Impaired adenylate cyclase signaling in acute myocardial ischemia: Impact on effectiveness of P2Y12 receptor antagonists.

INTRODUCTION: P2Y12 receptor antagonists reduce risk of thrombotic complications after stent implantation but increase bleeding risk. Activation of P2Y12 receptors by ADP causes Gi-protein-mediated inhibition of adenylate cyclase (AC), thus limiting platelet response to anti-aggregatory effect of prostacyclin (PGI2). However, P2Y12 blockade reverses this ADP-induced suppression of the platelet PGI2/AC signaling pathway. We previously demonstrated that impairment of this pathway predicts poor response to clopidogrel. OBJECTIVES: To identify clinical correlates of variability in PGI2/AC signaling, and to assess the impact of such variability on individual responses to the direct P2Y12 receptor antagonists ticagrelor (in vivo) and 2-methyl-thioadenosine-monophosphate (2MeSAMP) (in vitro). PATIENTS/METHODS: We compared the inhibitory effects of prostaglandin E1 (PGE1) and the PGI2 analog Iloprost (Ilt) on platelet aggregation in whole blood samples from healthy control subjects (n = 17), and patients with stable angina pectoris (SAP; n = 35) or acute coronary syndromes (ACS; n = 23), with or without associated diabetes/hyperglycemia. RESULTS: Compared to control subjects, patients with ACS and - to a lesser extent - those with SAP, exhibited impaired responses to PGE1, accentuated in the presence of hyperglycemia. Efficacy of ticagrelor treatment, measured as change in platelet reactivity index, was directly related to pre-treatment PGE1 response, both at univariate and multivariate analysis. There was a strong correlation between extent of inhibition of platelet aggregation, whether by PGE1 or Ilt, and the anti-aggregatory effect of 2MeSAMP in vitro. CONCLUSIONS: The integrity of PGI2/AC signaling, which is impaired in the presence of ACS and hyperglycemia, predetermines the anti-aggregatory efficiency of P2Y12 receptor antagonists.

A systematic review and meta-analysis of early goal-directed therapy for septic shock: the ARISE, ProCESS and ProMISe Investigators.

PURPOSE: To determine whether early goal-directed therapy (EGDT) reduces mortality compared with other resuscitation strategies for patients presenting to the emergency department (ED) with septic shock. METHODS: Using a search strategy of PubMed, EmBase and CENTRAL, we selected all relevant randomised clinical trials published from January 2000 to January 2015. We translated non-English papers and contacted authors as necessary. Our primary analysis generated a pooled odds ratio (OR) from a fixed-effect model. Sensitivity analyses explored the effect of including non-ED studies, adjusting for study quality, and conducting a random-effects model. Secondary outcomes included organ support and hospital and ICU length of stay. RESULTS: From 2395 initially eligible abstracts, five randomised clinical trials (n = 4735 patients) met all criteria and generally scored high for quality except for lack of blinding. There was no effect on the primary mortality outcome (EGDT: 23.2% [495/2134] versus control: 22.4% [582/2601]; pooled OR 1.01 [95% CI 0.88-1.16], P = 0.9, with heterogeneity [I(2) = 57%; P = 0.055]). The pooled estimate of 90-day mortality from the three recent multicentre studies (n = 4063) also showed no difference [pooled OR 0.99 (95% CI 0.86-1.15), P = 0.93] with no heterogeneity (I(2) = 0.0%; P = 0.97). EGDT increased vasopressor use (OR 1.25 [95% CI 1.10-1.41]; P < 0.001) and ICU admission [OR 2.19 (95% CI 1.82-2.65); P < 0.001]. Including six non-ED randomised trials increased heterogeneity (I(2) = 71%; P < 0.001) but did not change overall results [pooled OR 0.94 (95% CI 0.82 to 1.07); P = 0.33]. CONCLUSION: EGDT is not superior to usual care for ED patients with septic shock but is associated with increased utilisation of ICU resources.

Crystal structure of carboxypeptidase A complexed with D-cysteine at 1.75 A - inhibitor-induced conformational changes.

D-Cysteine differs from the antiarthritis drug D-penicillamine by only two methyl groups on the beta-carbon yet inhibits carboxypeptidase A (CPD) by a distinct mechanism: D-cysteine binds tightly to the active site zinc, while D-penicillamine catalyzes metal removal. To investigate the structural basis for this difference, we solved the crystal structure of carboxypeptidase A complexed with D-cysteine (D-Cys) at 1.75-A resolution. D-Cys binds the active site zinc with a sulfur ligand and forms additional interactions with surrounding side chains of the enzyme. The structure explains the difference in potency between D-Cys and L-Cys and provides insight into the mechanism of D-penicillamine inhibition. D-Cys binding induces a concerted motion of the side chains around the zinc ion, similar to that found in other carboxypeptidase-inhibitor crystal structures and along a limited path. Analysis of concerted motions of CPD and CPD-inhibitor crystal structures reveals a clustering of these structures into distinct groups. Using the restricted conformational flexibility of a drug target in this type of analysis could greatly enhance efficiency in drug design.

Inhibition of carboxypeptidase A by D-penicillamine: mechanism and implications for drug design.

Zinc metalloprotease inhibitors are usually designed to inactivate the enzyme by forming a stable ternary complex with the enzyme and active-site zinc. D-Cysteine inhibits carboxypeptidase, ZnCPD, by forming such a complex, with a K(i) of 2.3 microM. In contrast, the antiarthritis drug D-penicillamine, D-PEN, which differs from D-Cys only by the presence of two methyl groups on the beta-carbon, inhibits ZnCPD by promoting the release of the active-site zinc. We have given the name catalytic chelator to such inhibitors. Inhibition is a two-step process characterized by formation of a complex with the enzyme (K(i(initial)) = 1.2 mM) followed by release of the active-site zinc at rates up to 420-fold faster than the spontaneous release. The initial rate of substrate hydrolysis at completion of the second step also depends on D-PEN concentration, reflecting formation of a thermodynamic equilibrium governed by the stability constants of chelator and apocarboxypeptidase for zinc (K(i(final)) = 0.25 mM). The interaction of D-PEN and D-Cys with the active-site metal has been examined by replacing the active-site zinc by a chromophoric cobalt atom. Both inhibitors perturb the d-d transitions of CoCPD in the 500-600 nm region within milliseconds of mixing but only the CoCPD.D-Cys complex displays a strong S --> Co(II) charge-transfer band at 340 nm indicative of a metal-sulfur bond. While the D-Cys complex is stable, the CoCPD.D-PEN complex breaks down to apoenzyme and Co(D-PEN)(2) with a half-life of 0.5 s. D-PEN is the first drug found to inhibit a metalloprotease by increasing the dissociation rate constant of the active-site metal. The ability of D-PEN to catalyze metal removal from carboxypeptidase A and other zinc proteases suggests a possible mechanism of action in arthritis and Wilson's disease and may also underlie complications associated with its clinical use.

Hyperglycemia in hummingbirds and its consequences for hemoglobin glycation.

We measured levels of glucose and glycated hemoglobin in the blood of three of the world's smallest nectarivorous birds, the Anna's (Calypte anna), Costa's (Calypte costae), and ruby-throated hummingbirds (Archilochus colubris). Plasma glucose levels of hummingbirds that were fasted overnight (17 mM) were higher than those in any mammal and are among the highest ever measured in a fasting vertebrate. Glucose levels in hummingbirds just after feeding were extreme, rising as high as 42 mM. The surprisingly high blood glucose concentrations in hummingbirds were accompanied by glycated hemoglobin levels that are the highest ever measured in birds but are lower than those of non-diabetic humans. How hummingbirds tolerate blood glucose levels that cause serious neurological and microvascular pathologies in diabetic humans and animals remains unknown.