Right ventricular failure--insights provided by a new model of chronic pulmonary hypertension

Challenges in the development of chronic pulmonary hypertension models in large animals

Pulmonary hypertension (PH) results in significant morbidity and mortality. Chronic PH animal models may advance the study of PH's mechanisms, evolution, and therapy. In this report, we describe the challenges and successes in developing three models of chronic PH in large animals: two models (one canine and one swine) utilized repeated infusions of ceramic microspheres into the pulmonary vascular bed, and the third model employed a surgical aorto-pulmonary shunt. In the canine model, seven dogs underwent microsphere infusions that resulted in progressive elevation of pulmonary arterial pressure over a few months. In this model, pulmonary endoarterial tissue was obtained for histology. In the aorto-pulmonary shunt swine model, 17 pigs developed systemic level pulmonary pressures after 2-3 months. In this model, pulmonary endoarterial tissue was sequentially obtained to assess for changes in gene and microRNA expression. In the swine microsphere infusion model, three pigs developed only a modest chronic increase in pulmonary arterial pressure, despite repeated infusions of microspheres (up to 40 in one animal). The main purpose of this model was for vasodilator testing, which was performed successfully immediately after acute microsphere infusions. Chronic PH in large animal models can be successfully created; however, a model's characteristics need to match the investigational goals.

Characterization of a murine model of monocrotaline pyrrole-induced acute lung injury

Background

New animal models of chronic pulmonary hypertension in mice are needed. The injection of monocrotaline is an established model of pulmonary hypertension in rats. The aim of this study was to establish a murine model of pulmonary hypertension by injection of the active metabolite, monocrotaline pyrrole.

Methods

Survival studies, computed tomographic scanning, histology, bronchoalveolar lavage were performed, and arterial blood gases and hemodynamics were measured in animals which received an intravenous injection of different doses of monocrotaline pyrrole.

Results

Monocrotaline pyrrole induced pulmonary hypertension in Sprague Dawley rats. When injected into mice, monocrotaline pyrrole induced dose-dependant mortality in C57Bl6/N and BALB/c mice (dose range 6–15 mg/kg bodyweight). At a dose of 10 mg/kg bodyweight, mice developed a typical early-phase acute lung injury, characterized by lung edema, neutrophil influx, hypoxemia and reduced lung compliance. In the late phase, monocrotaline pyrrole injection resulted in limited lung fibrosis and no obvious pulmonary hypertension.

Conclusion

Monocrotaline and monocrotaline pyrrole pneumotoxicity substantially differs between the animal species.

3D anatomical variations of hepatic vasculature and bile duct for right lateral sector of liver with special reference to transplantation

To achieve a safer living related liver transplantation (LRLT) using the right lateral sector, anatomical variations of the portal vein, hepatic artery and bile duct for the right lateral sector and their three dimentional (3D) relationship were assessed by integrated 3D-CT images. 52 patients who underwent contrast enhanced multi-detector row CT (MD-CT) and MD-CT cholangiography were enrolled. Data from contrast enhanced MD-CT were used to reconstruct the 3D images of the hepatic artery and portal vein. 3D images reconstructed from MD-CT data of the hepatic artery, portal vein and bile duct were integrated into a single image. The dual branching of the right lateral portal vein was observed in 22 (42.3%) patients. Three (5.8%) had dual right lateral ducts and 14 (26.9%) had dual right lateral arteries. Among them, "south-turning" artery and "north-turning" bile duct was observed in 22 (42.3%). "South-turning" artery and "south-turning" bile duct were 3 (5.8%). "North-turning" artery and "north-turning" bile duct were 2 (7.4%). Only 27 (51.9%) had single portal vein, bile duct and artery for the right lateral sector, those were preferable as candidates for right lateral sector graft transplantation. 3D anatomical variations of portal vein, artery and bile duct for the right lateral sector were complexed, and only half of the donor candidates had preferable hepatic structures for right lateral sector graft transplantation. Understanding of the 3D hepatic structures by 3D-CT may contribute to a better definition of anatomical contraindications for LRLT which may further results in more safe and widely applied right lateral sector graft LRLT.

Decreased left ventricular function, myocarditis, and coronary arteriolar medial thickening following monocrotaline administration in adult rats

Decreased right as well as left ventricular function can be associated with pulmonary hypertension (PH). Numerous investigations have examined cardiac function following induction of pulmonary hypertension with monocrotaline (MCT) assuming that MCT has no direct cardiac effect. We tested this assumption by examining left ventricular function and histology of isolated and perfused hearts from MCT-treated rats. Experiments were performed on 50 male Sprague-Dawley rats [348 +/- 6 g (SD)]. Thirty-seven rats received MCT (50 mg/kg sc; MCT group) while the remainder did not (Control group). Three weeks later, pulmonary artery pressure was assessed echocardiographically in 20 MCT and 8 Control rats. The hearts were then excised and perfused in the constant pressure Langendorff mode to determine peak left ventricular pressure (LVP), the peak instantaneous rate of pressure increase (+dP/dtmax) and decrease (-dP/dtmax), as well as the rate pressure product (RPP). Histological sections were subsequently examined. Pulmonary artery pressure was higher in the MCT-treated group compared with the Control group [12.9 +/- 6 vs. 51 +/- 35.3 mmHg (P < 0.01)]. Left ventricular systolic function and diastolic relaxation were decreased in the MCT group compared with the Control group (+dP/dtmax 4,178 +/- 388 vs. 2,801 +/- 503 mmHg/s, LVP 115 +/- 11 vs. 83 +/- 14 mmHg, RPP 33,688 +/- 1,910 vs. 23,541 +/- 3,858 beats x min(-1) x mmHg(-1), -dP/dtmax -3,036 +/- 247 vs. -2,091 +/- 389 mmHg/s; P < 0.0001). The impairment of cardiac function was associated with myocarditis and coronary arteriolar medial thickening. Similarly depressed ventricular function and inflammatory infiltration was seen in 12 rats 7 days after MCT administration. Our findings appear unrelated to the degree of PH and indicate a direct cardiotoxic effect of MCT.

Progress in living donor liver transplantation

Living donor liver transplantation (LDLT) has the capacity to reduce the current discrepancy between the number of patients on the transplant waiting list and the number of available organ donors. For pediatric patients, LDLT has clearly reduced the number of waiting list deaths, providing compelling evidence for an increase in LDLT programs. This review discusses many of the recent advances in LDLT.

The effect of liver graft-body weight ratio on the core temperature of pediatric patients during liver transplantation

The left lateral segment of the liver from an adult living donor sometimes is relatively too large for a small pediatric recipient. It currently is unknown whether a high graft-recipient body weight ratio (GRWR) has a significant effect on core temperature during the anhepatic and reperfusion phases of living donor liver transplantation (LDLT). Seventy-two pediatric patients undergoing LDLT were divided into two groups according to body weight. Group I (GI) consisted of patients with a body weight greater than 10 kg, and group II (GII), less than 10 kg. Core temperature, measured as nasopharyngeal temperature (NT), was compared between groups at induction of anesthesia, hourly during the following 6 hours, as the lowest core temperature at the anhepatic phase, 5 and 30 minutes after reperfusion, and the last 2 hours before the end of the operation. Mild hypothermia of 35.8 degrees C +/- 0.7 degrees C and 35.9 degrees C +/- 0.4 degrees C for GI and GII was noted after induction of anesthesia, respectively; this increased +/- 1 degrees C in the following 6 hours. In the anhepatic and reperfusion phases, a sudden and significant decrease in NT was observed in both groups. This decrease in NT was significantly greater in GII than GI. In conclusion, a sudden decrease in core temperature was observed during the anhepatic and reperfusion phases of LDLT in pediatric patients, likely caused by placement of the cold liver graft, which is flushed with 4 degrees C lactated Ringer's solution during vessel reconstruction, in the anhepatic phase and return of venous blood through the cold preserved liver in the reperfusion phase. Core temperatures of pediatric patients with a body weight less than 10 kg in GII, who received grafts with a high GRWR, were more affected than those in GI.

Living-donor liver transplantation: 12 years of experience in Asia

Living-donor liver transplantation has provided a solution to the severe lack of cadaveric grafts for the replacement of livers afflicted with end-stage cirrhosis, fulminant disease, or inborn errors of metabolism. The pioneering experience in Japan in the early 1990s helped open wide the avenues of a new branch of science that is technically demanding and whose benefits are clearly dramatic. The need for alternative sources of liver grafts was common to the entire Asian region and, fortunately, the option of obtaining partial liver grafts from live donors had already become tenable. By the second half of the past decade, living-donor liver transplant programs had been successfully established in Hong Kong, Taiwan, and Korea. More than 1,500 cases have been performed over a 12-year period. This report describes the cumulative experience in living-donor liver transplantation in Asia on the basis of data from five major liver transplant centers.

Minimal blood loss living donor hepatectomy

BACKGROUND

Donor hepatectomy with maximal safety while preserving graft viability is of principal concern in living donor liver transplantation. There are compelling reasons for avoiding blood transfusion, even with autologous blood, to avoid the potential risks it imposes on healthy donors. This study aims to describe the surgical technique and clinical outcomes of living donor hepatectomy with minimal blood loss requiring no blood transfusion.

METHODS

Donor hepatectomy was performed in 30 living donors according to a detailed preoperative imaging study of the vascular and biliary anatomy. Liver parenchymal transection was carried out with strict adherence to a meticulous surgical technique without vascular inflow occlusion to either side of the liver. Pre-, intra-, and postoperative data were gathered, and factors related to blood loss were analyzed retrospectively.

RESULTS

The intraoperative blood loss ranged from 20 to 300 ml with a mean of 72.0+/-58.9 ml (median, 55 ml), and neither homologous nor autologous blood transfusion was required in any of the donors intra- and postoperatively. All 30 donors were discharged with minimal complications, and remain well at a mean follow-up of 24 months after donation. Excellent graft viability was verified by the fact that all 30 recipients are alive and well with a few manageable complications. The actual graft and patient survival are both 100% at the time of writing.

CONCLUSIONS

Regardless of the extent of donor hepatectomy, blood loss can and should be kept to a minimum, and living donor hepatectomy without blood transfusion is a realistic objective.

Combined therapy with inhaled nitric oxide and intravenous vasodilators during acute and chronic experimental pulmonary hypertension

Both inhaled nitric oxide (NO) and IV vasodilators decrease pulmonary hypertension, but the effects of combination therapy are unknown. We studied the response to inhaled NO (100 ppm) alone, IV vasodilator alone, and combined therapy during acute (U46619-induced) and chronic (monocrotaline-induced) pulmonary hypertension in the pentobarbital-anesthetized rat. Vasodilator doses were 1.0, 3.2, 10, and 32 microg x kg(-1) x min(-1) sodium nitroprusside (SNP); 50, 100, 150, 200, and 300 microg x kg(-1) x min(-1) adenosine; or 25, 50, 150, 200, and 300 ng x kg(-1) x min(-1) prostacyclin. In the absence of IV vasodilator therapy, inhaled NO decreased mean pulmonary artery pressure without decreasing mean systemic arterial pressure. In both acute and chronic pulmonary hypertension, the addition of inhaled NO to the largest dose of adenosine or prostacyclin, but not of SNP, decreased pulmonary artery pressure. Because inhaled NO and SNP activate guanylyl cyclase and adenosine and prostacyclin activate adenylyl cyclase, the results suggest that adding inhaled NO to a vasodilator not dependent on guanylyl cyclase may produce additional selective pulmonary vasodilation.

IMPLICATIONS

In therapy of pulmonary hypertension, inhaled nitric oxide should produce additional selective pulmonary vasodilation when combined with a vasodilator whose mechanism of action is not dependent on cyclic guanosine 3',5'-monophosphate.

Chronic pulmonary hypertension--the monocrotaline model and involvement of the hemostatic system

Monocrotaline (MCT) is a toxic pyrrolizidine alkaloid of plant origin. Administration of small doses of MCT or its active metabolite, monocrotaline pyrrole (MCTP), to rats causes delayed and progressive lung injury characterized by pulmonary vascular remodeling, pulmonary hypertension, and compensatory right heart hypertrophy. The lesions induced by MCT(P) administration in rats are similar to those observed in certain chronic pulmonary vascular diseases of people. This review begins with a synopsis of the hemostatic system, emphasizing the role of endothelium since endothelial cell dysfunction likely underlies the pathogenesis of MCT(P)-induced pneumotoxicity. MCT toxicology is discussed, focusing on morphologic, pulmonary mechanical, hemodynamic, and biochemical and molecular alterations that occur after toxicant exposure. Fibrin and platelet thrombosis of the pulmonary microvasculature occurs after administration of MCT(P) to rats, and several investigators have hypothesized that thrombi contribute to the lung injury and pulmonary hypertension. The evidence for involvement of the various components of the hemostatic system in MCT(P)-induced vascular injury and remodeling is reviewed. Current evidence is consistent with involvement of platelets and an altered fibrinolytic system, yet much remains to be learned about specific events and signals in the vascular pathogenesis.

Prolonged inhaled NO attenuates hypoxic, but not monocrotaline-induced, pulmonary vascular remodeling in rats

In concentrations of 10-20 ppm, inhaled nitric oxide (NO) decreases pulmonary artery pressure and attenuates vascular remodeling in pulmonary hypertensive rats. Because NO is potentially toxic, it is important to know whether lower concentrations attenuate vascular remodeling produced by different etiologies. Therefore, we determined the effects of prolonged, small-dose inhaled NO administration on hypoxic and monocrotaline (MCT)-induced pulmonary vascular remodeling. Rats were subjected to normoxia, hypoxia (normobaric 10% oxygen), or hypoxia plus NO in concentrations of 50 ppb, 200 ppb, 2 ppm, 20 ppm, and 100 ppm for 3 wk. A second group of normoxic rats was given MCT (60 mg/kg intraperitoneally) alone or in the presence of 2, 20, and 100 ppm of NO. Subsequently, pulmonary artery smooth muscle thickness and the number of muscular arteries (percentage of total arteries) were determined. Right ventricular hypertrophy was determined by right to left ventricle plus septum weight ratio (RV/LV + S). Pulmonary artery smooth muscle thickness and the percent muscular arteries were increased by hypoxia and MCT. The hypoxic increase in thickness was attenuated by all concentrations of NO, with 100 ppm being greatest, whereas NO had no effect on MCT rats. NO attenuated the increase in percent muscular arteries in hypoxic but not MCT rats. The RV/LV + S was increased by hypoxia and MCT compared with normoxia. Hypoxia-induced RV hypertrophy was decreased by all concentrations of inhaled NO, although attenuation with 50 ppb was less than with 200 ppb, 20 ppm, and 100 ppm. In MCT rats 2 and 100 ppm NO increased RV hypertrophy, whereas 20 ppm had no effect. In conclusion, inhaled NO in concentrations as low as 50 ppb attenuates the pulmonary vascular remodeling and RV hypertrophy secondary to hypoxia. In contrast, concentrations as high as 100 ppm do not attenuate MCT-induced pulmonary remodeling. These results demonstrate that extremely low concentrations of NO may attenuate remodeling but that the effectiveness is dependent on the mechanism inducing pulmonary remodeling.

IMPLICATIONS

The authors determined whether inhaled NO, a selective pulmonary vasodilator, attenuates pulmonary vascular remodeling caused by two models of pulmonary hypertension: chronic hypoxia and monocrotaline injection. Analysis of pulmonary vascular morphology suggests that very low concentrations of NO effectively attenuate hypoxic remodeling but that NO is not effective in monocrotaline-induced pulmonary remodeling.