Distinct Effects of Carrageenan and High-Fat Consumption on the Mechanisms of Insulin Resistance in Nonobese and Obese Models of Type 2 Diabetes

Common food additive carrageenan inhibits proglucagon expression and GLP-1 secretion by human enteroendocrine L-cells

Proglucagon mRNA expression and GLP-1 secretion by cultured human L-cells (NCI-H716) were inhibited following exposure to λ-carrageenan, a commonly used additive in processed foods. Carrageenan is composed of sulfated or unsulfated galactose residues linked in alternating alpha-1,3 and beta-1,4 bonds and resembles the endogenous sulfated glycosaminoglycans. However, carrageenan has unusual alpha-1,3-galactosidic bonds, which are not innate to human cells and are implicated in immune responses. Exposure to carrageenan predictably causes inflammation, and carrageenan impairs glucose tolerance and contributes to insulin resistance. When cultured human L-cells were deprived overnight of glucose and serum and then exposed to high glucose, 10% FBS, and λ-carrageenan (1 µg/ml) for 10 minutes, 1 h, and 24 h, mRNA expression of proglucagon and secretion of GLP-1 were significantly reduced, compared to control cells not exposed to carrageenan. mRNA expression of proglucagon by mouse L-cells (STC-1) was also significantly reduced and supports the findings in the human cells. Exposure of co-cultured human intestinal epithelial cells (LS174T) to the spent media of the carrageenan-treated L-cells led to a decline in mRNA expression of GLUT-2 at 24 h. These findings suggest that ingestion of carrageenan-containing processed foods may impair the production of GLP-1, counteract the effect of GLP-1 receptor agonists and induce secondary effects on intestinal epithelial cells.

Exogenous recombinant N-acetylgalactosamine-4-sulfatase (Arylsulfatase B; ARSB) inhibits progression of B16F10 cutaneous melanomas and modulates cell signaling

In the syngeneic, subcutaneous B16F10 mouse model of malignant melanoma, treatment with exogenous ARSB markedly reduced tumor size and extended survival. In vivo experiments showed that local treatment with exogenous N-acetylgalactosamine-4-sulfatase (Arylsulfatase B; ARSB) led to reduced tumor growth over time (p < 0.0001) and improved the probability of survival up to 21 days (p = 0.0391). Tumor tissue from the treated mice had lower chondroitin 4-sulfate (C4S) content and lower sulfotransferase activity. The free galectin-3 declined, and the SHP2 activity increased, due to altered binding with chondroitin 4-sulfate. These changes induced effects on transcription, which were mediated by Sp1, phospho-ERK1/2, and phospho-p38 MAPK. Reduced mRNA expression of chondroitin sulfate proteoglycan 4 (CSPG4), carbohydrate sulfotransferase 15 (N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase), and matrix metalloproteinases 2 and 9 resulted. Experiments in the human melanoma cell line A375 demonstrated similar responses to exogenous ARSB as in the tumors, and inverse effects followed ARSB siRNA. ARSB, which removes the 4-sulfate group at the non-reducing end of C4S, acts as a tumor suppressor, and treatment with exogenous ARSB impacts on vital cell signaling and reduces the expression of critical genes associated with melanoma progression.

Capsaicin combined with dietary fiber prevents high-fat diet associated aberrant lipid metabolism by improving the structure of intestinal flora

Capsaicin (CAP) and dietary fibers are natural active ingredients that given separately do positively affect obesity and metabolic diseases. However, it was unknown whether their combined administration might further improve blood lipids and gut flora composition. To test this hypothesis we administered capsaicin plus dietary fibers (CAP + DFs) to male rats on a high-fat diet and analyzed any changes in the intestinal microbiota make up, metabolites, and blood indexes. Our results showed that combining CAP with dietary fibers more intensely reduced total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C). CAP + DFs also increased gut bacteria variety, and the abundance of several beneficial bacterial strains, including Allobaculum and Akkermansia, while reducing harmful strains such as Desulfovibrio. Additionally, CAP + DFs significantly increased arginine levels and caused short-chain fatty acids accumulation in the contents of the cecal portion of rats' gut. In conclusion, notwithstanding the rats were kept on a high-fat diet, adding CAP + DFs to the chow further improved, as compared with CAP alone, the lipidemia and increased the gut beneficial bacterial strains, while reducing the harmful ones.

Molecular environment and atypical function: What do we know about enzymes associated with Mucopolysaccharidoses?

Mucopolysaccharidoses are a group of lysosomal storage disorders caused by deficiency of enzymes involved in glycosaminoglycans degradation. Relationship between mucopolysaccharidoses and related enzymes has been clarified clearly. Based on such relationship, lots of therapies have been commercialized or are in the process of research and development. However, many potential treatments failed, because those treatments did not demonstrate expected efficacy or safety data. Molecular environment of enzyme, which is essential for their expression and activity, is fundamental for efficacy of therapy. In addition to enzyme activities, mucopolysaccharidoses-related enzymes have other atypical functions, such as regulation, which may cause side effects. This review tried to discuss molecular environment and atypical function of enzymes that are associated with mucopolysaccharidoses, which is very important for the efficacy and safety of potential therapies.

Food-grade carrageenans and their implications in health and disease

Food additives, often used to guarantee the texture, shelf-life, taste, and appearance of processed foods, have gained widespread attention due to their increased link to the growing incidence of chronic diseases. As one of the most common additives, carrageenans have been used in human diets for hundreds of years. While classified as generally recognized as safe (GRAS) for human consumption, numerous studies since the 1980s have suggested that carrageenans, particularly those with random coil conformations, may have adverse effects on gastrointestinal health, including aggravating intestinal inflammation. While these studies have provided some evidence of adverse effects, the topic is still controversial. Some have suggested that the negative consequence of the consumption of carrageenans may be structure dependent. Furthermore, pre-existing conditions may predispose individuals to varied outcomes of carrageenan intake. In this review, structure-function relationships of various carrageenans in the context of food safety are discussed. We reviewed the molecular mechanisms by which carrageenans exert their biological effects. We summarized the findings associated with carrageenan intake in animal models and clinical trials. Moreover, we examined the interactions between carrageenans and the gut microbiome in the pathogenesis of gastrointestinal disorders. This review argues for personalized guidance on carrageenan intake based on individuals' health status. Future research efforts that aim to close the knowledge gap on the effect of low-dose and chronic carrageenan intake as well as interactions among food additives should be conducive to the improved safety profile of carrageenans in processed food products.

Galectins as modulators of receptor tyrosine kinases signaling in health and disease

Receptor tyrosine kinases (RTKs) constitute a large group of cell surface proteins that mediate communication of cells with extracellular environment. RTKs recognize external signals and transfer information to the cell interior, modulating key cellular activities, like metabolism, proliferation, motility, or death. To ensure balanced stream of signals the activity of RTKs is tightly regulated by numerous mechanisms, including receptor expression and degradation, ligand specificity and availability, engagement of co-receptors, cellular trafficking of the receptors or their post-translational modifications. One of the most widespread post-translational modifications of RTKs is glycosylation of their extracellular domains. The sugar chains attached to RTKs form a new layer of information, so called glyco-code that is read by galectins, carbohydrate binding proteins. Galectins are family of fifteen lectins implicated in immune response, inflammation, cell division, motility and death. The versatility of cellular activities attributed to galectins is a result of their high abundance and diversity of their cellular targets. A various sugar specificity of galectins and the differential ability of galectin family members to form oligomers affect the spatial distribution and the function of their cellular targets. Importantly, galectins and RTKs are tightly linked to the development, progression and metastasis of various cancers. A growing number of studies points on the close cooperation between RTKs and galectins in eliciting specific cellular responses. This review focuses on the identified complexes between galectins and RTK members and discusses their relevance for the cell physiology both in healthy tissues and in cancer.

ι-Carrageenan Tetrasaccharide from ι-Carrageenan Inhibits Islet β Cell Apoptosis Via the Upregulation of GLP-1 to Inhibit the Mitochondrial Apoptosis Pathway

ι-Carrageenan performs diversified biological activities but has low bioavailability. ι-Carrageenan tetrasaccharide (ιCTs), a novel marine oligosaccharide prepared by the marine enzyme Cgi82A, was investigated for its effects on insulin resistance in high-fat and high-sucrose diet mice. Oral administration of ιCTs (ιCTs-L 30.0 mg/kg·bw, ιCTs-H 90.0 mg/kg·bw) decreased fasting blood glucose by 35.1% ± 1.41 (P < 0.01) and 27.4% ± 0.420 (P < 0.05), and enhanced glucose tolerance. Besides, ιCTs-L ameliorated islet vacuolization, decreased the β cell apoptosis by 21.8% ± 0.200 (P < 0.05), and promoted insulin secretion by 5.41% ± 0.0173 (P < 0.01) through pancreatic hematoxylin and eosin (H&E) staining, TUNEL staining, and insulin-glucagon immunostaining analysis. Interestingly, ιCTs-L and ιCTs-H treatment increased the incretin GLP-1 content in serum by 22.1% ± 0.402 (P < 0.01) and 10.7% ± 0.0935 (P < 0.05) respectively, through regulating the bile acid levels, which contributed to the inhibition of β cell apoptosis. Mechanically, ιCTs upregulated the expression of the GLP-1 receptor (GLP-1R) and protein kinase A (PKA) in the GLP-1/cAMP/PKA signaling pathway, and further inhibited the expression of cytochrome C and caspase 3 in the mitochondrial apoptotic pathway. In conclusion, this study suggested that ιCTs alleviated insulin resistance by GLP-1-mediated inhibition of β cell apoptosis and proposed a new strategy for developing potential functional foods that prevent insulin resistance.

Immunological effects of Chondrus armatus carrageenans and their low molecular weight degradation products

Ability of high molecular weight (HMW) κ- and λ-carrageenans of the red marine algae Chondrus armatus and their low molecular weight degradation products (LMWDPs) (0.7-20 and 10-170 kDa respectively) to influence functional properties (motility and phagocytosis) of murine peritoneal macrophages was assessed in this study as an in vitro and a weeklong feeding experiment. We demonstrated that, with an exception of one, all carrageenan samples at 100 μg/ml increased cellular motility and dose-dependently decreased phagocytic activity; LMWDPs of λ-carrageenan suppressed motility and had no effect on phagocytosis. Oral administration of all the carrageenan samples at 100 μg/kg/day for 7 days to mice had no effect on their clinical appearance, body weight, weight of their liver, spleen or thymus or development of noticeable changes to their inner organs. All samples induced a shift of the cell composition of the peritoneal cavity towards macrophages. Consumption of LMWDPs of κ-carrageenan resulted in development of leukopenia, however, no changes to relative WBC count were introduced by either of the samples. All samples decreased murine peritoneal macrophages phagocytic activity, with λ-samples possessing higher efficacy than their κ-counterparts; all LMWDPs stimulated peritoneal macrophages motility, with κ-samples possessing higher efficacy than their λ-counterparts In conclusion, we have shown that κ- and λ-carrageenans of the C. armatus and their LMWDPs suppress phagocytotic activity of peritoneal macrophages under both in vitro and in vivo conditions. This allows them to be viewed as pharmacologically active substances andpropagates the need for their further investigation as such.

Carrageenan-Free Diet Shows Improved Glucose Tolerance and Insulin Signaling in Prediabetes: A Randomized, Pilot Clinical Trial

OBJECTIVES

Carrageenan is well known to cause inflammation and is used in laboratory experiments to study mediators and treatments of inflammation. However, carrageenan is added to hundreds of processed foods to improve texture. Previous work indicated that low concentrations of carrageenan in drinking water caused marked glucose intolerance and insulin resistance in a mouse model. This exploratory, clinical study tested the impact of the no-carrageenan diet in prediabetes. Research Design and Methods. Participants with prediabetes (n = 13), defined as HbA1c of 5.7%-6.4%, enrolled in a 12-week, randomized, parallel-arm, feeding trial. One group (n = 8) was provided all meals and snacks with no carrageenan. A second group (n = 5) received a similar diet with equivalent content of protein, fat, and carbohydrate, but with carrageenan. Blood samples were collected at baseline and during oral glucose tolerance tests at 6 and 12 weeks. The primary outcome measure was changed in %HbA1c between baseline and 12 weeks. Statistical analysis included paired and unpaired t-tests, correlations, and 2 × 2 ANOVAs.

RESULTS

Subjects on no carrageenan had declines in HbA1c and HOMA-IR (p = 0.006, p = 0.026; paired t-test, two tailed). They had increases in C-peptide (p = 0.029) and Matsuda Index (2.1 ± 0.7 to 4.8 ± 2.3; p = 0.052) and declines in serum IL-8, serum galectin-3, and neutrophil phospho-(Ser307/312)-IRS1 (p = 0.049, p = 0.003, and p = 0.006; paired t-tests, two tailed). Subjects on the diet with carrageenan had no significant changes in these parameters. Significant differences between no-carrageenan and carrageenan-containing diet groups for changes from baseline to 12 weeks occurred in C-peptide, phospho-Ser-IRS1, phospho-AKT1, and mononuclear cell arylsulfatase B (p = 0.007, p = 0.038, p = 0.0012, and p = 0.0008; 2 × 2 ANOVA). Significant correlations were evident between several of the variables.

CONCLUSIONS

Findings indicate improvement in HbA1c and HOMA-IR in participants on no-carrageenan diets, but not in participants on carrageenan-containing diets. Significant differences between groups suggest that removing carrageenan may improve insulin signaling and glucose tolerance. Larger studies are needed to further consider the impact of carrageenan on development of diabetes.