The antioxidative, anti-inflammatory, and antitumor properties of ginger (Zingiber officinale
Roscoe, Zingiberaceae) have been reported in previous studies (1
). Various clinical trials have evaluated ginger extracts to decrease lipid levels (6
), treat arthritis (7
), prevent nausea and vomiting (9
), and reduce pain in women with primary dysmenorrhea (12
). However, clinical studies using ginger extracts produced mixed or moderate/marginal benefits. For instance, Chaiyakunapruk et al
) demonstrated that administration of ginger at a dose of 1 g was more effective than placebo for the prevention of postoperative nausea and vomiting and postoperative vomiting. In contrast, Betz et al
) concluded that there was no clear evidence for the efficacy of ginger in the treatment of postoperative nausea and vomiting and of kinetosis. Bliddal et al
) showed that 170-mg daily dosing for 3 weeks of ginger powder did not show significant benefit over placebo in relieving pain in patients with osteoarthritis. Hoewever, a 6-week treatment with 510 mg of ginger extract daily dosing produced moderate effect on reducing pain in the knee in patients with osteoarthritis (16
Ginger contains volatile oils (~1% to 3%) and non-volatile pungent components oleoresin (1
). A variety of active components were identified in the oleoresin of ginger including gingerols and shogaols. Gingerols are a series of homologues with varied unbranched alkyl chain length, whereas shogaols are a series of homologues derived from gingerols with dehydration at the C-5 and C-4 during long-term storage or thermal processing. Other active compounds from the oleoresin portion of ginger were also reported, such as -paradol; - and -dehydrogingerdione; - and -gingerdione; -, -, -, and -gingerdiol; -methylgingerdiol; zingerone; -hydroxyshogaol; -, -, and -dehydroshogaol; and diarylheptanoids (17
). Among these compounds, gingerols and shogaols are the major constituents of oleoresin, while the other compounds are present in a limited amount, accounting for 1–10% of the overall amount of gingerols and shogaols (19
). Gingerols (especially 6-gingerol) are the major components in the fresh ginger rhizome. The amount of shogaols is increased in the dried ginger, as evidenced by the reduction of the ratio of 6-gingerol to 6-shogaol from 10:1 in fresh ginger to 1:1 in dried ginger (17
Since ginger extracts contain various components, it would be important to identify which compounds are responsible for their pharmacological effects. It was demonstrated that 6-, 8-, and 10-gingerols and 6-shogaol showed efficacy in anti-inflammatory, antibacterial, antipyretic, antilipidemic, antitumorigenic, and antiangiogenic effects (5
). In addition, 6-gingerol was shown to inhibit leukotriene A4
H) and suppress anchorage-independent cancer cell growth in colorectal cancer cells (HCT116 and HT29) with IC50
’s of 50 and 35 μM, respectively (28
). Sang et al
) demonstrated that 6-, 8-, and 10-shogaols exhibited much higher antiproliferative potency than 6-, 8-, and 10-gingerols against human lung cancer cells (H-1299) with IC50
’s of 8 μM for 6-shogaol and 150 μM for 6-gingerol. In addition, 10-gingerol was the most potent among the gingerols (19
). Furthermore, Dugasani et al
) found that 6-shogaol showed the most potent efficacy of antioxidative activity with an IC50
of about 8 μM, while 6, 8, and 10-gingerols had IC50
’s of 28, 20, and 12 μM, respectively.
In most of the clinical trials, the content of active ingredients in the ginger extract was not measured. The use of non-standardized ginger extracts in different clinical studies partly explain the mixed results of the clinical studies in addition to the different study designs and dose regimens. A study by Schwertner et al
. showed that variable amount of 6-gingerol, 6-shogaol, 8-gingerol, and 10-gingerol in various brands of ginger root dietary supplements (7
). In these different products, 6-gingerol ranged from 0.00 to 9.43 mg/g, 6-shogaol ranged from 0.16 to 2.18 mg/g, 8-gingerol ranged from 0.00 to 1.10 mg/g, and 10 gingerol ranged from 0.00 to 1.40 mg/g.
Furthermore, despite the numerous studies of the pharmacological effects of the ginger extracts in the human clinical trials, there are limited studies of the pharmacokinetics of the ginger active constituents in human biological matrices. The concentrations of 6-, 8-, and 10-gingerols and 6-shogaol for their efficacy in vivo
are still largely unknown. In our previous study, we developed a HPLC method to determine the concentrations of 6-, 8-, and 10-gingerols and 6-shogaol in healthy human subjects who received oral dose of ginger extracts at 2.0 g per day (1
). However, due to the low sensitivity of the HPLC method with low limit of quantification (LLOQ) ranging from 0.10 to 0.25 μg/mL for the four analytes, we did not detect any of these four compounds in the plasma, although we detected the glucuronide conjugates of the four analytes. No sulfate conjugates of 8-gingerol, 10-gingerol, and 6-shogaol were detected. Thus, a more sensitive method for the quantification of 6-, 8-, and 10-gingerols and 6-shogaol and their metabolites is desired to characterize the pharmacokinetics of the active ingredients of ginger in human.
In this study, we developed and validated a LC-MS/MS method for the quantification of 6-, 8-, and 10-gingerols and 6-shogaol simultaneously, with the LLOQ ranging from 2 to 5 ng/mL. We further utilized this method to analyze human plasma samples and detected low concentrations of free 10-gingerol and 6-shogaol, while most of the 6-, 8-, and 10-gingerols and 6-shogaol existed in plasma as glucuronide and sulfate metabolites. The pharmacokinetics of 6-, 8-, and 10-gingerols and 6-shogaol and their metabolites were analyzed. The half-lives of all compounds and their metabolites were between 1 and 3 h (Fig. ).
Chemical structures of 6-, 8-, and 10-gingerols, 6-shogaol, and internal standard pelargonic acid vanillylamide (PAV)