Pomegranate & Nasturtium for Chemoprevention

Posted: May 2021
Author: Phil Rasmussen |  M.Pharm., M.P.S., Dip. Herb. Med.; M.N.I.M.H.(UK),  F.N.Z.A.M.H. 
 

The health promoting and medicinal properties of pomegranate have been intensively researched over the past decade, and it seems that the more scientists look the more they are finding about this famous fruit.  This month, we thought it useful to talk about some of the research on this plant as well as that on nasturtium, a plant grown here in New Zealand, of relevance to both a preventive and treatment strategy for patients with or at risk of developing prostate cancer.

Pomegranate (Punica granatum), was one of the earliest fruits from warmer parts of the world to become popular in Europe. Native to the Middle East, it is used traditionally in the treatment of dysentery and diarrhoea. Recent studies have shown it to have benefits also in treating numerous other conditions, due in part to its antioxidant, anti-inflammatory, antimicrobial and anticancer properties^{(1, 2, 3)}.

Multiple therapeutically active polyphenols are found in the fruits of pomegranate, including anthocyanins and anthocyanidins, flavones, flavonoids and flavonols. The rind or peels, which are often discarded when juice products are prepared, are also rich in useful phytochemicals and have a high content of hydrolysable ellagitannins such as punicalagin, ellagic acid and punicic acid.

Phytomed’s Pomegranate extract is made using both the dried inner fruit and rind of Punica granatum, but we extract these two plant parts separately using different methods to try and optimize the phytochemical content of each extract, before combining them in a ratio of one part rind to two parts of fruit, to produce an extract closely resembling the fresh whole fruit itself.

Anticancer properties

Dietary factors are increasingly linked with the risks of certain cancers^{(4, 5, 6)}. While the incidence of prostate cancer in Asian countries is low compared to the West, this incidence increases by as much as 20-fold in Asian immigrants to the United States. Their adoption of a Western diet, a reduced intake of soy, tea, fish, fruits and vegetables, and increased intake of red meat and fat-rich foods, are thought to be largely contributory^{(7, 8)}.

Many foods rich in polyphenols have been associated with cancer prevention, effects attributable largely to their antioxidant and free radical scavenging properties.  Pomegranate is one of these, and anti-cancer effects have been measured in vitro for pomegranate fruit extracts using a wide range of different cancer cell lines, including ovarian⁽⁹⁾, bladder⁽¹⁰⁾, thyroid⁽¹¹⁾, breast⁽¹²⁾ and prostate cancer, and multiple melanoma⁽¹³⁾.

Flavonoid-rich polyphenol fractions have been reported to exert anti-proliferative, anti-invasive, anti-inflammatory and other anti-cancer actions in prostate cancer cells in vitro and in animal studies^{(2, 14)}. Pomegranate extracts also have anti-angiogenic activities⁽¹⁵⁾, and may suppress the final steps of carcinogenesis and metastasis^{(5, 16, 17)}.

There is growing evidence of an influence of the gut microbiota on prostate cancer initiation and/or progression mechanisms through the regulation of chronic inflammation, apoptotic processes, cytokines, and hormonal production⁽¹⁸⁾. Ellagitannins are bioactive polyphenols and a principle component of pomegranate peels, and other foods such as seeds, nuts and berries with chemopreventive potential against prostate and other cancers. Too large to be absorbed into the bloodstream intact, they are partially hydrolyzed in the gut to ellagic acid. Ellagic acid and its metabolite urolithin A, produced by colonic microflora, have demonstrated significant antioxidant and anticancer effects, including antiproliferative and apoptotic activities^{(19, 20)}.

At least 6 clinical trials involving prostate cancer patients have been undertaken, and while these suggest daily ingestion of pomegranate extracts can produce a significant slowing of PSA increase^{(2, 21, 22, 23, 24)}, further trials with larger patient numbers and longer treatment durations are required.

A recent review has also found potential applications to help protect against breast cancer⁽¹²⁾. This is supported by a significant number of studies including reports that pomegranate extracts induce cell cycle arrest in the G0/G1 phase, and induce cytotoxicity in a dose- and time-dependent manner. Inhibitory effects of pomegranate juice on bladder cancer development, have also been reported recently in rats⁽¹⁰⁾. Correction of the expression of pro-inflammatory cytokines and suppression of angiogenesis were associated with these benefits.

Nasturtium (Tropaelum majus)

This plant also has outstanding antioxidant activity due to its rich content of phenolic compounds, including anthocyanin and vitamin C.  Glucosinolates are also key constituents, which are hydrolysed to isothiocyanates which then act as potent inducers of phase II detoxifying enzymes and subsequently confer protection against oxidative stress and chronic inflammation⁽²⁵⁾. Many isothiocyanates also have antibacterial activities, which contribute to the traditional use of nasturtium for infections of the upper respiratory tract and urinary tract⁽²⁶⁾.

Possible applications in the prevention or treatment of various cancers are also likely for the aerial parts of nasturtium. The glucosinolate glucotropaeolin (found also in cruciferous vegetables) is metabolized within the body to benzyl isothiocyanate. Benzyl isothiocyanate is well absorbed into the bloodstream following oral ingestion of nasturtium by humans, and exhibits promising anticancer activity against cultured lung, breast, liver, prostate, brain, colon, melanoma, oral and ovarian cancer cells in vitro, as well as prevents chemically induced carcinogenesis in rodents^{(26, 27)}. It has also been shown to slow prostate cancer development in mice⁽²⁸⁾.

Enhancement of the in vitro cytotoxic effects of the chemotherapy drug cisplatin (but not 5-fluorouracil) in gastric cancer cells, has additionally been recently reported for benzyl isothiocyanate in time- and concentration-dependent manners⁽²⁹⁾. Dietary intake of the related plant watercress (Tropaelum officinale), has also been implicated with helping to reverse resistance to cisplatin in biliary cancer patients⁽³⁰⁾. Use of nasturtium as an adjunct to some chemotherapy medications may therefore have value.

Treatment of a mouse cell line with adipocyte-like characteristics (used in research on fat tissue) with an ethanolic extract of nasturtium, produced a concentration-dependent reduction in lipid accumulation, and inhibited the expression of various proteins associated with differentiation of fat cells. This suggests potential usefulness also in the prevention and treatment of obesity⁽²⁶⁾. As obesity is sometimes associated with various cancers including prostate cancer^{(31, 32)}, such effects could provide further benefits in patients at risk of cancer, for regular usage of nasturtium.

While their efficacy as treatments or adjunctive agents with conventional treatment needs to be further evaluated with well designed human clinical trials, evidence to date supports the regular use of both pomegranate and nasturtium, as a potential means to help prevent or slow down the progression of prostate cancer.
 

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