ApoM Ameliorates AAI-HSR Induced Microvascular Leakage

Acute alcohol intoxication (AAI) worsens hypotension and edema associated with hemorrhagic shock and fluid resuscitation (HSR). Apolipoprotein M (ApoM) is a lipocalin residing in plasma HDL and acts as a carrier of the endothelial-protective lipid, sphingosine-1-phosphate (S1P). We tested the hypothesis that ApoM administration reduces HSR-induced microvascular leakage. The ability of 0.1 mg/kg S1P, 0.4 mg/kg ApoM, or their combination to reduce AAI-HSR-induced microvascular leakage was tested using an established rat model of AAI-HSR combined with intravital microscopy. Transendothelial electrical resistance (TER) of human umbilical vein endothelial cell (HUVEC) monolayers served as an in vitro model of endothelial barrier function. Changes in TER after 0.1 µM S1P, 1.0 µM ApoM, or their combination were compared to control. Immunofluorescence staining of junctional VE-Cadherin in HUVEC monolayers was also assessed to evaluate junction integrity by comparing control, 75 mM alcohol, 0.1 µM S1P, 1.0 µM ApoM or their combination after 75 mM alcohol conditioning. A pull-down assay with ApoM-treated HUVEC was used to determine ApoM-bound proteins. The Rac1 G-LISA assay was used to verify if the ApoM causes Rac1 activation. The results show that compared to sham, combined AAI and HSR significantly increased microvascular leakage. Administration of S1P or ApoM alone or in combination during resuscitation significantly decreased microvascular leakage near the level of sham controls. In HUVEC monolayers, S1P, ApoM, and S1P + ApoM all significantly increased TER. ApoM also improved the junctional integrity of VE-cadherin compromised by alcohol. The small GTPase Rac1 was found to bind with ApoM in HUVEC and was significantly activated within 5 min of ApoM addition. The findings suggest that fluid resuscitation with ApoM ameliorates AAI-HSR-induced microvascular leakage. The mechanism involves stabilizing VE-Cadherin junction integrity, which could be caused by Rac1 activation. NIHR35GM145379 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.