Plasma xanthine oxidase activity is related to increased sodium and left ventricular hypertrophy in resistant hypertension

Hitting the (bio)mark part 1: selecting and measuring biomarkers in cardiovascular research

Cardiovascular studies, including nursing research, frequently integrate biomarkers for diagnostic, prognostic, monitoring, and therapeutic insights. However, effective utilization of biomarker data demands careful consideration. In the study design phase, researchers must select biomarkers that align with study objectives while considering resources and logistical factors. Additionally, a nuanced understanding of disease pathophysiology and biomarker characteristics is needed. During data collection, suitable experimental conditions and assays need to be defined. Whether researchers opt to manage these steps internally or outsource some, a comprehensive understanding of biomarker selection and experiments remains crucial. In this article, part 1 of 2, we provide an overview of considerations for the design to measurement phases of biomarker studies.

The hydrogen sulfide donor 4-carboxyphenyl-isothiocyanate decreases blood pressure and promotes cardioprotective effect through reduction of oxidative stress and nuclear factor kappa B/matrix metalloproteinase (MMP)-2 axis in hypertension

AIMS

Our aim was to evaluate whether the hydrogen sulfide (H2S) donor, 4-carboxyphenyl-isothiocyanate (4-CPI), exerts cardioprotective effect in the two kidney- one clip (2K-1C) rats through oxidative stress and MMP-2 activity attenuation and compare it with the classical H2S donor, Sodium Hydrosulfide (NaHS).

MATERIALS AND METHODS

Renovascular hypertension (two kidneys-one clip; 2K-1C) was surgically induced in male Wistar rats. After two weeks, normotensive (2K) and hypertensive rats were intraperitoneally treated with vehicle (0.6 % dimethyl sulfoxide), NaHS (0.24 mg/Kg/day) or with 4-CPI (0.24 mg/Kg/day), for more 4 weeks. Systolic blood pressure (SBP) was evaluated weekly by tail-cuff plethysmography. Heart function was assessed by using the Millar catheter. Cardiac hypertrophy and fibrosis were evaluated by hematoxylin and eosin, and Picrosirius Red staining, respectively. The H2S was analyzed using WSP-1 fluorimetry and the cardiac oxidative stress was measured by lucigenin chemiluminescence and Amplex Red. MMP-2 activity was measured by in-gel gelatin or in situ zymography assays. Nox1, gp91phox, MMP-2 and the phospho-p65 subunit (Serine 279) nuclear factor kappa B (NF-κB) levels were evaluated by Western blotting.

KEY FINDINGS

4-CPI reduced blood pressure in hypertensive rats, decreased cardiac remodeling and promoted cardioprotection through the enhancement of cardiac H2S levels. An attenuation of oxidative stress, with inactivation of the p65-NF-κB/MMP-2 axis was similarly observed after NaHS or 4-CPI treatment in 2K-1C hypertension.

SIGNIFICANCE

H2S is a mediator that promotes cardioprotective effects and decreases blood pressure, and 4-CPI seems to be a good candidate to reverse the maladaptive remodeling and cardiac dysfunction in renovascular hypertension.

Emerging Roles of Xanthine Oxidoreductase in Chronic Kidney Disease

Xanthine Oxidoreductase (XOR) is a ubiquitous, essential enzyme responsible for the terminal steps of purine catabolism, ultimately producing uric acid that is eliminated by the kidneys. XOR is also a physiological source of superoxide ion, hydrogen peroxide, and nitric oxide, which can function as second messengers in the activation of various physiological pathways, as well as contribute to the development and the progression of chronic conditions including kidney diseases, which are increasing in prevalence worldwide. XOR activity can promote oxidative distress, endothelial dysfunction, and inflammation through the biological effects of reactive oxygen species; nitric oxide and uric acid are the major products of XOR activity. However, the complex relationship of these reactions in disease settings has long been debated, and the environmental influences and genetics remain largely unknown. In this review, we give an overview of the biochemistry, biology, environmental, and current clinical impact of XOR in the kidney. Finally, we highlight recent genetic studies linking XOR and risk for kidney disease, igniting enthusiasm for future biomarker development and novel therapeutic approaches targeting XOR.

Hitting the (bio)mark part 2: analyzing, interpreting, and reporting biomarker data in cardiovascular research

Incorporating biomarkers into cardiovascular studies, including nursing research, is a common approach when identifying underlying mechanisms and providing targets for intervention. However, effective utilization of biomarker data demands careful consideration. In the analysis, interpretation, and reporting phase, there are many facets to consider, including non-normality of the data, normalization procedures, and potential confounding influences of other clinical data. Furthermore, as many studies focus on patient-reported outcomes, it is important that the analysis and interpretation of biomarkers in relation to patient-reported outcomes is rigorous and reproducible. In this article, part 2 of 2, we provide an overview of considerations for the analysis, interpretation, and reporting phases of biomarker studies. We also provide an example of these steps.

Inflammation and hypertension: Underlying mechanisms and emerging understandings

Hypertension remains a major contributor to cardiovascular disease (CVD), a leading cause of global death. One of the major insults that drive increased blood pressure is inflammation. While it is the body's defensive response against some homeostatic imbalances, inflammation, when dysregulated, can be very deleterious. In this review, we highlight and discuss the causative relationship between inflammation and hypertension. We critically discuss how the interplay between inflammation and reactive oxygen species evokes endothelial damage and dysfunction, ultimately leading to narrowing and stiffness of blood vessels. This, along with phenotypic switching of the vascular smooth muscle cells and the abnormal increase in extracellular matrix deposition further exacerbates arterial stiffness and noncompliance. We also discuss how hyperhomocysteinemia and microRNA act as links between inflammation and hypertension. The premises we discuss suggest that the blue-sky scenarios for targeting the underlying mechanisms of hypertension necessitate further research.

Interstitial Collagen Loss, Myocardial Remodeling, and Function in Primary Mitral Regurgitation

Interstitial collagen loss and cardiomyocyte ultrastructural damage accounts for left ventricular (LV) sphericity and decrease in LV twist and circumferential strain. Normal LV diastolic function belies significantly abnormal left atrial (LA) function and early LV diastolic untwist rate. This underscores the complex interplay of LV and LA myocardial remodeling and function in the pathophysiology of primary mitral regurgitation. In this study, we connect LA function with LV systolic and diastolic myocardial remodeling and function using cardiac magnetic resonance tissue tagging in primary mitral regurgitation.

Racial Differences in XO (Xanthine Oxidase) and Mitochondrial DNA Damage-Associated Molecular Patterns in Resistant Hypertension

BACKGROUND

We previously reported increased plasma XO (xanthine oxidase) activity in patients with resistant hypertension. Increased XO can cause mitochondrial DNA damage and promote release of fragments called mitochondrial DNA damage-associated molecular patterns (mtDNA DAMPs). Here, we report racial differences in XO activity and mtDNA DAMPs in Black and White adults with resistant hypertension.

METHODS

This retrospective study includes 91 resistant hypertension patients (44% Black, 47% female) with blood pressure >140/90 mm Hg on ≥4 medications and 37 normotensive controls (30% Black, 54% female) with plasma XO activity, mtDNA DAMPs, and magnetic resonance imaging of left ventricular morphology and function.

RESULTS

Black-resistant hypertension patients were younger (mean age 52±10 versus 59±10 years; P=0.001), with higher XO activity and left ventricular wall thickness, and worse diastolic dysfunction than White resistant hypertension patients. Urinary sodium excretion (mg/24 hour per kg) was positively related to left ventricular end-diastolic volume (r=0.527, P=0.001) and left ventricular mass (r=0.394, P=0.02) among Black but not White resistant hypertension patients. Patients with resistant hypertension had increased mtDNA DAMPs versus controls (P<0.001), with Black mtDNA DAMPS greater than Whites (P<0.001). Transmission electron microscopy of skeletal muscle biopsies in resistant hypertension patients demonstrates mitochondria cristae lysis, myofibrillar loss, large lipid droplets, and glycogen accumulation.

CONCLUSIONS

These data warrant a large study to examine the role of XO and mitochondrial mtDNA DAMPs in cardiac remodeling and heart failure in Black adults with resistant hypertension.

Sulfide and transition metals - A partnership for life

Sulfide and transition metals often came together in Biology. The variety of possible structural combinations enabled living organisms to evolve an array of highly versatile metal-sulfide centers to fulfill different physiological roles. The ubiquitous iron‑sulfur centers, with their structural, redox, and functional diversity, are certainly the best-known partners, but other metal-sulfide centers, involving copper, nickel, molybdenum or tungsten, are equally crucial for Life. This review provides a concise overview of the exclusive sulfide properties as a metal ligand, with emphasis on the structural aspects and biosynthesis. Sulfide as catalyst and as a substrate is discussed. Different enzymes are considered, including xanthine oxidase, formate dehydrogenases, nitrogenases and carbon monoxide dehydrogenases. The sulfide effect on the activity and function of iron‑sulfur, heme and zinc proteins is also addressed.

Oxidative stress in cardiac hypertrophy: From molecular mechanisms to novel therapeutic targets

When faced with increased workload the heart undergoes remodelling, where it increases its muscle mass in an attempt to preserve normal function. This is referred to as cardiac hypertrophy and if sustained, can lead to impaired contractile function. Experimental evidence supports oxidative stress as a critical inducer of both genetic and acquired forms of cardiac hypertrophy, a finding which is reinforced by elevated levels of circulating oxidative stress markers in patients with cardiac hypertrophy. These observations formed the basis for using antioxidants as a therapeutic means to attenuate cardiac hypertrophy and improve clinical outcomes. However, the use of antioxidant therapies in the clinical setting has been associated with inconsistent results, despite antioxidants having been shown to exert protection in several animal models of cardiac hypertrophy. This has forced us to revaluate the mechanisms, both upstream and downstream of oxidative stress, where recent studies demonstrate that apart from conventional mediators of oxidative stress, metabolic disturbances, mitochondrial dysfunction and inflammation as well as dysregulated autophagy and protein homeostasis contribute to disease pathophysiology through mechanisms involving oxidative stress. Importantly, novel therapeutic targets have been identified to counteract oxidative stress and attenuate cardiac hypertrophy but more interestingly, the repurposing of drugs commonly used to treat metabolic disorders, hypertension, peripheral vascular disease, sleep disorders and arthritis have also been shown to improve cardiac function through suppression of oxidative stress. Here, we review the latest literature on these novel mechanisms and intervention strategies with the aim of better understanding the complexities of oxidative stress for more precise targeted therapeutic approaches to prevent cardiac hypertrophy.

Xanthine oxidase inhibition attenuates doxorubicin-induced cardiotoxicity in mice

Accumulating evidence suggests that high serum uric acid (UA) is associated with left ventricular (LV) dysfunction. Although xanthine oxidase (XO) activation is a critical regulatory mechanism of the terminal step in ATP and purine degradation, the pathophysiological role of cardiac tissue XO in LV dysfunction remains unclear. We herein investigated the role and functional significance of tissue XO activity in doxorubicin-induced cardiotoxicity. Either doxorubicin (10 mg/kg) or vehicle was intraperitonially administered in a single injection to mice. Mice were treated with or without oral XO-inhibitors (febuxostat 3 mg/kg/day or topiroxostat 5 mg/kg/day) for 8 days starting 24 h before doxorubicin injection. Cardiac tissue XO activity measured by a highly sensitive assay with liquid chromatography/mass spectrometry and cardiac UA content were significantly increased in doxorubicin-treated mice at day 7 and dramatically reduced by XO-inhibitors. Accordingly, XO-inhibitors substantially improved LV ejection fraction (assessed by echocardiography) and LV developed pressure (assessed by ex vivo Langendorff heart perfusion) impaired by doxorubicin administration. This was associated with an increase in XO-derived hydrogen peroxide production with concomitant upregulation of apoptotic and ferroptotic pathways, all of which were reduced by XO-inhibitors. Furthermore, metabolome analyses revealed enhanced purine metabolism in doxorubicin-treated hearts, and XO-inhibitors suppressed the serial metabolic reaction of hypoxanthine-xanthine-UA, the paths of ATP and purine degradation. In summary, doxorubicin administration induces cardiac tissue XO activation associated with impaired LV function. XO-inhibitors attenuate doxorubicin-induced cardiotoxicity through inhibition of XO-derived oxidative stress and cell death signals as well as the maintenance of cardiac energy metabolism associated with modulation of the purine metabolic pathway.

Relationship between serum uric acid level and vascular injury markers in hemodialysis patients

PURPOSE

It has been reported that hyperuricemia causes vascular endothelial injury. Most hemodialysis patients present with hyperuricemia and also with vascular injury, resulting in cardiovascular diseases (CVD). However, the association of serum uric acid (sUA) with vascular injury markers in hemodialysis patients remains unclear. This study aimed to investigate this and discuss the mechanism by which uric acid causes vascular injury.

METHODS

We enrolled 48 Japanese maintenance hemodialysis patients without any history of CVD. The association between sUA level and three vascular injury markers (reactive hyperemia index [RHI], ankle-brachial index [ABI], and cardio ankle vascular index [CAVI]) was investigated by linear- and logistic regression analyses.

RESULTS

The median natural logarithm RHI (LnRHI) was 0.36. Linear regression analysis revealed a significant positive correlation between sUA level and LnRHI (β = 0.42, p = 0.001) in all patients. Moreover, a significant, strongly positive correlation was observed between sUA and LnRHI in patients who were treated with xanthine oxidase inhibitors (XOIs) (β = 0.75, p = 0.001). Further, the linear analysis showed a significant negative correlation between sUA level and CAVI in patients who were treated with XOIs (β = - 0.52, p = 0.049). sUA level was not significantly associated with ABI abnormality.

CONCLUSIONS

It is possible that a high level of sUA is significantly associated with better vascular endothelial function and condition of vascular tone in hemodialysis patients who were treated with XOIs. The findings suggest a significant paradox between sUA level and vascular endothelial function in hemodialysis patients; however, the opposite has been reported in patients without hemodialysis.

Cardio-renal protective effect of the xanthine oxidase inhibitor febuxostat in the 5/6 nephrectomy model with hyperuricemia

Although hyperuricemia has been shown to be associated with the progression of cardiovascular disorder and chronic kidney disease (CKD), there is conflicting evidence as to whether xanthine oxidase (XO) inhibitors confer organ protection besides lowering serum urate levels. In this study, we addressed the cardio-renal effects of XO inhibition in rodent CKD model with hyperuricemia. Sprague-Dawley rats underwent 5/6 nephrectomy and received a uricase inhibitor oxonic acid for 8 weeks (RK + HUA rats). In some rats, a XO inhibitor febuxostat was administered orally. Compared with control group, RK + HUA group showed a significant increase in albuminuria and renal injury. Febuxostat reduced serum uric acid as well as urinary albumin levels. Histological and immunohistochemical analysis of the kidney revealed that febuxostat alleviated glomerular, tubulointerstitial, and arteriolar injury in RK + HUA rats. Moreover, in the heart, RK + HUA showed individual myofiber hypertrophy and cardiac fibrosis, which was significantly attenuated by febuxostat. We found that renal injury and the indices of cardiac changes were well correlated, confirming the cardio-renal interaction in this model. Finally, NF-E2-related factor 2 (Nrf2) and the downstream target heme oxygenase-1 (HO-1) protein levels were increased both in the heart and in the kidney in RK + HUA rats, and these changes were alleviated by febuxostat, suggesting that tissue oxidative stress burden was attenuated by the treatment. These data demonstrate that febuxostat protects against cardiac and renal injury in RK + HUA rats, and underscore the pathological importance of XO in the cardio-renal interaction.

Pathological Roles of Mitochondrial Oxidative Stress and Mitochondrial Dynamics in Cardiac Microvascular Ischemia/Reperfusion Injury

Mitochondria are key regulators of cell fate through controlling ATP generation and releasing pro-apoptotic factors. Cardiac ischemia/reperfusion (I/R) injury to the coronary microcirculation has manifestations ranging in severity from reversible edema to interstitial hemorrhage. A number of mechanisms have been proposed to explain the cardiac microvascular I/R injury including edema, impaired vasomotion, coronary microembolization, and capillary destruction. In contrast to their role in cell types with higher energy demands, mitochondria in endothelial cells primarily function in signaling cellular responses to environmental cues. It is clear that abnormal mitochondrial signatures, including mitochondrial oxidative stress, mitochondrial fission, mitochondrial fusion, and mitophagy, play a substantial role in endothelial cell function. While the pathogenic role of each of these mitochondrial alterations in the endothelial cells I/R injury remains complex, profiling of mitochondrial oxidative stress and mitochondrial dynamics in endothelial cell dysfunction may offer promising potential targets in the search for novel diagnostics and therapeutics in cardiac microvascular I/R injury. The objective of this review is to discuss the role of mitochondrial oxidative stress on cardiac microvascular endothelial cells dysfunction. Mitochondrial dynamics, including mitochondrial fission and fusion, are critically discussed to understand their roles in endothelial cell survival. Finally, mitophagy, as a degradative mechanism for damaged mitochondria, is summarized to figure out its contribution to the progression of microvascular I/R injury.

Beneficial effects of Codonopsis lanceolata extract on systolic blood pressure levels in prehypertensive adults: A double-blind, randomized controlled trial

Codonopsis lanceolata (CL) extract was shown to have antihypertensive effects in hypertensive rats. This randomized controlled trial was designed to investigate the ability of CL extract to prevent hypertension (HTN) in prehypertensive subjects. Eighty subjects aged 19-60 years with a systolic blood pressure (BP) of 120-139 mmHg and a diastolic BP of 80-89 mmHg were recruited over 3 months. Subjects were randomized 1:1 to a CL group and a placebo (PL) group and administered CL extract and starch, respectively, for 6 weeks. (BP) was measured and blood sampled at baseline and at the end of the trial. Relative to baseline, systolic BP was significantly decreased, and catalase activity was significantly increased following CL treatment in both the elevated systolic BP and stage 1 HTN subgroups. In the elevated systolic BP subgroup, serum nitrite concentration relative to baseline was significantly increased in CL compared to PL treated subjects (p = .038). In subjects with stage 1 HTN, high sensitivity C-reactive protein (p = .020) and malondialdehyde (p = .039) showed significantly greater reductions from baseline in the CL than in the PL group. In summary, CL was effective in preventing endothelial dysfunction, inflammation, and lipid peroxidation in prehypertensive subjects, with these effects differing according to baseline systolic BP levels.