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ABSTRACT: Hydrogen sulfide (H2S), affects vascular resistance; however, its effect on the hepatic microcirculation has not been investigated. Hepatic sinusoidal perfusion is dysregulated during sepsis contributing to liver injury. Therefore, we determined the contribution of endogenous H2S to hepatic microcirculatory dysfunction in endotoxemia. Portal infusion of H2S increased portal pressure in vivo (6.8 ± 0.2 mmHg before H2S vs. 8.6 ± 0.8 mmHg, P<0.05). Using intravital microscopy, we observed decreased sinusoidal diameter (6.2 ± 0.27 μm before H2S vs. 5.7 ± 0.3 μm after H2S, P<0.05) and increased sinusoidal heterogeneity during H2S infusion (P<.05) and net constriction. Since hepatic H2S is elevated during sepsis, we used the cystathionine γ lyase (CSE) inhibitor, dl-propargylglycine (PAG), to determine the contribution of H2S to the hypersensitization of the sinusoid to endothelin 1 (ET-1). PAG treatment significantly attenuated the sinusoidal sensitization to ET-1 in endotoxin treated animals. ET-1 infusion increased portal pressure to 175% of baseline in endotoxemic animals which was reduced to 143% following PAG (P<0.05). PAG abrogated the increase in sinusoidal constriction after ET-1 infusion in LPS-treated rats (30.9% reduction in LPS rats vs. 11.6% in PAG/LPS rats, P<0.05). Moreover, PAG treatment attenuated the increase in NADH fluorescence following ET-1 exposure during endotoxemia (61 grey scale units LPS vs. 21 units in PAG/LPS, P<0.05) suggesting an improvement in hepatic oxygen availability. This study is the first to demonstrate a vasoconstrictor action of H2S on the hepatic sinusoid and provides a possible mechanism for the protective effect of PAG treatment during sepsis.
AJP Gastrointestinal and Liver Physiology 03/2013; · 3.43 Impact Factor
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ABSTRACT: Despite being protective in many disease states, H2S contributes to organ injury in sepsis. Like the other gasotransmitters, nitric oxide (NO) and carbon monoxide (CO), H2S is a modulator of the microcirculation. Since microcirculatory dysfunction is a main cause of organ injury during sepsis, the present study was designed to test the effect of H2S on microvascular dysfunction in isolated, perfused livers. In most microcirculatory beds, endotoxin activates the endothelium resulting in hyporesponsiveness to catecholamines and a derangement in blood flow distribution. We demonstrate that H2S treatment attenuates the increase in portal pressure during infusion of the α1adrenergic agonist, phenylephrine (PE) (P<0.01). H2S almost completely negated the increase in portal pressure in livers isolated from endotoxemic rats. Treatment with an inhibitor of endogenous H2S, dl-propargylglycine (PAG), reversed LPS induced hyporesponsiveness to PE. Since hepatic microcirculatory dysfunction is associated with excessive sinusoidal vasoconstriction and not dilation, we investigated whether H2S affects endothelin 1 (ET-1) induced vasoconstriction in isolated livers. Contrary to PE treatment, H2S did not affect the increase in portal pressure during infusion of ET-1 nor did it attenuate the hypersensitization of the liver to ET-1 during endotoxemia. Hepatic resistance in control rats was increased by PAG treatment during ET-1 infusion, but this increase was not exacerbated during endotoxemia. We monitored hepatic O2 consumption to assess the effect of vascular changes on oxygen consumption following ET-1 treatment. Low dose ET-1 infusion caused an increase in hepatic O2 consumption, whereas low dose ET-1 infusion decreased O2 consumption in endotoxemic livers. Interestingly, while we observed no effect of PAG on the vascular response to ET-1 infusion during endotoxemia, PAG treatment did maintain O2, suggesting a more complex effect of H2S inhibition. In summary, the discrepancies between the hepatic response to PE and ET-1 suggest that H2S differentially contributes to microcirculatory dysfunction in the systemic and hepatic microcirculations. We propose that this is due to H2S exerting a differential vasoactive function on presinusoidal and sinusoidal sites within the liver. Moreover, our findings suggest that H2S may contribute to the progression of sepsis by contributing to microvascular failure.
Shock (Augusta, Ga.) 11/2012; · 2.87 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 10/2012; 38(4):335-6. · 2.87 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 01/2012; 37(1):1-3. · 2.87 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 11/2011; 36(5):433-4. · 2.87 Impact Factor
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ABSTRACT: Activated protein C (aPC) promotes fibrinolysis while inhibiting coagulation and inflammation. In septic patients, aPC levels are depleted, and aPC treatment has emerged as a therapeutic option. To better understand the mechanism(s) by which aPC improves survival in sepsis, we sought to determine the effect of aPC treatment on hepatic vasoactive gene and protein expression, leading to changes in hepatic vascular responsiveness in a septic animal model. Under anesthesia, rats underwent sham or cecal ligation and puncture followed by aPC treatment (1 mg/kg, twice daily, i.v.). Treatment with aPC significantly decreased hepatic endothelin 1 (ET-1)/ET A receptor mRNA and protein expression. To determine the effect of aPC on hepatic microvasculature, ET-1-induced changes in liver microcirculation were assessed by intravital microscopy. This approach demonstrated aPC significantly improved hepatic perfusion index in the animals that underwent cecal ligation and puncture in the absence of significant changes in portal venous pressure. Furthermore, although aPC did not affect ET-1-dependent sinusoidal vasoconstriction, aPC induced hepatoprotective effects via enhanced red blood cell velocity. Collectively, these data demonstrate aPC ameliorates ET-1-dependent changes in hepatic microcirculation and improves hepatic function in the setting of sepsis.
Shock (Augusta, Ga.) 08/2011; 36(4):361-9. · 2.87 Impact Factor
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ABSTRACT: The liver is likely exposed to high levels of hydrogen sulfide (H2S) from endogenous hepatic synthesis and exogenous sources from the gastrointestinal tract. Little is known about the consequence of H2S exposure on the liver or hepatic regulation of H2S levels. We hypothesized that the liver has a high capacity to metabolize H2S and that H2S oxidation is decreased during sepsis, a condition in which hepatic O2 is limited and H2S synthesis is increased. Using a nonrecirculating isolated and perfused liver system, we demonstrated rapid hepatic H2S metabolism up to an infusion concentration of 200' μM H2S. Hydrogen sulfide metabolism was associated with an increase in O2 consumption from a baseline 96.7 ± 7.6 μmol O2/min/kg to 109 ± 7.4 μmol O2/min/kg at an infusion concentration of 150 μM H2S (P < 0.001). Removal of O2 from the perfusate decreased H2S clearance from a maximal 97% to only 23%. Livers isolated from rats subjected to cecal ligation and puncture (CLP) did not differ significantly from control livers in their capacity to metabolize H2S, suggesting that H2S oxidation remains a priority during sepsis. To test whether H2S induces O2 consumption in vivo, intravital microscopy was utilized to monitor the oxygen content in the hepatic microenvironment. Infusion of H2S increased the NADH/NAD+ ratio (645 gray-scale-unit increase, P = 0.035) and decreased hepatic O2 availability visualized with Ru(Phen)3(2+) (439 gray-scale-unit increase, P = 0.040). We conclude that the liver has a high hepatic capacity for H2S metabolism. Moreover, H2S oxidation consumes available oxygen and may exacerbate the tissue hypoxia associated with sepsis.
Shock (Augusta, Ga.) 05/2011; 36(3):242-50. · 2.87 Impact Factor
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ABSTRACT: Hepatic fibrosis is characterized by excess type I collagen deposition and exacerbated inflammatory response. Naltrexone, an opioid receptor antagonist used for treating alcohol abuse, attenuates hepatocellular injury in fibrotic animal models, which can be accompanied by deleterious side effects. Additionally, opioid neurotransmission is upregulated in patients with inflammatory liver disease. Several derivatives of Naltrexone, Nalmefene (Nal) and JKB-119, exert immunomodulatory activity; however, unlike Nal, JKB-119 does not show significant opioid receptor antagonism. To delineate the potential hepatoprotective effects of these compounds, we investigated if JKB-119 and Nal could modulate activation of hepatic stellate cells (HSCs), primary effector cells that secrete type I collagen and inflammatory mediators during liver injury. Our results demonstrated that Nal or JKB-119 treatment decreased smooth muscle α-actin, a marker of HSC activation, mRNA and protein expression. Despite decreased collagen mRNA expression, both compounds increased intracellular collagen protein expression; however, inhibition of collagen secretion was observed. To address a possible mechanism for suppressed collagen secretion or retention of intracellular collagen, endoplasmic (ER) protein expression and matrix metalloproteinase (MMP) activity were examined. While no change in ER protein expression (Grp78, PDI, Hsp47) was observed, MMP13 mRNA expression was dramatically increased. In an acute LPS inflammatory injury animal model, JKB-119 treatment decreased liver injury (ALT), plasma TNFα and PMN liver infiltration. Overall, these results suggest that JKB-119 can directly inhibit HSC activation attributed to anti-inflammatory activity and may, therefore, attenuate inflammation associated with HSC activation and liver disease.
Biochemical pharmacology 02/2011; 81(8):996-1003. · 4.25 Impact Factor
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Machine Learning in Medical Imaging - Second International Workshop, MLMI 2011, Held in Conjunction with MICCAI 2011, Toronto, Canada, September 18, 2011. Proceedings; 01/2011
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Mark G Clemens
Shock (Augusta, Ga.) 09/2010; 34(3):215-6. · 2.87 Impact Factor
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ABSTRACT: IL-27 is a heterodimeric cytokine composed of p28 and Epstein Barr virus induced gene 3 (Ebi3) protein subunits. In the present study, we questioned whether murine gammaherpesvirus 68 (HV-68) could induce expression of Ebi3, p28, and IL-27 in this mouse model of an EBV-like infection. Cultured macrophages and dendritic cells exposed to HV-68 upregulated p28 mRNA expression and increased secretion of the p28 and IL-27 (p28+Ebi3) proteins. B220(+) and CD11b(+) cells also upregulated p28 mRNA expression following in vivo infection with this virus. Surprisingly, no significant increases in p28 or IL-27 protein production were observed in vivo during the acute or mononucleosis phases of the disease. The possibility that HV-68-induced upregulation of p28 mRNA expression primed cells for IL-27 secretion was suggested by the ability of a TLR4 agonist to augment cytokine production. When cultured macrophages and dendritic cells were exposed to virus plus a suboptimal dose of LPS, increased levels of p28 protein expression were observed. More importantly, when latently infected mice were challenged with a sublethal dose of LPS, augmented p28 and IL-27 protein production occurred. Using a model of sepsis, mice latently infected with HV-68 had exaggerated p28 protein production when compared to mice that were singularly infected or subjected to cecal ligation and puncture. Taken together, these studies define expression of HV-68 induced IL-27, and suggest that mice latently infected with this gammaherpesvirus will have exaggerated responses when confronted with other stimuli capable of inducing this member of the IL-12 family of cytokines.
Cytokine 08/2010; 51(2):184-94. · 3.02 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 04/2010; 33(4):341-3. · 2.87 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 03/2010; 33(3):227-8. · 2.87 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 01/2010; 33(1):3-4. · 2.87 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 01/2010; 33(1):1-2. · 2.87 Impact Factor
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ABSTRACT: Endothelin-1 (ET-1) plays a key role in the regulation of endothelial nitric oxide synthase (eNOS) activation in liver sinusoidal endothelial cells (LSECs). In the presence of endotoxin, an increase in caveolin-1 (Cav-1) expression impairs ET-1/eNOS signaling; however, the molecular mechanism is unknown. The objective of this study was to investigate the molecular mechanism of Cav-1 in the regulation of LPS suppression of ET-1-mediated eNOS activation in LSECs by examining the effect of caveolae disruption using methyl-beta-cyclodextrin (CD) and filipin. Treatment with 5 mM CD for 30 min increased eNOS activity (+255%, P < 0.05). A dose (0.25 microg/ml) of filipin for 30 min produced a similar effect (+111%, P < 0.05). CD induced the perinuclear localization of Cav-1 and eNOS and stimulated NO production in the same region. Readdition of 0.5 mM cholesterol to saturate CD reversed these effects. Both the combined treatment with CD and ET-1 (CD + ET-1) and with filipin and ET-1 stimulated eNOS activity; however, pretreatment with endotoxin (LPS) abrogated these effects. Following LPS pretreatment, CD + ET-1 failed to stimulate eNOS activity (+51%, P > 0.05), which contributed to the reduced levels of eNOS-Ser1177 phosphorylation and eNOS-Thr495 dephosphorylation, the LPS/CD-induced overexpression and translocation of Cav-1 in the perinuclear region, and the increased perinuclear colocalization of eNOS with Cav-1. These results supported the hypothesis that Cav-1 mediates the action of endotoxin in suppressing ET-1-mediated eNOS activation and demonstrated that the manipulation of caveolae produces significant effects on ET-1-mediated eNOS activity in LSECs.
AJP Gastrointestinal and Liver Physiology 11/2009; 297(5):G930-9. · 3.43 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 07/2009; 31(6):543-4. · 2.87 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 06/2009; 31(5):435-7. · 2.87 Impact Factor
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Mark G Clemens
Shock (Augusta, Ga.) 02/2009; 31(1):1-2. · 2.87 Impact Factor
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ABSTRACT: Sepsis remains a serious complication after trauma. Although hepatic microvascular dysfunction occurs during trauma and sepsis, the mechanism responsible is unclear. Since Kupffer cells can provide the signals that regulate the hepatic response in inflammation and contribute to multiple organ failure, this study investigated the role of Kupffer cells in the imbalance of the expression of vasoactive and inflammatory mediators during trauma and sepsis.
The Kupffer cells were inactivated by gadolinium chloride (GdCl(3), 7.5 mg/kg body weight, i.v.) 1 and 2 d before surgery. The animals then underwent femur fracture (FFx) followed 48 h later by cecal ligation and puncture (CLP). After 24 h, blood was obtained to determine the alanine aminotransferase (ALT) activity. Liver samples were also taken for RT-PCR analysis of the mRNA for genes of interest.
Serum ALT levels increased in FFx and CLP. This increase was potentiated by FFx + CLP and was attenuated by GdCl(3). The mRNA expression levels in the FFx showed no change in the ET(A), ET(B), iNOS, and HO-1, and showed a slight increase of 2.6-fold, 2.2-fold, and 2.8-fold for ET-1, eNOS, and TNF-alpha, respectively. The ET-1 mRNA expression level increased after CLP and FFx + CLP. The ET(A) mRNA level showed no change, whereas the ET(B) transcripts increased after CLP. This increase was potentiated after FFx + CLP, and was attenuated by GdCl(3). After CLP alone, iNOS, eNOS, and TNF-alpha mRNA expression levels were increased 20.3-fold, 5.8-fold, and 11.9-fold, respectively. This increase was potentiated after FFx + CLP, and was attenuated by GdCl(3). HO-1 mRNA expression significantly increased after FFx + CLP, and this increase was attenuated by GdCl(3).
Mild trauma alone causes little change in the expression of vasoactive mediators while sequential injury potentiates the imbalanced gene expression induced by sepsis. Kupffer cells might be essential for hepatic microvascular dysfunction after sequential stress.
Journal of Surgical Research 12/2008; 158(1):104-11. · 2.25 Impact Factor
