Transient hyperammonemia due to L-asparaginase therapy in children with acute lymphoblastic leukemia or non-Hodgkin lymphoma

Treatment and outcomes of symptomatic hyperammonemia following asparaginase therapy in children with acute lymphoblastic leukemia

Hyperammonemia has been reported following asparaginase administration, consistent with the mechanisms of asparaginase, which catabolizes asparagine to aspartic acid and ammonia, and secondarily converts glutamine to glutamate and ammonia. However, there are only a few reports on the treatment of these patients, which varies widely from watchful waiting to treatment with lactulose, protein restriction, sodium benzoate, and phenylbutyrate to dialysis. While many patients with reported asparaginase-induced hyperammonemia (AIH) are asymptomatic, some have severe complications and even fatal outcomes despite medical intervention. Here, we present a cohort of five pediatric patients with symptomatic AIH, which occurred after switching patients from polyethylene glycolated (PEG)- asparaginase to recombinant Crisantaspase Pseudomonas fluorescens (4 patients) or Erwinia (1 patient) asparaginase, and discuss their subsequent management, metabolic workup, and genetic testing. We developed an institutional management plan, which gradually evolved based on our local experience and previous treatment modalities. Because of the significant reduction in glutamine levels after asparaginase administration, sodium benzoate should be used as a first-line ammonia scavenger for symptomatic AIH instead of sodium phenylacetate or phenylbutyrate. This approach facilitated continuation of asparaginase doses, which is known to improve cancer outcomes. We also discuss the potential contribution of genetic modifiers to AIH. Our data highlights the need for increased awareness of symptomatic AIH, especially when an asparaginase with higher glutaminase activity is used, and its prompt management. The utility and efficacy of this management approach should be systematically investigated in a larger cohort of patients.

Asparaginase: How to Better Manage Toxicities in Adults

PURPOSE OF REVIEW

This review aims to help oncologists who predominantly treat adults better understand and manage asparaginase associated toxicities and prevent unnecessary discontinuation or reluctance of its use.

RECENT FINDINGS

Given the data supporting the benefit of incorporating multiple doses of asparaginase in pediatric type regimens, it is prudent to promote deeper understanding of this drug, particularly its toxicities, and its use so as to optimize treatment of ALL. Although asparaginase is associated with a variety of toxicities, the vast majority are not life threatening and do not preclude repeat dosing of this important drug. Understanding the pharmacology and toxicity profile of asparaginase is critical to dosing asparaginase appropriately in order to minimize these toxicities.

A glance at transient hyperammonemia of the newborn: Pathophysiology, diagnosis, and treatment: A review

Hyperammonemia is the excessive accumulation of ammonia in the blood, and is usually defined as a plasma level above 100 µmol/L in neonates or above 50 µmol/L in term infants, children, and adolescents. Patients with hyperammonemia usually experience life-threatening neuropsychiatric symptoms, especially newborns. It is routinely caused by inherited metabolic diseases and also by acquired disorders, such as liver failure, portosystemic shunting, gastrointestinal hemorrhage, ureterosigmoidostomy, renal tubular acidosis, hypoxic ischemic encephalopathy, infections with urea-metabolizing organisms, and some drugs. Transient hyperammonemia of the newborn (THAN) is a special type of hyperammonemia acknowledged in the field of metabolic disease as an inwell-defined or well-understood entity, which can be diagnosed only after the exclusion of genetic and acquired causes of hyperammonemia. Although the prognosis for THAN is good, timely identification and treatment are essential. Currently, THAN is underdiagnosed and much less is mentioned for early diagnosis and vigorous treatment. Herein, we present common themes that emerge from the pathogenesis, diagnosis, and management of THAN, based on current evidence. When a newborn presents with sepsis, intracranial hemorrhage, or asphyxia that cannot explain coma and seizures, doctors should always keep this disease in mind.

SOHO State of the Art Updates and Next Questions | Asparaginase-Understanding and Overcoming Toxicities in Adults with ALL

The adoption of pediatric-inspired regimens in young adults with newly diagnosed acute lymphoblastic leukemia (ALL) has significantly improved their survival outcomes. Pediatric-inspired regimens in ALL rely profoundly on delivering adequate dosing of non-myelosuppressive drugs of which asparaginase, a bacterial derived agent, is a key component. Asparaginase therapy is associated with a spectrum of unique toxicities that are observed more frequently in adult patients compared to children with ALL, and this observation has contributed to the reluctance of adult oncologists to administer the drug to their patients. Understanding the breadth of asparaginase toxicity and the associated risk factors may help in preventing severe manifestations and allow safer treatment for adults with ALL. In this review, we will discuss the different formulations of asparaginase and the appropriate dosing in adults with ALL. We will further discuss the frequency and risk factors for individual toxicities of asparaginase along with strategies for their prevention and management.

Multiple Asparaginase Infusions Cause Increasingly Severe Acute Hyperammonemia

Adverse reactions during and shortly after infusing asparaginase for the treatment of acute lymphoblastic leukemia can increase in severity with later doses, limiting further use and increasing relapse risk. Although asparaginase is associated with hyperammonemia, the magnitude of the increase in serum ammonia immediately after the infusion and in response to multiple infusions has not been examined. The concurrence of hyperammonemia and infusion reactions was studied using weaned juvenile pigs that received 12 infusions of Erwinia asparaginase (Erwinase; 1250 U/kg) over 28 days, with two 5-day recovery periods without asparaginase after the eighth and eleventh doses. Infusion reactions and prolonged hyperammonemia (>50 µM ammonia 48 h after the infusion) began after the fourth dose and increased with later doses. Dense sampling for 60 min revealed an acute phase of hyperammonemia that peaked within 20 min after starting the first infusion (298 + 62 µM) and lasted less than 1 h, without apparent symptoms. A pronounced acute hyperammonemia after the final infusion (1260 + 250 µM) coincided with severe symptoms and one mortality during the infusion. The previously unrecognized acute phase of hyperammonemia associated with asparaginase infusion coincides with infusion reactions. The juvenile pig is a translational animal model for understanding the causes of acute and chronic hyperammonemia, differentiating from hypersensitivity reactions, and for improving infusion protocols to reduce acute hyperammonemia and to allow the continued use of asparaginase.

Novel Insights on the Use of L-Asparaginase as an Efficient and Safe Anti-Cancer Therapy

Simple Summary

L-asparaginase (L-ASNase) therapy is key for achieving the very high cure rate of pediatric acute lymphoblastic leukemia (ALL), yet its use is mostly confined to this indication. One main reason preventing the expansion of today’s FDA-approved L-ASNases to solid cancers is their high toxicity and side effects, which become especially challenging in adult patients. The design of optimized L-ASNase molecules provides opportunities to overcome these unwanted toxicities. An additional challenge to broader application of L-ASNases is how cells can counter the pharmacological effect of this drug and the identification of L-ASNases resistance mechanisms. In this review, we discuss recent insights into L-ASNase adverse effects, resistance mechanisms, and how novel L-ASNase variants and drug combinations can expand its clinical applicability, with a focus on both hematological and solid tumors.

Abstract

L-Asparaginase (L-ASNase) is an enzyme that hydrolyses the amino acid asparagine into aspartic acid and ammonia. Systemic administration of bacterial L-ASNase is successfully used to lower the bioavailability of this non-essential amino acid and to eradicate rapidly proliferating cancer cells with a high demand for exogenous asparagine. Currently, it is a cornerstone drug in the treatment of the most common pediatric cancer, acute lymphoblastic leukemia (ALL). Since these lymphoblasts lack the expression of asparagine synthetase (ASNS), these cells depend on the uptake of extracellular asparagine for survival. Interestingly, recent reports have illustrated that L-ASNase may also have clinical potential for the treatment of other aggressive subtypes of hematological or solid cancers. However, immunogenic and other severe adverse side effects limit optimal clinical use and often lead to treatment discontinuation. The design of optimized and novel L-ASNase formulations provides opportunities to overcome these limitations. In addition, identification of multiple L-ASNase resistance mechanisms, including ASNS promoter reactivation and desensitization, has fueled research into promising novel drug combinations to overcome chemoresistance. In this review, we discuss recent insights into L-ASNase adverse effects, resistance both in hematological and solid tumors, and how novel L-ASNase variants and drug combinations can expand its clinical applicability.

Transient Hyperammonemic Encephalopathy in a Child with Relapsed Acute Lymphoblastic Leukemia and Severe Tumor Lysis Syndrome

Idiopathic hyperammonemia (IHA) is a severe condition, which has been reported in intensive chemotherapy and bone marrow transplantation. This case elucidates the diagnostic dilemma in children undergoing initiation of chemotherapy and developing severe disorders of qualitative and quantitative consciousness in the presence of hyperammonemia (HA) and lactic acidosis. The role of mitoxantrone as a causative agent for IHA in children is elusive. Children undergoing chemotherapy are often in a poor general condition, and the clinical presentation of HA is heterogeneous. This case should be a reminder for clinicians to check for HA in children with tumor lysis syndrome and acute neurological deterioration.

Ammonia level as a proxy of asparaginase inactivation in children: A strategy for classification of infusion reactions

INTRODUCTION

Allergic hypersensitivity reactions related to enzyme asparaginase may occur during intravenous infusion of drugs and other adverse reactions (non-allergic hypersensitivity and hyperammonemia), which do not require discontinuation of therapy as the first case. It makes differential diagnoses between infusion reactions essential to assure the team regarding the right decision to make after the adverse event. This study evaluated a pharmacovigilance strategy of differentiating infusion reactions to asparaginase in pediatric patients, based on the measurement of serum ammonia and the classification of the reactions by clinical symptoms and severity.

METHODOLOGY

We included children, diagnosed with ALL, and treated with native Escherichia coli asparaginase in a university hospital. The professional team monitored and evaluated all asparaginase infusions for continuity of treatment (rechallenge), seeing the measurement of serum ammonia and classification of reactions for type and severity grade. Data from this monitoring was collected retrospectively. Chi-square and Mann-Whitney tests were used to compare the ratios between serum ammonia concentration posterior and before asparaginase infusion.

RESULTS

245 infusions in 32 patients were monitored, and 19 reactions were observed in 17 children (53%). Three children have hyperammonemia and continue their treatment. The variation of the serum ammonia levels before and after the infusion was statistically significant, comparing the groups with no reaction or hyperammonemia versus the group with the hypersensitivity reaction.

CONCLUSION

The pharmacovigilance strategy applied in the hospital investigated was a useful and inexpensive tool that supported clinical decision-making and enabled the maintenance of asparaginase therapy for three (9,4%) patients followed up.

Asparaginase Toxicities: Identification and Management in Patients With Acute Lymphoblastic Leukemia

BACKGROUND

Acute lymphoblastic leukemia (ALL) is a common cancer in children, and outcomes have greatly improved because of the refinement of multiagent chemotherapy regimens that include intensified asparaginase therapy. Asparaginase, a cornerstone of modern pediatric chemotherapy regimens for ALL and asparaginase-containing protocols, is increasingly used in adolescent and adult patients historically treated with asparaginase-free regimens. 
.

OBJECTIVES

This article is an overview of commonly encountered asparaginase-
associated toxicities and offers recommendations for treatment management.
.

METHODS

A literature review was conducted, reviewing asparaginase and common toxicities, specifically hypersensitivity, pancreatitis, thrombosis, hyperbilirubinemia, and hyperglycemia.
.

FINDINGS

The rapid identification and management of common asparaginase-associated adverse events can reduce symptom severity and limit potential interruptions to therapy, possibly improving outcomes.

Symptomatic Hyperammonemia With Erwinia chrysanthemi-derived Asparaginase in Pediatric Leukemia Patients

Erwinia chrysanthemi-derived asparaginase is increasingly integral to acute lymphoblastic leukemia therapy. In our series, 16% of patients developed symptomatic hyperammonemia following Erwinia administration with symptoms including refractory nausea, vomiting, profound fatigue, malaise, and coma. This series of patients receiving Erwinia indicates higher than expected incidence of hyperammonemia, correlation between ammonia and asparaginase levels and therapeutic asparaginase activity levels despite dose reduction. The series provides evidence for investigation into which patients require intervention to prevent toxicity, which patients may have ammonia levels used as an asparaginase activity surrogate and which patients may achieve equivalent efficacy with abridged dosing.

A Novel l-Asparaginase with low l-Glutaminase Coactivity Is Highly Efficacious against Both T- and B-cell Acute Lymphoblastic Leukemias In Vivo

Acute lymphoblastic leukemia (ALL) is the most common type of pediatric cancer, although about 4 of every 10 cases occur in adults. The enzyme drug l-asparaginase serves as a cornerstone of ALL therapy and exploits the asparagine dependency of ALL cells. In addition to hydrolyzing the amino acid l-asparagine, all FDA-approved l-asparaginases also have significant l-glutaminase coactivity. Since several reports suggest that l-glutamine depletion correlates with many of the side effects of these drugs, enzyme variants with reduced l-glutaminase coactivity might be clinically beneficial if their antileukemic activity would be preserved. Here we show that novel low l-glutaminase variants developed on the backbone of the FDA-approved Erwinia chrysanthemi l-asparaginase were highly efficacious against both T- and B-cell ALL, while displaying reduced acute toxicity features. These results support the development of a new generation of safer l-asparaginases without l-glutaminase activity for the treatment of human ALL.Significance: A new l-asparaginase-based therapy is less toxic compared with FDA-approved high l-glutaminase enzymes Cancer Res; 78(6); 1549-60. ©2018 AACR.

Severe pegaspargase hypersensitivity reaction rates (grade ≥3) with intravenous infusion vs. intramuscular injection: analysis of 54,280 doses administered to 16,534 patients on children's oncology group (COG) clinical trials

PEGylated asparaginase (pegaspargase) can be administered via intramuscular (IM) injection or intravenous (IV) infusion with a hypersensitivity reaction (HSR) incidence ranging 3-41%. We evaluated grade ≥3 HSRs when given IM vs. IV on six Children's Oncology Group (COG) leukemia trials (2003-2015) to determine differences in HSR rates. 54,280 doses were administered to 16,534 patients. Considering all doses of pegaspargase during induction, consolidation, and delayed intensification, grade ≥3 HSR rate with IM injection was 5.4% (n = 482/8981) compared to 3.2% for IV (n = 245/7553) (p < .0001). If only the second and third doses of pegaspargase were analyzed, where the majority of grade ≥3 HSRs occur, the rate following IM injection was 10.1% (n = 459/4534) compared to 5.0% (n = 222/4443) for IV (p < .0001). On standardized treatment protocols conducted by the COG during 2003-2015, grade ≥3 HSR rates to pegaspargase occurred less frequently with IV infusion than IM injection.

Reactions related to asparaginase infusion in a 10-year retrospective cohort

INTRODUCTION

Although it is an essential component of the treatment of acute lymphoid leukemia in children, asparaginase causes adverse reactions that sometimes make it impossible to use it fully. Hypersensitivity reactions are the most frequent and may lead to early discontinuation of treatment. The present study aimed to investigate suspicions of adverse reactions during the infusion of asparaginase in a pediatric cohort.

METHODS

A retrospective observational study was carried out at a university pediatric institute in the state of Rio de Janeiro. Information regarding clinical features and characteristics of adverse reactions was collected from hospital medical records. Suspicions of adverse reactions were classified regarding causality and severity.

RESULTS

Seventy-three suspicions of adverse reactions were recorded during asparaginase infusion in 72 children in the study period. Allergic hypersensitivity reactions were suspected in 60.5% of the cases. Of these, 25% of the reactions occurred during induction and 61.1% in concomitant use with vincristine, findings that diverge from other studies. High-risk classification and younger age were considered risk factors for these reactions. A total of 72.4% of the reactions were classified as grade 1 or 2, which suggest that not all are related to antibody formation; this highlights the importance of differential diagnosis with other reactions, such as non-allergic hypersensitivity and hyperammonemia.

CONCLUSION

The implementation of the differential diagnosis of reactions related to infusion of asparaginase with ammonia dosage and classification of the grade of reactions is crucial to facilitate the identification and proper management of each type of reaction.

Acute central nervous system complications and ammonium levels in adult patients with acute lymphoblastic leukemia receiving l-asparaginase

We analyzed ammonium levels and acute central nervous complications in adult patients receiving chemotherapy for acute lymphoblastic leukemia with or without asparaginase (l-asp). Twenty patients with a median age of 40.3 years were included. Ammonium-levels were measured during 88 chemotherapy cycles, 60 cycles (68%) with l-asp, and 28 cycles (32%) without l-asp. Ammonium was elevated in 87% of all l-asp containing cycles, with median ammonium levels of 169 μmol/l (interquartile range (IQR) 91-269 μmol/l). These values were higher when compared to ammonium levels at baseline (31.5 μmol/l, IQR 24-40 μmol/l, p < .001), and when compared to levels in cycles without l-asp (30 μmol/l, IQR 19-41 μmol/l, p < .001). Acute hyperammonemic encephalopathy was diagnosed in one patient, and encephalopathy for other reasons, but with hyperammonemia as a possible contributing factor in four patients. In conclusion, ammonium levels are elevated in all adult patients receiving l-asparaginase, but only some patients will present symptoms of encephalopathy.

Benzoate and Sorbate Salts: A Systematic Review of the Potential Hazards of These Invaluable Preservatives and the Expanding Spectrum of Clinical Uses for Sodium Benzoate

Sodium benzoate and potassium sorbate are extremely useful agents for food and beverage preservation, yet concerns remain over their complete safety. Benzoate can react with the ascorbic acid in drinks to produce the carcinogen benzene. A few children develop allergy to this additive while, as a competitive inhibitor of D-amino acid oxidase, benzoate can also influence neurotransmission and cognitive functioning. Model organism and cell culture studies have raised some issues. Benzoate has been found to exert teratogenic and neurotoxic effects on zebrafish embryos. In addition, benzoate and sorbate are reported to cause chromosome aberrations in cultured human lymphocytes; also to be potently mutagenic toward the mitochondrial DNA in aerobic yeast cells. Whether the substantial human consumption of these compounds could significantly increase levels of such damages in man is still unclear. There is no firm evidence that it is a risk factor in type 2 diabetes. The clinical administration of sodium benzoate is of proven benefit for many patients with urea cycle disorders, while recent studies indicate it may also be advantageous in the treatment of multiple sclerosis, schizophrenia, early-stage Alzheimer's disease and Parkinson's disease. Nevertheless, exposure to high amounts of this agent should be approached with caution, especially since it has the potential to generate a shortage of glycine which, in turn, can negatively influence brain neurochemistry. We discuss here how a small fraction of the population might be rendered-either through their genes or a chronic medical condition-particularly susceptible to any adverse effects of sodium benzoate.

From the Children's Oncology Group: Evidence-Based Recommendations for PEG-Asparaginase Nurse Monitoring, Hypersensitivity Reaction Management, and Patient/Family Education

PEG-aspariginase is a backbone chemotherapy agent in pediatric acute lymphoblastic leukemia and in some non-Hodgkin lymphoma therapies. Nurses lack standardized guidelines for monitoring patients receiving PEG-asparaginase and for educating patients/families about hypersensitivity reaction risks. An electronic search of 6 databases using publication years 2000-2015 and multiple professional organizations and clinical resources was conducted. Evidence sources were reviewed for topic applicability. Each of the final 23 sources was appraised by 2 team members. The GRADE (Grading of Recommendations Assessment, Development and Evaluation) system was used to assign a quality and strength rating for each recommendation. Multiple recommendations were developed: 4 relating to nurse monitoring of patients during and after drug administration, 8 guiding hypersensitivity reaction management, and 4 concerning patient/family educational content. These strong recommendations were based on moderate, low, or very-low-quality evidence. Several recommendations relied on generalized drug hypersensitivity guidelines. Additional research is needed to safely guide PEG-asparaginase monitoring, hypersensitivity reaction management, and patient/family education. Nurses administering PEG-asparaginase play a critical role in the early identification and management of hypersensitivity reactions.

Immunology of infusion reactions in the treatment of patients with acute lymphoblastic leukemia

Infusion reactions are potentially dose-limiting adverse events associated with intravenous administration of several common agents used to treat patients with acute lymphoblastic leukemia. True clinical hypersensitivity reactions are antibody-mediated and can occur only after repeated exposure to an antigen. Conversely, anaphylactoid infusion reactions are nonantibody-mediated and often occur on the initial exposure to a drug. Cytokine-release syndrome comprises a subset of nonantibody-mediated infusion reactions associated with the use of monoclonal antibodies and immune therapies. Clinical symptoms of hypersensitivity reactions and nonantibody-mediated infusion reactions heavily overlap and can be difficult to distinguish in practice. Regardless of the underlying mechanism, any infusion reaction can negatively affect treatment efficacy and patient safety. These events require prompt response, and potentially, modification of subsequent therapy.

Asparaginase-associated toxicity in children with acute lymphoblastic leukemia

Asparaginase is an integral component of multiagent chemotherapy regimens for the treatment of children with acute lymphoblastic leukemia. Positive outcomes are seen in patients who are able to complete their entire prescribed course of asparaginase therapy. Toxicities associated with asparaginase use include hypersensitivity (clinical and subclinical), pancreatitis, thrombosis, encephalopathy, and liver dysfunction. Depending on the nature and severity of the toxicity, asparaginase therapy may be altered or discontinued in some patients. Clinical hypersensitivity is the most common asparaginase-associated toxicity requiring treatment discontinuation, occurring in up to 30% of patients receiving Escherichia coli-derived asparaginase. The ability to rapidly identify and manage asparaginase-associated toxicity will help ensure patients receive the maximal benefit from asparaginase therapy. This review will provide an overview of the common toxicities associated with asparaginase use and recommendations for treatment management.

Idiopathic Hyperammonemia That Developed During Initial Treatment With Steroid in a Patient With Newly Diagnosed Leukemia

Idiopathic hyperammonemia (IHA) has been described as a complication of intensive chemotherapy for the treatment of hematologic malignancy but has subsequently been found in patients undergoing bone marrow transplantation and in those with solid tumors treated with 5-fluorouracil. Although IHA is a rare complication, it is sometimes associated with high mortality in hematologic malignancies. Here we report the case of a 15-year-old boy in whom hyperammonemia developed during the initial treatment with prednisolone for newly diagnosed acute lymphoblastic leukemia and who survived after early detection and oral lactulose therapy. To the best of our knowledge, this is the first report of IHA that was not induced by intensive chemotherapy, stem cell transplantation, or asparaginase therapy in a patient with newly diagnosed leukemia, but developed during an initial treatment with a steroid. Early detection of IHA by measuring the plasma ammonia level in patients with neurological symptoms may improve the outcome.

Ammonia metabolism and hyperammonemic disorders

Human adults produce around 1000 mmol of ammonia daily. Some is reutilized in biosynthesis. The remainder is waste and neurotoxic. Eventually most is excreted in urine as urea, together with ammonia used as a buffer. In extrahepatic tissues, ammonia is incorporated into nontoxic glutamine and released into blood. Large amounts are metabolized by the kidneys and small intestine. In the intestine, this yields ammonia, which is sequestered in portal blood and transported to the liver for ureagenesis, and citrulline, which is converted to arginine by the kidneys. The amazing developments in NMR imaging and spectroscopy and molecular biology have confirmed concepts derived from early studies in animals and cell cultures. The processes involved are exquisitely tuned. When they are faulty, ammonia accumulates. Severe acute hyperammonemia causes a rapidly progressive, often fatal, encephalopathy with brain edema. Chronic milder hyperammonemia causes a neuropsychiatric illness. Survivors of severe neonatal hyperammonemia have structural brain damage. Proposed explanations for brain edema are an increase in astrocyte osmolality, generally attributed to glutamine accumulation, and cytotoxic oxidative/nitrosative damage. However, ammonia neurotoxicity is multifactorial, with disturbances also in neurotransmitters, energy production, anaplerosis, cerebral blood flow, potassium, and sodium. Around 90% of hyperammonemic patients have liver disease. Inherited defects are rare. They are being recognized increasingly in adults. Deficiencies of urea cycle enzymes, citrin, and pyruvate carboxylase demonstrate the roles of isolated pathways in ammonia metabolism. Phenylbutyrate is used routinely to treat inherited urea cycle disorders, and its use for hepatic encephalopathy is under investigation.

Hyperammonemia secondary to asparaginase: A case series

OBJECTIVE

To report on hyperammonemia noted in a series of patients receiving asparaginase products at our institution.

SUMMARY OF CASES

We present four patients who experienced symptomatic hyperammonemia after receiving either pegaspargase (three patients) or Erwinia asparaginase (one patient). Presenting symptoms included lethargy, difficulty awakening, confusion, dizziness, numbness and tingling, hallucinations, and paranoia. All patients were treated with lactulose, which led to a decrease in ammonia level and resolution of symptoms.

DISCUSSION

Hyperammonemia secondary to asparaginase products has been reported in the literature. The signs and symptoms of increased ammonia should be included in consent documents and discussed with patients and their families. Monitoring of ammonia or asparagine levels may help individualize therapy with asparaginase products in the future.

CONCLUSION

Hyperammonemia can occur during treatment of acute lymphoblastic leukemia with asparaginase products. Lactulose appears to be a useful treatment strategy. Further study is warranted to determine whether dose modifications are required for pegaspargase in some patients. Whether these dose modifications would be in the dose itself or frequency of administration remains to be determined.

Clinical utility of ammonia concentration as a diagnostic test in monitoring of the treatment with L-asparaginase in children with acute lymphoblastic leukemia

L-asparaginase (ASP) is an enzyme used as one of the basic regimens in the acute lymphoblastic leukemia (ALL) therapy. Because of the possibility of the enzyme inactivation by antibodies, monitoring of ASP activity is essential. The aim of the study was to examine if plasma concentration of ammonia, a direct product of the reaction catalyzed by ASP, can be used in the assessment of ASP activity. A group of 87 patients with acute lymphoblastic leukemia treated in the Department of Pediatric Oncology and Hematology in Krakow was enrolled to the study. ASP activity and ammonia concentration were measured after ASP administrations during induction. A positive correlation was found between the ammonia concentration and ASP activity (R = 0.44; P < 0.0001) and between the medium values of ammonia concentration and ASP activity (R = 0.56; P < 0.0001). The analysis of ROC curves revealed the moderate accuracy of the ammonia concentration values in the ASP activity assessment. It was also found that the medium value of ammonia concentrations can be useful in identification of the patients with low (<100 IU/L) and undetectable (<30 IU/L) ASP activity. The plasma ammonia concentration may reflect ASP activity and can be useful when a direct measurement of the activity is unavailable.

Clinical and biochemical aspects of primary and secondary hyperammonemic disorders

An increased concentration of ammonia is a non-specific laboratory sign indicating the presence of potentially toxic free ammonia that is not normally removed. This does occur in many different conditions for which hyperammonemia is a surrogate marker. Hyperammonemia can occur due to increased production or impaired detoxification of ammonia and should, if associated with clinical symptoms, be regarded as an emergency. The conditions can be classified into primary or secondary hyperammonemias depending on the underlying pathophysiology. If the urea cycle is directly affected by a defect of any of the involved enzymes or transporters, this results in primary hyperammonemia. If however the function of the urea cycle is inhibited by toxic metabolites or by substrate deficiencies, the situation is described as secondary hyperammonemia. For removal of ammonia, mammals require the action of glutamine synthetase in addition to the urea cycle, in order to ensure lowering of plasma ammonia concentrations to the normal range. Independent of its etiology, hyperammonemia may result in irreversible brain damage if not treated early and thoroughly. Thus, early recognition of a hyperammonemic state and immediate initiation of the specific management are of utmost importance. The main prognostic factors are, irrespective of the underlying cause, the duration of the hyperammonemic coma and the extent of ammonia accumulation. This paper will discuss the biochemical background of primary and secondary hyperammonemia and will give an overview of the various underlying conditions including a brief clinical outline and information on the genetic backgrounds.

Arginase treatment prevents the recovery of canine lymphoma and osteosarcoma cells resistant to the toxic effects of prolonged arginine deprivation

Rapidly growing tumor cells require a nutrient-rich environment in order to thrive, therefore, restricting access to certain key amino acids, such as arginine, often results in the death of malignant cells, which frequently display defective cell cycle check-point control. Healthy cells, by contrast, become quiescent and remain viable under arginine restriction, displaying full recovery upon return to arginine-rich conditions. The use of arginase therapy to restrict available arginine for selectively targeting malignant cells is currently under investigation in human clinical trials. However, the suitability of this approach for veterinary uses is unexplored. As a prelude to in vivo studies in canine malignancies, we examined the in vitro effects of arginine-deprivation on canine lymphoid and osteosarcoma cell lines. Two lymphoid and 2 osteosarcoma cell lines were unable to recover following 6 days of arginine deprivation, but all remaining cell lines displayed full recovery upon return to arginine-rich culture conditions. These remaining cell lines all proved susceptible to cell death following the addition of arginase to the cultures. The lymphoid lines were particularly sensitive to arginase, becoming unrecoverable after just 3 days of treatment. Two of the osteosarcoma lines were also susceptible over this time-frame; however the other 3 lines required 6-8 days of arginase treatment to prevent recovery. In contrast, adult progenitor cells from the bone marrow of a healthy dog were able to recover fully following 9 days of culture in arginase. Over 3 days in culture, arginase was more effective than asparaginase in inducing the death of lymphoid lines. These results strongly suggest that short-term arginase treatment warrants further investigation as a therapy for lymphoid malignancies and osteosarcomas in dogs.

High incidence of symptomatic hyperammonemia in children with acute lymphoblastic leukemia receiving pegylated asparaginase

Asparaginase is a mainstay of treatment of childhood acute lymphoblastic leukemia. Pegylation of asparaginase extends its biological half-life and has been introduced in the newest treatment protocols aiming to further increase treatment success. Hyperammonemia is a recognized side effect of asparaginase treatment, but little is known about its incidence and clinical relevance. Alerted by a patient with severe hyperammonemia after introduction of the new acute lymphoblastic leukemia protocol, we analyzed blood samples and clinical data of eight consecutive patients receiving pegylated asparaginase (PEG-asparaginase) during their treatment of acute lymphoblastic leukemia. All patients showed hyperammonemia (>50 μmol/L) and seven patients (88 %) showed ammonia concentrations > 100 μmol/L. Maximum ammonia concentrations ranged from 89 to 400 μmol/L. Symptoms varied from mild anorexia and nausea to headache, vomiting, dizziness, and lethargy and led to early interruption of PEG-asparaginase in three patients. No evidence of urea cycle malfunction was found, so overproduction of ammonia through hydrolysis of plasma asparagine and glutamine seems to be the main cause. Interestingly, ammonia concentrations correlated with triglyceride values (r = 0.68, p < 0.0001), suggesting increased overall toxicity.The prolonged half-life of PEG-asparaginase may be responsible for the high incidence of hyperammonemia and warrants future studies to define optimal dosing schedules based on ammonia concentrations and individual asparagine and asparaginase measurements.

Severe hyperammonaemia in adults not explained by liver disease

Ammonia is produced continuously in the body. It crosses the blood-brain barrier readily and at increased concentration it is toxic to the brain. A highly integrated system protects against this: ammonia produced during metabolism is detoxified temporarily by incorporation into the non-toxic amino acid glutamine. This is transported safely in the circulation to the small intestine, where ammonia is released, carried directly to the liver in the portal blood, converted to non-toxic urea and finally excreted in urine. As a result, plasma concentrations of ammonia in the systemic circulation are normally very low (<40 μmol/L). Hyperammonaemia develops if the urea cycle cannot control the ammonia load. This occurs when the load is excessive, portal blood from the intestines bypasses the liver and/or the urea cycle functions poorly. By far, the commonest cause is liver damage. This review focuses on other causes in adults. Because they are much less common, the diagnosis may be missed or delayed, with disastrous consequences. There is effective treatment for most of them, but it must be instituted promptly to avoid fatality or long-term neurological damage. Of particular concern are unsuspected inherited defects of the urea cycle and fatty acid oxidation presenting with catastrophic illness in previously normal individuals. Early identification of the problem is the challenge.

Acute hyperammonemia after L-asparaginase administration in a dog

OBJECTIVE

To describe a previously unreported and potentially fatal complication of L-asparaginase (L-asp) administration in a dog.

CASE SUMMARY

A 7-year-old, 6.6 kg, female spayed Beagle presented with a 1-week history of progressive inappetance and lethargy. Diagnostic tests identified the presence of stage Vb lymphoma and liver dysfunction. The dog was treated with L-asp at 400 IU/kg, corticosteroids, and IV fluids. Within 12 hours the dog became depressed, vomited, and developed abdominal pain. Within 24 hours, the dog's mentation progressed from obtunded to comatose; subsequently the dog developed a "decerebrate posture." Blood ammonia concentrations exceeded 1,000 μmol/L (1,700 μg/dL). Treatment with broad-spectrum antimicrobials, lactulose enemas, and continuous renal replacement therapy were initiated without response and the dog suffered cardiopulmonary arrest.

NEW OR UNIQUE INFORMATION PROVIDED

The purpose of this report is to describe the development of severe hyperammonemia after L-asp therapy in a dog, which has not been previously reported in the literature. Given the rapid progression and fatal outcome observed in this case, early recognition may be crucial for management and treatment of this complication.