Influence of intermittent hypoxia on myocardial and hepatic P-glycoprotein expression in a rodent model

Regulation of P-Glycoprotein during Oxidative Stress

P-glycoprotein (Pgp, ABCB1, MDR1) is an efflux transporter protein that removes molecules from the cells (outflow) into the extracellular space. Pgp plays an important role in pharmacokinetics, ensuring the absorption, distribution, and excretion of drugs and its substrates, as well as in the transport of endogenous molecules (steroid and thyroid hormones). It also contributes to tumor cell resistance to chemotherapy. In this review, we summarize the mechanisms of Pgp regulation during oxidative stress. The currently available data suggest that Pgp has a complex variety of regulatory mechanisms under oxidative stress, involving many transcription factors, the main ones being Nrf2 and Nf-kB. These factors often overlap, and some can be activated under certain conditions, such as the deposition of oxidation products, depending on the severity of oxidative stress. In most cases, the expression of Pgp increases due to increased transcription and translation, but under severe oxidative stress, it can also decrease due to the oxidation of amino acids in its molecule. At the same time, Pgp acts as a protector against oxidative stress, eliminating the causative factors and removing its by-products, as well as participating in signaling pathways.

Altitude effect on Propofol Pharmacokinetics in Rats

BACKGROUND

Propofol is an intravenous agent for clinical anesthesia. As the influence of the hypobaric-hypoxic environment (Qinghai-Tibetan region, altitude: 2800-4300 m, PaO2: 15.1-12.4 kPa) on the metabolism of Propofol is complex, the research results on the metabolic characteristics of Propofol in high-altitude areas remain unclear. This study aimed to investigate the pharmacokinetic characteristics of Propofol in a high-altitude hypoxic environment using animal experiments.

METHODS

Rats were randomly divided into three groups: high-altitude, medium-altitude, and plain groups. The time of disappearance and recovery of the rat righting reflex was recorded as the time of anesthesia induction and awakening, respectively. The plasma concentration of Propofol was determined by gas chromatography-mass spectrometry. A pharmacokinetic analysis software was used to analyze the blood-drug concentrations and obtain the pharmacokinetic parameters.

RESULTS

We observed that when Propofol anesthetizes rats, the anesthesia induction time was shortened, and the recovery time was prolonged with increased altitude. Compared with the plain group, the clearance of Propofol decreased, whereas the half-life, area under the concentration-time curve, peak plasma concentration, and average residence time extension increased.

CONCLUSION

The pharmacokinetic characteristics of Propofol are significantly altered in high-altitude hypoxic environments.

Loss of Blood-Brain Barrier Integrity in an In Vitro Model Subjected to Intermittent Hypoxia: Is Reversion Possible with a HIF-1α Pathway Inhibitor?

Several sleep-related breathing disorders provoke repeated hypoxia stresses, which potentially lead to neurological diseases, such as cognitive impairment. Nevertheless, consequences of repeated intermittent hypoxia on the blood-brain barrier (BBB) are less recognized. This study compared two methods of intermittent hypoxia induction on the cerebral endothelium of the BBB: one using hydralazine and the other using a hypoxia chamber. These cycles were performed on an endothelial cell and astrocyte coculture model. Na-Fl permeability, tight junction protein, and ABC transporters (P-gp and MRP-1) content were evaluated with or without HIF-1 inhibitors YC-1. Our results demonstrated that hydralazine as well as intermittent physical hypoxia progressively altered BBB integrity, as shown by an increase in Na-Fl permeability. This alteration was accompanied by a decrease in concentration of tight junction proteins ZO-1 and claudin-5. In turn, microvascular endothelial cells up-regulated the expression of P-gp and MRP-1. An alteration was also found under hydralazine after the third cycle. On the other hand, the third intermittent hypoxia exposure showed a preservation of BBB characteristics. Furthermore, inhibition of HIF-1α with YC-1 prevented BBB dysfunction after hydralazine treatment. In the case of physical intermittent hypoxia, we observed an incomplete reversion suggesting that other biological mechanisms may be involved in BBB dysfunction. In conclusion, intermittent hypoxia led to an alteration of the BBB model with an adaptation observed after the third cycle.

Molecular modeling in cardiovascular pharmacology: Current state of the art and perspectives

Molecular modeling in pharmacology is a promising emerging tool for exploring drug interactions with cellular components. Recent advances in molecular simulations, big data analysis, and artificial intelligence (AI) have opened new opportunities for rationalizing drug interactions with their pharmacological targets. Despite the obvious utility and increasing impact of computational approaches, their development is not progressing at the same speed in different fields of pharmacology. Here, we review current in silico techniques used in cardiovascular diseases (CVDs), cardiological drug discovery, and assessment of cardiotoxicity. In silico techniques are paving the way to a new era in cardiovascular medicine, but their use somewhat lags behind that in other fields.

Triglyceride-induced cardiac lipotoxicity is mitigated by Silybum marianum

BACKGROUND AND AIMS

Silybum marianum (SM) is an herbal product with cytoprotective and antioxidant properties. We have previously demonstrated that SM ameliorates ventricular remodeling and improves cardiac performance. Here, we evaluated whether SM could exert beneficial effects against cardiac lipotoxicity in a pig model of closed-chest myocardial infarction (MI).

METHODS

Study 1 investigated the effect of SM administration on lipid profile and any potential SM-related adverse effects. Animals received SM or placebo during 10 days and were afterward sacrificed. Study 2 evaluated the effectiveness of SM daily administration in reducing cardiac lipotoxicity in animals subjected to a 1.5h myocardial infarction (MI), who were subsequently reperfused for 2.5h and euthanized or kept under study for three weeks and then sacrificed.

RESULTS

Animals administered a 10-day SM regime presented a sharp decline in plasma triglyceride levels vs. controls, with no other modifications in lipid profile. The decrease in triglyceride concentration was accompanied by a marked reduction in triglyceride intestinal absorption and glycoprotein-P expression. Three weeks post-MI the triglyceride content in the ischemic myocardium of the SM-treated animals was significantly lower than in the ischemic myocardium of placebo-controls. This effect was associated with an enhanced cardiac expression of PPARγ and triglyceride clearance receptors. This long-term SM-administration induced a lower expression of lipid receptors in subcutaneous adipose tissue. No SM-related side-effects were registered.

CONCLUSION

SM administration reduces plasma triglyceride levels through attenuation of triglyceride intestinal absorption and modulates cardiac lipotoxicity in the ischemic myocardium, likely contributing to improve ventricular remodeling.

In utero gene expression in the Slc39a8(neo/neo) knockdown mouse

Slc39a8 encodes ZIP8, a divalent cation/bicarbonate symporter expressed in pluripotent mouse embryonic stem cells, and therefore ubiquitous in adult tissues; ZIP8 influxes Zn²⁺, Mn²⁺ and Fe²⁺. Slc39a8(neo/neo) knockdown mice exhibit 10-15% of wild-type ZIP8 mRNA and protein levels, and show pleiotropic phenotype of stunted growth, neonatal lethality, multi-organ dysmorphogenesis, and dysregulated hematopoiesis manifested as severe anemia. Herein we performed RNA-seq analysis of gestational day (GD)13.5 yolk sac and placenta, and GD16.5 liver, kidney, lung, heart and cerebellum, comparing Slc39a8(neo/neo) with Slc39a8(+/+) wild-type. Meta-data analysis of differentially-expressed genes revealed 29 unique genes from all tissues - having enriched GO categories associated with hematopoiesis and hypoxia and KEGG categories of complement, response to infection, and coagulation cascade - consistent with dysregulated hematopoietic stem cell fate. Based on transcription factor (TF) profiles in the JASPAR database, and searching for TF-binding sites enriched by Pscan, we identified numerous genes encoding zinc-finger and other TFs associated with hematopoietic stem cell functions. We conclude that, in this mouse model, deficient ZIP8-mediated divalent cation transport affects zinc-finger (e.g. GATA proteins) and other TFs interacting with GATA proteins (e.g. TAL1), predominantly in yolk sac. These data strongly support the phenotype of dysmorphogenesis and anemia seen in Slc39a8(neo/neo) mice in utero.

Altered gene expression of hepatic cytochrome P450 in a rat model of intermittent hypoxia with emphysema

Patients with respiratory overlap syndrome (OS), defined as concomitant chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, may exhibit an increased blood concentration of ingested drugs. This poor elimination of drugs is primarily attributed to downregulated gene expression of the drug‑metabolizing cytochrome P450 enzymes (CYPs) in the liver. However, the underlying mechanisms of the decreased expression of CYPs in OS are poorly understood. In order to address this, a rat model of intermittent hypoxia with emphysema was evaluated in the present study, by analyzing liver gene expression using the reverse transcription‑quantitative polymerase chain reaction. Intermittent hypoxia and cigarette smoke exposure caused upregulation of hepatic inflammatory cytokines, while CYPs were downregulated. This downregulation of CYPs was associated with an increase in nuclear factor (NF)‑κB expression and a decrease in the expression of nuclear receptors pregnane X receptor, constitutive androstane receptor and glucocorticoid receptor, which are the upstream regulatory molecules of CYPs. The results of the present study indicated that, during the development of OS, systematic inflammatory reactions may downregulate hepatic CYP gene expression via the NF‑κB signaling pathway.

Characterizing the binding interactions between P-glycoprotein and eight known cardiovascular transport substrates

The multidrug efflux pump P-glycoprotein (Pgp) is upregulated in cardiomyocytes following chronic ischemia from infarction and hypoxia caused by sleep apnea. This report summarizes the molecular dynamic studies performed on eight cardiovascular drugs to determine their corresponding binding sites on mouse Pgp. Selected Pgp transport ligands include: Amiodarone, Bepridil, Diltiazem, Dipyridamole, Nicardipine, Nifedipine, Propranolol, and Quinidine. Extensive molecular dynamic equilibration simulations were performed to determine drug docking interactions. Distinct binding sites were not observed, but rather a binding belt was seen with multiple residues playing a role in each studied drug's stable docking. Three key drug–protein interactions were identified: hydrogen bonding, hydrophobic packing, and the formation of a “cage” of aromatic residues around the drug. After drug stabilization, water molecules were observed to leak into the binding belt and condense around the drug. Water influx into the binding domain of Pgp may play a role in catalytic transition and drug expulsion. The cytoplasmic recruitment theory was also tested, and the drugs were observed to interact with conserved loops of residues with a strong affinity. A free energy change of astronomical value is required to recruit the drug from the cytoplasm to the binding belt within the transmembrane domain of Pgp.

MDR1 will play a key role in pharmacokinetic changes under hypoxia at high altitude and its potential regulatory networks

Some newest studies indicated that drug transports may play the key role in pharmacokinetics changes under hypoxia at high altitude; MDR1 is now known to affect the disposition of many administered drugs and make a major contribution to absorption, distribution, metabolism, excretion. Different expression of MDR1 is frequently found in different normal tissues and tumor cells; it is important to better understand how MDR1 is regulated under hypoxia, which seems to be a complex and highly controlled process. Several signaling pathways and transcription factors have been described as being involved in the regulation of MDR1 expression, such as MAPK/ERK, nuclear factor-kappaB, hypoxia-inducible factor-1a, pregnane × receptor, constitutive androstane receptor and microRNA. Recently, researches have been increasingly appreciating long non-coding RNAs (lncRNAs) as an integral component of gene regulatory networks. lncRNAs play crucial roles in various biological processes ranging from epigenetic gene regulation, transcriptional control, post-transcriptional regulation, pre-mRNA processing and nuclear organization. A last recent research showed that H19 gene non-coding RNA is believed to induce P-glycoprotein expression under hypoxia.

Early gated SPECT adenosine myocardial perfusion imaging may influence the therapeutic management of patients with coronary artery disease

AIM

The aim of the study was to investigate whether myocardial perfusion imaging at 15 min after injection (T15) is more accurate in detecting coronary artery disease than that at 45 min (T45).

PATIENTS AND METHODS

Two-day stress/rest 99mTc-tetrofosmin gated SPECT was performed at T15 and T45 in 50 patients. Coronary angiography was considered when poststress and resting images were discordant. Tracer washout rates were calculated for the myocardium, liver, and subdiaphragmatic region. Perfusion sum difference scores were derived using QPS software.

RESULTS

T15 and T45 were discordant in 18/50 (36%) patients. In 16/18 patients (89%) discordant deficits were more apparent at T15. A total of 13/16 patients underwent coronary angiography, of whom 12 had coronary artery disease. Poststress, but not resting, left ventricular ejection fraction was lower at T15 (P=0.02). Sum difference scores were higher at T15 [2.2 (1.9)] than at T45 [1.6 (1.7); P<0.05]. Tracer washout rates from the liver [46 (13.3)%] and subdiaphragmatic region [36 (21.3)%] were significant (P<0.0001), but there was no change in myocardial activity.

CONCLUSION

T15 detected more abnormalities than did T45. The reduction in left ventricular ejection fraction after stress may result from adenosine-induced poststunning at T15. Accordingly, the T15 protocol may be useful in the assessment of hibernating myocardium. Contrasting myocardial and hepatic washout rates may be attributable to differential ABC transporter expression.

Obstructive sleep apnea and cognitive impairment: addressing the blood-brain barrier

Increasing data support a connection between obstructive sleep apnea (OSA) and cognitive impairment but a causal link has yet to be established. Although neuronal loss has been linked to cognitive impairment, emerging theories propose that changes in synaptic plasticity can cause cognitive impairment. Studies demonstrate that disruption to the blood-brain barrier (BBB), which is uniquely structured to tightly maintain homeostasis inside the brain, leads to changes in the brain's microenvironment and affects synaptic plasticity. Cyclical intermittent hypoxia is a stressor that could disrupt the BBB via molecular responses already known to occur in either OSA patients or animal models of intermittent hypoxia. However, we do not yet know if or how intermittent hypoxia can cause cognitive impairment by mechanisms operating at the BBB. Therefore, we propose that initially, adaptive homeostatic responses at the BBB occur in response to increased oxygen and nutrient demand, specifically through regulation of influx and efflux BBB transporters that alter microvessel permeability. We further hypothesize that although these responses are initially adaptive, these changes in BBB transporters can have long-term consequences that disrupt the brain's microenvironment and alter synaptic plasticity leading to cognitive impairment.

Prenatal endotoxemia and placental drug transport in the mouse: placental size-specific effects

Lipopolysaccharide (LPS) in high doses inhibits placental multidrug resistance P-glycoprotein (P-gp - Abcb1a/b) and breast cancer resistance protein (BCRP - Abcg2). This potentially impairs fetal protection against harmful factors in the maternal circulation. However, it is unknown whether LPS exposure, at doses that mimic sub-lethal clinical infection, alters placental multidrug resistance. We hypothesized that sub-lethal (fetal) LPS exposure reduces placental P-gp activity. Acute LPS (n = 19;150 µg/kg; ip) or vehicle (n = 19) were given to C57BL/6 mice at E15.5 and E17.5. Placentas and fetal-units were collected 4 and 24 h following injection. Chronic LPS (n = 6; 5 µg/kg/day; ip) or vehicle (n = 5) were administered from E11.5–15.5 and tissues were collected 4 h after final treatment. P-gp activity was assessed by [³H]digoxin accumulation. Placental Abcb1a/b, Abcg2, interleukin-6 (Il-6), Tnf-α, Il-10 and toll-like receptor-4 (Tlr-4) mRNA were measured by qPCR. Maternal plasma IL-6 was determined. At E15.5, maternal IL-6 was elevated 4 h after single (p<0.001) and chronic (p<0.05) LPS, but levels had returned to baseline by 24 h. Placental Il-6 mRNA was also increased after acute and chronic LPS treatments (p<0.05), whereas Abcb1a/b and Abcg2 mRNA were unaffected. However, fetal [³H]digoxin accumulation was increased (p<0.05) 4 h after acute LPS, and maternal [³H]digoxin myocardial accumulation was increased (p<0.05) in mice exposed to chronic LPS treatments. There was a negative correlation between fetal [³H]digoxin accumulation and placental size (p<0.0001). Acute and chronic sub-lethal LPS exposure resulted in a robust inflammatory response in the maternal systemic circulation and placenta. Acute infection decreased placental P-gp activity in a time- and gestational age-dependent manner. Chronic LPS decreased P-gp activity in the maternal myocardium and there was a trend for fetuses with smaller placentas to accumulate more P-gp substrate than their larger counterparts. Collectively, we demonstrate that acute sub-lethal LPS exposure during pregnancy impairs fetal protection against potentially harmful xenobiotics in the maternal circulation.