Prazosin improves neurogenic acute heart failure through downregulation of fibroblast growth factor 23 in rat hearts

Jun-Yen Pan; Wen-Hsien Lu; Chieh-Jen Wu; Ching-Jiunn Tseng; Hsin-Hung Chen

doi:10.4103/cjp.cjp_9_22

ORIGINAL ARTICLE

Year : 2022 | Volume : 65 | Issue : 4 | Page : 179-186

Prazosin improves neurogenic acute heart failure through downregulation of fibroblast growth factor 23 in rat hearts

Jun-Yen Pan¹, Wen-Hsien Lu², Chieh-Jen Wu¹, Ching-Jiunn Tseng³, Hsin-Hung Chen⁴
¹ Division of Cardiovascular Surgery, Department of Surgery, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan
² Department of Pediatrics, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan
³ Department of Medical Education and Research, Kaohsiung Veterans General Hospital, Kaohsiung; Department of Medical Research, China Medical University Hospital, China Medical University, Taichung, Taiwan
⁴ Department of Medical Education and Research, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan

Date of Submission	10-Feb-2022
Date of Decision	06-May-2022
Date of Acceptance	07-Jul-2022
Date of Web Publication	26-Aug-2022

Correspondence Address:
Dr. Hsin-Hung Chen
Department of Medical Education and Research, Kaohsiung Veterans General Hospital, No. 386, Dazhong 1^st Rd., Zuoying Dist., Kaohsiung City 813414
Taiwan

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/cjp.cjp_9_22

Abstract

Bilateral nucleus tractus solitarii (NTS) lesions, possibly caused by enterovirus 71 infection, cause severe neurogenic hypertension, leading to acute heart failure (HF), pulmonary edema, and death within hours. Alpha-adrenergic blockers attenuate blood pressure and ameliorate HF and pulmonary edema, thereby prolonging survival time. However, the molecular mechanisms of these blockers are not clear. In this study, we investigated these mechanisms in a rat model of 6-hydroxydopamine (6-OHDA)-induced HF. Sprague–Dawley rats were treated with prazosin 10 min after the microinjection of 6-OHDA into the NTS. Immunohistochemistry and dihydroethidium (DHE) staining were used for analysis. In the cardiac tissue of 6-OHDA-induced HF, in situ expression of tumor necrosis factor-alpha (TNF-α), fibroblast growth factor-23 (FGF23), and FGF receptor 1 (FGFR1) increased, but in situ expression of Vitamin D receptor (VDR) decreased. DHE staining revealed several heart cells with high reactive oxygen species production. Prazosin treatment decreased TNF-α, FGF23, and FGFR1 expression in the heart of rats with 6-OHDA-induced HF. It also prevented cardiomyopathy caused by 6-OHDA-induced bilateral NTS lesions by inhibiting the FGF23-FGFR1 pathway and downregulating TNF-α expression. In situ, FGF23, FGFR1, VDR, superoxide, and TNF-α in the heart were found to be involved in acute HF in our rat model of 6-OHDA-induced bilateral NTS lesions. These findings are potentially useful for treating fatal enterovirus 71 infection-induced NTS lesions and HF.

Keywords: 6-Hydroxydopamine, alpha-adrenergic blockers, anti-inflammation, cardiomyopathy, fibroblast growth factor 23, heart failure

How to cite this article:
Pan JY, Lu WH, Wu CJ, Tseng CJ, Chen HH. Prazosin improves neurogenic acute heart failure through downregulation of fibroblast growth factor 23 in rat hearts. Chin J Physiol 2022;65:179-86

How to cite this URL:
Pan JY, Lu WH, Wu CJ, Tseng CJ, Chen HH. Prazosin improves neurogenic acute heart failure through downregulation of fibroblast growth factor 23 in rat hearts. Chin J Physiol [serial online] 2022 [cited 2023 Dec 7];65:179-86. Available from: https://www.cjphysiology.org/text.asp?2022/65/4/179/354800

Introduction

The nucleus tractus solitarii (NTS) constitutes a principal site of baroreceptor termination and exhibits a critical function in the process of integrating inhibitory regulation within the sympathetic nervous system.^[1] De Caro et al. reported a sudden decrease in cardiac output in five adults who had selective bilateral lesions of the NTS, and this decrease engendered decreased cerebral blood flow due to reduced systemic blood pressure. They also observed that these adults exhibited short survival intervals after acute heart failure (HF).^[2] Bilateral lesions affecting the NTS may cause sudden death due to cardiac arrest by inducing fatal cardiac arrhythmias and myocardial lesions.^[3] Clinically, enterovirus 71 infection-induced HF and lung failure are considered neurogenic in origin because they are associated with brainstem encephalitis. Enterovirus 71 causes severe damage in the NTS area, inhibiting its modulation of autonomic neurons in the medulla. Hexamethonium (a ganglionic blocker) prevents the acute release of catecholamines, reducing serum catecholamine levels, and attenuates cardiopulmonary injury in 6-hydroxydopamine (6-OHDA)-induced acute HF.^[4] However, hexamethonium has adverse effects, which result from the inhibition of both parasympathetic and sympathetic stimuli at preganglionic sites. Bilateral NTS lesion-induced acute fulminating hypertension can be attributed to peripheral vascular resistance enhancement, and it is primarily mediated by alpha-adrenergic receptors.^[5] Adrenergic receptors regulate the postganglionic sympathetic system and are targeted by catecholamines, especially epinephrine and norepinephrine. In clinical practice, alpha-blockers are typically applied for hypertension treatment, and beta-blockers reportedly alleviate left ventricular remodeling, thus improving clinical outcomes.^[6]

Incident HF is associated with high fibroblast growth factor-23 (FGF23) levels.^[7],[8] FGF23 can promote profibrotic factor secretion in myocytes, consequently inducing pathways related to fibrosis in fibroblasts and then causing cardiac fibrosis.^[9] Systemic knockout of FGF23 causes serious calcifications of vascular and soft tissues, and reduces serum phosphate levels, osteopenia, and generalized atrophy of assorted tissues, leading to a shortened lifespan.^[10],[11] The protective cardiovascular effects of adrenergic blockers in acute HF and the mechanisms of these effects remain unclear. Accordingly, in this study, we probed (1) the distinct effects of prazosin, an alpha-blocker, on pathological changes in the heart and (2) FGF23 regulation of myofibrillar degeneration in neurogenic HF caused by 6-OHDA-induced NTS lesions using a rat model of 6-OHDA-induced HF. We hypothesized that alpha 1-adrenergic blockers markedly attenuate acute myocardial injury caused by 6-OHDA-induced bilateral NTS lesions and that a link exists between FGF23 expression and klotho activity, which causes myofibrillar degeneration. The study findings may be useful for the clinical application of alpha-adrenergic blockers for treating neurogenic acute HF.

Materials and Methods

Experiments and animals

We procured male Sprague–Dawley rats aged 8 weeks from the National Science Council Animal Facility and maintained them in cages placed in the animal room located on the premises of Kaohsiung Veterans General Hospital (Kaohsiung, Taiwan, ROC). The aforementioned room was set to have the following conditions: a 12-h on/12-h off lighting cycle and a 23°C–24°C. They were provided normal rat chow (Ralston Purina Co., St. Louis, MO, USA) and tap water ad libitum; a 1-week acclimatization (to the housing conditions) period was allowed. Kaohsiung Veterans General Hospital's Research Animal Facility Committee (VGHKS-2020-A015) ratified our animal research protocols, and we followed US National Research Council's Guide for the Care and Use of Laboratory Animals.^[12]

Based on a previous study,^[13] we assigned the rats to one of the following three groups: a sham group (Group 1) in which the NTS was bilaterally microinjected with vehicle (0.8% ascorbic acid in saline), and the rats were sacrificed after 6 h; 6-OHDA group (Group 2) in which the NTS was bilaterally microinjected with 6-OHDA (30 μg; Sigma-Aldrich, St. Louis, MO, USA) dissolved in the vehicle, and the rats were sacrificed after sacrificed; and prazosin group (Group 3) in which the alpha 1-adrenergic blocker prazosin (0.15 mg/kg, iv; Sigma-Aldrich) was infused one dose through the femoral vein 10 min after the microinjection of the NTS with 6-OHDA, and the rats were sacrificed after sacrificed.

6-OHDA microinjection into the rat nucleus tractus solitarii

Using a stereotaxic instrument (Kopf Instruments, Tujunga, CA, USA), we maintained each rat's head downward at 45° and exposed the medulla's dorsal surface by executing a craniotomy process. We ensured that rats rested for a minimum of 1 h before the experiments. The rats were microinjected with 6-OHDA into the NTS by employing single-barrel glass pipettes (0.031-inch OD, 0.006-inch ID; Richland Glass, Co., Inc., Vineland, NJ, USA). Specifically, we attached these pipettes onto a stereotaxic holder and connected them to a microsyringe (Hamilton) through polyvinyl tubing.^[14]

After identifying the NTS,^[15],[16] we inserted an L-glutamate (0.154 nmol/60 nL)-containing pipette into it at the following coordinates: 0.0 mm anteroposterior, 0.5 mm mediolateral, and 0.4 mm vertical relative to the obex. After this microinjection process, we noted specific blood pressure (35 mmHg) and heart rate (50 beats/min) reductions.

Immunohistochemical and histological analyses

We sacrificed each rat and then promptly excised its heart^[4] and maintained the derived specimens in 10% formalin for 5 days, followed by blocking, paraffin embedding, and slicing into sections measuring 4 μm. Immunohistochemical analysis of the heart tissues was performed after the sections were deparaffinized for 1 h in an oven at 70°C. In addition, we microwaved the derived sections in citric buffer (10 mmol/L, pH 6.0), quenched them in 30% H₂O₂–methanol, blocked them in 3% goat serum, and subjected them to overnight incubation at 4°C with several antibodies: anti-FGF23 antibody (MAB26291, 1:100, Minneapolis, MN, USA), anti–FGF receptor 1 (FGFR1) antibody (60325-1-Ig, 1:500, Rosemont, IL, USA), anti-klotho antibody (28100-1-AP, 1:50, Rosemont, IL, USA), anti-Vitamin D receptor (VDR) antibody (ab109234, Abcam, Cambridge, MA, USA), and anti-tumor necrosis factor-alpha (TNF-α) antibody (PA1079, 1:50, Boster Biological Technology, Woburn, MA, USA). We subsequently subjected the sections to a 1-h incubation process with biotinylated secondary antibodies (1:200; Vector Laboratories, Burlingame, CA, USA), in addition to subjecting them to a 30-min incubation process at 25°C in the AB complex (1:100; Vector Laboratories). We employed a 3,3′-diaminobenzidine substrate kit (Vector Laboratories) to visualize the derived sections, and we counterstained them with hematoxylin. Finally, to capture images of the sections, we employed a charge-coupled device camera-equipped Olympus BX51 (Olympus, Tokyo, Japan) microscope.

The results of IHC staining were scored using a semi-quantitative approach based on staining intensity and percentage. In brief, the proportion of positivity was scored as 0 when the percentage of positive cells was <5%; (1) when it was 5%–25%; (2) when it was 26%–50%; (3) when it was 51%–75%; and (4) when it was >75%. The intensity was scored as 0 when no positive cells were identified; weak staining as (1); moderate as (2), and strong as (3). Thereafter, two scores were added to obtain a final score, which ranged from 0 to 7.

In situ detection of reactive oxygen species in the nucleus tractus solitarii

We performed dihydroethidium (DHE) staining (Invitrogen, Carlsbad, CA, USA) to detect endogenous in vivo reactive oxygen species (ROS) production. We subsequently subjected deparaffinized slices (5 μm) to 30-min staining with 1 μM DHE in the dark at 37°C. We finally observed the derived samples under an LSM 5 PASCAL confocal microscope (Carl Zeiss, Göttingen, Germany) for analysis.

Picrosirius red staining and fluorescence intensity quantification

Paraffin-embedded rat heart sections were de-waxed, and then stained with a picrosirius red staining kit (ab245887; Abcam, Cambridge, UK), according to the manufacturer's instructions. After staining, the sections were observed and imaged with an Olympus microscope (BX 51) equipped with bright-field, fluorescence (TRITC) and polarized light. ZEN (blue edition, 2.3 vision, Carl Zeiss) was employed to quantify fluorescence intensity; the polarized light intensity of the images was quantified based on the color threshold; and the collagen content was measured using ImageJ (National Institutes of Health, Bethesda, MD, USA).

Statistical analysis

We expressed group data as mean ± standard deviation, and SPSS Statistics Version 20.0 (IBM Corp., Armonk, NY, USA) was used for all statistical analyses. We implemented two-way analysis of variance by considering treatment, time, and interactions as the effects (with Tukey's post hoc test) to analyze FGF23, FGFR1, klotho, and VDR parameters. Results with P < 0.05 were considered statistically significant (two-tailed).

Results

Nucleus tractus solitarii lesions enhance fibroblast growth factor-23-fibroblast growth factor receptor 1 expressions in the heart of rats with neurogenic acute heart failure

The results indicated that 6-OHDA-induced NTS lesions could promote FGF23 and FGFR1 expression in the heart in situ [Figure 1]a and [Figure 1]b and that treatment with the α-blocker prazosin attenuated FGF23 and FGFR1 expression in the heart following 6-OHDA-induced neurogenic acute HF [Figure 1]c and [Figure 1]d.

Figure 1: Quantitative analysis of FGF23 and FGFR1 in the heart, with or without prazosin treatment, after 6-OHDA-induced neurogenic HF. Immunohistochemistry of the heart for (a) FGF23 and (b) FGFR1 showing that the microinjection of 6-OHDA into the NTS enhanced heart FGF23 and FGFR1 expression levels in in situ. Treatment with prazosin significantly reduced (c) FGF23 and (d) FGFR1 expression in the heart through 6-OHDA-induced acute HF. Values are expressed as mean ± SEM, n = 9–11. *P < 0.05 versus the sham group; ^#P < 0.05 versus the 6-OHDA group. Scale bar represents 100 μm. 6-OHDA: 6-Hydroxydopamine, FGF23: Fibroblast growth factor 23, FGFR1: FGF receptor 1, HF: Heart failure, NTS: Nucleus tractus solitarii.

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Nucleus tractus solitarii lesions do not change klotho expression but inhibit Vitamin D receptor expression in the heart in neurogenic acute heart failure

We determined whether FGF23 and klotho exhibit potential direct influences on the heart that may in turn lead to neurogenic acute HF development and progression. To confirm the involvement of klotho in the FGF23-FGFR1 signaling pathway of the heart following 6-OHDA-induced neurogenic acute HF, we subjected paraffin-embedded heart sections to immunohistochemical staining and analysis using klotho antibodies. These results indicated that 6-OHDA-induced NTS lesions do not alter klotho expression in the heart in situ [Figure 2]a; however, treatment with prazosin could decrease klotho expression in the heart by 6-OHDA-induced NTS lesions [Figure 2]c. We also determined whether VDR is involved in the FGF23-mediated regulation of neurogenic acute HF development and advancement. We found that 6-OHDA-induced NTS lesions decreased VDR expression in the heart in situ [Figure 2]b. Although α-blockers may modulate Vitamin D-VDR mechanisms, treatment with prazosin did not change VDR expression in the heart in 6-OHDA-induced neurogenic acute HF [Figure 2]d.

Figure 2: Quantitative analysis of klotho and VDR in the heart, with or without prazosin treatment, after 6-OHDA-induced neurogenic HF. (a) Immunohistochemistry of the heart for klotho showed that the microinjection of 6-OHDA into the NTS did not change klotho expression in the heart in situ. (b) Immunohistochemistry of the heart for VDR revealed that the microinjection of 6-OHDA into the NTS significantly reduced VDR expression in the heart in situ. (c) Treatment with prazosin significantly reduced klotho expression in the heart following the microinjection of 6-OHDA into the NTS. (d) Treatment with prazosin did not change VDR expression in the heart after the microinjection of 6-OHDA into the NTS. Values are expressed as mean ± SEM, n = 9. *P < 0.05 versus the sham group; ^#P < 0.05 versus the 6-OHDA group. Scale bar represents 100 μm. 6-OHDA: 6-Hydroxydopamine, VDR: Vitamin D receptor, HF: Heart failure, NTS: Nucleus tractus solitarii.

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Alpha 1-adrenoceptor blocker protects against neurogenic acute heart failure by ameliorating inflammation in the heart

We investigated whether FGF23 induces oxidative stress, inflammation, or fibrosis in the heart, leading to cardiomyocyte necrosis in neurogenic acute HF. DHE staining revealed cardiomyocytes with a high DHE fluorescence activity in 6-OHDA-induced neurogenic acute HF [Figure 3]a; prazosin treatment did not inhibit DHE activity in the heart [Figure 3]c. In addition, we subjected paraffin-embedded heart sections to immunohistochemical staining and analysis using TNF-α antibodies. The results indicated that 6-OHDA-induced NTS lesions could induce TNF-α expression in the heart in situ [Figure 3]b, and treatment with prazosin could attenuate TNF-α expression in the heart following 6-OHDA-induced neurogenic acute HF [Figure 3]d. Finally, we conducted picrosirius red staining to confirm the occurrence of pathological cardiac damage following cardiac fibrosis-induced neurogenic acute HF. We observed that in the hearts of the rats in all three groups, collagen appeared red in light and fluorescence microscopy and exhibited yellow-orange/green birefringence in polarized light microscopy [Figure 4]a. Fluorescence intensity [Figure 4]b and polarized light quantitative [Figure 4]c analyses showed that the collagen bundles in the heart of the rats in all three groups remained unchanged following 6-OHDA-induced neurogenic acute HF.

Figure 3: In situ qualitative and quantitative evaluations of ROS and TNF-α production in the heart, with or without prazosin treatment, after 6-OHDA-induced neurogenic HF. (a) Results derived after the observation of DHE-treated brain sections under a confocal microscope after treatment with prazosin. (b) Immunohistochemistry of the heart for TNF-α revealed that the microinjection of 6-OHDA into the NTS enhanced TNF-α expression in the heart in situ. (c) Bar graph illustrates the level of superoxide production following treatment with prazosin. Superoxide production significantly decreased in the 6-OHDA-induced NTS lesion, but no significant difference was observed in superoxide production in the heart after the administration of prazosin. (d) Treatment with prazosin significantly reduced TNF-α expression in the heart through 6-OHDA-induced acute HF. Values are expressed as mean ± SEM, n = 9–11. *P < 0.05 versus the control group; ^#P < 0.05 versus the 6-OHDA group. Scale bar represents 100 μm. 6-OHDA: 6-Hydroxydopamine, ROS: Reactive oxygen species, DHE: Dihydroethidium, TNF-α: Tumor necrosis factor-alpha, HF: Heart failure, NTS: Nucleus tractus solitarii.

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Figure 4: Qualitative and quantitative analyses of fibrosis in the heart in situ, with or without prazosin treatment, after 6-OHDA-induced neurogenic HF. (a) Heart tissue stained with picrosirius red to visualize collagen in the heart after 6-OHDA-induced neurogenic HF. (b) Quantification of collagen in the heart using picrosirius red fluorescence indicated that the collagen content did not change in the heart among the groups. (c) As detected by polarized light microscopy, the collagen content did not change in the heart among the groups. Values are expressed as mean ± SEM, n = 9–11. 6-OHDA + prazosin group. Scale bar = 100 μm. 6-OHDA: 6-Hydroxydopamine, HF: Heart failure.

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Discussion

Brain damage exhibits a close relationship with heart dysfunction.^[17],[18] In our rat model of 6-OHDA-induced neurogenic HF, prazosin showed the ability to inhibit cardiac hypercontractility and pathological changes in necrosis of the contraction band, which was caused by the attenuation of FGF23, FGFR1, superoxide, and TNF-α expression in the heart.^[13] Compared with the findings of our previous study,^[4] the ganglionic blocker treatment of the 6-OHDA-treated model decreased the release of catecholamines, preserved cardiac output, and prevented the development of pulmonary edema.^[19] Rather than attempting to reduce serum norepinephrine and epinephrine levels in the current study, we assessed the respective effects and distinct mechanisms of alpha-adrenergic blockers. Furthermore, our previous study^[13] revealed that prazosin alone was valuable for prolonging survival by reducing increased vascular resistance^[20] to maintain cardiac output. Accordingly, through the inhibition of TNF-α-FGF23-FGFR1-ROS signaling, these mechanisms may prevent cardiac damage resulting from catecholamine-induced necrosis following 6-OHDA-induced neurogenic HF.

A previous study showed that increased expression of FGF23 is significantly and independently associated with poor clinical outcomes.^[21] The prognostic influence of FGF23 on (cardiovascular) mortality has numerous possible explanations, including the contribution of increased FGF23 level to endothelial dysfunction;^[22] stimulation of the renin–angiotensin system;^[23] and development of arterial stiffness,^[22] vascular calcification,^[24] inflammation,^[25] and left ventricular hypertrophy (LVH). Moreover, researchers have paid attention to left ventricular dysfunction because of its association with increased FGF23 level. FGF23 has been shown to function in LVH pathogenesis as children diagnosed with X-linked hypophosphatemic rickets, which is an X-linked disease involving FGF23 overexpression as well as consecutive hypophosphatemia, exhibited signs of LVH.^[26] In this study, 6-OHDA microinjected into the bilateral NTS induced acute HF and upregulated FGF23 and FGFR1 expression in the heart, suggesting increased FGF23-FGFR1 level is associated with acute HF (indicating its role as a potential biomarker) and, subsequently, with increased mortality [Figure 1].

Several studies have investigated whether the FGF23–LVH association is causative or purely associative, drawing the conclusion that FGF23 is a component of the causal pathway of LVH development.^{[8],[27],[28],[29]} When neonatal rat ventricular myocytes were subjected to in vitro treatment using various FGF23 concentrations for 48 h, morphometric hypertrophy was induced. The aforementioned histological changes occurred along with gene expression profile changes, reflecting pathological hypertrophy. Faul et al. conducted a study in klotho-null mice and reported that even when klotho was not expressed, treatment using FGF23 induced LVH to a similar extent as that observed in wild-type mice.^[8] Xie et al. also reported the klotho-independent effect of FGF23 on cardiomyocytes, but other research groups have suggested that klotho deficiency, rather than increased FGF23 expression, causes cardiac hypertrophy.^[30] The current study showed that the FGF23-FGFR1 pathway is involved in acute HF development and that the alpha 1-adrenoceptor antagonist prazosin improves cardiac damage by mediating this effect. Moreover, klotho is not involved in the FGF23-FGFR1 pathway in the heart with 6-OHDA-induced acute HF [Figure 2].

As established by in vitro and in vivo (animal) studies, alpha 1-adrenergic receptors mediate cardiovascular protective effects through several adaptive mechanisms, including the inhibition of myocardial cell death, enhanced protein synthesis, increased glucose metabolism, and positive inotropy.^{[31],[32],[33]} Kawai et al. indicated that sympathetic activation enhances FGF23 expression in the bone.^[34] The present study clearly demonstrated that 6-OHDA microinjected into the bilateral NTS induced acute HF and in situ FGF23-FGFR1 expression in the heart and possibly enhanced neurogenic cardiac damage. FGF23 is secreted by osteocytes and primarily targets the kidney to regulate phosphate reabsorption, 1,25-dihydroxyvitamin D production and catabolism, and α-klotho (an anti-aging hormone) expression.^[35] Furthermore, FGF23 serves as a counter-regulatory hormone for 1,25-dihydroxyvitamin D in a bone–kidney endocrine loop. Vitamin D stimulates the FGF23 gene's promoter region by acting on its specific receptor (VDR).^[36] VDR-knockout mice showed impaired cardiac relaxation and contractility and developed LVH.^[37],[38] Here, we investigated molecular mechanisms that are related to the beneficial effects of Vitamin D/VDR against cardiovascular disease.

The present study shows that 6-OHDA microinjected into the bilateral NTS induced acute HF and reduced VDR expression in the heart, which potentially caused cardiac injury through enhancement of the FGF23-FGFR1 pathway, thereby inhibiting the Vitamin D-VDR pathway [Figure 2]b. A recent study indicated that the activation of RAAS can induce FGF23 synthesis.^[39] Furthermore, 1,25-dihydroxyvitamin D suppresses renin, consequently preventing RAAS activation.^[40] The relationship of FGF23 with RAAS activation is intriguing and might constitute a promising target pathway for the therapeutic intervention of FGF23-mediated cardiac pathology. The study also indicated that increased plasma FGF23 level exhibited an independent association with increased aldosterone level, less successful uptitration of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, and increased risks of mortality and hospitalization due to HF. However, no significant association was observed between the employment of a beta-blocker and high FGF23 levels. Nevertheless, further research is required to confirm the mechanisms that underpin the process through which cardiac FGF23 interacts with the local RAAS in the heart to induce cardiac remodeling and impair diastolic function.

FGF23 treatment enhances ROS production by activating the NADPH oxidase 2/p67phox/p47phox/Rac1 signaling complex.^[41] Therefore, FGF23-induced NO synthesis is inhibited, and superoxide formation inhibits superoxide degradation in CKD.^[42] Consequently, enhanced circulation and locally synthesized FGF23 could promote endothelial dysfunction and may further affect the progression of cardiovascular disease in CKD. Our study showed that through the relationship of FGF23-FGFR1-ROS, 6-OHDA may induce acute HF, but prazosin only improved FGF23-FGFR1 molecule association mechanisms, and the association with ROS production was not evident [Figure 2] and [Figure 3]. Chronic inflammation in cardiac fibroblasts also reportedly induces FGF23 expression in the heart,^[43] suggesting that the chronic inflammation-induced cardiac FGF23 expression could be caused by a paracrine signaling mechanism.^[44] Han et al. indicted that FGF23 stimulates TNF-α expression via the activation of FGFR1 signaling in macrophages.^[45] TNF-α also enhances FGF23 gene transcription in osteocytes in vitro.^[46] Our study also showed a higher in situ TNF-α expression in the heart, which was improved by prazosin, indicating that inflammation upregulated FGF23-FGFR1-ROS mechanisms and led to acute HF in the 6-OHDA-induced neurogenic acute HF rat model. Hence, these results show that using an alpha-blocker can prevent acute HF by inhibiting the FGF23-FGFR1-TNF-α pathway. However, the cardioprotective mechanisms do not involve the klotho or Vitamin D signaling pathway [Figure 2] and [Figure 3].

Conclusion

Overall, prazosin inhibited the FGF23-FGFR1 relationship and downregulated inflammation in the heart through independent klotho and VitDR expression, which prevented cardiac damage in 6-OHDA-induced neurogenic acute HF [Figure 5]. Therefore, these findings will be potentially applicable clinically for treating enterovirus 71 infection-induced NTS lesions, improving HF and reducing mortality associated with HF.

Figure 5: Proposed mechanism by which prazosin prolongs survival time through the negative regulation of TNF-α, FGF23, and FGFR1 in the heart after 6-OHDA-induced neurogenic acute HF. Translational models of fatal enterovirus 71 infections were simulated such that acute HF and pulmonary edema and death occurred within hours of bilateral NTS microinjection of rats with 6-OHDA.^[19] (a) Severe neurologic acute HF in situ enhanced TNF-α-FGF23-FGFR1-ROS molecule association mechanism and attenuated VDR expression in the heart after 6-OHDA-induced neurogenic acute HF. (b) Prazosin mediated anti-inflammatory effects on the heart and improved neurogenic cardiac damage resulting from catecholamine-induced necrosis caused by 6-OHDA. The cardioprotective mechanisms appeared to involve strong and independent associations between decreased FGF23 and TNF-α levels as well as an anti-inflammatory influence, but the association with klotho or Vitamin D was much less evident. 6-OHDA: 6-Hydroxydopamine, NE: Norepinephrine, FGF23: Fibroblast growth factor 23, FGFR1: FGF receptor 1, TNF-α: Tumor necrosis factor-alpha, VDR: Vitamin D receptor, HF: Heart failure.

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Acknowledgment

We are grateful to Hui-Yu Chang for the technical assistance and invaluable inputs for this manuscript.

Financial support and sponsorship

This work was supported by the Ministry of Science and Technology (MOST 110-2320-B-075B-001-MY3) and Kaohsiung Veterans General Hospital (VGHKS108-076, VGHKS109-095, KSVGH110-085, KSVGH110-150, and KSVGH111-152).

Conflicts of interest

There are no conflicts of interest.

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