Primary bile acid malabsorption (PBAM) is an idiopathic intestinal disorder associated with congenital diarrhea, steatorrhea, interruption of the enterohepatic circulation of bile acids, and reduced plasma cholesterol levels. The molecular basis of PBAM is unknown, and several conflicting mechanisms have been postulated. In this study, we cloned the human ileal Na ϩ /bile acid cotransporter gene ( SLC10A2 ) and employed single-stranded conformation polymorphism analysis to screen for PBAM-associated mutations. Four polymorphisms were identified and sequenced in a family with congenital PBAM. One allele encoded an A171S missense mutation and a mutated donor splice site for exon 3. The other allele encoded two missense mutations at conserved amino acid positions, L243P and T262M. In transfected COS cells, the L243P, T262M, and double mutant (L243P/ T262M) did not affect transporter protein expression or trafficking to the plasma membrane; however, transport of taurocholate and other bile acids was abolished. In contrast, the A171S mutation had no effect on taurocholate uptake. The dysfunctional mutations were not detected in 104 unaffected control subjects, whereas the A171S was present in 28% of that population. These findings establish that SLC10A2 mutations can cause PBAM and underscore the ileal Na ϩ /bile acid cotransporter's role in intestinal reclamation of bile acids. ( J. Clin. Invest . 1997. 99:1880-1887.)

The enterohepatic circulation of bile acids is maintained by Na+-dependent transport mechanisms. To better understand these processes, a full-length human ileal Na+-bile acid cotransporter cDNA was identified using rapid amplification of cDNA ends and genomic cloning techniques. Using Northern blot analysis to determine its tissue expression, we readily detected the ileal Na+-bile acid cotransporter mRNA in terminal ileum and kidney. Direct cloning and mapping of the transcriptional start sites confirmed that the kidney cDNA was identical to the ileal Na+-bile acid cotransporter. In transiently transfected COS cells, ileal Na+-bile acid cotransporter-mediated taurocholate uptake was strictly Na+ dependent and chloride independent. Analysis of the substrate specificity in transfected COS or CHO cells showed that both conjugated and unconjugated bile acids are efficiently transported. When the inhibition constants for other potential substrates such as estrone-3-sulfate were determined, the ileal Na+-bile acid cotransporter exhibited a narrower substrate specificity than the related liver Na+-bile acid cotransporter. Whereas the multispecific liver Na+-bile acid cotransporter may participate in hepatic clearance of organic anion metabolites and xenobiotics, the ileal and renal Na+-bile acid cotransporter retains a narrow specificity for reclamation of bile acids.

is an immunostimulatory cytokine with antitumor activity in preclinical animal models. A phase I study of recombinant human IL-18 (rhIL-18) was done to determine the toxicity, pharmacokinetics, and biological activities of rhIL-18 in patients with advanced cancer. Experimental Design: Cohorts of patients were given escalating doses of rhIL-18, each administered as a 2-hour i.v. infusion on 5 consecutive days. Toxicities were graded using standard criteria. Serial blood samples were obtained for pharmacokinetic and pharmacodynamic measurements. Results: Twenty-eight patients (21with renal cell cancer, 6 with melanoma, and 1with Hodgkin's lymphoma) were given rhIL-18 in doses ranging from 3 to 1,000 Ag/kg. Common side effects included chills, fever, nausea, headache, and hypotension. Common laboratory abnormalities included transient, asymptomatic grade 1to 2 neutropenia, thrombocytopenia, anemia, hypoalbuminemia, hyponatremia, and elevations in liver transaminases. One patient in the100 Ag/kg cohort experienced transient grade 3 hypotension and grade 2 bradycardia during the first infusion of rhIL-18. No other dose-limiting toxicities were observed. Plasma concentrations of rhIL-18 increased with increasing dose, and 2.5-fold accumulation was observed with repeated dosing. Biological effects of rhIL-18 included transient lymphopenia and increased expression of activation antigens onlymphocytes and monocytes. Increases in serum concentrations of IFN-g, granulocyte macrophage colony-stimulating factor, IL-18 bindingprotein, and soluble Fasligand were observed. Two patients experiencedunconfirmed partial responses after rhIL-18 treatment. Conclusions: rhIL-18 can be safely given in biologically active doses to patients with advanced cancer. A maximum tolerated dose of rhIL-18 was not determined. Further clinical studies of rhIL-18 are warranted. Interleukin (IL)-18 is an immunostimulatory cytokine thatregulates both innate and adaptive immune responses (1, 2). The effects of IL-18 are mediated through a specific cell surface receptor complex composed of at least two subunits, an a chain (IL-1Rrp1) and a h chain (AcPL; ref. IL-18 has antitumor activity in animal models (8 -12). Regression of tumors in IL-18-treated animals is not dependent on the presence of IFN-g or IL-12 but seems to require an intact Fas/Fas ligand pathway (9, 10). The antitumor effects of IL-18 in multiple animal models provided the rationale for investigation of recombinant human (rh) IL-18 in cancer immunotherapy. We describe the results of the first clinical trial of rhIL-18 in patients with cancer. Materials and MethodsPatient selection. Eligible patients included adults (ages >18 years) with histologically confirmed, locally advanced, or metastatic solid tumor or lymphoma that was measurable and refractory to standard