E-64  (Synonyms: Proteinase inhibitor E 64)

The Cathepsin B activity is determined using Z-Arg-Arg-4mβNA as substrate with slight modifications. The crude extract is pre-incubated at 37°C for 5 min in 50 mM sodium acetate buffer, pH 5.0 containing 1 mM EDTA and 5 mM DTT. The substrate (final concentration, 100 μM) is added to make the final assay volume of 1 mL. The reaction mixture is incubated at 37°C for 30 min. The reaction is terminated by adding equal volume of stopping reagent containing Fast Garnet GBC salt (1 mg/mL), 10 mM pHMB and 50 mM EDTA, pH 6.0. The extraction of product, β-napthylamine (β-NA), is carried out with n-butanol. After complete layer separation, the absorbance is measured in n-butanol layer and activity is calculated using molar extinction coefficient of β-napthylamine solution as 31.5 M/cm per sec at 520 nm. One unit of enzyme activity is defined as the amount of enzyme liberating 1 μmol of βNA per minute at 37°C. The half maximal inhibitory concentration (IC₅₀) is calculated by plotting the graph between the different concentration of E-64 and the % inhibition in cathepsin B activity. Here, IC₅₀ indicates the concentration of the E-64 required to inhibit the parasitic cathepsin B activity by half^[2].

MCE has not independently confirmed the accuracy of these methods. They are for reference only.

Mice^[3]
The NOD/LtJ and BDC2.5 T cell receptor (TCR) transgenic NOD mice are used to study the effects of treatment with anti-serpin B13 monoclonal antibody (mAb). Four-week-old female NOD/LtJ mice are injected intravenously four times over a period of 10 days with anti-serpin B13 mAb (100 μg/injection). In addition, during the same period, some animals are also injected intraperitoneally with the protease inhibitor E64 at 10 mg/kg/day for several days. Control mice are treated with diluent (a sterilized PBS solution containing 10% DMSO) and control IgG. The solutions containing E64 or DMSO are prepared immediately before use. Twenty-four hours after the last injection, the mice are killed, and cells from their lymphoid organs and pancreatic islets are subjected to FACS analysis.
Rats^[4]
Seven-week old male Dahl Salt Sensitive rats (SS/JrHsdMcwi) are used. Briefly, 8-week old anesthetized SS rats have their left femoral artery and vein catheterized. Both catheters are fixed and exteriorized from the back of the neck and the arterial line is connected to a heparinized saline infusion pump that is in line with a blood pressure transducer, and the venous line is connected to a saline infusion pump. Animals are allowed 360° movement using a tether-swivel system. This preparation allowed chronic venous infusion and arterial blood pressure measurement in conscious, freely moving rats. A stable baseline blood pressure is obtained for 4 days prior to switching both groups to an 8.0% NaCl diet and the simultaneous addition of E-64 (1 mg/day; 280 mM stock in DMSO) or the vehicle (DMSO in saline) control to the venous catheter. Daily MAP is calculated by averaging MAP taken every min over the beginning 3 h period of the rat sleep cycle.

MCE has not independently confirmed the accuracy of these methods. They are for reference only.

• [1]. Matsumoto K, et al. Structural basis of inhibition of cysteine proteases by E-64 and its derivatives. Biopolymers. 1999;51(1):99-107.  [Content Brief]

  [2]. Wadhawan M, et al. Inhibition of cathepsin B by E-64 induces oxidative stress and apoptosis in filarial parasite. PLoS One. 2014 Mar 25;9(3):e93161.  [Content Brief]

  [3]. Baldzizhar R, et al. Anti-serpin antibody-mediated regulation of proteases in autoimmune diabetes. J Biol Chem. 2013 Jan 18;288(3):1612-9.  [Content Brief]

  [4]. Blass G, et al. Chronic cathepsin inhibition by E-64 in Dahl salt-sensitive rats. Physiol Rep. 2016 Sep;4(17). pii: e12950.  [Content Brief]