Anti-diarrhoeal therapeutic potential and safety assessment of sulphated polysaccharide fraction from Gracilaria intermedia seaweed in mice

Natural products for the treatment of neurodegenerative diseases

BACKGROUND

Neurodegenerative diseases are among the most common diseases in older adults worldwide. Alzheimer's disease (AD) and Parkinson's disease (PD) are two of the most common neurodegenerative diseases, and are accompanied by cerebral cortical atrophy, neuronal loss, protein accumulation, and excessive accumulation of metal ions. Natural products exhibit outstanding performance in improving cerebral circulatory disorders, promoting cerebral haematoma absorption, repairing damaged nerve tissue, and improving damaged nerve function. In recent years, studies have shown that neuroinflammatory mechanisms and signalling pathways closely related to the occurrence and development of neurological diseases include microglial activation, nuclear factor-κB (NF-κB) pathway, mitogen activated protein kinases (MAPK) pathway, reactive oxygen pathway, nucleotide binding oligomerisation domain-like receptor protein3 (NLRP3) inflammasomes, toll-like receptor4 (TLR4) pathway, nuclear factor erythroid 2-related factor 2 (Nrf2)/hemeoxygenase-1 (HO-1) pathway, phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway, and intestinal flora. Therefore, this study considered the mechanism of neurological diseases as the starting point to review the mechanism of action of natural products in the prevention and treatment of AD and PD in recent years to provide a theoretical basis for clinical prevention and treatment.

AIM

Natural products are a promising source of novel lead structures that have long been used to treat various nervous system diseases.

METHODOLOGY

This review collected literature on neurological diseases and natural products from 2012 to 2022, which were mainly searched through databases such as ScienceDirect, Springer, PubMed, SciFinder, China National Knowledge Infrastructure (CNKI), Wanfang, Google Scholar, and Baidu Academic. The following keywords were searched: neurological disorders, natural products, signalling pathway, mechanism of action.

RESULTS

This review summarises the pathogenesis of degenerative neurological diseases, recent findings on natural products used in neurodegenerative diseases, and the molecular mechanisms underlying these effects.

Research progress in the preparation, structural characterization, bioactivities, and potential applications of sulfated agarans from the genus Gracilaria

The genus Gracilaria produces 80% of the world's industrial agar. Agar of this genus is a promising biologically active polymer, which has been used in the human diet and folk medicine, alternative for weight loss, treatment of diarrhea, etc. With more attention paid to the genus Gracilaria-sulfated agarans (GSAs), they exhibited multitudinous health benefits in antioxidant, antiviral, antibacterial, prebiotics, anti-tumor, anticoagulant, and antidiabetic. Various preparation procedures of GSAs making the diversities of structure and biological activity. Therefore, this review summarized the isolation, identification, bioactivity potentials, and applications of GSAs, providing a reference to the development of GSAs in functional food and pharmaceutical industry. PRACTICAL APPLICATIONS: The genus Gracilaria is known as a raw material for agar extraction. GSAs are food-grade agaran with the properties of thermoreversible gels at low concentrations, which are commonly used as an additive for making candies as well as raw material for making soup and snacks. They are used in folk medicine to treat diarrhea and other diseases. As an important bioactive macromolecule, GSAs have various biological activities (such as antioxidant, antiviral, antibacterial, probiotic, anti-tumor, anticoagulant, and antidiabetic activities), and have the potential to be developed as functional food and medicine. They could also be used to create innovative agar-based products such as antibacterial films and drug carriers.

Insights into agar and secondary metabolite pathways from the genome of the red alga Gracilaria domingensis (Rhodophyta, Gracilariales)

Gracilariales is a clade of florideophycean red macroalgae known for being the main source of agar. We present a de novo genome assembly and annotation of Gracilaria domingensis, an agarophyte alga with flattened thallus widely distributed along Central and South American Atlantic intertidal zones. In addition to structural analysis, an organizational comparison was done with other Rhodophyta genomes. The nuclear genome has 78 Mbp, with 11,437 predicted coding genes, 4,075 of which did not have hits in sequence databases. We also predicted 1,567 noncoding RNAs, distributed in 14 classes. The plastid and mitochondrion genome structures were also obtained. Genes related to agar synthesis were identified. Genes for type II galactose sulfurylases could not be found. Genes related to ascorbate synthesis were found. These results suggest an intricate connection of cell wall polysaccharide synthesis and the redox systems through the use of L-galactose in Rhodophyta. The genome of G. domingensis should be valuable to phycological and aquacultural research, as it is the first tropical and Western Atlantic red macroalgal genome to be sequenced.

Preventive Effect of Depolymerized Sulfated Galactans from Eucheuma serra on Enterotoxigenic Escherichia coli-Caused Diarrhea via Modulating Intestinal Flora in Mice

In this work, the preventive effect of depolymerized sulfated polysaccharides from Eucheuma serra (DESP) on bacterial diarrhea by regulating intestinal flora was investigated in vivo. Based on the enterotoxigenic Escherichia coli (ETEC)-infected mouse diarrhea model, DESP at doses ranging from 50 mg/kg to 200 mg/kg alleviated weight loss and decreased the diarrhea rate and diarrhea index. Serological tests showed that the levels of inflammation-related factors were effectively suppressed. Furthermore, the repaired intestinal mucosa was verified by morphology and pathological tissue section observations. Compared with the model group, the richness and diversity of the intestinal flora in the DESP group increased according to the 16S rRNA high-throughput sequencing of the gut microbiota. Specifically, Firmicutes and Actinobacteria increased, and Proteobacteria decreased after DESP administration. At the family level, DESP effectively improved the abundance of Lactobacillaceae, Bifidobacteriaceae, and Lachnospiraceae, while significantly inhibiting the growth of Enterobacteriaceae. Therefore, the antimicrobial diarrhea function of DESP may be related to the regulation of intestinal microbiota.

Sulfated polysaccharide from Gracilaria caudata reduces hypernociception and inflammatory response during arthritis in rodents

Polysaccharide from marine alga Gracilaria caudata has potential health benefits, such as anti-inflammatory, gastroprotective and antidiarrheal effects. Here, we investigated the effect of a sulfated polysaccharide from G. caudata (SP-GC) on hypernociception and inflammatory response in arthritis models. The animals received SP-GC (3, 10 or 30 mg/kg) 1 h before tibio-tarsal injection of zymosan. Hypernociception, histopathology, edema, vascular permeability, myeloperoxidase (MPO) activity, cell influx, interleukin (IL)-1β and nitric oxide (NO) levels were evaluated in acute phase. In another protocol, animals received SP-GC (30 mg/kg) 2 h post-complete Freund's adjuvant (CFA). Hypernociception, edema and arthritis index were determined in acute, sub-chronic and chronic phases. Rota-rod test measured the motor performance. SP-GC significantly reduced, in a dose-dependent manner, the zymosan-induced hypernociception with maximal effect at 30 mg/kg. The microscopic inflammation, joint edema, MPO activity, cell influx, IL-1β and NO levels were also reduced by SP-GC. In the CFA-induced arthritis, SP-GC inhibits the hypernociception, edema and arthritic index in acute, sub-chronic and chronic phases. SP-GC did not alter the motor performance of animals. In conclusion, SP-GC exerts protective effect in models of arthritis due to the modulation of cell influx, IL-1β and NO levels, culminating in the reduction of hypernociception and edema.

Antidiarrheal activity of farnesol in rodents: Pharmacological actions and molecular docking

Diarrhea is a condition in which the individual has about three or more daily bowel movements, followed by changes in stool consistency. It is currently considered as one of the worst public health problems due to the number of cases and deaths involved and difficulty of treatment. Thus, the use of natural products is an alternative for new treatments. Among these possibilities is Farnesol (C₁₅H₂₆O), a sesquiterpene found in different herbal species that has known biological activities. The objective of this study was to evaluate the antidiarrheal activity of Farnesol (FOH). Initially, FOH activity was evaluated in models of diarrhea and enteropooling induced by castor oil and PGE₂. To evaluate motility, the opioid and cholinergic pathways were studied. In addition, the effect of FOH was investigated in the secretion model in intestinal loops treated with cholera toxin. FOH was evaluated for the ability to absorb fluids in intestinal loops and interact with GM1 receptors using the ELISA method and molecular docking. The dose of 50 mg/kg of FOH showed the best results in all antidiarrheal activity tests with castor oil and PGE₂, being considered as the standard dose, reducing motility by anticholinergic mechanisms. There was a reduction in fluid secretion when FOH interacted directly with GM1 receptors; cholera toxin and molecular docking showed strong interaction between farnesol and these targets. In view of the results presented, the antidiarrheal activity occurs through anticholinergic, anti-inflammatory and anti-secretory action, making farnesol a potential candidate for the development of a new drug to treat diarrheal diseases.

In vitro fermentation of Gracilaria lemaneiformis sulfated polysaccharides and its agaro-oligosaccharides by human fecal inocula and its impact on microbiota

The fermentation behaviour of sulfated polysaccharides (GLP) and their agaro-oligosaccharides (GLO) derived from Gracilaria lemaneiformis were examined. During in vitro fermentation, GLP and GLO increased the concentrations of short chain fatty acids (SCFAs) and modulated the composition and diversity of gut microorganisms compared with control groups. GLP increased the abundance of Bacteroidetes and decreased the abundance of Firmicutes, while GLO increased the abundance of Firmicutes and Actinobacteria. Moreover, the abundances of potential pathogenic bacteria were reduced. Molecular weight and intrinsic viscosity of GLP decreased significantly from 2.15 × 10⁵ to 1.22 × 10⁵ Da, 374.45-113.91 mL/g, respectively. Furthermore, GLP was degraded into smaller degree of polymerization of oligosaccharides, with no significant change observed in GLO. Overall, this study revealed GLP and GLO could be beneficial for gastrointestinal tract by producing SCFAs and modulating intestinal microbes, indicating GLP and GLO are potentially sources of prebiotics in functional foods.

Biopolymer Extracted from Anadenanthera colubrina (Red Angico Gum) Exerts Therapeutic Potential in Mice: Antidiarrheal Activity and Safety Assessment

Anadenanthera colubrina var. cebil (Griseb.) Altschul (Fabaceae family), commonly known as the red angico tree, is a medicinal plant found throughout Brazil’s semi-arid area. In this study, a chemical analysis was performed to investigate the antidiarrheal activity and safety profile of red angico gum (RAG), a biopolymer extracted from the trunk exudate of A. colubrina. Upon FT-IR spectroscopy, RAG showed bands in the regions of 1608 cm⁻¹, 1368 cm⁻¹, and 1029 cm⁻¹, which relate to the vibration of O–H water molecules, deformation vibration of C-O bands, and vibration of the polysaccharide C-O band, respectively, all of which are relevant to glycosidic bonds. The peak molar mass of RAG was 1.89 × 10⁵ g/mol, with the zeta potential indicating electronegativity. RAG demonstrated high yield and solubility with a low degree of impurity. Pre-treatment with RAG reduced the total diarrheal stool and enteropooling. RAG also enhanced Na+/K+-ATPase activity and reduced gastrointestinal transit, and thereby inhibited intestinal smooth muscle contractions. Enzyme-Linked Immunosorbent Assay (ELISA) demonstrated that RAG can interact with GM1 receptors and can also reduce E. coli-induced diarrhea in vivo. Moreover, RAG did not induce any signs of toxicity in mice. These results suggest that RAG is a possible candidate for the treatment of diarrheal diseases.

The anti-diarrhea activity of red algae-originated sulphated polysaccharides on ETEC-K88 infected mice

Polysaccharides from red algae Porphyra haitanensis and Gracilaria lemaneiformis possess various bioactive functions, however, their anti-diarrhea activity remains incompletely defined. In the current study, sulphated polysaccharides were extracted by high pressure treatment plus ethanol precipitation from these two algae, and named PHSP_(hp) and GLSP_(hp), respectively. PHSP_(hp) and GLSP_(hp) showed decreased viscosity and molecular weight. Meanwhile, they have a certain immunomodulatory effect on wound healing and migration of RAW264.7 cells. Moreover, they significantly increased the secretion of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). A BALB/c model infected by enterotoxigenic Escherichia coli (ETEC)-K88 was also established to evaluate the anti-diarrhea activity of PHSP_(hp) and GLSP_(hp). The results showed that PHSP_(hp) and GLSP_(hp) were able to alleviate mice diarrhea symptoms. Meanwhile, they inhibited the release of pro-inflammatory cytokines and suppressed the secretion of immunoglobulin A via reducing the population of B cells. In addition, the nitroblue tetrazolium levels of mouse serum were decreased. Taken together, PHSP_(hp) and GLSP_(hp) alleviated the inflammatory response of ETEC-K88-induced diarrhea through both specific and non-specific immunity. Sulphated polysaccharides from red algae may be used as functional food components for remitting diarrhea.

Polysaccharides from red algae Porphyra haitanensis and Gracilaria lemaneiformis possess various bioactive functions, however, their anti-diarrhea activity remains incompletely defined.

Antidiarrheal activity of α-terpineol in mice

Diarrhea is one of the leading causes of infant death in the world accounting for high child mortality rate. It is also present in different pathophysiologies related to several etiological agents. The aim of this study is to investigate the antidiarrheal effect of α -Terpineol (α-TPN) in different diarrhea models in rodents. The antidiarrheal effect of α-TPN in the treatment of acute diarrhea and enteropooling induced by castor oil or PGE₂ in Swiss mice pretreated orally with saline (NaCl 0.9%), Loperamide (5 mg/kg) and α-TPN (6.25, 12.5, 25 and 50 mg/kg) was analyzed. Additionally, parameters of severity, total weight of faeces and post-treatment for 4 h were evaluated. Modulation of the opioid and cholinergic pathways was performed and intestinal transit model using activated charcoal as marker was also used. The effect of α-TPN on secretory diarrhea was investigated using the model of fluid secretion in intestinal loops isolated from cholera toxin-treated mice. α-TPN showed antidiarrheal effect (*p < 0.05), reducing the total stool amount (*55%, *48%, *44%, *24%) and diarrheal (*47%, *66%; *56%, 10%) respectively for the doses tested. All doses investigated in the enteropooling test presented significant changes (*46%, *78%, *66%, *41% respectively) in relation to the control. α-TPN through the muscarinic pathway reduced the gastrointestinal transit (*31%), besides inhibiting PGE₂-induced diarrhea (*39%). α-TPN also reduced fluid formation and loss of Cl^- ions, by interacting directly with GM1 receptors and cholera toxin, thus increasing the uptake of intestinal fluids. The results suggest an anti-diarrheal activity of α-TPN due to its anticholinergic action, ability to block PGE₂ and GM1 receptors and interaction with cholera toxin in secretory diarrhea, making it a promising candidate drug for the treatment of diarrheal diseases.

Antidiarrheal activity of a novel sulfated polysaccharide from the red seaweed Gracilaria cervicornis

ETHNOPHARMACOLOGICAL RELEVANCE

The use of marine seaweeds as a source of natural compounds with medicinal purposes is increasing in Western countries in the last decades, becoming an important alternative in the traditional medicine of many developing countries, where diarrhea still remains a severe public health problem, with high rates of mortality and morbidity. Sulfated polysaccharides (PLS) extracted from red seaweeds can exhibit therapeutic effects for the treatment of gastrointestinal disorders. Thus, the pharmacological properties of the PLS from Gracilaria cervicornis, an endemic seaweed found in the Brazilian northeast coast, was evaluated as an alternative natural medication for diarrhea.

AIM OF THE STUDY

This study aimed to evaluate the antidiarrheal activity of sulfated polysaccharides (PLS) extracted from the red seaweed G. cervicornis in Swiss mice pre-treated with castor oil or cholera toxin.

MATERIALS AND METHODS

The seaweed Gracilaria cervicornis was collected at Flecheiras beach (city of Trairí, State of Ceará, Brazil) and the PLS was obtained through enzymatic extraction and administered in mice (25-30 g) before diarrhea induction with castor oil or cholera toxin. For the evaluation of the total number of fecal output and diarrheal feces, the animals were placed in cages lined with adsorbent material. The evaluation of intestinal fluid accumulation (enteropooling) on castor oil-induced diarrhea in mice occurred by dissecting the small intestine and measuring its volume. The determination of Na⁺/K⁺-ATPase activity was measured in the small intestine supernatants by colorimetry, using commercial biochemistry kits. The gastrointestinal motility was evaluated utilizing an activated charcoal as a food tracer. The intestinal fluid secretion and chloride ion concentration were evaluated in intestinal closed loops in mice with cholera toxin-induced secretory diarrhea. The binding ability of PLS with GM1 and/or cholera toxin was evaluated by an Enzyme-Linked Immunosorbent Assay (ELISA).

RESULTS

The G. cervicornis PLS showed antidiarrheal effects in both acute and secretory diarrhea, reducing the total number of fecal output, diarrheic stools, intestinal fluid accumulation, and increasing small intestine Na⁺/K⁺-ATPase activity on castor oil-induced diarrhea. However, the PLS did not affect gastrointestinal motility, indicating that this compound has a different action mechanism than loperamide. In secretory diarrhea, the PLS decreased intestinal fluid secretion and small intestine chloride excretion, binding with GM1 and/or cholera toxin and blocking their attachment to the enterocyte cell surface.

CONCLUSIONS

In conclusion, PLS has a significant antidiarrheal effect in acute and secretory diarrhea. Further investigation is needed towards its use as a natural medicine to treat diarrhea.

Preliminary characterization of the structure and immunostimulatory and anti-aging properties of the polysaccharide fraction ofHaematococcus pluvialis

In this study, a polysaccharide fraction (HPP-c3-s1) was obtained from Haematococcus pluvialis using DEAE-52 anion exchange and Sephacryl S400 chromatographies. The structure of HPP-c3-s1 was partially characterized and its biological activity was investigated. HPP-c3-s1 is a homogeneous polysaccharide with a molecular weight of 23 413 kDa as determined by high-performance gel permeation chromatography and polyacrylamide gel electrophoresis. Periodate oxidation and Smith degradation analysis combined with GC-MS determined that HPP-c3-s1 contains 1 → 2, 1 → 3, 1 → 4, and probably a few 1 → 6 glycosyl linkages. Fourier transform infrared spectroscopy and nuclear magnetic resonance analyses indicate HPP-c3-s1 is a pyranose containing an amino and O-acetyl group. The sugar chains in HPP-c3-s1 contain both α and β glycosidic configurations, where the β configuration is the primary form. It was observed that the HPP-c3-s1 nanostructure had linear and branched forms at a concentration of 5 μg mL⁻¹ and created different sized aggregates at a higher concentration of 50 μg mL⁻¹. Furthermore, HPP-c3-s1 had significant immunostimulatory effects on splenocytes and B lymphocytes. In assays assessing anti-aging effects, HPP-c3-s1 extended the mean survival of Caenorhabditis elegans without adversely affecting reproduction. In addition, treatment with HPP-c3-s1 resulted in delays in age-related physiologic parameters, including body movement, rates of head swing and body bending, and accumulation of intestinal lipofuscinosis in C. elegans. Overall, these results suggest HPP-c3-s1 has remarkable immunomodulatory and anti-aging properties that may serve as the basis for development of functional foods and dietary supplements.

HPP-c3-s1 is a pyranose with an average molecular weights of 23 413 kDa, which exhibited siginificant immunomodulatory and anti-aging activities.