Here we report for the first time that EGCG has robust inhibitory effects on ELT3 cells in vitro and in a nude mouse model. The increased efficacy of EGCG towards inhibition of ELT3 cells growth in vitro was dose-dependent and was mediated through apoptosis and inhibition of proliferation at various EGCG concentrations. Recent studies have demonstrated a wide variety of positive effects of EGCG on diverse physiological and pathological situations. Several mechanisms for EGCG bioactivities have been proposed. For example the anti-tumor effects of EGCG seem to be mediated through decreasing the activities of Cdk2 and Cdk4;20
inducing apoptosis in a variety of tumor cells21-23
; as well as blocking telomerase.24
EGCG also inhibits matrix metalloproteinases, in particular MMP-2 and MMP-9, which along with their antiangiogenic properties can block tumor cells invasion.25-28
Actually, EGCG modulate tumor cell proliferation through multiple signal pathways.29
We have recently reported higher expression of Catechol-O-methyltransferase (COMT) in human uterine fibroid tissues compared to adjacent normal myometrium.30-32
Additionally we reported that higher incidence of functional high activity COMT polymorphic markers might explain the increased prevalence of uterine fibroids in African Americans.30
We have also reported that selective COMT inhibitors are able to inhibit proliferation in both human and rat uterine leiomyoma cells.30
Interestingly, the steric structure of EGCG enable it to exert a strong inhibition of COMT activity as a substrate or by tightly binding with COMT.33-35
We propose that the strong anti-leiomyoma effects of EGCG could conceivable be mediated via COMT inhibition.
Although EGCG appears to affect many biological processes of various cell types, the dose and action of orally administered EGCG might differ from direct effects on cells in vitro. The great majority of EGCG in vitro studies, including ours, have shown in vitro activities at dosages from 10-100 μM, substantially higher than those obtainable in vivo. These results do not reflect typical catechin level found in animal or human plasma. Although there was a remarkable dose-dependent antiproliferation effect of EGCG on ELT3 cells in vitro, the in vivo procedure might not be as clear-cut due to the individual differences in ingestion, absorption and metabolism. That is why the evaluation of EGCG utility against fibroid tumors in vivo in an animal model was critical. Several animal studies have been done on metabolism and pharmacokinetic profile of EGCG in vivo. After intragastric administration of EGCG in rats at dose of 75mg/kg, the plasma bioavailability of EGCG was about 1.6%, while high levels were observed in the intestine and kidney.36
In the mice model, after administration of EGCG intragastrically at 163.8 μmol/kg, the plasma bioavailability of EGCG was about 26.5% after one dose consumption, higher than previously reported in rats.37
In humans, the maximum plasma concentration of EGCG was 77.9 ng/ml, after oral administration of a single dose of EGCG (2mg/kg).38
Other studies also found that in healthy individual, the plasma level of EGCG reached at 0.1-5.0 μM after moderate green tea consumption.37-39
Since catechins are relatively unstable and differ quantitatively during experiments, it is difficult to compare the relation of ingested dose and biological effect between studies. Nevertheless, several animal experiments have shown promising antitumor effects of orally administered EGCG or other green tea extracts.24,40,41
Theoretically, higher plasma level of EGCG might be reached by taking high dose of EGCG, however, studies showed that consumption of higher level of EGCG dose did not necessarily give substantially higher plasma concentration.41,42
It is highly encouraging that in our work, a relatively modest dose of EGCG of 1.25mg/mouse/day delivered in drinking water was successful in inducing a dramatic and sustained reduction in fibroid tumor size up to 8 weeks of treatment. The EGCG is a nontoxic, natural anticancer agent, and it appears to be safe and typically associated with minimal innocent side effects. Recently, healthy individuals who consumed decaffeinated, purified 800mg of EGCG daily for 4 weeks reported mild side effects such as upset stomach, nausea, abdominal pain, headache, and dizziness.43
A higher oral dose of 1600mg EGCG was also used without reported toxicity.44
In our studies, there was no observed liver or kidney tissue changes as examined by H&E staining in EGCG treated group after 8 weeks treatment (data not shown).
On the basis of the present study, we conclude that EGCG and green tea extract may have potential as oral agents for prevention or treatment of uterine leiomyoma. EGCG might be particularly useful for long term use in women low fibroid tumor burden to arrest tumor progression and avoid the development of severe symptoms necessitating major surgery. Further evaluation of EGCG in well designed clinical trials in women with uterine fibroids is warranted.