Evaluation of Vascular Reactivity in Alzheimer’s Disease via Iontophoresis of Vasoactive Compounds Thomas Budinger, M.D., Ph.D. Jonathan Maltz, Ph.D. William Jagust, M.D. Jamie Eberling, Ph.D. Bruce Miller, M.D.

Hypothesis Altered dilatory response of brain vasculature is an important factor in the development of AD. This altered response is systemic and affects the peripheral circulation as well as the brain.

Hypothesis suggested by 1. Increased incidence of AD in patients with cardiovascular disease. 2. Acetylcholine and nitric oxide (NO) biochemistry is significantly altered in the AD brain. These agents are important mediators of vasodilation throughout the body.

Objective To test the hypothesis that peripheral vasoactivity is altered in AD by evaluating the cutaneous vasodilatory response to vasoactive agents.

We are studying the effects of - Acetylcholine (ACh) - Methacholine (MCh) - Sodium nitroprusside (SNP) on the cutaneous vasculature of the human forearm. All elicit vasodilation via the relaxing action of NO on smooth muscle.

ACh, MCh and SNP ACh: - Relaxes vascular smooth muscle primarily via receptor stimulation of endothelial cells, which then release NO. MCh: - Same mode of action as ACh. - More stable. Seems to act directly on smooth muscle as well as on endothelial cells. - Preferential muscarinic agonist. SNP: - Releases NO on decomposition. - Acts by directly relaxing smooth muscle.

Iontophoresis: Quantitative drug delivery

Perfusion response to iontophoresis

Laser Doppler imaging: Quantitative measurement of perfusion

Laser Doppler perfusion imaging

Laser Doppler imaging of perfusion response to iontophoresis

Typical response to ACh

Review of previous work Two studies have investigated cutaneous vasoactivity in AD: Hörnqvist et al., Gerontology 33(6), 1987 Algotsson et al., Neurobiology of Aging 16(4), 1995

Hörnqvist et al. (1987): Subject selection 12 AD/SDAT patients Age: 52-84, mean 71 Severe dementia, hospitalized 13 controls with various dermatoses Age: 52-82, mean 70 Nicotine and caffeine allowed

Hörnqvist et al.

Hörnqvist et al.: Results AgentActionAD vs Control Phenylephrine  1 -agonist AD slightly reduced Isoproterenol  1 -agonist AD reduced p<0.001 MethacholineMuscarinic agonist Not significant

Algotsson et al. (1995): Subject selection 15 AD patients MMSE > Age-matched controls Subjects lived at home

Algotsson et al.

Algotsson et al.: Results AgentActionAD vs Control Sodium nitroprusside NO donor to smooth muscle AD reduced (not significant) Isoproterenol  1 -agonist AD reduced p < 0.01 AcetylcholineEndothelium dependent vasodilator AD reduced p < 0.05

Our study: Subject selection 9 AD patients, age , mean on donepezil (Aricept) 5 mg 3 on donepezil 10 mg MMSE range: , mean controls, age , mean hour fast Lipid panel performed Subjects lived at home

Dose 110  A for 60 seconds All solutions: 0.5 – 1 mM

Results AgentActionAD vs Control MethacholineMuscarinic agonist AD increased 42% p < 0.05 AcetylcholineEndothelium dependent vasodilator AD increased 41% p < 0.16 Sodium nitroprusside NO donor to smooth muscle AD increased 35% p < 0.14

Mean response vs. time

Time-integrals of perfusion responses

Donepezil dose dependence

Conclusion Perfusion response to MCh significantly increased in AD under donepezil therapy. Enhanced response to cholinergic agonists is opposite of what Algotsson et al. observed. It is impossible to evaluate original hypothesis in this patient population. Weak negative correlation observed between donepezil dose and response to MCh.

Proposed explanation AChEis delay the metabolic breakdown of cholinergic agonists in cutaneous tissue. This leads to enhanced and prolonged vasodilation. Results suggest MCh perfusion studies may be useful in monitoring acetylcholinesterase inhibitor therapy.

Future plans New UCSF-study, monitoring AChEi-therapy in AD/IVD. Study of recently diagnosed, untreated subjects. Acknowledgements We thank Matthew Darmalingum for assisting in these experiments and in the preparation of this presentation. This study was performed under NIH grant AG and DOE OBER contract DE-AC03-76SF0098.