Ferulic acid (FA) and p-coumaric acid (CA) are absorbed by the monocarboxylic acid transporter (MCT) in Caco-2 cells, although gallic acid (GA) is not. Therefore, the MCT is selective for certain phenolic acids. Absorption of orally administered CA and GA in rats was studied to obtain serum pharmacokinetic profiles and to investigate their intestinal absorption characteristics in vivo. Rats were administered 100 micromol/kg body weight of CA and GA, and blood was collected from the portal vein and abdominal artery after administration. CA, GA, and their metabolites were quantified with a highly selective and sensitive coulometric detection method using high-performance liquid chromatography-electrochemical detection. Ingested CA was rapidly absorbed in the gastrointestinal tract in an intact form. The serum concentration of intact CA in the portal vein peaked 10 min after dosing (C(max) was 165.7 micromol/L). In contrast, GA was slowly absorbed, with a t(max) for intact GA of 60 min and a C(max) of 0.71 micromol/L. The area under the curve for intact CA and GA was calculated from the serum concentration profile in the portal vein to be 2991.3 and 42.6 micromol min L(-)(1), respectively. The relative bioavailability of CA against GA was about 70. This is the first demonstration that absorption efficiency of CA is much higher than that of GA in vivo. The absorption characteristics of CA are clearly different from those of GA. These findings are in good agreement with the results obtained in vitro using a Caco-2 cell system.

p-Coumaric and ferulic acid are actively taken up by monocarboxylic acid transporter (MCT), whereas gallic acid, caffeic acid (CA), and rosmarinic acid (RA) are absorbed by paracellular diffusion in human intestinal Caco-2 cells, although CA has low affinity for MCT. We previously demonstrated that p-coumaric acid has a much higher absorption efficiency than gallic acid in rats, owing to the MCT-mediated absorption of p-coumaric acid in vivo (J. Agric. Food Chem. 2004, 52, 2527−2532). Here, absorption of orally administered CA and RA in rats has been studied to investigate their intestinal absorption characteristics and pharmacokinetics in vivo and to compare the results with those of p-coumaric and gallic acids obtained under identical conditions. Rats were given 100 μmol/kg body weight of CA and RA, and blood was collected from the portal vein and abdominal artery after administration. CA, RA, and their metabolites were quantified by a coulometric detection method using HPLC−ECD. The serum concentration of intact CA and RA in the portal vein peaked at 10 min after administration, with a C max of 11.24 μmol/L for CA and 1.36 μmol/L for RA. The area under the curve (AUC) for intact CA and RA in the portal vein was calculated from the serum concentration−time profile to be 585.0 and 60.4 μmol min L-1, respectively. The absorption efficiency of CA was about 9.7-fold higher than that of RA. Overall, the absorption efficiency of these compounds in vivo increases in the order:  gallic acid = RA < CA < p-coumaric acid, which is in good agreement with results obtained in Caco-2 cells in vitro. Keywords: Caffeic acid; rosmarinic acid; monocarboxylic acid transporter; intestinal absorption; rats

Artepillin C (AC), an active ingredient of Brazilian propolis, permeates intact across Caco-2 cells by transcellular passive diffusion. The permeation of AC across Caco-2 cells is as efficient as that of phenolic acids and the microbial metabolites of poorly absorbed polyphenols, which are actively absorbed by the monocarboxylic acid transporter (MCT) (Biochim. Biophys. Acta 2005, 1713, 138-144). Here, the absorption of orally administered AC in rats has been studied to evaluate its pharmacokinetics and bioavailability in vivo in comparison with those of p-coumaric acid (CA), a substrate of MCT. Rats were given 100 micromol/kg of body weight of AC or CA, and blood was subsequently collected from the portal vein and abdominal artery. AC, CA, and their metabolites were quantified by coulometric detection using HPLC-ECD. The serum concentration of intact AC and CA in the portal vein peaked at 5-10 min after administration, with a C(max) of 19.7 micromol/L for AC and 74.8 micromol/L for CA. The area under the curve (AUC) for intact AC and CA in the portal vein was calculated from the serum concentration as 182.6 and 3057.3 micromol.min.L(-1), respectively. The absorption efficiency of CA was about 17-fold higher than that of AC. Furthermore, the bioavailability of CA was about 278-fold higher than that of AC, and the ratio of AUC in the abdominal artery to AUC in the portal vein was 0.04 and 0.70, for AC and CA, respectively. Thus, AC is likely to be more susceptible to hepatic elimination than is CA. The bioactive compound of AC in vivo should be investigated further.

To achieve quality control of therapeutic proteins, it is important to compare their biological potency with their clinical effects.1) Therefore, an animal-based assay is preferred for measuring their bioactivity. However, the use of laboratory animals poses ethical concerns, is time consuming and requires skilled staff and sophisticated experimental facilities. Furthermore, in vivo bioassays have low precision and accuracy, and hence, there is a need for an alternative assay method to estimate in vivo bioactivity.To date, attempts have been made to replace traditional bioassays with physicochemical techniques for potency determination of insulin and growth hormone because it is possible to design and validate manufacturing processes in the production of properly folded materials.2,3) Potency of these pharmaceutical preparations can be calculated using the content assay with HPLC, which quantifies the peak area of a product against that of a reference standard of known potency. The results of the HPLC assay have been shown to correlate well with those of the bioassay.2,3) In addition, the HPLC assay is rapid, precise and less labour intensive than the bioassay. However, for some glycoproteins, alternative assay methods using a quantitative charge-based separation technique, such as isoelectric focusing (IEF) and capillary zone electrophoresis (CZE), have been shown to be feasible for estimating in vivo bioactivity 4,5) because negatively charged sialic acid residues are critical for in vivo bioactivity. For example, Mulders et al. 4) reported that quantitative assessment of the isoform distribution by IEF may provide a method for predicting in vivo biological potency of preparations containing recombinant human follicle-stimulating hormone (rhFSH). Close correlation between results of experimental in vivo bioactivities and IEF-predicted in vivo bioactivities suggest that the only factor affecting prediction of biological potency is the result of quantitative isoform distribution in rhFSH.Erythropoietin (EPO) is a glycoprotein hormone that regulates the red blood cell level by stimulating maturation of erythroid precursor cells. 6) Recombinant human EPO (rhEPO) produced in Chinese hamster ovary (CHO) cells is extensively used for serve anaemia therapy.7) EPO comprises a 165-amino acid protein with 40% of its molecular weight accounted for by carbohydrates.8,9) EPO contains three Nglycans located on Asn residues at positions 24, 38, and 83 and one mucin-type O-glycan located on the Ser-126 residue. The N-linked carbohydrates comprise bi-, tri-and tetraantennary oligosaccharides, which typically terminate with a negatively charged sialic acid residue. 10,11) Because of the variable number of sialic acid residues, the product of EPO usually exists as a mixture of isoforms with different isoelectric points. Several studies have reported that sialic acid residues are critical for in vivo bioactivity of EPO.12,13) Isoforms having a higher sialic acid content are seen to display higher in vivo bioactivity, longer seru...

Those data strongly suggest that eperisone may be metabolized to HMO by CYP1A in rat intestinal microsomes during the first-pass through the epithelium of the small intestine.

KRN321 is a hyperglycosylated analogue of recombinant human erythropoietin (rHuEPO, epoetin alfa), and its absorption, distribution, and excretion have been studied after a single intravenous and subcutaneous administration of 125I-KRN321 at a dose of 0.5 microg kg-1 to male rats. The half-lives of immunoreactive radioactivity in the terminal phase after intravenous and subcutaneous administration were 14.05 and 14.36 h, respectively, and the bioavailability rate after subcutaneous administration was 47%. The total radioactivity in tissues was lower than that in the serum in all tissues excluding the thyroid gland and skin at the injection site (subcutaneous administration). The maximum concentrations were observed in the bone marrow or skin at the injection site followed by the thyroid gland, kidneys, adrenal glands, spleen, lungs, stomach and bladder. The radioactivity found in trichloroacetic acid-precipitated fractions suggested that a high-molecular weight compound, unchanged or mixed with endogenous protein, distributed to the tissues after administration. The whole-body autoradiographic findings in both groups were in agreement with the tissue distribution mentioned above. The blood cell uptake of KRN321 was low for both groups. The excretion ratios of radioactivity into urine and faeces up to 168 h were 71.4 and 14.1% after the intravenous administration and 74.9 and 12.0% after the subcutaneous administration. There was no difference in the excretion profile of radioactivity between the two groups.

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