Bufadienolides from parotoid gland secretions of Cuban toad Peltophryne fustiger (Bufonidae): Inhibition of human kidney Na+/K+-ATPase activity

• Ten metabolites were isolated from gland secretions of Peltophryne fustiger.
• Arenobufagin is the major bufadienolide in this toad secretion.
• Arenobufagin and bufalin were 100 times more potent than ψ-bufarenogin.

Parotoid gland secretions of toad species are a vast reservoir of bioactive molecules with a wide range of biological properties. Herein, for the first time, it is described the isolation by preparative reversed-phase HPLC and the structure elucidation by NMR spectroscopy and/or mass spectrometry of nine major bufadienolides from parotoid gland secretions of the Cuban endemic toad Peltophryne fustiger: ψ-bufarenogin, gamabufotalin, bufarenogin, arenobufagin, 3-(N-suberoylargininyl) marinobufagin, bufotalinin, telocinobufagin, marinobufagin and bufalin. In addition, the secretion was analyzed by UPLC-MS/MS which also allowed the identification of azelayl arginine. The effect of arenobufagin, bufalin and ψ-bufarenogin on Na+/K+-ATPase activity in a human kidney preparation was evaluated. These bufadienolides fully inhibited the Na+/K+-ATPase in a concentration-dependent manner, although arenobufagin (IC50 = 28.3 nM) and bufalin (IC50 = 28.7 nM) were 100 times more potent than ψ-bufarenogin (IC50 = 3020 nM). These results provided evidence about the importance of the hydroxylation at position C-14 in the bufadienolide skeleton for the inhibitory activity on the Na+/K+-ATPase.

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