Trypsin is inhibited by phytocompounds liquiritin and terpinen-4-ol from the herb Glycyrrhiza glabra: in vitro and in silico studies

Serine proteases are a class of hydrolytic enzymes involved in various physiological functions like digestion, coagulation, fibrinolysis and immunity. The present study evaluates the serine protease inhibitory potential of phytochemicals liquiritin and terpinen-4-ol present in the herb Glycyrrhiza glabra L. using trypsin as the model enzyme. In silico studies showed that both the compounds have a significant binding affinity towards trypsin with a binding energy of -26.66 kcal/mol and -19.79 kcal/mol for liquiritin and terpinen-4-ol, respectively. Their binding affinity was confirmed through in vitro enzyme inhibition assays. The mode of inhibition was found to be uncompetitive. In order to explain the mode of inhibition, docking of the ligands to the enzyme-substrate complex was also done and binding energy was calculated after MD simulation. The energy values showed that the binding affinities of these compounds towards the enzyme substrate complex are more than that towards the enzyme alone. This explains the uncompetitive mode of inhibition.Communicated by Ramaswamy H. Sarma.

Unveiling the molecular basis of lobeline's allosteric regulation of NMDAR: insights from molecular modeling

Neurological and psychiatric disorders contribute significantly to the global disease burden, adversely affecting the quality of life for both patients and their families. Impaired glutamatergic signaling is considered to be a major cause for most of the neurological and psychiatric disorders. Glutamate receptors are over activated in excitotoxic conditions, leading to dysregulation of Ca2+ homeostasis, triggering the production of free radicals and oxidative stress, mitochondrial dysfunction and eventually cell death. Excitotoxicity primarily results from the overactivity of NMDARs, a subtype of ionotropic glutamate receptors, due to their pronounced Ca2+ permeability and conductance characteristics. NMDAR antagonists are suggested to have therapeutic use as they can prevent excitotoxicity. Our previous studies demonstrated lobeline, an alkaloid, exerts neuroprotective action in excitotoxic conditions by blocking NMDAR. However, the atomic level interactions of lobeline with NMDAR was not characterized yet. Structural comparison of lobeline with a known NMDAR antagonist ifenprodil, followed by molecular docking and dynamics simulations revealed that lobeline could bind to the ifenprodil binding site i.e., in the heterodimer interface of GluN1-GluN2B subunits and exert ifenprodil like activities. By in silico structure guided modifications on lobeline and subsequent free energy calculations, we propose putative NMDAR antagonists derived from lobeline.

Investigating the disease-modifying properties of sclerotiorin in Alzheimer's therapy using acetylcholinesterase inhibition

Alzheimer's disease (AD) is a progressive neurodegenerative disorder caused due to the damage and loss of neurons in specific brain regions. It is the most common form of dementia observed in older people. The symptoms start with memory loss and gradually cause the inability to speak and do day-to-day activities. The cost of caring for those affected individuals is huge and is probably beyond most developing countries capability. Current pharmacotherapy for AD includes compounds that aim to increase neurotransmitters at nerve endings. This can be achieved by cholinergic neurotransmission through inhibition of the cholinesterase enzyme. The current research aims to find natural substances that can be used as drugs to treat AD. The present work identifies and explains compounds with considerable Acetylcholinesterase (AChE) inhibitory activities. The pigment was extracted from the Penicillium mallochii ARA1 (MT373688.1) strain using ethyl acetate, and the active compound was identified using chromatographic techniques followed by structural confirmation with NMR. AChE inhibition experiments, enzyme kinetics, and molecular dynamics simulation studies were done to explain the pharmacological and pharmacodynamic properties. We identified that the compound sclerotiorin in the pigment has AChE inhibitory activity. The compound is stable and can bind to the enzyme non-competitively. Sclerotiorin obeys all the drug-likeliness parameters and can be developed as a promising drug in treating AD.

Lipoxygenase inhibitory synthetic derivatives of methyl gallate regulate gene expressions of COX-2 and cytokines to reduce animal model arthritis

Mammalian lipoxygenases (LOXs) are involved in the biosynthesis of mediators of anaphylactic reactions and have been implicated in cell maturation, the pathogenesis of bronchial asthma, atherosclerosis, rheumatoid arthritis, cardiovascular diseases, Alzheimer's disease and osteoporosis. Hence LOX inhibition in chronic conditions can lead to reducing the disease progression, which can be a good target for treating these diseases. The present study deals with designing methyl gallate derivatives and their anti-inflammatory effect by in silico, in vitro and in vivo methods. Designed derivatives were docked against LOX enzyme, and molecular dynamic simulations were carried out. Following the synthesis of derivatives, in vitro LOX inhibition assay, enzyme kinetics and fluorescence quenching studies were performed. One of the derivatives of methyl gallate (MGSD 1) was demonstrated as an anti-inflammatory agent for the treatment of rheumatoid arthritis in the animal model. Amelioration of Freund's complete adjuvant (FCA)-induced arthritis by methyl gallate and its derivative with a concentration of 10-40 mg.kg-1 has been assessed in vivo in a 28-day-long study. TNF-α and COX-2 gene expression were also studied. Methyl gallate synthetic derivatives (MGSDs) inhibited LOX with an IC50 of 100 nM, 304 nM, and 226 nM for MGSD 1, MGSD 2, and MGSD 3, respectively. Fluorescence quenching methods also prove their binding characteristics, and 200 ns simulations studies showed that the RMSDs for the entire complex were less than 2.8 Å. The in vivo results showed that methyl gallate was required approximately five times diclofenac for the same level of effect, and the synthesised (MGSD 1) compound required only approximately 1/12 of diclofenac for the same level of effect in in-vivo studies. The preeminent expression of COX-2 and TNF-α genes was significantly decreased after the treatment of the methyl gallate derivative. Hence, the in vivo results showed that the referenced synthetic derivative might have more arthritis-reducing properties than the parent compound methyl gallate and is more potent than the standard drug diclofenac, with no apparent induced toxicity.

Role of taraxerone isolated from Leucas lavandulifolia, as an immunomodulator

ETHNOPHARMACOLOGICAL RELEVANCE

The Indian tradition system of medicine enlists a large number of plants for basic health care. Leucas lavandulifolia is mentioned in the ayurvedic medicinal system and also used among the folklores. The plant is used for the treatment of fever, asthma, psoriasis, dermatitis and healing snake bites. The scientific validation of the plant for their traditional use in different immune related disorders are yet to be explored.

AIM OF THE STUDY

The study aims to isolate immunomodulatory active compound from Leucas lavandulifolia and evaluating its efficiency in immune related disorders.

MATERIALS AND METHODS

The immunomodulatory activity of the phytocompound is evaluated through in vitro and in vivo studies. The compound purification and identification were done by chromatography and LC/Q-TOF respectively. Its immunomodulatory activity was evaluated in cells like PBMC, neutrophils and macrophages by MTT assay and cell cycle analysis. Animal studies were performed on Swiss albino mice. The levels of IL-4 and IL-6 cytokines were also evaluated in both in vitro and in vivo models.

RESULTS

Leucas lavandulifolia stem portion was found to have good modulatory property. An active immunomodulator was isolated from the methanol extract of the plant. LC/Q-TOF data revealed the isolated compound to be taraxerone. In PBMC, the compound was capable of suppressing the proliferation rate of the compound indicated by a decrease in cell numbers. The activated IL-4 and IL-6 production was also suppressed actively at 25 μg/ml of taraxerone. Similar inhibitory effects were seen in RAW 264.7 and THP-1 macrophage cell lines. An IC₅₀ value of 17.5 μg/ml was obtained for taraxerone in LPS stimulated RAW 264.7 macrophage cell lines. The NO level, IL-4, IL-6 and phagocytosis in the LPS stimulated macrophage was effectively lowered by 25 μg/ml of taraxerone. In PMA stimulated THP-1 Macrophage Cell Lines, taraxerone was capable of suppressing the cell number and IL-6. The compound didn't show any effect on IL-4 levels. The compound exhibited an immunosuppressive activity in PHA induced PMN cells by suppressing the respiratory burst and interleukins IL-4 and IL-6. TX could also suppress the proliferation of DNCB induced monocyte cells and IL-4. The haematological parameters exhibited a significant suppression for the high dose group of taraxerone. The antibody titre and phagocytic index was suppressed by the high dose group, whereas the low dose group did not have any effect. So taraxerone at 50 mg/kg body weight is capable of modulating the B-lymphocytes and macrophages. But the compound has exhibited insignificant effect on the DTH hypersensitivity response and organ index.

CONCLUSION

Taraxerone at high concentration was capable of suppressing stimulated PBMC, macrophage and PMN. The activated nitric oxide, IL-4, IL-6 production and phagocytosis was also suppressed. The haematological parameters, antibody titre and phagocytic index was also lowered in antigenically challenged mice. The terpenoid taraxerone exhibits a good modulatory effect on the immune system and proves to be a potent drug for the treatment of many allergic disorders.

Neuroprotective derivatives of tacrine that target NMDA receptor and acetyl cholinesterase - Design, synthesis and biological evaluation

The complex and multifactorial nature of neuropsychiatric diseases demands multi-target drugs that can intervene with various sub-pathologies underlying disease progression. Targeting the impairments in cholinergic and glutamatergic neurotransmissions with small molecules has been suggested as one of the potential disease-modifying approaches for Alzheimer’s disease (AD). Tacrine, a potent inhibitor of acetylcholinesterase (AChE) is the first FDA approved drug for the treatment of AD. Tacrine is also a low affinity antagonist of N-methyl-D-aspartate receptor (NMDAR). However, tacrine was withdrawn from its clinical use later due to its hepatotoxicity. With an aim to develop novel high affinity multi-target directed ligands (MTDLs) against AChE and NMDAR, with reduced hepatotoxicity, we performed in silico structure-based modifications on tacrine, chemical synthesis of the derivatives and in vitro validation of their activities. Nineteen such derivatives showed inhibition with IC₅₀ values in the range of 18.53 ± 2.09 – 184.09 ± 19.23 nM against AChE and 0.27 ± 0.05 – 38.84 ± 9.64 μM against NMDAR. Some of the selected compounds also protected rat primary cortical neurons from glutamate induced excitotoxicity. Two of the tacrine derived MTDLs, 201 and 208 exhibited in vivo efficacy in rats by protecting against behavioral impairment induced by administration of the excitotoxic agent, monosodium glutamate. Additionally, several of these synthesized compounds also exhibited promising inhibitory activitiy against butyrylcholinesterase. MTDL-201 was also devoid of hepatotoxicity in vivo. Given the therapeutic potential of MTDLs in disease-modifying therapy, our studies revealed several promising MTDLs among which 201 appears to be a potential candidate for immediate preclinical evaluations.

Identification of sustainable trypsin active-site inhibitors from Nigrospora sphaerica strain AVA-1

Trypsin is a protein-digesting enzyme that is essential for the growth and regeneration of bone, muscle, cartilage, skin, and blood. The trypsin inhibitors have various role in diseases such as inflammation, Alzheimer's disease, pancreatitis, rheumatoid arthritis, cancer prognosis, metastasis and so forth. From 10 endophytic fungi isolated, we were able to screen only one strain with the required activity. The fungus with activity was obtained as an endophyte from Dendrophthoe falcata and was later identified as Nigrospora sphaerica. The activity was checked by enzyme assays using trypsin. The fungus was fermented and the metabolites were extracted and further purified by bioassay-guided chromatographic methods and the compound isolated was identified using gas chromatography-mass spectrometry. The compound was identified as quercetin. Docking studies were employed to study the interaction. The absorption, distribution, metabolism, and excretion analysis showed satisfactory results and the compound has no AMES and hepatotoxicity. This study reveals the ability of N. sphaerica to produce bioactive compound quercetin has been identified as a potential candidate for trypsin inhibition. The present communication describes the first report claiming that N. sphaerica strain AVA-1 can produce quercetin and it can be considered as a sustainable source of trypsin active-site inhibitors.

Chemical similarity assisted search for acetylcholinesterase inhibitors: Molecular modeling and evaluation of their neuroprotective properties

Alzheimer's disease (AD) is an obstinate and progressive neurodegenerative disorder, mainly characterized by cognitive decline. Increasing number of AD patients and the lack of promising treatment strategies demands novel therapeutic agents to combat various disease pathologies in AD. Recent progresses in understanding molecular mechanisms in AD helped researchers to streamline the various therapeutic approaches. Inhibiting acetylcholinesterase (AChE) activity has emerged as one of the potential treatment strategies. The present study discusses the identification of two potent AChE inhibitors (ZINC11709541 and ZINC11996936) from ZINC database through conventional in silico approaches and their in vitro validations. These inhibitors have strong preferences towards AChE than butyrylcholinesterase (BChE) and didn't evoke any significant reduction in the cell viability of HEK-293 cells and primary cortical neurons. Furthermore, promising neuroprotective properties has also been displayed against glutamate induced excitotoxicity in primary cortical neurons. The present study proposes two potential drug lead compounds for the treatment of AD, that can be used for further studies and preclinical evaluation.

Repurposing simeprevir, calpain inhibitor IV and a cathepsin F inhibitor against SARS-CoV-2 and insights into their interactions with Mpro

The world has come to a sudden halt due to the incessant spread of a viral pneumonia dubbed COVID-19 caused by the beta-coronavirus, SARS-CoV-2. The main protease of SARS-CoV-2 plays a key role in the replication and propagation of the virus in the host cells. Inhibiting the protease blocks the replication of the virus; therefore it is considered as an attractive therapeutic target. Here we describe the screening of the DrugBank database, a public repository for small molecule therapeutics, to identify approved or experimental phase drugs that can be repurposed against the main protease of SARS-CoV-2. The initial screening was performed on more than 13,000 drug entries in the target database using an energy optimised pharmacophore hypothesis AARRR. A sub-set of the molecules selected based on the fitness score was further screened using molecular docking by sequentially filtering the molecules through the high throughput virtual screening, extra precision and standard precision docking modalities. The best hits were subjected to binding free energy estimation using the MM-GBSA method. Approved drugs viz, Cobicistat, Larotrectinib and Simeprevir were identified as potential candidates for repurposing. Drugs in the discovery phase identified as inhibitors include the known cysteine protease inhibitors, Calpain inhibitor IV and an experimental cathepsin F inhibitor. In order to analyse the stability of the binding interactions, the known cysteine protease inhibitors viz, Simeprevir, calpain inhibitor IV and the cathepsin F inhibitor in complex M^pro were subjected to molecular dynamics simulations at 100 ns. Based on the results Simeprevir was found to be a strong inhibitor of SARS-CoV-2 M^pro.Communicated by Ramaswamy H. Sarma.

Isozymes inhibited by active site blocking: versatility of calcium indifferent hesperidin binding to phospholipase A2 and its significance

sPLA₂ is released under inflammatory conditions from neutrophils, basophils and T-cells. They cleave the cellular phospholipids leading to the release of arachidonic acid and there by provide intermediates for biosynthesis of inflammatory mediators. The focus of this study is on the interaction of hesperidin, a natural flavonoid with Group IB, IIA, and V and X isozymes of sPLA₂. Affinity of hesperidin towards PLA₂ isozymes was analyzed through enzymatic studies and molecular modeling. The experiments showed that hesperidin competitively inhibited PLA₂ with IC₅₀ of 5.1 µM. Molecular modeling studies revealed the association of hesperidin with the docking scores -6.90, -9.53, -5.63 and -8.29 kcal for isozymes Group IB, IIA, V and X of PLA₂ respectively. Their binding energy values were calculated as -20.25, -21.63, -21.66 and -33.43 kcal for the Group IB, IIA, V and X respectively. Structural model for Group V was made by homology modeling since no structural coordinates were available. Molecular dynamics studies were carried out to evaluate the structural stability of protein ligand complex. The analyses showed that hesperidin blocked the entry of the substrate to the active site of PLA₂ and it was indifferent to the differences of the isozymes. Hence, hesperidin might serve as lead for designing highly specific anti-inflammatory drugs directed to the PLA₂ isozyme specific to various diseases, with IC₅₀ value of therapeutic significance.

Structural characterization of a novel derivative of myricetin from Mimosa pudica as an anti-proliferative agent for the treatment of cancer

The study was initiated to determine the anticancer activity of a novel compound isolated from the plant Mimosa pudica. The structure of the compound was identified as a derivative of myricetin having alkyl, hydroxy alkyl and methyl substitutions on the basis of spectral evidences (UV-vis, FT-IR, ¹H NMR and Mass spectra). The isolated compound was interpreted as 2-(2',6'-dimethyl-3',4',5'-alkyl or hydroxy alkyl substituted phenyl)-3-oxy-(alkyl or hydoxy alkyl)- 5,7-dihydroxy-chromen-4-one. In vitro evaluation of anticancer activity against human lung adenocarcinoma cell line (A549) and human erythroleukemic cell line (K562) were conducted using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. In vivo anticancer activity was determined against Dalton's Ascites Lymphoma (DAL) in Swiss albino mice. The mice were treated with intraperitoneal administration of the compound at 25mg/kg and 100mg/kg body weight and were compared with the normal, DAL control and standard drug cyclophosphamide treated groups. The histology revealed that the compound could protect the cellular architecture of liver and kidney. The results from the in vitro, in vivo and histological examinations confirmed the ethnopharmacological significance of the isolated compound and could be considered further for the development of an effective drug against cancer.