Hypothalamic S-Nitrosylation Contributes to the Counter-Regulatory Response Impairment following Recurrent Hypoglycemia

Abstract

AimsHypoglycemia is a severe side effect of intensive insulin therapy. Recurrent hypoglycemia (RH) impairs the counter-regulatory response (CRR) which restores euglycemia. During hypoglycemia, ventromedial hypothalamus (VMH) production of nitric oxide (NO) and activation of its receptor soluble guanylyl cyclase (sGC) are critical for the CRR. Hypoglycemia also increases brain reactive oxygen species (ROS) production. NO production in the presence of ROS causes protein S-nitrosylation. S-nitrosylation of sGC impairs its function and induces desensitization to NO. We hypothesized that during hypoglycemia, the interaction between NO and ROS increases VMH sGC S-nitrosylation levels and impairs the CRR to subsequent episodes of hypoglycemia. VMH ROS production and S-nitrosylation were quantified following three consecutive daily episodes of insulin-hypoglycemia (RH model). The CRR was evaluated in rats in response to acute insulin-induced hypoglycemia or via hypoglycemic-hyperinsulinemic clamps. Pretreatment with the anti-oxidant N-acetyl-cysteine (NAC) was used to prevent increased VMH S-nitrosylation.ResultsAcute insulin-hypoglycemia increased VMH ROS levels by 49±6.3%. RH increased VMH sGC S-nitrosylation. Increasing VMH S-nitrosylation with intracerebroventricular injection of the nitrosylating agent S-nitroso-L-cysteine (CSNO) was associated with decreased glucagon secretion during hypoglycemic clamp. Finally, in RH rats pre-treated with NAC (0.5% in drinking water for 9 days) hypoglycemia-induced VMH ROS production was prevented and glucagon and epinephrine production was not blunted in response to subsequent insulin-hypoglycemia.ConclusionThese data suggest that NAC may be clinically useful in preventing impaired CRR in patients undergoing intensive-insulin therapy.

Direct effects of recurrent hypoglycaemia on adrenal catecholamine release

“…14,15,19,20,25,35 The time course and magnitude of IIH were similar with or without RH, and in this respect, our data differ from some reports in which the degree of hypoglycaemia becomes more severe with RH. 19,23 The magnitude of the elevation of plasma EPI concentration produced by acute IIH in our study is also less pronounced than reported in the literature during similar levels of hypoglycaemia in non-diabetic rats.…”

“…19,23 The magnitude of the elevation of plasma EPI concentration produced by acute IIH in our study is also less pronounced than reported in the literature during similar levels of hypoglycaemia in non-diabetic rats. 19,24,25,35,[51][52][53] This difference may be explained by the lower dose of insulin used to attain hypoglycaemia in our studies. As illustrated in Figure S7(a), and reported from the Beverly laboratory, 54 a similar time course of blood glucose decline can be attained using different doses of insulin, but with a lower dose, recovery towards euglycaemia begins sooner.…”

“…Thus, our RH protocol reduces the sympatho-adrenal response to IIH, similar to previous reports. 15,[19][20][21]23,25 Adrenal CAT release evoked by splanchnic nerve stimulation after RH Most studies investigating the blunting of the EPI response produced by RH have focused on brain loci that regulate EPI secretion; 15,[19][20][21][22][23][24][25] however, much less is known about the effect of RH on the functional properties of peripheral components of the sympatho-adrenal axis. To address this issue, this study investigated adrenal CAT release in nondiabetic rats subjected to RH.…”

“…A similar protocol has been used previously to show that the function of brain regions involved in glucosensing is affected by RH. 21,24,25 Even a single episode of antecedent hypoglycaemia can also affect central 23 and peripheral components 36 of the sympatho-adrenal axis. Nonetheless, whether any temporal relationship exists between the development of defects in central and peripheral components of the sympathetic nervous system during RH is unknown.…”

Pine Bark Extract Protects Against Oxidative Stress Induced By Recurrent Hypoglycemia In Rats.

“…Recurrent Hypoglycemia is achieved due to increased insulin doses for patients with diabetes type I or may be as a result of a congenital deformity of the metabolic processes or birth defects in insulin secretion for people who have diabetes. Several previous studies showed that hypoglycemia can cause oxidative stress by increasing reactive oxygen species (ROS) which caused brain tissue injury and death [2] [3] [4] [5] or by increasing the production of lipid peroxidation products (LPO) such as MDA [6] [7] [8] and the deficiency in the activity of SOD as well as the depletion of GSH content in the crust and hippocampus areas of the brain of mice [6] [8]. Pine bark extract (PBE) has many phenolic compounds such as catechins and epicatechins with beneficial impacts for human health.PBE from the French maritime pine tree (Pycnogenol, PY); Pinus pinaster.…”