Anticoagulation with argatroban using hemoclot™ targets is safe and effective in CARDS patients receiving venovenous extracorporeal membrane oxygenation: An exploratory bi-centric cohort study

Direct thrombin inhibitors, including argatroban, are increasingly used for anticoagulation during venovenous extracorporeal membrane oxygenation (VV ECMO). In many centers activated partial thromboplastin time (aPTT) is used for monitoring, but it can be affected by several confounders. The aim of this study was to evaluate the safety and efficacy of anticoagulation with argatroban titrated according to diluted thrombin time targets (hemoclot™ assay) compared to anti-Xa guided anticoagulation with unfractionated heparin (UFH).

METHODS

This cohort study included adults at two tertiary care centers who required VV ECMO for severe COVID-19-related acute respiratory distress syndrome (CARDS). Patients received center-dependent argatroban or UFH for anticoagulation during ECMO. Argatroban was guided following a hemoclot™ target range of 0.4-0.6 μg/ml. UFH was guided by anti-factor Xa (antiXa) levels (0.2-0.3 IU/ml). The primary outcome was safety of argatroban compared to UFH, assessed by time to first clinically relevant bleeding event or death during ECMO. Secondary outcomes included efficacy (time to thromboembolism) and feasibility (proportion of anticoagulation targets within range).

RESULTS

From 2019 to 2021 57 patients were included in the study with 27 patients (47 %) receiving argatroban and 30 patients (53 %) receiving UFH. The time to the first clinically relevant bleeding or death during ECMO was similar between groups (HR (argatroban vs. UFH): 1.012, 95 % CI 0.44-2.35, p = 0.978). Argatroban was associated with a decreased risk for thromboembolism compared to UFH (HR 0.494 (95 % CI 0.26-0.95; p = 0.034)). The overall proportion of anticoagulation within target ranges was not different between groups (46 % (23-54 %) vs. 46 % (37 %-57 %), p = 0.45).

CONCLUSION

Anticoagulation with argatroban according to hemoclot™ targets (0.4-0.6 μg/ml) compared to antiXa guided UFH (0.2-0.3 IU/ml) is safe and may prolong thromboembolism-free time in patients with severe ARDS requiring VV ECMO.

Precursor-directed biosynthesis and biological activity of tripropeptin Cpip, a new tripropeptin C analog containing pipecolic acid

Tripropeptin C, a non-ribosomal cyclic lipopeptide containing three proline residues, exhibits excellent efficacy in the mouse-methicillin-resistant Staphylococcus aureus septicemia model. Since tripropeptins contain L-prolyl-D-proline and, as a result, are known to form a hairpin structure in proteins, it was of interest to determine whether this substructure contributes to their antibacterial activity. In this study, prolines in tripropeptin C were replaced with pipecolic acid(s) using precursor-directed biosynthesis. Only a new tripropeptin analog, tripropeptin Cpip, which has one L-pipecolic acid in place of L-proline, was isolated. The in vitro antimicrobial activity of the new analog was approximately two to four times weaker activity against Gram-positive bacteria, including drug-resistant species, compared with that of tripropeptin C. These results suggest that the L-prolyl-D-proline substructure plays an important role in the observed potency of tripropeptins.

Association of Argatroban Dose With Coagulation Laboratory Test in Patients on Extracorporeal Membrane Oxygenation: Activated Clotting Time vs Activated Partial Thromboplastin Time

BACKGROUND

Only some studies have directly compared and analyzed the roles of activated partial thromboplastin time (aPTT) and activated clotting time (ACT) in coagulation monitoring during argatroban administration.

OBJECTIVES

This study aims to assess the correlation of argatroban dose with ACT and aPTT values and to identify the optimal coagulation test for argatroban dose adjustment.

METHODS

We evaluated 55 patients on extracorporeal membrane oxygenation (ECMO) who received argatroban for more than 72 hours. The correlation between argatroban dose and aPTT and ACT values was evaluated. To compare argatroban dose and bleeding events according to liver dysfunction, the patients were divided into 2 groups based on alanine aminotransferase and total bilirubin.

RESULTS

Among the 55 patients, a total of 459 doses and coagulation tests were evaluated. The aPTT and ACT values showed a weak correlation with argatroban dose, with the Pearson correlation coefficients of 0.261 (P < 0.001) and 0.194 (P = 0.001), respectively. The agreement between the target 150 to 180 seconds for ACT and 55 to 75 seconds for aPTT was observed in 140 patients (46.1%). Twenty-four patients (43.6%) had liver dysfunction when they started argatroban. The median argatroban dose was lower in the liver dysfunction group than in the control group (0.094 mcg/kg/min vs 0.169 mcg/kg/min, P = 0.020). Difference was not observed between the 2 groups in the amount of red blood cell (0.47 vs 0.43 pack, P = 0.909) and platelet (0.60 vs 0.08 pack, P = 0.079) transfusion per day.

CONCLUSION AND RELEVANCE

A weak correlation was observed between argatroban dose and the aPTT and ACT values. However, the agreement between aPTT and ACT was only 46.1% regarding the scope of target range. Further research is necessary to determine how to assess the optimal argatroban dose for patients administered argatroban while undergoing ECMO at the intensive care unit.

Direct thrombin inhibitors fail to reverse the negative effects of heparin on lung growth and function after murine left pneumonectomy

Neonates with congenital diaphragmatic hernia (CDH) frequently require cardiopulmonary bypass and systemic anticoagulation. We previously demonstrated that even subtherapeutic heparin impairs lung growth and function in a murine model of compensatory lung growth (CLG). The direct thrombin inhibitors (DTIs) bivalirudin and argatroban preserved growth in this model. Although DTIs are increasingly used for systemic anticoagulation clinically, patients with CDH may still receive heparin. In this experiment, lung endothelial cell proliferation was assessed following treatment with heparin-alone or mixed with increasing concentrations of bivalirudin or argatroban. The effects of subtherapeutic heparin with or without DTIs in the CLG model were also investigated. C57BL/6J mice underwent left pneumonectomy and subcutaneous implantation of osmotic pumps. Pumps were preloaded with normal saline, bivalirudin, or argatroban; treated animals received daily intraperitoneal low-dose heparin. In vitro, heparin-alone decreased endothelial cell proliferation and increased apoptosis. The effect of heparin on proliferation, but not apoptosis, was reversed by the addition of bivalirudin and argatroban. In vivo, low-dose heparin decreased lung volume compared with saline-treated controls. All three groups that received heparin demonstrated decreased lung function on pulmonary function testing and impaired exercise performance on treadmill tolerance testing. These findings correlated with decreases in alveolarization, vascularization, angiogenic signaling, and gene expression in the heparin-exposed groups. Together, these data suggest that bivalirudin and argatroban fail to reverse the inhibitory effects of subtherapeutic heparin on lung growth and function. Clinical studies on the impact of low-dose heparin with DTIs on CDH outcomes are warranted.NEW & NOTEWORTHY Infants with pulmonary hypoplasia frequently require cardiopulmonary bypass and systemic anticoagulation. We investigate the effects of simultaneous exposure to heparin and direct thrombin inhibitors (DTIs) on lung growth and pulmonary function in a murine model of compensatory lung growth (CGL). Our data suggest that DTIs fail to reverse the inhibitory effects of subtherapeutic heparin on lung growth and function. Clinical studies on the impact of heparin with DTIs on clinical outcomes are thus warranted.

Argatroban Use in Pediatric Patients Supported by Paracorporeal Ventricular Assist Devices

Direct thrombin inhibitor (DTI) use has been associated with decreased stroke and death rates in children on ventricular assist devices (VADs). Most information about DTI use for children on VADs has focused on bivalirudin with limited data on argatroban. We hypothesized that, compared to unfractionated heparin (UFH), argatroban would be associated with decreased bleeding, stroke, and death rates in children on VADs. We retrospectively collected data from patients <18 years old on paracorporeal VADs at Children's Wisconsin between January 1, 2010 and July 1, 2021. We divided patients into cohorts based on anticoagulation strategy with heparin or argatroban. Definitions of bleeding and neurologic events were the same as in other published reports on this population. We compared categorical variables with the χ 2 or Fisher's exact test, and continuous variables with the Mann-Whitney U test. Nineteen children were anticoagulated with argatroban, and 16 with heparin. Demographics between groups were not significantly different. Stroke, bleeding, and death rates did not differ between patients treated with UFH versus argatroban. The study population was complex with a high rate of extracorporeal membrane oxygenation (ECMO) use before VAD support, which likely impacted our findings. Our study does not support argatroban as a superior alternative anticoagulant compared to UFH in children requiring VADs.

Can the combination of antiplatelet or alteplase thrombolytic therapy with argatroban benefit patients suffering from acute stroke? a systematic review, meta-analysis, and meta-regression

BACKGROUND

The effectiveness of administering argatroban as a treatment approach following antiplatelet therapy or alteplase thrombolytic therapy in patients with acute stroke is presently uncertain. However, it is important to highlight the potential benefits of combining this medication with known thrombolytics or antiplatelet therapy. One notable advantage of argatroban is its short half-life, which helps minimize excessive anticoagulation and risk of bleeding complications in inadvertent cases of hemorrhagic stroke. By conducting a meticulous review and meta-analysis, we aim to further explore the common use of argatroban and examine the plausible advantages of combining this medication with established thrombolytic and antiplatelet therapies.

METHOD

In this study, we performed a rigorous and methodical search for both randomized controlled trials and retrospective analyses. Our main objective was to analyze the impact of argatroban on the occurrence of hemorrhagic events and the mRS scores of 0-2. We utilized a meta-analysis to assess the relative risk (RR) associated with using argatroban versus not using it.

RESULTS

In this study, we analyzed data from 11 different studies, encompassing a total of 8,635 patients. Out of these patients, 3999(46.3%) received argatroban treatment while the remaining 4636(53.7%)did not. The primary outcome of 90-day functional independence (modified Rankin scale (mRS) score≤2) showed that the risk ratio (RR) for patients using argatroban after alteplase thrombolytic therapy compared to those not using argatroban was(RR, 1.00 ([95% CI, 0.92-1.09]; P = 0.97), indicating no statistical significance. However, for patients using argatroban after antiplatelet therapy, was (RR,1.09 [95% CI, 1.04-1.14]; P = 0.0001), which was statistically significant. In terms of hemorrhagic events, the RR for patients using argatroban compared to those not using argatroban was (RR,1.08 [95% CI, 0.88-1.33]; P = 0.46), indicating no statistical significance.

CONCLUSION

The results of this study suggest that further research into combination therapy with argatroban and antiplatelet agents may be warranted, however more rigorous RCTs are needed to definitively evaluate the effects of combination treatment.

R97 at "Handlebar" Binding Mode in Active Pocket Plays an Important Role in Fe(II)/α-Ketoglutaric Acid-Dependent Dioxygenase cis-P3H-Mediated Selective Synthesis of (2S,3R)-3-Hydroxypipecolic Acid

Pipecolic acid (Pip) and its derivative hydroxypipecolic acids, such as (2S,3R)-3-hydroxypipecolic acid (cis-3-L-HyPip), are components of many natural and synthetic bioactive molecules. Fe(II)/α-ketoglutaric acid (Fe(II)/2-OG)-dependent dioxygenases can catalyze the hydroxylation of pipecolic acid. However, the available enzymes with desired activity and selectivity are limited. Herein, we compare the possible candidates in the Fe(II)/2-OG-dependent dioxygenase family, and cis-P3H is selected for potentially catalyzing selective hydroxylation of L-Pip. cis-P3H was further engineered to increase its catalytic efficiency toward L-Pip. By analyzing the structural confirmation and residue composition in substrate-binding pocket, a "handlebar" mode of molecular interactions is proposed. Using molecular docking, virtual mutation analysis, and dynamic simulations, R97, E112, L57, and G282 were identified as the key residues for subsequent site-directed saturation mutagenesis of cis-P3H. Consequently, the variant R97M showed an increased catalytic efficiency toward L-Pip. In this study, the k_cat/K_m value of the positive mutant R97M was about 1.83-fold that of the wild type. The mutation R97M would break the salt bridge between R97 and L-Pip and weaken the positive-positive interaction between R97 and R95. Therefore, the force on the amino and carboxyl groups of L-Pip was lightly balanced, allowing the molecule to be stabilized in the active pocket. These results provide a potential way of improving cis-P3H catalytic activity through rational protein engineering.

Atrial Fibrillation in a Patient with Heparin-induced Thrombocytopenia Successfully Treated by Radiofrequency Catheter Ablation Using a Direct Thrombin Inhibitor

A 74-year-old man was admitted to our hospital to undergo radiofrequency catheter ablation (RFCA) of persistent atrial fibrillation (AF). We found that he had a history of heparin-induced thrombocytopenia (HIT). Thus, a direct thrombin inhibitor, Argatroban Hydrate (Argatroban^®), was used instead of heparin as anticoagulation therapy during the RFCA procedure. Finally, the AF was successfully treated by RFCA without any complications. Given these findings, the direct thrombin inhibitor Argatroban^® may be effective and feasible for anticoagulation therapy during RFCA procedures for AF in patients with HIT, such as the present case.

Pipecolic Acid, a Putative Mediator of the Encephalopathy of Cerebral Malaria and the Experimental Model of Cerebral Malaria

BACKGROUND

We explored a metabolic etiology of cerebral malaria (CM) coma.

METHODS

Plasma metabolites were compared between Malawian children with CM and mild Plasmodium falciparum malaria. A candidate molecule was further studied in animal models of malaria.

RESULTS

Clinically abnormal concentrations of pipecolic acid (PA) were present in CM plasma, and nearly normal in mild malaria samples. PA is renally cleared and the elevated PA blood levels were associated with renal insufficiency, which was present only in CM subjects. Prior studies demonstrate that PA has neuromodulatory effects and is generated by malaria parasites. PA brain levels in Plasmodium berghei ANKA-infected animals in the experimental cerebral malaria (ECM) model inversely correlated with normal behavior and correlated with blood-brain barrier (BBB) permeability. Mice infected with malaria species that do not induce neurological abnormalities or manifest BBB permeability had elevated plasma PA levels similar to ECM plasma at 7 days postinfection; however, they had low PA levels in the brain compared to ECM mice brains at 7 days postinfection.

CONCLUSIONS

Our model suggests that malaria-generated PA induces coma in CM and in ECM. The role of BBB permeability and the mechanisms of PA neuromodulation in CM will require additional investigation.

Metabolic regulation of systemic acquired resistance

Plants achieve an optimal balance between growth and defense by a fine-tuned biosynthesis and metabolic inactivation of immune-stimulating small molecules. Recent research illustrates that three common hubs are involved in the cooperative regulation of systemic acquired resistance (SAR) by the defense hormones N-hydroxypipecolic acid (NHP) and salicylic acid (SA). First, a common set of regulatory proteins is involved in their biosynthesis. Second, NHP and SA are glucosylated by the same glycosyltransferase, UGT76B1, and thereby inactivated in concert. And third, NHP confers immunity via the SA receptor NPR1 to reprogram plants at the level of transcription and primes plants for an enhanced defense capacity. An overview of SA and NHP metabolism is provided, and their contribution to long-distance signaling in SAR is discussed.

Exogenous pipecolic acid modulates plant defence responses against Podosphaera xanthii and Pseudomonas syringae pv. lachrymans in cucumber (Cucumis sativus L.)

Systemic acquired resistance (SAR) is a long-lasting and broad-based resistance that can be activated following infection with (a)virulent pathogens and treatment with exogenous elicitors. Pipecolic acid (Pip), a Lys-derived non-protein amino acid, naturally occurs in many different plant species, and its N-hydroxylated derivative, N-hydroxypipecolic acid (NHP), acts as a crucial regulator of SAR. In the present study, we conducted a systemic analysis of the defence responses of a series of D,L-Pip-pretreated Cucumis sativus L. against Podosphaera xanthii (P. xanthii) and Pseudomonas syringae pv. lachrymans (Psl). The effects of D,L-Pip on ROS metabolism, defence-related gene expression, SA accumulation and activity of defence-related enzymes were evaluated. We show that exogenously applied D,L-Pip successfully induces SAR in cucumber against P. xanthii and Psl, but not Fusarium oxysporum f. sp. cucumerinum (Foc). Exogenous application of D,L-Pip via the root system is sufficient to activate the accumulation of free and conjugated salicylic acid (SA), and earlier and stronger upregulation of SAR-associated gene transcription upon P. xanthii infection. Furthermore, D,L-Pip treatment and subsequent pathogen inoculation promote hydrogen peroxide and superoxide accumulation, as well as Rboh transcription activation in cucumber plants, suggesting that D,L-Pip-triggered ROS production might be involved in enhanced defence reactions against P. xanthii. We also demonstrate that D,L-Pip pretreatment increases the activity of defence-associated enzymes, including peroxidase, chitinase and β-1,3-glucanase. The results presented in this report provide promising features of Pip as an elicitor in cucumber and call for further studies that may uncover its potential in production areas against different phytopathogens.

A quest for long-distance signals: the epidermis as central regulator of pipecolic acid-associated systemic acquired resistance

This article comments on: Jiang SC, Engle NL, Banday ZZ, Cecchini NM, Jung HW, Tschaplinski TJ, Greenberg JT. 2021. ALD1 accumulation in Arabidopsis epidermal plastids confers local and non-autonomous disease resistance. Journal of Experimental Botany 72, 2710–2726.

Biosynthesis of Nonimmunosuppressive ProlylFK506 Analogues with Neurite Outgrowth and Synaptogenic Activity

Separating the immunosuppressive activity of FK506 (1) from its neurotrophic activity is required to develop FK506 analogues as drugs for the treatment of neuronal diseases. Two new FK506 analogues, 9-deoxo-36,37-dihydro-prolylFK506 (2) and 9-deoxo-31-O-demethyl-36,37-dihydro-prolylFK506 (3) containing a proline moiety instead of the pipecolate ring at C-1 and modifications at the C-9/C-31 and C-36-C-37 positions, respectively, were biosynthesized, and their biological activities were evaluated. The proline substitution in 9-deoxo-36,37-dihydroFK506 and 9-deoxo-31-O-demethyl-36,37-dihydroFK506 reduced immunosuppressive activity by more than 120-fold, as previously observed. Compared with FK506 (1), 2 and 3 exhibited ∼1.2 × 105- and 2.2 × 105-fold reductions in immunosuppressive activity, respectively, whereas they retained almost identical neurite outgrowth activity. Furthermore, these compounds significantly increased the strength of synaptic transmission, confirming that replacement of the pipecolate ring with a proline is critical to reduce the strong immunosuppressive activity of FK506 (1) while enhancing its neurotrophic activity.

Metabolite profiling identified pipecolic acid as an important component of peanut seed resistance against Aspergillus flavus infection

In a previous study, we identified a halotolerant rhizobacterium belonging to the genus Klebsiella (MBE02) that protected peanut seeds from Aspergillus flavus infection. Here, we investigated the mechanisms underlying the effect of MBE02 against A. flavus via untargeted metabolite profiling of peanut seeds treated with MBE02, A. flavus, or MBE02+A. flavus. Thirty-five metabolites were differentially accumulated across the three treatments (compared to the control), and the levels of pipecolic acid (Pip) were reduced upon A. flavus treatment only. We validated the function of Pip against A. flavus using multiple resistant and susceptible peanut cultivars. Pip accumulation was strongly associated with the resistant genotypes that also accumulated several mRNAs of the ALD1-like gene in the Pip biosynthesis pathway. Furthermore, exogenous treatment of a susceptible peanut cultivar with Pip reduced A. flavus infection in the seeds. Our findings indicate that Pip is a key component of peanut resistance to A. flavus.

Inducible biosynthesis and immune function of the systemic acquired resistance inducer N-hydroxypipecolic acid in monocotyledonous and dicotyledonous plants

Recent work has provided evidence for the occurrence of N-hydroxypipecolic acid (NHP) in Arabidopsis thaliana, characterized its pathogen-inducible biosynthesis by a three-step metabolic sequence from l-lysine, and established a central role for NHP in the regulation of systemic acquired resistance. Here, we show that NHP is biosynthesized in several other plant species in response to microbial attack, generally together with its direct metabolic precursor pipecolic acid and the phenolic immune signal salicylic acid. For example, NHP accumulates locally in inoculated leaves and systemically in distant leaves of cucumber in response to Pseudomonas syringae attack, in Pseudomonas-challenged tobacco and soybean leaves, in tomato inoculated with the oomycete Phytophthora infestans, in leaves of the monocot Brachypodium distachyon infected with bacterial (Xanthomonas translucens) and fungal (Magnaporthe oryzae) pathogens, and in M. oryzae-inoculated barley. Notably, resistance assays indicate that NHP acts as a potent inducer of acquired resistance to bacterial and fungal infection in distinct monocotyledonous and dicotyledonous species. Pronounced systemic accumulation of NHP in leaf phloem sap of locally inoculated cucumber supports a function for NHP as a phloem-mobile immune signal. Our study thus generalizes the existence and function of an NHP resistance pathway in plant systemic acquired resistance.

N-hydroxypipecolic acid: a general and conserved activator of systemic plant immunity

This article comments on: Schnake A, Hartmann M, Schreiber S, Malik J, Brahmann L, Yildiz I, von Dahlen J, Rose LE, Schaffrath U, Zeier J. 2020. Inducible biosynthesis and immune function of the systemic acquired resistance inducer N-hydroxypipecolic acid in monocotyledonous and dicotyledonous plants. Journal of Experimental Botany 71, 6444–6459.

JMJ14 encoded H3K4 demethylase modulates immune responses by regulating defence gene expression and pipecolic acid levels

Epigenetic modifications have emerged as an important mechanism underlying plant defence against pathogens. We examined the role of JMJ14, a Jumonji (JMJ) domain-containing H3K4 demethylase, in local and systemic plant immune responses in Arabidopsis. The function of JMJ14 in local or systemic defence response was investigated by pathogen growth assays and by analysing expression and H3K4me3 enrichments of key defence genes using qPCR and ChIP-qPCR. Salicylic acid (SA) and pipecolic acid (Pip) levels were quantified and function of JMJ14 in SA- and Pip-mediated defences was analysed in Col-0 and jmj14 plants. jmj14 mutants were compromised in both local and systemic defences. JMJ14 positively regulates pathogen-induced H3K4me3 enrichment and expression of defence genes involved in SA- and Pip-mediated defence pathways. Consequently, loss of JMJ14 results in attenuated defence gene expression and reduced Pip accumulation during establishment of systemic acquired resistance (SAR). Exogenous Pip partially restored SAR in jmj14 plants, suggesting that JMJ14 regulated Pip biosynthesis and other downstream factors regulate SAR in jmj14 plants. JMJ14 positively modulates defence gene expressions and Pip levels in Arabidopsis.

Management of Anticoagulation with Impella® Percutaneous Ventricular Assist Devices and Review of New Literature

Cardiogenic shock is a life-threatening condition that may occur secondary to a variety of cardiac conditions, and may require temporary support with percutaneous ventricular devices like the Impella®. Anticoagulation in patients with Impella® devices can often be complicated due to unpredictable purge flow rates, pre-existing coagulopathy, or heparin allergies. The purpose of this article is to discuss the various options for anticoagulation in the setting of Impella®. The article will also describe recent updates (2014-current) in literature surrounding anticoagulation therapy for Impella® devices. At total of 228 articles were initially obtained through the PubMed search, with inclusion of 6 articles. A total of 51 patients had data in the six studies that were included in the review. Heparin for anticoagulation in the purge solution, at two different dextrose concentrations (5% and 20%), was associated with similar therapeutic activated partial thromboplastin time rates, thrombotic and bleeding events. One case series described the use of argatroban in the purge solution for anticoagulation in two patients with suspected heparin-induced thrombocytopenia, without bleeding or thrombotic complications. Pump thrombosis was not reported in any of the six studies. Anticoagulation in the setting of mechanical circulatory support devices is a challenging aspect of critical care. Institutions should have set protocols that clearly define the options for anticoagulation. Future studies that look at longer durations of support and possible operation of the Impella® device with a heparin-free purge solution are needed.

N-hydroxypipecolic acid and salicylic acid: a metabolic duo for systemic acquired resistance

Recent research has established that the pipecolate pathway, a three-step biochemical sequence from l-lysine to N-hydroxypipecolic acid (NHP), is central for plant systemic acquired resistance (SAR). NHP orchestrates SAR establishment in concert with the immune signal salicylic acid (SA). Here, we outline the biochemistry of NHP formation from l-Lys and address novel progress on SA biosynthesis in Arabidopsis and other plant species. In Arabidopsis, the pathogen-inducible pipecolate and salicylate pathways are activated by common and distinct regulatory elements and mutual interactions between both metabolic branches exist. The mode of action of NHP in SAR involves direct induction of SAR gene expression, signal amplification, priming for enhanced defense activation and positive interplay with SA signaling to ensure elevated plant immunity.

Evaluation of empiric versus nomogram-based direct thrombin inhibitor management in patients with suspected heparin-induced thrombocytopenia

The aim of this study was to evaluate a direct thrombin inhibitor (DTI) titration protocol in patients with suspected HIT. This observational study compared patients treated with argatroban or bivalirudin according to the University of Colorado Hospital DTI titration protocol versus a control group treated prior to protocol implementation. Protocol patients had DTI initial doses based on organ function and fixed dosage adjustments of 10, 25, or 50%. Initial doses and titrations in the control group were made per physician discretion. A total of 130 patients were enrolled: 47 in the protocol group and 83 in the control group (median age 54 years, 63% male, 78% critically ill, and 54% received argatroban). Goal aPTT was achieved with initial DTI dose in 64% of protocol patients and 46% of control patients (P = 0.07). Median (IQR) time to goal aPTT was reduced in the protocol group compared to the control group [5 hr (2-10 hr) vs. 13 hr (6-29 hr); P < 0.0001]. Median time to dose stabilization was 10 hr (6-27 hr) and 22 hr (13-40 hr) in the protocol and control groups, respectively; P < 0.0001. Median number of titrations to goal was 0 (0-1) versus 1 (0-4), respectively; P = 0.02. Median percentage of aPTT values in goal was 67% (41-100%) versus 53% (33-76%), respectively; P = 0.027. The DTI titration protocol shortened time to achieve goal aPTT, reduced time to dose stabilization, decreased the number of titrations required to achieve aPTT goal, and improved the percentage of aPTT values in goal range.

Essentials of anticoagulation in hemodialysis

Numerous acquired hemostatic abnormalities have been identified in renal insufficiency. Hemodialysis procedures add to these disturbances as they repetitively imply turbulent blood flow, high shear stress, and contact of blood to artificial surfaces. This nonphysiological environment leads to activation of platelets, leukocytes, and the coagulation cascade, resulting in fouling of the membrane and ultimately in clotting of fibers and the whole hemodialyzer. Anticoagulation in hemodialysis is targeted to prevent this activation of coagulation during the procedure. Most agents inhibit the plasmatic coagulation cascade. Still commonly used is unfractionated heparin, followed by low-molecular-weight heparin preparations with distinct advantages. Immune-mediated heparin-induced thrombocytopenia constitutes a potentially life-threatening complication of heparin therapy requiring immediate switch to nonheparin alternative anticoagulants. Danaparoid, lepirudin, and argatroban are currently being used for alternative anticoagulation, all of which possess both advantages and limitations. In the past, empirical strategies reducing or avoiding heparin were applied for patients at bleeding risk, whereas nowadays regional citrate anticoagulation is increasingly used to prevent bleeding by allowing procedures without any systemic anticoagulation. Avoidance of clotting within the whole hemodialyzer circuit is not granted. Specific knowledge of the mechanisms of coagulation, the targets of the anticoagulants in use, and their respective characteristics constitutes the basis for individualized anticoagulation aimed at achieving full patency of the circuit throughout the procedure. Patency of the circuit is an important prerequisite for optimal hemodialysis quality.

Oscillatory potentials of the slow-sequence multifocal ERG in primates extracted using the Matching Pursuit method

This study used the Matching Pursuit (MP) method, a time-frequency analysis, to identify and characterize oscillatory potentials (OPs) in the primate electroretinogram (ERG). When the slow-sequence mfERG from the macular region of the retina was matched with Gabor functions, OPs were identified in two distinct bands: a high-frequency band peaking around 150 Hz that contributes to early OPs, and a low-frequency band peaking around 80 Hz that contributes to both early and late OPs. Pharmacological blockade and experimental glaucoma studies showed that the high-frequency OPs depend upon sodium-dependent spiking activity of retinal ganglion cells, whereas the low-frequency OPs depend primarily upon non-spiking activity of amacrine cells, and more distal retinal activity.

Acute D2/D3 dopaminergic agonism but chronic D2/D3 antagonism prevents NMDA antagonist neurotoxicity

BACKGROUND

Antagonists of the N-methyl-D-aspartate (NMDA) glutamate receptor, most likely by producing disinhibtion in complex circuits, acutely produce psychosis and cognitive disturbances in humans, and neurotoxicity in rodents. Studies examining NMDA Receptor Hypofunction (NRHypo) neurotoxicity in animals, therefore, may provide insights into the pathophysiology of psychotic disorders. Dopaminergic D2 and/or D3 agents can modify psychosis over days to weeks, suggesting involvement of these transmitter system(s).

METHODS

We studied the ability of D2/D3 agonists and antagonists to modify NRHypo neurotoxicity both after a one-time acute exposure and after chronic daily exposure.

RESULTS

Here we report that D2/D3 dopamine agonists, probably via D3 receptors, prevent NRHypo neurotoxicity when given acutely. The protective effect with D2/D3 agonists is not seen after chronic daily dosing. In contrast, the antipsychotic haloperidol does not affect NRHypo neurotoxicity when given acutely at D2/D3 doses. However, after chronic daily dosing of 1, 3, or 5 weeks, haloperidol does prevent NRHypo neurotoxicity with longer durations producing greater protection.

CONCLUSIONS

Understanding the changes that occur in the NRHypo circuit after chronic exposure to dopaminergic agents could provide important clues into the pathophysiology of psychotic disorders.

Contribution of retinal neurons to d-wave of primate photopic electroretinograms

The purpose of this study was to determine the contribution of different types of retinal neurons to the d-wave of the primate electroretinogram using pharmacological agents. NMDA + TTX was used to suppress inner retinal activity, and APB and PDA to block the activity of the ON- and OFF-pathways, respectively. Results indicated that the inner retinal neurons had a small but certain contribution to the d-wave. The initial rapid phase of the d-wave originates from the activity of the cone OFF-pathway nearly exclusively, and the later slow phase is shaped by the cone photoreceptors. The cone ON-pathway acts in a direction opposite to that of the other components.

Hyperpipecolic acidaemia: a diagnostic tool for peroxisomal disorders

Peroxisomal disorders include a complex spectrum of diseases, characterized by a high heterogeneity from both the clinical and the biochemical points of view. Specific assays are required for the study of peroxisome metabolism. Among these, pipecolic acid evaluation is considered as a supplementary test. We have established the diagnostic role of pipecolic acid in 30 patients affected by a peroxisomal defect (5 Zellweger syndromes, 10 Infantile Refsum diseases, 1 neonatal adrenoleukodystrophy, 6 patients affected by a peroxisomal biogenesis disorder with unclassified phenotype, 1 case of rhizomelic chondrodysplasia punctata (RCDP), 2 acyl-CoA oxidase deficiencies, 2 bifunctional enzyme deficiencies, 2 Refsum diseases, and 1 beta-oxidation deficiency). Pipecolic acid was increased in all generalized peroxisomal disorders, while normal pipecolic acid with abnormal very long chain fatty acid concentrations was strong evidence for a single peroxisomal enzyme deficiency. Unexpectedly, hyperpipecolic acidaemia was found also in a child affected by RCDP and in two patients with Refsum disease. In six patients the suggestion of a peroxisomal disorder was raised by the fortuitous finding of a pipecolic acid peak in amino acid chromatography, routinely performed as a general metabolic screening. For all patients, pipecolic acid proved to be a useful parameter in the biochemical classification of peroxisomal disorders.

Glutaric aciduria type III: a distinctive non-disease?

Glutaric aciduria type III is a rare metabolic abnormality leading to persistent isolated glutaric acid excretion. We report the clinical and biochemical phenotypes of three affected children. The first patient is a boy with dysmorphic features and a chromosomal deletion (monosomy 6q26-qter) in whom a persistent glutaric aciduria (500 mmol/mol creatinine, normal <10) was detected during a routine metabolic investigation. The second boy suffered from acute gastroenteritis and hyperthyroidism, when an excessively high urinary glutaric acid excretion was identified (1460 mmol/mol creatinine). The third patient is a girl with constantly elevated glutaric acid in her urine (290 mmol/mol creatinine) but no symptoms of significant disease. In all our patients, glutaric aciduria type I (glutaryl-CoA dehydrogenase deficiency), glutaric aciduria type II (multiple acyl-CoA dehydrogenation defect), and secondary forms of glutaric aciduria (for example due to intestinal infections or mitochondrial dysfunction) could be excluded. Loading with the precursor amino acid lysine in all patients as well as with pipecolic acid in the third case led to an increase in urinary glutaric acid excretion, proving the endogenous origin of glutarate. Glutaric aciduria type III (a defect reported to be caused by peroxisomal glutaryl-CoA oxidase deficiency) is our presumptive diagnosis. However, peroxisomal glutaryl-CoA oxidase is not well characterized and no reliable approach for the direct determination of this enzyme is available to us. To our knowledge, in the English language literature only a single patient with glutaric aciduria type III has been described. Our cases reported here confirm the earlier assumption that glutaric aciduria type III is not related to a distinctive phenotype. Glutaric aciduria type III appears to be a rare metabolic abnormality, presumably of peroxisomal metabolism. However, its pathophysiological impact still needs further investigation.

Spatiotemporal dynamics of fibrin formation and spreading of active thrombin entering non-recalcified plasma by diffusion

The spatiotemporal dynamics of clot growth was studied in non-stirred non-recalcified plasma where thrombin entered by diffusion. Under these conditions, the clot rapidly grew for 30-45 min and then stopped growing on reaching 0.4-0.5 mm in size. The dynamics of clot growth and its size almost did not depend on the thrombin concentration in the range from 50 to 400 nM. FITC-thrombin was shown to permeate the growing clot. The clot size in antithrombin-deficient plasma increases with decreasing antithrombin concentration, being 1.5 mm in the plasma depleted of antithrombin to 5% of its initial level. The data on the spatial distribution of amidolytic activity in the growth zone of the clot suggested that thrombin was not the sole source of this activity. Analysis showed that this additional activity arising during thrombin diffusion into plasma was largely accounted for by thrombin-alpha(2)-macroglobulin complex.

Evaluation of argatroban and DUP 714 as anticoagulants for blood gas, electrolyte and ionized calcium analyses

The objective of this study was to determine if the thrombin inhibitors Argatroban and DUP 714 could anticoagulate whole blood without influencing the analyses of blood gases, electrolytes, ionized calcium or CO-oximetry. The anticoagulant potency of DUP 714 (0.5-68 micromol/l) and Argatroban (1.5-390 micromol/l) was evaluated using the activated partial thromboplastin time (APTT), prothrombin time (PT) and whole blood clot time (WBCT). APTT and the PT were measured using a Behring Fibrintimer. APTT was found to be more sensitive to prolongation by both of the thrombin inhibitors than were the PT or WBCT assays. DUP 714 was found to a more potent anticoagulant than Argatroban. DUP 714 anticoagulated specimens (>2.2 micromol/l) did not clot for at least 2 days, whereas Argatroban preserved specimens (390 micromol/l) clotted within 5.5 h of collection. No statistically significant changes in the measurement of pH, PCO2, PO2, Na, K, ionized calcium, oxyhaemoglobin, deoxyhaemoglobin, methaemoglobin or carboxyhaemoglobin (measured using a Corning 288 Blood Gas/Electrolyte Analyzer and a Coming 270 CO-oximeter) were detected in DUP 714 (34 micromol/l) or Argatroban (390 micromol/l) anticoagulated whole blood specimens. In conclusion, DUP 714 and Argatroban are suitable anticoagulants for preserving blood prior to blood gas and electrolyte analyses.

Argatroban as an anticoagulant for both hematologic and chemical tests

Argatroban possesses strong antithrombin-like activity. We evaluated the usefulness of argatroban in anticoagulating specimens for routine laboratory tests. Results using blood anticoagulated with argatroban corresponded well with the results of blood treated with ethylendiamine tetra-acetic acid (EDTA) in the complete blood count (CBC), including the WBC differential count and morphology of blood cells, when the CBC was performed within 2 hr of blood collection. Clinical chemistry results from argatroban-treated samples were similar to results obtained with serum specimens. Thus, argatroban may be a useful anticoagulant for emergency laboratory medicine.

Proline control of the feeding reaction of Cordylophora

The colonial hydroid Cordylophora is a carnivore whose feeding is induced by substances released from captured prey. An active molecule, probably the only one, has been isolated from a fraction of the laboratory food of Cordylophora, brine shrimp larvae, and identified on paper chromatograms as the imino acid proline. Reagent proline induces the feeding reaction at 10^-5M. The reaction is specific in that only two α-imino acids very closely related to proline were found to possess significant activity: azetidine-2-carboxylic acid and pipecolic acid. The response to proline is inhibited by magnesium ions and enhanced by phosphate. Since previous studies have shown that the feeding reactions of Hydra, Physalia, and Campanularia are controlled by reduced glutathione, the phylogenetic implications of the proline control of feeding in Cordylophora are discussed. The feeding reactions of both Cordylophora and Hydra are also induced by proteases, suggesting similar mechanisms of induction in the two hydroids.

Use of thrombin inhibitors ex vivo allows critical care clinical chemistry and hematology testing on common specimens

OBJECTIVE

To evaluate the suitability of the thrombin inhibitors PPACK (D-phenylalanyl-L-prolyl-L-arginine chloromethylketone) or Argatroban for anticoagulation of blood prior to critical care testing of whole blood or plasma.

DESIGN AND METHODS

Initially we evaluated the effect of PPACK (0-200 microM) or Argatroban (0-590 microM) on serum glucose, urea, creatinine, calcium and electrolyte tests on two chemistry analyzers (Hitachi 717 and Ektachem 700XR). Subsequently plasma and serum from whole blood samples containing either heparin 15,000 IU/L or PPACK 75 microM or Argatroban 245 microM or no anticoagulant were tested and compared. We analysed and compared whole blood containing either PPACK 75 microM or Argatroban 245 microM or ethylenediaminetetraacetic acid (EDTA) using a Coulter STK-R hematology analyzer at intervals for 90 minutes.

RESULTS

The measurement of electrolytes, urea, creatinine, calcium or glucose was unaffected by either Argatroban or PPACK in either serum or anticoagulant-specific plasmas (p > 0.05). For specimens from individual donors, serum potassium was higher than plasma potassium, irrespective of anticoagulant used. Clinically equivalent complete blood counts were achieved for 60 minutes using EDTA-whole blood, or whole blood containing 245 microM Argatroban or 75 microM PPACK. However automated differential white cell counting was not reliable with either form of thrombin inhibitor-whole blood. Argatroban-anticoagulated blood demonstrated concentration and time dependent changes in platelet counts, whereas platelet counts were stable in blood containing 75 microM PPACK for up to 90 minutes.

CONCLUSION

Specimens of blood anticoagulated with either 75 microM PPACK or 245 microM Argatroban can be used for either critical care chemistry or hematology testing.

Anti-thrombogenic effects of 2-hydroxyethylmethacrylate-styrene block copolymer and argatroban in synthetic small-caliber vascular grafts in a rabbit inferior vena cava model

The high anti-thrombogenicity of 2-hydroxyethylmethacrylate (HEMA)-styrene block copolymer (HS) and argatroban-coated polyurethane tubes in a rabbit inferior vena cava model is reported. Polyurethane tubes (i.d. 3.0 mm, o.d. 4.0 mm, 12.5 cm) were implanted into the inferior vena cavas of 36 rabbits, weighing 2.5 to 3.5 kg, using the sleeve anastomotic technique. The animals were divided into four groups according to the type of prosthesis: uncoated tubes (Group 1, n = 9); HS-coated tubes (Group 2, n = 9); heparin-coated tubes (Group 3, n = 9); and HS/argatroban-coated tubes (Group 4, n = 9). Patency was evaluated at 1 week by ultrasonic flowmetry and microscopic examination of the grafts. Patency rates were 0 percent (0/9) in Group 1; 56 percent (5/9) in Group 2; 67 percent (6/9) in Group 3; and 100 percent (9/9) in Group 4 Groups 2 and 3 animals demonstrated statistically significantly superior patency compared to those of Group 1. Group 4 animals exhibited significantly superior anti-thrombogenicity compared to those of both Groups 1 and 2. Although Group 3 animals had an excellent patency rate, transmission and scanning electron microscopic views showed a thick protein layer and activated platelets adhering to the surface of Group 3 vessels. On the contrary, only a thin protein layer was noted in Group 4 animals. The HS-treated surface combined with the argatroban slow-release system exhibited excellent anti-thrombogenicity under venous-flow conditions.

[Experimental epidural and conduction anesthesia with azacaine]

Experimental studies were undertaken to examine azacaine used in mice during conduction anesthesia and in rabbits during epidural anesthesia in 0.75, 2 and 0.75, 1% solutions, respectively. It was found that azacaine in the above doses is 1.5-3.5-fold superior to 2% solutions of lidocaine (xycaine) and trimecaine (mesocaine) in their effect duration. Histological studies of the rabbit spinal cord after epidural azacaine administration revealed no significant changes in brain tissues.

An evaluation of prothrombin assay method using MD805 by means of warfarin-treated plasma

The prothrombin assay method using the synthetic thrombin-inhibitor MD805 was standardized by fixing the concentrations of MD805 and S-2238 through their extinction coefficients (epsilon 333 for MD805 and epsilon 316 for S-2238). The prothrombin assay was directly proportional to the concentration of plasma up to 200% of the normal level and was not significantly influenced by the variety of three kinds of commercially available tissue thromboplastin preparations. Using plasma from Warfarin-treated patients and healthy volunteers, the correlation was studied between the prothrombin assay and the conventional coagulation tests such as Prothrombin time (INR), Thrombotest and Hepaplastintest (Normotest), and the correlation coefficients of -0.85, 0.81 and 0.94 were obtained respectively. FUT-175 and MD805 in the test plasma hardly affected the prothrombin assay in the concentration ranges which affected remarkably the conventional coagulation tests. These results indicated that the prothrombin assay was useful for monitoring the hyper- or hypoprothrombin state even on anticoagulant therapy. Eighteen healthy volunteers at 18 to 20 years old showed the mean and standard deviation of 0.96 +/- 0.097.

Neuronal protection correlates with prevention of calcium-calmodulin binding in rats

We correlated the efficacy of several clinically relevant pharmacotherapies with their ability to prevent calcium influx into neurons and subsequent binding to calmodulin. We studied the administration of CGS 19755, nimodipine, nicardipine, and combinations of these drugs before or immediately after ischemia in globally ischemic rats. Calcium-calmodulin binding was graded by an immunohistochemical assay after 2 and 24 hours of reperfusion (n = 5-6 at each time period), and histologic damage was graded by light microscopy after 72 hours of reperfusion (n = 6). Calcium-calmodulin binding correlated with the severity of delayed histologic damage in various brain regions. In untreated ischemic control rats, marked calcium-calmodulin binding was seen in CA1 and CA3 after 24 hours of reperfusion (p less than or equal to 0.01). Administered before ischemia, CGS 19755 prevented calcium-calmodulin binding across all brain regions after 2 and 24 hours of reperfusion compared with controls (p less than or equal to 0.05). This effect was most prominent in CA3 and CA1, where the drug also reduced delayed neuronal damage (p less than or equal to 0.05). Lower doses or postischemic administration of CGS 19755, nimodipine, nicardipine, and a combination of postischemic CGS 19755 and nicardipine had a more limited effect on calcium-calmodulin binding and did not protect against delayed neuronal damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesic, anesthetic, and respiratory effects of the competitive N-methyl-D-aspartate (NMDA) antagonist CGS 19755 in rhesus monkeys

The competitive excitatory amino acid antagonist cis-4-phosphonomethyl-2-piperidine-carboxylic acid (CGS 19755) increased the latency for monkeys to remove their tails from warm water (analgesia); larger doses produced ataxia, loss of righting, salivation, and eliminated reactivity to stimulation (anesthesia). CGS 19755 decreased tidal volume and had little effect on frequency of respiration. Although longer lasting, the effects of CGS 19755 were similar to the effects of ketamine, suggesting these effects result from actions at the NMDA receptor complex.

Stereoselectivity and mode of inhibition of phosphoinositide-coupled excitatory amino acid receptors by 2-amino-3-phosphonopropionic acid

DL-2-Amino-3-phosphonopropionic acid, a phosphonate-substituted derivative of aspartic acid, has been shown to be an inhibitor of excitatory amino acid-stimulated phosphoinositide hydrolysis in rat brain slices. In this study, the enantiomers of 2-amino-3-phosphonopropionic acid were synthesized and used to further characterize the stereoselectivity and mechanism of interaction of this compound for inhibiting phosphoinositide-coupled (metabotropic) excitatory amino acid receptors. L-2-Amino-3-phosphonopropionic acid was 3-5 times more potent than D-2-amino-3-phosphonopropionic acid as an inhibitor of ibotenate-stimulated [3H]inositol monophosphate formation in slices of the rat hippocampus or quisqualate-stimulated [3H]inositol monophosphate formation in neonatal rat cerebral cortical slices. Carbachol-stimulated phosphoinositide hydrolysis was not inhibited by L-2-amino-3-phosphonopropionic acid, and L-2-amino-3-phosphonopropionic acid had no appreciable affinity for ionotropic excitatory amino acid receptors at concentrations required to inhibit metabotropic excitatory amino acid responses. The inhibitory effects of L-2-amino-3-phosphonopropionic acid or L-2-amino-4-phosphonobutyric acid on phosphoinositide hydrolysis were not competitive, because they could not be surmounted by increasing concentrations of ibotenate or quisqualate. L-2-Amino-3-phosphonopropionic acid inhibition also could not be prevented by washing the tissue before incubation with ibotenate. Thus, L-2-amino-3-phosphonopropionic acid is a stereoselective inhibitor of metabotropic excitatory amino acid receptors with little affinity for ionotropic receptors. However, the inhibitory effects of L-2-amino-3-phosphonopropionic acid or L-2-amino-4-phosphonobutyric acid were not readily reversed, and the site at which they act to inhibit metabotropic excitatory amino acid receptors remains to be determined.

CGS-19755, a competitive NMDA receptor antagonist, reduces calcium-calmodulin binding and improves outcome after global cerebral ischemia

We evaluated several doses of cis-4-(phosphonomethyl)-2-piperidine-carboxylic acid (CGS-19755), a potent competitive N-methyl-D-aspartate (NMDA) receptor antagonist, systemically administered either before or after 20 to 30 minutes of global ischemia in rats. We measured outcome by mortality, histological damage by light microscopy, and learning ability on an eight-arm maze, and determined the drug's mechanism of action by an immunohistochemical assay of calcium-calmodulin binding. High-dose treatment begun prior to ischemia resulted in reduced cellular damage in severely ischemic hippocampal tissue, but also caused high mortality due to respiratory depression. Treatment begun 30 minutes after ischemia resulted in little histological protection but significantly improved learning ability when tested 1 month after ischemia, and did not increase mortality. Furthermore, CGS-19755, 10 mg/kg intraperitoneally, begun either before or after ischemia substantially reduced calcium influx into ischemic neurons as evidenced by reduced calcium-calmodulin binding. We conclude that CGS-19755 prevents calcium entry into ischemic neurons and may be effective therapy for very acute cerebral ischemia.

N-methyl-D-aspartate antagonist reduces stroke size and regional glucose metabolism

Pharmacological inhibition of cell excitation during focal ischemia was studied in the rat middle cerebral artery occlusion model. The potent and selective N-methyl-D-aspartate antagonist CGS 19755, administered 5 minutes prior to or 5 minutes following permanent middle cerebral artery occlusion, caused a substantial decrease in infarct size, which was associated with reduction of postischemic cerebral glucose hypermetabolism. These data support a role for excitation-induced hypermetabolism in the pathogenesis of infarction following focal cerebrovascular occlusion.

N-methyl-D-aspartate antagonism and phencyclidine-like activity: a drug discrimination analysis

The experiments examined the ability of competitive N-methyl-D-aspartate (NMDA) antagonists (CPP, CGS 19755), noncompetitive NMDA antagonists [phencyclidine (PCP), ketamine, MK-801], other putative excitatory amino acid antagonists (ifenprodil, PK 26124), and anticonvulsants (pentobarbital, chlordiazepoxide) to antagonize the discriminative stimulus (DS) effects of NMDA and to produce PCP-like DS effects. Rats were trained to discriminate NMDA (40 mg/kg) from saline. The DS effects of NMDA were blocked by the competitive NMDA antagonists but were antagonized at best partially by the other drugs tested. The response rate decreasing effects of NMDA were attenuated to varied extents by both the competitive and the noncompetitive NMDA antagonists. Some competitive and noncompetitive NMDA antagonists partially mimicked NMDA. To further examine their NMDA-antagonist properties, the compounds were also tested for antagonism of NMDA (160 mg/kg)-induced lethality in mice; only the competitive and noncompetitive NMDA antagonists completely protected against NMDA-induced lethality. In rats discriminating PCP (2.5 mg/kg) from saline, the competitive NMDA antagonists produced less drug-appropriate responding than the noncompetitive NMDA antagonists but more than was produced by the other drugs tested. The extent to which compounds antagonize behavioral effects of NMDA and produce PCP-like DS effects may depend partly on the effect measured and on the component of the NMDA receptor complex with which they interact. Although the competitive NMDA antagonists were more effective in blocking NMDA than the other drugs tested, they failed to act as pure antagonists of the DS effects of NMDA.

Substitution of proline with pipecolic acid at the scissile bond converts a peptide substrate of HIV proteinase into a selective inhibitor

The nonapeptide H-Val-Ser-Gln-Asn-Tyr-Pro-Ile-Val-Gln-NH2 containing the retroviral Tyr-Pro cleavage site is a good substrate for the proteinase of human immunodeficiency viruses but it is not readily hydrolyzed by other nonviral proteinases including the structurally related pepsin-like aspartic proteinases. Replacing the Pro by L-pipecolic acid (2-piperidinecarboxylic acid) converted the substrate into an effective inhibitor of HIV-1 and HIV-2 proteinases with IC50 of approximately 1 microM. This compound showed a high degree of selectivity in that it did not inhibit cathepsin D and renin.

Protection by NMDA antagonists against selective cell loss following transient ischaemia

We have administered antagonists acting competitively or noncompetitively at the N-methyl-D-aspartate receptor after a short period of incomplete ischaemia and evaluated selective neuronal loss in the CA1 region of the rat hippocampus. The competitive antagonists D-(-)-2-amino-7-phosphonoheptanoate (2APH); 100 or 330 mg/kg; 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP); 3.3 or 10 mg/kg; and CGS 19755 (cis-4-phosphonomethyl-2-piperidine carboxylate) 3.3 or 10 mg/kg; and the noncompetitive antagonists MK801 [+)5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate), 0.3, 1, or 3 mg/kg, and dextrorphan, 2, 6, 18, or 54 mg/kg, were administered intraperitoneally 15 min and 5 h after a 10-min incomplete ischaemia period; additionally MK801 (1 or 3 mg/kg) and CGS 19755 (10 or 30 mg/kg) were administered 5 and 10 h postischaemia. Seven days after ischaemia, the brains were fixed by perfusion. CA1 pyramidal cell counts were performed on Nissl-stained sections using an ocular grid piece. Ventilated (no ischaemia) control animals had a mean of 406 +/- 13 CA1 neurones/3 grid lengths. Ischaemia reduced this mean to 157 +/- 23. A significant protective effect against this cell loss was seen after two injections (at 15 min and 5 h postischaemia) of 2APH, CPP (10 mg/kg), CGS 19755 (10 mg/kg), MK801 (1 mg/kg), and dextrophan (54 mg/kg). Delayed injection (5 and 10 h postischaemia) of CGS 19755 (10 and 30 mg/kg) and MK801 (1 and 3 mg/kg) did not provide any protection against pyramidal cell loss.