Constituents from Maytenus Ilicifolia Leaves and Bioguided Fractionation for Gastroprotective Activity

Maytenus ilicifolia Mart. ex Reissek é tradicionalmente usada no Brasil para o tratamento de úlcera gástrica. O presente trabalho relata a investigação fitoquímica de um extrato etanólico de folhas de M. ilicifolia (EEMIL) visando o isolamento de constituintes que foram usados como marcadores químicos para monitorar o fracionamento de um extrato aquoso liofilizado de folhas de M. ilicifolia (LAEMIL). De EEMIL, quatro flavonóides foram isolados, compreendendo o triglicosídeo flavônico mauritianina (1), trifolina (2), hyperina (4), e epi-catequina (5). O fracionamento de LAEMIL levou a 5 frações, fornecendo um derivado tetraglicosilado de canferol (3), além do galactitol (6). LAEMIL e suas frações foram avaliadas quanto aos efeitos sobre o volume e pH da secreção gástrica em ratos. Análise por CLAE (Cromatografia Líquida de Alta Eficiência) revelou que somente frações contendo o trie tetra-glicosídeos flavônicos 1 e 3 causaram aumento significativo de volume gástrico e pH, indicando que esses glicosídeos têm importante papel sob o efeito gastroprotetor de folhas de M. ilicifolia.


Introduction
Maytenus ilicifolia Mart.ex.Reissek belongs to the Celastraceae, a pantropical family.The species is popularly known as "espinheira-santa", being found in Southern Brazil, and its leaves are traditionally used to treat dispepsy and gastric ulcers. 1 The antiulcerogenic activity of M. ilicifolia leaves is well documented.Its aqueous extract causes significant reduction in the number of gastric ulcers induced by both indomethacin and cold-restraint stress in rats.3][4] Investigation of the possible mechanism of action of LAEMIL showed that, as in the case of cimetidine, it antagonises histamine H 2 receptors, although other mechanisms cannot be ruled out. 5 M. ilicifolia leaves showed neither toxic nor teratologic effects when a lyophilized aqueous extract was administered for long periods of time (up to 3 months) and at high doses to rats and mice. 6[9][10][11] We have previously reported the phytochemical study of an infusion of M. ilicifolia leaves when three known flavonoid glycosides and a novel flavonoid tetra-glycoside were isolated. 8We have also reported the anti-inflammatory and antiulcerogenic activities of n-hexane and ethyl acetate extracts from M. ilicifolia leaves and have postulated a correlation between these pharmacological effects and flavonoids. 12Recently, Baggio and collaborators reported the potent in vivo gastroprotective properties of a flavonoidrich fraction separated from the leaves of M. ilicifolia, containing galactitol (25%), epicatechin (3.1%) and catechin (2%) as major constituents, which was correlated with the in vitro inhibition of rabbit gastric H + ,K + -ATPase activity. 13Aiming to further the investigation on the bioactive constituents from M. ilicifolia leaves we have carried out a phytochemical investigation of an ethanol extract of M. ilicifolia leaves (EEMIL) for the isolation of compounds which were further used as chemical markers to monitor an activity-guided fractionation of a lyophilized aqueous extract of M. ilicifolia leaves (LAEMIL).Finally, HPLC analyses of LAEMIL and its chromatographic fractions were carried out, aiming at establishing a correlation between gastroprotective effect and chemical composition.

Experimental
General experimental procedures 1 H and 13 C NMR spectra were registered in a Bruker DRX-600 and in a Bruker Advance DRX-400 apparatus.Mass spectra were registered in a FINNIGAN MAT90 spectrometer operating with ionization energy of 159 eV, at positive and negative modes.IR and UV-Vis spectra were registered in the spectrophotometers Shimadzu IR-408, in KBr discs, and Shimadzu UV-160A, respectively.Melting points were determined in a MQAPF-301 apparatus (Microquímica, Brazil).Column chromatography (CC) was undertaken over Macherey Naneg SC6 poliamide, silica gel Merck 60 (0.063-0.200 mm) and Sephadex LH-20 (Pharmacia).A DCC Cromatograph Buchi 670 apparatus was employed for countercurrent chromatography.Silica gel chromatofoils 60 F 254 (Merck) were used for TLC analyses.

Plant material
Leaves of M. ilicifolia were collected from native populations, at the municipality of Lapa, State of Paraná, Brazil, by the agricultural engineer Paulo Guilherme Ribeiro, Instituto Agronômico do Paraná -IAPAR, on June 1999.A voucher specimen was deposited at the Herbarium of the Universidade Federal de Londrina, Londrina, State of Paraná, Brazil (code number FUEL 21881).After drying at room temperature for 5 days, the leaves were ground in a knife mill.
Isolation of compounds 1, 2, 4 and 5 from EEMIL EEMIL (191.0 g) was obtained by percolation of the dried powder from M. ilicifolia leaves (959 g) after previous sequential extraction with n-hexane and ethyl acetate.A portion of EEMIL (24 g) was submitted to chromatography over Sephadex LH-20 columns (12 × 2 g, each column) eluted with methanol; fractions were combined into 6 groups according to their TLC analysis.Group 2 (fractions 7-11; 4.4 g) was chromatographed on a poliamide column eluted with water followed by water:methanol solutions with increasing contents of methanol (20-70%) and finishing with methanol.The collected fractions (298, 25 mL each) were combined according to their TLC analysis.Fractions 14-191 (1.3 g; eluted with water:methanol, 4:1) were dissolved in methanol (25 mL), filtered and injected onto a DCC apparatus.The lower layer of a mixture of chloroform:methanol:water, (8:10:5), thoroughly equilibrated in a separation funnel by repeated vigorous shaking, was used as stationary phase.The upper layer of this mixture was used as mobile phase and it was pumped into the column at a flow-rate of 0.5 mL/min affording 234 fractions (25 mL each).The DCC fractions were appropriately combined and after recrystallization (methanol:acetone, 1:1) afforded compound 1 (380 mg).Group 4 (fractions 15-21; 4.7 g) from the initial Sephadex LH-20 column, after successive injections of aliquots (4 × 1.0 g) onto the DCC apparatus employing the same system as described here, and combination of these fractions according to TLC profiles, afforded 7 groups.Re-chromatograhy on Sephadex LH-20 columns and/or recrystallizations of fractions 2, 3 and 4 afforded compounds 2 (20 mg, recrystallization from methanol), 4 (12 mg, recrystallization in methanol) and 5 (540 mg, recrystallization from water).

Preparation of LAEMIL
LAEMIL was prepared according to the traditional use, as described by Carlini. 2 Boiling water was added to dried leaves powder (400 g) of M. ilicifolia, in the proportion of 3 g leaves:100 mL water and the flask was kept covered for 15 min.The aqueous extract was separated by filtration in a Buchner funnel and was lyophilized, yielding 78 g (19.5%).

HPLC analysis of LAEMIL and fractions F1 -F 5
Analyses were carried out on a Merck-Hitachi apparatus (Germany) composed of pump L6200-A, automatic injector AS-2000A, UV-Vis detector L-4250 and integrator D-2500.An ODS column (150 x 4.0 mm, i.d. 5 mm) was employed (Merck Darmstadt, Germany), at a temperature of 40 °C and flow rate of 1.0 mL/min.UV-Vis detection was set at 254 nm.A linear gradient of water (A) and methanol (B) was employed (0−35 min, 0-90% B) followed by 10 min of isocratic elution.Solvents used were of HPLC grade (Merck Darmstadt, Germany) and were degassed by sonication before use.Samples were dissolved in methanol to concentrations of 3.0 mg/mL (LAEMIL) and 1 mg/mL (F1-F5 and compounds 1-5), under sonication, for 15 min.After centrifugation at 10,000 r.p.m., the sample solutions (20 mL) were automatically injected onto the HPLC apparatus.

Animals
Male Wistar rats (3-4 months age) weighing 300-350 g were provided by Animal House of the Departamento de Psicobiologia, Universidade Federal de São Paulo (UNIFESP) and were kept in polypropylene cages (32 × 40 × 18 cm, 4 animals per cage) in rooms with 12 h light/ dark cycle (lights on at 6:00 a.m.), at controlled temperature (23 ± 2 °C).Food and water were available ad libitum.The Committee of Ethics in Research of UNIFESP approved the experimental protocol (CEP 297/00).

Determination of gastric secretion volume and pH
To groups of 7 or 8 rats, which were fasted overnight before experiments, were administered (i.p.) water (control group), LAEMIL (140 mg/kg) and fractions (F1 -F5) from poliamide column (14 mg/kg each).After 1 h, the animals were sacrificed in a CO 2 chamber; their stomachs were ligated 2 cm below the pylorus and a small incision was made near the pylorus to collect the gastric juice.The volume was measured and pH determinations were done by using pH indicator paper strips (Spezialind.Kator, pH 2.5-4.5 and 4.0-7.0,Merck, Darmstadt).

Statistical analyses
One-way ANOVA method, followed by multiple comparisons was used to analyze the results.The statistical significance considered was p < 0.05 (confidence limit: 95%).

Results and Discussion
EEMIL was initially submitted to chromatography on a Sephadex LH-20 column and the fractions obtained were rechromatographed on poliamide columns and on a DCC apparatus to yield compounds 1, 2, 4 and 5 (Figure 1).We have previously isolated one of these compounds from an infusion of M. ilicifolia leaves, the known tri-glycoside kaempferol   4) and epi-catechin (5) were recently described for this species. 10,13][16] LAEMIL was prepared according to the traditional use of the species, as described by Carlini, 2 and was submitted to chromatography on a poliamide column eluted with a gradient of water and methanol, affording 5 fractions (F1 -F5).On concentration of F1, the poliol galactitol (dulcitol) (6) crystallized out, being identified as the major constituent and representing about 75% of LAEMIL.F2 and F3, after successive fractionations on Sephadex LH-20 and silica gel columns, besides recrystallization, afforded the previously known tri-glycoside 1 along with the tetra-glycoside kaempferol which, when firstly isolated from M. ilicifolia leaves, represented a novel compound and was fully characterized, chemically and spectrometrically. 8AEMIL and the fractions from the poliamide column (F1 -F5) were analyzed by TLC and RP-HPLC, employing compounds 1-5 as chemical markers.Flavonoid glycosides 1 and 3 showed close retention times (RT = 21.75 and 21.66 min) when injected separately, while for 2, 4 and 5 very distinct peaks were observed (RT = 24.22,22.75 and 14.92 min, respectively).A mixture of compounds 1-5, analyzed in the same conditions, displayed only 4 peaks with superposition of the signals of 1 and 3 (RT = 21.96min).The HPLC fingerprint obtained for LAEMIL revealed an intense peak at 21.78 min, corresponding to the coelution of 1 and 3, besides peaks at 24.50, 22.86 and 15.07 min, which were attributed to compounds 2, 4 and 5, respectively.HPLC chromatography profiles registered for F1 -F5 (Figure 2), followed by coinjection of each fraction with compounds 1-5, showed that F1 contains none of the chemical markers, a result further confirmed by the absence of flavonoid spots on TLC plates.On the other hand, F2 and F3 showed intense peaks with RT at 21.72 and 21.75 min, corresponding to the kaempferol glycosides 1 and 3. Trifolin (2), hyperin (4) and epi-catechin (5) showed more intense peaks in F4 (RT 24.47, 22.70 and 14.90 min, respectively) than in F5 (RT = 24.55,22.83 and 14.96 min).Proanthocyanidins were detected by TLC (spray reagent: 1% vanillin-methanol solution; eluent: 8% hydrochloric acid-methanol) in fractions F4 and F5, but were not isolated in the present investigation although previously reported in M. ilicifolia. 18AEMIL and the fractions derived from it (F1 -F5) were evaluated in rats for their effects on gastric secretion volume and pH (Table 1).A significant increase in gastric secretion volume and pH was observed for LAEMIL and these data were higher for F2 and F3 though they had been assayed in doses ten times smaller to that of LAEMIL.F1 and F4 did not differ significantly from the control group.In its turn, F5 increased the gastric secretion volume but no significant effect was observed on the pH.] LAEMIL was prepared according to Carlini's recipe 2 and the evaluation of the gastric secretion volume and pH was carried out at his own laboratory confirming its possible gastroproptective and antiulcerogenic effects.

Conclusions
The flavonoid tri-and tetra-glycosides 1 and 3 obtained from a poliamide column of LAEMIL, and that are present in the active fractions F2 and F3, may be the main phenolic constituents responsible for the gastroprotective effect of M. ilicifolia leaves.These two phenolics can be considered as the chemical and pharmacological markers for an aqueous extract of M. ilicifolia leaves and their signals clearly stand out in its HPLC chromatography profile.Compounds 2, 4, 5 and proanthocyanidins (condensed tannins) would make a less important contribution to LAEMIL gastroprotective effect since they have been shown to be predominant in F4 and F5 which have not disclosed significant activity on gastric volume and pH of rats.Finally, a contribution of galactitol for the gastroprotective/antiulcerogenic effect of this plant species should not be underestimated once it is the major constituent of LAEMIL (75%) and therefore could influence the absorption of the active compounds, since it is used in the production of slow release microcapsules of antiulcer drugs.

Figure 1 .
Figure 1.Chemical structures of compounds isolated from M. ilicifolia leaves.For the isolation of 1a and 1b, see Leite et al. 8 (2001).

Table 1 .
Effect on gastric secretion volume (mL) and pH of rats pretreated (i.p.) with LAEMIL and F1 -F5 Statistically different from control group (p < 0.05). a