Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 1995
Publication Date: N/A
Interpretive Summary: Conceptus losses in swine normally occur during maternal recognition of pregnancy and under crowded uterine conditions further losses occur between day 30-40 of pregnancy. Factors involved in these losses are not known. Endometrial secretion of an iron containing protein called uteroferrin increases during these two periods of pregnancy. Iron containing proteins, ,when combined with vitamin C are known to cause oxidation of fats. Oxidation of the fats contained in cells is lethal. Thus uteroferrin, if it is capable of oxidation of fats in cells, could cause conceptus loss by increased oxidation of cellular fats. As a first step to investigate this hypothesis, the ability of uteroferrin to cause the oxidation of fats isolated from reproductive tissues was determined. Results indicated that uteroferrin is capable of causing this chemical reaction. Further experiments to determine possible conceptus defense mechanisms were also performed. Results indicate that transferrin (another iron binding protei which does not cause oxidation of fats), vitamin A binding protein (a protein present in high concentrations in the intrauterine environment), and the uteroferrin-associated proteins (known to bind uteroferrin), all inhibited fat oxidation caused by uteroferrin. These results indicate that uteroferrin can cause oxidation of fats collected from reproductive tissues, consistent with the hypothesis that uteroferrin may be responsible for some conceptus losses.
Technical Abstract: Iron containing proteins catalyze lipid peroxidation when combined with either H2O2 or ascorbic acid. Microsomal membranes prepared from day 13 endometrial and conceptus tissues (5 pigs) and from day 30 endometrial, placental, fetal liver and fetus minus fetal liver tissues (5 pigs) were subjected to the following in vitro treatments (1) no treatment, (2) 50 uM ascorbic acid (ASC), (3) 100 uM uteroferrin (UF), (4) 50 uM ASC + 100 uM U (5) 50 uM ASC + 100 uM UF + 10 uM apotransferrin (transferrin with no iron bound; ATF), (6) 50 uM ASC + 100 uM UF + 10 uM holo-transferrin (transferrin saturated with iron; HTF) and (7-10) membranes preincubated for 3 h at 0 C with no treatment (7), 50 uM fetuin (8), 50 uM holoRBP (9, RBP with retinol bound) or 50 uM apoRBP (10, RBP with no retinol bound) followed by incubation with 50 uM ASC and 100 uM UF. Lipid peroxidation was measured in the samples as thiobarbituric acid reactive substances (TBARS). Combined ASC and UF caused a large increase (p<0.05) in TBARS in all membranes except day 30 placental membranes. Addition of ATF, but not HTF, decreased TBARS production in all membrane preparations. Holo-RBP, but not fetuin or apoRBP, decreased (p<0.05) TBARS production in all but day 30 endometrial membranes. In other experiments, when combined with ASC, UF/UF-associated protein complex catalyzed less (p<0.01) lipid peroxidation in fetal liver microsomal membranes than free UF. These results indicate that (1) UF combined with ASC catalyzes lipid peroxidation in reproductive tissue microsomal membranes and (2) ATF, holo-RBP and the UF-associated proteins inhibit this reaction.