Background: Interleukin-37 (IL-37) is a new member of IL-1 cytokine family with a defined role as a negative feedback inhibitor of pro-inflammatory responses. IL-37 has yet to be evaluated in non-immune neurological diseases like ischemic or hemorrhagic stroke. This study aimed to measure the urine and serum IL-37 levels in patients with acute ischemic stroke.
Method: Twelve patients consented for the study. Two sets of serum and urine samples were obtained and analyzed; one upon admission to the hospital, and the second the next morning after overnight fasting. The trends in serum level of IL-37 in 5 stroke patients, while trends in urine level of 6 patients were available, measured by real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). Prior studies with healthy volunteers as control group have consistently showed IL-37 plasma level around or less than 65 pg/ml with maximum normal levels on ELISA approximated at 130 pg/ml.
Results: IL-37 level in urine in stroke patients ranged from 297 - 4467. IL-37 levels were in the range of 300s to 1000s in patients with ischemic stroke compared with reported healthy controls in literature where the level was always less than 90. Three of these 10 patients presented within 3 hours of stroke onset with IL-37 serum levels being 2655 pg/ml, 3517 pg/ml and 5235 pg/ml. In all others, it ranged much less than that, with the trend of delayed presentation giving less IL-37 levels, both in urine and serum. There were no clear differences found in patients with or without tPA, diabetes, hyperlipidemia and high blood pressure in our small study.
Conclusion: The study shows a rather stable elevation of IL-37 levels post-ischemic stroke, which if compared to available data from other studies, is 3-10 times elevated after acute ischemic stroke with an uptrend in the first few days. IL-37 plays some role in mediating post-stroke inflammation with significant rise in serum and urine IL-37 levels suggesting a key role of this novel cytokine in post-stroke pathology. This is the first ever reported study measuring and trending IL-37 levels in human plasma after an acute ischemic stroke.