Spermidine is a natural polyamine which was shown to prolong lifespan of organisms and to improve cardiac and cognitive function. Spermidine was also reported to reduce inflammation and modulate T-cells. Autophagy is one of the mechanisms that spermidine exerts its effect. Autophagy is vital for β-cell homeostasis and autophagy deficiency was reported to lead to exacerbated diabetes in mice. The effect of spermidine in type 1 diabetes pathogenesis remains to be elucidated. Therefore, we examined the effect of spermidine treatment in non-obese diabetic (NOD) mice, a mouse model for type 1 diabetes. NOD mice were given untreated or spermidine-treated water ad libitum from 4 weeks of age until diabetes onset or 35 weeks of age. We found that treatment with 10 mM spermidine led to higher diabetes incidence in NOD mice despite unchanged pancreatic insulitis. Spermidine modulated tissue polyamine levels and elevated signs of autophagy in pancreas. Spermidine led to increased proportion of pro-inflammatory T-cells in pancreatic lymph nodes (pLN) in diabetic mice. Spermidine elevated the proportion of regulatory T-cells in early onset mice, whereas it reduced the proportion of regulatory T-cells in late onset mice. In summary spermidine treatment led to higher diabetes incidence and elevated proportion of T-cells in pLN.

Beta-cell apoptosis is a hallmark of type 1 diabetes (T1D) and type 2 diabetes (T2D). In T2D loss of autophagy has been associated to increased apoptosis and diminished beta-cell mass. In autoimmunity, dysfunctional autophagy alters negative selection of T cells in thymus driving autoreactive immune cells into periphery. Autophagy contributes to presentation of antigens in antigen presenting cells shaping the repertoire of peptides presented to T cells. The aim of this project is to investigate the role of autophagy in the etiology of T1D. To investigate the effect of spermidine (SPD, a known inducer of autophagy) in vivo, non-obese diabetic (NOD) mice received spermidine (10 mM; n=30) or pure drinking water (n=28) from the age of 4 weeks until the age of 35 weeks or diabetes onset. Mice were analyzed for diabetes rate, autophagy markers (LC3-II to LC3-I ratio and p62) and immune cell phenotype in spleen and blood. Spermidine led to a higher diabetes rate in SPD group (80 %) compared to control group (60,7 %) with p-value of 0,026 (log-rank test). Autophagy was induced by diabetes (plasma glucose > 200 mg/dL) and by age. Autophagy levels were higher at 21-35 weeks in old diabetic animals compared to nondiabetic animals at 35 weeks and compared to young diabetic animals at 14-20 weeks (p< 0,0001, and p< 0,0001, respectively). Spermidine treatment increased autophagy levels in pancreas, but diabetic mice at 21-35 weeks still had higher autophagy levels compared to nondiabetic animals at week 35. (LC3-II/LC3-I: p < 0,05; p62: p < 0,05). Spermidine elevated the frequency of natural killer cells in spleen (p < 0,01) and blood (p < 0,01), natural killer T cells (p < 0,01), naïve CD4+ T cells (p < 0,01), naïve CD8+ T cells (p < 0,01) and central memory CD4+ T cells (p < 0,01) in blood. Our experiments indicate that autophagy is induced upon T1D and spermidine-induced autophagy might increase diabetes incidence. Immune cell phenotyping revealed that spermidine promotes immune cells potentially provoking inflammation. Disclosure C. Karacay: None. P. Kotzbeck: None. B. Prietl: None. C. Harer: None. T. Pieber: Advisory Panel; Self; ADOCIA, Arecor, AstraZeneca, Eli Lilly and Company, Novo Nordisk A/S, Sanofi. Research Support; Self; AstraZeneca, Novo Nordisk A/S. Speaker’s Bureau; Self; Novo Nordisk A/S, Roche Diagnostics K.K.

Intermittent caloric restriction has the potential for improving metabolic and cardiovascular markers in rodents and humans, as well as longevity (in rodents). Furthermore, an intermittent caloric restriction regime that mimics prolonged fasting (fasting mimicking diet, FMD) has been linked to proliferation of β-cells in diabetic mice. Aim of the study was to assess the effect of FMD in female C57BL/6J mice on glucose tolerance, body and organ weight, measured at the end of the fasting and at the end of the refeeding period. We administered three weekly cycles of FMD (1st day 50%-, 2nd-3rd day 10% of daily calorie intake) followed by 4 days of refeeding ad libitum after every cycle to 20 mice at 12 weeks of age. In the second FMD cycle an intraperitoneal glucose tolerance test (IGTT) was performed either after fasting or after the 3rd refeeding day. Control animals (n=10) were fed a standard chow ad libitum. Animals were sacrificed and tissues collected after the 3rd FMD cycle, precisely 7 days after the IGTT. Compared to controls, FMD animals weighed less after the 1st, 2nd and 3rd cycle (mean differences ±SE (%): 18.9±1.8, 17.2±1.8, 15.1±1.8; p<0.001). After refeeding, bodyweight returned to levels of age matched control animals. IGTT revealed impaired glucose tolerance after fasting compared to refeeding (mean difference ±SE (mg/dL): min30: 76.4±21.8, min60: 68.7±14.3; p<0.05). Liver weight was reduced by 21.6±4.1% (p<0.001) after fasting and increased by 9.7±2.5% (p<0.001) after refeeding compared to age matched controls. Our study reveals impaired glucose tolerance at the end of the fasting period compared to the end of the refeeding period in healthy mice exposed to three cycles of FMD. Our data support previous findings that prolonged fasting rather reduces insulin secretory capacity of the ß-cell than changing insulin sensitivity, indicating to a fast adaptive cellular mechanism in ß-cells during prolonged fasting. Disclosure C. Harer: None. J. Krstic: None. P. Kotzbeck: None. C. Karacay: None. A. Prokesch: None. T. Pieber: Advisory Panel; Self; ADOCIA, Arecor, AstraZeneca, Eli Lilly and Company, Novo Nordisk A/S, Sanofi. Research Support; Self; AstraZeneca, Novo Nordisk A/S. Speaker’s Bureau; Self; Novo Nordisk A/S, Roche Diagnostics K.K.