Calcium antagonistic properties of the cyclooxygenase-2 inhibitor nimesulide in human myometrial myocytes

Peptidomics analysis of myometrium tissues in term labor compared with term nonlabor

Preterm birth (PTB) is a major cause of neonatal mortality, with a poorly understood etiology. The regular contraction of the myometrium was considered as contributing to the etiology of the onset of labor, especially PTB. Thus, studying the mechanism of myometrium contraction is very important for understanding the initiation of labor and also for preventing PTB. Using liquid chromatography-mass spectrometry, we found 322 significantly differential peptides in myometrium tissues between term nonlabor and term labor groups (absolute fold change ≥ 2 and P < .05). We next analyzed length, molecular weights, isoelectric point, and cleavage site of all the different peptides. We, next, analyzed the functions of different peptides through their precursor proteins by Gene Ontology, enrichment and canonical pathway analysis. The results indicated that the extracellular matrix (ECM) played a major role in biological process, the cellular component, and molecular function categories, and revealed that ECM remodeling played a vital role in myometrial contraction. In addition, some known signaling, such as corticotropin-releasing hormone signaling and calcium signaling were proven to be involved in this process. Ingenuity Pathways Analysis upstream regulator analysis suggested that some of the known molecules, which reportedly were very important in labor onset, were included, for example, nuclear factor κB, tubulin, and phosphoinositide 3-kinase. We also identified 23 peptides derived from the precursor protein TITIN, of which 21 peptides sequences from TITIN were located in functional domains. These results suggested that peptides play an important role in labor onset and provide further insight into PTB therapy.

The Regulation of Interleukin-6 Secretion by Prostanoids and Members of the Tumor Necrosis Factor Superfamily in Fresh Villous Fragments of Term Human Placenta

OBJECTIVE

To determine whether prostanoids, nonsteroidal anti-inflammatory drugs (NSAIDs), and members of the tumor necrosis factor superfamily can regulate placental secretion of interleukin-6 (IL-6) and whether labor influences any such effects.

METHODS

Villous fragments of term, human placenta were kept in culture for up to 4 hours, and IL-6 concentrations were measured in the supernatant. We assessed the effects of the following prostanoids: PGE(2), PGF(2alpha), thromboxane A(2) mimetic (U-46619), and carbacyclin, a stable prostacyclin analogue (all at 1 microM); NSAIDs: indomethacin (150 microM) or nimesulide (100 microM); and Fas ligand (5 ng/mL).

RESULTS

Secretion (mean +/- standard error) of IL-6 was, for control conditions, 1.92 +/- 0.28 fmol/mg wet weight per 3 hours; for PGE(2), 3.57 +/- 0.29 fmol/mg wet weight per 3 hours, P <.01; and for carbacyclin, 3.11 +/- 0.44 fmol/mg wet weight per 3 hours, P <.01. Incubation with PGF(2alpha) or the thromboxane A(2) analogue, U46619, had no effect on IL-6 secretion under these conditions. Fas ligand stimulated IL-6 secretion (3.06 +/- 0.38 fmol/mg wet weight per 3 hours, P <.05). Labor did not alter the effects of prostanoids or FasL. The effects of NSAIDs were assessed over 4 hours. Secretion (median, interquartile range) was, under control conditions 3.26, 2.83-6.23 fmol/mg wet weight per 4 hours, with indomethacin 1.4, 1.28-3.21 (P <.05), and with nimesulide 0.75, 0.50-1.56 fmol/mg wet weight per 4 hours. The magnitude of the effect of Fas ligand in the presence of NSAIDs depended on whether the placentas were delivered before or after labor.

CONCLUSION

Prostanoids, NSAIDs, and the Fas ligand regulate placental IL-6 secretion. Although the effects of individual agents did not vary with the presence or absence of labor, modulation of IL-6 secretion by labor became apparent when agents were combined.

Involvement of electron and hydrogen transfers through redox metabolism on activity and toxicity of the nimesulide

An electronic study of nimesulide was performed by using density functional theory calculations. The activities of the six different derivatives were related with electron donating or accepting capacities. All compounds which had nitro moiety had low electron donating and high electron accepting capacities. However, the reduced derivative of nimesulide have more electron donating capacity than other compounds. The highest spin density contribution in nitro and lowest spin density contribution on phenoxyl moieties can be related with preferential metabolism by reduction when compared with the oxidation. The redox behavior between nitro and amino groups can be related with anti-inflammatory mechanism of nimesulide. These results explain the redox influence of nitro moiety on biological metabolism and mechanism of nimesulide.

Computational modeling of inhibition of voltage-gated Ca channels: identification of different effects on uterine and cardiac action potentials

The uterus and heart share the important physiological feature whereby contractile activation of the muscle tissue is regulated by the generation of periodic, spontaneous electrical action potentials (APs). Preterm birth arising from premature uterine contractions is a major complication of pregnancy and there remains a need to pursue avenues of research that facilitate the use of drugs, tocolytics, to limit these inappropriate contractions without deleterious actions on cardiac electrical excitation. A novel approach is to make use of mathematical models of uterine and cardiac APs, which incorporate many ionic currents contributing to the AP forms, and test the cell-specific responses to interventions. We have used three such models-of uterine smooth muscle cells (USMC), cardiac sinoatrial node cells (SAN), and ventricular cells-to investigate the relative effects of reducing two important voltage-gated Ca currents-the L-type (ICaL) and T-type (ICaT) Ca currents. Reduction of ICaL (10%) alone, or ICaT (40%) alone, blunted USMC APs with little effect on ventricular APs and only mild effects on SAN activity. Larger reductions in either current further attenuated the USMC APs but with also greater effects on SAN APs. Encouragingly, a combination of ICaL and ICaT reduction did blunt USMC APs as intended with little detriment to APs of either cardiac cell type. Subsequent overlapping maps of ICaL and ICaT inhibition profiles from each model revealed a range of combined reductions of ICaL and ICaT over which an appreciable diminution of USMC APs could be achieved with no deleterious action on cardiac SAN or ventricular APs. This novel approach illustrates the potential for computational biology to inform us of possible uterine and cardiac cell-specific mechanisms. Incorporating such computational approaches in future studies directed at designing new, or repurposing existing, tocolytics will be beneficial for establishing a desired uterine specificity of action.

The effect of trichostatin-A and tumor necrosis factor on expression of splice variants of the MaxiK and L-type channels in human myometrium

The onset of human parturition is associated with up-regulation of pro-inflammatory cytokines including tumor necrosis factor (TNF) as well as changes in ion flux, principally Ca²⁺ and K⁺, across the myometrial myocytes membrane. Elevation of intra-cellular Ca²⁺ from the sarcoplasmic reticulum opens L-type Ca²⁺ channels (LTCCs); in turn this increased calcium level activates MaxiK channels leading to relaxation. While the nature of how this cross-talk is governed remains unclear, our previous work demonstrated that the pro-inflammatory cytokine, TNF, and the histone deacetylase inhibitor, Trichostatin-A (TSA), exerted opposing effects on the expression of the pro-quiescent Gαs gene in human myometrial cells. Consequently, in this study we demonstrate that the different channel splice variants for both MaxiK and LTCC are expressed in primary myometrial myocytes. MaxiK mRNA expression was sensitive to TSA stimulation, this causing repression of the M1, M3, and M4 splice variants. A small but not statistically significantly increase in MaxiK expression was also seen in response to TNF. In contrast to this, expression of LTCC splice variants was seen to be influenced by both TNF and TSA. TNF induced overall increase in total LTCC expression while TSA stimulated a dual effect: causing induction of LTCC exon 8 expression but repressing expression of other LTCC splice variants including that encoding exons 30, 31, 33, and 34, exons 30–34 and exons 40–43. The significance of these observations is discussed herein.

A computational model of the ionic currents, Ca2+ dynamics and action potentials underlying contraction of isolated uterine smooth muscle

Uterine contractions during labor are discretely regulated by rhythmic action potentials (AP) of varying duration and form that serve to determine calcium-dependent force production. We have employed a computational biology approach to develop a fuller understanding of the complexity of excitation-contraction (E-C) coupling of uterine smooth muscle cells (USMC). Our overall aim is to establish a mathematical platform of sufficient biophysical detail to quantitatively describe known uterine E-C coupling parameters and thereby inform future empirical investigations of physiological and pathophysiological mechanisms governing normal and dysfunctional labors. From published and unpublished data we construct mathematical models for fourteen ionic currents of USMCs: currents (L- and T-type), current, an hyperpolarization-activated current, three voltage-gated currents, two -activated current, -activated current, non-specific cation current, - exchanger, - pump and background current. The magnitudes and kinetics of each current system in a spindle shaped single cell with a specified surface area∶volume ratio is described by differential equations, in terms of maximal conductances, electrochemical gradient, voltage-dependent activation/inactivation gating variables and temporal changes in intracellular computed from known fluxes. These quantifications are validated by the reconstruction of the individual experimental ionic currents obtained under voltage-clamp. Phasic contraction is modeled in relation to the time constant of changing . This integrated model is validated by its reconstruction of the different USMC AP configurations (spikes, plateau and bursts of spikes), the change from bursting to plateau type AP produced by estradiol and of simultaneous experimental recordings of spontaneous AP, and phasic force. In summary, our advanced mathematical model provides a powerful tool to investigate the physiological ionic mechanisms underlying the genesis of uterine electrical E-C coupling of labor and parturition. This will furnish the evolution of descriptive and predictive quantitative models of myometrial electrogenesis at the whole cell and tissue levels.

Role of T-type Ca Channels in the Spontaneous Phasic Contraction of Pregnant Rat Uterine Smooth Muscle

Although extracellular Ca(2+) entry through the voltage-dependent Ca(2+) channels plays an important role in the spontaneous phasic contractions of the pregnant rat myometrium, the role of the T-type Ca(2+) channels has yet to be fully identified. The aim of this study was to investigate the role of the T-type Ca(2+) channel in the spontaneous phasic contractions of the rat myometrium. Spontaneous phasic contractions and [Ca(2+)](i) were measured simultaneously in the longitudinal strips of female Sprague-Dawley rats late in their pregnancy (on day 18~20 of gestation: term=22 days). The expression of T-type Ca(2+) channel mRNAs or protein levels was measured. Cumulative addition of low concentrations (<1 microM) of nifedipine, a L-type Ca(2+) channel blocker, produced a decrease in the amplitude of the spontaneous Ca(2+) transients and contractions with no significant change in frequency. The mRNAs and proteins encoding two subunits (alpha1G, alpha1H) of the T-type Ca(2+) channels were expressed in longitudinal muscle layer of rat myometrium. Cumulative addition of mibefradil, NNC 55-0396 or nickel induced a concentration-dependent inhibition of the amplitude and frequency of the spontaneous Ca(2+) transients and contractions. Mibefradil, NNC 55-0396 or nickel also attenuated the slope of rising phase of spontaneous Ca(2+) transients consistent with the reduction of the frequency. It is concluded that T-type Ca(2+) channels are expressed in the pregnant rat myometrium and may play a key role for the regulation of the frequency of spontaneous phasic contractions.

Characterization of the molecular and electrophysiological properties of the T-type calcium channel in human myometrium

Rises in intracellular calcium are essential for contraction of human myometrial smooth muscle (HMSM) and hence parturition. The T-type calcium channel may play a role in this process. The aim was to investigate the role of the T-type calcium channel in HMSM by characterizing mRNA expression, protein localization, electrophysiological properties and function of the channel subunits Cav3.1(alpha1G), Cav3.2(alpha1H), and Cav3.3(alpha1I). QRT-PCR, immunohistochemistry, electrophysiology and invitro contractility were performed on human myometrial samples from term, preterm, labour and not in labour. QRT-PCR analysis of Cav3.1, Cav3.2 and Cav3.3 demonstrated expression of Cav3.1 and Cav3.2 with no significant change (P>0.05) associated with gestation or labour status. Immunohistochemistry localized Cav3.1 to myometrial and vascular smooth muscle cells whilst Cav3.2 localized to vascular endothelial cells and invading leucocytes. Voltage clamp studies demonstrated a T-type current in 55% of cells. Nickel block of T-type current was voltage sensitive (IC50 of 118.57+/-68.9 microM at -30 mV). Activation and inactivation curves of ICa currents in cells expressing T-type channels overlapped demonstrating steady state window currents at the resting membrane potential of myometrium at term. Current clamp analysis demonstrated that hyperpolarizing pulses to a membrane potential greater than -80 mV elicited rebound calcium spikes that were blocked reversibly by 100 microM nickel. Contractility studies demonstrated a reversible decrease in contraction frequency during application of 100 microM nickel (P<0.05). We conclude that the primary T-type subunit expressed in some MSMCs is Cav3.1. We found that application of 100 microM nickel to spontaneously contracting human myometrium reversibly slows contraction frequency.

Effect of selective vs. non-selective cyclo-oxygenase inhibitors on fetal membrane prostaglandin synthesis

Increased expression of the inducible isoform of cyclo-oxygenase (COX-2) and prostaglandin output from fetal membranes is a key stage in human parturition. Prostaglandin production can be inhibited by non-steroidal anti-inflammatory drugs (NSAIDs), but these may also inhibit cyclo-oxygenase enzymes in fetal tissues, and hence cause potentially serious side effects. We have compared the concentrations of NSAIDs that inhibit maximal PGE2 synthesis from intact human fetal membrane explants in vitro with those found in human plasma after standard anti-inflammatory treatment. The concentrations of all six drugs that caused a 50% inhibition of fetal membrane prostaglandin output were lower than average plasma levels achieved during treatment. This effect was greatest for nimesulide and indomethacin, indicating that these drugs require further study at low doses in vivo, as this could achieve the same tocolytic effect with diminished adverse fetal effect. These drugs were also the most potent inhibitors of fetal membrane prostaglandin output, consistent with their effects on COX-2 activity.

Effect of nimesulide on gastric acid secretion in the mouse stomach in vitro

Nimesulide, a selective inhibitor of cyclooxygenase-2, has been reported to cause less gastric damage, compared to other NSAIDs. We investigated the effect of nimesulide on basal gastric acid secretion, a contributing factor in NSAID-induced gastric damage, and histamine, pentagastrin, 5-methylfurmethide, isobutyl methylxanthine or high K(+) stimulated acid secretion in the isolated mouse stomach. The stomachs, removed from mice, were transferred into an organ bath and continuously perfused. Changes in pH following the addition of secretagogues were measured by a pH electrode system. The effects of nimesulide on basal and secretagogues-stimulated acid secretion were compared to those of indomethacin. Nimesulide (1 microM to 100 microM) produced a rightward concentration-dependent shift and reduction of maximum acid secretion of all the agonist-stimulated acid secretion curves. Indomethacin was only effective at the higher concentration of 100 microM. Compared to their effects singly, nimesulide (20 microM) and famotidine (0.15 microM) together caused a further shift without further reduction in maximum acid output of the histamine-stimulated curve, suggesting that nimesulide was not acting at the histamine H(2)-receptor. Nimesulide concentration-dependent reduction of stimulated acid secretion in the isolated mouse stomach was not by antagonism of the histamine H(2) receptor and is probably beyond the level of adenylate cyclase stimulation. A direct effect on the calcium channel is demonstrated.

Nimesulide reduces interleukin-1beta-induced cyclooxygenase-2 gene expression in human synovial fibroblasts

OBJECTIVE

To characterize the effects of nimesulide (NIM) on basal and induced cyclo-oxygenase-2 (COX-2) gene expression in human synovial fibroblasts (HSF) and to define the intracellular mechanisms that mediate the changes in COX-2 expression and synthesis in response to the drug.

DESIGN

HSF were incubated with NIM and NS-398 (0, 0.03, 0.3, 3 microg/ml) in the absence or presence of the COX-2 inducers interleukin-1beta (IL-1beta) or endotoxin (LPS). Treated cells were analysed for COX-2 mRNA and protein by Northern and Western blotting analysis, respectively. Putative transcriptional, post-transcriptional, and signaling effects of NIM on basal and induced-COX-2 expression were investigated by human COX-2 promoter studies, calcium studies, reactive oxygen species (ROS) evaluations, electrophoretic mobility shift analysis (EMSA) and half-life studies of COX-2 mRNA.

RESULTS

NIM inhibited IL-1beta-induced COX-2 expression and protein at sub and therapeutic concentrations (0.03-0.3 microg/ml) while the non-specific NSAID, naproxen, did not. Both drugs suppressed PGE2 release by about 95%. NIM had no effect on (1) IL-1beta-induced increases in NF-kappaB or c/EBP signaling, or (2) human COX-2 promoter activity. Stability of induced COX-2 mRNA was unaffected by NIM treatments. Pre-treatment of cells with O(2)radical scavengers (e.g. PDTC) or with Ca(++)channel blockers (e.g. verapamil) had a modest effect on IL-1beta-induced COX-2 expression. NIM blocked ionomycin+thapsigargin and H(2)O(2)-induced increases in COX-2 protein synthesis.

CONCLUSION

NIM inhibits cytokine-induced COX-2 expression and protein at sub and therapeutic concentrations. At least part of this activity may be the result of NIM inhibition of calcium and/or free radical generation induced by cytokines.

Nimesulide: an NSAID that preferentially inhibits COX-2, and has various unique pharmacological activities

Nimesulide is a NSAID with good anti-inflammatory, analgesic and antipyretic activities expected of such compounds. However, in addition it has some unique therapeutic and pharmacological activities. The novel therapeutic aspects include a relatively low toxicity to the gastrointestinal tract and kidneys, it can be given to most patients who experience respiratory problems with other NSAIDs, and the onset of analgesia is comparatively quick. The main novel pharmacological actions obtained using nimesulide in vivo at therapeutic doses, or in vitro at concentrations within the therapeutic range of free (unbound) drug, include: a preferential inhibition of prostaglandin synthesis via COX-2, and reductions in cytokine action/release, histamine release, the release of enzymes that degrade cartilage, and the release of superoxide anions and other toxic substances from neutrophils. Interactions with other drugs are few and of little or no clinical significance.