Integrated transcriptomic landscape of the effect of anti-steatotic treatments in high-fat diet mouse models of non-alcoholic fatty liver disease

High-fat diet (HFD) mouse models are widely used in research to develop medications to treat non-alcoholic fatty liver disease (NAFLD), as they mimic the steatosis, inflammation, and hepatic fibrosis typically found in this complex human disease. The aims of this study were to identify a complete transcriptomic signature of these mouse models and to characterize the transcriptional impact exerted by different experimental anti-steatotic treatments. For this reason, we conducted a systematic review and meta-analysis of liver transcriptomic studies performed in HFD-fed C57BL/6J mice, comparing them with control mice and HFD-fed mice receiving potential anti-steatotic treatments. Analyzing 21 studies broaching 24 different treatments, we obtained a robust HFD transcriptomic signature that included 2,670 differentially expressed genes and 2,567 modified gene ontology biological processes. Treated HFD mice generally showed a reversion of this HFD signature, although the extent varied depending on the treatment. The biological processes most frequently reversed were those related to lipid metabolism, response to stress, and immune system, whereas processes related to nitrogen compound metabolism were generally not reversed. When comparing this HFD signature with a signature of human NAFLD progression, we identified 62 genes that were common to both; 10 belonged to the group that were reversed by treatments. Altered expression of most of these 10 genes was confirmed in vitro in hepatocytes and hepatic stellate cells exposed to a lipotoxic or a profibrogenic stimulus, respectively. In conclusion, this study provides a vast amount of information about transcriptomic changes induced during the progression and regression of NAFLD and identifies some relevant targets. Our results may help in the assessment of treatment efficacy, the discovery of unmet therapeutic targets, and the search for novel biomarkers. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Benefits of rilpivirine for liver stiffness in HIV/HCV-coinfected patients

BACKGROUND

Rilpivirine (RPV) is an antiretroviral drug characterized by good tolerability and a favorable liver safety profile. Recent research has shown that RPV ameliorates liver fibrosis in animal models of various chronic liver diseases. Our study aimed to analyze the effect of RPV on liver fibrosis by assessing changes in liver stiffness using transient elastography.

METHODS

Retrospective cohort study of HIV-infected patients who were exposed and not exposed to RPV. The change in liver stiffness during the period between two transient elastography measurements was analyzed and compared for patients exposed and not exposed to RPV.

RESULTS

We selected 118 RPV-exposed and 118 non-RPV-exposed HIV-infected patients. Median time between transient elastography (TE) measurements was 50 (29-68) months. A repeated-measures general linear model based on the main clinical characteristics revealed a significant decrease in the TE value of -0.8kPa in non-RPV-exposed patients (p=0.254) and -1.6kPa in the RPV-exposed group (p<0.001). The subgroup analysis showed a significant reduction in the TE value only patients cured of hepatitis C (RPV-exposed, -2.8kPa [p<0.001]; non-RPV-exposed, -1.1kPa [p=0.22]).

CONCLUSION

RPV-based antiretroviral regimens significantly reduced liver stiffness, as measured by TE, in patients cured of chronic hepatitis C.

Anti-inflammatory and immunomodulating effects of rilpivirine: Relevance for the therapeutics of chronic liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease (CLD) worldwide and inflammation is key to its progression/resolution. As we have previously described that rilpivirine (RPV) is hepatoprotective in murine models of CLD, here we determine the molecular mechanisms involved, focusing on its anti-inflammatory and immunomodulating properties. They were evaluated in vitro (human hepatic cell lines of the major hepatic cell types), in vivo (liver samples from a murine nutritional model of NAFLD) and ex vivo (peripheral blood mononuclear cells -PBMC- from patients with CLD). Transcriptomic analysis of liver samples from NAFLD mice showed RPV down-regulated biological processes associated with the inflammatory response (NF-κB/IκB signaling and mitogen-activated protein kinase -MAPK- activity) and leukocyte chemotaxis and migration. We observed a decrease in Adgre1 and Ccr2 expression and in the number of CCR2 + cells in the periportal areas of RPV-treated NAFLD mice. This RPV-induced effect on the CCL2/CCR2 axis was confirmed in vitro. A similar result was also obtained with CXCL10/IP10, one of the main chemokines in the liver. RPV also diminished activation of MAP kinases p38 and JNK. In addition, RPV inhibited the NLRP3 inflammasome pathway in vitro, decreasing NLRP3 protein expression, caspase-1 activation and IL-1β gene expression. RPV was also proven anti-inflammatory in PBMC from patients with CLD treated ex vivo. In conclusion, beyond its well-described role in antiretroviral therapy, RPV manifests anti-inflammatory and immunoregulatory effects, a finding that could be of great relevance for the search of novel targets or repositioning strategies for CLD.

Novel Therapeutic Approaches to Liver Fibrosis Based on Targeting Oxidative Stress

Chronic liver disease (CLD) constitutes a growing global health issue, with no effective treatments currently available. Oxidative stress closely interacts with other cellular and molecular processes to trigger stress pathways in different hepatic cells and fuel the development of liver fibrosis. Therefore, inhibition of reactive oxygen species (ROS)-mediated effects and modulation of major antioxidant responses to counteract oxidative stress-induced damage have emerged as interesting targets to prevent or ameliorate liver injury. Although many preclinical studies have shown that dietary supplements with antioxidant properties can significantly prevent CLD progression in animal models, this strategy has not proved effective to significantly reduce fibrosis when translated into clinical trials. Novel and more specific therapeutic approaches are thus required to alleviate oxidative stress and reduce liver fibrosis. We have reviewed the relevant literature concerning the crucial role of alterations in redox homeostasis in different hepatic cell types during the progression of CLD and discussed current pharmacological approaches to ameliorate fibrosis by reducing oxidative stress focusing on selective modulation of enzymatic oxidant sources, antioxidant systems and ROS-mediated pathogenic processes.

Implication of autophagy in the antifibrogenic effect of Rilpivirine: when more is less

As the main extracellular matrix-producing cells, activated hepatic stellate cells (HSC) are fundamental mediators of liver fibrosis (LF), and understanding their activation/inactivation mechanisms is paramount to the search for novel therapeutics. The antiretroviral drug Rilpivirine (RPV) has demonstrated a hepatoprotective effect in several animal models of chronic liver injury that is related to its antifibrogenic and apoptotic action in HSC. In the present study, we evaluated whether autophagy is implicated in the hepatoprotective action of RPV, as autophagy plays an important role in HSC transdifferentiation. We employed two standard mouse models of chronic liver injury - fatty liver disease and carbon tetrachloride (CCl₄)-induced hepatotoxicity -and cultured HSC activated with the profibrotic cytokine TGF-β. RPV enhanced autophagy in the whole liver of both mouse models and in activated HSC, evident in the protein expression of autophagy markers, increased autophagosome content and lysosomal mass. Moreover, increased autophagic flux was observed in RPV-exposed HSC as revealed by tandem fluorescence-tagged LC3 and p62 and analysis of LC3-II accumulation in cells exposed to the lysosomal inhibitor chloroquine. Importantly, autophagy was involved in the cytotoxic effect of RPV on HSC, though in a differential manner. Pharmacological inhibition of autophagy by 3-methyladenine (3-MA) did not affect the diminishing effect of RPV on viability, while treatment with wortmannin or depletion of specific autophagy proteins (ATG5, Beclin-1 and SQSTM1/p62) rescued the detrimental effect of high concentrations of RPV on the viability of activated HSC. Finally, we also provide evidence that RPV compromises the viability of TGF-β-induced HSC independently of its antifibrogenic effect, observed as reduced collagen 1A1 synthesis, and that this effect does not include RPV´s modulation of autophagy. In summary, as a contributor to the mechanisms involved in the hepatoprotective action of RPV, autophagy may be a good candidate to explore when developing novel therapeutics for LF.

Down-Regulation of the Longevity-Associated Protein SIRT1 in Peripheral Blood Mononuclear Cells of Treated HIV Patients

The activity of sirtuin 1 (SIRT1), a class III histone deacetylase with a critical role in several biological functions, decreases with age and its deficiency is associated with many inflammatory and age-related diseases. It also regulates the chronic immune activation and viral latency during an HIV infection. The life-span and particularly the health span of HIV patients are substantially shortened; however, the participation of SIRT1 in these effects is not clear. We performed a prospective cross-sectional monocentric study that included 70 HIV-infected patients and 43 BMI-, age- and sex-matched uninfected individuals. We found that in the PBMCs of the HIV patients, SIRT1 mRNA levels were significantly lower (p < 0.0001). This decrease, which was corroborated at the protein level, occurred irrespectively of the antiretroviral regimen these patients received and was not significantly related to the general, HIV-related or comorbidity-related parameters. The levels of the major mitochondrial sirtuin SIRT3 were not altered. Moreover, the strong correlations of SIRT1 with the leukocyte markers CD8A and CD19 present in the uninfected individuals were absent in the HIV patients. In conclusion, this study showed that the PBMCs of the HIV patients displayed diminished SIRT1 levels and altered correlations of SIRT1 with markers of CD8⁺ T cells and B cells, findings which may be relevant for understanding the complex pathogenic milieu in HIV patients.

Macrophages Modulate Hepatic Injury Involving NLRP3 Inflammasome: The Example of Efavirenz

Drug-induced liver injury (DILI) constitutes a clinical challenge due to the incomplete characterization of the mechanisms involved and potential risk factors. Efavirenz, an anti-HIV drug, induces deleterious actions in hepatocytes that could underlie induction of the NLRP3 inflammasome, an important regulator of inflammatory responses during liver injury. We assessed the potential of efavirenz to modulate the inflammatory and fibrogenic responses of major liver cell types involved in DILI. The effects of efavirenz were evaluated both in vitro and in vivo. Efavirenz triggered inflammation in hepatocytes, in a process that involved NF-κB and the NLRP3 inflammasome, and activated hepatic stellate cells (HSCs), thereby enhancing expression of inflammatory and fibrogenic markers. The NLRP3 inflammasome was not altered in efavirenz-treated macrophages, but these cells polarized towards the anti-inflammatory M2 phenotype and displayed upregulated anti-inflammatory mediators. Conversely, no evidence of damage was observed in efavirenz-treated animals, except when macrophages were depleted, which resulted in the in vivo manifestation of the deleterious effects detected in hepatocytes and HSCs. Efavirenz elicits a cell-specific activation of the NLRP3 inflammasome in hepatocytes and HSCs, but macrophages appear to counteract efavirenz-induced liver injury. Our results highlight the dynamic nature of the interaction among liver cell populations and emphasize the potential of targeting macrophage polarization as a strategy to treat NLRP3 inflammasome-induced liver injury.

NNRTI and Liver Damage: Evidence of Their Association and the Mechanisms Involved

Due to the improved effectiveness and safety of combined antiretroviral therapy, human immunodeficiency virus (HIV) infection has become a manageable, chronic condition rather than a mortal disease. However, HIV patients are at increased risk of experiencing non-AIDS-defining illnesses, with liver-related injury standing out as one of the leading causes of death among these patients. In addition to more HIV-specific processes, such as antiretroviral drug-related toxicity and direct injury to the liver by the virus itself, its pathogenesis is related to conditions that are also common in the general population, such as alcoholic and non-alcoholic fatty liver disease, viral hepatitis, and ageing. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are essential components of combined anti-HIV treatment due to their unique antiviral activity, high specificity, and acceptable toxicity. While first-generation NNRTIs (nevirapine and efavirenz) have been related largely to liver toxicity, those belonging to the second generation (etravirine, rilpivirine and doravirine) seem to be generally safe for the liver. Indeed, there is preclinical evidence of rilpivirine being hepatoprotective in different models of liver injury, independently of the presence of HIV. The present study aims to review the mechanisms by which currently available anti-HIV drugs belonging to the NNRTI family may participate in the development of liver disease.

Understanding the implication of autophagy in the activation of hepatic stellate cells in liver fibrosis: are we there yet?

Liver fibrosis (LF) occurs as a result of persistent liver injury and can be defined as a pathologic, chronic, wound-healing process in which functional parenchyma is progressively replaced by fibrotic tissue. As a phenomenon involved in the majority of chronic liver diseases, and therefore prevalent, it exerts a significant impact on public health. This impact becomes even more patent given the lack of a specific pharmacological therapy, with LF only being ameliorated or prevented through the use of agents that alleviate the underlying causes. Hepatic stellate cells (HSCs) are fundamental mediators of LF, which, activated in response to pro-fibrotic stimuli, transdifferentiate from a quiescent phenotype into myofibroblasts that deposit large amounts of fibrotic tissue and mediate pro-inflammatory effects. In recent years, much effort has been devoted to understanding the mechanisms through which HSCs are activated or inactivated. Using cell culture and/or different animal models, numerous studies have shown that autophagy is enhanced during the fibrogenic process and have provided specific evidence to pinpoint the fundamental role of autophagy in HSC activation. This effect involves - though may not be limited to - the autophagic degradation of lipid droplets. Several hepatoprotective agents have been shown to reverse the autophagic alteration present in LF, but clinical confirmation of these effects is pending. On the other hand, there is evidence that implicates autophagy in several anti-fibrotic mechanisms in HSCs that stimulate HSC cell cycle arrest and cell death or prevent the generation of pro-fibrotic mediators, including excess collagen accumulation. The objective of this review is to offer a comprehensive analysis of published evidence of the role of autophagy in HSC activation and to provide hints for possible therapeutic targets for the treatment and/or prevention of LF related to autophagy. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Apoptosis of Hepatocytes: Relevance for HIV-Infected Patients under Treatment

Due to medical advances over the past few decades, human immunodeficiency virus (HIV) infection, once a devastatingly mortal pandemic, has become a manageable chronic condition. However, available antiretroviral treatments (cART) cannot fully restore immune health and, consequently, a number of inflammation-associated and/or immunodeficiency complications have manifested themselves in treated HIV-infected patients. Among these chronic, non-AIDS (acquired immune deficiency syndrome)-related conditions, liver disease is one of the deadliest, proving to be fatal for 15–17% of these individuals. Aside from the presence of liver-related comorbidities, including metabolic disturbances and co-infections, HIV itself and the adverse effects of cART are the main factors that contribute to hepatic cell injury, inflammation, and fibrosis. Among the molecular mechanisms that are activated in the liver during HIV infection, apoptotic cell death of hepatocytes stands out as a key pathogenic player. In this review, we will discuss the evidence and potential mechanisms involved in the apoptosis of hepatocytes induced by HIV, HIV-encoded proteins, or cART. Some antiretroviral drugs, especially the older generation, can induce apoptosis of hepatic cells, which occurs through a variety of mechanisms, such as mitochondrial dysfunction, increased production of reactive oxygen species (ROS), and induction of endoplasmic reticulum (ER) stress and unfolded protein response (UPR), all of which ultimately lead to caspase activation and cell death.

Rilpivirine attenuates liver fibrosis through selective STAT1-mediated apoptosis in hepatic stellate cells

OBJECTIVE

Liver fibrosis constitutes a major health problem worldwide due to its rapidly increasing prevalence and the lack of specific and effective treatments. Growing evidence suggests that signalling through cytokine-activated Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathways regulates liver fibrosis and regeneration. Rilpivirine (RPV) is a widely used anti-HIV drug not reported to produce hepatotoxicity. We aimed to describe the potential hepatoprotective effects of RPV in different models of chronic liver injury, focusing on JAK-STAT signalling regulation.

DESIGN

The effects of RPV on hepatic steatosis, inflammation and fibrogenesis were studied in a nutritional mouse model of non-alcoholic fatty liver disease, carbon tetrachloride-induced fibrosis and bile duct ligation-induced fibrosis. Primary human hepatic stellate cells (hHSC) and human cell lines LX-2 and Hep3B were used to investigate the underlying molecular mechanisms.

RESULTS

RPV exerted a clear anti-inflammatory and antifibrotic effect in all the in vivo models of liver injury employed, and enhanced STAT3-dependent proliferation in hepatocytes and apoptosis in HSC through selective STAT1 activation. These results were reproduced in vitro; RPV undermined STAT3 activation and triggered STAT1-mediated pathways and apoptosis in HSC. Interestingly, this selective pro-apoptotic effect completely disappeared when STAT1 was silenced. Conditioned medium experiments showed that HSC apoptosis activated STAT3 in hepatocytes in an interleukin-6-dependent mechanism.

CONCLUSION

RPV ameliorates liver fibrosis through selective STAT1-dependent induction of apoptosis in HSC, which exert paracrinal effects in hepatocytes, thus promoting liver regeneration. RPV's actions may represent an effective strategy to treat chronic liver diseases of different aetiologies and help identify novel therapeutic targets.

Abacavir Induces Arterial Thrombosis in a Murine Model

Background

The purinergic system is known to underlie prothrombotic and proinflammatory vascular programs, making the profile of experimental actions demonstrated by abacavir compatible with thrombogenesis. However, direct evidence of a prothrombotic effect by the drug has been lacking.

Methods

The present study appraised the effects of abacavir in a well-validated animal model of arterial thrombosis. The role of ATP-P2X7 receptors in the actions of the drug was also assessed, and the actions of recognized vascular-damaging agents and other nucleoside reverse-transcriptase inhibitors (NRTIs) were evaluated and compared to those of abacavir.

Results

Abacavir dose-dependently promoted thrombus formation. This effect was reversed by a P2X7-receptor antagonist and was nonexistent in P2X7 knockout mice. The effects of abacavir were similar to those of diclofenac and rofecoxib. Other NRTIs had no thrombosis-related effects.

Conclusion

Abacavir promotes arterial thrombosis through interference with purinergic signaling, suggesting a possible biological mechanism for the clinical association of abacavir with cardiovascular diseases.

Transcriptome-based repurposing of apigenin as a potential anti-fibrotic agent targeting hepatic stellate cells

We have used a computational approach to identify anti-fibrotic therapies by querying a transcriptome. A transcriptome signature of activated hepatic stellate cells (HSCs), the primary collagen-secreting cell in liver, and queried against a transcriptomic database that quantifies changes in gene expression in response to 1,309 FDA-approved drugs and bioactives (CMap). The flavonoid apigenin was among 9 top-ranked compounds predicted to have anti-fibrotic activity; indeed, apigenin dose-dependently reduced collagen I in the human HSC line, TWNT-4. To identify proteins mediating apigenin's effect, we next overlapped a 122-gene signature unique to HSCs with a list of 160 genes encoding proteins that are known to interact with apigenin, which identified C1QTNF2, encoding for Complement C1q tumor necrosis factor-related protein 2, a secreted adipocytokine with metabolic effects in liver. To validate its disease relevance, C1QTNF2 expression is reduced during hepatic stellate cell activation in culture and in a mouse model of alcoholic liver injury in vivo, and its expression correlates with better clinical outcomes in patients with hepatitis C cirrhosis (n = 216), suggesting it may have a protective role in cirrhosis progression.These findings reinforce the value of computational approaches to drug discovery for hepatic fibrosis, and identify C1QTNF2 as a potential mediator of apigenin's anti-fibrotic activity.

The purine analogues abacavir and didanosine increase acetaminophen-induced hepatotoxicity by enhancing mitochondrial dysfunction

BACKGROUND

NRTIs are essential components of HIV therapy with well-documented, long-term mitochondrial toxicity in hepatic cells, but whose acute effects on mitochondria are unclear. As acetaminophen-induced hepatotoxicity also involves mitochondrial interference, we hypothesized that it would be exacerbated in the context of ART.

METHODS

We evaluated the acute effects of clinically relevant concentrations of the most widely used NRTIs, alone or combined with acetaminophen, on mitochondrial function and cellular viability.

RESULTS

The purine analogues abacavir and didanosine produced an immediate and concentration-dependent inhibition of oxygen consumption and complex I and III activity. This inhibition was accompanied by an undermining of mitochondrial function, with increased production of reactive oxygen species and reduction of mitochondrial membrane potential and intracellular ATP levels. However, this interference did not compromise cell survival. Co-administration with concentrations of acetaminophen below those considered hepatotoxic exacerbated the deleterious effects of both compounds on mitochondrial function and compromised cellular viability, showing a clear correlation with diminished glutathione levels.

CONCLUSIONS

The simultaneous presence of purine analogues and low concentrations of acetaminophen significantly potentiates mitochondrial dysfunction, increasing the risk of liver injury. This new mechanism is relevant given the liver's susceptibility to mitochondrial dysfunction-related toxicity and the tendency of the HIV infection to increase oxidative stress.

Is Autophagy Altered in the Leukocytes of Type 2 Diabetic Patients?

It is unknown whether autophagy is altered in the leukocytes of type 2 diabetes (T2D) patients and whether oxidative and endoplasmic reticulum (ER) stresses regulate this mechanism. We studied anthropometric and metabolic parameters and evaluated oxidative stress, chromatin condensation, ER stress, and autophagy parameters in leukocytes of 103 T2D patients versus 109 sex- and age-matched controls. Patients showed increases in glucose, insulin, homeostasis model assessment of insulin resistance, and glycated hemoglobin (HbA1c) compared with controls (p < 0.001). Leukocytes displayed enhanced total and mitochondrial reactive oxygen species (ROS), reduced mitochondrial mass, and increased chromatin condensation (p < 0.05). ER stress was also activated in diabetic patients, who displayed augmented glucose-regulated protein 78 kDa (GRP78), phosphorylated eukaryotic translation initiation factor 2, subunit 1 alpha (P-eIF2α), and activating transcription factor 6 (ATF6) levels (p < 0.05). We also observed an increase in the autophagy markers, microtubule-associated protein light chain 3 (LC3)-II and Beclin 1 (p < 0.05), and significant positive correlations between Beclin 1 and total ROS (r = 0.667), GRP78 (r = 0.925) and P-eIF2α (r = 0.644), and between LC3-II and P-eIF2α (r = 0.636) and ATF6 (r = 0.601). Our results lead to the hypothesis that autophagy is activated in the leukocytes of T2D patients and that both oxidative and ER stress signaling pathways may be implicated in the induction of autophagy.

Lack of mitochondrial toxicity of darunavir, raltegravir and rilpivirine in neurons and hepatocytes: a comparison with efavirenz

OBJECTIVES

Growing evidence associates the non-nucleoside reverse transcriptase inhibitor efavirenz with several adverse events. Newer antiretrovirals, such as the integrase inhibitor raltegravir, the non-nucleoside reverse transcriptase inhibitor rilpivirine and the protease inhibitor darunavir, claim to have a better toxicological profile than efavirenz while producing similar levels of efficacy and virological suppression. The objective of this study was to determine the in vitro toxicological profile of these three new antiretrovirals by evaluating their effects on the mitochondrial and cellular parameters altered by efavirenz in hepatocytes and neurons.

METHODS

Hep3B cells and primary rat neurons were treated with clinically relevant concentrations of efavirenz, darunavir, rilpivirine or raltegravir. Parameters of mitochondrial function, cytotoxicity and oxidative and endoplasmic reticulum stress were assessed using standard cell biology techniques.

RESULTS

None of the new compounds altered the mitochondrial function of hepatic cells or neurons, while efavirenz decreased mitochondrial membrane potential and enhanced superoxide production in both cell types, effects that are known to significantly compromise the functioning of mitochondria, cell viability and, ultimately, cell number. Of the four drugs assayed, efavirenz was the only one to alter the protein expression of LC3-II, an indicator of autophagy, and CHOP, a marker of endoplasmic reticulum stress and the unfolded protein response.

CONCLUSIONS

Darunavir, rilpivirine and raltegravir do not induce toxic effects on Hep3B cells and primary rat neurons, which suggests a safer hepatic and neurological profile than that of efavirenz.

Mitochondrial toxicity in HAART: an overview of in vitro evidence

The combined antiretroviral therapeutic approach currently employed for the treatment of HIV infection, known as Higly Active Antiretroviral Therapy (HAART), has dramatically reduced AIDS-related morbidity and mortality. However, the adverse reactions associated with the long term use of this therapy have now become a major issue and researchers have focused on understanding the cellular mechanisms underlying these drug-induced detrimental effects which englobe a large list of different events including rash and hypersensibility reactions, hepatotoxicity, metabolic disturbances including lipodystrophy, and other metabolic syndrome-like disturbances such as hyperlactatemia, hyperlipedimia, insulin resistance and pancreatitis. Other events include CNS toxic effects, peripheral neuropathies as well as nephrotoxicity and increased risk of cardiovascular diseases. Many of these reactions have been shown to develop as e result of mitochondrial dysfunction. The mitochondrial effect of N(t)RTI (Nucleos(t)ide Reverse Transcriptase Inhibitors) class of drugs, which has been widely studied, is believed to originate from the inhibitory action of these drugs on DNA polymerase gamma, the enzyme responsible for replication of mitochondrial DNA. However, additional mitochondrial targets have also been described and need to be considered. As to NNRTI (Non-Nucleoside-Transcriptase Inhibitor) or PI (Protease Inhibitors), evidence of the implication of mitochondria has also been reported, however the details of the mechanisms underlying these actions are still not fully known. This review covers the current knowledge of mitochondrial toxicities, particularly the available in vitro evidence, regarding the most commonly used groups of HIV drugs. Novel findings of mtDNA-independent mitochondrial dysfunction have received special attention.

Metabolomics of the effect of AMPK activation by AICAR on human umbilical vein endothelial cells

AMP-activated protein kinase (AMPK) is a metabolic master switch expressed in a great number of cells and tissues. AMPK is thought to modulate the cellular response to different stresses that increase cellular AMP concentration. The adenosine analog, 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) is an AMPK activator used in many studies to assess the effects of AMPK activation on cellular metabolism and function. However, the effect of AICAR on cell metabolism reaches many different pathways and metabolites, some of which do not seem to be fully related to AMPK activation. We have now for the first time used NMR metabolomics on human umbilical vein endothelial cells (HUVEC) for the study of the global metabolic impact of AMPK activation by AICAR. In our study, incubation with AICAR activates AMPK and is associated with, among others, broad metabolic alterations in energy metabolism and phospholipid biosynthesis. Using NMR spectroscopy and metabolic network tools, we analyzed the connections between the different metabolic switches activated by AICAR. Our approach reveals a strong interconnection between different phospholipid precursors and oxidation by-products. Metabolomics profiling is a useful tool for detecting major metabolic alterations, generating new hypotheses and provides some insight about the different molecular correlations in a complex system. The present study shows that AICAR induces metabolic effects in cell metabolism well beyond energy production pathways.

Mitochondrial interference by anti-HIV drugs: mechanisms beyond Pol-γ inhibition

The combined pharmacological approach to the treatment of HIV infection, known as highly active antiretroviral therapy (HAART), has dramatically reduced AIDS-related morbidity and mortality. However, its use has been associated with serious adverse reactions, of which those resulting from mitochondrial dysfunction are particularly widespread. Nucleos(t)ide-reverse transcriptase inhibitors (NRTIs) have long been considered the main source of HAART-related mitochondrial toxicity due to their ability to inhibit Pol-γ, the DNA polymerase responsible for the synthesis of mitochondrial DNA. Nevertheless, accumulating evidence points to a more complex relationship between these organelles and NRTIs. Also, alternative pathways by which other groups of anti-HIV drugs (non-nucleoside reverse transcriptase inhibitors and protease inhibitors) interfere with mitochondria have been suggested, although their implications, both pharmacological and clinical, are open to debate. This review aims to provide a comprehensive overview of the mechanisms and factors which influence the mitochondrial involvement in the toxicity of all three major classes of anti-HIV drugs.

Inhibition of mitochondrial function by efavirenz increases lipid content in hepatic cells

Efavirenz (EFV) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) widely used in human immunodeficiency virus (HIV) infection therapy. It has been associated with hepatotoxic effects and alterations in lipid and body fat composition. Given the importance of the liver in lipid regulation, we have evaluated the effects of clinically used concentrations of EFV on the mitochondria and lipid metabolism of human hepatic cells in vitro. Mitochondrial function was rapidly undermined by EFV to an extent that varied with the concentration employed; in particular, respiration and intracellular adenosine triphosphate (ATP) levels were reduced whereas reactive oxygen species (ROS) production increased. Results in isolated mitochondria suggest that the mechanism responsible for these actions was a specific inhibition of complex I of the respiratory chain. The reduction in energy production triggered a compensatory mechanism mediated by the enzyme adenosine monophosphate-activated protein kinase (AMPK), the master switch of cellular bioenergetics. Fluorescence and nuclear magnetic resonance demonstrated a rapid intracellular increase of neutral lipids, usually in the form of droplets. This was prevented by the AMPK inhibitor compound C and by removal of fatty acids from the culture medium. These effects were not reproduced by Nevirapine, another NNRTI. EFV is clinically coadministered with two nucleoside reverse transcriptase inhibitors. Evaluation of one of the most common combination, EFV/Lamivudine/Abacavir, revealed that the effects of EFV on ROS production were enhanced.

CONCLUSION

Clinical concentrations of EFV induce bioenergetic stress in hepatic cells by acutely inhibiting mitochondrial function. This new mechanism of mitochondrial interference leads to an accumulation of lipids in the cytoplasm that is mediated by activation of AMPK.

Gastric antisecretory drugs induce leukocyte-endothelial cell interactions through gastrin release and activation of CCK-2 receptors

Antisecretory drugs are effective antiulcer agents, but its chronic use generates hypergastrinemia and accelerates the development of atrophic gastritis in Helicobacter pylori-positive patients. We have recently shown that gastrin exerts a proinflammatory effect in rats through CCK-2 receptor activation that contributes to the inflammation induced by H. pylori. The present study was designed to examine whether gastrin hypersecretion in response to treatment with antisecretory drugs induces an inflammatory response that could promote mucosal atrophy. The effects of omeprazole or famotidine on leukocyte/endothelial cell interactions in vivo were analyzed in rat mesenteric venules using intravital microscopy. Administration of a single dose of omeprazole or famotidine acutely increased gastrinemia and leukocyte rolling and adhesion, but not emigration into the interstitium. Daily treatment with omeprazole for a short period (3 days) induced a similar response, but when this treatment was extended to 14 days and a steady hyper-gastrinemic state was established, increased leukocyte rolling, adhesion, and emigration was observed. Pretreatment with the CCK-2 receptor antagonist proglumide prevented these inflammatory events in all cases. Leukocytes from rats treated with omeprazole showed increased expression of CD11b/CD18 initially in granulocytes (3-day protocol) and later in monocytes and lymphocytes (14-day protocol). These changes were not observed in animals pretreated with proglumide, and they were not reproduced by incubation of leukocytes from untreated animals in vitro with gastrin. Thus, hypergastrinemia induced by chronic treatment with antisecretory drugs may promote inflammation, which could partly explain their worsening effect in corpus gastritis observed in H. pylori-infected patients.