Marco Limone
Matteo Simoncini
PLANT DESCRIPTION
Euphorbia Tirucalli (also known as Aveloz, Firestick Plants, Indian Tree Spurge, Naked Lady, Pencil Tree, Sticks on Fire or Milk Bush) is a shrub that grows in semi-arid tropical climates.
It has a wide distribution in Africa, being prominently present in northeastern, central and southern Africa. It may also be native in other parts of the continent as well as some surrounding islands and the Arabian peninsula and has been introduced to many other tropical regions. Its status in India is uncertain. It grows in dry areas, and is often used to feed cattle or as hedging.
ACTIVE MOLECULES DESCRIPTION
The irritant and tumor-promoting constituents of latex of Euphorbia tirucalli originating from South Africa were isolated. They were identified as irritant ingenane and tigliane type diterpene esters derived from unsaturated aliphatic acids and acetic acid and the polyfunctional diterpene parent alcohols 4-deoxyphorbol, phorbol and ingenol, respectively.
On the active principles of the spurge family Euphorbiaceae. 1985
Phorbol
Various esters of phorbol have important biological properties, the most notable of which is the capacity to act as tumor promoters through activation of protein kinase C. They mimic diacylglycerols, glycerol derivatives in which two hydroxyl groups have reacted with fatty acids to form esters.
Protein kinase C as the receptor for the phorbol ester tumor promoters: sixth Rhoads memorial award lecture. 1988
CLASSIFICATION
| Kingdom: | Plantae |
| Angiosperms |
| Eudicots |
| Rosids |
| Order: | Malpighiales |
| Family: | Euphorbiaceae |
| Genus: | Euphorbia |
| Species: | E. tirucalli |
INDICATIONS
E. tirucalli has uses in traditional medicine in many cultures. It has been used for cancer, excrescence, tumors, and warts in such diverse places as Brazil, India, Indonesia, and Malaysia. It has also been used as for asthma, cough, earache, neuralgia, rheumatism, toothache, and warts in India and Malaysia.
E. tirucalli has been promoted as an anticancer agent, but research shows that it suppresses the immune system, promotes tumor growth, and leads to the development of certain types of cancer. Euphorbia tirucalli has also been associated with Burkitt's lymphoma and is thought to be a cofactor of the disease rather than a treatment.
Aveloz. 2011
Burkitt's lymphoma, an Epstein-Barr virus (EBV)-associated non-Hodgkin's malignant lymphoma is endemic in an area of Africa known as the Lymphoma Belt. This zone is demarcated by climatic requirements of temperature and rainfall. EBV-activating plant factors are among several co-factors which have been proposed for the development of epidemic Burkitt's Lymphoma (eBL). The distribution of Euphorbia tirucalli, a plant which possesses EBV-activating substances and can induce the characteristic 8:14 translocation of eBL in EBV-infected lymphoblastic cell lines in vitro, conforms closely to the climatic requirements of the Lymphoma.
Are plant factors a missing link in the evolution of endemic Burkitt's lymphoma? 1993
The lymphoma belt: Burkitt's lymphoma is endemic in regions with mean minimum temperatures that exceed 15·5°C and yearly rainfall of higher than 50 mL, which stretch from about 10° north to 10° south of the equator.
Is endemic Burkitt's lymphoma an alliance between three infections and a tumour promoter? 2004
MOLECULAR MECHANISM
EBV is necessary
Chinese and African Euphorbiaceae plant extracts were shown to have a markedly enhancing effect on Epstein-Barr virus (EBV)-induced transformation of human lymphocytes. When 5 × 105 cord blood lymphocytes were seeded into the semisolid agar medium immediately after EBV exposure, 3–10 times more transformed colonies developed in the presence of the plant extracts at their optimal doses. When a smaller number of 5 × 104 cells were seeded, transformed colonies were also observed in the presence of the plant extracts but not in their absence. All of the colonies picked up from the agar medium were EBV-determined nuclear antigen (EBNA)-positive and showed the typical blastoid morphology. There were no colonies detected in the EBV-uninfected cultures with the extracts, indicating that the virus was required for the promotion by these plant extracts of this lymphocyte transformation.
Chinese and African Euphorbiaceae plant extracts: Markedly enhancing effect on Epstein-Barr virus-induced transformation. 1983
Cellular Immunity
4-deoxyphorbol ester reduced EBV-specific cytotoxic T-cell function. Furthermore, the B lymphocytes dually exposed to EBV and 4-deoxyphorbol ester were resistant to EBV-specific T cell cytotoxicity, through down-regulation of latent membrane protein 1 (LMP1), the major target to EBV-specific cytotoxic T-cells.
African Burkitt's lymphoma: a plant, Euphorbia tirucalli, reduces Epstein-Barr virus-specific cellular immunity. 1994
Myc and Bcl2 regulation
E. tirucalli is able to reactivate EBV and determine chromosomal alterations, which leads to c-MYC altered expression. The existence of genomic alterations might determine the accumulation of further genetic alteration, which could eventually lead to a transformed phenotype.
Though the specific chromosomal translocations present in Burkitt's lymphoma were not detected after E. tirucalli exposure, we observed the occurrence of polysomies involving chromosome 8, as demonstrated by the existence of multiple signals for MYC by FISH, which may result in overexpression of c-MYC, both at the mRNA and the protein level. In addition, increased expression for BCL2 was also observed, even in the absence of any genetic translocations involving this gene.
All together, our results suggest that E. tirucalli, through EBV reactivation and induction of genetic alterations leading to MYC overexpression, could contribute to the malignant transformation process.
EBV Reactivation and Chromosomal Polysomies: Euphorbia tirucalli as a Possible Cofactor in Endemic Burkitt Lymphoma. 2012
Dual exposure to Epstein-Barr virus and purified 4-deoxyphorbol ester derived from the plant Euphorbia tirucalli induced a high frequency of chromosomal rearrangements in human B lymphocytes in vitro. Rearrangements most commonly affected chromosome 8, the chromosome most often showing structural changes in Burkitt's lymphoma (BL) cells.
Chromosome translocation and c-MYC activation by Epstein-Barr virus and Euphorbia tirucalli in B lymphocytes. 1991
EBV promoters of plant origin gaining access to the body, could, theoretically, increase the number of EBV-carrying B cells and potentiate changes associated with cellular transformation. An extract of Euphorbia tirucalli has been shown to induce continuous mitosis and chromosomal rearrangements in EBV-infected B lymphocytes in vitro. Chromosomal abnormalities were seen in more than 10% of cell divisions in the course of one year. Approximately 10% of these abnormalities were the characteristic 8:14 translocation seen in BL involving activation of the c-myc oncogene. Such cells were tumorigenic when injected into nude mice. The chromosomal changes induced by the E. tirucalli extracts were only seen in the presence of EBV infection. Euphorbia tirucalli is thus apparently acting both as an EBV promoter and a translocation-inducer.
Are plant factors a missing link in the evolution of endemic Burkitt's lymphoma? 1993
Lytic cycle and PKC
Very dilute concentrations of unpurified E. tirucalli latex induced viral reactivation trough the expression of EBV lytic cycle genes in a dose-dependent way.
Unpurified E. tirucalli latex could reactivate the viral lytic cycle in a manner analogous to TPA (12-O-tetradecanoylphorbol-13-acetate, also called phorbol-12-myristate-13-acetate or PMA).
E. tirucalli induces EBV lytic cycle gene transcription by activation of protein kinase C (PKC). The activation of E. tirucalli latex-induced lytic gene expression was inhibited in the presence of 100 mM PKC-Inhibitor. These suggest that E. tirucalli latex-induced lytic cycle gene expression occurs through the activation of a PKC pathway.
Activation of the Epstein-Barr virus lytic cycle by the latex of the plant Euphorbia tirucalli. 2003
A panel of TPA structural analogs, encompassing tiglians with different spectra of biological activities, was assayed on a number of EBV-positive B-lymphoid cell lines. Lytic cycle induction correlated with the capacity to activate PKC, not with tumor promoter status; some nonpromoting tiglians were as efficient as TPA in inducing lytic cycle antigen expression.
The pseudosubstrate peptide PKC completely and specifically blocked tiglian-induced entry of the cells into the lytic cycle. The evidence both from TPA analogs and from enzyme inhibition studies therefore indicates that the pathway linking TPA treatment to lytic cycle induction involves active PKC. Interestingly, inhibition of PKC had no effect upon the spontaneous entry into lytic cycle which occurs in naturally productive cell lines, suggesting that spontaneous entry is signalled by another route.
Induction of Epstein-Barr virus lytic cycle by tumor-promoting and non-tumor-promoting phorbol esters requires active protein kinase C. 1991
Treatment with nocodazole, which provokes the depolymerization of microtubules, induces the expression of two EBV lytic cycle proteins, Zta and EA-D, in EBV-positive nasopharyngeal carcinoma cells. Notably, the induction of Zta by nocodazole was mediated by transcriptional upregulation via protein kinase C (PKC).
Induction of EBV reactivation via disturbing microtubule polymerization depends on the activity of PKC and its downstream signalling partners p38 MAPK and JNK in cells.
Microtubule depolymerization activates the Epstein-Barr virus lytic cycle through protein kinase C pathways in nasopharyngeal carcinoma cells.
Although the previous article talks about nasopharyngeal carcinoma and not about Burkitt's Lymphoma, it shows how PKC induction (also obtainable with phorbol esters) can lead to EBV reactivation. 2013
Epstein-Barr virus (EBV) undergoes latent and lytic replication cycles, and its reactivation from latency to lytic replication is initiated by expression of the two viral immediate-early transactivators, Zta and Rta.In vitro, reactivation of EBV can be induced by anti-immunoglobulin, tetradecanoyl phorbol acetate, and histone deacetylase inhibitor (HDACi). We have discovered that protein kinase C delta (PKC) is required specifically for EBV reactivation by HDACi. Overexpression of PKC is sufficient to induce the activity of the Zta promoter (Zp) but not of the Rta promoter (Rp). Deletion analysis revealed that the ZID element of Zp is important for PKC activation. Moreover, the Sp1 putative sequence on ZID is essential for PKC-induced Zp activity, and the physiological binding of Sp1 on ZID has been confirmed. After HDACi treatment, activated PKC can phosphorylate Sp1 at serine residues and might result in dissociation of the HDAC2 repressor from ZID. HDACi-mediated HDAC2-Sp1 dissociation can be inhibited by the PKC inhibitor, Rotterlin. Furthermore, overexpression of HDAC2 can suppress the HDACi-induced Zp activity. Consequently, we hypothesize that HDACi induces PKC activation, causing phosphorylation of Sp1, and that the interplay between PKC and Sp1 results in the release of HDAC2 repressor from Zp and initiation of Zta expression.
Interplay between PKC and Sp1 on Histone Deacetylase Inhibitor-Mediated Epstein-Barr Virus Reactivation. 2011
EBV reactivation induced by BCR signaling is mainly mediated through PI3K and PKC, whereas MAPK might be involved in later stages of viral replication.
The results indicate that inhibition of PI3K, MAPK, NF-kB pathways, and to some extent cyclin-dependent kinases (CDKs) significantly reduced EBV replication.
Protein kinase inhibitors that inhibit induction of lytic program and replication of Epstein-Barr Virus. 2012
CONCLUSIONS
Euphorbia Tirucalli has been related to Burkitt's Lymphoma because of its geographical distribution and its molecular mechanisms of action. Several ways seem implicated in this phenomenon and all of them need EBV infection in B lymphocytes: reduction in cellular immunity, myc and bcl2 overexpression, activation of EBV lytic cycle. These alterations lead to an increased probability of translocation, in particular 8:14, which can be considered pathognomonic of Burkitt's Lymphoma. However, the main mechanism involved in malignant transformation appear to be the activation of EBV lytic cycle, through PKC activation. Indeed, several studies demonstrate that inhibition of PKC and its downstream molecules prevents EBV reactivation. To explain this associations, we noticed that compounds contained in Euphorbia Tirucalli (e.g. phorbol esters) activate PKC in a Diacylglicerol similar manner; furthermore, we found many evidences that PKC pathway plays a key role in reactivation of EBV lytic cycle, even if it is activated in different ways.
