Effect of food additive E171 (titanium dioxide) on the development of colorectal cancer, an early biomarkers research.

The food additive E171 (titanium dioxide) is present at significant levels
mainly in sweets, cookies, icing and chewing gum. Consumers are exposed between
1 and 2 mg/kg bw/day depending on the age, it is important to evaluate the
potential risk of this compound on human health. E171 comprised titanium
dioxide (TiO2) particles of various sizes, among others in the nanoparticle
size range. TiO2 is not considered genotoxic, but in an animal model in which
colon cancer is induced by the genotoxicant AOM (Azoxymethane), E171 was able
to dramatically enhance the tumour formation induced by AOM.
The intervention study that is described in this METC protocol is done in the
context of a project that aims to establish the potential risk of stimulation
of the development of colorectal cancer in humans due to ingestion of the food
additive E171. The hypothesis for the mechanism that may explain the effect is
that E171 induces inflammation in the colon, and that the inflammatory
condition would facilitate the development of colorectal cancer. The
intervention study aims at measuring inflammatory and genomic markers that may
be early indicators of the development of colorectal cancer. The information
yielded by this study will allow to extrapolate the findings in animals
concerning the facilitation of the development of colorectal cancer to humans,
and perform a risk assessment. The selection of markers to be used in the
intervention study will be based pervious animal and in vitro experiments.

In this intervention study, the primary aim is to evaluate the influence of
E171 exposure on the gene expression profile in rectal biopsies. In addition,
inflammatory markers such as ROS in the rectal epithelium will be measured as
secondary outcome.

This human volunteer study has a cross-over design with only healthy volunteers
divided in 2 groups, one that will start with the control period and the other
one that will start with the intervention period. Each participant will undergo
proctoscopy after each study period, rectal biopsies and rectal swap will be
taken. In addition, subjects will be asked to donate blood.

During the study, the subjects will follow two different periods: a two weeks
control period and a two weeks intervention period.
The aim of the control period is to reduce to a minimum the exposure to E171.
Therefore, the subjects will be given a list of tiO2-containing products to
avoid during these two weeks.
The aim of the intervention period is to observe the effect of E171 in the
colon, by making a gene expression profile and measuring biomarkers of exposure
to E171. For this, the subjects will be given yoghurt to eat 3 times a day in
which a normal daily amount of E171 will be added.

The burden / risk / benefit associated with participation will be as follows:

-2 colonic biopsies (after each study period (control and intervention
period)). Biopsies will be collected by proctoscopy and therefore no specific
preparation is necessary. This procedure is used daily in medical practice and
is a relatively safe examination method. Complications are very rare. Bleeding
may occur from biopsies, but is minimal and stops quickly. If rectal bleeding
persists, the volunteer must report this immediately.
-2 rectal swaps; this procedure is without any specific risk;
- 2 blood samples will be collected (one sample after each study period). The
risks related to the collection of these samples are minimal;
- keeping a dietary registration.