Boldo (Peumus boldus) is a chilean tree traditionally employed in folk medicine due to its properties (anti-inflammatory, antipiretic, spasmolytic, antioxidant, antiproliferative, hepatoprotective, alongside others), and it has been the only plant with medicinal purposes accepted in the EU. These faculties have been attributed to active compounds found in leaves and barks. The compound’s presence has fomented the use of this tree in international pharmacopoeia. It is worth saying that the most important active compound is boldine, an aporphine alkaloid, which has been deeply investigated by different authors and approaches.
O´brien et al (2006) highlights that the active compound (boldine) has pharmacological activities, such as cytoprotective, anti-tumour promoting, anti inflammatory, antipyretic and antiplatelet, have been associated with the ability of boldine to scavenge highly reactive free radicals.The study affirmed that boldine effectively inhibit the spontaneous autoxidation of brain membrane lipids. Thus, it acts as an efficient HO* scavenger, and antioxidant molecule.
Likewise, some researches have appointed that the alkaloid inhibits nitric oxide production by the mitochondria, and does not react with superoxide radicals. It has also been reported that boldine prevents the non enzymatic peroxidation of microsomal lipids initiated by Fe2+ or the enzyme-catalyzed peroxidation initiated by Fe3+- ATP with NADPH or NADH as co-factor or initiated by CCI4 plus NADPH as cofactor.
Finally, it is noticeable to say that free radical-mediated oxidative events in the ethiogenesis of various cardiovascular, tumoral, inflammatory and neurodegenerative pathologies exalts the importance of the boldine’s antioxidant effect to prevent further spreading of the features previously mentioned.
Gerhardt et al (2009) studied the boldine effect against cell glioma lines (U138-MG, U87-MG and C6). It states that boldine has a capacity to decrease the number of cells in U138-MG, U87- MG and C6 glioma lineages. This reduction in cell number in response to boldine treatment can be explained by two hypotheses: (1) cell death or (2) reduced cell proliferation. Then, It was also observed necrotic cell lines in the C6 lineage after boldine treatment. The same effect was not seen at low concentrations in U138- MG and U87-MG lineages.
In comparison to control, comet assay results from U138- MG did not show DNA damage after boldine treatment. In addition, the data suggests that boldine may not affect hippocampal cells to the extent that it affects tumor cells. Lastly, apart from the fact that this findings may need in vivo studies, the results of boldine are particularly appealing because tumor- specific effects play a crucial role in anti-cancer therapies.
Lau et al (2013), who investigated about the endothelial function in diabetic db/db mice, asserts two ideas: demonstrates that endothelial dysfunction in diabetic mice was accompanied by augmented oxidative/nitrosative stress and BMP4 up-regulation, restoring the impaired endothelial function in db/db mice and inhibited ROS overproduction and BMP4 up-regulation. It also states that boldine is effective in inhibiting the AT, receptor- mediated cellular signalling cascade and in ameliorating endothelial dysfunction in diabetic mice. The findings further suggest a therapeutic potential of boldine-containing medicinal herbs in alleviating diabetic vasculopathy.
Paydar et al (2014) evaluated boldine for its cytotoxic effect in human breast cancer cells using the MTT cell viability assay. The cytotoxic effect of boldine was also confirmed by measuring lactate dehydrogenase release from boldine-treated cells. In the same line, it was observed both cellular shrinkage and DNA fragmentation, supporting the observation that treatment with boldine leads to apoptosis rather than necrosis in MDA-MB 231 breast cancer cells.
Gerhardt et al (2014) studied the mechanism of boldine on bladder cancer proliferation and cell death. One of the available options is that boldine acts interfering with proteins involved in g2 progression to mitosis thus blocking cells in g2/M when evaluating cell cycle distribution. On the other hand, the ERK signaling pathway is known to play a critical role in cellular proliferation, it was necessary to determine if boldine inhibits cell growth via the regulation of the ERK pathway in T24 cells. Results showed that boldine significantly inhibited ERK phosphorylation.
Consequently, ERK, AKT, and GSK3b are important proteins in the generation of an antiapoptotic response in cells, the inactivation or ERK and AKT, and activation of GSK-3b appears to be accountable for the death by apoptosis of T24 bladder carcinoma cells induced by boldine treatment. PI3K/AKT and MAPK/ERK pathways activation have been regarded as important key players in BC carcinogenesis.
Moreover, once the ERK pathway is known to be important in cell proliferation, whereas the AKT pathway has been more strongly implicated in cell survival, and both are activated in BC cells, targeting both pathways becomes an important strategy to avoid cancer cell proliferation and stimulate cancer cell death. To summarize, it has potential implications in the development of adjuvant therapeutic strategies using boldine in conjunction with established chemotherapy regimens.
Noureini & Wink (2015) investigated the dose-dependent cytotoxic effects of boldine in Hep-G2 cells-telomerase inhibition and apoptosis induction. This study show the beneficial antiproliferative properties of boldine suppressing immortality of Hep-G2 cells without toxic concentrations, through inhibition of telomerase and induction of senescence. At high concentrations, boldine induces apoptosis. This comes from a recent study in induction of cell cycle arrest and apoptosis in human bladder cancer cells by boldine via regulation of ERK/AKT, and GSK-3b. Another study shows the use of boldine at specific dosis, significantly reducing tumor size. This approaches may suggest that boldine, a potent and hardly toxic antioxidant, could serve as a valuable anti-cancer agent.
Yi et al (2017) emphasized the contribution of reactive gliosis to the pathological phenotype of Alzheimer’s disease (AD), opening the way for therapeutic strategies targeting the glial cells instead of neurons. In such context, connexin hemichannels were proposed recently as potential targets since neuronal suffering is alleviated when connexin expression is genetically suppressed in astrocytes of a murine model of AD. Also, there is much evidence that indicates that hemichannels (HCs) can be important players in pathological processes by providing a paracrine pathway targeting neuronal activity and survival.
Consequently, long-term oral administration if boldine in AD mice prevented the increase in glial hemichannel activity, astrocytic Ca2+ signal, ATP and glutamate release and alleviated hippocampal neuronal suffering. These findings highlight the important pathological role of hemichannels in AD mice. The neuroprotective effect of boldine treatment might provide the basis for future pharmacological strategies that target glial hemichannels to reduce neuronal damage in neurodegenerative diseases.
Ahmad et al (2019), stated that boldine, a natural alkaloid compound, was shown to have anticancer properties on various types of cancer cells, but the anti-telomerase property was poorly understood. It also suggests the ability of boldine in targeting telomerase on the human colon cancer cell line, HCT 116, by analyzing the expression of hTERT and hTERC. Boldine was shown to have a time-and dose- dependent cytotoxic effect on HCT 116 cell lines in SRB assay. In addition, exposure to boldine induced down-regulation of hTERT and hTERC genes expression, as well as hTERT protein expression in HCT 116 cell line. From this point of view, the ability of boldine in targeting telomerase is more clearly understood and can be used as a therapeutic agent for the treatment of human colon carcinoma.
Subramaniam et al (2019) studied hepatocellular carcinoma, seeing it as a multifaceted pathology- accompanying chronic liver disease and cirrhosis (considering HCC is the fifth most commonly occurring cancer globally). As this issue can be treated in various ways such as chemotherapy and radiotherapy, they may cause adverse effects with a high degree of mortality. The idea of demanding for an alternate medicine has been increasing.
This study concludes that boldine has an impressive antioxidant property by protecting the cells from oxidative stress. Boldine promoted caspase-dependent mitochondrial apoptosis in HCC rats; it was confirmed by mRNA and protein expression. Immunoblot analysis also revealed that boldine initiated the caspase cascade through the intrinsic pathway by increasing the protein expression of Bax, cytochrome c, and cleaved caspase 3 in a rat model of carcinogen-induced liver tissues. It authenticates that boldine has splendid antiproliferative and apoptotic properties on cancerous cells.