Continuous administration of organic nitrate decreases hepatic cytochrome P450

Metabolomic Signatures of Exposure to Nitrate and Trihalomethanes in Drinking Water and Colorectal Cancer Risk in a Spanish Multicentric Study (MCC-Spain)

We investigated the metabolomic profile associated with exposure to trihalomethanes (THMs) and nitrate in drinking water and with colorectal cancer risk in 296 cases and 295 controls from the Multi Case-Control Spain project. Untargeted metabolomic analysis was conducted in blood samples using ultrahigh-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. A variety of univariate and multivariate association analyses were conducted after data quality control, normalization, and imputation. Linear regression and partial least-squares analyses were conducted for chloroform, brominated THMs, total THMs, and nitrate among controls and for case-control status, together with a N-integration model discriminating colorectal cancer cases from controls through interrogation of correlations between the exposure variables and the metabolomic features. Results revealed a total of 568 metabolomic features associated with at least one water contaminant or colorectal cancer. Annotated metabolites and pathway analysis suggest a number of pathways as potentially involved in the link between exposure to these water contaminants and colorectal cancer, including nicotinamide, cytochrome P-450, and tyrosine metabolism. These findings provide insights into the underlying biological mechanisms and potential biomarkers associated with water contaminant exposure and colorectal cancer risk. Further research in this area is needed to better understand the causal relationship and the public health implications.

Vascular biotransformation of organic nitrates is independent of cytochrome P450 monooxygenases

BACKGROUND AND PURPOSE

Organic nitrates such as nitroglycerin (NTG) or pentaerythritol tetranitrate (PETN) have been used for over a century in the treatment of angina or ischaemic heart disease. These compounds are prodrugs which release their nitrovasodilators upon enzymic bioactivation by aldehyde dehydrogenase (ALDH2) or cytochromes P450 (CYP). Whereas ALDH2 is known to directly activate organic nitrates in vessels, the contribution of vascular CYPs is unknown and was studied here.

EXPERIMENTAL APPROACH

As all CYPs depend on cytochrome P450 reductase (POR) as electron donor, we generated a smooth muscle cell-specific, inducible knockout mouse of POR (smcPOR^-/- ) to investigate the contribution of POR/CYP to vascular biotransformation of organic nitrates.

KEY RESULTS

Microsomes containing recombinant CYPs expressed in human vascular tissues released nitrite from NTG and PETN with CYP2C9 and CYP2C8 being most efficient. SFK525, a CYP suicide inhibitor, blocked this effect. smcPOR^-/- mice exhibited no obvious cardiovascular phenotype (normal cardiac weight and endothelium-dependent relaxation) and plasma and vascular nitrite production was similar to control (CTL) animals. NTG- and PETN-induced relaxation of isolated endothelium-intact or endothelium-denuded vessels were identical between CTL and smcPOR^-/- . Likewise, nitrite release from organic nitrates in aortic rings was not affected by deletion of POR in smooth muscle cells (SMCs). In contrast, inhibition of ALDH2 by benomyl (10 μM) inhibited NTG-induced nitrite production and relaxation. Deletion of POR did not modulate this response.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that metabolism by vascular CYPs does not contribute to the pharmacological function of organic nitrates.

Regulation of cytochrome P450 enzyme activity and expression by nitric oxide in the context of inflammatory disease

Many hepatic cytochrome P450 enzymes and their associated drug metabolizing activities are down-regulated in disease states, and much of this has been associated with inflammatory cytokines and their signaling pathways. One such pathway is the induction of inducible nitric oxide synthase (NOS2) and generation of nitric oxide (NO) in many tissues and cells including the liver and hepatocytes. Experiments in the 1990s demonstrated that NO could bind to and inhibit P450 enzymes, and suggested that inhibition of NOS could attenuate, and NO generation could mimic, the down-regulation by inflammatory stimuli of not only P450 catalytic activities but also of mRNA expression and protein levels of certain P450 enzymes. This review will summarize and examine the evidence that NO functionally inhibits and down-regulates P450 enzymes in vivo and in vitro, with a particular focus on the mechanisms by which these effects are achieved.

Nitrate: An Environmental Endocrine Disruptor? A Review of Evidence and Research Needs

Nitrate is heavily used as an agricultural fertilizer and is today a ubiquitous environmental pollutant. Environmental endocrine effects caused by nitrate have received increasing attention over the last 15 years. Nitrate is hypothesized to interfere with thyroid and steroid hormone homeostasis and developmental and reproductive end points. The current review focuses on aquatic ecotoxicology with emphasis on field and laboratory controlled in vitro and in vivo studies. Furthermore, nitrate is just one of several forms of nitrogen that is present in the environment and many of these are quickly interconvertible. Therefore, the focus is additionally confined to the oxidized nitrogen species (nitrate, nitrite and nitric oxide). We reviewed 26 environmental toxicology studies and our main findings are (1) nitrate has endocrine disrupting properties and hypotheses for mechanisms exist, which warrants for further investigations; (2) there are issues determining actual nitrate-speciation and abundance is not quantified in a number of studies, making links to speciation-specific effects difficult; and (3) more advanced analytical chemistry methodologies are needed both for exposure assessment and in the determination of endocrine biomarkers.

Nitric oxide-regulated proteolysis of human CYP2B6 via the ubiquitin-proteasome system

We showed previously that rat cytochrome P450 CYP2B1 undergoes NO-dependent proteasomal degradation in response to inflammatory stimuli, and that the related human enzyme CYP2B6 is also down-regulated by NO in primary human hepatocytes. To investigate the mechanism of CYP2B6 down-regulation, we made several cell lines (HeLa and HuH7 cells) in which native CYP2B6 or CYP2B6 with a C-terminal V5 tag (CYP2B6V5) are expressed from a lentiviral vector with a cytomegalovirus promoter. Native CYP2B6 protein was rapidly down-regulated in HeLa cells within 3h of treatment with the NO donor (Z)-1-[2-(2-Aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate, while its mRNA level was not down-regulated. Treatment of the cells with the NO donor (Z)-1-[N-(3-aminopropyl)-N-(3-ammoniopropyl)amino]diazen-1-ium-1,2-diolate also resulted in rapid down-regulation of CYP2B6 activity, measured as the formation of 7-hydroxy-4-trifluoromethylcoumarin, as well as 2B6 protein in the CYP2B6 HeLa cell line. CYP2B6V5 was also down-regulated by NO donors in HuH7 cells. Down-regulation was observed in the presence of cycloheximide, demonstrating that this occurs via a post-translational mechanism. We generated a HeLa cell line expressing both CYP2B6V5 and human nitric oxide synthase 2 (NOS2), the latter under positive control by tetracycline. The cellular NO produced by doxycycline treatment also effectively down-regulated CYP2B6 protein, which was blocked by the co-treatment with the NOS2 competitive inhibitor L-N^G-nitroarginine methyl ester (L-NAME). We next investigated the proteolytic enzymes responsible for NO-dependent CYP2B6 degradation. Neither calpain inhibitors (N-Acetyl-L-leucyl-L-leucyl-L-norleucinal, carbobenzoxy-valinyl-phenylalaninal), nor lysosomal protease inhibitors (3-methyladenine and chloroquine) inhibited the NO dependent CYP2B6V5 down-regulation. The proteasome inhibitors MG132 and bortezomib attenuated, but did not completely block the NO-induced down-regulation in the HuH7 cell line. However, when cells were co-treated with NO donor and proteasome inhibitors, high molecular mass species could be detected on native CYP2B6 as well as CYP2B6V5 Western blots. Further investigation demonstrated that CYP2B6 protein was polyubiquitinated and this was dramatically enhanced by co-treatment with NO donor and bortezomib. Taken together, our data demonstrate that CYP2B6 is down-regulated in an NO-dependent manner via ubiquitination and proteasomal degradation.

Repeated Dosing with NCX1404, a Nitric Oxide-Donating Pregabalin, Re-establishes Normal Nociceptive Responses in Mice with Streptozotocin-Induced Painful Diabetic Neuropathy

NCX1404 [(3S)-5-methyl-3-(((1-(4-(nitrooxy)butanoyloxy)ethoxy)carbonylamino) methyl)hexanoic acid] is a novel nitric oxide (NO)-donating pregabalin that is readily absorbed and processed in vivo to pregabalin and NO. We determined the antiallodynic response of NCX1404 after acute or after 7, 14, and 21 days of repeated daily oral dosing in mice with streptozotocin (STZ)-induced painful diabetic neuropathy (PDN). Pregabalin and its combination with the NO donor isosorbide mononitrate (ISMN) were used for comparison. The blood levels of pregabalin and nitrites, used as surrogate marker of NO release, after NCX1404 or pregabalin dosing were monitored in parallel experiments using liquid chromatography with tandem mass spectrometry (LC-MS/MS). NCX1404 and pregabalin resulted in similar pregabalin levels as it was their antiallodynic activity after acute dosing in STZ mice. However, NCX1404 resulted in disease-modifying properties when administered daily for 21 days, as indicated by the time- and dose-dependent reversal of STZ-induced mechanical allodynia (paw withdrawal threshold [PWT]Veh_21d= 1.3 ± 0.15 g for vehicle; PWTNCX1404_21d= 1.4 ± 0.5 g, 2.9 ± 0.2 g* and 4.1 ± 0.2 g*, respectively for 19, 63, and 190μmol/kg, oral gavage [PO] of NCX1404; *P< 0.05 versus vehicle). This effect was not shared by pregabalin at equimolar doses (190μmol/kg, PO, PWTPregab_21d= 1.4 ± 0.1 g*, *P< 0.05 versus equimolar NCX1404). In addition, the NO donor ISMN (52.3μmol/kg, PO) alone or combined with pregabalin (63μmol/kg) was active at 7 days (PWTVeh_7d= 1.7 ± 0.16 g; PWTISMN_7d= 3.9 ± 0.34 g*; PWTPregab_7d= 1.3 ± 0.07 g; PWTISMN+pregab_7d= 3.8 ± 0.29 g*; *P< 0.05) but not at later time points. The long-term effect of NCX1404 was independent of residual drug exposure and lasted for several days after the treatment was stopped. In summary, like pregabalin, NCX1404 is an effective antiallodynic agent. Differently from pregabalin, repeated dosing of NCX1404 re-established normal nociceptive responses in STZ-induced PDN in mice.

Concomitant nitrates enhance clopidogrel response during dual anti-platelet therapy

BACKGROUND

Despite advances in modern anti-platelet strategies, clopidogrel still remains the cornerstone of dual anti-platelet therapy (DAPT) in patients undergoing percutaneous coronary interventions (PCI). There is some inconclusive evidence that response after clopidogrel may be impacted by concomitant medications, potentially affecting clinical outcomes. Sustained released nitrates (SRN) are commonly used together with clopidogrel in post-PCI setting for mild vasodilatation and nitric oxide-induced platelet inhibition.

METHODS

We prospectively enrolled 458 patients (64.5 ± 9.6 years old, and 73.4% males) following PCI undergoing DAPT with clopidogrel and aspirin. Platelet reactivity was assessed by the VerifyNow™ P2Y12 assay at the maintenance outpatient setting.

RESULTS

Concomitant SRN (n=266) significantly (p=0.008) enhanced platelet inhibition after DAPT (251.6 ± 80.9PRU) when compared (232.1 ± 73.5PRU) to the SRN-free (n=192) patients. Multivariate logistic regression analysis with the cut-off value of 253 PRU for defining heightened platelet reactivity confirmed independent correlation of more potent platelet inhibition during DAPT and use of SRN (Relative risk=1.675; Odds ratio [1.059-2.648]; p=0.027). In contrast, statins, calcium-channel blockers, beta blockers, angiotensin receptor blockers, ACE-inhibitors, diuretics, and anti-diabetic agents did not significantly impact platelet inhibition following DAPT.

CONCLUSION

The synergic ability of SRN to enhance response during DAPT may have important clinical implications with regard to better cardiovascular protection, but extra bleeding risks, requiring further confirmation in a large randomized study.

Organic Nitrate Therapy, Nitrate Tolerance, and Nitrate-Induced Endothelial Dysfunction: Emphasis on Redox Biology and Oxidative Stress

Organic nitrates, such as nitroglycerin (GTN), isosorbide-5-mononitrate and isosorbide dinitrate, and pentaerithrityl tetranitrate (PETN), when given acutely, have potent vasodilator effects improving symptoms in patients with acute and chronic congestive heart failure, stable coronary artery disease, acute coronary syndromes, or arterial hypertension. The mechanisms underlying vasodilation include the release of •NO or a related compound in response to intracellular bioactivation (for GTN, the mitochondrial aldehyde dehydrogenase [ALDH-2]) and activation of the enzyme, soluble guanylyl cyclase. Increasing cyclic guanosine-3',-5'-monophosphate (cGMP) levels lead to an activation of the cGMP-dependent kinase I, thereby causing the relaxation of the vascular smooth muscle by decreasing intracellular calcium concentrations. The hemodynamic and anti-ischemic effects of organic nitrates are rapidly lost upon long-term (low-dose) administration due to the rapid development of tolerance and endothelial dysfunction, which is in most cases linked to increased intracellular oxidative stress. Enzymatic sources of reactive oxygen species under nitrate therapy include mitochondria, NADPH oxidases, and an uncoupled •NO synthase. Acute high-dose challenges with organic nitrates cause a similar loss of potency (tachyphylaxis), but with distinct pathomechanism. The differences among organic nitrates are highlighted regarding their potency to induce oxidative stress and subsequent tolerance and endothelial dysfunction. We also address pleiotropic effects of organic nitrates, for example, their capacity to stimulate antioxidant pathways like those demonstrated for PETN, all of which may prevent adverse effects in response to long-term therapy. Based on these considerations, we will discuss and present some preclinical data on how the nitrate of the future should be designed.

Rhabdomyolysis developing secondary to atorvastatin therapy in a patient with liver cirrhosis

Atorvastatin is a lipid lowering agent that is widely used worldwide. Rhabdomyolysis is a rare but serious side effect that may lead to renal failure and dangerous electrolyte abnormalities in patients with decreased hepatic clearance of atorvastatin. We herein report the case of a patient with liver cirrhosis receiving atorvastatin therapy for ischemic heart disease and hyperlipidemia who developed rhabdomyolysis and acute renal failure.

Embryos as targets of endocrine disrupting contaminants in wildlife

Environmental contaminants are now a ubiquitous part of the ecological landscape, and a growing literature describes the ability of many of these chemicals to alter the developmental trajectory of the embryo. Because many environmental pollutants readily bioaccumulate in lipid rich tissues, wildlife can attain considerable body burdens. Embryos are often exposed to these pollutants through maternal transfer, and a growing number of studies report long-term or permanent developmental consequences. Many biological mechanisms are reportedly affected by environmental contaminants in the developing embryo and fetus, including neurodevelopment, steroidogenesis, gonadal differentiation, and liver function. Embryos are not exposed to one chemical at a time, but are chronically exposed to many chemicals simultaneously. Mixture studies show that for some developmental disorders, mixtures of chemicals cause a more deleterious response than would be predicted from their individual toxicities. Synergistic responses to low dose mixtures make it difficult to estimate developmental outcomes, and as such, traditional toxicity testing often results in an underestimate of exposure risks. In addition, the knowledge that biological systems do not necessarily respond in a dose-dependent fashion, and that very low doses of a chemical can prove more harmful than higher doses, has created a paradigm shift in studies of environmental contaminant-induced dysfunction. Although laboratory studies are critical for providing dose-response relationships and determining specific mechanisms involved in disease etiology, wildlife sentinels more accurately reflect the genetic diversity of real world exposure conditions, and continue to alert scientists and health professionals alike of the consequences of developmental exposures to environmental pollutants.

Organic nitrates and nitrate tolerance--state of the art and future developments

The hemodynamic and antiischemic effects of nitroglycerin (GTN) are lost upon chronic administration due to the rapid development of nitrate tolerance. The mechanism of this phenomenon has puzzled several generations of scientists, but recent findings have led to novel hypotheses. The formation of reactive oxygen and nitrogen species in the mitochondria and the subsequent inhibition of the nitrate-bioactivating enzyme mitochondrial aldehyde dehydrogenase (ALDH-2) appear to play a central role, at least for GTN, that is, bioactivated by ALDH-2. Importantly, these findings provide the opportunity to reconcile the two "traditional" hypotheses of nitrate tolerance, that is, the one postulating a decreased bioactivation and the concurrent one suggesting a role of oxidative stress. Furthermore, recent animal and human experimental studies suggest that the organic nitrates are not a homogeneous group but demonstrate a broad diversity with regard to induction of vascular dysfunction, oxidative stress, and other side effects. In the past, attempts to avoid nitrate-induced side effects have focused on administration schedules that would allow a "nitrate-free interval"; in the future, the role of co-therapies with antioxidant compounds and of activation of endogeneous protective pathways such as the heme oxygenase 1 (HO-1) will need to be explored. However, the development of new nitrates, for example, tolerance-free aminoalkyl nitrates or combination of nitrate groups with established cardiovascular drugs like ACE inhibitors or AT(1)-receptor blockers (hybrid molecules) may be of great clinical interest.

Atorvastatin restores endothelial function in offspring of protein-restricted rats in a cholesterol-independent manner

Maternal protein restriction in rats leads to endothelial dysfunction and decreased NO bioavailability in the offspring. Statins (3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors) are recognized to have pleiotropic actions including increasing NO bioavailability and reducing inflammation and oxidative damage. This study assessed statin treatment on vascular function in a model of endothelial dysfunction, which is independent of dyslipidemia. Wistar rats were fed a control (18% casein) or protein-restricted (9% casein) diet throughout pregnancy. At weaning, a subset of the protein-restricted group was given atorvastatin (10 mg/kg per day) in the drinking water. At 145 days of age, offspring were euthanized by CO(2) inhalation. Plasma samples were collected for markers of inflammation, vascular reactivity of the thoracic aorta, and small mesenteric arteries were assessed on the wire myograph, and tissues were snap frozen for molecular biology analysis. Thoracic aorta endothelial-dependent vasodilatation was attenuated in the male offspring from both protein-restricted groups compared with controls (P<0.05) but was similar in females (P value not significant). Endothelial-dependent dilatation of mesenteric arteries was attenuated in male and female protein-restricted offspring (P<0.05) and was corrected by atorvastatin. Maternal protein restriction increased plasma inflammatory markers granulocyte chemotactic protein, lipocalin-2, and beta(2)-microglobulin in male and C-reactive protein in female offspring (P<0.05). Atorvastatin had no effect on inflammatory markers in the males but restored C-reactive protein to control levels in the females (P<0.05). Aortic and mesenteric artery mRNA levels of endothelial NO synthase, superoxide dismutase 1, and tumor necrosis factor-alpha were unchanged. These data suggest that atorvastatin can restore endothelial function in this model, but its effects are gender specific and dependent on the vascular bed.

Heme oxygenase-1 and the vascular bed: from molecular mechanisms to therapeutic opportunities

Heme oxygenase-1, an enzyme degrading heme to carbon monoxide, iron, and biliverdin, has been recognized as playing a crucial role in cellular defense against stressful conditions, not only related to heme release. HO-1 protects endothelial cells from apoptosis, is involved in blood-vessel relaxation regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in blood-vessel formation by means of angiogenesis and vasculogenesis. The latter functions link HO-1 not only to cardiovascular ischemia but also to many other conditions that, like development, wound healing, or cancer, are dependent on neovascularization. The aim of this comprehensive review is to address the mechanisms of HO-1 regulation and function in cardiovascular physiology and pathology and to demonstrate some possible applications of the vast knowledge generated so far. Recent data provide powerful evidence for the involvement of HO-1 in the therapeutic effect of drugs used in cardiovascular diseases. Novel studies open the possibilities of application of HO-1 for gene and cell therapy. Therefore, research in forthcoming years should help to elucidate both the real role of HO-1 in the effect of drugs and the clinical feasibility of HO-1-based cell and gene therapy, creating the effective therapeutic avenues for this refined antioxidant system.

CO and NO in medicine

The occurrence, role and consequences of CO and NO in biological systems are reviewed. This includes their syntheses by heme oxygenases and NO synthases, their biological targets and the physiological effects of their signals. The use of CO and NO gases in medicine are discussed and methods of delivery are illustrated with particular emphasis on the therapeutic properties of compounds that generate controlled amounts of NO and CO in vivo.

Mitochondrial and cellular heme-dependent proteins as targets for the bioactive function of the heme oxygenase/carbon monoxide system

The toxic effect of high concentrations of CO gas in living organisms is coherently typified at biochemical levels by the high affinity of CO for hemoglobin and cytochromes, heme-dependent proteins that are indispensable for oxygen transport and mitochondrial respiration. However, the basal production of CO during heme degradation and the ability of heme oxygenase-1 (HO-1) to increase CO availability pose the question of how this gaseous molecule interacts with metal centers within the intracellular milieu to serve as one of the most unconventional signaling mediators. Emerging evidence indicates that the diverse and multifaceted beneficial effects exerted by "low concentrations" of CO cannot be explained solely by the activation of classic prototypic targets (i.e., guanylate cyclase/potassium channels) but entails the dynamic and concerted activation/inhibition of a group of CO-responsive proteins. As the complexity of the temporal and spatial action of CO is progressively being appreciated, this review aims to (a) highlight the current knowledge on certain metal-containing proteins that interact directly with CO; (b) analyze the latest notions on their functional role in response to CO; and finally (c) propose a rational view on the mode these CO targets may interrelate with and be regulated by the HO/CO pathway.

Vitamin E deficiency accelerates nitrate tolerance via a decrease in cardiac P450 expression and increased oxidative stress

Organic nitrates, such as nitroglycerin (NTG), have been used to relieve the symptoms of angina pectoris. However, their biochemical mechanisms of action, particularly in relation to the development of tolerance, are incompletely defined. It has been reported that supplemental antioxidants such as vitamin E attenuate the development of nitrate tolerance. Therefore, we examined the role of vitamin E in the regulation of nitrate tolerance. Continuous NTG infusion induced nitrate tolerance in rats after 48 h, and vitamin E concentrations decreased in a time-dependent manner in tissues and plasma. Vitamin E supplementation (0.5 g/kg diet) maintained higher concentrations of vitamin E during NTG infusion. The onset and extent of the tolerance, estimated by the decrease in blood pressure following NTG bolus injection during the infusion of NTG, were accentuated in the vitamin E-deficient group. Vitamin E supplementation inhibited nitrate tolerance 48 h after NTG infusion. Cardiac P450 expression (CYP1A2) assessed by immunoblotting, markedly decreased 48 h after NTG administration in control rats. The supplementation of vitamin E significantly attenuated the decrease in P450. Treatment of NTG enhanced vascular superoxide production (L-012 chemiluminescence, DHE fluorescence). The peak of lipid peroxidation and free radical generation in the heart was reached before tolerance developed. In contrast, vitamin E-deficient hearts had lower P450 expression and higher free radical generation than control hearts. To evaluate other vitamin E-inhibitable mechanisms of nitrate tolerance, we studied the NO-cGMP pathway. NTG markedly reduced the vasodilator-stimulated phosphoprotein (VASP) serine 239 phosphorylation (specific substrate of cGMP-activated protein kinase I; cGK-I) in tolerant hearts. Vitamin E inhibited the depletion of pVASP. In conclusion, because continuous NTG infusion causes vitamin E depletion as well as nitrate tolerance, vitamin E deficiency may further accelerate nitrate tolerance via an increase in oxidative stress, the reduced bioconversion because of decreased P450 expression, and impairment of the NO/cGMP pathway in tolerant heart tissues.

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.