Pyrrole-protein adducts – A biomarker of pyrrolizidine alkaloid-induced hepatotoxicity

Pyrrolizidine alkaloids (PAs) are phytotoxins identified in over 6000 plant species worldwide. Approximately 600 toxic PAs and PA N-oxides have been identified in about 3% flowering plants. PAs can cause toxicities in different organs particularly in the liver. The metabolic activation of PAs is catalyzed by hepatic cytochrome P450 and generates reactive pyrrolic metabolites that bind to cellular proteins to form pyrrole-protein adducts leading to PA-induced hepatotoxicity. The mechanisms that pyrrole-protein adducts induce toxicities have not been fully characterized. Methods for qualitative and quantitative detection of pyrrole-protein adducts have been developed and applied for the clinical diagnosis of PA exposure and PA-induced liver injury. This mini-review addresses the mechanisms of PA-induced hepatotoxicity mediated by pyrrole-protein adducts, the analytical methods for the detection of pyrrole-protein adducts, and the development of pyrrole-protein adducts as the mechanism-based biomarker of PA exposure and PA-induced hepatotoxicity.     

The novel role of β-aescin in attenuating CCl4-induced hepatotoxicity in rats

Context: β-Aescin has anti-inflammatory, anti-oxidant and antiedematous properties.

Objective: The present study investigated the hepatoprotective effect and underlying mechanisms of β-aescin in CCl₄-induced liver damage.

Materials and methods: Thirty-five Wistar rats were divided into six groups: normal control, CCl₄ control, silymarin (50?mg/kg, p.o) and β-aescin (0.9, 1.8 and 3.6?mg/kg, i.p.) treatment for 14 d. CCl₄ (1?mL/kg, i.p. for 3 d) was administered to produce hepatic damage. Ponderal changes and liver marker enzymes were estimated. Hepatic oxidative and nitrosative stress was estimated by levels of thiobarbituric acid reactive substances (TBARS), glutathione (GSH) and nitrite/nitrate. Serum TGF-β1 and TNF-α were estimated by ELISA technique. Hepatic collagen and histopathological studies were carried out.

Results: β-Aescin (3.6?mg/kg) markedly decreased CCl₄-induced increased levels of ALT, AST, ALP (71.77 versus 206.7, 71.39 versus 171.82, 121.20 versus 259?IU/L, respectively), total bilirubin (0.41 versus 1.35?mg/dL), TBARS (2.0 versus 8.83?nmol MDA/mg protein), nitrite/nitrate (352.50 versus 745.15?μg/mL) and increased CCl₄-induced decreased GSH levels (0.095 versus 0.048?μmol/mg protein). β-Aescin (3.6?mg/kg) induced focal regenerative changes in liver and markedly decreased TBARS (2.0 versus 8.83?nmol MDA/mg protein), nitrite/nitrate (352.50 versus 745.15?μg/mL), TGF-β1 (92.28 versus 152.1?pg/mL), collagen content (110.75 versus 301.74?μmol/100?mg tissue) and TNF-α (92.82 versus 170.56?pg/mL) when compared with CCl₄ control.

Discussion and conclusion: The findings suggest that β-aescin has a protective effect on CCl₄-induced liver injury, exhibited via its anti-inflammatory, antioxidative, antinitrosative and antifibrotic properties inducing repair regeneration of liver. Hence, it can be used as a promising hepatoprotective agent.     

The intriguing role of Rifaximin in gut barrier chronic inflammation and in the treatment of Crohn’s disease

Introduction: The gastrointestinal tract acts as a functional unit organized as a semipermeable multilayer system, in which commensal gut microbiota represents the anatomical barrier. Recently, several studies have highlighted the involvement of gut microbiota in inflammatory bowel diseases (IBD) pathogenesis, in sustaining gut barrier chronic inflammation, and in conditioning disease course and therapeutical response. This evidence provides a rationale for treating patients with gut microbiota modifiers. Among these, Rifaximin represents a non-traditional antibiotic able to act as a ‘eubiotic’ on intestinal barrier.

Area covered: The purpose of this narrative review is to explore the impact of Rifaximin on gut barrier and gut microbiota in IBD, in particular in Crohn’s disease (CD), and to analyze its potential therapeutic applications.

Expert opinion: The possibility of a beneficial activity of Rifaximin in chronic intestinal inflammation and CD has been debated and evaluated with different studies having obtained promising but still preliminary data. Larger trials are therefore needed. This gut-specific antibiotic could represent an alternative to systemic antibiotics thanks to its favorable safety profile and promising efficacy data. Rifaximin could exert, when appropriate, a synergic effect with immunomodulators in IBD, acting on both the microbial and the immunological sides of gut barrier impairment.     

Maternal separation as a model of brain–gut axis dysfunction

Rationale  

Early life stress has been implicated in many psychiatric disorders ranging from depression to anxiety. Maternal separation in rodents is a well-studied model of early life stress. However, stress during this critical period also induces alterations in many systems throughout the body. Thus, a variety of other disorders that are associated with adverse early life events are often comorbid with psychiatric illnesses, suggesting a common underlying aetiology. Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is thought to involve a dysfunctional interaction between the brain and the gut. Essential aspects of the brain–gut axis include spinal pathways, the hypothalamic pituitary adrenal axis, the immune system, as well as the enteric microbiota. Accumulating evidence suggest that stress, especially in early life, is a predisposing factor to IBS.     

The gut–brain interaction in opioid tolerance

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Regulation of the brain–gut axis by group III metabotropic glutamate receptors

l-glutamate is produced by a great variety of peripheral tissues in both health and disease. Like other components of the glutamatergic system, metabotropic glutamate (mGlu) receptors also have a widespread distribution outside the central nervous system (CNS). In particular, group III mGlu receptors have been recently found in human stomach and colon revealing an extraordinary potential for these receptors in the treatment of peripheral disorders, including gastrointestinal dysfunction. The significance of these findings is that pharmacological tools originally designed for mGlu receptors in the CNS may also be directed towards new disease targets in the periphery. Targeting mGlu receptors can also be beneficial in the treatment of disorders involving central components together with gastrointestinal dysfunction, such as irritable bowel syndrome, which can be co-morbid with anxiety and depression. Conversely, the development of more specific therapeutic approaches for mGlu ligands both centrally as in the gut will depend on the elucidation of tissue-specific elements in mGlu receptor signalling.     

Effects of prednisolone on behavior and hypothalamic–pituitary–interrenal axis activity in zebrafish

Prednisolone is a synthetic glucocorticoid used clinically for treating allergies, inflammation, and autoimmune diseases. Long-term prednisolone use has been shown to have negative effects on physiology and mood. We aimed to study the pharmacology and toxicology of glucocorticoid-like drugs by investigating behavioral and hypothalamic–pituitary–interrenal (HPI) axis effects in a zebrafish model. Zebrafish embryos 24 h post fertilization were exposed to 25 μM prednisolone. Their behavior was investigated 5 days post fertilization (dpf), and their HPI axis-related activity and related neurotransmitter levels were investigated 3, 4, 5, and 6 dpf. The behavior results showed that exposure to prednisolone resulted in decreased autonomic activity and low sensitivity to light. qRT-PCR and ELISA results showed decreased activity of the HPI axis and increased secretion of dopamine and serotonin after exposure to prednisolone. This study provides us with new insights into understanding the effects of glucocorticoids on the HPI axis.     

Hypothalamic–pituitary–adrenal axis and ethanol modulation of deoxycorticosterone levels in cynomolgus monkeys

Rationale The metabolites of deoxycorticosterone (DOC) and progesterone, allotetrahydrodeoxycorticosterone and allopregnanolone, are potent endogenous neuroactive steroids that are increased in rodent brain and plasma after hypothalamic–pituitary–adrenal (HPA) axis activation by acute stress or ethanol administration. However, little data are available for male nonhuman primates.Objective To determine DOC concentrations in plasma samples from 11 monkeys following challenge of the HPA axis with naloxone, corticotropin-releasing factor (CRF), dexamethasone, adrenocorticotropic hormone (ACTH) following dexamethasone pretreatment and ethanol.Methods DOC levels were measured in monkey plasma by radioimmunoassay.Results DOC levels were increased after naloxone (125 μg/kg and 375 μg/kg, respectively) and CRF administration (1 μg/kg), and decreased following dexamethasone (130 μg/kg) administration. ACTH (10 ng/kg) challenge, 4–6 h after 0.5 mg/kg dexamethasone, and administration of ethanol (1.0 g/kg and 1.5 g/kg) had no effect on DOC concentrations. DOC levels were positively correlated with cortisol and ACTH levels after the naloxone (375 μg/kg), CRF, and ACTH challenges. Finally, the suppression of DOC levels measured after dexamethasone was negatively correlated with subsequent alcohol self-administration.Conclusions These results suggest that DOC levels in monkeys are regulated by the HPA axis and may contribute to physiological responses following activation.     

The role of chalcones in suppression of NF-κB-mediated inflammation and cancer

Although consumption of fruits, vegetables, spices, cereals and pulses has been associated with lower incidence of cancer and other chronic diseases, how these dietary agents and their active ingredients minimize these diseases, is not fully understood. Whether it is oranges, kawa, hops, water-lilly, locorice, wax apple or mulberry, they are all connected by a group of aromatic ketones, called chalcones (1,3-diaryl-2-propen-1-ones). Some of the most significant chalcones identified from these plants include flavokawin, butein, xanthoangelol, 4-hydroxyderricin, cardamonin, 2',4'-dihydroxychalcone, isoliquiritigenin, isosalipurposide, and naringenin chalcone. These chalcones have been linked with immunomodulation, antibacterial, antifungal, antiviral, anti-inflammatory, antioxidant, anticancer, and antidiabetic activities. The current review, however, deals with the role of various chalcones in inflammation that controls both the immune system and tumorigenesis. Inflammatory pathways have been shown to mediate the survival, proliferation, invasion, angiogenesis and metastasis of tumors. How these chalcones modulate inflammatory pathways, tumorigenesis and immune system is the focus of this review.     

The role of hexokinase in cardioprotection – mechanism and potential for translation

Mitochondrial permeability transition pore (mPTP) opening plays a critical role in cardiac reperfusion injury and its prevention is cardioprotective. Tumour cell mitochondria usually have high levels of hexokinase isoform 2 (HK2) bound to their outer mitochondrial membranes (OMM) and HK2 binding to heart mitochondria has also been implicated in resistance to reperfusion injury. HK2 dissociates from heart mitochondria during ischaemia, and the extent of this correlates with the infarct size on reperfusion. Here we review the mechanisms and regulations of HK2 binding to mitochondria and how this inhibits mPTP opening and consequent reperfusion injury. Major determinants of HK2 dissociation are the elevated glucose‐6‐phosphate concentrations and decreased pH in ischaemia. These are modulated by the myriad of signalling pathways implicated in preconditioning protocols as a result of a decrease in pre‐ischaemic glycogen content. Loss of mitochondrial HK2 during ischaemia is associated with permeabilization of the OMM to cytochrome c, which leads to greater reactive oxygen species production and mPTP opening during reperfusion. Potential interactions between HK2 and OMM proteins associated with mitochondrial fission (e.g. Drp1) and apoptosis (B‐cell lymphoma 2 family members) in these processes are examined. Also considered is the role of HK2 binding in stabilizing contact sites between the OMM and the inner membrane. Breakage of these during ischaemia is proposed to facilitate cytochrome c loss during ischaemia while increasing mPTP opening and compromising cellular bioenergetics during reperfusion. We end by highlighting the many unanswered questions and discussing the potential of modulating mitochondrial HK2 binding as a pharmacological target.

Linked Articles

This article is part of a themed section on Conditioning the Heart – Pathways to Translation. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue‐8

Abbreviations

Akt

also known as PKB

AMPK

AMP‐activated PK

ANT

adenine nucleotide translocase

Bad

Bcl‐2‐associated death promoter

Bak

Bcl‐2 homologous antagonist/killer

Bax

Bcl‐2‐like protein 4

Bcl‐2

B‐cell lymphoma 2

Bcl‐xL

Bcl‐2‐extra large

CK

creatine kinase

CsA

cyclosporine A

CyP‐D

cyclophilin D

Drp1

dynamin‐related protein 1

G‐6‐P

glucose‐6‐phosphate

GSK3β

glycogen synthase kinase 3β

HK

hexokinase

I/R

ischaemia/reperfusion

IF1

ATP synthase inhibitor factor 1

IMM

inner mitochondrial membrane

IP

ischaemic preconditioning

mPTP

mitochondrial permeability transition pore

OMM

outer mitochondrial membrane

Opa‐1

optic athrophy 1

PCr

phosphocreatine

PPIase

peptidylprolyl isomerase

ROS

reactive oxygen species

SR

sarcoplasmic reticulum

T₀

time of ischaemic rigor start

TAT‐HK2

cell‐permeable peptide of HK2 binding domain

TP

temperature preconditioning

TSPO

translocator protein of the outer membrane

VDAC

voltage‐dependent anion channel

Tables of Links

The role of PPAR alpha in perfluorooctanoic acid induced developmental cardiotoxicity and l-carnitine mediated protection–Results of in ovo gene silencing

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant. This study established an in ovo peroxisome proliferator-activated receptor alpha (PPAR alpha) silencing model in chicken embryo heart, and investigated the role of PPAR alpha in PFOA induced developmental cardiotoxicity. The in ovo silencing was achieved by introducing lentivirus expressing PPAR alpha siRNA into ED2 chicken embryo via microinjection (0.05 ul/g egg weight). Transfection efficacy was confirmed by fluorescent microscopy and western blotting. To assess the developmental cardiotoxicity, cardiac function (heart rate) and morphology (right ventricular wall thickness) were measured in D1 hatchling chickens. 2 mg/kg (egg weight) PFOA exposure at ED0 induced significant elevation of heart rate and thinning of right ventricular wall thickness in D1 hatchling chickens. PPAR alpha silencing did not prevent PFOA-induced elevation of heart rate; however, it did significantly increase the right ventricular wall thickness as compared to PFOA exposed animals. Meanwhile, PPAR alpha silencing did not abolish the protective effects exerted by exposure to 100 mg/kg (egg weight) l-carnitine. In conclusion, PFOA-induced heart rate elevation is likely PPAR alpha independent, while the right ventricular wall thinning seems to be PPAR alpha dependent. The protective effects of l-carnitine do not require PPAR alpha.     

Evidence-based policy? The re-medicalization of cannabis and the role of expert committees in the UK, 1972–1982

BackgroundCannabis was introduced to the UK as a medical product in the nineteenth century. However, with questions over its safety, efficacy, and possible harms its medical role diminished and by the 1950s it was viewed as a drug of misuse. Nonetheless, scientific and lay knowledge around cannabis expanded from the 1960s and cannabis re-appeared in different therapeutic forms. In re-medicalizing cannabis, science-policy transfer proved important and was enabled by the developing mechanism of expert committees, most notably the Advisory Council on the Misuse of Drugs (ACMD).MethodsThis article draws upon previously unknown archival material on the ACMD held at the National Archives and covers the period 1972–1982. It considers how expert groups were established, their membership, and the evolving discussion over therapeutic cannabis within the broader drug policy debate.ResultsThree distinct periods emerged: 1972–1976 with the creation of the Working Group on Cannabis; 1977–1979 when the Working Group focused on potential amendments to the Misuse of Drugs Act and recommended downgrading cannabis from Class B to Class C; 1980–1982 when the Expert Group on the Effects of Cannabis recommended downgrading cannabis and encouraged research into cannabis as a medicine. Sources reveal that driven by drug control imperatives the ACMD stimulated research on cannabis leading to increased research on medical applications.ConclusionExpert advice was critical in the process of re-medicalization. Initially, discourse occurred in the closed expert committees of the ACMD. The drug problem had been framed under the criminal justice system but as the limitations of this were revealed, and there was continuing uncertainty over cannabis’ impact, new approaches to cannabis were sought. It was this combination of more relaxed attitudes towards cannabis, research incentives, as well as a developing desire to draw medical needs away from discussion of drug control that was to allow re-medicalization to develop.     

An evaluation of the protective role of α-tocopherol on free radical induced hepatotoxicity and nephrotoxicity due to chromium in rats

Aim:

To avert the health problems induced by many environmental pollutants, available antioxidants have been evaluated. The present study was aimed to investigate whether α-tocopherol could protect the hexavalent chromium (Cr VI)-induced peroxidation in the liver and kidney and to explore the underlying mechanism of the same.

Materials and Methods:

A total of 24 Wistar adult female rats were equally divided into four groups. Group 1 served as control while Groups 2 and 3 were administered K₂Cr₂O₇(10 mg/kg b.wt. s.c. single dose). In addition to (Cr VI), Group 3 also received α-tocopherol (125 mg/kg, daily) by oral gavage for 14 days. Group 4 was maintained as α-tocopherol control (dose as above). At the end of 14 days, blood samples were drawn for hematology. Subsequently, all the rats were sacrificed to collect liver and kidney samples for assay of tissue peroxidation markers, antioxidant markers and functional markers and histopathology.

Results:

Administration of chromium (Cr VI) in Group 2 significantly (P < 0.05) reduced the antioxidant markers such as superoxide dismutase and reduced glutathione along with significant (P < 0.05) increase in peroxidation markers such as malondialdehyde and protein carbonyls in the liver and kidney as compared with other groups. The functional markers in serum such as total protein was decreased significantly (P < 0.05), whereas other functional markers viz. alanine transaminase, blood urea nitrogen and creatinine were increased significantly (P < 0.05) in Group 2 as compared with the other groups. Significant (P < 0.05) decrease in hemoglobin, packed cell volume, total erythrocyte count, mean corpuscular volume, mean corpuscular hemoglobin and total leukocyte count were observed in Cr VI treated Group 2 rats. Prominent pathological changes were observed in the liver and kidney of Group 2. Co-treatment with α-tocopherol in Group 3 rats significantly (P < 0.05) reversed the Cr VI induced changes. The parameters in the study in Group 4 did not differ as compared with Group 1.

Conclusions:

α–tocopherol exhibited protective effect against Cr VI-induced damage to the liver and kidney by inhibition of lipid peroxidation owing its antioxidant activity.KEY WORDS: α-tocopherol, chromium (Cr VI), kidney, lipid peroxidation, liver     

The perceived role and skills of pharmacists in asthma management after in‐house training

Objective: To evaluate perceived roles and skills of pharmacists in asthma management before and after a training intervention that consisted of six inhouse training sessions. Method: Altogether 315 pharmacists in the intervention group and 121 pharmacists in the control group participated in the study. The data on study variables were collected by a questionnaire during the first and last training sessions.Main outcome measures: Pharmacists' perceptions of their role, perceived skills, estimates of patients receiving counselling and experienced problems.Results: Based on their ratings for 16 topics, the pharmacists' perceptions about their role in counselling asthma patients remained rather stable. Handling of the inhalers and inhalation technique were considered as the most important aspects of counselling and issues dealing with the disease were regarded as the least important. Using a selfrated scale (410 scale), pharmacists' perceived counselling skills improved in the intervention group (6.5 vs 7.6), but not in the control group (6.5 vs 6.4). In the intervention group, the pharmacists' estimates of the proportion of new users of asthma medicines receiving counselling increased from 48% to 61% and that of old users from 18% to 26%. Before the training, the most commonly experienced problem in counselling was the pharmacists' lack of knowledge and skills. After the training, pharmacists experienced problems mainly with communication. Conclusion: When pharmacists are included in the support system for any patient group, their capabilities of fulfilling their role have to be assessed. In particular, communication skills and outcomeoriented counselling require attention.     

The role of heat shock protein 90 in modulating ischemia–reperfusion injury in the kidney

Introduction: Kidney transplantation is the gold standard treatment for end-stage renal disease. Ischemia–reperfusion injury (IRI) is an unavoidable consequence of the transplantation procedure and is responsible for delayed graft function and poorer long-term outcomes.

Areas covered: Pharmacological induction of heat shock protein (Hsp) expression is an emerging pre-conditioning strategy aimed at reducing IRI following renal transplantation. Hsp90 inhibition up-regulates protective Hsps (especially Hsp70) and potentially down-regulates NF-κB by disruption of the IκB kinase (IKK) complex. However, the clinical application of Hsp90 inhibitors is currently limited by their toxicity profile and the exact mechanism of protection conferred is unknown. Toll-like receptor 4 (TLR4) is a further regulator of NF-κB and recent studies suggest TLR4 plays a dominant role in mediating kidney damage following IRI. The full interaction of Hsps with TLRs is yet to be delineated and whether TLR4 signalling can be targeted by Hsp90 inhibition in IRI remains uncertain.

Expert opinion: Pharmacological pre-conditioning by Hsp90 inhibition involves direct treatment to the kidney donor and/or organ, which aims to reduce injury prior to the onset of ischemia. The major challenges going forward are to establish the exact mechanism of protection offered by these drugs and the investgiation of less toxic analogues that could be safely translated into human studies.     

The role of δ-opioid receptors in learning and memory underlying the development of addiction

Opioids are important endogenous ligands that exist in both invertebrates and vertebrates and signal by activation of opioid receptors to produce analgesia and reward or pleasure. The μ-opioid receptor is the best known of the opioid receptors and mediates the acute analgesic effects of opiates, while the δ-opioid receptor (DOR) has been less well studied and has been linked to effects that follow from chronic use of opiates such as stress, inflammation and anxiety. Recently, DORs have been shown to play an essential role in emotions and increasing evidence points to a role in learning actions and outcomes. The process of learning and memory in addiction has been proposed to involve strengthening of specific brain circuits when a drug is paired with a context or environment. The DOR is highly expressed in the hippocampus, amygdala, striatum and other basal ganglia structures known to participate in learning and memory. In this review, we will focus on the role of the DOR and its potential role in learning and memory underlying the development of addiction.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2