The association of desaturase 9 and plasma fatty acid composition with insulin resistance–associated factors in female adolescents

Abstract

Desaturase 9 (Δ9), which converts saturated fatty acids (SFAs) into monounsaturated fatty acids, is an important component in leptin-mediated energy homeostasis in rodent models. Few human studies, however, have been performed regarding the clinical relevance of Δ9, particularly whether Δ9 is involved in the relationship between blood fatty acid profiles and insulin resistance–associated factors. The aim of the present study was to examine fatty acid data from 178 apparently healthy female adolescents and determine whether (a) Δ9 has independent associations with adiposity, insulin resistance level, and fasting plasma polyunsaturated fatty acids (PUFAs); (b) Δ9 is a predictor of fasting blood lipid profile; and (c) the associations between fasting plasma fatty acid component and insulin resistance level are independent of abdominal obesity level. Desaturase 9-16 (surrogate of Δ9 as calculated by plasma ratio C16:1 n-7/C16:0) correlated with waist girth (r = .160, P < .05), homeostasis model assessment of insulin resistance (HOMA-IR) (r = .201, P < .01), plasma PUFAs (eg, C20:4 n-6 [r = −.269, P < .001], C22:6 n-3 [r = −.274, P < .001]). After adjustment for dietary SFAs, Δ9-16 had stronger correlation with waist (r = .227, P < .01) and significant correlation with PUFAs, whereas it had a nonsignificant correlation with HOMA-IR. The same pattern was observed with Δ9-18 (surrogate of Δ9 as calculated by plasma ratio C18:1 n-9/C18:0). After adjustment for dietary SFAs, waist, and HOMA-IR, Δ9-16 and Δ9-18 were still positive predictors of triglyceride (both P < .001) and apolipoprotein B (Δ9-18, P < .001; Δ9-16, P = .052). After adjustment for waist, HOMA-IR only remained a positive determinant of medium-chain SFAs (C14:0, P < .001; C16:0, P < .05); but it emerged to be inversely related to C20:4 n-6 (P < 0.1). The positive and independent associations of medium-chain SFAs with insulin resistance level suggest their vital roles in diabetes pathogenesis, whereas certain PUFAs such as C20:4 n-6 appear to be protective. The observed associations of Δ9 with adiposity and plasma lipid profile in these apparently healthy female adolescents support the concept derived from rodent models that Δ9 activity is independently reflective of higher body mass index and higher circulatory triglyceride levels.