NotebookLM - patho

Physiological Effects & Mechanisms of Neurotransmitters

Acetylcholine (ACh): Often called the "rest and relax" neurotransmitter, ACh regulates learning, memory, motor control, and autonomic nervous system (ANS) activity.

• Receptors: Nicotinic (ligand-gated ion channels; excitatory) and Muscarinic (G-protein coupled receptors; varied signaling responses).

• Pro-Cholinergic Effects: Supports memory function, induces miosis and dizziness, activates skeletal muscle at the neuromuscular junction (NMJ via nicotinic receptors), and produces "WET" SLUDGE effects (salivation, lacrimation, urination, defecation, GI upset, emesis).

• Anti-Cholinergic Effects: Produces "DRY" symptoms (dry mouth, dry eyes, urinary retention, constipation), drowsiness, impaired memory and cognition, mydriasis (blurred vision), increased heart rate, agitation, hallucinations, and skeletal muscle block

Molecular Drug Targets at Cholinergic Synapses

• Acetylcholinesterase (AChE): An enzyme located in the synaptic cleft that breaks down ACh into choline and acetate. AChE is the only mechanism for terminating synaptic ACh activity (reuptake applies only to choline). Inhibiting AChE (via donepezil, rivastigmine, galantamine) increases synaptic ACh availability.

• Muscarinic Receptors: GPCRs present postsynaptically; targeted by muscarinic agonists (e.g., pilocarpine, carbachol, bethanechol) or antagonists (e.g., atropine, diphenhydramine)

• Nicotinic Receptors: Ligand-gated channels present post synaptically; targeted directly by nicotine-replacement therapy agents.

• Choline Transporter (ChT) & ChAT: Pre-synaptic uptake of choline and synthesis of ACh via Choline Acetyltransferase

Loss of Cholinergic Neurons & ACh Levels in Memory Pathways

Alzheimer’s disease (AD) neurodegeneration selectively damages cholinergic projection pathways to two main brain regions:

1. Hippocampus: Responsible for learning and memory.

2. Cortex: Responsible for cognition and executive function.

Pathological Cascade:

1. Loss of presynaptic cholinergic neurons projecting to these pathways.

2. Loss of nicotinic and muscarinic receptors on remaining active neurons.

3. Loss of postsynaptic target neurons.

Net Effect: A severe decrease in cholinergic transmission throughout these circuits, directly causing the progressive memory loss and cognitive deficits characteristic of AD

Modified Amyloid Theory, A$\beta$42, APOE, Tau & Neuroinflammation

• APP Cleavage & Abeta42: Amyloid Precursor Protein (APP) is processed by secretases into either non-toxic Abeta40 or toxic Abeta42.

• APOE Clearance: Apolipoprotein E (APOE) molecules shuttle cholesterol and clear Abeta proteins. Abeta42 is cleared poorly, and the APOE4 isoform is the least effective at clearance.

• Oligomers & Plaques: Uncleared Abeta42 accumulates into soluble oligomers and extracellular amyloid plaques. Soluble Abeta42 oligomers are highly neurotoxic.

• Tau Protein & Tangles: Hyperphosphorylated tau detaches from microtubules (disrupting intracellular transport) and forms intracellular neurofibrillary tangles. Misfolded tau spreads cell-to-cell, exacerbating toxicity.

• Neuroinflammation & Excitotoxicity: Soluble Abeta42 oligomers promote NMDA receptor overstimulation (excitotoxicity) and trigger microglial damage/local neuroinflammation. Combined, these drivers lead to physical neurodegeneration (tissue loss) in the hippocampus and cortex

Theory Behind Anti-Abeta42 Monoclonal Antibodies & Anti-Inflammatory Treatments

• Anti-Abeta42 Monoclonal Antibodies (Disease-Modifying Immunotherapies):

  • MOA: Bind directly to Abeta42 species to reduce toxic oligomers and remove amyloid plaque buildup, aiming to slow the rate of clinical disease progression.

  • Drugs:

    • Lecanemab (Leqembi): Targets soluble proto-fibrils/fibrils.

    • Donanemab (Kisunla): Targets insoluble aggregated amyloid plaques.

  • Risk/ADE: ARIA (Amyloid-Related Imaging Abnormalities), which occurs when antibodies target amyloid in blood vessel walls, reducing vascular structural integrity and increasing blood-brain barrier (BBB) permeability.

• Anti-Inflammatory & Regenerative Targets:

  • Experimental strategies aim to attenuate microglial attack, reduce free radical damage, and block neuroinflammation.

  • Investigational Example: Lomecel-B (bone-marrow-derived medicinal signaling cell product) secretes immunomodulatory and regenerative factors to foster anti-inflammatory responses

Differences in MOA Between the Three AD Drug Classes

Anti-Abeta42 Monoclonal Antibodies (Disease-Modifying):

• MOA: Bind soluble/insoluble Abeta42 to clear plaques and diminish oligomer neurotoxicity.

• Clinical Effect: Aimed at slowing neurodegeneration and disease progression2.

NMDA Receptor Channel Blockers (Symptomatic):

• MOA: Uncompetitive antagonist (channel blocker) at overactive NMDA receptors, limiting pathological Ca2+ entry and reducing excitotoxicity.

• Clinical Effect: Symptomatic relief only; slows clinical functional decline by protecting surviving neurons without halting underlying neurodegeneration.

• Drug: Memantine (Namenda).

Reversible Acetylcholinesterase (AChE) Inhibitors (Symptomatic):

• MOA: Reversibly inhibit AChE to prevent ACh breakdown and elevate synaptic ACh levels across all cholinergic synapses

• Clinical Effect: Symptomatic relief only (improves memory and cognition).

• Key Limitation: Because AChEIs require presynaptic ACh release to work, their effectiveness wanes as presynaptic cholinergic neurons die off.

• Drugs: Donepezil (Aricept), Rivastigmine (Exelon), Galantamine (Razadyne)

Pro- and Anti-Cholinergic Drug Classifications & MOAs

Pro-Cholinergic Drugs:

• AChE Inhibitors: Donepezil, Rivastigmine, Galantamine, and Namzaric (combination Memantine + Donepezil).

• Muscarinic Agonists (Pro-muscarinic only): Pilocarpine, Carbachol, Bethanechol.

• Nicotinic Agonists (Pro-nicotinic only): Nicotine-replacement therapy agents.

Anti-Cholinergic Drugs:

• Muscarinic Antagonists: Atropine, Diphenhydramine, and overactive bladder agents. Produce central and peripheral anti-cholinergic adverse effects