Therapeutic Potential of Medicinal Plant Proteins: Present Status and Future Perspectives

Identification and Characterization of Neuroprotective Properties of Thaumatin-like Protein 1a from Annurca Apple Flesh Polyphenol Extract

BACKGROUND

Alzheimer's disease (AD) and Parkinson's disease (PD) are multifactorial neurodegenerative disorders that are mostly treated with drugs inhibiting key enzymes of cholinergic and aminergic neurotransmission, such as acetyl and butyryl cholinesterase (AChE, BuChE) or monoamine oxidases (MAO)-A/B, and of Aβ1-40 aggregation. Diet plant components with multitarget functions are promising compounds in the prevention of AD and PD. Our aim was to identify neuroprotective compounds from Annurca apple polyphenol extract (AFPE).

METHODS

AFPE was fractionated by gel filtration, and the eluted peaks were subjected to chemical analyses (i.e., RP-HPLC and mass spectrometry), determination of inhibitory enzyme activity and cell effects by MTT, and morphology assays.

RESULTS

In AFPE, we identified thaumatin-like protein 1a, belonging to the pathogenesis-related protein (PR) family. This protein showed the best inhibitory activity on AChE, MAO-A (IC50 = 5.53 µM and 1.71 µM, respectively), and Aβ1-40 fibril aggregation (IC50 = 9.16 µM), compared to AFPE and other polyphenol-containing fractions. Among the latter, Peak 4 reverted Aβ fibril formation (IC50 = 104.87 µM). Moreover, thaumatin-like protein 1a protected AGS and MKN-28 cells from serum-deprivation-induced stress conditions.

CONCLUSIONS

We showed that AFPE exerted neuroprotective functions not only through its polyphenols but also through thaumatin-like protein 1a, which acted like a multitarget molecule.

Investigation of Epilobium hirsutum L. Optimized Extract's Anti-Inflammatory and Antitumor Potential

Epilobium hirsutum L., commonly known as hairy willowherb, is a perennial herbaceous plant native to Europe and Asia. In Romania, the Epilobium genus includes 17 species that are used in folk medicine for various purposes. This study aimed to investigate the anti-inflammatory and antitumor potential of the optimized extract of Epilobium hirsutum (EH) in animal models. The first study investigated the anti-inflammatory properties of EH optimized extract and the model used was carrageenan-induced paw inflammation. Wistar rats were divided into three groups: negative control, positive control treated with indomethacin, and a group treated with the extract. Oxidative stress markers, cytokine levels, and protein expressions were assessed. The extract demonstrated anti-inflammatory properties comparable to those of the control group. In the second study, the antitumor effects of the extract were assessed using the tumor model of Ehrlich ascites carcinoma. Swiss albino mice with Ehrlich ascites were divided into four groups: negative, positive treated with cyclophosphamide (Cph), Group 3 treated with Cph and EH optimized extract, and Group 4 treated with extract alone. Samples from the ascites fluid, liver, and heart were analyzed to evaluate oxidative stress, inflammation, and cancer markers. The extract showed a reduction in tumor-associated inflammation and oxidative stress. Overall, the EH optimized extract exhibited promising anti-inflammatory and antitumor effects in the animal models studied. These findings suggest its potential as a natural adjuvant therapeutic agent for addressing inflammation and oxidative stress induced by different pathologies.

A Review: The Antiviral Activity of Cyclic Peptides

In the design and development of therapeutic agents, macromolecules with restricted structures have stronger competitive edges than linear biological entities since cyclization can overcome the limitations of linear structures. The common issues of linear peptides include susceptibility to degradation of the peptidase enzyme, off-target effects, and necessity of routine dosing, leading to instability and ineffectiveness. The unique conformational constraint of cyclic peptides provides a larger surface area to interact with the target at the same time, improving the membrane permeability and in vivo stability compared to their linear counterparts. Currently, cyclic peptides have been reported to possess various activities, such as antifungal, antiviral and antimicrobial activities. To date, there is emerging interest in cyclic peptide therapeutics, and increasing numbers of clinically approved cyclic peptide drugs are available on the market. In this review, the medical significance of cyclic peptides in the defence against viral infections will be highlighted. Except for chikungunya virus, which lacks specific antiviral treatment, all the viral diseases targeted in this review are those with effective treatments yet with certain limitations to date. Thus, strategies and approaches to optimise the antiviral effect of cyclic peptides will be discussed along with their respective outcomes. Apart from isolated naturally occurring cyclic peptides, chemically synthesized or modified cyclic peptides with antiviral activities targeting coronavirus, herpes simplex viruses, human immunodeficiency virus, Ebola virus, influenza virus, dengue virus, five main hepatitis viruses, termed as type A, B, C, D and E and chikungunya virus will be reviewed herein.

Graphical Abstract

Luffa operculata seed proteins: Identification by LC-ESI-MS/MS and biotechnological potential against Candida albicans and C. krusei

L: operculata is a plant commonly found in the North and Northeast of Brazil. Although the regional population knows its medicinal potential, there are few scientific studies about its antimicrobial potential. Thus, this study aimed to characterize the proteins from L. operculata seeds extracted using different solutions and evaluate their antimicrobial potentials. The protein extracts obtained with NaCl and sodium acetate buffer presented the best inhibitory activities against Candida albicans and C. krusei. The study of the mechanism of action revealed proteins from L. operculata seeds induced pore formation on the membrane and ROS overaccumulation. Scanning Electron Microscopy images also showed severe morphological changes in Candida albicans and C. krusei. Proteins from L.operculata seeds did not show antibacterial activity. The enzymatic assays revealed the presence of proteolytic enzymes, serine and cysteine protease inhibitors, and chitinases in both protein extracts. Proteomic analysis by LC-ESI-MS/MS identified 57 proteins related to many biological processes, such as defense to (a)biotic stress, energetic metabolism, protein folding, and nucleotide metabolism. In conclusion, the L. operculata seed proteins have biotechnological potential against the human pathogenic yeasts Candida albicans and C. krusei.

The Updated Review on Plant Peptides and Their Applications in Human Health

Biologically active plant peptides, consisting of secondary metabolites, are compounds (amino acids) utilized by plants in their defense arsenal. Enzymatic processes and metabolic pathways secrete these plant peptides. They are also known for their medicinal value and have been incorporated in therapeutics of major human diseases. Nevertheless, its limitations (low bioavailability, high cytotoxicity, poor absorption, low abundance, improper metabolism, etc.) have demanded a need to explore further and discover other new plant compounds that overcome these limitations. Keeping this in mind, therapeutic plant proteins can be excellent remedial substitutes for bodily affliction. A multitude of these peptides demonstrates anti-carcinogenic, anti-microbial, anti-HIV, and neuro-regulating properties. This article's main aim is to list out and report the status of various therapeutic plant peptides and their prospective status as peptide-based drugs for multiple diseases (infectious and non-infectious). The feasibility of these compounds in the imminent future has also been discussed.

Therapeutic peptides of Mucuna pruriens L.: Anti-genotoxic molecules against human hepatocellular carcinoma and hepatitis C virus

To assist the development of new therapeutic strategies for several disorders, biologically active peptides/proteins obtained from plant sources can be considered. Current study expected to determine the biological activities of peptide fractions of Mucuna pruriens against hepatocellular carcinoma cell lines (HepG2/ADM, HepG2, SMMC-7721, and QGY-7703), as well as normal cell line to prove their selectivity. Moreover, anti-genotoxicity and antiviral activity against the hepatitis C virus (HCV) were assessed. The methods of this study were to isolate the peptides of M. pruriens and hydrolysate fractionation via fractionated pepsin-pancreatin hydrolysates by ultrafiltration/high-performance ultrafiltration cell, identify anti-hepatoma activity of peptide fractions human liver cancer and normal cells by (3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide) (MTT) assay, determine anti-HCV, and assess anti-genotoxic effect of peptide fractions against damage that induced via alkylating agent methyl methanesulphonate in human mononuclear cells. The results showed that the fraction 5-10 kDa has been reported to exhibit significant cytotoxic activity against HepG2 and QGY-7703. It was proven that both of 5-10 and >10 kDa fractions are active against HCV. The cytotoxic concentration (CC50) of 5-10 kDa against the cell line was 703.04 ± 5.21 µg/ml. Anti-genotoxic activities of the peptide fractions were evaluated as mean values for the analyzed comet images. In this regard, the highest activity of protecting DNA damages was observed by the peptide fraction of 5-10 kDa. This study revealed the potential ability of peptide fractions of M. pruriens for the treatment of liver cancer, HCV, and high activities of protecting DNA damages.