Antioxidant and Amine Oxidase Inhibitory Activities of Hydroxyurea

Flavonoids Isolated from Vitex grandifolia, an Underutilized Vegetable, Exert Monoamine A & B Inhibitory and Anti-inflammatory Effects and Their Structure-activity Relationship

Objectives

Vitex grandifolia belongs to family Lamiaceae; it consists of flowering plants and it is also called the mint family. The Yoruba people of southwest Nigeria called it "Oriri" or "Efo oriri". This plant is classified as an underutilized vegetable and little is known about its phytochemistry or its biological evaluations.

Materials and Methods

Methanol extracts of the dried leaves and stem of the plant were subjected to fractionation and isolation using vacuum layer and column chromatography methods. The structures of the compounds were elucidated using spectroscopic techniques including IR, 1D-, and 2D-NMR and by comparison with the data reported in the literature. They were evaluated in vitro for the inhibition of monoamine recombinant human MAO-A and -B and anti-inflammatory activities.

Results

Three known flavonoids were isolated from the methanolic extract of the leaves of V. grandifolia for the first time to the best of our knowledge, i.e. isoorientin (1), orientin (2), and isovitexin (3). Most of the isolated compounds showed selective inhibition of monoamine oxidase B, inhibition of MAO-B by isoorientin (1) and orientin (2) were 9-fold more potent (IC₅₀ (μg/mL) of 11.08 and 11.04) compared to the inhibition of MAO-A (IC₅₀ (μg/mL) of ˃100), while clorgyline and deprenyl were used as positive standards. The isolated flavonoids displayed good activity against the NF-ﭏb assay with IC₅₀ (μg/mL) of 8.9, 12, and 18. This study establishes a link between the structure and the biological activities on the basis of the different patterns of substitution, particularly the C2=C3 double bond and the position of glucose moiety.

Conclusion

This study is the first to establish the phytochemistry of the polar part of V. grandifolia and the anti-inflammatory and neuroprotective role of these isolated compounds.

Benzo[b]tiophen-3-ol derivatives as effective inhibitors of human monoamine oxidase: design, synthesis, and biological activity

A series of benzo[b]thiophen-3-ols were synthesised and investigated as potential human monoamine oxidase (hMAO) inhibitors in vitro as well as ex vivo in rat cortex synaptosomes by means of evaluation of 3,4-dihydroxyphenylacetic acid/dopamine (DOPAC/DA) ratio and lactate dehydrogenase (LDH) activity. Most of these compounds possessed high selectivity for the MAO-B isoform and a discrete antioxidant and chelating potential. Molecular docking studies of all the compounds underscored potential binding site interactions suitable for MAO inhibition activity, and suggested structural requirements to further improve the activity of this scaffold by chemical modification of the aryl substituents. Starting from this heterocyclic nucleus, novel lead compounds for the treatment of neurodegenerative disease could be developed.

Theobromine and related methylxanthines as inhibitors of Primary Amine Oxidase

Methylxanthines are among the most widely consumed drugs in the world and evidence of their health benefits has been growing in recent years. Primary Amine Oxidase (PrAO) has been recognized as a therapeutic target for the amelioration of inflammatory, vascular, and neurodegenerative diseases. Previous work in our laboratories showed that caffeine inhibited Bovine PrAO with a Ki of 1.0 mM using benzylamine as substrate. This study aimed to extend our previous work and explore the possibility that related methylxanthines might influence PrAO activity. While paraxanthine, theophylline, and 7-methylxanthine had little effect on PrAO, theobromine was a noncompetitive inhibitor with a Ki of 276 ± 44 µM. The specific structural elements of methylxanthines that are required for inhibition allow us to suggest that their binding site on PrAO may be a target for therapeutics. The health benefits associated with dietary methylxanthine consumption could involve PrAO inhibition. PRACTICAL APPLICATIONS: Inhibition of PrAO by methylxanthines may be significant in conferring health benefits. The design of PrAO inhibitors based on the structural motifs identified in this study (N-methylation at specific locations) is indicated. Existing therapeutics based on a core xanthine structure can be evaluated for their effects on PrAO. PrAO inhibition must be considered as a potential mediator of the beneficial health effects of some methylxanthines. If inhibition in human tissues is comparable to, or greater than, that found in these studies it points to an important role for these compounds in human health.

Potential involvement of ubiquitin-proteasome system dysfunction associated with oxidative stress in the pathogenesis of sickle cell disease

The ubiquitin-proteasome system (UPS) is an important intracellular proteolytic pathway responsible for the degradation of proteins and oxidative damage; hence it plays a central role in maintaining homeostasis of red blood cells (RBCs). The present study investigated the levels of polyubiquitination, the function of proteasomes and effect of hydroxycarbamide (HC) therapy in RBCs from sickle cell disease (SCD) patients. Polyubiquitinated proteins were found to be elevated in untreated SCD (UT-SCD) patients compared to those in HC-treated SCD patients (HC-SCD) and controls. Activities of β1 and β2 subunits were a little higher in UT-SCD patients, and much higher proteolytic activities were observed in all three subunits (β1, β2 and β5) of RBCs in HC-SCD patients compared to those of UT-SCD patients and controls, although the protein levels of these subunits remained approximately the same. It is notable that, despite HC therapy, some patients showed persistent complications and accumulation of polyubiquitinated proteins. The enhanced proteasomal activity among HC-treated patients might remove the polyubiquitinated protein and could be one of the important mechanisms of therapeutic action. These findings could be useful to understand the pathophysiology of SCD and its clinical heterogeneity and identify a suitable therapeutic target for the better management of these patients.

Antiglycation, radical scavenging, and semicarbazide-sensitive amine oxidase inhibitory activities of acetohydroxamic acid in vitro

Advanced glycation endproducts (AGEs) can promote intracellular reactive oxygen species production, and the levels of AGEs are highly correlated with cardiovascular disease and diabetes complications. Acetohydroxamic acid (acetH) is a bacterial urease inhibitor drug used to treat kidney stones and infections in the urinary tract, and hydroxyurea (HU) is a drug used for antineoplasm and sickle cell diseases. Both acetH and HU are hydroxamic acid derivatives. It was found that acetH and HU at 2.5 or 5 mM showed anti-AGE formation by lowering the AGEs' fluorescent intensities and N^ε-(carboxymethyl)lysine formation in bovine serum albumin/galactose models, and both showed better and significant differences (P<0.05) compared to the positive control of aminoguanidine. Regarding radical scavenging activities, the half-inhibition concentrations (IC₅₀) of acetH against α,α-diphenyl-β-picrylhydrazyl radical and hydroxyl radical were 34.86 and 104.42 μM, respectively. The IC₅₀ of acetH against semicarbazide-sensitive amine oxidase was 10.56 μM, and acetH showed noncompetitive inhibition respective to the substrates (benzylamine). The antiglycation, antioxidant, and semicarbazide-sensitive amine oxidase inhibitory activities of acetH prove that it has the potential for treating cardiovascular disease and diabetes complications and it needs further investigation in animal models.

Glycine hydroxamate inhibits tyrosinase activity and melanin contents through downregulating cAMP/PKA signaling pathways

Among the eight amino acid hydroxamates tested, Glycine hydroxamate (GH) was the best inhibitor of mushroom tyrosinase (TYR). With L-tyrosine as substrate, the GH inhibition of the monophenolase activity of the mushroom TYR was noncompetitive. GH decreased not only TYR protein expression, but also melanin content, tyrosinase-related protein (TRP)-1, TRP-2, and microphthalmia-associated transcription factor (MITF) expression in B16F10 melanoma cells while in the presence of α-melanocyte-stimulating hormone (α-MSH). GH also significantly decreased the isobutylmethylxanthine (IBMX)-induced increase in melanin content, which was not prevented by the ERK inhibitor PD98059. These results suggest GH has the potential for use in cosmetic hypopigmentation.

Influence of βS allele in the lipid peroxidation and antioxidant capacity parameters

INTRODUCTION

The oxidative process plays a fundamental role in the pathophysiology of sickle cell anemia (SCA), and population and environmental characteristics may influence redox balance. The aim of this study was to evaluate lipid peroxidation and antioxidant capacity in Brazilian Hb S carriers undergoing different therapies.

METHODS

Blood samples from 270 individuals were analyzed (Hb SS, n = 68; Hb AS, n = 53, and Hb AA, n = 149). Hemoglobin genotypes were assessed through cytological, electrophoretic, chromatographic, and molecular methods. Plasma lipid peroxidation and antioxidant capacity were measured by spectrophotometric methods.

RESULTS

Patients with SCA who used iron-chelating drugs combined with hydroxyurea, associated with regular transfusions, showed lower levels of TBARS (P ≤ 0.05), higher levels of TEAC (P ≤ 0.01), and lower TBARS/TEAC ratio (R = 255.8). The redox profile of Hb AS subjects was not statistically different (P > 0.05) from that of Hb AA subjects.

CONCLUSION

The data suggest that oxidative stress is lower in the patients with SCA who received regular blood transfusions associated with the combined use of HU and iron chelators than the group received only HU. The redox system of the Hb AS carriers is compatible with the control group.

The influence of hydroxyurea on oxidative stress in sickle cell anemia

OBJECTIVE

The oxidative stress in 20 sickle cell anemia patients taking hydroxyurea and 13 sickle cell anemia patients who did not take hydroxyurea was compared with a control group of 96 individuals without any hemoglobinopathy.

METHODS

Oxidative stress was assessed by thiobarbituric acid reactive species production, the Trolox-equivalent antioxidant capacity and plasma glutathione levels.

RESULTS

Thiobarbituric acid reactive species values were higher in patients without specific medication, followed by patients taking hydroxyurea and the Control Group (p < 0.0001). The antioxidant capacity was higher in patients taking hydroxyurea and lower in the Control Group (p = 0.0002 for Trolox-equivalent antioxidant capacity and p < 0.0292 for plasma glutathione). Thiobarbituric acid reactive species levels were correlated with higher hemoglobin S levels (r = 0.55; p = 0.0040) and lower hemoglobin F concentrations(r = -0.52; p = 0.0067). On the other hand, plasma glutathione levels were negatively correlated with hemoglobin S levels (r = -0.49; p = 0.0111) and positively associated with hemoglobin F values (r = 0.56; p = 0.0031).

CONCLUSION

Sickle cell anemia patients have high oxidative stress and, conversely, increased antioxidant activity. The increase in hemoglobin F levels provided by hydroxyurea and its antioxidant action may explain the reduction in lipid peroxidation and increased antioxidant defenses in these individuals.

Antioxidant and semicarbazide-sensitive amine oxidase inhibitory activities of glucuronic acid hydroxamate

The antioxidant and inhibitory activities of glucuronic acid (GluA) and its synthesized 1-methoxyl-6-glucuronic acid hydroxamate (GluA-NHOH) against semicarbazide-sensitive amine oxidase (SSAO) were investigated. The scavenging activities of GluA-NHOH against 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radicals (half-inhibition concentration [IC₅₀], 152μM) and hydroxyl radicals (IC₅₀, 70nM) were determined. The protective activities of GluA-NHOH against hydroxyl radical-mediated calf thymus DNA damage and peroxynitrite-mediated dihydrorhodamine oxidation were also investigated. GluA-NHOH, but not GluA, exhibited dose-dependent protective activities. GluA-NHOH, but not GluA, effectively inhibited bovine SSAO activities in a dose-dependent manner, and was further confirmed by AO activity stains on an acrylamide gel. GluA-NHOH showed mixed noncompetitive inhibition of bovine SSAO with respect to benzylamine (substrate) and benzylamine-SSAO (substrate-enzyme complex). The V_max^' and K_m^' values were reduced in the presence of GluA-NHOH (0.04mM).