Losartan protects the lung from chronic cellular damage induced by fat embolism (LB512)

In a rat model of fat embolism (FE) induced by i.v. triolein (T), severe lung damage develops up to 10 weeks post treatment1. The damage which is reduced by concomitant administration of the angiotensin II type 1 receptor blocker losartan (Los)2 was associated with an elevated level of renin in the lungs.3 Reports indicate that mast cells (MCs) are associated with the renin increase observed in the lungs.4 FE damage, however, is not limited to the lungs. Hearts of the same rats had severe inflammation of the coronary arteries with medial thickening, reduced lumen patency, adventitial fibrosis, and myocardial inflammation, which was also blocked by Los.5 We have now extended our investigation of the heart to the potential role of mast cells (MCs) in the pathogenesis of cardiovascular damage.Twenty‐two Sprague Dawley rats (~300 gm BW) received either T (0.2 mL i.v.) or saline. Six weeks later, half of the rats of each subgroup were given Los or saline). Four weeks later (10 weeks post T injection), rats were euthanized with isoflurane, and necropsied. Hearts were fixed in 10% formalin and stained with H&E (morphometric scoring), trichrome (fibrosis) and CD 11‐c kit (MCs). On each heart slide 10 photographs were taken at random at 400× and MCs counted by two pathologists unaware of the slide identity.Severe vasculitis, perivascular fibrosis, and myocardial inflammation were present in the hearts of T treated rats vs saline controls. Los markedly reduced this damage, but had no effect on MCs in the presence of absence of T. MC number. T caused a non‐significant increase in MCs number compared to saline controls (20.7 +/− 5.3 vs 13.1 +/− 5.1: mean +/− STdev). The results suggest that, although MCs are present in hearts of rats 10 weeks after T where vascular inflammation and histopathological damage is similar to that observed in the lungs, their number is more modestly increased and not affected by Los treatment.The trend of an increase in MCs in the heart 10 weeks after T suggests a potential role of MCs in the pathogenesis of cardiovascular damage. Despite the severe inflammatory and vascular response and the protective effect of Los from perivascular fibrosis, the role of MCs in the heart at this late time after T may suggest different pathways or time course for histopathological changes compared to the lungs. It remains to be seen if the appearance of MCs in the heart after T is greater at earlier time points when the lung pathology is also greater.Support or Funding InformationMary Katherine Geldmacher Research Foundation, St. Louis, MO; This work was supported by a CTSA grant from NCRR and NCATS awarded to the University of Kansas Medical Center for Frontiers: The Heartland Institute for Clinical and Translational Research # TL1TR000120. The contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH, NCRR, or NCATS.

an on Mast Cells in the Hearts of Rats 10 Weeks after Fat Embolism with Triolein

Fletcher,

Poisner,

Hamidpour

et al. 2016

Absence of Mast Cells in the Kidneys of Rats Subjected to Fat Embolism Despite their Presence in the Lungs and Heart

Patel,

Fletcher,

Poisner

et al. 2016

In a rat model of fat embolism (FE) induced by i.v. injection of triolein (T), we have shown that the lungs, hearts and kidneys demonstrate severe histopathological damage characterized by organ inflammation and arterial constriction. 1,2,3 Such damage is present up to 10 weeks after injection.1 The renin angiotensin system (RAS) plays a role in the pathogenesis of the damage since captopril (an ACE inhibitor) and losartan (Los), an angiotensin‐II type 1 receptor blocker, prevented the damage.4 After T injection, an increase in renin stain was observed in the kidney juxta‐glomerular apparatus (JXTG)5 and in the lungs.6 The renin overexpression may be related to an increased number of mast cells (MCs),7 and indeed we found an increased number of these cells 10 weeks post T injection in the lungs of the rats.8 MCs in lower numbers were also observed in hearts of the same rats, but LOS did not reduce their number.9 On the basis of these observations, we decided to evaluate the potential presence of MCs in kidneys after T injection.Twenty‐two Sprague Dawley rats (~300 gm BW) received either T (0.2 mL i.v.) or saline. Six weeks later, half of the rats were given i.p. injection of Los and the remainder received saline. Four weeks later (10 weeks post T injection), rats were anesthetized with isoflurane, sacrificed, and necropsied. Tissues were fixed in 10% formalin and stained with H&E (morphometric scoring), Trichrome (fibrosis) and CD 11‐c kit (MCs). On each slide, 10 photographs were taken at random at 400× and MCs evaluated by two pathologists unaware of the slide identity.After T injection, we observed severe arterial damage with increased medial thickness and reduced lumen patency. Glomeruli showed increased cellularity, thickening of basal membrane, and crescent formation. Scattered chronic inflammatory cells and erythrocytes were seen in the tubuli. The damage was moderately reduced by Los treatment. MCs were not seen in any of the animals.In the kidneys, despite the high presence of renin in the JXTG and severe vasculitis after T injection, we could not identify MCs at 10 weeks even with a very specific staining method. This is in contrast with the presence of MCs that we have found in the lungs and heart. The absence of MCs in the kidneys at 10 weeks may reflect different pathogenic mechanisms or a time course different from that of the lungs or heart.Support or Funding InformationM. K. Geldmacher Foundation, St. Louis, MO; This work was supported by a CTSA grant from NCRR and NCATS awarded to the University of Kansas Medical Center for Frontiers: The Heartland Institute for Clinical and Translational Research # TL1TR000120. The contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH, NCRR, or NCATS.

Losartan Blocks the Recruitment of Mast Cells in the Lungs of Rats Subjected to Fat Embolism with or without a Second Hit with LPS

Poisner,

Hamidpour,

et al. 2016

In a rat model of pulmonary fat embolism (FE) using triolein (T), we have shown that the long term histopathological effects of triolein‐induced FE extend to 10 weeks and are inhibited by losartan (LOS), an angiotensin II type 1 receptor blocker1 and augmented by a second hit with LPS2. These effects are associated with an increase in renin staining at 6 weeks3. Since other workers have implicated pulmonary mast cells (MC) in local renin‐angiotensin (RAS)‐mediated pulmonary pathology4, we examined whether FE in our model was associated with an increase in MC number and if their appearance would be blocked by LOS and modified by a second hit with LPS. 36 Sprague‐Dawley rats were treated with T (0.2 ml i.v.) or saline. After 6 weeks, half of the groups were given saline or LPS 0.1 ml (3 mg/kg) i.p., followed 1 hour later with saline or LOS (10 mg/kg i.p.), followed by LOS in the drinking water (50 mg/l). 4 weeks later (10 weeks after T), the animals were necropsied after isoflurane anesthesia. Lungs were fixed in 10% formalin and stained with H&E for morphometric scoring and for mast cells using CD11 (c‐kit). Portions of the lungs were frozen and stained for fat using Oil Red O. Two pathologists unaware of the slides’ identity took 10 photographs at random in each slide at 400× and then counted the mast cell number.MC number increased in T‐treated rats compared to saline controls (57.2 +/− 2.5 vs 20.0 +/− 2.3) (mean+/− SEM) (p=0.005). The MC count when T was followed by LPS rose to 66.8 +/− 14.5 (p=0.001 compared to saline). LPS or LOS alone did not cause a significant increase in MC (35.0 +/− 8.5 and 28.2 +/− 2.6, respectively.) The increases in MC caused by T and T+LPS were both blocked by LOS: (T+LOS 14.9 +/− 2.9; T+LPS+LOS 32.5 +/− 4.6; p=0.75 and 0.99 compared to LOS alone.The appearance of fat globules at 10 weeks was greatly reduced from what we reported for rats at 6 weeks3 but they were increased in T‐treated rats compared to saline controls.The results support suggestions that MC‐associated renin through its eventual product angiotensin II plays an important role in the histopathological changes produced by FE and the second hit with LPS. In addition, the presence of fat globules in the lungs 10 weeks after the initial challenge with T suggests that their continued presence may be important for the enhanced presence of MC in response to low grade inflammation. A role for macrophage signaling in this sequence is also supported5.Support or Funding InformationMary Katherine Geldmacher Research Foundation, St. Louis, MO