Brefeldin A: Miracle and CurseResearch Paper

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Upside and Downside of Brefeldin A

Brefeldin A (BFA) is a versatile compound in common use in many cell biological research laboratories around the world and has been very useful in dissecting signal transduction pathways in mammalian and plant cells (Nebenfuhr, Ritzenthaler, & Robinson, 2002). Preparations of BFA are derived from the fungus Penicillium brefeldianum or synthesized chemically (Sigma, n.d.; MycoBank, 2015). In the laboratory, BFA can be used to block protein transport from the endoplasmic reticulum to the Golgi (EMD Millipore, 2015). BFA performs this function specifically and reversibly, without affecting endocytosis or lysosome functions. BFA also has antifungal, antiviral, and macrolide antibiotic activity and is currently under development as a possible chemotherapeutic agent for cancer treatment (ChemSpider, 2015). This report will examine the chemical properties of BFA, its synthesis, applications, and hazards in more detail below.

Chemical Properties

Figure 1.

Brefeldin A chemical structure. The molecular formula of BFA is C16H24O4 and the average mass is 280.359 Da (ChemSpider, 2015). There are a large number of names and synonyms, but the IUPAC identifier is (1R,2E,6S,10E,11aS,13S,14aR)-1,13-Dihydroxy-6-methyl-1,6,7,8,9,11a,12,13,14,14a-decahydro-4H-cyclopenta[f]oxacyclotridecin-4-one. Synonyms include ?,4-Dihydroxy-2-(6-hydroxy-1-heptenyl)-4-cyclopentanecrotonic acid ?-Lactone, ascotoxin, cyanaein, decumbin, and nectrolide, to name a few. The Merck Index number is 1374 (Royal Society of Chemistry, 2013, p. 1378). The boiling point is 492.7±45.0 "C at 760 mmHg and the flash point is 180.8±22.2 "C (ChemSpider, 2015). The vapor pressure is 0.56 hPa at 20 "C and BFA has a density of 1.100 g/cm3 (Sigma, n.d.). The melting and freezing point is 18.4 "C. The chemical structure of BFA is shown in Figure 1 and the carbon ring structure is evident. BFA is typically dissolved in dimethyl sulfoxide due to its hydrophobicity and forms a clear, colorless liquid (Sigma, n.d.). Commercial concentrations are typically 10.0 mg/ml. The LD50 in mice was reported to be 250 mg/Kg (Japan Antibiotics Research Association, 1981), although this seems to be the only report examining BFA toxicity in a purified form.

Producing Brefeldin A

BFA is a metabolite and can therefore be isolated from fungal growth medium (Wang et al., 2012). BFA can also be chemically synthesized in the laboratory, but obtaining an optically pure reagent requires a complex series of reactions and purification steps. For this reason, the dominant method of obtaining BFA for research and commercial applications is the isolation and purification of this reagent from P. brefeldianum growth media. Documentation of a standard method of purification does not exist, but published reports suggest reversed-phase chromatography or high-speed counter-current chromatography with electrospray ionization mass spectrometry are feasible methods; however, yields are low and costs high. Wang and colleagues (2012) recently published an alternative method using macroporous resins, a common substrate for purifying of antibiotics. After method optimization, the adsorbent of choice turned out to be HZ830. This was then packed into a chromatography column for use. The Freundlich isotherm model was used as the model for static adsorption and once eluted, BFA was crystallized and recrystallized in acetone to produce a product with greater than 99% purity. In addition, the yields were high and costs low.

BFA Applications

P. brefeldianum is a toxic fungus and BFA an organic metabolite that has profound effects on mammalian cells (Chardin & McCormick, 1999). BFA is a fast-acting and reversible toxin that induces Golgi disassembly and redistribution to the endoplasmic reticulum (ER). As a result, protein translation from the ER to the Golgi is inhibited. The molecular targets of BFA are small G. proteins belonging to the Arf family. When bound to GTP, Arf proteins recruit and assemble the coat protein complexes involved in selecting proteins for transport. Arf proteins also act as scaffolding proteins to drive the formation of small vesicles derived from the ER. The vesicles fuse and form the intermediate compartment where protein sorting takes place. Proteins destined to be secreted will enter the anterograde transport system; whereas proteins destined to be recycled enter the retrograde transport system and return to the ER. In the presence of BFA, Arf proteins cannot promote the formation of the COPI coat and these proteins are released into the cytosol. Importantly, BFA readily crosses the plasma membrane of mammalian cells, an important consideration for medicinal applications. Eventually, the Golgi collapses and is redistributed to the ER, which underlies its antifungal and antiviral activities (Wang et al., 2012). BFA has also been shown to have anti-tumor activity against a number of cancers and is currently being developed for therapeutic applications.

Although BFA cannot enter wild-type yeast cells, mutant strains have been created that allow entry and BFA treatment revealed a mechanism of action surprisingly similar to what occurs in mammalian cells (Chardin & McCormick, 1999). The three proteins affected, Gea1, Gea2, and Sec7, all contain a guanine nucleotide exchange domain which is required for normal Golgi trafficking; however, contrary to expectations, BFA stabilizes the Arf1-GDP/Sec7 complex by becoming incorporated into the complex. The overall effect is that Arf1-DGP acts as a dominant-negative mutant by trapping the Arf1 exchange factors and preventing exchange factors from activating other Arf1 proteins.

The G-protein Ras, when bound to GDP, will be targeted by exchange factors (Chardin & McCormick, 1999). These exchange factors bind to GDP-Ras, which lowers GDP affinity and promotes its release. Once GDP is released, Ras can then bind GTP, which in turn induces a conformational change displacing the exchange factor. RasN17 is a mutant protein with low affinity for GTP; therefore, GTP cannot bind RasN17 and displace the exchange factor. Since exchange factors are expressed at lower levels, a few RasN17 proteins can derail the Ras signal transduction pathway by acting in a dominant-negative manner.

In an analogous fashion, BFA binds to the Arf1-GDP/Sec7 complex to produce a dominant-negative effect because it inhibits protein translocation from the ER to the Golgi (Chardin & McCormick, 1999). The reason cancer researchers are excited about BFA is because BFA or its derivatives may only need to be used in small dosages to be effective, due to its dominant-negative activity. In addition, the mechanism of BFA activity suggests any G-protein signal transduction pathway can be selectively targeted in a similar manner if the right BFA derivative can be developed (e.g., Seehafer et al., 2013).

Hazards

Penicillium is a common environmental mold that contaminates indoor spaces and food (Lillard, 2004). The preferred environment is damp spaces and growth can be detected by rapidly growing conidial structures producing a strong musty odor. Indoor, Penicillium contamination can be found in carpets, fiberglass insulation, and wall paper. If the offending species produces mycotoxins like BFA then exposure can lead to the development of asthma. Symptoms of acute exposure include edema and bronchial spasms, while chronic exposure can lead to the development of pulmonary emphysema. Since a number of different toxigenic molds can elicit these symptoms, symptoms alone are insufficient for determining the mold species responsible for toxin exposure.

While P. brefeldianum represents a significant health threat if exposed to high concentrations of its toxins, other more dangerous Penicillium species may be cohabitating with P. brefeldianum (Lillard, 2004). P. aurantiogriseum produces the neurotoxin verrucosidin and the mycotoxin penicillic acid, which upon exposure will cause neurologic, liver, and kidney disease. This health threat was uncovered after laboratory mice were fed contaminated corn. Other toxins produced by this mold include ergosterol, tremortin A and B, tremorgen, puberulic acid, puberulonic acid, and malic acid. Exposure to these toxins can cause DNA damage and permanent neurological and physical deficits.

Another species, P. marneffei, represents a significant health hazard because the mold can lead to the development of systemic infection if inhaled, touched, or ingested (Lillard, 2004). Symptoms include fever, anemia, skin lesions, liver disease, gastrointestinal distress, and pulmonary inflammation. This fungus is unique among environmental molds because it can adopt a yeast-like growth cycle inside tissue at body temperature. Fortunately, effective treatments for both contaminated surfaces and infections are available.

Conclusions

BFA may turn out to be a miracle drug, based on research findings to date. The possible applications include antifungal, antiviral, antibiotic, and anti-tumor. The mechanism of action has been well-characterized and research is currently underway to develop derivatives with different specificities. Among the more promising discoveries is that BFA derivatives may be capable of inhibiting an entire G-protein pathway at small doses, because it functions in dominant-negative fashion by sequestering exchange factors. The potency of BFA is also a tribute to the toxigenic nature of Penicillium species, which represent a significant health hazard to humans, pets, and livestock.

References

Chardin, P., & McCormick, F. (1999). Brefeldin A: The advantage of being uncompetitive. Cell, 97, 153-5.

ChemSpider. (2015). (+)-brefeldin A. Retrieved from http://www.chemspider.com/Chemical-Structure.4449949.html.

EMD Millipore. (2015). 203729 | (+)-Brefeldin A, Eupenicillium brefeldianum -- CAS 20350-15-6 -- Calbiochem. Retrieved from https://www.emdmillipore.com/U.S./en/product/%28%2B%29-Brefeldin-A%2C-Eupenicillium-brefeldianum-CAS-20350-15-6-Calbiochem,EMD_BIO-203729?bd=1.

Japan Antibiotics Research Association. (1981). JJANAX Japanese Journal of Antibiotics, 34, 51.

Lillard, S. (2004). Penicillium. Retrieved from http://www.mold-help.org/content/view/424/.

MycoBank. (2015). Penicillium brefeldianum. Retrieved from http://www.mycobank.org/Biolomics.aspx?Table=Mycobank&MycoBankNr_=258851.

Nebenfuhr, A., Ritzenthaler, C., & Robinson, D.G. (2002). Brefeldin A: Deciphering an enigmatic inhibitor of secretion. Plant Physiology, 130, 1102-8.

Royal Society of Chemistry. (2013). Merck Index. Cambridge, UK: Royal Society… [END OF PREVIEW]

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