Endothelin-1 induces vasoconstriction and nitric oxide release via endothelin ET(B) receptors in isolated perfused rat liver

Selective gene expression profiling contributes to a better understanding of the molecular pathways underlying the histological changes observed after RHMVL

Background

In previous studies, five vasoactive drugs were investigated for their effect on the recovery process after extended liver resection without observing relevant improvements. We hypothesized that an analysis of gene expression could help to identify potentially druggable pathways and could support the selection of promising drug candidates.

Methods

Liver samples obtained from rats after combined 70% partial hepatectomy and right median hepatic vein ligation (n = 6/group) sacrificed at 0 h, 24 h, 48 h, and 7days were selected for this study. Liver samples were collected from differentially perfused regions of the median lobe (obstruction-zone, border-zone, normal-zone). Gene expression profiling of marker genes regulating hepatic hemodynamics, vascular remodeling, and liver regeneration was performed with microfluidic chips. We used 3 technical replicates from each sample. Raw data were normalized using LEMming and differentially expressed genes were identified using LIMMA.

Results

The strongest differences were found in obstruction-zone at 24 h and 48 h postoperatively compared to all other groups. mRNA expression of marker genes from hepatic hemodynamics pathways (iNOS,Ptgs2,Edn1) was most upregulated.

Conclusion

These upregulated genes suggest a strong vasoconstrictive effect promoting arterial hypoperfusion in the obstruction-zone. Reducing iNOS expression using selective iNOS inhibitors seems to be a promising approach to promote vasodilation and liver regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01364-z.

Rho-Proteins and Downstream Pathways as Potential Targets in Sepsis and Septic Shock: What Have We Learned from Basic Research

Sepsis and septic shock are associated with acute and sustained impairment in the function of the cardiovascular system, kidneys, lungs, liver, and brain, among others. Despite the significant advances in prevention and treatment, sepsis and septic shock sepsis remain global health problems with elevated mortality rates. Rho proteins can interact with a considerable number of targets, directly affecting cellular contractility, actin filament assembly and growing, cell motility and migration, cytoskeleton rearrangement, and actin polymerization, physiological functions that are intensively impaired during inflammatory conditions, such as the one that occurs in sepsis. In the last few decades, Rho proteins and their downstream pathways have been investigated in sepsis-associated experimental models. The most frequently used experimental design included the exposure to bacterial lipopolysaccharide (LPS), in both in vitro and in vivo approaches, but experiments using the cecal ligation and puncture (CLP) model of sepsis have also been performed. The findings described in this review indicate that Rho proteins, mainly RhoA and Rac1, are associated with the development of crucial sepsis-associated dysfunction in different systems and cells, including the endothelium, vessels, and heart. Notably, the data found in the literature suggest that either the inhibition or activation of Rho proteins and associated pathways might be desirable in sepsis and septic shock, accordingly with the cellular system evaluated. This review included the main findings, relevance, and limitations of the current knowledge connecting Rho proteins and sepsis-associated experimental models.

Tezosentan normalizes hepatomesenteric perfusion in a porcine model of cardiac tamponade

BACKGROUND

To investigate endothelin-1 (ET-1)-dependent hepatic and mesenteric vasoconstriction, and oxygen and lactate fluxes in an acute, fixed low cardiac output (CO) state.

METHODS

Sixteen anesthetized, mechanically ventilated pigs were studied. Cardiac tamponade was established to reduce portal venous blood flow (Q(PV)) to 2/3 of the baseline value. CO, hepatic artery blood flow (Q(HA)), Q(PV), hepatic laser-Doppler flow (LDF), hepatic venous and portal pressure, and hepatic and mesenteric oxygen and lactate fluxes were measured. Hepatic arterial (R(HA)), portal (R(HP)) and mesenteric (R(mes)) vascular resistances were calculated. The combined ET(A)-ET(B) receptor antagonist tezosentan (RO 61-0612) or normal saline vehicle was infused in the low CO state. Measurements were made at baseline, after 30, 60, 90 min of tamponade, and 30, 60, 90 min following the infusion of tesozentan at 1 mg/kg/h.

RESULTS

Tamponade decreased CO, Q(PV), Q(HA), LDF, hepatic and mesenteric oxygen delivery, while hepatic and mesenteric oxygen extraction and lactate release increased. R(HA), R(HP) and R(mes) all increased. Ninety minutes after tesozentan, Q(PV), LDF and hepatic and mesenteric oxygen delivery and extraction increased approaching baseline values, but no effect was seen on CO or Q(HA). Hepatic and mesenteric handling of lactate converted to extraction. R(HA), R(HP) and R(mes) returned to baseline values. No changes were observed in these variables among control animals not receiving tesozentan.

CONCLUSION

In a porcine model of acute splanchnic hypoperfusion, unselective ET-1 blockade restored hepatomesenteric perfusion and reversed lactate metabolism. These observations might be relevant when considering liver protection in low CO states.

Liver perfusion in sepsis, septic shock, and multiorgan failure

Sepsis causes significant alterations in the hepatic macro- and microcirculation. Diverging views exist on global hepatic blood flow during experimental sepsis because of the large variety in animal and sepsis models. Fluid-resuscitated clinical sepsis is characterized by ongoing liver ischemia due to a defective oxygen extraction despite enhanced perfusion. The effects of vasoactive agents on the hepatosplanchnic circulation are variable, mostly anecdotal, and depend on baseline perfusion, time of drug administration, and use of concomitant medication. Microvascular blood flow disturbances are thought to play a pivotal role in the development of sepsis-induced multiorgan failure. Redistribution of intrahepatic blood flow in concert with a complex interplay between sinusoidal endothelial cells, liver macrophages, and passing leukocytes lead to a decreased perfusion and blood flow velocity in the liver sinusoids. Activation and dysfunction of the endothelial cell barrier with subsequent invasion of neutrophils and formation of microthrombi further enhance liver tissue ischemia and damage. Substances that regulate (micro)vascular tone, such as nitric oxide, endothelin-1, and carbon monoxide, are highly active during sepsis. Possible interactions between these mediators are not well understood, and their therapeutic manipulation produces equivocal or disappointing results. Whether and how standard resuscitation therapy influences the hepatic microvascular response to sepsis is unknown. Indirect evidence supports the concept that improving the microcirculation may prevent or ameliorate sepsis-induced organ failure.

Role of nitric oxide in the expression of hepatic vascular stress genes in response to sepsis

This study examined the role of nitric oxide (NO) on the expression of the hepatic vasoregulatory gene during polymicrobial sepsis. Aminoguanidine (AG, 100 mg/kg) or Nomega-nitro-L-arginine methyl ester (L-NAME, 100 mg/kg) was injected intraperitoneally at 0, 3, 6, 10, and 20 h after a cecal ligation and puncture (CLP). The heart rate increased 24 h after the CLP, and this increase was attenuated by L-NAME and further attenuated by AG. The mean arterial pressure in the CLP animals did not change significantly 24 h after the onset of sepsis but was increased after the L-NAME injection. Sepsis increased the serum aminotransferase levels, which were attenuated by AG but augmented by L-NAME. CLP increased the mRNA level of the ET-1 and ETB receptors in the liver. This increase was prevented by AG but augmented by L-NAME. The level of iNOS and HO-1 mRNA expression were increased by CLP, which was prevented by both AG and L-NAME. The level of TNF-alpha and COX-2 mRNA expression increased after CLP, and was attenuated by AG. These results show that iNOS and eNOS are regulated differently in sepsis. While eNOS appears to have a protective role in liver microcirculation, the strong upregulation of iNOS might contribute to a microvascular dysfunction and hepatic injury.

Sensitivity to endothelin-1 is decreased in isolated livers of endothelial constitutive nitric oxide synthase knockout mice

Background

Hepatic sinusoidal resistance is regulated by vasoactive factors including endothelin-1 (ET-1) and nitric oxide (NO). In the absence of NO, vasoconstrictor response to endothelin is expected to predominate. Therefore, we hypothesized sensitivity to endothelin to be increased in mice lacking the endothelial cell NO synthase gene. Response of vascular resistance to endothelin was assessed in the in situ perfused liver of endothelial constitutive nitric oxide synthase (ecNOS) knockout and wild type mice. Livers were also harvested for RNA and protein isolation for quantitative PCR and Western blotting, respectively. The expression of endothelin receptors, isoenzymes of NO synthase, heme-oxygenase and adrenomedullin was quantified.

Results

Endothelin increased hepatic vascular resistance in a dose-dependent manner in both strains; however, this increase was significantly less in ecNOS knockout mice at physiologic concentrations. Expression of heme-oxygenases and adrenomedullin was similar in both groups, whereas inducible nitric oxide synthase (iNOS) protein was not detectable in either strain. mRNA levels of pre-pro-endothelin-1 and ET_B receptor were comparable in both strains, while mRNA for ET_A receptor was decreased in ecNOS knockouts.

Conclusion

Livers of ecNOS knockout mice have a decreased sensitivity to endothelin at physiologic concentrations; this is associated with a decreased expression of ET_A receptors, but not with other factors, such as iNOS, ET_B receptors, adrenomedullin or heme-oxygenase. Further studies targeting adaptive changes in ET_A receptor distribution and/or intracellular signaling downstream of the receptor are indicated.

Different effects of optical isomers of the 5-HT1A receptor antagonist pyrapyridolol against postischemic guinea-pig myocardial dysfunction and apoptosis through the mitochondrial permeability transition pore

The recovery (%) of the left ventricular developed pressure by (S)-(-)-pyrapyridolol (5 x 10(-8) M) (90.7%), an optical isomer of a new 5-HT1A receptor antagonist, was greater than that by (R)-(+)-pyrapyridolol (66.2%, control: 34.4%) against ischemia-reperfusion injury in perfused Langendorff guinea-pig hearts. In the perfused mitochondrial preparation, (S)-(-)-pyrapyridolol inhibited the mitochondrial Ca2+ (Cam) elevation that was brought about by the change of Ca2+ content or pH of perfusate, similar to findings with cyclosporin A, well known to be an inhibitor of the mitochondrial permeability transition pore (MPTP). The mitochondrial K(ATP) channel opener, diazoxide, also inhibited the Cam elevation, but the mitochondrial K(ATP) channel antagonist, 5-hydroxydecanoic acid, attenuated it. There were significantly fewer numbers of TUNEL-positive cells in these (S)-(-)-pyrapyridolol-treated hearts than the control or (R)-(+)-pyrapyridolol, with decreases of the caspase-3 activity. Therefore, these results suggest that (S)-(-)-pyrapyridolol likely inhibits the opening of the MPTP by preventing the Cam overload induced apoptosis related to endogenous 5-HT accumulation in ischemia-reperfusion hearts.

Oxygenated and reoxygenated tumors show better local control in radiation therapy for cervical cancer

The presence of hypoxic cells is one of the major factors affecting resistance against radiation therapy. In the clinical setting, little information exists as to the relationship between intratumoral oxygen partial pressure (pO(2)) and outcome. This study involved 30 consecutive patients with cervical cancer, who were treated with a combination of external and high-dose rate intracavitary irradiation. The pO(2) was measured before radiation therapy and at 9 Gy, using a needle-type polarographic oxygen electrode. The mean intratumoral pO(2) before radiation therapy was 17.3 +/- 10.8 mm Hg. The 3-year local control rates of patients with pO(2)< or = 20 mm Hg and pO(2) > 20 mm Hg before radiation therapy were 52% and 100%, respectively, representing a significant difference (P= 0.035). At 9 Gy, mean intratumoral pO(2) was 23.6 +/- 9.1 mm Hg, a significant increase compared to the value before radiation therapy (P= 0.006). The 3-year local control rates of tumors with pO(2)< or = 20 mm Hg and pO(2) > 20 mm Hg at 9 Gy were 35% and 93%, respectively, representing a significant difference (P= 0.001). The significantly better local control for oxygenated tumors at 9 Gy as well as before radiation therapy indicated that the oxygen effect and reoxygenation by radiation played an important role in local control in radiation therapy for cervical cancer.

Protective effects of sarpogrelate, a 5-HT2A antagonist, against postischemic myocardial dysfunction in guinea-pig hearts

The protective effects of sarpogrelate (SG), a 5-HT2A antagonist, were investigated in perfused guinea-pig Langendorff hearts subjected to ischemia and reperfusion. Changes in cellular levels of high phosphorous energy, NO and Ca2+ in the heart together with simultaneous recordings of left ventricular developed pressure (LVDP) were monitored using an nitric oxide (NO) electrode, fluorometry and 31P-NMR. The recovery of LVDP from ischemia by reperfusion was 30.1% in the control, while the treatment with SG (5 x 10(-7) M) in pre- and post-ischemia hearts produced a gradual increase to 73.1 and 53.6%, respectively. At the final stage of ischemia, the intracellular concentration of Ca2+ ([Ca2+]i) and release of NO increased with no twitching and remained at a high steady level. The addition of SG increased the transient NO signal (TNO) level at the end of ischemia compared with the control, but [Ca2+]i during ischemia decreased. Meanwhile, mitochondrial Ca2+ uptake on acidification or Ca2+ content changes of the perfusate was suppressed by pre-treatment with SG or the KATP channel opener diazoxide, but not the KATP channel blocker 5-HD. The myocardial NO elevated with 5-HT in normal Langendorff hearts was suppressed by the treatment with SG. Therefore, the existence of the 5HT2A receptor in a Langendorff heart was anticipated. By in vitro EPR, SG was found to directly quench the hydroxy radical. Thus, these findings suggested that the 5-HT2A receptor induced in ischemia-reperfusion plays an important role in the mitochondrial KATP channel of hearts in close relation with NO and active oxygen radicals.

Effects of endothelin-1 on hepatic stellate cell proliferation, collagen synthesis and secretion, intracellular free calcium concentration

AIM: To explore the effects of endothelin-1 (ET-1) on hepatic stellate cells (HSCs) DNA uptake, DNA synthesis, collagen synthesis and secretion, inward whole-cell calcium concentration ([Ca²⁺]_i) as well as the blocking effect of verapamil on ET-1-stimulated release of inward calcium (Ca²⁺) of HSC in vitro.

METHODS: Rat hepatic stellate cells (HSCs) were isolated and cultivated. ³H-TdR and ³H-proline incorporation used for testing DNA uptake and synthesis, collagen synthesis and secretion of HSCs cultured in vitro; Fluorescent calcium indicator Fura-2/AM was used to measure [Ca²⁺]_i inward HSCs.

RESULTS: ET-1 at the concentration of 5 × 10^-8 mol/L, caused significant increase both in HSC DNA synthesis (2247 ± 344 cpm, P < 0.05) and DNA uptake (P < 0.05) when compared with the control group. ET-1 could also increase collagen synthesis (P < 0.05 vs control group) and collagen secretion (P < 0.05 vs control group). Besides, inward HSC [Ca²⁺] _i reached a peak concentration (422 ± 98 mol/L, P < 0.001) at 2 min and then went down slowly to165 ± 51 mol/L (P < 0.01) at 25 min from resting state (39 ± 4 mol/L) after treated with ET-1. Verapamil (5 mol/L) blocked ET-1-activated [Ca²⁺]_i inward HSCs compared with control group (P < 0.05). Fura-2/AM loaded HSC was suspended in no Ca²⁺ buffer containing 1 mol/L EGTA, 5 min later, 10^-8 mol/L of ET-1 was added, [Ca²⁺]_i inward HSCs rose from resting state to peak 399 ± 123 mol/L, then began to come down by the time of 20 min. It could also raise [Ca²⁺]_i inward HSCs even without Ca²⁺ in extracellular fluid, and had a remarkable dose-effect relationship (P < 0.05). Meanwhile, verapamil could restrain the action of ET-1 (P < 0.05).

CONCLUSION: Actions of ET-1 on collagen metabolism of HSCs may depend on the transportation of inward whole-cell calcium.

Sphingosine 1-phosphate enhances portal pressure in isolated perfused liver via S1P2 with Rho activation

Although structural changes are most important to determine vascular resistance in portal hypertension, vasoactive mediators also contribute to its regulation. Hepatic stellate cells (HSCs) are assumed to play a role in modulating intrahepatic vascular resistance based on their residence in the space of Disse and capacity to contract. Because sphingosine 1-phosphate (S1P) has been shown to stimulate HSC contractility, we wondered if S1P could regulate portal pressure. S1P at 0.5-5 microM increased portal pressure in isolated rat perfused liver. This effect was abrogated in the presence of a binding antagonist for S1P2, JTE-013. Perfusion of isolated rat liver with 5 microM S1P increased Rho activity in the liver, and co-perfusion with JTE-013 cancelled S1P-induced Rho activation. Because S1P is present in human plasma at approximately 0.2 microM, S1P might readily regulate portal vascular tone in physiological and pathological status. The antagonist for S1P2 merits consideration for treatment of portal hypertension.

Role of kupffer cells in the vasoregulatory gene expression during hepatic ischemia/reperfusion

Hepatic microcirculatory failure is a major component of reperfusion injury in the liver. Recent data provided some evidence that endothelium-derived vasoconstrictors and vasodilators may be functionally important to the control of the total hepatic blood flow under these conditions of circulatory failure. Since Kupffer cells provide signals that regulate the hepatic response in ischemia/reperfusion (I/R), the aim of this study was to investigate the role of Kupffer cells in the I/R-induced imbalance of vasoregulatory gene expression. Rats were subjected to 60 min hepatic ischemia, followed by 5 h of reperfusion. The Kupffer cells were inactivated by gadolinium chloride (GdCl3, 7.5 mg/kg body weight, intravenously) 1 day prior to ischemia. Liver samples were obtained 5 hrs after reperfusion for RT-PCR analysis of the mRNA for genes of interest: endothelin-1 (ET-1), its receptors ETA and ETB, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and heme oxygenase-1 (HO-1). ET-1 mRNA expression was increased by I/R. mRNA levels for ETA receptors showed no change, whereas ETB receptor transcripts increased in the I/R group. The increases in ET-1 and ETB mRNA were not prevented by the GdCl3 pretreatment. The mRNA levels for iNOS and eNOS significantly increased within the I/R group with no significant difference between the I/R group and the GdCl3-treated I/R group. HO-1 mRNA expression significantly increased in the I/R group and this increase was attenuated by GdCl3. In conclusion, we have demonstrated that an imbalance in hepatic vasoregulatory gene expression occurs during I/R. Our findings suggest that the activation of Kupffer cells is not required for I/R-induced hepatic microvascular dysfunction.

Correlations between in vivo tumor weight, oxygen pressure, 31P NMR spectroscopy, hypoxic microenvironment marking by beta-D-iodinated azomycin galactopyranoside (beta-D-IAZGP), and radiation sensitivity

PURPOSE

The purpose of this study is to evaluate the amount of hypoxic fraction in a rodent tumor by means of polarographic oxygen electrode, phosphorus-31 magnetic resonance spectroscopy (31P-MRS), and a newly synthesized hypoxic marker, beta-D-iodinated azomycin galactopyranoside (beta-D-IAZGP). We also investigated the radiosensitivity for tumors of different weights.

METHODS AND MATERIALS

Murine mammary carcinoma cells, FM3A, were subcutaneously implanted into the back of 5-week-old male C3H/He mice. beta-D-IAZGP radiolabeled with 123I or with 125I was injected intravenously into tumor-bearing mice, and marker distribution was measured by nuclear medicine procedures. Radiosensitivity of the tumor was measured by the in vivo/in vitro clonogenic assay. Tumor oxygenation status was also measured directly by polarographic oxygen electrodes and indirectly estimated from 31P-MR spectra.

RESULTS

Higher accumulation of 123I-beta-D-IAZGP was observed in the tumors than in normal tissues at 24 h after administration. As to biodistribution of 125I-beta-D-IAZGP, the tumor/blood ratio varied widely, but correlated significantly with tumor weight. Mean oxygen pressure (pO2) values and ratios of nucleoside triphosphate beta to inorganic phosphate (beta-ATP/Pi) and of phosphocreatine to inorganic phosphate (PCr/Pi) decreased significantly with the increase in tumor volume. As tumor volume increased, the surviving fraction of cells from tumors irradiated in vivo increased significantly.

CONCLUSIONS

The increase in tumor volume was significantly correlated with a reduction in mean pO2, a decrease in the ratios of beta-ATP/Pi or PCr/Pi, an increase in uptake of beta-D-IAZGP, and an increase in radioresistance. Because the uptake of beta-D-IAZGP can be measured noninvasively by nuclear medicine techniques, it could be clinically useful for monitoring hypoxia in human tumors.

Potentiated hepatic microcirculatory response to endothelin-1 during polymicrobial sepsis

We conducted this study to elucidate the role of endothelins (ET-1) in mediating the hepatic microcirculatory dysfunction observed in response to sepsis. Following 24 h of cecal ligation and puncture (CLP), we performed intravital microscopy both in vivo and on isolated perfused livers. Portal resistance increased in response to ET-1 in both sham and septic rats, with no significant difference between the two in either in vivo or in isolated livers. Sinusoidal volumetric flow (Qs) was evaluated using red blood cell velocity (V(RBC)) and sinusoidal diameter (Ds) to determine microvascular hemodynamic integrity. Qs decreased in response to ET-1 in livers from CLP rats compared with sham (P < 0.05, CLP vs. sham) in both in vivo and isolated livers. In vivo infusion of ET-1 resulted in greater constriction of sinusoids in the CLP group compared with sham (P < 0.05), resulting in higher sinusoidal resistance. Microvascular hyper-responsiveness was accompanied by hepatocellular injury in CLP rats, but not in sham rats. RT-PCR was performed to measure mRNA levels of ET-1, its receptors ET(A) and ET(B), inducible and constitutive nitric oxide (NO) synthase (iNOS and eNOS, respectively), and heme oxygenase 1 (HO-1). After CLP, both ET-1 and ET(B) mRNA increased, whereas ET(A) mRNA tended to decrease, although the change was not statistically significant. Livers from CLP rats showed no significant change in levels of eNOS mRNA, but showed a significant increase in iNOS expression (13.5-fold over sham). There was no change in the level of HO-1 mRNA between sham and CLP groups. Taken together, these results suggest that sepsis sensitizes the hepatic microcirculation to ET-1. More importantly, an impaired microcirculatory flow due to ET-1 in sepsis contributes to hepatic injury. Further, localized imbalances between endothelins and NO may mediate the altered microvascular response during sepsis.

Protective effects of antioxidative serotonin derivatives isolated from safflower against postischemic myocardial dysfunction

N-(p-Coumaroyl)serotonin (C) and N-feruroylserotonin (F) with antioxidative activity are present in safflower oil. The protective effects of C and F were investigated in perfused guinea-pig Langendorff hearts subjected to ischemia and reperfusion. Changes in cellular levels of high phosphorous energy, NO and Ca2+ in the heart together with simultaneous recordings of left ventricular developed pressure (LVDP) were monitored by an nitric oxide (NO) electrode, fluorometry and 31P-NMR. The rate of recovery of LVDP from ischemia by reperfusion was 30.8% in the control, while in the presence of C or F a gradual increase to 63.2 or 61.0% was observed. Changes of transient NO signals (TNO) released from heart tissue in one contraction (LVDP) were observed to be upside-down with respect to transient fura-2-Ca2+ signals (TCa) and transient O2 signals detected with a pO2 electrode. At the final stage of ischemia, the intracellular concentration of Ca2+ ([Ca2+]i) and the release of NO increased with no twitching and remained at a high steady level. The addition of C increased the NO level at the end of ischemia compared with the control, but [Ca2+]i during ischemia decreased. On reperfusion, the increased diastolic level of TCa and TNO returned rapidly to the control level with the recovery of LVDP. By in vitro EPR, C and F were found to directly quench the activity of active radicals. Therefore, it is concluded that the antioxidant effects of two derivatives isolated from safflower play an important role in ischemia-reperfusion hearts in close relation with NO.

Function of the endothelinB receptor in cardiovascular physiology and pathophysiology

One of the two receptors by which the potent vasoactive effects of endothelin (ET)-1 are mediated is the ET(B) receptor (ET(BR)), which is found in several tissues, but, more importantly from a cardiovascular point of view, on the endothelial cell. The endothelial cell also has the unique capability of releasing ET-1, as well as other factors, such as the endothelial-derived relaxing factors and prostacyclin, which counteract the myotropic effects of the peptide. The secretory and contractile responses to ET-1 rely on G-protein-coupled ET(BR)s, as well as ET(A)-G-protein-coupled receptor-like proteins. The mitogenic properties of ET-1 via ET(A) receptors (ET(AR)s) coupled to mitogen-activated protein kinases and tyrosine kinases on the vascular smooth muscle may occur in conjunction with the anti-apoptotic characteristics of the endothelial ET(BR)s. Interestingly, most of the relevant antagonists and agonists for both ET(AR)s and ET(BR)s have been developed by the pharmaceutical industry. This highlights the therapeutical potential of compounds that act on ET receptors. In normal as well as in physiopathological conditions, the ET(BR) plays an important role in the control of vascular tone, and must be taken into account when using ET receptor antagonists for the treatment of cardiovascular diseases. For the management of congestive heart failure, renal failure and primary pulmonary hypertension, the most recent literature supports the use of selective ET(AR) antagonists rather than mixed antagonists of ET(AR)s and ET(BR)s. Nonetheless, validation of this view will have to await the first clinical trials comparing the actions of ET(A) to mixed ET(A)/ET(B) receptor antagonists.

Endothelin 1 impairs oxygen delivery in livers from LPS-primed animals

Endothelin 1 (ET-1) is a potent vasoactive peptide that acts at sinusoidal and extrasinusoidal sites in the liver. Sensitivity to ET-1 increases in LPS-primed animals and is associated with impaired liver microcirculation in these animals. We hypothesized that LPS priming leads to an exacerbation in the impaired oxygen delivery in response to intraportal infusion of ET-1. Rats were studied 24 h after LPS injection (1 mg/kg, i.p.). Surface PO2 was determined using a recently developed technology of O2 mapping. The baseline portal pressure was higher in LPS-primed animals (P < 0.05), and increased to'similar magnitude as sham animals after a 10-min infusion of ET-1. The resultant portal pressure remained elevated in LPS compared to sham animals. There was no significant difference in baseline mean arterial pressure, and no significant systemic response to ET-1 in either group. In contrast to the macrohemodynamic, the decrease in tissue surface PO2 in response to ET-1 infusion was potentiated by LPS treatment (increased from baseline levels 33.8+/-9 to 46.8+/-8.3 in sham; 42.3+/-9.1 to 69+/-6.5 gray scale units in LPS; P < 0.01, sham vs. LPS) at end of infusion of ET-1 for 10 min. This indicates tissue hypoxia in response to ET-1, which is exacerbated in livers from LPS-primed animals compared to sham. Frequency distribution analysis showed a shift in mode from lower intensity (higher PO2) to areas with higher fluorescent intensity ranges (lower PO2), indicating areas with shut down in perfusion in LPS-treated animals. In the whole liver, ET-1 suppressed oxygen consumption, and this response was potentiated by LPS pretreatment. We propose that ET-1 impairs oxygen delivery in the liver during endotoxemia, resulting in areas of focal hypoxia. This response is possibly due to potentiated action of ET-1 at both sinusoidal and extrasinusoidal sites in the liver during endotoxemia.

Enhanced expression of endothelial nitric oxide synthase and caveolin-1 in human cirrhosis

BACKGROUND/AIMS

Nitric oxide is synthesized in diverse mammalian tissues by a family of calmodulin-dependent nitric oxide synthases (NOS). Caveolin, the principal structural protein in caveolae, interacts with endothelial NOS (eNOS) leading to enzyme inhibition by a reversible process modulated by Ca++ -calmodulin. The aim of the present study was to examine the localizations of eNOS and caveolin-1 at protein level in normal human liver tissue, and how the expressions are altered in cirrhotic liver.

METHODS

Fresh liver specimens were obtained from hepatic surgeries. Normal portions resected from cases of carcinoma metastasized to the liver were used as control specimens, and cirrhotic portions resected from cases of hepatocellular carcinoma with hepatitis C-related cirrhosis were used as cirrhotic specimens. Anti-eNOS and anticaveolin-1 antibodies were used for immunohistochemistry and Western blotting. Immunoelectron microscopy was conducted on ultra thin sections using immunoglobulin-gold combined with silver staining.

RESULTS

Immunohistochemistry revealed that both eNOS and caveolin-1 were sparsely expressed on hepatic sinusoidal lining in normal liver specimens, and these findings were confirmed by Western blot. Both immunohistochemistry and Western blotting demonstrated over-expression of eNOS and caveolin-1 in cirrhotic liver specimens. Morphometric analysis of immunogold particle labeling for eNOS and caveolin-1 was performed on immunoelectron micrographs. In normal liver tissue, hepatic stellate cells and sinusoidal endothelial cells (SEC) expressed low levels of caveolin-1, and SEC expressed a very low level of eNOS. In cirrhotic liver, both caveolin-1 and eNOS expressions were significantly increased by approximately four-fold on SEC compared to normal liver.

CONCLUSION

In cirrhotic human liver, marked increase of caveolin-1 in perisinusoidal cells may promote caveolin-eNOS binding and reduce the activity of eNOS despite an increased eNOS expression, leading to impaired NO production and increased hepatic microvascular tone.

Hipertensão portal esquistossomótica avaliação do fluxo sangüíneo portal antes e após tratamento cirúrgico

OBJETIVO: Avaliar o fluxo sangüíneo portal na esquistossomose hepato-esplênica e o efeito tardio do tratamento cirúrgico na hemodinâmica portal. MÉTODO: Foram estudados 64 pacientes por Doppler dúplex: grupo I (pacientes com hipertensão portal esquistossomótica); grupo II (pacientes submetidos a desconexão ázigo-portal com esplenectomia) e grupo III (pacientes submetidos derivação esplenorrenal distal). RESULTADOS: O fluxo da veia porta foi maior no grupo I (1954,46 ± 693,73ml/min) e foi menor no grupo III (639,55 ± 285,86ml/min), neste correlacionou-se com o tempo pós-operatório (r=-0,67, p=0,0005). O fluxo sangüíneo portal do grupo II (1097,18 ± 342,12ml/min) foi semelhante ao de indivíduos normais. As mesmas alterações foram verificadas com relação ao diâmetro da veia porta nos grupos I, II, e III (cm): 1,46 ± 0,23; 1,12 ± 0,22; 0,93 ± 0,20, respectivamente. CONCLUSÕES: Estes dados sugerem que: 1) Existe hiperfluxo portal na fisiopatologia da hipertensão portal esquistossomótica; 2) o tratamento cirúrgico interferiu na hemodinâmica portal, diminuindo o fluxo sangüíneo da veia porta; 3) Esta redução do fluxo sangüíneo portal correlacionou-se com o tempo de seguimento pós-operatório no grupo III mas não no grupo II.

Novel nitric oxide donor (FK409) ameliorates liver damage during extended liver resection with warm ischemia in dogs

BACKGROUND

Nitric oxide attenuates ischemia-reperfusion injury by maintaining organ circulation through its actions as a vasoregulator, an inhibitor of platelet aggregation, and an attenuator of leukocyte adhesion. Otherwise, the harmful effects of enhanced nitric oxide production induced by inducible nitric oxide synthase mediate ischemia-reperfusion injury. FK409 has been characterized as a spontaneous nitric oxide donor. The aim of this study was to evaluate the effects of FK409 on extended liver resection with ischemia using a canine model.

STUDY DESIGN

Adult mongrel dogs were subjected to 60 minutes of warm ischemia by partial inflow occlusion. After reperfusion the nonischemic lobes were resected and the remnant liver function was evaluated. The dogs were divided into two groups: the control group (n = 7) and the FK409 group (n = 6), which was given FK409 through the portal vein.

RESULTS

The hepatic tissue blood flow, serum liver enzymes levels, and serum endothelin-1 level after reperfusion were significantly better in the FK409 group than in the control group. Electron microscopy demonstrated that endothelial cells and Ito cells were well-preserved in the FK409 group. The 3-day survival rate was statistically better in the FK409 group (67%) than in the control group (14%).

CONCLUSIONS

FK409 appears to have protective effects during extended liver resection with ischemia.

Endotoxin treatment causes an upregulation of the endothelin system in the liver: amelioration of increased portal resistance by endothelin receptor antagonism

BACKGROUND

Mechanisms underlying hepatic microcirculatory failure during endotoxemia are incompletely understood. Because endothelin-1 (ET-1) has been implicated in endotoxin-induced liver injury, we investigated the hepatic ET-1 system in endotoxin-treated rats.

METHODS

Rats were treated with endotoxin (Escherichia coli lipopolysaccharide; 3 mg/kg, i.p.), and various determinations were made 24 h later.

RESULTS

Endotoxin treatment caused 11.2 +/- 1.6% weight loss, a decrease in mean arterial pressure (MAP; 96 +/- 5 mmHg vs 108 +/- 3 mmHg; P < 0.05) and an increase in portal pressure (11.6 +/- 1.3 mmHg vs 7.4 +/- 1 mmHg; P < 0.02). No significant changes in the serum levels of liver enzymes or hepatocellular necrosis were observed. Endotoxin caused increases in hepatic ET-1 (from 345 +/- 31 to 565 +/- 38 pg/g; P < 0.01), ET-1 receptor density (from 179 +/- 16 to 340 +/- 26 fmol/mg; P < 0.02), and mRNA expression of preproendothelin-1, and ET(A) and ET(B) receptors. While the serum nitric oxide (nitrite +/- nitrate) concentration was increased in endotoxin-treated rats, that of ET-1 remained unchanged. A mixed ET(A)/ET(B) receptor antagonist, TAK-044 (10 mg/kg, i.v.), reduced the weight loss from 11.2 +/- 1.6% to 5.9 +/- 2.9% (P < 0.05) and the portal pressure from 11.6 +/- 1.3 mmHg to 8.6 +/- 0.7 mmHg (P < 0.05) in endotoxin-treated rats. The mixed ET(A)/ET(B) receptor antagonist also caused an increase in serum ET-1 concentration, but did not affect serum nitric oxide and MAP in endotoxin-treated rats.

CONCLUSIONS

These results suggest that the upregulated hepatic ET-1 system is an important mechanism of increased portal resistance and related complications of endotoxemia.

Levels of circulating endothelin-1 and nitrates/nitrites in patients with virus-related hepatocellular carcinoma

A balance between endothelins (ET) and nitric oxide (NO) might interfere with liver haemodynamics and disease progression in various liver diseases. Increased levels of endothelin 1 (ET-1) and nitrites and nitrates (NOx, the end products of NO metabolism) have been reported in hepatocellular carcinoma (HCC), but the balance has not been studied. The purpose of this study was to assess the ratio of NOx to ET-1 in patients with virus-related hepatocellular carcinoma and to investigate its correlation with the extent of the disease. Eighteen patients with virus-related HCC (six Okuda stage I, six Okuda stage II and six Okuda stage III) were included in the study and were compared with 22 patients with viral cirrhosis (14 decompensated, eight compensated) and seven normal controls. ET-1 was measured with an ELISA assay and NOx with a modification of the Griess reaction. Patients with virus-related HCC had the highest levels of circulating ET-1 and NOx (13.24 +/- 0.82 pg/ml and 112.28 +/- 18.56 micromol/l) compared to compensated cirrhosis (9.47 +/- 0.50 pg/ml, P < 0.004 and 54.47 +/- 2.36 micromol/l, P < 0.01), decompensated cirrhosis (9.57 +/- 0.32 pg/ml, P < 0.001 and 90.20 +/- 11.23 micromol/l, NS) and normal controls (8.84 +/- 0.61 pg/ml, P < 0.001 and 51.17 +/- 6.18 micromol/l, P < 0.01). There was a significant increase of ET-1 and NOx at HCC stage III compared to HCC stages I and II, cirhotics and controls. HCC stage III patients also had a NOx/ET-1 ratio that was higher than HCC stages I and II patients, normal controls and patients with compensated cirrhosis. Virus-related HCC patients have high levels of circulating ET-1, compared to compensated or decompensated cirrhosis. Highest levels of ET-1 are produced in Okuda III tumours. NOx are also increased but only in Okuda stage III tumours. The NOx/ET-1 ratio is increased in virus-related HCC and DC. This increase may account for the known increase in tumour blood flow.

Endotoxin causes up-regulation of endothelin receptors in cultured hepatic stellate cells via nitric oxide-dependent and -independent mechanisms

Hepatic stellate cells (HSC) and their transformed phenotype found in the chronically injured liver play important roles in hepatic physiology and pathology. HSC produce and react to a potent contractile peptide endothelin-1 (ET-1) and also synthesize a vasorelaxant nitric oxide (NO) upon stimulation with endotoxin. However, whether endotoxin affects ET-1 system of HSC and if this is a mechanism of endotoxin-induced hepatic injury is not known. We characterized synthesis of ET-1 and NO and ET-1 receptors in cultured quiescent and transformed HSC subjected to endotoxin treatment. Endotoxin (1 - 1000 ng ml(-1)) stimulated synthesis of ET-1 and NO and up-regulated ET-1 receptors in both cell types. Inhibition of NO synthesis by N(G)-monomethyl-L-homoarginine strongly inhibited endotoxin-induced increase in ET-1 receptors in transformed HSC but produced small additional increase in quiescent HSC. Inhibition of soluble guanylyl cyclase by 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalin-1-one blocked the effect of endotoxin on ET-1 receptors in both cell types. Moreover, ET-1 receptors were increased in both cell types during earlier time points (1 - 4 h) of endotoxin treatment in the absence of the stimulation of NO synthesis. These results demonstrate that endotoxin up-regulates ET-1 receptors in HSC by NO-dependent and -independent mechanisms. Such effects of endotoxin can be of importance in acute endotoxemia and during chronic injury of the liver.

Functional significance of endothelin B receptors in mediating sinusoidal and extrasinusoidal effects of endothelins in the intact rat liver

Endothelins (ET) are important regulators of the hepatic microcirculation that act through different receptor subtypes. We investigated functional significance of ET(B) receptors in mediating microhemodynamic effects of ETs in normal and endotoxin (lipopolysaccharide [LPS])-primed rat liver. LPS priming (Escherichia coli O26:B6; 1 mg. kg(-1)) selectively increased ET(B) mRNA and led to a shift in available receptors to the ET(B) subtype. IRL 1620 (an ET(B) agonist) increased portal pressure in a dose-dependent manner, and the increase in ET(B) expression was associated with prolonged portal pressor response in isolated livers. However, lactate dehydrogenase (LDH) release was attenuated and sinusoidal blood flow was better maintained upon ET(B) stimulation in vivo. In isolated livers, portal constriction as well as release of LDH, were substantially increased in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS). In vivo microscopic assessment of sinusoidal perfusion during ET(B) stimulation revealed a disruption of the flow pattern including frequent reversal of the flow direction without significant sinusoid constriction. Sinusoidal flow decreased even further after discontinuation of IRL 1620. Both effects were mediated at extrasinusoidal sites that probably included postsinusoidal sites. However, after pretreatment with L-NAME, IRL 1620 evoked a significant sinusoidal constriction that colocalized with the body of the stellate cell. We propose that ET(B1)-induced NOS activity attenuates ET(B2) (and presumably ET(A))-mediated portal pressor response and stellate cell constriction. Transcriptional activation of the ET(B) gene may have a permissive effect on liver blood flow and protect against hepatocellular damage under pathophysiological conditions associated with endotoxemia.

Role of endothelin-1 and constitutive nitric oxide synthase in gastric mucosal resistance to indomethacin injury: effect of antiulcer agents

BACKGROUND

Endothelin-1 (ET-1) and nitric oxide, recognized key mediators implicated in the pathophysiology of gastric mucosal injury, are known to exert opposing effects on the inflammatory processes mediated by regulatory cytokines. In this study we investigated the mucosal expression of ET-1 and interleukin-4 (IL-4) and the activity of constitutive nitric oxide synthase (cNOS) during indomethacin-induced gastric mucosal injury and evaluated the effect of antiulcer agents, omeprazole and sucralfate, on this process.

METHODS

The experiments were conducted with groups of rats pretreated intragastrically with omeprazole (40 mg/kg), sucralfate (200 mg/kg), or vehicle, followed 30 min later by an intragastric dose of indomethacin (60 mg/kg). The animals were killed 2 h later, and their mucosal tissue subjected to macroscopic damage assessment, ET-1 and IL-4 expression assay, and the measurement of cNOS activity.

RESULTS

In the absence of antiulcer agents, indomethacin caused multiple hemorrhagic lesions and extensive epithelial cell apoptosis, accompanied by a 20.7% reduction in IL-4, a 3.1-fold increase in mucosal expression of ET-1, and a 4.2-fold decrease in cNOS. Pretreatment with a gastroprotective agent, sucralfate, produced a 59.7% reduction in the mucosal damage caused by indomethacin, a 41.2% decrease in epithelial cell apoptosis, and a 56.5% reduction in ET-1, whereas the expression of IL-4 increased by 29.3% and that of cNOS showed a 3.3-fold increase. In contrast, the pretreatment with a proton pump inhibitor, omeprazole, led to only a 10.5% reduction in the extent of mucosal damage caused by indomethacin and a 13% decrease in apoptosis, whereas the expression of cNOS increased by 68.7% and ET-1 by 12.2%, and the level of IL-4 remained essentially unchanged.

CONCLUSIONS

The results suggest that an increase in the vasoconstrictive ET-1 level combined with a decrease in regulatory cytokine, IL-4, and a loss of compensatory action by cNOS may be responsible for the gastric mucosal injury caused by indomethacin. Our findings also indicate the value of sucralfate in countering the untoward gastrointestinal side effects of nonsteroidal anti-inflammatory drug therapy.