A novel immunogen to modulate cytokine production and promote immune system reconstitution in HIV-AIDS.

This 'proof of concept' study was implemented in anticipation of identifying and testing a novel antigen of human origin as a potential immunogen in a paradigm that emphasizes immunomodulation and immune system reconstitution as requisites to the development of an effective human immunodeficiency virus (HIV)-acquired immune deficiency syndrome vaccine. Fifteen HIV-infected, highly active antiretroviral therapy (HAART) naive, otherwise healthy male seropositive patients were stratified by [CD4+] into 3 groups of 5 patients: group 1 >500/mm; group 2 > 250/mm but <500/mm; and group 3 < 250/mm. Five healthy male subjects were used as controls. Replicate peripheral blood mononuclear cell (PBMC) [H]thymidine uptake phytohemaglutinin-stimulated proliferation studies, and serum cytokine assays were carried out in the presence or absence of Kveim antigen at dilutions ranging from 0.001 to 100 µg/mL. Serum cytokines [interleukin-2 (IL-2), IL-4, IL-6, interferon gamma, and tumor necrosis factor alpha] were assayed using standardized methodology. Nonparametric statistical analyses and linear regression analysis were used to test for statistical significance and strength of associations. PBMCs harvested from HIV-infected patients and incubated, ex vivo, demonstrated reproducible, antigen concentration-dependent changes in cytokine production over a range of antigen concentrations (0.001-100 µg/mL) in contrast to antigen-naive PBMCs and controls. Significant correlations were demonstrated between antigen concentration and the amount of cytokines secreted. The magnitude of the cytokine response and the patterns of cytokine secretion were HIV group-specific and could be used to identify and distinguish between the 3 groups of HIV-infected subjects. A shift toward the production of type 1-like (Th1) cytokines characteristically seen in systemic sarcoidosis and associated with effective HAART was seen when patterns of cytokine secretion were compared between antigen exposed and antigen-naive PBMCs. PBMCs harvested from seropositive HIV-infected patients and exposed to the Kveim antigen have the following properties: (1) They demonstrate proliferation and exhibit an antigen concentration-dependent secretion of cytokines. The magnitude of the cytokine response can be used to identify and distinguish between groups of seropositive patients stratified by [CD4+]. (2) These PBMCs secrete cytokines in patterns suggestive of a shift to a type 1-like (Th1) response characteristic of HAART and sarcoidosis as opposed to the type 2-like (Th2) cytokine profile characteristic of HIV-acquired immune deficiency syndrome.

Single-dose gentamicin clearance is a predictor of creatinine clearance in spinal man.

To identify a radionuclide-free, SCI (spinal cord injury) population-specific method for estimating renal function utilizing the total body clearance of gentamicin as a measure of creatinine clearance (CL(cr)) and glomerular filtration rate (GFR). To incorporate SCI population-specific patient variables into a predictive model for estimating CLcr and GFR. A retrolective study of gentamicin clearance as a measure of GFR in patients with SCI. Each patient had received a single, intravenous dose of gentamicin. Simultaneously, a 24-hour creatinine clearance (CL(cr-24)) was obtained. Experimentally measured total body clearance of a single intravenous administration of gentamicin (CL(gent-iv)) was estimated from PK analyses of gentamicin disposition in patients with SCI. Comparisons were made between CL(gent-iv) and predictors of GFR derived from a SCI population-specific nomogram (SCI-psn), the method of Cockcroft and Gault (C-G), CL(cr-24), and a multiplicative statistical model. A multiplicative model, calculated gentamicin clearance (CL(gent-calc)), that incorporates SCI population-specific characteristics to predict CL(cr-24) and GFR was derived from a multivariate nonlinear regression analysis, and the strengths of association between CL(gent-iv) and CL(gent-calc), and estimates of GFR derived from the method of C-G, SCI-psn, and CL(cr-24) were tested. The best predictive performance was demonstrated for CL(gent-iv) and the multiplicative model, CL(gent-calc), when tested against CL(cr-24) or the SCI-psn, supporting our premise that CL(gent-iv) can be used to estimate GFR in SCI. CL(gent-iv) and CL(gent-calc) outperformed CL(cr-24), the method of C-G, and the SCI-psn as predictors of GFR. The multiplicative model produced estimates of CL(gent-iv) which were more precise and less biased than CL(cr-24), the standard radiation-free predictor of GFR in patients with SCI, the SCI-psn, and the C-G equation. In this preliminary study, the clearance of gentamicin administered intravenously, CL(gent-iv), correlated highly with simultaneously measured CL(cr-24). CL(gent-iv) and our predictive model, CL(gent-calc), are more precise and less biased predictors of GFR in SCI than CL(cr-24). CL(gent-iv) and CL(gent-calc) seem to be clinically useful alternatives to CL(cr-24), the method of C-G, and the SCI-psn.

Effects of long-term 4-aminopyridine therapy on glucose tolerance and glucokinetics in patients with spinal cord injury.

STUDY OBJECTIVE: To assess the effects of the potassium channel blocker, 4-aminopyridine, on glucose tolerance and glucokinetics in patients with spinal cord injury. DESIGN: Prospective, dose level-blinded study. SETTING: University-affiliated, tertiary-level care, Veterans Affairs medical center, and a university-affiliated research center. PATIENTS: Thirty-one patients with spinal cord injury of more than 1 year's duration. INTERVENTION: In a fasting state, patients ingested 75 g of glucose and completed a 5-hour oral glucose tolerance test before and after 6 months of treatment with an oral, immediate-release formulation of 4-aminopyridine. MEASUREMENTS AND MAIN RESULTS: The time course of glucose plasma concentrations during the oral glucose tolerance tests was profiled for each patient, and glucokinetic parameters were estimated. Results were compared at baseline and after 6 months of treatment with 4-aminopyridine. Of the 31 patients, 29 (94%) had impaired glucose tolerance at baseline. After 6 months of treatment with 4-aminopyridine, 12 (41%) of the 29 patients had a 2-hour postprandial glucose level that no longer supported a diagnosis of impaired glucose tolerance. No significant changes or clinically important trends were seen in fasting blood glucose concentrations or in other glucokinetic parameters in these patients. CONCLUSIONS: The long-term administration of an oral, immediate-release formulation of 4-aminopyridine to patients with longstanding spinal cord injury was associated with readily discernible, potentially clinically significant improvements in glucose tolerance. Because impaired glucose tolerance is a common finding in patients with spinal cord injury, more research, including randomized controlled trials with large study populations, is warranted on this potential treatment.

Immunoactivation and altered intercellular communication mediate the pathophysiology of spinal cord injury.

Evidence and inferences from clinical research, clinical observation, and literature review support an etiologic paradigm for the pathophysiology of spinal cord injury (SCI). According to this paradigm, changes in immunoregulation and in the activation of cytokines or intercellular adhesion molecules (ICAMs) contribute to many of the comorbidities, metabolic changes, and pathophysiologic sequelae observed after traumatic SCI. Cytokines and ICAMs are endogenously secreted molecules that serve as intercellular signals and immunoregulators. They modulate the activity of cells and influence the organization and function of tissues or organs. These intercellular signals are posited as molecular links between the damaged, decentralized nervous system of SCI and the acquired autonomic failure, neuroendocrine-immunoregulatory dysfunction, diminished central nervous system (CNS) regenerative capacity, and broad spectrum of pathology, organ failure, and generalized impairment of homeostasis caused by trauma to the spinal cord. These highly bioactive molecules may also mediate or facilitate the intralesional CNS axonal damage and peripheral neurologic deficits sustained at time of acute CNS injury. Ultimately, it should be possible to develop treatments that will block or modulate the local and systemic expression of cytokine or ICAM bioactivity. Such treatments might aid victims of SCI by diminishing overall morbidity or mortality, helping restore sensorimotor function and homeostasis, and enhancing longevity and quality of life.

Effects of 4-aminopyridine on cardiac repolarization, PR interval, and heart rate in patients with spinal cord injury.

STUDY OBJECTIVE: To determine the effects of 4-aminopyridine (4-AP) on heart rate and PR, QT, and QTc intervals in patients with longstanding spinal cord injury (SCI). DESIGN: Randomized, active-treatment-controlled, dose level-blinded study, with allocation concealed. SETTING: University-affiliated, tertiary care medical center. PATIENTS: Sixty otherwise healthy male and female outpatients with traumatic SCI of more than 1 year's duration. Intervention. Oral administration and dose titration to tolerance of an immediate-release formulation of 4-AP. MEASUREMENTS AND MAIN RESULTS: The PR interval, heart rate, QT interval, and QTc interval obtained from standard 12-lead electrocardiograms (ECGs) at baseline (before administration of 4-AP) and after 1 month of treatment were compared. The QTc intervals were derived by using Bazett's formula (equation) incorporated into standard computerized analyses of 12-lead ECG printouts. The paired t test was performed to test for the significance of differences between means and variances. No statistically significant differences were noted in heart rate or between ECG time intervals measured at baseline and after 1 month of treatment with 4-AP among all patients with SCI or between subgroups stratified by injury level (tetraplegia, paraplegia) or sex. CONCLUSION: During the 1-month period that 4-AP was administered, the heart rate and PR, QT, and QTc intervals all remained unchanged and stayed well within normal range in comparison to literature-derived control values. 4-Aminopyridine does not appear to influence the length of cardiac time intervals or heart rate and, hence, is unlikely to cause potentially life-threatening ventricular dysrrhythmias when administered long-term and taken orally in dosages of up to 30 mg/day. Specifically, cardiac repolarization (QTc interval) is unaffected in patients with SCI who continuously receive 4-AP for up to 1 month.

4-aminopyridine influences heart rate variability in long-standing spinal cord injury.

Humans with traumatic spinal myelopathy exhibit intralesional conduction block and autonomic failure as pathophysiologic sequelae of their injury. Analysis of heart rate variability (HRV) provides a means of assessing changes in the function of the autonomic nervous system (ANS) and the cardiac sequelae of injury. Thirteen patients with long-standing spinal cord injury (SCI) and 13 able-bodied controls were studied. Each patient received a single 10-mg dose of an immediate release (IR) formulation of 4-aminopyridine (4-AP). Twenty-four hour heart rate (HR) and HRV data were acquired using a Holter ambulatory electrocardiographic (ECG) monitor. Analysis of acquired data was carried out using a minicomputer programmed to separate ECG R-R intervals into frequency patterns that appear as peaks dispersed along a frequency range of 0.0 to 1.0 Hz. Twenty-four hour baseline, pretreatment low-frequency (LF) HRV power was diminished in all patients with SCI compared with able-bodied-controls and was significantly decreased in tetraplegic patients (P = 0.03). This difference in LF HRV power disappeared during the 24 hours immediately after administration of 4-AP, and mean LF HRV power in tetraplegic patients became indistinguishable from LF HRV power in controls. 4-Aminopyridine appears to influence ANS function and LF HRV in humans with long-standing SCI.

A Nonparametric Alternative to Modeling Population Pharmacokinetics in Patients with Spinal Cord Injury: Comparison with the Standard Two-Stage Method.

The estimation of population-specific pharmacokinetic parameters from sparse of fragmentary data obtained during routine patient care is a powerful analytical tool in drug development and therapeutic drug monitoring. The Nonparametric Expectation Maximization program (NPEM) performs this function and generates robust parameter estimates which are distribution-free and unconstrained by assumption-rich parametric, for example, Gaussian, analyses. We compared standard two-stage method (STS) estimates of amikacin pharmacokinetic parameters (V, CL) derived from a sampling rich strategy (11 patients with spinal cord injury, SCI; 7 able-bodied controls) to estimates of pharmacokinetic parameters obtained from an NPEM one-compartment analysis incorporating the 11 optimally sampled SCI patients and 8 sparse data sets (19 patients with SCI; 7 controls). The STS (n = 11) and NPEM (n = 19) analyses provided similar V and CL parameter estimates in patients with SCI: 0.20 plus minus 0.04 L kg(minus sign1), 0.93 plus minus 0.24 ml min(minus sign1) kg(minus sign1) and 0.20 plus minus 0.06 L kg(minus sign1), 1.12 plus minus 0.26 ml min(minus sign1) kg(minus sign1), respectively. NPEM is a useful, user-friendly, distribution-free computational program for estimating the central tendency and interindividual variability of amikacin pharmacokinetic parameters in spinal cord injured humans.