In vitro characterization of the human biotransformation of marine derived anti-cancer drugs

Cancer is the second cause of death in The Netherlands. Although the treatment options over the past few decades have substantially improved, the cure rate for patients with advanced cancer remains low. In addition, hopefully new therapies will induce less severe side effects compared to the present therapies. Overall, new anti cancer drugs are still very much needed to improve treatment outcome of patients. Many active cytotoxic agents originate from natural resources, mainly plants (e.g. paclitaxel originates from the Taxus tree). The search for marine compounds started 50 years ago and new compounds isolated from various marine sources have been described as anti-cancer agent and some have already entered clinical studies. In this thesis, three novel marine derived anti cancer drugs were investigated, i.e. thiocoraline, aplidine, and ET-743. Thiocoraline is derived form the Micromonospora marina, which grows in the Mozambique strait. Aplidine originates from the Mediterranean tunicate Aplidium albicans and ET 743 from the Ecteinascidia turbinata from the Caribbean. All three anti-cancer drugs showed promising activity against various tumor types in preclinical studies. Aplidine and ET-743 have already entered clinical trials and thiocoraline will be investigated in patients in the near future. Little is known about the biotransformation of thiocoraline, aplidine, and ET 743 in the human body. Information on the enzymes involved and the knowledge of the patient enzyme activity may help to improve the treatment of the individual patient and reduction of side effects. Therefore, it is important to elucidate the involvement of the different enzymes with the biotransformation of the anti-cancer drugs thiocoraline, aplidine, and ET 743. The research is focused on the elucidation of the human biotransformation pathways of these drugs. Furthermore, the toxicity of the metabolites was investigated to elucidate if bioactivation or bioinactivation occurred. The cytochrome P450 enzyme 3A4 was found to be very important in the biotransformation of thiocoraline and CYP2C8 was involved to a lesser extent. UGT1A1 and 1A9 were involved in the conjugation of thiocoraline. No involvement of other phase II enzymes was found. Furthermore, the metabolites formed from the CYP reaction were further conjugated by the phase II enzymes UGT, SULT, and GST. Aplidine was mainly metabolized by CYP3A4, but also by CYP2A6, 2E1, and 4A11. Four metabolites were identified from which three were specifically formed by CYP3A4 and one by CYP2A6. Only the UGTs 1A3 and 1A9 were involved in the direct conjugation of aplidine. The metabolites formed by CYP were further conjugated by UGT, SULT, and GST. Cell culture experiments showed that the aplidine metabolites were less toxic compared to aplidine, thus aplidine was bioinactivated by these enzymes. ET-743 was also mainly metabolized by CYP3A4 and a number of other CYPs played a minor role, namely CYP2C9, 2C19, 2D6, and 2E1. In addition, ET-743 was conjugated by GST and UGT. The metabolites formed by cytochrome P450 were less toxic compared to ET-743 itself in cell culture experiments, thus ET-743 was bioinactivated by the CYPs involved in its biotransformation. The studies performed to unravel the biotransformation of the here investigated marine derived anti-cancer agents may help to improve clinical evaluation of anti cancer activity and safety of these drugs

Fate in digestion in vitro of several food components, including some toxic compounds coming from omega-3 and omega-6 lipids

In this study it was proved the formation of oxygenated alpha,beta-unsaturated aldehydes (OaßUAs) of 6, 7, 9 and 10 carbon atoms during the thermal treatment (190 °C with aeration) of a commercial vegetable oil rich in omega-3 and omega-6 acyl groups, which also contained small amounts of added proteins and carbohydrates to produce barbecue aroma when heated. The OaßUAs detected by Solid Phase Microextraction (SPME) followed by Gas Chromatography/Mass Spectrometry (GC/MS) were: 4-hydroxy-2-hexenal, 4-oxo-2-hexenal and 4,5-epoxy-2-heptenals, coming from omega-3 acyl groups; and 4-hydroxy-2-nonenal, 4-oxo-2-nonenal and 4,5-epoxy-2-decenals, coming from omega-6 acyl groups. Mixtures of this oil, either thermodegraded or not, with standard food were submitted to an in vitro digestion model. The study of the digestion products obtained revealed that OaßUAs remained unaltered, being bioaccessible in the gastrointestinal tract and so able to reach the systemic circulation. Besides, it was evidenced that during digestion Maillard, esterification and oxidation reactions take place

Effects of probiotic bacteria on the bioaccessibility of aflatoxin B1 and ochratoxin A using an in vitro digestion model under fed conditions

PubMedID: 20183052In the present study, we aimed at determining the release of aflatoxin B1 (AFB1) and ochratoxin A (OTA) from different food products in the gastro-intestinal tract in the absence and presence of probiotics, a possible adsorbent. The average bioaccessibility of AFB1 and OTA without probiotics was about 90%, and 30%, respectively, depending on several factors, such as food product, contamination level, compound and type of contamination (spiked versus naturally contaminated). The six probiotic bacteria showed varying binding capacity to AFB1 and OTA depending on the bacterial strain, toxin studied, type of food and contamination level. A reduction to a maximum of 37% and 73% as observed for the bioaccessibility of AFB1 and OTA in the presence of probiotic bacteria, respectively. This is the first report on the effect of probiotic bacteria on reducing the fraction of mycotoxins available for absorption in the gastrointestinal tract from different food products. © Taylor & Francis Group, LLC.This study was supported financially by the Centre for Substances and Integrated Risk Assessment, National Institute for Public Health and the Environment, The Netherlands. We greatly thank Menno Duits for his technical assistance in the use of in vitro digestion model and Erwin van de Kamp for helping with the AFB1 and OTA experiments, both from the Laboratory for Food and Residue Analysis. Dr. Janine Ezendam from the Laboratory for Toxicology, Pathology and Genetics is kindly acknowledged for providing L. casei Shirota strain and culturing of the probiotics. Many thanks to Prof. Arthur Ouwehand (Danisco Ltd) and Nestle-Switzerland for supplying the bacterial strains. We also thank Martien Spanjer and others of the Food and Safety Authority for providing the aflatoxin and ochratoxin contaminated food products

Bioaccessibility of vitamin A, vitamin C and folic acid from dietary supplements fortified food and infant formula

In the Netherlands, vitamin intake occurs mainly via food and for some vitamins also via fortified food. In addition, some people take dietary supplements. Information on the bioavailability of vitamins is important for a good estimation of the actual exposure to vitamins. Furthermore, for a reliable intake estimation, it is important to know the accurateness of the claimed vitamin concentration on the product label. In the current study, the amount of vitamin A, vitamin C, and folic acid in different products and their maximum bioavailability (bioaccessibility) were investigated. In about half of the products, the amount of vitamins significantly deviated from the declared amounts. The vitamin bioaccessibility ranged fro

Implementation of toxicokinetics in toxicity studies e Toxicokinetics of 4-methylanisole and its metabolites in juvenile and adult rats

The current risk assessment of compounds is generally based on external exposure and effect relationships. External doses are often not representative for internal exposure concentrations. The aim of this study was to show how the implementation of toxicokinetics in a scheduled toxicity study contributes to improved data interpretation without additional use of animals and to the three goals of the 3R principles for animal testing. Toxicokinetic analyses were implemented in a rat developmental immunotoxicity study with 4-methylanisole without interfering with the outcome of the study and without the use of additional animals. 4-Methylanisole and its metabolites were analysed in plasma of adult rats and in pups at postnatal day 10. 4-Methylanisole has a short half-life in adult animals and the plasma concentrations increased more than proportional with increasing dose. The metabolic profile appeared to be different at low dose as compared to high dose. This information on the dose-proportionality of the internal exposure is crucial for the interpretation of the toxicity data and helps to identify the toxic agent and the appropriate dose metric. The metabolism was similar in adult and juvenile animals. Large inter-individual variability in adult animals, as observed for 4-methylanisole, may hamper dose–response analyses of the results. In addition, 4-metylanisole was excreted via milk, but concentrations in the juvenile animals appeared to be 20- to 100-fold lower than via direct gavage exposure. The toxicokinetic parameters support the data interpretation, among others by providing better insight into internal exposures. Subsequently, it will help to prevent testing of irrelevant exposure scenarios and exposure concentrations. Overall, implementation of kinetics with limited effort provides useful information to support the interpretation of toxicological data and can contribute to reduction and refinement of animal testing