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Biomedical subjects

J J Harding

Publications and source records attributed to J J Harding.

At least 55 records · Page 3Linked to original sources
PubMed1996

Molecular masses of gamma-crystallins.

Bovine gamma-crystallins were isolated and analysed by electrospray mass spectrometry (ESMS). The mass of gamma II-crystallin was as predicted from the amino acid sequence and the mass of gamma IIIb-crystallin was close, but the mass of gamma IVa-crystallin was 59 Da greater than that expected. gamma IVa-Crystallin was digested with cyanogen bromide and the fragments were isolated before analysis by ESMS. The masses of the fragments did not correspond to the published sequence. The published sequence of gamma IVa-crystallin, which has been used to predict its three-dimensional structure, is incorrect.

Animals↗
PubMed1996

Lens proteins changes induced by sugars and pyridoxal phosphate.

Glucose, galactose and pyridoxal phosphate (PLP) bind to lens protein amino groups causing changes in absorbance and fluorescence spectra and inducing aggregation. Sugars and PLP simultaneously cause an increase in fluorophore and chromophore formation, but a decreased aggregation, compared to PLP alone. PLP binds to lens protein amino groups decreasing the sugar binding, but in preventing glycation by PLP attention should be paid to the consequences of its own binding to proteins in diabetes.

Animals↗
PubMed1995

Molecular chaperones protect against glycation-induced inactivation of glucose-6-phosphate dehydrogenase.

Glucose-6-phosphate dehydrogenase is inactivated slowly by reaction with sugars (glycation), a process thought to be important in the development of diabetic complications. A major protein from the ocular lens, alpha-crystallin. which exhibits some chaperone-like properties, protects against this inactivation. The well-known molecular chaperone GroEL (chaperonin 60 from Escherichia coli) also protects. On a molar basis, alpha-crystallin is better than GroEL at protecting against glycation-induced inactivation of glucose-6-phosphate dehydrogenase. The relative amounts of enzyme/chaperone indicate that each molecule of alpha-crystallin binds two molecules of the damaged enzyme. This supports the view that alpha-crystallin has a chaperone-like structure as well as a chaperone-like function.

Chaperonin 60↗
PubMed1995

The reaction of methylglyoxal with human and bovine lens proteins.

Methylglyoxal is an endogenous metabolite that increases in diabetes and has been implicated in some of its long-term complications such as retinopathy, neuropathy and cataract. We investigated the reaction of methylglyoxal with isolated human and bovine lens crystallins (alpha, beta H, beta L and gamma). After 7 days incubation at 37 degrees C and pH 6.9, the reaction of methylglyoxal with lens proteins yielded stable adducts that exhibited fluorescent properties. SDS-polyacrylamide gel electrophoresis was used to monitor aggregation and crosslinking of the modified protein and autoradiography showed that [14C]methylglyoxal was incorporated into all the protein bands. Bovine gamma-crystallin was the most reactive towards methylglyoxal. Reaction of methylglyoxal with bovine gamma II-crystallin, which is found mainly in the lens nucleus, could alter the change surface network of the molecule, resulting in aggregation, increased light scattering and hence cataract. Modification of gamma II-crystallin by methylglyoxal produced an overall loss of positive charge and an increase in molecular weight and non-disulfide covalent crosslinking. Amino acid analysis of the modified gamma II-crystallin showed a loss of 47% of arginine residues.

Amino Acids↗
PubMed1995

Epidemiology, pathophysiology, and world blindness.

This year the role of diabetes and therefore of sugars in cataract has remained a dominant theme in the literature, but there has been a renewed interest in lens enzymes. Epidemiological studies have confirmed that cataract is the overwhelming cause of blindness in the third world, and identified association with another age-related disease. The possible protective effect of estrogens was surprising. The role of poor nutrition in cataract development, and conversely the possibility of decreasing the burden of cataract by improving nutrition or providing vitamin supplements has attracted much attention although we must await clinical trials for definitive answers.

Blindness↗
PubMed1994

Binding of glucose, galactose and pyridoxal phosphate to lens crystallins.

Glycation of proteins plays an important role in diabetic complications. Both glucose and galactose were shown to bind progressively to lens crystallins with decreased binding in the presence of increasing concentrations of pyridoxal 5-phosphate (PLP). In longer term incubations (10 mM sugar for 21 days) glucose produced no significant yellowing of the protein, that is no detectable advanced glycation products, but pyridoxal phosphate (15 mM) caused an increased absorbance at 325 nm. This increase was greater in the presence of glucose. It appears that PLP becomes firmly attached to the protein and that this binding is enhanced in the presence of glucose or galactose. Changes produced by sodium borohydride indicate that the PLP is attached to protein amino groups as a Schiff base. Incubation of lens crystallins with PLP also led to increased fluorescence which was greater when sugar was present. However, borohydride experiments indicated that glucose and galactose may decrease the formation of non-reducible adducts of PLP. The decreased glycation in the presence of PLP supports the notion that it might be useful in prevention of diabetic complications, but the reaction of PLP itself with protein is less encouraging.

Animals↗
PubMed1994

Identification of the site of glycation of gamma-II-crystallin by (14C)-fructose.

Cataract formation in diabetes may be via non-enzymic glycosylation (glycation) of lens proteins due to increased concentrations of sugars present in the lenses of diabetic patients. The objective of this project was to identify the site(s) of glycation of bovine gamma-II-crystallin by [14C]fructose. gamma-II-crystallin was isolated from soluble lens nucleus proteins by gel chromatography, followed by ion-exchange chromatography and was then glycated by incubation with [14C]fructose. Radioactively labelled gamma-II-crystallin was cleaved with trypsin. Affinity chromatography of the tryptic peptides gave a single main peak containing the majority of the radioactivity. This indicated that fructose had reacted at a single site on the protein. Amino acid analysis of this peptide showed it to contain only lysine and a trace amount of glycine. By relating the results of the amino acid analysis to the amino acid sequence of gamma-II-crystallin, it was concluded that the labelled peptide corresponded to the N-terminal dipeptide. The site of glycation of bovine gamma-II-crystallin by fructose was thereby identified as the alpha-NH2 group of the N-terminal glycine.

Animals↗
PubMed1994

Case of a 29-year-old nurse with factitious disorder. The utility of psychiatric intervention on a general medical floor.

A 29-year-old nurse was treated for septic arthritis of the knee. She was suspected of producing this infection and others. The consultation-liaison team intervened early, and the patient was treated in individual outpatient psychotherapy for 1 year. Her course was complicated by criminal behavior and a suicide attempt, prompting relocation to her home town. The patient demonstrated a strong need to be nurtured, as noted in other cases of factitious disorders. An overview of factitious disorders is presented, and guidelines for managing these difficult patients in the hospital are provided.

Adult↗
PubMed1993

The reaction of malondialdehyde with lens proteins and the protective effect of aspirin.

Malondialdehyde, a product of lipid peroxidation and a by-product of thromboxane synthesis increases in human cataract. Malondialdehyde bound to soluble lens proteins over 4 h of incubation. Pre-incubation of lens proteins with aspirin offered protection against reaction with MDA. Gel chromatography was used to monitor aggregation of the modified protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the reaction with malondialdehyde led to non-disulphide covalent cross-linking of gamma-crystallin, which was decreased by incubation with aspirin. Malondialdehyde has two carbonyl groups which could react with primary amino groups, forming Schiff-base conjugates and covalently cross-link proteins. The modification and cross-linking could initiate the cataractogenic process.

Acetaminophen↗
PubMed1993

The lens in diabetes.

This paper reviews the changes which occur in the human lens in diabetes. They include refractive changes and cataract and age-related increases in thickness, curvatures, light scattering, autofluorescence and yellowing. The incidence of cataract is greatly increased over the age of 50 years, slightly more so in women, compared with non-diabetics. Experimental models of sugar cataract provide some evidence for the mechanism of the uncommon, but morphologically distinct, juvenile form of human diabetic cataract, where an osmotic mechanism due to sugar alcohol accumulation has been thoroughly studied in diabetic or galactose-fed rats. The discrepancy between the ready accumulation of sugar alcohol in the lens in model systems and the very slow kinetics of aldose reductase (AR) has not been satisfactorily explained and suggests that the mechanism of polyol formation is not yet fully understood in mammalian systems. The activity of AR in the human lens lies mainly in the epithelium and there appears to be a marginal expectation that sufficient sorbitol accumulates in cortical lens fibres to explain the lens swelling and cataract on an osmotic basis. This is even more so in the cataracts of adult diabetics, which resemble those of age-related non-diabetic cataracts in appearance. The very low levels of sorbitol in adult diabetic lenses make an osmotic mechanism for the increased risk of cataract even less likely. Other mechanisms, including glycation and oxidative stress, are discussed. The occurrence of cataract is a predictor for increased mortality in the diabetic.

Adolescent↗