Diabetogenic action of alloxan-like derivatives of uric acid

Serum uric acid, mortality and glucose control in patients with Type 2 diabetes mellitus: a PreCIS database study

AIMS

To determine the association of serum uric acid with all-cause mortality and hyperglycaemia in patients with Type 2 diabetes.

METHODS

Retrospective cohort analysis of 535 consecutive patients who had uric acid determinations between 1998 and 2004 and whose subsequent vital status was determined at a median of 4.5 years. The association with mortality was analysed with Cox proportional hazards models. The incremental predictive value of uric acid was examined with concordance indexes. The proportional risk of mortality was represented with the Kaplan-Meier survival curves by uric acid quartiles.

RESULTS

We studied 370 men and 165 women aged 59.3 +/- 11.5 years. Mean uric acid was 371.7 +/- 106.2 micromol/l. Patients with glycated haemoglobin (HbA(1c)) > or = 9% had lower uric acid vs. the rest (342.2 +/- 112.1 vs. 383.5 +/- 106.2, P = 0.002). Overall mortality was 10.8%. For each 59 micromol/l increase in uric acid there was a 41% increase in risk of death (unadjusted analysis). The association of uric acid with mortality remained after adjustment for covariates (hazard ratio = 1.21, 95% confidence interval 1.07-1.45) and after gender subanalyses. Uric acid increased the accuracy of prediction when added to a model including Framingham risk factors, components of metabolic syndrome and fibrinogen (P = 0.03). Mortality was higher in patients taking diuretics vs. the rest (15.9 vs. 7.3%), but uric acid predicted mortality in both subgroups.

CONCLUSIONS

Serum uric acid predicts mortality in Type 2 diabetic patients regardless of gender, HbA(1c), renal function and diuretic use. Intervention studies should determine whether uric acid is a potential therapeutic target or only a marker of mortality risk.

Uric acid may inhibit glucose-induced insulin secretion via binding to an essential arginine residue in rat pancreatic β-cells

Uric acid (1a) suppresses basal insulin release in isolated rat pancreatic islets and inhibition of glucose-stimulated insulin secretion (GSIS) occurs right at hyperuricaemic levels (0.4 mM). Conversely, 1 mM guanidinium urate (2a) was completely ineffective, strongly suggesting that binding to an essential arginine residue triggers the inhibitory effect. A specific recognition of 1a molecule at the crucial beta-cell receptor is probably involved in the blocking glucose signal transduction.

Applications of high-performance liquid chromatography in bacteriology. I. Determination of metabolites

The chemotaxonomic approach to the identification of pathogenic bacteria for clinical purposes is surveyed. Primary interest is focused on the applications of HPLC to the determination of metabolic products from anaerobic bacteria. The use of HPLC is attractive as different classes of short-chain acids can be determined in a single analysis. Chromatographic conditions are extensively described, emphasizing the effects of changing variables on the HPLC profiles of analytes. The application of labelling procedures to bacterial metabolites can markedly increase the sensitivity of the analysis of pathological fluids. HPLC appears to be potentially useful in clinical bacteriology for the diagnosis of anaerobic infections.

Structure-activity relationships of alloxan-like compounds derived from uric acid

The diabetogenic activity of a range of alloxan-like compounds derived from uric acid has been investigated. The classes of derivatives were: 5-substituted-isouric acids; 4,5-disubstituted-4, 5-dihydrouric acids; 5-substituted-pseudouric acids; salts of dehydro-uramil hydrate; salts of dehydro-isouramil hydrate; alloxan derivatives. Compounds were tested by intravenous injection into rats and diabetogenic activity assessed by production of persistent hyperglycaemia and glycosuria. The only essential structural feature common to all active compounds was the presence of a quinonoid pyrimidine system or its hydrated equivalent. The presence of the five-membered ring of uric acid (or an opened form thereof) did not abolish and in some compounds enhanced diabetogenic activity.

Effects of dehydrouramil on protein phosphorylation and insulin secretion in rat islets of Langerhans

Dehydrouramil hydrate hydrochloride (DHU), a stable analogue of alloxan, inhibited the phosphorylation of an endogenous protein of Mr 53,000 catalysed by a Ca2+-calmodulin-dependent protein kinase in extracts of islets of Langerhans. The concentration of DHU required for 50% inhibition was 0.09 mM. DHU did not inhibit islet cyclic AMP-dependent protein kinase and caused only slight inhibition of Ca2+-phospholipid-dependent protein kinase. Inhibition of Ca2+-calmodulin-dependent protein kinase was neither prevented nor reversed by dithiothreitol. DHU did not affect the ability of calmodulin to activate cyclic AMP phosphodiesterase. In intact islets, pre-exposure to DHU impaired the insulin-secretory response to glucose and blocked the potentiatory effect on insulin secretion of forskolin, an activator of adenylate cyclase, and of tetradecanoylphorbol acetate (TPA), an activator of Ca2+-phospholipid-dependent protein kinase. The increase in islet cyclic AMP elicited by forskolin was not affected by DHU. The data are consistent with the hypothesis that protein phosphorylation catalysed by a Ca2+-calmodulin-dependent protein kinase may play a central role in the regulation of insulin secretion.

Host and environmental interactions in diabetes mellitus

A number of current issues in diabetes research are reviewed from an epidemiologic viewpoint. Though many advances have been made in our understanding of the causes of insulin-dependent diabetes mellitus (IDDM), there are many unresolved issues which could benefit from epidemiologic research. These include study of the 36-fold geographic variation in IDDM incidence seen across the world, perhaps by the development of registries, and the placing into a population perspective recent genetic and autoimmune findings concerning IDDM etiology. Epidemiologic considerations should also be incorporated into future trials of immunotherapy for IDDM. Despite considerable research, very little is known about risk factors and genetic environmental interactions in non-insulin dependent diabetes. Large scale prospective epidemiologic studies are, therefore, needed to delineate the potential roles of factors such as diet and physical activity, and how these interact with genetic predisposition.

Diabetogenic action of alloxan-like compounds: cytotoxic effects of 5-hydroxy-pseudouric acid and dehydrouramil hydrate hydrochloride on rat pancreatic beta cells

The effects on islet morphology and blood glucose concentration of intravenous administration of alloxan to rats have been compared with those of two new diabetogenic agents, 5-hydroxy-pseudouric acid (5-HPUA) and dehydrouramil hydrate hydrochloride (DHU). Administration of alloxan (0.35 mmol/kg) caused a classical triphasic change in blood glucose characterised by initial hyperglycaemia, subsequent hypoglycaemia and a delayed persistent hyperglycaemia. In contrast, 5-HPUA and DHU elicited persistent hyperglycaemia as early as 30 min after administration. Morphological evidence for degranulation, pyknosis, necrosis and widening of pericapillary spaces was obtained with all three agents. However, both 5-HPUA and DHU elicit considerably more rapid and extensive changes than alloxan, with evidence for extensive pyknosis occurring as early as 15 min after administration of DHU and 5-HPUA compared with 24 h for alloxan. The more marked potency of DHU and 5-HPUA may be at least partially attributable to the greater stability of these agents compared with alloxan, since solutions of DHU or 5-HPUA kept for 15 min prior to administration retained full diabetogenic activity, whereas similar treatment of alloxan solution completely abolished its diabetogenic activity. Since both 5-HPUA and DHU are potential metabolites of uric acid, their marked diabetogenic potency raises the possibility of a role for uric acid metabolites in the pathogenesis of diabetes mellitus.

Anaerobic degradation of uric acid via pyrimidine derivatives by selenium-starved cells of Clostridium purinolyticum

Clostridium purinolyticum decomposed uric acid via pyrimidine derivatives under selenium starvation conditions. Products were acetate, formate, glycine, ammonia, and CO2. 4,5-Diaminouracil could be identified as an intermediate after converting the labile substance into 6,7-dimethyllumazine. The breakdown of uric acid was inhibited by EDTA. High-pressure liquid chromatography methods have been developed for the simultaneous determination of uric acid, 4,5-diaminouracil, and 6,7-dimethyllumazine. The significance of the new pathway is discussed.