Pulmonary hypertension (PH) is a cardiopulmonary disease characterized by vasoconstriction, pulmonary vascular remodeling, and endothelial dysfunction leading to increased afterload of the right ventricle (RV) that culminates in RV hypertrophy (RVH). Initially, the cardiac output is maintained during hypertrophy but with sustained pressure and vascular resistance, the RV dilates leading to right heart failure.[1,2] Cellular events in the remodeling of RV include myocyte hypertrophy, alteration in metabolism, apoptosis, remodeling of the extracellular matrix, abnormalities in natriuretic peptides, and inflammation. Current treatment options for PAH are mainly directed to promoting pulmonary artery vasodilation, reducing RV afterload. Present therapeutic options are prostanoids, endothelin receptor antagonists, phosphodiesterase 5 inhibitors, soluble guanylate cyclase stimulants and less often, calcium channel blockers in responders to acute vasoreactivity.[4-6]
Free fatty acids (FFAs) like palmitate are synthesized from malonyl-CoA in a reaction catalyzed by fatty acid synthase (FASN). As per recent studies, increased FASN expression and long chain fatty acid uptake has been reported in myocardial dysfunction in obesity.[8-10] Further, FASN knockout in macrophages has been demonstrated to attenuate atherosclerotic plaque development and leading to enhanced regression of pre-established atherosclerotic plaques in diet-induced atherosclerosis in apoE null mice by induction of LXRa responsible for cholesterol efflux and decreased expression of PPARg.[11,12] As per another set of findings, increased FASN expression has also been reported in myocardial dysfunction and heart failure induced by abdominal aortic constriction in mice that leads to increased cardiomyocyte death.
Myocardial dependence on fatty acids as an energy source is dogma in cardiac physiology and in normoxic conditions, fatty acids are the key energy source (providing ~60–70%) required by the heart, with glucose, lactate, and ketones.[14,15] In addition to generating high-energy phosphates, fatty acids also serve complex structural and signaling roles in the heart, but how intracellular lipid diversity is coordinated is unknown. Several recent studies have demonstrated that metabolic remodeling, such as, aerobic glycolysis, fatty acid oxidation, and the tricarboxylic acid (TCA) cycle,[15,16] are associated with PAH and leads to lipotoxicity. Previous reports have shown that FFAs, like palmitate, play an important role in various cardiovascular disorders like atherosclerosis, cardiac hypertrophy, and heart failure. Palmitate readily induces apoptosis in rat neonatal cardiomyocytes by causing the mitochondrial membrane depolarization.[18-20] Palmitate also decreases the oxidative metabolism of fatty acids and causes an increase in the intracellular second messenger ceramide paralleling a decrease in complex III activity leading to cytochrome c release and causing apoptosis in myocyte.[22-24] The fatty acid is also critically involved in the formation and destabilization of atherosclerotic plaques.[25-27] However, the precise role of FASN in cardiac hypertrophy is not known. Therefore, the present study was designed to explore the mechanism behind the role of FASN in cardiac hypertrophy associated with PH.
MATERIALS AND METHODS
Male Wistar rats (250–260 g) were received from the Animal House Facility, KIET School of Pharmacy, Ghaziabad, Uttar Pradesh, India and kept under hygienic conditions in the transient facility. The experimental protocol was approved by the Institutional Animal Ethics Committee, (IAEC Registration No./CPCSEA, IAEC/KSOP/2022/06) of KIET School of Pharmacy, Ghaziabad (UP). The animals were kept under standard laboratory conditions, that is, temperature (23 ± 2°C) and relative humidity (60 ± 5%), with a 12 h light/12 h dark cycle with free access to food and water. Animals were acclimatized to laboratory conditions before the test. Each animal was used once in the experiments. All the experiments were performed between 09:00 and 1700 h. Experimental protocol was approved by Institutional Animal Ethics Committee and was conducted according to the Indian National Science Academy Guidelines for the use and care of experimental animals.
Study design and PAH induction
PAH was induced by a subcutaneous injection of monocrotaline (60 mg/kg). Monocrotaline (Sigma-Aldrich Co, St. Louis, MO, USA) was dissolved in 1 M HCl, and the pH was adjusted to 7.4 with 1 M NaOH. The complete study plan is as depicted in Figure 1. PAH was induced in 60 male rats, mean weight 250–260 g. Two weeks after monocrotaline injection, the rats were randomly assigned to different experimental groups as mentioned in Table 1 and all the dose selection and treatment schedule were based on the previous literature.[28,29] Drugs were dissolved in vehicle (hydroxypropylmethyl cellulose 0.5% + polyethylene glycol 400 1.3%, 5 mL/kg) and given by oral gavage as per Table 1.
Systolic blood pressure
Systolic blood pressure (SBP; mmHg) and heart rate (bpm) were measured with a tail-cuff method in consciously trained animals (BP2000 SERIES II, Blood Pressure Analysis System). To evaluate the effects of treatments on blood pressure, non-invasive SBP measurements were made in all the animals, one week after starting treatments and 2 h after the gavage.
Blood sampling, ALT, creatinine, troponin, natriuretic peptide, and collagen assays
Blood samples were drawn on the last day from the right jugular vein under mild anesthesia (isoflurane 5% + O2 1.3%) immediately before euthanasia. Blood was immediately centrifuged, and plasma was aliquoted (200 mL) and stored at −70°C for biomarker assays. Hs-cTnT was measured with an electrochemiluminescence assay (Cobas, Roche Diagnostics, Rotkreuz, CH). NT-proANP was assayed with a validated ELISA kit (Biomedica BI-20892) following the manufacturer’s recommendations. Cellular collagen levels were estimated by fluorometric assay kit (MAK322, Merck, St. Louis USA) as per the manufacturer’s protocol. Furthermore, plasma levels of creatinine and ALT activity were measured with an enzymatic assay (Cobas, Roche Diagnostics, Rotkreuz, CH) and a colorimetric assay (Alanine transaminase activity assay kit, Cayman Chemical Company, USA).
Rats were euthanized by 2.5 M KCl intravenous injection under anesthesia and the heart and lungs were excised, with careful dissection from surrounding tissues. The left ventricle (LV) with the septum was separated from the RV and they were both weighed. The RV-free wall was fixed by immersion in 10% buffered formalin and embedded in paraffin. The samples were stored for further analyses. RV hypertrophy was calculated with the Fulton index as the ratio of RV to LV-free wall + interventricular septum (S) weight. H and E stained cardiac tissue sections are scored by a blinded observer using a previously published system for the following measures: crypt architecture (normal, 0– severe crypt distortion with loss of entire crypts, 3), degree of inflammatory cell infiltration (normal, 0 – dense inflammatory infiltrate, 3), muscle thickening (base of crypt sits on the muscularis mucosae, 0 – marked muscle thickening present, 3), and crypt abscess (absent, 0 – present, 1). The histological damage score is the sum of each individual score.
Morphometric analysis of pulmonary arteries
The circumferential actin smooth muscle antibody positive staining around vessels revealed the medial area, representing the area between the internal elastic lamina and the external elastic lamina, indicative of vessel muscularization. To assess the type of remodeling of muscular pulmonary arteries, vessels were analyzed with a computerized morphometric system (Leica DMD108, Leica Microsystems, Wetzlar, Germany). For each animal at least 20 distal (intra-acinar) pulmonary arteries 30 to 80 mm in diameter were selected at magnification ×100 in randomly selected fields and examined for the degree of muscularization. Each small artery was classified as: N = nonmuscularized (no apparent muscle); P = partially muscularized (with only a crescent of muscle) and M = muscularized (with a complete medial coat of muscle), as literature.
To assess the effects of treatments, sample size was calculated for the primary endpoint of the study, namely RVSP. In the sample size calculation, to have statistical significant observation, we have 10 animals per experimental group, to detect a 35% reduction of RVSP in treated animals, assuming a two-tail a level of 0.05, b error 75% and 25% mortality. The data were analyzed by applying one-way ANOVA, followed by Tukey’s test, respectively (GraphPad Software, La Jolla, CA). All the values are expressed as mean ± SD. In all the tests, the criterion for statistical significance was P < 0.05.
Effect of Triclosan on systolic blood pressure and mortality
MCT treatment leads to significant increase in the SBP and mortality index as demonstrated in the Figure 2. Further treatment with Triclosan 3, 10, and 30 mg/kg, p.o., b.i.d., significantly decrease the SBP, and which is comparable to the Macitentan (MCT 10) 10 mg/kg, o.d. While Triclosan 1 mg/kg, p.o., b.i.d., was not able to produce any significant effect on both mortality and RSVP. In terms of mortality index, mortality was 35% in the MCT group, 30%, 25%, 20% respectively at 3, 10, and 30 mg/kg dose of Triclosan and 15% in the M10 group [Figure 2].
Effect of Triclosan on total cardiac wt., RV wt., left ventricle + Septum wt., and RV/LV+S ratio
Different cardiac masses such as total cardiac wt., RV wt., LV + Septum wt., and ratio of RV/LV+S at death are shown in Figure 3a-d. In rats treated with MCT there was a significant increase in the total cardiac wt. [Figure 3a], RV wt. [Figure 3b], and RV/LV + S ratio [Figure 3d], while there was no significant difference was observed in case LV+Septum wt. [Figure 3c] Further treatment with Triclosan 3, 10, and 30 mg/kg, p.o., b.i.d., significantly restores (in dose dependent manner) the cardiac wt., RV wt., and RV/LV+S ratio, while Triclosan 1 mg/kg, p.o., b.i.d., was not able to produce any significant effect on any of the masses. Further effect of Triclosan at 30 mg/kg, p.o., b.i.d. was comparable with Macitentan (MCT 10) 10 mg/kg, o.d. [Figure 3a-d].
Effect of Triclosan on ALT, creatinine, troponin, natriuretic peptide, and collagen levels
Monocrotaline treatment leads to significant increase in the different biomarkers (ALT, creatinine, troponin, natriuretic peptide and collagen) as compared to naive group animals. Further treatment with Triclosan 3, 10, and 30 mg/kg, p.o., b.i.d., significantly restores (in dose dependent manner) the ALT [Figure 4a], creatinine [Figure 4b], troponin [Figure 5a], natriuretic peptide [Figure 5b] and collagen [Figure 6a and 6b] levels. Further, Triclosan 1 mg/kg, p.o., b.i.d., was not able to produce any significant effect on any of these biomarkers (ALT, creatinine, troponin, natriuretic peptide and collagen) masses. Further effect of Triclosan at 30 mg/kg, p.o., b.i.d. was comparable with Macitentan (MCT 10) 10 mg/kg, o.d. [Figures 4 and 6].
Effect of Triclosan on Morphometric analysis of pulmonary arteries
Monocrotaline treatment leads to significant increase in the muscularization of pulmonary arteries as compared to naive group animals. Further treatment with Triclosan 3, 10, and 30 mg/kg, p.o., b.i.d., significantly restores (in dose dependent manner) the normal architecture of the pulmonary arteries [Figure 7]. While, Triclosan 1 mg/kg, p.o., b.i.d., was not able to produce any significant effect on tissue remodeling. Further effect of Triclosan at 30 mg/kg, p.o., b.i.d. was comparable with Macitentan (MCT 10) 10 mg/kg, o.d. [Figure 7].
Effect of Triclosan on gross cardiac histological alteration in heart
Animals exposed to MCT treatment, showed more histological damage (more cellular infiltration, greater distortion/damage to crypt architecture) compared to Naïve animals (mean ± SEM) Figure 8. Triclosan 3, 10, and 30 mg/kg, p.o., b.i.d., treatment were able to show reversal of histological damage as compared to the control group. While, Triclosan 1 mg/kg, p.o., b.i.d., was not able to produce any significant effect. Further, Macitentan (MCT 10) 10 mg/kg, o.d. also reverses the histological alteration [Figure 8].
This study examined triclosan first time in an experimental rat model of PAH induced by monocrotaline. The main findings are that triclosan improved several RV hemodynamic and biochemical and morphological/histological abnormalities, and blunted pulmonary arteriolar wall thickening more than macitentan. PAH is a rare disease with slow progression involving multiple pathogenic processes. A critical adaptation of the RV to the high pressure and increased pulmonary resistance during PH is to increase wall thickness by accumulating muscle mass resulting in right ventricular hypertrophy and leading to heart failure. Similarly, in our study, cardiac hypertrophy was demonstrated by different parameters such as morphometric analysis and histological alterations following MCT treatment and as reported in other studies also.[34,35] As per literature cardiac hypertrophy was accompanied by increased expression and activity of FASN and RV of MCT-treated rats, an observation supported by previous reports which show increased FASN expression in cardiac dysfunction.[11,36,37] Further as per literature, inhibition of FASN (by siRNA and C75) reduced the cardiac hypertrophy both in in vitro and in vivo conditions in different study.
FASNN plays a central role in vascular smooth muscle cell (VSMC) hypercontraction through the inhibition of myosin phosphatase followed by an increase of myosin light chain phosphorylation, affecting suppression of VSMC proliferation, macrophage infiltration, enhanced VSMC apoptosis, and amelioration of endothelial dysfunction. Review of literature have shown that increased level of FFAs increases cardiac hypertrophy resulting in heart failure.[33-35,40] In our study, Triclosan treatment restore the various physiological, biochemical and histological alterations as demonstrated by various parameters.
Further as per literature, decreased glucose oxidation and increased glycolysis associated with metabolic dysfunction in cardiac dysfunction. Clinical evidences also indicate a shift from oxidative phosphorylation to glycolytic metabolism in the RV dysfunction in PAH. The inhibition of FASN has demonstrated to restore the normal vasculature in heart and activity. Decreased the glycolysis markers in hypoxic cardiomyocyte indicating the metabolic shift towards glucose oxidation which is beneficial in cardiac hypertrophy. Previous report has shown that there is a reciprocal relationship between glucose oxidation and fatty acid oxidation (FAO) and inhibiting FAO is beneficial in RVH because FAO uses 12% more oxygen than glucose oxidation to generate the same amount of ATP.[43,44] As per literature, increased levels of hs-cTnt and NT-proANP are also responsible for the transport of fatty acids into the mitochondria for b oxidation and these increased levels are attenuated by FASN inhibition. This decreased FAO could be the reason behind the protective effect of FASN inhibition on cardiac hypertrophy as the previous reports demonstrated that inhibition of FAO, either by FAO inhibitor (like Trimetazidine) or CPT-1 inhibitors, offered protection in RVH induced by pulmonary artery banding and in clinical studies in cardiomyopathy.[15,36,39,40]
In monocrotaline-injected rats sustained vasoconstriction contributes substantially to the increased pulmonary vascular resistance and mediates pulmonary artery medial and adventitial thickening, and small arteries muscularization. As per previous studies, in monocrotaline-induced PAH in rats there was a significant reduction of the arteriolar medial wall thickness in pulmonary resistance vessels and significant attenuation of RV hypertrophy with Triclosan treatment. These results suggested that this agent not only inhibits the vasoconstriction but also slows the progression of pulmonary vascular and right ventricular remodeling. Further Triclosan treatment bring down increased SBP and the proportion of muscularized pulmonary arteries (30–75 mm in diameter). In present study macitentan 10 mg/kg, started one day after monocrotaline, significantly prevented RV-free wall end-diastolic thickening, RV systolic function impairment, and pulmonary arteriolar wall remodeling.[47-49]
Findings of the present study demonstrated the efficacy of Triclosan “FASN inhibitor” in monocrotaline-induced PAH model in rat. Further the efficacy was comparable to macitentan, so we govern further studies to establish “FASN inhibitor as a potential therapeutic approach” for management of PAH.
In conclusion, finding of the present study demonstrated the efficacy of “Triclosan” in monocrotaline-induced PAH model in rat. Therefore, we hypothesize the “FASN inhibitor” as a therapeutic approach for the management of PAH and recommend further studies to establish FASN inhibitor for management of PAH.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
The author gratefully acknowledged the faculty of KIET School of Pharmacy, Ghaziabad (UP) for carrying out the experimental work in the laboratory, without which this work may not be feasible.
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