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Biomedical subjects

C M Adams

Publications and source records attributed to C M Adams.

At least 19 recordsLinked to original sources
PubMed2004

Consistent cytotoxic-T-lymphocyte targeting of immunodominant regions in human immunodeficiency virus across multiple ethnicities.

Although there is increasing evidence that virus-specific cytotoxic-T-lymphocyte (CTL) responses play an important role in the control of human immunodeficiency virus (HIV) replication in vivo, only scarce CTL data are available for the ethnic populations currently most affected by the epidemic. In this study, we examined the CD8(+)-T-cell responses in African-American, Caucasian, Hispanic, and Caribbean populations in which clade B virus dominates and analyzed the potential factors influencing immune recognition. Total HIV-specific CD8(+)-T-cell responses were determined by enzyme-linked immunospot assays in 150 HIV-infected individuals by using a clade B consensus sequence peptide set spanning all HIV proteins. A total of 88% of the 410 tested peptides were recognized, and Nef- and Gag-specific responses dominated the total response for each ethnicity in terms of both breadth and magnitude. Three dominantly targeted regions within these proteins that were recognized by >90% of individuals in each ethnicity were identified. Overall, the total breadth and magnitude of CD8(+)-T-cell responses correlated with individuals' CD4 counts but not with viral loads. The frequency of recognition for each peptide was highly correlated with the relative conservation of the peptide sequence, the presence of predicted immunoproteasomal cleavage sites within the C-terminal half of the peptide, and a reduced frequency of amino acids that impair binding of optimal epitopes to the restricting class I molecules. The present study thus identifies factors that contribute to the immunogenicity of these highly targeted and relatively conserved sequences in HIV that may represent promising vaccine candidates for ethnically heterogeneous populations.

AIDS Vaccines↗
PubMed2001

Dissociation of reward anticipation and outcome with event-related fMRI.

Reward processing involves both appetitive and consummatory phases. We sought to examine whether reward anticipation vs outcomes would recruit different regions of ventral forebrain circuitry using event-related fMRI. Nine healthy volunteers participated in a monetary incentive delays task in which they either responded to a cued target for monetary reward, responded to a cued target for no reward, or did not respond to a cued target during scanning. Multiple regression analyses indicated that while anticipation of reward vs non-reward activated foci in the ventral striatum, reward vs non-reward outcomes activated foci in the ventromedial frontal cortex. These findings suggest that reward anticipation and outcomes may differentially recruit distinct regions that lie along the trajectory of ascending dopamine projections.

Adult↗
PubMed2001

Anticipation of increasing monetary reward selectively recruits nucleus accumbens.

Comparative studies have implicated the nucleus accumbens (NAcc) in the anticipation of incentives, but the relative responsiveness of this neural substrate during anticipation of rewards versus punishments remains unclear. Using event-related functional magnetic resonance imaging, we investigated whether the anticipation of increasing monetary rewards and punishments would increase NAcc blood oxygen level-dependent contrast (hereafter, "activation") in eight healthy volunteers. Whereas anticipation of increasing rewards elicited both increasing self-reported happiness and NAcc activation, anticipation of increasing punishment elicited neither. However, anticipation of both rewards and punishments activated a different striatal region (the medial caudate). At the highest reward level ($5.00), NAcc activation was correlated with individual differences in self-reported happiness elicited by the reward cues. These findings suggest that whereas other striatal areas may code for expected incentive magnitude, a region in the NAcc codes for expected positive incentive value.

Adult↗
PubMed2001

Total synthesis of (-)-cylindrocyclophanes A and F exploiting the reversible nature of the olefin cross metathesis reaction.

Efficient total syntheses of the C(2)-symmetric (-)-cylindrocyclophanes A and F (1a and 1f) have been achieved. The initial strategy featured the use of a common advanced intermediate to assemble in stepwise fashion the required macrocycle of 1f, exploiting in turn a Myers reductive coupling followed by ring-closing metathesis. In a second-generation strategy, a remarkable cross olefin metathesis dimerization cascade was discovered and exploited to assemble the requisite [7,7]-paracyclophane macrocycles of both 1a and 1f from dienyl monomers. The successful syntheses also featured the effective use of the Danheiser annulation to construct substrates for both the Myers reductive coupling and the metathesis dimerizations strategies. Finally, the Kowalski two-step chain homologation of esters to siloxyalkynes proved superior over the original one-step protocol.

Alkenes↗
PubMed1999

Mucosal T lymphocyte numbers are selectively reduced in integrin alpha E (CD103)-deficient mice.

The mucosal lymphocyte integrin alpha E(CD103)beta 7 is thought to be important for intraepithelial lymphocyte (IEL) localization or function. We cloned the murine integrin gene encoding alpha E, localized it to chromosome 11, and generated integrin alpha E-deficient mice. In alpha E-/- mice, intestinal and vaginal IEL numbers were reduced, consistent with the known binding of alpha E beta 7 to E-cadherin expressed on epithelial cells. However, it was surprising that lamina propria T lymphocyte numbers were diminished, as E-cadherin is not expressed in the lamina propria. In contrast, peribronchial, intrapulmonary, Peyer's patch, and splenic T lymphocyte numbers were not reduced in alpha E-deficient mice. Thus, alpha E beta 7 was important for generating or maintaining the gut and vaginal T lymphocytes located diffusely within the epithelium or lamina propria but not for generating the gut-associated organized lymphoid tissues. Finally, the impact of alpha E deficiency upon intestinal IEL numbers was greater at 3-4 wk of life than in younger animals, and affected the TCR alpha beta+ CD8+ T cells more than the gamma delta T cells or the TCR alpha beta+ CD4+CD8- population. These findings suggest that alpha E beta 7 is involved in the expansion/recruitment of TCR alpha beta+ CD8+ IEL following microbial colonization. Integrin alpha E-deficient mice will provide an important tool for studying the role of alpha E beta 7 and of alpha E beta 7-expressing mucosal T lymphocytes in vivo.

Animals↗
PubMed1999

Paradoxical stimulation of a DEG/ENaC channel by amiloride.

Extracellular amiloride inhibits all known DEG/ENaC ion channels, including BNC1, a proton-activated human neuronal cation channel. Earlier studies showed that protons cause a conformational change that activates BNC1 and exposes residue 430 to the extracellular solution. Here we demonstrate that, in addition to blocking BNC1, amiloride also exposes residue 430. This result suggested that, like protons, amiloride might be capable of activating the channel. To test this hypothesis, we introduced a mutation in the BNC1 pore that reduces amiloride block, and found that amiloride stimulated these channels. Amiloride inhibition was voltage-dependent, suggesting block within the pore, whereas stimulation was not, suggesting binding to an extracellular site. These data show that amiloride can have two distinct effects on BNC1, and they suggest two different interaction sites. The results suggest that extracellular amiloride binding may have a stimulatory effect similar to that of protons in BNC1 or extracellular ligands in other DEG/ENaC channels.

Acid Sensing Ion Channels↗
PubMed1999

Tetraethylammonium block of the BNC1 channel.

The brain Na+ channel-1 (BNC1, also known as MDEG1 or ASIC2) is a member of the DEG/ENaC cation channel family. Mutation of a specific residue (Gly430) that lies N-terminal to the second membrane-spanning domain activates BNC1 and converts it from a Na+-selective channel to one permeable to both Na+ and K+. Because all K+ channels are blocked by tetraethylammonium (TEA), we asked if TEA would inhibit BNC1 with a mutation at residue 430. External TEA blocked BNC1 when residue 430 was a Val or a Thr. Block was steeply voltage-dependent and was reduced when current was outward, suggesting multi-ion block within the channel pore. Block was dependent on the size of the quaternary ammonium; the smaller tetramethylammonium blocked with similar properties, whereas the larger tetrapropylammonium had little effect. When residue 430 was Phe, the effects of tetramethylammonium and tetrapropylammonium were not altered. In contrast, block by TEA was much less voltage-dependent, suggesting that the Phe mutation introduced a new TEA binding site located approximately 30% of the way across the electric field. These results provide insight into the structure and function of BNC1 and suggest that TEA may be a useful tool to probe function of this channel family.

Acid Sensing Ion Channels↗
PubMed1998

Protons activate brain Na+ channel 1 by inducing a conformational change that exposes a residue associated with neurodegeneration.

BNC1 is a mammalian neuronal cation channel in the novel DEG/ENaC ion channel family. BNC1 channels are transiently activated by extracellular protons and are constitutively activated by insertion of large residues, such as valine, in place of Gly-430; residue 430 is a site where analogous mutations in some Caenorhabditis elegans family members cause a swelling neurodegeneration. Mutation of Gly-430 to a small amino acid, cysteine, neither generated constitutive currents nor allowed modification of this residue by sulfhydryl-reactive methanethiosulfonate (MTS) compounds. However, when protons activated the channel, Cys-430 became accessible to extracellular MTS reagents, which modified Cys-430 to generate constitutive currents. Fluorescent MTS reagents also labeled Cys-430 in activated channels. These data indicate that protons induce a reversible conformational change that activates BNC1 thereby exposing residue 430 to the extracellular solution. Once Cys-430 is modified with a large chemical group, the channel is prevented from relaxing back to the inactive state. These results link ligand-dependent activation and activation by mutations that cause neurodegeneration.

Amino Acid Substitution↗
PubMed1998

Inhibition of the epithelial Na+ channel by interaction of Nedd4 with a PY motif deleted in Liddle's syndrome.

The epithelial Na+ channel (ENaC) plays a critical role in Na+ absorption in the kidney and other epithelia. Mutations in the C terminus of the beta or gammaENaC subunits increase renal Na+ absorption, causing Liddle's syndrome, an inherited form of hypertension. These mutations delete or disrupt a PY motif that was recently shown to interact with Nedd4, a ubiquitin-protein ligase expressed in epithelia. We found that Nedd4 inhibited ENaC when they were coexpressed in Xenopus oocytes. Liddle's syndrome-associated mutations that prevent the interaction between Nedd4 and ENaC abolished inhibition, suggesting that a direct interaction is required for inhibition by Nedd4. Inhibition also required activity of a ubiquitin ligase domain within the C terminus of Nedd4. Nedd4 had no detectable effect on the single channel properties of ENaC. Rather, Nedd4 decreased cell surface expression of both ENaC and a chimeric protein containing the C terminus of the beta subunit. Decreased surface expression resulted from an increase in the rate of degradation of the channel complex. Thus, interaction of Nedd4 with the C terminus of ENaC inhibits Na+ absorption, and loss of this interaction may play a role in the pathogenesis of Liddle's syndrome and other forms of hypertension.

Animals↗
PubMed1998

Ripped pocket and pickpocket, novel Drosophila DEG/ENaC subunits expressed in early development and in mechanosensory neurons.

Drosophila melanogaster has proven to be a good model for understanding the physiology of ion channels. We identified two novel Drosophila DEG/ ENaC proteins, Pickpocket (PPK) and Ripped Pocket (RPK). Both appear to be ion channel subunits. Expression of RPK generated multimeric Na+ channels that were dominantly activated by a mutation associated with neurodegeneration. Amiloride and gadolinium, which block mechanosensation in vivo, inhibited RPK channels. Although PPK did not form channels on its own, it associated with and reduced the current generated by a related human brain Na+ channel. RPK transcripts were abundant in early stage embryos, suggesting a role in development. In contrast, PPK was found in sensory dendrites of a subset of peripheral neurons in late stage embryos and early larvae. In insects, such multiple dendritic neurons play key roles in touch sensation and proprioception and their morphology resembles human mechanosensory free nerve endings. These results suggest that PPK may be a channel subunit involved in mechanosensation.

Amiloride↗
PubMed1997

Interactions between subunits of the human epithelial sodium channel.

The human epithelial sodium channel (hENaC) mediates Na+ transport across the apical membrane of epithelia, and mutations in hENaC result in hypertensive and salt-wasting diseases. In heterologous expression systems, maximal hENaC function requires co-expression of three homologous proteins, the alpha, beta, and gammahENaC subunits, suggesting that hENaC subunits interact to form a multimeric channel complex. Using a co-immunoprecipitation assay, we found that hENaC subunits associated tightly to form homo- and heteromeric complexes and that the association between subunits occurred early in channel biosynthesis. Deletion analysis of gammahENaC revealed that the N terminus was sufficient but not necessary for co-precipitation of alphahENaC, and that both the N terminus and the second transmembrane segment (M2) were required for gamma subunit function. The biochemical studies were supported by functional studies. Co-expression of gamma subunits lacking M2 with full-length hENaC subunits revealed an inhibitory effect on hENaC channel function that appeared to be mediated by the cytoplasmic N terminus of gamma, and was consistent with the assembly of nonfunctional subunits into the channel complex. We conclude that the N terminus of gammahENaC is involved in channel assembly.

Animals↗
PubMed1995

Mechanism by which Liddle's syndrome mutations increase activity of a human epithelial Na+ channel.

Liddle's syndrome is an inherited form of hypertension caused by mutations that truncate the C-terminus of human epithelial Na+ channel (hENaC) subunits. Expression of truncated beta and gamma hENaC subunits increased Na+ current. However, truncation did not alter single-channel conductance or open state probability, suggesting there were more channels in the plasma membrane. Moreover, truncation of the C-terminus of the beta subunit increased apical cell-surface expression of hENaC in a renal epithelium. We identified a conserved motif in the C-terminus of all three subunits that, when mutated, reproduced the effect of Liddle's truncations. Further, both truncation of the C-terminus and mutation of the conserved C-terminal motif increased surface expression of chimeric proteins containing the C-terminus of beta hENaC. Thus, by deleting a conserved motif, Liddle's mutations increase the number of Na+ channels in the apical membrane, which increases renal Na+ absorption and creates a predisposition to hypertension.

Amiloride↗
PubMed1993

Identification of high intraocular pressure responders to topical ophthalmic corticosteroids.

To locate suitable candidates to study the intraocular pressure (IOP) effects of new ocular steroids, healthy volunteers must be challenged with topically applied steroids to verify that such individuals are indeed high "steroid responders"; that is, they respond with IOP elevations of at least 5 mmHg during a 4- to 6-week challenge with the topically applied steroid. We used first-degree offspring of individuals with primary open-angle glaucoma to develop a model to identify high steroid responders to topical ophthalmic prednisolone. We conducted a prospective, randomized, open-label, placebo-controlled study of prednisolone phosphate 1.0% in which 13 subjects received either topical prednisolone phosphate 4 times daily to the right eye and placebo to the left eye, or vice versa. Baseline evaluations occurred on study Day 0, and follow-up examinations were on Days 7, 14, 21, 28, 35, and 42. The medications were administered continuously for 6 weeks or until the IOP rose > or = 10 mmHg. After the effect of diurnal variation in IOP was taken into account, 4 of the 13 subjects (31%) had a maximum elevation in IOP of 4 mmHg or less, 7 subjects (54%) showed maximum elevations in IOP of 5 to 9 mmHg, and 2 subjects (15%) had a maximum IOP elevation of > or = 10 mmHg. Thus, a cumulative total of 9 subjects (69%) had IOP elevations of at least 5 mmHg and could be classified as moderate to high steroid responders. This model should become useful as a productive source of subjects for studies evaluating the effect on IOP of new ocular steroids.

Adult↗
PubMed1988

Beta-blockade by sotalol in early myocardial infarction decreases ventricular arrhythmias without increasing left ventricular volume.

Although early beta-blockade in acute myocardial infarction (AMI) may have potential benefits owing to an anti-arrhythmic effect and limitation of infarct size, the haemodynamic effects are not well characterised. Accordingly, we studied the effects of intravenous beta-blockade by sotalol in AMI, commencing a mean of 6 hours after the onset of chest pain, with particular reference to systemic haemodynamic changes and left ventricular (LV) volumes. Thirty patients were randomised to a control group or to sotalol therapy starting with 40 mg and increasing to 120 mg, followed by the maximal dose tolerated every 6 hours for 72 hours. Sotalol reduced heart rate and mean blood pressure without elevating pulmonary wedge pressure or increasing enzymatic infarct size. Sotalol also decreased the incidence of ventricular tachycardia (P less than 0.001). An important new finding was that there was no increase in the LV volume measured by radionuclide techniques. Therefore intravenous sotalol safely achieved its beneficial effects without causing LV dilatation.

Adult↗