Increase in plasma ceramide levels via secretory sphingomyelinase activity in streptozotocin-induced diabetic rats

Abstract

Ceramide mediates apoptosis and is upregulated by oxidative stress. To reveal the causative agent of diabetes-induced complications, we examined the changes in ceramide metabolism during diabetes. Two and 8 weeks after intraperitoneal injection of streptozotocin (STZ: 40 mg kg À1 body weight) to rats, tissue ceramide levels were analyzed by liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS). Blood glucose was significantly increased 2 weeks after STZ administration. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), and blood urea nitrogen (BUN) levels were also increased in the diabetic rats, suggesting that hepatic and renal damage was induced by STZ administration. Vitamin C, an indicator of oxidative stress, was significantly decreased in the plasma, liver, and kidney of rats 2 weeks after STZ administration. Although no differences in hepatic ceramide levels were observed between the control and diabetic rats, plasma and renal ceramide levels were significantly increased 8 weeks after STZ administration. In the liver and kidney, acid and neutral sphingomyelinase (SMase) activities were not increased, while secretory sphingomyelinase (sSMase) activity was increased in the plasma of diabetic rats after STZ administration. These data indicated that STZ administration induced the increase in plasma ceramide levels via the increase in sSMase activity. It was suggested that increased plasma ceramide levels were involved in the renal damage induced by STZ in diabetic rats accompanied with the enhancement of oxidative stress.

Increase in Secretory Sphingomyelinase Activity and Specific Ceramides in the Aorta of Apolipoprotein E Knockout Mice during Aging

“…Similar results were obtained in diabetic rats. 17) These observations suggested that aging did not affect hepatic ceramide metabolism.…”

“…Excessive cholesterol intake increased plasma ceramides in apolipoprotein E knockout mice (apoE −/− ), a typical animal model for atherosclerosis. 16) In addition, we previously reported that the increase in plasma ceramide level was caused by increased activity of sSMase in the streptozotocin-induced diabetic rats, 17) thus suggesting that the elevation of plasma ceramide was an important factor in atherogenesis. sSMase activity also increased in response to stimulation of macrophages obtained from patients with chronic heart failure 18) and type 2 diabetes.…”

“…17,22) For sSMase analysis, a 800 µL assay mixture consisted of 15 µL of plasma and 785 µL of an assay buffer (0.1 mm ZnSO 4 , 1 nmol NBD C 6 -SM, 0.1% NP-40/62, 0.1 m sodium acetate buffer at pH 5.0) was incubated for 2 h at 37°C. The reaction was stopped by adding 1 mL of methanol.…”

Strong Inhibition of Secretory Sphingomyelinase by Catechins, Particularly by (&minus;)-Epicatechin 3-<i>O</i>-Gallate and (&minus;)-3&prime;-<i>O</i>-Methylepigallocatechin 3-<i>O</i>-Gallate

“…Previously, we demonstrated that increased sSMase activity resulted in an increase of the ceramide in the plasma of diabetic and atherosclerotic murine models which had been exposed to systemic oxidative stress (17,18). These results suggest that inhibition of sSMase activity is effective in the prevention of these diseases.…”

“…Change in sSMase activity by the redox state. sSMase activities were measured using NBD C 6-SM as a substrate, as previously described (17,18). To examine the effect of oxidation on sSMase activity, 100 mL of rat plasma was incubated with 500 mL of H2O2 solution at 0, 10, 100, and 1,000 mm final concentrations for 15 min at 37˚C in 20 mm Tris-HCl buffer (pH 7.5) (the oxidized sample).…”