Analysing the effect caused by increasing the molecular volume in M1-AChR receptor agonists and antagonists: a structural and computational study

M1 muscarinic acetylcholine receptor (M1-AChR), a member of the G protein-coupled receptors (GPCR) family, plays a crucial role in learning and memory, making it an important drug target for Alzheimer's disease (AD) and schizophrenia. M1-AChR activation and deactivation have shown modifying effects in AD and PD preclinical models, respectively. However, understanding the pharmacology associated with M1-AChR activation or deactivation is complex, because of the low selectivity among muscarinic subtypes, hampering their therapeutic applications. In this regard, we constructed two quantitative structure-activity relationship (QSAR) models, one for M1-AChR agonists (total and partial), and the other for the antagonists. The binding mode of 59 structurally different compounds, including agonists and antagonists with experimental binding affinity values (pKi), were analyzed employing computational molecular docking over different structures of M1-AChR. Furthermore, we considered the interaction energy (Einter), the number of rotatable bonds (NRB), and lipophilicity (ilogP) for the construction of the QSAR model for agonists (R2 = 89.64, QLMO2 = 78, and Qext2 = 79.1). For the QSAR model of antagonists (R2 = 88.44, QLMO2 = 82, and Qext2 = 78.1) we considered the Einter, the fraction of sp3 carbons fCsp3, and lipophilicity (MlogP). Our results suggest that the ligand volume is a determinant to establish its biological activity (agonist or antagonist), causing changes in binding energy, and determining the affinity for M1-AChR.

Clavulanic Acid and its Potential Therapeutic Effects on the Central Nervous System

Clavulanic acid (CLAV) is a non-antibiotic β-lactam that has been used since the late 1970s as a β-lactamase inhibitor in combination with amoxicillin, another ß-lactam with antibiotic activity. Its long-observed adverse reaction profile allows it to say that CLAV is a well-tolerated drug with mainly mild adverse reactions. Interestingly, in 2005, it was discovered that β-lactams enhance the astrocytic expression of GLT-1, a glutamate transporter essential for maintaining synaptic glutamate homeostasis involved in several pathologies of the central nervous system (CNS). This finding, along with a favorable pharmacokinetic profile, prompted the appearance of several studies that intended to evaluate the effect of CLAV in preclinical disease models. Studies have revealed that CLAV can increase GLT-1 expression in the nucleus accumbens (NAcc), medial prefrontal cortex (PFC), and spinal cord of rodents, to affect glutamate and dopaminergic neurotransmission, and exert an anti-inflammatory effect by modulating the levels of the cytokines TNF-α and interleukin 10 (IL-10). CLAV has been tested with positive results in preclinical models of epilepsy, addiction, stroke, neuropathic and inflammatory pain, dementia, Parkinson's disease, and sexual and anxiety behavior. These properties make CLAV a potential therapeutic drug if repurposed. Therefore, this review aims to gather information on CLAV's effect on preclinical neurological disease models and to give some perspectives on its potential therapeutic use in some diseases of the CNS.