Effect of repeated doses of ATP on serum protein pattern and fat content of the liver in experimental diabetes

ATP Secretion and Metabolism in Regulating Pancreatic Beta Cell Functions and Hepatic Glycolipid Metabolism

Diabetes (DM), especially type 2 diabetes (T2DM) has become one of the major diseases severely threatening public health worldwide. Islet beta cell dysfunctions and peripheral insulin resistance including liver and muscle metabolic disorder play decisive roles in the pathogenesis of T2DM. Particularly, increased hepatic gluconeogenesis due to insulin deficiency or resistance is the central event in the development of fasting hyperglycemia. To maintain or restore the functions of islet beta cells and suppress hepatic gluconeogenesis is crucial for delaying or even stopping the progression of T2DM and diabetic complications. As the key energy outcome of mitochondrial oxidative phosphorylation, adenosine triphosphate (ATP) plays vital roles in the process of almost all the biological activities including metabolic regulation. Cellular adenosine triphosphate participates intracellular energy transfer in all forms of life. Recently, it had also been revealed that ATP can be released by islet beta cells and hepatocytes, and the released ATP and its degraded products including ADP, AMP and adenosine act as important signaling molecules to regulate islet beta cell functions and hepatic glycolipid metabolism via the activation of P2 receptors (ATP receptors). In this review, the latest findings regarding the roles and mechanisms of intracellular and extracellular ATP in regulating islet functions and hepatic glycolipid metabolism would be briefly summarized and discussed.

Purinergic signalling in the liver in health and disease

Purinergic signalling is involved in both the physiology and pathophysiology of the liver. Hepatocytes, Kupffer cells, vascular endothelial cells and smooth muscle cells, stellate cells and cholangiocytes all express purinoceptor subtypes activated by adenosine, adenosine 5'-triphosphate, adenosine diphosphate, uridine 5'-triphosphate or UDP. Purinoceptors mediate bile secretion, glycogen and lipid metabolism and indirectly release of insulin. Mechanical stress results in release of ATP from hepatocytes and Kupffer cells and ATP is also released as a cotransmitter with noradrenaline from sympathetic nerves supplying the liver. Ecto-nucleotidases play important roles in the signalling process. Changes in purinergic signalling occur in vascular injury, inflammation, insulin resistance, hepatic fibrosis, cirrhosis, diabetes, hepatitis, liver regeneration following injury or transplantation and cancer. Purinergic therapeutic strategies for the treatment of these pathologies are being explored.

Purinergic signalling and diabetes

The pancreas is an organ with a central role in nutrient breakdown, nutrient sensing and release of hormones regulating whole body nutrient homeostasis. In diabetes mellitus, the balance is broken-cells can be starving in the midst of plenty. There are indications that the incidence of diabetes type 1 and 2, and possibly pancreatogenic diabetes, is rising globally. Events leading to insulin secretion and action are complex, but there is emerging evidence that intracellular nucleotides and nucleotides are not only important as intracellular energy molecules but also as extracellular signalling molecules in purinergic signalling cascades. This signalling takes place at the level of the pancreas, where the close apposition of various cells-endocrine, exocrine, stromal and immune cells-contributes to the integrated function. Following an introduction to diabetes, the pancreas and purinergic signalling, we will focus on the role of purinergic signalling and its changes associated with diabetes in the pancreas and selected tissues/organ systems affected by hyperglycaemia and other stress molecules of diabetes. Since this is the first review of this kind, a comprehensive historical angle is taken, and common and divergent roles of receptors for nucleotides and nucleosides in different organ systems will be given. This integrated picture will aid our understanding of the challenges of the potential and currently used drugs targeted to specific organ/cells or disorders associated with diabetes.

Serum enzyme changes due to trace amounts of some transition metal ions on the induction of experimental diabetes

The intravenous injection of zinc chloride immediately before and 15 minutes after alloxan or dithizone prevented the usual hyperglycaemia observed 24 hours after induction of diabetes. The intravenous injection of manganese chloride prevented any marked rise of blood glucose, while chromium and cobalt chlorides lowered the blood glucose level to a certain extent. In alloxan diabetic rats, serum GOT and GPT levels were significantly higher than normal. The serum GOT levels were higher in animals injected with chromium than cobalt, zinc and manganese; while serum GPT levels were higher in cobalt than in chromium, zinc and manganese. In dithizone diabetes, serum GOT and GPT were increased in animals injected with cobalt than chromium, zinc and manganese. Alloxan diabetic rats showed lower serum alkaline phosphatase levels and higher in animals injected with cobalt than chromium, zinc and manganese. For dithizone, there are statistically significant differences in all cases. In alloxan diabetes, coeruloplasmin was higher than normal, while intravenous injection of dithizone was without effect on serum coeruloplasmin.

Evaluation of the effect of lead exposure on the liver in Egyptian lead tank welders

In a group of Egyptian lead tank welders who were exposed to lead fumes for periods to 22 years the changes in serum lipids and some of the liver function tests which may elucidate the effect of lead on the liver were investigated. The results revealed increased blood lead level associated with decreased blood haemoglobin and increased urinary excretion of delta amino levulinic acid. However, no clinical abnormalities were recorded in the exposed group of the present work. Thus the increase in serum triglycerides and B-lipoprotein together with the lowering of the phospholipid/cholesterol ratio which were found may indicate premature development of atherosclerosis. Indirect evidence of the beginning of liver fattening was also provided by the increase in serum GOT, GPT, LDH enzymes and decreased albumin/globulin ratio besides the changes in serum lipid values. It is concluded therefore that lead poisoning may have a vascular as well as hepato-toxic action.