Biomedical subjects

E Terzi

Publications and source records attributed to E Terzi.

17 recordsLinked to original sources

PubMed2006

[Optical quality after refractive corneal surgery].

Correction of myopia, hyperopia and astigmatism within its indicated margin by means of refractive corneal surgical procedures such as LASIK and surface ablation (e.g. PRK) is one of the standard procedures in ophthalmology. Now that advances in the fields of surgical techniques and the technical devices employed have further progressed in terms of safety and predictability, research also focuses on optical quality. "Optical quality" is not a clearly defined parameter, but can be captured indirectly by means of directly measured data. One has to start with the anatomical properties of the eye, which determine the optical images on the retinal level. The quality of the retinal image influences the eye's function, i.e. acuity and contrast perception. Finally, there is the subjective perception of the image we receive. "Optical quality" as such is reflected by the patient's evaluation of this image perception. Three phenomena are especially responsible for deterioration of the quality of the retinal image: diffraction, aberrations and dispersion. Some of the methods for measuring optical quality are subjective questionnaires, functional testing procedures for measuring visual acuity and contrast sensitivity, optical measuring procedures for the determination of optical quality, as well as biomicroscopy, aberrometry and corneal topography for assessing anatomical changes.

Cornea↗

PubMed2006

Treatment of irritable bowel syndrome. A case control experience.

AIM: As optimal therapy for irritable bowel syndrome (IBS) remains elusive, current approach to therapy is based on symptomatic treatment. With this case-control experience we wanted to determine the beneficial effect in IBS patients of a dietary integrator (IBS Active), composed of L-tryptophan, inulin, angelica, vegetal charcoal, vitamin PP, group B vitamins (B1, B2, B6) and probiotics (Lactobacillus sporogenes, Lactobacillus acidophilus, Streptococcus thermophilus). METHODS: The treatment group comprised 37 patients (11 men and 27 women; mean age, 44.3+/-5.1 years) given IBS Active (440 mg bid) over a mean period of 6 months (range, 5-8). The control group comprised 28 patients (6 men and 22 women; mean age, 48.6+/-3.7 years) who were instructed to continue their customary therapy for 6 months (range, 5-7). All subjects were assessed for the presence of abdominal pain and/or distension, constipation, diarrhea and alternating constipation and diarrhea. RESULTS: Compared with baseline values, the reduction in abdominal pain in the treatment group was 62% (P<0.0001), 55% (P<0.0001) in abdominal distension, 58% (P=0.05) in constipation, 33% (P=0.3) in diarrhea, and 62% (P=0.01) in alternation constipation and diarrhea. Compared with baseline values, no statistically significant reduction in symptoms was found in the control group. Post-treatment comparison between the two groups showed that the study product had reduced symptoms and that the difference was statistically significant for abdominal pain (P<0.000001), abdominal distension (P=0.003) and constipation (P=0.03). CONCLUSIONS: The use of IBS Active led to a significant improvement in pain symptoms, abdominal distension and regulation of bowel movement in IBS patients. Further study is needed to evaluate the long-term benefit of the study product.

Abdominal Pain↗

PubMed2005

[Frankfurt-Freiburg Contrast and Acuity Test System (FF-CATS). A new test to determine contrast sensitivity under variable ambient and glare luminance levels].

BACKGROUND: The purpose of the present study was to evaluate a computerized test for measurement of contrast sensitivity thresholds under variable ambient and glare luminance levels. METHODS: A total of 40 eyes of 40 healthy subjects were examined with the FF-CATS and the Functional Acuity Contrast Test (FACT) at 0.167 cd/m(-2) (mesopic) and 167 cd/m(-2) (photopic). Measurements were performed twice with and without glare in a randomized fashion. Tests were evaluated according to three criteria: (1) repeatability, (2) discriminative ability, and (3) validity. RESULTS: The FF-CATS showed a higher discriminative ability between the two groups compared to the FACT charts. Under photopic conditions, the COR value was 0.39 for the FF-CATS and 0.26 for the FACT charts; under mesopic illumination, the COR value for the FF-CATS was 0.46 and 0.36 for the FACT charts. CONCLUSION: The FF-CATS is a reliable, sensitive, valid, and flexible test system for the determination of visual acuity and contrast sensitivity thresholds under variable ambient and glare luminance conditions.

Adult↗

PubMed2005

[Intraocular lenses for the correction of refraction errors. Part II. Phakic posterior chamber lenses and refractive lens exchange with posterior chamber lens implantation].

In this overview, the current status of intraocular lens surgery to correct refractive error is reviewed. The interventions are divided into additive surgery with intraocular lens implantation without extraction of the crystalline lens (phakic intraocular lens, PIOL) or removal of the crystalline lens with implantation of an IOL (refractive lens exchange, RLE). Phakic IOLs are constructed as angle-supported or iris-fixated anterior chamber lenses and posterior chamber lenses which are fixated in the ciliary sulcus. The implantation of phakic IOLs has been demonstrated to be an effective, safe, predictable and stable procedure to correct higher refractive errors. Complications are rare and differ for the three types of PIOL; for posterior chamber lenses these are mainly cataract formation and pigment dispersion. RLE is preferable in cases of high ametropia in which the natural lens has lost its accommodative effect. The main complications for myopic RLA include retinal detachment, while hyperopic refractive lens exchange may be associated with surgical problems in the narrower anterior eye segment.

Humans↗

PubMed2004

Size distribution of trace elements and polycyclic aromatic hydrocarbons in fly ashes generated in Greek lignite-fired power plants.

The fly ashes arrested by the electrostatic precipitators of four large lignite-fired Greek power stations (total installed capacity 4048 MW) were investigated regarding the distribution of 27 major, minor and trace elements and 13 polycyclic aromatic hydrocarbons (PAHs) in six size ranges from <40 to >105 microm. An inverse relationship of concentration with particle size was observed for trace elements, such as As, Se, Zn, Pb, Cd, as well as for Ca, whereas the distribution of the matrix elements Al, Si, Ti, Fe, Mg was fairly flat up to 105 microm with relative enrichment or depletion in larger particle sizes. A reverse relationship of concentration with particle size was also revealed for all PAHs, particularly the heavier compounds. The percent mass of all elements and PAH species in the suspendable fraction (<63 microm) was between 25 and 30%. In all fly ashes, the PAH mixture was dominated by 4-ring species (48-62%) followed by 3-ring compounds (38-41%), whereas the carcinogenic 5- and 6-ring PAHs were less abundant (2-11%). Fly ash PAH concentrations were found to correlate strongly with the concentrations of certain trace elements either positively (e.g. Ba) or negatively (Mg, Cr, V, U) thus suggesting that some lignite elements might promote or prevent PAH formation during combustion. The suspendable fly ash fraction (<63 microm) was found to contain 6-35% of the total mass of individual elements and 10-57% of the total mass of individual PAH components.

Journal Article↗

PubMed2004

[Higher order aberrations after implantation of an iris claw pIOL (Ophtec Artisan) in the phakic eye].

BACKGROUND: The purpose of the present study is to demonstrate the change of higher order wavefront aberrations (HOA) after implantation of an iris claw pIOL. METHODS: Thirteen eyes of seven patients were examined preoperatively and 1 month after implantation of an Artisan lens. The mean preoperative spherical equivalent was -10.69+/-1.92 D (-7.63 to -14.88 D). The diameter of the IOL optic was 6 mm and the lens was inserted though a tunnel incision at 12 o'clock. The root mean square (RMS) wavefront error was computed for all aberrations of the third to fifth order for pupil diameters of 3.5 and 6 mm. RESULTS: On average, HOA RMS changed for a 3.5 mm pupil by 0.037+/-0.089 microm (6 mm pupil: 0.405+/-0.245 microm). Third-order aberrations changed by 0.031+/-0.098 microm (0.320+/-0.269 microm). For both pupil diameters, a notable increase of Z 3,-3 of 0.117+/-0.085 microm (0.596+/-0.350 microm) could be observed depending on the distance between the limbus and incision. Fourth-order aberrations changed on average by 0.018+/-0.037 microm (0.280+/-0.143 microm), namely Z 4,0 increased by 0.025+/-0.034 microm (0.296+/-0.164 microm). CONCLUSION: After implantation of the Artisan lens HOA increased slightly. Particularly induction of Z 3,-3 and Z 4,0 contribute to the increase of HOA. The induction of trefoil ( Z 3,-3) is a result of the incision, whereas the increase of spherical aberration is due to the implant.

Adult↗

PubMed2001

Treatment of epidermodysplasia verruciformis with a combination of acitretin and interferon alfa-2a.

Epidermodysplasia verruciformis (EV) is an autosomal recessive disease characterized by the lifelong eruption of disseminated verrucae-like lesions. Numerous treatment modalities have been used to treat EV without benefit. Recently, retinoid and interferon therapies have been found to be of value in the treatment of EV. We present a case of EV that was treated with a combination of acitretin and interferon alfa-2a.

Acitretin↗

PubMed1997

Interaction of Alzheimer beta-amyloid peptide(1-40) with lipid membranes.

The beta-amyloid peptide beta AP(1-40), a 40-amino acid residues peptide, is one of the major components of Alzheimer's amyloid deposits. beta AP(1-40) exhibits only a limited solubility in aqueous solution and undergoes a concentration-dependent, cooperative random coil reversible beta-structure transition for Cpep > 10 microM [Terzi, E., Hölzemann, G., and Seelig, J. (1995) J. Mol. Biol. 252, 633-642]. In the presence of acidic lipid, the equilibrium is shifted further toward beta-structured aggregates. We have now characterized the lipid-peptide interaction using circular dichroism (CD) spectroscopy, lipid monolayers, and deuterium and phosphorus-31 solid-state nuclear magnetic resonance (NMR). CD spectroscopy revealed a distinct interaction between beta AP(1-40) and negatively charged unilamellar vesicles. In addition to the random coil reversible beta-structured aggregate equilibrium at low lipid-to-peptide (L/P) ratios, a beta-structure -->alpha-helix transition was observed at L/P > 55. beta AP(1-40) was found to insert into acidic monolayers provided the lateral pressure was low (20 mN/m). The extent of incorporation increased distinctly with the content of acidic lipid in the monolayer. However, at a lipid packing density equivalent to that of a bilayer (lateral pressure > or = 32 mN/m), no insertion of beta AP(1-40) was observed. The lipid molecular structure in the presence of beta AP(1-40) was studied with NMR. Phosphatidylcholine (PC) was selectively deuterated at the choline headgroup and at the cis-double bond of the oleic acyl chain and mixed with phosphatidylglycerol (PG). Phosphorus-31 NMR showed that the lipid phase retained the bilayer structure at all lipid-to-protein ratios. Deuterium NMR revealed no change in the headgroup conformation of the choline moiety or in the flexibility and ordering of the hydrocarbon chains upon the addition of beta AP-(1-40). It can be concluded that beta AP(1-40) binds electrostatically to the outer envelope of the polar headgroup region without penetrating between the polar groups. The data suggest a new mechanism of helix formation induced by the proper alignment of five positive charges of beta AP(1-40) on the negatively charged membrane template.

Amino Acid Sequence↗

PubMed1997

Inhibition of the electrostatic interaction between beta-amyloid peptide and membranes prevents beta-amyloid-induced toxicity.

The accumulation of beta-amyloid peptides (Abeta) into senile plaques is one of the hallmarks of Alzheimer disease. Aggregated Abeta is toxic to cells in culture and this has been considered to be the cause of neurodegeneration that occurs in the Alzheimer disease brain. The discovery of compounds that prevent Abeta toxicity may lead to a better understanding of the processes involved and ultimately to possible therapeutic drugs. Low nanomolar concentrations of Abeta1-42 and the toxic fragment Abeta25-35 have been demonstrated to render cells more sensitive to subsequent insults as manifested by an increased sensitivity to formazan crystals following MTT (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) reduction. Formation of the toxic beta-sheet conformation by Abeta peptides is increased by negatively charged membranes. Here we demonstrate that phloretin and exifone, dipolar compounds that decrease the effective negative charge of membranes, prevent association of Abeta1-40 and Abeta25-35 to negatively charged lipid vesicles and Abeta induced cell toxicity. These results suggest that Abeta toxicity is mediated through a nonspecific physicochemical interaction with cell membranes.

Amyloid beta-Peptides↗

PubMed1995

Self-association of beta-amyloid peptide (1-40) in solution and binding to lipid membranes.

The beta-amyloid peptide (beta AP), a 39 to 43 residue peptide, is the major component of Alzheimer plaques. Using circular dichroism spectroscopy, titration calorimetry, and analytical ultracentrifugation we have analyzed the self-association of beta AP(1-40) in aqueous solution and the binding of beta AP(1-40) to negatively charged lipid vesicles. The CD spectra of both aggregation and membrane binding are characterized by an isodichroic point at 212 nm, indicating a simple two-state equilibrium for both cases. In aqueous solution beta AP(1-40) exhibits a reversible, concentration-dependent random coil<-->beta-structure transition which can be described by a cooperative aggregation model with an association constant of s = 1.05 x 10(4)M-1 and a nucleation parameter of sigma = 0.012. A similar conformational change is observed upon addition of lipid. At a given peptide concentration, the addition of negatively charged, small unilamellar vesicles also induces a conformational change from a random coil conformation to a conformation with 40 to 60% beta-structure. The binding isotherm can be measured with high sensitivity titration calorimetry. It is approximately linear in the initial binding phase and exhibits an apparent saturation behaviour. The apparent binding constant decreases with concentration from Kapp approximately 2100 M-1 at low concentration to 700 M-1 at the highest concentration measured. Peptide penetration into the lipid membrane and peptide aggregation at the membrane surface are proposed as possible mechanisms to explain the lipid-induced random coil<-->beta-structure transition.

Amyloid beta-Peptides↗

PubMed1994

Alzheimer beta-amyloid peptide 25-35: electrostatic interactions with phospholipid membranes.

The role of lipids in the aggregation of three Alzheimer model peptides was investigated with circular dichroism spectroscopy and high-sensitivity titration calorimetry under conditions of low ionic strength. In solution, the peptides beta AP(25-35)OH and beta AP(25-35Nle)NH2 exhibit a reversible random-coil<-->beta-sheet (or beta-structured aggregate) transition. Addition of lipid vesicles containing negatively charged lipids shifts the random-coil<-->beta-sheet equilibrium almost completely toward beta-sheet structure, which can be explained by the specific conditions created at the membrane surface: the cationic peptides are attracted to the negatively charged membrane, and the increase in peptide concentration together with the partial alignment of the peptide molecules then facilitates beta-sheet formation. The third peptide, beta AP-(25-35)NH2, also binds to the lipid membrane but was found to adopt an essentially random-coil structure, both with and without lipids. A quantitative characterization of the binding equilibrium was possible with high-sensitivity titration calorimetry. All three peptides exhibited exothermic binding enthalpies which varied between delta H approximately -2 kcal/mol for beta AP(25-35)OH and -8 kcal/mol for beta AP(25-35)NH2. The apparent binding constants, calculated with bulk concentrations, were large and varied between 500 and 5 x 10(4) M-1, depending on the experimental conditions. However, after correction for electrostatic charge effects using the Gouy-Chapman theory, the intrinsic binding constants were found to be constant and much smaller with K approximately 2-10 M-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer Disease↗

PubMed1994

Reversible random coil-beta-sheet transition of the Alzheimer beta-amyloid fragment (25-35).

The beta-amyloid protein (39-43 amino acid residues) is the major constituent of the amyloid deposits found in brain of patients with Alzheimer's disease. Using circular dichroism spectroscopy, we have studied the secondary structure and the aggregation of fragment 25-35 of the beta-amyloid protein (beta AP(25-35)OH) under a variety of conditions. beta AP(25-35)OH in solution at pH 4.0 or 5.5 exhibits a concentration-dependent random coil<-->beta-sheet transition. The equilibrium is characterized spectroscopically by an isodichroic point and can be described quantitatively by a simple association model with association constants between 1.8 x 10(4) M-1 (non-cooperative model, nucleation parameter sigma = 1) and 2.9 x 10(4) M-1 (cooperative model, sigma = 0.2). The enthalpy of association is delta H approximately -3 kcal/mol as determined by titration calorimetry. The equilibrium is shifted completely toward beta-structured fibrils at pH 7.4 where the Met-35 carboxyl group is fully charged. In contrast, removal of the charged carboxy terminus by amidation locks the equilibrium in the random coil conformation. Model calculations suggest an antiparallel beta-sheet structure involving residues 28-35 which is stabilized at both ends of the beta-sheet by ion pairs formed between Lys-28 and Met-35. Removal of fibrils via millipore filtration leads to solutions with random coil monomers only. Seeding these solutions with a few fibrils establishes a new random coil<-->beta-sheet equilibrium.

Alzheimer Disease↗

PubMed1994

Further studies into the Boc/solid-phase synthesis of Ser(P)- and Thr(P)-containing peptides.

The Ser(P)-containing peptide corresponding to phospholamban 11-19, Ac-Ala-Ile-Arg-Arg-Ala-Ser(P)-Thr-Ile-Glu-NH2, was prepared by the use of Boc-Ser(PO3Ph2)-OH in Boc/solid-phase peptide synthesis followed by HF cleavage of the peptide from the polystyrene resin and subsequent platinum-mediated hydrogenolytic cleavage of the phenyl phosphate groups. A study of the HF deprotection step showed that extensive dephosphorylation of the Ser(PO3Ph2)-residue occurred using three commonly used HF conditions and gave rise to large quantities of the Ser-containing peptide. The subsequent study of model peptide systems under standard HF conditions established firstly that the extent of dephosphorylation was dependent on the HF-contact time, and secondly that the Ser(PO3Ph2) residue underwent dephosphorylation at a slightly higher rate than the Thr(PO3Ph2) residue.

Amino Acid Sequence↗

PubMed1992

Evidence for a phosphorylation-induced conformational change in phospholamban cytoplasmic domain by CD analysis.

Phospholamban (PLB), an integral membrane protein of cardiac sarcoplasmic reticulum (SR), is described as the regulator of the Ca(2+)-ATPase pump, via its phosphorylation-dephosphorylation of Ser-16. Recently it has been shown that a direct interaction between the N-terminal hydrophilic domain of PLB and Ca(2+)-ATPase may be one of the mechanisms of regulation. In order to show that this interaction could be modulated by a phosphorylation-induced conformational change in PLB, we ran CD studies on the synthetic peptide PLB(2-33) in its phosphorylated and non-phosphorylated forms, at various pHs, concentrations and in the absence or presence of trifluoroethanol. The results show a clear difference in structure of the phosphorylated and non-phosphorylated peptide.

Adenosine Triphosphatases↗

PubMed1991

Revision of the amino acid sequence of the smallest bc1 complex subunit: use of fast atom bombardment mass spectrometry and mass-analysed ion kinetic energy spectrum analysis.

We have isolated the smallest bc1 complex subunit from an acidic chloroform/methanol extract of bovine cardiac muscle. The identification of the polypeptide was made possible by classical Edman degradation and amino acid analysis. The measurement of its exact molecular weight by fast atom bombardment mass spectrometry (m/z 6519.8), the characterization of a tryptophan cleavage peptide and pepsic peptides by mass measurements and by mass-analysed ion kinetic energy spectrum analysis allow rectification of the amino acid sequence of the smallest bc1 complex subunit. We found a serine residue instead of Gln 22 and tryptophan residues in place of Ser 34 and Ser 38.

Amino Acid Sequence↗

PubMed1990

Isolation and amino acid sequence of a novel 6.8-kDa mitochondrial proteolipid from beef heart. Use of FAB-MS for molecular mass determination.

We have isolated a 6.8 kDa proteolipid from an acidic chloroform/methanol extract of bovine cardiac muscle. The molecular mass of the polypeptide was measured by fast atom bombardment-mass spectrometry (FAB-MS) (m/z6834.1). Its amino acid sequence was partly determined by direct sequencing and completed by characterization of cyanogen bromide and tryptic fragments (sequencing, FAB-MS and amino acid analysis). The polypeptide consists of 60 amino acid residues. Polyclonal antibodies raised in rabbit allowed its localization by electroimmunoblotting in mitochondria.

Amino Acid Sequence↗

PubMedDate not supplied

Domain formation induced by lipid-ion and lipid-peptide interactions.

High sensitivity titration calorimetry was performed for metal ions such as calcium and lanthanum and for different types of Alzheimer peptides. Ca2+ adsorbs to mixed phosphatidylcholine (PC)/phosphatidylglycerol (PG) membranes with an endothermic reaction enthalpy of delta H approximately +0.1 kcal/mol. La3+ binds to sonified PC vesicles with a reaction enthalpy of delta H approximately + 1.8 kcal/mol. The binding constants are of the order of 10 M-1 for Ca2+ and 4 x 10(3) M-1 for La3+. The role of lipids in the random coil<-->beta-sheet equilibrium of different types of Alzheimer model peptides was investigated with circular dichroism (CD) and high sensitivity titration calorimetry. Alzheimer peptide beta AP(1-40)OH and several fragments of this peptide undergo a concentration-dependent, co-operative random coil<-->beta-sheet transition in solution which can be described by a linear association model with a nucleation parameter sigma approximately 0.2-0.01 and a growth parameter s approximately 10(4) M-1. Addition of sonified lipid vesicles containing negatively charged lipids shifts the equilibrium towards the beta-sheet conformation. This can be explained by an aggregation phenomenon at the lipid/water interphase. The cationic peptides are attracted to the negatively charged membrane surface causing a local increase in peptide concentration. The high peptide concentration, together with the ordering of the peptide molecules on the membrane surface, facilitates beta-sheet formation, constituting the first experimental evidence for the induction of beta-sheet formation via the membrane surface. The binding of Alzheimer peptide fragments to the lipid membrane is accompanied by an exothermic heat of reaction with delta H in the range -2 - -8 kcal/mol.

Adsorption↗