Oral Supplementation with the Polyamine Spermidine Affects Hepatic but Not Pulmonary Lipid Metabolism in Lean but Not Obese Mice

Abstract

The polyamine spermidine is discussed as a caloric restriction mimetic and therapeutic option for obesity and related comorbidities. This study tested oral spermidine supplementation with regard to the systemic, hepatic and pulmonary lipid metabolism under different diet conditions. Male C57BL/6 mice were fed a purified control (CD), high sucrose (HSD) or high fat (HFD) diet with (-S) or without spermidine for 30 weeks. In CD-fed mice, spermidine decreased body and adipose tissue weights and reduced hepatic lipid content. The HSD induced hepatic lipid synthesis and accumulation and hypercholesterolemia. This was not affected by spermidine supplementation, but body weight and blood glucose were lower in HSD-S compared to HSD. HFD-fed mice showed higher body and fat depot weights, prediabetes, hypercholesterolemia and severe liver steatosis, which were not altered by spermidine. Within the liver, spermidine diminished hepatic expression of lipogenic transcription factors SREBF1 and 2 under HSD and HFD and affected the expression of other lipid-related enzymes. In contrast, diet and spermidine exerted only minor effects on pulmonary parameters. Thus, oral spermidine supplementation affects lipid metabolism in a diet-dependent manner, with significant reductions in body fat and weight under physiological nutrition and positive effects on weight and blood glucose under high sucrose intake, but no impact on dietary fat-related parameters.

Keywords: caloric restriction mimetic; diet-induced obesity; high fat diet; high sucrose diet; liver lipid metabolism; lung lipid metabolism; spermidine.

Figure 1

Experimental design. OGTT, oral glucose tolerance test; CD, control diet; HSD, high sucrose diet; HFD, high fat diet.

Figure 2

Effects of diets and spermidine on body weight, calorie intake and fat depots. (A) Diet-related effects on body weight gain. (B–D) Spermidine-related effects on body weight gain in respective diet groups. (E) Final body weights after 30 weeks. (F) Diet-related effects on calorie intake per week. (G–I) Spermidine-related effects on calorie intake per week in respective diet groups. (J) Mean calorie intake per week over 30 weeks. (K–M) Fat depot weights. (A–D,F–I) Values are group means ± SD; CD n = 10, CD-S n = 10, HSD n = 10, HSD-S n = 9, HFD n = 8, HFD-S n = 9; data were compared separately for diet and spermidine effects by 2W-RM-ANOVA followed by Tukey test; p-values < 0.05 are indicated by * for dietary effect or # for spermidine effect. (E,J–L) Data shown as values of individual mice, group means are indicated by horizontal lines; data were compared by 2W-ANOVA followed by Tukey test; * p < 0.05, ** p < 0.01, *** p < 0.001. CD, control diet; HSD, high sucrose diet; HFD, high fat diet; -S, spermidine.

Figure 3

Effects of diets and spermidine on glucose homeostasis. (A) Diet-related effects on glucose tolerance. (B–D) Spermidine-related effects on glucose tolerance in respective diet groups. (E) Area under the curve (AUC) values for glucose tolerance curves. (F) Fasting plasma glucose concentrations. (G) Fasting plasma insulin concentrations. (H) HOMA insulin resistance related to body weight. (I) Insulin sensitivity measured by 1/insulin related to body weight. (A–D) Values are group means ± SD; CD n = 10, CD-S n = 10, HSD n = 10, HSD-S n = 9, HFD n = 8, HFD-S n = 9; data were compared separately for diet and spermidine effects by 2W-RM-ANOVA followed by Tukey test; p-values < 0.05 are indicated by * for dietary effect or # for spermidine effect. (E–I) Data shown as values of individual mice, group means are indicated by horizontal lines; data were compared by 2W-ANOVA followed by Tukey test; * p < 0.05, ** p < 0.01, *** p < 0.001. CD, control diet; HSD, high sucrose diet; HFD, high fat diet; -S, spermidine.

Figure 4

Effects of diets and spermidine on circulating lipids and enzymes. (A–D) Fasting plasma total cholesterol concentrations. (E–H) Fasting plasma HDL cholesterol concentrations. (I–L) Fasting plasma LDL cholesterol concentrations. (M–P) Fasting plasma triglyceride concentrations. (Q–T) Fasting plasma alanine transaminase concentrations. (U–X) Fasting plasma aspartate transaminase concentrations. Values are group means ± SD; CD n = 10, CD-S n = 10, HSD n = 10, HSD-S n = 9, HFD n = 8, HFD-S n = 9. Data were compared separately for diet and spermidine effects by 2W-RM-ANOVA followed by Tukey test; p-values < 0.05 are indicated by * for dietary effect or # for spermidine effect. CD, control diet; HSD, high sucrose diet; HFD, high fat diet; -S, spermidine.

Figure 5

Effects of diets and spermidine on hepatic and pulmonary expression profiles of lipid metabolism-related proteins. (A,B) Sterol regulatory element binding transcription factors 1 and 2; peroxisome proliferator-activated receptor α. (C,D) ATP citrate lyase; acetyl-CoA carboxylase α; fatty acid synthase. (E,G) Glycerol-3-phosphate acyltransferase. (F,H) Adipose triglyceride lipase. (I,J) Carnitine palmitoyltransferase 1α; mitochondrial trifunctional protein, subunits α and β. Shown are fold expression values given as group means ± SD; n = 5 for every group. Data were compared by 2W-ANOVA followed by Tukey test; p-values < 0.05 are indicated by * for significant difference compared to CD (dietary effect) or # for significant difference compared to respective non-supplemented diet group (spermidine effect). CD, control diet; HSD, high sucrose diet; HFD, high fat diet; -S, spermidine.

Figure 6

Effects of diets and spermidine on hepatic and pulmonary lipid accumulation. (A) Liver weight. (B) Percentage of area occupied by lipid droplets in the liver. (C) Representative light microscopy images of toluidine blue stained liver sections, scale bar = 50 µm. (D) Lung volume. (E) Percentage of area occupied by lipid droplets in alveolar septa. (F) Representative electron microscopy images of the pulmonary septal region, scale bar = 1 µm. (A,B,D,E) Data shown as values of individual mice, group means are indicated by horizontal lines; data were compared by 2W-ANOVA followed by Tukey test; * p < 0.05, ** p < 0.01, *** p < 0.001. CD, control diet; HSD, high sucrose diet; HFD, high fat diet; -S, spermidine; *, LD; HC, hepatocyte; IF, interstitial fibroblast; AT1, epithelial type 1 cell; EC, endothelial cell.