Structural and functional studies of Arabidopsis thaliana glutamate dehydrogenase isoform 2 demonstrate enzyme dynamics and identify its calcium binding site

Glutamate dehydrogenase (GDH) is an enzyme at the crossroad of plant nitrogen and carbon metabolism. GDH catalyzes the conversion of 2-oxoglutarate into glutamate (2OG → Glu), utilizing ammonia as cosubstrate and NADH as coenzyme. The GDH reaction is reversible, meaning that the NAD+-dependent reaction (Glu → 2OG) releases ammonia. In Arabidopsis thaliana, three GDH isoforms exist, AtGDH1, AtGDH2, and AtGDH3. The subject of this work is AtGDH2. Previous reports have suggested that enzymes homologous to AtGDH2 contain a calcium-binding EF-hand motif located in the coenzyme binding domain. Here, we show that while AtGDH2 indeed does bind calcium, the binding occurs elsewhere and the region predicted to be the EF-hand motif has a completely different structure. As the true calcium binding site is > 20 Å away from the active site, it seems to play a structural, rather than catalytic role. We also performed comparative kinetic characterization of AtGDH1 and AtGDH2 using spectroscopic methods and isothermal titration calorimetry, to note that the isoenzymes generally exhibit similar behavior, with calcium having only a minor effect. However, the spatial and temporal changes in the gene expression profiles of the three AtGDH genes point to AtGDH2 as the most prevalent isoform.

Glutamate dehydrogenase: Potential therapeutic targets for neurodegenerative disease

Glutamate dehydrogenase (GDH) is a key enzyme in mammalian glutamate metabolism. It is located at the intersection of multiple metabolic pathways and participates in a variety of cellular activities. GDH activity is strictly regulated by a variety of allosteric compounds. Here, we review the unique distribution and expressions of GDH in the brain nervous system. GDH plays an essential role in the glutamate-glutamine-GABA cycle between astrocytes and neurons. The dysfunction of GDH may induce the occurrence of many neurodegenerative diseases, such as Parkinson's disease, epilepsy, Alzheimer's disease, schizophrenia, and frontotemporal dementia. GDH activators and gene therapy have been found to protect neurons and improve motor disorders in neurodegenerative diseases caused by glutamate metabolism disorders. To date, no medicine has been discovered that specifically targets neurodegenerative diseases, although several potential medicines are used clinically. Targeting GDH to treat neurodegenerative diseases is expected to provide new insights and treatment strategies.

Study of Alzheimer's disease- and frontotemporal dementia-associated genes in the Cretan Aging Cohort

Using exome sequencing, we analyzed 196 participants of the Cretan Aging Cohort (CAC; 95 with Alzheimer's disease [AD], 20 with mild cognitive impairment [MCI], and 81 cognitively normal controls). The APOE ε4 allele was more common in AD patients (23.2%) than in controls (7.4%; p < 0.01) and the PSEN2 p.Arg29His and p.Cys391Arg variants were found in 3 AD and 1 MCI patient, respectively. Also, we found the frontotemporal dementia (FTD)-associated TARDBP gene p.Ile383Val variant in 2 elderly patients diagnosed with AD and in 2 patients, non CAC members, with the amyotrophic lateral sclerosis/FTD phenotype. Furthermore, the p.Ser498Ala variant in the positively selected GLUD2 gene was less frequent in AD patients (2.11%) than in controls (16%; p < 0.01), suggesting a possible protective effect. While the same trend was found in another local replication cohort (n = 406) and in section of the ADNI cohort (n = 808), this finding did not reach statistical significance and therefore it should be considered preliminary. Our results attest to the value of genetic testing to study aged adults with AD phenotype.

A strategy for nitrogen conversion in aquaculture water based on poly-γ-glutamic acid synthesis

Ammonia and nitrite are nitrogenous pollutants in aquaculture effluents, which pose a major threat to the health of aquatic animals. In this study, we developed a nitrogen conversion strategy based on synthesis of poly-γ-glutamic acid (γ-PGA) by Bacillus subtilis NX-2. The nitrogen removal efficiency of NX-2 was closely related to synthesizing γ-PGA, and was positively correlated with the inoculum level. The degradation rates of ammonia nitrogen and nitrite at 10⁴ CFU/mL were 84.42 % and 62.56 %, respectively. Through adaptive laboratory evolution (ALE) experiment, we obtained a strain named ALE 5 M with ammonia degradation rate of 98.03 % and nitrite of 93.62 % at the inoculum level of 10⁴ CFU/mL. Transcriptome analysis showed that the strain was more likely to produce γ-PGA after ALE. By enzyme activity and qPCR analysis, we confirmed that ALE 5 M degraded ammonia nitrogen through γ-PGA synthesis, which provided a new way for nitrogen removal in aquaculture water.

Links of platelet glutamate and glutathione metabolism with attenuated positive and negative symptoms in depressed patients at clinical high risk for psychosis

Aim of the study is to reveal clinical and biological correlations in patients with adolescent depression and attenuated psychotic symptoms. Activity of platelet enzymes involved in glutamate-, glutathione- and energy metabolism was evaluated in control group and in the patients, because these systems are suspected as related to pathogenesis of psychosis. Adolescents (78 men, 16-25 years old) hospitalized with the first acute depressive state composed two groups: with prevalence of attenuated psychotic positive or negative symptoms (Gr1 and Gr2, 48 and 30 patients, respectively). Control group comprised 20 mentally healthy men of 19-25 years old. Gr1 differed significantly from Gr2 in scores by the Scale of Prodromal Symptoms (SOPS) for positive symptoms, p < 0.001, for disorganization symptoms, p < 0.003, and for total SOPS score, p < 0.001, before the treatment started. When patients from either Gr1 or Gr2 were compared with the control group, significantly decreased baseline activities of platelet glutamate dehydrogenase (GDH), glutathione reductase (GR) and glutathione S-transferase (GST) were found (p < 0.0001). Different correlations were found between baseline enzymatic activities in Gr1 and Gr2: GDH activity correlated with GR activity in Gr1 (R = 0.37), and with GST activity in Gr2 (R = 0.70). Significant correlations were found only in Gr2 between the delta of scores by SOPS negative symptoms (SOPS-N) under treatment and baseline GDH, GST, and GR activities (R = - 0.36, R = - 0.60, and R = 0.38, respectively). The found correlations of the baseline enzymatic activity levels with the value of the decrease (delta) in SOPS-N scores under the treatment represent interest for the prediction of the pharmacotherapy efficiency.

Long-term 1,2-dimethylhydrazine triggers pathological remodeling of colon mucosa through repression of sestrin2, nuclear factor (erythroid-derived 2)-like 2, and sirtuin4 stimulating mitochondrial stress and metabolic reprogramming

1,2-Dimethylhydrazine (DMH) is a plant toxicant that enters the food web through the diet. It is biotransformed into azoxymethane, a colon carcinogen, during the first hepatic passage. In mice, this study assessed the role of glutamate dehydrogenase (GDH), a key glutaminolysis enzyme in DMH-induced colorectal cancer (CRC). Colon samples were taken from mice given 6 or 15 weekly doses of 20 mg/kg DMH and serially sacrificed. Repeated DMH doses induced early aberrant crypt foci that evolved into irreversible adenocarcinomas over 24 weeks, along with an increase in GDH and lactate dehydrogenase activities (+ 122%, + 238%, P < 0.001), indicating a switch to aerobic glycolysis and glutaminolysis. Transcriptional downregulation of the endogenous GDH inhibitor, sirtuin4, and two redox regulators, mitochondrial sestrin2 and nuclear factor (erythroid derivative 2)-like 2 (- 26% and - 22%, P < 0, 05; and - 30%, P < 0.01), exacerbated mitochondrial stress by boosting mitochondrial superoxide dismutase activity (+ 240% (P < 0.001) while depressing catalase activity and GSH levels (- 57% and - 60%, P < 0.001). In vitro, allosteric GDH inhibition by 50 µM epigallocatechin gallate decreased human carcinoma (HCT-116) cells' viability, clonogenicity, and migration (- 43% and - 57%, P < 0.001, 41%, P < 0.05), while stimulating ROS release (+ 57%, P < 0.001). Dimethylfumarate (DMF), a linear electrophile and mitochondrial fumarate analog, rebalanced ROS levels (- 34%, P < 0.05) and improved GDH activity, cell viability, and tumorogenic capacity (+ 20%, 20%, P < 0.001; and 33%, P < 0.05). Thus, the pathological remodeling of colon mucosa is supported by metabolic reprogramming bypassing uncoupled mitochondria. DMF highlights the critical role of electrophile response elements in modulating redox mithormesis and redox homeostasis during CRC.

Arabidopsis thaliana sirtuins control proliferation and glutamate dehydrogenase activity

Sirtuins are part of a gene family of NAD-dependent deacylases that act on histone and non-histone proteins and control a variety of activities in all living organisms. Their roles are mainly related to energy metabolism and include lifetime regulation, DNA repair, stress resistance, and proliferation. A large amount of knowledge concerning animal sirtuins is available, but data about their plant counterparts are scarce. Plants possess few sirtuins that have, like in animals, a recognized role in stress defense and metabolism regulation. However, engagement in proliferation control, which has been demonstrated for mammalian sirtuins, has not been reported for plant sirtuins so far. In this work, srt1 and srt2 Arabidopsis mutant seedlings have been used to evaluate in vivo the role of sirtuins in cell proliferation and regulation of glutamate dehydrogenase, an enzyme demonstrated to be involved in the control of cell cycle in SIRT4-defective human cells. Moreover, bioinformatic analyses have been performed to elucidate sequence, structure, and function relationships between Arabidopsis sirtuins and between each of them and the closest mammalian homolog. We found that cell proliferation and GDH activity are higher in mutant seedlings, suggesting that both sirtuins exert a physiological inhibitory role in these processes. In addition, mutant seedlings show plant growth and root system improvement, in line with metabolic data. Our data also indicate that utilization of an easy to manipulate organism, such as Arabidopsis plant, can help to shed light on the molecular mechanisms underlying the function of genes present in interkingdom species.

Transcriptomic and enzymatic analysis reveals the roles of glutamate dehydrogenase in Corynebacterium glutamicum

Glutamate dehydrogenase (Gdh), catalyzing the reversible conversion between 2-oxoglutarate and glutamate, plays an important role in the connection of nitrogen and carbon metabolism. Yet little is known about these enzymes in the amino acid-manufacturing Corynebacterium glutamicum. In the present study, we firstly identified the enzymatic characteristics of two Gdhs (GdhA and GdhB). The results showed that both GdhA and GdhB prefers NADPH as a coenzyme and have higher affinity for 2-OG than glutamate. The growth characteristics of gdhAΔ mutant and gdhBΔ mutant, gdhABΔ mutant showed GdhA serves as the main conduit for ammonium assimilation, and GdhB is the main glutamate- metabolizing enzyme in C. glutamicum. The full-genome transcriptomic analysis was used to investigate physiological response of C. glutamicum to the glutamate as nitrogen source, and gdh deletion. The results showed that the nitrogen starvation response was elicited when glutamine served as the sole nitrogen source. gdhAΔBΔ double deletion trigger a partially deregulated nitrogen starvation response, in which genes involved in nitrogen assimilation showed obviously upregulated in a certain extent. On the other hand, the genes of phosphotransferase system (PTS) and glycolysis pathway, most genes in pentose phosphate pathway were significantly upregulated, indicating that gdh deficiency initiated the enhancement of the absorption and metabolism of carbon sources. We believed that our results in this study will give new insights on the molecular mechanism of Gdh activity cross-talks with carbon and nitrogen metabolism, also setting a new background for further flux redistribution applied research of biotechnological interest.

Metabolic engineering of Corynebacterium glutamicum for acetate-based itaconic acid production

BACKGROUND

Itaconic acid is a promising platform chemical for a bio-based polymer industry. Today, itaconic acid is biotechnologically produced with Aspergillus terreus at industrial scale from sugars. The production of fuels but also of chemicals from food substrates is a dilemma since future processes should rely on carbon sources which do not compete for food or feed. Therefore, the production of chemicals from alternative substrates such as acetate is desirable to develop novel value chains in the bioeconomy.

RESULTS

In this study, Corynebacterium glutamicum ATCC 13032 was engineered to efficiently produce itaconic acid from the non-food substrate acetate. Therefore, we rewired the central carbon and nitrogen metabolism by inactivating the transcriptional regulator RamB, reducing the activity of isocitrate dehydrogenase, deletion of the gdh gene encoding glutamate dehydrogenase and overexpression of cis-aconitate decarboxylase (CAD) from A. terreus optimized for expression in C. glutamicum. The final strain C. glutamicum ΔramB Δgdh IDH^R453C (pEKEx2-malEcad_opt) produced 3.43 ± 0.59 g itaconic acid L^-1 with a product yield of 81 ± 9 mmol mol^-1 during small-scale cultivations in nitrogen-limited minimal medium containing acetate as sole carbon and energy source. Lowering the cultivation temperature from 30 °C to 25 °C improved CAD activity and further increased the titer and product yield to 5.01 ± 0.67 g L^-1 and 116 ± 15 mmol mol^-1, respectively. The latter corresponds to 35% of the theoretical maximum and so far represents the highest product yield for acetate-based itaconic acid production. Further, the optimized strain C. glutamicum ΔramB Δgdh IDH^R453C (pEKEx2-malEcad_opt), produced 3.38 ± 0.28 g itaconic acid L^-1 at 25 °C from an acetate-containing aqueous side-stream of fast pyrolysis.

CONCLUSION

As shown in this study, acetate represents a suitable non-food carbon source for itaconic acid production with C. glutamicum. Tailoring the central carbon and nitrogen metabolism enabled the efficient production of itaconic acid from acetate and therefore this study offers useful design principles to genetically engineer C. glutamicum for other products from acetate.

GDH promotes isoprenaline-induced cardiac hypertrophy by activating mTOR signaling via elevation of α-ketoglutarate level

Numerous studies reveal that metabolism dysfunction contributes to the development of pathological cardiac hypertrophy. While the abnormal lipid and glucose utilization in cardiomyocytes responding to hypertrophic stimuli have been extensively studied, the alteration and implication of glutaminolysis are rarely discussed. In the present work, we provide the first evidence that glutamate dehydrogenase (GDH), an enzyme that catalyzes conversion of glutamate into ɑ-ketoglutarate (AKG), participates in isoprenaline (ISO)-induced cardiac hypertrophy through activating mammalian target of rapamycin (mTOR) signaling. The expression and activity of GDH were enhanced in cultured cardiomyocytes and rat hearts following ISO treatment. Overexpression of GDH, but not its enzymatically inactive mutant, provoked cardiac hypertrophy. In contrast, GDH knockdown could relieve ISO-triggered hypertrophic responses. The intracellular AKG level was elevated by ISO or GDH overexpression, which led to increased phosphorylation of mTOR and downstream effector ribosomal protein S6 kinase (S6K). Exogenous supplement of AKG also resulted in mTOR activation and cardiomyocyte hypertrophy. However, incubation with rapamycin, an mTOR inhibitor, attenuated hypertrophic responses in cardiomyocytes. Furthermore, GDH silencing protected rats from ISO-induced cardiac hypertrophy. These findings give a further insight into the role of GDH in cardiac hypertrophy and suggest it as a potential target for hypertrophy-related cardiomyopathy.

Sodium butyrate reduces ammonia emissions through glutamate metabolic pathways in cecal microorganisms of laying hens

Ammonia emission is an important problem that needs to be solved in laying hen industries. Sodium butyrate (SB) is considered to have potential for reducing ammonia production because of its ability to improve nitrogen metabolism. In this in vitro fermentation study, we presented a correlation analysis of the metatranscriptome and metaproteome of lay hen cecal microorganisms, in order to identify important proteins and pathways involved in ammonia production reduction due to sodium butyrate supplementation. The results showed that sodium butyrate supplement decreased the production of ammonia by 26.22% as compared with the non-sodium butyrate supplementation (CK) group. The SB group exhibited a lower concentration of ammonium nitrogen (NH₄⁺-N) and a decreased pH. Sodium butyrate promoted the uric acid concentration and lowered the uricase activity in the fermentation broth of laying hens cecal content. Notably, the 'alanine, aspartate and glutamate metabolism' category was more abundant in the SB group. The addition of sodium butyrate increased the expression of glutamate dehydrogenase (GDH) gene in cecal microbiota (e.g., Ruminococcus sp. and Bacteroides sp.) in vitro. The metaproteome analysis results showed that the expression of GDH with NADPH as coenzyme (NADPH-GDH) was up-regulated in cecal microbiota by sodium butyrate supplement. Our results indicate that sodium butyrate can affect glutamate metabolism through regulating the expression of glutamate dehydrogenase in cecal microorganisms, thereby reducing ammonia production. This study reveals that glutamate dehydrogenase-mediated glutamate metabolism play a key role in ammonia emission reduction in laying hen and provide theoretical basis for further developing ammonia production reduction approach.

Combined active pocket and hinge region engineering to develop an NADPH-dependent phenylglycine dehydrogenase

NADPH-dependent amino acid dehydrogenases (AADHs) are favorable enzymes to construct artificial biosynthetic pathways in whole-cell for high-value noncanonical amino acids (NcAAs) production. Glutamate dehydrogenases (GluDHs) represent attractive candidates for the development of novel NADPH-dependent AADHs. Here, we report the development of a novel NADPH-dependent phenylglycine dehydrogenase by combining active pocket engineering and hinge region engineering of a GluDH from Pseudomonas putida (PpGluDH). The active pocket of PpGluDH was firstly tailored to optimize its binding mode with bulky substrate α-oxobenzeneacetic acid (α-OA), and then, the hinge region was further engineered to tune the protein conformational dynamics, which finally resulted in a mutant M3 (T196A/T121I/L123D) with a 103-fold increase of catalytic efficiency (k_cat/K_m) toward α-OA. The M3 mutant exhibited high catalytic performance in both in vitro biocatalysis preparation and in vivo biosynthesis of l-phenylglycine, indicating its promising practical applications. Our results demonstrated that co-engineering of the active pocket and hinge region is an effective strategy for developing novel NADPH-dependent AADHs from GluDHs for NcAAs production.

Rational engineering of cofactor specificity of glutamate dehydrogenase for poly-γ-glutamic acid synthesis in Bacillus licheniformis

Poly-γ-glutamic acid (γ-PGA) is a multifunctional biopolymer mainly produced by Bacillus. The cofactor specificity of enzymes plays a critical role in regulating metabolic process and metabolite production. Here, we present a novel approach for switching cofactor specificity of glutamate dehydrogenase RocG from nicotinamide adenine dinucleotide phosphate (NADPH) to nicotinamide adenine dinucleotide (NADH) to improve γ-PGA production. Firstly, 3D structural modeling and molecular docking were performed to predict the binding modes of NADH and NADPH. Several site-specific mutants based on the conventional and Random Accelerated Molecular Dynamics simulations were obtained to alter cofactor specificity. Then, the effects of RocG variants overexpressions on γ-PGA production were evaluated. Compared to the wild-type, the mutant RocG^D276E showed highest increase in γ-PGA yield, increased by 40.50%. Meanwhile, yields of main by-products acetoin and 2,3-butandieol were decreased by 21.70% and 16.53%, respectively. Finally, the results of enzymatic properties confirmed that glutamate dehydrogenase mutant RocG^D276E exhibited the higher affinity for NADH, caused a shift in coenzyme preference from NADPH to NADH, with a catalytic efficiency comparable with NADPH-dependent RocG. Taken together, this research demonstrated that switching the cofactor preference of glutamate dehydrogenase via rational design was an effective strategy for high-level production of γ-PGA in Bacillus licheniformis.

Gene migration of giardiasis in Iran; a microevolutionary scale for reflecting transmission patterns of Giardia lamblia assemblages in symptomatic patients

In the microevolutionary scale of Giardia lamblia, the gene migration indicates how G. lamblia assemblages have transmitted between adjacent counties. 33 positive fecal samples were taken from patients suffering gastrointestinal disorders (nausea, bloating, burping constipation and fatty diarrhea) at Tabriz and Ardabil cities, where located in the cold regions of northwest Iran. Following parasitological examinations, DNA samples were extracted, amplified and digested by single-step PCR-RFLP assay, targeting the glutamate dehydrogenase (gdh) locus to distinguish within and between assemblages A and B. PCR products were directly sequenced to reconfirm their heterogeneity traits and phylogenetic analysis. Of the 33 isolates, 81.9% (n: 27), 9% (n: 3) and 9% (n: 3) were successfully identified as assemblages A (genotype AII), B (genotype BIII) and the mixed of genotypes AII and B, respectively. Despite the presence of heterogeneous clinical backgrounds, a low genetic diversity of sub-assemblage AII was identified among symptomatic cases. A low value of pairwise fixation index showed that G. lamblia sub-assemblage AII is not genetically differentiated among northwest regions of Iran. The occurrence of haplotypes TAB-1/ARD-1 between two regional populations indicates that there is a dawn of G. lamblia gene flow due to transfer of alleles through host mobility and/or ecological alterations. To assess the hypothetical evolutionary scenario, further studies are essential for multilocus genotyping of G. lamblia in tropical regions of Iran and neighboring countries.

A cost of illness comparison for toxigenic Clostridioides difficile diagnosis algorithms in developing countries

BACKGROUND

Availability of several commercial tests with different Clostridioides difficile targets contributes to uncertainty and controversies around the optimal diagnostic algorithm. While numerous studies have estimated the financial impact of C. difficile infection, models to guide testing strategies decisions in developing countries, where economic value significantly impacts clinical practice, are currently not available.

AIM

To determine the cost of illness of different C. difficile infection (CDI) diagnostic strategies in developing countries.

METHODS

Cost-comparison analysis was performed to compare eleven different algorithms of CDI diagnosis. The basis of calculation was a hypothetical cohort of 1000 adult inpatients suspected of CDI. We analyzed turnaround time of test results (i.e., time from taking sample to results emission), test performance (i.e., sensitivity and specificity) and testing costs. Patients were divided in true positive, false positive, true negative and false negative in order to integrate test performance and economics effects. Additional medical costs were calculated: costs of hygiene, medication, length of stay and intensive care unit costs, based on a Brazilian University Hospital costs. CDI prevalence was considered 22.64%.

FINDINGS

From laboratory-assisted tests, simultaneous glutamate dehydrogenase (GDH) and toxin A/B rapid immunoassay arbitrated by nucleic acid amplification test (NAAT) presented the lowest cost of illness (450,038.70 USD), whereas standalone NAAT had the highest (523,709.55 USD). Empirical diagnosis only presented the highest overall cost (809,605.44 USD).

CONCLUSION

The two-step algorithm with simultaneous GDH and toxin A/B rapid immunoassay arbitrated by NAAT seems to be the best strategy for CDI diagnosis in developing countries.

Crystal structure of glutamate dehydrogenase 3 from Candida albicans

Glutamate dehydrogenase 3 from Candida albicans (CaGdh3) catalyzes the reversible oxidative deamination of l-glutamate, playing an important role in the yeast-to-hyphal transition of C. albicans. Here we report the crystal structures of CaGdh3 and its complex with α-ketoglutarate and NADPH. CaGdh3 exists as a hexamer, with each subunit containing two domains. The substrate and coenzyme bind in the cleft between the two domains and their binding induces a conformational change in CaGdh3. Our results will help to understand the catalytic mechanism of CaGdh3 and will provide a structural basis for the design of antifungal drugs targeting the CaGdh3 pathway.

Is Clostridioides difficile toxins detection necessary when the glutamate dehydrogenase enzyme is detected?

INTRODUCTION

Clostridioides difficile causes diarrhea and pseudomembranous colitis. Its diagnosis is made with glutamate dehydrogenase (GDH) or toxins A and B detection and is confirmed with nucleic acid amplification tests.

OBJECTIVE

To define if GDH determination is redundant to that of toxins.

METHODS

Retrospective, observational study in diarrheal stools of patients with suspected Clostridioides difficile infection. Toxins and GDH were determined by immunochromatography. Bayesian simulation was performed with likelihood ratios; a p-value < 0.05 was regarded as significant.

RESULTS

329 GDH and toxin A and B results were analyzed. Clostridioides difficile infection prevalence was 18.2 %. Sensitivity and specificity of the GDH test were 0.90 and 0.89, respectively. Positive likelihood ratio was 8.9, and negative was 0.11.

CONCLUSIONS

A negative GDH result considerably reduces the probability of infection but does not rule it out. Clostridioides difficile toxins detection may be necessary in institutions where nucleic acid amplification is not affordable or accessible.

Application of a dissolved oxygen control strategy to increase the expression of Streptococcus suis glutamate dehydrogenase in Escherichia coli

The accumulation of acetate in Escherichia coli inhibits cell growth and desired protein synthesis, and cell density and protein expression are increased by reduction of acetate excretion. Dissolved oxygen (DO) is an important parameter for acetate synthesis, and the accumulation of acetate is inversely correlated to DO level. In this study, the effect of DO levels on glutamate dehydrogenase (GDH) expression was investigated, and then different DO control strategies were tested for effects on GDH expression. DO control strategy IV (50% 0-9 h, 30% 9-18 h) provided the highest cell density (15.43 g/L) and GDH concentration (3.42 g/L), values 1.59- and 1.99-times higher than those achieved at 10% DO. The accumulation of acetate was 2.24 g/L with DO control strategy IV, a decrease of 40.74% relative to that achieved for growth at 10% DO. Additionally, under DO control strategy IV, there was lower expression of PoxB, a key enzyme for acetate synthesis, at both the transcriptional and translational level. At the same time, higher transcription and protein expression levels were observed for a glyoxylate shunt gene (aceA), an acetate uptake gene (acs), gluconeogensis and anaplerotic pathways genes (pckA, ppsA, ppc, and sfcA), and a TCA cycle gene (gltA). The flux of acetate with DO strategy IV was 8.4%, a decrease of 62.33% compared with the flux at 10% DO. This decrease represents both lower flux for acetate synthesis and increased flux of reused acetate.

The razor clam Sinonovacula constricta uses the strategy of conversion of toxic ammonia to glutamine in response to high environmental ammonia exposure

High ammonia can inhibit the survival and growth, and even cause mortality of razor clam (S. constricta). The accumulation of ammonia to lethal concentrations in some invertebrates may be partially prevented by converting some of the ammonia into glutamine (Gln). Glutamine dehydrogenase (GDH) and glutamine synthetase (GS) have been widely implicated a central role in response to ammonia stress. However, the molecular and physiological response of GDH and GS to ammonia alterations has not yet been determined in clams. To investigate the possible participatory role of GDH and GS genes in altered ammonia conditions, we have cloned their gene sequences and examined the mRNA expression and western blotting under ammonia exposure in S. constricta (ScGDH and ScGS), and detected the levels of GS and GDH, and the content of glutamate (Glu) and Gln. The full-length cDNA of ScGDH was 3924 bp, with a 1629 bp open reading frame (ORF) encoding a 542 amino-acid polypeptide. The complete cDNA sequence for ScGS had 2739 bp with an ORF of 1110 bp encoding 369 amino acids. To investigate ammonia detoxification strategies, the clams were exposed to ammonia for 96 h at four different concentrations (0, 100, 140, and 180 mg/L). Exposure to ammonia resulted in a significant increase of glutamate concentration and Gln in the haemocytes. GDH activity, GDH relative mRNA and protein expression, GS activity, GS relative mRNA and protein expression increased significantly and showed a pronounced time and dosage interaction in the liver. The results suggested that the protective strategies of Gln formation existed in S. constricta, which could convert ammonia to non- or less toxic nitrogenous compounds on the exposure of ammonia. Glutamate content in the haemocytes increased significantly, which is to ensure sufficient Glu to meet the needs for GS to catalyze the conversion of ammonia to Gln. We proposed that the induction of Glu synthesis-related genes and the subsequent formation of the active protein occurred in preparation for the increased capacity of the body to convert ammonia, into Gln. The results of this study suggested that GDH and GS play an important role in the synthesis of Gln, emphasizing, the protective strategies of Gln formation in S. constricta convert ammonia to nontoxic or less toxic nitrogenous compounds upon exposure to ammonia.

Ammonia inhibits energy metabolism in astrocytes in a rapid and glutamate dehydrogenase 2-dependent manner

Astrocyte dysfunction is a primary factor in hepatic encephalopathy (HE) impairing neuronal activity under hyperammonemia. In particular, the early events causing ammonia-induced toxicity to astrocytes are not well understood. Using established cellular HE models, we show that mitochondria rapidly undergo fragmentation in a reversible manner upon hyperammonemia. Further, in our analyses, within a timescale of minutes, mitochondrial respiration and glycolysis were hampered, which occurred in a pH-independent manner. Using metabolomics, an accumulation of glucose and numerous amino acids, including branched chain amino acids, was observed. Metabolomic tracking of 15N-labeled ammonia showed rapid incorporation of 15N into glutamate and glutamate-derived amino acids. Downregulating human GLUD2 [encoding mitochondrial glutamate dehydrogenase 2 (GDH2)], inhibiting GDH2 activity by SIRT4 overexpression, and supplementing cells with glutamate or glutamine alleviated ammonia-induced inhibition of mitochondrial respiration. Metabolomic tracking of 13C-glutamine showed that hyperammonemia can inhibit anaplerosis of tricarboxylic acid (TCA) cycle intermediates. Contrary to its classical anaplerotic role, we show that, under hyperammonemia, GDH2 catalyzes the removal of ammonia by reductive amination of α-ketoglutarate, which efficiently and rapidly inhibits the TCA cycle. Overall, we propose a critical GDH2-dependent mechanism in HE models that helps to remove ammonia, but also impairs energy metabolism in mitochondria rapidly.

Effects of lead, cadmium and zinc on protein changes in Silene vulgaris shoots cultured in vitro

In the present research, Silene vulgaris as a representative species growing on both unpolluted and heavy metal (HM) polluted terrains were used to identify ecotype-specific responses to metallic stress. Growth, cell ultrastructure and element accumulations were compared between non-metallicolous (NM), calamine (CAL) and serpentine (SER) specimens untreated with HMs and treated with Pb, Cd and Zn ions under in vitro conditions. Moreover, proteins' modifications related to their level, carbonylation and degradations via vacuolar proteases were verified and linked with potential mechanisms to cope with ions toxicity. Our experiment revealed diversified strategy of HM uptake in NM and both metallicolous ecotypes, in which antagonistic relationship of Zn and Pb/Cd ions provided survival benefits for the whole organism. Despite this similarity, growth rate and metabolic pathways induced in CAL and SER shoots varied significantly. Exposition to HMs in CAL culture led to drop in protein level by approximately 16% compared to the control. This parameter nearly correlated with the enhanced activity of proteases at pH 5.2 as well as possible glutamate changes to proline and reduced glutathione, resulting in intensified growth and first signs of cell senescence. In turn, SER shoots were characterized by growth retardation (to 53% of the control), although protein level and carbonylation were not modified, while a deeper insight into protein network showed its remodeling towards production of polyamines and 2-oxoglutarate delivered to the Krebs cycle. Contrary, an uncontrolled HM influx in NM shoots contributed to morpho-structural disorders accompanied by an increase activity of proteases involved in the degradation of oxidized proteins, what pointed to metal-induced autophagy. Taken together, S. vulgaris ecotypes respond to stress by triggering various mechanisms engaged their survival and/or death under HM treatment.

A 2-step algorithm combining glutamate dehydrogenase and nucleic acid amplification tests for the detection of Clostridioides difficile in stool specimens

The optimized diagnosis algorithm of Clostridioides difficile infection (CDI) is worldwide concerns. The purpose of this study was to assess the toxigenic C. difficile test performance and propose an optimal laboratory workflow for the diagnosis of CDI in mild virulent epidemic areas. Diarrhea samples collected from patients were analyzed by glutamate dehydrogenase (GDH), toxin AB (CDAB), and nucleic acid amplification test (NAAT). We assessed the performance of GDH, the GDH-CDAB algorithm, and the GDH-NAAT algorithm using toxigenic culture (TC) as a reference method. In this study, 186 diarrhea samples were collected. The numbers of TC-positive and TC-negative samples were 39 and 147, respectively. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and kappa of the GDH assay were 100%, 80.3%, 57.4%, 100%, and 0.63; of the GDH-CDAB algorithm were 48.7%, 97.3%, 82.6%, 87.7%, and 0.54; and of the GDH-NAAT algorithm were 74.4%, 100%, 100%, 93.6%, and 0.82, respectively. The GDH-NAAT algorithm has great concordance with TC in detecting toxigenic C. difficile (kappa = 0.82), while the sensitivity of the GDH-CDAB algorithm was too low to meet the demand of CDI diagnosis clinically. GDH-NAAT algorithm is recommended for the detection of toxigenic C. difficile with high specificity, increased sensitivity, and cost-effective.

Molecular prevalence and genotyping of Giardia duodenalis in cattle in Central Anatolia Region of Turkey

The molecular prevalence and genotypes of Giardia duodenalis in cattle were investigated. A total of 450 fecal samples were collected from cattle in three provinces of Central Anatolia from August 2017 to July 2019. Genomic DNA was extracted from the fecal samples and used in molecular analysis carried out by nested PCR analyses of the β-giardin (bg) gene of G. duodenalis. Positive samples were further analyzed by nested PCR at two gene loci (triosephosphate isomerase (tpi) and glutamate dehydrogenase (gdh)) for genotyping of G. duodenalis isolates. PCR analyses of the bg gene indicated that the overall prevalence of G. duodenalis was 30.2%. However, lower rates were determined with PCR analyses for gdh and tpi loci. The sequence analyses of the bg, gdh, and tpi genes revealed the presence of zoonotic assemblage A and livestock-specific assemblage E. Combined-sequence analyses revealed that assemblage E was the most common in the study area. Our study provides the first data on the wide prevalence of livestock-specific assemblages E in cattle in Turkey. The prevalence of assemblage A in cattle also reveals the importance of cattle for zoonotic transmission of giardiasis in Turkey.

Glutamate dehydrogenase inhibits tumor growth in gastric cancer through the Notch signaling pathway

Glutamate dehydrogenase (GDH) is a key enzyme in glutaminolysis and can regulate allosteric functions. Immunohistochemical study found that GDH expressed in gastric cancer cell cytoplasm and membrane, and a few located in the nucleus, ranging from light yellow to tan to sepia. According to the analysis by Kaplan Meier survival curve and the Log-Rank test, the median survival of GDH high expression in patients was 51.7 months with 95% confidence intervals (CI) was 41.138-55.262. The expression level of GDH was significantly reduced after silencing GDH gene in gastric cancer cells and tissues. Further, after silencing GDH gene, gastric cancer cell migration and invasion ability were decreased significantly. Protein expression of. In addition, tumor growth was significantly reduced after silencing GDH gene. In vivo and in vitro experiments suggest that GDH can decrease gastric cancer cell migration and invasion, thus inhibiting tumor growth.

Hyperinsulinism associated with GLUD1 mutation: allosteric regulation and functional characterization of p.G446V glutamate dehydrogenase

Background

Gain-of-function mutations in the GLUD1 gene, encoding for glutamate dehydrogenase (GDH), result in the hyperinsulinism/hyperammonemia HI/HA syndrome. HI/HA patients present with harmful hypoglycemia secondary to protein-induced HI and elevated plasma ammonia levels. These symptoms may be accompanied by seizures and mental retardation. GDH is a mitochondrial enzyme that catalyzes the oxidative deamination of glutamate to α-ketoglutarate, under allosteric regulations mediated by its inhibitor GTP and its activator ADP. The present study investigated the functional properties of the GDH-G446V variant (alias c.1496G > T, p.(Gly499Val) (NM_005271.4)) in patient-derived lymphoblastoid cells.

Results

The calculated energy barrier between the opened and closed state of the enzyme was 41% lower in GDH-G446V compared to wild-type GDH, pointing to altered allosteric regulation. Computational analysis indicated conformational changes of GDH-G446V in the antenna region that is crucial for allosteric regulators. Enzymatic activity measured in patient-derived lymphoblastoid cells showed impaired allosteric responses of GDH-G446V to both regulators GTP and ADP. In particular, as opposed to control lymphoblastoid cells, GDH-G446V cells were not responsive to GTP in the lower range of ADP concentrations. Assessment of the metabolic rate revealed higher mitochondrial respiration in response to GDH-dependent substrates in the GDH-G446V lymphoblastoid cells compared to control cells. This indicates a shift toward glutaminolysis for energy provision in cells carrying the GDH-G446V variant.

Conclusions

Substitution of the small amino acid glycine for the hydrophobic branched-chain valine altered the allosteric sensitivity to both inhibitory action of GTP and activation by ADP, rendering cells metabolically responsive to glutamine.

Glutamate dehydrogenase mediated amino acid metabolism after ammonium uptake enhances rice growth under aeration condition

Aeration stimulates the rice growth and nitrogen (N) metabolism; in which, the glutamate accumulation limited by the glutamate dehydrogenase pathway after ammonia uptake may control root N metabolism during aeration. Increasing rhizosphere oxygen content greatly improves rice growth and biomass. To study the intrinsic mechanism involved in nitrogen (N) metabolism, a hydroponic experiment was conducted by supplying two different oxygen levels to two different rice genotypes. Compared to the hypoxia-resistant cultivar (Nip; japonica rice 'Nipponbare'), the hypoxia-sensitive cultivar (U502; upland rice 'Upland 502') presented with severe oxidative damage under the lack of aeration. However, aeration significantly reduced root oxidative damage by enhancing root antioxidant capacity and leaf photosynthesis especially in U502, and significantly increased nitrate (NO₃^-) and ammonia (NH₄⁺) uptake and upregulated the expression of the genes controlling these processes. Additional NO₃^- was mainly incorporated into amino acids in the leaves whereas NH₄⁺ assimilation occurred mostly in the roots. The ¹⁵N gas chromatography-mass spectrometry analysis demonstrated that aeration had no influence on the compositions of the individual amino acids derived from ¹⁵NO₃^- in the roots, but increased labeled glutamic acid (Glu), asparagine, γ-aminobutyric acid, and alanine in ¹⁵NH₄⁺-treated roots. Aeration inhibited root glutamate synthetase activity but this did not inhibit ¹⁵N-Glu production from ¹⁵NH₄⁺. In contrast, aeration upregulated isocitrate dehydrogenase and glutamate dehydrogenase. These mechanisms and soluble carbohydrates may constitute an alternative pathway for Glu production in which amino acid metabolism is enhanced after NH₄⁺ uptake during aeration. Therefore, the rice growth-enhancing effect of aeration is closely correlated with root redox equilibrium, N uptake, and amino acid metabolism. Glutamic acid accumulation is limited by the glutamate dehydrogenase pathway after NH₄⁺ uptake and may control root N metabolism during aeration.

Prevalence and genotypic characterization of Giardia duodenalis isolates from asymptomatic school-going children in Lusaka, Zambia

Giardia duodenalis is one of the most common causes of diarrhea in humans with about 250–300 million cases per year. It is considered to be a species complex comprising of eight genetic assemblages (A to H), with assemblages A and B being the major causes of human infections. In this study we carried out genotypic characterization of G. duodenalis isolates detected in asymptomatic school-going children aged 3–16 years. Between May and September 2017, a total of 329 fecal samples were collected from school-going children from Chawama compound of Lusaka City and were screened for Giardia by microscopic examination. All microscopically positive fecal samples were analyzed by semi-nested polymerase chain reaction (PCR) targeting the glutamate dehydrogenase (gdh) gene. Genotyping of amplified PCR products was conducted by restriction fragment length polymorphism (RFLP) and DNA sequence analysis. Microscopically, Giardia was found in 10% (33/329) of fecal samples. The PCR-RFLP analysis of the gdh gene revealed assemblages A and B in 27.3% (9/33) and 72.7% (24/33), respectively. Furthermore, analysis with restriction enzymes identified sub-assemblages AII (27.3%, 9/33), BIII (12.1%, 4/33), BIV (51.5%, 17/33) and mixed infections of BIII and BIV (9.1%, 3/33). Phylogenetic analysis showed the clustering of 27.6% (8/29) and 72.4% (21/29) of Zambian Giardia gdh gene sequences into assemblages A and B, respectively. This study has revealed the presence of both assemblage A and B and that spread of G. duodenalis in school-going children appears to be mostly through anthroponotic transmission. To our knowledge, this is the first report of genotypic characterization of G. duodenalis identified in Zambia.

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Giardia duodenalis infection observed in asymptomatic children

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First report of genotypes circulating in Zambia

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Presence of sub-assemblages AII, BIII and BIV

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Co-infection with sub-assemblages BIII and BIV reported

Metabolic adjustments during compatible interaction between barley genotypes and stripe rust pathogen

Stripe rust is a fungal disease that has devastated the barley production for a long time. The present study focused on the role of β-glucan, PR proteins, diamine oxidase (DAO), polyamine oxidase (PAO), key enzymes and metabolites of phenol and proline metabolism in the stripe rust resistance of barley. RD2901 with resistant behavior against stripe rust showed increased levels of PR proteins, phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL) along with the accumulation of β-glucan and lignin which strengthen the plant cell wall during plant-pathogen interaction. It also depicted the enhanced activities of glutamate dehydrogenase (GDH) and ornithine aminotransferase (OAT) coupled with the increased amounts of proline, glycine betaine and choline after infection with M-race of P. striiformis f. sp. hordei. On the contrary, the sensitive genotype Jyoti was unable to enhance the activities of most of these enzymes except PAL and OAT so that it showed an increase in lignin and choline contents only. Secondly, the increase in lignin content was less as compared to the tolerant genotype. Hence, it can be inferred that these key metabolites and enzymes of various metabolic pathways may contribute to the resistance of barley against stripe rust pathogen. This study suggested that these key enzymes and their metabolites could serve as markers for the characterization of plant defensive state that is essential for crop protection.

Canagliflozin impairs blood reperfusion of ischaemic lower limb partially by inhibiting the retention and paracrine function of bone marrow derived mesenchymal stem cells

Background

Canagliflozin (CANA) administration increases the risk of lower limb amputation in the clinic. The present study aimed to investigate whether and how CANA interferes with the intracellular physiological processes of bone marrow derived mesenchymal stem cells (BM-MSCs) and its contribution to ischaemic lower limb.

Methods

The in vivo blood flow recovery in ischaemic lower limbs following CANA treatment was evaluated. The cellular function of BM-MSCs after CANA treatment were also assessed in vitro. In silico docking analysis and mutant substitution assay were conducted to confirm the interaction of CANA with glutamate dehydrogenase 1 (GDH1).

Findings

Following CANA treatment, attenuated angiogenesis and hampered blood flow recovery in the ischaemic region were detected in diabetic and non-diabetic mice, and inhibition of the proliferation and migration of BM-MSCs were also observed. CANA was involved in mitochondrial respiratory malfunction in BM-MSCs and the inhibition of ATP production, cytochrome c release and vessel endothelial growth factor A (VEGFA) secretion, which may contribute to reductions in the tissue repair capacity of BM-MSCs. The detrimental effects of CANA on MSCs result from the inhibition of GDH1 by CANA (evidenced by in silico docking analysis and H199A-GDH1/N392A-GDH1 mutant substitution).

Interpretation

Our work highlights that the inhibition of GDH1 activity by CANA interferes with the metabolic activity of the mitochondria, and this interference deteriorates the retention of and VEGFA secretion by MSCs.

Funding

National Natural Science Foundation of China, Natural Science Foundation of Zhejiang Province and Wenzhou Science and Technology Bureau Foundation.

GAD1 but not GAD2 polymorphisms are associated with heroin addiction phenotypes

INTRODUCTION

Heroin addiction is a chronic complex brain disease that contains multiple phenotypes, which vary widely among addicts and may be affected by genetic factors. A total of 801 unrelated heroin addicts were recruited and divided into different subgroups according to eight phenotypes of heroin addiction. Polymorphisms in GAD1 (rs3762555, rs3762556, rs3791878, rs3749034, rs11532313 and rs769395) and GAD2 (rs2839669, rs2839670 and rs2236418) were genotyped using the SNaPshot assay. Associations between genetic variants and the eight phenotypes were mainly assessed by binary logistic regression.

RESULTS

We found that the frequencies of G allele of GAD1 rs3749034 and rs3762555 were associated with daily dose of methadone use and memory change after heroin addiction. The C allele frequency of GAD1 rs3762556 was associated with lower daily dose of methadone use. In GAD1, SNPs rs3762556, rs3762555, rs3791878 and rs3749034 had strong linkage, and the frequency of the C-G-C-A haplotype was higher in the lower dose of methadone group. Patients with the TT genotype of rs11542313 were maintained on lower dose of methadone than patients with the CC genotype. The G alleles of rs3762555 and rs3749034 were lower, while the T allele of rs11542313 was higher, in the memory decreased group. The results of association analyses of GAD2 with phenotypes of heroin addiction showed no significant differences.

CONCLUSION

GAD1 polymorphisms were associated with phenotypes of heroin addiction, especially the daily dose of methadone use and memory change in the Han Chinese population. These results may provide individualized guidance for the treatment of heroin addiction.

Stimulus-Secretion Coupling in Beta-Cells: From Basic to Bedside

Insulin secretion in humans is usually induced by mixed meals, which upon ingestion, increase the plasma concentration of glucose, fatty acids, amino acids, and incretins like glucagon-like peptide 1. Beta-cells can stay in the off-mode, ready-mode or on-mode; the mode-switching being determined by the open state probability of the ATP-sensitive potassium channels, and the activity of enzymes like glucokinase, and glutamate dehydrogenase. Mitochondrial metabolism is critical for insulin secretion. A sound understanding of the intermediary metabolism, electrophysiology, and cell signaling is essential for comprehension of the entire spectrum of the stimulus-secretion coupling. Depolarization brought about by inhibition of the ATP sensitive potassium channel, together with the inward depolarizing currents through the transient receptor potential (TRP) channels, leads to electrical activities, opening of the voltage-gated calcium channels, and exocytosis of insulin. Calcium- and cAMP-signaling elicited by depolarization, and activation of G-protein-coupled receptors, including the free fatty acid receptors, are intricately connected in the form of networks at different levels. Activation of the glucagon-like peptide 1 receptor augments insulin secretion by amplifying calcium signals by calcium induced calcium release (CICR). In the treatment of type 2 diabetes, use of the sulfonylureas that act on the ATP sensitive potassium channel, damages the beta cells, which eventually fail; these drugs do not improve the cardiovascular outcomes. In contrast, drugs acting through the glucagon-like peptide-1 receptor protect the beta-cells, and improve cardiovascular outcomes. The use of the glucagon-like peptide 1 receptor agonists is increasing and that of sulfonylurea is decreasing. A better understanding of the stimulus-secretion coupling may lead to the discovery of other molecular targets for development of drugs for the prevention and treatment of type 2 diabetes.

Arabidopsis thaliana mutants devoid of chloroplast glutamine synthetase (GS2) have non-lethal phenotype under photorespiratory conditions

Chloroplast located Glutamine Synthetase (GS2) is believed to play a major role in the reassimilation of ammonium generated by photorespiration, being GS2 knockout mutants unable to grow under photorespiratory conditions (low-CO₂ atmosphere) in the species characterized so far (Barley, Lotus). To investigate the importance of GS2 in A. thaliana nitrogen metabolism mutant plants devoid of this GS isoenzyme were characterized. It was shown that GS2 mutants although smaller, slightly chlorotic and with the nitrogen metabolism impaired, were able to grow and complete their life cycle under ordinary air conditions. Surprisingly, GS2 mutants were more tolerant to salt stress than wild-type plants. The lack of GS2 seems to be compensated by higher expression of some GS cytosolic isogenes, namely GLN1;2 and GLN1;3 and by glutamate dehydrogenase, whose activity and expression is enhanced in the GS2 mutant plants and might account for the increased tolerance to salt stress. Under conditions that minimize photorespiration (CO2-enriched atmosphere) plant growth and ammonium assimilation impairment is less evident in the GS2 mutant plants and is accompanied by an adjustment of levels of expression of the cytosolic isogenes, with an increase in the expression of GLN1;3 and a decrease in the expression of the GLN1;1 and GLN1;2. Altogether the results confirm a major role of GS2 in the assimilation of ammonium released during photorespiration, but suggest a redundancy of activity with cytosolic GSs and GDH and further support the involvement of the chloroplastic isoenzyme in primary nitrogen assimilation and plant growth and development in A. thaliana.

Tomato roots exhibit in vivo glutamate dehydrogenase aminating capacity in response to excess ammonium supply

In higher plants ammonium (NH₄⁺) assimilation occurs mainly through the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway. Nevertheless, when plants are exposed to stress conditions, such as excess of ammonium, the contribution of alternative routes of ammonium assimilation such as glutamate dehydrogenase (GDH) and asparagine synthetase (AS) activities might serve as detoxification mechanisms. In this work, the in vivo functions of these pathways were studied after supplying an excess of ammonium to tomato (Solanum lycopersicum L. cv. Agora Hybrid F1) roots previously adapted to grow under either nitrate or ammonium nutrition. The short-term incorporation of labelled ammonium (¹⁵NH₄⁺) into the main amino acids was determined by GC-MS in the presence or absence of methionine sulphoximine (MSX) and azaserine (AZA), inhibitors of GS and GOGAT activities, respectively. Tomato roots were able to respond rapidly to excess ammonium by enhancing ammonium assimilation regardless of the previous nutritional regime to which the plant was adapted to grow. The assimilation of ¹⁵NH₄⁺ could take place through pathways other than GS/GOGAT, since the inhibition of GS and GOGAT did not completely impede the incorporation of the labelled nitrogen into major amino acids. The in vivo formation of Asn by AS was shown to be exclusively Gln-dependent since the root was unable to incorporate ¹⁵NH₄⁺ directly into Asn. On the other hand, an in vivo aminating capacity was revealed for GDH, since newly labelled Glu synthesis occurred even when GS and/or GOGAT activities were inhibited. The aminating GDH activity in tomato roots responded to an excess ammonium supply independently of the previous nutritional regime to which the plant had been subjected.

Hyperthermia potentiates cisplatin cytotoxicity and negative effects on mitochondrial functions in OVCAR-3 cells

The aim of this study was to determine the effects of hyperthermia, cisplatin and their combination on mitochondrial functions such as glutamate dehydrogenase (GDH) activity and mitochondrial respiration rates, as well as survival of cultured ovarian adenocarcinoma OVCAR-3 cells. Cells treated for 1 h with hyperthermia (40 and 43 °C) or cisplatin (IC50) or a combination of both treatments were left for recovery at 37 °C temperature for 24 h or 48 h. The obtained results revealed that 43 °C hyperthermia potentiated effects of cisplatin treatment: combinatory treatment more strongly suppressed GDH activity and expression, mitochondrial functions, and decreased survival of OVCAR-3 cells in comparison to separate single treatments. We obtained evidence that in the OVCAR-3 cell line GDH was directly activated by hyperthermia (cisplatin eliminated this effect); however, this effect was followed by GDH inhibition after 48 h recovery. A combination of 43 °C hyperthermia with cisplatin induced stronger GDH inhibition in comparison to separate treatments, and negative effects exerted on GDH activity correlated with suppression of mitochondrial respiration with glutamate + malate. Cisplatin did not induce uncoupling of oxidative phosphorylation in OVCAR-3 cells but induced impairment of the outer mitochondrial membrane in combination with 43 °C hyperthermia. Hyperthermia (43 °C) potentiated cytotoxicity of cisplatin in an OVCAR-3 cell line.

Interaction of cyanate uptake by rice seedlings with nitrate assimilation: gene expression analysis

Cyanate (CNO^-) has been produced in the environment through either natural or anthropogenic sources. However, due to industrialization, it has been led more over-loads. In this study, interaction of CNO^- uptake by rice seedlings with nitrate assimilation was investigated using gene expression analysis after an acute phytotoxicity assay. Our results showed that CNO^- exposure caused inhibition on relative growth rates of plants. CNO^- analysis demonstrated that rice seedlings had higher potential for CNO^- uptake and the removal rates showed a zero-order kinetic. PCR analysis exposed that OsCYN transcript was not significantly induced by CNO^- treatments in rice tissues and CNO^- exposure also repressed gene expression of the collaborative enzyme carbonic anhydrase (CA), suggesting that assimilation of CNO^- initiated by the enzyme cyanase (CYN) in rice seedlings was an enzyme-limitation reaction. Gene expression of other enzymes involved in nitrate metabolism was tissue-specific under CNO^- exposure, suggesting that rice seedlings were able to trigger its intrinsic regulative and responsive mechanisms to cope up with uneven N conditions. Significant upregulation of three OsGDH isogenes, except for OsGDH1 in roots, was detected in both rice materials with enhancing CNO^- concentrations, suggesting that GDH may play a primary role to maintain the balance of C and N in plants under CNO^- exposure. In conclusion, because the innate pool of CYN activity was non-sufficient to degrade exogenous CNO^- by rice seedlings, CNO-derived ammonium only can serve as a supporting N source to support growth of rice seedling under non-effective doses of CNO^- exposure.

Impact of climate change on the American lobster (Homarus americanus): Physiological responses to combined exposure of elevated temperature and pCO2

The physiological consequences of exposing marine organisms to predicted future ocean scenarios, i.e. simultaneous increase in temperature and pCO₂, have only recently begun to be investigated. Adult American lobster (Homarus americanus) were exposed to either current (16 °C, 47 Pa pCO₂, pH 8.10) or predicted year 2300 (20 °C, 948 Pa pCO₂, pH 7.10) ocean parameters for 14-16 days prior to assessing physiological changes in their hemolymph parameters as well as whole animal ammonia excretion and resting metabolic rate. Acclimation of lobster simultaneously to elevated pCO₂ and temperature induced a prolonged respiratory acidosis that was only partially compensated for via accumulation of extracellular HCO₃^- and ammonia. Furthermore, acclimated animals possessed significantly higher ammonia excretion and oxygen consumption rates suggesting that future ocean scenarios may increase basal energetic demands on H. americanus. Enzyme activity related to protein metabolism (glutamine dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) in hepatopancreas and muscle tissue were unaltered in future ocean scenario exposed animals; however, muscular citrate synthase activity was reduced suggesting that, while protein catabolism may be unchanged, the net energetic output of muscle may be compromised in future scenarios. Overall, H. americanus acclimated to ocean conditions predicted for the year 2300 appear to be incapable of fully compensating against climate change-related acid-base challenges and experience an increase in metabolic waste excretion and oxygen consumption. Combining our study with past literature on H. americanus suggests that the whole lifecycle from larvae to adult stages is at risk of severe growth, survival and reproductive consequences due to climate change.

Molecular Genotyping of Giardia duodenalis in Humans in the Andimeshk County, Southwestern Iran

INTRODUCTION

Giardia duodenalis, one of the most common intestinal protozoa, infects a wide range of vertebrates, including humans and animals.

MATERIALS AND METHODS

In this study, 84 Giardia duodenalis positive stool samples were collected from 3580 patients attending the Imam Ali Hospital and two public health centers in Andimeshk County, southwestern Iran. Stool samples were examined initially by microscopy, and then G. duodenalis was confirmed by SSU rRNA gene and genotypes were determined by amplification of the gdh and β-giardin genes.

RESULTS

The SSU rRNA, gdh, and β-giardin genes were successfully amplified in 89.3%, 58.3%, and 51.2% samples, respectively. Of the positive samples for gdh and β-giardin, 40 isolates were successfully sequenced. Twenty-three isolates belonged to assemblage A, sub-assemblage AII, and 17 belonged to assemblage B. Of the 24 successfully amplified asymptomatic cases, 12 belonged to assemblage A and 12 belonged to assemblage B.

CONCLUSION

The current study found that 64.3% of the patients were asymptomatic. From an epidemiological point of view, the high percentage of asymptomatic patients is important because of their role in the transmission of Giardia. The predominant assemblage was assemblage A, sub-assemblage AII. In general, therefore, it seems that most infections are probably transmitted by anthroponotic pathways in the region.

DIFF QUIK CHEK COMPLETE and RIDASCREEN Assays

Various commercial assays have recently been developed for detecting glutamate dehydrogenase (GDH) and/or toxin A/B to diagnose Clostridioides difficile infection (CDI). We compared the performance of two assays for the simultaneous detection of C. difficile GDH and toxin A/B, using 150 stool samples: C. DIFF QUIK CHEK COMPLETE (QCC; TechLab, Blacksburg, VA, USA) and RIDASCREEN Clostridium difficile GDH (RC-GDH) and Toxin A/B (RC-Toxin A/B; R-Biopharm, Darmstadt, Germany). For GDH detection, QCC and RC-GDH showed satisfactory sensitivity (95.7% and 94.3%, respectively) and specificity (92.5% and 93.8%, respectively) compared with C. difficile culture. For toxin A/B detection, QCC showed higher sensitivity than RC-Toxin A/B (60.0% vs 33.3%, P<0.001) compared with toxigenic C. difficile culture. When the results of QCC or RC-GDH+RC-Toxin A/B were used as the first step of a two-step algorithm for diagnosing CDI, QCC permitted more accurate discrimination than RC of positive or negative results for CDI (77.3% and 65.3%, respectively). QCC is useful for the simultaneous detection of C. difficile GDH and toxin A/B as a part of the two-step algorithm for diagnosing CDI.

GDH and toxin immunoassay for the diagnosis of Clostridioides (Clostridium) difficile infection is not a 'one size fit all' screening test

Diagnosing Clostridioides (Clostridium) difficile infection is challenged by lack of a clear gold standard. We sought to determine if the two-step algorithm (screening GDH and toxin lateral flow assay followed by tcdB PCR) would have adequate clinical performance at a tertiary care center. Of 486 patients, 310 (63.8%) were immunocompromised. Of 150 PCR-positive specimens, 52 (34.7%) were toxin-positive and 126 (84.0%) were GDH positive. Positive GDH or toxin results corresponded to lower PCR cycle threshold values (P < 0.01). PCR-positive patients had more frequently documented antibiotic usage (78.4% vs 66.9%, P = 0.05) and diarrhea (91.0% vs. 79.4%, P < 0.01) and less frequent alternate etiologies of diarrhea (27.3% vs. 41.1%, P = 0.004) or laxative use (24.6% vs 36.1%, P = 0.02). Toxin positivity was associated with antibiotic use (P < 0.01), but not with neutropenia, diarrhea, malignancy, or chemotherapy (P > 0.05). The application of the 2-step algorithm should be thoroughly evaluated in immunocompromised patient populations before implementation.

A promising voltammetric biosensor based on glutamate dehydrogenase/Fe3O4/graphene/chitosan nanobiocomposite for sensitive ammonium determination in PM2.5

A novel NH₄⁺ voltammetric electrochemical biosensor was constructed by immobilizing glutamate dehydrogenase (GLDH)/Fe₃O₄/graphene (GR)/chitosan (CS) nanobiocomposite onto a glassy carbon electrode (GCE). On the GLDH/Fe₃O₄/GR/CS/GCE, GLDH catalyzed the reversible reaction, i.e., the reductive amination of α-ketoglutaric acid and the oxidative deamination of L-glutamate. The electrons produced in the enzymatic reactions were transferred to the surface of the electrode via the [Fe(CN)₆]^3-/4- couple, which helped for the amplification of the electrochemical signal. The electrochemical detection of NH₄⁺ was based on the fact that the enhanced response current was proportional to the NH₄⁺ concentration. Owing to the combination of the advantages of the synergistic effects of Fe₃O₄ nanospheres, GR and CS, a promising platform for NH₄⁺ sensing was provided. Under optimum conditions, the introduced biosensor had a linear range of 0.4-2.0 μM for NH₄⁺ with the detection and quantification limits of 0.08 and 0.27 μM, respectively. Moreover, the biosensor exhibited good sensitivity and excellent reproducibility. It could retain 91.8% of its original response after two weeks of storage at 4 °C, suggesting satisfactory stability. Additionally, the proposed biosensor was successfully applied to detect NH₄⁺ levels in PM_2.5 samples, indicating its feasibility for application in NH₄⁺monitoring in the environmental fields.

Propylselen inhibits cancer cell growth by targeting glutamate dehydrogenase at the NADP+ binding site

High levels of glutamate dehydrogenase (GDH) activity are associated with hypoglycemia, cancer, and Parkinson's disease. Propylselen was synthesized to investigate its mechanism of GDH inhibition in comparison with Ebselen and Epigallocatechin gallate (EGCG). Because Ebselen was found to crosslink with the peptide (AA299-341) at the active site of E.coli GDH, the Cys, Pro, and Lys residues of the corresponding peptide were mutagenized to Ala residues. Using enzyme kinetics and biomolecular interaction assays, we found that the conserved GDH P320 residue is important for propylselen binding, C321 for Ebselen binding, and K341 for EGCG binding. In addition, these 3 mutations abolished NADP⁺ binding to E. coli GDH in the absence of glutamate substrate, but in the presence of glutamate, the catalytic activity of the mutants was reduced only by 2-4 fold, indicating that a substrate-induced fit mechanism exists in E. coli GDH. Furthermore, biochemical analysis showed that NADP⁺ had high affinity (Kd of 77 nM) for GDH; by targeting the NADP binding site, propylselen effectively inhibited both E. coli and human GDH activity and improved anticancer activity.

A thermophilic microorganism from Deception Island, Antarctica with a thermostable glutamate dehydrogenase activity

BACKGROUND

The Antarctic continent is a source of extreme microorganisms. Millions of years of isolation have produced unique biodiversity with adaptive responses to its extreme environment. Although the Antarctic climate is mainly cold, the presence of several geothermal sites, including thermal springs, fumaroles, hot soils and hydrothermal vents, provides ideal environments for the development of thermophilic and hyperthermophilic microorganisms. Their enzymes, called thermoenzymes, are the focus of interest in both academic and industrial research, mainly due to their high thermal activity and stability. Glutamate dehydrogenase, is an enzyme that plays a key role in the metabolism of carbon and nitrogen catalyzing reversibly the oxidative deamination of glutamate to alpha-ketoglutarate and ammonium. It belongs to the family of oxidoreductases, is widely distributed and it has been highly regarded for use as biosensors, particularly for their specificity and ability to operate in photochemical and electrochemical systems. However, the use of enzymes as biosensors is relatively problematic due to their instability to high temperatures, organic solvents and denaturing agents. The purpose of this study is to present the partial characterization of a thermophilic microorganism isolated from Deception Island, Antarctica, that displays glutamate dehydrogenase activity.

RESULTS

In this work, we report the isolation of a thermophilic microorganism called PID15 from samples of Deception Island collected during the Antarctic Scientific Expedition ECA 46. This microorganism is a thermophile that grows optimally at 50 °C and pH 8.0. Scanning electron microscopy shows rod cells of 2.0 to 8.0 µm of length. Phylogenetic analysis of 16S rRNA gene revealed that this microorganism is closely related to Bacillus gelatini. This microorganism contains a thermostable glutamate dehydrogenase with optimal activity at pH 8.0 and temperatures for its activity from 37 to 50 °C, range of temperature of interest for biotechnological applications. This glutamate dehydrogenase is a highly thermostable enzyme.

CONCLUSION

This is the first report of a microorganism from Antarctica containing a thermostable glutamate dehydrogenase that maintains its activity in a broad range of temperatures making it of potential interest for biotechnological applications.

The pleiotropic effects of the glutamate dehydrogenase (GDH) pathway in Saccharomyces cerevisiae

Ammonium assimilation is linked to fundamental cellular processes that include the synthesis of non-essential amino acids like glutamate and glutamine. In Saccharomyces cerevisiae glutamate can be synthesized from α-ketoglutarate and ammonium through the action of NADP-dependent glutamate dehydrogenases Gdh1 and Gdh3. Gdh1 and Gdh3 are evolutionarily adapted isoforms and cover the anabolic role of the GDH-pathway. Here, we review the role and function of the GDH pathway in glutamate metabolism and we discuss the additional contributions of the pathway in chromatin regulation, nitrogen catabolite repression, ROS-mediated apoptosis, iron deficiency and sphingolipid-dependent actin cytoskeleton modulation in S.cerevisiae. The pleiotropic effects of GDH pathway in yeast biology highlight the importance of glutamate homeostasis in vital cellular processes and reveal new features for conserved enzymes that were primarily characterized for their metabolic capacity. These newly described features constitute insights that can be utilized for challenges regarding genetic engineering of glutamate homeostasis and maintenance of redox balances, biosynthesis of important metabolites and production of organic substrates. We also conclude that the discussed  pleiotropic features intersect with basic metabolism and set a new background for further glutamate-dependent applied research of biotechnological interest.

Development of an aptamer-based field effect transistor biosensor for quantitative detection of Plasmodium falciparum glutamate dehydrogenase in serum samples

There has been a continuous strive to develop portable, stable, sensitive and low cost detection system for malaria to meet the demand of effective screening actions in developing countries where the disease is most endemic. Herein, we report an aptamer-based field effect transistor (aptaFET) biosensor, developed by using an extended gate field effect transistor with inter-digitated gold microelectrodes (IDµE) for the detection of the malaria biomarker Plasmodium falciparum glutamate dehydrogenase (PfGDH) in serum samples. A 90 mer long ssDNA aptamer (NG3) selective to PfGDH was used in the aptaFET to capture the target protein. The intrinsic surface net charge of the captured protein led to change in gate potential of the aptaFET device, which could be correlated to the concentration of the protein. This biosensor exhibited a sensitive response in broad dynamic range of 100 fM -10 nM with limits of detection of 16.7 pM and 48.6 pM in spiked buffer and serum samples, respectively. The high selectivity of the biosensor for PfGDH was verified by testing relevant analogous human and parasitic proteins on the device. Overall, the results validated the application potential of the developed aptaFET for diagnosis of both symptomatic and asymptomatic malaria.

Prevalence of Clostridium Difficile-Associated Diarrhoea in Hospitalised Patients (Results of a Russian Prospective Multicentre Study)

Introduction

The objective of the study was to evaluate the prevalence of Clostridium difficile-associated diarrhoea (CDAD) among hospitalised patients with antibiotic-associated diarrhoea (AAD) in general and by specific types of medical care and hospital units.

Methods

A prospective, cross-sectional, non-interventional, multicentre study. The main inclusion criteria were: patient age ≥ 18 years, hospital stay of at least 48 h, current antibiotic therapy or antibiotic therapy within the previous 30 days, loose stools (Bristol stool types 5–7 and stool frequency ≥ 3 within ≤ 24 consecutive hours or exceeding normal for the patient) and signed informed consent form. The stool sample was taken to the local (study site) microbiology laboratory for detection of glutamate dehydrogenase (GDH) and toxins A/B using enzyme immunoassay (EIA) stool test.

Results

From April 2016 to April 2017, a total of 1245 patients from 12 large hospitals were enrolled in the study. Data on 81 patients were excluded from the analysis for different reasons. Data on 1164 patients (45.2% males and 54.8% females) with a mean age of 54.9 years (range 18–95 years) were analysed. Length of hospitalisation was 2–188 days (median, 8 days). The EIA stool test showed CDAD-positive results in 21.7% (253/1164) patients. The patients were from surgery units (546/1164), internal medicine units (510/1164) and intensive care units (108/1164). The prevalence of CDAD among patients from surgery, internal medicine and intensive care units was 26.2, 17.8 and 17.6%, respectively. Oncology, gastroenterology, septic surgery, oncohaematology and general medical hospital units accounted for more than 75% of all patients included; the prevalence of CDAD by those hospital units was 11.3, 15.0, 39.2, 17.6, and 27.2%, respectively. The proportion of GDH-positive and toxin A/B-negative patients by the rapid stool test result was 16.8% (196/1164). The prevalence of CDAD varied widely between the hospitals (from 0 to 44.3%).

Conclusions

The prevalence of CDAD among hospitalised patients with AAD in this study was 21.7% (95% confidence interval: 14.8 and 28.7%). The percentage of CDAD varied widely between hospitals and by specific types of medical care and hospital units.

Administration of chitosan-tripolyphosphate-DNA nanoparticles to knockdown glutamate dehydrogenase expression impairs transdeamination and gluconeogenesis in the liver

Glutamate dehydrogenase (GDH) plays a major role in amino acid catabolism. To increase the current knowledge of GDH function, we analysed the effect of GDH silencing on liver intermediary metabolism from gilthead sea bream (Sparus aurata). Sequencing of GDH cDNA from S. aurata revealed high homology with its vertebrate orthologues and allowed us to design short hairpin RNAs (shRNAs) to knockdown GDH expression. Following validation of shRNA-dependent downregulation of S. aurata GDH in vitro, chitosan-tripolyphosphate (TPP) nanoparticles complexed with a plasmid encoding a selected shRNA (pCpG-sh2GDH) were produced to address the effect of GDH silencing on S. aurata liver metabolism. Seventy-two hours following intraperitoneal administration of chitosan-TPP-pCpG-sh2GDH, GDH mRNA levels and immunodetectable protein decreased in the liver, leading to reduced GDH activity in both oxidative and reductive reactions to about 53-55 % of control values. GDH silencing decreased glutamate, glutamine and aspartate aminotransferase activity, while increased 2-oxoglutarate content, 2-oxoglutarate dehydrogenase activity and 6-phosphofructo-1-kinase/fructose-1,6-bisphosphatase activity ratio. Our findings show for the first time that GDH silencing reduces transdeamination and gluconeogenesis in the liver, hindering the use of amino acids as gluconeogenic substrates and enabling protein sparing and metabolisation of dietary carbohydrates, which would reduce environmental impact and production costs of aquaculture.

Rational modification of tricarboxylic acid cycle for improving L-lysine production in Corynebacterium glutamicum

BACKGROUND

Oxaloacetate (OAA) and L-glutamate are essential precursors for the biosynthesis of L-lysine. Reasonable control of all potentially rate-limiting steps, including the precursors supply rate, is of vital importance to maximize the efficiency of L-lysine fermentation process.

RESULTS

In this paper, we have rationally engineered the tricarboxylic acid (TCA) cycle that increased the carbon yield (from 36.18 to 59.65%), final titer (from 14.47 ± 0.41 to 23.86 ± 2.16 g L-1) and productivity (from 0.30 to 0.50 g L-1 h-1) of L-lysine by Corynebacterium glutamicum in shake-flask fermentation because of improving the OAA and L-glutamate availability. To do this, the phosphoenolpyruvate-pyruvate-oxaloacetate (PEP-pyruvate-OAA) node's genes ppc and pyc were inserted in the genes pck and odx loci, the P1 promoter of the TCA cycle's gene gltA was deleted, and the nature promoter of glutamate dehydrogenase-coding gene gdh was replaced by Ptac-M promoter that resulted in the final engineered strain C. glutamicum JL-69Ptac-M gdh. Furthermore, the suitable addition of biotin accelerates the L-lysine production in strain JL-69Ptac-M gdh because it elastically adjusts the carbon flux for cell growth and precursor supply. The final strain JL-69Ptac-M gdh could produce 181.5 ± 11.74 g L-1 of L-lysine with a productivity of 3.78 g L-1 h-1 and maximal specific production rate (qLys, max.) of 0.73 ± 0.16 g g-1 h-1 in fed-batch culture during adding 2.4 mg L-1 biotin with four times.

CONCLUSIONS

Our results reveal that sufficient biomass, OAA and L-glutamate are equally important in the development of L-lysine high-yielding strain, and it is the first time to verify that fed-batch biotin plays a positive role in improving L-lysine production.

Molecular detection and identification of Giardia duodenalis in cattle of Urmia, northwest of Iran

Giardia duodenalis is one of the most prevalent intestinal protozoa infecting humans and domestic animals. The aim of this study was to identify subspecies of G. duodenalis by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method from fecal samples of naturally infected cattle in the Urmia, West Azerbaijan province, Iran. Overall, 246 fecal specimens were collected from the cattle (diarrheic and healthy) and microscopically examined for G. duodenalis. The PCR-RFLP analysis of glutamate dehydrogenase (gdh) locus was used to identify the genotypes found in cattle. In this method, 432 bp expected size was amplified and then specific restriction NlaIV enzyme was used for subspecies detection. Totally, 23 (9.34%) specimens were microscopically positive for giardia cyst out of 246 examined samples. The PCR-RFLP analysis revealed that 19 samples (82.60%) have the genotype E and 4 samples (17.39%) belong to the subgroup AI. Our findings indicated that G. duodenalis infection is prevalent in cattle of Urmia and the non-zoonotic genotype E predominates in cattle in this region.

A Reagentless, Screen-Printed Amperometric Biosensor for the Determination of Glutamate in Food and Clinical Applications

A reagentless biosensor has been successfully developed to measure glutamate in food and clinical samples. The enzyme, glutamate dehydrogenase (GLDH) and the cofactor, nicotinamide adenine dinucleotide (NAD⁺) are fully integrated onto the surface of a Meldola's Blue screen-printed carbon electrode (MB-SPCE). The biological components are immobilized by utilizing unpurified multi-walled carbon nanotubes (MWCNT's) mixed with the biopolymer chitosan (CHIT), which are drop-coated onto the surface of the MB-SPCE in a layer-by-layer fashion. Meldola's Blue mediator is also incorporated into the biosensor cocktail in order to increase and facilitate electron shuttling between the reaction layers and the surface of the electrode. The loadings of each component are optimized by using amperometry in stirred solution at a low fixed potential of +0.1 V. The optimum temperature and pH are also determined using this technique. Quantification of glutamate in real samples is performed using the method of standard addition. The method of standard addition involves the addition of a sample containing an unknown concentration of glutamate, followed by additions of known concentrations of glutamate to a buffered solution in the cell. The currents generated by each addition are then plotted and the resulting line is extrapolated in order to determine the concentration of glutamate in the sample (Pemberton et al., Biosens Bioelectron 24:1246-1252, 2009). This layer-by-layer approach holds promise as a generic platform for the fabrication of reagentless biosensors.

Accuracy of a diagnostic model based on serum biochemical parameters in detecting cows at an increased risk of chronic fascioliasis

In adult cattle Fasciola hepatica infection usually follows a chronic subclinical course, and reduces both the milk yield and milk quality, resulting in considerable financial losses. Effective control of the disease is based on reliable identification of asymptomatically infected individuals, which now requires special parasitological or serological diagnostic tests. It is also known that F. hepatica infection induces alterations in some serum biochemical parameters. Therefore, the study was conducted to develop a model based on serum biochemical parameters allowing to identify cows at higher risk of chronic fascioliasis. Six hundred sixty eight adult dairy cows from 97 herds located in central and northeastern Poland were clinically examined, and blood and fecal samples from them were collected for a routine monitoring of fascioliasis and metabolic profile. Using the combination of fecal sedimentation test and indirect ELISA based on excretory/secretory products 203 cows, apparently healthy in clinical examination, were definitively classed as affected by (47 cows, 23.2%) or free from (156 cows, 76.8%) chronic fascioliasis. Their serum was screened for the activity of 4 enzymes (γ-glutamyl transpeptidase, glutamate dehydrogenase, aspartate aminotransferase, creatine kinase) and concentration of 18 other components (total bilirubin, total protein, albumin, globulin, urea, glucose, non-esterified fatty acids, β-hydroxybutyrate, sodium, potassium, chloride, calcium, magnesium, copper, zinc, iron, selenium, and haptoglobin). Logistic regression analysis was used to build 4 multivariable models allowing for identification of cows at risk of chronic fascioliasis. Then, the accuracy was compared between the models using the area under the receiver operating characteristic curve (AUROC), and an optimal cut-off value was determined for the most accurate model using Youden J index. The most accurate proved to be the model based on glutamate dehydrogenase activity and globulin, urea (all three positively linked with risk of chronic fascioliasis), and selenium concentration (negatively linked) adjusted by the access to pasture and cow's age. At the optimal cut-off of 0.37 this model had sensitivity of 85.1% (CI 95%:72.3%, 92.6%), specificity of 90.4% (CI 95%:84.7%, 94.1%), positive likelihood ratio of 8.8 (CI 95%:5.4, 14.5), and negative likelihood ratio of 0.16 (CI 95%:0.08, 0.33). This model performed significantly better than model including only γ-glutamyl transpeptidase or model including both γ-glutamyl transpeptidase and aspartate aminotransferase (both also adjusted by the access to pasture and cow's age), and was the only model which performed significantly better than the basic model based solely on the access to pasture and cow's age.