In vivo arginine production and nitric oxide synthesis in pregnant Indian women with normal and low body mass indices

L-Arginine supplementation in pregnancy: a systematic review of maternal and fetal outcomes

BACKGROUND/AIM OF THE STUDY

L-Arginine (L-Arg)/Nitric Oxide (NO) system is involved in the pathophysiology of relevant Obstetric conditions. This review aims at summarizing the effects of L-Arg supplementation in pregnancy looking at safety and efficacy.

METHODS

We conducted a systematic review of the literature utilizing PubMed for studies published from inception to September 2022. The search included human and animal studies where L-Arg was supplemented pre-conceptionally or during pregnancy, by either oral or intravenous route. The main perinatal outcomes were focused.

RESULTS

Among 1028 publications, 51 studies were eligible for inclusion, 25 were performed in women, and the remnant in animals. Compared to controls/placebo, the supplementation with L-Arg reduced the development of pre-eclampsia (four studies), decreased blood pressure, and reduced the need for antihypertensive drugs in women with Hypertensive Disorders of Pregnancy (HDP, eight studies). In women carrying growth retarded fetuses, L-Arg improved fetoplacental circulation, birth weight and neonatal outcomes (five studies), while in the case of threatened preterm birth, L-Arg reduced uterine contractions (two studies). In several animal species, L-Arg supplementation in pregnancy improved reproductive performance by increasing the litter number and size. Moreover, in pre-eclamptic and metabolic syndrome experimental models, maternal hypertension and fetal growth were improved.

CONCLUSION

L-Arg displays biological activities in pregnancies complicated by HDP and growth restriction, both in women and animal models. L-Arg administration is safe and could be a candidate as an intervention beneficial to maternal and fetal outcomes, at least in moderate clinical disorders.

Arginine Metabolism Is Altered in Adults with A-β + Ketosis-Prone Diabetes

Background

A-β + ketosis-prone diabetes (KPD) is a subset of type 2 diabetes in which patients have severe but reversible β cell dysfunction of unknown etiology. Plasma metabolomic analysis indicates that abnormal arginine metabolism may be involved.

Objective

The objective of this study was to determine the relation between gut microbiome and arginine metabolism and the relation between arginine availability and β cell function in KPD patients compared with control participants.

Methods

Kinetics of arginine and related metabolites were measured with stable isotope tracers, and insulin secretory responses to arginine and glucose were determined under euglycemic and hyperglycemic conditions in 6 KPD patients and 6 age-, gender-, and body mass index-matched control participants. Glucose potentiation of arginine-induced insulin secretion was performed in a different set of 6 KPD and 3 control participants.

Results

Arginine availability was higher in KPD patients during euglycemia [53.5 ± 4.3 (mean ± SEM) compared with 40.3 ± 2.4 μmol · kg lean body mass (LBM)-1 · h-1, P = 0.03] but declined more in response to hyperglycemia (Δ 10.15 ± 2.6 compared with Δ 3.20 ± 1.3 μmol · kg LBM-1 · h-1, P = 0.041). During hyperglycemia, ornithine flux was not different between groups but after an arginine bolus, plasma ornithine AUC trended higher in KPD patients (3360 ± 294 compared with 2584 ± 259 min · μmol · L-1, P = 0.08). In both euglycemia and hyperglycemia, the first-phase insulin responses to glucose stimulation were lower in KPD patients (euglycemic insulin AUC 282 ± 108 compared with 926 ± 257 min · μU · mL-1, P = 0.02; hyperglycemic insulin AUC 358 ± 79 compared with 866 ± 292 min · μU · mL-1, P = 0.05), but exogenous arginine restored first-phase insulin secretion in KPD patients to the level of control participants.

Conclusion

Compared with control participants, KPD patients have increased arginine availability in the euglycemic state, indicating a higher requirement. This is compromised during hyperglycemia, with an inadequate supply of arginine to sustain metabolic functions such as insulin secretion. Exogenous arginine administration restores a normal insulin secretory response.

Assessment of nitrite oxide and maternal-fetal Doppler parameters during pregnancy

OBJECTIVE

The objective was to evaluate and compare the whole blood nitrite concentration in the three trimesters of pregnancy. Additionally, we investigate whether there is any relation between nitrite concentrations and Doppler ultrasound analysis of some maternal and fetal vessels.

METHODS

Thirty-three healthy pregnant women were examined at the first (11-14 weeks), second (20-24 weeks) and third trimester (34-36 weeks) of pregnancy. In the three exams, we determined the maternal whole blood nitrite concentration and uterine arteries Doppler analysis to determine pulsatility index (PI), and resistance index (RI). In the second and third trimester we also performed fetal umbilical and middle cerebral arteries PI and RI. We compared the concentrations of nitrite in three trimesters and correlated with Doppler parameters.

RESULTS

No difference was observed in the whole blood nitrite concentrations across trimesters: 151.70 ± 77.90 nmol/ml, 142.10 ± 73.50 nmol/ml and 147.10 ± 87.30 nmol/ml; first, second and third trimesters, respectively. We found no difference in correlation between whole blood nitrite concentration and Doppler parameters from the evaluated vessels.

CONCLUSIONS

In healthy pregnant women, the nitrite concentrations did not change across gestational trimesters and there was also no strong correlation with Doppler impedance indices from maternal uterine arteries and fetal umbilical and middle cerebral arteries.

Is the serum l-arginine level during early pregnancy a predictor of pregnancy-induced hypertension?

The objective of this study was to determine the concentration of serum l-arginine in healthy pregnant women and infant cord blood and to compare them with those in patients with pregnancy-induced hypertension (PIH). The serum concentration of l-arginine in normal pregnant women at early gestation (n = 186) was determined and analyzed based on maternal factors such as the age, pre-pregnancy body mass index (BMI), smoking and alcohol habits before pregnancy. Similarly, the concentration of cord blood of the newborns (n = 142) was also analyzed. These values were compared with those in the PIH group (n = 21). The potential risk factors for PIH were also estimated. The serum concentration of l-arginine at early gestation in normal pregnant women (88.65 ± 19.96 µM) was not affected by the maternal age and BMI before pregnancy. A lower l-arginine concentration at early gestation (<70 µM) significantly elevated PIH risk [adjusted odds ratio (OR) = 4.26, 95% CI 1.29-14.50]. In addition, either women with large body mass before pregnancy (BMI>25 kg/m(2)) or primipara women also showed a significant association with PIH risk [adjusted OR = 10.55 (2.95-40.68); 5.25 (1.72-19.15), respectively]. In conclusion, a lower l-arginine concentration at early gestation, overweight before pregnancy (BMI>25 kg/m(2)) and primipara could predict to the development of PIH.

The Microbiome, Intestinal Function, and Arginine Metabolism of Healthy Indian Women Are Different from Those of American and Jamaican Women

BACKGROUND

Indian women have slower arginine flux during pregnancy compared with American and Jamaican women. Arginine is a semi-essential amino acid that becomes essential during periods of rapid lean tissue deposition. It is synthesized only from citrulline, a nondietary amino acid produced mainly in the gut. The gut is therefore a key site of arginine and citrulline metabolism, and gut microbiota may affect their metabolism.

OBJECTIVE

The objective of this study was to identify differences in the gut microbiota of nonpregnant American, Indian, and Jamaican women and characterize the relations between the gut microbiota, gut function, and citrulline and arginine metabolism.

METHODS

Thirty healthy American, Indian, and Jamaican women (n = 10/group), aged 28.3 ± 0.8 y, were infused intravenously with [guanidino-15N2]arginine, [5,5-2H2]citrulline, and [15N2]ornithine and given oral [U-13C6]arginine in the fasting and postprandial states. Fecal bacterial communities were characterized by 16S rRNA gene sequencing.

RESULTS

In the fasting state, Indian women had lower citrulline flux than did American and Jamaican women [7.0 ± 0.4 compared with 9.1 ± 0.4 and 8.9 ± 0.2 μmol ⋅ kg fat-free mass (FFM)-1 ⋅ h-1, P = 0.01] and greater enteral arginine conversion to ornithine than did American women (1.4 ± 0.11 compared with 1.0 ± 0.08 μmol ⋅ kg FFM-1 ⋅ h-1, P = 0.04). They also had lower mannitol excretion than American and Jamaican women (154 ± 37.1 compared with 372 ± 51.8 and 410 ± 39.6 mg/6 h, P < 0.01). Three dominant stool community types characterized by increased abundances of the genera Prevotella, Bacteroides, and Bacteroides with Clostridium were identified. Indian women had increased mean relative abundances of Prevotella (42%) compared to American and Jamaican women (7% and < 1%, P = 0.03) which were associated with diet, impaired intestinal absorptive capacity, and arginine flux.

CONCLUSIONS

These findings suggest that dysregulated intestinal function and a unique gut microbiome may contribute to altered arginine metabolism in Indian women.

Measurement of in vivo nitric oxide synthesis in humans using stable isotopic methods: a systematic review

Stable isotopic methods are considered the "gold standard" for the measurement of rates of in vivo NO production. However, values reported for healthy human individuals differ by more than 1 order of magnitude. The reason for the apparent variability in NO production is unclear. The primary aim of this review was to evaluate and compare the rates of in vivo NO production in health and disease using stable isotope methods. Articles were retrieved using the PubMed electronic database. Information on concentrations, isotopic enrichments of fluxes, and conversion rates of molecules involved in the NO metabolic pathway was extracted from selected articles; 35 articles were included in the final analysis. Three protocols were identified, including the arginine-citrulline, the arginine-nitrate, and the oxygen-nitrate protocols. The arginine-citrulline protocol showed a wider variability compared to the arginine-nitrate and oxygen-nitrate protocols. The direction of the association between disease state and rate of NO production was essentially determined by the etiopathogenesis of the disorder (inflammatory, metabolic, vascular). Considerable variation in methodologies used to assess whole-body NO synthesis in humans exists. The precision of several aspects of the techniques and the validity of some assumptions made remain unknown, and there is a paucity of information about physiological rates of NO production from childhood over adolescence to old age.

Intraoperative evaluation of revascularization effect on ischemic muscle hemodynamics using near-infrared diffuse optical spectroscopies

Arterial revascularization in patients with peripheral arterial disease (PAD) reestablishes large arterial blood supply to the ischemic muscles in lower extremities via bypass grafts or percutaneous transluminal angioplasty (PTA). Currently no gold standard is available for assessment of revascularization effects in lower extremity muscles. This study tests a novel near-infrared diffuse correlation spectroscopy flow-oximeter for monitoring of blood flow and oxygenation changes in medial gastrocnemius (calf) muscles during arterial revascularization. Twelve limbs with PAD undergoing revascularization were measured using a sterilized fiber-optic probe taped on top of the calf muscle. The optical measurement demonstrated sensitivity to dynamic physiological events, such as arterial clamping/releasing during bypass graft and balloon inflation/deflation during PTA. Significant elevations in calf muscle blood flow were observed after revascularization in patients with bypass graft (+48.1 ± 17.5%) and patients with PTA (+43.2 ± 11.0%), whereas acute post-revascularization effects in muscle oxygenation were not evident. The decoupling of flow and oxygenation after revascularization emphasizes the need for simultaneous measurement of both parameters. The acute elevations/improvements in calf muscle blood flow were associated with significant improvements in symptoms and functions. In total, the investigation corroborates potential of the optical methods for objectively assessing the success of arterial revascularization.

Regulation of nitric oxide production in health and disease

PURPOSE OF REVIEW

The purpose of this review is to highlight recent publications examining nitric oxide production in health and disease and its association with clinical nutrition and alterations in metabolism.

RECENT FINDINGS

The role of the cofactor tetrahydrobiopterin in nitric oxide production and its relation with arginine availability is indicated as an important explanation for the arginine paradox. This offers potential for nitric oxide regulation by dietary factors such as arginine or its precursors and vitamin C. Because diets with a high saturated fat content induce high plasma fatty acid levels, endothelial nitric oxide production is often impaired due to a reduction in nitric oxide synthase 3 phosphorylation. Increasing the arginine availability by arginine therapy or arginase inhibition was, therefore, proposed as a potential therapy to treat hypertension. Recent studies in septic patients and transgenic mice models found that inadequate de-novo arginine production from citrulline reduces nitric oxide production. Citrulline supplementation may, therefore, be a novel therapeutic approach in conditions of arginine deficiency.

SUMMARY

Both lack and excess of nitric oxide production in diseases can have various important implications in which dietary factors can play a modulating role. Future research is needed to expand our understanding of the regulation and adequate measurement of nitric oxide production at the organ level and by the different nitric oxide synthase isoforms, also in relation to clinical nutrition.