Evaluation of red blood cell labelling methods based on a statistical model for red blood cell survival

The Chemical Scaffold of Theranostic Radiopharmaceuticals: Radionuclide, Bifunctional Chelator, and Pharmacokinetics Modifying Linker

Therapeutic radiopharmaceuticals have been researched extensively in the last decade as a result of the growing research interest in personalized medicine to improve diagnostic accuracy and intensify intensive therapy while limiting side effects. Radiometal-based drugs are of substantial interest because of their greater versatility for clinical translation compared to non-metal radionuclides. This paper comprehensively discusses various components commonly used as chemical scaffolds to build radiopharmaceutical agents, i.e., radionuclides, pharmacokinetic-modifying linkers, and chelators, whose characteristics are explained and can be used as a guide for the researcher.

Modelling haemoglobin incremental loss on chronic red blood cell transfusions

BACKGROUND AND OBJECTIVES

Understanding the impact of red blood cell (RBC) lifespan, initial RBC removal, and transfusion intervals on patient haemoglobin (Hb) levels and total iron exposure is not accessible for chronic transfusion scenarios. This article introduces the first model to help clinicians optimize chronic transfusion intervals to minimize transfusion frequency.

MATERIALS AND METHODS

Hb levels and iron exposure from multiple transfusions were calculated from Weibull residual lifespan distributions, the fraction effete RBC removed within 24-h (X_e ) and the nominal Hb increment. Two-unit transfusions of RBCs initiated at patient [Hb] = 7 g/dl were modelled for different RBC lifespans and transfusion intervals from 18 to 90 days, and X_e from 0.1 to 0.5.

RESULTS

Increased X_e requires shorter transfusion intervals to achieve steady-state [Hb] of 9 g/dl as follows: 30 days between transfusions at X_e  = 0.5, 36 days at X_e  = 0.4, 42 days at X_e  = 0.3, 48 days at X_e  = 0.2 and 54 days at X_e  = 0.1. The same transfusion interval/X_e pairs result in a steady-state [Hb] = 8 g/dl when the RBC lifespan was halved. By reducing transfused RBC increment loss from 30% to 10%, annual transfusions were decreased by 22% with iron addition decreased by 24%. Acute dosing of iron occurs at the higher values of X_e on the day after a transfusion event.

CONCLUSION

Systematic trends in fractional Hb incremental loss X_e have been modelled and have a significant and calculatable impact on transfusion intervals and associated introduction of iron.

Lysophosphatidic Acid-Activated Calcium Signaling Is Elevated in Red Cells from Sickle Cell Disease Patients

(1) Background: It is known that sickle cells contain a higher amount of Ca2+ compared to healthy red blood cells (RBCs). The increased Ca2+ is associated with the most severe symptom of sickle cell disease (SCD), the vaso-occlusive crisis (VOC). The Ca2+ entry pathway received the name of Psickle but its molecular identity remains only partly resolved. We aimed to map the involved Ca2+ signaling to provide putative pharmacological targets for treatment. (2) Methods: The main technique applied was Ca2+ imaging of RBCs from healthy donors, SCD patients and a number of transgenic mouse models in comparison to wild-type mice. Life-cell Ca2+ imaging was applied to monitor responses to pharmacological targeting of the elements of signaling cascades. Infection as a trigger of VOC was imitated by stimulation of RBCs with lysophosphatidic acid (LPA). These measurements were complemented with biochemical assays. (3) Results: Ca2+ entry into SCD RBCs in response to LPA stimulation exceeded that of healthy donors. LPA receptor 4 levels were increased in SCD RBCs. Their activation was followed by the activation of Gi protein, which in turn triggered opening of TRPC6 and CaV2.1 channels via a protein kinase Cα and a MAP kinase pathway, respectively. (4) Conclusions: We found a new Ca2+ signaling cascade that is increased in SCD patients and identified new pharmacological targets that might be promising in addressing the most severe symptom of SCD, the VOC.

Shortened red blood cell age in patients with end-stage renal disease who were receiving haemodialysis: a cross-sectional study

Background

The causes of anaemia in patients with end-stage renal disease include a relative deficiency in erythropoietin production and complex clinical conditions. We aimed to investigate the underlying mechanisms of anaemia in patients with end-stage renal disease who were undergoing maintenance dialysis by measuring erythrocyte creatine levels.

Methods

In a cross-sectional study, we evaluated 69 patients with end-stage renal disease who were receiving haemodialysis (n = 55) or peritoneal dialysis (n = 14). Erythrocyte creatine level, a quantitative marker of mean red blood cell (RBC) age, was measured.

Results

The mean RBC age was significantly shorter in the haemodialysis group than in the peritoneal dialysis group (47.7 days vs. 59.8 days, p < 0.0001), although the haemoglobin levels were comparable between the groups. A Spearman correlation coefficient analysis revealed that shortened RBC age positively correlated with transferrin saturation (r = 0.54), ferritin level (r = 0.47), and haptoglobin level (r = 0.39) but inversely related with reticulocyte (r = − 0.36), weekly doses of erythropoiesis-stimulating agents (ESAs; r = − 0.62), erythropoietin resistance index (r = − 0.64), and intradialytic ultrafiltration rate (r = − 0.32).

Conclusions

Shortened RBC age was observed in patients who were receiving maintenance haemodialysis and was associated with iron deficiency, greater haptoglobin consumption, higher ESA requirements, and poor erythropoietin responsiveness, as well as with greater intradialytic fluid extraction.

Understanding quasi-apoptosis of the most numerous enucleated components of blood needs detailed molecular autopsy

Erythrocytes are the most numerous cells in human body and their function of oxygen transport is pivotal to human physiology. However, being enucleated, they are often referred to as a sac of molecules and their cellularity is challenged. Interestingly, their programmed death stands a testimony to their cell-hood. They are capable of self-execution after a defined life span by both cell-specific mechanism and that resembling the cytoplasmic events in apoptosis of nucleated cells. Since the execution process lacks the nuclear and mitochondrial events in apoptosis, it has been referred to as quasi-apoptosis or eryptosis. Several studies on molecular mechanisms underlying death of erythrocytes have been reported. The data has generated a non-cohesive sketch of the process. The lacunae in the present knowledge need to be filled to gain deeper insight into the mechanism of physiological ageing and death of erythrocytes, as well as the effect of age of organism on RBCs survival. This would entail how the most numerous cells in the human body die and enable a better understanding of signaling mechanisms of their senescence and premature eryptosis observed in individuals of advanced age.

Age-structured population model of cell survival

Age-structured cell population model was introduced to describe cell survival. The impact of the environment on the cell population is represented by drug plasma concentration. A key model variable is the hazard of cell removal that is a subject to the environment effect. The model is capable of describing cohort and random labeling cell survival data. In addition, it accounts for cell loss due to labeling of cell sample, but it lacks ability to describe the effect of label elution on the survival data. The model was applied to red blood cell (RBC) survival data in two groups of Wistar rats obtained by two techniques: cohort labeling using ¹⁴C-glycine (N = 4) and random labeling using biotin (N = 8). The Weibull probability density function was selected for the RBC lifespan distribution. The data were simultaneously fitted by the mixed effects model implemented in Monolix 4.3.3. The estimated typical values of RBC lifespan and age were 53.7 and 27.8 days, respectively. A noticeable effect of biotinylation on RBC survival was observed that resulted in a significant difference between the means of individual RBC lifespan for two groups. The model provides a mechanistic framework flexible enough to account for various experimental designs to generate the cell survival data. Despite model qualification using animal data, the model has the same potential to be applied to cell survival data analysis in humans.

Characterization of Anti-Dal Alloantibodies Following Sensitization of Two Dal-Negative Dogs

Since its discovery, the immunogenicity of the Dal blood type has not been further investigated. The aim of this study was to better characterize anti- Dal alloantibodies produced following sensitization of Dal-negative dogs, notably their rate of appearance, the agglutination titer over time, and their immunoglobulin class. A secondary objective was to obtain polyclonal anti- Dal alloantibodies to increase the availability of Dal blood typing. Of 100 healthy laboratory Beagles tested, 2 Dal-negative dogs were identified as recipients. Ten healthy Dal-positive dogs were investigated as potential blood donors. All dogs were extensively blood typed for DEA 1, 3, 4, 5, and 7, as well as for Dal. Then, the recipients were transfused uneventfully with 10 ml/kg of Dal-positive but otherwise compatible packed red blood cells. Posttransfusion blood samples were collected routinely over a minimum of 1 year. Using a gel column technology, anti- Dal alloantibodies were detected as early as 4 days posttransfusion and remained detectable 2 years posttransfusion, with maximum agglutination titers reached at 1 and 2 months posttransfusion. The immunoglobulin class was IgG. The immunogenicity and clinical significance of the Dal blood type were confirmed. The results support the recommendations that previously transfused dogs be crossmatched starting 4 days posttransfusion and for the animal’s lifetime. The polyclonal anti- Dal antibodies produced will allow blood typing of a significant number of dogs, especially transfused dogs facing blood incompatibilities and canine blood donors.

Mathematical modeling of erythrocyte chimerism informs genetic intervention strategies for sickle cell disease

Recent advances in gene therapy and genome-engineering technologies offer the opportunity to correct sickle cell disease (SCD), a heritable disorder caused by a point mutation in the β-globin gene. The developmental switch from fetal γ-globin to adult β-globin is governed in part by the transcription factor (TF) BCL11A. This TF has been proposed as a therapeutic target for reactivation of γ-globin and concomitant reduction of β-sickle globin. In this and other approaches, genetic alteration of a portion of the hematopoietic stem cell (HSC) compartment leads to a mixture of sickling and corrected red blood cells (RBCs) in periphery. To reverse the sickling phenotype, a certain proportion of corrected RBCs is necessary; the degree of HSC alteration required to achieve a desired fraction of corrected RBCs remains unknown. To address this issue, we developed a mathematical model describing aging and survival of sickle-susceptible and normal RBCs; the former can have a selective survival advantage leading to their overrepresentation. We identified the level of bone marrow chimerism required for successful stem cell-based gene therapies in SCD. Our findings were further informed using an experimental mouse model, where we transplanted mixtures of Berkeley SCD and normal murine bone marrow cells to establish chimeric grafts in murine hosts. Our integrative theoretical and experimental approach identifies the target frequency of HSC alterations required for effective treatment of sickling syndromes in humans. Our work replaces episodic observations of such target frequencies with a mathematical modeling framework that covers a large and continuous spectrum of chimerism conditions. Am. J. Hematol. 91:931-937, 2016. © 2016 Wiley Periodicals, Inc.

Models for the red blood cell lifespan

The lifespan of red blood cells (RBCs) plays an important role in the study and interpretation of various clinical conditions. Yet, confusion about the meanings of fundamental terms related to cell survival and their quantification still exists in the literature. To address these issues, we started from a compartmental model of RBC populations based on an arbitrary full lifespan distribution, carefully defined the residual lifespan, current age, and excess lifespan of the RBC population, and then derived the distributions of these parameters. For a set of residual survival data from biotin-labeled RBCs, we fit models based on Weibull, gamma, and lognormal distributions, using nonlinear mixed effects modeling and parametric bootstrapping. From the estimated Weibull, gamma, and lognormal parameters we computed the respective population mean full lifespans (95 % confidence interval): 115.60 (109.17-121.66), 116.71 (110.81-122.51), and 116.79 (111.23-122.75) days together with the standard deviations of the full lifespans: 24.77 (20.82-28.81), 24.30 (20.53-28.33), and 24.19 (20.43-27.73). We then estimated the 95th percentiles of the lifespan distributions (a surrogate for the maximum lifespan): 153.95 (150.02-158.36), 159.51 (155.09-164.00), and 160.40 (156.00-165.58) days, the mean current ages (or the mean residual lifespans): 60.45 (58.18-62.85), 60.82 (58.77-63.33), and 57.26 (54.33-60.61) days, and the residual half-lives: 57.97 (54.96-60.90), 58.36 (55.45-61.26), and 58.40 (55.62-61.37) days, for the Weibull, gamma, and lognormal models respectively. Corresponding estimates were obtained for the individual subjects. The three models provide equally excellent goodness-of-fit, reliable estimation, and physiologically plausible values of the directly interpretable RBC survival parameters.

Distributed transit compartments for arbitrary lifespan distributions in aging populations

Transit compartment models (TCM) are often used to describe aging populations where every individual has its own lifespan. However, in the TCM approach these lifespans are gamma-distributed which is a serious limitation because often the Weibull or more complex distributions are realistic. Therefore, we extend the TCM concept to approximately describe any lifespan distribution and call this generalized concept distributed transit compartment models (DTCMs). The validity of DTCMs is obtained by convergence investigations. From the mechanistic perspective the transit rates are directly controlled by the lifespan distribution. Further, DTCMs could be used to approximate the convolution of a signal with a probability density function. As example a stimulatory effect of a drug in an aging population with a Weibull-distributed lifespan is presented where distribution and model parameters are estimated based on simulated data.

A semi-mechanistic red blood cell survival model provides some insight into red blood cell destruction mechanisms

Most mathematical models developed for the survival of haematological cell populations, in particular red blood cells (RBCs), follow the principle of parsimony. They focus on the predominant destruction mechanism of age-related cell death (senescence) and do not account for within subject variability in the RBC lifespan. However, assessment of the underlying physiological destruction mechanisms can be of interest in pathological conditions that affect RBC survival, for example sickle cell anaemia or anaemia of chronic kidney disease. We have previously proposed a semi-mechanistic RBC survival model which accounts for four different types of RBC destruction mechanisms. In this work, it is shown that the proposed model in combination with informative RBC survival data is able to provide a deeper insight into RBC destruction mechanisms. The proposed model was applied in a non-linear mixed effect modelling framework to biotin derived RBC survival data available from literature. Three mechanisms were estimable based on the available data of twelve subjects, including random destruction, senescence and destruction due to delayed failure. It was possible to identify three subjects with a decreased RBC survival in the study population. These three subjects all showed differences in the contribution of the estimated destruction mechanisms: an increased random destruction, versus an accelerated senescence, versus a combination of both.

Modeling red blood cell survival data

Anaemia of chronic kidney disease (CKD) is a common complication in patients with renal impairment, especially in end-stage renal failure. As well as erythropoietin deficiency, decreased red blood cell survival is a contributing factor. However, it remains unclear which mechanism underlies the altered survival of red blood cells (RBCs). In this work a previously developed statistical model for RBC survival was applied to clinical data obtained from 14 patients with CKD undergoing hemodialysis as well as 14 healthy controls using radioactive chromium (⁵¹Cr) as random labelling method. A classical two-stage approach and a full population analysis were applied to estimate the key parameters controlling random destruction and senescence in the model. Estimating random destruction was preferred over estimating an accelerated senescence in both approaches and both groups as it provided the better fit to the data. Due to significant nonspecific random loss of the label from the cells that cannot be quantified directly only a relative RBC survival can be obtained from data using ⁵¹Cr as labelling method. Nevertheless, RBC survival was found to be significantly reduced in CKD patients compared to the controls with a relative reduction of 20-30% depending on the analysis method used.