Solution- and solid-phase synthesis and anti-HIV activity of maslinic acid derivatives containing amino acids and peptides

Bioactivities and Structure-Activity Relationships of Maslinic Acid Derivatives: A Review

Maslinic acid has a variety of biological activities, such as anti-tumor, hypoglycemic, anti-inflammatory, and anti-parasitic. In order to enhance the biological activity of maslinic acid, scholars have carried out a lot of structural modifications, and found some more valuable maslinic acid derivatives. In this paper, the structural modification, biological activity, and structure-activity relationship of maslinic acid were reviewed, providing references for the development of maslinic acid.

Molecular Dynamics Study on Selected Bioactive Phytochemicals as Potential Inhibitors of HIV-1 Subtype C Protease

Acquired immunodeficiency syndrome (AIDS), one of the deadliest global diseases, is caused by the Human Immunodeficiency Virus (HIV). To date, there are no known conventional drugs that can cure HIV/AIDS, and this has prompted continuous scientific efforts in the search for novel and potent anti-HIV therapies. In this study, molecular dynamics simulation (MDS) and computational techniques were employed to investigate the inhibitory potential of bioactive compounds from selected South African indigenous plants against HIV-1 subtype C protease (HIVpro). Of the eight compounds (CMG, MA, UA, CA, BA, UAA, OAA and OA) evaluated, only six (CMG (-9.9 kcal/mol), MA (-9.3 kcal/mol), CA (-9.0 kcal/mol), BA (-8.3 kcal/mol), UAA (-8.5 kcal/mol), and OA (-8.6 kcal/mol)) showed favourable activities against HIVpro and binding landscapes like the reference FDA-approved drugs, Lopinavir (LPV) and Darunavir (DRV), with CMG and MA having the highest binding affinities. Using the structural analysis (root-mean-square deviation (RMSD), fluctuation (RMSF), and radius of gyration (RoG) of the bound complexes with HIVpro after 350 ns, structural evidence was observed, indicating that the six compounds are potential lead candidates for inhibiting HIVpro. This finding was further corroborated by the structural analysis of the enzyme-ligand complexe systems, where structural mechanisms of stability, flexibility, and compactness of the study metabolites were established following binding with HIVpro. Furthermore, the ligand interaction plots revealed that the metabolites interacted hydrophobically with the active site amino residues, with identification of other key residues implicated in HIVpro inhibition for drug design. Overall, this is the first computational report on the anti-HIV-1 activities of CMG and MA, with efforts on their in vitro and in vivo evaluations underway. Judging by the binding affinity, the degree of stability, and compactness of the lead metabolites (CMG, MA, CA, BA, OA, and UAA), they could be concomitantly explored with conventional HIVpro inhibitors in enhancing their therapeutic activities against the HIV-1 serotype.

Self-Assembled Maslinic Acid Attenuates Doxorobucin Induced Cytotoxicity via Nrf2 Signaling Pathway: An In Vitro and In Silico Study in Human Healthy Cells

The clinical applications of some well-known chemotherapeutic drugs for cancer treatment have been restricted nowadays owing to their adverse effects on many physiological systems. In this experimental study, maslinic acid (MA) isolated from Olea europaea (Olive) fruit extract was used to mitigate the cytotoxicity induced by Doxorubicin (DOX) in human healthy peripheral blood mononuclear cells (hPBMCs). Self-assembled maslinic acid (SA-MA) was obtained in ethanol-water mixture (35.5 mM: 4:1 v/v). The morphology of SA-MA was analyzed by various physicochemical characterization techniques, which revealed its micro-metric vesicular architecture as well as nano-vesicular appearances. In this study, treatment of hPBMCs with DOX has been found to generate severe intracellular oxidative stress, which was significantly mitigated after pre-treatment with SA-MA. Alteration of hPBMC morphologies after DOX treatment was also restored notably by pre-treatment with SA-MA. Furthermore, pentoxifylline (TNF-α inhibitor) and indomethacin (COX-2 inhibitor) were used to investigate the responsible pathway by which SA-MA protected hPBMCs from DOX-induced cellular stress. Restoration of hPBMC viability above 92% in both cases confirmed that SA-MA protected the cells by inhibiting inflammatory pathways generated by DOX treatment. Subsequently, in molecular docking study, it was also evaluated that MA could successfully bind with the pocket region of Keap1, while Nrf2 was capable of upregulating cytoprotecting genes.

Novel Biotransformation of Maslinic Acid to MA-2-O-β-D-Glucoside by UDP-Glycosyltransferases from Bacillus subtilis

Maslinic acid (MA) is a pentacyclic triterpenoid which originates from olive and other plants. Though MA possesses multiple biological activities, it has limitations due to its poor water solubility. YojK, YjiC, and UGT109A3 UDP-glycosyltransferases (UGTs) from Bacillus subtilis (B. subtilis) were utilized to catalyze the conjugation of MA with UDP-Glucose to generate a new MA glycosylation product, MA-2-O-β-D-glucoside (MA-2-O-β-D-Glu). The experimental results indicated that the resultant water solubility of MA-2-O-β-D-Glu is 1.69 times higher than that of MA. In addition, the recombinant YojK showed maximum activity at 40 °C with a pH range of 8.0−10.0, while the recombinant YjiC showed maximum activity at 45 °C with a pH of 8.0, and the recombinant UGT109A3 showed maximum activity at 40 °C with a pH of 8.0. Mg2+ is an important factor for efficient catalysis by three recombinant glycosyltransferases. The chemical conversion rate of the recombinant YojK, YjiC, and UGT109A3 is nearly 100% at their optimum pH, temperature, and metal ions. Furthermore, eight essential residues of three UGTs for MA glycosylation modification were further determined by molecular docking and site-directed mutagenesis. Thus, efficient glycosylation modification improves the water solubility of MA and provides a new potential method for the glycosylation modification of other pentacyclic triterpenoids.

Nutraceutical Role of Polyphenols and Triterpenes Present in the Extracts of Fruits and Leaves of Olea europaea as Antioxidants, Anti-Infectives and Anticancer Agents on Healthy Growth

There is currently a worldwide consensus and recognition of the undoubted health benefits of the so-called Mediterranean diet, with its intake being associated with a lower risk of mortality. The most important characteristics of this type of diet are based on the consumption of significant amounts of fruit, vegetables, legumes, and nuts, which provide, in addition to some active ingredients, fiber and a proportion of vegetable protein, together with extra virgin olive oil (EVOO) as the main sources of vegetable fat. Fish and meat from poultry and other small farm animals are the main sources of protein. One of the main components, as already mentioned, is EVOO, which is rich in monounsaturated fatty acids and to a lesser extent in polyunsaturated fatty acids. The intake of this type of nutrient also provides an important set of phytochemicals whose health potential is widely spread and agreed upon. These phytochemicals include significant amounts of anthocyanins, stilbenes, flavonoids, phenolic acids, and terpenes of varying complexities. Therefore, the inclusion in the diet of this type of molecules, with a proven healthy effect, provides an unquestionable preventive and/or curative activity on an important group of pathologies related to cardiovascular, infectious, and cancerous diseases, as well as those related to the metabolic syndrome. The aim of this review is therefore to shed light on the nutraceutical role of two of the main phytochemicals present in Olea europaea fruit and leaf extracts, polyphenols, and triterpenes, on healthy animal growth. Their immunomodulatory, anti-infective, antioxidant, anti-aging, and anti-carcinogenic capabilities show them to be potential nutraceuticals, providing healthy growth.

Maslinic acid activates renal AMPK/SIRT1 signaling pathway and protects against diabetic nephropathy in mice

BACKGROUND

Diabetic nephropathy has been a devastating complication. Clinically, there is an urgent need for nephroprotective agents to delay the onset of diabetic nephropathy and ameliorate its symptoms. Maslinic acid is a pentacyclic triterpene acid with protective effect on multiple organs against oxidative stress and inflammation. In this research, we hypothesized that maslinic acid protects renal function against diabetic nephropathy.

METHODS

C57BL/6 J male mice administrated with 50 mg/kg of Streptozocin (STZ) daily were used to establish diabetic mouse model (blood glucose levels > 300 mg/dL). Urinary levels of albumin, total proteins, and creatinine were analyzed by an automatic analyzer. H&E staining was used to evaluate renal damage. qRT-PCR and ELISA were performed to investigate the inflammation and oxidative stress in renal tissues. Western blot was used to assess the activation of AMPK signaling.

RESULTS

Maslinic acid treatment alleviated the loss of body weight and blood glucose in diabetic mice. Renal structure and function were protected by maslinic acid in diabetic mice. 20 mg/kg maslinic acid treatment for 8 weeks significantly alleviated the oxidative stress and inflammation in the kidney of diabetic rats. Maslinic acid treatment activated the renal AMPK/SIRT1 signaling pathway.

CONCLUSION

Maslinic acid ameliorates diabetic nephropathy and activates the renal AMPK/SIRT1 signaling pathway.

Maslinic Acid Inhibits Cervical Intraepithelial Neoplasia by Suppressing Interleukin-6 and Enhancing Apoptosis in a Mouse Model

BACKGROUND

Cervical intraepithelial neoplasia (CIN) directly precedes cervical cancer, and elevated proinflammatory cytokine interleukins (IL)-6 is implicated in CIN.

OBJECTIVE

As maslinic acid exhibits anti-IL-6 property, the present study sought to determine the effect of maslinic acid on CIN in vitro and in vivo using cell cultures and mouse CIN models, respectively.

METHODS

The dose-effect of maslinic acid on HeLa cells, a human cervical cancer cell line, was first evaluated, including cytotoxicity, IL-6 secretion, IL-6 receptor (IL-6R) expression, proliferation potential and apoptosis status. A mouse model of CIN was also established, which was then subjected to increasing doses of maslinic acid treatment, followed by assessment of serum IL-6 level, cervical expression of IL-6R, and the proliferation potential and apoptosis of cervical tissues.

RESULTS

Maslinic acid dose-dependently inhibited cell growth and proliferation potential, reduced IL-6 secretion, cervical expression of IL-6R and induced apoptosis of HeLa cells in vitro. In the CIN mouse model, serum IL-6 level and cervical expression of IL-6R were elevated, which could be repressed by maslinic acid administration dose-dependently. Additionally, maslinic acid treatment in the CIN mice could also restore the otherwise increased proliferation potential and reduced apoptosis in the cervical tissues.

CONCLUSION

Maslinic acid exhibits potent anti-IL-6 property in the CIN mouse model, and alleviates the disease-related abnormality in proliferation potential and apoptosis state of the cervical tissue cells, demonstrating its usefulness as a promising agent in treating CIN.

Advances in Research on the Preparation and Biological Activity of Maslinic Acid

Maslinic acid, a pentacyclic triterpene acid, is mainly isolated from olives. Maslinic acid and its derivatives exhibit a broad range of biological properties, such as anti-inflammatory, anticancer, anti-diabetic, antimicrobial, neuroprotective and hepatoprotective activities. In this minireview, the progress of research on maslinic acid with regard to its bioactivities, extraction, semisynthetic preparation and patents is reported. The relationships between the structure and the activity of maslinic acid and its derivatives are also discussed.

Strong Inhibitory Activity and Action Modes of Synthetic Maslinic Acid Derivative on Highly Pathogenic Coronaviruses: COVID-19 Drug Candidate

In late December 2019, a novel coronavirus, namely severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), escaped the animal-human interface and emerged as an ongoing global pandemic with severe flu-like illness, commonly known as coronavirus disease 2019 (COVID-19). In this study, a molecular docking study was carried out for seventeen (17) structural analogues prepared from natural maslinic and oleanolic acids, screened against SARS-CoV-2 main protease. Furthermore, we experimentally validated the virtual data by measuring the half-maximal cytotoxic and inhibitory concentrations of each compound. Interestingly, the chlorinated isoxazole linked maslinic acid (compound 17) showed promising antiviral activity at micromolar non-toxic concentrations. Thoughtfully, we showed that compound 17 mainly impairs the viral replication of SARS-CoV-2. Furthermore, a very promising SAR study for the examined compounds was concluded, which could be used by medicinal chemists in the near future for the design and synthesis of potential anti-SARS-CoV-2 candidates. Our results could be very promising for performing further additional in vitro and in vivo studies on the tested compound (17) before further licensing for COVID-19 treatment.

In search of therapeutic candidates for HIV/AIDS: rational approaches, design strategies, structure-activity relationship and mechanistic insights

The HIV/AIDS pandemic is a serious threat to the health and development of mankind, which has affected about 37.9 million people worldwide. The increasing negative health, economic and social impacts of this disease have led to the search for new therapeutic candidates for the mitigation of AIDS/HIV. However, to date, there is still no treatment that can cure this disease. Furthermore, the clinically available drugs have numerous severe side effects. Hence, the synthesis of novel agents from natural leads is one of the rational approaches to obtain new drugs in modern medicinal chemistry. This review article is an effort to summarize recent developments with regards to the discovery of novel analogs with promising biological potential against HIV/AIDS. Herein, we also aim to discuss prospective directions on the progress of more credible and specific analogues. Besides presenting design strategies, the present communication also highlights the structure-activity relationship together with the structural features of the most promising molecules, their IC50 values, mechanistic insights and some interesting key findings revealed during their biological evaluation. The interactions with the amino acid residues of the enzymes responsible for HIV-1 inhibition are also discussed. This collection will be of great interest for researchers working in this area.

Olive-Derived Triterpenes Suppress SARS COV-2 Main Protease: A Promising Scaffold for Future Therapeutics

SARS CoV-2 pandemic is still considered a global health disaster, and newly emerged variants keep growing. A number of promising vaccines have been recently developed as a protective measure; however, cost-effective treatments are also of great importance to support this critical situation. Previously, betulinic acid has shown promising antiviral activity against SARS CoV via targeting its main protease. Herein, we investigated the inhibitory potential of this compound together with three other triterpene congeners (i.e., ursolic acid, maslinic acid, and betulin) derived from olive leaves against the viral main protease (Mpro) of the currently widespread SARS CoV-2. Interestingly, betulinic, ursolic, and maslinic acids showed significant inhibitory activity (IC50 = 3.22-14.55 µM), while betulin was far less active (IC50 = 89.67 µM). A comprehensive in-silico analysis (i.e., ensemble docking, molecular dynamic simulation, and binding-free energy calculation) was then performed to describe the binding mode of these compounds with the enzyme catalytic active site and determine the main essential structural features required for their inhibitory activity. Results presented in this communication indicated that this class of compounds could be considered as a promising lead scaffold for developing cost-effective anti-SARS CoV-2 therapeutics.

Recent advances in natural anti-HIV triterpenoids and analogs

The human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic is one of the world's most serious health challenges. Although combination antiretroviral therapy provides effective viral suppression, current medicines used against HIV cannot completely eradicate the infectious disease and often have associated toxicities and severe side effects in addition to causing drug resistance. Therefore, the continued development of new antiviral agents with diverse structures and novel mechanisms of action remains a vital need for the management of HIV/AIDS. Natural products are an important source of drug discovery, and certain triterpenes and their analogs have demonstrated potential as pharmaceutical precursors for the treatment of HIV. Over the past decade, natural triterpenoids and analogs have been extensively studied to find new anti-HIV drugs. This review discusses the anti-HIV triterpenoids and analogs reported during the period of 2009-2019. The article includes not only a comprehensive review of the recent anti-HIV agent development from the perspective of medicinal chemistry, but also discusses structure-activity relationship analyses of the described triterpenoids.

The cytotoxicity of oleanane derived aminocarboxamides depends on their aminoalkyl substituents

Several oligo-methylene diamine derived carboxamides of oleanolic and maslinic acid have been prepared, and substitutions of the terminal primary amine as well as variations of the length of alkyl chain of the diamine moiety were made. Biological evaluation of their cytotoxic activity was performed using photometric sulforhodamin B assays employing a panel of different human cancer cell lines. These experiments showed most of the carboxamides to be cytotoxic with EC₅₀ values below 10 µM. Prolongation of the alkyl chain length initially reduced EC₅₀ values to a minimum, but a decrease in cytotoxicity was observed for longer alkyl chains. Variation of substituents at the terminal nitrogen atom, however, did not influence EC₅₀ values at all. Noteworthy results were obtained particularly for compounds 4, 6 and 23 as indicated by EC₅₀ values lower than 2 µM, and in case of a maslinic derivative 23 even an increased tumor/non-tumor cell selectivity was observed. These compounds were further investigated using fluorescence microscopy and flow cytometry analysis, which revealed 6 to show indications of apoptosis.

Maslinic Acid Enhances Immune Responses in Leukemic Mice Through Macrophage Phagocytosis and Natural Killer Cell Activities In Vivo

BACKGROUND/AIM

Maslinic acid (MA), a pentacyclic triterpene extracted from wax-like coatings of olives, has been shown to reduce cancer cell number through induction of autophagy and apoptosis in many human cancer cells including human leukemia HL-60 cells. In the present study, we investigated whether or not MA affects immune responses in a leukemia mouse model.

MATERIALS AND METHODS

WEHI-3 cells were intraperitonealIy (i.p.) injected into normal BALB/c mice to develop leukemia. Mice were then treated by i.p. injection with MA at different doses (0, 8, 16 and 32 mg/kg) for 2 weeks. After treatment, all animals were weighed and blood, liver and spleen tissues were weighed. Blood or spleen both were used for determination of cell markers or phagocytosis, natural killer (NK) cell activities and T- and B-cell proliferation, respectively, by using a flow cytometric assay.

RESULTS

MA did not significantly affect body, liver, and spleen weights. However, MA increased markers of T-cells (at 16 mg/kg treatment) and monocytes (at 32 mg/kg treatment), but reduced B-cell markers (at 8 mg/kg treatment); MA did not significantly affect cell marker of macrophages. Furthermore, MA increased phagocytosis by macrophages from peripheral blood mononuclear cells and peritoneal cavity at 32 mg/kg treatment and increased NK cell activity at target cell:splenocyte ratio of 25:1 but did not affect B- and T-cell proliferation.

CONCLUSION

MA increased immune responses by enhancing macrophage phagocytosis and NK cell activities in leukemic mice.

Imidazo[1,2-a]quinoxalines Derivatives Grafted with Amino Acids: Synthesis and Evaluation on A375 Melanoma Cells

Imiqualines (imidazoquinoxaline derivatives) are anticancer compounds with high cytotoxic activities on melanoma cell lines. The first generation of imiqualines, with two lead compounds (EAPB0203 and EAPB0503), shows remarkable in vitro (IC₅₀ = 1 570 nM and IC₅₀ = 200 nM, respectively, on the A375 melanoma cell line) and in vivo activity on melanoma xenografts. The second generation derivatives, EAPB02302 and EAPB02303, are more active, with IC₅₀ = 60 nM and IC₅₀ = 10 nM, respectively, on A375 melanoma cell line. The aim of this study was to optimize the bioavailability of imiqualine derivatives, without losing their intrinsic activity. For that, we achieved chemical modulation on the second generation of imiqualines by conjugating amino acids on position 4. A new series of twenty-five compounds was efficiently synthesized by using microwave assistance and tested for its activity on the A375 cell line. In the new series, compounds 11a, 9d and 11b show cytotoxic activities less than second generation compounds, but similar to that of the first generation ones (IC₅₀ = 403 nM, IC₅₀ = 128 nM and IC₅₀ = 584 nM, respectively). The presence of an amino acid leads to significant enhancement of the water solubility for improved drugability.

Maslinic acid protects against lipopolysaccharide/d-galactosamine-induced acute liver injury in mice

Acute liver injury is a life-threatening syndrome that often caused by hepatocyte damage. In this study, we investigated the protective effects of maslinic acid (MA) on lipopolysaccharide (LPS)/d-galactosamine (D-gal)-induced acute liver injury and clarified its mechanism. Mice acute liver injury model was induced by given LPS and D-gal and MA was given intraperitoneally 1 h before LPS and D-gal. Our results showed that MA protected against liver injury by attenuating liver histopathologic changes, serum AST and ALT levels. The increased inflammatory cytokines TNF-α and IL-6 in serum and liver tissues were also inhibited by MA. The level of MDA and the activity of MPO in liver tissues were up-regulated by LPS/D-gal and dose-dependently inhibited by MA. Furthermore, MA attenuated hepatic NF-κB protein expression and increased hepatic Nrf2 and HO-1 protein expression. Taken together, MA offers a protective role against LPS/D-gal-induced liver injury through suppressing NF-κB and activating Nrf2 signaling pathways.

Maslinic acid suppresses the growth of human gastric cells by inducing apoptosis via inhibition of the interleukin-6 mediated Janus kinase/signal transducer and activator of transcription 3 signaling pathway

The present study aimed to determine whether maslinic acid effectively inhibits the proliferation of MKN28 cells, and to investigate the mechanisms underlying its antitumor functions. MKN28 cell viability was evaluated using a Cell Counting Kit-8, cell proliferation was analyzed by a colony formation assay and flow cytometry was used to investigate the rate of apoptosis. Western blot analysis was performed in order to determine the differential expression levels of Janus kinase (JAK), signal transducer and activator of transcription 3 (STAT3) and apoptosis associated proteins B-cell lymphoma 2 (Bcl-2), Bcl-2 associated X protein (Bax) and Bcl-2 associated agonist of cell death (Bad). Interleukin-6 (IL-6) concentration was evaluated using ELISA. IL-6 and anti-IL-6 antibodies were used to investigate the role of IL-6 in MKN28 cells treated with maslinic acid proliferation, and the STAT3 phosphorylation rates. The results demonstrated that maslinic acid treatment significantly reduced cell proliferation, induced apoptosis and was accompanied by a significant decrease in Bcl-2, Bax and Bad expression levels. Maslinic acid treatment also resulted in the downregulation of phosphorylated-STAT3 and JAK2, and significantly inhibited the protein expression of IL-6. Maslinic acid is able to inhibit MKN28 cell proliferation and the phosphorylation of STAT3 by downregulating the expression of IL-6. These results suggest that maslinic acid suppresses the growth of MKN28 cells by inducing apoptosis via its inhibition of the IL-6/JAK/STAT3 signaling cascade.

Maslinic Acid Inhibits Proliferation of Renal Cell Carcinoma Cell Lines and Suppresses Angiogenesis of Endothelial Cells

Despite the introduction of many novel therapeutics in clinical practice, metastatic renal cell carcinoma (RCC) remains a treatment-resistant cancer. As red and processed meat are considered risk factors for RCC, and a vegetable-rich diet is thought to reduce this risk, research into plant-based therapeutics may provide valuable complementary or alternative therapeutics for the management of RCC. Herein, we present the antiproliferative and antiangiogenic effects of maslinic acid, which occurs naturally in edible plants, particularly in olive fruits, and also in a variety of medicinal plants. Human RCC cell lines (ACHN, Caki-1, and SN12K1), endothelial cells (human umbilical vein endothelial cell line [HUVEC]), and primary cultures of kidney proximal tubular epithelial cells (PTEC) were treated with maslinic acid. Maslinic acid was relatively less toxic to PTEC when compared with RCC under similar experimental conditions. In RCC cell lines, maslinic acid induced a significant reduction in proliferation, proliferating cell nuclear antigen, and colony formation. In HUVEC, maslinic acid induced a significant reduction in capillary tube formation in vitro and vascular endothelial growth factor. This study provides a rationale for incorporating a maslinic acid–rich diet either to reduce the risk of developing kidney cancer or as an adjunct to existing antiangiogenic therapy to improve efficacy.

Mechanistic Perspectives of Maslinic Acid in Targeting Inflammation

Chronic inflammation drives the development of various pathological diseases such as rheumatoid arthritis, atherosclerosis, multiple sclerosis, and cancer. The arachidonic acid pathway represents one of the major mechanisms for inflammation. Prostaglandins (PGs) are lipid products generated from arachidonic acid by the action of cyclooxygenase (COX) enzymes and their activity is blocked by nonsteroidal anti-inflammatory drugs (NSAIDS). The use of natural compounds in regulation of COX activity/prostaglandins production is receiving increasing attention. In Mediterranean diet, olive oil and table olives contain significant dietary sources of maslinic acid. Maslinic acid is arising as a safe and novel natural pentacyclic triterpene which has protective effects against chronic inflammatory diseases in various in vivo and in vitro experimental models. Understanding the anti-inflammatory mechanism of maslinic acid is crucial for its development as a potential dietary nutraceutical. This review focuses on the mechanistic action of maslinic acid in regulating the inflammation pathways through modulation of the arachidonic acid metabolism including the nuclear factor-kappa B (NF-κB)/COX-2 expression, upstream protein kinase signaling, and phospholipase A₂ enzyme activity. Further investigations may provide insight into the mechanism of maslinic acid in regulating the molecular targets and their associated pathways in response to specific inflammatory stimuli.

The Potential of Sub-Saharan African Plants in the Management of Human Immunodeficiency Virus Infections: A Review

Acquired immunodeficiency syndrome, caused by human immunodeficiency virus (HIV), is a leading cause of mortality and morbidity in Sub-Saharan Africa, particularly in Southern Africa. Phytomedicines are an integral part of African health care. The Southern African flora is composed of at least 23 400 taxa. Despite this richness, only a handful of botanical products have been assessed for activities against HIV. This study aimed to summarize the potential of Sub-Saharan African plants, based on their composition and the established bioactivities, as sources of agents to manage HIV symptoms and as retroviral therapy. At least 109 plant species from 42 families and 94 genera that are found in Southern Africa were shown to have potential or actual activities against HIV. Only 12 of these plant species from 6 families and 10 genera were shown to harbour anti-HIV properties. Phytochemicals that include β-sitosterols, terpenoids, glycosides, saponins, flavonoids, triterpenoids, tannins and alkaloids, which harbour anti-HIV properties, were found to have a near cosmopolitan presence across the plant families in the region. Bioactivities of multiple phytochemicals are comparable to those for standard allopathic antiretroviral drugs. Research to determine the anti-HIV activities of the identified and other plants, including clinical trials, is long overdue.

Effect of the solvent and the sample preparation on the determination of triterpene compounds in two-phase olive-mill-waste samples

A simple and rapid extraction method has been employed to determine several value-added compounds, mainly triterpenes, in two-phase olive-mill-waste samples. The compounds were extracted with methanol or ethyl acetate, and the initial fresh samples were treated for classic techniques such as drying, drying and oil extraction, and drying and sifting of the olive stones. For the identification and quantitation of the compounds, an ultra performance liquid chromatography-mass spectrometry method was employed. The best results of the triterpenic compound content were achieved by extraction with methanol from the fresh sample for the oleanolic and ursolic acids, and erythrodiol and uvaol; and from the dried-extracted sample for the maslinic acid. Conversely, the best results for the linoleic acid content were reached by extraction with ethyl acetate from the dried-sifted sample. These are remarkable processes that make the solid wastes from the olive-oil industry reach a high added value.

Antimicrobial peptides: an alternative for innovative medicines?

Antimicrobial peptides are small molecules with activity against bacteria, yeasts, fungi, viruses, bacteria, and even tumor cells that make these molecules attractive as therapeutic agents. Due to the alarming increase of antimicrobial resistance, interest in alternative antimicrobial agents has led to the exploitation of antimicrobial peptides, both synthetic and from natural sources. Thus, many peptide-based drugs are currently commercially available for the treatment of numerous ailments, such as hepatitis C, myeloma, skin infections, and diabetes. Initial barriers are being increasingly overcome with the development of cost-effective, more stable peptides. Herein, we review the available strategies for their synthesis, bioinformatics tools for the rational design of antimicrobial peptides with enhanced therapeutic indices, hurdles and shortcomings limiting the large-scale production of AMPs, as well as the challenges that the pharmaceutical industry faces on their use as therapeutic agents.

Amino acid derivatives of ligustrazine-oleanolic acid as new cytotoxic agents

A series of novel ligustrazine-oleanolic acid (TOA) derivatives were designed, and synthesized by conjugating amino acids to the 3-hydroxy group of TOA by ester bonds. Their cytotoxicity was evaluated on four cancer cell lines (HepG2, HT-29, Hela and BGC-823) by standard MTT assays. The ClogP values were calculated by means of computer simulation, and logP values of both 3β-glycine ester olean-12-en-28-oic acid-3,5,6-trimethylpyrazin-2-methyl ester (6a) and TOA were determined using a shake flask-ultraviolet spectrophotometry method. It was found that 6a and the 3β-L-lysine ester-6g not only displayed good cytotoxicity (IC50<3.5 μM) but also possessed better hydrophilicity than TOA. Moreover, 6a (IC50=4.884 μM) had lower nephrotoxicity than both 6g (IC50=2.310 μM) and cisplatin (CDDP, IC50=3.691 μM) on MDCK cells. Combining Giemsa and DAPI staining, it was further verified that 6a could induce HepG2 apoptosis via nuclei fragmentation and had lower nephrotoxicity. In addition, the structure-activity relationships of these derivatives are briefly discussed.

Solid-phase library synthesis of bi-functional derivatives of oleanolic and maslinic acids and their cytotoxicity on three cancer cell lines

A wide set of 264 compounds has been semisynthesized with high yields and purities. These compounds have been obtained through easy synthetic processes based on a solid-phase combinatorial methodology. All the members of this library have one central core of a natural pentacyclic triterpene (oleanolic or maslinic acid) and differ by 6 amino acids, coupled with the carboxyl group at C-28 of the triterpenoid skeleton, and by 10 different acyl groups attached to the hydroxyl groups of the A-ring of these molecules. According to the literature on the outstanding and promising pharmacological activities of other similar terpene derivatives, some of these compounds have been tested for their cytotoxic effects on the proliferation of three cancer cell lines: B16-F10, HT29, and Hep G2. In general, we have found that around 70% of the compounds tested show cytotoxicity in all three of the cell lines selected; around 60% of the cytotoxic compounds are more effective than their corresponding precursors, that is, oleanolic (OA) or maslinic (MA) acids; and nearly 50% of the cytotoxic derivatives have IC50 values between 2- to 320-fold lower than their corresponding precursor (OA or MA).

Maslinic acid protects vascular smooth muscle cells from oxidative stress through Akt/Nrf2/HO-1 pathway

Maslinic acid (MA) is a natural triterpenoid widely distributed in edible and medicinal plants and has been demonstrated to possess bioactivity. However, its effect on vascular smooth muscle cells (VSMC) has not been explored yet. In this study, we found that heme oxygenase-1 (HO-1) expression was increased in VSMCs treated with MA. Furthermore, MA was found to induce Akt activation in a dose- and time-dependent manner. Wortmannin suppression of Akt was able to abolish HO-1 upregulation in VSMCs, suggesting the requirement of Akt activation for MA effect on HO-1. Further investigation indicated that Akt activation resulted in the elevated expression of Nrf2, a HO-1 promoter, in MA-treated VMSCs. Finally, we found that MA was able to protect VSMCs from oxidative stress induced by H2O2. Blocking the activation of Akt/Nrf2/HO-1 was able to compromise the protective effect of MA on VSMCs. Collectively, we provided evidence that MA protected VMSCs from oxidative stress through Akt/Nrf2/HO-1 pathway.

Antioxidant effects of maslinic acid in livers, hearts and kidneys of streptozotocin-induced diabetic rats: effects on kidney function

Studies indicate that hyperglycemia-induced oxidative stress triggers the development of microvascular and macrovascular complications in diabetes. Accordingly, we hypothesized that maslinic acid (MA) prevents these complications due to its antioxidant properties. We, therefore, investigated the effects of 5-week MA treatment of streptozotocin (STZ)-induced diabetic rats on anti-oxidative status of cardiac, hepatic and renal tissues as well as on kidney function. Proximal tubular effects of MA were studied in anesthetized rats challenged with hypotonic saline after a 3.5 h equilibration for 4 h of 1 h control, 1.5 h treatment and 1.5 h recovery periods using lithium clearance. MA was added to the infusate during the treatment period. Oral glucose tolerance responses to MA were monitored in rats given a glucose load after an 18 h fast. Compared with untreated diabetic rats, MA-treated diabetic animals exhibited significantly low malondialdehyde (MDA, a marker of lipid peroxidation) and increased the activity of antioxidant enzymes; superoxide dismutase and glutathione peroxidase in hepatic, cardiac and renal tissues. The expressions of gastrocnemius muscle GLUT4 and kidney GLUT1 and GLUT2 were assessed to elucidate the mechanism of the hypoglycemic effects of MA. MA-treatment diminished the expression of GLUT1 and GLUT2 in diabetic kidney and reduced glycemia values of diabetic rats. MA administration increased urinary Na+ outputs and additionally the FENa indicating that at least part of the overall reduction in Na+ reabsorption occurred in the proximal tubules. These results suggest antioxidant effects of MA can ameliorate oxidative stress and improve kidney function in diabetes mellitus.

Esters and amides of maslinic acid trigger apoptosis in human tumor cells and alter their mode of action with respect to the substitution pattern at C-28

Cancer is one of the most commonly diagnosed diseases worldwide; its mortality rate is high, and there is still a demand for the development of antitumor active drugs. Triterpenoic acids show many pharmacological effects, among them antitumor activity. One of these, maslinic acid-1 is of interest because of its antitumor profile. It is not only cytotoxic but also triggers apoptosis in various human tumor cell lines. To improve the cytotoxicity of parent 1 we set out to synthesize a series of esters and amides differing in structure and lipophilicity. These compounds were tested in a sulforhodamine B assay for cytotoxicity, and screened for their ability to induce apoptosis using an acridine orange/propidium iodide assay, DNA laddering and cell cycle experiments. Esters containing small-chain, lipophilic residues increased the cytotoxicity whereas amides as well long-chain esters led to a decrease in activity. The antitumor activity seems to be independent from the substitution pattern at position C-28 for esters and amides but alters their mode of action.

Biotransformation of oleanolic and maslinic acids by Rhizomucor miehei

Microbial transformation of oleanolic acid by Rhizomucor miehei produced three metabolites. A known compound, a 30-hydroxyl derivative (queretaroic acid), and two 7β,30- and 1β,30-dihydroxylated metabolites, respectively. The action of the same fungus (R. miehei) on maslinic acid produced an olean-11-en-28,13β-olide derivative, a metabolite hydroxylated at C-30, an 11-oxo derivative, and two metabolites with an 11α,12α-epoxy group, hydroxylated or not at C-30. Their structures were elucidated by extensive analyses of their spectroscopic data, and also by chemical correlations.

Hyptis verticillata Jacq: a review of its traditional uses, phytochemistry, pharmacology and toxicology

ETHNOPHARMACOLOGICAL RELEVANCE

Hyptis verticillata Jacq. (Lamiaceae) (John Charles) is an important medicinal plant with a long history of traditional use, originating in Central America and now extending from Florida to Colombia and across the Caribbean. Records of its earliest use date back to the ancient Mayan and Aztec cultures of Mesoamerica. There is no indication that this plant is being used outside of the Americas.

AIM OF THE REVIEW

This review aims to provide a comprehensive overview of the traditional use, phytochemistry, pharmacological activity and toxicology of Hyptis verticillata and to highlight the opportunities for greater development of the plant's medicinal properties at a local and international level.

MATERIALS AND METHODS

An extensive and systematic review of the literature was undertaken and all relevant abstracts and full-text articles analysed and included in the review.

KEY FINDINGS

A wide range of traditional uses are cited in the literature, from internal uses for conditions affecting the respiratory system, digestive tract and gynaecological system to external uses for conditions affecting the skin and musculoskeletal system. Pharmacological studies to date have demonstrated significant activity which support the traditional use of the plant as an antiinflammatory, antimicrobial, antisecretory agent and hormone modulator. In addition studies have identified anti-cancer, acaricidal, insecticidal and molluscicidal activity. No clinical trials had been completed at the time of this review. A number of key phytochemicals have been isolated, identified and published to date including: 17 lignans; 4 triterpenes; 11 diterpenes, 3 sesquiterpenes, 3 monoterpenes, 2 flavonoids, 1 polyphenol and 1 alkaloid. Nine of these phytochemicals are novel to Hyptis verticillata. Plant extracts and isolated phytochemicals exhibit a broad range of activities that include: antimitotic; antiproliferative; cytotoxic; antioxidant; antiinflammatory; antibacterial; antifungal; antiviral; anti-HIV; antisecretory; hepatoprotective; insecticidal and acaricidal.

CONCLUSIONS

Hyptis verticillata is a medicinal plant with current widespread traditional use in the Americas that warrants further research, clinical trials and product development to fully exploit its medicinal value.

Maslinic acid-enriched diet decreases intestinal tumorigenesis in Apc(Min/+) mice through transcriptomic and metabolomic reprogramming

Chemoprevention is a pragmatic approach to reduce the risk of colorectal cancer, one of the leading causes of cancer-related death in western countries. In this regard, maslinic acid (MA), a pentacyclic triterpene extracted from wax-like coatings of olives, is known to inhibit proliferation and induce apoptosis in colon cancer cell lines without affecting normal intestinal cells. The present study evaluated the chemopreventive efficacy and associated mechanisms of maslinic acid treatment on spontaneous intestinal tumorigenesis in Apc^Min/+ mice. Twenty-two mice were randomized into 2 groups: control group and MA group, fed with a maslinic acid–supplemented diet for six weeks. MA treatment reduced total intestinal polyp formation by 45% (P<0.01). Putative molecular mechanisms associated with suppressing intestinal polyposis in Apc^Min/+ mice were investigated by comparing microarray expression profiles of MA-treated and control mice and by analyzing the serum metabolic profile using NMR techniques. The different expression phenotype induced by MA suggested that it exerts its chemopreventive action mainly by inhibiting cell-survival signaling and inflammation. These changes eventually induce G1-phase cell cycle arrest and apoptosis. Moreover, the metabolic changes induced by MA treatment were associated with a protective profile against intestinal tumorigenesis. These results show the efficacy and underlying mechanisms of MA against intestinal tumor development in the Apc^Min/+ mice model, suggesting its chemopreventive potential against colorectal cancer.

Multi-targeted activity of maslinic acid as an antimalarial natural compound

Most drugs against malaria that are available or under development target a single process of the parasite infective cycle, favouring the appearance of resistant mutants which are easily spread in areas under chemotherapeutic treatments. Maslinic acid (MA) is a low toxic natural pentacyclic triterpene for which a wide variety of biological and therapeutic activities have been reported. Previous work revealed that Plasmodium falciparum erythrocytic cultures were inhibited by MA, which was able to hinder the maturation from ring to schizont stage and, as a consequence, prevent the release of merozoites and the subsequent invasion. We show here that MA effectively inhibits the proteolytic processing of the merozoite surface protein complex, probably by inhibition of PfSUB1. In addition, MA was also found to inhibit metalloproteases of the M16 family by a non-chelating mechanism, suggesting the possible hindrance of plasmodial metalloproteases belonging to that family, such as falcilysin and apicoplast peptide-processing proteases. Finally, in silico target screening was used to search for other potential binding targets that may have remained undetected. Among the targets identified, the method recovered two for which experimental activity could be confirmed, and suggested several putative new targets to which MA could have affinity. One of these unreported targets, phospholipase A2, was shown to be partially inhibited by MA. These results suggest that MA may behave as a multi-targeted drug against the intra-erythrocytic cycle of Plasmodium, providing a new tool to investigate the synergistic effect of inhibiting several unrelated processes with a single compound, a new concept in antimalarial research.

Design and synthesis of a dual linker for solid phase synthesis of oleanolic acid derivatives

A hydrophilic amino-terminated poly(ethylene glycol)-type dual linker for solid phase synthesis of oleanolic acid derivatives using trityl chloride resin was designed and synthesized for the first time. Model reactions in both liquid and solid phase were performed to show the feasibility of its selective cleavage at two different sites. The biological assay results indicated that the long and flexible alkyl ether functionality in the linker is less likely to be critical for the binding event. Following the successful solid-phase synthesis of model compounds, the potential of this dual linker in reaction monitoring and target identification is deemed worthy of further study.

Parasitostatic effect of maslinic acid. I. Growth arrest of Plasmodium falciparum intraerythrocytic stages

Background

Natural products have played an important role as leads for the development of new drugs against malaria. Recent studies have shown that maslinic acid (MA), a natural triterpene obtained from olive pomace, which displays multiple biological and antimicrobial activities, also exerts inhibitory effects on the development of some Apicomplexan, including Eimeria, Toxoplasma and Neospora. To ascertain if MA displays anti-malarial activity, the main objective of this study was to asses the effect of MA on Plasmodium falciparum-infected erythrocytes in vitro.

Methods

Synchronized P. falciparum-infected erythrocyte cultures were incubated under different conditions with MA, and compared to chloroquine and atovaquone treated cultures. The effects on parasite growth were determined by monitoring the parasitaemia and the accumulation of the different infective stages visualized in thin blood smears.

Results

MA inhibits the growth of P. falciparum Dd2 and 3D7 strains in infected erythrocytes in, dose-dependent manner, leading to the accumulation of immature forms at IC₅₀ concentrations, while higher doses produced non-viable parasite cells. MA-treated infected-erythrocyte cultures were compared to those treated with chloroquine or atovaquone, showing significant differences in the pattern of accumulation of parasitic stages. Transient MA treatment at different parasite stages showed that the compound targeted intra-erythrocytic processes from early-ring to schizont stage. These results indicate that MA has a parasitostatic effect, which does not inactivate permanently P. falciparum, as the removal of the compound allowed the infection to continue

Conclusions

MA displays anti-malarial activity at multiple intraerythrocytic stages of the parasite and, depending on the dose and incubation time, behaves as a plasmodial parasitostatic compound. This novel parasitostatic effect appears to be unrelated to previous mechanisms proposed for current anti-malarial drugs, and may be relevant to uncover new prospective plasmodial targets and opens novel possibilities of therapies associated to host immune response.

Astrocytic glutamate transporter-dependent neuroprotection against glutamate toxicity: an in vitro study of maslinic acid

The astrocytic glutamate transporters GLAST/EAAT1 and GLT-1/EAAT2 are crucial for the removal of glutamate from the synaptic cleft and are essential for maintaining a low concentration of extracellular glutamate in the brain. Enhanced transporter expression is neuroprotective. In the present study, we tested the neuropotective effects of maslinic acid, a natural product from the Olea europaea plant, on cultures of primary neurons from the cerebral cortex. Studies showed that astrocyte-conditioned medium from maslinic acid-treated astrocytes dose-dependently promoted neuron survival during glutamate toxicity by enhancing extracellular glutamate clearance. Real-time PCR and western blot analysis revealed that maslinic acid pre-treatment significantly increased the expression of GLAST and GLT-1 at the protein and mRNA levels. In addition, this neuroprotection was abolished by the glutamate transporter inhibitor, L-Threohydroxy aspartate (THA), in a co-culture of astrocytes and neurons. These findings suggest that maslinic acid regulates the extracellular glutamate concentration by increasing the expression of astrocytic glutamate transporters, which may, in turn, provide neuroprotection.

Action of a pentacyclic triterpenoid, maslinic acid, against Toxoplasma gondii

The action of maslinic acid (2alpha,3beta-dihydroxyolean-12-en-28-oic acid) (1), a pentacyclic derivative present in the pressed fruits of the olive (Olea europaea), has been studied against the tachyzoites of Toxoplasma gondii. The capability of tachyzoites to infect Vero cells treated with 1 was affected. The LD(50) values were 58.2 muM for the isolated tachyzoites and 236 muM for the noninfected Vero cells. Zymograms of the T. gondii proteases incubated with 1 showed a dosage-dependent inhibition of some of the proteases. The parasites treated with 1 showed gliding motility and ultrastructural alterations. The present findings suggest that protease activity of the parasite required for cell invasion is the action target for maslinic acid (1).