Clinical practice. NTBC therapy for tyrosinemia type 1: how much is enough?

Clinical experience with hepatorenal tyrosinemia from a single Egyptian center

Although very recently, in Egypt, sick newborn screening has included screening for hepatorenal tyrosinemia, yet, it is not yet included in nationwide neonatal screening and hence diagnosis may be delayed. The aim of this study was to analyze data of all cases presenting with hepatorenal tyrosinemia to the Pediatric Hepatology Unit, Cairo University, Egypt from 2006 to 2019. Data were retrieved from patients’ files including age of onset of symptoms, clinical signs, blood counts, liver functions, serum phosphorous, alpha-fetoprotein, succinylacetone and abdominal ultrasound. During this period, 76 patients were diagnosed with hepatorenal tyrosinemia if succinylacetone in dry blood spot was elevated above 1 μmol/L. These 76 cases came from 70 families; consanguinity was reported in 61 families. In our cohort we reported 30 affected siblings with a similar clinical presentation, who died undiagnosed. Presentation was acute in 26%, subacute in 30% and chronic in 43%. Abdominal distention was the commonest presenting symptom (52.6%). Coagulopathy was the commonest derangement in liver functions; hyperbilirubinemia and raised transaminases were less common. Ultrasound findings included hepatic focal lesions in 47% and enlarged echogenic kidneys in 39% and 45.3% respectively. Only 20 children were treated with Nitisinone because of unavailability and high costs; seven out of them underwent liver transplantation. In conclusion, although hepatorenal tyrosinemia is a rare inborn error of metabolism, in a large population country with high rate of consanguinity; this disease is not uncommonly diagnosed. The current treatment is not readily available because of the costs in a resource-limited country. Neonatal screening and subsidization of the costly medication need to be considered.

NTBC Treatment Monitoring in Chilean Patients with Tyrosinemia Type 1 and Its Association with Biochemical Parameters and Liver Biomarkers

Treatment and follow-up in Hereditary Tyrosinemia type 1 (HT-1) patients require comprehensive clinical and dietary management, which involves drug therapy with NTBC and the laboratory monitoring of parameters, including NTBC levels, succinylacetone (SA), amino acids, and various biomarkers of liver and kidney function. Good adherence to treatment and optimal adjustment of the NTBC dose, according to clinical manifestations and laboratory parameters, can prevent severe liver complications such as hepatocarcinogenesis (HCC). We analyzed several laboratory parameters for 15 HT-1 patients over one year of follow-up in a cohort that included long-term NTBC-treated patients (more than 20 years), as well as short-term patients (one year). Based on this analysis, we described the overall adherence by our cohort of 70% adherence to drug and dietary treatment. A positive correlation was found between blood and plasma NTBC concentration with a conversion factor of 2.57. Nonetheless, there was no correlation of the NTBC level with SA levels, αFP, liver biomarkers, and amino acids in paired samples analysis. By separating according to the range of the NTBC concentration, we therefore determined the mean concentration of each biochemical marker, for NTBC ranges above 15–25 μmol/L. SA in urine and αFP showed mean levels within controlled parameters in our group of patients. Future studies analyzing a longer follow-up period, as well as SA determination in the blood, are encouraged to confirm the present findings.

Clinical utilization of dried blood spot nitisinone (NTBC) and succinylacetone (SA) concentrations in hereditary tyrosinaemia type 1 - A UK centre experience

BACKGROUND

Dried blood spot monitoring of nitisinone and succinylacetone in hereditary tyrosinaemia type 1 patients is not widely available in the United Kingdom. Currently, biochemical monitoring utilizes urinary succinylacetone, blood spot tyrosine and phenylalanine monitoring, which can lack in convenience and accuracy, respectively.

METHODS

We report the development of a dried blood spot assay for nitisinone and succinylacetone and analysed retrospective clinical and biochemical data for hereditary tyrosinaemia type 1 patients from a single UK centre.

RESULTS

A total of 13 hereditary tyrosinaemia type 1 patients were evaluated. Eleven presented with liver dysfunction (two with associated renal tubulopathy) and two were detected by early sibling screening. All patients (age 0.03-22 months) were commenced on a tyrosine-/phenylalanine-restricted diet and nitisinone at diagnosis. Ten patients were on twice daily dosing and three were on single daily dosing at the start of monitoring. One patient from each dosing group swapped between dosing regimens at 20 years of age and 8 months of age, respectively. A total of 684 dried blood spot samples were analysed; 80% of nitisinone concentrations were between 9.2 and 27 µmol/L when succinylacetone was <0.3 µmol/L. Patients on twice daily dosing regimens had significantly higher nitisinone concentration compared with those on once daily dosing (P < 0.0001). The median dose required in the twice daily doing group was significantly lower when compared with once daily dosing.

CONCLUSIONS

Dried blood spot monitoring for nitisinone and succinylacetone concentrations in hereditary tyrosinaemia type 1 patients is a rapid and convenient method which allows physicians to individualize treatment plans and observe adherence to treatment.

Long-Term Outcomes and Practical Considerations in the Pharmacological Management of Tyrosinemia Type 1

Tyrosinemia type 1 (TT1) is a rare metabolic disease caused by a defect in tyrosine catabolism. TT1 is clinically characterized by acute liver failure, development of hepatocellular carcinoma, renal and neurological problems, and consequently an extremely poor outcome. This review showed that the introduction of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) in 1992 has revolutionized the outcome of TT1 patients, especially when started pre-clinically. If started early, NTBC can prevent liver failure, renal problems, and neurological attacks and decrease the risk for hepatocellular carcinoma. NTBC has been shown to be safe and well tolerated, although the long-term effectiveness of treatment with NTBC needs to be awaited. The high tyrosine concentrations caused by treatment with NTBC could result in ophthalmological and skin problems and requires life-long dietary restriction of tyrosine and its precursor phenylalanine, which could be strenuous to adhere to. In addition, neurocognitive problems have been reported since the introduction of NTBC, with hypothesized but as yet unproven pathophysiological mechanisms. Further research should be done to investigate the possible relationship between important clinical outcomes and blood concentrations of biochemical parameters such as phenylalanine, tyrosine, succinylacetone, and NTBC, and to develop clear guidelines for treatment and follow-up with reliable measurements. This all in order to ultimately improve the combined NTBC and dietary treatment and limit possible complications such as hepatocellular carcinoma development, neurocognitive problems, and impaired quality of life.

Dose-Finding Studies Among Orphan Drugs Approved in the EU: A Retrospective Analysis

In the development process for new drugs, dose‐finding studies are of major importance. Absence of these studies may lead to failed phase 3 trials and delayed marketing authorization. In our study we investigated to what extent dose‐finding studies are performed in the case of orphan drugs for metabolic and oncologic indications. We identified all orphan drugs that were authorized until August 1, 2017. European Public Assessment Reports were used to extract the final dose used in the summary of product characteristics, involvement of healthy volunteers, study type, end points used, number of patients, number of doses, studies in special populations, and dose used for phase 3 studies. Each drug was checked for major objections and dose changes postmarketing. We included 49 orphan drugs, of which 28 were indicated for metabolic disorders and 21 for oncologic indications. Dose‐finding studies were performed in 32 orphan drugs, and studies in healthy volunteers in 26. The absence of dose‐finding studies was mostly due to the rarity of the disease. In this case the dose was determined based on factors such as animal studies or clinical experience. Dose‐related major objections were raised for 9 orphan drugs. Postmarketing dose‐finding studies were conducted in 18 orphan drugs, but dose changes were applied in only 2 drugs. In conclusion, dose‐finding studies in the case of metabolic and oncologic orphan drugs were conducted in the development programs of two thirds of orphan drugs. Dose‐finding studies performed postmarketing suggest that registered doses are not always optimal. It is thus important to perform more robust dose‐finding studies both pre‐ and postmarketing.

NTBC and Correction of Renal Dysfunction

Hereditary tyrosinemia type 1 (HT1) is characterized by severe progressive liver disease and renal tubular dysfunction. Kidney involvement is characterized by hypophosphatemic rickets and Fanconi syndrome. Different animal models were useful to investigate the pathophysiology of the disease and the effects of NTBC therapy on liver and kidney function. NTBC has revolutionized the prognosis of HT1 and its acute and chronic effects on renal tubular function have been proved, with normalization of tubular function within a few weeks, particularly hypophosphatemia and proteinuria. NTBC therapy is highly effective in improving renal function both at short and long-term. However, its efficacy critically depends on the age at start of treatment with normal outcome in patients diagnosed at birth by newborn screening.

Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations

Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems and long term risks for hepatocellular carcinoma. An effective medical treatment with 2-[2-nitro-4-trifluoromethylbenzoyl]-1,3-cyclohexanedione (NTBC) exists but requires early identification of affected children for optimal long-term results. Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1. If identified early and treated appropriately, the majority of affected infants can remain asymptomatic. A clinical management scheme is needed for infants with HT-1 identified by NBS or clinical symptoms. To this end, a group of 11 clinical practitioners, including eight biochemical genetics physicians, two metabolic dietitian nutritionists, and a clinical psychologist, from the United States and Canada, with experience in providing care for patients with HT-1, initiated an evidence- and consensus-based process to establish uniform recommendations for identification and treatment of HT-1. Recommendations were developed from a literature review, practitioner management survey, and nominal group process involving two face-to-face meetings. There was strong consensus in favor of NBS for HT-1, using blood succinylacetone as a marker, followed by diagnostic confirmation and early treatment with NTBC and diet. Consensus recommendations for both immediate and long-term clinical follow-up of positive diagnoses via both newborn screening and clinical symptomatic presentation are provided.

Experience of a Single Center in NTBC Use in Management of Hereditary Tyrosinemia Type I in Libya

Background:

Hereditary Tyrosinemia type I (HTI) is a metabolic disease caused by deficiency of fumarylacetoacetate hydrolase enzyme.

Objectives:

This study reports beside its clinical and biochemical presentation, the outcome of NTBC [2- (2-nitro-4-trifloro-methylbenzoyl)-1, 3-cyclohexanedion] treatment of the disease and evaluates its biochemical markers in 16 pediatric Libyan patients.

Patients and Methods:

The diagnosis was based on presence of high tyrosine levels in blood and succinylacetone in urine.

Results:

The consanguinity rate was 81.2%, the median age at onset, at diagnosis and at starting treatment were 4.5, 8, and 9.5 months respectively. At presentation hepatomegaly, jaundice, rickets and high gamma glutamyl transferase (GGT) were observed in 87.5% of patients. All patients had extremely high alpha fetoprotein (AFP) and high alkaline phosphatase (ALP) levels. Fifteen patients were treated with NTBC, normalization of PT (Prothrombine time) was achieved in average in 14 days. The other biochemical parameters of liver function (transaminases, GGT, ALP, bilirubin and albumin) took longer to improve and several months to be normalized. Survival rate with NTBC was 86.6%. Patients who started treatment in a median of 3 months post onset observed a fast drop of AFP in 90.6% of patients (P = 0.003). Abnormal liver function and rickets were the common presentations, GGT was an early cholestatic sensitive test. ALP was constantly high even in asymptomatic patients.

Conclusions:

In HT1 a faster dropping of AFP is a marker of good prognosis.

Hereditary tyrosinemia type 1 in Turkey: twenty year single-center experience

BACKGROUND

Hereditary tyrosinemia type 1(HT1) is a chronic disorder leading to severe hepatic, renal and peripheral nerve damage if left untreated. Despite nitisinone treatment HT1 still carries the risks of hepatocellular carcinoma (HCC) and neuropsychological outcome.

METHODS

A retrospective single center study was carried out based on the phenotype, therapy and outcome in 38 Turkish patients with HT1 diagnosed during the last 20 years.

RESULTS

None of the patients was diagnosed on newborn screening. The patients were grouped according to acute, subacute and chronic forms of the disorder. The main clinical manifestations were hepatosplenomegaly, liver and renal tubular dysfunction. Thirty-six patients were treated with nitisinone. The mean duration of nitisinone treatment was 64 months and the mean dosage was 1.2 mg/kg/day. Dietary compliance problems were frequent. Eleven patients had cognitive evaluation (mean total IQ, 84 points). Six patients had living donor liver transplantation despite nitisinone treatment: three due to suspected HCC, two for non-compliance to diet, and one for both, at a median age of 90 months.

CONCLUSION

Nitisinone treatment is effective and improves both short- and long-term prognosis of HT1. Early diagnosis on newborn screening is needed because delay in treatment increases the risk of the persistence of hepatic disease and HCC. Interruption of the drug can lead to re-occurrence of hepatocellular damage and neurological crisis. Increased α-fetoprotein and new hypoechoic nodule formation are the warning signs for HCC.

Clinical outcome of hepatocyte transplantation in four pediatric patients with inherited metabolic diseases

Hepatocyte transplantation (HT) has become an effective therapy for patients with metabolic inborn errors. We report the clinical outcome of four children with metabolic inborn errors that underwent HT, describing the cell infusion protocol and the metabolic outcome of transplanted patients. Cryopreserved hepatocytes were used as this allows scheduling of treatments. Functional competence (viability, cell attachment, major cytochrome P450 and UDP-glucuronosyltransferase 1A1 activities, and urea synthesis) and microbiological safety of cell batches were assessed prior to clinical use. Four pediatric patients with liver metabolic diseases [ornithine transcarbamylase (OTC) deficiency, Crigler-Najjar (CNI) syndrome, glycogen storage disease Ia (GSD-Ia), and tyrosinemia type I (TYR-I)] underwent HT. Indication for HT was based on severity of disease, deterioration of quality of life, and benefits for the patients, with the ultimate goal to improve their clinical status whenever liver transplantation (LT) was not indicated or to bridge LT. Cells were infused into the portal vein while monitoring portal flow. The protocol included antibiotic prophylaxis and immunosuppressant therapy. After HT, analytical data on the disease were obtained. The OTC-deficient patient showed a sustained decrease in plasma ammonia levels and increased urea production after HT. Further cell infusions could not be administered given a fatal nosocomial fungus sepsis 2 weeks after the last HT. The CNI and GSD-Ia patients improved their clinical status after HT. They displayed reduced serum bilirubin levels (by ca. 50%) and absence of hypoglycaemic episodes, respectively. In both cases, the HT contributed to stabilize their clinical status as LT was not indicated. In the infant with TYR-I, HT stabilized temporarily the biochemical parameters, resulting in the amelioration of his clinical status while diagnosis of the disease was unequivocally confirmed by full gene sequencing. In this patient, HT served as a bridge therapy to LT.

Recommendations for the management of tyrosinaemia type 1

The management of tyrosinaemia type 1 (HT1, fumarylacetoacetase deficiency) has been revolutionised by the introduction of nitisinone but dietary treatment remains essential and the management is not easy. In this review detailed recommendations for the management are made based on expert opinion, published case reports and investigational studies as the evidence base is limited and there are no prospective controlled studies.

The added value of this paper is that it summarises in detail current clinical knowledge about HT1 and makes recommendations for the management.

Recommendations for the management of tyrosinaemia type 1

The management of tyrosinaemia type 1 (HT1, fumarylacetoacetase deficiency) has been revolutionised by the introduction of nitisinone but dietary treatment remains essential and the management is not easy. In this review detailed recommendations for the management are made based on expert opinion, published case reports and investigational studies as the evidence base is limited and there are no prospective controlled studies.The added value of this paper is that it summarises in detail current clinical knowledge about HT1 and makes recommendations for the management.

Plasma succinylacetone is persistently raised after liver transplantation in tyrosinaemia type 1

BACKGROUND

Tyrosinaemia type 1 (HT1) is a rare disorder leading to accumulation of toxic metabolites such as succinylacetone (SA) and a high risk of hepatocellular carcinoma. Children with HT1 traditionally required liver transplantation (OLT) and while the need for this has been reduced by the introduction of nitisinone some still require OLT. SA inhibits the enzyme porphobilinogen (PBG) synthase and its activity can be used as a marker of active SA. Elevated urinary SA post OLT has been reported previously. This study describes a novel finding of elevated plasma SA following OLT for HT1.

METHODS

A retrospective analysis was performed of patients treated for HT1 at our institution from 1989-2010.

RESULTS

Thirteen patients had an OLT for HT1. In patients who received nitisinone prior to OLT, mean urinary and plasma SA were elevated prior to treatment but normalised by the time of OLT (p ≤ 0.01). Mean PBG synthase activity increased from 0.032 to 0.99 nkat/gHb (ref range 0.58-1.25) at the time of OLT (p < 0.01). Mean urinary SA in patients not treated with nitisinone was also elevated prior to OLT; plasma levels and PBG synthase activity were not available prior to OLT for this group. Following OLT, mean urinary and plasma SA were elevated in all for the duration of follow-up and associated with low-normal PBG synthase activity.

CONCLUSION

Urinary and plasma SA levels are elevated following OLT for HT1. Low-normal PBG synthase activity suggests the plasma SA may be active. The clinical significance of this is unclear.

Single dose NTBC-treatment of hereditary tyrosinemia type I

NTBC (2-(2-nitro-4-trifluoromethylbenzoyl)-1,3cyclohexanedione) is the mainstay of treatment in tyrosinemia type 1 (HT 1). The current recommendation is to divide the total daily dose of NTBC into two doses. We monitored the plasma NTBC concentrations in a series of seven patients who were changed from multiple divided doses to a single daily dose of NTBC. Two additional patients were started on a single daily dose of NTBC after the diagnosis of HT 1 was established. In three patients, NTBC kinetics were performed over 6 and 24 hours, respectively. The use of multiple divided doses or a single daily dose did not significantly affect plasma NTBC concentrations or the mean daily dose needed to attain therapeutic plasma NTBC concentrations. Moreover, kinetic studies demonstrated that plasma NTBC concentrations were completely stable over a period of 24 hours with a single dose regimen, as expected given the known NTBC plasma half life of 54 hours. Although these preliminary results need to be confirmed in more patients, our findings show that administration of NTBC in a single daily dose may be as effective as a multiple-dose regimen in reaching therapeutic plasma NTBC concentrations and suppressing succinylacetone formation in patients with HT 1. In fact, single dose treatment may increase patients' compliance with the drug treatment and improve metabolic control.

Medical management of chronic liver diseases in children (part I): focus on curable or potentially curable diseases

The management of children with chronic liver disease (CLD) mandates a multidisciplinary approach. CLDs can be classified into 'potentially' curable, treatable non-curable, and end-stage diseases. Goals pertaining to the management of CLDs can be divided into prevention or minimization of progressive liver damage in curable CLD by treating the primary cause; prevention or control of complications in treatable CLD; and prediction of the outcome in end-stage CLD in order to deliver definitive therapy by surgical procedures, including liver transplantation. Curative, specific therapies aimed at the primary causes of CLDs are, if possible, best considered by a pediatric hepatologist. Medical management of CLDs in children will be reviewed in two parts, with part I (this article) specifically focusing on 'potentially' curable CLDs. Dietary modification is the cornerstone of management for galactosemia, hereditary fructose intolerance, and certain glycogen storage diseases, as well as non-alcoholic steatohepatitis. It is also essential in tyrosinemia, in addition to nitisinone [2-(nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione] therapy, as well as in Wilson disease along with copper-chelating agents such as D-penicillamine, triethylenetetramine dihydrochloride, and ammonium tetrathiomolybdate. Zinc and antioxidants are adjuvant drugs in Wilson disease. New advances in chronic viral hepatitis have been made with the advent of oral antivirals. In children, currently available drugs for the treatment of chronic hepatitis B virus infection are standard interferon (IFN)-α-2, pegylated IFN-α-2 (PG-IFN), and lamivudine. In adults, adefovir and entecavir have also been licensed, whereas telbivudine, emtricitabine, tenofovir disoproxil fumarate, clevudine, and thymosin α-1 are currently undergoing clinical testing. For chronic hepatitis C virus infection, the most accepted treatment is PG-IFN plus ribavirin. Corticosteroids, with or without azathioprine, remain the basic strategy for inducing remission in autoimmune hepatitis. Ciclosporin (cyclosporine) and other immune suppressants may be used for patients who do not achieve remission, or who have significant side effects, with corticosteroid/azathioprine therapy. The above therapies can prevent, or at least minimize, progression of liver damage, particularly if started early, leading to an almost normal quality of life in affected children.

Identification of mutations causing hereditary tyrosinemia type I in patients of Middle Eastern origin

Hereditary Tyrosinemia Type 1 (HT1) is an autosomal recessive disorder resulting from a deficiency of fumarylacetoacetase caused by mutations in the fumarylacetoacetate hydrolase (FAH) gene. We detected 11 novel and 6 previously described pathogenic mutations in a cohort of 43 patients originating from the Middle East with the acute form HT1. All of the mutations were homozygous and we did not find the presence of a "founder mutation".

Tyrosinemia type 1 in Spain: mutational analysis, treatment and long-term outcome

BACKGROUND

Tyrosinemia type 1 (HT1) is a rare but treatable disease. The aim of the present study was to review the efficacy of long-term treatment of HT1 with nitisinone, expand knowledge about the clinical spectrum of the disease and assess a possible genotype-phenotype correlation.

METHODS

A retrospective multicenter study was carried out based on questionnaires on genotype, phenotype, therapy and outcome in 34 Spanish patients with HT1.

RESULTS

The main manifestations that led to the diagnosis were acute liver failure (55.8%), asymptomatic hepatomegaly (44.1%) and renal tubular dysfunction (29.4%). Laboratory analysis indicated a marked increase of α-fetoprotein and coagulopathy. The most common mutation was IVS6-1(G > T; 66.6% of 24/34 patients for whom mutation analysis was available) and these patients presented less nephrocalcinosis and more hepatomegaly at diagnosis; two novel mutations (c.974C>T, c.398A>T) were found. The mean duration of treatment was 6.73 years. Dietary compliance was very good in 47.1% and good in 20.6%; nitisinone treatment adherence was very good in 85.2% of cases. Mean dose of nitisinone was 0.87 mg/kg per day with average plasma levels of 45.67 µmol/L. Only one patient required liver transplantation after nitisinone and none had hepatocellular carcinoma.

CONCLUSIONS

Treatment with nitisinone has improved the prognosis of HT1, and compliance is good. In Spain, screening for HT1 by plasma tyrosine and urine succinylacetone determination may be implemented with IVS6-1(G > T) mutational analysis. A correlation between low frequency of nephrocalcinosis and IVS6-1(G > T) mutation was observed.

Hereditary tyrosinemia type 1 from a single center in Egypt: clinical study of 22 cases

BACKGROUND

Hereditary tyrosinemia type 1 (HT1) is an increasingly recognized inborn error of metabolism among Egyptian children. This study was undertaken to define the presenting clinical, biochemical and imaging features and outcome of 2-(2-motrp-4-trifluoromethylbenzoyl)-1, 3-cyclohexanedione (NTBC) therapy and liver transplantation in a cohort of Egyptian children diagnosed with HT1.

METHODS

The study was carried out at the Pediatric Hepatology Unit at Cairo University Children's Hospital. HT1 was diagnosed by quantification of succinylacetone (SA) in dry blood spots.

RESULTS

Twenty-two patients were diagnosed with HT1 in a period of 3 years from August 2006 to July 2009. Infants with focal hepatic lesions and hepatomegaly (n=13) were younger at diagnosis than those with rickets (n=5) (median age: 3.25 vs. 10 months; P=0.05). Alpha fetoprotein was highly elevated in all children. Seven children died within a few weeks of diagnosis before therapy was initiated. Ten children were treated with NTBC. The response to NTBC treatment was apparent by a steep drop in serum alpha fetoprotein (AFP) and undetectable SA in urine within 2 months. Three children underwent living donor liver transplantation after treatment with NTBC for 10, 18 and 22 months respectively, despite adequate response to therapy because of financial issues. The explanted livers were all cirrhotic with no dysplasia or malignant transformation.

CONCLUSIONS

Focal hepatic lesions are the commonest presentation of HT1 patients and they present at an earlier age than rickets. NTBC is effective but very expensive. Liver transplantation is still considered in HT1 patients.

Comparison of plasma and dry blood spots as samples for the determination of nitisinone (NTBC) by high-performance liquid chromatography-tandem mass spectrometry. Study of the stability of the samples at different temperatures

Tyrosinemia is an inborn error of metabolism characterized by the accumulation of tyrosine as well as toxic by-products. NTBC or nitisinone is a drug currently used for the treatment of tyrosinemia that avoids the formation of these toxic substances. This paper presents the determination of NTBC in plasma and dry blood spots by high-performance liquid chromatography (HPLC) coupled to tandem mass spectrometry. The concentration of NTBC in matched plasma-dry blood spots was compared and the study of degradation of NTBC in plasma and dry spots at different temperatures is presented.

METHOD

For sample preparation, plasma proteins were precipitated with acetonitrile and 3-mm discs were extracted with methanol. ESI(+) was used as inozation method and the analytes were detected by multiple reaction monitoring using the transitions 330>218 for NTBC and 340>228 for mesotrione, used as internal standard.

RESULTS

There is good correlation between concentrations obtained in dry blood spots and plasma (r(2)=0.83), although values are 2.4 times higher in plasma samples. NTBC in plasma is stable at least for 45 days frozen at -30°C and refrigerated at 4°C. However, it shows slow decomposition at room temperature, approximately 30% after 45 days. The method shows good precision, accuracy and linearity and the detection limit is 50 nmol/L and paper samples are appropriate for the monitorization of NTBC.

Monitoring tyrosinaemia type I: Blood spot test for nitisinone (NTBC)

BACKGROUND

Quantification of nitisinone, 2-(nitro-4-trifluoromethylbenzoyl)1,3-cyclohexanedione (NTBC) has been repeatedly described. Nevertheless monitoring of NTBC has not yet become part of routine therapy surveillance in tyrosinaemia type I (OMIM 276700). We developed a blood spot test to facilitate collection and transport of samples. Furthermore, the test material can be used for determination of other parameters like tyrosine and succinylacetone.

METHOD

For quantification of NTBC in blood spots filter paper discs of 3.2mm diameter were extracted with 150 μL methanol containing mesotrione as internal standard (IS). Analysis was done by UPLC-MS/MS on a Xevo mass spectrometer (ESI+), (MRM). Parent ions were 330.05 for NTBC and 340.05 for IS, daughter ions were m/z 217.95 and m/z 125.95 for NTBC, and m/z 227.95 and m/z 103.95 for IS.

RESULTS

The calibration curve for NTBC in blood spots was linear from 0.1 μmol/L to 100 μmol/L. Recovery exceeded 73.1%, CV intraday and interday were below 9.6%. Instrumental run time was 2.5 min. Sensitivity of the method was 0.1 μmol/L. NTBC concentrations in plasma were higher than in blood spots by a factor of 1.56 ± 0.13.

CONCLUSION

As demonstrated in patients with tyrosinaemia type I quantification of NTBC by UPLC-MS/MS in blood spots is feasible and gives valuable information for monitoring NTBC treatment.