Characterization, origin and evolution of alpha-fetoprotein and albumin in postnatal rat brain

Serum AFP levels in patients suffering from 47 different types of cancers and noncancer diseases

Alpha-fetoprotein (AFP) is a glycoprotein and belongs to the gene family of serum albumins. The serum AFP levels were found to be elevated in the sera of liver cancer patients in 1964 and were subsequently developed and used as a liver cancer biomarker. However, elevated serum AFP levels have been observed in patients suffering from other cancer and noncancer diseases. Up to date, a systematic comparison of the serum AFP levels in different diseases has not been reported. In current study, 66,682 clinical lab test results of serum AFP levels from healthy individuals and patients with 47 different types of diseases during the past 5 years were retrieved and analyzed. Based on the mean (SD), median, and p (-Log₁₀p) values, we found that patients suffering from liver, breast, esophagus, cervical, pancreatic, endometrial, gastric, lung, rectum cancers in addition to noncancer diseases cirrhosis, nephrotic syndrome, and gastritis had significantly (p<0.05) increased, whereas patients suffering from multiple myeloma, Wilms' tumor, and other 22 types of noncancer diseases had significantly decreased median serum AFP levels than that of healthy controls. Moreover, patients with liver cancer, cirrhosis, lymphoma, bone fracture, and Wilms' tumor had highest mean serum AFP levels and the biggest SD values. In summary, the increased serum AFP levels were most evident but not specific for liver cancer patients. The potential clinical use of the increased or decreased serum AFP levels for other types of cancer and noncancer diseases and the molecular mechanisms behind our current findings need to be investigated.

Developmental time course of estradiol, testosterone, and dihydrotestosterone levels in discrete regions of male and female rat brain

The prevailing view of sexual differentiation of mammalian brain is that androgen synthesized in the fetal and neonatal testis and aromatized centrally during a perinatal sensitive period is the sole source of brain estradiol and the primary determinant of sex differences. Subregions of the diencephalon are among the most sexually dimorphic in the brain, and there are well-established sex differences in the amount of testosterone and estradiol measured in the hypothalamus and preoptic area during the perinatal period. We previously reported unexpectedly high estradiol in the hippocampus and cortex of both male and female newborn rat. This prompted a thorough investigation of the developmental profile of steroids in the rat brain using RIA to quantify the level of estradiol, testosterone, and dihydrotestosterone in discrete subregions of the brain from embryonic d 19 to adulthood. Plasma estradiol levels from individual animals were assessed when sufficient sample was available. A significant sex difference in hypothalamic testosterone prior to birth was consistent with previous findings. Postnatally, there was a distinct pattern of changing steroid concentrations in each brain region, and these were unrelated to circulating steroid. Removal of the gonads and adrenals at birth did not significantly reduce steroids in any brain region assayed 3 d later. Aromatase activity was detectable in all brain areas at birth, and the difference in activity level paralleled the observed regional differences in estradiol content. Based on these findings, we propose that steroidogenesis in the brain, independent of peripherally derived precursors, may play a critical role in mammalian brain development of both sexes, beyond the establishment of sex differences.

Cellular transfer of macromolecules across the developing choroid plexus of Monodelphis domestica

Choroid plexus epithelial cells secrete cerebrospinal fluid (CSF) and transfer molecules from blood into CSF. Tight junctions between choroidal epithelial cells are functionally effective from early in development: the route of transfer is suggested to be transcellular. Routes of transfer for endogenous and exogenous plasma proteins and dextrans were studied in Monodelphis domestica (opossum). Pups at postnatal (P) days 1-65 and young adults were injected with biotinylated dextrans (3-70 kDa) and/or foetal protein fetuin. CSF, plasma and brain samples were collected from terminally anaesthetized animals. Choroid plexus cells containing plasma proteins were detected immunocytochemically. Numbers of plasma protein-positive epithelial cells increased to adult levels by P28, but their percentage of plexus cells declined. Numbers of cells positive for biotinylated probes increased with age, while their percentage remained constant. Colocalization studies showed specificity for individual proteins in some epithelial cells. Biotinylated probes and endogenous proteins colocalized in about 10% of cells in younger animals, increasing towards 100% by adulthood. Injections of markers into the ventricles demonstrated that protein is transferred only from blood into CSF, whereas dextrans pass in both directions. These results indicate that protein and lipid-insoluble markers are transferred by separate mechanisms present in choroid plexuses from the earliest stage of brain development, and transfer of proteins from plasma across choroid plexus epithelial cells contributes to the high protein concentration in CSF in the immature brain.

Biological roles of alpha-fetoprotein during pregnancy and perinatal development

The use of alpha-fetoprotein (AFP) as a serum marker in cancer actually predates its employment in the detection of congenital defects; however, the latter use of AFP as a fetal defect marker has propelled its clinical utilization. Although the serum-marker capacity of AFP has long been exploited, less is known of the biological activities of this oncofetal protein during fetal and perinatal development. In the present review, the biological activities of AFP are discussed in light of this glycoprotein's presence in various biological fluid compartments: embryonic and fetal tissues, serum, urine, and reproductive fluids. After a review of the histochemical detection of AFP in various cells and tissues during development, AFP concentrations within various biological fluids were discussed in the context of gestational age and anatomic location. Discussion follows concerning the relationships and roles of AFP in developmental events such as erthyropoiesis, histogenesis/organogenesis, and ligand binding and in developmental disorders such as hypothyroidism, folate deficiencies, and acquired immunodeficiency disorder (AIDS). Based on its association with so many types of birth defects, malformations, and congenital anomalies, AFP can be viewed as a molecular "troubleshooter" until signal transduction pathways are established during pregnancy and prenatal development. The review concludes with a discussion of the place of AFP in the rapidly expanding field of proteomics.

Fatty acid desaturation: effect of alphafetoprotein on alpha-linolenic acid conversion by fetal rat hepatocytes

Freshly isolated fetal hepatocytes transformed 4.3, 8.5 and 19.2 pmol/min/10(6) cells of stearic, linoleic and alpha-linolenic acids, respectively, complexed to albumin or alpha-fetoprotein (AFP), to more unsaturated derivatives. Thus, fetal hepatocytes displayed high elongase and delta9, delta6, delta5-desaturase activities, as well as an ability to synthesize hexaene derivatives. Desaturase activities decreased when the time of culture of fetal hepatocytes (previous to incubation with the substrate) was prolonged, being practically undetectable after 24 h of culture. However, the rate of fatty acid uptake remained nearly constant. When AFP was used as the carrier the amount of hexaene fatty acid derivatives of alpha-linolenic acid recovered in cells was reduced up to 50% by albumin. This effect was associated with an increase of radioactivity found in the culture medium of hepatocytes incubated with AFP compared to albumin. Both observations taken together could be explained by an efflux of hexaene derivatives from cells caused by AFP.

Effect of alpha-fetoprotein and albumin on the uptake of polyunsaturated fatty acids by rat hepatoma cells and fetal rat hepatocytes

The uptake of polyunsaturated fatty acids by rat hepatoma cells and fetal hepatocytes has been studied using albumin and alpha-fetoprotein (AFP) as carrier proteins. Both types of cells took up linoleic (18:2(n-6)) and linolenic (18:3(n-3)) fatty acids at the same rate when they were added complexed either to albumin or AFP at a 1:1 molar ratio. At 37 degrees C a greater incorporation of arachidonic acid (20:4(n-6)) and mainly docosahexaenoic acid (22:6(n-3)) was observed when these acids were bound to albumin (6.5 nmol 20:4(n-6); 6.4 nmol 22:6(n-3) /million cells) as compared to AFP (5.5 nmol 20:4(n-6); 4.3 nmol 22:6(n-3)/million cells). The 20:4(n-6) and 22:6(n-3) uptake seems to be inversely related to the apparent association constants (k'a) between these fatty acids and both proteins (1.3 and 1.5 x 10(-7) M-1 20:4(n-6) and 22:6(n-3) for albumin; 6.4 and 54.0 x 10(-7) M-1 20:4(n-6) and 22:6(n-3) for AFP). Experiments carried out at 4 degrees C indicated that binding of 20:4(n-6) (0.83 nmol/million cells in presence of albumin; 2.16 nmol/million cells in presence of AFP) and 22:6(n-3) (0.83 nmol/million cells in presence of albumin; 1.32 nmol/million cells in presence of AFP) by cell membranes was also inversely related to the k'a of these proteins. At 4 degrees C, the k'a of AFP and albumin for 20:4(n-6) and 22:6(n-3) changed considerably (12.7 and 9.6 x 10(-7) M-1 20:4(n-6) and 22:6(n-3) for albumin; 3.9 and 14.6 x 10(-7) M-1 20:4(n-6) and 22:6(n-3) for AFP) with respect to the k'a calculated at 37 degrees C. Hence, k'a values were higher for albumin and lower for AFP than the corresponding values at 37 degrees C. It was concluded that uptake by cells and interaction of fatty acids with cell membranes depend mainly on the k'a of fatty acids and carrier proteins at equilibrium.

Chemistry and biology of alpha-fetoprotein

Alpha-Fetoprotein (AFP) is a product of specific fetal tissues and of neoplastic cells of hepatocyte or germ cell origin in adults. This protein belongs to a gene family that is phylogenetically most closely related to serum albumin. Its primary, secondary, and tertiary structural aspects appear similar to the three-domain concept proposed for the latter protein. The primary sequence of AFP departs most widely from serum albumin in the first 135 amino acid residues, with about 42% of the remaining 590 residues of the human proteins being identical. Some evidence exists that there are limited sequence differences in the AFP of a given animal species. AFP shows considerable charge heterogeneity that appears to relate mostly to its glycoid moiety. The proteins of some species such as the rat show more pronounced heterogeneities than that of humans. The variations in extent and type of glycosylations are evidenced by differences in the binding to various lectins. These interactions are being extensively explored in attempts to differentiate the sources of the protein produced by various normal and neoplastic cells and may provide valuable diagnostic methods. AFP, like serum albumin, shows relatively strong binding affinities for a variety of ligands. The most notable difference is the strong preferential binding of polyunsaturated fatty acids by AFP. This protein may play a role in transporting these substances to developing and to malignant cells. Various agents affect the synthesis of this protein both by specific fetal tissues and by neoplastic cells. Marked differences in the responses of cells, particularly those of neoplastic types, are indicative of variations in the genetic factors responsible for control of its synthesis. The subject of the genomic repression of the synthesis of AFP seen in fetal life upon maturation of the liver and the reoccurrence of synthesis upon malignant conversion of hepatocytes and of certain germ cells are of particular interest. The regulation of the closely related AFP and albumin genes is providing a powerful and attractive model to examine molecular events in the activation and inactivation of specific genes during development and in oncogenic processes. Extensive measurements of AFP during pregnancy and in the course of neoplasias, notably hepatoma, are being made to aid in following changes in such developments. Various specific physiological roles for this protein are also being proposed. One of these is its possible action in the regulation of immune processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Fatty acids bound to alpha-fetoprotein and albumin during rat development

The time-course levels and composition of the fatty acids bound to rat alpha-fetoprotein (AFP) and albumin from several sources, were determined throughout development, and related to the intake of lipids from milk and the compositional changes in brain and liver fatty acids. The major fatty acids bound to AFP were acids bound to AFP were polyunsaturated and mainly docosahexaenoic acid (22:6(n-3], either from fetal serum (23.1%) or whole fetuses (21.6%), whereas palmitic (34.1%) and oleic (29.9%) acids were the main acids bound to albumin from the same sources. Amniotic fluid AFP contained less fatty acids (0.8 mol/mol protein) than that of fetal serum (1.4 mol/mol protein), and especially noticeable was a reduced amount of 22:6 (9.6%). Both AFP-concanavalin A microforms showed identical fatty acid composition. Levels of 22:6 bound to AFP decreased quickly after birth until a minimum at 8-10 days, increasing moderately thereafter. This minimum is coincident in time with a maximal accumulation of this fatty acid by brain and a loss of 22:6 by liver. Except for colostrum, levels of 22:6 in milk lipids were low and fairly constant, but always greater than those of its precursor, linolenic acid (18:3 (n-3]. These results support a specialized role of AFP in the plasma transport and tissue delivery of polyunsaturated fatty acids, and mainly docosahexaenoic acid.

Fetuin as a marker of cortical plate cells in the fetal cow neocortex: a comparison of the distribution of fetuin, alpha 2HS-glycoprotein, alpha-fetoprotein and albumin during early development

Fetuin, alpha 2HS-glycoprotein (alpha 2HS), alpha-fetoprotein (AFP) and albumin have been shown to be present in some regions of the neocortex in two early stages of development of the cow brain using PAP immunocytochemistry. In the pre-cortical plate stage fibres of the primordial plexiform layer stained positively for fetuin. No staining was seen for albumin but plasma and cerebrospinal fluid (CSF) were positive for alpha 2HS and AFP. In the early cortical plate stage the strongest fetuin positive staining was seen in the earliest formed cells of the plate. alpha 2HS staining was much less intense but similar in distribution. The possible role of fetuin, or related glycoproteins, in cortical plate differentiation is discussed. Staining for AFP and for albumin was seen mainly in the ventricular zone and marginal zone fibres, and had a similar distribution and intensity for both proteins. Plasma and CSF stained for all four proteins. Tests showed some cross-reactivity between fetuin and anti-alpha 2HS and, to a much lesser extent, between antisera to AFP and albumin and antigens denatured by fixation.

Thyroxine-induced changes in the glycosylation pattern and in brain and serum levels of rat alpha-fetoprotein

We have studied the effect of thyroid disfunction during the postnatal period, on the serum and brain levels of rat alpha-fetoprotein (AFP) and albumin. Hypothyroidism was induced by treatment of pregnant rats and their newborn pups with 2-mercapto-1-methylimidazole(methimazole). Hyperthyroidism was provoked in newborns by daily injections of thyroxine (0.25 micrograms/g body wt) from the 3rd postnatal day weaning. Impaired growth, lower brain size, altered behaviour and morphological features observed were according to an altered thyroid status. Hypothyroid rats showed a significantly reduction in serum AFP concentration (78% of control values at 8 days of age) and a slight increase in that of albumin. level could be appreciated. Thyroxine supplementation (0.2 micrograms/rat/day) corrected most of these alterations. Hyperthyroidism induced a drastic fall in both serum and brain AFP levels (about 48% of the corresponding control values). Albumin concentration in serum was augmented significantly from the 12th postnatal day, but its brain levels did not change significantly. In hyperthyroid rats, a significant reduction (37% relative to controls) in the concanavalin A-non reactive microform of AFP, was observed. This alteration of the glycosylation pattern of AFP could be due to the inhibition by thyroxine of the activity of the hepatic enzyme GlcNAc-transferase III.

alpha-Fetoprotein and albumin gene expression in brain and other tissues of fetal and adult rats

Quantitative measurement of messenger RNA (mRNA) for alpha-fetoprotein (AFP) and albumin in developing rat liver and in different fetal and adult tissues reveals a close correlation between the previously determined rate of protein synthesis and mRNA levels. mRNA for AFP and albumin exists in fetal intestine, lung, liver and kidney whereas there are no such transcripts in fetal brain or heart. There are no mRNA transcripts for AFP in any adult organs other than the liver. The lack of mRNA AFP in fetal brain tissue indicates that the AFP found in fetal brain cells is absorbed from the serum. This finding supports the hypothesis that AFP may serve as a carrier protein to deliver bound molecules, such as non-esterified fatty acids, to brain cells at a specific time during development.

The distribution of native albumin and foreign albumin injected into lateral ventricles of prenatal and neonatal rat forebrains

Several plasma proteins are found within the cells of the developing brain of many species, with a distribution pattern which changes during development, but the origin of such proteins is in dispute. The experiments described here were designed to test the hypothesis that some developing brain cells are able to take up plasma proteins. The distribution of the plasma protein albumin has been studied in the rat forebrain from the 14th day of gestation until birth. Although present within the cerebrospinal fluid and plasma from the earliest age studied, albumin was not seen within cells of the developing forebrain until day 16E or 17E. A foreign protein, sheep albumin, was injected into the ventricles at days 14E, 16E, 18E, 20E and on the day of birth. Sheep albumin can be detected in the presence of rat albumin because the antibody to sheep albumin does not cross-react with rat albumin. The sheep albumin was taken up very rapidly into cells of the ventricular zone at the later but not the earlier ages, thus mimicking the distribution of the naturally occurring rat albumin. After the foreign albumin had been left within the ventricle for several hours, some of the cells of the cortical plate also contained the protein, again mimicking the normal distribution of albumin. These findings suggest that the presence of albumin within cells of the developing rat forebrain can largely be attributed to uptake rather than synthesis.

The uptake of alpha-foetoprotein by C-1300 mouse neuroblastoma cells

Recent immunocytochemical and biochemical studies have shown the intracellular uptake of alpha-foetoprotein (AFP) by most neural crest and neural tube derivatives of developing mammals and birds. The neural crest origin of neuroblastomas has been known for a long time. While many mouse neuroblastoma cell lines can express several neuronal properties, other lines lack specialized neural functions and may re-express embryonal or foetal antigens, suggesting some reversion towards an earlier stage of differentiation. We have therefore tested the C-1300 Jackson mouse neuroblastoma cell line for its ability to incorporate AFP. The results obtained confirm the significant internalization of protein by these cells, both in vitro and in vivo. External photoscans of mice bearing tumours after injection with [131I]-AFP have proven the usefulness of the protein as a radiotracer for neuroblastoma localization.

Cell-type-specific receptors for alpha-fetoprotein in a mouse T-lymphoma cell line

Binding and uptake of alpha-fetoprotein (AFP) by mouse T-lymphoma YAC-1 cells exhibited the characteristics of receptor-mediated endocytosis. The binding saturation curve obtained by incubating YAC-1 cells at 4 degrees C with 125I-labeled AFP at different concentrations (50 ng/ml to 2.5 mg/ml) showed three saturation plateaus. AFP binding was inhibited by unlabeled mouse, rat, or bovine AFP and, to a lesser extent, by rat or bovine serum albumin. No significant competition was observed with transferrin, alpha 2-macroglobulin, IgG, or ovalbumin. Scatchard analysis suggested the presence of three types of receptor sites with a Kd of 2.2 X 10(-9) M (approximately equal to 700 sites per cell), 8.6 X 10(-7) M (approximately equal to 210,000 sites per cell), and 5.7 X 10(-6) M (approximately equal to 910,000 sites per cell), respectively. At 37 degrees C, AFP was rapidly internalized and could be localized in the cytoplasm after incubation of cells with fluoresceinated AFP. After a short residence time, AFP was released undegraded from the cells. Normal adult thymocytes and T lymphocytes, which are counterparts of YAC-1 cells, did not show any significant uptake of AFP. On the other hand, a small subpopulation of fetal and newborn thymocytes was labeled by fluoresceinated AFP.

Alpha-fetoprotein receptors in a human breast cancer cell line

Evidence is presented for the existence of specific receptors for alpha-fetoprotein on the surface of MCF-7 human breast cancer cells. At 4 degrees C, the binding of alpha-fetoprotein to these cells displayed a biphasic saturation curve. Scatchard analysis revealed the presence of at least two binding sites with dissociation constants of 4.5 X 10(-9) M (2,000 sites/cell) and 1.3 X 10(-8) M (135,000 sites/cell), respectively. Binding was inhibited by 85% in the presence of a 5,000-fold excess of unlabeled alpha-fetoprotein and by 50% with the same excess of serum albumin. Competition by other serum proteins was not significant. At 37 degrees C, alpha-fetoprotein was endocytosed and the uptake curve reached a plateau after 3-4 hours of incubation.

Incorporation of radiolabelled alphafetoprotein in the brain and other tissues of the developing rat

The time course of uptake and autoradiographic localization of alphafetoprotein (AFP) were studied in the brain and other organs of fetuses, neonates and young rats injected with homologous radiolabelled AFP. Comparative data of radioactivity accumulation in the brain relative to that of several tissues (blood, liver, tongue, small intestine) showed bimodal patterns reflecting two periods of more active incorporation, with a maximum before the 16th day of fetal development. In brain autoradiographs, the strongest labelling was observed in 17-day-old fetuses 24 h after injection into the mother of [125I]AFP. The labelling included all regions of the brain. The results presented here give experimental support to the hypothesis that the presence of AFP in the developing nervous system of mammals and birds is primarily due to protein uptake rather than in situ synthesis.

Selective localization of alpha-fetoprotein and serum albumin within the sensory ganglia cells of developing chicken

The presence of alpha-fetoprotein (AFP) and serum albumin (SA) has been described within developing brain cells of mammals and chicken. In order to avoid the influence of the choroid plexuses in the transport, via the cerebrospinal fluid, of these proteins to brain cells, we studied the presence of AFP and SA within chicken sensory ganglion cells during ontogeny using the indirect immunoperoxidase technique. Our results show that before day 9 of egg incubation, both AFP and SA can be detected within the trigeminal and spinal ganglia cells. Henceforth, the labeling for AFP starts decreasing in the spinal ganglia but not in the trigeminal ganglion. The labeling for SA remains constant in both structures. Differences between AFP and SA staining in the spinal ganglia are maximal on day 11 of incubation, when AFP is no longer detected. It is concluded that at this time, the uptake of AFP by spinal ganglia cells is switched-off while SA is still taken up. As the blood concentration of both proteins is similar at this time, the finding reported here gives support to the advanced hypothesis suggesting the presence of specific receptors for AFP and/or SA in embryonic neural cells.

Long-chain fatty acids bound to alpha-fetoprotein and to serum albumin from fetal and adult pig

1. Pig alpha-fetoprotein (AFP) and albumin were isolated from fetal serum by DEAE-Sephadex ion exchange chromatography combined with Cibacron Blue-Sepharose and trypsin-Sepharose adsorptions. 2. AFP, fetal albumin and adult albumin carried 2.6, 2.4, and 1.9 moles of fatty acids per mole of protein, respectively. 3. Most of fatty acids bound to AFP were polyunsaturated: mainly arachidonic (20:4, n-6) and docosahexaenoic (22:6, n-3) acids, which accounted respectively for 21.7 and 18.8% of the total fatty acids. 4. By contrast, the fatty acids found in the albumins (fetal and adult) were preferentially saturated and monounsaturated. 5. Arachidonic acid was a minor component in both albumins, and no docosahexaenoic acid was detected.