Apigenin is a member of a group of plant compounds known as flavonoids. Like luteolin, nobiletin, and tangeretin, apigenin is classified as a flavone. Apigenin occurs in many plants and is relatively abundant in celery, artichoke, parsley, and chamomile.
With over 6,000 flavonoids identified so far, what makes apigenin stand out?
Early Research with Apigenin
Investigation into apigenin’s properties began in the 1980s. In 1984, it was reported that apigenin inhibited platelet aggregation by depressing the cyclooxygenase (COX) pathway, which is involved in inflammation.1 During the same year, it was reported that apigenin inhibited the aromatization of testosterone and androstenedione to estrogens.2 This was confirmed in 1999 in a study that found the greatest aromatase-inhibitory property for apigenin out of 28 flavonoids tested.3
It was also demonstrated in early research to inhibit the release of histamine from basophils, a type of white blood cell.4 Additionally, apigenin was shown to have an antiviral effect against herpes simplex 1 and 2.5
The Many Anti-Cancer Properties of Apigenin
Early evaluation of apigenin’s potential anticancer properties found potent antiproliferative effects against human breast cancer cells in vitro.6 The flavonoids’s inhibitory effect against the formation of hydrogen peroxide and 8-hydroxy-2′-deoxyguanosine (a measure of oxidative stress) has been suggested as contributing to its cancer preventive effects.7
In human anaplastic thyroid cancer cells, apigenin induced apoptosis (programmed cell death) and inhibited cell growth, leading the researchers to conclude that “Apigenin may provide a new approach for the treatment of human anaplastic thyroid carcinoma for which no effective therapy is presently available.”8 Apigenin has also induced apoptosisin human leukemia cells,9 cervical carcinoma cells10, neuroblastoma,11 gastric,12 liver13, lung14, and prostate cancer cells.15
In a study of human pancreatic cancer cells, pretreatment with apigenin enhanced the antiproliferative effects of chemotherapeutic drugs.16 “Apigenin alone induced cell death in two aggressive human pancreatic cancer cell lines,” noted study coauthor Elvira de Mejia. “But we received the best results when we pretreated cancer cells with apigenin for 24 hours, then applied the chemotherapeutic drug gemcitabine for 36 hours.”17
An investigation of the association between the intake of five common dietary flavonoids and the risk of ovarian cancer reported that only apigenin appeared to have an impact.18 Womenwhose intake was among the top one-fifth of a group of 1,141 cases and 1,183 matched controls had a 28% lower adjusted risk of the disease compared with those whose intake was among the lowest fifth.
In one study, patients who had undergone surgery for colon cancer or polyps were treated with a combination of apigenin and epigallocatechin-gallate (a flavonoid found in green tea) or received no supplementation. After three to four years, there were no incidences of cancer recurrence among flavonoid-treated patients compared with a 20% rate among untreated subjects.19
In a review of apigenin’s impact on gastrointestinal cancers, É. C. Lefort and J. Blay observed that “Apigenin has been shown to inhibit cell growth, sensitize cancer cells to elimination by apoptosis, and hinder the development of blood vessels to serve the growing tumor. It also has actions that alter the relationship of the cancer cells with their microenvironment. Apigenin is able to reduce cancer cell glucose uptake, inhibit remodeling of the extracellular matrix, inhibit cell adhesion molecules that participate in cancer progression, and oppose chemokine signaling pathways that direct the course of metastasis into other locations. As such, apigenin may provide some additional benefit beyond existing drugs in slowing the emergence of metastatic disease.”20
Apigenin Helps to Eliminate Parasites
The tropical disease known as Leishmaniasis affects over 12 million people worldwide. Apigenin has been shown to help destroy the protozoa that cause the disease by several mechanisms, indicating that it could be useful in this widespread and neglected disease.21 Orally administered apigenin decreased parasite load and lesion size in mice infected with cutaneous Leishmaniasis without otherwise impacting the animals’ overall health.22
The Neurological Effects of Apigenin
The calming effect of chamomile tea may be due to the presence of apigenin. In 1990, researchers in Argentina reported that some flavonoids have an effect on the central nervous system, including apigenin.23 In 2015, a team from Brazil identified the ability for apigenin to improve neuron formation and connectivity in research involving human stem cells.24 Researchers Steven K. Rehen and colleagues observed an increase in the number of neural progenitor cells and connections in treated versus untreated cells and concluded that apigenin acts through estrogen receptor signaling.
Apigenin for the Skin and Hair
Significantly, apigenin and apigenin 7-O-beta-glucoside have been found to penetrate not only the skin surface, but into deeper skin layers, which implies that the flavones may have more than a cosmetic effect on the skin.25 Indeed, apigenin was recently found to promote collagen synthesis, which decreases in association with skin aging, in cell cultures and in mice.26
Apigeninhas also shown promise for supporting hair growth.27 Evaluation of the effects of apigenin in human epidermal keratinocytes resulted in a decrease in androgen-inducible TGF-beta1, which mediates hair growth suppression in androgenetic hair loss, while increasing the proliferation of epidermal keratinocytes and dermal papilla cells. The researchers concluded that “…[t]hese findings suggest that apigenin, which is known to have antioxidant, anti-inflammatory, and anti-tumor properties, stimulates hair growth through downregulation of the TGF-beta1 gene.”
The majority of research involving apigenin has revealed complex and diverse cellular and molecular effects. It is to be hoped that the positive findings revealed over the past decades will stimulate clinical trials to evaluate the potential benefits of this most promising flavonoid.
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