Rapid discovery of chemical constituents and absorbed components in rat serum after oral administration of Fuzi-Lizhong pill based on high-throughput HPLC-Q-TOF/MS analysis

Background Fuzi-Lizhong pill (FZLZP), which was first recorded in the Classic–“Taiping Huimin Heji Ju Fang” of the Song Dynasty, has been widely used to treat gastrointestinal disease in clinic for thousands of years in China. However, an in-depth understanding of the chemical constituents of FZLZP and its potential bioactive constituents is lacking. Methods A simple, sensitive and selective method of high-performance liquid chromatography coupled with quadrupole-time-of-flight high-definition mass spectrometry (HPLC-Q-TOF/MS) and automated data analysis (Agilent MassHunter Qualitative Analysis B.06.00 Workstation Software) was developed to simultaneously identify the chemical constituents of FZLZP and the absorbed prototypes as well as the metabolites in rat serum after the oral administration of FZLZP. Results Sixty-seven compounds, including alkaloids, flavonoids, triterpenes, gingerols, phenylpropanoids and volatile oil, in the FZLZP extract were tentatively characterized by comparing the retention time and mass spectrometry data and retrieving the reference literatures. Additionally, 23 prototype compounds and 3 metabolites in the rat serum samples were identified after oral administration of FZLZP, which might be the potential active components in vivo. In addition, the absorption of alkaloids decreased when Aconitum carmichaeli Debx. was in the form of combined application as a prescription compared to when it was in the form of herb powder. Conclusions Herein, the chemical constituent in vitro and the absorbed compounds in the serum of a traditional Chinese formula, Fuzi-Lizhong pill, were fully characterized using a rapid and comprehensive analysis approach based on high-performance liquid chromatography combined with quadrupole time-of-flight mass spectrometry coupled to MassHunter Qualitative Analysis software data processing approach. The results provide helpful chemical information on FZLZP for further pharmacology and active mechanism research. In view of the bioactive constitutes that basically were derived from these absorbed compounds in vivo, this work could provide a useful strategy to explore the bioactive substances of traditional Chinese medicine. Electronic supplementary material The online version of this article (10.1186/s13020-019-0227-z) contains supplementary material, which is available to authorized users.

In our previous research, we focused on the dissolution behaviour of FZLZP in vitro and the results showed that some constituents in Aconitum carmichaeli Debx. and Glycyrrhiza uralensis Fisch., such as benzoylaconine, liquiritin and glycyrrhizic acid, were dissolved well in vitro [16][17][18]. While FZLZP has the so-called active ingredients, there are no empirical data to prove their effectiveness as bioactive compounds. According to the theory of serum pharmacochemistry, while there are multiple components in herbs, only compounds that are absorbed into the blood have the possibility of showing pharmacological bioactivities [19][20][21][22][23][24]. Therefore, simultaneous identification of systematic chemical constituents in vitro and potential active components in the blood of FZLZP are indispensable.
It was reported that the main components in Aconitum carmichaeli Debx. are monoester diterpenoid alkaloids (MDAs) and diester diterpenoid alkaloids (DDAs), which are toxicity and efficacy compounds and should be highly concerned [21]. Due to the toxicity, Fuzi is usually used in combination with other herbs as a prescription. Some researcher considered the combination to cause the reduction of the absorption of toxic compounds [21,25]. As a typical combination, however, there are no detailed studies of this mechanism and the compound variations of FZLZP. The strategy of serum thermochemistry can provide us the accurate qualitative and the preliminary quantitative information for exploring the quantitative change of alkaloids and toxicity reducing mechanism.
Currently, LC-MS is widely applied for the analysis of herbal constituents in vitro and in vivo because of its superior sensitivity, selectivity and ability to conclusively identify the compounds [26][27][28][29]. In this study, an approach of high-performance liquid chromatography (HPLC) quadrupole time-of-flight mass spectrometry (QTOF-MS) based on serum pharmacochemistry was developed to identify the phytochemical constituents of FZLZP and multiple absorbed components in rat serum.

Preparation of FZLZP extract samples for LC/MS analysis
FZLZP (1.5 g) was weighed and reflux-extracted with 50 mL 70% ethanol for 1 h. Then, the filtered supernatant sample was rotary evaporated at 40 °C to a concentration of 15 mL, and was centrifuged at 5000 revolutions/min (rpm) for 5 min. The solution was filtered through a 0.22μm membrane for further analysis.

Animal handling and serum sample preparation
Eighteen male Sprague-Dawley rats (200 ± 20 g) were obtained from the Sichuan Dashuo Biotechnology Co., Ltd. and were randomly divided into three groups of 6 rats each (group A, FZLZP group for dosed rat serum; group B, Fuzi powder (FZP) group for dosed rat serum; group C, control group for blank rat serum). The animal facilities and protocols conformed to the Care and Use of Laboratory Animals published by the National Institutes of Health. The experiment was approved by the ethical committee of Chengdu University of TCM (No.20161105). The rats were housed in an animal room with a controlled environment (20-25 °C, 65-69% relative humidity, 12 h dark-light cycle), and were given water and fed normal food for 1 week before the experiment. All animals were fasted overnight before the experiments and had free access to water.
The FZLZP was dissolved in 0.5% CMC-Na and were grinded to prepare the FZLZP suspension (150 mg crude drug/mL). Fuzi powder was dissolved in 0.5% CMC-Na to prepare the FZPsuspension (23 mg crude drug/mL, the concentration of FuZi was calculated by the ratio in FZLZP). Group A was intragastric administration 1.5 g/ kg body weight of FZLZP suspension for 3 days. Group B was intragastric administration 0.23 g/kg body weight of FZP suspension for 3 days. Group C was intragastric administration with an equivalent volume of 0.5% CMC-Na. Blood samples were collected from the abdominal aorta 45 min after oral administration on the 3rd day and were placed at room temperature for 1 h until solidification. Then, samples were centrifuged at 3000 rpm for 10 min at 4 °C. All samples were stored at − 80 °C until analysis. Three times methanol was added to the 2 mL serum samples, vortexed and then, centrifuged at 12,000 rpm for 20 min. The supernatant was dried with nitrogen gas. The residue was redissolved in 50 μL methanol, vortexed and then, centrifuged at 12,000 rpm for 20 min, and the filtrate was used as the LC/MS sample. 10 µL aliquot was injected for HPLC/MS analysis.

Establishment of FZLZP database
By searching databases, such as PubMed of the US National Library Medicine and the National Institutes of Health, SciFinder Scholar of American Chemical Society and the Chinese National Knowledge Infrastructure (CNKI) of Tsinghua University, all components reported in the literature on Aconitum carmichaeli Debx., Codonopsis pilosula (Franch.) Nannf., Atractylodes macrocephala Koidz., Glycyrrhiza uralensis Fisch. and Zingiber officinale Rosc. were summarized in an Agilent PCDL software Ver. B.06.00 (Agilent Technologies Inc.) to establish a database, which includes the name, molecular formula, chemical structure and literatures of each published known compound.

Characterization of chemical constituents from FZLZP
Using the optimal conditions described above, all information on the MS data that was obtained from the robust HPLC-TOF-MS analysis, indicated the retention time and precise molecular mass and provided the MS/ MS data. The protonated molecular weights of all target compounds were calculated within an error of 5 ppm. The base peak chromatogram (BPC) of the FZLZP extract sample in positive and negative ion modes are shown in Fig. 1A, and the data were processed by the Agilent MassHunter Qualitative Analysis B.06.00 Workstation Software with the "find compounds by molecular formula" tool. A total of 73 peaks were obtained, and 67 compounds were identified or tentatively characterized by comparing the t R values and the MS fragment characteristics of the compounds.
The reference standards are summarized in Table 1 and their fragmentation mechanism are proposed in Fig. 2 Table 2. Besides, all the structures of the compounds identified are shown in Figs. 3 and 4. The deriving herb for each compound was also assigned. The majority of constituents are identified as alkaloids, flavonoids, triterpenes, gingerols, phenylpropanoids and volatile oil.

Identification of the bioactive chemical prototype constituents in rat serum
As the results of constituents in rat serum show in Table 3, by comparing the t R values and MS fragment characteristics between compounds in serum and compounds in FZLZP extract, 10 alkaloid components sourced from Aconitum carmichaeli Debx. were identified, including benzoylaconine, benzoylmesaconine, benzoylhypaconine, mesaconitine, Hypaconitine, fuziline, neoline, talatisamine, chasmanine, and 14-acetyltalatizamine. These constituents have been reported as parts of the main constituents with significant effects of analgesia, anti-inflammation, thermogenesis and increasing blood oxygen in Fuzi [34,35]. The MS data of the (+) ESI-MS spectra are shown in Table 3. For example, MS 2 spectra of compound 19 in Table 2 Table 3 Table 3 was identified as the absorbed prototype of Fuziline in rat serum. The other alkaloid components were identified in a similar way.
Six compounds sourced from Glycyrrhiza uralensis Fisch. were identified, including 3 flavonoids, namely, liquiritigenin, isoliquiritigenin, and formononetin and 2 triterpenes, namely, glycyrrhetinic acid and glycyrrhizic acid. The MS data of the (+)ESI-MS spectra are shown in Table 3. For example, MS 2 spectra of compound 48 in Table 2 Table 3 Table 3 was identified as the absorbed prototype of Isoliquiritigenin in rat serum. Furthermore, liquiritin or isoliquiritin may also have been found, but further comparison with reference compounds is needed to identify these isomers. The flavonoids and triterpenes in Glycyrrhiza uralensis Fisch. have been reported as having significant anti-inflammatory, abirritation and immunoregulation effects [36][37][38].
7-Hydroxycoumarin, atractylenolide I and atractylenolide II have been identified as bioactive chemical constituents sourced form Atractylodes macrocephala Koidz. (Baizhu) and were found as the main institutes with the effect of anti-inflammatory, antitumor and gastrointestinal regulation in Baizhu [39][40][41][42]. The MS data of the (+) ESI-MS spectra are shown in Table 3. For example, MS 2 spectra of compound 26 in Table 2 Table 3 Table 3 was identified as the absorbed prototype of 7-hydroxycoumarin in rat serum.
6-Gingerdione, 6-gingerol and 6-shogaol sourced from Zingiber officinale Rosc (Ganjiang) were identified and were reported as having obvious antioxidant, anti-inflammatory, gastrointestinal protective and antitumor effects [43,44]. The MS data of the (+) ESI-MS spectra are shown in Table 3 Table 3 was identified as the absorbed prototype of 6-gingerdione in rat serum.
One compound was sourced from Codonopsis pilosula (Franch.) Nannf. (Dangshen) and was identified as l-pyroglutamic acid. MS 2 spectra of compound 1 in Table 2 Table 3 was identified as the absorbed prototype of l-pyroglutamic acid in rat serum.

Identification of the bioactive metabolites in rat serum
Based on a comparison of the information for ions, 8 peaks were detected only in dosed serum and were assigned to metabolites. Detailed information about the elemental compositions, retention times, and the characteristic fragment ions of metabolites are shown in Table 3. Alkaloid-, phenylpropanoids-and gingerolsrelated metabolites are the main metabolic constituents of FZPLP absorbed in vivo, and the main metabolic pathways in vivo were glucuronide conjugation and glucuronide. Identification of the corresponding fragment ions was obvious. For example, compound 4 (24.357 min) in Table 3 Table 1 and compound 29 in Table 2. Therefore, the peak was identified tentatively as a glucuronide conjugation metabolite of liquiritigenin. Similarly, compound 13 (the t R 33.165 min) in Table 3 has the similar retention time compared with the reference standard 6 in Table 1 and compound 48 in Table 2. And it produced [M + H] + at m/z 433 and MS 2 yielded a major ion at m/z 257 (− 176, Da with the loss of C 6 H 8 O 6 ) in the positive ion mode. Therefore, the peak was identified tentatively as a glucuronide conjugation metabolite of isoliquiritigenin. The possible structures of metabolites were elucidated as described above. All of the structures of metabolites were identified, and the MS data of the (+) ESI-MS spectra are shown in Table 3. This article reports these metabolites of FZLZP for the first time. The bioactivities are the subject of ongoing research.

Alkaloids difference between Group A and Group B
As the result shows in Fig. 5a, 10 kinds of alkaloids were detected in Group A. Most of them were trace amounts in vivo, which indicated the alkaloids' poor absorption in the prescription. Conversely, unlike Group A, the amount of the alkaloids in vivo increased obviously in Group B (Fig. 5b). The difference indicated that the absorption amount of alkaloids in the prescription can be decreased compared to the absorption amount of alkaloids in the herb powder.

Discussion
To obtain LC chromatograms of lower pressure, greater baseline stability, better resolution and higher ionization efficiency, methanol and acetonitrile and series of concentrations of aqueous formic acid solution were prepared for analysis. The best result was achieved when the mobile phase consisted of 0.1% formic acid aqueous solution and methanol. Both positive and negative modes were investigated, and the results showed that the positive ion mode was more sensitive and could provide more information for both extract samples and serum samples analyses.
FZLZP is a formula composed under the guidance of traditional Chinese medicine theory. According to TCM theory, Aconitum carmichaeli Debx. is the "monarch drug" and the main herb in FZLZP recipe to warm middle jiao and eliminate cold. This was confirmed in this research with 10 constituents among 23 prototype components sourced from Aconitum carmichaeli Debx., which maintains the maximum bioactive compounds. Glycyrrhiza uralensis Fisch. is frequently prescribed in combination with other herbs to decrease toxicity and to increase efficacy. In this recipe, it is the "envoy drug" and is considered to be the paramount assistant herb, which can detoxify the toxicity of aconitum. In this study, we found that Glycyrrhiza uralensis Fisch. was the second most-absorbed herb. The results that some compounds absorbed well in vivo derived from Aconitum carmichaeli Debx. and Glycyrrhiza uralensis Fisch. are consistent with our previous studies that they were dissolved very well in vitro [16].
Alkaloids in Fuzi herb are the toxicity as well as the efficacy compounds. The prescriptions which contains Fuzi herb should be highly concerned. In our study, the results on the differences in alkaloids between Group A and Group B show that the amount of absorption of bioactive constituents in Fuzi can be significantly reduced when this herb is used as part of a prescription rather than used alone. We think there are two reasons.