Saturated fatty acids induce inflammation in blood vessels

Significance

Cyclooxygenase-2 (COX-2) catalyzes the biosynthesis of prostanoids that trigger several normal effects during physiological conditions in the human vasculature. However, in pathophysiological conditions the inflammation induced by COX-2 activity may contribute to the development of unstable atherosclerotic plaques or increase the risk of ischemic stroke and heart attack. COX-2 expression is classically induced by cytokines and endotoxins (e.g. lipopolysaccharides), but more recent studies have demonstrated a “sterile” pathway induced by dietary free fatty acids (FFAs) resulting in proinflammatory mediator expression in the human vasculature. Although some researchers have demonstrated the effect of FFAs on the proinflammatory mediator expression of nitric oxide synthase, tumor necrosis factor-α, and interleukin-6 in vascular smooth muscle cells, there is little to no information about the effect of FFAs on the expression, activity, and regulation of COX-2 in the human vasculature. One of the most widespread FFAs in animal and plant food sources is palmitic acid. This necessitates the investigation of its effect on vascular health. Current research suggests palmitate, the anion of palmitic acid at physiological pH, can induce the expression of certain inflammatory markers in the vascular smooth muscle, adipose microvascular endothelial cells and myoblast cell lines of a mouse.

Recently, University of Arizona scientists: Puneet Raman, Lakshmi Madhavpeddi, and Professor Rayna J. Gonzales from the Department of Basic Medical Sciences demonstrated that palmitate elicits a dose-dependent increase in COX-2 protein expression and modulates the regulation of COX-2 activity through the modification of post-translational glycosylation. The work is published in the American Journal of Physiology-Cell Physiology.

The authors observed that the treatment of human primary vascular smooth muscle cells with palmitate resulted in a dose-dependent increase in COX-2 protein levels. They also observed an increase in the more glycosylated form of COX-2, coupled with an increase in the production of downstream inflammatory marker prostaglandin E2 in human primary vascular smooth muscle cells. These effects were attenuated by the treatment of human primary vascular smooth muscle cells with multiple glycosylation inhibitors (tunicamycin and glucosamine hydrochloride). Quantitative increases in cell density and morphological changes were also noted with palmitate treatment, changes that were attenuated by treatment with a functional selective COX-2 inhibitor (NS-398).

“Our research is one of the initial steps in clarifying the link between high fat diet and vascular disease,” Raman said in a statement to Medicine Innovates. “We found a novel mechanism for the inflammation caused by the most common dietary saturated fat. Looking forward, we would like to investigate how other pharmacologic agents can impact the glycosylation and activity of COX-2, a key inflammatory mediator, with the goal of reducing or preventing inflammatory changes in the blood vessel wall. We also see the importance of understanding how unsaturated fatty acids, the ‘healthy fats’, may impact this inflammatory process.”

The University of Arizona study provide compelling evidence that palmitate increases the total protein levels of COX-2 and elicits the regulation of COX-2 activity through posttranslational modification processes that involve glycosylation. These findings will advance further studies on the specific mechanism(s) of palmitate-induced vascular inflammation in the human vasculature for the identification of new potential therapeutic targets for cardiovascular diseases.

 

Medicine-Innovates-Figure-2019-Raman-Gonzales
Proposed mechanism of how palmitic acid, the most abundant dietary saturated fat, contributes to deleterious effects on blood vessel health.

About the author

Puneet Raman, B.S.
4th Year Medical Student
University of Arizona College of Medicine – Phoenix

Puneet Raman was born and raised in Chandler, AZ and graduated as the valedictorian from Chandler High School. He attended Duke University for his undergraduate education and earned a B.A. in History and B.S. in Biology. He worked for a local start-up education technology company, Picmonic, in Tempe AZ while completing his pre-med requirements. He began working in the laboratory of Dr. Rayna Gonzales in 2013 until matriculating as a first year medical student at the University of Arizona College of Medicine – Phoenix in 2015. He has continued his research in Dr. Gonzales’ laboratory through his medical school Scholarly Project requirement.

For his Scholarly Project, Puneet has focused on investigating the exact mechanism by which fatty acids elicit inflammation. He studies a prominent mediator of vascular inflammation, the inducible inflammatory enzyme, cyclooxygenase-2 (COX-2). Under normal physiologic conditions, COX-2 is expressed minimally, however it can be induced in pathophysiological conditions such as cerebrovascular and cardiovascular disease states. To understand how COX-2 contributes to pro-inflammatory induction by palmitic acid, the most abundant dietary saturated fatty acid, Puneet is investigating the mechanisms by which a high fat diet induces inflammation via COX-2 using a primary human vascular cell culture model.

His work has been supported by a Sarver Heart Center medical student award and a University of Arizona College of Medicine Valley Research Partnership P1 grant. Puneet has been recognized nationally for his work including being awarded first place in the American Society for Pharmacology and Experimental Therapeutics (ASPET) Division of Cardiovascular Pharmacology Graduate Student Best Poster Competition at Experimental Biology in 2017.

About the author

Rayna J. Gonzales, Ph.D.
Associate Professor
University of Arizona College of Medicine – Phoenix

Dr. Rayna J. Gonzales received her bachelor’s degree from New Mexico State University and her master’s degree from the University of New Mexico in the Department of Biology. She later received her doctorate degree in Biomedical Sciences from the University of New Mexico School of Medicine with a research focus in vascular biology. Her doctoral research was funded by a National Institutes of Health Training Grant and by an American Physiological Society Porter Development Fellowship. She was recruited by Dr. Sue P. Duckles at the University of California Irvine School of Medicine in the Department of Pharmacology for her post-doctoral training. Dr. Gonzales addressed the role of androgens in mediating cerebrovascular function during hypoxic injury. This work was supported by an American Heart Association (AHA) Post-doctoral fellowship and later by an AHA Scientist Development Award.

In 2007, Dr. Gonzales accepted a position as an Assistant Professor at the University of Arizona College of Medicine – Phoenix as a founding faculty member. In 2013 she was promoted to Associate Professor with tenure in the Department of Basic Medical Sciences. In her current role she leads a research team in investigating potential therapeutic targets to attenuate the development and progression of cerebrovascular endothelial and vascular smooth muscle inflammation during acute cerebral ischemia. When exposed to hypoxic or ischemic stress, the cerebral vasculature expresses proinflammatory mediators such as cyclooxygenase-2 (COX-2), which produces vasoactive agents that are deleterious to vascular function and circulatory health.

The current study reports the discovery of palmitic acid, the major nutrient saturated fatty acid that is also made in the body from sugar precursors, as a novel inducer and posttranslational modifier of COX-2. Indeed, during the development and progression of inflammatory responses to mediators of sterile inflammation such as or during acute ischemic induced cytokine release, dietary palmitate potentiates vascular inflammation both by inducing COX-2 enzyme protein and by activating the proinflammatory enzyme via posttranslational glycosylation. This insight reveals a mechanism whereby, beyond raising cholesterol levels to form plaque, saturated fat exacerbates vascular inflammation and potentially leads to the dislodging of plaque to precipitate ischemic stroke. In total, Dr. Gonzales has authored 30 peer reviewed journal articles and is currently funded by the American Heart Association.

Reference

Raman, P., Madhavpeddi, L., and Gonzales, R.J. Palmitate induces glycosylation of cyclooxygenase-2 in primary human vascular smooth muscle cells, American Journal of Physiology- Cell Physiology 314 (2018) C545–C553

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