Nicotinamide Modulates Mitochondrial Membrane Potential and Cysteine Protease Activity during Cerebral Vascular Endothelial Cell Injury

Abstract

Microvascular endothelial cell (EC) apoptosis or programmed cell death (PCD) during free radical injury may be involved in the development of cerebral ischemic and degenerative diseases. Yet, the cellular mechanisms that mediate cerebral EC injury require further definition. We therefore used the agent nicotinamide as an investigative tool in EC cultures to examine the role of free radical nitric oxide (NO)-induced PCD. EC injury was evaluated by the trypan blue dye exclusion method, DNA fragmentation, membrane phosphatidylserine (PS) exposure, cysteine protease activity, mitochondrial membrane potential, and mitogen-activated protein kinase phosphorylation. We demonstrate that cerebrovascular PCD consists of two distinct pathways that involve the degradation of genomic DNA and the exposure of membrane PS residues. Each of these pathways is reversible in nature and is controlled independently by caspase 8, caspase 1, and caspase 3. As a cytoprotectant, nicotinamide is novel in the vascular system and functions at two levels. Nicotinamide not only maintains the mitochondrial membrane potential and the prevention of cytochrome c release, but also prevents the induction of caspase-8-, caspase-1- and caspase-3-like activities linked to the DNA repair enzyme poly(ADP-ribose) polymerase through mechanisms that are independent from the MAP kinase systems of p38 and JNK. The work begins to identify therapeutic strategies for the protection of the cerebral vasculature during both acute and chronic degenerative disorders.

Triple play: Promoting neurovascular longevity with nicotinamide, WNT, and erythropoietin in diabetes mellitus

“…Potentially relevant to diabetic patients with renal failure, nicotinamide also has been shown to reduce intestinal absorption of phosphate and prevent the development of hyperphosphatemia and progressive renal dysfunction [81]. In animal and cell culture studies, nicotinamide also can maintain normal fasting blood glucose in animals with streptozotocin-induced diabetes [82,83], reduce peripheral nerve injury during elevated glucose [84], lead to the remission of type 1 DM in mice with acetyl-l-carnitine [85], and can inhibit oxidative stress pathways that lead to apoptosis [63, [86][87][88][89].…”

“…For example, nicotinamide can protect the function of the blood brain barrier [94,95], influence arteriolar dilatation and blood flow [96], potentially lead to decreased atherosclerotic plaque through inhibition of poly(ADP-ribose) polymerase [97], and promote platelet production through megakaryocyte maturation [98]. Nicotinamide also can maintain EC viability during reactive oxygen species exposure [42,87,99,100]. Nicotinamide is believed to be responsible for the preservation of cerebral [101] and endocardial [102,103] ECs during models of oxidative stress [102,103].…”

“…Nicotinamide can preserve mitochondrial NAD-linked respiration and block the depolarization of the mitochondrial membrane [62,87]. Interestingly, nicotinamide appears to act directly at the level of mitochondrial membrane pore formation to prevent cytochrome c release [62,87].…”

“…Nicotinamide blocks membrane PS externalization during a variety of insults that involve anoxia, free radical exposure, and oxygen-glucose deprivation [62,87,99]. Nicotinamide regulates membrane PS exposure and microglial activation through activation of Akt, a central pathway for cytoprotection [92].…”

Stress in the brain: novel cellular mechanisms of injury linked to Alzheimer's disease

“…Furthermore, oxidative stress can significantly increase chromosomal aberrations and micronuclei [26,39] and lead to the activation of apoptotic pathways in ECs [38,116,193]. ECs that are exposed to oxidative stress incur both DNA fragmentation and membrane PS externalization during exposure to insults, such as hypoxia, oxidants, and free radicals [9,28,38,39,124].…”