NO Answer to Alzheimer's Disease?

Harnessing Passive Pulsatile Shear Stress for Alzheimer's Disease Prevention and Intervention

 Alzheimer's disease (AD) affects more than 40 million people worldwide and is the leading cause of dementia. This disease is a challenge for both patients and caregivers and puts a significant strain on the global healthcare system. To address this issue, the Lancet Commission recommends focusing on reducing modifiable lifestyle risk factors such as hypertension, diabetes, and physical inactivity. Passive pulsatile shear stress (PPSS) interventions, which use devices like whole-body periodic acceleration, periodic acceleration along the Z-axis (pGz), and the Jogging Device, have shown significant systemic and cellular effects in preclinical and clinical models which address these modifiable risks factors. Based on this, we propose that PPSS could be a potential non-pharmacological and non-invasive preventive or therapeutic strategy for AD. We perform a comprehensive review of the biological basis based on all publications of PPSS using these devices and demonstrate their effects on the various aspects of AD. We draw from this comprehensive analysis to support our hypothesis. We then delve into the possible application of PPSS as an innovative intervention. We discuss how PPSS holds promise in ameliorating hypertension and diabetes while mitigating physical inactivity, potentially offering a holistic approach to AD prevention and management.

The effect of water immersion during exercise on cerebral blood flow

INTRODUCTION

Regular exercise induces recurrent increases in cerebrovascular perfusion. In peripheral arteries, such episodic increases in perfusion are responsible for improvement in arterial function and health. We examined the hypothesis that exercise during immersion augments cerebral blood flow velocity compared with intensity-matched land-based exercise.

METHODS

Fifteen normotensive participants were recruited (26 ± 4 yr, 24.3 ± 1.9 kg·m). We continuously assessed mean arterial blood pressure, HR, stroke volume, oxygen consumption, and blood flow velocities through the middle and posterior cerebral arteries before, during, and after 20-min bouts of water- and land-based stepping exercise of matched intensity. The order in which the exercise conditions were performed was randomized between subjects. Water-based exercise was performed in 30°C water to the level of the right atrium.

RESULTS

The water- and land-based exercise bouts were closely matched for oxygen consumption (13.3 mL·kg·min (95% confidence interval (CI), 12.2-14.6) vs 13.5 mL·kg·min (95% CI, 12.1-14.8), P = 0.89) and HR (95 bpm (95% CI, 90-101) vs 96 bpm (95% CI, 91-102), P = 0.65). Compared with land-based exercise, water-based exercise induced an increase in middle cerebral artery blood flow velocity (74 cm·s (95% CI, 66-81) vs 67 cm·s (95% CI, 60-74) P < 0.001), posterior cerebral artery blood flow velocity (47 cm·s (95% CI, 40-53) vs 43 cm·s (95% CI, 37-49), P < 0.001), mean arterial blood pressure (106 mm Hg (95% CI, 100-111) vs 101 mm Hg (95% CI, 95-106), P < 0.001), and partial pressure of expired CO2 (P ≤ 0.001).

CONCLUSIONS

Our findings suggest that water-based exercise augments cerebral blood flow, relative to land-based exercise of similar intensity, in healthy humans.

Cardiovascular responses to water immersion in humans: impact on cerebral perfusion

Episodic increases in cerebrovascular perfusion and shear stress may have beneficial impacts on endothelial function that improve brain health. We hypothesized that water immersion to the level of the right atrium in humans would increase cerebral perfusion. We continuously measured, in 9 young (means ± SD, 24.6 ± 2.0 yr) healthy men, systemic hemodynamic variables along with blood flows in the common carotid and middle and posterior cerebral arteries during controlled filling and emptying of a water tank to the level of the right atrium. Mean arterial pressure (80 ± 9 vs. 91 ± 12 mmHg, P < 0.05), cardiac output (4.8 ± 0.7 vs. 5.1 ± 0.6 l/min, P < 0.05) and end-tidal carbon dioxide (PetCO2, 39.5 ± 2.0 vs. 44.4 ± 3.5 mmHg, P < 0.05) increased with water immersion, along with middle (59 ± 6 vs. 64 ± 6 cm/s, P < 0.05) and posterior cerebral artery blood flow velocities (41 ± 9 vs. 44 ± 10 cm/s, P < 0.05). These changes were reversed when the tank was emptied. Water immersion is associated with hemodynamic and PetCO2 changes, which increase cerebral blood velocities in humans. This study provides an evidence base for future studies to examine the potential additive effect of exercise in water on improving cerebrovascular health.

Modulating nitric oxide signaling in the CNS for Alzheimer's disease therapy

Nitric oxide (NO)/solube GC (sGC)/cGMP signaling is important for modulating synaptic transmission and plasticity in the hippocampus and cerebral cortex, which are critical for learning and memory. Physiological concentrations of NO also elicit anti-apoptotic/prosurvival effects against various neurotoxic challenges and brain insults through multiple mechanisms. Depression of the NO/sGC pathway is a feature of Alzheimer's disease (AD), attributed to amyloid-β neuropathology, and altered expression and activity of NOS, sGC and PDE enzymes. Different classes of NO-releasing hybrid drugs, including nomethiazoles, NO-NSAIDs and NO-acetylcholinesterase inhibitors were designed to deliver low concentrations of exogenous NO to the CNS while targeting other underlying disease mechanisms, such as excitotoxicity, neuro-inflammation and acetylcholine deficiency, respectively. Incorporating a NO-donating moiety may also reduce gastrointestinal and liver toxicity of the parent drugs. Progress has also been made in targeting downstream sGC and PDE enzymes. The PDE9 inhibitor PF-04447943 has completed Phase II clinical trials for AD. The search for effective NO-donating hybrid drugs, CNS-targeting sGC stimulators/activators and selective PDE inhibitors is an important goal for pharmacotherapy that manipulates NO biochemical pathways involved in cognitive function and neuroprotection. Rigorous preclinical validation of target engagement, and optimization of pharmacokinetic and toxicity profiles are likely to advance more drug candidates into clinical trials for mild cognitive impairment and early stage AD.

Involvement of nitric oxide in granisetron improving effect on scopolamine-induced memory impairment in mice

Granisetron, a serotonin 5-HT(3) receptor antagonist, widely used as an antiemetic drug following chemotherapy, has been found to improve learning and memory. In this study, effects of granisetron on spatial recognition memory and fear memory and the involvement of nitric oxide (NO) have been determined in a Y-maze and passive avoidance test. Granisetron (3, 10mg/kg, intraperitoneally) was administered to scopolamine-induced memory-impaired mice prior to acquisition, consolidation and retrieval phases, either in the presence or in the absence of a non-specific NO synthase inhibitor, l-NAME (3, 10mg/kg, intraperitoneally); a specific inducible NO synthase (iNOS) inhibitor, aminoguanidine (100mg/kg); and a NO precursor, l-arginine (750 mg/kg). It is demonstrated that granisetron improved memory acquisition in a dose-dependent manner, but it was ineffective on consolidation and retrieval phases of memory. The beneficial effect of granisetron (10mg/kg) on memory acquisition was significantly reversed by l-NAME (10mg/kg) and aminoguanidine (100mg/kg); however, l-arginine (750 mg/kg) did not potentiate the effect of sub-effective dose of granisetron (3mg/kg) in memory acquisition phase. It is concluded that nitric oxide is probably involved in improvement of memory acquisition by granisetron in both spatial recognition memory and fear memory. This article is part of a Special Issue entitled The Cognitive Neuroscience.

Vascular effects of exercise: endothelial adaptations beyond active muscle beds

Endothelial adaptations to exercise training are not exclusively conferred within the active muscle beds. Herein, we summarize key studies that have evaluated the impact of chronic exercise on the endothelium of vasculatures perfusing nonworking skeletal muscle, brain, viscera, and skin, concluding with discussion of potential mechanisms driving these endothelial adaptations.