084P Brighton
Winter Meeting December 2007 |
The effect of raspberry leaf extract on the biotransformation of fluorogenic substrates by human cytochromes P450
Shirley Ho, Alison Holloway, Denis Crankshaw
McMaster University, Hamilton, Ontario, Canada
Preparations of red raspberry leaf (RRL) are widely promoted for use in pregnancy to facilitate labour. Indeed there is clinical evidence to suggest that RRL taken during pregnancy can shorten the second stage of labour (Simpson et al, 2001). RRL contains a number of polyphenols, a class of compounds known to affect the activity of cytochromes P450 (CYP). Thus RRL might serve as a chemo-preventative agent by inhibiting the formation of carcinogens by CYP1A1, or it may provoke adverse drug reactions by inhibiting the biotransformation of pharmaceuticals by other CYPs. To test these possibilities we have quantified the effect of three different preparations of RRL on the biotransformation of fluorogenic substrates by recombinant human CYPs and compared these to three of the major polyphenolic constituents of RRL, ellagic acid, kaempferol and quercetin.
Raspberry herbal tea, capsules and liquid extract (40% ethanol, hereafter referred to as tincture) were obtained from local sources. Aqueous extracts of tea and capsule contents were prepared and centrifuged to remove particulate matter. These extracts, the tincture, and the pure polyphenols were then tested for effects on the biotransformation of 7-ethoxyresorufin by CYP1A1, 3-cyano-7-ethoxycoumarin by CYP1A2 & CYP2C19, and 7-benzyloxyquinoline by CYP3A4. Incubations of substrates with human CYPs were performed in black 96-well plates under linear conditions at 37°C in the presence of an NADPH regenerating system. The formation of product was monitored kinetically by measurement of fluorescence intensity at the appropriate wavelengths.
The maximum concentrations of RRL used was 250 μg/mL. Results are given in Table 1 where pIC50 values are in g/mL. Values are means ± s.e.mean from three experiments performed in duplicate.
Table 1
|
CYP1A1 |
CYP1A2 |
CYP3A4 |
CYP2C19 |
|
pIC50 |
pIC50 |
pIC50 |
pIC50 |
| Raspberry tea |
No effect |
No effect |
No effect |
No effect |
| Raspberry capsule |
Heteroactivation |
5.9 ± 0.5 |
No effect |
No effect |
| Raspberry tincture |
Heteroactivation |
4.4 ± 0.1 |
3.9 ± 0.1 |
3.8 ± 0.1 |
| Ellagic acid |
No effect |
5.4 ± 0.1 |
No effect |
No effect |
| Kaempferol |
6.7 ± 0.1 |
6.8 ± 0.1 |
5.9 ± 0.2 |
5.4 ± 0.2 |
| Quercetin |
6.7 ± 0.2 |
5.9 ± 0.1 |
5.8 ± 0.1 |
5.6 ± 0.1 |
RRL is, at best, a poor inhibitor of the human CYPs that we have investigated. There is a small potential for interaction between RRL and drugs metabolized by CYP1A2. However, we predict that moderate consumption of the herbal preparations will not provoke adverse drug reactions that involve CYP2C19 or 3A4. Heteroactivation of CYP1A1 by some RRL preparations makes prediction of their in vivo effects difficult (Anger et al, 2005).
Simpson, M. et al (2001) J. Midwifery Women’s Health 46:51-59
Anger, D. et al (2005) Br.J.Pharmacol. 145:926-933
Supported by Sick Kids Foundation & CIHR
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