Pharmacogenomic biomarker information on drug labels of the Spanish Agency of Medicines and Sanitary products: evaluation and comparison with other regulatory agencies.

This work aimed to analyse the pharmacogenetic information in the Spanish Drug Regulatory Agency (AEMPS) Summary of Products Characteristics (SmPC), evaluating the presence of pharmacogenetic biomarkers, as well as the associated recommendations. A total of 55.4% of the 1891 drug labels reviewed included information on pharmacogenetic biomarker(s). Pharmacogenomic information appears most frequently in the "antineoplastic and immunomodulating agents", "nervous system", and "cardiovascular system" Anatomical Therapeutic Chemical groups. A total of 509 different pharmacogenetic biomarkers were found, of which CYP450 enzymes accounted for almost 34% of the total drug-biomarker associations evaluated. A total of 3679 drug-biomarker pairs were identified, 102 of which were at the 1A level (PharmGKB® classification system), and 33.33% of these drug-pharmacogenetic biomarker pairs were assigned to "actionable PGx", 12.75% to "informative PGx", 4.9% to "testing recommended", and 4.9% to "testing required". The rate of coincidence in the assigned PGx level of recommendation between the AEMPS and regulatory agencies included in the PharmGKB® Drug Label Annotations database (i.e., the FDA, EMA, SWISS Medic, PMDA, and HCSC) ranged from 45% to 65%, being 'actionable level' the most frequent. On the other hand, discrepancies between agencies did not exceed 35%. This study highlights the presence of relevant pharmacogenetic information on Spanish drug labels, which would help avoid interactions, toxicity, or lack of treatment efficacy.

Prospective study of sexual function and analysis of risk factors after rectal cancer surgery.

AIM: The aim of this study was to assess the evolution of sexual function over time after rectal cancer surgery and to identify risk factors that may have an impact on the deterioration of postoperative function. METHOD: This was a prospective cohort study of sexual function after rectal cancer surgery using the International Index of Erectile Function (IIEF) and Female Sexual Function Index (FSFI) preoperatively and at 6 and 12 months after surgery. Predictive factors of worsening were identified by univariate and multivariate analysis. RESULTS: One hundred and one patients were included (56 men and 45 women). In men, the average IIEF showed decreased erectile function and intercourse satisfaction at 6 months (respectively 21.58 ± 7.18 to 16.60 ± 7.96, p = 0.002 and 10.87 ± 2.94, to 8.09 ± 4.45, p = 0.002) with recovery at 1 year. As a percentage, erectile dysfunction increased from the preoperative value to 6 months (64.5% vs 87.1%, p = 0.022) and was observed in 72% at 1 year. Patients with moderate to severe dysfunction increased from 22% preoperatively to 58% (p = 0.009) at 6 months and 44% at 1 year (p < 0.0001). Neoadjuvant chemoradiotherapy (OR 5.4, 95% CI 0.9-29.6; p = 0.041) and erectile worsening at 6 months (OR 20, 95% CI 1.6-238; p = 0.004) were independent factors for worse function at 6 or 12 months, respectively. No significant worsening of the FSFI was found, although there was an improvement in lubrication and orgasm. CONCLUSION: Temporary deterioration of erectile function in men is common at 6 months after surgery and chemoradiotherapy is the only predictive factor. Furthermore, patients who remain dysfunctional show an increase in the severity of symptoms in relation to the preoperative period.

Mannheimia haemolytica and Bibersteinia trehalosi Serotypes Isolated from Merino Breed Lambs in Extremadura (Southwestern Spain).

Pneumonia caused by Mannheimia haemolytica is an important disease in ruminants. Because of its economic significance, several methods have been developed to study the pathogenicity and epidemiology of M. haemolytica. In this study, bacterial isolates of M. haemolytica and Bibersteinia trehalosi identified from the lungs of sheep were serotyped by means of indirect haemagglutination. Of the 598 lungs studied, 34 isolates were identified and serotyped. In decreasing order, M. haemolytica serotypes were: not typable (50 %), A1 (17.65 %), A7 (11.76 %), A6 (5.88 %), and A12, A2, A5 and A9 (each representing 2.94 %). The only B. trehalosi serotype was T4 (2.94 %). Serotypes A1, A6 and A7 of M. haemolytica were the most commonly isolated from pneumonic sheep producing greater changes in the lungs and having important implications for sheep production.

Analysis of immunogenetics interlaboratory comparisons' success rates. External quality assurance system of the Spanish Society for Immunology GECLID-SEI.

Background: For many years, transplantation outcomes were uncertain and not hopeful, until histocompatibility testing spread. Common criteria for histocompatibility assays and communications' improvement allowed an efficient organ sharing system. The possibility of organ exchanges is closely linked to the importance of interlaboratory comparisons for histocompatibility and immunogenetics methods. The external proficiency testing (EPT) systems are the most powerful quality assurance tools. They help achieve harmonization of analyses, set a standard of performance, and a common interpretation. Methods: The external quality assurance program for diagnostic immunology laboratories (Garantía Externa de Calidad para Laboratorios de Inmunología Diagnóstica, GECLID) program nowadays runs 13 external quality assurance (EQA) histocompatibility and immunogenetics schemes, with the first of them from 2011 to date: serological and molecular: low- and high-resolution human leukocyte antigen (HLA), human platelet antigen (HPA), and killer inhibitory receptor (KIR) typing(HLA-B*27, HLA-B*57:01, and coeliac disease-related HLA), cell-dependent cytotoxicity (CDC) and flow cytometry (FC) crossmatches, anti-HLA and anti-HPA antibodies, and chimerism. Results: A total of 85 laboratories participated in this subprogram in the last 12 years reporting over 1.69 M results: 1.46 M for anti-HLA and anti-HPA antibodies, 203.810 molecular typing data (HLA, HPA, and KIR genes), 2.372 for chimerism analyses, and 39.352 for crossmatches. Based on the European Federation for Immunogenetics (EFI) standards for EPT providers, the mean success rates ranged from 99.2% for molecular typing schemes and antibodies and 94.8% for chimerism, was 96.7% regarding crossmatches, and was 98.9% in serological typing. In 2022, 61.3% of the participating laboratories successfully passed every HLA EQA scheme, although 87.9% annual reports were satisfactory. Most penalties were due to nomenclature errors or misreporting of the risk associated to HLA and disease. Conclusion: This EQA confirms the reliability of HLA and immunogenetics assays in routine care. There is little heterogeneity of results of different assays used by participating laboratories, even when in-house assays are used. Reliability of test results is reasonably granted.

Persistence of SARS-CoV-2 total immunoglobulins in a series of convalescent plasma and blood donors.

BACKGROUND: The vast majority of COVID-19 cases both symptomatic and asymptomatic develop immunity after COVID-19 contagion. Whether lasting differences exist between infection and vaccination boosted immunity is yet to be known. The aim of this study was to determine how long total anti-SARS-CoV2 antibodies due to past infection persist in peripheral blood and whether sex, age or haematological features can influence their lasting. MATERIAL AND METHODS: A series of 2421 donations either of SARS-CoV-2 convalescent plasma or whole blood from 1107 repeat donors from January 2020 to March 2021 was analysed. An automated chemiluminescence immunoassay for total antibodies recognizing the nucleocapsid protein of SARS-CoV-2 in human serum and plasma was performed. Sex, age, blood group, blood cell counts and percentages and immunoglobulin concentrations were extracted from electronic recordings. Blood donation is allowed after a minimum of one-month post symptom's relapse. Donors were 69.7% males and their average age was 46. The 250 donors who had later donations after a positive one underwent further analysis. Both qualitative (positivity) and quantitative (rise or decline of optical density regarding consecutive donations) outcomes were evaluated. RESULTS AND DISCUSSION: In 97.6% of donors with follow-up, anti-SARS-CoV-2 protein N total antibodies remained positive at the end of a follow-up period of 12.4 weeks median time (1-46, SD = 9.65) after the first positive determination. The blood group was not related to antibody waning. Lower lymphocyte counts and higher neutrophils would help predict future waning or decay of antibodies. Most recovered donors maintain their total anti-SARS-CoV-2 N protein antibodies for at least 16 weeks (at least one month must have been awaited from infection resolution to blood donation). The 10 individuals that could be followed up longer than 40 weeks (approximately 44 weeks after symptom's relapse) were all still positive.

Epithelial component and intraepithelial lymphocytes of conjunctiva-associated lymphoid tissue in healthy children.

Conjunctiva-associated lymphoid tissue (CALT) plays a key role in protecting the eye surface by initiating and regulating immune responses. The aim of this study was to investigate in healthy children the proportion of intraepithelial lymphocytes (IELs), the degree of viability and/or apoptosis and cell proliferation in three different topographic areas of the conjunctiva. Superior tarsal, superior bulbar, and inferior tarsal-bulbarfornix conjunctival cells were collected by brush cytology (BC) from 24 healthy paediatric subjects (13 boys and 11 girls, mean age 6±2 years) who were to undergo strabismus correction surgery under general anaesthesia. Subsequently, these cells were analysed phenotypically and functionally by flow cytometry (FC). Flow cytometry analysis showed that not all the cells obtained by BC were of the epithelial lineage, but that there was a population of CD45+ cells (IELs) regularly present in the conjunctiva of healthy children. These IELs were mostly T-lymphocytes (CD3+) and B-lymphocytes (CD19+), with higher levels of T-lymphocytes (CD3+) in the upper areas than in the inferior tarsal-bulbar-fornix, where the highest levels of B-lymphocytes (CD19+) were found. In the apoptosis assay, two groups of cell populations were differentiated by cell size and complexity (cytoplasmic granularity), with more complex cells predominating in the upper areas of the conjunctiva and less complex cells being more abundant in the inferior tarsal-bulbar-fornix. Finally, the proliferative capacity of the conjunctival epithelium was significantly higher in the upper tarsal zone than in the rest of the zones analysed. These results suggest that the epithelial component and the IELs of CALT are also regularly present in the conjunctiva of the healthy child, varying in phenotype, viability and cell proliferation according to the different conjunctival regions analysed, which could lead us to believe that each conjunctival zone plays a different, specific role in the regulation of the immune response at the ocular level.

Impact of sulfur starvation on cysteine biosynthesis in T-DNA mutants deficient for compartment-specific serine-acetyltransferase.

Sulfur plays a pivotal role in the cellular metabolism of many organisms. In plants, the uptake and assimilation of sulfate is strongly regulated at the transcriptional level. Regulatory factors are the demand of reduced sulfur in organic or non-organic form and the level of O-acetylserine (OAS), the carbon precursor for cysteine biosynthesis. In plants, cysteine is synthesized by action of the cysteine-synthase complex (CSC) containing serine acetyltransferase (SAT) and O-acetylserine-(thiol)-lyase (OASTL). Both enzymes are located in plastids, mitochondria and the cytosol. The function of the compartmentation of the CSC to regulate sulfate uptake and assimilation is still not clearly resolved. To address this question, we analyzed Arabidopsis thaliana mutants for the plastidic and cytosolic SAT isoenzymes under sulfur starvation conditions. In addition, subcellular metabolite analysis by non-aqueous fractionation revealed distinct changes in subcellular metabolite distribution upon short-term sulfur starvation. Metabolite and transcript analyses of SERAT1.1 and SERAT2.1 mutants [previously analyzed in Krueger et al. (Plant Cell Environ 32:349-367, 2009)] grown under sulfur starvation conditions indicate that both isoenzymes do not contribute directly to the transcriptional regulation of genes involved in sulfate uptake and assimilation. Here, we summarize the current knowledge about the regulation of cysteine biosynthesis and the contribution of the different compartments to this metabolic process. We relate hypotheses and views of the regulation of cysteine biosynthesis with our results of applying sulfur starvation to mutants impaired in compartment-specific cysteine biosynthetic enzymes.

Analysis of cytosolic and plastidic serine acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for cysteine biosynthesis in Arabidopsis.

In plants, the enzymes for cysteine synthesis serine acetyltransferase (SAT) and O-acetylserine-(thiol)-lyase (OASTL) are present in the cytosol, plastids and mitochondria. However, it is still not clearly resolved to what extent the different compartments are involved in cysteine biosynthesis and how compartmentation influences the regulation of this biosynthetic pathway. To address these questions, we analysed Arabidopsis thaliana T-DNA insertion mutants for cytosolic and plastidic SAT isoforms. In addition, the subcellular distribution of enzyme activities and metabolite concentrations implicated in cysteine and glutathione biosynthesis were revealed by non-aqueous fractionation (NAF). We demonstrate that cytosolic SERAT1.1 and plastidic SERAT2.1 do not contribute to cysteine biosynthesis to a major extent, but may function to overcome transport limitations of O-acetylserine (OAS) from mitochondria. Substantiated by predominantly cytosolic cysteine pools, considerable amounts of sulphide and presence of OAS in the cytosol, our results suggest that the cytosol is the principal site for cysteine biosynthesis. Subcellular metabolite analysis further indicated efficient transport of cysteine, gamma-glutamylcysteine and glutathione between the compartments. With respect to regulation of cysteine biosynthesis, estimation of subcellular OAS and sulphide concentrations established that OAS is limiting for cysteine biosynthesis and that SAT is mainly present bound in the cysteine-synthase complex.

[Influence of mutations of proteinase-activated receptors F2R/PAR1 and F2RL1/PAR2 on inflammatory bowel disease]. / Influencia de las mutaciones de los receptores activados por proteinasa F2R/PAR1 y F2RL1/PAR2 en la enfermedad inflamatoria intestinal.

BACKGROUND AND OBJECTIVE: Inflammatory bowel disease (IBD) is a polygenic complex trait. The expression and presence in biopsiae from IBD patients points to a putative role of these genes in genetic susceptibility to IBD. This is the first association study on these genes in relation with IBD. PATIENTS AND METHOD: Two polymorphisms were analyzed within F2R/PAR1 and another one mapping to F2RL1/PAR2 in 778 healthy controls and 943 IBD cases (Crohn's disease and ulcerative colitis patients from 2 cohorts from Madrid and Granada). RESULTS: No significant differences in the distribution of the PARs' polymorphisms were found. CONCLUSIONS: There is no evidence of association of the analyzed polymorphisms with IBD risk.

MDR1 polymorphisms and response to azathioprine therapy in patients with Crohn's disease.

BACKGROUND: To investigate the contribution of multidrug resistance 1 (MDR1) gene pharmacogenetics (G2677T/A and C3435T) to the efficacy of azathioprine in inducing remission in patients with Crohn's disease (CD). METHODS: A cohort of 327 unrelated Spanish patients with CD recruited from a single center was studied. All patients were rigorously followed up for at least 2 years (mean time, 11.5 years). A case-control analysis of MDR1 G2677T/A and C3435T SNPs and 2 loci haplotypes in 112 steroid-dependent CD patients treated with azathioprine was performed. Patients were classified on the basis of response to azathioprine. RESULTS: A total 76 patients treated with azathioprine for longer than 3 months were included. Remission was achieved in 42 CD patients (55.3%). A higher frequency of the 2677TT genotype was found in nonresponders than in responders (17.65% versus 7.14%; OR = 2.8; 95% CI; 0.6-12.1; P = 0.11). Nonresponders to azathioprine were found to have a higher frequency of the 3435TT genotype than did CD patients who had achieved clinical remission (17.64% versus 4.76%; OR = 4.3; 95% CI, 0.8-22.8; P = 0.06). The 2677T/3435T haplotype was also more abundant in nonresponders (29.4% versus 20.2%), whereas the 2677G/3435C haplotype was more frequent in responders (58.3% versus 47.1%). Lack of response to azathioprine therapy in CD patients was 1.8-fold greater in carriers of the 2677T/3435T haplotype than in carriers of the 2677G/3435C haplotype (OR = 1.8; 95% CI, 0.82-3.9; P = 0.14). CONCLUSIONS: The results of our study indicate higher frequencies of the 2677TT and 3435TT genotypes and the 2677T/3435T haplotype in CD patients who did not respond to azathioprine. Additional replications in independent populations would confirm the real impact of these polymorphisms in response to azathioprine therapy.

MDR1 gene: susceptibility in Spanish Crohn's disease and ulcerative colitis patients.

BACKGROUND: The multidrug resistance MDR1 gene codes for a membrane transporter associated with inflammatory bowel disease. The polymorphism Ala893Ser/Thr (G2677T/A) previously showed significant association with Crohn's disease (CD) and the Ile1145Ile (C3435T) with ulcerative colitis (UC). We studied the association of both polymorphisms in an independent population to reveal the impact of the MDR1 gene on predisposition to inflammatory bowel disease. METHODS: Case-control study with 321 CD and 330 UC white Spanish patients recruited from the same center, and 352 healthy ethnically matched controls. RESULTS: A significant association of MDR1 C3435T with CD was observed (CC vs (CT + TT): P = 0.007; OR [95% CI] = 1.58 [1.12-2.23]). A CD susceptibility haplotype 2677T/C3435 was identified. No difference between UC patients as a whole and controls could be detected. CONCLUSIONS: New evidence supports the role of the MDR1 gene on CD susceptibility. Therefore, considering our results and those from others, the MDR1 gene behaves as a common risk factor for both CD and UC. We discovered that the C3435 allele conferring susceptibility to CD is different from the described 3435T UC risk allele.

Increased cysteine availability is essential for cadmium tolerance and accumulation in Arabidopsis thaliana.

Employing genetic transformation using an Atcys-3A cDNA construct expressing the cytosolic O-acetylserine(thiol)lyase (OASTL), we obtained two Arabidopsis lines with different capabilities for supplying cysteine under metal stress conditions. Lines 1-2 and 10-10, grown under standard conditions, showed similar levels of cysteine and glutathione (GSH) to those of the wild-type. However, in the presence of cadmium, line 10-10 showed significantly higher levels. The increased thiol content allowed line 10-10 to survive under severe heavy metal stress conditions (up to 400 microm of cadmium in the growth medium), and resulted in an accumulation of cadmium in the leaves to a level similar to that of metal hyperaccumulator plants. Investigation of the epidermal leaf surface clearly showed that most of the cadmium had accumulated in the trichomes. Furthermore, line 10-10 was able to accumulate more cadmium in its trichomes than the wild-type, whereas line 1-2 showed a reduced capacity for cadmium accumulation. Our results suggest that an increased rate of cysteine biosynthesis is responsible for the enhanced cadmium tolerance and accumulation in trichome leaves. Thus, molecular engineering of the cysteine biosynthesis pathway, together with modification of the number of leaf trichomes, may have considerable potential in increasing heavy metal accumulation for phytoremediation purposes.

Efficacy of a brief multifactorial adherence-based intervention in reducing blood pressure: a randomized clinical trial.

BACKGROUND: Lowering blood pressure (BP) by antihypertensive (AHT) drugs reduces the risks of cardiovascular events, stroke, and total mortality. However, poor adherence to AHT medications reduces their effectiveness and increases the risk of adverse events. OBJECTIVE: To evaluate the effectiveness of a multifactorial adherence-based intervention in a primary care setting in lowering BP. METHODS/DESIGN: Multicenter parallel randomized controlled trial. Thirty two nurses in 28 primary care centers of three Spanish regions. Patients aged 18-80 years, taking AHT drugs with uncontrolled BP (n=221) were randomized to a control group (usual care) or a multifactorial adherence-based intervention including nurse-led motivational interviews, pill reminders, family support, BP self-recording, and simplification of the dosing regimen by a pharmacist. MAIN OUTCOME MEASURES: The primary outcome was 12-month blinded measure of systolic BP (mean of three measurements). The secondary outcomes were 12-month diastolic BP and proportion of patients with adequately controlled BP. RESULTS: One hundred and fourteen patients were allocated to the intervention group and 109 to the control group. At 12 months, 212 (89%) participants completed the study. The systolic BP in the intervention group was 151.3 versus 153.7 in the control group (P=0.294). The diastolic BP did not differ between groups (83.4 versus 83.6). Of the patients in the control group, 9.2% achieved BP control versus a 15.8% in the intervention group. The relative risk for achieving BP control was 1.72 (95% confidence interval: 0.83-3.56). CONCLUSION: A multifactorial intervention based on improving adherence in patients with uncontrolled hypertension failed to find evidence of effectiveness in lowering systolic BP. TRIAL REGISTRATION: ISRCTN21229328.

[Phospholipase and proteinase production by Malassezia pachydermatis isolated in dogs with and without otitis]. / Producción de fosfolipasa y proteinasa en cepas de Malassezia pachydermatis aisladas de perros con otitis y sin otitis.

BACKGROUND: Malassezia pachydermatis is part of the skin microbiota of dogs and cats. M. pachydermatis has been associated with external otitis and seborrhoeic dermatitis, reported more often in dogs than in cats. When the physical, chemical or immunological mechanisms of the skin are altered, M. pachydermatis could act as a pathogen. Thus, several virulence factors, such as the ability to produce esterase, lipase, lipoxygenase, protease, chondroitin sulphatase, and hyaluronidase, have been studied. AIMS: In the present study, we aim to identify the phospholipase activity measured at pH 6.3, and the proteinase activity measured at pH 6.3 and pH 6.8 (pH from ears of dogs with external otitis) of M. pachydermatis strains isolated from dogs with and without external otitis. METHODS: The phospholipase activity was measured using a semi-quantitative method with egg yolk, and the proteinase activity with a semi-quantitative method using bovine serum albumin agar. The study was performed on 96 isolates of M. pachydermatis, 43 isolated from dogs without clinical symptoms of otitis, and 52 isolated from dogs with otitis. RESULTS: In our study, 75.8% of the isolates showed phospholipase activity at pH 6.3, and 81 and 97.9% of them showed proteinase activity measured at pH 6.3 and 6.8, respectively. A higher phospholipase activity was detected in strains isolated from dogs with otitis. The proteinase activity was increased at a pH of 6.8 (97.9%) in comparison to a pH of 6.3 (81%). CONCLUSIONS: Our results suggest that the phospholipase activity may play an important role in the invasion of host tissues in chronic canine otitis cases. The proteinase activity results obtained in this study suggest that a reduction in the pH of the treatment may improve its efficacy in the resolution of M. pachydermatis otitis.

Overexpression and activation of EGFR and VEGFR2 in medullary thyroid carcinomas is related to metastasis.

Therapeutic options for patients with metastatic medullary thyroid carcinoma (MTC) are limited due to lack of effective treatments. Thus, there is a need to thoroughly characterize the pathways of molecular pathogenesis and to identify potential targets for therapy in MTC. Since epidermal growth factor receptor (EGFR) seems to play a crucial role for RET activation, a key feature of MTCs, and several promising EGFR/vascular endothelial growth factor receptor 2 (VEGFR2)-targeted drugs have been developed, the present study was designed to investigate whether these proteins are altered in MTCs. We used a well-characterized series of 153 MTCs to evaluate EGFR activation by sequencing and FISH analysis, and to perform EGFR and VEGFR2 immunohistochemistry. EGFR tyrosine kinase domain mutations were not a feature of MTCs; however, EGFR polysomy and a strong EGFR expression were detected in 15 and 13% of the tumors respectively. Interestingly, EGFR was significantly overexpressed in metastases compared with primary tumors (35 vs 9%, P=0.002). We also studied whether specific RET mutations were associated with EGFR status, and found a decrease in EGFR polysomies (P=0.006) and a tendency towards lower EGFR expression for the most aggressive RET mutations (918, 883). Concerning VEGFR2, metastasis showed a higher expression than primary tumors (P=2.8 x 10(-8)). In this first study investigating the relationship between EGFR, RET, and VEGFR2 in a large MTC series, we found an activation of EGFR and VEGFR2 in metastasis, using both independent and matched primary/metastasis samples. This suggests that some MTC patients may benefit from existing anti-EGFR/VEFGR2 therapies, although additional preclinical and clinical evidence is needed.

Cytosolic cysteine in redox signaling.

CYSTEINE BIOSYNTHESIS IN PLANTS TAKES PLACE IN THE THREE CELLULAR COMPARTMENTS WITH AUTONOMOUS PROTEIN BIOSYNTHESIS MACHINERY: cytosol, plastids and mitochondria. This sulfur-containing molecule is synthesized sequentially in these compartments by two enzymatic families, the serine acetyltransferases and the O-acetylserine(thiol) lyases. Each family consists of several isoforms that differ in subcellular localization and abundance. Why so many isoforms are required in plant cell for cysteine biosynthesis has remained unknown to date. The characterization of gene-specific knockout mutants has started to address this question. In our recent work, we have performed a detailed analysis of the Arabidopsis oas-a1 null mutant and showed that the antioxidant capacity of the cytosol is compromised, highlighting the contribution of cytosolic Cys in redox signaling.

Knocking out cytosolic cysteine synthesis compromises the antioxidant capacity of the cytosol to maintain discrete concentrations of hydrogen peroxide in Arabidopsis.

Plant cells contain different O-acetylserine(thiol)lyase (OASTL) enzymes involved in cysteine (Cys) biosynthesis and located in different subcellular compartments. These enzymes are made up of a complex variety of isoforms resulting in different subcellular Cys pools. To unravel the contribution of cytosolic Cys to plant metabolism, we characterized the knockout oas-a1.1 and osa-a1.2 mutants, deficient in the most abundant cytosolic OASTL isoform in Arabidopsis (Arabidopsis thaliana). Total intracellular Cys and glutathione concentrations were reduced, and the glutathione redox state was shifted in favor of its oxidized form. Interestingly, the capability of the mutants to chelate heavy metals did not differ from that of the wild type, but the mutants have an enhanced sensitivity to cadmium. With the aim of establishing the metabolic network most influenced by the cytosolic Cys pool, we used the ATH1 GeneChip for evaluation of differentially expressed genes in the oas-a1.1 mutant grown under nonstress conditions. The transcriptomic footprints of mutant plants had predicted functions associated with various physiological responses that are dependent on reactive oxygen species and suggested that the mutant was oxidatively stressed. Evidences that the mutation caused a perturbation in H2O2 homeostasis are that, in the knockout, H2O2 production was localized in shoots and roots; spontaneous cell death lesions occurred in the leaves; and lignification and guaiacol peroxidase activity were significantly increased. All these findings indicate that a deficiency of OAS-A1 in the cytosol promotes a perturbation in H2O2 homeostasis and that Cys is an important determinant of the antioxidative capacity of the cytosol in Arabidopsis.