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In recent decades, microdialysis technology has been used to conduct studies to monitor the concentration and content of endogenous and exogenous substances in many tissues. The technology has gradually shown that it can directly and online reflect the characteristics of a substance in tissues and organs, while microdialysis technology is safe for tissues and organs, because the damage caused by the body is well tolerated. This paper mainly reviews the principle of microdialysis technology and its application in clinical research fields such as disease progression monitoring, and prospects the application prospect of this technology in occupational disease research.
2.1 temperature
2.2 membrane area and molecular weight cut off
2.3 concentration of dialysis material
2.4 composition of perfusate
2.5 perfusion rate
2.6 Collecting sample tube distortion
3.1 drug delivery plan design
3.2 Brain injury monitoring
3. 3 monitoring of other diseases
A review of the application of microdialysis technology in life sciences
A review of the application of microdialysis technology in life sciences
Summary:
Microdialysis technology is an experimental technique developed in the past 40 or 50 years. Because it can accurately acquire the metabolism and excretion information of local tissues through the exchange and exchange of dialysate and extracellular fluid, it is in biological and medical research. Get more and more applications. At present, most of the literature focuses on the use of microdialysis technology to study tissue cell metabolism, cytokines and media excretion. In fact, the information available using this technology goes far beyond this. Detailed information on medicines, pesticides, metal elements, environmental pollutants and metabolites of these substances in important organ tissues can be obtained using this technology. Therefore, microdialysis technology seems to have a broader development in the field of environmental and occupational medicine. This article gives an overview of its basic principles and applications.
1 basic principle of microdialysis
The term microdilaysis originated in the late 1950s and was used to describe an extraction technique similar to dialysis. Originally used for biochemical micro-tests, people can separate cholesterol from less than 1mL of plasma, and then gradually applied to other fields. In 1974, UNGERSTEDE and PYCOCK first used this technique to study the neurotransmitter dopamine in rat brain. At present, it has become an important experimental research technique for the analysis of the concentration changes of endogenous and exogenous chemicals in ex vivo or in vivo experiments.
The microdialysis experiment technology uses a semi-permeable membrane with a fiber to intercept the properties of different relative molecular masses to make a micro-dialysis probe (microdidisissis probe MDP), which is buried in the tissue area to be tested, and then infused into the probe at a constant rate. Isotonic perfusate with similar composition of tissue fluid; when the perfusate flows through the dialysis membrane at the front end of the probe, the biologically active substance with a relatively small molecular mass in the tissue outside the probe membrane will diffuse from the membrane into the membrane according to the concentration gradient, and The perfusate is drained from the probe; the dialysate is received in an orderly manner at a certain time interval, and the concentration of the biologically active substance to be tested in the dialysate is continuously detected by a high-sensitivity chemical detection system, thereby effectively monitoring the living tissue or the specific tissue region of the human body. Dynamic changes in extracellular biologically active substances.
Early microdialysis probes (mostly simple dialysis fiber tubes or u-type probes and type I probes) have great damage to tissues; in recent years, a new type of concentric I-type probe can be widely used in the brain, blood vessels and important tissues. Dialysis analysis. The sample to be collected can flow out through the semi-permeable membrane at the tip of the probe into the collection tube (outer tube) to form a "dialysis solution". When the perfusate flows through the dialysis membrane, different molecules are different depending on the concentration of the perfusate or diffuse out of the perfusate (called "reverse dialysis") or from the extra-tissue fluid (return)
Receive) dialysate.
After all, the concentration of the substance to be tested by microdialysis cannot accurately represent the actual concentration of the substance in the examined tissue; and since the perfusion solution containing the component to be tested is continuously perfused, the equilibrium state is never reached, suggesting that the microdialysis is obtained. The concentration detected by the liquid can only be the “fragment†of the true concentration of the body fluid in the site. The concentration of the substance in the examined tissue should be constantly greater than the concentration of the substance in the perfusate. The ratio of the two is the so-called “relative recovery rateâ€. ".
2 Main factors affecting the relative recovery rate of microdialysis
The diffusion rate of the material of the permeable membrane is proportional to the temperature l3, according to the StokesEinstein equation: the diffusion coefficient D = kh (6II), where kb is the Boltzmann constant, the diffusion coefficient is proportional to the temperature (T), and the liquid viscosity (å©) is inversely proportional to the particle diameter and is a circumferential coefficient, indicating that the higher the temperature, the higher the permeability of the dialysis material.
Only substances with a relative molecular mass lower than the dialysis membrane rejection threshold can pass through the dialysis membrane. From the reliability of the experiment, only the relative molecular mass is less than 1/4 of the dialysis membrane rejection threshold, and the relative recovery rate is only in the experiment. Significant.
According to Fick's law of diffusion, it is easy to understand that the higher the concentration of the substance to be dialyzed, the higher the relative recovery.
In the microdialysis experiment, the ambient temperature, the permeability of the membrane, the substances to be dialyzed have been determined, and the composition of the perfusate can be varied according to the needs of the experiment. The preparation process of the perfusate should be selected according to the characteristics of the substance to be permeated, in order to obtain the best analytical results. At present, artificial cerebrospinal fluid (ACSF), Ringer's solution or Krebs solution is used as the perfusion solution for brain microdialysis, and physiological saline is used as the non-neural tissue perfusion solution. Different dialysis samples can be added to the perfusate according to their properties to facilitate sample analysis. For the determination of peptide active substances, 0.5% bovine serum albumin can be added to the perfusate to reduce its adhesion to the dialysis system; monoamine neurotransmitters and their metabolites in light, room temperature and pH>3.5 It is easily oxidized under conditions, and a small amount of acetic acid can be added to the sample collection tube to keep the pH of the collected sample liquid below 3.5, and the sample is collected in an ice bath and protected from light, which can effectively avoid the norepinephrine in the sample. Oxidation of substances such as din, dopamine and serotonin. The above control of the factors affecting the recovery rate not only increases the types of substances detectable by microdialysis, but also helps to reduce system errors.
Another important factor affecting relative recovery is the dialysis perfusion rate. In general, low flow rates increase relative recovery and high flow rates reduce recovery. However, KJELLSTROM et al. found in experiments in 1998 that sometimes the experimental results would be contrary to this: when the flow rate is <1gL/min, the relative recovery of leukotrienes will decrease, and the authors believe that the dialysis membrane may be under the flow rate conditions. The absorption process is related to changes. Due to the relatively small collection volume of microdialysis experimental samples and limited by analytical methods, low flow rate sampling is often difficult to meet experimental requirements; however, larger flow rates (such as 10gL/min or higher) may cause "ultrafiltration". The phenomenon, that is, at a higher flow rate, the sample obtained is not a physical diffusion of the active ingredient, but a "net flow" resulting from a high filtration pressure formed by a high flow rate. Therefore, the flow rate of the perfusate in the microdialysis experiment should generally be controlled at 0.5 to 5 gL/min.
Compared with in vitro experiments, the relative recovery rate in the body microdialysis experiment will be reduced, because in the experimental experiment, the microdialysis experimental pipeline itself also has some resistance, especially when the experimental animals are free to move, the pipeline may be distorted. At this time, the resistance is more
Large, the experimental results obtained may be distorted.
3 microdialysis technology in the clinical field
The efficacy of anticancer drugs is closely related to the drug concentration in tumor tissues. In the past, the concentration of the drug in the tumor was difficult to measure directly, so the blood concentration was usually used to predict and evaluate the anticancer effect of the drug, but due to the special physiological condition of the tumor tissue.
In most cases, the drug concentration of the tumor is not consistent with the plasma concentration. Microdialysis technology can directly take samples in tumor tissues, so it has a great advantage in designing anticancer drug dosing programs and studying the metabolism of anticancer drugs in tumors.
Potential.
Since the 1990s, microdialysis technology has been increasingly used in brain injury and surgical monitoring, providing clinical information on brain damage and changes in brain metabolism during craniocerebral surgery. In 1966, BITO et al first used microdialysis technology to implant a semi-permeable membrane device filled with liquid into dogs. In 1992, PERSSON and HILLERED used microdialysis technology for neurological intensive care for the first time. Changes in energy metabolism-related substances and some amino acids in patients with severe brain injury and a patient with severe subarachnoid hemorrhage during disease progression and drug intervention. In 2003, only Shi et al. first reported the use of microdialysis technology in China to observe the changes of metabolites in the intercellular fluid of 7 patients with craniocerebral trauma, and the effect of hypothermia treatment on the above indicators. In recent years, there have been reports in the literature on the use of microdialysis technology to study aneurysmal rupture caused by aneurysmal subarachnoid hemorrhage, in the case of cerebral vasospasm, cerebral ischemia or delayed ischemic neurological dysfunction, brain extracellular fluid The change in biochemical substances. Microdialysis monitoring provides more information about brain metabolism and is safe and reliable.
In addition to ischemic monitoring after traumatic brain injury, microdialysis technology is also used to monitor the concentration of troponin T and aspartate aminotransferase in patients after cardiac surgery for up to 100 hE. The changes in the above-mentioned indicators in the myocardium are in good agreement with the changes in the electrocardiogram; it takes 1 hour for the above indicators to reach the peak in the serum, and the microdialysis technique can be detected at any time. Intestinal ischemia is another serious and difficult to diagnose condition, especially before the onset of clinical symptoms, and can now be monitored using microdialysis techniques. In plastic surgery, microdialysis technology can be used to detect early reconstruction of the flap with or without ischemia.
4 outlook
Environmental and occupational toxicants have become an important hotspot in current medical research, with a wide variety and complex mechanisms. Establish more optimized and sensitive detection and evaluation methods to further understand its impact on human health and its mechanism of action, in order to propose reasonable preventive and therapeutic measures to reduce the harm of these poisons to the human body. Long-term low-dose exposure is a characteristic of environmental or occupational toxicant exposure, which causes physiological and biochemical changes to be hidden. At present, there are still no effective and sensitive evaluation methods and analytical methods. Microdialysis test technology has slight trauma, does not damage the integrity of the body, and is not easy to cause tissue infection and volume change of tissue parts. It can be continuously sampled for a long time, and the sample is relatively pure (no biological macromolecules such as protein and enzyme) can be pretreated. Online sample analysis is performed, and the results can truly represent the concentration of the target content of the sampling site, and information about the intermediate process of metabolism can be obtained. With the advancement of microdialysis technology and the accumulation of practical experience, it is expected that in the near future, microdialysis technology will be rapidly involved in the field of environmental and occupational medicine, and this medical science will get a more powerful tool.
(Source: Environmental and Occupational Medicine, Vol. 25, No. 1 of Sekiri, etc.)