1. Investigations of the mechanisms of absorption of lycopene from the gastro-intestinal tract of the rat.
Faisal W., O'Driscoll C. M. and Griffin B. T.1
1Pharmaceutics, School of Pharmacy, University College Cork, Ireland
INTRODUCTION
Epidemiological studies which assess plasma lycopene levels and prostate cancer risk support a 25-30% reduction in risk. However, the findings of a number of dietary based studies which have compared patients with a high intake of lycopene rich foods and prostate cancer risk fail to conclusively show a reduction in risk. Giovannucci (2005) suggested that primary reasons for these differing scientific opinions lies in the variability in uptake of lycopene from dietary food stuffs[1]. Lycopene is an highly lipophilic carotenoid (clog P = 17.6), therfore solubilisation within the gastrointestinal contents is considered to be a crucial step in the oral absorption process. The oral bioavailability of highely lipophilic compounds is known to enhanced by lipid based formulations[2]. The impact of intestinal lymphatic transport on overall bioavailability of this extremely lipophilic compound remains to be explored.
Figure 3: Comparison of cumulative %dose transported in intestinal lymph versus time following administration of Fasted and Fed State Simulated intestinal Fluid (Mean±SE n≥5).
Figure 6: Lycopene plasma concentration (ng/ml) versus time profiles in lymph cannulated and non-lymph cannulated rat (Mean±SE, n≥4).
The extent of intestinal lymphatic transport of lycopene was consistently higher in FeSSIF compared to FaSSIF (Figure 3). The differences however were not statistically significant.
Cannulation and collection of intestinal lymph (i.e. lymph removed) resulted in a significant reduction in systematic plasma concentrations of lycopene (Figure 6).
Aims
To compare the saturation solubilities of lycopene in a range of bio-relevant media and lipid based micellar formulations. To estimate the degree of intestinal lymphatic transport of lycopene in the rat. To assess the contribution of lymphatic transport on overall oral bioavailability, comparative bioavailability studies in lymph cannulated (i.e. lymph removed and quantitified) and sham operated rats were compared.
Table 2: Comparison of lycopene bioavailability and lymph transport (Mean±SE, n≥4) in lymph and non-lymph cannulated rats following administration of FeSSIF.
Plasma data in lymph cannulated
Plasma data in non-lymph cannulated rat
AUC0-8 id
29.03±7.28ng.hr/ml
186.69±39.28ng.hr/ml
AUC0-8 iv
N/A
±439.17ng.hr/ml
%Bioavailability *
0.294±0.0073%
1.84±0.393%
%dose transported
in lymph
3.4±1.14%
Total (lymph+plasma)
3.694±1.15%
Methods
Saturation solubilities of lycopene in fasted and fed state simulated intestinal and gastric fluids (FaSSGF, FeSSGF, FaSSIF and FeSSIF) were determined. Saturation solubilities of lycopene in simple and mixed micelles of 2% bile salt and 2% cremophor with long chain (1% oleic acid) or medium chain (1% decanoic acid) fatty acid were assessed. The extent of intestinal lymphatic transport is determined in the mesenteric lymph duct cannulated anaesthetised rat model[3]. Lycopene levels in lymph/ plasma were analyzed by HPLC. Triglyceride (TG) levels in intestinal lymph were analyzed by colorimetric assay.
Figure 4: Comparison of cumulative %dose transported in intestinal lymph versus time following administration of 2% bile salt+ 1% oleic acid mixed micelles and 2% bile salt+ 1% decanoic acid mixed micelles (Mean±SE n≥5).
*Total bioavailability = AUC0-8 id *Doseiv /AUC0-8 iv *Doseid
Overall bioavailability of lycopene in rats was low (Table 2).
Collection and removal of the intestinal lymph resulted in an 84% reduction in the overall bioavailability of lycopene.
Long chain fatty acid mixed micelles enhanced the extent of intestinal lymphatic uptake of lycopene to a greater extent (2.25 fold greater) compared to medium chain fatty acid bile salt mixed micelles (p< 0.05)(Figure 4).
Results
Conclusion
Lipid based formulations enhance saturation solubility of lycopene.
The extent of intestinal lymphatic transport of lycopene in the rat ranged from 0.6 to 3.4% of the administered dose.
Intestinal lymphatic transport of lycopene is highly correlated with the extent of intestinal lymphatic transport of triglyceride, confirming that lycopene transport in the lymph is associated with the TG rich lipoproteins.
Lycopene bioavailability after intraduodenal infusion of FeSSIF media in anaesthesized rats was 1.84 ± 0.393%.
Comparison of plasma profiles in lymph cannulated and non lymph cannulated rats confirm that the intestinal lymphatic transport route is the major uptake mechanisms of lycopene from the gastro-intestinal tract.
Figure 1: Saturation solubility of lycopene in Fasted and Fed state simulated physiological fluids (intestinal and gastric) and its comparable buffers (i.e. blank) (Mean±SE).
Saturation solubilities of lycopene are higher in fed versus fasted state simulated physiological fluids. Lycopene displays greater solubility at low pH (Figure 1).
Figure 5: Correlation between lycopene transport rate (ng/hr) and triglyceride transport rate (mg/hr) in lymph following administration of 2% bile salt 1% Oleic acid (LCFA) and 1% Decanoic acid (MCFA) mixed micelle formulation (Mean±SE n≥5).
A strong positive correlation (r2>0.96) between intestinal lycopene levels and intestinal TG levels was demonstrated for the bile salt mixed micelle formulations (Figure 5).
References
Table 1: Cumulative transport of triglyceride in intestinal lymph and cumulative lymph flow as a function of administered formulation after 8 hours (mean  S.E., n5)
Giovannucci E, Tomato Products, Lycopene, and Prostate Cancer: a Review of the Epidemiological Literature. Journal of Nutrition 135: 2030S-2031S, 2005.
O'Driscoll, CM, 2002, Lipid based formulations for intestinal lymphatic delivery: European Journal of Pharmaceutical Sciences, v. 15, p
Griffin, B.T., O'Driscoll, C.M., A Comparison of Intestinal Lymphatic Transport and Systemic Bioavailability of Saquinavir From Three Lipid-Based Formulations in the Anaesthetised Rat Model. Journal of Pharmacy and Pharmacology 58,
Formulation
Cumulative Mass of total triglyceride (mg)
Cumulative triglyceride transport (mg)
Cumulative lymph flow (ml)
Saline, Control
14.42.16
7.29 1.04
LCFA bile salt mixed micelles
52.624.66
38.21
9.31 1.18
MCFA bile salt mixed micelles
30.932.24
16.52
6.860.83
FaSSIF
21.311.41
6.91
5.650.83
FeSSIF
27.824.41
13.42
6.470.67
Figure 2: Saturation solubility of lycopene (mcg/ml) in Simple micelle, Mixed micelles with long chain fatty acid (LCFA) and Mixed micelles with medium chain fatty acid (MCFA) of 2% Bile salt and 2% Cremophor (Mean±SE)
The saturation solubility of lycopene was higher in mixed versus simple micellar sysytems (Figure 2).