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Hepatology. 2009 Jan;49(1):141-50. doi: 10.1002/hep.22604.

Cystathionine beta-synthase as a carbon monoxide-sensitive regulator of bile excretion.

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1
Department of Biochemistry and Integrative Medical Biology, Department of Surgery, School of Medicine, Keio University, Tokyo, Japan.

Abstract

Carbon monoxide (CO) is a stress-inducible gas generated by heme oxygenase (HO) eliciting adaptive responses against toxicants; however, mechanisms for its reception remain unknown. Serendipitous observation in metabolome analysis in CO-overproducing livers suggested roles of cystathionine beta-synthase (CBS) that rate-limits transsulfuration pathway and H(2)S generation, for the gas-responsive receptor. Studies using recombinant CBS indicated that CO binds to the prosthetic heme, stabilizing 6-coordinated CO-Fe(II)-histidine complex to block the activity, whereas nitric oxide (NO) forms 5-coordinated structure without inhibiting it. The CO-overproducing livers down-regulated H(2)S to stimulate HCO(3) (-)-dependent choleresis: these responses were attenuated by blocking HO or by donating H(2)S. Livers of heterozygous CBS knockout mice neither down-regulated H(2)S nor exhibited the choleresis while overproducing CO. In the mouse model of estradiol-induced cholestasis, CO overproduction by inducing HO-1 significantly improved the bile output through stimulating HCO(3) (-) excretion; such a choleretic response did not occur in the knockout mice.

CONCLUSION:

Results collected from metabolome analyses suggested that CBS serves as a CO-sensitive modulator of H(2)S to support biliary excretion, shedding light on a putative role of the enzyme for stress-elicited adaptive response against bile-dependent detoxification processes.

PMID:
19085910
DOI:
10.1002/hep.22604
[Indexed for MEDLINE]
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