A unifying theory of refractive error development

While retinal defocus is believed to be myopigenic in nature, the underlying mechanism has remained elusive. We recently constructed a theory of refractive error development to investigate its fundamental properties. Our Incremental Retinal-Defocus Theory is based on the principle that the change in retinal-defocus magnitude during an increment of genetically-programmed ocular growth provides the requisite sign for the appropriate alteration in subsequent environmentally-induced ocular growth. This theory was tested under five experimental conditions: lenses, diffusers, occlusion, crystalline lens removal, and prolonged nearwork. Predictions of the theory were consistent with previous animal and human experimental findings. In addition, simulations using a MATLAB/SIMULINK model supported our theory by demonstrating quantitatively the appropriate directional changes in ocular growth rate. Thus, our Incremental Retinal-Defocus Theory provides a simple and logical unifying concept underlying the mechanism for the development of refractive error.     

Serum modulates the intracellular calcium response of primary cultured bone cells to shear flow

We investigated the effect of newborn bovine serum on the intracellular calcium [Ca²⁺]_i response of primary cultured bone cells stimulated by fluid flow. As it has been previously established that these cells exhibit [Ca²⁺]_i responses to fluid flow shear stress in saline media without growth factors or other chemically stimulatory factors, we hypothesized that the addition of serum to the flow medium would enhance the mechanosensitivity of the cells. We examined the effect of a short-term (10–15 min) exposure of the cells to 2 and 10% serum prior to flow stimulation (pretreated) compared to not exposing the cells prior to flow stimulation (unpretreated). The cells were subjected to a well-defined, 90-s flow stimulus with shear stress levels ranging from 0.02 to 3.5 Pa in a laminar flow chamber using a saline medium supplemented with 2 or 10% serum. For pretreatment, the serum concentration was the same from pre-flow to flow exposure. We observed a differential effect in the magnitude of the peak [Ca²⁺]_i response modulated by the concentration of serum in the pre-flow medium. Additionally, ATP-supplemented flow was examined as a comparison to the serum-supplemented flow and exhibited a similar trend in the peak [Ca²⁺]_i flow response that was dependent on ATP concentration and pre-flow exposure conditions. These findings demonstrate that under the conditions of this study, chemical agonist exposure can modulate the [Ca²⁺]_i response in bone cells subjected to fluid flow-induced shear stress.     

Effects of Ellagic Acid by Oral Administration on N-Acetylation and Metabolism of 2-Aminofluorene in Rat Brain Tissues

Numerous studies have demonstrated that the Acetyl Coenzyme A-dependent arylamine NAT enzyme exist in many tissues of experimental animals including humans, and that NAT has been shown to be exist in mouse brain tissue. Increased NAT activity levels are associated with increased sensitivity to the mutagenic effects of arylamine carcinogens. Attenuation of liver NAT activity is related to breast and bladder cancer processes. Therefore, the effects of ellagic acid (EA) on the in vitro and in vivo N-acetylation of 2-aminofluorene (AF) were investigated in cerebrum, cerebellum and pineal gland tissues from male Sprague-Dawley rats. For in vitro examination, cytosols with or without EA (0.5–500 M) co-treatment decreased 7–72%, 15–63% and 10–78% of AF acetylation for cerebrum, cerebellum and pineal gland tissues, respectively. For in vivo examination, EA and AF at the same time treated groups with all 3 examined tissues did show significant differences (the changes of total amounts of AF and AF metabolites based on the Anova analysis) when compared to the ones without EA cotreatment rats. The pretreatment of male rats with EA (10 mg/kg) 24 hr prior to the administration of AF (50 mg/kg) (one day of EA administration suffice to induce large changes in phase II enzyme activity) resulted in a 76% decrease in total AF and metabolites in pineal gland but did not show significant differences in cerebrum and cerebellum tissues. This is the first demonstration to show that EA decreases the N-acetylation of carcinogens in rat brain tissues.     

Paeonol promoted 2-aminofluorene and p-aminobenzoic acid acetylations by mononuclear leucocytes from Sprague-Dawley rats

Following exposure of rats to the arylamine carcinogen 2-aminofluorene, DNA-carcinogen adducts were found in the target tissues of the liver and bladder, and also in circulating leucocytes. This work investigated how paeonol affects arylamine (2-aminofluorene and p-aminobenzoic acid) acetylations in rat leucocytes. Evidence is presented showing that rat mononuclear leucocytes are capable of acetylating 2-aminofluorene and p-aminobenzoic acid. Paeonol promoted 2-aminofluorene and p-aminobenzoic acid acetylation. Cultured lymphocytes produced about twice as much N-acetyl-2-aminofluorene from 2-aminofluorene and 2.2-fold as much N-acetyl-p-aminobenzoic acid from p-aminobenzoic acid as monocytes. After cotreatment with paeonol, the lymphocyte and monocyte cultures indicated that paeonol did increase 2-aminofluorene and p-aminobenzoic acid acetylations.     

The two sides of enzyme-substrate specificity: lessons from the aspartic proteinases

Like most proteolytic enzymes, the aspartic proteinases bind substrates and most inhibitors within an extended active site cleft. Bound ligands typically adopt a beta-strand conformation. Interactions with groups on both sides of the cleft determine the primary as well as secondary specificity of the enzymes. We have pursued the discovery of the sometimes subtle distinctions between members of the aspartic proteinase family by two routes. In the first case, we have constructed sets of oligopeptide substrates with systematic variation in each position to assess interactions at one position at a time. In the second type of experiment, we have altered residues of the enzymes in order to test theories of selectivity. The combination of the two approaches has provided a better understanding of the forces involved in determining specificity of enzyme action.     

Chondrocyte extracellular matrix synthesis and turnover are influenced by static compression in a new alginate disk culture system

The goal of this study was to examine the effects of mechanical compression on chondrocyte biosynthesis of extracellular matrix (ECM) components during culture in a new alginate disk culture system. Specifically, we have examined chondrocyte biosynthesis rates, and the structure of aggrecan core protein species present in the cell-associated matrix (CM), in the further removed matrix (FRM) and in the surrounding culture medium. In this alginate disk culture system, chondrocytes can be subjected to mechanical deformations similar to those experienced in vivo. Our results show that over an 8-week culture period, chondrocytes synthesize a functional ECM and can respond to mechanical forces similarly to chondrocytes maintained in native cartilage. In the alginate disk system, static compression was shown to decrease and dynamic compression to increase synthesis of aggrecan of bovine chondrocytes. Western blot analysis of the core proteins of aggrecan molecules identified a number of different species that were present in different relative amounts in the CM, FRM, and medium. Over 21 days of culture, the predominant form of aggrecan found in the ECM was a full-length link-stabilized species. In addition, our data show that the application of 40 h of static compression caused an increase in the proportion of newly synthesized aggrecan molecules released into the medium. However, this was not accompanied by a significant change in the size and composition of aggrecan and aggrecan fragments in the different compartments, suggesting that mechanical compression did not alter the catabolic pathways. Together, these data show that chondrocyte function is maintained in an alginate disk culture system and that this culture system is a useful model to examine chondrocyte ECM assembly and some aspects of catabolism normally found in vivo.     

Gastric mucosal damage induced by arecoline seizure in rats

In an attempt to know the relation of seizure and gastric mucosal damage, we challenged arecoline (ACL) centrally to induce seizure and investigated gastric hemorrhagic injury in acid-irrigated stomachs of rats. The protective effects of several drugs also were evaluated. After deprivation of food for 24 h, rats were received laparotomy under diethylether-anesthesia. Both pylorus sphincters and carotid esophagus were ligated. The forestomach was equipped with a cannula for gastric irrigation. After recovery from anesthesia (approximately 1 h), the stomach was irrigated for 2 h with an acid solution containing 100 mM HCl and 54 mM NaCl or the same volume of normal saline. Intracerebroventricular (i.c.v.) ACL (0, 1, 3 or 10 mg/kg dissolved in 10 microl of CSF) was challenged to rats immediately after gastric irrigation. The seizure in rats was produced by ACL in a dose-related manner. The ulcerogenic parameters such as decrease of gastric mucosal glutathione levels and increase of histamine concentrations and lipid peroxide generations as well as the raise of luminal hemoglobin contents and exacerbated mucosal lesions were obtained depending on the doses of ACL challenged. These ulcerogenic parameters produced in ACL (10 mg/kg, i.c.v.) seizure rats were markedly ameliorated by gastric vagotomy or central anticholinergics. Intraperitoneal ketotifen, zinc sulfate, diphenhydramine or cimetidine also produced significant (p<0.05) inhibitions of these ulcerogenic parameters in ACL seizure rats. In conclusion, central ACL seizure may produce gastric oxidative stress and hemorrhagic lesions via vagal nervous activation and histamine release in acid-irrigated stomachs of rats.     

Ammonium, calcium, and leaf senescence in rice

The possible involvement of calcium in the regulation of ammonium-promoted senescence of detached rice leaves was investigated. Calcium effectively reduced ammonium-promoted senescence of detached rice leaves. The effect of ammonium on the senescence was also significantly reduced by the calcium ionophore A23187. Ammonium-promoted senescence of detached rice leaves may be mediated through blocking the entrance of calcium ions into the cytosol.