Moderate doses of conjugated linoleic acid reduce fat gain, maintain insulin sensitivity without impairing inflammatory adipose tissue status in mice fed a high-fat diet

Abstract

Background: The enrichment of diet with nutrients with potential benefits on body composition is a strategy to combat obesity. Conjugated linoleic acid (CLA) due its beneficial effects on body composition and inflammatory processes becomes an interesting candidate, since the promotion and impairment of obesity is closely linked to a low-grade inflammation state of adipose tissue. Previously we reported the favourable effects of moderate doses of CLA mixture on body composition and inflammatory status of adipose tissue in mice fed a standard-fat diet. In the present study we assessed the potential beneficial effects of CLA mixture (cis-9, trans-11 and trans-10, cis-12, 50:50) in mice fed a high-fat diet.

Methods: Two doses were assayed: 0.15 g (CLA1) and 0.5 g CLA/kg body weight (CLA2) for the first 30 days of the study and then animals received a double amount for another 35 days.

Results: The lowest dose (CLA1) had minor effects on body composition, plasma parameters and gene expression. However, a clear reduction in fat accumulation was achieved by CLA2, accompanied by a reduction in leptin, adiponectin and non-esterified fatty acids (NEFA) plasma concentrations. Insulin sensitivity was maintained despite a slight increase in fasting glucose and insulin plasma concentrations. The study of gene expression both in adipocytes and in the stromal vascular fraction (SVF) suggested that CLA may reduce either the infiltration of macrophages in adipose tissue or the induction of expression of pro-inflammatory cytokines.

Conclusion: In conclusion, the use of moderate doses of an equimolar mix of the two main CLA isomers reduces body fat content, improves plasma lipid profile, maintains insulin sensitivity (despite a moderate degree of hyperinsulinaemia) without the promotion of inflammatory markers in adipose tissue of mice fed a high-fat diet.

Figure 1

Effects of CLA on body weight gain in mice. Mice received a daily dose of CLA equivalent to 3 mg CLA/animal in CLA1 group and 10 mg/animal in CLA2 group for the first 30 d and 6 mg CLA/animal in CLA1 group and 20 mg/animal in CLA2 group for the last 35 d of treatment. Data are means ± SEM of 8 mice. Repeated-measures analysis of variance of body weight gain associated with CLA treatment was significant with respect to the control (P < 0.05). No differences between doses were found. x2dose: indicates the point from which the double dose was given.

Figure 2

Contribution of mature adipocytes isolated from epididymal fat depot to the expression of target mRNA in CLA treated mice. Epididymal adipose tissue was digested by collagenase and then separated into mature adipocytes and stromal vascular fraction. Expression levels of target genes of each fraction were measured by real time PCR and normalized by the internal housekeeping gene 18S rRNA. Expression data in adipocytes, derived from equal amount of RNA (Table 4), were referred to the total RNA content in the adipocyte fraction. Data, means ± SEM of 7-8 mice, are represented as fold induction over control group. Mean values with unlike letters are significantly different (P < 0.01); ANOVA followed by LSD test.

Figure 3

Contribution of SVF cells isolated from epididymal fat depot to the expression of target mRNA in CLA mice. Epididymal adipose tissue was digested by collagenase and then separated into mature adipocytes and stromal vascular fraction. Expression levels of target genes of each fraction were measured by real time PCR and normalized by the internal housekeeping gene 18S rRNA. Expression data in the stromal vascular fraction (SVF), derived from equal amount of RNA (Table 4) were referred to the total RNA content in SVF. Data, means ± SEM of 6-8 mice, are represented as fold induction over control group. Mean values with unlike letters are significantly different (P < 0.01); ANOVA followed by LSD test.