Effect of catechin on dietary AGEs absorption and cytotoxicity in Caco-2 cells

Absorption and intracellular accumulation of food-borne dicarbonyl precursors of advanced glycation end-product in a Caco-2 human cell transwell model

This study aimed to better understand whether and how the reactive 1,2-dicarbonyl precursors of advanced glycation end products (AGEs), glyoxal (GO) and methylglyoxal (MGO), cross the intestinal barrier by studying their transport in the in vitro Caco-2 transwell system. The results reveal that GO, MGO and Nε-(carboxymethyl)lysine (CML), the latter studied for comparison, are transported across the intestinal cell layer via both active and passive transport and accumulate in the cells, albeit all to a limited extent. Besides, the transport of the dicarbonyl compounds was only partially affected by the presence of amino acids and protein, suggesting that scavenging by a food matrix will not fully prevent their intestinal absorption. Our study provides new insights into the absorption of the two major food-borne dicarbonyl AGE precursors and provides evidence of their potential systemic bioavailability but also of factors limiting their contribution to the overall exposome.

Amelioration activity of the high bioaccessible chrysanthemum (Gongju) phenolics on alcohol-induced oxidative injury in AML-12 cells

The main bioavailable phenolics from of Gongju (GJ) and their mechanism for hepato-protection remain unclear. To select the GJ phenolics with high bioavailability, chrysanthemum digestion and Caco-2 cells were used and their hepato-protective potential were examined by using AML-12 cells. The digestive recovery and small intestinal transit rate of the main phenolic compounds ranged from 28.52 to 69.53% and 6.57% ∼ 15.50%, respectively. Among them, chlorogenic acid, 3,5-dicaffeoylquinic acid, and 1,5-dicaffeoylquinic acid, showed higher small intestinal transit rates and digestive recoveries. Furthermore, we found that by increasing intracellular Catalase (CAT) and Superoxide dismutase (SOD) viability and lowering Malondialdehyde (MDA) level (P < 0.05), 3,5-dicaffeoylquinic acid significantly mitigated the oxidative damage of AML-12 liver cells more than the other two phenolics. Our results demonstrated that 3,5-dicaffeoylquninic acid was the primary phenolic compounds in GJ that effectively reduced liver damage, providing a theoretical basis for the development of GJ as a potentially useful resource for hepatoprotective diet.

The inhibitory effects of endophytic metabolites on glycated proteins under non-communicable disease conditions: A review

Protein glycation in human body is closely linked to the onset/progression of diabetes associated complications. These glycated proteins are commonly known as advanced glycation end products (AGEs). Recent literature has also highlighted the involvement of AGEs in other non-communicable diseases (NCDs) such as cardiovascular, cancer, and Alzheimer's diseases and explored the impact of plant metabolites on AGEs formation. However, the significance of endophytic metabolites against AGEs has recently garnered attention but has not been thoroughly summarized thus far. Therefore, the objective of this review is to provide a comprehensive overview of the importance of endophytic metabolites in combating AGEs under NCDs conditions. Additionally, this review aims to elucidate the processes of AGEs formation, absorption, metabolism, and their harmful effects. Collectively, endophytic metabolites play a crucial role in modulating signaling pathways and enhancing the digestibility properties of gut microbiota (GM) by targeting on AGEs/RAGE (receptor for AGEs) axis. Furthermore, these metabolites exhibit anti-AGEs activities similar to those derived from host plants, but at a lower cost and higher production rate. The use of endophytes as a source of such metabolites offers a risk-free and sustainable approach that holds substantial potential for the treatment and management of NCDs.

Modulating intestinal health: Impact of chitooligosaccharide molecular weight on suppressing RAGE expression and inflammatory response in methylglyoxal-induced advanced glycation end-products

The accumulation of methylglyoxal (MGO) produced in high-temperature processed foods and excessive production in the body contributes to intestinal barrier dysfunction. In this study, we investigated the effects of chitooligosaccharides (COSs) of different molecular weights (<1 kDa, 1-3 kDa, 3-5 kDa, 5-10 kDa, and >10 kDa) on MGO-induced intestinal barrier dysfunction. We investigated the effect of COSs on inhibiting intracellular MGO accumulation/MGO-derived AGEs production and regulating the receptor for AGE (RAGE)-mediated downstream protein expression, including proteins related to apoptosis and inflammation, intestinal barrier integrity, and paracellular permeability. Pretreatment with COSs ameliorated MGO-induced increased RAGE protein expression, activation of apoptotic cascade/inflammatory response, loss of intestinal epithelial barrier integrity, and increased paracellular permeability, ameliorating intestinal dysfunction through MGO scavenging. 1-3 kDa COSs most effectively ameliorated MGO-induced intestinal dysfunction. Our results suggest the potential of COSs in improving intestinal health by ameliorating intestinal barrier dysfunction by acting as an MGO scavenger and highlighting the need for the optimization of the molecular weight of COSs to optimize its protective effects.

Comparative Study of the Effects of Dietary-Free and -Bound Nε-Carboxymethyllysine on Gut Microbiota and Intestinal Barrier

Nε-carboxymethyllysine (CML) is produced by a nonenzymatic reaction between reducing sugar and ε-amino group of lysine in food and exists as free and bound forms with varying digestibility and absorption properties in vivo, causing diverse interactions with gut microbiota. The effects of different forms of dietary CML on the gut microbiota and intestinal barrier of mice were explored. Mice were exposed to free and bound CML for 12 weeks, and colonic morphology, gut microbiota, fecal short-chain fatty acids (SCFAs), intestinal barrier, and receptor for AGE (RAGE) signaling cascades were measured. The results indicated that dietary-free CML increased the relative abundance of SCFA-producing genera including Blautia, Faecalibacterium, Agathobacter, and Roseburia. In contrast, dietary-bound CML mainly increased the relative abundance of Akkermansia. Moreover, dietary-free and -bound CML promoted the gene and protein expression of zonula occludens-1 and claudin-1. Additionally, the intake of free and bound CML caused an upregulation of RAGE expression but did not activate downstream inflammatory pathways due to the upregulation of oligosaccharyl transferase complex protein 48 (AGER1) expression, indicating a delicate balance between protective and proinflammatory effects in vivo. Dietary-free and -bound CML could modulate the gut microbiota community and increase tight-junction expression, and dietary-free CML might exert a higher potential benefit on gut microbiota and SCFAs than dietary-bound CML.

Impact of dietary plant flavonoids on 7,8-dihydroxyflavone transepithelial transport in human intestinal Caco-2 cells

7,8-dihydroxyflavone (7,8-DHF) is a biologically active flavone with various physiological activities, including neuroprotection, anti-inflammation, and weight loss. Previous studies have found that the efflux protein P-glycoprotein (P-gp) significantly affects the transepithelial transport of 7,8-DHF in the intestine, resulting in its low oral bioavailability. Based on this, in this study, a Caco-2 monolayer cell model was used to investigate 14 dietary plant flavonoids as potential P-gp inhibitors, and their effects on the transepithelial transport and in vitro digestion of 7,8-DHF were explored. The results showed that among the 14 plant flavonoids, hesperetin, epigallocatechin gallate, fisetin, kaempferol, quercetin, and isoorientin increased and the apparent permeability coefficients (P app) of 7,8-DHF at AP → BL direction and lowered P app value at BL → AP direction to varying degrees, reducing the efflux ratio of 7,8-DHF less than 1.5. In particular, kaempferol and quercetin exhibited the best effect on promoting the transepithelial transport of 7,8-DHF, especially when used at molar concentration ratios of 1:1 and 1:2 with 7,8-DHF. This is beneficial for improving the oral bioavailability of 7,8-DHF. Meanwhile, 7,8-DHF was found to maintain structural stability in simulated saliva, gastric juice, and intestinal juice, and its stability was not affected by the coexistence of quercetin and kaempferol. Overall, this study provided a theoretical basis for seeking natural and safe P-gp inhibitors to improve the oral absorption of natural products.

Inhibition of advance glycation end products formation, gastrointestinal digestion, absorption and toxicity: A comprehensive review

Advanced glycation end-products (AGEs) are the final products of the non-enzymatic interaction between reducing sugars and amino groups in proteins, lipids and nucleic acids. In numerous diseases, such as diabetes, neuropathy, atherosclerosis, aging, nephropathy, retinopathy, and chronic renal illness, accumulation of AGEs has been proposed as a pathogenic mechanism of inflammation, oxidative stress, and structural tissue damage leading to chronic vascular issues. Current studies on the inhibition of AGEs mainly focused on food processing. However, there are few studies on the inhibition of AGEs during digestion, absorption and metabolism although there are still plenty of AGEs in our body with our daily diet. This review comprehensively expounded AGEs inhibition mechanism based on the whole process of digestion, absorption and metabolism by polyphenols, amino acids, hydrophilic colloid, carnosine and other new anti-glycation agents. Our study will provide a ground-breaking perspective on mediation or inhibition AGEs.

Molecular Mechanism of Lotus Seedpod Oligomeric Procyanidins Inhibiting the Absorption of Oligopeptide-Advanced Glycation End Products

Research on advanced glycation end product (AGEs) inhibition has generally focused on food processing, but many protein-AGEs will still be taken. Oligopeptide (OLP)-AGEs, as the main form after digestion, will damage human health once absorbed. Here, we investigated the ability of lotus seedpod oligomeric procyanidins (LSOPC) to inhibit the absorption of the OLP-AGEs and elucidated the underlying mechanism. Our results showed that the inhibition rate of LSOPC on the absorption of OLP-AGEs was about 50 ± 5.38%. 0.1, 0.2, and 0.3 mg/mL could upregulate the expression of ZO-1 and downregulate the expression of PepT1 and clathrin. Molecular docking showed that LSOPC could compete with the binding of OLP-AGEs to PepT1 and AP-2, thus inhibiting the absorption of OLP-AGEs. Furthermore, the interaction of LSOPC with the OLP-AGEs reduced the surface hydrophobicity of OLP-AGEs. It altered the secondary structure of the OLP-AGEs, thus weakening the affinity of the OLP-AGEs to the transporter protein to inhibit the absorption of OLP-AGEs. Together, our data revealed potential mechanisms by which LSOPC inhibit the absorption of OLP-AGEs and opened up new perspectives on the application of LSOPC in reducing the increasing health risks posed by OLP-AGEs.

Different Structures of Arabinoxylan Hydrolysates Alleviated Caco-2 Cell Barrier Damage by Regulating the TLRs/MyD88/NF-κB Pathway

Arabinoxylan (AX) has been associated with alleviating intestinal barrier damage, and different structures of AX give rise to different effects on the intestinal barrier. This study investigated the main structural characteristics of AX, whose functional properties are attributed to alleviating intestinal barrier damage, and clarified their underlying mechanisms. An in vitro Caco-2 cell model was established to investigate the intestinal barrier effects of AX with various degrees of substitution (Ds) and molecular weight (Mw), with an added MyD88 inhibitor to verify the signaling pathways. Arabinoxylan treated with endo-1,4-β-xylanase (AXX) with higher Ds and Mw showed stronger physiological activity, which might be correlated with the uronic acid and bound ferulic acid contents in AXX. Moreover, AXX alleviated the intestinal barrier damage by upregulating the transepithelial electrical resistance (TER) and alleviating the decrease of claudin-1 (p < 0.05). AXX regulated the expression of inflammatory factors IL-2, TNF-α, IL-6 and IL-10 (p < 0.05). In addition, AXX reduced the intestinal barrier damage induced via inhibiting the TLRs/MyD88/NF-κB pathway and activating the TLRs/PKC pathway. Thus, AX with higher Ds and Mw might be better in alleviating intestinal barrier damage, and MyD88 might be the key point of AXX to identify these signaling pathways.

Investigation of the Phenolic Component Bioavailability Using the In Vitro Digestion/Caco-2 Cell Model, as well as the Antioxidant Activity in Chinese Red Wine

Red wine is a well-known alcoholic beverage, and is known to have phenolic compounds (PCs), which contribute to its antioxidant activity and have other beneficial advantages for human health. The aim of this study was to evaluate the effect of the simulated gastro-intestinal digestion and the Caco-2 transepithelial transport assay on the PCs, bioavailability, and the antioxidant capacity of red wines. The contents of PCs in red wine were significantly reduced during most of the digestion phases. Phenolic acid had the greatest permeability, while the flavonols had the weakest. The bioavailability of PCs ranged from 2.08 to 24.01%. The result of the partial least squares structural equation model showed that the three phenols were positively correlated with the antioxidant activity of red wine. The contribution of anthocyanins was the largest (0.8667).

High Molecular Weight Fucoidan Restores Intestinal Integrity by Regulating Inflammation and Tight Junction Loss Induced by Methylglyoxal-Derived Hydroimidazolone-1

Fucoidan from brown seaweeds has several biological effects, including preserving intestinal integrity. To investigate the intestinal protective properties of high molecular weight fucoidan (HMWF) from Undaria pinnatifida on intestinal integrity dysfunction caused by methylglyoxal-derived hydroimidazolone-1 (MG-H1), one of the dietary advanced-glycation end products (dAGEs) in the human-colon carcinoma-cell line (Caco-2) cells and ICR mice. According to research, dAGEs may damage the intestinal barrier by increasing gut permeability. The findings of the study showed that HMWF + MG-H1 treatment reduced by 16.8% the amount of reactive oxygen species generated by MG-H1 treatment alone. Furthermore, HMWF + MGH-1 treatment reduced MG-H1-induced monolayer integrity disruption, as measured by alterations in transepithelial electrical resistance (135% vs. 75.5%) and fluorescein isothiocyanate incorporation (1.40 × 10^-6 cm/s vs. 3.80 cm/s). HMWF treatment prevented the MG-H1-induced expression of tight junction markers, including zonula occludens-1, occludin, and claudin-1 in Caco-2 cells and mouse colon tissues at the mRNA and protein level. Also, in Caco-2 and MG-H1-treated mice, HMWF plays an important role in preventing receptor for AGEs (RAGE)-mediated intestinal damage. In addition, HMWF inhibited the nuclear factor kappa B activation and its target genes leading to intestinal inflammation. These findings suggest that HMWF with price competitiveness could play an important role in preventing AGEs-induced intestinal barrier dysfunction.

Bioactivity-guided isolation of the major anthocyanin from Lycium ruthenicum Murr. fruit and its antioxidant activity and neuroprotective effects in vitro and in vivo

Lycium ruthenicum Murr. fruit (LRF) is an edible berry known for its rich anthocyanin content. Our previous study has shown that LRF-derived anthocyanins have neuroprotective effects in rats, which may be due to their effective antioxidant activity. Therefore, this study performed online HPLC-DPPH screening as a bioactivity-guided method for the preparative separation of anthocyanins from LRF. Finally, the main fraction was isolated and identified as petunidin-3,5-O-diglucoside (Pn3G5G). Pn3G5G exhibited strong antioxidant capacity during DPPH and ABTS free radical scavenge assays. Furthermore, Pn3G5G exhibited protective effects on Nε-carboxymethyllysine (CML)-treated Neuro-2a cells by enhancing cell viability in a dose-dependent manner. CML-induced apoptosis was also reduced by Pn3G5G potentially by suppressing oxidative stress and inflammation. More importantly, Pn3G5G significantly improved cognitive impairment, neuroinflammation and neuronal apoptosis in D-galactose-induced aging mice. The result suggests the development of Pn3G5G as a healthcare product or a potent dietary supplement with antioxidant and neuroprotective effects.

Comparison of metabolic fate, target organs, and microbiota interactions of free and bound dietary advanced glycation end products

Increased intake of Western diets and ultra-processed foods is accompanied by increased intake of advanced glycation end products (AGEs). AGEs can be generated exogenously in the thermal processing of food and endogenously in the human body, which associated with various chronic diseases. In food, AGEs can be divided into free and bound forms, which differ in their bioavailability, digestion, absorption, gut microbial interactions and untargeted metabolites. We summarized the measurements and contents of free and bound AGE in foods. Moreover, the ingestion, digestion, absorption, excretion, gut microbiota interactions, and metabolites and metabolic pathways between free and bound AGEs based on animal and human studies were compared. Bound AGEs were predominant in most of the selected foods, while beer and soy sauce were rich in free AGEs. Only 10%-30% of AGEs were absorbed into the systemic circulation when orally administered. The excretion of ingested free and bound AGEs was approximately 90% and 60%, respectively. Dietary free CML has a detrimental effect on gut microbiota composition, while bound AGEs have both detrimental and beneficial impacts. Free and bound dietary AGEs changed amino acid metabolism, energy metabolism and carbohydrate metabolism. And besides, bound dietary AGEs altered vitamin metabolism, and glycerolipid metabolism.

Herbal Medicine, Gut Microbiota, and COVID-19

Coronavirus Disease 19 (COVID-19) is a respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which has grown to a worldwide pandemic with substantial mortality. The symptoms of COVID-19 range from mild flu-like symptoms, including cough and fever, to life threatening complications. There are still quite a number of patients with COVID-19 showed enteric symptoms including nausea, vomiting, and diarrhea. The gastrointestinal tract may be one of the target organs of SARS-CoV-2. Angiotensin converting enzyme 2 (ACE2) is the main receptor of SARS-CoV-2 virus, which is significantly expressed in intestinal cells. ACE2 links amino acid malnutrition to microbial ecology and intestinal inflammation. Intestinal flora imbalance and endotoxemia may accelerate the progression of COVID-19. Many herbs have demonstrated properties relevant to the treatment of COVID-19, by supporting organs and systems of the body affected by the virus. Herbs can restore the structure of the intestinal flora, which may further modulate the immune function after SARS-CoV-2 infection. Regulation of intestinal flora by herbal medicine may be helpful for the treatment and recovery of the disease. Understanding the role of herbs that regulate intestinal flora in fighting respiratory virus infections and maintaining intestinal flora balance can provide new ideas for preventing and treating COVID-19.