Centella asiatica water extract inhibits [iPLA.sub.2] and [cPLA.sub.2] activities in rat cerebellum.

Abstract

Centella asiatica (L.) Urb an is distributed widely in South America and Asia and is known as a therapeutic agent in folk medicine, capable of improving memory and treating several neurological disorders. Asiaticoside is one of the compounds found in C. asiatica leaves that is suggested to be responsible for its pharmacological potential. Phospholipase [A.sub.2] ([PLA.sub.2] is a group of enzymes that has abnormal activity in the central nervous system in some neuropsychiatric diseases. In this work, the asiaticoside present in C. asiatica water extract was quantified by HPLC analysis. We also evaluated the activity of subtypes [PLA.sub.2] in cerebellar samples from rats after C. asiatica water extract treatment using a radioenzymatic assay. Asiaticoside was the major compound (84%) found in Centella water extract. We found a dose-dependent inhibitory effect of C. asiatica water extract on the activity of [Ca.sup.2+] -independent [PLA.sub.2] ([iPLA.sub.2]) and cytosolic [PLA.sub.2] ([cPLA.sub.2]). The inhibition of these enzymes in the brain suggests that C. asiatica may be useful to treat conditions associated with increased [PLA.sub.2] activity in the brain, such as epilepsy, stroke, multiple sclerosis and other neuropsychiatric disorders. [c] 2008 Elsevier GmbH. All rights reserved.

Keywords: Centella asiatica; Umbelliferae; [PLA.sub.2]; Rat; Cerebellum; Neuropsychiatric disorders

Introduction

Centella asiatica (L.) Urban is a member of the Umbelliferae family that has been used for centuries in traditional medicine to treat psychiatric disorders, asthma, leprosy, ulcers, and eczema, and to promote wound healing (Brinkhaus et al., 2000; Chen et al., 2006; Wijeweera et al., 2006).

C. asiatica contains not only triterpene glycosides such as asiaticoside and madecassoside (Matsuda et al., 2001), but also asiatic and madecassic acids that have been identified using thin layer chromatography and mass spectrometry (Bonfill et al., 2006). Asiaticoside (Fig. 1) is transformed into asiatic acid in vivo by hydrolysis. Asiatic acid induces apoptosis and cell cycle arrest in different types of cancer (Hsu et al., 2005; Park et al, 2007).

[FIGURE 1 OMITTED]

Phospholipases [A.sub.2] ([PLA.sub.2]) are a family of key enzymes in the metabolism of phospholipids. In the brain, these enzymes preferentially cleave membrane phosphatidylcholine to release free arachidonic acid (AA) and lysophosphatidylcholine, which are important mediators necessary for memory processing (Farooqui et al., 1997). Accordingly, alterations in [PLA.sub.2] activity have been described in different neuropsychiatric disorders (Gattaz et al., 1987, 2004; Yegin et al., 2002; Forlenza et al., 2007). Different [PLA.sub.2] enzymes were identified in mammalian tissues (Kudo, 2004) and classified according to their structure, cellular function, subcellular localization and enzymatic properties (Sun et al., 2004; Farooqui et al., 2006). Stimulus-induced AA liberation is thought to be mediated mainly by secretory [PLA.sub.2] (s[PLA.sub.2]) and by cytosolic [PLA.sub.2] ([cPLA.sub.2]), whereas group VI [Ca.sup.2+] -independent [PLA.sub.2] ([iPLA.sub.2]) has been suggested to contribute to phospholipid remodeling (Murakami et al., 1998).

Our group explored the effects of C. asiatica water extract on activity of subtypes of [PLA.sub.2] in brain tissue from rats, and quantified by HPLC a possible molecule responsible for the activity. The asiaticoside present in the water extract of C. asiatica inhibited both [iPLA.sub.2] and [cPLA.sub.2] activities in rat cerebellum.

Material and methods

Cerebellum samples

Adult male Wistar rats (n = 8) (2.0-2.5 months old; weighing 250-300 g each) were obtained from the Federal University of Sao Paulo. The local Ethics Committee on Animal Experimentation approved the experimental protocol, following the international ethical principles for animal experimentation. The rats were killed by decapitation and the brain was rapidly withdrawn, the cerebellum was dissected and homogenized in 10 vol. of 5mM Tris--HCl buffer pH 7.4. Aliquots for [PLA.sub.2] activity determinations were separated and frozen at -70[degrees]C until use. Total protein levels were determined in the samples using to the method of Lowry et al. (1951).

Centella asiatica extract

C. asiatica (L.) Urban fresh plant was collected on the Campus of the Federal University of Juiz de Fora (UFJF)-Brazil, and authenticated by Dr. Fatima Regina Goncalves Salimena from the Botanic Department, UFJF. A voucher specimen (no. 24.610) is deposited at CESJ of the UFJF.

The aqueous extract was prepared by infusion of C. asiatica (200 g) in ultrapure water (41) followed by cold maceration for 24 h. The solution was filtered and then freeze-dried to yield a residue that was stored at -70[degrees]C until use. In order to carry out the radio-enzymatic assay, aqueous residue was re-suspended with 5 mM Tris-HCl buffer pH 7.4 to obtain a concentration of 0-500 [micro]g/ml.

Determination of asiaticoside by HPLC

HPLC analysis was used to determine the concentration of asiaticoside in Centella extract. Centella extract powder was dissolved in mobile phase and filtered by 0.22 [micro]m membrane (Millipore Corp., Bedford, MA, USA). The chromatographic system used consisted of a high-pressure pump (LC-10AT), a controller system (SCL-10A), a diode array detector (SPD-M10A) set at 204 nm, a degasser (DGU14A), an autoinjector (SIL-10AF) and a data processor (LC-lOAdvp) all from Shimadzu (Japan). Separation was performed on a CN column (Shimadzu; 250x4.6 m[m.sup.2] ID, 5-[micro]m particle size). Isocratic elution of mobile phase was performed using a mixture of 0.5% phosphoric acid solution and acetronitrile (1:4, v/v) and pumped at a flow rate of 2.0 ml/min. Calibration plots (weighted regression line) were obtained from linear least-squares regression analysis plotting of peak-area ratios (asiaticoside/internal standard) versus the HPLC grade asiaticoside (Carl Roth, Germany) concentrations (31.5-500 [micro]g/ml) in the column. The concentration of asiaticoside in Centella extract was calculated from the averaged peak-area ratios of the asiaticoside and internal standard (boldine - Pharmacopeia, Brazil) obtained from triplicate injections of 25 [micro]1 of Centella extract (boldine 100 [micro]g/ml).

[PLA.sub.2] subtypes activities by radioenzymatic assay

The substrate used was L-[alpha]-l-palmitoyl-2-arachidonyl-phosphatidyl-choline labeled with [1-[.sup.14]C] in the arachidonyl tail at position sn-2 ([.sup.14] C-PC) (48 mCi/mmol specific activity, Perkin-Elmer, Boston, MA, USA) previously diluted 1:10 (v/v) in a 0.14 g/ml solution of the buthylated hydroxytoluene prepared in toluol-etha-nol (1:1, v/v). Prior to reaction, [.sup.14]C-PC solution was nitrogen evaporated (0.075 [micro]Ci/sample), resuspended in 0.3mg/ml human albumin solution and homogenized by sonication.

Total homogenates of brain tissue were diluted to a protein concentration of 1.5 mg/ml with 50 mM Tris-HCl (pH 8.5 for s[PLA.sub.2] and [cPLA.sub.2] or pH 7.5 for [iPLA.sub.2]). The assay samples containing 100mM Tris-HCl buffer (pH 8.5 or 7.5), 1 [micro]M Ca[Cl.sub.2] (for [cPLA.sub.2] and i[[PLA.sub.2]) or 2mM for s[PLA.sub.2], 100 [micro]M BEL (Biomol, Plymouth Meeting, PA), 300[micro]g of protein from diluted homogenates, C. asiatica extract (0-500[micro]g/ml) and 0.075[micro] Ci arachidonyl-[1.sup.-14]C-PC. After an incubation time of 15 min at 37 [degrees]C, the reaction was stopped by adding a mixture of HCI-isopropanol (1:12, v/v). The liberated [1-[.sup.-14]C] AA was then extracted. Finally, the radioactivity of [.sup.14]C-AA was measured in a liquid scintillation counter (Tri-Carb 2100 TR; Packard, Meriden, CT, USA) and used for calculating the [PLA.sub.2] activities, which are expressed in pmol mg protein [min.sup.-1]. All experiments were performed in triplicate.

Statistical analysis

Data from [PLA.sub.2] activity determinations are reported as mean [+ or -] standard error of the mean (SEM). One-way ANOVA was followed by Bonferroni's method using Statistical Package for Social Sciences version 10.0 (SPSS Inc., Chicago, IL, USA) software. Probability level of statistical significance was set at p < 0.05.

Results

HPLC analysis of asiaticoside standard showed a single peak at 204 nm with a retention time of 0.821 min. Centella extract showed a peak with the same wavelength and retention time of the asiaticoside standard, while the retention time of boldine was 2.677 min. The concentration of asiaticoside found in Centella extract powder (250[micro]g/ml) submitted to chromatographic analysis (n = 3) was 211 [micro]g/ml, calculated from the averaged peak-area ratios of the asiaticoside standard and boldine. As the main component in this extract, the concentration of asiaticoside was 84% (w/w). Other compounds were not detected by this HPLC method.

We found a dose-dependent inhibitory effect of C. asiatica water extract (125-500[micro]g/ml) on [iPLA.sub.2] activity (Fig. 2). At 500 [micro]g/ml, the value of inhibition of [iPLA.sub.2] activity was maximal at 96%, whereas with 250[micro]g/ml the inhibition was 85% and with 125[micro]g/ml was 39%, as compared to control. Centella water extract (12.5-500[micro]g/ml) also showed a dose-dependent inhibition of [cPLA.sub.2] activity (Fig. 3). At 500[micro]g/ml, the value of inhibition of [cPLA.sub.2] activity was maximal at 77%, as compared to control (without C. asiatica water extract). Interestingly, s[PLA.sub.2] activity was undetected, probably because its activity in the cerebellum is very low, below the detection limit of our assay (0.01 pMol/mg protein/min) (data not shown).

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Discussion

In the present study, we found that C. asiatica water extract inhibited 96% and 77% of the activity of [iPLA.sub.2] and [cPLA.sub.2], respectively. The first number is especially interesting due to our previous findings that [iPLA.sub.2] is responsible for about 80% of all [PLA.sub.2] activity in the brain (unpublished results). In our experiments, we identified asiaticoside as major compound (84%) present in Centella water extract by HPLC.

The interest of C. asiatica effectiveness in the treatment of neurodegenerative disorders is increasing. Subathra et al. (2005) reported that C. asiatica prevents oxidative damage, improving antioxidant status in the brain. Kim et al. (2004) reported that asiatic acid improves acetylcholine synthesis, which is fundamental to memory processes. Kumar and Gupta (2003) reported that C. asiatica water extract dose-dependently normalized brain enzyme levels of malondialdehyde, catalase and glutathione, whereas derivatives of asiaticoside and asiatic acid showed a protective effect against beta amyloid-induced neurotoxicity (Inhee et al., 1999; Sang-sup et al., 2000).

Our findings suggest that C. asiatica may be useful in the treatment of disorders associated with an increment of [PLA.sub.2] activity in the brain. Increased brain [PLA.sub.2] activity results in profound changes in the physicochemical properties of neuronal membranes, which influence, for instance, signal transduction, synthesis and release of neurotransmitters, receptor function and neuronal viability (Sun et al., 2004). These mechanisms may underlie a number of conditions in which increased [PLA.sub.2] activity has been described, including schizophrenia (Gattaz et al., 1987; Smesny et al., 2005), epilepsy (Yegin et al., 2002), Parkinson's disease and multiple sclerosis (review in Farooqui et al., 2006).

Novel, potent and specific inhibitors of [PLA.sub.2] are emerging as potential therapeutic agents for neuroin-flammation and oxidative stress. The need for specific and nontoxic potent inhibitors provides a new impetus for research in this field. C. asiatica water extract is an excellent candidate, with pharmacological activities in brain and with a very low toxicity as attested by its long popular use as a natural product in the treatment of neuropsychiatric disorders.

Acknowledgment

The Laboratory of Neuroscience receives financial support from the Associacao Beneficente Alzira Denise Herzog da Silva.

References

Bonfill, M., Mangas, S., Cusido, R.M., Osuna, L., Pinol, M.T., Palazon, J., 2006. Identification of triterpenoid compounds of Centella asiatica by thin-layer chromatography and mass spectrometry. Biomed. Chromatogr. 20, 151-153.

Brinkhaus, B., Lindner, M., Schuppan, D., Hahn, E.G., 2000. Chemical, pharmacological and clinical profile of the East Asian medical plant Centella asiatica. Phytomedicine 7 (5), 427-448.

Chen, S.W., Wang, W.J., Li, W.J., Wang, R., Li, Y.L., Huang, Y.N., Liang, X., 2006. Anxiolytic-like effect of asiaticoside in mice. Pharmacol. Biochem. Behav. 85, 339-344.

Farooqui, A.A., Yang, H.C., Rosenberger, T.A., Horrocks, L.A., 1997. Phospholipase [A.sub.2] and its role in brain tissue. J. Neurochem. 69, 889-901.

Farooqui, A.A., Ong, W.Y., Horrocks, L.A., 2006. Inhibitors of brain phospholipase [A.sub.2] activity: their neuropharmacological effects and therapeutic importance for the treatment of neurologic disorders. Pharmacol. Rev. 58, 591-620.

Forlenza, O.V., Schaeffer, E.L., Gattaz, W.F., 2007. The role of phospholipase [A.sub.2] in neuronal homeostasis and memory formation: implications for the pathogenesis of Alzheimer's disease. J. Neural Transmission 114, 231-238.

Gattaz, W.F., Kollisch, M., Thuren, T., Virtanen, J. A., Kinnunen, P.K., 1987. Increased plasma phospholipase [A.sub.2] activity in schizophrenic patients: reduction after neuroleptic therapy. Biol. Psychiatry 22, 421-426.

Gattaz, W.F., Forlenza, O.V., Talib, L.L., Barbosa, N.R., Bottino, CM., 2004. Platelet phospholipase [A.sub.2] activity in Alzheimer's disease and mild cognitive impairment. J. Neural Transmission 111, 591-601.

Hsu, Y.L., Kuo, P.L., Lin, L.T., Lin, C.C., 2005. Asiatic acid, a triterpene, induces apoptosis and cell cycle arrest through activation of extracellular signal-regulated kinase and p38 mitogen-activated protein kinase pathways in human breast cancer cells. J. Pharmacol. Exp. Ther. 313, 333-344.

Inhee, M.J., Eun, S.J., Hwan, Y.S., Kyoon, H., Young, K.J., Keun, P.H., Sang-Sup, J., Whan, J.M., 1999. Protective effects of asiaticoside derivatives against beta-amyloid neurotoxicity. J. Neurosci. Res. 58, 417-425.

Kim, S.R., Koo, K.A., Lee, M.K., Park, H.G., Sang-sup, J.. Cha, K., Kim, Y.C., 2004. Asiatic acid derivatives enhance cognitive performance partly by improving acetylcholine synthesis. J. Pharm. Pharmacol. 56, 1275-1282.

Kudo, I., 2004. Diversity of phospholipase [A.sub.2] enzymes. Foreword. Biol. Pharm. Bull. 27, 1157.

Kumar, M.H.V., Gupta, Y.K., 2003. Effect of Centella asiatica on cognition and oxidative stress in an intracerebroventricular streptozotocin model of Alzheimer's disease in rats. Clin. Exp. Pharmacol. Physiol. 30, 336-342.

Lowry, O.H., Rowebrough, N.J., Farr, L.A., Randall, R.J., 1951. Protein measurement with the Folin phenol reagent. J,Biol. Chem. 193, 265-275.

Matsuda, H., Morikawa, T., Ueda, H., Yoshikawa, M., 2001. Medicinal foodstuffs. XXVII. Saponin constituents Gotu Kola (2): structures of new ursane-and oleanane-type triterpene oligoglycosides, centellasaponin B, C, and D, from Centella asiatica cultivated in Sri Lanka. Chem. Pharm. Bull. 49, 1368-1371.

Murakami, M., Shimbara, S., Kambe, T., Kuwata, H., Winstead, M.V., Tischfield, J.A., Kudo, I., 1998. The functions of five distinct mammalian phospholipase A2s in regulating arachidonic acid release. J. Biol. Chem. 23, 14411-14423.

Park, B.C., Paek, S.H., Lee, Y.S., Kim, S.J., Lee, E.S., Choi, H.G., Yong, C.S., Kim, J.A., 2007. Inhibitory effects of asiatic acid on 7,12-dimethylbenz [alpha]anthracene and 12-0-tetradecanoylphorbol 13-acetate-induced tumor promotion in mice. Biol. Pharm. Bull. 30, 176-179.

Sang-Sup, J., Chi-Hyoung, Y., Doo-Yeon, L., Heeman, K., Inhee, M.J., Min, W.J., Heesung, C., Young-Hoon, J., Heedoo, K., Hyeung-Geun, P., 2000. Structure-activity relationship study of asiatic acid derivatives against beta amyloid (A-[beta])-induced neurotoxicity. Bioorg. Med. Chem. Lett. 10, 119-121.

Smesny, S., Kinder, D., Willhardt, I., Rosburg, T., Lasch, J., Berger, G., Sauer, H., 2005. Increased calcium-independent phospholipase [A.sub.2] activity in first but not in multiepisode chronic schizophrenia. Biol. Psychiatry 57, 399-405.

Subathra, M., Shila, S., Devi, M.A., Panneerselvam, C., 2005. Emerging role of Centella asiatica in improving age-related neurological antioxidant status. Exp. Gerontol. 40, 707-715.

Sun, G.Y., Xu. J.F., Jensen, M.D., Simonyi, A., 2004. Phospholipase [A.sub.2] in the central nervous system: implications for neurodegenerative diseases. J. Lipid Res. 45, 205-213.

Wijeweera, P., Arnason, J.T., Koszycki, D., Merali, Z., 2006. Evaluation of anxiolytic properties of Gotukola - (Centella asiatica) extracts and asiaticoside in rat behavioral models. Phytomedicine 13, 668-676.

Yegin, A., Akbas, S.H., Ozben, T., Korgun, D.K., 2002. Secretory phospholipase [A.sub.2] and phospholipids in neural membranes in an experimental epilepsy model. Acta Neurol. Scand. 106, 258-262.

(a) Nucleo de Identificacao e Quaqntificacao Analitica (NIQUA), Faculty of Pharmacy and Biochemistry, Federal University of Juiz de Fora (UFJF), Minas Gerais, Brazil

(b) Laboratory of Neuroscience, Department and Institute of Psychiatry, Faculty of Medicine, University of Sao Paulo (USP). Sao Paulo, Brazil

* Corresponding author at: Department of Psychiatry, University of Sao Paulo. Rua Dr. Ovidio Pires de Campos, 785, Cerqueira Cesar, Sao Paulo, SP, Brazil. Tel.: + 55 11 30697283; fax: + 55 11 30698010. E-mail address: [e-mail] (W.F. Gattaz).

0944-7113/$-see front matter[C]2008 Elsevier GmbH. All rights reserved. doi:10.10l6/j.phymed.2008.02.007

N.R. Barbosa (a), (b), F. Pittella (a), W.F. Gattaz (b), (*)