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BMJ Case Reports Dec 2021Alkaptonuria (AKU) is a rare autosomal recessive disorder with a global incidence of 1 in 250 000 to 1 million people worldwide. It results from a deficiency of the...
Alkaptonuria (AKU) is a rare autosomal recessive disorder with a global incidence of 1 in 250 000 to 1 million people worldwide. It results from a deficiency of the enzyme homogentisic acid (HGA) oxidase which when absent, leads to an accumulation of HGA. Without this enzymatic degradation, HGA deposits in connective tissues resulting in pigmentation (ochronosis), plaque formation and accelerated cartilage destruction. With this, many patients who suffer from AKU develop ochronotic arthropathies, tendon ruptures, fractures, and chronic joint pain. Similarly, patients can develop cardiac valvular dysfunction and interstitial renal disease. Our two cases highlight the array of pathologies seen in AKU and, in light of newly published research, give us a platform from which we can discuss the developments in management of this rare disease.
Topics: Alkaptonuria; Cartilage, Articular; Homogentisic Acid; Humans; Ochronosis; Rare Diseases
PubMed: 34876442
DOI: 10.1136/bcr-2021-244240 -
Metabolites Sep 2022Metabolomic analyses in alkaptonuria (AKU) have recently revealed alternative pathways in phenylalanine-tyrosine (phe-tyr) metabolism from biotransformation of...
Metabolomic analyses in alkaptonuria (AKU) have recently revealed alternative pathways in phenylalanine-tyrosine (phe-tyr) metabolism from biotransformation of homogentisic acid (HGA), the active molecule in this disease. The aim of this research was to study the phe-tyr metabolic pathway and whether the metabolites upstream of HGA, increased in nitisinone-treated patients, also undergo phase 1 and 2 biotransformation reactions. Metabolomic analyses were performed on serum and urine from patients partaking in the SONIA 2 phase 3 international randomised-controlled trial of nitisinone in AKU (EudraCT no. 2013-001633-41). Serum and urine samples were taken from the same patients at baseline (pre-nitisinone) then at 24 and 48 months on nitisinone treatment (patients N = 47 serum; 53 urine) or no treatment (patients N = 45 serum; 50 urine). Targeted feature extraction was performed to specifically mine data for the entire complement of theoretically predicted phase 1 and 2 biotransformation products derived from phenylalanine, tyrosine, 4-hydroxyphenylpyruvic acid and 4-hydroxyphenyllactic acid, in addition to phenylalanine-derived metabolites with known increases in phenylketonuria. In total, we observed 13 phase 1 and 2 biotransformation products from phenylalanine through to HGA. Each of these products were observed in urine and two were detected in serum. The derivatives of the metabolites upstream of HGA were markedly increased in urine of nitisinone-treated patients (fold change 1.2-16.2) and increases in 12 of these compounds were directly proportional to the degree of nitisinone-induced hypertyrosinaemia (correlation coefficient with serum tyrosine = 0.2-0.7). Increases in the urinary phenylalanine metabolites were also observed across consecutive visits in the treated group. Nitisinone treatment results in marked increases in a wider network of phe-tyr metabolites than shown before. This network comprises alternative biotransformation products from the major metabolites of this pathway, produced by reactions including hydration (phase 1) and bioconjugation (phase 2) of acetyl, methyl, acetylcysteine, glucuronide, glycine and sulfate groups. We propose that these alternative routes of phe-tyr metabolism, predominantly in urine, minimise tyrosinaemia as well as phenylalanaemia.
PubMed: 36295829
DOI: 10.3390/metabo12100927 -
Human Molecular Genetics Dec 2019Alkaptonuria is an inherited disease caused by homogentisate 1,2-dioxygenase (HGD) deficiency. Circulating homogentisic acid (HGA) is elevated and deposits in connective...
Conditional targeting in mice reveals that hepatic homogentisate 1,2-dioxygenase activity is essential in reducing circulating homogentisic acid and for effective therapy in the genetic disease alkaptonuria.
Alkaptonuria is an inherited disease caused by homogentisate 1,2-dioxygenase (HGD) deficiency. Circulating homogentisic acid (HGA) is elevated and deposits in connective tissues as ochronotic pigment. In this study, we aimed to define developmental and adult HGD tissue expression and determine the location and amount of gene activity required to lower circulating HGA and rescue the alkaptonuria phenotype. We generated an alkaptonuria mouse model using a knockout-first design for the disruption of the HGD gene. Hgd tm1a -/- mice showed elevated HGA and ochronosis in adulthood. LacZ staining driven by the endogenous HGD promoter was localised to only liver parenchymal cells and kidney proximal tubules in adulthood, commencing at E12.5 and E15.5 respectively. Following removal of the gene trap cassette to obtain a normal mouse with a floxed 6th HGD exon, a double transgenic was then created with Mx1-Cre which conditionally deleted HGD in liver in a dose dependent manner. 20% of HGD mRNA remaining in liver did not rescue the disease, suggesting that we need more than 20% of liver HGD to correct the disease in gene therapy. Kidney HGD activity which remained intact reduced urinary HGA, most likely by increased absorption, but did not reduce plasma HGA nor did it prevent ochronosis. In addition, downstream metabolites of exogenous 13C6-HGA, were detected in heterozygous plasma, revealing that hepatocytes take up and metabolise HGA. This novel alkaptonuria mouse model demonstrated the importance of targeting liver for therapeutic intervention, supported by our observation that hepatocytes take up and metabolise HGA.
Topics: Alkaptonuria; Animals; Disease Models, Animal; Gene Knockout Techniques; Homogentisate 1,2-Dioxygenase; Homogentisic Acid; Liver; Male; Mice; Mice, Transgenic; Promoter Regions, Genetic
PubMed: 31600782
DOI: 10.1093/hmg/ddz234 -
JIMD Reports Sep 2020Increased homogentisic acid (HGA) causes ochronosis. Nitisinone decreases HGA. The aim was to study the effect of nitisinone on the ochronosis progression.
BACKGROUND
Increased homogentisic acid (HGA) causes ochronosis. Nitisinone decreases HGA. The aim was to study the effect of nitisinone on the ochronosis progression.
METHODS
Photographs of the eyes and ears were acquired from patients attending the National Alkaptonuria Centre (NAC) at V-1 (pre-baseline visit), V0 (baseline visit when 2 mg nitisinone was commenced), and yearly at V1, V2, and V3 visits. Photographs were inspected for evolution of ochronotic pigment and also scored categorically to derive eye, ear, and combined ochronosis scores. An ear cartilage biopsy was also carried out at V0 and one year after V3 (V4) and ochronotic pigment was assessed and quantitated. Visits were compared for changes in pigment. Fasting blood and 24-hour urine samples were collected for measurement of HGA.
RESULTS
There were 80 AKU patients at V0, and 52, 47, and 40 at V1, V2, and V3 in the group with variable numbers (VAR Group) respectively; 23 patients attended once before V0, in the V-1 visit. Photographs of patients show increase in eye pigment between V-1 and V0, followed by decrease post-nitisinone at V1, V2, and V3. Ear and combined ochronosis semiquantitative scoring showed an increase between V-1 and V0 ( < .01), followed by a decrease at V1, V2, and V3, in the VAR group ( < .01). Ochronotic pigment in ear biopsy between V0 and V4 showed a 19.1% decrease ( < .05).
CONCLUSIONS
Nitisinone decreases HGA and partially reverses ochronosis.
PubMed: 32904992
DOI: 10.1002/jmd2.12137 -
Orthopedic Reviews Jun 2020Patients with alkaptonuria can present ochronotic degenerative arthropathy due to the accumulation of pigments in the cartilages. Ochronotic arthropathy initially...
Patients with alkaptonuria can present ochronotic degenerative arthropathy due to the accumulation of pigments in the cartilages. Ochronotic arthropathy initially affects the spine, then there is the involvement of the other large joints, with greater frequency of the knees. In this article we will present two patients with alkaptonuria who have been effectively treated with knee and hip replacement, comparing our experience with what is available in the literature.
PubMed: 32913615
DOI: 10.4081/or.2020.8687 -
International Journal of Molecular... Feb 2021Pyomelanin mimics from homogentisic acid (HGA) and gentisic acid (GA) were biosynthesized by the oxidative enzyme laccase at physiological pH to obtain water soluble...
Pyomelanin mimics from homogentisic acid (HGA) and gentisic acid (GA) were biosynthesized by the oxidative enzyme laccase at physiological pH to obtain water soluble melanins. The pigments show brown-black color, broad band visible light absorption, a persistent paramagnetism and high antioxidant activity. The EPR approach shows that at least two different radical species are present in both cases, contributing to the paramagnetism of the samples. This achievement can also shed light on the composition of the ochronotic pigment in the Alkaptonuria disease. On the other hand, these soluble pyomelanin mimics, sharing physico-chemical properties with eumelanin, can represent a suitable alternative to replace the insoluble melanin pigment in biotechnological applications.
Topics: Antioxidants; Biotechnology; Fungal Proteins; Gentisates; Homogentisic Acid; Laccase; Melanins; Polyporaceae
PubMed: 33572316
DOI: 10.3390/ijms22041739 -
Molecules (Basel, Switzerland) Sep 2021Nitisinone (NTBC) is used in the treatment of disorders affecting the tyrosine pathway, including hereditary tyrosinemia type I, alkaptonuria, and neuroblastoma. An...
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.
Topics: Adsorption; Cyclohexanones; Enzyme Inhibitors; Humans; Nitrobenzoates; Polymerization; Polymers; Silica Gel; Silicon Dioxide; Solid Phase Extraction; beta-Cyclodextrins
PubMed: 34641489
DOI: 10.3390/molecules26195945 -
Calcified Tissue International Feb 2021Alkaptonuria (AKU) is characterised by increased circulating homogentisic acid and deposition of ochronotic pigment in collagen-rich connective tissues (ochronosis),...
Alkaptonuria (AKU) is characterised by increased circulating homogentisic acid and deposition of ochronotic pigment in collagen-rich connective tissues (ochronosis), stiffening the tissue. This process over many years leads to a painful and severe osteoarthropathy, particularly affecting the cartilage of the spine and large weight bearing joints. Evidence in human AKU tissue suggests that pigment binds to collagen. The exposed collagen hypothesis suggests that collagen is initially protected from ochronosis, and that ageing and mechanical loading causes loss of protective molecules, allowing pigment binding. Schmorl's staining has previously demonstrated knee joint ochronosis in AKU mice. This study documents more comprehensively the anatomical distribution of ochronosis in two AKU mouse models (BALB/c Hgd, Hgd tm1a), using Schmorl's staining. Progression of knee joint pigmentation with age in the two AKU mouse models was comparable. Within the knee, hip, shoulder, elbow and wrist joints, pigmentation was associated with chondrons of calcified cartilage. Pigmented chondrons were identified in calcified endplates of intervertebral discs and the calcified knee joint meniscus, suggesting that calcified tissues are more susceptible to pigmentation. There were significantly more pigmented chondrons in lumbar versus tail intervertebral disc endplates (p = 0.002) and clusters of pigmented chondrons were observed at the insertions of ligaments and tendons. These observations suggest that loading/strain may be associated with increased pigmentation but needs further experimental investigation. The calcified cartilage may be the first joint tissue to acquire matrix damage, most likely to collagen, through normal ageing and physiological loading, as it is the first to become susceptible to pigmentation.
Topics: Alkaptonuria; Animals; Cartilage; Chondrocytes; Female; Male; Mice; Mice, Inbred BALB C; Mice, Knockout; Ochronosis; Pigmentation
PubMed: 33057760
DOI: 10.1007/s00223-020-00764-6 -
Molecular Genetics and Metabolism... Mar 2022Although changes in the tyrosine pathway during nitisinone therapy are known, a complete characterization of the induced tyrosinaemia is lacking to improve disease...
BACKGROUND
Although changes in the tyrosine pathway during nitisinone therapy are known, a complete characterization of the induced tyrosinaemia is lacking to improve disease management.
PATIENTS AND METHODS
Our research aims were addressed by 24-h blood sampling. 40 patients with alkaptonuria (AKU), treated with 0, 1, 2, 4 and 8 mg nitisinone daily ( = 8), were studied over four weeks. Serum homogentisic acid (sHGA), tyrosine (sTYR), phenylalanine (sPHE), hydroxyphenylpyruvate (sHPPA), hydroxyphenyllactate (sHPLA) and nitisinone (sNIT) were measured at baseline and after four weeks.
RESULTS
sNIT showed a clear dose-proportional response. sTYR increased markedly but with less clear-cut dose responses after nitisinone. Fasting and average 24-h (C) sTYR responses were similar. Individual patient sTYR 24-h profiles showed significant fluctuations during nitisinone therapy. At week 4, sTYR, sHPPA and sHPPL all showed dose-related increases compared to V0, with the greatest difference between 1 and 8 mg nitisinone seen for HPLA, while there was no change from V0 in sPHE. sHGA decreased to values around the lower limit of quantitation.
DISCUSSION
There was sustained tyrosinaemia after four weeks of nitisinone therapy with significant fluctuations over the day in individual patients. Diet and degree of conversion of HPPA to HPLA may determine extent of nitisinone-induced tyrosinaemia.
CONCLUSION
A fasting blood sample is recommended to monitor sTYR during nitisinone therapy Adaptations in HPPA metabolites as well as the inhibition of tyrosine aminotransferase could be contributing factors generating tyrosinaemia during nitisinone therapy.
PubMed: 35242577
DOI: 10.1016/j.ymgmr.2022.100846 -
Journal of Anaesthesiology, Clinical... 2022
PubMed: 35706646
DOI: 10.4103/joacp.JOACP_115_20