Comparison of rat and human alkaline phosphatase isoenzymes and isoforms using HPLC and electrophoresis

Alkaline Phosphatase-Instructed Peptide Assemblies for Imaging and Therapeutic Applications

Self-assembly, a powerful strategy for constructing highly stable and well-ordered supramolecular structures, widely exists in nature and in living systems. Peptides are frequently used as building blocks in the self-assembly process due to their advantageous characteristics, such as ease of synthesis, tunable mechanical stability, good biosafety, and biodegradability. Among the initiators for peptide self-assembly, enzymes are excellent candidates for guiding this process under mild reaction conditions. As a crucial and commonly used biomarker, alkaline phosphatase (ALP) cleaves phosphate groups, triggering a hydrophilicity-to-hydrophobicity transformation that induces peptide self-assembly. In recent years, ALP-instructed peptide self-assembly has made breakthroughs in biological imaging and therapy, inspiring the development of self-assembly biomaterials for diagnosis and therapeutics. In this review, we highlight the most recent advancements in ALP-instructed peptide assemblies and provide perspectives on their potential impact. Finally, we briefly discuss the ongoing challenges for future research in this field.

Differential glycosylation of tissue non-specific alkaline phosphatase in mesenchymal stromal cells differentiated into either an osteoblastic or adipocytic phenotype

It has long been known that tissue non-specific alkaline phosphatase (TNAP) is essential for the correct formation of bone, as altered expression or function of this enzyme results in hypophosphatasia, a disease characterised by compromised bone structure, density and strength. However, recent evidence strongly suggests that the enzyme also has a role in lipid accrual and adipogenesis, a function that seems far removed from bone formation. Given that mesenchymal stromal cells (MSCs) are progenitors of both osteoblasts and adipocytes, the question arises of how TNAP is regulated to potentially have a different function when MSCs undergo either osteogenesis or adipogenesis. As the primary protein sequence is unchanged for the enzyme during both types of differentiation, any differences in function must be attributed to post-translational modification and/or localisation. We therefore examined the location of TNAP in bone- or adipose-derived MSCs differentiated into an adipocytic phenotype and compared the glycosylation state of the enzyme in MSCs differentiated into either osteoblasts or adipocytes. TNAP was found to co-locate with perilipin around lipid droplets in MSCs from bone, subcutaneous- and visceral adipose tissue during adipocytic differentiation. Treatment of TNAP with wheat germ lectin followed by electrophoresis showed minor differences in glycosylation between the phosphatase isolated from cells from these tissues, whereas electrophoresis after neuraminidase digestion highlighted differential glycosylation between cell types and during adipogenesis and osteoblastogenesis. This infers that post-translational modification of TNAP is altered during differentiation and is dependent on the eventual phenotype of the cells.

A new perspective on the function of Tissue Non-Specific Alkaline Phosphatase: from bone mineralization to intra-cellular lipid accumulation

Tissue-nonspecific alkaline phosphatase (TNAP) is one of four isozymes, which include germ cell, placental and intestinal alkaline phosphatases. The TNAP isozyme has 3 isoforms (liver, bone and kidney) which differ by tissue expression and glycosylation pattern. Despite a long history of investigation, the exact function of TNAP in many tissues is largely unknown. Only the bone isoform has been well characterised during mineralization where the enzyme hydrolyses pyrophosphate to inorganic phosphate, which combines with calcium to form hydroxyapatite crystals deposited as new bone. The inorganic phosphate also increases gene expression of proteins that support tissue mineralization. Recent studies have shown that TNAP is expressed in preadipocytes from several species, and that inhibition of TNAP activity causes attenuation of intracellular lipid accumulation in these and other lipid-storing cells. The mechanism by which TNAP stimulates lipid accumulation is not known; however, proteins that are important for controlling phosphate levels in bone are also expressed in adipocytes. This review examines the evidence that inorganic phosphate generated by TNAP promotes transcription that enhances the expression of the regulators of lipid storage and consequently, that TNAP has a major function of lipid metabolism.

Biodistribution and toxicity of orally administered poly (lactic-co-glycolic) acid nanoparticles to F344 rats for 21 days

Aim: Quantify the biodistribution and assess the toxicity of PLGA (poly-lactic-co-glycolic acid) and surface-modified PLGA chitosan (PLGA/Chi) nanoparticles (NPs) orally administered for 7, 14 and 21 days to F344 rats. Materials & methods: Fluorescent NPs were tracked in F344 rat tissues, and toxicity was evaluated by alkaline phosphatase and alanine transaminase levels, and by histologic examination of tissue samples. Results: Biodistribution of PLGA and PLGA/Chi were similar, with highest amounts found in the intestine and liver. Alkaline phosphatase increased significantly in treated rats. Mild histological differences were detected in the intestine and liver. Conclusion: PLGA and PLGA/Chi NPs behaved similarly presenting minimal toxicity in the liver and intestine, but not in kidney, lung and brain.

The role of intestinal alkaline phosphatase in pediatric inflammatory bowel and celiac diseases

Intestinal alkaline phosphatase enzyme plays a pivotal role in the maintenance of intestinal mucosal barrier integrity with the detoxification capacity of lipopolysaccharide, the ligand of Toll-like receptor 4. The inappropriate immune responses and the damage of the mucosal barrier may contribute to the initiation of inflammatory bowel and celiac diseases. In the inflamed colonic mucosa of children with inflammatory bowel disease and in the duodenal mucosa of newly diagnosed children with celiac disease, the decreased intestinal alkaline phosphatase and increased Toll-like receptor 4 protein expression may generate enhanced lipopolysaccharide activity, which may strengthen tissue damaging processes. The enhancement of intestinal alkaline phosphatase activity in an animal model of colitis and in therapy resistant, adult patients with ulcerative colitis reduced the symptoms of intestinal inflammation. In accordance with these results, the targeted intestinal administration of the enzyme in the two examined disorders may be a supplemental therapeutic option in the future. Orv. Hetil., 2012, 153, 1389–1395.

Intestinal alkaline phosphatase: multiple biological roles in maintenance of intestinal homeostasis and modulation by diet

The diverse nature of intestinal alkaline phosphatase (IAP) functions has remained elusive, and it is only recently that four additional major functions of IAP have been revealed. The present review analyzes the earlier literature on the dietary factors modulating IAP activity in light of these new findings. IAP regulates lipid absorption across the apical membrane of enterocytes, participates in the regulation of bicarbonate secretion and of duodenal surface pH, limits bacterial transepithelial passage, and finally controls bacterial endotoxin-induced inflammation by dephosphorylation, thus detoxifying intestinal lipopolysaccharide. Many dietary components, including fat, protein, and carbohydrate, modulate IAP expression or activity and may be combined to sustain a high level of IAP activity. In conclusion, IAP has a pivotal role in intestinal homeostasis and its activity could be increased through the diet. This is especially true in pathological situations (e.g., inflammatory bowel diseases) in which the involvement of commensal bacteria is suspected and when intestinal AP is too low to detoxify a sufficient amount of bacterial lipopolysaccharide.

Analysis of human bone alkaline phosphatase isoforms: Comparison of isoelectric focusing and ion-exchange high-performance liquid chromatography

BACKGROUND

Several isoforms of alkaline phosphatase (ALP) can be identified in human tissues and serum after separation by anion-exchange HPLC and isoelectric focusing (IEF).

METHODS

We purified four soluble bone ALP (BALP) isoforms (B/I, B1x, B1 and B2) from human SaOS-2 cells, determined their specific pI values by broad range IEF (pH 3.5-9.5), compared these with commercial preparations of bone, intestinal and liver ALPs and established the effects of neuraminidase and wheat germ lectin (WGA) on enzyme activity.

RESULTS

Whilst the isoforms B1x (pI=4.48), B1 (pI=4.32) and B2 (pI=4.12) resolved as well-defined bands, B/I resolved as a complex (pI=4.85-6.84). Neuraminidase altered the migration of all BALP isoforms to pI=6.84 and abolished their binding to the anion-exchange matrix, but increased their enzymatic activities by 11-20%. WGA precipitated the BALP isoforms in IEF gels and the HPLC column and attenuated their enzymatic activities by 54-73%. IEF resolved the commercial BALP into 2 major bands (pI=4.41 and 4.55).

CONCLUSIONS

Migration of BALP isoforms is similar in IEF and anion-exchange HPLC and dependent on sialic acid content. HPLC is preferable in smaller scale research applications where samples containing mixtures of BALP isoforms are analysed. Circulating liver ALP (pI=3.85) can be resolved from BALP by either method. IEF represents a simpler approach for routine purposes even though some overlapping of the isoforms may occur.