Although hops are most famous for producing the bitter flavour in beer, this plant has been used since ancient times to treat digestive complaints and for its slight narcotic and sedative actions. The climbing nature of the herb influenced its common name, as this is derived from the Anglo-Saxon hoppan, which means ‘to climb’.
Common hops, European hops, hop strobile, hopfen, houblon, humulus, lupulus, lupulin
Botanical Name / Family
Humulus lupulus (family Cannabinaceae)
Plant Part Used
Resinous bitter principles (mostly alpha-bitter and beta-bitter acids) and their oxidative degradation products, polyphenolic condensed tannins, volatile oil, polysaccharides, mainly monoterpenes and sesquiterpenes, flavonoids (xanthohumol, isoxantholumol, kaempferol, quercetin and rutin), phenolic acids, and amino acids.
A long history of use within well-established systems of traditional medicine, together with scientific testing, have suggested that hops have significant sedative activity. A recent in vivo study found that both the extract of hops and a fraction containing alpha-bitter acids had significant sedative properties in mice. Both extracts were also found to have an antidepressant action.
Hops extract and hops oil have activity against the Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) and the fungus Trichophyton mentagrophytes var. interdigitale, but almost no activity against the Gram-negative bacterium Escherichia coli and the yeast Candida albicans. A review of the antimicrobial properties concluded that hops were also effective against the parasite Plasmodium falciparum and a range of viruses including HSV types 1 and 2, cytomegalovirus and HIV. The mechanism of anti-HIV activity is not fully understood, but it is thought that the flavonoid xanthohumol may inhibit transcription.
Hops showed significant competitive binding to alpha and beta oestrogen receptors and upregulation of progesterone receptors in vitro. Theoestrogenic activity is thought to be due to the constituent 8-prenylnaringenin, which is converted by intestinal microflora from isoxanthohumol.
POSSIBLE CHEMOPREVENTATIVE EFFECTS
A chalcone flavonoid, xanthohumol and a flavone isomer of xanthohumol found in hops act as antiproliferative agents in vitro. In vitro data has demonstrated that hops induces detoxification enzymes, in particular quinone reductase, which may contribute to its chemoprotective effects. A review concluded that this compound has the ability to protect in the initiation, promotion and progression stages of cancer.
CYTOCHROME P450 INDUCTION
Colupulone, a beta-bitter acid, was reported to induce the cytochrome P450 system and increase mRNA levels of cytochrome 2B and 3A in rats. Another study found that the flavonoids from hops inhibit the cytochrome P450 system in humans, in particular cytochromes 1A1, 1 b1, 1A2, but not 2E1 or 3A4. A recent review concluded that hops inhibits phase 1 detoxification and enhances phase two by inducing quinone reductase. The clinical significance of these findings is unknown.
Hops may demonstrate an anti-inflammatory action. The chalones, including xanthohumol, from hops significantly reduced NO by suppressing iNOS in mouse macrophage cells. Xanthohumol has also been reported to inhibit COX-1 and COX-2 activity.