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Biomedical subjects

Donald W Landry

Publications and source records attributed to Donald W Landry.

At least 19 recordsLinked to original sources
PubMed2006

Rapid and robust protection against cocaine-induced lethality in rats by the bacterial cocaine esterase.

There is no approved means to prevent the toxic actions of cocaine. Cocaine esterase (CocE) is found in a rhodococcal strain of bacteria that grows in the rhizosphere soil around the coca plant and has been found to hydrolyze cocaine in vitro. The esteratic activity of CocE (0.1-1.0 mg, i.v.) was characterized and confirmed in vivo by assessing its ability to prevent cocaine-induced convulsions and lethality in the rat. The therapeutic efficiency of the enzyme was demonstrated by the increasing dose of cocaine (100-1000 mg/kg, i.p.) required to produce toxic effects after a single intravenous injection of CocE. The enzyme demonstrated rapid kinetics for cocaine degradation in rat and human serum. Two catalytically inactive mutants of CocE (S117A or Y44F) failed to protect rats from the toxic effects of cocaine, confirming the protective effects are due to hydrolytic activity. However, butyrylcholinesterase, an endogenous cocaine-hydrolyzing enzyme, was inactive (1.3-13 mg, i.v.) in this rat toxicity procedure. Furthermore, CocE did not block the lethality of WIN-35065-2 (560 mg/kg, i.p.), a cocaine analog that lacks the benzoyl ester moiety targeted by CocE. This characterization of CocE provides preliminary evidence that the enzyme could serve as a suitable antidote to cocaine toxicity in humans.

Animals↗
PubMed2006

Identification of small-molecule inhibitors of the Abeta-ABAD interaction.

The interaction of amyloid beta peptide (Abeta) and Abeta-binding alcohol dehydrogenase (ABAD) was recently implicated in the pathogenesis of Alzheimer's disease (AD). Using an ELISA-based screening assay, we identified frentizole, an FDA-approved immunosuppressive drug, as a novel inhibitor of the Abeta-ABAD interaction. Analysis of the frentizole structure-activity relationship led to identification of a novel benzothiazole urea with a 30-fold improvement in potency.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed2005

First-principle studies of intermolecular and intramolecular catalysis of protonated cocaine.

We have performed a series of first-principles electronic structure calculations to examine the reaction pathways and the corresponding free energy barriers for the ester hydrolysis of protonated cocaine in its chair and boat conformations. The calculated free energy barriers for the benzoyl ester hydrolysis of protonated chair cocaine are close to the corresponding barriers calculated for the benzoyl ester hydrolysis of neutral cocaine. However, the free energy barrier calculated for the methyl ester hydrolysis of protonated cocaine in its chair conformation is significantly lower than for the methyl ester hydrolysis of neutral cocaine and for the dominant pathway of the benzoyl ester hydrolysis of protonated cocaine. The significant decrease of the free energy barrier, approximately 4 kcal/mol, is attributed to the intramolecular acid catalysis of the methyl ester hydrolysis of protonated cocaine, because the transition state structure is stabilized by the strong hydrogen bond between the carbonyl oxygen of the methyl ester moiety and the protonated tropane N. The relative magnitudes of the free energy barriers calculated for different pathways of the ester hydrolysis of protonated chair cocaine are consistent with the experimental kinetic data for cocaine hydrolysis under physiologic conditions. Similar intramolecular acid catalysis also occurs for the benzoyl ester hydrolysis of (protonated) boat cocaine in the physiologic condition, although the contribution of the intramolecular hydrogen bonding to transition state stabilization is negligible. Nonetheless, the predictability of the intramolecular hydrogen bonding could be useful in generating antibody-based catalysts that recruit cocaine to the boat conformation and an analog that elicited antibodies to approximate the protonated tropane N and the benzoyl O more closely than the natural boat conformer might increase the contribution from hydrogen bonding. Such a stable analog of the transition state for intramolecular catalysis of cocaine benzoyl-ester hydrolysis was synthesized and used to successfully elicit a number of anticocaine catalytic antibodies.

Antibodies, Catalytic↗
PubMed2005

Enhancing calstabin binding to ryanodine receptors improves cardiac and skeletal muscle function in heart failure.

Abnormalities in intracellular calcium release and reuptake are responsible for decreased contractility in heart failure (HF). We have previously shown that cardiac ryanodine receptors (RyRs) are protein kinase A-hyperphosphorylated and depleted of the regulatory subunit calstabin-2 in HF. Moreover, similar alterations in skeletal muscle RyR have been linked to increased fatigability in HF. To determine whether restoration of calstabin binding to RyR may ameliorate cardiac and skeletal muscle dysfunction in HF, we treated WT and calstabin-2-/- mice subjected to myocardial infarction (MI) with JTV519. JTV519, a 1,4-benzothiazepine, is a member of a class of drugs known as calcium channel stabilizers, previously shown to increase calstabin binding to RyR. Echocardiography at 21 days after MI demonstrated a significant increase in ejection fraction in WT mice treated with JTV519 (45.8 +/- 5.1%) compared with placebo (31.1 +/- 3.1%; P < 0.05). Coimmunoprecipitation experiments revealed increased amounts of calstabin-2 bound to the RyR2 channel in JTV519-treated WT mice. However, JTV519 did not show any of these beneficial effects in calstabin-2-/- mice with MI. Additionally, JTV519 improved skeletal muscle fatigue in WT and calstabin-2-/- mice with HF by increasing the binding of calstabin-1 to RyR1. The observation that treatment with JTV519 improved cardiac function in WT but not calstabin-2-/- mice indicates that calstabin-2 binding to RyR2 is required for the beneficial effects in failing hearts. We conclude that JTV519 may provide a specific way to treat the cardiac and skeletal muscle myopathy in HF by increasing calstabin binding to RyR.

Analysis of Variance↗
PubMed2004

Sudden death in familial polymorphic ventricular tachycardia associated with calcium release channel (ryanodine receptor) leak.

BACKGROUND: Familial polymorphic ventricular tachycardia (FPVT) is characterized by exercise-induced arrhythmias and sudden cardiac death due to missense mutations in the cardiac ryanodine receptor (RyR2), an intracellular Ca2+ release channel required for excitation-contraction coupling in the heart. METHODS AND RESULTS: Three RyR2 missense mutations, P2328S, Q4201R, and V4653F, which occur in Finnish families, result in similar mortality rates of approximately 33% by age 35 years and a threshold heart rate of 130 bpm, above which exercise induces ventricular arrhythmias. Exercise activates the sympathetic nervous system, increasing cardiac performance as part of the fight-or-flight stress response. We simulated the effects of exercise on mutant RyR2 channels using protein kinase A (PKA) phosphorylation. All 3 RyR2 mutations exhibited decreased binding of calstabin2 (FKBP12.6), a subunit that stabilizes the closed state of the channel. After PKA phosphorylation, FPVT-mutant RyR2 channels showed a significant gain-of-function defect consistent with leaky Ca2+ release channels and a significant rightward shift in the half-maximal inhibitory Mg2+ concentration (IC50). Treatment with the experimental drug JTV519 enhanced binding of calstabin2 to RyR2 and normalized channel function. CONCLUSIONS: Sympathetic activation during exercise induces ventricular arrhythmias above a threshold heart rate in RyR2 mutation carriers. Simulating the downstream effects of the sympathetic activation by PKA phosphorylation of RyR2 channels containing these FPVT missense mutations produced a consistent gain-of-function defect. RyR2 function and calstabin2 depletion were rescued by JTV519, suggesting stabilization of the RyR2 channel complex may represent a molecular target for the treatment and prevention of exercise-induced arrhythmias and sudden death in these patients.

Adult↗
PubMed2004

Protection from cardiac arrhythmia through ryanodine receptor-stabilizing protein calstabin2.

Ventricular arrhythmias can cause sudden cardiac death (SCD) in patients with normal hearts and in those with underlying disease such as heart failure. In animals with heart failure and in patients with inherited forms of exercise-induced SCD, depletion of the channel-stabilizing protein calstabin2 (FKBP12.6) from the ryanodine receptor-calcium release channel (RyR2) complex causes an intracellular Ca2+ leak that can trigger fatal cardiac arrhythmias. A derivative of 1,4-benzothiazepine (JTV519) increased the affinity of calstabin2 for RyR2, which stabilized the closed state of RyR2 and prevented the Ca2+ leak that triggers arrhythmias. Thus, enhancing the binding of calstabin2 to RyR2 may be a therapeutic strategy for common ventricular arrhythmias.

Animals↗
PubMed2004

Insights into shock.

Explore the source record for details and available documents.

Adenosine Triphosphate↗
PubMed2004

Heterogeneity of the vasoconstrictor effect of vasopressin in septic shock.

OBJECTIVE: To determine whether pressor doses of vasopressin impair organ blood flow in endotoxic shock. DESIGN: Graded doses of vasopressin or phenylephrine, starting at the clinically recommended doses for pressure support in septic shock, were intravenously infused during endotoxic shock. SETTING: University hospital surgical research laboratory. SUBJECTS: Twelve random-bred female Yorkshire pigs. INTERVENTIONS: We measured mean arterial pressure, cardiac output, heart rate, pulmonary artery occlusion pressure, and carotid, mesenteric, renal, and iliac blood flows. MEASUREMENTS AND MAIN RESULTS: Low doses of vasopressin (typically used in the clinical management of septic shock) raised arterial pressure by increasing systemic vascular resistance without a significant preferential effect in the circulations measured. However, moderately greater doses of vasopressin had a very heterogeneous vasoconstrictor action; although there was no significant vasoconstriction in the carotid and iliac circulations, mesenteric and renal blood flows decreased markedly. Furthermore, at pressor doses vasopressin improved cerebral perfusion. CONCLUSIONS: The vasoconstrictor action of exogenous low-dose vasopressin in endotoxic shock does not impair blood flow to any of the vascular beds examined. However, moderately higher doses of vasopressin may induce ischemia in the mesenteric and renal circulations. The data indicate that the safe dose range for exogenous vasopressin in septic shock is narrow and support the current practice of fixed low-dose administration, generally 0.04 units/min and in no case exceeding 0.1 units/min.

Animals↗
PubMed2004

Embryonic death and the creation of human embryonic stem cells.

The creation of human embryonic stem cells through the destruction of a human embryo pits the value of a potential therapeutic tool against that of an early human life. This contest of values has resulted in a polarized debate that neglects areas of common interest and perspective. We suggest that a common ground for pursuing research on human embryonic stem cells can be found by reconsidering the death of the human embryo and by applying to this research the ethical norms of essential organ donation.

Beginning of Human Life↗
PubMed2003

Substrate-assisted antibody catalysis.

A new strategy in transition-state analog design is demonstrated to elicit catalytic antibodies. The strategy is based on substrate-assisted antibody catalysis and utilizes analogs designed to mimic the transition-state for intramolecular catalysis and thereby favor antibodies that can recruit catalytic groups from substrate. The hydrolysis of the benzoyl ester of cocaine provides an illustration. The benzoyl ester of cocaine is distant from the protonated nitrogen in the stable chair conformer but proximate in the strained boat form. An antibody stabilizing the boat form and approximating ester and amine could catalyze ester hydrolysis. To mimic the transition-state for the intramolecular catalysis, we synthesized a cocaine analog that replaces this ester with a methylenephenylphosphinate bridge to the tropane nitrogen. This bridged analog elicited 85 cocaine esterases out of 450 anti-analog antibodies-a performance markedly superior to that of a simple phosphonate ester-based analog with an identical tether. The correspondence of the analog to a "high energy" conformer eliminated product inhibition. For certain polyfunctional targets, substrate assistance can be an effective strategy for eliciting catalytic antibodies.

Alkalies↗
PubMed2003

Science review: Vasopressin and the cardiovascular system part 1--receptor physiology.

Vasopressin is emerging as a rational therapy for vasodilatory shock states. Unlike other vasoconstrictor agents, vasopressin also has vasodilatory properties. The goal of the present review is to explore the vascular actions of vasopressin. In part 1 of the review we discuss structure, signaling pathways, and tissue distributions of the classic vasopressin receptors, namely V1 vascular, V2 renal, V3 pituitary and oxytocin receptors, and the P2 class of purinoreceptors. Knowledge of the function and distribution of vasopressin receptors is key to understanding the seemingly contradictory actions of vasopressin on the vascular system. In part 2 of the review we discuss the effects of vasopressin on vascular smooth muscle and the heart, and we summarize clinical studies of vasopressin in shock states.

Humans↗
PubMed2003

Science Review: Vasopressin and the cardiovascular system part 2 - clinical physiology.

Vasopressin is emerging as a rational therapy for vasodilatory shock states. In part 1 of the review we discussed the structure and function of the various vasopressin receptors. In part 2 we discuss vascular smooth muscle contraction pathways with an emphasis on the effects of vasopressin on ATP-sensitive K+ channels, nitric oxide pathways, and interaction with adrenergic agents. We explore the complex and contradictory studies of vasopressin on cardiac inotropy and coronary vascular tone. Finally, we summarize the clinical studies of vasopressin in shock states, which to date have been relatively small and have focused on physiologic outcomes. Because of potential adverse effects of vasopressin, clinical use of vasopressin in vasodilatory shock should await a randomized controlled trial of the effect of vasopressin's effect on outcomes such as organ failure and mortality.

Animals↗
PubMed2003

Cross-reactive arrays based on three-way junctions.

We report herein a novel system for the parallel processing of molecular recognition events utilizing arrays of oligonucleotide-based fluorescent sensors to characterize hydrophobic molecules in solution. The binding domains of the sensors were based on three-way junctions that utilize double helical stems as framework regions to reliably fold regardless of variations in or around the binding domain. A reporting domain was introduced by the specific substitution of a single phosphodiester group with a phosphorothioate, followed by selective functionalization with a fluorophore. The sensors were organized into cross-reactive arrays to yield characteristic fingerprints for samples containing hydrophobic molecules. The fingerprints can be used to characterize steroids in solution, including complex biologically important fluids. Arrays have the potential for clinical applications such as the detection of gross errors in steroidogenesis.

Biosensing Techniques↗
PubMed2003

Fundamental reaction mechanism for cocaine hydrolysis in human butyrylcholinesterase.

Butyrylcholinesterase (BChE)-cocaine binding and the fundamental pathway for BChE-catalyzed hydrolysis of cocaine have been studied by molecular modeling, molecular dynamics (MD) simulations, and ab initio calculations. Modeling and simulations indicate that the structures of the prereactive BChE/substrate complexes for (-)-cocaine and (+)-cocaine are all similar to that of the corresponding prereactive BChE/butyrylcholine (BCh) complex. The overall binding of BChE with (-)-cocaine and (+)-cocaine is also similar to that proposed with butyrylthiocholine and succinyldithiocholine, i.e., (-)- or (+)-cocaine first slides down the substrate-binding gorge to bind to Trp-82 and stands vertically in the gorge between Asp-70 and Trp-82 (nonprereactive complex) and then rotates to a position in the catalytic site within a favorable distance for nucleophilic attack and hydrolysis by Ser-198 (prereactive complex). In the prereactive complex, cocaine lies horizontally at the bottom of the gorge. The fundamental catalytic hydrolysis pathway, consisting of acylation and deacylation stages similar to those for ester hydrolysis by other serine hydrolases, was proposed on the basis of the simulated prereactive complex and confirmed theoretically by ab initio reaction coordinate calculations. Both the acylation and deacylation follow a double-proton-transfer mechanism. The calculated energetic results show that within the chemical reaction process the highest energy barrier and Gibbs free energy barrier are all associated with the first step of deacylation. The calculated ratio of the rate constant (k(cat)) for the catalytic hydrolysis to that (k(0)) for the spontaneous hydrolysis is approximately 9.0 x 10(7). The estimated k(cat)/k(0) value of approximately 9.0 x 10(7) is in excellent agreement with the experimentally derived k(cat)/k(0) value of approximately 7.2 x 10(7) for (+)-cocaine, whereas it is approximately 2000 times larger than the experimentally derived k(cat)/k(0) value of approximately 4.4 x 10(4) for (-)-cocaine. All of the results suggest that the rate-determining step of the BChE-catalyzed hydrolysis of (+)-cocaine is the first step of deacylation, whereas for (-)-cocaine the change from the nonprereactive complex to the prereactive complex is rate-determining and has a Gibbs free energy barrier higher than that for the first step of deacylation by approximately 4 kcal/mol. A further analysis of the structural changes from the nonprereactive complex to the prereactive complex reveals specific amino acid residues hindering the structural changes, providing initial clues for the rational design of BChE mutants with improved catalytic activity for (-)-cocaine.

Butyrylcholinesterase↗
PubMed2003

A double-blind randomized trial: prophylactic vasopressin reduces hypotension after cardiopulmonary bypass.

BACKGROUND: Inhibition of angiotensin-converting enzyme (ACE) predisposes patients to vasodilatory hypotension after cardiopulmonary bypass (CPB). This hypotension has been correlated with arginine vasopressin deficiency and can be corrected by its replacement. In patients receiving ACE inhibition, we investigated whether initiation of vasopressin before CPB would diminish post-CPB hypotension and catecholamine use by avoiding vasopressin deficiency. METHODS: Cardiac surgical patients on ACE inhibitor therapy were randomized to receive vasopressin (0.03 U/min) (n = 13) or an equal volume of normal saline (n = 14) starting 20 minutes before CPB. RESULTS: Vasopressin did not change pre-CPB mean arterial pressure or pulmonary artery pressure. After CPB, the vasopressin group had a lower peak norepinephrine dose than the placebo group (4.6 +/- 2.5 versus 7.3 +/- 3.5 microg/min, p = 0.03), a shorter period on catecholamines (5 +/- 6 versus 11 +/- 7 hours, p = 0.03), fewer hypotensive episodes (1 +/- 1 versus 4 +/- 2, p < 0.01), and a shorter intensive care unit length of stay (1.2 +/- 0.4 versus 2.1 +/- 1.4 days, p = 0.03). CONCLUSIONS: In this cohort, prophylactic administration of vasopressin, at a dose without a vasopressor effect pre-CPB, reduced post-CPB hypotension and vasoconstrictor requirements, and was associated with a shorter intensive care unit stay.

Adult↗