Anti-plasmodial and anti-inflammatory activities of cyclotide-rich extract and fraction of Oldenlandia affinis (R. & S.) D.C. (Rubiaceae)

Phytochemistry, pharmacology, and medical uses of Oldenlandia (family Rubaceae): a review

The Oldenlandia genus comprises approximately 240 species of plants, yet only a limited number of these have been investigated for their chemical composition and medicinal properties. These species contain a wide range of compounds such as iridoids, anthraquinones, triterpenes, phytosterols, flavonoids, anthocyanidins, vitamins, essential oils, phenolic acids, and coumarins. These diverse phytochemical profiles underscore the pharmacological potential of Oldenlandia plants for various medical purposes. Among other chemical constituents, ursolic acid stands out as the most important active compound in Oldenlandia, owing to its proven anticancer, anti-inflammatory, antimicrobial, and hepatoprotective properties. The evaluation of Oldenlandia's pharmacological prospects indicates that the holistic utilization of the entire plant yields the most significant effects. Oldenlandia diffusa showcases anticancer and anti-inflammatory capabilities attributed to its varying constituents. Across a broad spectrum of pharmacological capacities, anticancer research predominates, constituting the majority of medical uses. Oldenlandia diffusa emerges as a standout for its remarkable anticancer effects against diverse malignancies. Antioxidant applications follow, with O. corymbosa demonstrating potent antioxidant properties alongside O. umbellata and O. diffusa. Subsequent priority lies in anti-inflammatory studies, wherein O. diffusa exhibits noteworthy efficacy, trailed by O. corymbosa also takes the lead in antimicrobial activity, with O. umbellata as a strong contender. Additional investigation is essential to ascertain the relative significance of these species in various pharmacological applications. This comprehensive assessment underscores the multifaceted potential of Oldenlandia as a versatile herbal resource, offering diverse pharmacological capacities. The call for sustained exploration and research remains essential to unlock the full extent of Oldenlandia's medicinal benefits.

Ethnopharmacology, phytochemistry and a new chemotaxonomic marker in Oldenlandia affinis (Roem. & Schult.) DC. Rubiaceae

The proper documentation of ethnopharmacological application of widely used indigenous plants and their phytochemical analysis has positively impacted the drug discovery pipeline. Medicinal plants with potential commercial value and prospects for clinical application need to be properly identified and authenticated to avoid confusion, adulteration and substitution. Oldenlandia affinis (OA) has continued to attract scientific attention following the discovery of extremely stable cyclotides (circular peptides) that are not expressed in many investigated members of the contentious genus, Oldenlandia (synonym – Hedyotis); yet there is a lack of an elaborate review covering some broader aspects of its traditional uses, ethnopharmacology and phytochemistry of the species. More importantly, the age long but lingering confusion and taxonomic inconsistencies common to the Oldenlandia–Hedyotis debate could foster species mismatching, increase cases of misidentification, promote adulteration of OA and thereby limit its proper clinical application. Here, we aim to reveal the extent of indigenous use of and research on OA from 1960 till date, unveil knowledge gaps, document hitherto unknown traditional applications, ethnopharmacological uses, pharmacological properties, and reported phytochemical profile. In addition, to encourage proper selection and utilization of genuine crude drug, the chemotaxonomically important phytoconstituents of OA have been presented and the modern approach of chemophenetic study of OA proposed to resolve the lack of consensus in the taxonomy of OA as well as the morphologically and anatomically close members of the taxon. The abundant cyclotide expression in OA represents a new chemotaxonomic marker for its unambiguous identification, utilization and reproducibility of research findings on the species.

Antiplasmodial, antimalarial activities and toxicity of African medicinal plants: a systematic review of literature

BACKGROUND

Malaria still constitutes a major public health menace, especially in tropical and subtropical countries. Close to half a million people mainly children in Africa, die every year from the disease. With the rising resistance to frontline drugs (artemisinin-based combinations), there is a need to accelerate the discovery and development of newer anti-malarial drugs. A systematic review was conducted to identify the African medicinal plants with significant antiplasmodial and/or anti-malarial activity, toxicity, as wells as assessing the variation in their activity between study designs (in vitro and in vivo).

METHODS

Key health-related databases including Google Scholar, PubMed, PubMed Central, and Science Direct were searched for relevant literature on the antiplasmodial and anti-malarial activities of African medicinal plants.

RESULTS

In total, 200 research articles were identified, a majority of which were studies conducted in Nigeria. The selected research articles constituted 722 independent experiments evaluating 502 plant species. Of the 722 studies, 81.9%, 12.4%, and 5.5% were in vitro, in vivo, and combined in vitro and in vivo, respectively. The most frequently investigated plant species were Azadirachta indica, Zanthoxylum chalybeum, Picrilima nitida, and Nauclea latifolia meanwhile Fabaceae, Euphorbiaceae, Annonaceae, Rubiaceae, Rutaceae, Meliaceae, and Lamiaceae were the most frequently investigated plant families. Overall, 248 (34.3%), 241 (33.4%), and 233 (32.3%) of the studies reported very good, good, and moderate activity, respectively. Alchornea cordifolia, Flueggea virosa, Cryptolepis sanguinolenta, Zanthoxylum chalybeum, and Maytenus senegalensis gave consistently very good activity across the different studies. In all, only 31 (4.3%) of studies involved pure compounds and these had significantly (p = 0.044) higher antiplasmodial activity relative to crude extracts. Out of the 198 plant species tested for toxicity, 52 (26.3%) demonstrated some degree of toxicity, with toxicity most frequently reported with Azadirachta indica and Vernonia amygdalina. These species were equally the most frequently inactive plants reported. The leaves were the most frequently reported toxic part of plants used. Furthermore, toxicity was observed to decrease with increasing antiplasmodial activity.

CONCLUSIONS

Although there are many indigenous plants with considerable antiplasmodial and anti-malarial activity, the progress in the development of new anti-malarial drugs from African medicinal plants is still slothful, with only one clinical trial with Cochlospermum planchonii (Bixaceae) conducted to date. There is, therefore, the need to scale up anti-malarial drug discovery in the African region.

Therapeutic Potentials of Antiviral Plants Used in Traditional African Medicine With COVID-19 in Focus: A Nigerian Perspective

The coronavirus disease 2019 (COVID-19) pandemic is caused by an infectious novel strain of coronavirus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which was earlier referred to as 2019-nCoV. The respiratory disease is the most consequential global public health crisis of the 21st century whose level of negative impact increasingly experienced globally has not been recorded since World War II. Up till now, there has been no specific globally authorized antiviral drug, vaccines, supplement or herbal remedy available for the treatment of this lethal disease except preventive measures, supportive care and non-specific treatment options adopted in different countries via divergent approaches to halt the pandemic. However, many of these interventions have been documented to show some level of success particularly the Traditional Chinese Medicine while there is paucity of well reported studies on the impact of the widely embraced Traditional African Medicines (TAM) adopted so far for the prevention, management and treatment of COVID-19. We carried out a detailed review of publicly available data, information and claims on the potentials of indigenous plants used in Sub-Saharan Africa as antiviral remedies with potentials for the prevention and management of COVID-19. In this review, we have provided a holistic report on evidence-based antiviral and promising anti-SARS-CoV-2 properties of African medicinal plants based on in silico evidence, in vitro assays and in vivo experiments alongside the available data on their mechanistic pharmacology. In addition, we have unveiled knowledge gaps, provided an update on the effort of African Scientific community toward demystifying the dreadful SARS-CoV-2 micro-enemy of man and have documented popular anti-COVID-19 herbal claims emanating from the continent for the management of COVID-19 while the risk potentials of herb-drug interaction of antiviral phytomedicines when used in combination with orthodox drugs have also been highlighted. This review exercise may lend enough credence to the potential value of African medicinal plants as possible leads in anti-COVID-19 drug discovery through research and development.

Amino acid-derived defense metabolites from plants: A potential source to facilitate novel antimicrobial development

For millennia, humanity has relied on plants for its medicines, and modern pharmacology continues to reexamine and mine plant metabolites for novel compounds and to guide improvements in biological activity, bioavailability, and chemical stability. The critical problem of antibiotic resistance and increasing exposure to viral and parasitic diseases has spurred renewed interest into drug treatments for infectious diseases. In this context, an urgent revival of natural product discovery is globally underway with special attention directed toward the numerous and chemically diverse plant defensive compounds such as phytoalexins and phytoanticipins that combat herbivores, microbial pathogens, or competing plants. Moreover, advancements in “omics,” chemistry, and heterologous expression systems have facilitated the purification and characterization of plant metabolites and the identification of possible therapeutic targets. In this review, we describe several important amino acid–derived classes of plant defensive compounds, including antimicrobial peptides (e.g., defensins, thionins, and knottins), alkaloids, nonproteogenic amino acids, and phenylpropanoids as potential drug leads, examining their mechanisms of action, therapeutic targets, and structure–function relationships. Given their potent antibacterial, antifungal, antiparasitic, and antiviral properties, which can be superior to existing drugs, phytoalexins and phytoanticipins are an excellent resource to facilitate the rational design and development of antimicrobial drugs.

Cyclotides: From Structure to Function

This Review explores the class of plant-derived macrocyclic peptides called cyclotides. We include an account of their discovery, characterization, and distribution in the plant kingdom as well as a detailed analysis of their sequences and structures, biosynthesis and chemical synthesis, biological functions, and applications. These macrocyclic peptides are around 30 amino acids in size and are characterized by their head-to-tail cyclic backbone and cystine knot motif, which render them to be exceptionally stable, with resistance to thermal or enzymatic degradation. Routes to their chemical synthesis have been developed over the past two decades, and this capability has facilitated a wide range of mutagenesis and structure-activity relationship studies. In turn, these studies have both led to an increased understanding of their mechanisms of action as well as facilitated a range of applications in agriculture and medicine, as ecofriendly crop protection agents, and as drug leads or scaffolds for pharmaceutical design. Our overall objective in this Review is to provide readers with a comprehensive overview of cyclotides that we hope will stimulate further work on this fascinating family of peptides.

The Potential of the Cyclotide Scaffold for Drug Development

Cyclotides are a novel class of micro-proteins (≈30-40 residues long) with a unique topology containing a head-to-tail cyclized backbone structure further stabilized by three disulfide bonds that form a cystine knot. This unique molecular framework makes them exceptionally stable to physical, chemical, and biological degradation compared to linear peptides of similar size. The cyclotides are also highly tolerant to sequence variability, aside from the conserved residues forming the cystine knot, and are orally bioavailable and able to cross cellular membranes to modulate intracellular protein-protein interactions (PPIs), both in vitro and in vivo. These unique properties make them ideal scaffolds for many biotechnological applications, including drug discovery. This review provides an overview of the properties of cyclotides and their potential for the development of novel peptide-based therapeutics. The selective disruption of PPIs still remains a very challenging task, as the interacting surfaces are relatively large and flat. The use of the cell-permeable highly constrained polypeptide molecular frameworks, such as the cyclotide scaffold, has shown great promise, as it provides unique pharmacological properties. The use of molecular techniques, such as epitope grafting, and molecular evolution have shown to be highly effective for the selection of bioactive cyclotides. However, despite successes in employing cyclotides to target PPIs, some of the challenges to move them into the clinic still remain.

Cyanobacterial peptides as a tour de force in the chemical space of antiparasitic agents

Parasites are scarcely addressed target for antimicrobial peptides despite their big impact in health and global economy. The notion of antimicrobial peptides is frequently associated to the innate immune defense of vertebrates and invertebrate vectors, as the ultimate recipients of the parasite infection. These antiparasite peptides are produced by ribosomal synthesis, with few post-translational modifications, and their diversity come mostly from their amino acid sequence. For many of them permeabilization of the cell membrane of the targeted pathogen is crucial for their microbicidal mechanism. In contrast, cyanobacterial peptides are produced either by ribosomal or non-ribosomal biosynthesis. Quite often, they undergo heavy modifications, such as the inclusion of non-proteinogenic amino acids, lipid acylation, cyclation, N^α-methylation, or heterocyclic rings. Furthermore, the few targets identified for cyanobacterial peptides in parasites are intracellular. Some cyanobacterial antiparasite peptides are active at picomolar concentrations, whereas those from higher eukaryotes usually work in the micromolar range. In all, cyanobacterial peptides are an appealing target to develop new antiparasite therapies and a challenge in the invention of new synthetic methods for peptides. This review aims to provide an updated appraisal of antiparasite cyanobacterial peptides and to establish a side-by -side comparison with those antiparasite peptides from higher eukaryotes.