Dietary polyunsaturated fatty acids and their metabolites: Implications for diabetes pathophysiology, prevention, and treatment

Gαz-independent and -dependent Improvements With EPA Supplementation on the Early Type 1 Diabetes Phenotype of NOD Mice

Prostaglandin E2 (PGE2) is a key mediator of inflammation and is derived from the omega-6 polyunsaturated fatty acid, arachidonic acid (AA). In the β-cell, the PGE2 receptor, Prostaglandin EP3 receptor (EP3), is coupled to the unique heterotrimeric G protein alpha subunit, Gɑz to reduce the production of cyclic adenosine monophosphate (cAMP), a key signaling molecule that activates β-cell function, proliferation, and survival pathways. Nonobese diabetic (NOD) mice are a strong model of type 1 diabetes (T1D), and NOD mice lacking Gɑz are protected from hyperglycemia. Therefore, limiting systemic PGE2 production could potentially improve both the inflammatory and β-cell dysfunction phenotype of T1D. Here, we sought to evaluate the effect of eicosapentaenoic acid (EPA) feeding, which limits PGE2 production, on the early T1D phenotype of NOD mice in the presence and absence of Gαz. Wild-type and Gαz knockout NOD mice were fed a control or EPA-enriched diet for 12 weeks, beginning at age 4 to 5 weeks. Oral glucose tolerance, splenic T-cell populations, islet cytokine/chemokine gene expression, islet insulitis, measurements of β-cell mass, and measurements of β-cell function were quantified. EPA diet feeding and Gɑz loss independently improved different aspects of the early NOD T1D phenotype and coordinated to alter the expression of certain cytokine/chemokine genes and enhance incretin-potentiated insulin secretion. Our results shed critical light on the Gαz-dependent and -independent effects of dietary EPA enrichment and provide a rationale for future research into novel pharmacological and dietary adjuvant therapies for T1D.

Adherence to diet with higher dietary diabetes risk reduction score is associated with reduced risk of type 2 diabetes incident in Iranian adults

BACKGROUND

The Dietary diabetes risk reduction score (DDRRS) has recently been considered by researchers as a diet quality index to predict the risk of chronic diseases, such as type 2 diabetes (T2D). In this study, we aimed to assess the association of DDRRS with T2D risk in Iranian adults.

METHODS

Subjects aged ≥ 40 years without T2D (n = 2081) were selected for the current study from participants of the Tehran Lipid and Glucose Study (2009-2011) and followed for a mean of 6.01 years. We used the food frequency questionnaire to determine the DDRRS that is characterized by eight components, including higher consumption of nuts, cereal fiber, coffee, and polyunsaturated to saturated fat ratio and lower consumption of red or processed meats, trans fats, sugar-sweetened beverages, and high glycemic index foods. The multivariable logistic regression analysis was used to determine the odds ratio (ORs) and 95% confidence interval (CI) of T2D across the DDRRS tertiles.

RESULTS

The mean ± SD age of individuals was 50.4 ± 8.2 years at baseline. The Median (25-75 interquartile range) DDRRS of the study population was 24(22-27). During the study follow-up, 233(11.2%) new cases of T2D were ascertained. In the age and sex-adjusted model, the odds of T2D were decreased across tertiles of DDRRS (OR = 0.68; 95%CI: 0.48-0.97, P for trend = 0.037). Based on the multivariable-adjusted model, after controlling all potential confounders, the risk of T2D is reduced across tertiles of DDRRS (OR = 0.66; 95%CI: 0.44-0.98, P for trend = 0.047). Also, higher scores (lower consumption) of red and processed meat (OR = 0.59; 95%CI: 0.39-0.88, P = 0.012) and sugar-sweetened beverages (OR = 0.49; 95%CI: 0.32-0.76, P = 0.002) as DDRRS components were associated with decreased T2D incident.

CONCLUSIONS

Our findings suggested that a diet with a higher score of DDRRS may be related to reducing the risk of T2D in Iranian adults.

Plasma Prostaglandin E2 Metabolite Levels Predict Type 2 Diabetes Status and One-Year Therapeutic Response Independent of Clinical Markers of Inflammation

Over half of patients with type 2 diabetes (T2D) are unable to achieve blood glucose targets despite therapeutic compliance, significantly increasing their risk of long-term complications. Discovering ways to identify and properly treat these individuals is a critical problem in the field. The arachidonic acid metabolite, prostaglandin E₂ (PGE₂), has shown great promise as a biomarker of β-cell dysfunction in T2D. PGE₂ synthesis, secretion, and downstream signaling are all upregulated in pancreatic islets isolated from T2D mice and human organ donors. In these islets, preventing β-cell PGE₂ signaling via a prostaglandin EP3 receptor antagonist significantly improves their glucose-stimulated and hormone-potentiated insulin secretion response. In this clinical cohort study, 167 participants, 35 non-diabetic, and 132 with T2D, were recruited from the University of Wisconsin Hospital and Clinics. At enrollment, a standard set of demographic, biometric, and clinical measurements were performed to quantify obesity status and glucose control. C reactive protein was measured to exclude acute inflammation/illness, and white cell count (WBC), erythrocyte sedimentation rate (ESR), and fasting triglycerides were used as markers of systemic inflammation. Finally, a plasma sample for research was used to determine circulating PGE₂ metabolite (PGEM) levels. At baseline, PGEM levels were not correlated with WBC and triglycerides, only weakly correlated with ESR, and were the strongest predictor of T2D disease status. One year after enrollment, blood glucose management was assessed by chart review, with a clinically-relevant change in hemoglobin A1c (HbA1c) defined as ≥0.5%. PGEM levels were strongly predictive of therapeutic response, independent of age, obesity, glucose control, and systemic inflammation at enrollment. Our results provide strong support for future research in this area.

Investigating the Role of EPA and DHA on Cellular Oxidative Stress; Profiling Antidiabetic and Antihypertensive Potential

Background

Polyunsaturated fatty acids (PUFAs) remain part of the diet and are essential for growth and development. Furthermore, omega - 3 fatty acids boost various cardiovascular disease risk factors as well as lower blood pressure and cholesterol levels. The effects of PUFAs on glycemia in type 2 diabetes patients are unclear. In the present study, the anti-diabetic and anti-hypertensive potential of eicosapentenoic acid (EPA) and docosahexaenoic acid (DHA)-two polyunsaturated fatty acids-were examined.

Material and Methods

Using 3T3-L1 pre-adipocyte cells fed with PUFAs, the antioxidant capacity of EPA and DHA was assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay/test. The DPPH activity of EPA and DHA was 49.72 and 50.51%, respectively, indicating a reduction in oxidative stress. The number, size, and total lipid content of adipocytes in adipose tissue were used to study the anti-diabetic effect of EPA and DHA. Both PUFAs were revealed to have a much lower capacity for cell lysis of 3T3-L1 pre-adipocytes when compared to propylene glycol monomethyl ether acetate (PMA). In 3T3-L1 pre-adipocyte cells that had been treated with EPA and DHA, the gene expression profiles for ATP synthase 6 were examined.

Results

The results demonstrated a similar trend of reducing total lipid content in 3T3-L1 pre-adipocyte cells treated with EPA and DHA. The amount of cell lysis was then examined for 3T3-L1 pre-adipocyte cells exposed to DHA and EPA, and the results showed 38.45% and 41.26%, respectively. In the 3T3-L1 pre-adipocyte cells, treatment with PUFAs, EPA, and DHA dramatically lowered total lipid content after 48 hours. The study also revealed that exposing 3T3-L1 pre-adipocyte cells to EPA at 90 g/ml for 48 hours reduced the total lipid content by a significant amount.

Conclusion

According to the findings, EPA and DHA therapy reversed oxidative stress in mitochondria and upregulated the ATP synthase 6 gene. This discovery shows how EPA and DHA have anti-diabetic and hypertension properties.

Prostaglandin EP3 receptor signaling is required to prevent insulin hypersecretion and metabolic dysfunction in a non-obese mouse model of insulin resistance

When homozygous for the Leptin^Ob mutation (Ob), Black-and-Tan Brachyury (BTBR) mice become morbidly obese and severely insulin resistant, and by 10 wk of age, frankly diabetic. Previous work has shown prostaglandin EP3 receptor (EP3) expression and activity is upregulated in islets from BTBR-Ob mice as compared with lean controls, actively contributing to their β-cell dysfunction. In this work, we aimed to test the impact of β-cell-specific EP3 loss on the BTBR-Ob phenotype by crossing Ptger3 floxed mice with the rat insulin promoter (RIP)-Cre^Herr driver strain. Instead, germline recombination of the floxed allele in the founder mouse-an event whose prevalence we identified as directly associated with underlying insulin resistance of the background strain-generated a full-body knockout. Full-body EP3 loss provided no diabetes protection to BTBR-Ob mice but, unexpectedly, significantly worsened BTBR-lean insulin resistance and glucose tolerance. This in vivo phenotype was not associated with changes in β-cell fractional area or markers of β-cell replication ex vivo. Instead, EP3-null BTBR-lean islets had essentially uncontrolled insulin hypersecretion. The selective upregulation of constitutively active EP3 splice variants in islets from young, lean BTBR mice as compared with C57BL/6J, where no phenotype of EP3 loss has been observed, provides a potential explanation for the hypersecretion phenotype. In support of this, high islet EP3 expression in Balb/c females versus Balb/c males was fully consistent with their sexually dimorphic metabolic phenotype after loss of EP3-coupled Gα_z protein. Taken together, our findings provide a new dimension to the understanding of EP3 as a critical brake on insulin secretion.NEW & NOTEWORTHY Islet prostaglandin EP3 receptor (EP3) signaling is well known as upregulated in the pathophysiological conditions of type 2 diabetes, contributing to β-cell dysfunction. Unexpected findings in mouse models of non-obese insulin sensitivity and resistance provide a new dimension to our understanding of EP3 as a key modulator of insulin secretion. A previously unknown relationship between mouse insulin resistance and the penetrance of rat insulin promoter-driven germline floxed allele recombination is critical to consider when creating β-cell-specific knockouts.

Agonist-independent Gαz activity negatively regulates beta-cell compensation in a diet-induced obesity model of type 2 diabetes

The inhibitory G protein alpha-subunit (Gα_z) is an important modulator of beta-cell function. Full-body Gα_z-null mice are protected from hyperglycemia and glucose intolerance after long-term high-fat diet (HFD) feeding. In this study, at a time point in the feeding regimen where WT mice are only mildly glucose intolerant, transcriptomics analyses reveal islets from HFD-fed Gα_z KO mice have a dramatically altered gene expression pattern as compared with WT HFD-fed mice, with entire gene pathways not only being more strongly upregulated or downregulated versus control-diet fed groups but actually reversed in direction. Genes involved in the “pancreatic secretion” pathway are the most strongly differentially regulated: a finding that correlates with enhanced islet insulin secretion and decreased glucagon secretion at the study end. The protection of Gα_z-null mice from HFD-induced diabetes is beta-cell autonomous, as beta cell–specific Gα_z-null mice phenocopy the full-body KOs. The glucose-stimulated and incretin-potentiated insulin secretion response of islets from HFD-fed beta cell–specific Gα_z-null mice is significantly improved as compared with islets from HFD-fed WT controls, which, along with no impact of Gα_z loss or HFD feeding on beta-cell proliferation or surrogates of beta-cell mass, supports a secretion-specific mechanism. Gα_z is coupled to the prostaglandin EP3 receptor in pancreatic beta cells. We confirm the EP3γ splice variant has both constitutive and agonist-sensitive activity to inhibit cAMP production and downstream beta-cell function, with both activities being dependent on the presence of beta-cell Gα_z.

The Combination of Whole Cell Lipidomics Analysis and Single Cell Confocal Imaging of Fluidity and Micropolarity Provides Insight into Stress-Induced Lipid Turnover in Subcellular Organelles of Pancreatic Beta Cells

Modern omics techniques reveal molecular structures and cellular networks of tissues and cells in unprecedented detail. Recent advances in single cell analysis have further revolutionized all disciplines in cellular and molecular biology. These methods have also been employed in current investigations on the structure and function of insulin secreting beta cells under normal and pathological conditions that lead to an impaired glucose tolerance and type 2 diabetes. Proteomic and transcriptomic analyses have pointed to significant alterations in protein expression and function in beta cells exposed to diabetes like conditions (e.g., high glucose and/or saturated fatty acids levels). These nutritional overload stressful conditions are often defined as glucolipotoxic due to the progressive damage they cause to the cells. Our recent studies on the rat insulinoma-derived INS-1E beta cell line point to differential effects of such conditions in the phospholipid bilayers in beta cells. This review focuses on confocal microscopy-based detection of these profound alterations in the plasma membrane and membranes of insulin granules and lipid droplets in single beta cells under such nutritional load conditions.