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Objective To determine the mechanisms of inflammation‐induced left ventricular (LV) remodeling and effects of blocking circulating tumor necrosis factor alpha (TNF‐α) in a model of systemic inflammation. Methods Seventy Sprague‐Dawley rats were divided into three groups: the control group, the collagen‐induced arthritis (CIA) group, and the anti‐TNF‐α group. Inflammation was induced in the CIA and anti‐TNF‐α groups. Following the onset of arthritis, the anti‐TNF‐α group received the TNF‐α inhibitor, etanercept, for 6 weeks. LV geometry and function were assessed with echocardiography. Circulating inflammatory markers were measured by ELISA and LV gene expression was assessed by comparative TaqMan® polymerase chain reaction. Results The LV relative gene expression of pro‐fibrotic genes, transforming growth factor β (TGFβ) (p = 0.03), collagen I (Col1) (p < 0.0001), and lysyl oxidase (LOX) (p = 0.002), was increased in the CIA group compared with controls, consistent with increased relative wall thickness (p = 0.0009). Col1 and LOX expression in the anti‐TNF‐α group were similar to controls (both, p > 0.05) and tended to be lower compared to the CIA group (p = 0.06 and p = 0.08, respectively), and may, in part, contribute to the decreased relative wall thickness in the anti‐TNF‐α group compared to the CIA group (p = 0.03). In the CIA group, the relative gene expression of matrix metalloproteinase 2 (MMP2) and MMP9 was increased compared to control (p = 0.04) and anti‐TNF‐α (p < 0.0001) groups, respectively. Conclusion Chronic systemic inflammation induces fibrosis and dysregulated LV extracellular matrix remodeling by increasing local cardiac pro‐fibrotic gene expression, which is partially mediated by TNF‐α. Inflammation‐induced LV diastolic dysfunction is likely independent of myocardial fibrosis.

Background Titin phosphorylation contributes to left ventricular (LV) diastolic dysfunction. The independent effects of inflammation on the molecular pathways that regulate titin phosphorylation are unclear. Methods We investigated the effects of collagen-induced inflammation and subsequent tumor necrosis factor-α (TNF-α) inhibition on mRNA expression of genes involved in regulating titin phosphorylation in 70 Sprague-Dawley rats. LV diastolic function was assessed with echocardiography. Circulating inflammatory markers were quantified by enzyme-linked immunosorbent assay and relative LV gene expression was assessed by Taqman® polymerase chain reaction. Differences in normally distributed variables between the groups were determined by two-way analysis of variance (ANOVA), followed by Tukey post-hoc tests. For non-normally distributed variables, group differences were determined by Kruskal–Wallis tests. Results Collagen inoculation increased LV relative mRNA expression of vascular cell adhesion molecule 1 (VCAM1), pentraxin 3 (PTX3), and inducible nitric oxide synthase (iNOS) compared to controls, indicating local microvascular inflammation. Collagen inoculation decreased soluble guanylate cyclase alpha-2 (sGCα2) and soluble guanylate cyclase beta-2 (sGCβ2) expression, suggesting downregulation of nitric oxide-soluble guanylate cyclase-cyclic guanosine monophosphate (NO-sGC-cGMP) signaling. Inhibiting TNF-α prevented collagen-induced changes in VCAM1, iNOS, sGCα2 and sGCβ2 expression. Collagen inoculation increased protein phosphatase 5 (PP5) expression. Like LV diastolic dysfunction, increased PP5 expression was not prevented by TNF-α inhibition. Conclusion Inflammation-induced LV diastolic dysfunction may be mediated by a TNF-α-independent increase in PP5 expression and dephosphorylation of the N2-Bus stretch element of titin, rather than by TNF-α-induced downregulation of NO-sGC-cGMP pathway-dependent titin phosphorylation. The steady rise in number of patients with inflammation-induced diastolic dysfunction, coupled with low success rates of current therapies warrants a better understanding of the systemic signals and molecular pathways responsible for decreased titin phosphorylation in development of LV diastolic dysfunction. The therapeutic potential of inhibiting PP5 upregulation in LV diastolic dysfunction requires investigation.

Background: Interleukin-6 (IL-6) receptor blockers improve systemic inflammation however, their inconsistent effects on lipid metabolism and drug-induced liver injuries warrant further investigation. This study aimed to determine the effects of IL-6 receptor blocker therapy on lipid metabolism and liver morphology in collagen-induced arthritis. Methods: Methods: Sixty-three Sprague-Dawley rats were divided into control (n=24), inflammation (n=24), and IL-6 blocker (n=15) groups. Inflammation was induced in the inflammation and IL-6-blocker groups using Bovine type-II collagen and incomplete Freund’s adjuvant. At first signs of arthritis, the IL-6 blocker group received an IL-6 blocker, tocilizumab for six weeks. Serum concentrations of low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and ATP-binding cassette transporter-A1 (ABCA1) were measured. Liver fibrosis was determined by histological stains and liver enzymes were measured using the colorimetric-chemistry analyzer. Results: In the inflammation group, HDL-C and ABCA1 were reduced compared to control (p<0.0001 and p=0.04, respectively) and IL-6 blocker (p=0.0003 and p<0.0001, respectively) groups. LDL-C was increased in the inflammation compared to control (p=0.02). Markers of liver fibrosis were increased in the IL-6 blocker group compared to control and inflammation groups (picrosirius red collagen area fraction: p<0.0001 and p=0.0008, respectively; Masson’s trichrome collagen area fraction: p=0.0002 and p=0.01, respectively). Alkaline phosphatase concentrations were increased in the IL-6 blocker group compared to the control (p<0.0001) and inflammation (p=0.002) groups. Conclusion: IL-6 blockers ameliorated inflammation-induced lipid metabolism impairments, however they induced liver fibrosis. Although IL-6 blockers may reduce inflammation-induced metabolic impairments in chronic inflammatory disorders, routine monitoring of liver function is warranted while on treatment.

Elevated systemic inflammation contributes to pathogenesis of heart failure with preserved ejection fraction (HFpEF), but molecular mechanisms are poorly understood. Although left ventricular (LV) diastolic dysfunction is the main cause of HFpEF, subclinical systolic dysfunction also contributes. We have previously shown that rats with collagen-induced arthritis (CIA) have systemic inflammation, LV diastolic dysfunction, and that increased circulating TNF-a contributes to inflammation-induced HFpEF pathogenesis, but does not mediate LV diastolic dysfunction in CIA rats. Contribution of systemic inflammation to dysfunction of the active process of LV diastolic and systolic function are unknown. In the present study, we used the CIA rat model to investigate the effects of systemic inflammation and TNF-a blockade on systolic function, and mRNA expression of genes involved in active diastolic relaxation and of myosin heavy chain (MyHC) isoforms. Collagen inoculation and TNF-a blockade did not affect LV mRNA expression of genes that mediate active LV diastolic function. Collagen-induced inflammation impaired LV global longitudinal strain (P = 0.03) and velocity (P = 0.04). This impairment of systolic function was prevented by TNF-a blockade. Collagen inoculation decreased mRNA expression of a-MyHC (Myh6, P = 0.03) and increased expression of b-MyHC (Myh7, P = 0.0002), a marker, which is upregulated in failing hearts. TNF-a blockade prevented this MyHC isoformswitch. These results show that increased circulating TNF-a changes the relative expression of MyHC isoforms, favoring b-MyHC, which may underlie changes in contractile function that impair systolic function. Our results indicate that TNF-a initiates early-stage LV systolic, rather than LV diastolic dysfunction.