Efficacy of low dose nitisinone in the management of alkaptonuria

Alkaptonuria

Alkaptonuria is a rare inborn error of metabolism caused by the deficiency of homogentisate 1,2-dioxygenase activity. The consequent homogentisic acid (HGA) accumulation in body fluids and tissues leads to a multisystemic and highly debilitating disease whose main features are dark urine, ochronosis (HGA-derived pigment in collagen-rich connective tissues), and a painful and severe form of osteoarthropathy. Other clinical manifestations are extremely variable and include kidney and prostate stones, aortic stenosis, bone fractures, and tendon, ligament and/or muscle ruptures. As an autosomal recessive disorder, alkaptonuria affects men and women equally. Debilitating symptoms appear around the third decade of life, but a proper and timely diagnosis is often delayed due to their non-specific nature and a lack of knowledge among physicians. In later stages, patients' quality of life might be seriously compromised and further complicated by comorbidities. Thus, appropriate management of alkaptonuria requires a multidisciplinary approach, and periodic clinical evaluation is advised to monitor disease progression, complications and/or comorbidities, and to enable prompt intervention. Treatment options are patient-tailored and include a combination of medications, physical therapy and surgery. Current basic and clinical research focuses on improving patient management and developing innovative therapies and implementing precision medicine strategies.

Homogentisate 1,2-dioxygenase (HGD) gene variants in young Egyptian patients with alkaptonuria

Alkaptonuria (AKU) is a rare autosomal recessive metabolic disorder caused by pathogenic variants in the homogentisate 1,2-dioxygenase (HGD) gene. This leads to a deficient HGD enzyme with the consequent accumulation of homogentisic acid (HGA) in different tissues causing complications in various organs, particularly in joints, heart valves and kidneys. The genetic basis of AKU in Egypt is completely unknown. We evaluated the clinical and genetic spectrum of six pediatric and adolescents AKU patients from four unrelated Egyptian families. All probands had a high level of HGA in urine by qualitative GC/MS before genetic confirmation by Sanger sequencing. Recruited AKU patients were four females and two males (median age 13 years). We identified four different pathogenic missense variants within HGD gene. Detected variants included a novel variant c.1079G > T;p.(Gly360Val) and three recurrent variants; c.1078G > C;p.(Gly360Arg), c.808G > A;p.(Gly270Arg) and c.473C > T;p.(Pro158Leu). All identified variants were properly segregating in the four families consistent with autosomal recessive inheritance. In this study, we reported the phenotypic and genotypic spectrum of alkaptonuria for the first time in Egypt. We further enriched the HGD-variant database with another novel pathogenic variant. The recent availability of nitisinone may promote the need for genetic confirmation at younger ages to start therapy earlier and prevent serious complications.

Ochronotic arthropathy in the context of spondyloarthritis differential diagnosis: a case-based review

Alkaptonuria is a disease often forgotten because of its rarity. Its pathogenic mechanism is the deficiency of one of the enzymes of the tyrosine degradation pathway-homogentisate-1, 2-dioxygenase, which sequelae is accumulation and deposition of its metabolite homogentisic acid in connective tissues and urine. Alkaptonuria presents as a clinical triad-darkening urine upon prolonged exposure to air, pigmentation of connective tissues and debilitating arthropathy. We present a case report of a 67-year old patient with alkaptonuria who presented with the clinical triad, but was mistakenly diagnosed as having ankylosing spondylitis in the past. Currently there is no treatment for the disease hence the management strategy was focused on symptoms control with analgesics, physical therapy, dietary modification, vitamin C supplementation, and joint arthroplasty. Alkaptonuria's clinical features are extensively described in the literature and despite the fact that it is a rare disease, due to the similar radiographic changes with spondyloarthropathies, it should be included in the differential diagnosis in young patients presenting with severe joint involvement. Early recognition of the disease is necessary since its natural evolution is joint destruction leading to significant reduction in the quality of life. Alkaptonuria's articular features in the spine and peripheral tissues are well described using the classical imaging techniques. Musculoskeletal ultrasonography shows a characteristic set of findings in the soft tissues, including synovium, cartilage, tendons and entheses.

Long-term follow-up of alkaptonuria patients: single center experience

OBJECTIVES

Alkaptonuria is a rare autosomal recessive genetic disorder resulting from the deficiency of homogentisate 1,2 dioxygenase (HGD), the third enzyme in the tyrosine degradation pathway. Homogentisic acid produced in excess oxidizes into ochronotic pigment polymer. Accumulation of this pigment in various tissues leads to systemic disease.

METHODS

Clinical, laboratory, molecular findings and treatment characteristics of 35 patients followed up in Ege University Pediatric Nutrition, and Metabolism Department with the diagnosis of alkaptonuria were evaluated retrospectively.

RESULTS

Twenty-four males (68.57%) and 11 females (31.42%) with a confirmed diagnosis of alkaptonuria from 32 different families were included in the study. We identified 11 different genetic variants; six of these were novel. c.1033C>T, c.676G>A, c.664G>A, c.731_734del, c.1009G>T, c.859_862delins ATAC were not previously reported in the literature. 24 (68.57%) patients only adhered to a low-protein diet in our study group. Seven (20%) patients initiated a low protein diet and NTBC therapy. Mean urinary HGA decreased by 88.7% with nitisinone. No statistical changes were detected in urinary HGA excretion with the low protein diet group.

CONCLUSIONS

In our study, alkaptonuria patients were diagnosed at different ages, from infancy to adulthood, and progressed with other systemic involvement in the follow-up. Since the initial period is asymptomatic, giving potentially effective treatment from an early age is under discussion. Raising disease awareness is very important in reducing disease mortality and morbidity rates.

Impact of Nitisinone on the Cerebrospinal Fluid Metabolome of a Murine Model of Alkaptonuria

Background: Nitisinone-induced hypertyrosinaemia is well documented in Alkaptonuria (AKU), and there is uncertainty over whether it may contribute to a decline in cognitive function and/or mood by altering neurotransmitter metabolism. The aim of this work was to evaluate the impact of nitisinone on the cerebrospinal fluid (CSF) metabolome in a murine model of AKU, with a view to providing additional insight into metabolic changes that occur following treatment with nitisinone. Methods: 17 CSF samples were collected from BALB/c Hgd−/− mice (n = 8, treated with nitisinone—4 mg/L and n = 9, no treatment). Samples were diluted 1:1 with deionised water and analysed using a 1290 Infinity II liquid chromatography system coupled to a 6550 quadrupole time-of-flight mass spectrometry (Agilent, Cheadle, UK). Raw data were processed using a targeted feature extraction algorithm and an established in-house accurate mass retention time database. Matched entities (±10 ppm theoretical accurate mass and ±0.3 min retention time window) were filtered based on their frequency and variability. Experimental groups were compared using a moderated t-test with Benjamini−Hochberg false-discovery rate adjustment. Results: L-Tyrosine, N-acetyl-L-tyrosine, γ-glutamyl-L-tyrosine, p-hydroxyphenylacetic acid, and 3-(4-hydroxyphenyl)lactic acid were shown to increase in abundance (log2 fold change 2.6−6.9, 3/5 were significant p < 0.05) in the mice that received nitisinone. Several other metabolites of interest were matched, but no significant differences were observed, including the aromatic amino acids phenylalanine and tryptophan, and monoamine metabolites adrenaline, 3-methoxy-4-hydroxyphenylglycol, and octopamine. Conclusions: Evaluation of the CSF metabolome of a murine model of AKU revealed a significant increase in the abundance of a limited number of metabolites following treatment with nitisinone. Further work is required to understand the significance of these findings and the mechanisms by which the altered metabolite abundances occur.

Long‐term low dose nitisinone therapy in adults with alkaptonuria shows no cognitive decline or increased severity of depression

Little is documented on whether nitisinone‐induced hypertyrosinaemia alters cognitive functioning or leads to worsening depression in alkaptonuria (AKU). Wechsler Adult Intelligence Scale‐IV (WAIS‐IV) and Beck Depression Inventory‐II (BDI‐II) assessments were performed before and annually following treatment with nitisinone 2 mg daily to assess the impact on cognitive functioning and severity of depression. Serum tyrosine concentrations were also measured annually. WAIS‐IV: 63 patients (27 females/36 males: mean age[years] [±standard deviation, range] 55.7[13.7, 26–79]; 60.3[9.6, 19–75]) were included at baseline for assessment of: verbal comprehension (VC), perceptual reasoning (PR), working memory (WM), and processing speed (PS) using separate indices. Over the 6‐year period studied 43, 39, 36, 29, 26 and 15 patients had annual assessments. Using a longitudinal model (age and sex adjusted) no significant differences were observed in any of the indices over this period, apart from VC which showed a significant increase after adjustment for sex (p < 0.05). BDI‐II: 74 patients (32 females/42 males: mean age[years] [±standard deviation, range] 56.1[13.2, 26–79]; 42 males, 51.5[16.3, 19–70]) were included at baseline. Over the 7‐year period studied 48, 47, 38, 34, 32, 24 and 12 patients had annual assessments. No significant differences in BDI‐II scores were observed when compared to baseline. Hypertyrosinaemia was observed in all patients following treatment with nitisinone (p < 0.001, at all annual visits). Serum tyrosine was not correlated with WAIS‐IV sub‐test indices or BDI‐II scores pre‐ or post‐nitisinone therapy. These findings suggest that treatment with nitisinone does not affect cognitive functioning and or lead to increased severity of depression.

Comparing nitisinone 2 mg and 10 mg in the treatment of alkaptonuria-An approach using statistical modelling

BACKGROUND

Outcomes from studies employing nitisinone 10 mg and 2 mg in alkaptonuria were compared.

PATIENTS AND METHODS

Sixty-nine patients in each of the nitisinone (10 mg daily) and controls of suitability of nitisinone in alkaptonuria 2 (SONIA 2), as well as 37 and 23 in nitisinone (2 mg daily) and control cohorts at the National Alkaptonuria Centre (NAC), respectively, were followed up for 4 years. Severity of alkaptonuria (AKU) was assessed by the AKU Severity Score Index (AKUSSI). 24-h urine homogentisic acid (uHGA24), serum HGA (sHGA), serum tyrosine (sTYR) and serum nitisinone (sNIT) were also analysed at each time point. Dietetic support was used in the NAC, but not in SONIA 2. Safety outcomes were also compared. All statistical analyses were post hoc.

RESULTS

The slope of the AKUSSI was 0.55, 0.19, 0.30, and 0.06 per month in the control NAC, nitisinone NAC, control SONIA 2, and nitisinone SONIA 2 cohorts, respectively. The intersection of the slopes on the x-axis was -132, -411, -295, and - 1460 months, respectively. The control and nitisinone slope comparisons were statistically significant both in the NAC (p < 0.001) and the SONIA 2 (p < 0.001). Corneal keratopathy occurred in 3 and 10 patients in the NAC and SONIA 2, respectively.

DISCUSSION

The nitisinone 10 mg dose decreased disease progression more than the 2 mg dose although the incidence of corneal keratopathy was 14.5% and 4.9%, respectively.

CONCLUSION

Nitisinone 10 mg decreased urine and serum HGA, increased serum tyrosine, and decreased disease progression more than 2 mg. Low-protein dietetic support may be needed to mitigate tyrosinaemia following nitisinone.

HIGHLIGHTS

Nitisinone 10 mg apparently slows alkaptonuria disease progression more than 2 mg in adults.Corneal keratopathy during nitisinone therapy was more common in men.Serum nitisinone concentrations increased significantly over time.Nitisinone may inhibit cytochrome P450 self catabolism.

Influence of nitisinone and its metabolites on l-tyrosine metabolism in a model system

Nitisinone (NTBC) is currently used for the treatment of tyrosinemia type 1, a rare disease. It also exhibits potential in the treatment of other orphan diseases as well as nervous system disorders - this is however limited by its side effects. In all living organisms, NTBC inhibits 4-hydroxyphenylpyruvate dioxygenase activity, thereby affecting l-tyrosine (L-TYR) catabolism, which results in the therapeutic effect. The NTBC metabolites formed in patient's body is one of the causes of its side effects. The influence of NTBC and its metabolites; 2-amino-4-(trifluoromethyl)benzoic acid, 2-nitro-4-(trifluoromethyl)benzoic acid, and cyclohexane-1,3-dione on L-TYR catabolism was investigated in Raphanus sativus var. longipinnatus. Based on targeted LC-MS/MS analysis the concentration of NTBC and its metabolites in exposed plant tissues was determined. Based on non-targeted LC-MS/MS analysis the concentrations of products of L-TYR catabolism: levodopa, epinephrine, norepinephrine, normetanephrine, dopamine, tyramine and vitamins C, B5 and B6, additionally leucine and valine were identified as influenced by the NTBC or its metabolites. NTBC and its metabolites influenced L-TYR catabolism differently. Particularly significant changes were found in the content of epinephrine and normetanephrine: in the plant tissues exposed to NTBC, an increase in the content of these neurotransmitters was found (+42%), whereas in the plant treated with 2-amino-4-(trifluoromethyl)benzoic acid or 2-nitro-4-(trifluoromethyl)benzoic acid a decrease in concentration (-39% and 55%, respectively) was observed. Cyclohexane-1,3-dione does not influence epinephrine and normetanephrine concentration. The conclusions of this study provide a platform for expanded research on the causes of side effects of NTBC treatment.

Efficacy of Phenylalanine- and Tyrosine-Restricted Diet in Alkaptonuria Patients on Nitisinone Treatment: Case Series and Review of Literature

INTRODUCTION

Nitisinone used in alkaptonuria (AKU) can result in keratopathy due to strongly increased tyrosine levels.

METHODS

This study aimed to investigate nutritional status and changes in plasma tyrosine and phenylalanine and urinary homogentisic acid (u-HGA) levels in 8 adult AKU patients (mean age, 56.3 ± 4.7 years) who were on tyrosine/phenylalanine-restricted diet together with 2 mg/day nitisinone.

RESULTS

The treatment period was 23.4 ± 6.9 months. Daily dietary protein intake was restricted to 0.8-1.0 g/kg/day. Daily tyrosine intake was restricted to 260-450 mg/day for females and 330-550 mg/day for males. Tyrosine/phenylalanine-free amino acid supplements accounted for an average of 56.1% of daily protein intake. The following assessments were performed: anthropometric and plasma tyrosine level measurements every 2 months; ophthalmological examination every 6 months, and nutritional laboratory analyses and measurements of plasma amino acids and u-HGA once in a year. It was targeted to keep the plasma tyrosine level <500 μmol/L. The plasma tyrosine level was <100 μmol/L before the treatment in all patients and around a mean of 582.5 ± 194.8 μmol/L during the treatment. The diet was rearranged if a plasma tyrosine level of >700 μmol/L was detected. The u-HGA level before and after the 1st year of treatment was 1,429.3 ± 1,073.4 mmol/mol creatinine and 33.6 ± 9.5 mmol/mol creatinine, respectively. None of the patients developed keratopathy or experienced weight loss and protein or micronutrient deficiency.

CONCLUSION

AKU patients should receive tyrosine/phenylalanine-restricted diet for reducing plasma tyrosine level to the safe range. Tyrosine/phenylalanine-free amino acid supplements can be safely used to enhance dietary compliance. Keratopathy and nutrient deficiency should be frequently monitored.

β-Cyclodextrin Derivative Grafted on Silica Gel Represents a New Polymeric Sorbent for Extracting Nitisinone from Model Physiological Fluids

Nitisinone (NTBC) is used in the treatment of disorders affecting the tyrosine pathway, including hereditary tyrosinemia type I, alkaptonuria, and neuroblastoma. An inappropriate dosage of this therapeutic drug causes side effects; therefore, it is necessary to develop a rapid and sensitive method to monitor the content of NTBC in patients' blood. This study aimed to develop anew polymeric sorbent containing β-cyclodextrin (β-CD) derivatives grafted on silica gel to effectively extract NTBC from model physiological fluids. The inclusion complex formed between β-CD and NTBC was examined by proton nuclear magnetic resonance spectroscopy. The novel sorbents with derivatives of β-CD were prepared on modified silica gel using styrene as a comonomer, ethylene glycol dimethacrylate as a crosslinking agent, and 2,2'-azo-bis-isobutyronitrile as a polymerization initiator. The obtained products were characterized via Fourier transform infrared spectroscopy and then used as sorbents as part of a solid phase extraction technique. High NTBC recovery (70%indicated that the developed polymeric sorbent may be suitable for extracting this compound from patients' blood samples.

Preventive use of nitisinone in alkaptonuria

Alkaptonuria (AKU, OMIM 203500) is a rare congenital disorder caused by a deficiency of the enzyme homogentisate-1,2,-dioxygenase. The long-term consequences of AKU are joint problems, cardiac valve abnormalities and renal problems. Landmark intervention studies with nitisinone 10 mg daily, suppressing an upstream enzyme activity, demonstrated its beneficial effects in AKU patients with established complications, which usually start to develop in the fourth decade. Lower dose of nitisinone in the range of 0.2–2 mg daily will already reduce urinary homogentisic acid (uHGA) excretion by > 90%, which may prevent AKU-related complications earlier in the course of the disease while limiting the possibility of side-effects related to the increase of plasma tyrosine levels caused by nitisinone. Future preventive studies should establish the lowest possible dose for an individual patient, the best age to start treatment and also collect evidence to which level uHGA excretion should be reduced to prevent complications.

A case report of pregnancy in untreated alkaptonuria - Focus on urinary tissue remodelling markers

A 34-year old woman with alkaptonuria had an elective pregnancy, during which she collected urine samples over the duration of her pregnancy until parturition. She had been attending the National Alkaptonuria Centre from the age of 31 years and continued to attend after delivery for a further three annual visits. Data from her NAC visits as well as urine samples collected during pregnancy were analysed. Urine CTX-1/urine creatinine, urine αCTX-I/ urine creatinine, urine CTX-II/ urine creatinine, and urine C3M/urine creatinine all showed a rapid increase early in pregnancy, returning to baseline before increasing in late pregnancy, indicating significant remodelling of bone, subchondral bone, cartilage and other organs and connective tissue rich in collagens I, II and III. The pattern of tissue remodelling in AKU pregnancy has been described for the very first time. Further research is needed to understand pregnancy in AKU.

Alkaptonuria in Turkey: Clinical and molecular characteristics of 66 patients

Alkaptonuria (AKU) is an inborn error of metabolism caused by the deficiency of homogentisate 1,2-dioxygenase (HGD) as a result of a defect in the HGD gene. HGD enzyme deficiency results in accumulation of homogentisic acid (HGA) in the body, which in turn leads to multisystemic clinical symptoms. The present study aimed to investigate the presenting symptoms, age at diagnosis, and clinical and genetic characteristics of AKU patients followed-up in different centers in Turkey. In this cross-sectional, multicenter, descriptive study, medical records of 66 AKU patients were retrospectively evaluated. Patients' data regarding demographic, clinical and genetic characteristics were recorded. HGD database (http://hgddatabase.cvtisr.sk/) was used to identify HGD gene variants. Of the patients, 37 (56.1%) presented with isolated dark urine and 29 (43.9%) were diagnosed based on the clinical symptoms or family screening. One of these patients was on follow-up for 2 years due to Parkinsonism and was diagnosed with AKU on further analyses. Signs of ochronosis such as joint pain, low back pain and renal stones developed in childhood in 7 patients. Eight patients were diagnosed with depression via psychiatric evaluation. There were 14 (21.2%) patients operated on for ochronosis. The most frequent mutation observed in the patients was c.175delA, which was followed by c.674G > A and c.1007-2A > T mutations. Four novel mutations (c.189G > A, c.549+1G > T, c.1188+1G > A, and c.334 T > G) were identified in the patients included in the study. In addition to the known signs such as dark urine and skin pigmentation, symptoms involving different systems such as neurological findings and depression can also be encountered in AKU patients. The presence of a change in urine color needs to be questioned in patients presenting with different symptoms such as arthralgia/arthritis, renal stones or low-back pain, particularly in childhood, when skin ochronosis is not pronounced, and further examination should be performed.

Laboratory monitoring of patients with hereditary tyrosinemia type I

BACKGROUND

The prognosis of patients with Hereditary Tyrosinemia Type 1 (HT-1) has greatly improved with early detection through newborn screening and the introduction of nitisinone (NTBC) therapy. A recent guideline calls for periodic monitoring of biochemical markers and NTBC levels to tailor treatment; however, this is currently only achieved through a combination of clinical laboratory tests. We developed a multiplexed assay measuring relevant amino acids, succinylacetone (SUAC), and NTBC in dried blood spots (DBS) to facilitate treatment monitoring.

METHODS

Tyrosine, phenylalanine, methionine, NTBC and SUAC were eluted from DBS with methanol containing internal standards for each analyte and analyzed by liquid chromatography tandem mass spectrometry over 6.5 min in the multiple reaction monitoring positive mode.

RESULTS

Pre-analytical and analytical factors were studied and demonstrated a reliable assay. Chromatography resolved an unknown substance that falsely elevates SUAC concentrations and was present in all samples. To establish control and disease ranges, the method was applied to DBS collected from controls (n = 284) and affected patients before (n = 2) and after initiation of treatment (n = 29). In the treated patients SUAC concentrations were within the normal range over a wide range of NTBC levels.

CONCLUSIONS

This assay enables combined, accurate measurement of revelevant metabolites and NTBC in order to simplify treatment monitoring of patients with HT-1. In addition, the use of DBS allows for specimen collection at home to facilitate more standardization in relation to drug and dietary treatment.

Fatal acute haemolysis and methaemoglobinaemia in a man with renal failure and Alkaptonuria - Is nitisinone the solution?

Haemolysis and methaemoglobinaemia (MetHb) are rare metabolic complications that can occur in Alkaptonuria (AKU), for which there is no curative treatment. Presented is a case of a man who had AKU, and serves as a reminder of life-threatening complications that can occur with haemolysis and MetHb. This case presents an opportunity to revisit important considerations relating to the investigation and treatment of haemolysis and MetHb with a view to raising awareness, and in doing so hopefully reducing the uniformly fatal outcome. Additionally it is proposed that treatment of haemolysis and MetHb with nitisinone is considered as a potentially lifesaving treatment as it is believed that reducing the concentration of circulating homogentisic acid will reduce oxidative stress.