Heme oxygenase-1 induction by hemin prevents oxidative stress-induced acute cholestasis in the rat.

We previously demonstrated in in vitro and ex vivo models that physiological concentrations of unconjugated bilirubin (BR) prevent oxidative stress (OS)-induced hepatocanalicular dysfunction and cholestasis. Here, we aimed to ascertain, in the whole rat, whether a similar cholestatic OS injury can be counteracted by heme oxygenase-1 (HO-1) induction that consequently elevates endogenous BR levels. This was achieved through the administration of hemin, an inducer of HO-1, the rate-limiting step in BR generation. We found that BR peaked between 6 and 8 h after hemin administration. During this time period, HO-1 induction fully prevented the pro-oxidant tert-butylhydroperoxide (tBuOOH)-induced drop in bile flow, and in the biliary excretion of bile salts and glutathione, the two main driving forces of bile flow; this was associated with preservation of the membrane localization of their respective canalicular transporters, bile salt export pump (Bsep) and multidrug resistance-associated protein 2 (Mrp2), which are otherwise endocytosed by OS. HO-1 induction counteracted the oxidation of intracellular proteins and membrane lipids induced by tBuOOH, and fully prevented the increase in the oxidized-to-total glutathione (GSHt) ratio, a sensitive parameter of hepatocellular OS. Compensatory elevations of the activity of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were also prevented. We conclude that in vivo HO-1 induction protects the liver from acute oxidative injury, thus preventing consequent cholestasis. This reveals an important role for the induction of HO-1 and the consequently elevated levels of BR in preserving biliary secretory function under OS conditions, thus representing a novel therapeutic tool to limit the cholestatic injury that bears an oxidative background.

Physiological concentrations of unconjugated bilirubin prevent oxidative stress-induced hepatocanalicular dysfunction and cholestasis.

Bilirubin is an endogenous antioxidant with cytoprotective properties, and several studies highlight its potential in the treatment of pro-oxidant diseases. We demonstrated that oxidative stress (OS), a key feature in most hepatopathies, induces cholestasis by actin cytoskeleton disarrangement and further endocytic internalization of key canalicular transporters, such as the bile salt export pump (Bsep) and the multidrug resistance-associated protein 2 (Mrp2) . Here, we evaluated the capability of physiological concentrations of unconjugated bilirubin (UB) to limit OS and the impairment in biliary secretory function induced by the model pro-oxidant agent, tert-butylhydroperoxide (tBuOOH). UB fully prevented the formation of reactive oxygen species and membrane lipid peroxidation induced by tBuOOH in isolated rat hepatocytes. In the isolated rat hepatocyte couplet model, UB (17.1 µM) prevented the endocytic internalization of Bsep and Mrp2 and the impairment in their secretory function induced by tBuOOH. UB also prevented actin disarrangement, as evaluated by both plasma membrane bleb formation and actin fluorescent staining. Finally, UB prevented tBuOOH-induced cPKC activation. Experiments in isolated perfused rat livers showed that UB prevents the increase in oxidized glutathione biliary excretion and the drop in bile flow and the biliary excretion of specific Bsep and Mrp2 substrates. We conclude that physiological concentrations of UB are sufficient to prevent the biliary secretory failure induced by OS, by counteracting actin disarrangement and the consequent internalization of canalicular transporters relevant to normal bile formation. This reveals an important role for UB in preserving biliary secretory function under OS conditions.

Complement activation and disease: protective effects of hyperbilirubinaemia.

Complement, an important effector mechanism of the immune system, is an enzymatic cascade of approx. 30 serum proteins leading to the amplification of a specific humoral response. It can be activated through the classical or alternative pathways, or through the mannose-binding lectin pathway. The activation of the classical pathway is initiated by the binding of the C1 component to antigen-bound antibodies, known as immunocomplexes. C1 is a complex of one molecule of C1q, two molecules of C1r and two molecules of C1s. C1q contains three copies of a Y-shaped fundamental unit with globular heads included in its structure, which play a major role in the interaction with the Fc portion of immunoglobulins. Deficient or exacerbated activation of the complement system leads to diseases of variable severity, and pharmacological inhibition of the complement system is considered as a therapeutic strategy to ameliorate the inflammatory effects of exacerbated complement activation. Bilirubin is a product of haem degradation by the concerted action of haem oxygenase, which converts haem into biliverdin, and biliverdin reductase, which reduces biliverdin to UCB (unconjugated bilirubin). UCB exerts both cytoprotective and cytotoxic effects in a variety of tissues and cells, acting either as an antioxidant at low concentrations or as an oxidant at high concentrations. In the present review, we describe in detail the anti-complement properties of bilirubin, occurring at levels above the UCB concentrations found in normal human serum, as a beneficial effect of potential clinical relevance. We provide evidence that UCB interferes with the interaction between C1q and immunoglobulins, thus inhibiting the initial step in the activation of complement through the classical pathway. A molecular model is proposed for the interaction between UCB and C1q.

Protective role of unconjugated bilirubin on complement-mediated hepatocytolysis.

Hyperbilirubinemia and complement-mediated immune attack on hepatocyte membrane are common features of certain hepatic diseases. To assess whether unconjugated bilirubin (UB) counteracts complement-mediated hepatocytolysis, we first generated a rabbit polyclonal antibody (Ab) against rat hepatocyte plasma membrane (RHPM). An assay performed with isolated rat hepatocytes in the presence of the polyclonal Ab and rat serum as complement donor demonstrated that UB inhibits cell lysis, as lactate dehydrogenase release into the medium was inhibited by the pigment in a dose-dependent manner. Immunofluorescence microscopy studies showed that UB significantly attenuates the binding of C3 to the hepatocyte-Ab complex. Further enzyme immunoassay studies showed that UB interferes the binding of C1q to purified anti-RHPM IgG, also in a dose-dependent manner. A dot-blot assay showed that [14C]-UB binds to C1q and human serum albumin (HSA) to a similar extent. A differential spectrum analysis of UB in the presence of C1q further confirmed that the pigment interacts with this protein. In conclusion, we demonstrated an inhibitory action of UB on complement-mediated Ab-induced hepatocytolysis, this action being evidenced at pathophysiological pigment concentrations (171 microM and higher). A direct binding of the pigment to C1q is likely involved.

Evaluation of urinary N-acetyl-beta-D-glucosaminidase as a marker of early renal damage in patients with type 2 diabetes mellitus.

OBJECTIVE: To evaluate the clinical usefulness of urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion for the detection of early tubular damage in type 2 diabetes mellitus (T2DM). SUBJECTS AND METHODS: Thirty six patients with T2DM were divided into two groups based on urinary albumin to creatinine ratio (ACR): normoalbuminuria (ACR <30 mg/g; n=19) and microalbuminuria (ACR =30-300 mg/g; n=17). The following parameters were determined in both groups: urinary NAG and albumin, serum and urine creatinine, fasting plasma glucose and glycated hemoglobin (HbA1c). RESULTS: Urinary NAG levels [Units/g creatinine; median (range)] were significantly increased in microalbuminuria group [17.0 (5.9 - 23.3)] compared to normoalbuminuria group [4.4 (1.5 - 9.2)] (P<0.001). No differences between groups were observed in fasting glucose, HbA1c, serum creatinine levels and estimated glomerular filtration rates (eGFR). Urinary NAG positively correlated with ACR (r=0.628; p<0.0001), while no significant association was observed between NAG and glycemia, HbA1c, serum creatinine and eGFR. CONCLUSIONS: The increase of urinary NAG at the microalbuminuria stage of diabetic nephropathy (DN) suggests that tubular dysfunction is already present in this period. The significant positive association between urinary NAG excretion and ACR indicates the possible clinical application of urinary NAG as a complementary marker for early detection of DN in T2DM.

Unconjugated bilirubin inhibits C1 esterase activity.

OBJECTIVE: To evaluate if unconjugated bilirubin (UB) inhibits C1 esterase activity. DESIGN AND METHODS: Esterase activity was evaluated by C1-mediated hydrolysis of N-acetyl-L-tyrosine ethyl ester, and binding of UB to C1r and C1s was assessed by dot-blot analysis. RESULTS: UB inhibited C1 enzymatic activity. C1r, C1s and human serum albumin bound [(14)C]-UB to a similar extent. CONCLUSIONS: UB inhibits C1 esterase activity, apparently due to a direct pigment-protein interaction. This could explain the inhibitory action of UB on complement activation.

Evaluation of urinary N-acetyl-beta-D-glucosaminidase as a marker of early renal damage in patients with type 2 diabetes mellitus / Avaliação da N-acetil-beta-D-glucosaminidase urinária como marcador de dano renal precoce em pacientes com diabetes melito tipo 2

Objective To evaluate the clinical usefulness of urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion for the detection of early tubular damage in type 2 diabetes mellitus (T2DM). Subjects and methods Thirty six patients with T2DM were divided into two groups based on urinary albumin to creatinine ratio (ACR): normoalbuminuria (ACR <30 mg/g; n=19) and microalbuminuria (ACR =30‐300 mg/g; n=17). The following parameters were determined in both groups: urinary NAG and albumin, serum and urine creatinine, fasting plasma glucose and glycated hemoglobin (HbA1c). Results Urinary NAG levels [Units/g creatinine; median (range)] were significantly increased in microalbuminuria group [17.0 (5.9 - 23.3)] compared to normoalbuminuria group [4.4 (1.5 - 9.2)] (P<0.001). No differences between groups were observed in fasting glucose, HbA1c, serum creatinine levels and estimated glomerular filtration rates (eGFR). Urinary NAG positively correlated with ACR (r=0.628; p<0.0001), while no significant association was observed between NAG and glycemia, HbA1c, serum creatinine and eGFR. Conclusions The increase of urinary NAG at the microalbuminuria stage of diabetic nephropathy (DN) suggests that tubular dysfunction is already present in this period. The significant positive association between urinary NAG excretion and ACR indicates the possible clinical application of urinary NAG as a complementary marker for early detection of DN in T2DM. .

Objetivo Avaliar a utilidade clínica da excreção urinária da N-acetil-beta-D-glucosaminidase (NAG) para a detecção de dano tubular precoce no diabetes melito tipo 2 (DM2). Sujeitos e métodos Foram estudados trinta e seis pacientes com DM2 que se dividiram em dois grupos com base na excreção urinária de albumina (EUA): normoalbuminúrico (EUA <30 mg/g de creatinina; n=19) e microalbuminúrico (EUA =30‐300 mg/g de creatinina; n=17). Em ambos os grupos foram determinados os seguintes parâmetros: NAG e albumina urinária, creatinina sérica e urinária, glicemia de jejum e hemoglobina glicada (HbA1c). Resultados Os níveis de NAG urinária [unidades/g de creatinina; mediana (intervalo interquartílico)] foram significativamente maiores no grupo microalbuminúrico [17,0 (5,9 - 23,3)] em comparação com o grupo normoalbuminúrico [4,4 (1,5 - 9,2)] (p<0,001). Não se observaram diferenças significativas entre os dois grupos nos níveis de glicemia de jejum, HbA1c, creatinina sérica e taxa de filtração glomerular estimada (TFGe). A NAG urinária se correlacionou positivamente com o EUA (r=0,628, p<0,0001), não sendo observada associação significativa da NAG com glicemia, HbA1c, creatinina sérica e TFGe. Conclusões O aumento da NAG urinária na fase de microalbuminúria da nefropatia diabética (ND) sugere que a disfunção tubular já está presente nesse período. A associação positiva significativa entre a excreção urinária da NAG e EUA indica a possível aplicação clínica da NAG urinária como marcador complementar para a detecção precoce da ND no DM2. .

Estudio de la reactividad antigênica en muestras de sangre congeladas / Study of antigen in frozen blood sample

Se conoce relativamente bien el tiempo de vida útil de muestras de sangre conservadas a bajas temperaturas para uso transfusional. El objetivo de nuestro trabajo fue investigar en muestras de sangre congeladas las modificaciones de la actividad de los antígenos eritrocitarios como reactivos inmunohematológicos. Se estudiaron el antígeno A del sistema ABO y el antígeno D del sistema Rh en sangre de dadores normales (n = 3) utilizando ACD como anticoagulante. Las muestras se fraccionaron en alícuotas que se congelaron inmediatamente. Se determinó el título, el score y la cuantificación de la hemaglutinación a intervalos regulares (7 días). El deterioro del antígeno A sólo es demostrable por la técnica de cuantificación de la hemaglutinación. La pérdida de la reactividad del antígeno D se evidencia en los valores del título y del score, obteniéndose mayor grado de significado al aplicar el método óptico. Además, los resultados obtenidos indican la ventaja del uso de la técnica de cuantificación de la hemaglutinación que puede ser utilizada en laboratorios no especializados