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

Desaturase 9 (Delta 9), 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 Delta 9, particularly whether Delta 9 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) Delta 9 has independent associations with adiposity, insulin resistance level, and fasting plasma polyunsaturated fatty acids (PUFAs); (b) Delta 9 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 Delta 9 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, Delta 9-16 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 Delta 9-18 (surrogate of Delta 9 as calculated by plasma ratio C18:1 n-9/C18:0). After adjustment for dietary SFAs, waist, and HOMA-IR, Delta 9-16 and Delta 9-18 were still positive predictors of triglyceride (both P < .001) and apolipoprotein B (Delta 9-18, P < .001; Delta 9-16, 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 Delta 9 with adiposity and plasma lipid profile in these apparently healthy female adolescents support the concept derived from rodent models that Delta 9 activity is independently reflective of higher body mass index and higher circulatory triglyceride levels.