Effect of hypoxia alone or combined with inflammation and 3-methylcholanthrene on hepatic cytochrome P450 in conscious rabbits

New strategy for rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments

High-altitude hypoxic environments have critical implications on cardiovascular system function as well as blood pressure regulation. Such environments place patients with hypertension at risk by activating the sympathetic nervous system, which leads to an increase in blood pressure. In addition, the high-altitude hypoxic environment alters the in vivo metabolism and antihypertensive effects of antihypertensive drugs, which changes the activity and expression of drug-metabolizing enzymes and drug transporters. The present study reviewed the pharmacodynamics and pharmacokinetics of antihypertensive drugs and its effects on patients with hypertension in a high-altitude hypoxic environment. It also proposes a new strategy for the rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments. The increase in blood pressure on exposure to a high-altitude hypoxic environment was mainly dependent on increased sympathetic nervous system activity. Blood pressure also increased proportionally to altitude, whilst ambulatory blood pressure increased more than conventional blood pressure, especially at night. High-altitude hypoxia can reduce the activities and expression of drug-metabolizing enzymes, such as CYP1A1, CYP1A2, CYP3A1, and CYP2E1, while increasing those of CYP2D1, CYP2D6, and CYP3A6. Drug transporter changes were related to tissue type, hypoxic degree, and hypoxic exposure time. Furthermore, the effects of high-altitude hypoxia on drug-metabolism enzymes and transporters altered drug pharmacokinetics, causing changes in pharmacodynamic responses. These findings suggest that high-altitude hypoxic environments affect the blood pressure, pharmacokinetics, and pharmacodynamics of antihypertensive drugs. The optimal hypertension treatment plan and safe and effective medication strategy should be formulated considering high-altitude hypoxic environments.

High-altitude Hypoxia Influences the Activities of the Drug-Metabolizing Enzyme CYP3A1 and the Pharmacokinetics of Four Cardiovascular System Drugs

(1) Background: High-altitude hypoxia has been shown to affect the pharmacokinetic properties of drugs. Although there is a high incidence of cardiovascular disease among individuals living in high-altitude areas, studies on the effect of high-altitude hypoxia on the pharmacokinetic properties of cardiovascular drugs are limited. (2) Methods: The aim of this study was to evaluate the pharmacokinetics of nifedipine, bosentan, simvastatin, sildenafil, and their respective main metabolites, dehydronifedipine, hydroxybosentan, simvastatin hydroxy acid, and N-desmethyl sildenafil, in rats exposed to high-altitude hypoxia. Additionally, the protein and mRNA expression of cytochrome P450 3A1 (CYP3A1), a drug-metabolizing enzyme, were examined. (3) Results: There were significant changes in the pharmacokinetic properties of the drugs in rats exposed to high-altitude hypoxia, as evidenced by an increase in the area under the curve (AUC) and the half-life (t_1/2z) and a decrease in total plasma clearance (CL_z/F). However, most of these changes were reversed when the rats returned to a normoxic environment. Additionally, there was a significant decrease in CYP3A1 expression in rats exposed to high-altitude hypoxia at both the protein and mRNA levels. (4) Conclusions: High-altitude hypoxia suppressed the metabolism of the drugs, indicating that the pharmacokinetics of the drugs should be re-examined, and the optimal dose should be reassessed in patients living in high-altitude areas.

Intermittent Hypoxia Inhibits Hepatic CYP1a2 Expression and Delays Aminophylline Metabolism

Purpose

In this study, we aimed to determine the effects of intermittent hypoxia (IH) on hepatic cytochrome P450 1A2 (CYP1A2) expression and the pharmacokinetics of CYP1A2-mediated aminophylline and warfarin in vitro and in a rabbit model of obstructive sleep apnea.

Materials

Human normal liver (LO-2) cells were exposed to 30 min each of 1%, 1–21%, 21%, and 21–1% O₂, and then, CYP1A2 expression and drug concentrations were analyzed. We compared the pharmacokinetic parameters of drugs administered to normoxic rabbits and those exposed to 10 min of IH during which the oxygen level fluctuated from 21% to 8%–10% (n = 10 per group).

Result

s. The expression of CYP1A2 protein in vitro was significantly reduced in the IH compared with the normoxic cells (0.56 ± 0.11 vs. 1.27 ± 0.17, p < 0.001). Aminophylline was more abundant in cell culture supernatants after 48 h of IH than in those under normoxia. The T_1/2, AUC_0–24 h, and Ke values for aminophylline were significantly higher in the IH group.

Conclusion

Intermittent hypoxia inhibits hepatic CYP1A2 expression and delays aminophylline metabolism, suggesting that the impact of IH on the expression of CYP enzymes should be closely monitored in clinical practice.

Gut Microbiota as the Potential Mechanism to Mediate Drug Metabolism Under High-Altitude Hypoxia

BACKGROUND

The characteristics of pharmacokinetics and the activity and expression of drug-metabolizing enzymes and transporters significantly change under a high-altitude hypoxic environment. Gut microbiota is an important factor affecting the metabolism of drugs through direct or indirect effects, changing the bioavailability, biological activity, or toxicity of drugs and further affecting the efficacy and safety of drugs in vivo. A high-altitude hypoxic environment significantly changes the structure and diversity of gut microbiota, which may play a key role in drug metabolism under a high-altitude hypoxic environment.

METHODS

An investigation was carried out by reviewing published studies to determine the role of gut microbiota in the regulation of drug-metabolizing enzymes and transporters. Data and information on expression change in gut microbiota, drug-metabolizing enzymes and transporters under a high-altitude hypoxic environment were explored and proposed.

RESULTS

High-altitude hypoxia is an important environmental factor that can adjust the structure of the gut microbiota and change the diversity of intestinal microbes. It was speculated that the gut microbiota could regulate drug-metabolizing enzymes through two potential mechanisms, the first being through direct regulation of the metabolism of drugs in vivo and the second being indirect, i.e., through the regulation of drug-metabolizing enzymes and transporters, thereby affecting the activity of drugs.

CONCLUSION

This article reviews the effects of high-altitude hypoxia on the gut microbiota and the effects of these changes on drug metabolism.

Exposure to High-Altitude Environment is Associated with Drug Transporters Change: miR-873-5p-Mediated Alteration of Function and Expression Levels of Drug Transporters under Hypoxia

Hypoxia is the main characteristic of a high-altitude environment, affect ing drug metabolism. However, so far, the mechanism of miRNA involved in the regulation of drug metabolism and transporters under high-altitude hypoxia is still unclear. This study aims to investigate the function s and expression levels of multidrug resistance protein 1 ( MDR1 ), m ultidrug resistance-associated protein 2 ( MRP2 ), breast cancer resistance protein ( BCRP ) , peptide transport 1 (PEPT1), and organic anion-transporting polypeptides 2B1 (OATP2B1) in rats and Caco-2 cells after exposure to high - altitude hypoxia. The protein and mRNA expression of MDR1 , MRP2, BCRP, PEPT1, and OATP2B1 were determined by Western blot and qPCR. The function s of MDR1 , MRP2, BCRP, PEPT1, and OATP2B1 were evaluated by determining the effective intestinal permeability and a bsorption rate constants of their specific substrates in rats under high-altitude hypoxia , and uptake and transport studies were performed on Caco-2 cells . To screen the miRNA associated with hypoxia, Caco-2 cells were examined by high throughput sequencing . We observed that the miR-873-5p was significantly decreased under hypoxia and might target MDR1 and pregnane X receptor ( PXR). To clarify whether miR-873-5p regulates MDR1 and pregnane X receptor (PXR) under hypoxia, Caco-2 cells were transfected with mimics or inhibitors of miR-873-5p and negative control (NC). The function and expression of drug transporters were found to be significantly increased in rats and Caco-2 cells under hypoxia. We found that miR-873-5p regulated MDR1 and PXR expression. Herein, it is shown that miRNA may affect the expression of drug transporter and nuclear receptor under hypoxia. Significance Statement This study explores if alterations to the microRNAs, induced by high-altitude hypoxia, can be translated to altered drug transporters. Among miRNAs, which show a significant change in a hypoxic environment, miR-873-5p can act on the MDR1 gene; however, there are multiple miRNAs that can act on the PXR. We speculate that the miRNA-PXR-Drug transporter axis is important in the physiological disposition of drugs. The results of this study are anticipated to be helpful for rational pharmaceutical use in high - altitude environments .

Reduced theophylline clearance due to hepatic congestion secondary to right heart failure - A population pharmacokinetic study

Theophylline, a beneficial drug with bronchodilatory and anti-inflammatory effects, is used for the treatment of respiratory diseases. Pulmonary (PC) and hepatic congestion (HC) are secondary to the development of left- and right-sided heart failure (HF), respectively. This study aimed to evaluate the effects of PC and HC on theophylline clearance (CL) by population pharmacokinetic (PPK) analysis with consideration of the severity of HF assessed by the New York Heart Association (NYHA) functional classification. We obtained 710 minimum steady-state concentrations from 201 Japanese bronchial asthma patients with and without HF. PPK analysis was performed by NONMEM. In the analysis, the left ventricular ejection fraction, smoking (SMK), clarithromycin (CAM), sex, and age were also considered as covariates. The final model of apparent theophylline clearance (CL/F) was as follows: CL/F (L/hr/kg) = 0.0465 × 1.40^SMK × 0.870^CAM × 0.863^{HC(+)NYHA II} × 0.634^{HC(+)NYHA III} × 0.586^{HC(-)NYHA IV} × 0.467^{HC(+)NYHA IV}. SMK is a well-known factor that markedly enhances theophylline clearance through the induction of CYP1A enzymes, while CAM has been reported to inhibit CYP3A4. The final model indicates that HF patients with HC show reduced clearance of theophylline depending on the severity of HF. In this study, no effects of PC were observed.

The activity, protein, and mRNA expression of CYP2E1 and CYP3A1 in rats after exposure to acute and chronic high altitude hypoxia

The effects of exposure to acute and chronic high altitude hypoxia on the activity and expression of CYP2E1 and CYP3A1 were examined in rats. Rats were divided into low altitude (LA, 400 m), acute moderate altitude hypoxia (AMH, 2800 m), chronic moderate altitude hypoxia (CMH, 2800 m), acute high altitude hypoxia (AHH, 4300 m), and chronic high altitude hypoxia groups (CHH, 4300 m). Probe drugs were administrated orally to all five groups. Then the serum concentration of probe drug and its metabolite was determined by RP-HPLC. The activity of CYP2E1 and CYP3A1 was evaluated using the ratio of the metabolite to chlorzoxazone and testosterone, respectively. ELISA and real-time PCR were used to analyze the protein and mRNA expression of CYP2E1 and CYP3A1 in liver microsomes, respectively. Chronic high altitude hypoxia caused significant decreases in the activity and protein and mRNA expression of rat CYP2E1 and CYP3A1 in vivo. Acute high altitude hypoxia was not found to change the activity, protein or mRNA expression of rat CYP2E1 or CYP3A1. This study showed significant changes in the activity and protein and mRNA expression of CYP2E1 or CYP3A1 in rats after exposure to chronic high altitude hypoxia.

Effect of erythropoietin on hepatic cytochrome P450 expression and function in an adenine-fed rat model of chronic kidney disease

BACKGROUND AND PURPOSE

Erythropoietin (EPO) is used to treat anaemia associated with chronic kidney disease (CKD). Hypoxia is associated with anaemia and is known to cause a decrease in cytochrome P450 (P450) expression. As EPO production is regulated by hypoxia, we investigated the role of EPO on P450 expression and function.

EXPERIMENTAL APPROACH

Male Wistar rats were subjected to a 0.7% adenine diet for 4 weeks to induce CKD. The diet continued for an additional 2 weeks while rats received EPO by i.p. injection every other day. Following euthanasia, hepatic P450 mRNA and protein expression were determined. Hepatic enzyme activity of selected P450s was determined and chromatin immunoprecipitation was used to characterize binding of nuclear receptors involved in the transcriptional regulation of CYP2C and CYP3A.

KEY RESULTS

EPO administration decreased hepatic mRNA and protein expression of CYP3A2 (P < 0.05), but not CYP2C11. Similarly, EPO administration decreased CYP3A2 protein expression by 81% (P < 0.001). A 32% decrease (P < 0.05) in hepatic CYP3A enzymatic activity (Vmax ) was observed for the formation of 6βOH-testosterone in the EPO-treated group. Decreases in RNA pol II recruitment (P < 0.01), hepatocyte nuclear factor 4α binding (P < 0.05) and pregnane X receptor binding (P < 0.01) to the promoter region of CYP3A were also observed in EPO-treated rats.

CONCLUSIONS AND IMPLICATIONS

Our data show that EPO decreases the expression and function of CYP3A, but not CYP2C in rat liver.

Effect of exposure to acute and chronic high-altitude hypoxia on the activity and expression of CYP1A2, CYP2D6, CYP2C9, CYP2C19 and NAT2 in rats

We investigated the effect of exposure to acute and chronic high-altitude hypoxia (AHH and CHH) on the activity and expression of CYP1A2, CYP2D6, CYP2C9, CYP2C19 and NAT2 in rats. The rats were divided into plain (400 m), acute middle-altitude hypoxia (2,800 m), chronic middle-altitude hypoxia (2,800 m), AHH (4,300 m) and CHH (4,300 m). After probe drugs had been orally administered to the rats of the 5 groups, the serum or urine concentration of the probe drug and its metabolite was determined by reversed-phase HPLC. The activity of cytochrome P450 isozyme and NAT2 was evaluated by the ratio of the metabolite to the probe drug. The ELISA and real-time PCR were used to analyze the protein and mRNA expression of cytochrome P450 isozyme and NAT2, respectively. AHH and CHH caused significant decreases in the activity and protein and mRNA expression of rat CYP1A2 in vivo. AHH downregulates the activity and mRNA expression of rat NAT2 in vivo, and CHH upregulates the activity and protein and mRNA expression of rat CYP2D6. AHH and CHH did not change the expression of CYP2C9 and CYP2C19 in rats. This study found significant changes in the activity and protein and mRNA expression of CYP1A2, CYP2D6 and NAT2 in rats in the special environment of high-altitude hypoxia.

Effect of intermittent hypobaric hypoxia on efficacy & clearance of drugs

BACKGROUND & OBJECTIVES

People travelling to high altitude for occupational, recreational or religious purposes are mostly healthy and fit but sometimes they use drugs for common ailments like influenza, acute mountain sickness or chronic disease like diabetes. Limitation of oxygen at high altitude may compromise metabolism of drugs. Hence, we undertook this study to assess the effect of hypobaric hypoxia on some commonly used drugs in rats and rabbits.

METHODS

Effect of intermittent hypobaric hypoxia on phenotypic expression of anesthetic drugs pentabarbitone, thiopentone and zoxazolamine (sleeping time) was assessed in rats exposed to 282.4 mm Hg equivalent to 25000 feet in a decompression chamber. Plasma clearance of some commonly used drugs was investigated in rabbits exposed to 429 mm Hg equivalent to 15000 feet. Pharmacokinetic parameters were computed by plotting drug concentration versus time curve on semi log scale.

RESULTS

A significant delay in regaining rightening reflex was observed in rats exposed to intermittent hypobaric hypoxia in response to zoxazolamine, pentobarbitone and thiopentone sodium. Pharmacokinetics of acetyl salicylic acid, gentamicin, phenobarbitone and acetazolamide showed increase in plasma half life (t 1/2), decrease in elimination rate constant (k el) and hence prolonged residence of these drugs in hypoxic animals.

INTERPRETATION & CONCLUSIONS

This experimental study showed that hypoxia altered therapeutic effectiveness and clearance of several drugs, in rats and rabbits exposed to intermittent hypobaric hypoxia. s0 uch studies need to be done in human volunteers to see the effect of hypoxia on pharmacokinetics of some common drugs.

The gastrointestinal effects that may follow the administration of theophylline reflect the pharmacodynamic profiles of both the parent drug and its metabolites

This study investigates the effect of theophylline along the rabbit gastrointestinal tract in comparison with the pharmacodynamic effect produced by the combined application of its three major metabolites. At concentrations up to 10(-3) m, theophylline relaxed, in a declining order from the lower oesophageal sphincter (LOS) to pylorus, all regions of the upper gastrointestinal tract, but only the ascending colon from the intestinal regions studied. At concentrations higher than 10(-3) m, instead of relaxing, theophylline strongly contracted the antrum and pylorus. In all three small intestinal regions, at concentrations up to 10(-3) m, theophylline produced a weak contraction, which at higher concentrations became very strong, and at 10(-2) m was comparable to that produced by a supramaximal dose of acetylcholine. The additive relaxing effect resulting from the combined application of the theophylline's metabolites was, from oesophagus to pylorus, weaker than that produced by theophylline, while on the ascending colon it was comparable to that of the parent drug. In contrast, the additive contractile effect of the metabolites on the three small intestinal regions was four to five times higher the one produced by theophylline. In conclusion, this study shows that the additive effect of the combined application of theophylline's major metabolites on the rabbit gastrointestinal tract plays a major role in the final response of the intestine, and a minor one in the final responses of the gastric regions, while both the parent drug and the metabolites contribute to the final responses of the oesophagus and LOS.

Relaxing and contracting effects of theophylline's metabolites on the rabbit upper gastrointestinal tract

The present study, aimed to clarify whether the gastrointestinal adverse effects following administration of the bronchodilator theophylline are owing to the action of the drug itself or its metabolites, investigates the pharmacodymanic effects of theophylline's metabolites on the spontaneous contractility in the rabbit upper gastrointestinal tract. Comparative examination reveals that while two of the metabolites, namely 1-methylxanthine (1-MX) and 3-methylxanthine (3-MX), cause a similar, but less pronounced than the parent drug, concentration-dependent relaxation on the isolated oesophagus, lower oesophageal sphincter (LOS), fundus, antrum and pylorus, the remaining two metabolites, 1,3-dimethyluric acid (1,3-DMU) and 1-methyluric acid (1-MU), produce either a weak stimulating effect, or an even weaker relaxation. The relaxation which is muscle-mediated, non-adrenergic non-cholinergic (NANC) and nitric oxide (NO)-independent is probably mediated via inhibition of the metabolites on phosphodiesterases (PDEs), while a presynaptic cholinergic pathway is involved in the weak stimulating effect. The effects of all substances are additive. As a consequence, the net result of the cumulative action of all metabolites in the oesophagus, LOS, antrum and pylorus is, at 10(-3) m, comparable with that of theophylline, but in the fundus it is lower than that of the parent drug, because in the latter tissue the stimulating effect of 1,3-DMU and 1-MU counteracts the relaxing effect of the other two metabolites. However, combination of the parent drug with its metabolites leads to a considerable relaxation in all the gastrointestinal regions extending from the oesophagus to pylorus. Conclusively, upper gastrointestinal adverse effects following theophylline's administration are also because of theophylline's metabolites.

Animal models of acute moderate hypoxia are associated with a down-regulation of CYP1A1, 1A2, 2B4, 2C5, and 2C16 and up-regulation of CYP3A6 and P-glycoprotein in liver

In humans, indirect evidence suggests that hypoxia reduces the rate of biotransformation of drugs cleared by cytochrome P450 (P450) subfamilies CYP1A, 2B, and 2C. The aim of this study was to assess whether acute moderate hypoxia modulates the expression of CYP2B4, 2C5, and 2C16 in vivo, and to determine whether the changes in hepatic P450 are conveyed by serum mediators. Moreover, because hypoxia increases the expression of P-glycoprotein in vitro, we examined whether in vivo acute moderate hypoxia modulates the expression of several membrane transporters in the liver. Rabbits and rats were exposed to a fractional concentration of oxygen of 8% for 48 h to generate a stable arterial partial pressure of O2 of 34 +/- 1 mm Hg. Compared with rabbits breathing room air, hypoxia in rabbits reduced the amount of CYP1A1, 1A2, 2B4, 2C5, and 2C16 proteins and increased the expression of CYP3A6. Sera of rabbits with hypoxia were fractionated by size exclusion chromatography, the fractions were tested for their ability to modify the expression of P450 isoforms, and serum mediators were identified through neutralization experiments. The serum mediators responsible for the down-regulation of P450 isoforms were interferon-gamma, interleukin-1beta (IL-1beta), and IL-2. In vivo, in rats, hypoxia increased the mRNA and protein expression of P-glycoprotein but did not affect the mRNA of breast cancer resistance protein and organic anion-transporting polypeptide 2. It is concluded that in vivo, hypoxia down-regulates rabbit hepatic CYP1A1, 1A2, 2B4, 2C5, and 2C16 and up-regulates CYP3A6. CYP3A11 and P-glycoprotein were up-regulated in the livers of hypoxic rats.

Down-regulation of aryl hydrocarbon receptor-regulated genes by tumor necrosis factor-alpha and lipopolysaccharide in murine hepatoma Hepa 1c1c7 cells

Although much is known concerning the effects of inflammation and oxidative stress on the cytochrome P450 1A1 (CYP1A1), little is known about the modulation of other aryl hydrocarbon receptor (AHR)-regulated genes such as glutathione-S-transferase Ya (GST Ya) and NAD(P)H:quinone oxidoreductase (QOR) by inflammation. In the present study, the effect of tumor necrosis factor (TNF)-alpha and lipopolysaccharides (LPS) on the constitutive and inducible expression of the AHR-regulated genes cyp1a1, GST Ya, and QOR was determined in murine hepatoma Hepa 1c1c7 (WT), AHR-deficient (C12), and AHR nuclear translocator protein (ARNT)-deficient (C4) cells. We found that both TNF-alpha and LPS strongly repressed the constitutive expression and the beta-naphthoflavone-mediated induction of cyp1a1, GST Ya, and QOR in WT but not in C12 and C4 cells. The induction of GST Ya and QOR activities and mRNA levels by phenolic antioxidant, tert-butylhydroquinone, through the antioxidant response element was not significantly affected by TNF-alpha or LPS. In addition, a significant increase in reactive oxygen species was observed in WT, C12, and C4 cells treated with TNF-alpha or LPS which was completely prevented by tert-butylhydroquinone. These results show that the down-regulation of AHR-regulated genes by TNF-alpha and LPS is dependent on the presence of both heterodimeric transcription factors, AHR and ARNT. Furthermore, reactive oxygen species may be involved in the down-regulation of AHR-regulated genes.

Possible pathomechanisms of sudden infant death syndrome: key role of chronic hypoxia, infection/inflammation states, cytokine irregularities, and metabolic trauma in genetically predisposed infants

Chronic hypoxia, viral infections/bacterial toxins, inflammation states, biochemical disorders, and genetic abnormalities are the most likely trigger of sudden infant death syndrome (SIDS). Autopsy studies have shown increased pulmonary density of macrophages and markedly more eosinophils in the lungs accompanied by increased T and B lymphocytes. The elevated levels of immunoglobulins, about 20% more muscle in the pulmonary arteries, increased airway smooth muscle cells, and increased fetal hemoglobin and erythropoietin are evidence of chronic hypoxia before death. Other abnormal findings included mucosal immune stimulation of the tracheal wall, duodenal mucosa, and palatine tonsils, and circulating interferon. Low normal or higher blood levels of cortisol often with petechiae on intrathoracic organs, depleted maternal IgG antibodies to endotoxin core (EndoCAb) and early IgM EndoCAb triggered, partial deletions of the C4 gene, and frequent IL-10-592*A polymorphism in SIDS victims as well as possible hypoxia-induced decreased production of antiinflammatory, antiimmune, and antifibrotic cytokine IL-10, may be responsible for the excessive reactions to otherwise harmless infections. In SIDS infants, during chronic hypoxia and times of infection/inflammation, several proinflammatory cytokines are released in large quantities, sometimes also representing a potential source of tissue damage if their production is not sufficiently well controlled, eg, by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). These proinflammatory cytokines down-regulate gene expression of major cytochrome P-450 and/or other enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity, thus affecting metabolism of several endogenous lipophilic substances, such as steroids, lipid-soluble vitamins, prostaglandins, leukotrienes, thromboxanes, and exogenous substances. In SIDS victims, chronic hypoxia, TNF-alpha and other inflammatory cytokines, and arachidonic acid (AA) as well as n-3 polyunsaturated fatty acids (FA), stimulated and/or augmented superoxide generation by polymorphonuclear leukocytes, which contributed to tissue damage. Chronic hypoxia, increased amounts of nonheme iron in the liver and adrenals of these infants, enhanced activity of CYP2C9 regarded as the functional source of reactive oxygen species (ROS) in some endothelial cells, and nicotine accumulation in tissues also intensified production of ROS. These increased quantities of proinflammatory cytokines, ROS, AA, and nitric oxide (NO) also resulted in suppression of many CYP450 and other enzymes, eg, phosphoenolpyruvate carboxykinase (PEPCK), an enzyme important in the metabolism of FA during gluconeogenesis and glyceroneogenesis. PEPCK deficit found in SIDS infants (caused also by vitamin A deficiency) and eventually enhanced by PACAP lipolysis of adipocyte triglycerides resulted in an increased FA level in blood because of their impaired reesterification to triacylglycerol in adipocytes. In turn, the overproduction and release of FA into the blood of SIDS victims could lead to the metabolic syndrome and an early phase of type 2 diabetes. This is probably the reason for the secondary overexpression of the hepatic CYP2C8/9 content and activity reported in SIDS infants, which intensified AA metabolism. Pulmonary edema and petechial hemorrhages often present in SIDS victims may be the result of the vascular leak syndrome caused by IL-2 and IFN-alpha. Chronic hypoxia with the release of proinflammatory mediators IL-1alpha, IL-1beta and IL-6, and overloading of the cardiovascular and respiratory systems due to the narrowing airways and small pulmonary arteries of these children could also contribute to the development of these abnormalities. Moreover, chronic hypoxia of SIDS infants induced also production of hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulated synthesis and release of different growth factors by vascular endothelial cells and intensified subclinical inflammatory reactions in the central nervous system, perhaps potentiated also by PACAP and VIP gene mutations. These processes could lead to the development of brainstem gliosis and disorders in the release of neuromediators important for physiologic sleep regulation. All these changes as well as eventual PACAP abnormalities could result in disturbed homeostatic control of the cardiovascular and respiratory responses of SIDS victims, which, combined with the nicotine effects and metabolic trauma, finally lead to death in these often genetically predisposed children.

Cytochrome P450 enzyme-mediated drug metabolism at exposure to acute hypoxia (corresponding to an altitude of 4,500�m)

OBJECTIVE

To investigate the effect of acute hypoxia and concomitant changes in portal blood flow on the disposition of drugs mainly metabolized by the cytochrome P(450) enzymes (CYP) 3A4 (verapamil) and CYP1A2 (theophylline).

METHODS

Twenty healthy male participants were studied on two 14-h study days in a normobaric hypoxic chamber and were allocated randomly to one of two groups receiving short infusions of either theophylline (6 mg kg (-1) body weight) or verapamil (5 mg) intravenously. According to a randomized, cross-over design, participants were once exposed to normoxia and once to hypoxia (12% oxygen corresponding to the ambient( P)O(2) at an altitude of 4,500 m above sea level). The concentrations of theophylline, 1,3-dimethyluric acid, verapamil, and norverapamil were determined in serial blood samples by means of liquid chromatography-mass spectrometry (LC/MS/MS). Portal blood flow was assessed by transabdominal duplex ultrasonography.

RESULTS

Acute hypoxia did not alter the pharmacokinetics of theophylline [half-life+/-SD: 9.29+/-1.77 versus 9.39+/-1.40 (hypoxia)], 1,3-dimethyluric acid (12.9+/-4.72 versus 15.1+/-8.59), verapamil (2.00+/-0.98 versus 1.79+/-0.58), or norverapamil (7.98+/-2.94 versus 9.91+/-6.40). Individual changes of elimination half-life and changes in capillary oxygen saturation,( P)O(2), or portal vein flow were not correlated. Portal vein flow was unaffected by hypoxia.

CONCLUSIONS

Acute hypoxia corresponding to hypoxia at altitudes of 4,500 m does not impair the metabolism mediated by CYP1A2 or CYP3A4. At rapid ascent to and short-term stay at altitudes up to 4,500 m, the doses of drugs metabolized by these CYPs do therefore not require dose modification, and major changes in the disposition of already administered drugs are not to be expected.

Signal transduction pathways implicated in the decrease in CYP1A1, 1A2 and 3A6 activity produced by serum from rabbits and humans with an inflammatory reaction

Incubation of serum from rabbits with a turpentine-induced inflammatory reaction and from humans with an upper respiratory viral infection with hepatocytes from rabbits with a turpentine-induced inflammatory reaction for 4h reduces total cytochrome P450 content and activity of cytochrome P450 isoforms CYP1A1/1A2 and 3A6 without affecting the expression of these proteins. To document the signal transduction pathways implicated in the decrease in CYP1A1/1A2 and 3A6 activity, hepatocytes from rabbits with a turpentine-induced inflammatory reaction were incubated with serum from rabbits with a turpentine-induced inflammatory reaction, serum from individuals with a viral infection and interleukin-6 for 4h in presence of inhibitors of protein kinases. The sera-induced decrease in CYP1A1/1A2 and 3A6 activity was partially prevented by the inhibition of Janus-associated protein tyrosine kinase, double-stranded RNA-dependent protein kinase, protein kinase C, and p42/44 mitogen-activated protein kinase. The serum from rabbits with a turpentine-induced inflammatory reaction increased the phosphorylation of Erk1/2, effect prevented by PD98059 but not by bis-indolylmaleimide, a specific inhibitor of protein kinase C. The results demonstrated that the decrease in total cytochrome P450 content and in CYP1A1/1A2 and 3A6 activity by sera and interleukin-6 involves the activation of protein tyrosine kinases, p42/44 mitogen-activated protein kinase and protein kinase C. Indirect evidence supported that nitric oxide is implicated in the decrease in activity of these enzymes.

Hypoxia-inducible factor-1 and activator protein-1 modulate the upregulation of CYP3A6 induced by hypoxia

1. Moderate hypoxia in vivo and serum from rabbits subjected to moderate hypoxia (SHYPO) in vitro reduce CYP1A1 and 1A2 p450 isoforms and upregulate CYP3A6. The aim of this project was to investigate the signal transduction pathways implicated in the upregulation of CYP3A6 expression by hypoxia. 2. Hypoxia in vivo and SHYPO in vitro increased the expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and c-jun, as well as CYP3A6. By electrophoresis mobility shift assay, it was shown that HIF-1 and activator protein-1 (AP-1) bind to CYP3A6 oligonucleotide probe after exposure to hypoxia in vivo and SHYPO in vitro. The effects of hypoxia in vivo or SHYPO in vitro were reproduced by CoCl2 and lead acetate, activators of HIF-1 and AP-1, respectively. 2. PD98059, a p42/44 MAPK inhibitor, prevented the increase of CYP3A6 and c-jun, but did not impede the increase of HIF-1alpha and binding to CYP3A6 oligonucleotide probe. Genistein, an inhibitor of protein tyrosine kinases (PTKs), prevented the increase in HIF-1alpha, c-jun and CYP3A6, as well as HIF-1 and AP-1 binding to CYP3A6 oligonucleotide probe. Moreover, hypoxia in vivo induced constitutive androstane receptor (CAR) as well as CAR binding to the CYP3A6 oligonucleotide probe, but not the pregnane X receptor. 4. In conclusion, hypoxia in vivo and SHYPO induce the expression of CYP3A6. The in vitro induction of CYP3A6 by SHYPO is PTK- and p42/44 MAPK-dependent. The present data support the hypothesis that HIF-1 and AP-1 are part of the signalling pathway leading to CYP3A6 induction by hypoxia.

Hepatic cytochrome P450 2E1 activity in nondiabetic patients with nonalcoholic steatohepatitis

Cytochrome P450 2E1 (CYP2E1) plays an important role in the pathogenesis of nonalcoholic steatohepatitis (NASH) in animal models, but its role in the pathogenesis of human NASH is unclear. Therefore, we measured hepatic CYP2E1 activity and its correlates in a cohort of nondiabetic patients with NASH (NDN) and controls to explore its role in the pathogenesis of human NASH. Hepatic CYP2E1 activity was assessed using the oral clearance (CL(PO)) of chlorzoxazone (CHZ) in 20 NDN and 17 age, gender, and body mass index (BMI)-matched controls. The relationship between hepatic CYP2E1 activity and demographic and anthropometric variables; fasting levels of insulin, glucose, lipids, and beta-OH butyrate; insulin resistance; and nocturnal hypoxemia was assessed. Furthermore, expression of CYP2E1 in the peripheral lymphocytes was assessed using reverse transcription-polymerase chain reaction (RT-PCR). The CL(PO) of CHZ was significantly (P =.03) greater in NDN (41 +/- 12 L/h) compared with controls (33 +/- 16 L/h). Lymphocyte CYP2E1 messenger RNA was significantly higher in NDN compared with controls (11.5 x 10(3) +/- 10 x 10(3) vs. 2.6 x 10(3) +/- 1.2 x 10(3) molecules/microg total RNA, respectively, P <.001). On univariate analysis, BMI, respiratory quotient, high-density lipoprotein, triglycerides, insulin, insulin resistance, hypoxemia, and beta-OH butyrate significantly correlated with hepatic CYP2E1 activity. However, on stepwise regression analysis, only nocturnal hypoxemia (r = 0.50, P =.009) and beta-OH butyrate (r = 0.37, P =.04) were independent predictors of hepatic CYP2E1 activity. In conclusion, hepatic CYP2E1 activity and lymphocyte CYP2E1 expression are enhanced in NDN. The significant correlations noted between CYP2E1 and hypoxemia and beta-OH butyrate suggest that these factors play a role in increased CYP2E1 activity that is seen in patients with NASH.

Hypoxia-induced down-regulation of CYP1A1/1A2 and up-regulation of CYP3A6 involves serum mediators

1. Acute moderate hypoxia modifies the catalytic activity and expression of certain isoenzymes of hepatic cytochrome P450 (P450). The aim of this study was to document whether hypoxia affects hepatic P450 directly or through the release of serum mediators. 2. Rabbits were subjected to a FiO(2) of 8% for 48 h, sacrificed, and serum and hepatocytes were isolated; hepatocytes from control and rabbits with hypoxia were incubated with serum from control and hypoxic rabbits for 4 and 24 h, and total P450 content, CYP1A1, 1A2 and 3A6 activities and expressions were assessed. Sera were fractionated by size exclusion chromatography and fractions tested for their ability to modify activity and amount of P450, and serum mediators were identified through neutralization experiments. 3. Total serum and fractions with proteins of 15-23 and 65-94 kDa of M(r) reduced P450 content and expression of CYP1A1, 1A2 and 3A6, as well as CYP1A1, 1A2 and 3A6 mRNA. Total serum and the fraction with 32-44 kDa proteins increased CYP3A6 activity and protein and mRNA. The serum mediators implicated in the decrease in activity and expression of CYP1A1, 1A2 and 3A6 were interferon-gamma (IFN-gamma), interleukin-1beta (IL-1beta) and IL-2. Erythropoietin (Epo) was partly responsible for the increase in P450 content and CYP3A6 expression. 4. In conclusion, acute moderate hypoxia diminishes the activity and expression of CYP1A1, 1A2 and CYP1A1, 1A2 mRNA, and increases CYP3A6 protein, activity and CYP3A6 mRNA. Several mechanisms contribute to these changes in P450, among them the release of cytokines acting as serum mediators.

Nitric oxide-mediated regulation of chemosensitivity in cancer cells

BACKGROUND

Hypoxia in tumors is associated with malignant progression, metastatic spread, and increased resistance to radiotherapy and chemotherapy. Molecular O(2) is required for the cellular production of nitric oxide (NO) by the enzyme NO synthase (NOS), and NO may block components of the adaptive response to hypoxia. Hence, we hypothesized that hypoxia increases drug resistance in tumor cells by inhibiting endogenous NO production.

METHODS

Human breast carcinoma (MDA-MB-231) and mouse melanoma (B16F10) cells were pre-exposed to 20% O(2), 5% O(2), or 1% O(2), incubated with a pharmacologic inhibitor of endogenous NO production, and then treated with chemotherapeutic agents. Resistance was assessed by colony-formation assays, and western blot analysis was used to measure NOS protein levels. All P values were two-sided.

RESULTS

Incubation of MDA-MB-231 tumor cells in 1% O(2) maximally increased their resistance to doxorubicin and 5-fluorouracil by 8.5-fold (P =.002) and 2.3-fold (P =.002), respectively, compared with incubation in 20% O(2). B16F10 mouse melanoma cells preincubated in 1% O(2) (versus 20% O(2)) for 12 hours exhibited a twofold increase in resistance to doxorubicin (P<.001). The rapid acquisition of drug resistance after exposure to 1% O(2) could be mimicked by incubating the MDA-MB-231 cells for 12 hours with the NOS inhibitor N(G)-monomethyl-Larginine (fivefold increase; P<.001). Conversely, replacement of NO activity by use of the NO-mimetic glyceryl trinitrate (GTN) and diethylenetriamine NO adduct produced statistically significant attenuations in the development of resistance of 59% (P<.001) and 40% (P<.001), respectively, in MDA-MB-231 cells. Treatment of B16F10 cells with GTN produced a 58% reduction in resistance (P<.001). MDA-MB-231 cells expressed all three isoforms of the NOS enzyme at levels that were not altered by exposure to hypoxia.

CONCLUSIONS

NO mediates chemosensitivity in tumor cells, and hypoxia-induced drug resistance appears to result, in part, from downstream suppression of endogenous NO production. These results raise the possibility that administration of small doses of NO mimetics could be used as an adjuvant in chemotherapy.

Cytochrome P450 inactivation by serum from humans with a viral infection and serum from rabbits with a turpentine-induced inflammation: the role of cytokines

Serum from humans with an acute upper respiratory viral infection and from rabbits with turpentine-induced inflammation reduce the catalytic activity of hepatic cytochrome P450 (P450). The aim of this study was to identify the serum mediators responsible for the decrease in P450 activity. Rabbit and human sera were fractionated by size exclusion chromatography and the fractions tested for their ability to reduce the activity and amount of P450 after 4 h of incubation with hepatocytes from turpentine-treated rabbits (H(INF)). Rabbit and human sera decreased P450 activity by around 40% without any change in the amount of CYP1A1 and 1A2 apoproteins. In rabbit serum, the fraction containing proteins of M(r) 23-15 kDa decreased P450 content by 41%, but did not alter the amount of the apoproteins. Anti-IL-6 antibody added to the M(r) 23-15 kDa fraction restored P450 content to 97% of control values, while anti-IL-1beta, TNF-alpha and IFN-gamma antibodies had no effect. Supporting the role of IL-6, incubation of H(INF) in the presence of IL-6 for 4 h reduced P450 content by 40%. In human serum, the fraction containing proteins of M(r) >95 kDa lowered P450 content by 43% without modifying the amounts of CYP1A1/2. Neutralization experiments showed that IFN-gamma, IL-6, and IL-1beta contributed to the decrease in P450 content. In conclusion, the present results demonstrate that IL-6, and IFN-gamma, IL-6 and IL-1beta are the serum mediators released in vivo by a turpentine-induced inflammatory reaction in the rabbit and an upper respiratory viral infection in humans, respectively, inactivating hepatic P450.

21-aminosteroids prevent the down-regulation of hepatic cytochrome P450 induced by hypoxia and inflammation in conscious rabbits

1 This study was conducted to assess whether a 21-aminosteroid, U74389G, could prevent the down-regulation of hepatic cytochrome P450 (P450) induced by acute moderate hypoxia or an inflammatory reaction. 2 The rabbits of two groups (n = 6 per group) were subjected to acute moderate hypoxia (PaO2 approximately 35 mmHg), one pre-treated with U74389G (3 mg kg-1 i.v. every 6 h, for 48 h). The rabbits of two other groups received 5 ml of turpentine s.c., one of them being pre-treated with U74389G (3 mg kg-1 i.v. every 6 h, for 72 h). The kinetics of theophylline (2.5 mg kg-1) were assessed to evaluate the activity of the P450. Once the rabbits were sacrificed, the P450 content and the amount of thiobarbituric acid reactive substances (TBARS), a marker of lipid peroxidation, were estimated in the liver. 3 Compared with control rabbits, hypoxia and inflammation increased theophylline plasma concentrations, as a result of a decrease in theophylline systemic clearance (P<0.05). Both experimental conditions reduced hepatic content of P450 by 40-50% (P<0.05) and increased the amount of hepatic TBARS by around 50% (P<0.05). Pre-treatment with U74389G prevented the hypoxia- and inflammation-induced decrease in theophylline systemic clearance, the down-regulation of hepatic P450, and the increase in liver TBARS. 4 It is concluded that in the rabbit, U74389G prevents hepatic P450 depression produced by acute moderate hypoxia and a turpentine-induced inflammatory reaction, possibly by eliciting a radical quenching antioxidant activity.