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Biomedical subjects

C Stefan

Publications and source records attributed to C Stefan.

At least 55 records · Page 3Linked to original sources
PubMed1999

[The vitreoretinal complications of cataract surgery].

The paper reports a retrospective study performed between January 1996 and January 1999 which comprised 423 patients who underwent eye cataract surgery. Vitreoretinal complications (retinal detachment, cystoid macular edema, choroidal detachment, endophthalmitis, luxation of the lens into the vitreous body) were related to age, sex, other general and local diseases and surgical complications, like disruption of the posterior capsule. The study presents also vitreoretinal complications after Nd:YAG laser posterior capsulotomy. The outcomes of the study show that 18 cases (4.25%) had retinal detachment, 11 (2.60%) had cystoid macular edema, 2 cases had endophthalmitis, while choroidal detachment and luxation of the lens into the vitreous body were reported each in 1 case. Retinal detachment following Neodymium:YAG laser capsulotomy (performed in 109 cases) was found in 2 cases. All of those vitreoretinal complications were reported with a higher incidence in patients with vascular diseases (diabetes mellitus, arterial hypertension, angiosclerosis) and also in patients who had axial lengths of 25 mm or greater.

Aged↗
PubMed1998

Growth-related expression of the ectonucleotide pyrophosphatase PC-1 in rat liver.

Plasma cell differentiation antigen-1 (PC-1) is a 5'-ectonucleotide pyrophosphatase that has been implicated in various processes including insulin- and nucleotide-mediated signaling and cell growth. We show here that the expression of both PC-1 mRNA and protein in rat liver and in hepatoma cells is strictly growth-related. Thus, the level of PC-1 in FAO hepatoma cells increased with the cell density. PC-1 was not expressed in the neonatal rat liver, but gradually appeared in the first weeks of age, to reach adult levels around the weaning period. Furthermore, PC-1 protein and mRNA largely disappeared from the liver within 24 hours following a hepatectomy of 70%, but re-appeared in the later phases (3-15 days) of the ensuing regeneration period. An equally rapid loss of PC-1 protein and mRNA could also be provoked in normal livers by the administration of the translational inhibitor, cycloheximide, but the transcriptional inhibitors, actinomycin D and alpha-amanitin, did not show these effects. Nuclear run-on assays revealed that the loss of PC-1 mRNA after hepatectomy or after the administration of cycloheximide was not caused by a decreased transcription of the PC-1 gene, suggesting that the level of PC-1 is controlled by an mRNA-stabilizing protein that is lost after hepatectomy and has a high turnover.

Aging↗
PubMed1998

[The use of viscoelastic compounds in cataract surgery].

The viscoelastic substances are very useful generally in cataract surgery, but absolutely useful in phacoemulsification. In present is used for viscoelastic compounds two terms that assemble the rheologic and physics-chemical properties: is said about the viscoelastic substance that is cohesive and dispersive (respective cohesivity or dispersivity property). Thus both types of viscoelastic substances--cohesive and dispersive--is used, sequentially, in one system. This double technique provides a fluid, heterogeneous work environment, which differ from the other techniques that use only one viscoelastic substance and provide a fluid, homogeneous work environment.

Cataract Extraction↗
PubMed1998

[Vascular risk factors in glaucoma].

The study realised in the Eye Clinic of the Central Military Hospital during February 1995-November 1997 analyses the impact of the vascular risk factors on the evolution of the primary glaucoma. The group consists in 533 patients which primary open angle glaucoma, from which 90.6% patients with primary open angle glaucoma and 9.3% with normal tension glaucoma. The assessment of the patients in order to identify the vascular risk factors it was performed on the basis of anamnestic questionnaire, following: degenerative vasculopathies, spastic vasculopathies, arterial hypotension and coronary insufficiency. 70.5% of the patients presented minimum one vascular risk factor. In the case of the patients with primary open angle glaucoma, we found a high frequency of the degenerative vasculopathies. In the patients with normal tension glaucoma the most frequent factor were: arterial hypotension and spastic vasculopathies. The coronary insufficiency had equal distribution in the primary open angle glaucoma and normal tension glaucoma. The parameters of the disease were affected faster in the patients with vascular risk factors. The outcomes of the study allow to estimate that the screening of the vascular risk factors has a distinct importance in the evolution and accurate treatment of glaucoma.

Aged↗
PubMed1998

[Cataract and the exfoliative syndrome].

Exfoliation syndrome is more frequently in the older age and represents a risk factor for cataract surgery. This paper presents the results of a clinical trial made on 436 patients with troubles of transparency of the lens who were investigate in our clinic during January 1995-January 1997, and in whom, clinic and paraclinic exams have not revealed any associated ocular disease. In 14% of these patients who presented troubles of transparency of the lens were found uni- or bilateral exfoliation. The authors present the treatment applied both in patients in clinical follow-up (50% of patients with exfoliation syndrome develop secondary glaucoma) and patients who underwent surgical treatment. The patients with exfoliation syndrome and cataract have had a high risk to develop intra- and postoperative complications. The surgical treatment suggested by authors is extracapsular cataract extraction, either or without lens implantation and peripheral iridectomy which represents a compulsory step.

Aged↗
PubMed1997

[Pseudoexfoliative glaucoma].

The pseudoexfoliative glaucoma was find in our study at approximately 10% of the patients. Both clinical evolution and treatment results were less good at the patients with pseudoexfoliative glaucoma.

Adult↗
PubMed1997

[Pseudotumoral tuberculous choroiditis].

It is presented a case of a secondary tumoral retinal detachment that clinical examination and all paraclinical investigation go for a choroidal malignant melanoma. The anatomopathological examination of the enucleated eyeball has surprisingly put in evidence some choroidal consumptive lesions.

Adult↗
PubMed1996

Threonine autophosphorylation and nucleotidylation of the hepatic membrane protein PC-1.

The membrane protein plasma-cell-differentiation antigen 1 (PC-1) has been described as a phosphodiesterase-I/nucleotide pyrophosphatase and as an autophosphorylating protein kinase. It has been suggested, however, that PC-1 is not a real protein kinase and that the autophosphorylated enzyme represents a nucleotidylated derivative, which is formed on Thr238 (murine PC-1) as a catalytic intermediate during ATP hydrolysis [Belli, S.I., Mercuri, F.A., Sali, A.& Goding, J.W. (1995) Eur. J. Biochem. 228, 669-676]. We have investigated the proposed multifunctional role of PC-1 and show here that ATP hydrolysis and autophosphorylation represent two distinct catalytic reactions. The enzyme was radiolabeled when various concentrations (1-260 microM) of [alpha-32P]ATP or [alpha-32P]ADP, but not [gamma-32P]ATP, were used as substrates for the formation of the pyrophosphatase catalytic intermediate, especially in the presence of imidazole, which interferes with the hydrolysis of the nucleotidylated enzyme. In contrast, autoradiography revealed autophosphorylation only with [gamma-32P]ATP as the phosphoryl donor, and autophosphorylation has been shown to occur only at ATP concentrations below 5 microM. Autophosphorylation could also be differentiated from nucleotidylation by its higher resistance to alkaline treatment and its more basic pH optimum. An intestinal nucleotide pyrophosphatase with a structurally related catalytic site could not be autophosphorylated, which shows that autophosphorylation is not an intrinsic property of the nucleotide pyrophosphatase reaction. Autophosphorylation of PC-1 was associated with inactivation of its phosphodiesterase-I/nucleotide-pyrophosphatase activity. We propose that autophosphorylation of PC-1 on Thr238 at low ATP concentrations serves as an autoregulatory mechanism that makes Thr238 unavailable for participation in the hydrolysis of extracellular nucleotides when they become scarce.

Adenine Nucleotides↗
PubMed1996

The inhibition of the insulin receptor by the receptor protein PC-1 is not specific and results from the hydrolysis of ATP.

The membrane protein plasma cell differentiation antigen 1 (PC-1) has been purified as an inhibitor of insulin receptor tyrosine kinase activity and has been implicated in the pathogenesis of NIDDM. However, we show here that PC-1 is a general protein kinase inhibitor in vitro and that this inhibition results from the hydrolysis of ATP by the intrinsic nucleotide pyrophosphatase activity of PC-1. Thus, the inhibition diminished with increasing ATP concentrations, and it was nullified when the ATP concentration was kept constant with a regenerating system or when ATP was added repetitively. When care was taken to avoid ATP depletion, PC-1 did not affect the insulin sensitivity of insulin receptor autophosphorylation. We conclude that the reported inhibition of insulin signaling by PC-1 does not result from a direct inhibition of the insulin receptor kinase activity.

Adenosine Triphosphate↗
PubMed1996

Intracellular redox changes during apoptosis.

In the current paradigm for apoptotic cell death, the activity of a family of proteases related to interleukin 1-beta converting enzyme (ICE) orchestrates the multiple downstream events (such as cell shrinkage and chromatin degradation) that comprise apoptosis. A variety of stimuli can induce this type of cell death. One of the most reproducible inducers is mild oxidative stress, although it is unclear how an oxidative stimulus activates ICE-like proteases. Oxidative modification of proteins and lipids have also been observed in cells undergoing apoptosis in response to non-oxidative stimuli, suggesting that intracellular oxidation may be a general feature of the effector phase of apoptosis. However, attempts to consistently detect a requirement for reactive oxygen species in apoptosis have been inconclusive. Recent experiments revealing that apoptosis is typically accompanied by a depletion of intracellular reduced glutathione (GSH) are also discussed. In JURKATT lymphocytes treated with antibodies to the Fas/APO-1 surface receptor, this depletion results from an accelerated efflux of the reduced thiol rather than any intracellular oxidation. As GSH is the most abundant cytosolic reductant, we propose that its efflux may provide a non-oxidative mechanism by which the reducing environment of apoptotic cells is lost. An increase in oxidative damage to proteins and lipids would then result even in the absence of an increase in the production of oxidants. This may explain the seemingly contradictory findings that increased oxidative stress is not required for apoptosis even though antioxidants often inhibit the process and peroxidised products accumulate in apoptotic cells.

Journal Article↗
PubMed1995

Signalling mechanisms and oxidative stress in apoptosis.

A variety of stimuli can induce cells to undergo apoptotic death. One of the most reproducible inducers is mild oxidative stress, be it via exposure to hydrogen peroxide, redox-cycling quinones or thiol-alkylating agents. Oxidative modifications of proteins and lipids have also been observed in cells undergoing apoptosis in response to non-oxidative stimuli such as glucocorticoids or topoisomerase II inhibitors. This suggests that some unidentified oxidative changes occur during apoptosis in many, if not all, cases. However, recent experiments demonstrating apparently normal apoptosis even when cells are cultured at low oxygen tensions show that reactive oxygen species cannot be essential mediators of this type of cell death. Experiments revealing that apoptosis is typically accompanied by a depletion of intracellular reduced glutathione (GSH) are also discussed. As GSH depletion will lower a cell's capacity to buffer against endogenous oxidants, we propose that it contributes to the increased oxidative damage commonly observed to accompany apoptosis. In addition, it may set a time limit on continued mitochondrial function (and thus indirectly on total ATP levels and membrane integrity) in apoptotic cells, and thereby explain the often observed 'secondary necrosis' of cells undergoing apoptosis in vitro.

Animals↗
PubMed1991

Molecular cloning and characterization of the gene encoding the adenine methyltransferase M.CviRI from Chlorella virus XZ-6E.

The gene encoding the DNA methyltransferase M.CviRI from Chlorella virus XZ-6E was cloned and expressed in Escherichia coli. M.CviRI methylates adenine in TGCA sequences. DNA containing the M.CviRI gene was sequenced and a single open reading frame of 1137 bp was identified which could code for a polypeptide of 379 amino acids with a predicted molecular weight of 42,814. Comparison of the M.CviRI predicted amino acid sequence with another Chlorella virus and 14 bacterial adenine methyltransferases revealed extensive similarity to the other Chlorella virus enzyme.

Amino Acid Sequence↗
PubMed1991

A comparative study on involvement of tPA activity in ovulation induced by hCG and GnRH agonist in hypophysectomized rats.

A GnRH agonist (5-50 micrograms) is capable of inducing ovulation in PMSG-primed hypophysectomized immature rats, as is the case in hCG-induced ovulation, but 2-4 h earlier than hCG. GnRH-induced ovulation is effectively blocked by the concomitant administration of the GnRH-antagonist which failed to interfere with hCG-induced ovulation, indicating that GnRH and its agonists do not share a receptor with LH/hCG. Like hCG, GnRH is also capable of inducing tissue type (tPA), but not urokinase type (uPA) PA. The plasminogen activator activity in ovarian homogenates and the granulosa and theca-interstitial cells increase in a time-dependent manner, reaching maximum levels just prior to ovulation. Similar to hCG, GnRH also increases tPA activity in cumulus-oocyte complexes in a time-dependent fashion.

Animals↗
PubMed1982

[Lipid electrophoresis in the alcoholic. Features and usefulness in the diagnosis of various degrees of alcoholic liver diseases].

Reference is made to the importance of assessing serum lipoproteins by conventional agarose gel electrophoresis in the preliminary diagnosis of the degree of severity of a liver disease. A comparison is made between lipidogram changes in 48 alcoholic patients with the liver histologies following needle biopsy according to Menghini. The conclusion is drawn that in acute and chronic alcoholic liver disease there is a characteristic lipidogram profile, marked by a double "camel's hump" in the bands due to predominance of the beta and prebeta-lipoprotein fractions. This, in turn, is related to the liver steatosis observed bioptically. In macro and micronodular cirrhosis, however, examination of the electrophoretic lipid fractions is frequently unhelpful. Attention is drawn to the appearance of the alpha fraction as a presumably pointer to the condition in question. It is felt that this conventional, simple evaluation of lipoproteins is a valuable diagnostic test in assessing the seriousness of alcoholic liver disease.

Adult↗
PubMed1982

An investigation of the construct validity of the Bannister-Fransella Grid Test of Schizophrenic Thought Disorder.

An attempt was made to demonstrate the construct validity of the Grid Test in a psychiatric population by showing that: (a) judgements of thought disorder based on the Grid Test were associated with judgements based on a clinical interview; (b) Grid Test scores were not associated with measures of other forms of psychopathology, intelligence, or memory. Results of a principal components factor analysis confirmed both hypothesis, supporting the validity of the Grid Test as a measure of thought disorder.

Diagnosis, Differential↗