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Physiological functions of organic cation transporters (OCTs) in the placenta include transporting essential nutrients from the maternal to fetal circulations. OCTN2 transports carnitine with high affinity, and the transport of several drugs has also been shown to be mediated by this transporter. In this work, the role of phosphorylation and dephosphorylation mechanisms in regulating OCTN2 was investigated by observing the effects of various activators and inhibitors of kinases and phosphatases on the uptake of carnitine in BeWo cells, a human choriocarcinoma trophoblast cell line frequently used as an in vitro model of the rate-limiting barrier for maternal-fetal exchange. Preincubation with genistein resulted in significant increases in both alkaline phosphatase (ALP) activity and carnitine uptake. Levamisole, an ALP inhibitor, caused a more substantial decrease in carnitine uptake than expected from its corresponding decrease in ALP activity. It was determined that levamisole competitively inhibits carnitine uptake, with a K(i) value of 1.01+/-0.05mM, and this effect has a greater role in decreasing carnitine uptake than any indirect effects of ALP inhibition upon OCTN2 function. Progesterone also competitively inhibited carnitine uptake (K(i)=48.6+/-5.0muM), but had no effect on ALP activity in BeWo cells.

This study demonstrates the upregulation of alkaline phosphatase and the mechanisms involved in experimental colitis. All models of ileal and colonic inflammation examined, which were characterized by significant oxidative stress and neutrophil infiltration, resulted in an increase in alkaline phosphatase activity which was attributable to both epithelial cells and cells of the lamina propria, mainly leukocytes. The increase in alkaline phosphatase sensitivity to the inhibitors levamisole and homoarginine, together with changes in the apparent molecular size and in the sialization of the enzyme, indicated a change in the isoform expressed. An increase in tissue non-specific alkaline phosphatase expression was observed by Western blotting. Treatment with the bone/kidney alkaline phosphatase inhibitor levamisole or a monoclonal antibody resulted in significant protection from colonic inflammation. Taken together, these results indicate that the kidney isoform is a marker of intestinal inflammation and that it might even constitute a target for pharmacological intervention.

We studied the effect of bromolevamisole (BL) and other imidazo [2,1-b] thiazole derivatives--bromodexamisole (BD) and levamisole (LV)--on adenylate cyclase (AC) activity. BL and BD both inhibited forskolin-activated human thyroid AC, while LV had no effect. This inhibition was non-stereospecific and the IC50 values, as measured with 1 mM ATP and 40 microM forskolin, were 0.95 and 0.80 mM for BL and BD, respectively. In contrast, human thyroid alkaline phosphatase (ALP) inhibition was stereospecific, with IC50 values of 0.0012 mM for BL and 0.9 mM for BD. LV was a 10-fold weaker inhibitor of ALP than BL. These results show that ALP inhibition is not correlated with forskolin-activated AC inhibition. Furthermore, in the presence of a competitive inhibitor of GTP (0.1 mM guanosine 5'-O-(2-thiodiphosphate), BL retained its antagonizing effect on forskolin-activated AC which suggests a direct action on the catalytic subunit. The inhibition was of the mixed type, indicating a complex interaction between BL and AC. Glucagon-activated AC activity in rat liver membranes was also inhibited by BL, although to a slightly lesser degree than thyroid stimulating hormone (TSH)-activated AC from human thyroid for a given BL concentration. In cultured human thyroid cells, BL (0.25 mM) induced a potent decrease in cAMP accumulation after 2 hr of stimulation by TSH. Taken together, these results show that BL inhibits AC and that this inhibition is not organ-specific.

We tested the inhibitory effects of phenothiazine derivatives on bone in vivo and osteoblastic cells in vitro. Chlorpromazine (CPZ) and trifluoperazine (TFPZ) dose-dependently decreased alkaline phosphatase activity in calvariae of rats: half-maximal inhibitory effects of CPZ and TFPZ were at 2.0 and 4.0 mg/kg, respectively. These effects were more specific for calvaria and ileum than for liver and duodenum. CPZ inhibited the proliferation of osteoblastic clone MC3T3-E1 cells to a greater extent than that of liver epithelial clone RLC-18(4) cells in vitro. CPZ, TFPZ and perphenazine (PNZ) also affected rather specifically alkaline phosphatase activity and collagen synthesis and were not cytotoxic. These in vivo and in vitro findings suggest inhibitory effects on osteoblastic cell function(s). However, promethazine (PMZ) had little effect in vivo and in vitro. In addition, increases in serum calcium and phosphate induced by CPZ indicate its possible involvement in bone resorption.

Growth plate chondrocytes in primary culture release alkaline phosphatase (AP)-rich matrix vesicles (MV) into the culture medium. While these are thought to derive from the plasma membrane by a membrane fusion-dependent process, the mechanism is not fully understood. Recently, a cytosolic protein, synexin, has been shown to promote membrane fusion in a number of systems, and thus may be involved in MV formation. Since the action of synexin is selectively inhibited by trifluoperazine (TFP) and other phenothiazines, we examined the effects of these drugs, and imipramine, on cellular AP production and formation of AP-containing MV by cultured chondrocytes. In addition, we studied the effect on cell division, protein biosynthesis, and incorporation of palmitate into cellular and MV lipids. All of the drugs reduced cellular AP in a concentration-dependent manner; however, at the higher levels, chlorpromazine (CPZ) and TFP caused a transient sharp rise in MV AP activity. At IC50 levels, the drugs were more inhibitory to cellular AP than to MV AP, appearing to enhance significantly the transfer of available cellular AP into MV. In contrast, the drugs stimulated incorporation of [3H]palmitate into cellular lipids, but either had no effect on, or actually inhibited, incorporation of the fatty acid into MV. At these levels, the drugs had little effect on cell division and protein biosynthesis. The inhibitory effect of IC50 levels of CPZ on palmitate incorporation into MV appears to have resulted from impairment of vesicle formation per se, since at these levels the drug stimulated incorporation of the fatty acid into the cells. The transient stimulatory effect of higher levels of CPZ on MV AP levels, and the enhanced transfer of AP into MV by the drugs generally, may result from the effect of the drugs on membrane structure. Since TFP was not inhibitory to MV formation, it is doubtful that synexin was directly involved.

Analogues of bromo-levamisole and guanidine derivatives including cimetidine are examined in vitro in order to investigate their comparative inhibition, towards alkaline phosphatase (ALP) from human liver and diamine-oxidase (DAO) from human placenta. Bromo-levamisole, considered as a potent selective uncompetitive inhibitor of ALP (Ki, 2.8.10(-6) M at pH 10.5) is shown to be a noncompetitive inhibitor of DAO (Ki = 7.10(-4) M). According to the structure-inhibition relationship, the imidazole ring is important for ALP and DAO inhibition. The phenyl ring of bromo-levamisole is required for ALP inhibition but not for DAO inhibition, which is mediated mainly by aminoguanidine or guanidine groups. These results have allowed the selection of cimetidine, an H2-antagonist but also an immunomodulating compound, as inhibitor of these two enzymes. Cimetidine is an uncompetitive inhibitor of ALP (Ki = 3.2.10(-3) M at pH 10.5), and a good inhibitor of DAO (I50 = 3.8.10(-4) M). The Ki of ALP is commonly calculated at pH 10.5, but to study the role of the enzyme at the physiological pH, the inhibition has also been performed at pH 7.4. The Ki values are only slightly affected by this pH variation. So far several compounds, including levamisole, imidazole, theophylline and aminoguanidine are known to possess immunomodulating activities in vivo and/or in vitro and inhibit ALP and/or DAO. Therefore, it seems reasonable to assume that the inhibition of enzymes is involved in the immunomodulating effects of these drugs, when the ranges of active concentrations are similar for these properties.