Heparin use in a rat hemorrhagic shock model induces biologic activity in mesenteric lymph separate from shock

Why Do Men Accumulate Abdominal Visceral Fat?

Men have a higher tendency to accumulate abdominal visceral fat compared to pre-menopausal women. The accumulation of abdominal visceral fat in men, which is a strong independent predictor of mortality, is mainly due to the higher dietary fat uptake by their abdominal visceral fat. Since dietary fat is absorbed by the enterocytes and transported to the circulation in the forms of chylomicrons and very low density lipoproteins (VLDLs), it is crucial to understand how these lipoproteins are different between men and women. The chylomicrons in men are generally bigger in size and more in quantity than those in women. During the postprandial state, these chylomicrons congest the lamina propria and the low-pressure lymphatics. In this paper, we propose that this congestion predisposes the chylomicron triglycerides to hydrolysis by lipoprotein lipase (LPL). The liberated fatty acids are then stored by the nearby abdominal visceral adipocytes, leading to the accumulation of abdominal visceral fat. These mechanisms perhaps explain why men, through their bigger and higher production of chylomicrons, are more likely to accumulate abdominal visceral fat than pre-menopausal women. This accumulation eventually leads to belly enlargement, which confers men their apple-shaped body.

Group VIB Ca(2+)-independent phospholipase A(2γ) is associated with acute lung injury following trauma and hemorrhagic shock

BACKGROUND

Gut-derived mediators are carried via mesenteric lymph duct into systemic circulation after trauma/hemorrhagic shock (T/HS), thus leading to acute lung injury (ALI)/multiple-organ dysfunction syndrome. Phospholipase A2 (PLA(2)) is a key enzyme for the production of lipid mediators in posthemorrhagic shock mesenteric lymph (PHSML). However, the precise functions of PLA(2) subtype, such as cytosolic PLA(2), secretory PLA(2), and Ca-independent PLA(2), in the acute phase of inflammation have remained unclear. Our previous study has suggested that the activation of Group VIB Ca-independent PLA(2γ) (PLA(2γ)) may be associated with increased lyso-phosphatidylcholines (LPCs) in the PHSML. Therefore, our purpose was to verify the role of iPLA(2γ) on the production of 2-polyunsaturated LPC species and the pathogenesis of T/HS-induced ALI using an iPLA(2γ)-specific inhibitor, R-(E)-6-(bromoethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one (R-BEL).

METHODS

Male Sprague-Dawley rats were anesthetized and cannulated in blood vessels and mesenteric lymph duct. Animals in the T/HS group underwent a midline laparotomy plus hemorrhagic shock (mean arterial pressure, 35 mm Hg, 30 minutes) and 2-hour resuscitation with shed blood and 2× normal saline. Trauma/sham shock rats were performed the identical procedure without hemorrhage. R-BEL or DMSO was administered 30 minutes before T/HS or trauma/sham shock. Polyunsaturated LPCs and arachidonic acid in the PHSML were analyzed with a liquid chromatography/electrospray ionization-mass spectrometry. Furthermore, ALI was assessed by lung vascular permeability, myeloperoxidase activity, and histology.

RESULTS

T/HS increased 2-polyunsaturated LPCs and arachidonic acid in the PHSML. The R-BEL pretreatment significantly decreased these lipids and also inhibited ALI.

CONCLUSION

The iPLA(2γ) enzyme is possibly involved in the pathogenesis of ALI following T/HS through the mesenteric lymph pathway.

Redefining the gut as the motor of critical illness

The gut is hypothesized to play a central role in the progression of sepsis and multiple organ dysfunction syndrome. Critical illness alters gut integrity by increasing epithelial apoptosis and permeability and by decreasing epithelial proliferation and mucus integrity. Additionally, toxic gut-derived lymph induces distant organ injury. Although the endogenous microflora ordinarily exist in a symbiotic relationship with the gut epithelium, severe physiological insults alter this relationship, leading to induction of virulence factors in the microbiome, which, in turn, can perpetuate or worsen critical illness. This review highlights newly discovered ways in which the gut acts as the motor that perpetuates the systemic inflammatory response in critical illness.

Role of lipase-generated free fatty acids in converting mesenteric lymph from a noncytotoxic to a cytotoxic fluid

Recent studies have shown that mesenteric lymph plays a very important role in the development of multiple-organ dysfunction syndrome under critical conditions. Great efforts have been made to identify the biologically active molecules in the lymph. We used a trauma-hemorrhagic shock (T/HS) model and the superior mesenteric artery occlusion (SMAO) model, representing a global and a localized intestinal ischemia-reperfusion insult, respectively, to investigate the role of free fatty acids (FFAs) in the cytotoxicity of mesenteric lymph in rats. Lymph was collected before, during, and after (post) shock or SMAO. The post-T/HS and SMAO lymph, but not the sham lymph, manifested cytotoxicity for human umbilical vein endothelial cells (HUVECs). HUVEC cytotoxicity was associated with increased FFAs, especially the FFA-to-protein ratio. Addition of albumin, especially delipidated albumin, reduced this cytotoxicity. Lipase treatment of trauma-sham shock (T/SS) lymph converted it from a noncytotoxic to a cytotoxic fluid, and its toxicity correlated with the FFA-to-protein ratio in a fashion similar to that of the T/HS lymph, further suggesting that FFAs were the key components leading to HUVEC cytotoxicity. Analysis of lymph by gas chromatography revealed that the main FFAs in the post-T/HS or lipase-treated T/SS lymph were palmitic, stearic, oleic, and linoleic acids. When added to the cell culture at levels comparable to those in T/HS lymph, all these FFAs were cytotoxic, with linoleic acid being the most potent. In conclusion, this study suggests that lipase-generated FFAs are the key components resulting in the cytotoxicity of T/HS and SMAO mesenteric lymph.

Regional citrate anticoagulation for hemorrhage experiments in rats

INTRODUCTION

Hemorrhage alone without concomitant trauma often results in a hypercoagulable state that makes it difficult to prevent clotting within the blood withdrawal catheters. Although systemic administration of heparin can ameliorate this problem, heparin use has many additional actions that may confound interpretation of the hemorrhage experiments. The problem can be resolved by the use of a dual lumen catheter that anticoagulates only the blood within the withdrawal circuit. We describe the design of such a catheter and evaluate its function in studies of hemorrhagic shock in rats.

MATERIALS AND METHODS

Construction directions are provided for the dual lumen catheter along with a commercial source. The catheters were connected to computer controllable infusion syringes. Either citrate or heparin was used for regional extracorporeal anticoagulation. Rats were anesthetized and hemorrhaged to 40mmHg for more than 15min through the use of a computer program written in Labview. Ionized calcium measurements were obtained pre- and posthemorrhage.

RESULTS

The catheters remained patent throughout the experiments. There was no significant difference in the ionized calcium whether citrate or heparin was used for extracorporeal anticoagulation.

CONCLUSION

The dual lumen catheters are suitable for the study of hemorrhagic shock in rats without the need for systemic anticoagulation. The catheters can be used with computer-controlled hemorrhage procedures.

Anticoagulants influence the in vitro activity and composition of shock lymph but not its in vivo activity

Many models of trauma-hemorrhagic shock (T/HS) involve the reinfusion of anticoagulated shed blood. Our recent observation that the anticoagulant heparin induces increased mesenteric lymph lipase activity and consequent in vitro endothelial cell cytotoxicity prompted us to investigate the effect of heparin-induced lipase activity on organ injury in vivo as well as the effects of other anticoagulants on mesenteric lymph bioactivity in vitro and in vivo. To investigate this issue, rats subjected to trauma-hemorrhage had their shed blood anticoagulated with heparin, the synthetic anticoagulant arixtra (fondaparinux sodium), or citrate. Arixtra, in contrast to heparin, did not increase lymph lipase activity or result in high levels of endothelial cytotoxicity. Yet, the arixtra-treated rats subjected to T/HS still manifested lung injury, neutrophil priming, and red blood cell dysfunction, which was totally abrogated by lymph duct ligation. Furthermore, the injection of T/HS mesenteric lymph, but not sham-shock lymph, collected from the arixtra rats into control mice recreated the pattern of lung injury, polymorphonucleocyte (PMN) priming, and red blood cell dysfunction observed after actual shock. Consistent with these observations, citrate-anticoagulated rats subjected to T/HS developed lung injury, and the injection of mesenteric lymph from the citrate-anticoagulated T/HS rats into control mice also resulted in lung injury. Based on these results, several conclusions can be drawn. First, heparin-induced increased mesenteric lymph lipase activity is not responsible for the in vivo effects of T/HS mesenteric lymph. Second, heparin should be avoided as an anticoagulant when studying the biology or composition of mesenteric lymph because of its ability to cause increases in lymph lipase activity that increase the in vitro cytotoxicity of these lymph samples.

Activated platelets in heparinized shed blood: the "second hit" of acute lung injury in trauma/hemorrhagic shock models

The return of heparinized shed blood (SB) in trauma/hemorrhagic shock (T/HS) models remains controversial because of potential anti-inflammatory properties. Although ubiquitous as an anticoagulant, heparin is ineffective on cellular coagulation as an antithrombotic agent. Therefore, we hypothesized that returning heparinized SB would paradoxically enhance acute lung injury (ALI) after T/HS because of the infusion of activated platelets. Sprague-Dawley rats, anesthetized with pentobarbital, underwent laparotomy and hemorrhage-induced shock (MAP of 30 mmHg × 45 min). Animals were resuscitated with a combination of normal saline and returned SB. Shed blood was collected in either 80 U/kg of heparin, 800 U/kg of heparin, or citrate or diluted 1:8 with normal saline. An additional group of animals were pretreated with a platelet P2Y12 receptor antagonist (clopidogrel) before T/HS. Bronchoalveolar lavage, lung myeloperoxidase assays, pulmonary immunofluorescence, and blood smears were conducted. Bronchoalveolar lavage protein increased in animals resuscitated with heparinized SB (T/HS + 80 U/kg Hep 1.62 ± 0.29, T/HS + 800 U/kg Hep 1.30 ± 0.15 vs. T/SS 0.51 ± 0.16 and T/HS Citrate 0.7 ± 0.09) (P < 0.0001). Blood smears and platelet function assays revealed platelet aggregates and increased platelet activation. Animals pretreated with a platelet P2Y12 receptor antagonist were protected from postinjury ALI (P < 0.0001). Animals with return of SB had increased pulmonary polymorphonuclear leukocyte sequestration (P < 0.0001). Pulmonary immunofluorescence demonstrated microthrombi only in the T/HS group receiving heparinized SB (P < 0.0001). The return of heparinized SB functions as a "second hit" to enhance ALI, with activated platelets propagating microthrombi and pulmonary polymorphonuclear leukocyte recruitment.