Chronic isofenphos poisoning: case report of agnogenic myeloid metaplasia with a rapid progression into acute myeloid leukemia

Chromosomal aberrations in human lymphocytes exposed to the anticholinesterase pesticide isofenphos with mechanisms of leukemogenesis

Human lymphocytes were exposed to the leukemogenic pesticide isofenphos (IFP) to investigate its effects on chromosomal DNA and cholinergic homeostasis using cholinesterase activity as a marker. Isolated peripheral lymphocytes were administered concentrations of IFP ranging from 0.1 ng/ml to 10 microg/ml. The absence (Group 1) and presence (Group 2) of DNA repair inhibitors 4 mM hydroxyurea (HU), 40 microM cytosine arabinoside (ARA-C) and an NADPH regenerating system (NRS) (Group 3) were analyzed at 1, 6 and 24 h by single cell gel electrophoresis using the comet assay. Significant damage to DNA directly from IFP at 1 h by remarkably low concentrations was observed in Group 1, escalating in Group 2 with DNA repair inhibition, while Group 3 disruptions were highest due to the presence of the NRS P-450 microsomal fraction conducive to producing reactive IFP-oxon and N-desalkyl metabolites. The extent of DNA aberrations increased further in parallel within the groups at 6 and 24 h. Male and female chemical sensitivities were similar on average (P < 0.01). Cholinesterase activity measured in a satellite group was inhibited with 0.1 microg/ml IFP by 69, 62, and 48% at 1, 6, and 24 h, respectively, indicating gradual induction of compensatory synthesis. Restoration of cholinergic homeostasis may be exceptionally impaired at higher IFP concentrations from acetyl-CoA depletion [Leuk. Res. 25 (2001) 883]. In summary, these studies reveal that exposure to the organophosphate pesticide isofenphos induces human DNA mutation beyond endogenous repair capacity and disrupts cholinergic nuclear signaling affectively constructing the mutator phenotype of leukemogenesis.

Isofenphos induced metabolic changes in K562 myeloid blast cells

The organophosphate pesticide, isofenphos, is associated with human myeloid leukemia. In this study we describe metabolic changes in K562 myeloid blast cells from exposure to varying concentrations of isofenphos using the stable [1,2-13C(2)]glucose isotope as the single tracer and biological mass spectrometry. Isofenphos (1, 10, 100 microg/ml/72 h) treated K562 cells showed increases of 10.7, 33.8 and 39.7% in lactate production as well as a 14.2% increase (1 microg/ml/72 h) in 13C incorporation into nucleic acid ribose from glucose. Concomitantly, we observed a decrease in glucose oxidation and the synthesis of glutamate, palmitate and stearate from glucose. Our results demonstrate that this organophosphate pesticide exerts a leukemogenic effect by the recruitment of glucose carbons for nucleic acid synthesis thus promoting proliferation simultaneous with poor differentiation. The imbalanced metabolic phenotype with a severe defect in glucose oxidation, lipid and amino acid synthesis concurrent with de novo synthesis of nucleic acids in response to isofenphos treatment conforms to the invasive proliferating phenotype observed in TGF-beta treated lung epithelial carcinoma cells.