Piergiorgio Pietta

Application of micellar electrokinetic capillary chromatography to the determination of flavonoid drugs

The use of micellar electrokinetic capillary chromatography is described for the determination of flavonol-3-O-glycosides. A 72-cm fused-silica capillary column and a 50 mM sodium dodecyl sulphate-20 mM sodium borate running buffer (pH 8.3) were used for the electrophoretic separations. The samples were injected onto the capillary column in the range 10–1000 pg. Results are given for quercetin-, kaempferol- and isorhamnetin-3-O-glycosides and for a standardized Ginkgo biloba extract. The results are compared with those obtained by reversed-phase high-performance liquid chromatography.

Relationship between rate and extent of catechin absorption and plasma antioxidant status.

Flavonoids are described to exert a large array of biological activities, which are mostly ascribed to their radical‐scavenging, metal chelating and enzyme modulation ability. Most of these evidences have been obtained by in vitro studies on individual compounds and at doses largely exceeding those dietary. Little is known about a possible relationship between rate and extent of the absorption and modifications of plasma antioxidants. To elucidate this aspect, human volunteers were supplemented with single doses of green tea catechins in free (Greense‐lect™) or phosphotipid complex form (Greenselect™ Phytosomer®) equivalent to 400 mg epigallocatechingallate (EGCg). EGCg was chosen as biomarker for green tea catechin absorption, and its time course plasma concentration was correlated to the subsequent percent variations of plasma ascorbate, total glutathione, α‐tocopherol, β‐carotene and Total Radical Antioxidant Parameter (TRAP). Green tea catechins were absorbed more extensively when administered as phospholipid complex rather than as free catechins. Single dose intake of both forms of catechins produced a transient decrease (10‐20%) of plasma ascorbate and total glutathione and an increase of plasma TRAP (16‐19%). These variations were consistent with the plasmatic levels of EGCg, ascorbate and total glutathione.

Electrospray characterization of selected medicinal plant extracts

Extracts of selected medicinal plants were examined by electrospray mass spectrometry (ESI-MS). This technique allowed identification of the main components of each extract, thereby providing a typical finger-print of the examined plants. More specifically, anthocyanins (Vaccinium myrtillus), isoflavones (Glycine max, soybean), flavonol-glycosides and terpenes (Ginkgo biloba), triterpenes (Centella asiatica), caffeoyl-quinic acids (Cynara scolymus, artichoke), ginsenosides (Panax ginseng), catechins (Camellia sinensis, green tea) and flavones and flavanones (Propolis) were detected rapidly at levels in the range of 0.1-1 microg/ml, using 0.2-1 mg/ml of each medicinal plant extract.

Identification of Ginkgo biloba flavonol metabolites after oral administration to humans

An extract of Ginkgo biloba leaves (EGb) was given to healthy volunteers. Urine samples were collected for 3 days, and blood samples were withdrawn every 30 min for 5 h. The samples were purified through SPE C18 cartridges and analyzed by reversed-phase LC-diode array detection for the presence of EGb metabolites. Only urine samples contained detectable amounts of substituted benzoic acids, i.e., 4-hydroxybenzoic acid conjugate, 4-hydroxyhippuric acid, 3-methoxy-4-hydroxyhippuric acid, 3,4-dihydroxybenzoic acid, 4-hydroxybenzoic acid, hippuric acid and 3-methoxy-4-hydroxybenzoic acid (vanillic acid). In contrast to rats no phenylacetic acid or phenylpropionic acid derivatives were found in urine, thus indicating that in humans a more extensive metabolism takes place. As for rats the metabolites found in human urines accounted for less than 30% of the flavonoids given. The same procedure was applied to blood samples, and no metabolites could be detected.

Separation of flavonol-2-O-glycosides from Calendula officinalis and Sambucus nigra by high-performance liquid and micellar electrokinetic capillary chromatography

Calendula officinalis and Sambucus nigra flowers were analysed by reversed-phase high-performance liquid chromatography (RP-HPLC) and micellar electrokinetic capillary chromatography (MECC). RP-HPLC was performed on C8 Aquapore RP 300 columns with eluents containing 2-propanol and tetrahydrofuran. MECC was carried out on a 72-cm fused-silica capillary using sodium dodecyl sulphate and sodium borate (pH 8.3) as the running buffer. The results obtained by these techniques are compared.

Identification of flavonoids from Ginkgo biloba L., Anthemis nobilis L. and Equisetum arvense L. by high-performance liquid chromatography with diode-array UV detection

Naturally occurring flavonoids can be separated by reversed-phase high-performance liquid chromatography (HPLC) using 2-propanol and tetrahydrofuran. A development of this approach is described for the HPLC of Ginkgo biloba, Anthemis nobilis and Equisetum arvense. Peaks related to previously reported compounds were identified by co-chromatography with authentic standards and/or by diode-array detection. Tentative assignments of unknown peaks are presented.

High performance liquid chromatography/electrospray mass spectrometry of Hypericum perforatum extracts

Hypericum perforatum L. (St. Johns Wort) is a widely distributed herbaceous perennial plant which has been well known as a medicinal plant since antiquity. In recent years, H. perforatum has received increasing attention for the treatment of depression and other neuralgic disorders. The main constituents of H. perforatum extract include flavonoids, naphthodianthrones, phloroglucinols, essential oils and xanthones. The present work reports the analysis of naphthodianthrones and phloroglucinols in H. perforatum extracts by means of high performance liquid chromatography (HPLC) coupled simultaneously to a diode array detector (DAD) and electrospray mass spectrometry (ESI-MS). Hypericin, pseudohypericin, hyperforin and adhyperforin were separated and identified on the base of their on-line UV and mass spectra. Quantitative analysis of hypericin derivatives in different extracts of H. perforatum using DAD and MS detectors was performed. In addition, direct infusion ESI-MS of H. perforatum extracts was applied to obtain rapid mass fingerprints of constituents present in the sample.

High-performance liquid chromatography and micellar electrokinetic chromatography of flavonol glycosides from Tilia

The determination of nine different flavonol glycosides from Tilia using reversed-phase high-performance liquid chromatography (HPLC) and micellar electrokinetic chromatography (MEKC) is described. The analytes were monitored by on-line diode-array UV detection to identify peaks as quercetin or kaempferol derivatives. MEKC is confirmed as a useful complementary technique to HPLC.

Identification of flavonoid metabolites after oral administration to rats of a Ginkgo biloba extract

An extract of Ginkgo biloba leaves (EGb) was administered by gastric probe to Wistar female rats, and urine and faeces samples were collected for 5 days and whole blood samples were withdrawn every 30 min for 6 h. After purification with SPE C18 cartridges, the samples were analysed by reversed-phase LC-diode array detection (LC-DAD) for residual flavonoid glycosides, aglycones and metabolites. No glycosides or aglycones were detected in urine, faeces or blood and extensive degradation of EGb flavonoids within 24 h was detected. Among the seven different phenylalkyl acids detected by LC-DAD, 3,4-dihydroxyphenylacetic acid (I), hippuric acid (II), 3-hydroxyphenylacetic acid (III), homovanillic acid (IV) and benzoic acid (VII) were directly confirmed by on-line mass spectrometry using an electrospray interface (ES-MS). Peaks V and VI needed to be collected and separately examined and they were found to be 3-(4-hydrophenyl)propionic acid and 3-(3-hydrophenyl)propionic acid, respectively. As further evidence, the identity of metabolites I, II, III, IV, V and VII was confirmed by co-chromatography with authentic standards.

Liquid chromatography/electrospray mass spectrometry of bioactive terpenoids in Ginkgo biloba L.

Standardized extracts of Ginkgo biloba leaves are mainly used in the treatment of peripheral and celebral circulation disorders, and also as a remedy against asthma, coughs, bladder inflammation, blenorrhagia and alcohol abuse. The leaf extracts contain biflavones, flavonol glycosides and terpene lactones. This paper reports a method based on liquid chromatography coupled with electrospray mass spectrometry for the analysis of terpenoids in G. biloba extracts. This method allows the rapid isocratic separation of underivatized ginkgolides (GA, GB, GC and GJ) and bilobalide at very low levels (10 pg on the column) and their quantitative detection by external standardization with relative standard deviations of 3 and 5% for intra- and inter-day analyses, respectively.