This study aimed to investigate the pharmacological potential of cubiu extract, a tropical fruit of Solanum sessiliflorum and native to the Amazon region. Cubiu is rich in fiber, minerals, iron, niacin, citric acid, and pectin 26, and the presence of phenolic compounds stands out in its composition, including chlorogenic acid and, more specifically, 5-caffeoylquinic acid as the major compound 3. In agreement with the above, we also found phenolic compounds in the cubiu extract, with 5-caffeoylquinic acid being the major compound. Hence, it is seen that Solanaceae plants have caffeoylquinic acids in their composition to which are attributed several of their biological activities that benefit human health 27.
We first investigated the antimicrobial activity of the cubiu extract. From a curve with concentrations of 0.01, 0.03, 0.1, 0.3, 1, 3, 10, and 30 mg/mL of cubiu extract, we showed that 10 and 30 mg/mL have bacteriostatic and bactericidal activity against Aeromonas caviae, Sphingomonas paucimobilis, P. aeruginosa (PA01), which are bacteria that affect various tissues, e.g., the skin, and cause mild and severe infections in hospitals 28–30.
Furthermore, knowing that PA01 is a multidrug-resistant biofilm-producing bacterium 31, we also tested the cubiu extract effectiveness in inhibiting biofilm formation and destroying this biofilm when previously formed by PA01. We evidenced that the cubiu extract was effectively in the inhibition biofilm formation by PA01 and destroy the biofilm previously formed by this bacterium at all concentrations tested (15mg/mL and 30mg/mL). Biofilm is mainly associated with prolonged infections and an important mechanism used by microorganisms to survive antibiotic treatments. Additionally, the biofilm formed by PA01 is closely related to infections in chronic skin wounds 31,32.
Various conventional antimicrobial agents have become less effective against microorganisms as they have become increasingly resistant, making the search for new alternatives with antimicrobial activity indispensable. Thus, research with medicinal plants is a crucial alternative to treat different infectious diseases, as many of these plants have bioactive components with antimicrobial properties 33,34. Therefore, plant extracts and their constituents are being used to combat numerous resistance mechanisms of microorganisms 35,36.
Given this scenario, we can highlight the potential use of the cubiu extract as a bacteriostatic and bactericidal agent to prevent and treat bacterial biofilms, and the antimicrobial potential exerted by this fruit can be justified by the phenolic substances in its chemical matrix. Among the bioactive substances, phenolic substances are highly relevant concerning antimicrobial properties 37. In a similar study, Rodrigues et al. 38 corroborate our findings by demonstrating that pitanga (Eugenia uniflora L.) extract was effective against bacterial biofilm, attributing this result to the presence of phenolic substances in the fruit extract.
Evidence suggests that the possible mechanism of antimicrobial compounds is related to the cascade of reactions involving the bacterial cell 39,40. These reactions may involve the antioxidant capacity of phenolic compounds, which may be important in the antimicrobial mode of action since these natural compounds can reduce the production of essential metabolites for microorganism survival under stress conditions. Hence, it is plausible that the cubiu extract attached and incorporate itself to the biofilm structure, impairing signaling pathways and inducing the disruption of cell membrane 41,42.
Knowing that concentrations of 10 and 30 mg/mL of cubiu extract have promising biological activities, it is vital to verify if these concentrations are safe to use. Therefore, we followed up on the toxicity study of the cubiu extract using PBMC, and our findings revealed that the cubiu extract did not present toxicity due to maintaining hemolysis and blood coagulation patterns within the biological range. In addition, the cubiu extract did not cause alterations or damage to double-stranded DNA, alter NO levels, and improved cell viability. Moreover, Hernandes et al. 43 reported that cubiu does not present cytotoxic or genotoxic effects, further echoing that its safe to consume.
Furthermore, the cubiu extract at the tested concentrations decrease ROS total levels, thus demonstrating antioxidant action. Kaunda et al. 44 also reported that different species of the genus Solanum exhibit antioxidant properties, and Morais et al. 27 described Solanaceae species as having antioxidant potential mainly due to their chemical matrices, including phenolic substances. These, in turn, are widely known for their antioxidant and chelating properties 45.
High ROS levels, at the expense of the body’s antioxidant capacity, are known to cause oxidative stress, promoting cellular damage in plasma membranes, lipids, and proteins and even culminating in cell death. Moreover, oxidative stress is closely linked with the inflammatory response since lipid peroxidation causes inflammatory enzymes such as cyclooxygenase and lipoxygenase to be stimulated and induces leukocytes to release pro-inflammatory cytokines 46. Cytokines are importants inflammatory mediators and can be pro-inflammatory, thus being responsible for manifesting and propagating inflammatory (e.g., IL-1, IL-6, TNF-α and INF-g) or anti-inflammatory (e.g., IL-10) responses and acting as an inhibitor of the inflammatory process 47,48.
The phenolic substances present in Solanaceae plants also provide anti-inflammatory properties 27, as demonstrated herein with the cubiu extract. Therefore, by using PBMCs, we aimed to verify the anti-inflammatory properties of the cubiu extract against PHA, a natural agent inducer of inflammatory responses 23. From this experiment, it was possible to evidence that the cubiu extract (10 and 30 mg/mL) has anti-inflammatory activity, restoring cell viability, maintaining NO levels unchanged, decreasing pro-inflammatory cytokine levels (IL-1, IL-6, TNF-a and INF-g), and increasing anti-inflammatory cytokine levels (IL-10).
Phenolic substances have anti-inflammatory activity given their ability to inhibit enzymes such as prostaglandin synthetase, lipoxygenase, and cyclooxygenase, which are involved in the inflammatory process. Moreover, it is also known that chlorogenic acid, which is present in the composition of cubiu, interferes with the response of leukocytes to chemokines, also preventing the interaction with adhesion molecules involved in cell migration during the inflammatory process 49.
In addition, the anti-inflammatory activity of cubiu was also evidenced in the scratch assay using HFF-1 cells, as both cubiu extract concentrations decreased pro-inflammatory cytokine levels (IL-1, IL-6, TNF-a, and INF-g) and increased anti-inflammatory cytokine levels (IL-10). Furthermore, the scratch assay demonstrated the skin wound healing potential of the cubiu extract. It is known that phenolic substances present in natural extracts have skin wound healing properties 50,51. The cubiu is popularly used for skin wound healing 4,5, albeit without scientific data so far. The present study is the pioneer to prove this activity, as shown herein, both concentrations (10 and 30 mg/mL) of the cubiu extract improved skin wound healing.
It is widely known that treatments that improve skin wound healing should promote antimicrobial, anti-inflammatory, and antioxidant activities since infections, prolonged inflammatory processes, and oxidative stress delay the skin wound healing process 7,8. As for the cubiu extract, we proved that all of these indispensable properties that enhance skin wound healing are found in it, therefore justifying the significant skin wound healing potential of this tropical fruit at the concentrations tested. This is the first research to prove that cubiu extract is an important compound for use in the skin diseases, promoting skin wound healing, antimicrobial and anti-inflammatory activities.