ELEVATED PHENYLACETIC ACID LEVELS DO NOT CORRELATE WITH ADVERSE EVENTS IN PATIENTS WITH UREA CYCLE DISORDERS OR HEPATIC ENCEPHALOPATHY AND CAN BE PREDICTED BASED ON THE PLASMA PAA TO PAGN RATIO

Background Phenylacetic acid (PAA) is the active moiety in sodium phenylbutyrate (NaPBA) and glycerol phenylbutyrate (GPB, HPN-100), both are approved for treatment of urea cycle disorders (UCDs) - rare genetic disorders characterized by hyperammonemia. PAA is conjugated with glutamine in the liver to form phenylacetyleglutamine (PAGN), which is excreted in urine. PAA plasma levels ≥500 μg/dL have been reported to be associated with reversible neurological adverse events (AEs) in cancer patients receiving PAA intravenously. Therefore, we have investigated the relationship between PAA levels and neurological AEs in patients treated with these PAA pro-drugs as well as approaches to identifying patients most likely to experience high PAA levels. Methods The relationship between nervous system AEs, PAA levels and the ratio of plasma PAA to PAGN were examined in 4683 blood samples taken serially from: [1] healthy adults [2], UCD patients ≥2 months of age, and [3] patients with cirrhosis and hepatic encephalopathy (HE). The plasma ratio of PAA to PAGN was analyzed with respect to its utility in identifying patients at risk of high PAA values. Results Only 0.2% (11) of 4683 samples exceeded 500 ug/ml. There was no relationship between neurological AEs and PAA levels in UCD or HE patients, but transient AEs including headache and nausea that correlated with PAA levels were observed in healthy adults. Irrespective of population, a curvilinear relationship was observed between PAA levels and the plasma PAA:PAGN ratio, and a ratio > 2.5 (both in μg/mL) in a random blood draw identified patients at risk for PAA levels > 500 μg/ml. Conclusions The presence of a relationship between PAA levels and reversible AEs in healthy adults but not in UCD or HE patients may reflect intrinsic differences among the populations and/or metabolic adaptation with continued dosing. The plasma PAA:PAGN ratio is a functional measure of the rate of PAA metabolism and represents a useful dosing biomarker

Mechanisms of T cell organotropism

F.M.M.-B. is supported by the British Heart Foundation, the Medical Research Council of the UK and the Gates Foundation

Effect of antisense oligonucleotides on the expression of hepatocellular bile acid and organic anion uptake systems in Xenopus laevis oocytes

A Na(+)-dependent bile acid (Na+/taurocholate co-transporting polypeptide; Ntcp) and a Na(+)-independent bromosulphophthalein (BSP)/bile acid uptake system (organic-anion-transporting polypeptide; oatp) have been cloned from rat liver by using functional expression cloning in Xenopus laevis oocytes. To evaluate the extent to which these cloned transporters could account for overall hepatic bile acid and BSP uptake, we used antisense oligonucleotides to inhibit the expression of Ntcp and oatp in Xenopus laevis oocytes injected with total rat liver mRNA. An Ntcp-specific antisense oligonucleotide co-injected with total rat liver mRNA blocked the expression of Na(+)-dependent taurocholate uptake by approx. 95%. In contrast, an oatp-specific antisense oligonucleotide when co-injected with total rat liver mRNA had no effect on the expression of Na(+)-dependent taurocholate uptake, but it blocked Na(+)-independent uptake of taurocholate by approx. 80% and of BSP by 50%. Assuming similar expression of hepatocellular bile acid and organic anion transporters in Xenopus laevis oocytes, these results indicate that Ntcp and oatp respectively represent the major, if not the only, Na(+)-dependent and Na(+)-independent taurocholate uptake systems in rat liver. By contrast, the cloned oatp accounts for only half of BSP transport, suggesting that there must be additional, non-bile acid transporting organic anion uptake systems in rat liver