PubMed Health⌕ Search

Biomedical subjects

S Milstein

Publications and source records attributed to S Milstein.

At least 19 recordsLinked to original sources
PubMed1998

Thermodynamic characterization of an intermediate state of human growth hormone.

The thermal denaturation of recombinant human growth hormone (rhGH) was studied by differential scanning calorimetry and circular dichroism spectroscopy (CD). The thermal unfolding is reversible only below pH 3.5, and under these conditions a single two-state transition was observed between 0 and 100 degrees C. The magnitudes of the deltaH and deltaCp of this transition indicate that it corresponds to a partial unfolding of rhGH. This is also supported by CD data, which show that significant secondary structure remains after the unfolding. Above pH 3.5 the thermal denaturation is irreversible due to the aggregation of rhGH upon unfolding. This aggregation is prevented in aqueous solutions of alcohols such as n-propanol, 2-propanol, or 1,2-propanediol (propylene glycol), which suggests that the self-association of rhGH is caused by hydrophobic interactions. In addition, it was found that the native state of rhGH is stable in relatively high concentrations of propylene glycol (up to 45% v/v at pH 7-8 or 30% at pH 3) and that under these conditions the thermal unfolding is cooperative and corresponds to a transition from the native state to a partially folded state, as observed at acidic pH in the absence of alcohols. In higher concentrations of propylene glycol, the tertiary structure of rhGH is disrupted and the cooperativity of the unfolding decreases. Moreover, the CD and DSC data indicate that a partially folded intermediate with essentially native secondary structure and disordered tertiary structure becomes significantly populated in 70-80% propylene glycol.

Calorimetry, Differential Scanning↗
PubMed1997

The influence of molecular conformation upon the self-assembly of cyclohexane diamide diacids.

BACKGROUND: Information regarding the self-association of small peptide motifs can be used in the design of peptide microstructures. Previous work in our laboratories illustrated the self-association of certain diamide diacids into microcapsules. In this report a series of cyclohexane diamide diacids are investigated. The cyclohexylene (R-C6H10-R) system (with its axial and equatorial requirements) provided an opportunity to study the influence of molecular conformation upon the self-aggregation process. RESULTS: Condensation of the respective cis- and trans-1,2-, 1,3-, and 1,4- cyclohexane dicarboxylic acid platforms with two equivalents of a L-Phe ester followed by deprotection gave the desired diamide diacids. Basic solutions of cis-1,2-, trans-1,3-, and cis-1,4-diamide diacids generated solid microspheres when acidified to pH 2.4. Molecular modeling revealed that 1,3-diaxial interactions favor a helical turn within these diamides. CONCLUSIONS: Access to 'complementary' molecular geometries is needed to self-associate into microscopic architectures.

Amides↗
PubMed1997

Right atrial appendage to right ventricle accessory atrioventricular connection: a case report.

Atrial and ventricular attachments of accessory atrioventricular connections have classically been localized to adjacent atrial and ventricular tissues, and this principle is responsible for the widespread success of radiofrequency catheter ablation. We present anatomical evidence of an unusually located accessory atrioventricular connection, which bridged the atrioventricular ring epicardially, directly from the base of the right atrial appendage to the right ventricle. This observation might offer a new insight into unusual accessory atrioventricular connection locations and may explain why some endocardial radiofrequency catheter ablation procedures might fail.

Adult↗
PubMed1996

Neural influence on protein kinase C isoform expression in skeletal muscle.

Protein kinase C (PKC) is a family of enzymes involved in synapse formation and signal transduction at the neuromuscular junction. Two PKC isoforms, classical PKC alpha and novel PKC theta, have been shown to be enriched in skeletal muscle or localized to the endplate. We examined the role of nerve in regulating the expression of these PKC isoforms in rat skeletal muscle by denervating diaphragm muscle and measuring PKC protein expression at various postoperative times. nPKC theta protein levels decreased 65% after denervation, whereas cPKC alpha levels increased 80% compared with control hemidiaphragms. These results suggest that innervation regulates PKC theta and alpha isoform expression in skeletal muscle. To explore further how nerve regulates PKC expression, we characterized PKC isoform expression in rat myotubes deprived of neural input. Myoblast expression of nPKC theta was low, and the increase in nPKC theta expression that occurred during differentiation into myotubes resulted in levels of nPKC theta significantly below adult skeletal muscle. cPKC alpha expression in myoblastic increased during differentiation to levels that exceeded expression in adult skeletal muscle. Coculturing myotubes within neuroblastoma X glioma hybrid clonal cell line (NG108-15) increased nPKC theta expression, but not cPKC alpha, suggesting that nPKC theta in skeletal muscle and myotubes is regulated by nerve contact or by a factor(s) provided by nerve. Treating myotubes with tetrodotoxin did not affect either basal- or NG108-15 cell-stimulated nPKC theta expression. Together these results suggest that expression of nPKC theta in skeletal muscle is regulated by a transynaptic interaction with nerve that specifically influences nPKC theta expression.

Animals↗
PubMed1996

4-[4-[(2-Hydroxybenzoyl)amino]phenyl]butyric acid as a novel oral delivery agent for recombinant human growth hormone.

A series of N-acetylated, non-alpha, aromatic amino acids was prepared and shown to promote the absorption of recombinant human growth hormone (rhGH) from the gastrointestinal tract. Seventy compounds in this family were tested in vivo in rats. Of the compounds tested, 4-[4-[(2-hydroxybenzoyl)amino]phenyl]butyric acid was identified as a preclinical candidate and was used to demonstrate the oral delivery of rhGH in primates. A significant positive correlation was found between the relative log k' of the delivery agents, as determined by HPLC on an immobilized artificial membrane (IAM) column, and serum rhGH concentrations following oral or colonic dosing in rats. Structure-activity relationships have also been developed on the basis of electronic effects and hydrogen-bonding characteristics of the aromatic amide substituents.

Administration, Oral↗
PubMed1996

Radiation doses during pediatric radiofrequency catheter ablation procedures.

Because RF catheter ablation procedures may be lengthy and are commonly performed in young patients, concern has arisen about radiation dose in this group of patients. This article investigates radiation doses in pediatric patients undergoing RF catheter ablation. Standard fluoroscopic equipment used for diagnostic electrophysiological catheterization studies is technologically capable of dose rates as high as 90 milligray (mGy) per minute to skin and adjacent lung and 260 mGy/min to vertebral bone. Dose rates of this magnitude when used for extended periods of time have been known to cause erythema, pneumonitis, and retardation of bone growth. We measured skin dose rates of nine pediatric patients undergoing RF catheter ablation for tachycardia and calculated doses to the skin using standard dosimetric methods. Fluoroscopic techniques and equipment were studied using a patient simulating phantom. Overlap of fluoroscopic fields was checked using radiotherapy portal verification film, and regions in which doses overlapped from multiple angle exposures were verified using a treatment planning computer. Patient skin dose rates ranged from 6.2-49 mGy/min for patients ranging in age from 2-20 years. Maximum skin doses ranged from 0.09-2.35 Gy. Our data demonstrate the need to directly measure dose rates for individual fluoroscopic equipment and procedural techniques in order to determine whether limitations need to be set for procedural times.

Adolescent↗
PubMed1994

Therapeutic and diagnostic utility of adenosine during tachycardia evaluation in children.

Adenosine has become the drug of choice for termination of regular, normal QRS tachycardia. Initial studies in adult and pediatric patients have shown that the drug is effective for tachycardias using the atrioventricular (AV) node as an integral part of the tachycardia circuit and has few serious side effects. Experience with adenosine administration in children was reviewed to examine the diagnostic and therapeutic usefulness, effective dose, and adverse effects of adenosine. Adenosine was administered to 38 children during 50 separate electrophysiologic evaluations. Eleven patients had structural or acquired heart disease. Tachycardia mechanisms included orthodromic-reciprocating tachycardia using an accessory AV connection (23 patients), primary atrial tachycardia (6 patients), AV node reentrant tachycardia (3 patients), ventricular tachycardia (2 patients), postoperative junctional tachycardia (1 patient), and antidromic-reciprocating tachycardia (1 patient). Adenosine successfully terminated 51 of 53 episodes (96%) of tachycardia using the AV node, 5 of 10 primary atrial tachycardias, 1 of 1 junctional tachycardia, and 1 of 3 ventricular tachycardias. Reinitiation of tachycardia was seen after 16 of 58 successful terminations (28%), reducing the effectiveness to 39 of 53 (74%) for tachycardia requiring the AV node. Average effective dose was 132 micrograms/kg, range 50 to 250 micrograms/kg, and was slightly higher for peripheral (147 micrograms/kg) than for central (120 micrograms/kg) administration. Significant complications occurred in 4 of 38 patients, including atrial fibrillation, accelerated ventricular tachycardia, apnea, and 1 minute of asystole. Although adenosine is useful therapeutically and diagnostically in children with tachycardia, its effectiveness is limited by tachycardia reinitiation and adverse effects. Higher doses may be required for peripheral intravenous administration.

Adenosine↗
PubMed1993

Oral immunization of rats with proteinoid microspheres encapsulating influenza virus antigens.

Influenza virus antigen microspheres were prepared by a pH-dependent process using a protein-like polymer (proteinoid) made by thermal condensation of amino acids. The efficacy of these preparations to induce specific IgG responses when used as oral vaccines in rats was evaluated. A single enteric dose of M1 entrapped in proteinoid microspheres was able to induce a significant IgG response to M1 as early as 2 weeks postdosing, while rats dosed orally with the same M1 total dose (no microspheres) showed no detectable antibody response. An unencapsulated hemagglutinin and neuraminidase (HA-NA) preparation induced a moderate anti HA-NA IgG response. A single enteric dose of HA-NA spheres induced a response in 33% of the rats; this response was up to eight times higher than that observed in the rats dosed with unencapsulated antigen.

Administration, Oral↗
PubMed1993

Anatomical mechanisms explaining damage to pacemaker leads, defibrillator leads, and failure of central venous catheters adjacent to the sternoclavicular joint.

The literature suggests that approximately 93% of all pacemaker lead fractures occur in the segment of the lead lateral to the venous entry, and costoclavicular compression has been implicated. While blood vessels can be compressed by movements of the clavicle, our research suggests that lead and catheter damage in that region is caused by soft tissue entrapment rather than bony contact. Dissection of eight cadavers with ten leads revealed that two entered the cephalic vein, and were not included in the study. Of the other eight leads, four passed through the subclavius muscle, two through the costoclavicular ligament, and two through both these structures before entering the subclavian, internal jugular, or brachiocephalic vein. Anatomical studies demonstrated that entrapment by the subclavius muscle or the costoclavicular ligament could cause repeated flexing of leads during movements of the pectoral girdle. Cineradiology of patients with position dependent catheter occlusion confirmed entrapment by the subclavius muscle. Soft tissue entrapment imposes a static load upon leads and catheters, and repeated flexure about the point of entrapment may be responsible for damage previously attributed to cyclic costoclavicular compression.

Arm↗
PubMed1993

Tetrahydrobiopterin is required for cytokine-induced nitric oxide production in a murine macrophage cell line (RAW 264).

The murine macrophage cell line RAW 264 constitutively synthesizes tetrahydrobiopterin (BH4), the cofactor required for the hydroxylation of the aromatic amino acids and for the production of nitric oxide. Stimulation of the cells with interferon-gamma and lipopolysaccharide induced the production of nitric oxide and increased BH4 levels further. When the cells were stimulated in the presence of 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of BH4 biosynthesis, biopterin levels decreased by 90% within 6 hr, whereas nitrite production was essentially unaffected. Pretreatment of the cells for 12 hr with DAHP decreased intracellular BH4 concentrations by > 95% yet inhibited the cytokine-stimulated production of nitric oxide by only 50%. However, pretreatment with DAHP plus N-acetylserotonin, an inhibitor of sepiapterin reductase, the terminal enzyme of the BH4 biosynthetic pathway, decreased biopterin levels by > 99% and inhibited nitric oxide synthesis by 90%. This inhibition could be reversed by loading the cells with dihydrobiopterin, a precursor of BH4 via the dihydrofolate reductase salvage pathway. In addition, these studies revealed that N-acetylserotonin has a direct inhibitory effect on nitric oxide synthesis, acting in a BH4-independent manner. The results presented here support previous suggestions, based on experiments with isolated enzymes, that BH4 is absolutely required for cytokine-stimulated nitric oxide production in macrophages and they suggest that only a small fraction of the total intracellular BH4 pool in macrophages is utilized in the production of fully active nitric oxide synthase.

Amino Acid Oxidoreductases↗
PubMed1993

Adult day care centres in British Columbia: client characteristics, reasons for referral and reasons for non-attendance.

This paper discusses a 1989 study of new admissions to 22 adult day care centres in British Columbia and compares it to similar studies in the U.S. The B.C. study investigated clients' characteristics, reasons for referral to the centres, and why some referrals did not attend. Of the new admissions, 63% were female and 30% lived alone. Compared to those in American studies, B.C. clients were older and more likely to live with a spouse. The primary medical conditions of B.C. clients were related to diseases of the circulatory system. As for daily activities, 58% could not bathe without supervision and 43% required assistance with dressing. Some 37% were unable to prepare their own meals; 31% needed help with housekeeping and 62% with shopping. The proportion of clients with mental diseases (38%) was similar to that in American adult day care centres. The three most common reasons for referring clients to adult day care centres were: to assist those who were socially isolated; to give family caregivers some respite; and to give clients emotional help. Perceptions varied as to why referred clients did not attend: for continuing care staff there were psychosocial factors; for adult day care staff it was related to characteristics of the service delivery system; and clients themselves cited functional, physical and operational factors (e.g., problems related to hearing and vision, transportation or physical barriers).

Activities of Daily Living↗
PubMed1993

Adult Day Care centres in British Columbia: models, characteristics and services.

Adult Day Care (ADC) is increasingly being recognized as an important sub-system of the continuing care system. This paper reviews models developed in the United States and Britain and compares them, and the services they offer, with centres in British Columbia, Canada. Data on British Columbia are from a study in which all 49 centres in the province provided detailed information about their staffing, operating characteristics, activities and services. The study found B.C. compared favourably in providing services needed by ADC clients. Key differences between the B.C. centres and those in the U.S. and U.K. were: a larger proportion of B.C. centres were not affiliated with any other organization; B.C. centres admitted a range of clients and were less likely to cater exclusively to special needs groups; and, B.C. centres were more likely than centres in the U.S. to provide a number of services such as: dental care, transportation, bathing and physiotherapy.

Adult↗
PubMed1992

Reproducibility of head-up tilt-table testing for eliciting susceptibility to neurally mediated syncope in patients without structural heart disease.

Head-up tilt testing has gained acceptance as a tool for assessing susceptibility to neurally mediated syncopal syndromes (e.g., vasovagal syncope), and is currently being evaluated as a means of testing therapeutic interventions in these conditions. To assess reproducibility of head-up tilt testing and thereby assess the potential of such testing for immediate evaluation of a planned treatment, findings during 2 sequential 80 degrees head-up tilt tests were compared in 23 patients (age range 6.5 to 74 years) undergoing evaluation of syncope of unknown origin. Upright tilt was performed initially in the absence of drugs, and repeated if necessary during pharmacologic provocation by means of isoproterenol infusions of 1 and 3 micrograms/min (tilt 1). End points were syncope, maximal tolerated isoproterenol dose, or a tilt duration of 10 minutes. The second tilt test (tilt 2) was conducted after approximately 30 minutes of supine rest using the maximal provocative conditions used in tilt 1. Fifteen of 23 patients (65%) developed syncope in either tilt 1 or 2, while 8 of 23 (35%) remained asymptomatic. Tilt testing results were concordant (i.e., positive in both tests, or negative in both tests) in 20 of 23 (87%) patients. Concordance was, however, less among tilt-positive patients (12 of 15, 80%) since 3 patients were tilt-positive in tilt 1 only.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Syncope: causes, clinical evaluation, and current therapy.

Syncope is a common clinical problem comprising the sudden loss of both consciousness and postural tone, with a subsequent spontaneous and relatively prompt recovery. Often it is difficult to differentiate a true syncopal spell from other conditions, such as seizure disorders, or from some simple accidents. Even more difficult is the identification of the cause of syncopal episodes. Nonetheless, establishing a definitive diagnosis ia an important task given the high risk of recurrent symptoms. Careful use of noninvasive and invasive cardiovascular studies (including electrophysiologic testing and tilt-table testing) along with selected hematologic, biochemical, and neurologic studies provides, in the majority of cases, the most effective strategy for obtaining a specific diagnosis and for directing therapy.

Diagnosis, Differential↗
PubMed1991

Indications for modification of coexisting dual atrioventricular node pathways in patients undergoing surgical ablation of accessory atrioventricular connections.

Concomitant susceptibility to atrioventricular (AV) node reentrant tachycardia has been demonstrated in certain patients having reentrant tachycardia utilizing accessory AV connections. For those patients undergoing accessory connection ablation, AV node surgical modification may be warranted during the same operative procedure. To assess indications for a combined operative procedure, this study evaluated potential predictors of subsequent spontaneous AV node reentrant tachycardia in patients undergoing ablation of accessory AV connections. Among 62 consecutive patients undergoing surgical ablation of an accessory AV connection, 13 (21%) manifested dual AV node pathways. The latter were identified preoperatively in five patients (four with concealed and one with bidirectional accessory connections) and postoperatively in seven (all seven with bidirectional accessory connections). In one patient with a bidirectional accessory connection, dual AV node pathways could not be demonstrated preoperatively, but AV node reentrant tachycardia was induced. Operative ablation of an accessory connection was successful in all patients. However, postoperatively, 2 of the 13 patients had inducible AV node reentrant tachycardia, 5 had AV node "echo" beats and 6 had no inducible arrhythmia. During 26 +/- 7 months of follow-up study, the two patients with inducible AV node reentrant tachycardia postoperatively had symptomatic AV node reentrant tachycardia. In addition, the one patient with inducible AV node reentrant tachycardia preoperatively had recurrence of this tachycardia 4 months after attempted surgical modification of the AV node. Consequently, although dual AV node pathways appear to be common in patients undergoing surgical ablation of an accessory AV connection (21%), only a small group (3 of 13) of these patients are at risk for subsequent clinical AV node reentrant tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗