Microorganisms (microorganisms) is a generic term for a class of tiny organisms that are tiny in size, simple in structure, mostly unicellular, and must be observed morphologically with a microscope [1]. It includes bacteria, viruses, actinomycetes, rickettsia, chlamydia, mycoplasma, spirochetes, fungi, protozoa, and unicellular algae in 10 major groups. It is closely related to human life, such as the pathogenesis of human diseases, the production of antibiotics, and the immune status of the organism. How to control the harmful aspects of microorganisms and use their beneficial aspects is a topic that has been studied for many years. There are many methods to control microorganisms, and this paper provides a review of PhotodynamicTherapy (PDT) for the treatment of bacterial and viral diseases.
Bacterial and viral characteristics and their control
Characteristics of bacteria
Bacteria are a large group of microorganisms, which are prokaryotes. They have the following characteristics [2]: (1) many species and wide distribution; (2) fast reproduction and strong metabolism, such as the general bacteria reproduce one generation in 20-30 minutes; (3) small individuals and large effects, which can only be detected by light microscope magnification of 40-100 times; (4) easy mutation, as a result of mutation, the characteristics of the offspring are different from those of the parents, and this characteristic can make the pathogenic bacteria develop drug resistance, which has adverse effects on clinical treatment. (4) easy to mutate. Most human and animal diseases are almost always caused by bacteria, so it poses a serious risk to human health. Any bacteria that can cause disease in humans or animals is called pathogenic bacteria or pathogenic bacteria (pathogenicbacteria). The pathogenic bacteria invade the organism and grow and multiply in a certain area. Due to the different power of the two sides and the influence of environmental factors, sometimes they show clinical symptoms, sometimes they do not show clinical symptoms and show hidden infection or carrier state. So the pathogenic bacteria invade the body does not necessarily cause disease, whether it can cause mainly depends on the pathogenic role of pathogenic bacteria, the body resistance (i.e. immunity) and the environment and other three major factors. The pathogenicity of pathogenic bacteria is closely related to their virulence, the number of invasive organisms and the route of invasion. According to the Gram staining method, bacteria are often classified into Gram-positive and Gram-negative bacteria. Currently, it is believed that Gram-negative bacteria have a high content of lipids and a low content of peptidoglycan in the cell wall. In Gram-positive bacteria, the pore size of the peptidoglycan layer in the cell wall was reduced due to the high peptidoglycan content and low lipid content. This staining method has important significance in bacterial classification and clinical drug selection.
Current status of antibacterial conventional therapy
The main methods of bacterial control are currently physical and chemical. Physical methods of disinfection and sterilization include mechanical decontamination, thermal sterilization, and radiation irradiation. Some physical factors can achieve the requirement of sterilization (sterilization) i.e. killing or removing all living organisms, but it is only applicable to some instruments, utensils, air, etc. for preventive disinfection. It is basically not applicable to the human body that has been infected with pathogenic bacteria. Chemical methods can be divided into chemical disinfectants and chemotherapeutic agents. There are many types of chemical disinfectants, including: halogens, phenols and their derivatives, alcohols, alkylating agents, oxidizing agents, heavy metals, surfactants, acids and bases, dyes, etc., each with different antibacterial effects. In summary, there are the following aspects: (1) oxidation and hydrolysis of microbial cell components; (2) production of salts in combination with cellular proteins; (3) coagulation and denaturation of proteins; (4) inactivation of enzymes through interference; (5) alteration of membrane permeability; and (6) cell rupture. Chemical disinfectants have the same scope of application as physical disinfection, but they rarely meet the requirements for sterilization; they can only remove pathogenic microorganisms from the object, i.e., disinfection. It is also not suitable for the treatment of people infected with pathogens. The most important feature of chemotherapeutic agents (chemotherapyagents) is that they selectively kill or inhibit bacteria with no or less toxicity to the organism. The best example of selective toxicity is penicillin, which inhibits the synthesis of cell walls, which is not toxic to humans because human and animal cells do not have cell walls. This is not the case with chemical disinfectants, such as phenols that make proteins coagulate, which are toxic to all cells without selectivity. The current chemotherapeutic agents include mainly sulfonamides, antibiotics and others. The mechanism is mainly through interfering with bacterial metabolism, acting on cell wall synthesis, acting on nucleic acid synthesis, affecting protein synthesis, interfering with cell membrane function and other ways to play antibacterial effect. Although it has strong antibacterial activity, high selectivity and broad antibacterial spectrum, the use of chemotherapeutic agents still has four major clinical problems to be solved: toxicity, allergy (allergic reaction), secondary infection and drug resistance. Among them, the problem of drug resistance greatly affects the clinical efficacy.
Characteristics of viruses
Virus is a non-cellular microorganism. It is one of the smallest classes of pathogenic factors and is clearly different from other microorganisms. It has the following characteristics [3]: (1) It is extremely small and is the smallest living organism known to date. (2) It has no cellular structure and consists of a nucleic acid and a protein shell. Each virus contains only one nucleic acid: DNA or RNA.(3) It is strictly parasitic on living host cells. Cannot reproduce by transverse division, but proliferate by replication. Because they do not have a complete enzyme system, they cannot metabolize independently and must rely on the host cell for their own nucleic acid and protein synthesis to reproduce offspring. (4) Infectious, most viruses are capable of causing disease in humans, animals and plants. It is estimated that about 75% of human infectious diseases are caused by viruses.
Current status of antiviral conventional therapy
There are currently two approaches to controlling viral infections: one is prevention-based, with widespread use of vaccines (live attenuated or inactivated vaccines), which have been experienced for many years, but because there are many types of viruses and they are prone to mutation, it is not yet possible to produce a variety of effective vaccines against all types of viruses. Another is the application of chemotherapeutic agents, but unfortunately there is still no ideal drug to control the virus, the reason for this is that the relationship between the host cells and the virus is too close, and drugs with strong antiviral effects are bound to have a high toxicity to the host cells.
PDT antibacterial therapy
At present, antibacterial and antiviral treatments have some of the above-mentioned problems to be solved, and people began to seek new methods for treatment. Since bacteria and viruses have the characteristics of fast growth and reproduction like tumors, a new method for treating tumors, photodynamic therapy (PDT), was thought of. pDT has made great clinical progress in treating tumors, and now people have also made breakthroughs in PDT for many non-tumor diseases, such as treatment of erythema nodosum [4], restenosis after angioplasty [5], and rheumatoid arthritis [6-9], etc. PDT antimicrobial therapy has been under investigation and is currently used mainly to prevent contamination of blood products, especially viral contamination. Although many technical problems remain to be solved, in vitro studies have demonstrated that this method can be effective antibacterial (including drug-resistant bacteria), antiviral, and available with a variety of photosensitizers, both natural and synthetic.
Bertoloni et al [10] found in 1984 that bacteria could be killed by the PDT method. Several studies [11-12] found that Gram-positive bacteria are more sensitive to PDT than Gram-negative bacteria. Some reports [13] on Gram-negative bacteria with high doses of photosensitizers can also damage them, but some reports [14] showed that Gram-negative bacteria are resistant to PDT unless the permeability of its cell wall is changed.Minnock et al [15] demonstrated that Gram-negative Escherichia coli and Pseudomonas aeruginosa are as sensitive to PDT as Gram-positive bacteria. This was analyzed to be due to the different cell wall structures of Gram-positive and negative bacteria.
Dahi et al [16] used rosebengal as a photosensitizer and killed P. aeruginosa as a target organism and observed the distribution of rosebengal on bacteria by fluorescence reaction and found that it was mainly on the membrane system, especially on the cell wall, rather than in the cell body. This suggests that the principle of PDT antibacterial therapy may be based on the use of photosensitizers selectively trapped in bacteria, mainly located on the bacterial cell wall and cell membrane, which then produce singlet oxygen and other reactive oxygen species (ROS) upon laser irradiation to directly damage the bacterial cell wall and membrane system, affecting their metabolism and leading to bacterial death.
Schafer et al [17] used rosebengal as a photosensitizer and E. coli, Actinomyces and Bacillus as target organisms and found that the temperature and pH of incubation of cells with the photosensitizer had an effect on the photosensitization effect. Bacillus, as an inactive system, was not sensitive to PDT. The results suggest that DNA is not a target of PDT, while the bacterial cytosol appears to be a target of PDT attack.Vander et al [18] co-incubated Haemophilus parainfluenzae with ALA and irradiated with 630 nm laser, the bacterial survival number decreased significantly, while the bacterial survival number of the control group without ALA did not change, concluding that PDT can kill Haemophilus parainfluenzae under in vitro conditions.Hillson et al [19] mice were used as a model for in vivo PDT treatment of gastrointestinal Helicobacter infection, and microfluoroscopic observation of photosensitizer distribution revealed that fluorescence was maximally concentrated on the infected bacterial mucosa, wrapping the bacteria, and the results proved that the energy of PDT to kill Helicobacter could not damage the mucosa beneath it, concluding that PDT could be used to kill Helicobacter on mucosal epithelium.
As bacteria gather in the periodontium to form plaque to attack the periodontal mucosa, mechanical methods are commonly used to wash away the plaque, while applying antimicrobials and antiseptics. Wilson et al [20] demonstrated that plaque could be eliminated by PDT without harming the normal periodontal mucosa, and Soukos et al [21] designed a test using a polyllysine (PL) conjugate with Chlorine6 (Ce6) as a photosensitizer, which had positive, neutral, and negative charges on the surface, and used the three The three conjugates were incubated with Gram-positive and Gram-negative bacteria causing oral periodontal plaque, respectively, and irradiated with red light at 671 nm for 10 min after incubation for 1 min. For Gram-positive bacteria, the bactericidal rate of the cationically charged photosensitizer was greater than 99.99% without damaging mucosal epithelial cells. For Gram-negative bacteria, the bactericidal rate was 99% with cationically charged photosensitizers, 91% with neutrally charged photosensitizers, and 76% with anionically charged photosensitizers. The results suggest that the cationically charged photosensitizer PL-Ce6 conjugate may have a good application in PDT for periodontal treatment.
PDT for bone marrow transplant decontamination
Autologous and allogeneic bone marrow transplantation is often used to treat leukemia and other humoral tumors. Autologous bone marrow transplantation has several advantages, significantly avoiding the risk of rejection, viral infections and lymphoid tissue proliferation disorders. Unfortunately, however, the relapse rate is high [22].
PDT is a new technique for ex vivo bone marrow transplantation decontamination and several photosensitizers have been used in studies including DHE, BPD, CIAIPc and MC540.Bone marrow transplantation involves suspension of individual cells susceptible to damage by photosensitization reactions.MC540 has been widely used in clinical studies and this dye preferentially binds leukemic cells, lymphoma cells and some viral infections. PDT reduces promyelocytic leukemia cells by up to 8Log under conditions that preserve 50% of pluripotent stem hematopoietic cells [23]. Purification of non-Hodgkin’s lymphoma has been investigated [24], and MC540-mediated PDT reduced non-Hodgkin’s lymphoma cells by 4-5Log in an in vitro trial with a photosensitizer dose that ensured 50% normal hematopoietic progenitor cells.MC540 was the first photosensitizer used in clinical trials, and it was found to be several times larger than the dose used in preclinical trials. In addition, MC540-mediated photosensitization was found to suppress T and B cell immunity [25]. Thus, it can cause immunosuppression in autochthonous bone marrow transplantation and significantly reduce immune rejection in allogeneic bone marrow transplantation.
PDT against viral-like diseases
The first study of PDT for viruses was on phages, and the penetration of photosensitizers was found to be a variable factor. Several animal viruses, including adenovirus and cowpox virus, can be inhibited by PDT. Resistant viruses incubated with photosensitizers can become susceptible to PDT with increased viral capsid permeability [26]. The earliest patients were suffering from cutaneous herpes simplex virus with a neutral red dye photosensitizer and white light [27].PDT antiviral therapy is still in preclinical studies with trials of different photosensitizers and light irradiation.
Papillomavirus.
Papilloma is a rapidly growing benign epithelial tumor caused by papillomavirus that can become severe and life-threatening. It is usually removed surgically, but is prone to recurrence and prolongs the course of the disease [28]. The disease is equally prevalent in children and adults, and PDT has been considered as an effective treatment for laryngeal papilloma.
Shikowitz et al. first took Dutch rabbit papilloma virus, inoculated it in cottontail rabbits to make an animal model of papilloma virus, administered hematoporphyrin derivative (HPD) intravenously and irradiated with white light, resulting in significant tumor regression. They [30] used DHE as a photosensitizer and PDT to treat an animal model of cottontail rabbit papilloma mediated by Dutch rabbit papilloma virus. The tumor did not recur and no tumor was seen on biopsy of normal tissue near the lesion, and no tumor virus was detected by DNA testing after 18 months of observation. They [31] treated this laryngeal papillomavirus patient with PDT since 1988 and randomized 81 patients aged 4 to 74 years with moderate to severe disease into a PDT-treated group of 48 and a control group of 33. The control group received conventional antiviral therapy, while half of the patients in the PDT group were given DHE 3.25 mg/kg, and the other half were given DHE 4.25 mg/kg, administered 48 to 72 hours prior to photoluminescence. The results showed a significant regression of the tumor in the PDT group compared to the control group, which was more pronounced in the group given DHE4.25 mg/kg.
Karrer et al. treated a 65-year-old woman with 5-aminolevulinic acid (5-ALA) as a photosensitizer and PDT. The patient had multiple warty lesions on her hands and upper extremities. The history was 45 years, with a history of basal cell carcinoma, and electronic section showed papillomavirus infection. 20% 5-ALA was injected intravenously, and the lesion area was irradiated with 580-740 nm laser at a power density of 160 Mw/cm2. after PDT, blistering and crusting appeared, but healed quickly, with no scar formation after 5 weeks, with remarkable results. after 6 months, local biopsy showed no papillomavirus, and the tissue was completely After 12 months, there was recurrence in individual lesion areas. They concluded that although the long-term efficacy of this method of treatment is not certain, it should be a good method for the immediate treatment.
Abramson et al [33] treated 33 patients with laryngeal papillomavirus with DHE as a photosensitizer and PDT and no recurrence even in the most severe cases.Feyh et al [34] treated 21 patients with recurrent laryngeal papillomavirus infection occurring in head and neck tumors with HPD as a photosensitizer and PDT and showed a cure rate of 95% at 4 years.Although this result is exciting, the PDT does not eliminate the potential for papillomavirus infection in normal tissues. Moreover, the common skin and genital damage caused by PDT has not been controlled.
Human immunodeficiency virus (HIV) and blood-borne viruses
There is some data to demonstrate that PDT is effective in removing disease-causing viruses from the blood without damage to the cells in the blood and to the blood as a whole. Susceptible viruses include human immunodeficiency virus I (HIV-I), herpes simplex virus (HSV), human cytomegalovirus, and monkey virus.
PDT inhibits viral photosensitizers such as DHE, BPD, Aluminiumphthalocyanine, and MC540.Photosensitization inhibition is thought to result from the action of lipids and proteins on the oxidized viral capsid.MC540 antiviral mechanisms have been investigated [38,39],and current evidence suggests that MC540-mediated PDT damages the viral capsid, which is a component that connects components of the viral parasitic host cell and determines the ability of the virus to adhere to and penetrate the host cell. Because these photosensitizers do not target nucleic acids within the virus, PDT is ineffective against viruses without capsid encapsulation, such as poliovirus I and human adenovirus I. These photosensitizers may not contact viral DNA, and they do not have mitogenic properties.
PDT is considered a promising method for pre-transfusion decontamination and disinfection of blood pathogenic organisms. It is valued because of its low cost and simple method. Of course, it is acceptable that some coagulation proteins such as coagulation factor VIII and Willebrand factor are inactivated by the action of PDT [40].Mathews et al [35] found that DHE and BPD-mediated PDT treatment of virus-contaminated blood did not damage erythrocytes, complement and immunoglobulins.Sieber et al [36] demonstrated that MC540-mediated PDT killed the virus while injuring very few erythrocytes, factor VIII, and willebrands factor. After BPD-mediated PDT of blood naturally infected with virus, the virus that had not yet invaded the host and the virus-infected leukocytes scattered in the blood were effectively killed, while erythrocytes and uninfected leukocytes were uninjured.
Benhur et al. performed PDT with Phthalocyanines and red light in blood before transfusion and found that it prevented red blood cell infection, but a possible complication was red blood cell aggregation. In contrast, it was prevented by pre-addition of antioxidants. north et al [37] found potassium leakage and IgG antibody binding in red blood cells after PDT treatment, suggesting some possible red blood cell damage. This observation, combined with the incomplete killing of HIV found in their trial, suggests that the use of PDT as a commercial sterilized blood or blood product may be a long way off. However, it is feasible as a prior means.
Since active cells are sensitive to PDT and HIV replicates only in active CD4T lymphocytes, this point facilitates PDT treatment. It is suggested that PDT may be used as a method to reduce HIV in patients, and that in vitro treatment of blood or leukocytes from HIV-infected patients may stabilize or improve immune function due to viral suppression and modulation of leukocyte activity. Therefore PDT may be a beneficial treatment in this regard.
Benhur et al. used SilliconphthalocyaninePc4 as a photosensitizer and performed PDT on blood containing HIV-infected erythrocytes and lymphocytes, irradiated with red light from 600 to 800 nm at an energy density of 90 J/cm2, and controlled blood was subjected to electrophoresis to record characteristic DNA ladders, and it was observed that 30 minutes after illumination The toning was recorded with a toning kit and flow cytometry, and 3 hours after 10.5 J/cm2 irradiation, about 92.5% of HIV-infected cells showed cell toning and eventually 99% of cells died.
Hebeda et al. observed the efficacy of PDT in the treatment of human acquired immunodeficiency syndrome (AIDS)-associated Kaposi’s sarcoma. 9 homosexual patients were treated with Photofrin injected at 2 mg/kg body weight, with a light dose of 120 J/cm2 in 5 patients and 70 J/cm2 in the remaining 4. 83 areas of skin lesions were observed 3 to 8 months after treatment, and significant efficacy was found with The tumor disappeared. The response was stronger in the head lesions than in the limb lesions, and the size of the tumor was inversely proportional to the intensity of the response. However, strong systemic side effects, such as scar formation and hyperpigmentation, were observed in the 120 J/cm2 group. Therefore, they believe that PDT can treat this disease, but it is not appropriate to use 70-120 J/cm2 light dose.
Problems that remain to be solved
Although PDT has many advantages in the treatment of bacterial and viral diseases, the author believes that there are also many issues that need further discussion before it is formally used in the clinic: First, a large number of trials have focused on in vitro cultures of bacteria and viruses, individually used in animal models and patients, and have achieved some efficacy, but the mechanism has not been fully elucidated. However, the mechanism has not yet been fully elucidated. There is still a gap until the method is really widely used in patients infected with bacterial and viral diseases, and clinical observation is needed. Secondly, most of the current studies target infections on the body surface or the inner surface of cavernous organs (e.g. respiratory tract, digestive tract, etc.), and for infections in substantive organs (e.g. liver, etc.), it is still difficult to solve them due to the current PDT conditions. Again, in order to seek the best effect of treatment, there are a series of problems in choosing laser and photosensitizer, including the selection of photosensitizer, entry diameter, dose and administration time, and an optimal photosensitizer has not been found yet. The choice of light source, irradiation time, power, level, and irradiation method will also vary in results. Finally, after PDT causes bacterial or viral necrosis, the necrotic tissue will release some inflammatory mediators, whether it can cause secondary inflammation and how it affects the disease remains to be seen.
Summary and outlook
Although PDT treatment for bacterial and viral diseases is in the preclinical exploration stage and some problems still need to be solved, the method is based on the pathological basis of bacterial and viral diseases, which is the rapid growth and multiplication of bacteria and viruses to attack the host, and the characteristics of specific retention of photosensitizers in bacteria and viruses. As a new type of therapy that selectively kills diseased tissues without harming normal tissues, it is simple, less invasive and less expensive than other therapies. With the emergence of newer photosensitizers and more suitable lasers, the future of PDT for bacterial and viral diseases will become brighter and brighter. It is believed that in the near future, it will be effective in treating many patients with bacterial and viral infections.