Critical role of vitamin D in sulfate homeostasis: regulation of the sodium-sulfate cotransporter by 1,25-dihydroxyvitamin D3.

As the fourth most abundant anion in the body, sulfate plays an essential role in numerous physiological processes. One key protein involved in transcellular transport of sulfate is the sodium-sulfate cotransporter NaSi-1, and previous studies suggest that vitamin D modulates sulfate homeostasis by regulating NaSi-1 expression. In the present study, we found that, in mice lacking the vitamin D receptor (VDR), NaSi-1 expression in the kidney was reduced by 72% but intestinal NaSi-1 levels remained unchanged. In connection with these findings, urinary sulfate excretion was increased by 42% whereas serum sulfate concentration was reduced by 50% in VDR knockout mice. Moreover, levels of hepatic glutathione and skeletal sulfated proteoglycans were also reduced by 18 and 45%, respectively, in the mutant mice. Similar results were observed in VDR knockout mice after their blood ionized calcium levels and rachitic bone phenotype were normalized by dietary means, indicating that vitamin D regulation of NaSi-1 expression and sulfate metabolism is independent of its role in calcium metabolism. Treatment of wild-type mice with 1,25-dihydroxyvitamin D3 or vitamin D analog markedly stimulated renal NaSi-1 mRNA expression. These data provide strong in vivo evidence that vitamin D plays a critical role in sulfate homeostasis. However, the observation that serum sulfate and skeletal proteoglycan levels in normocalcemic VDR knockout mice remained low in the absence of rickets and osteomalacia suggests that the contribution of sulfate deficiency to development of rickets and osteomalacia is minimal.

Ursodeoxycholic acid inhibits Ras mutations, wild-type Ras activation, and cyclooxygenase-2 expression in colon cancer.

K-ras mutations occur frequently in colon cancer and contribute to autonomous growth. In the azoxymethane (AOM) model of colon cancer, in addition to K-ras mutations, we have shown that wild-type (WT) Ras can be activated by upstream pathways, including, e.g., signaling by ErbB receptors. Tumors with mutant or activated WT Ras had increased cyclooxygenase-2 (Cox-2) expression. We have also shown that ursodeoxycholic acid (UDCA) prevented AOM-induced colon cancer and suppressed Cox-2 induction. In this study, we examined the role of Ras in Cox-2 inhibition by UDCA. Rats were fed AIN-76A chow alone, or supplemented with 0.4% UDCA, and received 20 mg/kg AOM i.p. weekly x 2 weeks. At 40 weeks, rats were sacrificed, and tumors were harvested. K-ras mutations were assessed by primer-mediated RFLP, allele-specific oligonucleotide hybridization, and direct DNA sequencing. Ras was immunoprecipitated and defined as activated if [Ras - GTP/(Ras - GTP + Ras - GDP)] was >3 SD above normal colonocytes. Cox-2 mRNA was determined by reverse transcription-PCR, and protein expression was assessed by Western blotting and immunostaining. In the AOM alone group, Ras was activated by mutations in 8 of 30 (27%) tumors, and WT Ras was activated in 7 of 30 (23%) tumors. UDCA significantly suppressed the incidence of tumors with mutant Ras (1 of 31, 3.2%; P < 0.05) and totally abolished the development of tumors with activated WT Ras (0 of 10; P < 0.05). In the AOM alone group, Cox-2 was up-regulated >50-fold in tumors with normal Ras activity and further enhanced in tumors with mutant or signaling-activated Ras. UDCA significantly inhibited Cox-2 protein and mRNA levels in tumors with normal Ras activity. In summary, we have shown for the first time that UDCA suppressed the development of tumors with Ras mutations and blocked activation of WT Ras. Furthermore, UDCA inhibited Cox-2 induction by Ras-dependent and -independent mechanisms.

Serum phosphorus levels predict clinical outcome in fulminant hepatic failure.

The aim of this pilot study was to evaluate the incidence of hypophosphatemia and its association with clinical outcome in fulminant hepatic failure (FHF). Patients with FHF referred for orthotopic liver transplantation (OLT) between January, 1991 and May, 2002 were identified. FHF was defined as the development of coagulopathy and encephalopathy within 8 weeks of onset of jaundice. Demographic and laboratory data, including serum phosphate, calcium, magnesium, creatinine, and PT/INR were obtained from medical records. Clinical outcomes (death, OLT, or hepatic recovery) and associated morbidities (renal failure, bleeding, and sepsis) also were noted. Thirty-eight patients, 8 men and 30 women, aged 34 +/- 4 years, were included in the study. Hypophosphatemia (< 2.5 mg/dL) developed in 33 of 38 (87%) patients within 10 days of referral. Twelve patients (32%) died, 14 patients (37%) underwent OLT, and 12 patients (32%) recovered. The mean nadir serum phosphorus level was significantly lower in those who recovered compared with those who either died or required OLT (1.18 +/- 0.54 versus 1.79 +/- 1.00 mg/dL; P =.02). A trend toward lower mean serum phosphorus level also was noted in those who recovered compared with those who died (1.18 +/- 0.54 versus 1.96 +/- 1.35 mg/dL; P =.09). Serum phosphorus levels > 2.5 mg/dL was a predictor of mortality, and when used alone, was equivalent to the King's College Criteria. In conclusion, hypophosphatemia occurred frequently in patients with FHF. Lower serum phosphorus levels were observed in patients who recovered as compared with those who died or required OLT, and may be associated with recovery of hepatic function. The greater decline in serum phosphorus level in those who recover hepatic function may represent cellular use of phosphorus during hepatocyte regeneration.