Glucose Bolus Research Articles

2002-P: A Long-Acting GLP-1 and Y2-Receptor Dual Agonist Improves Body Weight and Glucose Control in Obese and Diabetic Rodent Models

Bariatric surgery can result in profound weight loss and remission of type 2 diabetes. Following meal consumption post-surgery, patients exhibit an exaggerated increase in the circulating levels of the enteroendocrine L-cell peptides peptide YY (PYY) and glucagon-like peptide-1 (GLP-1). We have developed a long-acting PYY Y2 and GLP-1 receptor agonist (GLP-1-Fc-PYY), which exerted potent effects on improving glucose metabolism and body weight loss in diabetic db/db mice and diet-induced obese (DIO) mice. Administration of GLP-1-Fc-PYY to diabetic db/db mice for 28 days normalized HbA1c levels (4.3%) compared to vehicle controls (9.1%), and exceeded that observed with Fc-GLP-1 monotherapy treatment (7.2%). GLP-1-Fc-PYY administration also preserved circulating insulin levels and increased pancreatic insulin content in db/db mice, which was not observed in mice treated with Fc-GLP-1. Administration of GLP-1-Fc-PYY for 21 days in DIO mice resulted in a 28% (p<0.0001) decrease in body weight, whereas vehicle-treated mice gained 13% and Fc-GLP-1-treated mice only exhibited a 13% reduction in body weight. To further characterize the GLP-1-Fc-PYY molecule, DIO GLP-1R knockout (KO) mice were treated for 13 days, and effects on body weight loss were partially attenuated in GLP-1R KO mice (10% BW loss), compared to wild type mice (32% BW loss). Additionally, when GLP-1R KO DIO mice were challenged with an IP glucose bolus following sub-chronic GLP-1-Fc-PYY treatment, the improvement in glucose excursion was lost compared to wild type mice. DIO Y2R KO mice treated for 11 days with GLP-1-Fc-PYY had attenuated BW loss (9%) compared to wild type mice (32%). These data suggest that GLP-1-Fc-PYY is a balanced dual agonist with in vivo activity at both the GLP-1 and Y2 receptors. GLP-1-Fc-PYY therefore represents a PYY/GLP-1 long-acting dual agonist that produces robust bariatric surgery-like weight loss and antidiabetic efficacy in relevant rodent models. Disclosure S. Oldham: Employee; Self; AstraZeneca. Stock/Shareholder; Self; AstraZeneca. V.G. Howard: Employee; Self; AstraZeneca. Stock/Shareholder; Self; AstraZeneca. S. Will: Employee; Self; AstraZeneca. Stock/Shareholder; Self; AstraZeneca. D.C. Hornigold: Employee; Self; AstraZeneca. Stock/Shareholder; Self; AstraZeneca. C.J. Rhodes: Employee; Self; AstraZeneca, MedImmune. S. Madalli: None. I. Sermadiras: None. J. Naylor: Employee; Self; MedImmune. Stock/Shareholder; Self; AstraZeneca. C. Rivera: None.

SAT-024 Adipose Specific Inactivation of Aromatase is Sufficient to Cause Adiposity and Impaired Glucose Tolerance in Mice

Aromatase synthesizes estrogens from androgens. While the gonads are major sites of aromatase expression, it is expressed in multiple other organs including adipose tissue, brain and bone. In global aromatase knockouts in mice, studied by us, or man aromatase deficiency there are phenotypes of adiposity and low bone mass as well as varying degrees of insulin resistance. Breast cancer patients treated with aromatase inhibitors (AIs) also develop adiposity and low bone mass. Thus, it remains unclear the role of site specific aromatase activity in the phenotypes observed in chemically or genetically induced aromatase deficiency. To begin to understand the relative contributions of tissue specific aromatase activity and develop a model that will be useful for understanding and developing therapeutic strategies for ailments in aromatase inhibitor therapy, we have developed mouse models with tissue specific aromatase inactivation. Embryonic stem cells were purchased from EUCOMM. Using standard methods and appropriate breeding strategies we generated C57Bl6 mice with Lox P sites flanking Exon 2 in the aromatase gene (Arom fl/fl). Mice with adipose specific inactivation of aromatase were generated by interbreeding Arom fl/fl mice with mice expressing Cre recombinase driven by the adiponectin promoter (AdipoCre). We measured body composition by dual energy x-ray absorptiometry (Lunar PIXIMus 2). As a first step in examining glucose homeostasis we performed oral glucose tolerance tests. All mice were fed normal chow and the study was approved by the local IACUC. Female mice aged 4-6 months were studied with at least 4 animals in each group. Arom fl/fl mice were compared as controls for the AdipoCre+; Arom fl/fl mice. Mean body weight was higher in fat specific aromatase knockout female mice (33.6 vs 21.6, p<0.05). On DEXA Mean %Body fat was higher in female AdipoCre+;Arom fl/fl mice (29.3% vs. 17.3%, p<0.05). Following a 16h fast female mice with adipose specific aromatase inactivation had higher fasting blood glucose levels (93.3+/-10.3 vs 74.5+/-10, p=0.03). For the glucose tolerance test, a bolus of glucose (2 g/kg) was delivered into the stomach by a gavage needleand blood was sampled at 0, 5, 10, 20, 30, 60, 90, 120, and 180 min for plasma glucose analyses. On OGTT peak glucose levels were higher and did not return to baseline. Insulin tolerance tests will be performed to further understand the mechanism of impaired glucose homeostasis. Male mice with fat specific aromatase inactivation showed similar patterns in higher body weight, percent body fat and glucose levels but the phenotype was more variable. In summary, fat specific aromatase inactivation is sufficient to cause adiposity and impaired glucose homeostasis. The observed phenotype in females is more robust than we have observed in the global knockout.

Flock differences in the impact of maternal dietary restriction on offspring growth and glucose tolerance in female offspring

Variable impacts of in-utero programming stimuli on postnatal offspring development suggest that genotype may play a role in this response. In this study, ewes from two flocks of similar breeding but adapted for 6–8 generations to one of two markedly different production environments were utilized (Baggs ewes - nomadic lifestyle and limited nutrition; UW ewes - sedentary lifestyle and adequate nutrition). Ewes from each flock were fed 50% (nutrient restricted) or 100% (control) National Research Council (NRC) requirements between day 28 and 78 of gestation; some ewes in each dietary group were then necropsied. Remaining ewes were fed 100% NRC requirements from day 79 to term. Weights of singleton female fetuses were reduced (P < 0.05) in nutrient restricted UW ewes compared to control UW ewes on day 78. Two month old ewe lambs from nutrient restricted UW ewes had greater (P < 0.05) baseline glucose concentrations, and exhibited greater (P < 0.05) glucose and insulin concentrations to an intravenous glucose bolus than lambs from control UW ewes. From 4 to 12 months of age, ewe lambs from nutrient restricted UW ewes were heavier (P < 0.05) than lambs from control UW ewes. In contrast, no differences in fetal weight, baseline glucose, glucose and insulin concentration to an intravenous glucose bolus, or body weight were observed for nutrient restricted and control Baggs ewes. These data suggest that a multigenerational adaptation of ewes to different production systems impacts their ability to protect their fetus against a bout of early to mid-gestational nutrient restriction.

Portal milieu and the interplay of multiple antidiabetic effects after gastric bypass surgery.

Diabetes is a worldwide health problem. Roux-en-Y gastric bypass (RYGB) leads to rapid resolution of type 2 diabetes (T2D). Decreased hepatic insulin resistance is key, but underlying mechanisms are poorly understood. We hypothesized that changes in intestinal function and subsequent changes in portal venous milieu drive some of these postoperative benefits. We therefore aimed to evaluate postoperative changes in portal milieu. Two rat strains, healthy [Sprague-Dawley (SD)] and obese diabetic [Zucker diabetic fatty (ZDF)] rats, underwent RYGB or control surgery. After 4 wk, portal and systemic blood was sampled before and during an intestinal glucose bolus to investigate changes in intestinal glucose absorption (Gabsorp) and utilization (Gutil), and intestinal secretion of incretins and glucagon-like peptide-2 (GLP-2). Hepatic activity of dipeptidyl peptidase-4 (DPP4), which degrades incretins, was also measured. RYGB decreased Gabsorp in both rat strains. Gutil increased in SD rats and decreased in ZDF rats. In both strains, there was increased expression of intestinal hexokinase and gluconeogenesis enzymes. Systemic incretin and GLP-2 levels also increased after RYGB. This occurred without an increase in secretion. Hepatic DPP4 activity and expression were unchanged. RYGB perturbs multiple intestinal pathways, leading to decreased intestinal glucose absorption and increased incretin levels in both healthy and diabetic animals. In diabetic rats, intestinal glucose balance shifts toward glucose release. The portal vein as the gut-liver axis may integrate these intestinal changes to contribute to rapid changes in hepatic glucose and hormone handling. This fresh insight into the surgical physiology of RYGB raises the hope of less invasive alternatives. NEW & NOTEWORTHY Portal milieu after gastric bypass surgery is an underinvestigated area. Roux-en-Y gastric bypass perturbs multiple intestinal pathways, reducing intestinal glucose absorption and increasing incretin levels. In diabetic rats, the intestine becomes a net releaser of glucose, increasing portal glucose levels. The portal vein as the gut-liver axis may integrate these intestinal changes to contribute to changes in hepatic glucose handling. This fresh insight raises the hope of less invasive alternatives.

Glucose Tolerance and Plasma Non-Esterified Fatty Acid Levels in Chickens Selected for Low Body Weight, Red Junglefowl, and their Reciprocal Cross.

Responses of an individual to food deprivation, such as a 16-h fast, are complex, and are influenced by environmental and genetic factors. Domestication is an ongoing process during which adaptations to changing environments occur over generations. Food deprivation by their caretakers is less for domestic chickens than for their junglefowl ancestors. Unlike domestic chicken, the junglefowl adapted over generations to periods of food deprivation, which may be reflected in differences in metabolic responses to brief periods without food. Here, we compared the blood glucose and plasma levels of non-esterified fatty acids (NEFA) among four populations when deprived of feed for 16 h. The four populations included a domestic White Rock experimental line (LWS) maintained for generations under ad libitum feeding, adult red junglefowl (RJF), and a reciprocal cross of the lines. Although there were significant differences in adult (31-week) body weight between the RJF (683 g) and LWS (1282 g), with the weight of F1 crosses being intermediate, the amount of abdominal fat relative to body weight was similar for all populations. Patterns for blood glucose responses to a glucose bolus after a 16-h fast were similar for the initial and final points in the parental and cross populations. However, RJF reached their peak faster than LWS, with the reciprocal cross intermediate to the parental populations. Plasma NEFA concentrations were higher after the 16-h fast than in fed states, with no population differences for the fasting state. However, in the fed state, NEFA levels were lesser for LWS than for others, which was reflected further in percentage change from fed to fasted. This larger change in LWS suggests differences in mobilization of energy substrates and implies that during domestication or development of the LWS line, thresholds for responses to acute stressors may have increased.

Effect of Endurance Conditioning on Insulin-mediated Glucose Clearance in Dogs.

Physical activity has been shown to improve insulin sensitivity in subjects with insulin resistance, but the effect of athletic conditioning on subjects with normal insulin sensitivity has received less scrutiny. Because strenuous exercise can be limited by the availability of substrates, it is reasonable to hypothesize that conditioning would increase the capacity for muscle uptake of substrates like glucose and to the extent that improvement in this process would include upregulation of the portions of the glucose uptake pathway in muscle, this increased capacity would also be reflected in insulin sensitivity. Therefore, we tested the hypothesis that conditioning for endurance exercise would result in increased insulin sensitivity using elite racing sled dogs. A frequent-sampled intravenous glucose tolerance test was performed on these dogs before and after a full 7-month season of conditioning in preparation for a 1600-km race. Compared with the results in unconditioned dogs, conditioned dogs rapidly cleared the intravenous glucose bolus through increases in both glucose mediated (7.6%·min ± 3.4%·min vs 3.0%·min ± 2.2%·min, P = 0.008) and insulin-mediated (36.3 ± 18.4 × 10 L·min·mU vs 11.5 ± 8.0 × 10 L·min·mU, P = 0.007) mechanisms. The more modest increase in serum insulin after the intravenous glucose bolus in conditioned dogs failed to suppress lipolysis and serum concentrations of nonesterified fatty acids remained constant in the conditioned dogs throughout the 4-h test. These results, in particular the increase in insulin-independent peripheral uptake of glucose, describe novel alterations in metabolism induced by athletic conditioning that arguably result in near-continuous provision of oxidizable substrates to peripheral muscle in support of sustained muscular work typical of these dogs.

Glucose, fructosamine, and insulin measurements in saliva of dogs: variations after an experimental glucose administration

The aim of this study was to evaluate if glucose, fructosamine, and insulin levels can be measured in saliva of dogs and assess the changes in these compounds after an experimental glucose administration. Automated spectrophotometric assays for glucose and fructosamine and an ELISA assay for insulin measurements were validated in saliva of dogs, by evaluating precision, accuracy, and limits of detection. In addition, an intravenous glucose bolus was administrated to 10 beagles and fasting serum and saliva samples were obtained immediately before and 5, 10, 20, 30, and 45 min after glucose infusion. The results of the between-run imprecision gave mean CVs of 6.16, 9.40, and 3.10% for glucose, fructosamine, and insulin, respectively. Linearity under dilution showed coefficient of correlation of 0.999, 0.994, and 0.990 for glucose, fructosamine, and insulin, respectively. The LDs were 0.04 mg/dL, 4.08 μmol/L, and 0.02 μg/mL for glucose, fructosamine, and insulin, respectively. The glucose administration caused an increase in serum and salivary levels of glucose with a peak in salivary levels at 30 min and of insulin with a peak in salivary levels at 45 min, while fructosamine did not change. No correlations between serum and salivary concentrations were found for any compound. It is concluded that glucose, fructosamine, and insulin can be measured in saliva of dogs, and an experimental administration of glucose in this species can lead to increases in glucose and insulin in saliva.

Nrf2-related gene expression is impaired during a glucose challenge in type II diabetic rat hearts

Diabetic hearts are susceptible to damage from inappropriate activation of the renin angiotensin system (RAS) and hyperglycemic events both of which contribute to increased oxidant production. Prolonged elevation of oxidants impairs mitochondrial enzyme function, further contributing to metabolic derangement. Nuclear factor erythriod-2-related factor 2 (Nrf2) induces antioxidant genes including those for glutathione (GSH) synthesis following translocation to the nucleus. We hypothesized that an acute elevation in glucose impairs Nrf2-related gene expression in diabetic hearts, while AT1 antagonism would aid in Nrf2-mediated antioxidant production and energy replenishment. We used four groups (n = 6–8/group) of 25-week-old rats: 1) LETO (lean strain-control), 2) type II diabetic OLETF, 3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d × 8 wks), and 4) ARBM (4 weeks on ARB, 4 weeks off) to study the effects of acutely elevated glucose on cardiac mitochondrial function and Nrf2 signaling in the diabetic heart. Animals were gavaged with a glucose bolus (2 g/kg) and groups were dissected at T0, T180, and T360 minutes. Nrf2 mRNA was 32% lower in OLETF rats compared to LETO and remained suppressed in response to glucose. LETO Nrf2 mRNA increased 25% at T360 in response to glucose while no changes were observed in diabetic hearts. GCLC and GCLM mRNA decreased in diabetic hearts 33% and 44% respectively and remained suppressed in response to glucose while ARB treatment increased GCLM transcripts 90% at T180. These data illustrate that during T2DM and in response to glucose, cardiac Nrf2′s adaptive response to environmental stressors such as glucose is impaired in diabetic hearts and that ARB treatment may aid Nrf2′s impaired dynamic response.

Effects of overconditioning on pancreatic insulin secretory capacity, fat infiltration, and the number and size of islets in dairy cows at the end of the dry period

In the present study, we tested the hypothesis that overconditioning in dairy cows at the end of the dry period leads to infiltration of fat and alterations of the insulin secretory capacity of the pancreas. Pregnant Holstein Friesian dairy cows were selected based on body condition score (BCS) at the start of the dry period. Body condition score varied between cows to have optimal conditioned (2.5 < BCS ≤3.5, n = 5) and overconditioned (3.5 < BCS ≤5, n = 5) cows. All animals underwent an intravenous glucose tolerance test (IVGTT) at an average of 260 d of gestation to measure the pancreatic insulin secretory capacity and assess peripheral insulin sensitivity regarding glucose metabolism. Eight days after the IVGTT, animals were slaughtered. The pancreas was dissected and weighed and tissue samples were taken for histological analysis. Results revealed that overconditioning in dairy cows led to fat infiltration in the pancreas and an increase in size of pancreatic islets expressed relative to the total area of pancreatic tissue. In addition, results revealed a positive correlation between serum fatty acid concentration and peak insulin concentration and area and number of pancreatic islets expressed relative to the total area of pancreatic tissue. The IVGTT revealed that overconditioned animals have a higher insulin secretory capacity of the pancreas, as demonstrated by higher peak insulin concentration, higher acute insulin response to glucose, and higher area under the curve (AUC) for insulin compared with optimal conditioned cows. A higher AUC for glucose during the first 60 min following administration of the glucose bolus in overconditioned cows indicates an insulin-resistant state regarding glucose metabolism. Our results suggest that the pancreas of overconditioned dairy cows at the end of gestation compensates for the concomitantly elevated level of peripheral insulin resistance by greater secretion of insulin.

Mealtime insulin bolus adherence and glycemic control in adolescents on insulin pump therapy.

Poor self-management contributes to insufficient glycemic control in adolescents with type 1 diabetes (T1DM). We assessed the effects on glycemic control of adherence to self-measurement of blood glucose (SMBG) and insulin boluses in 90 adolescents with T1DM on insulin pump therapy over a 2-month period. We compared the number of insulin boluses and SMBGs around main meals to the "gold standard" of optimal diabetes management (SMBGs and a bolus before each main meal and SMBG before bedtime). The mean (95% CI) HbA1c levels were 2.9(1.7 to 4.0)mmol/mol lower for every additional insulin bolus and 3.1(1.6 to 4.5)mmol/mol lower for every additional SMBG. Patients performing SMBG and bolusing around each main meal had considerably lower HbA1c levels than those unable to do (95% CI for difference 4.3 to 10.4mmol/mol and 11.5 to 20.1mmol/mol respectively). For each additional mealtime bolus/day, the odds ratio of achieving target HbA1c levels of <58mmol/mol was 6.73 (95% CI 2.94-15.38), after adjustment for gender, age, diabetes duration, and affective responses to SMBG in a multiple logistic regression model.Conclusion: Glycemic control in adolescents with T1DM on insulin pump therapy is strongly dependent on adherence to insulin boluses around mealtimes. What is Known: • In mixed groups of children and adolescents, insulin bolus frequency and self-monitoring of blood glucose (SMBG) frequency were determinants of HbA1c levels. • Adherence to insulin boluses and SMBG is particularly challenging in adolescents. What is New: • In adolescents on insulin pump therapy, each additional insulin bolus, particularly around mealtime, was significantly associated with approximately 3mmol/mol lower HbA1c levels. • This beneficial effect of mealtime bolusing was strongest for the evening meal.

Investigating the Association Between Diabetes Distress and Self-Management Behaviors.

Diabetes distress has been linked with suboptimal glycemic control in patients with type 1 diabetes. We evaluated the effect of diabetes distress on self-management behaviors in patients using insulin pumps. We analyzed the impact of diabetes distress on self-management behaviors using pump downloads from 129 adults treated with continuous subcutaneous insulin infusion (CSII) at a single hospital clinic. Exclusion criteria were CSII treatment <6 months, pregnancy, hemoglobinopathy, and continuous glucose monitoring/sensor use. People were categorized into three groups based on the Diabetes Distress Scale-2 (DDS-2) score: < 2.5, 2.5-3.9, > 4. Participants had a mean age of 45.2 ± 19.0 years; duration of diabetes 26.6 ± 16.2 years; duration of CSII 6.0 ± 3.5 years; HbA1c 8.0 ± 1.2%; and DDS-2 score 2.7 ± 1.3. Self-monitoring blood glucose (SMBG) frequency and bolus wizard usage was similar between groups. Patients with higher distress had higher HbA1c (7.7 ± 0.9 vs. 8.0 ± 0.9 vs. 8.7 ± 1.8; P = 0.004), lower frequency of set changes (4.7 ± 1.3vs. 4.8 ± 1.9 vs. 3.8 ± 1.1; P = .025), a greater number of appointments booked (5.8 ± 4.4 vs. 8.6 ± 4.8 vs. 8.1 ± 6.9; P = .021), and a greater number of appointments missed (1.9 ± 1.3 vs. 2.5 ± 1.5 vs. 3.8 ± 4.1; P = .004). Although in some patients, high distress may be caused by reduced self-management, in our highly trained, pump-using patients, high distress was associated with suboptimal biomedical outcomes despite appropriate self-management behaviors. Future work should further explore the relationships between diabetes distress, self-management, and glycemic control.

Synchronized Microfluidic System to Dynamically Assess Pancreatic Islet Function beyond Glucose-Stimulated Insulin Secretion

The endocrine function of pancreatic islets goes beyond glucose stimulated insulin secretion (GSIS). Besides glucose, dynamic regulation through a variety of incretin hormones, drugs, and metabolites have been shown to modulate insulin secretion. The most commonly applied ex vivo and in vitro methodologies to study islet function are static in nature; carried out in standard well formats for extended incubation times. This approach ignores the dynamic nature of secretion and regulation thereof, and limits the complexity of scientific questions that may be posed. In the last decade several groups have begun using microfluidic devices to assess islet function in a dynamic environment, which aims to mimic a physiological bolus of glucose followed by imaging and secretory analysis. Thus far no commercial research device has been made available to the scientific community, requiring the in-house development of microfluidic islet analysis systems by groups aiming to take a more in-depth view of pancreatic islet function. We have developed a fabrication processes for poly-methyl methacrylate (PMMA) microfluidic chips, with micromilled channels and pockets into which islets will be hydrostatically trapped. These optically clear chips allow for direct fluorescent imaging of the trapped islets, with real-time calcium flux (Fura-2-AM) and mitochondrial potential (Rhodamine 123) assays. Using the I2C (Inter-Integrated Circuit, NXP Semiconductors) protocol, we are able to synchronize several microcontrolled syringe pumps (and a fraction collector) to produce precise concentrations of glucose, hormones, metabolites, and factors of interest in a time-dependent manner. This system has applications in our study of the effects of bariatric surgery (in rodents) on pancreatic islet function, as well as the mechanisms by which myokines may directly regulate pancreatic endocrine function. Disclosure S. Nieuwoudt: None. R. McDowell: None. H. Zhang: None. J.P. Kirwan: None.

Dapagliflozin Improves Insulin Sensitivity in the Obese Prediabetic Canine

SGLT2 inhibition has positive effects on glucose balance, reducing fasting and postprandial glucose levels, however little is known about the effects of SGLT2 inhibitors on lipid levels. PKPD simulation for this canine model was applied for dose selection of dapagliflozin (dapa). Seven dogs were fed a high fat diet for 6 weeks, then received a single low dose of streptozotocin (18.5mg/kg) to induce mild type 2 diabetes. Animals were exposed to dapa (n=4, 1.25mg/kg) or placebo (n=3) once per day for 6 weeks, while remaining on the high fat diet. Animals were then subjected to the intravenous glucose tolerance test (IVGTT) to assess glucose tolerance and insulin response to glucose, and the euglycemic hyperinsulinemic clamp protocol in conjunction with tracer infusions to evaluate adipose tissue, skeletal muscle and hepatic insulin sensitivity. In the IVGTT, modeling techniques are used to estimate the acute insulin response to a glucose bolus, which was not altered with dapa treatment, but insulin sensitivity was significantly improved compared to placebo-treated animals (dapa 0.54±0.22, control -0.95±0.51mU/l-1.minute-1, p=0.05). The glucose infusion required for euglycemia during steady state in the clamp was decreased with dapa (dapa -3.0±1.05, control 1.53±1.28 mg/minute/kg, change from pre-drug timepoint, P=0.038), supporting the IVGTT results. Urinary glucose disposal rate during the clamp was inconsistent. There is a trend towards higher FFA levels in dapa-treated animals under noninsulin stimulated conditions (P=0.054). These may be a regulator of hepatic glucose production, or reflect a switch towards lipid utilization. We conclude that 6 weeks of dapa treatment improves insulin sensitivity in a canine model of mild type 2 diabetes. Further studies on lipid metabolism, body fat deposition and insulin clearance are on-going. Disclosure R.L. Paszkiewicz: None. R.N. Bergman: Advisory Panel; Self; Ingredion, Inc.. Research Support; Self; AstraZeneca. Consultant; Self; GI Dynamics Inc.. Research Support; Self; National Institute of Diabetes and Digestive and Kidney Diseases. Consultant; Self; Novo Nordisk A/S. I. Asare Bediako: None. H.J. Mkrtchyan: None. V. Gopaul: Employee; Self; AstraZeneca. H. Yang: Employee; Self; AstraZeneca. E. Lundborg: Employee; Self; AstraZeneca. S. Kim: None. I. Formentini: Employee; Self; AstraZeneca. C.M. Kolka: Research Support; Self; AstraZeneca.

Electrical stimulation of renal nerves for modulating urine glucose excretion in rats

BackgroundThe role of the kidney in glucose homeostasis has gained global interest. Kidneys are innervated by renal nerves, and renal denervation animal models have shown improved glucose regulation. We hypothesized that stimulation of renal nerves at kilohertz frequencies, which can block propagation of action potentials, would increase urine glucose excretion. Conversely, we hypothesized that low frequency stimulation, which has been shown to increase renal nerve activity, would decrease urine glucose excretion.MethodsWe performed non-survival experiments on male rats under thiobutabarbital anesthesia. A cuff electrode was placed around the left renal artery, encircling the renal nerves. Ureters were cannulated bilaterally to obtain urine samples from each kidney independently for comparison. Renal nerves were stimulated at kilohertz frequencies (1–50 kHz) or low frequencies (2–5 Hz), with intravenous administration of a glucose bolus shortly into the 25–40-min stimulation period. Urine samples were collected at 5–10-min intervals, and colorimetric assays were used to quantify glucose excretion and concentration between stimulated and non-stimulated kidneys. A Kruskal-Wallis test was performed across all stimulation frequencies (α = 0.05), followed by a post-hoc Wilcoxon rank sum test with Bonferroni correction (α = 0.005).ResultsFor kilohertz frequency trials, the stimulated kidney yielded a higher average total urine glucose excretion at 33 kHz (+ 24.5%; n = 9) than 1 kHz (− 5.9%; n = 6) and 50 kHz (+ 2.3%; n = 14). In low frequency stimulation trials, 5 Hz stimulation led to a lower average total urine glucose excretion (− 40.4%; n = 6) than 2 Hz (− 27.2%; n = 5). The average total urine glucose excretion between 33 kHz and 5 Hz was statistically significant (p < 0.005). Similar outcomes were observed for urine flow rate, which may suggest an associated response. No trends or statistical significance were observed for urine glucose concentrations.ConclusionTo our knowledge, this is the first study to investigate electrical stimulation of renal nerves to modulate urine glucose excretion. Our experimental results show that stimulation of renal nerves may modulate urine glucose excretion, however, this response may be associated with urine flow rate. Future work is needed to examine the underlying mechanisms and identify approaches for enhancing regulation of glucose excretion.

Physiological hyperinsulinemia caused by acute hyperglycemia minimizes renal sodium loss by direct action on kidneys.

This study used acute, renal artery insulin infusion in conscious rats to test the hypothesis that hyperinsulinemia attenuates glucose-induced natriuresis by a direct renal mechanism. We reported previously that hyperinsulinemia was required to prevent ad libitum eating or an acute glucose bolus from causing excessive renal sodium loss. Rats were instrumented with renal artery, aortic, and femoral vein catheters and Data Sciences International blood pressure telemeters and were housed in metabolic cages. Insulin was clamped chronically at normal levels in two groups [vehicle infused (irV) and insulin infused (irI)] by administering streptozotocin and then infusing insulin intravenously 24 h/day to maintain normal blood glucose. Bolus glucose administration was used as a meal substitute to produce hyperglycemia that was not different between groups, and urinary sodium excretion (UNaV) was measured over the next 4 h. In the irV and control (C) rats, vehicle was infused in the renal artery during that period, whereas insulin was infused in the renal artery of the irI rats. Plasma insulin increased significantly in C rats but not in either of the clamped groups. UNaV in the irV rats, which could not increase circulating insulin levels, was approximately threefold greater than in C rats, similar to our previous report. However, allowing the kidney of irI rats to experience hyperinsulinemia via the renal artery insulin infusion completely prevented this, with no blood pressure differences. These data support our hypothesis that meal-induced increases in plasma insulin are a major component of normal sodium homeostasis, and that this occurs by direct action of insulin on the kidney.

Generalized sensitivity analysis of the minimal model of the intravenous glucose tolerance test

Generalized sensitivity functions characterize the sensitivity of the parameter estimates with respect to the nominal parameters. We observe from the generalized sensitivity analysis of the minimal model of the intravenous glucose tolerance test that the measurements of insulin, 62 min after the administration of the glucose bolus into the experimental subject’s body, possess no information about the parameter estimates. The glucose measurements possess the information about the parameter estimates up to three hours. These observations have been verified by the parameter estimation of the minimal model. The standard errors of the estimates and crude Monte Carlo process also confirm this observation.

Acute hypertensive stress imaged by cardiac hyperpolarized [1-13 C]pyruvate magnetic resonance.

Deranged metabolism is now recognized as a key causal factor in a variety of heart diseases, and is being studied extensively. However, invasive methods may alter metabolism, and conventional imaging techniques measure tracer uptake but not downstream metabolism. These challenges may be overcome by hyperpolarized MR, a noninvasive technique currently crossing the threshold into human trials. The aim of this study was to image metabolic changes in the heart in response to endogastric glucose bolus and to acute hypertension. Five postprandial pigs were scanned with hyperpolarized [1-13 C]pyruvate cardiac MR at baseline, after oral glucose bolus, and after infusion of angiotensin-II. No effect of glucose bolus was seen using hyperpolarized [1-13 C]pyruvate MR despite changes in circulating substrates. During angiotensin-II infusion, blood pressure increased 179% (P = 0.008) and ejection fraction decreased from 54 ± 2% to 47 ± 6% (P = 0.03) The hemodynamic changes were accompanied by increases in the hyperpolarized [1-13 C]pyruvate MR derived ratios of lactate/alanine (from 0.58 ± 0.13 to 0.78 ± 0.06, P = 0.03) and bicarbonate/alanine (from 0.55 ± 0.12 to 0.91 ± 0.14, P = 0.007). Glucose loading did not alter cardiac metabolism, but during acute hypertensive stress, cardiac aerobic, carbohydrate metabolism, and pyruvate-lactate exchange was altered. Hyperpolarized MR allows noninvasive evaluation of acute changes in cardiac metabolism. However, hemodynamics must be taken into account when interpreting the results.

Acute glycemic changes in brain and subcutaneous tissue measured by continuous glucose monitoring system in hereditary hypertriglyceridemic rat.

Parallel glucose measurements in blood and other different tissues give us knowledge about dynamics of glycemia changes, which depend on vascularization, distribution space and local utilization by tissues. Such information is important for the understanding of glucose homeostasis and regulation. The aim of our study was to determine the time-lag between blood, brain, and adipose tissue during rapid glucose changes in a male hHTG rat (n=15). The CGMS sensor Guardian RT (Minimed/Medtronic, USA) was inserted into the brain and into the abdominal subcutaneous tissue. Fixed insulin and variable rate of glucose infusion was used to maintain euglycemia during sensor calibration period. At 0 min, 0.5 g/kg of bolus of glucose was administered, and at 50 min, 5 IU/kg of bolus of insulin was administered. Further glucose and insulin infusion was stopped at this time. The experiment was finished at 130 min and animals were euthanized. The time-shift between glycemia changes in blood, brain, and subcutaneous tissue was calculated by identification of the ideal correlation function. Moreover, the time to achieve 90 % of the maximum glucose excursion after intervention (T90) was measured to compare our data with the literature. The time-lag blood vs. brain and blood vs. subcutaneous tissue was 10 (10; 15) min and 15 (15; 25) min, respectively. The difference was statistically significant (P=0.01). T90 after glucose bolus in brain and subcutaneous tissue was 10 min (8.75; 15) and 15 min (13.75; 21.25), respectively. T90 after insulin bolus in brain and subcutaneous tissue was 10 min (10; 15) and 20 min (20; 27.5), respectively. To the contrary, with literature, our results showed earlier glucose level changes in brain in comparison with subcutaneous tissue after glucose and insulin boluses. Our results suggest that glucose dynamics is different within monitored tissues under rapid changing glucose level and we can expect similar behavior in humans. Improved knowledge about glucose distribution and dynamics is important for avoiding hypoglycemia.

On‐Line Control of Glucose Concentration in High‐Yielding Mammalian Cell Cultures Enabled Through Oxygen Transfer Rate Measurements

Glucose control is vital to ensure consistent growth and protein production in mammalian cell cultures. The typical fed-batch glucose control strategy involving bolus glucose additions based on infrequent off-line daily samples results in cells experiencing significant glucose concentration fluctuations that can influence product quality and growth. This study proposes an on-line method to control and manipulate glucose utilizing readily available process measurements. The method generates a correlation between the cumulative oxygen transfer rate and the cumulative glucose consumed. This correlation generates an on-line prediction of glucose that has been successfully incorporated into a control algorithm manipulating the glucose feed-rate. This advanced process control (APC) strategy enables the glucose concentration to be maintained at an adjustable set-point and has been found to significantly reduce the deviation in glucose concentration in comparison to conventional operation. This method has been validated to produce various therapeutic proteins across cell lines with different glucose consumption demands and is successfully demonstrated on micro (15 mL), laboratory (7 L), and pilot (50 L) scale systems. This novel APC strategy is simple to implement and offers the potential to significantly enhance the glucose control strategy for scales spanning micro-scale systems through to full scale industrial bioreactors.

Glucose Modulates Human Ventral Tegmental Activity in Response to Sexual Stimuli

BackgroundAttribution of salience to sexual stimuli is mediated by the dopaminergic midbrain, including the ventral tegmental area (VTA). The existence of glucose-sensing neurons in the VTA, as suggested by animal studies, offers the opportunity to modulate aberrant salience coding involved in sexual disorders such as sexual addiction. Recent neuroimaging work supported that VTA activity in humans can be modulated by intravenously infusing a small bolus of glucose. However, that study used appetitive food stimuli, leaving the possibility that glucose modulation of VTA-mediated salience coding might be bound to this class of stimuli. AimTo test whether glucose-modulatory effects generalize to food-unrelated stimuli despite being in the class of primary reinforcers. MethodsDuring functional imaging, 37 healthy men were exposed to images showing nude or clothed female upper bodies. At the end of the 1st quarter (∼6 minutes) of the experiment, 18 participants received a small amount of intravenously infused glucose. ResultsBefore glucose administration, VTA activity was higher for nude than for clothed female stimuli. After infusion of glucose, this pattern reversed such that VTA activity was higher for clothed than for nude female stimuli. The effect was at its maximum approximately 7 to 12 minutes after glucose infusion, changing back during the experiment’s 4th phase. In another 19 participants not treated with glucose, VTA activity was consistently higher for nude than for clothed female stimuli throughout the experiment. ConclusionThe present findings show that glucose modulates VTA-mediated salience coding of sexual stimuli. These results suggest that glucose might affect salience coding in a stimulus-general way. However, future studies are necessary to address the question of whether glucose modulation also affects the VTA’s salience coding of secondary reinforcers.Ulrich M, Stauβ P, Grön G. Glucose Modulates Human Ventral Tegmental Activity in Response to Sexual Stimuli. J Sex Med 2018;15:20–28.