The objective of this study was to evaluate the efficacy of
melatonin to affect mild
inflammation in the
metabolic syndrome (MS) induced by a high-fat diet in rats. Adult Wistar male rats were divided into four groups (n = 16/group): (i) control diet (3% fat); (ii) high-fat (35%) diet; (iii) high-fat diet +
melatonin; and (iv)
melatonin. Rats had free access to high-fat or control chow and one of the following drinking solutions for 10 wk: (a) tap water; (b) 25 μg/mL of
melatonin. Plasma
interleukin (IL)-1β,
IL-4,
IL-6,
IL-10,
tumor necrosis factor (TNF)-α,
interferon (IFN)-γ, and
C-reactive protein (CRP) were measured at two time intervals, that is, the middle of daylight period and the middle of the scotophase. In addition, a number of somatic and metabolic components employed clinically to monitor the MS were measured.
Melatonin decreased the augmented circulating levels of IL-1β,
IL-6, TNF-α, IFN-γ, and CRP seen in obese rats and restored the depressed levels of
IL-4 and
IL-10. Rats fed with the high-fat diet showed significantly higher
body weights and augmented systolic blood pressure from the third and fourth week onwards, respectively,
melatonin effectively preventing these changes. In high-fat-fed rats, circulating
low-density lipoprotein-cholesterol, total
cholesterol, and
triglyceride concentration augmented significantly,
melatonin being effective to counteract these changes.
Melatonin-treated rats showed a decreased
insulin resistance, the highest values of plasma
high-density lipoprotein-cholesterol, and the lowest values of plasma
uric acid. The results indicate that
melatonin is able to normalize the altered biochemical pro-inflammatory profile seen in rats fed with a high-fat diet.