The differential diagnosis of acute renal failure (ARF) and chronic renal failure (CRF) may be possible by measuring urinary dipeptidase (Udpase) activity and serum creatinine (Scr) concentration. When the mass test of 246 individuals was examined on a 2-dimensional plot of Udpase (y-axis) versus Scr (x-axis) with the data obtained from healthy volunteers (n = 189), ARF (n = 19) and CRF (n = 38) patients, the characteristic distribution of each group was obvious. It is summarized by the mean values of healthy volunteers (1.44 +/- 0.39 mg/dL, 1.19 (0.59 mU/mL), ARF (6.04 +/- 5.04 mg/dL, 0.12 +/- 0.08 mU/mL), and CRF patients (8.72 +/- 2.93 mg/dL, 0.81 +/- 0.44 mU/mL). The healthy volunteers are distributed along the y-axis and the ARF patients the x-axis, thus separating the two groups 90 degrees apart. The CRF patients are scattered away from both x-, and y-axis. This 2-dimensional approach is thought to be very useful for the differential diagnosis of ARF suggesting Udpase as a new member of the marker enzymes of renal disease.

Amphipathic and hydrophilic forms of human renal dipeptidase and urinary dipeptidase were purified by affinity chromatography using cilastatin, a dipeptidase inhibitor, as the ligand. The sequence analyses of the first ten amino acids of renal and urinary dipeptidases were shown to be identical, and they are Asp-Phe-Phe-Arg-Asp-Glu-Ala-Glu-Arg-Ile. Unambiguous results of amino acid sequencing, the molecular weight of native protein (190 kD), the molecular weight of subunit (47.7 kD) and a single band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicate that the enzymes are composed of homotetramers. This is the most direct evidence that urinary dipeptidase is the released form of renal dipeptidase. In fact, they are the same enzymes.

Effects of several drugs on rabbit renal proximal tubules were examined for the applicability of renal dipeptidase (RDPase, EC 3. 4. 13. 11) release as a model system to study nephrotoxicity. The proximal tubule prepared by the method of Taub (1990) released RDPase spontaneously in the control experiment which was confirmed by Western blotting. RDPase was also released from cisplatin, lipopolysaccharide (LPS), and indomethacin-treated tubules. Gentamicin inhibited RDPase release in a concentration-dependent manner. This RDPase release system may not be a general model to screen nephrotoxicity but could be a useful source of RDPase purification in a simple and inexpensive way.

The stability of DA-1131 to renal dipeptidase (RDPase) (EC 3.4.13.19) was compared with that of imipenem and meropenem by V max /K m ratios as an index of the enzyme's preference for substrates. Our results showed a decreasing order of imipenem (6.24), meropenem (2.41), and DA-1131 (1.39). The biochemical evaluation of DA-1131 as the least preferred substrate of RDPase suggests its potential use as a novel ␤-lactam antibiotic which may be usable without coadministration of RDPase inhibitors once its clinical suitability is proven.Imipenem (N-formimidoylthienamycin), developed by Merck Sharp & Dohme, West Point, Pa., was highly effective against bacterial species resistant to most ␤-lactam antibiotics with unusually high potency against gram-positive as well as gramnegative bacteria (8,21,23). It is degraded, though, in the kidneys of various animals, resulting in a reduced antibacterial activity. The enzyme responsible for this metabolism was shown to be renal dipeptidase (RDPase, also called renal dehydropeptidase I) (EC 3.4.13.19) located in the brush-border membrane of renal proximal tubules (8,9,20). Cilastatin, Z-2-(2,2-dimethylcyclopropanecarboxamido)-2-butenoic acid, is a specific competitive inhibitor of RDPase and is well matched in its pharmacokinetic properties for coadministration with imipenem (8,22). Therefore, imipenem is designed to be coadministered with cilastatin to suppress RDPase for its clinical use, and they are now manufactured in a 1:1 combination.Meropenemhept-2-ene-2-carboxylic acid, which was introduced in the late 1980s, though relatively less active against gram-positive bacteria than imipenem (1,4,6,7), is stable in the presence of RDPase as judged by its V max /K m ratio. Thus, it is currently in clinical use without coadministration of an RDPase inhibitor.DA 237, 1996). DA-1131 has been examined in many aspects, including pharmacokinetics under various conditions in animals (10,12,13,16,17,18,19), in the renal excretion mechanism (14, 15), and in nephrotoxicity-related studies (11).We measured the kinetic parameters of imipenem, meropenem, and DA-1131 in relation to human RDPase and the RDPases of various animals to examine the stability of DA-1131 in reference to the two well-established ␤-lactam antibiotics, imipenem and meropenem.DA-1131 and meropenem were supplied by Dong-A Research Laboratory. Imipenem and cilastatin were obtained from Merck Sharp & Dohme. Human RDPase was purified to homogeneity with a 2,029-fold purification, and RDPases from animal sources were purified or partially purified according to the method previously described (24).RDPase-catalyzed hydrolysis of imipenem, meropenem, and DA-1131 was measured in the presence and absence of cilastatin (0.15 M) according to the method described by Kim and Campbell (9) by measuring the decrease in absorbance at 298 nm and 37°C as a function of time for 2.5 min. Substrate concentration was varied over a range of 1.25 to 3.3 mM in 3-(N-morpholino)propanesulfonic acid, pH 7.1. One microgram of purified RDPase was employ...