Growth of B95-8 cells and expression of Epstein-Barr virus lytic phase in serum-free medium.

Epstein-Barr virus (EBV)-transformed tamarin (Saguinus oedipus) cells (B95-8) were selected for growth in medium with reduced serum and then transferred to serum-free medium which consisted of RPMI 1640 supplemented with insulin, transferrin, and selenium. Serum-free cells in continuous passage for 1 year had a morphology, growth rate, and culture density which approached those of B95-8 cells grown with serum. The cells expressed virus-induced antigens, including the EBV-associated DNA polymerase. Cells exposed to EBV-inducing agents, n-butyric acid and phorbol 12-myristate-13-acetate, produced transforming virus with titers comparable to those of cultures grown with serum. These findings demonstrate that serum is neither required for the growth of B95-8 cells nor necessary for induction or full expression of the EBV lytic phase in these cells.     

The frequency of gonadotropin-releasing hormone secretion regulates expression of alpha and luteinizing hormone beta-subunit messenger ribonucleic acids in male rats

The influence of GnRH pulse frequency on LH subunit mRNA concentrations was examined in castrate, testosterone-replaced male rats. GnRH pulses (25 ng/pulse) or saline to controls, were given via a carotid cannula at intervals of 7.5-240 min for 48 h. alpha and LH beta mRNA concentrations were 109 +/- 23 and 30 +/- 5 pg cDNA bound/100 micrograms pituitary DNA, respectively, in saline controls. GnRH pulse intervals of 15, 30, and 60 min resulted in elevated alpha and LH beta mRNAs (P less than 0.01) and maximum responses (4-fold, alpha; 3-fold, LH beta) were seen after the 30-min pulses. Acute LH release to the last GnRH pulse was seen after the 15-, 30-, and 60-min pulse intervals. In contrast, LH subunit mRNAs were not increased and acute LH release was markedly impaired after the rapid (7.5 min) or slower (120 and 240 min) pulse intervals. Equalization of total GnRH dose/48 h using the 7.5- and 240-min intervals did not increase LH subunit mRNAs to levels produced by the optimal 30-min interval. These data indicate that the frequency of the pulsatile GnRH stimulus regulates expression of alpha and LH beta mRNAs in male rats. Further, GnRH pulse frequencies that increase subunit mRNA concentrations are associated with continuing LH responsiveness to GnRH.     

Acetaldehyde-mediated hepatic lipid peroxidation: role of superoxide and ferritin

Evidence in alcoholics as well as in experimental models support the role of hepatic lipid peroxidation in the pathogenesis of alcohol-induced liver injury, but the mechanism of this injury is not fully delineated. Previous studies of the metabolism of ethanol by alcohol dehydrogenase revealed iron mobilization from ferritin that was markedly stimulated by superoxide radical generation by xanthine oxidase. Peroxidation of hepatic lipid membranes (assessed as malondialdehyde production) was studied during in vitro alcohol metabolism by alcohol dehydrogenase. Peroxidation was initiated by acetaldehyde-xanthine oxidase, stimulated by ferritin, and inhibited by superoxide dismutase or chelation or iron with desferrioxamine. In conclusion, lipid peroxidation may be initiated during the metabolism of ethanol by alcohol dehydrogenase by an iron-dependent acetaldehyde-xanthine oxidase mechanism.     

Pyridinium crosslinks of bone collagen and their location in peptides isolated from rat femur

The relative proportions of pyridinoline and deoxypyridinoline in bone showed large species variations, although the total number of pyridinium crosslinks in rat, rabbit and bovine bone collagen was only 25-30% of that found in articular cartilage. Three pyridinium-containing peptides were isolated from cyanogen bromide digests of rat femoral bone and were characterized by their Mr values and amino-acid compositions. The results showed that pyridinoline and its deoxy analogue were equally distributed at two locations stabilizing the 4D stagger through interactions involving both the N- and C-terminal telopeptide regions. Less than stoichiometric amounts of pyridinium crosslinks were present in the peptides, suggesting that the isolated peptides contained additional (unidentified) maturation products of the bifunctional, reducible crosslinks.     

Catabolism of neurotensin in the epithelial layer of porcine small intestine

The mammalian small intestine is both a source and a site of degradation of neurotensin. Metabolites produced by incubation of the peptide with dispersed enterocytes from porcine small intestine were isolated by high-performance liquid chromatography and identified by amino-acid analysis. The principal sites of cleavage were at the Tyr-11-Ile-12 bond, generating neurotensin-(1-11), and at the Pro-10-Tyr-11 bond, generating neurotensin-(1-10). The corresponding COOH-terminal fragments, neurotensin-(11-13) and -(12-13) were metabolized further. Formation of neurotensin-(1-11) and -(1-10) was completely inhibited by phosphoramidon (Ki = 6 nM), an inhibitor of endopeptidase 24.11, but not by captopril, an inhibitor of peptidyl dipeptidase A. Incubation of neurotensin with purified endopeptidase 24.11 from pig stomach also resulted in cleavage of the Tyr-11-Ile-12 and Pro-10-Tyr-11 bonds. A minor pathway of cell-surface-mediated degradation was the phosphoramidon-insensitive cleavage of the Tyr-3-Glu-4 bond, generating neurotensin-(1-3) and neurotensin-(4-13). No evidence for specific binding sites (putative receptors) for neurotensin was found either on the intact enterocyte or on vesicles prepared from the basolateral membranes of the cells. Neurotensin-(1-8), the major circulating metabolite, was not formed when neurotensin(1-13) was incubated with cells, but represented a major metabolite (together with neurotensin-(1-10] when neurotensin-(1-11) was used as substrate. The study has shown that degradation of neurotensin in the epithelial layer of the small intestine is mediated principally through the action of endopeptidase 24.11, but this enzyme is probably not responsible for the production of the neurotensin fragments detected in the circulation.     

Hydrolysis of N3-methyl-2'-deoxycytidine: model compound for reactivity of protonated cytosine residues in DNA

Protonation of cytosine residues at physiological pH may occur in DNA as a consequence of both alkylation and aberrant base-pair formation. When cytosine derivatives are protonated, they undergo hydrolysis reactions at elevated rates and can either deaminate to form the corresponding uracil derivatives or depyrimidinate generating abasic sites. The kinetic parameters for reaction of protonated cytosine are derived by studying the hydrolysis of N3-methyl-2'-deoxycytidine (m3dC), a cytosine analogue which is predominantly protonated at physiological pH. Both deamination and depyrimidimation reaction rates are shown to be linearly dependent upon the fraction of protonated molecules. We present here thermodynamic parameters which allow determination of hydrolysis rates of m3dC as functions of pH and temperature. Protonation of cytosine residues in DNA, as induced by aberrant base-pair formation or base modification, may accelerate the rate of both deamination and depyrimidation up to several thousand-fold under physiological conditions.