Relaxin Reverses Cardiac and Renal Fibrosis in Spontaneously Hypertensive Rats

Abstract

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.

Relaxin remodels fibrotic healing following myocardial infarction

“…35 At both time points studied, the levels of MMP-13 in the infarcted heart were consistently elevated across different regions following relaxin treatment, which is a likely contributing factor for the relaxin-mediated reduction of collagen. Hence, these findings, which are consistent with those of our previous studies, 6,10,11,18 suggest that the mechanisms associated with relaxin's ability to alter post-infarct fibrotic healing involve its ability to (i) suppress the expression and influence of profibrotic factors (such as TGF-b1), that promote fibrogenesis; (ii) inhibit myofibroblast differentiation and hence, myofibroblast-induced collagen synthesis; and (iii) augment MMP-13-induced collagen breakdown; with these combined actions favoring a net reduction in aberrant collagen content.…”

“…Relaxin-treated mice had a smaller LV area and lower AVF, changes very likely due to a significantly increased heart rate level (Po0.05 vs MI þ VEH groups at days 7 and 30), a finding consistent with previous reports in other rodent models. 18,26 Hemodynamic measurements (Table 3) confirmed the relaxin-induced increment in heart rate at days 7 and 30 (Po0.01 vs sham and MI þ VEH groups). MI resulted in Figure 2).…”

“…Interestingly, relaxin therapy did not significantly affect the extent of hypertrophy in this infarct model, which is consistent with findings in other in vitro and in vivo models. 18,37 The safety of interfering with fibrotic healing in the infarcted heart also remains unknown. Ventricular rupture, a fatal complication of MI, 38 is only experimentally seen in mice within the first week of injury.…”

“…It should be noted, however, that the dose of relaxin used (which produces circulating relaxin levels of 20-40 ng/ml; see Williams et al 19 and Samuel et al 20 ) significantly elevated HR, consistent with previous findings in other rodent models. 6,18,26 While interfering with some functional parameters that are sensitive to rate changes, such as Tau, a higher HR in treated animals would negatively impact on the infarcted heart. Again though, the relaxininduced higher level of HR did not appear to have any deleterious effects in the diseased heart, based on the similar extent of LV remodeling and dysfunction in MI þ RLX vs MI þ VEH mice, matched by IS.…”

“…Sham-operated mice were also separated to control for the day 7 (n ¼ 17) and day 30 (n ¼ 9) treatment groups. The dose of H2 relaxin used had previously been shown to successfully prevent and/or reverse fibrosis progression in several other experimental models of heart disease, 6,10,11,18 and produce 20-40 ng/ml of circulating H2 relaxin in rodents. 19,20 The effects of H2 relaxin alone on sham-operated animals was not assessed based on previous studies consistently demonstrating that relaxin does not affect basal collagen turnover.…”