Relaxin deficiency attenuates pregnancy-induced adaptation of the mesenteric artery to angiotensin II in mice

Therapeutic potential of relaxin or relaxin mimetics in managing cardiovascular complications of diabetes

Diabetes mellitus is a metabolic disease with an escalating global prevalence. Despite the abundance and relative efficacies of current therapeutic approaches, they primarily focus on attaining the intended glycaemic targets, but patients ultimately still suffer from various diabetes-associated complications such as retinopathy, nephropathy, cardiomyopathy, and atherosclerosis. There is a need to explore innovative and effective diabetic treatment strategies that not only address the condition itself but also combat its complications. One promising option is the reproductive hormone relaxin, an endogenous ligand of the RXFP1 receptor. Relaxin is known to exert beneficial actions on the cardiovascular system through its vasoprotective, anti-inflammatory and anti-fibrotic effects. Nevertheless, the native relaxin peptide exhibits a short biological half-life, limiting its therapeutic potential. Recently, several relaxin mimetics and innovative delivery technologies have been developed to extend its biological half-life and efficacy. The current review provides a comprehensive landscape of the cardiovascular effects of relaxin, focusing on its potential therapeutic applications in managing complications associated with diabetes. The latest advancements in the development of relaxin mimetics and delivery methods for the treatment of cardiometabolic disorders are also discussed.

Relaxin elicits renoprotective actions accompanied by increasing bile acid levels in streptozotocin-induced diabetic mice

BACKGROUND

The peptide hormone relaxin has potent anti-fibrotic and anti-inflammatory properties in various organs, including the kidneys. However, the protective effects of relaxin in the context of diabetic kidney complications remain controversial. Here, we aimed to evaluate the effects of relaxin treatment on key markers of kidney fibrosis, oxidative stress, and inflammation and their subsequent impact on bile acid metabolism in the streptozotocin-induced diabetes mouse model.

METHODS AND RESULTS

Male mice were randomly allocated to placebo-treated control, placebo-treated diabetes or relaxin-treated diabetes groups (0.5 mg/kg/d, final 2 weeks of diabetes). After 12 weeks of diabetes or sham, the kidney cortex was harvested for metabolomic and gene expression analyses. Diabetic mice exhibited significant hyperglycaemia and increased circulating levels of creatine, hypoxanthine and trimethylamine N-oxide in the plasma. This was accompanied by increased expression of key markers of oxidative stress (Txnip), inflammation (Ccl2 and Il6) and fibrosis (Col1a1, Mmp2 and Fn1) in the diabetic kidney cortex. Relaxin treatment for the final 2 weeks of diabetes significantly reduced these key markers of renal fibrosis, inflammation, and oxidative stress in diabetic mice. Furthermore, relaxin treatment significantly increased the levels of bile acid metabolites, deoxycholic acid and sodium glycodeoxycholic acid, which may in part contribute to the renoprotective action of relaxin in diabetes.

CONCLUSION

In summary, this study shows the therapeutic potential of relaxin and that it may be used as an adjunctive treatment for diabetic kidney complications.

Placental Dysfunction in Assisted Reproductive Pregnancies: Perinatal, Neonatal and Adult Life Outcomes

Obstetric and newborn outcomes of assisted reproductive technology (ART) pregnancies are associated with significative prevalence of maternal and neonatal adverse health conditions, such as cardiovascular and metabolic diseases. These data are interpreted as anomalies in placentation involving a dysregulation of several molecular factors and pathways. It is not clear which extent of the observed placental alterations are the result of ART and which originate from infertility itself. These two aspects probably act synergically for the final obstetric risk. Data show that mechanisms of inappropriate trophoblast invasion and consequent altered vascular remodeling sustain several clinical conditions, leading to obstetric and perinatal risks often found in ART pregnancies, such as preeclampsia, fetal growth restriction and placenta previa or accreta. The roles of factors such as VEGF, GATA3, PIGF, sFLT-1, sEndoglin, EGFL7, melatonin and of ART conditions, such as short or long embryo cultures, trophectoderm biopsy, embryo cryopreservation, and supraphysiologic endometrium preparation, are discussed. Inflammatory local conditions and epigenetic influence on embryos of ART procedures are important research topics since they may have important consequences on obstetric risk. Prevention and treatment of these conditions represent new frontiers for clinicians and biologists involved in ART, and synergic actions with researchers at molecular levels are advocated.

Pressurized Hot Water Extraction of Okra Seeds Reveals Antioxidant, Antidiabetic and Vasoprotective Activities

Abelmoschus esculentus L. Moench (okra) is a commonly consumed vegetable that consists of the seeds and peel component which are rich in polyphenolic compounds. The aim of this study is to utilize pressurized hot water extraction (PHWE) for the extraction of bioactive phytochemicals from different parts of okra. A single step PHWE was performed at various temperatures (60 °C, 80 °C, 100 °C and 120 °C) to determine which extraction temperature exhibits the optimum phytochemical profile, antioxidant and antidiabetic activities. The optimum temperature for PHWE extraction was determined at 80 °C and the biological activities of the different parts of okra (Inner Skin, Outer Skin and Seeds) were characterized using antioxidant (DPPH and ABTS), α-glucosidase and vasoprotective assays. Using PHWE, the different parts of okra displayed distinct phytochemical profiles, which consist of primarily polyphenolic compounds. The okra Seeds were shown to have the most antioxidant capacity and antidiabetic effects compared to other okra parts, likely to be attributed to their higher levels of polyphenolic compounds. Similarly, okra Seeds also reduced vascular inflammation by downregulating TNFα-stimulated VCAM-1 and SELE expression. Furthermore, metabolite profiling by LC/MS also provided evidence of the cytoprotective effect of okra Seeds in endothelial cells. Therefore, the use of PHWE may be an alternative approach for the environmentally friendly extraction and evaluation of plant extracts for functional food applications.

Impact of trophectoderm biopsy on obstetric and perinatal outcomes following frozen-thawed embryo transfer cycles

STUDY QUESTION

Does trophectoderm biopsy for preimplantation genetic testing (PGT) increase the risk of obstetric or perinatal complications in frozen-thawed embryo transfer (FET) cycles?

SUMMARY ANSWER

Trophectoderm biopsy may increase the risk of hypertensive disorders of pregnancy (HDP) in pregnancies following FET cycles.

WHAT IS KNOWN ALREADY

Trophectoderm biopsy has replaced blastomere biopsy as the standard of care to procure cells for PGT analysis. Recently, there has been concern that trophectoderm biopsy may adversely impact obstetric and perinatal outcomes. Previous studies examining this question are limited by use of inappropriate control groups, small sample size or reporting on data that no longer reflects current IVF practice.

STUDY DESIGN, SIZE, DURATION

This was a retrospective cohort study conducted at a single university-affiliated fertility center. A total of 756 patients who underwent FET with transfer of previously vitrified blastocysts that had either trophectoderm biopsy or were unbiopsied and resulted in a singleton live birth between 2013 and 2019 were included.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Obstetric and perinatal outcomes for patients aged 20-44 years who underwent FET with transfer of previously vitrified blastocysts that were either biopsied (n = 241) or unbiopsied (n = 515) were analyzed. Primary outcome was odds of placentation disorders including HDP and rate of fetal growth restriction (FGR). Binary logistic regression was performed to control for potential covariates.

MAIN RESULTS AND THE ROLE OF CHANCE

The biopsy group was significantly older, had fewer anovulatory patients, was more often nulliparous and had fewer embryos transferred compared to the unbiopsied group. After controlling for potential covariates, the probability of developing HDP was significantly higher in the biopsy group compared with unbiopsied group (adjusted odds ratio (aOR) 1.943, 95% CI 1.072-3.521; P = 0.029).There was no significant difference between groups in the probability of placenta previa or placenta accreta. There was also no significant difference in the rate of FGR (aOR 1.397; 95% CI, 0.815-2.395; P = 0.224) or the proportion of low (aOR 0.603; 95% CI, 0.336-1.084; P = 0.091) or very low (aOR 2.948; 95% CI, 0.613-14.177; P = 0.177) birthweight infants comparing biopsied to unbiopsied groups.

LIMITATIONS, REASON FOR CAUTION

This was a retrospective study performed at a single fertility center, which may limit the generalizability of our findings.

WIDER IMPLICATIONS OF THE FINDINGS

Trophectoderm biopsy may increase the risk of HDP in FET cycles, however, a prospective multicenter randomized trial should be performed to confirm these findings.

STUDY FUNDING/COMPETING INTEREST(S)

No specific funding was obtained for this study. The authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

NA.

Kinetics of Postpartum Mesenteric Artery Structure and Function Relative to Pregnancy and Lactation in Mice

Epidemiological evidence suggests that normal pregnancy in women is associated with decreased cardiovascular risk in later life. Clinical studies have provided evidence that alterations in vascular function and structure are detectable long after delivery. To understand these findings, we examined mesenteric artery reactivity at both early (3 days and 2–4 weeks) and late (12 weeks) postpartum (PP) time points in relation to late pregnancy (LP) and lactation. Vessels from virgin controls, LP, PP, and nursing and non-nursing mothers were tested for responses to phenylephrine (PE), high potassium solutions (high K⁺), and acetylcholine (ACh). Passive arterial distensibility, vessel dimensions, and collagen and elastin content were evaluated for the studied groups. We observed that (1) there was a significant inhibition of vascular reactivity to PE in LP, 3 days and 2 weeks PP vessels that returned to pre-pregnancy levels at 4 and 12 weeks PP; (2) inhibition of NO production in PP vessels restored PE-induced constriction to pre-pregnancy levels; (3) vasodilator responses to ACh were similar at all PP periods; (4) LP and early PP was associated with a persistent increase in arterial distensibility that correlates with a PP-induced reduction in wall collagen, and regressed to pre-conception levels at 12 weeks PP; (5) vessels from non-nursing PP mice demonstrated an increased PE reactivity, diminished responses to ACh, and reduced distensibility compared to breastfeeding mice. These studies provide a timeframe for mesenteric artery adaptations that occur during pregnancy and extend to the PP period, but which may be modified by PP events.

Antioxidant and Cytoprotective Effect of Quinoa (Chenopodium quinoa Willd.) with Pressurized Hot Water Extraction (PHWE)

Quinoa is widely noted for its nutritional value. The seed is the main edible part of the plant and exists in at least three different colors: white, red and black. This study utilized a pressurized hot water extraction (PHWE) for the extraction of phytochemicals from quinoa. Chemical fingerprints with LC/UV and LC/MS using a targeted approach and pattern recognition tools were used to evaluate the quinoa extracts. The antioxidant properties for various types of quinoa were evaluated using DPPH assay, ABTS assay and the cytoprotective effect of quinoa extracts were investigated in HMEC-1 cell line. Distinctive chemical profiles obtained from black and red quinoa were well correlated with the antioxidant activities and cytoprotective effects. The combination of PHWE, chemical standardization with LC/UV and LC/MS, pattern recognition tools and biological assay provided an approach for the evaluation and eventual production of quinoa extracts for functional food.

Plasticity of the Maternal Vasculature During Pregnancy

Maternal cardiovascular changes during pregnancy include an expansion of plasma volume, increased cardiac output, decreased peripheral resistance, and increased uteroplacental blood flow. These adaptations facilitate the progressive increase in uteroplacental perfusion that is required for normal fetal growth and development, prevent the development of hypertension, and provide a reserve of blood in anticipation of the significant blood loss associated with parturition. Each woman's genotype and phenotype determine her ability to adapt in response to molecular signals that emanate from the fetoplacental unit. Here, we provide an overview of the major hemodynamic and cardiac changes and then consider regional changes in the splanchnic, renal, cerebral, and uterine circulations in terms of endothelial and vascular smooth muscle cell plasticity. Although consideration of gestational disease is beyond the scope of this review, aberrant signaling and/or maternal responsiveness contribute to the etiology of several common gestational diseases such as preeclampsia, intrauterine growth restriction, and gestational diabetes.

Maternal and perinatal outcomes in programmed versus natural vitrified-warmed blastocyst transfer cycles

RESEARCH QUESTION

Do maternal and perinatal outcomes differ between natural and programmed frozen embryo transfer (FET) cycles?

DESIGN

Retrospective cohort study at a university-affiliated fertility centre including 775 patients who underwent programmed or natural FET cycles resulting in a singleton live birth using blastocysts vitrified between 2013 and 2018.

RESULTS

A total of 384 natural and 391 programmed FET singleton pregnancies were analysed. Programmed FET resulted in higher overall maternal complications (32.2% [126/391] versus 18.8% [72/384]; P < 0.01), including higher probability of hypertensive disorders of pregnancy (HDP) (15.3% [60/391] versus 6.3% [24/384]; P < 0.01), preterm premature rupture of membranes (2.6% [10/391] versus 0.3% [1/384]; P = 0.02) and caesarean delivery (53.2% [206/387] versus 42.8% [163/381]; P = 0.03) compared with natural FET. After controlling for potential confounders, including age, body mass index, parity, smoking status, history of diabetes or chronic hypertension, infertility diagnosis, number of embryos transferred and use of preimplantation genetic testing, the adjusted odds ratio for HDP was 2.39 (95% CI 1.37 to 4.17) and for overall maternal complications was 2.21 (95% CI 1.51 to 3.22) comparing programmed with natural FET groups. The groups did not significantly differ for any perinatal outcomes analysed, including birth weight (3357.9 ± 671.6 g versus 3318.4 ± 616.2 g; P = 0.40) or rate of birth defects (1.5% [6/391] versus 2.1% [8/384]; P = 0.57), respectively.

CONCLUSION

Vitrified-warmed blastocyst transfer in a programmed cycle resulted in a twofold higher probability of HDP compared with transfer in a natural cycle. Natural FET cycle should, therefore, be recommended as first line for all eligible patients undergoing FET to reduce the risk of HDP.

The Novel Small-molecule Annexin-A1 Mimetic, Compound 17b, Elicits Vasoprotective Actions in Streptozotocin-induced Diabetic Mice

The formyl peptide receptor (FPR) family are a group of G-protein coupled receptors that play an important role in the regulation of inflammatory processes. It is well-established that activation of FPRs can have cardioprotective properties. Recently, more stable small-molecule FPR1/2 agonists have been described, including both Compound 17b (Cmpd17b) and Compound 43 (Cmpd43). Both agonists activate a range of signals downstream of FPR1/2 activation in human-engineered FPR-expressing cells, including ERK1/2 and Akt. Importantly, Cmpd17b (but not Cmpd43) favours bias away from intracellular Ca²⁺ mobilisation in this context, which has been associated with greater cardioprotection in response to Cmpd17b over Cmpd43. However, it is unknown whether these FPR agonists impact vascular physiology and/or elicit vasoprotective effects in the context of diabetes. First, we localized FPR1 and FPR2 receptors predominantly in vascular smooth muscle cells in the aortae of male C57BL/6 mice. We then analysed the vascular effects of Cmpd17b and Cmpd43 on the aorta using wire-myography. Cmpd17b but not Cmpd43 evoked a concentration-dependent relaxation of the mouse aorta. Removal of the endothelium or blockade of endothelium-derived relaxing factors using pharmacological inhibitors had no effect on Cmpd17b-evoked relaxation, demonstrating that its direct vasodilator actions were endothelium-independent. In aortae primed with elevated K⁺ concentration, increasing concentrations of CaCl₂ evoked concentration-dependent contraction that is abolished by Cmpd17b, suggesting the involvement of the inhibition of Ca²⁺ mobilisation via voltage-gated calcium channels. Treatment with Cmpd17b for eight weeks reversed endothelial dysfunction in STZ-induced diabetic aorta through the upregulation of vasodilator prostanoids. Our data indicate that Cmpd17b is a direct endothelium-independent vasodilator, and a vasoprotective molecule in the context of diabetes.

Relaxin reduces endothelium-derived vasoconstriction in hypertension: Revealing new therapeutic insights

BACKGROUND AND PURPOSE

Endothelium-derived vasoconstriction is a hallmark of vascular dysfunction in hypertension. In some cases, an overproduction of endothelium-derived prostacyclin (PGI₂ ) can cause contraction rather than relaxation. Relaxin is well known for its vasoprotective actions, but the possibility that this peptide could also reverse endothelium-derived vasoconstriction has never been investigated. We tested the hypothesis that short-term relaxin treatment mitigates endothelium-derived vasoconstriction in spontaneously hypertensive rats (SHR).

EXPERIMENTAL APPROACH

Male Wistar Kyoto rats (WKY) and SHR were subcutaneously infused with either vehicle (20 mmol·L^-1 sodium acetate) or relaxin (13.3 μg·kg^-1 ·hr^-1 ) using osmotic minipumps for 3 days. Vascular reactivity to the endothelium-dependent agonist ACh was assessed in vitro by wire myography. Quantitative PCR and LC-MS were used to identify changes in gene expression of prostanoid pathways and PG production, respectively.

KEY RESULTS

Relaxin treatment ameliorated hypertension-induced endothelial dysfunction by increasing NO-dependent relaxation and reducing endothelium-dependent contraction. Notably, short-term relaxin treatment up-regulated mesenteric PGI₂ receptor (IP) expression, permitting PGI₂ -IP-mediated vasorelaxation. In the aorta, reversal of contraction was accompanied by suppression of the hypertension-induced increase in prostanoid-producing enzymes and reduction in PGI₂ -evoked contractions.

CONCLUSIONS AND IMPLICATIONS

Relaxin has region-dependent vasoprotective actions in hypertension. Specifically, relaxin has distinct effects on endothelium-derived contracting factors and their associated vasoconstrictor pathways in mesenteric arteries and the aorta. Taken together, these observations reveal the potential of relaxin as a new therapeutic agent for vascular disorders that are associated with endothelium-derived vasoconstriction including hypertension.

Recent developments in relaxin mimetics as therapeutics for cardiovascular diseases

Cardiovascular disease is the most common cause of mortality worldwide, accounting for almost 50% of all deaths globally. Vascular endothelial dysfunction and fibrosis are critical in the pathophysiology of cardiovascular disease. Relaxin, an insulin-like peptide, is known to have beneficial actions in the cardiovascular system through its vasoprotective and anti-fibrotic effects. However, relaxin has several limitations of peptide-based drugs such as poor oral bioavailability, laborious, and expensive to synthesize. This review will focus on recent developments in relaxin mimetics, their pharmacology, associated signalling mechanisms, and their therapeutic potential for the management and treatment of cardiovascular disease.

Sympathetic nervous system control of vascular function and blood pressure during pregnancy and preeclampsia

: Proper vascular tone and blood pressure regulation during pregnancy are important for immediate and long-term cardiovascular health of the mother and her offspring. Preeclampsia is clinically defined as new-onset maternal hypertension accompanied by cardiovascular, renal, and/or neural abnormalities presenting in the second half of pregnancy. There is strong evidence to support that preeclampsia is mediated by attenuations in uteroplacental vascular remodeling and increases in vasoconstriction with subsequent placental ischemia/reperfusion-induced release of hypertensive substances into the maternal circulation. These include antiangiogenic and pro-inflammatory factors. There is also evidence implicating increased sympathetic nervous system activity (SNA) in this maternal disorder, but this mostly includes data correlating severity of disease with catecholamine levels and elevated muscle SNA. These measurements have not confirmed a causative role for SNA in the pathogenesis of preeclampsia. Therefore, studies are needed to provide a comprehensive understanding of SNA and its control of vascular function and blood pressure regulation during normal pregnancy in order to set the stage for exploring the mechanisms mediating the exaggerated SNA and signaling during preeclampsia. This review examines the role of SNA in control of uteroplacental vascular tone and blood pressure regulation during normal pregnancy. Furthermore, it is proposed that over-activation of the SNA contributes to altered uteroplacental vascular tone and perfusion leading to placental ischemic events and modulates the systemic vasoconstriction and hypertensive responses to soluble placenta ischemic factors. Recognizing the integrative role and importance of SNA in the pathophysiology of preeclampsia will advance our understanding of this maternal disorder.

Targeting the vascular dysfunction: Potential treatments for preeclampsia

Preeclampsia is a pregnancy-specific disorder, primarily characterized by new-onset hypertension in combination with a variety of other maternal or fetal signs. The pathophysiological mechanisms underlying the disease are still not entirely clear. Systemic maternal vascular dysfunction underlies the clinical features of preeclampsia. It is a result of oxidative stress and the actions of excessive anti-angiogenic factors, such as soluble fms-like tyrosine kinase, soluble endoglin, and activin A, released by a dysfunctional placenta. The vascular dysfunction then leads to impaired regulation and secretion of relaxation factors and an increase in sensitivity/production of constrictors. This results in a more constricted vasculature rather than the relaxed vasodilated state associated with normal pregnancy. Currently, the only effective "treatment" for preeclampsia is delivery of the placenta and therefore the baby. Often, this means a preterm delivery to save the life of the mother, with all the attendant risks and burdens associated with fetal prematurity. To lessen this burden, there is a pressing need for more effective treatments that target the maternal vascular dysfunction that underlies the hypertension. This review details the vascular effects of key drugs undergoing clinical assessment as potential treatments for women with preeclampsia.

The Role of Placental Hormones in Mediating Maternal Adaptations to Support Pregnancy and Lactation

During pregnancy, the mother must adapt her body systems to support nutrient and oxygen supply for growth of the baby in utero and during the subsequent lactation. These include changes in the cardiovascular, pulmonary, immune and metabolic systems of the mother. Failure to appropriately adjust maternal physiology to the pregnant state may result in pregnancy complications, including gestational diabetes and abnormal birth weight, which can further lead to a range of medically significant complications for the mother and baby. The placenta, which forms the functional interface separating the maternal and fetal circulations, is important for mediating adaptations in maternal physiology. It secretes a plethora of hormones into the maternal circulation which modulate her physiology and transfers the oxygen and nutrients available to the fetus for growth. Among these placental hormones, the prolactin-growth hormone family, steroids and neuropeptides play critical roles in driving maternal physiological adaptations during pregnancy. This review examines the changes that occur in maternal physiology in response to pregnancy and the significance of placental hormone production in mediating such changes.

Evidence of proteinuria, but no other characteristics of pre-eclampsia, in relaxin-deficient mice

Pre-eclampsia (PE) is a leading cause of maternal and fetal death, characterised by an imbalance of placental growth factors and hypertension at >20 weeks gestation. Impaired maternal systemic vascular adaptations and fetal growth restriction are features of both PE and pregnant relaxin-deficient (Rln^-/-) mice. The aim of the present study was to investigate whether these phenotypes in Rln^-/- mice are associated with abnormal placental growth factor expression, increased soluble fms-like tyrosine kinase-1 (sFlt-1), proteinuria and/or hypertension during pregnancy. In addition, we examined relaxin and relaxin receptor (relaxin/insulin like family peptide receptor 1 (RXFP1)) mRNA expression in placentas of women with PE. There was no significant difference in placental vascular endothelial growth factor A (VegfA) and placenta growth factor (Plgf) gene expression between Rln^-/- and wild-type mice. Circulating plasma sFlt-1 concentrations in pregnant mice of both genotypes and ages were increased compared with non-pregnant mice but were lower in younger pregnant Rln^-/- mice compared with aged-matched Rln^+/+ mice. Aged pregnant Rln^-/- mice had higher urinary albumin:creatinine ratios compared with age-matched Rln^+/+ mice, indicative of proteinuria. Systolic and diastolic blood pressures did not differ between genotypes. In addition, PE in women was not associated with altered placental mRNA expression of RLN2 or RXFP1 at term. Overall, the data demonstrate that pregnant Rln^-/- mice do not have the typical characteristics of PE. However, these mice show evidence of proteinuria, but we suggest that this results from systemic renal vascular dysfunction before pregnancy.

Relaxin as a Therapeutic Target for the Cardiovascular Complications of Diabetes

Cardiovascular complications are the major cause of mortality in patients with diabetes. This is closely associated with both macrovascular and microvascular complications of diabetes, which lead to organ injuries in diabetic patients. Previous studies have consistently demonstrated the beneficial effects of relaxin treatment for protection of the vasculature, with evidence of antioxidant and anti-remodeling actions. Relaxin enhances nitric oxide, prostacyclin and endothelium-derived hyperpolarization (EDH)-type-mediated relaxation in various vascular beds. These effects of relaxin on the systemic vasculature, coupled with its cardiac actions, reduce pulmonary capillary wedge pressure and pulmonary artery pressure. This results in an overall decrease in systemic and pulmonary vascular resistance in heart failure patients. The anti-fibrotic actions of relaxin are well established, a desirable property in the context of diabetes. Further, relaxin ameliorates diabetic wound healing, with accelerated angiogenesis and vasculogenesis. Relaxin-mediated stimulation of vascular endothelial growth factor (VEGF) and stromal cell-derived factor 1-α, as well as regulation of metalloproteinase expression, ameliorates cardiovascular fibrosis in diabetic mice. In the heart, relaxin is a cardioprotective molecule in several experimental animal models, exerting anti-fibrotic, anti-hypertrophy and anti-apoptotic effects in diabetic pathologies. Collectively, these studies provide a foundation to propose the therapeutic potential for relaxin as an adjunctive agent in the prevention or treatment of diabetes-induced cardiovascular complications. This review provides a comprehensive overview of the beneficial effects of relaxin, and identifies its therapeutic possibilities for alleviating diabetes-related cardiovascular injury.

Relaxin Deficiency Leads to Uterine Artery Dysfunction During Pregnancy in Mice

The uterine vasculature undergoes profound adaptations in response to pregnancy. Augmentation of endothelial vasodilator function and reduced smooth muscle reactivity are factors contributing to uterine artery adaptation and are critical for adequate placental perfusion. The peptide hormone relaxin has an important role in mediating the normal maternal renal vascular adaptations during pregnancy through a reduction in myogenic tone and an increase in flow-mediated vasodilation. Little is known however about the influence of endogenous relaxin on the uterine artery during pregnancy. We tested the hypothesis that relaxin deficiency increases myogenic tone and impairs endothelial vasodilator function in uterine arteries of late pregnant relaxin deficient (Rln^−/−) mice. Reactivity of main uterine arteries from non-pregnant and late pregnant wild-type (Rln^+/+) and Rln^−/− mice was studied using pressure and wire myography and changes in gene expression explored using PCR. Myogenic tone was indistinguishable in arteries from non-pregnant mice. In late pregnancy uterine artery myogenic tone was halved in Rln^+/+ mice (P < 0.0001), an adaptation that failed to occur in arteries from pregnant Rln^−/− mice. The role of vasodilator prostanoids in the regulation of myogenic tone was significantly reduced in arteries of pregnant Rln^−/− mice (P = 0.02). Agonist-mediated endothelium-dependent vasodilation was significantly impaired in non-pregnant Rln^−/− mice. With pregnancy, differences in total endothelial vasodilator function were resolved, although there remained an underlying deficiency in the role of vasodilator prostanoids and alterations to the contributions of calcium-activated K⁺ channels. Fetuses of late pregnant Rln^−/− mice were ~10% lighter (P < 0.001) than those of Rln^+/+ mice. In conclusion, relaxin deficiency is associated with failed suppression of uterine artery myogenic tone in pregnancy, which likely contributes to reduced uteroplacental perfusion and fetal growth restriction.

Relaxin treatment reduces angiotensin II-induced vasoconstriction in pregnancy and protects against endothelial dysfunction†

The peptide relaxin has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in cardiovascular disease. In this study, we tested the hypothesis that relaxin treatment alleviates systemic vascular dysfunction characteristic of hypertensive diseases of pregnancy. We investigated vascular effects and mechanisms of relaxin action in (i) pregnant relaxin-deficient (Rln-/-) mice with enhanced responses to angiotensin II (AngII) and (ii) arteries pre-incubated ex vivo in trophoblast conditioned media (TCM) to induce endothelial dysfunction. Pregnant Rln-/- mice received 0.5 μg/h recombinant human H2 relaxin (rhRLX: n = 5) or placebo (20 nM sodium acetate; n = 7) subcutaneously via osmotic minipumps for 5 days prior to gestational day 17.5. This treatment protocol significantly reduced AngII-mediated contraction of mesenteric arteries and increased plasma 6-keto prostaglandin F1α. These vascular effects were endothelium independent and likely involve smooth muscle-derived vasodilator prostanoids. In the second study, mesenteric arteries were incubated ex vivo for 24 h at 37°C in TCM, which contained high levels of soluble Flt-1 (>20 ng/ml) and soluble Eng (>1 ng/ml). TCM incubation caused significant reduction in endothelium-dependent relaxation and increased sensitivity to AngII. Co-incubation of arteries with rhRLX for 24 h (n = 6-16/treatment) prevented endothelial dysfunction but had no effect on AngII-mediated contraction. In conclusion, relaxin treatment prevents and/or reverses vascular dysfunction in mesenteric arteries, but acts through different vascular pathways depending on duration of relaxin treatment and type of vascular dysfunction. Overall, our data suggest that relaxin is a potential therapeutic to alleviate maternal systemic vascular dysfunction associated with hypertensive diseases in pregnant women.

Serelaxin as a novel therapeutic opposing fibrosis and contraction in lung diseases

The most common therapies for asthma and other chronic lung diseases are anti-inflammatory agents and bronchodilators. While these drugs oppose disease symptoms, they do not reverse established structural changes in the airways and their therapeutic efficacy is reduced with increasing disease severity. The peptide hormone, relaxin, is a Relaxin Family Peptide Receptor 1 (RXFP1) receptor agonist with unique combined effects in the lung that differentiates it from these existing therapies. Relaxin has previously been reported to have cardioprotective effects in acute heart failure as well anti-fibrotic actions in several organs. This review focuses on recent experimental evidence of the beneficial effects of chronic relaxin treatment in animal models of airways disease demonstrating inhibition of airway hyperresponsiveness and reversal of established fibrosis, consistent with potential therapeutic benefit. Of particular interest, accumulating evidence demonstrates that relaxin can also acutely oppose contraction by reducing the release of mast cell-derived bronchoconstrictors and by directly eliciting bronchodilation. When used in combination, chronic and acute treatment with relaxin has been shown to enhance responsiveness to both glucocorticoids and β₂-adrenoceptor agonists respectively. While the mechanisms underlying these beneficial actions remain to be fully elucidated, translation of these promising combined preclinical findings is critical in the development of relaxin as a novel alternative or adjunct therapeutic opposing multiple aspects of airway pathology in lung diseases.

Abnormal extracellular matrix remodelling in the cervix of pregnant relaxin-deficient mice is not associated with reduced matrix metalloproteinase expression or activity

Relaxin regulates cervical extracellular matrix (ECM) remodelling during pregnancy by modifying collagen and other ECM molecules by unknown mechanisms. We hypothesised that abnormal collagen remodelling in the cervix of pregnant relaxin-deficient (Rln1−/−) mice is due to excessive collagen (Col1a1 and Col3a1) and decreased matrix metalloproteinases (Mmp2, Mmp9, Mmp13 and Mmp7) and oestrogen receptors (Esr1 and Esr2). Quantitative polymerase chain reaction, gelatinase zymography, MMP activity assays and histological staining evaluated changes in ECM in pregnant wildtype (Rln1+/+) and Rln1−/− mice. Cervical Col1a1, Col3a1 and total collagen increased in Rln1−/− mice and were higher at term compared with Rln1+/+ mice. This was not correlated with a decrease in gelatinase (Mmp2, Mmp9) expression or activity, Mmp7 or Mmp13 expression, which were all significantly higher in Rln1−/− mice. In late pregnancy, circulating MMP2 and MMP9 were unchanged. Esr1 expression was highest in Rln1+/+ and Rln1−/− mice in late pregnancy, coinciding with a decrease in Esr2 in Rln1+/+ but not Rln1−/− mice. The relaxin receptor (Rxfp1) decreased slightly in late-pregnant Rln1+/+ mice, but was significantly higher in Rln1−/− mice. In summary, relaxin deficiency results in increased cervical collagen in late pregnancy, which is not explained by a reduction in Mmp expression or activity or decreased Rxfp1. However, an imbalance between Esr1 and Esr2 may be involved.

Serelaxin treatment reverses vascular dysfunction and left ventricular hypertrophy in a mouse model of Type 1 diabetes

Serelaxin prevents endothelial dysfunction in the mouse aorta ex vivo and inhibits apoptosis in cardiomyocytes under acute hyperglycaemia. Less is known about the effects of serelaxin in an in vivo mouse model of diabetes. Therefore, we tested the hypothesis in streptozotocin (STZ)-treated mice that serelaxin is able to reverse diabetes-induced vascular dysfunction and cardiac remodelling. Mice were divided into citrate buffer + placebo, STZ + placebo and STZ + serelaxin (0.5 mg/kg/d, 2 weeks) groups. After 12 weeks of diabetes, sensitivity to the endothelium-dependent agonist acetylcholine (ACh) was reduced in the mesenteric artery. This was accompanied by an enhanced vasoconstrictor prostanoid contribution and a decrease in endothelium-derived hyperpolarisation (EDH)-mediated relaxation. Serelaxin restored endothelial function by increasing nitric oxide (NO)-mediated relaxation but not EDH. It also normalised the contribution of vasoconstrictor prostanoids to endothelial dysfunction and suppressed diabetes-induced hyper-responsiveness of the mesenteric artery to angiotensin II. Similarly, diabetes reduced ACh-evoked NO-mediated relaxation in the aorta which was reversed by serelaxin. In the left ventricle, diabetes promoted apoptosis, hypertrophy and fibrosis; serelaxin treatment reversed this ventricular apoptosis and hypertrophy, but had no effect on fibrosis. In summary, serelaxin reversed diabetes-induced endothelial dysfunction by enhancing NO-mediated relaxation in the mouse vasculature and attenuating left ventricular hypertrophy and apoptosis.

Vascular actions of relaxin: nitric oxide and beyond

The peptide hormone relaxin regulates the essential maternal haemodynamic adaptations in early pregnancy through direct actions on the renal and systemic vasculature. These vascular actions of relaxin occur mainly through endothelium-derived NO-mediated vasodilator pathways and improvements in arterial compliance in small resistance-size arteries. This work catalysed a plethora of studies which revealed quite heterogeneous responses across the different regions of the vasculature, and also uncovered NO-independent mechanisms of relaxin action. In this review, we first describe the role of endogenous relaxin in maintaining normal vascular function, largely referring to work in pregnant and male relaxin-deficient animals. We then discuss the diversity of mechanisms mediating relaxin action in different vascular beds, including the involvement of prostanoids, VEGF, endothelium-derived hyperpolarisation and antioxidant activity in addition to the classic NO-mediated vasodilatory pathway. We conclude the review with current perspectives on the vascular remodelling capabilities of relaxin.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Serelaxin: A Novel Therapeutic for Vascular Diseases

Vascular dysfunction is an important hallmark of cardiovascular disease. It is characterized by increased sensitivity to vasoconstrictors, decreases in the endothelium-derived vasodilators nitric oxide (NO) and prostacyclin (PGI2), and endothelium-derived hyperpolarization (EDH). Serelaxin (recombinant human relaxin) has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in acute heart failure. In this review we first describe the contribution of endogenous relaxin to vascular homeostasis. We then provide a comprehensive overview of the novel mechanisms of serelaxin action in blood vessels that differentiate it from other vasodilator drugs and explain how this peptide could be used more widely as a therapeutic to alleviate vascular dysfunction in several cardiovascular diseases.