Okadaic acid and its interaction with sodium, potassium, magnesium and calcium ions: Complex formation and transport across a liquid membrane

Pergamon

PII: SOO41-0101(96)00199-7

OKADAIC ACID AND ITS INTERACTION WITH SODIUM, POTASSIUM, MAGNESIUM AND CALCIUM

IONS: COMPLEX FORMATION AND TRANSPORT ACROSS A LIQUID MEMBRANE

MOHAMED BLAGHEN,’ AMINA BOUHALLAOUI,’ HAMID TALEB.’

HALIMA IDRISSI.’ FOUZIA TAGMOUTI.’ MOHAMED TALBI’ and KHADIJA FELLAT-ZARROUCK’

‘Unitb de Bloindustrie et Toxlcologie MolCculaire. Dbpartement de Biologic, Unirerslti Hasan II Ai’n-Chock. FacultC des Sciences. Km8. route Eljadida Maaril: B.P. 5366. Casablanca.

Morocco; XJnitk de Pharmacognosic. Facultk de Medecine et de Pharmacie, Casablanca, Morocco; and ‘Instltut Scxntitiquc dcs P&ha Maritimes. Casablanca. Morocco

M. Blaghen. A. Bouhallaoui, t-1. Taleb, H. Idrissi. F. Tagmouti, M. Talbi and K. Fellat-Zarrouck. Okadaic acid and its interaction with sodiutn, potassium, magnesium and calcium ions: complex formation and transport across a liquid membrane. Tosicorz 35, X43--847, 1997:--Okadaic acid, a macrocyclic: polyether compound, was shown to mediate the transfer of Na ’ , K + . ME’+ and Ca’ + ions from aqueous solution to an organic phase, with a preference for Na’

ions. A kinetic study of the transport of these ions across a liquid membrane showed that the Na ’ ion was more rapidly transported than the other ions and that the Na- ion flux was dependent on the okadaic acid concentration.

‘t’ 1997 Elsevier Science Ltd

Okadaic acid, an algal toxin which is sometimes present in seafood, is known to induce diarrhoeic shellfish poisoning (DSP). The toxin was reported and identified in 1982 (Murakami et al.. 1982), and was also isolated from a black sponge, Hulichond~ir~ okatlui.

in Japan (Tachibana et ul., 1981). More details concerning its isolation. chemistry and biological activity appeared later (Murakami et al.. 1982: Murata et al., 1982; Tachibana rf ul.. 1981; Yasumoto, 1990; Ozaki (‘1 ol., 19X7). Certain biochemical properties have been discussed more recently (Cohen rt [il.. 1990; Fernandez. 1993; Suganuma et ul., 1988). It has been demonstrated that okadaic acid is a potent tumour promoter and that it causes increased phosphorylation of several proteins and disturbance of several cellular functions, such as smooth muscle contraction, fatty acid biosynthesis, protein synthesis and catecholamine synthesis and secretion. Recently. its neurotoxic efiects. including the possible involvement of voltage-sensitive calcium channels and the excitatory amino- acid

(EAA) receptor, have been described (Fernandei, 1993).

844 M. BLAGHEh P/ (I/

In this paper, we show that okadaic acid is able to transfer Na . K , Mg’ and C’a’ ’ ions from aqueous picrate solution into an organic medium and to facilitate the transport of these cation metals through a chloroform liquid membrane model.

MATER1AL.S AND METHODS

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The interaction between Na . K ’ Mg” and C‘;I’ IOM and okadalc acid war jtutllcd using the extl-actton procedure described by FrensdorW (I 97 I ).

Five mlllilitres of an aqueous \olution. conai\ting of It) ’ M metnl picrate and 5 x IO ’ M metal nltratc. and 5 ml of ;L chloroform solution of okadalc acid at concentrationr of 0.5 x 10 ” alld I .i x IO were placed 111 a beaker, and the organic layer ~vas stirred at con\tanr speed. The rate of complex i’ormCition was monitor-ed b? measuI-ing the decrcasc in absorption at 355 nn~ of the metal pica-ate in the .tlqueow wlut~on.

Experiments on the transport of \odlum and potawum ions were carrlcd out in a cylindrical glaa cell (3 2 cm 1.~1.) containing a cylindrical glass-walled tube (2 cm i.d ) separating two aqueous phascc (phase 1 and phaw II:

SW figure?) (Behr and Lehn. 1973). Aqueous phase I ctrnsi?ted of 10 ’ M metal picratc. 0.05 M metal nitrate and 5 x IO ’ metal hydroxide in 4 ml of double-distilled water, while aqueous phase II conwted of 5 ml of double-dIstilled water. These two phases WI-e separated by 7 ml of chloroform containmg okadalc acid

concrntr,ition 01‘ 0.9 X IO Mar ISx IO M 7hc ahwrption at 355 nm of the metal picrate-transported aqueous phase II wa\ meawred at regular itme Intervals.

RESIiLTS 4hD DISCUSSION

Because of their ability to form selective complexes with various metal cations, macrocyclic polyethers have attracted attention in the fields of both chemistry and biology.

These compounds are characterized by a hydrophobic cavity in which metal cations can be selectively bound. depending ^on their ionic diameter. Antibiotic ionophores, such as monensin, contain tetrahydrofuran and tel.rahydropyran units, the former of which is thought to have potential activit] as a macrocyclic chain component because of its greater donor ability and its favourable lipophilic propertics.

The ability of okadaic acid to conlplex Na . K ’ . Mg‘ and Ca’ ’ ions wus examined by equilibration of a chloroform solution of the acid with ^an aqueous picrate solution.

The metal picrate salt. insoluble in chlorotbrm, was then extractlzd as an okadaic acid complex and the decrease in absorption of thl.: picrate in the aqueous phase used to estimate the complexing eAiciency of okadaic acid for these cations. All of the metal ions tested formed complexes, but with dilrerent ntfinities (Fig. 1 ). The order of reactivity was Na > Ca’ ’ > Mg’ ’ . K Thus, after 5 min 60% of the Nit was complexed by the acid but only 10% of the K ’ and \/Ig‘ and 20% of the Ca’ vIere complexed at this period.

The rate of complex formation is dependent on the okadaic acid concentration (Fig. 2).

In order to study the ionophoric properties of okadaic acid, we tested its ability to act as a carrier in the transport of Na + . K + . Mg’ or Ca’ ’ 101~s through a liquid membrane.

In the system used. the metal picrate in aqueous phase I moved, as a complex. through the chloroform solution contarning okadaic acid and was released into aqueous phase 11.

In this system. Na ’ . K ’ . Mg’ ’ and Ca’- ions were transported by okadaic acid into aqueous phase II with marked selectivity. the order being Na ’ > CX’ . Mg’ ’ . K Again.

sodium was transported more effecti~~ely than any of the other cations tested and transport

rate was dependent on the concentration of okadaic acid (Fig. 3): alter 10 min, the

concentrations of Na ’ transported were h x 10 7 M and 2.5 x IO ” M at okadaic acid

concentrations of 0.9 x 10 ” M and I .X Y IO ’ M. respectively. In conlrol experiments without okadaic acid, no transport occurred.

In general, ionophores may be considered as molecules with various types of backbone

containing strategically spaced oxygen atoms. This backbone is able to assume critical

conformations that concentrate oxygen atoms in it cavity into which a complexible cation

may fit more or less snugly. As with the carboxylic ionophores. the ability of okadaic acid

to extract and transport Na ’ . K . Mg’ and c’a’ ions is depcndcnt con its structural

properties. Okadaic acid shows structural similarities \vith other ionophore antibiotics

(Pointud c/ (I/.. 19X2; Sandeaux PI ol.. I%-?). Ionophores. e.g. moncnsin, alborixin and

grisonexin, like okadaic acid contain :I carboxylic group. hydroxyl groups and

X46 M. BLAGHEN 01 rrl

o.on

0 IO 20 Xl 41) 50

Time (mln)

Fig. 3. Sodium. potaatium. calcium and magneu~um ions transportea by okadaic acid.

Sodium value\ (0.0) are at oh;id;rtc aad conccntration~ of 1.X x IO ’ M and 0.Y k 10 ” M.

respectively. C‘oncentration or pota\u~um (~1). c:dcium (C) and magnchium (A) ions transported through ;I chlorolhrm bari-ler containing okadaic acid at 1.X < IO ” M

tetrahydrofuran and tetrahydropyran units, which play an important role in the transport and complex formation process.

Further studies in biological systems m the presence of Na ’ . K ’ , Mg’ and (I‘a’ + should provide additional evidence for okaclaic acid-mediated selective complex formation and transport.

A~,/\rroi~,/~,r/~c~r?lcrr/.\ -~ This stud) VG> supported bq C’N R Morocco. We arc grateful for helpf’ul discussions with Professors J. P. Vernoux and S. C. f’uwux f2to We would like to thank fSPM ibr his glt of okadalc acid.

Dr L.. houss~ and K. B. Filali I’OI their i~chnical a~crstancc and Dr .Jamal Eddinc f’or hi3 help with writing the

manuscript.

Okad,Cc Acid and Ion Transport 847 Sandceux, R., Sandeaux. J.. Garach, C. and Brun. B. (1982) ‘Transport of Na by monensin across bimolecular

lipid membranes. Bioc~lrrn~. hiopll~ .\. .,l~,itr 684, 127 132.

Suganuma. M.. Fujiki, H.. Suguri. H.. Yobhizawa. S.. Hiroto. M.. Nakayasu, M.. OJika, hl.. Wakamatsu. K..

Yamada, K. and Sugimura, T. (1988) Okadalc acid- an additIonal non phosphol-12 tetradecanoate-I 3 acetate type tumor promoter. Proc. rurf~. .3wd. SC,;. I ‘.,~.A. 85, 176% 1771.

Tachibana. K.. Schever, P. J., Tsukltani. ‘r’.. Kikuchi. M., V,m Engen, D., Cleardy. J., Gopichand. Y. and Schmith. F. J. (1981) Okadaic acid. a cytotoxic pvlyether from two marine sponges of genus I~c//ic./~orlclriri.

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