Relationship Between Fasting Plasma Glucagon Level and Renal Function-A Cross-Sectional Study in Individuals With Type 2 Diabetes

Impaired Incretin Homeostasis in Nondiabetic Moderate-to-Severe CKD

Key Points

Total incretin levels and incretin response during oral glucose tolerance testing were significantly higher among patients with moderate-to-severe nondiabetic patients with CKD compared with healthy people. Unlike in healthy individuals, increased incretin response was not correlated with insulin response and coincided with persistently greater glucagon levels to oral glucose tolerance testing in CKD. Disruption in the incretin system and glucagon dynamics may contribute to metabolic complications in moderate-to-severe CKD.

Background

Incretins are regulators of insulin secretion and glucose homeostasis metabolized by dipeptidyl peptidase-4 (DPP-4). CKD may modify incretin release, metabolism, or response.

Methods

We performed 2-hour oral glucose tolerance testing in 59 people with nondiabetic CKD (eGFR <60 ml/min per 1.73 m2) and 39 matched controls. We measured total area under the curve and incremental area under the curve (iAUC) of plasma total glucagon-like peptide-1 (GLP-1) and total glucose-dependent insulinotropic polypeptide (GIP). Fasting DPP-4 levels and activity were measured. Linear regression was used to adjust for demographic, body composition, and lifestyle factors.

Results

Mean (SD) eGFR was 38±13 and 89±17 ml/min per 1.73 m2 in patients with CKD and controls, respectively. GLP-1 total area under the curve and GIP iAUC were higher in patients with CKD than controls with a mean of 1531±1452 versus 1364±1484 pM×min and 62,370±33,453 versus 42,365±25,061 pg×min/ml, respectively. After adjustment, CKD was associated with 15,271 pM×min/ml greater GIP iAUC (95% confidence intervals [CIs], 387 to 30,154) compared with controls. Adjustment for covariates attenuated associations of CKD with higher GLP-1 iAUC (adjusted difference, 122; 95% CI, −619 to 864). Plasma glucagon levels were higher at 30 minutes (mean difference, 1.6; 95% CI, 0.3 to 2.8 mg/dl) and 120 minutes (mean difference, 0.84; 95% CI, 0.2 to 1.5 mg/dl) in patients with CKD compared with controls. There were no differences in insulin levels or plasma DPP-4 activity or levels between groups.

Conclusions

Overall, incretin response to oral glucose is preserved or augmented in moderate-to-severe CKD, without apparent differences in circulating DPP-4 concentration or activity. However, neither insulin secretion nor glucagon suppression is enhanced.

Glucagon receptor activation contributes to the development of kidney injury

The underlying causes of diabetic kidney disease are still largely unknown. New insights into the contributing causes of diabetic nephropathy are important to prevent this complication. Hyperglycemia and hypertension are some of the risk factors for diabetic nephropathy. However, the incidence of diabetic nephropathy is increasing despite efforts to normalize blood glucose levels and blood pressure. Therefore, other factors should be investigated as causes of diabetic nephropathy. We investigated whether long-term increased plasma levels of glucagon contribute to the development of pathophysiological changes in kidney function as seen in patients with diabetic nephropathy. Using mouse models of chronic activation and inactivation of glucagon receptor signaling, we investigated whether glucagon is involved in changes in renal function, renal structure, and transcriptional changes. We found several histopathological changes in the kidney, such as thickening of the parietal layer of Bowman's capsule, glomerular mesangial cell expansion, and significant albuminuria in the mice with activated glucagon receptor signaling. Opposite effects on mesangial area expansion and the development of albuminuria were demonstrated in mice with glucagon receptor inactivation. RNA sequencing data revealed that transcription of genes related to fatty acid metabolism, podocytes, Na+-K+-ATPase, and sodium/glucose transport was significantly changed in mice with activated glucagon receptor signaling. These data implicate that glucagon receptor signaling is involved in the development of kidney injury, as seen in type 2 diabetes, and that glucagon receptor is a potential therapeutic target in the treatment of diabetes. NEW & NOTEWORTHY This study suggests that the glucagon receptor is a potential therapeutic target in the treatment of diabetic kidney disease. We show, in mice, that long-term treatment with a glucagon analog showed not only pathophysiological changes and changes in renal function but also transcriptional changes in the kidneys, whereas opposite effects were demonstrated in mice with glucagon receptor inactivation. Therefore, the use of glucagon in a treatment regimen requires investigation of possible metabolic and renal abnormalities.

Glucagon Clearance Is Decreased in Chronic Kidney Disease but Preserved in Liver Cirrhosis

It is not completely clear which organs are responsible for glucagon elimination in humans, and disturbances in the elimination of glucagon could contribute to the hyperglucagonemia observed in chronic liver disease and chronic kidney disease (CKD). Here, we evaluated kinetics and metabolic effects of exogenous glucagon in individuals with stage 4 CKD (n = 16), individuals with Child-Pugh A-C cirrhosis (n = 16), and matched control individuals (n = 16), before, during, and after a 60-min glucagon infusion (4 ng/kg/min). Individuals with CKD exhibited a significantly lower mean metabolic clearance rate of glucagon (14.0 [95% CI 12.2;15.7] mL/kg/min) compared with both individuals with cirrhosis (19.7 [18.1;21.3] mL/kg/min, P < 0.001) and control individuals (20.4 [18.1;22.7] mL/kg/min, P < 0.001). Glucagon half-life was significantly prolonged in the CKD group (7.5 [6.9;8.2] min) compared with individuals with cirrhosis (5.7 [5.2;6.3] min, P = 0.002) and control individuals (5.7 [5.2;6.3] min, P < 0.001). No difference in the effects of exogenous glucagon on plasma glucose, amino acids, or triglycerides was observed between groups. In conclusion, CKD, but not liver cirrhosis, leads to a significant reduction in glucagon clearance, supporting the kidneys as a primary site for human glucagon elimination.

ARTICLE HIGHLIGHTS

The effect of exogenous glucagon on circulating amino acids in individuals with and without type 2 diabetes and obesity

Objective

In obesity and type 2 diabetes, hyperglucagonaemia may be caused by elevated levels of glucagonotropic amino acids due to hepatic glucagon resistance at the level of amino acid turnover. Here, we investigated the effect of exogenous glucagon on circulating amino acids in obese and non-obese individuals with and without type 2 diabetes.

Design

This was a post hoc analysis in a glucagon infusion study performed in individuals with type 2 diabetes (n = 16) and in age, sex, and body mass index-matched control individuals without diabetes (n = 16). Each group comprised two subgroups of eight individuals with and without obesity, respectively.

Methods

All participants received a 1-h glucagon infusion (4 ng/kg/min) in the overnight fasted state. Plasma amino acid concentrations were measured with frequent intervals.

Results

Compared to the control subgroup without obesity, baseline total amino acid levels were elevated in the control subgroup with obesity and in the type 2 diabetes subgroup without obesity. In all subgroups, amino acid levels decreased by up to 20% in response to glucagon infusion, which resulted in high physiological steady-state glucagon levels (mean concentration: 74 pmol/L, 95% CI [68;79] pmol/L). Following correction for multiple testing, no intergroup differences in changes in amino acid levels reached significance.

Conclusion

Obesity and type 2 diabetes status was associated with elevated fasting levels of total amino acids. The glucagon infusion decreased circulating amino acid levels similarly in all subgroups, without significant differences in the response to exogenous glucagon between individuals with and without obesity and type 2 diabetes.

Significance statement

The hormone glucagon stimulates glucose production from the liver, which may promote hyperglycaemia if glucagon levels are abnormally elevated, as is often seen in type 2 diabetes and obesity. Glucagon levels are closely linked to, and influenced by, the levels of circulating amino acids. To further investigate this link, we measured amino acid levels in individuals with and without obesity and type 2 diabetes before and during an infusion of glucagon. We found that circulating amino acid levels were higher in type 2 diabetes and obesity, and that glucagon infusion decreased amino acid levels in both individuals with and without type 2 diabetes and obesity. The study adds novel information to the link between circulating levels of glucagon and amino acids.

Impaired incretin homeostasis in non-diabetic moderate-severe CKD

Background

Incretins are regulators of insulin secretion and glucose homeostasis that are metabolized by dipeptidyl peptidase-4 (DPP-4). Moderate-severe CKD may modify incretin release, metabolism, or response.

Methods

We performed 2-hour oral glucose tolerance testing (OGTT) in 59 people with non-diabetic CKD (eGFR<60 ml/min per 1.73 m2) and 39 matched controls. We measured total (tAUC) and incremental (iAUC) area under the curve of plasma total glucagon-like peptide-1 (GLP-1) and total glucose-dependent insulinotropic polypeptide (GIP). Fasting DPP-4 levels and activity were measured. Linear regression was used to adjust for demographic, body composition, and lifestyle factors.

Results

Mean eGFR was 38 ±13 and 89 ±17ml/min per 1.73 m2 in CKD and controls. GLP-1 iAUC and GIP iAUC were higher in CKD than controls with a mean of 1531 ±1452 versus 1364 ±1484 pMxmin, and 62370 ±33453 versus 42365 ±25061 pgxmin/ml, respectively. After adjustment, CKD was associated with 15271 pMxmin/ml greater GIP iAUC (95% CI 387, 30154) compared to controls. Adjustment for covariates attenuated associations of CKD with higher GLP-1 iAUC (adjusted difference, 122, 95% CI -619, 864). Plasma glucagon levels were higher at 30 minutes (mean difference, 1.6, 95% CI 0.3, 2.8 mg/dl) and 120 minutes (mean difference, 0.84, 95% CI 0.2, 1.5 mg/dl) in CKD compared to controls. There were no differences in insulin levels or plasma DPP-4 activity or levels between groups.

Conclusion

Incretin response to oral glucose is preserved or augmented in moderate-severe CKD, without apparent differences in circulating DPP-4 concentration or activity. However, neither insulin secretion nor glucagon suppression are enhanced.

Temporal Profile of Kynurenine Pathway Metabolites in a Rodent Model of Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is an early onset genetic disorder characterized by numerous renal cysts resulting in end stage renal disease. Our study aimed to determine if metabolic reprogramming and tryptophan (Trp) metabolism via the kynurenine pathway (KP) is a critical dysregulated pathway in PKD. Using the Lewis polycystic kidney (LPK) rat model of PKD and Lewis controls, we profiled temporal trends for KP metabolites in plasma, urine, and kidney tissues from 6- and 12-week-old mixed sex animals using liquid and gas chromatography, minimum n = 5 per cohort. A greater kynurenine (KYN) concentration was observed in LPK kidney and plasma of 12-week rats compared to age matched Lewis controls (P ⩽ .05). LPK kidneys also showed an age effect (P ⩽ .05) with KYN being greater in 12-week versus 6-week LPK. The metabolites xanthurenic acid (XA), 3-hydroxykynurenine (3-HK), and 3-hydroxyanthranilic acid (3-HAA) were significantly greater in the plasma of 12-week LPK rats compared to age matched Lewis controls (P ⩽ .05). Plasma XA and 3-HK also showed an age effect (P ⩽ .05) being greater in 12-week versus 6-week LPK. We further describe a decrease in Trp levels in LPK plasma and kidney (strain effect P ⩽ .05). There were no differences in KP metabolites in urine between cohorts. Using the ratio of product and substrates in the KP, a significant age-strain effect (P ⩽ .05) was observed in the activity of the KYN/Trp ratio (tryptophan-2,3-dioxygenase [TDO] or indoleamine-2,3-dioxygenase [IDO] activity), kynurenine 3-monooxygenase (KMO), KAT A (kynurenine aminotransferase A), KAT B, total KAT, total KYNU (kynureninase), KYNU A, KYNU B, and total KYNU within LPK kidneys, supporting an activated KP. Confirmation of the activation of these enzymes will require verification through orthogonal techniques. In conclusion, we have demonstrated an up-regulation of the KP in alignment with progression of renal impairment in the LPK rat model, suggesting that KP activation may be a critical contributor to the pathobiology of PKD.

The Effect of Nutrition and Exercise on Body Composition, Exercise Capacity, and Physical Functioning in Advanced CKD Patients

Patients with stages 4 and 5 chronic kidney disease (CKD), and particularly chronic dialysis patients, commonly are found to have substantially reduced daily physical activity in comparison to age- and sex-matched normal adults. This reduction in physical activity is associated with a major decrease in physical exercise capacity and physical performance. The CKD patients are often physically deconditioned, and protein energy wasting (PEW) and frailty are commonly present. These disorders are of major concern because physical dysfunction, muscle atrophy, and reduced muscle strength are associated with poor quality of life and increased morbidity and mortality in CKD and chronic dialysis patients. Many randomized controlled clinical trials indicate that when CKD and chronic dialysis are provided nutritional supplements or undergo exercise training their skeletal muscle mass and exercise capacity often increase. It is not known whether the rise in skeletal muscle mass and exercise capacity associated with nutritional support or exercise training will reduce morbidity or mortality rates. A limitation of these clinical trials is that the sample sizes of the different treatment groups were small. The aim of this review is to discuss the effects of nutrition and exercise on body composition, exercise capacity, and physical functioning in advanced CKD patients.

The association of glucagon with disease severity and progression in patients with autosomal dominant polycystic kidney disease: an observational cohort study

Background

Mammalian target of rapamycin (mTOR) inhibitors and ketogenesis have been shown to ameliorate disease progression in experimental autosomal dominant polycystic kidney disease (ADPKD). Glucagon is known to lower mTOR activity and stimulate ketogenesis. We hypothesized that in ADPKD patients, higher endogenous glucagon is associated with less disease severity and progression.

Methods

Data were analysed from 664 Dutch ADPKD patients participating in the Developing Intervention Strategies to Halt Progression of ADPKD observational cohort, including patients >18 years of age with an estimated glomerular filtration rate (eGFR) ≥15 mL/min/1.73 m² and excluding patients with concomitant diseases or medication use that may impact the natural course of ADPKD. The association between glucagon and disease severity and progression was tested using multivariate linear regression and mixed modelling, respectively.

Results

The median glucagon concentration was 5.0 pmol/L [interquartile range (IQR) 3.4-7.2) and differed significantly between females and males [4.3 pmol/L (IQR 2.9-6.0) and 6.6 (4.5-9.5), P < 0.001, respectively]. Intrasubject stability of glucagon in 30 patients showed a strong correlation (Pearson's correlation coefficient 0.893; P < 0.001). Moreover, glucagon showed significant associations with known determinants (sex, body mass index and copeptin; all P < 0.01) and known downstream effects (glucose, haemoglobin A1c and cholesterol; all P < 0.05), suggesting that glucagon was measured reliably. Cross-sectionally, glucagon was associated with eGFR and height-adjusted total kidney volume, but in the opposite direction of our hypothesis, and these lost significance after adjustment for confounders. Glucagon was not associated with an annual decline in kidney function or growth in kidney volume.

Conclusions

These data do not provide evidence for a role of endogenous glucagon as a protective hormone in ADPKD. Intervention studies are needed to determine the relation between glucagon and ADPKD.

Glucagon Clearance is Preserved in Type 2 Diabetes

Hyperglucagonemia is a common observation in both obesity and type 2 diabetes, and the etiology is primarily thought to be hypersecretion of glucagon. We investigated whether altered elimination kinetics of glucagon could contribute to the hyperglucagonemia in type 2 diabetes and obesity. Individuals with type 2 diabetes and preserved kidney function (8 with and 8 without obesity) and matched control individuals (8 with and 8 without obesity) were recruited. Each participant underwent a 1-hour glucagon infusion (4 ng/kg/min), achieving steady-state plasma glucagon concentrations, followed by a 1-hour wash-out period. Plasma levels, the metabolic clearance rate (MCR), half-life (T½) and volume of distribution of glucagon were evaluated and a pharmacokinetic model was constructed. Glucagon MCR and volume of distribution were significantly higher in the type 2 diabetes group compared to the control group, while no significant differences between the groups were found in glucagon T½. Individuals with obesity had neither a significantly decreased MCR, T½, nor volume of distribution of glucagon. In our pharmacokinetic model, glucagon MCR associated positively with fasting plasma glucose and negatively with body weight. In conclusion, our results suggest that impaired glucagon clearance is not a fundamental part of the hyperglucagonemia observed in obesity and type 2 diabetes.

Association of Glucagon With Obesity, Glycemic Control and Renal Function in Adults With Type 2 Diabetes Mellitus

OBJECTIVES

In this study, we used a double-antibody sandwich enzyme-linked immunosorbent assay to assess the association between blood glucagon levels and indices of obesity, glycemic control and renal function in patients with type 2 diabetes mellitus (T2DM).

METHODS

This investigation was a cross-sectional study on inpatients with T2DM who had plasma glucagon levels measured during hospitalization. Associations of fasting glucagon levels (G₀), 120-minute postbreakfast plasma glucagon (G₁₂₀), fasting glucagon/C-peptide ratio (G₀/CPR₀) and postbreakfast glucagon/C-peptide ratio (G₁₂₀/CPR₁₂₀) with clinical data were evaluated using multiple regression analysis.

RESULTS

A total of 345 patients were enrolled in the study. G₀, and G₁₂₀ were significantly and positively associated with serum C-peptide levels. Moreover, G₀ and G₁₂₀ were positively associated with waist circumference, and G₀ was negatively associated with duration of diabetes mellitus. Interestingly, both G₀ and G₁₂₀ were negatively associated with the estimated glomerular filtration rate. In addition, G₁₂₀/CPR₁₂₀ was positively associated with duration of diabetes mellitus and glycoalbumin levels.

CONCLUSIONS

The balance between glucagon and insulin secretion is significantly associated with abdominal obesity and important for maintaining glucose homeostasis. Postprandial hyperglucagonemia could also be related to deterioration of renal function.

Frequency and Causes of False-Positive Elevated Plasma Concentrations of Fasting Gut Hormones in a Specialist Neuroendocrine Tumor Center

INTRODUCTION

In the UK, the fasting plasma concentrations of a panel of gut hormones (comprising vasoactive intestinal peptide (VIP), gastrin, pancreatic polypeptide (PP), glucagon, somatostatin and chromogranin A) are measured to evaluate patients who have or who (due to unexplained and compatible symptoms) are suspected of having neuroendocrine tumors (NETs). False positive elevated hormone concentrations are sometimes found.

OBJECTIVE

To evaluate the frequency and implications of false positive fasting gut hormone results.

METHODS

Retrospective audit of fasting gut hormone profile results at a large UK university teaching hospital over 12 months.

RESULTS

Fasting gut hormone concentrations were measured in 231 patients during 2017. No NETs were found in the 88 patients who had this test performed only to investigate symptoms. 31 false positive gastrin, 8 false positive chromogranin A, two false positive glucagon, three false positive somatostatin, one false positive PP, and one false positive VIP results were found. We extended the audit for glucagon and somatostatin for an additional two years and found seven probable false-positive raised glucagon concentrations and four probable false-positive elevated plasma somatostatin concentrations in total.

CONCLUSIONS

False-positive elevations of plasma gastrin and chromogranin A were common and causes such as proton pump inhibitor use or inadequate fasting accounted for most cases. Elevated plasma concentrations of the other gut hormones were also detected in patients who had no other evidence of NET. Other diagnoses (e.g. cirrhosis and medullary thyroid carcinoma for hypersomatostatinemia and type 2 diabetes mellitus, pancreatitis, liver or renal impairment for hyperglucagonemia) may cause these false positive results.