Sweet-Tasting Natural Proteins Brazzein and Monellin: Safe Sugar Substitutes for the Food Industry

This article presents the results of a comprehensive toxicity assessment of brazzein and monellin, yeast-produced recombinant sweet-tasting proteins. Excessive sugar consumption is one of the leading dietary and nutritional problems in the world, resulting in health complications such as obesity, high blood pressure, and cardiovascular disease. Although artificial small-molecule sweeteners widely replace sugar in food, their safety and long-term health effects remain debatable. Many sweet-tasting proteins, including thaumatin, miraculin, pentadin, curculin, mabinlin, brazzein, and monellin have been found in tropical plants. These proteins, such as brazzein and monellin, are thousands-fold sweeter than sucrose. Multiple reports have presented preparations of recombinant sweet-tasting proteins. A thorough and comprehensive assessment of their toxicity and safety is necessary to introduce and apply sweet-tasting proteins in the food industry. We experimentally assessed acute, subchronic, and chronic toxicity effects, as well as allergenic and mutagenic properties of recombinant brazzein and monellin. Our study was performed on three mammalian species (mice, rats, and guinea pigs). Assessment of animals' physiological, biochemical, hematological, morphological, and behavioral indices allows us to assert that monellin and brazzein are safe and nontoxic for the mammalian organism, which opens vast opportunities for their application in the food industry as sugar alternatives.

iPSC-derived cells lack immune tolerance to autologous NK-cells due to imbalance in ligands for activating and inhibitory NK-cell receptors

BACKGROUND

Dozens of transplants generated from pluripotent stem cells are currently in clinical trials. The creation of patient-specific iPSCs makes personalized therapy possible due to their main advantage of immunotolerance. However, some reports have claimed recently that aberrant gene expression followed by proteome alterations and neoantigen formation can result in iPSCs recognition by autologous T-cells. Meanwhile, the possibility of NK-cell activation has not been previously considered. This study focused on the comparison of autologous and allogeneic immune response to iPSC-derived cells and isogeneic parental somatic cells used for reprogramming.

METHODS

We established an isogeneic cell model consisting of parental dermal fibroblasts, fibroblast-like iPSC-derivatives (iPS-fibro) and iPS-fibro lacking beta-2-microglobulin (B2M). Using the cells obtained from two patients, we analyzed the activation of autologous and allogeneic T-lymphocytes and NK-cells co-cultured with target cells.

RESULTS

Here we report that cells differentiated from iPSCs can be recognized by NK-cells rather than by autologous T-cells. We observed that iPS-fibro elicited a high level of NK-cell degranulation and cytotoxicity, while isogeneic parental skin fibroblasts used to obtain iPSCs barely triggered an NK-cell response. iPSC-derivatives with B2M knockout did not cause an additional increase in NK-cell activation, although they were devoid of HLA-I, the major inhibitory molecules for NK-cells. Transcriptome analysis revealed a significant imbalance of ligands for activating and inhibitory NK-cell receptors in iPS-fibro. Compared to parental fibroblasts, iPSC-derivatives had a reduced expression of HLA-I simultaneously with an increased gene expression of major activating ligands, such as MICA, NECTIN2, and PVR. The lack of inhibitory signals might be due to insufficient maturity of cells differentiated from iPSCs. In addition, we showed that pretreatment of iPS-fibro with proinflammatory cytokine IFNγ restored the ligand imbalance, thereby reducing the degranulation and cytotoxicity of NK-cells.

CONCLUSION

In summary, we showed that iPSC-derived cells can be sensitive to the cytotoxic potential of autologous NK-cells regardless of HLA-I status. Thus, the balance of ligands for NK-cell receptors should be considered prior to iPSC-based cell therapies. Trial registration Not applicable.

Survival of human cells in tissue-engineered constructs stored at room temperature

Tissue-engineered constructs (TECs), the dermal equivalent (DE) and the skin equivalent (SE), are allogenic equivalents of the skin and derm used to treat critical skin loss. Selection of storage conditions that contribute to longer shelf life, thereby expanding the possibilities of logistics and use, is one of the major issues related to the TECs development. The study was aimed to determine the shelf life of the DE and SE TECs stored in normal saline at room temperature by assessing morphology and viability of the cells on their surface, along with the levels of endothelial growth factor (VEGF) secreted by these cells. Using the MTT assay and staining with vital dye, we discovered the following: when TECs of both types were stored in normal saline, the cells viability and metabolic activity decreased by more than 50% by days 3–4 of storage. Furthermore, these decreased faster in DEs than in SEs. Morphology of the cells isolated from DEs and SEs after the 3-day storage remained unchanged. Mesenchymal stem cells on the surface of TECs kept producing VEGF after TECs culture medium was changed for saline solution (confirmed by immunofluorescence assay), which could indicate that the cells retained essential secretory activity.

Deeper insights into transcriptional features of cancer-associated fibroblasts: An integrated meta-analysis of single-cell and bulk RNA-sequencing data

Cancer-associated fibroblasts (CAFs) have long been known as one of the most important players in tumor initiation and progression. Even so, there is an incomplete understanding of the identification of CAFs among tumor microenvironment cells as the list of CAF marker genes varies greatly in the literature, therefore it is imperative to find a better way to identify reliable markers of CAFs. To this end, we summarized a large number of single-cell RNA-sequencing data of multiple tumor types and corresponding normal tissues. As a result, for 9 different types of cancer, we identified CAF-specific gene expression signatures and found 10 protein markers that showed strongly positive staining of tumor stroma according to the analysis of IHC images from the Human Protein Atlas database. Our results give an insight into selecting the most appropriate combination of cancer-associated fibroblast markers. Furthermore, comparison of different approaches for studying differences between cancer-associated and normal fibroblasts (NFs) illustrates the superiority of transcriptome analysis of fibroblasts obtained from fresh tissue samples. Using single-cell RNA sequencing data, we identified common differences in gene expression patterns between normal and cancer-associated fibroblasts, which do not depend on the type of tumor.

[Experimental stem cell replacement transplantation in retinal pigment epithelium atrophy]

PURPOSE

To develop and evaluate the results of the modified surgical technique for transplantation of retinal pigment epithelium (RPE) differentiated from human induced pluripotent stem cells (iPSC-RPE) in the form of a cell suspension into the subretinal space of rabbits with previously induced RPE atrophy.

MATERIAL AND METHODS

The study was conducted on 10 New Zealand albino rabbits (20 eyes). One month after modeling RPE atrophy and retinal degeneration, rabbits were subjected to subretinal transplantation of iPSC-RPE cells in the form of a cell suspension. To prevent reflux of iPSC-RPE into the vitreal cavity, the injection site was sealed with 2-3 drops of autologous platelet-rich plasma (PRP). All rabbits underwent spectral optical coherence tomography (SOCT) and autofluorescence studies on the Heidelberg Spectralis system («Heidelberg Engineering», Germany). Enucleated animal eyes were studied with morphological and immunohistochemical methods.

RESULTS

In this study we developed and evaluated a modified surgical technique of transplantation of iPSC-RPE in the form of a cell suspension into the subretinal space of rabbits with induced RPE atrophy. It was found that the use of PRP helps seal the defect and prevents cell suspension reflux into the vitreous cavity, effectively minimizing intra- and postoperative complications. Morphological in vivo study and examination of histological sections showed that implantable iPSC-RPEs were correctly integrated and adhered to the choroid in the surgery site. Immunohistochemical analysis involving fluorescence-marked antibodies confirmed the survival of iPSC-RPE integrated into the retina of model animals.

CONCLUSION

This method improves the technology of iPSC-RPE transplantation on preclinical stages of the study, revealing new prospects in the treatment of degenerative diseases of the retina and the possibility of a personalized approach.

Derivation of induced pluripotent stem cells line (RCPCMi007-A-1) with inactivation of the beta-2-microglobulin gene by CRISPR/Cas9 genome editing

The mismatch of HLA haplotypes between donor and recipient adversely affects the outcome of tissue transplantation. TheB2Mgene knockout (B2M-KO) disrupts the HLA I heterodimer formation; therefore,B2M-KO cells have reduced immunogenicity to allogeneic CD8⁺ T cells. Thus, theB2M-KO IPSCs and their derivatives can potentially solve a problem of the immunological compatibility in allogeneic transplantations. Using CRISPR/Cas9-mediated genome editing, we generated a human B2M-KO iPSC line (RCPCMi007-A-1). The RCPCMi007-A-1 iPSCs express pluripotency markers, have typical stem cell morphology, maintain normal karyotype, and the ability to differentiate into three germ layers.

Propionate Induces Virulent Properties of Crohn's Disease-Associated Escherichia coli

Crohn's disease (CD) is a severe chronic immune-mediated granulomatous inflammatory disease of the gastrointestinal tract. The mechanisms of CD pathogenesis remain obscure. Metagenomic analysis of samples from CD patients revealed that several of them have the elevated level of Escherichia coli with adhesive-invasive phenotype (AIEC). Previously, we isolated an E. coli strain CD isolate ZvL2 from a patient with CD, which features AIEC phenotype. Here, we demonstrate that prolonged growth on propionate containing medium stimulates virulent properties of CD isolate ZvL2, while prolonged growth on glucose reduces these properties to levels indistinguishable from laboratory strain K-12 MG1655. Propionate presence also boosts the ability of CD isolate ZvL2 to penetrate and colonize macrophages. The effect of propionate is reversible, re-passaging of CD isolate on M9 medium supplemented with glucose leads to the loss of its virulent properties. Proteome analysis of CD isolate ZvL2 growth in medium supplemented with propionate or glucose revealed that propionate induces expression porins OmpA and OmpW, transcription factors PhoP and OmpR, and universal stress protein UspE, which were previously found to be important for macrophage colonization by enteropathogenic bacteria.

[The Role of Mutant RNA in the Pathogenesis of Huntington's Disease and Other Polyglutamine Diseases]

Polyglutamine diseases are rare, inherited neurodegenerative pathologies that arise as a result of expansion of trinucleotide CAG repeats in the coding segment of certain genes. This expansion leads to the appearance of mRNA with abnormally long repetitive CAG triplets (mCAG-RNA) and proteins with polyglutamine (PolyQ) tracts in the cells, which is why these pathologies are commonly termed polyglutamine diseases, or PolyQ diseases. To date, nine PolyQ diseases have been described: Huntington's disease, dentatorubral pallidoluysian atrophy (DRPLA), spinal and bulbar muscular atrophy (SBMA), and six different types of spinocerebellar ataxia (SCA 1,2,3,6,7, and 17). PolyQ diseases lead to serious, constantly progressing dysfunctions of the nervous and/or muscular systems, and there currently exists no efficacious therapy for any of them. Recent studies have convincingly shown that mCAG-RNA can actively participate in the pathological process during the development of PolyQ diseases. Mutant RNA is involved in a wide range of molecular mechanisms, ultimately leading to disruption of the functions of transcription, splicing, translation, cytosol structure, RNA transport from the nucleus to the cytoplasm, and, finally, to neurodegeneration. This review discusses the involvement of mutant mCAG-RNA in neurodegenerative processes in PolyQ diseases.

[At Home among Strangers: Is It Possible to Create Hypoimmunogenic Pluripotent Stem Cell Lines?]

Human pluripotent stem cells, which include embryonic stem cells and induced pluripotent cells (iPSCs), are capable of unlimited division and differentiation into all cells of the body. These cells are considered as a potential source of various types of cells for transplantations. The use of autologous iPSCs is not potentially associated with immune rejection and does not require immunosuppression required for allogeneic grafts. However, the high cost of this technology and the duration of obtaining iPSCs and differentiated cells may limit the use of autologous iPSCs in clinical practice. In addition, full equivalence and immunological compatibility of autologous iPSCs and their derivatives have been repeatedly questioned. One approach to solving the problem of the immunological compatibility of allogeneic derivatives of iPSCs can be the establishment of cell lines with reduced immunogenicity. Differentiated derivatives of such iPSCs may be suitable for transplantation to any patient. This review discusses the strategies for evading immune surveillance in normal and tumor processes that can be used to establish stem cell lines with reduced immunogenicity.

"Necessity Is the Mother of Invention" or Inexpensive, Reliable, and Reproducible Protocol for Generating Organoids

Organoids are three-dimensional (3D) cell cultures that replicate some of the key features of morphology, spatial architecture, and functions of a particular organ. Organoids can be generated from both adult and pluripotent stem cells (PSCs), and complex organoids can also be obtained by combining different types of cells, including differentiated cells. The ability of pluripotent cells to self-organize into organotypic structures containing several cell subtypes specific for a particular organ was used for creating organoids of the brain, eye, kidney, intestine, and other organs. Despite the advantages of using PSCs for obtaining organoids, an essential shortcoming that prevents their widespread use has been a low yield when they are obtained from a PSC monolayer culture and a large variation in size. This leads to great heterogeneity on further differentiation. In this article, we describe our own protocol for generating standardized organoids, with emphasis on a method for generating brain organoids, which allows scaling-up experiments and makes their cultivation less expensive and easier.

Synergy of optimized administration sequence and timing of active DC immunotherapy with a PD1 checkpoint inhibitor in a mouse model of renal cell carcinoma

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Background: AGS-003 is an immunotherapy consisting of autologous dendritic cells electroporated with amplified total tumor RNA plus synthetic CD40L RNA and is currently being tested in combination with standard of care to extend survival of newly diagnosed metastatic renal cell carcinoma (RCC) patients in the Phase 3 ADAPT clinical trial. We set out to establish a model system based on the Renca mouse model to more thoroughly study the AGS-003 mechanism of action and identify optimal combination therapies, including with a PD1 checkpoint inhibitor (aPD1 CPI). Methods: Mouse DC precursors were processed in a similar manner to how human monocytes are processed to manufacture AGS-003. Mature DCs were injected s.c. to treat BALB/c mice in an orthotopic syngeneic RCC model. This model system was utilized to test the efficacy and mechanism of action of the AGS-003-like homologous mouse DCs in combination with a murine monoclonal antibody PD1 CPI (anti-mPD1). Results: Murine DCs with similar properties to AGS-003 in combination with anti-mPD1 and sunitinib, resulted in recruitment and migration of lymphocytes into the tumor microenvironment and an increase in peripheral blood CD8+CD28+CD45RA- memory T cells in vivo. Multiple combination dosing strategies were tested and only one dosing regimen (DCs administered prophylactically followed by aPD1 mAb administered therapeutically) showed a substantial synergistic effect (67 days median OS) while all other DC/aPD1 dosing combinations did not exceed the efficacy of DC monotherapy treatment (44.5-48 days median OS). Control animals treated with PBS had a median OS of 29 days. Conclusions: These data demonstrate the importance of the administration sequence for active immunotherapy and aPD1 CPI combination therapy. Our data suggest that the cellular immune response must be initiated and established prior to administration of the aPD1 CPI/sunitinib combination therapy in order to observe synergy in this RCC mouse model. This model may be useful to explore additional combination therapies and effective treatment regimens with other therapeutic agents to guide future clinical development.

[Allocation of precursor germinal cells from the tissue of the human ovaries]

The article present the results of a study on the allocation of precursor germinal cells from tissue of human ovaries obtained during various gynecological operations. Two series of cell culture were isolated from tissue of tunica albuginea. The cell lines were identified and characterized by PCR012-method, immunocytochemical staining and histological examination. The study provided data reliably confirming the presence of precursor cells in the ovarian tissue of women in their reproductive years.

Mouse hepatocytes retain the expression of the main differentiation markers during culturing on collagen-chitosan matrices

Mouse hepatocytes cultured on artificial 3D collagen-chitosan biopolymer matrices retained the expression of hepatocyte markers for 14 days.

[Comparison of sevoflurane and propofol anesthesia for aortocoronary bypass surgery without artificial circulation]

The purpose of the study was to compare the effectiveness of sevoflurane and propofol during combined anesthesia with epidural component during aortocoronary bypass surgery without artificial circulation.

MATERIALS AND METHODS

The study included 24 patients with ischemic heart disease. All patients underwent aortocoronary bypass surgery on the working heart (from 1 to 5 bypasses) under combined anesthesia (propofol or sevoflurane with epidural anesthesia with the use of ropicavaine and fentanyl). Induction of anesthesia was carried out by midasolam 0.06 mg/kg, propofol 1-1.5 mg/kg, fentanyl 2.5 mcg/kg, myorelaxation was reached by pipecuronium bromide 0.1 mg/kg. Patients were randomized into propofol group (n = 12) and sevoflurane group (n = 12). Both groups received low flow anesthesia (1l/min) with the use of Drager Primus anesthesia workstation. Anesthesia in the first group was maintained by propofol 3-5 mg/kg/h, in the second group by sevoflurane 0.5-3 vol.%. In both groups additional fentanyl was administered in the dose of 1.2 -1.5 mcg/kg/h.

RESULTS

In the postoperative period the increase of the stroke volume and decrease of blood plasma lactate were noticed in the sevoflurane group. The postoperative pain, 6 hours after the aortocoronary bypass surgery in the control group was evidently higher according to Visual Analogue Scale.

CONCLUSION

Use of sevorane as a component of combined anesthesia during aortocoronary bypass surgery allows to improve the performance of the myocardium, reduce the severity of hypoperfusion in the perioperative period and reduce the severity of pain after the surgery compared to propofol anesthesia.

Human embryonic stem cell lines isolation, cultivation, and characterization

A large number of human embryonic stem cell (hESC) lines have been derived worldwide since the first hESC line establishment in 1998. Despite many common characteristics, most important of which is the pluripotency, hESC lines vary significantly in their transcriptional profiles, genetic, and epigenetic state. These differences may arise both from individual genetics of the cell lines and from variations in their handling such as isolation and cultivation. In order to minimize the latter differences, the standardized protocols of cultivation and inter-laboratory comprehensive studies should be performed. In this report, we summarized our experience of derivation and characterization of hESC lines as well as of adaptation of hESCs to novel cultivation protocols. We have successfully derived five hESC lines and characterized them by previously established criteria, including expression of specific markers and the capacity to differentiate both in vitro and in vivo. Four of these lines, namely hESM01-04, were initially derived using mouse fibroblasts as a feeder and currently are maintained under feeder-free, serum-free conditions using mTeSR1 and Matrigel. The fifth line, hESMK05 was derived in feeder-free, serum-free conditions using mTeSR1 and Matrigel. Cell lines retain their pluripotent status and normal karyotype for more than 70 passages and are available to the scientific community.

Single transpulmonary thermodilution and continuous monitoring of central venous oxygen saturation during off-pump coronary surgery

BACKGROUND

Off-pump coronary artery bypass grafting (OPCAB) requires thorough monitoring of hemodynamics and oxygen transport. Our aim was to find out whether therapeutic guidance during and after OPCAB, using an algorithm based on advanced monitoring, influences perioperative hemodynamic and fluid management as well as the length of post-operative ICU and hospital stay.

METHODS

Patients were randomized into two groups of hemodynamic monitoring: the conventional monitoring (CM) group (n=20) and the advanced monitoring (AM) group (n=20). In the CM group, therapy was guided by central venous pressure, mean arterial pressure (MAP) and heart rate (HR), and in the AM group by the intrathoracic blood volume index, MAP, HR, central venous oxygen saturation (ScvO(2)) and cardiac index (CI). The measurements were performed before and during surgery, and at 2, 4 and 6 h post-operatively.

RESULTS

In the AM group, colloids and dobutamine were given more frequently and were accompanied by increments in ScvO(2), CI and oxygen delivery compared with baseline. The percentage of ephedrine administration was higher in the CM group. The algorithm guided by AM decreased time until achieving the status of 'fit for ICU discharge' and post-operative hospital stay by 15% and 25%, respectively.

CONCLUSIONS

A goal-directed algorithm based on advanced hemodynamic monitoring and continuous measurement of ScvO(2) facilitates early detection and correction of hemodynamic changes and influences the strategy for fluid therapy that can improve the course of post-operative period after coronary artery bypass grafting on the beating heart.

[Different sensitivity of inbred mice to hepatocarcinogen ortho-aminoazotoluene may be due to differences in the negative control mechanisms of hepatocyte proliferation]

A most convenient model to study mechanisms of live organism response to chemical carcinogens is tumor induction in murine liver by aminoazodyes, in particular by ortho-aminoazotoluene (OAT). We studied both early and late stages of hepatocarcinogenesis on several lines of inbred mice differing in sensibility to OAT. By means of autoradiography, we examined proliferative activity of hepatocytes obtained from the liver of sensitive (A/He, DD, SWR) and resistant to OAT AKR, CC57Br, BALB/c lines of mice, which were injected carcinogen. The level of p53, p21Cip1, bax, mdm2, cyclin G, gadd45 genes expression in the liver of mice of different lines given OAT injection was studied by multiplex PCR method. Carcinogen caused a decrease of hepatocyte proliferative activity induced by partial hypatectomy (PHE), and an increase in p53, p21Cip, bax, mdm2, and cyclin G genes within mice of A/He, DD and SWR lines. Cell fusion experiments on hepatocytes obtained from regenerating murine liver sensitive to A/He line carcinogen and given long-time OAT administrations with resting and proliferating fibroblasts of NIH 3T3 mice revealed no obvious suppression of DNA synthesis in heterokaryons. Unlike, in fusion experiments on serum-stimulated fibroblasts with hepatocytes obtained from the liver of BALB/c line mice also given OAT suppression of DNA synthesis in stimulated fibroblasts in heterokaryons was observed 15 days following PHE. These results enable us to conclude that OAT administrations break negative endogenous mechanisms of hepatocyte proliferation control in the liver of mice sensitive to carcinogenes.

[Inhibitors of protein biosynthesis can stimulate proliferation of mouse hepatocytes in vitro]

Hepatocyte proliferation in the liver regenerating after partial hepatectomy ceases when the organ is restored, and the mechanism of this phenomenon is still unclear. In the experiments on fusing hepatocytes from the regenerated mouse liver (15 days after partial hepatectomy) with NIH 3T3 mouse fibroblasts, we revealed no DNA synthesis in the nuclei of stimulated fibroblasts in heterokaryons (in the presence of hepatocyte nuclei), whereas DNA synthesis in nonfused cells was undisturbed. In this work, our purpose was to find out whether the suppression of DNA synthesis in heterokaryons could be due to the appearance in hepatocytes of some endogenous factors having an inhibitory effect on proliferation. To this end, hepatocytes from the mouse liver regenerated after partial hepatectomy were treated with cycloheximide for 1-4 h and were then fused with stimulated fibroblasts. Such a short-term treatment of hepatocytes with cycloheximide proved to result in the loss of their ability to inhibit DNA synthesis in the nuclei of stimulated or quiescent fibroblasts in heterokaryons, but hepatocytes proper actively proliferated in the medium with a low serum content (0.2%). When the mice with the liver regenerated after partial hepatectomy were treated with a single sublethal dose of cycloheximide (3 mg/kg), their hepatocytes taken two days after this treatment had no inhibitory effect. Puromycin, another inhibitor o protein synthesis, had the same effect on hepatocytes. These results may be interpreted as evidence that the final stage of liver regeneration after damage is controlled by the factors having a negative effect on cell proliferation.

Dobutamine prevents experimental postintoxication liver cirrhosis in mice

Various chronic inflammatory and necrotic processes in the liver parenchyma are accompanied by pathological morphofunctional changes, which are associated with hepatocyte death and hyperplasia of the connective tissue. Regeneration of the liver parenchyma should include not only prevention of fibrosis, but also stimulation of hepatocyte proliferation. The adrenoceptor agonist dobutamine stimulated proliferative activity of cultured hepatocytes and prevented the development of postintoxication liver cirrhosis in mice produced by chronic poisoning with CCl(4).

[Hepatocytes in heterokaryons can suppress entry into the S-period of fibroblast nuclei from murine NIH 3T3 cells]

Mouse liver regeneration after partial hepatectomy can be considered as a spectacular example of controlled tissue increase. In this study serum-deprived (0.2%) resting and serum-stimulated (10%) proliferating NIH 3T3 mouse fibroblasts were fused with primary hepatocytes isolated from normal (intact) and regenerating adult mouse liver at different times after partial hepatectomy (1-15 days) to elucidate mechanisms of liver cell proliferation cessation at the regeneration end. DNA synthesis was investigated in the nuclei of heterokaryons and non-fused cells using radioautography. Hepatocytes isolated from regenerating liver within 1-12 days following operation did not retard the entry of stimulated fibroblast nuclei into the S-period. In contrast, hepatocytes isolated within 15 days after hepatectomy were found to have inhibitory effect on the entry of stimulated fibroblast nuclei into the S-period in heterokaryons. Preincubation of these hepatocytes with cyclocheximide for 2-4 h abolished their ability to suppress DNA synthesis in stimulated fibroblast nuclei in heterokaryons. Possible reasons of inhibitory effect of differentiated cells in heterokaryos are discussed. The data obtained enable us to conclude that the mechanism of proliferative process control in regenerating hepatocytes seems to be stopped being affected by the intracellular growth inhibitors, whose formation depends on protein synthesis.

[Avoidance conditioned-reflex behavior in rats chronically administered leucine enkephalin and its synthetic tetrapeptide analog into the neostriatum]

The three-week daily administration of 5 and 15 micrograms leu-enkephalin and its synthetic tetrapeptide analogue into the rat neostriatum led to an inhibition of avoidance conditioning in shuttlebox. Starting on the 10th day of the synthetic analogue injections, a motor excitation and a stereotyped behaviour were observed. No withdrawal effects were found. The tetrapeptide analogue was more effective than the natural leu-enkephalin in the same dose. A possible dopaminergic mechanism involved in the enkephalin long-term treatment, is discussed.