HbSS Genotype Research Articles

Effects of hydroxyurea treatment on cerebral oxygenation in adult patients with sickle cell disease: an open-label pilot study

In patients with sickle cell disease (SCD), cerebral oxygen saturation (rSO(2)) has been reported to be below normal and to increase after red blood cell transfusion. This study was designed to determine the effects of long-term and short-term hydroxyurea (HU) treatment on cerebral oxygenation in patients with SCD. This open-label pilot study was conducted at the Department of Anesthesiology and the Center for Sickle Cell Disease, College of Medicine, Howard University, Washington, DC. Adult African American outpatients with SCD and hemoglobin (Hb) genotype HbSS (homozygous sickle Hb) who were receiving long-term (>6 months) HU treatment (15-30 mg/kg . d PO) or who had never received this treatment (control group) were enrolled. Patients in the treated and control groups were matched for age, sex, race, and Hb genotype. Cerebral oximetry (near-infrared spectroscopy) was performed to determine rSO(2) index. In a separate analysis to determine the effects of short-term HU treatment on cerebral oxygenation, hospitalized patients with SCD and vaso-occlusive crisis (VOC)receiving long-term therapy with HU were enrolled. We performed cerebral and pulse (fingernail) oximetry to determine rSO (2)index and arterial oxygen saturation (SpO(2)) after the administration of a single oral dose of HU (500-mg tablet) alone and again after dosing concomitantly with inhaled oxygen. The study enrolled 11 patients in the HU group (6 women, 5 men; mean [SD] age, 37 [8] years) and 20 controls (8 women, 12 men; mean [SD] age, 35 [6] years). Mean (SD) rSO(2) index was significantly increased (but still low) in patients receiving long-term HU treatment compared with controls (46.1% [6.6%] vs 41.2% [7.6%]; P< 0.025). Hb concentration (9.6 [1.4] g/dL vs 8.5 [1.2] g/dL; P< 0.027), hematocrit (28% [3%] vs 24% [4%]; P < 0.028), and mean corpuscular volume (102% [7%] vs 89% [8%]; P < 0.027) also were significantly higher in the HU group compared with controls. In 8 patients with SCD and VOC (6 men, 2 women; mean [SD] age, 28 [5] years), single-dose HU, either alone or in combination with inhaled oxygen, did not significantly affect cerebral oxygenation, and SpO(2) failed to correlate with rSO(2) index in these patients. The results of this open-label pilot study in patients with SCD suggest that the low cerebral oxygenation in these patients is significantly improved but not normalized with long-term HU treatment. A single dose of HU, either alone or in combination with inhaled oxygen, did not appear to influence cerebral oxygenation in patients with VOC.

Studies on the effect of aqueous extracts of &lt;i&gt;Garcinia kola&lt;/i&gt; seeds on human erythrocytes adenosine triphosphatases of HbAA, HbAS and HbSS genotypes

The activities of the membrane-bound ATPases (Na + , K + -ATPase: E. C. 3.6.1.37; Ca 2+ -ATPase: E. C. 3.6.1.38, and Mg 2+ -ATPase: E. C. 3.6.1.3) were determined in erythrocytes obtained from HbAA, HbAS and HbSS genotypes. For Na + , K + -ATPase and Ca 2+ -ATPase, the activity trend was HbAA > HbAS > HbSS while for Mg 2+ -ATPase, the trend was HbSS > HbAS > HbAA. The aqueous extract of Garcinia kola seed increased the activity of Na + , K + -ATPase and Ca 2+ -ATPase in the three genotypes with the trend of HbSS > HbAS > HbAA. Phenylalanine, a known anti-sickling agent, showed similar activating effect as the extract. In contrast, both the extract and phenylalanine decreased the activity of Mg 2+ -ATPase from all the genotypes, showing the trend of HbSS > HbAS > HbAA. The three ATPases obeyed Michaelis-Menten kinetics. The apparent K m for the three different genotypes for ATP were similar for the ATPases with the values of 5.62+0.02, 5.27+0.02 and 4.65+0.03 mM ATP-Na 2 for (Na + , K + )- ; Ca 2+ -; and Mg 2+ -ATPases, respectively. An activation constant of 0.317 g/ml of extract, for the Ca 2+ -ATPase of HbSS erythrocyte was obtained while the inhibition constant, K i , of the extract on Mg 2+ -ATPase from HbSS erythrocyte by the extract was 1.23 g/ml of extract. These findings are of significance to the suggested use of the aqueous extract of G. kola seeds in ameliorating sickle cell crisis. Key Words: adenosine triphosphatases, erythrocytes, genotypes, phenylalanine Global Jnl Medical Sciences Vol.2(2) 2003: 107-114

Binding of ovarian steroids to erythrocytes in patients with sickle cell disease; effects on cell sickling and osmotic fragility

Ovarian steroids appear to influence the manifestations of sickle cell disease (SCD); oestrogens can adversely affect erythrocyte function, whereas progestogens may inhibit sickling and decrease the osmotic fragility of erythrocytes. The aims of the present studies were: (i) to characterise the binding of oestradiol and progesterone to erythrocytes from women with HbSS, HbSC and HbAA genotypes; (ii) to investigate whether steroids modulate susceptibility to sickling or osmotic fragility of HbSS and HbAA erythrocytes. Erythrocytes were incubated for 1 h with [ 3 H ]-steroids at 4 and 37 °C. Binding of both oestradiol and progesterone was independent of temperature and steroid concentration, but was decreased by sequential “washing” of erythrocytes in fresh incubation buffer. Binding capacity was 80±6% greater for oestradiol (versus progesterone) in all three genotypes, and binding of both steroids was decreased by ≥70% in HbSS erythrocytes compared to HbSC or HbAA erythrocytes. Pre-incubation of erythrocytes with 35 μM oestradiol or 30 μM progesterone had no significant effect on susceptibility of HbSS and HbAA erythrocytes to sickling, or on osmotic fragility. We conclude that both oestradiol and progesterone bind in a low affinity, non-saturable manner to erythrocytes with decreased binding in cells from women with HbSS. However, steroid binding does not affect susceptibility to sickling or osmotic fragility irrespective of haemoglobin genotype.

Priapism in sickle-cell disease; incidence, risk factors and complications - an international multicentre study.

To define the incidence, risk factors and complications of priapism in a large population of patients with sickle-cell anaemia in five centres in the UK and Nigeria, as priapism is common among these patients, but the precise characteristics of the condition in this population are poorly documented. A questionnaire was developed and administered to patients with sickle-cell disease. Questions were designed to define the incidence, nature, precipitants, duration, treatment and complications of priapism. A distinction was made between acute (severe) priapism and the recurrent, 'stuttering' type. The questionnaire was completed by 130 patients (mean age 25 years, sd 11, range 4-66) from the five centres; 102 (78%) were homozygous Hb SS genotype, 19 (15%) were Hb SC genotype and two (1.5%) were Hb Salpha-thalassaemia. Of the patients, 46 (35%) reported a history of priapism, and of these, 33 (72%) had a history of stuttering priapism, while 24 (52%) had had an acute episode of priapism. The mean age of onset of priapism was 15 years, with 75% of patients having the first episode before their 20th birthday. Sexual activity was the most frequent precipitating factor, with fever and/or dehydration being the next most common. Of the 46 patients, 10 (21%) with a history of priapism reported having erectile dysfunction. A similar proportion reported dissatisfaction with sexual intercourse, including a fear of engaging in sexual activity. The incidence of priapism among patients with sickle-cell anaemia is high (35%). The implications of priapism for erectile and sexual function are significant and documented in this large series. The treatment of this condition in these patients remains unstandardised. This study highlights the need for an increased awareness of the problems associated with priapism among patients, families and medical professionals.

Haemoglobin C protects against clinical Plasmodium falciparum malaria.

Haemoglobin C (HbC; beta6Glu --> Lys) is common in malarious areas of West Africa, especially in Burkina Faso. Conclusive evidence exists on the protective role against severe malaria of haemoglobin S (HbS; beta6Glu --> Val) heterozygosity, whereas conflicting results for the HbC trait have been reported and no epidemiological data exist on the possible role of the HbCC genotype. In vitro studies suggested that HbCC erythrocytes fail to support the growth of P. falciparum but HbC homozygotes with high P. falciparum parasitaemias have been observed. Here we show, in a large case-control study performed in Burkina Faso on 4,348 Mossi subjects, that HbC is associated with a 29% reduction in risk of clinical malaria in HbAC heterozygotes (P = 0.0008) and of 93% in HbCC homozygotes (P = 0.0011). These findings, together with the limited pathology of HbAC and HbCC compared to the severely disadvantaged HbSS and HbSC genotypes and the low betaS gene frequency in the geographic epicentre of betaC, support the hypothesis that, in the long term and in the absence of malaria control, HbC would replace HbS in central West Africa.

Studies in the compartmentalization of trace elements in the blood of patients with sickle cell anaemia using PIXE technique

Concentrations of trace elements in the whole blood, plasma and erythrocytes of 77 individuals (20 carrying the HbSS genotype, 21 with HbAS and 36 with HbAA) were determined using a PIXE facility employing a 2 MeV proton beam. Up to 16 elements were detected in some or all of the samples. The skewness of elemental distribution was measured for each element in the three bloodflow compartments. Most of the essential elements, apart from selenium were distinctly packed in either the erythrocytes or the plasma. Results of the t-test employed to compare elemental values between sickle cell subjects and matched controls show similar patterns in the three compartments for some of the elements. The results are compared with previous work using INAA.

Whole body protein turnover and resting metabolic rate in homozygous sickle cell disease.

1. Whole body protein turnover and resting metabolic rate were measured in six adults with homozygous sickle cell disease (genotype HbSS) and in six normal adults (genotype HbAA) of similar age. 2. Turnover was measured with prime/intermittent oral doses of [15N]glycine over 18 h and resting energy expenditure was measured by indirect calorimetry. 3. In HbSS, nitrogen flux (0.9 +/- 0.08 g day-1), protein synthesis (6.0 +/- 0.5 g day-1 kg-1) and protein degradation (5.6 +/- 0.5 g day-1 kg-1) were significantly increased compared with HbAA nitrogen (flux 0.5 +/- 0.02 g day-1 kg-1, protein synthesis 3.2 +/- 0.2 g day-1 kg-1 and protein degradation 2.8 +/- 0.2 g day-1 kg-1). 4. Resting energy expenditure was significantly higher in HbSS compared with HbAA when expressed per unit of body weight (115 +/- 3 and 94 +/- 4 kJ day-1 kg-1, respectively) or weight 0.75(317 +/- 6 and 269 +/- 8 kJ day-1 kg-0.75, respectively). 5. The increase in protein turnover and energy expenditure suggest that patients with HbSS exist in a hypermetabolic state that requires greater dietary energy compared with HbAA.

Erythrocyte density distribution in sickle cell anemia.

Density distributions were determined for sickle cell erythrocytes from 27 patients with HbSS genotype using the phthalate ester microcapillary differential flotation method of Danon and Marikovsky. Mean density distribution curves showed HbSS erythrocytes to have trimodal populations with significant increases in both dense and light cell fractions when compared to 20 normal controls of HbAA genotype (p less than 0.05). Irreversibly sickled cell (ISC) and reticulocyte counts were compared with density distributions. Integrated unit areas under the dense cell population curves correlated with ISC percentages, while corresponding unit areas for light populations correlated to a lesser extent with reticulocyte percentages. Mean cell density, D50, varied widely among patients and correlated poorly with the ISC or reticulocyte percentage; however, D50 did correlate with the net change in integrated unit areas. Several patients had repeated density distributions over a 2-year time period. All HbSS patients showed increased but variable dense cell fractions which could not be definitively correlated with the clinical state of the patient. Transfusion reproducibly resulted in a lowering of the dense cell fraction. Erythrocytes from the HbSC patients showed a uniform increase in density and absence of the large dense cell fraction seen in most HbSS patients. This method provides a simple means for quantitation of the light and dense cell fraction in blood of patients with sickling disorders and displays the profile of erythrocyte density heterogeneity for the individual sickle cell patient.

Admissions to hospital of children with sickle-cell anaemia: a study in south London.

Admissions to hospital of 171 children with sickle-cell anaemia, genotype Hb SS, were reviewed over a 20-year period. Altogether 887 admissions occurred in 797 patient-years. The commonest cause of admission was painful vaso-occlusive crisis. Appreciable morbidity also resulted from pulmonary disease, infection, and anaemic episodes. The complications resulting in the most severe illness were acute splenic sequestration, pneumococcal meningitis, and some episodes of erythroid hypoplasia resulting in very low haemoglobin concentrations. Most deaths occurred in children aged under 5. Mortality and morbidity could be reduced by measures including prophylaxis of pneumococcal infections and more active treatment of seemingly minor illness in children with sickle-cell anaemia.