The Rapid Development and Early Success of Covid 19 Vaccines Have Raised Hopes for Accelerating the Cancer Treatment Mechanism.

The Covid-19 pandemic has brought about rapid change in medical science. The production of new generation vaccines for this disease has surprised even their most optimistic supporters. Not only have these vaccines proven to be effective, but the importance of this disease and pandemic situation also significantly shortened the long-standing process of validating such products. Vaccination is a type of immunotherapy. Researchers have long been looking at vaccines as a possible treatment for cancer (Geynisman et al., 2014). In the same way that vaccines work against infectious diseases, attempts are being made to develop vaccines to identify specific proteins on cancer cells. This helps the immune system recognize and attack cancer cells. Cancer vaccines may help: I) Prevent the growth of cancer cells (Bialkowski et al., 2016), II) Prevent recurrence of cancer (Stanton and Disis, 2015), III) Destroy cancer cells left over from other treatments. The following types of cancer vaccines are being studied: Antigen Vaccines. These vaccines are made from specific proteins or antigens of cancerous cells. Their purpose is to stimulate the immune system to attack cancer cells (Tagliamonte et al., 2014). Whole-Cell Vaccines. A whole-cell vaccine uses the entire cancer cell, not just a specific molecule (antigen), to generate the vaccine. (Keenan and Jaffee, 2012).Dendritic Cell Vaccines. Dendritic cells help the immune system identify abnormal cells, such as cancerous cells. Dendritic cells are grown with cancer cells in the laboratory to produce the vaccine. The vaccine then stimulates the immune system to attack cancer. (Wang et al., 2014; Mastelic-Gavillet et al., 2019). DNA Vaccines. These vaccines are made from DNA fragments of cancer cells. They can be injected into the body to facilitate immune system cells can better respond and kill cancer cells (Gatti-Mays et al., 2017).Other Types of Cancer Vaccines. such as Anti idiotype vaccines. This vaccine stimulates the body to generate antibodies against cancerous cells. An example of an anti-idiotype antibody is Racotumomab or Vaxira (Cancer, 2016). However, conditions and considerations after Corona does not seem to be the same as before. The current pandemic situation has also led to major changes in the pharmaceutical and Vaccine production process and international protocols. Some of the most critical issues that can accelerate the introduction of cancer vaccines are: 1. Typical drug and vaccine development timeline. A typical vaccine needs 5 to 10 years and sometimes longer to design secure funding, and get approval (Figure 1). Less than 10 percent of new drugs, which are entered in the different phases of clinical trials, are advanced to approval by the Food and Drug Administration (FDA)(Cancer, 2020a). However, now the situation is not normal. Dozens of Covid 19 vaccines are starting clinical trials. Some of them use RNA and DNA technology, which delivers the body with missions to produce its antibodies against the virus. There are already at least 254 therapies and 95 vaccines related to Covid-19 being explored. However, it seems that the experiences gained in this pandemic, and advances in technology, may be effective in shortening the production path of other vaccines and drugs and the process of its approval at the national and international levels in the future. In Figure 2, the time course of production of conventional vaccines in comparison with Covid 19 vaccines (Cancer, 2020b) is shown.2. The introduction of messenger RNA (mRNA) technology into the field of prevention and treatment. Over the past decades, this technology has been considered an excellent alternative to conventional vaccination methods. Proper potency and low side effects, the possibility of fast production and relatively low production cost are its advantages. However, until recently, the instability of this molecule has been a major problem in its application. This research was started many years ago by two companies that played a significant role in developing the first Covid vaccines, so BioNTech and Moderna were able to quickly transfer their experience in the field of Covid vaccine development (Pardi et al., 2018; Moderna, 2020). Figure 3 shows how mRNA vaccines work. Bout Pfizer – BioNTech and Moderna mRNA vaccines were more than 90 % effective in preclinical stages. Millions of doses of these two vaccines are currently being injected into eligible individuals worldwide. 3. Considering the use of artificial intelligence in assessing the effectiveness of vaccines. There are always doubts about the effectiveness of the new drug in treating the disease. Once the vaccine is widely available, we will know more about its effectiveness versus it works under carefully controlled scientific testing conditions. Vaccines will continue to be monitored after use. The data collected helps professionals understand how they work in different groups of people (depending on factors such as age, ethnicity, and people with different health conditions) and also the length of protection provided by the vaccine. Artificial intelligence (AI) is an emerging field, which reaches everywhere and not only as a beneficial industrial tool but also as a practical tool in medical science and plays a crucial role in developing the computation vision, risk assessment, diagnostic, prognostic, etc. models in the field of medicine (Amisha et al., 2019). According to the wide range of AI applications in the analysis of different types of data, it can be used in vaccine production, safety assessments, clinical and preclinical studies and Covid 19 vaccines adverse reactions (CDC, 2019). Indeed, most cancer vaccines are therapeutic, rather than prophylactic, and seek to stimulate cell-mediated responses, such as those from CTLs, capable of clearing or reducing tumor burden. There are currently FDA-approved products for helping cancer treatment such as BREYANZI, TECARTUS and YESCARTA for lymphoma, IMLYGIC for melanoma, KYMRIAH for acute lymphoblastic leukemia, and PROVENGE for prostate cancer. Over the past decade, most of BioNTech's activities have been in the field of cancer vaccine design and production for melanoma (two clinical trials), breast cancer (one clinical trial), and the rest concerning viral and veterinary vaccines (two clinical trials). Also Maderno company has been working on Individualized cancer vaccines (one clinical trials), and vaccines for viral infections such as Zika and Influenza and veterinary vaccines (several clinical trials) (Pardi et al., 2018). Therefore, it can be said, mRNA technology that has been the subject of much research into the treatment of cancer has been shifted and rapidly used to produce and use the Covid 19 vaccine. The current pandemic situation has necessitated the acceleration of Covid 19 vaccines and drugs and national and international protocols for their approval. If the currently produced vaccines can continue to be as successful as the preclinical and early phase studies, these changes and evolution have raised hopes for accelerating the use of these technologies and mechanisms in the field of cancer and other diseases vaccines, including HIV and influenza.

Combination therapy with TiO2 nanoparticles and cisplatin enhances chemotherapy response in murine melanoma models

Background Despite recent progressions in the treatment of melanoma, the response to conventional therapies and the long-term survival in melanoma patients still remain poor. Recently, the use of nanoparticles (NPs) has been highlighted for promoting the chemotherapeutic effects of cytotoxic drugs in melanoma. The aim of this study is to mechanistically evaluate the potential of titanium dioxide (TiO2) nanoparticles (NPs) for enhancing chemotherapy effects in in vitro and in vivo models of murine melanoma. Methods The F10 melanoma cells were exposed to different concentrations of TiO2 NPs and/or cisplatin, then cell growth, cell viability, and cell death were evaluated. In parallel, C57BL/6 syngeneic melanoma mice were treated by TiO2 NPs and/or cisplatin, and then drug responses, tumor size and mice’s organs were studied pathologically. Autophagy was examined by evaluating the formation of autophagosomes and gene expression levels of autophagy markers (ATG5 and ATG6) by fluorescent microscopy and qPCR, respectively. Results Nontoxic concentrations of TiO2 NPs (50 µg/ml) promote anti-proliferative and cytotoxic effects of cisplatin in F10 melanoma cells, which is mediated through the induction of autophagy and necrotic cell death. Whereas TiO2 NPs have no cytotoxic or metastatic effects in melanoma mice, its combination with cisplatin enhances drug responses (up to 50%), leading to higher inhibition of tumor growth compared with each monotherapy. Conclusion The combination of TiO2 NP with cisplatin enhances chemotherapy response in both in vitro and in vivo melanoma models. In addition, autophagy plays an essential role during sensitizing melanoma cells to chemotherapy (AU)

Combination therapy with TiO2 nanoparticles and cisplatin enhances chemotherapy response in murine melanoma models.

BACKGROUND: Despite recent progressions in the treatment of melanoma, the response to conventional therapies and the long-term survival in melanoma patients still remain poor. Recently, the use of nanoparticles (NPs) has been highlighted for promoting the chemotherapeutic effects of cytotoxic drugs in melanoma. The aim of this study is to mechanistically evaluate the potential of titanium dioxide (TiO2) nanoparticles (NPs) for enhancing chemotherapy effects in in vitro and in vivo models of murine melanoma. METHODS: The F10 melanoma cells were exposed to different concentrations of TiO2 NPs and/or cisplatin, then cell growth, cell viability, and cell death were evaluated. In parallel, C57BL/6 syngeneic melanoma mice were treated by TiO2 NPs and/or cisplatin, and then drug responses, tumor size and mice's organs were studied pathologically. Autophagy was examined by evaluating the formation of autophagosomes and gene expression levels of autophagy markers (ATG5 and ATG6) by fluorescent microscopy and qPCR, respectively. RESULTS: Nontoxic concentrations of TiO2 NPs (50 µg/ml) promote anti-proliferative and cytotoxic effects of cisplatin in F10 melanoma cells, which is mediated through the induction of autophagy and necrotic cell death. Whereas TiO2 NPs have no cytotoxic or metastatic effects in melanoma mice, its combination with cisplatin enhances drug responses (up to 50%), leading to higher inhibition of tumor growth compared with each monotherapy. CONCLUSION: The combination of TiO2 NP with cisplatin enhances chemotherapy response in both in vitro and in vivo melanoma models. In addition, autophagy plays an essential role during sensitizing melanoma cells to chemotherapy.

Effect of Gamma Irradiation on Microbial Decontamination, Crude Nutrient Content, and Mineral Nutrient Composition of Laboratory Animal Diets.

Laboratory animal models are an important part of test design. Certain conditions such as microbial contamination in diets of these models could affect the results of experiments. One of the most important routes that predispose to contamination is generated through feeding of laboratory animals. This study aimed to show the effect of gamma irradiation in reducing bacteria concentrations, crude nutrient content, and concentrations of some minerals and trace elements in laboratory animal diets. Large-sized pellets with 10–15 mm diameter (commonly used for rats and hamsters) and small-sized pellets with 3–5 mm diameter (used for rabbits and guinea pigs) along with skimmed milk powder (SMP) as a food additive were exposed to gamma irradiation with different doses ranging from 3 to 30 kGy. The total microbial contamination and any possible changes in some mineral nutrient composition and the crude nutrient content were determined pre- and post-irradiation. Our data revealed that 25 kGy in pelleted diets and 18 kGy in SKM had superior effects in the reduction of bacterial contamination with little change in crude nutrient content and minerals and trace elements in nutrient requirements of laboratory animals. According to the results, gamma irradiation had minimal effects on crude nutrient content and the concentrations of some minerals and trace elements of laboratory animal diets, and it also eliminated bacterial and fungal contamination load. By using gamma irradiation, this method could yield a favorable outcome in controlling microbial contamination of animal diets.

Evaluation of the NOX5 protein expression and oxidative stress in sperm from asthenozoospermic men compared to normozoospermic men.

PURPOSE: NADPH oxidase 5 (NOX5), the main isoform of NOX in spermatozoa, has been recognized as the main active generators of reactive oxygen species (ROS), including superoxide anion (O 2 -. ) and hydrogen peroxide (H2O2). ROS have been shown to play important roles in many physiological and pathological conditions in spermatozoa. The present study aims to investigate the alterations of NOX5 protein expression and oxidative stress (OS) status in asthenozoospermic men compared to normozoospermic men. METHODS: Semen samples were collected from 25 asthenozoospermic men and 28 normozoospermic men. In this study, NOX5 protein expression was evaluated by Western blotting. An OS status was evaluated by measuring of ROS (O 2 -. and H2O2), DNA damage and plasma membrane integrity in spermatozoa. RESULTS: The protein expression of NOX5 (p < 0.0001) was remarkably higher in asthenozoospermic men in comparison to normozoospermic men. In addition, the percentages of intracellular O 2 -. (p < 0.0001), H2O2 (p < 0.0001) in viable spermatozoa, apoptotic sperm cells with altered plasma membrane (p < 0.001) and DNA damage (p = 0.001) were significantly increased in asthenozoospermic men compared to normozoospermic men. CONCLUSIONS: The present study provides evidence that the overexpression of NOX5 protein may induce excessive ROS production and oxidative stress damages to DNA and plasma membrane integrity in asthenozoospermic men.

The Characteristics of an Ovine Lymphoid Cell-Line sensitive to Vaccinal Infectious Bursal Disease Virus Strain.

Infectious bursal disease (IBD), also known as Gumboro disease, is a globally well-known disease with a significant socio-economic effect. For control of IBD, several commercial egg- and cell-based vaccines are prepared. The cell-based IBD vaccines are significantly cost-effective; however, it is essential to confirm their safety and efficacy. The main cell line used to product the cell-based IBD vaccines, is a primary chicken embryo fibroblast (CEF). Nevertheless, manipulation of CEF is extremely challenging and time-consuming. This study aimed to characterize a sensitive suspension cell culture from ovine lymphoid, according to WHO technical report series; No. 978, Annex III. This authentication covered the growth curves, sensitivity, stability, karyotyping and identifying the adventitious agents. This cell line passed all defined tests and was considered as a suitable one for IBD vaccine preparation in a large scale.

Can calcitonin nasal spray reduce the risk of recurrence of central giant cell granuloma of the jaws? A double-blind clinical trial.

Recurrence is a major problem following the treatment of aggressive central giant cell granuloma (CGCG). The aim of this study was to compare the frequency of recurrence between patients who received calcitonin nasal spray after curettage of CGCGs and those who did not. A double-blind clinical trial was designed. Patients were allocated to one of two groups: those in the calcitonin group underwent curettage and received calcitonin salmon nasal spray 200IU/day once a day for 3 months after surgery; those in the control group underwent curettage of CGCGs and received a placebo once a day for 3 months after surgery. All patients were followed for 5 years after surgery. Twenty-four patients were treated in the two groups. There was no difference in age, sex, tumour size, or tumour location between the two groups (P>0.05). Eight of the 24 patients (33.3%) had recurrences during the follow-up period: one in the calcitonin group (9.1%) and seven in the control group (53.8%). Analysis of the data demonstrated a significant difference between the two study groups (P=0.033). It appears that calcitonin nasal spray may reduce the frequency of recurrence in aggressive CGCGs in the mandible and maxilla.

Evaluation of immunological interaction between spermatozoa and fallopian tube epithelial cells.

Toll-like receptors (TLR) are one of the major compartments of innate immune system. It was revealed that the TLR have relevance in ovulation, sperm capacitation and fertilisation. So, in this study, the expression of TLR, their adaptor molecules and cytokines in human fallopian tube cell line under the effect of human normal spermatozoa was evaluated. TLR mRNA and protein were evaluated in OE-E6/E7 cell line. Semen samples from 10 donors were collected and co-incubated with OE-E6/E7 cell line and used as sperm group, and cell line without spermatozoa was used as control group. Afterwards, the level of TLR, their adaptor molecule and cytokine mRNA expression was compared using qPCR in sperm and control groups, and supernatant was used for ELISA. To determine whether elevated cytokine reaction to spermatozoa in OE-E6/E7 cell line is mediated via TLR, TLR3 function-blocking antibody was used. OE-E6/E7 cell line expressed TLR1-6 genes and proteins. TLR expressions, especially TLR3 and TLR5, in OE-E6/E7 cell line under the effect of spermatozoa were significantly higher. Also, levels of adaptor molecules and cytokine production were increased in sperm group than in control group (P < 0.05). So, it may be hypothesised that TLR are essential for spermatozoa and fallopian tube immunological interaction and for preparing safe environment for important events in fallopian tube.

Antioxidant effect of manganese on the testis structure and sperm parameters of formalin-treated mice.

Manganese inhibits oxidative stress damage. The aim of this study was to investigate the protective role of manganese on testis structure and sperm parameters in adult mice exposed to formaldehyde (FA). Twenty adult male NMRI mice were selected and randomly divided into four groups: (i) control; (ii) sham; (iii) 'FA'-exposed group; and (iv) 'FA and manganese chloride'-exposed group. The FA-exposed groups received 10 mg kg(-1) FA daily for 14 days, and manganese chloride was just injected intraperitoneally 5 mg kg(-1) on 2nd weeks. Mice were sacrificed, and spermatozoa were collected from the cauda of the right epididymis and analysed for count, motility, morphology and viability. The other testicular tissues were weighed and prepared for histological examination upon removal. Seminiferous tubules, lumen diameters and epithelium thickness were also measured. The findings revealed that FA significantly reduced the testicular weight, sperm count, motility, viability and normal morphology compared with control group (P ≤ 0.05). In addition, seminiferous tubules atrophied and seminiferous epithelial cells disintegrated in the FA group in comparison with the control group (P ≤ 0.05). However, manganese improved the testicular structure and sperm parameters in FA-treated mice testes (P ≤ 0.05). According to the results, manganese may improve and protect mice epididymal sperm parameters and testis structure treated with FA respectively.

Detectability of Her2 positive tumors using monoclonal antibody conjugated iron oxide nanoparticles in MRI.

Detecting an imaging signal from a small number of cells is vital when a disease needs to be diagnosed in an early stage of development. Molecular and genetic information from cancer cell types provide a guide for specific imaging based on gene expression and their activities on the cell membrane. Various physical and biological parameters affect the capability of an imaging system to provide an efficient procedure for biomarker imaging. Iron oxide based magnetic nanoparticles conjugated to breast cancer monoclonal antibody (Her2) were used as a specific contrast agent for detection of the tumor cells in nude mice models. All processes for the nanoparticle synthesis, antibody development, and conjugation strategies were designed and evaluated in the current work. The final engineered product was found to be without precipitate containing 20 microg antibody/mg magnetic nanoparticles at 10 mg Fe/ml solution. This contrast agent has a high affinity for the BT474 breast cancer cells. MRI images of nude mice bearing tumor cells confirm this specific biomarker based imaging protocol.

Early spontaneous immortalization and loss of plasticity of rabbit bone marrow mesenchymal stem cells.

OBJECTIVES: Bone marrow-derived mesenchymal stem cells (BM-MSC) have been widely used for cell therapy and tissue engineering purposes. However, there are still controversies concerning safety of application of these cells after in vitro expansion. Therefore, we aimed to investigate the characteristics of rabbit BM-MSC during long-term culture. MATERIALS AND METHODS: In this study, we have examined growth kinetics, morphological changes, differentiation potential and chromosomal abnormalities, as well as tumour formation potential of rabbit BM-MSC in long-term culture. RESULTS AND CONCLUSION: We found that shortly after isolation, proliferation rate of rabbit BM-MSC decreases until they enter a dormant phase. During this period of quiescence, the cells are large and multinucleate. After some weeks of dormancy we found that several small mononuclear cells originated from each large multinucleate cell. These newly formed cells proliferated rapidly but had inferior differentiation potential. Although they were immortal, they did not have the capability for tumour formation in soft agar assay or in nude mice. This is the first report of spontaneous, non-tumorigenic immortalization of BM-MSC in rabbits. The phenomenon raises more concern for meticulous monitoring and quality control for using rabbit BM-MSC in cell-based therapies and tissue engineering experiments.

MR relaxivity measurement of iron oxide nano-particles for MR lymphography applications.

The aim of this study was to assess the T1, T2 and T2* relaxivity of Ultrasmall Super Paramagnetic Iron Oxide (USPIO) nano-particles in vitro and in vivo in rat models with magnetic resonance imaging at 1.5T. First, relaxation properties of USPIO nano-particles at different doses were measured using related SE and GRE MR imaging protocols. The relation between dose and relaxation were observed which is linear; Higher dose of the nano-particles means higher relaxivity. Based on this relation, an optimum protocol can be proposed for obtaining the best image contrast at each situation. Then detection ability of MRI protocols was studied for USPIO nano-particles with injection of the particles in the rat. The optimum MR protocols were used to observe the signal change of lymph nodes in rat.

Enhancement of indomethacin-induced gastric damage by mouth breathing in rabbits.

Previous studies have reported that mouth breathing is associated with respiratory acidosis. Regarding to the reports that renal elimination of weak acids such as indomethacin is pH dependent, this study was carried out to evaluate the role of mouth breathing on plasma level of indomethacin and indomethacin-induced gastric damage in rabbits. Mouth breathing was induced by surgical ligation of nostrils under general anesthesia. One day after the operation, arterial blood samples were collected for acid-base balance analysis and indomethacin was administered intraperitoneally in a single dose of 40mg/kg. The animals were killed 4h after indomethacin administration and blood samples were collected for spectrofluorometric determination of indomethacin in plasma. The results showed that indomethacin induces more severe gastric damage in nose obstructed rabbits compared with sham and unoperated (UNOP) animals. Acid-base analysis revealed a respiratory acidosis in nose obstructed rabbits and indomethacin level of plasma was significantly higher in nose obstructed animals in comparison with control rabbits. The study shows that mouth breathing can increase the potentiation of indomethacin-induced gastric mucosal damage that may be due to higher level of indomethacin in plasma of nose obstructed animals.

Preconditioning of the rat random-pattern skin flap: modulation by opioids.

Opioid receptors have been implicated in protecting several organ systems from ischaemic events. The authors have studied the effects of opioid receptors on random-pattern skin flap survival. Sixty-nine male Sprague-Dawley rats were used. Bipedicled dorsal skin flaps (2 x 8 cm) were elevated at the midline. Different doses of morphine (0.01, 0.1, 1 and 5 mg/flap) were administered locally in the cranial half of the flap and systemically through intraperitoneal injections (5 and 10 mg/kg). In another experiment, 0.4 mg/flap of naloxone was injected followed by 5 mg/flap injection of morphine to determine whether the effect of morphine is receptor mediated. The role of the opioid receptors in the ischaemic preconditioning (IPC) phenomenon was investigated by administration of naloxone (0.4 mg/flap) 1 h before clamping the cranial pedicle for 20 min followed by 40 min of reperfusion. Appropriate control groups were included. The cranial pedicle was cut 2 h after saline or drug administration in all groups and flap survival area was evaluated on the seventh postoperative day. Local administration of morphine in higher doses (1 and 5 mg/flap) significantly reduced the amount of flap necrosis when compared to that of the control cohort (P < 0.05). Naloxone abolished this protective effect of morphine. Furthermore naloxone significantly decreased the anti-ischaemic effect of the IPC. Systemic administrations of morphine had no significant effect on flap survival area in compare with the control group.

In vitro and in vivo hemocompatibility evaluation of graphite coated polyester vascular grafts.

Attempts have been made in this study to prepare a homogeneous and stable coating of graphite on polyester vascular grafts (GPVG) using an electrophoresis method to evaluate thromboresistant and blood compatibility of GPVG in comparison to non-coated PVG and InterGard (collagen sealed PVG) as control. Lactate dehydrogenase (LDH) activity measurement was carried out on all PVG types to evaluate platelet adhesion. To examine tissue reaction GPVG and non-coated sheets of knitted polyester fabric were implanted simultaneously in the dorsal flank of rats subcutaneously. The GPVG, non-coated and control were implanted in descending aorta as end-to-end or end-to-side implantation substitution in 25 sheep for 4-60 weeks. Results showed that the graphite coating on polyester vascular grafts reduced the number of adherent platelets and prevent platelet activation and spreading on the surface in comparison with non-coated and control. Pathological investigation showed inflammatory reactions were totally resolved after 12 weeks and there was no difference in the tissue reaction between graphite coated, non-coated and control patches. All grafts remained patent and there was no significant difference in patency rate between these three types of PVG. We found that GPVG has no need for pre-clotting and it showed lower platelet aggregation, thinner capsule formation and lower calcification after 15 months. However, suturing of GPVG was more difficult in comparison with the other types.

Isocyanate-terminated urethane prepolymer as bioadhesive material: evaluation of bioadhesion and biocompatibility, in vitro and in vivo assays.

Attempts have been made to evaluate the degree of bioadhesion and biocompatibility of a synthesized urethane prepolymer with specially tailored microstructure. Wetting behaviour and extent of interfacial adhesion of the prepared prepolymer towards biological substrates were examined by in vitro methods. The former was carried out by measuring the contact angle between drops of the prepolymer liquid and a biological surface, while the latter was determined from the force between the prepolymer and tissue model or mucus. The obtained results exhibited good tissue wettability and bioadhesion by the prepolymer. Preliminary evaluation of biocompatibility for the uncatalytically cured prepolymer films was performed by cytotoxicity and histotoxicity experiments. Results showed a significant growth for the adhered L929 fibroblast cells within a period of 5 days incubation. Also, no severe inflammatory tissue response towards the samples implanted in rabbit for 16 weeks was seen. These observations can support the potentiality of the designed urethane prepolymer to be applied as hemostatic agent.

Naloxone is protective against indomethacin-induced gastric damage in cholestatic rats.

We compared indomethacin-induced gastric damage in three groups of rats-bile duct-ligated, sham-operated, and unoperated-and evaluated the role of the opioid system by blocking the effects of endogenous opioids with naloxone. Indomethacin was administered orally in a dose-dependent manner at 10, 30, and 45 mg/ kg. Naloxone was administered intraperitoneally in several doses of 0.5 and 1 mg/kg, starting 30 min before indomethacin (10mg/kg) administration and continued every 30 min. The animals were killed 4h after indomethacin administration. Indomethacin induced more severe gastric damage in bile duct-ligated rats than in sham and unoperated animals, and administration of naloxone (1 mg/kg) every 30 min inhibited the potentiation of indomethacin-induced gastric damage in bile duct-ligated rats, but not in the control groups (sham-operated and unoperated rats). Plasma indomethacin level was also measured, by fluorometry, but showed no significant difference between the groups. Endogenous opioids have been reported to accumulate in plasma of cholestatic animals, and, considering the results of this study, we suggest the opioid system plays an important pathophysiologic role in the pathogenesis of peptic ulcers in cholestatic subjects.