Glucagon-like peptide-1, glucose-dependent insulinotropic polypeptide, and glucagon receptor poly-agonists: a new era in obesity pharmacotherapy.

Achieving successful long-term weight loss with lifestyle modification in people with obesity is difficult and underscores the need for effective pharmacotherapy. Since 1947, a total of 18 medications have been approved by the US Food and Drug Administration for treating obesity; however, only 5 remain available for long-term use in the US. Semaglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist approved in 2021, demonstrated much greater weight loss than previous medications, which stimulated the development of poly-agonists that combine GLP-1 receptor agonism with glucose-dependent insulinotropic polypeptide (GIP) and glucagon receptor agonism. The potential of this approach was recently demonstrated by the extraordinary weight loss achieved by tirzepatide, a GLP-1/GIP receptor dual agonist. The therapeutic efficacy of poly-agonists is likely to change the treatment paradigm for obesity. However, the use of medications for obesity, as for other chronic diseases, will likely require lifelong treatment, which makes it important to analyze the long-term efficacy, safety, and economic implications of chronic pharmacotherapy.

Insulin Receptor Autoantibody-mediated Hypoglycemia in a Woman With Mixed Connective Tissue Disease.

Autoantibodies to the insulin receptor are rare and typically cause severe insulin resistance and hyperglycemia, a condition termed type B insulin resistance. Uncommonly, antibodies to the insulin receptor can cause hypoglycemia. We present the case of a woman who developed recurrent severe hypoglycemia and myopathy, was found to have insulin receptor autoantibodies and mixed connective tissue disease, and had resolution of hypoglycemia with immunosuppression. A 55-year-old woman with a history of obesity, hypertension, and prior hemorrhagic stroke presented with recurrent severe hypoglycemia. A diagnostic fast resulted in hypoinsulinemic hypoketotic hypoglycemia. Adrenal function was intact. Progressive myopathy had developed simultaneously with her hypoglycemia, and rheumatologic evaluation revealed mixed connective tissue disease. The plasma acylcarnitine profile was normal, extensive oncologic evaluation including insulin-like growth factor 2 measurement was unrevealing, and anti-insulin antibody testing was negative. Ultimately, anti-insulin receptor antibodies were found to be present. The patient was treated with glucocorticoids and rituximab. Eight weeks after initiation of immunosuppression, the insulin receptor antibody titer had decreased and hypoglycemia had resolved. Eight months after diagnosis, the patient remained free of severe hypoglycemia despite tapering of glucocorticoids to a near-physiologic dose. Though antibodies to the insulin receptor typically cause severe insulin resistance, this patient had no evidence of insulin resistance and instead presented with recurrent severe hypoglycemia, which responded to glucocorticoids and rituximab. The diagnosis of insulin receptor antibody-mediated hypoglycemia is rare but should be considered in patients with systemic autoimmune disease, including mixed connective tissue disease, in the appropriate clinical context.

Effect of elexacaftor-tezacaftor-ivacaftor on body weight and metabolic parameters in adults with cystic fibrosis.

BACKGROUND: Though weight gain has been reported in some clinical trials of CFTR modulators, the effect of elexacaftor-tezacaftor-ivacaftor on body weight, body mass index (BMI), blood pressure, lipids and glycemic control in the real-world setting remains incompletely described. METHODS: We performed a single-center, retrospective, observational analysis of the effect of elexacaftor-tezacaftor-ivacaftor on body weight and cardiometabolic parameters in 134 adult CF patients of the Washington University Adult Cystic Fibrosis Center. Body weight, BMI, and blood pressure were extracted from outpatient clinic visits for the year preceding and the period following the initiation of elexacaftor-tezacaftor-ivacaftor. Other metabolic parameters were extracted at baseline and at latest available follow-up. RESULTS: A mean of 12.2 months of follow-up data was available for analysis. The mean rate of change in BMI was 1.47 kg/m2/yr (95% CI, 1.08 to 1.87) greater after initiation of elexacaftor-tezacaftor-ivacaftor. Significant increases in blood pressure were observed. In those without CFRD, random blood glucose and hemoglobin A1c were decreased after elexacaftor-tezacaftor-ivacaftor initiation. In those with CFRD, elexacaftor-tezacaftor-ivacaftor increased serum total cholesterol, HDL-cholesterol, and LDL-cholesterol. CONCLUSIONS: In this single-center, retrospective, observational study of 134 adults with CF, initiation of elexacaftor-tezacaftor-ivacaftor was associated with increases in BMI at a mean follow up of 12.2 months. Changes in other cardiometabolic risk factors were also observed. Widespread use of elexacaftor-tezacaftor-ivacaftor may be expected to increase the incidence of overnutrition in the CF population.

Distinct Hepatic PKA and CDK Signaling Pathways Control Activity-Independent Pyruvate Kinase Phosphorylation and Hepatic Glucose Production.

Pyruvate kinase is an important enzyme in glycolysis and a key metabolic control point. We recently observed a pyruvate kinase liver isoform (PKL) phosphorylation site at S113 that correlates with insulin resistance in rats on a 3 day high-fat diet (HFD) and suggests additional control points for PKL activity. However, in contrast to the classical model of PKL regulation, neither authentically phosphorylated PKL at S12 nor S113 alone is sufficient to alter enzyme kinetics or structure. Instead, we show that cyclin-dependent kinases (CDKs) are activated by the HFD and responsible for PKL phosphorylation at position S113 in addition to other targets. These CDKs control PKL nuclear retention, alter cytosolic PKL activity, and ultimately influence glucose production. These results change our view of PKL regulation and highlight a previously unrecognized pathway of hepatic CDK activity and metabolic control points that may be important in insulin resistance and type 2 diabetes.

PKCε contributes to lipid-induced insulin resistance through cross talk with p70S6K and through previously unknown regulators of insulin signaling.

Insulin resistance drives the development of type 2 diabetes (T2D). In liver, diacylglycerol (DAG) is a key mediator of lipid-induced insulin resistance. DAG activates protein kinase C ε (PKCε), which phosphorylates and inhibits the insulin receptor. In rats, a 3-day high-fat diet produces hepatic insulin resistance through this mechanism, and knockdown of hepatic PKCε protects against high-fat diet-induced hepatic insulin resistance. Here, we employed a systems-level approach to uncover additional signaling pathways involved in high-fat diet-induced hepatic insulin resistance. We used quantitative phosphoproteomics to map global in vivo changes in hepatic protein phosphorylation in chow-fed, high-fat-fed, and high-fat-fed with PKCε knockdown rats to distinguish the impact of lipid- and PKCε-induced protein phosphorylation. This was followed by a functional siRNA-based screen to determine which dynamically regulated phosphoproteins may be involved in canonical insulin signaling. Direct PKCε substrates were identified by motif analysis of phosphoproteomics data and validated using a large-scale in vitro kinase assay. These substrates included the p70S6K substrates RPS6 and IRS1, which suggested cross talk between PKCε and p70S6K in high-fat diet-induced hepatic insulin resistance. These results identify an expanded set of proteins through which PKCε may drive high-fat diet-induced hepatic insulin resistance that may direct new therapeutic approaches for T2D.

MARCH1 regulates insulin sensitivity by controlling cell surface insulin receptor levels.

Insulin resistance is a key driver of type 2 diabetes (T2D) and is characterized by defective insulin receptor (INSR) signalling. Although surface INSR downregulation is a well-established contributor to insulin resistance, the underlying molecular mechanisms remain obscure. Here we show that the E3 ubiquitin ligase MARCH1 impairs cellular insulin action by degrading cell surface INSR. Using a large-scale RNA interference screen, we identify MARCH1 as a negative regulator of INSR signalling. March1 loss-of-function enhances, and March1 overexpression impairs, hepatic insulin sensitivity in mice. MARCH1 ubiquitinates INSR to decrease cell surface INSR levels, but unlike other INSR ubiquitin ligases, MARCH1 acts in the basal state rather than after insulin stimulation. Thus, MARCH1 may help set the basal gain of insulin signalling. MARCH1 expression is increased in white adipose tissue of obese humans, suggesting that MARCH1 contributes to the pathophysiology of T2D and could be a new therapeutic target.

ApoA5 knockdown improves whole-body insulin sensitivity in high-fat-fed mice by reducing ectopic lipid content.

ApoA5 has a critical role in the regulation of plasma TG concentrations. In order to determine whether ApoA5 also impacts ectopic lipid deposition in liver and skeletal muscle, as well as tissue insulin sensitivity, we treated mice with an antisense oligonucleotide (ASO) to decrease hepatic expression of ApoA5. ASO treatment reduced ApoA5 protein expression in liver by 60-70%. ApoA5 ASO-treated mice displayed approximately 3-fold higher plasma TG concentrations, which were associated with decreased plasma TG clearance. Furthermore, ApoA5 ASO-treated mice fed a high-fat diet (HFD) exhibited reduced liver and skeletal muscle TG uptake and reduced liver and muscle TG and diacylglycerol (DAG) content. HFD-fed ApoA5 ASO-treated mice were protected from HFD-induced insulin resistance, as assessed by hyperinsulinemic-euglycemic clamps. This protection could be attributed to increases in both hepatic and peripheral insulin responsiveness associated with decreased DAG activation of protein kinase C (PKC)-ε and PKCθ in liver and muscle, respectively, and increased insulin-stimulated AKT2 pho-sphory-lation in these tissues. In summary, these studies demonstrate a novel role for ApoA5 as a modulator of susceptibility to diet-induced liver and muscle insulin resistance through regulation of ectopic lipid accumulation in liver and skeletal muscle.