Structure, enzymatic activities, glycation and therapeutic potential of human serum albumin: A natural cargo

Tolperisone hydrochloride (TH) has muscle relaxant activity and has been widely used for several years in clinical practice to treat pathologically high skeletal muscle tone (spasticity) and related pains. The current study was designed to explore the binding efficacy of TH with human serum albumin (HSA) using multispectrscopic, calorimetric approach, FRET, esterase-like activity, and a molecular docking method. A reduction in fluorescence emission at 340 nm of HSA was attributed to fluorescence quenching by TH via a static quenching type. Binding constants ( Kb) were evaluated at different temperatures, and obtained Kb values were ∼104 M-1, which demonstrated moderately strong affinity of TH for HSA. A calculated negative Δ G° value indicated spontaneous binding of TH to HSA. Far-UV CD spectroscopy revealed that the α-helix content was increased after TH binding. The binding distance between donor and acceptor was calculated to be 2.11 nm based on Forster's resonance energy transfer theory. ITC results revealed TH interacted with HSA via hydrophobic interactions and hydrogen bonding. The thermal stability of HSA was studied using DSC, and results showed that in the presence of TH the structure of HSA was significantly more thermostable. The esterase-like activity of HSA showed fixed Vmax and increased Km suggesting that TH binds with HSA in a competitive manner. Furthermore, molecular docking results revealed TH binds in the cavity of HSA, that is, subdomain IIA (Sudlow site I), and that it hydrogen bonds with K199 and H242 of HSA. Binding studies of drugs with HSA are potentially useful for elucidating chemico-biological interactions that can be utilized in the drug design, pharmaceutical, pharmacology, and biochemistry fields. This extensive study provides additional insight of ligand binding and structural changes induced in HSA relevant to the biological activity of HSA in vivo.

Binding of Tolperisone Hydrochloride with Human Serum Albumin: Effects on the Conformation, Thermodynamics, and Activity of HSA

The focus of perioperative pain management should be to attempt to minimise the nociceptive input and reduce the risk of transition to central sensitisation. Gabapentinoids are being increasingly used as adjuncts for management of perioperative pain. Although gabapentinoids are classed as calcium channel blockers, their mechanisms of action are poorly understood. The analgesic effect in neuropathic pain is well evidenced but the role in postoperative pain is less certain. Medline and EMBASE database searches were conducted to identify studies relating to mechanisms of action and effects in experimental animal models of inflammatory and postoperative pain and human models of experimental pain. The effects of gabapentinoids may be attributed to depression of dorsal horn sensitivity through a multitude of mechanisms. They inhibit calcium mediated neurotransmitter release through effects on α2δ-1 subunits. They inhibit forward trafficking of α2δ-1 from the dorsal root ganglion, their recycling from endosomal compartments, thrombospondin mediated processes and stimulate glutamate uptake by excitatory amino acid transporters. Mechanisms not directly related to neurotransmitter release at dorsal horn include inhibition of descending serotonergic facilitation, stimulation of descending inhibition, anti-inflammatory actions, and influence on the affective component of pain. Gabapentinoids are effective analgesics in most animal models of inflammation and postoperative pain but effects in human models are variable.

Analgesic mechanisms of gabapentinoids and effects in experimental pain models: a narrative review

Polymer conjugation of proteins as a synthetic post-translational modification to impact their stability and activity.

Tuberculosis is a ravaging disease killing one person in every 1.5 minutes in India alone. Someone in the world is newly infected with TB bacilli every second. Overall, one-third of the world's population is currently infected with the TB bacillus. Left untreated, each person with active TB disease will infect on average between 10 and 15 people every year. 450 000 new MDR-TB cases are estimated to occur every year. Estimated 5% of TB patients are HIV infected. Although the complete genome sequence of the causative pathogen _Mycobacterium tuberculosis_ was published about a decade ago and many years of painstaking efforts have been invested, we are still far from having a good, fast acting drug and vaccine which confers long lasting protection. Despite increasing investment, led by charities including the Gates Foundation, no novel drugs for TB have entered the market for many years.Novel mechanisms for attracting funding, particularly private sector funding, into this research area are desperately needed. We wish to bring in the power of genomics, computational technologies and participation of young and brilliant talent from Universities and Industrial partners with a strong inclination to apply a concerted effort to address this important scourge. All researchers contribute data on tuberculosis drug targets and active molecules through a copyleft agreement; anyone who is prepared to keep to this may participate. All the data is Clickwrap protected and credit sharing will be based on a novel and flexible micro-attribution system. This system is aimed at providing due credit through an active process. Various levels of investigators shall have appropriate levels of rights, recognition and responsibilities. Another valuable aspect is the partnerships of Industry with belief in Open Source systems and models. We name this concerted effort to tackle this dreaded disease as Open Source Drug Discovery for Tuberculosis.

Open Source Drug Discovery

The albumin molecule, in contrast to many other plasma proteins, is not covered with a carbohydrate moiety and can bind and transport various molecules of endogenous and exogenous origin. The enzymatic activity of albumin, the existence of which many scientists perceive skeptically, is much less studied. In toxicology, understanding the mechanistic interactions of organophosphates with albumin is a special problem, and its solution could help in the development of new types of antidotes. In the present work, the history of the issue is briefly examined, then our in silico data on the interaction of human serum albumin with soman, as well as comparative in silico data of human and bovine serum albumin activities in relation to paraoxon, are presented. Information is given on the substrate specificity of albumin and we consider the possibility of its affiliation to certain classes in the nomenclature of enzymes.

https://www.mdpi.com/1420-3049/22/7/1201/pdf

Serum Albumin Binding and Esterase Activity: Mechanistic Interactions with Organophosphates.

Being one of the main proteins in the human body and many animal species, albumin plays a decisive role in the transport of various ions-electrically neutral and charged molecules-and in maintaining the colloidal osmotic pressure of the blood. Albumin is able to bind to almost all known drugs, as well as many nutraceuticals and toxic substances, largely determining their pharmaco- and toxicokinetics. Albumin of humans and respective representatives in cattle and rodents have their own structural features that determine species differences in functional properties. However, albumin is not only passive, but also an active participant of pharmacokinetic and toxicokinetic processes, possessing a number of enzymatic activities. Numerous experiments have shown esterase or pseudoesterase activity of albumin towards a number of endogeneous and exogeneous esters. Due to the free thiol group of Cys34, albumin can serve as a trap for reactive oxygen and nitrogen species, thus participating in redox processes. Glycated albumin makes a significant contribution to the pathogenesis of diabetes and other diseases. The interaction of albumin with blood cells, blood vessels and tissue cells outside the vascular bed is of great importance. Interactions with endothelial glycocalyx and vascular endothelial cells largely determine the integrative role of albumin. This review considers the esterase, antioxidant, transporting and signaling properties of albumin, as well as its structural and functional modifications and their significance in the pathogenesis of certain diseases.

Serum Albumin in Health and Disease: Esterase, Antioxidant, Transporting and Signaling Properties.

As a carrier of many biologically active compounds, blood is exposed to oxidants to a greater extent than the intracellular environment. Serum albumin plays a key role in antioxidant defence under both normal and oxidative stress conditions. This review evaluates data published in the literature and from our own research on the mechanisms of the enzymatic and non-enzymatic activities of albumin that determine its participation in redox modulation of plasma and intercellular fluid. For the first time, the results of numerous clinical, biochemical, spectroscopic and computational experiments devoted to the study of allosteric modulation of the functional properties of the protein associated with its participation in antioxidant defence are analysed. It has been concluded that it is fundamentally possible to regulate the antioxidant properties of albumin with various ligands, and the binding and/or enzymatic features of the protein by changing its redox status. The perspectives for using the antioxidant properties of albumin in practice are discussed.

https://www.mdpi.com/2076-3921/9/10/966/pdf

The Universal Soldier: Enzymatic and Non-Enzymatic Antioxidant Functions of Serum Albumin.

Clinical observations have shown that patients with chronic neuropathic pain or itch exhibit symptoms of increased anxiety, depression and cognitive impairment. Such patients need corrective therapy with antidepressants, antipsychotics or anticonvulsants. It is known that some psychotropic drugs are also effective for the treatment of neuropathic pain and pruritus syndromes due to interaction with the secondary molecular targets. Our own clinical studies have identified antipruritic and/or analgesic efficacy of the following compounds: tianeptine (atypical tricyclic antidepressant), citalopram (selective serotonin reuptake inhibitor), mianserin (tetracyclic antidepressant), carbamazepine (anticonvulsant), trazodone (serotonin antagonist and reuptake inhibitor), and chlorprothixene (antipsychotic). Venlafaxine (serotonin-norepinephrine reuptake inhibitor) is known to have an analgesic effect too. The mechanism of such effect of these drugs is not fully understood. Herein we review and correlate the literature data on analgesic/antipruritic activity with pharmacological profile of these compounds.

https://www.mdpi.com/1424-8247/12/2/99/pdf

Psychotropic Drugs for the Management of Chronic Pain and Itch.

Although the tricyclic antidepressant amitriptyline (ATL) is widely used in the clinic, the mechanism underlying its high therapeutic efficacy against neuropathic pain remains unclear. NMDA receptors (NMDARs) represent a target for ATL and are involved in sensitization of neuropathic pain. Here we describe two actions of ATL on NMDARs: 1) enhancement of Ca2+-dependent desensitization and 2) trapping channel block. Inhibition of NMDARs by ATL was found to be dependent upon external Ca2+ concentration ([Ca2+]) in a voltage-independent manner, with an IC50 of 0.72 μM in 4 mM [Ca2+]. The ATL IC50 value increased exponentially with decreasing [Ca2+], with an e-fold change observed per 0.69 mM decrease in [Ca2+]. Loading neurons with BAPTA abolished Ca2+-dependent inhibition, suggesting that Ca2+ affects NMDARs from the cytosol. Since there is one known Ca2+-dependent process in gating of NMDARs, we conclude that ATL most likely promotes Ca2+-dependent desensitization. We also found ATL to be a trapping open-channel blocker of NMDARs with an IC50 of 220 µM at 0 mV. An e-fold change in ATL IC50 was observed to occur with a voltage shift of 50 mV in 0.25 mM [Ca2+]. Thus, we disclose here a robust dependence of ATL potency on extracellular [Ca2+], and demonstrate that ATL bound in the NMDAR pore can be trapped by closure of the channel.

/pdf/dual-action-of-amitriptyline-on-nmda-receptors-enhancement-rm8h0ym2vg.pdf

Daria A. Belinskaia

Papers

Serum Albumin Binding and Esterase Activity: Mechanistic Interactions with Organophosphates.

Serum Albumin in Health and Disease: Esterase, Antioxidant, Transporting and Signaling Properties.

The Universal Soldier: Enzymatic and Non-Enzymatic Antioxidant Functions of Serum Albumin.

Psychotropic Drugs for the Management of Chronic Pain and Itch.

Dual action of amitriptyline on NMDA receptors: enhancement of Ca-dependent desensitization and trapping channel block.