Objective: Increased interleukin-6 plasma levels have been reported in metabolic syndrome (MS); nevertheless, it is unclear whether interleukin-6 activity is exerted through direct signalling only or also through the "trans-signalling". This issue is important to clarify since signalling and "trans-signalling" affect different tissues. We investigated the relationship between MS and the interleukin-6 system in an older population.
Methods: Data from 997 older community dwelling individuals (age ≥ 65 years; females: 56.2%) enrolled the InChianti study were analysed. Interleukin-6, soluble interleukin-6 receptor (sIL-6r), and soluble glycoprotein 130 (sgp130) were measured on plasma by ELISA. MS was defined by the NCEP ATP III criteria; 309 individuals (31%) resulted affected by MS.
Results: Subjects with MS had higher interleukin-6 and sgp130 levels compared to controls; a trend toward higher levels of sIL-6R was also observed. The risk of having MS was increased in individuals with high sIL-6r or/and sgp130 levels, independent of age, gender, and interleukin-6 levels. Elevated sgp130 levels were associated with higher plasma glucose, HOMA, triglycerides, and with diabetes both in subjects with and without MS. Although the risk of high sgp130 levels was generally associated with MS (O.R.: 1.77, 95%C.I.: 1.39-2.25), this excess of risk was not present in MS phenotypes excluding the criteria "elevated glucose" or "elevated triglycerides". Furthermore, the association between sgp130 and MS disappeared after adjustment for HOMA.
Conclusions: We found that older individuals with MS have increased sgp130 plasma levels compared with controls; nevertheless, our data suggest that this association might be mediated by insulin resistance.
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