Acute Free-Iron Exposure Does Not Explain the Impaired Haemorheology Associated with Haemochromatosis

A Matched-Cohort Analysis of Outcomes in Patients with Hereditary Hemochromatosis After Anterior Cervical Discectomy and Fusion

BACKGROUND

Hereditary hemochromatosis (HH) is a common autosomal recessive disorder. This disease affects gut iron transport, leading to iron overload, which affects immune function, coagulation mechanics, and bone health. Within the spine, HH contributes to decreased bone mineral density and accelerated intervertebral disc degeneration. The purpose of this study was to discover the differences in the rates of common 90-day postoperative complications and 1-year and 2-year surgical outcomes in patients with and without HH after anterior cervical discectomy and fusion (ACDF).

METHODS

Using the PearlDiver database, patients with active diagnoses of HH before ACDF were matched to patients without HH using a 1:5 ratio on the basis of age, sex, body mass index, and comorbidities. Postoperative complications were assessed at 90 days, and 1-year and 2-year surgical outcomes were assessed. All outcomes and complications were analyzed using multivariate logistic regression with significance achieved at P < 0.05.

RESULTS

Patients with HH had significantly higher rates of 1-year and 2-year reoperation rates compared with patients without HH (29.19% vs. 3.94% and 37.1% vs. 5.93%, respectively; P < 0.001). The rates of 90-day postoperative complications significantly increased in patients with HH including dysphagia, pneumonia, cerebrovascular accident, deep vein thrombosis, acute kidney injury, urinary tract infection, hyponatremia, surgical site infection, iatrogenic deformity, emergency department visit, and hospital readmission.

CONCLUSIONS

Patients with HH undergoing ACDF showed increased 90-day postoperative complications and significantly increased rates of 1-year and 2-year reoperation compared with patients without HH. These findings suggest that iron overload may contribute to adverse outcomes in patients with HH undergoing 1-level and 2-level ACDF.

Blood donation for iron removal in individuals with HFE mutations: study of efficacy and safety and short review on hemochromatosis and blood donation

Background

Elevated serum ferritin with/without HFE variants in asymptomatic persons leads frequently to referral for blood donation. Hemochromatosis (p.C282Y/p.C282Y) only requires treatment. We evaluated safety and feasibility of iron removal in healthy persons with elevated ferritin and HFE variants using blood donation procedures.

Materials and methods

Thirty subjects with ferritin >200 ng/mL (women) or >300 ng/mL (men) with p.C282Y/p.C282Y, p.C282Y/p.H63D or p.H63D/p.H63D were randomized to weekly phlebotomy (removal of 450 mL whole blood) or erythrapheresis (removal of 360 mL red blood cells) every 14 days. The ferritin target was <100 ng/mL. A full blood count and ferritin were measured at each visit. Hemoglobin (Hb) ≥140 g/L was required at inclusion. If Hb dropped to <120 g/L (women) or <130 g/L (men), procedures were postponed (7 or 14 days). Primary endpoint was the number of procedures needed to the ferritin target; secondary objectives were duration of treatment and compliance. The treatment effect was tested with Poisson regression; number of procedures and treatment duration were compared between study arms with the Kruskal-Wallis test.

Results

Twenty-five of 30 participants were men (83%); mean age was 47 years (SD 10.5), mean BMI 26.6 kg/m2 (SD 3.6); 17 had p.C282Y/p.C282Y, nine p.C282Y/p.H63D, four p.H63D/p.H63D. Median baseline Hb was 150 g/L (IQR 144, 1,559), median ferritin 504 ng/mL (IQR 406,620). Twenty-seven subjects completed the study. Treatment arm (p < 0.001) and HFE variant (p = 0.007) influenced the primary endpoint significantly. To ferritin levels <100 ng/mL, a median number of 7.5 (IQR 6.2, 9.8) phlebotomies and 4.0 (IQR 3.0, 5.8) erythraphereses (p = 0.001) was needed during a median of 66.5 days (IQR 49,103) and 78.5 days (IQR 46139), respectively (p = 0.448). Low Hb was the principal reason for protocol violation; anemia occurred in 13 participants (48%). Immediate complications were infrequent; fatigue was reported after 25% of phlebotomies and 45% of erythraphereses. Thirty-five procedures were postponed because of low Hb and 15 for non-medical reasons. The median interval was 7.0 (IQR 7.7) and 14.0 (IQR 14, 20) days between phlebotomies and erythraphereses, respectively.

Conclusion

Blood donation procedures remove iron effectively in HC, but frequent treatments cause Hb decrease and fatigue that can impair feasibility.

Red blood cell sublethal damage: haemocompatibility is not the absence of haemolysis

Blood is a complex fluid owing to its two-phase suspension of formed cellular elements within a protein-rich plasma. Vital to its role in distributing nutrients throughout the circulatory system, the mechanical properties of blood - and particularly red blood cells (RBC)-primarily determine bulk flow characteristics and microcirculatory flux. Various factors impair the physical properties of RBC, including cellular senescence, many diseases, and exposure to mechanical forces. Indeed, the latter is increasingly relevant following the advent of modern life support, such as mechanical circulatory support (MCS), which induce unique interactions between blood and artificial environments that leave blood cells with the signature of aging, albeit accelerated, and crucially underlie various serious complications, including death. Accumulating evidence indicates that these complications appear to be associated with mechanical shear forces present within MCS that are not extreme enough to overtly rupture cells, yet may still induce "sublethal" injury and "fatigue" to vital blood constituents. Impaired RBC physical properties following elevated shear exposure-a hallmark of sublethal injury to blood-are notable and may explain, at least in part, systemic complications and premature mortality associated with MCS. Design of optimal next-generation MCS devices thus requires consideration of biocompatibility and blood-device interactions to minimize potential blood complications and promote clinical success. Presented herein is a contemporary understanding of "blood damage," with emphasis on shear exposures that alter microrheological function but do not overtly destroy cells (ie, sublethal damage). Identification of key cellular factors perturbed by supraphysiological shear exposure are examined, offering potential pathways to enhance design of MCS and blood-contacting medical devices.

Metabolic Influences Modulating Erythrocyte Deformability and Eryptosis

Many factors in the surrounding environment have been reported to influence erythrocyte deformability. It is likely that some influences represent reversible changes in erythrocyte rigidity that may be involved in physiological regulation, while others represent the early stages of eryptosis, i.e., the red cell self-programmed death. For example, erythrocyte rigidification during exercise is probably a reversible physiological mechanism, while the alterations of red blood cells (RBCs) observed in pathological conditions (inflammation, type 2 diabetes, and sickle-cell disease) are more likely to lead to eryptosis. The splenic clearance of rigid erythrocytes is the major regulator of RBC deformability. The physicochemical characteristics of the surrounding environment (thermal injury, pH, osmolality, oxidative stress, and plasma protein profile) also play a major role. However, there are many other factors that influence RBC deformability and eryptosis. In this comprehensive review, we discuss the various elements and circulating molecules that might influence RBCs and modify their deformability: purinergic signaling, gasotransmitters such as nitric oxide (NO), divalent cations (magnesium, zinc, and Fe2+), lactate, ketone bodies, blood lipids, and several circulating hormones. Meal composition (caloric and carbohydrate intake) also modifies RBC deformability. Therefore, RBC deformability appears to be under the influence of many factors. This suggests that several homeostatic regulatory loops adapt the red cell rigidity to the physiological conditions in order to cope with the need for oxygen or fuel delivery to tissues. Furthermore, many conditions appear to irreversibly damage red cells, resulting in their destruction and removal from the blood. These two categories of modifications to erythrocyte deformability should thus be differentiated.

Impact of small fractions of abnormal erythrocytes on blood rheology

Red blood cell (RBC) populations are inherently heterogeneous, given mature RBC lack the transcriptional machinery to re-synthesize proteins affected during in vivo aging. Clearance of older, less functional cells thus aids in maintaining consistent hemorheological properties. Scenarios occur, however, where portions of mechanically impaired RBC are re-introduced into blood (e.g., damaged from circulatory support, blood transfusion) and may alter whole blood fluid behavior. Given such perturbations are associated with poor clinical outcomes, determining the tolerable level of abnormal RBC in blood is valuable. Thus, the current study aimed to define the critical threshold of blood fluid properties to re-infused physically-impaired RBC. Cell mechanics of RBC were impaired through membrane cross-linking (glutaraldehyde) or intracellular oxidation (phenazine methosulfate). Mechanically impaired RBC were progressively re-introduced into the native cell population. Negative alterations of cellular deformability and high shear blood viscosity were observed following additions of only 1-5% rigidified RBC. Low-shear blood viscosity was conversely decreased following addition of glutaraldehyde-treated cells; high-resolution microscopy of these mixed cell populations revealed decreased capacity to form reversible aggregates and decreased aggregate size. Mixed RBC populations, when exposed to supraphysiological shear, presented with compounded mechanical impairment. Collectively, key determinants of blood flow behavior are sensitive to mechanical perturbations in RBC, even when only 1-5% of the cell population is affected. Given this fraction is well-below the volume of rigidified RBC introduced during circulatory support or transfusion practice, it is plausible that some adverse events following surgery and/or transfusion may be related to impaired blood fluidity.

Hemochromatosis alters the sensitivity of red blood cells to mechanical stress

BACKGROUND

Hemochromatosis (HH) is characterized by chronic iron accumulation, leading to deleterious effects to various organ systems. A common approach to managing iron load involves large-volume venesection. Some countries authorize HH venesections to be used in the development of transfusable blood products, although concerns remain regarding suitability. Due to the high oxidative load associated with hyperferritinemia, it has been proposed that HH blood products may be susceptible to mechanical damage. This is particularly relevant given that typical blood product destinations (eg, transfusion, cardiopulmonary bypass) expose blood to supraphysiologic levels of mechanical stress. We sought to explore the mechanical tolerance of red blood cells (RBC) derived from HH venesections to varied magnitudes and durations of sublethal shear stress.

STUDY DESIGN AND METHODS

Initially, 110 individuals with HH were recruited; to eliminate the effects of comorbidities, only those who were untreated and uncomplicated were included for comparisons with age-matched healthy controls (Con). RBC were exposed to 25 discrete magnitudes (1-64 Pa) and durations (1-64 seconds) of shear stress. Cellular deformability was assessed before, and immediately after, each shear exposure.

RESULTS

In the absence of prior shear exposure, RBC deformability of HH was significantly decreased by 11.5%, compared with Con. For both HH and Con, supraphysiologic shear exposure significantly impaired RBC deformability, although the rate and magnitude of deterioration were elevated for HH.

CONCLUSION

Given that blood products are commonly exposed to high-shear environments (eg, during high-volume transfusion), venesections from asymptomatic and untreated individuals with HH appear suboptimal for the development of therapeutic RBCs.

Mechanical sensitivity of red blood cells improves in individuals with hemochromatosis following venesection therapy

BACKGROUND

Individuals with hereditary hemochromatosis (HH) receive frequent blood withdrawals (ie, venesections) as part of their primary treatment to assist in normalizing blood iron levels. It remains unclear whether this source of blood is suitable for use in blood product development, as current data indicate that red blood cell (RBC) deformability, both before and after shear stress exposure, is impaired in individuals with HH, relative to healthy controls. Given that venesection therapy is known to significantly reduce circulating iron levels in individuals with HH, the current study examined whether venesection therapy is effective at improving RBC mechanical properties, both before and after shear stress exposure, in individuals with HH.

STUDY DESIGN AND METHODS

Blood samples were initially collected from untreated HH patients (age, 61 ± 9 years; 14% female) undergoing their first venesection, and then again during their second (approx. 9 weeks later) and third (approx. 16 weeks later) venesections. RBC deformability was measured at each time point with a commercial ektacytometer. Moreover, to determine cell responses to mechanical stimuli, the mechanical sensitivity of blood samples was determined at each time point.

RESULTS

The salient findings indicate that venesection therapy used for managing plasma ferritin concentration significantly improves the cellular deformability of RBC in individuals with HH. Further, the sensitivity of RBC to supraphysiological mechanical stress is decreased (ie, improved) in a dose-response fashion with routine venesection.

CONCLUSION

While cellular mechanics of RBC from individuals with HH are impaired when untreated, venesection therapy significantly improves cellular properties of RBC, supporting the use of venesections in blood product development from individuals with well-managed HH.

Beyond oxygen transport: active role of erythrocytes in the regulation of blood flow

It was classically thought that the function of mammalian red blood cells (RBCs) was limited to serving as a vehicle for oxygen, given the cells' abundance of cytosolic hemoglobin. Over the past decades, however, accumulating evidence indicates that RBCs have the capacity to sense low-oxygen tensions in hypoxic tissues, and, subsequently, release signaling molecules that influence the distribution of blood flow. The precise mechanisms that facilitate RBC modulation of blood flow are still being elucidated, although recent evidence indicates involvement of 1) adenosine triphosphate, capable of binding to purinergic receptors located on the vascular wall before initiating nitric oxide (NO; a powerful vasodilator) production in endothelial cells, and/or 2) nonvascular NO, which is now known to have several modes of production within RBCs, including an enzymatic process via a unique isoform of NO synthase (i.e., RBC-NOS), which has potential effects on the vascular smooth muscle. The physical properties of RBCs, including their tendency to form three-dimensional structures in low shear flow (i.e., aggregation) and their capacity to elongate in high shear flow (i.e., deformability), are only recently being viewed as mechanotransductive processes, with profound effects on vascular reactivity and tissue perfusion. Recent developments in intracellular signaling in RBCs, and the subsequent effects on the mechanical properties of blood, and blood flow, thus present a vivid expansion on the classic perspective of these abundant cells.

Red blood cell tolerance to shear stress above and below the subhemolytic threshold

Mechanical circulatory support device (MCS) design has improved over the years and yet blood damage (e.g., hemolysis) remains a problem. Accumulating evidence indicates a subhemolytic threshold for red blood cells (RBC)-a threshold at which RBC deformability is impaired prior to hemolysis. The current study aimed to assess the deformability of RBC exposed to supra-physiological shear stresses that are typical of MCS devices and assess whether a method used to estimate an individualized subhemolytic threshold, accurately demarcates whether future application of shear stress was damaging. Suspensions of RBC were "conditioned" with discrete magnitudes of shear stress (5-100 Pa) for specific durations (1-16 s). Cellular deformability was subsequently measured via ektacytometry and a mechanical sensitivity (MS) index was calculated to identify the subhemolytic threshold. Thereafter, fresh RBC suspensions were exposed to a magnitude of shear stress 10 Pa above, 10 Pa below, or matched to a donor's previously estimated subhemolytic threshold for a given duration (1, 4, 16 s) to ascertain the sensitivity of the subhemolytic threshold. The MS index of RBC was significantly impaired following exposure to 10 Pa above the subhemolytic threshold (p < 0.0001), and significantly enhanced following exposure to 10 Pa below the subhemolytic threshold (p < 0.01). For all shear conditions, there was no significant increase in free hemoglobin. Functional assessments of RBC may be useful when conducting biocompatibility testing of MCS devices, to detect trauma to blood prior to overt cell rupture being induced.

Blood rheology as a mirror of endocrine and metabolic homeostasis in health and disease1

Rheological properties of plasma and blood cells are markedly influenced by the surrounding milieu: physicochemical factors, metabolism and hormones. Acid/base status, osmolality, lipid status, plasma protein pattern, oxidative stress induced by increased free radicals production, endothelium-derived factors such as nitric oxide (NO), achidonic acid derivatives modulate both red blood cell (RBC) and white cell mechanics. Therefore, regulatory axes involving liver, endothelium, kidney, pancreas, adrenal gland, endocrine heart, adipose tissue, pituitary gland, and surely other tissues play important roles in the regulation of blood fluidity. A comprehensive picture of all this complex network of regulatory loops is still unavailable but current progress of knowledge suggest that some attempts can currently be made.

Prediction of the level and duration of shear stress exposure that induces subhemolytic damage to erythrocytes

BACKGROUND

Current generation mechanical circulatory assist devices are designed to minimize high shears to blood for prolonged durations to avoid hemolysis. However, red blood cells (RBC) demonstrate impaired capacity to deform when exposed to shear stress (SS) well below the "hemolytic threshold".

OBJECTIVE

We endeavored to identify how changes in the magnitude and duration of SS exposure alter RBC deformability and subsequently develop a model to predict erythrocyte subhemolytic damage.

METHODS

RBC suspensions were exposed to discrete magnitudes of SS (1-64 Pa) for specific durations (1-64 s), immediately prior to RBC deformability being measured. Analyses included exploring the maximal RBC deformation (EImax) and SS required for half EImax (SS1/2). A surface-mesh was interpolated onto the raw data to predict impaired RBC deformability.

RESULTS

When SS was applied at <16Pa, limited changes were observed. When RBC were exposed to 32 Pa, mild impairments in EImax and SS1/2 occurred, although 64 Pa caused a dramatic impairment of RBC deformability. A clear relation between SS duration and magnitude was determined, which could predict impaired RBC deformability.

CONCLUSION

The present results provide a model that may be used to predict whether RBC deformability is decreased following exposure to a given level and duration of SS, and may guide design of future generations of mechanical circulatory assist devices.