Helix-enhancing propensity of fluoro and alkyl alcohols: influence of pH,temperature and cosolvent concentration on the helical conformation of peptides

We have analyzed the effects of trifluoroethanol (TFE) and three other alcohols(1-propanol, 2-propanol and hexafluoro-2-propanol) on S-peptide (residues 1–20) of ribonuclease A, an analog of S-peptide (QHM → AAA, Sa-peptide) and TC-peptide (residues 295–316) of thermolysin to assess the helix-enhancing propensity of fluoro and alkyl alcohols under different environmental conditions of cosolvent concentration, pH and temperature by circular dichroism (CD). The dependence of cosolvent concentration on helix-induction showed a plateauing effect in all cases. 1-Propanol and 2-propanol were as effective as TFE in all the three peptides. Hexafluoro-2-propanol (HFIP) was a better helix enhancer in all cases however, the relative effectiveness varied with the peptide sequence. The alcohol transitions were analyzed assuming a two-state transition. The free energy decreased linearly in the cosolvent concentration range of 0–5 m for all the three peptides. The m-value (constant of proportionality) varied between peptides but was similar for any given peptide for TFE, 1-propanol or 2-propanol. The m-values of HFIP for all three peptides was much higher compared to other cosolvents. The isothermal cosolvent helix-induction curves for the three peptides exhibited similar features of shape and character for 1-propanol, 2-propanol and TFE. The additivity of cosolvent-induced helix formation was observed for different blends of alkyl and/or fluoro cosolvents. The pH-dependence of helix formation was observed in both TFE and 1-propanol solutions for S-peptide and TC-peptide, respectively, while in Sa-peptide, which was designed to perturb the pH-effect, helix formation was unaffected. The overall results provide some insight into the mechanism of cosolvent-mediated helix-enhancement in protein segments and are likely to facilitate optimization of conditions for cosolvent usage in chemistry and biology.     

Associations between proteins and heavy metals in urine at low environmental exposures: Evidence of reverse causality

Heavy metals can cause renal effects on vulnerable populations but it is uncertain whether these metals still pose health risks at the low exposure levels now prevailing in most industrialized countries.     

Associations between proteins and heavy metals in urine at low environmental exposures: evidence of reverse causality

Mitochondria represent a possible drug target with unexplored therapeutic and toxicological potential. The possibility was suggested that antidepressants, mood stabilizers and other drugs may show some therapeutic and/or toxic effects through their action on mitochondrial functions. There are no sufficient data about the effect of these drugs on mitochondrial respiration in the brain. We investigated the in vitro effects of amitriptyline, fluoxetine, tianeptine, ketamine, lithium, valproate, olanzapine, chlorpromazine and propranolol on mitochondrial respiration in crude mitochondrial fractions of pig brains. Respiration was energized using substrates of complex I or complex II and dose dependent drug-induced changes in mitochondrial respiratory rate were measured by high-resolution respirometry. Antidepressants, but not mood stabilizers, ketamine and propranolol were found to inhibit mitochondrial respiratory rate. The effective dose of antidepressants reaching half the maximal respiratory rate was in the range of 0.07-0.46mmol/L. Partial inhibition was found for all inhibitors. Differences between individual drugs with similar physicochemical properties indicate selectivity of drug-induced changes in mitochondrial respiratory rate. Our findings suggest that mood stabilizers do not interfere with brain mitochondrial respiration, whereas direct mitochondrial targeting is involved in mechanisms of action of pharmacologically different antidepressants.     

Trace enrichment on a metal-loaded thiol stationary phase in liquid chromatography: effect of analyte structure and pH value on the (de)sorption behaviour

In order to obtain more information on the (de)sorption processes on a metal-loaded thiol phase, various compounds containing heterocyclic nitrogen atoms have been studied. Adenine and adenosine, which contain no carbonyl groups in a position ortho to the ring nitrogen, were chosen to study the role of the binding donor atoms and, therefore, of the ‘minimum’ structure required for efficient pH-dependent (de)sorption. The results indicate that a single heterocyclic nitrogen atom, preferably with a high pK_a value, is sufficient to provide pH-dependent (de)sorption on chelating phases loaded with soft metal ions, such as Ag(I) or Hg(II), which can profitably be used in an on-line combination with column liquid chromatography. Barbiturates were chosen on the basis of their structural similarity with the earlier studied (halogenated) uracil derivatives. The (de)sorption behaviour of the barbiturates was studied as a function of the pH, the metal ion [Cu(II), Ag(I), Hg(II), Pd(II)] bound to the stationary phase and the type of stationary phase. The combined data show that the pK_a value of an analyte and the stability constant of the complex formed with the metal ion sorbed on the stationary phase give a reliable indication of the optimum (de)sorption pH. Application of this principle is demonstrated by the determination of four barbiturates in plasma.     

PRL-8-53: Enhanced learning and subsequent retention in humans as a result of low oral doses of new psychotropic agent

The effect of 3-(2-benzylmethylaminoethyl) benzoic acid methyl ester hydrochloride (PRL-8-53) on learning and on retention of verbal information in human subjects was investigated. Using the serial anticipation method under double-blind conditions it was found that PRL-8-53 causes slight improvement of acquisition. Retention of verbal information was found improved to a statistically significant degree (most P values better than 0.01, some better than 0.001). No significant changes were found for either visual reaction time or motor control after drug when compared with placebo values.     

The induction of stress proteins (hsp) in Oniscus asellus (Isopoda) as a molecular marker of multiple heavy metal exposure: I. Principles and toxicological assessment

The induction of stress-70 (hsp70) and stress-60 (hsp60, chaperonin 60) in the terrestrial woodlouse, Oniscus asellus, after exposure to various heavy metals and heavy metal combinations was investigated by means of standard Western-blot using monoclonal antibodies. The expression of stress-70 was found to react much more sensitively to metal contamination than that of stress-60. The general course of the stress-70 response to increasing metal concentration was found to be similar for all treatments. Based on the obtained results, this course could be divided into three zones: in the first zone, the expression of stress-70 proteins was only marginally increased by comparatively low metal concentrations; in the second zone, strong induction of stress-70 occurred and the ability of the heat shock system to react to increased metal concentrations reached its climax; and in the third, non-compensation zone, a further increase in heavy metal concentration resulted in a decline of stress-70 levels, which can be interpreted as a result of pathological tissue damage. Combinations of metals were found to increase the stress- 70 level more intensely than related concentrations of singularly applied metals. Based on these studies, a ranking scheme of increasing toxicological impact of a variety of heavy metal combinations was composed     

An alkylpolyglucoside surfactant as a prospective pharmaceutical excipient for topical formulations: The influence of oil polarity on the colloidal structure and hydrocortisone in vitro/in vivo permeation

There is a growing need for research into new skin- and environment-friendly surfactants. This paper focuses on a natural surfactant of an alkylpolyglucoside type, which can form both thermotropic and lyotropic liquid-crystalline phases. The aim of this study was to relate some physicochemical properties (characterised by polarisation and transmission electron microscopy, thermal analysis and rheology) of the three formulations based on cetearyl glucoside and cetearyl alcohol, to the results of in vitro and in vivo bioavailability of hydrocortisone (HC). The three formulations contained oils of different polarity (medium chain triglycerides: MG, isopropyl myristate: IPM and light liquid paraffin: LP), respectively. In vitro permeation was followed through the artificial skin constructs (ASC), while the parameters measured in vivo were erythema index: EI (using instrumental human skin blanching assay), transepidermal water loss (TEWL) and stratum corneum hydration (SCH). The vehicles based on cetearyl glucoside and cetearyl alcohol showed a complex colloidal structure of lamellar liquid-crystalline and lamellar gel-crystalline type, depending on oil polarity. Rheological profile of the vehicle was directly related to the in vitro profile of the HC permeation. In vivo results suggested that the vehicle with MG retarded the HC permeation, whereas less polar IPM and non-polar LP enhanced it. It is suggested that the enhancement is achieved either by a direct interaction with lipid lamellae of the SC or indirectly by improving skin hydration.

There were no adverse effects during in vivo study, which indicates a good safety profile of this alkylpolyglucoside surfactant.     

The induction of stress proteins (hsp) in Oniscus asellus (Isopoda) as a molecular marker of multiple heavy metal exposure. II: Joint toxicity and transfer to field situations

In laboratory toxicity tests, woodlice (Oniscus asellus) exposed to a variety of different combinations of the metals cadmium, lead, and zinc exhibited a broad range in intensity of the induction of the 70 kDa stress protein (hsp70, stress-70). Using two-dimensional isobolograms and the toxic unit concept, it could be shown that cadmium and lead as well as cadmium and zinc or lead and zinc act as synergists and cause superadditive effects on the stress response of these animals. Using a three- dimensional isobologram based on the stress-70 level in response to numerous combinations of all three tested metals, transfer to the field could be achieved: data obtained from O. asellus populations abundant at field sites, the soils of which are influenced mainly by different concentrations of these heavy metals, were found to fit this laboratory test-based model     

The partial D<Subscript>2</Subscript>-like dopamine receptor agonist terguride acts as a functional antagonist in states of high and low dopaminergic tone: evidence from preweanling rats

Rationale In adult rats, the partial D₂-like agonist terguride acts as an antagonist at normosensitive D₂-like post-synaptic receptors, while it acts as an agonist at the same receptors during states of low dopaminergic tone.Objective The purpose of the present study was to determine whether partial D₂-like agonists exhibit both antagonistic and agonistic actions during the preweanling period.Methods In experiments 1 and 2 (examining the agonistic actions of terguride), preweanling rats were either given an escalating regimen of amphetamine to induce a state of amphetamine withdrawal or pretreated with the tyrosine hydroxylase inhibitor AMPT. Distance traveled was measured after rats were injected with saline, terguride (0.4–1.6 mg/kg), or the full D₂-like receptor agonist NPA (0.01 mg/kg). In experiment 3 (examining the antagonistic actions of terguride), preweanling rats were pretreated with terguride 30 min before they were tested with saline, NPA (0.05 mg/kg), or amphetamine (1.5 mg/kg).Results NPA had an exaggerated locomotor activating effect when tested under conditions of amphetamine withdrawal, while the partial D₂-like agonist did not enhance distance traveled under any circumstance. Similarly, NPA increased and terguride did not affect the distance-traveled scores of AMPT-pretreated rats. In experiment 3, terguride pretreatment significantly reduced the distance traveled of amphetamine-treated and NPA-treated rats.Conclusions The behavioral evidence indicates that, during the preweanling period, terguride antagonizes D₂-like post-synaptic receptors in a state of high dopaminergic tone; however, there is no evidence that terguride is capable of stimulating D₂-like post-synaptic receptors during states of low dopaminergic tone.