Transglutaminases (Tg) are a family of enzymes that crosslink glutamine and lysine amino acids to form an irreversible (γ-glutamyl) lysine dipeptide bond. Tissue type transglutaminase (tTg) is upregulated and released in the rat kidney following subtotal nephrectomy (SNx) which induces kidney scarring (Johnson et al., 1997). We describe the effect of a Tg inhibitor, with both intracellular and extracellular activity, on kidney scarring and renal function in the SNx rat.

Male Wistar rats (250-300g) underwent 5/6 subtotal nephrectomy under halothane anaesthesia during which time a fenestrated cannula was inserted and fixed in the remnant kidney. The Tg inhibitor , 1,3-dimethyl-2-[(2-oxopropyl)thio]imidazolium iodide (Freund et al., 1994) was synthesised and a 50mM solution delivered, from an osmotic minipump (Alzet 2ml4) inserted into a subcutaneous pocket, by renal tissue infusion. This equated to a daily dose of 2.5mg/kg. Pumps were changed every 4 weeks, the study lasting for 12 weeks (n=6 per group). Tg activity was measured in renal homogenates using a [¹⁴C] putrescine incorporation assay. Kidney scarring was assessed from Masson's trichrome staining and collagen III immunohistochemistry. Kidney function was determined from creatinine clearance and proteinuria.

The Tg inhibitor produced a significant decrease in renal Tg enzyme activity ( 45.4 ± 1.4 vs 31.3 ± 6.0 units/mg/protein, P<0.05) decreasing the renal content of (γ -glutamyl)lysine crosslink (0.35 ± 0.14 vs 0.13 ± 0.05 nmol/mg protein, P<0.05). Kidney scarring in SNx rats receiving the Tg inhibitor, was significantly reduced compared to vehicle treated SNx controls when measured using multiphase image analysis for either Masson's trichrome stained sections (2.55 ± 0.37 vs 0.75 ± 0.34 stained area/nuclear area, P<0.001) or collagen III immunohistochemistry (1.34 ± 0.26 vs 0.56 ± 0.08 stained area/nuclear area, P<0.05). Creatinine clearance was significantly higher in SNx rats treated with the Tg inhibitor (0.37 ± 0.18 vs 0.86 ± 0.05 ml/min, P<0.05) proteinuria however, was slightly increased not decreased by the Tg inhibitor (672 ± 64 vs 836 ± 93 mg/24 hours).

Treatment with a Tg inhibitor, delivered by renal tissue infusion, slowed the progression of scarring in the remnant rat kidney, improving the decline in the glomerular filtration rate. Interestingly, this occurred in the absence of any decrease in proteinuria. Tg inhibitors may reduce kidney scarring by inhibiting the deposition of extracellular matrix proteins. Tg inhibitors may therefore be of potential benefit to the treatment of chronic renal failure.

Freund, K et al., (1994) Biochemistry, 33, 10109-10119.
Johnson, T et al., (1997) J. Clin. Invest., 99, 2950-2960.

TSJ is a Senior Research Fellow of the National Kidney Research Fund.