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The metabolism and disposition of U-14C-erythritol was examined in four groups of three male and three female, nonfasted rats each. The rats of groups A and D were germfree; the rats of groups B and C were kept under conventional conditions. The rats of group B received an erythritol-supplemented diet for 3 weeks prior to the experiment (adapted rats). The rats of groups A, C, and D were kept on an ordinary diet which was sterile for groups A and D (not adapted rats). On the day of the experiment, each rat was dosed with U-14C-erythritol by gavage (5 μCi/kg body wt; sp act 50 (μCi/g erythritol). The radiochemical purity of the erythritol was 96.43% for groups A-C. Group D, which was attached to the study after evaluation of the results of groups A-C, received a more purified erythritol with a radiochemical purity of 99.46% because the data of group A pointed to a possible interference by a 14C-labeled impurity in the commercial 14C-erythritol. After dosing, respiratory CO2 and urine were collected from each rat at regular intervals for 24 hr. At termination, feces were also collected. The animals were killed and intestinal contents, organs, tissues, and the remaining carcass processed for determination of 14C. 14C was excreted rapidly in the urine of all groups (range of groups A-D: 47.3-60.6% of the administered dose within the first 4 hr). Total 24-hr urinary excretion varied between 67.0% (group B) and 81.4% (group D). HPLC analysis of the urine showed that more than 96% of the eluted radiolabel represented erythritol. Conventional, adapted rats expired more 14CO2 than conventional, unadapted rats [10.9% (B) vs 6.7% (C)]. Germfree rats expired much less 14CO2 [0.8% (A) and 0.3% (D)]. In germfree rats, 14CO2 expiration started shortly after dosing, reaching half of the 24-hr excretion after about 2.5 hr. In conventional rats 14CO2 expiration started with a delay of about 2 hr reaching half the 24-hr excretion after 4-6 hr. The excretion of 14C with feces was similar in all groups (8.3% on average of all rats). Slightly more 14C was retained in the intestinal contents of germfree than conventional rats (1.9 vs 0.5%). The body retention was higher in conventional than in germfree rats (3.4 vs 2.0%). In group D, body retention was lowest (1.6%). The total recovery of 14C was similar in all groups (95.6%, average of all rats). It is concluded that ingested erythritol is efficiently absorbed mainly from the small intestine, is not metabolized to a relevant extent in the body, and is excreted unchanged in the urine. The fraction of erythritol not absorbed is fermented by the gut microflora to intermediate products which are largely absorbed and metabolized. The data support a proposed physiological energy value for erythritol of about 0.5 kcal/g. © 1996 Academic Press, Inc.

In contrast to primary hepatocytes, estimating carrier-mediated hepatic disposition by using a panel of single transfected cell-lines provides direct information on the contribution of the individual transporters to the net disposition. The most direct way to correct for differences in transporter abundance between cell-lines and tissue is by using absolute protein quantification. In the present study, the performance of this strategy to predict human hepatic uptake transport was investigated and compared with traditional scaling from primary human hepatocytes. Rosuvastatin was used as a model compound. The uptake activity was measured in HEK293 cell-lines stably overexpressing OATP1B1⁄1a, OATP1B3 or OATP2B1, the major transporters involved in human hepatic uptake of rosuvastatin, or expressing OATP1B1⁄15, associated with reduced hepatic uptake of rosuvastatin. The abundance of these transporter proteins in the outer membranes of HEK293-cells, in human primary hepatocytes and in human liver tissue was determined by LC–MS/MS. The measured activity, corrected for protein abundance and scaled to the whole liver, gave a very accurate prediction of the hepatic intrinsic clearance observed in vivo. Embedded in a PBPK model describing the hepatic disposition and enterohepatic circulation, the collec- tive in vitro data resulted in a good explanation of the observed oral and intravenous pharmacokinetic profiles of rosuvastatin. The model allowed simulation of the effect of polymorphic variants of OATP1B1 on rosuvastatin pharmacokinetics. These results encourage a larger scale validation. This approach may facilitate prediction of drug–drug interactions, scaling of transporter processes across subpopulations (children, diseased patients), and may be extended to tissues for which primary cells may be more difficult to obtain. Chemicals/CAS: rosuvastatin, 147098-18-8, 147098-20-2 Manufacturers: Moravek, United States

The absorption, disposition, metabolism, and excretion of 14C-labeled γ-cyclodextrin ([14C]γ-CD) was examined in four separate experiments with Wistar rats. In experiment 1, [14C]γ-CD (25 μCi, 600 mg/kg body wt) was administered intravenously to four male and four female conventional rats. In experiment 2, [14C]γ- CD (25 μCi, 1000 mg/kg body wt) was given by gavage to four male and four female germ-free rats. In experiments 3 and 4, [14C]γ-CD (25 and 100 μCi, respectively, 1000 mg/kg body wt) was given to four male and four female conventional rats by gavage. In all experiments, 14C was measured in respiratory CO2, urine, feces contents of the gastrointestinal tract, blood, main organs, and residual carcass. The chemical identity of the 14C-labeled compounds was examined by HPLC in urine (experiments 1-4), blood (experiments 1 and 4), and samples of intestinal contents (experiments 3 and 4). Recovered 14C was expressed as a percentage of the administered dose. Total recovery of 14C varied between about 90% (experiments 3 and 4) and 100% (experiments 1 and 2). Experiment 1 showed that about 90% of intravenously administered γ-CD is excreted in urine within 24 h. During the first 2 h after dosing, plasma 14C levels decreased rapidly (t( 1/4 ), 15-20 min). The remaining 10% of the dose was probably excreted into the gastrointestinal tract with bile and saliva. In addition, some [14C]γ-CD may have been degraded by plasma and tissue amylases. Since glucose is the common product of systemic hydrolysis and intestinal digestion, it is not possible to quantitate the relative flux of [14C]γ-CD through these two pathways. Upon oral administration of [14C]γ-CD to germ-free rats (experiment 2), about 66% of the label was expired as CO2 within 24 h. The rate of 14C exhalation reached a maximum at 90 min after dosing and then declined steadily. In the urine, and in the contents of the cecum and colon collected at 24 h, [14C]γ-CD was not found (except for a trace in the cecum of females). In conventional rats (experiments 3 and 4), a similar, fast appearance of respiratory 14CO2, was observed. There was no delayed formation of 14CO2 due to incomplete digestion and subsequent microbial fermentation in the cecum and colon. In pooled urine collected at 4 h after dosing, a small amount of unchanged [14C]γ-CD was detected (experiment 4). From this result, it was estimated that less than 0.02% of ingested intact γ-CD was absorbed and excreted with the urine. It is concluded from the data that ingested [14C]γ-CD is rapidly and essentially completely digested in the small intestine to absorbable [14C]glucose. The absorption of intact [14C]γ-CD by passive diffusion is very low (<0.02%). Therefore, the metabolism of γ-CD resembles closely that of starch or linear dextrins.