Tadalafil inhibits the cAMP stimulated glucose output in the rat liver

doi:10.1016/j.cbi.2014.05.020

Chemico-Biological Interactions

Volume 220, 5 September 2014, Pages 1-11

https://doi.org/10.1016/j.cbi.2014.05.020 Get rights and content

Highlights

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Tadalafil decreases cAMP stimulated glucose output in the rat liver.
•
The glycogen phosphorylase a activity is diminished.
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Glucokinase and glucose 6-phosphatase are stimulated.
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A glucose/glucose 6-phosphatase futile cycle is stimulated.

Abstract

The purpose of the present work was to verify if tadalafil affects hepatic glucose output, one of the primary targets of cAMP, in the isolated perfused rat liver. No effects on glycogen catabolism and oxygen uptake were found under basal conditions for tadalafil concentrations in the range between 0.25 and 10 μM. However, tadalafil had a clear and time-dependent inhibitory effect on the cAMP- and glucagon-stimulated glucose release. Constant infusion of tadalafil in the range between 0.25 and 10 μM eventually abolished 100% of the stimulatory action of those effectors. The tadalafil concentrations producing half-maximal rates of inhibition of the cAMP and glucagon stimulated glycogenolysis were 0.46 ± 0.04 and 1.07 ± 0.16 μM, respectively. These concentrations are close to the plasma peak concentrations in patients after ingestion of 20 mg tadalafil. The drug also diminished the activity of glycogen phosphorylase a and increased the activities of glucose 6-phosphatase, glucokinase, pyruvate kinase and glucose 6-phosphate dehydrogenase. These actions occurred only in the cellular environment. Tadalafil did not affect binding of cAMP to protein kinase A. Diminution of cAMP-stimulated glucose output is the opposite of what can be expected from a phosphodiesterase inhibition, the most common effect attributed to tadalafil. Diminution of glucose output by tadalafil can be attributed (a) to an interference with glycogen phosphorylase stimulation and (b) to an increased futile cycling of glucose 6-phosphate and glucose with a concomitant increased flow of hexose units into cellular metabolic pathways. The effects described in the present work may prove to represent important side effects of tadalafil.

Graphical abstract

Introduction

Tadalafil belongs to the type 5 class of phosphodiesterase inhibitors (PDE5). The PDE5 decomposes and reduces the cellular levels of the second messenger cGMP in several tissues [1]. It is utilized mainly for treating erectile dysfunction [2], which is related to age and physiological factors, and appears as a secondary effect of many pathologies [3], [4], [5] and as a collateral effect of antidepressives which inhibit serotonin reabsorption [6]. The increase in the cellular levels of cGMP in response to nitric oxide causes relaxing of the smooth muscles of the cavernous bodies of the penis, resulting in an increased local blood flow and, consequently, erection [7], [8]. Tadalafil has also been used for treating pulmonary hypertension, benign prostatic hyperplasia, cardioprotection, and for improving glucose uptake in diabetic patients [9], [10], [11], [12], [13], [14], [15].

The liver cells do not possess PDE5, but they present at least four different isoenzymes, namely PDE1, PDE2, PDE3 and PDE11 [16], [17], [18], [19], [20]. The latter is the second most sensitive to tadalafil [16]. It is also relatively unspecific in that it hydrolyzes both cAMP and cGMP [16]. Up to now there is no experimental evidence of any kind about an action of tadalafil on the liver functions or metabolism, excepting a weak interaction with medication drugs metabolized by cytochrome P450 [21]. However, there are two reports about a metabolic action of another phosphodiesterase inhibitor, similar to tadalafil, namely sildenafil. In isolated rat hepatocytes, sildenafil inhibits gluconeogenesis from alanine [22] and intraperitoneal administration of sildenafil to rats diminishes hepatic glycogenolysis [23]. These observations with sildenafil are surprising because inhibition of hepatic gluconeogenesis and glycogenolysis is the opposite of what one would expected in the case of a phosphodiesterase inhibition. Since cAMP stimulates both gluconeogenesis and glycogenolysis [24], [26], inhibition of its hydrolysis should enhance stimulation because its steady-state cellular concentration should increase [24]. For this reason we decided to undertake a systematic investigation of a possible action of tadalafil on basic metabolic pathways in the liver linked in some way to glucose homeostasis and that are influenced by cAMP. Tadalafil was chosen because this compound has the longest half-life of all the structural analogs currently used for treating erectile dysfunction [1], [2], [3], [4]. The experimental model used in the present work was the isolated perfused rat liver, a system in which true metabolic steady-states can be established under conditions that are much closer to the physiological situation than isolated and cultured cells [27], [28]. The cellular cAMP levels were increased by direct infusion of the compound, which is effectively transported across the cell membrane [26], but also by infusing glucagon, the classical cAMP-generating hormone in the cellular environment [24]. The results should improve our current understanding of the overall effects of tadalafil.

Section snippets

Materials

The liver perfusion apparatus was built in the workshops of the University of Maringá [27]. Tadalafil was purchased at the Farmácia Medicinal (Maringá, Brazil) which obtained the product from Ideal Farma Indústria e Comércio de Produtos Farmacêuticos Ltda (Anápolis, Goiás, Brazil). According to the validated quantification certificate from Ideal Farma, the purity of the sample was 99.6%, as revealed by high performance chromatography. Prior to our experiments spectral analyses in the UV range

Effects of tadalafil on the metabolic actions of cAMP

In the first experiments a possible action of tadalafil on basic metabolic pathways in the perfused liver was investigated. Fig. 1 shows a typical experiment in which glycogen catabolism and oxygen uptake were measured in livers from fed rats being perfused with substrate-free perfusion fluid. Under these conditions the liver respires at the expense of endogenous fatty acids and promotes the degradation of endogenous glycogen to glucose and lactate plus pyruvate [27], [28]. Fig. 1 shows that

Discussion

The results allow to conclude that tadalafil inhibits glucose output in the liver when the latter was stimulated by cAMP or by a hormone that acts via cAMP (glucagon). Tadalafil probably interferes in some way with the mechanism of action of cAMP, but it is difficult to attribute this action to an inhibition of phosphodiesterases. A significant inhibition of cAMP hydrolysis should produce the opposite of what was observed, more precisely, a stimulation of glucose output because such an effect

Conflict of Interest

The authors declare that there are no conflicts of interest.

Transparency Document

Acknowledgements

This work was supported by Grants from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). Vanessa Rodrigues Vilela was a fellowship recipient of the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

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The concentrations of tadalafil causing half-maximal inhibition of cAMP- and glucagon-stimulated glucose release, 0.46 ± 0.04 and 1.07 ± 0.16 μM, respectively, are similar to plasma peak concentrations in humans following a 20 mg oral dose. Furthermore, tadalafil reduced glycogen phosphorylase activity and increased glucose-6-phosphatase, glucokinase, pyruvate kinase and glucose-6-phosphate dehydrogenase activities [14E]. The authors speculate that, even in the presence of phosphodiesterase inhibition, tadalafil-induced reduction in glucose output is the result of altered glycogen phosphorylase activity and/or increased futile cycling of glucose-6-phosphate and glucose with concomitant increased flow of hexose units in cellular metabolic pathways.
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Tadalafil inhibits the cAMP stimulated glucose output in the rat liver

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Effects of tadalafil on the metabolic actions of cAMP

Discussion

Conflict of Interest

Transparency Document

Acknowledgements

PDE-5 inhibition and sexual response: pharmacological mechanisms and clinical outcomes

Annu. Rev. Sex Res.

The discovery of tadalafil: a novel and highly selective PDE5 inhibitor

J. Med. Chem.

Sexual dysfunction in United States: prevalence and predictors

JAMA

Do vardenafil and tadalafil have advantages over sildenafil in the treatment of erectile dysfunction?

Int. J. Impot. Res.

Erectile dysfunction

InnovAiT

Effects of SSRIs on sexual function: a critical review

J. Clin. Psychopharmacol.

Anatomy, physiology, and pathophysiology of erectile dysfunction

J. Sex. Med.

Comparison of phosphodiesterase type 5 (PDE5) inhibitors

Int. J. Clin. Pract.

Urodynamic effects of once daily tadalafil in men with lower urinary tract symptoms secondary to clinical benign prostatic hyperplasia: a randomized, placebo controlled 12-week clinical trial

J. Urol.

Tadalafil therapy for pulmonary arterial hypertension

Circulation

Phosphodiesterase-5 inhibitor, tadalafila, protects against myocardial ischemia/reperfusion through protein-kinase g-dependent generation of hydrogen sulfide

Circulation

The phosphodiesterase-5 inhibitor tadalafil reduces myocardial infarct size

Int. J. Impot. Res.

Chronic inhibition of cyclic GMP phosphodiesterase 5A prevents and reverses cardiac hypertrophy

Nat. Med.

Tadalafil increases muscle capillary recruitment and forearm glucose uptake in women with type 2 diabetes

Diabetologia

Phosphodiesterase 5 inhibition improves β-cell function in metabolic syndrome

Diabetes Care

Potency, selectivity, and consequences of nonselectivity of PDE inhibition

Int. J. Impot. Res.

Cyclic nucleotide phosphodiesterases: functional implications of multiple isoforms

Physiol. Rev.

Cyclic nucleotide phospho-diesterases: relating structure and function

Prog. Nucleic Acid Res. Mol. Biol.

PDE4 cAMP phosphodiesterases: modular enzymes that orchestrate signaling cross-talk, desensitization and compartmentalization

Biochem. J.

Update on phosphodiesterase (PDE) isoenzymes as pharmacologic targets in urology: present and future

Eur. Urol.

Redefining the role of long-acting phosphodiesterase inhibitor tadalafil in the treatment of diabetic erectile dysfunction

Curr. Diabetes Rev.

Effects of phosphodiesterase 3,4,5 inhibitors on hepatocyte cAMP levels, glycogenolysis, gluconeogenesis, and susceptibility to a mitochondrial toxin

Mol. Cell. Biochem.

Effects of sildenafil a phosphodiesterase 5 inhibitor on rat liver cell key enzymes of gluconeogenesis and glycogenolysis

Int. J. Pharmacol.

Production, uptake and metabolic effects of cAMP in the bivascularly perfused rat liver

Biochem. Pharmacol.

Modeling the transformation of exogenously supplied [3H]cAMP in the perfused rat liver

Res. Comm. Mol. Pathol. Pharmacol.

Transport of cyclic AMP and synthetic analogs in the perfused rat liver

Biochem. Pharmacol.

O estudo do metabolismo no fígado em perfusão

Hemoglobin-free perfusion of rat liver

Modeling the transformation of exogenously supplied [³H]cAMP in the perfused rat liver