The Effects of Glucagon on Hepatic Metabolism

T2DM and prediabetes are characterized by abnormal post-prandial suppression of glucagon, which contributes to postprandial hyperglycemia by increasing EGP. Although these effects are magnified by decreased and delayed insulin secretion, they are also apparent when insulin secretion is intact. In rodents, altered glucagon signaling changes α-cell function and mass - an effect mediated by changes in circulating AA concentrations. Are the elevated concentrations of branched-chain AA and other AA metabolites in T2DM a cause or an effect of global α-cell dysfunction? Could altered glucagon signaling precipitate a vicious cycle resulting in T2DM?

• Glucagon response study (Drug), also known as Glucagon: Please see information in group descriptions

Primary outcomes

• Rate of Amino Acid Catabolism in the Presence / Absence of Glucagon [0 minutes, 120 minutes, 240 minutes]: Amino acid catabolism assessed by leucine reamination, a surrogate measure of leucine oxidation, during fasting (0 minutes), intermediate glucagon infusion (120 minutes), and high glucagon infusion (240 minutes).

Secondary outcomes

• Effect of Diabetes on Amino-acid Catabolism [240 minutes of study]: Tracer-dependent measurement of amino-acid clearance
• Splanchnic Balance of Essential Amino Acids During Fasting and Glucagon Infusion [0 Minutes, 120 Minutes, 240 Minutes]: Splanchnic balance of essential amino acids calculated from the arteriovenous concentration difference across the liver multiplied by splanchnic blood flow. Measurements were obtained during fasting (0 minutes), intermediate glucagon infusion (120 minutes), and high glucagon infusion (240 minutes) to evaluate the effect of obesity and hepatic steatosis on glucagon-mediated amino acid metabolism.
• Splanchnic Balance of Nonessential Amino Acids During Fasting and Glucagon Infusion [0 Minutes, 120 Minutes, 240 Minutes]: Splanchnic balance of nonessential amino acids calculated from the arteriovenous concentration difference across the liver multiplied by splanchnic blood flow. Measurements were obtained during fasting (0 minutes), intermediate glucagon infusion (120 minutes), and high glucagon infusion (240 minutes) to evaluate the effect of obesity and hepatic steatosis on glucagon-mediated amino acid metabolism.

Sex: All, ages: 25 Years to 65 Years, accepts healthy volunteers

Inclusion Criteria - Obese Subjects with Type 2 Diabetes:

* Type 2 diabetes
* BMI ≥ 28 Kg/M2
* Managed by diet alone or a combination of metformin and/or sulfonylurea
* Willing to stop glucose-lowering medication for 3 weeks prior to participation and willing to self-monitor their fasting glucose during this time
* No history of micro- or macrovascular complications of T2DM

Exclusion Criteria - Obese Subjects with Type 2 Diabetes:

* Age < 25 or > 65 years
* HbA1c ≥ 8.5%
* BMI ≤ 28 Kg/M2
* For female subjects: positive pregnancy test at the time of enrollment or study
* History of prior upper abdominal surgery such as adjustable gastric banding, pyloroplasty and vagotomy.
* Active systemic illness or malignancy.
* Symptomatic macrovascular or microvascular disease.
* Known contraindications to MRI
* Hematocrit < 35%
* History of uncontrolled thyroid disease
* Consumption of > 2 alcohol drinks per day or > 14 per week or a positive AUDIT questionnaire.
* Allergy to iodine
* Thrombocytopenia, history of bleeding disorder or use of anticoagulation
* Subjects with treatment change or significant weight change (≥ 10%) in the prior 3 months.

Inclusion Criteria - Obese subjects without Type 2 Diabetes:

-Obese subjects without type 2 diabetes but are age, sex and weight-matched (BMI ≥ 28 Kg/M2) with subjects who have T2DM

Exclusion Criteria - Obese Subjects without Type 2 Diabetes:

* Age < 25 or > 65 years (match subjects with T2DM)
* HbA1c ≥ 6.5%
* BMI ≤ 28 Kg/M2
* Use of any glucose-lowering agents
* For female subjects: positive pregnancy test at the time of enrollment or study
* History of prior upper abdominal surgery such as adjustable gastric banding, pyloroplasty and vagotomy.
* Active systemic illness or malignancy.
* Symptomatic macrovascular or microvascular disease.
* Known contraindications to MRI
* Hematocrit < 35%
* History of uncontrolled thyroid disease.
* Consumption of > 2 alcohol drinks per day or > 14 per week or a positive AUDIT questionnaire.
* Allergy to iodine
* Thrombocytopenia, history of bleeding disorder or use of anticoagulation

Inclusion Criteria - Lean subjects without Diabetes:

-Subjects who do not have type 2 diabetes but are age and sex but are not weight-matched (BMI ≤ 25 Kg/M2) with subjects who have T2DM

Exclusion Criteria - Lean subjects without Diabetes:

* Age < 25 or > 65 years (match subjects with T2DM)
* HbA1c ≥ 6.5%
* BMI ≥ 25 Kg/M2 unless % body fat is < 20% in males and < 30% in females.
* Use of any glucose-lowering agents
* For female subjects: positive pregnancy test at the time of enrollment or study
* History of prior upper abdominal surgery such as adjustable gastric banding, pyloroplasty and vagotomy.
* Active systemic illness or malignancy.
* Symptomatic macrovascular or microvascular disease.
* Known contraindications to MRI
* Hematocrit < 35%
* History of uncontrolled thyroid disease.
* Consumption of > 2 alcohol drinks per day or > 14 per week or a positive AUDIT questionnaire.
* Liver fat content ≥ 5% as determined by MRI using the proton density fat fraction (PDFF) technique.
* Allergy to iodine
* Thrombocytopenia, history of bleeding disorder or use of anticoagulation

Participant flow

Outcome results

• Rate of Amino Acid Catabolism in the Presence / Absence of Glucagon (Primary), Mean, mmol/min: Healthy Adults 17 +/- 2; Obese Adults Protein Density Fat Fraction (PDFF) < 5% 26 +/- 5; Obese Subjects Protein Density Fat Fraction (PDFF) > 5% 20 +/- 6; Adults With Type 2 Diabetes Protein Density Fat Fraction (PDFF) < 5% ; Adults With Type 2 Diabetes Protein Density Fat Fraction (PDFF) > 5%
• Effect of Diabetes on Amino-acid Catabolism (Secondary)
• Splanchnic Balance of Essential Amino Acids During Fasting and Glucagon Infusion (Secondary), Mean, nmol/min: Healthy Adults 1.1 +/- 5.3; Obese Adults Protein Density Fat Fraction (PDFF) < 5% 2.0 +/- 2.3; Obese Subjects Protein Density Fat Fraction (PDFF) > 5% 0.5 +/- 3.0; Adults With Type 2 Diabetes Protein Density Fat Fraction (PDFF) < 5% ; Adults With Type 2 Diabetes Protein Density Fat Fraction (PDFF) > 5%
• Splanchnic Balance of Nonessential Amino Acids During Fasting and Glucagon Infusion (Secondary), Mean, nmol/min: Healthy Adults -2.1 +/- 9.0; Obese Adults Protein Density Fat Fraction (PDFF) < 5% 13.8 +/- 4.5; Adults With Type 2 Diabetes Protein Density Fat Fraction (PDFF) < 5% 5.7 +/- 4.8; Adults With Type 2 Diabetes Protein Density Fat Fraction (PDFF) > 5% ; Obese Adults Protein Density Fat Fraction (PDFF) > 5%

Adverse events

Time frame: Adverse events were collected from the time of informed consent through study completion, approximately 4 weeks.

Other adverse events by term

• Study Protocol and Statistical Analysis Plan (PDF, 2025-01-23)
• Informed Consent Form (PDF, 2025-02-26)

• Adrian Vella, Principal investigator, Mayo Clinic

NIH grants: R01DK116231