Hypoalbuminemia as a predictor of acute kidney injury during colistin treatment

This study aimed to assess the predictors of acute kidney injury (AKI) during colistin therapy in a cohort of patients with bloodstream infections (BSI) due to colistin-susceptible Gram-negative bacteria, focusing on the role of serum albumin levels. The study consisted of two parts: (1) a multicentre retrospective clinical study to assess the predictors of AKI during colistin therapy, defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria; and (2) bioinformatic and biochemical characterization of the possible interaction between human serum albumin and colistin. Among the 170 patients included in the study, 71 (42%), 35 (21%), and 11 (6%) developed KDIGO stage 1 (K1-AKI), KDIGO stage 2 (K2-AKI), and KDIGO stage 3 (K3-AKI), respectively. In multivariable analyses, serum albumin <2.5 g/dL was independently associated with K1-AKI (subdistribution hazard ratio [sHR] 1.85, 95% confidence interval [CI] 1.17\u20132.93, p = 0.009) and K2-AKI (sHR 2.37, 95% CI 1.15\u20134.87, p = 0.019). Bioinformatic and biochemical analyses provided additional information nurturing the discussion on how hypoalbuminemia favors development of AKI during colistin therapy. In conclusion, severe hypoalbuminemia independently predicted AKI during colistin therapy in a large cohort of patients with BSI due to colistin-susceptible Gram-negative bacteria. Further study is needed to clarify the underlying causal pathways

A possible molecular mechanism for parasitic inhibition by lactoferrin

Transferrins (Tfs) belong to a family of iron-binding glycoproteins possessing similar aminoacid sequence though they have different biological functions and locations. Lactoferrin (Lf) is expressed and secreted from glandular epithelial cells and from mature neutrophiles of mammalian and it is an important component of the aspecific host defence or natural immunity, including resistance to parasitic infections. Serum transferrin (sTf) is synthesized by the liver of mammals and secreted into the blood stream; its primary function is iron transport. Ovotransferrin (Otrf), synthesized by avians, displays both iron transport and protective functions. Parasites synthesize papain-like cysteine proteases that are relevant for the virulence and pathogenicity of parasites, being involved in several aspects of the parasite life cycle, it is therefore possible that the antiparasitic activity of Lf could be due to the inhibition of parasitic papain-like cysteine protease that we have recently observed. In this study we have investigated the thermodynamic parameters of hLf, bLf and Otrf inhibition of the parasitic papain-like type I cysteine proteases from Leishmania infantum, Trypanosoma cruzi and Trypanosoma brucei. bLf, hLf and Otrf, both in the apo- and olo-forms, showed time- and concentration-dependent inhibition of the catalytic activity of papain and of type I proteases from L.infantum, T. cruzi and T. brucei. The KI values observed for bLf and hLf inhibition of L. infantum, T. cruzi and T. brucei proteases were in the nanomolar range (KI = 3.1 nM), lower than KI values observed for papain inhibition (KI = 24 nM). Otrf showed lower inhibition of cysteine proteases (KI = 0.6 µM). On the contrary, sTf did not display any inhibition towards parasitic proteases, according to its different role in mammals. The inhibition of parasitic cysteine proteases by hLf, bLf and Otrf appeared to conform to a competitive mechanism. The observed pH optimum for bLf inhibition of parasitic proteases was around neutrality, while it was acidic for hLf and alkaline for Otrf. The further quantitative analysis of pH dependence of the intrinsic ligand-independent inhibition constant KI allowed the evaluation of pKa values that define the acid-base equilibrium of amino acidic residue(s) modulating the enzyme(s)-inhibitor recognition events. SDS-PAGE showed that hLf, bLf and Otrf were easily degraded by either papain or parasitic type I protease during the assay incubation time (few minutes) and it is likely that one or more protease inhibitory peptides were generated from protein hydrolysis. As a matter of fact, a sequence present near the C-terminus of human (hLf) and bovine (bLf) lactoferrin shows homology with the sequence of the active site of cystatins, which are competitive inhibitors of papain-like cysteine proteases. The same sequence is present, though with lower homology, in Otrf and, with even lower homology, in sTf. Therefore, we have charactherized by MALDI-TOF the profile of Lf cleavage by papain and preliminary data suggest the presence of a cystatin-like peptide in two proteolytic fragments of hLf and in one proteolytic fragment of bLf.Le transferrine (Tfs) sono una famiglia di glicoproteine in grado di legare reversibilmente il ferro, e presentano un’elevata omologia di sequenza tra tutti i membri di questa famiglia. In particolare la lattoferrina (Lf) è prodotta e secreta nelle cellule ghiandolari epiteliali ed è presente nei granuli dei granulociti neutrofili dei mammiferi. Essa rappresenta un’importante componente della difesa immunitaria aspecifica dell’ospite. La siero transferrina (sTf) invece è sintetizzata nel fegato, ed è coinvolta unicamente nel trasporto del ferro. L’ovotransferrina (Otrf), l’omologa aviaria della Lf , svolge sia una funzione di difesa che di trasporto del ferro. Le proteasi a cisteina papaina-simili da protozoi e metazoi parassiti, secretorie e di membrana, partecipano ai processi di morfogenesi degli organismi patogeni, sono implicate nell’invasione delle cellule e dei tessuti da parte dei parassiti, riducono la risposta immunitaria dell’ospite e costituiscono uno dei fattori più rilevanti nelle patologie associate alle infestazioni da parassiti. Pertanto, a fronte della capacità della Lf di svolgere un’azione antiparassitaria, noi abbiamo ipotizzato che la Lf possa svolgere tale azione grazie all’inattivazione delle suddette proteasi a cisteina. Nel presente lavoro abbiamo studiato le proprietà termodinamiche dell’inibizione delle proteasi a cisteina di alcuni parassiti, quali Leishmania infantum, Tripanosoma cruzi e Trypanosoma brucei. Tale studio è stato esteso anche verso la papaina, capostipite di questa famiglia. Innanzitutto è emerso una maggiore affinità delle transferrine studiate (bLf, hLf e Otrf, in forma apo e olo) verso le proteasi parassitarie (KI = 3.1 nM) rispetto a quella verso la papaina (KI = 24 nM). Otrf risulta essere l’inibitore con minore affinità (KI = 0.6 µM). Inoltre è emerso che la sTf non è in grado di svolgere un’azione inibitoria, coerentemente con la sua funzione nei mammiferi. L’inibizione di tutte le proteasi risulta essere conforme ad un meccanismo di inibizione competitivo. Da un’analisi della dipendenza del pH dei suddetti fenomeni di inibizione si è osservato una maggiore attività della bLf a pH fisiologico mentre la hLf inibisce più efficacemente a valori di pH acidi (pH = 5.0) e la Otrf a valori di pH alcalini (pH = 9.0). La dipendenza dal pH del parametro KI relativo all’interazione degli inibitori studiati con gli enzimi, ha permesso di evidenziare la variazione di diversi valori di pKa, ascrivibili ad eventi di protonazione e deprotonazione di differenti gruppi ionizzabili. Inoltre si è osservato, a seguito di SDS-page, una parziale idrolisi della Lf e della Otrf durante diverse incubazioni con la papaina e con le proteasi parassitarie, e l’insieme di tali dati suggerisce la liberazione di un peptide, che può quindi inibire competitivamente le suddette proteasi a cisteina. A supporto di tale ipotesi, si è osservato in presenza della porzione C-terminale della Lf, una sequenza aminoacidica che presenta un’elevata omologia con il sito attivo delle cistatine, una (super)famiglia di proteina, riconosciute essere gli inibitori reversibili per eccellenza delle proteasi a cisteina papaina-simili. Abbiamo quindi caratterizzato, mediante MALDI TOF, il profilo di idrolisi della Lf ad opera della papaina, ed è stata riscontrata la presenza di frammenti contenenti tale sequenza cistatinosimile, sia nella bLf che nell’hLf

Antifungal and Antiparasitic Activities of Lactoferrin

The first function attributed to lactoferrin, an iron-binding protein belonging to the non-immune natural defences, was antimicrobial activity related to its capability of sequestering iron. Many other antimicrobial and antiviral functions have been ascribed to lactoferrin. In vitro activity towards human pathogenic fungi on the part of both human and bovine lactoferrin has been well documented as well. The antifungal activity appears to be related to lactoferrin interference with the fungal cell surface rather than iron deprivation and some host-mediated mechanisms of action cannot be ruled out. Lactoferrin also displays anti-parasitic activity, although the molecular mechanisms of such activity are even more complex

Cholesterol homeostasis failure in the brain: implications for synaptic dysfunction and cognitive decline

Cholesterol is one of the most important molecules in cell physiology because of its involvement in several biological processes: for instance, it determines both physical and biochemical properties of cell membranes and proteins. Disruption to cholesterol homeostasis leads to coronary heart disease, atherosclerosis and metabolic syndrome. Strong evidence suggests that cholesterol also has a crucial role in the brain as various neurological and neurodegenerative disorders, including Alzheimer's, Huntington's and Parkinson diseases are associated with disruptions to cholesterol homeostasis. Here, we summarize the current knowledge about the role cholesterol plays at synaptic junctions and the pathological consequences caused by disruptions in the homeostatic maintenance of this compound

The Nutraceutical Properties of Ovotransferrin and Its Potential Utilization as a Functional Food

Ovotransferrin or conalbumin belong to the transferrin protein family and is endowed with both iron-transfer and protective activities. In addition to its well-known antibacterial properties, ovotransferrin displays other protective roles similar to those already ascertained for the homologous mammalian lactoferrin. These additional functions, in many cases not directly related to iron binding, are also displayed by the peptides derived from partial hydrolysis of ovotransferrin, suggesting a direct relationship between egg consumption and human health

Lactoferrin from milk: Nutraceutical and pharmacological properties

Lactoferrin is an iron-binding protein present in large quantities in colostrum and in breast milk, in external secretions and in polymorphonuclear leukocytes. Lactoferrin’s main function is non-immune protection. Among several protective activities shown by lactoferrin, those displayed by orally administered lactoferrin are: (i) antimicrobial activity, which has been presumed due to iron deprivation, but more recently attributed also to a specific interaction with the bacterial cell wall and extended to viruses and parasites; (ii) immunomodulatory activity, with a direct effect on the development of the immune system in the newborn, together with a specific antinflammatory effects; (iii) a more recently discovered anticancer activity. It is worth noting that most of the protective activities of lactoferrin have been found, sometimes to a greater extent, also in peptides derived from limited proteolysis of lactoferrin that could be generated after lactoferrin ingestion. Lactoferrin could therefore be considered an ideal nutraceutic product because of its relatively cheap production from bovine milk and of its widely recognized tolerance after ingestion, along with its well demonstrated protective activities. The most important protective activities shown by orally administered bovine lactoferrin are reviewed in this article

Human plasma lipocalins and serum albumin: Plasma alternative carriers?

Lipocalins are an evolutionarily conserved family of proteins that bind and transport a variety of exogenous and endogenous ligands. Lipocalins share a conserved eight anti-parallel β-sheet structure. Among the different lipocalins identified in humans, α-1-acid glycoprotein (AGP), apolipoprotein D (apoD), apolipoprotein M (apoM), α1-microglobulin (α1-m) and retinol-binding protein (RBP) are plasma proteins. In particular, AGP is the most important transporter for basic and neutral drugs, apoD, apoM, and RBP mainly bind endogenous molecules such as progesterone, pregnenolone, bilirubin, sphingosine-1-phosphate, and retinol, while α1-m binds the heme. Human serum albumin (HSA) is a monomeric all-α protein that binds endogenous and exogenous molecules like fatty acids, heme, and acidic drugs. Changes in the plasmatic levels of lipocalins and HSA are responsible for the onset of pathological conditions associated with an altered drug transport and delivery. This, however, does not necessary result in potential adverse effects in patients becausemany drugs can bind both HSA and lipocalins, and therefore mutual compensatory binding mechanisms can be hypothesized. Here, molecular and clinical aspects of ligand transport by plasma lipocalins and HSA are reviewed, with special attention to their role as alterative carriers in health and disease

Nutraceutical Peptides from Lactoferrin

Lactoferrin belongs to the transferrin protein superfamily and is a major component of the mammalian innate immune system. Proteolytic cleavage of either human or bovine lactoferrin results in the generation of several peptides, most of which manifest the protective activities of Lactoferrin. It is worth noting that these peptides may be naturally produced in the human intestine after milk ingestion. Interestingly, peptides deriving from proteolytic cleavage of Ovotransferrin, a Lactoferrin homologous protein present in reptiles and birds, displays the same protective activities. This mini-review summarizes the most relevant protective activities of peptides deriving from Lactoferrin and Ovotransferrin

Different disulfide bridge connectivity drives alternative folds in highly homologous Brassicaceae trypsin inhibitors

Low-molecular-mass trypsin inhibitors from Arabidopsis thaliana, Brassica napus var. oleifera, and Sinapis alba L. (ATTI, RTI, and MTI, respectively) display more than 69% amino acid sequence identity. Among others, the amino acid sequence Cys-Ala-Pro-Arg-Ile building up the inhibitor reactive site, and the eight Cys residues forming four disulfide bridges are conserved. However, the disulfide bridge connectivity of RTI and MTI (C1-C3, C2-C4, C5-C6, and C7-C8) is different from that of ATTI Cys (C1-C8, C2-C5, C3-C6, and C4-C7). Despite the different disulfide bridge connectivity, the reactive site loop of ATTI, RTI, and MTI is solvent exposed permitting trypsin recognition. Structural considerations here reported suggest that proteins showing high amino acid sequence identity and common functional properties could display different three-dimensional structures. This may reflect high inhibitor plasticity in relation to plant-pathogen interactions, plant tissue development as well as the different redox potential of cell compartments