Biomedical subjects

J Alexander

Publications and source records attributed to J Alexander.

At least 307 records · Page 17Linked to original sources

PubMed1994

In vitro formation and degradation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) protein adducts.

Adduct formation between the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and rat serum albumin (RSA) was studied in vitro using hepatic microsomes isolated from polychlorinated biphenyl-induced rats. With 1-methyl-2-nitro-6-phenylimidazo[4,5-b]pyridine (2-nitro-PhIP) as starting material, four main products were formed. Pretreatment of RSA with beta-mercaptoethanol markedly increased the yield of one of them. In this adduct, the C-2 of PhIP was linked to cysteine of RSA at position 34 in a C-S linkage. With N2-acetoxy-PhIP as starting material, unstable conjugates were formed with RSA as well as with glutathione (GSH) and cysteine. The suggested structures of the GSH and cysteine conjugates, GSH-S-N2-PhIP and cysteine-S-N2-PhIP respectively, are based on mass spectra and UV spectra. The degradation of the conjugates of GSH and cysteine as well as of the protein adduct were monitored. They all resulted in the same degradation product, identified as 2-amino-5-hydroxy-1-methyl-6-phenylimidazo[4,5-b]pyridine (5-hydroxy-PhIP).

Animals↗

PubMed1994

TCR antagonism and T cell tolerance can be independently induced in a DR-restricted, hemagglutinin-specific T cell clone.

The outcome of TCR engagement with peptide-MHC is of central importance for the immune response of the host. TCR antagonism is one phenomenon known which is characterized by selective inhibition of T cell responses by non-stimulatory antigen analogs. T cell anergy is another state resulting in T cell unresponsiveness, generally characterized by lack of proliferation and lymphokine production. In the present study, the relationship between TCR antagonism and T cell anergy was examined by using protocols known to induce either phenomenon. Re-isolation experiments demonstrated that antagonized T cells were not tolerized, in that they were fully capable of responding to a subsequent antigen challenge. Conversely, while high doses of soluble antigen could efficiently induce T cell tolerance, TCR antagonists, either alone or in conjunction with suboptimal antigen doses, could not. Taken together, these data demonstrate that TCR antagonism and T cell tolerance are phenomena independent of each other.

Antigen-Presenting Cells↗

PubMed1994

False aneurysm of the medial inferior genicular artery after intramedullary nailing of the tibia.

Although rare, arterial false aneurysm about the knee has been a well-documented complication of many types of surgery. False aneurysms have been reported after such procedures as open meniscectomy, synovectomy, arthroscopy, total knee arthroplasty, and proximal tibial osteosynthesis. Arteries injured in these procedures have included the popliteal artery and the descending, medial superior, medial inferior, lateral superior, and lateral inferior genicular arteries. An extensive review of the literature showed no cases of false aneurysm after intramedullary nailing of the tibia.

Adult↗

PubMed1994

Influence of macrophage resistance gene Lsh/Ity/Bcg (candidate Nramp) on Toxoplasma gondii infection in mice.

Functional studies have shown that the murine macrophage resistance gene Lsh/Ity/Bcg (candidate Nramp) regulates macrophage priming/activation for antimicrobial activity via the tumour necrosis factor-alpha (TNF-alpha)-dependent production of reactive nitrogen intermediates. Since Toxoplasma gondii also parasitizes macrophages, is a stimulator of endogenous TNF-alpha release, and is sensitive to nitric oxide-mediated killing in activated macrophages, studies were carried out using chromosome 1 congenic mouse strains to determine whether Lsh influences T. gondii infection. Two interesting observations were made: (i) contrary to expectation, mice carrying the Lsh-resistant allele died earlier over the acute phase of infection than Lsh-susceptible mice; and (ii) Lsh-resistant mice which survived this acute phase of infection showed lower brain cyst numbers than the Lsh-susceptible mice. Whilst the latter occurred independently of route of inoculation (oral, intraperitoneal, or subcutaneous), the former was influenced both by the route of inoculation and the genetic background on which the Lsh-resistant allele had been isolated. Hence, following oral administration of 20 brain cysts of the RRA strain of T. gondii, mice carrying the Lsh-resistant allele on a B10 genetic background showed a significantly enhanced rate of mortality over the acute (first 8-12 days) phase of infection than B10 Lsh-susceptible mice. Although this acute phase of infection in B10 background mice was accompanied by an increase in serum TNF-alpha levels in both Lsh-resistant and -susceptible mouse strains, early mortality preceded the TNF-alpha peak, and administration of neutralizing rabbit anti-TNF-alpha did not significantly enhance survival. Hence, inflammatory mediators other than TNF-alpha appear to be responsible for the increased rate of acute mortality observed in resistant mice. Infection intraperitoneally led to delayed mortality in B10 mice, with the mean time to 50% mortality now being significantly longer in Lsh-resistant than in Lsh-susceptible mice. On a BALB genetic background, it was the i.p. route of infection which led to acute mortality and more rapid death in the Lsh-resistant strain. When a less virulent inoculum was used and mortality delayed, Lsh-susceptible mice died more rapidly, and i.p. administration of rabbit anti-TNF-alpha led to 100% mortality between days 8 and 10 of infection in both susceptible and resistant mouse strains, consistent with a crucial protective role for TNF-alpha during this phase of infection.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

The demonstration of an essential role for macrophages in the in vivo generation of IgG2a antibodies.

BALB/c mice were depleted of macrophages by intravenous inoculation of dichloromethylene diphosphonate entrapped in liposomes 24 h before primary and 24 h before secondary sensitization intravenously with 100 micrograms bovine serum albumin (BSA) or ovalbumin (OVA). The effectiveness of macrophage depletion was confirmed by immunocytochemistry. Five days and 14 days after secondary challenge with BSA, plasma samples from these and control mice inoculated with empty liposomes were examined for the production of BSA-specific IgG1 and IgG2a antibodies. Macrophage depletion resulted in a significantly increased production of the Th2 lymphocyte-associated IgG1 isotype, while the production of specific IgG2a antibodies, produced under the influence of Th1 cells, was totally ablated. Similar results were obtained when OVA was used as the test antigen. Furthermore, analysis of interferon-gamma (IFN-gamma) production after antigen or concanavalin A (Con A) restimulation in vitro indicated that macrophage depletion in vivo significantly reduced production of this Th1 cell-associated cytokine. These results provide strong in vivo and in vitro evidence for the macrophage being the antigen-presenting cell population responsible for Th1 cell activation.

Animals↗

PubMed1994

Temporal differences in the expression of mRNA for IL-10 and IFN-gamma in the brains and spleens of C57BL/10 mice infected with Toxoplasma gondii.

C57BL/10 Sc Sn (B10) mice infected orally with Toxoplasma gondii tissue cysts were killed at regular intervals up to day 116 post infection (p.i.) and their brains excised. These were used either to count the total number of cysts in the brain, for RNA purification or histopathological studies. Mortality levels in a parallel group of T. gondii infected B10 mice were also monitored and regular plasma samples taken to measure specific antibody production. Seventy per cent of mice died within the first 35 days of infection. Thereafter deaths were infrequent. Inflammation in the brain was apparent from day 10 onwards and by day 25 there was widespread astrocyte activation, perivascular cuffing, meningitis and extensive encephalitis. Total cyst numbers increased rapidly from day 15 to day 35 when they peaked. By day 60, however, cyst numbers had dropped dramatically and this decrease continued through to day 116. Using the polymerase chain reaction mRNA transcripts for IFN-gamma were detected from the first time point sampled, day 25 p.i., until the end of the study. Transcripts for IL-10, an inhibitor of IFN-gamma production, release and activity, were not detected until day 70. The predominant antibody detected against T. gondii was IgG2a but not IgG1. Significantly transcripts for IFN-gamma were found in the spleens of infected but not non-infected animals. Our results suggest that an inflammatory response associated with IFN-gamma production in B10 mice eventually controls T. gondii infection. After the cyst burden has dropped dramatically transcripts for IL-10 are detected in the brain, perhaps to suppress inflammation, and limit pathology.

Animals↗

PubMed1994

Developing theories of mind: understanding concepts and relations between mental activities.

The purpose of the study was to expand our knowledge of older children's understanding of the unique features and potential relations existing among mental activities. 8- and 10-year-olds as well as adults were asked to rate the similarity of pairs of mental activity scenarios in terms of how their mind would be used for each one. The scenarios involved primarily Prospective Memory, List Memory, Recognition Memory, Comprehension, Interference, Planning, Comparison, or Selective Attention. There was a developing tendency to organize mental activities on the degree to which memory was a component of the activity. Several distinctions were also more likely to be made with age: the distinction between recall and recognition, the distinction between the roles of internal and external cues in mediating cognitive activity, and the distinction among the various roles of attentional processes in regulating input from the sensory world. Together, these findings suggest that a constructivist theory of mind develops in later childhood.

Adolescent↗

PubMed1994

Antigen analogs/MHC complexes as specific T cell receptor antagonists.

Recent studies demonstrated that antigen analogs can act as powerful and specific inhibitors of T cell activation, leading to the formulation of the concept that antigen analog/MHC complexes may act as antagonists of the T cell receptor (TCR). TCR antagonism appears to be associated with engagement of the TCR below a crucial affinity threshold necessary for full T cell activation. Studies addressing the molecular mechanism of this effect suggest that TCR antagonists could act by interfering with membrane-related events (such as proper receptor clustering) that might precede intracellular signaling. Discovery of the TCR antagonism phenomenon also suggested a possible rational approach to antigen-specific immunointervention in allergies and autoimmune diseases. The feasibility of such an approach is now being actively investigated. Finally, TCR antagonist peptides may provide a useful tool to probe TCR-peptide/MHC interactions involved in the process of thymic education.

Animals↗

PubMed1994

Parenting and childrearing attitudes among high school students.

A descriptive study to assess parenting and childrearing attitudes was conducted among 502 high school students in a greater metropolitan area in the Southeast. The Adult-Adolescent Parenting Inventory (Bavolek, 1984) was used to identify students' scores on four constructs associated with abusive parenting: inappropriate parental expectations, lack of empathy toward the child, value of physical punishment, and parent-child role reversal. Several group differences were found by sex, race, grade, and birth order. Ten percent of students scored consistently low and could be targeted for education programs to increase parenting knowledge and skill.

Adolescent↗

PubMed1994

Metabolism of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b] pyridine (PhIP) in isolated liver cells from guinea pig, hamster, mouse, and rat.

The metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the most abundant compound of the aminoimidazoazaarens (AIA) group of mutagens/carcinogens isolated from the crust of fried and broiled meat, was examined in freshly isolated hepatocytes from untreated rat, mouse, hamster, and guinea pig. Activation was evaluated by the total level of covalent binding of PhIP to macromolecules. Rat hepatocytes had the lowest rate of metabolism, both to reactive and detoxified metabolites. The products were identified as 4'-PhIP-sulfate, PhIP-glucuronide, and N(OH)-PhIP-glucuronide. The ring hydroxylation rate was much greater in mouse hepatocytes, the main products being 4'-PhIP-sulfate and 4-hydroxy-PhIP. The level of covalent binding in the mouse hepatocytes exceeded those of the rat and guinea pig at high doses of PhIP. An extensive metabolism was seen in guinea pig hepatocytes, the major products being 4'-PhIP-sulfate, 4'-O-PhIP glucuronide, PhIP-glucuronide, and N(OH)-PhIP-glucuronide. In addition, several other unknown metabolites were formed. However, the amount of covalent binding in guinea pig hepatocytes was similar to that in rat hepatocytes. Covalent binding of PhIP metabolites was highest in hamster hepatocytes. Three of the main metabolites were identified as 4'-PhIP-sulfate, 4'-O-PhIP-glucuronide, and PhIP-glucuronide, but several unknown PhIP metabolites also were formed. Only minor amounts of N(OH)-PhIP-glucuronide were produced in the hamster. The present study shows that both the direct detoxification of PhIP and further conjugation of the 2-hydroxylamino-PhIP to reactive and/or detoxified metabolites are important for the resulting covalent binding.

Animals↗

PubMed1994

A survey of preferred approach to inguinal hernia repair: laparoscopic or inguinal incision?

The recent interest in laparoscopic surgery has raised some concerns that large numbers of surgeons were recommending this "minimally invasive" approach in procedures such as inguinal herniorrhaphy before the availability of adequate data regarding safety and benefits. To determine current experience and preference levels for laparoscopic inguinal herniorrhaphy (LH), we conducted a mail survey of New Jersey surgeons. Of 531 respondents, 430 (81%) preferred a traditional inguinal incision approach over a laparoscopic approach (8%). Of 344 general surgeon respondents, 227 (66%) had experience with laparoscopic cholecystectomy, but only 56 (16%) had experience with LH. This latter group had performed only an average of 9.2 laparoscopic herniorrhaphies, with a median of five cases. Most of these 56 surgeons with LH experience indicated a preference for inguinal incision herniorrhaphy although 19 surgeons who had performed 10 or more LH cases showed a slight preference for LH (11 to 8). The primary reasons for choosing LH included "less pain" and "quicker recovery." The primary reasons for choosing inguinal incision herniorrhaphy included having a "better known procedure" and avoiding general anesthesia. Our survey indicates that the laparoscopic approach to inguinal hernia repair has currently accumulated few proponents in the surgical community since many surgeons are waiting for more data on the procedure.

Hernia, Inguinal↗

PubMed1993

The inhibition of different T cell lines specific for the same antigen with TCR antagonist peptides.

To further understand and evaluate the phenomenon of TCR antagonism, we wished to determine whether analogs of an antigenic determinant could antagonize a specific polyclonal response. To this end, the ability of TCR antagonist peptides to inhibit a panel of five different DR4w4-restricted, influenza hemagglutinin 307-319-specific T cell lines was examined. An analysis of their V beta and J beta usage indicated that each of these five T cell lines expressed different TCR. A series of HA 307-319 single amino acid substituted analogs were used to determine the fine Ag specificities of the different lines. Ag analogs that demonstrated little or no stimulatory capacity were then examined for their ability to act as TCR antagonists by inhibiting the proliferative response of these five lines. Overall, 17 different peptide analogs capable of antagonizing at least one T cell line were identified. Although no single analog was capable of inhibiting all five T cell lines, two different analogs were identified that were capable of inhibiting four of five of the T cell specificities examined.

Amino Acid Sequence↗

PubMed1993

[Vitamin A and toxicity. Should pregnant women and small children reduce their intake of liver products and vitamin A?].

It has been recognized for many years that high doses of vitamin A-metabolites may be teratogenic. Recently, it was found that the content of vitamin A in liver and liver products was much higher than the value prescribed in dietary tables. Thus, in many countries, health personnel advised pregnant women to reduce their intake of liver and liver products. Officials in Norway, however, have not given similar advice to Norwegian women. The background for this point of view is discussed in the present paper.

Female↗

PubMed1993

A linoleate-enriched cheese product reduces low-density lipoprotein in moderately hypercholesterolemic adults.

OBJECTIVE: To test the effect of substituting a modified-fat cheese product into the diets of hypercholesterolemic adults. DESIGN: A 4-month, randomized, double-blind, crossover substitution trial. SETTING: General community outpatient study. PARTICIPANTS: Twenty-six healthy adult volunteers (17 men, 9 women) with moderate hypercholesterolemia (total cholesterol > 5.69 mmol/L but < 7.24 mmol/L). INTERVENTION: Daily substitution of 100 g of cheese, either partial skim-milk mozzarella or modified-fat (vegetable oil) mozzarella cheese product, into participants' normal diets. Participants consumed an assigned cheese for 2 months, at which time they crossed over to consume the other study cheese. MAIN OUTCOME MEASURES: Plasma lipid and apolipoprotein levels were measured at baseline and at 2 and 4 months after initiation of the study. Compliance was assessed by body weight and by biweekly dietary records and interviews. RESULTS: No differences in weight or in the amount or type of calories consumed were found during the study. No statistically significant changes in lipid values resulted from consumption of mozzarella cheese. Modified-fat cheese substitution resulted in a decreased low-density lipoprotein cholesterol level when compared with levels at both baseline (-0.28 mmol/L; 95% Cl, -0.14 to -0.42 mmol/L) and during consumption of the skim-milk mozzarella cheese (-0.38 mmol/L; 95% Cl, -0.2 to -0.70 mmol/L). Findings for total cholesterol were similar. High-density lipoprotein cholesterol, plasma triglyceride, and apolipoprotein A-l and B-100 levels were unaltered. Both sexes responded similarly. CONCLUSIONS: A linoleate-enriched cheese product, in the absence of any other changes in diet or habits, substituted into the normal diets of hypercholesterolemic adults reduced low-density lipoprotein and plasma cholesterol levels.

Adult↗

PubMed1993

Intracellular transport of class I MHC molecules in antigen processing mutant cell lines.

Intracellular transport and stability of class I MHC glycoproteins depends on the assembly of H chain, beta 2-microglobulin, and peptide. The Ag processing mutant cell lines T2 and RMA-S have defects in peptide loading of class I, resulting in reduced cell surface expression of class I molecules. Expression of class I molecules in the murine cell line RMA-S can be induced at 26 degrees C, suggesting that they are transported to the cell surface, but are unstable. However, most human class I molecules in T2 are poorly expressed at the cell surface, even at 26 degrees C. To directly compare the transport of human and mouse alleles in RMA-S and T2, the human alleles HLA-A2, A3, and B27 were transfected into RMA-S along with human beta 2-microglobulin, and the mouse alleles H-2Kb and Db were transfected into T2. Surface expression of HLA-A3 and B27 in RMA-S remained less than 10% of wild-type levels at 26 degrees C. H-2Kb and Db in both cell lines, however, were expressed at 20 to 30% wild-type levels at 37 degrees C and could be induced to wild-type levels at 26 degrees C or with peptides. The selective expression of murine class I glycoproteins at the cell surface of T2 is not because of their greater stability when associated with human beta 2m, since H-2Kb and Db H chain/human beta 2m complexes dissociate more rapidly in vitro than HLA-A3 and B27 complexes. These results suggest that the difference in transport between human and mouse class I in T2 reflects a fundamental structural property of the class I glycoproteins.

Alleles↗

PubMed1993

Effect of T-cell receptor antagonism on interaction between T cells and antigen-presenting cells and on T-cell signaling events.

T-cell receptor (TCR) antagonism induced by complexes of antigen analogue with major histocompatibility complex (MHC) molecules results in efficient inhibition of antigen-dependent T-cell responses. We have investigated some of the possible mechanisms by which TCR antagonists bound to the MHC molecules of antigen-presenting cells (APCs) can inhibit T-cell activation. Using a nonstimulatory analogue of the antigenic peptide influenza hemagglutinin-(307-319), we showed that MHC/antagonist complexes completely inhibit very early intracellular events of antigen-dependent T-cell activation, such as inositol phosphate turnover and Ca2+ influx. In a parallel series of experiments, the effect of TCR antagonist peptide on membrane-related activation events was also investigated. It was found that MHC/antagonist complexes on the surface of APCs did not induce stable conjugates with T cells and, most interestingly, did not inhibit antigen-induced conjugate formation. Thus, our data suggest that antagonistic peptides do not interfere with the cellular events that are required for stable T-cell/APC conjugate formation but do inhibit early biochemical events required for T-cell proliferation. The data are discussed with respect to the role of surface receptor clustering in TCR antagonism.

Animals↗

PubMed1993

Alterations in mitochondrial branched-chain amino acid metabolism in brain in acute hyperammonemic states.

Production of 14CO2 and [14C]branched-chain keto acids (BCKA) was determined from [U-14C]branched-chain amino acids along with the activities of branched-chain amino acid transaminase (BCAA-T) and branched-chain keto acid dehydrogenase (BCKA-DH) in mitochondria isolated from the cerebral cortex of normal and hyperammonemic rats. Results indicated that the production of CO2, but not of keto acids, was suppressed while the activities of BCAA-T and BCKA-DH were not adversely affected in the mitochondria of hyperammonemic rats. Suppression in the oxidation of BCAA in hyperammonemic states was found to be due to increased efflux of BCKA from mitochondria.

Amino Acid Oxidoreductases↗

PubMed1993

Functional consequences of engagement of the T cell receptor by low affinity ligands.

The mechanisms involved in TCR antagonism by Ag analog/MHC have been analyzed. A detailed structure-activity relationship study indicated that modification of any of the major T cell contact residues of the peptide molecule can yield a powerful antagonist. It was also shown that as the analog structure increased in similarity to the Ag, the capacity to antagonize Ag-TCR interaction increased up to the point that the analogs themselves became antigenic. These data strongly suggest an affinity-related mechanism whereby a certain affinity is required for signaling through the TCR, and that below this level there can be sufficient affinity to engage the receptor such that triggering does not occur and antagonism can be detected. Taking advantage of this information, antagonist peptides active down to the 10 nM range were engineered. Thus, this approach demonstrates for the first time a rational approach to designing effective, selective low m.w. compounds with high potential in treatment of allergies and autoimmune diseases.

Amino Acids↗