A sensitive method for the colorimetric determination of urea

Enzyme Cascade with Horseradish Peroxidase Readout for High-Throughput Screening and Engineering of Human Arginase-1

We report an enzyme cascade with horseradish peroxidase-based readout for screening human arginase-1 (hArg1) activity. We combined the four enzymes hArg1, ornithine decarboxylase, putrescine oxidase, and horseradish peroxidase in a reaction cascade that generated colorimetric or fluorescent signals in response to hArg1 activity and used this cascade to assay wild-type and variant hArg1 sequences as soluble enzymes and displayed on the surface of Escherichia coli. We screened a curated 13-member hArg1 library covering mutations that modified the electrostatic environment surrounding catalytic residues D128 and H141, and identified the R21E variant with a 13% enhanced catalytic turnover rate compared to wild type. Our scalable one-pot single-step arginase assay with continuous kinetic readout is amenable to high-throughput screening and directed evolution of arginase libraries and testing drug candidates for arginase inhibition.

A new and accessible instrumentation to determine urea in UHT milk using digital image analysis

This research demonstrates the development, optimization and application of a new low-cost detection system, based on digital image analysis, for the detection of urea in ultra-high-temperature (UHT) milk samples. The apparatus built in the laboratory, allows the capture of images through a simple system built by polyvinyl chloride (PVC) tubes, a digital microscope and a peristaltic mini-pump, after the colorimetric reaction between urea and diacetylmonoxime (butane-2,3-dionammonoxime). The red, green and blue (RGB) and hue, saturation and value (HSV) color systems were studied, with the saturation channel of the HSV color system selected as the analytical signal. Subsequently, the experimental chemical conditions were evaluated through multivariate experimental designs and the optimal conditions were defined. The proposed method was validated, and the detection and quantification limits presented by the method were 0.35 mg L^-1 and 0.52 mg L^-1, respectively; precision, ranged between 1.6  and 2.8 %. The results were compared with those obtained using the mid-infrared technique and no statistically significant differences were observed at a 95 % confidence level. The proposed method was applied to eight UHT milk samples that presented urea content ranging from 187 to 386 mg L^-1. The mean values obtained are in agreement with values presented in other studies for the determination of urea in milk. The results indicated that the system described and validated here is promising and can be applied to assess the authenticity and quality of milk.

An Update on Arginase Inhibitors and Inhibitory Assays

Arginase, which converts arginine into ornithine and urea, is a promising therapeutic target. Arginase is involved in cardiovascular diseases, parasitic infections and, through a critical role in immunity, in some cancers. There is a need to develop effective arginase inhibitors and therefore efforts to identify and optimize new inhibitors are increasing. Several methods of evaluating arginase activity are available, but few directly measure the product. Radiometric assays need to separate urea and dying reactions require acidic conditions and sometimes heating. Hence, there are a variety of different approaches available, and each approach has its own limits and benefits. In this review, we provide an update on arginase inhibitors, followed by a discussion on available arginase assays and alternative methods, with a focus on the intrinsic biases and parameters that are likely to impact results.

Potentiometric urea biosensors

Excess nitrogen in the body is converted to urea in the liver, and urea is disposed as a waste product in urine. Urea concentration can change in body fluids such as blood due to the presence of certain disorders. Therefore, the determination of urea is of high importance in various areas including medical diagnosis, as well as food quality control and environmental monitoring. Potentiometric sensors have certain advantages over their alternatives, such as rapidity, portability, cost effectiveness, high sensitivity, easy operation and simple apparatus. Potentiometric urea biosensors based on enzyme urease have been developed using various materials including nanoparticles and films, and also using different methodologies. In this review, we covered potentiometric urea biosensors reported in the literature, and touched upon their certain structure characteristics and performance parameters including detection limit, working concentration range, response time and lifetime, all of which are of practical importance. Each potentiometric urea biosensor has its own advantages and drawbacks, thus the selection of appropriate method depends on the sample to be analyzed, its urea concentration range and other requirements of the particular application. Further research is needed in order to optimize the performance of these devices and to broaden their applicability.

Protective effect of Vernonia amygdalina Delile against doxorubicin-induced cardiotoxicity

Doxorubicin has been used as an anticancer drug and has already indicated effective in the treatment of cancer. The incidence of cardiotoxicity due to doxorubicin was approximately 11%, resulting in the limited use of doxorubicin. Cardiac protection during doxorubicin therapy is needed because it can reduce the incidence of heart failure. Vernonia amygdalina (VA) is traditionally used by Indonesians as a traditional medicine and contains many secondary metabolites, including vernolide, vernodalol, vernoamygdalin, vernolepin, luteolin, luteolin 7-O-beta-glucoronoside and luteolin 7-O-glucoside. The pharmacological activity of VA has been widely studied, including its antimalarial, antidiabetic, anticancer, hepatoprotective, nephroprotective, and antioxidant activities. This research aimed to determine the antioxidant 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, total phenol, total flavonoid, and cardioprotective effects of Vernonia Amygdalina. Negative control was only intraperitoneal injection of doxorubicin (20 mg/kgbw) on the eight day while quercetin (85 mg/kgbw) and ethanol extract of Vernonia amygdalina (EEVA) 100, 200, 400 mg/kgbw dose are orally administered for eight consecutive days. Both quercetin and EEVA groups were also injected with doxorubicin (20 mg/kgbw) on the same day. On the following day, rats were injected with ketamine HCL 75 mg/kgbw and were dissected for heart blood collected. The blood collected 3 ml from each rat was analyzed for biochemical parameters. The analyzed biochemical parameters were Aspartate transaminase (AST), Alanine transaminase (ALT), Ureum, Creatinine, Creatinine kinase-MB (CK-MB), Lactate dehydrogenase (LDH), Troponin T, Brain natriuretic peptide (BNP), and antioxidant parameter Superoxide Dismutase (SOD). The result showed that EEVA antioxidant activity was 40.51 ± 4.89 μg/mL, total flavonoid was 3.79 ± 0.61 mg QE/g extract, and total phenol was 281.575 ± 1.069 mg GAE/g extract. Quercetin (85 mg/kgbw) and EEVA (400 mg/kgbw) reduce AST, ALT, Ureum, Creatinine, CK- MB, LDH, Troponin T, BNP significantly and increase rats' SOD level compared with negative control. So that, this study explicates that EEVA potentials as cardioprotective agent against doxorubicin by reducing biochemical parameters.

Amelioration of diethylnitrosamine (DEN) induced renal oxidative stress and inflammation by Carissa carandas embedded silver nanoparticles in rodents

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Phytofabricated silver nanoparticles (CCAgNPs) were biosynthesized and characterized.

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CCAgNPs were evaluated against diethylnitrosamine induced renal cancer.

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Silver nanoparticles have an antioxidant property.

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Silver nanoparticles unveiled a therapeutic effect against renal cancer in vivo.

Introduction

Inflammation and oxidative stress are the main factors ascribed with interruption in the process of renal tissue impairment. The toxicity of different types of nitrosamine is well recognized in animals and humans. Administration of the smallest quantities of diethylnitrosamine or dimethylnitrosamine either orally or parenterally results into renal damage. Therapeutic effects of phytofabricated silver nanoparticles of Carissa carandas aqueous extract has been scrutinised in current study for the assessment of renal cancer activity in animal model.

Methodology

Phytofabricated silver nanoparticles were characterized by using different instrumentation. Nephroprotective activity of silver nanoparticles at different doses was evaluated against N-diethylnitrosamine (200 mg/kg b.w., intraperitoneal) in animal model. Serum and renal homogenate were taken to evaluate the renal toxicity markers, oxidative stress, and antioxidant parameter, proinflammatory cytokines and histopathological study.

Result

Significant outcomes of silver nanoparticles in dose dependent manner down regulated the elevated serum marker, tumour marker enzymes and histopathology observation of repaired tissue assured the renal cancer activity in animals. In addition, profile of enzymatic and non-enzymatic antioxidant, proinflammatory cytokines and tumour promotion marker also favours the anticancer property of silver nanoparticles.

Conclusion

The data of current study reveals silver nanoparticles ameliorates renal oxidative stress and carcinogenesis which was induced by N-diethylnitrosamine and accredited to antioxidant and anticancer activities of phytofabricated nanoparticles by biological approach.

Reno-Hepatoprotective and Antidiabetic Properties of Methanol Leaf Extract of Laportea Aestuans in Wistar Rats

Toxicities due to exposure to arsenic-contaminated water and the occurrence of diabetes mellitus are major health concerns. Treatment of these concerns using therapeutic measures have recorded limited success. Traditionally, Laportea aestuans (LA) has been used in managing various diseases. Hence, we investigated the reno-hepatoprotective/antidiabetic potentials of methanol leaf extract of LA (MeLELA) in male Wistar rats. Thirty rats (100-150 g) were equally distributed into 6 groups: Group I (vehicle-treated); group II received 2.5 mg/kg sodium arsenite (SA) thrice a week for 2 weeks; group III received streptozotocin (STZ, 50 mg/kg once); group IV received 200 mg/kg LA daily for 14 days; group V received SA and LA; group VI received STZ and LA. Sodium arsenite and STZ induced reno-hepatotoxicity and diabetes, respectively. Phytochemical screening, biomarkers/enzyme activities, blood glucose levels, micronucleus assay, kidney, liver and pancreas histologies were determined according to standard procedures. Alkaloids, carotenoids and flavonoids were present in abundance. Both SA-and STZ-treated groups recorded significant (p < 0.05) reductions in serum protein concentrations, while co-treatment with LA significantly restored the levels. The SA-induced significant increase in creatinine/urea levels were significantly reduced by LA. Co-treatment of each of SA-and STZ-treated groups, respectively, with LA significantly decreased the elevated serum alanine and aspartate aminotransferases' activities. Increased blood glucose level in diabetic group was remarkably lowered by LA. Also, the SA-induced frequency of micronucleated polychromatic erythrocytes was significantly ameliorated by LA. Conclusively, LA is protective against SA-induced toxicity and STZ-induced diabetes in Wistar rats.

Rational design, engineer, and characterization of a novel pegylated single isomer human arginase for arginine depriving anti-cancer treatment

AIMS

Arginine depleting enzymes are found effective to treat arginine-auxotrophic cancers and therapy-resistant malignancies, alone or in combination with cytotoxic agents or immune checkpoint inhibitors. We aim to select and validate a long-lasting, safe and effective PEGylated and cobalt-chelated arginase conjugated at the selective cysteine residue as a therapeutic agent against cancers.

MAIN METHODS

Exploring pharmacokinetic and pharmacodynamic properties of the three arginase conjugates with different PEG modality (20 kDa linear as A20L, 20 kDa branched as A20Y, and 40 kDa branched as A40Y) by cell-based and animal studies.

KEY FINDINGS

Arginase conjugates showed comparable systemic half-lives, about 20 h in rats and mice. The extended half-life of PEGylated arginase was concurrent with the integrity of conjugates of which PEG and protein moieties remain attached in bloodstream for 72 h after drug administration. Arginase modified with a linear 20 kDa PEG (A20L) was chosen as the lead candidate (PT01). In vitro assays confirmed the very potent cytotoxicity of PT01 against cancer cell lines of breast, prostate, and pancreas origin. In MIA PaCa-2 pancreatic and PC-3 prostate tumor xenograft models, weekly infusion of the PT01 at 5 and 10 mg/kg induced significant tumor growth inhibition of 44-67%. All mice experienced dose-dependent but rapidly reversible weight loss following each weekly dose, suggesting tolerable toxicity.

SIGNIFICANCE

These non-clinical data support PT01 as the lead candidate for clinical development that may benefit cancer patients by providing an alternative cytotoxic mechanism.

Can Enterocin M in Combination with Sage Extract Have Beneficial Effect on Microbiota, Blood Biochemistry, Phagocytic Activity and Jejunal Morphometry in Broiler Rabbits?

Simple Summary

The weaning period is one of the most critical phases in a rabbit’s life, when rabbits are most sensitive to various spoilage agents, often with fatal outcome. Preventing these post-weaning alimentary disturbances and improving gut health through the use of natural substances has become an area of research activity in rabbit nutrition. The possibilities of “in vivo” administration of bacteriocins in rabbits are often limited. Our study focused therefore on improving rabbits’ health using enterocin M and sage extract, alone and also in combination, mainly to determine their effect on the microbiota, phagocytic activity, serum biochemistry, and morphometry of rabbits. The antibacterial effect of both additives was observed in the gastrointestinal tract of rabbits. Several biochemical parameters (increased in total proteins (TPs) using enterocin (Ent) M, reduction of alanine aminotransferase (ALT) using sage and its hypocholesteremic effect alone and in combination with EntM, and improvement of mineral levels) were optimized. All additives, but mostly EntM, showed a tendency to improve the jejunal morphological parameters.

Abstract

The present study investigated the effects of enterocin (Ent) M and sage extract alone and also in combination on the gut microflora, phagocytic activity, blood biochemistry, and morphometry of rabbits. Sixty-four rabbits (aged five weeks, M91 meatline, both sexes) were divided into three experimental groups: E (EntM; 50 µL/animal/day), S (sage; 10 µL/animal/day), and E + S (EntM + sage) groups and control group (C). The additives were administered in drinking water for a period of 21 days. Dietary supplementation of EntM and sage significantly reduced the coliforms (E: p < 0.001; S: p < 0.001; E + S: p < 0.001) in feces, while simultaneous addition of EntM and sage decreased enterococci (E + S: p < 0.0001), lactic acid bacteria (E + S: p < 0.01), and coagulase-positive staphylococci (E + S: p < 0.0001) in the appendix. Sage addition reduced HDL (S: p < 0.001) and LDL cholesterol (S: p < 0.001; E + S: p < 0.001), LDL/HDL ratio (S: p < 0.001; E + S: p < 0.01), and increased urea (S: p < 0.01; E + S: p < 0.001) and creatinine (S: p < 0.001; E + S: p < 0.001) in serum. EntM and sage application, alone or in combination, improve the jejunal morphometry (p < 0.0001) in rabbits.

Resveratrol Supplementation Protects Against Nicotine-Induced Kidney Injury

Prolonged exposure to nicotine accelerates onset and progression of renal diseases in habitual cigarette smokers. Exposure to nicotine, either via active or passive smoking is strongly shown to enhance renal oxidative stress and augment kidney failure in various animal models. In this study, we investigated the effects of resveratrol supplementation on nicotine-induced kidney injury and oxidative stress in a rat model. Male Sprague-Dawley rats were given nicotine (0.6 mg/kg, i.p.) alone or in combination with either resveratrol (8 mg/kg, i.p.), or angiotensin II type I receptor blocker, irbesartan (10 mg/kg, p.o.) for 28 days. Upon completion of treatment, kidneys were investigated for changes in structure, kidney injury markers and oxidative stress. Administration of nicotine alone for 28 days resulted in significant renal impairment as shown by marked increase in plasma creatinine, blood urea nitrogen (BUN) and oxidative stress. Co-administration with resveratrol however successfully attenuated these changes, with a concomitant increase in renal antioxidants such as glutathione similar to the conventionally used angiotensin II receptor blocker, irbesartan. These data altogether suggest that targeting renal oxidative stress with resveratrol could alleviate nicotine-induced renal injury. Antioxidants may be clinically important for management of renal function in habitual smokers.

Feasibility of biodiesel production and CO2 emission reduction by Monoraphidium dybowskii LB50 under semi-continuous culture with open raceway ponds in the desert area

BACKGROUND

Compared with other general energy crops, microalgae are more compatible with desert conditions. In addition, microalgae cultivated in desert regions can be used to develop biodiesel. Therefore, screening oil-rich microalgae, and researching the algae growth, CO₂ fixation and oil yield in desert areas not only effectively utilize the idle desertification lands and other resources, but also reduce CO₂ emission.

RESULTS

Monoraphidium dybowskii LB50 can be efficiently cultured in the desert area using light resources, and lipid yield can be effectively improved using two-stage induction and semi-continuous culture modes in open raceway ponds (ORPs). Lipid content (LC) and lipid productivity (LP) were increased by 20% under two-stage industrial salt induction, whereas biomass productivity (BP) increased by 80% to enhance LP under semi-continuous mode in 5 m² ORPs. After 3 years of operation, M. dybowskii LB50 was successfully and stably cultivated under semi-continuous mode for a month during five cycles of repeated culture in a 200 m² ORP in the desert area. This culture mode reduced the supply of the original species. The BP and CO₂ fixation rate were maintained at 18 and 33 g m^-2 day^-1, respectively. Moreover, LC decreased only during the fifth cycle of repeated culture. Evaporation occurred at 0.9-1.8 L m^-2 day^-1, which corresponded to 6.5-13% of evaporation loss rate. Semi-continuous and two-stage salt induction culture modes can reduce energy consumption and increase energy balance through the energy consumption analysis of life cycle.

CONCLUSION

This study demonstrates the feasibility of combining biodiesel production and CO₂ fixation using microalgae grown as feedstock under culture modes with ORPs by using the resources in the desert area. The understanding of evaporation loss and the sustainability of semi-continuous culture render this approach practically viable. The novel strategy may be a promising alternative to existing technology for CO₂ emission reduction and biofuel production.

Novel Route for Agmatine Catabolism in Aspergillus niger: 4-Guanidinobutyrase Assay

The enzyme 4-guanidinobutyrase (GBase) catalyzes the hydrolysis of 4-guanidinobutyric acid (GB) to 4-aminobutyric acid (GABA) and urea. Here we describe methods to estimate urea and GABA that were suitably adapted from the published literature. The urea is determined by colorimetric assay using modified Archibald's method. However, the low sensitivity of this method often renders it impractical to perform fine kinetic analysis. To overcome this limitation, a high sensitive method for detecting GABA is exploited that can even detect 1 μM of GABA in the assay mixture. The samples are deproteinized by perchloric acid (PCA) and potassium hydroxide treatment prior to HPLC analysis of GABA. The method involves a pre-column derivatization with o-phthalaldehyde (OPA) in combination with the thiol 3-mercaptopropionic acid (MPA). The fluorescent GABA derivative is then detected after reversed phase high performance liquid chromatography (RP-HPLC) using isocratic elution. The protocols described here are broadly applicable to other biological samples involving urea and GABA as metabolites.

The effect of an unsaturated-fat diet on cataract formation in streptozotocin-induced diabetic rats

1. Cataract formation in streptozotocin-induced diabetes in rats was reduced by approximately 85% when a diet rich in maize oil (300 g/kg diet) (fat diet) was given, thus confirming results of earlier studies. However, the concentration of sorbitol in the lens of diabetic animals remained high, the values for diabetic rats given the standard diet and the fat diet being 65 and 40 μmol/g protein respectively.

2. With the standard diet, the fatty acid profile of the triglycerides of the epididymal fat pads was characterized by a greater relative proportion of saturated fatty acids for the diabetic animals compared to that for the normal animals. The fat diet moderated the tendency towards saturation in the diabetic animals.

3. The fat diet had other effects on the diabetic animals; these included a reduced mortality rate, increased body-weight, a decrease in the daily water intake, and in the daily urinary excretion of glucose and urea.

4. In the diabetic animals the fat diet had no effect on the specific activities in the liver of hexokinase (EC 2.7.1.1), glucokinase (EC 2.7.1.2), phosphofructokinase (EC 2.7.1.11) and pyruvate kinase (EC 2.7.1.40). However, the specific activity of glucose-6-phosphatase (EC 3.1.3.9) was reduced, while that of malate dehydrogenase (decarboxylating) (NADP) (EC 1.1.1.40) was increased. The NAD+: NADH ratio, as calculated from liver pyruvate and lactate concentrations, tended to increase.

5. The results suggested that the fat diet moderated the long-term metabolic effects of diabetes.

The effect of green tea on opposing toxicity of acrylamide on kidney function

Purpose

The purpose of this paper is to investigate the effects of green tea extract on kidney function tests, in male rats that received different doses of acrylamide (AA).

Design/methodology/approach

Animals were dispensed at random to one of the following treatments: group 1 served as control, whereas groups 2, 3 received seven, 14 mg/100 g B.W/day of AA, respectively, in drinking water for 15 and 30 days. Group 4 received green tea 1.5 percent concentration and groups 5, 6 received seven, 14 mg/100 g B.W/day in a mixture with green tea for 15 and 30 days.

Findings

Serum urea and creatinine significantly increase with AA. However, Total protein, albumin and A/G ratio showed significant drop in all treated groups when compared with control. Supplementation of rats with antioxidant (green tea) enhanced the general health condition, reduced the severity of genotoxic effect and the alteration in blood and serum parameters produced by AA.

Practical implications

The authors suggest that green tea may deliver a cushion for long therapeutic option against toxins-induced nephrotoxicity without damaging side effects.

Originality/value

The study uses green tea as a natural antioxidant source. Epigallocatechin-3 gallate is the most plentiful catechin preserved in green tea and a high source of flavonoids. Flavonoids are a group of phenolic products of plant metabolism with high antioxidant properties to reduce nephrotoxicity without side effects.

Structure and function of non-native metal clusters in human arginase I

Various binuclear metal ion clusters and complexes have been reconstituted in crystalline human arginase I by removing the Mn(2+)(2) cluster of the wild-type enzyme with metal chelators and subsequently soaking the crystalline apoenzyme in buffer solutions containing NiCl(2) or ZnCl(2). X-ray crystal structures of these metal ion variants are correlated with catalytic activity measurements that reveal differences resulting from metal ion substitution. Additionally, treatment of crystalline Mn(2+)(2)-human arginase I with Zn(2+) reveals for the first time the structural basis for inhibition by Zn(2+), which forms a carboxylate-histidine-Zn(2+) triad with H141 and E277. The imidazole side chain of H141 is known to be hyper-reactive, and its chemical modification or mutagenesis is known to similarly compromise catalysis. The reactive substrate analogue 2(S)-amino-6-boronohexanoic acid (ABH) binds as a tetrahedral boronate anion to Mn(2+)(2), Co(2+)(2), Ni(2+)(2), and Zn(2+)(2) clusters in human arginase I, and it can be stabilized by a third inhibitory Zn(2+) ion coordinated by H141. Because ABH binds as an analogue of the tetrahedral intermediate and its flanking transition states in catalysis, this implies that the various metallo-substituted enzymes are capable of some level of catalysis with an actual substrate. Accordingly, we establish the following trend for turnover number (k(cat)) and catalytic efficiency (k(cat)/K(M)): Mn(2+) > Ni(2+) ≈ Co(2+) ≫ Zn(2+). Therefore, Mn(2+) is required for optimal catalysis by human arginase I.

Engineering reduced-immunogenicity enzymes for amino acid depletion therapy in cancer

Cancer has become the leading cause of death in the developed world and has remained one of the most difficult diseases to treat. One of the difficulties in treating cancer is that conventional chemotherapies often have unacceptable toxicities toward normal cells at the doses required to kill tumor cells. Thus, the demand for new and improved tumor specific therapeutics for the treatment of cancer remains high. Alterations to cellular metabolism constitute a nearly universal feature of many types of cancer cells. In particular, many tumors exhibit deficiencies in one or more amino acid synthesis or salvage pathways forcing a reliance on the extracellular pool of these amino acids to satisfy protein biosynthesis demands. Therefore, one treatment modality that satisfies the objective of developing cancer cell-selective therapeutics is the systemic depletion of that tumor-essential amino acid, which can result in tumor apoptosis with minimal side effects to normal cells. While this strategy was initially suggested over 50 years ago, it has been recently experiencing a renaissance owing to advances in protein engineering technology, and more sophisticated approaches to studying the metabolic differences between tumorigenic and normal cells. Dietary restriction is typically not sufficient to achieve a therapeutically relevant level of amino acid depletion for cancer treatment. Therefore, intravenous administration of enzymes is used to mediate the degradation of such amino acids for therapeutic purposes. Unfortunately, the human genome does not encode enzymes with the requisite catalytic or pharmacological properties necessary for therapeutic purposes. The use of heterologous enzymes has been explored extensively both in animal studies and in clinical trials. However, heterologous enzymes are immunogenic and elicit adverse responses ranging from anaphylactic shock to antibody-mediated enzyme inactivation, and therefore have had limited utility. The one notable exception is Escherichia colil-asparaginase II (EcAII), which has been FDA-approved for the treatment of childhood acute lymphoblastic leukemia. The use of engineered human enzymes, to which natural tolerance is likely to prevent recognition by the adaptive immune system, offers a novel approach for capitalizing on the promising strategy of systemic depletion of tumor-essential amino acids. In this work, we review several strategies that we have developed to: (i) reduce the immunogenicity of a nonhuman enzyme, (ii) engineer human enzymes for novel catalytic specificities, and (iii) improve the pharmacological characteristics of a human enzyme that exhibits the requisite substrate specificity for amino acid degradation but exhibits low activity and stability under physiological conditions.

Integrative analysis of metabolite and transcript abundance during the short-term response to saline and oxidative stress in the brown alga Ectocarpus siliculosus

The model brown alga Ectocarpus siliculosus undergoes extensive transcriptomic changes in response to abiotic stress, many of them related to primary metabolism and particularly to amino acid biosynthesis and degradation. In this study we seek to improve our knowledge of the mechanisms underlying the stress tolerance of this alga, in particular with regard to compatible osmolytes, by examining the effects of these changes on metabolite concentrations. We performed extensive metabolic profiling (urea, amino acids, sugars, polyols, organic acids, fatty acids) of Ectocarpus samples subjected to short-term hyposaline, hypersaline and oxidative stress, and integrated the results with previously published transcriptomic data. The most pronounced changes in metabolite concentrations occurred under hypersaline stress: both mannitol and proline were accumulated, but their low final concentrations indicate that, in this stress condition, both compounds are not likely to significantly contribute to osmoregulation at the level of the entire cell. Urea and trehalose were not detected in any of our samples. We also observed a shift in fatty acid composition from n-3 to n-6 fatty acids under high salinities, and demonstrated the salt stress-induced accumulation of small amounts of γ-aminobutyric acid (GABA). GABA could be synthesized in E. siliculosus through a salt stress-induced putrescine-degradation pathway.

Replacing Mn(2+) with Co(2+) in human arginase i enhances cytotoxicity toward l-arginine auxotrophic cancer cell lines

Replacing the two Mn(2+) ions normally present in human Arginase I with Co(2+) resulted in a significantly lowered K(M) value without a concomitant reduction in k(cat). In addition, the pH dependence of the reaction was shifted from a pK(a) of 8.5 to a pK(a) of 7.5. The combination of these effects led to a 10-fold increase in overall catalytic activity (k(cat)/K(M)) at pH 7.4, close to the pH of human serum. Just as important for therapeutic applications, Co(2+) substitution lead to significantly increased serum stability of the enzyme. Our data can be explained by direct coordination of l-Arg to one of the Co(2+) ions during reaction, consistent with previously reported model studies. In vitro cytotoxicity experiments verified that the Co(2+)-substituted human Arg I displays an approximately 12- to 15-fold lower IC(50) value for the killing of human hepatocellular carcinoma and melanoma cell lines and thus constitutes a promising new candidate for the treatment of l-Arg auxotrophic tumors.

Analytical methods for measuring urea in pharmaceutical formulations

Two new methods are described for the routine determination of urea that utilize HPTLC-densitometry and colorimetry. The methods involve derivatization of urea with p-dimethylaminobenzaldehyde to a yellow-coloured compound. Validation of the methods was accomplished with respect to linearity, accuracy, reproducibility and limit of detection/quantification. Both methods were compared with an enzymatic method previously described in the literature and were found to be in close agreement. The proposed methods have the advantages of being simple, rapid and involve a single step sample preparation. Under experimental conditions HPTLC was the most sensitive method.

The Prague Hypertensive Rat: a new model of genetic hypertension

Several animal models of genetic hypertension have been developed but not all of them possess a closely related control strain. Therefore, a new model based on Wistar rats is described in which both hypertensive and normotensive lines were bred from a single parental pair. Several basic data on the two lines (called the Prague Hypertensive Rat, PHR, and the Prague Normotensive Rat, PNR) are given. PNR had a longer survival compared with PHR. At the age of 7 weeks, systolic blood pressure was 161 +/- 14 mmHg in PHR males and 109 +/- 9 mmHg in PNR males. Its further increase with age was very slow in PNR but very steep in PHR. Typical left ventricular cardiac hypertrophy developed in PHR in which cardiac output was not significantly different from that of PNR but total peripheral resistance was higher. Kidney weight was also greater in PHR than in PNR. There was no difference in basic renal functions except of proteinuria which was higher in PHR than in PNR. No differences were observed in extracellular and interstitial fluid volumes whereas plasma and blood volumes were slightly but significantly greater in PHR than in PNR suggesting a shift of extracellular fluid towards the intravascular compartment. This hypertensive model the parameters of which resemble to those of human essential hypertension should be especially suitable for cross-transplantation studies.

Effect of some simple manoeuvres on the course of acute renal failure after gentamycin treatment in rats

For a period of 5 days, Wistar rats received Gentamycin (G), 100 mg/kg b.w./day i.m. Three days after the last injection, the rats were sacrificed and the plasma concentrations of urea (PU) and creatinine (PCr) were determined. Both values were significantly higher than in the control rats receiving vehicle only. The increase was substantially greater in females than in males. The rats drinking isotonic NaCl solution instead of water 7 days prior to G showed near normal PU and PCr values; drinking of NaHCO3 had a similar protective effect. Isotonic sucrose solution was without any influence. The rats drinking Ca gluconate or NH4Cl solutions had similar or higher PU and PCr values as rats drinking water, but their body weight and overall condition markedly deteriorated. Brattleboro rats with diabetes insipidus exhibited a very similar course as Wistar rats; there was also no significant difference between the former and their heterozygous non-insipidic litter mates.

Urea handling by the medullary collecting duct of the rat kidney during hydropenia and urea infusion

Previous micropuncture studies of distal tubule fluid and ureteral urine have indicated a varying degree of urea reabsorption in the collecting duct. In the present experiments the microcatheterization technique was used to directly determine urea, Na, K, total solute and fluid reabsorption along the length of the medullary collecting duct in anesthetized hydropenic rats and in rats given low dose urea infusion (Purea 18.9 mM/l). In hydropenic rats, the remaining fraction of filtered urea did not change significantly along the collecting duct, as indicated both by regression analysis of all samples and by comparison of paired samples from the corticomedullary junction and papillary tip. During low dose urea infusion, urine osmolality increased in proportion to the increase in urea concentration and again there was no net urea reabsorption between the beginning and end of the duct. However, during urea infusion, analysis of samples from the beginning, mid-zone, and end of the collecting duct indicated that urea entry occurred in the proximal portion of the duct (beginning to mid-zone, P less than 0.01) and that urea reabsorption occurred in the distal portion (mid-zone to end, P less than 0.01). The lack of significant net urea reabsorption along the duct despite the excretion of moderately concentrated urine, has despite the excretion of moderately concentrated urine, has implications for the concept of medullary urea recycling and for models of the urinary concentrating mechanism. The finding of functional heterogeneity with respect to urea handling in the collecting duct in vivo, with both reabsorption are secretion being demonstrated, raises the possibility that internal recycling of urea in the medullary collecting duct itself may contribute to maintenance of a high papillary interstitial urea concentration.

Improvements in the determination of urea using diacetyl monoxime; methods with and without deproteinisation

A rapid and reproducible method is described for measurement of urea in biological materials (after deproteinisation) and in serum (without deproteinisation). Urea is colorimetrically determined with diacetyl monoxime and thiosemicarbazide in the presence of sulphuric acid, phosphoric acid and ferric chloride. The sensitivity of the colorimetric reaction and stability of the colour are enhanced over existing related procedures and the serum blank diminished, enabling urea to be precisely measured in micro amounts (1--5 microliters) of serum.

The effects of a high fat diet on chronic streptozotocin-diabetic rats

The effects of a high fat diet (30% (w/w) corn oil) on chronic streptozotocin-diabetic rats were investigated at the whole body level and at the enzyme level. The diet caused significant decreases in the extent of polydipsia (66% decrease), polyphagia (49%), polyuria (67%) and glycosuria (70%). The activities of selected hepatic enzymes from the glycolytic, gluconeogenic, ureogenic and lipogenic clusters were determined. The fat diet caused significant decreases (range: 47 to 54%) in the activity of the ureogenic enzymes carbamyl phosphate synthetase, ornithine transcarbamylase and arginase; had no effect on the glycolytic enzymes glucokinase, hexokinase and pyruvate kinase; partially decreased the diabetes-induced elevated activities of the gluconeogenic enzymes phosphoenolpyruvate carboxykinase (63% decrease), serine dehydratase (90%), alanine aminotransferase (31%) and aspartate aminotransferase (65%), and partially reversed the activity of one lipogenic enzyme, ATP citrate lyase.

The excretion of urea by the larvae of Spodoptera mauritia Boisd. (Noctuidae: Lepidoptera) during development

The concentration of urea in the excreta of the 6th instar larvae of Spodoptera mauritia varies from 4.017 +/- 0.541 to 31.052 +/- 1.193 mumoles/g dry excreta (mean +/- SE). The observation confirms that urea excreted is of metabolic origin.

Investigation of reaction intermediates of the urea-diacetylmonoxime reaction

1. An investigation of the intermediates of the urea-diacetylmonoxime reaction and the isolation of the protochromogen has been described. A comparative spectral study of the protochromogen with that of the literature values suggested the structure of the protochromogen to be a diureide. 2. The diureides of 1-phenyl-1,2-propanedione-monoxime and 2,3-pentanedione were synthesized and their visible, U.V., I.R., NMR, and mass desorption spectrometry data were analyzed. The study suggests that the structure of each of these compound is that of a diureide. When these diureides were redissolved in acid media, they gave the color expected of the corresponding chromogens found from the respective diketones and urea. 3. The 3a-methyl-6a-phenyl-glycoluril was synthesized by a base-catalyzed reaction. When this glycoluril was dissolved in concentrated HCl, a pink color was obtained, similar to that of the corresponding diureide. These studies indicate that both the diureide and the glycoluril (if formed at all in acid-catalyzed reaction) are converted to the same chromogen, possibly via a rearrangement. 4. When 2,3-butanedionemonoximethiosemicarbazone was reacted with urea in acid medium, characteristic spectral data were obtained which were very similar to those of the urea-diacetylmonoximethiosemicarbazide reaction. This tends to indicate that the possible structures of the protochromogens are similar and of the open chain diureide type.

Some photoreactions of isolated cytochrome b-559

Cytochrome b-559 was isolated from spinach and the alga Bumilleriopsis filiformis (Xanthophyceae) and characterized by functional properties: (a) It was active as electron acceptor in a diaphorase system using NADPH as donor and ferredoxin and ferredoxin-NADP reductase as redox proteins. (b) It exhibited photooxidation with Photosystem-I particles, when illuminated with 707 nm light. (c) It was photooxidized by Photosystem-II particles and 652 nm light at room temperature. Light greater than 702 nm was ineffective. The data corroborate previous reports on redox reactions of bound cytochrome b-559.

Renal function tests: what do they mean? A review of renal anatomy, biochemistry, and physiology

Renal physiology, biochemistry, and anatomy are reviewed. For the most part, those aspects of these disciplines will be discussed which relate directly to the question of the evaluation of nephrotoxicity. In addition, emphasis is placed on those procedures and techniques which are useful in the evaluation of nephrotoxicity. A detailed discussion of histological and anatomical considerations is not given, since this is probably the least useful criterion for evaluation of renal damage. This information is intended as background for the remainder of the symposium which will be directed toward an understanding of specific nephrotoxicity phenomena.