METHODS
Male Wistar rats that are 10-12 weeks old and weighing 250-350 g were divided into four groups: control,
RT alone, RT+ATX, and ATX alone as Groups 1, 2, 3, and 4, respectively. RT was given to the
abdomen as one fraction of 8 Gy, and ATX was given as 4 mg/kg for 7 days before RT. Intestinal tissues
were taken 24 h after the last ATX injection and radiation for histopathologic, immunohistochemical
examination, and oxidative stress measurement.
RESULTS
Oxidative stress index and oxidant status decreased with ATX administration in the radiation group
where an increase was reported in total antioxidant status. ATX treatment decreased the pathological
expressions observed in the proprial and epithelial cells of the intestinal villi in the RT group. Similarly,
RT exposure increased TNF-? expression while ATX treatment decreased the immunoreaction.
CONCLUSION
Our results demonstrate that radiation induces apoptosis and histopathologic intestinal mucosal changes
which leads to an increase in oxidative stress. ATX significantly ameliorates radiation-induced reactions
with its superior antioxidant properties and additional anti-inflammatory and antiapoptotic activities.
Keywords: Astaxanthin; oxidative stress; radiation-induced intestinal toxicity
Ionizing radiation (IR) can cause a prominent increment
of intracellular reactive oxygen species (ROS),
which causes a consequential intensive oxidative stress.
Excess of these molecules causes irreversible damage
to DNA, lipids, and proteins. They oxidize the cellular
components with consequential tissue damages that
lead to cell death via apoptosis.[
This justifies investigating efficient antioxidant molecules
to prevent radiation-induced damage mediated
by ROS and apoptosis. Therefore, various antioxidant
compounds against radiation-induced oxidative stress
became important targets of the investigation for radioprotective
intend.[
ATX, a natural antioxidant that is a xanthophyll
carotenoid of the carotenoid family member, is predominantly
found in marine organisms or water plants
such as fungi, microalgae, and other seafood.[
Many studies reported hepatoprotective, antioxidative,
anti-inflammatory, immunomodulatory, antidiabetic,
and antitumor activity of ATX, with no determined
toxicity or side effects. Consequentially, it is
widely used as a potential therapeutic agent in many
indications.[
Zhao and colleagues demonstrated the protective
effect of ATX administration before irradiation on liver
cells in terms of oxidative deterioration and DNA damage
in irradiated mice.[
The antioxidant activity of other carotenoids has
been investigated in reviews and meta-analyses; however,
ATX has not been sufficiently searched yet.[
In this study, we investigated whether oral ATX administration
could reduce the radiosensitivity of intestinal
tissue via evaluating the changes in inflammatory markers
[caspase 3, tumor necrosis factor-alpha (TNF-α)], and
biochemical markers of oxidative stress [total antioxidant
status (TAS) and total oxidant status (TOS)]. We also
sought radiation-induced histopathological and immunohistochemical
changes in intestinal tissue.
ATX: Astaxanthin ; TNF: Tumor necrosis factor; MCP: Monocyte chemoattractant protein; ICAM: Intracellulary adhesion molecule; ROS:
Reactive oxygen species; HO: Hydrogene oxide; NADH: Nicotinamide adenine dinucleotide; NQO-1: NAD (P) H dehyhdrogenes quinon
1; SOD: Superoxide dismutase ; CAT: Catalase; GP: Gluthation peroxidase ; GST: Gluthation; MnSOD: Manganese superoxide dismutase;
BCLXL: B cell lymphoma extralarge protein; BAK: Pro-apoptotic Bcl-2 protein; BAX: Bcl-2-associated X protein; Cyt: Cytochrome.
Rat food ingredients: raw oil 3%, ash 6.95%, lysine 1.3%, phosphorus 0.74%, protein 23.50%, cellulose 6.75%, methionine 0.43%, calcium 0.62%, and sodium 0.04%.
All procedures of the study were approved by the Animal Care and Ethics Committee of the Suleyman Demirel University (01-05/January 7, 2021). This study was supported by the Scientific Research Projects Coordination Unit of Suleyman Demirel University with project code TSG-2020-8134.
During the procedure, no weight loss of more than 15% was detected, which required stopping the experiment.
Groups of Animals
I. Control group (n=8): This group was anesthetized
with intraperitoneal 90 mg/kg ketamine and 10 mg/
kg xylazine for sham radiation and had 1 mL saline
solution with oral gavage for 7 days.
II. RT group (n=8): This group underwent a single dose of 8 Gy X-ray abdominal radiation after being anesthetized and had 1 mL saline solution with oral gavage for 7 days.
III. RT+ATX group (n=8): This group underwent radiation after being anesthetized and had 1 mL of 4 mg/kg ATX solution via oral gavage for 7 days.
IV. ATX Group (n=8): This group was anesthetized for sham radiation and had 1 mL of 4 mg/kg ATX solution via oral gavage for 7 days.
ATX was used in a wide range of doses (2 µg/kg-100
mg/kg), which can be attributed to the difference in the
searched effects in studies such as inhibiting proliferation,
inducing apoptosis, and mitigation of radiation-induced
hematopoietic system injury after TBI.[
Kim and Kim determined variable effects of ATX
on oxidative stress with different doses in their review.
[
Irradiation
Treatment plans were created using the Eclipse
treatment planning system. Beam's eye view is shown
in Figure
Incision and Tissue Evaluation
Measurement of Oxidative Stress Parameters
TAS analysis: Dark blue-green 2,2'-azino-bis(3-
ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical is
reduced to colorless ABTS form via antioxidants in the
sample.
The total level of antioxidants in the sample is evaluated
according to the difference in absorbance at 660 nm. The determined antioxidative effect of the sample is
expressed as millimolar Trolox equivalent per liter.[
TOS analysis: Ferrous ion-dianisidine complex turns
into ferric ion via the oxidants in the sample. A colored
complex is formed by the interaction of ferric ions with
xylenol orange in an acidic medium. A spectrophotometric
method is used to measure the color intensity, which
relatively shows the total amount of oxidative species.
Hydrogen peroxide was used for the calibration of the
assay. The results were reported as micromolar hydrogen
peroxide equivalent per liter (µmol H2O2 equiv./L).[
Histopathological Examination
Immunohistochemical Examination
For immunohistochemical analysis, sections were
separately investigated for each antibody. To evaluate the
severity of the immunohistochemical reaction of cells
with markers, semiquantitative analysis was performed
using a grading score ranging from 0 to 3 as follows:
0=negative, 1=weak and focal, 2=weak and diffuse, and
3=strong and diffuse. For evaluation, 10 different areas
under 40× objective magnification in each section were
examined. Morphometric analyses and microphotography
were performed via Database Manual Cell Sens Life
Science Imaging Software System (Olympus Co., Tokyo,
Japan). The results were saved and statistically analyzed.
Statistical Analysis
Radiation was given using a Varian DHX linear accelerator
with a fixed source to a surface distance of
98.5 cm and a single field size of 20 cm×21 cm, which
covers the body of the rat. Anisotropic Analytical Algorithm
dose calculation algorithm and 6 MV X-ray
beam were used in the planning process, and 8 Gy
with 600 MU/min was prescribed for irradiation. For
investigating radiation-induced gastrointestinal adverse
effects, 8.4, 9.4, and 10.4 Gy were administered
in a study by Saha et al.[
The surgical procedure was done 24 h after the last
ATX administration under anesthesia. Following an
abdominal incision, a part of the ileum was taken and
stored at -20°C for biochemical analysis and embedded
in a 10% solution of formaldehyde for histopathologic
and immunohistochemical analysis.
Intestinal tissue samples were homogenized with Ultra
Turrax Janke & Kunkel T-25 homogenizer (IKA®-
Werke, Germany) for oxidant-antioxidant analysis.
TAS and TOS were measured spectrophotometrically
(Beckman Coulter AU 5800, Beckman Coulter, USA)
using standard kits (Rel Assay Diagnostics, Gaziantep,
Turkey). Oxidative stress index (OSI) was calculated
using the formula: OSI=TOS/TAS.[25]
Ileum samples were gently removed and fixed in a 10%
solution of neutral formalin. After 24 h of fixation, tissue
samples were trimmed and transferred to the tissue-processing
cassette. Then, samples are processed with an automatic
tissue processor (Leica ASP300S, Wetzlar, Germany)
and embedded in paraffin wax. Sections of 5-µm thickness were taken from the paraffin blocks by a rotary
microtome (Leica RM2155, Leica Microsystems, Wetzlar,
Germany). The sections were stained with hematoxylineosin
coverslip and examined under a light microscope.
In the morphometric analysis of the intestines, the height
and width of the villus were measured in each rat.
For immunohistochemical examination, two series of
sections taken from all blocks of the intestine drawn on
poly-L-lysine coated slides were stained immunohistochemically
for caspase-3 [anti-caspase-3 antibody (E-
8): sc-7272] and TNF-α (anti-TNFα antibody (52B83):
sc-52746, 1/100 dilution] Santa Cruz (Texas, USA) expression
according to the manufacturer's instruction.
The sections were incubated with primary antibodies
for 60 min, and immunohistochemical analysis was
done by a conjugate of a biotinylated secondary antibody
and streptavidin-alkaline phosphatase. EXPOSE Mouse and Rabbit Specific HRP/DAB Detection IHC
kit (ab80436) (Abcam, Cambridge, UK) was used as
the secondary antibody. Diaminobenzidine (DAB) was
used as the chromogen. For negative controls, instead
of a primary antibody, antigen dilution solution was
used. A specialized pathologist from another university
performed all processes on blinded samples.
For statistical analysis, the immunohistochemical
scores of the groups were compared using the one-way
ANOVA Duncan test (SPSS-22.00 package program).
The level of significance was considered at p<0.05.
The differences between the means of groups carrying different letters between the groups are statistically significant, p<0.001. Data are
expressed as mean±standard deviation. One-way ANOVA LSD test was performed. TOS: Total oxidant status; TAS: Total antioxidant
status; OSI: Oxidative stress index; RT: Radiation; ATX: Astaxanthin
ATX Decreased Histopathological Findings Induced
by Radiation
In the histopathological analyses of the intestinal samples,
no histological abnormalities were reported in the
control group. Histological analysis showed that radiation
caused crypt damage and inflammatory reaction
at the mucosal layer. Shortened and fused villi were
noticed in the intestinal mucosa in addition to irregular
proliferation. Inflammatory cell infiltrations at the
propria mucosa were the other marked finding in the
RT group. ATX treatment decreased the pathological
findings in the RT+ATX group. Normal tissue histology
was seen in the ATX group (Fig.
RT: Radiation; ATX: Astaxanthin; HE: hematoxylin and eosin.
The differences between the means
of groups carrying different letters
between the groups are statistically
significant, p<0.001. RT: Radiation;
ATX: Astaxanthin; TNF: Tumor necrosis
factor; Cas-3: Caspase-3.
ATX Decreased TNF-α and Caspase-3 Expression
At the immunohistochemical analysis, increased expressions
were observed in proprial and epithelial cells
of the intestinal villi in the RT group while very slight
to no expression in the control group. Decreased caspase-
3 expressions were observed in the RT+ATX group
(p<0.001). No or slight expressions were noticed in the
ATX group (Fig.
RT: Radiation; ATX: Astaxanthin.
Data expressed mean±standard deviation. One-way ANOVA Duncan test was performed.
This remarkable sensitivity of the intestine is attributed to the retainable intensive proliferative activity of the epithelial cell compartment.
Radiation-induced gastrointestinal toxicity is mainly
a result of massive apoptosis in crypt epithelial cells
and villus stromal cells, which leads to a consequential
mucosal barrier dispersal followed by intestinal bleeding,
electrolyte imbalance, and even sepsis.[
IR causes free radical excess through the lysis of water
molecules and causes cell death by DNA damage
after interacting with tissues. Intracellular antioxidant
expression increases to reduce the cellular damage due
to free radicals formed after IR exposure. Therefore,
natural products with potential antioxidant and immune-
stimulant activity became the subject of recent
investigations as effective radioprotectors.[
ATX is approved as a food colorant[
Many previous studies proved the anticancer effect
of ATX via decreasing mRNA and protein levels of
MMP-2 and MMP-9, inducing apoptosis and regulating
the expressions of NF-κ B, and inhibiting invasion and
angiogenesis through downregulation of JAK-2/STAT-
3 leading to inhibition of tumor development and progression.[
In our study, we assessed TAS, TOS, OSI, histopathological
changes, and immunohistochemical marker
variations in the intestinal tissues to detect the radioprotective
effect of ATX on intestinal injury after abdominopelvic
irradiation.
Oxidative stress is known to be one of the major
mediators of radiation damage, and protection of redox balance facilitates tissue recovery [
In a study with 50 mice in five groups, the protective
effect of Haematococcus pluvialis (containing ATX)
against any antioxidative system damage and DNA
damage induced by Co60 gamma-rays. In line with our
results, superoxide dismutase and other oxidative stress
products were higher in the model group than in the
control group. Compared with the control group, the same contents were decreased (p<0.01) in all Haematococcus
pluvialis groups. Conclusively, ATX was suggested
as a protector against oxidative deterioration and
DNA damage in mice induced by gamma-rays.[
Shortened and fused villi, irregular proliferation in
intestinal mucosa, and inflammatory cell infiltrations
at the propria mucosa were the histological changes
revealing radiation-caused crypt damage and inflammatory
reaction at the mucosal layer induced by radiation.
The addition of ATX to the RT group decreased
the pathological findings caused by RT.
Goblet cells are a quantitatively important population
of the small intestine epithelium.[
Immunohistochemical expression was increased in
proprial and epithelial cells of intestinal villi in the RT
group. However, in the RT+ATX group, expressions
were decreased. No or slight expressions were noticed
in the ATX-only group (Fig.
TNF-α is a major regulator for the activation of proinflammatory
cytokines and mediates phosphorylation
of kinases, which induces transcription of inflammatory
mediators.[
Similar to the above-mentioned studies, we observed
an increased TNF-α expression with RT exposure,
but immunoreaction in the intestinal tissue is decreased
with ATX.
Giris et al.[
Limitations of the Study
An important limitation of our study is that no data in
terms of ROS such as SOD, catalase, and glutathione
in the intestinal pathological tissue section were given.
Another issue to be mentioned is the absence of gene
expression analysis for other inflammatory cytokines
such as IL-6, IL-1Β, and TNF-α.
Peer-review: Externally peer-reviewed.
Conflict of Interest: All authors declared no conflict of interest.
Ethics Committee Approval: The study was approved by the Animal Care and Ethics Committee of the Suleyman Demirel University (no: 01-05, date: 07/01/2021).
Financial Support: None declared.
Authorship contributions: Concept - E.E.Ö.; Design - Ö.Ö.; Supervision - E.E.Ö.; Funding - None; Materials - İ.İ.; Data collection and/or processing - E.E.Ö.; Data analysis and/or interpretation - E.E.Ö.; Literature search - İ.Ç.; Writing - E.E.Ö.; Critical review - İ.Ç.