Short- versus Long-Sarafotoxins: Two Structurally Related Snake Toxins with Very Different in vivo Haemodynamic Effects

Abstract

Sarafotoxin-m (24 amino acids) from the venom of Atractaspis microlepidota microlepidota was the first long-sarafotoxin to be identified, while sarafotoxin-b (21 aa) is a short-sarafotoxin from Atractaspis engaddensis. Despite the presence of three additional C-terminus residues in sarafotoxin-m, these two peptides display a high sequence homology and share similar three-dimensional structures. However, unlike sarafotoxin-b, sarafotoxin-m shows a very low in vitro affinity for endothelin receptors, but still has a very high in vivo toxicity in mammals, similar to that of sarafotoxin-b. We have previously demonstrated, in vitro, the crucial role of the C-terminus extension in terms of pharmacological profiles and receptor affinities of long- versus short-sarafotoxins. One possible hypothesis to explain the high in vivo toxicity of sarafotoxin-m could be that its C-terminus extension is processed in vivo, resulting in short-like sarafotoxin. To address this possibility, we investigated, in the present study, the in vivo cardiovascular effects of sarafotoxin-b, sarafotoxin-m and sarafotoxin-m-Cter (sarafotoxin-m without the C -terminus extension). Male Wistar rats were anaesthetised and mechanically ventilated. Invasive haemodynamic measurements and echocardiographic measurements of left and right ventricular function were performed. The rats were divided into four groups that respectively received intravenous injections of: saline, sarafotoxin-b (one LD50), sarafotoxin-m (one LD50) or sarafotoxin-m-Cter (one LD50). All measurements were performed at baseline, at 1 minute (+1) and at 6 minutes (+6) after injection.

Results: Sarafotoxin-b and sarafotoxin-m-Cter decreased cardiac output and impaired left ventricle systolic and diastolic function, whilst sarafotoxin-m decreased cardiac output, increased airway pressures and led to acute right ventricular dilatation associated with a decreased tricuspid annulus peak systolic velocity. Sarafotoxin-b and sarafotoxin-m-Cter appear to exert toxic effects via impairment of left ventricular function, whilst sarafotoxin-m increases airway pressures and impairs right ventricular function. These results do not support the hypothesis of an in vivo processing of long sarafotoxins.

Fig 1. Effects of the toxins on global haemodynamic indices and airway pressure.

Toxins or saline were perfused at baseline. Haemodynamic measurements were recorded at baseline and at 1 min and 6 min post-toxin. The dots represent the median and interquartile range. n = 15 for Saline group; n = 16 for SRTX-b; n = 13 for SRTX-m; n = 12 for SRTX–m-Cter. *p<0.05 versus baseline

Fig 2. Effects of the toxins on left ventricular function indices.

Toxins or saline were perfused at baseline. Haemodynamic measurements were recorded at baseline, and at 1 min and 6 min post-toxin. The left ventricular area shortening and Tei index were recorded using Doppler echocardiography. +dp/dt max and Tau were recorded using a catheter placed in the left ventricle. The decrease in left ventricular area shortening and +dp/dt max indicated impairment of left ventricular systolic function. The increased Tei index reflected impairment of global left ventricular function, whereas the increase in Tau indicated impairment of left ventricular diastolic function. The dots represent the median and interquartile range. n = 15 for Saline; n = 16 for SRTX-b; n = 13 for SRTX-m; n = 12 for SRTX–m-Cter. *p<0.05 versus baseline

Fig 3. Effects of the toxins on right ventricular function indices evaluated by Doppler echocardiography.

Toxins or saline were perfused at baseline. Haemodynamic measurements were recorded at baseline and at 1 min and 6 min post-toxin. The ratio of the right ventricle diastolic area to the left ventricle diastolic area increases in case of acute right ventricular dilatation. This dilatation is a sign of right ventricular dysfunction. The peak systolic velocity of the tricuspid annulus (S wave) is a parameter of right ventricular systolic function. A decrease in this velocity is consistent with a right ventricular systolic dysfunction. The dots represent the median and interquartile range. n = 15 for Saline; n = 16 for SRTX-b; n = 13 for SRTX-m; n = 12 for SRTX–m-Cter. *p<0.05 vs baseline