URAT1-selective inhibition ameliorates insulin resistance by attenuating diet-induced hepatic steatosis and BAT whitening in mice

Background

Accumulating evidence suggests that high uric acid is strongly associated with obesity and metabolic syndrome and drives the development of non-alcoholic fatty liver disease (NAFLD) and insulin resistance. Although urate transporter-1 (URAT1), which is primarily expressed in the kidney, plays a critical role in the development of hyperuricemia, its pathophysiological implication in NAFLD and insulin resistance remains unclear.

Objectives

We hypothesizes that URAT1 plays an important role in obesity-induced metabolic disorders, and URAT1-selective inhibitor treatment ameliorates systemic insulin resistance, NAFLD and adipose tissue dysfunction using diet-induced obese mice.

Methods

Mice fed a high-fat diet (HFD) for 16 to 18 weeks or a normal-fat diet (NFD) were treated with or without a novel oral URAT1-selective inhibitor (dotinurad [50 mg/kg/day]) for another 4 weeks.

Results

Dotinurad administration significantly ameliorated HFD-induced obesity and insulin resistance. We found that URAT1 was also expressed in the liver and brown adipose tissue (BAT) other than kidney. HFD markedly induced NAFLD, which was characterized by severe hepatic steatosis, as well as the elevation of serum ALT activity and tissue inflammatory cytokine genes (Ccl2 and TNFα), all of which were attenuated by dotinurad. Likewise, HFD significantly increased URAT1 expression in BAT, resulting in the lipid accumulation (whitening of BAT) and increased production of tissue reactive oxygen species, which were reduced by dotinurad via UCP1 activation.

Conclusions

A novel URAT1-selective inhibitor, dotinurad, ameliorates insulin resistance by attenuating hepatic steatosis and promoting rebrowning of lipid-rich BAT in HFD-induced obese mice. URAT1 serves as a key regulator of the pathophysiology of metabolic syndrome, and may be a new therapeutic target for insulin-resistant individuals, particularly those with concomitant NAFLD.

Funding Acknowledgement

Type of funding sources: None.

Xanthine oxidase inhibition attenuates doxorubicin-induced cardiotoxicity in mice

Background

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.

Objectives

We hypothesized that cardiac XO is activated in doxorubicin-induced LV dysfunction, and XO inhibitors ameliorate LV function by inhibiting cell death signals as well as by modifying cardiac purine metabolism.

Methods

Either doxorubicin (10 mg/kg) or vehicle was intraperitonially administered in a single injection to ICR 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 hours before doxorubicin-injection. The LV function was assessed by echocardiography at day 6 and by ex vivo heart perfusion at day 7.

Results

Cardiac tissue XO activity measured by a highly sensitive assay with liquid chromatography/mass spectrometry (n=8 each) and cardiac UA content (n=3–6) were significantly increased in doxorubicin-treated mice at day 7 and dramatically reduced by XO inhibitors. Accordingly, XO inhibitors substantially improved LV ejection fraction (n=8 each) and LV developed pressure (n=9 each) that had been impaired by doxorubicin administration. Intriguingly, the expression of GPX4, a negative regulator of ferroptosis, was decreased in doxorubicin-treated hearts but improved by XO inhibitors (n=6 each). Furthermore, metabolome analyses revealed an enhanced purine metabolism in doxorubicin-treated hearts, and XO inhibitors suppressed the serial metabolic reaction of hypoxanthine–xanthine–UA.

Conclusions

Doxorubicin administration induces cardiac tissue XO activation associated with an impaired LV function. XO inhibition attenuates the doxorubicin-induced cardiotoxicity partly through an anti-ferroptotic effect and the conservation of tissue ATP levels by modulating purine metabolism. The present study suggests that pharmacological XO inhibition represents a potential therapeutic strategy for the treatment of doxorubicin-induced cardiotoxicity.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): This study was supported in part by grants-in-aid for Ministry of Education Culture, Sports, Science and Technology.

Biphasic action of aldosterone on Akt signaling in cardiomyocytes

Both aldosterone and Akt signaling play pivotal roles in the pathogenesis of heart failure. However, little is known about the correlation between them. We herein investigated whether aldosterone interacts with Akt signaling in a coordinated manner in cardiomyocytes. Neonatal rat cardiomyocytes were stimulated with aldosterone for either a short (10-min) or long (24-h) time. The phosphorylation of Akt and its downstream effector, GSK3β, were transiently increased after short-term stimulation, which was blocked by either PI3K or Na(+)/H(+) exchanger inhibitors, but not by the mineralocorticoid receptor antagonist, eplerenone. Long-term stimulation also significantly increased Akt-GSK3β phosphorylation and this effect was reduced by eplerenone. Thus, these results suggest that aldosterone activates Akt signaling via a biphasic reaction that occurs through different cascades. To understand the significance of the rapid action of aldosterone, cardiomyocytes were exposed to hydrogen peroxide for from 10 to 60 min. A short-term aldosterone stimulation (for up to 30 min) significantly protected cardiomyocytes from oxidative stress-induced cellular damage. Eplerenone did not abrogate this beneficial effect, while a PI3K inhibitor did. Therefore, during the early phase, aldosterone has favorable effects on cardiomyocytes, partly by acute activation of a mineralocorticoid receptor-independent cascade through the Na(+)/H(+) exchanger, PI3K, and Akt. In contrast, its persistent activity produces pathological effects partly by chronic Akt activation in a mineralocorticoid receptor-dependent manner.

Angiographic features at ischemia- or infarct-related sites in patients with acute coronary syndrome: morphology changing in a relatively short time

OBJECTIVES

Coronary cineangiography was reviewed in patients with acute coronary syndrome to investigate whether angiographic features at identifiable ischemia- or infarct-related lesions can change in terms of luminal diameter and morphology in a short period after development, and whether the amount of thrombus with/without underlying ruptured plaque is the major determinant.

METHODS

The present study included 72 patients with unstable angina, 118 with acute myocardial infarction (< 1 month after onset) and 137 with old myocardial infarction (> or = 1 month after onset). The coronary angiographic findings were compared with those from patients with stable effort angina. The groups of patients were subdivided into two groups based on whether antiplatelet and/or anticoagulant therapy, or fibrinolytic therapy with subsequent anticoagulant agents (antiplatelet and/or anticoagulant, or fibrinolytic therapy) were administered. The morphologies of the ischemia- or infarct-related lesions were classified as totally occlusive, simple (Type I lesion) or complex. Complex lesions were further subdivided into Type IIa lesions indicative of the presence of thrombus accumulation with/without an underlying ruptured atheromatous plaque, e.g., narrowing with irregular, poorly defined or hazy borders, sharp leading or trailing edges that overhang or are perpendicular to vessel walls, and globular endoluminal negative images, Type IIb lesions with two or more serial, closely spaced narrowings together with multiple irregularities, and Type IIc lesions indicative of the presence of some parts of ruptured plaque with a smaller amount of thrombus, e.g., luminal narrowing with extraluminal contrast pooling, single or paired short thin linear radiolucencies with/without a variable degree of outpouching, and narrowing with definite outpouching with/without radiolucency, and Type IId lesions showing narrowing with morphology not included in Type IIa-IIc lesions. The coronary angiographic findings were related to the elapsed time before the coronary angiographic study, and whether each patient underwent antiplatelet and/or anticoagulant, or fibrinolytic therapy.

RESULTS

Ischemia- or infarct-related lesions were totally occlusive in 9.7% of patients with unstable angina, 40.7% of those with acute myocardial infarction and 21.9% of those with old myocardial infarction. Total occlusion was significantly more prevalent in patients with acute myocardial infarction than in those with stable effort angina (23.9%, p < 0.05), and total occlusion was more frequent in patients without antiplatelet and/or anticoagulant, or fibrinolytic drugs (50.6% vs 17.1%, p < 0.01). The presence of total occlusion decreased with time after development, and the decrease was more significant with the use of antiplatelet and/or anticoagulant, or fibrinolytic drugs. Type IIa morphology was significantly prevalent immediately after the initial episode, and Type IIa and IIc morphologies increased in the late period, and were more frequent with the use of antiplatelet and/or anticoagulant, or fibrinolytic drugs.

CONCLUSIONS

The severity of the luminal diameter at ischemia- or infarct-related lesions sites can progress or even regress in a relatively short period in patients with acute coronary syndrome, and the amount of accumulated thrombus with/without underlying ruptured plaque is a major determinant of luminal diameter narrowing and angiographic morphology.

Microvascular angina in a patient with aortic stenosis

A 39-year-old woman had exercise-induced ST segment depression associated with chest pain. Cardiac evaluation revealed moderate aortic stenosis (AS), related to the bicuspid valves, with an aortic mean pressure gradient of 22 mmHg, a calculated aortic valve area of 1.3 cm2 and normal left ventricular (LV) peak systolic and end-diastolic pressures, but no LV hypertrophy, resulting in normal LV wall stress. Although the coronary arteries were angiographically normal, rapid atrial pacing and an intracoronary papaverine injection revealed a significantly decreased coronary flow reserve (CFR), which may have played an important role in the pathogenesis of angina pectoris in this patient. Though the CFR is usually decreased in patients with AS, as well as in microvascular angina, in this particular case, it appeared to have decreased as a consequence of microvascular dysfunction rather than of AS-related mechanisms.

Angiographic coronary morphology in patients with ischemic heart disease

OBJECTIVES

To determine whether ischemia- or infarct-related arteries (IRAs) are accompanied by certain findings specific to clinical settings, coronary cineangiography was reviewed of 71 patients with stable effort angina pectoris (SAP), 72 with unstable angina pectoris (UAP), 118 with acute myocardial infarction (AMI) and 137 with old myocardial infarction (OMI).

METHODS

The morphology of identifiable ischemia- or infarct-related lesions (IRLs) was classified as totally occlusive, and simple (Type I lesion) or complex (Type II lesion). Complex lesions were subdivided into Type IIa lesions (narrowing with irregular, poorly defined or hazy borders, sharp leading or trailing edges that overhang or are perpendicular to vessel walls, and globular endoluminal negative images), Type IIb (2 or more serial, closely spaced narrowings together with multiple irregularities), Type IIc (luminal narrowing with extraluminal contrast pooling, single or paired short thin linear radiolucencies with or without a variable degree of outpouching, and narrowing with definite outpouching with or without radiolucency), and Type IId (narrowing with morphology not included in Types IIa-IIc).

RESULTS

Total occlusive lesions among identifiable IRLs occurred at 17 sites (23.9%) in patients with SAP, 7 (9.7%) with UAP, 48 (40.7%) with AMI and 30 (21.9%) with OMI. The mean diameter stenosis of identifiable IRLs was 89.4% in patients with SAP, 92.0% with UAP, 93.1% with AMI, and 87.4% with OMI. Patent identifiable IRLs in patients with SAP had a significantly higher frequency of Type I lesions (29 sites, 40.8%) compared with those with UAP, AMI and OMI (p < 0.01), followed by a relatively lower occurrence of Types IIa 12 (16.9%), IIb 8 (11.3%), IIc 3 (4.2%) and IId 2 (2.9%) lesions. Patients with UAP were characterized by a higher occurrence of Type IIa (34 sites, 47.2%, p < 0.01) and IIc (13 sites, 18.1%, p < 0.01) lesions compared with those with SAP. Patients with AMI had total occlusion (48 sites, 40.7%, p < 0.05) and Type IIa lesion (38 sites, 32.2%, p < 0.05) more frequently than those with SAP. Patients with OMI showed fewer total occlusions (30 sites, 21.9%), same occurrence of Type IIa lesion (39 sites, 28.5%), and higher occurrence of IIb (23 sites, 16.8%) and IIc (20 sites, 14.6%) than those with AMI.

CONCLUSIONS

This analysis of coronary cineangiographies from patients with UAP, AMI and OMI, which share a common pathogenesis, shows that IRAs, especially IRLs, are associated with certain morphology specific to clinical settings, and that the morphology and severity of stenosis could change in a short period. The present results may improve coronary cineangiography interpretation about pathophysiological issues in vivo affecting coronary circulation.

[Coronary angiography provides considerable in vivo pathophysiological information on coronary artery disease]

Coronary cineangiography (CAG) has various limitations and pitfalls, but is widely accepted for evaluating coronary circulation. The interpretation of CAG focuses mainly on the extent and location of coronary artery disease. However, CAG can also provide considerable and varied in vivo pathophysiological information on coronary artery disease as follows: Certain in vivo angiographic coronary morphologies are indicative of histological findings, such as ruptured atheromatous plaque with/without overlying thrombus. Such morphologies are commonly found in patent ischemia- or infarct-related arteries of patients with acute coronary events in both the acute phase and one month after standard medication, and the diseased portion with the morphology is highly specific to the culprit site. The rupture of plaque and overlaid thrombus is just as important in patients with acute coronary events who survive as in patients who die. Diseased sites with complex lesions are prone to progress toward clinical ischemic episodes. The severity of coronary narrowing immediately after acute coronary events does not influence later left ventricular function if antegrade coronary blood flow without distal filling delay is preserved. Coronary stenosis induced by plaque rupture and superimposed thrombus is likely to improve or disappear with time and/or anticoagulant administration with/without antiplatelet therapy. Such information derived from CAG may improve the understanding and suggest optimal therapeutic strategies of coronary artery disease for individual patients.

Indoxyl-beta-D-glucuronide, the primary emitter of low-level chemiluminescence in plasma of hemodialysis patients

Characteristic light emission induced by the oxidation of hydroxyl radicals has been found in plasma of hemodialysis patients (Agatsuma et al., Clin Chem 1992;38:48-55). We purified a primary emitter, a chemiluminescent component peaking at 430 nm, by anion-exchange chromatography and reversed-phase HPLC. By using proton nuclear magnetic resonance and authentic indoxyl compounds, we determined the primary emitter to be indoxyl-beta-D-glucuronide. Absorption and fluorescence spectra of the purified sample coincided well with those of authentic indoxyl-beta-D-glucuronide, as did the peak in the chemiluminescence emission spectrum. Retention time of the purified sample on reversed-phase HPLC, measured by fluorescence, was also in accordance with that of indoxyl-beta-D-glucuronide. To our knowledge, this is the first identification of a primary emitter of low-level chemiluminescence from a biological source.

Indoxyl-beta-D-glucuronide, the primary emitter of low-level chemiluminescence in plasma of hemodialysis patients

Characteristic light emission induced by the oxidation of hydroxyl radicals has been found in plasma of hemodialysis patients (Agatsuma et al., Clin Chem 1992;38:48-55). We purified a primary emitter, a chemiluminescent component peaking at 430 nm, by anion-exchange chromatography and reversed-phase HPLC. By using proton nuclear magnetic resonance and authentic indoxyl compounds, we determined the primary emitter to be indoxyl-beta-D-glucuronide. Absorption and fluorescence spectra of the purified sample coincided well with those of authentic indoxyl-beta-D-glucuronide, as did the peak in the chemiluminescence emission spectrum. Retention time of the purified sample on reversed-phase HPLC, measured by fluorescence, was also in accordance with that of indoxyl-beta-D-glucuronide. To our knowledge, this is the first identification of a primary emitter of low-level chemiluminescence from a biological source.

Chemiluminescence in the crude extracts of soybean seedlings. Postulated mechanism on the formation of hydroperoxide intermediates

It has been reported that weak chemiluminescence (CL) from crude extracts of soybean seedlings is remarkably enhanced with the addition of various aldehydes (Biochim. Biophys. Acta 1058, 209-216). The reactivity of certain emitter(s) with oxygen species was examined in the autoclaved extracts of seedlings. When samples were reduced by the addition of hydrosulfite, two different types of reactivities in CL were defined. One type showed an initial rapid increase and a subsequent fast decay in CL upon mixing with oxygen. This rapid increase in CL intensity was independent of the presence of aldehydes, and was significantly suppressed by SOD. However, the subsequent slow decay phase in CL was dependent on the presence of aldehydes. In the sample reduced more moderately by borohydride, the same slow decay of CL appeared upon mixing with acetaldehyde and oxygen. This second type of CL was not inhibited by active oxygen scavengers. Hydrogen peroxide added to unreduced (oxidized) samples also elicited CL. Three types of primary emitters may be oxidized to form transient hydroperoxide, and excited for light emission by slightly different ways: two of them are excited by abstraction of one atomic oxygen from the hydroperoxy intermediate with aldehyde or hydrogen peroxide, leading to formation of an excited hydroxide intermediate. The third is excited directly on the binding of superoxide anion to the reduced primary emitter.

Bilirubin chemiluminescence induced by the attack of active oxygen species

Ultraweak chemiluminescence (CL) from bilirubin occurs in the presence of triplet oxygen and is stimulated by the addition of aldehydes. Active oxygen species also enhance bilirubin CL, in the absence of aldehydes. An inhibitory effect of active oxygen scavengers on the CL indicated that active oxygens generated from the decomposition of added hydrogen peroxide or from the xanthine-xanthine oxidase reaction contributed to the CL from bilirubin molecules. However, the contribution of singlet oxygen to the CL disappeared in the presence of formaldehyde. This suggested that the scission of tetrapyrrole bonds via a dioxetane intermediate or the production of triplet carbonyls from the oxidation of aldehydes by singlet oxygen was not involved in the CL, at least in the presence of formaldehyde. The spectrum of CL induced by the generation of active oxygen was the same as that from the aldehyde-enhanced CL reaction. We propose that the formation of a hydroperoxide (and/or hydroxide) bilirubin intermediate, but not a dioxetane, may be involved in the excitation of bilirubin molecules for CL.

Hydroxyl radical-induced characteristic chemiluminescent spectra from plasma of hemodialysis patients

Plasma from hemodialysis patients evoked weak photon emissions (chemiluminescence) in a characteristic emission spectrum with a peak at 430 nm, attributed to attack by hydroxyl radicals generated from the iron-catalyzed breakdown of hydrogen peroxide (Fenton reaction), whereas plasma from normal healthy subjects showed a rather weak red chemiluminescence peak at around 680 nm, similar to that resulting from attack by hydroxyl radicals. However, the addition of hydrogen peroxide in the absence of divalent irons induced almost the same red chemiluminescent emission spectrum in both plasmas. The HPLC-gel-filtration chromatography carried out with both plasmas revealed that a primary emitter evoking a peak emission at 430 nm was located in the fraction of lower-molecular-mass substances in fractionated plasma from hemodialysis patients. In contrast, the elution peaks evoking red chemiluminescence with the addition of hydrogen peroxide were mainly observed for the higher-molecular-mass fraction, as determined by gel chromatography of both plasmas. Therefore, the observation of a chemiluminescence peak at 430 nm, induced by the generation of hydroxyl radicals, correlated well with chemiluminescent emissions in plasma samples from patients with chronic renal failure. Spectral analyses of clinical samples that show weak chemiluminescence by forced oxidation by such an active oxygen may provide a new and more sensitive method for diagnosing metabolic disorders.

Effect of column temperature on the retention of peropyrene-type polycyclic aromatic hydrocarbons on various chemically bonded stationary phases in reversed-phase liquid chromatography

The effect of column temperature on the reversed-phase retention of polycyclic aromatic hydrocarbons has been investigated using various chemically bonded phases. Four solutes, coronene, tetrabenzo[a,cd,j,lm]perylene, tetrabenzo[a,cd,f,lm]perylene and benzo[lm]phenanthro[4,5,6-abcd]perylene, were used as the test probes. The temperature dependences of the retention are almost linear (the logarithm of capacity factor is proportional to the reciprocal of the column absolute temperature) with monomeric C18, monomeric C18 with endcapping and diphenyl bonded phases, while non-linear behaviour was observed with polymeric C18 phases. These differences in behaviour of the stationary phases are interpreted in terms of their structural differences.

[Gastric carcinoma with prominent reactive lymphoid hyperplasia; report of two cases with an immunohistological study]

An immunohistological study using a Leu 7 antibody, which is a marker for human NK and K cells, was carried out in two cases of gastric carcinomas with prominent reactive hyperplasia. The patients were a 72-year-old man and a 55-year-old man who had shown good postoperative courses in spite of the advanced stage of their tumors. There were many scattered Leu 7 positive cells in the lymphoid hyperplasia, predominantly in the germinal centers and the peri-follicles. The number of Leu 7 positive cells were even more pronounced in a patient whose condition was more advanced. These findings suggest that lymphoid hyperplasia, particularly with regard to the NK and K cell response, plays a significant role in the clinical benignity of the tumors.

Elution behaviour of planar and non-planar polycyclic aromatic hydrocarbons on various chemically bonded stationary phases in liquid chromatography

The elution behaviour of planar and non-planar polycyclic aromatic hydrocarbons has been studied on various stationary phases in reversed-phase and normal-phase liquid chromatography. The results show that the elution behaviours of the isomer sets which have distinctly different planarities such as triphenylene, triphenylmethane or o-terphenyl reflect the characteristics of the chemically bonded stationary phases. The phases studied included polymeric C18, monomeric C18 (with end capping), monomeric C18 (without end capping), triphenyl, naphthylethyl and pyrenylethyl phases.

Elution behaviour of peropyrene-type polycyclic aromatic hydrocarbons in various chemically bonded stationary phases in reversed-phase liquid chromatography

The elution behaviour of polycyclic aromatic hydrocarbons (PAHs, 13 of the 16 U.S. Environmental Protection Agency priority pollutants and peropyrene types) was studied on several chemically bonded stationary phases (octadecylsilicas, di- and triphenylsilicas, naphthylethylsilica and pyrenylethylsilica) under reversed-phase conditions. The results showed that the elution order of peropyrene-type PAHs is highly dependent on the degree of planarity of the solute and on the orderlines of the bonded phases, whereas no definite differences were found in the retention behaviour of the 13 small PAHs on various stationary phases. The characteristics of all the stationary phases could be classified by statistical cluster analysis.