Intestinalni i sistemski imunski efekti oralnog unosa kadmijuma kod pacova
Intestinal and systemic immune effects of oral cadmium intake in rats
Authors:
Ninkov, MarinaContributors
Popov Aleksandrov, AleksandraKataranovski, Milena
Popov Aleksandrov, Aleksandra
Kataranovski, Milena
Matović, Vesna
Document Type:
Doctoral thesis (Published version)
Metadata
Show full item recordAbstract:
Cadmium (Cd) is a heavy metal which is found in every part of the environment,
it does not have any known biological function and has an adverse effect upon the living
systems. The most common way of Cd exposure is orally, through contaminated water
and food, where the prime target of this metal toxicity is the gastrointestinal tract. It is
known that Cd causes damage to intestinal tissue and disrupts the epithelial barrier
function which is necessary for maintaining immune homeostasis, however, the
immunotoxicity mechanisms in this region have not been examined sufficiently.
Additionally, it is known that Cd toxic effects may depend also on genetic background /
strain of experimental animals, but the strain-dependent differences in intestinal toxicity
of oral Cd intake have not been examined to date.
This dissertation was aimed at characterization of the effect of subchronic oral
Cd administration on rat’s intestinal immune system. Rats were, for 30 days, orally (in
drinking water) exposed to Cd in the form of cadmium chloride (CdCl2) at
concentration of 5 ppm (5 mg Cd/l) and 50 ppm and (50 mg Cd/l) of Cd, which
corresponds to the doses present in the environment. Within the local
immunomodulatory Cd effect, basic parameters of immune response in duodenum
(region of greatest Cd absorption) and in mesenteric lymph nodes (MLN) which drain
intestine, were investigated. The indicators of tissue damage, oxidative stress and
inflammatory changes were tested in duodenum, whereas in the MLN basic phenotype
characteristics and parameters of this lymph tissue cells' activities (cellularity,
proliferation, cytokine responses, and innate-immune cell activity) were tested. Besides
the local, the systemic response to oral Cd intake was tested as well, including humoral
and cellular parameters of the inflammatory reaction in blood (changes in hematological
parameters, presence of inflammatory mediators and oxidative stress), as well as
oxidative stress and basic characteristics of the innate and adaptive immune response in
the spleen, a lymph organ in which immune response to blood borne antigens are
generated. Aiming to test the contribution of genetic background to intestinal and
systemic immunotoxicity of oral Cd exposure, local and systemic effects were analyzed
in two rat strains, Dark Agouti (DA) and Albino Oxford (AO), which establish
qualitatively and/or quantitative different immune response to the same stimuli.
The study has shown that oral Cd treatment leads to dose-dependent
accumulation of this metal in intestine, MLN and spleen, similarly in DA and AO rats,
which demonstrates that genetic background has no effect on the metal deposition
levels. Despite similar Cd concentrations in the intestine of both rat strains, more
pronounced mononuclear leukocytes infiltrates in intestinal tissue, higher degree of
enterocytes necrosis [measured by increased necrosis marker HMGB1 (High mobility
group box 1) molecule] and the increased production of proinflammatory cytokines
(tumor necrosis factor/TNF, interferone-gamma/IFN-γ, interleukin-17/IL-17) were
shown in intestinal tissue of DA rats compared to rats of AO strain. The change in
activity of basic enzymes of anti-oxidative defense (superoxide dismutase/SOD and
catalase/CAT), in intestine of DA rats and SOD in AO rats, which depicts host tissue
attempt to counterattack reactive oxygen species (ROS) and limit tissue damage, as well
as glutathione-s-transferase/GST (the enzyme responsible for electrophilic substances
binding, such as Cd, to the reduced form of glutathione, GSH), was also more expressed
in rats of DA strain. Such type of changes is probably in the background of the
increased level of lipid peroxides (measured by the changes of malondialdehyde/MDA)
in AO rats. Oral Cd treatment results in reduced prevalence of lactobacilli in DA rats'
intestine which may contribute to the development of proinflammatory cytokine
response to Cd, whereas relative preservation of commensal flora in AO rats (along
with significant increase in prevalence of L. johnsonii and L. Murinus) might be of
significance for preservation of gut barrier integrity and absence of the local
inflammatory cytokine response in this strain of rats.
Oral Cd treatment affected the MLN activity in both strains of rats (increase of
MLN mass and cellularity, ROS production). Nevertheless, Cd induced
metalotioneinas/MT gene expression as well as proinflammatory immune response
(MLN cells' proliferative activity, oxidative activities, Th1/Type1 and Th17/Type17
response) and inhibited anti-inflammatory response (interleukine-10/IL-10 gene
expression and production) only in MLN of DA rats. Higher degree of intestinal
epithelium damage and necrosis observed in DA treated rats (compared to AO rats) is
the most likely factor which stimulated proinflammatory response in MLN of DA rats.
The changes in MLN of DA rats indicate that Cd disrupts the tolerogenic immune
environment in the gut by induction of both innate and the acquired immune responses.
Although the investigation of the systemic effect of orally administered Cd
indicated, in general, slight effect of the metal on the basic hematological and
biochemical parameters in the peripheral blood, the effect on anti-oxidative activities of
erythrocytes in both strains of rats was noticed. The increased levels of HMGB1
molecule in blood of DA rats only, suggests higher degree of organs damage and
inflammatory character of immune response to Cd in this strain of rats.
Although the same quantity of Cd is deposited in MLN and spleen, the response
in these two immune organs differs, showing that the micro environment of the
examined tissue is also of great importance in observing Cd effects. Unlike MLN, the
oral Cd administration did not affect spleen mass and cellularity but it resulted in
reduced viability and reduced proliferative activity of spleen cells, whereas, similar as in
MLN, the increased oxidative activity of spleen cells (activity of
myeloperoxidase/MPO, nitrogen-oxide/NO production) was noted and the increase of
non-stimulated production of proinflammatory cytokines (interleukine-1 beta/ IL-1ß,
IFN-γ, IL-17) was noted, only in DA rats. This proinflammatory cytokine response of
spleen cells in DA rats may be associated with increased level of HMBG1 molecule in
the spleen. More pronounced proinflammatory response to oral Cd administration in gut
as well as in MLN and spleen of DA rats in comparison to AO rats (in which similar
concentrations of deposited Cd were found) show that DA rats are more susceptible to
oral subchronic administration of this metal.
The results of this study contribute to the understanding of the mechanisms
which underlie the toxic Cd effects on immune response in intestine, for the first time
showing the effect of this metal on homeostasis of innate and adaptive components of
immune response in MLN. At the same time, this study has also shown the significance
of tissue in expressing Cd toxicity. Also, for the first time, this study has indicated the
effect of genetic background on orally administered Cd effects, suggesting the
significance of careful selection of experimental animals to be used in the analysis of
immunotoxic effects of this metal.
Keywords:
Oral cadmium administration; Intestinal immune response; Mesenteric lymph nodes; Spleen; DA and AO rats; Strain differences; ImmunotoxicitySource:
University of Belgrade, Faculty of Biology, 2016, 1-139Funding / projects:
- Immunomodulatory effects of environmental xenobiotics and biotic factors on the populations of mouse-like rodents (RS-MESTD-Basic Research (BR or ON)-173039)
URI
http://uvidok.rcub.bg.ac.rs/handle/123456789/1680https://radar.ibiss.bg.ac.rs/handle/123456789/2517