Abstract
Background: The demand for essential oils (EOs) has been steadily growing over the years. This is mirrored by a substantial increase in research concerned with EOs also in the field of inflammatory and neuropathic pain. The purpose of this present systematic review and meta-analysis is to investigate the preclinical evidence in favor of the working hypothesis of the analgesic properties of EOs, elucidating whether there is a consistent rational basis for translation into clinical settings. Methods: A literature search has been conducted on databases relevant for medical scientific literature, i.e., PubMed/MEDLINE, Scopus, and Web of Science from database inception until November 2, 2020, following the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) criteria for systematic reviews and meta-analyses. Results: The search was conducted in order to answer the following PICOS (participants/population, interventions, comparisons, outcomes, and study design) question: are EOs efficacious in reducing acute nociceptive pain and/or neuropathic pain in mice experimental models? The search retrieved 2,491 records, leaving 954 studies to screen after the removal of duplicates. The title and abstract of all 954 studies were screened, which left 127 records to evaluate in full text. Of these, 30 articles were eligible for inclusion. Conclusion: Most studies (27) assessed the analgesic properties of EOs on acute nociceptive pain models, e.g. the acetic acid writhings test, the formalin test, and the hot plate test. Unfortunately, efficacy in neuropathic pain models, which are a more suitable model for human conditions of chronic pain, had fewer results (only three studies). Moreover, some methodologies raised concerns in terms of the risk of bias. Therefore, EOs with proven efficacy in both types of pain were corroborated by methodologically consistent studies, like the EO of bergamot, which should be studied in clinical trials to enhance the translational impact of preclinical modeling on clinical pain research.
Highlights
Essential oils (EOs) containing components in exact proportion contributing synergically to the whole plant effect, have been used in traditional medicine for centuries since The Divine Farmer’s Materia Medica, the first text of Chinese Traditional Medicine, representing a form of combinatorial medicine (Li and Weng, 2017)
Identifying the year 1880 as this field emerged (Wood and Reichut, 1880), we found a remarkable increase in publications concerned with EOs up to 2020 (Figures 1A,B) (see (Scuteri et al, 2017a))
Modulation of the γ-aminobutyric acid (GABA) neurotransmission and blockade of neuronal voltage-gated sodium channels (Na + channels) as well as activity on serotonergic neurotransmission are proposed as mechanisms involved in the action of EOs endowed with anxiolytic and anti-nociceptive properties like bergamot essential oil (BEO) (Rombolà et al, 2017; Scuteri et al, 2018a; Scuteri et al, 2019a; Scuteri et al, 2019b; Rombolà et al, 2019; Rombola et al, 2020), lavender essential oil (LEO) (Lopez et al, 2017), and melissa (Abuhamdah et al, 2008; Awad et al, 2009)
Summary
Essential oils (EOs) containing components in exact proportion contributing synergically to the whole plant effect, have been used in traditional medicine for centuries since The Divine Farmer’s Materia Medica, the first text of Chinese Traditional Medicine, representing a form of combinatorial medicine (Li and Weng, 2017). There has been a remarkable increase in the import of EOs by the European market from 2011–2018 (Eurostat) and it is estimated that the demand for essential oils in the global market will grow by 7.5% from 2020 to 2027 (GVR, 2020) These data are mirrored by the steady increase of research on EOs that pave the way for the development of these products. The demand for essential oils (EOs) has been steadily growing over the years This is mirrored by a substantial increase in research concerned with EOs in the field of inflammatory and neuropathic pain. The purpose of this present systematic review and meta-analysis is to investigate the preclinical evidence in favor of the working hypothesis of the analgesic properties of EOs, elucidating whether there is a consistent rational basis for translation into clinical settings
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