Specific role of NAD+ biosynthesis reduction mediated mitochondrial dysfunction in vascular endothelial injury induced by chronic intermittent hypoxia.

OBJECTIVE: Cardiovascular diseases (CVD) are prevalent among those with obstructive sleep apnea (OSA) and are the leading cause of death in these individuals. However, due to clinical confounders, the mechanism by which OSA induces CVD is still unclear. Previous studies have shown that chronic intermittent hypoxia (CIH) and high cholesterol diet (HCD) induce distinct characteristics of atherosclerotic plaques, highlighting the specific mechanisms involved in CIH-induced vascular endothelial injury. MATERIALS AND METHODS: This study aims to investigate whether nicotinamide adenine dinucleotide (NAD+) biosynthesis reduction-mediated mitochondrial dysfunction is responsible for vascular endothelial injury induced by CIH and to elucidate its specific role in this process. Models were established to stimulate human umbilical vein endothelial cells (HUVECs) with CIH and oxidized low-density lipoprotein (ox-LDL), and the NAD+ biosynthesis-related indicators, such as NAD+ levels and nicotinamide phosphoribosyltransferase (NAMPT) enzyme activity, were measured in this model. Additionally, interventions were performed by supplementing NAD+ levels with nicotinamide mononucleotide (NMN), inhibiting NAD+ synthesis with FK866, and evaluating mitochondrial function, oxidative stress status, vascular constriction and dilation function, and endothelial adhesion function in these models. A comparative study was conducted to assess the effects of these interventions. RESULTS: We found that under CIH conditions, NAMPT enzyme activity was inhibited, leading to a reduction in NAD+ biosynthesis and a decrease in NAD+/NADH ratio. At the same time, CIH caused mitochondrial dysfunction in HUVECs, including a decrease in adenosine triphosphate (ATP) content and mitochondrial membrane potential, as well as the activity of respiratory chain complex I and III, induced an increase in oxidative stress levels in endothelial cells, impaired vascular constriction and dilation function, and significantly increased expression of adhesion factors. The impact of CIH on endothelial cell-related mitochondrial function and endothelial function was restored by supplementing NMN. Although ox-LDL also causes multi-level endothelial injury, it does not involve the NAD+ pathway, as there were no significant changes in the related indicators, and the impaired endothelial function under ox-LDL conditions was not restored by supplementing NMN. CONCLUSIONS: CIH-induced vascular endothelial injury may be associated with NAD+ biosynthesis reduction-mediated mitochondrial dysfunction. Supplementing NAD+ precursors to increase its levels may be a potential intervention to ameliorate CIH-induced vascular endothelial injury, while it does not have a significant effect on endothelial injury caused by ox-LDL.

[Building up of an animal model of conditioned immunosuppression and analysis of its possible mechanism].

In the present study, camphor odor and intraperitoneal (ip) injection of cyclophosphamide (CY) were used as conditional and unconditional stimulus, respectively, in mice. Mice were exposed to camphor odor for 1 h in their cage in a closed area followed by an ip injection of CY (75 mg.kg-1). This association trial session was repeated once on the next day. Delayed type hypersensitivity response (DTH) was induced as follows: six days after the second association trial session the mice were sensitized by smearing dinitrochlorobenezene (DNCB) on their abdominal skin. The mice were challenged by smearing DNCB on the left ear 5 days after the antigen sensitization. The left and right ears were removed 24 h after the challenge and weighed, the weight ratio of left/right ears was calculated for identification of the response. The ratio was 1.30 +/- 0.113 (+/- s, P < 0.001), indicating that the challenged ear was heavier than the other and DTH was induced. In the unconditioned response (UCR) group, CY (75 mg.kg-1) was given 24 h prior to the challenge and the ratio was 1.09 +/- 0.024 (P < 0.001) indicating that DTH was suppressed by unconditional stimulus (CY). In the conditioned response (CR) group mice were reexposed to camphor odor 24 h prior to the challenge and normal saline was injected instead of CY. The ratio was 1.13 +/- 0.074 (P < 0.001), indicating that DTH was also suppressed by conditional stimulus (camphor odor). These results show that a conditioned immunosuppressive response was induced. In the experiment, many other groups, including unconditioned response group, CYE group and camphor control group, were described in more details in the text. In order to further analyse the mechanisms of the conditioned response, the blood from the mice in CR group was obtained 6 h after reexposure to camphor odor and the serum was injected to normal mice 6 h prior to the challenge. DTH was found to be suppressed significantly when compared with the mice injected with normal serum. The conditioned serum was dialyzed against a membrane with a 10,000 molecular weight cut off. The suppressive activity of the conditioned serum disappeared, suggesting that the molecular weight of the suppressive element in the serum was probably less than 10,000 kDa.

[Effect of intracerebroventricular injection of IL-1 beta on generation of immuno-suppressive factor in lymphocytes in stressed mice].

Our previous work showed that a suppressive factor (a protein with large molecular weight) in serum was induced by restraint stress in mice and rats, which suppressed Con A induced lymphocyte proliferation. It was also found that the generation of serum suppressive factor was under control of the central nervous system. Our further study showed that intracerebroventricular (icv) injection of interleukin 1 receptor antagonist (IL-1Ra) antagonised the generation of serum suppressive factor induced by restraint stress and icv injection of interleukin-1 beta (IL-1 beta) increased the generation of the suppressive factor. Our experiment also showed that the serum suppressive factor induced by restraint stress was first made in lymph tissue and then released into blood. The present work was designed to investigate the role of IL-1 in the brain in generation of the suppressive factor in lymph node in mice. Icv injection of IL-1 beta (1 pg/mouse) was shown to significantly increase the generation of the suppressive factor in lymph node. Icv injection of IL-1Ra, however, antagonised generation of the suppressive factor. In mice without restraint stress, both the suppressive factor in serum and in lymph node were found to be induced in dose-dependent manner by icv injection of IL-1 beta. Taken together, these results suggest that IL-1 beta in brain played a very important role in generation of the suppressive factor in lymph node. The positive correlation between the suppressive action of lymph node and of serum added to the evidence that lymph tissue is probably the source of the serum suppressive factor.