Apocynin attenuates isoproterenol-induced myocardial injury and fibrogenesis

The Alzheimer's Disease Brain, Its Microvasculature, and NADPH Oxidase

The deterioration of the brain's microvasculature, particularly in the hippocampus, appears to be a very early event in the development of Alzheimer's disease (AD), preceding even the deposition of amyloid-β. A damaged microvasculature reduces the supply of oxygen and glucose to this region and limits the production of energy, ATP. The damage may be a function of the rise with age in the expression and activity of NADPH oxidase (NOX) in these microvessels. This rise renders these vessels vulnerable to the effects of oxidative stress and inflammation. The rise in NOX activity with age is even more marked in the AD brain where an inverse correlation has been demonstrated between NOX activity and cognitive ability. Apocynin, a putative NOX inhibitor, has been shown to block the damaging effects of NOX activation. Apocynin acts as a strong scavenger of H2O2, and as a weak scavenger of superoxide. Like apocynin, sodium oxybate (SO) has also been shown to block the toxic effects of NOX activation. The application of SO generates NADPH and ATP. SO inhibits oxidative stress and maintains normal cerebral ATP levels under hypoxic conditions. Moreover, it acts epigenetically to attenuate the expression of NOX. SO may delay the onset and slow the progress of AD by suppling energy and maintaining an antioxidative environment in the brain throughout the night. The slow wave activity produced by SO may also activate the glymphatic system and promote the clearance of amyloid-β from the brain.

Neuroprotective role of apocynin against pentylenetetrazole kindling epilepsy and associated comorbidities in mice by suppression of ROS/RNS

Epilepsy is a neurological disease that transpires due to the unusual synchronized neuronal discharge within the central nervous system, which drives repetitious unprovoked seizures. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is a complex enzyme accountable for reactive oxygen species (ROS) production, neurodegeneration, neurotoxicity, memory impairment, vitiates normal cellular processes, long term potentiation, and thus, implicated in the pathogenesis of epilepsy. Therefore, the present study was sketched to examine the neuroprotective effect of apocynin, NADPH oxidase inhibitor in pentylenetetrazole kindling epilepsy, and induced comorbidities in mice. Mice (either sex) were given pentylenetetrazole (35 mg/kg, i.p.) every other day up to 29 days, and a challenge test was executed on the 33^rd day. Pretreatment with apocynin (25, 50, and 100 mg/kg, i.p.) was carried out from 1^st to 33^rd day. Rotarod and open field test were performed on the 1^st, 10^th, 20^th, and 30^th days of the study. Animals were tutored on the morris water maze from 30^th to 33^rd day, and the retention was registered on the 34^th day. Tail suspension test and elevated plus maze were sequentially performed on the 32^nd and 33^rd day of the study. On the 34^th day, animals were sacrificed, and their brains were isolated to conduct biochemical estimation. NADPH oxidase activation due to chronic pentylenetetrazole treatment resulted in generalized tonic-clonic seizures, enhanced oxidative stress, remodeled neurotransmitters' level, and resulted in comorbidities (anxiety, depression, and memory impairment). Pretreatment with apocynin significantly restricted the pentylenetetrazole induced seizure severity, ROS production, neurotransmitter alteration, and comorbid conditions by inhibiting the NADPH oxidase enzyme.

Putative anti-inflammatory, antioxidant, and anti-apoptotic roles of the natural tissue guardian methyl palmitate against isoproterenol-induced myocardial injury in rats

Background

Myocardial injury is considered as a worldwide main cause of morbidity and mortality. The present study aimed to investigate the probable cardioprotective activity of the naturally occurring endogenous fatty acid ester methyl palmitate (MP) against isoproterenol (ISO)-induced myocardial injury in rats and the possible underlying molecular mechanisms. The study was carried out in two consecutive sets of experiments; the first set screened the cardioprotective dose of MP in ISO-intoxicated rats. In the second set, forty male Sprague Dawley rats received either MP (150 mg/kg, p.o) three times/week for 2 weeks and/or 2 consecutive doses of ISO separated by 24 h (85 mg/kg, s.c) on the 13th and 14th days. Different cardiotoxicity and oxidative stress markers were assessed. Furthermore, endothelial nitric oxide synthase (eNOS) levels were determined. For detection of apoptosis, Bax, Bcl-2, and caspase 3 were estimated. To assess inflammation, toll-like receptor 4 (TLR-4) and tumor necrosis factor-alpha (TNF-α) were measured using ELISA. Meanwhile, nuclear factor kappa B (NF-kB) and cyclooxygenase-2 (COX-2) were detected immunohistochemically.

Results

Pretreatment with MP significantly ameliorated the cardiotoxicity and oxidative stress markers. It also markedly elevated eNOS content, decreased apoptotic marker expression, and mitigated TLR-4 activation and other inflammatory markers. Electrocardiography and histopathological examination also confirmed the cardioprotective effect of MP.

Conclusion

The findings of this study indicated that MP possesses a potent cardioprotective activity against ISO-induced myocardial injury through its significant antioxidant, anti-apoptotic, anti-inflammatory, and vasodilatation activities.

Graphical abstract

AQP4-knockout aggravation of isoprenaline-induced myocardial injury is mediated by p66Shc and endoplasmic reticulum stress

Aquaporin 4 (AQP4) is a type of water channel protein that maintains the water balance of cardiomyocytes. However, the physiological role of AQP4 in cardiovascular disease is poorly understood. We wanted to explore whether p66Shc and endoplasmic reticulum stress participates in AQP4 knockout (KO)-mediated cardiac injury. There were two types of mice: AQP4 knockout and wild-type mice. Each type was randomly divided into three groups: Control group, isoprenaline stimulation group (ISO, 1 mg/kg, s.c., 5 days), and apocynin treatment group (APO, 100 mg/kg, p.o., 3 days). H9c2 rat cardiomyocytes were cultured for RNA interference of AQP4. Results showed increased left ventricular weight index and more severe myocardial inflammation were induced in AQP4 knockout mice relative to wild-type mice, accompanied by significantly increased levels of the oxidative stress biomarkers MDA and NOX4. In addition, the expressions of p66Shc, ER stress markers PERK, GRP78 and CHOP and proinflammatory factors such as ET_A , IL6 and TNFα were upregulated in the myocardium of AQP4 knockout mice or AQP4 siRNA treated cardiomyocytes, whereas CASQ2 was downregulated. ISO stimulation aggravated these abnormalities, which were significantly attenuated by apocynin. This study showed that AQP4 knockout mice were susceptible to cardiac injury induced by ISO. The mechanism was closely connected with p66Shc and proinflammatory factors. Endoplasmic reticulum stress was also involved in the pathological process.

Luteolin-7-diglucuronide attenuates isoproterenol-induced myocardial injury and fibrosis in mice

Myocardial injury and ensuing fibrotic alterations impair normal heart architecture and cause cardiac dysfunction. Oxidative stress has been recognized as a key player in the pathogenesis of cardiac injury and progression of cardiac dysfunction, and promoting fibrosis. In the current study we investigated whether luteolin-7-diglucuronide (L7DG), a naturally occurring antioxidant found in edible plants, could attenuate isoproterenol (ISO)-induced myocardial injury and fibrosis in mice and the underlying mechanisms. Myocardial injury and fibrosis were induced in mice via injection of ISO (5 mg·kg^-1·d^-1, ip) for 5 or 10 d. Two treatment regimens (pretreatment and posttreatment) were employed to administer L7DG (5-40 mg·kg^-1·d^-1, ip) into the mice. After the mice were euthanized, morphological examinations of heart sections revealed that both L7DG pretreatment and posttreatment regimens significantly attenuated ISO-induced myocardial injury and fibrosis. But the pretreatment regimen caused better protection against ISO-induced myocardial fibrosis than the posttreatment regimen. Furthermore, L7DG pretreatment blocked ISO-stimulated expression of the genes (Cyba, Cybb, Ncf1, Ncf4 and Rac2) encoding the enzymatic subunits of NADPH oxidase, which was the primary source of oxidant production in mammalian cells. Moreover, L7DG pretreatment significantly suppressed ISO-stimulated expression of collagen genes Col1a1, Col1a2, Col3a1, and Col12a1 and non-collagen extracellular matrix genes fibrillin-1, elastin, collagen triple helix repeat containing 1 and connective tissue growth factor. In addition, L7DG pretreatment almost reversed ISO-altered expression of microRNAs that were crosstalking with TGFβ-mediated fibrosis, including miR-29c-3p, miR-29c-5p, miR-30c-3p, miR-30c-5p and miR-21. The current study demonstrated for the first time that L7DG is pharmacologically effective in protecting the heart against developing ISO-induced injury and fibrosis, justifying further evaluation of L7DG as a cardioprotective agent to treat related cardiovascular diseases.

Inhibition of Pin1 alleviates myocardial fibrosis and dysfunction in STZ-induced diabetic mice

Therapeutic management of diabetic myocardial fibrosis remains an unsolved clinical problem. Pin1, a peptidyl-prolyl isomerase, impacts diverse cellular processes and plays a pivotal role in regulating cardiac pathophysiology. Here we investigate the potential mechanism of action of Pin1 and its role in diabetes-induced myocardial fibrosis and dysfunction in mice. Cardiac Pin1, transforming growth factor β1 (TGF-β1), α-smooth muscle actin (α-SMA) and extracellular matrix deposits (collagen I and III) are found to be increased in diabetic mice, which are effectively prevented by Pin1 inhibition by juglone. Pin1 inhibition alleviates cardiac fibrosis and dysfunction. In vitro, high glucose increases Pin1 expression with an accompanying increase in phospho-Akt (Ser 473), p-Smad2, p-Smad3, TGF-β1, and α-SMA in cardiac fibroblasts (CFs). These increases are effectively prevented by the inhibition of Pin1 by juglone. Furthermore, Pin1 inhibition inhibits HG-induced CF proliferation and migration. Our results indicate that Pin1 inhibition attenuates cardiac extracellular matrix deposition by regulating the phosphorylation of Akt, TGF-β1/Smads, MMP activities, and α-SMA expression in diabetic mice.

Treatment with Rhus tripartita extract curtails isoproterenol-elicited cardiotoxicity and oxidative stress in rats

BACKGROUND

Consumption of plant-derived nutraceuticals and crude drugs in traditional medicine is widely believed to confer beneficial effects in thwarting the progression of cardiovascular diseases. Rhus tripartita (family Anacardiaceae) has been traditionally used to treat a wide range of ailments.

METHODS

In the present study we investigated the protective effects of an alcoholic extract of the stem part of Rhus tripartita male genotype (RTSM) on experimentally induced myocardial injury in rats. To this end, cardiac injury was induced by administration of isoproterenol (ISO) and serum enzyme markers, lipid profiles and cardiac tissue redox status were determined following RTSM treatment (250 and 500 mg/kg).

RESULTS

As a result, RTSM treatment significantly mitigated ISO-triggered upregulation of cardiac-specific markers of injury creatine kinase and lactate dehydrogenase. RTSM treatment significantly attenuated ISO-induced increase in serum cholesterol and triglycerides as well alterations in serum lipoproteins. Determination of oxidative balance showed that RTSM treatment significantly blunted ISO-induced increase in malondialdehyde and decrease in nonprotein sulfhydryl in cardiac tissue. Six compounds were isolated and identified as gallocatechin 1, taxifolin 2, myricetin-3-O-β-glucoside 3, catechin 4, epicatechin 5, and 3',8-binaringenin 6. Compound 6 was isolated for the first time from the stem part of Rhus tripartita. Furthermore, RTSM treatment enhanced the survival fraction of cardiac cells exposed to oxidative stress in vitro.

CONCLUSION

We conclude that the antioxidant properties of RTSM treatment underpin its cardioprotective pharmacological effects, thus, providing biological evidence for the treatment of cardiovascular diseases using Rhus tripartita in indigenous medicine.

Apocynin inhibits Toll-like receptor-4-mediated activation of NF-κB by suppressing the Akt and mTOR pathways

Microbial product lipopolysaccharide has been shown to be involved in the pathogenesis of inflammatory skin diseases. Apocynin has demonstrated to have an anti-inflammatory effect. However, the effect of apocynin on the Toll-like receptor-4-dependent activation of Akt, mammalian target of rapamycin (mTOR), and nuclear factor (NF)-κB pathway, which is involved in productions of inflammatory mediators in keratinocytes, has not been studied. Using human keratinocytes, we investigated the effect of apocynin on the inflammatory mediator production in relation to the Toll-like receptor-4-mediated-Akt/mTOR and NF-κB pathways, which regulates the transcription genes involved in immune and inflammatory responses. Apocynin, Akt inhibitor SH-5, Bay 11-7085 and N-acetylcysteine each attenuated the lipopolysaccharide-induced production of cytokines, PGE₂, and chemokines, changes in the levels of Toll-like receptor-4, p-Akt, mTOR, and NF-κB, and production of reactive oxygen species in keratinocytes. The results show that apocynin appears to attenuate the lipopolysaccharide-stimulated production of inflammatory mediators in keratinocytes by suppressing the Toll-like receptor-4-mediated activation of the Akt, mTOR, and NF-κB pathways. The effect of apocynin appears to be attributed to its inhibitory effect on the production of reactive oxygen species. Apocynin appears to attenuate the microbial product-mediated inflammatory skin diseases.

Acute Catecholamine Exposure Causes Reversible Myocyte Injury Without Cardiac Regeneration

RATIONALE

Catecholamines increase cardiac contractility, but exposure to high concentrations or prolonged exposures can cause cardiac injury. A recent study demonstrated that a single subcutaneous injection of isoproterenol (ISO; 200 mg/kg) in mice causes acute myocyte death (8%-10%) with complete cardiac repair within a month. Cardiac regeneration was via endogenous cKit(+) cardiac stem cell-mediated new myocyte formation.

OBJECTIVE

Our goal was to validate this simple injury/regeneration system and use it to study the biology of newly forming adult cardiac myocytes.

METHODS AND RESULTS

C57BL/6 mice (n=173) were treated with single injections of vehicle, 200 or 300 mg/kg ISO, or 2 daily doses of 200 mg/kg ISO for 6 days. Echocardiography revealed transiently increased systolic function and unaltered diastolic function 1 day after single ISO injection. Single ISO injections also caused membrane injury in ≈10% of myocytes, but few of these myocytes appeared to be necrotic. Circulating troponin I levels after ISO were elevated, further documenting myocyte damage. However, myocyte apoptosis was not increased after ISO injury. Heart weight to body weight ratio and fibrosis were also not altered 28 days after ISO injection. Single- or multiple-dose ISO injury was not associated with an increase in the percentage of 5-ethynyl-2'-deoxyuridine-labeled myocytes. Furthermore, ISO injections did not increase new myocytes in cKit(+/Cre)×R-GFP transgenic mice.

CONCLUSIONS

A single dose of ISO causes injury in ≈10% of the cardiomyocytes. However, most of these myocytes seem to recover and do not elicit cKit(+) cardiac stem cell-derived myocyte regeneration.

Changes in interconnected pathways implicating microRNAs are associated with the activity of apocynin in attenuating myocardial fibrogenesis

Myocardial fibrosis is the endpoint pathology common to many cardiovascular disorders. We have previously shown that apocynin (APO), a naturally occurring NADPH oxidase inhibitor, significantly prevents the development of isoproterenol (ISO)-induced myocardial injury and fibrogenesis. The current study investigated the changes in microRNAs (miRNAs) and their potential implication in the cardioprotective effects of APO. Integrative analyses of whole-genome miRNA and gene expression profiles were first performed, revealing that altered expression of miRNAs likely contributed to dysregulated expression of genes associated with multiple interconnected fibrogenic signaling pathways. Importantly, APO treatment exhibited a broad impact on these signaling pathways, which could in part be mediated through miRNA-mediated gene expression regulation. The expression of differentially expressed miRNAs was further validated by real-time PCR analyses. Consistent with the data from miRNA array, compared to that from vehicle-treated normal controls, significantly decreased expression of miR-10b, miR-29c*, miR-30c-1*, miR-30e*, miR-148b, miR-181d, miR-218 and miR-3107* was observed in ISO-challenged vehicle-treated mouse hearts. In contrast, significantly increased expression of these miRNAs was observed in ISO-challenged APO-treated hearts compared to that from ISO-challenged vehicle-treated mice. Moreover, increased expression of miR-21 was observed as a result of ISO administration, which was significantly reduced by APO treatment. Altered protein levels of Col1, TIMP1, Rac2 and gp91(phox) were also validated. Lastly, APO treatment was shown to attenuate pre-established myocardial fibrosis induced by ISO. The results therefore demonstrated for the first time that complex changes in miRNA-mRNA interactome network are associated with the protective effects of APO against ISO-induced myocardial injury and fibrogenesis.