Design of an adaptive randomized clinical trial of intravenous citrulline for sickle cell pain crisis in the emergency department

Background

Vaso-occlusive pain crisis (VOC) is the most frequent cause for Emergency Department (ED) visits and hospital admissions for patients with sickle cell disease (SCD). Nitric oxide plays a critical role in the pathogenesis of vaso-occlusion. The amino acid, citrulline, is the main endothelial nitric oxide booster that offers the potential to ameliorate vaso-occlusion and decrease the risk of hospitalization.

Objective

In this two-part study, the goal of the first part is to determine the pharmacokinetic profile of intravenous (IV) l-citrulline and optimal dose for the second part of the study, which is to determine the efficacy and tolerability of the intervention in patients with SCD.

Design

A phase I/IIA open-label dose-finding study with subsequent double-blind, placebo-controlled, randomized Study of l-citrulline in children and adolescents with SCD presenting to the ED in VOC.

Methods

Part 1: Subjects experiencing VOC are enrolled in an open-label, ascending dose of IV l-citrulline to identify the optimum dose with endpoints of pharmacokinetic parameters, pain scores, reduction of opioid use, quality of life, proportion admitted to the hospital for treatment of pain, readmission rates, and assessment of adverse events. Part 2 of the trial is a double-blind, placebo-controlled adaptive "pick-the-winner" design to evaluate the efficacy and tolerability of IV l-citrulline in patients with SCD while receiving standard of care therapy for VOC.

Summary

This ED based sickle cell adaptive trial will determine the optimal dose for IV citrulline and whether the intervention improves outcome as a potential novel therapy for VOC in SCD.

Development of a robust 30-minute reverse-phase high pressure liquid chromatography method to measure amino acids using widely available equipment and its comparison to current clinical ion-exchange chromatography measurement

We have developed a fast and accurate method that uses a small volume of sample to determine over 25 of the typically reported amino acids in human plasma. Samples were prepped with a single step using a spin filter to remove proteins, avoiding the decreased sensitivity from dilution in acid precipitation. Using a reverse phase (RP) High Performance Liquid Chromatography (HPLC) system with O-phthaldehyde (OPA) as the pre-column derivatization reagent, and UV detection at 338 nm, we did a direct comparison with the most common ion exchange/ninhydrin method used in clinical labs on the same plasma samples with 95% concurrence, analysis of amino acid standard solutions returned 99% concurrence. With a sample preparation time of 30 min, utilizing less than 25 μl of sample and with a chromatography run of 30 min, this method can substantially increase access to analysis in both clinical and research laboratories using instruments that are more widely available.

Synopsis

We describe a rapid and easily deployed method for sensitive amino measurement in biological samples.

Urinary phenylacetylglutamine as dosing biomarker for patients with urea cycle disorders

We have analyzed pharmacokinetic data for glycerol phenylbutyrate (also GT4P or HPN-100) and sodium phenylbutyrate with respect to possible dosing biomarkers in patients with urea cycle disorders (UCD).

STUDY DESIGN

These analyses are based on over 3000 urine and plasma data points from 54 adult and 11 pediatric UCD patients (ages 6-17) who participated in three clinical studies comparing ammonia control and pharmacokinetics during steady state treatment with glycerol phenylbutyrate or sodium phenylbutyrate. All patients received phenylbutyric acid equivalent doses of glycerol phenylbutyrate or sodium phenylbutyrate in a cross over fashion and underwent 24-hour blood samples and urine sampling for phenylbutyric acid, phenylacetic acid and phenylacetylglutamine.

RESULTS

Patients received phenylbutyric acid equivalent doses of glycerol phenylbutyrate ranging from 1.5 to 31.8 g/day and of sodium phenylbutyrate ranging from 1.3 to 31.7 g/day. Plasma metabolite levels varied widely, with average fluctuation indices ranging from 1979% to 5690% for phenylbutyric acid, 843% to 3931% for phenylacetic acid, and 881% to 1434% for phenylacetylglutamine. Mean percent recovery of phenylbutyric acid as urinary phenylacetylglutamine was 66.4 and 69.0 for pediatric patients and 68.7 and 71.4 for adult patients on glycerol phenylbutyrate and sodium phenylbutyrate, respectively. The correlation with dose was strongest for urinary phenylacetylglutamine excretion, either as morning spot urine (r = 0.730, p < 0.001) or as total 24-hour excretion (r = 0.791 p<0.001), followed by plasma phenylacetylglutamine AUC(24-hour), plasma phenylacetic acid AUC(24-hour) and phenylbutyric acid AUC(24-hour). Plasma phenylacetic acid levels in adult and pediatric patients did not show a consistent relationship with either urinary phenylacetylglutamine or ammonia control.

CONCLUSION

The findings are collectively consistent with substantial yet variable pre-systemic (1st pass) conversion of phenylbutyric acid to phenylacetic acid and/or phenylacetylglutamine. The variability of blood metabolite levels during the day, their weaker correlation with dose, the need for multiple blood samples to capture trough and peak, and the inconsistency between phenylacetic acid and urinary phenylacetylglutamine as a marker of waste nitrogen scavenging limit the utility of plasma levels for therapeutic monitoring. By contrast, 24-hour urinary phenylacetylglutamine and morning spot urine phenylacetylglutamine correlate strongly with dose and appear to be clinically useful non-invasive biomarkers for compliance and therapeutic monitoring.

Recommendations for locus-specific databases and their curation

Expert curation and complete collection of mutations in genes that affect human health is essential for proper genetic healthcare and research. Expert curation is given by the curators of gene-specific mutation databases or locus-specific databases (LSDBs). While there are over 700 such databases, they vary in their content, completeness, time available for curation, and the expertise of the curator. Curation and LSDBs have been discussed, written about, and protocols have been provided for over 10 years, but there have been no formal recommendations for the ideal form of these entities. This work initiates a discussion on this topic to assist future efforts in human genetics. Further discussion is welcome.

Neurological implications of urea cycle disorders

The urea cycle disorders constitute a group of rare congenital disorders caused by a deficiency of the enzymes or transport proteins required to remove ammonia from the body. Via a series of biochemical steps, nitrogen, the waste product of protein metabolism, is removed from the blood and converted into urea. A consequence of these disorders is hyperammonaemia, resulting in central nervous system dysfunction with mental status changes, brain oedema, seizures, coma, and potentially death. Both acute and chronic hyperammonaemia result in alterations of neurotransmitter systems. In acute hyperammonaemia, activation of the NMDA receptor leads to excitotoxic cell death, changes in energy metabolism and alterations in protein expression of the astrocyte that affect volume regulation and contribute to oedema. Neuropathological evaluation demonstrates alterations in the astrocyte morphology. Imaging studies, in particular (1)H MRS, can reveal markers of impaired metabolism such as elevations of glutamine and reduction of myoinositol. In contrast, chronic hyperammonaemia leads to adaptive responses in the NMDA receptor and impairments in the glutamate-nitric oxide-cGMP pathway, leading to alterations in cognition and learning. Therapy of acute hyperammonaemia has relied on ammonia-lowering agents but in recent years there has been considerable interest in neuroprotective strategies. Recent studies have suggested restoration of learning abilities by pharmacological manipulation of brain cGMP with phosphodiesterase inhibitors. Thus, both strategies are intriguing areas for potential investigation in human urea cycle disorders.

Interstitial deletion of chromosome 2q32-34 associated with multiple congenital anomalies and a urea cycle defect (CPS I deficiency)

A de novo deletion of the long arm of chromosome 2 at 2q31-33 was observed in the fetal amniocyte G-banded karyotype performed because of possible multiple malformations identified by ultrasound at 23 weeks gestation. Two days after the uneventful term delivery of a 2.45 kg male, the neonate experienced cardiopulmonary decompensation and biochemical changes compatible with carbamoyl phosphate synthetase I (CPS I) deficiency (elevated ammonia with a peak of 948 micromol/L, deficiency of citrulline, and no increase in orotic acid). The child died on day 3 of life. Physical anomalies confirmed at autopsy included double superior vena cava, ectopic adrenal tissue, and metatarsus adductus. The autopsy also revealed histologic evidence consistent with CPS deficiency, most notably microvesicular steatosis of the liver and Alzheimer's Type II changes with hypertrophic astrocytes in the basal ganglia. A postnatal lymphocyte karyotype confirmed the chromosome 2q31-33 deletion. Enzyme analysis on postmortem liver tissue confirmed the diagnosis of CPS deficiency. CPS I is reported to be mapped to 2q35 by NCBI (http://www.ncbi.nlm.nih.gov/mapview/) and 2q34 by ENSEMBL (http://www.ensembl.org/). The UCSC Human Genome Browser July 2003 assembly also places the gene at 2q34 (http://genome.UCSC.edu/). Fluorescence in situ hybridization (FISH) analysis with a BAC clone (RP11-349G4) of CPS I demonstrated that one copy of the gene was deleted in this infant. Using additional probes corresponding to the bands in the region of deletion, we identified the deleted region as 2q32-2q34. Our observations support the CPS I map position (ENSEMBL, UCSC) at 2q34. Additionally, potential conditions associated with deletions narrowly defined by standard cytogenetic techniques merit consideration in prenatal counseling. As demonstrated here, deletions may not only result in malformations and mental retardation but also increase the likelihood of revealing mutated genes located in the undeleted region of the homologous chromosome.

Current strategies for the management of neonatal urea cycle disorders

The treatment of newborns with urea cycle disorders has evolved over the years into a complex multidisciplinary effort. The complexity derives from the number of issues that must be addressed simultaneously. At the Urea Cycle Disorders Consensus Meeting held in Washington, D.C., a panel of physicians and other professionals with extensive experience in this field was assembled to bring some systematization to this task. This manuscript is a condensation of the collective opinion and experience of that group. The outcome of untreated or poorly treated patients with urea cycle disorders is universally bad. Although a favorable outcome is not always feasible, even with the best therapy, the methods outlined here should help treat such a patient by drawing on the experience of others who have treated patients with urea cycle disorders. This article does not purport to be the final word in treating children with these disorders. However, by establishing some common ground, new methods can be tried and compared with existing ones. In a future that holds the prospect of gene therapy "cures" for these diseases, striving for the best possible outcome in the critical newborn period is a worthy goal.

Proceedings of a consensus conference for the management of patients with urea cycle disorders

In an effort to develop standards for the treatment of patients with urea cycle disorders, a consensus conference was held in Washington, DC, from April 27-29, 2000. Conference participants included physicians, scientists, nurses, dieticians, and a genetic counselor, all experts in their various medical fields in these diseases. Representatives from the Food and Drug Administration and the National Urea Cycle Disorders Foundation, a parents support group, also participated in the conference. The goals set forth for the conference were to (1) reach a consensus on diagnostic and therapeutic guidelines for urea cycle disorders with the most up-to-date information and the experience of experts in the field, (2) establish a collaborative network of health care professionals to advance the cause of patients with urea cycle disorders in the areas of clinical management and research, and (3) provide help to health care providers in the recognition and management of these complex disorders by publishing the proceedings of the conference in a widely read journal. The articles that follow this introduction represent the current state of knowledge on the topics addressed in the conference and a summary of the discussions that followed each of the presentations. With input from all the participants, we tried to cover those topics that were believed to be the most relevant both to the experts and to patients. As the reader will appreciate, many unresolved and controversial issues pertaining to treatment have yet to be studied by rigorous scientific methods. On the other hand, there are many issues on which the panel agreed. In many instances the availability of reliable information on the respective topics determined whether consensus could be reached.

Effective hemodialysis and hemofiltration driven by an extracorporeal membrane oxygenation pump in infants with hyperammonemia

Two infants with urea cycle disorders had life-threatening hyperammonemia within the first 5 days of life. Both patients were small for dates, poorly oxygenated, and hemodynamically unstable. We employed a combination of extracorporeal oxygenation and hemodialysis to provide high-flow filtration in a controlled system to rapidly detoxify both patients.

Molecular cloning, sequencing, chromosomal localization, and tissue distribution of the human Na+/H+ exchanger (SLC9A2)

The Na+/H+ exchangers belong to a family of transport proteins involved in intracellular pH regulation and vectorial sodium transport across various epithelial tissues. We have cloned a unique isoform (NHE-2) by screening a rat intestinal cDNA library utilizing a human NHE-1 fragment. In this report we describe molecular cloning of the human Na+/H+ exchanger (NHE-2, HGMW-approved symbol SLC9A2). The cDNA encodes a protein of 698 amino acid residues. Human NHE-2 is widely distributed in tissues of the gastrointestinal tract, kidney, heart, testes, uterus, and adrenal glands. Hydropathy plot indicates that the translated protein is predicted to have 10 transmembrane domains with three potential N-glycosylation sites and four potential cAMP- and cGMP-dependent protein kinase phosphorylation sites. This cDNA maps the location of the gene encoding NHE-2 to human chromosome 2q11.2.

In vivo molecular analysis of lymphokines involved in the murine immune response during Schistosoma mansoni infection. I. IL-4 mRNA, not IL-2 mRNA, is abundant in the granulomatous livers, mesenteric lymph nodes, and spleens of infected mice

Using Northern Blot analysis, the endogenous levels of IL-4 and IL-2 mRNA in the spleens, mesenteric lymph nodes, and granulomatous livers of male CBA/J mice in the acute phase of infection with Schistosoma mansoni have been quantified. High levels of IL-4 mRNA were detected in all three tissues from infected mice, whereas none was detected in tissues from normal, uninfected, age-matched mice. Isolation of the granulomas from the livers of infected mice and subsequent extraction of total RNA from these lesions resulted in a 70-fold enrichment of IL-4 message compared with the whole, unseparated granulomatous liver tissue. Hence, the predominant source of the IL-4 mRNA detected in livers from infected mice appears to be the schistosome egg-induced granulomas within these livers. In contrast, IL-2 mRNA was never detected in any of these tissues from either infected or normal mice. Control experiments were performed that ruled out the possibility that this inability to detect IL-2 mRNA was due to a difference in the efficacy of the IL-4 and IL-2 probes or due to a selective lability of IL-2 message. These data imply that IL-4-producing, Th2 lymphocytes are active in and possibly integral to the granulomatous, delayed-type hypersensitivity response characteristic of this infection, and directly challenges the current hypothesis that delayed-type hypersensitivity responses are exclusively mediated by Th1 lymphocytes.

In vivo molecular analysis of lymphokines involved in the murine immune response during Schistosoma mansoni infection. I. IL-4 mRNA, not IL-2 mRNA, is abundant in the granulomatous livers, mesenteric lymph nodes, and spleens of infected mice

Using Northern Blot analysis, the endogenous levels of IL-4 and IL-2 mRNA in the spleens, mesenteric lymph nodes, and granulomatous livers of male CBA/J mice in the acute phase of infection with Schistosoma mansoni have been quantified. High levels of IL-4 mRNA were detected in all three tissues from infected mice, whereas none was detected in tissues from normal, uninfected, age-matched mice. Isolation of the granulomas from the livers of infected mice and subsequent extraction of total RNA from these lesions resulted in a 70-fold enrichment of IL-4 message compared with the whole, unseparated granulomatous liver tissue. Hence, the predominant source of the IL-4 mRNA detected in livers from infected mice appears to be the schistosome egg-induced granulomas within these livers. In contrast, IL-2 mRNA was never detected in any of these tissues from either infected or normal mice. Control experiments were performed that ruled out the possibility that this inability to detect IL-2 mRNA was due to a difference in the efficacy of the IL-4 and IL-2 probes or due to a selective lability of IL-2 message. These data imply that IL-4-producing, Th2 lymphocytes are active in and possibly integral to the granulomatous, delayed-type hypersensitivity response characteristic of this infection, and directly challenges the current hypothesis that delayed-type hypersensitivity responses are exclusively mediated by Th1 lymphocytes.