The cytotoxic effects of brown Cuban propolis depend on the nemorosone content and may be mediated by mitochondrial uncoupling

A review of nemorosone: Chemistry and biological properties

Nemorosone is a bicyclic polyprenylated acylphloroglucinol derivative originally isolated from Clusia spp. and it can be obtained through chemical synthesis employing different synthetic strategies. Since its discovery, it has attracted great attention both from a biological and chemical viewpoint. In the present article, we attempted to review various chemical and biological topics around nemorosone, with an emphasis on its antiproliferative activities. For this purpose, relevant data was collected from different scientific databases including Google Scholar, PubMed, Scopus and ISI Web of Knowledge. This natural compound has shown activity against several types of malignancies such as leukemia, human colorectal, pancreatic, and breast cancer because it modulates multiple molecular pathways. Nemorosone has both cytostatic and cytotoxic activity and it also seems to induce apoptosis and ferroptosis. Additionally, it has antimicrobial capabilities against Gram-positive bacteria and parasites belonging to genus Leishmania. Its promising antiproliferative pre-clinical effects deserve further attention for anticancer and anti-parasitic drug development and translation to the clinic.

Molecular Mechanisms of Nemorosone-Induced Ferroptosis in Cancer Cells

Ferroptosis is an iron-dependent cell death-driven by excessive peroxidation of polyunsaturated fatty acids (PUFAs) of membranes. A growing body of evidence suggests the induction of ferroptosis as a cutting-edge strategy in cancer treatment research. Despite the essential role of mitochondria in cellular metabolism, bioenergetics, and cell death, their function in ferroptosis is still poorly understood. Recently, mitochondria were elucidated as an important component in cysteine-deprivation-induced (CDI) ferroptosis, which provides novel targets in the search for new ferroptosis-inducing compounds (FINs). Here, we identified the natural mitochondrial uncoupler nemorosone as a ferroptosis inducer in cancer cells. Interestingly, nemorosone triggers ferroptosis by a double-edged mechanism. In addition to decreasing the glutathione (GSH) levels by blocking the System xc cystine/glutamate antiporter (SLC7A11), nemorosone increases the intracellular labile Fe²⁺ pool via heme oxygenase-1 (HMOX1) induction. Interestingly, a structural variant of nemorosone (O-methylated nemorosone), having lost the capacity to uncouple mitochondrial respiration, does not trigger cell death anymore, suggesting that the mitochondrial bioenergetic disruption via mitochondrial uncoupling is necessary for nemorosone-induced ferroptosis. Our results open novel opportunities for cancer cell killing by mitochondrial uncoupling-induced ferroptosis.

From propolis to nanopropolis: An exemplary journey and a paradigm shift of a resinous substance produced by bees

Propolis, a natural resinous mixture produced by honey bees is poised with diverse biological activities. Owing to the presence of flavonoids, phenolic acids, terpenes, and sesquiterpenes, propolis has garnered versatile applications in pharmaceutical industry. The biopharmaceutical issues associated with propolis often beset its use as being too hydrophobic in nature; it is not absorbed in the body well. To combat the problem, various nanotechnological approaches for the development of novel drug delivery systems are generally applied to improve its bioavailability. This paradigm shift and transition of conventional propolis to nanopropolis are evident from the literature wherein a multitude of studies are available on nanopropolis with improved bioavailability profile. These approaches include preparation of gold nanoparticles, silver nanoparticles, magnetic nanoparticles, liposomes, liquid crystalline formulations, solid lipid nanoparticles, mesoporous silica nanoparticles, etc. Nanopropolis has further been explored to assess the potential benefits of propolis for the development of futuristic useful products such as sunscreens, creams, mouthwashes, toothpastes, and nutritional supplements with improved solubility, bioavailability, and penetration profiles. However, more high-quality clinical studies assessing the effects of propolis either alone or in combination with synthetic drugs as well as natural products are warranted and its safety needs to be firmly established.

Bicyclic polyprenylated acylphloroglucinols and their derivatives: structural modification, structure-activity relationship, biological activity and mechanism of action

Bicyclic polyprenylated acylphloroglucinols (BPAPs), the principal bioactive benzophenone products isolated from plants of genera Garcinia and Hypericum, have attracted noticeable attention from the synthetic and biological communities due to their fascinating chemical structures and promising biological activities. However, the potential drug interaction, undesired physiochemical properties and toxicity have limited their potential use and development. In the last decade, pharmaceutical research on the structural modifications, structure-activity relationships (SARs) and mechanisms of action of BPAPs has been greatly developed to overcome the challenges. A comprehensive review of these scientific literature is extremely needed to give an overview of the rapidly emerging area and facilitate research related to BPAPs. This review, containing over 226 references, covers the progress made in the chemical synthesis-based structure modifications, SARs and the mechanism of action of BPAPs in vivo and vitro. The most relevant articles will focus on the discovery of lead compounds via synthetic modifications and the important BPAPs for which the direct targets have been deciphered. From this review, several key points of the SARs and mode of actions of this novel class of compounds have been summarized. The perspective and future direction of the research on BPAPs are concluded. This review would be helpful to get a better grasp of medicinal research of BPAPs and become a compelling guide for chemists dedicated to the synthesis of these compounds.

Cuban Brown Propolis Interferes in the Crosstalk between Colorectal Cancer Cells and M2 Macrophages

Tumor-associated macrophages (TAMs), primarily the M2 phenotype, are involved in the progression and metastasis of colorectal cancer (CRC). Cuban brown propolis (Cp) and its main component Nemorosone (Nem) displays an antiproliferative effect on different cancer cells, including CRC cell lines. However, whether Cp and Nem could exploit its effect on CRC cells by targeting their relationship with TAMs remains to be elucidated. In this study, we differentiated the human monocytic THP-1 cells to M2 macrophages and confirmed this transition by immunofluorescence (IF) staining, qRT-PCR and zymography. An MTT assay was performed to determine the effect of Cp and Nem on the viability of CRC HT-29 cells co-cultured with M2 macrophages. Furthermore, the migration and invasion abilities of HT-29 cells were determined by Transwell assays and the expression levels of epithelial–mesenchymal transition (EMT) markers were analyzed by IF staining. We demonstrated that Cp and Nem reduced the viability of M2 macrophages and, accordingly, the activity of the MMP-9 metalloprotein. Moreover, we demonstrated that M2 macrophages produce soluble factors that positively regulate HT-29 cell growth, migration and invasion. These M2-mediated effects were counteracted by Cp and Nem treatments, which also played a role in regulating the expression of the EMT markers E-cadherin and vimentin. Taken together, our results indicate that Nem contained in Cp interferes in the crosstalk between CRC cells and TAMs, by targeting M2 macrophages.

Cytotoxic and apoptotic effects of ethanolic propolis extract on C6 glioma cells

Propolis is a natural resinous substance obtained from beehives, and emerging evidence supports that it has antitumor, antiinflammatory, antioxidant, and antimicrobial activities. The aim of the study is to examine the cytotoxic, antioxidant, and apoptotic features of ethanolic propolis extract (PE) on C6 glioma cells. The cells were treated with ethanolic PE at various concentrations for 24 hours, after which the total antioxidant status (TAS) and total oxidant status; malondialdehyde, protein carbonyl, 8-hydroxy-2'-deoxyguanosine, and glutathione (GSH) levels; Cu/Zn-superoxide dismutase (Cu/Zn-SOD) activity; and apoptotic markers were measured. Ethanolic PE at 100, 250, and 500 μg/mL concentrations showed optimal activity on C6 glioma cells. TAS and GSH levels were significantly increased in C6 glioma cells treated with 100 and 500 μg/mL PE compared to control cells (P < .05). Similarly, the activity of Cu/Zn-SOD was higher in C6 glioma cells treated with 250 or 500 μg/mL ethanolic PE compared to control cells (P < .05), as was the caspase-3 mRNA expression level. The highest levels of caspase-8 and -9 expression were in C6 glioma cells treated with 500 μg/mL PE. Collectively, our results indicate that ethanolic PE has cytotoxic and apoptotic effects on C6 glioma cells. Furthermore, it may provide a protective role in the antioxidant defense system. PE shows potential for development as a natural antioxidant and apoptotic agent for the treatment of brain tumors.

The Cuban Propolis Component Nemorosone Inhibits Proliferation and Metastatic Properties of Human Colorectal Cancer Cells

The majority of deaths related to colorectal cancer (CRC) are associated with the metastatic process. Alternative therapeutic strategies, such as traditional folk remedies, deserve attention for their potential ability to attenuate the invasiveness of CRC cells. The aim of this study is to investigate the biological activity of brown Cuban propolis (CP) and its main component nemorosone (NEM) and to describe the molecular mechanism(s) by which they inhibit proliferation and metastatic potential of 2 CRC cell lines, i.e., HT-29 and LoVo. Our results show that CP and NEM significantly decreased cell viability and inhibited clonogenic capacity of CRC cells in a dose and time-dependent manner, by arresting the cell cycle in the G0/G1 phase and inducing apoptosis. Furthermore, CP and NEM downregulated BCL2 gene expression and upregulated the expression of the proapoptotic genes TP53 and BAX, with a consequent activation of caspase 3/7. They also attenuated cell migration and invasion by inhibiting MMP9 activity, increasing E-cadherin and decreasing β-catenin and vimentin expression, proteins involved in the epithelial–mesenchymal transition (EMT). In conclusion NEM, besides displaying antiproliferative activity on CRC cells, is able to decrease their metastatic potential by modulating EMT-related molecules. These finding provide new insight about the mechanism(s) of the antitumoral properties of CP, due to NEM content.

Hypolipidemic Activities of Two Pentapeptides (VIAPW and IRWWW) from Miiuy Croaker (Miichthys miiuy) Muscle on Lipid Accumulation in HepG2 Cells through Regulation of AMPK Pathway

In this work, the hypolipidemic activities of two pentapeptides (VIAPW and IRWWW) from miiuy croaker (Miichthys miiuy) muscle on oleic acid (OA)-induced lipid accumulation in HepG2 cells were investigated. VIAPW and IRWWW could significantly inhibit lipid accumulation induced by OA and decreased intracellular levels of intracellular triglyceride (TG) and total cholesterol (TC) in a dose-effect dependence manner. At the concentration of 100 μm, the TG levels of VIAPW (0.201 ± 0.006 mm) and IRWWW (0.186 ± 0.005 mm) were very (p < 0.01) and extremely (p < 0.001) significantly lower than those (0.247 ± 0.004 mm) of the OA model group; the levels of TC of VIAPW (45.88 ± 0.74 μg/mg protein) and IRWWW (41.02 ± 0.14 μg/mg protein) were very (p < 0.01) and extremely (p < 0.001) significantly lower than that (53.45 ± 0.10μg/mg protein) of the OA model group (p < 0.01). The hypolipidemic mechanisms of VIAPW and IRWWW were to down-regulate the expression levels of genes of SREBP-1c, SREBP-2, FAS, ACC, and HMGR in lipid synthesis and to up-regulate the expression levels of genes of PPARα, ACOX-1, and CPT-1 in lipid oxidation. These results suggested that VIAPW and IRWWW could play their hypolipidemic activities in HepG2 cells through regulation of AMPK pathway and act as hypolipidemic nutrient ingredients applied in public healthy and functional foods.

Development of propolis nanoparticles for the treatment of bovine mastitis: in vitro studies on antimicrobial and cytotoxic activities

This study describes the development of propolis nanoparticles (PNP) to treat bovine mastitis. Three PNP prepared with varying concentrations of propolis (5% and 7%, w/v) and the surfactants [poloxamer (1%, 3%, and 4%, w/v) and soy lecithin (0.25%, 0.7%, and 1%, w/v)]. PNP were characterized according to their size, polydispersity, zeta potential, pH, morphology, and physical stability. PNP were evaluated for their in vitro antimicrobial and cytotoxic effects. PNP obtained were spherical with a monodisperse distribution (polydispersity index < 0.2) and an average particle size between 181 and 201 nm. Stability studies showed that PNP were stable over 150 d. The encapsulation efficiency of total phenolic content varied between 73% and 91%. The chromatographic profile of phenolic compounds from PNP showed selective encapsulation efficiency according to the polarity of compounds. All PNP showed antimicrobial activity against Staphylococcus aureus with a minimum inhibitory concentration ranging from 156 to 310 μg mL−1. The IC50 (the concentration responsible for reduction of cellular viability by half) for epithelial cells of bovine mammary gland (MAC-T, mammary alveolar cell-T) varied from 122.2 to 268.4 μg mL−1. Results showed that PNP represent a promising nanocarrier for high concentrations of propolis extract in a stable aqueous medium, while, at the same time, presenting antimicrobial activity accompanied by moderate cytotoxicity to the MAC-T cells.

Nemorosone inhibits the proliferation and migration of hepatocellular carcinoma cells

AIMS

In the tumor microenvironment, dysregulated immune cells could promote tumor progression, invasion and metastasis, by establishing a symbiotic relationship with cancer cells. A pivotal role is played by monocyte recruitment and induction of tumor-associated macrophages (TAMs), which provide immunosuppression and tumorigenesis. The effect of nemorosone, an antiproliferative phytocomponent present in Cuban Propolis, on TAM-induced tumor progression remains to be elucidated. Here we investigated the symbiotic relationship between monocytic leukemia THP-1 and hepatocellular carcinoma HepG2 cells, and the role of nemorosone in preventing TAM-induced tumor growth.

MAIN METHODS

Macrophage differentiation induced by HepG2-conditioned medium was assessed by flow cytometry, analysis of secreted molecules and cytokine expression. The effect of nemorosone and/or conditioned THP-1-medium on HepG2 proliferation was evaluated by MTT assay, colony formation, cells cycle and migration assays.

KEY FINDINGS

HepG2 cells induced THP-1 recruitment and differentiation to macrophages. When compared with control THP-1 cells, differentiated THP-1 showed a significant increase of the matrix metalloproteinases MMP-2 and MMP-9 expression (P < 0.01), and slightly induced HepG2 cells growth. This effect was counteracted by nemorosone, which also significantly inhibited colony formation (P < 0.01) and migratory capacity of HepG2 cells, driving a high percentage of cells (80%) to the G0/G1 phase.

SIGNIFICANCE

HepG2-conditioned medium is a suitable model for THP-1 modulation and differentiation. Moreover, nemorosone significantly inhibits the proliferation of HepG2 cells, both in presence and absence of the soluble factors secreted by TAMs. Further studies are needed to elucidate the role of this natural compound in the HCC-TAM relationship.