7. Nicotinamide adenine dinucleotide phosphate oxidase

#### 7.1 NADPH oxidase

The heart has the highest oxygen uptake rate in the human body, and the oxygen consumption is normally 8–13 mL 100 gˉ <sup>1</sup> minˉ <sup>1</sup> at rest [82]. The cellular sources in the genesis of ROS in the heart include cardiac myocytes, endothelial cells, and neutrophils. Within cardiac myocytes, ROS can be produced by several mechanisms, including the transport of mitochondrial electrons, NADPH oxidase (nicotinamide adenine dinucleotide phosphate oxidase), and xanthine dehydrogenase/xanthine oxidase. To meet the high demand for ATP synthesis, cardiac myocytes therefore have the highest volume density of mitochondria in the entire human body.

NADPH oxidase with its isoforms generically called NOX is the major source of ROS (reactive oxygen species) in biological systems. NOX proteins are involved in a plethora of pathophysiological conditions, so it is important to note that the functions of NOX proteins in different tissues are influenced by the activity of other oxidases and peroxidases, such as myeloperoxidase, xanthine oxidase, and hemoxygenase [83].

In the heart, the cardiomyocyte NADPH oxidase seems to be the main source of production of ROS from the heart in failure [84, 85].

NADPH oxidases are present in phagocytes and in a wide variety of nonphagocytic cells. NADPH generates superoxide by transferring electrons from NADPH into the cell through the membrane and coupling them to molecular oxygen to produce superoxide anion. Structurally, NADPH oxidase is an enzyme that has several components: it includes two integral membrane proteins, the glycoprotein gp. 1 Phox and the adapter protein p22 (phox), which together form the heterodimeric b558 flavocytochrome that form the nucleus of the enzyme. During the resting state, the multidomain regulatory subunits p40P (phox), p47 (phox), and p67 (Phox) are located in the cytosol organized as a complex. Activation of phagocytic NADPH oxidase occurs through a complex series of protein interactions.

The products that activate it are angiotensin II, endothelin-1, TNF-α, and mechanical forces. The cardiomyocyte NADPH oxidase and any other NADPH oxidase when stimulated generates large amounts of (O•2), which dismutes to H2O2; both in the tissue presence of iron and H2O2, increase the production of ROS, lead to the production of the HO• radical; these are highly reactive and can induce peroxidative damage of molecules within reach such as lipids, proteins, carbohydrates, nucleic acids, and membranes, resulting in the increase of reactive substances thiobarbituric acid (TBARS) in patients with heart failure.

This suggests that some pro-inflammatory products can activate a pathway to generate oxidative stress damage through the NADPH oxidase and increase the biological damage to the heart by ROS which correlates with left ventricular dysfunction [86]. Even more, the fact that NADPH oxidase is activated by pro-inflammatory products suggests a link with the genesis of oxidative stress.

Of the infectious processes in the heart on the balance of oxidants and antioxidants in the myocardium little is known. IE in which heart valves are usually affected, generating refractory congestive heart failure, is accompanied by a very important inflammatory response, both local and systemic with high circulating concentrations of IL-6, IL-2R, and IL-1β [87]. In the case of infective endocarditis, the interaction of the infectious agent and its products (chemotactic, formylated, and lipopolysaccharide peptides) with monocytes and polymorphonuclear cells can increase the production of ROS through the activation of NADPH oxidase, secondary to the inflammatory state.

IE induces an increase of pro-inflammatory cytokines, being able to stimulate ROS production in the myocardium and peroxidative damage to several molecules. The substances reactive to thiobarbituric acid (TBAR), in a study comparing cardiac tissue from patients with IE and patients with valvular heart disease (VHD) of rheumatic etiology; TBARs were increased 10 times more in IE than their controls with VHD [88].

#### 8. Inducible nitric oxide synthase

In sepsis, endotoxins and cytokines stimulate the expression of inducible nitric oxide synthase (iNOS) and the overproduction of nitric oxide (NO) in various tissues; it also stimulates the excessive activity of NADPH oxidase that facilitates the expression of iNOS to produce large amounts of NO. The NADPH oxidases derived from ROS by activating the Jak2-IRF1 and JNK-AP1 pathways are necessary for the induction of iNOS. The main mechanism that regulates the activity of iNOS is the modulation of the transcription of the iNOS gene. The NO derived from iNOS and its metabolite peroxynitrite can contribute to the pathological alterations observed in sepsis, such as endothelial dysfunction, hypotension, and multiple organ failure [89].

The peroxynitrite anion ONOO�

$$\mathrm{H\_2O\_2} + \mathrm{NO\_2}^- \rightarrow \mathrm{ONOO}^- + \mathrm{H\_2O} \tag{6}$$

$$\bullet \mathrm{O}\_{2}^{-} + \bullet \mathrm{NO} \rightarrow \mathrm{ONO}\_{2}^{-} \tag{7}$$

#### 9. Metabolome and proteome

The composition of metabolites such as amino acids, intermediate products of the Krebs cycle, and acylcarnitines (metabolome) and protein complement expressed in cells, tissues, or body fluids (proteome) of survivors of sepsis and non-survivors was analyzed in patients who studied with sepsis by three different pathogens, S. pneumoniae, S. aureus, or E. coli. The main differences between survivors and nonsurvivors were those highlighted in their metabolome and proteome. For example, nine proteins involved in the transport of fatty acids were decreased in non-survivors of sepsis, suggesting a defect in β-oxidation. The nonacceptance and nonuse of fatty acids by the mitochondria led to an accumulation of acylcarnitines in the plasma; another predictive marker is that glycolysis and gluconeogenesis were also markedly different. Survivors of sepsis showed decreased levels of citrate, malate, glycerol, glycerol 3-phosphate, phosphate, and glucogenic and ketogenic amino acids, while non-survivors showed elevated levels of citrate, malate, pyruvate, dihydroxyacetone, lactate, phosphate, and gluconeogenic amino acids [90]. That is to say that the pathways for the transport of fatty acids, as well as glycolysis and gluconeogenesis, are damaged, so the substrate is low, and they are not used by the mitochondria.

#### 10. Acetylome

Acetylome analysis identified a subpopulation of mitochondrial proteins that was sensitive to changes in the NADH/NAD+ ratio. Hyperacetylation induced by Infective Endocarditis: Inflammatory Response, Genetic Susceptibility, Oxidative Stress… DOI: http://dx.doi.org/10.5772/intechopen.84908

mitochondrial dysfunction is a positive regulator of pathological remodeling in the heart of mice with primary or acquired mitochondrial dysfunction, as well as in humans with heart failure. Hyperacetylation of mitochondrial malate–aspartate shuttle (MAS) proteins impaired the transport and oxidation of cytosolic NADH in the mitochondria, resulting in altered cytosolic redox state and energy deficiency. Furthermore, acetylation of oligomycin-sensitive conferring protein at lysine-70 in adenosine triphosphate synthase complex promoted its interaction with cyclophilin D and sensitized the opening of mitochondrial permeability transition pore. There are two different mechanisms that point to the proteins of hyperacetylation, i.e., MAS and the regulators of mitochondrial permeability transition pore (mPTP), which mediate an increase in heart failure. Both could be fixed by normalizing the NAD+ redox balance either genetically or pharmacologically [91].

#### 11. Q and cytochrome c

Q and cytochrome c (Cytc) are mobile. Q diffuses rapidly within the membrane, while cytochrome c is a soluble protein that contains a peptide sequence located at the C-terminus of the protein [92] that allows it to cross the cell membranes in a nontraditional way. This property of Cytc was used in a study in mice, which were subject to ligation and cecal puncture; they underwent sepsis and damage to mitochondrial respiration, which was restored with the injection i.v. of Cytc [93]. The treatment led to an uptake of Cytc into the cardiomyocytes, and survival increased from 15% for the sepsis control group to about 50% in mice that were also injected with Cytc [94].

### 12. Deregulated apoptosis and multiple organ failure

The death of cells of the immune system by deregulated apoptosis contributes to the dysfunction of the immune system and multiple organ failure (MOF) which is observed in sepsis. The immune cells most affected by this dysregulated apoptotic cell death appear to be lymphocytes [95]. Extensive lymphocytic apoptosis mediated by caspase-3 in sepsis may contribute to impaired immune response in septic patients [96]. Lymphocyte loss occurs by both death receptor and mitochondrialmediated apoptosis, suggesting that there may be multiple triggers for lymphocyte apoptosis [97, 98].

Apoptosis in the immune system is a pathological event in sepsis which has been considered a therapeutic goal. Studies on sepsis in experimental animals suggest that the loss of lymphocytes during sepsis may be due to deregulated apoptosis and that it appears to be secondary to a variety of mediators that carry out both "intrinsic" and "extrinsic" cell death pathways.

In experimental animals, lymphocyte apoptosis is frequently seen 12 h after the onset of experimental polymicrobial sepsis in the thymus, spleen, and lymphoid tissues associated with the intestine. It has been suggested that deregulated lymphocytic apoptosis results in reduced septic survival through loss of lymphocytes, resulting in multiple organ failure and ultimately death. Lymphocyte apoptosis in the thymus appears to occur 4 h after the onset of sepsis and is independent of the effects of endotoxin or death receptors. Apoptosis in the spleen appears to be particularly important in mortality from sepsis, by an increase of the splenic apoptosis of lymphocytes in experimental animals after the cecal ligation and puncture (CLP) which results in a reduced survival [99].

In septic humans apoptosis does not seem to be generalized, since in these patients only extensive lymphocytic apoptosis was demonstrated, which suggests a damaged immune response, suggesting that other mechanisms apart from cell death participate in the conditions associated with mortality [100]. For example, hyperglycemia induces the expression of leukocyte adhesion molecules, such as the intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM), which is suppressed by treatment with insulin. Another example is the impairment induced by hyperglycemia in the function of neutrophils, including chemotaxis, phagocytosis, and respiratory function, which is attenuated with insulin [101].

#### 13. Conclusions

As we observed, the epidemiology of IE has changed over time. S. aureus is currently the most important pathological agent as a cause of IE [4, 102]. The age group with greater participation is the older adult due to their comorbidities, especially cardiac ones, with the need for valve prosthesis placement, and vascular approach for the placement of cardiac pacemakers.

The existence of an immunogenetic influence in the risk and outcomes of infectious diseases has been well stablished. In the cases of IE and sepsis, investigation is ongoing to clearly define the specific genetic anomalies that contribute to this influence. The study of SNPs has been a good start in the understanding of the phenomena; nevertheless at the light of the information derived from their study, they do not seem sufficient to explain the whole participation of genetics in the sepsis and IE equation. Other types of genetic abnormalities might also participate, and it might be worth exploring [103]. Even though there is a large body of studies with positive results, there are also lots of contradictory and conflicting findings that make it difficult to make definitive conclusions. Even more, according to a systematic review made to determine the methodological quality of SNP association studies with sepsis, most of the studies could improve a lot methodologically speaking in terms of control group selection, genetic assay technique, study blinding, statistical interpretation, study replication, study size, and power.

Finally, the sequence of events that begin with an infectious state, such as IE, alerts and promotes inflammation through the immune system, both cellular and humoral to eliminate the infectious agent; however, this has the ability to evade the immune system.

In its evolution, the germ also generated the possibility of survival through the acquisition of resistance to external agents, such as antibiotics, which can perpetuate the septic process, increasing the production of reactive O2 species both locally (cell-mitochondria) and systemic level (neutrophil-monocytes-macrophageendothelium) together with the products that generate the interaction infectious agent-immune system.

The activity of antioxidant enzymes is exceeded, so that ROS cannot be eliminated, generating a state of oxidative stress, with a profound effect on the mitochondrial level by breaking the chain of electron transport, and, consequently, the genesis of the energy is compromised.

The repercussion of this sequence of events, both at the cardiac level and at the systemic level, is manifested by the failure of one or several organs.

In a schematic way, the sequence of events of a patient with IE who has a severe evolution and finally dies of multiple organ failure is shown (Figure 3).

Different studies explore areas of compromise such as metabolome and proteome in which it is observed that glycolysis, gluconeogenesis, and fatty acid

Infective Endocarditis: Inflammatory Response, Genetic Susceptibility, Oxidative Stress… DOI: http://dx.doi.org/10.5772/intechopen.84908

#### Figure 3.

Schematic representation of the sequence of events of a patient with IE who has a severe evolution and finally dies of multiple organ failure.

transport are damaged, so the substrate is low and the few substrates are not used by the mitochondria, which generates attention in processes to be repaired.

In another (acetylome) the possibility of normalizing the NAD + redox balance is observed both genetically and pharmacologically in the treatment of heart failure [91].

The observations of the behavior of cytochrome c, being a mobile complex molecule and crossing cell membranes, made it possible for cytochrome c to enter into cardiomyocytes to improve mitochondrial respiration, improving the survival of septic mice [92–94]. This open a very attractive opportunity in the treatment of septic patients with heart failure as in IE when in the future we use complex molecules, i.v., in the treatment of these patients.

There are still many areas in which it is necessary to continue researching in the clinical area as well as in the bacteriological, biochemical, and biomolecular areas in addition to other types of tools to observe systemic inflammation, through mathematical modulation and systems-based models of inflammation [104, 105], and the severity of a septic patient due to the complexity of losing the cardiac bioelectrical signal and how it recovers the complexity if the patient survives the septic event have also been considered [106].
