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Biomedical subjects

J Barnett

Publications and source records attributed to J Barnett.

At least 19 recordsLinked to original sources
PubMed1992

Regulated expression of the human acetylated low density lipoprotein receptor gene and isolation of promoter sequences.

The acetylated low density lipoprotein (AcLDL) receptor is expressed on tissue macrophages after their differentiation from monocyte precursors and has been proposed to play a role in the generation of foam cells in atherosclerotic lesions. In the present studies, THP-1 human monocytic leukemia cells were used to investigate mechanisms responsible for expression of the AcLDL receptor gene after treatment with phorbol 12-myristate 13-acetate (TPA). TPA-dependent accumulation of AcLDL receptor mRNA was not detected until after a lag phase of 12 hr and was blocked by concurrent treatment with cycloheximide. In addition, the TPA-dependent induction of AcLDL receptor activity and mRNA levels was inhibited by retinoic acid and dexamethasone treatment. Isolation and sequence analysis of the promoter regions for the human and bovine AcLDL receptor genes indicated high sequence similarity. Binding sites for AP-1 proteins or other known transcription factors were not conserved between the two species, suggesting that novel factors are required for AcLDL receptor expression.

Base Sequence↗
PubMed1991

Extracorporeal lithotripsy. An important adjunct in the nonoperative management of retained or recurrent bile duct stones.

Retained or recurrent bile duct stones can be successfully removed in up to 80% to 85% of patients with the use of percutaneous or endoscopic techniques. However, problems related to difficult biliary access, large stones, and biliary strictures may decrease the success rate of this approach. We evaluated the safety and efficacy of extracorporeal shock-wave lithotripsy (ESWL) in 16 patients with complicated biliary stones treated prospectively over a 24-month period. Successful stone fragmentation was achieved in 15 patients (94%) using a Dornier HM3 lithotripter (average of 2290 shocks at 22 kV). Three patients (19%) required a second ESWL treatment. Biliary clearance of stone fragments was spontaneous in seven (43%) of the patients and required additional treatment in eight (57%) of the patients. Complications from ESWL were minor and included transient hematuria and ecchymoses at the skin entry site. Extracorporeal shock-wave lithotripsy failed in one patient (6%) with a biliary stricture and surgery was required. At hospital discharge, all patients were asymptomatic and stone free. Treatment with ESWL appears to be a safe and effective adjunct for selected patients with complex biliary stone disease.

Adult↗
PubMed1991

Physicochemical characterization of recombinant human nerve growth factor produced in insect cells with a baculovirus vector.

Recombinant human nerve growth factor (rhNGF) secreted by insect cells was purified by ion-exchange and reversed-phase chromatography to near homogeneity. The N-terminus of the secreted molecule was analogous to that of mouse salivary gland NGF. In its native conformation, the insect cell produced rhNGF molecules were homodimers consisting of 120 amino acid polypeptide chains. Mature rhNGF was found not to be significantly glycosylated (less than 0.08 mol of N-acetylglucosamine/mol of protein). The rhNGF was homogeneous with regard to molecular weight and amino acid sequence. Isoelectric focusing resolved the rhNGF into one major and one minor component. Because rhNGF from insect cells can be obtained in large quantities, purified to near homogeneity, and is similar to natural NGF with regard to physicochemical properties and biological activity, it is suitable for further evaluation in animal models as a therapeutic molecule for neurodegenerative diseases such as Alzheimer's disease.

Amino Acid Sequence↗
PubMed1990

High-density lipoprotein inhibits the oxidative modification of low-density lipoprotein.

Oxidatively modified low-density lipoprotein (LDL), generated as a result of incubation of LDL with specific cells (e.g., endothelial cells, EC) or redox metals like copper, has been suggested to be an atherogenic form of LDL. Epidemiological evidence suggests that higher concentrations of plasma high-density lipoprotein (HDL) are protective against the disease. The effect of HDL on the generation of the oxidatively modified LDL is described in the current study. Incubation of HDL with endothelial cells, or with copper, produced much lower amounts of thiobarbituric acid-reactive products (TBARS) as compared to incubations that contained LDL at equal protein concentrations. Such incubations also did not result in an enhanced degradation of the incubated HDL by macrophages in contrast to similarly incubated LDL. On the other hand, inclusion of HDL in the incubations that contained labeled LDL had a profound inhibitory effect on the subsequent degradation of the incubated LDL by the macrophages while having no effect on the generation of TBARS or the formation of conjugated dienes. This inhibition was not due to the modification of HDL as suggested by the following findings. (A) There was no enhanced macrophage degradation of the HDL incubated with EC or copper alone, together with LDL, despite an increased generation of TBARS. (B) HDL with the lysine groups blocked (acetyl HDL, malondialdehyde (MDA) HDL) was still able to prevent the modification of LDL and (C) acetyl HDL and MDA-HDL competed poorly for the degradation of oxidatively modified LDL. It is suggested that HDL may play a protective role in atherogenesis by preventing the generation of an oxidatively modified LDL. The mechanism of action of HDL may involve exchange of lipid peroxidation products between the lipoproteins.

Animals↗
PubMed1990

Synthetic HIV-2 protease cleaves the GAG precursor of HIV-1 with the same specificity as HIV-1 protease.

A 99-amino acid protein having the deduced sequence of the protease from human immunodeficiency virus type 2 (HIV-2) was synthesized by the solid phase method and tested for specificity. The folded peptide catalyzes specific processing of a recombinant 43-kDa GAG precursor protein (F-16) of HIV-1. Although the protease of HIV-2 shares only 48% amino acid identity with that of HIV-1, the HIV-2 enzyme exhibits the same specificity toward the HIV-1 GAG precursor. Fragments of 34, 32, 24, 10, and 9 kDa were generated from F-16 GAG incubated with the protease. N-terminal amino acid sequence analysis of proteolytic fragments indicate that cleavage sites recognized by HIV-2 protease are identical to those of HIV-1 protease. The verified cleavage sites in F-16 GAG appear to be processed independently, as indicated by the formation of the intermediate fragments P32 and P34 in nearly equal ratios. The site nearest the amino terminus is quite conserved between the two viral GAG proteins (...VSQNY-PIVQN...in HIV-1,...KGGNY-PVQHV...in HIV-2). In contrast, the putative second site (...IPFAA-AQQKG...) of HIV-2 GAG shares minimal sequence identity with site 2 of HIV-1 GAG (...SATIM-MQRGN...). These sequence variations in the substrates suggest higher order structural features that may influence recognition by the proteases. Pepstatin A inhibits HIV-2 protease, whereas 1,10-phenanthroline and phenylmethylsulfonylfluoride do not; these results are in agreement with the finding that proteases of HIV and other retroviruses are aspartyl proteases.

Amino Acid Sequence↗
PubMed1990

Human beta nerve growth factor obtained from a baculovirus expression system has potent in vitro and in vivo neurotrophic activity.

A baculovirus expression vector, which contains the coding sequences for human prepro (beta) nerve growth factor under control of the viral polyhedrin promoter, was constructed. Upon infection of insect cells with the recombinant virus, mature human beta nerve growth factor (rhNGF) was released into the culture fluid. The mature rhNGF was biologically active since rat pheochromocytoma (PC12) and human neuroblastoma (SH-SY5Y) cells were induced to extend neurites upon treatment with this material. This activity was abolished by treating with antiserum prepared against mature mouse beta NGF (mNGF). When compared with mNGF, rhNGF more rapidly elicited the differentiation response in both PC12 and SH-SY5Y cells. In an in vivo assay of cholinergic cell survival, rhNGF was nearly as potent as mNGF in protecting cholinergic neurons from degeneration following a fimbria-fornix lesion. These results show that the baculovirus expression system provides quantities of biologically potent human beta NGF suitable for a comprehensive program of research to ascertain beta NGF's potential as a therapeutic agent for the treatment of Alzheimer's disease.

Animals↗
PubMed1990

Low density lipoprotein rich in oleic acid is protected against oxidative modification: implications for dietary prevention of atherosclerosis.

Oxidative modification of low density lipoprotein (LDL) enhances its potential atherogenicity in several ways, notably by enhancing its uptake into macrophages. In vivo studies in the rabbit show that inhibition of LDL oxidation slows the progression of atherosclerotic lesions. In the present studies, rabbits were fed either a newly developed variant sunflower oil (Trisun 80), containing more than 80% oleic acid and only 8% linoleic acid, or conventional sunflower oil, containing only 20% oleic acid and 67% linoleic acid. LDL isolated from the plasma of animals fed the variant sunflower oil was highly enriched in oleic acid and very low in linoleic acid. These oleate-rich LDL particles were remarkably resistant to oxidative modification. Even after 16-hr exposure to copper-induced oxidation or 24-hr incubation with cultured endothelial cells, macrophage uptake of the LDL was only marginally enhanced. The results suggest that diets sufficiently enriched in oleic acid, in addition to their LDL-lowering effect, may slow the progression of atherosclerosis by generating LDL that is highly resistant to oxidative modification.

Animals↗
PubMed1990

Phospholipase A2 activity of low density lipoprotein: evidence for an intrinsic phospholipase A2 activity of apoprotein B-100.

During oxidative modification of low density lipoprotein (LDL) there is extensive degradation of phosphatidylcholine (PtdCho) to lysophosphatidylcholine (lyso-PtdCho), with the removal of fatty acids from the 2 position. The phospholipase A2 (PLA2) activity responsible for hydrolysis is closely associated with LDL. By use of lipoxygenase-oxidized 2-[1-14C]linoleoyl PtdCho as the substrate and delipidated apoprotein B (apo-B), evidence is presented to show that (i) the activity is destroyed progressively during the oxidative modification of LDL; (ii) p-bromophenacyl bromide (pBPB), a histidine modifier that inhibits the oxidative modification of LDL, also substantially inhibits the PLA2 activity; and (iii) photooxidation of LDL in the presence of Rose Bengal completely inactivates the enzyme with concomitant loss of apo-B histidine residues. High molecular weight proteins from delipidated LDL, separated by polyacrylamide gel electrophoresis, showed PLA2 activity. It is suggested that apo-B itself may possess PLA2 activity.

Amino Acids↗
PubMed1990

Changes in MMPI profile levels of chronic low back pain patients following successful treatment.

The present study evaluated changes in the Minnesota Multiphasic Personality Inventory (MMPI) profile levels of chronic low back pain (CLBP) patients following successful treatment for their disability. A total of 69 patients were evaluated at admission and 6 months after completing the treatment program. Results demonstrated significant decreases of the Hysteria, Depression, and Hypochondriasis scales toward normal ranges at the 6-month evaluation. These results indicate that MMPI profile levels of CLBP patients are significantly reduced to normal ranges following successful treatment.

Adult↗
PubMed1989

Strategy of acne therapy with long-term antibiotics.

A study of the outcome of conventional antibiotic treatment in 543 patients with acne was performed. All were treated initially with erythromycin 1 g/day and topical 5% benzoyl peroxide. The median improvement at 6 months was 78%, with an interquartile range of 67-90%. Four-hundred and eight of the 492 who completed 6 months' treatment showed over 50% improvement and 247 of the 279 patients treated for a subsequent 6 months with benzoyl peroxide alone, continued to do well. Another subgroup of 174 patients, was continued for 6 months with systemic antibiotic and 5% benozyl peroxide. No significant benefit was gained, however, by maintaining successfully treated patients on a further 6 months of systemic antibiotics. Of the 84 patients who did less well, 18 were given alternative treatment (Diane, isotretinoin). The other 60, subsequently referred to as slow responders, were continued on antibiotics (erythromycin, 31; minocin, 29; cotrimoxazole, 4; trimethoprim, 2) and benzoyl peroxide. Those prescribed minocycline for the second 6 months appeared to have greater benefit (64%) than those receiving erythromycin (57%). This level of improvement was still lower than that seen in those who responded well within 6 months (78%). Of the risk factors analysed, the poorest response occurred in males with truncal acne. Age at presentation, duration and severity did not adversely affect therapeutic outcome. Side-effects were minimal.

Acne Vulgaris↗
PubMed1988

Teratological evaluations of atrazine technical, a triazine herbicide, in rats and rabbits.

Atrazine technical was evaluated for its embryotoxic, fetotoxic, and teratogenic potential in both rats and rabbits. The compound was orally administered at doses of 0, 10, 70, or 700 mg/kg.d to groups of rats on gestational d 6-15, while rabbits were administered doses of 0, 1, 5, or 75 mg/kg.d on gestational d 7-19. Maternal toxicity was observed at doses greater than or equal to 70 mg/kg.d in rats and at doses greater than or equal to 5 mg/kg.d in rabbits. Minor fetal effects, concurrent with maternal toxicity, were observed in rats at doses greater than or equal to 70 mg/kg.d. Among rabbits, fetal effects concurrent with severe maternal toxicity were only observed at the 75 mg/kg.d dose level. There were no adverse maternal or fetal effects in either rats or rabbits at the low dose levels. These findings indicated that pregnant rabbits were more sensitive than pregnant rats to the effects produced by atrazine technical and the compound was not teratogenic at maternally toxic dose levels in either species.

Abnormalities, Drug-Induced↗
PubMed1987

Use of directed mutagenesis to probe the role of tyrosine 198 in the catalytic mechanism of carboxypeptidase A.

Derivatization of Tyr198 in carboxypeptidase A (CPA) results in lowered catalytic activity toward peptide substrates (Cueni, L., and Riordan, J.F. (1978) Biochemistry 17, 1834-1842). We have synthesized via directed mutagenesis a rat CPA variant [Phe198] CPA containing a Tyr198-to-Phe substitution in order to test whether the phenolic hydroxyl plays a critical role in catalysis. A double mutant [Phe193, Phe248]CPA in which both Tyr198 and Tyr248 have been replaced by phenylalanine has also been engineered. Enzymatic characterization of [Phe198]CPA indicates that the Tyr198 hydroxyl is not obligatory for the hydrolysis of peptide and ester substrates. Furthermore, parallel studies with [Phe198, Phe248]CPA show that simultaneous removal of both the Tyr198 and Tyr248 hydroxyls does not abolish catalytic activity. Analysis of the acetylated derivatives of [Phe198]CPA, [Phe248]CPA, and [Phe198, Phe248]CPA establishes that Tyr198 and Tyr248 are the active site tyrosines which are modified by N-acetylimidazole. In addition, the perturbations of enzymatic activity which accompany acetylation of native CPA can be largely assigned to derivatization of Tyr248. The changes in the kinetic constants of substrate hydrolysis due to the Tyr198-to-Phe substitution are manifested as small decreases in the kcat values, but the Km values are essentially unaffected. This exclusive effect on the kcat values suggests that the Tyr198 hydroxyl participates in catalysis by stabilizing the rate-determining transition-state complex.

Amino Acid Sequence↗
PubMed1986

Million Behavioral Health Inventory: its utility in predicting physical function in patients with low back pain.

The present study evaluated the use of psychologic measures, in particular, the relatively new Million Behavioral Health Inventory (MBHI), in predicting change in physical function of chronic low back pain patients undergoing a functional restoration program. The first 134 consecutive patients completing this program were assessed. Results demonstrated that various clinical scales of the MBHI were predictive of improvement in physical function. In addition, various scales enabled discrimination between patients who completed the program and those who prematurely dropped out. Although this inventory shows promise in helping to predict response to treatment, no single psychologic test can reliably be used as the sole predictor in clinical cases.

Adult↗
PubMed1986

Aleukemic leukemia cutis.

A 46-year-old man presented with nodular skin lesions, a biopsy specimen of which demonstrated a poorly differentiated malignancy. Touch preparations with histochemical staining and electron microscopy confirmed leukemia cutis. Results from a bone marrow aspirate disclosed focal areas of increased myeloblasts, and cytogenetic analysis revealed an abnormal karyotype as follows 46,XY, t(1;2) (q44p13). Antileukemic therapy resulted in prompt disappearance of the skin nodules, and a return of the patient's bone marrow to normal was noted, but after six months of intensive chemotherapy leukemia cutis recurred without morphologically identifiable leukemia in the bone marrow. The patient underwent successful bone marrow transplantation from an HLA-identical sibling but died 70 days after the transplant from disseminated aspergillosis.

Acute Disease↗
PubMed1985

Essential role of phospholipase A2 activity in endothelial cell-induced modification of low density lipoprotein.

Previous studies have established that incubation of low density lipoprotein (LDL) with cultured endothelial cells (EC) converts it to a new form (EC-modified LDL) that is now recognized by a specific receptor on macrophages (the acetyl LDL receptor) and is taken up and degraded 3-10 times more rapidly than native LDL (biological modification). The formation of EC-modified LDL depended on generation of free radicals with consequent peroxidation of LDL lipids and was accompanied by extensive hydrolysis of LDL phosphatidylcholine at the 2-position. The present studies show that p-bromophenacyl bromide, a site-specific irreversible inhibitor of phospholipase A2 activity, blocks this hydrolysis and, at the same time, the enhanced macrophage degradation. We show further that during EC modification the apoprotein B of LDL undergoes considerable modification and that this also is prevented by the phospholipase inhibitor. Finally, as reported previously, changes similar to those observed on incubation of LDL with EC can be induced by incubation in the absence of cells but in the presence of a sufficiently high concentration of Cu2+. This also is accompanied by hydrolysis of phosphatidylcholine at the 2-position and breakdown of apoprotein B. These changes are also inhibited by p-bromophenacyl bromide, suggesting the presence of a phospholipase A2 activity associated with LDL as it is isolated. A hypothesis is presented linking lipid peroxidation, phosphatidylcholine hydrolysis, and changes in the LDL apoprotein during EC modification.

Acetophenones↗