Dong Hee Na

Evaluation of metabolism-mediated herb-drug interactions

As the use of herbal medicines increases, the public health consequences of drug-herb interactions are becoming more significant. Herbal medicines share the same drug metabolizing enzymes and drug transporters, including cytochrome P450 enzymes (CYPs), glucuronosyltransferases (UGTs), and P-glycoprotein, with several clinically important drugs. Interactions of several commonly used herbal medicines, such as Ginko biloba, milk thistle, and St. John’s wort, with therapeutic drugs including warfarin, midazolam, alprazolam, indinavir, saquinavir, digoxin, nifedipine, cyclosporine, tacrolimus, irinotecan, and imatinib in humans have been reported. Many of these drugs have very narrow therapeutic indices. As the herb-drug interactions can significantly alter pharmacokinetic and pharmacodynamic properties of administered drugs, the drugs interacting with herbal medicines should be identified by appropriate in vitro and in vivo methods. A good understanding of the mechanisms of herb-drug interactions is also essential for assessing and minimizing clinical risks. In vitro methods are useful for providing mechanistic information and evaluating multiple components in herbal medicines. This review describes major factors affecting the metabolism of herbal medicines, mechanisms of herb-drug interactions mediated by CYPs and UGTs, and several in vitro methods to assess the herb-drug interactions. Finally, drug interactions of Ginkgo biloba and St. John’s wort, as representative herbal medicines, are described.

Gastroretentive drug delivery system of DA-6034, a new flavonoid derivative, for the treatment of gastritis.

A gastroretentive drug delivery system of DA-6034, a new synthetic flavonoid derivative, for the treatment of gastritis was developed by using effervescent floating matrix system (EFMS). The therapeutic limitations of DA-6034 caused by its low solubility in acidic conditions were overcome by using the EFMS, which was designed to cause tablets to float in gastric fluid and release the drug continuously. The release of DA-6034 from tablets in acidic media was significantly improved by using EFMS, which is attributed to the effect of the solubilizers and the alkalizing agent such as sodium bicarbonate used as gas generating agent. DA-6034 EFMS tablets showed enhanced gastroprotective effects in gastric ulcer-induced beagle dogs, indicating the therapeutic potential of EFMS tablets for the treatment of gastritis.

Effect of Molecular Size of PEGylated Recombinant Human Epidermal Growth Factor on the Biological Activity and Stability in Rat Wound Tissue

The purpose of this study was to investigate the effect of size of polyethylene glycol (PEG) conjugated to recombinant human epidermal growth factor (rhEGF) on its stability in skin wound tissue and in vitro biological activity to find the desirable conjugate as topical therapeutic agent for wound healing. Site-specific PEGylation at N-terminus of rhEGF was performed with monomethoxy PEG-Butyraldehyde derivatives (MW 2, 5, and 20 kDa). Mono-PEG-rhEGFs retained 60–70% of biological activity of native rhEGF, and the effect of PEG size was not significant. The improvement of stability in the rat skin wound tissue was dependent on the increase of the PEG size attached. The degradation half-lives of native rhEGF, mono-PEG-2K-, −5K-, and −20K-rhEGFs were 1.1, 3.1, 5.2, and 41.5 hr, respectively. Therefore, mono-PEG-20K-rhEGF was considered to be the most desirable in terms of the increase of stability and the preservation of biological activity. This study suggests that the high molecular weight PEG at N-terminus of rhEGF would give a satisfactory stabilizing effect and thus may improve therapeutic efficacy in clinical use.The purpose of this study was to investigate the effect of size of polyethylene glycol (PEG) conjugated to recombinant human epidermal growth factor (rhEGF) on its stability in skin wound tissue and in vitro biological activity to find the desirable conjugate as topical therapeutic agent for wound healing. Site-specific PEGylation at N-terminus of rhEGF was performed with monomethoxy PEG-Butyraldehyde derivatives (MW 2, 5, and 20 kDa). Mono-PEG-rhEGFs retained 60-70% of biological activity of native rhEGF, and the effect of PEG size was not significant. The improvement of stability in the rat skin wound tissue was dependent on the increase of the PEG size attached. The degradation half-lives of native rhEGF, mono-PEG-2K-, -5K-, and -20K-rhEGFs were 1.1, 3.1, 5.2, and 41.5 hr, respectively. Therefore, mono-PEG-20K-rhEGF was considered to be the most desirable in terms of the increase of stability and the preservation of biological activity. This study suggests that the high molecular weight PEG at N-terminus of rhEGF would give a satisfactory stabilizing effect and thus may improve therapeutic efficacy in clinical use.

Optimization of octreotide PEGylation by monitoring with fast reversed-phase high-performance liquid chromatography.

The purpose of this study was to develop a fast reversed-phase high-performance liquid chromatography (HPLC) method for monitoring the octreotide PEGylation reaction in order to find optimal conditions for the production of the desired mono-PEGylated octreotide. The fast HPLC method could separate the positional isomers of two mono-PEGylated octreotides, di-PEGylated octreotide, and unmodified octreotide within 4.5 min. The PEGylation pattern was monitored at various pH conditions and molar ratios of reactants to allow optimization of the PEGylation reaction conditions for the production of N-terminally mono-PEGylated octreotide.

Reversible blocking of amino groups of octreotide for the inhibition of formation of acylated peptide impurities in poly(lactide-co-glycolide) delivery systems.

The purpose of this study was to develop a novel method to inhibit the formation of acylated peptide impurities in poly(d,l-lactide-co-glycolide) (PLGA) formulations by reversely blocking the amino groups of octreotide with maleic anhydride (MA). Two mono-MA conjugates with different modification sites (N terminus and Lys residue) and di-MA conjugate of octreotide were prepared and isolated by reversed-phase high-performance liquid chromatography (RP-HPLC). The polymer interaction of peptides and the formation of acylated peptides were monitored by RP-HPLC. The stability of MA-octreotide conjugates in PLGA films was studied in 0.1xa0M phosphate buffer (pHxa07.4) at 37°C. The conjugation of MA to octreotide substantially inhibited the interaction of peptide with PLGA polymer and the subsequent formation of acylated peptide impurities. The MA-octreotides were successfully converted to intact octreotide as pH drops by PLGA hydrolysis. In PLGA films, MA-octreotide also showed complete inhibition of peptide acylation. In conclusion, MA conjugation provides a viable approach for stabilizing peptides in PLGA delivery systems.

Effect of PEGylation on stability of peptide in poly(lactide-co-glycolide) microspheres

The purpose of this study was to evaluate the effect of PEGylation on the stabilization of peptide in poly(D,L-lactide-co-glycolide) (PLGA) microspheres for sustained release delivery. As model peptide, growth hormone-releasing peptide-6 (GHRP-6) was conjugated with succinimidyl propionate monomethoxy poly(ethylene glycol) (PEG) with an average molecular weight of 2000 Da. The mono-PEG-GHRP-6 was separated by ion-exchange chromatography, and its molecular mass was identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The microspheres encapsulating native GHRP-6 or mono-PEG-GHRP-6 were prepared using the single oil-in-water emulsion solvent evaporation method. During incubation in a 0.1 M phosphate buffer (pH 7.4) for one month at 37°C, native GHRP-6 microspheres were identified to form several acylated peptides by reversed-phase HPLC and MALDI-TOF MS, whereas the mono-PEG-GHRP-6 microspheres was not affected from peptide acylation by PLGA. This study demonstrates that PEGylation can stabilize peptide against the acylation reaction occurred in PLGA microspheres.

Quantitative determination of major phlorotannins in Ecklonia stolonifera.

Ecklonia stolonifera is a rich source of phlorotannins, which are responsible for the potent pharmacological effects associated with this seaweed. The purpose of this study was to develop a reversed-phase high-performance liquid chromatography method for the simultaneous determination of three major phlorotannins, eckol, dieckol, and phlorofucofuroeckol-A, in the extracts of Ecklonia stolonifera. The optimal chromatographic conditions were achieved on a Thermo Hypersil Gold C-18 column (250 × 4.6 mm i.d., 5 μm) using linear gradient elution of acetonitrile and water containing 0.1% formic acid at UV 254 nm. The separated phlorotannins were identified by liquid chromatography-mass spectrometry. The high-performance liquid chromatography method showed good linearity (r2 > 0.998), precision (1.4–9.5%), and accuracy (93.9–108.7%). The limits of detection ranged from 0.06 to 0.30 μg/mL and the lower limits of quantitation ranged from 0.2 to 1.0 μg/mL. Among phlorotannins, dieckol was the most abundant in both ethanol and ethyl acetate extracts of Ecklonia stolonifera.

Separation of positional isomers of mono-poly(ethylene glycol)-modified octreotides by reversed-phase high-performance liquid chromatography

The purpose of this study was to develop a reversed-phase high-performance liquid chromatographic method (RP-HPLC) for separating each positional isomer from low- to high-molecular-weight mono-PEGylated octreotides prepared by polyethylene glycol (PEG) derivatives with various molecular weights (2, 5, or 20kDa). In the gradient elution using acetonitrile and 10mM phosphate buffer at pH 7.0 on a Phenomenex Gemini C-18 column (250mmx4.6mm id, 5microm), each positional isomer of the mono-PEGylated octreotides was completely resolved with good resolution (PEG-2K: 7.6, PEG-5K: 6.6, and PEG-20K: 3.1). The optimal RP-HPLC condition also resolved the degradation products of mono-PEG-octreotide isomers in thermal stability studies at 55 degrees C and enzymatic stability studies with trypsin. In conclusion, the developed RP-HPLC method will be valuable for studying the effect of PEGylation site and the attached PEG size on the physicochemical and pharmacological properties of PEGylated octreotides.

Application of microchip CGE for the analysis of PEG-modified recombinant human granulocyte-colony stimulating factors.

The purpose of this study was to evaluate the microchip CGE (MCGE) for the analysis of PEG‐modified granulocyte‐colony stimulating factor (PEG‐G‐CSF) prepared with PEG‐aldehydes. The unmodified and PEG‐modified G‐CSFs were analyzed by Protein 80 and 230 Labchips on the Agilent 2100 Bioanalyzer. The MCGE allowed size‐based separation and quantitation of PEG‐G‐CSF. The Protein 80 Labchip was useful for PEG‐5K‐G‐CSF, while the Protein 230 Labchip was more suitable for PEG‐20K‐G‐CSF. The MCGE was also used to monitor a search for optimal PEG‐modification (PEGylation) conditions to produce mono‐PEG‐G‐CSF. This study demonstrates the usefulness of MCGE for monitoring and optimizing the PEGylation of G‐CSF with the advantages of speed, minimal sample consumption, and automatic quantitation.

Microchip electrophoresis for monitoring covalent attachment of poly(ethylene glycol) to proteins

A microchip electrophoretic method was applied to monitor and characterize the covalent attachment of poly(ethylene glycol) (PEGylation) of two proteins, alpha-lactalbumin and bovine serum albumin, using several poly(ethylene glycol) (PEG) derivatives with molecular weights from 1 to 20 kDa. This method effectively separated multi-PEGylated proteins in a size-based manner and allowed monitoring of the PEGylation pattern with the advantages of high speed, minimal sample consumption, and high reproducibility. Microchip electrophoresis would be a very useful tool for protein PEGylation studies such as reaction monitoring, purity checks, and characterization of PEGylated protein products.