The effects of purification and serum proteins on the organ identifying properties of alkaline phosphatases from canine tissues

Quantitation of skeletal alkaline phosphatase isoenzyme activity in canine serum

Pursuing the hypothesis that quantitation of skeletal alkaline phosphatase (ALP) activity in canine serum would provide an index of the rate of bone formation, we compared three methods for isoenzyme-specific identification of skeletal ALP activity in canine serum: heat inactivation, wheat germ agglutinin (WGA) precipitation, and concanavalin A (ConA) precipitation. ALP isoenzyme activities were extracted from canine bone, intestine, and liver, diluted into heat-inactivated canine serum (i.e., serum without ALP activity), and used as calibrators of ALP isoenzyme activities. Differential sensitivity to inhibition by 10 mM L-homoarginine was used to distinguish intestinal ALP activity from hepatic and skeletal ALP activities (i.e., 9, 80, and 72% inhibition, respectively). To allow resolution of skeletal ALP activity from hepatic ALP activity, we tested two established methods (heat inactivation and WGA precipitation) and a novel method, ConA precipitation. The organ-derived skeletal and hepatic ALP isoenzyme activities were used to compare these three methods with respect to linearity, isoenzyme separation, and precision. All three methods were linear, but the WGA and ConA methods afforded greater isoenzyme separation and precision. The relative extent of isoenzyme separation (i.e., the difference in percentage remaining skeletal and hepatic ALP isoenzyme activities) averaged 23, 40, and 47% remaining ALP activity for the heat, WGA, and ConA methods, respectively. However, when these methods were applied to the quantitation of skeletal ALP activity in sera from 10 young and 10 adult beagles, the WGA method was found to be unacceptable because most of the results fell outside the range of the WGA assay calibrators (i.e., greater than 100% skeletal ALP activity). The heat and ConA methods showed that the amount of skeletal ALP activity in the beagle sera decreased with age, both as ALP activity per liter and as percentage of total serum ALP activity (p less than 0.001 for each). Skeletal ALP activity levels determined by ConA were correlated with values determined by heat inactivation (r = 0.87, p less than 0.001) but not with WGA-determined levels (r = 0.26). Intestinal ALP activity was detected in only 1 of these 20 sera. We conclude that ConA precipitation can be used for quantitation of skeletal ALP activity in beagle serum.

Subcellular location of corticosteroid-induced alkaline phosphatase in canine hepatocytes

Dogs received either 4 mg/kg of prednisone or sterile saline daily for 32 days. Serum samples were assayed every 4 days for total alkaline phosphatase (ALP) and corticosteroid-induced ALP isoenzyme (CIALP) activity. The initial and major increase of serum ALP was attributed to the liver isoenzyme of ALP (LALP), however, CIALP began to increase by day 8 and was significantly increased by day 24. Prior to treatment and on day 32, sections of liver from control and prednisone-treated dogs were stained for ALP activity after blocking the staining activity of LALP with levamisole. The staining activity of CIALP was compared to the staining activity of LALP in liver sections from control dogs and from dogs in which the bile duct was ligated. It was determined that CIALP was located in that area of the hepatocyte membranes which comprise the bile canaliculi.

Separation and heat stability of the corticosteroid-induced and hepatic alkaline phosphatase isoenzymes in canine plasma

A convenient method has been developed for the separation of alkaline phosphates (AP) isoenzymes from canine plasma. The various forms of AP activity were extracted by ethanol and separated on an anion exchanger by fast protein liquid chromatography. In this way a complete discrimination was achieved between the increase in plasma AP activity due to liver disease and that due to corticosteroid induction. The corticosteroid-induced form of AP could be separated from the other isoenzymes because of its relative heat stability at 65 degrees C. A quantitation of the contribution of liver and corticosteroid-induced AP isoenzymes to the total plasma AP activity could be made from the respective heat inactivation plots. The separation of the isoenzymes may be valuable in the purification of the different isoenzymes for further characterization.