Protection from chronic stress- and depressive symptom-induced vascular endothelial dysfunction in female rats is abolished by preexisting metabolic disease

Cerebrovascular dysfunction and depressive symptoms in preclinical models: insights from a scoping review

Although existing literature supports associations between cerebrovascular dysfunction and the emergence of depression and depressive symptoms, relatively little is known about underlying mechanistic pathways that may explain potential relationships. As such, an integrated understanding of these relationships in preclinical models could provide insight into the nature of the relationship, basic mechanistic linkages, and areas in which additional investment should be targeted. This scoping review was conducted in MEDLINE, EMBASE, and Scopus to outline the relationship between depressive symptoms and cerebrovascular dysfunction in preclinical animal models with an additional focus on the areas above. From 3,438 articles initially identified, 15 studies met the inclusion criteria and were included in the review. All studies reported a positive association between the severity of markers for cerebrovascular dysfunction and that for depressive symptoms in rodent models and this spanned all models for either pathology. Specific mechanistic links between the two such as chronic inflammation, elevated vascular oxidant stress, and altered serotonergic signaling were highlighted. Notably, almost all studies addressed outcomes in male animals, with a near complete lack of data from females, and there was little consistency in terms of how cerebrovascular dysfunction was assessed. Across nearly all studies was a lack of clarity for any "cause and effect" relationship between depressive symptoms and cerebrovascular dysfunction. At this time, it is reasonable to conclude that a correlative relationship clearly exists between the two, and future investigation will be required to parse out more specific aspects of this relationship.NEW & NOTEWORTHY This scoping review presents a structured evaluation of all relevant existing literature linking cerebral vasculopathy to depressive symptom emergence in preclinical models. Results support a definite connection between vascular dysfunction and depressive symptoms, highlighting the importance of chronic elevations in inflammation and oxidant stress, and impaired serotonergic signaling. The review also identified significant knowledge gaps addressing male versus female differences and limited clear mechanistic links between cerebral vasculopathy and depressive symptoms.

Thromboxane-induced cerebral microvascular rarefaction predicts depressive symptom emergence in metabolic disease

Previous studies have suggested that the loss of microvessel density in the peripheral circulation with evolving metabolic disease severity represents a significant contributor to impaired skeletal muscle oxygenation and fatigue-resistance. Based on this and our recent work, we hypothesized that cerebral microvascular rarefaction was initiated from the increased prooxidant and proinflammatory environment with metabolic disease and is predictive of the severity of the emergence of depressive symptoms in obese Zucker rats (OZRs). In male OZR, cerebrovascular rarefaction followed the emergence of elevated oxidant and inflammatory environments characterized by increased vascular production of thromboxane A2 (TxA2). The subsequent emergence of depressive symptoms in OZR was associated with the timing and severity of the rarefaction. Chronic intervention with antioxidant (TEMPOL) or anti-inflammation (pentoxifylline) therapy blunted the severity of rarefaction and depressive symptoms, although the effectiveness was limited. Blockade of TxA2 production (dazmegrel) or action (SQ-29548) resulted in a stronger therapeutic effect, suggesting that vascular production and action represent a significant contributor to rarefaction and the emergence of depressive symptoms with chronic metabolic disease (although other pathways clearly contribute as well). A de novo biosimulation of cerebrovascular oxygenation in the face of progressive rarefaction demonstrates the increased probability of generating hypoxic regions within the microvascular networks, which could contribute to impaired neuronal metabolism and the emergence of depressive symptoms. The results of the present study also implicate the potential importance of aggressive prodromic intervention in reducing the severity of chronic complications arising from metabolic disease.NEW & NOTEWORTHY With clinical studies linking vascular disease risk to depressive symptom emergence, we used obese Zucker rats, a model of chronic metabolic disease, to identify potential mechanistic links between these two negative outcomes. Depressive symptom severity correlated with the extent of cerebrovascular rarefaction, after increased vascular oxidant stress/inflammation and TxA2 production. Anti-TxA2 interventions prevasculopathy blunted rarefaction and depressive symptoms, while biosimulation indicated that cerebrovascular rarefaction increased hypoxia within capillary networks as a potential contributing mechanism.

The development of peripheral microvasculopathy with chronic metabolic disease in obese Zucker rats: a retrograde emergence?

The study of peripheral vasculopathy with chronic metabolic disease is challenged by divergent contributions from spatial (the level of resolution or specific tissue being studied) and temporal origins (evolution of the developing impairments in time). Over many years of studying the development of skeletal muscle vasculopathy and its functional implications, we may be at the point of presenting an integrated conceptual model that addresses these challenges within the obese Zucker rat (OZR) model. At the early stages of metabolic disease, where systemic markers of elevated cardiovascular disease risk are present, the only evidence of vascular dysfunction is at postcapillary and collecting venules, where leukocyte adhesion/rolling is elevated with impaired venular endothelial function. As metabolic disease severity and duration increases, reduced microvessel density becomes evident as well as increased variability in microvascular hematocrit. Subsequently, hemodynamic impairments to distal arteriolar networks emerge, manifesting as increasing perfusion heterogeneity and impaired arteriolar reactivity. This retrograde "wave of dysfunction" continues, creating a condition wherein deficiencies to the distal arteriolar, capillary, and venular microcirculation stabilize and impairments to proximal arteriolar reactivity, wall mechanics, and perfusion distribution evolve. This proximal arteriolar dysfunction parallels increasing failure in fatigue resistance, hyperemic responses, and O2 uptake within self-perfused skeletal muscle. Taken together, these results present a conceptual model for the retrograde development of peripheral vasculopathy with chronic metabolic disease and provide insight into the timing and targeting of interventional strategies to improve health outcomes.NEW & NOTEWORTHY Working from an established database spanning multiple scales and times, we studied progression of peripheral microvascular dysfunction in chronic metabolic disease. The data implicate the postcapillary venular endothelium as the initiating site for vasculopathy. Indicators of dysfunction, spanning network structures, hemodynamics, vascular reactivity, and perfusion progress in an insidious retrograde manner to present as functional impairments to muscle blood flow and performance much later. The silent vasculopathy progression may provide insight into clinical treatment challenges.

Short-term salicylate treatment improves microvascular endothelium-dependent dilation in young adults with major depressive disorder

Reactive oxygen species (ROS)-mediated reductions in nitric oxide (NO)-dependent dilation are evident in adults with major depressive disorder (MDD); however, the upstream mechanisms remain unclear. Here, we hypothesized that nuclear factor-κB (NF-κB) activation-induced ROS production contributes to microvascular endothelial dysfunction in MDD. Thirteen treatment-naive adults with MDD (6 women; 19-23 yr) and 10 healthy nondepressed adults (HAs; 5 women; 20-25 yr) were tested before and after (open-label design) systemic NF-κB knockdown (nonacetylated salicylate; 3,000-4,500 mg/day × 4 days). Red cell flux (laser Doppler flowmetry) was measured during graded intradermal microdialysis perfusion of the endothelium-dependent agonist acetylcholine (ACh), alone and in combination with NO synthase inhibition [NG-nitro-l-arginine methyl ester (l-NAME)] or ROS scavenging (apocynin). Serum salicylate concentrations following treatment were not different between groups (22.8 ± 7.4 HAs vs. 20.8 ± 4.3 mg/dL MDD; P = 0.46). When compared with HAs, the NO-dependent component of ACh-induced dilation was blunted in adults with MDD before (P = 0.023), but not after (P = 0.27), salsalate treatment. In adults with MDD, the magnitude of improvement in endothelium-dependent dilation following salsalate treatment was inversely related to the degree of functional impairment at baseline (R2 = 0.43; P = 0.025). Localized ROS scavenging improved NO-dependent dilation before (P < 0.01), but not after (P > 0.05), salsalate treatment. Salsalate did not alter systemic concentrations of pro- or anti-inflammatory cytokines (all P > 0.05). These data suggest that NF-κB activation, via increased vascular ROS production, contributes to blunted NO-dependent dilation in young adults with MDD but otherwise free of clinical disease. These data provide the first direct evidence for a mechanistic role of vascular inflammation-associated endothelial dysfunction in human depression.NEW & NOTEWORTHY Our data indicate that short-term treatment with therapeutic doses of the nuclear factor-κB (NF-κB) inhibitor salsalate improved nitric oxide (NO)-mediated endothelium-dependent dilation in adults with major depressive disorder (MDD). In adults with MDD, acute localized scavenging of reactive oxygen species (ROS) with apocynin improved NO-dependent dilation before, but not after, salsalate administration. These data suggest that activation of NF-κB, in part via stimulation of vascular ROS production, contributes to blunted NO-mediated endothelium-dependent dilation in young adults with MDD.

Mitochondrial DNA integrity and function are critical for endothelium-dependent vasodilation in rats with metabolic syndrome

Endothelial dysfunction in diabetes is generally attributed to oxidative stress, but this view is challenged by observations showing antioxidants do not eliminate diabetic vasculopathy. As an alternative to oxidative stress-induced dysfunction, we interrogated if impaired mitochondrial function in endothelial cells is central to endothelial dysfunction in the metabolic syndrome. We observed reduced coronary arteriolar vasodilation to the endothelium-dependent dilator, acetylcholine (Ach), in Zucker Obese Fatty rats (ZOF, 34 ± 15% [mean ± standard deviation] 10-3 M) compared to Zucker Lean rats (ZLN, 98 ± 11%). This reduction in dilation occurred concomitantly with mitochondrial DNA (mtDNA) strand lesions and reduced mitochondrial complex activities in the endothelium of ZOF versus ZLN. To demonstrate endothelial dysfunction is linked to impaired mitochondrial function, administration of a cell-permeable, mitochondria-directed endonuclease (mt-tat-EndoIII), to repair oxidatively modified DNA in ZOF, restored mitochondrial function and vasodilation to Ach (94 ± 13%). Conversely, administration of a cell-permeable, mitochondria-directed exonuclease (mt-tat-ExoIII) produced mtDNA strand breaks in ZLN, reduced mitochondrial complex activities and vasodilation to Ach in ZLN (42 ± 16%). To demonstrate that mitochondrial function is central to endothelium-dependent vasodilation, we introduced (via electroporation) liver mitochondria (from ZLN) into the endothelium of a mesenteric vessel from ZOF and restored endothelium-dependent dilation to vasoactive intestinal peptide (VIP at 10-5 M, 4 ± 3% vasodilation before mitochondrial transfer and 48 ± 36% after transfer). Finally, to demonstrate mitochondrial function is key to endothelium-dependent dilation, we administered oligomycin (mitochondrial ATP synthase inhibitor) and observed a reduction in endothelium-dependent dilation. We conclude that mitochondrial function is critical for endothelium-dependent vasodilation.

Role of Perivascular Adipose Tissue and Exercise on Arterial Function with Obesity

Adipose tissue and arterial dysfunction are common in the obese state. Perivascular adipose tissue (PVAT) plays an important role in mediating arterial health, and with obesity, the PVAT dysfunction negatively affects arterial health. Exercise training exerts direct and beneficial effects on PVAT, providing an additional and novel pathway by which exercise can improve arterial health in diseased populations.

Chronic stress and endothelial dysfunction: mechanisms, experimental challenges, and the way ahead

Although chronic stress is an important risk factor for cardiovascular diseases (CVD) onset, the underlying mechanisms driving such pathophysiological complications remain relatively unknown. Here, dysregulation of innate stress response systems and the effects of downstream mediators are strongly implicated, with the vascular endothelium emerging as a primary target of excessive glucocorticoid and catecholamine action. Therefore, this review article explores the development of stress-related endothelial dysfunction by focusing on the following: 1) assessing the phenomenon of stress and complexities surrounding this notion, 2) discussing mechanistic links between chronic stress and endothelial dysfunction, and 3) evaluating the utility of various preclinical models currently employed to study mechanisms underlying the onset of stress-mediated complications such as endothelial dysfunction. The data reveal that preclinical models play an important role in our efforts to gain an increased understanding of mechanisms underlying stress-mediated endothelial dysfunction. It is our understanding that this provides a good foundation going forward, and we propose that further efforts should be made to 1) more clearly define the concept of stress and 2) standardize protocols of animal models with specific guidelines to better indicate the mental complications that are simulated.

Oxidative Stress Contributes to Microvascular Endothelial Dysfunction in Men and Women With Major Depressive Disorder

RATIONALE

In rodent models of depression, oxidative stress-induced reductions in NO bioavailability contribute to impaired endothelium-dependent dilation. Endothelial dysfunction is evident in major depressive disorder (MDD); however, the molecular mediators remain undefined.

OBJECTIVE

We sought to translate preclinical findings to humans by testing the role of oxidative stress in mediating microvascular endothelial dysfunction, including potential modulatory influences of sex, in MDD.

METHODS AND RESULTS

Twenty-four treatment-naive, otherwise healthy, young adults with MDD (14 women; 18-23 years) and 20 healthy adults (10 women; 19-30 years) participated. Red blood cell flux (laser Doppler flowmetry) was measured during graded intradermal microdialysis perfusion of the endothelium-dependent agonist acetylcholine, alone and in combination with an NO synthase inhibitor (L-NAME), a superoxide scavenger (Tempol), and an NADPH oxidase inhibitor (apocynin), as well as during perfusion of the endothelium-independent agonist sodium nitroprusside. Tissue oxidative stress markers (eg, nitrotyrosine abundance, superoxide production) were also quantified. Endothelium-dependent dilation was blunted in MDD and mediated by reductions in NO-dependent dilation. Endothelium-independent dilation was likewise attenuated in MDD. In MDD, there were no sex differences in either NO-mediated endothelium-dependent dilation or endothelium-independent dilation. Acute scavenging of superoxide or inhibition of NADPH oxidase improved NO-dependent dilation in MDD. Expression and activity of oxidative stress markers were increased in MDD. In a subset of adults with MDD treated with a selective serotonin reuptake inhibitor for their depressive symptoms and in remission (n=8; 7 women; 19-37 years), NO-mediated endothelium-dependent dilation was preserved, but endothelium-independent dilation was impaired, compared with healthy adults.

CONCLUSIONS

Oxidative stress-induced reductions in NO-dependent dilation, as well as alterations in vascular smooth muscle function, directly contribute to microvascular dysfunction in MDD. Strategies targeting vascular oxidative stress may be viable therapeutic options for improving NO-mediated endothelial function and reducing cardiovascular risk in MDD.

Exercise training prevents the perivascular adipose tissue-induced aortic dysfunction with metabolic syndrome

The aim of the study was to determine the effects of exercise training on improving the thoracic perivascular adipose tissue (tPVAT) phenotype (inflammation, oxidative stress, and proteasome function) in metabolic syndrome and its subsequent actions on aortic function.

Methods

Lean and obese (model of metabolic syndrome) Zucker rats (n=8/group) underwent 8-weeks of control conditions or treadmill exercise (70% of max speed, 1 h/day, 5 days/week). At the end of the intervention, the tPVAT was removed and conditioned media was made. The cleaned aorta was attached to a force transducer to assess endothelium-dependent and independent dilation in the presence or absence of tPVAT-conditioned media. tPVAT gene expression, inflammatory /oxidative phenotype, and proteasome function were assessed.

Results

The main findings were that Ex induced: (1) a beige-like, anti-inflammatory tPVAT phenotype; (2) a greater abundance of ^•NO in tPVAT; (3) a reduction in tPVAT oxidant production; and (4) an improved tPVAT proteasome function. Regarding aortic function, endothelium-dependent dilation was greater in exercised lean and obese groups vs. controls (p < 0.05). Lean control tPVAT improved aortic relaxation, whereas obese control tPVAT decreased aortic relaxation. In contrast, the obese Ex-tPVAT increased aortic dilation, whereas the lean Ex-tPVAT did not affect aortic dilation.

Conclusion

Overall, exercise had the most dramatic impact on the obese tPVAT reflecting a change towards an environment with less oxidant load, less inflammation and improved proteasome function. Such beneficial changes to the tPVAT micro-environment with exercise likely played a significant role in mediating the improvement in aortic function in metabolic syndrome following 8 weeks of exercise.

Increased circulating microparticles in streptozotocin-induced diabetes propagate inflammation contributing to microvascular dysfunction

KEY POINTS

Circulating microparticles (MPs) are elevated in many cardiovascular diseases and have been considered as biomarkers of disease prognosis; however, current knowledge of MP functions has been mainly derived from in vitro studies and their precise impact on vascular inflammation and disease progression remains obscure. Using a diabetic rat model, we identified a >130-fold increase in MPs in plasma of diabetic rats compared to normal rats, the majority of which circulated as aggregates, expressing multiple cell markers and largely externalized phosphatidylserine; vascular images illustrate MP biogenesis and their manifestations in microvessels of diabetic rats. Using combined single microvessel perfusion and systemic cross-transfusion approaches, we delineated how diabetic MPs propagate inflammation in the vasculature and transform normal microvessels into an inflammatory phenotype observed in the microvessels of diabetic rats. Our observations derived from animal studies resembling conditions in diabetic patients, providing a mechanistic insight into MP-mediated pathogenesis of diabetes-associated multi-organ microvascular dysfunction.

ABSTRACT

In various cardiovascular diseases, microparticles (MPs), the membrane-derived vesicles released during cell activation, are markedly increased in the circulation. These MPs have been recognized to play diverse roles in the regulation of cellular functions. However, current knowledge of MP function has been largely derived from in vitro studies. The precise impact of disease-induced MPs on vascular inflammation and disease progression remains obscure. In this study we investigated the biogenesis, profile and functional roles of circulating MPs using a streptozotocin-induced diabetic rat model with well-characterized microvascular functions. Our study revealed a >130-fold increase in MPs in the plasma of diabetic rats compared to normal rats. The majority of these MPs originate from platelets, leukocytes and endothelial cells (ECs), and circulate as aggregates. Diabetic MPs show greater externalized phosphatidylserine (PS) than normal MPs. When diabetic plasma or isolated diabetic MPs were perfused into normal microvessels or systemically transfused into normal rats, MPs immediately adhered to endothelium and subsequently mediated leukocyte adhesion. These microvessels then exhibited augmented permeability responses to inflammatory mediators, replicating the microvascular manifestations observed in diabetic rats. These effects were abrogated when MPs were removed from diabetic plasma or when diabetic MPs were pre-coated with a lipid-binding protein, annexin V, suggesting externalized PS to be key in mediating MP interactions with endothelium and leukocytes. Our study demonstrated that the elevated MPs in diabetic plasma are actively involved in the propagation of vascular inflammation through their adhesive surfaces, providing mechanistic insight into the pathogenesis of multi-organ vascular dysfunction that commonly occurs in diabetic patients.

Short- and long-term administration of the non-steroidal mineralocorticoid receptor antagonist finerenone opposes metabolic syndrome-related cardio-renal dysfunction

AIM

To determine whether non-steroidal mineralocorticoid receptor (MR) antagonists oppose metabolic syndrome-related end-organ, i.e. cardiac, damage.

MATERIALS AND METHODS

In Zucker fa/fa rats, a rat model of metabolic syndrome, we assessed the effects of the non-steroidal MR antagonist finerenone (oral 2 mg/kg/day) on left ventricular (LV) function, haemodynamics and remodelling (using echocardiography, magnetic resonance imaging and biochemical methods).

RESULTS

Long-term (90 days) finerenone modified neither systolic blood pressure nor heart rate, but reduced LV end-diastolic pressure and LV end-diastolic pressure-volume relationship, without modifying LV end-systolic pressure and LV end-systolic pressure-volume relationship. Simultaneously, long-term finerenone reduced both LV systolic and diastolic diameters, associated with reductions in LV weight and LV collagen density, while proteinuria and renal nGAL expression were reduced. Short-term (7 days) finerenone improved LV haemodynamics and reduced LV systolic diameter, without modifying LV diastolic diameter. Moreover, short-term finerenone increased myocardial tissue perfusion and reduced myocardial reactive oxygen species, while plasma nitrite levels, an indicator of nitric oxide (NO) bio-availability, were increased.

CONCLUSIONS

In rats with metabolic syndrome, the non-steroidal MR antagonist finerenone opposed metabolic syndrome-related diastolic cardiac dysfunction and nephropathy. This involved acute effects, such as improved myocardial perfusion, reduced oxidative stress/increased NO bioavailability, as well as long-term effects, such as modifications in the myocardial structure.

Cerebrovascular dysfunction with stress and depression

Maintenance of adequate tissue perfusion through a dense network of cerebral microvessels is critical for the perseveration of normal brain function. Regulation of the cerebral blood flow has to ensure adequate delivery of nutrients and oxygen with moment-to-moment adjustments to avoid both hypo- and hyper-perfusion of the brain tissue. Even mild impairments of cerebral blood flow regulation can have significant implications on brain function. Evidence suggests that chronic stress and depression elicits multifaceted functional impairments to the cerebral microcirculation, which plays a critical role in brain health and the pathogenesis of stress-related cognitive impairment and cerebrovascular events. Identifying the functional and structural changes to the brain that are induced by stress is crucial for achieving a realistic understanding of how related illnesses, which are highly disabling and with a large economic cost, can be managed or reversed. This overview discusses the stress-induced alterations in neurovascular coupling with specific attention to cerebrovascular regulation (endothelial dependent and independent vasomotor function, microvessel density). The pathophysiological consequences of cerebral microvascular dysfunction with stress and depression are explored.