Systematic review on the anxiolytic and hypnotic effects of flower extracts in in vivo pre-clinical studies published from 2010 to 2020

Anxiety disorders are prevalent conditions in the world population, whose standard approaches include pharmacotherapy, psychotherapy, and combinations of these interventions. Different classes of psychopharmaceuticals are recommended as the first line of drugs to treat these disorders, which can have several adverse effects, treatment resistance, dependence, and drug-drug interactions making it necessary to search for new therapeutic agents. In particular, diazepam (DZP), a prototype drug from the group of benzodiazepines, has been commonly used and evaluated for its efficacy and safety in different anxiety disorders in clinical trials. DZP is also the most widely used reference standard in in vivo pharmacological assays of natural compounds. However, translating the results obtained in different rodent species and physiological anxiety tests instead of psychopathological animal models that can be of clinical application remains challenging. A systematic review of scientific articles published between 2010 and 2020 that included in vivo pre-clinical tests to define the anxiolytic, sedative and/or hypnotic effect of flower extracts is proposed. PRISMA and Rayyan were used for the selection of studies using four databases (Pubmed, Scopus, Web of Science, and QInsight), using the keywords: Animals, Anxiolytic, Diazepam, Elevated Plus Maze, Flower Extracts, Insomnia, In vivo, Mice, Open Field Test, Pre clinical and Sedative. The characteristics of anxiety studies in animal models, other studies related to locomotor activity, and the hypnotic effect of the extracts were compiled. Twenty-four articles were included, 21 of them performed the animal model of anxiety-like behavior of the elevated plus maze, seven the open field test, and six the light-dark box test. The locomotor activity was evaluated in 10 studies after the administration of the extracts to the animals to define their sedative effect, where only one defined that the extract (Matricaria chamomilla) had a sedative effect. The plants declared with this type of activity were Achyranthes aspera, Alcea aucheri, Brassica nigra, Cananga odorata, Carthamus tinctorius, Chrysanthemum indicum, Citrus aurantium, Couroupita guianensis, Echium amoenum, Erythrina berteroana, Gardenia jasminoides, Hibiscus tilliaceus, Lavandula officinalis, Lawsonia inermis, Matricaria chamomilla, Melia azedarach, Nerium oleander, Passiflora incarnata, Plumeria rubra, Salix aegyptiaca, Syzygium aromaticum, Tagetes erecta, Tilia americana. Although this review showed that some flower extracts have an anxiolytic effect as effective as diazepam, their therapeutic utility in anxiety disorders remains to be extensively demonstrated. Hence, more reliable and predictive behavioral tests and appropriate strategies for the experimental designs are needed to obtain more conclusive evidence with clinical significance.

Automated summary

Anxiety disorders are prevalent and require effective treatment approaches. Current standard approaches include pharmacotherapy and psychotherapy, but these interventions may have adverse effects and treatment resistance. This review examines the potential therapeutic effects of flower extracts in treating anxiety disorders, and suggests the need for more reliable and predictive behavioral tests to obtain conclusive evidence with clinical significance.