A bistable switch in pH in urease-loaded alginate beads.

A bistable switch from a low pH (unreacted "off") state to a high pH (reacted "on") state was obtained in enzyme-loaded gel beads in response to supra-threshold substrate concentrations.

On the origin of bistability in the Stage 2 of the Huang-Ferrell model of the MAPK signaling.

Mitogen-activated protein kinases (MAPKs) are important signal transducing enzymes, unique to eukaryotes, that are involved in many pathways of cellular regulation. Successive phosphorylation cascades mediated by MAPKs serve as sensitive switches initiating various cellular processes. Apart from this basic feature, the underlying reaction network is capable of displaying other nonlinear phenomena including bistable steady states and hysteresis as well as periodic oscillations. We show that from the mechanistic point of view, bistability is a consequence of interaction between single and double phosphorylation/dephosphorylation pathways in a Stage 2 subsystem of the Huang-Ferrell model. Within this subsystem we uncover the core subnetwork obtained by systematic reduction relying on the methods of stoichiometric network analysis. For the core model we show that there is either one stable steady state or three steady states of which two are stable and point out the role of interplay between the single and double phosphorylation subnetworks in generating bistability.

Degradation of tertiary alkylamines during chlorination/chloramination: implications for formation of aldehydes, nitriles, halonitroalkanes, and nitrosamines.

Drinking water utilities are exploring the use of waters impacted by wastewater effluents and agricultural runoff to meet the demands of growing populations. Due to the elevated organic nitrogen concentrations in these waters, the pathways responsible for transformation of organic nitrogen into toxic nitrogenous disinfection byproducts during chlorine and chloramine disinfection are of current concern. Tertiary alkylamines are important functional groups in human waste products and various consumer products that can be released to drinking water supplies via wastewater effluents. We investigated degradation pathways for model tertiary alkylamines during chlorination and chloramination. Our results indicate that tertiary alkylamines degrade nearly instantaneously during chlorination to form aldehydes and secondary alkylamines quantitatively, with no significant regioselectivity. Similar results were observed during chloramination, but the observed degradation rates were much slower, with lower yields of aldehydes. As these major products were fairly stable, these results explain why tertiary amines are significant precursors of secondary nitrosamines during chloramination. Trichloronitromethane formed at very low yields during chlorination, but was not observed during chloramination; monochloronitromethane and dichloronitromethane were never detected. Despite the significant yields of aldehydes during chloramination, our results indicated low nitrile yields bythe reaction between chloramines and aldehydes.

Enhanced nitrogenous disinfection byproduct formation near the breakpoint: implications for nitrification control.

Increasing the chlorine to ammonia molar ratio and breakpoint chlorination are two control strategies practiced by drinking water treatment utilities experiencing nitrification during chloramination. The first strategy will increase dichloramine formation, which increases nitrosamine formation. Moreover, our results indicate that dichloramine is also an important factor for nitrile formation. Near the breakpoint, nitrosamine formation is over an order of magnitude higher than that observed during chloramination. We propose that there are two nitrosamine formation pathways active in the breakpoint chlorination region: (i) a relatively slow reaction of dichloramine with amine precursors in the presence of dissolved oxygen and (ii) a fast reaction involving reactive breakpoint chlorination intermediates. Lastly, in the presence of nitrite, if breakpoint chlorination is conducted to achieve a significant free chlorine residual, nitrosamines and nitramines will form through a reaction with nitrite and hypochlorite. However, nitrosamine formation will be much lower than when breakpoint chlorination is conducted with no significant free chlorine residual.

Treatment of acromegaly with the GH receptor antagonist pegvisomant in clinical practice: safety and efficacy evaluation from the German Pegvisomant Observational Study.

OBJECTIVE: The GH receptor antagonist pegvisomant is a highly effective new treatment option in acromegaly. The German Pegvisomant Observational Study (GPOS) was started to monitor long-term safety and efficacy of pegvisomant as prescribed in clinical practice. DESIGN: GPOS is an observational, multi-center, surveillance study, which comprises non-interventional data collection. METHODS: Of the 229 patients included in the study, 90.4% had previous pituitary surgery, 43.2% were treated by radiation therapy, and 94.3% had previous medical therapy for acromegaly that had been discontinued mainly due to persistent IGF-I elevation or side effects. The intention-to-treat population included 177 patients with at least one post-baseline efficacy measurement. RESULTS: IGF-I levels decreased from 1.75+/-0.91-fold the upper limit of normal at baseline to 1.05+/- 0.62 at the 6-month visit, 0.96+/-0.60 at the 12-month visit, and to 0.89+/-0.41-fold after 24 months (P<0.0001). Mean duration of pegvisomant therapy was 51.8+/-35.8 weeks (median=51.9 weeks). IGF-I was normalized in 64.4% at 6 months with a median dose of 15.0 mg/day, in 70.9% at 12 months, and in 76.3% at 24 months. Fasting glucose levels improved from 114.4+/-45.9 to 101.5+/- 42.8 mg/dl after 6 months (P<0.01) and to 100.6+/-33.2 mg/ml after 12 months (P<0.01). General physical condition measured by specific signs and symptoms score improved significantly. Adverse events occurring in >1% were injection site reactions in 7.4%, elevated liver enzymes (>3 times of normal) in 5.2% (3.1% spontaneously normalized during continued treatment), reported increase of pituitary tumor volume in 5.2% (which was verified in 3.1%), and headache in 1.7%. CONCLUSIONS: Pegvisomant is generally well tolerated with a safety profile similar to that reported in clinical trials and can effectively reduce IGF-I in patients with acromegaly refractory to conventional therapy.

Nitrosamine formation pathway revisited: the importance of chloramine speciation and dissolved oxygen.

Nitrosamine formation during chloramination previously has been linked to a reaction between monochloramine and organic nitrogen precursors via unsymmetrical dialkylhydrazine intermediates. Our results demonstrate the critical importance of dichloramine and dissolved oxygen. We propose a new nitrosamine formation pathway in which dichloramine reacts with secondary amine precursors to form chlorinated unsymmetrical dialkylhydrazine intermediates. Oxidation of these intermediates by dissolved oxygen to form nitrosamines competes with their oxidation by chloramines. Even when preformed monochloramine was applied, our model explained nearly all N-nitrosodimethylamine formation from the traces of dichloramine formed via monochloramine disproportionation. We suggest that, in contrast to unsymmetrical dialkylhydrazines, the weak, nonpolar nature of the N-Cl linkage in chlorinated unsymmetrical dialkylhydrazine intermediates enables incorporation of dissolved oxygen to form nitrosamines. With the improved understanding of the nitrosamine formation pathway, strategies are suggested that could significantly reduce nitrosamine formation during chloramination.

Occurrence and fate of nitrosamines and nitrosamine precursors in wastewater-impacted surface waters using boron as a conservative tracer.

Using boron as a conservative tracer of municipal wastewater effluents, a mass balance was developed to determine river flowrates that requires only wastewater discharge flowrates and boron concentrations in wastewater effluents and in the river upstream and downstream of these discharges. Furthermore, this method permits calculation of the percentage of the river deriving from wastewater. This method could be useful within river sections featuring no independent data regarding river discharge. We assessed the decay of nitrate and N-nitrosodimethylamine (NDMA) precursors within an engineered treatment wetland and, using our boron analysis technique to account for dilution, within the Quinnipiac River (CT). Although both decayed with several day half-lives, their slow decay indicates they can persist to impact downstream drinking water supplies. Concentrations of NDMA and N-nitrosomorpholine (NMOR) were measurable within the river, but concentrations of four other nitrosamines, their precursors, and NMOR precursors were not detectable.

Elevated transaminases during medical treatment of acromegaly: a review of the German pegvisomant surveillance experience and a report of a patient with histologically proven chronic mild active hepatitis.

OBJECTIVE: The new GH receptor antagonist pegvisomant is the most effective medical therapy to normalize IGF-I levels in patients with acromegaly. Based on currently available data pegvisomant is well tolerated; however, treatment-induced elevation of transaminases has been reported and led to the necessity for drug discontinuation in some patients in the pivotal studies. The aim of this study was to evaluate and characterize the prevalence of elevated transaminases and to describe in detail the findings in a single case who required drug discontinuation because of elevation of transaminases which emerged during treatment and who underwent liver biopsy. DESIGN AND METHODS: Retrospective safety analyses were carried out on 142 patients with acromegaly receiving pegvisomant treatment in Germany between March 2003 and the end of 2004. Of these patients, 123 were documented in a post-marketing surveillance study, one case of elevated transaminases was reported spontaneously and the other patients were treated in a clinical study. RESULTS: Mean treatment duration with pegvisomant in the ongoing observational study at the end of 2004 was 28.3 +/- 19.9 (S.D.) weeks. Twelve out of the 142 patients had elevated transaminases above three times the upper limit of normal, likely caused by biliary obstruction in five of the patients. All patients but one affected by elevated transaminases had been previously treated with somatostatin analogues. In six out of 142 (4%) of patients, pegvisomant was permanently withdrawn because of elevated transaminases. The same number of patients showed a transient increase of transaminases with either spontaneous remission without dose modification (n = 4) or no re-increase of transaminases after temporary discontinuation and re-exposure (n = 2). The liver biopsy of one patient who was permanently withdrawn showed a chronic mild hepatitis with a mixed portal inflammation including eosinophilic granulocytes. CONCLUSIONS: Liver function tests should be regularly followed on pegvisomant treatment. Biliary complications, which may arise from restitution of normal gall bladder motility after cessation of somatostatin analogue treatment, need to be differentiated from pegvisomant-induced abnormalities. The histological pattern of the liver biopsy performed in one of the patients showed a mild chronic active hepatitis. The lack of dose dependency and rather low frequency of elevated transaminases in those cases where a biliary disorder was excluded render this reaction an idiosyncratic drug toxicity.

Influence of the order of reagent addition on NDMA formation during chloramination.

The formation of the potent carcinogen, N-nitrosodimethylamine (NDMA), during chlorine disinfection has caused significant concern among drinking water and wastewater recycling utilities practicing intentional or unintentional chloramination. Previous research modeled NDMA formation as arising from a reaction between monochloramine and organic nitrogen precursors, such as dimethylamine, via an unsymmetrical dimethylhydrazine (UDMH) intermediate. Contrary to the importance of monochloramine indicated by previous studies, hypochlorite formed an order of magnitude more NDMA than monochloramine when applied to a secondary municipal wastewater effluent containing excess ammonia. Experiments involving variation of the order that each reagent (i.e., hypochlorite, ammonium chloride, and dimethylamine) was added to solution suggest two factors that may be more important for NDMA formation than the presence of monochloramine: (i) the chlorination state of organic nitrogen precursors and (ii) the partial formation of dichloramine. Although dichloramine formation was most influenced by the pH conditions under which inorganic chloramine formation was performed, mixing effects related to the order of reagent addition may be important at full-scale plants. Chloramination strategies are suggested that may reduce NDMA formation by nearly an order of magnitude.

Excitability in chemical and biochemical pH-autocatalytic systems.

Using two different kinds of pH systems--the papain catalyzed hydrolysis of N-benzoyl-L-arginine ethyl ester in a membrane reactor and the bromate-sulfite-ferrocyanide (BSF) reaction in the CSTR--we study the relation among excitability, oscillations and bistability, and the ability of the system to respond to external periodic perturbations. Excitable properties of dynamical systems are examined in terms of a threshold set which is used to characterise dynamics in the reactor subject to external periodic stimuli. A precise definition and a method of calculating the threshold set are formulated. Two kinds of excitability distinguished by either direct or indirect initiation of the activatory process are found in both pH systems. Periodic pulsed perturbations of the BSF system display a nontrivial dependence of an excitation number on the forcing period. We examined this system also in oscillatory mode by looking at the phase shifts caused by single-pulse perturbations and constructing the phase transition curves (PTCs).

Dynamical properties of chemical systems near Hopf bifurcation points.

In this paper, we numerically investigate local properties of dynamical systems close to a Hopf bifurcation instability. We focus on chemical systems and present an approach based on the theory of normal forms for determining numerical estimates of the limit cycle that branches off at the Hopf bifurcation point. For several numerically ill-conditioned examples taken from chemical kinetics, we compare our results with those obtained by using traditional approaches where an approximation of the limit cycle is restricted to the center subspace spanned by critical eigenvectors, and show that inclusion of higher-order terms in the normal form expansion of the limit cycle provides a significant improvement of the limit cycle estimates. This result also provides an accurate initial estimate for subsequent numerical continuation of the limit cycle. (c) 2000 American Institute of Physics.

Upregulation of cholesterol synthesis after acute myocardial infarction--is cholesterol a positive acute phase reactant?

Acute myocardial infarction is associated with profound alterations in the plasma lipoprotein profile. The mechanism of these alterations is not clear, and both cholesterol biosynthesis up- and downregulation could possibly be a consequence of acute myocardial infarction. We determined plasma lipids, lipoproteins, apolipoproteins, and lathosterol-which is regarded as an estimate of whole body cholesterol biosynthesis in humans-concentrations in 34 patients (age 68+/-10 years, 24 male, 10 female) admitted to our hospital with acute MI and with onset of symptoms within the last 12 h. Samples were taken immediately after admission to the hospital, and 1, 2, and 10 days after admission. On the first day after admission there was a decrease in total cholesterol (C) by 14.1%, (P = 0.01), in LDL-C by 14.4% (P = 0.03), in HDL-C by 9.3% (NS), and in triglycerides by 19.5% (NS). Apolipoprotein B100 was reduced by 18.3% (P = 0.008), and apolipoprotein AI by 12.3% (NS). The lathosterol/cholesterol ratio was increased by 23.1% after 1 day, and by 28.7% after 2 days (P = 0.05). After 10 days, all variables except the apolipoproteins had essentially returned to baseline values. In conclusion, the changes in the plasma lipid profile after acute myocardial infarction are associated with a profound increase of whole body cholesterol biosynthesis as judged by the lathosterol/cholesterol ratio. These changes may possibly enhance the delivery of cholesterol to cells involved in tissue repair mechanisms after acute myocardial infarction.

Group psychotherapy for women molested in childhood: psychological and somatic symptoms and medical visits.

Molested women who completed a series of 16 weekly group psychotherapy sessions conducted by social workers improved substantially regarding various aspects of psychological functioning, including self-image, coping techniques, relationship issues, and mothering. In addition, there was significant improvement in all psychological symptom scales and all global indices of symptomatic distress measured by the SCL-90-R. Furthermore, the improvement was present immediately after therapy and, with the exception of the hostility score, persisted 1 year later. Although the somatization score was reduced, the number of visits for physical symptoms did not change. The patients studied manifested characteristics typical of previously surveyed women with a history of childhood abuse, including a frequent history of major surgery (Drossman et al., 1996; Longstreth & Wolde-Tsadik, 1993; Springs & Friedrich, 1992) and, in some, a previous problem with alcohol (Springs & Friedrich, 1992; Walker et al., 1995) or drugs (Longstreth & Wolde-Tsadik, 1993; Miller & McCluskey-Fawcett, 1993; Springs & Friedrich, 1992). Also, nearly one half of the subjects had irritable bowel syndrome, the prototypical functional bowel disorder (Drossman et al., 1995; Longstreth & Wolde-Tsadik, 1993; Scarinci et al., 1994; Walker et al., 1995). Most of their baseline SCL-90-R scores were > 1 SD above the nonpatient norms. A problem inherent in assessing the long-term benefit of this study and other group psychotherapy studies is the tendency for some patients to continue similar or different forms of therapy after completing the group sessions. More than one half of patients received subsequent therapy that could have influenced their status at 1-year follow-up. However, most of the symptom dimensions and all global indices were similar 1 year posttherapy in the women who did not receive more treatment as compared to results in the women who did. Patients who received additional therapy had higher somatization scores before, immediately after, and 1 year posttherapy; scores in the other group increased 1 year posttherapy. Although the indications for subsequent therapy were not surveyed, there was an association between additional psychological care seeking and somatization. Furthermore, improvement in psychological status reflected by the phobic-anxiety score immediately posttherapy may have contributed to the decision of some patients to seek subsequent therapy. In the group without additional treatment, the loss of some of the initial somatization improvement at 1 year may have contributed to the lack of reduction in medical care visits in the combined groups. We speculate that provision of additional therapy to more patients might have had a long-term effect on somatization and reduced medical visits. We obtained complete psychological data and nearly complete medical-visit data on our patients, and our survey included 1-year follow-up. Our survey did not meet rigorous methodological standards for an outcome study, however. We surveyed only a small number of patients and did not collect similar data on an untreated control group. It was not possible to distinguish health care visits for organic versus functional disorders, but such a distinction may be artificial, because psychological factors may influence health care seeking for "organic" illness. Because our measurements came from a subset of our patients who were willing to complete the survey questionnaires, we do not know how generalizable the findings are. There is increasing awareness among health care professionals that childhood sexual abuse is common and that it may have serious and long-term psychological and medical sequelae. Our data suggest that group psychotherapy by social workers for women victims may have long-lasting psychological and somatic symptom benefits. Reduction in health care usage was not found, and this outcome may require the identification and treatment of patients who need additi

The hepatic glutathione content and glutathione S-transferase activity in the pike (Esox lucius L.) and rat.

1. The content of glutathione and glutathione disulfide and the activity of the glutathione S-transferase were determined in the liver of pike and rat. 2. It was found that the liver of pike contains far less glutathione than the liver of rats, while the glutathione disulfide content was similar in both species. 3. The activity of the hepatic glutathione S-transferase was more effective in pike than in rats.