Abstract-The antifibrotic effects of the peptide hormone relaxin on cardiac and renal fibrosis were studied in 9-to 10-month-old male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Rats (nϭ8 to 9 per group) were allocated into 3 groups: WKY controls, vehicle-treated SHR (SHR-V), and relaxin-treated SHR (SHR-R). Relaxin (0.5 mg/kg per day) was administered via subcutaneously implanted osmotic mini-pumps over 2 weeks before hearts and kidneys were harvested for analysis. Collagen content was analyzed by hydroxyproline assay, gel electrophoresis, and quantitative histology. Zymography was used to determine matrix metalloproteinase (MMP) expression and Western blotting to determine proliferating cell nuclear antigen (PCNA) expression and ␣-smooth muscle actin (␣-SMA)/myofibroblast expression, whereas cardiac hypertrophy was assessed by myocyte size and real-time polymerase chain reaction of associated genes.

Since its discovery as a reproductive hormone 80 years ago, relaxin has been implicated in a number of pregnancy-related functions involving extracellular matrix (ECM) turnover and collagen degradation. It is now becoming evident that relaxin's ability to reduce matrix synthesis and increase ECM degradation has important implications in several nonreproductive organs, including the heart, lung, kidney, liver and skin. The identification of relaxin and RXFP1 (Relaxin family peptide receptor-1) mRNA and/or binding sites in cells or vessels of these nonreproductive tissues, has confirmed them as targets for relaxin binding and activity. Recent studies on Rln1 and Rxfp1 gene-knockout mice have established relaxin as an important naturally occurring and protective moderator of collagen turnover, leading to improved organ structure and function. Furthermore, through its ability to regulate the ECM and in particular, collagen at multiple levels, relaxin has emerged as a potent anti-fibrotic therapy, with rapid-occurring efficacy. It not only prevents fibrogenesis, but also reduces established scarring (fibrosis), which is a leading cause of organ failure and affects several tissues regardless of etiology. This chapter will summarize these coherent findings as a means of highlighting the significance and therapeutic potential of relaxin.

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The effect of endogenous relaxin on the development of cardiac hypertrophy, dysfunction, and fibrosis remains completely unknown. We addressed this question by subjecting relaxin-1 deficient (Rln1-/-) and littermate control (Rln1+/+) mice of both genders to chronic transverse aortic constriction (TAC). The extent of left ventricular (LV) remodeling and dysfunction were studied by serial echocardiography over an 8-wk period and by micromanometry. The degree of hypertrophy was estimated by LV weight, cardiomyocyte size, and expression of relevant genes. Cardiac fibrosis was determined by hydroxyproline assay and quantitative histology. Expression of endogenous relaxin during the course of TAC was also examined. In response to an 8-wk period of pressure overload, TAC mice of both genotypes developed significant LV hypertrophy, fibrosis, hypertrophy related gene profile, and signs indicating congestive heart failure when compared with respective sham controls. The severity of these alterations was not statistically different between the two genotypes of either gender. Relaxin mRNA expression was up-regulated, whereas that of its receptor was unchanged in the hypertrophic myocardium of wild-type mice. Collectively, the extent of pressure overload-induced LV hypertrophy, fibrosis, and dysfunction were comparable between Rln1+/+ and Rln1-/- mice. Thus, although up-regulated in its expression, endogenous relaxin had no significant effect on the progression of cardiac maladaptation and dysfunction in the setting of chronic pressure overload.

In this study, we determined the effects of relaxin and estrogen deficiency and estrogen replacement therapy (ERT) on the cardiac, renal, and pulmonary phenotypes of female relaxin gene knockout (Rln1-/-) and age-matched wild-type (Rln1+/+) mice. One-month-old Rln1+/+ and Rln1-/- mice were bilaterally ovariectomized or sham-operated and aged until 9 or 12 months. A subgroup of ovariectomized mice received ERT from 9 to 12 months of age. At the appropriate time points, heart, kidney, and lung tissues from these mice were collected and analyzed for changes in organ fibrosis, hypertrophy, and airway thickening. Neither ovariectomy nor ERT had any effect on cardiac or renal collagen concentration in all groups studied. In contrast, total lung collagen concentration and airway subepithelial collagen deposition were significantly increased in ovariectomized Rln1+/+ mice (P<0.05 vs. sham) and to a greater extent in ovariectomized Rln1-/- mice (P<0.01 vs. sham). Ovariectomy of Rln1+/+ mice also led to a significant increase in airway smooth muscle (SM) (lung) thickening, which was further exaggerated in Rln1-/- mice. Cardiac hypertrophy, evidenced by increased heart weight and expression of hypertrophy-related genes (all P<0.05 vs. sham) was only observed in Rln1-/- mice. These findings demonstrated an increased pathology in mice that were deficient of both relaxin and estrogen. ERT significantly decreased airway fibrosis, airway SM thickening, and cardiac hypertrophy when administered to ovariectomized Rln1-/- mice (all P<0.05 vs. ovariectomy alone). These findings suggest that relaxin and estrogen appear to play protective roles against airway fibrosis, airway SM thickening, and cardiac hypertrophy in female mice.

As a hallmark of heart disease, cardiac fibrosis contributes to the development of heart failure and arrhythmias and forms a key therapeutic target. There is a major unmet need for selective, potent, and safe antifibrotic drugs. Earlier studies revealed a cardiac fibrosis phenotype in relaxin-1-deficient mice. Recent studies in several rodent models of cardiac fibrosis have documented reversal of fibrosis by treatment with relaxin peptide or virally mediated relaxin gene delivery. In mice with surgically induced transmural myocardial infarction, relaxin therapy inhibited scar density. In these studies, however, functional benefits achieved by relaxin therapy were limited or less explored. Collectively, there is good experimental evidence that relaxin is able to reverse cardiac fibrosis due to distinct mechanisms. Future research needs to explore functional improvement following fibrosis reversal by relaxin and the usefulness of relaxin in antiarrhythmic or stem cell-based therapy.

Initially thought of as primarily a reproductive hormone, relaxin is emerging as a multi-functional factor in a broad range of target tissues including the cardiovascular, renal, and respiratory systems, in addition to the brain, skin, liver and other less studied organs. The ever-increasing detection of H2/relaxin and the newly discovered H3/relaxin-3 gene transcripts and/or immunostaining in several non-reproductive organs suggests that these tissues may act as nonovarian sources of relaxin production in numerous mammalian species. Furthermore, the recent discovery that the relaxin receptor was identified as an orphan leucine-rich repeat containing G-protein coupled receptor-7 (LGR7), and subsequent detection of LGR7 expression in several non-reproductive tissues have confirmed these organs as targets for relaxin binding and activity. This review, discusses evidence from several studies that collectively demonstrate the many diverse and vital roles that relaxin plays in male and non-pregnant female mammals, each with significant therapeutic and clinical implications. Relaxin has been reported to decrease extracellular matrix turnover, when stimulated by chemical, surgical and genetic means, in addition to organ scarring (fibrosis) in the heart, lung, kidney, liver and skin. Relaxin also protects many non-reproductive organs through its ability to promote vasodilation of the vasculature, angiogenesis and wound healing, while counteracting allergic reactions via its anti-inflammatory actions. Furthermore, the identification of relaxin peptides and receptors in numerous regions of the brain, involved in a range of sensory and autonomic functions has expanded the biological significance of the relaxin peptide family.

Objective: To examine the correlation between eating disorder (ED) symptoms and borderline personality disorder (BPD) traits in a sample of adolescents with eating disorders.Method: There were 168 participants (M age = 16.0 years; SD = 1.16) with a diagnosis of anorexia nervosa (AN) or Eating Disorder Not Otherwise Specified-AN type. Eating Disorder Examination (EDE) and the Borderline Personality Questionnaire (BPQ) were used to assess ED symptoms and BPD traits.Results: A total of 10 participants (6.6%) scored above the clinical cut-off for a likely diagnosis of BPD. A positive correlation was observed between BPQ total score and EDE global (r s = 0.64, p < .001). There were also positive correlations between the BPQ self-image and emptiness subscales and all EDE subscales. Similarly, the EDE eating concern subscale was correlated with all BPQ subscales.Discussion: Previous studies have demonstrated that some BPD traits (i.e., suicidality, impulsivity, anger) are co-morbid with ED but the link with other BPD traits has been poorly studied in adolescents and those with AN. These findings indicate that while the prevalence of BPD in adolescents with AN may be relatively low, ED symptom severity is closely related to severity of BPD traits, particularly identity disturbance and feelings of emptiness.