type II patients have a less severe form of the disease because The aim of this study was to test a possible form of of residual enzyme activity. Genetic analysis of a number of therapy that could be used in the management of uncon-Crigler-Najjar patients 3 has revealed that type I patients jugated hyperbilirubinemia. We hypothesized that unhave mutations in both alleles of the UGT1 gene that lead conjugated bilirubin (UCB) can permeate the intestinal to complete inactivation or absence of the enzyme, whereas, wall and can thus be secreted with the feces. We have in type II patients, the mutations in the gene may be such previously observed that UCB binds to amorphous calthat the enzyme has low residual activity (õ5%). Accumulacium phosphate in vitro. Orally ingested amorphous caltion of unconjugated bilirubin (UCB) is potentially toxic and, cium phosphate may act as a trapping agent for bilirubin if not treated, can lead to mental retardation and death. 4-6 in the intestine, thereby preventing back-diffusion Besides liver transplantation, the only therapy known so far across the intestinal wall. In this study, we tested whether feeding calcium phosphate leads to enhanced is phototherapy. Light in the blue range (wavelength range, excretion of unconjugated bilirubin in Gunn rats. When 400-500 nm) induces formation of photoproducts of bilirubin. a purified control diet was substituted by a high calcium These photoproducts can be excreted in bile. [7][8][9] Type II paphosphate diet, a decrease in bilirubin levels of 30% to tients can be treated with phenobarbital, an agent that is 50% in male Gunn rats and of 23% in female rats was thought to induce the residual activity of bilirubin-uridine observed. The fecal output of bilirubin was more than diphosphate-glucuronosyltransferase. Both therapies have doubled in Gunn rats in the first 3 days after the normal disadvantages, and phototherapy becomes less effective with diet had been replaced by the high calcium-phosphate age. [10][11][12][13] Therefore, the goal of our research was to find possidiet. The biological half-life of 3 H-labeled bilirubin in ble new therapies for this disease. Gunn rats have the same blood was 89.8 { 17.2 hours in rats fed the purified conenzyme deficiency as Crigler-Najjar patients and were used trol diet and 50.9 { 1.4 hours in rats fed the high calcium as a model for the disease. phosphate diet (P Å .004). After 30 weeks, plasma biliru-
In Gunn rats and in Crigler-Najjar patients, the plasma bin levels were still significantly lower in Gunn rats fed bilirubin level is constant. This indicates that an equilibrium a high calcium phosphate diet. No differences were exists between bilirubin production and excretion. The bilirufound in plasma concentrations of calcium, magnesium, bin production rate in Crigler-Najjar patients is equal to that phosphate, urea, and creatinine in both Gunn rats and in normal healthy individuals. 14 Thus, the amount of biliru-Wistar rats on control or high calcium phosphate diets. bin and bilirubin breakdown products excreted per day will This therapy might be useful in the management of be the same, despite the fact that the bilirubin pool is much Crigler-Najjar patients, for example, as an adjunct to larger and turnover of bilirubin is much slower in Gunn rats phototherapy. (HEPATOLOGY 1996;24:620-626.) and Crigler-Najjar patients. Consequently, alternative metabolic pathways for bilirubin must exist in patients with this syndrome. Two major hypotheses are postulated that may The Crigler-Najjar syndrome is an inherited disease in not be mutually exclusive. First, unconjugated bilirubin is which unconjugated bilirubin, the major breakdown product thought to be oxidized by microsomal mixed-function monoof hemoglobin, cannot be excreted by the body in the normal oxygenases in the liver, probably cytochrome P450 IA1. The way and accumulates in blood and tissues. 1,2 Normally, conjupolar breakdown products are subsequently excreted in bile. gation of bilirubin with glucuronic acid in the liver leads Stimulation of this putative pathway is possible by intraperito exposure of negative charges, which makes excretion of toneal administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin bilirubin in bile possible. In Crigler-Najjar patients, the enin Gunn rats. 15 Unfortunately, this drug is carcinogenic and zyme needed for this reaction, bilirubin-uridine diphosphate-glucuronosyltransferase, is deficient. Two types of cannot be used as a therapy for Crigler-Najjar disease. Until this disease are distinguished 2 : type I patients are the most now, no drug has been found that is equally effective but less severely affected because the enzyme activity is absent, and toxic. Second, UCB is thought to diffuse from the blood across the intestinal wall into the intestinal lumen and is excreted via the feces. 14,16 This pathway is not very efficient. From studies in rats, 17 neonates, 18 and humans [19][20][21] it is known that Abbreviations: UCB, unconjugated bilirubin; HPLC, high-pressure liquid chromatogra-UCB can be reabsorbed from the intestinal lumen. We invesphy.