Research Articles
Monocarboxylate Transporter Mediates Uptake of Lovastatin Acid in Rat Cultured Mesangial Cells

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ABSTRACT:

To clarify the uptake mechanism(s) for statins, we examined whether monocarboxylate transporter (MCT) contributed to the uptake of lovastatin acid by rat cultured mesangial cells. Expression of mRNAs for MCT1, 2, and 4 was confirmed in mesangial cells. The uptake of lovastatin acid by mesangial cells increased with decreasing extracellular pH. There was clear overshooting in lovastatin acid uptake by the ATP-depleted cells in the presence, but not in the absence, of an inwardly directed H+-gradient. The representative MCT substrates/inhibitors inhibited the lovastatin acid uptake. In particular, the inhibition of lovastatin acid uptake by L-lactic acid at the concentration of 80 mM reached 70%, and L-lactic acid and valproic acid inhibited the uptake competitively. On preloading of mesangial cells with L-lactic acid or valproic acid, the lovastatin acid uptake was significantly stimulated. The inhibition constant of L-lactic acid for the lovastatin acid uptake was 32 mM, and this value is comparable to the Michaelis constant (>20 mM) of L-lactic acid for MCT4 described elsewhere. These results demonstrate that lovastatin acid was largely taken up by mesangial cells via MCT, and suggest that MCT4 might contribute to lovastatin acid uptake in the cells. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association

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INTRODUCTION

Mesangial cells are a major constituent of the renal glomerulus and have complex biological functions. Their proliferation is believed to play an important role in the inflammatory response to glomerular injury, which is one of the general characteristics of various glomerular diseases, including proliferative glomerulonephritis, IgA nephropathy, and diabetic nephropathy.1., 2., 3. However, the mechanisms underlying the occurrence and development of proliferative nephritis remain unclear, being

Materials

Lovastatin was generously provided by Merck Sharp & Dohme Research Laboratories, Rahway, NJ. Lovastatin acid was prepared from its lacton form by hydrolysis in a 0.05 N NaOH solution with stirring at 20°C for 30 min. The hydrolyzed solution was adjusted to pH 7.4 with 0.2 N HCl and then stored at 4°C until use.4,11 The purity of lovastatin acid was >95%, as confirmed by high-performance liquid chromatography (HPLC). RPMI1640 medium, collagenase type I, and FBS were purchased from GIBCO

Expression of mRNAs for MCT Isoforms

The expression of mRNAs for MCT1, 2, 3, and 4 in rat cultured mesangial cells was examined by the RT-PCR method using specific primers for each isoform. As shown in Figure 1, there were mRNAs of MCT1, 2, and 4 in the mesangial cells.

Effect of Extracellular pH

The effect of the extracellular pH on lovastatin acid uptake by mesangial cells is shown in Figure 2. The rate of uptake of lovastatin acid apparently increased with decreasing extracellular pH, the maximum uptake rate being observed at pH 5.5. So, in the following

DISCUSSION

In our previous report,4 the carrier-mediated uptake of lovastatin acid by mesangial cells was estimated to be ∼90% of the total uptake, and contribution of nonspecific diffusion was thought to be negligible. Thus, we consider the results obtained in this study almostly reflect the carrier-mediated uptake of lovastatin acid by mesangial cells.

First, we confirmed the expression of MCT isoform(s) in rat cultured mesangial cells. As shown in Figure 1, there were messages for mRNAs of MCT1, 2, and

ACKNOWLEDGEMENTS

We are grateful to Merck Sharp & Dohme Research Laboratories for generously providing us with the lovastatin.

REFERENCES (31)

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