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S Kaufman

Publications and source records attributed to S Kaufman.

At least 109 records · Page 6Linked to original sources
PubMed1995

Further studies of the role of Ser-16 in the regulation of the activity of phenylalanine hydroxylase.

It was previously proposed that the activation of rat liver phenylalanine hydroxylase (EC 1.14.16.1) by cAMP-dependent protein kinase-mediated phosphorylation of Ser-16 is due to the introduction of the negatively charged phosphate group. To explore the validity of this proposal, we have applied site-directed mutagenesis to specifically replace Ser-16 with negatively charged amino acids, glutamic and aspartic; with polar uncharged amino acids, asparagine and glutamine; with the positively charged amino acid lysine; and with the nonpolar hydrophobic amino acid alanine. The wild-type and mutant enzymes were purified to homogeneity, and the importance of Ser-16 in the activation of phenylalanine hydroxylase was examined by comparing the state of activation of the phosphorylated form of the wild-type hydroxylase with that of the mutants. The kinetic studies carried out on the wild-type phosphorylated hydroxylase showed that all the activation could be accounted for by an increase in Vmax with no change in Km for either phenylalanine or the pterin cofactor. Replacement of Ser-16 with a negatively charged residue, glutamate of aspartate, resulted in the activation of the hydroxylase by 2- to 4-fold, whereas replacement with glutamine, asparagine, lysine, or alanine resulted in a much more modest increase. Further, lysolecithin was found to stimulate the phosphorylated hydroxylase and the mutant enzymes S16E and S16D by a factor of 6-7. In contrast, the mutants S16Q, S16N, and S16A all showed the same magnitude of activation as the wild-type with lysolecithin. Therefore, this study demonstrates that activation of the enzyme by phosphorylation of Ser-16 by cAMP-dependent protein kinase is due to the introduction of negative charge(s) and strongly suggests the involvement of electrostatic interaction between the regulatory and catalytic domains of the hydroxylase.

Amino Acid Sequence↗
PubMed1995

Study of the role of retinoblastoma protein in terminal differentiation of murine erythroleukemia cells.

Hexamethylenebisacetamide-induced terminal differentiation of Friend virus-transformed murine erythroleukemia (MEL) cells can be inhibited by okadaic acid, an inhibitor of type 1 and type 2A protein phosphatases. The inhibition is shown to be correlated with prevention of dephosphorylation of retinoblastoma protein (pRB) in cells and bypass of G1 prolongation in the cell cycle. These results suggest that pRB-mediated G1 prolongation is necessary for MEL cells to commit to terminal differentiation. However, further experiments demonstrate that the simple cell cycle exit is not sufficient for commitment to terminal differentiation. Induction of dephosphorylation of pRB and subsequent G1 prolongation by forskolin does not lead MEL cells to differentiate. Additional pRB has been expressed in MEL cells by transfection with a neo-resistant plasmid containing RB cDNA under the control of a cytomegalovirus promoter. Exogenously expressed pRB is hyperphosphorylated in logarithmically growing MEL cells without any noticeable change in growth rate between the transfected cell line and the parental cell line. This result suggests that pRB in MEL cells is regulated by protein kinases and protein phosphatases and not by transcription.

Acetamides↗
PubMed1995

Characteristics of the nitric oxide synthase-catalyzed conversion of arginine to N-hydroxyarginine, the first oxygenation step in the enzymic synthesis of nitric oxide.

The nitric oxide synthase-catalyzed conversion of L-arginine to L-citrulline and nitric oxide is known to be the sum of two partial reactions: oxygenation of arginine to N-hydroxyarginine, followed by oxygenation of N-hydroxyarginine to citrulline and nitric oxide. Whereas the conversion of N-hydroxyarginine to citrulline and nitric oxide has been the subject of a number of studies, the oxygenation of arginine to N-hydroxyarginine has received little attention. Here we show that substrate amounts of rat cerebellar nitric oxide synthase, in the absence of added NADPH, catalyze the conversion of arginine to N-hydroxyarginine as the dominant product. The product appears not to be tightly bound to the enzyme. A maximum of 0.16 mol of N-hydroxyarginine/mol of nitric oxide synthase subunit was formed. The reaction requires oxygen and the addition of Ca2+/calmodulin and is stimulated 3-fold by tetrahydrobiopterin. Upon addition of NADPH, citrulline is formed exclusively. Conversion of N-hydroxyarginine to citrulline, like the first partial reaction, requires Ca2+/calmodulin and is stimulated by tetrahydrobiopterin but differs from the first partial reaction in being completely dependent upon addition of NADPH. These results indicate that brain nitric oxide synthase contains an endogenous reductant that can support oxygenation of arginine but not of N-hydroxyarginine. The reductant is not NADPH, since the amount of nitric oxide synthase-bound NADPH is appreciably less than the amount required for N-hydroxyarginine synthesis. Possible candidates for this role are discussed in relation to proposed mechanisms of action of nitric oxide synthase.

Amino Acid Oxidoreductases↗
PubMed1995

A novel natriuretic, hypotensive factor derived from the spleen.

Previous experiments have shown that the reduction in plasma volume observed after administration of atrial natriuretic factor is abolished by splenectomy. In order to determine whether the spleen contains a factor that influences cardiorenal homeostasis, rat spleens were homogenized in phosphate-buffered saline, centrifuged, subjected to ultrafiltration (molecular weight cut-off 10,000), extracted on C18 affinity columns and dried. After reconstitution in isotonic saline, the extract was injected i.v. into conscious rats. In response to this extract, there was a dose-dependent diuresis, natriuresis, kaliuresis and chloruresis which plateaued during the second and third hours following administration. Solute-free water clearance was inversely related to urine output. Blood pressure fell significantly from 109 +/- 3 mm Hg to 103 +/- 3 mm Hg during the first 10 min. after injection of the extract, and tended to remain depressed thereafter. There was no accompanying increase in heart rate. We conclude that the mammalian spleen contains a natriuretic, hypotensive factor that may play a role in cardiorenal homeostasis.

Animals↗
PubMed1995

Improved survival with preoperative chemotherapy followed by resection uncompromised by tumor response for advanced squamous cell carcinoma of the head and neck.

BACKGROUND: A total of 93 patients were treated with one of two preoperative chemotherapy regimens over a 15-year period. The study supports the importance of strict adherence to guidelines for ablative surgery. METHODS: A single surgeon performed the surgery and evaluated each patient prior to treatment. The extent of the planned operation was documented. RESULTS: The 5-year absolute survival of 88 patients who completed the protocol was estimated at 55%. The 40 cisplatin/5-fluorouracil-treated patients exhibited a significantly better outcome than the 48 cisplatin/bleomycin-treated patients (76% versus 43%, respectively). Comparison of a subset of 37 patients with a matched group from the standard control arm of the Head and Neck Contracts Program demonstrated a statistically significant improvement in overall survival over standard treatment. CONCLUSIONS: These data suggest that strict adherence to preoperative chemotherapy planning of ablative uncompromised surgery contribute to improved survival. Selective rather than routine postoperative radiotherapy may be advantageous.

Antibiotics, Antineoplastic↗
PubMed1995

Monoaminergic effects of folinic acid, L-DOPA, and 5-hydroxytryptophan in dihydropteridine reductase deficiency.

Plasma and CSF concentrations of endogenous L-DOPA, catecholamines, and metabolites of monoamines were assayed in a patient with atypical phenylketonuria due to absent dihydropteridine reductase (DHPR), before and during treatment with folinic acid, Sinemet, and 5-hydroxytryptophan. The patient had low but detectable levels of L-DOPA, 3,4-dihydroxyphenylacetic acid (DOPAC), and 3,4-dihydroxyphenylglycol (DHPG) in plasma and low but detectable levels of these compounds and of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in CSF, with approximately normal plasma and CSF levels of norepinephrine [noradrenaline (NA)]. Folinic acid treatment approximately doubled plasma levels of L-DOPA, NA, DOPAC, and DHPG, compared with values during dietary phenylalanine restriction alone. Detection of L-DOPA, catecholamines, and monoamine metabolites in this patient indicates that monoamine synthesis in humans does not absolutely require DHPR. The results are consistent with the existence of an alternative biochemical pathway, with folinic acid treatment augmenting activity along this pathway. Low plasma levels of L-DOPA, DOPAC, and DHPG may reflect decreased catecholamine synthesis and turnover in sympathetic nerves, with compensatory increases in exocytotic release normalizing plasma NA levels.

5-Hydroxytryptophan↗
PubMed1995

Parallel induction of nitric oxide and tetrahydrobiopterin synthesis by cytokines in rat glial cells.

Activation of monocyte-derived macrophages with cytokines leads to the induction of nitric oxide synthase. Much less is known about the effects of cytokines on microglia, resident brain macrophages, or on astrocytes. In this study, we compared the induction by lipopolysaccharide, interferon-gamma, and tumor necrosis factor-alpha of nitric oxide production and synthesis of tetrahydrobiopterin, the required cofactor for nitric oxide synthase, in microglia and peritoneal macrophages. Activation of microglia induced parallel increases in nitric oxide and intracellular tetrahydrobiopterin levels, although induction of the latter appears to be somewhat more sensitive to diverse stimulators. As with macrophages, inducible nitric oxide production in microglia was blocked by inhibitors of tetrahydrobiopterin biosynthesis. Interleukin-2, an important component of the neuroimmunomodulatory system, was only a weak activator of microglia by itself but potently synergized with interferon-gamma to stimulate production of both nitric oxide and tetrahydrobiopterin. Astrocytes were also activated by lipopolysaccharide and combinations of cytokines but showed a somewhat different pattern of responses than microglia. Biopterin synthesis was increased to higher levels in astrocytes than in microglia, but maximal induction of nitric oxide production required higher concentrations of cytokines than microglia and the response was much lower. These results suggest that tetrahydrobiopterin synthesis in glial cells is a potential target for therapeutic intervention in acute CNS infections whose pathology may be mediated by overproduction of nitric oxide.

Animals↗
PubMed1995

Detection of high- and moderately high-level resistance to gentamicin and streptomycin in Enterococcus faecium by a disc diffusion method.

We evaluated an agar disc diffusion test for the detection of high-level (> or = 2000 mg/L) and moderately high-level resistance to gentamicin (MIC, > or = 128- < or = 1024 mg/L) and streptomycin (MIC, > or = 256- < or = 1024 micrograms/ml) with 70 clinical isolates of Enterococcus faecium. Results obtained using disks containing 120 micrograms gentamicin and 300 micrograms streptomycin were compared with MICs determined by an agar dilution method. Based on the scattergrams, the closest zone diameter correlations with MIC breakpoints were as follows: susceptible, > or = 16 mm; and resistant, < or = 10 mm, for both streptomycin and gentamicin. No major or very major errors were found with either aminoglycoside using these values. We conclude that agar disk diffusion test can be used to accurately detect high-level or moderately high-level gentamicin and streptomycin resistance in E. faecium.

Anti-Bacterial Agents↗
PubMed1995

Surgical approach to short-bowel syndrome. Experience in a population of 160 patients.

OBJECTIVE: The authors reviewed their experience with short-bowel syndrome to define the surgical approach to this problem in 160 patients. METHODS: Forty-eight adults and 112 children were evaluated over a 15-year period. RESULTS: Seventy-one patients (44%) adapted to resection and took enteral nutrition alone. Forty-four patients (28%) were supported by parenteral nutrition (PN). Forty-five patients (28%) have had 49 surgical procedures. Fifteen patients with adequate intestinal length (> 120 cm in adults) but dilated dysfunctional bowel underwent stricturoplasty (n = 4) or tapering (n = 11). Thirteen patients (87%) demonstrated clinical improvement. Fourteen patients with shorter remnants (90-120 cm) and rapid transit time received an artificial valve (n = 2) or a reversed segment (n = 1). All patients' conditions improved initially, but the reversed segment was revised or taken down. Fourteen patients with short remnants and dilated bowel underwent intestinal lengthening. Twelve patients' conditions improved (86%), one underwent transplantation, and one died. Sixteen patients with very short remnants (< 60 cm) and complications of PN underwent solitary intestine (n = 4) or combined liver-intestinal transplantation (n = 13). One-year graft survival was 65%. There have been five deaths. CONCLUSIONS: The surgical approach to short-bowel syndrome depends on the patient's age, remnant length and caliber, intestinal function, and PN-related complications. Nontransplant procedures have a role in the treatment of selected patients. Intestinal transplantation is emerging as a potential therapy for patients with significant PN-related complications.

Adolescent↗
PubMed1995

An 8-year study of resistance to amikacin in gram-negative bacilli isolates from patients with nosocomial infection at one hospital in Argentina.

Administration of either gentamicin or amikacin induced an increase in the number of amikacin-resistant (AR) isolates of certain Enterobacteriaceae and Acinetobacter species in a hospital in Buenos Aires. A total of 127 AR isolates was selected to study the molecular mechanisms of resistance involved. The aac(6')-Ic gene was found by dot-blot hybridisation in every Serratia marcescens isolate. A gene different from aac(6')-Ia, aac(6')-Ib and aac(6')-Ic encoding the AAC(6')-I activity was found in a 15.5-kb plasmid in Acinetobacter spp. Plasmids from 27 Enterobacteriaceae contained and aac(6')-Ib gene and 26 of these carried sequences related to the Tn1331 transposon, whereas one Escherichia coli plasmid showed homology in another fragment of the Tn1331 transposase. Because plasmids bearing the aac(6')-Ib gene were heterogeneous, dissemination of the aac(6')-Ib gene may have been due to transposition of Tn1331 rather than the spread of an epidemic plasmid. The rate of AR isolates varied within each species in spite of the presence of Tn1331, and it is likely, therefore, that this transposon may not be the sole factor responsible for the observed variation. The aph(3')-VIa gene (originally described in Acinetobacter spp.) was found with high frequency (80%) in this Acinetobacter population. Furthermore, this gene was found also in plasmids from 20% of other gram-negative organisms commonly involved in nosocomial infections in this hospital.

Acinetobacter↗
PubMed1995

Control of intravascular volume during pregnancy.

1. We wished to determine whether, during pregnancy, there is reduced renal response to atrial distension, whether secretion of atrial natriuretic factor (ANF) is suppressed and whether neural input from the atrial volume receptors to the central nervous system is altered. 2. Conscious, chronically instrumented female rats were used. Atrial distension was achieved by implanting small balloons positioned at the superior vena caval/right atrial junction; inflation of the balloon did not impede blood flow through the heart. 3. In virgin rats, atrial stretch caused increased urine volume, urine sodium and potassium output and decreased free water clearance. These responses were abolished during pregnancy. 4. In response to atrial stretch, plasma ANF levels increased significantly in virgin rats. No such secretory response was observed in the pregnant animals. 5. Distension of isolated atria derived from unmated and 7 day pregnant rats resulted in an increase in secretion of ANF into the perfusate. Atria from 14 and 21 day pregnant rats were unresponsive to distension. 6. Pretreatment with oestradiol (50 micrograms daily for 10 days) caused plasma ANF levels and ANF secretion by isolated perfused atria to increase. By contrast, testosterone pretreatment (15 mg twice weekly for 2 weeks) abolished stretch induced secretion of ANF by isolated atria. 7. C-fos activity in the paraventricular nucleus of virgin rats increased in response to atrial distension. This response was reduced in the 7 day pregnant rats and abolished at 21 days. 8. We conclude that there is attenuation of both hormonal and neural responses to atrial distension in the pregnant animal. This allows blood volume to increase without eliciting homeostatic mechanisms to eliminate the extra fluid.

Animals↗
PubMed1995

Effect of pregnancy on activation of central pathways following atrial distension.

Stimulation of the atrial volume receptors increases neural traffic to the ventrolateral medulla, which in turn sends output to, and receives input from, the lateral hypothalamic area. An integrated reflex and hormonal response is thus initiated. We wished to investigate first whether atrial distension results in activation of selected nuclei in the forebrain and, second, whether pregnancy modifies this response. Rats were implanted with indwelling intracardiac balloons positioned at the superior vena caval/right atrial junction. One week later, the balloons were inflated. The animals were then anesthetized, their brains fixed by perfusion, and the tissue prepared for visualization of c-fos activity. Atrial distension caused a significant increase in c-fos expression in the paraventricular nucleus, the medial preoptic area, and the lateral septum. This response was markedly attenuated in the pregnant animals. In conclusion, during pregnancy central pathways that are normally activated in responses to volume expansion, fail to respond to atrial distension. We propose that this allows blood volume to increase in the pregnant animal, without triggering homeostatic mechanisms.

Animals↗
PubMed1995

Interferon-alpha-2b with VMCP for induction in multiple myeloma: the Israel Myeloma Cooperative Group experience.

In 1988, a prospective, randomized multicenter study was initiated to determine the efficacy of a combined induction regimen with recombinant interferon-alpha-2b (IFN-alpha) and maintenance with IFN-alpha on the response and survival rates in multiple myeloma (MM) patients. Induction therapy consisted of VMCP (vincristine, melphalan, cyclophosphamide, prednisone), randomized to combine IFN-alpha at a dose of 2 x 10(6) U, 5 days per week throughout the induction period of 12 months. Patients who achieved plateau phase were subsequently randomized again between IFN alpha maintenance (2 x 10(6) U, 3 days a week) for 12 months and no maintenance therapy. Of the previously untreated patients, 84 were initially randomized for induction therapy, and 31 for the maintenance phase with IFN-alpha. Results of the cohort median survival, based on the intention to treat, have shown that those on the VMCP/IFN-alpha arm had a median survival of 53 months, compared with patients on the VMCP induction arm who a median survival of 26 months (P = 0.052). The median survival of stage 3 evaluable patients who were on the VMCP/IFN induction arm was 43 months, and 13 months for patients treated by VMCP alone (P = 0.008). No significant difference in survival was detected among patients in partial remission (after induction) who had a second IFN-alpha randomization at the plateau phase. Hematologic toxicity, mild to moderate fever, and fatigue were more common in the VMCP/IFN induction arm. The results show that VMCP/IFN is a well-tolerated treatment regimen, and is superior to VMCP for patients with stage 3 myeloma.

Adult↗
PubMed1995

-Prolonged fever syndrome and infection of abdominal aortic aneurysm due to Salmonella enteritidis.

Endovascular infection of atherosclerotic aorta is a rare event in the setting of aged patients with gram negative bacteremia of the salmonella group. Until the beginning of the 60s this meant an ominous diagnosis with an almost unavoidable fatal prognosis. Presently, this trend has been reverted, mostly due to an earlier diagnosis, the development of more sophisticated imaging techniques, the correct use of broad spectrum bactericidal antibiotics and prompt surgical management. Paradoxically, the incidence of arterial infections has increased in recent years, specially in old people with atherosclerotic abdominal aortic aneurysms, in whom infective endocarditis could not be demonstrated. We describe the case of a 65 year old man, with a history of longstanding non-insulin-dependent diabetes, presenting with protracted fever, weight loss and thigh pain. Blood cultures and serologic studies as well as several echocardiograms yielded negative results. An abdominal CT scan showed an infrarenal aortic aneurysm raising the clinical suspicion of arterial infection of abdominal aorta. The patient underwent surgery because of highly presumptive diagnosis of complicated aortic aneurysm. The resection was followed by an in situ graft. There was no evidence of disruption or gross collection. Samples of the aortic wall and perianeurysmatic fluid grew Salmonella enteritides. We describe the main etiopathogenic and clinic features of the entity highlighting the high sensitivity and specificity of the CT scan in the identification and characterization of infected aortic aneurysm. Certain features may firmly suggest this diagnosis without using preoperative aortography.

Aortic Aneurysm, Abdominal↗
PubMed1995

University of Nebraska Medical Center Liver Transplant Program.

The field of liver transplantation has evolved slowly over the past 5 years. The most important new additions to this field include new immunosuppressive agents and greatly broadened recipient selection criteria. The most compelling problem in transplantation today remains the lack of suitable donors. Innovative surgical techniques, such as auxiliary liver transplantation, extracorporeal support and living-related donation, represent new and important additions to the approach to patients with liver disease.

Academic Medical Centers↗