Cimetidine suppresses chemically induced experimental hepatic porphyria

Cimetidine Does Not Inhibit 5-Aminolevulinic Acid Synthase or Heme Oxygenase Activity: Implications for Treatment of Acute Intermittent Porphyria and Erythropoietic Protoporphyria

Acute intermittent porphyria (AIP) is characterized by acute neurovisceral attacks that are precipitated by the induction of hepatic 5-aminolevulinic acid synthase 1 (ALAS1). In erythropoietic protoporphyria (EPP), sun exposure leads to skin photosensitivity due to the overproduction of photoreactive porphyrins in bone marrow erythroid cells, where heme synthesis is primarily driven by the ALAS2 isozyme. Cimetidine has been suggested to be effective for the treatment of both AIP and EPP based on limited case reports. It has been proposed that cimetidine acts by inhibiting ALAS activity in liver and bone marrow for AIP and EPP, respectively, while it may also inhibit the hepatic activity of the heme catabolism enzyme, heme oxygenase (HO). Here, we show that cimetidine did not significantly modulate the activity or expression of endogenous ALAS or HO in wildtype mouse livers or bone marrow. Further, cimetidine did not effectively decrease hepatic ALAS activity or expression or plasma concentrations of the putative neurotoxic porphyrin precursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG), which were all markedly elevated during an induced acute attack in an AIP mouse model. These results show that cimetidine is not an efficacious treatment for acute attacks and suggest that its potential clinical benefit for EPP is not via ALAS inhibition.

Acute hepatic porphyrias: Current diagnosis & management

Each of the four acute hepatic porphyrias is due to mutation of an enzyme in the heme biosynthetic pathway. The accumulation of pathway intermediates that occur most notably when these diseases are active is the basis for screening and establishing a biochemical diagnosis of these rare disorders. Measurement of enzyme activities and especially DNA testing also are important for diagnosis. Suspicion of the diagnosis and specific testing, particularly measurement of urinary porphobilinogen, are often delayed because the symptoms are nonspecific, even when severe. Urinary porphyrins are also measured, but their elevation is much less specific. If porphobilinogen is elevated, second line testing will establish the type of acute porphyria. DNA testing identifies the familial mutation and enables screening of family members. Management includes removal of triggering factors whenever possible. Intravenous hemin is the most effective treatment for acute attacks. Carbohydrate loading is sometimes used for mild attacks. Cyclic attacks, if frequent, can be prevented by a GnRH analogue. Frequent noncyclic attacks are sometime preventable by scheduled (e.g. weekly) hemin infusions. Long term complications may include chronic pain, renal impairment and liver cancer. Other treatments, including RNA interference, are under development.

Cimetidine/lactulose therapy ameliorates erythropoietic protoporphyria-related liver injury

A 21-year-old Japanese man was admitted to our hospital because of severe abdominal pain and jaundice. He had been suffering from abdominal pain attacks and liver dysfunction since 18 years of age. Liver histology showed amorphous brown deposits in the sinusoidal space and significant periportal fibrosis without apparent hepatitis. Increased protoporphyrin in serum and feces and ferrochelatase gene mutation confirmed the final diagnosis of erythropoietic protoporphyria (EPP). Since ursodeoxycholic acid (UDCA) intake and glucose infusion are insufficient to ameliorate jaundice and abdominal attacks, cimetidine and lactulose were added in order to suppress hepatic delta-aminolevulinic acid synthase and limit re-absorption of protoporphyrin, respectively. Afterwards, the jaundice, liver dysfunction and abdominal symptoms improved and UDCA, cimetidine, and lactulose administration was continued. A repeat biopsy at 1.5 years after adding cimetidine/lactulose revealed marked attenuation of periportal fibrosis and protoporphyrin deposits. As far as we know, this is the first demonstration of histological improvement of EPP-induced liver abnormalities due to persistent cimetidine/lactulose administration. These treatments may be useful for EPP-related liver injury.

Interaction of cimetidine with P450 in a mouse model of hepatocarcinogenesis initiation

Many drugs and xenobiotics are lipophilic and they should be transformed into more polar water soluble compounds to be excreted. Cimetidine inhibits cytochrome P450. The aim of this study was to investigate the preventive and/or reversal action of cimetidine on cytochrome P450 induction and other metabolic alterations provoked by the carcinogen p-dimethylaminoazobenzene. A group of male CF1 mice received a standard laboratory diet and another group was placed on dietary p-dimethylaminoazobenzene (0.5% w w(-1). After 40 days of treatment, animals of both groups received p-dimethylaminoazobenzene and two weekly doses of cimetidine (120 mg kg(-1), i.p.) during a following period of 35 days. Cimetidine prevented and reversed delta-aminolevulinate synthetase induction and cytochrome P450 enhancement provoked by p-dimethylaminoazobenzene. However, cimetidine did not restore haem oxygenase activity decreased by p-dimethylaminoazobenzene. Enhancement in glutathione S-transferase activity provoked by p-dimethylaminoazobenzene, persisted in those animals then treated with cimetidine. This drug did not modify either increased lipid peroxidation or diminution of the natural antioxidant defence system (inferred by catalase activity) induced by p-dimethylaminoazobenzene. In conclusion, although cimetidine treatment partially prevented and reversed cytochrome P450 induction, and alteration on haem metabolism provoked by p-dimethylaminoazobenzene AB, it did not reverse liver damage or lipid peroxidation. These results further support our hypothesis on the necessary existence of a multiple biochemical pathway disturbance for the onset of hepatocarcinogenesis initiation.

Cimetidine in the treatment of acute intermittent porphyria

Treatment options for AIP remain limited. Although no single therapy has been proven superior in clinical trials, intravenous hemin appears to be more effective than increased carbohydrate intake, and remains the treatment of choice. At usual dosages the average wholesale price of hemin is $120-475 per day (for a patient weighing 70 kg), compared with $2.50 per day for cimetidine. Cimetidine may offer a more cost-effective and easily administered alternative to hemin therapy. The optimal dosage and duration of treatment with cimetidine have not been established and are likely to be patient-specific. Oral doses of 800 mg/d have been used. In addition to its potential for treatment, cimetidine may also have a role in prophylaxis of acute episodes by maintaining a baseline suppression of ALA synthase activity. Until well-designed, controlled clinical trials demonstrate its efficacy and compare it with other treatment options, cimetidine should be reserved for use only after standard treatment modalities have failed.