Humans use two sodium-ascorbate cotransporters (hSVCT1 and hSVCT2) for transporting the dietary essential micronutrient ascorbic acid, the reduced and active form of vitamin C. Although the human liver plays a pivotal role in regulating and maintaining vitamin C homeostasis, vitamin C transport physiology and regulation of the hSVCT systems in this organ have not been well defined. Thus, this research used a human hepatic cell line (HepG2), confirming certain results with primary human hepatocytes and determined the initial rate of ascorbic acid uptake to be Na(+) gradient, pH dependent, and saturable as a function of concentration over low and high micromolar ranges. Additionally, hSVCT2 protein and mRNA are expressed at higher levels in HepG2 cells and native human liver, and the cloned hSVCT2 promoter has more activity in HepG2 cells. Results using short interfering RNA suggest that in HepG2 cells, decreasing hSVCT2 message levels reduces the overall ascorbic acid uptake process more than decreasing hSVCT1 message levels. Activation of PKC intracellular regulatory pathways caused a downregulation in ascorbic acid uptake not mediated by a single predicted PKC-specific amino acid phosphorylation site in hSVCT1 or hSVCT2. However, PKC activation causes internalization of hSVCT1 but not hSVCT2. Examination of other intracellular regulatory pathways on ascorbic acid uptake determined that regulation also potentially occurs by PKA, PTK, and Ca(2+)/calmodulin, but not by nitric oxide-dependent pathways. These studies are the first to determine the overall ascorbic acid uptake process and relative expression, regulation, and contribution of the hSVCT systems in human liver epithelial cells.

This case describes a patient presenting with acute onset papilledema, subacute strokes resulting in upper extremity weakness and numbness, arthritis, maculopapular rash, depressed C4 and CH50, and a high titer anti-double-stranded DNA antibody. The patient was given the diagnosis of probable systemic lupus erythematosus, which was supported by the Systemic Lupus International Collaborating Clinics (SLICC) criteria. He was aggressively treated for neuropsychiatric lupus (NPSLE) with pulse dose steroids and a dose of intravenous cyclophosphamide. Blood cultures drawn on admission later grew out 2/4 bottles of Gram-variable bacteria, speciated as Brucella melitensis by PCR. Serum Brucella serologies were also positive. On further evaluation, the patient noted a history of eating unpasteurized cheese in Mexico. Given these additional findings, the patient's presentation was most consistent with a diagnosis of neurobrucellosis. Steroids were tapered off, no further doses of cyclophosphamide were given, and a prolonged course of intravenous and oral antibiotic therapy was administered, resulting in complete resolution of the patient's presenting symptoms.

Ascorbic acid (AA), the reduced active form of vitamin C, is transported by two sodium‐ascorbate co‐transporters (SVCT1 & 2). Humans do not synthesize AA and the essential micronutrient is both an antioxidant and cofactor for several enzymes. The human liver participates in regulating and maintaining body AA homeostasis. Using a human hepatic cell line (HepG2) we determined, the characteristics of AA uptake, the expression levels of the hSVCT systems and characterized the hSVCT promoters. The initial rate of ascorbic acid uptake by HepG2 cells was: 1) Na+ gradient, pH, and energy dependent, 2) saturable with a Km of 10μM 3) not inhibited by membrane transport inhibitors 4) not stimulated by glucocorticoids 5) PKC, PKA, PTK, Ca‐Camodulin dependant, but not NO dependant. Expression of hSVCT1 and hSVCT2 protein and mRNA in both HepG2 cells and human liver was determined; hSVCT2 is expressed at higher levels. Using cloned promoter fragments, transcriptional activity was determined in HepG2 cells and the minimal regions required for basal activity mapped. In addition, using promoter mutagenesis we determined that Hepatic Nuclear Factor sites in the hSVCT1 promoter and Sp1/KLF sites in the hSVCT2 promoter were essential for activities. Results from these studies are the first determination of the AA uptake process, relative expression of the hSVCT systems and characterization of the hSVCT promoters in human liver cells.

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