Cyclic nucleotides and calcium regulation in heart and smooth muscle cells

The Complexity and Multiplicity of the Specific cAMP Phosphodiesterase Family: PDE4, Open New Adapted Therapeutic Approaches

Cyclic nucleotides (cAMP, cGMP) play a major role in normal and pathologic signaling. Beyond receptors, cyclic nucleotide phosphodiesterases; (PDEs) rapidly convert the cyclic nucleotide in its respective 5'-nucleotide to control intracellular cAMP and/or cGMP levels to maintain a normal physiological state. However, in many pathologies, dysregulations of various PDEs (PDE1-PDE11) contribute mainly to organs and tissue failures related to uncontrolled phosphorylation cascade. Among these, PDE4 represents the greatest family, since it is constituted by 4 genes with multiple variants differently distributed at tissue, cellular and subcellular levels, allowing different fine-tuned regulations. Since the 1980s, pharmaceutical companies have developed PDE4 inhibitors (PDE4-I) to overcome cardiovascular diseases. Since, they have encountered many undesired problems, (emesis), they focused their research on other PDEs. Today, increases in the knowledge of complex PDE4 regulations in various tissues and pathologies, and the evolution in drug design, resulted in a renewal of PDE4-I development. The present review describes the recent PDE4-I development targeting cardiovascular diseases, obesity, diabetes, ulcerative colitis, and Crohn's disease, malignancies, fatty liver disease, osteoporosis, depression, as well as COVID-19. Today, the direct therapeutic approach of PDE4 is extended by developing allosteric inhibitors and protein/protein interactions allowing to act on the PDE interactome.

The Endocrine Function of the Heart: Physiology and Involvements of Natriuretic Peptides and Cyclic Nucleotide Phosphodiesterases in Heart Failure

Besides pumping, the heart participates in hydro-sodium homeostasis and systemic blood pressure regulation through its endocrine function mainly represented by the large family of natriuretic peptides (NPs), including essentially atrial natriuretic (ANP) and brain natriuretic peptides (BNP). Under normal conditions, these peptides are synthesized in response to atrial cardiomyocyte stretch, increase natriuresis, diuresis, and vascular permeability through binding of the second intracellular messenger’s guanosine 3′,5′-cyclic monophosphate (cGMP) to specific receptors. During heart failure (HF), the beneficial effects of the enhanced cardiac hormones secretion are reduced, in connection with renal resistance to NP. In addition, there is a BNP paradox characterized by a physiological inefficiency of the BNP forms assayed by current methods. In this context, it appears interesting to improve the efficiency of the cardiac natriuretic system by inhibiting cyclic nucleotide phosphodiesterases, responsible for the degradation of cGMP. Recent data support such a therapeutic approach which can improve the quality of life and the prognosis of patients with HF.

Cyclic nucleotide phosphodiesterase (PDE) isozymes as targets of the intracellular signalling network: benefits of PDE inhibitors in various diseases and perspectives for future therapeutic developments

Cyclic nucleotide phosphodiesterases (PDEs) that specifically inactivate the intracellular messengers cAMP and cGMP in a compartmentalized manner represent an important enzyme class constituted by 11 gene-related families of isozymes (PDE1 to PDE11). Downstream receptors, PDEs play a major role in controlling the signalosome at various levels of phosphorylations and protein/protein interactions. Due to the multiplicity of isozymes, their various intracellular regulations and their different cellular and subcellular distributions, PDEs represent interesting targets in intracellular pathways. Therefore, the investigation of PDE isozyme alterations related to various pathologies and the design of specific PDE inhibitors might lead to the development of new specific therapeutic strategies in numerous pathologies. This manuscript (i) overviews the different PDEs including their endogenous regulations and their specific inhibitors; (ii) analyses the intracellular implications of PDEs in regulating signalling cascades in pathogenesis, exemplified by two diseases affecting cell cycle and proliferation; and (iii) discusses perspectives for future therapeutic developments.

Myocardial effects of cyclic AMP phosphodiesterase inhibition are dampened in thyroxine-induced cardiac hypertrophy

We tested the hypothesis that the increase in myocardial O2 consumption (MVO2) and myocardial wall thickening in response to milrinone would not be limited by thyroxine (T4)-induced (0.5 mg/kg for 16 days) cardiac hypertrophy. Anesthetized open-chest New Zealand white rabbits were divided into four groups: control vehicle (CV, n = 5), control milrinone (CM, n = 8), T4 vehicle (T4V, n = 7), and T4 milrinone (T4M, n = 9). Vehicle or milrinone (10(-3) M) were topically applied to the left ventricular epicardium for 15 min. Coronary blood flow (radioactive microspheres) and O2 extraction (microspectrophotometry) were used to determine O2 consumption. Cyclic AMP levels were determined by radioimmunoassay. T4 increased the heart weight to body weight ratio from 2.6 +/- 0.1 to 3.1 +/- 0.1 (g/kg). T4 rabbits had significantly higher baseline heart rates, blood pressures, and dP/dtmax and both subepicardial (EPI) and subendocardial (ENDO) blood flows. Topical application of milrinone did not have significant hemodynamic effects in either group. Baseline cyclic AMP levels (pmol/g) in the EPI and ENDO myocytes were comparable between control and T4 rabbits (CVEPI = 599 +/- 34, CVENDO = 532 +/- 26, T4VEPI = 656 +/- 42, T4VENDO = 657 +/- 17). Milrinone increased cyclic AMP in all groups although the increases were less in the T4 rabbits (CMEPI = 742 +/- 115, CMENDO = 698 +/- 101, T4MEPI = 742 +/- 103, T4MENDO = 690 +/- 55). Baseline MVO2 (ml O2/min/100 g) was significantly higher in T4 rabbits than controls (T4VEPI = 17.7 +/- 3.5 vs CVEPI = 8.5 +/- 1.5, T4VENDO = 17.2 +/- 3.2 vs CVENDO = 9.2 +/- 1.5). Significant increases in MVO2 were noted with the addition of milrinone in control (CMEPI = 14.8 +/- 3.0, CMENDO = 13.5 +/- 1.6) and T4 (T4MEPI = 25.5 +/- 3.4, T4MENDO = 22.0 +/- 3.3) rabbits; however, the percentage increase in MVO2 was significantly greater in controls (CEPI = 73%, CENDO = 47%) than T4 (T4,EPI = 44%, T4,ENDO = 28%). Thus, although the cyclic AMP phosphodiesterase activity was comparable between T4 rabbit hearts and controls, the metabolic effects and cyclic AMP effects of milrinone were dampened in this form of hypertrophy.

Calcium-channel blockers and gastrointestinal motility: basic and clinical aspects

Several calcium-channel blockers currently in use for the treatment of cardiovascular disorders have recently been tested for their effects on gastrointestinal motility. The rationale for this approach centers on the concept that calcium-channel blockers are at least as potent in inhibiting intestinal smooth muscle as in relaxing vascular smooth muscle. This review will give an outline of the most recent findings on the role of calcium and calcium channels in smooth muscle and neuronal function in the digestive system. It will also consider the mechanisms by which calcium-channel blockers may affect gastrointestinal motility and assess potential clinical applications in gastroenterology. The main goal for researchers in this field will be the development of gut-selective agents, with no cardiovascular side effects.

Regulation of cytosolic free Ca2+ concentration in vascular smooth muscle cells by A- and C-kinases

The cytosolic free Ca2+ concentration [( Ca2+]i) was measured in cultured human umbilical vein smooth muscle cells using fura-2 as a Ca2+ indicator and microscopic digital image analysis system. Activation of cells with histamine and vasopressin resulted in a prompt though transient rise in [Ca2+]i 10- to 12-fold higher than the resting [Ca2+]i. The [Ca2+]i then declined rapidly during the first 30-40 seconds after hormonal stimulation and then gradually decreased to near resting levels in 2-3 minutes in the continued presence of hormones. The magnitude of the increase in peak [Ca2+]i was similar in buffered salt solution containing 1.8 mM Ca2+, zero Ca2+, and zero Ca2+ buffered salt solution containing 10 mM La3+, suggesting that receptor-mediated increase in [Ca2+]i is primarily due to the release of Ca2+ from the intracellular stores. Addition of La3+ produced oscillations in [Ca2+]i in approximately half the cells in response to both hormones. Addition of 10 microM forskolin did not significantly affect the resting [Ca2+]i, the hormone-stimulated peak [Ca2+]i, or the time course of hormone-stimulated [Ca2+]i transients. These data suggest that mechanisms involved in A-kinase-mediated smooth muscle relaxation may be subsequent to the changes in [Ca2+]i. Activation of C-kinase by 1 microM 12 deoxyphorbol 13-isobutyrate-20 acetate (DPBA) did not affect the resting [Ca2+]i, though it attenuated the histamine and vasopressin-mediated peak elevation in [Ca2+]i. Since DPBA inhibited the peak [Ca2+]i response to both the hormones to the same extent, it would appear that C-kinase activation may uncouple the receptor-mediated activation of phospholipase C.