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Biomedical subjects

J Karam

Publications and source records attributed to J Karam.

At least 19 recordsLinked to original sources
PubMed2006

Early and severe hyperparathyroidism associated with hypercalcemia after renal transplant treated with cinacalcet.

Bone disease is a common clinical problem following renal transplantation. In renal transplant recipients, multiple underlying factors determine the extent of bone loss and the subsequent risk of fractures. In addition to the well-recognized risk to bone disease posed by steroids, calcineurin inhibitors and pre-existing bone disease, persistent hyperparathyroidism (HPT) contributes to post-transplant bone loss. HPT is usually treated with vitamin D supplements combined with calcium. Patients whose HPT is associated with hypercalcemia pose a difficult therapeutic dilemma which often requires parathyroidectomy. Cinacalcet, a calcium mimetic agent, offers a unique pharmacologic approach to the treatment of patients with post-transplant hypercalcemia and HPT. In this paper, we describe the clinical course and biochemical changes in 10 renal transplant recipients with hypercalcemia and severe HPT early after renal transplantation treated with cinacalcet. Cinacalcet therapy corrected hypercalcemia and decreased parathyroid hormone (PTH) levels in all cases. A transient rise in the level of alkaline phosphatase was noted following initiation of cinacalcet therapy. In this patient population, correction of HPT was not permanent as discontinuing cinacalcet therapy led to a rapid rise in PTH level.

Administration, Oral↗
PubMed1999

Steady-state kinetic characterization of RB69 DNA polymerase mutants that affect dNTP incorporation.

The function of six highly conserved residues (Arg482, Lys483, Lys486, Lys560, Asn564, and Tyr567) in the fingers domain of bacteriophage RB69 DNA polymerase (RB69 gp43) were analyzed by kinetic studies with mutants in which each of these residues was replaced with Ala. Our results suggest that Arg482, Lys486, Lys560, and Asn564 contact the incoming dNTP during the nucleotidyl transfer reaction as judged by variations in apparent Km and kcat values for dNTP incorporation by these mutants compared to those for the exonuclease deficient parental polymerase under steady-state conditions. On the basis of our studies, as well as on the basis of the crystal structure of RB69 gp43, we propose that a conformational change in the fingers domain, which presumably occurs prior to polymerization, brings the side chains of Arg482, Lys486, Lys560, and Asn564 into the vicinity of the primer-template terminus where they can contact the triphosphate moiety of the incoming dNTP. In particular, on the basis of structural studies reported for the "closed" forms of two other DNA polymerases and from the kinetic studies reported here, we suggest that (i) Lys560 and Asn564 contact the nonbonding oxygens of the alpha and beta phosphates, respectively, and (ii) both Arg482 and Lys486 contact the gamma phosphate oxygens of the incoming dNTP of RB69 gp43 prior to the nucleotidyl transfer reaction. We also found that Ala substitutions at each of these four RB69 gp43 sites could incorporate dGDP as a substrate, although with markedly reduced efficiency compared to that with dGTP. In contrast in the parental exo- background, the K483A and Y567A substituted enzymes could not use dGDP as a substrate for primer extension. These results, taken together, are consistent with the putative roles of the four conserved residues in RB69 gp43 as stated above.

Alanine↗
PubMed1999

Early postoperative complications of splenectomy for hematologic disease.

Splenectomy may be indicated in a variety of hematologic diseases for diagnostic reasons, therapeutic reasons, or both. Most reviews reveal a high proportion of procedures performed as part of the staging process for Hodgkin disease. Splenectomy for myelofibrosis has been associated with an increased postoperative complication rate. Other determinants of morbidity have been splenic weight and operative blood loss. The authors reviewed a series of 83 adult patients from a prospective database established in 1991 to determine the incidence of early postoperative complications associated with splenectomy for hematologic disease and to analyze patient characteristics that may predict their occurrence. Morbidity that occurred within 30 days of splenectomy was considered to be an early postoperative complication. Operative estimated blood loss and incidence of postoperative complications were correlated with patient age, preoperative platelet count, splenic weight, and diagnosis of myelofibrosis as regression covariates. Indications for splenectomy were therapeutic in 76 patients (92%). Median splenic weight was 760 g, and 22 patients had massive splenomegaly. Patients with splenic weight more than 1,500 g had a significantly higher median estimated blood loss (300 ml; p = 0.02). Splenic weight was the main determinant of estimated blood loss in a multiple linear regression analysis (p = 0.02). Twenty-two patients (27%) experienced postoperative complications and five of those patients died (6%). Patients with myelofibrosis had the highest incidence of complications (50%) and the highest postoperative mortality (21%; p = 0.04). In a logistic regression model, estimated blood loss was the only variable significantly correlated with postoperative complications (p = 0.02). Splenectomy for hematologic disease is associated with an acceptable early postoperative complication rate, even when the indication is predominantly therapeutic. Patients at particularly high risk include those with elevated operative blood loss, massive splenomegaly, and myelofibrosis.

Adult↗
PubMed1994

Surgical treatment of multiple ventricular septal defects using a biologic glue.

The closure of multiple ventricular septal defects remains a surgical challenge. Mortality and morbidity are high. Left ventricular incision and multiple patches or stitches impair septal motion and function. We searched for a method that would cause minimal left ventricular and septal dysfunction. The use of fibrin seal for closing ventricular septal defects was considered. The method was first tested in animals so as to assess the internal resistance of the fibrin seal to stretching and fragmentation in addition to its adhesiveness and hence the absence of left-to-right embolization of the fibrin seal clot and the long-term success of the ventricular septal defect closure further to complete resorption of the ventricular septal defect clot. This experimental work was very satisfactory. Between April 1986 and September 1991, 15 children were operated on with the use of this technique. The overall hospital mortality rate was 6%. There were no reoperations for residual ventricular septal defects. All the long-term survivors (n = 13) were in excellent clinical condition with no or trivial residual shunt attested by color flow mapping investigation. This experimental and clinical experience suggests that satisfactory results can be achieved with the use of fibrin seal for the closure of multiple muscular ventricular septal defects.

Animals↗
PubMed1993

A new video-assisted thoracoscopic surgical technique for interruption of patient ductus arteriosus in infants and children.

Classic surgical interruption of patent ductus arteriosus was partially replaced by transcatheter endovascular closure in 1971. We describe a new technique for ductus closure by video-assisted thoracoscopic surgical interruption, derived from video-assisted endoscopic surgery. With the patient under general anesthesia and intubated, two 5 mm holes were made through the left thoracic wall. A video camera and specially devised surgical tools were introduced; such as scissors, dissectors, and clip appliers. The ductus was dissected, and two titanium clips were applied, completely interrupting the ductus. Thirty-eight patients were operated on from April 1991 to April 1992. Mean age was 23.3 months (range 1.5 to 90 months) and mean weight was 9.5 kg (range 2.4 to 25 kg). Six had associated lesions not necessitating immediate surgical treatment. All had successful closure of the patent ductus with the video-assisted technique, but two needed two such procedures, one because of incomplete immediate ductus closure and one because of partial opening of the clip after 24 hours. One patient had recurrent laryngeal nerve injury and four had pneumothorax on the left side. The usual hospital stay was 2 or 3 days. There were no other complications and no deaths. Video-assisted thoracoscopic surgical interruption was a rapid, safe, and successful technique for closure of the patent ductus arteriosus. Better dissection of the ductus decreased the risk of recurrent laryngeal nerve injury and that of clip opening. In the last 26 patients, in whom a 2 mm multiperforated catheter was used for chest drainage during the first hours, no pneumothoraces occurred. Video-assisted thoracoscopic interruption of the patent ductus arteriosus is feasible in low-weight infants, whereas transcatheter endovascular closure of the ductus usually is not possible. The technique will be applied to premature infants with new instruments designed for the size of these patients.

Child↗
PubMed1990

Binding of the bacteriophage T4 regA protein to mRNA targets: an initiator AUG is required.

Bacteriophage T4 regA protein translationally represses the synthesis of a subset of early phage-induced proteins. The protein binds to the translation initiation site of at least two mRNAs and prevents formation of the initiation complex. We show here that the protein binds to the translation initiation sites of other regA-sensitive mRNAs. Analysis of mRNA binding by filtration and nuclease protection assays shows that AUG is necessary but not sufficient for specific binding of regA protein to its mRNA targets. Anticipating the need for large quantities of regA protein for structural studies to further define the regA protein-RNA ligand interaction, we also report cloning the regA gene into a T4 overexpression system. The expression of regA protein in uninfected E. coli is lethal, so in our system regA driven by a strong T7 promoter is sequestered in a T4 phage until 'induction' by phage infection is desired. We have replaced the regA sensitive wild-type ribosome binding site with a strong insensitive ribosome binding site at an optimal distance from the regA initiation codon for maximizing expression. We have obtained large amounts of regA protein.

Base Sequence↗
PubMed1990

Intrauterine versus postnatal repair of created pulmonary artery stenosis in the lamb. Morphologic comparison.

Experimental lamb models were used for intrauterine creation of pulmonary artery stenosis and later intrauterine repair or postnatal repair. Intrauterine creation of pulmonary artery stenosis was performed in 23 fetal lambs at 90 +/- 1 days of gestation. Eight lambs underwent intrauterine repair of pulmonary artery stenosis at 135 +/- 1 days of gestation and were studied 110 +/- 13 days after repair. Seven lambs underwent postnatal repair at 57 +/- 9 days after birth and were studied 162 +/- 32 days after repair. Eight fetal lambs with unrepaired pulmonary artery stenosis were studied 89 +/- 18 days after birth. All study lambs were compared with normal control lambs. The systolic right ventricular pressure was significantly higher after unrepaired stenosis (78.6 +/- 6.8 mm Hg) than in other lambs, but there was no statistically significant difference after intrauterine repair (23.3 +/- 2.9 mm Hg), postnatal repair (25.9 +/- 3.4 mm Hg), and normal lambs (21.6 +/- 1.1 mm Hg). The systolic pulmonary artery pressure was also not statistically different in these three groups. The weight measurements were age-adjusted for comparison of postnatal and intrauterine repair with normal lambs. The adjusted heart weights were similar in the three groups. The comparison of the adjusted heart weight/adjusted body weight ratio (10(-3) showed a significantly higher ratio in postnatal repair (7.4 +/- 0.1) than in intrauterine repair (6.1 +/- 0.1). The adjusted right ventricular weight/adjusted left ventricular weight ratio was significantly higher in the postnatal repair group (0.71 +/- 0.01) than in both the intrauterine repair group (0.59 +/- 0.01) and normal lambs (0.59 +/- 0.01). The transverse myocyte diameter was not statistically different in all groups of animals and there were no ultrastructural changes even when the pulmonary stenosis was unrepaired. We conclude that intrauterine repair was more satisfactory than postnatal repair in terms of age-adjusted heart weight results, but we did not find any advantages of intrauterine repair in terms of histologic and ultrastructural changes.

Animals↗
PubMed1989

[Importance of peptide C determination in diabetes].

The peptide C, polypeptide secreted by the pancreas at the same time as insulin, presents a great interest in the evaluation of diabetic patients. First it allows a differentiation between insulin dependent diabetes (IDD) and non insulin dependent (NDD). A low and non stimulated levels of peptide C signifies an insulin dependence. Within the group of IDD patients the peptide C was low when the diabetes was discovered at a younger age and its secretion diminished as the diabetes progresses. The peptide C has also a prognostic interest in IDD. Low and non stimulable levels of peptide C signifies a difficult control of diabetes which needs two injections per day while high and stimulable levels will be seen in diabetes easy to control with one injection of insulin. Finally, values of peptide C does not permit to predict the onset of diabetic complications (retinopathy, acidocetosis) as well as the control of patients.

Adolescent↗
PubMed1988

DNA polymerase of bacteriophage T4 is an autogenous translational repressor.

In bacteriophage T4 the protein product of gene 43 (gp43) is a multifunctional DNA polymerase that is essential for replication of the phage genome. The protein harbors DNA-binding, deoxyribonucleotide-binding, DNA-synthesizing (polymerase) and 3'-exonucleolytic (editing) activities as well as a capacity to interact with several other T4-induced replication enzymes. In addition, the T4 gp43 is a repressor of its own synthesis in vivo. We show here that this protein is an autogenous repressor of translation, and we have localized its RNA-binding sequence (translational operator) to the translation initiation domain of gene 43 mRNA. This mechanism for regulation of T4 DNA polymerase expression underscores the ubiquity of translational repression in the control of T4 DNA replication. Many T4 DNA polymerase accessory proteins and nucleotide biosynthesis enzymes are regulated by the phage-induced translational repressor regA, while the T4 single-stranded DNA-binding protein (T4 gp32) is, like gp43, autogenously regulated at the translational level.

Base Sequence↗
PubMed1988

Autogenous regulation of the regA gene of bacteriophage T4: derepression of translation.

The regA gene of phage T4 encodes a translational repressor that inhibits utilization of its own mRNA as well as the translation of a number of other phage-induced mRNAs. In recombinant plasmids, autogenous translational repression limits production of the RegA protein when the cloned structural gene is expressed under control of a strong, plasmid-borne promoter (lambda PL). We have found that a genetic fusion which places the regA ribosome binding domain in proximity to active translation leads to partial derepression of wild-type RegA protein synthesis. The derepression is not due to increased synthesis of regA RNA, suggesting that it occurs at the translational level. Derepressed clones of the wild-type regA gene were used to overproduce and purify the repressor. In an in vitro assay the wild-type target was sensitive and a mutant target was resistant to inhibition by the added protein. The results suggest that the sensitivity of a regA-regulated cistron to translational repression may depend on the competition between ribosomes and RegA protein for overlapping recognition sequences in the translation initiation domain of the mRNA.

Cloning, Molecular↗
PubMed1987

Translational repression: biological activity of plasmid-encoded bacteriophage T4 RegA protein.

The RegA protein of bacteriophage T4 is a translational repressor that regulates expression of several phage early mRNAs. We have cloned wild-type and mutant alleles of the T4 regA gene under control of the heat-inducible, plasmid-borne leftward promoter (PL) of phage lambda. Expression of the cloned regA+ gene resulted in the synthesis of a protein that closely resembled phage-encoded RegA protein in biological properties. It repressed its own synthesis (autogenous translational control) as well as the synthesis of specific T4-encoded proteins that are known from other studies to be under RegA-mediated translational control. Cloned mutant alleles of regA exhibited derepressed synthesis of the mutant regA gene products and were ineffective in trans against RegA-sensitive mRNA targets. The effects of plasmid-encoded RegA proteins were also demonstrated in experiments using two compatible plasmids in uninfected Escherichia coli. The two-plasmid assays confirm the sensitivities of several cloned T4 genes to RegA-mediated translational repression and are well-suited for genetic analysis of RegA target sites. Repression specificity in this system was demonstrated by using wild-type and operator-constitutive translational initiation sites of T4 rIIB fused to lacZ. The results show that no additional T4 products are required for RegA-mediated translational repression. Additional evidence is provided for the proposal that uridine-rich mRNA sequences are preferred targets for the repressor. Surprisingly, plasmid-generated RegA protein represses the synthesis of some E. coli proteins and appears to enhance selectively the synthesis of others. The RegA protein may have multiple functions, and its binding sites are not restricted to phage mRNAs.

Base Sequence↗
PubMed1987

Bacteriophage T4 regA protein binds to mRNAs and prevents translation initiation.

The bacteriophage T4 regA protein is a translational repressor of a subset of phage mRNAs. We show here that purified regA protein binds specifically to target mRNAs near the initiating AUG and occludes binding of ribosomes. Translational repression by regA protein diminishes expression of many genes whose mRNA sequences around the initiating AUG codons are different. A comparison of nucleotide sequences from several regA-repressed mRNAs suggests that the initiating AUG is an important, but not sufficient, sequence for regA binding.

Base Sequence↗
PubMed1987

Genetic mapping of the amino-terminal domain of bacteriophage T4 DNA polymerase.

The DNA polymerase of bacteriophage T4 is a multifunctional enzyme that harbors DNA-binding, DNA-synthesizing and exonucleolytic activities. We have cloned in bacterial plasmids about 99% of the structural gene for this enzyme (T4 gene 43). The gene was cloned in six contiguous 5'-terminal DNA fragments that defined seven intragenic mapping regions. Escherichia coli hosts harboring recombinant plasmids carrying the gene 43 subsegments were used in marker-rescue experiments that assigned a large number of ts and nonsense polymerase mutations to different physical domains of the structural gene. Conspicuously, only one missense mutation in a large collection of mutants mapped in the 5'-terminal 450 base-pair segment of the approximately 2700 base-pair gene. To test if this indicated a DNA polymerase domain that is relatively noncritical for biological activity, we mutagenized a recombinant plasmid carrying this 5'-terminal region and generated new conditional-lethal mutations that mapped therein. We identified five new ts sites, some having mutated at high frequency (nitrosoguanidine hot spots). New ts mutations were also isolated in phage genes 62 and 44, which map upstream of gene 43 on the T4 chromosome. A preliminary examination of physiological consequences of the ts gene 43 mutations showed that they exhibit effects similar to those of ts lesions that map in other gene 43 segments: some were mutators, some derepressed gene 43 protein synthesis and they varied in the severity of their effects on T4-induced DNA synthesis at nonpermissive temperatures. The availability of the gene 43 clones should make it possible to isolate a variety of lesions that affect different activities of the T4 DNA polymerase and help to define the different domains of this multifunctional protein.

Cloning, Molecular↗
PubMed1987

Intrauterine creation and repair of pulmonary artery stenosis in the fetal lamb. Weight and ultrastructural changes of the ventricles.

Fetal lamb experimental models were employed for intrauterine creation and repair of pulmonary artery stenosis. The study group was composed of 51 fetal lambs including 29 models of pulmonary artery stenosis and 22 control lambs. Gestational age was 89 days at creation of pulmonary artery stenosis. Fourteen fetal lambs (Group A) were studied after creation of the stenosis at 131 days of gestation and compared to normal age-matched control lambs. The systolic right ventricular pressure was significantly higher after creation of pulmonary artery stenosis (76.6 +/- 17.8 versus 50.3 +/- 23.5 mm Hg), but the systolic pulmonary artery pressure was unchanged. The mean right ventricular weight and the mean right ventricular/left ventricular weight ratio were significantly greater after pulmonary artery stenosis than in normal control animals. The transverse myocyte diameter was not modified by pulmonary artery stenosis, but on electron microscopic study the myocytes appeared mature. Ten lambs (Group B) underwent intrauterine repair of pulmonary artery stenosis at 131 days of gestation without cardiopulmonary bypass. The pulmonary artery was clamped and patched. Immediately after repair the right ventricular pressure fell significantly from 85.8 +/- 18.9 to 62.2 +/- 14.6 mm Hg. At birth, 7 +/- 6 days after repair, Group B was compared to Group C (unrepaired pulmonary artery stenosis, five fetuses) and to normal control lambs. The mean right ventricular weight and the mean right ventricular/left ventricular weight ratio were not statistically different in Group B and in the control group. There were no ultrastructural changes after intrauterine repair. We conclude that intrauterine creation of pulmonary artery stenosis causes right ventricular hypertrophy with more mature myocytes. Intrauterine repair of pulmonary artery stenosis is feasible without cardiopulmonary bypass and rapidly abolishes the preponderance of right ventricular weight over left ventricular weight.

Animals↗
PubMed1984

The bacteriophage T4 regA gene: primary sequence of a translational repressor.

The regA gene product of bacteriophage T4 is an autogenously controlled translational regulatory protein that plays a role in differential inhibition (translational repression) of a subpopulation of T4-encoded "early" mRNA species. The structural gene for this polypeptide maps within a cluster of phage DNA replication genes, (genes 45-44-62-regA-43-42), all but one of which (gene 43) are under regA-mediated translational control. We have cloned the T4 regA gene, determined its nucleotide sequence, and identified the amino-terminal residues of a plasmid-encoded, hyperproduced regA protein. The results suggest that the T4 regA gene product is a 122 amino acid polypeptide that is mildly basic and hydrophilic in character; these features are consistent with known properties of regA protein derived from T4-infected cells. Computer-assisted analyses of the nucleotide sequences of the regA gene and its three upstream neighbors (genes 45, 44, and 62) suggest the existence of three translational initiation units in this four-gene cluster; one for gene 45, one for genes 44, 62 and regA, and one that serves only the regA gene. The analyses also suggest that the gene 44-62 translational unit harbors a stable RNA structure that obligates translational coupling of these two genes.

Amino Acid Sequence↗