Endocrinol Metab.  2023 Oct;38(5):557-567. 10.3803/EnM.2023.1672.

Protective Effects of Melatonin in High-Fat Diet-Induced Hepatic Steatosis via Decreased Intestinal Lipid Absorption and Hepatic Cholesterol Synthesis

• Ku H
• Kim Y
• Kim AL
• Lee G
• Choi Y
• Kim B

• KMID: 2546986
• DOI: http://doi.org/10.3803/EnM.2023.1672

Abstract

Background
The preventative effect of melatonin on the development of obesity and the progression of fatty liver under a high-fat diet (HFD) has been well elucidated through previous studies. We investigated the mechanism behind this effect regarding cholesterol biosynthesis and regulation of cholesterol levels.
Methods
Mice were divided into three groups: normal chow diet (NCD); HFD; and HFD and melatonin administration group (HFD+M). We assessed the serum lipid profile, mRNA expression levels of proteins involved in cholesterol synthesis and reabsorption in the liver and nutrient transporters in the intestines, and cytokine levels. Additionally, an in vitro experiment using HepG2 cells was performed.
Results
Expression of hepatic sterol regulatory element-binding protein 2 (SREBP-2), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), and low-density lipoprotein receptor (LDLR) demonstrated that melatonin administration significantly reduces hepatic cholesterol synthesis in mice fed an HFD. Expression of intestinal sodium-glucose transporter 1 (SGLT1), glucose transporter 2 (GLUT2), GLUT5, and Niemann-pick C1-like 1 (NPC1L1) demonstrated that melatonin administration significantly reduces intestinal carbohydrate and lipid absorption in mice fed an HFD. There were no differences in local and circulatory inflammatory cytokine levels among the NCD, HFD, and HFD+M group. HepG2 cells stimulated with palmitate showed reduced levels of SREBP, LDLR, and HMGCR indicating these results are due to the direct mechanistic effect of melatonin on hepatocytes.
Conclusion
Collectively, these data indicate the mechanism behind the protective effects of melatonin from weight gain and liver steatosis under HFD is through a reduction in intestinal caloric absorption and hepatic cholesterol synthesis highlighting its potential in the treatment of obesity and fatty liver disease.

Keyword

Melatonin; Fatty liver; Obesity; NPC1L1 protein

Figure

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  Fig. 1. Melatonin protects against high-fat diet (HFD)-induced obesity and fat deposit in the liver. (A) body weight changes through 17 weeks, (B) gross findings of visceral fat accumulation, (C) comparison of liver weights among groups, (D) histological lipid accumulation of liver with H&E (×100) and Oil red O (×200) staining at 17 weeks. HFD+M, high-fat diet with melatonin. aP<0.05 as compared to the control; bP=0.14 as compared to the HFD.

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  Fig. 2. Melatonin decreased high-fat diet (HFD)-induced low-density lipoprotein cholesterol elevation. Serum lipid profile at 6 weeks (A) total cholesterol, (B) triglyceride, (C) apolipoprotein A1 (ApoA1) lipoprotein, (D) apolipoprotein B (ApoB) lipoprotein. HFD+M, high-fat diet with melatonin. aP<0.05.

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  Fig. 3. Melatonin protect excess calories absorption via suppression of carbohydrate and lipid transporters’ expression in the intestine (A) sodium-glucose transporter 1 (SGLT1) which is brush border transporter of carbohydrate, (B) glucose transporter 5 (GLUT5) which is brush border transporter of carbohydrate (C) glucose transporter 2 (GLUT2) which is basolateral membrane transporter of carbohydrate, (D) Niemann-pick C1-like 1 (NPC1L1) which is intestinal and hepatic transporter of cholesterol. HFD, high-fat diet; HFD+M, high-fat diet with melatonin. aP<0.05.

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  Fig. 4. mRNA expression levels of genes involved in cholesterol metabolism in the liver. (A) sterol regulatory element-binding protein 2 (SREBP-2), (B) 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase (C) low-density lipoprotein receptor (LDLR). HFD, high-fat diet; HFD+M, high-fat diet with melatonin. aP<0.05.

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  Fig. 5. No differences among groups in circulatory and local inflammatory cytokines. (A) Serum interleukin 10 (IL-10), (B) serum tumor necrosis factor α (TNF-α), (C) serum IL-6, (D) liver IL-10, (E) liver TNF-α, and (F) liver IL-6. HFD, high-fat diet; HFD+M, high-fat diet with melatonin. aP<0.05.

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  Fig. 6. Melatonin directly inhibits palmitate-induced cholesterol synthesis in hepatocyte. (A) Hepatocytes were stimulated with palmitate for 6 hours in the absence or presence of melatonin. Levels of sterol regulatory element-binding protein (SREBP), low-density lipoprotein receptor (LDLR), 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) were analyzed by reverse transcriptase-polymerase chain reaction. (B) Levels of LDLR, HMGCoA were analyzed by Western blot. β-Actin were used as internal loading controls. (C) Immunofluorescent images were obtained with palmitate, melatonin, and both and were compared to the control (×800). FITC, fluorescein. aP<0.01.

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