Experimental testing of air filter efficiency against the SARS-CoV-2 virus: The role of droplet and airborne transmission.

Verifying the capacity of different types of air filters to stop the propagation of the SARS-CoV-2 virus has become a strategic element to contain viral spreading in enclosed spaces. This paper shows the results of experimental tests about the capacity of different commercial filter grades to stop SARS-CoV-2 propagation using inactivated virions. In the first test, the obtained results showed that the F8 filter blocks SARS-CoV-2 propagation if it encounters a flow devoid of liquid phase, i.e., a biphasic flow that can wet the filtering material. On the contrary, as shown in the second test, the SARS-CoV-2 virus propagates through the F8 filter if the droplet content in the air flow is enough to wet it. In these operational conditions, i.e., when the filter is wet by a flow with a high droplet content, the absolute H14 filter was also shown to fail to stop the transmission of the SARS-CoV-2 virus. Lastly, in the third test, the viral load was shown to be stopped when the pathway of the infected droplet is blocked.

Restriction Factors expression decreases in HIV-1 patients after cART.

Activation of interferon (IFN) mediated responses and the consequent expression of restriction factors (RFs) represent an early line of defense against HIV-1 infection. The levels of viral replication and the antiviral are among the determinants influencing RFs' expression pattern. A deeper understanding of the molecular mechanisms regulating RFs activity and their relationship with viral replication factors might lead to new therapeutic strategies based on the enhancement of immune response against the virus. The aim of this study is to perform a longitudinal evaluation of the variations in the levels of a group of selected RFs (APOBEC3G, BST2, TRIM5α, MX2, SAMHD1, SERINC3/5, IFI16 and STING) to determine the impact of cART on their expression in HIV-1 positive patients. Together with RFs expression, immunological and virological parameters (plasma HIV1-RNA load and total HIV1-DNA) were longitudinally evaluated in a cohorts fourteen HIV-1 cART na ve patients, who were evaluated at diagnosis (T0) and followed at 4 (T1) and 8 (T2) months after starting cART. Fourteen long-term treated patients who achieved sustained undetectable viremia for at least 2 years were also included in the study as a reference group. We observed a restoration of immunological conditions during cART, together with a progressive decrease of HIV1-RNA load, which became undetectable at 8 months after starting treatment. On the other hand, despite showing a trend towards decrease, total HIV1-DNA remained detectable after reaching viral suppression, similarly to what observed in long term treated patients. The expression of APOBEC3G, SAMHD1, BST2, IFI16, SERINC3, and SERINC5 was higher at the time of diagnosis and decreased significantly during therapy, reaching levels similar to the ones observed in virally suppressed patients. On the other hand, MX2 and TRIM5a high expression values up to T0, reaching lower levels immediately after the initiation of cART treatment. Correlation analysis showed a positive association between the expression levels of APOBEC3G, IFI16, MX2, SAMHD1, SERINC3 and TRIM5α with the HIV-1 viral load. On the contrary, no significant association was observed for BST2, SERINC5 and STING, even BST2 expression showed a tendency to correlate with viral load. We observed a tendency for a positive association of MX2, SAMHD1 and SERINC5 with the size of viral reservoir and a trend for a negative association for STING. STING appeared also as the only one factor whose expression correlates with the CD4 count and the CD4/CD8 ratio. Our data confirm the correlation between viral replication and expression of RFs, with, the levels of cellular defense proteins decreasing in parallel to the reduction of viral replication.

Multiple Sessions of High-Frequency Repetitive Transcranial Magnetic Stimulation as a Potential Treatment for Gambling Addiction: A 3-Month, Feasibility Study.

Gambling disorder (GD) is a behavioral addiction, in which dysfunctions in prefrontal activity have been proposed as relevant pathophysiological correlates. The aim of the present study was to preliminarily investigate the feasibility of a noninvasive neuromodulation intervention targeting the prefrontal cortex to treat GD in an open-label setting. We included 8 treatment-seeking patients with GD (7 males; 1 female; mean age: 40.6 ± 11.2). The study consisted of 3 phases: (1) outpatient screening phase, (2) 2-week intensive repetitive transcranial magnetic stimulation (rTMS) treatment phase (twice daily, 5 days/week for 2 weeks); and (3) 3-month maintenance follow-up phase (twice daily, once a week). Each high-frequency (15 Hz) rTMS session was delivered targeting the left dorsolateral prefrontal cortex. GD severity and treatment response were assessed at the baseline and during the follow-up. No relevant side effect was reported. We found a 71.2% Gambling Symptom Assessment Scale mean score reduction after 2 weeks of rTMS treatment; the days spent gambling decreased from 19.63 ± 7.96 to 0.13 ± 0.35 days. Clinical improvements were maintained throughout the study period. The lack of a control group limits the interpretation of these results. In conclusion, these results consolidate the rationale that rTMS interventions deserve further investigation as a potential treatment for GD. These protocols should be tested in larger randomized controlled studies, to determine the real benefits of neuromodulation in the clinical course of patients with GD. Registration Number: ClinicalTrials.gov Identifier NCT03336879.

Environmental Contamination by SARS-CoV-2 During Noninvasive Ventilation in COVID-19.

BACKGROUND: Environmental contamination by SARS-CoV-2 from patients with COVID-19 undergoing noninvasive ventilation (NIV) in the ICU is still under investigation. This study set out to investigate the presence of SARS-CoV-2 on surfaces near subjects receiving NIV in the ICU under controlled conditions (ie, use of dual-limb circuits, filters, adequate room ventilation). METHODS: This was a single-center, prospective, observational study in the ICU of a tertiary teaching hospital. Four surface sampling areas, at increasing distance from subject's face, were identified; and each one was sampled at fixed intervals: 6, 12, and 24 h. The presence of SARS-CoV-2 was detected with real-time reverse transcriptase-polymerase-chain-reaction (RT-PCR) test on environmental swabs; the RT-PCR assay targeted the SARS-CoV-2 virus nucleocapsid N1 and N2 genes and the human RNase P gene as internal control. RESULTS: In a total of 256 collected samples, none were positive for SARS-CoV-2 genetic material, whereas 21 samples (8.2%) tested positive for RNase P, thus demonstrating the presence of genetic material unrelated to SARS-CoV-2. CONCLUSIONS: Our data show that application of NIV in an appropriate environment and with correct precautions leads to no sign of surface environmental contamination. Accordingly, our data support the idea that use of NIV in the ICU is safe both for health care workers and for other patients.

Associations of adverse childhood and lifetime experiences with sleep quality and duration among women in midlife.

OBJECTIVES: Many women experience sleep problems during midlife. Associations of adverse lifetime experiences-more common among women-with sleep outcomes are understudied. METHODS: We studied 476 women enrolled in Project Viva 1999-2002. At enrollment, participants reported any lifetime history of abuse and/or financial hardship. At midlife follow-up ∼20 years later, they reported a history of up to 10 adverse childhood experiences (ACEs); 7-day sleep quality (patient-reported outcomes measurement information system sleep disturbance and sleep-related impairment T-scores); and past month average sleep duration. We examined associations of adverse experiences with sleep outcomes, adjusted for childhood sociodemographic variables. We also explored mediation by current depression and anxiety symptoms, hot flash severity, general health, and body mass index. RESULTS: ACEs were common: 301 women (63%) reported one or more. Each additional ACE was associated with higher midlife sleep disturbance (adjusted ß = 0.65 points, 95% confidence interval [CI]: 0.27, 1.02) and sleep-related impairment (0.98, 95% CI: 0.54, 1.41) T-scores, and with sleep duration <6 hour/night (odds ratio 1.19, 95% CI: 1.00, 1.42), but not with continuous sleep duration (-2 minutes, 95% CI: -5, 1). Adverse experiences in adulthood were less consistently associated with sleep quality but were associated with sleep duration, for example, financial hardship during the index pregnancy was associated with 75 minutes (95% CI: -120, -29) shorter sleep duration 2 decades later. Associations of ACEs with sleep disturbance and sleep-related impairment were mediated by midlife depression anxiety and physical health but not by hot flash severity or body mass index. CONCLUSIONS: Adverse lifetime experiences have deleterious associations with sleep duration and quality in midlife women.

The role of setting for ketamine abuse: clinical and preclinical evidence.

Drug abuse is often seen as a unitary phenomenon, partly as a result of the discovery over the past three decades of shared mechanisms of action for addictive substances. Yet the pattern of drug taking is often very different from drug to drug. This is particularly evident in the case of 'club drugs', such as ketamine. Although the number of ketamine abusers is relatively small in the general population, it is quite substantial in some settings. In particular, ketamine abuse is almost exclusively limited to clubs and large music parties, which suggests a major role of context in modulating the reward effects of this drug. This review focuses on recent preclinical and clinical findings, including previously unpublished data, that provide evidence that, even under controlled conditions, ketamine reward is a function of the setting of drug taking.

Identifying and characterizing binding sites on the irreversible inhibition of human glutathione S-transferase P1-1 by S-thiocarbamoylation.

Human glutathione S-transferase P1-1 (hGST P1-1) is involved in cell detoxification processes through the conjugation of its natural substrate, reduced glutathione (GSH), with xenobiotics. GSTs are known to be overexpressed in tumors, and naturally occurring isothiocyanates, such as benzyl isothiocyanate (BITC), are effective cancer chemopreventive compounds. To identify and characterize the potential inhibitory mechanisms of GST P1-1 induced by isothiocyanate conjugates, we studied the binding of GST P1-1 and some cysteine mutants to the BITC-SG conjugate as well as to the synthetic S-(N-benzylcarbamoylmethyl)glutathione conjugate (BC-SG). We report here the inactivation of GST P1-1 through the covalent modification of two Cys47 residues per dimer and one Cys101. The evidence has been compiled by isothermal titration calorimetry (ITC) and electrospray ionization mass spectrometry (ESI-MS). ITC experiments suggest that the BITC-SG conjugate generates adducts with Cys47 and Cys101 at physiological temperatures through a corresponding kinetic process, in which the BITC moiety is covalently bound to these enzyme cysteines through an S-thiocarbamoylation reaction. ESI-MS analysis of the BITC-SG incubated enzymes indicates that although the Cys47 in each subunit is covalently attached to the BITC ligand moiety, only one of the Cys101 residues in the dimer is so attached. A plausible mechanism is given for the emergence of inactivation through the kinetic processes with both cysteines. Likewise, our molecular docking simulations suggest that steric hindrance is the reason why only one Cys101 per dimer is covalently modified by BITC-SG. No covalent inactivation of GST P1-1 with the BC-SG inhibitor has been observed. The affinities and inhibitory potencies for both conjugates are high and very similar, but slightly lower for BC-SG. Thus, we conclude that the presence of the sulfur atom from the isothiocyanate moiety in BITC-SG is crucial for its irreversible inhibition of GST P1-1.

Treatment of doxorubicin-resistant MCF7/Dx cells with nitric oxide causes histone glutathionylation and reversal of drug resistance.

Acquired drug resistance was found to be suppressed in the doxorubicin-resistant breast cancer cell line MCF7/Dx after pre-treatment with GSNO (nitrosoglutathione). The effect was accompanied by enhanced protein glutathionylation and accumulation of doxorubicin in the nucleus. Among the glutathionylated proteins, we identified three members of the histone family; this is, to our knowledge, the first time that histone glutathionylation has been reported. Formation of the potential NO donor dinitrosyl-diglutathionyl-iron complex, bound to GSTP1-1 (glutathione transferase P1-1), was observed in both MCF7/Dx cells and drug-sensitive MCF7 cells to a similar extent. In contrast, histone glutathionylation was found to be markedly increased in the resistant MCF7/Dx cells, which also showed a 14-fold higher amount of GSTP1-1 and increased glutathione concentration compared with MCF7 cells. These results suggest that the increased cytotoxic effect of combined doxorubicin and GSNO treatment involves the glutathionylation of histones through a mechanism that requires high glutathione levels and increased expression of GSTP1-1. Owing to the critical role of histones in the regulation of gene expression, the implication of this finding may go beyond the phenomenon of doxorubicin resistance.

Repetitive transcranial magnetic stimulation in treatment-seeking subjects with cocaine use disorder: A randomized, double-blind, sham-controlled trial.

BACKGROUND: Cocaine use disorder (CUD) is a chronic and relapsing brain disorder with no approved treatments. Repetitive transcranial magnetic stimulation (rTMS) has shown promising results in open label and single-blind studies, reducing cocaine craving and consumption. Although, large randomized, double-blind, controlled trials are still missing. OBJECTIVE: This multi-center, randomized, double-blind, sham-controlled study was designed to evaluate the safety and efficacy of multiple sessions of active rTMS compared to sham stimulation in patients with CUD. METHODS: rTMS (15 Hz, 2 daily sessions for 5 days/week,for a total of 20 stimulation sessions) was delivered over the left DLPFC for two weeks of continuous treatment followed by 12 weeks of maintenance (1 day/week, twice a day), in a double-blind, randomized sham-controlled design. Our primary outcomes included self-reported cue-induced craving and cocaine consumption, as measured by percentage of negative urine tests. Our secondary outcomes included: 1) changes in depressive symptoms; 2) changes in cocaine withdrawal symptoms; and 3) changes in self-reported days of cocaine use. RESULTS: Forty-two outpatients with CUD were enrolled in the active rTMS group and 38 patients in the sham group. We observed a significant decrease in self-reported cue-induced cocaine craving and consumption in both the active rTMS and sham, whereas no main effect of treatment was found. However, the active rTMS group showed greater changes in depressive symptoms. The improvement on depressive symptomatology was particularly marked among patients receiving a total number of rTMS sessions greater than 40 and those reporting more severe depressive symptoms at baseline. CONCLUSIONS: A significant improvement of CUD symptoms during active rTMS treatment was observed. However, we did not observe significant differences in cocaine craving and consumption between treatment groups, highlighting the complexity of factors contributing to CUD maintenance. A significant improvement in depressive symptoms was observed in favour of the active group. Clinical trial registration details:clinicaltrials.govidentifierNCT03333460.

Diuretic drug binding to human glutathione transferase P1-1: potential role of Cys-101 revealed in the double mutant C47S/Y108V.

The diuretic drug ethacrynic acid (EA), both an inhibitor and substrate of pi class glutathione S-transferase (GST P1-1), has been tested in clinical trials as an adjuvant in chemotherapy. We recently studied the role of the active site residue Tyr-108 in binding EA to the enzyme and found that the analysis was complicated by covalent binding of this drug to the highly reactive Cys-47. Previous attempts to eliminate this binding by chemical modification yielded ambiguous results and therefore we decided here to produce a double mutant C47S/Y108V by site directed mutagenesis and further expression in Escherichia coli and the interaction of EA and its GSH conjugate (EASG) examined by calorimetric studies and X-ray diffraction. Surprisingly, in the absence of Cys-47, Cys-101 (located at the dimer interface) becomes a target for modification by EA, albeit at a lower conjugation rate than Cys-47. The Cys-47 → Ser mutation in the double mutant enzyme induces a positive cooperativity between the two subunits when ligands with affinity to G-site bind to enzyme. However, this mutation does not seem to affect the thermodynamic properties of ligand binding to the electrophilic binding site (H-site) and the thermal or chemical stability of this double mutant does not significantly affect the unfolding mechanism in either the absence or presence of ligand. Crystal structures of apo and an EASG complex are essentially identical with a few exceptions in the H-site and in the water network at the dimer interface.

Glutathione transferases and glutathionylated hemoglobin in workers exposed to low doses of 1,3-butadiene.

We evaluated glutathione transferase (GST) activities and the levels of glutathionylated hemoglobin in the RBC of 42 workers exposed to 1,3-butadiene in a petrochemical plant, using 43 workers not exposed to 1,3-butadiene and 82 foresters as internal and external controls, respectively. Median 1,3-butadiene exposure levels were 1.5, 0.4, and 0.1 microg/m3 in 1,3-butadiene-exposed workers, in workers not directly exposed to 1,3-butadiene, and in foresters, respectively. In addition, we determined in the peripheral blood lymphocytes of the same individuals the presence of GST polymorphic genes GSTT1 and GSTM1 and the distribution of GSTP1 allelic variants. Comparing the mean values observed in petrochemical workers with those of control foresters, we found a marked decrease of GST enzymatic activity and a significant increase of glutathionylated hemoglobin in the petrochemical workers. A weak but significant negative correlation was found between levels of 1,3-butadiene exposure and GST activity, whereas a positive correlation was found between 1,3-butadiene exposure and glutathionylated hemoglobin. A negative correlation was also observed between GST activity and glutathionylated hemoglobin. No influence of confounders was observed. Using a multiple linear regression model, up to 50.6% and 41.9% of the variability observed in glutathionylated hemoglobin and GST activity, respectively, were explained by 1,3-butadiene exposure, working setting, and GSTT1 genotype. These results indicate that occupational exposure to 1,3-butadiene induces an oxidative stress that impairs the GST balance in RBC, and suggest that GST activity and glutathionylated hemoglobin could be recommended as promising biomarkers of effect in petrochemical workers.

Early changes in renal hemodynamics in children with diabetes: Doppler sonographic findings.

PURPOSE: Although clinically evident diabetes-related microvascular complications are extremely rare in childhood, early functional and structural abnormalities may be present a few years after the onset of the disease. Renal Doppler resistance index (RI) is widely used for the evaluation of blood flow in renal parenchymal diseases. This study was designed to investigate the possible alteration of intrarenal Doppler RI in children with diabetes compared with healthy children. METHODS: The study was performed in 42 children with diabetes (age range, 6-18 years) and in 41 age-matched healthy controls, all having normal renal function. RI was measured with Doppler sonography in interlobular renal arteries. RESULTS: RI values were significantly greater in children with diabetes than in age-matched healthy controls (0.64 +/- 0.03 versus 0.60 +/- 0.04, P < 0.035). RI correlated positively with HbA1c (P < 0.001, r = 0.42) and diabetes duration (P < 0.05, r = 0.39). CONCLUSION: Early changes in renal hemodynamics are detectable on Doppler sonography in children with diabetes without any evidence of renal dysfunction and may suggest a preclinical stage of diabetic nephropathy.

Serum and urinary nitrites and nitrates and Doppler sonography in children with diabetes.

OBJECTIVE: The aim of the present study was to evaluate serum and urinary nitric oxide (NO) concentrations in children and adolescents with diabetes compared with age-matched healthy control subjects to find out whether Doppler ultrasonography could be used to detect changes in renal resistive indexes (RIs) in children with diabetes and to assess whether there are correlations between these parameters and NO excretion. RESEARCH DESIGN AND METHODS: We studied 42 children with type 1 diabetes and 41 matched healthy control subjects, both divided into prepubertal or pubertal children. Serum and urinary nitrite and nitrate (NO2-+NO3-) concentrations were evaluated as an index of NO production. Doppler ultrasonographic registration of intrarenal RI was performed. RESULTS: Compared with healthy control subjects, children with diabetes had significantly increased concentrations of serum (30.26 +/- 6.52 vs. 24.47 +/- 7.27 mmol/l, P = 0.001) and urinary NO2-+NO3- (345.07 +/- 151.35 vs. 245.86 +/- 80.25 mmol/l, P = 0.002); the same was true for Doppler RI values (0.64 +/- 0.03 vs. 0.60 +/- 0.04, P = 0.035). This occurs in both prepubertal and the pubertal children. A significant positive correlation was found between serum and urinary NO2-+NO3- levels (P = 0.002, r = 0.374). Serum NO2-+NO3- concentrations also correlated positively with Doppler RI (P = 0.032, r = 0.262) and HbA1c (A1C) (P = 0.004, r = 0.329); urinary NO2-+NO3- concentrations correlated positively with A1C (P = 0.001, r = 0.394). Doppler RI correlated positively with A1C (P = 0.000, r = 0.424). CONCLUSIONS: This study demonstrates that in children with diabetes, chronic hyperglycemia may act through a mechanism that involves increased NO production and/or action and contributes to generating intrarenal hemodynamic abnormalities, which are detectable by Doppler ultrasonography even in early diabetic nephropathy.

National Institute on Alcohol Abuse and Alcoholism and the study of fetal alcohol spectrum disorders. The International Consortium.

Fetal alcohol syndrome (FAS) is a large and rapidly increasing public health problem worldwide. Aside the full-blown FAS, multiple terms are used to describe the continuum of effects that result from prenatal exposure to alcohol, including the whole fetal alcohol spectrum disorders (FASD). The revised Institute of Medicine (IOM) Diagnostic Classification System and the diagnostic criteria for FAS and FASD are reported, as well as the formation of the four-state FAS International Consortium and its aims, as the development of an information base that systematizes data collection that helps to determine at-high-risk populations, and to implement and test a scientific-based prevention/intervention model for at risk women. The Consortium was further enlarged, with the inclusion of some more states (including Italy), leading to the formation of the International Consortium for the Investigation of FASD. The objectives of the Consortium are reported, as well as its previous activities, the South Africa and Italy Projects (active case ascertainment initiatives), and its future activities.

Fetal alcohol syndrome disorders: experience on the field. The Lazio study preliminary report.

In Italy, little is known about the problems related to alcohol drinking during pregnancy. In this paper, the Italian literature about this subject is briefly reviewed. This first Italian experience of a field study, aimed to the assessment of the prevalence of fetal alcohol syndrome (FAS) and fetal alcohol spectrum disorders (FASD) in an area in the Rome province (Lazio region) is reported. This in-field study was performed in the school years 2003-2004 and 2004-2005 in cooperation with American researchers, most from University of New Mexico (Albuquerque), and Italian researchers from University "la Sapienza" of Rome. First grade children (n(o) = 1,086) of primary school were contacted to enter in the in-school study for the detection of FAS and FASD and were examined by the experts team of clinicians, pediatrics, psychologists. Preliminary consideration and the implications of this study for FASD prevention are discussed.

Glutathione transferases and neurodegenerative diseases.

There is substantial agreement that the unbalance between oxidant and antioxidant species may affect the onset and/or the course of a number of common diseases including Parkinson's and Alzheimer's diseases. Many studies suggest a crucial role for oxidative stress in the first phase of aging, or in the pathogenesis of various diseases including neurological ones. Particularly, the role exerted by glutathione and glutathione-related enzymes (Glutathione Transferases) in the nervous system appears more relevant, this latter tissue being much more vulnerable to toxins and oxidative stress than other tissues such as liver, kidney or muscle. The present review addresses the question by focusing on the results obtained by specimens from patients or by in vitro studies using cells or animal models related to Parkinson's and Alzheimer's diseases. In general, there is an association between glutathione depletion and Parkinson's or Alzheimer's disease. In addition, a significant decrease of glutathione transferase activity in selected areas of brain and in ventricular cerebrospinal fluid was found. For some glutathione transferase genes there is also a correlation between polymorphisms and onset/outcome of neurodegenerative diseases. Thus, there is a general agreement about the protective effect exerted by glutathione and glutathione transferases but no clear answer about the mechanisms underlying this crucial role in the insurgence of neurodegenerative diseases.

Influence of the H-site residue 108 on human glutathione transferase P1-1 ligand binding: structure-thermodynamic relationships and thermal stability.

The effect of the Y108V mutation of human glutathione S-transferase P1-1 (hGST P1-1) on the binding of the diuretic drug ethacrynic acid (EA) and its glutathione conjugate (EASG) was investigated by calorimetric, spectrofluorimetric, and crystallographic studies. The mutation Tyr 108 --> Val resulted in a 3D-structure very similar to the wild type (wt) enzyme, where both the hydrophobic ligand binding site (H-site) and glutathione binding site (G-site) are unchanged except for the mutation itself. However, due to a slight increase in the hydrophobicity of the H-site, as a consequence of the mutation, an increase in the entropy was observed. The Y108V mutation does not affect the affinity of EASG for the enzyme, which has a higher affinity (K(d) approximately 0.5 microM) when compared with those of the parent compounds, K(d) (EA) approximately 13 microM, K(d) (GSH) approximately 25 microM. The EA moiety of the conjugate binds in the H-site of Y108V mutant in a fashion completely different to those observed in the crystal structures of the EA or EASG wt complex structures. We further demonstrate that the Delta C(p) values of binding can also be correlated with the potential stacking interactions between ligand and residues located in the binding sites as predicted from crystal structures. Moreover, the mutation does not significantly affect the global stability of the enzyme. Our results demonstrate that calorimetric measurements maybe useful in determining the preference of binding (the binding mode) for a drug to a specific site of the enzyme, even in the absence of structural information.

The anti-cancer drug chlorambucil as a substrate for the human polymorphic enzyme glutathione transferase P1-1: kinetic properties and crystallographic characterisation of allelic variants.

The commonly used anti-cancer drug chlorambucil is the primary treatment for patients with chronic lymphocytic leukaemia. Chlorambucil has been shown to be detoxified by human glutathione transferase Pi (GST P1-1), an enzyme that is often found over-expressed in cancer tissues. The allelic variants of GST P1-1 are associated with differing susceptibilities to leukaemia and differ markedly in their efficiency in catalysing glutathione (GSH) conjugation reactions. Here, we perform detailed kinetic studies of the allelic variants with the aid of three representative co-substrates. We show that the differing catalytic properties of the variants are highly substrate-dependent. We show also that all variants exhibit the same temperature stability in the range 10 degrees C to 45 degrees C. We have determined the crystal structures of GST P1-1 in complex with chlorambucil and its GSH conjugate for two of these allelic variants that have different residues at positions 104 and 113. Chlorambucil is found to bind in a non-productive mode to the substrate-binding site (H-site) in the absence of GSH. This result suggests that under certain stress conditions where GSH levels are low, GST P1-1 can inactivate the drug by sequestering it from the surrounding medium. However, in the presence of GSH, chlorambucil binds in the H-site in a productive mode and undergoes a conjugation reaction with GSH present in the crystal. The crystal structure of the GSH-chlorambucil complex bound to the *C variant is identical with the *A variant ruling out the hypothesis that primary structure differences between the variants cause structural changes at the active site. Finally, we show that chlorambucil is a very poor inhibitor of the enzyme in contrast to ethacrynic acid, which binds to the enzyme in a similar fashion but can act as both substrate and inhibitor.