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We have recently shown in vitro that the peroxisomal fraction of a rat liver homogenate has the highest capacity to beta-oxidize prostaglandins. In order to evaluate the relative importance of peroxisomes for this conversion also in vivo, we administered [3H]prostaglandin F2 alpha to an infant suffering from Zellweger syndrome, a congenital disorder characterized by the absence of intact peroxisomes. As a control, labeled compound was administered to two healthy volunteers. Urine was collected, fractionated on a SEP-PAK C18 cartridge, and subjected to reversed-phase high-performance liquid chromatography. The Zellweger patient was found to excrete prostaglandin metabolites considerably less polar than those of the control subjects. The major urinary metabolite in the control subjects was practically absent in the urine from the Zellweger patient. The major urinary prostaglandin F2 alpha metabolite from the Zellweger patient was identified as an omega-oxidized C20-prostaglandin, 9,11-dihydroxy-15-oxoprost-5-ene-1,20-dioic acid. The major urinary prostaglandin F2 alpha metabolite from the control subjects had chromatographic properties of a tetranor (C16) prostaglandin, in accordance with earlier published data. The present results, in combination with our previous in vitro data, indicate that peroxisomal beta-oxidation is of major importance for in vivo chain shortening of prostaglandins.

Based on in vitro work with rat liver, we recently suggested that the peroxisomal fraction is most important for the oxidation of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) into cholic acid. The cerebro-hepato-renal syndrome of Zellweger is a fatal recessive autosomal disorder, the most characteristic histological feature of which is a virtual absence of peroxisomes in liver and kidneys. This disease offers a unique opportunity to evaluate the relative importance of peroxisomes in bile acid biosynthesis. A child with Zellweger syndrome was studied in the present work. In accordance with previous work, there was a considerable accumulation of THCA, 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acid (24-OH-THCA), 3 alpha, 7 alpha, 12 alpha-trihydroxy-27-carboxymethyl-5 beta-cholestan-26-oic acid (C29-dicarboxylic acid), and 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid in serum. In addition, a tetrahydroxylated 5 beta-cholestanoic acid with all the hydroxyl groups in the steroid nucleus was found. 3H-Labeled 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol was administered intravenously together with 14C-labeled cholic acid. There was a rapid incorporation of 3H in THCA and a slow incorporation into cholic acid. The specific radioactivity of 3H in THCA was about one magnitude higher than that in cholic acid. The conversion was evaluated by following the increasing ratio between 3H and 14C in biliary cholic acid. The rate of incorporation of 3H in cholic acid was considerably less than previously reported in experiments with healthy subjects, and the maximal conversion of the triol into cholic acid was only 15-20%. About the same rate of conversion was found after oral administration of 3H-THCA. Both in the experiment with 3H-5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol and with 3H-THCA, there was an efficient incorporation of 3H in the above unidentified tetrahydroxylated 5 beta-cholestanoic acid. There was only slow incorporation of radioactivity into 24-OH-THCA and into the C29-dicarboxylic acid. From the specific activity decay curve of 14C in cholic acid obtained after intravenous injection of 14C-cholic acid, the pool size of cholic acid was calculated to be 24 mg/m2 and the daily production rate to 9 mg/m2 per d. This corresponds to a reduction of approximately 85 and 90%, respectively, when compared with normal infants. It is concluded that liver peroxisomes are essential in the normal conversion of THCA to cholic acid. In the Zellweger syndrome this conversion is defective and as a consequence the accumulated THCA is either excreted as such or transformed into other metabolites by hydroxylation or side chain elongation. The accumulation of THCA, as well as the similar rate of conversion of 5 beta-cholestane-3 alpha,7 alpha.12 alpha-triol and THCA into cholic acid, support the contention that the 26-hydroxylase pathway with intermediate formation of THCA is the most important pathway for formation of cholic acid in man.

The last step in bile acid formation involves conversion of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) into cholic acid and 3 alpha,7 alpha-dihydroxy-5 beta-cholestanoic acid (DHCA) into chenodeoxycholic acid. The peroxisomal fraction of rat and human liver has the highest capacity to catalyze these reactions. Infants with Zellweger syndrome lack liver peroxisomes, and accumulate 5 beta-cholestanoic acids in bile and serum. We recently showed that such an infant had reduced capacity to convert a cholic acid precursor, 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol into cholic acid. 7 alpha-Hydroxy-4-cholesten-3-one is a common precursor for both cholic acid and chenodeoxycholic acid. Intravenous administration of [3H]7 alpha-hydroxy-4-cholesten-3-one to an infant with Zellweger syndrome led to a rapid incorporation of 3H into biliary THCA but only 10% of 3H was incorporated into cholic acid after 48 h. The incorporation of 3H into DHCA was only 25% of that into THCA and the incorporation into chenodeoxycholic acid approximately 50% of that in cholic acid. The conversion of intravenously administered [3H]THCA into cholic acid in another infant with Zellweger syndrome was only 7%. There was a slow conversion of THCA into 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-C29-dicarboxylic acid. The pool size of both cholic- and chenodeoxycholic acid was markedly reduced. Preparations of liver from two patients with Zellweger syndrome had no capacity to catalyze conversion of THCA into cholic acid. There was, however, a small conversion of DHCA into chenodeoxycholic acid and into THCA. It is concluded that liver peroxisomes are important both for the conversion of THCA into cholic acid and DHCA into chenodeoxycholic acid.