中国P站

In the past 50 years, dietary habits have changed worldwide. In fact, the 2022 Global Nutrition report estimated that intake of fruit and vegetable is 60% and 40% lower than recommended, respectively. In addition, more than half of the population is exceeding the recommended intake for saturated fat and added sugar. Because of the above, in the past 30 years, the average consumption of calories in the world has increased by 280 kcal/day/person [1]. The energy imbalance between consumed and expended calories is considered the main cause of obesity. A new study released from the Lancet, showed that since 1990, obesity in adults has doubled and it has quadruple among children and young adults, resulting in more than 1 billion people living with obesity worldwide. Obesity is characterized by excess Adipose Tissue (AT) deposition, frequently accompanied by chronic low level inflammation. Low-levels of chronic inflammation contribute to the development and progression of obesity-associated diseases via alteration of:

• Redox-signaling pathways, causing oxidative stress.
• Intestinal barrier integrity, causing intestinal permeabilization and endotoxemia.
• The gut microbiota, causing dysbiosis.
• Mitochondrial dynamics, causing mitochondrial dysfunction [2].

Mitochondria are the master regulators of energy homeostasis. Mitochondrial dynamics is tightly regulated by two phenomena, fission and fusion. In inflammatory conditions, derived from excess of nutrients and/or excess production of oxidants, mitochondria undergo architectural alterations leading to an imbalance between fission and fusion triggering mitochondrial dysfunction [3].

White AT (WAT) is the most abundant type of fat present in the body. WAT adipocytes are characterized by a single fat droplet and few cellular organelles. On the contrary, Brown AT (BAT) contains a large number of fat droplets and mitochondria. Thus, BAT is a high metabolically active tissue, being specialized in adaptive thermogenesis. The transition from WAT to BAT is a process called browning. This process is characterized by an increase in the number of adipocyte mitochondria with thermogenic capacity [4]. Emerging evidence have shown the beneficial effects of polyphenols consumption on WAT browning via an increase of thermogenesis and lipolysis [5,6]. Thus, stimulation of WAT browning, especially though dietary intervention, could be a potential therapeutic approach to prevent, mitigate, and treat obesity-associated non-communicable diseases, such as Type 2 Diabetes (T2D), Non-Alcoholic Fatty Liver Disease (NAFLD) and Insulin Resistance (IR).

Given the above, this mini-review will focus on the potential benefits of Anthocyanins (AC), in promoting WAT browning. It will also address their potential mechanisms of action, with particular focus on their capacity to prevent High-Fat Diet (HFD)/obesityassociated mitochondrial dysfunction.

Anthocyanins (AC)

Anthocyanidins are characterized by a basic flavonoid structure (C6-C3-C6) with a positive charge on the B ring (Figure 1). In nature anthocyanidins mostly exist in glycosylated forms, called Anthocyanins (AC). The different hydroxyl groups on the C ring define not only the different types of AC, such as cyanidin, delphinidin, peonidin, petunidin, malvidin, and pelargonin, but also their biological actions (Figure 1B). Among all the different types of AC, cyanidin and delphinidin were found to mitigate HFD-induced intestinal permeability, hypertriglyceridemia, parameters of insulin resistance, inflammation, and endotoxemia, both in pre-clinical and clinical studies [7-9]. Furthermore, cyanidin-(C3G) and Delphinidin-3-O-Glucoside (D3G) and their metabolites have the capacity to mitigate mitochondrial dysfunction and promote WAT browning in part through the activation of cyclic adenosine monophosphate/cAMP-dependent protein kinase (cAMP/PKA), 5' AMP-activated Protein Kinase/peroxisome proliferator-activated receptor gamma coactivator-1 alpha (AMPK/PGC-1α), and AMPK/ Sirtuin-1 (SIRT-1) signaling pathways. Besides the mitigating effects of C3G on the dysmetabolism associated with obesity and consumption of HFDs, it has been observed that C3G stimulated the differentiation of 3T3-L1 cells pre-adipocytes via the regulation of thermogenesis by increasing Uncoupling Protein-1 (UCP-1), PGC-1α, and PR Domain Containing 16 (PRDM16) expression, and cAMP levels. Additionally, C3G, D3G, and the cyanidin metabolite Protocatechuic Acid (PCA) increased cAMP levels and activates the PKA pathway in GluTag cells.

 

Figure 1: Chemical structure of anthocyanidins. A) Basic structure of anthocyanidins; B) Distribution of hydroxyl and methoxyl groups defining the six most common anthocyanins (AC): cyanidin, delphinidin, peonidin, malvidin, pelargonidin, and petunidin.

Anthocyanins and the browning of the white adipose tissue

Among all the different AT pads, Subcutaneous WAT (sWAT) is the one more prone to browning. Browning of the WAT is an adaptive and reversible response to an environmental stimulus, such as cold, exercise, and diet. During browning, WAT depots develop features that resemble BAT, in fact, adipocytes present a multilocular appearance, increased mitochondrial number, and increased expression of thermogenesis-regulated proteins like UCP-1. UCP-1 overexpression is associated with an increase in mitochondrial biogenesis. Mitochondrial biogenesis is regulated by several proteins, i.e., PGC-1α, PRDM16, and peroxisome Proliferator-Activated Receptor Gamma (PPARγ). PPARγ, widely expressed in the AT, has the capacity to regulate thermogenesis, lipids metabolism, and insulin sensitivity. Thus, PPARγ induces WAT browning by stabilizing PRDM16, which is responsible for activating genes involved in thermogenesis. PDRM16 is essential for sWAT browning and its actions are regulated through its interaction with PGC-1α. PGC-1α is a key player in adaptive thermogenesis by regulating UCP-1 gene transcription. Evidence showed that consumption of HFDs and the associated obesity leads to an enlargement of sWAT adipocyte size, decreases the expression of indicators of mitochondrial number, as well as of mtDNA, and decreases the expression of UCP-1 and of genes involved in mitochondrial biogenesis (PGC-1α, PRDM16, and PPARγ). In contrast, consumption of AC improves thermogenesis and mitochondrial biogenesis. Thus, supplementation with AC (cyanidin and delphinidin) and the cyanidin metabolite vanillic acid mitigated obesity-associated decreased gene expression of markers of mitochondrial number, biogenesis, and thermogenesis in sWAT of mice fed HFD or high fructose diets. Interestingly, mice fed the control diet added with AC showed an increased expression of PGC-1α, PRDM16, PPARγ, and UCP-1 in sWAT compared to control diet-fed mice. These results suggest that selected AC and their metabolites, could be used as a strategy to improve thermogenesis and mitochondrial biogenesis the context of obesity, but also in healthy conditions.

In vitro studies, using 3T3-L1 pre and mature adipocytes, with or without stimulation with fatty acids, showed that treatment with C3G, D3G, their main gut metabolites or AC natural oligomer, promoted thermogenesis and mitochondria biogenesis by increasing the expression of PPARγ, PRDM16, PGC-1α, and UCP-1.

Even when sWAT browning is mainly dependent on the activation of the β3-adrenergic receptor (β3-AR) cascade, other signaling pathways have been recently identified to play a key role in WAT browning WAT, i.e., cAMP/PKA, AMPK/PGC-1α, and AMPK/ SIRT-1. All these pathways lead to increased expression of UCP-1 and increased mitochondria biogenesis via PGC-1α and by deacetylating PPARγ, improving the PPARγ-PRDM16 interaction required for the induction of thermogenic genes.

The stimulation of β3-AR by cold exposure leads to increased levels of cAMP and PKA phosphorylation. Activation of this cAMP/PKA pathway triggers p38 phosphorylation, which leads to an increased expression of PCG1α, and activating thermogenesis via UCP-1 transcription and PPARγ activation. Choi et al. demonstrated that AC extracted from skin grapes (AC natural oligomer) activated browning of mature 3T3-L1 via stimulation of β3-AR/PKA/p38 pathway. In addition, it was observed that AC oligomer increased CREB protein levels, leading to increase expression of UCP-1, independently of p38 activation. Activation of CREB seems to be ERK-mediated. Thus, this work showed that the AC oligomer increased the activation of ERK in vitro, which plays a key role in the activation of UCP-1 and PCG-1α. Furthermore, Matsukawa et al. showed that C3G promote beiging phenotypes in pre-adipocyte 3T3- L1 cells, increasing cAMP levels. In the same line, but in mature 3T3- L1 cells, it was recently observed that C3G, but not D3G and their gut metabolites, prevented palmitate-induced decrease of cAMP levels. This suggests that different ACs could be promoting browning through other mechanisms besides the stimulation of the β3-AR. Thus, it has been shown that C3G, D3G and their metabolites mitigated palmitatemediated decreased activation of PKA, which can be activated by free intracellular Ca2+ independently of β3-AR and cAMP pathways.

Under stress conditions associated with HFDs and obesity, i.e., inflammation and oxidative stress, AMP activates AMPK (Thr172), which regulates PGC-1α-associated mitochondrial biogenesis and UCP-1 expression (AMPK/PGC-1α pathways). In this regard, C3G and D3G, mitigate fatty acid-mediated decreased activation of AMPK both in mice fed a HFD and in mature 3T3-L1 adipocytes treated with palmitate.

SIRT-1 is another master regulator of energy metabolism, increasing the activation and expression of PGC-1α, promoting lipolysis and inhibiting adipogenesis through the regulation of PPARγ and AMPK. SIRT-1 induces WAT thermogenesis via AMPK/SIRT-1/ PGC-1α pathways. C3G and its gut metabolite, PCA, also act on this pathway mitigating palmitate-mediated decreased expression of SIRT-1 in mature 3T3-L1 cells.

Overall, recent findings in vivo and in vitro using pre and mature adipocytes, suggest that select AC, especially C3G and D3G, promote mitochondria biogenesis and thermogenesis via activation of different signaling pathways, in a context of HFDs and obesity (Figure 2).

 

Figure 2: Anthocyanins (AC) mechanisms of action on the white adipose tissue browning in the context of obesity. AC consumption improves obesity-impaired mitochondrial biogenesis and thermogenesis via regulation of different signaling pathways.

Anthocyanins and mitochondrial dynamics

Mitochondrial biogenesis and thermogenesis are associated with changes in mitochondria dynamics. Thus, mitochondria undergo continuous processes of fission, fusion, and mitophagy, which determine the quality and quantity of mitochondrial within cells as well as their function. Fission and fusion processes are tightly regulated by different proteins. Mitochondrial fusion is coordinated in both the outer and inner mitochondrial membranes by mitofusins (MFN-1 and MFN-2) and OPA1, respectively. Mitochondrial fission is regulated by outer mitochondrial membrane proteins, including Drp-1, Fis-1, and MFF. When mitochondrial damage occurs, a quality control system regulated by PINK1, Parkin, and BNIP3/NIX is activated, leading to mitochondria degradation by mitophagy, a process that exclusively eliminates damaged mitochondria. Alterations of mitochondrial dynamics lead to the development and progression of different obesity-associated pathologies, including T2D, NAFLD, IR, cancer, and cardiovascular diseases. Thus, it was observed that consumption of HFDs and obesity can reduce mitochondrial function by altering the activity of proteins involved in mitochondrial dynamics. Although some evidence show how polyphenols consumption could modulate mitochondrial dynamics, there is limited evidence on the effect of AC consumption on mitochondrial function in the context of obesity. It was recently observed that supplementation with an AC-rich extract, composed mainly by cyanidin and delphinidin, mitigated HFD/obesity-induced decrease in the protein levels of MFN-2, OPA1, Fis-1, and MFF, inhibition of Drp1 activation, and decreased expression of the mitophagy receptor BNIP3L/NIX in sWAT. Furthermore, a study from Ramirez et al. showed that consumption of a delphinidin-rich extract, improved BAT mitochondrial function in obese mice via modulation of OPA1 expression and Drp1 phosphorylation.

All together these few findings in pre-clinical studies using HFD as a model of obesity, provide promising evidence that consumption of AC could mitigate obesity-associated mitochondrial dysfunction (Figure 3).

 

Figure 3: Anthocyanins (AC) consumption on high-fat diet/ obesity-associated mitochondrial dysfunction. AC consumption restores obesity-altered mitochondrial function via modulation key mitochondrial dynamics-associated proteins involved in fusion, fission, and mitophagy

This mini-review provides a general overview on the effects of consumption of AC and their mechanisms of action on the browning of WAT and mitochondrial function. Even though a large amount of evidence showed that polyphenols consumption could be used as a strategy to ameliorate obesity-associated diseases, there are only a few in vitro and pre-clinical studies showing the role of AC in the mitigation of obesity-associated impaired WAT mitochondrial biogenesis and function. Pre-clinical studies have shown that selected AC, especially cyanidin and delphinidin, can improve body weight gain, in part via modulation of key regulator of mitochondrial biogenesis and thermogenesis. Furthermore, AC supplementation can improve the mitochondrial dysfunction caused by HFD consumption and associated obesity.

Main findings from in vitro studies, performed in pre- and in mature adipocytes, highlighted how different types of AC, especially C3G and D3G, and their gut metabolites can improve mitochondrial biogenesis and thermogenesis via different pathways. Differences in the mechanisms of action of particular ACs on WAT browning could be due to their different chemical structures.

In summary, the overall results support the concept that increasing consumption of fruit and vegetables, especially those rich in selected AC (i.e., cyanidin and delphinidin) can promote WAT browning via modulation of mitochondrial biogenesis and thermogenesis and can regulate mitochondria dynamics in the context of HFD/obesityinduced dysmetabolism. Because of limited available studies, there is an urgent need to further investigate the potential relevance of AC consumption as a strategy to mitigate HFD/obesity-associated alterations of mitochondrial dynamics and biogenesis, particularly in clinical trials.

Figures were generated with BioRender.com

1. Cremonini E, Iglesias DE, Kang J, Lombardo GE, Mostofinejad Z, et al. (2020) Arch Biochem Biophys 690: 108505.

   [] [] []

2. Chen W, Zhao H, Li Y (2023) . Signal Transduct Target Ther 8: 333.

   [] [] []

3. Machado SA, Pasquarelli-do-Nascimento G, da Silva DS, Farias GR, de Oliveira Santos I, et al. (2022) . Nutr Metab 19: 61.

   [] [] []

4. Lanzi CR, Perdicaro DJ, Landa MS, Fontana A, Antoniolli A, et al. (2018) J Nutr Biochem 56: 224-233.

   [] [] []

5. Silvester AJ, Aseer KR, Yun JW (2019) J Nutr Biochem 64: 1-12.

   [] [] []

6. Daveri E, Cremonini E, Mastaloudis A, Hester SN, Wood SM, et al. (2018) Redox Biol 18: 16-24.

   [] [] []

7. Iglesias DE, Cremonini E, Hester SN, Wood SM, Bartlett M, et al. (2022) Free Radic Biol Med 188: 71-82.

   [] [] []

8. Cremonini E, Daveri E, Mastaloudis A, Adamo AM, Mills D, et al. (2019) Redox Biol 26: 101269.

   [] [] []

9. Cremonini E, Daveri E, Iglesias DE, Kang J, Wang Z, et al. (2022) . Redox Biol 51: 102273.

   [] [] []