Possible involvement of Fas/FasL-dependent apoptotic pathway in α-bisabolol induced cardiotoxicity in zebrafish embryos

Highlights

• α-Bisabolol induces developmental toxicity in zebrafish embryos.

• α-Bisabolol has adverse effects on the cardiac development in zebrafish embryos.

• α-Bisabolol triggers apoptosis in the zebrafsh heart.

• α-Bisabolol alters the expression of cardiac development-related genes.

Abstract

α-Bisabolol, an unsaturated monocyclic sesquiterpene alcohol, is a common ingredient in many pharmaceuticals and personal care products (PPCPs). Despite being widely used, little is known about its toxic effects on organisms and aquatic environment. In this study, we investigated the developmental toxicity of α-Bisabolol, especially its effects on the cardiac development using zebrafish embryos as a model. Embryos at 4 h post-fertilization (hpf) were exposed to 10, 30, 50, 70, 90, and 100 μM α-Bisabolol until 144 hpf. α-Bisabolol caused phenotypic defects and the most striking one is the heart malformation. Treatment of α-Bisabolol significantly increased the cardiac malformation rate, the SV-BA distance, as well as the pericardial edema area, and reduced heart rate in a concentration-dependent manner. Notably, considerable numbers of apoptotic cells were mainly observed in the heart region of zebrafish treated with α-Bisabolol. Further study on α-Bisabolol induced apoptosis in the zebrafsh heart suggested that an activation of Fas/FasL-dependent apoptotic pathway. Taken together, our study investigated the cardiotoxicity of α-Bisabolol on zebrafish embryonic development and its underlying molecular mechanism, shedding light on the full understanding of α-Bisabolol toxicity on living organisms and its environmental impact.

Introduction

α-Bisabolol is a natural monocyclic sesquiterpene alcohol, isolated from several plants including arnica, sage, and chamomile and has been demonstrated to have anti-inflammatory, antimicrobial, antinociceptive, anti-tumor, and pro-apoptotic properties (Barreto et al., 2016; Quintanilha et al., 2017; Popovic et al., 2014; Leite et al., 2018; Cavalieri et al., 2011; Kim et al., 2011a). Because of its diverse biological activities, α-Bisabolol is known to be a common additive in over 1000 pharmaceuticals and personal care products (PPCPs), including dental care products, moisturizing skin care products, sunscreens, antiperspirants, makeup products, baby lotion, household cleaners and detergents, anti-inflammatory and anti-irritant pharmaceuticals (Fiume, 2017; Bhatia et al., 2008; Russell and Jacob, 2010).

In recent years, concerns for PPCPs that may contain environmentally hazardous ingredients have been raised due to their universal consumption and improper disposal (Yang et al., 2017). PPCPs are generally released into aquatic environments through domestic wastewater, hospital discharges, and manufacturer disposal (Dai et al., 2015). Although α-Bisabolol is a widely used ingredient of PPCPs, little is known about its toxic effects on in vivo organisms and aquatic environment. European Chemicals Agency (ECHA) reported that α-Bisabolol is hazardous to aquatic environment. Based on the previous studies in mammals, the oral LD₅₀ of α-Bisabolol in mice and rats is approximately 14 g/kg and the intraperitoneal LD₅₀ in mice is 0.633 g/kg (Bhatia et al., 2008). α-Bisabolol exhibits slight developmental and maternal toxicity on mammals, such as reduction in body weight gains and in number of live fetuses (Bhatia et al., 2008). Moreover, α-Bisabolol shows cytotoxicity (Corpas-Lopez et al., 2016; Rigo and Vinante, 2016). Recently, accumulating studies indicated that α-Bisabolol has pro-apoptotic activity. It has been reported that α-bisabolol binds to the pro-apoptotic Bcl-2 family protein BID, thereby induce apoptosis (Darra et al., 2008). In human acute leukemia cells, α-Bisabolol disrupts the mitochondrial membrane potential and triggers apoptosis (Cavalieri et al., 2011). α-Bisabolol induces dose- and time-dependent apoptosis in human liver carcinoma cells via a Fas-related pathway (Chen et al., 2010). Notably, previous studies showed that α-Bisabolol is able to selectively induce apoptosis (Cavalieri et al., 2009), suggesting its toxic effects may vary in different models and more efficacious toxicity investigation is in desperate need.

Zebrafish (Danio rerio) is a prominent model for developmental and toxicological studies (Dumitrescu et al., 2017; Li et al., 2017; Raimondo et al., 2014; Ellis et al., 2014; Liu et al., 2016; Al-Habsi et al., 2016), especially suitable for investigating cardiovascular development and cardiotoxicity (Sarmah and Marrs, 2016; Peterson and Macrae, 2012; Hamilton et al., 2014). One major advantage with this animal model is that zebrafish embryos are not completely dependent on a functional cardiovascular system for their development. They are able to survive the first 7 days of their development without cardiovascular function. Cardiac defects do not cause immediate lethality as in many vertebrate models, allowing the analysis of embryos with severe cardiovascular defects (Stainier, 2001). Moreover, the transparency of the zebrafish embryos permits cardiac development and abnormalities to be readily observed (Heideman et al., 2005). Therefore, zebrafish model was used in this study to investigate the toxic effects of α-Bisabolol, a widespread ingredient of PPCPs.

In the present study, we utilized zebrafish embryos as a model to study the developmental toxicity of α-Bisabolol. As a result, its toxic effects on the heart were revealed. Our findings suggested that α-Bisabolol caused the cardiotoxicity through an activation of Fas/FasL-dependent apoptotic pathway in zebrafish embryos.