Cellular interactions between L-arginine and asymmetric dimethylarginine: Transport and metabolism

CHronic hypERtension and L-citRulline studY (CHERRY): an Early-Phase Randomised Controlled Trial in Pregnancy

Oral supplementation with L-citrulline, which is sequentially converted to L-arginine then nitric oxide, improves vascular biomarkers and reduces blood pressure in non-pregnant, hypertensive human cohorts and pregnant mice with a pre-eclampsia-like syndrome. This early-phase randomised feasibility trial assessed the acceptability of L-citrulline supplementation to pregnant women with chronic hypertension and its effects on maternal BP and other vascular outcomes. Pregnant women with chronic hypertension were randomised at 12-16 weeks to receive 3-g L-citrulline twice daily (n = 24) or placebo (n = 12) for 8 weeks. Pregnant women reported high acceptability of oral L-citrulline. Treatment increased maternal plasma levels of citrulline, arginine and the arginine:asymmetric dimethylarginine ratio, particularly in women reporting good compliance. L-citrulline had no effect on diastolic BP (L-citrulline: - 1.82 95% CI (- 5.86, 2.22) vs placebo: - 5.00 95% CI (- 12.76, 2.76)), uterine artery Doppler or angiogenic biomarkers. Although there was no effect on BP, retrospectively, this study was underpowered to detect BP changes < 9 mmHg, limiting the conclusions about biological effects. The increase in arginine:asymmetric dimethylarginine ratio was less than in non-pregnant populations, which likely reflects altered pharmacokinetics of pregnancy, and further pharmacokinetic assessment of L-citrulline in pregnancy is advised.Trial Registration EudraCT 2015-005792-25 (2017-12-22) and ISRCTN12695929 (2018-09-20).

The effect of nitric oxide, endothelial nitric oxide synthetase, and asymmetric dimethylarginine in hemorrhoidal disease

AIM

The aim of this study was to examine the roles of nitric oxide (NOx), endothelial nitric oxide synthetase (eNOS), and asymmetric dimethylarginine (ADMA), which is the major endogenous inhibitor of nitric oxide synthases (NOS), in the pathophysiology of hemorrhoidal disease.

METHODS

This study included 54 patients with grades 3 and 4 internal hemorrhoidal disease and 54 patients without the disease who attended the General Surgery Clinic. NOx, eNOS, and ADMA levels were measured with the Enzyme-Linked ImmunoSorbent Assay (ELISA) method.

RESULTS

The patients had higher NO and eNOS levels and lower ADMA levels than the control subjects (p<0.001). A significant highly positive correlation was found between NO and eNOS (p<0.001). Nevertheless, there was a highly negative correlation between ADMA and NO-eNOS(p<0.001, p<0.001).

CONCLUSION

This preliminary study reveals that higher NOx and eNOS activities and lower ADMA levels in the rectal mucosa are observed in patients with hemorrhoidal disease than in those with normal rectal tissue. The imbalance between endothelium-derived relaxing factors, such as NO and endogenous competitive inhibitor of NOS, ADMA, may cause hemorrhoidal disease. Our study proposes that hemorrhoids display apparent vascular dilatation and present with bleeding or swelling. ADMA is an effective NOS inhibitor and may be a promising therapeutic option for hemorrhoidal disease.

A correlation between the fluctuations of cytokine concentrations measured in the morning and evening and the circadian blood pressure rhythm in patients with stage II essential hypertension

Today, increasing attention is being paid to the role of circadian rhythms in pathology. There are time-of-day-dependent immune markers that provide valuable information about disease progression. The aim of this study was to measure evening and morning concentrations of a few cytokines (interleukins, adhesion molecules, tumor necrosis/growth factors, etc.) in the peripheral blood of patients with stage II essential hypertension and to investigate how they correlate with a nocturnal blood pressure decline. Blood samples were collected from 90 patients with stage II EH at 7:00 a.m. and 8:00 p.m. Cytokine concentrations were measured using immunoassays. Based on 24-h blood pressure monitoring, the patients were distributed into 3 groups: dippers, non-dippers and night-peakers. The morning to evening ratios of cytokine concentrations in patients with EH differed from those in healthy controls due to an increase in the evening concentrations of somnogenic cytokines (IL1β, IL1α) and LIF, sLIFr, and M-CSF whose daily fluctuations patterns remain understudied. On the whole, the fluctuation patterns of the measured cytokines in patients with stage II EH who had had the condition for 10 to 14 years and were receiving no antihypertensive treatment at the time of our study differed from those displayed by healthy controls. A twenty percent rise in the evening concentrations of IL1α, LIF, sLIFr, M-CSF, and erythropoietin contributes significantly to pathological blood pressure rhythms (as demonstrated by the groups of non-dippers and night-peakers) in patients with stage II EH receiving no antihypertensive therapy. Understanding the pathophysiological role of cytokine levels and their fluctuations over a 24-h cycle could inspire new methods for EH prevention and reduce end-organ damage.

Investigating a correlation between the levels of peripheral blood cytokines and the risk for cardiovascular complications in patients with stage II essential hypertension

Essential hypertension (EH) is one of the most common modifiable risk factors for cardiovascular diseases and death. The aim of this study was to investigate a correlation between the levels of some cytokines (interleukins, adhesion molecules, tumor necrosis and growth factors, etc.) in the peripheral blood of patients with stage II EH and the rate of complications (myocardial infarction, acute cerebrovascular events, and transient ischemic attacks) occurring in a 5-year follow-up period. Twenty-eight cytokines were measured using ELISA, including IL1β, IL1α, IL1ra, IL18, IL18BP, IL37, IL6, sIL6r, LIF, sLIFr, IGF-1, IGFBP-1, TNFα, sTNF-RI, sVCAM-1, IL17, IL2, IL4, IL10, TGF-β1, IL8, CX3CL1, CXCL10, INFγ, M-CSF, IL34, VEGF-A, and erythropoietin, and a few vasoactive peptides, including NО, iNOS, eNOS, ADMA, SDMA, Nt-proСNP, and Nt-proBNP, in the peripheral blood samples of 200 patients with stage II EH who had been suffering from this condition for 10 to 14 years and were receiving comparable therapies to bring their blood pressure down. The patients were followed up for 5 years to keep track of complications. The retrospective analysis revealed that the group of patients who developed complications during the 5-year follow-up period exhibited a decline in the levels of IL1ra (р < 0.001) and IL10 (р < 0.001) and a rise in IL1β (р < 0.001), TNFα (р < 0.001) and M-CSF (р < 0.001) in comparison with the group of those who did not develop any complications. The multivariate Cox regression analysis was applied to the following parameters: IL1β > 18.8 pg/ml; IL1ra < 511 pg/ml; IL6 > 23.8 pg/ml; IL10 < 26.3 pg/ml; 389 pg/ml < M-CSF < 453 pg/ml; ADMA > 0.86 μmol/L; total cholesterol > 4.9 mmol/L; LDL> 3.0 mmol/L; HDL in men < 1.0 mmol/L; HDL in women < 1.2 mmol/L. The analysis revealed that M-CSF in the range from 389 to 453 pg/ml (р < 0.001) and LDL above 3.0 mmol/L (р < 0.01) correlated with an increase in the risk for end-organ damage in stage II EH. Changes in the cytokine levels can be regarded as a predictor of myocardial and cerebral damage in patients with stage II EH. Measurement of peripheral blood M-CSF can be included into the classic risk assessment schemes for the cardiovascular complications in the studied cohort of patients.

Metabolic pathways of L-arginine and therapeutic consequences in tumors

Difference in the metabolism of normal and cancer cells inspires to search for new, more specific and less toxic therapies than those currently used. The development of tumors is conditioned by genetic changes in cancer-transformed cells, immunological tolerance and immunosuppression. At the initial stages of carcinogenesis, the immune system shows anti-tumor activity, however later, cancer disrupts the function of Th1/Th17/Th2 lymphocytes by regulatory T (Treg) cells, tumor-associated macrophages (TAMs), and myeloid-derived suppressor cells (MDSCs) and finally causes immunosuppression. Recently, much attention has been devoted to the influence of l-arginine metabolism disorders on both carcinogenesis and the immune system. l-Arginine is essential for the maturation of the T cell receptor zeta (TCRζ), and its absence deprives T-cells of the ability to interact with tumor antigens. MDSCs deplete l-arginine due to a high expression of arginase 1 (ARG1) and their number increases 4-10 times depending on the type of the cancer. L-Arginine has been shown to be essential for the survival and progression of arginine auxotrophic tumors. However, the progression of arginine non-auxotrophic tumors is independent of exogenous l-arginine, because these tumors have arginine-succinate synthetase (ASS1) activity and are available to produce l-arginine from citrulline. Clinical studies have confirmed the high efficacy of arginine auxotrophic tumors therapy based on the elimination of l-arginine. However, l-arginine supplementation may improve the results of treatment of patients with arginine non-auxotrophic cancer. This review is an attempt to explain the seemingly contradictory results of oncological therapies based on the deprivation or supplementation of l-arginine.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

Small molecule inhibition of DDAH1 significantly attenuates triple negative breast cancer cell vasculogenic mimicry in vitro

Dimethylarginine dimethylaminohydrolase 1 (DDAH1) is a key enzyme involved in the metabolism of the endogenous nitric oxide synthase (NOS) inhibitors asymmetric dimethylarginine (ADMA) and monomethyl arginine (L-NMMA). Increased DDAH1 expression and subsequent increased NO production have been recently linked to cancer. Specifically, DDAH1 is implicated in establishment of a vascular network by tumour cells, vasculogenic mimicry (VM), which is strongly associated with tumour progression and poor patient prognosis. The use of DDAH1 inhibitors as potential therapeutic agents thus represents a growing field of interest. Here we describe a UPLC-MS assay to quantify stability and intracellular concentration of two small molecule DDAH1 inhibitors synthesised by our group, ZST316 and ZST152, following incubation with MDA-MB-231 breast cancer cells. In an in vitro assay of VM, both DDAH1 inhibitors significantly attenuated formation of capillary-like tube structures in a dose-dependent fashion. This was not due to cell toxicity or altered cell proliferation, but may be due in part to inhibition of cell migration. Mechanistically, we demonstrate significant modulation of the endogenous DDAH/ADMA/NO pathway following exposure of 100 μM ZST316 or ZST152: a 40% increase in the DDAH1 substrate ADMA, and a 38% decrease in the DDAH1 product l-citrulline. This study represents the first evidence for therapeutic inhibition of DDAH1 by small molecules in breast cancer.