Inhibitors of sodium-dependent glucose-transporter 2 (including dapagliflozin) represent intensively investigated drugs in the field of diabetes. SGLT-2 inhibition limits glucose reabsorption in renal tubular cells, hereby increasing the amount of glucose excreted via urine in the hyperglycemic state. Its mechanisms of action are independent of insulin, the indispensable standard of care in Type 1 Diabetes (T1D). Several international diabetes experts highlighted the need for adjunct therapies in T1D.

Subcutaneous application of insulin is non-physiological. Most significant, subcutaneous insulin substitution does not address the bi-hormonal character of T1D. The loss of pancreatic beta cells and subsequent endogenous insulin production uncouples alpha cell derived glucagon secretion from its paracrine suppressor. Consequently, excess glucagon concentrations occur in the fasting and the postprandial state, which promotes hyperglycemia, requires higher doses of subcutaneous insulin, and promotes glycaemic variability.

Recent studies on SGLT-2 inhibition in T1D showed better glycemic control compared to placebo, whereas a higher risk for the development of diabetic ketoacidosis was observed. Knowledge about the underlying mechanisms is scarce. Studies showed that SGLT-inhibition increased Glucagon-like-peptide 1 (GLP-1) in T1D, an incretin hormone capable of suppressing glucagon. On the other side, total concentrations of ketone bodies were higher following SGLT-2 inhibition, irrespective of ongoing subcutaneous or intravenous insulin substitution. The present study aims to investigate the effect of SGLT-2 inhibitor dapagliflozin on hormonal regulators of glucose homeostasis and ketogenesis in T1D. The primary endpoint is the difference of GLP-1 during oral glucose tolerance test clamps (OGGTc). Secondary endpoints comprise total ketone body concentrations, free fatty acids, glucagon, and somatostatin during OGTTc and hyperinsulinemic, euglycemic clamps (HEC) following dapagliflozin and placebo. The study recruits male and female patients with T1DM in a randomized, open label, cross-over intervention study.

Inclusion Criteria:

• Informed Consent as documented by signature
• Duration of T1DM > 5 years
• Male or female sex
• Body mass index (BMI) between 20 and 29 kg/m2
• Adherence to safe contraception during the study and for 2 weeks after completion of the study protocol. Safe contraception comprises double barrier methods (hormonal contraception [like: oral contraceptive pills or intrauterine contraceptive devices] together with a mechanical barrier [like: condom, diaphragm]).

Exclusion Criteria:

• Contraindications to SGLT-2 inhibitors
• Contraindications to lactose
• Diagnosis of renal and/or hepatic dysfunction
• History of malignancy of any kind
• Intake of drugs influencing glucose homeostasis during the last three months (steroids, metformin, sulfonylureas, thiazolidinedione)
• Known or suspected non-compliance, drug or alcohol abuse.
• Inadequate vein status on both forearms
• Active smoker (defined as ≥1 or more cigarettes or nicotine-containing equivalents per day)
• Known pregnancy, positive plasma beta-HCG test prior to study inclusion or intention to become pregnant during the study period.
• Women who are breast feeding
• Lack of safe contraception
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant

According to Swiss National Fund (SNF) policy on Open Research Data, Data will be uploaded to an open data registry.