Chronic L-Name-Treatment Produces Hypertension by Different Mechanisms in Peripheral Tissues and Brain: Role of Central eNOS

Current insights and future perspectives of flavonoids: A promising antihypertensive approach

Hypertension, or high blood pressure (BP), is a complex disease influenced by various risk factors. It is characterized by persistent elevation of BP levels, typically exceeding 140/90 mmHg. Endothelial dysfunction and reduced nitric oxide (NO) bioavailability play crucial roles in hypertension development. L-NG-nitro arginine methyl ester (L-NAME), an analog of L-arginine, inhibits endothelial NO synthase (eNOS) enzymes, leading to decreased NO production and increased BP. Animal models exposed to L-NAME manifest hypertension, making it a useful design for studying the hypertension condition. Natural products have gained interest as alternative approaches for managing hypertension. Flavonoids, abundant in fruits, vegetables, and other plant sources, have potential cardiovascular benefits, including antihypertensive effects. Flavonoids have been extensively studied in cell cultures, animal models, and, to lesser extent, in human trials to evaluate their effectiveness against L-NAME-induced hypertension. This comprehensive review summarizes the antihypertensive activity of specific flavonoids, including quercetin, luteolin, rutin, troxerutin, apigenin, and chrysin, in L-NAME-induced hypertension models. Flavonoids possess antioxidant properties that mitigate oxidative stress, a major contributor to endothelial dysfunction and hypertension. They enhance endothelial function by promoting NO bioavailability, vasodilation, and the preservation of vascular homeostasis. Flavonoids also modulate vasoactive factors involved in BP regulation, such as angiotensin-converting enzyme (ACE) and endothelin-1. Moreover, they exhibit anti-inflammatory effects, attenuating inflammation-mediated hypertension. This review provides compelling evidence for the antihypertensive potential of flavonoids against L-NAME-induced hypertension. Their multifaceted mechanisms of action suggest their ability to target multiple pathways involved in hypertension development. Nonetheless, the reviewed studies contribute to the evidence supporting the useful of flavonoids for hypertension prevention and treatment. In conclusion, flavonoids represent a promising class of natural compounds for combating hypertension. This comprehensive review serves as a valuable resource summarizing the current knowledge on the antihypertensive effects of specific flavonoids, facilitating further investigation and guiding the development of novel therapeutic strategies for hypertension management.

Drying temperature affects the hypolipidemic, antioxidant, and antihypertensive potential of Hibiscus sabdariffa calyx in rats induced with L-NAME

The effects of different drying temperatures on the hypolipidemic, antioxidant, and antihypertensive potential of Hibiscus sabdariffa calyx was evaluated. The calyx were dried under different temperature conditions (- 58 °C, 30 °C, 40 °C, and 50 °C), and extracted with a solvent mixture of ethanol and water (1:4 % w/v). To induce hypertension, the rats were administered with 40 mg/kg body weight dose of N-nitro L-arginine methyl-ester (L-NAME), via the intra-gastric route. H. sabdariffa extract was administered orally, at varying doses (250, 500, and 1000 mg/kg) to the rats. Afterwards, the hypolipidemic, antioxidant, and antihypertensive potentials of the extracts were evaluated using standard validated methods. Induction with L-NAME significantly (p < 0.05) increased the total cholesterol, triglyceride, and LDL levels, significantly decreased the HDL levels; significantly (p < 0.05) increased the levels of LPO/MDA, H2O2, and decreased GPx, and SOD activities; significantly (p < 0.05) increased the pressures (diastolic and systolic); significantly (p < 0.05) increased ACE and arginase activities, glucose level, and significantly decreased nitric oxide activity. Treatment with H. sabdariffa extract significantly (p < 0.05) reversed these trends in the hypertensive experimental rats. The hypolipidemic, antioxidant, and antihypertensive properties of the extract from the calyx of H. sabdariffa, which varies with the drying temperatures of the calyx, portends its potential as a curative agent in the treatment of hypertensive conditions, and other cardiovascular diseases.

Co-administration of metformin and/or glibenclamide with losartan reverse NG-nitro-l-arginine-methyl ester-streptozotocin-induced hypertensive diabetes and haemodynamic sequelae in rats

Over the years, there have been opinions on whether to reduced blood pressure (BP) to a different levels in patients with diabetes mellitus. Hence, this study investigated the efficacy of the co-administration of losartan (angiotensin receptor blocking antihypertensive agent) with metformin and/or glibenclamide (antidiabetic agents) on hypertensive-diabetic experimental rats induced by N^G-nitro-l-arginine-methyl-ester hydrochloride (l-NAME), and streptozotocin (STZ). STZ (45 mg/kg, i.p.)-induced diabetic rats combined with l-NAME (40 mg/kg, p.o.)-induced hypertension were allotted into different groups. Group 1 received distilled water (10 mL/kg) and served as normal control, group 2 comprised hypertensive diabetic rats with distilled water, groups 3-5 were hypertensive-diabetic rats but received combination treatments of losartan + metformin, losartan + glibenclamide, and losartan + metformin + glibenclamide daily for 8 weeks, respectively. Our finding revealed no changes in the body weights, but there was a significant increase in fasting blood sugar levels in l-NAME - STZ-induced hypertensive-diabetes, which were lowered by losartan + metformin, losartan + glibenclamide, and losartan + metformin + glibenclamide treatments. Moreover, the increased systolic-BP, mean arterial pressure but not diastolic-BP and heart rate by l-NAME + STZ were attenuated more significantly by losartan + metformin + glibenclamide between weeks 2-8 relative to hypertensive-diabetic control. l-NAME + STZ-induced elevated levels of lactate dehydrogenase and creatinine kinase, were differentially reversed by losartan + metformin, losartan + glibenclamide, and losartan + metformin + glibenclamide. However, l-NAME + STZ-induced decreased nitrite level was significantly restored by all treatments, suggesting increased nitrergic transmission. Additionally, l-NAME + STZ-induced degeneration of pancreatic islet and myocardial cells were dramatically alleviated by losartan + metformin + glibenclamide treatments. Our findings suggest hyperglycemia with raised systolic-BP should be managed with losartan combined with both metformin and glibenclamide than single combination of losartan with antidiabetics.

Antihypertensive Effect of Kolaviron, a Bioflavonoid From Garcinia kola, in L-NAME Induced Hypertension in Rats

The antihypertensive effect of Kolaviron (KV) has been demonstrated in ethanol- and sucrose-model of hypertension in our previous studies. However, there remains a need to further confirm and validate this effect in other models of hypertension. This study was devised to appraise the antihypertensive action of KV in N(G)-nitro-L-arginine methyl ester (L-NAME) induced experimental format of hypertension. Thirty-six (36) male Wistar rats were divided into 6 groups of 6 animals each. Group I represents the control group while Group II animals received L-NAME 40 mg/kg only. Groups III to V animals received L-NAME 40 mg/kg and 50, 100, and 200 mg/kg KV, respectively. Group VI animals received L-NAME 40 mg/kg and 0.14 mg/kg Lisinopril (LIS). Treatment was done orally for 28 days after which blood pressure was determined via the invasive method. After this, vital organs and blood were retrieved for analysis. KV and LIS elicited significant contraction ( P < .01-.001) in blood pressure producing up to 27%, 24%, and 22% reduction in systolic blood pressure, diastolic blood pressure, and mean arterial pressure, respectively. In addition, KV elicited a notable rise ( P < .05-.001) in catalase, reduced glutathione, and superoxide dismutase in the blood and vital organs. Results from this study further demonstrate and confirm that KV possesses notable blood pressure-lowering effect possibly through its well-documented antioxidant effect. Additional studies are advocated to validate the results from this study and determine the precise mechanism for the antihypertensive action of KV.

Parboiled Germinated Brown Rice Improves Cardiac Structure and Gene Expression in Hypertensive Rats

Hypertension leads to oxidative stress, inflammation, and fibrosis. The suppression of these indicators may be one treatment approach. Parboiled germinated brown rice (PGBR), obtained by steaming germinated Jasmine rice, reduces oxidative stress and inflammation in vivo. PGBR contains more bioactive compounds than brown rice (BR) and white rice (WR). Anti-hypertensive benefits of PGBR have been predicted, but research is lacking. The anti-hypertensive effects of PGBR were investigated in the downstream gene network of hypertension pathogenesis, including the renin-angiotensin system, fibrosis, oxidative stress production, and antioxidant enzymes in N-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats. To strengthen our findings, the cardiac structure was also studied. PGBR-exposed rats showed significant reductions in systolic blood pressure (SBP) compared to the hypertensive group. WR did not reduce SBP because of the loss of bioactive compounds during intensive milling. PGBR also reduced the expression of the angiotensin type 1 receptor (AT1R), transforming growth factor-β (TGF-β), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX4), which contribute to the renin-angiotensin system, fibrosis, and oxidative stress production, respectively. Losartan (Los, an anti-hypertensive drug)-treated rats also exhibited similar gene expression, implying that PGBR may reduce hypertension using the same downstream target as Los. Our data also indicated that PGBR reduced cardiac lesions, such as the cardiomyopathy induced by L-NAME. This is the first report on the anti-hypertensive effects of PGBR in vivo by the suppression of the renin response, fibrosis, and improved cardiac structure.

Anti-Hypertensive Activity of Some Selected Unani Formulations: An Evidence-Based Approach for Verification of Traditional Unani Claims Using LC-MS/MS for the Evaluation of Clinically Relevant Blood Parameters in Laboratory Rats

Background: Systemic arterial hypertension, which is associated with an increased risk of cardiovascular disease(CVD), is the most significant modifiable risk factor for mortality and morbidity worldwide. WHO has recognized Unanipathy as an alternate system of medicine. The aim of the present study is to investigate the anti-hypertensive activity of some selected unani formulations using L-NAME model. Method: Group I or hypertensive control group: L-NAME administered for 7 days and left for the next 7 days; Group II or KASgroup: L-NAME administered (i.p) for 7 days and L-NAME + KAS (1000 mg/kg b.w) for the next 7 days; Group III or DMM group: L-NAME administered (i.p) for 7 days and L-NAME + DMM (2000 mg/kg b.w) for the next 7 days; Group IV or MSR group: L-NAME administered (i.p) for 7 days and L-NAME + MSR (300 mg/kg b.w) for the next 7 days; Group V or HJ group: L-NAME administered (i.p) for 7 days and L-NAME + HJ (113 mg/kg b.w) for the next 7 days; Group VI or KGS group: L-NAME administered (i.p) for 7 days and L-NAME +KGS (2000 mg/kg b.w) for the next 7 days. Non-invasive systolic blood pressure and RR-interval (ECG) was measured. Plasma was investigated forsodium, potassium, nitrite, ANP, adrenaline, noradrenaline and aldosterone on day 0, 7 and 14 using LC-MS/MS. Result: Treatment showed a non-significant lowreduction in SBP (systolic blood pressure) of KAS, MSR and HJ while that of DMM was quite significant (p < 0.05), but in the case of KGS, SBP increased. DMM on day 14 significantly (p < 0.05) reduced plasma nitrite while no significant plasma Na+ was noted. In the case of both DMM and KGS, potassium increased significantly (p < 0.05) on day 14. No significant changes in plasma ANP and aldosterone was observed against DMM and KGS while blood levels of adrenaline and noradrenaline significantly (p < 0.05) changed. No significant change in body weight was found. Conclusions: L-NAME KAS, MSR and HJ showed no change in SBP while DMM showed a significant reduction in SBP with decreased plasma nitrite. Probably, DMM may have anti-hypertensive activity mediated through NO inhibition while KGS may involve central sympathomimetic action.

Investigating the effect of Fenofibrate on biomarkers of vascular inflammation in L-NAME induced hypertensive rats

This study aims to evaluate the impact of fenofibrate on the levels of (IL-6, hsCRP, Lp-PLA2, sCD40L, and cystatin C) in hypertensive rats. Twenty-four rats were divided into two groups each of twelve. The first group served as the normotensive group, while the second group was regarded as the hypertensive group. Each group was further divided into two subgroups (control and treated). The control subgroups only received a placebo and the treated subgroups were given fenofibrate 30 mg/kg daily orally by gastric gavage for 4 weeks. The level of hsCRP, IL6, and Lp-PLA2 significantly increased, but sCD40L and cystatin C levels were not changed in hypertensive rats. Fenofibrate has significantly reduced the levels of hsCRP and Lp-LPA2 in hypertensive rats while IL6 and sCD40s have not been changed in both groups. In conclusion, Fenofibrate has revealed a pleiotropic anti-inflammatory effect by reducing the level of hsCRP and Lp-LPA2 in hypertensive rats.

Ziziphus Oxyphylla hydro-methanolic extract ameliorates hypertension in L-NAME induced hypertensive rats through NO/cGMP pathway and suppression of oxidative stress related inflammatory biomarkers

ETHNOPHARMACOLOGICAL RELEVANCE

Ziziphus Oxyphylla belongs to family Ziziphus and has been used traditionally in hypertension. It is enriched with quercetin and kaempferol derivatives, catechin and cyclopeptide alkaloids.

AIM

The current research evaluates the antihypertensive potential of aqueous methanolic extract of Z. oxyphylla (AMEZO) in NG-nitro-L-arginine methyl ester (LNAME) induced hypertension in rats.

MATERIAL AND METHODOLOGY

Phytochemical analysis of AMEZO was carried out using high performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS/MS). Antihypertensive activities of AMEZO (200 and 400 mg/kg) and Kaempferol were assessed in L-NAME (185 μmol/kg, intraperitoneal) injected hypertensive rats. In normotensive rats, blood pressure was assessed using Power Lab data system. Serum and tissue samples were preserved for estimation of nitric oxide (NO), Cyclic guanosine monophosphate (cGMP), interleukin-6 (IL-6), tumor necrosis factor (TNF- α) and oxidative stress markers respectively. mRNA levels of eNOS, ACE, COX-2 and NF-kB genes were assessed through qPCR.

RESULTS

The HPLC and ESI-MS/MS identified kaempferol, quercetin, catechin, ceanothic acid, zizybernalic acid and oxyphylline F. Chronic administration of AMEZO and kaempferol in L-NAME induced hypertensive rats significantly (p < 0.001) reduced systolic, diastolic and mean blood pressure. AMEZO and kaempferol caused meaningfully improved (p < 0.001) serum NO and cGMP levels. AMEZO administration also noticeably decrease the elevated IL-6 and TNF- α concentration in hypertensive animals. Administration of AMEZO and kaempferol also improved oxidative stress markers (MDA, CAT, SOD, GSH). The antihypertensive activity of AMEZO also resulted in upregulation of eNOS and downregulation of ACE.

CONCLUSION

These data depict that AMEZO and kaempferol showed antihypertensive activity in LNAME induced hypertensive rats possibly mediated through improvement in NO and cGMP levels, modulation of mRNA expression of eNOS, ACE, COX-2 and NF-kB and suppression of oxidative stress related inflammatory markers, proposing a defensive role in cardiovascular diseases.

Evaluation of Oxidative Stress Biomarkers, Pro-Inflammatory Cytokines, and Histological Changes in Experimental Hypertension, Dyslipidemia, and Type 1 Diabetes Mellitus

The present study aims to compare the oxidative stress biomarkers, pro-inflammatory cytokines, and histological changes induced by three cardiovascular risk factors, namely, hypertension, dyslipidemia, and type 1 diabetes mellitus. Hypertension was induced with 40 mg/kg body weight (b.w.) of N omega-nitro-L-arginine-methyl (L-NAME) administered orally. Dyslipidemia was induced by the administration of a diet with a high cholesterol (2%) content. Diabetes mellitus was induced by intraperitoneal administration of a single dose of streptozocin (65 mg/kg). Malondialdehyde (MDA) and total oxidative status (TOS) are increased by all three cardiovascular risk factors (up to 207%). The indirect assessment of NO synthesis (NOx) is observed to be reduced after L-NAME administration (43%), and dyslipidemia induction (16%), while type 1 diabetes mellitus is associated with the highest levels of NOx (increased 112%). Hypertension, dyslipidemia, and type 1 diabetes reduced the total antioxidative capacity (TAC) and total thiol (SH) levels (up to 57%). The values of evaluated pro-inflammatory cytokines, tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β), assessed from the ascending aorta were elevated by all three cardiovascular risk factors, with the highest levels induced by type 1 diabetes mellitus (up to 259%). The histopathological examination of the ascending and descending aorta revealed reversible pro-atherogenic changes consisting of the accumulation of lipid droplets in the subendothelial connective tissue on rats with hypertension and dyslipidemia. Irreversible pro-atherogenic changes consisting of a reduction of the specific elasticity of the arteries were observed in rats with type 1 diabetes mellitus. Type 1 diabetes mellitus demonstrates an alteration of the oxidative stress parameters, the elevation of tissue levels of the pro-inflammatory cytokines and causing irreversible pro-atherogenic changes on the aortic wall.

Interaction between Angiotensinase Activities in Pituitary and Adrenal Glands of Wistar-Kyoto and Spontaneously Hypertensive Rats under Hypotensive or Hypertensive Treatments

In the present study, we analyzed the activity of several aminopeptidases (angiotensinases) involved in the metabolism of various angiotensin peptides, in pituitary and adrenal glands of untreated Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) or treated with the antihypertensive drugs captopril and propranolol or with the L-Arginine hypertensive analogue L-NG-Nitroarginine Methyl Ester (L-NAME). Intra- and inter-gland correlations between angiotensinase activities were also calculated. Membrane-bound alanyl-, cystinyl-, and glutamyl-aminopeptidase activities were determined fluorometrically using aminoacyl-β-naphthylamide as substrates. Depending on the type of angiotensinase analyzed, the results reflect a complex picture showing substantial differences between glands, strains, and treatments. Alanyl-aminopeptidase responsible for the metabolism of Ang III to Ang IV appears to be the most active angiotensinase in both pituitary and adrenals of WKY and particularly in SHR. Independently of treatment, most positive correlations are observed in the pituitary gland of WKY whereas such positive correlations are predominant in adrenals of SHR. Negative inter-gland correlations were observed in control SHR and L-NAME treated WKY. Positive inter-gland correlations were observed in captopril-treated SHR and propranolol-treated WKY. These results may reflect additional mechanisms for increasing or decreasing systolic blood pressure in WKY or SHR.

Butterfly Pea Flower (Clitoria ternatea Linn.) Extract Ameliorates Cardiovascular Dysfunction and Oxidative Stress in Nitric Oxide-Deficient Hypertensive Rats

In this study, we examine whether Clitoria ternatea Linn. (CT) can prevent Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME)-induced cardiac and vascular dysfunction in rats. Male Sprague Dawley rats were given L-NAME (40 mg/kg, drinking water) and orally administered with CT extract (300 mg/kg/day) or lisinopril (2.5 mg/kg/day) for 5 weeks. The main phytochemical components of the CT extract were found to be flavonoids. The CT extract alleviated the high blood pressure in rats receiving L-NAME. Decreased vasorelaxation responses to acetylcholine and enhanced contractile responses to sympathetic nerve stimulation in aortic rings and mesenteric vascular beds of L-NAME treated rats were ameliorated by CT extract supplementation. Left ventricular hypertrophy and dysfunction were developed in L-NAME rats, which were partially prevented by CT extract treatment. The CT extract alleviated upregulated endothelial nitric oxide synthase expression, decreased plasma nitrate/nitrite levels, and increased oxidative stress in L-NAME rats. It suppressed high levels of serum angiotensin-converting enzyme activity, plasma angiotensin II, and cardiac angiotensin II type 1 receptor, NADPH oxidases 2, nuclear factor-kappa B, and tumor necrosis factor-alpha expression. The CT extract, therefore, partially prevented L-NAME-induced hypertension and cardiovascular alterations in rats. These effects might be related to a reduction in the oxidative stress and renin-angiotensin system activation due to L-NAME in rats.