Effect of Rapamycin on Contractility of Lymphatic Vessel and Energy Metabolism of Lymphatic Muscle Cells

Abstract

Proper functioning of lymphatic vessels (LV) is necessary for the transport of fluids, proteins, and metabolites from the interstitium via lymph nodes to the blood circulation. To achieve all these functions, lymphatic vessels use muscle cells for contractions and endothelial cells to precisely tune these contractions. Moreover, lymphatic vessels play important roles in antigen and immune cell trafficking to provide sufficient immune responses. During a solid organ transplantation, the body's immune system has a strong tendency to reject the organ transplant. Therefore, immunosuppressive drugs are used for tolerance induction to lower the activity of the immune system to accept the organ transplant. Rapamycin is a potent immunosuppressant that can disrupt cytokine signaling, which contributes to the proliferation of lymphocytes. Potential but unusual side effects of using Rapamycin include lymphatic disorders. Several cases were observed wherein transplant recipients exhibited delayed drainage of lymph, lymphatic obstruction, and complete blockage of lymphatic vessels. Cases such as these suggest that more research must be conducted to investigate the mechanism of these effects and possible prophylaxis and treatment of these complications. We investigated the effect of rapamycin on contractility of rat mesenteric lymphatic vessels and lymphatic muscle cell (LMC) metabolism. Rapamycin at 10^-5M after 1Hr of application decreased tone of LV at transmural pressure of 1cm H2O by 4.1 ± 2.9%, and decreased contractile amplitude by 7.8 ± 3.5% and 10.2 ± 4.2% at pressures 3 and 5 cm H2O respectively. Rapamycin at 10^-5M after 1Hr of application decreased LMC ATP production by 0.012 ± 0.002 pmol/min/ug, maximal oxygen consumption rate by 0.027 ± 0.006 pmol/min/ug, spare mitochondrial capacity by 0.025 ± 0.005 pmol/min/ug, coupling efficiency by 33.9 ± 6.1% and increased proton leak by 0.009 ± 0.002 pmol/min/ug. Rapamycin also increased basal extracellular acidification rate (ECAR) by 0.011 ± 0.003 pmol/min/ug. Therefore, rapamycin in high concentration could possibly lead to mitochondrial uncoupling that might reflect changes in contractility. Moreover, an increase in the ECAR can indicate shifting glucose fermentation to lactate that could progress to pathological LV remodeling in the future.