جستجوی مقالات مرتبط با کلیدواژه "هیالورونیک اسید" در نشریات گروه "زیست شناسی"

The naked mole rat (Heterocephalus glaber) displays exceptional longevity, with a maximum lifespan exceeding 30 years. This is the longest reported lifespan for a rodent species and is especially striking considering the small body mass of the naked mole rat. In comparison, a similarly sized house mouse has a maximum lifespan of 4 years. In addition to their longevity, naked mole rats show an unusual resistance to cancer. Multi-year observations of large naked mole-rat colonies did not detect a single incidence of cancer. Here we identify a mechanism responsible for the naked mole rat's cancer resistance. We found that naked mole-rat fibroblasts secrete extremely high-molecular-mass hyaluronan (HA), which is over five times larger than human or mouse HA. This high-molecular-mass HA accumulates abundantly in naked mole-rat tissues owing to the decreased activity of HA-degrading enzymes and a unique sequence of hyaluronan synthase 2 (HAS2). Furthermore, the naked mole-rat cells are more sensitive to HA signaling, as they have a higher affinity to HA compared with mouse or human cells. Perturbation of the signaling pathways sufficient for malignant transformation of mouse fibroblasts fails to transform naked mole-rat cells. However, once high-molecular-mass HA is removed by either knocking down HAS2 or overexpressing the HA-degrading enzyme, HYAL2, naked mole-rat cells become susceptible to malignant transformation and readily form tumours in mice. We speculate that naked mole rats have evolved a higher concentration of HA in the skin to provide skin elasticity needed for life in underground tunnels. This trait may have then been co-opted to provide cancer resistance and longevity to this species.

Hyaluronic acid (HA) is a natural and linear polymer that finds a wide-range of applications in medicine, cosmetics, and nutraceuticals because of excellent viscoelasticity, high moisture retention capacity, high biocompatibility and non-toxicity. HA has been recently produced in industrial scale by Streptococcal species. Streptococci are nutritionally fastidious lactic acid bacteria and cannot synthesize some amino acids. Therefore, it is necessary to study and select some commercial culture media for their growth. In this study, HA production and hyaluronidase activity of S. zooepidemicus ATCC 43079 in three culture media were investigated. Regarding the detrimental effect of this enzyme on HA amount, 6-O-Palmitoyl-L-ascorbic acid as hyaluronidase inhibitor was added to culture medium during fermentation. The effect of three variables consisted of glucose concentration, yeast extract concentration and medium pH each at 3 levels were considered and (response surface methodology (RSM) was used for statistical design of experiments to study the HA production by this strain. The results showed that maximum HA production was obtained when glucose concentration, yeast extract concentration and pH were 21.2 g L-1, 43.6 g L-1 and 6.6, respectively. Under optimum conditions, HA was produced as 370±15 mg L-1 which was ~150% more than of HA concentration in basal medium (150±10 mg L-1) and productivity reached 56.74 g L-1 h-1 that was increased 2 fold compared to central point.

Hyaluronic acid (HA) is a natural linear polysaccharide with excellent viscoelasticity, high water retention capacity and biocompatibility finding wide-range of application in medicine, drug delivery and cosmetics. Currently, microbial fermentation is used for industrial HA production. The present study reports screening and optimization of HA production by clinical Streptococcus equisimilis group C and G (GCS and GGS) isolates from Iranian patients.

The 11 S.equisimilis strains including 9 GCS and 2 GGS were characterized and primary HA production was quantified by carbazol assay. Accordingly, three strains were selected for further optimization. The effect of pH on HA yields at 12 points ranging from 3.1-7.5 and glucose concentrations ranging from 0.3-15 mg/ml at 11 points at optimized pH were determined for selected strains.

The range of HA concentration among 11 strains was 216.6-729.7 µg/ml. The three higher producer strains including GCS-08, GGS-88 and GGS132 with an average production of 573.0, 579.7 and 729.7 µg/ml, respectively was selected. The HA concentrations at optimized pH of selected strains were (6.5, 744.3 µg/ml), (4.8, 598.9 µg/ml) and (6.8, 1041.8 µg/ml) respectively. Cultivation at 15 mg/ml of glucose led to increasing HA yield by GCS-08:1096.4, GGS-88:1234.3 and GGS-132:1993.6 µg/ml.

The findings showed the significant effect of pH and direct correlation of glucose concentration on HA production that can increase the yield up to 2.73 folds. Identification of high producer strain at pH 4.8 would be an advantage for HA production under unusual condition at industrial scale.

Hyaluronic acid (HA) is a major component of the extracellular epithelial, neural and connective tissue of vertebrates, as well as of extracellular microorganisms. This polysaccharide has specific applications in ophthalmology, orthopedic, cosmetics and tissue engineering due to features such as high viscosity and biocompatibility. Animal tissues and streptococci have a major role in producing hyaluronic acid, but because of problems such as protein contamination and the presence of endotoxin, attention has been drawn to the GRAS bacteria for producing hyaluronic acid. Lactobacilli are probiotic bacteria that have diverse uses. The production of biochemical macromolecules by this group of bacteria is a priority because they are GRAS. Hyaluronic acid production for the first time in these GRAS bacteria including Lactobacillus acidophilus PTCC1643, Lactobacillus rhamnosus PTCC1637, Lactobacillus casei PTCC1608 and Streptococcus thermophilus PTCC1738 were investigated. In the first step, Hyaluronic acid was isolated from specific culture medium and partially purified by ethanol precipitation daily for 96 hours. Carbazole method was used to measure the production of hyaluronic acid. Based on results, Lactobacillus rhamnosus produced about 0.4 g/l of hyaluronic acid at 96 hours. The increase of HA was also investigated using optimization culture medium by Taguchi design. By using this method, the optimum points of the factors were determined and the hyaluronic acid production increased by 162%.