Maria R Negrão

Alkaline phosphatase from rat liver and kidney is differentially modulated

OBJECTIVE To investigate the effect of inhibitors of alkaline phosphatase (ALP) and modulators of P-glycoprotein (Pgp), multidrug resistance protein (MRP) and hepatic taurocholate uptake on the activity of tissue-nonspecific ALP (TNALP) in liver and kidney. DESIGN AND RESULTS ALP activity was determined in rat liver and kidney homogenates. Levamisole had a stronger inhibitory effect on renal TNALP than on the hepatic isoform. 1,3-dimethylxanthine (theophylline) almost abolished renal TNALP activity whereas its effect on hepatic TNALP was less intense. 3-isobutyl-1-methylxanthine (IBMX) and lidocaine produced opposite effects, activating hepatic TNALP and inhibiting the kidney isoform. Quinidine significantly inhibited renal TNALP without affecting hepatic TNALP. Kaempferol activated both liver and kidney isoforms, the effect being more pronounced on hepatic TNALP. CONCLUSIONS a) renal TNALP seems to be more sensitive to inhibition than hepatic TNALP, b) TNALP activity studies should take into account the source of ALP isoform and c) ALP pharmacological manipulation in vivo may produce different and even opposite effects in different tissues/organs.

Characterization of rat heart alkaline phosphatase isoenzymes and modulation of activity

Alkaline phosphatase (ALP) is important in calcification and its expression seems to be associated with the inflammatory process. We investigated the in vitro acute effects of compounds used for the prevention or treatment of cardiovascular diseases on total ALP activity from male Wistar rat heart homogenate. ALP activity was determined by quantifying, at 410 nm, the p-nitrophenol released from p-nitrophenylphosphate (substrate in Tris buffer, pH 10.4). Using specific inhibitors of ALP activity and the reverse transcription-polymerase chain reaction, we showed that the rat heart had high ALP activity (31.73 +/- 3.43 nmol p-nitrophenol.mg protein-1.min-1): mainly tissue-nonspecific ALP but also tissue-specific intestinal ALP type II. Both ALP isoenzymes presented myocardial localization (striated pattern) by immunofluorescence. ALP was inhibited a) strongly by 0.5 mM levamisole, 2 mM theophylline and 2 mM aspirin (91, 77 and 84%, respectively) and b) less strongly by 2 mM L-phenylalanine, 100 mL polyphenol-rich beverages and 0.5 mM progesterone (24, 21 to 29 and 11%, respectively). beta-estradiol and caffeine (0.5 and 2 mM) had no effect; 0.5 mM simvastatin and 2 mM atenolol activated ALP (32 and 36%, respectively). Propranolol (2 mM) tended to activate ALP activity and corticosterone activated (18%) and inhibited (13%) (0.5 and 2 mM, respectively). We report, for the first time, that the rat heart expresses intestinal ALP type II and has high total ALP activity. ALP activity was inhibited by compounds used in the prevention of cardiovascular pathology. ALP manipulation in vivo may constitute an additional target for intervention in cardiovascular diseases.

Physiologic Concentrations of Bile Salts Inhibit Rat Hepatic Alkaline Phosphatase but Not the Intestinal Isoenzyme

OBJECTIVE The effect of bile salts on alkaline phosphatase (EC 3.1.3.1) activity from Wistar rat liver, duodenum, jejunum, and serum was investigated. DESIGN AND RESULTS For concentrations higher than 1 mM conjugated bile salts (glycocholate, glycochenodeoxycholate, taurocholate, taurodeoxycholate, and taurochenodeoxycholate) inhibited hepatic ALP but, up to concentrations of 10 mM, had no effect on intestinal ALP. Also cholate, deoxycholate, and chenodeoxycholate, within the same concentration range, did not have any effect on intestinal ALP. ALP inhibition induced by conjugated bile salts was significantly higher in serum of starved rats than in serum of fed animals, what is in good agreement with the known higher proportion of hepatic ALP and lower proportion of intestinal ALP in serum of starved rats. CONCLUSIONS Bile salts can, thus, be used to help discriminating between tissue-nonspecific and intestinal ALP isoenzymes and identifying pathologic conditions where the relative quantities of these isoenzymes are altered in serum. Inhibition of hepatic ALP by physiologic concentrations of bile salts may bear some relation to the bile salts effects on their own enterohepatic circulation and/or biosynthesis.

Comment on: Hosogai et al. (2007) Adipose Tissue Hypoxia in Obesity and Its Impact on Adipocytokine Dysregulation. Diabetes 56:901–911, 2007

In their most opportune and valuable article (1), Hosogai et al. provide a clear and quite extensive concatenation of data that indicate a very important role for hypoperfusion and hypoxia of adipose tissue in the dysregulated production of adipocytokines and metabolic syndrome. We had previously published a study on the role of adipocyte rupture—the more facile the bigger the adipocyte—in the inflammatory process …