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Biomedical subjects

J J Harding

Publications and source records attributed to J J Harding.

At least 73 records · Page 4Linked to original sources
PubMed1993

Diabetes, glaucoma, sex, and cataract: analysis of combined data from two case control studies.

Data from two case control studies in Oxfordshire were combined and analysed. The combined study covered 1940 subjects, 723 cases, and 1217 controls, between the ages of 50 and 79 with a response rate of 97% for cases and 94% for controls. Diabetes was shown to be a powerful and highly significant risk factor for cataract with a relative risk of 5.04. More than 11% of cataracts in Oxfordshire are attributable to diabetes. The relative risk did not increase significantly with age within the range 50 to 79 years but was higher in females than in males. For females with diabetes the relative risk was 7.85 with 95% confidence interval from 4.30 to 14.3 compared with 3.42 with confidence interval from 2.05 to 5.71 for males with diabetes. Diabetes remained a powerful risk factor when other identified risk factors had been controlled for. No known mechanism for the development of diabetic complications provides an explanation for the excess risk in females. Combination of the two studies led to better estimates of the relative risk of glaucoma as a risk factor for cataract (3.96 with 95% confidence interval from 2.35 to 6.68). The relative risk appeared to be greater in women than in men but this difference was not statistically significant. There was no significant change in risk with age. Glaucoma is a powerful and independent risk factor for cataract in both sexes and may be responsible for 5% of all cataracts in our area.

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PubMed1992

Glycation (non-enzymic glycosylation) inactivates glutathione reductase.

Non-enzymic binding of sugars to proteins (glycation) is a common biological phenomenon that is increased in diabetes. Most work has been directed towards structural proteins which may be present for many years and would continue to accumulate sugar residues. As glycation is a non-specific reaction, other proteins such as enzymes will also be susceptible to glycation and could well display altered activity. We investigated the effect of various sugars whose concentrations increase in diabetes in insulin-independent tissues on glutathione reductase, an enzyme that maintains the GSH level in cells. Glucose, glucose 6-phosphate and fructose all displayed a time-dependent inhibition of glutathione reductase activity, suggesting that these sugars glycate this enzyme. Aspirin gave some protection against the loss of activity induced by glucose.

Acetaminophen↗
PubMed1992

Prevention of cataract in diabetic rats by aspirin, paracetamol (acetaminophen) and ibuprofen.

Evidence from epidemiological, in vitro and animal studies has accumulated to support the idea that aspirin, ibuprofen and paracetamol protect against cataract. In this study rats made diabetic with streptozotocin were given these drugs in their drinking solution for up to 160 days. All three drugs delayed cataract formation assessed by slit-lamp examination for a large part of this time. Blood glucose levels were a little lower in diabetic rats treated with aspirin and ibuprofen than in untreated diabetic rats although all groups remained diabetic. Similarly, the increased glycation (non-enzymic glycosylation) of lens proteins caused by diabetes was less in the diabetic rats treated with aspirin and ibuprofen. The fall in glutathione induced by diabetes was also alleviated by aspirin and ibuprofen. Paracetamol appeared to afford similar protection against the biochemical changes but its effect was not statistically significant. The decrease in glutathione and increase in glycation were related to the progression of lens opacification. The greatest loss of glutathione occurred at an early stage, whereas glycation had its greatest change at the later stages--nuclear and mature cataract. These results encourage the view that ibuprofen, aspirin and paracetamol could protect against cataract in man: a hypothesis that could be tested in a properly-conducted clinical trial.

Acetaminophen↗
PubMed1991

Investigations of ibuprofen and paracetamol binding to lens proteins to explore their protective role against cataract.

There is evidence that ibuprofen and paracetamol can act as anti-cataract drugs. [14C]-Ibuprofen labelled at the methyl group of the propanoic acid moiety was synthesized. The labelled ibuprofen was found to bind non-covalently to alpha-crystallin but not to beta- and gamma-crystallin of the bovine lens. Labelled paracetamol binds to total lens soluble proteins. Both drugs penetrate into the lens cortex and nucleus within 24 hr. Affinity chromatographic studies suggest that the lipophilic isobutyl group of ibuprofen hinders binding to the lens proteins. Hence, in the light of weak binding of ibuprofen and paracetamol and strong binding of the ibuprofen analogue used in the affinity chromatography, it is suggested, in this paper, that the protection against cataract by these analgesics is possibly due to their metabolites interacting with the lens proteins.

Acetaminophen↗
PubMed1991

Non-enzymic modification of lens proteins by glucose and fructose: effects of ibuprofen.

Cataract is the major cause of blindness worldwide. Non-enzymic modification of lens proteins leading to a disruption of their short range order is an important route to cataract formation. A reaction between lens proteins and a compound found in the lens indicates a potential role for that compound in cataract formation. The reactions of glucose and fructose with lens protein in vitro were investigated. Fructose bound to lens protein at pH 6.9 in a time-dependent fashion over a period of 20 days. The reactions of both glucose and fructose with lens proteins and bovine serum albumin led to the formation of coloured and fluorescent compounds. The formation of such compounds was greater with fructose than with glucose. The kinetics of the reactions of lens proteins and bovine serum albumin with fructose as measured by the formation of the above compounds were not identical. This point must be appreciated when attempting to extrapolate from results obtained with bovine serum albumin as to the reactions of lens proteins. The incubation of lens proteins with fructose led to an enhancement of protein aggregation. The implications of the reactions between lens proteins and fructose for the formation of cataract in diabetics are discussed. Ibuprofen intake is associated with protection against cataract. At relatively high concentrations (10-20 mM) ibuprofen decreased the binding of fructose to lens protein: this decrease was statistically significant at selected times (Student's t-test, P less than 0.05). The formation of fluorescent compounds in the presence of fructose was also decreased by ibuprofen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Post-translational modification of lens proteins in cataract.

Evidence supporting the role of non-enzymic post-translational modification of lens proteins in cataract is reported as presented at a meeting in Bydgoszcz, Poland in August 1990. Glycation and carbamylation have been studied intensively recently. Both produce modified proteins with properties similar to those of 'molten-globule' intermediates of protein folding and unfolding pathways.

Cataract↗
PubMed1990

The effects of aminoguanidine on the glycation (non-enzymic glycosylation) of lens proteins.

Aminoguanidine is being studied as a possible drug to prevent diabetic complications, by blocking the reactive carbonyl group of the Amadori product formed by glycation (non-enzymic glycosylation) of proteins. Thus it prevents the later browning and cross-linking steps. In the present work we show that labelled aminoguanidine becomes bound to glycated lens proteins. We also show that aminoguanidine inhibits the first steps of glycation of lens proteins but has no effect on carbamylation, the reaction with cyanate. It appears, therefore, that aminoguanidine can prevent glycation as well as the browning reactions, and may do so not by acting on the proteins, as other putative anti-cataract drugs do, but by decreasing the concentration of the active aldehyde form of the sugars.

Animals↗
PubMed1990

Ibuprofen, a putative anti-cataract drug, protects the lens against cyanate and galactose.

Cataract, the major cause of blindness world-wide, may be caused partly by modification of lens proteins by carbamylation and non-enzymic glycosylation (glycation) in some patients. Aspirin has been found to protect against these modifications and to prevent cyanate-induced opacification occurring in whole rate lenses. Ibuprofen is an aspirin-like anti-inflammatory drug which appeared as a protective factor against cataract in an Oxford case-control study. The binding of cyanate, galactose and glucose 6-phosphate to lens proteins, and the effect of ibuprofen on this reaction was investigated, as was cyanate-induced opacification in whole rat lenses. Labelled metabolite was incubated with bovine lens homogenate in the presence and absence of ibuprofen, and the incorporation of label into the lens homogenate was followed. Simultaneous and preincubation experiments were performed. Intact rat lenses were incubated in culture medium with and without cyanate and ibuprofen. The phase separation temperature was noted as the temperature at which opacity first appeared on cooling. Cyanate, galactose and glucose 6-phosphate bind progressively to lens proteins. Simultaneous incubation with ibuprofen reduces cyanate and galactose binding but not glucose 6-phosphate. Ibuprofen protects against opacities due to cyanate-induced phase separation. Ibuprofen has protected against cataract in the models of cataractogenesis in this study. It appears to have a different mechanism of action from that of aspirin. These studies provide some support for the idea, based on epidemiological findings, that ibuprofen might be a useful anti-cataract drug.

Animals↗
PubMed1989

Site of carbamoylation of bovine gamma-II-crystallin by potassium [14C]cyanate.

One possible route to cataract formation may be via the carbamoylation of lens proteins due to increased concentrations of cyanate in the body resulting from uraemia associated with renal failure and with severe diarrhoea. Carbamoylation of gamma-II-crystallin, which is found in the lens core, could alter the surface charge network of the molecules, resulting in aggregation, increased light-scattering and hence cataract. We have attempted to locate the site(s) of carbamoylation in gamma-II-crystallin. gamma-II-Crystallin was isolated by gel chromatography and ion-exchange chromatography. gamma-II-Crystallin was then carbamoylated by incubation with potassium [14C]cyanate, followed by citraconylation and digestion with trypsin to give peptides that were separated by high-resolution ion-exchange chromatography. The amino acid compositions of the radioactive peptides were compared with the expected peptide composition for gamma-II-crystallin. The radioactive peptide compositions, which agreed with the theoretical peptides, all matched with the N-terminal region of gamma-II-crystallin and had in common the presence of the N-terminal glycine residue. It appears that the alpha-amino group of the N-terminal glycine was the main site of carbamoylation. This site forms part of the charge network on the surface of gamma-II-crystallin.

Amino Acids↗
PubMed1989

Pinpointing the sites of hydroxylysine glycosides in peptide alpha 1-CB7 of bovine corneal collagen, and their possible role in determining fibril diameter and thus transparency.

Two cyanogen bromide fragments (alpha 1-CB7 and alpha 1-CB8) of bovine corneal stromal collagen have been isolated and characterized. These added to those characterized in our previous work account for 95% of the amino acid sequence of the alpha 1(1)-chain. The hydroxylysine glycoside content of each fragment was determined and in this way the general distribution of glycoside over the entire molecule was deduced accounting for all the galactosylhydroxylysine and most of the glucosylgalactosylhydroxylysine of this heavily glycosylated type I collagen. The characterization of fragments alpha 1-CB7 and alpha 1-CB8 has enabled us to resolve the controversy over the relative mobilities of these fragments on SDS gels. Fragment alpha 1-CB7 of bovine corneal collagen was digested by trypsin and by staphylococcal proteinase V8. The resultant peptides were isolated by gel and ion-exchange chromatography and identified in relation to the known amino acid sequence of type I collagen. The hydroxylysine glycosides were determined in the relevant peptides providing a complete account of their distribution along this part of the collagen molecule. Most of the glycoside was found in the gap region of collagen especially near the edges of the axial holes where it could act as a peg to facilitate fibre formation. In addition, some glycoside was found in the overlap region where, being unable to fit into axial holes, it might impede the growth of the fibre and, with other glycoside of the overlap region, might be responsible for the narrow fibres of corneal collagen that are essential for corneal transparency. This glycoside, with that previously found in the peptide alpha 1-CB3 is the only hydroxylysine glycoside identified in the overlap region of a type I collagen.

Amino Acid Sequence↗
PubMed1989

The non-enzymic glycosylation of bovine lens proteins by glucosamine and its inhibition by aspirin, ibuprofen and glutathione.

Cataract is a long-term complication of diabetes mellitus. Diabetics have increased glucosamine levels and it is possible that the non-enzymic glycosylation of the lens structural proteins by glucosamine induces conformational changes in the lens that contribute to cataract formation. Aspirin and aspirin-like analgesics may protect against glycosylation. In this paper the binding of glucosamine to bovine lens proteins and the effects of aspirin, paracetamol and ibuprofen on this reaction were investigated. Significant binding of glucosamine to the lens proteins was found. Gel-chromatography indicated that beta H-crystallin was most reactive to the amino-sugar. Of the analgesics studied, aspirin was the most effective inhibitor of glycosylation, followed by the other anti-inflammatory drug, ibuprofen. Preincubation of the lens homogenate with aspirin was no more effective at decreasing binding of glucosamine than was simultaneous incubation with aspirin. Glutathione significantly inhibited glucosamine binding. Glucosamine is active in non-enzymic glycosylation but the reaction can be inhibited by agents thought to protect against cataract.

Animals↗
PubMed1989

Non-enzymic post-translational modification of proteins in aging. A review.

Various non-enzymic post-translational changes to proteins occur in vivo and some of these progress with aging. These changes are reviewed and linked to a number of age-related diseases, and to alterations in the charge distribution on protein surfaces. Modification by cyanate and by glucose 6-phosphate causes a partial unfolding of proteins, with loss of tertiary structure but retention of secondary structure. These products are reminiscent of the intermediate state observed during folding and unfolding of some proteins.

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