C. Alvin Head

Sickle cell disease and anesthesia.

IN October 1902, a “peculiar anomaly in human red blood corpuscles. . .came to notice in the histologic laboratory of the Ohio State University,” Columbus, Ohio. “Examination disclosed the fact that the colored corpuscles in the sample recently drawn by (a) student from his own finger that were elliptical and not circular.” Similar erythrocyte abnormalities were reported in North African Arab subjects shortly afterwards. In November 1910 James B Herrick, M.D. (Professor Of Medicine, Rush Medical College, Chicago, Illinois; 1861–1954) published a detailed case report. This described a patient with jaundice, shortness of breath, lymphadenopathy, dark urine, leg ulcers, epigastria pain, and anemia associated with these same types of “peculiar elongated and sickle-shaped red blood corpuscles.” This classic report was the first unequivocal clinical description in Western scientific literature of sickle cell disease (SCD), a set of closely related hemoglobinopathies that have in common the inheritance of mutant hemoglobin S (fig. 1). Clinically, SCD is characterized by chronic hemolytic anemia, recurrent episodes of intermittent vasoocclusion and severe pain, progressive organ damage, and a striking variation of expression. In 1927, Hahn and Gillespie noted that the eponymous deformation or sickling of the erythrocytes was induced by deoxygenation and reversed with reoxygenation. The clinical segue was a hypothesis that vasoocclusion was triggered by delayed passage of erythrocytes through the microcirculation, leading to a “vicious cycle” of increased sickling, mechanical obstruction to flow, further sickling, vasoocclusion, and infarction. In 1955, the first major review of the anesthetic implications of SCD acknowledged the high incidence of serious and potentially fatal exacerbations of the disease after surgical procedures. The avoidance of factors said to increase erythrocyte sickling and precipitate the vicious cycle has been the traditional foundation of anesthetic management of SCD. The century after the discovery of the peculiar anomaly has seen an immense expansion in the understanding of the complex relationship between these peculiar erythrocytes and the clinical expression of the disease. This article briefly summarizes advances made in understanding of the disease pathophysiology, describes salient clinical features relevant to the anesthesiologist, and reviews data from the perioperative period, emphasizing a new anesthetic approach to this old problem.

Inhibition of cell adhesion by anti–P-selectin aptamer: a new potential therapeutic agent for sickle cell disease

Adhesive interactions between circulating sickle red blood cells (RBCs), leukocytes, and endothelial cells are major pathophysiologic events in sickle cell disease (SCD). To develop new therapeutics that efficiently inhibit adhesive interactions, we generated an anti-P-selectin aptamer and examined its effects on cell adhesion using knockout-transgenic SCD model mice. Aptamers, single-stranded oligonucleotides that bind molecular targets with high affinity and specificity, are emerging as new therapeutics for cardiovascular and hematologic disorders. In vitro studies found that the anti-P-selectin aptamer exhibits high specificity to mouse P-selectin but not other selectins. SCD mice were injected with the anti-P-selectin aptamer, and cell adhesion was observed under hypoxia. The anti-P-selectin aptamer inhibited the adhesion of sickle RBCs and leukocytes to endothelial cells by 90% and 80%, respectively. The anti-P-selectin aptamer also increased microvascular flow velocities and reduced the leukocyte rolling flux. SCD mice treated with the anti-P-selectin aptamer demonstrated a reduced mortality rate associated with the experimental procedures compared with control mice. These results demonstrate that anti-P-selectin aptamer efficiently inhibits the adhesion of both sickle RBCs and leukocytes to endothelial cells in SCD model mice, suggesting a critical role for P-selectin in cell adhesion. Anti-P-selectin aptamer may be useful as a novel therapeutic agent for SCD.

Beneficial effects of nitric oxide breathing in adult patients with sickle cell crisis

Pain from vaso-occlusive crisis (VOC) is the major cause of hospitalization in patients with sickle cell disease (SCD). The beneficial therapeutic effects of inhaled nitric oxide (NO) on the pathophysiology of SCD have been reported. A double-blind, randomized, placebo-controlled clinical trial was conducted to determine whether NO breathing reduces acute VOC pain in adult patients and to study the safety of inhaled NO. Twenty-three patients experiencing acute VOC were enrolled. After randomization but before treatment, five were found to not meet final eligibility criteria. Nine patients were assigned to inhaled NO (80 ppm) and nine to placebo (21% O2). Primary outcome was the mean change in pain scores after 4 hr of inhalation, measured on a 10-cm visual analog scale (VAS). Both groups had similar baseline VAS pain scores but inhaled NO significantly reduced pain scores compared with placebo (P 5 0.02) at the end of NO inhalation. Secondary outcome was parenteral morphine use at baseline, 4, and 6 hr. Parenteral morphine use was lower in the inhaled NO group, but the difference was not statistically significant.Safety assessments included systolic blood pressure measurements,pulse oximetry readings, concentration of delivered nitrogen dioxide, and concentration of methemoglobin (metHb). None of these NO toxicities was observed.

L-citrulline protects from kidney damage in type 1 diabetic mice

Rationale: Diabetic nephropathy (DN) is a major cause of end-stage renal disease, associated with endothelial dysfunction. Chronic supplementation of l-arginine (l-arg), the substrate for endothelial nitric oxide synthase (eNOS), failed to improve vascular function. l-Citrulline (l-cit) supplementation not only increases l-arg synthesis, but also inhibits cytosolic arginase I, a competitor of eNOS for the use of l-arg, in the vasculature. Aims: To investigate whether l-cit treatment reduces DN in streptozotocin (STZ)-induced type 1 diabetes (T1D) in mice and rats and to study its effects on arginase II (ArgII) function, the main renal isoform. Methods: STZ-C57BL6 mice received l-cit or vehicle supplemented in the drinking water. For comparative analysis, diabetic ArgII knock out mice and l-cit-treated STZ-rats were evaluated. Results: l-Citrulline exerted protective effects in kidneys of STZ-rats, and markedly reduced urinary albumin excretion, tubulo-interstitial fibrosis, and kidney hypertrophy, observed in untreated diabetic mice. Intriguingly, l-cit treatment was accompanied by a sustained elevation of tubular ArgII at 16 weeks and significantly enhanced plasma levels of the anti-inflammatory cytokine IL-10. Diabetic ArgII knock out mice showed greater blood urea nitrogen levels, hypertrophy, and dilated tubules than diabetic wild type (WT) mice. Despite a marked reduction in collagen deposition in ArgII knock out mice, their albuminuria was not significantly different from diabetic WT animals. l-Cit also restored nitric oxide/reactive oxygen species balance and barrier function in high glucose-treated monolayers of human glomerular endothelial cells. Moreover, l-cit also has the ability to establish an anti-inflammatory profile, characterized by increased IL-10 and reduced IL-1β and IL-12(p70) generation in the human proximal tubular cells. Conclusion: l-Citrulline supplementation established an anti-inflammatory profile and significantly preserved the nephron function during T1D.

Inhaled nitric oxide for treatment of sickle cell stroke

STROKE is a highly fatal complication of sickle cell disease (SCD) in children, particularly between the ages of 4 and 15 yr. Children with SCD carry a 300-fold increased risk for stroke; consequently, sickle cell anemia is the most common cause of childhood stroke. We report the case of a 13-yr-old African-American boy diagnosed at age 6 months old with hemoglobin SS disease, who had a nonhemorrhagic stroke after a routine anesthetic and was treated with inhaled nitric oxide (INO).

The proinflammatory cytokine GM-CSF downregulates fetal hemoglobin expression by attenuating the cAMP-dependent pathway in sickle cell disease

Although reduction in leukocyte counts following hydroxyurea therapy in sickle cell disease (SCD) predicts fetal hemoglobin (HbF) response, the underlying mechanism remains unknown. We previously reported that leukocyte counts are regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) in SCD patients. Here we examined the roles of GM-CSF in the regulation of HbF expression in SCD. Upon the analysis of retrospective data in 372 patients, HbF levels were inversely correlated with leukocyte counts and GM-CSF levels in SCD patients without hydroxyurea therapy, while HbF increments after hydroxyurea therapy correlated with a reduction in leukocyte counts, suggesting a negative effect of GM-CSF on HbF expression. Consistently, in vitro studies using primary erythroblasts showed that the addition of GM-CSF to erythroid cells decreased HbF expression. We next examined the intracellular signaling pathway through which GM-CSF reduced HbF expression. Treatment of erythroid cells with GM-CSF resulted in the reduction of intracellular cAMP levels and abrogated phosphorylation of cAMP response-element-binding-protein, suggesting attenuation of the cAMP-dependent pathway, while the phosphorylation levels of mitogen-activated protein kinases were not affected. This is compatible with our studies showing a role for the cAMP-dependent pathway in HbF expression. Together, these results demonstrate that GM-CSF plays a role in regulating both leukocyte count and HbF expression in SCD. Reduction in GM-CSF levels upon hydroxyurea therapy may be critical for efficient HbF induction. The results showing the involvement of GM-CSF in HbF expression may suggest possible mechanisms for hydroxyurea resistance in SCD.

Nitric oxide reduces sickle hemoglobin polymerization: Potential role of nitric oxide-induced charge alteration in depolymerization

We previously demonstrated that inhaling nitric oxide (NO) increases the oxygen affinity of sickle red blood cells (RBCs) in patients with sickle cell disease (SCD). Our recent studies found that NO lowered the P(50) values of sickle hemoglobin (HbS) hemolysates but did not increase methemoglobin (metHb) levels, supporting the role of NO, but not metHb, in the oxygen affinity of HbS. Here we examine the mechanism by which NO increases HbS oxygen affinity. Because anti-sickling agents increase sickle RBC oxygen affinity, we first determined whether NO exhibits anti-sickling properties. The viscosity of HbS hemolysates, measured by falling ball assays, increased upon deoxygenation; NO treatment reduced the increment. Multiphoton microscopic analyses showed smaller HbS polymers in deoxygenated sickle RBCs and HbS hemolysates exposed to NO. These results suggest that NO inhibits HbS polymer formation and has anti-sickling properties. Furthermore, we found that HbS treated with NO exhibits an isoelectric point similar to that of HbA, suggesting that NO alters the electric charge of HbS. NO-HbS adducts had the same elution time as HbA upon high performance liquid chromatography analysis. This study demonstrates that NO may disrupt HbS polymers by abolishing the excess positive charge of HbS, resulting in increased oxygen affinity.