Amino Acid Availability of a Dairy and Vegetable Protein Blend Compared to Single Casein, Whey, Soy, and Pea Proteins: A Double-Blind, Cross-Over Trial

Protein quality is important for patients needing medical nutrition, especially those dependent on tube feeding. A blend of dairy and vegetable proteins (35% whey, 25% casein, 20% soy, 20% pea; P4) developed to obtain a more balanced amino acid profile with higher chemical scores, was compared to its constituent single proteins. Fourteen healthy elderly subjects received P4, whey, casein, soy, and pea (18 g/360 mL bolus) on five separate visits. Blood samples were collected at baseline until 240 min after intake. Amino acid availability was calculated using incremental maximal concentration (iCmax) and area under the curve (iAUC). Availability for P4 as a sum of all amino acids was similar to casein (iCmax and iAUC) and whey (iCmax) and higher vs. soy (iCmax and iAUC) and pea (iCmax). Individual amino acid availability (iCmax and iAUC) showed different profiles reflecting the composition of the protein sources: availability of leucine and methionine was higher for P4 vs. soy and pea; availability of arginine was higher for P4 vs. casein and whey. Conclusions: The P4 amino acid profile was reflected in post-prandial plasma levels and may be regarded as more balanced compared to the constituent single proteins.

Metabolomic changes demonstrate reduced bioavailability of tyrosine and altered metabolism of tryptophan via the kynurenine pathway with ingestion of medical foods in phenylketonuria

BACKGROUND

Deficiencies of the monoamine neurotransmitters, such as dopamine synthesized from Tyr and serotonin synthesized from Trp, are of concern in PKU. Our objective was to utilize metabolomics analysis to assess monoamine metabolites in subjects with PKU consuming amino acid medical foods (AA-MF) and glycomacropeptide medical foods (GMP-MF).

METHODS

Subjects with PKU consumed a low-Phe diet combined with AA-MF or GMP-MF for 3weeks each in a randomized, controlled, crossover study. Metabolomic analysis was conducted by Metabolon, Inc. on plasma (n=18) and urine (n=9) samples. Catecholamines and 6-sulfatoxymelatonin were measured in 24-h urine samples.

RESULTS

Intake of Tyr and Trp was ~50% higher with AA-MF, and AA-MF were consumed in larger quantities, less frequently during the day compared with GMP-MF. Performance on neuropsychological tests and concentrations of neurotransmitters derived from Tyr and Trp were not significantly different with AA-MF or GMP-MF. Plasma serotonin levels of gut origin were higher in subjects with variant compared with classical PKU, and with GMP-MF compared with AA-MF in subjects with variant PKU. Metabolomics analysis identified higher levels of microbiome-derived compounds synthesized from Tyr, such as phenol sulfate, and higher levels of compounds synthesized from Trp in the kynurenine pathway, such as quinolinic acid, with ingestion of AA-MF compared with GMP-MF.

CONCLUSIONS

The Tyr from AA-MF is less bioavailable due, in part, to greater degradation by intestinal microbes compared with the Tyr from prebiotic GMP-MF. Research is needed to understand how metabolism of Trp via the kynurenine pathway and changes in the intestinal microbiota affect health for individuals with PKU. This trial is registered at www.clinicaltrials.gov as NCT01428258.

Casein and other tumor markers in relation to cancer of the breast

Five tumor markers can be simultaneously determined in the serum by radioimmunoassay: carcinoembryonal antigen (CEA), alpha-fetoprotein (alpha-FP), human chorionic gonadotropin (HCG), beta-subunit of HCG (beta-HCG) and kappa-casein. In a series of 935 healthy subjects, these antigens remain detectable or are detected within very precise limits. At the start of the clinical evolution of breast cancer, the incidence of pathological concentrations is increased as compared with the highest level observed in normal subjects. This high incidence is mainly due to a concomitant determination of CEA, kappa-casein, HCG and beta-HCG. The alpha-FP test is never positive, while the kappa-casein concentration is particularly high in the first clinical stages of breast cancer and with metastases. The concomitant determination of these tumor markers may be a biological element contributing to the diagnosis of neoplasia, although it is neither an absolute nor a specific criterium. Indeed, a pathological concentration of at least one antigen was observed in 5.5% of the subjects presenting with benign mastopathy. When metastases occur (25 patients), the incidence of pathological concentrations of at least one antigen increases: 88%, the absolute values of these levels increasing simultaneously. The determination of the antigen concentration therefore allows an evaluation of the extension of the disease. Surgical removal reduces the incidence of positivity of these antigens to 34%. Persistence of pathological levels seems to be related to a possibility of relapse or metastatic spreading. Finally, chemotherapy and radiotherapy applied on a tumor which is not excised, does not decrease the incidence of positivity of the tumoral markers, although their levels seem to fluctuate with the clinical evolution.

Analysis of polymorphism in the bovine casein genes by use of the polymerase chain reaction

Methods have been devised for detecting polymorphisms in the bovine beta- and kappa-casein genes using the polymerase chain reaction (PCR) followed either by restriction enzyme digestion (to reveal a restriction fragment length polymorphism (RFLP] or by hybridization of an allele-specific oligonucleotide. These methods, as well as being faster and more sensitive than traditional RFLP methods, are of more general applicability since they can detect any change in DNA sequence. They require only a small sample of blood or semen and are applicable to animals of any age or sex. These methods make possible large-scale screening and thus selection for alleles at these loci. Typing of blood DNA can give erroneous results when the animal concerned is a twin; however, this can be overcome by retesting using milk or semen. Analysis of the kappa-casein genotype of Holstein-Friesian bulls gives frequencies for the A and B alleles of 0.80 and 0.20 respectively. Selection in favour of the B allele, which is superior for cheese production, could thus have a large effect. The A3 and B alleles at the beta-casein locus have been shown to be rare in the Holstein-Friesian population. Linkage disequilibrium exists between beta-casein B and kappa-casein B.

A Model of Net Amino Acid Absorption and Utilization by the Portal-Drained Viscera of the Lactating Dairy Cow

A more complete understanding of amino acid (AA) metabolism by the various tissues of the body is required to improve upon current systems for predicting the use of absorbed AA. The objective of this work was to construct and parameterize a model of net removal of AA by the portal-drained viscera (PDV). Six cows were prepared with arterial, portal, and hepatic catheters and infused abomasally with 0, 200, 400, or 600 g of casein daily. Casein infusion increased milk yield quadratically and tended to increase milk protein yield quadratically. Arterial concentrations of a number of essential AA increased linearly with respect to infusion amount. When infused casein was assumed to have a true digestion coefficient of 0.95, the minimum likely true digestion coefficient for noninfused duodenal protein was found to be 0.80. Net PDV use of AA appeared to be linearly related to total supply (arterial plus absorption), and extraction percentages ranged from 0.5 to 7.25% for essential AA. Prediction errors for portal vein AA concentrations ranged from 4 to 9% of the observed mean concentrations. Removal of AA by PDV represented approximately 33% of total postabsorptive catabolic use, including use during absorption but excluding use for milk protein synthesis, and was apparently adequate to support endogenous N losses in feces of 18.4 g/d. As 69% of this use was from arterial blood, increased PDV catabolism of AA in part represents increased absorption of AA in excess of amounts required by other body tissues. Based on the present model, increased anabolic use of AA in the mammary and other tissues would reduce the catabolic use of AA by the PDV.

Changes in serum lipoprotein lipids and their fatty acid compositions and lipid peroxidation in growing rats fed soybean protein versus casein with or without cholesterol

OBJECTIVE

We compared the effects of diets based on soybean protein and casein supplemented or not supplemented with 0.1% cholesterol on plasma lipoprotein lipid amounts and their fatty acid compositions, lecithin:cholesterol acyl-transferase activity, and lipid peroxidation.

METHODS

The composition and concentration of lipid and apolipoprotein in different lipoprotein classes, plasma LCAT activity, and lipid peroxidation were determined in rats fed 20% highly purified soybean protein or casein with or without 0.1% cholesterol for 2 mo.

RESULTS

Soybean protein and casein diets with or without cholesterol had similar plasma total cholesterol concentrations. Soybean protein consumption diminished very low-density lipoprotein particle number, as measured by diminished contents of very low-density lipoprotein triacylglycerol, phospholipid, and apolipoprotein-B100. Lecithin:cholesterol acyl-transferase activity was not significantly modified by either protein. The soybean protein diet decreased the linoleate desaturation index (20:4[omega-6]/18:2[omega-6]) in liver and high-density lipoprotein fraction 2-3-phospholipids but enhanced red blood cell resistance against free radical attack. Addition of cholesterol to both protein diets decreased concentrations of high-density lipoprotein fraction 2-3 cholesterol. Lecithin:cholesterol acyl-transferase activity tended to be greater after cholesterol feeding, likely due to the enhanced high-density lipoprotein fraction 2-3 apolipoprotein-AI, a cofactor activator for lecithin:cholesterol acyl-transferase. Regardless of dietary protein source, cholesterol supplementation decreased the linoleate desaturation index in liver and plasma lipoprotein lipids and red blood cell resistance to free radical attack.

CONCLUSIONS

Our results suggest that the dietary protein origin affects lipid peroxidation and polyunsaturated fatty acid biosynthesis and distribution among liver and different lipoprotein lipid classes, but plays only a minor role in the regulation of plasma and lipoprotein cholesterol concentrations. Providing dietary cholesterol (0.1%) with casein or soybean protein attenuates the effects of these proteins, with the exception of plasma cholesterol.

Peptide fragments released from Phe-caseinomacropeptide in vivo in the rat

The aim of this study was to investigate the pharmacokinetics of bovine Phe-caseinomacropeptide (Phe-CMP) in the rat after oral administration. This polypeptide was monophosphorylated and mainly nonglycosylated: Phe-CMP-1P. During gastrointestinal digestion and absorption, Phe-CMP-1P was degraded. Intact Phe-CMP-1P and CMP-1P were rapidly released from the stomach. In contrast, partial hydrolysis by pancreatic enzymes was observed. In vitro hydrolysis by brush-border membrane vesicles also indicated that the peptide was degraded. In the blood, "CMP-immunoreactive material" appeared rapidly, reaching a maximum level of 5.5 microg/ml at 60 min.

Caseinomacropeptide specifically stimulates exocrine pancreatic secretion in the anesthetized rat

The effect of caseinomacropeptide (CMP) (the [106-169] fragment of kappa-casein produced during digestion of milk protein), was studied in anesthetized rats using bile diversion for a pure pancreatic juice collection system. Intraduodenal administration of CMP induced a dose-related specific stimulation of pancreatic secretion which was nearly abolished by devazepide, atropine, hexamethonium, vagotomy or perivagal capsaicin pretreatment. Moreover, CMP did not inhibit in vitro trypsin activity. These results demonstrate that CMP is more likely to stimulate pancreatic secretion specifically through cholecystokinin release and activation of a vago-vagal cholinergic reflex loop than by inhibition of luminal trypsin, in anesthetized rats.

Comparative study of glycine, alanine or casein as inert nitrogen sources in endotoxemic rats

Pharmacological effects of dietary amino acids (AA) and peptides must be compared to an isonitrogenous control that is as inert as possible. To establish a rationale for the choice of such a control, potential metabolic and nutritional effects of three currently used nitrogenous controls (glycine, alanine, and casein) were evaluated in an endotoxemic rat model that has well-defined alterations in AA and protein metabolism. Five-week-old male Sprague-Dawley rats (113 +/- 1 g) were randomly assigned to four groups and received at d 0 an intraperitoneal injection of endotoxin (3 mg/kg). After withdrawal of food for 24 h, the rats were enterally refed for 48 h with a liquid diet (Osmolite((R))) supplemented with 0.19 g N. kg(-1). d(-1) in the form of glycine [lipopolysaccharide (LPS)-GLY group], alanine (LPS-ALA group) or casein (LPS-CAS group). One group (LPS group) received only Osmolite((R)). Plasma, two skeletal muscles, the liver and the intestine were then removed. Body and tissue weights and tissue protein contents did not differ among the four groups. Intestine histomorphometry showed no significant difference among groups. Jejunal hydrolase activities were significantly affected by the nitrogenous supplementations, but no effect was observed in the ileum. Only limited significant effects were observed on plasma and tissue-free AA concentrations, except for an accumulation of glycine in the plasma and tissues from the LPS-GLY group, compared to other groups. Overall, whereas glycine as a nitrogenous control should be used with care, either alanine or casein may be used as the "placebo," with the choice depending on the study to be performed.

A murine model of IgE-mediated cow's milk hypersensitivity

BACKGROUND

Cow's milk allergy (CMA) is one of the leading causes of food allergy in children. Understanding the mechanisms involved in the development of CMA has been hampered by the lack of suitable animal models.

OBJECTIVE

We sought to develop a mouse model of IgE-mediated cow's milk hypersensitivity (CMH) that mimics the clinical features of immediate CMA in humans.

METHODS

Three-week-old C3H/HeJ mice were sensitized by intragastric administration of cow's milk (CM) plus cholera toxin and boosted 5 times at weekly intervals.

RESULTS

CM-specific IgE antibody levels were significantly increased at 3 weeks and peaked at 6 weeks after the initial feeding. Intragastric challenge with CM at week 6 elicited systemic anaphylaxis accompanied by vascular leakage, significantly increased plasma histamine, and increased intestinal permeability to casein. Histologic examination of intestinal tissue revealed marked vascular congestion, edema, and sloughing of enterocytes. The role of IgE in mediating CMH was confirmed by abrogation of passive cutaneous anaphylaxis reactions by heat inactivation of immune sera. Development of IgE-mediated CMH in this model is likely to be TH2 cell mediated because in vitro stimulation of spleen cells from mice allergic to CM induced significant increases in the levels of IL-4 and IL-5, but not IFN-gamma.

CONCLUSION

This model should provide a useful tool for evaluating the immunopathogenic mechanisms involved in CMA and for exploring new therapeutic approaches.

Casein peptide release and passage to the blood in humans during digestion of milk or yogurt

In adult humans, after milk or yogurt ingestion, many peptides derived from alpha s1-, beta- or kappa-caseins were detected in stomach, including the kappa-caseinoglycopeptide, an inhibitor of platelet aggregation. Smaller peptides derived from casein and lactoferrin were recovered from duodenum. Two long peptides, the kappa-caseinoglycopeptide and the N-terminal peptide of alpha s1-casein, were absorbed and detected in plasma. These results support the concept that food-born peptides could have physiological activities in man.

Differential effects of protein restriction on gamma-glutamyltranspeptidase [EC 2.3.2.2] activity in young and mature rats

Gamma-glutamyltranspeptidase (GGT, EC 2.3.2.2) activity was determined in the plasma and liver of 40 young (50 days old) and 40 mature (300 days old) male Wistar rats, after a protein restriction period of 28 days. Casein protein levels used were: 1%, 3%, 5%, 7% and 28% (control). Weanling rats submitted to protein-free diet and adult rats submitted to that and other low-protein diets (1%, 3% or 5% casein) presented weight reductions (-0.38 +/- 0.07 g/day and -0.98 +/- 0.19 g/day, respectively). Only in young animals did these weight reductions parallel those of food consumption (37 +/- 12% of control), plasma protein (52 +/- 11% of control), plasma albumin (70 +/- 12% of control), hepatic RNA (68 +/- 7% of control) and protein (71 +/- 8% of control). A marked effect of the protein restriction, increasing the GGT activity, was also observed only in young rats. A significant (P < 0.05) rise was promoted by the protein-free diet in the plasma GGT (2.83 +/- 1.39 vs 0.69 +/- 0.50 mU/ml for control) and by both the protein-free and 3% casein diets, in the liver GGT (respectively, 16.00 +/- 6.72 and 7.75 +/- 3.49 vs 0.94 +/- 0.57 U/g protein for control). The different results obtained for young in relation to mature animals could be explained by the reduction of both protein and sulfur-containing amino acid requirements with aging.

Characterization of an antithrombotic peptide from kappa-casein in newborn plasma after milk ingestion

Bovine and human kappa-caseinoglycopeptides, two antithrombotic peptides derived from the corresponding kappa-caseins, were detected in physiologically active concentrations in the plasma of 5-d-old newborn infants after ingestion of cow's-milk-based formula or human milk respectively. It is suggested that these two bioactive peptides are released from milk proteins during digestion.

Enzyme-linked immunosorbent assay of colostral IgG transported into lymph and plasma in neonatal pigs

Amounts of colostral proteins in lymph and plasma were estimated by an enzyme-linked immunosorbent assay (ELISA) after infusion of bovine colostrum into the duodenal lumen in nonsuckling neonatal pigs. The rate of immunoglobulin (Ig) G transport in lymph of the thoracic duct reached the maximal level (4.7 +/- 1.3 mg.15 min-1.kg body wt-1) within 3 h after the duodenal infusion. The rate of small protein (SP) transport more slowly increased than that of IgG. On the contrary, casein remained in the much lower level in lymph. IgG concentration in plasma increased gradually and reached a plateau level (2.5 +/- 0.9 g/l) 5 h after the infusion, but the levels of SP and casein were slowly and slightly increased in plasma. The IgG-to-casein and SP-to-casein ratios in lymph and plasma were 161:15:1 and 128:12:1 4 h after the infusion, respectively, and much higher than the value in the colostrum (IgG/SP/casein = 15:4:1). These results indicate 1) that IgG transported via lymph flow after absorption through the small intestine is faster than that via blood flow, 2) that the concentration of absorbed IgG is higher than that of absorbed SP and much higher than the concentration of absorbed casein both in the lymph and plasma, and 3) that total amount of colostral protein transported via blood flow is larger than that transported via lymph flow.

Mammary gland differentiation in hypophysectomized, pregnant mice treated with corticosterone and thyroxine

Swiss Webster mice were hypophysectomized or sham-operated on Day 11 of pregnancy. The animals were fitted s.c. with osmotic minipumps containing either corticosterone (B) dissolved in Molecusol (Pharmatec, Alachua, FL) or the vehicle alone immediately after they were hypophysectomized. Animals in some of the experimental groups also received thyroxine (T4) in their drinking water. The mice were killed on Day 18 of gestation, and mammary tissue was homogenized and extracted for assessment of DNA, RNA, alpha-lactalbumin, and alpha-casein. Serum was assayed for placental lactogen-I (PL-I), and placental lactogen-II (PL-II), B, and T4. The concentration of PL-II in serum was elevated in the hypophysectomized mice, whereas the PL-I concentration did not differ among experimental groups. Hypophysectomy decreased both T4 and B concentrations in serum, and administration of these hormones restored their serum concentrations to normal or, in some cases, somewhat higher than normal levels. Hypophysectomy reduced the total RNA content and RNA/DNA ratio of the mammary gland, but treatment with B alone or with B and T4 restored RNA levels to those of sham-operated animals. T4 alone was ineffective in restoring RNA levels. Sham-operated animals that received hormonal treatment (B and T4) had the highest levels of RNA in the mammary tissue. Hypophysectomized animals had reduced content and concentration of alpha-lactalbumin in the mammary gland as compared to all other experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicological evaluation of rapeseed products in a subacute feeding study in rats

Groups of 15 male rats were fed ad libitum for 4 weeks standard diet containing 0, 2.5, 5 or 10% rapeseed protein isolate (RPI), 2.5, 5 or 10% rapeseed extraction residue (RER) or 10% casein. Body weight gain and food intake were recorded weekly. Clinical chemistry analyses, haematology, urinalysis, organ weights and histology were performed terminally. Serum alanine aminotransferase was decreased by RPI, RER and casein, while serum albumin only increased in rats fed RER. Microscopic examinations revealed abnormalities in liver and kidneys of animals at the 10% RPI, RER and casein levels. The absolute liver weights showed increases in the 5 and 10% RER groups and in the 10% RPI group. The relative kidney weights were reduced at all RER levels and in the 2.5% RPI group. Antithyroid activity of the rapeseed products were not noted.

[Problem of assimilation of isolated fish protein]

Ion-exchange chromatography was used to study the content of free amino acids in the blood serum of the portal and hepatic veins 0.5, 1, 2 and 3 h after oral administration of isolated fish protein (IFP) to white rats. The rate of IFP decomposition was estimated in the system of immobilized enzymes. It has been found that all amino acids of IFP are accessible and well assimilated in the body. Concentrations of arginine, lysine, ornithine, ramified and aromatic amino acids reached their maximum values more rapidly after administration of IFP than casein. However, the process of IFP production led to the reduction of the isolate digestion rate under the effect of peptidases as compared to the untreated fish and casein, as the result of which the total content of IFP amino acids in the blood was decreased 2 h after IFP administration, and the time of the isolated protein digestion in the body was extended.

Relationship of milk proteins in blood with somatic cell counts in milk of dairy cows

Intramammary leucocytosis was induced by injection of Escherichia coli endotoxin via the teat canal in three lactating Holstein cows. Concentrations of alpha-lactalbumin and casein in blood serum were measured, and somatic cell concentration and yield and composition of milk were determined. Endotoxin injection elicited mean increases of 100-fold in somatic cell concentration and 50% in protein concentration, whereas milk yield declined 5-fold and lactose concentration was halved. Concentrations of alpha-lactalbumin and casein in blood rose from 80 to 1909 and 0 to 1231 ng/ml, respectively. By 96 h postinjection, all variables were approximately equal to those preinjection. In a second study, concentration of alpha-lactalbumin was determined in blood of lactating cows in two herds (n = 332) and related to milk somatic cell count. Concentrations of alpha-lactalbumin in blood were correlated with somatic cell counts (r = .60). Mean concentrations of alpha-lactalbumin increased with increasing cell count even at low somatic cell concentrations (25 to 250 X 10(3)). Concentrations of milk proteins in blood serum apparently reflect competency of the blood-milk barrier and may therefore yield an indirect measure of udder health.

Human beta-casomorphin-8 immunoreactive material in the plasma of women during pregnancy and after delivery

A method for the extraction of human beta-casomorphin-8 immunoreactive material from human plasma and a radioimmunoassay for its determination in the plasma extracts were developed. Blood was collected from 34 men, from 35 non-pregnant women, from 35 pregnant women and from 138 women after delivery and plasma extracts were assayed for the presence of human beta-casomorphin-8 immunoreactive materials. No human beta-casomorphin-8 immunoreactive material was detected in the plasma of men or non-pregnant women, whereas such material was found in the plasma of 26 out of 35 pregnant women and in the plasma of 100 out of 138 women after parturition. Material collected from women after delivery was characterized by gel filtration and high-performance liquid chromatography (HPLC) and was found to be of different composition in various individuals; its components, one of which coeluted with human beta-casein from the HPLC column, have apparently higher molecular weights than human beta-casomorphin-8. Some of these compounds seem to be very stable against enzymatic degradation at 37 degrees C in human plasma, whereas human beta-casomorphin-8 proved to be degraded very fast under identical conditions. A physiological significance of mammary products of the beta-casomorphin type during pregnancy or after parturition is suggested.

[Comparison of specific IgE levels versus various milk proteins in 76 eczematous children]

Among 76 eczematous children, we realized a RAST test for whole milk and milk specific proteins: lactalbumin, lactoglobulin and casein. One of these RAST tests, at least, was positive for 27 children. Whole milk RAST test is the most frequently positive (77%) but some non specific reactions seem to interfere: only three children are clinically milk sensitive. Among specific proteins, lactalbumin is more frequently positive (59%) than lactoglobulin (51%) and casein (18%). Eczematous children with positive milk RAST tests, if compared to other eczematous children, have currently more mite allergies and positive egg RAST tests. They have a tendency (non significative) to be more frequently breast fed. The positivity of milk RAST tests seems to belong to a polysensitization and infrequently concerns a clinical allergy.

Dietary bovine antigens and immune complex formation after intravenous immunoglobulin in common varied immunodeficiency

Previously we have shown that the sera of hypogammaglobulinemic patients may contain large amounts of antigenically intact foreign protein of dietary origin, presumably due to the absence of an adequate gastrointestinal secretory immune barrier. In these studies we show that the intravenous infusion of immunoglobulin in these patients may result in high levels of immune complexes postinfusion and that at least one constituent of these complexes is likely to be bovine casein.

Inhibition of adenylate cyclase by transglutaminase-catalyzed reactions in pigeon erythrocyte ghosts

We report the occurrence in pigeon erythrocytes of a soluble Ca2+-dependent transglutaminase (TGase) activity. The effect of the erythrocyte ghost protein modifications, determined by TGase-catalyzed reactions, on adenylate cyclase, phospholipid methyltransferase I and II activities and on the lipidic matrix fluidity of the membrane was investigated by using a purified guinea pig liver TGase preparation. The results showed a significant inhibitory effect of such modifications both on the basal and on the variously stimulated (by NaF, Gpp(NH)p alone or in the presence of 1-isoproterenol) adenylate cyclase activity. By contrast, both the phospholipid methylation and the fluidity of the lipidic matrix of the membrane were unaffected by TGase-mediated reactions. These data suggest a new possible inhibitory mechanism of the cyclic AMP synthesis which might be triggered by the enhancement of the cytosolic Ca2+ concentration.

Interaction of casein with human polymorphonuclear cells

Attachment of 125I-casein to PMN cells was investigated. Iodination did not decrease the chemotactic effect of casein. 125I-casein binding was increasing toward a maximum reached at about 45 min at 24, and 37 degrees C. At 4 degrees C the binding was proportional to time for 45 min. No saturation was achieved even at 15 mg/ml casein. About 40% of casein remained attached to PMN in a casein-free medium after 60 min, at 37 degrees C. Pretreatment of the cells with trypsin or butanol, or the presence of indomethacin, azide, and PMSF did not affect the binding of casein. The hydrophobic amino acid, leucin counteracted the attachment of casein. Our data show that at chemotactic doses casein is bound specifically to cell membranes by hydrophobic forces. The induction of chemotaxis may be due to micellar casein-membrane lipid complexes.

Dietary protein antigenemia in humoral immunodeficiency. Correlation with splenomegaly

Enhanced gastrointestinal absorption of dietary substances is an important feature of normal neonatal life that also exists in particular disease states such as selective IgA deficiency and atopic allergy. In these studies, it is shown that patients with hypogammaglobulinemia have increased absorption of dietary bovine antigens and that most patients have large amounts of these proteins present in the serum even after an overnight fast. The amounts of such proteins were found to be correlated with spleen size and/or peripheral lymphoid hypertrophy. Interestingly, three patients with X-linked agammaglobulinemia did not have detectable amounts of these proteins in the serum nor did they have splenomegaly or lymphadenopathy. It is speculated that hypogammaglobulinemic patients have a specific gastrointestinal mucosal lesion that permits the chronic excessive absorption of dietary antigens and may result in lymphoid hypertrophy.

[Experimental data on milk casein absorption into the blood in the early postnatal period of development]

Blood absorption of unchanged molecules of the food protein casein was studied. Of 18 test serum samples withdrawn from portal blood of a satiated lamb, only 8 contained casein-like protein that had an immunoelectrophoretic mobility of casein and provided a reaction identical to that of casein preparation. Casein hydrolysis products did not interact with anticasein serum. The evidence obtained warrants the conclusion that under normal physiological conditions an insignificant part of casein may be absorbed unchanged by blood from the intestinal lumen during the early postnatal development.

Casein production by human breast cancer

Casein was measured in the sera of breast cancer patients, in breast cancer tumors, and in breast cancer cells in long-term tissue culture using a sensitive and specific radioimmunoassay. Levels present in breast cancer sera were not elevated above control values. Eight of forty-seven (17%) of the tumor samples tested were positive for casein, the highest level representing 0.003% of the soluble protein. When seven human breast cancer cell lines were assayed for casein, the results were uniformly negative even under conditions of stimulation by lactogenic hormones. In addition, direct immunoprecipitation of labeled cellular protein supported the negative result of the radioimmunoassay. Thus it appears that casein production is not a common characteristic of most human breast cancers.