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D P Davis

Publications and source records attributed to D P Davis.

At least 19 recordsLinked to original sources
PubMed2001

Both the environment and somatic mutations govern the aggregation pathway of pathogenic immunoglobulin light chain.

Deposition of monoclonal immunoglobulin light chain (LC) aggregates in tissues is the hallmark of a class of fatal diseases with no effective treatment. In the most prevalent diseases two different types of LC aggregates are observed: fibrillar deposits in LC amyloidosis (AL) and granular aggregates in LC deposition disease (LCDD). The mechanisms by which a given LC forms either type of aggregate are not understood. Although some LCs are more aggregation-prone than others, this does not appear to be due to specific sequence determinants, but more likely from global properties that can be introduced by multiple somatic mutations. Moreover, a single LC isotype can sometimes form both fibrillar and granular aggregates within the same patient. To better understand how the different aggregation pathways arise, we developed a series of in vitro assays to analyze the formation of distinct aggregate types. The recombinant kappa IV LC (SMA) assembles into fibrils when agitated. We now show that SMA can also form granular aggregates upon exposure to copper, and that this aggregation can occur not only in vitro, but also in cells. A constellation of somatic mutations, consisting of His89/His94/Gln96, is sufficient to confer sensitivity to copper on wild-type kappa IV proteins. The formation of both types of aggregates is inhibited by synthetic peptides derived from the LC variable domain. However, the peptide that inhibits fibrillar aggregation is different from the peptide that inhibits copper-induced aggregation. Thus, distinct molecular surfaces of the LC underly each type of aggregate. We conclude that both the intrinsic properties of the sequence and extrinsic conditions govern the aggregation pathway of a LC.

Amino Acid Sequence↗
PubMed2001

Hsp70 and antifibrillogenic peptides promote degradation and inhibit intracellular aggregation of amyloidogenic light chains.

In light chain (LC) amyloidosis an immunoglobulin LC assembles into fibrils that are deposited in various tissues. Little is known about how these fibrils form in vivo. We previously showed that a known amyloidogenic LC, SMA, can give rise to amyloid fibrils in vitro when a segment of one of its beta sheets undergoes a conformational change, exposing an Hsp70 binding site. To examine SMA aggregation in vivo, we expressed it and its wild-type counterpart, LEN, in COS cells. While LEN is rapidly oxidized and subsequently secreted, newly synthesized SMA remains in the reduced state. Most SMA molecules are dislocated out of the ER into the cytosol, where they are ubiquitinylated and degraded by proteasomes. A parallel pathway for molecules that are not degraded is condensation into perinuclear aggresomes that are surrounded by vimentin-containing intermediate filaments and are dependent upon intact microtubules. Inhibition of proteasome activity shifts the balance toward aggresome formation. Intracellular aggregation is decreased and targeting to proteasomes improved by overexpression of the cytosolic chaperone Hsp70. Importantly, transduction into the cell of an Hsp70 target peptide, derived from the LC sequence, also reduces aggresome formation and increases SMA degradation. These results demonstrate that an amyloidogenic LC can aggregate intracellularly despite the common presentation of extracellular aggregates, and that a similar molecular surface mediates both in vitro fibril formation and in vivo aggregation. Furthermore, rationally designed peptides can be used to suppress this aggregation and may provide a feasible therapeutic approach.

Amino Acid Sequence↗
PubMed2001

Effect of surgical cricothyrotomy on the unstable cervical spine in a cadaver model of intubation.

Cricothyrotomy is indicated for patients who require an immediate airway and in whom orotracheal or nasotracheal intubation is unsuccessful or contraindicated. Cricothyrotomy is considered safe with cervical spine (c-spine) injury; however, the amount of c-spine movement that occurs during the procedure has not been determined. In this experimental study, an established cadaver model of c-spine injury was used to quantify movement during cricothyrotomy. A complete C5--6 transection was performed by using an osteotome on 13 fresh-frozen cadavers. Standard open cricothyrotomy was performed on each cadaver, with c-spine images recorded in real time on fluoroscopy, then transferred to video and Kodachrome still images. Outcome measures included movement across the C5--6 site with regard to angulation expressed in degrees of rotation and linear measures of axial distraction and anterior-posterior (AP) displacement expressed as a proportion of C5 body width. Data were analyzed by using descriptive statistics to determine mean change from baseline in each of three planes of movement. Significance was assumed if 95% confidence intervals did not include zero. A significant amount of movement was observed with regard to AP displacement (6.3% of C5 width) and axial distraction (-4.5% of C5 width, indicating narrowing of the intervertebral space). These correspond to 1--2 mm AP displacement and less than 1 mm axial compression. No significant angular displacement was observed. In conclusion, cricothyrotomy results in a small but significant amount of movement across an unstable c-spine injury in a cadaver model. This degree of movement is less than the threshold for clinical significance.

Cadaver↗
PubMed2001

Exercise-associated hyponatremia in marathon runners: a two-year experience.

This study was conducted to better define the pathophysiology, risk factors, and therapeutic approach to exercise-associated hyponatremia. Medical records from all participants in the 1998 Suzuki Rock 'N' Roll Marathon who presented to 14 Emergency Departments (EDs) were retrospectively reviewed to identify risk factors for the development of hyponatremia. Hyponatremic patients were compared to other runners with regard to race time and to other marathon participants seen in the ED with regard to gender, clinical signs of dehydration, and use of nonsteroidal anti-inflammatory drugs (NSAIDs). An original treatment algorithm incorporating the early use of hypertonic saline (HTS) was evaluated prospectively in our own ED for participants in the 1999 marathon to evaluate improvements in sodium correction rate and incidence of complications. A total of 26 patients from the 1998 and 1999 marathons were hyponatremic [serum sodium (SNa) < or =135 mEq/L] including 15 with severe hyponatremia (SNa < or = 125 mEq/L). Three developed seizures and required intubation and admission to an intensive care unit. Hyponatremic patients were more likely to be female, use NSAIDS, and have slower finishing times. Hyponatremic runners reported drinking "as much as possible" during and after the race and were less likely to have clinical signs of dehydration. An inverse relationship between initial SNa and time of presentation was observed, with late presentation predicting lower SNa values. The use of HTS in selected 1999 patients resulted in faster SNa correction times and fewer complications than observed for 1998 patients. It is concluded that the development of exercise-associated hyponatremia is associated with excessive fluid consumption during and after extreme athletic events. Additional risk factors include female gender, slower race times, and NSAID use. The use of HTS in selected patients seems to be safe and efficacious.

Adult↗
PubMed2000

Safety and efficacy of the Rapid Four-Step Technique for cricothyrotomy using a Bair Claw.

The Rapid Four-Step Technique (RFST) has been demonstrated to be faster than standard open crico thyrotomy technique, but may have a higher incidence of cricoid injury with tracheal hook traction applied caudad. The "Bair Claw" is a novel device that may help eliminate these complications. This randomized, experimental trial used a fresh-frozen cadaver model of cricothyrotomy to compare speed and safety between RFST using a Bair Claw and standard open technique. Outcome measures included time to definitive airway, size of largest endotracheal (ET) tube able to be passed, and incidence of complications. We observed that RFST using a Bair Claw was significantly faster than standard open technique. There was no significant difference with regard to size of ET tube able to be passed with RFST using a Bair Claw versus standard open technique, and there was no damage to trachea or larynx observed with either technique. We concluded that RFST using a Bair Claw is faster and appears to be equally safe when compared to standard open technique in a fresh-frozen cadaver model of cricothyrotomy. The two techniques were equal with regard to maximal ET tube size.

Cadaver↗
PubMed2000

Effects of cervical spine immobilization technique and laryngoscope blade selection on an unstable cervical spine in a cadaver model of intubation.

STUDY OBJECTIVE: Orotracheal intubation (OTI) is commonly used to establish a definitive airway in major trauma victims, with several different cervical spine immobilization techniques and laryngoscope blade types used. This experimental, randomized, crossover trial evaluated the effects of manual in-line stabilization and cervical collar immobilization and 3 different laryngoscope blades on cervical spine movement during OTI in a cadaver model of cervical spine injury. METHODS: A complete C5-C6 transection was performed by using an osteotome on 14 fresh-frozen cadavers. OTI was performed in a randomized crossover fashion by using both immobilization techniques and each of 3 laryngoscope blades: the Miller straight blade, the Macintosh curved blade, and the Corazelli-London-McCoy hinged blade. Intubations were recorded in real time on fluoroscopy and then transferred to video and color still images. Outcome measures included movement across C5-C6 with regard to angulation expressed in degrees of rotation and axial distraction and anteroposterior displacement with values expressed as a proportion of C5 body width. Cormack-Lehane visualization grades were also recorded as a secondary outcome measure. Data were analyzed by using multivariate analysis of variance to test for differences between immobilization techniques and between laryngoscope blades and to detect for interactions. Significance was assumed for P values of less than.05. RESULTS: Manual in-line stabilization resulted in significantly less movement than cervical collar immobilization during OTI with regard to anteroposterior displacement. Use of the Miller straight blade resulted in significantly less movement than each of the other 2 blades with regard to axial distraction. The Cormack-Lehane grade was significantly better with manual in-line stabilization versus cervical collar immobilization; no differences were observed between blades. CONCLUSION: Manual in-line stabilization results in less cervical subluxation and allows better vocal cord visualization during OTI in a cadaver model of cervical spine injury. The Miller laryngoscope blade allowed less axial distraction than the Macintosh or Corzelli-London-McCoy blades. The clinical significance of this degree of movement is unclear.

Cadaver↗
PubMed1999

Mapping the major interaction between binding protein and Ig light chains to sites within the variable domain.

Newly synthesized Ig chains are known to interact in vivo with the binding protein (BiP), a major peptide-binding chaperone in the endoplasmic reticulum. The predominant interactions between the light chain and BiP are observed early in the folding pathway, when the light chain is either completely reduced, or has only one disulfide bond. In this study, we describe the in vitro reconstitution of BiP binding to the variable domain of light chains (VL). Binding of deliberately unfolded VL was dramatically more avid than that of folded VL, mimicking the interaction in vivo. Furthermore, VL binding was inhibited by addition of ATP, was competed with excess unlabeled VL, and was demonstrated with several different VL proteins. Using this assay, peptides derived from the VL sequence were tested experimentally for their ability to bind BiP. Four peptides from both beta sheets of VL were shown to bind BiP specifically, two with significantly higher affinity. As few as these two peptide sites, one from each beta sheet of VL, are sufficient to explain the association of BiP with the entire light chain. These results suggest how BiP directs the folding of Ig in vivo and how it may be used in shaping the B cell repertoire.

Animals↗
PubMed1998

Intracellular pH and chemoresponse to NH4+ in Paramecium.

Paramecium are attracted to ammonium chloride solutions relative to sodium chloride control solutions, but little is known about the mechanisms by which attraction is evoked. A known effect of ammonium solutions in other cell types is an alteration of intracellular pH. We show here that intracellular pH is elevated upon initial exposure to 5 mM NH4Cl, but appears to decline within 10 minutes, both in wild type cells and in two mutants which do not show sustained attraction to NH4Cl using the standard behavioral assay, the T-maze. We also present quantitative values of swimming parameters that underlie the response to NH4Cl.

Ammonium Chloride↗
PubMed1998

Reversal of midazolam-induced laryngospasm with flumazenil.

Midazolam is a commonly used benzodiazepine that is ideal for conscious sedation during a variety of procedures. Laryngospasm is listed by the manufacturer as a rare side effect of midazolam. Flumazenil is a competitive inhibitor of the benzodiazepines that is available for reversal at the end of such a procedure or when too much sedation has been achieved. We present a case of a 61-year-old man who was to undergo conscious sedation before cardioversion. Shortly after receiving midazolam, he developed laryngospasm and resultant respiratory distress; the laryngospasm was reversed by a small dose of flumazenil. The symptoms recurred after approximately 25 minutes and were again reversed with flumazenil. Neither midazolam-induced laryngospasm nor its reversal with flumazenil have previously been reported. A brief discussion regarding laryngospasm and the use of flumazenil are included.

Anti-Anxiety Agents↗
PubMed1998

Association of gonadotropin receptor precursors with the protein folding chaperone calnexin.

The lutropin/choriogonadotropin receptor (LHR) and follitropin receptor (FSHR) are members of the superfamily of G protein-coupled receptors. The carboxyl half of each receptor is composed of the classical seven membrane spanning regions connected by intracellular and extracellular loops. In addition, each receptor contains a large extracellular domain. Despite the complexity of the structure of G protein-coupled receptors, little is known about how these receptors assume their correct conformations during biosynthesis. Although the role of chaperone proteins in the folding of other proteins has been well documented, their role in the folding of G protein-coupled receptors has been an enigma. To better understand the folding of the LH and FSH receptors, we examined their association with the general chaperone proteins calnexin, binding protein (BiP), and the 94-kDa glucose-regulated protein (GRP94). Clonal 293 cell lines expressing comparably high levels of each receptor were solubilized, and the extracts were incubated with the appropriate antibody bound to Protein A-sepharose beads. Experiments were performed using two approaches: 1) coimmunoprecipitation of receptor/chaperone complexes with one of the antireceptor antibodies, then SDS-PAGE and Western blotting using either anticalnexin or anti-KDEL (which recognizes BiP and GRP94) antibodies; or 2) coimmunoprecipitation of receptor/chaperone complexes with anticalnexin or anti-KDEL, then Western blotting with one of the antireceptor antibodies. Using these protocols, we found that the immature forms of both the rLHR and rFSHR are associated with calnexin, but little or no association was observed for either receptor with BiP or GRP94. These experiments show that the precursor forms of the wild-type LHR and FSHR can associate with calnexin, raising the possibility that this chaperone protein may facilitate in the folding of the gonadotropin receptors.

Calcium-Binding Proteins↗
PubMed1997

The six N-linked carbohydrates of the lutropin/choriogonadotropin receptor are not absolutely required for correct folding, cell surface expression, hormone binding, or signal transduction.

Using two separate methods, we have determined that all six potential sites for N-linked glycosylation on the rat lutropin/choriogonadotropin receptor (rLHR) contain carbohydrates. The functional roles of the carbohydrates were analyzed initially through the use of two nonglycosylated receptor mutants rLHR(N(77,152,173,269,277,291)Q) and rLHR(N(77,152,269,277,291)Q;T(175)A). Although Western blot analyses demonstrated both mutant receptors to be stably expressed, little or no hCG binding activity could be detected in detergent solubilized extracts of 293 cells expressing either nonglycosylated LHR mutant. Although this loss of hCG binding was concluded to be due to misfolding, it was unknown whether this misfolding was due to the absence of carbohydrates or to the multiple amino acid substitutions that had been introduced into the polypeptide. To differentiate between these possibilities, hCG binding assays were performed with nonglycosylated receptors obtained after tunicamycin treatment of cells expressing the wild-type rLHR. Even though these wild-type receptors were confirmed to be devoid of all N-linked carbohydrates by Western blots, they were found to bind hCG with a normal high affinity. In addition, tunicamycin-derived, nonglycosylated LHRs were present at the cell surface and exhibited a phenotype consistent with mature receptors due to their capability to mediate hCG-stimulated cAMP production as well as bind oLH with high affinity. These results indicate that the loss of high affinity hormone binding by rLHR(N(77,152,173,269,277,291)Q) and rLHR(N(77,152,269,277,291)Q;T(175)A) is simply due to the collective amino acid substitutions rather than to the absence of carbohydrates. Therefore, N-linked carbohydrates are not absolutely required for the proper folding of the rLHR into a mature receptor capable of binding hormone and signaling. These results are in marked contrast to the follitropin receptor (FSHR), a very similar receptor which has been shown to strictly require N-linked carbohydrates for folding of the nascent protein.

Animals↗
PubMed1996

Maternal reproductive effects of oral salicylic acid in Sprague-Dawley rats.

Clinical and experimental evidence indicates that exposure to relative ly large doses of acetylsalicylic acid (ASA) prolongs parturition. However, little is known about the dose-response relationship for salicylate-related effects on labor and gestation. As well, the relative potency of salicylic acid (SA) as compared with ASA for these reproductive effects has not been well investigated. This study was designed to define a dose-response relationship for salicylic acid (SA) effects on labor and gestation times in Sprague-Dawley rats. Pregnant females received oral doses of 20,80, or 200 mg/kg/day sodium salicylate, or 260 mg/kg/day acetylsalicylic acid (ASA), as a positive control, on days 15 through 21 of gestation (sperm positive = day 0). Onset of labor was followed in each animal beginning on day 21 of gestation. The data failed to demonstrate a substantial potency difference between ASA and SA but some differences in toxicity were observed. Relative to controls, gestation times were unaffected by SA. SA treatment resulted in a dose-related trend towards increased duration of labor which was statistically significant at 200 mg/kg/day of SA. ASA treatment of pregnant females resulted in both prolonged labor and gestation times. Both the highest administered dose of SA and ASA treatment contributed to increased maternal peripartum death. Overall, the study confirms a dose-response relationship for SA-induced maternal reproductive effects and supports a no observable effect level (NOEL) for this compound of 80 mg/kg/day for adverse effects on parturition.

Administration, Oral↗
PubMed1995

Role of alterations in Ca(2+)-associated signaling pathways in the immunotoxicity of polycyclic aromatic hydrocarbons.

Polycyclic aromatic hydrocarbons (PAHs) are an important class of environmental pollutants that are known to be carcinogenic and immunotoxic. The effects of PAHs on the immune system of various animals and models have been studied for at least 30 yr. Despite these efforts, the mechanism or mechanisms by which PAHs exert their effects on the immune system are still largely unknown. During recent years, the molecular events associated with lymphocyte activation and receptor-mediated signaling have become increasingly clear. Substantial progress has been made in understanding the molecular and cellular bases for toxicant-induced immune cell injury. Understanding mechanisms of drug or chemical effects on the immune system is an important area of research in the field of immunotoxicology, and indeed in all fields of toxicology. Mechanistic toxicology plays an important role in risk assessment and extrapolation of potential human health effects. In this review, we have summarized recent evidence that has examined the effects of PAHs on the immune system of animals and humans. In particular, we have focused on the effects of PAHs on cell signaling in lymphoid cells and have examined the hypothesis that PAHs alter lymphocyte activation via calcium-dependent mechanisms. Previously published reports are discussed, and new data obtained with murine B cells and cell lines are presented demonstrating the relationship between alterations in intracellular calcium and immune dysregulation. These data demonstrate a strong association between PAH-induced alterations in B- and T-lymphocyte activation and changes in calcium homeostasis.

Animals↗
PubMed1991

Suppression of local gut-associated and splenic mitogen responsiveness of lymphoid cells following oral exposure of B6C3F1 mice to 7,12-dimethylbenz[a]anthracene.

In these studies, the mitogen responsiveness of lymphocytes obtained from local gut-associated lymphoid tissues (GALT) and the spleen were evaluated following a 5-day exposure to 7,12-dimethylbenz(a)anthracene (DMBA) at doses of 50 or 150 mg/kg. Phytohemagglutinin and lipopolysaccharide (LPS) responses were suppressed in all lymphoid tissues studied. However, the LPS response in mesenteric lymph nodes and Peyer's Patches seemed to be the most sensitive indicator of immunotoxicity, indicating that B cells appear to be particularly sensitive to DMBA toxicity in the GALT. These studies demonstrate that both splenic tissues and GALT are important targets of immunotoxicity following oral administration of DMBA. Based upon these and past studies we conclude that the total administered dose of DMBA is a more important determinant of immunotoxicity than the length of exposure.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1990

Density of itch mite, Sarcoptes scabiei (Acari: Sarcoptidae) and temporal development of cutaneous hypersensitivity in swine mange.

Experimental infestations of Sarcoptes scabiei (De Geer) were established to study development of cutaneous hypersensitivity in pigs. Forty-eight pigs in six isolation rooms were used in two trials lasting 51 and 65 days, respectively. Treatments of 0 (control), 100 (low dose), and 1000 mites (high dose) per pig were randomly assigned to rooms. Intradermal skin tests with a sterile mite extract were done weekly to assess hypersensitivity. Control pigs never responded to the extract, whereas most infested pigs progressed through phases of (1) no response, (2) delayed hypersensitivity alone, (3) immediate and delayed hypersensitivity together, and (4) immediate hypersensitivity alone. High-dose pigs developed delayed and immediate hypersensitivity sooner than low-dose pigs (P less than 0.005). When related to cumulative mite-days, a measure of exposure to mite antigens, low-dose and high-dose pigs developed delayed responses after experiencing the same level of exposure. Thereafter, immediate responses developed sooner in low-dose pigs, suggesting that immediate hypersensitivity develops at a rate that is independent of rate of antigen exposure.

Animals↗