Hyperhomocysteinemia is related to a decreased blood level of vitamin B12 in the second and third trimester of normal pregnancy.

Hyperhomocysteinemia has been associated with several pregnancy complications. We have investigated the variation of plasma total homocysteine (tHcys) during the 2 last trimesters of normal pregnancy and related it to blood vitamin B12 and folate and to the excretion of the degraded intrinsic factor receptor (IFCR) in urine, in a follow-up study of 15 cases. A significant rise in tHcys was observed between the beginning of the second trimester and the third trimester with respective values (median) 6.1, 5.8 and 6.7 micromol/l (p = 0.038). The tHcys/albumin ratio also increased significantly, while no correlation was found between albumin and folate blood concentration. In contrast, a significant decrease in vitamin B12 was observed (279, 225 and 199 pmol/l, between the 4th and 6th, and the 6th and 9th month, respectively (p = 0.017-0.002)). A significant negative correlation was found between tHcys between the 4th and 9th month of pregnancy and the ratio of vitamin B12 between the 4th and 9th month of pregnancy (r = 0.55, p = 0.037). The urine excretion of IFCR was increased and was not related to vitamin B12 and tHcys. In conclusion, we have observed a rise in tHcys between the beginning of the second trimester and the third trimester of pregnancy which was related to the decreased blood level of vitamin B12. Subclinical deficiency of vitamin B12 should be further investigated in pregnant women who remain on inadequate diet.

Production of gastric intrinsic factor, transcobalamin, and haptocorrin in opossum kidney cells.

Opossum kidney epithelial cells were shown previously to synthesize and secrete two cobalamin (Cbl)-binding proteins, presumed to be haptocorrin (Hc) and transcobalamin II (TCII). The present study examines the hypothesis that renal tubular cells also produce intrinsic factor (IF), and this production provides an explanation for the presence of IF in urine. By using antisera raised against human IF and against TCII, the presence of TCII was confirmed, and that of IF discovered in the media of opossum kidney (OK) cells in culture. The apparent molecular weight of IF and TCII was 68 and 43 kDa, respectively. Immunoreactivity on Western blot of the putative IF protein was blocked by recombinant human IF. When proteins secreted into the media were separated electrophoretically under nondenaturing conditions after binding with [(57)Co]Cbl, a broad major band migrated at a relative front independently of recombinant IF or TCII, and probably represents Hc, as the Cbl binding is blocked by cobinamide. Small amounts of bound [(57)Co]Cbl migrated in the position of both IF and TCII, when cobinamide was present. The presence of IF and TCII in OK cells was confirmed by immunohistology. Specific reactivity for IF (blocked by recombinant IF) was found in proximal tubules of opossum kidney, but not in other portions of the nephron, confirming the ability of anti-human IF antiserum to detect opossum IF. A 732-bp fragment of IF, nearly identical in sequence to rat IF, was isolated by RT-PCR from opossum kidney mRNA, and Western blot confirmed the presence of IF protein. The presence of IF was also documented in rat kidney by isolation of an RT-PCR fragment, immunocytochemistry, and Western blot. IF should be added to the list of renal (proximal) tubular antigens that are shared by other epithelia.

An enzyme immunoassay for intrinsic factor in urine.

An enzyme immunoassay for intrinsic factor has been used on urine. The assay can measure intrinsic factor in native urine from healthy people and from patients with pernicious anaemia with no antibodies. The urinary intrinsic factor concentration in healthy individuals ranged from 40 to 54 pmol/l. Intrinsic factor antibodies, demonstrated by testing the recovery of added intrinsic factor, interfered with the assay. Cobalamin at high concentrations also affected the assay result. A low intrinsic factor concentration or the presence of antibodies to intrinsic factor was found in the urine of individuals with pernicious anaemia.

Cobalamin-binding proteins in human urine: identification and quantitation.

The urinary cobalamin (Cbl) binders were examined by gel filtration of concentrated urine on Sephadex G-200, alone and together with immunoglobulins against human Cbl binders. The 11 urine specimens from 10 persons studied had a free Cbl-binding capacity of 0.76 to 30.0 pmol/L (mean 6.6 pmol/L). Gel filtration with buffer preventing association of the Cbl binders gave peaks with elution volumes characteristic of serum transcobalamin and haptocorrin. When concentrated urine specimens were run together with immunoglobulins, the findings confirmed the presence of haptocorrin and transcobalamin and, in addition, of intrinsic factor. The presence of intrinsic factor was confirmed by incubating urine with an ion exchanger gel and by showing that an eluate of the gel reacted with the corresponding immunoglobulin. Part of the urinary intrinsic factor detected by radioimmunoassay was able to bind 57Co-Cbl; the rest appeared to be saturated with endogenous Cbl and possibly partly incapable of binding Cbl. All the free Cbl-binding capacity of urine concentrate could be blocked with adenine cyanocobamide, but only half with cobinamide; cobinamide blocked all the urinary haptocorrin but only part of the transcobalamin and none of the intrinsic factor eluted from the ion exchanger gel.