Behavioral and physiological effects of acute and chronic kava exposure in adult zebrafish

Highlights

• Kava (Piper methysticum) is a medicinal plant containing kavalactones with potent neuroactive effects.

• However, their pharmacological effects and molecular targets remain poorly understood.

• Zebrafish (Danio rerio) is a new powerful model organism for neuroscience and drug discovery.

• Acute kava evoked overt sedation, elevated brain monoamines and reduced whole-body cortisol levels.

• Chronic kava evoked similar behavioral effects and upregulated neuroglial biomarker genes

Abstract

Kava kava (Piper methysticum) is a medicinal plant containing kavalactones that exert potent sedative, analgesic and anti-stress action. However, their pharmacological effects and molecular targets remain poorly understood. The zebrafish (Danio rerio) has recently emerged as a powerful new model organism for neuroscience research and drug discovery. Here, we evaluate the effects of acute and chronic exposure to kava and kavalactones on adult zebrafish anxiety, aggression and sociality, as well as on their neurochemical, neuroendocrine and genomic responses. Supporting evolutionarily conserved molecular targets, acute kava and kavalactones evoked dose-dependent behavioral inhibition, upregulated brain expression of early protooncogenes c-fos and c-jun, elevated brain monoamines and lowered whole-body cortisol. Chronic 7-day kava exposure evoked similar behavioral effects, did not alter cortisol levels, and failed to evoke withdrawal-like states upon discontinuation. However, chronic kava upregulated several microglial (iNOS, Egr-2, CD11b), astrocytal (C3, C4B, S100a), epigenetic (ncoa-1) and pro-inflammatory (IL-1β, IL-6, TNFa) biomarker genes, downregulated CD206 and IL-4, and did not affect major apoptotic genes in the brain. Collectively, this study supports robust, evolutionarily conserved behavioral and physiological effects of kava and kavalactones in zebrafish, implicates brain monoamines in their acute effects, and provides novel important insights into potential role of neuroglial and epigenetic mechanisms in long-term kava use.

Introduction

Kava kava (Piper methysticum) is a perennial plant native to the Pacific islands, with a long history of medicinal use in the region (Volgin et al., 2020). Extracts from kava roots play an important role in social rituals and traditional medicine (Shaver and Sosis, 2014; Singh, 1992), relaxing body and improving mood and sleep (Chua et al., 2016; Brown et al., 2007; Herberg, 1993; Paul et al., 2008; Singh, 2004). The main bioactive components of kava are a group of phenolic polyketones, kavalactones (Volgin et al., 2020; Wang et al., 2019), including six major pharmacologically active kavalactones - kavain, methysticin, 7,8-dihydromethysticin, yangonin, desmethoxyyangonin and 5,6-dihydrokavain (Jerome et al., 2011). Like kava extracts, kavalactones potently modulate human CNS, and can be used for alleviating anxiety, insomnia and pain (Volgin et al., 2020; Wheatley, 2010). Some of these effects can be attributed to central inhibition via positive modulation by kavalactones of gamma-aminobutyric acid (GABA)-A receptors (Chua et al., 2016).

Due to its unique and generally safe anxiolytic effects, recreational kava use is widespread worldwide (Baker, 2020; Volgin et al., 2020), showing anxiolytic, analgesic, anti-depressant and sleep-improving properties (Ooi et al., 2018; Savage et al., 2015; Shinomiya et al., 2005). However, its growing clinical and societal importance as a used and abused substance (tightly controlled in some countries worldwide) necessitates further translational research of kava CNS action (Volgin et al., 2020).

Various experimental (animal) models are a valuable tool in neuroscience and CNS drug screening (McArthur, 2010), and can be used to study neuroactive effects of kava. For example, strong sleep-enhancing and anxiolytic effects of kava have already been reported in rodents and chicks (Shinomiya et al., 2005; Smith et al., 2001), with similar action evoked by kavalactones (see (Volgin et al., 2020) for review). It is generally understood that kava lowers neuronal excitation and promotes inhibitory neurotransmitter signaling (Volgin et al., 2020). However, the exact pharmacological effects and specific molecular targets of kava and kavalactone remain poorly understood, necessitating further pre-clinical and clinical investigation.

Complementing rodent studies, the zebrafish (Danio rerio) has become a promising novel model organism in biomedical research due to genetic tractability, small size, easy maintenance, fast development and high genetic and physiological homology to humans (Volgin et al., 2019). Zebrafish are also an important tool in translational neuroscience research, possessing robust behavioral phenotypes and high sensitivity to stress and various genetic, epigenetic and pharmacological manipulations (Cachat et al., 2011; Kalueff et al., 2013; Kalueff et al., 2014; Stewart et al., 2014). Capitalizing on this powerful aquatic in-vivo vertebrate model system, here we assess pharmacological effects of kava and kavalactones on adult zebrafish behavior, neurochemistry, physiology and CNS gene expression, aiming to evaluate their potential mechanisms and targets for further clinical applications.