Samantha Adamson DiGruccio

Aims: Use of sodium‐glucose cotransporter 2 inhibitors (SGLT2i) in patients with type 1 diabetes (T1D) is limited by increased risk of ketoacidosis. We aimed to determine metabolic pathways affected by SGLT2i treatment in adults with T1D during ketosis induced by insulin withdrawal. Materials and Methods: Plasma metabolomic and lipidomic analysis by ultra‐high‐performance liquid chromatography/mass spectrometry was performed at baseline and after supervised insulin withdrawal in 17 adults with T1D treated with usual care (UC) and (DP) dapagliflozin (10 mg daily for 14 days). Results: Plasma glucose levels were lower, and ketone levels were higher after insulin withdrawal in DP compared to UC. Pathway analysis of differentially altered metabolites revealed that DP altered amino acids and TCA cycle metabolites during ketosis. DP treatment increased citrate and aconitate at baseline, with a trend towards increased branched chain ketoacids and acylcarnitines. Citrate, aconitate, α‐ketoglutarate and malate were increased during insulin withdrawal after UC whereas insulin withdrawal after DP resulted in unchanged α‐ketoglutarate and malate and significantly decreased fumarate and succinate. Acetylcarnitine was significantly higher during insulin withdrawal after DP compared to UC. DP effected subtle changes in amino acids and amino acid derivatives. Symmetric dimethylarginine and pseudouridine were significantly elevated at baseline and after insulin withdrawal after DP. Lipidomics revealed increased very long TG species in DP and differences in phospholipids, particularly phosphatidylcholine. Conclusion: In adults with T1D, dapagliflozin alters TCA cycle metabolites, amino acid metabolites and certain lipids during insulin withdrawal. Future work will validate findings and further investigate the metabolic basis of SGLT2i‐mediated ketoacidosis risk.

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are mainstay therapies for diabetes and obesity, acting in part by enhancing glucose-dependent insulin secretion. While the primary cilium is a known signaling compartment for certain G-protein coupled receptors (GPCRs), its role in the β-cell response to incretins remains undefined. Here, we show that primary cilia are essential for GLP-1R signaling. Loss of β-cell cilia in mouse and human islets severely impaired GLP-1-potentiated insulin secretion, an effect preceded by blunted whole-cell cAMP and Ca²⁺ responses. Immunofluorescence and immunogold scanning electron microscopy revealed endogenous GLP-1R localized to the primary cilium. Critically, disrupting ciliary GPCR trafficking via Tulp3 knockdown – while preserving cilia structure – recapitulated the signaling and secretory deficits, demonstrating a specific requirement for the ciliary receptor pool. These findings establish the primary cilium as a non-redundant signaling compartment for GLP-1R and uncover a new layer of subcellular organization in incretin action in β cells.

Background: Breath acetone (BrACE) is an end product of ketone metabolism that is measurable by noninvasive breath ketone analyzers. We assessed the correlation between capillary blood β-hydroxybutyrate (BOHB) and BrACE in people with type 1 diabetes during 14 days of outpatient care with and without dapagliflozin treatment and during supervised insulin withdrawal studies with and without dapagliflozin. Methods: In this randomized crossover study, participants completed two 14-day outpatient periods with or without dapagliflozin 10 mg daily. Each 14-day unsupervised outpatient period was followed by a 1-day supervised insulin withdrawal study. Paired BOHB and BrACE measurements were obtained 3 times daily during outpatient periods, then hourly during supervised insulin withdrawal. The correlation between BrACE and BOHB was assessed by Spearman’s ρ. Results: Twenty people with type 1 diabetes completed the study. During outpatient periods, BrACE and BOHB were moderately correlated (n = 1425 paired readings; ρ = .41; 95% CI = 0.36 to 0.45; P < .0001). However, BrACE and BOHB were strongly correlated during insulin withdrawal (n = 246 paired values, ρ = .81; 95% CI = 0.77 to 0.85). In ROC analysis, BrACE > 5 ppm demonstrated optimal sensitivity (93%) and specificity (87%) for detecting capillary BOHB ≥ 1.5 mmol/L. No serious adverse events occurred. Conclusions: In adults with type 1 diabetes, measurement of breath acetone provides a noninvasive estimate of blood BOHB concentration. The correlation between BrACE and BOHB was suboptimal during unsupervised outpatient care, but was strong during supervised insulin withdrawal. Trial registration: clinicaltrials.gov (NCT05541484)

Background: Breath acetone (BrACE) is an end product of ketone metabolism that is measurable by noninvasive breath ketone analyzers. We assessed the correlation between capillary blood β-hydroxybutyrate (BOHB) and BrACE in people with type 1 diabetes (T1D) during 14 days of outpatient care with and without dapagliflozin treatment and during supervised insulin withdrawal studies with and without dapagliflozin. Methods: In this randomized crossover study, participants completed 14-day two outpatient periods with or without dapagliflozin 10 mg daily. Each 14-day unsupervised outpatient period was followed by a one-day supervised insulin withdrawal study. Paired BOHB and BrACE measurements were obtained three times daily during outpatient periods, then hourly during supervised insulin withdrawal. The correlation between BrACE and BOHB was assessed by Spearman’s ρ. Results: Twenty people with T1D completed the study. During outpatient periods, BrACE and BOHB were moderately correlated (n=1425 paired readings; ρ = 0.41; 95% CI: 0.36 to 0.45; P < 0.0001). However, BrACE and BOHB were strongly correlated during insulin withdrawal (n=246 paired values, ρ = 0.81; 95% CI: 0.77 to 0.85). In ROC analysis, BrACE > 5 ppm demonstrated optimal sensitivity (93%) and specificity (87%) for detecting capillary BOHB ≥ 1.5 mmol/L. No serious adverse events occurred. Conclusions: In adults with T1D, measurement of breath acetone provides a noninvasive estimate of blood BOHB concentration. The correlation between BrACE and BOHB was suboptimal during unsupervised outpatient care, but was strong during supervised insulin withdrawal. Trial registration: clinicaltrials.gov ( NCT05541484 )

Somatostatin is a paracrine modulator of insulin secretion and beta cell function with pleotropic effects on glucose homeostasis. The mechanism of somatostatin-mediated communication between delta and beta cells is not well-understood, which we address in this study via the ciliary somatostatin receptor 3 (SSTR3). Primary cilia are membrane organelles that act as signaling hubs in islets by virtue of their subcellular location and enrichment in signaling proteins such as G-protein coupled receptors (GPCRs). We show that SSTR3, a ciliary GPCR, mediates somatostatin suppression of insulin secretion in mouse islets. Quantitative analysis of calcium flux using a mouse model of genetically encoded beta cell-specific GCaMP6f calcium reporter shows that somatostatin signaling alters beta cell calcium flux after physiologic glucose stimulation, an effect that depends on endogenous SSTR3 expression and the presence of intact primary cilia on beta cells. Comparative in vitro studies using SSTR isoform antagonists demonstrate a role for SSTR3 in mediating somatostatin regulation of insulin secretion in mouse islets. Our findings support a model in which ciliary SSTR3 mediates a distinct pathway of delta-to-beta cell regulatory crosstalk and may serve as a target for paracrine modulation.