Improving Riparin-A Dissolution through a Laponite Based Nanohybrid.

(1) Background: Riparin-A presents several pharmacological activities already elucidated, such as antimicrobial modulator, antileishmania, anxiolytic, anti-inflammatory, antinociceptive, and antioxidant. Even with important bioactive effects, the applicability of Riparin-A is limited due to its low solubility in water, impairing its dissolution in biological fluids. Thus, the objective of this study was to develop a nanohybrid based on Riparin-A and Laponite to obtain a better dissolution profile and evaluate its cytotoxic potential. (2) Methods: The formation of a hybrid system was highlighted by X-ray powder diffraction, infrared spectroscopy, and thermal analysis. Solubility, dissolution, and cytotoxicity studies were performed; (3) Results: An increase in the solubility and aqueous dissolution rate of Riparin-A was observed in the presence of clay. Diffractometric analysis of the hybrid system suggests the amorphization of Riparin-A, and thermal analyses indicated attenuation of decomposition and melting of the Riparin-A after interaction with clay. Furthermore, the nanosystem did not exhibit cytotoxic activity on normal and tumorigenic lines. (4) Conclusions: These results are promising for the development of the Riparin-A/Laponite nanosystem for therapeutic purposes, suggesting an increase in the range of possible routes of administration and bioavailability of this bioactive compound.

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.

Antifungal and Antibiofilm Activity of Riparin III against Dermatophytes.

The ability of dermatophytes to develop biofilms is possibly involved in therapeutic failure because biofilms impair drug effectiveness in the infected tissues. Research to find new drugs with antibiofilm activity against dermatophytes is crucial. In this way, riparins, a class of alkaloids that contain an amide group, are promising antifungal compounds. In this study, we evaluated the antifungal and antibiofilm activity of riparin III (RIP3) against Trichophyton rubrum, Microsporum canis, and Nannizzia gypsea strains. We used ciclopirox (CPX) as a positive control. The effects of RIP3 on fungal growth were evaluated by the microdilution technique. The quantification of the biofilm biomass in vitro was assessed by crystal violet, and the biofilm viability was assessed by quantifying the CFU number. The ex vivo model was performed on human nail fragments, which were evaluated by visualization under light microscopy and by quantifying the CFU number (viability). Finally, we evaluated whether RIP3 inhibits sulfite production in T. rubrum. RIP3 inhibited the growth of T. rubrum and M. canis from 128 mg/L and N. gypsea from 256 mg/L. The results showed that RIP3 is a fungicide. Regarding antibiofilm activity, RIP3 inhibited biofilm formation and viability in vitro and ex vivo. Moreover, RIP3 inhibited the secretion of sulfite significantly and was more potent than CPX. In conclusion, the results indicate that RIP3 is a promising antifungal agent against biofilms of dermatophytes and might inhibit sulfite secretion, one relevant virulence factor.

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.

Is Riparin III a promising drug in the treatment for depression?

Stress is crucially related to the pathophysiology of mood disorders, including depression. Since the effectiveness and number of the current pharmacological options still presents significant limitations, research on new substances is paramount. In rodents, several findings have indicated that corticosterone administration induces the manifestation of behavioral and neurochemical aspects of depression. Recently, riparin III has shown antidepressant-like properties in trials performed on animal models. Thus, our goal was to investigate the effects of riparin III on behavioral tests, monoamines levels, oxidative stress and cytokines levels in chronic corticosterone-induced model of depression. To do this, female swiss mice were treated with subcutaneous administration of corticosterone for 22 days. In addition, for the last 10 days, riparin III or fluvoxamine were also administered per os in specific test groups. Control groups received subcutaneous saline injections or distilled water per os. At the end of the timeline, the animals were killed and their hippocampi, prefrontal cortex, and striatum dissected for neurochemical analysis. Brain changes following corticosterone administration were confirmed, and riparin III could reversed the most abnormal behavioral and neurochemical corticosterone-induced alterations. These results suggest the potential antioxidant, anti-inflammatory and antidepressant effects of riparin III after a chronic stress exposure.

Riparin II potentials the effect of ephedrine on inflammation and remodelling in the airway of rats suffering from asthma by regulating transforming growth factor-ß/Smad3 signalling pathway.

Asthma is a chronic obstructive lung disorder involving hyperresponsive lung tissue. This study evaluated the protective effects of riparin II against asthma and determined the synergistic effects of riparin II with ephedrine in treatment of asthma. Asthma was induced by intraperitoneal injection of Al(OH)3 (100 mg) with ovalbumin 1 mg/kg and subsequent exposure to 2% ovalbumin aerosol for 1 week. All animals were treated with riparin II 50 mg/kg and ephedrine 25 mg/kg alone and in combination for the duration of the study. Interleukin levels were assessed in the serum and bronchoalveolar lavage fluid (BALF) of asthmatic rats, while inflammatory cell infiltration was determined in the lungs. Airway remodelling was determined by assessing the lung tissue expression levels of transforming growth factor beta 1 (TGF-ß1), Smad, and collagen I in asthmatic rats. There were lower levels of cytokines in the serum and BALF in riparin II-treated rats than in negative control rats. Moreover, inflammatory cell and IgE levels were reduced while interferon level was enhanced in the lungs of riparin II-treated rats, compared to negative control rats. These data reveal that treatment with riparin II ameliorates the altered expression of TGF-ß1, Smad, and collagen I in lung tissue of asthmatic rats. In conclusion, riparin II treatment alone and in combination with ephedrine ameliorated the hyperresponsiveness of lung tissue due to reductions in airway remodelling and inflammation in asthmatic rats.

Antimicrobial activity and biofilm inhibition of riparins I, II and III and ultrastructural changes in multidrug-resistant bacteria of medical importance.

Natural products have been used to treat various infections; however, the development of antimicrobials has made natural products in disuse. Riparin I, II and III are natural alkamide isolated from Aniba riparia (Ness) Mez (Lauraceae), that exhibit economic importance and it is used in traditional medicine, and popularly known as "louro". This study investigated the cytotoxicity, antimicrobial and antibiofilm activity, and ultrastructural changes in vitro by riparins I, II and III in Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa. We analyzed the cytotoxicity by MTT assay in Vero cells and hemolytic action verified in human erythrocytes. The antimicrobial activity was determined by microdilution in broth against ATCC strains, identifying the susceptible species. Subsequently, only the MDR isolates of sensitive bacterial species were evaluated regarding its biofilm formation and ultrastructural changes. Riparin I presented low cytotoxicity and hemolytic percentage ranging from of 9.01%-12.97%. Only the riparin III that showed antimicrobial activity against MDR clinical isolates, and significant reduction in biofilm formation in S. aureus. Moreover, the riparin III promoted ultrastructural changes in bacterial cells, such as elongated cellular without bacterial septum, cells with a rugged appearance on the cell surface and cytoplasmic material extravasation. As has been noted riparin III has an inhibitory potential against biofilm formation in S. aureus, besides having antimicrobial activity and promoting ultrastructural changes in MDR clinical isolates. Thus, riparin III is an interesting alternative for further studies aiming to develop new therapeutic options.

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.

The neuroprotective effect of Riparin IV on oxidative stress and neuroinflammation related to chronic stress-induced cognitive impairment.

BACKGROUND: Cognitive impairment is identified as one of the diagnostic criteria for major depressive disorder and can extensively affect the quality of life of patients. Based on these findings, this study aimed to investigate the possible effects of Riparin IV (Rip IV) on cognitive impairment induced by chronic administration of corticosterone in mice. METHODS: Female Swiss mice were divided into four groups: control (Control), corticosterone (Cort), Riparin IV (Cort + Rip IV), and Fluvoxamine (Cort + Flu). Three groups were administered corticosterone (20 mg/kg) subcutaneously during the 22-day study, while the control group received only vehicle. After the 14th day, the groups were administered medications: Riparin IV (Rip IV), fluvoxamine (Flu), or distilled water, by gavage, 1 h after the subcutaneous injections. After treatment, mice underwent behavioral testing, and brain areas were removed for oxidative stress and cytokine content assays. RESULTS: The results revealed that Cort-treated mice developed a cognitive impairment and exhibited a neuroinflammatory profile with an oxidative load and Th1/Th2 cytokine imbalance. Rip IV treatment significantly ameliorated the cognitive deficit induced by Cort and displayed a neuroprotective effect. CONCLUSION: The antidepressant-like ability of Rip IV treatment against chronic Cort-induced stress may be due to its potential to mitigate inflammatory damage and oxidative stress. The antioxidant and anti-inflammatory effect observed indicates Rip IV as a possible drug for antidepressant treatment of non-responsive patients with severe and cognitive symptoms.

Involvement of monoaminergic targets in the antidepressant- and anxiolytic-like effects of the synthetic alkamide riparin IV: Elucidation of further mechanisms through pharmacological, neurochemistry and computational approaches.

Despite recent advances, current antidepressants have considerable limitations: late onset of action and the high profile of refractoriness. Biomedical research with natural products has gained growing interest in the last years, and had provide useful candidates for new antidepressants. Riparins are a group of natural alkamides obtained from Aniba riparia, which had marked neuroactive effects, mainly as antidepressant and antinociceptive agents. We made modifications of the basic structure of riparins, originating a synthetic alkamide, also known as riparin IV (RipIV). RipIV demonstrated a superior analgesic effect than its congeners and a marked antidepressant-like effect. However, the basic mechanism for the central effects of RipIV remains unknown. Here, we aimed to investigate the participation of monoaminergic neurotransmission targets in the antidepressant-like effects of RipIV. To do this, we applied a combined approach of experimental (classical pharmacology and neurochemistry) and computer-aided techniques. Our results demonstrated that RipIV presented antidepressant- and anxiolytic-like effects without modifying locomotion and motor coordination of mice. Also, RipIV increased brain monoamines and their metabolite levels. At the higher dose (100 mg/kg), RipIV increased serotonin concentrations in all studied brain areas, while at the lower one (50 mg/kg), it increased mainly dopamine and noradrenaline levels. When tested with selective receptor antagonists, RipIV antidepressant effect showed dependence of the activation of multiple targets, including D1 and D2 dopamine receptors, 5-HT2A/2, 5-HT3 receptors and α2 adrenergic receptors. Molecular docking demonstrated favorable binding conformation and affinity of RipIV to monoamine oxidase B (MAO-B), serotonin transporter (SERT), α1 receptor, D2 receptor, dopamine transporter (DAT) and at some extent GABA-A receptor. RipIV also presented a computationally predicted favorable pharmacokinetic profile. Therefore, this study demonstrated the involvement of monoaminergic targets in the mechanism of RipIV antidepressant-like action, and provide evidence of it as a promising new antidepressant.