title: Selectivity of commonly used pharmacological inhibitors for cystathionine β synthase (CBS) and cystathionine γ lyase (CSE).
abstract: OBJECTIVE
  Hydrogen sulfide (H₂S) is a signalling molecule that belongs to the gasotransmitter family. Two major sources for endogenous enzymatic production of H₂S are cystathionine β synthase (CBS) and cystathionine γ lyase (CSE). In the present study, we examined the selectivity of commonly used pharmacological inhibitors of H₂S biosynthesis towards CSE and CBS.
  
  
  METHODS
  To address this question, human CSE or CBS enzymes were expressed and purified from Escherichia coli as fusion proteins with GSH-S-transferase. After purification, the activity of the recombinant enzymes was tested using the methylene blue method.
  
  
  RESULTS
  β-Cyanoalanine (BCA) was more potent in inhibiting CSE than propargylglycine (PAG) (IC₅₀ 14 ± 0.2 μM vs. 40 ± 8 μM respectively). Similar to PAG, L-aminoethoxyvinylglycine (AVG) only inhibited CSE, but did so at much lower concentrations. On the other hand, aminooxyacetic acid (AOAA), a frequently used CBS inhibitor, was more potent in inhibiting CSE compared with BCA and PAG (IC₅₀ 1.1 ± 0.1 μM); the IC₅₀ for AOAA for inhibiting CBS was 8.5 ± 0.7 μM. In line with our biochemical observations, relaxation to L-cysteine was blocked by AOAA in aortic rings that lacked CBS expression. Trifluoroalanine and hydroxylamine, two compounds that have also been used to block H₂S biosynthesis, blocked the activity of CBS and CSE. Trifluoroalanine had a fourfold lower IC₅₀ for CBS versus CSE, while hydroxylamine was 60-fold more selective against CSE.
  
  
  CONCLUSIONS
  In conclusion, although PAG, AVG and BCA exhibit selectivity in inhibiting CSE versus CBS, no selective pharmacological CBS inhibitor is currently available.
authors.affiliation: Department of Pharmacy, Laboratory of Molecular Pharmacology, University of Patras, Patras, Greece.
authors.forename: Antonia
authors.initials: A
authors.lastname: Asimakopoulou
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Panopoulos
authors.forename: Christos T
authors.initials: CT
authors.lastname: Chasapis
authors.forename: Ciro
authors.initials: C
authors.lastname: Coletta
authors.forename: Zongmin
authors.initials: Z
authors.lastname: Zhou
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Cirino
authors.forename: Athanassios
authors.initials: A
authors.lastname: Giannis
authors.forename: Csaba
authors.initials: C
authors.lastname: Szabo
authors.forename: Georgios A
authors.initials: GA
authors.lastname: Spyroulias
authors.forename: Andreas
authors.initials: A
authors.lastname: Papapetropoulos
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives / Q000494:pharmacology; D000480:Alkynes / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D003541:Cystathionine beta-Synthase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D003542:Cystathionine gamma-Lyase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005982:Glutathione Transferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D006862:Hydrogen Sulfide / Q000032:analysis / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D014664:Vasodilation / Q000187:drug effects
chemical_list: D000480:Alkynes; D004791:Enzyme Inhibitors; D020030:Nitric Oxide Donors; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D009569:Nitric Oxide; C009055:propargylglycine; C004631:3-cyanoalanine; D005982:Glutathione Transferase; D003541:Cystathionine beta-Synthase; D003542:Cystathionine gamma-Lyase; D000409:Alanine; C088137:aminoethoxyvinylglycine; D005998:Glycine; D006862:Hydrogen Sulfide