You-Lin Tain

Melatonin prevents hypertension and increased asymmetric dimethylarginine in young spontaneous hypertensive rats

Abstract:  Nitric oxide (NO) deficiency is associated with development of hypertension. We examined whether melatonin protects against the blood pressure increase is because of the restoration of the NO pathway. Spontaneous hypertensive rats (SHR) and control normotensive Wistar Kyoto (WKY) rats aged 4 weeks were assigned to four groups (N = 6 for each group): untreated SHR and WKY, melatonin‐treated SHR and WKY. Melatonin‐treated rats received 0.01% melatonin in drinking water for 8 wks. All rats were sacrificed at 12 wk of age. SHR had higher blood pressure than WKY, which melatonin prevented. Plasma asymmetric dimethylarginine (ADMA) levels were elevated in SHR, combined with a reduction in plasma L‐arginine to ADMA ratio (AAR). In the kidney, L‐arginine, ADMA, and AAR were not different between SHR and WKY rats, whereas L‐citrulline level was increased in SHR. Melatonin decreased plasma ADMA level and restored plasma AAR. Renal dimethylarginine dimethylaminohydrolase (DDAH, ADMA‐metabolizing enzyme) activity was lower in SHR than WKY rats, which melatonin therapy prevented. Also, melatonin elevated both L‐arginine and ADMA but reduced L‐citrulline level in the kidney in SHR, which was associated with the prevention of reduced renal argininosuccinate lyase (ASL) expression in SHR. Moreover, melatonin reduced the degree of oxidative damaged DNA product, 8‐ hydroxydeoxyguanosine (8‐OHdG) immunostaining in SHR. The observed antihypertensive effects of melatonin in young SHR are because of the restoration of the NO pathway by reduction of plasma ADMA, restoration of plasma AAR, preservation of renal L‐Arg availability, and attenuation of oxidative stress.

Effects of maternal l-citrulline supplementation on renal function and blood pressure in offspring exposed to maternal caloric restriction: The impact of nitric oxide pathway

Maternal undernutrition can cause reduced nephron number and glomerular hypertrophy, consequently leading to adult kidney disease. We intended to elucidate whether NO deficiency evolves to kidney disease vulnerability in offspring from mothers with caloric restriction diets and whether maternal L-citrulline (L-Cit) supplementation can prevent this. Using a rat model with 50% caloric restriction, four groups of 3-month-old male offspring were sacrificed to determine their renal outcome: control, caloric restriction (CR), control treated with 0.25% L-citrulline solution during the whole period of pregnancy and lactation (Cit), and CR treated in the same way (CR+Cit group). The CR group had low nephron numbers, increased glomerular diameter, and an increased plasma creatinine level compared with the control group. Maternal L-Cit supplementation prevented these effects. The CR+Cit and Cit groups developed hypertension beginning at 4 and 8weeks of age, respectively. Plasma asymmetric and symmetric dimethylarginine (ADMA and SDMA) levels were increased, but L-arginine/ADMA ratios (AAR) were decreased in the CR group vs the control group. This was prevented by maternal L-Cit supplementation. Renal cortical neuronal NOS-alpha (nNOSalpha) protein abundance was significantly decreased in the Cit and CR+Cit groups. Collectively, reduced nephron number, reduced renal nNOSalpha expression, increased ADMA, and decreased AAR contribute to the developmental programming of adult kidney disease and hypertension. Although maternal L-Cit supplementation prevents caloric restriction-induced low nephron number and renal dysfunction, it also induces hypertension.

Melatonin blocks oxidative stress-induced increased asymmetric dimethylarginine

Asymmetric dimethylarginine (ADMA) is a competitive inhibitor of nitric oxide synthase, and its increase is associated with many systemic diseases. We recently found that increases in plasma and hepatic ADMA levels were associated with oxidative stress in young bile-duct-ligation (BDL) rats; these increases were prevented by melatonin therapy. Therefore, we used an in vivo BDL model and in vitro cultured hepatocytes to elucidate the protective mechanisms of melatonin against oxidative stress-induced increase in ADMA. We found that the presence of reactive oxygen species (ROS) in young rats with BDL leads to downregulation of dimethylarginine dimethyaminohydrolase (DDAH)-1 and -2 as well as DDAH activity. Melatonin prevented ADMA increases in the liver mainly by regulating DDAH-1 and -2. The expression and activity of DDAH were suppressed in vitro by superoxide and hydrogen peroxide (H(2)O(2)) in a time-dependent manner, whereas melatonin could block H(2)O(2)-induced downregulation of DDAH-2 as well as decreased DDAH activity, thereby preventing increases in hepatic ADMA. Our findings reveal a mechanistic basis of DDAH downregulation by ROS and suggest that melatonin might be a potential therapy for various diseases with elevated cellular ADMA.

Asymmetric dimethylarginine: clinical applications in pediatric medicine.

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS). Growing evidence indicates that ADMA plays an important role in the initiation and progression of a variety of adulthood diseases, especially in the cardiovascular and renal systems. However, the study of ADMA in pediatric diseases has just begun. This review provides an overview of potential clinical applications of ADMA in pediatric practice, with an emphasis on the following areas: the biochemistry and pathophysiology of ADMA; clinical ramifications of elevated ADMA levels in pediatric population; age-related normal reference ranges of ADMA; methodology for measuring ADMA; current and potential agents to reduce ADMA; and the problems that must be addressed before use of ADMA in pediatric medicine. ADMA will soon be available for use as a biomarker and therapeutic target in the pediatric population.

Melatonin prevents maternal fructose intake-induced programmed hypertension in the offspring: roles of nitric oxide and arachidonic acid metabolites

Fructose intake has increased globally and is linked to hypertension. Melatonin was reported to prevent hypertension development. In this study, we examined whether maternal high fructose (HF) intake causes programmed hypertension and whether melatonin therapy confers protection against the process, with a focus on the link to epigenetic changes in the kidney using next‐generation RNA sequencing (NGS) technology. Pregnant Sprague–Dawley rats received regular chow or chow supplemented with HF (60% diet by weight) alone or with additional 0.01% melatonin in drinking water during the whole period of pregnancy and lactation. Male offspring were assigned to four groups: control, HF, control + melatonin (M), and HF + M. Maternal HF caused increases in blood pressure (BP) in the 12‐wk‐old offspring. Melatonin therapy blunted the HF‐induced programmed hypertension and increased nitric oxide (NO) level in the kidney. The identified differential expressed gene (DEGs) that are related to regulation of BP included Ephx2, Col1a2, Gucy1a3, Npr3, Aqp2, Hba‐a2, and Ptgs1. Of which, melatonin therapy inhibited expression and activity of soluble epoxide hydrolase (SEH, Ephx2 gene encoding protein). In addition, we found genes in arachidonic acid metabolism were potentially involved in the HF‐induced programmed hypertension and were affected by melatonin therapy. Together, our data suggest that the beneficial effects of melatonin are attributed to its ability to increase NO level in the kidney, epigenetic regulation of genes related to BP control, and inhibition of SEH expression. The roles of DEGs by the NGS in long‐term epigenetic changes in the adult offspring kidney require further clarification.

Splice variants of neuronal nitric oxide synthase are present in the rat kidney

BACKGROUND Decreased renal cortical neuronal NO synthase (nNOS) abundance/activity correlates with progression of chronic kidney disease (CKD) in a number of animal models. METHODS Western blotting with both N-terminal and C-terminal antibodies, immunoprecipitation, proteomics, RT-PCR and in situ hybridization were used to identify nNOS splice variants in the rat kidney. RESULTS We have identified two nNOS proteins and transcripts in the rat kidney; nNOSalpha (approximately 160 kDa) and nNOSbeta (approximately 140 kDa), a catalytically active exon-2 deletion variant, lacking both the PDZ and protein inhibitor of nNOS (PIN) domains. We also report that nNOSbeta protein abundance is increased in the kidney at 11 weeks following 5/6th nephrectomy (5/6NX)-induced CKD while nNOSalpha protein abundance is diminished. The transcript data parallel the protein data in 5/6NX. By in situ hybridization, there is abundant nNOSalpha mRNA widely distributed throughout the normal kidney cortex, with very sparse nNOSbeta mRNA confined to a few proximal tubules. In a second injury model (6 weeks after 5/6 renal mass reduction by combined right kidney ablation and infarction of approximately 2/3 of the left kidney; 5/6 A/I), nNOSalpha mRNA almost disappears from the kidney cortex while nNOSbeta mRNA abundance increases in tubules and tubulo-interstitium. CONCLUSION The renal cortical nNOSbeta protein is present in low abundance in the normal kidney and increases with injury, in an inverse pattern of change with the nNOSalpha.

Asymmetric dimethylarginine is associated with developmental programming of adult kidney disease and hypertension in offspring of streptozotocin-treated mothers.

Diabetes mellitus complicates pregnancies, leading to diseases in adult life in the offspring. Asymmetric dimethylarginine (ADMA) is increased in diabetes mellitus, kidney disease, and hypertension. We tested whether maternal diabetes causes increased ADMA in rats, resulting in kidney disease and hypertension in the adult offspring, and whether these can be prevented by maternal citrulline supplementation. Newborn female and pregnant Sprague-Dawley rats were injected with streptozotocin (STZ), which made up the nSTZ and STZ models, respectively. For the STZ model, 4 groups of male offspring were killed at age 3 months: the control, STZ, and Cit and STZ+Cit (control and STZ rats treated with 0.25% l-citrulline solution, respectively) groups. The nSTZ rats had lower nephron numbers. The renal level of ADMA was higher in the nSTZ rats than in controls. The STZ group developed kidney injury, renal hypertrophy, and elevated blood pressure at the age of 12 weeks. These conditions were found to be associated with increased ADMA levels, decreased nitric oxide (NO) production, and decreased dimethylarginine dimethylaminohydrolase (DDAH) activity in the kidney. In addition, ADMA caused a nephron deficit in cultured rat metanephroi. Maternal citrulline supplementation prevented hypertension and kidney injury, increased the renal DDAH-2 protein level, and restored the levels of ADMA and NO in the STZ+Cit group. Reduced nephron number and increased ADMA contribute to adult kidney disease and hypertension in offspring of mothers with STZ-induced diabetes. Manipulation of the ADMA-NO pathway by citrulline supplementation may be a potential approach to prevent these conditions.

Melatonin utility in neonates and children

Melatonin (N-acetyl-5-methoxytryptamine) is an endogenously produced indoleamine secreted by the pineal gland and the secretion is suppressed by light. Melatonin is a highly effective antioxidant, free radical scavenger, and has anti-inflammatory effect. Plenty of evidence supports the utility of melatonin in adults for cancer, neurodegenerative disorders, and aging. In children and neonates, melatonin has been used widely, including for respiratory distress syndrome, bronchopulmonary dysplasia, periventricular leukomalacia (PVL), hypoxia-ischemia encephalopathy and sepsis. In addition, melatonin can be used in childhood sleep and seizure disorders, and in neonates and children receiving surgery. This review article discusses the utility of melatonin in neonates and children.

Roles of Melatonin in Fetal Programming in Compromised Pregnancies

Compromised pregnancies such as those associated with gestational diabetes mellitus, intrauterine growth retardation, preeclampsia, maternal undernutrition, and maternal stress may negatively affect fetal development. Such pregnancies may induce oxidative stress to the fetus and alter fetal development through the epigenetic process that may affect development at a later stage. Melatonin is an oxidant scavenger that reverses oxidative stress during the prenatal period. Moreover, the role of melatonin in epigenetic modifications in the field of developmental programming has been studied extensively. Here, we describe the physiological function of melatonin in pregnancy and discuss the roles of melatonin in fetal programming in compromised pregnancies, focusing on its involvement in redox and epigenetic mechanisms.

Roles of nitric oxide and asymmetric dimethylarginine in pregnancy and fetal programming.

Nitric oxide (NO) regulates placental blood flow and actively participates in trophoblast invasion and placental development. Asymmetric dimethylarginine (ADMA) can inhibit NO synthase, which generates NO. ADMA has been associated with uterine artery flow disturbances such as preeclampsia. Substantial experimental evidence has reliably supported the hypothesis that an adverse in utero environment plays a role in postnatal physiological and pathophysiological programming. Growing evidence suggests that the placental nitrergic system is involved in epigenetic fetal programming. In this review, we discuss the roles of NO and ADMA in normal and compromised pregnancies as well as the link between placental insufficiency and epigenetic fetal programming.