Vaccination of African penguins (Spheniscus demersus) against high-pathogenicity avian influenza.

BACKGROUND: High-pathogenicity avian influenza (HPAI) has become a conservation threat to wild birds. Therefore, suitable vaccine technology and practical application methods require investigation. METHODS: Twenty-four African penguins (Spheniscus demersus) were vaccinated with either a conventional inactivated clade 2.3.4.4b H5N8 HPAI whole virus or a tobacco leaf-produced H5 haemagglutinin-based virus-like particle (VLP). Six birds received a second dose of the inactivated vaccine. Antibody responses were assessed and compared by employing haemagglutination inhibition tests. RESULTS: A second dose of inactivated vaccine was required to induce antibody titres above the level required to suppress virus shedding, while a single dose of VLP vaccine produced these levels by day 14, and one bird still had antibodies on day 430. LIMITATIONS: Bacterial contamination of the VLP vaccine limited the monitoring period and sample size in that treatment group, and it was not possible to perform a challenge study with field virus. CONCLUSION: VLP vaccines offer a more practical option than inactivated whole viruses, especially in logistically challenging situations involving wild birds.

Drug Burden Index and Its Association With Hip Fracture Among Older Adults: A National Population-Based Study.

BACKGROUND: The Drug Burden Index (DBI) calculates the total sedative and anticholinergic load of prescribed medications and is associated with functional decline and hip fractures in older adults. However, it is unknown if confounding factors influence the relationship between the DBI and hip fractures. The objective of this study was to evaluate the association between the DBI and hip fractures, after correcting for mortality and multiple potential confounding factors. METHODS: A competing-risks regression analysis conducted on a prospectively recruited New Zealand community-dwelling older population who had a standardized (International Resident Assessment Instrument) assessment between September 1, 2012, and October 31, 2015, the study's end date. Outcome measures were survival status and hip fracture, with time-varying DBI exposure derived from 90-day time intervals. The multivariable competing-risks regression model was adjusted for a large number of medical comorbidities and activities of daily living. RESULTS: Among 70,553 adults assessed, 2,249 (3.2%) experienced at least one hip fracture, 20,194 (28.6%) died without experiencing a fracture, and 48,110 (68.2%) survived without a fracture. The mean follow-up time was 14.9 months (range: 1 day, 37.9 months). The overall DBI distribution was highly skewed, with median time-varying DBI exposure ranging from 0.93 (Q1 = 0.0, Q3 = 1.84) to 0.96 (Q1 = 0.0, Q3 = 1.90). DBI was significantly related to fracture incidence in unadjusted (p < .001) and adjusted (p < .001) analyses. The estimated subhazard ratio was 1.52 (95% confidence interval: 1.28-1.81) for those with DBI > 3 compared with those with DBI = 0 in the adjusted analysis. CONCLUSIONS: In this study, increasing DBI was associated with a higher likelihood of fractures after accounting for the competing risk of mortality and adjusting for confounders. The results of this unique study are important in validating the DBI as a guide for medication management and it could help reduce the risk of hip fractures in older adults.

Pharmacotherapy in Older Adults with Cardiovascular Disease: Report from an American College of Cardiology, American Geriatrics Society, and National Institute on Aging Workshop.

OBJECTIVES: To identify the top priority areas for research to optimize pharmacotherapy in older adults with cardiovascular disease (CVD). DESIGN: Consensus meeting. SETTING: Multidisciplinary workshop supported by the National Institute on Aging, the American College of Cardiology, and the American Geriatrics Society, February 6-7, 2017. PARTICIPANTS: Leaders in the Cardiology and Geriatrics communities, (officers in professional societies, journal editors, clinical trialists, Division chiefs), representatives from the NIA; National Heart, Lung, and Blood Institute; Food and Drug Administration; Centers for Medicare and Medicaid Services, Alliance for Academic Internal Medicine, Patient-Centered Outcomes Research Institute, Agency for Healthcare Research and Quality, pharmaceutical industry, and trainees and early career faculty with interests in geriatric cardiology. MEASUREMENTS: Summary of workshop proceedings and recommendations. RESULTS: To better align older adults' healthcare preferences with their care, research is needed to improve skills in patient engagement and communication. Similarly, to coordinate and meet the needs of older adults with multiple comorbidities encountering multiple healthcare providers and systems, systems and disciplines must be integrated. The lack of data from efficacy trials of CVD medications relevant to the majority of older adults creates uncertainty in determining the risks and benefits of many CVD therapies; thus, developing evidence-based guidelines for older adults with CVD is a top research priority. Polypharmacy and medication nonadherence lead to poor outcomes in older people, making research on appropriate prescribing and deprescribing to reduce polypharmacy and methods to improve adherence to beneficial therapies a priority. CONCLUSION: The needs and circumstances of older adults with CVD differ from those that the current medical system has been designed to meet. Optimizing pharmacotherapy in older adults will require new data from traditional and pragmatic research to determine optimal CVD therapy, reduce polypharmacy, increase adherence, and meet person-centered goals. Better integration of the multiple systems and disciplines involved in the care of older adults will be essential to implement and disseminate best practices. J Am Geriatr Soc 67:371-380, 2019.

Drug Burden and its Association with Falls Among Older Adults in New Zealand: A National Population Cross-Sectional Study.

BACKGROUND: Adverse outcomes associated with advanced diseases are often exacerbated by polypharmacy. OBJECTIVES: The current study investigated an association between exposure to anticholinergic and sedative medicines and falls in community-dwelling older people, after controlling for potential confounders. METHODS: We conducted a retrospective cross-sectional study of a continuously recruited national cohort of community-dwelling New Zealanders aged 65 years and over. Participants had an International Resident Assessment Instrument-Home Care (interRAI-HC) assessment between 1 September 2012 and 31 January 2016. InterRAI-HC is a comprehensive, multi-domain, standardised assessment. This study captured 18 variables, including fall frequency, from the interRAI. These data were deterministically matched with the Drug Burden Index (DBI) for each participant, derived from an anonymised national dispensed pharmaceuticals database. DBI groupings were statistically ascertained, and ordinal regression models employed. RESULTS: Overall, there were 71,856 participants, with a mean age of 82.7 years (range 65-106); 43,802 (61.0%) were female, and 63,578 (88.5%) were New Zealand European. In unadjusted and adjusted analyses, DBI groupings were related to falls (p < 0.001). A DBI score > 3 was associated with a 41% increase in falls compared with a DBI score of 0 (p < 0.001). There was a 'dose-response' relationship between DBI levels and falls risk. CONCLUSIONS: DBI was found to be independently and positively associated with a greater risk of falls in this cohort after adjustment for 18 known confounders. We suggest that the DBI could be a valuable tool for clinicians to use alongside electronic prescribing to help reduce falls in older people.

Logic-Based and Cellular Pharmacodynamic Modeling of Bortezomib Responses in U266 Human Myeloma Cells.

Systems models of biological networks show promise for informing drug target selection/qualification, identifying lead compounds and factors regulating disease progression, rationalizing combinatorial regimens, and explaining sources of intersubject variability and adverse drug reactions. However, most models of biological systems are qualitative and are not easily coupled with dynamical models of drug exposure-response relationships. In this proof-of-concept study, logic-based modeling of signal transduction pathways in U266 multiple myeloma (MM) cells is used to guide the development of a simple dynamical model linking bortezomib exposure to cellular outcomes. Bortezomib is a commonly used first-line agent in MM treatment; however, knowledge of the signal transduction pathways regulating bortezomib-mediated cell cytotoxicity is incomplete. A Boolean network model of 66 nodes was constructed that includes major survival and apoptotic pathways and was updated using responses to several chemical probes. Simulated responses to bortezomib were in good agreement with experimental data, and a reduction algorithm was used to identify key signaling proteins. Bortezomib-mediated apoptosis was not associated with suppression of nuclear factor κB (NFκB) protein inhibition in this cell line, which contradicts a major hypothesis of bortezomib pharmacodynamics. A pharmacodynamic model was developed that included three critical proteins (phospho-NFκB, BclxL, and cleaved poly (ADP ribose) polymerase). Model-fitted protein dynamics and cell proliferation profiles agreed with experimental data, and the model-predicted IC50 (3.5 nM) is comparable to the experimental value (1.5 nM). The cell-based pharmacodynamic model successfully links bortezomib exposure to MM cellular proliferation via protein dynamics, and this model may show utility in exploring bortezomib-based combination regimens.

Effect of obesity on the pharmacokinetics of drugs in humans.

The prevalence of obesity has dramatically increased in recent years and now includes a significant proportion of the world's children, adolescents and adults. Obesity is linked to a number of co-morbidities, the most prominent being type 2 diabetes mellitus. While many agents are available to treat these conditions, the current knowledge regarding their disposition in the obese remains limited. Over the years, both direct and indirect methodologies have been utilized to assess body composition. Commonly used direct measures include underwater weighing, skinfold measurement, bioelectrical impedance analysis and dual-energy x-ray absorptiometry. Unfortunately, these methods are not readily available to the majority of clinicians. As a result, a number of indirect measures to assess body composition have been developed. Indirect measures rely on patient attributes such as height, bodyweight and sex. These size metrics are often utilized clinically and include body mass index (BMI), body surface area (BSA), ideal bodyweight (IBW), percent IBW, adjusted bodyweight, lean bodyweight (LBW) and predicted normal weight (PNWT). An understanding of how the volume of distribution (V(d)) of a drug changes in the obese is critical, as this parameter determines loading-dose selection. The V(d) of a drug is dependent upon its physiochemical properties, the degree of plasma protein binding and tissue blood flow. Obesity does not appear to have an impact on drug binding to albumin; however, data regarding alpha(1)-acid glycoprotein binding have been contradictory. A reduction in tissue blood flow and alterations in cardiac structure and function have been noted in obese individuals. At the present time, a universal size descriptor to describe the V(d) of all drugs in obese and lean individuals does not exist. Drug clearance (CL) is the primary determinant to consider when designing a maintenance dose regimen. CL is largely controlled by hepatic and renal physiology. In the obese, increases in cytochrome P450 2E1 activity and phase II conjugation activity have been observed. The effects of obesity on renal tubular secretion, tubular reabsorption, and glomerular filtration have not been fully elucidated. As with the V(d), a single, well validated size metric to characterize drug CL in the obese does not currently exist. Therefore, clinicians should apply a weight-normalized maintenance dose, using a size descriptor that corrects for differences in absolute CL between obese and non-obese individuals. The elimination half-life (t((1/2))) of a drug depends on both the V(d) and CL. Since the V(d) and CL are biologically independent entities, changes in the t((1/2)) of a drug in obese individuals can reflect changes in the V(d), the CL, or both. This review also examines recent publications that investigated the disposition of several classes of drugs in the obese--antibacterials, anticoagulants, antidiabetics, anticancer agents and neuromuscular blockers. In conclusion, pharmacokinetic data in obese patients do not exist for the majority of drugs. In situations where such information is available, clinicians should design treatment regimens that account for any significant differences in the CL and V(d) in the obese.

Stereochemistry of an agonist determines coupling preference of beta2-adrenoceptor to different G proteins in cardiomyocytes.

A fundamental question regarding receptor-G protein interaction is whether different agonists can lead a receptor to different intracellular signaling pathways. Our previous studies have demonstrated that although most beta(2)-adrenoceptor agonists activate both G(s) and G(i) proteins, fenoterol, a full agonist of beta(2)-adrenoceptor, selectively activates G(s) protein. Fenoterol contains two chiral centers and may exist as four stereoisomers. We have synthesized a series of stereoisomers of fenoterol and its derivatives and characterized their receptor binding and pharmacological properties. We tested the hypothesis that the stereochemistry of an agonist determines selectivity of receptor coupling to different G protein(s). We found that the R,R isomers of fenoterol and methoxyfenoterol exhibited more potent effects to increase cardiomyocyte contraction than their S,R isomers. It is noteworthy that although (R,R)-fenoterol and (R,R)-methoxyfenoterol preferentially activate G(s) signaling, their S,R isomers were able to activate both G(s) and G(i) proteins as evidenced by the robust pertussis toxin sensitivities of their effects on cardiomyocyte contraction and on phosphorylation of extracellular signal-regulated kinase 1/2. The differential G protein selectivities of the fenoterol stereoisomers were further confirmed by photoaffinity labeling studies on G(s),G(i2), and G(i3) proteins. The inefficient G(i) signaling with the R,R isomers is not caused by the inability of the R,R isomers to trigger the protein kinase A (PKA)-mediated phosphorylation of the beta(2)-adrenoceptor, because the R,R isomers also markedly increased phosphorylation of the receptor at serine 262 by PKA. We conclude that in addition to receptor subtype and phosphorylation status, the stereochemistry of a given agonist plays an important role in determining receptor-G protein selectivity and downstream signaling events.

Molecular, biologic, and pharmacokinetic properties of monoclonal antibodies: impact of these parameters on early clinical development.

Currently, 14 intact, unconjugated, monoclonal antibodies (Mabs) are approved for therapeutic use in the United States, and more than 100 Mabs are presently undergoing clinical development or regulatory review. Mabs are large molecular weight glycoproteins that embody structural, biochemical, and pharmacologic properties distinct from other biologics or chemically synthesized compounds. Early therapeutic Mabs were murine proteins, and clinical testing of these agents revealed serious immune-mediated toxicities. The side effect profile of murine Mab therapeutic agents restricted the clinical development of these agents to indications with high morbidity and/or mortality (ie, oncology, graft vs host rejection). Advances in genetic engineering and protein expression technologies resulted in the development of Mabs composed either predominately (ie, mouse/human chimeric, "humanized") or completely (ie, "fully human" Mabs) of the human amino acid sequence. The production of chimeric, humanized, and fully human Mabs significantly reduced the immune-mediated toxicities and expanded the utility for these agents in numerous therapeutic areas, particularly in chronic disorders requiring either long-term administration (ie, rheumatoid arthritis) or treatment upon the flare up of disease (Crohn's disease, psoriasis). This review provides an overview of the molecular, biochemical, and pharmacokinetic properties and clinical development history of Mabs and details how these factors currently affect the scope and design of early clinical development strategies for these drug candidates. Emphasis is placed on the criteria for selecting appropriate subject populations for phase I testing of Mabs.

Differential role of the alpha1C subunit tails in regulation of the Cav1.2 channel by membrane potential, beta subunits, and Ca2+ ions.

Voltage-gated Ca(v)1.2 channels are composed of the pore-forming alpha1C and auxiliary beta and alpha2delta subunits. Voltage-dependent conformational rearrangements of the alpha1C subunit C-tail have been implicated in Ca2+ signal transduction. In contrast, the alpha1C N-tail demonstrates limited voltage-gated mobility. We have asked whether these properties are critical for the channel function. Here we report that transient anchoring of the alpha1C subunit C-tail in the plasma membrane inhibits Ca2+-dependent and slow voltage-dependent inactivation. Both alpha2delta and beta subunits remain essential for the functional channel. In contrast, if alpha1C subunits with are expressed alpha2delta but in the absence of a beta subunit, plasma membrane anchoring of the alpha1C N terminus or its deletion inhibit both voltage- and Ca2+-dependent inactivation of the current. The following findings all corroborate the importance of the alpha1C N-tail/beta interaction: (i) co-expression of beta restores inactivation properties, (ii) release of the alpha1C N terminus inhibits the beta-deficient channel, and (iii) voltage-gated mobility of the alpha1C N-tail vis a vis the plasma membrane is increased in the beta-deficient (silent) channel. Together, these data argue that both the alpha1C N- and C-tails have important but different roles in the voltage- and Ca2+-dependent inactivation, as well as beta subunit modulation of the channel. The alpha1C N-tail may have a role in the channel trafficking and is a target of the beta subunit modulation. The beta subunit facilitates voltage gating by competing with the N-tail and constraining its voltage-dependent rearrangements. Thus, cross-talk between the alpha1C C and N termini, beta subunit, and the cytoplasmic pore region confers the multifactorial regulation of Ca(v)1.2 channels.

New short splice variants of the human cardiac Cavbeta2 subunit: redefining the major functional motifs implemented in modulation of the Cav1.2 channel.

Two new short splice variants of the Ca2+ channel beta2 subunit were cloned from human heart poly(A)(+) mRNA. The 410-amino acid beta2f subunit is encoded by exons 1A, 2A, 3, 4, 12, 13, and 14 of the human Cavbeta2 gene and lacks the protein kinase A phosphorylation site, the beta-interaction domain (De Waard, M., Pragnell, M., and Campbell, K. P. (1994) Neuron 13, 495-503), 40% of the beta-SH3 domain, and 73% of the guanylate kinase domain of the putative membrane-associated guanylate kinases module (McGee, A. W., Nunziato, D. A., Maltez, J. M., Prehoda, K. E., Pitt, G. S., and Bredt, D. S. (2004) Neuron 42, 89-99), and helix alpha3 of the alpha1-subunit binding pocket (Van Petegem F., Clark, K. A., Chatelain, F. C., and Minor, D. L., Jr. (2004) Nature 429, 671-675). The beta2g transcript has two potential initiation codons. With the second ATG codon, it generates the 164-amino acid beta2Deltag subunit encoded essentially by the distal part of exon 14, and thus beta2Deltag completely lacks any of the above motifs. Immunoprecipitation analysis confirmed stable association of beta2f and beta2Deltag with the alpha1C subunit. The plasma membrane localization of beta2f and beta2Deltag was substantially increased by co-expression of the alpha1C,77 and alpha2delta subunits. In COS1 cells, beta2f and beta2Deltag increased plasma membrane targeting of the pore-forming alpha1C subunit and differentially facilitated (beta2f > beta2Deltag) the voltage gating of otherwise silent Cav1.2 channels. We conclude that it is unlikely that the beta-interaction domain, membrane-associated guanylate kinases module, and the alpha1-subunit binding pocket helix alpha3 are essential for the interaction of the alpha1C and beta2 subunits and suggest that in addition to the alpha1-subunit binding pocket helices alpha5 and alpha8, a yet unresolved C-terminal beta2 region plays a crucial role.

Exendin-4 pharmacodynamics: insights from the hyperglycemic clamp technique.

The purpose of this study is to ascertain the pharmacodynamic properties of exendin-4, a glucose-dependent insulinotropic agent, from plasma glucose and insulin concentration-time profiles following a 60-min intravenous infusion in healthy and type 2 diabetic subjects. Plasma glucose and insulin concentrations were obtained from a previous clinical study, whereby a hyperglycemic clamp was established and maintained in healthy (n = 7) and type 2 diabetic (n = 7) volunteers (plasma glucose raised 5.4 mM above fasting level). Exendin-4 was infused (0.15 pmol/kg/min) during the 2nd hour of a 5-h clamp. A physiological pharmacodynamic model was developed and fitted to individual glucose and insulin responses simultaneously. Because drug concentrations were unavailable, hypothetical pharmacokinetic driving functions were approximated during the modeling process and used to enhance a proportionality constant relating elevated glucose and the rate of second-phase insulin release. Exendin-4 infusions produced substantial insulin release in both subject populations that required higher glucose infusion rates to maintain stable hyperglycemia. Observed plasma glucose-insulin profiles were well characterized by the final pharmacodynamic model. Apparent exendin-4 elimination rate constants for healthy and diabetic subjects were similar (0.0386 +/- 0.0192 and 0.0460 +/- 0.0145 min(-1)). Capacity and sensitivity parameters of drug effect were 2-fold lower in diabetic subjects, but mean differences were not statistically significant. Simulations confirm that diabetic subjects exhibit a reduced capacity to enhance second-phase insulin release in response to exendin-4 compared with healthy subjects. Type 2 diabetic subjects demonstrate a significant response to exendin-4, but to a lesser extent than nondiabetic subjects, despite comparable measures of apparent drug exposure and efficacy.

Kullback-Leibler clustering of continuous wavelet transform measures of heart rate variability.

Power spectral analysis of beat-to-beat heart rate variability (HRV) has provided a useful means of understanding the interplay between autonomic and cardiovascular functionality. Despite their utility, commonly employed frequency-domain techniques are limited in their prerequisite for stationary signals and their inability to account for temporal changes in the power spectral and/or frequency properties of signals. The purpose of this study is to develop an algorithm that utilizes continuous wavelet transform (CWT) parameters as inputs to a Kohonen self-organizing map (SOM), providing a method of clustering subjects with similar wavelet transform signatures. Continuous interbeat-intervals were recorded (Portapres monitor at 200 Hz) during a perception of affect test in 79 African-American volunteers (ages 21-83), where after a 5-min baseline, participants evaluated emotional expressions in sentences and pictures of faces, followed by a 5-min recovery. Individual HRV biosignals from each session were pre-processed (artifact replacement and signal resampling at 2 Hz) and a CWT was applied (db9 wavelet basis function over 32 scales). Standard deviations of resulting wavelet coefficients at each scale were calculated, normalized, and used as inputs into a SOM with Kullback-Leibler divergence as the dissimilarity measure used for clustering. Differences in subject demographics between two final clusters were assessed via two-independent-groups t-tests or chi-square or Fisher's exact tests of contingency tables. Significant differences were found for age, initial systolic blood pressure, smoking status, and mean s.d. of coefficients in the high frequency band (0.15-0.4 Hz). These findings may have clinical significance and the developed algorithm provides an alternative means of analyzing HRV data originating from populations with complex covariates.

Abciximab pharmacodynamic model with neural networks used to integrate sources of patient variability.

OBJECTIVE: Our objective was to develop a computational model for predicting abciximab-induced inhibition of ex vivo platelet aggregation from the administered dose and readily available patient clinical characteristics by use of a neural network approach. METHODS: A back-propagation neural network was designed to establish the relationship between abciximab dosing, patient clinical history, and effect (inhibition of 20 micromol/L adenosine diphosphate-induced ex vivo platelet aggregation). The neural network was trained by use of data from 8 (out of 47) patients undergoing coronary angioplasty and 30 healthy individuals. Final neuron connection weights were used to evaluate significant patient covariates. The final neural network was validated via (1) predicting the effects of the validation database (remaining 39 patients) and (2) predicting the individual patient doses to achieve 20% of baseline platelet aggregation. RESULTS: The trained neural network successfully captured the complex pharmacodynamic profiles of abciximab without specifying a structural model and identified several patient covariates that significantly contribute to establishing the abciximab dose-effect relationship, including stable angina with nitrate treatment, previous myocardial infarction, and smoking. A wide distribution of individual bolus doses of abciximab was predicted, suggesting the potential for dosing individualization while improving the risk of adverse drug events. The mean predicted dose (16.9 mg) was in agreement with the results from a previously published concentration-effect relationship for abciximab (18.9 +/- 2.0 mg). CONCLUSIONS: These findings suggest the usefulness of neural network methods to individualize dosing for drugs with a narrow therapeutic index when real-time measures of drug concentration and effect are unavailable, but future clinical studies are required for prospective validation.

Simultaneous modeling of abciximab plasma concentrations and ex vivo pharmacodynamics in patients undergoing coronary angioplasty.

An integrated structural pharmacokinetic/pharmacodynamic (PK/PD) model was developed for the glycoprotein IIb/IIIa antagonist abciximab administered to patients undergoing percutaneous transluminal coronary angioplasty. PK/PD data, in the form of plasma abciximab concentrations and ex vivo platelet aggregation in the presence of 20 microM adenosine diphosphate, were obtained from two previously conducted clinical studies. Study 1 consisted of patients who were given abciximab as a single intravenous injection of 0.25 mg/kg (n = 32). Patients in study 2 received an identical bolus dose, followed by a 36-h infusion at 0.125 microg/kg/min (n = 15). The PK component of the final model included drug-receptor binding, nonspecific distribution, and linear systemic clearance, whereas the PD module assumed that ex vivo dynamics were controlled by free plasma drug concentration. Mean PK/PD data from both studies were fitted simultaneously using nonlinear regression. PK profiles from both studies show rapidly decreasing plasma abciximab concentrations at early time points, but with extended terminal disposition phases. The maximum effect (Emax = 83.6%) was achieved rapidly and gradually returned to baseline values, although inhibition could be measured long after abciximab concentrations dropped below the detection limit. The final model well described the resulting PK/PD profiles and allowed for parameter estimation with relatively small coefficients of variation. Simulations were conducted to assess predicted receptor-occupancy and effects of selected parameters on PK/PD profiles. Models such as the one developed in this study demonstrate how drug binding to pharmacological targets may influence the PK of certain drugs and also provide a suitable paradigm for defining the PK/PD relationships of similar compounds.

Effects of endothelial nitric oxide synthase gene polymorphisms on platelet function, nitric oxide release, and interactions with estradiol.

Impaired platelet-derived nitric oxide (NO) contributes to acute coronary syndromes by enhancing platelet recruitment and thrombus formation. Polymorphic variants of the endothelial NO synthase (eNOS) gene have been associated with cardiovascular diseases. To examine whether eNOS variants affect platelet-derived NO and platelet function, and to assess the effects of estradiol on platelet function, we studied platelets from 47 healthy caucasians who were genotyped for eNOS polymorphisms in the promoter region (T-786 C), in intron 4, and in exon 7 (Glu298Asp). Platelet aggregation, platelet-derived NO and superoxide production were measured in control samples and samples pretreated with 17-alpha-estradiol (10 nmol/l). The occurrence of variants in the promoter region (P = 0.002) or in exon 7 (P = 0.007), but not in intron 4 (P > 0.05), were associated with lower levels of platelet-derived NO. An increased (P = 0.047) release of superoxide was observed with platelets from subjects with the variant in the promoter region, but not with other eNOS genetic variants. The eNOS gene polymorphisms did not affect ADP-induced platelet aggregation (P > 0.05). However, estradiol significantly increased platelet aggregation (P = 0.004), and platelet-derived superoxide (P = 0.047) in individuals homozygous for the variant in exon 7, but not in subject with other genotypes. These data demonstrate that the eNOS variants in the promoter region and in exon 7 decrease platelet-derived NO and that estradiol significantly increases platelet aggregation in homozygous for the variant in exon 7 but not in subjects with other genotypes, suggesting that eNOS variants may influence the thrombotic response.

Pharmacodynamics of abciximab during angioplasty: comparison to healthy subjects.

OBJECTIVES: Our objectives were to compare and contrast abciximab concentration-effect relationships in healthy volunteer participants with those in patients with coronary atherosclerosis undergoing elective coronary angioplasty. We also aimed to establish abciximab plasma concentrations associated with 80% inhibition of platelet aggregation. METHODS: Abciximab clearance and concentration-effect relationships were determined from two separate clinical studies, one in 30 healthy subjects aged 21 to 66 years and the other in 32 patients aged 44 to 74 years before they underwent elective coronary angioplasty. After abciximab administration, abciximab plasma concentrations, platelet glycoprotein IIb/IIIa (GP IIb/IIIa) receptor occupancy, and degree of inhibition of platelet aggregation in the presence of 5-micromol/L and 20-micromol/L adenosine diphosphate was determined. With an E(max) (receptor occupancy) or inhibitory E(max) (inhibition of platelet aggregation) model, abciximab concentrations required for 80% receptor occupancy and 80% inhibition of platelet aggregation were determined. RESULTS: Abciximab steady-state clearance in healthy participants was 183 +/- 72 ml/min (mean +/- SD), and single-dose clearance in patients undergoing angioplasty was 405 +/- 240 ml/min (mean +/- SD). Abciximab concentration required for 80% GP IIb/IIIa receptor occupancy was 35.2 +/- 2.4 versus 72.8 +/- 6.4 ng/ml in healthy participants versus patients (P <.01). Concentrations required for 80% inhibition of platelet aggregation stimulated by 5-micromol/L adenosine diphosphate were 25.6 +/- 1.6 versus 68.9 +/- 9.2 ng/ml (P <.01). Similarly, the concentrations required for 80% inhibition of platelet aggregation stimulated by 20-micromol/L adenosine diphosphate were 56.0 +/- 3.2 versus 141 +/- 16.8 ng/ml (P <.01). CONCLUSION: Approximately 2-fold greater abciximab exposure is required to achieve the same degree of GP IIb/IIIa occupancy and inhibition of platelet aggregation in patients undergoing angioplasty as compared with healthy participants. The difference between groups may be related either to different states of basal platelet activation or to the effect of heparin that patients received as part of the angioplasty procedure. A therapeutic concentration range for patients is 100 to 175 ng/ml, because this is the concentration consistent with >80% inhibition of platelet aggregation when 20-micromol/L adenosine diphosphate is used as the aggregating stimulus.

Pharmacodynamic profile of short-term readministration of abciximab in healthy subjects.

OBJECTIVE: The purpose of the study was to establish a rebolus regimen for abciximab that restores pharmacologic glycoprotein (GP) IIb/IIIa receptor blockade within a short time frame (up to 48 hours) after completion of an initial treatment. METHODS AND RESULTS: The study was a single-center, nonrandomized, open-label dose escalation trial in healthy volunteers (n = 30). Each subject received a 0.25 mg/kg bolus and a 0.125 microg/kg per minute infusion of abciximab, followed by incremental bolus doses of the agent at 15-minute intervals up to 48 hours (10 per group) after completion of the infusion, (maximal cumulative rebolus dose of 0.25 mg/kg). Pharmacodynamic measurements (GP IIb/IIIa receptor blockade, turbidimetric and whole blood platelet aggregation with use of a rapid platelet function assay [RPFA]) were obtained at periodic intervals during and after administration of the abciximab bolus and infusion. At the time of the first rebolus, pharmacodynamic measurements were attained immediately before administration of each rebolus and 15 minutes after the last rebolus dose. In subjects who received reboluses 12 hours after infusion, a cumulative dose of 0.05 mg/kg restored >80% blockade of GP IIb/IIIa receptors and >80% inhibition of turbidimetric (5 and 20 micromol/L adenosine diphosphate) and RPFA aggregation in 10 of 10 subjects. At 24 hours after treatment, a cumulative abciximab bolus dose of 0.1 mg/kg restored >80% blockade of all 4 pharmacodynamic measurements in 10 of 10 subjects. At 48 hours after treatment, a cumulative bolus dose of 0.15 mg/kg restored >80% blockade of all 4 pharmacodynamic measurements in 10 of 10 subjects. CONCLUSIONS: A fraction of the bolus of abciximab restored pharmacologic (>80%) GP IIb/IIIa receptor blockade when readministered at various postinfusion time points. These observations suggest that in the setting where acute readministration of abciximab is required less than a full bolus dose of the agent is warranted.