Serum myeloperoxidase in leukaemia and polycythaemia vera

Degradation of vincristine by myeloperoxidase and hypochlorous acid in children with acute lymphoblastic leukemia

Vincristine (VCR) is an effective drug against acute lymphoblastic leukemia (ALL), many solid tumors, but not acute myeloid leukemia. It has been hypothesized that resistance of myeloblasts to VCR is related to myeloperoxidase (MPO) and production of hypochlorous acid (HOCl). We investigated the relationship between VCR degradation and MPO expression and serum HOCl concentrations in pediatric patients with ALL, lymphoma and solid tumors. We studied the sera from 43 children, of which 23 were newly diagnosed and as yet untreated cancer patients, 10 on chemotherapy and 10 healthy control subjects. Patients' sera were incubated with VCR alone or in the presence of taurine (T) or acetaminophen (APAP) and post-incubation VCR and HOCL concentrations were measured. Significant correlations between serum MPO expression, HOCl concentrations and VCR degradation were seen. In the chemotherapy group, MPO-positive patients produced high levels of HOCl and reciprocally low post-incubation VCR levels. HOCl and VCR concentrations in this group were significantly different than other groups studied. Both APAP and T inhibited VCR degradation in the sera of the chemotherapy group but not to the same degree. The effects seen here were consistent for both ALL and the lymphoma/solid tumor cases. Our results indicate that HOCl can increase VCR degradation in vitro in the serum and this effect is significantly more pronounced in pediatric patients undergoing chemotherapy.

Vincristine degradation by serum from leukemic patients: role of myeloperoxidase

Myeloperoxidase (MPO) has been shown to catalyze the in vitro degradation of vincristine (VCR). Given that MPO is a lysosomal enzyme that can be released into the circulation by both normal activated and leukemic myeloid cells, we investigated the possibility that sera from patients with acute myeloblastic leukemia (AML) might exhibit an increased capacity to degrade VCR. 31 serum samples (23 from patients with acute myeloblastic leukemia and 8 from patients with other conditions) were analyzed after incubation with ((3)H)VCR by using HPLC. Sera from patients with AML demonstrated an increased ability to breakdown VCR when compared to either normal sera or to sera from patients with lymphoid leukemias. VCR degradation was significantly increased by adding hydrogen peroxide, an electron donor for MPO, to the sera and was almost completely inhibited by adding 1 mM acetaminophen, an inhibitor of MPO. VCR peroxidation in the presence of hydrogen peroxide correlated both with the number of leukemic blasts in the circulation at the time the sera were obtained and with serum MPO concentrations determined by an immunoassay. These data suggest that the inactivity of VCR in AML may be due in part to its rapid peroxidation to inactive species by the MPO of leukemic myeloblasts.

Self-labeling of human polymorphonuclear leucocyte myeloperoxidase with 125iodine

In order to obtain a radioimmunoassay (RIA) technique for the measurement of human plasma myeloperoxidase (MPO), we purified the enzyme from polymorphonuclear granulocytes (neutrophils), and compared three methods of labeling it with 125Iodine:chloramine T, lactoperoxidase, and an original technique of 'self labeling' based on the ability of the enzyme to oxidize and bind 125I in the presence of H2O2. The chloramine T technique produced a degraded protein, as well shown by a high non-specific binding of tracer to antibody. The lactoperoxidase technique did not succeed in labeling MPO with an adequate specific activity. In contrast, the self-labeling method gave a stable tracer with a specific activity of 23 microCi/micrograms MPO (85 MBq), a satisfactory level of immunoreactivity, and a low-specific binding (less than or equal to 3%). After labeling, purification of tracer was achieved by gel filtration chromatography in phosphate buffer (0.05 M; pH7) to which 0.1% poly-L-lysine was added. The labeled molecule remained stable for 40 days and could be used for RIA with a polyclonal antibody raised in rabbits.

Tissue peroxidase in the normal and neoplastic salivary gland

Peroxidase activity was measured by two colorimetric methods in six neoplastic tumors of the parotid salivary gland. When p-phenylenediamine was used as the hydrogen donor co-substrate, peroxidase activity was absent or reduced from 6 to 22% of normal in these tumors. Cross reactivity with normal peroxidase antibody could not be demonstrated in tumors exhibiting negative activity. Two neoplastic salivary glands had well-described, encapsulated tumors which showed reduced peroxidase activity when compared with the normal uninvolved portion. However, when guaiacol was substituted for p-phenylenediamine, normal activity was recorded. After dialysis, peroxidase activity was not enhanced. Mixing experiments showed no effect of the tumor extract on the peroxidase activity of normal saliva, nor on salivary gland supernatant. Normal salivary gland peroxidase was inhibited 90% by 10(-2) g/L amino-triazole, but neoplastic tumors were inhibited less (13 and 73%). It is suggested that peroxidase is a simple marker for the detection of neoplasia and can be of value in the differentiation of benign tumors.

Diagnostic and prognostic significance of serum measurements of lactoferrin, lysozyme and myeloperoxidase in acute myeloid leukemia (AML): recognition of a new variant, high-lactoferrin AML

92 patients with acute myeloid leukemia were classified according to the FAB classification (M1 n = 20, M2 n = 43, M3 n = 1, M4 n = 19, M5a n = 2, M5b n = 2, and M6 n = 5 patients). Serum measurements of lactoferrin (LF), myeloperoxidase (MPO) and lysozyme (LYS) were performed before the start of treatment. LF was significantly lower in M1 when compared with M2 but not as compared to M4, MPO was significantly higher in M2 and M4 than in M1, but comparable MPO levels were found in M2 and M4. LYS was significantly elevated in M2 in comparison with M1, and in M4 when compared to both M1 and M2. Polymorphonuclear granulocytes (PMNs) in M1 were significantly reduced when compared with M2 and M4, whereas mononuclear cells were significantly increased in M4 in comparison with both M1 and M2. FAB classification did not generate any prognostic information. When the patients were, instead, subdivided according to LF levels were found prognostically significant differences. Of patients below 100 micrograms/l, 44% went into remission as compared to 77% with LF from 101 to 400 micrograms/l. In patients with LF levels above 400 micrograms/l the remission frequency was only 14%. Multivariate statistical analysis on the data further suggested that lactoferrin may be used as an independent prognostic indicator. We conclude that although determination of the serum-levels of lactoferrin, lysozyme and myeloperoxidase in certain cases may be valuable as a supplement to the morphological examination of acute myeloid leukemia, it is evident that none of the three determinations can be used alone to distinguish between the FAB groups.

Molecular forms of myeloperoxidase in human plasma

A radioimmunoassay for myeloperoxidase was established with the use of affinity-purified anti-(human myeloperoxidase) immunoglobulins. By the use of ion-exchange followed by immunoaffinity chromatography a preparation of immunoreactive, catalytically active myeloperoxidase was obtained from fresh human plasma. In non-denaturing gel electrophoresis, the plasma preparation showed about four catalytically active components of mobility very similar to that of the granulocyte enzyme. SDS/polyacrylamide-gel electrophoresis combined with protein blotting showed that the two polypeptides of strongest antigenicity in the plasma preparation corresponded in Mr to the large and the small subunits of the granulocyte enzyme. In addition, the plasma preparation contained a higher-Mr immunoreactive polypeptide, possibly a precursor form of the enzyme, together with another of Mr similar to that of the large subunit of eosinophil peroxidase.

Serum-levels of lactoferrin, lysozyme and myeloperoxidase in normal, infection-prone and leukemic children

Serum levels of lactoferrin, lysozyme and myeloperoxidase have been established in 31 healthy children. On average, serum lactoferrin was 330 micrograms/1, serum lysozyme 1638 micrograms/1 and serum myeloperoxidase 174 micrograms/1. Serum myeloperoxidase was, on average, significantly higher in children than in adults (p = 0.01), whereas serum lactoferrin and serum lysozyme were equal to those of adults. In a group of infection-prone children (n = 31), both serum lactoferrin and serum myeloperoxidase, but not the serum lysozyme levels, were significantly lower (p less than 0.001 and p = 0.002, respectively) than those of the reference children in spite of normal intracellular contents and even somewhat higher peripheral blood polymorphonuclear counts. Based on the assumption that serum lactoferrin and serum myeloperoxidase reflect turnover and activity of neutrophil granulocytes, the findings could suggest reduction in these respects and could be one contributing factor to the high infection propensity of these children. Serum levels of the three proteins have also been measured in 10 children with suspected or various forms of manifest leukemia. It is suggested that the levels reflect turnover and stage of maturation of the myeloid and monocytic cells and could, therefore, aid in the understanding and diagnosis of these diseases.

Serum and plasma myeloperoxidase, elastase and lactoferrin content in acute myeloid leukaemia

Myeloperoxidase (MPO) and elastase, restricted to azurophil granules of neutrophils, as well as lactoferrin, restricted to specific granules of neutrophils, were determined in plasma and serum from patients with acute myeloid leukaemia (AML). Highly sensitive radio immuno assays were developed for detection of these proteins. Serum MPO was increased in 12/35 and decreased in 2/35 patients without correlation to WBC or neutrophil counts; these levels may reflect an abnormal production by leukaemic blasts or ineffective granulopoiesis in the bone marrow. Serum elastase was increased in 6/22 patients. Serum lactoferrin was decreased in 12/25 patients without correlation to neutrophil counts probably reflecting abnormal production. Serum elastase and MPO showed a covariation in chronic myeloid leukaemia but not in AML; the latter finding may indicate that the synthesis of these two proteins is not synchronized in AML-cells. Sequential studies of patients with AML demonstrated fluctuations of serum MPO and lactoferrin during remission most likely because of chemotherapeutic pertubation. Although a limited number of patients has been studied it is suggested that serum lactoferrin may be of help for prediction of relapse in AML.

Myeloperoxidase and lactoferrin of blood neutrophils and plasma in chronic granulocytic leukaemia

Myeloperoxidase, restricted to primary granules, and lactoferrin, restricted to secondary granules, were determined in plasma and neutrophils of peripheral blood in chronic granulocytic leukaemia (CGL). Plasma myeloperoxidase was increased 2-3 times while plasma lactoferrin increased 2-8 times. This discrepancy indicates different modes of release or elimination. A correlation was found between the leucocyte count and plasma myeloperoxidase or lactoferrin. A correlation was also found between cellular and plasma levels of lactoferrin but not for myeloperoxidase indicating the source for plasma lactoferrin to be circulating leucocytes, which may not be the case for plasma myeloperoxidase. Decreased neutrophil lactoferrin was found in 71% of the CGL cases while myeloperoxidase was decreased in 18%. Serial studies on individual CGL subjects showed low cellular lactoferrin during phases with rapidly expanding leucocytosis indicating defective maturation of neutrophils or abnormal release because of prolonged intravascular life-span.

Plasma myeloperoxidase and lactoferrin measured by radioimmunoassay: relations to neutrophil kinetics

In 31 patients, covering a wide range of blood neutrophil counts and turnover rates, the plasma concentrations of myeloperoxidase and lactoferrin have been measured with radioimmunoassays and compared to neutrophil kinetic parameters, measured with DF32P-labeled neutrophils. It was found that the plasma concentrations of both proteins correlated significantly with the total number of neutrophils in the blood (TBGP=total blood granulocyte pool) as well as with the neutrophil turnover rate (GTR=granulocyte turnover rate), which is evidence that neutrophilic granulocytes are the main suppliers of myeloperoxidase and lactoferrin to the plasma. In contrast to the previously demonstrated better relationship between the GTR and plasma lysozyme, a protein also originating in neutrophil granules, both myeloperoxidase and lactoferrin correlated better with the TBGP. These differences may reflect differences in the mode of release of intragranular proteins from neutrophils to the plasma. The correlation of the plasma lactoferrin concentration with the TBGP was so good as to suggest its use in the clinical assessment of the TBGP.