Glucagon-like peptide-1 does not have acute effects on central or renal hemodynamics in patients with type 2 diabetes without nephropathy

The GLP-1-mediated gut-kidney cross talk in humans: mechanistic insight

Incretin-based therapy is an antidiabetic and antiobesity approach mimicking glucagon-like peptide-1 (GLP-1) with additional end-organ protection. This review solely focuses on randomized, controlled mechanistic human studies, investigating the renal effects of GLP-1. There is no consensus about the localization of GLP-1 receptors (GLP-1Rs) in human kidneys. Rodent and primate data suggest GLP-1R distribution in smooth muscle cells in the preglomerular vasculature. Native GLP-1 and GLP-1R agonists elicit renal effects. Independently of renal plasma flow and glomerular filtration rate, GLP-1 has a natriuretic effect but only during volume expansion. This is associated with high renal extraction of GLP-1, suppression of angiotensin II, and increased medullary as well as cortical perfusion. These observations may potentially indicate that impaired GLP-1 sensing could establish a connection between salt sensitivity and insulin resistance. It is concluded that a functional GLP-1 kidney axis exists in humans, which may play a role in renoprotection.

Separate and combined effects of semaglutide and empagliflozin on kidney oxygenation and perfusion in people with type 2 diabetes: a randomised trial

AIMS/HYPOTHESIS

Glucagon-like peptide-1 receptor agonists (GLP-1ras) and sodium-glucose cotransporter 2 inhibitors (SGLT2is) have shown kidney-protective effects. Improved kidney oxygenation and haemodynamic changes are suggested mechanisms; however, human data are scarce. We therefore investigated whether semaglutide (GLP-1ra), empagliflozin (SGLT2i) or their combination improve kidney oxygenation and perfusion.

METHODS

The trial was undertaken at Aarhus University Hospital, Denmark. A total of 120 people with type 2 diabetes (HbA1c ≥48 mmol/mol [6.5%]) and at high risk of CVD (age ≥50 years) were randomised into four parallel groups (n=30 in each group) for 32 weeks: 1.0 mg semaglutide (open label); 10 mg empagliflozin (blinded to participants, caregivers, examiners and outcome assessors); their combination (1.0 mg semaglutide open label plus 10 mg empagliflozin blinded to participants, caregivers, examiners and outcome assessors); and placebo tablet (blinded to participants, caregivers, examiners and outcome assessors). Sequentially numbered, sealed envelopes containing computer-generated randomisation codes, provided by Glostrup Pharmacy, Glostrup, Denmark, determined the intervention. The two co-primary outcomes were change in kidney oxygenation and change in arterial stiffness. This paper reports on kidney oxygenation, for which 80 individuals as prespecified, 20 in each group, underwent MRI. We primarily hypothesised that kidney oxygenation would be improved in the active treatment groups compared with placebo after 32 weeks. Secondary outcomes included changes in kidney perfusion, erythropoietin, haematocrit, urine albumin/creatinine ratio (UACR) and GFR (measured using technetium-99m) compared with baseline and between treatment groups at week 32.

RESULTS

Our model estimated a common baseline R2* value across all four groups in the cortex and the medulla. At baseline, the value was 24.5 (95% CI 23.9, 24.9) Hz in the medulla. After 32 weeks, the R2* values in the medulla were estimated to be 25.4 (95% CI 24.7, 26.2) Hz in the empagliflozin group and 24.5 (95% CI 23.9, 25.1) Hz in the placebo group (p=0.016) (higher R2* corresponds to a lower oxygenation). Semaglutide decreased perfusion in both the cortex and the medulla. Empagliflozin increased erythropoietin and haematocrit. All three active treatments decreased GFR but not UACR. Ten serious adverse events were reported, among them two occurrences of semaglutide-associated obstipation.

CONCLUSIONS/INTERPRETATION

Our hypothesis, that semaglutide, empagliflozin or their combination improve kidney oxygenation, was rejected. On the contrary, empagliflozin induced a reduction in medullary kidney oxygenation. Semaglutide substantially reduced kidney perfusion without affecting oxygenation.

TRIAL REGISTRATION

Clinicaltrialsregister.eu EudraCT 2019-000781-38 FUNDING: Novo Nordisk Foundation, Central Denmark Region Research Fund and Danish Medical Associations Research Foundation.

The blood pressure lowering effects of glucagon-like peptide-1 receptor agonists: A mini-review of the potential mechanisms

The incretin hormone glucagon-like peptide 1 (GLP-1) is a key component of the signaling mechanisms promoting glucose homeostasis. Clinical and experimental studies demonstrated that GLP-1 receptor agonists, including GLP-1 itself, have favorable effects on blood pressure and reduce the risk of major cardiovascular events, independently of their effect on glycemic control. GLP-1 receptors are present in the hypothalamus and brainstem, the carotid body, the vasculature, and the kidneys. These organs are involved in blood pressure regulation, have their function altered in hypertension, and are positively benefited by the treatment with GLP-1 receptor agonists. Here, we discuss the potential mechanisms whereby activation of GLP-1R signaling exerts blood pressure-lowering effects beyond glycemic control.

GLP-1 Promotes Cortical and Medullary Perfusion in the Human Kidney and Maintains Renal Oxygenation During NaCl Loading

Background GLP-1 (glucagon-like peptide-1) receptor agonists exert beneficial long-term effects on cardiovascular and renal outcomes. In humans, the natriuretic effect of GLP-1 depends on GLP-1 receptor interaction, is accompanied by suppression of angiotensin II, and is independent of changes in renal plasma flow. In rodents, angiotensin II constricts vasa recta and lowers medullary perfusion. The current randomized, controlled, crossover study was designed to test the hypothesis that GLP-1 increases renal medullary perfusion in healthy humans. Methods and Results Healthy male participants (n=10, aged 27±4 years) ingested a fixed sodium intake for 4 days and were examined twice during a 1-hour infusion of either GLP-1 (1.5 pmol/kg per minute) or placebo together with infusion of 0.9% NaCl (750 mL/h). Interleaved measurements of renal arterial blood flow, oxygenation (R₂*), and perfusion were acquired in the renal cortex and medulla during infusions, using magnetic resonance imaging. GLP-1 infusion increased medullary perfusion (32±7%, P<0.001) and cortical perfusion (13±4%, P<0.001) compared with placebo. Here, NaCl infusion decreased medullary perfusion (-5±2%, P=0.007), whereas cortical perfusion remained unchanged. R₂* values increased by 3±2% (P=0.025) in the medulla and 4±1% (P=0.008) in the cortex during placebo, indicative of decreased oxygenation, but remained unchanged during GLP-1. Blood flow in the renal artery was not altered significantly by either intervention. Conclusions GLP-1 increases predominantly medullary but also cortical perfusion in the healthy human kidney and maintains renal oxygenation during NaCl loading. In perspective, suppression of angiotensin II by GLP-1 may account for the increase in regional perfusion. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT04337268.

Nephroprotective Effects of Semaglutide as Mono- and Combination Treatment with Lisinopril in a Mouse Model of Hypertension-Accelerated Diabetic Kidney Disease

Background: Obesity, hyperglycemia and hypertension are critical risk factors for development of diabetic kidney disease (DKD). Emerging evidence suggests that glucagon-like peptide-1 receptor (GLP-1R) agonists improve cardiovascular and renal outcomes in type 2 diabetes patients. Here, we characterized the effect of the long-acting GLP-1R agonist semaglutide alone and in combination with an ACE inhibitor (lisinopril) in a model of hypertension-accelerated, advanced DKD facilitated by adeno-associated virus-mediated renin overexpression (ReninAAV) in uninephrectomized (UNx) female diabetic db/db mice. Methods: Female db/db mice received a single intravenous injection of ReninAAV 1 week prior to UNx. Six weeks post-nephrectomy, db/db UNx-ReninAAV mice were administered (q.d.) vehicle, semaglutide (30 nmol/kg, s.c.) or semaglutide (30 nmol/kg, s.c.) + lisinopril (30 mg/kg, p.o.) for 11 weeks. Endpoints included blood pressure, plasma/urine biochemistry, kidney histopathology and RNA sequencing. Results: Vehicle-dosed db/db UNx-ReninAAV mice developed hallmarks of DKD characterized by severe albuminuria and advanced glomerulosclerosis. Semaglutide robustly reduced hyperglycemia, hypertension and albuminuria concurrent with notable improvements in glomerulosclerosis severity, podocyte filtration slit density, urine/renal kidney injury molecule-1 (KIM-1) levels and gene expression markers of inflammation and fibrogenesis in db/db UNx-ReninAAV mice. Co-administration of lisinopril further ameliorated hypertension and glomerulosclerosis. Conclusions: Semaglutide improves disease hallmarks in the db/db UNx-ReninAAV mouse model of advanced DKD. Further benefits on renal outcomes were obtained by adjunctive antihypertensive standard of care. Collectively, our study supports the development of semaglutide for management of DKD.

Effect of a 3-Week Treatment with GLP-1 Receptor Agonists on Vasoactive Hormones in Euvolemic Participants

CONTEXT

Glucagon-like-peptide-1 receptor agonists (GLP-1 RAs) exert cardiovascular benefits by reducing plasma glucose, body weight, and blood pressure. The blood pressure-lowering effect may be mediated by angiotensin II (ANG II) suppression and consecutive natriuresis. However, the role of ANG II and other vasoactive hormones on GLP-1 RA treatment has not been clearly defined.

OBJECTIVE

This work aimed to investigate the effect of a 3-week treatment with the GLP-1 RA dulaglutide on vasoactive hormones, that is, renin, ANG II, aldosterone, mid-regional proatrial natriuretic peptide (MP-proANP), and natriuresis in euvolemic participants.

METHODS

Randomized, double-blinded, placebo-controlled, crossover trials were conducted at University Hospital Basel, Switzerland. A total of 54 euvolemic participants, including 20 healthy individuals and 34 patients with primary polydipsia, received a subcutaneous injection of dulaglutide (Trulicity) 1.5 mg and placebo (0.9% sodium chloride) once weekly over a 3-week treatment phase.

RESULTS

After a 3-week treatment phase, dulaglutide showed no effect on plasma renin, plasma ANG II, or plasma aldosterone levels in comparison to placebo. Natriuresis remained unchanged or decreased on dulaglutide depending on the measured parameter. Dulaglutide significantly decreased plasma MR-proANP levels (treatment effect: 10.60 pmol/L; 95% CI, -14.70 to -7.90; P < .001) and systolic blood pressure (median: 3 mm Hg; 95% CI, -5 to 0; P = .036), whereas heart rate increased (median: 5 bpm; 95% CI, 3-11; P < .001).

CONCLUSION

In euvolemic participants, a 3-week treatment of dulaglutide reduced systolic blood pressure independently of plasma renin, ANG II, or aldosterone levels and urinary sodium excretion. The reduction in MR-proANP might be secondary to reduced arterial pulse pressure.

Glucagon-Like Peptide-1 Receptor Agonists-Use in Clinical Practice

In the past 2 decades, eight glucagon-like peptide-1 receptor agonists (GLP-1RAs) have been approved for the management of type 2 diabetes, each with its peculiar molecular structure, pharmacokinetics, and metabolic effects. Along with their marked glucose-lowering actions, which occur both at fasting and in the postprandial phase without an increased risk of hypoglycemia, GLP-1RAs have provided marked reductions in body weight and ancillary improvements in blood pressure and lipid profile. Recent cardiovascular outcome trials have established the benefits of GLP-1RAs on major cardiovascular events and all-cause mortality, independent of glucose control, with minor effects on preventing hospitalization for heart failure. Novel evidence is also emerging on the protection of GLP-1RAs against diabetic kidney disease, mainly preventing the onset of macroalbuminuria. Several mechanisms have been proposed to explain the cardiorenal protective properties of GLP-1RAs, which may be direct or mediated by additional hemodynamic and anti-inflammatory/antioxidant effects. With their favorable cardiometabolic properties and safety profile, GLP-1RAs may offer an ideal pharmacological option for the management of diabetic kidney disease. In this review, we discuss pharmacokinetic properties, glucometabolic effects, and cardioprotective actions of GLP-1RAs, highlighting the available evidence for a kidney protective role and the proposed mechanisms.

Inquiry into the short- and long-term effects of Roux-en-Y gastric bypass on the glomerular filtration rate

Bariatric surgery is known to attenuate glomerular hyperfiltration over the long term and thereby protect the kidney from mechanical damage. Whether this effect is directly related to weight loss or is independent of weight as are some of its other beneficial metabolic effects is not known. We explored this question in a preliminary study that directly measured glomerular filtration rate (GFR) before, immediately after, and again many months after Roux-en-Y gastric bypass after large weight loss had occurred. We simultaneously measured stimulated circulating glucagon-like peptide-1, which is upregulated after Roux-en-Y gastric bypass and is a putative mediator of GFR after bariatric surgery. We found no weight-independent effect of Roux-en-Y gastric bypass on GFR nor an association between circulating GLP-1 levels and GFR. These findings, if confirmed in larger studies, will help steer future enquiries in this area.

Activation of the renal GLP-1R leads to expression of Ren1 in the renal vascular tree

The GLP‐1 receptor (GLP‐1R) in the kidney is expressed exclusively in vascular smooth muscle cells in arteries and arterioles. Downstream effects of the activation of the renal vascular GLP‐1R are elusive but may involve regulation of the renin‐angiotensin‐aldosterone system (RAAS). The expression of Ren1 in the mouse renal vasculature was investigated by in situ hybridization after a single subcutaneous dose of liraglutide, semaglutide and after repeated injections of liraglutide. Single and repeated exposure to GLP‐1R agonists induced expression of Ren1 in the renal vascular smooth muscle cell compartment compared with vehicle injected controls (p < .0001) for both semaglutide and liraglutide. The present data show a robust induction of Ren1 expression in the vascular smooth muscle cells of the kidney after single and repeated GLP‐1R activation and this renin recruitment may be involved in the effects of GLP‐1R agonist treatment on kidney disease.

Renoprotection in diabetic kidney disease: can incretin-based therapies deliver?

PURPOSE OF REVIEW

Incretin-based therapies mimic or augment the gut-hormone glucagon-like peptide (GLP)-1 and, due to their glucose-lowering potential and beneficial safety profile, as well as their cardiovascular safety and/or protection, are prescribed on a large scale to treat individuals with type 2 diabetes (T2D). However, whether the two drug-classes that belong to this category, respectively GLP-1 receptor agonists and dipeptidyl peptidase (DPP)-4 inhibitors, also reduce the risk of diabetic kidney disease (DKD) is at present heavily debated. This review aims to discuss the current evidence.

RECENT FINDINGS

Evidence from land-mark cardiovascular safety trials, conducted in people with T2D at high-cardiovascular risk but with normal kidney function, suggest that both drug-classes have excellent renal safety profiles. In contrast to DPP-4 inhibitors, it seems that GLP-1 receptor agonists reduce albuminuria and possibly induce a reduction of estimated glomerular filtration rate decline. However, the trials were not properly designed to test renal outcomes.

SUMMARY

A dedicated renal trial involving a GLP-1 receptor agonist has recently commenced and will answer the question whether these drugs will be effective to reduce DKD. Moreover, ongoing mechanism-of-action studies are focusing on the renal physiological effects of GLP-1, as the effects on particularly albuminuria reduction remain currently unexplained.

The Renal Extraction and the Natriuretic Action of GLP-1 in Humans Depend on Interaction With the GLP-1 Receptor

PURPOSE

The natriuretic effect of glucagon-like peptide-1 (GLP-1) in humans is independent of changes in renal plasma flow (RPF) and glomerular filtration rate (GFR) but may involve suppression of angiotensin II (ANG II) and a significant (~45%) renal extraction of GLP-1. The current study was designed to investigate the consequences for the renal extraction and the natriuretic effect of blocking GLP-1 receptors with the specific GLP-1 receptor antagonist, Exendin 9-39 (Ex 9-39).

METHODS

Under fixed sodium intake for 4 days before each study day, 6 healthy male participants were recruited from our recent study where GLP-1 or vehicle was infused (1). In the present new experiments, participants were examined during a 3-hour infusion of GLP-1 (1.5 pmol/kg/min) together with a 3.5-hour infusion of Ex 9-39 (900 pmol/kg/min). Timed urine collections were conducted throughout the experiments. Renal extraction of GLP-1 as well as RPF and GFR were measured via Fick's principle after catheterization of a renal vein. Arterial plasma renin, ANG II, and aldosterone concentrations were measured.

RESULTS

Co-infusion of Ex 9-39 significantly reduced renal extraction of GLP-1 to ~25% compared with GLP-1 infusion alone (~45%). Urinary sodium excretions remained at baseline levels during co-infusion of Ex 9-39 as well as vehicle. By contrast, GLP-1 infusion alone resulted in a 2-fold increase in natriuresis. Ex 9-39 abolished the GLP-1-induced decrease in arterial ANG II concentrations. RPF and GFR remained unchanged during all experiments.

CONCLUSIONS

Renal extraction of GLP-1 and its effect on natriuresis are both dependent on GLP-1 receptor activation in healthy humans.

Hematopoietic cell- versus enterocyte-derived dipeptidyl peptidase-4 differentially regulates triglyceride excursion in mice

Postprandial triglycerides (TGs) are elevated in people with type 2 diabetes (T2D). Glucose-lowering agents, such as glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, also reduce postprandial TG excursion. Although the glucose-lowering mechanisms of DPP-4 have been extensively studied, how the reduction of DPP-4 activity improves lipid tolerance remains unclear. Here, we demonstrate that gut-selective and systemic inhibition of DPP-4 activity reduces postprandial TG excursion in young mice. Genetic inactivation of Dpp4 simultaneously within endothelial cells and hematopoietic cells using Tie2-Cre reduced intestinal lipoprotein secretion under regular chow diet conditions. Bone marrow transplantation revealed a key role for hematopoietic cells in modulation of lipid responses arising from genetic reduction of DPP-4 activity. Unexpectedly, deletion of Dpp4 in enterocytes increased TG excursion in high-fat diet–fed (HFD-fed) mice. Moreover, chemical reduction of DPP-4 activity and increased levels of GLP-1 were uncoupled from TG excursion in older or HFD-fed mice, yet lipid tolerance remained improved in older Dpp4^–/– and Dpp4^EC–/– mice. Taken together, this study defines roles for specific DPP-4 compartments, age, and diet as modifiers of DPP-4 activity linked to control of gut lipid metabolism.

Gut-selective and systemic inhibition of dipeptidyl peptidase-4 activity reveals roles in gut lipid metabolism.

Increased oral sodium chloride intake in humans amplifies selectively postprandial GLP-1 but not GIP, CCK, and gastrin in plasma

Human studies have demonstrated that physiologically relevant changes in circulating glucagon-like peptide-1 (GLP-1) elicit a rapid increase in renal sodium excretion when combined with expansion of the extracellular fluid volume. Other studies support the involvement of various gastrointestinal hormones, e.g., gastrin and cholecystokinin (CCK) in a gut-kidney axis, responsible for a rapid-acting feed-forward natriuretic mechanism. This study was designed to investigate the hypothesis that the postprandial GLP-1 plasma concentration is sensitive to the sodium content in the meal. Under fixed sodium intake for 4 days prior to each experimental day, 10 lean healthy male participants were examined twice in random order after a 12-hr fasting period. Arterial blood samples were collected at 10-20-min intervals for 140 min after 75 grams of oral glucose + 6 grams of oral sodium chloride (NaCl) load versus 75 grams of glucose alone. Twenty-four-hour baseline urinary sodium excretions were similar between study days. Arterial GLP-1 levels increased during both oral glucose loads and were significantly higher at the 40-80 min period during glucose + NaCl compared to glucose alone. The postprandial arterial responses of CCK, gastrin, and glucose-dependent insulinotropic polypeptide as well as glucose, insulin, and C-peptide did not differ between the two study days. Arterial renin, aldosterone, and natriuretic peptides levels did not change within subjects or between study days. Angiotensin II levels were significantly lower at the time GLP-1 was higher (60-80 min) during glucose + NaCl. Sodium intake in addition to a glucose load selectively amplifies the postprandial GLP-1 plasma concentration. Thus, GLP-1 may be part of an acute feed-forward mechanism for natriuresis.

Glucagon-like peptide-1 receptors in the kidney: impact on renal autoregulation

Glucagon-like peptide-1 (GLP-1) and strategies based on this blood sugar-reducing and appetite-suppressing hormone are used to treat obesity and type 2 diabetes. However, the GLP-1 receptor (GLP-1R) is also present in the kidney, where it influences renal function. The effect of GLP-1 on the kidney varies between humans and rodents. The effect of GLP-1 on kidney function also seems to vary depending on its concentration and the physiological or pathological state of the kidney. In studies with rodents or humans, acute infusion of pharmacological doses of GLP-1 stimulates natriuresis and diuresis. However, the effect on the renal vasculature is less clear. In rodents, GLP-1 infusion increases renal plasma flow and glomerular filtration rate, suggesting renal vasodilation. In humans, only a subset of the study participants exhibits increased renal plasma flow and glomerular filtration rate. Differential status of kidney function and changes in renal vascular resistance of the preglomerular arterioles may account for the different responses of the human study participants. Because renal function in patients with type 2 diabetes is already at risk or compromised, understanding the effects of GLP-1R activation on kidney function in these patients is particularly important. This review examines the distribution of GLP-1R in the kidney and the effects elicited by GLP-1 or GLP-1R agonists. By integrating results from acute and chronic studies in healthy individuals and patients with type 2 diabetes along with those from rodent studies, we provide insight into how GLP-1R activation affects renal function and autoregulation.

Extracellular Fluid Volume Expansion Uncovers a Natriuretic Action of GLP-1: A Functional GLP-1-Renal Axis in Man

PURPOSE

We have previously demonstrated that glucagon-like peptide-1 (GLP-1) does not affect renal hemodynamics or function under baseline conditions in healthy participants and in patients with type 2 diabetes mellitus. However, it is possible that GLP-1 promotes natriuresis under conditions with addition of salt and water to the extracellular fluid. The current study was designed to investigate a possible GLP-1-renal axis, inducing natriuresis in healthy, volume-loaded participants.

METHODS

Under fixed sodium intake, eight healthy men were examined twice in random order during a 3-hour infusion of either GLP-1 (1.5 pmol/kg/min) or vehicle together with an intravenous infusion of 0.9% NaCl. Timed urine collections were conducted throughout the experiments. Renal plasma flow (RPF), glomerular filtration rate (GFR), and uptake and release of hormones and ions were measured via Fick's principle.

RESULTS

During GLP-1 infusion, urinary sodium and osmolar excretions increased significantly compared with vehicle. Plasma renin levels decreased similarly on both days, whereas angiotensin II (ANG II) levels decreased significantly only during GLP-1 infusion. RPF and GFR remained unchanged on both days.

CONCLUSIONS

In volume-loaded participants, GLP-1 induces natriuresis, probably brought about via a tubular mechanism secondary to suppression of ANG II, independent of renal hemodynamics, supporting the existence of a GLP-1-renal axis.

The incretin pathway as a therapeutic target in diabetic kidney disease: a clinical focus on GLP-1 receptor agonists

Diabetic kidney disease (DKD) remains the main cause for chronic kidney disease (CKD) and end-stage kidney disease (ESKD) worldwide. Both CKD and ESKD lead to major increases in risk of cardiovascular disease and death in people with diabetes. Despite optimal management of lifestyle, glucose levels and hypertension, residual risk remains high, indicating that additional therapies to mitigate the burden of the disease are desired. In past decades, new treatment options for the management of diabetes have emerged, of which some have showed promising renoprotective potential. This review discusses current understanding of the renal effects of glucagon-like peptide receptor agonists and their potential use in prevention and treatment of DKD.

The potential and pitfalls of GLP-1 receptor agonists for renal protection in type 2 diabetes

Glucagon-Like Peptide-1 Receptor agonists (GLP-1 RA) offer substantial benefits for the management of glucose levels in type 2 diabetes. In addition, recent data from clinical trials have demonstrated that treatment with Glucagon-Like Peptide-1 Receptor agonists (GLP-1 RA) are also able to reduce new onset macroalbuminuria. These benefits may be consistent with the known effects of GLP-1 RA on traditional risk factors for progressive kidney disease including glucose lowering, blood pressure lowering, reduced insulin levels and weight reduction. However, emerging evidence suggests that GLP-1 RA can also have direct effects in the kidney, including inhibiting NHE3-dependent sodium reabsorption in the proximal tubule. Additional effects on the intrarenal renin angiotensin system, ischaemia/hypoxia, inflammation, apoptosis and neural signalling may also contribute to renal benefits. The extent to which these effects are mediated by the GLP-1R remains to be established. Recent studies confirm that the metabolic products of GLP-1 retain important antioxidant and anti-apoptotic activities that are GLP-1 R independent. Moreover the divergent peptide sequences of the currently available GLP-1 RA may mean that divergent reno-protective efficacy could be anticipated from different GLP-1 RA on this basis. Kidney disease is an important and deadly clinical outcome, and one worth preventing. Although both experimental and clinical data now support the possibility of renoprotective effects arising from treatment with GLP-1 RA, further work is needed to optimise these effects. A logical synergism with SGLT2 inhibition also exists, and at least in the short term, this combination approach may become the most useful way to protect the kidney in type 2 diabetes.

Glucagon-like peptide-1 elicits vasodilation in adipose tissue and skeletal muscle in healthy men

In healthy subjects, we recently demonstrated that during acute administration of GLP-1, cardiac output increased significantly, whereas renal blood flow remained constant. We therefore hypothesize that GLP-1 induces vasodilation in other organs, for example, adipose tissue, skeletal muscle, and/or splanchnic tissues. Nine healthy men were examined twice in random order during a 2-hour infusion of either GLP-1 (1.5 pmol kg^-1 min^-1) or saline. Cardiac output was continuously estimated noninvasively concomitantly with measurement of intra-arterial blood pressure. Subcutaneous, abdominal adipose tissue blood flow (ATBF) was measured by the ¹³³Xenon clearance technique. Leg and splanchnic blood flow were measured by Fick's Principle, using indocyanine green as indicator. In the GLP-1 study, cardiac output increased significantly together with a significant increase in arterial pulse pressure and heart rate compared with the saline study. Subcutaneous, abdominal ATBF and leg blood flow increased significantly during the GLP-1 infusion compared with saline, whereas splanchnic blood flow response did not differ between the studies. We conclude that in healthy subjects, GLP-1 increases cardiac output acutely due to a GLP-1-induced vasodilation in adipose tissue and skeletal muscle together with an increase in cardiac work.

Postprandial renal haemodynamic effect of lixisenatide vs once-daily insulin-glulisine in patients with type 2 diabetes on insulin-glargine: An 8-week, randomised, open-label trial

AIM

To determine whether lixisenatide, a prandial short-acting glucagon-like peptide receptor agonist (GLP-1RA), ameliorates postprandial glomerular hyperfiltration in patients with type 2 diabetes mellitus (T2DM) compared with insulin-glulisine (iGlu).

METHODS

Postprandial renal haemodynamic effects of 8-week treatment with lixisenatide 20 µg vs once-daily titrated iGlu were measured in 35 overweight patients with T2DM inadequately controlled on insulin-glargine, with or without metformin [mean ± SD age 62 ± 7 years, HbA1c 8.0% ± 0.9%, estimated glomerular filtration rate (GFR) 85 ± 12 mL/min/1.73 m² , median (IQR) urinary albumin/creatinine ratio 1.5 (0.9-3.0) mg/mmol]. After a standardised breakfast, GFR (primary endpoint) and effective renal plasma flow (ERPF) were determined by inulin and para-aminohippuric acid renal clearance, respectively, based on timed urine sampling. Intrarenal haemodynamic functions were estimated using Gomez equations.

RESULTS

Compared with iGlu, lixisenatide did not affect GFR [+0.1 mL/min/1.73 m² (95% CI -9 to 9)], ERPF [-17 mL/min/1.73 m² (-61 to 26)], other (intra-)renal haemodynamics or renal damage markers, but increased fractional sodium excretion [+0.25% (0.09-0.41)] and urinary pH [+0.7 (0.3-1.2)]. Plasma renin, angiotensin-II and aldosterone were unchanged. Lixisenatide and iGlu reduced HbA1c similarly, by 0.8% ± 0.1% and 0.6% ± 0.1%, respectively, while postprandial glucose was lower with lixisenatide (P = .002). Compared with iGlu, lixisenatide reduced bodyweight [-1.4 kg (-2.5 to -0.2)] and increased postprandial mean arterial pressure [+9 mm Hg (4-14)].

CONCLUSION

Eight-week lixisenatide treatment does not affect postprandial (intra-)renal haemodynamics compared with iGlu when added to insulin-glargine in patients with T2DM without overt nephropathy. Prolonged lixisenatide treatment has a sustained natriuretic effect, which is in contrast to previous reports on long-acting GLP-1RA, reduces body weight and increases postprandial blood pressure compared with iGlu.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT02276196.

Natriuretic peptides in the control of lipid metabolism and insulin sensitivity

Natriuretic peptides have long been known for their cardiovascular function. However, a growing body of evidence emphasizes the role of natriuretic peptides in human substrate and energy metabolism, thereby connecting the heart with several insulin-sensitive organs like adipose tissue, skeletal muscle and liver. Obesity may be associated with an impaired regulation of the natriuretic peptide system, also indicated as a natriuretic handicap. Evidence points towards a contribution of this natriuretic handicap to the development of obesity, type 2 diabetes mellitus and cardiometabolic complications, although the causal relationship is not fully understood. Nevertheless, targeting the natriuretic peptide pathway may improve metabolic health in obesity and type 2 diabetes mellitus. This review will focus on current literature regarding the metabolic roles of natriuretic peptides with emphasis on lipid metabolism and insulin sensitivity. Furthermore, it will be discussed how exercise and lifestyle intervention may modulate the natriuretic peptide-related metabolic effects.

GLP-1 and the kidney: from physiology to pharmacology and outcomes in diabetes

The gastrointestinal tract - the largest endocrine network in human physiology - orchestrates signals from the external environment to maintain neural and hormonal control of homeostasis. Advances in understanding entero-endocrine cell biology in health and disease have important translational relevance. The gut-derived incretin hormone glucagon-like peptide 1 (GLP-1) is secreted upon meal ingestion and controls glucose metabolism by modulating pancreatic islet cell function, food intake and gastrointestinal motility, amongst other effects. The observation that the insulinotropic actions of GLP-1 are reduced in type 2 diabetes mellitus (T2DM) led to the development of incretin-based therapies - GLP-1 receptor agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors - for the treatment of hyperglycaemia in these patients. Considerable interest exists in identifying effects of these drugs beyond glucose-lowering, possibly resulting in improved macrovascular and microvascular outcomes, including in diabetic kidney disease. As GLP-1 has been implicated as a mediator in the putative gut-renal axis (a rapid-acting feed-forward loop that regulates postprandial fluid and electrolyte homeostasis), direct actions on the kidney have been proposed. Here, we review the role of GLP-1 and the actions of associated therapies on glucose metabolism, the gut-renal axis, classical renal risk factors, and renal end points in randomized controlled trials of GLP-1 receptor agonists and DPP-4 inhibitors in patients with T2DM.

A sandwich ELISA for measurement of the primary glucagon-like peptide-1 metabolite

Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted from the gastrointestinal tract. It is best known for its glucose-dependent insulinotropic effects. GLP-1 is secreted in its intact (active) form (7-36NH₂) but is rapidly degraded by the dipeptidyl peptidase 4 (DPP-4) enzyme, converting >90% to the primary metabolite (9-36NH₂) before reaching the targets via the circulation. Although originally thought to be inactive or antagonistic, GLP-1 9-36NH₂ may have independent actions, and it is therefore relevant to be able to measure it. Because reliable assays were not available, we developed a sandwich ELISA recognizing both GLP-1 9-36NH₂ and nonamidated GLP-1 9-37. The ELISA was validated using analytical assay validation guidelines and by comparing it to a subtraction-based method, hitherto employed for estimation of GLP-1 9-36NH₂ Its accuracy was evaluated from measurements of plasma obtained during intravenous infusions (1.5 pmol × kg^-1 × min^-1) of GLP-1 7-36NH₂ in healthy subjects and patients with type 2 diabetes. Plasma levels of the endogenous GLP-1 metabolite increased during a meal challenge in patients with type 2 diabetes, and treatment with a DPP-4 inhibitor fully blocked its formation. Accurate measurements of the GLP-1 metabolite may contribute to understanding its physiology and role of GLP-1 in diabetes.

Effects of the glucagon-like peptide-1 receptor agonist liraglutide on 24-h ambulatory blood pressure in patients with type 2 diabetes and stable coronary artery disease: a randomized, double-blind, placebo-controlled, crossover study

OBJECTIVE

The glucagon-like peptide-1 receptor agonist liraglutide has been shown to reduce blood pressure (BP) in clinical trials using office BP measurements. However, the effects of liraglutide on 24-h BP and on the diurnal variation in BP have not been explored sufficiently.

METHODS

Forty-one patients with type 2 diabetes and stable coronary artery disease were randomized to receive liraglutide or placebo to a backbone therapy of metformin in this double-blind, placebo-controlled 12 along with 12 weeks crossover study. Ambulatory blood pressure monitoring (ABPM) was performed at the start and end of each intervention.

RESULTS

Twenty-four individuals completed all 24-h BP measurements. Liraglutide, when compared with placebo, did not induce any significant changes in mean 24-h SBP [difference +1.8 mmHg (95% confidence interval, 95% CI: -4.33 to 7.93)] or DBP [+4.2 mmHg (-0.74 to 9.17)]. Twenty-four-hour BP profiles revealed a trend for increase in evening SBP and DBP [+9.2 mmHg (95% CI: 1.1-17.2) and +9.7 mmHg (95% CI: 3.9-15.5), respectively]. Mean heart rate significantly increased after liraglutide [+7.6 bpm (95% CI: 2.56-12.62)]. Liraglutide did not affect the BP variability or the nocturnal BP dipping.

CONCLUSIONS

We could not demonstrate any BP-lowering effect of liraglutide when using 24-h ABPM. Liraglutide exhibited diurnal variation in the effect on BP without affecting the BP variability or nocturnal BP dipping.

Differential effects of glucagon-like peptide-1 receptor agonists on heart rate

While glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are known to increase heart rate (HR), it is insufficiently recognized that the extent varies greatly between the various agonists and is affected by the assessment methods employed. Here we review published data from 24-h time-averaged HR monitoring in healthy individuals and subjects with type 2 diabetes mellitus (T2DM) treated with either short-acting GLP-1 RAs, lixisenatide or exenatide, or long-acting GLP-1 RAs, exenatide LAR, liraglutide, albiglutide, or dulaglutide (N = 1112; active-treatment arms). HR effects observed in two independent head-to-head trials of lixisenatide and liraglutide (N = 202; active-treatment arms) are also reviewed. Short-acting GLP-1 RAs, exenatide and lixisenatide, are associated with a transient (1-12 h) mean placebo- and baseline-adjusted 24-h HR increase of 1-3 beats per minute (bpm). Conversely, long-acting GLP-1 RAs are associated with more pronounced increases in mean 24-h HR; the highest seen with liraglutide and albiglutide at 6-10 bpm compared with dulaglutide and exenatide LAR at 3-4 bpm. For both liraglutide and dulaglutide, HR increases were recorded during both the day and at night. In two head-to-head comparisons, a small, transient mean increase in HR from baseline was observed with lixisenatide; liraglutide induced a substantially greater increase that remained significantly elevated over 24 h. The underlying mechanism for increased HR remains to be elucidated; however, it could be related to a direct effect at the sinus node and/or stimulation of the sympathetic nervous system, with this effect related to the duration of action of the respective GLP-1 RAs. In conclusion, this review indicates that the effects on HR differ within the class of GLP-1 RAs: short-acting GLP-1 RAs are associated with a modest and transient HR increase before returning to baseline levels, while some long-acting GLP-1 RAs are associated with a more pronounced and sustained increase during the day and night. Findings from recently completed trials indicate that a GLP-1 RA-induced increase in HR, regardless of magnitude, does not present an increased cardiovascular risk for subjects with T2DM, although a pronounced increase in HR may be associated with adverse clinical outcomes in those with advanced heart failure.

Renal Effects of DPP-4 Inhibitor Sitagliptin or GLP-1 Receptor Agonist Liraglutide in Overweight Patients With Type 2 Diabetes: A 12-Week, Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVE

To investigate effects of dipeptidyl peptidase-4 inhibitor (DPP-4I) sitagliptin or glucagon-like peptide 1 (GLP-1) receptor agonist liraglutide treatment on renal hemodynamics, tubular functions, and markers of renal damage in overweight patients with type 2 diabetes without chronic kidney disease (CKD).

RESEARCH DESIGN AND METHODS

In this 12-week, randomized, double-blind trial, 55 insulin-naïve patients with type 2 diabetes (mean ± SEM: age 63 ± 7 years, BMI 31.8 ± 4.1 kg/m², glomerular filtration rate [GFR] 83 ± 16 mL/min/1.73 m²; median [interquartile range]: albumin-to-creatinine ratio (ACR) 1.09 mg/mmol [0.47-3.31]) received sitagliptin (100 mg/day), liraglutide (1.8 mg/day), or matching placebos. GFR (primary end point) and effective renal plasma flow (ERPF) were determined by inulin and para-aminohippuric acid clearance, respectively. Intrarenal hemodynamic variables were estimated. Absolute and fractional excretions of sodium (FE_Na), potassium, and urea (FE_U) and renal damage markers (ACR, neutrophil gelatinase-associated lipocalin [NGAL], and kidney injury molecule-1 [KIM-1]) were measured. Plasma renin concentration (PRC) and glycated hemoglobin (HbA_1c) were assessed. At weeks 2 and 6, estimated GFR and fractional electrolyte excretions were determined.

RESULTS

At week 12, GFR was not affected by sitagliptin (-6 mL/min/1.73 m² [95% CI -14 to 3], P = 0.17) or liraglutide (+3 mL/min/1.73 m² [-5 to 11], P = 0.46), compared with placebo. Sitagliptin modestly reduced estimated glomerular hydraulic pressure (P_GLO; P = 0.043). ERPF, other intrarenal hemodynamic variables, renal damage markers, and PRC did not change for both treatments. Both agents reduced HbA_1c. Only at week 2, sitagliptin increased FE_Na and FE_U (P = 0.005).

CONCLUSIONS

Twelve-week treatment with sitagliptin or liraglutide does not affect measured renal hemodynamics. No sustained changes in tubular functions or alteration in renal damage markers were observed. The validity and clinical relevance of the slight sitagliptin-induced P_GLO reduction remains speculative.