Fen Zhuge

Astaxanthin prevents and reverses diet-induced insulin resistance and steatohepatitis in mice: A comparison with vitamin E.

Hepatic insulin resistance and nonalcoholic steatohepatitis (NASH) could be caused by excessive hepatic lipid accumulation and peroxidation. Vitamin E has become a standard treatment for NASH. However, astaxanthin, an antioxidant carotenoid, inhibits lipid peroxidation more potently than vitamin E. Here, we compared the effects of astaxanthin and vitamin E in NASH. We first demonstrated that astaxanthin ameliorated hepatic steatosis in both genetically (ob/ob) and high-fat-diet-induced obese mice. In a lipotoxic model of NASH: mice fed a high-cholesterol and high-fat diet, astaxanthin alleviated excessive hepatic lipid accumulation and peroxidation, increased the proportion of M1-type macrophages/Kupffer cells, and activated stellate cells to improve hepatic inflammation and fibrosis. Moreover, astaxanthin caused an M2-dominant shift in macrophages/Kupffer cells and a subsequent reduction in CD4+ and CD8+ T cell recruitment in the liver, which contributed to improved insulin resistance and hepatic inflammation. Importantly, astaxanthin reversed insulin resistance, as well as hepatic inflammation and fibrosis, in pre-existing NASH. Overall, astaxanthin was more effective at both preventing and treating NASH compared with vitamin E in mice. Furthermore, astaxanthin improved hepatic steatosis and tended to ameliorate the progression of NASH in biopsy-proven human subjects. These results suggest that astaxanthin might be a novel and promising treatment for NASH.

DPP-4 inhibition by linagliptin attenuates obesity-related inflammation and insulin resistance by regulating M1/M2 macrophage polarization

Dipeptidyl peptidase 4 (DPP-4) cleaves a large number of chemokine and peptide hormones involved in the regulation of the immune system. Additionally, DPP-4 may also be involved in macrophage-mediated inflammation and insulin resistance. Thus, the current study investigated the effect of linagliptin, an inhibitor of DPP-4, on macrophage migration and polarization in white adipose tissue (WAT) and liver of high-fat diet–induced obese (DIO) mice. DPP-4+ macrophages in lean and obese mice were quantified by fluorescence-activated cell sorting (FACS) analysis. DPP-4 was predominantly expressed in F4/80+ macrophages in crown-like structures compared with adipocytes in WAT of DIO mice. FACS analysis also revealed that, compared with chow-fed mice, DIO mice exhibited a significant increase in DPP-4+ expression in cells within adipose tissue macrophages (ATMs), particularly M1 ATMs. Linagliptin showed a greater DPP-4 inhibition and antioxidative capacity than sitagliptin and reduced M1-polarized macrophage migration while inducing an M2-dominant shift of macrophages within WAT and liver, thereby attenuating obesity-induced inflammation and insulin resistance. Loss of macrophage inflammatory protein-1α, a chemokine and DPP-4 substrate, in DIO mice abrogated M2 macrophage-polarizing and insulin-sensitizing effects of linagliptin. Therefore, the inhibition of DPP-4 by linagliptin reduced obesity-related insulin resistance and inflammation by regulating M1/M2 macrophage status.

Differential Roles of Breakfast and Supper in Rats of a Daily Three-Meal Schedule Upon Circadian Regulation and Physiology

The timing of meals has been suggested to play an important role in circadian regulation and metabolic health. Three meals a day is a well-established human feeding habit, which in todays lifestyle may or may not be followed. The aim of this study was to test whether the absence of breakfast or supper significantly affects the circadian system and physiological function. The authors developed a rat model for their daily three meals study, whereby animals were divided into three groups (three meals, TM; no first meal, NF; no last meal, NL) all fed with the same amount of food every day. Rats in the NF group displayed significantly decreased levels of plasma triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and glucose in the activity phase, accompanied by delayed circadian phases of hepatic peripheral clock and downstream metabolic genes. Rats in the NL group showed lower concentration of plasma TC, HDL-C, and glucose in the rest phase, plus reduced adipose tissue accumulation and body weight gain. Real-time polymerase chain reaction (PCR) analysis indicated an attenuated rhythm in the food-entraining pathway, including down-regulated expression of the clock genes Per2, Bmal1, and Rev-erbα, which may further contribute to the delayed and decreased expression of FAS in lipogenesis in this group. Our findings are consistent with the conclusion that the daily first meal determines the circadian phasing of peripheral clocks, such as in the liver, whereas the daily last meal tightly couples to lipid metabolism and adipose tissue accumulation, which suggests differential physiological effects and function of the respective meal timings. (Author correspondence: azwfu2003@yahoo.com.cn)

Novel Action of Carotenoids on Non-Alcoholic Fatty Liver Disease: Macrophage Polarization and Liver Homeostasis

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease. It is characterized by a wide spectrum of hepatic changes, which may progress to non-alcoholic steatohepatitis (NASH) and cirrhosis. NAFLD is considered a hepatic manifestation of metabolic syndrome; however, mechanisms underlying the onset and progression of NAFLD are still unclear. Resident and recruited macrophages are key players in the homeostatic function of the liver and in the progression of NAFLD to NASH. Progress has been made in understanding the molecular mechanisms underlying the polarized activation of macrophages. New NAFLD therapies will likely involve modification of macrophage polarization by restraining M1 activation or driving M2 activation. Carotenoids are potent antioxidants and anti-inflammatory micronutrients that have been used to prevent and treat NAFLD. In addition to their antioxidative action, carotenoids can regulate macrophage polarization and thereby halt the progression of NASH. In this review, we summarize the molecular mechanisms of macrophage polarization and the function of liver macrophages/Kupffer cells in NAFLD. From our review, we propose that dietary carotenoids, such as β-cryptoxanthin and astaxanthin, be used to prevent or treat NAFLD through the regulation of macrophage polarization and liver homeostasis.

SGLT2 Inhibition by Empagliflozin Promotes Fat Utilization and Browning and Attenuates Inflammation and Insulin Resistance by Polarizing M2 Macrophages in Diet-induced Obese Mice

Sodium-glucose cotransporter (SGLT) 2 inhibitors increase urinary glucose excretion (UGE), leading to blood glucose reductions and weight loss. However, the impacts of SGLT2 inhibition on energy homeostasis and obesity-induced insulin resistance are less well known. Here, we show that empagliflozin, a SGLT2 inhibitor, enhanced energy expenditure and attenuated inflammation and insulin resistance in high-fat-diet-induced obese (DIO) mice. C57BL/6J mice were pair-fed a high-fat diet (HFD) or a HFD with empagliflozin for 16 weeks. Empagliflozin administration increased UGE in the DIO mice, whereas it suppressed HFD-induced weight gain, insulin resistance, and hepatic steatosis. Moreover, empagliflozin shifted energy metabolism towards fat utilization, elevated AMP-activated protein kinase and acetyl-CoA carbolxylase phosphorylation in skeletal muscle, and increased hepatic and plasma fibroblast growth factor 21 levels. Importantly, empagliflozin increased energy expenditure, heat production, and the expression of uncoupling protein 1 in brown fat and in inguinal and epididymal white adipose tissue (WAT). Furthermore, empagliflozin reduced M1-polarized macrophage accumulation while inducing the anti-inflammatory M2 phenotype of macrophages within WAT and liver, lowering plasma TNFα levels and attenuating obesity-related chronic inflammation. Thus, empagliflozin suppressed weight gain by enhancing fat utilization and browning and attenuated obesity-induced inflammation and insulin resistance by polarizing M2 macrophages in WAT and liver.

Glucoraphanin Ameliorates Obesity and Insulin Resistance Through Adipose Tissue Browning and Reduction of Metabolic Endotoxemia in Mice

Low-grade sustained inflammation links obesity to insulin resistance and nonalcoholic fatty liver disease (NAFLD). However, therapeutic approaches to improve systemic energy balance and chronic inflammation in obesity are limited. Pharmacological activation of nuclear factor (erythroid-derived 2)–like 2 (Nrf2) alleviates obesity and insulin resistance in mice; however, Nrf2 inducers are not clinically available owing to safety concerns. Thus, we examined whether dietary glucoraphanin, a stable precursor of the Nrf2 inducer sulforaphane, ameliorates systemic energy balance, chronic inflammation, insulin resistance, and NAFLD in high-fat diet (HFD)–fed mice. Glucoraphanin supplementation attenuated weight gain, decreased hepatic steatosis, and improved glucose tolerance and insulin sensitivity in HFD-fed wild-type mice but not in HFD-fed Nrf2 knockout mice. Compared with vehicle-treated controls, glucoraphanin-treated HFD-fed mice had lower plasma lipopolysaccharide levels and decreased relative abundance of the gram-negative bacteria family Desulfovibrionaceae in their gut microbiomes. In HFD-fed mice, glucoraphanin increased energy expenditure and the protein expression of uncoupling protein 1 (Ucp1) in inguinal and epididymal adipose depots. Additionally, in this group, glucoraphanin attenuated hepatic lipogenic gene expression, lipid peroxidation, classically activated M1-like macrophage accumulation, and inflammatory signaling pathways. By promoting fat browning, limiting metabolic endotoxemia-related chronic inflammation, and modulating redox stress, glucoraphanin may mitigate obesity, insulin resistance, and NAFLD.

Enhanced effect of daytime restricted feeding on the circadian rhythm of streptozotocin-induced type 2 diabetic rats

There is increasing awareness of the link between impaired circadian clocks and multiple metabolic diseases. However, the impairment of the circadian clock by type 2 diabetes has not been fully elucidated. To understand whether and how the function of circadian clock is impaired under the diabetic condition, we examined not only the expression of circadian genes in the heart and pineal gland but also the behavioral rhythm of type 2 diabetic and control rats in both the nighttime restricted feeding (NRF) and daytime restricted feeding (DRF) conditions. In the NRF condition, the circadian expression of clock genes in the heart and pineal gland was conserved in the diabetic rats, being similar to that in the control rats. DRF shifted the circadian phases of peripheral clock genes more efficiently in the diabetic rats than those in the control rats. Moreover, the activity rhythm of rats in the diabetic group was completely shifted from the dark phase to the light phase after 5 days of DRF treatment, whereas the activity rhythm of rats in the control group was still under the control of the suprachiasmatic nucleus (SCN) after the same DRF treatment. Furthermore, the serum glucose rhythm of type 2 diabetic rats was also shifted and controlled by the external feeding schedule, ignoring the SCN rhythm. Therefore, DRF shows stronger effect on the reentrainment of circadian rhythm in the type 2 diabetic rats, suggesting that the circadian system in diabetes is unstable and more easily shifted by feeding stimuli.

Significant dissociation of expression patterns of the basic helix-loop-helix transcription factors Dec1 and Dec2 in rat kidney.

SUMMARY Dec1 and Dec2 are regulators of the mammalian molecular clock that show robust circadian rhythms in the suprachiasmatic nucleus and various peripheral tissues. Although the expression of Dec1 and Dec2 is altered by multiple stimuli in different organs, their transcriptional regulatory mechanisms have not been fully elucidated for the kidney. In the present study, we describe for the first time significant dissociation of expression patterns with arrhythmic expression of Dec1 and rhythmic expression of Dec2 in rat kidney under a normal light–dark (LD) cycle. Daytime restricted feeding (RF) significantly altered the expression patterns of these two clock genes, and even induced circadian expression of Dec1 with an amplitude of 2.2 on day 3 and 4.2 on day 7. However, when a reversed feeding schedule was coupled with a reversed LD cycle, the expression of Dec1 but not Dec2 reverted to being arrhythmic. Moreover, exogenous injection of the glucocorticoid analogue dexamethasone (Dex) at certain times of the day resulted in rhythmic expression of Dec1, which was similar to that seen following RF for 7 days. In contrast, endogenous disruption of glucocorticoids by adrenalectomy abolished RF-induced rhythmic expression of Dec1 in the kidney. These observations suggest the existence of a glucocorticoid gating mechanism in the circadian expression of Dec1 in rat kidney.

A porcine placental extract prevents steatohepatitis by suppressing activation of macrophages and stellate cells in mice

Nonalcoholic fatty liver disease (NAFLD) is caused by ectopic fat accumulation in the liver. NAFLD is associated with hepatic inflammation and oxidative stress, resulting in nonalcoholic steatohepatitis (NASH) with advanced fibrosis. Placental extracts have been used to treat various chronic diseases due to their antioxidative effect. However, the effects of the extracts on the development of NASH have yet to be elucidated. Here, we demonstrated that supplementation with an oral porcine placental extract (PPE) attenuated lipid accumulation and peroxidation, insulin resistance, inflammatory and stress signaling, and fibrogenesis in the liver of NASH model mice fed a high-cholesterol and high-fat diet. The PPE reduced the number of M1-like liver macrophages, but increased the number of anti-inflammatory M2-like macrophages, resulting in a predominance of M2 over M1 macrophage populations in the liver of NASH mice. Accordingly, the PPE suppressed lipopolysaccharide-induced M1 polarization in isolated murine peritoneal macrophages, whereas it facilitated interleukin 4-induced M2 polarization. Furthermore, the PPE reduced the hepatic stellate cell (HSC) activation associated with the attenuated transforming growth factor-β/Smad3 signaling, both in the liver of NASH mice and in RI-T cells, a HSC line. The PPE may be a potential approach to prevent NASH by limiting lipid peroxidation, promoting M2 macrophage polarization, and attenuating HSC activation.