Quercetin, a natural product supplement, impairs mitochondrial bioenergetics and locomotor behavior in larval zebrafish (Danio rerio)

- Quercetin is a natural product that can have both beneficial and adverse effects.
- Zebrafish embryos exposed to quercetin displayed high survival but curved spines.
- Quercetin impacted mitochondrial bioenergetics.
- Quercetin decreased locomotion of larvae at the highest concentration investigated.
- Quercetin altered transcripts related to muscle activity, specifically myosin isoforms.

Quercetin is a natural product that is sold as a supplement in health food stores. While there are reported benefits for this flavonoid as a dietary supplement due to antioxidant properties, the full scope of its biological interactions has not been fully addressed. To learn more about the mechanisms of action related to quercetin, we exposed zebrafish (Danio rerio) embryos to 1 and 10 μg/L quercetin for 96 h starting at 3 h post fertilization. Quercetin up to 10 μg/L did not induce significant mortality in developing fish, but did increase prevalence of an upward-curved dorsal plane in hatched larvae. To determine whether this developmental defect was potentially related to mitochondrial bioenergetics during development, we measured oxygen consumption rate in whole embryos following a 24-hour exposure to quercetin. Basal mitochondrial and ATP-linked respiration were decreased at 1 and 10 μg/L quercetin, and maximal respiration was decreased at 10 μg/L quercetin, suggesting that quercetin impairs mitochondrial bioenergetics. This is proposed to be related to the deformities observed during development. Due to the fact that ATP production was affected by quercetin, larval behaviors related to locomotion were investigated, as well as transcriptional responses of six myogenesis transcripts. Quercetin at 10 μg/L significantly reduced the swimming velocity of zebrafish larvae. The expression levels of both myostatin A (mstna) and myogenic differentiation (myoD) were also altered by quercetin. Mstna, an inhibitory factor for myogenesis, was significantly increased at 1 μg/L quercetin exposure, while myoD, a stimulatory factor for myogenesis, was significantly increased at 10 μg/L quercetin exposure. There were no changes in transcripts related to apoptosis (bcl2, bax, casp3, casp7), but we did observe a decrease in mRNA levels for catalase (cat) in fish exposed to each dose, supporting an oxidative stress response. Our data support the hypothesis that quercetin may affect locomotion and induce deformities in zebrafish larvae by diminishing ATP production and by altering the expression of transcripts related to muscle formation and activity.