Differential effects of doxorubicin on atrial natriuretic peptide expression in vivo and in vitro

Doxorubicin (Dox) is a potent anti-cancer agent with cardiotoxic side-effects but the mechanism of its cardiotoxicity and its effect on expression of the vasoactive atrial natriuretic peptide (ANP), an important marker for cardiac hypertrophy, are little understood. The present study examined Dox-induced changes in vivo in hearts of 6 mongrel dogs and 5 Sprague-Dawley rats and in vitro in cardiac cultures of neonatal rats. Quantitative RT-PCR analysis using gamma 32-p labeled primers for beta-actin, phospholamban (PLB) and ANP showed a selective 5-fold increase of ANP mRNA in Dox-treated dog hearts in comparison to controls. Similarly, northern analysis of GAPD, beta-actin, cardiac alpha-actin and ANP gave a selective 4.5-fold increase in ANP transcripts in Dox-treated rat hearts. On the other hand, there was a selective decrease (approximately 39 percent) of ANP transcripts in Dox-treated cardiac cultures relative to controls. Immunohistochemistry localized the ANP changes both in tissue sections and in cultures to the cardiomyocytes. The data clearly showed that Dox selectively increases ANP expression in dog and rat hearts in absence of cardiocyte hypertrophy but selectively decreases it in cardiac cultures. This differential effect of Dox on cardiocytes in vivo and in vitro should be a useful parameter for studies of transcriptional control of ANP expression.

Ventricular myosin light chain-2 gene expression in developing heart of chicken embryos

Recent gene knock-out studies in mice have suggested that ventricular myosin light chain-2 (vMLC2) has a role in the regulation of cardiogenic development and that perturbation in expression of vMLC2 is linked to the onset of dilated cardiomyopathy. In an attempt to develop an avian model for such studies, we examined the expression pattern of vMLC2 in chicken embryos at various stages and analyzed the effect of antisense oligonucleotide-mediated interference of vMLC2 function in cultures of whole embryos. Our results showed vMLC2 to be a specific marker for ventricular chamber throughout chicken embryonic development and antisense vMLC2 treatment of primitive streak stage (stage 4) embryos to produce pronounced dilation of heart tube with severe deficiency in formation of striated myofibrils. Further studies with antisense mRNA techniques of whole embryo cultures should, therefore, be useful to evaluate the role of vMLC2 and other putative regulatory factors in cardiac myofibrillogenesis.