Date of Award

2019

Degree Name

Biomedical Sciences

College

Joan C. Edwards School of Medicine

Type of Degree

Ph.D.

Document Type

Dissertation

First Advisor

Dr. Uma Sundaram, Committee Chairperson

Second Advisor

Dr. Subha Arthur

Third Advisor

Dr. Richard Egleton

Fourth Advisor

Dr. Sandrine Pierre

Fifth Advisor

Dr. Travis Salisbury

Abstract

Background: Alcohol consumption leads to a variety of different health consequences including cardiovascular disease, cancer and malnutrition. This malnutrition is in part due to a sub-optimal diet but also due to the malabsorption of nutrients along the small intestine. Many studies have shown that ethanol directly decreases nutrient absorption along the small intestine; however, few studies have investigated the effect of a moderate dose of ethanol on the transmembrane nutrient co-transporters that line the brush border membrane of the small intestine. The primary fuel source for the small intestine, glutamine, as well as for the entire body, glucose, are absorbed by the sodium-dependent nutrient co-transporters: Na-glutamine co-transport (B0AT1) and Naglucose co-transport (SGLT1), respectively. Both B0AT1 and SGLT1 are present in the brush border membrane of intestinal absorptive villus, but not crypt cells. The effect of moderate ethanol consumption on B0AT1 and SGLT1 in intestinal epithelial cells is not known.

Methods: Rat intestinal epithelial cells (IEC-18) were exposed to 8.64 mM ethanol over 1, 3, 6, and 12 hours. Sixteen-week-old Sprague Dawley rats were administered an intragastric gavage of 2 g/kg ethanol over 1, 3, and 6 hours. Sodium-dependent 3H-glutamine and 3H-O-methyl-D-glucose uptakes were conducted to determine B0AT1 and SGLT1 activities, respectively. Na-K-ATPase activity was measured as a function of inorganic phosphate release and with 86rubidium uptake. Protein expression was analyzed by Western blot analysis and immunohistochemical staining.

Results: Ethanol significantly decreased glutamine absorption, glucose absorption and Na-KATPase activity in enterocytes. Kinetic studies showed a decrease in Vmax values for B0AT1 in vitro, but an increase in Km values for SGLT1 in vitro and in vivo. Western blots and immunohistochemistry data support these findings. Ethanol did not change Na-H exchange in vitro. Acetaldehyde alone did not change glutamine or glucose uptake in vitro.

Conclusions: Moderate ethanol significantly inhibits B0AT1 and SGLT1 in intestinal epithelial cells. This occurs through two separate mechanisms: B0AT1 is reduced via a decrease in co-transporter number while SGLT1 is diminished via a decrease in co-transporter affinity for glucose. Moreover, both B0AT1 and SGLT1 are further inhibited at the intact cellular level secondary to the decreased sodium-gradient. Overall, glutamine and glucose absorption by enterocytes is significantly affected by moderate ethanol, which may help describe the onset of alcoholic malnutrition.

Subject(s)

Alcohol -- Physiological effect.

Membranes (Biology) -- Research.

Cell receptors -- Research.

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