Organ specific properties for human urinary alkaline phosphatases

Atypical alkaline phosphatase isozymes in serum and urine of patients with renal failure

BACKGROUND

Alkaline phosphatases (ALPs) originating from different organs are frequently detected in the serum and urine of patients with renal failure.

METHODS

We investigated the characteristics of ALPs in the serum and urine of 108 patients with chronic renal failure (CRF) and of 106 healthy control subjects.

RESULTS

In polyacrylamide gel electrophoresis, three atypical ALP bands in serum of patients were designated as atypical-s1, -s2 and -s3, respectively. In contrast, five atypical bands (u1, u2, u3, u4 and u5) were detected in the urine of patients. The atypical ALPs were electrophoretically isolated and assayed to determine their biochemical properties, i.e., neuraminidase sensitivity, heat stability, reactivity to anti-intestinal or anti-tissue nonspecific ALP antibodies, molecular sizes and sugar chain heterogeneities. From these results, we found that atypical-s1 and -s2 were the intestinal-type ALP, while s3 was the tissue-unspecific type ALP. Atypical-u1, -u2 and -u3 were high-molecular type ALPs, which we suggested as the ones that originated from the intestine. Atypical-u4, a tissue-unspecific type ALP, was detected with considerable frequency in the urine of patients. In patients with CRF, the appearance of these atypical ALPs was accompanied by a deterioration of the creatinine clearance.

CONCLUSIONS

The appearance of atypical ALPs in the serum and urine of patients with CRF may be a useful marker for renal disease.

Specific gel electrophoresis method detects two isoforms of human intestinal alkaline phosphatase

We have demonstrated that the 6.0% polyacrylamide disc gel electrophoresis (PAGE) method in the presence of 1% Triton X-100 clearly separated both normal molecular mass intestinal alkaline phosphatase (NIAP) and bone alkaline phosphatase (BAP) in serum regardless of the ABO blood group and the secretor status of the subjects. From the results under the usual 7.5% PAGE condition, overlapping mobilities of NIAP and BAP were found in particular in nonsecretor subjects after a high-fat meal. Under the above conditions, the apparent BAP percentage three hours after a meal was higher in nonsecretors than in subjects under fasting conditions, because NIAP activity in serum rose sharply following a high-fat meal. In contrast, under our 6.0% PAGE method, the NIAP and BAP were clearly separated from each other regardless of whether the subjects were fasting or had ingested a high-fat meal. In addition, an elevated level of the circulating NIAP can be another marker for patients with liver cirrhosis. Considering all these factors, the 6.0% PAGE method proposed by us is not only a useful method for the separation of intestinal alkaline phosphatase (IAP) isoforms, but can also be useful for the analysis of other usual AP isozymes.

Measurement of bone-specific alkaline phosphatase by an immunoselective enzyme assay method

We evaluated a new immunoselective enzyme assay of bone-specific alkaline phosphatase (ALP). The monoclonal antibody used in this assay was raised against purified bone-specific ALP obtained from SAOS-2 human osteosarcoma cell line. Calibration was based on the enzyme's own activity. The relative activity of the antibody was 100% with bone ALP, 8.7% with liver ALP, and 0% with placental and intestinal ALPs. Intra- and inter-assay coefficients of variation were less than 4%. The sensitivity of the assay was 0.7 U/L, and the linearity extended from 2 to 140 U/L. The recovery of bone-specific ALP standard added to serum was 94-106%. The correlation coefficient between this method and the polyacrylamide gel (PAG) electrophoretic method was 0.94. The mean value of bone-specific ALP in 89 healthy adults (mean age 29 years, SD 5 years) was 18.5 U/L (SD 4.1 U/L). Interestingly, mean bone-specific ALP activities in 60 premenopausal women (mean age 39 years, SD 8 years) and 70 postmenopausal women (mean age 57 years, SD 5 years) were 20.3 U/L (SD 6.5 U/L) and 31.1 U/L (SD 11.1 U/L), respectively. The age-related increase in bone-specific ALP was significant and more pronounced in women (P < 0.01). We conclude that this new immunoassay of bone-specific ALP would be useful for clinical investigation of patients with osteoporosis or other metabolic diseases of bone.

Alkaline phosphatase isozymes of serum and urine and urinary protein in young men before and after running 3 km

Urine samples were collected from seven healthy male students 1 h before (control fraction) and 5-15 min (5-15 min fraction), 1 h (1-h fraction) and 3 h (3-h fraction) after running 3 km at a perceived exertion equal to approximately 15-17 Borg's scale. Venous blood was also collected from the subjects 1 h before and 1 h after the run. Urine was studied by measuring protein excretion, patterns of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of proteins, total alkaline phosphatase (ALP) excretion, intestinal alkaline phosphatase (IAP) excretion and ALP isozyme analysis by PAGE. Serum ALP was studied by measuring the total ALP activity and isozyme analysis by PAGE. The following results were observed: firstly, an increase was seen in the excretion of total protein, total ALP and IAP after the exercise. Statistical significance was seen in the first two of these parameters; secondly, albumin was the only detectable protein band in the control, 5-15 min and 3-h fraction by SDS-PAGE; thirdly, no significant changes were seen in total ALP activity and ALP isozymes in the serum; and fourthly, three to five ALP bands (bands 1, 2, 3, 4 and 5, from the cathodal side) were detected in the zymograms of urinary ALP. Bands 1-3 were high molecular mass ALP. Bands 4 and 5 were intestine-like and liver-like ALP, respectively. An increase of ALP activity of high molecular mass ALP and/or decrease of that of band 5 or appearance of band 4 were seen in the 1-h fraction, in comparison to the control fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences between the sugar moieties of liver- and bone-type alkaline phosphatases: a re-evaluation

We re-evaluated the differences between the sugar moieties of liver and bone alkaline phosphatases (ALPs). Sialic acid was added to ALP sugar moieties by alpha 2,3- or 2,6-sialyltransferase treatment of the asialo-form ALP (neuraminidase-treated ALP). Asialo-bone ALP was converted to a liver-like ALP by the 2,6-sialyltransferase treatment. The resulting liver-like ALP was less susceptible to neuraminidase than non-treated bone ALP, but was still labile to heat exposure at 56 degrees C like non-treated bone ALP. However, after the O-linked sugar moiety had been released by additional treatment with O-glycanase the liver-like ALP became more heat stable at 56 degrees C, like non-treated liver ALP. Non-treated liver ALP reacted specifically with anti-liver ALP monoclonal antibody, and non-treated bone ALP reacted with both anti-liver and anti-bone ALP antibodies. The asialo-bone ALP still reacted with anti-bone ALP antibody, whereas the asialo-form liver ALP showed little, if any, reaction with anti-liver and anti-bone ALP antibodies. Neuraminidase and O-glycanase-treated bone ALP reacted less with anti-bone ALP antibody. After O-glycanase treatment, bone ALP molecules deprived of an O-linked sugar moiety had a molecular size and heat stability similar to liver ALP. The difference between liver and bone ALP molecules may be due not only to their manner of sialic acid linkage but also to the attachment of the O-linked sugar moiety.

A case of benign familial hyperphosphatasemia of intestinal origin

We recently encountered a case of hyperphosphatasemia, in which > 90% of serum alkaline phosphatase (ALP) was of intestinal origin. The patient, a 51-year-old man, was found to have hyperphosphatasemia (2,341 U/L) during a routine medical check-up. All other laboratory tests and physical findings were normal. The agarose gel electrophoresis pattern of the patient's serum ALP was identical to that of common intestinal ALP from healthy adults, and only a single band of intestinal ALP was detected by immunoaffinity electrophoresis. In addition, 89% of total ALP was defined as intestinal ALP by an immunoprecipitation method. The molecular mass of the ALP was 154 kDa, almost identical with that of adult duodenal ALP. Analysis of the sugar chain structure showed an increased la fraction (74%) compared with adult duodenal ALP. Genealogical study revealed that two persons in the 5 members of the proband's family had hyperphosphatasemia of intestinal origin, indicating possible autosomal dominant inheritance.

Intestinal type alkaline phosphatase hyperphosphatasemia associated with liver cirrhosis

Hyperphosphatasemia due to increased intestinal type serum alkaline phosphatase was noted in a 48-year-old male who had asymptomatic liver cirrhosis. The alkaline phosphatase activity in the serum was 828 U/l (our reference range in adults: 57-194 U/l), 94% of which was of the intestinal type as measured by an immunoprecipitation method. The intestinal component of alkaline phosphatase was separated into two major and some minor components using electrophoresis and isoelectrofocusing. One of the major components had similar mobility to that of a standard intestinal enzyme purified from adult intestine. The components were heat-labile and neuraminidase-resistant. Serial lectin affinity chromatography, however, indicated that sugar chain compositions of the alkaline phosphatase were different from those of the standard tissue intestinal enzyme. These results and further enzymological studies suggest that the patient's serum alkaline phosphatase basically consisted of several intestine-like isoforms.

Liver-like alkaline phosphatase in the tissue-unspecific type enzyme found in rabbit organs

Rabbit liver and kidney tissues are known to produce an intestinal-like alkaline phosphatase (IAP-like enzyme) as a dominant isozyme, with a minor isozyme of tissue-unspecific type (UAP), unlike humans and other mammalians. We investigated immunohistochemically and biochemically these unique isozymes in the rabbit liver and bone, and compared them with the human isozyme. In rabbit liver, UAP was found to be localized only in the apical part of the membrane of cells lining the bile duct, whereas IAP-like enzyme was found in the sinusoidal membrane of hepatocytes. Rabbit liver UAP was separated from IAP-like enzyme by DEAE-cellulose column chromatography. Rabbit bone tissue contained only one UAP isozyme. The two UAPs were biochemically and physicochemically compared with human liver AP. Both UAPs reacted with an anti-human liver AP monoclonal antibody, not with an anti-human bone AP monoclonal antibody, indicating that both enzymes have the same antigenicity as human liver AP. Rabbit liver and bone UAPs had similar N-linked sugar-chain heterogeneities to the respective human enzymes. In addition, rabbit bone AP also had an O-linked sugar chain, as did human bone AP, unlike rabbit and human liver APs.

Purification and partial characterization of intestinal-like alkaline phosphatase in rabbit kidney

Two types of alkaline phosphatase (AP) isozymes in rabbit kidney, a major intestinal-like type and a minor tissue-unspecific type, have been identified. The former enzyme was purified from rabbit kidney by immunoaffinity chromatography using monoclonal anti-human intestinal AP antibody. The purified enzyme yielded a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the apparent molecular size of its monomer subunit was found to be 72,000. Three amino acid residues within the first 16 N-terminal amino acid residues were different in purified AP and human intestinal AP. Although the rabbit enzyme possessed some peptide bands identical to those of human adult intestinal AP after Staphylococcus aureus V8 protease digestion, the enzyme did not react with monoclonal antibody against human adult intestinal AP alone, whereas it did react with monoclonal antibody against both human adult and fetal intestinal APs. The affinity of the enzyme for concanavalin A was identical to that of the fetal intestinal AP, but different from that of the adult enzyme. These results indicate that the antigenicity and certain properties of purified rabbit AP are more like those of human fetal intestinal AP or Kasahara isozyme, so-called intestinal-like AP, than like human adult intestinal AP.

Developmental changes in the antigenicity and sugar-chain heterogeneity of rabbit alkaline phosphatases

1. Rabbit alkaline phosphatases (APs) clearly fused with the anti-human AP antibodies. In particular, fetal liver and kidney APs reacted slightly less with the anti-intestinal AP antibody as did adult enzymes, suggesting that intestinal AP-like isozyme is expressed at earlier stages of gestation in rabbit liver and kidney. 2. Immunohistochemical data indicated that intestinal AP-like isozyme in the kidney was mainly localized in the distal convoluted tubules and slightly in the proximal straight tubules, whereas liver/bone/kidney AP-like enzyme was found more in the glomeruli and interstitial capillary walls as a major component. 3. The sugar-chain heterogeneity of adult and fetal rabbit APs displayed organ-specificity as did of rat and human APs. Moreover, in fetal development, the expression of high-mannose type or hybrid type sugar chains precedes the expression of complex type sugar chains in fetal development.

Similarity of the sugar moiety of human alkaline phosphatases between the kidney cortex and duodenum, or medulla and ileum

Characteristics of human renal cortex and medulla alkaline phosphatase (ALP) were compared. Enzymatic and hydrophobic properties of both ALPs were almost similar. However, the results of concanavalin A affinity chromatography and wheat germ agglutinin affinity electrophoresis, exhibited that sugar chain structure(s) might be different between the cortex and medulla ALPs. In addition, the molecular mass and substrate specificity differed from each other, and these results of cortex and medulla ALPs were well accordant with those of human duodenal and ileal ALPs, respectively, as described previously (Clin Chim Acta 1987;163:279-287).