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Inducible nitric oxide synthase (iNOS) in the human heart: expression and localization in congestive heart failure
N G Vejlstrup1, A Bouloumie, S Boesgaard
1Medical Department B, University of Copenhagen, Denmark.
Abstract:
The inducible nitric oxide (NO) synthase (iNOS or NOS2) generates a prolonged release of large amounts of NO which may be cytotoxic and/or inhibit myocyte contractility. It has been suggested that this mechanism specifically contributes to heart failure caused by dilated cardiomyopathy (DCM). To test this hypothesis we compared the myocardial amount and localization of iNOS in myocardial biopsies from patients with heart failure caused by either DCM or ischemic heart disease (IHD). During heart transplantation, myocardial biopsies collected from the diseased heart after explantation were frozen in liquid nitrogen. Twenty-two patients in NYHA class III-IV were included (DCM: n = 8; IHD: n = 14). In each biopsy, iNOS expression was assessed using reverse transcription polymerase chain reaction (RT-PCR), and visualized by immunohistochemistry. iNOS was detected in all biopsies. Intriguingly, the amount of iNOS mRNA (shown as iNOS cDNA normalized to GADPH cDNA) did not differ significantly between the two groups (DCM 30 +/- 7; IHD 20 +/- 6, mean +/- S.E.M., P > 0.05). Similarly, no inter-group differences in the amount of iNOS protein (Western) were observed. iNOS was invariably located to vascular endothelial and smooth muscle cells. In addition, an iNOS reaction in relation to the myocyte membrane was found in 4 of the 22 patients. These four patients (two from each group) had significantly (P < 0.05) higher iNOS/GADPH ratios (54 +/- 20) than patients without myocyte membrane iNOS reaction (17 +/- 15). In conclusion, iNOS is expressed in the myocardium of all patients with heart failure caused by either DCM or IHD. iNOS is located primarily and invariably in the endothelium and vascular smooth muscle cells of the myocardial vasculature and its expression appears to be associated with the condition of heart failure per se rather than related to the heart failure etiology.
Insights
Inducible nitric oxide synthase (iNOS) is present in all heart failure patients, regardless of cause. Its location in vascular cells, not myocytes, suggests iNOS contributes to heart failure generally, not specific types like dilated cardiomyopathy.
Area of Science:
- Cardiovascular Research
- Molecular Biology
- Pathophysiology
Background:
- Inducible nitric oxide synthase (iNOS) produces nitric oxide (NO), potentially impacting heart function.
- iNOS has been hypothesized to play a specific role in heart failure due to dilated cardiomyopathy (DCM).
Purpose of the Study:
- To compare myocardial iNOS expression and localization in patients with heart failure from DCM versus ischemic heart disease (IHD).
- To investigate if iNOS contributes specifically to DCM-related heart failure.
Main Methods:
- Myocardial biopsies were obtained from heart failure patients during transplantation.
- iNOS expression was quantified using reverse transcription polymerase chain reaction (RT-PCR) and visualized via immunohistochemistry.
- iNOS localization was assessed in relation to vascular cells and myocytes.
Main Results:
- iNOS was detected in all heart failure patient biopsies, irrespective of etiology (DCM or IHD).
- Myocardial iNOS mRNA levels did not significantly differ between DCM and IHD groups.
- iNOS was primarily localized to vascular endothelial and smooth muscle cells, with some association with myocyte membranes in a subset of patients.
Conclusions:
- iNOS is expressed in the myocardium of all heart failure patients studied.
- iNOS localization is predominantly in vascular cells, suggesting a general role in heart failure pathophysiology.
- The findings do not support a specific role for iNOS in DCM etiology over IHD.