D-limonene (LIM) is a common monoterpene compound, principally found in citrus essential oils. This study investigated the anti-obesity effect of LIM on the 5′-adenosine monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway in 3T3-L1 adipocytes and high-calorie diet-induced obese rats and confirmed the optimally effective dose of LIM. The 3T3-L1 adipocytes were treated with 0.05–0.4 mg/mL LIM for 10 days and oil red O and triglyceride (TG) content were used to determine the levels of lipid accumulation. The results showed that more than 0.05 mg/mL LIM inhibited lipid accumulation by reducing oil red O in 3T3-L1 adipocytes. Masses of 0.2 and 0.4 mg/mL LIM also decreased the TG contents in 3T3-L1 adipocytes. On the other hand, Wistar rats were given high-calorie diets, combined with LLIM (154 mg/kg) and HLIM (1000 mg/kg) treatments, for 16 weeks. The result shows that LLIM and HLIM decreased body weight, total fat tissue weight, and serum low-density lipoprotein-cholesterol (LDLc) levels. HLIM reduced serum TG and increased serum lipase and high-density lipoprotein-cholesterol (HDLc) levels. Moreover, the anti-obesity metabolic pathway showed that LIM (>0.05 mg/mL) in 3T3-L1 adipocytes and LIM (>154 mg/kg) in high-calorie diet-induced obese rats could activate the AMPK signaling pathway. The activated AMPK regulated the mRNA expression related to adipogenesis (PPARγ, C/EBPα, FABP4), lipogenesis (SREBP-1c, ACC, FAS), and lipolysis (ATGL, HSL) to inhibit obesity. This finding demonstrates that LIM has anti-obesity properties. Namely, it is seen that LIM acts by regulating the AMPK signaling pathway in 3T3-L1 adipocytes and high-calorie diet-induced obese rats. In terms of dose–response, LIM (154 mg/kg) would be an optimal effective dose for anti-obesity induced by a high-calorie diet.

Lemon (Citrus limon) has antioxidant, immunoregulatory, and blood lipid-lowering properties. This study aimed to determine the effect of the lemon fermented product (LFP) which is lemon fermented with Lactobacillus OPC1 to prevent obesity. The inhibition of lipid accumulation in 3T3-L1 adipocytes is examined using a Wistar rat model fed a high-fat diet to verify the anti-obesity efficacy and mechanism of LFP. Here, it was observed that LFP reduced cell proliferation and inhibited the lipid accumulation (8.3%) of 3T3-L1 adipocytes. Additionally, LFP reduced body weight (9.7%) and fat tissue weight (25.7%) of rats; reduced serum TG (17.0%), FFA (17.9%), glucose (29.3%) and ketone body (6.8%); and increased serum HDL-C (17.6%) and lipase activity (17.8%). LFP regulated the mRNA expression of genes related to lipid metabolism (PPARγ, C/EBPα, SREBP-1c, HSL, ATGL, FAS, and AMPK). Therefore, LFP reduces body weight and lipid accumulation by regulating the mRNA expression of genes related to lipid metabolism. Overall, our results implicate LFP as a potential dietary supplement for the prevention of obesity.

Nostoc commune is an edible terrestrial blue-green alga. It has shown many beneficial effects on human health. This study aimed to investigate the phytochemical assay of N. commune ethanol extract (NEE) and its anti-obesity effects. The effect of a high-calorie diet on lipid accumulation in 3T3-L1 preadipocytes is investigated, and a Wistar rat model is used to demonstrate the anti-obesity effect of NEE and its mechanism. The results showed that the NEE has phytochemical compounds, such as total polyphenol, total flavonoids, and total terpenoids. NEE was also shown to suppress cell proliferation and lipid accumulation (26.9%) in 3T3-L1 preadipocytes. Furthermore, NEE reduced the body weight (13.5%), fat tissue weight (13.3%), and the serum FFA (19.4%), TG (14.2%), TC (11.8%), and LDL-C (16.4%) of rats. In histopathology, NEE was shown to diminish the size of adipocytes and hepatic lipid droplets. The NEE downregulated the mRNA expression of adipogenesis (PPAR-γ, SREBP-1c) and lipid lysis-related genes (ATGL, HSL) in epididymal adipose tissue. The NEE also upregulated the mRNA expression of β-oxidation related genes (AMPK, CPT-1, PPAR-α) in the liver. Overall, this study suggests NEE has the potential to be developed as a functional food for anti-obesity.