Antioxidant and Antidiabetic Properties of a Thinned-Nectarine-Based Nanoformulation in a Pancreatic β-Cell Line

Pancreatic β-cells play a crucial role in maintaining glucose homeostasis, although they are susceptible to oxidative damage, which can ultimately impair their functionality. Thinned nectarines (TNs) have gained increasing interest due to their high polyphenol and abscisic acid (ABA) content, both of which possess antidiabetic properties. Nevertheless, the efficacy of these bioactive compounds may be compromised by limited stability and bioavailability in vivo. This study aimed to develop nanoformulations (NFs) containing pure ABA or a TN extract (TNE) at an equivalent ABA concentration. Subsequently, the insulinotropic and antioxidant potential of the NFs and their unformulated (free) forms were compared in MIN-6 pancreatic cells exposed to varying glucose (5.5 mM and 20 mM) and iron (100 µM) concentrations. NF-TNE treatment exhibited enhanced antioxidant activity compared to free TNE, while ABA-based groups showed no significant antioxidant activity. Moreover, MIN6 cells incubated with both high glucose and iron levels demonstrated significantly higher insulin AUC levels after treatment with all samples, with NF-TNE displaying the most pronounced effect. In conclusion, these results highlight the additional beneficial potential of TNE due to the synergistic combination of bioactive compounds and demonstrate the significant advantage of using a nanoformulation approach to further increase the benefits of this and similar phytobioactive molecules.

Baseline and recurrent exposure to the standard dose of artemisinin-based combination therapies (ACTs) induces oxidative stress and liver damage in mice (BALB/c)

Background

In malaria-endemic countries, repeated intake of artemisinin-based combination therapies (ACTs) is rampant and driven by drug resistance, improper usage, and easy accessibility. Stress effects and potential liver toxicity due to the frequent therapeutic use of ACTs have not been extensively studied. Here, we investigated the effects of repeated treatment with standard doses of the commonly used ACTs artemether/lumefantrine (A/L) and artesunate-amodiaquine (A/A) on oxidative stress and liver function markers in male mice (BALB/c).

Methods

Forty Five mice were divided into three groups: control, A/L, and A/A. The drugs were administered three days in a row per week, and the regimen was repeated every two weeks for a total of six cycles. The levels of oxidative stress and liver function markers were measured in both plasma and liver tissue after initial (baseline) and repeated exposures for the second, third, and sixth cycles.

Results

Exposure to A/L or A/A caused a significant (p < 0.001) increase in plasma malondialdehyde (MDA) levels after the first and repeated exposure periods. However, Hepatic MDA levels increased significantly (p < 0.01) only after the sixth exposure to A/A. Following either single or repeated exposure to A/L or A/A, plasma and liver glutathione peroxidase (GPx) and catalase (CAT) activities, plasma aspartate and alanine transaminase, alkaline phosphatase activity, and bilirubin levels increased, whereas total plasma protein levels decreased significantly (p < 0.001). Varying degrees of hepatocyte degeneration and blood vessel congestion were observed in liver tissues after a single or repeated treatment period.

Conclusion

Irrespective of single or repeated exposure to therapeutic doses of A/L or A/A, plasma oxidative stress and liver damage were observed. However, long-term repeated A/A exposure can led to hepatic stress. Compensatory processes involving GPx and CAT activities may help reduce the observed stress.

Non-alcoholic fatty liver disease: Immunological mechanisms and current treatments

Non-alcoholic fatty liver disease (NAFLD) causes significant global disease burden and is a leading cause of mortality. NAFLD induces a myriad of aberrant changes in hepatocytes at both the cellular and molecular level. Although the disease spectrum of NAFLD is widely recognised, the precise triggers for disease progression are still to be fully elucidated. Furthermore, the propagation to cirrhosis is poorly understood. Whilst some progress in terms of treatment options have been explored, an incomplete understanding of the hepatic cellular and molecular alterations limits their clinical utility. We have therefore reviewed some of the key pathways responsible for the pathogenesis of NAFLD such as innate and adaptative immunity, lipotoxicity and fibrogenesis, and highlighted current trials and treatment options for NAFLD patients.

Alcoholic liver disease: Current insights into cellular mechanisms

Alcoholic liver disease (ALD) due to chronic alcohol consumption is a significant global disease burden and a leading cause of mortality. Alcohol abuse induces a myriad of aberrant changes in hepatocytes at both the cellular and molecular level. Although the disease spectrum of ALD is widely recognized, the precise triggers for disease progression are still to be fully elucidated. Oxidative stress, mitochondrial dysfunction, gut dysbiosis and altered immune system response plays an important role in disease pathogenesis, triggering the activation of inflammatory pathways and apoptosis. Despite many recent clinical studies treatment options for ALD are limited, especially at the alcoholic hepatitis stage. We have therefore reviewed some of the key pathways involved in the pathogenesis of ALD and highlighted current trials for treating patients.

Excessive Iron Induces Oxidative Stress Promoting Cellular Perturbations and Insulin Secretory Dysfunction in MIN6 Beta Cells

Exposure to high levels of glucose and iron are co-related to reactive oxygen species (ROS) generation and dysregulation of insulin synthesis and secretion, although the precise mechanisms are not well clarified. The focus of this study was to examine the consequences of exposure to high iron levels on MIN6 β-cells. MIN6 pseudoislets were exposed to 20 µM (control) or 100 µM (high) iron at predefined glucose levels (5.5 mM and 11 mM) at various time points (3, 24, 48, and 72 h). Total iron content was estimated by a colourimetric FerroZine™ assay in presence or absence of transferrin-bound iron. Cell viability was assessed by a resazurin dye-based assay, and ROS-mediated cellular oxidative stress was assessed by estimating malondialdehyde levels. β-cell iron absorption was determined by a ferritin immunoassay. Cellular insulin release and content was measured by an insulin immunoassay. Expression of SNAP-25, a key protein in the core SNARE complex that modulates vesicle exocytosis, was measured by immunoblotting. Our results demonstrate that exposure to high iron levels resulted in a 15-fold (48 h) and 4-fold (72 h) increase in cellular iron accumulation. These observations were consistent with data from oxidative stress analysis which demonstrated 2.7-fold higher levels of lipid peroxidation. Furthermore, exposure to supraphysiological (11 mM) levels of glucose and high iron (100 µM) at 72 h exerted the most detrimental effect on the MIN6 β-cell viability. The effect of high iron exposure on total cellular iron content was identical in the presence or absence of transferrin. High iron exposure (100 µM) resulted in a decrease of MIN6 insulin secretion (64% reduction) as well as cellular insulin content (10% reduction). Finally, a significant reduction in MIN6 β-cell SNAP-25 protein expression was evident at 48 h upon exposure to 100 µM iron. Our data suggest that exposure to high iron and glucose concentrations results in cellular oxidative damage and may initiate insulin secretory dysfunction in pancreatic β-cells by modulation of the exocytotic machinery.

Hepcidin secretion was not directly proportional to intracellular iron-loading in recombinant-TfR1 HepG2 cells: short communication

Hepcidin is the master regulator of systemic iron homeostasis and its dysregulation is observed in several chronic liver diseases. Unlike the extracellular iron-sensing mechanisms, the intracellular iron-sensing mechanisms in the hepatocytes that lead to hepcidin induction and secretion are incompletely understood. Here, we aimed to understand the direct role of intracellular iron-loading on hepcidin mRNA and peptide secretion using our previously characterised recombinant HepG2 cells that over-express the cell-surface iron-importer protein transferrin receptor-1. Gene expression of hepcidin (HAMP) was determined by real-time PCR. Intracellular iron levels and secreted hepcidin peptide levels were measured by ferrozine assay and immunoassay, respectively. These measurements were compared in the recombinant and wild-type HepG2 cells under basal conditions at 30 min, 2 h, 4 h and 24 h. Data showed that in the recombinant cells, intracellular iron content was higher than wild-type cells at 30 min (3.1-fold, p < 0.01), 2 h (4.6-fold, p < 0.01), 4 h (4.6-fold, p < 0.01) and 24 h (1.9-fold, p < 0.01). Hepcidin (HAMP) mRNA expression was higher than wild-type cells at 30 min (5.9-fold; p = 0.05) and 24 h (6.1-fold; p < 0.03), but at 4 h, the expression was lower than that in wild-type cells (p < 0.05). However, hepcidin secretion levels in the recombinant cells were similar to those in wild-type cells at all time-points, except at 4 h, when the level was lower than wild-type cells (p < 0.01). High intracellular iron in recombinant HepG2 cells did not proportionally increase hepcidin peptide secretion. This suggests a limited role of elevated intracellular iron in hepcidin secretion.

High omega arachidonic acid/docosahexaenoic acid ratio induces mitochondrial dysfunction and altered lipid metabolism in human hepatoma cells

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a common cause of liver disease worldwide and is a growing epidemic. A high ratio of omega-6 fatty acids to omega-3 fatty acids in the diet has been implicated in the development of NAFLD. However, the inflicted cellular pathology remains unknown. A high ratio may promote lipogenic pathways and contribute to reactive oxygen species (ROS)-mediated damage, perhaps leading to mitochondrial dysfunction. Therefore, these parameters were investigated to understand their contribution to NAFLD development.

AIM

To examine the effect of increasing ratios of omega-6:3 fatty acids on mitochondrial function and lipid metabolism mediators.

METHODS

HepG2-derived VL-17A cells were treated with normal (1:1, 4:1) and high (15:1, 25:1) ratios of omega-6: omega-3 fatty acids [arachidonic acid (AA): docosahexaenoic acid (DHA)] at various time points. Mitochondrial activity and function were examined via MTT assay and Seahorse XF24 analyzer, respectively. Triglyceride accumulation was determined by using EnzyChrom™ and levels of ROS were measured by fluorescence intensity. Protein expression of the mediators of lipogenic, lipolytic and endocannabinoid pathways was assessed by Western blotting.

RESULTS

High AA:DHA ratio decreased mitochondrial activity (P < 0.01; up to 80%) and promoted intracellular triglyceride accumulation (P < 0.05; 40%-70%). Mechanistically, it altered the mediators of lipid metabolism; increased the expression of stearoyl-CoA desaturase (P < 0.05; 22%-35%), decreased the expression of peroxisome proliferator-activated receptor-alpha (P < 0.05; 30%-40%) and increased the expression of cannabinoid receptor 1 (P < 0.05; 31%). Furthermore, the high ratio increased ROS production (P < 0.01; 74%-115%) and reduced mitochondrial respiratory functions such as basal and maximal respiration, ATP production, spare respiratory capacity and proton leak (P < 0.01; 35%-68%).

CONCLUSION

High AA:DHA ratio induced triglyceride accumulation, increased oxidative stress and disrupted mitochondrial functions. Stimulation of lipogenic and steroidal transcription factors may partly mediate these effects and contribute to NAFLD development.

Mucosa-associated invariant T cells link intestinal immunity with antibacterial immune defects in alcoholic liver disease

BACKGROUND/AIMS

Intestinal permeability with systemic distribution of bacterial products are central in the immunopathogenesis of alcoholic liver disease (ALD), yet links with intestinal immunity remain elusive. Mucosa-associated invariant T cells (MAIT) are found in liver, blood and intestinal mucosa and are a key component of antibacterial host defences. Their role in ALD is unknown.

METHODS/DESIGN

We analysed frequency, phenotype, transcriptional regulation and function of blood MAIT cells in severe alcoholic hepatitis (SAH), alcohol-related cirrhosis (ARC) and healthy controls (HC). We also examined direct impact of ethanol, bacterial products from faecal extracts and antigenic hyperstimulation on MAIT cell functionality. Presence of MAIT cells in colon and liver was assessed by quantitative PCR and immunohistochemistry/gene expression respectively.

RESULTS

In ARC and SAH, blood MAIT cells were dramatically depleted, hyperactivated and displayed defective antibacterial cytokine/cytotoxic responses. These correlated with suppression of lineage-specific transcription factors and hyperexpression of homing receptors in the liver with intrahepatic preservation of MAIT cells in ALD. These alterations were stronger in SAH, where surrogate markers of bacterial infection and microbial translocation were higher than ARC. Ethanol exposure in vitro, in vivo alcohol withdrawal and treatment with Escherichia coli had no effect on MAIT cell frequencies, whereas exposure to faecal bacteria/antigens induced functional impairments comparable with blood MAIT cells from ALD and significant MAIT cell depletion, which was not observed in other T cell compartments.

CONCLUSIONS

In ALD, the antibacterial potency of MAIT cells is compromised as a consequence of contact with microbial products and microbiota, suggesting that the 'leaky' gut observed in ALD drives MAIT cell dysfunction and susceptibility to infection in these patients.

Erratum to: HFE mRNA expression is responsive to intracellular and extracellular iron loading: short communication

The original article has been changed to reflect the correct co-author name: Sebastien Farnaud. The original article was corrected.

HFE mRNA expression is responsive to intracellular and extracellular iron loading: short communication

In liver hepatocytes, the HFE gene regulates cellular and systemic iron homeostasis by modulating cellular iron-uptake and producing the iron-hormone hepcidin in response to systemic iron elevation. However, the mechanism of iron-sensing in hepatocytes remain enigmatic. Therefore, to study the effect of iron on HFE and hepcidin (HAMP) expressions under distinct extracellular and intracellular iron-loading, we examined the effect of holotransferrin treatment (1, 2, 5 and 8 g/L for 6 h) on intracellular iron levels, and mRNA expressions of HFE and HAMP in wild-type HepG2 and previously characterized iron-loaded recombinant-TfR1 HepG2 cells. Gene expression was analyzed by real-time PCR and intracellular iron was measured by ferrozine assay. Data showed that in the wild-type cells, where intracellular iron content remained unchanged, HFE expression remained unaltered at low holotransferrin treatments but was upregulated upon 5 g/L (p < 0.04) and 8 g/L (p = 0.05) treatments. HAMP expression showed alternating elevations and increased upon 1 g/L (p < 0.05) and 5 g/L (p < 0.05). However, in the recombinant cells that showed higher intracellular iron levels than wild-type cells, HFE and HAMP expressions were elevated only at low 1 g/L treatment (p < 0.03) and were repressed at 2 g/L treatment (p < 0.03). Under holotransferrin-untreated conditions, the iron-loaded recombinant cells showed higher expressions of HFE (p < 0.03) and HAMP (p = 0.05) than wild-type cells. HFE mRNA was independently elevated by extracellular and intracellular iron-excess. Thus, it may be involved in sensing both, extracellular and intracellular iron. Repression of HAMP expression under simultaneous intracellular and extracellular iron-loading resembles non-hereditary iron-excess pathologies.

Iron Enhances Hepatic Fibrogenesis and Activates Transforming Growth Factor-β Signaling in Murine Hepatic Stellate Cells

BACKGROUND

Although excess iron induces oxidative stress in the liver, it is unclear whether it directly activates the hepatic stellate cells (HSC).

MATERIALS AND METHODS

We evaluated the effects of excess iron on fibrogenesis and transforming growth factor beta (TGF-β) signaling in murine HSC. Cells were treated with holotransferrin (0.005-5g/L) for 24 hours, with or without the iron chelator deferoxamine (10µM). Gene expressions (α-SMA, Col1-α1, Serpine-1, TGF-β, Hif1-α, Tfrc and Slc40a1) were analyzed by quantitative real time-polymerase chain reaction, whereas TfR1, ferroportin, ferritin, vimentin, collagen, TGF-β RII and phospho-Smad2 proteins were evaluated by immunofluorescence, Western blot and enzyme-linked immunosorbent assay.

RESULTS

HSC expressed the iron-uptake protein transferrin receptor 1 (TfR1) and the iron-export protein ferroportin. Holotransferrin upregulated TfR1 expression by 1.8-fold (P < 0.03) and ferritin accumulation (iron storage) by 2-fold (P < 0.01), and activated HSC with 2-fold elevations (P < 0.03) in α-SMA messenger RNA and collagen secretion, and a 1.6-fold increase (P < 0.01) in vimentin protein. Moreover, holotransferrin activated the TGF-β pathway with TGF-β messenger RNA elevated 1.6-fold (P = 0.05), and protein levels of TGF-β RII and phospho-Smad2 increased by 1.8-fold (P < 0.01) and 1.6-fold (P < 0.01), respectively. In contrast, iron chelation decreased ferritin levels by 30% (P < 0.03), inhibited collagen secretion by 60% (P < 0.01), repressed fibrogenic genes α-SMA (0.2-fold; P < 0.05) and TGF-β (0.4-fold; P < 0.01) and reduced levels of TGF-β RII and phospho-Smad2 proteins.

CONCLUSIONS

HSC express iron-transport proteins. Holotransferrin (iron) activates HSC fibrogenesis and the TGF-β pathway, whereas iron depletion by chelation reverses this, suggesting that this could be a useful adjunct therapy for patients with fibrosis. Further studies in primary human HSC and animal models are necessary to confirm this.

Characterization of hepcidin response to holotransferrin in novel recombinant TfR1 HepG2 cells

Hepcidin is the key regulator of systemic iron homeostasis. The iron-sensing mechanisms and the role of intracellular iron in modulating hepatic hepcidin secretion are unclear. Therefore, we created a novel cell line, recombinant-TfR1 HepG2, expressing iron-response-element-independent TFRC mRNA to promote cellular iron-overload and examined the effect of excess holotransferrin (5g/L) on cell-surface TfR1, iron content, hepcidin secretion and mRNA expressions of TFRC, HAMP, SLC40A1, HFE and TFR2. Results showed that the recombinant cells exceeded levels of cell-surface TfR1 in wild-type cells under basal (2.8-fold; p<0.03) and holotransferrin-supplemented conditions for 24h and 48h (4.4- and 7.5-fold, respectively; p<0.01). Also, these cells showed higher intracellular iron content than wild-type cells under basal (3-fold; p<0.03) and holotransferrin-supplemented conditions (6.6-fold at 4h; p<0.01). However, hepcidin secretion was not higher than wild-type cells. Moreover, holotransferrin treatment to recombinant cells did not elevate HAMP responses compared to untreated or wild-type cells. In conclusion, increased intracellular iron content in recombinant cells did not increase hepcidin responses compared to wild-type cells, resembling hemochromatosis. Furthermore, TFR2 expression altered within 4h of treatment, while HFE expression altered later at 24h and 48h, suggesting that TFR2 may function prior to HFE in HAMP regulation.

Regional Increase in the Expression of the BCAT Proteins in Alzheimer's Disease Brain: Implications in Glutamate Toxicity

BACKGROUND

The human branched chain aminotransferases (hBCATm, mitochondrial and hBCATc, cytosolic) are major contributors to brain glutamate production. This excitatory neurotransmitter is thought to contribute to neurotoxicity in neurodegenerative conditions such as Alzheimer's disease (AD) but the expression of hBCAT in this disease has not previously been investigated.

OBJECTIVE

The objective of investigating hBCAT expression is to gain insight into potential metabolic pathways that may be dysregulated in AD brain, which would contribute to glutamate toxicity.

METHODS

Western blot analysis and immunohistochemistry were used to determine the expression and localization of hBCAT in postmortem frontal and temporal cortex from AD and matched control brains.

RESULTS

Western blot analysis demonstrated a significant regional increase in hBCATc expression in the hippocampus (↑ 36%; p-values of 0.012), with an increase of ↑ 160% reported for hBCATm in the frontal and temporal cortex (p-values = 4.22 × 10⁻⁴ and 2.79 × 10⁻⁵, respectively) in AD relative to matched controls, with evidence of post-translational modifications to hBCATm, more prominent in AD samples. Using immunohistochemistry, a significant increase in immunopositive labelling of hBCATc was observed in the CA1 and CA4 region of the hippocampus (p-values = 0.011 and 0.026, respectively) correlating with western blot analysis. Moreover, the level of hBCATm in the frontal and temporal cortex correlated significantly with disease severity, as indicated by Braak staging (p-values = 5.63 × 10⁻⁶ and 9.29 × 10⁻⁵, respectively).

CONCLUSION

The expression of the hBCAT proteins is significantly elevated in AD brain. This may modulate glutamate production and toxicity, and thereby play a role in the pathogenesis of the disease.

Characterisation of hepcidin response to holotransferrin treatment in CHO TRVb-1 cells

Iron overload coupled with low hepcidin levels are characteristics of hereditary haemochromatosis. To understand the role of transferrin receptor (TFR) and intracellular iron in hepcidin secretion, Chinese hamster ovary transferrin receptor variant (CHO TRVb-1) cells were used that express iron-response-element-depleted human TFRC mRNA (TFRC∆IRE). Results showed that CHO TRVb-1 cells expressed higher basal levels of cell-surface TFR1 than HepG2 cells (2.2-fold; p < 0.01) and following 5 g/L holotransferrin treatment maintained constitutive over-expression at 24h and 48 h, contrasting the HepG2 cells where the receptor levels significantly declined. Despite this, the intracellular iron content was neither higher than HepG2 cells nor increased over time under basal or holotransferrin-treated conditions. Interestingly, hepcidin secretion in CHO TRVb-1 cells exceeded basal levels at all time-points (p < 0.02) and matched levels in HepG2 cells following treatment. While TFRC mRNA expression showed expected elevation (2h, p < 0.03; 4h; p < 0.05), slc40a1 mRNA expression was also elevated (2 h, p < 0.05; 4 h, p < 0.03), unlike the HepG2 cells. In conclusion, the CHO TRVb-1 cells prevented cellular iron-overload by elevating slc40a1 expression, thereby highlighting its significance in the absence of iron-regulated TFRC mRNA. Furthermore, hepcidin response to holotransferrin treatment was similar to HepG2 cells and resembled the human physiological response.

New insights into the role of the branched-chain aminotransferase proteins in the human brain

The human cytosolic branched-chain aminotransferase (hBCATc) enzyme is strategically located in glutamatergic neurons, where it is thought to provide approximately 30% of de novo nitrogen for brain glutamate synthesis. In health, glutamate plays a dominant role in facilitating learning and memory. However, in patients with Alzheimer's disease (AD), synaptic levels of glutamate become toxic, resulting in a direct increase in postsynaptic neuronal calcium, causing a cascade of events that contributes to the destruction of neuronal integrity and cell death, pathological features of AD. Our group is the first to map the hBCAT proteins to the human brain, where cell-specific compartmentation indicates key roles for these proteins in regulating glutamate homeostasis. Moreover, increased expression of hBCAT was observed in the brains of patients with AD relative to matched controls. We reflect on the importance of the redox-active CXXC motif, which confers novel roles for the hBCAT proteins, particularly with respect to substrate channeling and protein folding. This implies that, in addition to their role in glutamate metabolism, these proteins have additional functional roles that might impact redox cell signaling. This review discusses how these proteins behave as potential neuroprotectors during periods of oxidative stress. These findings are particularly important because an increase in misfolded proteins, linked to increased oxidative stress, occurs in several neurodegenerative conditions. Together, these studies give an overview of the diverse role that these proteins play in brain metabolism, in which a dysregulation of their expression may contribute to neurodegenerative conditions such as AD.

The branched-chain aminotransferase proteins: novel redox chaperones for protein disulfide isomerase--implications in Alzheimer's disease

AIMS

The human branched-chain aminotransferase proteins (hBCATm and hBCATc) are regulated through oxidation and S-nitrosation. However, it remains unknown whether they share common redox characteristics to enzymes such as protein disulfide isomerase (PDI) in terms of regulating cellular repair and protein misfolding.

RESULTS

Here, similar to PDI, the hBCAT proteins showed dithiol-disulfide isomerase activity that was mediated through an S-glutathionylated mechanism. Site-directed mutagenesis of the active thiols of the CXXC motif demonstrates that they are fundamental to optimal protein folding. Far Western analysis indicated that both hBCAT proteins can associate with PDI. Co-immunoprecipitation studies demonstrated that hBCATm directly binds to PDI in IMR-32 cells and the human brain. Electron and confocal microscopy validated the expression of PDI in mitochondria (using Mia40 as a mitochondrial control), where both PDI and Mia40 were found to be co-localized with hBCATm. Under conditions of oxidative stress, this interaction is decreased, suggesting that the proposed chaperone role for hBCATm may be perturbed. Moreover, immunohistochemistry studies show that PDI and hBCAT are expressed in the same neuronal and endothelial cells of the vasculature of the human brain, supporting a physiological role for this binding.

INNOVATION

This study identifies a novel redox role for hBCAT and confirms that hBCATm differentially binds to PDI under cellular stress.

CONCLUSION

These studies indicate that hBCAT may play a role in the stress response of the cell as a novel redox chaperone, which, if compromised, may result in protein misfolding, creating aggregates as a key feature in neurodegenerative conditions such as Alzheimer's disease.

Hepatic mitochondrial dysfunction induced by fatty acids and ethanol

Understanding the key aspects of the pathogenesis of alcoholic fatty liver disease particularly alterations to mitochondrial function remains to be resolved. The role of fatty acids in this regard requires further investigation due to their involvement in fatty liver disease and obesity. This study aimed to characterize the early effects of saturated and unsaturated fatty acids alone on liver mitochondrial function and during concomitant ethanol exposure using isolated liver mitochondria and VA-13 cells (Hep G2 cells that efficiently express alcohol dehydrogenase). Liver mitochondria or VA-13 cells were treated with increasing concentrations of palmitic or arachidonic acid (1 to 160 μM) for 24 h with or without 100 mM ethanol. The results showed that in isolated liver mitochondria both palmitic and arachidonic acids significantly reduced state 3 respiration in a concentration-dependent manner (P<0.001), implicating their ionophoric activities. Increased ROS production occurred in a dose-dependent manner especially in the presence of rotenone (complex I inhibitor), which was significantly more prominent in arachidonic acid at 80 μM (+970%, P<0.001) than palmitic acid (+40%, P<0.01). In VA-13 cells, ethanol alone and both fatty acids (40 μM) were able to decrease the mitochondrial membrane potential and cellular ATP levels and increase lipid formation. ROS production was significantly increased with arachidonic acid (+110%, P<0.001) exhibiting a greater effect than palmitic acid (+39%, P<0.05). While in the presence of ethanol, the drop in the mitochondrial membrane potential, cellular ATP levels, and increased lipid formation were further enhanced by both fatty acids, but with greater effect in the case of arachidonic acid, which also correlated with significant cytotoxicity (P<0.001). This study confirms the ability of fatty acids to promote mitochondrial injury in the development of alcoholic fatty liver disease.

Effects of 4-hydroxynonenal on mitochondrial 3-hydroxy-3-methylglutaryl (HMG-CoA) synthase

Chronic ethanol consumption causes increased production of reactive oxygen species in hepatic mitochondria accompanied by elevations in products of lipid peroxidation such as 4-hydroxynonenal (4-HNE). In the current study we investigated the effects of chronic ethanol consumption on a prominent protein-4-HNE adduct in liver mitochondria. Male Sprague-Dawley rats were fed a liquid diet for 31 days in which ethanol constituted 36% of total calories. Immunoblot analyses of liver mitochondria from ethanol-fed and control animals, using an antibody to a 4-HNE-protein adduct, demonstrated elevated 4-HNE binding (+50%) to a mitochondrial protein of approximately 55 kDa due to chronic ethanol consumption. Analysis of this protein using AspN digestion and tandem mass spectrometry identified it as the mitochondrial form of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase. Activity of the activated form of this enzyme was unchanged in livers from ethanol-fed animals, but the protein level was elevated by 36%, which suggests a compensatory mechanism to maintain constant levels of synthase activity in the mitochondrion in the face of continuous inactivation by 4-HNE. Treatment of isolated mitochondria with 4-HNE demonstrated that the enzyme activity decreased as a function of 4-HNE concentration and with time of exposure. This study demonstrates that ethanol consumption increases the formation of a 4-HNE adduct with mitochondrial HMG-CoA synthase, which has the potential to inactivate the enzyme in situ.

PROTEIN ADDUCT SPECIES IN MUSCLE AND LIVER OF RATS FOLLOWING ACUTE ETHANOL ADMINISTRATION

AIMS

Previous immunohistochemical studies have shown that the post-translational formation of aldehyde-protein adducts may be an important process in the aetiology of alcohol-induced muscle disease. However, other studies have shown that in a variety of tissues, alcohol induces the formation of various other adduct species, including hybrid acetaldehyde-malondialdehyde-protein adducts and adducts with free radicals themselves, e.g. hydroxyethyl radical (HER)-protein adducts. Furthermore, acetaldehyde-protein adducts may be formed in reducing or non-reducing environments resulting in distinct molecular entities, each with unique features of stability and immunogenicity. Some in vitro studies have also suggested that unreduced adducts may be converted to reduced adducts in situ. Our objective was to test the hypothesis that in muscle a variety of different adduct species are formed after acute alcohol exposure and that unreduced adducts predominate.

METHODS

Rabbit polyclonal antibodies were raised against unreduced and reduced aldehydes and the HER-protein adducts. These were used to assay different adduct species in soleus (type I fibre-predominant) and plantaris (type II fibre-predominant) muscles and liver in four groups of rats administered acutely with either [A] saline (control); [B] cyanamide (an aldehyde dehydrogenase inhibitor); [C] ethanol; [D] cyanamide+ethanol.

RESULTS

Amounts of unreduced acetaldehyde and malondialdehyde adducts were increased in both muscles of alcohol-dosed rats. However there was no increase in the amounts of reduced acetaldehyde adducts, as detected by both the rabbit polyclonal antibody and the RT1.1 mouse monoclonal antibody. Furthermore, there was no detectable increase in malondialdehyde-acetaldehyde and HER-protein adducts. Similar results were obtained in the liver.

CONCLUSIONS

Adducts formed in skeletal muscle and liver of rats exposed acutely to ethanol are mainly unreduced acetaldehyde and malondialdehyde species.

Liver dysfunction induced by bile duct ligation and galactosamine injection alters cardiac protein synthesis

Liver disease has been shown to affect the cardiovascular system and may influence cardiac protein metabolism. This hypothesis was tested by measuring rates of cardiac protein synthesis in 2 models of liver disease in rats. The study consisted of 5 groups--group 1: control, injected with saline and fed ad libitum; group 2: acute liver injury, by dosage with 400 mg/kg galactosamine; group 3: injected with saline and pair-fed to group 2; group 4: chronic liver disease, using bile duct ligation; and group 5: sham-operated and pair-fed to group 4. Rates of cardiac protein synthesis were measured using the flooding dose technique. After 1 week, galactosamine injection caused the following cardiac changes, i.e. group (2) versus (3): an increased RNA content, RNA/DNA ratio, and RNA/protein ratio. However, there was no change in DNA or protein content, or protein/DNA ratio. There was an increase in the fractional rate of protein synthesis, and the absolute synthesis rate. Cellular efficiency was increased, but RNA activity remained unchanged. Comparison of groups 4 and 5 showed that bile duct ligation caused no change in any parameters measured. Although comparison of the ad libitum-fed group 1 with the bile duct ligation group 4 showed reduced cardiac weight, protein, and RNA content, with decreased right ventricular absolute synthesis rates; this was also seen in the pair-fed group 5, suggesting that these effects were due solely to reduced oral intake. Thus, although galactosamine-induced acute liver injury caused marked changes in cardiac biochemistry, bile duct ligation per se did not. This study also illustrates the importance of including a pair-fed group.

The acute and chronic effects of alcohol upon cardiac nucleotide status

The aim of the investigation was to ascertain the biochemical and morphological basis for the functional impairments in the heart due to alcohol. In chronic studies rats were fed a nutritionally complete liquid diet containing 35% of total calories as ethanol, controls were pair-fed identical amounts of the same diet in which ethanol was replaced by isocaloric glucose. In acute studies rats were injected with ethanol at a dose of 75 mmol/kg body weight. Pre-treatment of acute ethanol-dosed rats with cyanamide (ALDH inhibitor) was designed to raise acetaldehyde levels. In chronic studies ventricular adenine nucleotides, ATP, ADP and AMP; NAD(+), ATP ratios and the energy charge showed no alteration after 6 weeks of alcohol feeding. Light and electron microscopy sections indicated very little structural damage to muscle fibres and organelles (especially the mitochondria) in both atria and ventricles. Ventricular fibre diameters, throughout the different ranges, showed no significant differences between chronically alcohol and control-fed rats. In acute studies an increase in ventricular AMP levels (micromoles/g wet weight) occurred following cyanamide and cyanamide + ethanol treatment (+57%, p < 0.025 and +76%, p<0.01, respectively), but not as a consequence of ethanol alone. Cyanamide+ethanol caused marked elevation in ADP levels (+28%, p < 0.05) and again ethanol was without effect. ATP and GTP levels were not altered by any of the acute treatments. The energy charge was slightly reduced in both cyanamide and cyanamide+ethanol groups (-8%, p < 0.01 and -7%, p < 0.05, respectively), but not by ethanol alone. In conclusion, chronic alcohol appears to have minimal effects upon cardiac nucleotides which suggest that possible adaptive mechanisms are induced during the 6-week period and that alternative pathways other than defects in adenine nucleotide concentrations are involved in the pathogenesis of AHMD. The acute study suggests that the heart is resilient to toxic levels of alcohol and acetaldehyde in terms of ATP and GTP levels, despite the elevated AMP, ADP and GDP levels.

Emerging techniques in biomedical research and their application to alcohol toxicity

This article represents the proceedings of a symposium at the 2002 RSA-ISBRA Meeting in San Francisco. The chairs were Vinood B. Patel and Victor R. Preedy. The presentations were (1) Macromolecular structural analysis, by Vinood B. Patel; (2) Profiling and imaging of proteins in tissue sections using mass spectrometry as a discovery tool in biological research, by Pierre Chaurand and Richard M. Caprioli; (3) The use of SELDI ProteinChip trade mark arrays, by Brian M. Austen, Emma R. Frears, Francesca Manca, and Huw Davies; (4) DNA hybridization array technologies, by Kent E. Vrana; and (5) Adeno- and adeno-associated viral mediated gene transfer approaches for alcoholic liver disease, by Michael Wheeler. Concluding remarks were by Victor R. Preedy.