Glucagon, from past to present: a century of intensive research and controversies.

2022 corresponds to the 100th anniversary of the discovery of glucagon. This TimeCapsule aims to recall the main steps leading to the discovery, characterisation, and clinical importance of the so-called second pancreatic hormone. We describe the early historical findings in basic research (ie, discovery, purification, structure, α-cell origin, radioimmunoassay, glucagon gene [GCG], and glucagon receptor [GLR]), in which three future Nobel Prize laureates were actively involved. Considered as an anti-insulin hormone, glucagon was rapidly used to treat insulin-induced hypoglycaemic coma episodes in people with type 1 diabetes. A key step in the story of glucagon was the discovery of its role and the role of α cells in the physiology and pathophysiology (ie, paracrinopathy) of type 2 diabetes. This concept led to the design of different strategies targeting glucagon, among which GLP-1 receptor (GLP1R) agonists were a major breakthrough, and combination of inhibition of glucagon secretion with stimulation of insulin secretion (both in a glucose-dependent manner). Taking advantage of the glucagon-induced increase in energy metabolism, biased coagonists were developed. Besides the GLP-1 receptor, these coagonists also target the glucagon receptor to further promote weight loss. Thus, the 100-year story of glucagon has most probably not come to an end.

Investigational glucagon receptor antagonists in Phase I and II clinical trials for diabetes.

INTRODUCTION: Despite type 2 diabetes (T2D) being recognized as a bihormonal pancreatic disease, current therapies are mainly focusing on insulin, while targeting glucagon has been long dismissed. However, glucagon receptor (GCGr) antagonists are currently investigated in clinical trials. Area covered: Following a brief description of the rationale for antagonizing GCGr in T2D, lessons from GCGr knock-out mice and pharmacological means to antagonize GCGr, a detailed description of the main results obtained with GCGr antagonists in Phase I-II clinical trials is provided. The development of several small molecules has been discontinued, while new ones are currently considered as well as innovative approaches such as monoclonal antibodies or antisense oligonucleotides inhibiting GCGr gene expression. Their potential benefits but also limitations are discussed. Expert opinion: The proof-of-concept that antagonizing GCGr improves glucose control in T2D has been confirmed in humans. Nevertheless, some adverse events led to stopping the development of some of these GCGr antagonists. New approaches seem to have a better benefit/risk balance, although none has progressed to Phase III clinical trials so far. Pharmacotherapy of T2D is becoming a highly competitive field so that GCGr antagonists should provide clear advantages over numerous existing glucose-lowering medications before eventually reaching clinical practice.

Does insulin release kinins in rats?

Rat uterus maintained in situ was used as a bioassay of kinins possibly released in vivo by hyperglycaemia or insulin. Intravenous injections of bradykinin induced contractions of rat uterus which were suppressed by HOE 140, a bradykinin B2 receptor antagonist. Des-Arg9-bradykinin, a kinin B1 receptor agonist, did not elicit any response. After propranolol, the effects of bradykinin were enhanced and dose-dependent. This potentiation did not appear in adrenalectomized rats. Captopril, an angiotensin-converting enzyme (ACE) inhibitor, largely increased the effects of bradykinin. In animals pretreated with propranolol, captopril and atosiban, an oxytocin antagonist, intravenous infusion of glucose induced hyperglycaemia and after a delay increased the uterine contractile activity. This contractile effect of glucose was abolished by HOE 140. Infusion of insulin with glucose induced contractions of the uterus. These responses did not appear or were suppressed by HOE 140 or by soya bean trypsin inhibitor (SBTI), a plasma kallikrein inhibitor. These results are direct evidence that insulin induces a release of kinins.

Secondary prevention of macrovascular events in patients with type 2 diabetes in the PROactive Study (PROspective pioglitAzone Clinical Trial In macroVascular Events): a randomised controlled trial.

BACKGROUND: Patients with type 2 diabetes are at high risk of fatal and non-fatal myocardial infarction and stroke. There is indirect evidence that agonists of peroxisome proliferator-activated receptor gamma (PPAR gamma) could reduce macrovascular complications. Our aim, therefore, was to ascertain whether pioglitazone reduces macrovascular morbidity and mortality in high-risk patients with type 2 diabetes. METHODS: We did a prospective, randomised controlled trial in 5238 patients with type 2 diabetes who had evidence of macrovascular disease. We recruited patients from primary-care practices and hospitals. We assigned patients to oral pioglitazone titrated from 15 mg to 45 mg (n=2605) or matching placebo (n=2633), to be taken in addition to their glucose-lowering drugs and other medications. Our primary endpoint was the composite of all-cause mortality, non fatal myocardial infarction (including silent myocardial infarction), stroke, acute coronary syndrome, endovascular or surgical intervention in the coronary or leg arteries, and amputation above the ankle. Analysis was by intention to treat. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN NCT00174993. FINDINGS: Two patients were lost to follow-up, but were included in analyses. The average time of observation was 34.5 months. 514 of 2605 patients in the pioglitazone group and 572 of 2633 patients in the placebo group had at least one event in the primary composite endpoint (HR 0.90, 95% CI 0.80-1.02, p=0.095). The main secondary endpoint was the composite of all-cause mortality, non-fatal myocardial infarction, and stroke. 301 patients in the pioglitazone group and 358 in the placebo group reached this endpoint (0.84, 0.72-0.98, p=0.027). Overall safety and tolerability was good with no change in the safety profile of pioglitazone identified. 6% (149 of 2065) and 4% (108 of 2633) of those in the pioglitazone and placebo groups, respectively, were admitted to hospital with heart failure; mortality rates from heart failure did not differ between groups. INTERPRETATION: Pioglitazone reduces the composite of all-cause mortality, non-fatal myocardial infarction, and stroke in patients with type 2 diabetes who have a high risk of macrovascular events.

Modulation of the renal response to ACE inhibition by ACE insertion/deletion polymorphism during hyperglycemia in normotensive, normoalbuminuric type 1 diabetic patients.

ACE inhibition protects kidney function, but ACE insertion/deletion (I/D) polymorphism affects renal prognosis in type 1 diabetic patients. ACE genotype may influence the renal benefits of ACE inhibition. We studied the impact of ACE I/D polymorphism on the renal hemodynamic changes induced by ACE inhibition in type 1 diabetes. We studied renal hemodynamics (glomerular filtration rate [GFR], effective renal plasma flow [ERPF], filtration fraction [GFR/ERPF], mean arterial pressure [MAP], and total renal resistances [MAP/ERPF]) repeatedly during normoglycemia and then hyperglycemia in 12 normotensive, normoalbuminuric type 1 diabetes and the II genotype (associated with nephroprotection) versus 22 age- and sex-matched subjects with the ACE D allele after three randomly allocated 2- to 6-week periods on placebo, 1.25 mg/day ramipril, and 5 mg/day ramipril in a double-blind, cross-over study. During normoglycemia, the hemodynamic changes induced by ramipril were similar in both genotypes. During hyperglycemia, the changes induced by ramipril were accentuated in the II genotype group and attenuated dose dependently in the D allele group (treatment-genotype interaction P values for ERPF, 0.018; MAP, 0.018; and total renal resistances, 0.055). These results provide a basis to different renal responses to ACE inhibition according to ACE genotype in type 1 diabetes.

Different patterns of insulin resistance in relatives of type 1 diabetic patients with retinopathy or nephropathy: the Genesis France-Belgium Study.

OBJECTIVE: Insulin resistance may be a risk factor for diabetic microangiopathy, which may have a familial component. We carried out a family-based study to determine which components of the insulin resistance syndrome are associated with diabetic retinopathy and nephropathy in type 1 diabetes. RESEARCH DESIGN AND METHODS: The Genesis France-Belgium Study is a multicenter binational study designed to investigate the genetic factors involved in the microvascular complications of type 1 diabetes using a family-based design. Probands were type 1 diabetic patients with diabetic retinopathy (classified as background, preproliferative, or proliferative) and possibly diabetic nephropathy (absent, incipient, established, or advanced). The insulin resistance score of their first-degree relatives was calculated according to their BMI and history of arterial hypertension, lipid disorders, and type 2 diabetes. RESULTS: The insulin resistance score of relatives was positively correlated with the albumin excretion rate (P = 0.0009) and fasting plasma glucose (P = 0.0003) and HbA(1c) (P < 0.0001) concentrations. This score was higher in the relatives of probands with than in those without diabetic nephropathy (P = 0.0370). Similarly, it was higher in relatives of subjects with proliferative diabetic retinopathy than in those of probands without, even after controlling for subjects with versus without diabetic nephropathy (P = 0.0379). However, the components of the insulin resistance score in relatives differed according to the severity of diabetic retinopathy or nephropathy in the probands. Obesity and history of arterial hypertension were most common in relatives of probands with proliferative diabetic retinopathy, whereas obesity and history of lipid disorders were most common in the relatives of probands with diabetic nephropathy. CONCLUSIONS: Familial insulin resistance segregates with diabetic complications: lipid disorders and obesity segregate with diabetic nephropathy, whereas arterial hypertension and obesity segregate with diabetic retinopathy.

Hepatic insulin resistance in obese non-diabetic subjects and in type 2 diabetic patients.

OBJECTIVE: Obese non-diabetic patients are characterized by an extra-hepatic insulin resistance. Whether obese patients also have decreased hepatic insulin sensitivity remains controversial. RESEARCH METHODS AND PROCEDURES: To estimate their hepatic insulin sensitivity, we measured the rate of exogenous insulin infusion required to maintain mildly elevated glycemia in obese patients with type 2 diabetes, obese non-diabetic patients, and lean control subjects during constant infusions of somatostatin and physiological low-glucagon replacement infusions. To account for differences in insulin concentrations among the three groups of subjects, an additional protocol was also performed in healthy lean subjects with higher insulin infusion rates and exogenous dextrose infusion. RESULTS: The insulin infusion rate required to maintain glycemia at 8.5 mM was increased 4-fold in obese patients with type 2 diabetes and 1.5-fold in obese non-diabetic patients. The net endogenous glucose production (measured with 6,6-(2)H(2)-glucose) and total glucose output (measured with 2-(2)H(1)-glucose) were approximately 30% lower in the patients than in the lean subjects. Net endogenous glucose production and total glucose output were both markedly increased in both groups of obese patients compared with lean control subjects during hyperinsulinemia. DISCUSSION: Our data indicate that both obese non-diabetic and obese type 2 diabetic patients have a blunted suppressive action of insulin on glucose production, indicating hepatic and renal insulin resistance.