# PR toxin

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{{Chembox
| Name = PR toxin
| ImageFile1 = Penicillin Roquefort toxin.png
| ImageFile2 = PR-toxin-from-xtal-3D-bs-17.png
| IUPACName = (11''S'')-8,12-Dioxo-1β,2β:7,11-diepoxy-7α-eremophil-9-en-3β-yl acetate
| SystematicName = (1a''R'',2''R'',2′''R'',3''R'',3′''S'',3a''R'',7b''S'')-3′-Formyl-3,3′,3a-trimethyl-6-oxo-1a,2,3a,4,6,7b-hexahydro-3''H''-spiro[naphtho[1,2-''b'']oxirene-5,2′-oxiran]-2-yl acetate
| OtherNames = 
| Section1 = {{Chembox Identifiers
| PubChem = 440907
| CASNo = 56299-00-4
| UNII = F9W0X88AFM
| KEGG = C06079
| ChEBI = 7883
| ChEMBL = 4176158
| ChemSpiderID = 389737
| 3DMet= B01991
| StdInChI=1S/C17H20O6/c1-8-12(21-9(2)19)14-13(22-14)10-5-11(20)17(6-15(8,10)3)16(4,7-18)23-17/h5,7-8,12-14H,6H2,1-4H3/t8-,12+,13-,14+,15+,16+,17-/m0/s1
| StdInChIKey = GSPFUBNBRPVALJ-VIEAGMIOSA-N
| SMILES = C[C@H]1[C@H]([C@@H]2[C@@H](O2)C3=CC(=O)[C@@]4(C[C@]13C)[C@@](O4)(C)C=O)OC(=O)C
 }}
| Section2 = 
| Section3 = 
| Section4 = 
| Section5 = 
| Section6 = 
}}
'''Penicillin Roquefort toxin''' ('''PR toxin''') is a [mycotoxin](/source/mycotoxin) produced by the fungus ''[Penicillium roqueforti](/source/Penicillium_roqueforti)''. In 1973, PR toxin was first partially characterized by isolating moldy corn on which the fungi had grown.<ref name="Wei 111–114">{{Cite journal|last1=Wei|first1=R.D.|last2=Still|display-authors=1|date=1973-01-25|title=Isolation and Partial Characterization of a Mycotoxin from ''Penicillium roqueforti''|journal=American Society for Microbiology|volume=25|issue=1|pages=111–114|doi=10.1128/am.25.1.111-114.1973|pmid=4687064|pmc=380745}}</ref> Although its lethal dose was determined shortly after the isolation of the chemical, details of its toxic effects were not fully clarified until 1982 in a study with mice, rats, anesthetized cats and preparations of isolated rat [auricle](/source/Auricle_(anatomy))s.<ref>{{Cite journal|last1=Chen|first1=F.C.|last2=Wei|display-authors=1|date=1982|title=Acute toxicity of PR toxin, a mycotoxin from ''Penicillium roqueforti''|journal=Toxicon|volume=20|issue=2|pages=433–441|doi=10.1016/0041-0101(82)90006-x|pmid=7080052|bibcode=1982Txcn...20..433C }}</ref>

== Structure and reactivity ==
PR toxin contains multiple functional groups, including [acetoxy](/source/acetoxy) (CH<sub>3</sub>COO-), [aldehyde](/source/aldehyde) (-CHO), [α,β-unsaturated ketone](/source/enone) (-C=C-CO) and two [epoxide](/source/epoxide)s.<ref name=":2" /> The aldehyde group on C-12 is directly involved in the biological activity as removal leads to inactivation of the compound. The two epoxide groups do not play an important role, as removal showed no difference in activity. When exposed to air, PR toxin may decompose. How and why this happens, is however not known.<ref name=":0" />

== Synthesis ==
PR toxin is derived from the 15-carbon [hydrocarbon](/source/hydrocarbon) [aristolochene](/source/aristolochene), a [sesquiterpene](/source/sesquiterpene) produced from [farnesyl diphosphate](/source/farnesyl_diphosphate) catalyzed by the enzyme [aristolochene synthase](/source/aristolochene_synthase). Aristolochene then gains an alcohol, a ketone, and an additional alkene, mediated by [hydroxysterol oxidase](/source/hydroxysterol_oxidase) and [quinone oxidoreductase](/source/quinone_oxidoreductase).{{clarify|issue=which enzyme does what specific transformation?|date=January 2023}} Addition of the fused-[epoxide](/source/epoxide) oxygen by [P450 monooxygenase](/source/P450_monooxygenase) gives eremofortin&nbsp;B. Epoxidation of the [isopropenyl](/source/isopropenyl) sidechain, again by P450 monooxygenase, and addition of the [acetyl group](/source/acetyl_group) by an [acetyltransferase](/source/acetyltransferase) gives eremofortin&nbsp;A. A [short-chain oxidoreductase](/source/short-chain_oxidoreductase) oxidizes a [methyl group](/source/methyl_group) on the side-chain to eremofortin&nbsp;C, the [primary alcohol](/source/primary_alcohol) analog of PR toxin (incorrectly illustrated in the following diagram), which is then further oxidized by a [short-chain alcohol dehydrogenase](/source/short-chain_alcohol_dehydrogenase) to give the [aldehyde](/source/aldehyde).<ref name=":2" />

:alt=|frameless|600x600px

Eremofortin&nbsp;C has been isolated from microbial sources and found to be in a spontaneous equilibrium between an open-chain hydroxy–ketone structure and a [lactol](/source/lactol) form.<ref>{{cite journal |title= Eremofortin C, a new metabolite obtained from ''Penicillium roqueforti'' cultures and from biotransformation of PR toxin |first1= Serge |last1= Moreau |first2= Monique |last2= Cacan |first3= Alain |last3= Lablache-Combier |journal= J. Org. Chem. |year= 1997 |volume= 42 |issue= 15 |pages= 2632–2634 |doi= 10.1021/jo00435a023 |pmid= 874620 }}</ref>

:400px

== Genetic Regulation ==
Recent [genomic](/source/genomic) and [metabolomic](/source/metabolomic) studies have shown that PR toxin production in ''Penicillium roqueforti'' is transcriptionally regulated by the PR toxin biosynthetic gene cluster. This cluster spans approximately 25 kilobase pairs and contains eleven [open reading frames](/source/open_reading_frames) (ORFs). Key gene products include the ''ari1'' locus, which encodes the [rate-limiting enzyme](/source/rate-limiting_enzyme), aristolochene synthase (ORF2); two dehydrogenases (ORF1 and ORF4); quinone oxidase (ORF3); an oxidoreductase (ORF1); an acetyltransferase (ORF8); a transcriptional regulator (ORF10); and four cytochrome P450 monooxygenases (ORF5, ORF6, ORF9, and ORF11). The PR toxin biosynthetic gene cluster is generally conserved across ''Penicillium'' species, though not universally identical.<ref> Hidalgo, P.I., Poirier, E., Ullán, R.V. et al. ''Penicillium roqueforti'' PR toxin gene cluster characterization. Appl Microbiol Biotechnol 101, 2043–2056 (2017). https://doi.org/10.1007/s00253-016-7995-5 </ref> 

Commercial ''Penicillium roqueforti'' strains commonly used in blue cheese manufacturing exhibit lower PR toxin expression. In these strains, a frequent guanine-to-adenine (G→A) mutation in ORF11, encoding a cytochrome P450 monooxygenase, introduces a premature [stop codon](/source/stop_codon) which disrupts the final steps of PR toxin biosynthesis. This mutation leads to the accumulation of biosynthetic intermediates eremofortin A and B.<ref>Crequer, E., et al. Different Metabolite Profiles across Penicillium roqueforti Populations Associated with Ecological Niche Specialisation and Domestication. Preprint, 2024, Microbiology. https://doi.org/10.1101/2024.01.12.575369 </ref><ref>Caron, Thibault, et al. Generation of Diversity in the Blue Cheese Mold Penicillium roqueforti and Identification of Pleiotropic QTL for Key Cheese-Making Phenotypes. Preprint, 22 Feb. 2024, bioRxiv, https://doi.org/10.1101/2024.02.22.581506. </ref> The nonfunctional [allele](/source/allele) resulting from this [nonsense mutation](/source/nonsense_mutation) is thought to have become fixed in commercial ''Penicillium roqueforti'' via domestication; moreover, human selection or relaxed [selective pressure](/source/selective_pressure) occurred within the fungal-cheese environment. The mutation results in a phenotype considered favorable for food safety, as it  lowers the concentrations of PR toxin within unspoiled products.<ref name=":2" /><ref>Rojas-Aedo, J. F., Gil-Durán, C., Goity, A., Vaca, I., Levicán, G., Larrondo, L. F., & Chávez, R. (2018). The developmental regulator Pcz1 affects the production of secondary metabolites in the filamentous fungus Penicillium roqueforti. Microbiological Research, 212–213, 67–74. https://doi.org/10.1016/j.micres.2018.05.005 </ref> 

Furthermore, the [microaerophilic](/source/microaerophilic) conditions and the presence of [nitrogenous](/source/nitrogenous) compounds such as [amino acid](/source/amino_acid)s, [casein](/source/casein), [amines](/source/amines), and [ammonium salt](/source/ammonium_salt)s in the blue cheese milieu promote the degradation of PR toxin. When degraded, PR toxin forms metabolites PR acid (C<sub>17</sub>H<sub>20</sub>O<sub>7</sub>), PR imine (C<sub>17</sub>H<sub>21</sub>O<sub>5</sub>N), and PR amide (C<sub>17</sub>H<sub>21</sub>O<sub>6</sub>N)
which exhibit lower toxicity and are thought to have minimal deleterious effects on [chromatin](/source/chromatin) architecture and protein synthesis.<ref name=":2" /><ref>Vallone, L., Giardini, A., and Soncini, G. (2014). Secondary metabolites from Penicillium roqueforti, a starter for the production of Gorgonzola cheese. Ital. J. Food Saf. 3:2118. doi: 10.4081/ijfs.2014.2118 </ref> These degradation products, unlike PR toxin and its eremofortin derivatives, have been detected in blue cheeses with relative abundance and are considered less hazardous to human health.<ref>{{cite journal |last1=Hidalgo |first1=Pedro I. |title=Molecular characterization of the PR-toxin gene cluster in Penicillium roqueforti and Penicillium chrysogenum: Cross talk of secondary metabolite pathways |journal=Fungal Genetics and Biology |volume=56 |year=2014 |pages=69–78 |doi=10.1016/j.fgb.2013.10.009}} </ref><ref> Moreau, S., Lablache-Combier, A., and Biguet, J. (1980). Production of
eremofortins A, B, and C relative to formation of PR toxin by Penicillium roqueforti. Appl. Environ. Microbiol. 39, 770–776. </ref>

== Metabolism ==
Different experiments have shown the effects of the PR toxin on liver cells in culture (in vitro) and in the liver (in vivo).<ref name=":0">{{Cite journal|last1=Moule|first1=Y.|last2=Jemmali|display-authors=1|date=1976|title=Mechanism of the inhibition of transcription by pr toxin, a mycotoxin from ''Penicillium roqueforti''|url=https://www.sciencedirect.com/science/article/abs/pii/0009279776901010|journal=Chemico-Biological Interactions|volume=14|issue=3–4|pages=207–216|doi=10.1016/0009-2797(76)90101-0|pmid=182392|bibcode=1976CBI....14..207M |url-access=subscription}}</ref><ref name=":1">{{Cite journal|last1=Moulé|first1=Y|last2=Jemmali|display-authors=1|date=1978-04-15|title=Inhibition of protein synthesis by PR toxin, a mycotoxin from ''Penicillium roqueforti''|journal=FEBS Letters|volume=88|issue=2|pages=313–323|doi=10.1016/0014-5793(78)80207-5|pmid=648640|doi-access=free|bibcode=1978FEBSL..88..341M}}</ref><ref>{{Cite journal|last1=Aujard|first1=C.|last2=Morel-Chaney|display-authors=1|date=1979|title=Biochemical effects of PR toxin on rat liver mitochondrial respiration and oxidative phosphorylation|url=https://www.sciencedirect.com/science/article/abs/pii/000398618490420X|journal=Archives of Biochemistry and Biophysics|volume=230|issue=2|pages=400–411|doi=10.1016/0003-9861(84)90420-x|pmid=6324685|url-access=subscription}}</ref>

===In vitro===

The PR toxin caused an inhibition of the incorporation of amino acids. These results show that the toxin was responsible for altering the translating process. Together with some earlier experiments it has been proved that the PR toxin was indeed active on the cell metabolism.<ref name=":0" /><ref name=":1" /> Another interesting finding is the decreased activity of respiratory control and oxidative phosphorylation in the (isolated) mitochondria of the liver .

Apparently the amount of [polysomes](/source/Polysome) wasn't the determining factor, the inhibition was not decreased by increasing the amount of polysomes. The increase of pH 5 enzymes on the other hand, had a significant inhibitory effect. A higher concentration of pH 5 enzymes made the inhibitory effect less effective. These findings proved that the PR toxin was not altering the polysomes but in some way dysfunctions the pH 5 enzymes.<ref name=":1" />

===In vivo===

When the PR toxin was directly administered to rats, protein synthesis in the liver was not as high as it normally would be.<ref name=":1" /> This in vivo administration showed that the isolated cells from the rat's liver had a much lower transcriptional capacity.<ref name=":0" />

{{Expert needed|biology|paragraph|reason=poor wording, meaning not clear|date=March 2024}}
The process did not alter the uptake of amino acids in the liver, but the translational process was exclusively affected. The toxic effect of this toxin is as expected close with the fact that the process of protein synthesis is inhibited. However the real toxic effect could be that some required proteins aren't made in a proper amount.<ref name=":1" />

== Mechanism of action ==
Multiple experiments have shown the different effects of PR toxin: it can cause damage to the liver and kidney, can induce carcinogenicity, and can in vivo inhibit DNA replication, protein synthesis, and transcription.<ref name=":2">{{Cite journal|last1=Dubey|first1=M.K.|last2=Aamir|display-authors=1|date=2019-03-29|title=PR Toxin - Biosynthesis, Genetic Regulation, Toxicological Potential, Prevention and Control Measures: Overview and Challenges|journal=Frontiers in Pharmacology|volume=9|pages=288|doi=10.3389/fphar.2018.00288|pmid=29651243|pmc=5885497|doi-access=free}}</ref>{{better source needed|reason=Frontiers is potentially predatory publisher|date=October 2020}} Most experiments on the effect of the PR toxin focus on the inhibition of protein synthesis and impairment of the liver.<ref name=":0" /><ref name=":1" /><ref name=":2" />

The PR toxin dysfunctions the transcriptional process in the liver. RNA polymerases I & II, the two main RNA polymerase systems in the liver, are affected by the toxin. The toxin needs no further enzymatic conversion to exert its effects on these systems.<ref name=":0" /> The liver seems to be the most influenced organ by the PR toxin.

== Toxicity ==
The toxicity of PR toxin was measured both intraperitoneally as well as orally. The first determined median lethal dose of pure PR toxin intraperitoneal in weanling rats was 11&nbsp;mg/kg. The oral median lethal dose was 115&nbsp;mg/kg.<ref name="Wei 111–114"/> The same study reported that ten minutes after an oral dose of 160&nbsp;mg/kg, the animals experienced breathing problems that eventually led to death.

Acute Rat studies (mg/kg)

-        LDLo test, via oral route: 115

-        LD50 test, intraperitoneal route: 11.6

-        LD50 test, intravenous: 8.2

Acute Mouse studies (mg/kg)

-        LD50 test, via oral route: 72

-        LD50 test, intraperitoneal: 2

-        LD50 test, intravenous: 2

An acute human study has yet to be done, so no LD50 test results or doses are known yet. However, there is one case report from 1982 in which toxic effects are described on a human. This person was working in a factory in which the blue cheese was produced. The mold of ''Penicillium roqueforti'' was inhaled by this person and she developed hypersensitivity pneumonitis. Because of this lung inflammation, the person experienced among other things coughing, dyspnea, reduced lung volumes and [hypoxemia](/source/hypoxemia). Antibodies against the mold were found afterwards in serum and lavage fluid. However, the LD50 values have not yet been determined.<ref>{{Cite journal|last1=Campbell|first1=J.A.|last2=Kryda|display-authors=1|date=1983|title=Cheese worker's hypersensitivity pneumonitis.|journal=American Review of Respiratory Disease|volume=127|issue=4|pages=495–496|doi=10.1164/arrd.1983.127.4.495|pmid=6838056}}</ref>

== Effects on animals ==
Studies of the effects on animals were done on mice, rats, anesthetized cats and preparations of isolated rat auricle. Toxic effects in mice and rats included abdominal writhing, decrease of motor activity and respiration rate, weakness of the hind legs and ataxia.

The effects were different for the different ways PR toxin was taken up. When the median lethal dose was ingested orally, the pathology was described as swollen-gas filled stomach and intestines as well as edema and congestion in the lungs. The kidney showed degenerative changes as well as hemorrhage.

If PR toxin was injected intraperitoneally, cats, mice and rats developed [ascites](/source/ascites) fluid and edema of the lungs and scrotum. While intravenous injection showed, for the same animals, large volumes of pleural and pericardial volumes as well as lung edema.

In conclusion, the tissue cells and blood vessels were directly damaged by PR toxin. This caused leakage of fluid resulting among other things in edema of the lungs and ascites fluid. Also, the damage on the blood vessels resulted in increased capillary permeability. This increased permeability lead to a decrease in blood volume and direct damage to the vital organs including lungs, kidneys, liver and heart.<ref>{{Cite journal|last1=Chen|first1=F.C.|last2=Wei|display-authors=1|date=1982|title=Acute toxicity of PR toxin, a mycotoxin from ''Penicillium roqueforti''|journal=Toxicon|volume=20|issue=2|pages=433–441|doi=10.1016/0041-0101(82)90006-x|pmid=7080052|bibcode=1982Txcn...20..433C }}</ref>

== References ==
{{reflist}}

Category:Mycotoxins
Category:Epoxides
Category:Acetates
Category:Ketones
Category:Heterocyclic compounds with 4 rings
Category:Oxygen heterocycles

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Adapted from the Wikipedia article [PR toxin](https://en.wikipedia.org/wiki/PR_toxin) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/PR_toxin?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.