An array of brain protease activities and their modulation by the toxic effects of cyanamide

Brain proteolytic enzymes have been implicated in a

variety of disorders though most studies have focused on

a few components such as the ATP-ubiquitin pathway.

In this study we assayed a broad range of representative

proteolytic enzyme types, to address the hypothesis that

their activities are perturbed in cyanamide toxicity. We

dosed maleWistar rats (approximately 0.1 kg BW) with

either saline (0.15 mol/l NaCl) or cyanamide, an inhibitor

of aldehyde dehydrogenase (ALDH) (0.5 mmol/kg BW;

ip). After 3 h rats were killed and cerebellum dissected.

Using fluorimetry, we measured the activities

of the cytoplasmic enzymes alanyl-aminopeptidase

(ALAAP), arginyl-aminopeptidase (ARGAP), leucylaminopeptidase

(LEUAP), dipeptidyl-aminopeptidase

IV (DIA-IV), tripeptidyl aminopetidase (TRI-AP) and

proline endopeptidase (PROAP), as well as the lysosomal

enzymes cathepsins B (CATHB), D (CATHD),

H (CATHH) and L (CATHL), dipeptidyl aminopeptidases

I (DIA-I) and II (DIA-II) and proteasomal

chymotrypsin-like (PRCHY) and trypsin-like (PRTRP)

activities (Table 1).

There was a wide range of proteolytic activities

(Table 1). The highest activity was found in arginyl

aminopeptidase whereas proteosomal activities were

low. In response to cyanamide dosage in vivo, there were

significant increases in the in vitro activities of cerebellum

DIA-IV (P < 0.05). There were also reductions in

DIA-I and CATHL (P < 0.001).

In conclusions, impaired proteolysis may contribute

to, or reflect, the cellular toxicity of cyanamide.