Vegetarian lifestyle and monitoring of vitamin B-12 status

Vegetarians are at risk to develop deficiencies of some essential nutrients, especially vitamin B-12 (cobalamin). Cobalamin occurs in substantial amounts only in foods derived from animals and is essential for one-carbon metabolism and cell division. Low nutritional intake of vitamin B-12 may lead to negative balance and, finally, to functional deficiency when tissue stores of vitamin B-12 are depleted. Early diagnosis of vitamin B-12 deficiency seems to be useful because irreversible neurological damages may be prevented by cobalamin substitution. The search for a specific and sensitive test to diagnose vitamin B-12 deficiency is ongoing. Serum vitamin B-12 measurement is a widely applied standard method. However, the test has poor predictive value. Optimal monitoring of cobalamin status in vegetarians should include the measurement of homocysteine (HCY), methylmalonic acid (MMA), and holotranscobalamin II. Vitamin B-12 deficiency can be divided into four stages. In stages I and II, indicated by a low plasma level of holotranscobalamin II, the plasma and cell stores become depleted. Stage III is characterized by increased levels of HCY and MMA in addition to lowered holotranscobalamin II. In stage IV, clinical signs become recognizable like macroovalocytosis, elevated MCV of erythrocytes or lowered haemoglobin. In our investigations, we have found stage III of vitamin B-12 deficiency in over 60% of vegetarians, thus underlining the importance of cobalamin monitoring in this dietary group.

Holo-transcobalamin is an early marker of changes in cobalamin homeostasis. A randomized placebo-controlled study

BACKGROUND

We examined the effect of oral vitamin B(12) treatment on fluctuations in plasma total cobalamin and its binding proteins transcobalamin (TC) and haptocorrin (HC).

METHODS

Patients (n = 88; age range, 38-80 years) undergoing coronary angiography (part of the homocysteine-lowering Western Norway B-Vitamin Intervention Trial) were allocated to daily oral treatment with (a) vitamin B(12) (0.4 mg), folic acid (0.8 mg), and vitamin B(6) (40 mg); (b) vitamin B(12) and folic acid; (c) vitamin B(6); or (d) placebo. EDTA blood was obtained before treatment and 3, 14, 28, and 84 days thereafter.

RESULTS

The intraindividual variation for patients not treated with B(12) was approximately 10% for plasma total cobalamin, total TC, apo-TC, and apo-HC, and <20% for holo-TC and TC saturation. In B(12)-treated patients, the maximum change in concentrations was observed already after 3 days for total TC (-16%), holo-TC (+54%), and TC saturation (+82%). At this time holo-HC (+20%) and plasma total cobalamin (+28%) showed an initial burst, but had increased further at 84 days. All changes were highly significant compared with the control group (P <0.0001).

CONCLUSIONS

Oral vitamin B(12) treatment produces maximal effects on total TC, holo-TC, and TC saturation within 3 days, whereas maximal increases in holo-HC and plasma total cobalamin occur later. The results support the view that holo-TC is an early marker of changes in cobalamin homeostasis.

Megalin is essential for renal proximal tubule reabsorption and accumulation of transcobalamin-B(12)

Megalin has previously been shown to bind and mediate endocytosis of transcobalamin (TC)-B(12). However, the physiological significance of this has not been established, and other TC-B(12) binding proteins have been suggested to mediate renal uptake of this vitamin complex. The present study demonstrates by the use of megalin-deficient mice that megalin is, in fact, essential for the normal renal reabsorption of TC-vitamin B(12) and for renal accumulation of this highly conserved vitamin. Megalin-deficient mice excrete increased amounts of TC and B(12) in the urine, revealing a defective renal tubular uptake of TC-B(12). The urinary B(12) excretion is increased approximately 4-fold, resulting in an approximately 28-fold higher renal B(12) clearance. This is associated with an approximately 4-fold decrease in B(12) content in megalin-deficient kidney cortex. Thus megalin is important to prevent urinary loss of vitamin B(12). In addition, light- and electron-microscopic immunocytochemistry demonstrate lysosomal accumulation of B(12) in rat and mouse proximal tubules. In rats this accumulation is correlated with vitamin intake. Thus renal lysosomal B(12) accumulation is dependent on vitamin status, indicating a possible reserve function of this organelle in the rat kidney.

High serum cobalamin levels in the clinical setting--clinical associations and holo-transcobalamin changes

Whereas low cobalamin levels have been studied intensively, systematic information about high levels, especially in the clinical setting, is scarce. Therefore, a prospective comparison was done of 60 patients with high cobalamin levels and 75 with normal levels obtained by a hospital laboratory over a 2.5 month period. Associations with clinical disorders and laboratory test results were examined. Transcobalamin (TC) I and II were measured, especially the holoproteins (TC carrying circulating endogenous cobalamin) which were fractionated with microfine silica powder. High cobalamin levels (> 664 pmol/l; > 900 ng/l) occurred in 94 of 670 consecutive clinically requested assays (14%). The only independently significant associations with a high cobalamin level were renal failure among the clinical disorders (P=0.01), elevated serum creatinine (P=0.0001) and diminished albumin (P=0.0002) levels among laboratory tests. Both holo-TC I and holo-TC II levels were increased in renal failure (P=0.0001) but the increase was relatively greater in holo-TC II. The results indicate that high cobalamin levels are more frequent than low ones in clinical practice and appear to be associated often with renal failure. The elevation of both holo-TC II and holo-TC I suggests that several mechanisms are operative. The accumulation of holo-TC II suggests that cellular uptake of cobalamin by the abundant TC II receptors in the kidney may be impaired. The much better known association of high cobalamin levels with leucocytic disorders is rare, and no association was seen with liver disease.

Plasma total transcobalamin I. Ethnic/racial patterns and comparison with lactoferrin

Plasma total transcobalamin (TC) I levels were measured in 434 healthy volunteers by radioimmunoassay (RIA). The results were analyzed for demographic patterns and were compared with lactoferrin, cobalamin, homocysteine, and chemistry panel results. Plasma TC I was higher in blacks than in other ethnic/racial groups and higher in women than in men. TC I levels did not correlate with lactoferrin levels. Lactoferrin showed significant ethnic differences also, but, unlike TC I, its levels were highest in whites. TC I levels correlated with cobalamin but not homocysteine levels. Neither TC I nor lactoferrin correlated with chemistry panel results, including creatinine, total protein, albumin, lactate dehydrogenase, and alkaline phosphatase levels. The demonstration with an RIA that directly measures total TC I that plasma levels are significantly higher in blacks than in other groups may explain the well-known higher cobalamin levels in blacks. Surprisingly, plasma lactoferrin, which has the same cellular sources as TC I, does not correlate with plasma TC I levels and shows dissimilar demographic patterns; lactoferrin levels are highest in whites. These findings suggest that regulation and/or secretion of these 2 proteins differ even though their localization and expression patterns in myeloid precursors are similar.

Transcobalamin codon 259 polymorphism in HT-29 and Caco-2 cells and in Caucasians: relation to transcobalamin and homocysteine concentration in blood

Transcobalamin (TC) is the plasma transporter that delivers vitamin B(12) to cells. We have already reported that HT-29 and Caco-2 cells secrete different TC variants. HT-29 secretes 2 TC isoproteins (codon 259-Pro/Arg [259-P/R]), exhibiting unequal concentrations (TC 259-P > TC 259-R), and Caco-2 cells only secrete the phenotype 259-R. We investigated the relation between phenotypic and genetic TC polymorphism in HT-29 cells transfected with Caco-2 TC complementary DNA and in 159 healthy Caucasians. We found that codon 259-R is buried and, thus, the genetic polymorphism provides no explanation why the TCs from HT-29 and Caco-2 cells have different isoelectric points in nondenaturing isoelectric focusing (IEF). The newly translated TC in HT-29 cells from the Caco-2 complementary DNA recombinant plasmid had the same isoelectric point as the TC constitutively expressed in HT-29 cells, suggesting that TC phenotypic variability involves a specific cell folding of the protein. The codon 259 polymorphism was found to have a biallelic distribution: homozygotes P = 34.6%, heterozygotes R/P = 47.8%, and homozygotes R = 17.6%. In heterozygous samples, the IEF showed that the TC 259-P/TC 259-R ratio = 1.6. The blood apo-TC concentration of 259-P homozygous Caucasians was significantly higher than that of homozygous 259-R (P <.0001) and heterozygous (P <.0006) Caucasians. The heterozygotes 259-R/P had homocysteine concentration significantly higher than the homozygotes 259-R and 259-P (P =.02 and P =.01, respectively). In conclusion, TC codon-259 polymorphism affects TC plasma concentration and may interfere in vitamin B(12) cellular availability and homocysteine metabolism.

Measurement of transcobalamin by ELISA

BACKGROUND

Transcobalamin is essential for the cellular internalization of cobalamin. Methods to quantify the unsaturated protein are available, but few attempts have been made to develop methods to quantify the sum of unsaturated and cobalamin saturated transcobalamin.

METHODS

gamma-Globulins from two polyclonal rabbit antibodies against recombinant human transcobalamin were used as capture and detection antibodies, and recombinant human transcobalamin was used as calibrator in an ELISA design.

RESULTS

The ELISA is specific for transcobalamin and has a detection limit of <1.6 pmol/L. The imprecision (CV) is 4-6% for mean concentrations of 13-70 pmol/L. The central 95% interval for serum from healthy blood donors (n = 77) was approximately 600-1500 pmol/L and showed limited variation with age and sex. No correlation was observed between the marker of acute phase reaction, C-reactive protein, and transcobalamin in plasma.

CONCLUSIONS

The ELISA measures total transcobalamin in serum and thus can be used for measurement of transcobalamin in patients treated with cobalamin.

Holotranscobalamin - a sensitive marker of cobalamin malabsorption

BACKGROUND

No simple and reliable method of identifying patients with cobalamin malabsorption is available at present. The measurement of plasma holotranscobalamin, i.e. the metabolically active cobalamins bound to the transport protein transcobalamin, has been suggested as a means of fulfilling such criteria.

DESIGN

We describe a method that directly quantifies cobalamins attached to transcobalamin. The method is evaluated in patients referred for gastrointestinal examination because of suspected cobalamin malabsorption.

RESULTS

Of the 101 patients referred, all 48 with gastrointestinal conditions compatible with cobalamin malabsorption had plasma holotranscobalamin below 35 pmol L-1 (interval of 35-160pmol L-1). None of the patients with plasma holotranscobalamin above the lower reference limit had conditions compatible with cobalamin malabsorption.

CONCLUSION

The values obtained for plasma holotranscobalamin showed a better correlation with possible malabsorption than the values obtained for plasma cobalamins. The specificity of the test, however, needs to be elucidated further.

Atherogenesis and the homocysteine-folate-cobalamin triad: do we need standardized analyses?

BACKGROUND

Bioscientists, physicians and nutritionists are newly interested in the homocysteine-folate-cobalamin triad, in part because homocysteine may be important both in atherogenesis and thrombogenesis. Homocysteine imbalance may be an early marker for cobalamin disorders because cobalamin is a cofactor in remethylation of homocysteine to methionine.

METHODS

In 139 men and 32 women of similar mean age of 65 years, we measured markers which have been cited as risk for atherosclerosis: serum homocysteine, folate, total cobalamin, holotranscobalamin I and II, (TCI and TCII), total serum cholesterol (SCHOL), high density lipoprotein cholesterol (HDLC), triglycerides (STG) as well as red blood cell (RBC) folate, food records and body composition by whole body counting of potassium-forty (40K).

RESULTS

Statistical relationships among the data showed healthy women had lower mean serum homocysteine and their mean RBC folate and TCI and TCII were higher than men. Eighty-three subjects had TCII much lower than 60 pg/ml (subnormal), yet only 11 of these men and two women had total cobalamin < 200 pg/ml (abnormal). Fifty-two subjects with serum homocysteine greater than 17.5 nmol/ml had TCII less than 60 pg/ml, suggesting serum homocysteine may be a marker for early cobalamin negative balance. None of the subjects in the study had serum folate below abnormal values, i.e., less than 1.6 mg/ml. All subjects had RBC folate within normal range. Serum homocysteine showed inverse relationship with RBC folate and serum total cobalamin, TCI and TCII.

CONCLUSIONS

1) importance of using serum holotranscobalamin TCI and TCII as markers of cobalamin deficiency, 2) necessity to use documented quantitative components of dietary intake if strong comparisons are to be made among quantitative values of serum or plasma homocysteine, folate, cobalamin, and nutrients in food intake.

Transcobalamin II receptor imaging via radiolabeled diethylene-triaminepentaacetate cobalamin analogs

Rapidly dividing cells up-regulate the number of transcobalamin II receptors during DNA replication. We have developed diethylene-triaminepentaacetate (DTPA) cobalamin analogs for the purpose of imaging transcobalamin II receptors in malignant and nonmalignant tissue.

METHODS

Methyl-, adenosyl- and cyanocobalamin-b-(4-aminobutyl)-amide-DTPA analogs were synthesized. In vitro binding of the analogs to the transcobalamin proteins was assessed by the unsaturated vitamin B12 binding capacity assay and compared to DTPA and cyanocobalamin. The biodistribution of the 111In-DTPA cobalamin analogs was measured at 24 hr after injection into sarcoma-bearing mice and non-tumor-bearing mice and pigs.

RESULTS

Methyl-, adenosyl- and cyanocobalamin-b-(4-aminobutyl)-amide-DTPA analogs and DTPA were 94.0%, 90.4%, 66.4%, and 3.6%, respectively, as efficient in binding to the transcobalamin proteins when compared to cyanocobalamin. At 24 hr after administration, the cobalamin analogs had 5-17 times and 20-29 times, respectively, the amount of uptake within the resected tissue samples and transplanted sarcomas when compared to 111In-DTPA.

CONCLUSION

The radiolabeled DTPA cobalamin analogs are biologically active. Preliminary animal studies suggest that the analogs could be effective in vivo transcobalamin II receptor imaging agents.

Home parenteral nutrition and vitamin B12 status

The vitamin B12 status of 20 subjects who were on home parenteral nutrition after surgical or functional small bowel resection and were given 1000 micrograms cyanocobalamin every 3 mo was studied by comparing their plasma vitamin B12, homocysteine (HS), and methylmalonic acid (MMA) concentrations. The plasma vitamin B12 concentration (median 145 pmol/L, 95% confidence interval: 123-217) was subnormal in four cases and borderline in four others. In the "4low B12" group, the concentrations of the markers of vitamin B12 deficiency were in the normal range; HS 10.7 mumol/L (8.0-12.3); and MMA, 0.15 mumol/L (0.09-0.19). References values were HS, 10.0 mumol/L (9.4-12.6); and MMA, 0.16 mumol/L (0.10-0.19). Thus, there were no metabolic signs of vitamin B12 deficiency in these subjects on parenteral nutrition, despite the fact that their plasma vitamin B12 levels were low. Analysis of individual data showed that the four patients with low circulating B12 had markers of intracellular vitamin B12 deficiency in the normal range.

Crohn's disease and vitamin B12 metabolism

The concentrations of vitamin B12, its analogs, and the haptocorrin and transcobalamin carriers in 21 patients suffering from Crohn's disease and a group of controls (20 adults) were measured. There were no significant differences in the mean values for vitamin B12, total corrinoids (vitamin B12 + analogs), or vitamin B12 or total corrinoids bound to haptocorrin or transcobalamin of the Crohn's and control patients. There was a significant increase in the binding capacity of transcobalamin in the Crohn's patients compared to the controls (P < 0.001), but there was no difference in the binding capacities of haptocorrin. The serum concentrations of the markers of vitamin B12 status, homocysteine and methylmalonic acid, showed an increase (P < 0.01) in homocysteine in the Crohn's disease patients, but no change in methylmalonic acid. As the hyperhomocysteinemia was associated with normal folate concentrations, there may have been a defect in the activation of the enzyme due to altered intracellular vitamin B12 status.

Serum transcobalamin II level in glucose-6-phosphate dehydrogenase deficient subjects with typhoid fever

Transcobalamin II (TCII) is the vitamin B12 binding protein which is responsible for delivery of this vitamin to the tissues. High values for serum TCII have been reported in many clinical conditions. This paper describes the elevated serum TCII levels in three G-6-PD deficient patients with typhoid fever. They had severe hemolysis with hemoglobinuria associated with slight liver dysfunctions but without obvious increased serum creatinine and BUN concentrations. A remarkable increase in serum TCII level was observed during active hemolysis and decreased to the normal level within 2-3 days after hemolysis ceased. The mechanism of increased serum TCII during hemolysis is probably due to hemoglobinuria secondary to excessive hemolysis. As Hb is known to be efficiently reabsorbed by the proximal tubule cells and can competitively inhibit the tubular uptake of TCII-B12. It is possible that excess Hb interferes with TCII uptake and degradation at renal tubular cells. Therefore, the circulating TCII survival is prolonged resulting in the elevated TCII level. Furthermore, lysosomal degradation of newly synthesized TCII is a normal process that regulates the TCII secretion. Therefore, a reduced lysosome-mediated uptake of TCII-B12 by renal tubular cell may stimulate the TCII secretion as has been shown experimentally in vitro.

Transcobalamin from cow milk: isolation and physico-chemical properties

The concentration of endogenous cobalamin (Cbl) in cow milk was 3.3 nM while the Cbl-binding capacity was 0.05 nM. Both endogenous and newly added Cbl showed similar quantitative distribution between a 280 kDa protein complex (45%) and a 43 kDa Cbl-binder (55%). Long time incubation, as well as urea treatment, was accompanied by a slow release of the 43 kDa Cbl-binder from the 280 kDa fraction. No other Cbl-binding proteins appeared after these procedures. The 43 kDa binder from cow milk, depleted of the ligand by urea treatment, reacted with Cbl even in the presence of a B12-analogue cobinamide (Cbi) at the ratio Cbl:Cbi = 1:40. The stokes radius of the binder changed from 2.7 nm for the Cbl-free protein to 2.5 nm for the Cbl-saturated form and the Cbl-saturated binder was able to displace human transcobalamin (TC) from the TC-receptor. The interaction between the protein and Cbl was significantly suppressed at pH 2.0. The N-terminal sequence of the purified 43 kDa Cbl-binder revealed homology with TC from human and rabbit plasma. In conclusion we have shown that TC is the main Cbl-binding protein in cow milk. This is surprising, since previous studies on human and rat milk have shown another Cbl-binder, apo-haptocorrin, to be the dominating Cbl-binding protein.

Improved method for silver staining of glycoproteins in thin sodium dodecyl sulfate polyacrylamide gels

A method for detection of glycoproteins in thin sodium dodecyl sulfate polyacrylamide gels was developed by a combination of (i) initial periodic acid oxidation/Alcian blue staining and (ii) subsequent staining with silver nitrate. The procedure allowed detection of as little as 1.6 ng of alpha 1-acid glycoprotein and 8-40 ng of a polydisperse mucin sample, which is at least 10 times more sensitive than previously published methods. The method should be very useful for assessment of sample purity and detection of glycoproteins in dilute mixed samples.

Abnormally elevated serum transcobalamin II levels in patients with cerebral malaria

Transcobalamin II (TCII) levels have been reported to be elevated in patients with many clinical conditions including proliferative reticuloendothelial system. As reactive macrophage hyperplasia frequently occurs in patients with malaria, the objective of the present study was to determine TCII in patients with Plasmodium falciparum with cerebral symptoms. The studies were performed on 14 cerebral malaria patients as well as 60 normal subjects. The mean values of serum vitamin B12 and TCII levels were significantly higher in the patient group and 6 and 7 patients had serum vitamin B12 and TCII levels higher than the normal values. There was direct relationship between serum TCII levels and BUN or creatinine levels. These findings indicated that raised serum TCII level occurred only in patients with renal insufficiency. A decreased glomerular fiLtration rate reduced the amount of vitamin B12 and TCII-B12 that filtered through the glomeruli resulting in the reduced proximal tubular cells uptake and its degradation of TCII. This reduced lysosomal enzyme activity, therefore, prolongs the intravascular TCII survival and increased secretion of TCII into the circulation. Therefore, serum TCII levels were elevated in these cerebral malaria patients.

Serum vitamin B12 and transcobalamin levels in early HIV disease

A cohort of asymptomatic human immunodeficiency virus (HIV) seropositive patients was followed over a 2 1/2-year period, to establish changes in serum vitamin B12 (B12) concentrations. Serum B12, CD4 count, and clinical progression to acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) were measured. The unsaturated B12 binding capacities of the transcobalamins were also determined at the start of the study and compared to those from a homosexual HIV seronegative control group. The geometric mean of serum B12 in 218 asymptomatic HIV seropositive patients was significantly lower than of a homosexual HIV seronegative control group (P = 0.02) and the unsaturated B12 binding capacities of transcobalamins I and II were significantly higher in the asymptomatic patients compared with the same control group (P < 0.03, P < 0.0001, respectively). Fifty-nine of the asymptomatic HIV seropositive patients were followed over a 2 1/2-year period during which most had falling serum B12 levels (64%). Twelve patients progressed clinically to ARC or AIDS, of which nine had repeat serum B12 estimation prior to progression. All nine patients had or developed falling serum B12 levels without any evidence of an HIV-related bowel disorder. All patients progressing had falling CD4 counts. Subnormal serum B12 levels are common in HIV disease and occur at an early stage. B12 levels fall in most patients with time and may help predict those patients whose disease will progress the most rapidly.

Secretion of intrinsic factor from cultured rat gastric chief cells

Intrinsic factor (IF) is a vitamin B12 binding protein that is secreted from the gastric mucosa. We tested secretagogues which stimulate IF secretion in rat gastric perfusion and found that carbachol and cholecystokinin octapeptide (CCK-8) stimulated secretion, but histamine and tetragastrin did not. To confirm these results, we examined IF secretion from isolated rat chief cells. For this purpose, we established an enzyme immunoassay (EIA) using an avidin-biotin peroxidase complex to measure small amounts of IF. To prepare an anti-rat IF, IF was isolated from the stomach, and was injected into a rabbit for immunization. Rat gastric chief cells were isolated from the gastric mucosa with Dispase and a Percoll gradient centrifugation, and were cultured. We examined the effects of chemicals by adding them to culture dishes of chief cells in a CO2 incubator. Released IF in culture medium was determined by EIA. Carbachol, CCK-8 and secretin stimulated IF secretion from cultured chief cells, while histamine and tetragastrin did not; Forskolin and A23187 also stimulated the secretion. We concluded that carbachol and CCK-8 stimulated IF secretion via an increase of intracellular Ca2+ concentration and that secretin did so via a cAMP accumulation.

Effect of glycemic control on vitamin B12 metabolism in diabetes mellitus

To determine the effect of glycemic control on vitamin B12 (B12) metabolism in diabetes mellitus, we studied B12 metabolism in 19 diabetic patients with poor glycemic control and 15 normal individuals. The diabetic patients had significantly higher total B12 binding capacity (3303 +/- 963 pg/ml), higher serum B12 levels (1173 +/- 503 pg/ml) and unsaturated B12 binding capacity (2131 +/- 902 pg/ml) when compared with the normal controls, but there was no difference in R-binder levels and the B12 binding ratio between the two groups. During a 2-week admission to establish glycemic control, the fructosamine levels in the diabetic patients decreased from 556 to 428 mumol/l and the total B12 binding capacity as well as unsaturated B12 binding capacity were significantly improved to the normal range (P < 0.01), but serum B12 levels, R-binder levels and the B12 binding ratio were not changed. There was a significant association between serum fructosamine levels and the total B12 binding capacity in poorly controlled diabetic patients and the decrease of fructosamine was correlated significantly with the change of total B12 binding capacity and serum B12 levels in diabetic patients. These results indicate the effects of glycemic control on B12 metabolism in diabetes mellitus.

Structural and functional heterogeneity among peroxidase-negative granules in human neutrophils: identification of a distinct gelatinase-containing granule subset by combined immunocytochemistry and subcellular fractionation

The existence of separate gelatinase granules in human neutrophils has been a matter of debate in recent years. We have demonstrated that the 135-kD form of neutrophil gelatinase is a complex of 92-kD gelatinase and a novel 25-kD protein termed neutrophil gelatinase-associated lipocalin (NGAL) that, in addition to being complexed with part of the gelatinase, is localized in free form in peroxidase-negative specific granules. Because this association was not appreciated in earlier studies, we decided to reassess the ultrastructural localization of gelatinase using specific antibodies without immunoreactivity towards NGAL. Double-labeling immunogold electron microscopy was performed on frozen thin sections of human neutrophils. Twenty-four percent of all peroxidase-negative granules were labeled with antigelatinase antibody, but not with antilactoferrin antibody. These granules are defined as gelatinase granules. Sixteen percent reacted with antilactoferrin antibody but not with antigelatinase antibody. The rest (60%) reacted with both antibodies. All granules labeling for lactoferrin are defined as specific granules. Gelatinase granules were observed as round and oval forms of considerably smaller size than specific granules, and were less electron dense. Isolated granules obtained by subcellular fractionation were also examined by immunoelectron microscopy. This demonstrated that peroxidase-negative granules comprise a continuum from the most dense granules that contain lactoferrin but no gelatinase to the lightest that contain gelatinase but no lactoferrin. Thus, gelatinase granules do exist as a subpopulation of peroxidase-negative granules and may allow for exocytosis of gelatinase during neutrophil diapedesis without substantial mobilization of other peroxidase-negative granules, ie, specific granules.

Induction of differentiation of myeloid leukemic cells by busulphan: in vivo and in vitro observations

Treatment of a 74 year old patient with chronic myelogenous leukemia (CML) with busulphan resulted in an abrupt and pronounced decrease of the white blood cell (WBC) count with restoration of normal peripheral blood cell morphology and regression of splenomegaly. The Philadelphia positive (Ph+) clone was however still detectable. The alterations in the WBC count and morphology were not preceded by marrow hypoplasia but correlated closely with a marked decrease in the serum levels of Transcobalamin I (TC I), a vitamin B12-binding protein derived from immature myeloid precursors and a reciprocal rise in serum TC III, a vitamin B12-binding protein originating from terminally differentiated mature granulocytes. Studies on the HL-60 cell line showed that busulphan is capable of inducing leukemic cells to differentiate into granulocyte-like cells. These observations, taken together, suggest that in addition to its potent myelosuppressive effects, busulphan may induce apparent clinical remissions in some CML patients by promoting terminal cell differentiation.

Measurement of red blood cell-vitamin B12: a study of the correlation between intracellular B12 content and concentrations of plasma holotranscobalamin II

We have recently reported a new and rapid assay to measure plasma holotranscobalamin II (holo TC II) as a means of exploring vitamin B12 status. In order to further evaluate the significance of plasma holoTC II in determining tissue cobalamin, we have chosen the red blood cell-vitamin B12 (RBC-B12) assay as a measure of tissue vitamin B12 content and studied the relationship between RBC-B12 and plasma holoTC II levels. Plasma holoTC II and RBC-B12 concentrations were concomitantly assayed in 20 hematologically normal controls and cancer patients. In our groups of controls, the mean value of RBC-B12 was determined as 241 +/- 51 pg/ml of packed erythrocytes (PE) with a range varying from 180 to 355 pg/ml PE. Preliminary results obtained in 32 cancer patients revealed lower holoTC II and RBC-B12 levels than the control group and a required threshold value of 70 pg/ml of holoTC II in order to maintain a normal RBC-B12 greater than 180 pg/ml PE.

Correlations between holo-transcobalamin II, holo-haptocorrin, and total B12 in serum samples from healthy subjects and patients

AIMS

To study the correlations between total vitamin B12(B12), holo-haptocorrin, and holo-transcobalamin II (holo-TCII) concentrations in human sera; the association between reduced holo-TCII concentrations and macrocytosis attributable to B12 deficiency.

METHODS

Serum samples from 38 healthy volunteers, 113 patients with normal total serum B12 concentrations and 93 patients with low total serum B12 were studied. Holo-TCII was removed from whole serum by adsorption with amorphous precipitated silica, and both whole serum and adsorbed serum were assayed for B12 using the Becton Dickinson vitamin B12 [57Co] radioassay kit.

RESULTS

In all three groups of subjects studied there were strong correlations between the logarithms of the total serum B12 and the holo-haptocorrin concentrations with regression coefficients between 0.884 and 0.967. By contrast, the correlations between the logarithms of the total serum B12 and holo-TCII concentrations were weaker, especially in the patients with normal or low total serum B12, for whom the regression coefficients were 0.491 and 0.391, respectively. Analysis of the clinical records of a proportion of the patients studied indicated that there were many more patients with low holo-TCII concentrations than with haematological disturbances related to B12 deficiency.

CONCLUSIONS

The total serum B12 concentration is a relatively poor indicator of holo-TCII concentrations and, therefore, of the ability of serum to deliver B12 to tissues. Additional information regarding B12 values can therefore be gleaned from measuring holo-TCII concentrations in the serum. Low holo-TCII concentrations, however, are an early sign of negative B12 balance and are frequently unassociated with haematological abnormalities caused by B12 deficiency.

Mobilization of granules in neutrophils from patients with myeloproliferative disorders

Neutrophil granule subsets and dynamics were studied in 4 patients with polycythemia vera/myelofibrosis and 2 patients with chronic myelogenous leukemia. Alkaline phosphatase, a marker for the membrane of secretory vesicles (the most readily mobilizable pool of intracellular membranes in neutrophils) was highly elevated in the PV/MF patients and significantly reduced in the CML patients. In spite of this, the amount of secretory vesicles was normal as judged by the content of albumin, and of the membrane protein cytochrome b-245 and CD11b, both partially localized in secretory vesicles. Gelatinase granules were present in all patients. The azurophil granules were lighter than normal in both CML patients. SDS-PAGE protein profiles indicated absence of defensins from azurophil granules from 1 CML patient. In addition, a 41-42 kD doublet protein band was absent from 2 PV and 1 CML patient, and reduced in the other CML patient. No difference in mobilization of granules was observed between patient neutrophils and control neutrophils. Also, stimulation with 10(-8) mol/l N-formyl-methionyl-leucyl-phenylalanine induced normal increases in intracellular Ca2+ in patient neutrophils. These results indicate that stimulus-response coupling leading to granule exocytosis is intact in neutrophils from patients with myeloproliferative disorders.

Vitamin B12 transport proteins in patients with HIV-1 infection and AIDS

BACKGROUND

Low vitamin B12 levels (B12) are often observed in patients infected with human immunodeficiency virus type 1 (HIV-1). The causes underlying this finding are thought to be intestinal malabsorption and/or abnormalities in the vitamin plasma binding proteins (BP).

MATERIAL AND METHODS

Serum levels of B12 and BP were studied in eighty HIV-1-positive patients, 55 of whom met the diagnostic criteria for AIDS. Subjects were divided into various subgroups: non-AIDS HIV-1 positive versus AIDS; low serum B12 levels (DB12, < 150 pmol/L) versus normal serum B12 levels (NB12); and the results obtained were compared both between groups and with respect to a reference population (RF) of normal volunteers.

RESULTS

Low levels of serum B12 were found in 14 patients (17.5%), without differences between the AIDS and non-AIDS subgroups. The levels of holohaptocorrin (holoHP) were lower in the DB12 group than in the NB12 and RF groups (p < 0.01), and no differences were found between the AIDS and non-AIDS groups. The levels of apotranscobalamin (apoTC) were higher in the AIDS group than in the non-AIDs and RF subjects (p < 0.01), but no differences were found between the DB12 and NB12 groups. Likewise, no differences were noted in the levels of holoTC between the DB12 and NB12 groups. A positive correlation between neutrophil counts and free serum haptocorrin levels (apoHP) (rs = 0.36; p = 0.002), and a negative one between the former and the levels of apoTC (rs = -0.3; p = 0.009) were observed. Furthermore, a positive correlation was detected between the erythrocyte sedimentation rate and the levels of apoHP and TC.

CONCLUSIONS

Low serum levels of HP in HIV-1 positive patients could lead to the low levels of serum vitamin B12 frequently observed in this patient population, while the high levels of TC could merely represent a non-specific marker of inflammation (acute phase, reactant).

New assay for the rapid determination of plasma holotranscobalamin II levels: preliminary evaluation in cancer patients

We describe a new and rapid assay for the measurement of plasma B12 bound to transcobalamin II (holotranscobalamin II) using the property of adsorption of the polypeptides of apotranscobalamin II and holotranscobalamin II to the hydrophobic surface of microfine glass particles. Acid-washed microfine glass was used to separate vitamin B12 bound to the glycoproteins transcobalamin I and transcobalamin III (haptocorrin or R binder) from that bound to transcobalamin II. Sephadex gel filtration separation of 57Co-labelled vitamin B12 binders confirmed that > 90% of holotranscobalamin II can be removed from plasma holohaptocorrin by adsorption to microfine glass particles. Since only holotranscobalamin II is capable of delivering vitamin B12 to metabolizing cells, plasma holotranscobalamin II content reflects the availability of B12 to cells. Use of this test in cancer patients undergoing either chemotherapy or radiation therapy revealed evidence of early negative B12 balance that in some instances was induced by the treatment itself.

Cobalamin binding proteins in human seminal plasma

Transcobalamin (TC) and haptocorrin (HC) are present in normal seminal plasma in substance concentrations ten- to twenty-fold that in blood. The results are given in range and (median). The substance concentration of seminal plasma TC is 3.6-21.9 (8.4) nmol l-1 and of seminal plasma HC 1.4-8.6 (3.0) nmol l-1. Compared to normals the substance concentration of TC is significantly lowered in post-vasectomy seminal plasma 2.2-2.9 (5.3) nmol l-1. The Stokes radius and the isoelectric points of seminal plasma TC are identical to TC in blood.

FK 383 DS, a new silica gel for the determination of unsaturated haptocorrin and transcobalamin II in serum

The ability of selective absorption of the polypeptide transcobalamin II by silica gel was used for the determination of the unsaturated cobalamin binding capacity of haptocorrin and transcobalamin II. Two different silica gels, QUSO G 761 and FK 383 DS, were compared by Sephacryl gel-filtration and by determination of unsaturated haptocorrin and transcobalamin II from forty different patient sera. It was found that the silica gels act identically for this purpose.

Elevated serum transcobalamin levels in anaemia of rheumatoid arthritis: correlation with disease activity but not with serum tumour necrosis factor alpha and interleukin 6

Transcobalamin (TCII) and haptocorrins (TCI and III), tumour necrosis factor alpha (TNF), interleukin-6 (IL6) and parameters of disease activity were assessed in 20 rheumatoid arthritis (RA) patients without anaemia and 19 subjects with anaemia of chronic disease (ACD) in order to determine if there was a possible correlation between these parameters. TCII, TNF and IL6 correlated positively with RA disease activity parameters, whereas their serum levels were higher in the ACD patients. TC levels were not correlated with cytokine levels. Vitamin B12 serum levels were lower in ACD. We conclude that in RA, elevated serum TCII levels are possibly mediated by increased RA disease activity, but probably not by actions of TNF or IL6. Increased TCII levels found in ACD may be explained by the higher degree of RA activity in these patients, and could also be viewed as a compensatory reaction to anaemia or reduced vitamin B12 levels. However, these preliminary findings require further confirmation.

Enzyme-linked immunoassay of haptocorrin: analysis of milk and granulocytes

An enzyme-linked, sandwich-type immunoassay method was described for quantitive assay of haptocorrin. The ranges of haptocorrin concentrations measurable by the method were comparable with those by radioimmunoassay. Using the method, the mean +/- SD of haptocorrin was 4.83 +/- 1.23 micrograms/ml in the colostrum (4th and 5th days after parturition), 3.17 +/- 1.77 micrograms/ml in the mature milk, and 21 ng/10(4) granulocytes (634 ng/mg protein). Haptocorrin from milk showed a homogeneous band at 66 kDa on SDS polyacrylamide electrophoresis followed by immunoblotting, while that from the granulocytes exhibited several closely aligned bands at 80 kDa and one or two bands at around 20 kDa.

Portal and biliary phases of enterohepatic circulation of corrinoids in humans

The assimilation of labeled cobalamin and the transport of corrinoids in portal blood, peripheral venous blood, and bile were studied in eight cholecystectomized patients, after ingestion of a dose of cyano[57Co]cobalamin (0.5 microCi). The radioactivity appeared in the portal vein after a delay of 1.5-2 hours and in the peripheral vein 1 hour later. In bile, it reached a maximum at 24-72 hours; the excreted cobalamin corresponded to 1.42% +/- 0.92% of the dose ingested. The output of total corrinoids was 1.85 nmol/day. The high-performance liquid chromatography analysis of bile showed the presence of methylcobalamin, 5'-deoxyadenosylcobalamin, hydroxocobalamin, and an unknown corrinoid. This corrinoid bound to R binder but not to the intrinsic factor, and it had the same retention time as cobinamide. The R binder was the single cobalamin-binding protein found in bile. It was completely saturated in some periods of bile secretion. The corrinoids corresponding to such a period were eluted in Sephacryl S 300 gel filtration (Pharmacia Fine Chemicals, Uppsala, Sweden) in two peaks corresponding to saturated R binder and to free cobalamin. The mean level of total corrinoid was significantly higher in the portal vein (593 +/- 238 pmol/L) than in the peripheral vein (376 +/- 114 pmol/L) (P less than 0.01). This "cobalamin analogue" fraction was hypothetical because it was calculated from the difference between total corrinoid concentration and the so called "true cobalamin" concentration. This difference corresponded to the cobalamin analogue fraction. These data show that bile removes not only cobalamin but also cobalamin analogues and that R binder is the single carrier protein involved in their excretion.

Transcobalamins in the etiology of neural tube defects

In a sample of 79 pregnant women at risk offspring with neural tube defects (NTDs) and 158 controls, significantly increased median values were found for apo-transcobalamins I and II in amniotic fluid in the group at risk, thus confirming previous results. The findings may reflect a genetic disposition to NTDs associated with altered levels of apo-transcobalamins, and research on the etiology and mechanisms of NTDs should focus on these proteins.

Plasma vitamin B12 binding proteins correlate with disease activity in patients with rheumatoid arthritis

The unsaturated vitamin B12 (cobalamin) binding capacity (UB12BC), transcobalamin (TC) I, II and III were measured in plasma and synovial fluid of 55 patients (10 men and 45 women, 25-60 years of age) with rheumatoid arthritis. The vitamin B12 binding proteins in 55 clinically and haematologically normal subjects of similar age group and sex were also studied as controls. The mean plasma concentrations of UB12BC, TCI, II and III were all significantly raised in patients with rheumatoid arthritis (RA) as compared to the normal controls. The increase of all vitamin B12 binding proteins in these patients showed a positive correlation with the increase of total proteins and globulin concentrations, and a negative (inverse) correlation with the albumin concentrations in the plasma, suggesting that these biochemical changes may be systemic consequences of the inflammatory and immunological processes characteristic of rheumatoid arthritis. The UB12BC, TC I and TC III concentrations in the synovial fluid were significantly higher than the corresponding plasma concentrations of these vitamin B12 binding proteins in patients with RA. Vitamin B12 binding proteins in the synovial fluid in these patients were probably at least partly produced locally by inflammatory cells. The mean levels of plasma transcobalamins in patients with severe disease activity were significantly higher than in patients with median or least disease activity. Therefore these proteins may be further studied as possible additional markers of disease activity in patients with RA.

Blood transcobalamin levels in malignant hepatoma

Alpha-Fetoprotein (AFP) levels measured by RIA show a strong sensitivity for the biological diagnosis of malignant hepatoma (MH). However, this parameter lacks specificity. Previous observations of an alteration in vitamin B12 metabolism in the presence of hepatoma led us to study vitamin-B12-binding proteins. Vitamin B12, also called cobalamin, is transported in the blood by two proteins or transcobalamins: one is haptocorrin (HC), which is linked to most of the cobalamin, and the other is transcobalamin II, which is involved in tissue exchanges. In this work, the levels of AFP and transcobalamins were determined by RIA and radioisotope dilution assay, respectively. They were measured in patients with MH (group A) and in patients with other liver diseases (group B). Compared with group B, group A showed a significant increase in total serum HC (p less than 0.005). In conclusion, it was observed that MH is accompanied by increased levels of HC. The origin of these changes could be due to either an increase in HC synthesis or a catabolic defect.

Low holotranscobalamin II is the earliest serum marker for subnormal vitamin B12 (cobalamin) absorption in patients with AIDS

In AIDS, as previously found in pernicious anemia (PA), the earliest serum marker of subnormal vitamin B12 (cobalamin) absorption, and therefore of negative B12 balance, is low serum holotranscobalamin II (holo-TC II; B12-TC II) despite normal total serum B12 level, normal serum homocysteine, and normal classic (oral free radio-B12) Schilling test. This may be accompanied by subtle and insidious damage to hematopoietic, immunologic, neuropsychiatric, nutritional and alimentary systems, confirmed by correction on therapeutic trial with B12 therapy. Our studies suggest such selective B12 deficiency occurs in about half of the HIV-1 infected, in part due to frequent depression of B12 absorption by HIV-1 attack on the gastric mucosa and/or opportunistic infection attack on the small bowel, and in part due to a telescoping of the continuum of the stages of negative B12 balance in relation to damage to B12 delivery by the infective and/or systemic disease process. In AIDS, when total serum B12 is normal despite tissue depletion of B12, if the classic Schilling test does not reveal subnormal food B12 absorption, the food Schilling test does. We hypothesize that DNA-synthesizing cells of the hematopoietic, immunologic, neurologic and other systems which have surface receptors solely for holo-TC II, and which have low B12 stores, rapidly become dysfunctional due to B12 deficiency when holo-TC II is low, while cells (such as liver cells) which also have surface receptors for holohaptocorrin (B12-haptocorrin) remain B12-replete. We believe this to be another example of the concept of selective nutrient deficiency in one cell line but not another.

Increased apotranscobalamin II levels in rheumatoid arthritis

The distribution of endogenous cobalamin among serum cobalamin-binding proteins was studied in 30 patients with active rheumatoid arthritis (RA) and 27 in clinical remission. The mean total serum cobalamin concentration (holo-transcobalamin I and II) was similar in both groups of patients, whereas mean apotranscobalamin II was significantly increased in patients with active RA. The clinical significance of this finding is not yet established but it might be a useful parameter for the evaluation of disease activity in RA.

Mixed enzyme-linked immunosorbent assay (MELISA) for HLA class I antigen: a plasma membrane marker

This study introduces a simple, reproducible assay for HLA class I antigen using antibodies against beta 2-microglobulin and the heavy chain on HLA. The sandwich technique was named mixed enzyme-linked immunosorbent assay (MELISA), and was designed for identification of plasma membranes in neutrophil subcellular fractions. The subcellular localization of HLA was identical to that of other plasma membrane markers, [3H]concanavalin A and detergent-independent alkaline phosphatase, and was unchanged by stimulation of cells by weak and strong secretagogues. In addition to the presence as part of the HLA complex in the plasma membrane uncomplexed beta 2-microglobulin is present in the specific granules of neutrophils. However, the release of beta 2-microglobulin from intact neutrophils stimulated with formyl-methionylleucylphenylalanine was much higher than could be explained by exocytosis of specific granules. Subcellular fractionation studies demonstrated that beta 2-microglobulin is localized in fractions characterized by latent alkaline phosphatase and released from this novel secretory compartment in response to stimulation with formyl-methionylleucylphenylalanine.