Eric W. Dickson

Proinflammatory phenotype of perivascular adipocytes: influence of high-fat feeding.

Adipose tissue depots originate from distinct precursor cells, are functionally diverse, and modulate disease processes in a depot-specific manner. However, the functional properties of perivascular adipocytes, and their influence on disease of the blood vessel wall, remain to be determined. We show that human coronary perivascular adipocytes exhibit a reduced state of adipocytic differentiation as compared with adipocytes derived from subcutaneous and visceral (perirenal) adipose depots. Secretion of antiinflammatory adiponectin is markedly reduced, whereas that of proinflammatory cytokines interleukin-6, interleukin-8, and monocyte chemoattractant protein-1, is markedly increased in perivascular adipocytes. These depot-specific differences in adipocyte function are demonstrable in both freshly isolated adipose tissues and in vitro–differentiated adipocytes. Murine aortic arch perivascular adipose tissues likewise express lower levels of adipocyte-associated genes as compared with subcutaneous and visceral adipose tissues. Moreover, 2 weeks of high-fat feeding caused further reductions in adipocyte-associated gene expression, while upregulating proinflammatory gene expression, in perivascular adipose tissues. These changes were observed in the absence of macrophage recruitment to the perivascular adipose depot. We conclude that perivascular adipocytes exhibit reduced differentiation and a heightened proinflammatory state, properties that are intrinsic to the adipocytes residing in this depot. Dysfunction of perivascular adipose tissue induced by fat feeding suggests that this unique adipose depot is capable of linking metabolic signals to inflammation in the blood vessel wall.

Cardioprotection 'outside the box'--the evolving paradigm of remote preconditioning.

Abstract. Conventional ischemic preconditioning is the phenomenon whereby brief episodes of myocardial ischemia render the ischemic territory resistant to a subsequent, sustained ischemic insult. A growing body of evidence further indicates that brief ischemia applied in distant organs and tissues can also protect naïve, virgin myocardium from ischemic injury. In this review, we describe the initial observations that provided the impetus for the study of ‘remote preconditioning’, and summarize our current knowledge of the three facets of ‘preconditioning at a distance’ – intra-cardiac, inter-organ and transferred inter-cardiac preconditioning.

Ischemic preconditioning may be transferable via whole blood transfusion: preliminary evidence.

This research was designed to test the hypothesis that ischemic preconditioning can be transferred between animals via whole blood transfusion. Preconditioning at a distance refers to the reduction in myocardial infarct size seen when coronary artery occlusion is preceded by brief ischemic episodes of noncardiac tissue. Isolation of the trigger signal responsible for this effect may be useful in the diagnosis and treatment of acute coronary occlusive syndromes. Rabbits were paired by crossmatching blood samples prior to experimentation. Crossmatched pairs were placed into either preconditioned (P) or control sets. Rabbits in the preconditioned sets were further divided into donor (PD) and acceptor (PA) animals. PD animals underwent five episodes of circumflex and renal artery occlusion followed by reperfusion. Before and after each preconditioning episode, a whole blood exchange was performed between PD and PA animals. Alternatively, control rabbits underwent the same surgical procedures and time-sequenced transfusion without preconditioning. All animals then underwent prolonged circumflex occlusion (60 minutes) followed by reperfusion (30 minutes). The area of myocardium at risk (R) was determined by isotope-labeled microsphere injection. Infarct size (I) was determined by NBT staining. The percent infarct within the risk area (I/R) was then compared. The I/R was significantly lower in the PA (14.0% ± 12.2) and PD (14.3% ± 11.2) groups as compared with controls (61% ± 20.6). There was no significant difference between the tPA and TPD groups. In conclusion, the ischemic preconditioning effect can be transferred to nonpreconditioned animals via whole blood transfusion, suggesting a humoral mechanism for preconditioning at a distance.

Proenkephalin expression and enkephalin release are widely observed in non-neuronal tissues

Enkephalins are opioid peptides that are found at high levels in the brain and endocrine tissues. Studies have shown that enkephalins play an important role in behavior, pain, cardiac function, cellular growth, immunity, and ischemic tolerance. Our global hypothesis is that enkephalins are released from non-neuronal tissues in response to brief ischemia or exercise, and that this release contributes to cardioprotection. To identify tissues that could serve as potential sources of enkephalins, we used real-time PCR, Western blot analysis, ELISA, immunofluorescence microscopy, and ex vivo models of enkephalin release. We found widespread expression of preproenkephalin (pPENK) mRNA and production of the enkephalin precursor protein proenkephalin (PENK) in rat and mouse tissues, as well as in tissues and cells from humans and pigs. Immunofluorescence microscopy with anti-enkephalin antisera demonstrated immunoreactivity in rat tissues, including heart and skeletal muscle myocytes, intestinal and kidney epithelium, and intestinal smooth muscle cells. Finally, isolated tissue studies showed that heart, skeletal muscle, and intestine released enkephalins ex vivo. Together our studies indicate that multiple non-neuronal tissues produce PENK and release enkephalins. These data support the hypothesis that non-neuronal tissues could play a role in both local and systemic enkephalin-mediated effects.

Liquid ventilation with perfluorocarbons facilitates resumption of spontaneous circulation in a swine cardiac arrest model

BACKGROUND Induced external hypothermia during ventricular fibrillation (VF) improves resuscitation outcomes. Our objectives were twofold (1) to determine if very rapid hypothermia could be achieved by intrapulmonary administration of cold perfluorocarbons (PFC), thereby using the lungs as a vehicle for targeted cardiopulmonary hypothermia, and (2) to determine if this improved resuscitation success. METHODS Part 1: Nine female swine underwent static intrapulmonary instillation of cold perfluorocarbons (PFC) during electrically induced VF. Part 2: Thirty-three female swine in VF were immediately ventilated via total liquid ventilation (TLV) with pre-oxygenated cold PFC (-15 degrees C) or warm PFC (33 degrees C), while control swine received no ventilation during VF. All swine in both Parts 1 and 2 underwent VF arrest for 11 min, then defibrillation, ventilation and closed chest massage until resumption of spontaneous circulation (ROSC). The endpoint was continued spontaneous circulation for 1h without pharmacologic support. RESULTS Static intrapulmonary instillation of cold PFC achieved rapid cardiopulmonary hypothermia; pulmonary artery (PA) temperature of 33.5+/-0.2 degrees C was achieved by 10 min. Nine of 9 achieved ROSC. Hypothermia was achieved faster using TLV: at 6 min VF, cold TLV temperature was 32.9+/-0.4 degrees C vs. cold static instillation temperature 34.3+/-0.2 degrees C. Nine of 11 cold TLV swine achieved ROSC for 1h vs. 3 of 11 control swine (p=0.03). Warm PFC also appeared to be beneficial, with a trend toward greater achievement of ROSC than control (ROSC; warm PFC 8 of 11 vs. control 3 of 11, p=0.09). CONCLUSION Targeted cardiopulmonary intra-arrest moderate hypothermia was achieved rapidly by static intrapulmonary administration of cold PFC and more rapidly by total liquid ventilation with cold PFC; resumption of spontaneous circulation was facilitated. Warm PFC showed a trend toward facilitating ROSC.

Diazepam Inhibits Organophosphate‐induced Central Respiratory Depression

OBJECTIVES Current evidence suggests that mortality from acute organophosphate (OP) poisoning is partially mediated through central nervous system (CNS) respiratory center depression (CRD). However, the exact mechanism of OP-induced CRD is unknown. In these studies, the authors investigated the hypothesis that OP-induced CRD is the result of overstimulation of CNS respiratory centers. METHODS Wistar rats received prophylaxis with either normal saline (controls), atropine, the peripherally acting anticholinergics glycopyrrolate (GLYC), ipratropium bromide (IB), or the CNS respiratory center attenuator diazepam. To determine if a dual CNS/peripheral cholinergic mechanism is responsible for animal death, two additional groups received combination treatment with diazepam plus either IB or GLYC. All treatments were completed 5 minutes before OP with subcutaneous dichlorvos. Differences in 10-minute and 24-hour mortality were assessed by the Fisher exact test. RESULTS Dichlorvos poisoning resulted in profound fasciculations without obvious seizure in all cohorts. In controls and animals treated with peripherally acting anticholinergics, fasciculations were followed by sedation and respiratory arrest (0% 10-minute survival in all cohorts). In contrast, pretreatment with either atropine or diazepam significantly improved 10-minute survival (100% and 44%, respectively). Although GLYC or IB afforded no protection when given alone, when delivered in conjunction with diazepam, the combination significantly improved survival (both groups 88% at 24 hours), suggesting a dual CNS/pulmonary muscarinic mechanism of lethality. CONCLUSIONS The central respiratory depressant diazepam paradoxically attenuates organophosphate-induced respiratory depression, and when combined with peripherally acting anticholinergic agents, reduces mortality in a rat model of severe acute OP poisoning.

Partial Liquid Ventilation with Perfluorocarbon in the Treatment of Rats with Lethal Pneumococcal Pneumonia

Background Partial liquid ventilation with perfluorocarbon is a new therapeutic strategy to treat various lung disorders. The current study was undertaken to determine the efficacy of partial liquid ventilation with a perfluorocarbon (FC‐77) in the treatment of pneumococcal pneumonia in rats. Methods Male Wistar rats (weight, 275–300 g; n, 75) were infected via direct intratracheal inoculation with ca 109 colony‐forming units of viable Streptococcus pneumoniae, serotype 3, and 24 h after infection were placed into one of five groups, each containing 15 rats. The groups were (1) no treatment, (2) one intramuscular injection of penicillin G benzathine (200,000 U), (3) partial liquid ventilation with FC‐77, (4) partial liquid ventilation with FC‐77 and a single intramuscular dose of penicillin G benzathine (200,000 U), and (5) gas ventilation. Animals were observed every 24 h for survival. Results All untreated or gas‐ventilated animals or animals that received only partial liquid ventilation were dead by 7 days. Those receiving only partial liquid ventilation survived longer than untreated controls, but ultimately all succumbed by day 7. Survival was 40% for penicillin‐treated rats compared with controls (P < 0.05) and 80% for animals treated with both partial liquid ventilation and penicillin versus antibiotic alone (P < 0.05). Conclusions These observations suggest that partial liquid ventilation with perfluorocarbon in combination with antibiotic administration may be an effective therapeutic modality in pneumococcal pneumonia.

Liquid ventilation with perflubron in the treatment of rats with pneumococcal pneumonia.

Objective To determine the efficacy of liquid ventilation using a medical-grade perfluorocarbon (perflubron) combined with parenteral or intratracheal antibiotics in a rat model of pneumonia. Design Prospective, laboratory investigation. Setting Experimental laboratory in a university medical center. Subjects Wistar rats (n = 112). Interventions One day after intratracheal inoculation with Streptococcus pneumoniae, rats received one of five experimental treatments or no treatment (control): modified liquid ventilation (MLV), intramuscular ampicillin, MLV plus intramuscular ampicillin, MLV with intratracheal ampicillin, or MLV plus ampicillin PulmoSpheres. Measurements and Main Results Animals receiving MLV plus intramuscular ampicillin, MLV with intratracheal ampicillin, or MLV plus ampicillin PulmoSpheres had significantly improved 10-day survival rates (85%, 72%, and 72%, respectively) compared with all other groups (0% to 25%). Conclusions MLV in combination with either intramuscular, intratracheal, or PulmoSpheres ampicillin improved survival as compared with MLV alone or the same dose of antibiotics delivered intramuscularly.

Diphenhydramine as a protective agent in a rat model of acute, lethal organophosphate poisoning

OBJECTIVE To evaluate the effects of diphenhydramine chloride (DPH) on mortality in a rat model of acute, severe organophosphate poisoning (OP). METHODS Wistar rats (n = 40) were randomized to pretreatment with either normal saline (controls), 5 mg/kg atropine, 3 mg/kg DPH, 15 mg/kg DPH, or 30 mg/kg DPH given as a single intramuscular injection 5 minutes prior to a subcutaneous injection of 25 mg/kg dichlorvos (n = 8 per group). The primary endpoint was 10-minute survival. Survival at 24 hours was a secondary endpoint. Comparison of survival rates between groups was carried out by ANOVA and the Student-Newman-Keuls test. RESULTS Dichlorvos exposure resulted in profound fasciculations within 2 minutes of injection in all cohorts. In controls, fasciculations were followed by respiratory arrest within 10 minutes (0% survival). The rats receiving atropine pre-treatment exhibited similar fasciculations (nicotinic effects) without subsequent respiratory arrest, resulting in a significant improvement in survival (88%, p < 0.001). The DPH-treated rats exhibited a significant dose-dependent reduction in mortality, with the 3 mg/kg, 15 mg/kg, and 30 mg/kg groups demonstrating 0%, 25%, and 100% survival, respectively. There was no additional mortality between 10 minutes and 24 hours in any group. There was no significant difference in survival between the high-dose DPH and the atropine groups. CONCLUSIONS Diphenhydramine chloride significantly reduced mortality in rats with acute, severe dichlorvos exposure.

Low level bacterial endotoxin activates two distinct signaling pathways in human peripheral blood mononuclear cells

BackgroundBacterial endotoxin, long recognized as a potent pro-inflammatory mediator in acute infectious processes, has more recently been identified as a risk factor for atherosclerosis and other cardiovascular diseases. When endotoxin enters the bloodstream, one of the first cells activated is the circulating monocyte, which exhibits a wide range of pro-inflammatory responses.MethodsWe studied the effect of low doses of E. coli LPS on IL-8 release and superoxide formation by freshly isolated human peripheral blood mononuclear cells (PBMC).ResultsIL-8 release was consistently detectable at 10 pg/ml of endotoxin, reaching a maximum at 1 ng/ml, and was exclusively produced by monocytes; the lymphocytes neither produced IL-8, nor affected monocyte IL-8 release. Superoxide production was detectable at 30 pg/ml of endotoxin, reaching a maximum at 3 ng/ml. Peak respiratory burst activity was seen at 15-20 min, and superoxide levels returned to baseline by 1 h. IL-8 release was dependent on both membrane-associated CD14 (mCD14) and Toll-like receptor 4 (TLR4. Superoxide production was dependent on the presence of LBP, but was not significantly affected by a blocking antibody to TLR4. Moreover, treatment with lovastatin inhibited LPS-dependent IL-8 release and superoxide production.ConclusionsThese findings suggest that IL-8 release and the respiratory burst are regulated by distinct endotoxin-dependent signaling pathways in PBMC in low level of endotoxin exposure. Selectively modulating these pathways could lead to new approaches to treat chronic inflammatory diseases, such as atherosclerosis, while preserving the capacity of monocytes to respond to acute bacterial infections.