The following is a summary of “GIP Affects Hepatic Fat and Brown Adipose Tissue Thermogenesis but Not White Adipose Tissue Transcriptome in Type 1 Diabetes,” published in the December 2022 issue of Endocrinology & Metabolism by Heimbürger, et al.
It had been suggested that insulin-independent effects on lipid and bone metabolism can be achieved via glucose-dependent insulinotropic polypeptide (GIP). For a study, researchers sought to analyze how a 6-day subcutaneous GIP infusion affected the circulating lipids, white adipose tissue (WAT) and brown adipose tissue (BAT), the amount of fat in the liver, inflammatory markers, respiratory exchange ratio (RER), and bone homeostasis in type 1 diabetic patients.
Twenty type 1 diabetic males had a 6-day continuous subcutaneous infusion of GIP (6 pmol/kg/min) and placebo (saline) in a randomized, placebo-controlled, double-blind, crossover research with a 7-day washout interval in between.
Participants (26±8 years [mean±SD]; BMI 23.8±1.8 kg/m2; glycated hemoglobin A1c 51±10 mmol/mol [6.8±3.1%]) had temporarily higher circulating levels of nonesterified fatty acids (NEFA) during GIP infusion than during placebo (P = 0.0005), decreased RER (P = 0.009), an indication of higher fatty acid β-oxidation, and lower levels of the bone resorption marker C-terminal telopeptide (P = 0.000072) compared with placebo. Hepatic fat content rose by 12.6% (P = 0.007) after 6 days of GIP infusion, while supraclavicular skin temperature, a proxy for BAT activity, rose by 0.29 °C (P <0.000001) after the same period of time. In addition to the proteome, circulating lipid species, indicators of inflammation, and bone homeostasis, the WAT transcriptome profile was unaltered.
Men with type 1 diabetes who received subcutaneous GIP infusions for six days saw momentary decreases in bone resorption and increases in NEFA and β-oxidation. Further, without changing WAT transcriptomics, the circulating proteome, lipids, or inflammatory markers, hepatic fat content and supraclavicular skin temperature rose.