CharaCteristiCs of novel polymer based on pseudo-polyamino aCids Glula-dpG-peG 600 : bindinG of albumin , bioCompatibility , biodistribution and potential CrossinG the blood-brain barrier in rats

the aim of our work was to study biological properties of the polymer based on pseudo-polyamino acids GluLa-DPG-PEG600, its ability to bind albumin, as well as its localization in rat body and influence on physio logical and functional state of rat kidneys and liver. We have found the ability of Glula-DpG-peG600 to bind bovine serum albumin (BSa) using electrophoresis in 5% polyacrylamide gel. Structural and functional state of the liver and kidneys of rats after injections of polymer were investigated by histological analysis of organs and determination the activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, gamma-glutamyltransferase and content of cholesterol and creatinine in blood. Our results showed little toxic effect of GluLa-DPG-PEG600 on rat body. Using fluorescent microscopy we have studied polymer in complex with BSa distribution in rat body: after intravenous injection polymer are localized in kidneys and spleen, and after intramuscular – in liver and brain. It has been shown that polymer passed through the blood-brain barrier and are localized in the immune organ – spleen, indicating Glula-DpG-peG600 as a potential drug transporter.

N owadays, one of the main task for phar macy is development a novel polymeric compounds for drug delivery and other biomedical purposes [1].It has been developed poly mers based on amino acids with good biocompati bility like hydrogel based on poly γ-glutamic acid (γ-PGA) and ε-polylysine (ε-PL) or able to adsorb rare earth elements like sodium alginate hydrogel linked with poly-γ-glutamate [2,3].Scientists also developed specific polymers for drug delivery, for example lysinebased hydrogels for the oral delivery which are pHsensitive or safe detoxifying agent like poly(γ-glutamic acid) [4,5].We develop and research polymers based on pseudopolyamino acids which, like polymers based on amino acids, have good bio compatibility but are more stable for degradation.
Pseudo-polyamino acids -class of polymeric compounds based on natural amino acids.Their structure doesn't contain peptide bonds, ones can be changed to urethane, ester, anhydrite and other chemical bonds [6].Drug delivery systems based on pseudopolyamino acids with ester bonds are re spectable for research and developing.Pseudo-poly amino acids based on glycine, asparagine, arginine and lysine in complex with lactic acid are biodegra dable and have advanced cell adhesion [7][8][9].Pseu dopolyamino acids based on tyrosine in complexes with ZnO can be used in anticancer therapy [10,11].The main advantages of this class of polymers as drug transporters are their biodegradability and prolonged time of degradation that correlates with releasing of drugs active components (for example, polymers based on glycine and lactic acid are de composed for about 10 weeks) [7,8].Polymer Glu La-DPG-PEG600 based on glutamic acid with ester bonds was developed.Therefore, the main purpose of our study was to research polymer as drug trans porter particularly its ability to bind serum blood proteins, influence on rats and polymer distribution in their body.
For assessment of the ability of GluLa-DPG-PEG600 to bind serum blood proteins we tested 2% water dispersion of GluLa-DPG-PEG600 and the same dispersion with 1% water solution of BSA (molecular weight = 66 kDa) was tested by electro phoresis in 5% polyacrylamide gel [14].
GluLa-DPG-PEG600 influence on rat body were investigated by the analysis of histological structure of liver and kidneys.We also determined the activities of key indicators enzymes of liver and kidneys functional state -alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), γ-glutamyltransferase (GGT) and content of cholesterol and creatinine in blood.The animals were divided into 4 experimental groups of male aged 6 months rattus norvegicus var.alba.Each group consisted of 9 rats and weight of 1 animal was approximately 250300 g maintained under standard laboratory conditions.On the 1 st , 7 th and 14 th days of experiment, rats from first ex perimental group were intramuscularly injected by saline.In the same way, animals from second ex perimental group were intramuscularly injected by 0.3 ml 1% GluLa-DPG-PEG600, from third group -Fig. 1. Structure of Glula-DpG-peG600-F 0.3 ml 1% GluLa-DPG-PEG600 with 0.3 ml 1% BSA and fourth group -0.3 ml 1% BSA.On the 7 th , 14 th and 21 st days of experiment -rats from every experi mental group were anesthetized with chloroform and decapitated.Activities of alanine aminotransferase (ALT, EC 2.6.1.2),aspartate aminotransferase (AST, EC 2.6.1.1),alkaline phosphatase (ALP, EC 3.1.3.1),γ-glutamyl transferase (GGT, EC 2.3.2.2) and con tent of cholesterol and creatinine were determined in rat blood serum using biochemical analyser Hu maLyzer 2000 (Human®).Histological structure of liver and kidneys were investigated in accordance with methods [14].
Polymer distribution in rat body was studied by fluorescent microscopy.Complex of 2% water dispersion of GluLa-DPG-PEG600-F with 1% water solution of BSA was labeled with Alexa Fluor 555 fluorescent dye (ThermoFisher®) in ratio of 2.5:1 and maintained at 18 °C for 1 h.For this purpose 2 experimental groups and 1 control group of rattus norvegicus var.alba line Wistar, consisted of 3 rats and weight of 1 animal was approximately 250 300 g were formed.Rats from control group were intact.Rats from first experimental group were in travenously injected by 0.3 ml of water dispertion of GluLa-DPG-PEG600-F + BSА Alexa Fluor 555 complexes and euthanized at soft chloroform condi tion in 5 h after the injections.Second experimen tal group of rats were intramuscularly injected by 0.

results and discussion
The ability of GluLa-DPG-PEG600 to bind BSA was studied using electrophoresis in 5% po lyacrylamide gel (Fig. 2).Serum albumins are the main transporters for xenobiotics and nutrients in blood.The ability to bind BSA is a positive characteristic of synthesized polymers, as a drug trans porter.For example similar polymers -esters of microbial poly(γ-glutamic acid) can encapsulate erythromycin and α-chymotrypsin [15].It has been shown the ability of poly(γ-glutamic acid) to sorb al bumin molecules [16].
For assessment of the influence of GluLa-DPG-PEG600 on rat body, the structure and functional state of kidneys and liver were studied.
We have been found that on the 7 th day on experiment, rats from 1 st experimental group had increased with significant values p < 0.05, AST activi ty by 28%, (p < 0.01) ALT activity by 55%, (p < 0.05) ALP -on 13% and creatinine contentby 29% compared with control group animals.Rats from 2 nd experimental group had increased (p < 0.05) AST activity by 26%, (p < 0.01) ALTby 47%, (p < 0.05) GGT -by 34% and creatinine content -by 30%.3 rd experimental group of animals had unchanged enzymes activities, and creatinine content which were the same as in the control group of animals.Level of cholesterol was in the range of physiological fluctuations in rats from all experimen tal groups.
According to obtained results -increased ac tivities of AST and ALT are the indicators of the functional state of hepatocytes and may attest the defections of hepatocytes structure.The increased activity of GGT may be a sign of the distraction of the cells that forms intrahepatic bile ducts, while ALP -destruction of the cells that forms extrahe patic bile ducts on ultramicroscopic level.Increased level of creatinine in rats blood of the 1 st and 2 nd ex perimental groups compared with the control group of animals, may indicate the decreased glomerular filtration rate.Using histological analysis we have been found few sites of inflammation in ascending convoluted tubules of nephrons in animals from the 1 st and 2 nd experimental groups on the 7 th and 14 th days of the experiment, that accompanied by changes in enzyme activities (Fig. 5).
Increased activity of AST by 20% (p < 0.05) in rats blood from the 1 st experimental and by 25% (p < 0.05) in animals from the 2 nd group were de tected on the 14 th day of the experiment.We also detected increased ALT activity by 27% (p < 0.05) and 33% (p < 0.05) in rats from the 1 st and 2 nd ex perimental groups, while activities of AST and ALT in rats blood from the 3 rd group were the same as in control group.Activities of ALP, GGT, creatinine and cholesterol content in animals of all experimen tal groups were the same as in the control group.However, inflammation in ascending convoluted tubules of nephrons were detected in rats from the 2 nd experimental group that can be the result of de creased glomerular filtration rate.
It has been found, that on the 21 st day -level of activities of ALT AST ALP GGT and content of cre atinine and cholesterol in all groups of animals were in the range of physiological fluctuations.Investiga tion of rats liver and kidneys histological structure revealed that on the 21 st day of experiment -struc ture of organs from all experimental groups were without pathological changes.Using histological analysis we detected no changes of liver structure during the experiment.
The absence of the negative impact of GluLa-DPG-PEG600 on the 21 st day of the experiment shows that polymer has temporary toxic effect on rat body.The fact, that on the 14 th and 21 st days of experiments after two and three polymer injections toxic effect was reduced that may indicate adaptation processes in rat body.The nontoxicity and biocom patibility of this class of polymers are confirmed by several studies [17].In addition, amino acidbased polymers, such as polyglutamic acid, polyaspartic acid are widely used in biomedical application due to their biocompatibility, enhanced solubility and low profile cytotoxicity [18].
Polymer distribution in rat body was investi gated by fluorescent microscopy using fluorescein labeled polymer GluLa-DPG-PEG600-F in complex with BSA labeled Alexa Fluor 555 dye.Obtained re sults showed that polymer with BSA in 5 h after in travenous injection were localized in rat kidneys and  spleen (Fig. 6).In kidneys complexes were localized in the cortical layer and in the lumens of veins in a zone of proximal convoluted tubules.In the control group of rats, structures with the same luminescence were not detected (Fig. 6).Detection of polymer with BSA complexes in kidneys indicates that they are excreted by the kidney.Detection of GluLa-DPG-PEG600-F with BSA complexes in rat spleen is a positive charac teristic of polymer as a potential adjuvant for vac cine develop ment, because lymphocytes and antigen depen dent antibody differentiation processes take place in spleen and this immune organ can provide quick and effective immune response to vaccine an tigens.for example, other studies showed, that poly (γ-glutamic acid) nano-particles combined with mu cosal influen za virus hemagglutinin vaccine protects against influenza virus infection in mice and may have potential for clinical applications as a mucosal adjuvant [19].We found the localization of GluLa-DPG-PEG600-F + BSА Alexa Fluor 555 complexes in 16 h after intramuscular injections in rat brain and liver.Complexes were detected in liver lobules near hepatic vessels and inside it.In liver from control group of rats structures with the same fluorescence were absent (Fig. 6).

Fig. 6. Localization of GluLa-DPG-PEG600-F + BSА Alexa Fluor 555 complexes in rat kidneys and spleen in 5 h after intramuscular injections and in liver and brain in 16 h after intravenous injections: A -control group of rats, B -experimental group of rats (total magnification = 900x), 1 -luminescence of GluLa-DPG-peG600-F with BSa alexa Fluor, 2 -vein in a zone of proximal convoluted tubules, 3 -lymph node, 4 -liver blood vessel wall, 5 -luminescence of catecholamines
Luminescence of these complexes were detected in brain tissue in 16 h after intramuscular injec tions.In control group and experimental group of animals in brain tissues were detected luminescence of catecholamines (Fig. 6).Detection of GluLa-DPG-PEG600-F + BSA Alexa Fluor 555 complexes in brain indicates its ability to penetrate the blood brain barrier.Earlier, it has been shown that this class of polymers in complexes with albumins is able to form rodshaped particles with a hydrodynamic dia meter of 40-70 nm which can penetrate the bloodbrain barrier.That is because BSA molecules were adsorbed on the surface of GluLa-DPG-PEG600-F and acted as an additional stabilizer of a dispersed phase of the polymer which reduces the linear sizes of the particles by fragmentation of large particles into smaller [20].
In conclusions it has been found that polymer GluLa-DPG-PEG600 can bind bovine serum albu min that suggests its possible using as a potential transporter for proteins and their complexes.Glu La-DPG-PEG600 characterized by little short-term toxic effect on rat body, evidenced by increased activities of studied enzymes and minor pathologi cal changes in kidneys structure.Obtained results demonstrate that polymer is safe for rat body and applicable for further research as a drug transporter.
Analysis of polymer distribution in rat body revealed that polymer GluLa-DPG-PEG600 in com plexes with BSA are localized in rat kidney and spleen after intravenous injections that indicates that these complexes are excreted by the kidneys.This feature demonstrates the polymer as a potential adju vant for vaccine development.Polymer localization in liver and brain tissues after intramuscular injec tions indicates that polymer can penetrate blood brain barrier.There are important features of the polymer as a potential drug transporter.

F
3 ml of water dispertion of GluLa-DPG-PEG600-F + BSА Alexa Fluor 555 complexes and euthanized at soft chloroform condition in 16 h after the injec tions.Histological analysis of spleen, liver, brain and kidneys was conducted by cryostat.fluores cence of GluLa-DPG-PEG600-F + BSА Alexa fluor 555 complexes with 656 nm wavelength via Leica DM2500® microscope and Leica Application Suite® software was observed.Statistical processing DPG PEG600 GluLa of the investigation results was made using the pack of Microsoft Excel programs.All experiments were performed in accordance with the Ministry of Education and Science of Ukraine, order No 281 from 01.11.2000, the Europe an Convention for Protection of vertebrate Animals Used for Experimental and Other Scientific Purpo ses (18.03.1986),EU Directive No 609 (24.11.1986).