Interaction of rat alpha-fetoprotein and albumin with polyunsaturated and other fatty acids: determination of apparent association constants

Comprehensive approach to cancer immunotherapy - Simultaneous targeting of myeloid-derived suppressor cells and cancer cells with AFP conjugates

The immune system plays a pivotal role in combating diseases, including cancer, with monocytes emerging as key regulators of immune response dynamics. This article describes a novel strategy for cancer treatment centered on depleting myeloid-derived suppressor cells (MDSCs), to enhance the overall immune response while simultaneously targeting cancer cells directly. Alpha-fetoprotein (AFP) is an oncofetal protein that plays an important role in delivering nutrients to immature monocytes, embryonic, and cancer cells in a targeted manner. AFP can be repurposed, making it a vehicle for delivering toxins, rather than nutrients to kill cancer cells and deplete MDSCs in the tumor microenvironment (TME). Depleting monocytes not only stimulates the immune system but also improves the lymphocyte-to-monocyte ratio (LMR), often low in cancer patients. AFP combined with cytotoxic drugs, offers dual benefit-immune stimulation and targeted chemotherapy. Studies in xenograft models demonstrated high efficacy and safety of AFP-toxin conjugates, surpassing conventional targeted chemotherapy. Such conjugates have also been reported to provide superior efficacy and safety in cancer patients compared to chemotherapy. This approach, using AFP conjugated with toxins, either covalently or non-covalently, presents a safe and highly effective option for cancer immuno/chemotherapy.

A Historical Review of Brain Drug Delivery

The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.

The use of α-fetoprotein for the delivery of cytotoxic payloads to cancer cells

One approach to improving the activity of anticancer drugs is to bind them to the human α-fetoprotein (HAFP) that recognizes the tumor-associated cell-surface HAFP receptor. A drug can be bound to the HAFP by covalent conjugation or within a non-covalent complex. Specially designed linkers couple cytotoxins to the HAFP and ensure the stability of the HAFP-drug conjugate in the circulation and the activation of the drug in the cancer cell. On the other hand, AFP-drug non-covalent complexes can exploit the natural role of the AFP as a nutrition delivery "shuttle". In this article we review the design of HAFP-drug conjugates and AFP-drug complexes and their potential uses.

Alpha fetoprotein is increasing with age in ataxia-telangiectasia

The elevated serum alpha fetoprotein (AFP) concentration in ataxia-telangiectasia (A-T) patients has been known for decades, but the individual variation of AFP levels over time has not been studied. We have followed 12 patients (five girls and seven boys) for 1-12 years (mean 5.5 years) measuring in each patient AFP 2-8 (mean 4) times. Serum AFP levels were increased in all patients, mean 168.7 (range 40-373) kU/L, and without significant differences between the patients. There was a significant age related difference in the serum AFP level. A positive linear relationship (r=0.61, p=0.04) could be found between AFP level and age. Albumin levels were within normal range and did not change with age. Four patients had slightly increased aspartate aminotransferase (AST) levels. None of the patients had serological evidence of infectious hepatitis, and none had increased levels of carcinoembryonic antigen. Repeated standardized observations of gait function revealed no major difference in neurological deterioration between our patients. All had classical A-T disease and mainly truncating mutations; 21 out of 24 possible mutations were either frameshift or nonsense. Four were homozygous for the Norwegian ATM founder mutation. No correlation between serum AFP levels and the different ATM genotypes could be found. We conclude that serum AFP is not only elevated, but also is continuously increasing with age in patients with classical A-T disease.

Competitive binding of fatty acids and the fluorescent probe 1-8-anilinonaphthalene sulfonate to bovine beta-lactoglobulin

The use of spectroscopy in the study of fatty acids binding to bovine beta-lactoglobulin (BLG) appears to be a difficult task, as these acid compounds, assumed as the protein natural ligands, do not exhibit favorable optical response such as, for example, absorption or fluorescence. Therefore, the BLG fatty-acid equilibrium has been tackled by exploiting the competition between fatty acids and ANS, a widely used fluorescent hydrophobic probe, whose binding sites on the protein have been characterized recently. Two lifetime decays of the ANS-BLG complex have been found; the longer one has been attributed to the internal binding site and the shorter one to the external site. At increasing fatty acids concentration, the fractional weight associated with ANS bound to the internal site drops, in agreement with a model describing the competition of the dye with fatty acids, whereas the external site occupancy appears to be unaffected by the fatty acids binding to BLG. This model is supported by docking studies. An estimate of the acid-binding affinities for BLG has been obtained by implementing the fitting of the bound ANS intensities with a competitive binding model. A relevant dependence has been found upon the solution pH, in the range from 6 to 8, which correlates with the calyx accessibility modulated by the conformation of the EF loop. Fatty acids with longer aliphatic chains (palmitate and laurate) are found to display larger affinities for the protein and the interaction free energy nicely correlates with the number of contacts inside the protein calyx, in agreement with docking simulations.

Characterization of the vitamin E-binding properties of human plasma afamin

Human plasma afamin, the fourth member of the albumin gene family, is shown to be a specific binding protein for vitamin E. A radio ligand-binding assay followed by Scatchard and Hill analysis are used to show that afamin has a binding affinity for both alpha-tocopherol and gamma-tocopherol, two of the most important forms of vitamin E, in vitro. The binding-dissociation constant was determined to be 18 microM, indicating that afamin plays a role as vitamin E carrier in body fluids such as human plasma and follicular fluid under physiological conditions. Additionally, we demonstrate that afamin has multiple binding sites for both alpha- and gamma-tocopherol. Due to the large binding capacity of afamin for vitamin E, it might take over the role of vitamin E transport in body fluids under conditions where the lipoprotein system is not sufficient for vitamin E transport. To confirm the experimental results, we performed homology modeling and docking calculations on the predicted tertiary structure, which showed coincidence between calculated and in vitro results.

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.

Uptake of docosahexaenoic acid by microvessels from developing rat brain

Uptake of polyunsaturated fatty acids by the rat brain occurs mainly during the three weeks before weaning. Docosahexaenoic acid [22:6], the predominant polyunsaturated fatty acid in the adult brain, appears to be preferentially taken up from the circulation by both the adult and developing rat brain. To test the hypothesis that this preferential incorporation was mediated by the cerebral microvasculature, we compared the incorporation of 22:6 to a saturated fatty acid, palmitic acid [16:0], in freshly isolated rat brain microvessels from the pooled brains of entire litters of two-week-old rats (n = 8 litters). For each litter duplicate incubations with 2 microCi of [1-14C]22:6 or [1-14C]16:0 were performed in 60% autologous rat serum for 2 hr at 37 degrees C. [3H]Sucrose was included in each incubation, allowing correction for non-specific uptake and trapping. An average of 2.7 +/- 2.0% (SD) of the radioactivity from 16:0 was found in the microvessels after 2 hr, vs 0.9 +/- 0.6% for 22:6. This yielded a three-fold enrichment of 16:0 over 22:6 (P = 0.02, paired t-test). There was preferential incorporation of 22:6 into phosphatidylethanolamine and of 16:0 into phosphatidylcholine, although most of the label from either substrate remained as fatty acid after the 2 hr incubation. These results do not indicate that brain capillaries mediate the preferential incorporation of polyunsaturated fatty acids into brain tissue that was seen in intact young rats.

Effect of beta-lactoglobulin on the activity of pregastric lipase. A possible role for this protein in ruminant milk

The interaction of bovine beta-lactoglobulin with palmitic and oleic acids has been studied by a partition equilibrium method. Bovine beta-lactoglobulin displays only one high affinity binding site for fatty acids whose association constants for palmitic and oleic acids are 4.2 x 10(6) and 2.3 x 10(6) M-1, respectively. However, other binding sites with low affinity are also present. The existence of one high affinity binding site is in accordance with the amount of fatty acids naturally bound to beta-lactoglobulin isolated from milk. The effect of beta-lactoglobulin on ruminant pregastric lipases from a pharyngeal extract has been assayed. The activity of pharyngeal lipase on a triglyceride emulsion is increased about 200%, 250% and 190% in the presence of 10 mg/ml, 20 mg/ml and 40 mg/ml of beta-lactoglobulin, respectively, the last concentration representing that found physiologically in colostrum. Albumin, another ligand-binding protein, increases the activity of this enzyme to a lesser extent and high levels tend to inhibit enzyme action. These results indicate that beta-lactoglobulin could participate in the digestion of milk lipids during the neonatal period by enhancing the activity of pregastric lipase through removal of the fatty acids that inhibit this enzyme.

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.

Cytotoxicity of chlorambucil and chlorambucil-fatty acid conjugates against human lymphomas and normal human peripheral blood lymphocytes

The cytotoxic activity of chlorambucil (Chl) and of chlorambucil-fatty acid conjugates of different degree of unsaturation have been assayed in vitro upon two human lymphoma cell lines and comparatively, upon quiescent and mitogen-activated lymphocytes from healthy blood donors. The cell toxicity observed with Chl-arachidonic acid and Chl-docosahexaenoic acid against lymphoma cells was, at any experimental condition used, equal or higher than the individual toxic potential of either chlorambucil or fatty acids. The two conjugates, like chlorambucil alone, were toxic against mitogen-activated lymphocytes. Contrary to chlorambucil, Chl-arachidonic at any concentration tested, lacked of toxicity towards normal non-activated lymphocytes. Chl-oleic acid conjugate was, whatever the cell species tested, much less toxic than Chl alone. In conclusion, the coupling of chlorambucil with polyunsaturated fatty acids increases: (a) the selectivity against neoplastic versus quiescent lymphocytes and (b) the toxicity for B-lymphoma cells. The selective effect of Chl-fatty acid conjugates is discussed in relation with the expression of an AFP/AFP-receptor autocrine system in malignant lymphoblastoid cells and in mitogen-activated lymphocytes.

Relations between vitamin D and fatty acid binding properties of vitamin D-binding protein

The interaction of fatty acids with bovine vitamin D-binding protein (DBP) was studied using a partition equilibrium method. This protein has one high affinity site for binding of fatty acids with an association constant Ka = 7 x 10(5) M-1 for palmitic acid and Ka = 6 x 10(5) M-1 for arachidonic acid. Competition experiments showed that palmitic acid hardly competes with 25-hydroxycholecalciferol for binding to DBP. However, arachidonic acid showed comparatively a stronger competition for binding to this protein. The great difference in competition of palmitic and arachidonic acids with 25-hydroxycholecalciferol may be related to changes in DBP conformation promoted by the binding of different ligands.