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Effects of NO synthase inhibitors on the synovial microcirculation in the mouse knee joint
A Veihelmann1, F Krombach, H J Refior
1Department of Orthopedics, Ludwig Maximilians University of Munich, Germany. andyvei@lrz-muenchen.de
Abstract:
Production of nitric oxide by the inducible NO synthase (iNOS) is known to be enhanced in chronic joint inflammation and osteoarthritis as well as aseptic loosening of joint prostheses. Initial studies yielded promising results after inhibition of the nitric oxide synthase (NOS). However, the effect of NOS inhibition has not been studied at the site of the primary function of NO, the microcirculation of the synovium in vivo. Using our recently developed model for the in vivo study of synovial microcirculation in the mouse knee joint, the effects of selective versus nonselective inhibition of iNOS were investigated by means of intravital fluorescence microscopy. After resection of the patella tendon, the synovial fatty tissue was exposed for intravital microscopy. Diameter of arterioles, functional capillary density (FCD), diameter of venules, venular red blood cell velocity and leukocyte-endothelial cell interaction were quantitatively analyzed before, and 10 and 60 min after intravenous injection of NOS inhibitors [selective iNOS inhibitor N-iminoethyl-L-lysine (L-NIL), and nonselective NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME)]. Our results demonstrate that L-NAME causes a significant decrease in the arteriolar diameter and FCD associated with an increase in the leukocyte accumulation in the synovium in vivo. In contrast, L-NIL neither altered the microhemodynamics nor the leukocyte-endothelial cell interaction in the synovium, indicating its potential use for selective inhibition of iNOS in joint inflammation. Using our method, further studies will provide new insights into the unknown effect of NOS inhibition on the synovial microvasculature in inflammatory joint disease in vivo.
Insights
Nonselective inhibition of nitric oxide synthase (NOS) worsens joint microcirculation, while selective inhibition of inducible NOS (iNOS) shows potential for treating joint inflammation without adverse effects.
Area of Science:
- Orthopedics
- Vascular Biology
- Pharmacology
Background:
- Nitric oxide (NO) production increases in joint inflammation, osteoarthritis, and prosthesis loosening.
- Previous studies suggested benefits of nitric oxide synthase (NOS) inhibition.
- The impact of NOS inhibition on synovial microcirculation in vivo remains unexamined.
Purpose of the Study:
- To investigate the effects of selective and nonselective NOS inhibition on synovial microcirculation in a mouse knee joint model.
- To evaluate the impact of these inhibitors on arteriolar diameter, capillary density, venular function, and leukocyte interaction.
Main Methods:
- Utilized a novel in vivo mouse knee joint model for intravital fluorescence microscopy.
- Administered selective iNOS inhibitor (L-NIL) and nonselective NOS inhibitor (L-NAME).
- Quantitatively analyzed microhemodynamic parameters and leukocyte-endothelial cell interactions.
Main Results:
- L-NAME significantly reduced arteriolar diameter and functional capillary density (FCD).
- L-NAME increased leukocyte accumulation in the synovium.
- L-NIL did not alter microhemodynamics or leukocyte interaction, suggesting selective iNOS inhibition is safe.
Conclusions:
- Nonselective NOS inhibition negatively impacts synovial microcirculation.
- Selective iNOS inhibition with L-NIL demonstrates potential for treating joint inflammation without compromising microvascular function.
- This study provides a valuable model for further research into NOS inhibition in inflammatory joint diseases.