Session Title: Rheumatoid Arthritis: Animal Models
Session Type: Abstract Submissions (ACR)
Background/Purpose: Sufficient lymphatic drainage, which is partially controlled by an intrinsic lymphatic pulse, is an important mechanism to limit joint inflammation and destruction from arthritis. We reported recently that arthritic flare in TNF transgenic (TNF-Tg), a mouse model of inflammatory-erosive arthritis, coincides with the loss of the lymphatic pulse afferent to expanding draining lymph nodes, causing their collapse. From other models, the lymphatic pulse is known to be controlled by endothelia nitric oxide synthase (eNOS), and inhibited by inducible NOS (iNOS) expresses in Gr-1+ cells. To determine if this mechanism controls the lymphatic pulse and lymphatic drainage in inflammatory-erosive arthritis, we tested the hypotheses that: 1) Gr-1+/iNOS+ cells are present in the draining lymph nodes of flaring TNF-Tg mice; and 2) selective iNOS inhibition increases the lymphatic pulse and drainage from joints to draining lymph nodes.
Methods: Immunohistochemistry for Gr-1 and iNOS was performed on popliteal lymph node (PLN) frozen sections from WT and TNF-Tg mice. The lymphatic pulse and flow afferent to the PLN were quantified in TNF-Tg mice with collapsed PLN (>8-month-old) and WT controls (n=4 legs) via in vivo near infrared indocyanine green (NIR-ICG) imaging before and after saline (placebo), iNOS specific inhibitor L-NIL (4mg/kg), or general NOS inhibitor L-NAME (5mg/kg) was injected S.C. in footpad.
Results: Immunohistochemistry showed more iNOS expressing Gr-1+ cells in collapsed vs. expanding PLN (127 vs. 3 cells/mm2), and undetectable numbers in WT PLN. Saline did not change the lymphatic pulse in either WT or TNF-Tg mice. However, L-NIL significantly increased the pulse in TNF-Tg mice (from 0.42 +/- 0.84 to 2.19 +/- 0.77 pulse/min; p<0.05), but not in age-matched WT mice (0.96 +/- 1.42 to 3.13 +/- 2.36 pulse/min; p=0.08). Moreover, L-NIL significantly increase lymphatic flow in TNF-Tg vs. saline (73.48 +/- 8.9 vs, 53.25 +/- 12.72 % ICG clearance; p<0.05). In contrast, L-NAME decreased the clearance rate in both WT (27.77 +/- 13.78%) and TNF-Tg (9.07 +/- 33.65%), but did not significantly change the pulse rate.
Conclusion: We demonstrated that large numbers of iNOS expressing Gr-1+ cells exist in collapsed PLN of TNF-Tg mice with flaring inflammatory-erosive arthritis, and that the specific iNOS inhibitor L-NIL increased the lymphatic pulse and afferent lymphatic drainage. These results suggest that selective iNOS inhibition may be effective in ameliorating arthritic flare by improving lymphatic drainage, which is currently being tested in a prospective study of flaring TNF-Tg mice treated for 6-weeks with L-NIL, L-NAME, or placebo. The effects of these treatments on knee and ankle synovitis and focal joint bone erosion determined by CE-MRI, micro-CT and histology will be presented.
C. T. Ritchlin,
E. M. Schwarz,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/selective-inos-inhibition-increases-the-lymphatic-pulse-and-drainage-from-arthritic-joints-in-tnf-tg-mice/