Relaxin activates AMPK-AKT signaling and increases glucose uptake by cultured cardiomyocytes

PURPOSE

Many evidences show that the hormone relaxin plays a pivotal role in the physiology and pathology of the cardiovascular system. This pleiotropic hormone exerts regulatory functions through specific receptors in cardiovascular tissues: in experimental animal models it was shown to induce coronary vasodilation, prevent cardiac damage induced by ischemia/reperfusion and revert cardiac hypertrophy and fibrosis. A tight relationship between this hormone and important metabolic pathways has been suggested, but it is at present unknown if relaxin could regulate cardiac metabolism. Our aim was to study the possible effects of relaxin on cardiomyocyte metabolism.

METHODS

Neonatal rat cardiomyocytes were treated with relaxin and (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assays (MTT) were performed to assess metabolic activity; while 2-deoxy-D-[³H] glucose and BODIPY-labelled fatty acid incorporations were analyzed to measure glucose and fatty acid uptakes, and western blot was utilized to study the intracellular signaling pathways activated by the hormone.

RESULTS

We observed that relaxin at 10 ng/ml was able to increase the level of metabolic activity of cultured neonatal rat cardiomyocytes; the rate of 2-deoxy-D-[³H]glucose incorporation demonstrated that relaxin also induced an increase in glucose uptake. First evidence is also offered that relaxin can activate the master energy sensor and regulator AMPK in cardiomyocytes. Moreover, the treatment of cardiomyocytes with relaxin also induced dose-dependent increases in ERK1/2, AKT, and AS160 phosphorylation. That raise in AS160 phosphorylation induced by relaxin was prevented by the pretreatment with AMPK and AKT pathways inhibitors, indicating that both molecules play important roles in the relaxin effects reported.

CONCLUSION

Relaxin can regulate cardiomyocyte metabolism and activate AMPK, the central sensor of energy status that maintains cellular energy homeostasis, and also ERK and AKT, two molecular sensing nodes that coordinate dynamic responses of the cell's metabolic responses.

Effects of a selective histamine H₄R antagonist on inflammation in a model of carrageenan-induced pleurisy in the rat

The histamine H₄ receptor (H₄R), recently cloned and identified, is a G-protein coupled histamine receptor family expressed in immune cells which plays an important role in inflammation. Recent data evidentiated that H₄R antagonists can decrease airway inflammation and hyperreactivity in animal models of asthma. In the present study we evaluated the effect of the selective H₄R antagonist JNJ7777120 (JNJ) in carrageenan-induced pleurisy, an in vivo model of inflammation, well characterized for cellular and molecular mechanisms. Intra-pleural administration of λ-carrageenan (1% w/v in 0.2 ml sterile saline) determined an intense recruitment of leucocytes in pleural exudates and in lung tissues, activated inducible nitric oxide (NO) synthase and cyclooxygenase-2, thus increasing the generation of harmful autacoids such as NO and pro-inflammatory prostaglandins, PgE₂ and 6-ketoPgF(1α), increased cellular and DNA oxidative stress, measured as malondialdehyde and 8-OH-deoxyguanosine and the local generation of IL-1β and TNF-α. Moreover, the activity of caspase-3, an early marker of apoptosis was also activated by λ-carrageenan injection. The pre-treatment with JNJ (5-10 mg Kg⁻¹ b.wt., given intrapleurally), 60 min before carrageenan markedly reduced all the studied parameters. This study clearly demonstrated that histamine H₄R antagonists have anti-inflammatory effects and could have potential therapeutic application for the treatment of inflammatory diseases.

A new low molecular weight, MnII-containing scavenger of superoxide anion protects cardiac muscle cells from hypoxia/reoxygenation injury

Reperfusion injury after oxygen starvation is a key pathogenic step in ischemic diseases. It mainly consists in oxidative stress, related to mitochondrial derangement and enhanced generation of reactive oxygen species (ROS), mainly superoxide anion (O2(•2)), and peroxynitrite by cells exposed to hypoxia. This in vitro study evaluates whether Mn(II)(4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-diacetate).2H2O, or Mn(II)(Me2DO2A), a new low molecular weight, Mn(II)-containing O2(•) scavenger, has a direct protective action on H9c2 rat cardiac muscle cells subjected to hypoxia and reoxygenation. Mn(II)(Me2DO2A) (1 and 10 μmol/l) was added to the culture medium at reoxygenation and maintained for 2 h. In parallel experiments, the inactive congener Zn(II)(Me2DO2A), in which Zn(II) replaced the functional Mn(II) center in the same organic scaffold, was used as negative control. Mn(II)(Me2DO2A) (10 μmol/l) significantly increased cardiac muscle cell viability (trypan blue assay), improved mitochondrial activity (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide test, membrane potential Δψ), reduced apoptosis (mitochondrial permeability transition pore opening, caspase-3, terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling assay), decreased intracellular ROS levels (2',7'-dichlorodihydrofluorescein diacetate and MitoSOX assays), and decreased protein nitroxidation (nitrotyrosine [NT] expression) and DNA oxidation (8-hydroxy-deoxyguanosine levels). Of note, Zn(II)(Me2DO2A) had no protective effect. The mechanism of Mn(II)(Me2DO2A) relies on concentration-dependent removal of harmful O2(•) generated at reoxygenation from dysfunctional mitochondria in hypoxia-induced cells, as indicated by the MitoSOX assay. This study suggests that Mn(II)(Me2DO2A) is a promising antioxidant drug capable of reducing O2(•)-mediated cell oxidative stress which occurs at reoxygenation after hypoxia. In perspective, Mn(II)(Me2DO2A) might be used to reduce ischemia-reperfusion organ damage in acute vascular diseases, as well as to extend the viability of explanted organs before transplantation.

A selective antagonist of histamine H₄ receptors prevents antigen-induced airway inflammation and bronchoconstriction in guinea pigs: involvement of lipocortin-1

BACKGROUND AND PURPOSE

Among the pathogenic mechanisms of asthma, a role for oxidative/nitrosative stress has been well documented. Recent evidence suggests that histamine H₄ receptors play a modulatory role in allergic inflammation. Here we report the effects of compound JNJ 7777120 (JNJ), a selective H4 receptor antagonist, on antigen-induced airway inflammation, paying special attention to its effects on lipocortin-1 (LC-1/annexin-A1), a 37 kDA anti-inflammatory protein that plays a key role in the production of inflammatory mediators.

EXPERIMENTAL APPROACH

Ovalbumin (OA)-sensitized guinea pigs placed in a respiratory chamber were challenged with antigen. JNJ (5, 7.5 and 10 mg.kg⁻¹) was given i.p. for 4 days before antigen challenge. Respiratory parameters were recorded. Bronchoalveolar lavage (BAL) fluid was collected and lung specimens taken for further analyses 1 h after antigen challenge. In BAL fluid, levels of LC-1, PGD2 , LTB4 and TNF-α were measured. In lung tissue samples, myeloperoxidase, caspase-3 and Mn-superoxide dismutase activities and 8-hydroxy-2-deoxyguanosine levels were measured.

KEY RESULTS

OA challenge decreased LC-1 levels in BAL fluid, induced cough, dyspnoea and bronchoconstriction and increased PGD2 , LTB4 and TNF-α levels in lung tissue. Treatment with JNJ dose-dependently increased levels of LC-1, reduced respiratory abnormalities and lowered levels of PGD2 , LTB4 and TNF-α in BAL fluid.

CONCLUSIONS AND IMPLICATIONS

Antigen-induced asthma-like reactions in guinea pigs decreased levels of LC-1 and increased TNF-α and eicosanoid production. JNJ pretreatment reduced allergic asthmatic responses and airway inflammation, an effect associated with LC-1 up-regulation.

Developing ROS scavenging agents for pharmacological purposes: recent advances in design of manganese-based complexes with anti-inflammatory and anti- nociceptive activity

Reactive oxygen and nitrogen species, which are normal products of cell metabolism, may play a dual beneficial/deleterious role, depending on local concentration and mode of generation. As such, they have been identified as key pathogenic factors for many inflammatory and degenerative disorders, carcinogenesis, nociception and ageing. In this perspective, low molecular weight transition metal complexes with organic ligands have been and are still viewed as promising pharmaceutical agents with antioxidant/free radical scavenging properties, owing to their ability to interact and/or react with reactive oxygen or nitrogen species and counterbalance excessive endogenous free radical generation in biological systems. Among these compounds, manganese(II/III) complexes have resulted effective as ROS scavengers both in vitro and in vivo. In particular, Mn(III) complexes with porphyrins and salen derivatives as well as Mn(II) complexes with macrocyclic pentaamines and polyamine-polycarboxylic acids have been recently analyzed as ROS scavengers for therapeutic purposes. In this article, we summarize the chemical and biological properties of manganese complexes with low molecular weight synthetic ligands as scavengers of pro-oxidant species, with particular attention to the mechanisms operating at the metal center in the scavenging process. A proper design of the organic scaffolds may yield manganese complexes capable to catalyze different scavenging reactions, including superoxide and/or hydrogen peroxide dismutation and peroxynitrite decomposition. These manganese complexes can be viewed either as a novel class of drugs helpful to reduce oxidative tissue injury or as useful tools to get further light on the role played by ROS in biological systems.

Skeletal myoblasts for heart regeneration and repair: state of the art and perspectives on the mechanisms for functional cardiac benefits

Until recently, skeletal myoblasts (SkMBs) have been the most widely used cells in basic research and clinical trials of cell based therapy for cardiac repair and regeneration. Although SkMB engraftment into the post-infarcted heart has been consistently found to improve cardiac contractile function, the underlying therapeutic mechanisms remain still a matter of controversy and debate. This is basically because SkMBs do not attain a cardiac-like phenotype once homed into the diseased heart nor they form a contractile tissue functionally coupled with the surrounding viable myocardium. This issue of concern has generated the idea that the cardiotropic action of SkMBs may depend on the release of paracrine factors. However, the paracrine hypothesis still remains ill-defined, particularly concerning the identification of the whole spectrum of cell-derived soluble factors and details on their cardiac effects. In this context, the possibility to genetically engineering SkMBs to potentate their paracrine attitudes appears particularly attractive and is actually raising great expectation. Aim of the present review is not to cover all the aspects of cell-based therapy with SkMBs, as this has been the object of previous exhaustive reviews in this field. Rather, we focused on novel aspects underlying the interactions between SkMBs and the host cardiac tissues which may be relevant for directing the future basic and applied research on SkMB transplantation for post ischemic cardiac dysfunction.

Relationships between telocytes and cardiomyocytes during pre- and post-natal life

Evidence has been given that the adult heart contains a specific population of stromal cells lying in close spatial relationship with cardiomyocytes and with cardiac stem cells in sub-epicardial cardiogenic niches. Recently termed ‘telocytes’ because of their long cytoplasmic processes embracing the parenchymal cells, these cells have been postulated to be involved in heart morphogenesis. In our opinion, investigating the occurrence and morphology of telocytes during heart histogenesis may shed further light on this issue. Our findings show that typical telocytes are present in the mouse heart by early embryonic to adult life. These cells closely embrace the growing cardiomyocytes with their long, slender cytoplasmic processes. Hence, in the developing myocardium, telocytes may play nursing and guiding roles for myocardial precursors to form the correct three-dimensional tissue architectural pattern, as previously suggested.

Relaxin and nitric oxide signalling

The peptide hormone relaxin (RLX) has been shown to exert a variety of functions in both reproductive and non-reproductive tissues. The molecular mechanism of RLX on its target cells appears to involve multiple intracellular signalling systems, including the nitric oxide (NO) pathway. NO is an ubiquitous molecule synthesised from L-arginine under the catalytic action of different nitric oxide synthase (NOS) isoforms and its altered production has been reported to be involved in several diseases. RLX has been demonstrated to promote NO biosynthesis by up-regulating NOS expression; its influence on the different NOS appears to depend on the cell type studied. In addition to its physiological roles, RLX has been postulated as a potential therapeutic agent in several diseases. In particular, based on its property to promote NO biosynthesis, RLX may be regarded as a therapeutic tool in diseases characterized pathogenically by an impaired NO production. The aim of the present mini-review is to summarize and discuss the pathophysiological actions of RLX, strictly related to its ability to activate the endogenous NO pathway in reproductive and non-reproductive target organs.

Activation of cannabinoid receptors prevents antigen-induced asthma-like reaction in guinea pigs

In this study we evaluated the effects of the CB₁/CB₂ cannabinoid receptor agonist CP55, 940 (CP) on antigen-induced asthma-like reaction in sensitized guinea pigs and we tested the ability of the specific CB2 receptor antagonist SR144528 (SR) and CB1 receptor antagonist AM251 (AM) to interfere with the effects of CP. Ovalbumin-sensitized guinea pigs placed in a respiratory chamber were challenged with the antigen given by aerosol. CP (0.4 mg/kg b.wt.) was given i.p. 3 hrs before ovalbumin challenge. Sixty minutes before CP administration, some animals were treated i.p. with either AM, or SR, or both (0.1 mg/kg b.wt.). Respiratory parameters were recorded and quantified. Lung tissue specimens were then taken for histopathological and morphometric analyses and for eosinophilic major basic protein immunohistochemistry. Moreover, myeloperoxidase activity, 8-hydroxy-2-deoxyguanosine, cyclic adenosine monophosphate (cAMP) and guanosine monophosphate (cGMP) levels, and CB₁ and CB₂ receptor protein expression by Western blotting were evaluated in lung tissue extracts. In the bronchoalveolar lavage fluid, the levels of prostaglandin D₂ and tumour necrosis factor-α TNF-α were measured. Ovalbumin challenge caused marked abnormalities in the respiratory, morphological and biochemical parameters assayed. Treatment with CP significantly reduced these abnormalities. Pre-treatment with SR, AM or both reverted the protective effects of CP, indicating that both CB₁ and CB₂ receptors are involved in lung protection. The noted treatments did not change the expression of cannabinoid receptor proteins, as shown by Western blotting. These findings suggest that targeting cannabinoid receptors could be a novel preventative therapeutic strategy in asthmatic patients.

Reversal by relaxin of altered ileal spontaneous contractions in dystrophic (mdx) mice through a nitric oxide-mediated mechanism

Altered nitric oxide (NO) production/release is involved in gastrointestinal motor disorders occurring in dystrophic (mdx) mice. Since the hormone relaxin (RLX) can upregulate NO biosynthesis, its effects on spontaneous motility and NO synthase (NOS) expression in the ileum of dystrophic (mdx) mice were investigated. Mechanical responses of ileal preparations were recorded in vitro via force-displacement transducers. Evaluation of the expression of NOS isoforms was performed by immunohistochemistry and Western blot. Normal and mdx mice were distributed into three groups: untreated, RLX pretreated, and vehicle pretreated. Ileal preparations from the untreated animals showed spontaneous muscular contractions whose amplitude was significantly higher in mdx than in normal mice. Addition of RLX, alone or together with l-arginine, to the bath medium depressed the amplitude of the contractions in the mdx mice, thus reestablishing a motility pattern typical of the normal mice. The NOS inhibitor N(G)-nitro-L-arginine (L-NNA) or the guanylate cyclase inhibitor ODQ reversed the effects of RLX. In RLX-pretreated mdx mice, the amplitude of spontaneous motility was reduced, thus resembling that of the normal mice, and NOS II expression in the muscle coat was increased in respect to the vehicle-pretreated mdx animals. These results indicate that RLX can reverse the altered ileal motility of mdx mice to a normal pattern, likely by upregulating NOS II expression and NO biosynthesis in the ileal smooth muscle.

Protection from cardiac injury by induction of heme oxygenase-1 and nitric oxide synthase in a focal ischaemia-reperfusion model

The enzymes heme oxygenase (HO) generate carbon monoxide (CO) in living organisms during heme degradation. Carbon monoxide has recently been shown to dilate blood vessels and to possess anti-inflammatory properties. It is also known that nitric oxide (NO) donors ameliorate cardiac ischaemia-reperfusion injury in experimental models of global or focal ischaemia-reperfusion (FIR). The two gaseous mediators share the same mechanism of action via the stimulation of soluble guanylyl cyclase and the increase in cellular levels of cyclic GMP. We studied the effects of manipulating the HO system and the possible interaction between CO and NO in an experimental in vivo model of FIR in the rat heart. FIR-subjected rats had necrotic area in the left ventricle, ventricular arrhythmias and a shortening of survival time in comparison to sham-operated animals. Resident mast cells underwent a heavy degranulation, malonyldialdehyde was produced by myocardial cell membranes, and tissue calcium levels were increased. High levels of myeloperoxidase were also detected, suggesting a FIR-related inflammatory process. In animals pre-treated with the HO-1 inducer, hemin, all the biochemical and morphometric markers of FIR were minimized or fully abated. Consistently, the biochemical and morphometric markers of FIR were reversed in rats treated with the HO-1 blocker, ZnPP-IX, prior to hemin administration. Pre-treatment with hemin significantly increases the expression and activity of both cardiac HO-1 and iNOS, suggesting that CO and NO cooperate in the cardioprotective effect against FIR-induced damage, and that there is a therapeutic synergism between NO-donors and CO-releasing molecules, via the common stimulation of increase in cGMP levels and decrease in calcium overload.

Atomic force microscopy of histological sections using a chemical etching method

Physiology and pathology have a big deal on tissue morphology, and the intrinsic spatial resolution of an atomic force microscope (AFM) is able to observe ultrastructural details. In order to investigate cellular and subcellular structures in histological sections with the AFM, we used a new simple method for sample preparation, i.e. chemical etching of semithin sections from epoxy resin-embedded specimens: such treatment appears to melt the upper layers of the embedding resin; thus, removing the superficial roughness caused by the edge of the microtome knife and bringing into high relief the biological structures hidden in the bulk. Consecutive ultrathin sections embedded in epoxy resin were observed with a transmission electron microscope (TEM) to compare the different imaging properties on the same specimen sample. In this paper we report, as an example, our AFM and TEM images of two different tissue specimens, rat pancreas and skeletal muscle fibres, showing that most of the inner details are visible with the AFM. These results suggest that chemical etching of histological sections may be a simple, fast and cost-effective method for AFM imaging with ultrastructural resolution.

Atomic force microscopy of histological sections using a chemical etching method

Physiology and pathology have a big deal on tissue morphology, and the intrinsic spatial resolution of an atomic force microscope (AFM) is able to observe ultrastructural details. In order to investigate cellular and subcellular structures in histological sections with the AFM, we used a new simple method for sample preparation, i.e. chemical etching of semithin sections from epoxy resin-embedded specimens: such treatment appears to melt the upper layers of the embedding resin; thus, removing the superficial roughness caused by the edge of the microtome knife and bringing into high relief the biological structures hidden in the bulk. Consecutive ultrathin sections embedded in epoxy resin were observed with a transmission electron microscope (TEM) to compare the different imaging properties on the same specimen sample. In this paper we report, as an example, our AFM and TEM images of two different tissue specimens, rat pancreas and skeletal muscle fibres, showing that most of the inner details are visible with the AFM. These results suggest that chemical etching of histological sections may be a simple, fast and cost-effective method for AFM imaging with ultrastructural resolution.

Relaxin potentiates the expression of inducible nitric oxide synthase by endothelial cells from human umbilical vein in in vitro culture

The hormone relaxin (RLX), which can be detected in human venous cord blood, has been shown to be a potent vasodilator, acting through increased expression of inducible nitric oxide synthase (NOS II) and nitric oxide (NO) generation. This study aims at clarifying whether RLX, at concentrations of 100 and 1000 ng/ml for 6 or 12 h of exposure, can influence the expression of NOS isoforms in human umbilical vein endothelial cells (HUVEC) cultured in vitro. NOS mRNA expression was studied by quantitative real-time RT-PCR, NOS protein expression and activity was studied by Western blot and nitrite assay, and immunoreactive NOS localization was performed by confocal microscopy. Untreated HUVEC expressed all the NOS isoforms, especially the constitutive, endothelial-type NOS III and, to a lesser extent, NOS II and NOS I. RLX-treated cells showed an increased expression of NOS II, attaining a maximum with 1000 ng/ml RLX, which gave rise to increased NO generation, as shown by nitrite assay. This effect of RLX appears to be mediated by activation of NOS II transcription factor NF-kappaB, since it was abolished by the NF-kappaB inhibitors curcumin-95 and dexamethasone. These findings suggest that RLX in the umbilical vein might contribute to the NO-dependent regulation of vascular tone.

Protective effect of relaxin in cardiac anaphylaxis: involvement of the nitric oxide pathway

1 Relaxin (RLX) is a multifunctional hormone best known for its role in pregnancy and parturition, that has been also shown to influence coronary perfusion and mast cell activation through the generation of endogenous nitric oxide (NO). In this study we report on the effects of RLX on the biochemical and mechanical changes of ex vivo perfused hearts isolated from ovalbumin-sensitized guinea-pigs induced by challenge with the specific antigen. The possible involvement of NO in the RLX action has been also investigated. 2 A 30-min perfusion with RLX (30 ng ml(-1)) before ovalbumin challenge fully abated the positive chronotropic and inotropic effects evoked by anaphylactic reaction to the antigen. RLX also blunted the short-term coronary constriction following to antigen challenge. Conversely, perfusion with chemically inactivated RLX had no effect. 3 The release of histamine in the perfusate and the accumulation of calcium in heart tissue induced by antigen challenge were significantly decreased by RLX, while the amounts of nitrites in the perfusate were significantly increased, as were NO synthase activity and expression and cGMP levels in heart tissue. 4 These findings indicate that RLX has a protective effect in cardiac anaphylaxis which involves an up-regulation of the NO biosynthetic pathway.

Myenteric neurons and interstitial cells of Cajal of mouse colon express several nitric oxide synthase isoforms

Information on equipment and subcellular distribution of nitric oxide synthase (NOS) isoforms in myenteric neurons and pacemaker cells (ICC) might help to identify nitric oxide (NO) pathway(s) acting on gastrointestinal motility. In sections of mouse colon labelled with neuronal (n)NOS, endothelial (e)NOS and inducible (i)NOS antibodies, all myenteric neurons co-expressed eNOS and iNOS and a subpopulation of them co-expressed nNOS. ICC co-expressed nNOS and eNOS. In the neurons, nNOS-labeling was intracytoplasmatic, in the ICC at cell periphery. In both cell types, eNOS-labeling was on intracytoplasmatic granules, likely mitochondria. In conclusion, myenteric neurons and ICC co-express several NOS isoforms with specific subcellular distribution. Different nNOS splice variants are presumably present: intracytoplasmatic nNOSbeta and nNOSalpha producing neurogenic NO, plasma membrane-bound nNOSalpha producing ICCgenic NO. eNOS might be implicated in mitochondrial respiration and, in ICC, also in pacemaker activity. Neurons express iNOS also in basal condition.

Ultrastructural abnormalities of muscle spindles in the rat masseter muscle with malocclusion-induced damage

Human temporomandibular disorders due to disturbed occlusal mechanics are characterized by sensory, motor and autonomic symptoms, possibly related to muscle overwork and fatigue. Our previous study in rats with experimentally-induced malocclusion due to unilateral molar cusp amputation showed that the ipsilateral masseter muscles undergo morphological and biochemical changes consistent with muscle hypercontraction and ischemia. In the present study, the masseter muscle spindles of the same malocclusion-bearing rats were examined by electron microscopy. Sham-operated rats were used as controls. In the treated rats, clear-cut alterations of the muscle spindles were observed 26 days after surgery, when the extrafusal muscle showed the more severe damage. The fusal alterations affected predominantly capsular cells, intrafusal muscle fibers and sensory nerve endings. These results suggest that in the malocclusion-bearing rats, an abnormal reflex regulation of the motor activity of the masticatory muscles may take place. They also allow us to hypothesize that muscle spindle alterations might be involved in the pathogenesis of human temporomandibular disorders.

The vasorelaxant hormone relaxin induces changes in liver sinusoid microcirculation: a morphologic study in the rat

This study shows that specialized contractile endothelial cells exist in rat liver sinusoids which may be involved in the local control of hemodynamics and which are sensitive to vasoactive agents, including the vasorelaxant hormone relaxin. Male rats were treated with 10 microg relaxin for 4 days; phosphate-buffered saline (PBS)-treated rats were the controls. For comparison, rats treated with relaxin together with the NO-synthase inhibitor N(omega)-nitro-l -arginine methyl ester (L-NAME), and rats treated with the vasodilator taurodeoxycholic acid or the vasoconstrictor ethanol were investigated. Liver fragments were studied morphologically and morphometrically. In the control rats, peculiar contractile cells were present in the endothelial lining. These cells had abundant myofilaments and formed cytoplasmic blebs projecting into and often occluding the lumen. In the ethanol-treated rats, sinusoids were constricted and filled with cytoplasmic blebs. In the relaxin-treated rats, sinusoids were markedly dilated and the cytoplasmic blebs nearly disappeared. Similar findings were observed in the taurodeoxycholic acid-treated rats. The effects of relaxin were blunted by L-NAME, suggesting that the relaxin action involves an NO-mediated mechanism.

Dantrolene counteracts the masseter muscle damage induced by artificial occlusal wear: studies in a rat model

In previous studies, we showed that the introduction of occlusal alterations to rats results in masseter muscle abnormalities. Here, we investigate whether administration of the muscle relaxant dantrolene to rats with occlusal alteration could counteract the occurrence of such abnormalities. Rats underwent unilateral amputation of molar cusps to cause malocclusion. Some rats received dantrolene (10 mg/kg/day subcutaneously). The masseter muscles ipsilateral to the amputated molars were excised 26 days later. Sham-operated rats were used as controls. The tissue samples were studied by light and electron microscopy and morphometry. Moreover, tissue Ca2+ content, an index of muscle injury, was determined. In the absence of dantrolene, occlusal alteration leads to microvessel constriction, morphologic damage of masseter muscle fibers and blood capillaries, and elevation of tissue Ca2+ content. These changes were nearly abrogated by dantrolene, thus supporting it as a possible new therapeutic tool for the treatment of malocclusion-induced muscle diseases.

Relaxin causes changes of the liver. In vivo studies in rats

During pregnancy, the liver undergoes metabolic adjustments directed to fulfil the needs of the mother and the growing fetus. This study was designed to verify whether relaxin, a hormone related to pregnancy, may induce histochemical and ultrastructural modifications of hepatocytes which can be related to metabolic changes. Estrogen-primed female rats were treated with relaxin (10 microg in repository vehicle) for 18 h. Additional male rats were treated with relaxin (10 microg/day in PBS) for 4 days. Appropriate vehicle-treated rats were used as controls. After fasting, the rats were killed and liver fragments were processed for light and electron microscopy and for computer-assisted morphometry of PAS-positive glycogen deposits and acid phosphatase-reactive organelles. In both sexes, the relaxin-treated rats underwent a significant decrease in the amount of glycogen in the hepatocytes as compared with the controls. These changes were accompanied by an increase in smooth endoplasmic reticulum, endocytosis vesicles and lysosomes. These findings show that relaxin promotes glycogen depletion and induces morphological changes of hepatocytes which are consistent with functional activation. It is suggested that relaxin might play an important role in hepatic metabolic adjustments occurring during pregnancy.

Relaxin promotes differentiation of human breast cancer cells MCF-7 transplanted into nude mice

Previous studies showed that the hormone relaxin acts on human breast cancer MCF-7 cells in vitro by modulating cell proliferation and promoting cell differentiation toward a duct epithelial phenotype. The present study was designed to investigate whether relaxin retains these properties when acting in vivo on MCF-7 cell tumors developed in athymic nude mice. Mice bearing MCF-7 cell tumors transplanted under the mammary fat pad and estrogenized to sustain tumor growth were treated systemically with relaxin (10 microg/day) for 19 days. Vehicle-treated mice were used as controls. Thirty days later, the mice were sacrificed and tumor fragments were analyzed by light and electron microscopy and immunocytochemistry. Measurements of tumor volume were recorded weekly for the overall experimental period. The results obtained indicate that relaxin treatment promotes differentiation of tumor cells towards both myoepithelial-like and epithelial-like cells, as judged by the ultrastructural features of the cells and by the increased expression of smooth muscle actin and cadherins. Measurements of tumor size and of the number of cycling cells show that relaxin, at the doses and times of exposure used in this study, does not significantly influence tumor growth and cell proliferation.

Morphologic and biochemical changes of the masseter muscles induced by occlusal wear: studies in a rat model

Occlusal alterations may result in changes in the functional performance of masticatory muscles. In this study, we set up an experimental model in rats to examine whether masticatory muscle abnormalities occur after a malocclusion is induced. Rats underwent unilateral amputation of the molar cusps to simulate an occlusal wear situation. The masseter muscles ipsilateral and contralateral to the amputated molars were excised at different experimental times. Sham-operated rats were used as controls. The tissue samples were studied by light and electron microscopy and morphometry. Tissue calcium content, a biochemical index of muscle injury, was also determined. The results show that occlusal dysfunction leads to microvessel constriction and clear-cut morphologic damage of muscular fibers and blood capillary endothelium, as well as to elevation of tissue calcium content, in the ipsilateral masseter muscle. These changes are likely related to muscle fatigue and ischemia. The early signs of injury do not involve the entire muscle but are mostly restricted to tissue areas rich in type I (slow) muscle fibers, which are characterized by a predominantly aerobic metabolism. The muscle damage becomes more extended and severe with time. On the other hand, the contralateral muscles show only slight alterations which are reversible with time, possibly due to an adaptive response.

Relaxin up-regulates the nitric oxide biosynthetic pathway in the mouse uterus: involvement in the inhibition of myometrial contractility

The uterus is a site of nitric oxide (NO) production and expresses NO synthases (NOS), which are up-regulated during pregnancy. NO induces uterine quiescence, which is deemed necessary for the maintenance of pregnancy. Relaxin is known to promote uterine quiescence. Relaxin has also been shown to stimulate NO production in several targets. In this study we investigated the effects of relaxin on the NO biosynthetic pathway of the mouse uterus. Estrogenized mice were treated with relaxin (2 microg) for 18 h, and the uterine horns were used for determination of immunoreactive endothelial-type NOS and inducible NOS. Moreover, uterine strips from estrogenized mice were placed in an organ bath, and the effect of relaxin on K+-induced contracture was evaluated in the presence or absence of the NOS inhibitor nitro-L-arginine. Relaxin increases the expression of endothelial-type NOS in surface epithelium, glands, endometrial stromal cells, and myometrium, leaving inducible NOS expression unaffected. Moreover, relaxin inhibits myometrial contractility, and this effect is blunted by nitro-L-arginine, thus indicating that the L-arginine-NO pathway is involved in the relaxant action of relaxin on the myometrium. Because relaxin is elevated during pregnancy, it is suggested that relaxin has a physiological role in the up-regulation of uterine NO biosynthesis during pregnancy.

Relaxin favors the development of activated human T cells into Th1-like effectors

Differentiation of naive CD4+ helper T (Th) cells into Th1 or Th2 effectors, as characterized by their opposite pattern of cytokine production, can be influenced by several factors, including hormones. In this study, we demonstrate that porcine relaxin, at concentrations ranging from 10(-10) to 10(-6) M, favors the in vitro development of human antigen-specific T cells into Th1-like effectors and enhances both IFN-gamma mRNA expression and IFN-gamma production by established human T cell clones. The promoting effect of relaxin on the development of IFN-gamma-producing cells was not due to a relaxin-induced release of IL-12 and/or IFN-alpha by antigen-presenting cells. These results suggest that relaxin may contribute to the regulation of the immune homeostasis during pregnancy and may also play some role in counteracting Th2-dominated disorders.

Relaxin activates the L-arginine-nitric oxide pathway in vascular smooth muscle cells in culture

The peptide hormone relaxin (RLX) has been shown to elicit a powerful vasodilatory response in several target organs. This response is mediated by the stimulation of intrinsic nitric oxide (NO) generation. The present study was designed to clarify whether RLX directly promotes the relaxation of vascular smooth muscle cells through stimulation of NO generation. Vascular smooth muscle cells from bovine aortas were incubated with RLX at concentrations ranging from 1 nmol/L to 1 micromol/L. The expression and activity of NO synthase, production of NO, and the intracellular levels of cGMP and Ca2+ were determined. The cell morphology and signal transduction mechanisms of these bovine aortic smooth muscle cells in response to RLX were also studied. RLX stimulated the expression of immunoreactive inducible NO synthase and increased significantly and in a concentration-related fashion inducible NO synthase activity, NO generation, and intracellular cGMP levels. Concurrently, RLX significantly decreased cytosolic Ca2+ concentrations and caused changes in cell shape and the actin cytoskeleton that were consistent with cell relaxation. The signal transduction mechanisms leading to the enhanced expression of inducible NO synthase protein and activity caused by RLX involve the activation of tyrosine kinase, phosphatidylcholine-phospholipase C, and the transcription factor nuclear factor-kappaB, similar to bacterial endotoxins and proinflammatory cytokines. This study suggests that RLX is an endogenous agent capable of regulating vascular tone by activation of the L-arginine-NO pathway in vascular smooth muscle cells.

Relaxin protects against myocardial injury caused by ischemia and reperfusion in rat heart

Myocardial injury caused by ischemia and reperfusion comes from multiple pathogenic events, including endothelial damage, neutrophil extravasation into tissue, platelet and mast cell activation, and peroxidation of cell membrane lipids, which are followed by myocardial cell alterations resulting eventually in cell necrosis. The current study was designed to test the possible cardioprotective effect of the hormone relaxin, which has been found to cause coronary vessel dilation and to inhibit platelet and mast cell activation. Ischemia (for 30 minutes) was induced in rat hearts in vivo by ligature of the left anterior descending coronary artery; reperfusion (for 60 minutes or less if the rats died before this predetermined time) was induced by removal of the ligature. Relaxin (100 ng) was given intravenously 30 minutes before ischemia. The results obtained showed that relaxin strongly reduces 1) the extension of the myocardial areas affected by ischemia-reperfusion-induced damage, 2) ventricular arrhythmias, 3) mortality, 4) myocardial neutrophil number, 5) myeloperoxidase activity, a marker of neutrophil accumulation, 6) production of malonyldialdehyde, an end product of lipid peroxidation, 7) mast cell granule release, 8) calcium overload, and 9) morphological signs of myocardial cell injury. This study shows that relaxin can be regarded as an agent with a marked cardioprotective action against ischemia-reperfusion-induced myocardial injury.

Relaxin counteracts myocardial damage induced by ischemia-reperfusion in isolated guinea pig hearts: evidence for an involvement of nitric oxide

Relaxin was previously shown to cause coronary vasodilation and to inhibit mast cell activation through a stimulation of endogenous nitric oxide production. This suggests that relaxin may have beneficial effects on ischemia-reperfusion-induced myocardial injury, which is triggered by endothelial damage and impaired nitric oxide generation. In this study, we tested the effect of relaxin on isolated and perfused guinea pig hearts subjected to ischemia and reperfusion. Ischemia was induced by ligature of the left anterior descending coronary artery; removal of the ligature induced reperfusion. Relaxin, at the concentration of 30 ng/ml of perfusion fluid, causes: a significant increase in coronary flow and in nitric oxide generation; a significant decrease in malonyldialdehyde production and in calcium overload, both markers of myocardial injury; an inhibition of mast cell granule exocytosis and histamine release, which are known to contribute to myocardial damage; a reduction of ultrastructural abnormalities of myocardial cells; an improvement of heart contractility. The beneficial effects of relaxin were blunted by the NO synthase inhibitor L-NMMA. The current study provides first experimental evidence that relaxin has a powerful protective effect on the heart undergoing ischemia and reperfusion acting through a nitric oxide-driven mechanism.

Relaxin counteracts asthma-like reaction induced by inhaled antigen in sensitized guinea pigs

In previous studies, the peptide hormone relaxin (RLX) was found to inhibit mast cell secretion and platelet activation. It has been established that the release of mediators from these cells plays a central pathogenic role in allergic asthma. This prompted us to ascertain whether RLX may counteract the respiratory and histopathological abnormalities of the asthma-like reaction to inhaled antigen in sensitized guinea pigs. Guinea pigs were sensitized with ovalbumin and challenged with the same antigen given by aerosol. Some animals received RLX (30 microg/kg BW, twice daily for 4 days) before antigen challenge. Other animals received inactivated RLX in place of authentic RLX. Respiratory abnormalities, such as cough and dyspnea, were analyzed as were light and electron microscopic features of lung specimens. RLX was shown to reduce the severity of respiratory abnormalities, as well as histological alterations, mast cell degranulation, and leukocyte infiltration in sensitized guinea pigs exposed to ovalbumin aerosol. RLX was also found to promote dilation of alveolar blood capillaries and to reduce the thickness of the air-blood barrier. This study provides evidence for an antiasthmatic property of RLX and raises the possibility of new therapeutic strategies for allergic asthma in humans.

Relaxin and breast cancer

Relaxin is a peptide hormone of luteal origin with a broad range of biological activities on tissues and organs of the female reproductive system as well as on other targets not directly related to the reproductive function. The mammary gland is one of the major targets for relaxin, which has been shown to promote growth and differentiation of mammary parenchyma and stroma. Based on the recognition of the mammotrophic action of relaxin, further research could show that this peptide also influences the behaviour of breast cancer cells in vitro. In fact, when relaxin was added to the culture medium of MCF-7 breast adenocarcinoma cells for short exposure times it had a biphasic effect on their growth, stimulating cell proliferation at low, nanomolar concentrations and inhibiting it at high, micromolar concentrations. In the longer times, relaxin had a marked growth-inhibitory effect on MCF-7 cells at any concentration assayed, and concurrently promoted cell differentiation and expression of adhesion molecules which are known to binder the spreading ability of cancer cells. The positive effect of relaxin on MCF-7 cell differentiation was even enhanced when these cells were cocultured with myoepithelial cells, thus recreating a microenvironment reminiscent of the tissue architecture of the mammary ducts in vivo. Concerning the mechanisms of action of relaxin on MCF-7 cells, it seems that the growth-inhibiting and differentiation-promoting effects of the peptide are mediated through the activation of the synthetic pathway of nitric oxide.

Relaxin: a pleiotropic hormone

1. Relaxin is a peptide hormone of about 6000 Da belonging to the insulin family. Like insulin, relaxin is composed by two disulfide-linked chains, termed the A and B chains, the B chain bearing the receptor interaction site. 2. Relaxin is produced primarily by the corpus luteum, in both pregnant and nonpregnant females. It attains the highest plasma levels during pregnancy. In this condition, relaxin is also produced by the decidua and placenta. In males, relaxin is synthesized in the prostate and released in the seminal fluid. An additional source of relaxin has recently been identified in the heart atria. 3. Relaxin has a broad range of biologic activities, some of which have been known for a long time. These latter ones include: (a) the induction of collagen remodeling and consequent softening of the tissues of the birth canal in view of delivery; (b) the inhibition of uterine contractile activity; (c) the stimulation of growth and differentiation of the mammary gland. 4. In more recent years, novel sites of relaxin action have been recognized. In particular, it has been shown that relaxin: (a) regulates growth and differentiation of breast cancer cells in culture; (b) promotes dilation of blood vessels in several organs and tissues, including the uterus, the mammary gland, the lung and the heart; (c) has a chronotropic action on the heart; (d) inhibits the release of histamine by mast cells, thus being able to counteract experimental allergic asthma; (d) depresses aggregation of platelets and their release by megakaryocytes; (e) influences the secretion of hormones by the pituitary gland; and (f) contributes to the regulation of fluid balance. 5. Concerning the mechanisms of action of relaxin, stimulation of nitric oxide generation, with consequent rise in intracellular cyclic GMP levels, and stimulation of cyclic AMP production have been demonstrated to occur in the target cells and organs. 6. It may be expected that the next decade will provide answers about the utility of relaxin, in terms of insight into the actual physiologic functions of relaxin in the animal kingdom and especially in man, in view of possible therapeutic use of relaxin or relaxin-derived drugs in human disease, especially considering that human recombinant relaxin is now available for clinical experimentation.

Relaxin, a potent microcirculatory effector, is not angiogenic

The ability of relaxin (RLX), which is a potent microcirculatory effector in many species including the rat, to induce de novo angiogenesis in vascularized mammalian tissue was tested using the rat mesenteric-window angiogenesis assay. RLX was administered intraperitoneally on days 1-5 at doses of 0.33, 3.3 and 33 nM. Controls received the vehicle by the same route. Groups of animals were sacrificed at the end of the 1st, 2nd and 3rd weeks. Using computer-aided microscopic morphometry including image analysis, the response was quantified by sensitive, technically independent, highly reproducible methods in terms of the vascularized area (VA), a measure of microvascular spatial extension, and the microvascular length (MVL), a measure of microvascular density. The total MVL was computed from VA x MVL. The results obtained show that RLX did not cause significant changes in any of the variables tested, regardless of dose and observation time. These findings indicate that RLX is apparently unable to mediate significant de novo angiogenesis in the system used in contrast to previously tested angiogens such as basic fibroblast growth factor, vascular endothelial growth factor, isoform 165, and tumor necrosis factor-alpha. In previous studies, RLX has been shown to exert antitumor activity on breast cancer cells in vitro. In the search for a possible role for RLX as an anticancer agent in vivo, it is important to know that this peptide is not angiogenic, since de novo angiogenesis is known to be a prerequisite for tumor growth and metastatic spread.

In vitro modulation of MCF-7 breast cancer cell growth by myoepithelial cells

Growth and differentiation of MCF-7 breast adenocarcinoma cells were studied in mixed cultures of MCF-7 cells and PA 16/23 myoepithelial cells and in isolated cultures of MCF-7 cells grown in the absence and presence of conditioned medium of PA 16/23 cells. In the cocultures, the MCF-7 cells grew in smaller aggregates and showed a more differentiated phenotype than in the isolated cultures. The conditioned medium of PA 16/23 cells enhanced growth and reduced differentiation of the MCF-7 cells. Hence, a direct relationship between MCF-7 cells and PA 16/23 cells seems to play a leading role in influencing the behaviour of the former cells, thus overriding the opposite effects of soluble factors secreted by the PA 16/23 cells.

Relaxin activates the L-arginine-nitric oxide pathway in human breast cancer cells

Recently, we demonstrated that relaxin (RLX), a peptide hormone of ovarian origin, inhibits growth and promotes differentiation of MCF-7 breast adenocarcinoma cells. We also showed that RLX stimulates the production of nitric oxide (NO) in several cell types. NO has been reported to have antitumor activity by inhibiting proliferation, promoting differentiation, and reducing the metastatic spread of some tumor cell types. In this study, we aimed at evaluating whether RLX influences the L-arginine-NO pathway in MCF-7 cells. The cells were grown in the absence or presence of RLX at different concentrations, and cell proliferation, constitutive and inducible NO synthase activities, nitrite production, and intracellular levels of cyclic GMP were investigated. The results obtained indicate that RLX increases inducible NO synthase activity and potentiates NO production. This was accompanied by an elevation of intracellular cyclic GMP, which is known to mediate the cell response to NO. The RLX-induced activation of the L-arginine-NO pathway in the MCF-7 cells was inversely related to the rate of cell proliferation. These results suggest that the cytostatic effect of RLX on MCF-7 breast cancer cells may rely on its ability to stimulate endogenous production of NO.

Relaxin depresses platelet aggregation: in vitro studies on isolated human and rabbit platelets

BACKGROUND

Relaxin, a peptide hormone of ovarian origin, has been shown to cause a striking dilatory action on microvessels in different organs. In our recent studies, relaxin has been shown to stimulate the production of nitric oxide, a powerful vasodilatory agent, in several targets. Nitric oxide also inhibits platelet aggregation. This prompted us to search for a role of relaxin in platelet function.

EXPERIMENTAL DESIGN

The effect of relaxin on platelet aggregation was studied in isolated human and rabbit platelets. The samples were incubated with relaxin at different concentrations and then stimulated with collagen or thrombin. Aggregation and intracellular levels of cGMP and Ca2+ were determined. In some experiments, inhibitors or potentiators of nitric oxide activity were also used to clarify whether the mechanism of action of relaxin involves the L-arginine-nitric-oxide pathway. Electron microscopy of platelets treated and not treated with relaxin was also carried out.

RESULTS

Preincubation of the platelets with relaxin before stimulation with proaggregants resulted in a significant, concentration-dependent inhibition of platelet aggregation, accompanied by an elevation of intraplatelet cGMP and a decrease in the rise of cytosolic Ca2+ levels. The effect of relaxin appeared to be mediated through nitric oxide. Ultrastructurally, relaxin was shown to hinder the conformational changes and granule exocytosis usually occurring in platelets during aggregation.

CONCLUSIONS

This newly recognized antiaggregatory property of relaxin, together with the vasodilatory and hypotensive activities of the peptide demonstrated in previous studies, allows for this hormone to be regarded as a protective agent against thrombotic and hypertensive disorders of pregnancy and cardiovascular diseases.

Relaxin-induced increased coronary flow through stimulation of nitric oxide production

1. Relaxin (RLX) is a multifunctional hormone which, besides its role in pregnancy and parturition, has also been shown to influence the cardiovascular system. In this study, we investigated the effect of RLX on coronary flow of rat and guinea-pig hearts, isolated and perfused in a Langendorff apparatus. RLX was either added to the perfusion fluid at a concentration of 5 x 10(-9) M for a 20-min perfusion, or given as a bolus into the aortic cannula at concentrations of 10(-9) M, 5 x 10(-8) M dissolved in 1 ml of perfusion fluid. 2. RLX, given either for a 20-min perfusion or as a bolus in the aortic cannula to guinea-pig and rat isolated hearts, increased the coronary flow and the amount of nitrite, a stable end-product of nitric oxide (NO) metabolism, that appeared in the perfusates in a concentration-dependent fashion. 3. The increase in coronary flow and in nitrite in the perfusates induced by RLX was significantly reduced by pretreatment with the nitric oxide synthase (NOS) inhibitor, NG-monomethyl-L-arginine (L-NMMA, 10(-4) M). 4. The effects of RLX on coronary flow and nitrite amounts in the perfusates were compared with those induced by the endothelium-dependent vasodilator agent, acetylcholine (ACh, 10(-8)-10(-7) M), and by the endothelium-independent vasodilator agent, sodium nitroprusside (SNP, 10(-7)-10(-6) M). The results obtained show that RLX is more effective than ACh and SNP in increasing coronary flow. 5 The results of this study show that RLX increases coronary flow through stimulation of NO production; hence this hormone should be regarded as a novel agent capable of improving myocardial perfusion.