Polyamine regulation of atrial natriuretic peptide in cultured cardiocytes

Mechanism of polyamine toxicity in cultured cardiac myocytes

The goal of this study was to investigate the mechanism of polyamine-mediated injury to the cardiac myocytes isolated from neonatal rat hearts. The myocytes, cultured in Dulbecco's minimal essential medium-1% foetal calf serum (FBS), were exposed to spermidine or spermine. The toxicity to myocytes was determined by (a) increased release of creatine kinase (CPK) into the media and (b) decline in cell viability or functional activity. Spermidine, above 10 mum, increased the release of CPK into media, decreased cell viability and decreased the functional activity of the myocytes. The FBS exhibited polyamine oxidase activity and semicarbazide-sensitive amine oxidase activity. Aminoguanidine, MDL72,527 or semicarbazide, are the inhibitors of amine oxidases, polyamine oxidase (PAO) and semicarbazide-sensitive amine oxidase (SSAO), respectively. The addition of these inhibitors to the medium protected the myocytes from spermidine toxicity. To determine whether myocyte PAO is involved in polyamine toxicity, we used horse serum that contained high SSAO activity and negligible PAO activity. The myocyte extracts had negligible SSAO activity but high PAO activity. When myocytes were cultured in horse serum in lieu of FBS, spermine caused toxicity at above 100 mum. In horse serum, MDL72,527 and semicarbazide protected the myocytes from spermine toxicity. These observations show that extracellular amine oxidases and myocyte PAO are significant in mediation of polyamine toxicity.

Decrease of polyamine levels and enhancement of transglutaminase activity in selective reduction of B16-F10 melanoma cell proliferation induced by atrial natriuretic peptide

The atrial natriuretic peptide (ANP) at physiological levels reduced the proliferation of highly metastatic murine (B16-F10) and human (SK-MEL 110) melanoma cell lines whereas rat aortic smooth muscle (RASM) cells were unaffected. In RASM cells, the levels of proliferation markers (putrescine, spermidine and spermine) increase after 24 h of epidermal growth factor (EGF) stimulation (RASM-EGF), but strongly decrease after 24 h of exposition to ANP. The B16-F10 cell line, which received no EGF stimulation, showed a similar decrease in polyamine content after ANP treatment. Furthermore, the enzymatic activity of a differentiation marker (transglutaminase) was increased for both RASM-EGF and B16-F10 cells after 24 h of treatment with 10(-10) mol/l ANP, concomitantly with the observed inhibition of polyamine biosynthesis and cell growth. Data obtained on B16-F10 cells treated with 8Br-GMPc or with an ANP analogue (cANF) support the involvement of the type C ANP receptor (NRP-C) in hormone effects. From the overall results, it appears that ANP may play a role in the inhibition of cellular growth under hyperproliferative conditions, as shown for RASM-EGF cells. The B16-F10 melanoma cell line showed similar results, but in the absence of mitogen stimulation. This observation suggests that the constitutive hyperproliferative state of tumor cells may be a sufficient condition to favor the ANP inhibitory effects on cell growth. This finding is particularly interesting in the light of a possible use of ANP as a potential selective antineoplastic agent.