Micronuclei in blood lymphocytes and genetic polymorphism for GSTM1, GSTT1 and NAT2 in pesticide-exposed greenhouse workers.

The frequency of micronuclei (MN) in cultured peripheral lymphocytes was used as a biomarker of genotoxic effects in 34 Italian pesticide-exposed greenhouse workers and 33 unexposed referents matched with the exposed workers for age and smoking habits. The possible influence of the genetic polymorphisms of xenobiotic metabolizing enzymes glutathione S-transferase M1 (GSTM1), T1 (GSTT1), and N-acetyltransferase 2 (NAT2) was also evaluated. To restrict the analysis primarily to cells that have divided once in vitro, MN were scored only in cells showing label after a 42-h incubation with bromodeoxyuridine (BrdU), as detected by immunofluorescence (anti-BrdU technique). Two different concentrations of BrdU (0.5 and 1 microg/ml) were compared. Individual frequencies of micronucleated cells (MNCs) obtained with the two concentrations of BrdU significantly correlated with each other (r=0.55, P<0.001). Higher mean MNCs frequencies (per 1000 cells) were detected among exposed smokers (9.0 at 0.5 microg/ml BrdU and 7.8 at 1 microg/ml BrdU) than in smoking referents (6.3 and 5.9, respectively). In multiple regression analysis controlling for age, sex, smoking and genotypes, a significant elevation of MNC frequency (P=0.004 at 1 microg/ml BrdU; P=0.052 at 0.5 microg/ml BrdU) was observed in greenhouse workers with a work history of extensive pesticide spraying (n=17). Increased MNC frequencies were also associated with ageing at 0.5 microg/ml BrdU, with the GSTM1-positive genotype at both 1 (P=0.028) and 0.5 (P=0.056) microg/ml BrdU in all subjects, and with the NAT2 fast acetylator genotype in smokers at 0.5 microg/ml BrdU (P=0.043). The results indicate that MN rates are increased in greenhouse workers, especially in those involved in pesticide spraying. The GSTM1 positive and NAT2 fast genotypes appear to be associated with elevated MNC frequencies, which contradicts with earlier results on elevated chromosomal aberration rates in GSTM1 null smokers and NAT2 slow subjects.     

Dendritic I h Selectively Blocks Temporal Summation of Unsynchronized Distal Inputs in CA1 Pyramidal Neurons

The active dendritic conductances shape the input-output properties of many principal neurons in different brain regions, and the various ways in which they regulate neuronal excitability need to be investigated to better understand their functional consequences. Using a realistic model of a hippocampal CA1 pyramidal neuron, we show a major role for the hyperpolarization-activated current, Ih, in regulating the spike probability of a neuron when independent synaptic inputs are activated with different degrees of synchronization and at different distances from the soma. The results allowed us to make the experimentally testable prediction that the Ih in these neurons is needed to reduce neuronal excitability selectively for distal unsynchronized, but not for synchronized, inputs.     

Uptake kinetics of 99Tc in common duckweed

The uptake of the nuclear waste product technetium-99 was studied in common duckweed (Lemna minor). In addition to measurements, a model involving two compartments in duckweed with different chemical forms of technetium was derived. The model was tested by chemical speciation, i.e. differentiating between reduced Tc-compounds and Tc(VII)O(4)(-). The TcO(4)(-) concentrations measured were in good agreement with those predicted by the model. Two processes determine technetium uptake: (1) transport of Tc(VII)O(4)(-) across the cell membrane, and (2) reduction of Tc(VII). The TcO(4)(-) concentration in duckweed reaches a steady state within 2 h while reduced Tc-compounds are stored, as a result of absence of release or re-oxidation processes. Bioaccumulation kinetic properties were derived by varying 99Tc concentration, temperature, nutrient concentrations, and light intensity. The reduction of technetium in duckweed was highly correlated with light intensity and temperature. At 25 degrees C the maximum reduction rate was observed at light intensities above 200 μmol m(-2) s(-1) while half of the maximum transformation rate was reached at 41 μmol m(-2) s(-1). Transport of TcO(4)(-) over the cell membrane requires about 9.4 kJ mol(-1), indicating an active transport mechanism. However, this mechanism behaved as first-order kinetics instead of Michaelis-Menten kinetics between 1x10(-14) and 2.5x10(-5) mol l(-1) TcO(4)(-). Tc uptake could not be inhibited by 10(-3) mol l(-1) nitrate, phosphate, sulphate or chloride.     

Molecular implications of the human glutathione transferase A-4 gene (hGSTA4) polymorphisms in neurodegenerative diseases

Several lines of evidence, including an increased level of lipid peroxidation and the depletion of antioxidant molecules like as glutathione (GSH), indicate that oxidative stress plays an important role in the pathogenesis of several neurodegenerative disorders, such as Parkinson's disease (PD) and Alzheimer's disease (AD). We previously observed a significant increased level of DNA oxidative damage in peripheral blood cells of PD patients, with respect to controls, moreover, the activity of glutathione transferases (GSTs) measured in circulating plasma was higher in controls than in PD patients, suggesting a lower enzymatic protection in PD individuals. Among human GSTs, glutathione transferase A4-4 displays a high catalitic activity towards 4-hydroxy-2-nonenal (HNE), a marker of lipid peroxidation whose levels have been found significantly increased in the substantia nigra of Parkinson's disease patients, in respect to controls. We performed this study to determine the presence of allelic variants of functional interest in the coding region of the hGSTA4 gene on 60 PD patients and 60 healthy controls. By the combined effort of polymerase chain reaction/single-strand conformation polymorphisms (PCR/SSCP) techniques, we observed a single nucleotide polymorphism (SNP) G351A leading to the silent mutation Gln117Gln. No significant difference was observed in the distribution of this polymorphism between PD individuals and controls, moreover, we did not observe any other polymorphism in the hGSTA4 gene in our population. Further studies are required to test the role played by both factors regulating the level of the expression of the hGSTA4 gene and any possible post-translational modification of the protein, in the protection against oxidative damage in neuronal cells.