The conjugation of siRNA to molecules, which can be internalized into the cell via natural transport mechanisms, can result in the enhancement of siRNA cellular uptake. Herein, the carrier-free cellular uptake of nuclease-resistant anti-MDR1 siRNA equipped with lipophilic residues (cholesterol, lithocholic acid, oleyl alcohol and litocholic acid oleylamide) attached to the 5′-end of the sense strand via oligomethylene linker of various length was investigated. A convenient combination of H-phosphonate and phosphoramidite methods was developed for the synthesis of 5′-lipophilic conjugates of siRNAs. It was found that lipophilic siRNA are able to effectively penetrate into HEK293, HepG2 and KB-8-5 cancer cells when used in a micromolar concentration range. The efficiency of the uptake is dependent upon the type of lipophilic moiety, the length of the linker between the moiety and the siRNA and cell type. Among all the conjugates tested, the cholesterol-conjugated siRNAs with linkers containing from 6 to 10 carbon atoms demonstrate the optimal uptake and gene silencing properties: the shortening of the linker reduces the efficiency of the cellular uptake of siRNA conjugates, whereas the lengthening of the linker facilitates the uptake but retards the gene silencing effect and decreases the efficiency of the silencing.

The thermodynamic asymmetry of siRNA duplexes determines their silencing activity. Favorable asymmetry can be achieved by incorporation of mismatches into the 3' part of the sense strand, providing fork-siRNAs, which exhibit higher silencing activity and higher sensitivity to nucleases. Recently, we found that selective 2'-O-methyl modifications of the nuclease-sensitive sites of siRNA significantly improve its nuclease resistance without substantial loss of silencing activity. Here, we examined the impact of nucleotide mismatches and the number and location of 2'-O-methyl modifications on the silencing activity and nuclease resistance of anti-MDR1 siRNAs. We found that both nonmodified and selectively modified fork-siRNAs with 4 mismatches at the 3' end of the sense strand suppress the expression of target gene at lower effective concentrations than the parent siRNAs with classical duplex design. The selective modification of nuclease-sensitive sites significantly improved the stability of fork-siRNAs in the presence of serum. The selectively modified fork-siRNA duplexes provided inhibitory effect over a period of 12 days posttransfection, whereas the gene silencing activity of the nonmodified analogs expired within 6 days. Thus, selective chemical modifications and structural alteration of siRNA duplexes improve their silencing properties and significantly prolong the duration of their silencing effect.

Edited by Tamas DalmayKeywords: RNA interference siRNA Thermodynamic stability MDR1 2 0 -O-Methyl modification a b s t r a c tThe thermodynamic properties of siRNA duplexes are important for their silencing activity. siRNAs with high thermodynamic stability of both the central part of the duplex and in the whole, usually display low silencing activity. Destabilization of the central part of the siRNA duplex could increase its silencing activity. However, mismatches located in the central part of the duplex could substantially decrease the amount of RNAi efficacy, hindering active RISC formation and function. In this study, we examined the impact of duplex destabilization by nucleotide substitutions in the central part (7-10 nt counting from the 5 0 -end of the antisense strand) of the nuclease-resistant siRNA on its silencing activity.

The ongoing COVID-19 pandemic around the world and in Russia remains a major event of 2020. All over the world, research is being conducted to comprehensively study the patterns and manifestations of the epidemic  process. The main quantitative characteristics of SARS-CoV-2 transmission dynamics among the population, based on the data of official monitoring over the current situation, play an important role in the development of  the epidemiological surveillance system.The aim of this study is to explore the peculiarities of age-gender distribution of COVID-19 patients in Moscow.Material and methods. The data related to the epidemiological characteristics of age-gender structure of COVID-19 patients in Moscow between March 19, 2020 and April 15, 2020, at different stages of the  epidemic were retrospectively analyzed.Results and discussion. The mean age of COVID-19 patients in Moscow was 46,41±20,58 years. The gender ratio (male/female) among the patients was 52.7/47.3 %, wherein the indicators varied depending upon the  age. Male/female ratio in the age group “under 39” stood at 53.7/46.3 %, and “over 40 years of age” – at  39.3/60.7 %. The predominant age range among male cases was 19 to 39 years old – 35.4 %, while among female patients – 40–59 years (36.5 %). The age distribution of patients in Moscow is indicative of the fact that COVID-19 is a disease that primarily affects older age groups. The age structure of all COVID-19 cases during the observation period is characterized by predominance of adult patients over 19 years of age – 92,7 % (92,6–92,8 %), the share of patients aged 40–59 years is 35,7% (35,5–35,9 %). The differences in the age distribution in males and females are as follows: in the male cohort, the age groups 19–39 years old and 40–59 years old prevail – 35.4 % (35.1–35.7 %) and 34.9 % (34.6–35.2 %), respectively. The age group 40–59 years old – 36.5 % (36.3–36.8%) dominates in the female cohort.

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Aim. Identification of epidemiological patterns of the SARS-CoV-2 spread among the population of St. Petersburg during the one-year COVID-19 pandemic period.Materials and methods. The performed analysis focused on the dynamics of COVID-19 cases in St. Petersburg from 2/3/2020 to 4/4/2021 and on the gender-age profile of patients. The information about patients (age, gender, type of the disease, hospitalization, social, and occupational status) was obtained from the database containing the materials from statistical data form No. 058/u.Results. After one year, the dynamics of reported cases of COVID-19 in St. Petersburg shows two cycles of seasonal surge (spring and autumn-winter) and 8 epidemic periods. It has been found that there are no gender-age differences among COVID-19 patients, which can be seen from the relatively similar number of cases among men and women per 100,000 people in each age group during specific epidemic periods. The strong association between clinical manifestations of COVID-19 and the patients' age was detected: Severe cases were more frequently diagnosed in patients over 70 years, regardless of their gender identity. Based on the social and occupational status, the people who were most exposed to the COVID-19 epidemic process were retirees and people whose occupation was associated with health and safety of St. Petersburg. Among the COVID-19 patients, retirees accounted for 13.69% (men) and 17.67% (women). The proportion of healthcare workers was 3.67% (men) and 9.41% (women).Conclusion. It has been assumed that COVID-19 tends to be a seasonal disease featuring annual autumn-winter epidemic cycles. The study addressed prospects of preventive vaccination against COVID-19 in Russia and the importance of tracking the complications pathogenetically associated with the acute phase of the disease in the system of epidemiological surveillance.

Background.The COVID-19 epidemic in the Russian Federation, which began in March 2020, caused serious damage to health of the population and led to severe economic losses. By December 28, 2020, 3 078 035 cases of COVID-19 and 55 265 lethal outcomes were registered in the country. The population of all territorial subjects of the country is involved in the epidemic process of COVID-19. The severe epidemiological situation made it necessary to conduct an analysis to identify the factors that determine the high intensity of the epidemic process, as well as the population groups with the highest risk of SARS-CoV-2 infection. Aims to study the patterns of SARS-CoV-2 spread and the epidemiological features of the initial stage of the COVID-19 pandemic in the Russian Federation in 2020. Methods.An epidemiological analysis of the COVID-19 situation in the Russian Federation was carried out to determine the dynamics of morbidity, the gender proportion and age structure of patients, the proportion of hospitalized patients, the ratio of various forms of infection, the social and professional status of patients. Standard methods of descriptive statistics Microsoft Excel and STATISTICA 12.0 (StatSoft, USA) were used for statistical processing. The mean values were estimated with a 95% confidence interval [95% CI] (the exact Klopper Pearson method). Results.During the observation time (2020), several periods were identified in the dynamics of the new COVID-19 cases detection: the period of importation of SARS-CoV-2 and the increase in morbidity, the period of epidemic decline, the period of autumn growth, the period of sustained high incidence of COVID-19. It was found that people over 70 years of age are the group with the highest risk of infection and a more severe course of COVID-19. The presence of target contingents among social and professional groups of the population, which should include medical workers, retired person, employees of educational institutions, law enforcement agencies, transport, who require special attention and medical and social support, was shown. Conclusions.The analysis showed that the large-scale spread of COVID-19 requires in-depth epidemiological studies and the development of additional disease control measures, taking into account the dynamics of the incidence of this socially significant infection.

Kidney disease in pets is the most common problem that pet owners come to the veterinary clinic for. With age, the likelihood of kidney disease in domestic cats increases. It has been found that 20 to 50% of household cats older than 15 suffer from chronic renal failure. The authors studied chronic kidney disease of domestic cats in the metropolitan metropolis at the Monino veterinary clinic. The total sample consisted of 85 cats, of which, after clarification of the diagnosis (biochemical tests), experimental (n = 37) and control groups (n = 37) were formed. According to clinical analysis, the latter was assigned to a conditionally healthy group. The mean age of healthy cats in the control group was 4.95±0.22 years (median five years), and that of cats in the experimental group with renal insufficiency was 8.92±0.53 (median nine years). Ultrasound examination of the kidneys of domestic cats with chronic renal failure revealed diseases such as nephritis with a frequency of 32.4%, glomerulonephritis - 27.1, urolithiasis - 21.6 and pyelonephritis - 18.9%. Frequent clinical symptoms in domestic cats were: loss or lack of appetite - 54.1%, vomiting - 32.4%, pollakiuria with strangiuria - 10.8%, and lethargy - 10.8%. Thus, ultrasound diagnostics showed high information content in detecting renal failure in domestic cats. The diagnostic efficiency reached 97%. The ultrasound method has established itself as safe, painless and comfortable for a pet when examining the abdominal organs.