Aromatase activity after a short-course of letrozole administration in adult men at sea level and at high altitude (with or without excessive erythrocytosis)

Men living at high altitudes in Peru compared to sea level counterparts have erythrocytosis (hemoglobin 16-21 g/dl) or excessive erythrocytosis (hemoglobin>21 g/dl). High testosterone (T) levels in men at high altitude (HA) were associated with excessive erythrocytosis. High androgen levels could be due to a low aromatase activity or to an elevated rate of conversion from precursors to testosterone. The aim of this study was to evaluate aromatase activity and rate of conversion from precursors to testosterone before and after administration of the aromatase enzyme inhibitor letrozole (5 mg/day) for a 5-day period to men at HA and at sea level (SL). The response to short term aromatase inhibition was assessed in 30 adult men living at sea level, 31 native men at HA with erythrocytosis (Hb 16-21 g/dl), and 35 men at HA with excessive erythrocytosis (Hb>21 g/dl). Serum hormone levels, estradiol/testosterone, testosterone/androstenedione, and testosterone/dehydroepiandrosterone sulfate (DHEAS) ratios were measured. Men with erythrocytosis had lower basal serum T/androstenedione ratios than men with excessive erythrocytosis at HA and men at sea level. Men at HA with excessive erythrocytosis had higher T/DHEAS ratios than men with erythrocytosis and than those at sea level before and after letrozole administration. After letrozole administration, both groups of men at high altitude (with erythrocytosis or with excessive erythrocytosis) showed lower aromatase activities than those at sea level. In conclusion, higher serum testosterone levels in men with excessive erythrocytosis were associated with an increased rate of conversion from DHEAS to testosterone rather than to a lower aromatase activity.

Usefulness of JAK2V617F mutation in distinguishing idiopathic erythrocytosis from polycythemia vera

Idiopathic erythrocytosis (IE) is a primary erythrocytosis not fulfilling the criteria for polycythemia vera (PV) diagnosis. In order to verify the relationship between IE and PV, we screened JAK2V617F mutation in a consecutive series of 11 IE and, for comparison, in 15 PV. JAK2V617F mutation was screened by both cDNA sequencing and mutation specific PCR in both peripheral blood and bone marrow samples. All 11 IE tested negative for JAK2V617F mutation, which, conversely, occurred in 11/15 (73.3%) PV. Our results demonstrate that JAK2V617F is absent in IE and may represent a useful molecular marker for distinguishing IE from PV.

The incidence of the JAK2 V617F mutation in patients with idiopathic erythrocytosis

Sixty-three patients with erythrocytosis exhibiting a range of erythropoietin levels were screened for the JAK2 V617F mutation. One patient (1.6%) was found to have this mutation, and has remained stable for 9 years, suggesting that the JAK2 V617F mutation is rare in patients with idiopathic erythrocytosis.

A family with erythrocytosis establishes a role for prolyl hydroxylase domain protein 2 in oxygen homeostasis

The number of red blood cells is normally tightly regulated by a classic homeostatic mechanism based on oxygen sensing in the kidney. Decreased oxygen delivery resulting from anemia induces the production of erythropoietin, which increases red cell production and hence oxygen delivery. Investigations of erythropoietin regulation identified the transcription factor hypoxia-inducible factor (HIF). HIF is now recognized as being a key regulator of genes that function in a comprehensive range of processes besides erythropoiesis, including energy metabolism and angiogenesis. HIF itself is regulated through the alpha-subunit, which is hydroxylated in the presence of oxygen by a family of three prolyl hydroxylase domain proteins (PHDs)/HIF prolyl hydroxylases/egg-laying-defective nine enzymes. Hydroxylation allows capture by the von Hippel-Lindau tumor suppressor gene product, ubiquitination, and destruction by the proteasome. Here we describe an inherited mutation in a mammalian PHD enzyme. We show that this mutation in PHD2 results in a marked decrease in enzyme activity and is associated with familial erythrocytosis, identifying a previously unrecognized cause of this condition. Our findings indicate that PHD2 is critical for normal regulation of HIF in humans.

Red cell enzymes

Mutations leading to red cell enzyme deficiencies can be associated with diverse phenotypes that range from hemolytic anemia, methemoglobinemia, polycythemia, and neurological and developmental abnormalities. While most of these mutations occur sporadically, some such as common glucose-6-phosphate dehydrogenase (G6PD) mutants are endemic and rarely cause disease. Common G6PD mutants likely reached their prevalence because they provide some protection against severe malarial complications. In this review G6PD, pyruvate kinase, 5' nucleotidase, and cytochrome b5 reductase deficiencies will be discussed in greater detail. Limitations of commonly used screening tests for detection of these disorders will also be emphasized, as well as emerging knowledge about non-enzymatic function of the glycolytic enzymes.

Erythrocytosis due to bisphosphoglycerate mutase deficiency with concurrent glucose-6-phosphate dehydrogenase (G-6-PD) deficiency

A 28-year-old asymptomatic male of Iranian Jewish (Meshadi) heritage was found on routine exam to have an erythrocytosis (RBC = 6.22 x 10(12)/l, Hgb = 19.2 g/dl, Hct = 58.9%). Splenomegaly was absent on physical exam. There was no family history of erythrocytosis. His oxygen dissociation curve was left-shifted with a p50 of 19 mmHg (normal = 25-32 mmHg). Hemoglobin electrophoresis showed no abnormalities. DNA sequencing of the hemoglobin beta globin gene and both alpha globin genes did not reveal a mutation. A 2,3-bisphosphoglycerate (BPG) level was markedly decreased at 0.3 micromol/g Hb (normal = 11.4-19.4 micromol/g Hb). The patient's bisphosphoglycerate mutase (BPGM) enzyme activity was also markedly decreased at 0.16 IU/g Hb (normal = 4.13-5.43 IU/g Hb). A red cell enzyme panel revealed a markedly decreased G-6-PD level (0.3 U/g Hb, normal = 8.6-18.6 U/g Hb). His parents and a brother were also available for evaluation. Both parents showed normal 2,3-BPG levels but BPGM activity approximately 50% of normal. Paradoxically, the brother showed normal BPGM activity but a slightly decreased 2,3-BPG level. All family members had markedly decreased G-6-PD activity. DNA sequencing of the BPGM gene showed the propositus to be homozygous for 185 G-->A, Arg 62 Gln in exon 2. Thus, the erythrocytosis in this patient is secondary to low 2,3-BPG levels, due to a deficiency in BPG mutase. This appears due to consanguinity within this family.

Effects of chronic nitric oxide synthase inhibition on renal function and histology in polycythemic rats

Augmented endogenous nitric oxide (NO) production may ameliorate derangement of renal functions or glomerular damage in polycythemia. To investigate this possibility, we examined the effect of NO synthase inhibition with N omega-nitro-L-arginine methyl ester (L-NAME; 50 mg/dl in drinking water) on renal functions and histology in heminephrectomized Sprague-Dawley rats treated for 4 weeks with recombinant human erythropoietin (rh-EP; 500 IU/kg on alternate days). L-NAME elevated the blood pressure which was aggravated by concomitant rh-EP and was ameliorated by treatment with a nonpeptide angiotensin type 1 receptor blocker (CV116; 60 mg/kg in chow). The hematocrit level was prominently increased by rh-EP. The glomerular filtration rate was impaired by L-NAME alone, but was maintained by concomitant administration of rh-EP or CV116. Micropuncture experiments revealed that the glomerular capillary pressure was similarly elevated by L-NAME alone or in combination with rh-EP. L-NAME significantly, although not prominently, aggravated glomerular sclerosis observed with rh-EP alone, and concomitant CV116 ameliorated the glomerular damage. These results suggest that, in polycythemia, enhanced NO production buffers the glomerular damage, and the balance between NO and angiotensin II may play an important role in maintaining renal function and glomerular structure.

Red cell lipid peroxidation and antioxidant enzymes in iron deficiency

Whether iron deficient RBC in humans have a reduced, or an increased, susceptibility to lipid peroxidation was studied in the iron deficiency states of primary proliferative polycythaemia and iron deficiency anaemia and related to changes in the activities of iron-dependent and non-iron dependent antioxidant enzymes. Susceptibility of RBCs to lipid peroxidation was increased when expressed per g Hb. However, this was a result of the low RBC Hb giving an increased membrane lipid: Hb ratio in the incubations. Results were normal when expressed either per cell, or per ml, RBC. Glutathione reductase was normal. Increased RBC superoxide dismutase activity in iron deficiency may be explained by the younger RBC population and reductions in glutathione peroxidase and catalase activities by the microcytic hypochromic changes and the lack of availability of iron, respectively. There is no evidence of an increased susceptibility of RBC to lipid peroxidation in iron deficiency.

The effect of polycythemia and hypoxia on urinary N-acetyl-beta-D-glucosaminidase activity in newborns

Urinary N-acetyl-beta-D-glucosaminidase activity was assayed in fullterm and preterm polycythemic neonates, in preterm infants with hypoxia, and in healthy newborns. There were no significant differences between fullterm and preterm babies or between appropriate for gestational age and small for gestational age neonates in the normal group. N-acetyl-beta-D-glucosaminidase excretion on the first day of life was significantly raised in polycythemic newborns (P less than 0.01). Fourteen days after partial plasma exchange the enzyme activity returned to normal. N-acetyl-beta-D-glucosaminidase activities in preterm babies with respiratory distress syndrome were significantly (P less than 0.01) raised on the 1st, 2nd, 4th days and fell sharply to the 14th day. N-acetyl-beta-D-glucosaminidase isoenzyme studies revealed that urine samples taken from preterm babies with respiratory distress syndrome in the first week after birth contained increased amounts of intermediate and B isoenzyme forms while there was a concomitant reduction in the amount of the A form present.

The use of knowledge-based information systems for interpreting specialized clinical chemistry analyses--experience from erythrocyte enzymes and metabolites

A knowledge-based information system has been constructed to facilitate and standardize the interpretation of data obtained from specialized analyses in clinical chemistry. For illustration the system was applied to metabolic studies of erythrocytes from patients in whom hereditary disorders are suspected to explain the presence of a haemolytic anaemia or a polycythaemia. The study includes assay of the catalytic activity of 10 different enzymes and the concentration of some key metabolites. The knowledge-based system is an excellent tool for documentation, updating and transfer of knowledge of the interpretative process. This will reduce the risk of changes in this process being made without sound motivation and documentation. Furthermore, the statistical and graphic features of the system provide data for long-term quality assessment and insights into reference sample groups which are used to update decision levels.

The in vivo ageing of red cell enzymes: direct evidence of biphasic decay from polycythaemic rabbits with reticulocytosis

The rate at which the activities of red cell enzymes decay during maturation of the reticulocyte and ageing of the erythrocyte is poorly understood. It has recently been suggested that loss of enzyme activity may be rapid during reticulocyte maturation and occur slowly thereafter. We have now devised a rabbit model in which reticulocytosis is combined with transfusional polycythaemia. This makes it possible to follow the enzymatic activity of a cohort of reticulocytes without the interfering effect of newly formed cells. In this model the reticulocyte count of the experimental animals falls from about 60% to subnormal levels within 4 d. Red cell hexokinase activity declined rapidly with more than half of the activity being lost within 7 d, little change occurring thereafter. Glucose-6-phosphate dehydrogenase activity declined more gradually, but also followed a biphasic course. The fall of pyrimidine 5' nucleotidase activity was the slowest of the three age-dependent enzymes studied. This is consistent with our observations in children with transient erythroblastopenia of childhood, in which this enzyme, alone of the age-dependent enzymes, was found to be decreased in a senescent red cell population. In contrast to the three age-dependent enzymes studied, the activity of lactate dehydrogenase remained unchanged during the course of the experiment. These studies provide direct verification of the suggestion that the decline of red cell enzyme activities may be biphasic. They show, moreover, that enzyme decay is not only rapid in reticulocytes, but also in young erythrocytes.

Clinical significance of the isomorphic pattern of the isoenzymes of serum lactate dehydrogenase

Five hundred patients with the isomorphic pattern of the isoenzymes of serum lactate dehydrogenase (LDH) were surveyed. The isomorphic pattern of LDH isoenzymes is defined as a significant increase of total LDH with normal or low percentage of individual fractions, but with the LDH1:2 ratio less than unity. Diagnoses were, in descending order of frequency, cardiorespiratory diseases, malignancy, fracture, diseases of the central nervous system, infection/inflammation, hepatic cirrhosis and/or alcoholism, trauma without fracture, infectious mononucleosis, hypothyroidism, uremia, necrosis, pseudomononucleosis, viremia and intestinal obstruction. Incidence of increased serum activity in individuals without evidence of disease or drug explanation was 3 percent. Low PaO2 was observed in 88 percent of the 67 patients in whom it was measured.

[Activity of kidney tissue enzymes in phenylhydrazine anemia and post-transfusion polycythemia]

The activity of hexokinase, glucose-6-phosphoric dehydrogenase, lactic dehydrogenase, succinic dehydrogenase, acid and alkaline phosphatases was determined in the rat kidney tissue with phenylhydrazine anemia and posttransfusion polycytemia. The blood supply of the cortical and medullary layers of the kidneys was studied at the same time. The purpose of this work was to ascertain possible connections between the changes in the activity of the enzymes under study with the renal erythropoietin producing function of the kidneys. The blood supply of the kidneys of rats with phenylhydrazine anemia was sharply decreased, but it was markedly elevated in case of posttransfusion polycytemia. There were no significant changes in the activity of the mentioned enzymes. These data suggest that the activity of the kidney enzymes is not a controlling factor in the renal erythropoietin production.

Activity and Intracellular Localization of Lysosomal Acid Phosphatase in Lymphocytes from Patients with Hodgkin's Disease, Plasma Cell Myeloma and Primary Polycythemia

Using the cytochemical method after Barka and Anderson, activity and localization of lysosomal acid phosphatase (AP) was determined in peripheral-blood lymphocytes from 20 healthy subjects, 10 patients with Hodgkin's disease (HD), 10 patients with plasma cell myeloma (PCM), and 10 patients with primary polycythemia (PP). Total count of AP-positive lymphocytes was lowest in the patients with HD. Moreover, they showed a significant decrease of the absolute count of lymphocytes with well formed and more numerous AP-positive lysosomal granules. Analogous alterations in lymphocytes from patiens with PCM and those with PP were much less significant. The authors discuss the importance of the above-mentioned observations for evaluation on a cellular basis of lowered immunity of patients with lympho-proliferative and myelo-proliferative disorders, with special regard to AP as a T-cell marker.

Atypical intraerythrocytic pyruvate kinase in some haematological diseases

An atypical pyruvate kinase (PK) in erythrocytes was studied in a family with several different haematological diseases: non-spherocytic haemolysis, thrombocytopenia, myelofibrosis and polycythaemic traits. Atypical intraerythrocytic PK was also found in a group of non-related patients with myelofibrosis and polycythaemia vera. The atypical PK was characterised by abnormal urea inhibition and other relevant biochemical parameters.

Neutrophil alkaline phosphatase score in chronic granulocytic leukaemia: effects of splenectomy and antileukaemic drugs

Staining with naphthol AS phosphate and Fast Blue BB salt has been used for the estimation of neutrophil alkaline phosphatase (NAP) scores in patients with chronic granulocytic leukaemia (CGL). The very low scores found at diagnosis rise when the disease is treated, and there is some inverse correlation between the NAP score and the absolute neutrophil count. Patients treated intensively developed high NAP scores. Elective splenectomy performed during the chronic phase of CGL is followed by a pronounced but transient neutrophilia and a concurrent striking rise in the NAP score. Similar changes were observed in patients without CGL who underwent splenectomy. These observations can be explained by assuming that newly formed neutrophils in CGL have a normal content of NAP but are rapidly sequestered in non-circulating extramedullary pools, whereas the circulating neutrophil with a typically low NAP content is a relatively aged cell which has lost enzyme activity. In subjects with or without CGL, removal of the spleen, a major site of such pooling, temporarily permits the circulation of newly formed neutrophils but eventually other organs assume the sequestering functions of the spleen. Thus the aberrations of NAP score seen in CGL might be attributable not to an intrinsic cellular defect but to an exaggeration of the granulocyte storage phenomena which also occur in subjects without CGL.