Quantification of the flux of tyrosine pathway metabolites during nitisinone treatment of Alkaptonuria.

Nitisinone decreases homogentisic acid (HGA) in Alkaptonuria (AKU) by inhibiting the tyrosine metabolic pathway in humans. The effect of different daily doses of nitisinone on circulating and 24 h urinary excretion of phenylalanine (PA), tyrosine (TYR), hydroxyphenylpyruvate (HPPA), hydroxyphenyllactate (HPLA) and HGA in patients with AKU was studied over a four week period. Forty AKU patients, randomised into five groups of eight patients, received doses of 1, 2, 4 or 8 mg of nitisinone daily, or no drug (control). Metabolites were analysed by tandem mass spectrometry in 24 h urine and serum samples collected before and after nitisinone. Serum metabolites were corrected for total body water and the sum of 24 hr urine plus total body water metabolites of PA, TYR, HPPA, HPLA and HGA were determined. Body weight and urine urea were used to check on stability of diet and metabolism over the 4 weeks of study. The sum of quantities of urine metabolites (PA, TYR, HPPA, HPLA and HGA) were similar pre- and post-nitisinone. The sum of total body water metabolites were significantly higher post-nitisinone (p < 0.0001) at all doses. Similarly, combined 24 hr urine:total body water ratios for all analytes were significantly higher post-nitisinone, compared with pre-nitisinone baseline for all doses (p = 0.0002 - p < 0.0001). Significantly higher concentrations of metabolites from the tyrosine metabolic pathway were observed in a dose dependant manner following treatment with nitisinone and we speculate that, for the first time, experimental evidence of the metabolite pool that would otherwise be directed towards pigment formation, has been unmasked.

The effect of nitisinone on homogentisic acid and tyrosine: a two-year survey of patients attending the National Alkaptonuria Centre, Liverpool.

Background Alkaptonuria is a rare, debilitating autosomal recessive disorder affecting tyrosine metabolism. Deficiency of homogentisate 1,2-dioxygenase leads to increased homogentisic acid which is deposited as ochronotic pigment. Clinical sequelae include severe early onset osteoarthritis, increased renal and prostate stone formation and cardiac complications. Treatment has been largely based on analgaesia and arthroplasty. The National Alkaptonuria Centre in Liverpool has been using 2 mg nitisinone (NTBC) off-license for all patients in the United Kingdom with alkaptonuria and monitoring the tyrosine metabolite profiles. Methods Patients with confirmed alkaptonuria are commenced on 2 mg dose (alternative days) of NTBC for three months with daily dose thereafter. Metabolite measurement by LC-MS/MS is performed at baseline, day 4, three-months, six-months and one-year post-commencing NTBC. Thereafter, monitoring and clinical assessments are performed annually. Results Urine homogentisic acid concentration decreased from a mean baseline 20,557 µmol/24 h (95th percentile confidence interval 18,446-22,669 µmol/24 h) by on average 95.4% by six months, 94.8% at one year and 94.1% at two year monitoring. A concurrent reduction in serum homogentisic acid concentration of 83.2% compared to baseline was also measured. Serum tyrosine increased from normal adult reference interval to a mean ± SD of 594 ± 184 µmol /L at year-two monitoring with an increased urinary excretion from 103 ± 81 µmol /24 h at baseline to 1071 ± 726 µmol /24 h two years from therapy. Conclusions The data presented represent the first longitudinal survey of NTBC use in an NHS service setting and demonstrate the sustained effect of NTBC on the tyrosine metabolite profile.

Suitability Of Nitisinone In Alkaptonuria 1 (SONIA 1): an international, multicentre, randomised, open-label, no-treatment controlled, parallel-group, dose-response study to investigate the effect of once daily nitisinone on 24-h urinary homogentisic acid excretion in patients with alkaptonuria after 4 weeks of treatment.

BACKGROUND: Alkaptonuria (AKU) is a serious genetic disease characterised by premature spondyloarthropathy. Homogentisate-lowering therapy is being investigated for AKU. Nitisinone decreases homogentisic acid (HGA) in AKU but the dose-response relationship has not been previously studied. METHODS: Suitability Of Nitisinone In Alkaptonuria 1 (SONIA 1) was an international, multicentre, randomised, open-label, no-treatment controlled, parallel-group, dose-response study. The primary objective was to investigate the effect of different doses of nitisinone once daily on 24-h urinary HGA excretion (u-HGA24) in patients with AKU after 4 weeks of treatment. Forty patients were randomised into five groups of eight patients each, with groups receiving no treatment or 1 mg, 2 mg, 4 mg and 8 mg of nitisinone. FINDINGS: A clear dose-response relationship was observed between nitisinone and the urinary excretion of HGA. At 4 weeks, the adjusted geometric mean u-HGA24 was 31.53 mmol, 3.26 mmol, 1.44 mmol, 0.57 mmol and 0.15 mmol for the no treatment or 1 mg, 2 mg, 4 mg and 8 mg doses, respectively. For the most efficacious dose, 8 mg daily, this corresponds to a mean reduction of u-HGA24 of 98.8% compared with baseline. An increase in tyrosine levels was seen at all doses but the dose-response relationship was less clear than the effect on HGA. Despite tyrosinaemia, there were no safety concerns and no serious adverse events were reported over the 4 weeks of nitisinone therapy. CONCLUSIONS: In this study in patients with AKU, nitisinone therapy decreased urinary HGA excretion to low levels in a dose-dependent manner and was well tolerated within the studied dose range. TRIAL REGISTRATION NUMBER: EudraCT number: 2012-005340-24. Registered at ClinicalTrials.gov: NCTO1828463.

Serum markers in alkaptonuria: simultaneous analysis of homogentisic acid, tyrosine and nitisinone by liquid chromatography tandem mass spectrometry.

BACKGROUND: Alkaptonuria is a rare debilitating autosomal recessive disorder of tyrosine metabolism, where deficiency of homogentisate 1,2-dioxygenase results in increased homogentisic acid. Homogentisic acid is deposited as an ochronotic pigment in connective tissues, especially cartilage, leading to a severe early onset form of osteoarthritis, increased renal and prostatic stone formation and hardening of heart vessels. Treatment with the orphan drug, nitisinone, an inhibitor of 4-hydroxyphenylpyruvate dioxygenase has been shown to reduce urinary excretion of homogentisic acid. METHOD: A reverse phase liquid chromatography tandem mass spectrometry method has been developed to simultaneously analyse serum homogentisic acid, tyrosine and nitisinone. Using matrix-matched calibration standards, two product ion transitions were identified for each compound (homogentisic acid, tyrosine, nitisinone) and their respective isotopically labelled internal standards ((13)C6-homogentisic acid, d2-tyrosine, (13)C6-nitisinone). RESULTS: Intrabatch accuracy was 94-108% for homogentisic acid, 95-109% for tyrosine and 89-106% for nitisinone; interbatch accuracy (n = 20) was 88-108% for homogentisic acid, 91-104% for tyrosine and 88-103% for nitisinone. Precision, both intra- and interbatch were <12% for homogentisic acid and tyrosine, and <10% for nitisinone. Matrix effects observed with acidified serum were normalized by the internal standard (<10% coefficient of variation). Homogentisic acid, tyrosine and nitisinone proved stable after 24 h at room temp, three freeze-thaw cycles and 24 h at 4℃. The assay was linear to 500µmol/L homogentisic acid, 2000µmol/L tyrosine and 10µmol/L nitisinone; increased range was not required for clinical samples and no carryover was observed. CONCLUSIONS: The method developed and validated shows good precision, accuracy and linearity appropriate for the monitoring of alkaptonuria patients, pre- and post-nitisinone therapy.

Interferences of homogentisic acid (HGA) on routine clinical chemistry assays in serum and urine and the implications for biochemical monitoring of patients with alkaptonuria.

OBJECTIVES: We have assessed the effect of elevated concentrations of homogentisic acid (HGA) as in alkaptonuria (AKU), on a range of routine chemistry tests in serum and urine. DESIGN AND METHODS: HGA was added to pooled serum and a range of assays was analysed with Roche Modular chemistries. Effects on urine were assessed by diluting normal urine with urine from a patient with AKU, adding HGA to urine and after lowering output of urinary HGA with nitisinone treatment. RESULTS: Serum enzymatic creatinine showed 30% negative interference with 100µmol/L HGA and >50% at 400µmol/L. Serum urate 100 to 480µmol/L was reduced up to 20% at 100 and to 50% with 400µmol/L HGA. Serum cholesterol between 3 and 11mmol/L was reduced by 0.5mmol/L with 400µmol/L HGA. Urine enzymatic creatinine and urate with >2mmol/L HGA showed concentration dependent negative interference up to 80%. A positive interference in urine total protein by benzethonium turbidometric assay was observed, with 10mmol/L HGA equivalent to 1g/L protein. Jaffe creatinine, Na, K, Cl, Mg, Ca, phosphate, ALT, GGT, ALP activities and urea in serum and or urine were not affected by increases in HGA. CONCLUSIONS: To avoid interferences by HGA in alkaptonuria concentration of HGA should be established before samples are assayed with peroxidase assays and benzethonium urine protein.

A 3-year randomized therapeutic trial of nitisinone in alkaptonuria.

Alkaptonuria is a rare, autosomal recessive disorder of tyrosine degradation due to deficiency of the third enzyme in the catabolic pathway. As a result, homogentisic acid (HGA) accumulates and is excreted in gram quantities in the urine, which turns dark upon alkalization. The first symptoms, occurring in early adulthood, involve a painful, progressively debilitating arthritis of the spine and large joints. Cardiac valvular disease and renal and prostate stones occur later. Previously suggested therapies have failed to show benefit, and management remains symptomatic. Nitisinone, a potent inhibitor of the second enzyme in the tyrosine catabolic pathway, is considered a potential therapy; proof-of-principle studies showed 95% reduction in urinary HGA. Based on those findings, a prospective, randomized clinical trial was initiated in 2005 to evaluate 40 patients over a 36-month period. The primary outcome parameter was hip total range of motion with measures of musculoskeletal function serving as secondary parameters. Biochemically, this study consistently demonstrated 95% reduction of HGA in urine and plasma over the course of 3 years. Clinically, primary and secondary parameters did not prove benefit from the medication. Side effects were infrequent. This trial illustrates the remarkable tolerability of nitisinone, its biochemical efficacy, and the need to investigate its use in younger individuals prior to development of debilitating arthritis.

A metabolic cause of spinal deformity.

A 38-year-old man presented to our clinic with a 6-year history of chronic low back pain. Physical examination showed limited spine mobility; radiographs of the spine demonstrated narrowed disk spaces and calcifications. Lumbar spine magnetic resonance imaging showed Modic type II signal intensity changes in the bone marrow consistent with chronic disk degeneration. The finding of a massively elevated excretion of homogentisic acid (HGA) in the patient's urine confirmed the suspicion that the complaints were due to underlying alkaptonuria. Alkaptonuria (ochronosis) is an uncommon cause of backache and results from mutations in homogentisate 1,2-dioxygenase, an enzyme involved in tyrosine catabolism. Homogentisic acid accumulates in the plasma of the affected individuals, and HGA polymers deposit in connective tissues where they cause cartilage degeneration. So far, there is no proven treatment; but preclinical and phase I data with nitisinone, an inhibitor of HGA formation, are promising. Currently, the effects of nitisinone on joint mobility are being evaluated in a randomized trial. Clinicians involved in the care of musculoskeletal problems should be aware of this rare disorder, particularly because the correct diagnosis may have therapeutic implications.

Hip arthroplasty for ochronosis.

Alkaptonuria is a metabolic disorder in which homogentisic acid oxidase is absent. Therefore, homogentisic acid accumulates in cartilage and connective tissues. We can diagnose ochronotic arthropathy, a manifestation of long standing alkaptonuria, through careful radiological, physical, and laboratory examination. In this report, we describe 4 cases of ochronotic arthropathy to which we applied cementless total hip prosthesis due to severe hip involvement.

Use of nitisinone in patients with alkaptonuria.

Alkaptonuria, a rare autosomal recessive disorder caused by mutations in the HGD gene and deficiency of homogentisate 1,2 dioxygenase, is characterized by ochronosis, arthritis, and daily excretion of gram quantities of homogentisic acid (HGA). Nitisinone, an inhibitor of the enzyme 4-hydroxyphenylpyruvate dioxygenase, can drastically reduce urinary excretion of HGA in individuals with alkaptonuria. We investigated the safety and the HGA-depleting efficacy of nitisinone in an open-label, single-center study of 9 alkaptonuria patients (5 women, 4 men; 35-69 years of age) over the course of 3 to 4 months. Each patient received nitisinone in incremental doses, 0.35 mg bid followed by 1.05 mg bid, and remained on this dosage and a regular diet for 3 months. Nitisinone reduced urinary HGA levels from an average of 4.0 +/- 1.8 (SD) g/day to 0.2 +/- 0.2 g/day ( P < .001). The average plasma tyrosine concentration, initially 68 +/- 18 mmicro mol/L, rose to 760 +/- 181 micro mol/L ( P < .001). During the final week of the study, 5 patients adhered to a protein-restricted diet (40 g/day), and their mean plasma tyrosine level fell from 755 +/- 167 to 603 +/- 114 mu mol/L. Six of the 7 patients who received nitisinone for more than 1 week reported decreased pain in their affected joints. Weekly ophthalmologic examinations showed no signs of corneal toxicity. Adverse events included the passing of kidney stones, the recognition of symptoms related to aortic stenosis, and elevation of liver transaminase levels. We conclude that low-dose nitisinone effectively reduced urinary HGA levels in patients with alkaptonuria. Future long-term clinical trials are planned to determine the benefits of nitisinone in preventing joint deterioration and providing pain relief, and its long-term side effects.

Quantitation of homogentisic acid in normal human plasma.

A new stable isotope dilution gas chromatograph-mass spectrometric method of analysis of homogentisic acid is described. Using this method, homogentisic acid is measured for the first time in normal human plasma. The assay of sera from nine normal individuals yielded a range of values from 2.4 to 12 ng/ml. The method appears to be very sensitive and may be useful in the characterization of heterozygotes for alkaptonuria and other disorders of tyrosine degradation.

Homogentisic acid and structurally related compounds as intermediates in plasma soluble melanin formation and in tissue toxicities.

Homogentisic acid (HGA) spontaneously starts to undergo oxidation and polymerization soon after the beginning of incubation in human blood or plasma at 37 degrees C, and forms plasma soluble melanins (PSM). Haemolysis accompanies this process in blood. The addition of equimolar quantities of antioxidants delays this oxidation significantly (isoascorbic acid by 2:30-4:00 h; glutathione by 3:20-4:05 h; D-penicillamine by 5:00-5:45 h). HGA is a phenylalanine and tyrosine metabolite, related structurally to the catecholamines and other precursors of melanins. HGA is normally metabolized by the enzyme homogentisic acid oxidase. When this enzyme is genetically missing, part of HGA is excreted in the urine, another part polymerizes darkens many tissues (ochronosis), and produces widespread degenerative changes in cartilage and other connective tissues, joints, blood vessels, heart valves, kidneys and in other tissues. Collectively this disorder is known as alcaptonuria, for which no satisfactory treatment is known. The causes of both alcaptonuric arthritis and rheumatoid arthritis are thought to involve increased oxidative stress. Inflammation of joints and connective tissue damage are involved in both diseases. Oxygen radicals are suspected to cause inflammation and cellular damage. Hydroxyl radicals degrade hyaluronic acid (the viscous synovial fluid of joints). High levels of products of free radical reactions, with fluorescence excitation (ex) and emission (em) maxima in the wavelength ranges of those of PSM (ex 320-400 and em 400-470) were reported in the blood sera and synovial fluids of patients with rheumatoid arthritis.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral loading of homogentisic acid in controls and in obligate heterozygotes for hereditary tyrosinemia type I.

Homogentisic acid (HGA) (50 mg/kg) was given orally to 22 obligate heterozygotes for hereditary tyrosinemia type 1 (HT) and to 11 controls. After 1 h the mean +/- standard error (SE) plasma level of HGA was 30.42 +/- 1.41 micrograms/ml in carriers and 19.29 +/- 1.62 in controls. Mean +/- SE fasting delta-amino-levulinate dehydratase (delta-ALD) was 40.05 +/- 1.79 m microM/min/g Hb in carriers, much lower than the 60.81 +/- 5.11 found in controls. After 3 h this difference in levels of delta-ALD remained, with mean +/- SE values of 25.70 +/- 2.89 m microM/min/g Hb in carriers, compared with 48.83 +/- 5.37 in controls. Three-hour mean +/- SE excretion of fumarylacetone "equivalent" [FAc] in urine in carriers, 51.597 +/- 5.580 micrograms/mg/creatinine, was significantly higher than the 27.941 +/- 5.916 in controls. Three-hour excretion of succinylacetone "equivalent" [SAc] was also significantly higher in the urine of carriers. FAc in 3-h urine was identified by thin-layer chromatography and confirmed by gas chromatography/mass spectrometry. Multivariate stepwise discriminant analysis showed that the inclusion order of significant variables was as follows: HGA levels at 1 hr, fasting level of delta-ALD, residual level of HGA at 3 h, and 3-h excretion of [FAc]. Non-significant variables were HGA tolerance, levels of delta-ALD at 3 h, sex, and 3-h excretion of [SAc].(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis of alcaptonuria: rapid analysis of homogentisic acid by HPLC.

The clinical and biochemical features of five cases of alcaptonuria were reported. The concentration of homogentisic acid was determined in urine and also in plasma using a rapid, sensitive and specific HPLC method. In all five cases, the concentrations of homogentisic acid were elevated in urine rising up to 46.5 mmol/24 h. In plasma, homogentisic acid levels ranged from 33 to 38 mumols/l. In healthy individuals, homogentisic acid was not detectable in plasma and urine. The method described represents a very useful and suitable analytical tool for the diagnosis of alcaptonuria.

Effects of ascorbic acid in alkaptonuria: alterations in benzoquinone acetic acid and an ontogenic effect in infancy.

The effects of ascorbic acid on the excretion of homogentisic acid and its derivative benzoquinone acetic acid were studied in two adults and three infants. The administration of relatively large amounts of ascorbic acid to the adults was followed by a disappearance of benzoquinone acetic acid from the urine, whereas the level of excretion of homogentisic acid did not change. This could have relevance to the pathogenesis of ochronotic arthritis. In the 4-mo-old infant and the 5-mo-old infant ascorbic acid in the urine may have doubled the amount of homogentisic acid, presumably through an effect on the immature p-hydroxyphenylpyruvic acid oxidase. Dietary reduction of the intake of tyrosine and phenylalanine substantially reduced the excretion of homogentisic acid.

Homogentisic acid determined in biological fluids by HPLC.

In this rapid, specific, and sensitive high-performance liquid-chromatographic method of analysis for homogentisic acid in biological fluids, homogentisic acid is separated on a column of Nucleosil CN. This method, which we applied to the diagnosis of three cases of alcaptonuria, represents a suitable analytical tool for the diagnosis of alcaptonuria.