**6.2. The chronic mitochondrial toxic effect of doxorubicin**

The heart, skeletal muscle, and brain are reasonably active organs [14], so energy demand is very high. This is why the majority of energy production is based on mitochondria for maintaining heart function [80]. Therefore, organ failure can develop because of damage to mitochondrial function [14].

Mitochondria have a role in regulating cell survival and death, proliferation, and calcium and redox homeostasis. It is reported that the inner mitochondrial structure is different from tissue to tissue, based on their metabolic activities; even the structure is different in the same tissue [14]. For example, heart tissue has been indicated to have two types of mitochondria. One is located near the T tubule and SR, and the other is firmly located at a contractile component of myocytes. The dynamic of the organelle is limited due to its close relation with the cytoskeleton [14]. So, these two mitochondria present different features, including dynamic organization, calcium accumulation, functional capacity, and localization. Subsarcolemmal mitochondria are situated at the plasma membrane and have a role in supplying ATP to the ion pump. However, intermyofibrillar mitochondria are situated between the myofibrillar structure and produce energy for the contraction/relaxation function of the tissue [80].

Mitochondria have two shapes or morphologies: long and filamentous (fused) and short and punctuated (fragmented). The form is vital to respond to damage. For example, fused mitochondria are suggested for counteracting apoptosis, while fragmented mitochondria are susceptible to apoptosis [81]. Mitochondria have two structures: long tubules and small round vesicles [82].

Mitochondria are dynamic organelles and perform trafficking, fusion, and fission, called mitochondrial dynamics [14, 21, 83]. The importance of mitochondrial dynamics is that mitochondria have to divide from existing organelles and proliferate via growth [83]. There is a balance between the fission and fusion processes. If the balance shifts towards fission, it causes damage, including mitochondrial fragmentation, mitophagy, a rise in oxidative stress, and cell death [21]. This equilibrium could relate to a number of factors, e.g., cell conditions such as stress, cell compartmentation such as neuronal axons or dendrites, and mitochondrial function as well. The dynamic is crucial for mitochondrial morphogenesis [82]. The importance of dynamics is to scale up because of its role in mitochondrial function, apoptosis, or aging [83]. DOX also leads to senescence of cardiomyocytes by inhibition of Akt Ser473 phosphorylation [21].

Mitochondrial morphological alternation is claimed to provide some idea about DOX's degree of toxicity. For example, the morphological shift at organelles is displayed at the beginning of DOX toxicity on heart tissue. Mitochondria have a homeostatic balance between fission (divide) and fusion. Fission could cause mitophagy, apoptosis, and cell proliferation. However, fusion provides a homogeneous network of mitochondria. Imbalance of the mitochondrial dynamic causes it to lose cell function, e.g., when the shift towards fission could initiate apoptotic cell death due to severe ROS production. In contrast, the change towards fusion would increase mitochondrial dysfunction because of extinguishment of the mitophagy mechanism. The dynamic provides healthy, functional mitochondria and cells [39].

Eventually, mitochondrial collapse is inevitable, resulting in MMP dissipation, improvement in ROS production, inhibition of ATP production, and also oxygen utilization. A dose of 1 mg/kg of DOX has been reported to increase superoxide radicals within 2 h, although a 37 mg/m2 dose, which equals to 5–30 μM mitochondrial concentration, has the same effect on human

The heart, skeletal muscle, and brain are reasonably active organs [14], so energy demand is very high. This is why the majority of energy production is based on mitochondria for maintaining heart function [80]. Therefore, organ failure can develop because of damage to

Mitochondria have a role in regulating cell survival and death, proliferation, and calcium and redox homeostasis. It is reported that the inner mitochondrial structure is different from tissue to tissue, based on their metabolic activities; even the structure is different in the same tissue [14]. For example, heart tissue has been indicated to have two types of mitochondria. One is located near the T tubule and SR, and the other is firmly located at a contractile component of myocytes. The dynamic of the organelle is limited due to its close relation with the cytoskeleton [14]. So, these two mitochondria present different features, including dynamic organization, calcium accumulation, functional capacity, and localization. Subsarcolemmal mitochondria are situated at the plasma membrane and have a role in supplying ATP to the ion pump. However, intermyofibrillar mitochondria are situated between the myofibrillar

structure and produce energy for the contraction/relaxation function of the tissue [80].

Mitochondria have two shapes or morphologies: long and filamentous (fused) and short and punctuated (fragmented). The form is vital to respond to damage. For example, fused mitochondria are suggested for counteracting apoptosis, while fragmented mitochondria are susceptible to apoptosis [81]. Mitochondria have two structures: long tubules and small

Mitochondria are dynamic organelles and perform trafficking, fusion, and fission, called mitochondrial dynamics [14, 21, 83]. The importance of mitochondrial dynamics is that mitochondria have to divide from existing organelles and proliferate via growth [83]. There is a balance between the fission and fusion processes. If the balance shifts towards fission, it causes damage, including mitochondrial fragmentation, mitophagy, a rise in oxidative stress, and cell death [21]. This equilibrium could relate to a number of factors, e.g., cell conditions such as stress, cell compartmentation such as neuronal axons or dendrites, and mitochondrial function as well. The dynamic is crucial for mitochondrial morphogenesis [82]. The importance of dynamics is to scale up because of its role in mitochondrial function, apoptosis, or aging [83]. DOX also leads to senescence of cardiomyocytes by inhibition of Akt Ser473 phos-

Mitochondrial morphological alternation is claimed to provide some idea about DOX's degree of toxicity. For example, the morphological shift at organelles is displayed at the beginning of DOX toxicity on heart tissue. Mitochondria have a homeostatic balance between

**6.2. The chronic mitochondrial toxic effect of doxorubicin**

beings [44].

342 Mitochondrial Diseases

mitochondrial function [14].

round vesicles [82].

phorylation [21].

To maintain its function the heart prefers to metabolize fatty acid in mitochondria and peroxisomes via β-oxidation due to its high demand energy [14]. Mitochondrion starts energy production by the tricarboxylic acid cycle (TCA) in the ETS. Mitochondrial ATP is synthesized by ETS steps. Although TCA elements are placed in the mitochondrial matrix, except for succinate dehydrogenase, ETS elements having a spherical shape are present at the mitochondrial inner membrane and project to the mitochondrial matrix. The space between the inner and outer layer is called the intermembrane space or mitochondrial cytosol. A molecule with hydrophilic structure can transit the inner membrane as a requirement of the transport system. The outer membrane of mitochondria can pass through almost all particles less than 10,000 Da [10]. The respiratory chain is under the control of four complexes: complex I (NADH dehydrogenase), complex II (succinate dehydrogenase), complex III (cytochrome-*c* reductase), and complex IV(cytochrome-*c* oxidase) [34] (**Figure 5**). Complex V is ATP synthase [11]. After synthesis, ATP can be transferred from the inner mitochondrial membrane to the cytosol through ANT and the outer membrane VDAC. MPT induction opens the nonselective pores permitting the diffusion of a 1.5 kDa small molecule [14]. Electrons can be relocated from complex I (NADH dehydrogenase) and II (succinate dehydrogenase) to coenzyme Q10 with a quinine structure as DOX. Then, particles are moved to complex III, cytochrome-*c*, and complex IV. Eventually, oxygen can capture the particle, resulting in water synthesis (**Figure 5**). All ETS elements associated with the enzyme are placed near the matrix surface of the inner mitochondrial membranes. It has been reported that complex I and II could not reach the particles in the mitochondrial cytosol from any organ and any cancer cells, except the heart. The mitochondria of cardiac tissue has two position on the outer surface of inner mitochondrial membrane and faces the matrix [10]. However, overexposed DOX causes mitochondrial dysfunction, consisting of decreasing state 3 respiration, complex I, and ANT activities. Moreover, lengthy DOX treatment increases susceptibility to calcium, resulting in dissipation of MMP at low and high concentrations [13].

Bioenergetics failure may be primarily a mechanism of DOX cardiotoxicity [13]. So, the other molecular base of DOX toxicity on noncancerous tissue relies on the destruction of mtDNA. Oxidative stress leads to damage to mtDNA, especially heart tissue. Additionally, DOX represents the harmful effect of mtDNA much more than nuclear DNA. If the integrated knowledge that the mtDNA repair system is fragile vs. the nuclear DNA system, DOX is understood to be highly toxic to mitochondria [10]. The mitochondrial genome has 13 subunits of ETC codes, which are almost all of the ETC complex, except complex II, a succinate dehydrogenase encoded by nuclear DNA [13]. mtDNA has also been encoded by mitochondrial ribosomal and transfer RNA [10]. DOX damages mtDNA via elevation of ROS [13]. Oxidative damage of DNA has been evaluated by using 8-OHdG formation. After DOX treatment, 8-OHdG has been reported to reach a peak value at 24 h, but a baseline value at 14 days [13]. The chronic

Another chronic drug mechanism is associated with cardiolipin. DOX has high affinity for cardiolipin; therefore, DOX–cardiolipin complex formation interrupts the standard oxidative phosphorylation mechanism. DOX can be transformed into the semiquinone form by NADPH reductases in mitochondria. The opening of MTP led to swelling of mitochondria and depolarizing mitochondria membrane potential, structural and cytoskeleton disorganization, and mtDNA injury. Peroxisome proliferator-activated receptor-*c* coactivator-1α (PGC-1α) has a crucial role in mitochondrial biogenesis and oxidative metabolism [16]. Also, alternative posttranslational modification could participate in the alteration of mitochondrial function. Posttranslational modification through acetylation and deacetylation from lysine residues play a crucial role in regulating mitochondrial function. Mitochondrial proteins are modulated posttranslationally as sirtuin enzymes, sirtuin-3, -4, and -5, by deacetylation. Posttranslational modification can occur under redox stress and nutrient flux. Mitochondria

Mitochondria have sources of bioenergetics and ROS as well. This is why mitochondria become the target of multiple factors such as drugs, including DOX, and environmental compounds. PGC-1α plays an essential role in the regulation of mitochondrial function, including production of bioenergy and energy homeostasis. PGC-1α can regulate gene transcription, including mitochondrial services such as NRF-1, PPARa, and ERRa, which modulate and are divided into three groups of metabolic enzymes in the TCA cycle: antioxidant enzymes, other mitochondrial protein components of the ETC complexes, and mitochondrial transcription

When mitochondrial dysfunction occurs, i.e., enhancing ROS, reduction of ATP synthesis, a complex transcriptional network, including PGC-1α can be triggered to maintain cellular homeostasis. PGC-1α can transcript three groups of genes, which are mentioned above. Although PGC-1α's effect on three groups is suggested to have a minor impact at a low mitochondrial toxic concentration to alter ROS and ATP production, its effect on the groups is essential at a high level of mitochondrial toxins. It is reported that DOX's toxic effect is related to increasing mitochondrial ROS production and the most destructive impact of DOX appears

It is well known that heart tissue contains a high cell volume of mitochondria, almost 35% due to the requirement of energy supply because of maintaining the contraction function of the tissue [15]. The heart produces energy requirement by using β-oxidation of fatty acid in mitochondria. The cardiotoxicity of DOX might be related to swelling and destroy bioenergy from the organelle and myofibril of cardiac tissue. DOX also increases oxidative stress, resulting in enhancing mitochondria dysfunction. The other mechanism of DOX on mitochondrial malfunction is reported to be associated with the dissipation of mitochondrial ETC at different levels. So, NADH and succinate oxidase in cardiac tissue have been shown to be blocked by DOX treatment. Also, DOX separates complex I from ETC, resulting in the elevation of oxidative damage by producing semiquinone free radicals. Moreover, DOX might inhibit stage-3 and stage-4 respiration. The other mechanism for blocking mitochondrial function is related to the prevention of Mg-dependent F0F1-ATPase in muscle, including heart and


Mitochondrial Dysfunction Associated with Doxorubicin http://dx.doi.org/10.5772/intechopen.80284 345

express mostly sirtuin-3 and nuclear NAD+

factor A (TFAM) [38].

**6.3. Bioenergetics dysfunction induced by doxorubicin**

in cardiac tissue due to its accumulation in cardiac cells [38].

**Figure 5.** The effect of doxorubicin and its derivate on the electron transport system and mitochondrial energy production. Modified from Govender et al. [34].

effect of DOX on mitochondria has been reported to appear when it destroys mtDNA [44], mainly developing mtDNA deletion. The prevalence of the elimination has been reported to be between 33 and 80% at a low and high dose of DOX, respectively [10]. When DOX oxidizes mtDNA, mitochondria can no longer produce high-energy substrate, resulting from destroying to reproduce mtDNA [10]. This alternation is explained by DNA repair and elimination of damage to the genomic material, which changes or eliminates the protein function. Alternation or disappearance of mitochondrial protein function elevates ROS formation as well [13]. At this moment, we should take time to diagnose DOX's chronic cardiotoxic effect, e.g., heart failure, dilated cardiomyopathy, and congestive heart failure [10]. Moreover, mitochondrial complex I activity has been claimed to inhibit isolated mitochondria from cardiac tissue, but not hepatic tissue by chronic DOX therapy for 28 weeks. This notion has given rise to the thought that the drug's toxicity in mitochondria is cardioselective [10]. One study suggested that endurance exercises reduce DOX toxicity based on modulation of state 3 alternation at mitochondria. Also, the study reported that apoptosis induced by DOX could be counteracted by endurance exercises giving rise to a decline in apoptotic factors, such as Bax or Bax/Bcl-2 ratio. Moreover, DOX alters the ultrastructure of heart tissue by mitochondrial destruction, including damaging cristae and vacuoles, and causing distension and abnormal size and shape [80]. Mainly, the outer mitochondrial membrane plays a role in the transduction of signals, e.g., apoptotic [82]. Endurance exercises have been suggested to reverse the ultrastructural alternation, e.g., a rise in glycogen storage, and enhance cytosolic and mitochondrial sodium oxide dismutase. Due mostly to the sensitive oxidative stress of MPT, elevation of antioxidant by endurance exercises leads to decreased apoptosis induced by DOX [80].

Another chronic drug mechanism is associated with cardiolipin. DOX has high affinity for cardiolipin; therefore, DOX–cardiolipin complex formation interrupts the standard oxidative phosphorylation mechanism. DOX can be transformed into the semiquinone form by NADPH reductases in mitochondria. The opening of MTP led to swelling of mitochondria and depolarizing mitochondria membrane potential, structural and cytoskeleton disorganization, and mtDNA injury. Peroxisome proliferator-activated receptor-*c* coactivator-1α (PGC-1α) has a crucial role in mitochondrial biogenesis and oxidative metabolism [16]. Also, alternative posttranslational modification could participate in the alteration of mitochondrial function. Posttranslational modification through acetylation and deacetylation from lysine residues play a crucial role in regulating mitochondrial function. Mitochondrial proteins are modulated posttranslationally as sirtuin enzymes, sirtuin-3, -4, and -5, by deacetylation. Posttranslational modification can occur under redox stress and nutrient flux. Mitochondria express mostly sirtuin-3 and nuclear NAD+ -dependent histone deacetylase [34].
