Decreased liver peroxisomal β-oxidation accompanied by changes in brain fatty acid composition in aged rats

Spermidine - an old molecule with a new age-defying immune function

Polyamines - putrescine, spermidine, and spermine - are widely distributed aliphatic compounds known to regulate important biological processes in prokaryotic and eukaryotic cells. Therefore, spermidine insufficiency is associated with various physio-pathological processes, such as aging and cancers. Recent advances in immuno-metabolism and immunotherapy shed new light on the role of spermidine in immune cell regulation and anticancer responses. Here, we review novel works demonstrating that spermidine is produced by collective metabolic pathways of gut bacteria, bacteria-host co-metabolism, and by the host cells, including activated immune cells. We highlight the effectiveness of spermidine in enhancing antitumor responses in aged animals otherwise nonresponsive to immune checkpoint therapy and propose that spermidine supplementation could be used to enhance the efficacy of anti-PD-1 treatment.

Lipid and glucose metabolism in senescence

Senescence is an inevitable biological process. Disturbances in glucose and lipid metabolism are essential features of cellular senescence. Given the important roles of these types of metabolism, we review the evidence for how key metabolic enzymes influence senescence and how senescence-related secretory phenotypes, autophagy, apoptosis, insulin signaling pathways, and environmental factors modulate glucose and lipid homeostasis. We also discuss the metabolic alterations in abnormal senescence diseases and anti-cancer therapies that target senescence through metabolic interventions. Our work offers insights for developing pharmacological strategies to combat senescence and cancer.

Advances in Understanding of the Role of Lipid Metabolism in Aging

During aging, body adiposity increases with changes in the metabolism of lipids and their metabolite levels. Considering lipid metabolism, excess adiposity with increased lipotoxicity leads to various age-related diseases, including cardiovascular disease, cancer, arthritis, type 2 diabetes, and Alzheimer's disease. However, the multifaceted nature and complexities of lipid metabolism make it difficult to delineate its exact mechanism and role during aging. With advances in genetic engineering techniques, recent studies have demonstrated that changes in lipid metabolism are associated with aging and age-related diseases. Lipid accumulation and impaired fatty acid utilization in organs are associated with pathophysiological phenotypes of aging. Changes in adipokine levels contribute to aging by modulating changes in systemic metabolism and inflammation. Advances in lipidomic techniques have identified changes in lipid profiles that are associated with aging. Although it remains unclear how lipid metabolism is regulated during aging, or how lipid metabolites impact aging, evidence suggests a dynamic role for lipid metabolism and its metabolites as active participants of signaling pathways and regulators of gene expression. This review describes recent advances in our understanding of lipid metabolism in aging, including established findings and recent approaches.

Radix Polygoni Multiflori and Its Main Component Emodin Attenuate Non-Alcoholic Fatty Liver Disease in Zebrafish by Regulation of AMPK Signaling Pathway

Purpose

Nonalcoholic fatty liver disease (NAFLD) has become a predictor of death in many diseases. This study was carried out to investigate the therapeutic effect of Radix Polygoni Multiflori Preparata (RPMP) and its main component emodin on egg yolk powder-induced NAFLD in zebrafish. Further investigation was performed to explore whether emodin was the main component of RPMP for the treatment of NAFLD as well as the underlying therapeutic mechanism of RPMP and emodin.

Methods

Zebrafish were divided into control group, egg yolk powder group, RPMP group and emodin group. The obesity of zebrafish was evaluated by body weight, body length and BMI. The content of lipid was detected by triglyceride (TG), total cholesterol (TC) reagent kit and the fatty acid was detected by nonesterified free fatty acids (NEFA) reagent kit. HE staining was used to detect the histological structure of liver. Whole-mount Oil red O staining and Frozen oil red O staining were carried out to investigate the lipid accumulation in liver. KEGG and STRING databases were performed to analyze the potential role of AMPK between insulin resistance (IR) and fatty acid oxidation. Western blot and RT-qPCR were carried out for mechanism research.

Results

RPMP and emodin significantly reduced zebrafish weight, body length and BMI. Both RPMP and emodin treatment could reduce the lipid deposition in zebrafish liver. RPMP significantly reduced the content of TG. However, emodin significantly reduced the contents of TG, TC and NEFA in zebrafish with NAFLD. The protein interaction network indicated that AMPK participated in both IR and fatty acid oxidation. Further investigation indicated that RPMP and emodin reduced hepatic lipogenesis via up-regulating the expressions of phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT2), amp-activated protein kinase alpha (AMPKα), proliferator-activated receptor alpha (PPARα), carnitine palmitoyl transferase 1a (CPT-1a) and acyl-coenzyme A oxidase 1 (ACOX1).

Conclusion

These findings suggest that emodin is the main component of RPMP for the treatment of NAFLD, which is closely related to the regulation of AMPK signaling pathway which increases IR and fatty acid oxidation.

Short-Term Activation of Peroxisome Proliferator-Activated Receptors α and γ Induces Tissue-Specific Effects on Lipid Metabolism and Fatty Acid Composition in Male Wistar Rats

Dietary fatty acids (FAs) affect certain metabolic routes, including pathways controlled by the peroxisome proliferator-activated receptors (PPARs), but tissue-specific effects are not well-defined. Thus, the aim was to compare the metabolic response in hepatic, adipose, and cardiac tissues after treatment with specific PPAR agonists. Male Wistar rats were randomized into three groups: a control group receiving placebo (n=8); a PPARα agonist group receiving WY-14,643 (n=6); and a PPARγ agonist group receiving rosiglitazone (n=6) for 12 days. All animals received a low-fat standard chow diet and were given a daily dose of placebo or agonist orally. Lipids and FA methyl esters were measured in plasma, liver, and heart and gene expression was measured in liver and adipose tissue, while enzyme activities were measured in liver. Treatment with the PPARα agonist was associated with higher liver mass relative to body weight (liver index), lower plasma, and hepatic total cholesterol, as well as lower plasma carnitine and acylcarnitines, compared with control. In heart, PPARα activation leads to overall lower levels of free FAs and specific changes in certain FAs, compared with control. Furthermore, β-oxidation in liver and the enzymatic activities of well-known PPARα targeted genes were higher following PPARα administration. Overall, rats treated with the PPARα agonist had higher hepatic saturated FAs (SFAs) and monounsaturated FAs (MUFAs) and lower n-6 and n-3 PUFAs, compared to control. Treatment with the PPARγ agonist was associated with a lower liver index, lower plasma triglycerides (TAG) and phospholipids, and higher hepatic phospholipids, compared with control. PPARγ target genes were increased specifically in adipose tissue. Moreover, lower total cardiac FAs and SFA and higher cardiac n-6 PUFA were also associated with PPARγ activation. Altogether, there were characteristic effects of PPARα activation in liver and heart, as well as in plasma. PPARγ effects were not only confined to adipose tissue, but specific effects were also seen in liver, heart, and plasma. In conclusion, short-term treatment with PPAR agonists induced tissue-specific effects on FA composition in liver and heart. Moreover, both PPARα and PPARγ activation lowered plasma TAG and phospholipids, most likely through effects on liver and adipose tissue, respectively. In future studies we aim to reveal whether similar patterns can be found through diet-induced activation of specific pathways.

Quantitative Proteomics Reveals the Mechanism of Oxygen Treatment on Lenses of Alzheimer's Disease Model Mice

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease with well-characterized pathological features. Yet the underlying mechanisms have not been resolved and an effective therapeutic approach is lacking. Cerebral hypoxia is considered a risk factor of AD.

OBJECTIVE

We tested whether oxygen supplementation can relieve AD symptoms and how it affects the expression levels of proteins in the lens.

METHODS

Triple transgenic AD model (3xTg-AD) mice were divided into oxygen treated (OT) and control (Ctrl) groups. Their cognitive performances were tested in a Morris water maze (MWM) paradigm. Then, their eye lens tissues were subjected to quantitative proteomics analysis by the iTRAQ (isobaric tags for relative and absolute quantification) method. The up- and downregulated proteins were classified according to a Gene Ontology (GO) database in PANTHER. Behavioral and proteomic data were compared between the groups.

RESULTS

Mice in the OT group had better learning and memorizing performance compared with the Ctrl group in MWM test. Lenses from the OT group had 205 differentially regulated proteins, relative to lenses from the Ctrl group, including proteins that are involved in the clearance of amyloid β-protein.

CONCLUSION

The results of this study indicate that oxygen treatment can improve cognitive function in AD model mice and alters protein expression in a manner consistent with improved redox regulation.

Long-chain polyunsaturated fatty acids regulation of PPARs, signaling: Relationship to tissue development and aging

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that function as ligand-dependent transcription factors that can be activated by different types of fatty acids (FAs). Three isoforms of PPARs have been identify, namely, PPARα, PPARβ/δ, and PPARγ, which are able to bind long-chain polyunsaturated FAs (LCPUFAs), n-3 LCPUFAs being bound with greater affinity to achieve activation. FA binding induces a conformational change of the nuclear receptors, triggering the transcription of specific genes including those encoding for various metabolic and cellular processes such as FA β-oxidation and adipogenesis, thus representing key mediators of lipid homeostasis. In addition, PPARs have important roles during placental, embryonal, and fetal development, and in the regulation of processes related to aging comprising oxidative stress, inflammation, and neuroprotection. The aim of this review was to assess the role of FAs as PPARs ligands, in terms of their main functions associated with FA metabolism and their relevance in the prevention and treatment of related pathologies during human life span.

Medium-chain plasma acylcarnitines, ketone levels, cognition, and gray matter volumes in healthy elderly, mildly cognitively impaired, or Alzheimer's disease subjects

Aging, amyloid deposition, and tau-related pathology are key contributors to the onset and progression of Alzheimer's disease (AD). However, AD is also associated with brain hypometabolism and deficits of mitochondrial bioenergetics. Plasma acylcarnitines (ACCs) are indirect indices of altered fatty acid beta-oxidation, and ketogenesis has been found to be decreased on aging. Furthermore, in elderly subjects, alterations in plasma levels of specific ACCs have been suggested to predict conversion to mild cognitive impairment (MCI) or AD. In this study, we assayed plasma profiles of ACCs in a cohort of healthy elderly control, MCI subjects, and AD patients. Compared with healthy controls or MCI subjects, AD patients showed significant lower plasma levels of several medium-chain ACCs. Furthermore, in AD patients, these lower concentrations were associated with lower prefrontal gray matter volumes and the presence of cognitive impairment. Interestingly, lower levels of medium-chain ACCs were also found to be associated with lower plasma levels of 2-hydroxybutyric acid. Overall, these findings suggest that altered metabolism of medium-chain ACCs and impaired ketogenesis can be metabolic features of AD.

Basis of aggravated hepatic lipid metabolism by chronic stress in high-fat diet-fed rat

Our previous study has demonstrated that long-term stress, known as chronic stress (CS), can aggravate nonalcoholic fatty liver disease in high-fat diet (HFD)-fed rat. In this study, we tried to figure out which lipid metabolic pathways were impacted by CS in the HFD-fed rat. Male Sprague-Dawley rats (6 weeks of age, n = 8 per group) were fed with either standard diet or HFD with or without CS exposure for 8 weeks. Hepatic lipidosis, biochemical, hormonal, and lipid profile markers in serum and liver, and enzymes involved in de novo lipogenesis (DNL) of fatty acids (FAs) and cholesterol, β-oxidation, FAs uptake, triglycerides synthesis, and very low-density lipoprotein (VLDL) assembly in the liver were detected. CS exposure reduced hepatic lipidosis but further elevated hepatic VLDL content with aggravated dyslipidemia in the HFD-fed rats. There was a synergism between CS and HFD on VLDL production and dyslipidemia. PCR and western blot assays showed that CS exposure significantly promoted hepatic VLDL assembly in rats, especially in the HFD-fed rats, while it had little impact on DNL, β-oxidation, FAs uptake, and triglycerides synthesis in the HFD-fed rats. This phenomenon was in accordance with elevated serum glucocorticoid level. The critical influence of CS exposure on hepatic lipid metabolism in the HFD-fed rats is VLDL assembly which might be regulated by glucocorticoid.

Palmitic acid induces central leptin resistance and impairs hepatic glucose and lipid metabolism in male mice

The consumption of diets rich in saturated fat largely contributes to the development of obesity in modern societies. A diet high in saturated fats can induce inflammation and impair leptin signaling in the hypothalamus. However, the role of saturated fatty acids on hypothalamic leptin signaling, and hepatic glucose and lipid metabolism remains largely undiscovered. In this study, we investigated the effects of intracerebroventricular (icv) administration of a saturated fatty acid, palmitic acid (PA, C16:0), on central leptin sensitivity, hypothalamic leptin signaling, inflammatory molecules and hepatic energy metabolism in C57BL/6J male mice. We found that the icv administration of PA led to central leptin resistance, evidenced by the inhibition of central leptin's suppression of food intake. Central leptin resistance was concomitant with impaired hypothalamic leptin signaling (JAK2-STAT3, PKB/Akt-FOXO1) and a pro-inflammatory response (TNF-α, IL1-β, IL-6 and pIκBa) in the mediobasal hypothalamus and paraventricular hypothalamic nuclei. Furthermore, the pre-administration of icv PA blunted the effect of leptin-induced decreases in mRNA expression related to gluconeogenesis (G6Pase and PEPCK), glucose transportation (GLUT2) and lipogenesis (FAS and SCD1) in the liver of mice. Therefore, elevated central PA concentrations can induce pro-inflammatory responses and leptin resistance, which are associated with disorders of energy homeostasis in the liver as a result of diet-induced obesity.