We found a significant effect of a ginger root extract, in the dose and formulation used, to decrease our primary endpoint, the mean percent change in PGE2 levels in colon biopsies from subjects at normal risk for developing colorectal cancer when normalized to free AA. We did not, however, find a significant difference in PGE2 concentrations when normalized to protein. Similarly, we found no difference in the concentrations of 5-, 12-, 15-HETE, or 13-HODE when normalized per protein. However, when normalized per free AA there was a significance decrease in 5-HETE and decreases in both 12-, & 15-HETE approached significance. Eicosanoid levels per amount of protein reflect absolute concentrations of eicosanoids in the tissue; however, eicosanoid levels per amount of free AA could reflect enzymatic activity of the COX and LOX enzymes. In essence, when the catalytic enzymes, i.e. COX are blocked, less substrate is metabolized increasing the amount of AA and decreasing the eicosanoids. This may possibly imply some inhibition of COX-1, LOX-5, -12 and LOX-15-2 enzymes by ginger extract. However, rigorous kinetic experiments assessing COX and LOX enzymatic activity would need to be conducted to confirm this hypothesis. Linoleic acid was not quantified, making interpretation of 13-HODE levels difficult.
This study observed a 28.0% mean decrease in PGE2
normalized to free AA and a roughly 7% decrease when normalized to protein from baseline colon mucosal levels. To date, how much PGE2
concentration needs to be decreased in human colonic mucosa to prevent the occurrence of adenomas is unknown. While aspirin has been shown to both prevent adenomas and decrease colonic mucosal PGE2
no studies have combined these endpoints. Several studies have examined the effect of aspirin on production of PGE2
in human colonic mucosa showing anywhere from no reduction to an 85% decrease in PGE2
in colonic mucosa.33–37
Unlike aspirin, a study examining sulindac, another NSAID, did examine the effect on mucosal prostanoids and polyp occurrence in patients with genotypically affected familial adenomatous polyposis (FAP). On average, PGE2
concentrations in rectal biopsies in participants that received sulindac decreased significantly by 19.2% from baseline levels when taken for 48 months at doses of either 75 to 150 mg daily.38
In the sulindac arm, those participants that did not develop an adenoma had a 33.9% mean reduction in baseline PGE2
rectal mucosal concentrations compared to baseline levels, while those who received sulindac and developed a polyp had a slight increase of 2.4% from baseline PGE2
In contrast, taking difluoromethylornithine/sulindac for 3 years resulted in a 70 to 90% reduction in the recurrence of colorectal adenomas but this was not correlated with reductions in mucosal PGE2
, although higher baseline levels of PGE2
were associated with higher recurrence rates.39
Our results are more modest than those observed for aspirin, but only slightly lower than those observed for sulindac. Our results are most likely attenuated by lower baseline PGE2
levels because of our healthy normal risk for CRC sample and relatively short study duration of 28 days. Longer-term use in high-risk patients could possibly maximize the effect of ginger.
Previous to this study, ginger and ginger constituents’ anti-inflammatory effects on COX and LOX enzymes and their products had only been observed ex vivo
The only exception is in one study of rats where decreased serum levels of PGE2
were observed with ginger treatment.22
The present study indicates that oral ginger could have inhibitory effects on colon tissue COX and LOX enzymes in humans.
This study had several limitations. We had a small sample size of only 30 participants and this study was intended as a pilot to determine if a larger study with ginger extract was warranted. Also, our results had much larger standard deviations for all of the eicosanoids than anticipated, and as such we had inadequate sample size to detect meaningful changes in colon eicosanoid concentrations in several instances, especially when normalized to protein. The sample size of this study was based on the mean and standard deviation of PGE2
concentrations in human colon tissue determined by our group’s previous study using enzyme-linked immunosorbent assay (ELISA).33
The ELISA assay results indicated standard deviation of around 10% of the mean. In contrast, the LC/MS/MS assay, employed in our study had standard deviations that exceeded 100% of the mean. With this standard deviation, a post-hoc sample size analysis indicated that 61 subjects would be needed to detect a significant difference in PGE2
levels normalized to protein.
Despite the variability of the LC/MS/MS assay it provided several advantages over an ELISA. Mainly, with LC/MS/MS we could measure numerous eicosanoids and free AA simultaneously. The LC/MS/MS method is also more specific for a given analyte than ELISA as it avoids cross-reactivity issues inherent in ELISAs. Importantly, however, we did determine that our mean baseline PGE2
, 12-, 15-HETE and 13-HODE concentrations per protein derived from LC/MS/MS were similar to other studies,11, 32, 36
which used other methods to determine eicosanoid concentrations. Other studies using ELISA and gas chromatography-mass spectrometry also found high amounts of variability in colonic PGE2
concentrations, not dissimilar to our results.38, 41
One explanation for the high level of variability in our eicosanoid assays is the >15% between-day CV42
for all the eicosanoids except PGE2
and AA. However, assay batch had no significant effect on mean percent change for any eicosanoid when examined in linear models, and was thus not added to the final analysis. Another source of variability is the considerable dissimilarity of eicosanoids at different locations of the colon both between and within people.41
To help address this, we combined two biopsies from the same participant at the same time point, but it was in the same section of the colon.
Participants reported a high level of adherence in this study with an average intake of 100% of study medication, making it an unlikely source of variability. A recent study has also found that adenoma risk was not significantly associated with genetic variation in PGE2
synthase and prostaglandin dehydrogenase, however genetic variations in these key enzymes and associations with variation in levels of PGE2
were not examined.43
Similarly, no significant associations were found between age, body mass index, percentage of body fat, NSAID drug use, history of adenomas and family history of colon cancer with either baseline levels of mucosal PGE2
or change of PGE2
Another potential source of variability could be due to differences in absorption of key ginger constituents in human tissue. Limited research has been conducted examining the pharmacokinetics of ginger constituents in human blood and tissue. In one study a dose of 2.0 g of ginger extract led to detectable levels of all four of the main ginger constituents (6-, 8-, and 10-gingerols and 6-shogaols) in human plasma after a single oral dose.28
Some normal colon tissue samples were also determined to have detectable levels of 10-gingerols glucuronide and sulfate within 24 hours of the last dose of ingesting 2.0 g of ginger extract for 28 days. Presence of gingerols in tissue were affected by the length of time form the last dose of ginger extract due to the fast half-lives (between 1 to 3 hours) and clearance of the gingerols and shogaol in humans.44
These findings argue for large sample sizes, careful recording of when ginger was last consumed and the use of colonic biopsies taken at multiple time points to help draw meaningful conclusions that would otherwise be masked by the considerable variability in this marker.
Future studies of ginger root extract should focus on examining the mechanisms of action by which ginger extract is affecting the COX and LOX enzymes involved in the production of both the inflammatory and anti-inflammatory eicosanoids. In addition, the effect of ginger on microsomal prostaglandinE2
synthase-1 (mPGEs-1) and 15-hydroxyprostaglandin dehydrogenase (15-PGDH) should be considered as the role of both of these enzymes in PGE2
production and degradation are being recognized as increasingly important to governing tissue concentrations of PGE2
Subsequent studies should also examine the effect of ginger extract in people at high risk for CRC to determine if there is a differential or similar effect between normal and high-risk populations.
In conclusion, ginger appeared to be well tolerated. There were no differences between placebo and ginger for total adverse events (AE) or in common AE categories including fatigue, gastrointestinal effects or headaches. Participants reported a high level of adherence with all participants reporting taking at least 80% of their study medication. Ginger extract had no significant effect on colon concentrations of AA, PGE2, 5-, 12-, & 15-HETE or 13-HODE normalized to protein when compared to the placebo group. However, ginger extract did appear to have an inhibitory effect on COX and LOX-5, 12-, & 15-2 enzymes as observed by significant or close to significant decreases in the mean percent change in PGE2, 5-, 12-, & 15-HETE normalized to AA. Consequently, it would appear that ginger extract has an anti-inflammatory effect in the colon of persons at normal risk for CRC and warrants further study.