Protective efficacy of a sulfated sialyl lipid (NMSO3) against human rotavirus-induced diarrhea in a mouse model

Advances in the development of antivirals for rotavirus infection

Rotavirus (RV) causes 200,000 deaths per year and imposes a serious burden to public health and livestock farming worldwide. Currently, rehydration (oral and intravenous) remains the main strategy for the treatment of rotavirus gastroenteritis (RVGE), and no specific drugs are available. This review discusses the viral replication cycle in detail and outlines possible therapeutic approaches including immunotherapy, probiotic-assisted therapy, anti-enteric secretory drugs, Chinese medicine, and natural compounds. We present the latest advances in the field of rotavirus antivirals and highlights the potential use of Chinese medicine and natural compounds as therapeutic agents. This review provides an important reference for rotavirus prevention and treatment.

The Potential for Sialic Acid and Sialylated Glycoconjugates as Feed Additives to Enhance Pig Health and Production

Simple Summary

This review discusses the current challenges in the pig industry and the potential nutritional significance of sialic acid (Sia) and glycoconjugates (Sia-GC’s) for pig health and nutrition. Sia is a nine-carbon acidic sugar which is present in various organs and body fluids of humans and animals. Sias contribute to many beneficial biological functions including pathogen resistance, immunomodulation, gut microbiota development, gut maturation, anti-inflammation and neurodevelopment. The role of Sias in regulating the metabolism of pigs has seldom been reported. However, we have documented significant beneficial effects of specific Sia-GC’s on health and production performance of sows and piglets. These findings are reviewed in relation to other studies while noting the beneficial effects of the inclusion of Sia, Sia containing oligosaccharide or the sialo-protein lactoferrin in the diets of gilts and sows. The importance of the passive transfer of of Sia and Sia-GC’s through milk to the young and the implications for their growth and development is also reviewed. This information will assist in optimizing the composition of sow/gilt milk replacers designed to increases the survival of IUGR piglets or piglets with dams suffering from agalactia, a common problem in pig production systems worldwide.

Abstract

Swine are one of the most important agricultural species for human food production. Given the significant disease challenges confronting commercial pig farming systems, introduction of a new feed additive that can enhance animal performance by improving growth and immune status represents a major opportunity. One such candidate is sialic acid (Sia), a diverse family of nine-carbon acidic sugar, present in various organs and body fluid, as well as an essential structural and functional constituent of brain ganglioside of humans and animals. Sias are key monosaccharide and biomarker of sialylated milk oligosaccharide (Sia-MOS’s), sialylated glycoproteins and glycolipids in milk and all vertebrate cells. Sias accomplish many critical endogenous functions by virtue of their physiochemical properties and via recognition by intrinsic receptors. Human milk sialylated glycoconjugates (Sia-GC’s) are bioactive compounds known to act as prebiotics that promote gut microbiota development, gut maturation, pathogen resistance, immunomodulation, anti-inflammation and neurodevelopment. However, the importance of Sia in pig health, especially in the growth, development, immunity of developing piglet and in pig production remains unknown. This review aims to critically discuss the current status of knowledge of the biology and nutritional role of Sia and Sia-GC’s on health of both female sow and newborn piglets.

Broad-spectrum neutralization of avian influenza viruses by sialylated human milk oligosaccharides: in vivo assessment of 3'-sialyllactose against H9N2 in chickens

Two sialylated human milk oligosaccharides (SHMOs) 3'-sialyllactose (3'-SL) and 6'-sialyllactose (6'-SL) were accessed for their possible antiviral activity against six different subtypes of thirteen avian influenza (AI) viruses in vitro. 3'-SL exhibited promising antiviral activity against almost all subtypes of tested AI viruses in hemagglutination inhibition assay, whereas 6'-SL showed activity against few selected H1N1, H1N2, and H3N2 subtype strains. 3'-SL has minimum inhibitory concentration values of 15.62 mM or less in more than half of the viruses examined. 3'-SL also showed effective inactivation of H9N2 Korea isolate (A/Chicken/Korea/MS96/1996) at 12.5 mM concentration in Madin Darby Canine Kidney (MDCK) cell line. Thus, 3'-SL was further studied for in vivo study against H9N2 virus in pathogen free chicken experiment models. In vivo study exhibited improved clinical symptoms on H9N2 infected chickens when treated with 3'-SL. Moreover, treating chickens with 3'-SL resulted in complete elimination of H9N2 viruses within 24 h of virus infection (0.8 HAU of H9N2). Indirect ELISA assay confirmed complete wash-out of H9N2 viruses from the colon after neutralization by 3'-SL without entering the blood stream. These in vivo results open up possible applications of 3'-SL for the prevention of AI virus infections in birds by a simple cleansing mechanism.

Functional role and mechanisms of sialyllactose and other sialylated milk oligosaccharides

Human milk is a rich source of oligosaccharides. Acidic oligosaccharides, such as sialyllactose (SL), contain sialic acid (SA) residues. In human milk, approximately 73% of SA is bound to oligosaccharides, whereas only 3% is present in free form. Oligosaccharides are highly resistant to hydrolysis in the gastrointestinal tract. Only a small portion of the available oligosaccharides in breast milk is absorbed in the neonatal small intestine. SL and sialylated oligosaccharides are thought to have significant health benefits for the neonate, because of their roles in supporting resistance to pathogens, gut maturation, immune function, and cognitive development. The need for SA to allow proper development during the neonatal period is thought to exceed the endogenous synthesis. Therefore, these structures are important nutrients for the neonate. Based on the potential benefits, SL and sialylated oligosaccharides may be interesting components for application in infant nutrition. Once the hurdle of limited availability of these oligosaccharides has been overcome, their functionality can be explored in more detail, and supplementation of infant formula may become feasible.

Development of liposomal nanoconstructs targeting P-selectin (CD62P)-expressing cells by using a sulfated derivative of sialic acid

PURPOSE

NMSO3, a sulfated derivative of sialic acid, is a specific inhibitor for P-selectin (CD62P)-mediated cell adhesion. We attempted to apply liposomes modified with NMSO3 for selective targeting of activated platelets.

METHODS

The binding of fluorescently labeled NMSO3-containing liposomes (NMSO3-liposomes) to CHO cells expressing P-selectin (CHO-P cells) and activated platelets were examined. The distribution of NMSO3-liposomes incorporated into the cells was observed by fluorescence microscopy.

RESULTS

The binding assay revealed that NMSO3-liposomes specifically bound to immobilized P-selectin and CHO-P cells in a dose-dependent manner. The binding of NMSO3-liposomes to CHO-P cells was much stronger than that to the parental CHO-K1 cells. Fluorescence microscopic observation showed that NMSO3-liposomes were incorporated into CHO-P cells after the binding and distributed throughout the cytoplasm of the cell. NMSO3-liposomes bound more strongly to thrombin-activated platelets than to resting platelets, as assessed by flow cytometry.

CONCLUSIONS

These results suggest that NMSO3-liposomes can be applied for selective drug delivery to activated platelets.

Anti-rotavirus effects by combination therapy of stevioside and Sophora flavescens extract

Anti-rotaviral activities of Sophora flavescens extract (SFE) and stevioside (SV) from Stevia rebaudiana Bertoni either singly or in various combinations were examined in vitro and in vivo using a porcine rotavirus G5[P7] strain. Combination of SFE and SV inhibited in vitro virus replication more efficiently than each single treatment. In the piglet model, SV had no effect on rotavirus enteritis, whereas SFE improved but did not completely cure rotaviral enteritis. Interestingly, combination therapy of SFE and SV alleviated diarrhea, and markedly improved small intestinal lesion score and fecal virus shedding. Acute toxicity tests including the piglet lethal dose 50, and body weight, organ weight and pathological changes for the combination therapy did not show any adverse effect on the piglets. These preliminary data suggest that the combination therapy of SV and SFE is a potential curative medication for rotaviral diarrhea in pigs. Determination of the efficacy of this combination therapy in other species including humans needs to be addressed in the future.

Multiple-dose therapy with bovine colostrum confers significant protection against diarrhea in a mouse model of human rotavirus-induced gastrointestinal disease

Rotavirus is the most important etiologic agent of severe gastroenteritis. Previously, we reported that skimmed and concentrated bovine late colostrum (SCBLC) obtained from normal unimmunized cows at 6 to 7d after parturition effectively prevented against human rotavirus (HRV)-induced severe gastroenteritis in vivo, when administered as a single dose 60 min before viral inoculation. In the present study, we examined the efficacy of multiple administrations of SCBLC at smaller dosages after viral inoculation in vivo. We demonstrate that multiple administrations within 24h after virus inoculation resulted in earlier recovery from diarrheal symptoms, in an administration frequency-dependent manner. Furthermore, we investigated whether isolated IgG anti-HRV activity in SCBLC was equivalent to that of IgG isolated from bovine mature milk as measured by in vitro activity assays. We found that IgG-containing fractions from SCBLC and mature milk exhibited approximately the same level of anti-HRV activity. We concluded that the SCBLC contains a high level of IgG against HRV-induced severe gastroenteritis, which will be possible to use in protective effects in immunocompromised hosts, such as children and the elderly. Multiple doses of SCBLC during the early stages of infection or lower dosage of SCBLC given as a single dose both resulted in relief of diarrheal symptoms.

Targeting RSV with vaccines and small molecule drugs

Respiratory syncytial virus (RSV) is the most significant cause of pediatric respiratory infections. Palivizumab (Synagis®), a humanized monoclonal antibody, has been used successfully for a number of years to prevent severe RSV disease in at-risk infants. However, despite intense efforts, there is no approved vaccine or small molecule drug for RSV. As an enveloped virus, RSV must fuse its envelope with the host cell membrane, which is accomplished through the actions of the fusion (F) glycoprotein, with attachment help from the G glycoprotein. Because of their integral role in initiation of infection and their accessibility outside the lipid bilayer, these proteins have been popular targets in the discovery and development of antiviral compounds and vaccines against RSV. This review examines advances in the development of antiviral compounds and vaccine candidates.

Evaluation of antirotavirus activity of flavonoids

Flavonoids are dietary components and the most ubiquitous phenolic compounds found in nature, showing a range of pharmacological activities including antiviral action. This study describes the antiviral screening of 60 different flavones and flavonols against human rotavirus (Wa-1 strain) as well as their cytotoxicity in MA104 cells. Cytotoxicity was investigated by cell morphology assessment and antirotavirus activity by cytopathic effect inhibition. Results were expressed as CC₅₀ and IC₅₀, respectively, in order to calculate the selectivity index (SI = CC₅₀/IC₅₀) of each compound. Structure–activity relationships (SAR) were proposed based on antirotavirus activity.

In vitro and in vivo evaluation of the efficacy of bovine colostrum against human rotavirus infection

We found that skimmed and concentrated bovine late colostrum (SCBLC) obtained from normal cows at 6-7 d after parturition exhibited high potency in inhibiting replication of human rotavirus (HRV) in vitro. Furthermore, prophylactic oral administration of SCBLC once before inoculation of HRV prevented the development of diarrhea in suckling mice in vivo. SCBLC from normal cows might be useful in the prevention of HRV-induced severe gastroenteritis in immunocompromised hosts.

Role of sialic acids in rotavirus infection

Rotaviruses are the leading cause of childhood diarrhea. The entry of rotaviruses into the host cell is a complex process that includes several interactions of the outer layer proteins of the virus with different cell surface molecules. The fact that neuraminidase treatment of the cells, or preincubation of the virus with sialic acid-containing compounds decrease the infectivity of some rotavirus strains, suggested that these viruses interact with sialic acid on the cell surface. The infectivity of some other rotavirus strains is not affected by neuraminidase treatment of the cells, and therefore they are considered neuraminidase-resistant. However, the current evidence suggests that even these neuraminidase-resistant strains might interact with sialic acids located in context different from that of the sialic acids used by the neuraminidase-sensitive strains. This review summarizes our current knowledge of the rotavirus-sialic acid interaction, its structural basis, the specificity with which distinct rotavirus isolates interact with sialic acid-containing compounds, and also the potential use of these compounds as therapeutic agents.

The synthesis and biological evaluation of lactose-based sialylmimetics as inhibitors of rotaviral infection

Rotaviruses are the most significant cause of gastroenteritis in young children and are responsible for over 600,000 infant deaths annually. The rotaviral haemagglutinin protein (VP8*) of some strains has been implicated in early recognition and binding events of host cell-surface sialoglycoconjugates, and is therefore an attractive target for potential therapeutic intervention. Since N-acetylneuraminic acid alpha(2,3)-linked to galactose is believed to be the minimum binding epitope of rotavirus to host cells, we report here our development of an efficient and flexible synthetic route to a range of lactose-based sialylmimetics of alpha(2,3)-linked thiosialosides. These compounds were biologically evaluated as inhibitors of rotaviral infection using an in vitro neutralisation assay. The results suggest that these lactose-based sialylmimetics are not inhibitors of the rhesus rotavirus strain; however, they do exhibit modest inhibition of the human (Wa) strain, presumably through inhibition of the rotaviral adhesion process.

Supplemental dietary whey protein concentrate reduces rotavirus-induced disease symptoms in suckling mice

Rotavirus-induced diarrhea is a common infection that results in the death of nearly 500,000 children annually. Currently, no large-scale preventative treatments or vaccines exist. Because some whey protein concentrates (WPC) were shown to contain bioactive ingredients that may activate immune cells and/or prevent infection, the current study was conducted to assess whether the proprietary WPC IMUCARE (WPC-IC) could protect against rotavirus. Suckling BALB/c mice were treated by gavage once daily with WPC-IC or with the control protein bovine serum albumin from the age of 9 to 17 d, and were infected with murine rotavirus at the age of 11 d. Disease symptoms were graded as mild, moderate, or severe, and viral shedding was measured in fecal samples during the postinfection period. Severe diarrhea occurred in 63% of control mice; this was significantly reduced to 36% in WPC-IC-fed mice. Severe diarrhea occurred for a 4-d period in the control group but only for a 2-d period in the WPC-IC group. Although the mean viral load per mouse did not differ between the groups, the proportion of mice shedding high levels of the virus in the feces postinfection was significantly lower in the WPC-IC group on d 13, 16, and 17, and significantly higher on d 14. Rotavirus-specific antibody levels in serum and gut fluid did not differ between groups. Thus, prophylactic treatment with WPC-IC may reduce rotaviral disease by decreasing the prevalence of severe diarrhea and by decreasing the time period during which severe symptoms and high viral shedding occur.

Localization of sulfated sialic acids in the dentinal tubules during tooth formation in mice

Lectin-like properties of the major enamel protein amelogenin suggest that it binds to glycoconjugates in dentinal tubules released at the dentin-enamel junction (DEJ) during enamel formation. Therefore, a detailed mapping of glycosylation in dentinal tubules during tooth formation was undertaken using histochemistry and lectin-binding assays. The tubular content exhibited sialidase-susceptible gamma-metachromasia with Toluidine Blue (pH 2.5) and staining with Alcian Blue (pH 1.0). The presence of sulfate groups was confirmed by benzidine reactions (Bracco-Curti's and tetrazonium assays). Alpha2,3-, alpha2,6- and alpha2,8-sialidases entirely abolished staining with the benzidine reactions. The presence of sialic acids in dentinal tubules was confirmed with the Bial's reaction and sialidase-susceptible binding of Limax flavus lectin suggesting that sialic acids are the major sulfated sugars in the glycoconjguates. Immunostaining with the monoclonal antibody 5-D-4 before and after treatment with chondroitin-4- and chondroitin-6-sulfatase confirmed the presence of keratan sulfate (KS), a sialylated proteoglycan, in dentinal tubules. We suggest that sulfated sialic acids are part of the KSs. The sulfated glycoconjugates are also found in dentin and the DEJ but not in predentin suggesting that amelogenin binds to the sialoconjugate during enamel formation.

Coexpression of hepatitis C virus E1 and E2 chimeric envelope glycoproteins displays separable ligand sensitivity and increases pseudotype infectious titer

We have previously reported that a pseudotype virus generated by reconstitution of hepatitis C virus (HCV) chimeric envelope glycoprotein E1-G or E2-G on the surface of a temperature-sensitive mutant of vesicular stomatitis virus (VSVts045) interacts independently with mammalian cells to initiate infection. Here, we examined whether coexpression of both of the envelope glycoproteins on pseudotype particles would augment virus infectivity and/or alter the functional properties of the individual subunits. Stable transfectants of baby hamster kidney (BHK) epithelial cells expressing either one or both of the chimeric envelope glycoproteins of HCV on the cell surface were generated. The infectious titer of the VSV pseudotype, derived from a stable cell line incorporating both of the chimeric glycoproteins of HCV, was approximately 4- to 5-fold higher than that of a pseudotype bearing E1-G alone or approximately 25- to 30-fold higher than that of E2-G alone when assayed with a number of mammalian cell lines. Further studies suggested that that the E1-G/E2-G or E2-G pseudotype was more sensitive to the inhibitory effect of heparin than the E1-G pseudotype. Treatment of the E1-G/E2-G pseudotype with a negatively charged sulfated sialyl lipid (NMSO3) displayed a approximately 4-fold-higher sensitivity to neutralization than pseudotypes with either of the two individual glycoproteins. In contrast, VSVts045, used as a backbone for the generation of pseudotypes, displayed at least 20-fold-higher sensitivity to NMSO3-mediated inhibition of virus plaque formation. The effect of low-density lipoprotein on the E1-G pseudotype was greater than that apparent for the E1-G/E2-G pseudotype. The treatment of cells with monoclonal antibodies to CD81 displayed an inhibitory effect upon the pseudotype with E1-G/E2-G or with E2-G alone. Taken together, our results indicate that the HCV E1 and E2 glycoproteins have separable functional properties and that the presence of these two envelope glycoproteins on VSV/HCV pseudotype particles increases infectious titer.

Isolation and characterization of NMSO3-resistant mutants of respiratory syncytial virus

We obtained two mutant strains of respiratory syncytial virus (RSV) which showed resistance against NMSO3 after 15 and 33 passages, respectively, in HEp-2 cells in the presence of 6.8 microM of NMSO3. The EC50 values of NMSO3 for the resistant virus strains were 0.48 and 0.93 microM, that is 4.8-9.3 times higher than that of the parent strain (EC50 = 0.1 microM). The most resistant strain also showed resistance against heparin but was sensitive to dextran sulfate and a polyoxotungstate, PM-523. In order to determine whether the acquisition of resistance to NMSO3 was the result of the accumulation of genetic changes of virus, we sequenced the G- and F-protein genes. In comparison with the standard type of RSV strains, we identified changes of 10 amino acids in the G protein including those at the central conserved segment. However, we did not observe any particular changes in the amino acid sequence of the F-protein of the resistant strains. From these results, we conclude that NMSO3 inhibits the G-protein interaction to the receptor. The mutations in the G-protein may result in the observed phenotypic resistance of RSV towards NMSO3.

Inhibition of P-selectin-mediated cell adhesion by a sulfated derivative of sialic acid

P-selectin, a carbohydrate-binding cell adhesion molecule expressed on activated endothelial cells and platelets, plays a key role in the recruitment of leukocytes to inflammatory and hemorrhagic sites. It simultaneously recognizes a sialic acid-containing carbohydrate chain and the sulfated tyrosine residues of a specific counter-receptor expressed on the leukocyte surface. We examined the inhibitory effects of a synthetic sulfated derivative of sialic acid (NMSO3) on P-selectin-mediated cell adhesion and found the following: (1) P-selectin/IgG chimera bound to immobilized NMSO3. (2) The binding of P-selectin/IgG chimera to purified P-selectin glycoprotein ligand-1 was inhibited by soluble NMSO3. (3) The adhesion of HL60 cells to P-selectin-expressing CHO cells was inhibited by NMSO3. (4) NMSO3 inhibited P-selectin-induced tumor necrosis factor-alpha production in monocytes and activated platelet-induced generation of reactive oxygen species in neutrophils. In conclusion, NMSO3 acts as a specific inhibitor for P-selectin-mediated cell adhesion and for adhesion-dependent leukocyte activation.