Isozyme profile and tissue-origin of alkaline phosphatases in mouse serum

ArticleinBone 53(2) · January 2013with29 Reads
DOI: 10.1016/j.bone.2012.12.048 · Source: PubMed
Mouse serum alkaline phosphatase (ALP) is frequently measured and interpreted in mammalian bone research, however; little is known about the circulating ALPs in mice and their relation to human ALP isozymes and isoforms. Mouse ALP was extracted from liver, kidney, intestine, and bone from vertebra, femur and calvaria tissues. Serum from mixed strains of wild-type (WT) mice and from individual ALP knockout strains were investigated, i.e., Alpl(-/-) (a.k.a. Akp2 encoding tissue-nonspecific ALP or TNALP), Akp3(-/-) (encoding duodenum-specific intestinal ALP or dIALP), and Alpi(-/-) (a.k.a. Akp6 encoding global intestinal ALP or gIALP). The ALP isozymes and isoforms were identified by various techniques and quantified by high-performance liquid chromatography. Results from the WT and knockout mouse models revealed identical bone-specific ALP isoforms (B/I, B1, and B2) as found in human serum, but in addition mouse serum contains the B1x isoform only detected earlier in patients with chronic kidney disease and in human bone tissue. The two murine intestinal isozymes, dIALP and gIALP, were also identified in mouse serum. All four bone-specific ALP isoforms (B/I, B1x, B1, and B2) were identified in bone tissues from mice, in good correspondence with those found in human bones. All mouse tissues, except liver and colon, contained significant ALP activities. This is a notable difference as human liver contains vast amounts of ALP. Histochemical staining, Northern and Western blot analysis confirmed undetectable ALP expression in liver tissue. ALP activity staining showed some positive staining in the bile canaliculi for BALB/c and FVB/N WT mice, but not in C57Bl/6 and ICR mice. Taken together, while the main source of ALP in human serum originates from bone and liver, and a small fraction from intestine (<5%), mouse serum consists mostly of bone ALP, including all four isoforms, B/I, B1x, B1, and B2, and two intestinal ALP isozymes dIALP and gIALP. We suggest that the genetic nomenclature for the Alpl gene in mice (i.e., ALP liver) should be reconsidered since murine liver has undetectable amounts of ALP activity. These findings should pave the way for the development of user-friendly assays measuring circulating bone-specific ALP in mice models used in bone and mineral research.
    • "Marked decreases in serum total ALP activities were also present. Unlike in humans where bone and liver isozymes are the main contributors to the total serum ALP activity, mouse total ALP activity is comprised primarily of contributions of the bone and intestinal isozymes (Halling Linder et al. 2013). Intestinal ALP (iALP) is a brush-border-associated protein secreted by enterocytes and its activity is considered a valuable marker of crypt–villus differentiation (Sussman et al. 1989; Fevr et al. 2007). "
    [Show abstract] [Hide abstract] ABSTRACT: Activated Wnt/β-catenin signaling is frequently associated with colorectal cancer. Wnt inhibitors, including tankyrase inhibitors, are being explored as potential anticancer agents. Wnt signaling is also critical for intestinal tissue homeostasis, and Wnt inhibitors have been shown to cause intestinal toxicity in mice by affecting intestinal stem cells. This study sought to characterize the intestinal toxicity of tankyrase inhibitors, including reversibility, and to assess their therapeutic index. Novel tankyrase inhibitor G-631 caused dose-dependent intestinal toxicity with a therapeutic index < 1 after 14 days of dosing in mice. At a tolerated subtherapeutic dose level, the intestinal toxicity was composed of enteritis characterized by villus blunting, epithelial degeneration, and inflammation, which fully reversed after 14 days of recovery. Doubled exposure showed weak antitumor activity in a xenograft colorectal cancer model but also caused more severe intestinal toxicity characterized by multifocal-regionally extensive necrotizing and ulcerative enteritis leading to morbidity or moribundity in some animals. This toxicity was only partially reversed after 14 days of recovery, with evidence of crypt and villus regeneration, mildly blunted villi, and/or scarring in association with chronic inflammation of the submucosa. Therefore, the clinical utility of tankyrase inhibitors is likely limited by the on-target intestinal toxicity and a therapeutic index < 1 in mice.
    Full-text · Article · Dec 2015
    • "Akp5 gene), two different intestinal ALPs, i.e., the duodenum-specific IAP (dIAP) (Akp3 gene) and a global IALP (gIAP) (Alpi, a.k.a. Akp6 gene), and a putative pseudogene (Akp-ps1) [6]. dIAP has a clear role in the regulation of lipid uptake in the intestine [7], and its circulating levels increase significantly after fatty meals and high fat diet in rats [8,9]. "
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    Full-text · Article · Sep 2015
    • "Among such enzymes, alkaline phosphatase (ALP), a glycoprotein anchored to the cell membrane, is a good candidate for surface functionalization. There are a number of different isoforms of ALP, and it is expressed in many tissues, especially bone and liver, but also kidney and intestine [45] . It acts by splitting off phosphorus (an acidic mineral ) and so creating an alkaline pH. "
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    Full-text · Article · Jun 2014
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