In this study, 12-months treatment of dapagliflozin reduced plasma IL-1B level. To our knowledge, this is the first time that SGLT2 inhibitor is shown to lower IL-1B in a placebo-controlled double-blind randomized clinical trial. However, dapagliflozin treatment did not result in a change in plasma IL6, plasma TNFα or serum CRP, consistent with the majority of prior clinical studies [18]. Furthermore, dapaglifozin significantly increased plasma ketones and attenuated the decline of PBMC maximal OCR, which was previously shown to inversely correlate with IL-1B expression in chronic heart failure [14, 17]. Despite the improvements in circulatory inflammatory endpoints, we did not observe significant changes in CMRI measurements of myocardial fibrosis and strain in patients receiving dapagliflozin. Of note, in the placebo group, there was a trend of worsening T2 relaxation time (inflammation), which was not observed in the dapagliflozin group, suggesting dapagliflozin may attenuate the progression of cardiac inflammation.
IL-1B is an inducible pro-inflammatory cytokine made primarily by immune cells, such as monocytes and macrophages, to function in cardiac repair as well as injury [19]. Under the NFkB-mediated transcriptional regulation, Pro-IL-1B is produced and stored intracellularly. Activation of NLRP3 inflammasome results in the cleavage and maturation of IL-1B prior to secretion. IL-1B has been shown to worsen myocardial contractile function and relaxation and induce hypertrophy [20–23]. Furthermore, in multiple animal studies, SGLT2 inhibitor is shown to antagonize the NLRP3-IL-1B axis to improve cardiovascular outcomes [4], substantiating IL-1B’s role as a potential mediator of cardiac inflammation. The recent CANTOS trial subgroup analysis provides clinical evidence that circulating IL-1B is not just a bystander but actively contributes to heart failure pathogenesis. The conjecture is corroborated by a number of small clinical trials using anakinra, a recombinant IL-1 receptor antagonist. In these studies, anakinra is shown to reduce CRP and HF hospitalization in acute STEMI patients [24, 25] and enhance exercise capacity and LVEF in HF patient with elevated CRP [26].
PBMC mitochondrial respiration is an emerging biomarker of sterile inflammation [14, 27–29], particularly in the setting of heart failure, and was previously shown to inversely correlate with the expressions of proinflammatory cytokines, such as IL-1B [14, 17]. It is postulated that upon stimulation by circulating mitochondrial damage associated molecular patterns (MitoDAMPs), PBMC produces IL-6, leading to mitochondrial dysfunction and mitochondrial ROS production in an autocrine manner [14]. Mitochondrial ROS subsequently activates the NLRP3 inflammasome, resulting in the maturation and release of IL-1B family of cytokines [30]. In the current study, we observed that SGLT2 inhibitor sustains mitochondrial oxidative capacity of circulating immune cells, supporting the notion that PBMC may be a source of circulating IL-1B, and a potential therapeutic target in T2D. Together, our results are consistent with the proposed mechanism that SGLT2 inhibitor lowers systemic inflammation by increasing plasma ketones, which acts on peripheral immune cells (PBMCs) to inhibit NLRP3 inflammasome activation and IL-1B production [6]. Recently, transcriptomic analyses indicate that disruption of mitochondrial pathways (TCA cycle and oxidative phosphorylation) in circulating monocytes is a marker of elevated cardiovascular risk in T2D patients [31]. Whether and how mitochondrial dysfunction in circulating monocytes plays a role in the pathogenesis of T2D and heart failure is an area of active research.
In addition to anti-inflammation, SGLT2 inhibitors have a wide range of effects on hemodynamic, neurohormonal, metabolic and endothelial function. There are several potential direct and indirect pathways leading to improvement of cardiac structure and function and myocardial substrate utilization in T2D. For example, SGLT2 inhibitors provide glycemic control, reduce blood pressure, reduce arterial stiffness, decrease body weight and reduce visceral adiposity, which could indirectly lead to improved cardiac function in T2D patients [32]. On the cellular level, SGLT2 inhibitors could directly affect cardiac function by reducing oxidative stress, attenuating myocardial fibrosis [33, 34]. In this study we did not find a significant effect of dapagliflozin on strain when compared to placebo. We also did not find a significant change in strain measures in the placebo control group over a 12-month period; raising the question whether the enrolled T2D patients truly had underlying structural heart disease.
Myocardial T1 mapping methods are used to measure tissue fibrosis and reflects a composite signal from intracellular and extracellular compartments; however, T1 measurements can be confounded by renal clearance, hematocrit, and type and dosage of gadolinium [35]. To adjust for these factors, the most widely accepted approach to determine fibrosis is to measure ECV which has been shown to be a good measure of interstitial fibrosis. In the current study, we found that 12 months of SGLT2 inhibition compared to placebo did not alter ECV of T2D patients. Our findings are consistent with a prospective study which enrolled 35 T2D subjects: Before and after CMRI was performed following 6 months of Empagliflozin showed no significant effect on ECV [36]. Furthermore, in our study, SGLT2 inhibition did not change the level of plasma IL-10, a pro-fibrotic cytokine. While these results do not support the notion that the cardioprotective effects of SGLT2 inhibition is mediated via improving cardiac fibrosis, further studies are required to unravel the mechanism of action by which SGLT2 inhibitors enhance cardiac outcomes.
There are several strengths of this study. First, there was excellent adherence with treatment as evidenced by significant reduction in blood glucose, hemoglobin A1c, and BMI in subjects randomized to dapagliflozin (Table 3). Second, the randomized study design was a strength, since many previous studies on SGLT2 inhibitors utilized a prospective study design. Third, the use of circulating inflammatory endpoints as well as CMRI allowed for the assessment of anti-inflammatory effect of SGLT2 inhibitor at both the systemic and organ levels.
There are several limitations and weaknesses. First, this is a relatively small clinical trial which was not powered to detect smaller effect sizes. For example, while there is a trend that dapagliflozin attenuates the progression of cardiac inflammation (T2 relaxation time), the study is underpowered to detect a statistically significant difference. Second, previous animal studies of SGLT2 inhibition utilized direct pathologic examination of inflammation and fibrosis, whereas CMRI are known to be less sensitive in assessing these parameters. Third, the 12-month treatment period may not have been sufficient to result in detectable cardiac structural and functional changes, although in a prospective study, 3 months of SGLT2 inhibition was sufficient to demonstrate improvement in diastolic function [37]. Fourth, we did not have a matched, non-diabetic control group. Fifth, higher ECV values (greater than 32%) are associated with worse outcomes in patients with known myocarditis [38]. In contrast, the T2D cohort in our study had baseline ECV of 27–28%. To address the possibility that patients with higher baseline ECV would derive more benefits from SGLT2 inhibition, we performed a subgroup analysis in patients in the upper half of ECV values at baseline (ECV ~ 30%); however, in this cohort (N = 17) we still did not find a significant difference in ECV between the drug and placebo groups.
In conclusion we demonstrated that 12 months of daily dapagliflozin in T2D patients reduces circulating IL-1B, increases plasma ketones, and prevents the decline of PBMC mitochondrial maximal respiration, but does not improve cardiac fibrosis or strain by CMRI.