Context: A strong association between subclinical hypothyroidism (SCH) and atherosclerotic diseases, independent of the traditional risk factors, was noted.
Objective: The objective of the study was to evaluate the association between SCH and the inflammatory potential of atherosclerotic plaques as well as the role of L-T(4) replacement therapy (LTR) on regulation of plaque inflammation. EXPERIMENTAL DESIGN AND MAIN OUTCOME MEASURES: We examined the differences in macrophage content, proinflammatory cytokine infiltration, and oxidative stress between asymptomatic carotid plaques of patients with and without SCH and LTR.
Setting and participants: Plaques were obtained from 23 SCH patients with LTR (treated), 34 untreated SCH patients, and 30 control patients without SCH enlisted to undergo carotid endarterectomy for extracranial high-grade (>70%) internal carotid artery stenosis. Plaques were analyzed for macrophages, T lymphocytes, human leukocyte antigen (HLA)-DR(+) cells, nuclear factor-κB (NF-κB), inhibitory-κBβ (IκBβ), TNF-α, nitrotyrosine, matrix metalloproteinase-9 (MMP-9), and collagen content (immunohistochemistry and ELISA).
Results: Compared with control plaques, SCH plaques had more macrophages, T lymphocytes, and HLA-DR(+) cells, TNF-α, NF-κB, markers of oxidative stress (nitrotyrosine and O(2-) production), and MMP-9 (P < 0.01, for all), along with a lesser collagen content and IκBβ levels (P < 0.001). Compared with plaques from treated patients, plaques from untreated patients had more macrophages, T lymphocytes, HLA-DR(+) cells, TNF-α, NF-κB (P < 0.001), nitrotyrosine, O(2-) production, and MMP-9 (P < 0.01, for all), along with a lesser collagen content and IκBβ levels (P<0.001).
Conclusions: These data suggest a potential interplay between SCH and inflammatory activity in atherosclerotic plaque progression toward instability. Moreover, LTR might contribute to plaque stabilization by inhibiting the innate immunity-dependent plaque rupture in patients with SCH.