Interesterified palm oil promotes insulin resistance and altered insulin secretion and signaling in Swiss mice

Interesterified fats have been used to replace trans-fat in ultra-processed foods. However, their metabolic effects are not completely understood. Hence, this study aimed to investigate the effects related to glucose homeostasis in response to interesterified palm oil or refined palm oil intake. Four-week-old male Swiss mice were randomly divided into four experimental groups and fed the following diets for 8 weeks: a normocaloric and normolipidic diet containing refined palm oil (PO group) or interesterified palm oil (IPO group); a hypercaloric and high-fat diet containing refined PO (POHF group) or interesterified PO (IPOHF group). Metabolic parameters related to body mass, adiposity and food consumption showed no significant differences. As for glucose homeostasis parameters, interesterified palm oil diets (IPO and IPOHF) resulted in higher glucose intolerance than unmodified palm oil diets (PO and POHF). Euglycemic-hyperinsulinemic clamp assessment showed a higher endogenous glucose production in the IPO group compared with the PO group. Moreover, the IPO group showed significantly lower p-AKT protein content (in the muscle and liver tissues) when compared with the PO group. Analysis of glucose-stimulated static insulin secretion (11.1 mmol/L glucose) in isolated pancreatic islets showed a higher insulin secretion in animals fed interesterified fat diets (IPO and IPOHF) than in those fed with palm oil (PO and POHF). Interesterified palm oil, including in normolipidic diets, can impair insulin signaling in peripheral tissues and increase insulin secretion by β-cells, characterizing insulin resistance in mice.

[Role of fatty acids in the nervous control of energy balance]

Fatty acid (FA)-sensitive neurons are present in the brain, especially the hypothalamus, and play a key role in the neural control of energy and glucose homeostasis including feeding behavior, insulin secretion and action. Subpopulations of neurons in the ventromedial and arcuate hypothalamic nuclei are selectively either inhibited or activated by FA. Molecular effectors of these FA effects include ion channels such as chloride, potassium or calcium. In addition at least half of the FA responses in ventromedial hypothalamic neurons are mediated by interaction with FAT/CD36, a FA translocator/receptor that does not require intracellular metabolism to activate downstream signaling. Recently, an important role of lipoprotein lipase in FA sensing has also been demonstrated not only in hypothalamus, but also in the hippocampus and striatum. Finally, FA overload might impair neural control of energy homeostasis through enhanced ceramide synthesis and may contribute to obesity and/or type 2 diabetes pathogenesis in predisposed subjects.

A multiorgan map of metabolic, signaling, and inflammatory pathways that coordinately control fasting glycemia in mice

To identify the pathways that are coordinately regulated in pancreatic β cells, muscle, liver, and fat to control fasting glycemia we fed C57Bl/6, DBA/2, and Balb/c mice a regular chow or a high fat diet for 5, 13, and 33 days. Physiological, transcriptomic and lipidomic data were used in a data fusion approach to identify organ-specific pathways linked to fasting glycemia across all conditions investigated. In pancreatic islets, constant insulinemia despite higher glycemic levels was associated with reduced expression of hormone and neurotransmitter receptors, OXPHOS, cadherins, integrins, and gap junction mRNAs. Higher glycemia and insulin resistance were associated, in muscle, with decreased insulin signaling, glycolytic, Krebs' cycle, OXPHOS, and endo/exocytosis mRNAs; in hepatocytes, with reduced insulin signaling, branched chain amino acid catabolism and OXPHOS mRNAs; in adipose tissue, with increased innate immunity and lipid catabolism mRNAs. These data provide a resource for further studies of interorgan communication in glucose homeostasis.

Brain lipid sensing and the neural control of energy balance

The central nervous system continuously detects circulating concentrations of lipids such as fatty acids and troglycerides. Once information has been detected, the central nervous system can in turn participate in the control of energy balance and blood sugar levels and in particular regulate the secretion and action of insulin. Neurons capable of detecting circulating lipid variations are located in the hypothalamus and in other regions such as the nucleus accumbens, the striatum or the hippocampus. An excess of lipids will have deleterious effects and may induce central lipotoxicity, in particular following local production of ceramides and the appearance of neuroinflammation which may lead to metabolic diseases such as obesity and type 2 diabetes.

Disruption of Pituitary Gonadotrope Activity in Male Rats After Short- or Long-Term High-Fat Diets Is Not Associated With Pituitary Inflammation

Overnutrition is associated with the activation of inflammatory pathways in metabolically linked organs and an early hypothalamic inflammation is now known to disrupt the central control of metabolic function. Because we demonstrated that fatty acids (FA) target the pituitary and affect gonadotropin synthesis, we asked whether overnutrition induces pituitary inflammation that may contribute to obesity-associated disorders in the control of reproduction. We analyzed pituitary inflammation and hypothalamic-pituitary-testicular axis in male rats fed a short- (4 weeks) or long-term (20 weeks) high-fat diet. The effect of diet enrichment with the ω3 polyunsaturated FA, DHA, was also analyzed. After only 4 weeks and before weight gain of rats, high-fat diet caused a significant decrease in pituitary gonadotropin and hypothalamic GnRH transcript levels despite unchanged testosterone and inhibin B levels. Contrasting with the hypothalamus, there was no concomitant increases in gene expression of pituitary inflammatory mediators and even a reduction of prototypical cytokines such as interleukin-1β and TNF-α. No inflammation was still detected in the pituitary after 20 weeks although gonadotropin transcripts and circulating levels were still altered. Gonadotropins were the only pituitary hormones remaining affected at this stage of the regimen, underlying a differential susceptibility of pituitary lineages to metabolic disorders. DHA enrichment of the diet did not prevent alterations of gonadotrope activity due to either a long- or a short-term high-fat diet although it blocked early hypothalamic inflammation and attenuated several metabolic effects. Taken together, our findings suggest that high-fat diet-induced defects in gonadotrope activity in male rats occurred despite a lack of pituitary inflammation.

Fish oil minimises feed intake and improves insulin sensitivity in Zucker fa/fa rats

Long-chain n-3 PUFA (LC n-3 PUFA) prevent, in rodents, insulin resistance (IR) induced by a high-fat and/or fructose diet but not IR induced by glucocorticoids. In humans, contrasting effects have also been reported. We investigated their effects on insulin sensitivity, feed intake (FI) and body weight gain in genetically insulin resistant male obese (fa/fa) Zucker (ZO) rats during the development of obesity. ZO rats were fed a diet supplemented with 7 % fish oil (FO) + 1 % corn oil (CO) (wt/wt) (ZOFO), while the control group was fed a diet containing 8 % fat from CO (wt/wt) (ZOCO). Male lean Zucker (ZL) rats fed either FO (ZLFO) or CO (ZLCO) diet were used as controls. FO was a marine-derived TAG oil containing EPA 90 mg/g + DHA 430 mg/g. During an oral glucose tolerance test, glucose tolerance remained unaltered by FO while insulin response was reduced in ZOFO only. Liver insulin sensitivity (euglycaemic-hyperinsulinaemic clamp + 2 deoxyglucose) was improved in ZOFO rats, linked to changes in phosphoenolpyruvate carboxykinase expression, activity and glucose-6-phosphatase activity. FI in response to intra-carotid insulin/glucose infusion was decreased similarly in ZOFO and ZOCO. Hypothalamic ceramides levels were lower in ZOFO than in ZOCO. Our study demonstrates that LC n-3 PUFA can minimise weight gain, possibly by alleviating hypothalamic lipotoxicity, and liver IR in genetically obese Zucker rats.

A neuronal circuit driven by GLP-1 in the olfactory bulb regulates insulin secretion

Glucagon-like peptide 1 (GLP-1) stimulates insulin secretion and holds significant pharmacological potential. Nevertheless, the regulation of energy homeostasis by centrally-produced GLP-1 remains partially understood. Preproglucagon cells, known to release GLP-1, are found in the olfactory bulb (OB). We show that activating GLP-1 receptors (GLP-1R) in the OB stimulates insulin secretion in response to oral glucose in lean and diet-induced obese male mice. This is associated with reduced noradrenaline content in the pancreas and blocked by an α2-adrenergic receptor agonist, implicating functional involvement of the sympathetic nervous system (SNS). Inhibiting GABAA receptors in the paraventricular nucleus of the hypothalamus (PVN), the control centre of the SNS, abolishes the enhancing effect on insulin secretion induced by OB GLP-1R. Therefore, OB GLP-1-dependent regulation of insulin secretion relies on a relay within the PVN. This study provides evidence that OB GLP-1 signalling engages a top-down neural mechanism to control insulin secretion via the SNS.

Identification of integrated proteomics and transcriptomics signature of alcohol-associated liver disease using machine learning

Distinguishing between alcohol-associated hepatitis (AH) and alcohol-associated cirrhosis (AC) remains a diagnostic challenge. In this study, we used machine learning with transcriptomics and proteomics data from liver tissue and peripheral mononuclear blood cells (PBMCs) to classify patients with alcohol-associated liver disease. The conditions in the study were AH, AC, and healthy controls. We processed 98 PBMC RNAseq samples, 55 PBMC proteomic samples, 48 liver RNAseq samples, and 53 liver proteomic samples. First, we built separate classification and feature selection pipelines for transcriptomics and proteomics data. The liver tissue models were validated in independent liver tissue datasets. Next, we built integrated gene and protein expression models that allowed us to identify combined gene-protein biomarker panels. For liver tissue, we attained 90% nested-cross validation accuracy in our dataset and 82% accuracy in the independent validation dataset using transcriptomic data. We attained 100% nested-cross validation accuracy in our dataset and 61% accuracy in the independent validation dataset using proteomic data. For PBMCs, we attained 83% and 89% accuracy with transcriptomic and proteomic data, respectively. The integration of the two data types resulted in improved classification accuracy for PBMCs, but not liver tissue. We also identified the following gene-protein matches within the gene-protein biomarker panels: CLEC4M-CLC4M, GSTA1-GSTA2 for liver tissue and SELENBP1-SBP1 for PBMCs. In this study, machine learning models had high classification accuracy for both transcriptomics and proteomics data, across liver tissue and PBMCs. The integration of transcriptomics and proteomics into a multi-omics model yielded improvement in classification accuracy for the PBMC data. The set of integrated gene-protein biomarkers for PBMCs show promise toward developing a liquid biopsy for alcohol-associated liver disease.

Dietary docosahexaenoic acid (DHA) downregulates liver DHA synthesis by inhibiting eicosapentaenoic acid elongation

DHA is abundant in the brain where it regulates cell survival, neurogenesis, and neuroinflammation. DHA can be obtained from the diet or synthesized from alpha-linolenic acid (ALA; 18:3n-3) via a series of desaturation and elongation reactions occurring in the liver. Tracer studies suggest that dietary DHA can downregulate its own synthesis, but the mechanism remains undetermined and is the primary objective of this manuscript. First, we show by tracing 13C content (δ13C) of DHA via compound-specific isotope analysis, that following low dietary DHA, the brain receives DHA synthesized from ALA. We then show that dietary DHA increases mouse liver and serum EPA, which is dependant on ALA. Furthermore, by compound-specific isotope analysis we demonstrate that the source of increased EPA is slowed EPA metabolism, not increased DHA retroconversion as previously assumed. DHA feeding alone or with ALA lowered liver elongation of very long chain (ELOVL2, EPA elongation) enzyme activity despite no change in protein content. To further evaluate the role of ELOVL2, a liver-specific Elovl2 KO was generated showing that DHA feeding in the presence or absence of a functional liver ELOVL2 yields similar results. An enzyme competition assay for EPA elongation suggests both uncompetitive and noncompetitive inhibition by DHA depending on DHA levels. To translate our findings, we show that DHA supplementation in men and women increases EPA levels in a manner dependent on a SNP (rs953413) in the ELOVL2 gene. In conclusion, we identify a novel feedback inhibition pathway where dietary DHA downregulates its liver synthesis by inhibiting EPA elongation.

Correction to: Establishing a Reproducible Murine Animal Model of Single Anastomosis Duodenoileal Bypass with Sleeve Gastrectomy (SADl-S)

The first and last names of the authors were inverted in the original article. They are displayed correctly here.

Transcriptome atlases of rat brain regions and their adaptation to diabetes resolution following gastrectomy in the Goto-Kakizaki rat

Brain regions drive multiple physiological functions through specific gene expression patterns that adapt to environmental influences, drug treatments and disease conditions. To generate a detailed atlas of the brain transcriptome in the context of diabetes, we carried out RNA sequencing in hypothalamus, hippocampus, brainstem and striatum of the Goto-Kakizaki (GK) rat model of spontaneous type 2 diabetes, which was applied to identify gene transcription adaptation to improved glycemic control following vertical sleeve gastrectomy (VSG) in the GK. Over 19,000 distinct transcripts were detected in the rat brain, including 2794 which were consistently expressed in the four brain regions. Region-specific gene expression was identified in hypothalamus (n = 477), hippocampus (n = 468), brainstem (n = 1173) and striatum (n = 791), resulting in differential regulation of biological processes between regions. Differentially expressed genes between VSG and sham operated rats were only found in the hypothalamus and were predominantly involved in the regulation of endothelium and extracellular matrix. These results provide a detailed atlas of regional gene expression in the diabetic rat brain and suggest that the long term effects of gastrectomy-promoted diabetes remission involve functional changes in the hypothalamus endothelium.

Abstract 2238: A novel comprehensive breakpoint-targeted assay for clinically actionable RNA fusions and aberrant RNAs in solid tumors

Background: Gene fusions are major drivers of cancer and their accurate detection is key for supporting diagnosis and therapy selection. There are more than 65,000 annotated gene fusion events. Current fusions detection strategies are limited to amplicon panels querying only a small number of genes, or whole exome capture based assays, which can reduce sensitivity. With these technologies, multiple small panels are required to capture all relevant fusions, which is prohibitive for small biopsies like fine needle aspirates. Hence, clinical grade assays able to accurately detect a comprehensive set of the most clinically relevant gene fusions for solid tumors are needed.

Methods: We isolated total nucleic acid (TNA) from 141 FFPE tumor specimens or a control sample (Seraseq) and performed pair-ended, strand-specific hybridization-based RNA sequencing on a Next-Seq 500. We selected 252 fusion genes from NCCN and WHO guidelines, published clinical studies, and the 120 most frequent curated fusions in solid tumors from COSMIC (v91). These fusions are clinically relevant to most frequent cancers, including breast, colorectal, lung, lymphoma, pancreatic, prostate, salivary gland, sarcomas, and thyroid cancers. Chimeric probes were synthetized targeting fusion RNA sequences for 2230 selected breakpoints and exon junction regions of aberrant RNAs, including EGFRvIII, MET exon 14 skipping, ARv7 and ARv9. We also targeted the full coding region of 27 genes whose change in expression may suggest translocations and mutations, or have diagnostic value. Fusions were called by a custom pipeline using 3 fusion callers and a machine-learning algorithm. The PCR-based Archer FusionPlex assays and RT-PCR followed by Sanger were used as orthogonal validation methods.

Results: This single RNA fusion assay can detect at least 1194 unique known fusions pairs involving 1104 genes, as compared to 63 or 47 fusion genes from other commercially available NGS assays. On 141 FFPE samples from various tumor types, we detected 100/106 fusions reported in our CLIA laboratory Archer Sarcoma and Comprehensive Thyroid & Lung (CTL) panels. We also identified 41 additional high confidence fusions missed by Archer but confirmed by Sanger sequencing. Thus, the assay has 95.9% (141/147) sensitivity and 100% specificity, as all fusions were confirmed by either orthogonal assay. We also detected MET exon 14 skipping, EGFRvIII and ARv7 variants. Importantly, in two samples we detected MET exon 14 skipping not predicted from DNA mutation analysis showing the sensitivity of the approach. Notably, several of the 41 additional fusions are novel and were targeted by only one of the breakpoints.

Conclusion: We developed a novel and efficient breakpoint targeted fusion detection RNA-seq assay from extracted TNA from FFPE samples that can comprehensively profile thousands of clinically actionable RNA fusions and aberrant RNAs in solid tumors.

Citation Format: Fernando J. Lopez-Diaz, Steven P. Rivera, Chenyin Ou, Christophe Magnan, Brad Thomas, Tibor Gyuris, Yanglong Mou, Segun Jung, Madhuri Paul, Forrest Blocker, Shari Brown, Jacqueline Lekostaj, Ryan Bender, Sally Agersborg, Lawrence M. Weiss, Vincent Funari. A novel comprehensive breakpoint-targeted assay for clinically actionable RNA fusions and aberrant RNAs in solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2238.

Preterm birth: A neuroinflammatory origin for metabolic diseases?

Preterm birth and its related complications have become more and more common as neonatal medicine advances. The concept of "developmental origins of health and disease" has raised awareness of adverse perinatal events in the development of diseases later in life. To explore this concept, we propose that encephalopathy of prematurity (EoP) as a potential pro-inflammatory early life event becomes a novel risk factor for metabolic diseases in children/adolescents and adulthood. Here, we review epidemiological evidence that links preterm birth to metabolic diseases and discuss possible synergic roles of preterm birth and neuroinflammation from EoP in the development of metabolic diseases. In addition, we explore theoretical underlying mechanisms regarding developmental programming of the energy control system and HPA axis.

ABCG1 orchestrates adipose tissue macrophage plasticity and insulin resistance in obesity by rewiring saturated fatty acid pools

The mechanisms governing adipose tissue macrophage (ATM) metabolic adaptation during diet-induced obesity (DIO) are poorly understood. In obese adipose tissue, ATMs are exposed to lipid fluxes, which can influence the activation of specific inflammatory and metabolic programs and contribute to the development of obesity-associated insulin resistance and other metabolic disorders. In the present study, we demonstrate that the membrane ATP-binding cassette g1 (Abcg1) transporter controls the ATM functional response to fatty acids (FAs) carried by triglyceride-rich lipoproteins, which are abundant in high-energy diets. Mice genetically lacking Abcg1 in the myeloid lineage presented an ameliorated inflammatory status in adipose tissue and reduced insulin resistance. Abcg1-deficient ATMs exhibited a less inflammatory phenotype accompanied by a low bioenergetic profile and modified FA metabolism. A closer look at the ATM lipidome revealed a shift in the handling of FA pools, including a redirection of saturated FAs from membrane phospholipids to lipid droplets, leading to a reduction in membrane rigidity and neutralization of proinflammatory FAs. ATMs from human individuals with obesity presented the same reciprocal relationship between ABCG1 expression and this inflammatory and metabolic status. Abolition of this protective, anti-inflammatory phenotype in Abcg1-deficient ATMs was achieved through restoration of lipoprotein lipase (Lpl) activity, thus delineating the importance of the Abcg1/Lpl axis in controlling ATM metabolic inflammation. Overall, our study identifies the rewiring of FA pools by Abcg1 as a major pathway orchestrating ATM plasticity and insulin resistance in DIO.

Serotonergic neurons are involved in the counter-regulatory response to hypoglycemia

OBJECTIVES

Intensive insulin therapy provides optimal glycemic control in patients with diabetes. However, intensive insulin therapy causes so-called iatrogenic hypoglycemia as a major adverse effect. The ventromedial hypothalamus (VMH) has been described as the primary brain area initiating the counter-regulatory response (CRR). Nevertheless, the VMH receives projections from other brain areas which could participate in the regulation of the CRR. In particular, studies suggest a potential role of the serotonin (5-HT) network. Thus, the objective of this study was to determine the contribution of 5-HT neurons in CRR control.

METHODS

Complementary approaches have been used to test this hypothesis in quantifying the level of 5-HT in several brain areas by HPLC in response to insulin-induced hypoglycemia, measuring the electrical activity of dorsal raphe (DR) 5-HT neurons in response to insulin or decreased glucose level by patch-clamp electrophysiology; and measuring the CRR hormone glucagon as an index of the CRR to the modulation of the activity of 5-HT neurons using pharmacological or pharmacogenetic approaches.

RESULTS

HPLC measurements show that the 5HIAA/5HT ratio is increased in several brain regions including the VMH in response to insulin-induced hypoglycemia. Patch-clamp electrophysiological recordings show that insulin, but not decreased glucose level, increases the firing frequency of DR 5-HT neurons in the DR. In vivo, both the pharmacological inhibition of 5-HT neurons by intraperitoneal injection of the 5-HT1A receptor agonist 8-OH-DPAT or the chemogenetic inhibition of these neurons reduce glucagon secretion, suggesting an impaired CRR.

CONCLUSION

Taken together, these data highlight a new neuronal network involved in the regulation of the CRR. In particular, this study shows that DR 5-HT neurons detect iatrogenic hypoglycemia in response to the increased insulin level and may play an important role in the regulation of CRR.

Hormonal counterregulation failure in rats is related to previous hyperglycaemia-hyperinsulinaemia

Hyperglycaemia and hyperinsulinaemia were induced in rats by a continuous 48-h infusion with glucose. Discontinuation of glucose infusion resulted in marked, persistent hypoglycaemia. To further delineate the mechanism underlying this condition, we measured counterregulatory hormone levels, in vivo glucose kinetics (glucose production = rate of appearance = Ra; glucose utilization = rate of disappearance = Rd), and in vitro gluconeogenesis during the 48-h postinfusion period. Prior to cessation of glucose infusion, Rd was increased 6-fold when compared to control rats, whereas Ra was totally abolished. During the first hour after the end of glucose infusion, Ra increased and Rd decreased (but was still higher than Ra), inducing hypoglycaemia which stabilized after 1 h at ¿¿126¿¿3.5 mmol/l when both Ra and Rd became equal. Despite hypoglycaemia, plasma glucagon and catecholamine levels did not increase during the 3-to 36-h time interval. The increase in Ra during the first hour post-infusion was not related to changes in counterregulatory hormone response. The increase in glucose production was accounted for by glycogenolysis, as shown by total depletion in liver glycogen within 6 h and thereafter by gluconeogenesis. In vitro experiments using isolated hepatocytes suggested that gluconeogenesis was supported during the first 24 h by substrates entering the pathway beyond the step catalysed by the PEPCK enzyme. Thereafter, lactate became the major substrate, and this condition was associated with a progressive rise in glucagon concentration. It is concluded that 48 h of hyperglycaemia/hyperinsulinaemia resulted in a failure of counterregulatory hormonal response to hypoglycaemia. Yet, despite this lack of counterregulatory response, hepatic gluconeogenesis was stimulated in response to hypoglycaemia.

Western diet since adolescence impairs brain functional hyperemia at adulthood in mice: rescue by a balanced ω-3:ω-6 polyunsaturated fatty acids ratio

BACKGROUND/OBJECTIVE

Obesity is a devastating worldwide metabolic disease, with the highest prevalence in children and adolescents. Obesity impacts neuronal function but the fate of functional hyperemia, a vital mechanism making possible cerebral blood supply to active brain areas, is unknown in organisms fed a high-caloric Western Diet (WD) since adolescence.

SUBJECTS/METHODS

We mapped changes in cerebral blood volume (CBV) in the somatosensory cortex in response to whisker stimulation in adolescent, adult, and middle-aged mice fed a WD since adolescence. To this aim, we used non-invasive and high-resolution functional ultrasound imaging (fUS).

RESULTS

We efficiently mimicked the metabolic syndrome of adolescents in young mice with early weight gain, dysfunctional glucose homeostasis, and insulinemia. Functional hyperemia is compromised as early as 3 weeks of WD and remains impaired after that in adolescent mice. These findings highlight the cerebrovascular vulnerability to WD during adolescence. In WD, ω-6:ω-3 polyunsaturated fatty acids (PUFAs) ratio is unbalanced towards proinflammatory ω-6. A balanced ω-6:ω-3 PUFAs ratio in WD achieved by docosahexaenoic acid supplementation efficiently restores glucose homeostasis and functional hyperemia in adults.

CONCLUSIONS

WD triggers a rapid impairment in cerebrovascular activity in adolescence, which is maintained at older ages, and can be rescued by a PUFA-based nutraceutical approach.