Protective effects of Piper nigrum and Vinca rosea in alloxan induced diabetic rats.

In the present study aqueous extract of Piper nigrum seeds and Vinca rosea flowers were administered orally to alloxan induced diabetic rats once a day for 4 weeks. These treatments lead to significant lowering of blood sugar level and reduction in serum lipids. The levels of antioxidant enzymes, catalase and glutathione peroxidase decreased in alloxan induced diabetic rats however these levels returned to normal in insulin, P. nigrum and V. rosea treated rats. There was no significant difference in superoxide dismutase activity in all groups compared to controls. Lipid peroxidation levels were significantly higher in diabetic rats and it was slightly increased in insulin, P. nigrum and V. rosea treated rats as compared to control rat. These results suggest that oxidative stress plays a key role in diabetes, and treatment with P. nigrum and V. rosea are useful in controlling not only the glucose and lipid levels but these components may also be helpful in strengthening the antioxidants potential.

Characterisaton of human plasma thiol proteinase inhibitors.

Earlier, we had reported purification of three thiol proteinase inhibitors (TPI-1 of 70 kDa, TPI-3 of 195 kDa and TPI-4 of 497 kDa) from human plasma. In the present study we report that TPI-1 binds to papain in the stoichiometry ratio (E/I) of 1:1 while TPI-3 and TPI-4 bind in the ratio of 1.5:1 and 3.2:1 respectively. The K(m) for papain with BAPNA as substrate and Kcat/K(m) values for TPI-1, TPI-3 and TPI-4 were 2.7 x 10(-6) M, 0.84 nM/sec; 3.2 x 10(-6) M, 0.75 nM/sec; and 3.6 x 10(-6) M, 0.72 nM/sec respectively. The Ki values were found to be 1.48 nM for TPI-1, 0.133 nM for TPI-3 and 0.117 nM for TPI-4. The UV absorption and fluorescence emission spectra study suggest involvement of aromatic residues in the binding process. This study suggests that TPI-4 is the most potent inhibitor of thiol proteinases.

Purification and physicochemical studies of human plasma thiol proteinase inhibitors.

The physicochemical properties of thiol proteinase inhibitors (TPI) isolated from outdated human blood have been studied. A simple technique which includes ammonium sulphate precipitation, Sephadex G-200 gel filtration and ion-exchange chromatography led to the isolation of 4 isolates namely TPI-1, TPI-2, TPI-3 and TPI-4 having molecular mass of 70, 155, 195 and 497 kDa respectively. The latter two forms are the new isolates unreported previously. They exhibit similar pH stability, inhibition spectra with papain, cathepsin B and trypsin, antigenic properties and glycoprotein nature. The TPI-4, however, was found to be most heat stable showing no decrease in inhibitory activity when heated upto 70 degrees C for 30 min. Our work suggests that TPI-3 and TPI-4 are the oligomers of TPI-1.