Triterpenoids from Euphorbia maculata and Their Anti-Inflammatory Effects

Euphorbia maculata is a medicinal plant of the Euphorbiaceae family, which can produce anti-inflammatory and cancer chemopreventive agents of triterpenoids. The present study reports on the bioactive triterpenoids of this plant. Two new lanostane-type triterpenoids, named (3S,4S,7S,9R)-4-methyl-3,7-dihydroxy-7(8→9) abeo-lanost-24(28)-en-8-one (1) and 24-hydroperoxylanost-7,25-dien-3β-ol (2), together with 15 known triterpene derivatives, were isolated from Euphorbia maculata. The structures of the new compounds were determined on the basis of extensive spectroscopic data (UV, MS, 1H and 13C-NMR, and 2D NMR) analysis. All tetracyclic triterpenoids (1–11) were evaluated for their anti-inflammatory effects in the test of TPA-induced inflammation (1 μg/ear) in mice. The triterpenes exhibited significant anti-inflammatory activities.


Introduction
Euphorbia maculata L. is a plant of the Euphorbiaceae family, which is widely used as folk medicine throughout the world, especially in China, Japan, and Korea [1]. Many species of the genus Euphorbia have a variety of applications in traditional Chinese medicines (TCM). E. maculata is an annual herb that is commonly used for the treatment of diarrhea, hemoptysis, hematuria, and sore swollen [2]. Extracts of this plant has an antiplatelet activity via suppressing thromboxane B2 formation [3]. Previous phytochemical investigations of E. maculata yielded tannins, flavonol glycoside, and triterpenoids [4][5][6][7].
Naturally occurring triterpenoids possesses anti-tumor, anti-inflammatory, anti-proliferative, and anti-HIV activities. Many triterpenoids of different skeletons exhibited anti-inflammatory and inhibitory activities on tumor promotion induced by TPA [8][9][10]. As many tumor promoters can cause inflammatory symptoms, the inhibitory effect against TPA-induced ear inflammation has a close correlation with the inhibition of TPA-induced tumor promotion in a two-stage carcinogenesis. Thus, we chose the medicinal plants of the genus Euphorbia (Euphorbiaceae) which contained triterpenoids to study their chemical constituents and pharmacological activity [11]. We found that the lanostane-type triterpenes of E. kansui markedly possessed the inhibitory activity against TPA-induced inflammation, and the predominant triterpene in this plant, euphol, significantly inhibited the tumor-promoting activity induced by TPA [12].
In the course of our continuing search for anti-inflammatory compounds from plants [13][14][15][16], we focused on the Euphorbia maculata due to their medicinal use and began to clarify their anti-inflammatory principles. Herein, we describe the structural elucidation of the new triterpenoids and the anti-inflammatory activities of all tetracyclic isolated triterpenoids.

Structures
Compound 1 was isolated as a white solid. Its HREIMS spectrum showed a molecular ion peak at m/z 458.  Figure S2) and HMQC spectra ( Figure S3) disclosed the existence of thirty carbons including a ketone (δ C 215.1), two olefins (δ C 156.5 and 106.2), and two oxygenated methines (δ C 80.5 and 77.5). The aforementioned data suggested that 1 was a triterpenoid ( Figure 2). In the 1 H-1 H COSY spectrum ( Figure S5 Figure S4) from H-4 and H 3 -29 to C-3, and from H 2 -6 and H 2 -11 to C-7 indicated that the two hydroxyl groups were located at C-3 and C-7, respectively. Furthermore, the HMBC correlations from both H 3 -19 and H 2 -6 to C-5, C-9, C-10, and from H-7 to C-5, C-9 and C-10, as well as the 1 H-1 H COSY cross-peaks of H 2 -6/H-7 and H 2 -11/H 2 -12 suggested that the quaternary carbon C-9 was the connectivity of a spiro center. The ketone group was substituted at C-8, which was indicated by the HMBC correlations from H 3 -30 to C-8, C-13, and C-14, and from H 2 -11 to C-8.  (Figure 2, Figure S6). The NOESY correlations between H 3 -19 and H-2β, H-6β, and H 3 -18 indicated that these protons were at the same orientation. Furthermore, the orientations of the two hydroxyl groups were deduced as β on the basis of the NOE correlations between H-7 and H-5α, H-11α, and H 3 -30, and between H-3 and H-5α, and H 3 -29. The above NOE correlations also suggested that C-9 was R configuration. The C-ring was supposed to be a boat configuration based on the NOE correlations of H-5α with H-11β and H-17α with H 3 -30, which was the same as that of spiroinonotsuoxodiol. Based on the comparison of its NMR data with that of a spiro-triterpene in the literature [32], the structure of 1 was determined to be (3S,4S,7S,9R)-4-methyl-3,7-dihydroxy-7(8→9) abeo-lanost-24(28)-en-8-one ( Figure 1).

Anti-Inflammatory
The n-hexane extract of the whole plant of E. maculata inhibited the inflammatory ear oedema induced by TPA with the ID50 (50% inhibitory dose) value of 0.8 mM. All the tetracyclic triterpenoids were evaluated with respect to their anti-inflammatory activity against TPA-induced inflammation in mice, and the inhibitory effects were compared with indomethacin, a commercially available antiinflammatory drug, as shown in Table 1. Most of the tetracyclic triterpenoids exhibited a potent inhibitory activity, with ID50 values in the range of 87.1-1087 nM/ear, of which compound 8 showed the most potent inhibitory activity higher than indomethacin (ID50 838 nM/ear). The results indicated that compounds 8, 10, and 11 with only one methyl substitution at C-4 and a double bond at C-24 in the side chain possessed a stronger anti-inflammatory activity than the other tetracyclic triterpenoids.
Another tetracyclic triterpene, euphol isolated from E. kansui possessed both anti-inflammatory and anti-tumor promoting activities. Various triterpenoids of different skeletons have been demonstrated to inhibit the tumor-promoting activities induced by TPA. The inhibitory activity of euphol was similar to lupeol (16) [34]. Thus, we concluded that most triterpenes isolated from E. maculata probably inhibited the tumor-promoting activity by TPA.

General Experimental Procedures
Optical rotations were measured on a Jasco DIP-360 polarimeter. UV spectrum was obtained on a Jasco V-550 spectraphotometer (Tokyo, Japan). FAB-MS and HR-FAB-MS were obtained using a JEOLJMS-GC mate spectrometer (JEOL, Tokyo, Japan). NMR spectra were recorded using a JEOL

Anti-Inflammatory
The n-hexane extract of the whole plant of E. maculata inhibited the inflammatory ear oedema induced by TPA with the ID 50 (50% inhibitory dose) value of 0.8 mM. All the tetracyclic triterpenoids were evaluated with respect to their anti-inflammatory activity against TPA-induced inflammation in mice, and the inhibitory effects were compared with indomethacin, a commercially available anti-inflammatory drug, as shown in Table 1. Most of the tetracyclic triterpenoids exhibited a potent inhibitory activity, with ID 50 values in the range of 87.1-1087 nM/ear, of which compound 8 showed the most potent inhibitory activity higher than indomethacin (ID 50 838 nM/ear). The results indicated that compounds 8, 10, and 11 with only one methyl substitution at C-4 and a double bond at C-24 in the side chain possessed a stronger anti-inflammatory activity than the other tetracyclic triterpenoids.
Another tetracyclic triterpene, euphol isolated from E. kansui possessed both anti-inflammatory and anti-tumor promoting activities. Various triterpenoids of different skeletons have been demonstrated to inhibit the tumor-promoting activities induced by TPA. The inhibitory activity of euphol was similar to lupeol (16) [34]. Thus, we concluded that most triterpenes isolated from E. maculata probably inhibited the tumor-promoting activity by TPA.

Plant Material
The dried whole plant of Euphorbia maculata was collected in Medicinal Plant Garden of College of Pharmacy, Nihon University. The plant was authenticated by Prof. Yasukawa, College of Pharmacy, Nihon University, Chiba, Japan. A voucher specimen has been deposited in the College of Pharmacy, Nihon University, Chiba, Japan.

Extraction and Isolation
The dried whole plant of E. maculata (1.5 kg) was ground and extracted with MeOH (3 L × 24 h × 5) at room temperature. After the combined extract was evaporated under reduced pressure at 40 • C, the residue (32. The n-hexane extract was subjected to a silica gel column, eluting with a gradient of n-hexane/EtOAc, and then monitored on TLC to obtain five major fractions. Fraction 3 (4.  Table 2. All NMR spectra of 1 have been provided in the Supplementary Material.

Animals
Experiments were performed in accordance with the guidelines of the Institutional Animal Care and Use Committee of the College of Pharmacy, Nihon University, Chiba, Japan. Female ICR mice were purchased from Japan SLC Inc., Shizuoka, Japan, and housed in an air-conditioned specific pathogen free room (22-23 • C) lit from 08:00 to 22:00. Food and water were available ad libitum.

Assay of TPA Inflammation Ear Edema in Mice
TPA (1.7 nmol, 1 µg) dissolved in acetone (20 µL) was applied to the right ear only of ICR mice by means of a micropipette. A volume of 10 µL was delivered to both the inner and outer surface of the ear. The samples or their vehicles, CHCl 3 /MeOH (1:1, 20 µL), as a control, were applied topically about 30 min before TPA treatment. For ear thickness determinations, a pocket thickness gauge with a range of 0-9 mm, graduated at 0.01 mm intervals and modified so that the contact surface area was increased to reduce the tension, was applied to the tip of the ear. The ear thickness was measured before treatment (a) and 6 h after TPA treatment (b = TPA alone; b' = TPA plus sample). The following values were then calculated: • Edema A as induced by TPA alone (b-a) • Edema B as induced by TPA plus sample (b'-a) • Inhibitory ratio (IR) (%) = [(Edema A − Edema B)/Edema A] × 100 • Each value was the mean of individual determinations from five mice. The 50% inhibitory dose (ID 50 ) values were determined by the method of probit-graphic interpolation for four dose levels.

Conclusions
In this study, we isolated two new lanostane-type triterpennes, together with 15 known triterpenoids. We evaluated the anti-inflammatory activities of all the tetracyclic triterpenoids. Triterpenoids 1-11 isolated from E. maculata exhibited potent anti-inflammatory activities. Many triterpenes with different skeletons, such as oleanae-, ursane-, lupine-, lanostane-, and multiflorane-types, inhibited the tumor promoting activity of TPA. Therefore, these triterpenes might be the candidates for cancer chemopreventive agents.