Abstract
BackgroundD-limonene and its derivatives have demonstrated potential chemopreventive and anticancer activity in preclinical and clinical studies. The aim of this scoping review was to assess and critically appraise current literature on the effect of these bioactive citrus peel compounds on breast cancer in human trials and to identify knowledge gaps for exploration in future studies.MethodsThis study followed a scoping review framework. Peer-reviewed journal articles were included if they reported the effect of d-limonene or its derivatives on breast cancer in human subjects. Articles were retrieved from academic databases – PubMed, EMBASE, CINAHL, Web of Science, and Cochrane reviews – and iteratively through review of bibliographies of relevant manuscripts. Titles and abstracts were appraised against the aforementioned inclusion criteria in a first round of screening. Through consensus meetings and full article review by authors, a final set of studies were selected. Results were reported according to the PRISMA extension for scoping reviews.ResultsOur search strategy yielded 367 records. Following screening and adjudication, five articles reporting on phase 1(n = 2), phase 2 (n = 2) and both trial phases (n = 1) were included as the final dataset for this review. Trials evaluating the effect of d-limonene (n = 2) showed it was well tolerated in subjects. One study (n = 43 participants) showed d-limonene concentrated in breast tissue (mean 41.3 μg/g tissue) and reduction in tumor cyclin D1 expression, which is associated with tumor proliferation arrest. This study did not show meaningful change in serum biomarkers associated with breast cancer, except for a statistically significant increase in insulin-like growth factor-1 (IGF-I) levels. While elevation of IGF-I is associated with increased cancer risk, the clinical implication of this study remains uncertain given its short duration. Trials with perillyl alcohol (n = 3) showed low tolerance and no effect on breast cancer.ConclusionThis review demonstrated a dearth of clinical studies exploring the effect of d-limonene and its derivatives on breast cancer. Limited literature suggests d-limonene is safe and tolerable in human subjects compared to its derivative, perillyl alcohol. Our review demonstrates the need for additional well-powered placebo-controlled trials that assess d-limonene’s efficacy on breast cancer compared to other therapies.
Highlights
D-limonene and its derivatives have demonstrated potential chemopreventive and anticancer activity in preclinical and clinical studies
While other compounds in the citrus peel have been evaluated for anticancer activity, limonene, the simplest monocyclic monoterpene, shows substantial chemotherapeutic promise because: (1) it constitutes 3.8 wt% of dry orange peel, and about 90–95% of citrus oil [9]; (2) it is fat-soluble, allowing for absorption into fat tissue, thereby permitting for the monoterpene to accumulate in the body [10]; and (3) it is rapidly metabolized in humans in a fashion similar to animal models [11]
Peer-reviewed journal articles were included in the present study if they: (1) reported on the effect of d-limonene or any of its derivatives; (2) measured breast cancer as a key outcome; (3) were conducted among human subjects; 4) employed an experimental design, with or without a comparison; and (5) were published at any time before June 20, 2020
Summary
D-limonene and its derivatives have demonstrated potential chemopreventive and anticancer activity in preclinical and clinical studies. Depending on a confluence of factors – ranging from age, cancer type, and cancer stage – clinical treatment options for breast cancer include surgical interventions, chemotherapy, hormonal, biological, and radiation therapies. These currently available therapies are invasive, associated with severe side effects, and/or are expensive to administer [2,3,4]. Citrus fruits, including lemons, limes, oranges, tangerines, and grapefruits, are widely available at low cost These fruits contain bioactive compounds – including phenols, flavonoids and terpenes – which have demonstrated chemotherapeutic properties in relation to breast cancer [5,6,7,8]. While other compounds in the citrus peel have been evaluated for anticancer activity, limonene, the simplest monocyclic monoterpene, shows substantial chemotherapeutic promise because: (1) it constitutes 3.8 wt% of dry orange peel, and about 90–95% of citrus oil [9]; (2) it is fat-soluble, allowing for absorption into fat tissue, thereby permitting for the monoterpene to accumulate in the body [10]; and (3) it is rapidly metabolized in humans in a fashion similar to animal models [11]
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