Clarence P. Alfrey

The negative regulation of red cell mass by neocytolysis: Physiologic and pathophysiologic manifestations

We have uncovered a physiologic process which negatively regulates the red cell mass by selectively hemolyzing young circulating red blood cells. This allows fine control of the number of circulating red blood cells under steady-state conditions and relatively rapid adaptation to new environments. Neocytolysis is initiated by a fall in erythropoietin levels, so this hormone remains the major regulator of red cell mass both with anemia and with red cell excess. Physiologic situations in which there is increased neocytolysis include the emergence of newborns from the hypoxic uterine environment and the descent of polycythemic high-altitude dwellers to sea level. The process first became apparent while investigating the mechanism of the anemia that invariably occurs after spaceflight. Astronauts experience acute central plethora on entering microgravity resulting in erythropoietin suppression and neocytolysis, but the reduced blood volume and red cell mass become suddenly maladaptive on re-entry to earth’s gravity. The pathologic erythropoietin deficiency of renal disease precipitates neocytolysis, which explains the prolongation of red cell survival consistently resulting from erythropoietin therapy and points to optimally efficient erythropoietin dosing schedules. Implications should extend to a number of other physiologic and pathologic situations including polycythemias, hemolytic anemias, ‘blood-doping’ by elite athletes, and oxygen therapy. It is likely that erythropoietin influences endothelial cells which in turn signal reticuloendothelial phagocytes to destroy or permit the survival of young red cells marked by surface molecules. Ongoing studies to identify the molecular targets and cytokine intermediaries should facilitate detection, dissection and eventual therapeutic manipulation of the process.

The hemostatic defect produced by carbenicillin.

Abstract Blood coagulation and platelet function were examined in 17 human volunteers receiving doses of 300, 400 or 600 mg per kilogram per day of carbenicillin. Platelet function was also investigated in five patients receiving carbenicillin for the treatment of gram-negative infection. In volunteers, plasma coagulation remained normal. However, defective platelet function was seen in all volunteers and patients. Eleven of 11 volunteers demonstrated abnormal adenosine-diphosphate-induced platelet aggregation; six of 11 demonstrated abnormal l-epinephrine-induced aggregation, and five of 11 abnormal collagen-induced aggregation; in 14 of 20 studies, there was prolongation of bleeding time; seven of 11 volunteers had reduced clot retraction; eight of 11 had decreased prothrombin consumption. Prolongation of bleeding time and defective clot retraction appeared to be dose dependent. Three volunteers given 600 mg per kilogram per day and two patients given 340 and 375 mg per kilogram per day, respectively, e...

Neocytolysis contributes to the anemia of renal disease.

Neocytolysis is a recently described physiological process affecting the selective hemolysis of young red blood cells in circumstances of plethora. Erythropoietin (EPO) depression appears to initiate the process, providing the rationale to investigate its contributions to the anemia of renal disease. When EPO therapy was withheld, four of five stable hemodialysis patients showed chromium 51 (51Cr)-red cell survival patterns indicative of neocytolysis; red cell survival was short in the first 9 days, then normalized. Two of these four patients received oral 13C-glycine and 15N-glycine, and there was a suggestion of pathological isotope enrichment of stool porphyrins when EPO therapy was held, again supporting selective hemolysis of newly released red cells that take up the isotope (one patient had chronic hemolysis indicated by isotope studies of blood and stool). Thus, neocytolysis can contribute to the anemia of renal disease and explain some unresolved issues about such anemia. One implication is the prediction that intravenous bolus EPO therapy is metabolically and economically inefficient compared with lower doses administered more frequently subcutaneously.

Study of the Effects of Ticarcillin on Blood Coagulation and Platelet Function

Ticarcillin is a new semisynthetic penicillin similar to carbenicillin. Since carbenicillin has been shown to inhibit platelet function to such an extent that bleeding may accompany its use, an investigation of the effects of ticarcillin on hemostasis was made. The drug was administered to 17 human volunteers for periods of 3 to 10 days in intravenous doses of 100, 200, or 300 mg/kg per day (7 to 21 g/day). Serial studies of blood coagulation and platelet function indicated that coagulation was unaffected by ticarcillin but that platelet function became defective in all subjects. Abnormal platelet function was evidenced by lengthening of bleeding time (17 of 17 volunteers), depressed adenosine diphosphate-induced platelet aggregation (17 of 17), defective collagen-induced aggregation (15 of 17), and abnormal epinephrine-induced aggregation (10 of 17). Prothrombin consumption, due to reduced platelet procoagulant activity, was significantly decreased with a dose of 300 mg/kg per day. Comparison of results from this study with those from an earlier carbenicillin study revealed that ticarcillin at 300 mg/kg per day produces the same defects in hemostasis as does carbenicillin at 300 mg/kg per day, but that lower doses (100 or 200 mg/kg per day) of ticarcillin result in only a mild defect in platelet function. If the effective dose of ticarcillin is proven to be lower than the doses of carbenicillin currently employed for treatment of certain gram-negative infections, bleeding should not be a frequent complication of ticarcillin administration, when the drug is given to patients with normal renal function.

Erythropoietin Withdrawal Alters Interactions Between Young Red Blood Cells, Splenic Endothelial Cells, and Macrophages: An In Vitro Model of Neocytolysis

Background We have described the rapid destruction of young red blood cells (neocytolysis) in astronauts adapting to microgravity, in polycythemic high altitude dwellers who descend to sea level, and in patients with kidney disorders. This destruction results from a decrease in erythropoietin (EPO) production. We hypothesized that such EPO withdrawal could trigger physiological changes in cells other than red cell precursors and possibly lead to the uptake and destruction of young red cells by altering endothelial cell-macrophage interactions, most likely occurring in the spleen. Methods We identified EPO receptors on human splenic endothelial cells (HSEC) and investigated the responses of these cells to EPO withdrawal. Results A monolayer of HSEC, unlike human endothelial cells from aorta, glomerulus, or umbilical vein, demonstrated an increase in permeability upon EPO withdrawal that was accompanied by unique morphological changes. When HSEC were cultured with monocyte-derived macrophages (but not when either cell type was cultured alone), EPO withdrawal induced an increased ingestion of young red cells by macrophages when compared with the constant presence or absence of EPO. Conclusions HSEC may represent a unique cell type that is able to respond to EPO withdrawal by increasing permeability and interacting with phagocytic macrophages, which leads to neocytolysis.

Modulation of red cell mass by neocytolysis in space and on Earth

Abstract. Astronauts predictably experience anemia after return from space. Upon entering microgravity, the blood volume in the extremities pools centrally and plasma volume decreases, causing plethora and erythropoietin suppression. There ensues neocytolysis, selective hemolysis of the youngest circulating red cells, allowing rapid adaptation to the space environment but becoming maladaptive on re-entry to a gravitational field. The existence of this physiologic control process was confirmed in polycythemic high-altitude dwellers transported to sea level. Pathologic neocytolysis contributes to the anemia of renal failure. Understanding the process has implications for optimizing erythropoietin-dosing schedules and the therapy of other human disorders. Human and rodent models of neocytolysis are being created to help find out how interactions between endothelial cells, reticuloendothelial phagocytes and young erythrocytes are altered, and to shed light on the expression of surface adhesion molecules underlying this process. Thus, unraveling a problem for space travelers has uncovered a physiologic process controlling the red cell mass that can be applied to human disorders on Earth.

Influence of Cephalosporin Antibiotics on Blood Coagulation and Platelet Function

Administration of cephalothin to normal volunteers in maximal doses of 300 mg/kg per day resulted in a combined defect of platelet function and blood coagulation. No such abnormalities were evident after infusion of cefazolin or cephapirin at a maximal dosage of 200 mg/kg per day. The observed thrombocytopathy was similar to but less severe than that induced by carbenicillin or ticarcillin and was not reflected by a prolonged bleeding time test or impaired prothrombin consumption. Moreover, it was not a consistent finding in those persons receiving cephalothin. A separate defect involving blood coagulation appeared to result from delayed fibrinogen-fibrin polymerization and was evidenced by extended values of the activated partial thromboplastin and thrombin time tests. It remains uncertain whether the abnormalities described may constitute clinically important hemostatic disorders in patients with normal renal function receiving large doses of cephalosporin antibiotics.

Acquired factor IX deficiency in the nephrotic syndrome.

Abstract In a patient with the nephrotic syndrome prolonged whole blood clotting and defective intrinsic thromboplastin generation resulted from an acquired deficiency of factor IX. His urine and t...

Implications of Neocytolysis for Optimal Management of Anaemia in Chronic Kidney Disease

Erythropoietin is the major hormone regulator of erythrocyte production promoting the survival, as well as the differentiation and maturation, of erythroid progenitor cells. In addition to these well-characterized effects, it appears that an erythropoietin-responsive non-erythroid mechanism also mediates the selective destruction of young circulating erythrocytes (neocytes) when red cell mass becomes excessive – a process termed ‘neocytolysis’. Endothelial cells appear to respond to a rapid decrease in circulating levels of erythropoietin by secreting cytokines (including TGF-α), which signal reticuloendothelial phagocytes to destroy neocytes. The result is a more rapid decrease in red cell mass than can be explained by natural erythrocyte senescence alone. The current pharmacologic approach to treatment of anaemia in chronic kidney disease may cause neocytolysis and could keep therapy from reaching its full potential. Understanding neocytolysis and its relationship to fluctuating serum erythropoietin levels might help to better understand optimal treatment with erythropoietic agents.

Brucellosis with pancytopenia.

Abstract The unique occurrence of severe pancytopenia and splenomegaly in a young woman with brucellosis is reported. Hemoglobin was 6.2 g/100 ml; total leukocyte count, 2,200/mm3; platelet count, ...