Predictors of osteoclast activity in patients with sickle cell disease

Background

Bone changes are common in sickle cell disease, but the pathogenesis is not fully understood. Tartrate-resistant acid phosphatase (TRACP) type 5b is produced by bone-resorbing osteoclasts. In other forms of hemolytic anemia, increased iron stores are associated with osteoporosis. We hypothesized that transfusional iron overload would be associated with increased osteoclast activity in patients with sickle cell disease.

Design and Methods

We examined tartrate-resistant acid phosphatase 5b concentrations in patients with sickle cell disease and normal controls of similar age and sex distribution at steady state. Serum tartrate-resistant acid phosphatase 5b concentration was measured using an immunocapture enzyme assay and plasma concentrations of other cytokines were assayed using the Bio-Plex suspension array system. Tricuspid regurgitation velocity, an indirect measure of systolic pulmonary artery pressure, was determined by echocardiography.

Results

Tartrate-resistant acid phosphatase 5b concentrations were higher in 58 adults with sickle cell disease than in 22 controls (medians of 4.4 versus 2.4 U/L, respectively; P=0.0001). Among the patients with sickle cell disease, tartrate-resistant acid phosphatase 5b independently correlated with blood urea nitrogen (standardized beta=0.40, P=0.003), interleukin-8 (standardized beta=0.30, P=0.020), and chemokine C-C motif ligand 5 (standardized beta=−0.28, P=0.031) concentrations, but not with serum ferritin concentration. Frequent blood transfusions (>10 units in life time) were not associated with higher tartrate-resistant acid phosphatase 5b levels in multivariate analysis. There were strong correlations among tartrate-resistant acid phosphatase 5b, alkaline phosphatase and tricuspid regurgitation velocity (r>0.35, P<0.001).

Conclusions

Patients with sickle cell disease have increased osteoclast activity as reflected by serum tartrate-resistant acid phosphatase 5b concentrations. Our results may support a potential role of inflammation rather than increased iron stores in stimulating osteoclast activity in sickle cell disease. The positive relationships among tartrate-resistant acid phosphatase 5b, alkaline phosphatase and tricuspid regurgitation velocity raise the possibility of a common pathway in the pulmonary and bone complications of sickle cell disease.     

Malignancy in patients with sickle cell disease

Malignancy in patients with sickle cell disease (SCD) has been previously reported, but the types of cancer and its incidence remain undefined. With the advent of hydroxyurea therapy, there is concern about increasing the cancer risk for patients with SCD. The International Association of Sickle Cell Nurses and Physician Assistants identified 52 cases of cancer (49 patients) among 16,613 patients with SCD followed at 52 institutions. The median age at malignancy diagnosis was 34 years (range, 14 months-62 years). Twenty-one cases (40%) occurred in pediatric patients, primarily leukemia (n = 7) or Wilms' tumor (n = 5), with 15 children surviving. Most adults had solid tumors, especially carcinomas, and only nine were known to be alive. Three patients received hydroxyurea before the diagnosis of malignancy. These data provide essential baseline information for the accurate interpretation of future reports of malignancy in patients with SCD, especially those receiving hydroxyurea therapy.     

Pharmacogenetics of morphine: Potential implications in sickle cell disease

Morphine is frequently used to treat painful episodes associated with sickle cell disease (SCD) but may fail to provide adequate analgesia in many patients. This concise review focuses on unique disease related changes in physiologic variables associated with SCD that impacts pharmacokinetics and pharmacodynamics of morphine and may contribute to the variability in analgesia. Emerging evidence suggests that the allelic variants in the genes involving the opioid (UGT2B7, OPRM1, and ABCB1 genes) and nonopioid system (COMT gene) can alter the efficacy of morphine.     

Procoagulant activity in patients with sickle cell trait

Patients with sickle cell trait (STr) are usually considered to be asymptomatic. However, complications, including hypercoagulability, increased risk of venous thromboembolism and the exertional exercise syndrome with rhabdomyolysis and sudden death, have been described. The exact cause of these adverse events is unclear. We have investigated two patients, a set of monozygotic twins with STr, to establish their procoagulant activity status as a potential indicator of thrombotic risk. In-vivo thrombin generation was assessed by the measurement of prothrombin fragment 1 + 2 (F1 + 2) and thrombin-antithrombin complexes (TAT). D-dimer was used as a marker of fibrinolytic activity. The potential to generate thrombin was determined using an ex-vivo thrombin generation test (TGT). The impact of red blood cell (RBC)-derived microparticle shedding and RBC rheology were examined. TAT (>60 μg/l) and F1 + 2 (948 pmol/l) were markedly elevated in patient 2 but within the normal reference range in patient 1 (TAT = 2.5 μg/l; F1 + 2 = 138 pmol/l). D-dimer levels (0.9 mg/l FEU) were similarly elevated in both patients. TGT peak thrombin and endogenous thrombin potential (ETP) were elevated to similar degrees in both patients. Flow cytometric analysis for RBC-derived microparticles showed that both patients had elevated levels on two occasions. RBC deformability, blood viscosity and RBC aggregation were normal and similar in both patients. The results demonstrated different coagulation activity in the patients with one patient in a prothrombotic state, suggesting that there may be two levels of hypercoagulability in STr. Measurement of such differences would allow for separation of high and low-risk patients from serious complications.     

Echocardiographic findings in patients with sickle cell disease

Pulmonary hypertension is a complication of sickle cell disease that is associated with increased mortality. Whether this complication is associated with hemolysis has been questioned. Systolic pulmonary artery blood pressure can be estimated from echocardiography-determined tricuspid regurgitation velocity (TRV). A velocity of 2.5 m/s or higher suggests possible pulmonary hypertension. A retrospective review of hospital records from adult patients with sickle cell disease undergoing echocardiography in 2006 and 2007 was performed at a tertiary level hospital. Echocardiographic, demographic, and clinical laboratory data were collected. Echocardiographic results were available for 105 adult sickle cell patients. Of these, 62 (59%) had a TRV ≥2.5 m/s and 24 (22.8%) had a TRV ≥3.0 m/s. Mitral valve regurgitation was observed in 44% and left ventricular abnormalities (defined by either hypertrophy or dilation) in 28% of cases. Elevated TRV had independent and significant associations with greater age, higher serum lactate dehydrogenase (LDH) concentration, and lower hemoglobin concentration. We confirmed that elevated TRV is common among hospital-based adults with sickle cell disease. Significant, independent associations were found with both elevated LDH concentration and degree of anemia, suggesting that hemolytic and other mechanisms contribute to pulmonary hypertension in patients with sickle cell disease.     

Platelet activation in patients with sickle cell disease

Vascular occlusion and vasculopathy underlie much of the morbidity in patients with sickle cell anaemia. Platelets may play a role in this vasculopathy. Samples from 43 patients with sickle cell disease (SCD) were examined for evidence of platelet activation using fluorescent-labelled monoclonal antibodies and flow cytometry. There was increased expression of activation-dependent antigens on the platelets from patients with SCD compared to those from both Caucasian and African-American controls. In addition, SCD patients had increased levels of platelet microparticles. Platelets are activated in patients with sickle cell disease. The contribution of platelet activation to sickle cell pathophysiology is under active investigation in our laboratories.     

Sleep-disordered breathing in patients with sickle cell disease

Sickle cell disease is one of the most common hereditary hemoglobinopathies worldwide, and its vaso-occlusive and hemolytic crises cause considerable patient morbidity. A growing body of evidence has shown that sleep-disordered breathing, and in particular, obstructive sleep apnea, occurs at high frequency in the sickle cell population, and that there is significant overlap in the underlying pathophysiology of these two conditions. Through a variety of mechanisms including nocturnal hypoxemia and increased oxidative stress, production of pro-inflammatory cytokines, and endothelial dysfunction, sickle cell anemia and sleep-disordered breathing potentiate each other’s clinical effects and end-organ complications. Here, we will review the shared pathophysiologic mechanisms of these conditions and discuss their clinical sequelae. We will also examine the results of studies that have been carried out with clinical intervention of nocturnal hypoxemia in patients with sickle cell disease in the attempts to overcome the complications of the disease. Finally, we will propose the areas of investigation that merit further investigations in future in patients with sickle cell disease and sleep-disordered breathing.     

ADAMTS13 activity in sickle cell disease

Sickle red blood cell (SRBC)-endothelial adhesion plays a central role in sickle cell disease (SCD)-related vaso-occlusion. As unusually large von Willebrand factor (ULVWF) multimers mediate SRBC-endothelial adhesion, we investigated the activity of ADAMTS13, the metalloprotease responsible for cleaving ULVWF multimers, in SCD. ADAMTS13 activity was determined using a quantitative immunoblotting assay. VWF:Ag and VWF:RCo were determined using commercial assays. The high-molecular-weight VWF multimer percentage was determined by employing gel electrophoresis. ADAMTS13 activity was similar among asymptomatic patients (n = 8), patients at presentation with a painful crisis (n = 23), and healthy controls. ADAMTS13/VWF:Ag ratios were lower in patients compared to healthy HbAA controls, with the lowest values at presentation with a painful crisis (P = 0.02). Division of samples in those with VWF:RCo/VWF:Ag ratios < 0.70 and those with ratios >or= 0.70 revealed significantly more samples with ratios >or= 0.70 (P = 0.01) collected during painful crises. ULVWF multimers were detected in 6 patient samples and in 1 control sample. ADAMTS13/VWF:Ag ratios were inversely related to the duration of symptoms at presentation with an acute vaso-occlusive event (r(s)-0.67, P = 0.002). Although SCD is characterized by elevated VWF:Ag levels, no severe ADAMTS13 deficiency was detected in our patients.     

Monocyte phagocytic activity in sickle cell disease

The phagocytic activity of peripheral blood monocytes from sickle cell disease patients and normal controls was studied using a monocyte monolayer assay. Phagocytosis of antibody-coated red cells by monocytes from patients in stable condition and in normal controls did not differ significantly (7.1 +/- 1.5 vs. 5.3 +/- 0.9%). However, monocytes from sickle cell disease patients during vasoocclusive crises demonstrated increased phagocytic activity compared to the normal controls (11.0 +/- 2.7 vs. 5.3 +/- 0.9%, p less than 0.025). Numerous defects in immune response have been described in association with sickle cell disease. However, monocyte phagocytic activity is not deficient and is not a factor in the predisposition to infections.     

Folate supplementation and twinning in patients with sickle cell disease

Patients with sickle cell disease routinely take folic acid daily as a supplement to maintain effective erythropoiesis. One of the controversial effects of folic acid is its effect on twin gestation rates. In this report, we present our experience in patients with sickle cell disease and twin pregnancy. Our data show that twin pregnancies seem to be associated with folate supplementation.     

Cancer specific survival in patients with sickle cell disease

Sickle cell disease (SCD) patients have a higher incidence of certain cancers, but no studies have determined the impact of cancer on survival among SCD patients. SCD patients (n = 6423), identified from state-wide hospitalisation data, were linked to the California Cancer Registry (1988–2014). Multivariable Cox proportional hazards regression was used to examine survival. Among SCD patients, a cancer diagnosis was associated with a 3-fold increased hazard of death. Compared to matched cancer patients without SCD, SCD was associated with worse overall survival, but not cancer-specific survival, suggesting that SCD cancer patients should be treated with similar therapeutic intent.     

Cholelithiasis in Jamaican patients with homozygous sickle cell disease

The prevalence of cholelithiasis in Jamaican adults with SS disease was studied by plain abdominal radiograph in 206 patients and by oral cholecystogram in 126 (61%) of these patients. Gallstones were found in 57 (28%) of patients, were more common in females than males, and increased with age and hemolytic rate. The majority of gallstones were visible on the plain abdominal radiograph, only 17% of patients with gallstones having only radiolucent stones. Nonfunctioning oral cholecystograms were common (10%) in agreement with observations by previous workers. Gallstones were noted in the common bile duct in 2 patients. In general there was no clear relationship between the presence of cholelithiasis and clinical symptomatology. Complications, such as pancreatitis and malignant change in the gall bladder, recognized to be associated with cholelithiasis in the general population, have not been clearly related to cholelithiasis in SS disease. More information is needed before a logical policy can be evolved for surgical intervention in cholelithiasis in SS disease.     

Post-transfusion alloimmunization in patients with sickle cell disease.

The transfusion histories over a 33-month period of 50 patients with sickle cell disease were reviewed to determine the frequency of alloimmunization to red cell antigens following transfusion in these patients. There were 30 females and 20 males, aged 19--49 years. Eighteen (36%) were immunized of which thirteen were females. Five of the patients have formed only one antibody so far, while the other 13 have formed two or more. Thirty-six antibodies were identified: 16 against various Rh antigens, 12 anti-Lewis, 5 anti-Kell and one each of anti-Jka, -Fya and -M. The immunized patients received, on the average, more transfusions although there was a considerable degree of overlap between the immunized and nonimmunized groups. An approach to the hemotherapy of patients with sickle cell disease (SCD) is discussed.     

Nontransferrin-bound iron in transfused patients with sickle cell disease

The value of nontransferrin‐bound iron (NTBI) as an index of iron overload in patients with thalassemia has been evaluated; however, data in patients with sickle cell disease (SCD) is limited. NTBI levels were evaluated in a cross‐sectional study of 43 transfused patients with SCD. Patient charts were reviewed for demographics, status of the spleen, and total number of lifetime transfusions. All patients were chelation naïve and none of the patients had evidence of hepatitis B or C infection. Blood samples were taken for assessment of NTBI and serum ferritin (SF); liver iron concentration (LIC) was determined by R2 magnetic resonance imaging. NTBI levels were generally low with a median of ?0.01 μm (range ?2.56 to 6.37 μm ). Among study variables, NTBI levels were only significantly correlated to age and total number of lifetime transfusions, whereas LIC and SF only significantly correlated with total number of lifetime transfusions. On multivariate analysis, only total number of lifetime transfusions remained independently correlated with NTBI (P = 0.001), SF (P < 0.001), and LIC (P < 0.001). On multivariate stepwise linear regression analysis, SF was a better predictor of LIC than NTBI. In transfused patients with SCD, NTBI levels are low yet correlate significantly with transfusion burden. However, they offer poor predictability of LIC when compared with SF.     

Systemic lupus erythematosus in patients with sickle cell disease

Sickle cell disease (SCD) is a prevalent genetic disorder that includes sickle cell anemia (hemoglobin SS), hemoglobin SC, and hemoglobin Sb-thalassemia. Patients with SCD present with a defective activation of the alternate pathway of the complement system that increases the risk of capsulate bacteria infection and failure to eliminate antigens, predisposing these patients to autoimmune diseases. The authors describe three patients with SCD that developed systemic lupus erythematosus (SLE). In all patients, SLE diagnosis was delayed because symptoms were initially attributable to SCD. Physicians should be alerted to the possible development of SLE in patients with SCD to not delay the diagnosis and start appropriate treatment.     

Oxygen saturation with sleep in patients with sickle cell disease

Ear oximetry was used to monitor arterial oxygenation in seven patients who had a history of frequent admissions for sickle cell crisis and were taking narcotic analgesics. Five full-night studies and seven daytime "nap" studies were performed in which sleep state was monitored by electroencephalography, and respiratory rate and tidal volume were monitored by inductance plethysmography. For all patients the mean (+/- SEM) of the median oxygenation values was 93.3% +/- 0.4% during wakefulness and 91.4% +/- 0.8% during sleep. During wakefulness the lowest saturation was 90% +/- 0.5%; during sleep there was a fall in the lowest oxygen saturation to 86.5% +/- 0.9%. In all patients a fall in oxygen saturation was associated with a decrease in respiratory depth without a change in respiratory frequency. The results indicate that in sickle cell disease oxygen saturation is lower during sleep than during wakefulness and that hypoxemia can be attributed to a fall in tidal volume.