Multiparameter monitoring and analysis of in vivo ischemic and hypoxic heart

Potential therapy strategy: targeting mitochondrial dysfunction in sepsis

Recently, the definition of sepsis was concluded to be a life-threatening organ dysfunction caused by a dysregulated host response to infection. Severe patients always present with uncorrectable hypotension or hyperlactacidemia, which is defined as septic shock. The new definition emphasizes dysregulation of the host response and multiple organ dysfunction, which is partially attributed to metabolic disorders induced by energy crisis and oxidative stress. Mitochondria are a cellular organelle that are well known as the center of energy production, and mitochondrial damage or dysfunction is commonly induced in septic settings and is a predominant factor leading to a worse prognosis. In the present review, we determine the major mitochondrial disorders from morphology to functions in sepsis. In the following, several clinical or pre-clinical assays for monitoring mitochondrial function are demonstrated according to accumulated evidence, which is the first step of specific therapy targeting to modulate mitochondrial function. Accordingly, various reagents used for regulating mitochondrial enzyme activities and promoting biogenesis have been documented, among which mitochondria-targeted cation, TPP-conjugated antioxidants are the most valuable for future trials and clinical treatment to improve mitochondrial function as they may take advantage of the prognosis associated with septic complications.

Autofluorescence spectroscopy for NADH and flavoproteins redox state monitoring in the isolated rat heart subjected to ischemia-reperfusion

BACKGROUND

Reduction of myocardial ischemia-reperfusion injury in the patients undergoing cardiac surgery under cardiopulmonary bypass represents an important goal. Intraoperative monitoring of myocardial metabolic state using continuous registration of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) fluorescence might contribute to the solution of the problem. The successful application of fluorescent spectroscopy in the clinical field requires additional refinement of the technique, particularly using excitation of both NADH and FAD with different wavelengths.

METHODS

The experiments were performed on the isolated Langendorff-perfused rat hearts (n=28) subjected to either regional or global ischemia-reperfusion. Two principles of NADH and FAD autofluorescence (AF) measurement were used for ischemia monitoring: (1) analysis of photographs and videos obtained with multispectral organoscopy technique allowing the assessment of both spatial and temporal characteristics of the process (n=16); (2) continuous registration of tissue redox state in a representative area of the heart by application of local spectroscopy, assisted by fiber optic spectrometer (n=12).

RESULTS

It was found that regional myocardial ischemia resulted in a rapid, substantial increase in the intensity of NADH AF excited at 360nm in the ischemic versus non-ischemic area of the heart. The same result was obtained when the heart was made globally ischemic, while the restoration of perfusate flow completely reversed the increase in NADH AF. During the transition from ischemia to reperfusion, the spatial heterogeneity of myocardial AF was noted on video recordings, probably reflecting the microheterogeneity of myocardial blood flow. Local spectroscopy studies demonstrated opposite changes in the NADH and FAD AF during ischemia. Using both methodological approaches, we found that repetitive brief episodes of global myocardial ischemia resulted in progressive decrease in the magnitude of AF elevation, which might point to preconditioning effect.

CONCLUSIONS

The application of multispectral fluorescent organoscopy offers the advantage of monitoring myocardial redox state at the level of the entire heart. Local spectroscopy is characterized by better precision and, in addition, provides the unique opportunity to measure AF in different parts of the spectrum. AF measurements are non-invasive, rapid, and technically easy to perform. For future clinical applications, it might be recommended to combine the measurement of redox state of both NADH and FAD, using excitation wavelength and emission filter optimal for each fluorophore.

Monitoring tissue perfusion, oxygenation, and metabolism in critically ill patients

Alterations in oxygen transport and use are integral to the development of multiple organ failure; therefore, the ultimate goal of resuscitation is to restore effective tissue oxygenation and cellular metabolism. Hemodynamic monitoring is the cornerstone of management to promptly identify and appropriately manage (impending) organ dysfunction. Prospective randomized trials have confirmed outcome benefit when preemptive or early treatment is directed toward maintaining or restoring adequate tissue perfusion. However, treatment end points remain controversial, in large part because of current difficulties in determining what constitutes "optimal." Information gained from global whole-body monitoring may not detect regional organ perfusion abnormalities until they are well advanced. Conversely, the ideal "canary" organ that is readily accessible for monitoring, yet offers an early and sensitive indicator of tissue "unwellness," remains to be firmly identified. This review describes techniques available for real-time monitoring of tissue perfusion and metabolism and highlights novel developments that may complement or even supersede current tools.

Shedding light on mitochondrial function by real time monitoring of NADH fluorescence: I. Basic methodology and animal studies

Normal mitochondrial function in the process of metabolic energy production is a key factor in maintaining cellular activities. Many pathological conditions in animals, as well as in patients, are directly or indirectly related to dysfunction of the mitochondria. Monitoring the mitochondrial activity by measuring the autofluorescence of NADH has been the most practical approach since the 1950s. This review presents the principles and technological aspects, as well as typical results, accumulated in our laboratory since the early 1970s. We were able to apply the fiber-optic-based NADH fluorometry to many organs monitored in vivo under various pathophysiological conditions in animals. These studies were the basis for the development of clinical monitoring devices as presented in accompanying article. The encouraging experimental results in animals stimulated us to apply the same technology in patients after technological adaptations as described in the accompanying article. Our medical device was approved for clinical use by the FDA.

Use of NADH fluorescence to determine mitochondrial function in vivo

Normal mitochondrial function is a critical factor in maintaining cellular homeostasis in various organs of the body. Due to the involvement of mitochondrial dysfunction in many pathological states, the real-time in vivo monitoring of the mitochondrial metabolic state is crucially important. This type of monitoring in animal models as well as in patients provides real-time data that can help interpret experimental results or optimize patient treatment. In this paper we are summarizing the following items: (1) presenting the solid scientific ground underlying nicotine amide adenine dinucleotide (NADH) NADH fluorescence measurements based on published materials. (2) Presenting NADH fluorescence monitoring and its physiological significance. (3) Providing the reader with basic information on the methodologies of the fluorometers reflectometers. (4) Clarifying various factors affecting the monitored signals, including artifacts. (5) Presenting the potential use of monitoring mitochondrial function in vivo for the evaluation of drug development. The large numbers of publications by different groups testify to the valuable information gathered in various experimental conditions. The monitoring of NADH levels in the tissue provides the most important information on the metabolic state of the mitochondria in terms of energy production and intracellular oxygen levels. Although NADH signals are not calibrated in absolute units, their trend monitoring is important for the interpretation of physiological or pathological situations. To better understand the tissue function, the multiparametric approach has been developed where NADH serves as the key parameter to be monitored.

Mitochondrial function in vivo evaluated by NADH fluorescence: from animal models to human studies

Normal mitochondrial function is a critical factor in maintaining cellular homeostasis in various organs of the body. Due to the involvement of mitochondrial dysfunction in many pathological states, the real-time in vivo monitoring of the mitochondrial metabolic state is crucially important. This type of monitoring in animal models as well as in patients provides real-time data that can help interpret experimental results or optimize patient treatment. The goals of the present review are the following: 1) to provide an historical overview of NADH fluorescence monitoring and its physiological significance; 2) to present the solid scientific ground underlying NADH fluorescence measurements based on published materials; 3) to provide the reader with basic information on the methodologies used in the past and the current state of the art fluorometers; and 4) to clarify the various factors affecting monitored signals, including artifacts. The large numbers of publications by different groups testify to the valuable information gathered in various experimental conditions. The monitoring of NADH levels in the tissue provides the most important information on the metabolic state of the mitochondria in terms of energy production and intracellular oxygen levels. Although NADH signals are not calibrated in absolute units, their trend monitoring is important for the interpretation of physiological or pathological situations. To understand tissue function better, the multiparametric approach has been developed where NADH serves as the key parameter. The development of new light sources in UV and visible spectra has led to the development of small compact units applicable in clinical conditions for better diagnosis of patients.

Multiparametric monitoring of brain under elevated intracranial pressure in a rat model

Intracranial hypertension may develop in most patients exposed to traumatic head injury. In many cases, patients enduring elevated intracranial pressure (ICP) will incur morbidity or mortality. Several methods are used in animal models to investigate the influence of ICP elevation on physiological parameters. In this study, we developed a cisterna magna model by adding a mechanism for warming the mock cerebrospinal fluid (CSF) entering the cisterna space to a temperature of 37 degrees C and combined this method for ICP elevation with the multiparametric monitoring system (Multiprobe Assembly [MPA]). Using the MPA, we monitored, for the first time, mitochondrial NADH redox state as well as ionic homeostasis under elevated ICP in a rat model. In addition, we monitored cerebral blood flow (CBF) by laser Doppler flowmetry, ECoG (bipolar electrodes), and surface temperature. Blood pressure was measured in the cannulated femoral artery. The ICP (monitored by Camino probe) was elevated to 50-60 mm Hg for 13-15 min, followed by 2 h of recovery. The results show that CBF was decreased by 90%, while NADH was elevated by 80% as compared to the normoxic levels. Complete depolarization occurred as evidence by the decrease in extracellular Ca2+ and a significant increase in K+. All parameters recovered 10 min after reopening the cannula to the cisterna magna to air pressure. We conclude that ICP elevation through the cisterna magna infusion method, used simultaneously with multiparametric monitoring, supplies reliable information on the brain tissue metabolic state with intracranial hypertension in a rat model.