Chemical compositions and sleep-promoting activities of hop (Humulus lupulus L.) varieties.

Among natural products with sleep-promoting activity, hops have been used since ancient times as a tranquilizer and hypnotic agent. This study investigated the sleep-promoting effects of extracts of various hop (Humulus lupulus L.) varieties in invertebrate and vertebrate models. The content of α-acids, ß-acids, and xanthohumol was higher in hop 70% alcohol extracts than in hop hot water extracts. Among the alcohol extracts, Citra contained a high α-acid content (229.32 µg/mg), while Saphir showed high ß-acid and xanthohumol content (66.37 and 4.23 µg/mg, respectively). In Drosophila melanogaster, Simcoe and Mosaic water extracts and Saphir and Simcoe alcohol extracts significantly increased total nighttime sleep. Total sleep time of mice with pentobarbital-induced sleep was significantly increased by Simcoe and Mosaic water extracts and Saphir and Simcoe ethanol extracts compared to the normal group. Oral administration of Simcoe water extract and Saphir alcohol extract improved sleep in the caffeine-induced insomnia model and upregulated the mRNA expression of GABAA (gamma 2 subunit) and GABAB receptors in mouse brains. Additionally, Saphir alcohol extract significantly increased the GABA content in mouse brains. Simcoe water extract and Saphir ethanol extract modulated GABAergic signaling to improve sleep-related behaviors, including sleep duration.

GABAA Receptor-Mediated Sleep-Promoting Effect of Saaz-Saphir Hops Mixture Containing Xanthohumol and Humulone.

Hops contain flavonoids that have sedative and sleep-promoting activities such as α-acid, ß-acid, and xanthohumol. In this study, the sleep-enhancing activity of a Saaz-Saphir hops mixture was measured. In the caffeine-induced insomnia model, the administration of a Saaz-Saphir mixture increased the sleep time compared to Saaz or Saphir administration alone, which was attributed to the increase in NREM sleep time by the δ-wave increase. Oral administration of the Saaz-Saphir mixture for 3 weeks increased the γ-amino butyric acid (GABA) content in the brain and increased the expression of the GABAA receptor. As the GABA antagonists picrotoxin and bicuculline showed a decrease in sleep activity, it was confirmed that the GABAA receptor was involved in the Saaz-Saphir mixture activity. In addition, the GABAA receptor antagonist also reduced the sleep activity induced by xanthohumol and humulone contained in the Saaz-Saphir mixture. Therefore, xanthohumol and humulone contained in the Saaz-Saphir mixture showed sleep-promoting activity mediated by the GABAA receptors. The mixture of the Saaz and Saphir hop varieties may thus help mitigate sleep disturbances compared to other hop varieties.