that an extemporaneously prepared hydrocortisone suspension provides comparable cortisol exposures to commercially available tablet formulations in children and can be used to safely and effectively treat CAH.

Interrelationships among cortisol, 17-hydroxyprogesterone, and androstenendione exposures in the management of children with congenital adrenal hyperplasia.

UNLABELLED: Hydrocortisone is the standard replacement therapy for children with congenital adrenal hyperplasia (CAH). Relationships between cortisol exposures and pharmacodynamic responses of 17-hydroxyprogesterone and androstenedione exposures have not been systematically evaluated. OBJECTIVES: (1) Assess individual oral hydrocortisone pharmacokinetics; (2) relate the observed cortisol exposure in each subject to the observed exposures of 17-hydroxyprogesterone and androstenedione; (3) determine potential individualized treatment regimens based on each subject's pharmacokinetic and pharmacodynamic parameters. METHODS: Thirty-four patients (18 boys, 16 girls, aged 1.4 to 18.1 years) with CAH underwent 6-hour pharmacokinetic studies. Results were analyzed by noncompartmental methods to obtain the area under the curve (AUC) for cortisol, 17-hydroxyprogesterone, and androstenedione; maximum concentration and time-to-maximum concentration for cortisol; and minimum and time-to-minimum concentration for 17-hydroxyprogesterone and androstenedione. RESULTS: Mean (SD) cortisol half-life and Cmax were 1.01 (0.20) hours and 24.4 (5.4) µg/dL, respectively. The AUCs for cortisol, 17-hydroxyprogesterone and androstenedione were 40.8 (14.5) µg hour/dL, 29,490 (23,539) ng hour/dL, and 680 (795) ng hour/dL, respectively. No significant relationships existed between cortisol AUCs and the AUCs of either 17-hydroxyprogesterone (P=0.32) or androstenedione (P=0.99); nor were there differences between the change-from-baseline concentrations for cortisol with either 17-hydroxyprogesterone (P=0.80) or androstenedione (P=0.40). Cortisol simulations indicated that although four daily doses decreased 24-hour hypercortisolemia and hypocortisolemia, substantial periods of each remained. CONCLUSIONS: Concentration profiles of cortisol, 17-hydroxyprogesterone, and androstenedione are highly variable in children with CAH, and knowledge of them can assist in personalizing the therapy of CAH patients. Hydrocortisone's rapid half-life and the lack of a sustained-released product make it difficult to closely approximate normal circadian profiles.

Preliminary comparison of sertraline levels in postbariatric surgery patients versus matched nonsurgical cohort.

BACKGROUND: Roux-en-Y gastric bypass (RYGB) is the most frequent bariatric procedure performed in the United States, with thousands performed. Because of the changes to the gastrointestinal tract, the potential exists for clinically significant alterations in the absorption/bioavailability of ingested medications. The purpose of the present pilot trial was to determine to what extent RYGB alters the area under the plasma concentration/time curve (AUC(0-10.5)) of the antidepressant, sertraline at a community research center. METHODS: After an overnight fast, 5 postbariatric surgery and 5 nonsurgical control subjects matched for body mass index, age, and gender received 100 mg of sertraline. Plasma samples were obtained for 10.5 hours. The mean AUC(0-10.5), maximal plasma concentration, and the interval to the peak plasma level were obtained for both groups. RESULTS: The mean AUC(0-10.5) was significantly smaller for the postbariatric surgery group (124.4 ± 55.5 ng-hr/mL, range 62.0-198.1; P = .043) compared with the nonsurgical control group (314.8 ± 129.6 ng-hr/mL, range 194.8-508.7). The maximal plasma concentration was also significantly smaller for the postbariatric surgery group than for the nonsurgical control group (P = .043). CONCLUSION: To our knowledge, this is the first reported study exploring antidepressant pharmacokinetics after bariatric surgery. In the present trial, the AUC(0-10.5) and maximal plasma concentration were significantly smaller in the subjects who had undergone RYGB than in the matched subjects who had not. Additional investigation of the effects of bariatric surgery (RYGB, sleeve gastrectomy, and gastric banding) on the antidepressant pharmacokinetic parameters is warranted.

The intestinal absorption of a prodrug of the mGlu2/3 receptor agonist LY354740 is mediated by PEPT1: in situ rat intestinal perfusion studies.

LY354740 is a potent mGlu2/3 agonist with a limited oral bioavailability. Its alanyl prodrug, LY544344, showed high affinity to the intestinal peptide transporter PEPT1, and improved the oral bioavailability of LY354740 in various animal models. The aim of the present study was to investigate the mechanism of in vivo absorption of the dipeptidic prodrug LY544344. The permeabilities of LY544344 and LY354740 were examined in the rat in situ single-pass intestinal perfusion model. The intestinal absorptive flux of LY354740 was shown to be very low in comparison with LY544344. The absorptive flux of LY544344 could best be described by a Michaelis-Menten process in parallel with a linear process. The estimated parameters were: J(max) = 26.7 x 10(-5) micromol/(cm(2)-s), K(m) = 2.6 mM. The absorptive permeability of LY544344 was reduced to approximately 5% of control in the presence of excess Gly-Sar, a known PEPT1 substrate. Intracellular accumulation of LY354740 and LY544344, estimated postperfusion, showed high levels of LY354740 over LY544344 at all perfusate concentrations studied. However, there was a decline in the intracellular ratio of LY354740 to LY544344 at higher concentrations, suggesting that the metabolic activation to release LY354740 is saturable.

Intestinal metabolism: the role of enzyme localization in phenol metabolite kinetics.

The influence of enzyme localization and blood flow on intestinal elimination was evaluated in rats. Phenol was administered vascularly (approximately 1400 and 2500 microg) and luminally (intrajejunal bolus doses of approximately 100 and 1000 microg) to the recirculating in situ perfused intestine. The portal effluent and the reservoir were sampled. The intestinal extraction ratios for phenol at the low and high vascular doses were (mean +/- S.D., n = 3) 0.09 +/- 0.02 and 0.11 +/- 0.01, respectively. The perfusion flow rate was also varied from 5 to 12 ml/min at a vascular dose of approximately 2500 microg of phenol. The organ clearance at the lowest flow rate significantly exceeded those at the higher flow rates. The presence of a diffusional barrier at the mucosa-serosa interface was suggested. The calculated mean diffusional clearance of phenol was 1.11 ml/min. Sulfation was the predominant metabolic pathway after vascular administration of phenol. After luminal dosing, the intestinal intrinsic clearances of phenol at the low and high doses were 7.29 +/- 1.39 (n = 4) and 3.55 +/- 1.16 ml/min (n = 3), respectively, indicating saturation at the higher dose. Moreover, there was a decrease in the area under the curve ratio (metabolite/phenol) at the high luminal dose. Luminal administration, in general, produced greater glucuronidation. These data and STELLA simulations suggest that enzyme localization at both the cellular and tissue levels has a significant influence on intestinal metabolism.

Metabolism and pharmacokinetics of N'-nitrosonornicotine in the patas monkey.

N'-Nitrosonornicotine (NNN) is present in significant quantities in tobacco and tobacco smoke and is believed to play an important role as a cause of cancer in people who use tobacco products. Biomarkers of NNN uptake in humans such as urinary metabolites would be useful for assessing cancer risk. Previous studies, carried out almost exclusively in rodents, have characterized urinary metabolites of NNN, but none of these would be suitable as a biomarkers of NNN uptake in humans. Therefore, we studied NNN metabolism in the patas monkey. Monkeys were treated intravenously with [5-(3)H]NNN, which has tritium in the pyridine ring. Blood and urine samples were collected at timed intervals. Six urinary metabolites were observed by high-performance liquid chromatography (HPLC) and were identified by their spectral properties and/or comparison to appropriate standards as follows: metabolite (% of radioactivity eluting from HPLC +/- S.D., n = 3 monkeys); 4-hydroxy-4-(3-pyridyl)butyric acid (43.8 +/- 4.0); 4-oxo-4-(3-pyridyl) butyric acid (2.7 +/- 0.66); norcotinine (13.1 +/- 2.7); norcotinine-1N-oxide (16.5 +/- 1.3); 3'-hydroxynorcotinine (16.9 +/- 2.0); 3'-(O-beta-D-glucopyranuronosyl)hydroxynorcotinine (5.4 +/- 1.0); and unchanged NNN (0.63 +/- 0.15). The two major metabolites in serum were 4-hydroxy-4-(3-pyridyl)butyric acid and norcotinine. NNN was rapidly metabolized to 4-hydroxy-4-(3-pyridyl)butyric acid, whereas the formation of norcotinine and 3'-hydroxynorcotinine were somewhat delayed. The results of this study demonstrate substantial differences between NNN metabolism in the rodent and patas monkey. Metabolism of NNN to norcotinine and its derivatives was far more prevalent in the patas monkey than in the rat. 3'-Hydroxynorcotinine and its O-glucuronide may be formed from NNN via alpha-oximinonornicotine or isomyosmine. There was no evidence that it was formed via norcotinine, although this pathway could not be excluded. 3'-Hydroxynorcotinine could potentially be a biomarker of NNN uptake in humans.

Pharmacokinetics of amino acid phosphoramidate monoesters of zidovudine in rats.

In vitro studies have demonstrated that water-soluble, nontoxic phosphoramidates of azidothymidine (zidovudine [AZT]) have significant and specific anti-human immunodeficiency virus and anticancer activity. Although polar, these compounds are internalized and processed to the corresponding nucleoside monophosphates. Eight methyl amide and methyl ester phosphoramidate monoesters composed of D- or L-phenylalanine or tryptophan and AZT were synthesized. The plasma stability and protein binding studies were carried out in vitro. Then in vivo pharmacokinetic evaluations of six of the compounds were conducted. Sprague-Dawley rats received each compound by intravenous bolus dose, and serial blood and urine samples were collected. AZT and phosphoramidate concentrations in plasma and urine were quantitated by high-performance liquid chromatography with UV or fluorescence detection. Pharmacokinetic parameters were calculated by standard noncompartmental means. The plasma half-lives of the phosphoramidates were 10- to 20-fold longer than the half-life of AZT. Although the renal clearances of the phosphoramidates were similar to AZT, their total body clearances were significantly greater than that of AZT. The 3- to 15-fold-larger volume of distribution (Vss) for the phosphoramidates relative to AZT appeared to be dependent on the stereochemistry of the amino acid, with the largest values being associated with the L-amino acids. The increased Vss indicates a much greater tissue distribution of the phosphoramidate prodrugs than of AZT. Amino acid phosphoramidate monoesters of AZT have improved pharmacokinetic properties over AZT and significant potential as in vivo pronucleotides.

Disposition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in bile duct-cannulated rats: stereoselective metabolism and tissue distribution.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a chiral compound, and the primary metabolite of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a major carcinogen in tobacco smoke. The goal of the present work was to study the pharmacokinetics and stereoselective metabolism and tissue retention of NNK and NNAL in the rat. Groups of rats were dosed with [5-(3)H]NNK (n = 3) or racemic [5-(3)H]NNAL (n = 3) at a target dose of 8.45 micromol/kg and were killed at selected time points for tissue collection. Separate groups of rats (n =5 per group) received the same dose of either NNK or NNAL and serial sampling of blood, bile and urine was carried out over 24 h. All samples were analyzed by C(18) reversed-phase HPLC with gradient elution and radioflow detection. A gas chromatograph-thermal energy analyzer (GC-TEA) was used to separate the (R)-/(S)-NNAL enantiomers. Racemic NNAL and NNK had large volumes of distribution (321 +/- 137 ml for NNK and 2772 +/- 1423 ml for NNAL) and similar total body clearances (12.8 +/- 2.0 ml/min for NNK and 8.6 +/- 2.6 ml/min for NNAL). The results indicated that the enantiomers of NNAL are stereoselectively metabolized and excreted. The glucuronide of (R)-NNAL, ((R)-NNAL-Gluc) was identified as the major metabolite in the bile after administration of either NNK or NNAL. (R)-NNAL was the major NNAL enantiomer in the bile or urine samples. At 24 h after racemic NNAL administration, NNAL comprised an average of 75.4% of total radioactivity in the lung with an (S)-/(R)-ratio of >20. The stereoselective localization of (S)-NNAL to lung tissue may contribute to the lung selectivity of NNK carcinogenesis. The present studies suggest a need to look beyond metabolic activation as the sole mechanism for lung carcinogenesis.

Stereoselective metabolism and tissue retention in rats of the individual enantiomers of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), metabolites of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is reduced to its main metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in a reaction that is both stereoselective and reversible. (S)-NNAL has been shown to be equivalent to NNK in carcinogenic potency, and significantly more potent than (R)-NNAL. It was hypothesized that stereoselective differences in metabolism or tissue distribution contributed to the difference in carcinogenicity between the enantiomers. The individual NNAL enantiomers were therefore administered to bile duct-cannulated rats. Male Fisher F344 rats received i.v. doses of either (R)-NNAL (n = 10) or (S)-NNAL (n = 9) and bile, urine, blood and tissue samples were collected over 24 h. (R)/(S)-NNAL and metabolites were quantified by HPLC and radioflow detection. NNAL was also collected from the HPLC and silylated, and the two NNAL enantiomers were separated by chiral GC-TEA. (S)-NNAL had a much larger tissue distribution (Vss = 1792 +/- 570 ml) than did (R)-NNAL (Vss = 645 +/- 230 ml). Overall, (R)-NNAL tended to enter detoxification pathways, particularly glucuronidation, while reversible metabolism of (S)-NNAL to NNK was favored. For example, after (R)-NNAL administration, approximately 50% of the dose was excreted as (R)-NNAL-Gluc in bile and urine, and <5% was excreted as NNK or NNK metabolites. In contrast, only 10% of an (S)-NNAL dose was excreted as a glucuronide, while almost 20% of the (S)-NNAL dose was excreted as NNK or NNK metabolites. In tissues, particularly the lung, (S)-NNAL appeared to be stereoselectively retained. These findings suggest that the difference in carcinogenicity between the NNAL enantiomers may be attributed to stereoselective differences in tissue distribution and excretion.

Disposition and oral bioavailability in rats of an antiviral and antitumor amino acid phosphoramidate prodrug of AZT-monophosphate.

PURPOSE: The purpose of this study was to characterize the in vivo disposition of 3'-azido-2'-deoxythymidine-5'-methylamino-L-tryptophanylphosphoramidate (NMe-Trp-AZT), a potential pronucleotide of 3'-azido-2'-deoxythymidine monophosphate (AZT-MP). METHODS: The in vitro metabolic stability of NMe-Trp-AZT was evaluated in a wide variety of tissue homogenates. NMe-Trp-AZT was administered orally (n = 3) to female Sprague-Dawley rats. Its biliary excretion and intestinal permeability were also studied. RESULTS: Renal excretion of unchanged prodrug (16.4 +/- 5.6% of the total dose administered intravenously), its conversion to AZT (12.1 +/- 5.4% of total dose administered intravenously), and its biliary excretion (54.3 +/- 4.9% of the total dose up to 4 h after intravenous administration) accounted for most of the elimination of NMe-Trp-AZT. Significant amounts of AZT were found in both plasma and urine after oral administration of the prodrug. The prodrug itself was not permeable through the small intestinal wall but was slowly converted to AZT-MP in gastric fluids at low pH. CONCLUSIONS: The NMe-Trp-AZT prodrug itself was not orally bioavailable because of poor intestinal permeability; however, AZT was readily available in the systemic circulation after the oral administration of the prodrug. Modification of the phosphoramidate to promote intestinal uptake should lead to enhanced oral bioavailability of this and other nucleoside phosphoramidate monoesters.