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Biomedical subjects

R C Dickson

Publications and source records attributed to R C Dickson.

At least 55 records · Page 3Linked to original sources
PubMed1997

Suppressor gene analysis reveals an essential role for sphingolipids in transport of glycosylphosphatidylinositol-anchored proteins in Saccharomyces cerevisiae.

Sphingolipids are normally necessary for growth of Saccharomyces cerevisiae cells, but mutant strains that bypass the need for sphingolipids have been identified. Such bypass mutants fail to grow under stressful conditions, including low pH (pH 4.1), when they lack sphingolipids. To begin to understand why sphingolipids seem to be necessary for coping with low-pH stress, we screened a genomic library and selected a suppressor gene, CWP2 (cell wall protein 2), that when present in multiple copies partially compensates for the lack of sphingolipids and enhances survival at low pH. To explain these results, we present evidence that sphingolipids are required for a normal rate of transport of glycosylphosphatidylinositol (GPI)-anchored proteins, including Cwp2 and Gas1/Gpg1, from the endoplasmic reticulum (ER) to the Golgi apparatus. The effect of sphingolipids is specific for transport of GPI-anchored proteins because no effect on the rate of transport of carboxypeptidase Y, a non-GPI-anchored protein, was observed. Since the Gasl protein accumulated in the ER with a GPI anchor in cells lacking sphingolipids, we conclude that sphingolipids are not necessary for anchor attachment. Therefore, sphingolipids must be necessary for a step in formation of COPII vesicles or for their transport to the Golgi apparatus. Our data identify the Cwp2 protein as a vital component in protecting cells from the stress of low pH.

Biological Transport↗
PubMed1997

Quality of life of hepatitis B and C patients after liver transplantation.

Liver transplantation is an accepted treatment for end-stage liver disease due to hepatitis C (HCV), but remains controversial for patients with hepatitis B(HBV). Recently, the use of aggressive hepatitis B immunoglobulin (HBIg) to maintain hepatitis B surface antibody (anti-HBs) titers greater than 500 IU/L has been reported to improve outcome of transplantation for hepatitis B. The aim of this study was to compare the quality of life of patients transplanted for HBV using this regimen of HBIg immunoprophylaxis (group 1) to patients transplanted for HCV (group 2). The State-Trait Anxiety Inventory (STAI), Sickness Impact Profile (SIP), and a work survey were administered to two groups of patients. The STAI measured anxiety while the SIP evaluated physical and psychosocial function. Lower scores indicated less anxiety and dysfunction. Questions regarding hours worked prior to illness and hours worked after transplantation were administered to both groups. Group 1 included a majority of patients who were hepatitis B e antigen (HBeAg) positive prior to transplantation. Survey response was 13:16 (81%) for group 1; and 17:24 (72%) for group 2. Group 1 revealed significantly lower scores than group 2 on the STAI and the overall SIP score. Group 1 reported working similar hours after transplantation as prior to illness while group 2 did not. Thus, patients transplanted for HBV and treated with aggressive HBIg immunoprophylaxis attained a higher quality of life than patients transplanted for HCV.

Activities of Daily Living↗
PubMed1996

Sphingolipid synthesis: identification and characterization of mammalian cDNAs encoding the Lcb2 subunit of serine palmitoyltransferase.

Synthesis of the ceramide portion of sphingolipids in animals has been hypothesized to be tightly regulated thereby controlling the rate of de novo sphingolipid formation. Regulation is predicted to occur at the first and committed biosynthetic step catalyzed by serine palmitoyltransferase (SPT, EC 2.3.1.50). This hypothesis remains unproven because SPT has been refractory to purification and subsequent characterization. To begin to test this hypothesis we have used a genetic strategy to isolate LCB2 homologs from the yeasts Kluyveromyces lactis and Schizosaccharomyces pombe and a cDNA homolog from humans and mice. Identity is supported by overall amino acid sequence similarity between the predicted proteins and the known Saccharomyces cerevisiae Lcb2 protein. In addition, a motif of 56 residues from the human protein functionally substituted for the corresponding region of the S. cerevisiae Lcb2 protein. The 56 residue motif was found to be unique to Lcb2 proteins. Likewise, the base sequence encoding it is unique to the human genome. Finally, a peptide sequence in the motif is known to be part of the catalytic domain of all members of the aminolevulinate synthase superfamily of proteins of which Lcb2 is a member. These data argue that this motif is part of the catalytic domain of SPT and is a signature of Lcb2 proteins. The mammalian LCB2 cDNAs provide valuable reagents for studying the Lcb2 subunit of SPT and for studying how ceramide synthesis is regulated.

Acyltransferases↗
PubMed1996

Improved outcome of orthotopic liver transplantation for chronic hepatitis B cirrhosis with aggressive passive immunization.

Passive immunization with hepatitis B surface antibody (anti-HBs) is important to prevent hepatitis B virus (HBV) recurrence after orthotopic liver transplantation for chronic HBV cirrhosis. Hepatitis B immune globulin (HBIG) dosing regimens have been poorly defined, utilize numerous routes of administration, and result in a high rate of HBV relapse and mortality. Twenty-five of 27 (93%) patients transplanted (four retransplants) for chronic HBV cirrhosis show no evidence of recurrent HBV (range, 2-55 months). Anti-HBs titers necessary to minimize the risk of hepatitis B surface antigen detectability were >500 IU/L for days 0 to 7, >250 IU/L for days 8 to 90, and >100 IU/L thereafter. Pretransplant HBV E antigen (HBeAG)-positive patients required more HBIG to achieve these goals than HBeAG-negative individuals. The elimination of anti-HBs changed continually for the initial 3 posttransplant months. The anti-HBs half-life increased from 0.7 days to 14.1 days. Anti-HBs elimination was significantly different in HBeAG+ and HBeAG- patients for the first week, but was subsequently indistinguishable after week 1. After 3 months, the half-life was statistically less for HBeAG+ patients, but the difference did not influence the clinical treatment regimens. Quantitative hepatitis B DNA levels did not predict the amount of HBIG required. HBV recurrence after orthotopic liver transplantation can be reduced by aggressive passive immunization. Pharmacokinetic analysis of anti-Hbs elimination can improve immunoglobulin therapy and prevent recurrence of clinical hepatitis.

Adult↗
PubMed1996

Clinical and histologic patterns of early graft failure due to recurrnet hepatitis C in four patients after liver transplantation.

Hepatitis C viral recurrence after orthotopic liver transplantation is almost universal. Hepatitis C induced graft failure may occur, but the clinical and histologic profiles are not well defined. The aim of this study was to describe the pattern of early graft failure in patients with recurrent hepatitis C after liver transplantation. Thirty patients with hepatitis C underwent liver transplantation from October 1989 through September 1994. Four patients were excluded because of death (2 patients), graft failure unrelated to hepatitis C (1 patient), and lost to follow-up (1 patient). Hepatitis C recurred in 24 of the 26 remaining patients. In 4 patients with hepatitis C virus recurrence and cholestasis, graft failure developed at 5.25, 11.0, 11.0, and 18.5 months. The medical records and liver biopsies were reviewed. In all 4 patients, a histologic pattern characterized by centrilobular ballooning degeneration developed and progressed to involve more than two-thirds of the lobules. Moderate to severe cholestasis and bridging fibrosis were present in all grafts at explant. Two patients had portal inflammation on 3-month biopsies consistent with viral hepatitis. All patients had mild macrovesicular steatosis, but only 1 patient had significant lymphoid aggregates. No patient had evidence of hepatic artery thrombosis. One patient had potential drug-induced cholestasis. One patient had 3 episodes of rejection that were not believed to contribute to graft loss. All 4 patients developed clinical features of hepatic failure and were retransplanted. Two patients had early recurrence of graft failure. We conclude that a pattern of progressive centrilobular ballooning degeneration, bridging fibrosis, and cholestasis occurs in some patients with hepatitis with early graft failure, similar to fibrosing cholestatic hepatitis seen in some transplant patients with recurrent hepatitis B.

Adult↗
PubMed1996

Hepatitis C virus in body fluids after liver transplantation.

Recurrence of hepatitis C virus (HCV) after liver transplantation is common and is associated with high blood levels of HCV RNA. Higher blood levels of HCV may promote body fluid expression of the virus. We tested 152 body fluid specimens from 33 patients with chronic hepatitis C, 21 of whom had undergone prior liver transplantation. All patients had hepatitis C viremia, as determined by a reverse-transcription polymerase chain reaction (PCR) to the 5' noncoding region. The virus was quantitated in serum by the branched chain DNA assay (bDNA). Body fluids (33 sputum, 33 saliva, 33 urine, 32 tear, 9 vaginal, and 12 semen samples) were analyzed using PCR for HCV RNA. Serum HCV RNA by bDNA in the posttransplantation group was 255 +/- 229 x 10(5) compared with 50 +/- 56 x 10(5) eq/mL in the patients who did not undergo transplantation (P = .01). All urine, tear, and semen specimens were negative for HCV RNA. Five of 21 (24%) posttransplantation patients had detectable HCV RNA using PCR in oral secretions compared with 0 of 12 patients who did not undergo transplantation (not statistically significant). However, 5 of 11 patients with serum HCV RNA by bDNA results greater than 150 x 10(5) eq/mL had positive RNA in oral secretions compared to 0 of 22 patients with bDNA less than 150 x 10(5) eq/mL (P = .01). Posttransplantation patients were more likely to have bDNA levels exceeding 150 x 10(5) eq/mL (11 of 21 v 1 of 12, P = .03). Patients within the first year of transplantation were particularly prone to viral RNA levels exceeding 150 x 10(5) eq/mL (8 of 9 v 3 of 12, P = .01). We conclude that HCV RNA can occasionally be detected using PCR in oral secretions after liver transplantation. This is more likely during the first year posttransplantation when blood levels of HCV RNA often exceed 150 x 10(5) eq/mL by the branched chain DNA assay. Whether or not these observations represent an increased risk of transmission of infection during the early posttransplantation period is not certain.

Adult↗
PubMed1996

Accuracy and significance of pretransplant liver volume measured by magnetic resonance imaging.

Measurement of liver volume in patients with advanced liver disease is used to gauge the appropriate size of donor organs and may have prognostic value. We sought to determine the accuracy of magnetic resonance imaging (MRI) in measuring liver volume in 19 adult patients under consideration for liver transplantation. We also correlated the liver volume determination to the clinical severity of disease. Liver volume was measured at MRI by averaging the calculated volumes from coronal and transverse breath-hold T1-weighted images. These results were compared to the explanted liver volume measured by fluid displacement and the explant mass. The correlation coefficient for MRI liver volume and the explant displacement volume was 0.90. The mean liver volume for Child-Pugh class AB by MRI was 1986 +/- 568 mL (1002-2470 mL) compared to 1433 +/- 379 mL (540-1889 mL) in Child-Pugh class C patients (p = .02). We conclude that MRI offers an anatomically accurate means of determining adult liver volume in vivo. Lower mean liver volumes were observed in Child-Pugh class C patients. In addition to its ability to provide tumor screening and vascular assessment, MRI is able to provide accurate determinations of liver volume in patients undergoing liver transplant evaluations.

Adult↗
PubMed1996

Variation between centers in technique and guidelines for liver biopsy.

Hospitals have few published guidelines to follow when performing a liver biopsy. In 1992, we began revising our protocol in an effort to institute new guidelines for our teaching hospitals. To assess the current practice of liver biopsy, we sent 500 multilingual questionnaires to international academic centers, and 85 U.S. centers were surveyed by telephone. The survey assessed: 1) patient preparation, 2) technical aspects of the biopsy, and 3) post-procedural care. One hundred and eighty international centers and 85 U.S. centers responded (total = 265). We found a wide variation in the practice of this surgical procedure at both national and international centers. Many Asian centers (73%) performed a bleeding time prior to liver biopsy. This practice was seen in only 36% of the U.S. centers. Most centers preferred platelet counts of 50,000/mm3 and above. The aspiration needle was more widely used in the U.S. (74%) and in many international centers, but Asian centers (61%) preferred a cutting needle. Thirty percent of Japanese centers performed more than 50% of their liver biopsies laparoscopically. Few laparoscopies were done at other centers. While about a quarter of the reported U.S., European, Asian, and South American centers observed patients for 4-6 hours after a biopsy, the majority of centers observed patients 10 hours or more. In addition to the wide variation seen, this survey provided us with an academic view of the contemporary practice of liver biopsy and an insight into how to redefine our present guidelines.

Academic Medical Centers↗
PubMed1996

Isolation and composition of inositolphosphorylceramide-type sphingolipids of hyphal forms of Candida albicans.

Hyphal forms of the human pathogen Candida albicans have been found to contain substantial quantities of phosphosphingolipids. These lipids were fractionated into three classes by normal-phase high-performance liquid chromatography. The first class contained equimolar amounts of phosphorus, inositol, phytosphingosines, and fatty acids; their composition and chromatographic behavior suggest that these compounds are inositolphosphorylceramides. The second class contained equimolar amounts of phosphorus, mannosylinositol, phytosphingosines, and fatty acids; their composition and chromatographic behavior indicate that these compounds are mannosylinositolphosphorylceramides. The third class of compounds contained phosphorus, mannosylinositol, inositol, phytosphingosines, and fatty acids in a molar ratio of 2:1:1:1:1; their composition and chromatographic behavior indicate that these compounds are mannosyldiinositolphosphorylceramides. Molecular species in each class differ in the composition of long chain bases and fatty acids; the most abundant long chain bases were C18 and C20 phytosphingosines, and the most abundant fatty acids were hydroxy and nonhydroxy C24-26. The array of sphingolipids in C. albicans is similar to that of Saccharomyces cerevisiae. Sphingolipids have been shown to be essential in S. cerevisiae, thus these lipids, which are not present in animals, offer a potentially unique target for antifungal chemotherapy against C. albicans.

Alkalies↗
PubMed1995

Sexual, vertical and household transmission of hepatitis C.

Hepatitis C infection is one of the most common forms of chronic liver disease. This increasingly recognized infection often presents in asymptomatic or mildly symptomatic individuals who are otherwise functional. Although sexual, vertical (mother to infant) and household routes of transmission are of perhaps minor concern in an epidemiologic sense, these potential problems are of considerable concern to most patients. Appropriate counseling in this setting depends on fully informing these patients of the low but possible risk of transmission through these routes. In this article, we have reviewed the current literature regarding these sources of hepatitis C infection.

Disease Transmission, Infectious↗
PubMed1994

The LCB2 gene of Saccharomyces and the related LCB1 gene encode subunits of serine palmitoyltransferase, the initial enzyme in sphingolipid synthesis.

The first and committed step in synthesis of the ceramide moiety of sphingolipids is catalyzed by serine palmitoyltransferase (EC 2.3.1.50), which condenses palmitoyl-CoA and serine to form 3-ketosphinganine. This step is thought to be tightly regulated to control the synthesis of sphingolipids, but data supporting this hypothesis are lacking mainly because the enzyme has resisted purification and consequent characterization. Rather than attempting to purify the enzyme from normal cells, we have taken a different tack and opted to try and overproduce the enzyme to facilitate its purification. Here we demonstrate that overproduction in Saccharomyces cerevisiae requires expression of LCB1, a previously isolated yeast gene, and LCB2, the isolation and characterization of which we describe. Several lines of evidence argue that both genes encode subunits of the enzyme; however, biochemical evidence will be needed to substantiate this hypothesis. Although overproduction was modest, 2- to 4-fold, it should now be possible to devise improved overproduction vectors for yeast or other host organisms.

Acyltransferases↗
PubMed1994

Antenatal vitamin K therapy of the low-birth-weight infant.

OBJECTIVE: The purpose of our study was to determine whether maternal vitamin K1 administered antenatally improved global coagulation parameters and the levels of specific vitamin K-dependent proteins in low-birth-weight infants. STUDY DESIGN: Thirty-three preterm mothers admitted in labor were assigned in a prospective, blinded fashion to receive either intramuscular vitamin K1 (17) or placebo (16). At delivery cord blood samples were tested for prothrombin time, activated partial thromboplastin time, factor II and protein C activity, and antigen levels. Statistical analysis was by Student t test. RESULTS: No statistically significant differences could be demonstrated with regard to group mean values for global tests (prothrombin time, activated partial thromboplastin time) or specific vitamin K-dependent protein levels (factor II, protein C) in newborns whose mothers received antenatal vitamin K compared with those who did not. CONCLUSION: These results would suggest that antenatal vitamin K1 therapy to mothers < 32 weeks' gestation has no significant effect on the level of vitamin K-dependent factors in the fetus.

Adolescent↗
PubMed1993

A suppressor gene that enables Saccharomyces cerevisiae to grow without making sphingolipids encodes a protein that resembles an Escherichia coli fatty acyltransferase.

Saccharomyces cerevisiae normally requires sphingolipid biosynthesis for growth; however, mutant strains lacking sphingolipids have been isolated by suppression of a genetic defect in sphingolipid long chain base biosynthesis. To begin to understand the nature of the suppressor(s) we isolated and characterized a suppressor gene, SLC1 (sphingolipid compensation). DNA sequence analysis showed that the wild type SLC1 allele differs from the suppressor allele by a single nucleotide which changes Gln-44 in the predicted wild type protein to Leu4-4 in the predicted SLC1-1 suppressor protein. The predicted SLC1 protein sequence is homologous to the 1-acyl-sn-glycerol-3-phosphate acyltransferase of Escherichia coli encoded by the plsC gene. The homology extends to function as well since the SLC1 gene complements the growth defect in an E. coli strain mutated in plsC. These results suggest that the SLC1 protein has a fatty acyltransferase activity. SLC1 thus may be the first eucaryotic sn2-acylglyceride fatty acyltransferase gene to be cloned. SLC strains grown in the absence of long chain base make novel phosphatidylinositol derivatives (Lester, R. L., Wells, G. B., Oxford, G., and Dickson, R. C. (1993) J. Biol. Chem. 268, 845-856) having a C26 fatty acid at the sn-2 position and the same polar head groups as normal sphingolipids. We postulate that the SLC1 suppressor allele encodes a variant enzyme with an altered substrate specificity that enables it to use a C26 in place of a C16/18 fatty acid precursor to acylate the sn-2 position of inositol-containing glycerolipids.

Acyltransferases↗
PubMed1993

Autoregulation of GAL4 transcription is essential for rapid growth of Kluyveromyces lactis on lactose and galactose.

Transcriptional induction of genes in the lactose-galactose regulon of the yeast Kluyveromyces lactis requires the GAL4 transcription activator protein. Previous data indicated that the concentration of GAL4 was tightly regulated under basal, inducing, and glucose repressing conditions but the mechanisms were unknown. In this paper we demonstrate that transcription of the GAL4 gene (KI-GAL4) increases 3- to 4-fold during induction of the regulon. This increase requires a KI-GAL4 binding site, UASG, in front of the KI-GAL4 gene, indicating that the KI-GAL4 protein autoregulates transcription of its own gene. Our data demonstrate that the autoregulatory circuit is essential for full induction of the lactose-galactose regulon and, hence, for rapid growth on lactose or galactose. Other data indicate that basal transcription of the KI-GAL4 gene is governed by unidentified promoter elements. The existence of the autoregulatory circuit reveals an important difference between the lactose-galactose regulon and its homologue in Saccharomyces cerevisiae, the melibiose-galactose regulon. This difference may have evolved in response to different selective pressures encountered by the two organisms.

Base Sequence↗
PubMed1993

Mutant strains of Saccharomyces cerevisiae lacking sphingolipids synthesize novel inositol glycerophospholipids that mimic sphingolipid structures.

Mutant strains of Saccharomyces cerevisiae, termed SLC, make no detectable sphingolipids when cultured without a sphingolipid long chain base such as phytosphingosine (Dickson, R.C., Wells, G.B., Schmidt, A., and Lester, R.L. (1990) Mol. Cell. Biol. 10, 2176-2181). When grown with phytosphingosine they make sphingolipids in normal amounts. SLC strains carry a secondary suppressor mutation that bypasses the need to synthesize a long chain base. Hypothetically, the suppressor mutation could function by mutating a gene whose protein product required a sphingolipid for function, by increasing the level of one or more endogenous lipids, or by making new lipid(s). Here we demonstrate that SLC strains make novel inositol glycerophospholipids when cultured without a long chain base. The novel lipids are phosphatidylinositol (PI), mannosyl-PI, and inositol-P-(mannosyl-PI), containing 1 mol of C26 fatty acid, ordinarily found in yeast sphingolipids but not usually found in glycerophospholipids; the C26 fatty acid appears to be located at the SN-2 position of the glycerol. In addition, mono-fattyacyl versions of these three compounds were also identified. The polar head groups and hydrophobic portions of these novel lipids are strikingly similar to S. cerevisiae sphingolipids found in wild-type cells. We speculate that the novel lipids structurally mimic sphingolipids and thereby compensate for some sphingolipid function(s) necessary for growth.

Chromatography, High Pressure Liquid↗