Masayuki Nakano

BACKGROUND: Tumor necrosis factor-alpha (TNF-alpha) is a pleiotropic cytokine with a broad range of concentration-dependent effects. The recent observation that TNF-alpha is expressed by the cardiac myocyte after certain forms of stress suggests that TNF-alpha might contribute to the maintenance of normal tissue homeostasis after environmental injury. Accordingly, the purpose of this study was to examine the effects of TNF-alpha on protein synthesis in cultured adult cardiac myocytes. METHODS AND RESULTS: Cultured adult feline cardiac myocytes were stimulated with 10 to 1000 U/mL TNF-alpha to examine the effects of this cytokine on the rate of protein synthesis and degradation. Stimulation with TNF-alpha led to an accelerated rate of general protein synthesis and a time-dependent decrease in protein degradation in adult cardiac myocytes. The specificity of these findings was demonstrated by studies in which the effects of TNF-alpha on protein synthesis were blocked by a neutralizing anti-TNF-alpha antibody as well as studies in which TNF-alpha-conditioned medium had no effect on protein synthesis in myocytes. In addition to the TNF-alpha-induced increase in the general protein synthesis, stimulation with TNF-alpha led to a 2.4-fold increase in net actin protein synthesis and a 3.3-fold increase in net myosin heavy chain synthesis. Finally, the effects of TNF-alpha on adult cardiac myocytes were shown to be dependent on cell-substrate interaction, suggesting that the cell signaling pathways used by TNF-alpha are dependent on a preserved interaction between cell integrins and the extracellular matrix. CONCLUSIONS: The observation that TNF-alpha provokes a hypertrophic growth response in cardiac myocytes suggests that TNF-alpha may play an important role in myocardial homeostasis after environmental stress.

Tumor necrosis factor-alpha (TNF-alpha) mRNA and protein biosynthesis were examined in adult feline myocardium in the presence and absence of superimposed hemodynamic pressure overloading. A brief period of hemodynamic pressure overloading ex vivo resulted in de novo TNF-alpha mRNA expression within 30 minutes and de novo TNF-alpha protein production within 60 minutes; neither TNF-alpha mRNA nor protein was detected in hearts perfused at normal perfusion pressures. Moreover, TNF-alpha mRNA and protein biosynthesis were observed in myocyte and nonmyocyte cell types in the pressure-overloaded hearts. To determine whether a simple passive stretch of the myocardium was a sufficient stimulus for TNF-alpha biosynthesis, we examined TNF-alpha mRNA expression in stretched and unstretched papillary muscles. This study showed that myocardial stretch was a sufficient stimulus for the induction of TNF-alpha mRNA biosynthesis. The functional significance of the intramyocardial production of TNF-alpha was determined by examining cell motion in isolated contracting cardiac myocytes treated with superfusates from pressure-overloaded and control hearts. These studies showed that cell motion was depressed in myocytes treated with superfusates from the pressure-overloaded hearts but was normal with the superfusates from the control hearts. Finally, hemodynamic pressure overloading in vivo under physiological conditions was also shown to result in de novo intramyocardial TNF-alpha mRNA biosynthesis. In conclusion, this study constitutes the initial demonstration that the adult mammalian myocardium elaborates biologically active TNF-alpha, both ex vivo and in vivo, in response to hemodynamic pressure overloading.

We examined genetically determined oxidation polymorphisms of metoprolol and mephenytoin in 200 unrelated, healthy Japanese subjects and in 98 mainland Chinese subjects simultaneously. This examination was done according to the respective reported phenotyping criteria by use of the urinary metabolic ratio of metoprolol and of the percentage of excretion of 4-hydroxymephenytoin 8 hours after dose administration. The frequencies of occurrence of poor metabolizers (PMs) in the Japanese versus the Chinese subjects were 0.5% versus 0% for metoprolol and 22.5% versus 17.4% for mephenytoin, respectively. There were no statistically significant differences in these frequencies between the two Oriental populations. However, Chinese extensive metabolizers (EMs) showed a significantly lower excretion of alpha-hydroxymetoprolol (p less than 0.01) and 4-hydroxymephenytoin (p less than 0.001) than that of Japanese EMs, and the mode of the distribution histogram of the Chinese EMs for the two test probes was skewed compared with that of the Japanese EMs. The findings indicate that the two Far Eastern Oriental subject groups have a lower frequency of PM phenotype of debrisoquin/sparteine-type oxidation and a greater incidence of PM phenotype of mephenytoin oxidation compared with the respective frequencies reported from white subjects. However, the explanation for the observation that the metabolic capacities of the test drugs differed between the EMs of the two populations who had a similar ethnic origin and who resided in the same geographic area remains obscure.