Effects of N-nitro l-arginine methyl ester (l-NAME), a potent nitric oxide synthase inhibitor, on visual evoked potentials of rats exposed to different experimental stress models

Recent Developments in Drug Targets and Combination Therapy for the Clinical Management of Hypertension

Raised blood pressure is the most common complication worldwide that may lead to atherosclerosis and ischemic heart disease. Unhealthy lifestyles, smoking, alcohol consumption, junk food, and genetic disorders are some of the causes of hypertension. To treat this condition, numerous antihypertensive medications are available, either alone or in combination, that work via various mechanisms of action. Combinational therapy provides a certain advantage over monotherapy in the sense that it acts in multi mechanism mode and minimal drug amount is required to elicit the desired therapeutic effect. Such therapy is given to patients with systolic blood pressure greater than 20 mmHg and/or diastolic blood pressure exceeding 10 mmHg beyond the normal range, as well as those suffering from severe cardiovascular disease. The selection of antihypertensive medications, such as calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and low-dose diuretics, hinges on their ability to manage blood pressure effectively and reduce cardiovascular disease risks. This review provides insights into the diverse monotherapy and combination therapy approaches used for elevated blood pressure management. In addition, it offers an analysis of combination therapy versus monotherapy and discusses the current status of these therapies, from researchbased findings to clinical trials.

Human Nitric Oxide Synthase-Its Functions, Polymorphisms, and Inhibitors in the Context of Inflammation, Diabetes and Cardiovascular Diseases

In various diseases, there is an increased production of the free radicals needed to carry out certain physiological processes but their excessive amounts can cause oxidative stress and cell damage. Enzymes play a major role in the transformations associated with free radicals. One of them is nitric oxide synthase (NOS), which catalyzes the formation of nitric oxide (NO). This enzyme exists in three forms (NOS1, NOS2, NOS3), each encoded by a different gene. The following work presents the most important information on the NOS isoforms and their role in the human body, including NO synthesis in various tissues and cells, intercellular signaling and activities supporting the immune system and regulating blood vessel functions. The role of NOS in pathological conditions such as obesity, diabetes and heart disease is considered. Attention is also paid to the influence of the polymorphisms of these genes, encoding particular isoforms, on the development of these pathologies and the role of NOS inhibitors in the treatment of patients.

Age-dependent redox status in the brain stem of NO-deficient hypertensive rats

BACKGROUND

The brain stem contains important nuclei that control cardiovascular function via the sympathetic nervous system (SNS), which is strongly influenced by nitric oxide. Its biological activity is also largely determined by oxygen free radicals. Despite many experimental studies, the role of AT1R-NAD(P)H oxidase-superoxide pathway in NO-deficiency is not yet sufficiently clarified. We determined changes in free radical signaling and antioxidant and detoxification response in the brain stem of young and adult Wistar rats during chronic administration of exogenous NO inhibitors.

METHODS

Young (4 weeks) and adult (10 weeks) Wistar rats were treated with 7-nitroindazole (7-NI group, 10 mg/kg/day), a specific nNOS inhibitor, with N^G-nitro-L-arginine-methyl ester (L-NAME group, 50 mg/kg/day), a nonspecific NOS inhibitor, and with drinking water (Control group) during 6 weeks. Systolic blood pressure was measured by non-invasive plethysmography. Expression of genes (AT1R, AT2R, p22phox, SOD and NOS isoforms, HO-1, MDR1a, housekeeper GAPDH) was identified by real-time PCR. NOS activity was detected by conversion of [3H]-L-arginine to [3H]-L-citrulline and SOD activity was measured using UV VIS spectroscopy.

RESULTS

We observed a blood pressure elevation and decrease in NOS activity only after L-NAME application in both age groups. Gene expression of nNOS (youngs) and eNOS (adults) in the brain stem decreased after both inhibitors. The radical signaling pathway triggered by AT1R and p22phox was elevated in L-NAME adults, but not in young rats. Moreover, L-NAME-induced NOS inhibition increased antioxidant response, as indicated by the observed elevation of mRNA SOD3, HO-1, AT2R and MDR1a in adult rats. 7-NI did not have a significant effect on AT1R-NADPH oxidase-superoxide pathway, yet it affected antioxidant response of mRNA expression of SOD1 and stimulated total activity of SOD in young rats and mRNA expression of AT2R in adult rats.

CONCLUSION

Our results show that chronic NOS inhibition by two different NOS inhibitors has age-dependent effect on radical signaling and antioxidant/detoxificant response in Wistar rats. While 7-NI had neuroprotective effect in the brain stem of young Wistar rats, L-NAME- induced NOS inhibition evoked activation of AT1R-NAD(P)H oxidase pathway in adult Wistar rats. Triggering of the radical pathway was followed by activation of protective compensation mechanism at the gene expression level.

Novel Fluorescence Arginine Analogue as a Sensor for Direct Identification and Imaging of Nitric Oxide Synthase-like Enzymes in Plants

Nitric oxide synthase like enzyme (NOS-like enzyme), which produces nitric oxide, participates in many biological processes. However it remains unidentified and highly controversial that plants do possess a NOS-like enzyme. In this paper, a novel arginine analogue NP1 was designed and developed for the direct identification and real time tracking of NOS-like enzymes in plant by fluorescence sensing. It could bind NOS-like enzyme efficiently and enter the cell successfully. In vivo fluorescence response results directly proved that NOS-like enzymes did exist in tobacco leaf and would be stimulated by pathogen infection, which also provided a useful chemical tool for the study of the function of NOS-like enzyme in plants.

CHANGES IN VISUAL EVOKED POTENTIALS, LIPID PEROXIDATION AND ANTIOXIDANT ENZYMES IN RATS EXPOSED TO RESTRAINT STRESS: EFFECT OF L-CARNITINE

The purpose of our study was to investigate the effects of L-carnitine on lipid peroxidation, Visual Evoked Potentials (VEPs) and antioxidant enzyme activities such as superoxide dismutase and catalase in rats exposed to chronic restraint stress. Forty male Wistar rats, aged three months were used. They were equally divided into four groups: control (C), the group exposed to restraint stress (R), the group treated with L-carnitine(L) and the group exposed to stress and treated with L-carnitine (RL). Chronic restraint stress was applied for 21 days (1 h/day) and L-carnitine (50 mg/kg/day) was given by gavage to the L and RL groups for the same period. Brain and retina levels of thiobarbituric acid reactive substances (TBARS) were significantly increased in the R group and were not altered in the L group compared to the C group. Brain and retina TBARS levels were lower in the RL group than in the R group. Brain and retina superoxide dismutase and catalase activities were significantly decreased in the L and R groups compared to the C group. L-carnitine pretreatment had no significant effect on superoxide dismutase and catalase activity in the RL group. All latencies of VEP components were prolonged in the R and L groups with respect to the C group. L-carnitine increased the latencies of all VEP components in the L group whereas shortened them in the RL group compared to their control groups. L-carnitine may be a promising agent for the prevention of VEP and TBARS alterations caused by stress.

Nitroglycerin sensitises in healthy subjects CNS structures involved in migraine pathophysiology: evidence from a study of nociceptive blink reflexes and visual evoked potentials

Nitroglycerin (NTG), a NO donor, induces an attack in migraine patients approximately 4-6 h after administration. The causative mechanisms are not known, but the long delay leaves room for a central effect, such as a change in neuronal excitability and synaptic transmission of various CNS areas involved in pain and behaviour including trigeminal nucleus caudalis and monoaminergic brain stem nuclei. To explore the central action of NTG, we have studied its effects on amplitude and habituation of the nociceptive blink reflex (nBR) and the visual evoked potential (VEP) before, 1 h and 4 h after administration of NTG (1.2 mg sublingual) or placebo (vehicle sublingual) in two groups of 10 healthy volunteers. We found a significant decrease in nBR pain and reflex thresholds both 1 and 4 h post-NTG. At the 4 h time point R2 latency was shorter (p=0.04) and R2 response area increased (p<0.01) after NTG but not after placebo. Habituation tended to become more pronounced after both NTG and placebo administration. There was a significant amplitude increase in the 5th VEP block (p=0.03) at 1h after NTG and in the 1st block (p=0.04) at 4 h. VEP habituation was replaced by potentiation at both delays after NTG; the change in habituation slope was significant at 1h (p=0.02). There were no significant VEP changes in subjects who received sublingual placebo. In conclusion, we found that in healthy subjects sublingual NTG, but not its vehicle, induces changes in a trigeminal nociceptive reflex and an evoked cortical response which are comparable to those found immediately before and during an attack of migraine. These changes could be relevant for the attack-triggering effect of NTG in migraineurs.

Effect of aminoguanidine on visual evoked potentials (VEPs), antioxidant status and lipid peroxidation in rats exposed to chronic restraint stress

The purpose of the study was to investigate the effect of aminoguanidine (AG) on visual evoked potentials (VEPs), thiobarbituric acid reactive substances (TBARS), the activities of Cu, Zn superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GSH-Px) and catalase (CAT), and nitrite/nitrate levels. Forty healthy male Wistar rats, aged 3 months, were divided into four equal groups: Control (C), the group treated with aminoguanidine (A), the group exposed to restraint stress (S), the group exposed to restraint stress and treated with aminoguanidine (AS). Chronic restraint stress was applied for 21 days (1 h/day) and aminoguanidine (50 mg/kg/day) was injected intraperitoneally to the A and AS groups for the same period. Aminoguanidine treatment significantly decreased retina and brain TBARS levels in rats exposed to restraint stress compared to rats exposed to restraint stress alone. Aminoguanidine treatment produced a significant decrease in brain and retina nitrite and nitrate levels with respect to the control groups. Aminoguanidine increased all antioxidant enzyme activities in both brain and retina in rats exposed to restraint stress compared to rats exposed to restraint stress alone. All VEP components were significantly decreased in AG treated rats exposed to restraint stress compared to rats exposed to restraint stress alone. Our study clearly showed that AG has the potential to prevent changes caused by stress.

Effects of iloprost on visual evoked potentials and brain tissue oxidative stress after bilateral common carotid artery occlusion

Effects of iloprost on visual evoked potentials and oxidant/antioxidant status were evaluated after bilateral carotid artery occlusion. There were three experimental groups; Sham (S) group (n=10), bilateral common carotid artery occluded (BCCAO) group (n=10) and after bilateral common carotid artery occlusion, iloprost-treated (BCCAOI) group (n=10). Iloprost was administered (0.5ng/kg/day) for 10 days by intraperitoneal injection. N(2) and P(2) latencies (millisecond) and N(2)-P(2) (microV) amplitudes were recorded 10 days after operation for evaluating VEPs. The rats were sacrificed by decapitation immediately after recording of VEPs. Malondialdehyte (MDA), glutathione (GSH), Cu-Zn superoxide dysmutase (SOD) were studied spectrophotometricly. After BCCAO, MDA levels were increased, GSH and Cu-Zn SOD levels were decreased significantly, and abnormal VEPs parameters were observed. Iloprost treatment after BCCAO decreased MDA and increased GSH levels significantly. Low Cu-Zn SOD levels and impaired VEPs remained after iloprost treatment. Iloprost treatment may protect the brain tissue from oxidative damage during cerebral hypoperfusion.