Abstract
A newly synthesized isoquinolinesulfonamide, HMN-1180 (1-(5-isoquinolinylsulfonyl)-7-methylhomopiperazine), was shown to have selective inhibitory action against rat neuronal nitric oxide synthase (nNOS) with a Ki value of 5.4 μM. Kinetic analysis indicated that the inhibition was competitive with respect to l-arginine but not to calmodulin (CaM). However HMN-1180 exhibited no significant influence up to a concentration of 1 mM on activity of endothelial NOS (eNOS) and it was less active toward inducible NOS (iNOS) (IC50 > 100 μM). Moreover, nNOS bound to a HMN-1180-coupled Sepharose column, but eNOS and iNOS did not. These results suggest that inhibition of nNOS activity is due to direct binding of the compound to thel-arginine binding site of the synthase. Several HMN-1180 derivatives were synthesized and analyzed for their inhibitory actions against nNOS, eNOS and iNOS to cast light on its structure-activity relationships. The potency of inhibition proved dependent on the position of methyl group in the homopiperazine molecule. HMN-1180 was also found to inhibit glutamate stimulated NO production generated by nNOS in the human neuroblastoma cell line SK-N-MC, thus indicating that it is useful tool for elucidating the physiological role of nNOS in neuronal function.
Footnotes
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Send reprint requests to: Dr. Hiroyoshi Hidaka, Department of Pharmacology, Nagoya University School of Medicine, Showa-ku, Nagoya 466-8550,Japan. E-mail: hhidaka{at}tsuru.med.nagoya-u.ac.jp
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↵1 This work was supported in part by a Grant-in-Aid for Scientific Research on Priority Areas (to H.H.) and a Grant-in-Aid for Scientific Research (to Y.W.) from the Ministry of Education, Science, Sports and Culture.
- Abbreviations:
- NOS
- nitric oxide synthase
- CaM
- calmodulin
- PKA
- cAMP-dependent protein kinase
- CaMKII
- Ca++/CaM-dependent protein kinase II
- NADPH
- β-nicotinamide dinucleotide phosphate
- BH4
- (6R)-5, 6, 7, 8- tetrahydro-l-biopterin
- SDS-PAGE
- sodium dodecyl sulfate-polyacrylamide gel electrophoresis
- l-NAME
- N-nitro-l-arginine methyl ester
- PBS
- phosphate-buffered saline
- MEM
- minimum essential medium
- PVDF
- polyvinylidene difluoride
- CREB
- cyclic AMP response element binding protein
- Received April 21, 1998.
- Accepted July 8, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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