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Biomedical subjects

A C Allen

Publications and source records attributed to A C Allen.

At least 37 records · Page 2Linked to original sources
PubMed1999

Novel 3alpha-diphenylmethoxytropane analogs: selective dopamine uptake inhibitors with behavioral effects distinct from those of cocaine.

The pharmacological effects were assessed for a series of 3alpha-diphenylmethoxy-1alphaH,5alphaH-tropane analogs which have structural similarities to cocaine. Like cocaine, these compounds displaced [3H]WIN 35,428 binding from rat caudate and had affinities ranging from approximately 10-fold greater than cocaine (Ki=11.8 nM) to relatively low affinity (Ki=2000 nM). The compounds also inhibited dopamine uptake with potencies corresponding to their affinities for WIN 35,428 binding sites. Like the parent compound, benztropine, the 3alpha-(diphenylmethoxy)tropane analogs displaced [3H]pirenzepine from muscarinic M1 receptors with affinities ranging from 2 to 120 nM. Cocaine produced dose-related increases in locomotor activity (horizontal ambulation) in Swiss Webster mice, whereas the 3alpha-(diphenylmethoxy)tropane analogs generally had lower efficacy than cocaine. Compounds with fluoro-substituents in the phenyl rings generally were among those with efficacy approaching that of cocaine; those with chloro- and bromo-substituents were markedly less efficacious, despite having binding affinities comparable to those of the corresponding fluoro-substituted compounds. The 3alpha-(diphenylmethoxy)tropane analogs were also examined in rats trained to discriminate saline from cocaine (10 mg/kg, i.p.). Cocaine produced a dose-related increase in responding on the cocaine-appropriate lever, reaching 100% at 10 mg/kg. Only the 4',4"-difluoro-substituted analog produced effects similar to those of cocaine; the other compounds showed markedly reduced efficacy compared to cocaine. Drug interaction studies showed that the antimuscarinics, atropine and scopolamine, potentiated rather than attenuated the locomotor stimulant and cocaine-like discriminative-stimulus effects of cocaine, indicating that the antimuscarinic effects of the 3alpha-diphenylmethoxytropane analogs did not contribute to their diminished cocaine-like activity. Studies of the time course of selected compounds indicated that their reduced cocaine-like efficacy was likely not due to behavioral observations being conducted at an inopportune time period. Because none of the 3alpha-diphenylmethoxytropane analogs studied showed evidence that they were binding to more than one site, and because the structure activity relationships among these drugs are distinctly different from those obtained with cocaine, these data suggest that the 3alpha-diphenylmethoxytropane analogs are accessing a different binding domain than that accessed by cocaine. Binding to this domain may produce a behavioral profile that is distinct from that of the cocaine-like dopamine uptake inhibitors.

Animals↗
PubMed1998

Abnormal IgA glycosylation in Henoch-Schönlein purpura restricted to patients with clinical nephritis.

BACKGROUND: Glomerular deposition of IgA1 is a common feature of Henoch-Schönlein purpura, and is indistinguishable from that seen in IgA nephropathy. Serum IgA1 is abnormally O-glycosylated in IgA nephropathy, and this may contribute to mesangial IgA1 deposition and the development of glomerular injury. This altered O-glycosylation of IgA1 can be detected by its increased binding to the lectin Vicia villosa. METHODS: To investigate whether IgA1 is abnormally glycosylated in Henoch-Schönlein purpura, the binding of Vicia villosa lectin to serum IgA1 was studied in the following subject groups: IgA nephropathy; adults and children with Henoch-Schönlein purpura and nephritis; children with clinically diagnosed Henoch-Schönlein purpura but no renal involvement; adults and children with non-IgA associated glomerulonephritis; and matched controls. RESULTS: The abnormality of lectin binding seen in IgA nephropathy was also found in both adults and children with Henoch-Schönlein purpura with nephritis. However, the lectin binding of serum IgA1 from children with Henoch-Schönlein purpura lacking renal involvement did not differ from controls, and similarly, no abnormality of lectin binding was seen in patients with non-IgA associated glomerulonephritis. CONCLUSIONS: These data indicate that the abnormality of IgA1 O-glycosylation seen in IgA nephropathy is also found in Henoch-Schönlein purpura, but only in those subjects with renal involvement, while IgA1 O-glycosylation is normal in patients with other forms of renal disease. These findings lend strong support to a role for altered IgA1 O-glycosylation in the pathogenesis of IgA-associated glomerular disease.

Adolescent↗
PubMed1998

The nucleotide sequence of the IgA1 hinge region in IgA nephropathy.

BACKGROUND: Mesangial IgA1 deposition is characteristic of IgA nephropathy (IgAN). Structural abnormalities of the IgA1 glycoprotein may play a key role in its mesangial deposition, particularly the recently described abnormalities of O-glycosylation of the IgA1 hinge region. The mechanism of abnormal O-glycosylation has not yet been elucidated; it is not clear whether there is an alteration in the amino acid sequence of the hinge region, modifying the number of O-glycosylation sites available, or whether there is a post-translational defect in the glycosylation process. METHODS: The O-glycosylation of serum IgA1 from a series of patients with IgAN and matched controls was assessed by lectin binding assay. We then used dideoxy-sequencing of the PCR-amplified hinge region of the alpha1 heavy chain gene to compare the hinge region nucleotide sequence in IgAN and controls. We also compared cDNA transcripts of alpha1 hinge region mRNA to look for evidence for a transcriptional abnormality in IgAN. RESULTS: Lectin binding assays confirmed that the IgAN subjects used in this study did indeed display the previously reported abnormality of IgA1 O-glycosylation. However, the hinge region nucleotide sequence of the alpha1 gene was identical in IgAN and controls. There was also no difference in the sizes of cDNA transcripts of hinge region mRNA from patients with IgAN and controls. CONCLUSIONS: We found no evidence for any nucleotide sequence alteration or transcriptional abnormality of the alpha1 hinge region in IgAN, and we conclude that the O-glycosylation defect is post-translational.

Adolescent↗
PubMed1997

Henoch-Schönlein purpura with immunoglobulin A nephropathy and abnormalities of immunoglobulin A in a Wiskott-Aldrich syndrome carrier.

Abnormalities of immunoglobulin A1 (IgA1) glycosylation have been described in patients with IgA nephropathy (IgAN), whether primitive or secondary to Henoch-Schönlein purpura. The Wiskott-Aldrich syndrome, an X-linked recessive disorder, is associated with abnormalities of IgA. Renal involvement with mesangial IgA deposition identical to that found in IgAN has been reported during this affection. We report the case of a female carrier of the Wiskott-Aldrich syndrome presenting with Henoch-Schönlein purpura and abnormalities of IgA glycosylation, as previously reported in patients with IgAN. The galactosylation abnormalities of IgA could be linked to the patient's status as carrier of the Wiskott-Aldrich syndrome and could contribute to the pathogenesis of IgAN.

Adult↗
PubMed1997

Expression of the mucosal gamma delta T cell receptor V region repertoire in patients with IgA nephropathy.

IgA nephropathy (IgAN) is characterized by the deposition of IgA in the glomerular mesangium and often leads to progressive renal dysfunction and kidney failure. We have previously shown that the mesangial IgA is likely to derive from the bone marrow plasma cells, and suggested that a primary abnormality within the mucosal immune system may underly the pathogenesis of IgAN. This study has analyzed the T cell receptor (TCR) variable (V) region expression by gamma delta T cells in the intestinal mucosa of patients with IgAN. The V gamma and V delta usage of TCR transcripts was determined using a semiquantitative reverse transcriptase-PCR protocol. Primers specific for the four human V gamma and six V delta subfamilies were used each with a constant (C) gamma or C delta specific primer, and the PCR-amplified TCR transcripts were detected by Southern blotting and oligonucleotide hybridization. gamma delta TCR V region expression was determined in gut biopsies and peripheral blood of 11 patients with IgAN, and the TCR V gamma and V delta repertoires were compared to those in gut and peripheral blood of 11 control individuals. gamma delta T cells in normal blood predominantly expressed V gamma 2 (V gamma 9 gene) and V delta 2 gene segments whereas those in normal gut mainly expressed V gamma 3 and V delta 3. In IgAN patients, V delta 2 was also the predominant V delta gene utilized by peripheral blood gamma delta T cells, however, we observed a predominance of V gamma 3 and reduced V gamma 2 usage by these cells. gamma delta T cells in the gut of IgAN patients mainly used V gamma 3 and V delta 1. While the gamma and delta TCR V region repertoires did not differ significantly between the peripheral blood of patients and controls, there were significant differences in V gamma and V delta repertoire expression between IgAN and control gut biopsies. V gamma 3 gene expression was significantly decreased in IgAN gut compared to control gut (P = 0.023). In addition, there was a significant decrease in V delta 3 gene expression in IgAN gut compared to control gut (P = 0.043). These findings indicate that a subpopulation of gamma delta T cells, which represent the majority of gamma delta T cells in normal gut mucosa, are significantly diminished in the gut of patients with IgAN. This suggests that a "hole" in the mucosal gamma delta T cell repertoire may play a fundamental role in contributing to the pathogenesis of IgAN.

Adult↗
PubMed1997

Leucocyte beta 1,3 galactosyltransferase activity in IgA nephropathy.

BACKGROUND: Reduced galactosylation of the O-linked glycans of the IgA1 hinge region in IgAN has recently been described. To investigate the underlying defect resulting in this abnormality, we have measured the activity of beta 1,3 galactosyltransferase, the enzyme responsible for galactosylation of O-linked sugars. METHODS: A galactose-acceptor substrate was prepared from degalactosylated hinge region fragments of normal IgA1, and incubated with the T cell, B cell, and monocyte lysates from patients with IgAN and controls for acceptor regalactosylation. The extent of acceptor galactosylation was then measured with biotinylated Vicia villosa lectin (VV), which is specific for ungalactosylated moieties. Lectin binding of serum IgA from the same subjects was also measured. RESULTS: T cell and monocyte beta 1,3 galactosyltransferase activities did not differ between IgAN and control, but B cell lysates in IgAN showed significantly lower beta 1,3 galactosyltransferase activity than control (6.2 +/- 0.71 vs. 9.5 +/- 1.03 AU/microgram, P = 0.018). Furthermore, B cell beta 1,3 galactosyltransferase activity showed a negative correlation (r = -0.87, P = 0.002) with VV lectin binding of serum IgA in IgAN, but not controls. CONCLUSIONS: These data indicate that altered IgA1 O-galactosylation in IgAN results from a B cell-restricted reduction of beta 1,3 galactosyltransferase activity. This enzyme defect may be a fundamental pathogenic abnormality in IgAN.

Adult↗
PubMed1996

Increased dimeric IgA producing B cells in the bone marrow in IgA nephropathy determined by in situ hybridisation for J chain mRNA.

AIM: To investigate the possible role of the systemic IgA immune system in the pathogenesis of IgA nephropathy METHODS: J chain mRNA expression in the IgA cells of the bone marrow was studied. Bone marrow trephine biopsy specimens from seven patients with IgA nephropathy and seven matched controls were examined by (1) non-isotopic in situ hybridisation (ISH) and (2) combined immunofluorescence and non-isotopic ISH to identify the plasma cell type. Serum polymeric IgA was also determined using standard high pressure liquid chromatography and sandwich enzyme linked immunosorbent assay. RESULTS: Non-isotopic ISH revealed a similar number of J chain mRNA positive cells/unit length in biopsy specimens from patients (16.5 +/- 2.7 cells/mm) and controls (17.7 +/- 2.4 cells/mm). Combined immunofluorescence and ISH revealed a greater proportion of J chain mRNA positive IgA cells in patients (7.6 +/- 1.45%) compared with controls (3 +/- 0.8%). Serum polymeric IgA was similar in both patients (91 +/- 22 mg/l) and controls (77 +/- 24 mg/l). CONCLUSION: These data suggest that excess production of dimeric IgA occurs in the bone marrow in IgA nephropathy.

Adult↗
PubMed1996

Three homologs of rds/peripherin in Xenopus laevis photoreceptors that exhibit covalent and non-covalent interactions.

We have isolated and characterized three homologs of mammalian rds/peripherin from Xenopus retinae. One (xrds38) is likely the Xenopus ortholog, while the other two (xrds36 and -35) are more distant relatives. By immunocytochemical analysis of retinal sections, xrds38 is distributed in both rod and cone photoreceptors, while xrds36 and xrds35 are present in rods only. At the EM level, xrds38 is present specifically in the rims and incisures of rod and cone outer segment discs. All are N-glycosylated and form covalent dimers. Immunoprecipitation analysis showed that in rods, these three proteins interact to form heterotetrameric or higher-order complexes. The pattern of sequence conservation among the xrds proteins, mammalian rds/peripherin, and mammalian rom-1 suggest that the central portion of the intradiscal D2 loop contains the interacting structural elements.

Amino Acid Sequence↗
PubMed1995

Novel 4'-substituted and 4',4"-disubstituted 3 alpha-(diphenylmethoxy)tropane analogs as potent and selective dopamine uptake inhibitors.

A series of 4'-substituted and 4',4"-disubstituted 3 alpha-(diphenylmethoxy)tropane analogs were prepared as novel probes for the dopamine transporter. These compounds were evaluated in radiolabeled binding assays for the dopamine, norepinephrine, and serotonin transporters. All of these compounds monophasically displaced [3H]WIN 35,428 binding in rat caudate putamen with Ki values ranging from 11.8 to 2000 nM. The most potent compound in this series was 4',4"-difluoro 3 alpha-(diphenylmethoxy)tropane 7c with a Ki = 11.8 nM. All of the compounds inhibited dopamine uptake in rat caudate putamen (IC50 = 24-4456 nM) which correlated significantly (r = 0.907; p > 0.0001) with binding affinities at the dopamine transporter. None of the compounds demonstrated high-affinity binding at the norepinephrine (Ki > 4800 nM) or serotonin (Ki > 690 nM) transporters. Therefore, the most potent dopamine uptake inhibitors in this series were highly selective for the dopamine transporter. Preliminary behavioral studies of several of these analogs (7a-e) suggested that the compounds did not display a cocaine-like behavioral profile, despite their ability to inhibit dopamine uptake. The present data coupled with the observed differences from cocaine in structure-activity relationships suggested that the 3 alpha-(diphenylmethoxy)tropane analogs may be interacting at a different active site than cocaine on the dopamine transporter and that an additional binding domain might be exploited for the identification of potential therapeutics for the treatment of cocaine abuse.

Animals↗
PubMed1995

Retinal degeneration slow (rds) in mouse results from simple insertion of a t haplotype-specific element into protein-coding exon II.

Retinal degeneration slow (rds) is a semidominant mutation of mice that causes dysplasia and degeneration of rod and cone photoreceptors. Mutations in RDS, the human ortholog of the rds gene, are responsible for several inherited retinal dystrophies including a subset of retinitis pigmentosa. The normal rds locus encodes rds/peripherin, an integral membrane glycoprotein present in outer segment discs. Genomic libraries from wildtype and rds/rds mice were screened with an rds cDNA, and phage lambda clones that span the normal and mutant loci were mapped. We show that in mice, rds is caused by the insertion into exon II of a 9.2-kb repetitive genomic element that is very similar to the t haplotype-specific element in the H-2 complex. The entire element is included in the RNA products of the mutant locus. We present evidence that rds in mice represents a null allele.

Alleles↗
PubMed1995

Effects of cocaine, cocaine metabolites and cocaine pyrolysis products on the hindbrain cardiac and respiratory centers of the rabbit.

Hemodynamic and respiratory effects of vertebral artery or i.v. administration of cocaine, cocaine metabolites and cocaine pyrolysis products were measured in anesthetized rabbits. Vertebral artery administration of 1 mg of cocaine produced decreases in blood pressure and heart rate and respiratory arrest. Cocaethylene (1 mg), a cocaine metabolite produced following co-administration of cocaine and ethanol, had comparable effects except that the respiratory arrest following cocaethylene had a longer duration of action than did cocaine. A decrease in blood pressure was also observed following 1 mg of norcocaine; however, unlike cocaine, norcocaine did not affect respiration. Acute tolerance was not observed to any of the effects of 1 mg of cocaine, cocaethylene or norcocaine following vertebral artery administration. None of these compounds had significant effects following i.v. administration of the same dose. The cocaine metabolites benzoylecgonine and ecgonine methyl ester were without effect by either route in doses up to 3 mg. In contrast to cocaine, the cocaine pyrolysis products anhydroecgonine methyl ester (3 mg) and noranhydroecgonine methyl ester (3 mg) produced similar effects via both routes of administration. Both compounds produced decreases in blood pressure and heart rate and an increase in respiratory rate. Anhydroecgonine ethyl ester (3 mg), a metabolite hypothetically formed from the cocaine pyrolysis product in individuals co-administering ethanol, had effects similar to the other pyrolysis products, although its effects were not as prominent via the i.v. route of administration. Acute tolerance was observed upon administration of the cocaine pyrolysis products. These results indicate that the cocaine pyrolysis products do not share a common mechanism of action with either cocaine or the cocaine metabolites.

Animals↗
PubMed1995

Perinatal implications of shoulder dystocia.

OBJECTIVE: To assess the antecedents of shoulder dystocia, the risk of recurrence, and the perinatal morbidity associated with the different maneuvers used for its management. METHODS: We conducted a 10-year (1980-1989) retrospective case record review of all instances of shoulder dystocia in a teaching maternity hospital. RESULTS: There were 254 cases of shoulder dystocia in 40,518 vaginal cephalic deliveries (0.6%), with 33 cases (13.0%) of brachial plexus palsy and 13 fractures (5.1%). There were no perinatal deaths attributable to shoulder dystocia. The risk of shoulder dystocia was increased with prolonged pregnancy (threefold), prolonged second stage of labor (threefold), mid-forceps deliveries (tenfold), and increasing birth weight. Of the maneuvers used to deal with shoulder dystocia, strong downward traction on the head was significantly correlated with brachial plexus palsy compared with other individual methods of delivering the shoulders. There was only one case of recurrent shoulder dystocia in 80 women having 93 cephalic vaginal deliveries after their original delivery coded with shoulder dystocia. CONCLUSION: Shoulder dystocia is not a reliably predictable event in labor. Although the risk of shoulder dystocia is increased with prolonged pregnancy, prolonged second stage of labor, increasing birth weight, and mid-forcepts delivery, the majority of cases occur without these risk factors. Strong downward traction on the head is associated with the greatest degree of neonatal trauma, whereas McRoberts maneuver has the least. The risk of recurrent shoulder dystocia is low.

Birth Injuries↗
PubMed1995

Increased dimeric IgA-producing B cells in tonsils in IgA nephropathy determined by in situ hybridization for J chain mRNA.

The origin of mesangial IgA deposits in IgA nephropathy (IgAN) remains obscure. A significant proportion of deposited immunoglobulin is dimeric (J chain-positive). Previous studies of J chain expression within lymphoid tissue in IgAN have utilized antibodies which other investigators have found to be non-specific. To address this problem, we have developed and in situ hybridization (ISH) method for the detection of J chain mRNA within IgA plasma cells. Tonsils from 12 patients with IgAN and 12 controls were studied using (i) non-isotopic ISH for J chain mRNA, and (ii) combined immunofluorescence (IF) and fluorescent ISH. J chain mRNA-positive cells were identified in germinal centres, and within the subepithelial and interfollicular zones. A greater number of J chain mRNA-positive cells were found in the germinal centres of patients (mean 57.7 +/- 4.6 cells/10(5) micron2) compared with controls (mean 36.9 +/- 3.5 cells/10(5) micron2) (P < 0.001). Combined IF and fluorescent ISH showed a greater proportion of J chain mRNA-positive interfollicular IgA cells in patient tonsils (32 +/- 3.4%) compared with controls (21 +/- 2.3%; P < 0.02). These results indicate a shift towards dimeric IgA production in the tonsils in IgAN. In addition, the finding of excess numbers of J chain-positive Iga-negative cells within germinal centres suggests that an abnormality may be present at the B cell differentiation stage before IgA switching. These results further highlight immune abnormalities within the tonsil as a central feature of abnormal polymeric IgA biology in this common form of glomerulonephritis.

Adolescent↗
PubMed1995

Galactosylation of N- and O-linked carbohydrate moieties of IgA1 and IgG in IgA nephropathy.

The mechanism of IgA deposition in the kidneys in IgA nephropathy is unknown. Mesangial IgA is of the IgA1 subclass, and since no consistent antigenic target for the IgA1 has been described, we have investigated the glycosylation of the molecule, as a potential non-immunological abnormality which may contribute to its deposition. IgA1 is rich in carbohydrate, carrying N-linked moieties in common with IgG, but also O-linked sugars, which are rare in serum proteins, and not expressed by IgG or IgA2. Lectin binding assays were designed to examine the expression of terminal galactose on the N-linked carbohydrate chains of purified serum IgG and IgA1, and the O-linked sugars of IgA1 and C1 inhibitor (one of the very few other serum proteins with O-linked glycosylation). No evidence was found for abnormalities of N-linked glycosylation of either isotype in IgA nephropathy compared with matched controls. However, in IgA nephropathy, reduced terminal galactosylation of the hinge region O-linked moieties was demonstrated; this was not seen in C1 inhibitor, which showed normal or increased galactosylation of the O-linked sugars. This abnormality of IgA1 has considerable implications for the pathogenesis of IgA nephropathy, since the O-linked sugars lie in an important functional location within the IgA1 molecule, close to the ligand of Fc receptors. Changes in the carbohydrates in this site may therefore affect interactions with receptors and extracellular proteins, leading to anomalous handling of the IgA1 protein in this condition, including failure of normal clearance mechanisms, and mesangial deposition.

Adult↗
PubMed1994

Increased immunoglobulin A and immunoglobulin A1 cells in bone marrow trephine biopsy specimens in immunoglobulin A nephropathy.

The origin of mesangial immunoglobulin A (IgA) in IgA nephropathy remains unknown. To investigate potential abnormalities within the bone marrow in this condition, bone marrow trephine biopsy specimens from seven patients and matched controls were studied using two-color immunofluorescence. In addition, serum levels of IgA and IgA1 were determined by radial immunodiffusion. Serum levels of IgA and IgA1 were higher in patients than in controls (4.53 +/- 1.38 g/L v 2.56 +/- 1 g/L, P < 0.01 and 3.68 +/- 1.11 g/L v 1.92 +/- 0.7 g/L, P < 0.005, respectively). In addition, patient trephine biopsy specimens contained an increased percentage of IgA plasma cells (61.6% +/- 4.4%) compared with controls (47.3% +/- 2.5%) (P < 0.02). The proportion of IgA plasma cells bearing subclass IgA1 was also greater in the patient biopsy specimens (91.6% +/- 1.9%) compared with controls (81.4% +/- 2.7%) (P < 0.01). In patients a positive correlation between the percentage of marrow IgA plasma cells and serum IgA levels was found (r = 0.94, P < 0.002). However, our studies failed to demonstrate a similar correlation between serum IgA1 levels and IgA1 marrow cells. These findings support the hypothesis that mesangial IgA may derive from the bone marrow.

Adult↗
PubMed1994

Design of a potent and orally active nonpeptide platelet fibrinogen receptor (GPIIb/IIIa) antagonist.

The direct design of the potent nonpeptide platelet fibrinogen receptor (GPIIb/IIIa) antagonist, 8-[[[4- (aminoiminomethyl)phenyl]amino]carbonyl]-2,3,4,5-tetrahydro-3-oxo- 4- (2-phenylethyl)-1H-1,4-benzodiazepine-2-acetic acid, (3) (SB 207448), based on the structure and conformation of the potent and highly constrained cyclic peptide antagonist SK&F 107260 (2), has been reported [Ku et al., J. Am. Chem. Soc. 1993, 115, 8861]. While 3 displayed in vivo activity in the conscious dog following intravenous administration, it was not active following intraduodenal administration; activity was measured with an ex vivo platelet aggregation assay. The secondary amide in 3 was N-methylated in the expectation of increased absorption and bioavailability. The resulting tertiary amide, 4 (SB 208651), also showed high binding affinity for human GPIIb/IIIa and potent antiaggregatory activity in human platelet-rich plasma. Most importantly, 4 was active in vivo following intravenous and intraduodenal administration. Comparison of the iv and id inhibition curves suggests an apparent bioavailability of approximately 10%. Thus, 4 represents the first orally active compound in this series of potent, nonpeptide fibrinogen receptor antagonists.

Administration, Oral↗