INDUCTION OF INOS GENE-EXPRESSION BY MONOPHOSPHORYL LIPID-A - A PHARMACOLOGICAL APPROACH FOR MYOCARDIAL ADAPTATION TO ISCHEMIA

Using the concept that exposing a cell to an adverse environment (stre ss) results in the stimulation of its endogenous defense system, heart s have been adapted to ischemia by exposing them to diverse stresses. Recently, 24-h pretreatment of monophosphoryl lipid A (MLA), a chemica lly modified derivative of endotoxin, was found to render the hearts m ore tolerant to ischemic reperfusion injury. Since nitric oxide has re cently been implicated in myocardial preservation and since inducible nitric oxide synthetase (iNOS) was originally characterized in macroph ages and shown to be maximally induced by bacterial lipopolysaccharide s (endotoxin), we sought to determine whether MLA mediates its cardiop rotective effects through the iNOS expression. For this, rats were inj ected with MLA (300 mu g/kg) or vehicle (control), and after 24 h the animals were sacrificed and the isolated working hearts were made isch emic for 30 min followed by 30 min of reperfusion. MLA-treated hearts were found to be tolerant to ischemic reperfusion injury as evidenced by improved postischemic ventricular recovery. After 30 min of reperfu sion, left ventricular developed pressure (LVDP) and its maximum first derivative (LV(max)dp/dt) were 13.3+/-0.3 kPa and 537+/-13 kPa/s, res pectively, in the MLA-treated group, as compared with 10.2+/-20.4 kPa (p<0.05) and 447+/-11 kPa/s (p<0.05), respectively for the control gro up. Aortic flow and coronary flow were 20.1+/-1.4 ml/min and 19.1+/-0. 8 ml/min, respectively, in the MLA group, as compared with 9.5+/-0.8 m l/min (p<0.05) and 15.9+/-0.7 ml/min (p<0.05), respectively, for the u ntreated group. To examine the induction of the iNOS expression, RNAs were extracted from the control and MLA-treated hearts (after 2 4, 6, 8, 12 and 24 h of treatment) and Northern blot analysis was performed using specific cDNA probe for iNOS. A single band of approximately 4.6 kb corresponding to iNOS mRNA was detected after 4 h of MLA treatment , while the maximal iNOS expression was found between 6-8 h of MLA tre atment;The results of this study demonstrate that MLA induces the expr ession of iNOS and protects the myocardium from ischemic reperfusion i njury.