A Simple and Accurate Method for the Determination of Related Substances in Coenzyme Q10 Soft Capsules.

As a new dosage form, coenzyme Q10 (Co-Q10) soft capsules are easily absorbed and utilized by the human body. Co-Q10 soft capsules can effectively improve the bioavailability and reduce medical costs for patients. A main concern about Co-Q10 as an active pharmaceutical ingredient (API) is how to control the total quantity of related substances. In this article, according to the degradation pattern of the API, the most easily degradable impurity (impurity X) in the sample was prepared and its chemical structure was determined. Furthermore, a simple and accurate method was developed for the determination of related substances and to avert the interference of excipient ingredients in Co-Q10 soft capsules. The approach was validated adequately and the primary impurity X was confirmed accurately. The limit of total quantity of related substances (less than 1%) could be revised to the level of specific impurity X being no more than 0.5%, in this effective quality control method of Co-Q10 soft capsules. The revised level is suggested to be included in the corresponding standard of the supplement taken from the Pharmacopoeia of the People's Republic of China (2015 edition). This can provide a feasible method for the relevant enterprises and regulatory authorities to control the related substances of coenzyme Q10 soft capsules.

[Enantiomeric separation and impurity determination of valaciclovir hydrochloride].

OBJECTIVE: To determine the contents of L-enantiomer impurity in valaciclovir hydrochloride. METHODS: Valaciclovir enantiomers were separated and determined by using chiral high performance liquid chromatography. Chromatographic conditions were as follows:CROWNPAK(®) CR(+) chiral column (4 mm×150 mm, 5 µm), detection wavelength:254 nm, mobile phase:water-methanol-perchloric acid (19:1:0.1), flow rate:0.75 ml/min, sample injection volume:10 µl. RESULTS: D-valaciclovir was completely separated from L-enantiomer impurity. The contents of L-enantiomer impurity were 0.65%-2.62% on average in 8 batches of valaciclovir hydrochloride. CONCLUSION: Enantiomeric impurity contents in each batch of products were all meet criteria of United States Pharmacopeia, which can be used in criteria of Chinese Pharmacopeia as references.

Structure-metabolism relationships for the glucuronidation of flavonoids by UGT1A3 and UGT1A9.

OBJECTIVES: This study tries to find structure-metabolism relationships between flavonoids and human UGT1A3 and UGT1A9. METHODS: The glucuronidation of flavonoids was studied with recombinant UGT1A3 and UGT1A9, and the glucuronidation activity was determined by HPLC. KEY FINDINGS: Of the flavonoids studied, it was shown for the first time that baicalein, quercetin-3-OCH(2) OCH(3) , quercetin-4'-CH(3) , quercetin-3'-OCH(3) and quercetin-3'-Br are substrates of UGT1A3. Wogonin, baicalein, quercetin-4'-Cl, quercetin-3-OCH(2) OCH(3) , quercetin-3-O-arabinoside, quercetin-4'-CH(3) , quercetin-3'-OCH(3) and quercetin-3'-Br are the newly reported substrates of UGT1A9. The preferred substrates for UGT1A3 and UGT1A9 contain the hydroxyl group at the C7-position. The glycon and the position of the B ring have conspicuous influences on the glucuronidation activity, and other chemical structures of flavonoids have minor effects. CONCLUSIONS: From the quantitative study, UGT1A9 in general has higher glucuronidation efficiency than UGT1A3.

Stereoselective glucuronidation of propafenone and its analogues by human recombinant UGT1A9.

Stereoselective glucuronidation of propafenone and its beta-blocker analogues by human recombinant UGT1A3 and UGT1A9 from the recombinant baculovirus in insect sf9 cells was studied. The glucuronides produced in incubation mixtures were assayed by HPLC equipped with UV detector, and identified by beta-glucuronidase. The stereoselective glucuronidation was measured by pre-column 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocynate (GITC) derivatization HPLC method for propafenone and esomolol. In all of ten beta-blocker drugs studied, six showed the glucuronidation activity with UGT1A9, while four with UGT1A3. From roughly quantitative stereoselective glucuronidation study of racemic beta-blocker analogues by UGT1A9, propranolol had a high ratio of the ratios of S- to R-isomer glucuronide (S-G/R-G), about 4.3, the ratios of terbutaline, atenolol and esomolol were 3.3, 3.1 and 2.8 respectively, sotalol and propafenone were 2.3 and 2.0. In a word, S-isomers of these drugs were glucuronidated by human UGT1A9 much faster than their antipodes.

Glucuronidation of flavonoids by recombinant UGT1A3 and UGT1A9.

Flavonoids are highlighted for their potential roles in the prevention of oxidative stress-associated diseases. Their metabolisms in vivo, such as glucuronidation, are the key points to determine their health beneficial properties. In this paper, we tested the glucuronidation of nineteen flavonoids by both recombinant human UGT1A3 and UGT1A9. Eleven compounds could be catalyzed by both enzymes. In general, both enzymes showed moderate to high catalyzing activity to most flavonoid aglycones, while the catalyzing efficiency changed with structures. Each flavonoid produced more than one monoglucuronide with no diglucuronide detected by liquid chromatography-mass spectrometry (LC-MS). Enzymatic kinetic analysis indicated that the catalyzing efficiency (Vmax/Km) of UGT1A9 was higher than that of UGT1A3, suggesting its important role in flavonoid glucuronidation. Both human UGT1A3 and UGT1A9 preferred flavonoid aglycone to flavonoid glycoside, and their metabolism to arabinoside was stronger than to other glycosides. Of the flavonoids studied, it is the first time to report isorhamnetin, morin, silybin, kaempferol, daidzein, quercetin-3',4'-OCHO-, quercetin xylopyranoside and avicularin as substrates of UGT1A3. Apigenin, morin, daidzein, quercetin-3',4'-OCHO-, quercetin xylopyranoside and avicularin were the newly reported substrates of UGT1A9.

Stereoselective glucuronidation of carvedilol by Chinese liver microsomes.

OBJECTIVE: To study the stereoselective glucuronidation of carvedilol (CARV) by three Chinese liver microsomes. METHODS: The metabolites of CARV were identified by a hydrolysis reaction with beta-glucuronidase and HPLC-MS/MS. The enzyme kinetics for CARV enantiomers glucuronidation was determined by a reversed phase-high pressure liquid chromatography (RP-HPLC) assay using (S)-propafenone as internal standard after precolumn derivatization with 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylisothiocyanate. RESULTS: Two CARV glucuronides were found in three Chinese liver microsomes incubated with CARV. The non-linear regression analysis showed that the values of K(m) and V(max) for (S)-CARV and (R)-CARV enantiomers were (118+/-44) micromol/L, (2 500+/-833) pmol/(min.mg protein) and (24+/-7) micromol/L, (953+/-399) pmol/(min.mg protein), respectively. CONCLUSION: These results suggested that there was a significant (P<0.05) stereoselective glucuronidation of CARV enantiomers in three Chinese liver microsomes, which might partly explain the enantioselective pharmacokinetics of CARV.

Studies on the flavonoid substrates of human UDP-glucuronosyl transferase (UGT) 2B7.

Flavonoids are found in fruits, vegetables, nuts, seeds, herbs, spices, stems and flowers, as well as in tea and red wine. They are prominent components of citrus fruits and other food sources, are consumed regularly with the human diet, and have been shown to have many biological functions, including antioxidant and chelating properties. This study suggests features of the flavonoid structure necessary for it to act as a substrate of human UGT2B7. Generally speaking, flavonol has higher glucuronidation activity than flavones and isoflavones. Differences in C3' position have an important effect on UGT2B7 glucuronidation activity, and the various substituents have different influences on glucuronidation activity. For flavonol, the bulky group at C4' can enhance glucuronidation activity. Increasing the number of hydroxyl groups of flavonoids will increase their glucuronidation activity towards UGT2B7, while conjugation of glycon will weaken the activity, and hydroxyl position can also have an important role in activity. The high glucuronidation efficiency observed with many flavonoids suggests that the contribution of UGT2B7 to the metabolism of flavonoids may be significant. The results suggest that we should not only pay attention to glucuronidation activity, but should also attach importance to the regioselectivity of glucuronidation.