Carbaryl Modulates Chronobiological Behaviors via Melatonin Receptors
Authors: Glatfelter Grant , Rajnarayanan Rajendram V , Dubocovich Margarita L 
Published: June 2021

Humans are exposed to low levels of carbaryl and other carbamate insecticides found in household products, food, and water due to persistent and widespread use. Environmental and occupational exposure to carbamate pesticides is linked to metabolic disorders and sleep apnea, though it is not clear which biological targets contribute to disease pathology (Montgomery et al. 2008; James‐Todd et al., 2016; Baumert et al. 2017). Carbaryl binds to MT1 and MT2 G protein‐coupled receptors with varying efficacies and potencies as demonstrated by our team via in‐silico molecular modeling and in‐vitro bioassays (Popovska‐Gorevski et al. 2017; Jones et al. 2017 EB Abst; Glatfelter et al. 2017 EB Abst). We hypothesize that carbaryl may produce alterations in circadian rhythms through interactions with melatonin receptors that could contribute to the aforementioned disease symptomology, progression, and/or pathologies. Previous in‐vitro (1–100μM) and ex‐vivo (10 mg/kg, i.p.) experiments demonstrated specificity for competition of carbaryl for 2‐[125I]‐iodomelatonin binding to brain melatonin receptors and its ability to reach target brain areas controlling circadian rhythms in‐vivo (e.g. suprachiasmatic nucleus: SCN; Glatfelter et al. 2017 EB Abs). We tested the ability of carbaryl (10 mg/kg, i.p.) to phase shift onset of circadian running wheel activity when given at circadian time (CT) 10 (CT12 = onset of running wheel activity in constant dark) for 3 days in wild‐type C3H/HeN (C3H) mice. Our results indicate that carbaryl (0.81h ± 0.1; n=12; p<0.0001) and positive control melatonin (3mg/kg s.c.; 0.97h ± 0.2; n=4; p<0.001) significantly phase advance running wheel activity onset compared to vehicle (0.03h ± 0.04; n=7) treated controls (F2,20=18.46; p<0.05; Dunnet's Post Test). In the same paradigm, carbaryl (10 mg/kg i.p.) given 10 hrs before onset of running wheel activity in constant dark at CT 2 showed a phase delay (−1.2h ± 0.11; n=14; p<0.0001) similar to positive control melatonin (3mg/kg s.c. 1.3h ± 0.14; n=4; p<0.001) compared to vehicle (−0.12h ± 0.02; n=19) treated controls (F2,34=75.96; p<0.05; Dunnet's Post Test). These data demonstrate that carbaryl has the same periods of circadian sensitivity for phase shift at CT2 & CT10 as melatonin (Benloucif & Dubocovich 1996). A dose response curve for carbaryl (0.01 – 10 mg/kg i.p.) to phase advance circadian running wheel activity rhythms at CT10 reveals an ED50 value of 0.019 mg/kg, i.p. which is similar in magnitude to melatonin (ED50=0.024 mg/kg s.c. Dubocovich et al. 1998). Carbaryl (10 mg/kg i.p.) did not phase advance circadian running wheel activity rhythms in C3H MT1KO mice (−0.04h ± 0.04; n=18; n.s.) at CT10 compared to vehicle controls (−0.04h ± 0.03; n=19; t=0.12; n.s.) suggesting an MT1 dependent mechanism. We conclude that carbaryl phase shifts circadian activity rhythms via activation of MT1 melatonin receptors suggesting environmental or occupational exposure to this insecticide in the tested dose range could influence disease pathologies via modulation of circadian biology.Support or Funding InformationSupported by ES 023684 and UB Jacobs School of Medicine funds to MLD and RVR.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.