Nostoc muscorum is a novel source of microalgal lectins with potent antiviral activity against herpes simplex type-1

Mannose-specific plant and microbial lectins as antiviral agents: A review

Lectins are non-immunological carbohydrate-binding proteins classified on the basis of their structure, origin, and sugar specificity. The binding specificity of such proteins with the surface glycan moiety determines their activity and clinical applications. Thus, lectins hold great potential as diagnostic and drug discovery agents and as novel biopharmaceutical products. In recent years, significant advancements have been made in understanding plant and microbial lectins as therapeutic agents against various viral diseases. Among them, mannose-specific lectins have being proven as promising antiviral agents against a variety of viruses, such as HIV, Influenza, Herpes, Ebola, Hepatitis, Severe Acute Respiratory Syndrome Coronavirus-1 (SARS-CoV-1), Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV) and most recent Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). The binding of mannose-binding lectins (MBLs) from plants and microbes to high-mannose containing N-glycans (which may be simple or complex) of glycoproteins found on the surface of viruses has been found to be highly specific and mainly responsible for their antiviral activity. MBLs target various steps in the viral life cycle, including viral attachment, entry and replication. The present review discusses the brief classification and structure of lectins along with antiviral activity of various mannose-specific lectins from plants and microbial sources and their diagnostic and therapeutic applications against viral diseases.

Identification and statistical optimization of a novel alginate polymer extracted from newly isolated Synechocystis algini MNE ON864447 with antibacterial activity

Cyanobacteria are a potential source of promising secondary metabolites with different biological activities, including antibacterial, antiviral, antifungal, antiprotozoal, and anticancer activities. To combat the emergence of antibiotic resistance, there is an urgent requirement for new drugs, and cyanobacteria metabolites can constitute alternative new antibacterial medication. The chemical complexity of their exopolysaccharides indicates that they have the potential to be bioactive molecules with many biological activities. The present study aimed to produce and optimise a novel alginate polymer from a newly isolated cyanobacterium, S. algini MNE ON864447, in addition to its promising antibacterial activity. We successfully isolated a new cyanobacterium strain, S. algini MNE ON864447 from the Nile River, which produces alginate as an extracellular polymeric substance. The isolated cyanobacterial alginate was identified using a set of tests, including FTIR, TLC, HPLC, GC-MS, and 1H NMR. Plackett-Burman statistical design showed that working volume (X1), the incubation period (X2), and inoculum size (X3) are the most significant variables affecting the production of alginate. The highest alginate production (3.57 g/L) was obtained using 4% inoculum size in 400 mL medium/L conical flask after 20 days of the incubation period. The extracted alginate showed potent antibacterial activity against both Gram-negative and Gram-positive bacteria and Streptococcus mutants (NCTC10449) are the most sensitive tested pathogen for purified cyanobacterial alginate with inhibition zone diameters of 34 ± 0.1 mm at 10 mg/mL of purified alginate while Vibro cholera (NCTC 8021) the lowest sensitive one and showed inhibition zone diameters of 22.5 ± 0.05 mm at the same cyanobacterial alginate concentration. This antibacterial activity is a critical step in the development of antibacterial drugs and presents a new challenge to fight against multi-resistant bacteria.

Anti-inflammatory, remorin-like protein from green marine Macroalga Caulerpa sertularioides (S.G.Gmel.) M.Howe

The most prevalent natural source of hydrocolloids, cosmetics, medications, and nutraceuticals is marine seaweed (macroalgae). Numerous bioactivities, including antiviral, anticancer, anti-inflammatory, and immunomodulatory characteristics, have been found in bioactive substances such as polyphenols and sulfated and non-sulfated polysaccharides. As a result, new start-up projects and industries based on seaweed are emerging in all regions of the world with abundant marine biodiversity. In this current investigation, the anti-inflammatory activity of two different marine macroalgae Caulerpa racemosa (CR) and Caulerpa sertularioides (CS) was evaluated. Consequently, CS demonstrated more anti-inflammatory and antioxidant effects at a lower dose than CR. The IC50 value for DPPH inhibition was 456.1 μg/mL, and 180.9 μg/mL for CS and CR respectively. A similar result was obtained in the case of protein denaturation (PD), membrane stabilization (MS), and protease inhibition (PI) anti-inflammatory assays with 127.2 μg/mL, 135.5 μg/mL, and 71.88 μg/mL for CR, and 66.78 μg/mL, 88.96 μg/mL, and 59.54 μg/mL for CS respectively. Based on the SDS-PAGE, the molecular weight of lectin responsible for the anti-inflammatory activity was determined as 17 kDa. Protein mass fingerprinting was performed for the particular lectin by in-gel trypsin digestion, MALDI-MS analysis, and Mascot peptide mass fingerprinting. Because of this, the unidentified lectin protein was discovered to be a remorin-like protein that shared 65% of its sequence with the remorin-like protein of Aegilops tauschii subsp. tauschii. Therefore, it is the hitherto report on the presence of remorin-like protein from the green macroalga Caulerpa sertularioides.

Antiviral activity of red algae phycocolloids against herpes simplex virus type 2 in vitro

Herpes simplex virus type 2 (HSV-2) is a human infectious agent with significant impact on public health due to its high prevalence in the population and its ability to elicit a wide range of diseases, from mild to severe. Although several antiviral drugs, such as acyclovir, are currently available to treat HSV-2-related clinical manifestations, their effectiveness is poor. Therefore, the identification and development of new antiviral drugs against HSV-2 is necessary. Seaweeds are attractive candidates for such purposes because they are a vast source of natural products due to their highly diverse compounds, many with demonstrated biological activity. In this study, we evaluated the in vitro antiviral potential of red algae extracts obtained from Agarophyton chilense, Mazzaella laminarioides, Porphyridium cruentum, and Porphyridium purpureum against HSV-2. The phycocolloids agar and carrageenan obtained from the macroalgae dry biomass of A. chilense and M. laminarioides and the exopolysaccharides from P. cruentum and P. purpureum were evaluated. The cytotoxicity of these extracts and the surpluses obtained in the extraction process of the agar and carrageenans were evaluated in human epithelial cells (HeLa cells) in addition to their antiviral activity against HSV-2, which were used to calculate selectivity indexes (SIs). Several compounds displayed antiviral activity against HSV-2, but carrageenans were not considered as a potential antiviral therapeutic agent when compared to the other algae extracts with a SI of 23.3. Future assays in vivo models for HSV-2 infection should reveal the therapeutic potential of these algae compounds as new antivirals against this virus.