The origin of serum alkaline phosphatase in the rat

Effect of calcium on rat intestinal alkaline phosphatase activity and molecular aggregation

Two fractions of rat intestinal alkaline phosphatase (IAP) were detected by Western blot: 168 +/- 6 and 475 +/- 45 kDa. The low molecular weight fraction constitutes 43% of the isolated proteins exhibiting 82% of the enzymatic activity, and a heavier fraction constitutes 57% of the isolated proteins and has 18% of the enzymatic activity. Calcium produced an increase of the 475-kDa form to the detriment of the 168-kDa form. This work also describes the kinetic and structural changes of IAP as a function of calcium concentration. With [Ca2+] < 10 mmole/L, the Ca(2+)-IAP interaction fitted a binding model with 7.8 +/- 4.4 moles of Ca2+ /mole of protein, affinity constant = 19.1 +/- 8.4 L/mmole, and enzymatic activity increased as a linear function of [Ca2+] (r = 0.946 p < 0.01). On the other hand, with [Ca2+] > 10 mmole/L the data did not fit this model and, the enzymatic activity decreased as a function of [Ca2+] (r = - 0.703 p < 0.05).

The influence of fasting on blood glucose, triglycerides, cholesterol, and alkaline phosphatase in rats

Serum concentrations of glucose, cholesterol, triglycerides, and serum alkaline phosphatase activity were measured over different periods of time of food deprivation in male rats. Thirty percent of non-fasted rat's sera was found to be lipemic. At 16 hours of fasting, glucose levels dropped by 30% compared to the level of the non-fasting control group, and remained at a relatively constant level for up to 48 hours of fasting. Triglyceride concentrations decreased at 16 hours after fasting. Serum cholesterol levels were not changed at any of the fasting periods compared to the non-fasted control group. Alkaline phosphatase activity was decreased at 8 hours of fasting, with further declines in activity of the serum enzyme seen at 16, 24, and 48 hours of fasting. It was concluded that at 16 to 18 hours fasting, a non-absorptive state had been reached in male rats.

Reduced alkaline phosphatase activity in diabetic rat bone: a re-evaluation

We found previously that human bone alkaline phosphatase (AP) was glycated by aseptic incubation with glucose, and partially broken down by reactive oxygen species. In this study, we examined whether selective in vivo glycation of AP molecules occurred in bone tissue, using experimental diabetic rats induced by streptozotocin and spontaneously diabetic rats. Additionally, the effects of hyperlipidemia on bone AP activity were examined. Serum AP activity was significantly elevated after incipient onset of diabetes, and the increased activity originated from the intestinal isozyme. High levels of intestinal AP activity were also observed in rats with hyperlipidemia induced by feeding high-fat or high-fructose chow, but the AP activity in bone tissues was maintained at a constant level. AP activity in bone was reduced after the onset of diabetes. The resulting bone AP molecule bound to an aminophenylboronic acid column, which had affinity for glycated proteins, and contained smaller molecular sizes than the native bone AP. These results suggest that elevated levels of serum AP activity originated from the intestinal isozyme accompanied with hyperlipidemia induced by diabetes. In contrast, the reduced serum levels of AP activity in diabetic rats might be dependent on inactivation of bone AP, which was glycated, followed by partial breakdown of bone AP molecules, possibly due to reactive oxygen species.

Role of sodium azide in reducing nonspecific color development in enzyme immunoassays

Improved enzyme immunoassay (EIA) procedures achieved by incorporating sodium azide during predilution of serum samples in a solid-phase EIA for the detection of anti-Toxoplasma antibody in swine using a peroxidase conjugate and in all washes of a bovine brucellosis rapid card test EIA using alkaline phosphatase conjugate are reported. Without this modification, substantial background interference was encountered that showed direct correlation with the degree of hemolysis of the serum samples. Anti-Toxoplasma gondii antibody-negative samples, separated by subjective groupings based on degree of hemolysis, into "clear", "slight", and "gross/total" samples, had a mean +/- standard deviation of 0.150 +/- 0.072, 0.187 +/- 0.105, and 0.232 +/- 0.108, respectively. The incorporation of sodium azide during the initial step of serum dilution dramatically eliminated the background, giving a mean +/- standard deviation of 0.079 +/- 0.029, 0.076 +/- 0.022, and 0.081 +/- 0.029, respectively. The level of endogenous peroxidase activity, a possible factor for this nonspecific interference, was considerably elevated in some of the swine sera. The clear, slight, and gross/total categories had relative levels of 1%, 2%, and 51% peroxidase activity compared to the conjugate peroxidase activity of 100%. Whereas sodium azide could be used only in sample predilution in the swine toxoplasmosis peroxidase-conjugate test, in the bovine brucellosis alkaline phosphatase-conjugate card test it could be used in all wash cycles. Many brucellosis card test results were visually uninterpretable because of significant background color when the manufacturer's wash reagent was used. The substitution of a wash reagent containing sodium azide eliminated background color, giving a visually unambiguous test.

Synthesis and parallel secretion of rat intestinal alkaline phosphatase and a surfactant-like particle protein

Rat intestinal microvillous alkaline phosphatases are secreted bidirectionally from the enterocyte attached to a phospholipid-rich membrane (surfactant-like particle). To determine the intracellular pathways for newly synthesized alkaline phosphatases and for the extracellular enzyme-particle complex in the intestinal mucosa, pulse-chase experiments were performed. Synthesis of both isoforms of alkaline phosphatase in fasted rats peaked in the Golgi at 15-30 min and in the microvillous membrane at 60 min, without intermediate localization in the basolateral membranes. A second peak of incorporation was found at 15-30 min in scrapings obtained from the apical surface of the enterocytes. These results demonstrate a dominant direct Golgi-to-microvillous membrane transport for newly synthesized alkaline phosphatase. An additional precursor pool(s) appears responsible for the early appearance of enzyme in the lumen. Newly synthesized alkaline phosphatase isoforms and the 97-kDa protein of surfactant-like particles showed parallel patterns of appearance in enterocytes, luminal washings, and lamina propria after triacylglycerol feeding and were preferentially secreted into the lumen and lamina propria at times (5-7 h) when enterocyte content of these newly synthesized proteins had declined toward basal rates. Enhanced secretion of newly synthesized proteins for hours after fat feeding could explain the prolonged rise in serum and luminal washings of both the enzyme and the particle.

A 91-day feeding study in rats with caprenin

Caprenin, a randomized triglyceride primarily comprising caprylic (C8:0), capric (C10:0), and behenic (C22:0) acids, was administered in a semi-purified diet to weanling Sprague-Dawley rats (25/sex/group) at dose levels of 5.23, 10.23 or 15.00% (w/w) for 91 days. Corn oil was added at 8.96, 5.91 and 3.00%, respectively, to provide essential fatty acids and digestible fat calories. Corn oil alone (12.14%) and a blend of medium-chain triglyceride (MCT) oil plus corn oil (11.21 and 3.13%, respectively) served as controls. All diets were formulated to provide about 4000 kcal/kg of diet and 26.8% of digestible calories from fat by assuming that corn oil, MCT oil, and caprenin provided 9, 7 and 5 kcal/g, respectively. Survival, clinical signs, body weight, feed consumption, feed efficiency, organ weights, organ-to-body-weight ratios, organ-to-brain-weight ratios, haematological values and clinical chemistry parameters were evaluated in all groups. Histopathology of a full complement of tissues was evaluated in the corn oil and MCT oil control groups as well as the high-dose caprenin group. Additional rats (n = 5/sex/group) were included in the study to determine whether there was marked storage of C22:0 in heart, liver or perirenal fat at the end of the 91-day feeding period. No significant differences in body weight gain were measured with the balanced caloric diets, although feed conversion efficiency was reduced in the high-dose caprenin group. No adverse effects from the ingestion of caprenin were detected, nor were significant amounts of C22:0 present in the fat extracted from the selected fat depot sites. These results establish a no-observable-adverse-effect level (NOAEL) of more than 15% (w/w) caprenin in the diet (or more than 83% of total dietary fat), which is equal to a mean exposure level of more than 13.2 g/kg/day for male rats and more than 14.6 g/kg/day for female rats.

Analysis of a conjugate between anti-carcinoembryonic antigen monoclonal antibody and alkaline phosphatase for specific activation of the prodrug etoposide phosphate

The selective targeting of tumors by enzymes conjugated to monoclonal antibodies (mAb) may be an ideal approach to convert relatively nontoxic prodrugs into active agents at the tumour site. We used the anti-carcinoembryonic antigen mAb BW431/26 conjugated to alkaline phosphatase (AP) and phosphorylated etoposide (etoposide-P) as a prodrug to study the feasibility of this concept. Etoposide was phosphorylated with POCl3. Quantitative hydrolysis of etoposide-P to etoposide occurred within 10 min in the presence of AP. BW431/26 and AP were conjugated using a thioether bond. The AP conjugate retained 93% of its calculated activity. 125I-labelled AP conjugate did not show a reduction of immunoreactivity as determined by a cell-binding assay. SW1398 colon cancer cells were used to analyse the cytotoxicity of etoposide and etoposide-P. Etoposide (IC50 22 microM) was 100 times more toxic than etoposide-P (20% growth inhibition at 200 microM). Pretreatment of the cells with BW431/26-AP prior to etoposide-P exposure resulted in a dramatic increase in cytotoxicity (IC50 70 microM). The pharmacokinetics and tumour-localizing properties of BW431/27 and the AP conjugate were assessed in nude mice bearing SW1398 tumours. BW431/26 showed excellent tumour localization (10% of the injected dose/g tissue retained from 8 h to 120 h), whereas the AP conjugate showed a reduced tumour uptake (3%-0.3% of the injected dose/g tissue at 8-120 h), a faster clearance from the circulation and a high liver uptake. Radiolabelled AP showed a similar pharmacokinetic profile to the AP conjugate. Gel filtration analysis of blood, liver, and tumour samples indicated good stability of the conjugate.

Retinoid-induced hemorrhaging and bone toxicity in rats fed diets deficient in vitamin K

The recent increase in the clinical use of synthetic vitamin A compounds has led to concern of possible side effects. Some of these effects are known to be influenced by dietary levels of vitamin K. We therefore compared the toxic effects of 13-cis-retinoic acid (13cisRA), retinyl acetate (ROAc), and N-(4-hydroxyphenyl)retinamide (4HPR) in male Sprague-Dawley rats maintained on diets containing different levels of vitamin K. Animals were fed either an NIH-07 diet supplemented with menadione (3.1 ppm vitamin K3), an NIH-07 diet not supplemented with menadione, or an AIN-076 purified diet devoid of vitamin K. The retinoids had no effect on prothrombin times of animals fed the supplemented diet. When menadione was omitted from the diet, however, 4HPR-dosed animals had elevated prothrombin times. This effect was observed as early as Day 7 and was accompanied by one confirmed hemorrhagic death. 13cisRA-dosed animals showed no change in prothrombin times. In the high-dose ROAc group, there was a twofold increase in prothrombin times but only after prolonged dosing. In animals fed the NIH-07 diets, 13cisRA and ROAc induced multiple bone fractures at all dose levels. In contrast, 4HPR administered at the highest dose induced only one fracture in one animal. Animals fed the purified diet lost weight faster and diet sooner than those maintained on the other diets. Bone fractures were not observed in these animals because of early deaths resulting from hemorrhaging. For all retinoid-dosed groups maintained on the purified diet, changes in prothrombin times occured as early as 1 week. The order of effect was 4HPR greater than ROAc greater than 13cisRA, with increases in prothrombin times correlating with increases in hemorrhagic deaths. Hence, the degree of retinoid-induced hemorrhage, but not the incidence of bone fractures, was inversely related to vitamin K levels in the diet. 13cisRA and ROAc, but not 4HPR, caused a dose-dependent reduction in plasma osteocalcin, an effect that correlated with retinoid-induced bone effects. In contrast, serum alkaline phosphatase was elevated in animals dosed with 13cisRA or 4HPR but not in those dose with ROAc. For this enzyme, the electrophoretic pattern on agarose gel showed a decrease, compared to controls, in the major isozyme in serum of ROAc-dosed animals. Hence, plasma osteocalcin is a better predictor of retinoid-induced bone effects than serum alkaline phosphatase.

Blood appearance of rat alkaline phosphatase originating from the duodenum in vitro

The major source of rat serum alkaline phosphatase (ALP) is well known to be from the intestinal enzyme, but it is still unclear whether it is from the duodenal or the ileal enzyme. The organic origin was investigated by means of two-dimensional electrophoresis. Major isoelectric points and molecular masses for activities of duodenal enzyme treated with both phosphatidylinositol-specific phospholipase C and neuraminidase were identified apparently with those of the major serum enzyme. In organ culture, the normal duodenal enzyme was released in the highest amounts to the culture medium. These results indicate that the major source of serum ALP in adult rats is basically from the duodenal enzyme. On the other hand, lectin affinity chromatography for ALPs showed that the ALP in the medium from culture duodenum and liver had the same complex-type sugar chain as with the ALP in the duodenal tissue. Although the duodenal ALP induced by glucosamine in vitro had the hybrid-type chain, sugar chains of the induced ALP in the culture medium were of the complex type, indicating that medial ALPs possessing the same sugar chain as the native duodenal enzyme, complex type, are mainly released from their tissues in normal conditions.

The origin of plasma alkaline phosphatase activity in mice and rats

Swiss albino mice displayed the highest activity of alkaline phosphatase at 4-6 weeks with a precipitous decline by 18 weeks of age to a value seen in the mature animal. Circulating activity of alkaline phosphatase was significantly higher in the rat than the mouse in the fed state. With fasting, enzyme activity declined in the rat yet increased in the mouse. The net result was significantly higher plasma alkaline phosphatase activity in the mouse than the rat after the 48 hr fast. L-Phenylalanine inhibition of plasma alkaline phosphatase was greater in plasma from the rat than the mouse in the fed state. Yet in the fed condition, L-homoarginine and L-p-bromotetramisole inhibited alkaline phosphatase activity in plasma from mice to a greater extent than in rats. Heat inactivation as well as urea denaturation of alkaline phosphatase was significantly faster with plasma of the mouse than the rat in the fed state. Thus, it appears that the alkaline phosphatase isoenzyme of skeletal origin contributes a greater proportion of the circulating activity in the fed Swiss albino mouse than occurs in the Sprague-Dawley rat in which the intestinal isoenzyme plays a greater role in the fed condition.

The mechanisms relating to increases in plasma enzymes and isoenzymes in diseases of animals

Changes in plasma or serum enzymes and isoenzymes are useful indicators of tissue damage in many diseases. Enzyme increases are usually related to leakage of enzymes from damaged cells. The amount of increase depends on factors such as the concentration of enzyme in the cells, the rate of leakage of enzyme from cells and the rate of clearance of enzyme from plasma. There are important species variations in the tissue concentrations and plasma clearance rates of enzymes and isoenzymes.

Differential effects of phospholipids on skeletal alkaline phosphatase activity in extracts, in situ and in circulation

Human skeletal alkaline phosphatase (ALP) purified from human bone was subject to competitive inhibitions by phospholipids including cephalins, lecithins, and phosphatidylinositol. Ki values ranged from 0.7 to 1.5 mM, at pH 9.5. As previously shown, the enzyme was subject to uncompetitive inhibition by imidazole. The inhibitory phospholipids potentiated this effect, and altered the nature of the imidazole inhibition, from uncompetitive to mixed type, suggesting that imidazole was bound more efficiently to the enzyme-phospholipid complex than to the enzyme-substrate complex. No interactions were observed between phospholipids and other uncompetitive inhibitors of ALP. The skeletal ALP activity of cultured chick calvarial cells was assayed both in situ and in extracts. Like the extracted human isoenzyme, the extracted chick ALP was subject to competitive inhibition by cephalin (Ki = 0.3 mM at pH 9.3) and an inhibitory interaction between cephalin and imidazole, but the same isoenzyme showed neither effect in situ. The value of Km,PNPP at pH 9.5 for chick skeletal ALP was 1.5 mM in extracts and 7.1 mM in situ. When embryonic chick bones were cultured in vitro, skeletal ALP activity was released into the serum-free medium. Unlike the same isoenzyme extracted from the bones, the ALP activity in the medium was not inhibited by cephalin and showed no inhibitory interaction between cephalin and imidazole. Similarly, human serum ALP activities were not as sensitive to phospholipid inhibition as the same isoenzymes extracted from tissues. Human skeletal ALP extracted from bone was inhibited by cephalin, but the skeletal isoenzyme in Pagetic serum was not, suggesting that the potential for phospholipid interaction was altered during or after release from osteoblast cell membranes. The observation that extracted human skeletal ALP lost its potential for inhibition by phospholipids after treatment with phospholipase C further suggests that ALP activity may be released from cells during membrane turnover.

Alkaline phosphatase activity in chronic streptozotocin-induced insulin deficiency in the rat: effect of insulin replacement

Alterations in circulating alkaline phosphatase have been described in both man and the experimental animal with chronic insulin deficiency. We evaluated plasma and tissue alkaline phosphatase levels in freely-fed control, streptozotocin-induced diabetic and insulin-treated diabetic rats, seven weeks after the induction of diabetes. Circulating alkaline phosphatase activity was markedly elevated in the insulin deficient animal (p less than 0.001) and completely normalized following insulin administration. The elevated plasma alkaline phosphatase activity observed in the insulin deficient animals was heat-resistant and phenylalanine-sensitive, a pattern typical of the intestinal isoenzyme. Small intestinal alkaline phosphatase activity was significantly higher (p less than 0.01) in the diabetic animals, but comparable in the insulin-replaced and control rats. The intestinal isoenzyme activity was found to be strikingly insulin-sensitive; withholding insulin therapy for 36 hr prior to sacrifice resulted in an abrupt rise in both plasma and intestinal alkaline phosphatase values comparable to those observed in the insulin-deficient state. In contrast to these observations, skeletal alkaline phosphatase activity was decreased in the insulin deficient animal (p less than 0.01) and this abnormality was corrected by insulin replacement. Neither insulin deficiency nor insulin replacement resulted in any significant changes in the hepatic alkaline phosphatase isoenzyme.

Alkaline phosphatase isoenzymes in serum of rats during cholestasis

Alkaline phosphatase isoenzymes (API) in serum of rats during cholestasis are investigated. For comparison different membrane systems in liver are damaged. Proliferation of bile canaliculi, sinusoidal area, and endoplasmic reticulum, respectively, is induced by different toxic conditions. It is found that in cholestasis an API5 in serum arises which is not present in serum of normal rats, but can be detected in normal rat liver. Thus, it is not a de novo synthesis of this API. Under the condition connected with a proliferation of bile canaliculi we find this API5 in serum. Under different conditions without proliferation of bile canaliculi we do not find an increase of this API5. We assume, therefore, that API5 in cholestasis is produced by cells of the bile canaliculi rather than by liver parenchymal cells in the sinusoidal area. No difference is found in intra- or extrahepatic cholestasis.

Studies of rat alkaline phosphatase I. Development of methods for detecting isoenzymes

A manual system of various estimations of rat plasma alkaline phosphatase activity has been devised for small volumes of plasma which uses different inhibitors, compares the utilisation of two substrates and includes acrylamide gel electrophoresis. The different inhibitors etc. allow a degree of discrimination between alkaline phosphatase extracts of rat organs. The properties of isoenzymes, e.g. intestinal phosphatase, differ depending upon the environment in which they are studied. In conjunction, if necessary, with the methods described for the estimation of liver and intestinal alkaline phosphatase activity, it is hoped to use the system to discriminate between the isoenzymes present in the plasma alkaline phosphatase of rats in toxicological studies.

Changes in the alkaline phosphatase (EC 3.1.3.1) and inorganic pyrophosphatase (EC 3.6.1.1) activities of rat tissues during magnesium deficiency. The importance of controlling feeding pattern

1. The adoption of a meal-eating pattern of feeding by rats altered the alkaline phosphatase (EC 3.1.3.1) activity in serum and liver. It was therefore necessary to regulate the feeding pattern of both magnesium-deficient rats and control animals receiving a Mg-adequate diet in order to study the effect of the deficiency. 2. Mg deficiency decreased the activities of alkaline phosphatase and inorganic pyrophosphatase (EC 3.6.1.1) in serum, kidney and tibia, but increased them in spleen. 3. Addition of a standard concentration of exogenous Mg to tissue extracts usually increased the activity of corresponding enzymes from Mg-deficient and control rats by the same proportion, indicating that the main effect of the deficiency was on the amount of enzyme present rather than on the efficiency of its operation. 4. Certain quantitative differences in the response to exogenous Mg and the activity ratio, alkaline phosphatase:inorganic pyrophosphatase were found between tissues from Mg-deficient and control rats. The significance of these are discussed in relation to the association of the two enzymic activities with the same protein molecule, and the possible occurrence of isoenzymes.