Synthesis of block copolymers containing a carbon chain and a polypeptide block

The bifunctional initiators, bis(2-glycylaminophenyl) disulfide ( 1 ) and 2, 2′-azo-2,2′-dimethyl-dipropionohydrazide ( 2 ), were used to obtain polymeric initiators of two types: carbon chain initiators with amino end groups initiating the polymerization of amino acid N-carboxyanhydrides (NCAs) and symmetric polypeptide initiators containing ? S? S? or ? N?N? groups, which decompose on exposure to UV light or elevated temperature forming free radicals. These polymeric initiators were used to synthesize block copolymers (BC) containing carbon chain and polypeptide blocks of ABA and AB structures. It is shown that AB block copolymers are capable of aggregation to a much higher extent than those of ABA type. These BC can form liquid-crystalline polymer structures and undergo controlled biodegradation by enzymes.     

Restoration of gastrocnemius muscle in mdx mice of different age after injury and implantation of xenogenic muscle tissue

The intensity of regeneration of crossed gastrocnemius muscle was evaluated in two groups of mdx mice of different age 2 weeks after implantation of crushed muscle tissue from newborn rats into the wound defect area. The effect of xenoplasty manifested in increased weight of the damaged muscle. The effect was observed in mice aging 12–16 weeks but not in those aged 40–48-weeks. Structural changes in the skeletal muscle tissue intrinsic of mdx mice and augmenting with age were detected in intact mice before the experiment. Activity of muscle fiber regeneration in intact and injured muscle of 40–48-week-old mice was significantly lower than in 12–16-week-old ones. Myoblasts of the xenogenic transplant retained viability in recipient muscles for at least 2 weeks. Post-traumatic regeneration was stimulated in only 12–16-week animals. Xenoplasty was ineffective in older animals and even somewhat enhanced the destructive processes in the muscle. It seems that age-specific regeneration activity of the recipient skeletal muscle tissue should be taken into consideration in the development of effective strategy of cell therapy for progressive muscular dystrophy. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 8, pp. 216–220, August, 2006     

Cardiotropic effect of extracardiac transplantation of embryonic human myoblasts to mice with bradycardia: Various effects of cell material

Animals with bradycardia were detected in reproductive colony of mdx mice. Low pulse rate was associated with poor survival and predisposition to sudden death, but did not directly depend on the presence of dystrophin mutant gene or animal age. Heart rate increased in old mice with bradycardia after extracardial, intramuscular, and intravenous injection of human embryonic myoblasts. Stable normalization of the pulse was observed 2 weeks after transplantation, but early peak of heart rate was observed as early as 24 h after cell transplantation. Cell suspensions, which could contain stem cells (blood mononuclears and CD34⁺ lymphocytes), also corrected heart rhythm. Unlike the effect of myoblasts, cardiotropic effect of mononuclears was preceded by a period of tachycardia, while the effect of CD34⁺ lymphocytes was very unstable. The cardiotropic effect of myoblasts was combined with life span prolongation and certain “rejuvenation” in some animals. Erythrocytes and supernatant obtained during blood cell fractionation did not modify the heart rhythm in mice with bradycardia. After injection of myoblasts to mice with rare and normal pulses serum creatine kinase activity decreased with different rates. These data attest to a variety of biological effects of stem cells and/or their derivatives and to ambiguous mechanisms of these effects.__________This revised version was published online in July 2005 with the addition of the issue title and article categoryTranslated from Kletochnye Tekhnologii v Biologii i Meditsine, Vol. 1, No. 1, pp. 29–33, January, 2005     

Investigation of the polymerization of the N-carboxyanhydride of γ-benzyl L-glutamate,initiated by low-molecular-weight and polymeric initiators

N-carboxyanhydride of γ-benzyl L -glutamate (N-CA-γ-BG) was polymerized with the lowmolecular-weight initiators 2,2′-dithiodiglycinanilide ( 1 ) and 2,2′-azo-2,2′-dimethyldipropionohydrazide ( 2 ) and with poly(methyl methacrylate) (PMMA) of different molecular weights containing amino and hydrazide end groups, exhibiting different nucleophilicities. For comparison, the N-CA was also polymerized with initiators described in the literature. It could be shown that the induction period depends on the nucleophilicity of the end groups of the initiator. In contrast to the low-molecular-weight initiators, the polymerization of the N-CA with PMMA proceeds without acceleration.