Identification of N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine in the urine of a patient with cystathioninuria using LC/APCI-MS

Cystathionine protects against endoplasmic reticulum stress-induced lipid accumulation, tissue injury, and apoptotic cell death

Cystathionine (R-S-(2-amino-2-carboxyethyl)-l-homocysteine) is a non-proteinogenic thioether containing amino acid. In mammals, cystathionine is formed as an intermediate of the transsulfuration pathway by the condensation of serine and homocysteine (Hcy) in a reaction catalyzed by cystathionine β-synthase (CBS). Cystathionine is subsequently converted to cysteine plus ammonia and α-ketobutyrate by the action of cystathionine γ-lyase (CGL). Pathogenic mutations in CBS result in CBS-deficient homocystinuria (HCU) which, if untreated, results in mental retardation, thromboembolic complications and connective tissue disorders. Currently there is no known function for cystathionine other than serving as an intermediate in transsulfuration and to date, the possible contribution of the abolition of cystathionine synthesis to pathogenesis in HCU has not been investigated. Using both mouse and cell-culture models, we have found that cystathionine is capable of blocking the induction of hepatic steatosis and kidney injury, acute tubular necrosis, and apoptotic cell death by the endoplasmic reticulum stress inducing agent tunicamycin. Northern and Western blotting analysis indicate that the protective effects of cystathionine occur without any obvious alteration of the induction of the unfolded protein response. Our data constitute the first experimental evidence that the abolition of cystathionine synthesis may contribute to the pathology of HCU and that this compound has therapeutic potential for disease states where ER stress is implicated as a primary initiating pathogenic factor.

Priming effect of N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine in human neutrophils and tyrosyl phosphorylation of 45 kDa protein

Human peripheral blood polymorphonuclear leukocytes were preincubated with N-acetylcystathionine and N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine (NAc-OCPC) found in the urine of a patient with cystathioninuria. NAc-OCPC significantly enhanced the N-formyl-methionyl-leucyl-phenylalanine-induced superoxide generation, whereas N-acetylcystathionine did not enhance the superoxide generation. When the cells were incubated with NAc-OCPC, the tyrosyl phosphorylation of 45 kDa protein of the cell was markedly increased with time. The phosphorylation process was dependent on the concentration of NAc-OCPC. Both the superoxide generation and the tyrosyl phosphorylation of 45 kDa protein increased by NAc-OCPC were inhibited by genistein and herbimycin A, the inhibitors of protein tyrosine kinase, but were rather enhanced by staurosporine, an inhibitor of protein kinase C.