This review focuses specifically on matrix metalloproteinases (MMPs) and their role in physiological and pathological extracellular matrix (ECM) remodeling and degradation processes in the oral environment. A group of enzymes capable of degrading almost all ECM proteins, MMPs contribute to both normal and pathological tissue remodeling. The expression of different MMPs may be upregulated in pathological conditions such as inflammation and tumor invasion. The balance between activated MMPs and tissue inhibitors of metalloproteinases (TIMPs) controls the extent of ECM remodeling. Prior to mineralization, MMPs may participate in the organization of enamel and dentin organic matrix, or they may regulate mineralization by controlling the proteoglycan turnover. There is evidence indicating that MMPs could be involved in the etiology of enamel fluorosis and amelogenesis imperfecta. They seem to play a part in dentinal caries progression, since they have a crucial role in dentin collagen breakdown in caries lesions. MMPs have been identified in pulpal and periapical inflammation and are strongly correlated with periodontal diseases, since they are the major players in collagen breakdown during periodontal tissue destruction. The use of MMP inhibitors could help the prevention and treatment of many MMP-related oral diseases.
RESUMO -Objetivou-se avaliar a influência do tempo de incubação in situ e do tamanho de partículas sobre as estimativas das frações indigestíveis da matéria seca (MSi), da fibra em detergente neutro (FDNi) e da fibra em detergente ácido (FDAi) em alimentos e fezes bovinas. Avaliaram-se amostras de fubá de milho, casca de soja, farelo de trigo, farelo de soja, farelo de algodão, silagem de milho, capim-elefante, cana-de-açúcar, feno de capim-braquiária, palha de milho e fezes de bovinos alimentados com dietas com alto ou baixo nível de concentrado. As amostras foram processadas em moinho com peneiras de porosidade 1, 2 ou 3 mm e acondicionadas (20 mg MS/cm 2 de superfície) em sacos de tecido não-tecido (100 g/m 2 ) de dimensão 4 × 5 cm. Os materiais foram divididos em três grupos, de modo que as amostras de cada grupo foram incubadas no rúmen de três novilhas mestiças (Holandês × Zebu). O procedimento de incubação foi repetido três vezes e, a cada período, procedeu-se à incubação dos grupos em animais distintos. Foram utilizados os tempos: 0, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216, 240 e 312 horas. Os teores de MSi, FDNi e FDAi foram avaliados seqüencialmente para interpretação dos perfis de degradação por modelo logístico não-linear. Não houve efeito do tamanho de partículas sobre as estimativas de FDNi e FDAi. Verificaram-se efeitos dos tamanhos de partículas sobre a velocidade de degradação da MS da silagem de milho e do fubá de milho, da FDN da cana-de-açúcar, da silagem de milho e da palha de milho e sobre a velocidade de degradação da FDA da cana-de-açúcar. Para esses alimentos, o tamanho de partícula associou-se positivamente ao tempo necessário para estimar a fração indigestível. Tempos de incubação de 240 horas para MS e FDN e de 264 horas para FDA são recomendados para obtenção de estimativas exatas das frações indigestíveis. O uso de partículas de 2 mm é recomendado por proporcionar maior precisão das estimativas.Palavras-chave: fibra em detergente ácido indigestível, fibra em detergente neutro indigestível, matéria seca indigestível Influence of incubation time and particles size on indigestible compounds contents in cattle feeds and feces obtained by in situ proceduresABSTRACT -The aim of this work was to evaluate the effects of in situ incubation time and particles size on the estimates of indigestible fractions of dry matter (iDM), neutral detergent fiber (iNDF), and acid detergent fiber (iADF) in cattle feeds and feces. Samples of corn grain, wheat bran, corn silage, elephant grass, sugarcane, signal grass hay, corn straw, and feces obtained from cattle fed high and low concentrate diets were used. The samples were ground through 1 mm, 2 mm, and 3 mm screen sieve and put in 4 × 5 cm non-woven textile bags (20 mg DM/cm² of surface). The samples were divided in three groups, being each group incubated in the rumen of a crossbred heifer. The incubation procedure was conducted three times with the change of groups among animals. The following incubation times were used: 0, 12, 24, 48, 72, 96, 1...
RESUMO - Os efeitos de diferentes níveis de concentrado sobre o comportamento ingestivo foram estudados com cinco bezerros holandeses, inteiros, com idade e peso corporal médios iniciais de 10,8±0,8 meses e 233,4±26,1 kg PV. Os animais foram alojados em baias individuais e alimentados à vontade com dietas contendo 30, 45, 60, 75 e 90% de concentrado, com base na MS. As rações contendo, aproximadamente, 16% PB foram formuladas para taxa de ganho de peso de 1,0 kg/dia e compostas por farelo de soja, fubá de milho e feno de capim coast-cross. O delineamento experimental em blocos casualizados com cinco tratamentos, com duração de 20 dias, 12 dias de adaptação e quatro períodos de dois dias, relativos à coleta de dados foi usado. O tempo despendido em alimentação e ruminação diminuiu, e o tempo de ócio aumentou linearmente, em função do aumento dos níveis de concentrado. A eficiência de alimentação em g MS/h registrou comportamento quadrático, estimando-se o valor máximo em 826,81 g FDN/h, para o nível de 60,77% de concentrado. A elevação no nível de concentrado nas dietas aumentou linearmente a eficiência de ruminação em g MS/h, mas em g FDN/h decresceu linearmente. O número de bolos ruminais e de mastigações merícicas por dia decresceu linearmente. O número e o tempo de mastigação merícica por bolo registraram comportamento quadrático, estimando-se valores máximos de 73,79 mastigações e 66,61 segundos, por bolo ruminal, para os níveis de 48,51 e 54,44% de concentrado, respectivamente.
These data suggest that cognitive screening should take place in patients with advanced cancer because cognitive failure is highly prevalent in this population, is reversible in a significant proportion of patients, and the presence of sustained cognitive impairment is a poor prognosticator for discharge. However, these results need to be confirmed in prospective studies.
To understand the complex mechanisms of reaction, solvation, and diffusion that determine the chemistry of silica in solution, it is necessary to study first the silicate clusters that participate in these processes. We have investigated, by ab initio density functional methods, all silica-based clusters of the form Si x O y (OH) z , with a maximum of five silicon atoms and two intramolecular condensations, plus the six-silicon ring and the eightsilicon containing cube. In this article (part I), we report our results on the structure, charge distribution, and energy of the simpler clusters: the monomer Si(OH) 4 , the dimer Si 2 O(OH) 6 , the linear trimer Si 3 O 2 (OH) 8 , the ring trimer Si 3 O 3 (OH) 6 , the linear tetramer Si 4 O 3 (OH) 10 , the ring tetramer Si 4 O 4 (OH) 8 , the linear pentamer Si 5 O 4 (OH) 12 , and the cubic cage Si 8 O 12 (OH) 8 . We also present density functional results for aluminosilicate clusters: Al(OH) 4 -, Al 2 O(OH) 6 2-, and SiAlO(OH) 6 -. The results for the more complex clusters are presented in the subsequent article (part II). Our studies reveal a wide diversity of structures and consequently of charge distributions and energies for these clusters, that directly influence their chemical behavior, in particular the interaction with other clusters and with the solvent.
We report density functional calculations on the energies and conformations of complex silica-based clusters, after our analysis of the simpler clusters reported in part I. We report calculated structures, charge distributions, and energies of the noncyclic four-and five-silicon chains, the branched trimer and tetramer rings, the double trimer rings, the tetramer plus trimer rings, the five-and six-silicon rings; all calculations are at the local density level of approximation. The total condensation energy (from the monomer) to form a silica cluster in the gas phase depends essentially on its structure and size. Our results show that the stability of the noncyclic clusters decreases with the degree of branching, as observed experimentally. This trend is observed for both four-silicon and five-silicon clusters. As expected, the double ring clusters are quite unstable, which is especially marked for the double trimer rings. Formation of trimer-tetramer rings is energetically more favorable, particularly for the edge-linked cluster. The four-and six-silicon rings are more stable than the corresponding pentamer because of the relatively asymmetric arrangement of the latter.
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