Immunohistochemical Study of Glucose Transporter GLUT-5 in Duodenal Epithelium in Norm and in T-2 Mycotoxicosis

Although patterns of glucose transporter expression and notes about diseases leading to adaptive changes in intestinal fructose transport have been well-characterized, the connection between infection and fructose transportation has been lightly investigated. Up to now only few studies on GLUT-5 expression and function under pathological conditions in bird intestines have been carried out. The aim of our current research was to immunolocalize GLUT-5 in chicken duodenal epithelium in norm and during T-2 mycotoxicosis. Material from chicken (Gallus gallus domesticus) duodenum was collected from twelve seven-day-old female broilers, divided into control group and broilers with T-2 mycotoxicosis. The material was fixed with 10% formalin and thereafter embedded into paraffin; slices 7 μm in thickness were cut, followed by immunohistochemical staining, according to the manufacturers guidelines (IHC kit, Abcam, UK) using polyclonal primary antibody Rabbit anti-GLUT-5. Our study revealed the strong expression of GLUT-5 in the apical parts of the duodenal epithelial cells in the control group chickens and weak staining for GLUT-5 in the intestinal epithelium in the T-2 mycotoxicosis group. Our results confirmed decreased the expression of GLUT-5 in the duodenal epithelium during T-2 mycotoxicosis.


Introduction
[15] [16] T-2 mycotoxin, the basic type A trichothecene mycotoxin, has been regarded to be the most toxic trichothecene. In dynamic cell proliferation tissues, such as the gastrointestinal tissues, T-2 mycotoxin poses different toxic effects . It was shown that, in poultry, the T-2 toxin elicits genetic, cellular toxic and immunomodulatory effects, influencing the cells of the digestive, nervous and integumentary system, as well as on the impairment of poultry performance . Symptoms of T-2 mycotoxicosis in chicken manifest in growth retardation, lower feed intake, reduced egg production with thinner eggshells, impaired egg hatch, leucopenia and the cyanosis of the comb. Besides, T-2 mycotoxin is among to the most essential trichothecene mycotoxins, which occurs in several agricultural products , causing severe diseases and even death among humans and animals . Animals are exposed through food to T-2 mycotoxins, whose initial interaction is with the gut epithelium.
As animals are exposed through food to T-2 mycotoxins, one of the most deadly toxins of the trichothecene group and, due to the absence of data about the effect of mycotoxicosis on GLUT-5 in the intestines of birds during their first posthatching week, the aim of our current research was to immunolocalize GLUT-5 in the seven-day old chicken duodenal epithelium in norm and during T-2 mycotoxicosis.
In the gastrointestinal system, the glucose transporter expression is the greatest in the small intestine, where the absorption for monosaccharides depends on the sodium-dependent glucose transporter SGLUT1 and the facilitateddiffusion glucose transporters located in the intestinal epithelium . Identical expressions of GLUT2 and GLUT5 mRNA have been noticed from the proximal to middle parts of the small intestine where GLUT-5 is located on the apical membrane of epithelial cells. While galactose and glucose transport is mediated by SGLT1 , GLUT-5 only mediates the uptake of fructose , whose activity changes during pathological conditions. Generally, it was found that the activity and expression of GLUT-5 was reduced during inflammation and sepsis in rabbits . According to those authors lipopolysaccharide and tumor necrosis factor-α, as the main causes of sepsis, provoked decreased fructose absorption in the jejunum. In humans it has been noted that the infection caused by Helicobacter pylori also reduces the expression of intestinal GLUT-5 . Decreased expression of GLUT-5 in the duodenal epithelial cells in the T-2 mycotoxicosis group found in our study points towards reduced fructose transportation in the diseased gut epithelium.
The gastrointestinal organs are among the first organs coming into contact with mycotoxins of dietary origin. T-2 mycotoxin is a naturally occurring mold byproduct of Fusarium spp. fungus, toxic both to humans and animals. The ingestion of T-2 mycotoxin may occur because of the intake of moldy grains-barley, maize, rice, wheat, etc. The T-2 mycotoxin is specific because the systemic toxicity can result from different route of exposure-respiratory, oral and dermal . The T-2 toxin can be absorbed through human skin, unlike most biological toxins . Besides skin, it causes symptoms related to respiratory and gastrointestinal organs. The fact that it is delivered by water, droplets, aerosols from various dispersal systems and food also makes it a potential biological weapon . In vivo and in vitro T-2 mycotoxin can inhibit DNA and RNA, as well as inhibit protein synthesis 35 . These effects led to apoptosis in various tissues, including immune-and gastrointestinal systems . In immune systems, it inhibits erythropoiesis in the bone marrow and spleen by disturbing the antibody production . According to earlier research, T-2 mycotoxin is able to inhibit IL-2 and IL-5 production by T cells. It has been reported that low concentrations of T-2 mycotoxin ingestion changes Toll-like receptor activation, interfering with the initiation of the inflammatory immune responses against viruses and bacteria. Thus, the mycotoxins may increase the receptivity of animals and humans to infectious diseases . Mycotoxins elicit similar toxic effects among humans and animals. In bird intestines, various methods have been used to study the effects of toxins . Some data revealed the immuno-and cytotoxic effect of ochratoxin A on intestinal epithelium and MALT-system (mucosa-associated lymphoid tissue), modifying the intestinal barrier and thus increasing receptiveness to different associated diseases . A decreased glucose uptake has been registered after the oral administration of the T-2 toxin .
In our recent study decreased expression of GLUT-5 immunolocalized in the duodenal epithelial cells in one-week-old T-2 toxicated broilers, compared to the control group points towards reduced fructose transportation in the diseased gut epithelium after only three days of T-2 mycotoxin administration.