Insulin action in the human brain modulates whole-body metabolism by increasing peripheral insulin sensitivity and suppressing endogenous glucose production. In brain insulin resistance, this modulatory function of the brain is impaired. Experimental evidence from rodents and first observations in humans suggest major differences in brain insulin action between women and men. We therefore investigated effects of brain insulin delivery on peripheral metabolism in the follicular and luteal phase of the menstrual cycle. Eleven natural cycling women (age: 19-29 years, BMI: 17.8 - 23.8 kg/m²) underwent four hyperinsulinemic-euglycemic clamps. On two days during both the follicular and the luteal cycle phase, participants received intranasal insulin spray and placebo 90 min after initiation of the 210 min clamp in randomized, blinded order. Insulin spillover into the blood was mimicked by an appropriate iv insulin bolus on placebo days. The phase of the menstrual cycle interacted with the type of spray on the subsequent change of glucose infusion rates (GIR) (p=0.01). During the follicular phase, more glucose had to be infused after insulin delivery to the brain as nasal spray compared to placebo administration (p<0.0001; β=0.40±0.06). This difference remained significant after adjustment for plasma glucose and insulin concentrations (p<0.0001). During the luteal phase, GIR were only transiently higher after nasal insulin (p=0.005; β=0.16±0.06), but this depended on the circulating glucose and insulin levels as the difference was no longer present after respective adjustments (p=0.1). In the follicular phase of the menstrual cycle, insulin delivery to the brain improves peripheral insulin sensitivity in lean women, comparable to what has previously been described in lean men. However, this response was not detected in the luteal phase, suggesting brain insulin resistance. Brain insulin resistance could therefore contribute to the long known peripheral insulin resistance in the luteal phase of the menstrual cycle. Disclosure C.F.C. Benkendorff: None. J. Hummel: None. A. Vosseler: None. S. Kullmann: None. L. Fritsche: None. A.L. Birkenfeld: None. H. Preissl: None. H. Haering: None. A. Fritsche: None. A. Peter: None. R. Wagner: Advisory Panel; Self; Novo Nordisk A/S. Speaker’s Bureau; Self; Novo Nordisk A/S. Other Relationship; Self; Eli Lilly and Company. M. Heni: Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Sanofi. Speaker’s Bureau; Self; Novo Nordisk A/S. Funding German Federal Ministry of Education and Research (01GI0925)

Insulin action in the human brain reduces food intake, improves whole-body insulin sensitivity, and modulates adiposity. In most cases of obesity and diabetes, the brain becomes insulin resistant with impaired brain-derived modulation of peripheral metabolism. As treatment with the SGLT2-inhibitor empagliflozin not only improves glucose metabolism but also reduces body weight and cardiovascular risk, we hypothesized that improved brain insulin sensitivity could be involved. Methods: In this double blind study, 40 participants with prediabetes (according to ADA’s OGTT criteria) were 1:1 randomized to receive 25 mg empagliflozin qd or placebo (mean ± SD: age: 60 ± 9 years; BMI: 31.5 ± 3.8 kg/m²). Before and after 8 weeks of treatment, brain insulin sensitivity was assessed by functional MRI combined with the intranasal administration of insulin to the brain. Results: In healthy persons, intranasal insulin administration significantly decreases cerebral blood flow in the hypothalamus. In the current study, volunteers with prediabetes were unresponsive to this, as insulin could not induce hypothalamic inhibition prior treatment. We identified a significant interaction between treatment and the hypothalamic response to insulin (p<0.05, corrected for multiple comparisons). Post-hoc analyses showed that only participants on empagliflozin showed a significant insulin-induced decrease in hypothalamic blood flow after treatment. The group receiving placebo showed no such improvement. Conclusion: Our current results corroborate insulin resistance of the human hypothalamus in humans with prediabetes. Treatment with empagliflozin for 8 weeks was able to restore hypothalamic insulin sensitivity; a favorable response that could contribute to the positive effects of SGLT2 inhibitors. These findings reveal that brain insulin resistance is treatable by pharmacological interventions with potential benefits for cognition, adiposity, and whole-body metabolism. Disclosure M. Heni: Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Sanofi. Speaker’s Bureau; Self; Novo Nordisk A/S. S. Kullmann: None. R. Wagner: Advisory Panel; Self; Novo Nordisk A/S. Speaker’s Bureau; Self; Novo Nordisk A/S. Other Relationship; Self; Eli Lilly and Company. J. Hummel: None. C. Dannecker: None. A. Vosseler: None. L. Fritsche: None. K. Kantartzis: None. J. Machann: None. H. Haering: None. A. Fritsche: None. H. Preissl: None. Funding Boehringer Ingelheim

Background and Aims: Postprandial thermogenesis is thought to be important for the control of metabolism. This process could be reflected by minute changes in body temperature after glucose load. In this study, we measured body temperature before and its change during a glucose challenge and investigated the relationships with anthropometric and glycemic traits. Methods: We prospectively studied 383 volunteers (251 females, 132 males) with a mean age of 46.6 (SD ± 16) years and a BMI of 27.9 kg/m2 (SD ± 5.9). All participants underwent a 75 g oral glucose tolerance test (OGTT) and repeated bilateral measurements of intra-auricular temperature at time points 0, 30 and 120 minutes during the OGTT using a tympanic thermometer (Covidien Genius 2). Results: Baseline temperature was 0.17°C lower in males compared to females (p = 0.001) and inversely associated with age (p < 0.0001). During the OGTT, there was a significant increase in body temperature (0.18 ± 0.34°C). This response was present in females and males. BMI was negatively associated with the increase of temperature during the OGTT (p = 0.0147). Participants with higher BMI displayed higher fasting temperatures, but less increase of temperature during the OGTT. Body temperature was not associated with glycemia, insulin sensitivity or insulin secretion, neither in females nor males. Conclusions: There is a robust increase in body temperature during a glucose load that can be captured by intra-auricular temperature measurements. We did not detect any associations of the body temperature with glucose metabolism, arguing against a major contribution of the variability of body temperature in the pathogenesis of diabetes. However, the rise in temperature in response to oral glucose is reduced in obesity and might therefore be involved in body weight regulation. Disclosure A. Vosseler: None. L. Fritsche: None. J. Hummel: None. C. Dannecker: None. N. Stefan: None. A.L. Birkenfeld: None. H. Haering: None. A. Fritsche: None. R. Wagner: Advisory Panel; Self; Novo Nordisk A/S. Speaker’s Bureau; Self; Novo Nordisk A/S. Other Relationship; Self; Eli Lilly and Company. M. Heni: Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Sanofi. Speaker’s Bureau; Self; Novo Nordisk A/S. Funding German Federal Ministry of Education and Research (01GI0925)

Background: Pancreatic fat (PF) related beta-cell failure might play a role in the pathophysiology of type 2 diabetes (T2D). We hypothesized that the effect of PF on beta-cell function can be modeled as a gene x environment interaction. To this end, we investigated the association of PF with insulin secretion in subjects with different genetic predisposition for T2D. Methods: A genome-wide polygenic risk score (gwPRS) was computed combining summary statistics from a genome-wide association study with ∼900.000 participants and 480.000 genetic variants in our cohort. The interaction of MRI-measured PF with gwPRS was investigated in 376 nondiabetic participants. Results: PF interacted with gwPRS on insulin secretion after adjustment for confounders (p=0.001). In participants with low gwPRS, PF associated positively with insulin secretion. In participants with high gwPRS, there was a negative association with insulin secretion. Discussion: PF is a pathophysiologic factor potentially contributing to both primary insulin hypersecretion and impairment of insulin secretion, dependent on genetic predisposition. Disclosure B. Jaghutriz: None. M. Heni: Research Support; Self; Boehringer Ingelheim International GmbH, Sanofi. Speaker's Bureau; Self; Lilly Diabetes, Merck Sharp & Dohme Corp., Sanofi. J. Machann: None. F. Schick: None. S. Ullrich: Advisory Panel; Spouse/Partner; AstraZeneca, Boehringer Ingelheim International GmbH, Lilly Diabetes, Merck Sharp & Dohme Corp., Mylan, Novo Nordisk A/S. Consultant; Self; Boehringer Ingelheim Pharmaceuticals, Inc. H. Haering: None. A. Fritsche: None. R. Wagner: Other Relationship; Self; Lilly Diabetes, Novo Nordisk A/S. Funding German Federal Ministry of Education and Research

Insulin and dopamine signaling in the human brain are known modulators of whole-body glucose metabolism. Brain insulin resistance contributes to impaired postprandial glycemia and could predispose to type 2 diabetes. Experimental evidence suggests a crucial interaction between insulin and dopamine with dopaminergic dysfunction in brain insulin resistance. We now investigated the presence of such an interaction in the human brain. In 10 healthy young men (age 27±3 years, BMI 23.6±2.3 kg/m², HOMA-IR 1.8±1.1), we performed combined PET/MRI measurements using dynamic [11C]-Raclopride in combination with the intranasal application of 160 U insulin and placebo on two separate days in randomized, blinded order. Dopamine receptor binding potential as a measure of dopaminergic tone was estimated in regions of interests (ROI). Intranasal insulin delivery to the human brain increased dopamine receptor binding potential in the bilateral ventral and dorsal striatum, a major dopaminergic brain region (pFWE<0.001 cluster level). This response tended to be stronger in participants with higher BMI but was not statistically associated with HbA1c, fasting glucose, or HOMA-IR. Hence, insulin delivery to the human brain influences dopaminergic tone in the striatum. As earlier studies found insulin sensitivity of this region to be involved in the postprandial modulation of whole-body insulin sensitivity, the detected mechanism might be involved in the regulation of postprandial glycaemia. Alterations in this mechanism could therefore predispose to type 2 diabetes, a hypothesis that must be tested in further studies. Disclosure S. Kullmann: None. D. Blum: None. B. Jaghutriz: None. B. Bender: None. H. Haering: None. C. la Fougère: None. H. Preissl: None. A. Fritsche: None. M. Reimold: None. M. Heni: Research Support; Self; Boehringer Ingelheim International GmbH, Sanofi. Speaker's Bureau; Self; Lilly Diabetes, Merck Sharp & Dohme Corp., Sanofi. Funding German Federal Ministry of Education and Research

The link between type 2 diabetes and cognitive dysfunction appears to start in the prediabetic state. Although cross sectional studies have linked insulin resistance to impaired cognition, this mechanism has not yet been sufficiently studied longitudinally without confounding by overt diabetes (and its treatment). We investigated participants of the ‘Tübinger Evaluation of Risk Factors for Early Detection of Neurodegeneration’ (TREND) study longitudinally. Subjects underwent a comprehensive neurocognitive assessment battery at baseline and every 2 years afterwards (median follow-up 4.0 q1-3: 2.2-4.3 y). Subjects with an HbA1c of 5.6-6.5% without known diabetes were metabolically investigated by a five-point 75g oral glucose tolerance test (OGTT) with assessment of insulin sensitivity and insulin secretion (N=175). Subjects with newly diagnosed diabetes or with depression (BDI >20) were excluded (N=15). Data were analyzed by mixed models using sex, age and glycemic trait as fixed effects. Subject and time between measurements were used as random effects. Insulin sensitivity was negatively associated with the CERAD sum score (Consortium to Establish a Registry for Alzheimer's Disease) in a time-dependent manner (p=0.0057). This result is mainly driven by a worse performance in the memory domain due to declining insulin sensitivity (p=0.029). These interactions remained significant after adjusting for glycemia (p<0.04). No interactions between time and insulin sensitivity for executive, visuospatial or language domains were found. There was no association with insulin secretion. In summary, insulin resistance predicts cognitive decline, specifically memory impairment in prediabetic persons. Therefore, insulin resistance rather than sole elevation of blood glucose predispose neuro-cognitive impairment. Diabetes treatments that improve insulin sensitivity might therefore have the potential to postpone/prevent cognitive decline in diabetes. Disclosure C. Willmann: None. K. Brockmann: None. R. Wagner: Other Relationship; Self; Lilly Diabetes, Novo Nordisk A/S. S. Kullmann: None. H. Preissl: None. W. Maetzler: None. T. Gasser: Research Support; Self; National Institute on Aging. Other Relationship; Self; AbbVie Inc. G.W. Eschweiler: None. F.G. Metzger: None. A.J. Fallhgatter: None. H. Haering: None. A. Fritsche: None. M. Heni: Research Support; Self; Boehringer Ingelheim International GmbH, Sanofi. Speaker's Bureau; Self; Lilly Diabetes, Merck Sharp & Dohme Corp., Sanofi.

Mitochondria are dynamic organelles with diverse functions in tissues such as liver and skeletal muscle. To unravel the mitochondrial contribution to tissue-specific physiology, we performed a systematic comparison of the mitochondrial proteome and lipidome of mice and assessed the consequences hereof for respiration. Liver and skeletal muscle mitochondrial protein composition was studied by data-independent ultra-high-performance (UHP)LC-MS/MS-proteomics, and lipid profiles were compared by UHPLC-MS/MS lipidomics. Mitochondrial function was investigated by high-resolution respirometry in samples from mice and humans. Enzymes of pyruvate oxidation as well as several subunits of complex I, III, and ATP synthase were more abundant in muscle mitochondria. Muscle mitochondria were enriched in cardiolipins associated with higher oxidative phosphorylation capacity and flexibility, in particular CL(18:2)4 and 22:6-containing cardiolipins. In contrast, protein equipment of liver mitochondria indicated a shuttling of complex I substrates toward gluconeogenesis and ketogenesis and a higher preference for electron transfer via the flavoprotein quinone oxidoreductase pathway. Concordantly, muscle and liver mitochondria showed distinct respiratory substrate preferences. Muscle respired significantly more on the complex I substrates pyruvate and glutamate, whereas in liver maximal respiration was supported by complex II substrate succinate. This was a consistent finding in mouse liver and skeletal muscle mitochondria and human samples. Muscle mitochondria are tailored to produce ATP with a high capacity for complex I-linked substrates. Liver mitochondria are more connected to biosynthetic pathways, preferring fatty acids and succinate for oxidation. The physiologic diversity of mitochondria may help to understand tissue-specific disease pathologies and to develop therapies targeting mitochondrial function.