In vitro inhibition and eradication of multidrug-resistant Acinetobacter baumannii biofilms by riparin III and colistin combination.

Acinetobacter baumannii, a prominent emerging pathogen, is responsible for persistent and recurrent healthcare-associated infections (HAIs). Its bacterial resistance and virulence factors, such as biofilm formation, contribute to its survival in hospital environments. Combination therapy has proven to be an effective approach for controlling these infections; however, antimicrobial resistance and compound toxicity can hinder antimicrobial efficacy. Numerous in vitro studies have demonstrated the synergistic effect of antimicrobials and natural products against multidrug-resistant (MDR) A. baumannii biofilm. Riparin III, a natural alkamide derived from Aniba riparia (Nees) Mez., possesses various biological activities, including significant antimicrobial potential. Nonetheless, no reports are available on the use of this compound in conjunction with conventional antimicrobials. Hence, this study aimed to investigate the inhibition and eradication of A. baumannii MDR biofilm by combining riparin III and colistin, along with potential ultrastructural changes observed in vitro. Clinical isolates of A. baumannii, known for their robust biofilm production, were inhibited, or eradicated in the presence of the riparin III/colistin combination. Furthermore, the combination resulted in several ultrastructural alterations within the biofilm, such as elongated cells and coccus morphology, partial or complete disruption of the biofilm's extracellular matrix, and cells exhibiting cytoplasmic material extravasation. At the synergistic concentrations, the riparin III/colistin combination exhibited a low hemolytic percentage, ranging from 5.74% to 6.19%, exerting inhibitory and eradicating effects on the A. baumannii biofilm, accompanied by notable ultrastructural changes. These findings suggest its potential as a promising alternative for therapeutic purposes.

Antileishmanial activity of Riparin structural analogs of Aniba riparia: Biological evaluation, in silico Adme-Tox, and molecular docking.

We performed a biological evaluation of antileishmanial activity, in silico ADME-Tox profile, and molecular docking of riparins A-F. The antileishmanial activity was evaluated in Leishmania major promastigotes, whereas the cytotoxic activity was tested on murine macrophages. Computational parameters were predicted by in silico analysis. Molecular docking was performed with 18 L. major molecular targets. Riparins, especially RipC and RipE, showed cytotoxic activity in vitro toward L. major promastigotes and a high selectivity index. Riparins showed small differences in their physicochemical properties, such as polarity and aqueous solubility. LogP was an important parameter for the differences in the antileishmanial activity between the molecules. In molecular docking, the ligands displayed Ki < 1 µM for LmNMT and LmLEI. Significant molecular interactions were observed with residues from the active site and adjacent regions of such enzymes. Thus, riparins have the potential for application in antileishmanial therapy.

Neuroprotective and Antioxidant Effects of Riparin I in a Model of Depression Induced by Corticosterone in Female Mice.

BACKGROUND: Depression is a common, chronic, and often recurrent serious mood disorder. Conventional antidepressants present limitations that stimulate the search for new drugs. Antioxidant and neuroprotective substances are potential antidepressant agents. In this context, riparin I (RIP I) has presented promising results, emerging as a potential source of a new therapeutic drug. In this study, the antidepressant effect of RIP I was evaluated in an animal model of depression induced by corticosterone (CORT). The involvement of neuroprotective and antioxidant mechanisms in the generation of this effect was also assessed. METHODS: Female mice were submitted to CORT for 21 days and treated with RIP I in the last 7 days. Behavioral and neurochemical analyses were performed. RESULTS: The administration of RIP I reversed the depressive and psychotic-like behavior, as well as the cognitive impairment caused by CORT, in addition to regulating oxidative stress parameters and BDNF levels in depression-related brain areas. CONCLUSION: These findings suggest that RIP I can be a strong candidate for drugs in the treatment of depression.

Mechanism of the lethal effect of Riparin E against bacterial and yeast strains.

Riparins are alkamides naturally found in the fruits of Aniba riparia (Nees) Mez, but currently synthetic molecules as Riparin E (Rip-E) can be obtained. Potential biological of Rip-E as schistosomicidal agent against Schistosoma mansoni worms, as well as against Staphylococcus aureus strains has already been described. However, the mechanism of action related to antimicrobial activity of Rip-E against bacterial or fungi species has not yet been reported. This study had as objective to evaluate the Rip-E antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as against yeast species of clinical importance. Minimal inhibitory concentrations of the compound against bacterial and yeast strains were determined by microdilution method. To verify if a possible lethal effect caused by Rip-E were related to plasma membrane damage, microbial cells treated with Rip-E were stained with 7-aminoactinomycin D (7-AAD) and analyzed by flow cytometry. Rip-E showed a bactericide effect against Gram-positive species S. aureus and S. epidermidis, as well as, against Gram-negative species Escherichia coli and Salmonella enterica Typhimurium, but was inactive against Pseudomonas aeruginosa. Moreover, Rip-E showed activity against fungi species Candida albicans and C. tropicalis. S. aureus, E. coli and C. albicans cells treated with Rip-E were marked with 7-aminoactinomycin D (7-AAD) indicating that Rip-E can cause plasma membrane damage, acting as a potential microbicide agent for prevention or treatment of infectious diseases.

In vitro antileishmanial and immunomodulatory activities of the synthetic analogue riparin E.

Leishmaniases are infectious diseases caused by protozoa of the genus Leishmania, that may have different clinical manifestations. First line drugs used in the treatment of leishmaniosis are high costly, and are very aggressive requiring medical monitoring. Thus new therapeutic alternatives are needed and, in this context, natural products have been considered as a source of new antileishmania agents. Riparins are alkamides found in the unripe fruits of Aniba riparia. Several biological activities are described for this group of compounds, such as antimicrobial and antiparasitic potential. The objective of this work was to evaluate the anti-leishmania activity riparin E (Rip-E) in vitro, against promastigotes and internalized amastigotes of Leishmania amazonensis. Rip-E was able to inhibit promastigote cell growth (IC50 4.7 µg/ml) and to reduce the percentage of macrophages infected with amastigotes, reducing its infectivity (survival index) (IC50 1.3 µg/ml). The cytotoxicity against BALB/c murine macrophages was also assessed (CC50 50.6 µg/ml) and the selectivity index was 38.9. Rip-E also demonstrated immunomodulatory activity, evidenced by the increase of the phagocytic capacity and lysosomal activity. However, Rip-E did not affect directly the production of nitric oxide. These results suggest that Rip-E has antileishmania potential, by both its direct inhibitory effect and its ability to activate macrophages.

Psychopharmacological effects of riparin III from Aniba riparia (Nees) Mez. (Lauraceae) supported by metabolic approach and multivariate data analysis.

BACKGROUND: Currently there is a high prevalence of humor disorders such as anxiety and depression throughout the world, especially concerning advanced age patients. Aniba riparia (Nees) Mez. (Lauraceae), popular known as "louro", can be found from the Amazon through Guianas until the Andes. Previous studies have already reported the isolation of alkamide-type alkaloids such as riparin III (O-methyl-N-2,6-dyhydroxy-benzoyl tyramine) which has demonstrated anxiolytic and antidepressant-like effects in high doses by intraperitoneal administration. METHODS: Experimental protocol was conducted in order to analyze the anxiolytic-like effect of riparin III at lower doses by intravenous administration to Wistar rats (Rattus norvegicus) (n = 5). The experimental approach was designed to last 15 days, divided in 3 distinct periods of five days: control, anxiogenic and treatment periods. The anxiolytic-like effect was evaluated by experimental behavior tests such as open field and elevated plus-maze test, combined with urine metabolic footprint analysis. The urine was collected daily and analyzed by 1H NMR. Generated data were statistically treated by Principal Component Analysis in order to detect patterns among the distinct periods evaluated as well as biomarkers responsible for its distinction. RESULTS: It was observed on treatment group that cortisol, biomarker related to physiological stress was reduced, indicating anxiolytic-like effect of riparin III, probably through activation of 5-HT2A receptors, which was corroborated by behavioral tests. CONCLUSION: 1H NMR urine metabolic footprint combined with multivariate data analysis have demonstrated to be an important diagnostic tool to prove the anxiolytic-like effect of riparin III in a more efficient and pragmatic way.

Antinociceptive activity of Riparin II from Aniba riparia: Further elucidation of the possible mechanisms.

Riparin II (RipII) has an anti-inflammatory activity potentially due its ability to decrease TNF-α and IL-1ß production and its histamine antagonism. The objective of this study was to evaluate the role of RipII in the pain process and the possible antinociceptive mechanisms involved, using classic models of nociception. Male Swiss mice were used in the assays. Determinate the acute toxicity according to the OECD 425 test guideline. The models used were the acetic acid-, formalin-, hot plate and glutamate-induced nociception. For evaluation of antinociceptive effect, the involvement of TRPV1, TRPA1, TRPM8, ASICS, Bradykinin, PKC and PKA were performed using the paw licking using agonists. The acute toxicity study did not detect any clinical signs or changes in behavior or mortality. RipII, administered orally (25 and 50 mg/kg) caused a reduction of nociception induced by acetic acid, formalin (on the second phase) and glutamate. In the investigation of antinociceptive mechanism, we used capsaicin (2.2 µg/paw), cinnamaldehyde (10 nmol/paw), menthol (1.2 µmol/paw), ASICS (2% acetic acid, pH 1.98) and bradykinin (10 µg/paw). The results showed that TRPV1, TRPA1, TRPM8, ASICS and bradykinin play a role in the antinociceptive effect of RipII. The results also showed that PKA is involved too. These data demonstrate that RipII has a low or not toxicity and produced an important antinociceptive effect through mechanisms that probably involve an interaction, at least in part, TRPV1, TRPA1, TRPM8, ASICS, bradykinin and PKA participate in the RipII's antinociceptive effect.

Solid-State Form Characterization of Riparin I.

Riparin I is an alkamide with potential anxiolytic activity in preclinical studies. The characterization and understanding of solid-state properties play an importance role in drug development. For this work, the solid state of five riparin I batches (RIP-1, RIP-2, RIP-3, RIP-4, and RIP-5), obtained by the same synthesis process, were characterized by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), DSC-photovisual, Thermogravimetry (TG), Fourier Transform Infrared (FTIR), Pyrolysis (Pyr-GC/MS), X-ray Powder Diffraction (PXRD), and Solid-State Nuclear Magnetic Resonance (ssNMR) techniques. Batches of riparin I with different crystal habits resulting in crystallization impurities were observed, which can be attributed to the presence of triethylamine. The main differences were observed by DSC, PXRD, and ssNMR analysis. DSC curves of RIP-2 and RIP-3 presented endothermic peaks at different temperatures of fusion, which can be attributed to the mixture of different crystalline forms. PXRD and ssNMR results confirmed crystallinity differences. The results offer evidence of the importance of controlling the reproducibility of the synthesis in order to obtain the adequate morphology for therapeutic efficacy and avoiding future problems in quality control of riparin I products.

Evidence for the involvement of the serotonergic, noradrenergic, and dopaminergic systems in the antidepressant-like action of riparin III obtained from Aniba riparia (Nees) Mez (Lauraceae) in mice.

Previous work has shown that intraperitoneal administration of riparin III (ripIII) reduces immobility time in the forced swimming test (FST), which suggests potential antidepressant activity. As the mechanism of action is not completely understood, this study is aimed at investigating the antidepressant-like action of ripIII. Following intraperitoneal administration of ripIII at doses of 25 and 50 mg/kg, there were decreases in the immobility time in the FST and tail suspension test without accompanying changes in ambulation (data not shown). The pretreatment of mice with sulpiride (50 mg/kg, i.p.), prazosin (1 mg/kg, i.p.), yohimbine (1 mg/kg, i.p.), and p-chlorophenylalanine (PCPA, 100 mg/kg, i.p. for, four consecutive days) significantly prevented the anti-immobility effect of ripIII in the FST. On the other hand, the anti-immobility effect of ripIII (50 mg/kg, v.o.) was not altered by pretreatment of mice with SCH23390 (15 µg/kg, i.p.) Furthermore, ripIII potentiated the sleeping latency and sleeping time of the pentobarbital-induced sleeping time test and also potentiated apomorphine (16 mg/kg, i.p.)-induced hypothermia in mice. In conclusion, the present study provides evidence that the antidepressant-like effect of ripIII is dependent on its interaction with the serotonergic, noradrenergic (α1- and α2- receptors), and dopaminergic (dopamine D2 receptors) systems.