P-glycoprotein efflux transporter activity often displays biphasic dose-response relationships

Exposure to haloacetic acid disinfection by-products and male steroid hormones: An epidemiological and in vitro study

Haloacetic acids (HAAs) are ubiquitous in drinking water and have been associated with impaired male reproductive health. However, epidemiological evidence exploring the associations between HAA exposure and reproductive hormones among males is scarce. In the current study, the urinary concentrations of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), the internal exposure markers of HAAs, as well as sex hormones (testosterone [T], progesterone [P], and estradiol [E2]) were measured among 449 Chinese men. Moreover, in vitro experiments, designed to simulate the real-world scenarios of human exposure, were conducted to assess testosterone synthesis in the Leydig cell line MLTC-1 and testosterone metabolism in the hepatic cell line HepG2 in response to low-dose HAA exposure. The DCAA and TCAA urinary concentrations were found to be positively associated with urinary T, P, and E2 levels (all p < 0.001), but negatively associated with the ratio of urinary T to E2 (p < 0.05). Combined with in vitro experiments, the results suggest that environmentally-relevant doses of HAA stimulate sex hormone synthesis and steroidogenesis pathway gene expression in MLTC-1 cells. In addition, the inhibition of the key gene CYP3A4 involved in the testosterone phase Ⅰ catabolism, and induction of the gene UGT2B15 involved in testosterone phase Ⅱ glucuronide conjugation metabolism along with the ATP-binding cassette (ABC) transport genes (ABCC4 and ABCG2) in HepG2 cells could play a role in elevation of urinary hormone excretion upon low-dose exposure to HAAs. Our novel findings highlight that exposure to HAAs at environmentally-relevant concentrations is associated with increased synthesis and excretion of sex hormones in males, which potentially provides an alternative approach involving urinary hormones for the noninvasive evaluation of male reproductive health following exposure to DBPs.

Non-Nutritive Sweeteners Acesulfame Potassium and Sucralose Are Competitive Inhibitors of the Human P-glycoprotein/Multidrug Resistance Protein 1 (PGP/MDR1)

Non-nutritive sweeteners (NNS) are popular sugar replacements used in foods, beverages, and medications. Although NNS are considered safe by regulatory organizations, their effects on physiological processes such as detoxification are incompletely understood. Previous studies revealed that the NNS sucralose (Sucr) altered P-glycoprotein (PGP) expression in rat colon. We also demonstrated that early-life exposure to NNS Sucr and acesulfame potassium (AceK) compromises mouse liver detoxification. Building upon these initial discoveries, we investigated the impact of AceK and Sucr on the PGP transporter in human cells to assess whether NNS influence its key role in cellular detoxification and drug metabolism. We showed that AceK and Sucr acted as PGP inhibitors, competing for the natural substrate-binding pocket of PGP. Most importantly, this was observed after exposure to concentrations of NNS within expected levels from common foods and beverage consumption. This may suggest risks for NNS consumers, either when taking medications that require PGP as the primary detoxification transporter or during exposure to toxic compounds.

Hormesis: A potential strategic approach to the treatment of neurodegenerative disease

This review describes neuroprotective effects mediated by pre- and post-conditioning-induced processes that act via the quantitative features of the hormetic dose response. These lead to the development of acquired resilience that can protect neuronal systems from endogenous and exogenous stresses and insult. Particular attention is directed to issues of dose optimization, inter-individual variation, and potential ways to further study and employ hormetic-based preconditioning approaches in medical and public health efforts to treat and prevent neurodegenerative disease.

Leaf Extracts from Dillenia philippinensis Rolfe Exhibit Cytotoxic Activity to both Drug-Sensitive and Multidrug-Resistant Cancer Cells

Background:

Cancer is one of the leading causes of illness and death worldwide. Only palliative therapeutic options are available for many types of cancers, and most anticancer drugs in clinical use exhibit significant side effects. It is therefore important to develop new anticancer drugs that are more effective and less toxic. In this study, we evaluate the bioactivity of a Philippine endemic plant, “katmon” or Dillenia philippinensis, and its potential use in cancer therapy.

Methods:

The cytotoxicity of the crude leaf extract, partitions, and isocratic column chromatography fractions of Dillenia philippinensis was determined in vitro by MTT assay against drug-sensitive cancer cell lines MCF7 (human breast adenocarcinoma) and HCT 116 (human colorectal carcinoma), as well as against moderately multidrug resistant (MDR) cancer cell line HCT-15 (human colorectal carcinoma) and its highly MDR subline HCT-15/Dox. The selectivity of the extract to cancer cells was determined by computing for the selectivity index (SI) with respect to normal mouse embryonic fibroblasts (NIH/3T3) cell line. To check for a possible mechanism for overcoming cancer multiple drug resistance, Calcein-AM assay was performed to assess the activity of the extract against P-glycoprotein-activated efflux pump.

Results:

Dillenia philippinensis (DP1) fraction from the hexane partition exhibited cytotoxicity (IC₅₀< 30 µg/ml) against MCF7, HCT 116, HCT-15, and HCT-15/Dox cells. DP1 also exhibited a moderate level of selectivity against cancer cells over normal cells as supported by the SI computed from the IC₅₀ value obtained for the normal cell line. DP1 was able to inhibit P-glycoprotein (P-gp) activity in a dose-dependent manner, suggesting its possible role in targeting cancer cells with overexpressed P-gp.

Conclusion:

The present findings thus demonstrate the potential chemotherapeutic properties of D. philippinensis which can be promising for future drug development against cancer.

Toxicology of Avermectins and Milbemycins (Macrocyclic Lactones) and the Role of P-Glycoprotein in Dogs and Cats

Overdoses of macrocyclic lactones in dogs and cats can result in such signs as tremors, ataxia, seizures, coma, and blindness. Dogs with the ABCB1-1Δ gene defect are predisposed to macrocyclic lactone toxicosis at lower dosages than dogs without the defect. Intravenous lipid emulsion therapy has been suggested for treatment of macrocyclic lactone toxicosis but evidence of efficacy is limited. Initial decontamination and supportive care remain the mainstays of therapy for macrocyclic lactone toxicosis.

A Conformationally Gated Model of Methadone and Loperamide Transport by P-Glycoprotein

P-glycoprotein (Pgp) is a multidrug resistance transporter that limits the penetration of a wide range of neurotherapeutics into the brain including opioids. The diphenylpropylamine opioids methadone and loperamide are structurally similar, but loperamide has about a 4-fold higher Pgp-mediated transport rate. In addition to these differences, they showed significant differences in their effects on Pgp-mediated adenosine triphosphate (ATP) hydrolysis. The activation of Pgp-mediated ATP hydrolysis by methadone was monophasic, whereas loperamide activation of ATP hydrolysis was biphasic implying methadone has a single binding site and loperamide has 2 binding sites on Pgp. Quenching of tryptophan fluorescence with these drugs and digoxin showed competition between the opioids and that loperamide does not compete for the digoxin-binding site. Acrylamide quenching of tryptophan fluorescence to probe Pgp conformational changes revealed that methadone- and loperamide-induced conformational changes were distinct. These results were used to develop a model for Pgp-mediated transport of methadone and loperamide where opioid binding and conformational changes are used to explain the differences in the opioid transport rates between methadone and loperamide.

Exploring Jolkinol D Derivatives To Overcome Multidrug Resistance in Cancer

Macrocyclic monoacyl lathyrane derivatives bearing a benzoyl moiety were previously found to be strong ABCB1 modulators. To explore the effects of different substituents of the aromatic moiety, 14 new compounds (1.1-1.7, 1.10, and 2.1-2.4) were prepared from jolkinol D (1), obtained from Euphorbia piscatoria, and from jolkinodiol (2), its hydrolysis derivative. Compounds 1.8 and 1.9, having aliphatic moieties, were also obtained. The reversal of ABCB1-mediated MDR was evaluated through functional and chemosensitivity assays on the human ABCB1-gene-transfected L5178Y mouse T-lymphoma cell line. Structure-activity relationships showed that addition of electron-donating groups to the aromatic moiety improved the activity. The effects on the ATPase activity of the strongest modulator (1.3) and the inactive jolkinol D (1) were also investigated and compared. Moreover, in the chemosensitivity assay, most of the compounds interacted synergistically with doxorubicin. Compounds 1.1-1.10 and 2.1-2.4 were further assessed for their collateral sensitivity effect against the human cancer cells: EPG85-257 (gastric) and EPP85-181 (pancreatic), and the matching drug-selected cells EPG85-257RDB, EPG85-257RNOV, EPP85-181RDB, and EPP85-181RNOV. The most promising ones (1.8 and 1.10) along with compound 3, previously selected, were investigated as apoptosis inducers. The compounds were able to induce apoptosis through caspase-3 activation, with significant differences being observed between the parental and resistant cells.

Evaluation of the in vitro expression of ATP binding-cassette (ABC) proteins in an Ixodes ricinus cell line exposed to ivermectin

Background

Ticks are among the most important vectors of pathogens causing human and animal disease. Acaricides are used to control tick infestation, although there are increasing reports of resistance. Recently, over-expression of ATP-binding cassette (ABC) transporter proteins (P-glycoproteins, PgP) has been implicated in resistance to the acaricide ivermectin in the ticks Rhipicephalus (Boophilus) microplus and Rhipicephalus sanguineus sensu lato. Ixodid tick cell lines have been used to investigate drug resistance mechanisms. The aim of the present study was to evaluate expression of several PgPs in the Ixodes ricinus-derived cell line IRE/CTVM19 and to determine modulation of expression following treatment with ivermectin.

Findings

IRE/CTVM19 cells were treated with different concentrations of ivermectin (0, 11, 22 or 33 μM) and incubated for 10 days. Evaluation of viability and relative expression of ABCB1, ABCB6, ABCB8 and ABCB10 genes were carried out at day 10 post treatment. Cell viability ranged between 84 % and 92 % with no significant differences between untreated and treated cells. qRT-PCR showed that ABC pump expression was not significantly modulated by ivermectin treatment. Expression of the ABCB8 PgP subfamily revealed a biphasic trend, based on the ivermectin concentration. ABCB6 and ABCB10 gene expression was not modulated by ivermectin treatment and ABCB1 expression was not detected.

Conclusions

This is the first report of PgP expression in an I. ricinus-derived tick cell line. Development of an in vitro model for the study of acaricide resistance mechanisms would greatly facilitate screening for drug resistance in ticks.

A phase I pharmacokinetics study of lapatinib and tamoxifen in metastatic breast cancer (EORTC 10053 Lapatam study)

OBJECTIVE

This phase I study assessed the pharmacokinetic (PK), tolerability, safety and preliminary clinical activity of tamoxifen (T) and lapatinib (L) in patients with metastatic breast cancer (MBC).

METHODS

Patients (pts) with hormone receptor positive MBC, irrespective of HER-2 status, were randomly assigned to T → T + L group, tamoxifen in cycle 1 for 28 days then adding lapatinib on day 1 of cycle 2; or L → T + L group, lapatinib in cycle 1 for 14 days, then adding tamoxifen on day 1 of cycle 2 to evaluate the potential drug-drug PK interaction at steady-state. The dose of tamoxifen was 20 mg/day and lapatinib 1500 mg/day.

RESULTS

Twenty-five pts were enrolled of which 23 started treatment, five (22%) of them were HER-2 positive. Median age was 59 years and 96% had PS ≤1. Eleven (91.7%) pts in the T → T + L group and 10 (76.9%) in L → T + L group received at least 2 cycles of treatment. The most frequently reported drug-related adverse events (>25% of patients) were diarrhoea (62%), anaemia (56%), rash (52%), fatigue (52%), dermatology other (34%) and leukopenia (28%). Grade 3-4 drug-related toxicities were infrequent (<10%). No cardiotoxicity was observed. T plasma concentrations did not appeared to be affected by the presence of lapatinib. L steady-state plasma concentrations were 20% lower after 28 days of co-administration with T. Eight (36.4%) patients experienced stable disease and median progression free survival was 2.7 months.

CONCLUSIONS

The combination of L and T was safe and clinically active. T affected L plasma concentrations, which remained within the therapeutic index.

Acetaminophen inhibits intestinal p-glycoprotein transport activity

Repeated acetaminophen (AP) administration modulates intestinal P-glycoprotein (P-gp) expression. Whether AP can modulate P-gp activity in a short-term fashion is unknown. We investigated the acute effect of AP on rat intestinal P-gp activity in vivo and in vitro. In everted intestinal sacs, AP inhibited serosal-mucosal transport of rhodamine 123 (R123), a prototypical P-gp substrate. R123 efflux plotted against R123 concentration adjusted well to a sigmoidal curve. Vmax decreased 50% in the presence of AP, with no modification in EC50, or slope, ruling out the possibility of inhibition to be competitive. Inhibition by AP was absent at 0°C, consistent with interference of the active transport of R123 by AP. Additionally, AP showed no effect on normal localization of P-gp at the apical membrane of the enterocyte and neither affected paracellular permeability. Consistent with absence of a competitive inhibition, two further strategies strongly suggested that AP is not a P-gp substrate. First, serosal-mucosal transport of AP was not affected by the classical P-gp inhibitors verapamil or Psc 833. Second, AP accumulation was not different between P-gp knock-down and wild-type HepG2 cells. In vivo intestinal absorption of digoxin, another substrate of P-gp, was assessed in the presence or absence of AP (100 μM). Portal digoxin concentration was increased by 214%, in average, by AP, as compared with digoxin alone. In conclusion, AP inhibited P-gp activity, increasing intestinal absorption of digoxin, a prototypical substrate. These results suggest that therapeutic efficacy of P-gp substrates can be altered if coadministered with AP.

Hormesis: its impact on medicine and health

This article offers a broad assessment of the hormetic dose response and its relevance to biomedical researchers, physicians, the pharmaceutical industry, and public health scientists. This article contains a series of 61 questions followed by relatively brief but referenced responses that provides support for the conclusion that hormesis is a reproducible phenomenon, commonly observed, with a frequency far greater than other dose-response models such as the threshold and linear nonthreshold dose-response models. The article provides a detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how hormesis is currently being used within medicine and identifying how this concept could be further applied in the development of new therapeutic advances and in improved public health practices.

Toxicology of avermectins and milbemycins (macrocylic lactones) and the role of P-glycoprotein in dogs and cats

The macrocyclic lactones (MLs) are parasiticides able to kill a wide variety of arthropods and nematodes. They have a high margin of safety for labeled indications, and ivermectin has become the best-selling antiparasitic in the world. Dogs of certain breeds and mixtures of those breeds have a defect in the ABCB1 gene (formerly MDR1 gene) that results in a lack of functional P-glycoprotein, which leads to accumulation of the MLs in the central nervous system and a higher risk of adverse effects when exposed. There is no specific antidote for ML toxicosis so the most important part of treatment is good supportive care.

Cellular stress responses, hormetic phytochemicals and vitagenes in aging and longevity

Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This paper introduces the emerging role of exogenous molecules in hormetic-based neuroprotection and the mitochondrial redox signaling concept of hormesis and its applications to the field of neuroprotection and longevity. Maintenance of optimal long-term health conditions is accomplished by a complex network of longevity assurance processes that are controlled by vitagenes, a group of genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin and the sirtuin protein systems. Dietary antioxidants, such as polyphenols and L-carnitine/acetyl-L-carnitine, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. Hormesis provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose response relationships, their mechanistic foundations, their relationship to the concept of biological plasticity as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This paper describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways including sirtuin, Nrfs and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Hormesis, cellular stress response and vitagenes as critical determinants in aging and longevity

Understanding mechanisms of aging and determinants of life span will help to reduce age-related morbidity and facilitate healthy aging. Average lifespan has increased over the last centuries, as a consequence of medical and environmental factors, but maximal life span remains unchanged. Extension of maximal life span is currently possible in animal models with measures such as genetic manipulations and caloric restriction (CR). CR appears to prolong life by reducing reactive oxygen species (ROS)-mediated oxidative damage. But ROS formation, which is positively implicated in cellular stress response mechanisms, is a highly regulated process controlled by a complex network of intracellular signaling pathways. By sensing the intracellular nutrient and energy status, the functional state of mitochondria, and the concentration of ROS produced in mitochondria, the longevity network regulates life span across species by co-ordinating information flow along its convergent, divergent and multiply branched signaling pathways, including vitagenes which are genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin and the sirtuin protein systems. Dietary antioxidants, such as carnosine, carnitines or polyphenols, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. The hormetic dose-response, challenges long-standing beliefs about the nature of the dose-response in a lowdose zone, having the potential to affect significantly the design of pre-clinical studies and clinical trials as well as strategies for optimal patient dosing in the treatment of numerous diseases. Given the broad cytoprotective properties of the heat shock response there is now strong interest in discovering and developing pharmacological agents capable of inducing stress responses. In this review we discuss the most current and up to date understanding of the possible signaling mechanisms by which caloric restriction, as well hormetic caloric restriction-mimetics compounds by activating vitagenes can enhance defensive systems involved in bioenergetic and stress resistance homeostasis with consequent impact on longevity processes.

Cellular stress responses, the hormesis paradigm, and vitagenes: novel targets for therapeutic intervention in neurodegenerative disorders

Despite the capacity of chaperones and other homeostatic components to restore folding equilibrium, cells appear poorly adapted for chronic oxidative stress that increases in cancer and in metabolic and neurodegenerative diseases. Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This article introduces the concept of hormesis and its applications to the field of neuroprotection. It is argued that the hormetic dose response provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose-response relationships, their mechanistic foundations, and their relationship to the concept of biological plasticity, as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This article describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways, including sirtuin and Nrf2 and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. Particular attention is given to the emerging role of nitric oxide, carbon monoxide, and hydrogen sulfide gases in hormetic-based neuroprotection and their relationship to membrane radical dynamics and mitochondrial redox signaling.

Hormesis is central to toxicology, pharmacology and risk assessment

This paper summarizes numerous conceptual and experimental advances over the past two decades in the study of hormesis. Hormesis is now generally accepted as a real and reproducible biological phenomenon, being highly generalized and independent of biological model, endpoint measured and chemical class/physical stressor. The quantitative features of the hormetic dose response are generally highly consistent, regardless of the model and mechanism, and represent a quantitative index of biological plasticity at multiple levels of biological organization. The hormetic dose-response model has been demonstrated to make far more accurate predictions of responses in low dose zones than either the threshold or linear at low dose models. Numerous therapeutic agents widely used by humans are based on the hormetic dose response and its low dose stimulatory characteristics. It is expected that as low dose responses come to dominate toxicological research that risk assessment practices will incorporate hormetic concepts in the standard setting process.

Vitagenes, cellular stress response, and acetylcarnitine: relevance to hormesis

Modulation of endogenous cellular defense mechanisms via the stress response signaling represents an innovative approach to therapeutic intervention in diseases causing chronic damage, such as neurodegeneration and cancer. Protein thiols play a key role in redox sensing, and regulation of cellular redox state is crucial mediator of multiple metabolic, signaling, and transcriptional processes. Maintenance of optimal long-term health conditions is accomplished by a complex network of longevity assurance processes that are controlled by vitagenes, a group of genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin, and the sirtuin protein systems. Dietary antioxidants, such as polyphenols and L-carnitine/acetyl-L-carnitine, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. The hormetic dose-response, challenges long-standing beliefs about the nature of the dose-response in a low dose zone, having the potential to affect significantly the design of pre-clinical studies and clinical trials as well as strategies for optimal patient dosing in the treatment of numerous diseases. Given the broad cytoprotective properties of the heat shock response, there is now strong interest in discovering and developing pharmacological agents capable of inducing these responses. In this review we discuss the most current and up-to-date understanding of the possible signaling mechanisms by which acetylcarnitine by activating vitagenes can differentially modulate signal transduction cascades inducing apoptosis/cell death in abnormal cancer cells but at the same time enhancing defensive enzymes to protect against carcinogenesis and neurodegeneration in normal cells. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.