Cardiac autonomic neuropathy (CAN) is one of the earliest complications of type 2 diabetes (T2D), presenting a silent cause of cardiovascular morbidity and mortality. Recent research relates the pathogenesis of cardiovascular disease in T2D to an ensuing chronic, low-grade proinflammatory and pro-oxidative environment, being the hallmark of the metabolic syndrome. Metabolic inflammation emerges as adipose tissue inflammatory changes extending systemically, on the advent of hyperglycemia, to reach central regions of the brain. In light of changes in glucose and insulin homeostasis, dysbiosis or alteration of the gut microbiome (GM) emerges, further contributing to inflammatory processes through increased gut and blood–brain barrier permeability. Interestingly, studies reveal that the determinants of oxidative stress and inflammation progression exist at the crossroad of CAN manifestations, dictating their evolution along the natural course of T2D development. Indeed, sympathetic and parasympathetic deterioration was shown to correlate with markers of adipose, vascular, and systemic inflammation. Additionally, evidence points out that dysbiosis could promote a sympatho-excitatory state through differentially affecting the secretion of hormones and neuromodulators, such as norepinephrine, serotonin, and γ-aminobutyric acid, and acting along the renin–angiotensin–aldosterone axis. Emerging neuronal inflammation and concomitant autophagic defects in brainstem nuclei were described as possible underlying mechanisms of CAN in experimental models of metabolic syndrome and T2D. Drugs with anti-inflammatory characteristics provide potential avenues for targeting pathways involved in CAN initiation and progression. The aim of this review is to delineate the etiology of CAN in the context of a metabolic disorder characterized by elevated oxidative and inflammatory load.

Cardiometabolic syndrome (CMS) is a cluster of maladaptive cardiovascular, renal, thrombotic, inflammatory, and metabolic disorders. It confers a high risk of cardiovascular mortality and morbidity. CMS is triggered by major shifts in lifestyle and dietary habits with increased consumption of refined, calorie-dense diets. Evidence indicates that diet-induced CMS is linked to Adipose tissue (AT) inflammation. This led to the proposal that adipose inflammation may be involved in metabolic derangements, such as insulin resistance and poor glycemic control, as well as the contribution to the inflammatory process predisposing patients to increased cardiovascular risk. Therefore, in the absence of direct pharmacological interventions for the subclinical phase of CMS, time restricted feeding regimens were anticipated to alleviate early metabolic damage and subsequent comorbidities. These regimens, referred to as intermittent fasting (IF), showed a strong positive impact on the metabolic state of obese and non-obese human subjects and animal models, positive AT remodeling in face of overnutrition and high fat diet (HFD) consumption, and improved CV outcomes. Here, we summarize the available evidence on the role of adipose inflammation in triggering cardiovascular impairment in the context of diet induced CMS with an emphasis on the involvement of perivascular adipose tissue. As well, we propose some possible molecular pathways linking intermittent fasting to the ameliorative effect on adipose inflammation and cardiovascular dysfunction under such circumstances. We highlight a number of targets, whose function changes in perivascular adipose tissue inflammation and could be modified by intermittent fasting acting as a novel approach to ameliorate the inflammatory status.

The risk of cardiovascular complications in type 2 diabetes increases as early as in the prediabetic stage. Our previous studies showed that perivascular adipose tissue inflammation contributes to vascular and cardiac autonomic dysfunction in prediabetic rats. Intermittent fasting has been extensively studied in the management of metabolic diseases. Here, we aim to examine the impact of therapeutic fasting (TF) on the metabolic and cardiovascular stress among prediabetic rats. Male SD rats (4–5weeks) were randomly allocated into 3 dietary groups; control diet (C), high‐calorie (HC) diet and HC‐diet with TF, for 24 weeks. Rats were fed ad libitum in the first 12 weeks. Afterwards, the TF group was subjected to daily fasting from 7.00pm – 7.00am (during the dark period) for 12 weeks with free access to water, and to HC‐diet during the light phase. Daily food intake, body weight (BW), blood glucose (fasting FBG and random RBG), body composition (BC) (using NMR), HbA1c, serum insulin levels, echocardiographic parameters, and noninvasive blood pressure were measured. At week 24; rats were catheterized for invasive hemodynamic examination. Cardiac autonomic neuropathy (CAN) was assessed by measuring baroreceptor sensitivity (BRS) using the vasoactive method. After sacrifice, aortic contractility and endothelial function were assessed using organ bath experiments. Daily calorie intake was higher in the HC group compared to control with no difference in body weight, blood glucose level, HbA1c, and glucose tolerance. Similar to our previous observations, HC feeding led to an increased fat/lean ratio, increased serum insulin level, insulin resistance, increased vascular reactivity, and reduced endothelium‐dependent relaxation. Despite a lack of effect on daily calorie intake, the previous parameters were reversed by TF. As well, SBP was higher in the HC‐fed rats (137.7 vs. 119 mm Hg), which was reversed in TF rats. This could be explained based on the observed increase in vascular sensitivity to phenylephrine‐induced contraction (pEC50 5.95 vs. 5.53) and a reduced acetylcholine mediated endothelium‐dependent relaxation in HC rats. Both observations were normalized in TF rats. Moreover, HC‐fed rats showed parasympathetic CAN manifesting as reduced BRS (DMAP vs. DHR slope decreased to −0.15 from −0.4) that was reversed in TF. Our results indicate that HC feeding induced vascular and cardiac autonomic dysfunction secondary to perivascular adipose inflammation. TF reverses signs of cardiovascular impairment. Future studies will be conducted to assess the effect of TF on PVAT inflammation. Support or Funding Information Funded by AUB‐FM MPP grant #320148

Background The complexity of the interaction between metabolic dysfunction and cardiovascular complications has long been recognized to extend beyond simple perturbations of blood glucose levels. Yet, structured interventions targeting the root pathologies are not forthcoming. Growing evidence implicates the inflammatory changes occurring in perivascular adipose tissue (PVAT) as early instigators of cardiovascular deterioration. Methods and Results We used a nonobese prediabetic rat model with localized PVAT inflammation induced by hypercaloric diet feeding, which dilutes inorganic phosphorus (Pi) to energy ratio by 50%, to investigate whether Pi supplementation ameliorates the early metabolic impairment. A 12‐week Pi supplementation at concentrations equivalent to and twice as much as that in the control diet was performed. The localized PVAT inflammation was reversed in a dose‐dependent manner. The increased expression of UCP1 (uncoupling protein1), HIF‐1α (hypoxia inducible factor‐1α), and IL‐1β (interleukin‐1β), representing the hallmark of PVAT inflammation in this rat model, were reversed, with normalization of PVAT macrophage polarization. Pi supplementation restored the metabolic efficiency consistent with its putative role as an UCP1 inhibitor. Alongside, parasympathetic autonomic and cerebrovascular dysfunction function observed in the prediabetic model was reversed, together with the mitigation of multiple molecular and histological cardiovascular damage markers. Significantly, a Pi‐deficient control diet neither induced PVAT inflammation nor cardiovascular dysfunction, whereas Pi reinstatement in the diet after a 10‐week exposure to a hypercaloric low‐Pi diet ameliorated the dysfunction. Conclusions Our present results propose Pi supplementation as a simple intervention to reverse PVAT inflammation and its early cardiovascular consequences, possibly through the interference with hypercaloric‐induced increase in UCP1 expression/activity.

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Introduction: Cardiac autonomic neuropathy, a risk factor of cardiovascular mortality, is a common manifestation of prediabetes. Evidence points to perivascular adipose tissue inflammation as a quintessential instigator of cardiovascular dysfunction in metabolic impairment. Interventions tailored to ameliorate such subtle cardiovascular involvement have not been forthcoming. Data emerging from our laboratory implicate alteration of adipocyte mitochondrial bioenergetics, particularly an upregulation of uncoupling protein 1 (UCP1) expression and subsequent augmentation of adipose tissue hypoxia, as a potential culprit driving localized adipose inflammation. Hypothesis: Inhibition of UCP1-mediated thermogenesis or activation of the alternative thermogenic pathway, futile creatine cycling, through supplementation with phosphate or creatine monohydrate, respectively, may ameliorate the inflammatory phenotype observed in non-obese prediabetic rats. Methods: A non-obese prediabetic rat model, developed in our laboratory was used. This phenotype is evoked by 12 weeks of hypercaloric feeding causing localized perivascular inflammation in absence of systemic markers of inflammation. Cardioautonomic function was assessed by invasive hemodynamics. Localized adipose tissue inflammation and macrophage polarization were examined. Results: UCP1 inhibition by phosphate supplementation reversed the blunted parasympathetic baroreflex sensitivity observed in prediabetic rats. This was associated with the alleviation of perivascular adipose tissue hypoxia, inflammation, and altered macrophage polarization. These changes were accompanied by normalization of metabolic efficiency that increased in prediabetic rats due to UCP1 upregulation. Similar functional effects were observed after creatine supplementation without changes in metabolic efficiency. Conclusions: Bypassing UCP1-mediated thermogenesis upregulated by increased caloric intake alleviates cardioautonomic deterioration triggered by perivascular inflammation. This is achieved by UCP1 inhibition with a potential risk of increased metabolic efficiency and weight gain, or by activation of the alternative thermogenic pathway of creatine cycling.

Cardiac autonomic neuropathy (CAN) has been linked to negative outcomes in diabetic patients, where it is associated with a high risk of cardiac arrhythmia and sudden death. Our previous research showed that prediabetic rats develop CAN in absence of overt signs of metabolic derangement or change in body weight. This was associated with vascular dysfunction and perivascular adipose tissue (PVAT) inflammation, which preceded inflammatory changes in other adipose pools, possibly linked to increased Uncoupling protein 1 (UCP1) and hypoxia‐inducible factor (HIF1‐a) expression. In parallel, phosphate supplementation is a simple intervention to improve body weight, energy metabolism, and glucose tolerance. Moreover, inorganic phosphate acts as a UCP1 inhibitor. Here, we examined the role of phosphate supplementation in ameliorating the early signs of cardiovascular dysfunction in metabolically challenged rats. Male SD rats (5–6 weeks) were randomly allocated into four groups fed either control diet (group 1) or high‐calorie (HC) diet for 12 weeks with three different levels of dietary phosphate; group 2: low phosphate (LP)‐ 0.37 mg/KCal, group 3: intermediate phosphate (IP)‐0.7 mg/KCal, group 4: high phosphate (HP)‐ 1.5 mg/KCal. Daily food intake, body weight, and body composition were recorded. Serum insulin was measured by ELISA. Invasive hemodynamic measurements were done and baroreceptor sensitivity (BRS) was assessed by the vasoactive method. After sacrifice, organs were collected for immunohistochemistry and western blotting. No changes in caloric intake, body weight, blood pressure, and blood glucose levels were observed. However, rats on HC diet showed an increase in serum insulin level and fat/lean ratio. Consistent with our previous work, HC‐feeding was associated with significant reduction in parasympathetic BRS in both the LP and IP groups. This was also accompanied by a reduced left ventricular systolic function. On the cellular level, Oil Red O stain showed a significant increase in the diameter of PVAT adipocytes in LP condition, together with increased expression of HIF‐1α, IL‐1β and UCP‐1. Of note, inflammatory changes observed in the PVAT were not detected in neither white nor brown adipose tissue. Furthermore, higher macrophage infiltration and total ROS score in the PVAT, heart mid‐section and brainstem were observed in LP when compared to control. Our present results highlight a role of phosphate supplementation in the amelioration of the HC induced parasympathetic dysfunction. This could be due to the reported ability of dietary phosphate to improve the assimilation of fat and reduce adipose tissue hypoxia possibly via UCP1 inhibition. Support or Funding Information Funded by an AUB CRS grant IL1‐UCP1 for perivascular adipose tissue (PVAT), white adipose tissue (WAT), and brown adipose tissue (BAT)

Cardiovascular (CV) risk associated with metabolic dysfunction commences in early stages preceding the emergence of diagnostic markers. In this regard, a protective role of female sex hormones has been observed where males and postmenopausal females are at a higher risk of these complications. Our previous work on non-obese insulin resistant male rats revealed a crucial role for perivascular adipose tissue (PVAT) inflammation in developing CV dysfunction in early prediabetes. This resulted from PVAT hypoxia evoked by increased uncoupling protein 1 (UCP1) expression and adipocyte hypertrophy in response to a dietary metabolic challenge of mild hypercaloric (MHC) feeding . Here, we examined whether estrogen modulated MHC-induced PVAT dysfunction and its CV consequences. Male and female Sprague-Dawley rats (4-5weeks) were randomly allocated into 2 dietary groups: control or MHC diet for 24 weeks. To control for estrogen effect, bilateral ovariectomy was performed on female rat sub-groups after 12 weeks of feeding with or without daily treatment with an oral dose of 17 β -estradiol (E2) of 2.8 μg/ 100 gm of body weight for an additional 12 weeks. Daily food intake, body weight, body composition, blood glucose and insulin levels, echocardiographic parameters, and blood pressure were measured. At week 24; rats were catheterized for invasive hemodynamic examination. Cardiac autonomic neuropathy was assessed by measuring baroreceptor sensitivity using the vasoactive method. After sacrifice, aortic contractility and endothelial function were examined and molecular investigation were performed. Indeed, the absence of endogenous E2 seemed to precipitate an obese phenotype in MHC-fed female rats and instigate CV impairment together with hallmarks of early PVAT dysfunction reminiscent of those observed in male rats. Intriguingly, E2 replacement restored the protective phenotype observed in intact females. E2 treatment mitigated PVAT inflammation without affecting UCP1 expression levels possibly suggesting a direct anti-inflammatory role. Our results present a novel framework for the protective role of E2 interrupting the inflammatory machinery in PVAT, as well as the subsequent CV dysfunction in presence of a dietary metabolic challenge.