Rheological and Biological Properties of Adhesive Skin Secretions from Eupsophus vertebralis (Anura: Alsodidae)

Abstract

Skin secretions from Patagonian ground frogs, Eupsophus vertebralis, have previously been reported as a potent proteinaceous adhesive with potential biomedical applications. Here, we conducted a rheological analysis indicating the mechanical robustness of these secretions, with a storage modulus ranging from 1 to 10 Pa. In addition, antimicrobial and cytotoxicity assays were performed, revealing no antimicrobial activity against both the Gram-positive and Gram-negative bacteria. The cytotoxicity results were intriguing, as three samples showed no harm, and one exhibited a severe cytotoxic effect on the human cell line MG63. These properties, as indicated by these preliminary results, reinforce their potential for practical applications in the industrial and medical sectors.

Figure 1

Skin secretions from Eupsophus vertebralis after performing the solubility protocol (see text for details): (a) viscous mucus visual aspect of the secretion before drying, (b) film formed from the dried secretion, and (c) secretion grains formed after drying. Scale bar = 500 μm.

Figure 2

Fourier transform infrared (FTIR) spectroscopy of Eupsophus vertebralis secretions. Bands of amides I and II are shown. Voucher numbers of each specimen are indicated.

Figure 3

Rheological test of the Eupsophus vertebralis secretions. Stored deformation energy (storage module) and loss deformation energy lost (dissipated) through internal friction when flowing (loss module) are indicated for each specimen.

Figure 4

Cytotoxicity assays for Eupsophus vertebralis secretions using the MG63 cell line: (a) cell viability of indirect cytotoxicity tests using an extract of the secretion, following ISO 10993-5 standard, and (b) cell viability of direct cytotoxicity tests, where cells were in direct contact with the secretion (see text for details). Cell viability is shown at 24 h for direct tests and 24 and 48 h for indirect tests. The red line indicates 70% viability.

Figure 5

Cell adhesion surface test using the MG63 cell line and Eupsophus vertebralis secretions assays to: (a, b) EVPN1370 died samples (c, d) EVPN1040 dried samples, and (e, f) controls. Fluorescence of the nuclei labelled with DAPI (left) and light microscopy (right) is shown. Scale bar = 100 μm.