Efficacy and safety of once-daily nitisinone for patients with alkaptonuria (SONIA 2): an international, multicentre, open-label, randomised controlled trial

BACKGROUND

Alkaptonuria is a rare, genetic, multisystem disease characterised by the accumulation of homogentisic acid (HGA). No HGA-lowering therapy has been approved to date. The aim of SONIA 2 was to investigate the efficacy and safety of once-daily nitisinone for reducing HGA excretion in patients with alkaptonuria and to evaluate whether nitisinone has a clinical benefit.

METHODS

SONIA 2 was a 4-year, open-label, evaluator-blind, randomised, no treatment controlled, parallel-group study done at three sites in the UK, France, and Slovakia. Patients aged 25 years or older with confirmed alkaptonuria and any clinical disease manifestations were randomly assigned (1:1) to receive either oral nitisinone 10 mg daily or no treatment. Patients could not be masked to treatment due to colour changes in the urine, but the study was evaluator-blinded as far as possible. The primary endpoint was daily urinary HGA excretion (u-HGA₂₄) after 12 months. Clinical evaluation Alkaptonuria Severity Score Index (cAKUSSI) score was assessed at 12, 24, 36, and 48 months. Efficacy variables were analysed in all randomly assigned patients with a valid u-HGA₂₄ measurement at baseline. Safety variables were analysed in all randomly assigned patients. The study was registered at ClinicalTrials.gov (NCT01916382).

FINDINGS

Between May 7, 2014, and Feb 16, 2015, 139 patients were screened, of whom 138 were included in the study, with 69 patients randomly assigned to each group. 55 patients in the nitisinone group and 53 in the control group completed the study. u-HGA₂₄ at 12 months was significantly decreased by 99·7% in the nitisinone group compared with the control group (adjusted geometric mean ratio of nitisinone/control 0·003 [95% CI 0·003 to 0·004], p<0·0001). At 48 months, the increase in cAKUSSI score from baseline was significantly lower in the nitisinone group compared with the control group (adjusted mean difference -8·6 points [-16·0 to -1·2], p=0·023). 400 adverse events occurred in 59 (86%) patients in the nitisinone group and 284 events occurred in 57 (83%) patients in the control group. No treatment-related deaths occurred.

INTERPRETATION

Nitisinone 10 mg daily was well tolerated and effective in reducing urinary excretion of HGA. Nitisinone decreased ochronosis and improved clinical signs, indicating a slower disease progression.

FUNDING

European Commission Seventh Framework Programme.

Homogentisic acid is not only eliminated by glomerular filtration and tubular secretion but also produced in the kidney in alkaptonuria

The clinical effects of alkaptonuria (AKU) are delayed and ageing influences disease progression. Morbidity of AKU is secondary to high circulating homogentisic acid (HGA) and ochronosis. It is not known whether HGA is produced by or processed in the kidney in AKU. Data from AKU patients from four studies were merged to form a single AKU group. A control group of non-AKU subjects was generated by merging data from two non-AKU studies. Data were used to derive renal clearance and fractional excretion (FE) ratios for creatinine, HGA, phenylalanine (PHE) and tyrosine (TYR) using standard calculations, for comparison between the AKU and the control groups. There were 225 AKU patients in the AKU group and 52 in the non-AKU control group. Circulating HGA increased with age (P < 0.001), and was significantly associated with decreased HGA clearance (CL_HGA ) (P < 0.001) and FE_HGA (P < 0.001). CL_HGA and FE_HGA were increased beyond the theoretical maximum renal plasma flow, confirming renal production and emphasising the greater contribution of net tubular secretion than glomerular filtration to renal elimination of HGA. The kidneys are crucial to elimination of HGA. Elimination of HGA is impaired with age resulting in worsening disease over time. The kidney is an important site for production of HGA. Tubular secretion of HGA contributes more to elimination of HGA in AKU than glomerular filtration.

Extrahepatic manifestations of cholestasis

Pruritus, fatigue and metabolic bone disease represent three major extrahepatic manifestations of chronic cholestatic liver disease that considerably affect the patient's quality of life. The present article reviews pathogenetic aspects of and current therapeutic approaches to extrahepatic manifestations of cholestatic liver disease. Pathogenesis of pruritus of cholestasis remains poorly understood. The involvement of putative peripherally acting pruritogens, such as bile acids or endogenous opioids, is being discussed. More recently, central mechanisms, including an increased central opioidergic tone and pertubations in the serotonergic system have been proposed. Treatment of the underlying disease is beneficial also for the control of cholestasis-associated pruritus. Current therapeutic recommendations include ursodeoxycholic acid, cholestyramine, rifampicin and opioid antagonists. Liver transplantation may be indicated when severe pruritus is refractory to medical treatment. Fatigue is being recognized as the most frequent and one of the most disabling complaints in chronic cholestasis. Fatigue is presumably of central origin and its association with other neuropsychiatric disorders (e.g. depression, obsessive-compulsive disorders) is consistent with defective central neurotransmission. No specific therapies are currently available and a healthy lifestyle, regular sleep and avoidance of unnecessary stress and other precipiting factors are recommended. Antidepressant therapy may be warranted in selected patients. Osteopenia and osteoporosis are common in chronic cholestatic liver disease, whereas osteomalacia is rare. The pathophysiology of cholestasis-associated metabolic bone disease is regarded as multifactorial. Therapeutic recommendations include regular exercise, calcium and vitamin D supplementation in late stage disease, hormone replacement therapy in postmenopausal women and bisphosphonates.

Tauroursodeoxycholic acid mobilizes alpha-PKC after uptake in human HepG2 hepatoma cells

BACKGROUND

Tauroursodeoxycholic acid (TUDCA) may exert anticholestatic effects via Ca(++)- and alpha-protein kinase C (alpha-PKC)-dependent apical vesicular insertion of canalicular transporters in cholestatic hepatocytes (Hepatology 2001; 33: 1206-16). Tauroursodeoxycholic acid is mainly taken up into liver cells by Na(+)-taurocholate cotransporting polypeptide (Ntcp). Tauroursodeoxycholic acid selectively translocates alpha-PKC, a key mediator of regulated exocytosis, to hepatocellular membranes. It is unclear whether TUDCA exerts its effects on alpha-PKC after carrier-mediated uptake into liver cells or by interaction with extracellular/membraneous structures.

MATERIALS AND METHODS

Human hepatoblastoma HepG2 cells lacking Ntcp were stably transfected with pcDNA3.1/Ntcp or sham-transfected with pcDNA3.1 [+]. Distribution of alpha-PKC was studied using a Western blotting technique. Uptake of [(3)H]taurocholic acid (TCA) was determined radiochemically.

RESULTS

[(3)H]taurocholic acid uptake was approximately 180-fold higher in Ntcp-transfected than in sham-transfected cells. Phorbol 12-myristate 13-acetate (1 micromol L(-1); positive control) increased membrane binding of alpha-PKC by 34% in Ntcp-transfected and by 37% in sham-transfected cells. Tauroursodeoxycholic acid (10 micromol L(-1)) increased membrane-associated alpha-PKC by 19% in Ntcp-transfected, but not in sham-transfected cells (-13%). Taurocholic acid (10 micromol L(-1)) did not affect the distribution of alpha-PKC.

CONCLUSION

Carrier-mediated uptake is a prerequisite for TUDCA-induced translocation of alpha-PKC to hepatocellular membranes.