Exploiting three-dimensional human hepatic constructs to investigate the impact of rs174537 on fatty acid metabolism

The Modern Western Diet has been associated with the rise in metabolic and inflammatory diseases, including obesity, diabetes, and cardiovascular disease. This has been attributed, in part, to the increase in dietary omega-6 polyunsaturated fatty acid (PUFA) consumption, specifically linoleic acid (LA), arachidonic acid (ARA), and their subsequent metabolism to pro-inflammatory metabolites which may be driving human disease. Conversion of dietary LA to ARA is regulated by genetic variants near and within the fatty acid desaturase (FADS) haplotype block, most notably single nucleotide polymorphism rs174537 is strongly associated with FADS1 activity and expression. This variant and others within high linkage disequilibrium may potentially explain the diversity in both diet and inflammatory mediators that drive chronic inflammatory disease in human populations. Mechanistic exploration into this phenomenon using human hepatocytes is limited by current two-dimensional culture models that poorly replicate in vivo functionality. Therefore, we aimed to develop and characterize a three-dimensional hepatic construct for the study of human PUFA metabolism. Primary human hepatocytes cultured in 3D hydrogels were characterized for their capacity to represent basic lipid processing functions, including lipid esterification, de novo lipogenesis, and cholesterol efflux. They were then exposed to control and LA-enriched media and reproducibly displayed allele-specific metabolic activity of FADS1, based on genotype at rs174537. Hepatocytes derived from individuals homozygous with the minor allele at rs174537 (i.e., TT) displayed the slowest metabolic conversion of LA to ARA and significantly reduced FADS1 and FADS2 expression. These results support the feasibility of using 3D human hepatic cultures for the study of human PUFA and lipid metabolism and relevant gene-diet interactions, thereby enabling future nutrition targets in humans.

Impact of rs174537 on Critically Ill Patients with Acute Lung Injury: A Secondary Analysis of the OMEGA Randomized Clinical Trial

BACKGROUND

Nutrition in the intensive care unit is vital for patient care; however, immunomodulatory diets rich in PUFAs like γ-linolenic acid (GLA), EPA, and DHA remain controversial for patients with acute respiratory distress syndrome. We postulate that genetic variants impacting PUFA metabolism contribute to mixed responses to PUFA-rich diets.

OBJECTIVES

In this study, we aimed to test the effects of single nucleotide polymorphism (SNP) rs174537 on differential responses to PUFA-rich diets.

METHODS

We performed a secondary analysis of the OMEGA trial (NCT00609180) where 129 subjects received placebo control diets and 143 received omega-oil. DNA was extracted from buffy coats and used to genotype rs174537; plasma was used to quantitate PUFAs. We tested for SNP-diet interactions on PUFA concentrations, inflammatory biomarkers, and patient outcomes.

RESULTS

We observed that all individuals receiving omega-oil displayed significantly higher concentrations of GLA, EPA, and DHA (all P < 0.0001), but they did not vary by genotype at rs174537. Statistically significant SNP-diet interactions were observed on circulating DHA concentrations in African Americans. Specifically, African American T-allele carriers on placebo illustrated elevated DHA concentrations. Additionally, all individuals receiving omega-oil had higher concentrations of EPA-derived urinary F3-isoprostane (Caucasians: P = 0.0011; African Americans: P = 0.0002). Despite these findings, we did not detect any significant SNP-diet interactions on pulmonary functional metrics, clinical outcomes, and mortality.

CONCLUSIONS

This study highlights the importance of genetic and racial contributions to PUFA metabolism and inflammation. In particular, rs174537 had a significant impact on circulating DHA and urinary isoprostane concentrations. Given our relatively small sample size, further investigations in larger multiethnic cohorts are needed to evaluate the impact of rs174537 on fatty acid metabolism and downstream inflammation.

A Pilot Study Assessing the Impact of rs174537 on Circulating Polyunsaturated Fatty Acids and the Inflammatory Response in Patients with Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and disability in persons under age 45. The hallmark secondary injury profile after TBI involves dynamic interactions between inflammatory and metabolic pathways including fatty acids. Omega-3 polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) have been shown to provide neuroprotective benefits by minimizing neuroinflammation in rodents. These effects have been less conclusive in humans, however. We postulate genetic variants influencing PUFA metabolism in humans could contribute to these disparate findings. Therefore, we sought to (1) characterize the circulating PUFA response and (2) evaluate the impact of rs174537 on inflammation after TBI. A prospective, single-center, observational pilot study was conducted to collect blood samples from Level-1 trauma patients (N = 130) on admission and 24 h post-admission. Plasma was used to quantify PUFA levels and inflammatory cytokines. Deoxyribonucleic acid was extracted and genotyped at rs174537. Associations between PUFAs and inflammatory cytokines were analyzed for all trauma cases and stratified by race (Caucasians only), TBI (TBI: N = 47; non-TBI = 83) and rs174537 genotype (GG: N = 33, GT/TT: N = 44). Patients with TBI had higher plasma DHA levels compared with non-TBI at 24 h post-injury (p = 0.013). The SNP rs174537 was associated with both PUFA levels and inflammatory cytokines (p < 0.05). Specifically, TBI patients with GG genotype exhibited the highest plasma levels of DHA (1.33%) and interleukin-8 (121.5 ± 43.3 pg/mL), which were in turn associated with poorer outcomes. These data illustrate the impact of rs174537 on the post-TBI response. Further work is needed to ascertain how this genetic variant directly influences inflammation after trauma.