Plasma Semicarbazide-sensitive Amine Oxidase is Moderately Decreased by Pronounced Exogenous Hyperinsulinemia but is Not Associated with Insulin Sensitivity and Body Fat

Objective: Semicarbazide-sensitive amine oxidase (SSAO) is widely expressed in adipose tissue, where it may contribute to stimulation of glucose transport via GLUT4 recruitment. We tested the relationships of soluble SSAO, as reflected by its plasma activity, with insulin sensitivity and indices of body fat, and determined whether insulin is involved in regulating plasma SSAO activity.

Material And Methods: In 24 non-diabetic subjects, the relationships of plasma SSAO activity with insulin sensitivity (M-value and free fatty acid (FFA) suppression during a 3-h hyperinsulinemic (8.3 microU kg-1 s-1), euglycemic clamp), body mass index (BMI 25.5 +/- 3.1 kg m-2), waist-hip ratio and fat mass were assessed. In 16 subjects, the effect of insulin infusion, administered at a rate of 8.3 microU kg-1 s-1 during 3 h, followed by 3-h insulin infusion at a high rate of 41.7 microU kg-1 s-1 on plasma SSAO activity was determined. In the other 8 subjects, the response of plasma SSAO activity to 24-h insulin infused at 8.3 microU kg-1 s-1 was assessed.

Results: There were no relationships (all p > 0.10) of plasma SSAO activity (215 +/- 60 mU L-1) with the M-value or with any indices of body fat and FFA before and after insulin suppression. Plasma SSAO activity changed by -7.2 (95% CI, -14.5 to +0.2)% after 3 h (NS) and decreased by 10.1 (95% CI, 19.2 to 1)% after 6 h of insulin infusion (p < 0.05). Plasma SSAO activity did not significantly change after 8 h (change 0.4 (95% CI, -15.3 to +16.2)%, NS) and after 24 h (change -8.8 (95% CI, -27.4 to +9.7)%, NS) of insulin infusion.

Conclusions: It is unlikely that circulating SSAO is a clinically important marker of insulin sensitivity on glucose and fatty acid metabolism. The reduction in plasma SSAO activity in response to pronounced hyperinsulinemia suggests that insulin is involved in the regulation of the soluble form of this enzyme.