Manfred Braeter

Propiverine and metabolites: differences in binding to muscarinic receptors and in functional models of detrusor contraction

Propiverine is a commonly used antimuscarinic drug used as therapy for symptoms of an overactive bladder. Propiverine is extensively biotransformed into several metabolites that could contribute to its spasmolytic action. In fact, three propiverine metabolites (M-5, M-6 and M-14) have been shown to affect various detrusor functions, including contractile responses and L-type calcium-currents, in humans, pigs and mice, albeit with different potency. The aim of our study was to provide experimental evidence for the relationship between the binding of propiverine and its metabolites to human muscarinic receptor subtypes (hM1–hM5) expressed in chinese hamster ovary cells, and to examine the effects of these compounds on muscarinic receptor-mediated detrusor function. Propiverine, M-5, M-6 and M-14 bound to hM1–hM5 receptors with the same order of affinity for all five subtypes: M-6 > propiverine > M-14 > M-5. In HEK-293 cells expressing hM3, carbachol-induced release of intracellular Ca2+ ([Ca2+]i) was suppressed by propiverine and its metabolites; the respective concentration-response curves for carbachol-induced Ca2+-responses were shifted to the right. At higher concentrations, propiverine and M-14, but not M-5 and M-6, directly elevated [Ca2+]i. These results were confirmed for propiverine in human detrusor smooth muscle cells (hDSMC). Propiverine and the three metabolites decreased detrusor contractions evoked by electric field stimulation in a concentration-dependent manner, the order of potency being the same as the order of binding affinity. We conclude that, in comparison with the parent compound, loss of the aliphatic side chain in propiverine metabolites is associated with higher binding affinity to hM1–hM5 receptors and higher functional potency. Change from a tertiary to a secondary amine (M-14) results in lower binding affinity and reduced potency. Oxidation of the nitrogen (M-5) further lowers binding affinity as well as functional potency.

Pharmacodynamics of propiverine and three of its main metabolites on detrusor contraction

1 Besides its antimuscarinic effects, propiverine may possess an additional mode of action. We compared the effects of propiverine, three of its metabolites (M‐5, M‐6, M‐14) and atropine in human, pig and mouse urinary bladder preparations in order to elucidate the nature of a possible additional mode of action. 2 Like the parent compound, M‐5, M‐6 and M‐14 reduced to variable degrees the contractions elicited by electric field stimulation (EFS) of isolated, urothelium‐denuded detrusor strips. In mouse the atropine‐resistant and therefore the nonadrenergic, noncholinergic component of contractile response to EFS was reduced by M‐5, M‐14 and propiverine, but was hardly affected by M‐6. 3 Atropine, propiverine and M‐6 significantly shifted the cumulative concentration–response curves for carbachol (CCh) to higher concentrations. Atropine and M‐6 did not affect the maximum tension induced by CCh. Propiverine, M‐5 and M‐14 reduced the maximum CCh effect, suggesting at least one additional mode of action. This pattern of response was observed in all the three species, albeit with some differences in sensitivity to the various agents. 4 In freshly isolated human detrusor smooth muscle cells, propiverine and M‐14 inhibited the nifedipine‐sensitive L‐type calcium current (ICa) in a concentration‐dependent manner. In contrast, the effects of M‐5 and M‐6 on ICa were insignificant in the concentration range examined. 5 The investigated responses to propiverine and its metabolites suggest that impairment of maximum CCh‐induced contractions is due to strong effect on ICa and that this may be associated with the presence of the aliphatic side chain.

Effects of three metabolites of propiverine on voltage-dependent L-type calcium currents in human atrial myocytes.

The non-selective muscarinic receptor antagonist propiverine impairs L-type Ca(2+) currents (I(Ca,L)) in human detrusor smooth muscle cells and atrial cardiomyocytes. Here, we have investigated the effects of three metabolites of propiverine on human cardiac I(Ca,L). Propiverine reduced I(Ca)(,L) with a -logIC(50) [M] value of 4.1, M-5 only showed minor effect on I(Ca)(,L) at high concentrations, M-6 did not influence I(Ca)(,L) at all. Like the parent compound M-14 also reduced I(Ca)(,L) (-logIC(50) [M]=4.6). We conclude, that propiverine and M-14 reduce cardiac I(Ca)(,L) at higher concentrations than in detrusor cells and therefore preferentially reduce I(Ca)(,L) in the urinary bladder than in the heart.