EFFECTS OF MELATONIN ON BLOOD PRESSURE IN STRESS-INDUCED HYPERTENSION IN RATS

A neural perspective on the treatment of hypertension: the neurological network excitation and inhibition (E/I) imbalance in hypertension

Despite the increasing number of anti-hypertensive drugs have been developed and used in the clinical setting, persistent deficiencies persist, including issues such as lifelong dosage, combination therapy. Notwithstanding receiving the treatment under enduring these deficiencies, approximately 4 in 5 patients still fail to achieve reliable blood pressure (BP) control. The application of neuromodulation in the context of hypertension presents a pioneering strategy for addressing this condition, con-currently implying a potential central nervous mechanism underlying hypertension onset. We hypothesize that neurological networks, an essential component of maintaining appropriate neurological function, are involved in hypertension. Drawing on both peer-reviewed research and our laboratory investigations, we endeavor to investigate the underlying neural mechanisms involved in hypertension by identifying a close relationship between its onset of hypertension and an excitation and inhibition (E/I) imbalance. In addition to the involvement of excitatory glutamatergic and GABAergic inhibitory system, the pathogenesis of hypertension is also associated with Voltage-gated sodium channels (VGSCs, Nav)-mediated E/I balance. The overloading of glutamate or enhancement of glutamate receptors may be attributed to the E/I imbalance, ultimately triggering hypertension. GABA loss and GABA receptor dysfunction have also proven to be involved. Furthermore, we have identified that abnormalities in sodium channel expression and function alter neural excitability, thereby disturbing E/I balance and potentially serving as a mechanism underlying hypertension. These insights are expected to furnish potential strategies for the advancement of innovative anti-hypertensive therapies and a meaningful reference for the exploration of central nervous system (CNS) targets of anti-hypertensives.

Hypotensive effects of melatonin in rats: Focus on the model, measurement, application, and main mechanisms

The hypotensive effects of melatonin are based on a negative correlation between melatonin levels and blood pressure in humans. However, there is a positive correlation in nocturnal animals that are often used as experimental models in cardiovascular research, and the hypotensive effects and mechanism of melatonin action are often investigated in rats and mice. In rats, the hypotensive effects of melatonin have been studied in normotensive and spontaneously or experimentally induced hypertensive strains. In experimental animals, blood pressure is often measured indirectly during the light (passive) phase of the day by tail-cuff plethysmography, which has limitations regarding data quality and animal well-being compared to telemetry. Melatonin is administered to rats in drinking water, subcutaneously, intraperitoneally, or microinjected into specific brain areas at different times. Experimental data show that the hypotensive effects of melatonin depend on the experimental animal model, blood pressure measurement technique, and the route, time and duration of melatonin administration. The hypotensive effects of melatonin may be mediated through specific membrane G-coupled receptors located in the heart and arteries. Due to melatonin's lipophilic nature, its potential hypotensive effects can interfere with various regulatory mechanisms, such as nitric oxide and reactive oxygen species production and activation of the autonomic nervous and circadian systems. Based on the research conducted on rats, the cardiovascular effects of melatonin are modulatory, delayed, and indirect.

The Role of Melatonin in Chronic Kidney Disease and Its Associated Risk Factors: A New Tool in Our Arsenal?

BACKGROUND

The increasing incidence of chronic kidney disease (CKD), as a consequence of the high prevalence of arterial hypertension and type 2 diabetes mellitus (T2DM), warrants the need for developing effective treatment approaches. In this regard, the pineal gland-derived hormone melatonin may represent an appealing treatment approach of CKD and its associated risk factors.

SUMMARY

Targeting the adverse pathophysiology surrounding CKD and its associated risk factors has been the concept of pharmacologic treatment developed for its management. This review article aimed to present the role of melatonin in this direction, by providing an overview of melatonin's physiology followed by its effect as a therapeutic agent in arterial hypertension and T2DM.

KEY MESSAGES

Melatonin, the primary darkness hormone, possesses pleiotropic mechanisms of action which may have important implications in various pathologic states since its receptors are situated across various organ systems. As a treatment tool in arterial hypertension, melatonin may be efficacious in reducing both daytime and nocturnal blood pressure by influencing endothelial function, oxidative stress, the autonomic nervous system, and the renin-angiotensin system. Melatonin may also increase insulin sensitivity and β-cell function. However, late meal intake may be detrimental in glucose regulation, as consumption close to melatonin peak concentrations may induce hyperglycemia and insulin resistance. This finding may explain the inconsistent glycose regulation achieved with melatonin in clinical trials and meta-analyses. Additionally, the presence of genetic variants to melatonin receptor 2 may predispose to T2DM development. Finally, we present the available preclinical evidence supporting melatonin's efficacy in ameliorating CKD's pathophysiology since melatonin supplementation has not been adequately explored in patients with CKD. The combined use of stem cells with melatonin is an appealing therapeutic approach which ought to be assessed further.

Evidence for the Benefits of Melatonin in Cardiovascular Disease

The pineal gland is a neuroendocrine gland which produces melatonin, a neuroendocrine hormone with critical physiological roles in the circadian rhythm and sleep-wake cycle. Melatonin has been shown to possess anti-oxidant activity and neuroprotective properties. Numerous studies have shown that melatonin has significant functions in cardiovascular disease, and may have anti-aging properties. The ability of melatonin to decrease primary hypertension needs to be more extensively evaluated. Melatonin has shown significant benefits in reducing cardiac pathology, and preventing the death of cardiac muscle in response to ischemia-reperfusion in rodent species. Moreover, melatonin may also prevent the hypertrophy of the heart muscle under some circumstances, which in turn would lessen the development of heart failure. Several currently used conventional drugs show cardiotoxicity as an adverse effect. Recent rodent studies have shown that melatonin acts as an anti-oxidant and is effective in suppressing heart damage mediated by pharmacologic drugs. Therefore, melatonin has been shown to have cardioprotective activity in multiple animal and human studies. Herein, we summarize the most established benefits of melatonin in the cardiovascular system with a focus on the molecular mechanisms of action.

Overexpression of NaV1.6 in the rostral ventrolateral medulla in rats mediates stress-induced hypertension via glutamate regulation

BACKGROUND

The rostral ventrolateral medulla (RVLM) plays a key role in mediating the development of stress-induced hypertension (SIH). Furthermore, enhanced glutamate transport within glutamatergic neurons in the RVLM mediates pressor responses. Data from our previous studies suggest that the voltage-gated sodium channel NaV1.6 is overexpressed in neurons in the RVLM in SIH model rats and participates in the resulting elevation of blood pressure. However, previous studies have not investigated the relationship between NaV1.6 expression and glutamatergic neurons.

METHODS

Here, we constructed an SIH rat model by knocking down NaV1.6 via microinjection of clustered regularly interspaced short palindromic repeats (CRISPR) guide RNA into the RVLM. Glutamate-related markers were quantified by Western blotting and immunofluorescence, and blood pressure was measured in the rats.

RESULTS

Our findings showed that vesicular glutamate transporter 1 (VGluT1) protein expression in the RVLM was higher in SIH rats than in Control rats, and GAD67 protein expression in SIH rats was lower than that in Control rats. Therefore, the number of VGluT1-positive neurons increased, while the number of GAD67-labeled neurons decreased after stress. After knocking down NaV1.6 expression in the RVLM, VGluT1 expression and the number of VGluT1-positive neurons decreased relative to those in SIH rats, while GAD67 protein expression and the number of GAD67-labeled neurons increased relative to those in SIH rats.

CONCLUSIONS

These results indicate that overexpression of NaV1.6 in the RVLM may mediate the transport and transformation of glutamate in neurons, and NaV1.6 may participate in SIH.

TLR4/MyD88/NF-κB Signaling in the Rostral Ventrolateral Medulla Is Involved in the Depressor Effect of Candesartan in Stress-Induced Hypertensive Rats

This study aimed to investigate whether the proinflammatory and pressor effects of endogenous angiotensin II (AngII) are mediated by binding to the AngII type 1 receptor (AT₁R) and subsequently activating central Toll-like receptor 4 (TLR4) in the rostral ventrolateral medulla (RVLM) of stress-induced hypertensive rats (SIHR). The stress-induced hypertension (SIH) model was established by random electric foot shocks combined with noise stimulation. Mean arterial pressure, heart rate, plasma norepinephrine, and RVLM AngII and TLR4 increased in a time-dependent manner in SIHR. Pro-inflammatory cytokines (tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β)), myeloid differentiation factor 88 (MyD88), and nuclear factor (NF)-κB also increased, while anti-inflammatory cytokine IL-10 decreased in the RVLM of SIHR. These changes were attenuated by 14-day intracerebroventricular (ICV) infusion of VIPER (a TLR4 inhibitor) or candesartan (an AT₁R antagonist). Both TLR4 and AT₁R were expressed in the neurons and microglia in the RVLM of SIHR. Candesartan attenuated the expression of TLR4 in the RVLM of SIHR. This study demonstrated that endogenous AngII may activate AT₁R to upregulate TLR4/MyD88/NF-κB signaling and subsequently trigger an inflammatory response in the RVLM of SIHR, which in turn enhanced sympathetic activity and increased blood pressure.

Gut microbiota modulates stress-induced hypertension through the HPA axis

Stress is associated with an increased risk of hypertension, and the incidence of stress-related hypertension has risen rapidly in recent years; however, the underlying mechanisms remain elusive. Gut dysbiosis has been demonstrated to contribute to hypertension and hyperactivation of the hypothalamus-pituitary-adrenal (HPA) axis. Based on our previous findings showing the altered gut microbiota in the rats of stress-induced hypertension (SIH), the present study aims to investigate whether the stress-induced alteration in gut microbiota can lead to the dysfunction of the HPA axis which contributes to the development of SIH. SIH was developed in rats subjected to electric foot-shock combined with buzzer noise stressors. The gut microbiota of rats were deleted by administering an antibiotic cocktail containing ampicillin (1 g/L), vancomycin (500 mg/L), neomycin (1 g/L), and metronidazole (1 g/L) in drinking water. The serum levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were tested using enzyme-linked immunosorbent assay (ELISA). The mRNA expression of glucocorticoid receptor (GR) and corticotropin-releasing factor (CRF), CRFR1 and CRFR2 was detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The cellular protein expressions of corticotropin-releasing hormone (CRH), c-fos, and GR were examined by immunohistochemical staining. In the present study, SIH rats showed a hyperactive HPA axis as indicated by the increased CRH expression in the paraventricular nucleus (PVN) of the hypothalamus, the elevated serum ACTH or CORT concentrations, and increased adrenal gland index. The decreased GR expression and increased CRFR1 in the hypothalamus might underlie the hyperactivation of the HPA axis. The microbial deletion by antibiotics mitigated the hyperactivation of the HPA axis and attenuated the stress-induced elevation of blood pressure, indicating that the causal link of gut microbiota to SIH is mediated, at least in part, by the HPA axis activity. Our findings shed new light on the mechanisms underlying SIH.

Microglia-Derived NLRP3 Activation Mediates the Pressor Effect of Prorenin in the Rostral Ventrolateral Medulla of Stress-Induced Hypertensive Rats

Increased microglial activation and neuroinflammation within autonomic brain regions such as the rostral ventrolateral medulla (RVLM) have been implicated in stress-induced hypertension (SIH). Prorenin, a member of the brain renin-angiotensin system (RAS), can directly activate microglia. The present study aimed to investigate the effects of prorenin on microglial activation in the RVLM of SIH rats. Rats were subjected to intermittent electric foot-shocks plus noise, this stress was administered for 2 h twice daily for 15 consecutive days, and mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) were monitored. The results showed that MAP and RSNA were augmented, and this paralleled increased pro-inflammatory phenotype (M1) switching. Prorenin and its receptor (PRR) expression and the NLR family pyrin domain containing 3 (NLRP3) activation were increased in RVLM of SIH rats. In addition, PLX5622 (a microglial depletion agent), MCC950 (a NLRP3 inhibitor), and/or PRO20 (a (Pro)renin receptor antagonist) had antihypertensive effects in the rats. The NLRP3 expression in the RVLM was decreased in SIH rats treated with PLX5622. Mito-tracker staining showed translocation of NLRP3 from mitochondria to the cytoplasm in prorenin-stimulated microglia. Prorenin increased the ROS-triggering M1 phenotype-switching and NLRP3 activation, while MCC950 decreased the M1 polarization. In conclusion, upregulated prorenin in the RVLM may be involved in the pathogenesis of SIH, mediated by activation of the microglia-derived NLRP3 inflammasome. The link between prorenin and NLRP3 in microglia provides insights for the treatment of stress-related hypertension.

HMGB1/RAGE axis mediates stress-induced RVLM neuroinflammation in mice via impairing mitophagy flux in microglia

Background

Microglial mediated neuroinflammation in the rostral ventrolateral medulla (RVLM) plays roles in the etiology of stress-induced hypertension (SIH). It was reported that autophagy influenced inflammation via immunophenotypic switching of microglia. High-mobility group box 1 (HMGB1) acts as a regulator of autophagy and initiates the production of proinflammatory cytokines (PICs), but the underlying mechanisms remain unclear.

Methods

The stressed mice were subjected to intermittent electric foot shocks plus noises administered for 2 h twice daily for 15 consecutive days. In mice, blood pressure (BP) and renal sympathetic nerve activity (RSNA) were monitored by noninvasive tail-cuff method and platinum-iridium electrodes placed respectively. Microinjection of siRNA-HMGB1 (siHMGB1) into the RVLM of mice to study the effect of HMGB1 on microglia M1 activation was done. mRFP-GFP-tandem fluorescent LC3 (tf-LC3) vectors were transfected into the RVLM to evaluate the process of autolysosome formation/autophagy flux. The expression of RAB7, lysosomal-associated membrane protein 1 (LAMP1), and lysosomal pH change were used to evaluate lysosomal function in microglia. Mitophagy was identified by transmission electron microscopic observation or by checking LC3 and MitoTracker colocalization under a confocal microscope.

Results

We showed chronic stress increased cytoplasmic translocations of HMGB1 and upregulation of its receptor RAGE expression in microglia. The mitochondria injury, oxidative stress, and M1 polarization were attenuated in the RVLM of stressed Cre-CX3CR1/RAGE^fl/fl mice. The HMGB1/RAGE axis increased at the early stage of stress-induced mitophagy flux while impairing the late stages of mitophagy flux in microglia, as revealed by decreased GFP fluorescence quenching of GFP-RFP-LC3-II puncta and decreased colocalization of lysosomes with mitochondria. The expressions of RAB7 and LAMP1 were decreased in the stressed microglia, while knockout of RAGE reversed these effects and caused an increase in acidity of lysosomes. siHMGB1 in the RVLM resulted in BP lowering and RSNA decreasing in SIH mice. When the autophagy inducer, rapamycin, is used to facilitate the mitophagy flux, this treatment results in attenuated NF-κB activation and reduced PIC release in exogenous disulfide HMGB1 (ds-HMGB1)-stimulated microglia.

Conclusions

Collectively, we demonstrated that inhibition of the HMGB1/RAGE axis activation led to increased stress-induced mitophagy flux, hence reducing the activity of microglia-mediated neuroinflammation and consequently reduced the sympathetic vasoconstriction drive in the RVLM.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1673-3) contains supplementary material, which is available to authorized users.

The Role of Melatonin in Oxidative Stress, DNA Damage, Apoptosis and Angiogenesis in Fetal Eye under Preeclampsia and Melatonin Deficiency Stress

Aim: The aim of this study was to investigate the possible mechanisms of ocular damage induced by pinealectomy (PNX) and preeclampsia (PE), and to determine the cellular and molecular effects of melatonin treatment on oxidative stress, DNA damage, molecular chaperone responses, induction of apoptosis and angiogenesis in the fetal eye of both PNX and PNX+PE animals. Material and Methods: We analysed therapeutic potential of melatonin on fetal eye damage in PNX and PNX+PE animals using Malondialdehyde (MDA), Random Amplified Polymorphic DNA (RAPD), qRT-PCR and Western blot assays. Results: Our study presents three preliminary findings: (a) in fetal eye tissues, PNX and PNX+PE significantly induce oxidative damage to both DNA and protein contents, leading to a dramatic increase in caspase-dependent apoptotic signalling in both mitochondrial and death receptor pathways; (b) the same conditions trigger hypoxia biomarkers in addition to significant overexpression of HIF1-α, HIF1-β, MMP9 and VEGF genes in the fetal eye; (c) finally, melatonin regulates not only the expression of genes encoding antioxidant enzymes and increase in DNA damage as well as lipid peroxidation but also limits programmed cell death processes in the fetal eye of PNX and PNX+PE animals . Furthermore, melatonin can relatively modulate genes in the HIF1 family, TNF-α and VEGF, thus acting as a direct anti-angiogenic molecule. In conclusion, both PNX and PNX+PE induce ocular damage at both cellular and molecular levels in fetal eye tissue of rats. Conclusion: Our results clearly indicate the potential of melatonin as a preventative therapeutic intervention for fetal ocular damage triggered by both PNX and PNX+PE.

Melatonin decreases M1 polarization via attenuating mitochondrial oxidative damage depending on UCP2 pathway in prorenin-treated microglia

Accumulating evidence suggests that neuroinflammation and oxidative stress in cardiovascular center contribute to the pathological processes underlying hypertension. Microglia activation triggers the inflammation and oxidative stress. Melatonin is a documented potent anti-inflammatory regent and antioxidant, the underlying roles of melatonin in regulating microglia activation via mitochondria remain unclear. In present study, we investigated the protective role of melatonin in decreasing M1 phenotype switching via attenuating mitochondrial oxidative damage in dependence on uncoupling protein 2 (UCP2) pathway in microglia. Prorenin (20 nmol/L; 24 hr) was used to induce inflammation in cultured microglia. Mitochondrial morphology was detected by transmission electron microscope. The reactive oxygen species (ROS) production by using DCFH-DA fluorescence imaging and mitochondrial membrane potential (MMP, ΔΨm) was evaluated by JC-1 staining. The indicator of the redox status as the ratio of the amount of total NADP+ to total NADPH, and the expression of 6 subunits of NADPH oxidase is measured. The pro-inflammatory cytokines releasing was measured by qPCR. UCP2 and activated AMPKα (p-AMPKα) expression were examined by immunoblot. Melatonin (100 μM) markedly alleviated the M1 microglia phenotype shifting and abnormal mitochondria morphology. Melatonin attenuated prorenin-induced ΔΨm increasing and ROS overproduction. Melatonin decreased the redox ratio (NADP+/NADPH) and the p47phox and gp91phox subunits of NADPH oxidase expression in prorenin-treated microglia. These effects were reversed in the presence of UCP2 siRNA. Our results suggested that the protective effect of melatonin against prorenin-induced M1 phenotype switching via attenuating mitochondrial oxidative damage depending on UCP2 upregulation in prorenin-treated microglia.

Upregulation of AT1 Receptor Mediates a Pressor Effect Through ROS-SAPK/JNK Signaling in Glutamatergic Neurons of Rostral Ventrolateral Medulla in Rats With Stress-Induced Hypertension

The present study examined whether angiotensin II (Ang II) mediates the pressor effect through nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived reactive oxygen species (ROS)-mitogen-activated protein kinase (MAPK) signaling in the glutamatergic neurons of the rostral ventrolateral medulla (RVLM) in stress-induced hypertensive rats (SIHR). The SIHR model was established using electric foot-shocks combined with noises for 15 days. We observed that Ang II type 1 receptor (AT₁R) and the glutamatergic neurons co-localized in the RVLM of SIHR. Furthermore, glutamate levels in the intermediolateral column of the spinal cord were higher in SIHR than in controls. Microinjection of Ang II into the RVLM of SIHR activated stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK), extracellular signal-regulated protein kinase (ERK) 1/2, and p38MAPK. Compared with controls, the activation of SAPK/JNK, ERK1/2, p38MAPK, and ROS in the RVLM were higher in SIHR, an effect that was blocked by an NADPH oxidase inhibitor (apocynin) and an AT₁R antagonist (candesartan). RVLM microinjection of apocynin or a SAPK/JNK inhibitor (SP600125), but not an ERK1/2 inhibitor (U0126) or a p38MAPK inhibitor (SB203580), decreased AT₁R mRNA and mean arterial blood pressure (MABP) in SIHR. The increase of AT₁R protein expression and MABP was inhibited by intracerebroventricular infusion (ICV), for 14 days, of SP600125, but not U0126 or SB203580 in SIHR. We conclude that Ang II modulates the pressor effect through AT₁R-dependent ROS-SAPK/JNK signaling in glutamatergic neurons in the RVLM of SIHR.

Upregulation of Nav1.6 expression in the rostral ventrolateral medulla of stress-induced hypertensive rats

The rostral ventrolateral medulla (RVLM) plays a key role in mediating the development of stress-induced hypertension (SIH) by excitation and/or inhibition of sympathetic preganglionic neurons. The voltage-gated sodium channel Nav1.6 has been found to contribute to neuronal hyperexcitability. To examine the expression of Nav1.6 in the RVLM during SIH, a rat model was established by administering electric foot-shocks and noises. We found that Nav1.6 protein expression in the RVLM of SIH rats was higher than that of control rats, peaking at the tenth day of stress. Furthermore, we observed changes in blood pressure correlating with days of stress, with systolic blood pressure (SBP) found to reach a similarly timed peak at the tenth day of stress. Percentages of cells exhibiting colocalization of Nav1.6 with NeuN, a molecular marker of neurons, indicated a strong correlation between upregulation of Nav1.6 expression in NeuN-positive cells and SBP. The level of RSNA was significantly increased after 10 days of stress induction than control group. Compared with the SIHR, knockdown of Nav1.6 in RVLM of the SIHR decreased the level of SBP, heart rate (HR) and renal sympathetic nerve activity (RSNA). These results suggest that upregulated Nav1.6 expression within neurons in the RVLM of SIH rats may contribute to overactivation of the sympathetic system in response to SIH development.

Melatonin promotes sleep in mice by inhibiting orexin neurons in the perifornical lateral hypothalamus

Melatonin promotes sleep. However, the underlying mechanisms are unknown. Orexin neurons in the perifornical lateral hypothalamus (PFH) are pivotal for wake promotion. Does melatonin promote sleep by inhibiting orexin neurons? We used C57BL/6J mice and designed 4 experiments to address this question. Experiment 1 used double-labeled immunofluorescence and examined the presence of melatonin receptors on orexin neurons. Second, mice, implanted with bilateral guides targeted toward PFH and sleep-recording electrodes, were infused with melatonin (500 pmole/50 nL/side) at dark onset (onset of active period), and spontaneous bouts of sleep-wakefulness were examined. Third, mice, implanted with bilateral guides into the PFH, were infused with melatonin (500 pmole/50 nL/side) at dark onset and euthanized 2 hours later, to examine the activation of orexin neurons using c-Fos expression in orexin neurons. Fourth, mice, implanted with PFH bilateral guides and sleep-recording electrodes, were infused with melatonin receptor antagonist, luzindole (10 pmol/50 nL/side), at light onset (onset of sleep period), and spontaneous bouts of sleep-wakefulness were examined. Our results suggest that orexin neurons express MT1, but not MT2 receptors. Melatonin infusion into the PFH, at dark onset, site-specifically and significantly increased NREM sleep (43.7%, P = .003) and reduced wakefulness (12.3%, P = .013). Local melatonin infusion at dark onset inhibited orexin neurons as evident by a significant reduction (66%, P = .0004) in the number of orexin neurons expressing c-Fos. Finally, luzindole infusion-induced blockade of melatonin receptors in PFH at sleep onset significantly increased wakefulness (44.1%, P = .015). Based on these results, we suggest that melatonin may act via the MT1 receptors to inhibit orexin neurons and promote sleep.

Neuroinflammation contributes to autophagy flux blockage in the neurons of rostral ventrolateral medulla in stress-induced hypertension rats

BACKGROUND

Neuroinflammation plays hypertensive roles in the uninjured autonomic nuclei of the central nervous system, while its mechanisms remain unclear. The present study is to investigate the effect of neuroinflammation on autophagy in the neurons of the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of vasomotor tone reside.

METHODS

Stress-induced hypertension (SIH) was induced by electric foot-shock stressors with noise interventions in rats. Systolic blood pressure (SBP) and the power density of the low frequency (LF) component of the SAP spectrum were measured to reflect sympathetic vasomotor activity. Microglia activation and pro-inflammatory cytokines (PICs (IL-1β, TNF-α)) expression in the RVLM were measured by immunoblotting and immunostaining. Autophagy and autophagic vacuoles (AVs) were examined by autophagic marker (LC3 and p62) expression and transmission electron microscopy (TEM) image, respectively. Autophagy flux was evaluated by RFP-GFP-tandem fluorescent LC3 (tf-LC3) vectors transfected into the RVLM. Tissue levels of glutamate, gamma aminobutyric acid (GABA), and plasma levels of norepinephrine (NE) were measured by using high-performance liquid chromatography (HPLC) with electrochemical detection. The effects of the cisterna magna infused minocycline, a microglia activation inhibitor, on the abovementioned parameters were analyzed.

RESULTS

SIH rats showed increased SBP, plasma NE accompanied by an increase in LF component of the SBP spectrum. Microglia activation and PICs expression was increased in SIH rats. TEM demonstrated that stress led to the accumulation of AVs in the RVLM of SIH rats. In addition to the Tf-LC3 assay, the concurrent increased level of LC3-II and p62 suggested the impairment of autophagic flux in SIH rats. To the contrary, minocycline facilitated autophagic flux and induced a hypotensive effect with attenuated microglia activation and decreased PICs in the RVLM of SIH rats. Furthermore, SIH rats showed higher levels of glutamate and lower level of GABA in the RVLM, while minocycline attenuated the decrease in GABA and the increase in glutamate of SIH rats.

CONCLUSIONS

Collectively, we concluded that the neuroinflammation might impair autophagic flux and induced neural excitotoxicity in the RVLM neurons following SIH, which is involved in the development of SIH.

Effect of melatonin on blood pressure and nitric oxide generation in rats with metabolic syndrome

Melatonin, a multitasking indolamine, seems to be involved in a variety of physiological and metabolic processes via both receptor-mediated and receptor-independent mechanisms. The aim of our study was to find out whether melatonin can affect blood pressure (BP), nitric oxide synthase (NOS) activity, eNOS and nNOS protein expressions in rats with metabolic syndrome (SHR/cp). Rats were divided into four groups: 6-week-old male WKY andSHR/cp and age-matched WKY and SHR/cp treated with melatonin (10 mg/kg/day) for 3 weeks. BP was measured by tail-cuff plethysmography. NOS activity, eNOS and nNOS protein expressions were determined in the heart, aorta, brain cortex and cerebellum. MT(1) receptors were analyzed in the brain cortex and cerebellum. In SHR/cp rats, BP was decreased after melatonin treatment. In the same group, melatonin did not affect NOS activity and eNOS protein expression in the heart and aorta, while it increased both parameters in the brain cortex and cerebellum. Interestingly, melatonin elevated MT1 protein expression in the cerebellum. Neuronal NOS protein expression was not changed within the groups. In conclusion, increased NOS activity/eNOS upregulation in particular brain regions may contribute partially to BP decrease in SHR/cp rats after melatonin treatment. Participation of MT(1) receptors in this melatonin action may be supposed.

Melatonin and Human Cardiovascular Disease

The possible therapeutic role of melatonin in the pathophysiology of coronary artery disorder (CAD) is increasingly being recognized. In humans, exogenous melatonin has been shown to decrease nocturnal hypertension, improve systolic and diastolic blood pressure, reduce the pulsatility index in the internal carotid artery, decrease platelet aggregation, and reduce serum catecholamine levels. Low circulating levels of melatonin are reported in individuals with CAD, arterial hypertension, and congestive heart failure. This review assesses current literature on the cardiovascular effects of melatonin in humans. It can be concluded that melatonin deserves to be considered in clinical trials evaluating novel therapeutic interventions for cardiovascular disorders.

Day/night expression of MT1 and MT2 receptors in hypothalamic nuclei of the primate Sapajus apella

Melatonin is involved in the temporal organization of several physiological and behavioral events, controlled by hypothalamic nuclei, like sleep, feeding, reproduction and metabolic modulation and acts through two types of high-affinity G protein-coupled membrane receptors: MT₁ and MT₂. This study aimed to investigate the expression of MT₁ and MT₂ receptors proteins in four hypothalamic nuclei, i.e., SCN, supraoptic (SON), paraventricular (PVN) and anteroventral periventricular nuclei (AVPV), of the diurnal primate Sapajus apella using immunohistochemistry. Since these areas are involved in the expression of biological rhythms, they are candidates to have variations in their neurochemistry, so the MT₁ and MT₂ expression has been analyzed at a point in light and another in the dark phase. Both receptors were found to have day/night differences in the four hypothalamic nuclei with an apparent inverse expression in the SCN compared with the other areas. These differences could be related to the idea that the individual should be prepared to respond by different ways to melatonin signal within the several processes and can contribute to the efficacy of melatonin ligands or melatonin in therapies.

Chronic Stress Facilitates the Development of Deep Venous Thrombosis

The increasing pressure of modern social life intensifies the impact of stress on the development of cardiovascular diseases, which include deep venous thrombosis (DVT). Renal sympathetic denervation has been applied as one of the clinical approaches for the treatment of drug-resistant hypertension. In addition, the close relationship between oxidative stress and cardiovascular diseases has been well documented. The present study is designed to explore the mechanism by which the renal sympathetic nerve system and the oxidative stress affect the blood coagulation system in the development of DVT. Chronic foot shock model in rats was applied to mimic a state of physiological stress similar to humans. Our results showed that chronic foot shock procedure could promote DVT which may be through the activation of platelets aggregation. The aggravation of DVT and activation of platelets were alleviated by renal sympathetic denervation or antioxidant (Tempol) treatment. Concurrently, the denervation treatment could also reduce the levels of circulating oxidation factors in rats. These results demonstrate that both the renal sympathetic nerve system and the oxidative stress contribute to the development of DVT in response to chronic stress, which may provide novel strategy for treatment of clinic DVT patients.

Effect of electro-acupuncture on gene expression in heart of rats with stress-induced pre-hypertension based on gene chip technology

OBJECTIVE

To explore electro-acupuncture's (EA's) effect on gene expression in heart of rats with stress-induced pre-hypertension and try to reveal its biological mechanism based on gene chip technology.

METHODS

Twenty-seven Wistar male rats were randomly divided into 3 groups. The stress-induced hypertensive rat model was prepared by electric foot-shocks combined with generated noise. Molding cycle lasted for 14 days and EA intervene was applied,on rats in model + EA group during model preparation. Rat Gene 2.0 Sense Target Array technology was used for the determination of gene expression profiles and the screened key genes were verified by real-time quantitative polymerase chain reaction (RT-PCR) method.

RESULTS

Compared with blank control group, 390 genes were changed in model group; compared with model control group, 330 genes were changed in model+EA group. Significance analysis of gene function showed that the differentially expressed genes are those involved in biological process, molecular function and cellular components. RT-PCR result of the screened key genes is consistent with that of gene chip test.

CONCLUTION

EA could significantly lower blood pressure of stress-induced pre-hypertension rats and affect its gene expression profile in heart. Genes that related to the contraction of vascular smooth muscle may be involved in EA's anti-hypertensive mechanism.

A Study on Effect of Electroacupuncture on Gene Expression in Hypothalamus of Rats with Stress-Induced Prehypertension Based on Gene Chip Technology

Objective. To explore the effect of electroacupuncture (EA) on gene expression in the hypothalamus of rats with stress-induced prehypertension and try to reveal its biological mechanism with gene chip technology. Methods. The stress-induced hypertensive rat model was prepared by combining electric foot-shocks with generated noise. Molding cycle lasted for 14 days and EA intervention was applied on model + EA group during model preparation. Rat Gene 2.0 Array technology was used for the determination of gene expression profiles and the screened key genes were verified by real-time fluorescence quantitative PCR method. Results. Compared with the blank group, 234 genes were upregulated and 73 were downregulated in the model group. Compared with the model group, 110 genes were upregulated and 273 genes were downregulated in model + EA group. The PCR results of the key genes including HSPB1, P2RX4, PPP1R14A, and TH are consistent with that of gene chip test. Conclusion. EA could significantly lower blood pressure of stress-induced prehypertension rats and affect its gene expression profile in hypothalamus. Genes and their signal transduction pathway that related to the contraction of vascular smooth muscle, concentration of Ca(2+), and excitability of sympathetic nerve may be involved in EA's antihypertensive mechanism.

Role of the renin-angiotensin system, renal sympathetic nerve system, and oxidative stress in chronic foot shock-induced hypertension in rats

OBJECTIVE

The renin-angiotensin system (RAS) and renal sympathetic nerve system (RSNS) are involved in the development of hypertension. The present study is designed to explore the possible roles of the RAS and the RSNS in foot shock-induced hypertension.

METHODS

Male Sprague-Dawley rats were divided into six groups: control, foot shock, RSNS denervation, denervation plus foot shock, Captopril (angiotensin I converting enzyme inhibitor, ACE inhibitor) plus foot shock, and Tempol (superoxide dismutase mimetic) plus foot shock. Rats received foot shock for 14 days. We measured the quantity of thiobarbituric acid reactive substances (TBARS), corticosterone, renin, and angiotensin II (Ang II) in plasma, the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and renal noradrenaline content. RAS component mRNA and protein levels were quantified in the cerebral cortex and hypothalamus.

RESULTS

The two week foot shock treatment significantly increased systolic blood pressure, which was accompanied by an increase in angiotensinogen, renin, ACE1, and AT1a mRNA and protein expression in the cerebral cortex and hypothalamus, an increase of the plasma concentrations of renin, Ang II, corticosterone, and TBARS, as well as a decrease in plasma SOD and GSH-Px activities. Systolic blood pressure increase was suppressed by denervation of the RSNS or treatment with Captopril or Tempol. Interestingly, denervation or Tempol treatment both decreased main RAS components not only in the circulatory system, but also in the central nervous system. In addition, decreased antioxidant levels and increased TBARS and corticosterone levels were also partially restored by denervation or treatment with Tempol or Captopril.

CONCLUSIONS

RAS, RSNS and oxidative stress reciprocally potentiate to play important roles in the development of foot shock-induced hypertension.

Contribution of the renin-angiotensin system in chronic foot-shock induced hypertension in rats

AIMS

Chronic foot shock has been demonstrated to induce hypertension. The present study was designed to explore whether the renin-angiotensin system (RAS) plays a role in this process and the possible mechanisms involved in chronic-foot-shock-induced hypertension.

MAIN METHODS

Male Sprague-Dawley rats were subjected to a two-week foot shock with or without an angiotensin II (Ang II) type 1 receptor blocker (ARB, candesartan) or an angiotensin I converting enzyme inhibitor (ACEI, captopril). The expression of RAS components in the central nervous and circulatory systems was examined. Antioxidant levels in the plasma were monitored.

KEY FINDINGS

Two-week foot shock significantly increased systolic blood pressure (SBP). Angiotensinogen, angiotensin I converting enzyme (ACE)-1, ACE-2, angiotensin type 1a and type 1b receptors, and vasopressin (VAP) mRNA expression in the cerebral cortex and hypothalamus were increased along with the concentration of renin and Ang II in the plasma; these changes were accompanied by decreased glutathione peroxidase activity and increased lipid peroxidation levels and plasma corticosterone concentrations. Both candesartan and captopril suppressed not only the increases in SBP but also the increases in VAP expression in the hypothalamus and RAS components in the central nervous system and the circulatory system. The decreases in antioxidant levels and the increases in lipid peroxidation and corticosterone levels were also partially reversed by candesartan or captopril treatment.

SIGNIFICANCE

Chronic foot shock increases expression of the main RAS components, which play an important role in the development of high blood pressure through increased VAP levels, oxidative stress levels and stress hormone levels.

Melatonin reduces tachycardia in postural tachycardia syndrome: a randomized, crossover trial

BACKGROUND

Postural tachycardia syndrome (POTS) induces disabling chronic orthostatic intolerance with an excessive increase in heart rate (HR) upon standing, and many POTS patients have a hyperadrenergic state. Medications that restrain HR are a promising approach to this problem.

OBJECTIVE

We tested the hypothesis that melatonin will attenuate the tachycardia and improve symptom burden in patients with POTS.

METHODS

Patients with POTS (n = 78) underwent acute drug trials with melatonin 3 mg orally and placebo, on separate mornings, in a randomized crossover design. Blood pressure, HR, and symptoms were assessed while seated and after standing for up to 10 min prior to, and hourly for 4 h following study drug administration.

RESULTS

The reduction in standing HR was significantly greater 2 h after melatonin compared with placebo (P = 0.017). There was no significant difference in the reduction of systolic blood pressure between melatonin and placebo, either with standing or while seated. The symptom burden was not improved with melatonin compared with placebo.

CONCLUSION

Oral melatonin produced a modest decrease in standing tachycardia in POTS. Further research is needed to determine the effects of regular night-time use of this medication in POTS.

Peripheral and central effects of melatonin on blood pressure regulation

The pineal hormone, melatonin (N-acetyl-5-methoxytryptamine), shows potent receptor-dependent and -independent actions, which participate in blood pressure regulation. The antihypertensive effect of melatonin was demonstrated in experimental and clinical hypertension. Receptor-dependent effects are mediated predominantly through MT1 and MT2 G-protein coupled receptors. The pleiotropic receptor-independent effects of melatonin with a possible impact on blood pressure involve the reactive oxygen species (ROS) scavenging nature, activation and over-expression of several antioxidant enzymes or their protection from oxidative damage and the ability to increase the efficiency of the mitochondrial electron transport chain. Besides the interaction with the vascular system, this indolamine may exert part of its antihypertensive action through its interaction with the central nervous system (CNS). The imbalance between the sympathetic and parasympathetic vegetative system is an important pathophysiological disorder and therapeutic target in hypertension. Melatonin is protective in CNS on several different levels: It reduces free radical burden, improves endothelial dysfunction, reduces inflammation and shifts the balance between the sympathetic and parasympathetic system in favor of the parasympathetic system. The increased level of serum melatonin observed in some types of hypertension may be a counter-regulatory adaptive mechanism against the sympathetic overstimulation. Since melatonin acts favorably on different levels of hypertension, including organ protection and with minimal side effects, it could become regularly involved in the struggle against this widespread cardiovascular pathology.

The effect of melatonin on circadian blood pressure in patients with type 2 diabetes and essential hypertension

INTRODUCTION

The aim of this study was to evaluate the effect of melatonin on blood pressure in patients with essential hypertension receiving medical treatment and with type 2 diabetes in good metabolic control.

MATERIAL AND METHODS

The study lasted 8 weeks. Patients were equipped with a 24-hour ambulatory blood pressure monitor and took melatonin (3 mg a day in the evening) for 4 weeks. The patients were divided into four groups: group 1 (n = 32) including dippers, group 2 (n = 34) non-dippers treated with melatonin; and two control groups: group 3 (n = 28) including dippers and group 4 (n = 30) non-dippers treated without melatonin. After 4 weeks patients took melatonin for the next 4 weeks (5 mg a day). In each visit were analyzed: systolic, diastolic and mean blood pressure in both day and night time.

RESULTS

We observed that 29.5% non-dippers (n = 10) treated with melatonin in a dose of 3 mg/day achieved features of dippers compared to control group (p < 0.05). Five mg of melatonin per day restored normal diurnal blood pressure rhythm in 32.4% non-dippers (n = 11, p < 0.05). In non-dippers treated with melatonin significant decreases of diastolic, systolic and mean night blood pressure values (p < 0.05) were observed.

CONCLUSIONS

More than 30% of non-dippers with type 2 diabetes treated with melatonin were restored to the normal circadian rhythm of blood pressure. The effect of melatonin in both doses (3 mg and 5 mg) was significant for non-dippers only and included nocturnal systolic, diastolic and mean arterial pressure.

Effect of captopril and melatonin on fibrotic rebuilding of the aorta in 24 hour light-induced hypertension

Chronic continuous light exposure leads to melatonin deficiency along with complex neurohumoral activation resulting in hypertension development in rats. The aim of this study was to show, whether continuous light induces fibrotic rebuilding of the aorta and whether the treatment with melatonin or angiotensin converting enzyme inhibitor captopril can prevent these potential alterations. In a six-week experiment, 3-month-old Wistar rats were divided into 4 groups (ten per group): controls, rats exposed to continuous light, exposed to continuous light plus treated with captopril (100 mg/kg/24 h) and exposed to continuous light plus treated with melatonin (10 mg/kg/24 h). Systolic blood pressure (SBP) and collagen type I and III in the media of thoracic aorta were measured. Continuous light induced hypertension and fibrotic rebuilding of the aorta in terms of enhancement of collagen I and III concentration in the aortic media. Both captopril and melatonin prevented SBP rise and reduced collagen III concentration in the aorta. However, only melatonin reduced collagen I and the sum of collagen I and III in the aortic tissue. We conclude that in continuous light-induced hypertension, administration of melatonin, along with SBP reduction, decreases collagen I and III concentration in the aorta. It is suggested that antifibrotic effect of melatonin may reduce the stiffness of the aorta and small arteries and beneficially influence the nature of the pulse wave and peripheral vascular resistance.

Melatonin secretion is impaired in women with preeclampsia and an abnormal circadian blood pressure rhythm

Non-dipping circadian blood pressure (BP) is a common finding in preeclampsia, accompanied by adverse outcomes. Melatonin plays pivotal role in biological circadian rhythms. This study investigated the relationship between melatonin secretion and circadian BP rhythm in preeclampsia. Cases were women with preeclampsia treated between January 2006 and June 2007 in the University Hospital of Larissa. Volunteers with normal pregnancy, matched for chronological and gestational age, served as controls. Twenty-four hour ambulatory BP monitoring was applied. Serum melatonin and urine 6-sulfatoxymelatonin levels were determined in day and night time samples by enzyme-linked immunoassays. Measurements were repeated 2 months after delivery. Thirty-one women with preeclampsia and 20 controls were included. Twenty-one of the 31 women with preeclampsia were non-dippers. Compared to normal pregnancy, in preeclampsia there were significantly lower night time melatonin (48.4 ± 24.7 vs. 85.4 ± 26.9 pg/mL, p<0.001) levels. Adjustment for circadian BP rhythm status ascribed this finding exclusively to non-dippers (p<0.01). Two months after delivery, in 11 of the 21 non-dippers both circadian BP and melatonin secretion rhythm reappeared. In contrast, in cases with retained non-dipping status (n=10) melatonin secretion rhythm remained impaired: daytime versus night time melatonin (33.5 ± 13.0 vs. 28.0 ± 13.8 pg/mL, p=0.386). Urinary 6-sulfatoxymelatonin levels were, overall, similar to serum melatonin. Circadian BP and melatonin secretion rhythm follow parallel course in preeclampsia, both during pregnancy and, at least 2 months after delivery. Our findings may be not sufficient to implicate a putative therapeutic effect of melatonin, however, they clearly emphasize that its involvement in the pathogenesis of a non-dipping BP in preeclampsia needs intensive further investigation.

The effects of angiotensin II and angiotensin-(1-7) in the rostral ventrolateral medulla of rats on stress-induced hypertension

We have shown that angiotensin II (Ang II) and angiotensin-(1–7) [Ang-(1–7)] increased arterial blood pressure (BP) via glutamate release when microinjected into the rostral ventrolateral medulla (RVLM) in normotensive rats (control). In the present study, we tested the hypothesis that Ang II and Ang-(1–7) in the RVLM are differentially activated in stress-induced hypertension (SIH) by comparing the effects of microinjection of Ang II, Ang-(1–7), and their receptor antagonists on BP and amino acid release in SIH and control rats. We found that Ang II had greater pressor effect, and more excitatory (glutamate) and less inhibitory (taurine and γ-aminobutyric acid) amino acid release in SIH than in control animals. Losartan, a selective AT₁ receptor (AT₁R) antagonist, decreased mean BP in SIH but not in control rats. PD123319, a selective AT₂ receptor (AT₂R) antagonist, increased mean BP in control but not in SIH rats. However, Ang-(1–7) and its selective Mas receptor antagonist Ang779 evoked similar effects on BP and amino acid release in both SIH and control rats. Furthermore, we found that in the RVLM, AT₁R, ACE protein expression (western blot) and ACE mRNA (real-time PCR) were significantly higher, whereas AT₂R protein, ACE2 mRNA and protein expression were significantly lower in SIH than in control rats. Mas receptor expression was similar in the two groups. The results support our hypothesis and demonstrate that upregulation of Ang II by AT₁R, not Ang-(1–7), system in the RVLM causes hypertension in SIH rats by increasing excitatory and suppressing inhibitory amino acid release.

Orexin A regulates cardiovascular responses in stress-induced hypertensive rats

Several pieces of evidence indicate that the rostral ventrolateral medulla (RVLM) is probably one of the key neural structures mediating the pressor effects of orexins in the brain. Nitric oxide synthase/nitric oxide (NOS/NO) system in the RVLM modulates cardiovascular activities. Our experiments were designed to test the hypothesis that orexin-A (OXA) is involved in the mechanism of stress-induced hypertension (SIH) by adjusting NOS/NO system in the RVLM. The stress-induced hypertensive rats (SIHR) model was established by electric foot-shocks and noises. Here we examined the expression of OXA immunoreactive (OXA-IR) cells in the lateral hypothalamus (LH) and the protein level of orexin 1 receptor (OX1R) in the RVLM of SIHR, and we found that the expressions of OXA-IR and OX1R were higher than those of the control group. The double-staining immunohistochemical evidence showed that OX1R immunoreactive (OX1R-IR) cells and neuronal nitric oxide synthase (nNOS) or inducible nitric oxide synthase (iNOS) immunoreactive (IR) cells were co-localizated in the RVLM. Microinjection of OXA (10, 50, 100 pmol/100 nl) into the unilateral (right) RVLM of control rats or SIHR produced pressor and tachycardiac effects in a dose-dependent manner. SB-408124 (100 pmol/100 nl, an antagonist of OX1R) or TCS OX2 29 (100 pmol/100 nl, an antagonist of OX2R) partly abolished the cardiovascular effects of exogenously-administrated OXA into the RVLM of control rats and SIHR, and lowered the increased systolic blood pressure (SBP) and heart rate (HR) of SIHR, with no difference in statistical significance between the two antagonists' effects. Microinjection into the RVLM of both control and SIHR groups of 7-Ni (0.05 pmol/100 nl, nNOS inhibitor) or Methylene Blue [100 pmol/100 nl, an inhibitor of soluble guanylate cyclase (sGC)] suppressed the OXA-induced increase of SBP and HR, whereas microinjection of AG (1, 10, 100 pmol/100 nl) had no obvious effects on the OXA-induced increase of SBP and HR. Our results indicate that OXA in the RVLM may participate in the central regulation of cardiovascular activities in SIHR, and OX1R and OX2R both have important roles in it. The cardiovascular effects of OXA in the RVLM may be induced by nNOS-derived NO, which activated sGC-associated signaling pathway.

Cardiovascular effects of melatonin receptor agonists

INTRODUCTION

Melatonin synchronizes circadian rhythms with light/dark period and it was demonstrated to correct chronodisruption. Several melatonin receptor agonists with improved pharmacokinetics or increased receptor affinity are being developed, three of them are already in clinical use. However, the actions of melatonin extend beyond chronobiology to cardiovascular and metabolic systems as well. Given the high prevalence of cardiovascular disease and their common occurrence with chronodisruption, it is of utmost importance to classify the cardiometabolic effects of the newly approved and putative melatoninergic drugs.

AREAS COVERED

In the present review, the available (although very sparse) data on such effects, in particular by the approved (circadin, ramelteon, agomelatine) or clinically advanced (tasimelteon, piromelatine = Neu-P11, TIK-301) compounds are summarized. The authors have searched for an association with blood pressure, vascular reactivity, ischemia, myocardial and vascular remodeling and metabolic syndrome.

EXPERT OPINION

The data suggest that cardiovascular effects of melatonin are at least partly mediated via MT(1)/MT(2) receptors and associated with its chronobiotic action. Therefore, despite the sparse direct evidence, it is believed that these effects will be shared by melatonin analogs as well. With the expected approval of novel melatoninergic compounds, it is suggested that the investigation of their cardiovascular effects should no longer be neglected.

Synergism between melatonin and atorvastatin against endothelial cell damage induced by lipopolysaccharide

The beneficial effects of atorvastatin are based on both cholesterol-dependent and independent mechanisms. The latter probably include the ability of the estatin to enhance the expression of endothelial nitric oxide synthase (eNOS) and to cause a vasodilatation. In turn, the antioxidant and anti-inflammatory actions of melatonin are related to its vascular protection. In the present study, we investigated the efficacy of the combination of melatonin plus atorvastatin against endothelial cell damage induced by inflammation and oxidative stress injury. Human umbilical vein endothelial cells (HUVEC) were cultured with bacterial lipopolysaccharide (LPS) in the presence or absence of melatonin and/or atorvastatin. LPS inhibited eNOS mRNA and protein expression, which was reversed by atorvastatin and, to a lesser extent, by melatonin. Together, melatonin + atorvastatin induced higher eNOS protein expression than either compound alone. Melatonin, but not atorvastatin, reduced free radical generation, lipid peroxidation, and interleukin-6 levels induced by LPS. In the presence of atorvastatin, the effects of melatonin were maintained or even improved. These data suggest that melatonin improves the beneficial effects of atorvastatin and reduces its side effects in endothelial cells during inflammation and under conditions of oxidative stress.

The role of melatonin in glaucoma: implications concerning pathophysiological relevance and therapeutic potential

Glaucoma is a frequent ophthalmologic condition leading to chronic progressive optic neuropathy, which can result in visual impairment and blindness. In addition, glaucoma is associated with a dysregulation of circadian rhythms, as well as with a high incidence of sleep disorders, depression, and anxiety. However, because of their high comorbidity in older age, these conditions have not received much scientific attention and are often undertreated. In the current paper, we review the available literature on the role of melatonergic mechanisms in glaucoma, regulation of circadian rhythms, and depression. The literature is presented as a narrative review, providing an overview on the most important and clinically relevant publications. Recently, there has been evidence for a progressive loss of intrinsically photosensitive retinal ganglion cells (ipRGC) because of oxidative stress in glaucoma. As ipRGC are responsible for the photic transduction to the circadian system and subsequent melatonin secretion, and melatonin is involved in the pathophysiology of circadian desynchronization, sleep disorder, and depression, an impairment of photo-dependent melatonergic signaling may be a common pathway connecting glaucoma with these comorbidities. This fact, as well as the proven retinal neuroprotective role of melatonin, suggests that melatonergic drugs provide a potentially promising treatment strategy supplementing the management of intraocular pressure by pharmacological and surgical measures. Additionally, multidisciplinary treatment focusing on depression and normalization of circadian rhythms might be beneficial for glaucoma patients. Furthermore, glaucoma might be a useful model for studying the pathophysiological interactions between the melatonergic, circadian, and mood systems.

Beneficial effects of melatonin in cardiovascular disease

The experimental data obtained from both human and rodent studies suggest that melatonin may have utility in the treatment of several cardiovascular conditions. In particular, melatonin's use in reducing the severity of essential hypertension should be more widely considered. In rodent studies melatonin has been shown to be highly effective in limiting abnormal cardiac physiology and the loss of critical heart tissue resulting from ischemia/reperfusion injury. Melatonin may also be useful in reducing cardiac hypertrophy in some situations and thereby limiting the frequency of heart failure. Finally, some conventional drugs currently in use have cardiotoxicity as a side-effect. Based on studies in rodents, melatonin, due to its multiple anti-oxidative actions, is highly effective in abrogating drug-mediated damage to the heart. Taken together, the findings from human and animal studies support the consideration of melatonin as a cardioprotective agent.

Potential roles of melatonin and chronotherapy among the new trends in hypertension treatment

The number of well-controlled hypertensives is unacceptably low worldwide. Respecting the circadian variation of blood pressure, nontraditional antihypertensives, and treatment in early stages of hypertension are potential ways to improve hypertension therapy. First, prominent variations in circadian rhythm are characteristic for blood pressure. The revolutionary MAPEC (Ambulatory Blood Pressure Monitoring and Cardiovascular Events) study, in 3000 adult hypertensives investigates, whether chronotherapy influences the cardiovascular prognosis beyond blood pressure reduction per se. Second, melatonin, statins and aliskiren are hopeful drugs for hypertension treatment. Melatonin, through its scavenging and antioxidant effects, preservation of NO availability, sympatholytic effect or specific melatonin receptor activation exerts antihypertensive and anti-remodeling effects and may be useful especially in patients with nondipping nighttime blood pressure pattern or with nocturnal hypertension and in hypertensives with left ventricular hypertrophy (LVH). Owing to its multifunctional physiological actions, this indolamine may offer cardiovascular protection far beyond its hemodynamic benefit. Statins exert several pleiotropic effects through inhibition of small guanosine triphosphate-binding proteins such as Ras and Rho. Remarkably, statins reduce blood pressure in hypertensive patients and more importantly they attenuate LVH. Addition of statins should be considered for high-risk hypertensives, for hypertensives with LVH, and possibly for high-risk prehypertensive patients. The direct renin inhibitor, aliskiren, inhibits catalytic activity of renin molecules in circulation and in the kidney, thus lowering angiotensin II levels. Furthermore, aliskiren by modifying the prorenin conformation may prevent prorenin activation. At present, aliskiren should be considered in hypertensive patients not sufficiently controlled or intolerant to other inhibitors of renin-angiotensin system. Third, TROPHY (Trial of Preventing Hypertension) is the first pharmacological intervention for prehypertensive patients revealing that treatment with angiotensin II type 1 receptor blocker attenuates hypertension development and thus decreases the risk of cardiovascular events.