• Natural Product Sciences
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• v.8 no.2
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• pp.35-43
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• 2002

Glycosides of herbal medicines, such as glycyrrhizin, ginsenosides, kalopanaxsaponins, rutin and ponicirin, were studied regarding their metabolic fates and pharmacological actions in relation to intestinal bacteria using germ-free, gnotobiotic and conventional animals. When glycyrrhizin (GL) was orally administered, $18{\beta}-glycyrrhetinic\;acid\;(GA)$, not GL, was detected in plasma and intestinal contents of gnotobiotic and conventional rats. However, GA could not be detected in germ-free rats. When GL was incubated with human intestinal bacteria, it was directly metabolized to GA (>95%) or via $18{\beta}-glycyrrhetinic\;acid-3-{\beta}-D-glucuronide$(>5%). Orally administered GL was effective in gnotobiotic and conventional rats for liver injury induced by carbon tetrachloride, but was not effective in germ-free rats. When ginseng saponins were orally administered to human beings, compound K in the plasma was detected, but the other protopanxadiol saponins were not detected. The compound K was active for tumor metastasis and allergy. When kalopanaxsaponins were incubated with human intestinal microflora, they were metabolized to kalopanaxsaponin A, kalopanaxsaponin I and hederagenin. These metabolites were active for rheumatoid arthritis and diabetic mellitus while the other kalopanxsaponins were not. When flavonoid glycosides were orally administered to animals, aglycones and/or phenolic acids were detected in the urine. The metabolic pathways proceeded by intestinal bacteria rather than by liver or blood enzymes. These metabolites, aglycones and phenolic acids, showed antitumor, antiinflammatory and antiplatelet aggregation activities. These findings suggest that glycosides of herbal medicines are prodrugs.

• Archives of Pharmacal Research
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• v.21 no.1
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• pp.17-23
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• 1998

Flavonoid glycosides were metabolized to phenolic acids via aglycones by human intestinal microflora producing ${\alpha}$-rhamnosidase, exo-${\beta}$-glucosidase, endo- ${\beta}$-glucosidase and/or ${\beta}$-glucuronidase. Rutin, hesperidin, naringin and poncirin were transformed to their aglycones by the bacteria producing ${\alpha}$-rhamnosidase and ${\beta}$-glucosidase or endo- ${\beta}$-glucosidase, and baicatin, puerarin and daidzin were transformed to their aglycones by the bacteria producing ${\beta}$glucuronidase, C-glycosidase and ${\beta}$-glycosidase, respectively. Anti-platelet activity and cytotoxicity of the metabolites of flavonoid glycosides by human intestinal bacteria were more effective than those of the parental compounds. 3,4-Dihydroxyphenylacetic acid and 4-hydroxyl-phenylacetic acid were more effective than rutin and quercetin on anti-platelet aggregation activity. 2,4,6-Trihydroxybenzaidehyde, quercetin and ponciretin were more effective than rutin and ponciretin on the cytotoxicity for tumor cell lines. We insist that these flavonoid glycosides should be natural prodrugs.

• Archives of Pharmacal Research
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• v.25 no.2
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• pp.111-136
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• 2002

The prodrug and antedrug concepts, which were developed to overcome the physical and pharmacological shortcomings of various therapeutic classes of agents, employ diametrically different metabolic transformations. The prodrug undergoes a predictable metabolic activation prior to exhibiting its pharmacological effects in a target tissue while the antedrug undergoes metabolic deactivation in the systemic circulation upon leaving a target tissue. An increased therapeutic index is the aspiration for both approaches in designing as well as evaluation criteria. The recent research endeavors of prodrugs include the gene-directed and antibody-directed enzymatic activation of a molecule in a targeted tissue, organ specific delivery, improved bioavailabilities and cellular penetration of nucleotides. As for antedrugs, emphasis in research has been based upon the design and synthesis of systemically inactive molecule by incorporating a metabolically labile functional group into an active molecule.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1997.04a
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• pp.119-119
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• 1997

Valacyclovir is a L-valyl ester prodrug of acyclovir which is a highly effective and selective antiviral agent in the treatment of herpes virus diseases. Valacyclovir is rapidly and almost completely converted to acyclovir and increases the oral bioavailability of acyclovir three to five fold. However, the intestinal absorption mechanism of valacyclovir is not clear. If the improved absorption mechanism of valacyclovir is fully understood, it will provide a rationale of designing the amino acid ester prodrugs of polar drugs containing hydroxyl group. The main objective of our present study is to characterize the membrane transport mechanism of valacyclovir. Methods : Intestinal absorption of valacyclovir was investigated by using in-situ rat perfusion study and its wall permeability was estimated by modified boundary layer model. The membrane transport mechanism was also investigated through the uptake study in Caco-2 cells and in CHO-hPepTl cells. Results : In the rat perfusion study, the wall permeability of valacyclovir was ten times higher than acyclovir and showed concentration dependency, Valacyclovir also demonstrated a D,L stereo-selectivity with L-isomer having an approximately five-fold higher permeability than D-isomer. Mixed dipeptides and cephalexin, which are transported by dipeptide carriers, strongly competed with valacyclovir for the intestinal absorption, while L-valine did not show any competition with valacyclovir. This indicated that the intestinal absorption of valacyclovir could be dipeptide carrier-mediated. In addition, the competitive uptake study in Caco-2 cells presented that dipeptides reduced the valacyclovir uptake but valine did not. Also, in IC$\sub$50/ study, valacyclovir showed strong inhibition on the $^3$H-gly-sar uptake in CHO-hPepTl cells over-expressing a human intestinal peptide transporter. Taken together, the result from our present study indicated that valacyclovir utilized the peptide transporter for the intestinal absorption.

• Archives of Pharmacal Research
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• v.26 no.4
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• pp.258-263
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• 2003

Colon-specific delivery of glucocorticoids is highly desirable for the efficient treatment of inflammatory bowel disease. We synthesized prednisolone 21-sulfate sodium (PDS) as a colon-specific prodrug of prednisolone (PD) and investigated its properties using rats as test animals. We expected that introduction of sulfate ester as a sodium salt might increase the hydrophilicity and restrict the absorption in the GI tract. If PDS is stable and nonabsorbable in the upper intestine, it will be delivered to the colon as an intact form, where it hydrolyze by the sulfatase to release PD. Compared with PD, the solubility of PDS increased and the apparent partition coefficient decreased greatly. PDS was stable on incubation with pH 1.2 and 6.8 buffer solutions and with the contents of the stomach and small intestine. On incubation with the cecal contents, PDS decreased to 9.6％ of the dose in 10 h producing PD. The amount of PD increased to give a maximum 54％ of the dose and decreased. As a control, when PD was incubated with the cecal contents, it decreased to 29％ of the dose in 8 h, which implied that reduction of PD proceeded under such conditions. These results suggested that hydrolysis of PDS took place to produce and accumulate PD, which decreased by reduction as the incubation period extended. Our results suggested that PDS can be a promising colon-specific prodrug of PD, and sulfate ester group might serve as a potential colon-specific promoiety, especially for the drugs which are resistant to reduction in the colon.

• Asian Pacific Journal of Cancer Prevention
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• v.14 no.10
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• pp.5797-5804
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• 2013

In order to enhance the bioavailability of curcumin its conjugates with piperic acid and glycine were synthesized by esterifying the 4 and 4' phenolic hydroxyls, the sites of metabolic conjugation. Antiproliferative and apoptotic efficacy of synthesized conjugates was investigated in MCF-7 and MDA-MB-231 cell lines. $IC_{50}$ values of di-O-glycinoyl (CDG) and di-O-piperoyl (CDP) esters of curcumin were found to be comparable with that of curcumin. Both conjugates induced chromatin condensation fragmentation and apoptotic body formation. CDP exposure to MCF-7 cells induced apoptosis initiating loss of mitochondrial membrane potential (${\Delta}{\Psi}m$) followed by inhibition of translocation of transcription factor NF-${\kappa}B$ and release of Cytochrome-C. Reactive oxygen species (ROS) production was evaluated by fluorescent activated cell sorter. Change in ratio of Bcl2/Bclxl was observed, suggesting permeablization of mitochondrial membrane leading to the release of AIF, Smac and other apoptogenic molecules. DNA fragmentation as a hallmark for apoptosis was monitored by TUNEL as well as agrose gel electrophoresis. Thus, it was proven that conjugation does not affect the therapeutic potential of parent molecule in vitro, while these could work in vivo as prodrugs with enhanced pharmacokinetic profile. Pharmacokinetics of these molecules under in vivo conditions is a further scope of this study.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1993.04a
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• pp.71-71
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• 1993

Carboxylesterase is widely distributed in the tissues of vertebrates, insects, plants and mycobacteria. Among various tissues of animals and humans, the highest esterase activity with various substrates is found in the liver. Kidney has moderate carboxylesterase activity in the proximal tubules. Considerable esterase activity is also found in the small intestine epithet elial cells and serum of mammals. Besides these tissues, carboxylesterase has been found in the lung, testis, adipose tissue, nasal mucosa and even in the central nervous system. Hepatic microsomal carboxylesterase catalyzes the hydrolysis of a wide variety of endogenous and exogenous compounds such as carboxylester, thioester and aromatic amide. Since carboxylesterases are important for metabolic activation of prodrugs and detoxification of xenobiotics, differences in substrate specificity and immunological properties of this enzyme are important in connection with choosing a suitable laboratory animal for the evaluation of biotransformation and toxicity of drugs. On the other hand, liver, kidney, intestine and serum were found to contain multiple forms of carboxylesterases in animal species and humans. In fact, we have purified more than fifteen isoforms of carboxylesterases from microsomes of liver, kidney and intestinal mucosa of nine animal species and humans. and characteristics of these isoforms were compared each other in terms of their physical and immunochemical properties. On the other hand, we have reported that hepatic microsomal carboxylesterases are induced by many exogenous compounds such as phenobarbital, polycyclic aromatic hydrocarbons, Aroclor 1254, aminopyrine and clofibrate. Later, we showed that some isoforms of hepatic carboxylesterase were induced by glucocorticoids such as dexamethasone and 16 ${\alpha}$-carbonitrile, but other isoforms were rather inhibited by these compounds. These findings indicate that involvement of carboxylesterases in the metabolism and toxicity of drugs should be explained by the isoforms involved. Since 1991, we have carried out detailed research investigating the types of carboxylesterases involved in the metabolic activation of CPT-11, a derivative of camptothecin, to the active metabolite, SN-38. The results obtained strongly suggest that some isoforms of carboxylesterase of liver microsomes and intestinal mucosal membrane are exclusively involved in CPT-11 metabolism. In this symposium, the properties of carboxylesterase isoforms purified from liver, kidney and intestine of animal species and humans are outlined. In addition, metabolism of CPT-11, a novel antitumor agent, by carboxylesterases in relation to the effectiveness will also be discussed.

• Archives of Pharmacal Research
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• v.27 no.6
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• pp.662-669
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• 2004

The highly water-soluble monomethoxypoly(ethyleneglycol) (mPEG) prod rugs of cyciosporin A(CsA) were synthesized. These prod rugs were prepared by initially preparing intermediate in the form of carbonate at the 3'-positions of CsA with chloromethyl chloroformate, in the pres-ence of a base to provide a 3'-carbonated CsA intermediate. Reaction of the CsA intermediate with mPEG derivative in the presence of a base provides the desired water-soluble prod rugs. As a model, we chose molecular weight 5 kDa mPEG in the reaction with CsA to give water soluble prodrugs. To prove that the prod rug is decomposed in the body to produce CsA, the enzymatic hydrolysis test was conducted using human liver homogenate at $37^{\circ}C$. The prodrug was decomposed in human liver homogenate to produce the active material, CsA, and the hydrolysis half-life ($t_{1/2}$) of the prodrug, KI-306 was 2.2 minutes at $37^{\circ}C$. However, a demon-stration of non-enzymatic conversion in pH 7.4 phosphate buffer was provided by the fact that the half-life ($t_{1/2}$) is 21 hours at 37$^{\circ}C$. The hydrolysis test in rat whole blood was also conducted. The hydrolysis was seen with half-life ($t_{1/2}$) of about 9.9, 65.0, 14.2, 3.4, 2.1 9.5, and 1.6 minutes for KI-306, 309, 312, 313, 315, 316, and 317, respectively. This is the ideal for CsA prodrug. The pharmacokinetic study of the prodrug, KI-306, in comparison to the commer-cial product (Sandimmune Neoral Solution) was also carried out after single oral dose. Each rat received 7 mg／kg of CsA equivalent dose. Especially, the prodrug KI-306 exhibits higher AUC and $C_{max}$ than the conventional Neoral. The AUC and $C_{max}$ were increased nearly 1.5 fold. The kinetic value was also seen with $T_{max}$ of about 1.43 and 2.44 hours for KI-306 and Neoral, respectively.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.6
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• pp.349-354
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• 2006

The aromatic hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates many of the biological and toxicological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and related chemicals. The application of recombinant reporter plasmid such as the firefly luciferase gene has proven to be a very effective method to detect these chemicals. The bioassay system, CALUX, is sensitive in directly detecting AhR-agonists from a variety of environmental and biologic materials. However, responses of the AhR-dependent bioassays are dependent on the cell types used. Thus, we developed a sensitive bioassay using the recombinant mouse hepatoma cell (Hepa1c1c7) for the determination of dioxins. The recombinant cell line was stably transfected with firefly luciferase reporter gene (pGudLuc1.1). The transfected cells showed the highest induction of luciferase activity at 4.5 hr and a decrease beyond this time point. The system showed the highest sensitivity of detection ever reported. Upon TCDD exposure cells showed 2 fold increase at 10 pM and 7 fold increase at 100 pM, respectively. The passage number after the transfection played an important role in the sensitivity. The increase of passage number tended to increase the sensitivity of the cells up to 15. The media without phenol red showed a higher induction rate than with phenol red, suggesting the preferable use of phenol red-free media for the bioassay. Since each of the assays has unique characteristics that make them suitable for some screening applications and not others, development of sensitive bioanalytical methods based on a variety of cellular systems in a key to the successful determination of dioxins. The bioassay system developed in this study will contribute to further development of successful screening the AhR agonists among the environmental mixture. In addition, the rapid and sensitive nature of this cellular system can be applied as a valuable tool to screen the dioxin-like moieties among the prodrugs at the initial stage, thereby expediting the new drug discovery.

• BMB Reports
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• v.52 no.8
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• pp.508-513
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• 2019

In this study, the anti-inflammatory effects of ${\alpha}-lipoic$ acid (LA) and decursinol (Dec) hybrid compound LA-Dec were evaluated and compared with its prodrugs, LA and Dec. LA-Dec dose-dependently inhibited lipopolysaccharide (LPS)-induced nitric oxide (NO) generation in BV2 mouse microglial cells. On the other hand, no or mild inhibitory effect was shown by the Dec and LA, respectively. LA-Dec demonstrated dose-dependent protection from activation-induced cell death in BV2 cells. LA-Dec, but not LA or Dec individually, inhibited LPS-induced increased expressions of induced NO synthase (iNOS) and cyclooxygenase-2 (COX-2) proteins in a dose-dependent manner in both BV2 and mouse macrophage, RAW264.7 cells. Furthermore, LA-Dec inhibited LPS-induced expressions of iNOS, COX-2, interleukin-6, tumor necrosis $factor-{\alpha}$, and $interleukin-1{\beta}$ mRNA in BV2 cells, whereas the same concentration of LA or Dec was ineffective. Signaling studies demonstrated that LA-Dec inhibited LPS-activated signal transducer and activator of transcription 3 and protein kinase B activation, but not nuclear factor-kappa B or mitogen-activated protein kinase signaling. The data implicate LA-Dec hybrid compound as a potential therapeutic agent for inflammatory diseases of the peripheral and central nervous systems.