The Flavor Enhancer Maltol Increases Pigment Aggregation in Dermal and Neural Melanophores in Xenopus laevis Tadpoles

Abstract

Melanophores are pigmented cells that change the distribution of melanosomes, enabling animals to appear lighter or darker for camouflage, thermoregulation, and protection from ultraviolet radiation. A complex series of hormonal and neural mechanisms regulates melanophore pigment distribution, making these dynamic cells a valuable tool to screen toxicants as they rapidly respond to changes in the environment. We found that maltol, a naturally occurring flavor enhancer and fragrance agent, induces melanophore pigment aggregation in a dose-dependent manner in Xenopus laevis tadpoles.To determine if maltol affects camouflage adaptation, we placed tadpoles into maltol baths situated over either a white or a black background. Maltol induced pigment aggregation in a similar dose-dependent pattern regardless of background color. We also tested how maltol treatment compares to melatonin treatment and found that the degree of pigment aggregation induced by maltol is similar to treatment with melatonin but that maltol induces over a much longer time course. Last, maltol had no effect on mRNA expression in the brain of genes that regulate camouflage-related pigment aggregation. The present results suggest that maltol does not exert its effects via the camouflage adaptation mechanism or via melatoninrelated mechanisms. These results are the first to identify a putative toxicological effect of maltol exposure in vivo and rule out several mechanisms by which maltol may exert its effects on pigment aggregation. Environ Toxicol Chem 2020;39:381-395.

Cannabinoid receptor type 1 regulates sequential stages of migration and morphogenesis of neural crest cells and derivatives in chicken and frog embryos

“…Determining the effects of the CB1R agonist and antagonist ACEA and AM251 on melanophore density and morphology will provide initial insights into the mechanisms of CB1R on neural crest‐derived cells in tailbud stage frog embryos. The morphology of melanophores is a reflection of their subcellular pigment distribution (aggregated or dispersed), so any changes in the shape of these cells following treatment with ACEA and AM251 could additionally indicate whether CB1R regulates subcellular transport in this neural crest‐derived cell (Dahora et al, 2020).…”

“…Similar to neural crest cells in chicken embryos which showed a more clumped distribution following perturbation of CB1R signaling, the increase in melanophore density in frog embryos with pharmacological treatments against CB1R may result from an alteration of cell-to-cell adhesion (Elul et al, 2022). In addition, the morphology of melanophores is thought to reflect their subcellular distribution of melanin (aggregated or dispersed; Dahora et al, 2019). Melanin is transported through the melanophores via melanosomes in an acto-myosin-dependent manner (Dahora et al, 2019).…”

“…In addition, the morphology of melanophores is thought to reflect their subcellular distribution of melanin (aggregated or dispersed; Dahora et al, 2019). Melanin is transported through the melanophores via melanosomes in an acto-myosin-dependent manner (Dahora et al, 2019). Accordingly, the more stellate morphology of melanophores observed in frog embryos following modifications of CB1R signaling could, in turn, reflect increased dispersion of melanin in these cells due to alterations in acto-myosin-based transport processes.…”