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Biomedical subjects

T Turk

Publications and source records attributed to T Turk.

At least 19 recordsLinked to original sources
PubMed2006

[Nitrous-oxide sedation indispensable in the dental care of anxious people and the mentally impaired].

The long-term occupational exposure to high concentrations of nitrous oxide in health-care workers in a Dutch hospital, with probable adverse effects on their offspring, has triggered a discussion about the benefits and risks of nitrous oxide. In Dutch dentistry, nitrous-oxide sedation is a valuable and indispensable aid in the treatment of patients with challenging behaviour, such as those with mental impairment or in extremely-anxious adults and children. Nitrousoxide sedation can be used without risk to the dental team, provided that measures are taken for sufficient scavenging and room ventilation. A possible ban on nitrous oxide would be a major setback for specialty-care dentistry in the Netherlands.

Anesthesia, Dental↗
PubMed2006

3-Alkylpyridinium compounds as potential non-toxic antifouling agents.

To date, around thirty bioactive 3-alkylpyridinium compounds, either in monomeric or oligomeric forms, have been identified in marine sponges belonging to the order Haplosclerida In this work, we have reviewed their biological activities, which include mainly cytotoxicity, ichthyotoxicity, inhibition of bacterial growth, and enzyme inhibition. Most of these activities increase with the increasing degree of oligomerization of the corresponding 3-alkylpyridinium compound. It was shown recently that 3-alkylpyridines also exhibit promising antifouling activities. Linear 3-octylpyridinium polymers (Poly-APS), isolated from the Mediterranean sponge Reniera sarai, showed a non-toxic reversible mechanism of settlement inhibition of Balanus amphitrite cypris larvae with an EC50 of 0.27 microg/mL. At the same time, their toxicity towards the organisms used in the toxicity bioassays (B. amphitrite nauplii, microalga Tetraselmis suecica and larvae of Mytilus galloprovincialis) was almost negligible in comparison to commercially available and currently used booster biocides based on copper and zinc complexes with pyrithione. Poly-APS and some other natural 3-alkylpyridines were also found to be very effective in preventing microbial biofilm formation. Preliminary tests have confirmed that some monomeric and oligomeric synthetic analogues of poly-APS also exert antifouling activity, which makes these compounds promising candidates as new environmentally-friendly ingredients in the new generation of antifouling coatings.

Animals↗
PubMed2001

Characterization of parazoanthoxanthin A binding to a series of natural and synthetic host DNA duplexes.

Parazoanthoxanthin A is a fluorescent yellow nitrogenous pigment of the group of zoanthoxanthins, which show a broad range of biological activity. These include, among others, the ability to bind to DNA. In this study we have used a variety of spectroscopic (intrinsic fluorescence emission and UV-spectroscopy) and hydrodynamic techniques (viscometry) to characterize in more detail the binding of parazoanthoxanthin A to a variety of natural and synthetic DNA duplexes in different buffer conditions. Our results reveal the following five significant features: (i) Parazoanthoxanthin A exhibits two modes of DNA binding: One binding mode exhibits properties of intercalation, while the second binding mode is predominantly electrostatic in origin. (ii) The apparent binding "site size" for parazoanthoxanthin A near physiological salt concentration (100 mM NaCl) is in the range of 7 +/- 1 base pairs for natural genomic DNA duplexes (calf thymus and salmon testes DNA) and alternating synthetic polynucleotides (poly[d(AT)]. poly[d(AT)] and poly[d(GC)]. poly[d(GC)]). A slightly larger apparent binding site size of 9 +/- 1 bp was obtained for parazoanthoxanthin A binding to the synthetic homopolymer poly[d(A)]. poly[d(T)]. (iii) Near physiological salt concentration (100 mM NaCl) parazoanthoxanthin A binds with the same approximate binding affinity of 2-5 x 10(5) M(-1) to all DNA polymers studied. (iv) At low salt concentration, parazoanthoxanthin A preferentially binds alternating poly[d(AT)]. poly[d(AT)] and poly[d(GC)]. poly[d(GC)] host duplexes. (v) Parazoanthoxanthin A inhibits DNA polymerase in vitro.

Animals↗
PubMed2001

Antibacterial and anticholinesterase activities of aplysamine-4, a bromotyrosine-derived metabolite of a Red Sea marine sponge.

Aplysamine-4, a metabolite of likely bromotyrosine biogenesis, was isolated from an unidentified verongid sponge from the Red Sea. The compound was identified by heteronuclear magnetic resonance experiments, and by electrospray ionization tandem mass spectrometry. The compound exhibited moderate inhibitory activity on several Gram positive and Gram negative bacteria, and was also found to be a non-competitive reversible inhibitor of acetylcholinesterase. At pH 7.4, a Ki value of 16 and 2 microM was determined with electric eel and insect recombinant acetylcholinesterase, respectively. A deprotonated form of aplysamine-4 was obtained by alkaline treatment of the natural compound and it was shown to be less active than the protonated form.

Animals↗
PubMed2000

In vivo effects of head-to-tail 3-alkylpiridinium polymers isolated from the marine sponge Raniera sarai.

Water soluble polymeric 3-alkylpyridinium salts (poly APS; MW 18900 and 5520 Da) were isolated from the marine sponge Raniera sarai. In vitro it strongly inhibited acetyl cholinesterase (AChE) from different species (electric eel, horse serum, human erythrocytes). In our experiments the importance of anti AChE activity in the toxin lethality was evaluated. In vivo experiments were performed on male Wistar rats and ECG, blood pressure and breathing pattern were monitored. After i.v. application of lethal doses of the toxin ECG showed signs of hypo perfusion. Arterial blood pressure fell to mid-circulatory pressure, and breathing stopped after a few breaths At sublethal doses the toxin caused an increase of residual volume, prolongation of expiration, and bradycardia. Patho-anatomical examination revealed that the plugs in lung circulation may cause the death of experimental animals due to cardiorespiratory failure.

Animals↗
PubMed1999

AFM imaging of surface adsorbed polymeric 3-alkylpyridinium salts from the marine sponge Reniera sarai.

Bioactive 3-alkylpyridinium polymers (poly-APS) have recently been isolated from the marine sponge Reniera sarai. Previous results have shown that these molecules in aqueous solutions form supramolecular aggregates with an average hydrodynamic radius of 23 +/- 2 nm. To obtain additional evidences about the shape and the dimensions of poly-APS aggregates, we used atomic force microscopy (AFM) operating in tapping mode. The images clearly showed adsorbed aggregates with a lateral dimension of approximately 40 nm and a thickness of the order of approximately 1 nm. The distribution of volumes of the adsorbed aggregates is very similar to the distribution of hydrodynamic radii as obtained from the dynamic light scattering experiments. The volume distribution of these aggregates shows a maximum at 1750 nm3, which corresponds to a sphere with a radius of 7.5 nm.

Adsorption↗
PubMed1999

Characterization of hemolytic activity of 3-alkylpyridinium polymers from the marine sponge Reniera sarai.

Polymeric alkylpyridinium salts (poly-APS) isolated from the marine sponge Reniera sarai act as potent anticholinesterase agents; in addition they show moderate hemolytic and cytotoxic activities. The hemolytic activity of poly-APS is due to their detergent-like structure and behavior in aqueous solutions. In this work, the hemolytic activity of poly-APS is analyzed and compared to that of structurally-related monomeric cationic surfactants. The influence of different divalent cations and lipids on poly-APS induced hemolysis is discussed. The dimensions of lesions caused by poly-APS in erythrocyte membranes are determined by the use of osmotic protectants. Finally, the possible role of poly-APS in their natural environment is proposed.

Animals↗
PubMed1999

Interaction of 3-alkylpyridinium polymers from the sea sponge Reniera sarai with insect acetylcholinesterase.

3-Alkylpyridinium polymers (poly-APS), composed of 29 or 99 N-butyl-3-butyl pyridinium units, were isolated from the marine sponge Reniera sarai. They act as potent cholinesterase inhibitors. The inhibition kinetics pattern reveals several successive phases ending in irreversible inhibition of the enzyme. To provide more information on mechanism of inhibition, interaction of poly-APS and N-butyl-3-butyl pyridinium iodide (NBPI) with soluble dimeric and monomeric insect acetylcholinesterase (AChE) was studied by using enzyme intrinsic fluorescence and light scattering, conformational probes ANS and trypsin, and SDS-PAGE. Poly-APS quenched tryptophan fluorescence emission of AChE more extensively than NBPI. Both inhibitors exhibited a pseudo-Lehrer type of quenching. Interaction of poly-APS with dimeric AChE did not induce significant changes of the enzyme conformation as assayed by using the hydrophobic probe ANS and trypsin digestion. In contrast to NBPI, titration of both monomeric and dimeric AChE with poly-APS resulted in the appearance of large complexes detected by measuring light scattering. An excess of poly-APS produced AChE precipitation as proved on SDS-PAGE. None of the effects were observed with trypsin as a control. It was concluded that AChE aggregation and precipitation rather than the enzyme conformational changes accounted for the observed irreversible component of poly-APS inhibition.

Acetylcholinesterase↗
PubMed1999

Left atrial thrombus detection with multiplane transesophageal echocardiography: an echocardiographic study with surgical verification.

BACKGROUND AND AIM OF THE STUDY: The detection of left atrial thrombus (LAT) is especially important in patients being evaluated for percutaneous mitral valvuloplasty and elective cardioversion for atrial fibrillation. Transesophageal echocardiography (TEE) is widely used for this indication. This study was undertaken to validate the use of multiplane TEE to detect LAT in the setting of rheumatic mitral valve disease. METHODS: The study population comprised 262 patients (103 men, 159 women, mean age 42.2+/-13.1 years) who underwent open heart surgery for rheumatic mitral valvular disease between January 1994 and October 1997. Of these patients, 178 had mitral stenosis and 84 mitral regurgitation. All patients were examined with multiplane TEE less than three days before valvular surgery. RESULTS: The presence or absence of LAT was confirmed at surgery by direct inspection of the left atrium. Left atrial thrombi were detected by TEE in 34 patients (14 men, 20 women; mean age 51+/-8 years). The presence of all 34 thrombi found by multiplane TEE was confirmed during surgery. Only one thrombus was confirmed surgically among 228 patients shown thrombus-negative by multiplane TEE. The sensitivity, specificity, positive and negative predictive value and diagnostic accuracy for multiplane TEE were 97, 100, 100, 99.6 and 99.6%, respectively. CONCLUSION: Multiplane TEE is exquisitely sensitive for the detection of LAT.

Adult↗
PubMed1998

Inhibition of acetylcholinesterase by an alkylpyridinium polymer from the marine sponge, Reniera sarai.

Large polymeric 3-alkylpyridinium salts have been isolated from the marine sponge Reniera sarai. They are composed of N-butyl(3-butylpyridinium) repeating subunits, polymerized head-to-tail, and exist as a mixture of two main polymers with molecular weights without counterion of about 5520 and 18900. The monomer analogue of the inhibitor, N-butyl-3-butylpyridinium iodide has been synthesized. This molecule shows mixed reversible inhibition of acetylcholinesterase. The polymers also act as acetylcholinesterase inhibitors and show an unusual inhibition pattern. We tentatively describe it as quick initial reversible binding, followed by slow binding or irreversible inhibition of the enzyme. This kinetics suggests that there are several affinity binding sites on the acetylcholinesterase molecule where the polymer can bind. The first binding favors binding to other sites which leads to an apparently irreversibly linked enzyme-inhibitor complex.

Animals↗
PubMed1998

Anticholinesterase activity of the fluorescent zoanthid pigment, parazoanthoxanthin A.

A synthetic linear tetrazacyclopent(f)azulene compound, parazoanthoxanthin A (m.w. 214.2), strongly fluorescent pigment occurring in zoanthids, was characterized and assayed for anticholinesterase activity. The pigment, emitting fluorescence at lambda(em) 420 nm, was found to be a pure competitive inhibitor of cholinesterases. At pH 8.0, a Ki value of 19 and 26 microM was determined with insect recombinant, and electric eel acetylcholinesterase. Horse serum butyrylcholinesterase was less sensitive with a Ki of 70 microM.

Acetylcholinesterase↗
PubMed1997

Biological activities of aqueous extracts from marine sponges and cytotoxic effects of 3-alkylpyridinium polymers from Reniera sarai.

We screened the biological activity of 21 marine sponges collected in the northern Adriatic sea. Hemolytic, hemagglutinating, antimicrobial, cytotoxic, and anti-acetilcholinesterase activities of the extracts were monitored. We found that hemolytic activity was generally weak; only extracts from three sponge species possess considerable activity. Hemagglutinating activity was present in almost half of extracts but with little specificity against human erythrocytes of different blood groups. Detectable antimicrobial activity was present in only two extracts, while most of them possessed cytotoxic activity. Strong anti-cholinesterase activity was present only in one sample. 3-alkypyridinium polymers isolated from Reniera sarai were hemolytic and strongly cytotoxic against different cell lines with slightly expressed specificity against transformed cells.

Animals↗
PubMed1997

Characterization of anticholinesterase-active 3-alkylpyridinium polymers from the marine sponge Reniera sarai in aqueous solutions.

From the marine sponge Reniera sarai 3-alkylpyridinium oligomers and polymers have been isolated. 3-Alkylpyridinium polymers are potent anticholinesterase agents; in addition, they show hemolytic and cytotoxic activities. Oligomers with a molecular weight lower than 3000 Da do not possess any significant activity. We report structural characterization of 3-alkylpyridinium polymers and their behavior in aqueous solutions. We found that biologically active polymers are composed of head-to-tail 3-alkylpyridinium units. According to MALDI-TOF spectrometry two species of polymers exist, the smaller with a molecular weight of 5520 Da and the larger with a molecular weight of 18,900 Da. Both polymers are soluble only in water, while low molecular oligomers are readily soluble in organic solvents. Polymers form large water-dissolved supramolecular structures with an average hydrodynamic radius of 23 +/- 2 nm and, therefore, cannot be separated with size-exclusion chromatography.

Animals↗
PubMed1996

Pseudozoanthoxantin-like compound from Parazoanthus axinellae Adriaticus inhibits acetylcholinesterase.

Acetylcholinesterase is an enzyme responsible for the timely termination of acetylcholine action at muscarinic and nicotinic receptors, so it is essential for the normal function of cholinergic synapses. Naturally occurring acetylcholinesterase inhibitors are relatively rare, but several synthetic acetylcholinesterase inhibitors have been developed as potent remedies, pesticides, and neurotoxins. Here we describe the inhibition of soluble and membrane-bound cholinesterases with a recently isolated and purified acetylcholinesterase inhibitor isolated from the crust coral Parazoanthus axinellae Adriaticus. This substance with a novel chemical structure might serve as a new prototype of cholinesterase inhibitors.

Acetylcholinesterase↗
PubMed1996

Space maintainer effects on intercanine arch width and length.

In order to investigate the effects of space maintainers in intercanine arch width and length, twenty cases, characterized with the early loss of mandibular primary molars were selected and divided into two groups. The treatment group used removable space maintainers, while the other ten cases served as the control group. The first dental casts of the treatment and control groups were obtained when the primary canines were in the mouth. After the eruption of permanent canines second dental casts were obtained in both groups. Six measurements were made on the dental casts of each patient. No parameter was found to be statistically significant in the treatment group. In the control group the increase in intercanine arch width and perimeter were found to be statistically significant. Also the increase at the buccal and lingual bone measurements were found to be statistically significant. These results showed that space maintainers might cease the increase in intercanine arch width and length during the transition period between the primary and permanent canines.

Adolescent↗
PubMed1995

Inhibition of acetylcholinesterase by a pseudozoanthoxanthin-like compound isolated from the zoanthid Parazoanthus axinellae (O. Schmidt).

An ethanolic extract from a zoanthid crust coral Parazoanthus axinellae was lethal to mice and crabs and exhibited anticholinesterase activity. The isolation of several AChE inhibitors with the aid of RP-HPLC is described. The most abundant of the inhibitors present in the P. axinellae extract was identified as pseudozoanthoxanthin or an almost identical compound which belongs to the chemically well-characterized series of tetrazacyclopentazulene natural pigments from the genera Parazoanthus, Epizoanthus, Zoanthus and Palythoa. The inhibitor has a mol. wt of 242 and acts as a competitive inhibitor with a Ki of 4 microM. The inhibitor exhibited a strong blue fluorescence. In vivo action of crude extract and the isolated inhibitor showed a typical picture of systemic acetylcholinesterase inhibition. Atropinization of experimental animals prior to injection of the inhibitor almost entirely neutralized its activity.

Animals↗
PubMed1994

Primary and secondary structure of a pore-forming toxin from the sea anemone, Actinia equina L., and its association with lipid vesicles.

The complete amino acid sequence of equinatoxin II, a potent pore-forming toxin with hemolytic, cytotoxic and cardiotoxic activity from the venom of the sea anemone, Actinia equina L., is reported. In addition, circular dicroism was used to estimate the secondary structure of this toxin either in the water-soluble or in the membrane-anchored form. Equinatoxin II when in water was found to contain about 29-33% of alpha-helical structure, 53-58% of beta-strand+beta-turn and 10-16% of random structure. Upon association with phospholipids, in particular with sphingomyelin, a rearrangement of the secondary structure occurs resulting in an increase of the alpha-helix content. An amphiphilic alpha-helical segment is predicted at the N-terminus, which shares structural homology with membrane active peptides like melittin and viral fusion peptides. In analogy to the behaviour of these peptides we propose that at least part of the alpha-helix content increase of equinatoxin II is due to the insertion of its N-terminus into the lipid bilayer. As in the case of melittin, association of 3-4 equinatoxin molecules is necessary to induce membrane permeabilisation.

Amino Acid Sequence↗