Inactivation of glyceraldehyde 3-phosphate dehydrogenase by sugars, prednisolone-21-hemisuccinate, cyanate and other small molecules

Diabetes, diarrhoea, renal failure and glucocorticoid therapy have all been identified as independent risk factors for cataract. Increased post-translational modification of proteins, leading to inactivation of enzymes and induction of conformational changes within proteins could result in lens opacification and cataract. Aspirin has been associated with many beneficial effects, including protection against cataract, in-vivo. alpha-Crystallin has been shown to act as a molecular chaperone in-vitro. This lenticular protein prevented the thermal aggregation of other lens proteins in-vitro and has sequence and functional homology with the small heat shock proteins. Glyceraldehyde 3-phosphate dehydrogenase (GAP-DH) is constitutively expressed in tissues and is susceptible to chemical modification in-vivo. In-vitro incubations of GAP-DH with sugars, cyanate and prednisolone-21-hemisuccinate, all led to significant loss of enzyme activity with time in two buffer systems. Rapid inactivation occurred when GAP-DH was incubated with fructose 6-phosphate or prednisolone-21-hemisuccinate. Slower inactivation was observed when GAP-DH was incubated with fructose, glucose 6-phosphate or potassium cyanate. Glucose did not inactivate GAP-DH under the conditions of our experiments. Aspirin and ibuprofen were shown to inactivate GAP-DH very rapidly in-vitro. Bovine lenticular alpha-crystallin conferred no protection against GAP-DH inactivation. This is the first occasion that alpha-crystallin has been demonstrated to be unable to protect against inactivation in our chemical enzyme inactivation system. This may have implications for the susceptibility of lenticular GAP-DH to post-translational inactivation.     

Phase I clinical trial of the flavonoid quercetin: pharmacokinetics and evidence for in vivo tyrosine kinase inhibition

In the present open study, the long-term safety, tolerability, and efficacy of citalopram in the treatment of elderly people with emotional disturbances were studied. One hundred twenty-three elderly patients with symptoms of depression-anxiety were included. Most of the patients (76%) were demented. Fifty-two patients completed a 12-month treatment. Irritability, depressed mood, anxiety, restlessness, and fear-panic were significantly reduced. The severity of illness from baseline to Month 9 was rated as significantly improved. The side effects were infrequent and mostly mild.     

p53 activity is essential for normal development in Xenopus

BACKGROUND: The tumor suppressor p53 plays a key role in regulating the cell cycle and apoptosis in differentiated cells. Mutant mice lacking functional p53 develop normally but die from multiple neoplasms shortly after birth. There have been hints that p53 is involved in morphogenesis, but given the relatively normal development of p53 null mice, the significance of these data has been difficult to evaluate. To examine the role of p53 in vertebrate development, we have determined the results of blocking its activity in embryos of the frog Xenopus laevis. RESULTS: Two different methods have been used to block p53 protein activity in developing Xenopus embryos--ectopic expression of dominant-negative forms of human p53 and ectopic expression of the p53 negative regulator, Xenopus dm-2. In both instances, inhibition of p53 activity blocked the ability of Xenopus early blastomeres to undergo differentiation and resulted in the formation of large cellular masses reminiscent of tumors. The ability of mutant p53 to induce such developmental tumors was suppressed by co-injection with wild-type human or wild-type Xenopus p53. Cells expressing mutant p53 activated zygotic gene expression and underwent the mid-blastula transition normally. Such cells continued to divide at approximately normal rates but did not form normal embryonic tissues and never underwent terminal differentiation, remaining as large, yolk-filled cell masses that were often associated with the neural tube or epidermis. CONCLUSIONS: In Xenopus, the maternal stockpile of p53 mRNA and protein seems to be essential for normal development. Inhibiting p53 function results in an early block to differentiation. Although it is possible that mutant human p53 proteins have a dominant gain-of-function or neomorphic activity in Xenopus, and that this is responsible for the development of tumors, most of the evidence indicates that this is not the case. Whatever the basis of the block to differentiation, these results indicate that Xenopus embryos are a sensitive system in which to explore the role of p53 in normal development and in developmental tumors.     

Subunit composition of neurofilaments specifies axonal diameter

Neurofilaments (NFs), which are composed of NF-L, NF-M, and NF-H, are required for the development of normal axonal caliber, a property that in turn is a critical determinant of axonal conduction velocity. To investigate how each subunit contributes to the radial growth of axons, we used transgenic mice to alter the subunit composition of NFs. Increasing each NF subunit individually inhibits radial axonal growth, while increasing both NF-M and NF-H reduces growth even more severely. An increase in NF-L results in an increased filament number but reduced interfilament distance. Conversely, increasing NF-M, NF-H, or both reduces filament number, but does not alter nearest neighbor interfilament distance. Only a combined increase of NF-L with either NF-M or NF-H promotes radial axonal growth. These results demonstrate that both NF-M and NF-H play complementary roles with NF-L in determining normal axonal calibers.     

Steering without representation with the use of active fixation

This paper demonstrates the use of active fixation on both fixed and moving fixation points to guide a robot vehicle by means of a steering rule which, at large distances, sets the steering angle directly proportional to the deviation of gaze direction from translation direction. Steering a motor vehicle around a winding but otherwise uncluttered road has been observed by Land and Lee to involve repeated periods of visual fixation upon the tangent point of the inside of each bend. We suggest that proportional rule devised for steering in the robotic example appears applicable to the observed human performance data, providing an alternative explanation to the quadratic rule proposed by Land and Lee.     

Encapsulated islet cells: the role of direct and indirect presentation and the relevance to xenotransplantation and autoimmune recurrence

Immuno-isolation of islet tissue for the purpose of curing diabetes without immunosuppression is an attractive concept that has been extensively investigated over the last 20 years. Rather than give a detailed review of the past and present history of the immuno-isolation or encapsulation approach for islet transplantation, this paper will examine the concepts behind encapsulation, concentrating on the immune mechanisms involved.