Effects of warm and cold ischemia on mitochondrial functions in brain, liver and kidney

Mitochondrial Consequences of Organ Preservation Techniques during Liver Transplantation

Allograft ischemia during liver transplantation (LT) adversely affects the function of mitochondria, resulting in impairment of oxidative phosphorylation and compromised post-transplant recovery of the affected organ. Several preservation methods have been developed to improve donor organ quality; however, their effects on mitochondrial functions have not yet been compared. This study aimed to summarize the available data on mitochondrial effects of graft preservation methods in preclinical models of LT. Furthermore, a network meta-analysis was conducted to determine if any of these treatments provide a superior benefit, suggesting that they might be used on humans. A systematic search was conducted using electronic databases (EMBASE, MEDLINE (via PubMed), the Cochrane Central Register of Controlled Trials (CENTRAL) and Web of Science) for controlled animal studies using preservation methods for LT. The ATP content of the graft was the primary outcome, as this is an indicator overall mitochondrial function. Secondary outcomes were the respiratory activity of mitochondrial complexes, cytochrome c and aspartate aminotransferase (ALT) release. Both a random-effects model and the SYRCLE risk of bias analysis for animal studies were used. After a comprehensive search of the databases, 25 studies were enrolled in the analysis. Treatments that had the most significant protective effect on ATP content included hypothermic and subnormothermic machine perfusion (HMP and SNMP) (MD = −1.0, 95% CI: (−2.3, 0.3) and MD = −1.1, 95% CI: (−3.2, 1.02)), while the effects of warm ischemia (WI) without cold storage (WI) and normothermic machine perfusion (NMP) were less pronounced (MD = −1.8, 95% CI: (−2.9, −0.7) and MD = −2.1 MD; CI: (−4.6; 0.4)). The subgroup of static cold storage (SCS) with shorter preservation time (< 12 h) yielded better results than SCS ≥ 12 h, NMP and WI, in terms of ATP preservation and the respiratory capacity of complexes. HMP and SNMP stand out in terms of mitochondrial protection when compared to other treatments for LT in animals. The shorter storage time at lower temperatures, together with the dynamic preservation, provided superior protection for the grafts in terms of mitochondrial function. Additional clinical studies on human patients including marginal donors and longer ischemia times are needed to confirm any superiority of preservation methods with respect to mitochondrial function.

Renal Mitochondrial Response to Low Temperature in Non-Hibernating and Hibernating Species

SIGNIFICANCE

Therapeutic hypothermia is commonly applied to limit ischemic injury in organ transplantation, during cardiac and brain surgery and after cardiopulmonary resuscitation. In these procedures, the kidneys are particularly at risk for ischemia/reperfusion injury (IRI), likely due to their high rate of metabolism. Although hypothermia mitigates ischemic kidney injury, it is not a panacea. Residual mitochondrial failure is believed to be a key event triggering loss of cellular homeostasis, and potentially cell death. Subsequent rewarming generates large amounts of reactive oxygen species that aggravate organ injury. Recent Advances: Hibernators are able to withstand periods of profoundly reduced metabolism and body temperature ("torpor"), interspersed by brief periods of rewarming ("arousal") without signs of organ injury. Specific adaptations allow maintenance of mitochondrial homeostasis, limit oxidative stress, and protect against cell death. These adaptations consist of active suppression of mitochondrial function and upregulation of anti-oxidant enzymes and anti-apoptotic pathways.

CRITICAL ISSUES

Unraveling the precise molecular mechanisms that allow hibernators to cycle through torpor and arousal without precipitating organ injury may translate into novel pharmacological approaches to limit IRI in patients.

FUTURE DIRECTIONS

Although the precise signaling routes involved in natural hibernation are not yet fully understood, torpor-like hypothermic states with increased resistance to ischemia/reperfusion can be induced pharmacologically by 5'-adenosine monophosphate (5'-AMP), adenosine, and hydrogen sulfide (H₂S) in non-hibernators. In this review, we compare the molecular effects of hypothermia in non-hibernators with natural and pharmacologically induced torpor, to delineate how safe and reversible metabolic suppression may provide resistance to renal IRI. Antioxid. Redox Signal. 27, 599-617.

Altered mitochondrial functioning induced by preoperative fasting may underlie protection against renal ischemia/reperfusion injury

We reported previously that the robust protection against renal ischemia/reperfusion (I/R) injury in mice by fasting was largely initiated before the induction of renal I/R. In addition, we found that preoperative fasting downregulated the gene expression levels of complexes I, IV, and V of the mitochondrial oxidative phosphorylation (OXPHOS) system, while it did not change those of complexes II and III. Hence, we now investigated the effect of 3 days of fasting on the functioning of renal mitochondria in order to better understand our previous findings. Fasting did not affect mitochondrial density. Surprisingly, fasting significantly increased the protein expression of complex II of the mitochondrial OXPHOS system by 19%. Complex II-driven state 3 respiratory activity was significantly reduced by fasting (46%), which could be partially attributed to the significant decrease in the enzyme activity of complex II (16%). Fasting significantly inhibited Ca(2+) -dependent mitochondrial permeability transition pore opening that is directly linked to protection against renal I/R injury. The inhibition of the mitochondrial permeability transition pore did not involve the expression of the voltage-dependent anion channel by fasting. In conclusion, 3 days of fasting clearly induces the inhibition of complex II-driven mitochondrial respiration state 3 in part by decreasing the amount of functional complex II, and inhibits mitochondrial permeability transition pore opening. This might be a relevant sequence of events that could contribute to the protection of the kidney against I/R injury.

NMR analysis of the rat neurochemical changes induced by middle cerebral artery occlusion

Stroke is a leading cause of death and disability, affecting millions of people worldwide with almost 80% of them as ischemic stroke and understanding the multiple mechanisms underlying cerebral ischemia is essential for development of effective treatments. To understand metabolic changes induced by focal brain ischemia, we conducted a comparative analysis of metabolic composition of cerebral tissue from rats with sham-operation and middle cerebral artery occlusion (MCAO) using high-resolution nuclear magnetic resonance (NMR) spectroscopy. More than 40 metabolites were assigned including organic acids, amino acids, carbohydrates, choline, pyrimidine and purine metabolites. Our results showed that MCAO led to significant level decreases for glutamate, glutamine, aspartate, γ-aminobutyrate (GABA), taurine, malate, fumarate, acetate, phosphocreatine, and purine and pyrimidine metabolites such as inosine, hypoxanthine, xanthine, uracil and UDP/UTP, together with significant level increases for glucose in focal brain tissue extracts. This demonstrated that experimental ischemic stroke in rats caused extensive perturbation in tricarboxylic acid cycle, GABA shunt, and metabolisms of choline and nucleic acids. These findings provided essential information for our understandings of MCAO-caused biochemical alterations and demonstrated the metabolite composition analysis as a useful tool for understanding the neurochemistry of stroke.

ROS scavenging before 27 degrees C ischemia protects hearts and reduces mitochondrial ROS, Ca2+ overload, and changes in redox state

We have shown that cold perfusion of hearts generates reactive oxygen and nitrogen species (ROS/RNS). In this study, we determined 1) whether ROS scavenging only during cold perfusion before global ischemia improves mitochondrial and myocardial function, and 2) which ROS leads to compromised cardiac function during ischemia and reperfusion (I/R) injury. Using fluorescence spectrophotometry, we monitored redox balance (NADH and FAD), O(2)(*-) levels and mitochondrial Ca(2+) (m[Ca(2+)]) at the left ventricular wall in 120 guinea pig isolated hearts divided into control (Con), MnTBAP (a superoxide dismutase 2 mimetic), MnTBAP (M) + catalase (C) + glutathione (G) (MCG), C+G (CG), and N(G)-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) groups. After an initial period of warm perfusion, hearts were treated with drugs before and after at 27 degrees C. Drugs were washed out before 2 h at 27 degrees C ischemia and 2 h at 37 degrees C reperfusion. We found that on reperfusion the MnTBAP group had the worst functional recovery and largest infarction with the highest m[Ca(2+)], most oxidized redox state and increased ROS levels. The MCG group had the best recovery, the smallest infarction, the lowest ROS level, the lowest m[Ca(2+)], and the most reduced redox state. CG and L-NAME groups gave results intermediate to those of the MnTBAP and MCG groups. Our results indicate that the scavenging of cold-induced O(2)(*-) species to less toxic downstream products additionally protects during and after cold I/R by preserving mitochondrial function. Because MnTBAP treatment showed the worst functional return along with poor preservation of mitochondrial bioenergetics, accumulation of H(2)O(2) and/or hydroxyl radicals during cold perfusion may be involved in compromised function during subsequent cold I/R injury.

The contemporary role of antioxidant therapy in attenuating liver ischemia-reperfusion injury: a review

Oxidative stress is an important factor in many pathological conditions such as inflammation, cancer, ageing and organ response to ischemia-reperfusion. Humans have developed a complex antioxidant system to eliminate or attenuate oxidative stress. Liver ischemia-reperfusion injury occurs in a number of clinical settings, including liver surgery, transplantation, and hemorrhagic shock with subsequent fluid resuscitation, leading to significant morbidity and mortality. It is characterized by significant oxidative stress but accompanied with depletion of endogenous antioxidants. This review has 2 aims: firstly, to highlight the clinical significance of liver ischemia-reperfusion injury, the underlying mechanisms and the main pathways by which the antioxidants function, and secondly, to describe the new developments that are ongoing in antioxidant therapy and to present the experimental and clinical evidence about the role of antioxidants in modulating hepatic ischemia-reperfusion injury.

Protection by bilobalide of the ischaemia-induced alterations of the mitochondrial respiratory activity

Ischaemia is a common feature of most vascular diseases. There is evidence from experimental and clinical studies that Ginkgo biloba extract protects tissues from ischaemia/reperfusion damages. Bilobalide seems to be responsible, at least in part, for this activity. However, the mechanism of the protection afforded by bilobalide is not yet known. In this work, the effects of bilobalide on mitochondrial respiration were investigated during liver and brain ischaemia, since mitochondria alteration is an early event in ischaemia-induced damage. Bilobalide could prevent the decrease in respiratory activity induced by ischaemia in liver and in brain, both when glutamate/malate or succinate was used as substrate. Ischaemia decreased state 3 respiration rate and bilobalide prevented this decrease. While bilobalide was not able to prevent the decrease in adenine translocase activity, it protected complex I activity. Bilobalide allows mitochondria to maintain their respiratory activity in ischaemic conditions by protecting complex I and probably complex III activities. Hence, the energetic pool of tissues is preserved during the ischaemic period as well as its viability. This mechanism provides, a possible explanation for the anti-ischaemic properties of bilobalide and of Ginkgo biloba extract in therapeutic interventions.

Time-dependent impairment of mitochondrial function after storage and transplantation of rabbit kidneys

BACKGROUND

The mitochondrial respiratory chain is implicated as a major target of kidney damage after ischemia-reperfusion. This study measures changes in integrated mitochondrial function and in the activity of enzymes of the respiratory chain after cold storage and transplantation-reperfusion in vivo.

METHODS

Mitochondrial oxygen consumption and activities of respiratory chain enzymes and citrate synthase were measured in cortical mitochondria isolated from rabbit kidneys after 1-48 hr of cold ischemia with or without transplantation-reperfusion.

RESULTS

State 4 mitochondrial oxygen consumption was significantly increased after 48 hr of ischemia or 24-48 hr of ischemia with transplantation. Prolonged (24 or 48 hr) ischemic storage with and without transplantation caused a significant decrease in state 3 oxygen consumption, as did transplantation after 1, 24, and 48 hr of cold storage. Complex I and complex II-III activity decreased after 24 or 48 hr of ischemia, with transplantation having little additional effect. Complex IV activity was significantly decreased after 48 hr of ischemia, this decrease being exacerbated by transplantation-reperfusion. Complex V activity decreased significantly after 1 hr of ischemia and continued to decrease after 24-48 hr of ischemia. Transplantation after 1-24 hr (but not 48 hr) of ischemia resulted in partial recovery of complex V activity. Citrate synthase activity was decreased significantly only after 48 hr of ischemia and reperfusion, consistent with the loss of mitochondrial membrane integrity seen in electron micrographs of the transplanted 48-hr group.

CONCLUSIONS

These data suggest that individual rabbit kidney mitochondrial complexes have different susceptibilities to cold ischemic and reperfusion damage.

Characterization of neuroprotection from excitotoxicity by moderate and profound hypothermia in cultured cortical neurons unmasks a temperature-insensitive component of glutamate neurotoxicity

Although profound hypothermia has been used for decades to protect the human brain from hypoxic or ischemic insults, little is known about the underlying mechanism. We therefore report the first characterization of the effects of moderate (30 degrees C) and profound hypothermia (12 degrees to 20 degrees C) on excitotoxicity in cultured cortical neurons exposed to excitatory amino acids (EAA; glutamate, N-methyl-D-aspartate [NMDA], AMPA, or kainate) at different temperatures (12 degrees to 37 degrees C). Cooling neurons to 30 degrees C and 20 degrees C was neuroprotective, but cooling to 12 degrees C was toxic. The extent of protection depended on the temperature, the EAA receptor agonist employed, and the duration of the EAA challenge. Neurons challenged briefly (5 minutes) with all EAA were protected, as were neurons challenged for 60 minutes with NMDA, AMPA, or kainate. The protective effects of hypothermia (20 degrees and 30 degrees C) persisted after rewarming to 37 degrees C, but rewarming from 12 degrees C was deleterious. Surprisingly, however, prolonged (60 minutes) exposures to glutamate unmasked a temperature-insensitive component of glutamate neurotoxicity that was not seen with the other, synthetic EAA; this component was still mediated via NMDA receptors, not by ionotropic or metabotropic non-NMDA receptors. The temperature-insensitivity of glutamate toxicity was not explained by effects of hypothermia on EAA-evoked [Ca2+]i increases measured using high- and low-affinity Ca2+ indicators, nor by effects on mitochondrial production of reactive oxygen species. This first characterization of excitotoxicity at profoundly hypothermic temperatures reveals a previously unnoticed feature of glutamate neurotoxicity unseen with the other EAA, and also suggests that hypothermia protects the brain at the level of neurons by blocking, rather than slowing, excitotoxicity.

Impairment of hepatic mitochondrial respiratory function following storage and orthotopic transplantation of rat livers

Prolonged storage of organs for transplant results in tissue damage which may be compounded on reperfusion of the graft tissue. The effect of storage times was examined on hepatic mitochondrial oxygen consumption and activities of complexes I, II-III, IV, and V in mitochondria isolated from rat liver isografts stored for 25 min and 24 h pre- and posttransplantation. While Complex I activity was significantly (P < 0.05) inhibited under all the conditions studied, Complex II-III activity was only significantly (P < 0.05) reduced following transplantation of 24-h stored tissue. Complex IV activity remained unchanged under all the conditions studied. Although Complex V activity was significantly damaged within the first 25 min of ischemia, activity values were partially recovered to control levels following 3 h of reperfusion after transplantation. Prolonged (24 h) storage induced decreases in Complex V activity which were irrecoverable. Mitochondria subjected to 25 min ischemia alone also showed a significant (P < 0.01) decrease in NAD(+)-linked respiratory control indices due to a stimulated state 4 rate. The 24-h storage and transplantation brought about a significantly (P < 0.001) greater inhibition of respiratory control and state 3 respiration. FAD-linked respiration parameters were significantly (P < 0.05) affected in livers subjected to prolonged (24 h) storage or transplantation. These data suggest that a loss of membrane integrity coupled with an inhibition of Complexes I and V and an involvement of Complex II-III in 24-h stored hepatic transplants accounts for mitochondrial respiratory dysfunction in hepatic transplantation injury. No indication of Complex IV damage was found in this study. This study shows that damage to specific mitochondrial complexes occurs as a consequence of hypothermic ischemic injury.

Response of normal and reperfused livers to glucagon stimulation: NMR detection of blood flow and high-energy phosphates

The effects of glucagon on blood flow and high-energy phosphates in control and in rat livers damaged by ischemia were studied using in vivo nuclear magnetic resonance (NMR) spectroscopy. Normal livers and livers which had been made ischemic for 20, 40, and 60 min followed by 60 min of reperfusion were studied. Ischemia led to a loss in adenosine triphosphate (ATP) within 30 min. Reperfusion after 20 min of ischemia led to complete recovery of ATP. 60 min of reperfusion after 40 or 60 min of ischemia led to only a 76% and 48% recovery of ATP, respectively. Glucagon, at doses up to 2.5 mg/kg body weight, caused no changes in the inorganic phosphate (P(i)) to ATP ratio in normal livers as measured by 31P-NMR spectroscopy. In livers which had been made ischemic for 20, 40, or 60 min, glucagon caused an increase in the P(i)/ATP ratio of 18%, 40%, and 40%, respectively. 19F-NMR detection of the washout of trifluoromethane from liver was used to measure blood flow. Glucagon-stimulated flow in the normal liver in a dose-dependent manner, with 2.5 mg glucagon/kg body weight leading to a 95% increase in flow. Ischemia for 20, 40, and 60 min followed by 60 min of reperfusion led to hepatic blood flows which were 63%, 68%, and 58% lower than control liver. In reperfused livers, blood flow after glucagon-stimulation was reduced to 56%, 43%, and 48% of control glucagon-stimulated flow after 20, 40, and 60 min of ischemia. These results indicate that ischemia followed by reperfusion leads to decreases in hepatic blood flow prior to alterations in ATP and the response of the liver to glucagon is altered in the reperfused liver.

Preserved mitochondrial function by allopurinol despite deteriorated hemodynamics in warm ischemia-damaged canine liver

To investigate the pathophysiology of warm ischemia (WI) of the liver, the changes in hemodynamics and energy metabolism were studied during and after 60-min complete WI induced by total hepatic vascular exclusion (HVE) in the canine model. Hepatic arterial blood flow after WI was maintained at 76% of the pre-ischemic level, while portal blood flow was only 27% of the pre-ischemic level associated with increased portal vein pressure, which was twice the pre-ischemic level, resulting in a decrease of total hepatic blood flow to 46% of the pre-ischemic level. Concentration of tissue lipid peroxide increased after WI. Arterial blood ketone body ratio (AKBR), which reflects the hepatic mitochondrial redox state, could not recover to the pre-ischemic level after termination of WI. However, when 100 mg/kg of allopurinol (xanthine oxidase inhibitor) was administered intravenously 10 min prior to initiating WI, AKBR was restored to the pre-ischemic level at 30 min after WI in spite of the fact that allopurinol administration to one group produced no remarkable changes in the hepatic hemodynamics compared with the group without allopurinol treatment. Concentration of adenine nucleotides was significantly higher for the treated group at the end of and after WI than for the group without allopurinol treatment and was maintained at a higher level even after WI. Lipid peroxide production was suppressed. Electron microscopic examination revealed that allopurinol treatment could not prevent mitochondrial swelling. It is suggested that WI causes injury primarily to the portal sinusoidal circulation, resulting in portal congestion concomitant with high portal pressure after the release of WI. Allopurinol could prevent the deterioration of mitochondrial ATP metabolism, and was able to inhibit lipid peroxide production, resulting in the rapid recovery of mitochondrial redox state in spite of the fact that it produced no amelioration of hepatic hemodynamics and morphological alterations.

The effect of shock on blood oxidation-reduction potential

Oxidation-reduction (redox) potential measurements were made in the blood of rabbits subjected to hemorrhagic shock followed by treatment with a mild oxidizing agent (albumin). Control redox potential reading corrected for pH was -8.8 +/- 1.3 millivolts (mV) in arterial blood (A) and -18.0 +/- 2.0 mV in venous blood (V). This A-V difference indicated that hydrogen equivalents coming from muscle and other tissues were partially consumed in the lungs. A 20-mV drop on the V and a 13 mV on the A side was seen after shock. This did not fully return to control 2 h after return of the shed blood. Infusion of 2 g of albumin/kg/h raised the V redox potential to control, but it returned to untreated levels when the albumin was discontinued. The reductive load imposed on the animal by shock appeared to be large and not readily reversed by reperfusion or by the quantity of albumin given. Thus, it may be concluded that cellular respiration had not been adequately restored. This reductive load may impede recovery by suppression of cellular respiration and other cell and organ functions.

Energy metabolism and renal ischemia

In renal preservation, the longer the organ is cold stored the greater the damage to the organ. The mechanism of hypothermic-induced kidney injury is not known. In this study the effects of long-term preservation (up to 120 h) of the dog kidney on mitochondrial functions in an homogenate of kidney cortex tissue was investigated. Kidneys were exposed to either warm ischemia (0 to 90 min) cold ischemia (0, 72, 96, and 120 h). The mitochondrial oxygen uptake was measured in an homogenate. In both warm and cold ischemia there were changes in the mitochondrial utilization of oxygen. The changes were characterized as a decrease in uncoupler stimulated oxygen uptake by up to 40%, an increase in oligomycin-sensitive respiration by up to about 150%, and a decrease in the respiratory control ratio (uncoupler control ratio) from about 3 to 1. These changes in mitochondrial utilization of oxygen were partially reversed by including albumin in the respiration medium. Albumin binds free fatty acids and these may originate, during ischemia, from the action of phospholipases during ischemia. The changes in mitochondrial oxygen uptake may result from both the loss of membrane-bound phospholipids and the accumulation of free fatty acids. The changes in mitochondrial activity between 72 h (viable kidneys on transplantation) and 96 to 120 h preservation (nonviable kidneys) were not significant. Furthermore, reperfusion of kidneys preserved for 72 to 120 h resulted in a restoration of mitochondrial oxygen uptake to near normal (control) values. Thus, it does not appear that the limitation of successful long-term renal preservation is due to mitochondrial injury caused by cold ischemia.

Inhibition by taurine of the phosphorylation of specific synaptosomal proteins in the rat cortex: effects of taurine on the stimulation of calcium uptake in mitochondria and inhibition of phosphoinositide turnover

It has been previously observed that taurine inhibits PKC-activated phosphorylation of specific proteins including a approximately 20k Mr protein in rat cortical synaptosomes. In the present study, the mechanism of the above effects of taurine were investigated. In an intrasynaptosomal cytosol fraction obtained by subcellular fractionation, taurine did not have inhibitory effects on protein phosphorylation. However, taurine did inhibit the phosphorylation of the approximately 20k Mr protein in a reconstituted preparation containing intrasynaptosomal cytosol and mitochondria. Experiments measuring calcium uptake demonstrated that taurine increased the accumulation of 45Ca2+ in the mitochondrial fraction in incubation systems both in the absence and presence of added ATP. In addition, taurine inhibited the accumulation of 32P-labeled phosphatidic acid in synaptosomes indicative of a reduction in the levels of diacylglycerol. These results suggest that taurine may inhibit specific protein phosphorylation both by reducing cytosolic calcium levels and by inhibiting the turnover of phosphoinositides. These effects of taurine on the signal transduction cascade involving PKC and phosphoinositide metabolism indicate a potential biological role for taurine in the nervous system.

Intracerebral distribution of mitochondrial abnormalities in 21 cases of infantile spongy dystrophy

Using a monoclonal antibody to an inner mitochondrial membrane antigen and light microscopic immunohistochemistry, we investigated the distribution of increased immunostaining (mitochondrial anomalies, MA) on paraffin sections from 21 brains with infantile spongy dystrophy (Leigh's disease, 8; Canavan's disease, 4; Alpers' syndrome, 2; mixed spongy dystrophy, 7). Compared with an age-matched control group, MA were present in all cases of Leigh's disease (leptomeningeal and intracerebral endothelial and vascular smooth muscle cells, choroid plexus epithelia, ependymal cells, astrocytes or some neurons), in 2 cases of Canavan's disease and the Alpers' syndrome cases (astrocytes and occasionally some neurons). The MA were restricted to spongy areas in Canavan's disease and Alpers' syndrome, whereas they were distributed throughout the brain in Leigh's disease. In mixed spongy dystrophies the Leigh histology was associated with MA, but not the Canavan histology. Brains with Wernicke's encephalopathy (3 cases), adult infarction (3), and multicystic encephalopathy (5) showed no MA, but one with methylmalonaciduria did. Our results substantiate the classification of Leigh's disease as primary mitochondrial encephalopathy.