What Is Clozapine N-Oxide and How Is It Used?

Clozapine N-oxide (CNO) is a chemical compound primarily employed as a research tool, particularly in neuroscience. It possesses the chemical formula C18H19ClN4O2 and a molecular weight of 388.82 g/mol, sharing a structural similarity with the antipsychotic medication clozapine, but with an added N-oxide group. Its significance lies in its ability to manipulate neural activity in controlled laboratory settings, allowing scientists to investigate various brain functions and disease mechanisms. It interacts with specially engineered receptors, enabling precise control over specific cell populations.

The Connection to Clozapine

Clozapine N-oxide is a metabolite of clozapine, an antipsychotic medication used to treat conditions like schizophrenia. In the body, clozapine undergoes enzymatic processes that convert it into CNO.

A significant area of discussion in research involves CNO’s potential to convert back into active clozapine within the body. While CNO was initially considered pharmacologically inactive, studies show it can undergo “reverse metabolism” and revert to clozapine in animal models. The extent of this reconversion varies between species and individuals, introducing variability in experimental outcomes. This means clozapine, with its known pharmacological properties, might contribute to observed effects in CNO studies.

A Tool in Neuroscience Research

CNO plays a role in a neuroscience technique known as “chemogenetics,” using “Designer Receptors Exclusively Activated by Designer Drugs” (DREADDs). DREADDs are engineered receptors designed to respond only to specific external compounds like CNO. When researchers introduce DREADDs into particular brain cells, they can administer CNO to precisely activate or inhibit the activity of those specific neurons.

This precise control allows researchers to investigate the function of particular neural circuits in various physiological and pathological processes. By activating or inhibiting DREADD-expressing neurons, scientists can study their role in behaviors like feeding, memory, or the mechanisms underlying neurological diseases. For example, expressing an inhibitory DREADD in specific neurons of the arcuate nucleus in mice, followed by CNO injection, has been shown to reduce feeding behavior by 40%. This approach helps understand how specific neuronal populations contribute to complex brain functions.

Understanding Its Effects and Safety Profile

Clozapine N-oxide, when administered, reaches peak concentrations in plasma between 30 and 90 minutes, and remains detectable for up to four hours. It is a substrate for P-glycoprotein (P-gp), an efflux pump that can limit its entry into the central nervous system (CNS). This means CNO may not readily cross the blood-brain barrier in large quantities.

The conversion of CNO back to clozapine is a significant consideration for researchers. Clozapine itself is a pharmacologically active compound with multiple receptor targets in the brain, such as serotonergic and dopaminergic receptors. The levels of clozapine formed from CNO can be sufficient to activate these receptors, potentially leading to “off-target” effects that could confound experimental results. Careful interpretation of data and the inclusion of appropriate control groups are important when using CNO in research, especially to differentiate between effects caused by CNO activating DREADDs and those caused by its conversion to clozapine.