Diana L. Diesen

Endogenous S-nitrosothiols protect against myocardial injury

Despite substantial evidence that nitric oxide (NO) and/or endogenous S-nitrosothiols (SNOs) exert protective effects in a variety of cardiovascular diseases, the molecular details are largely unknown. Here we show that following left coronary artery ligation, mice with a targeted deletion of the S-nitrosoglutathione reductase gene (GSNOR−/−) have reduced myocardial infarct size, preserved ventricular systolic and diastolic function, and maintained tissue oxygenation. These profound physiological effects are associated with increases in myocardial capillary density and S-nitrosylation of the transcription factor hypoxia inducible factor-1α (HIF-1α) under normoxic conditions. We further show that S-nitrosylated HIF-1α binds to the vascular endothelial growth factor (VEGF) gene, thus identifying a role for GSNO in angiogenesis and myocardial protection. These results suggest innovative approaches to modulate angiogenesis and preserve cardiac function.

Hypoxic Vasodilation by Red Blood Cells. Evidence for an S-Nitrosothiol–Based Signal

Red blood cells (RBCs) have been ascribed an essential role in matching blood flow to local metabolic demand during hypoxic vasodilation. The vasodilatory function of RBCs evidently relies on the allosteric properties of hemoglobin (Hb), which couple the conformation of Hb to tissue oxygen tension (Po2) and thereby provide a basis for the graded vasodilatory activity that is inversely proportional to Hb oxygen saturation. Although a large body of evidence indicates that the Po2-coupled allosteric transition from R (oxy)-state to T (deoxy)-state subserves the release from Hb of vasodilatory nitric oxide (NO) bioactivity, it has not yet been determined whether the NO-based signal is a necessary and sufficient source of RBC-mediated vasoactivity and it has been suggested that ATP or nitrite may also contribute. We demonstrate here by bioassay that untreated human RBCs rapidly and substantially relax thoracic aorta from both rabbit and mouse at low Po2 (≈1% O2) but not at high Po2 (≈21% O2). RBC-mediated vasorelaxation is inhibited by prior depletion of S-nitroso-Hb, potentiated by low-molecular-weight thiols, and dependent on cGMP. Furthermore, these relaxations are largely endothelium-independent and unaffected by NO synthase inhibition or nitrite. Robust relaxations by RBCs are also elicited in the absence of endothelial, neuronal or inducible NO synthase. Finally, contractions that appear following resolution of RBC-mediated relaxations are dependent on NO derived from RBCs as well as the endothelium. Our results suggest that an S-nitrosothiol–based signal originating from RBCs mediates hypoxic vasodilation by RBCs, and that vasorelaxation by RBCs dominates NO-based vasoconstriction under hypoxic conditions.

Effectiveness of Laparoscopic Computer Simulator Versus Usage of Box Trainer for Endoscopic Surgery Training of Novices

OBJECTIVE Teaching of laparoscopic skills is a challenge in surgical training programs. Because of the highly technical nature and the steep learning curve, students and residents must learn laparoscopic skills before performing them in the operating room. To improve efficiency of learning and patient safety, research in simulation is essential. Two types of simulators currently in use include virtual reality and box trainers. Our study examined which simulator technique was most effective in teaching novice trainees laparoscopic techniques. DESIGN This is a prospective, randomized, blinded, controlled trial that enrolled fourth-year medical students and surgical interns to participate in a supervised 6-month laparoscopic training program with either computer simulators or box trainers. Subjects were randomized and trained on appropriate laparoscopic camera skills, instrument handling, object positioning, dissection, ligation, suturing, and knot tying. Students within one group were not allowed to practice, learn or train on the opposing trainers. At time points 0, 2, and 6 months all subjects completed a series of laparoscopic exercises in a live porcine model, which were captured on DVD and scored by blinded expert investigators. RESULTS Scores improved overall from the pretest to subsequent tests after training with no difference between the virtual reality and box simulator groups. In the medical students specifically, there was overall improvement, and improvement in the needle-transfer and knot-tying skills specifically, with no difference between the box simulator and virtual reality groups. For the interns, both groups showed significant overall improvement with no difference between the virtual reality and box simulator groups or on individual skills. CONCLUSIONS We conclude that laparoscopic simulator training improves surgical skills in novice trainees. We found both the box trainers and the virtual reality simulators are equally effective means of teaching laparoscopic skills to novice learners.

Nitric Oxide and Redox Regulation in the Liver: Part I. General Considerations and Redox Biology in Hepatitis

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are created in normal hepatocytes and are critical for normal physiologic processes, including oxidative respiration, growth, regeneration, apoptosis, and microsomal defense. When the levels of oxidation products exceed the capacity of normal antioxidant systems, oxidative stress occurs. This type of stress, in the form of ROS and RNS, can be damaging to all liver cells, including hepatocytes, Kupffer cells, stellate cells, and endothelial cells, through induction of inflammation, ischemia, fibrosis, necrosis, apoptosis, or through malignant transformation by damaging lipids, proteins, and/or DNA. In Part I of this review, we will discuss basic redox biology in the liver, including a review of ROS, RNS, and antioxidants, with a focus on nitric oxide as a common source of RNS. We will then review the evidence for oxidative stress as a mechanism of liver injury in hepatitis (alcoholic, viral, nonalcoholic). In Part II of this review, we will review oxidative stress in common pathophysiologic conditions, including ischemia/reperfusion injury, fibrosis, hepatocellular carcinoma, iron overload, Wilsons disease, sepsis, and acetaminophen overdose. Finally, biomarkers, proteomic, and antioxidant therapies will be discussed as areas for future therapeutic interventions.

Protocolized Approach to the Management of Congenital Diaphragmatic Hernia: Benefits of Reducing Variability in Care

PURPOSE Variable approaches to the care of infants with congenital diaphragmatic hernia (CDH) by multiple providers may contribute to inconsistent care. Our institution developed a comprehensive evidence-based protocol to standardize the management of CDH infants. This report reviews patient outcomes before and after the implementation of the protocol. METHODS Retrospective chart review of CDH infants managed with individualized care (preprotocol group, January 1997-December 2001, n = 22) or on the protocol (Protocol group, January 2002-July 2009, n = 47). Survival and other categorical variables were compared by chi(2) analysis, and continuous variables were compared using 1-sided analysis of variance analysis, with significance defined as P < .05. RESULTS Survival to discharge was significantly greater in the Protocol group (40/47; 85%) than the preprotocol group (12/22; 52%; P = .006), although mean gestational age, mean birth weight, and expected survival were not statistically different between the 2 groups. The use of supportive therapies, including high-frequency jet ventilation, inhaled nitric oxide, and extracorporeal life support, was similar between groups as well. CONCLUSIONS Since the implementation of a management protocol for infants with CDH, survival has improved significantly compared with expected survival and preprotocol controls. Reduction in the variability of care through use of an evidence-based protocol may improve the survival of CDH infants.

Nitric Oxide and Redox Regulation in the Liver: Part II Redox biology in Pathologic Hepatocytes and Implications for intervention

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are created in normal hepatocytes and are critical for normal physiologic processes, including oxidative respiration, growth, regeneration, apoptosis, and microsomal defense. When the levels of oxidation products exceed the capacity of normal antioxidant systems, oxidative stress occurs. This type of stress, in the form of ROS and RNS, can be damaging to all liver cells, including hepatocytes, Kupffer cells, stellate cells, and endothelial cells, through induction of inflammation, ischemia, fibrosis, necrosis, apoptosis, or through malignant transformation by damaging lipids, proteins, and/or DNA. In Part I of this review, we will discuss basic redox biology in the liver, including a review of ROS, RNS, and antioxidants, with a focus on nitric oxide as a common source of RNS. We will then review the evidence for oxidative stress as a mechanism of liver injury in hepatitis (alcoholic, viral, nonalcoholic). In Part II of this review, we will review oxidative stress in common pathophysiologic conditions, including ischemia/reperfusion injury, fibrosis, hepatocellular carcinoma, iron overload, Wilsons disease, sepsis, and acetaminophen overdose. Finally, biomarkers, proteomic, and antioxidant therapies will be discussed as areas for future therapeutic interventions.

Predictors of patients who will develop prolonged occult hypoperfusion following blunt trauma.

BACKGROUND Prolonged occult hypoperfusion or POH (serum lactate >2.4 mmol/L persisting >12 hours from admission) represents a reversible risk factor for adverse outcomes following traumatic injury. We hypothesized that patients at increased risk for POH could be identified at the time of admission. METHODS Prospective data from adult trauma admissions between January 1, 1998 and December 31, 2000 were analyzed. Potential risk factors for POH were determined by univariate analysis (p < or =0.10= significant). Significant factors were tested in a logistic regression model (LR) (p < or =0.05= significant). The predictive ability of the LR was tested by receiver operating curve (ROC) analysis (p < or =0.05= significant). RESULTS Three hundred seventy-eight patients were analyzed, 129 with POH. Injury Severity Score (ISS), emergency department Glasgow Coma Scale score, hypotension, and the individual Abbreviated Injury Scale score (AIS) for Head (H), Abdominal/Pelvic Viscera (A) and Pelvis/Bony Extremity (P) were significantly associated with POH. LR demonstrated that ISS, A-AIS > or =3 and P-AIS > or =3 were independent predictors of POH (p <0.05). ROC analysis of the LR equation was statistically significant (Area=0.69, p <0.001). CONCLUSIONS We identified factors at admission that placed patients at higher risk for developing POH. Select patients may benefit from rapid, aggressive monitoring and resuscitation, possibly preventing POH and its associated morbidity and mortality.

Low volume is associated with worse patient outcomes for pediatric liver transplant centers.

BACKGROUND An inverse association between hospital procedure volume and postoperative mortality has been demonstrated for a variety of pediatric surgical procedures. The objective of our study was to determine whether such an association exists for pediatric liver transplantation. METHODS We performed a retrospective analysis of pediatric liver transplant procedures included in the Scientific Registry of Transplant Recipients over a 7.5-year time period from July 1, 2000, through December 31, 2007. Pediatric liver transplant centers were divided into three volume categories (high, middle, low) based on absolute annual volume. Mean 1-year patient survival rates and aggregate 1-year observed-to-expected (O:E) patient death ratios were calculated for each hospital volume category and then compared using ordered logistic regression and chi square analyses. RESULTS High-volume pediatric liver transplant centers achieved significantly lower aggregate 1-year O:E patient death ratios than low-volume centers. When freestanding childrens hospitals (FCH), childrens hospitals within adult hospitals (CAH), and other centers (OC) were considered separately, we found that a significant volume-outcomes association existed among OC centers but not among FCH or CAH centers. Low-volume OC centers, which represent 41.6% of all pediatric liver transplant centers and perform 10% of all pediatric liver transplantation, had the least favorable aggregate 1-year O:E patient death ratio of all groups. CONCLUSIONS We demonstrate that a significant center volume-outcomes relationship exists among OC pediatric liver transplant centers but not among FCH or CAH centers. These findings support the possible institution of minimum annual procedure volume requirements for OC pediatric liver transplant centers.

Pediatric melanoma: a single-institution experience of 150 patients

PURPOSE Differentiating pigmented skin lesions from malignant melanoma in the pediatric population has been a challenge. Despite guidelines describing clinical features and histopathologic criteria to distinguish these lesions, misdiagnoses still occur. We report our experience over 30 years in a pediatric population with malignant melanoma. METHODS We performed a retrospective review of 150 pediatric patients treated for malignant melanoma between 1973 and 2007 at our institution. Outcomes measured included age, Breslow thickness, Clark level of invasion, tumor location, local and distant failure rates, and overall survival. RESULTS One hundred fifty pediatric patients were evaluated. The mean age was 15.1 years. The mean Breslow thickness was 2.05 mm and corresponding Clark level of invasion was 3.47. There were 43 known recurrences (29%); 29 distant, 14 nodal, and 7 local. Overall survival was 84% with a mean follow-up of 8.5 years. Sixteen patients (10.7%) were incorrectly diagnosed on initial pathologic examination. Overall survival in the misdiagnosed group was 66%. CONCLUSION Pigmented skin lesions in the pediatric population represent a diagnostic challenge to pathologists and clinicians. Improvements in diagnostic techniques with rigorous characterization, as well as increased physician awareness, should lead to a reduction in errors of diagnosis.

S-nitrosylation therapy to improve oxygen delivery of banked blood

From the perspectives of disease transmission and sterility maintenance, the world’s blood supplies are generally safe. However, in multiple clinical settings, red blood cell (RBC) transfusions are associated with adverse cardiovascular events and multiorgan injury. Because ∼85 million units of blood are administered worldwide each year, transfusion-related morbidity and mortality is a major public health concern. Blood undergoes multiple biochemical changes during storage, but the relevance of these changes to unfavorable outcomes is unclear. Banked blood shows reduced levels of S-nitrosohemoglobin (SNO-Hb), which in turn impairs the ability of stored RBCs to effect hypoxic vasodilation. We therefore reasoned that transfusion of SNO-Hb–deficient blood may exacerbate, rather than correct, impairments in tissue oxygenation, and that restoration of SNO-Hb levels would improve transfusion efficacy. Notably in mice, administration of banked RBCs decreased skeletal muscle pO2, but infusion of renitrosylated cells maintained tissue oxygenation. In rats, hemorrhage-induced reductions in muscle pO2 were corrected by SNO-Hb–repleted RBCs, but not by control, stored RBCs. In anemic awake sheep, stored renitrosylated, but not control RBCs, produced sustained improvements in O2 delivery; in anesthetized sheep, decrements in hemodynamic status, renal blood flow, and kidney function incurred following transfusion of banked blood were also prevented by renitrosylation. Collectively, our findings lend support to the idea that transfusions may be causally linked to ischemic events and suggest a simple approach to prevention (i.e., SNO-Hb repletion). If these data are replicated in clinical trials, renitrosylation therapy could have significant therapeutic impact on the care of millions of patients.