Optimization of HPLC and MS conditions
To obtain chromatograms with good resolution of adjacent peaks, some HPLC analytical parameters including separation column, mobile phase and its elution mode were all investigated. Several trials were tried to achieve the good separation which included three kinds of C
18 reversed-phase columns (Agilent ZOR-BAX, HiQ, Kromasil) and three gradient elution systems of methanol-water, acetonitrile-water and acetonitrile-methanol-water. The ratio of acetonitrile and methanol were selected at 50 to 8 and 0.5 % ammonium acetate aqueous solution were most suitable for the eluting solvent system as well as adequate for further MS/MS analysis in all the samples. MS parameters including spray voltage, capillary temperature, sheath gas and auxiliary gas pressure were optimized by analyzed the extract of FA. The optimized analysis methods to identify the chemical constituents in FA were developed by ESI-MS/MS in positive mode. In this study, chemical constituents in the extract of FA were scanned in positive and negative ion mode. As shown in
Figure 1, it was found that the negative ion mode was more sensitive than the positive ion mode for flavonoid glycoside while the positive ion mode was more suitable for most polymethoxylated flavones.
Chromatograms of the extract of Fructus Aurantii by LC-MS/MS. (A) TIC chromatogram in positive ESI mode.(B) TIC chromatogram in negative ESI mode.(C) TIC chromatogram in negative ESI mode of MSn.(D) TIC chromatogram in ESI positive mode of MSn. (E)HPLC chromatogram at 254 nm. (F) HPLC chromatogram at 230 nm. (G) HPLC chromatogram at 280 nm
MS and UV analysis in the extract of FA
In the analysis condition, the screening and further identification of main components in the extract of FA were conducted by HPLC-ESI-MS/MS in both the positive and negative ion modes and UV chromatograms at 230, 254 and 280 nm were set to gain the full chemical information. Thirty-one components were identified tentatively by comparing their UV spectrum, molecular weight and MS fragmentation behavior and the data were listed in
Table 1.
| Peak | RT(min) | MS
| MS/MS
| Identification |
|---|
| [M+H]+ | [M-H]- | [M+H]+ | [M-H]- |
|---|
| 1 | 15.6 | 168 | - | [168]: 124 | | Synephrine |
| 2 | 18.9 | 152 | - | [152]: 108 | | N-methyltyramine |
| 3 | 20.5 | - | 741 | | [741]: 579, 433, 271 | O-triglycosyl naringenin |
| 4 | 21.9 | - | 741 | | [741]: 579, 433, 271 | O-triglycosyl flavones |
| 5 | 23.1 | - | 771 | | [771]: 609, 463, 301 | O-triglycosyl hesperetin |
| 6 | 25.0 | - | 595 | | [595]: 433, 287 | Neoeriocitrin |
| 7 | 26.2 | - | 595 | | [595]: 433, 287 | Neoeriocitrin |
| 8 | 29.8 | - | 579 | | [579]: 433, 417, 271 | Narirutin |
| 9 | 32.2 | - | 579 | | [579]: 433, 417, 271 | Naringin |
| 10 | 34.3 | - | 609 | | [609]: 463, 301 | Hesperidin |
| 11 | 37.8 | - | 609 | | [609]: 463, 301 | Neohesperidin |
| 12 | 61.9 | - | 593 | | [593]: 447, 431, 287 | Poncirin |
| 13 | 63.6 | - | 271 | | [271]: 256 | Naringenin |
| 14 | 65.9 | - | 301 | | [301]: 287 | Hesperetin |
| 15 | 70.1 | 392 | | [392]: 373 | | Trihydroxy-tetramethoxyflavone |
| 16 | 71.2 | 389 | | [389]: 374 | | Monohydroxy-pentamethoxyflavone |
| 17 | 71.5 | | 227 | | - | Seselin |
| 18 | 71.8 | 433 | | [433]: 418, 403 | | Heptamethoxyflavone |
| 19 | 72.4 | 403 | | [403]: 388, 373 | | Hexamethoxyflavone |
| 20 | 73.6 | 373 | | [373]: 358, 297 | | Pentamethoxyflavone |
| 21 | 74.4 | 343 | | [343]: 313, 285 | | Tetramethoxyflavone |
| 22 | 75.4 | 433 | | [433]: 418, 403 | | Heptamethoxyflavone |
| 23 | 76.1 | 403 | | [403]: 388, 373 | | Hexamethoxyflavone |
| 24 | 77.9 | 403 | | [403]: 388, 373 | | Hexamethoxyflavone |
| 25 | 78.4 | 343 | | [343]: 328, 313 | | Tetramethoxyflavone |
| 26 | 80.8 | 433 | | [433]: 428, 403 | | Heptamethoxyflavone |
| 27 | 82.9 | 419 | | [419]: 404, 489 | | Monohydroxy-hexamethoxyflavone |
| 28 | 83.4 | 373 | | [373]: 358, 297 | | Pentamethoxyflavone |
| 29 | 87.4 | 389 | | [389]: 374, 259 | | Monohydroxy-pentamethoxyflavone |
| 30 | 87.7 | 405 | | [405]: 390, 375 | | Hexamethoxyflavone |
| 31 | 88.8 | 433 | | [433]: 428, 403 | | Heptamethoxyflavone |
According to the literatures (
15-
18), the dominant fragmentation pathways of authentic compounds were studied. All authentic constituents displayed [M+H]
+ in positive ion mode and [M-H]
- in negative mode. As for glycosides, there were two signals produced which corresponding to the pseudomolecular ions and its protonated aglycones in negative ion mode. In this study,
O-triglycosyl and
O-diglycosyl flavonoid glycosides were identified by analysis of the fragmentation pathways in MS/MS. The molecule ion at m/z 741, a
O-triglycosyl flavonoid glycosides in negative ion mode showed MS
2 fragment ion at m/z 579 due to the loss of the glucose reside, while
O-diglycosyl flavonoid glycosides displayed MS
2 fragment ion at m/z 417 due to the loss of glucose resides. Two
O-triglycosyl naringenins, narirutin and naringin gave the major product ion at m/z 271 which was identified the protonated aglycones of these four components. The results were consistent with our previous study.
A plenty of ploymethoxylated flavones were investigated in this detected conditions. In positive mode, the pseudomolecular ions of ploymethoxylated flavones were more selective and more sensitive than in negative mode. According to their UV spectra and MS fragmentation characters (
19-
21), the pseudomolecular [M+H]
+ ion at m/z at 373, 389, 359, 403 were tentatively identified as ploymethoxylated flavones. The MS
2 fragment ion predominantly loss the different number of methyl radical and gave the ions at m/z [M-CH
3+H]
+ or [M-2CH
3+H]
+. Except the fragment of loss of methyl radical, m/z [M-CH
3-H
2O+H]
+, [M-CH
3-CO+H]
+, [M-2CH
3-H
2O+H]
+ and [M-2CH
3-CO+H]
+ were detected in the literatures. In this study, 31 components were investigated in the methanol of FA. So the analysis methods were utilized for the further identification of the biological samples after oral admhinistration of the extract of Fructus Aurantii in rats.
Analysis of the biological samples
To elucidate the chemical constituents responsible for the pharmacological activity, it is essential to study the components profile
in-vivo after administration (
22,
23). The full scanning of constituents in rat plasma, urine and feced were analyzed by the same analysis method of the extract of FA. To avoid the interference of the endogenous, various sample preparation methods including protein precipitation with acetonitrile, methanol and liquid-liquid extraction were test to optimize an efficient clean up of the biological samples for obtaining better recovery of the target compounds. Finally, liquid-liquid extraction with ethyl acetate was chosen to prepare three kinds of the biological samples due to its simple, efficient and less interference from the endogenous matrixes.
Figures 2 and
3 displayed TIC chromatograms of the blank and drug-containing biological samples in positive and negative modes. By comparing the RT values, UV spectrum and MS/MS ion fragments characteristics of the peaks with the constituents detected in the extract of FA, the parent constituents were identified and some metabolites were observed in rat biological samples. Different kinds of components detected in biological samples were summarized in
Tables 2 and
3. Compared with blank samples, 18 parent components and 11 potential metabolites were detected in the dosed rat biological samples. Although the parent and metabolites components in three kinds of biological samples were not consistent, it could be generally divided into three groups: flavonoid glycosides, their glucuronides and ploymethoxylated flavones.
As previous research shown that the major components detected in the plasma were flavonoid glycoside and their glucuronides (
24), and polymethoxylated flavones (
25) were also found absorbed
in-vivo. In dosed plasma, only three flavonoid glycosides including naringin, neohesperidin, poncirin were found, while six flavonoid glycosides were detected in rats urine samples and six in the feces. These components were marked in
Table 2. Triglycosyl naringenin was only found in feces but not in the plasma and urine samples. It can be concluded that this compound is not absorbed from intestinal tract. It is interested that ploymethoxylated flavones were detected in the plasma and urine samples. However, there were no ploymethoxylated flavones in rat feces. Therefore, they are completely absorbed. Tong
et al. (
26) investigated the pharmacokinetic of naringin, hesperidin, neohesperidin, naringenin and hesperetin in rat plasma after oral FA extract. The
Cmax and AUC of naringenin and hesperetin were higher significantly than that of flavanone glycosides. It is not glycoside but aglycone may play more important role
in-vivo.
Eleven metabolites were identified by the approach shown in
Figures 2 and
3. Five flavone glucuronides were detected as the metabolites of polymethoxylated flavones. Except naringenin glucuronide and hesperetin glucuronide, which were detected consistence with the literatures, M3, M5 and M6 were identified as metabolites of polymethoxylated flavones glucuronide. According to previous reports, the major metabolites of polymethoxylated flavones were demethylated products of the parent components and their glucuronides (
27). Components M7-M11 was identified as the demethylated products of polymethoxylated flavones. Except M4, M10 metabolites were detected in dosed plasma, while only four metabolites were investigated in the urine samples and no metabolites were detected in the feced.
TIC Chromatograms of rat biological samples after oral administration of the extract of Fructus Aurantii in positive ESI mode. (A) TIC chromatogram of the extract of Fructus Aurantii; (B) TIC chromatogram of the rat plasma after oral administration (b: blank plasma); (C) TIC chromatogram of the rat urine after oral administration (c: blank urine); (D) TIC chromatogram of the rat faces after oral administration (c: blank feces).
TIC Chromatograms of rat biological samples after oral administration of the extract of Fructus Aurantii in positive ESI mode. (A) TIC chromatogram of the extract of Fructus Aurantii; (B) TIC chromatogram of the rat plasma after oral administration (b: blank plasma); (C) TIC chromatogram of the rat urine after oral administration (c: blank urine); (D) TIC chromatogram of the rat faces after oral administration (c: blank feces).
| Peak | Component Name | TR(min) | MS
| MS/MS
| Identification | P | U | F |
|---|
| [M+H]+ | [M-H]- | [M+H]+ | [M-H]- |
|---|
| P1 | 3 | 20.5 | | 741 | | [741]: 579, 433,271 | O-triglycosyl naringenin | | | + |
| P2 | 6 | 25.0 | | 595 | | [595]: 433, 287 | Neoeriocitrin | | | + |
| P3 | 7 | 26.2 | | 595 | | [595]: 433, 287 | Neoeriocitrin | | | + |
| P4 | 8 | 29.8 | 581 | 579 | | [579]: 433, 417, 271 | Narirutin | | + | |
| P5 | 9 | 32.2 | 581 | 579 | | [579]: 433, 417, 271 | Naringin | + | + | + |
| P6 | 10 | 34.3 | | 609 | | [609]: 433,417,271 | Hesperidin | | + | |
| P7 | 11 | 37.8 | | 609 | | [609]: 433,417,271 | Poncirin | | + | + |
| P8 | 12 | 61.9 | | 593 | | [593]: 447,431,287 | Naringenin | + | + | |
| P9 | 13 | 63.6 | | 271 | | [271]: 256 | Neohesperidin | | + | |
| P10 | 14 | 65.9 | | 301 | | [301]: 287 | Hesperetin | | + | |
| P11 | 15 | 70.1 | 392 | | [392]:377, 362 | | Trihydroxy-tetramethoxyflavone | + | + | |
| P12 | 16 | 71.2 | 389 | | [389]:374, 359 | | Monohydroxy-pentamethoxyflavone | + | | |
| P13 | 20 | 73.6 | 373 | | [373]:358, 343 | | Pentamethoxyflavone | + | + | |
| P14 | 21 | 74.4 | 343 | | [343]:328, 313 | | Tetramethoxyflavone | + | + | |
| P15 | 24 | 77.9 | 403 | | [403]:388, 373 | | Hexamethoxyflavone | + | + | |
| P16 | 25 | 78.4 | 343 | | [343]:328, 313 | | Tetramethoxyflavone | + | + | |
| P17 | 26 | 80.8 | 432 | | [432]:417, 402 | | Heptamethoxyflavone | + | + | |
| P18 | 28 | 83.4 | 373 | | [373]:358, 343 | | Pentamethoxyflavone | + | + | |
| Peak | TR(min) | [M+H]+
| P | U | F |
|---|
| MS | MS/MS |
|---|
| M 1 | 22.5 | 449 | [449]: 273, 153 | + | + | |
| M 2 | 22.9 | 449 | [449]: 273, 153 | + | + | |
| M 3 | 29.4 | 535 | [535]: 359, 328 | + | | |
| M 4 | 31.5 | 354 | | | + | |
| M 5 | 31.9 | 565 | [565]: 389, 359, 328 | + | | |
| M 6 | 43.1 | 581 | [581]: 405, 390 | + | + | |
| M 7 | 58.9 | 389 | [389]: 359, 327 | + | | |
| M 8 | 62.4 | 329 | [329]: 299 | + | | |
| M 9 | 63.0 | 419 | [419]: 403, 389 | + | | |
| M 10 | 65.0 | 359 | [359]: 329, 298 | + | | |
| M 11 | 65.5 | 329 | [329]: 268 | + | | |
MS spectrum of the reference substances. (a) neohesperidin; (b) hesperidin; (c) naringin; (d) narirutin
Structures of main identified compounds from the extracts of F. aurantii