Levamisole inhibition of alkaline phosphatase and 5'-nucleotidase of bovine milk fat globule membranes

Structure, Biological Functions, Separation, Properties, and Potential Applications of Milk Fat Globule Membrane (MFGM): A Review

BACKGROUND

The milk fat globule membrane (MFGM) is a thin film that exists within the milk emulsion, suspended on the surface of milk fat globules, and comprises a diverse array of bioactive components. Recent advancements in MFGM research have sparked a growing interest in its biological characteristics and health-related functions. Thorough exploration and utilization of MFGM as a significant bioactive constituent in milk emulsion can profoundly impact human health in a positive manner. Scope and approach: This review comprehensively examines the current progress in understanding the structure, composition, physicochemical properties, methods of separation and purification, and biological activity of MFGM. Additionally, it underscores the vast potential of MFGM in the development of additives and drug delivery systems, with a particular focus on harnessing the surface activity and stability of proteins and phospholipids present on the MFGM for the production of natural emulsifiers and drug encapsulation materials.

KEY FINDINGS AND CONCLUSIONS

MFGM harbors numerous active substances that possess diverse physiological functions, including the promotion of digestion, maintenance of the intestinal mucosal barrier, and facilitation of nerve development. Typically employed as a dietary supplement in infant formula, MFGM's exceptional surface activity has propelled its advancement toward becoming a natural emulsifier or encapsulation material. This surface activity is primarily derived from the amphiphilicity of polar lipids and the stability exhibited by highly glycosylated proteins.

Milk fat: opportunities, challenges and innovation

Milk fat is a high-value milk component that is processed mainly as butter, cheese, cream and whole milk powder. It is projected that approximately 35 million tonnes of milk fat will be produced globally by 2025. This surplus, enhances the need for diversification of milk fat products and the milk pool in general. Infant milk formula producers, for instance, have incorporated enzyme modified ("humanised") milk fat and fat globule phospholipids to better mimic human milk fat structures. Minor components like mono- and di-glycerides from milk fat are increasingly utilized as emulsifiers, replacing palm esters in premium-priced food products. This review examines the chemistry of milk fat and the technologies employed for its modification, fractionation and enrichment. Emerging processing technologies such as ultrasound, high pressure processing, supercritical fluid extraction and fractionation, can be employed to improve the nutritional and functional attributes of milk fat. The potential of recent developments in biological intervention, through dietary manipulation of milk fatty acid profiles in cattle also offers significant promise. Finally, this review provides evidence to help redress the imbalance in reported associations between milk fat consumption and human health, and elucidates the health benefits associated with consumption of milk fat and dairy products.

Structure-Activity Relationship of Purine and Pyrimidine Nucleotides as Ecto-5'-Nucleotidase (CD73) Inhibitors

Cluster of differentiation 73 (CD73) converts adenosine 5'-monophosphate to immunosuppressive adenosine, and its inhibition was proposed as a new strategy for cancer treatment. We synthesized 5'- O-[(phosphonomethyl)phosphonic acid] derivatives of purine and pyrimidine nucleosides, which represent nucleoside diphosphate analogues, and compared their CD73 inhibitory potencies. In the adenine series, most ribose modifications and 1-deaza and 3-deaza were detrimental, but 7-deaza was tolerated. Uracil substitution with N³-methyl, but not larger groups, or 2-thio, was tolerated. 1,2-Diphosphono-ethyl modifications were not tolerated. N⁴-(Aryl)alkyloxy-cytosine derivatives, especially with bulky benzyloxy substituents, showed increased potency. Among the most potent inhibitors were the 5'- O-[(phosphonomethyl)phosphonic acid] derivatives of 5-fluorouridine (4l), N⁴-benzoyl-cytidine (7f), N⁴-[ O-(4-benzyloxy)]-cytidine (9h), and N⁴-[ O-(4-naphth-2-ylmethyloxy)]-cytidine (9e) ( K_i values 5-10 nM at human CD73). Selected compounds tested at the two uridine diphosphate-activated P2Y receptor subtypes showed high CD73 selectivity, especially those with large nucleobase substituents. These nucleotide analogues are among the most potent CD73 inhibitors reported and may be considered for development as parenteral drugs.

Anthelmintic Drugs: Their Efficacy and Cost-Effectiveness in Different Parity Cattle

Gastrointestinal nematodes are responsible for economic losses in bovines and are characterized by reduced milk production, decreased working efficiency, and even death. In our study, the effect of different anthelmintic treatments on nematode control in different parity cattle (Friesian crossbreds) at calving and their effect on milk yield were evaluated. The economics of anthelmintics and farm benefits in terms of increased milk production after deworming was also calculated. We screened cattle of first and second parity for nematodes. Animals were randomly selected in each group. In first parity animals, there were 23 positive cattle found, which were divided into 3 different groups, while in second parity animals there were 20 positive cattle which were also divided into 3 groups. For treatment of gastrointestinal nematodes, we used albendazole (velbazine) at 10 mg/kg body weight and levamisole (Nilverm®) at 7.5 mg/kg. In this study, both drugs were found effective in controlling nematode infections in cattle. Percentage reduction of eggs per gram (EPG) by albendazole was 48.20, 85.34, and 93.90% and 51.54, 81.43, 91.74% on day 7, 14, and 21 in first and second parity animals, respectively. Percentage reduction of EPG by levamisole was 44.45, 76.92, and 88.03% and 46.60, 73.78, 85.43% on day 7, 14, and 21 in first and second parity animals, respectively. The average increase in milk production in albendazole-treated groups was 0.39 and 0.92 L per day while increases in levamisole treated groups were 0.27 and 0.55 L per day in first and second parity cattle, respectively. After treatment, albendazole increased the milk fat by 0.07 and 0.1% while levamisole decreased by 0.02 and 0.05% in first and second parity cattle, respectively. It is concluded that anthelmintic treatments of recently calved cattle have a significant effect on milk production due to the nematode control. Milk production increased significantly in second parity cattle following anthelmintic treatment as compared to first parity animals. Levamisole had a negative effect on fat concentration in cattle while albendazole-treated cattle showed a positive effect. Albendazole has been found more efficient in reducing EPG of helminths in both parity animals as compared to levamisole-treated animals while the cost-benefit ratio of levamisole was greater than albendazole.

[Identification of thiamine monophosphate hydrolyzing enzymes in chicken liver]

In animals, thiamine monophosphate (TMP) is an intermediate on the path of thiamine diphosphate, the coenzyme form of vitamin B1, degradation. The enzymes involved in TMP metabolism in animal tissues are not identified hitherto. The aim of this work was to study TMP hydrolysis in chicken liver. Two phosphatases have been found to contribute to TMP hydrolysis in liver homogenate. The first one, possessing a maximal activity at pH 6.0, is soluble, whereas the second one represents a membrane-bound enzyme with a pH optimum of 9.0. Membrane-bound TMPase activity was enhanced 1.7-fold by 5 mM Mg2+ ions and strongly inhibited by levamisole in uncompetitive manner with K1 of 53 μM, indicating the involvement of alkaline phosphatase. An apparent Km of alkaline phosphatase for TMP was calculated from the Hanes plot to be 0.6 mM. The soluble TMPase has an apparent Km of 0.7 mM; this enzyme is Mg2+ independent and insensitive to levamisole. As estimated by gel filtration on a Toyopearl HW-55 column, the soluble enzyme has a molecular mass of 17.8 kDa, TMPase activity being eluted simultaneously with peaks of flavinmononucleotide and p-nitrophenyl phosphatase activity. Thus, TMP appears to be a physiological substrate for a low-molecular weight acid phosphatase, also known as low-molecular-weight protein phosphotyrosine phosphatase.

cAMP- and Ca2+-independent activation of cystic fibrosis transmembrane conductance regulator channels by phenylimidazothiazole drugs

Patch-clamp, iodide efflux, and biochemical techniques were used to evaluate the ability of phenylimidazothiazoles to open normal and mutated cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels and to investigate the mechanism of activation. As reported previously for bromotetramisole, levamisole activated wild-type CFTR channels stably expressed in Chinese hamster ovary cells in the absence of other secretagogues and without elevating intracellular cAMP or calcium. The protein kinase A (PKA) inhibitor N - (2-(p-bromocinnamylamino)ethyl)-5-isoquinolinesul-fonamid e abolished activation by forskolin but only partially inhibited stimulation by levamisole, suggesting the involvement of other kinases. CFTR channels bearing mutations at multiple phosphorylation sites, in the membrane domains, and in the first nucleotide binding domain (including the disease-causing mutations G551D and DeltaF508) all responded to phenylimidazothiazoles. Moreover, levamisole and bromotetramisole increased the activity of wild-type and mutant channels already exposed to PKA + MgATP, consistent with the inhibition of a constitutive, membrane-associated phosphatase activity. We conclude that phenylimidazothiazole drugs can open normal and mutated CFTR channels by stabilization of phosphoforms of CFTR that are produced by basal activity of PKA and alternative protein kinases. If similar stimulation is observed in humans in vivo, phenylimidazothiazoles may be useful in the development of pharmacological therapies for cystic fibrosis.

Characterization and localization of an ATP-diphosphohydrolase on the external surface of the tegument of Schistosoma mansoni

An ATP-diphosphohydrolase (EC 3.6.1.5) was identified in the tegumental fraction isolated from Schistosoma mansoni worms. Both ATP and ADP were hydrolyzed to AMP at similar rates by the enzyme. Other nucleotides were also degraded by the tegument enzyme, revealing a broad substrate specificity. Electrophoretic separation of tegumental proteins under non-denaturing conditions followed by addition of ATP or ADP as substrate revealed a single band of activity with similar mobility. In addition, similar heat-inactivation profiles were obtained for ATPase or ADPase activities, indicating that a single enzyme is responsible for degrading both nucleotides. The enzyme was not inhibited by vanadate, levamisole, tetramisole, ouabain or sodium azide. The ADPase activity was not affected by adenosine (5')-pentaphospho-(5')-adenosine (Ap5A) or by an excess of glucose and hexokinase used as an ATP-trapping system, thus excluding the presence of any significant adenylate kinase activity. The ATP-diphosphohydrolase displayed micromolar affinities for both Mg2+ and Ca2+, and the calcium-activated enzyme was inhibited by millimolar Mg2+. In intact live worms a calcium phosphate precipitate was formed on the outer tegumental surface upon incubation of the worms with either ATP or ADP, indicating the ectolocalization of this enzyme. In addition, ultrastructural histochemical localization of the enzyme was obtained. A distinct deposition of lead phosphate granules on the outer surface of the tegument was observed by electron microscopy, in the presence of either ATP or ADP as substrate. It is suggested that the ATP-diphosphohydrolase could regulate the concentration of purine nucleotides around the parasites and hence enable them to escape the host hemostasis by preventing ADP-induced platelet activation.

Purification and properties of alkaline phosphatase in the lactating bovine mammary gland

Alkaline phosphatase has been purified 1400-fold from homogenates of lactating bovine mammary tissue. The purification procedure included subcellular fractionation, solubilization with butanol, fractionation with acetone, chromatography on concanavalin A-Sepharose, DEAE cellulose, DEAE-Sephadex, and gel filtration on Sephadex G-200. The enzyme activity was measured with the substrate p-nitrophenylphosphate in three buffers, and the maximum rate occurred at pH 10. For maximum activity, Mg2+ was required. Substrate specificity studies at three pH values indicated that the enzyme had broad specificity. It catalyzed the hydrolysis of aliphatic and aromatic phosphates and pyrophosphates, but the phosphoprotein beta-casein was a poor substrate. Potent inhibitors of the enzyme were levamisole and sulfhydryl reagents (2-mercaptoethanol, dithiothreitol, and cysteine).

Alkaline phosphatase in the lactating bovine mammary gland and the milk fat globule membrane. Release by phosphatidylinositol-specific phospholipase C

1. Alkaline phosphatase is covalently bound to bovine mammary microsomal membranes and milk fat globule membranes through linkage to phosphatidylinositol as demonstrated by the release of alkaline phosphatase following treatment with phosphatidylinositol-specific phospholipase C. 2. The release of alkaline phosphatase from the pellet to the supernatant was demonstrated by enzyme assays and electrophoresis. 3. Electrophoresis of the solubilized enzymes showed that the alkaline phosphatase of the microsomal membranes contained several isozymes, while only one band with alkaline phosphatase activity was seen in the fat globule membrane. 4. Levamisole and homoarginine were potent inhibitors of the alkaline phosphatase activities in both membrane preparations and in bovine liver alkaline phosphatase, but not in calf intestinal alkaline phosphatase.

Subcellular and ultrastructural localization of alkaline phosphatase in lactating rat mammary glands

The subcellular fractions of lactating rat mammary glands were isolated by differential centrifugation. The mean specific activity of alkaline phosphatase in various fractions was in order greatest to least: microsomes, Golgi, mitochondria, nuclei, and cytosol. Alkaline phosphatase was examined cytochemically by transmission electron microscopy. Alkaline phosphatase activity was localized on myoepithelial membranes, basal and possibly lateral membranes of secretory epithelial cells, and endothelial cells. This finding agreed with biochemical data associating this enzyme activity with microsomes. However, intracellular activities could not be detected on Golgi, secretory vesicles, or apical plasma membranes. Saponin uncovered the activity in that portion of the endoplasmic reticulum of secretory cells adjacent to myoepithelial cells. The identify of this enzyme was further confirmed by selective inhibition studies using dithiothreitol and levamisole. Alkaline phosphatase activities were detected biochemically in lipid droplet "membranes" of secretory epithelium and fat globule membranes. Activity decreased with increasing globule size, indicating that milk alkaline phosphatase originates from lipid droplets of secretory epithelium. The predominance of alkaline phosphatase activity in myoepithelial cell plasma membranes suggests that this enzyme could be involved in cell surface reactions related to oxytocin-mediated milk ejection. In secretory epithelium, it was associated with basal and possibly lateral membranes and lipid droplets that lead to the secretion of milk fat.