Liver disease in erythropoietic protoporphyria: insights and implications for management
Liver disease in EPP
No study to date has specifically set out to document the natural history of liver disease or to identify risk factors in its causation in a large unselected cohort of unrelated patients with EPP. The largest studies reported so far have all been from single centres and many are subject to case selection bias resulting from local interest and expertise in the management of EPP‐related liver disease. Despite these shortcomings, these studies (summarised in table 22)) provide a useful starting point for further analysis of this topic.
Pathogenesis of liver disease in EPP
Irrespective of its origin, excess protoporphyrin is excreted by the liver into bile and enters an enterohepatic circulation. Protoporphyrin is a hydrophobic compound which is not filtered by the kidneys. When in excess, protoporphyrin becomes insoluble in bile and exerts cholestatic effects leading to architectural changes in the hepatobiliary system ranging from mild inflammation to fibrosis and cirrhosis.42 Even in early EPP, ultrastructural damage has been described in hepatocyte nuclei, endoplasmic reticulum, plasma membranes and bile canaliculi, associated with protoporphyrin crystals.43Significant intracellular precipitates of protoporphyrin, demonstrated in liver biopsy samples by fluorescent birefringence, are invariably present in protoporphyric liver disease.44
Exposure of cultured hepatocytes to protoporphyrin inhibits cell metabolism and increases cellular fragility.45 However, it remains unclear what effect protoporphyrin has on hepatocytes in vivo and how this relates to the development of liver disease. Bloomer et al32 found that liver FECH activity in EPP‐related end‐stage liver disease was reduced more than could be explained by the decrease in ferrochelatase protein, and concluded that the liver probably contributes to the overproduction of protoporphyrin that results in its own damage. In the absence of a clear explanation for occasional severe liver disease complicating EPP in humans, Nordmann46 speculated that patients may vary in their susceptibility to protoporphyrin‐induced liver damage. This is probably so, but host factors other than deficiency of FECH activity relevant to the onset and progression of liver disease are currently unknown. Recent murine studies (highlighted later in this review) have revealed that other genetic factors are relevant to this process. It is likely that quantitative trait loci analyses will shed more light on this important topic, with the growing recognition of the importance of such factors for many inherited diseases.
Hepatobiliary disease in humans with EPP may be described under the following headings:
- Mild liver disease;
- Deteriorating liver disease; and
- Terminal phase of EPP‐associated liver disease.
Protoporphyrin in bile may crystallise out forming stones. The original case of EPP described by Magnus in 1961 underwent a cholecystectomy at the age of 29 years and a solitary gallstone was identified.6Gallstones have subsequently been reported in EPP in many patients, including 2 patients in a series of 29 from Denmark,35 4 patients in a series of 32 reported from the USA,36 and 9 patients from a series of 200 reported from The Netherlands.37 Three of the patients in the series from the USA required cholecystectomy, and gallstones analysed from 2 of these cases revealed high levels of protoporphyrin.36Todd highlighted the fact that, when gallstones occur in children, EPP should be included in the differential diagnosis.47
Mild liver disease
There is wide variation in the severity of liver disease in EPP. Minor abnormalities in biochemical parameters of liver function are relatively common and include raised aspartate transaminase levels and approximately twofold increases in alkaline phosphatase and γ‐glutamyl transferase.44 A study of 32 patients with EPP included a single patient with abnormal liver function.36 Analysis of liver biopsies from this case and 4 patients with normal liver function revealed protoporphyrin deposition without evidence of fibrosis or infiltrates in all 5 samples.36 In contrast, liver biopsies from 7 cases of EPP without overt liver disease from The Netherlands showed protoporphyrin deposition and mild fibrosis in 3 cases; the remainder were normal.48 In a separate study Cripps et al also reported protoporphyrin deposition in liver biopsy specimens from 5 patients with EPP and normal liver function tests; portal and periportal fibrosis was identified in 2 of these 5 samples.49 An ultrastructural study of liver biopsy specimens obtained from 11 patients with EPP, 4 of whom had overt liver disease and 7 of whom did not, revealed significant pathological changes in all samples compared with normal controls.50 It was concluded that liver damage is an early and consistent feature of EPP.50 Finally, a study with histopathology and ultrastructural studies of liver biopsy samples obtained from 4 patients with EPP (1 with severe liver disease, 1 with mild liver disease and 2 without evidence of liver disease and with normal histopathology) showed characteristic crystal‐containing vacuoles on electron microscopy in all 4 cases.51 It therefore appears that protoporphyrin deposition in hepatocytes is invariable, whereas histological evidence of damage is less common; electron microscopy will, however, show ultrastructural evidence of damage in most, if not all, patients with EPP.
Deteriorating liver disease
Patients with EPP who manifest significant liver disease will progress to decompensated cirrhosis which, in the absence of liver transplantation, is fatal. Various treatments have been attempted to preserve liver function and break the cycle of rapid deterioration that occurs in this situation in order to avoid terminal liver failure, or at least to buy time until a donor liver becomes available. The different forms of treatment have been directed at specific pathogenetic mechanisms as follows:
- To increase the excretion of protoporphyrin into bile by the oral administration of the bile salts chenodeoxycholic acid50,52 or ursodeoxycholic acid.41
- To reduce protoporphyrin production by suppressing erythropoiesis using iron,53,54 red cell transfusions55 or infusion of haematin,56,65 all of which are intended to reduce the drive for haem synthesis.
- To reduce the pool of circulating plasma protoporphyrin by plasmapheresis,57,58 haemodialysis,59and exchange transfusions.55,60
- To reduce protoporphyrin levels by interrupting the enterohepatic circulation with administration of cholestyramine59,61 and activated charcoal.54,62
- To reverse oxidative stress in EPP by intravenous vitamin E therapy.63
One or more of these treatments are sometimes combined,58,59 and this is currently the practice before liver transplantation in order to optimise the environment into which the new liver is transplanted.64,65However, none of these treatments is effective in all cases, each has potential problems and none has been applied in sufficient numbers of patients to allow a rigorous evaluation of efficiency.
Treatment with bile acid appears to have only a modest effect on EPP‐associated liver disease. Administration of chenodeoxycholic acid resulted in no distinct improvement in ultrastructural assessment of organelle damage in EPP‐associated liver disease in three patients after 1 year of treatment,50 and its therapeutic efficacy in another study was doubtful.52 In spite of these reports, chenodeoxycholic acid continues to be used with other treatments for the treatment of acute liver decompensation before transplant surgery.64 Doss and Frank reported a patient who showed biochemical and clinical improvement from EPP‐induced decompensated liver cirrhosis following treatment with cholic acid.66
The role of iron treatment in EPP is unclear, with reports of significant efficacy53,54 but also reports of increased protoporphyrin levels in some patients.67,68 Furthermore, use of erythropoietin following orthotic liver transplantation in one patient was implicated in causing a great overproduction in protoporphyrin IX, prompting the authors to conclude that treatment with erythropoietin is risky and probably contraindicated in EPP.69 Transfusion therapy is probably the most widely reported and effective treatment for deteriorating liver function in EPP,55,70,71,72,73,74 but in one case it was implicated as the trigger for worsening liver function.75 Various hypertransfusion protocols for decompensating EPP have been used, ranging from 1 unit of blood per month for 5 months to a maximum of 1 unit every 2–7 days repeated 3–10 times.55,70,71,72,73,74 However, care is needed as transfused cells exposed to plasma protoporphyrin are more fragile than endogenous protoporphyrin‐loaded erythrocytes.75,76,77 The risk of haemolysis can be reduced by plasmapheresis conducted before transfusion and, in the context of liver transplantation, immediately before surgery.65 Exchange transfusion is seldom used and is reserved for severe or rapidly deteriorating cases. Intravenous haematin has been shown to reduce protoporphyrin levels56,66,78,79 and, more recently, haem‐albumin has been used successfully in combination with plasmapheresis before liver transplantation.65 Haemodialysis has only been used as a treatment in EPP‐related liver failure and was unsuccessful.59
The efficacy of oral cholestyramine was reported in two well documented cases.80,81 The therapeutic use of this agent in EPP‐related liver disease is seldom reported and, when used, it is usually in combination with other treatments.59,64 Some patients, however, fail to respond to this treatment.66 Cholestyramine was the main treatment used in a 36‐year‐old patient with EPP who developed liver disease but remained in good health until rapid deterioration in liver function 6 years later requiring liver transplantation.82Activated charcoal is another treatment aimed at preventing reabsorption of protoporphyrin from the gut, and has the merit of being cheap and safe, albeit unpalatable.54,62 Long‐term treatment (27 months) with this agent has been reported to be beneficial in reducing protoporphyrin levels and restoring liver function.62 Finally, intravenous vitamin E was reported to be effective at reversing severe EPP‐related liver disease in a single case report.63
Terminal phase of EPP‐associated liver disease
Deteriorating liver disease in EPP is characterised by chole‐stasis83 followed by jaundice and generalised upper abdominal pain.66 The spleen becomes enlarged and haemolysis may ensue.75 Rapidly worsening photosensitivity due to a further reduction in biliary free protoporphyrin excretion heralds the onset of fulminant disease which is seldom reversible and, in the absence of liver transplantation, usually leads to death. Acute liver failure may rarely be the presenting feature for EPP.85 Additionally, EPP‐related liver failure may sometimes be further complicated by the development of acute pancreatitis.86 In 1986 Bonkovsky and Schned87 summarised 21 fatal cases of EPP‐related liver failure reported in the literature, and Todd identified a further 8 cases in his comprehensive review in 1994.3 The majority of these fatal cases were over the age of 30, but two teenagers and an 11‐year‐old child were also included.3 In the last 10 years liver transplantation has increasingly been available as a treatment option but, despite this, patients have continued to die from EPP‐related liver failure.30,59,88
The cycle of deterioration which characterises fulminant hepatic failure in EPP has been recorded in detail in a number of individual case reports, but the initiating event (or events) remains unclear. What is known is that cholestasis induced by protoporphyrin leads to further accumulation of protoporphyrin,45 initiating a vicious cycle of worsening cholestasis and reduced protoporphyrin excretion.45 Haemolysis leads to increased erythropoiesis, hence increased de novo porphyrin formation by the bone marrow.75 Once this cycle is established, liver decompensation is rapid and liver failure ensues ((figsfigs 4 and 55).).
Liver transplantation in EPP
The first liver transplant for EPP‐related liver disease was carried out in 1980.11 Since then, more than 40 further liver transplants have been reported (table 33).). Published reports with clinical details of liver transplantation for EPP‐related liver disease include 41 patients (23 male) of age range 13–59 years (mean 39.2 years). The most recent figures from the European Liver Transplant Registry indicate that 19 liver transplants were performed in Europe for EPP between 1985 and 2003, 13 of whom have survived. The reasons for the deaths were gastrointestinal haemorrhage (n = 1), primary graft non‐function (n = 1), infection (n = 2) and unknown causes (n = 2) (V Karam, personal communication, July 2005).
McGuire et al84 have recently reported the outcome of 20 cases of EPP in the USA who underwent liver transplantation. Paediatric and adult survival rates were 100% and 85% respectively at 1 year, 75% and 69% at 5 years and 50% and 47% at 10 years. Recurrent EPP was noted in 11 of the 17 patients (65%) who survived more than 2 months after transplantation. Of the remaining 6 patients without evidence of recurrent EPP, serial monitoring of liver function has shown no evidence of cholestasis. The earliest interval at which recurrent disease was noted on liver biopsy was 8 months. Three patients were re‐transplanted for recurrent EPP‐associated liver disease at 1.8, 12.6 and 14.5 years. Three additional patients in this series died 61–73 months after liver transplantation, documented by extensive protoporphyrin deposits and bridging fibrosis or cirrhosis on liver biopsy. The high rate of recurrent EPP‐associated liver disease prompted the authors to recommend that bone marrow transplantation (soon after successful liver transplantation) should be considered in transplant recipients in order to correct the underlying defect and prevent this.
Liver transplantation restores normal liver function and thus the ability to excrete protoporphyrin via the biliary system. However, it does not correct the FECH enzyme deficiency in the bone marrow, which continues to be the source of significant overproduction of protoporphyrin. Transplanted patients therefore usually continue to have the symptoms of EPP and are at risk of developing EPP‐related liver disease in the transplanted liver;41,89,90,104 some patients have subsequently required a second transplant.84
A number of early patients with EPP who received a liver transplant developed life‐threatening phototoxic abdominal burns and wound dehiscence with severe haemolytic anaemia, since it had not been foreseen that prolonged visceral exposure to operating lamps would result in tissue phototoxicity analogous to that displayed in the skin under normal circumstances.82,106 Additional and unexpected complications included acute neuropathy82,101,106 resulting from high circulating protoporphyrin levels (neuropathy is not generally a feature of EPP as it is of other forms of porphyria), and acute protoporphyrin‐mediated damage to the transplanted liver resulting in delayed return of function as a result of these high circulating levels at the time of grafting.41,89,90 This led to recommendations for optimising the environment for the transplanted liver,58 which included the use of filtered theatre lights and short‐term measures aimed at keeping the level of protoporphyrin as low as possible in the immediate postoperative period.90,102 The introduction of such measures has reduced perioperative complications including haemolysis.76Furthermore, long‐term use of plasmapheresis and intravenous haem‐albumin has been advocated as a worthwhile therapeutic measure to prolong survival of the transplanted liver in the face of chronically raised protoporphyrin levels.105 There are increasing reports of medium‐term30,103,105 and long‐term104survival following EPP‐related liver transplantation. However, long‐term follow‐up of two patients with EPP who underwent liver transplantation for acute liver failure revealed protoporphyrin deposits and onset of fibrosis in the transplanted livers 8 months and 6 months after transplantation.104 Despite this, both patients remained in good health 7 years after surgery.104
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