Cotinine binding to nicotinic acetylcholine receptors in bovine chromaffin cell and rat brain membranes

Abstract

Cotinine is the major metabolite of nicotine. It has nicotine-like biological activity, but its potency is low. We studied cotinine binding to nicotinic receptors labelled with [3H]epibatidine. In membranes from cultured bovine chromaffin cells [3H]epibatidine bound to two apparent sites with K(d) values of 93 and 1400 pM. The low-affinity binding represented two-thirds of the binding sites. In rat frontal cortex and hippocampus homogenate membranes, only one apparent binding site was detected. The Kd values were 40 and 62 pM, in frontal cortex and hippocampus, respectively. Nicotine displaced [3H]epibatidine 10 times more potently from the brain than from the chromaffin cell membranes, and cotinine had over two orders of magnitude lower affinity than nicotine. In addition, the competitive nicotinic receptor antagonists methyllycaconitine and dihydro beta-erythroidine displaced [3H]epibatidine (100 pM and 1 nM) from the chromaffin cell membranes. Alpha-bungarotoxin did not affect the binding of 100 pM [3H]epibatidine. However, upon labelling with 1 nM [3H]epibatidine alpha-bungarotoxin (10 nM to 10 microM) displaced one-sixth of the bound radioligand. Our results demonstrate that 100 pM to 1 nM [3H]epibatidine labels mostly neuronal heteropentameric nicotinic receptors in bovine chromaffin cell membranes, and that cotinine is a low-affinity nicotinic ligand both in the adrenal chromaffin cell and in the brain receptors.

The nicotine metabolite, cotinine, attenuates glutamate (NMDA) antagonist-related effects on the performance of the five choice serial reaction time task (5C-SRTT) in rats

“…Moreover, in rats and mice, α 7 -nAChR activation enhances field stimulation-evoked glutamate currents [43, 44, 47, 48]. However, cotinine is also a low affinity ligand at heteromeric nAChRs including those composed of α3/α6β2 and α4β2-nAChR subunits [11, 12, 13, 18]. Importantly, selective ligands at α4β2-nAChRs (e.g., Sazetidine-A) have also been shown to attenuate impairments in tasks of sustained attention associated with MK-801 [49].…”

“…For example, cotinine was found to have very low potency in producing cardiovascular or respiratory effects [7], in altering electroencephalogram activation, or producing behavioral arousal [8], and it did not generalize to the discriminative stimulus properties of nicotine [9]. In nicotinic acetylcholine receptor (nAChR) binding assays, cotinine was also found to be approximately 100–1000 fold less potent than nicotine at displacing radiolabeled nAChR ligands in rodent brain preparations [10–13]. Moreover, in functional assays, cotinine was approximately 30–50 fold less potent than nicotine in evoking dopamine release in brain slices or synaptosomes [14].…”

Evaluation of nicotine and cotinine analogs as potential neuroprotective agents for Alzheimer’s disease

“…It has been reported that the neuroprotective effects of nicotine and acetylcholinesterase inhibitors (AChEIs) observed previously in Aβ 1–42 and glutamate neurotoxicity models is related to direct (nicotine) and indirect (AChEIs) effects at α 4 β 2 and α 7 nicotinic acetylcholine receptors (nAChRs) as well as effects on the PI3K-Akt pathway, activation of calcineurin, and L-type calcium channels. 27–30 In older nAChR binding assays, cotinine was found to be approximately 100–1000 fold less potent than nicotine at displacing radiolabeled nAChR ligands 31–34 , therefore, it appears unlikely that the neuroprotective effects of cotinine observed in the Aβ 1–42 neurotoxicity assay (i.e., at similar concentrations to nicotine) could be fully explained by direct effects at nAChRs. Interestingly, effectiveness of nicotine and cotinine and some other compounds (e.g., choline analogs) in memory-related behavioral tasks has been correlated with their effectiveness in producing nAChR desensitization.…”

Nicotine enhances ethanol-induced fat accumulation and collagen deposition but not inflammation in mouse liver

“…It is possible that nicotine metabolites produced by CYP2A5 enhance alcoholic fatty liver. On the other hand, metabolites of nicotine have a very low potency to bind to nAChRs (Vainio and Tuominen, 2001). Thus the cell-cell or organ-organ interaction as postulated above would be impaired.…”

“…Nicotine exerts its cellular functions in neuronal cells through nicotinic acetylcholine receptors (nAChRs) (Itier and Bertrand, 2001). Cotinine, a metabolite of nicotine, has much lower potency to bind to nAChR (Vainio and Tuominen, 2001). CYP2A6 is a major enzyme which metabolically inactivates nicotine in humans, while in mice the enzyme which inactivates nicotine is CYP2A5, a mouse ortholog of human CYP2A6 (Su and Ding, 2004).…”