Richard Donnelly

Protein kinase C activation: isozyme-specific effects on metabolism and cardiovascular complications in diabetes

Abstract Protein kinase C (PKC) is a family of multifunctional isoenzymes, activated by diacylglycerols (DAGs), which play a central role in signal transduction and intracellular crosstalk by phosphorylating at serine/threonine residues an array of substrates, including cell-surface receptors, enzymes, contractile proteins, transcription factors and other kinases. Individual isozymes vary in their pattern of tissue and subcellular distribution, function and Ca2+/phospholipid cofactor requirements, and in diabetes there is widespread activation of the DAG-PKC pathway in metabolic, cardiovascular and renal tissues. In liver, muscle and adipose tissue, PKC isozymes have been implicated both as mediators and inhibitors of insulin action. Activation of DAG-sensitive PKC isoforms, such as PKC-θ and PKC-ɛ, down-regulates insulin receptor signalling and could be an important biochemical mechanism linking dysregulated lipid metabolism and insulin resistance in muscle. On the other hand, atypical PKC isozymes, such as PKC-ζ and PKC-λ, have been identified as downstream targets of PI-3-kinase involved in insulin-stimulated glucose uptake, especially in adipocytes. Glucose-induced de novo synthesis of (palmitate-rich) DAG and sustained isozyme-selective PKC activation (especially but not exclusively PKC-β) has been strongly implicated in the pathogenesis of diabetic microangiopathy and macroangiopathy through a host of undesirable effects on endothelial function, VSM contractility and growth, angiogenesis, gene transcription (in part by MAP-kinase activation) and vascular permeability. Interventions that increase DAG metabolism (e. g. vitamin E) and/or inhibit PKC isozymes (e. g. the β-selective inhibitor LY333 531) ameliorate the biochemical and functional consequences of DAG-PKC activation in experimental diabetes, for example improving retinal blood flow and albuminuria in parallel with reductions in membrane-associated PKC isozyme activities. Thus, a greater understanding of the functional diversity and pathophysiological regulation of PKC isozymes is likely to have important clinical and therapeutic benefits. [Diabetologia (2001) 44: 659–673]

ABC of arterial and venous disease: Vascular complications of diabetes

Adults with diabetes have an annual mortality of about 5.4% (double the rate for non-diabetic adults), and their life expectancy is decreased on average by 5-10 years. Although the increased death rate is mainly due to cardiovascular disease, deaths from non-cardiovascular causes are also increased. A diagnosis of diabetes immediately increases the risk of developing various clinical complications that are largely irreversible and due to microvascular or macrovascular disease. Duration of diabetes is an important factor in the pathogenesis of complications, but other risk factors—for example, hypertension, cigarette smoking, and hypercholesterolaemia—interact with diabetes to affect the clinical course of microangiopathy and macroangiopathy. View this table: Vascular complications of diabetes View this table: Risk of morbidity associated with all types of diabetes mellitus A continuous relation exists between glycaemic control and the incidence and progression of microvascular complications. Hypertension and smoking also have an adverse effect on microvascular outcomes. In the diabetes control and complications trial—a landmark study in type 1 diabetes—the number of clinically important microvascular endpoints was reduced by 34-76% in patients allocated to intensive insulin (that is, a 10% mean reduction in glycated haemoglobin (HbA1c) concentration from 8.0% to 7.2%). However, these patients also had more hypoglycaemic episodes. Similarly, in the UK prospective diabetes study of patients with type 2 diabetes, an intensive glucose control policy that lowered glycated haemoglobin concentrations by an average of 0.9% compared with conventional treatment (median HbA1c 7.0% v 7.9%) resulted in a 25% reduction in the overall microvascular complication rate. It was estimated that for every 1% reduction in HbA1c concentration there is a 35% reduction in microvascular disease. Relation between glycaemic control (HbA1c) and risk of progression of microvascular complications (retinopathy) and severe hypoglycaemia in patients with type 1 diabetes. Data from the diabetes control and complications trial. Dotted lines represent 95% confidence …

Exenatide compared with long-acting insulin to achieve glycaemic control with minimal weight gain in patients with type 2 diabetes: results of the Helping Evaluate Exenatide in patients with diabetes compared with Long-Acting insulin (HEELA) study

Aim: The Helping Evaluate Exenatide in overweight patients with diabetes compared with Long‐Acting insulin (HEELA) study was designed to examine whether the glucagon‐like peptide‐1 (GLP‐1) receptor agonist, exenatide, could improve HbA1c (≤7.4%) with minimal weight gain (≤1 kg) compared with insulin glargine.

Sodium–glucose co‐transporter‐2 inhibitors: an emerging new class of oral antidiabetic drug

The sodium–glucose co‐transporter‐2 (SGLT2) is a low‐affinity transport system that is specifically expressed in the kidney and plays an important role in renal glucose reabsorption in the proximal tubule. Competitive inhibition of SGLT2 therefore represents an innovative therapeutic strategy for the treatment of hyperglycaemia and/or obesity in patients with type 1 or type 2 diabetes by enhancing glucose and energy loss through the urine. The observation that individuals with familial renal glycosuria maintain normal long‐term kidney function provides some reassurance that this mode of action will not adversely affect renal function. Intense research in this therapeutic area has led to the discovery of novel SGLT2 inhibitors, each with different chemical, pharmacodynamic and pharmacokinetic profiles. This review outlines the biology, expression and pleotropic activity of the SGLT system and the pharmacological profile of SGLT2 inhibitors and provides a summary of preclinical and limited clinical data available to characterize the efficacy, safety and potential clinical utility of SGLT2 inhibitors in the management of diabetes.

Dipeptidyl peptidase-IV inhibitors: a major new class of oral antidiabetic drug.

Exploiting the incretin effect to develop new glucose‐lowering treatments has become the focus of intense research. One successful approach has been the development of oral inhibitors of dipeptidyl peptidase‐IV (DPP‐IV). These drugs reversibly block DPP‐IV‐mediated inactivation of incretin hormones, for example, glucagon‐like peptide 1 (GLP‐1) and also other peptides that have alanine or proline as the penultimate N‐terminal amino acid. DPP‐IV inhibitors, therefore, increase circulating levels and prolong the biological activity of endogenous GLP‐1, but whether this is sufficient to fully explain the substantial reduction in haemoglobin A1c (HbA1c) and associated metabolic profile remains open to further investigation. DPP‐IV inhibitors such as vildagliptin and sitagliptin have been shown to be highly effective antihyperglycaemic agents that augment insulin secretion and reduce glucagon secretion via glucose‐dependent mechanisms. This review summarizes the major clinical trials with DPP‐IV inhibitors as monotherapy and as add‐on therapy in patients with type 2 diabetes. The magnitude of HbA1c reduction with DPP‐IV inhibitors depends upon the pretreatment HbA1c values, but there seems to be no change in body weight, and very low rates of hypoglycaemia and gastrointestinal disturbance with these agents. DPP‐IV inhibitors represent a major new class of oral antidiabetic drug and their metabolic profile offers a number of unique clinical advantages for the management of type 2 diabetes.

Resistin: an adipocyte‐derived hormone. Has it a role in diabetes and obesity?

Resistin is a 12.5 kDa cysteine-rich peptide that is secreted from adipocytes and present in the circulation. The discovery of resistin, together with other adipocytederived hormones, has prompted intense research into the role of fat-derived mediators in obesity-induced insulin resistance and type 2 diabetes. As the discovery and functional importance of resistin were first highlighted in Nature in 2001 [1], several follow-up studies have explored the cellular, physiological and clinical importance of resistin, but fundamental questions remain unclear and several inconsistencies have emerged. The purpose of this review is to summarize the experimental findings to date and to discuss the extent to which the original hypotheses relating to resistin have been confirmed or questioned.

Exendin-4 increases insulin sensitivity via a PI-3-kinase-dependent mechanism: contrasting effects of GLP-1.

The insulinotropic agent, exendin-4, is a long-acting analogue of glucagon-like peptide-1 (GLP-1) which improves glucose tolerance in humans and animals with diabetes, but the underlying mechanisms and the effects of exendin-4 on peripheral (muscle/fat) insulin action are unclear. Previous in vivo and clinical studies have been difficult to interpret because of complex, simultaneous changes in insulin and glucagon levels and possible effects on hepatic metabolism. Thus, the comparative effects of exendin-4 and GLP-1 on insulin-stimulated 2-[3H]deoxyglucose (2-DOG) uptake were measured in fully differentiated L6 myotubes and 3T3-adipocytes, including co-incubation with inhibitors of the PI-3-kinase (wortmannin) and mitogen-activated protein (MAP) kinase (PD098059) pathways. In L6 myotubes, there was a concentration-dependent and PI-3-kinase-dependent increase in insulin-stimulated 2-DOG uptake with exendin-4 and GLP-1, e.g. for exendin-4 the C(I-200) value (concentration of insulin required to increase 2-DOG uptake 2-fold) decreased from 1.3 +/- 1.4 x 10(-7)M (insulin alone, n=16) to 5.9 +/- 1.3 x 10(-8)M (insulin+exendin-4 0.1nM, n=18, P<0.03). A similar insulin-sensitizing effect was observed with exendin-4 in 3T3-adipocytes, but GLP-1 had no effect on adipocyte insulin sensitivity. In conclusion, this is the first direct evidence showing that exendin-4 increases insulin-stimulated glucose uptake in muscle and fat derived cells via a pathway that involves PI-3-kinase activation. Furthermore, the contrasting responses of exendin and GLP-1 in 3T3-adipocytes suggest that the peripheral insulin-sensitizing effect of exendin-4 (in contrast to the insulinotropic effect) does not involve the GLP-1 receptor pathway.

Pharmacokinetics of calcium antagonists.

Calcium antagonists are a biochemically heterogeneous group of drugs that share the property of blocking the entry of calcium into cells by voltage-operated channels in cardiac and smooth muscle. They are useful in the management of angina pectoris and hypertension. The drugs available at present include nifedipine, verapamil, and diltiazem. All three drugs have similar pharmacokinetic properties of low and variable bioavailability, high first-pass metabolism, short elimination half-life, and active metabolites. The pharmacokinetics of calcium antagonists are relevant, because in individual patients the intensity and duration of the pharmacological effect is related to the level of drug in plasma. Amlodipine is a new dihydropyridine calcium antagonist in advanced clinical development. It has a completely different pharmacokinetic profile. It is water soluble and photostable, and has a long half-life of 35-50 h. Amlodipine is slowly absorbed, its absolute bioavailability is high, and it is extensively metabolized in the liver. The long half-life is associated with a prolonged (greater than 24 h) duration of pharmacodynamic action. Amlodipine, because of its novel pharmacokinetics, may offer practical advantages over existing calcium antagonists in the long-term treatment of cardiovascular disease.

ABC of arterial and venous disease: Non-invasive methods of arterial and venous assessment

Although diagnostic and therapeutic decisions in patients with vascular disease are guided primarily by the history and physical examination, the use of non-invasive investigations has increased significantly in recent years, mainly as a result of technological advances in ultrasonography. This article describes the main investigative techniques. Handheld pencil Doppler being used to measure ankle brachial pressure index In the simplest form of ultrasonography, ultrasound is transmitted as a continuous beam from a probe that contains two piezoelectric crystals. The transmitting crystal produces ultrasound at a fixed frequency (set by the operator according to the depth of the vessel being examined), and the receiving crystal vibrates in response to reflected waves and produces an output voltage. Conventional B mode (brightness mode) ultrasonography records the ultrasound waves reflected from tissue interfaces, and a two dimensional picture is built up according to the reflective properties of the tissues. ### Doppler ultrasonography Ultrasound signals reflected off stationary surfaces retain the same frequency with which they were transmitted, but the principle underlying Doppler ultrasonography is that the frequency of signals reflected from moving objects such as red blood cells shifts in proportion to the velocity of the target. The output from a continuous wave Doppler ultrasonograph is usually presented as an audible signal, so that a sound is heard whenever there is movement of blood in the vessel being examined. Left: Doppler velocity waveforms:( a ) triphasic waveform in normal artery; ( b ) biphasic waveform, with increased velocity, through a mild stenosis;( c ) monophasic waveform, with greatly increased velocity, through tight stenosis; and ( d ) dampened monophasic waveform, with reduced velocity, recorded distal to tight stenosis. Right:Anatomical chart used to record position of stenoses, showing three stenoses with velocity increases of 7×, 4×, and 3× compared with adjacent unaffected arteries ### Pulsed ultrasonography Continuous wave ultrasonography provides little scope for restricting the area of …

Kinetic-dynamic relations and individual responses to enalapril.

Pharmacokinetic and pharmacodynamic variability largely account for interindividual differences in the response to antihypertensive drugs including angiotensin converting enzyme inhibitors. The factors determining the response to enalapril have been investigated in a placebo-controlled study in essential hypertension. The effects of placebo, the initial dose of enalapril, and long-term (1 and 6 weeks) treatment with enalapril were studied in 13 subjects. By using an integrated kinetic-dynamic model that incorporates a parameter for saturable protein binding, individual responses for blood pressure reduction and angiotensin converting enzyme inhibition were characterized in terms of the maximum effect (Emax) and the drug concentration required to produce 50% of Emax (Ce50). In individual subjects, plasma enalaprilat concentrations could be correlated with falls in blood pressure and changes in plasma angiotensin converting enzyme activity. For the group, Emax was -46.1 +/- 16.5 and -19.7 +/- 3.8 mm Hg for systolic and diastolic blood pressure, respectively, and the corresponding Ce50 values were 66.1 +/- 20.2 and 61.6 +/- 22.5 ng/ml. For angiotensin converting enzyme inhibition, Emax (%) and Ce50 (ng/ml) were, respectively, 102.4 +/- 5 and 19.8 +/- 13 after the first dose, 103 +/- 5 and 33.4 +/- 20.3 after 1 week, and 101.3 +/- 2.2 and 31.3 +/- 18.9 after 6 weeks. There was no relation between the responsiveness to enalapril (Emax or Ce50) and patient age or plasma renin activity, but there was a significant positive correlation between Emax and the pretreatment blood pressure. In individual subjects, Emax (first dose) was directly correlated with Emax after 1 and 6 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)