Glitazones regulate glutamine metabolism by inducing a cellular acidosis in MDCK cells

Abstract

-We studied the effect of the antihyperglycemic glitazones, ciglitazone, troglitazone, and rosiglitazone, on glutamine metabolism in renal tubule-derived Madin-Darby canine kidney (MDCK) cells. Troglitazone (25 M) enhanced glucose uptake and lactate production by 108 and 92% (both P Ͻ 0.001). Glutamine utilization was not inhibited, but alanine formation decreased and ammonium formation increased (both P Ͻ 0.005). The decrease in net alanine formation occurred with a change in alanine aminotransferase (ALT) reactants, from close to equilibrium to away from equilibrium, consistent with inhibition of ALT activity. A shift of glutamine's amino nitrogen from alanine into ammonium was confirmed by using L-[2-15 N]glutamine and measuring the [ 15 N]alanine and [15 N]ammonium production. The glitazone-induced shift from alanine to ammonium in glutamate metabolism was dose dependent, with troglitazone being twofold more potent than rosiglitazone and ciglitazone. All three glitazones induced a spontaneous cellular acidosis, reflecting impaired acid extrusion in responding to both an exogenous (NH 4 ϩ ) and an endogenous (lactic acid) load. Our findings are consistent with glitazones inducing a spontaneous cellular acidosis associated with a shift in glutamine amino nitrogen metabolism from predominantly anabolic into a catabolic pathway.

Troglitazone Acts on Cellular pH and DNA Synthesis through a Peroxisome Proliferator-Activated Receptor γ-Independent Mechanism in Breast Cancer-Derived Cell Lines

“…Therefore, depending on the concentration and physiologic conditions, the antitumorigenic action of TRO appears to involve both PPAR␥ and PPAR␥-independent pathways. Another apparent PPAR␥-independent action that may play an anticancer role is the ability of TRO to induce cellular acidosis, which we have demonstrated previously in normal cells (35)(36)(37). Our previous findings are consistent with glitazones inducing a spontaneous cellular acidosis associated with a shift in glutamine amino nitrogen metabolism from a predominantly anabolic to a catabolic pathway in canine mesangial cells (35).…”

“…We also assess the ability of TRO-induced acidosis to inhibit DNA synthesis in a dosedependent manner and partially independent from PPAR␥ activation. Our results present a novel action of TRO as an antiproliferative compound that broadens the spectrum of various PPAR␥-independent effects described previously (35)(36)(37).…”

“…Another apparent PPAR␥-independent action that may play an anticancer role is the ability of TRO to induce cellular acidosis, which we have demonstrated previously in normal cells (35)(36)(37). Our previous findings are consistent with glitazones inducing a spontaneous cellular acidosis associated with a shift in glutamine amino nitrogen metabolism from a predominantly anabolic to a catabolic pathway in canine mesangial cells (35). Consequently, we have shown that TRO induces a spontaneous cellular acidosis resulting from a reduction in cellular acid extrusion in murine mesangial cells (36).…”

“…We have shown previously that TRO induces cellular acidosis in nontumorigenic cells expressing either NHE1 or NHE3 (35)(36)(37). Based on these observations, we asked whether TRO would decrease pH i in breast carcinoma-derived cell lines MCF-7 and MDA-MB-231.…”

“…The chambers were placed uncapped inside a 60-mm covered tissue culture dish, incubated at 37°C in 5% CO 2 atmosphere, and allowed to gain confluence. The pH i was determined with the pH-sensitive fluorescent dye (2,7)-biscarboxyethyl-5(6)-carboxyfluorescein [BCECF (Molecular Probes, Eugene, OR)] assay performed at 37°C by spectrofluorometry as described previously (35,36). Changes in the emission ratio (490 nm/440 nm) were taken as an index of changes in pH i .…”