Nitric Oxide/Peroxynitrite Balance in Kidney – Effect of Diabetes and Obesity

Nitric oxide (NO) is a vasoprotective signaling molecule. Peroxynitrite (ONOO^-), the reaction product of the superoxide (O₂^-) with the nitric oxide, is the main cytotoxic component of nitroxidative stress. This work elucidated the [NO]/[ONOO^-] imbalance in the kidney of rats with type I and type II diabetes. Obesity factor has also been studied by induced high fat diet to rats before or after type II diabetes was established.

The releases of NO and ONOO^- were monitored in situ by placing NO and ONOO^- nanosensors near the surface (5 ± 2 µm) of medulla part of kidney slices. Intracellular L-arginine was measured by HPLC-fluorescence and eNOS protein levels were examined by immunological Western blotting analysis.

These studies clearly indicate that the [NO]/[ONOO^-] imbalance in the type I and type II diabetes is caused by uncoupled eNOS. The deficiency of intracellular L-argnine and tetrahydrobiopterin may be linked to eNOS uncoupling. At early stage of diabetes, the [NO]/[ONOO^-] balance could be restored after treatments with L-arginine and sepiapterin.

Obesity, itself, showed inhibitory effect on eNOS activity and NO release. However, obesity and type II diabetes increased hyperglycemia, hyperlipidaemia and eNOS uncoupling at the late stage. All of these factors lead to a severe [NO]/[ONOO^-] imbalance and form high oxidative/nitroxidative stress in kidney.

Different herbal drug treatments improved the [NO]/[ONOO^-] balance by different mechanisms. Corn silk, a hypercholesterol inhibitor, improved the [NO]/[ONOO^-] balance more significantly than ginseng at the early stage of type II diabetes. However, ginseng showed better effect than corn silk on the improvement of the [NO]/[ONOO^-] balance at the late stage.

Our overall results indicate that the function of endothelial nitric oxide synthase can be severely uncoupled in diabetic kidney. The uncoupled eNOS is the main generator of cytotoxic ONOO^-. An overproduction of ONOO^- and diminished generation of NO shifts unfavorably [NO]/[ONOO^-] balance in diabetes. This process can be significantly reversed or inhibited by treatment with L-arginine, sepiapterin, corn silk or ginseng. Therefore, these treatments can be potentially used for mollification of kidney capillary vascular injury induced by diabetes.