Lower Glucose Production Research Articles

Insulin sensitivity and skeletal muscle mitochondrial respiration in Black and White women with obesity.

Non-Hispanic black women (BW) have a greater risk of type 2 diabetes (T2D) and insulin resistance (IR) compared to non-Hispanic white women (WW). The mechanisms leading to these differences are not understood, and it is unclear whether synergistic effects of race and obesity impact disease risk. To understand the interaction of race and weight, hepatic and peripheral IR were compared in WW and BW with and without obesity. Hepatic and peripheral IR was measured by a labeled, hyperinsulinemic-euglycemic clamp in BW (n=32) and WW (n=32) with and without obesity. Measurements of body composition, cardiorespiratory fitness, and skeletal muscle (SM) respiration were completed. Data were analyzed by mixed model ANOVA. Subjects with obesity had greater hepatic and peripheral IR and lower SM respiration (P<0.001). Despite 14% greater insulin (P=0.066), BW tended to have lower peripheral glucose disposal (Rd; P=0.062), which was driven by women without obesity (P=0.002). BW had significantly lower glucose production (P=0.005), hepatic IR (P=0.024), and maximal coupled and uncoupled respiration (P<0.001) than WW. Maximal coupled and uncoupled SM mitochondrial respiration was strongly correlated with peripheral and hepatic IR (P<0.01). While BW without obesity had lower Rd than WW, race and obesity did not synergistically impact peripheral IR. Paradoxically, WW with obesity had greater hepatic IR compared to BW. Relationships between SM respiration and IR persisted across a range of body weight. These data provide support for therapies in BW, like exercise, that improve SM mitochondrial respiration to reduce IR and T2D risk.

Disruption of hepatic mitochondrial pyruvate and amino acid metabolism impairs gluconeogenesis and endurance exercise capacity in mice.

Exercise robustly increases the glucose demands of skeletal muscle. This demand is met by not only muscle glycogenolysis but also accelerated liver glucose production from hepatic glycogenolysis and gluconeogenesis to fuel mechanical work and prevent hypoglycemia during exercise. Hepatic gluconeogenesis during exercise is dependent on highly coordinated responses within and between muscle and liver. Specifically, exercise increases the rate at which gluconeogenic precursors such as pyruvate/lactate or amino acids are delivered from muscle to the liver, extracted by the liver, and channeled into glucose. Herein, we examined the effects of interrupting hepatic gluconeogenic efficiency and capacity on exercise performance by deleting mitochondrial pyruvate carrier 2 (MPC2) and/or alanine transaminase 2 (ALT2) in the liver of mice. We found that deletion of MPC2 or ALT2 alone did not significantly affect time to exhaustion or postexercise glucose concentrations in treadmill exercise tests, but mice lacking both MPC2 and ALT2 in hepatocytes (double knockout, DKO) reached exhaustion faster and exhibited lower circulating glucose during and after exercise. Use of 2H/1³C metabolic flux analyses demonstrated that DKO mice exhibited lower endogenous glucose production owing to decreased glycogenolysis and gluconeogenesis at rest and during exercise. Decreased gluconeogenesis was accompanied by lower anaplerotic, cataplerotic, and TCA cycle fluxes. Collectively, these findings demonstrate that the transition of the liver to the gluconeogenic mode is critical for preventing hypoglycemia and sustaining performance during exercise. The results also illustrate the need for interorgan cross talk during exercise as described by the Cahill and Cori cycles.NEW & NOTEWORTHY Martino and colleagues examined the effects of inhibiting hepatic gluconeogenesis on exercise performance and systemic metabolism during treadmill exercise in mice. Combined inhibition of gluconeogenesis from lactate/pyruvate and alanine impaired exercise endurance and led to hypoglycemia during and after exercise. In contrast, suppressing either pyruvate-mediated or alanine-mediated gluconeogenesis alone had no effect on these parameters. These findings provide new insight into the molecular nodes that coordinate the metabolic responses of muscle and liver during exercise.

Mechanisms by which sheep milk consumption ameliorates insulin resistance in high-fat diet-fed mice

Sheep milk is rich in fat, protein, vitamins and minerals and is also one of the most important sources of natural bioactives. Several biopeptides in sheep milk have been reported to possess antibacterial, antiviral and anti-inflammatory properties, and they may prevent type 2 diabetes (T2D), disease and cancer. However, the precise mechanism(s) underlying the protective role of sheep milk against T2D development remains unclear. Therefore, in the current study, we investigated the effect of sheep milk on insulin resistance and glucose intolerance in high-fat diet (HFD)-fed mice, by conducting intraperitoneal glucose tolerance tests, metabolic cage studies, genomic sequencing, polymerase chain reaction, and biochemical assays. Hyperinsulinemic–euglycemic clamp-based experiments revealed that mice consuming sheep milk exhibited lower hepatic glucose production than mice in the control group. These findings further elucidate the mechanism by which dietary supplementation with sheep milk alleviates HFD-induced systemic glucose intolerance.

Acute Activation of GFRAL in the Area Postrema Contributes to Glucose Regulation Independent of Weight.

GDF15 regulates energy balance and glucose homeostasis in rodents by activating its receptor GFRAL, expressed in the area postrema of the brain. However, whether GDF15-GFRAL signaling in the area postrema regulates glucose tolerance independent of changes in food intake and weight and contributes to the glucose-lowering effect of metformin remain unknown. Herein, we report that direct, acute GDF15 infusion into the area postrema of rats fed a high-fat diet increased intravenous glucose tolerance and insulin sensitivity to lower hepatic glucose production independent of changes in food intake, weight, and plasma insulin levels under conscious, unrestrained, and nonstressed conditions. In parallel, metformin infusion concurrently increased plasma GDF15 levels and glucose tolerance. Finally, a knockdown of GFRAL expression in the area postrema negated administration of GDF15, as well as metformin, to increase glucose tolerance independent of changes in food intake, weight, and plasma insulin levels. In summary, activation of GFRAL in the area postrema contributes to glucose regulation of GDF15 and metformin in vivo. Article Highlights

A glucose-sensing mechanism with glucose transporter 1 and pyruvate kinase in the area postrema regulates hepatic glucose production in rats

The area postrema (AP) of the brain is exposed to circulating metabolites and hormones. However, whether AP detects glucose changes to exert biological responses remains unknown. Its neighboring nuclei, the nucleus tractus solitarius (NTS), responds to acute glucose infusion by inhibiting hepatic glucose production, but the mechanism also remains elusive. Herein, we characterized AP and NTS glucose-sensing mechanisms. Infusion of glucose into the AP, like the NTS, of chow rats suppressed glucose production during the pancreatic (basal insulin)-euglycemic clamps. Glucose transporter 1 or pyruvate kinase lentiviral-mediated knockdown in the AP negated AP glucose infusion to lower glucose production, while the glucoregulatory effect of NTS glucose infusion was also negated by knocking down glucose transporter 1 or pyruvate kinase in the NTS. Furthermore, we determined that high-fat (HF) feeding disrupts glucose infusion to lower glucose production in association with a modest reduction in the expression of glucose transporter 1, but not pyruvate kinase, in the AP and NTS. However, pyruvate dehydrogenase activator dichloroacetate infusion into the AP or NTS that enhanced downstream pyruvate metabolism and recapitulated the glucoregulatory effect of glucose in chow rats still failed to lower glucose production in HF rats. We discovered that a glucose transporter 1- and pyruvate kinase-dependent glucose-sensing mechanism in the AP (as well as the NTS) lowers glucose production in chow rats and that HF disrupts the glucose-sensing mechanism that is downstream of pyruvate metabolism in the AP and NTS. These findings highlight the role of AP and NTS in mediating glucose to regulate hepatic glucose production.

Hepatocyte Rap1a contributes to obesity- and statin-associated hyperglycemia.

SUMMARYExcessive hepatic glucose production contributes to the development of hyperglycemia and is a key feature of type 2 diabetes. Here, we report that activation of hepatocyte Rap1a suppresses gluconeogenic gene expression and glucose production, whereas Rap1a silencing stimulates them. Rap1a activation is suppressed in obese mouse liver, and restoring its activity improves glucose intolerance. As Rap1a′s membrane localization and activation depends on its geranylgeranylation, which is inhibited by statins, we show that statin-treated hepatocytes and the human liver have lower active-Rap1a levels. Similar to Rap1a inhibition, statins stimulate hepatic gluconeogenesis and increase fasting blood glucose in obese mice. Geranylgeraniol treatment, which acts as the precursor for geranylgeranyl isoprenoids, restores Rap1a activity and improves statin-mediated glucose intolerance. Mechanistically, Rap1a activation induces actin polymerization, which suppresses gluconeogenesis by Akt-mediated FoxO1 inhibition. Thus, Rap1a regulates hepatic glucose homeostasis, and blocking its activity, via lowering geranylgeranyl isoprenoids, contributes to statin-induced glucose intolerance.

Short-term combined training reduces hepatic steatosis and improves hepatic insulin signaling

Hepatic steatosis is directly associated with hepatic inflammation and insulin resistance, which is correlated with hyperglycemia and type 2 diabetes mellitus (T2DM). Aerobic and strength training have been pointed out as efficient strategies against hepatic steatosis. However, little is known about the effects of the combination of those two protocols on hepatic steatosis. Therefore, this study aimed to evaluate the impact of short-term combined training (STCT) on glucose homeostasis and in the synthesis and oxidation of fat in the liver of obesity-induced mice with hepatic steatosis. Swiss mice were distributed into three groups: control lean (CTL), sedentary obese (OB), and combined training obese (CTO). The CTO group performed the STCT protocol, which consisted of strength and aerobic exercises in the same session. The protocol lasted seven days. The CTO group reduced the glucose levels and fatty liver when compared to the OB group. Interestingly, these results were observed even without reductions in body adiposity. CTO group also showed increased hepatic insulin sensitivity, with lower hepatic glucose production (HGP). STCT reduced the expression of the lipogenic genes Fasn and Scd1 and hepatic inflammation, as well as increased the ACC phosphorylation and the oxidative genes Cpt1a and Ppara, reverting the complications caused by obesity. Since this protocol increased lipid oxidation and reduced hepatic lipogenesis, regardless of body fat mass decrease, it can be considered an effective non-pharmacological strategy for the treatment of hepatic steatosis.

Comparing texture and digestion properties between white and brown rice of indica cultivars preferred by Chinese consumers

The consumption of good tasting rice, mainly soft-textured white rice with low amylose content, has substantially increased in China as living standards improve. However, this diet change may increase the risk of developing type II diabetes because the soft-textured white rice is generally less resistant to digestion and has a higher glycemic index. In contrast, intake of brown rice is inversely associated with type II diabetes risk. This study was conducted to test the possibility that brown rice processed from soft-textured cultivars has both acceptable texture and improved health benefits. Texture and digestion properties were compared between white and brown rice of five indica cultivars preferred by Chinese consumers. Mean hardness was 33% higher while mean springiness was 5% lower for cooked brown rice than for cooked white rice. As compared to cooked white rice, cooked brown rice had a 41% longer mean active digestion duration but 31% lower mean glucose production rate and 11% lower mean total glucose production from starch digestion. However, the differences in texture and starch digestion properties between cooked brown and white rice were affected by cultivar identity. Brown rice processed from suitable cultivars with both a relatively thinner bran layer and relatively higher grain amylose content met consumer requirements in terms of acceptable texture and improved health benefits.

Effects of Sodium Thiosulfate During Resuscitation From Trauma-and-Hemorrhage in Cystathionine Gamma Lyase (CSE) Knockout Mice.

Sodium thiosulfate (Na2S2O3) is a clinically established drug with antioxidant and sulphide-releasing properties. Na2S2O3 mediated neuro- and cardioprotective effects in ischemia/reperfusion models and anti-inflammatory effects in LPS-induced acute lung injury. Moreover, Na2S2O3 improved lung function during resuscitation from hemorrhagic shock in swine with pre-existing atherosclerosis, characterized by decreased expression of cystathionine γ-lyase (CSE), a major source of hydrogen sulfide (H2S) synthesis in the vasculature. Based on these findings, we investigated the effects of Na2S2O3 administration during resuscitation from trauma-and-hemorrhage in mice under conditions of whole body CSE deficit. After blast wave-induced blunt chest trauma and surgical instrumentation, CSE knockout (CSE-/-) mice underwent 1 h of hemorrhagic shock (MAP 35 ± 5 mm Hg). At the beginning of resuscitation comprising retransfusion, norepinephrine support and lung-protective mechanical ventilation, animals received either i.v. Na2S2O3 (0.45 mg g-1, n = 12) or vehicle (saline, n = 13). Hemodynamics, acid-base status, metabolism using stable isotopes, and visceral organ function were assessed. Blood and organs were collected for analysis of cytokines, mitochondrial respiratory capacity, and immunoblotting. Na2S2O3 treatment improved arterial paO2 (P = 0.03) coinciding with higher lung tissue glucocorticoid receptor expression. Norepinephrine requirements were lower in the Na2S2O3 group (P < 0.05), which was associated with lower endogenous glucose production and higher urine output. Na2S2O3 significantly increased renal tissue IκBα and heme oxygenase-1 expression, whereas it lowered kidney IL-6 and MCP-1 levels. Na2S2O3 exerted beneficial effects during resuscitation of murine trauma-and-hemorrhage in CSE-/- mice, confirming and extending the previously described organ-protective and anti-inflammatory properties of Na2S2O3. The findings make Na2S2O3 a potentially promising therapeutic option in the context of impaired CSE activity and/or reduced endogenous H2S availability.

Nutrient infusion in the dorsal vagal complex controls hepatic lipid and glucose metabolism in rats

SummaryHypothalamic regulation of lipid and glucose homeostasis is emerging, but whether the dorsal vagal complex (DVC) senses nutrients and regulates hepatic nutrient metabolism remains unclear. Here, we found in rats DVC oleic acid infusion suppressed hepatic secretion of triglyceride-rich very-low-density lipoprotein (VLDL-TG), which was disrupted by inhibiting DVC long-chain fatty acyl-CoA synthetase that in parallel disturbed lipid homeostasis during intravenous lipid infusion. DVC glucose infusion elevated local glucose levels similarly as intravenous glucose infusion and suppressed hepatic glucose production. This was independent of lactate metabolism as inhibiting lactate dehydrogenase failed to disrupt glucose sensing and neither could DVC lactate infusion recapitulate glucose effect. DVC oleic acid and glucose infusion failed to lower VLDL-TG secretion and glucose production in high-fat fed rats, while inhibiting DVC farnesoid X receptor enhanced oleic acid but not glucose sensing. Thus, an impairment of DVC nutrient sensing may lead to the disruption of lipid and glucose homeostasis in metabolic syndrome.

FXR in the dorsal vagal complex is sufficient and necessary for upper small intestinal microbiome-mediated changes of TCDCA to alter insulin action in rats

ObjectiveConjugated bile acids are metabolised by upper small intestinal microbiota, and serum levels of taurine-conjugated bile acids are elevated and correlated with insulin resistance in people with type 2 diabetes....

1898-P: Colonic Short-Chain Fatty Acids Lower Endogenous Glucose Production

Hyperglycemia is a hallmark characteristic of diabetes, resulting in elevated blood glucose levels, due in part to a chronic elevation in endogenous hepatic glucose production (GP). Recent work has highlighted the gut microbiota as a salient contributor to energy and glucose homeostasis. One potential mechanism may be through increased short-chain fatty acid (SCFA) signaling mechanisms. SCFAs are bacterial breakdown products of nondigestible dietary fibers, occurring mainly in the colon, and have been shown to improve glucose homeostasis. Interestingly, recent work has highlighted that ingested nutrients can activate small intestinal nutrient-sensing mechanisms to lower hepatic glucose production via a neuronal gut-brain-liver axis mediated via gut peptide signaling. However, no one has directly tested whether colonic SCFAs can regulate GP via a similar colonic neuronal mechanism. To test this, we directly infused SCFAs (acetate, propionate, butyrate; 10mM or 100mM) into the colon during a pancreatic euglycemic clamp, the gold standard for measuring endogenous glucose production and uptake, in high-fat diet (HFD) fed rats that we previously found to have diminished levels of SCFAs in the large intestine. Administration of either acetate, propionate or butyrate (10mM or 100mM) directly into the colon of HFD-fed rats resulted in an increased glucose infusion rate needed to maintain euglycemia, which was due to a significant decrease in endogenous GP compared to saline infusion. Furthermore, we found that this was mediated via GLP-1 receptor signaling, as co-administration of exendin-9 with either SCFA (10mM) abolished the GP-lowering effect. Additionally, portal levels of GLP-1 were significantly increased at the end of the pancreatic clamp in rats receiving infusion of acetate, butyrate, or propionate compared to saline. Taken together, this work demonstrates that colonic SCFAs can activate a GLP-1 receptor mediated pathway in the colon to lower endogenous GP. Disclosure A.I.L. Lane: None. S.N. Weninger: None. F. Duca: None. Funding National Institutes of Health (R01DK121804)

SAT-653 Exploring the Role of Brown Adipokines on Hepatic Insulin Resistance Using a Microfluidic Organ-On-Chip

The development of insulin resistance (IR) in liver is a key of pathophysiologic response in type 2 diabetes. Although insulin resistance impairs its ability to suppress hepatic glucose production, insulin regulation of lipogenesis is maintained (1). Currently available insulin sensitizers are effective at lowering glucose levels, but have significant adverse effect on weight gain due to triglyceride accumulation, which highlights a need to develop new therapeutic treatment options for type 2 diabetes. Brown adipose tissue (BAT) has been studied as a new target for anti-obesity and type 2 diabetes as BAT stimulation increases energy expenditure, reduces adiposity, and improves insulin sensitivity (2). However, the underlying mechanisms are not completely understood. To identify the role of BAT adipokines on hepatic insulin resistance, we developed an insulin resistant liver organ-on-chip model and then perfused primary mouse brown adipocyte conditioned media through the hepatocytes. Our results demonstrate that IR hepatocytes treated with brown adipocyte - conditioned media restores insulin sensitivity and improves glucose metabolism. This was verified by significantly increased expression of Phospho-Akt (Ser473) and glucose production gene markers (G6pc and PEPCK), lowered glucose production, increased glucose uptake, and increased glycogen synthesis in treated hepatocytes over IR group (p < 0.05). Our results also indicate that brown adipocyte - conditioned media treatment has the potential to suppress lipogenesis in hepatic insulin resistance. This was confirmed by significantly reduced expression of a lipogenesis gene marker (SREPB1) and fatty acid uptake in treated hepatocytes over IR group (p < 0.05). Current efforts are focused towards identifying the BAT adipokine via mass spectrometry. We conclude that BAT-derived endocrine factors could be a potential target for new drug discovery for obesity and type 2 diabetes treatment. Reference: (1) Langlet et al. Cell. 2017 Nov;171(4):824-835. (2) Subhadraw et al. Am J Physiol Endocrinol Metlab. 2015 Jun;308(12):E1043-E1055. Nothing to Disclose: NT, CL, AT, FZ, KK, JM, RC, AB

270-LB: Amelioration of Hepatic Insulin Resistance by Brown Adipocyte Secretion

Insulin resistance (IR) is a hallmark of T2D. In the IR state, insulin fails to inhibit hepatic glucose production yet promotes lipogenesis. Although thiazolidinediones can partially reinstate insulin sensitivity, there are concerns about long-term usage. Recent studies have shown positive effects of paracrine signaling from BAT transplant on metabolic homeostasis. Transplant of embryonic BAT into diabetic mice can improve glucose tolerance. However, the mechanisms are unclear. In this study, we show that brown adipocyte secretions can partially resolve hepatic IR. We cultured primary hepatocytes in a microfluidic organ-on-chip device. IR was induced by cytokine exposure and the cells were treated with brown adipocyte secretions among other controls. The group treated with brown adipocytes had restored insulin sensitivity. This was verified by an increased Akt phosphorylation (Figure 1), lowered glucose production, increased glucose uptake, and increased glycogen synthesis. We finally confirmed that genes important for glucose production (G6pc, PEPCK) and lipogenesis (SREBP1) were downregulated in the treated cells. We will present results from ongoing mechanistic studies. Our data imply that brown adipocyte secretions contain factors that regulate hepatic insulin sensitivity and could be potential targets for drug development. Disclosure A. Bhushan: None. N. Tanataweethum: None. C. Lee: None. F. Zhong: None. A. Trang: None. A. Budiman: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (DK095984NIH, P30DK020595)

115-OR: Epinephrine Contributes to Hypoglycemia-Associated Autonomic Failure (HAAF)

Recurrent hypoglycemia leads to HAAF, with blunted counterregulatory hormone responses to subsequent hypoglycemic episodes. A recent report suggested inter-individual differences in susceptibility to HAAF (JCEM 102:3571, 2017). Since adrenergic receptor blockade prevents HAAF (Diabetes 60:602, 2011), we investigated to what extent the rises in plasma epinephrine (EPI) associated with hypoglycemia predict the development of HAAF. Healthy non-diabetic subjects (n=18, age 43±2years, BMI 25±1 kg/m2) underwent two 2-hour hypoglycemic clamp studies (nadir 54mg/dl; 0-2h and 4-6 h) on Day 1 followed by a third 2-hour hypoglycemic clamp on Day 2. Twelve subjects (67%) developed HAAF by the third episode, as defined by at least 20% reductions in peak EPI levels (peak EPI 1st vs. 3rd episode: HAAF subjects 1072±156 vs. 530±87pg/ml, p&amp;lt;0.001). Importantly, peak EPI levels during the 1st hypoglycemic episode were ∼83% higher in the subjects who developed HAAF compared to those who did not (p=0.02). To specifically define the role of EPI in the pathogenesis of HAAF, we challenged an additional seven non-diabetic subjects (age 32±4 years, BMI 25±1 kg/m2) with two 2-hour infusions of EPI (0.03 μg/kg/min;0-2h and 4-6 h) on Day 1 followed by 200-minute stepped hypoglycemic clamps (90, 80, 70 and 60 mg/dl, each for 50 minutes) on Day 2. Compared to saline, EPI infusion on Day 1 induced 40% and 28% reductions in epinephrine response to hypoglycemia at the 70 and 60 mg/dl glucose steps on Day 2, respectively (all p&amp;lt;0.05). There were parallel reductions in hypoglycemic symptoms (all p&amp;lt;0.05). Furthermore, the rate of glucose infusion was higher at all steps after EPI infusion (all p&amp;lt;0.05), consistent with a trend towards lower endogenous glucose production (6,6-D2-glucose). Thus, rises in EPI similar to those seen with hypoglycemia reproduce key features of HAAF in non-diabetic subjects. Marked inter-individual variability in EPI levels in response to hypoglycemia may explain why some people are more prone to develop HAAF. Disclosure E. Lontchi Yimagou: None. S. Aleksic: None. L. Upadhyay: None. S. Sharma: None. M. Carey: None. A. Goyal: None. J. You: None. R. Hulkower: None. S. Murthi: None. W.G. Mitchell: None. H. Shamoon: None. M. Hawkins: Other Relationship; Self; Novo Nordisk Inc. Funding American Diabetes Association (1-18-PMF-024 to E.L.Y.); National Institutes of Health (R01DK079974)

104-OR: Glucoregulatory Effects of Hypothalamic Glucocorticoid Action In Vivo

Diabetes is characterized by dysregulated glucose homeostasis that leads to hyperglycemia, due in part to increased hepatic glucose production (GP) and insulin resistance. Excessive levels and/or action of glucocorticoids (GCs) are associated with obesity, insulin resistance, and hyperglycemia. We aim to delineate a mechanism of GC action in the mediobasal hypothalamus (MBH) that modulates GP in normal and pre-obese rodents. Male SD rats underwent stereotaxic MBH bilateral cannulation and intravenous (iv) and intraarterial catheterization to enable simultaneous direct infusions into the MBH, iv infusions, and blood sampling, respectively. Mildly hyperinsulinemic-euglycemic clamps with tracer dilution methodology combined with MBH GC infusion ± GC receptor (GR) inhibition enables measurement of GP and utilization while assessing MBH GC interaction with its MBH receptors independent of changes in plasma insulin, glucagon, and glucose levels. MBH GC infusion potently stimulates GP and lowers the requirement for exogenous glucose infusion without altering glucose utilization. This effect is mediated via GRs since co-infusion of GR antagonist mifepristone, or a HSP90 inhibitor, negates the ability of MBH GCs to increase GP. MBH GCs similarly increased glucose excursions during iv glucose tolerance tests, which was reversed with concomitant MBH mifepristone infusion. Rats fed with high fat diet (HFD) for 3 days had altered glucose kinetics and increased basal plasma corticosterone, insulin, and blood glucose levels without changes in body weight. Chronic MBH GR inhibition with MBH GR shRNA lowered GP compared to MBH mismatch control HFD rats with MBH vehicle infusions, suggesting that blocking excessive MBH GC action resulting from HFD-feeding attenuates GP to improve glucose homeostasis. We provide novel evidence that MBH GC action modulates GP in healthy and pre-obese rats. Importantly, targeted inhibition of MBH GC action may help improve glucose regulation in obesity-related metabolic disease. Disclosure E. Beaulieu-Bayne: None. M. Cardoso: None. H. Kim: None. S. Yang: None. J.T. Yue: None. Funding Diabetes Canada; Natural Sciences and Engineering Research Council of Canada; Alberta Diabetes Institute; Canadian Institutes of Health Research

Inhibition of upper small intestinal mTOR lowers plasma glucose levels by inhibiting glucose production

Glucose homeostasis is partly controlled by the energy sensor mechanistic target of rapamycin (mTOR) in the muscle and liver. However, whether mTOR in the small intestine affects glucose homeostasis in vivo remains unknown. Here, we first report that delivery of rapamycin or an adenovirus encoding the dominant negative acting mTOR-mutated protein into the upper small intestine is sufficient to inhibit small intestinal mTOR signaling and lower glucose production in rodents with high fat diet-induced insulin resistance. Second, we found that molecular activation of small intestinal mTOR blunts the glucose-lowering effect of the oral anti-diabetic agent metformin, while inhibiting small intestinal mTOR alone lowers plasma glucose levels by inhibiting glucose production in rodents with diabetes as well. Thus, these findings illustrate that inhibiting upper small intestinal mTOR is sufficient and necessary to lower glucose production and enhance glucose homeostasis, and thereby unveil a previously unappreciated glucose-lowering effect of small intestinal mTOR.

Inhibition of Upper Small Intestinal mTOR Lowers Plasma Glucose Levels by Inhibiting Hepatic Glucose Production

Energy-sensing signals in the gut play a significant role in glucose metabolism, affecting hepatic glucose production and/or overall blood glucose levels; any imbalance of this system may cause diabetes. Recently, we reported that metformin activates energy sensor protein, AMP-protein kinase, in the upper small intestine to exert its anti-diabetic effect in rodents via a gut-brain axis. Although metformin action in the gut is subsequently reported to lower glucose levels in humans with type 2 diabetes as well, the overall intestinal mechanisms remain elusive. The mechanistic target of rapamycin (mTOR), a highly conserved energy-sensing kinase protein, is inhibited by metformin in vitro, and over-activation of mTOR in the liver and skeletal muscle leads to insulin resistance in rodents. The role of upper small intestinal mTOR in glucose homeostasis and/or metformin action is, however, unknown. Here, we first report that direct delivery of the mTOR inhibitor rapamycin or an adenovirus encoding the dominant negative-acting mTOR-mutated protein into the upper small intestine is sufficient to lower hepatic glucose production during the pancreatic (basal insulin)-euglycemic clamps in rodents with a high-fat diet (HFD)-induced insulin resistance. Second, we found that molecular (via upper small intestinal-targeted viral injection of adenovirus that expresses the constitutively active mTOR proteins) activation of upper intestinal mTOR blunted the glucose-lowering effect of the first-line anti-diabetic medication metformin. Finally, and most importantly, direct inhibition of upper small intestinal mTOR is sufficient to restore glycemia by lowering glucose production in type 2 diabetic rodents. In summary, our findings illustrate that inhibiting upper small intestinal mTOR is sufficient and necessary to lower glucose production and restore glucose homeostasis, and, thereby, unveil a previously unappreciated anti-diabetic role of mTOR in the upper small intestine.

Increased Gluconeogenesis Is Not an Early Feature of Whole-Body Insulin Resistance in Black Women—The Federal Women Study

In contrast to white women, fasting hyperglycemia is not an early diabetes risk marker in black women. The etiology of this racial difference in risk is unknown but could be related to differences in rates of gluconeogenesis and hepatic fat in black women. Using stable isotope tracers [2H2O], [6,62H2]glucose, and ([2H5]glycerol), we partitioned basal glucose production into its two components (gluconeogenesis and glycogenolysis) and measured basal whole body lipolysis. Whole body (SI), hepatic (HIS) and adipose tissue insulin sensitivity were calculated in two groups of federally employed pre-menopausal women, without diabetes: 24 black and 19 white; age 37±6 (mean±SD), range 25-50y; BMI 33±6, range 24.9-45.2 kg/m2. Hepatic and visceral fat were measured by proton MRS. The prevalence of prediabetes (17% vs. 26%), age and BMI were similar in blacks and whites, all P&amp;gt;0.4). Black women had less fasting hyperglycemia (4% vs. 22%, P=0.1), lower visceral and hepatic fat (P&amp;lt;0.01) but similar SI, adipose tissue insulin sensitivity and whole body lipolysis (all P&amp;gt;0.5). Basal glucose, insulin and FFA concentrations were similar in both groups (P&amp;gt;0.05). Blacks had lower glucose production (2.52±0.34 vs. 2.75±0.28 mg·kglbm-1·min-1, P&amp;lt;0.05), fractional gluconeogenesis (57.6±10.6 vs. 66.3±11.4%, P=0.02), and absolute gluconeogenesis (1.44±0.28 vs. 1.77±0.31 mg·kglbm-1·min-1, P&amp;lt;0.01). HIS correlated with SI and hepatic fat (both r=0.5, P&amp;lt;0.01) and the relationship did not differ by race (P&amp;gt;0.05). However, at the same SI blacks had higher HIS (intercepts P&amp;lt;0.01). In summary, black women had relatively preserved HIS and lower hepatic fat, while white women had higher gluconeogenesis and hepatic fat associated with fasting hyperglycemia. Fasting glucose may be a poor early diabetes marker in black women because gluconeogenesis was low despite whole-body insulin resistance. Disclosure S.T. Chung: None. M.W. Haymond: Advisory Panel; Self; Zealand Pharma A/S. Other Relationship; Self; Xeris Pharmaceuticals, Inc.. A. Onuzuruike: None. L. Mabundo: None. H. Garraffo: None. P.J. Walter: None. A.B. Courville: None. A.M. Gharib: None. S. Chacko: None. A.E. Sumner: None.

Lactobacillus Gasseri in the Upper Small Intestine Impacts an ACSL3-Dependent Fatty Acid Sensing Pathway That Regulates Whole-Body Glucose Homeostasis

Long chain acyl CoA synthetase (ACSL)-dependent upper small intestinal lipid metabolism activates preabsorptive pathways to regulate metabolic homeostasis, but whether changes in the upper small intestinal microbiota alter specific fatty acid-dependent pathways to impact glucose homeostasis remains unknown. We here first find that upper small intestinal infusion of Intralipid, oleic acid, or linoleic acid preabsorptively increases glucose tolerance and lowers glucose production in rodents. High-fat feeding impairs preabsorptive fatty acid sensing and reduces upper small intestinal Lactobacillus gasseri levels and ACSL3 expression. Transplantation of healthy upper small intestinal microbiota to high-fat fed rodents restores Lactobacillus gasseri levels and fatty acid sensing via increased ACSL3 expression, while Lactobacillus gasseri probiotic administration to non-transplanted high-fat fed rodents is sufficient to restore upper small intestinal ACSL3 expression and fatty acid sensing. In summary, we unveil a glucoregulatory role of upper small intestinal Lactobacillus gasseri that impacts an ACSL3-dependent glucoregulatory fatty acid sensing pathway. Disclosure P.V. Bauer: None. F. Duca: None. T. Waise: None. H.J. Dranse: None. B.A. Rasmussen-Small: None. A. Puri: None. M. Rasti: None. T.K.T. Lam: None.