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

Abstract

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.

The gut microbiota contributes to a mouse model of spontaneous bile duct inflammation

“…ALP and AST serum levels on the contrary were elevated in GF mice. The use of ALP serum levels as a marker of biliary disease in mice has been somewhat debated [33,34] as the ALP levels measured in mice seem to be mostly bone-derived ALP isoforms, some intestinal ALP isoforms and close to no liver ALP, and it also varies between different mouse strains [35]. Intestinal ALP activity is increased in GF mice [36] and this could explain some of the discrepancies seen in our serum measurements.…”

Effects of 1.8 GHz radiofrequency field on microstructure and bone metabolism of femur in mice

“…Usually, serum ALP is used as an indicator of bone formation in mammalian bone research [Halling et al, ; Fink et al, ]. ALP could be produced in liver, bone, intestine, and kidney, and about 50% of total ALP was produced from bone in healthy adults [Kuo and Chen, ].…”

Alkaline Phosphatase and Hypophosphatasia

“…Their lifespan averaged 8.8 ± 2.3 days on the 129J background, and 10.6 ± 3.4 days on the 129J, C57Bl/6J hybrid background. Plasma of Alpl KO mice contains little ALP activity, which comes from the gut [ 46 ], whereas heterozygous Alpl +/ − mice have approximately 50 % the plasma ALP activity of wild-type (WT) mice and are healthy and fertile [ 44 ].…”

“…Magnification bars equal 100 μm. Taken from [ 46 ] and reproduced with permission from the Journal of Dental Research. g Scanning electron microscopy (SEM) analysis of incisors ( top ) and molars ( bottom ) of WT and KO mice at 20 days-of-age.…”