Identification of carrageenan in mammalian tissues: an analytical and histochemical study

The Antitumor Potential of λ-Carrageenan Oligosaccharides on Gastric Carcinoma by Immunomodulation

Gastric carcinoma is a frequently detected malignancy worldwide, while its mainstream drugs usually result in some adverse reactions, including immunosuppression. λ-carrageenan oligosaccharides (COS) have attracted increasing attention as potential anticancer agents due to their ability to enhance immune function. Our current work assessed the antitumor mechanism of λ-COS using BGC-823 cells. Our findings indicated that λ-COS alone did not have a significant impact on BGC-823 cells in vitro; however, it was effective in inhibiting tumor growth in vivo. When THP-1 cells were pre-incubated with λ-COS and used to condition the medium, BGC-823 cells in vitro displayed a concentration-dependent induction of cell apoptosis, nuclear damage, and the collapse of mitochondrial transmembrane potential. These findings suggested that the antineoplastic effect of λ-COS was primarily due to its immunoenhancement property. Treatment with λ-COS was found to significantly enhance the phagocytic capability of macrophages, increase the secretion of TNF-α and IFN-γ, and improve the indexes of spleen and thymus in BALB/c mice. In addition, λ-COS was found to inhibit the growth of BGC-823-derived tumors in vitro by activating the Par-4 signaling pathway, which may be stimulated by the combination of TNF-α and IFN-γ. When used in combination with 5-FU, λ-COS demonstrated enhanced anti-gastric carcinoma activity and improved the immunosuppression induced by 5-FU alone. These findings suggested that λ-COS could be used as an immune-modulating agent for chemotherapy.

Long-term kappa-carrageenan consumption leads to moderate metabolic disorder by blocking insulin binding

Carrageenan (CGN) is a common food additive, and questions have been raised regarding its safety for human consumption. The purpose of this study was to investigate the impact of κ-CGN on glucose intolerance and insulin resistance from the perspective that κ-CGN may interfere with insulin receptor function and affect insulin sensitivity and signaling, thereby leading to body weight loss. The health effects of κ-CGN on C57BL/6 mice were assessed over a 90-d period by monitoring changes in body weight, glucose tolerance, insulin tolerance, fasting glucose and insulin levels, and expression of insulin-pathway-related proteins. Furthermore, HepG2 cells were used to detect the binding of κ-CGN on insulin receptor and measure its effect on downstream signal transduction. In mice, κ-CGN treatment reduced weight gain without affecting food intake. Glucose and insulin tolerance tests revealed that κ-CGN treatment increased blood glucose levels and glycosylated hemoglobin levels, while hepatic and muscle glycogen levels were decreased, suggesting that κ-CGN affected glucose metabolism in mice. Interestingly, κ-CGN treatment did not cause typical diabetic symptoms in mice, as indicated by low levels of fasting and postprandial blood glucose, in addition to normal pancreatic tissue and insulin secretion. The binding studies revealed that κ-CGN could competitively bind to the insulin receptor with FITC-insulin and thereby disrupt PI3K and Akt activation, thus suppressing expression of glucose transporters and glycogen synthase. In summary, this study revealed that κ-CGN reduced weight gain without affecting food intake, but impaired glucose metabolism in mice by interfering with insulin binding to receptors, thereby affecting the sensitivity of insulin and inhibiting the insulin PI3K/AKT signaling pathway, causing non-diabetic weight gain reduction.

Degraded λ-carrageenan activates NF-κB and AP-1 pathways in macrophages and enhances LPS-induced TNF-α secretion through AP-1

BACKGROUND

Carrageenan (CGN), a high molecular weight sulfated polysaccharide, is a traditional ingredient used in food industry. Its degraded forms have been identified as potential carcinogens, although the mechanism remains unclear.

METHODS

The effects of degraded λ-carrageenan (λ-dCGN) on murine RAW264.7 cells and human THP-1-derived macrophage cells were investigated by studying its actions on tumor necrosis factor alpha (TNF-α) secretion, Toll-like receptor 4 (TLR4) expression, and activation of nuclear factor-κb (NF-κB) and activation protein-1 (AP-1) pathways.

RESULTS

We found that λ-dCGN was much stronger than native λ-CGN in the activation of macrophages to secrete TNF-α. Treatment of RAW264.7 cells with λ-dCGN resulted in the upregulation of TLR4, CD14 and MD-2 expressions, but it did not increase the binding of lipopolysacchride (LPS) with macrophages. Meanwhile, λ-dCGN treatment activated NF-κB via B-cell lymphoma/leukemia 10 (Bcl10) and nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) phosphorylation. In addition, λ-dCGN induced extracellular signal-regulated kinases/1/2/mitogen-activated protein kinases (ERK1/2/MAPK) and AP-1 activation. Interestingly, pretreatment of RAW264.7 cells with λ-dCGN markedly enhanced LPS-stimulated TNF-α secretion. This pretreatment resulted in the enhanced phosphorylation of ERK1/2 and c-Jun N-terminal kinase (JNK) and intensified activation of AP-1.

CONCLUSIONS

λ-dCGN induced an inflammatory reaction via both NF-κB and AP-1, and enhanced the inflammatory effect of LPS through AP-1 activation.

GENERAL SIGNIFICANCE

The study demonstrated the role of λ-dCGN to induce the inflammatory reaction and to aggravate the effect of LPS on macrophages, suggesting that λ-dCGN produced during food processing and gastric digestion may be a safety concern.

Review of harmful gastrointestinal effects of carrageenan in animal experiments

In this article I review the association between exposure to carrageenan and the occurrence of colonic ulcerations and gastrointestinal neoplasms in animal models. Although the International Agency for Research on Cancer in 1982 identified sufficient evidence for the carcinogenicity of degraded carrageenan in animals to regard it as posing a carcinogenic risk to humans, carrageenan is still used widely as a thickener, stabilizer, and texturizer in a variety of processed foods prevalent in the Western diet. I reviewed experimental data pertaining to carrageenan's effects with particular attention to the occurrence of ulcerations and neoplasms in association with exposure to carrageenan. In addition, I reviewed from established sources mechanisms for production of degraded carrageenan from undegraded or native carrageenan and data with regard to carrageenan intake. Review of these data demonstrated that exposure to undegraded as well as to degraded carrageenan was associated with the occurrence of intestinal ulcerations and neoplasms. This association may be attributed to contamination of undegraded carrageenan by components of low molecular weight, spontaneous metabolism of undegraded carrageenan by acid hydrolysis under conditions of normal digestion, or the interactions with intestinal bacteria. Although in 1972, the U.S. Food and Drug Administration considered restricting dietary carrageenan to an average molecular weight > 100,000, this resolution did not prevail, and no subsequent regulation has restricted use. Because of the acknowledged carcinogenic properties of degraded carrageenan in animal models and the cancer-promoting effects of undegraded carrageenan in experimental models, the widespread use of carrageenan in the Western diet should be reconsidered.

Syndecan-4 deficiency increases susceptibility to kappa-carrageenan-induced renal damage

SUMMARY

The expression and roles of syndecan-4 in the kidney were investigated. Syndecan-4 expression was detected in the ureteric bud invaginating into the metanephric mesenchyme at 11.5 gestational days, and remained in the collecting ducts, distal renal tubules, glomeruli, and some capillaries between renal tubules until the mature kidney stage. However, organogenesis of the kidney was normal in syndecan-4-deficient (Synd4[-/-]) mice. Although most renal functions of Synd4(-/-) mice were not impaired, a significant increase in susceptibility to kappa-carrageenan-induced renal damage was observed in these mice. kappa-Carrageenan was heavily deposited in the collecting ducts of Synd4(-/-) mice and caused obstructive nephropathy, leading to death of 7 of 24 Synd4(-/-) mice within 7 days after administration, whereas none of 24 Synd4(+/+) mice died. After administration of kappa-carrageenan, blood urea nitrogen of Synd4(-/-) mice was significantly higher than that of Synd4(+/+) mice. Thus, syndecan-4 may function to prevent kappa-carrageenan deposition in the collecting ducts.

Intestinal transport of some macromolecules in food

This review focuses on the intestinal transport of macromolecules in food. Although it is known that neonates have the ability to absorb proteins from the intestine as a means of passive immunization, it has generally been assumed that adults do not retain this capability. A number of studies have shown that the adult mammalian small intestine is capable of transporting a variety of macromolecules in food to a very limited extent. The evidence demonstrating the transport of test substances in the micron-size range across the adult intestinal epithelial barrier is examined for a number of food substances and environmental contaminants. It will be shown that macromolecules can be transported across this barrier by endocytosis; by uptake into the gut-associated lymphoid tissue, and possibly by uptake into the goblet cells. It is considered highly unlikely that large micron-sized particles pass between intestinal cells due to the integrity of the tight junctions between cells that exclude particles in this size range. Quantitative estimates for macromolecular uptake are included along with a discussion of the physiological parameters influencing macromolecular transport.

Effect of orally administered food-grade carrageenans on antibody-mediated and cell-mediated immunity in the inbred rat

Experiments were performed to investigate the immunological consequences associated with the persorption of poorly degradable carregeenans from the diet. Using an inbred strain of rat it was demonstrated histochemically, by the carrageenan-specific Alcian blue staining technique, that small quantities of food-grade carrageenans given at 0.5% in drinking-water for 90 days could penetrate the intestinal barrier of adult animals. This apparently occurred via an intact mucosa in the absence of inflammatory or pathological lesions. The carrageenan was demonstrated in macrophage-like cells present within the villi and lamina propria of the small intestine. The oral administration of kappa, lambda or iota food-grade carrageenans did not affect local (biliary) or systemic antibody responses to gut commensal microorganisms, or to orally-administered sheep erythrocytes. However, when sheep red blood cells were administered parenterally the ensuing anti-sheep red blood cell haemagglutinating antibody response was temporarily suppressed in carrageenan-fed rats. lambda-Carrageenan and iota-carrageenan both significantly (P less than or equal to 0.01 and P less than or equal to 0.05, respectively) reduced the mid-phase (14-28 days) haemagglutinin response; kappa-carrageenan (L100) was less effective but caused significant depression at day 21 (P less than or equal to 0.01). Individual responses were, however, within the control range 35 days after sheep erythrocyte administration, thus indicating the temporary nature of this effect. Although carrageenan administration depressed the anti-sheep erythrocyte antibody response, it did not affect T-cell immune competence as measured by the popliteal lymph node assay for graft-versus-host reactivity.

Electronmicroscopical detection of iota-carrageenan as its ruthenium red complex

Specific detection of iota-Carrageenan (i-CAR) at the ultrastructural level has been obtained by coupling with ruthenium red (RR) - an electron microscopic stain. The i-CAR-RR complex showed electron density on carbon layers. Peritoneal macrophages were treated with the complex and after 3 h it caused the same morphological changes in macrophages as iota-Carrageenan alone. On the surfaces of macrophages, fine filamentous electron dense material - the i-CAR-RR complex - was detected.

Histological and ultrastructural changes following carrageenan injection in the mouse

Mice were injected intravenously with either uncharacterised potassium carrageenan or purified iota carrageenan and tissue was examined by light and electron microscopy 1 hr and 24 hr later. The survival of animals injected with these carrageenans was monitored over a 6-month period. Histological examination of liver and kidney was carried out on animals which died during this time and in the surviving mice at 28 weeks. Histological and ultrastructural evidence of disseminated intravascular coagulation was observed within 24 hr of carrageenan injection. The changes were more severe in animals given potassium carrageenan. Electro-microscopic examination of liver revealed carrageenan within membrane-bound vacuoles in Küpffer cells. These cells were largely unaffected by phagocytosis of iota carrageenan but uptake of potassium carrageenan resulted in marked ultrastructural changes and occasional damage to adjacent hepatocytes. Mice given potassium carrageenan had the poorer long-term survival and many animals in this group showed chronic renal damage with features which suggested obstructive nephropathy. A smaller proportion of mice injected with iota carrageenan displayed similar changes. There was no evidence of long-term hepatotoxicity in either group although both types of carrageenan persisted within liver macrophages for at least 6 months after injection.

Stereomicroscopic and histologic changes in the colon of guinea pigs fed degraded carrageenan

A colitis-like state induced in Guinea Pigs fed degraded carrageenan orally. By means of a combined semimacroscopic and histologic technique the course of the disease was followed during 28 days. The changes were primarily seen and became most prominent in the caecum. The first lesions were observed following 24 hours of treatment as small rounded foci initially with degenerative changes and inflammation in the surface epithelium, later forming superficial focal ulcerations. Ulcerative changes gradually progressed during the experiment, forming linear and later large, geographical ulcerations. Topographically the ulcerative process was strongly related to the larger submucosal vessels. Nonulcerated parts of the mucosa were not changed until following 7-14 days of treatment. The mucosa became bulging, granulated and finally villus-like. Accumulation of macrophages was found under the surface epithelium after 7-17 days. Possible pathogenetic mechanisms are discussed, especially the development of the early lesions and the significance of the macrophages.