Advantages and Pitfalls of Antihyperglycemic Combination Pills as First-Line Therapy in the Management of Type 2 Diabetes.

Type 2 diabetes is a heterogeneous disease with multiple underlying pathophysiological processes. Several new antidiabetic agents are presently available for clinical use, yet very few clinical trials have been performed on the efficacy of combination pill therapy. Combination pill use is easily justified as a second-line therapy in which the advantages of added efficacy, enhanced adherence, and only modest increase in risk are recognized. In contrast, combination pill use as first-line therapy has some drawbacks, such as increased risk of hypoglycemia, difficulty in attribution of side effects to the constituents, and less than additive efficacy of the components of the pill. In general, combinations of drugs with synergistic mechanisms of action are preferable. However, the efficacy of currently available combination pills when used as first-line therapy is less than the sum of the efficacy of its components. The current guidelines recommend initiation of dual therapy in drug-naive individuals depending on baseline HbA1c at the time of diagnosis. When the HbA1c is above 8.5%-9%, the likelihood of achieving glycemic targets with a single agent diminishes sharply. These patients may be better candidates for treatment with a combination of antihyperglycemic agents as first-line therapy.

Diabetes mellitus in older adults.

The prevalence of diabetes mellitus increases with age and causes significant morbidity and poor quality of life in older adults. To review the current literature on the diagnosis and management of diabetes in the elderly, the relevant manuscripts were identified through a MEDLINE (2000-September 1, 2010) search of the English literature. The key phrase used was diabetes in older adults or diabetes in the elderly. The literature search was limited to core clinical journals that have accessible full texts. A total of 480 manuscripts were reviewed. Managing diabetes in older adults is a challenging task. Some features of the disease are unique to the older patient. Several new antidiabetic agents are now available for clinical use, and yet very few clinical trials have been carried out in this age group. For many older adults, maintaining independence is more important than adherence to published guidelines to prevent diabetes complications. The goals of diabetes care in older adults are to enhance quality of life without subjecting the residents to inappropriate interventions.

The antioxidant paradox in diabetes mellitus.

There is ample empiric evidence to indicate that oxidative stress contributes to the pathogenesis of coronary artery disease and has a key role in the onset and progression of diabetes and its complications. Diabetes leads to depletion of the cellular antioxidant defense system and is associated with an increase in the production of free radicals. Oxidative stress can be the result of multiple pathways. Some of these are related to substrate-driven overproduction of mitochondrial reactive oxygen species, advanced glycation end product formation, glucose autoxidation, and depletion of micronutrients and cellular elements with antioxidative properties. There are numerous observational studies in the literature showing a beneficial outcome of the consumption of antioxidant vitamins. However, the interventional trials portray a different picture. The divide between the robust experimental evidence of the pathogenetic role of increased oxidative load in diabetes and the overwhelming failure of antioxidants to show any health benefits in clinical trials may well be characterized as the "antioxidant paradox."

Age-related changes in rat cerebral occludin and zonula occludens-1 (ZO-1).

The endothelial or epithelial tight junctions create a rate-limiting barrier to diffusion of solutes. A major determinant of the barrier function is the density of tight junction proteins. Since aging is associated with significant alterations in the blood-brain barrier (BBB) it is possible that specific tight junction proteins may be altered in the cerebrum of aging rats. To test this hypothesis, Western and Northern blot analysis were carried out to measure the steady-state level of occludin and zonula occludens-one (ZO-1) proteins and their mRNA in cerebral tissue of 3-, 12- and 24-month-old rats. The cerebral occludin content in 24-month-old rats (732.5+/-99.9 arbitrary units) was significantly reduced compared to 12-month-old rats (1043.4+/-131.8) or 3-month-old rats (1021.4+/-62.8), P<0.01. The cerebral ZO-1 protein content in 24-month-old rats (161.7+/-8.1 arbitrary units) and 12-month-old rats (144.3+/-35.9) were not significantly reduced compared to 4-month-old rats (189.0+/-27.2). The occludin mRNA content relative to G3PDH mRNA was 1.11+/-0.05, 1.11+/-0.07 and 1.00+/-0.05 in 3-, 12- and 24-month-old rats, respectively. The differences did not achieve statistical significance. The ZO-1 mRNA content of cerebral tissue relative to G3PDH mRNA was significantly increased in 24-month-old rats compared to 3-month-old rats (1.280+/-0.030 vs. 0.956+/-0.038), P<0.001. It is concluded that aging in rats may alter the molecular anatomy of the BBB by altering the content of select structural proteins of tight junctions.

Dyslipidemia in type 2 diabetes: prevalence, pathophysiology, and management.

Dyslipidemia is one of the key risk factors for cardiovascular disease (CVD) in diabetes mellitus. Despite the mounting clinical trial data, the management of dyslipidemia other than lowering the low density lipoprotein cholesterol (LDL-c) continues to be controversial. The characteristic features of diabetic dyslipidemia are high plasma triglyceride concentration, reduced high density lipoprotein cholesterol (HDL-c) concentration, and increased concentration of small dense LDL particles. These changes are caused by increased free fatty acid flux secondary to insulin resistance and aggravated by increased inflammatory adipokines. The availability of several lipid-lowering drugs and nutritional supplements offers novel and effective options for achieving target lipid levels in people with diabetes. While initiation of drug therapy based on differences in the lipid profile is an option, most practice guidelines recommend statins as first-line therapy. Although the evidence for clinical utility of combination of statins with fibrates or nicotinic acid in reducing cardiovascular events remains inconclusive, the preponderance of evidence suggests that a subgroup who have high triglycerides and low HDL-c levels may benefit from combination therapy of statins and fibrates. The goal of therapy is to achieve at least 30-40 % reduction in LDL-c levels. Preferably the LDL-c should be less than 100 mg/dL in low-risk people and less than 70 mg/dL in those at high risk, including people with established CVD.

Induction of apolipoprotein A-I gene expression by glucagon-like peptide-1 and exendin-4 in hepatocytes but not intestinal cells.

OBJECTIVE: Diabetic dyslipidemia is an important risk factor for the development of macrovascular complications. Recent clinical trials suggest that diabetics treated with glucagon-like peptide-1 (GLP-1) have normalized lipid levels, including an increase in plasma high-density lipoprotein cholesterol (HDLc) levels. METHODS: To determine if GLP-1 (7-36 amide) and the GLP-1-like insulinotropic peptide exendin-4 regulate expression of apolipoprotein A-I (apo A-I), the primary anti-atherogenic component of high-density lipoprotein (HDL), HepG2 hepatocytes and Caco-2 intestinal cells, representative of tissues that express the majority of apo A-I, were treated with increasing amounts of each peptide and apo A-I gene expression was measured in the conditioned medium. RESULTS: Apo A-I secretion increased in both GLP-1 and exendin-4-treated HepG2, but not Caco-2 cells, and this was accompanied by similar changes in apo A-I mRNA levels and apo A-I promoter activity. Induction of apo A-I promoter activity by GLP-1 and exendin-4 required an SP1-responsive element. Hepatic ATP binding cassette protein A1 (ABCA1) expression, but not scavenger receptor class B type1 receptor expression was also induced by GLP-1 and exendin-4. CONCLUSIONS: These results suggest that GLP-1- and exendin-4-mediated changes in HDLc are likely due to changes in hepatic expression of apo A-I and ABCA1.

Nicotinic acid induces apolipoprotein A-I gene expression in HepG2 and Caco-2 cell lines.

The objective was to test the effect of nicotinic acid on apolipoprotein A-I (apo A-I) gene expression in hepatic (HepG2) and intestinal (Caco-2) cell lines. HepG2 and Caco-2 cells were treated with 0.1, 0.3, 1.0, 3.0, and 10 mmol/L of nicotinic acid; and apo A-I concentrations in conditioned media were measured with Western blots. Relative apo A-I messenger RNA (mRNA) levels, normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA, were measured with quantitative real-time polymerase chain reaction method. The nicotinic acid response element in the apo A-I promoter was identified using a series of apo A-I reporter plasmids containing deletion constructs of the promoter. In other experiments, HepG2 cells were also transfected with the apo A-I reporter plasmid and the hepatocyte nuclear factors 3α and ß expression plasmids. The apo A-I levels in conditioned media from HepG2 cells, apo A-I mRNA levels, and apo A-I promoter activity increased significantly following treatment with 1.0, 3.0, and 10 mmol/L nicotinic acid. Nicotinic acid-induced promoter activity required a region of the apo A-I gene located between -170 and -186 base pairs. Exogenous overexpression of the hepatocyte nuclear factors 3α and ß had no additive effect on apo A-I promoter. Apolipoprotein A-I concentrations in conditioned media and the apo A-I promoter activity were also significantly increased in Caco-2 intestinal cells. Nicotinic acid may increase apo A-I protein synthesis in the liver and small intestine. Induction of apo A-I gene by nicotinic acid requires a nicotinic acid responsive element in the apo A-I promoter.

Diabetes-related changes in rat cerebral occludin and zonula occludens-1 (ZO-1) expression.

The endothelial or epithelial tight junctions create a barrier to diffusion of solutes. Since experimental diabetes mellitus is associated with considerable alterations in the blood-brain barrier (BBB), it is possible that specific tight junction proteins may be altered in diabetes. To test this hypothesis, Western and Northern blot analysis were carried out to measure the steady-state level of occludin and zonula occludens-one (ZO-1) proteins and mRNA levels in cerebral tissue of streptozotocin-induced diabetic rats and the results were compared to insulin treated diabetic rats and vehicle injected control rats. The cerebral occludin content in diabetic rats (115.4 +/- 18.6 arbitrary units) was significantly reduced compared to insulin-treated diabetic rats (649.1 +/- 141.2) or control rats (552.9 +/- 82.9), p < 0.001. The ZO-1 content of cerebral tissue from diabetic rats (1,240.6 +/- 199.7 arbitrary units) was not significantly altered compared to controls (1,310.8 +/- 256.9). The cerebral occludin mRNA content relative to G3PDH mRNA was 1.35 +/- 0.07 and 1.34 +/- 0.19 in control and diabetic rats respectively. The cerebral ZO-1 mRNA content relative to G3PDH mRNA in diabetic and control rats was 1.135 +/- 0.123 and 0.956 +/- 0.038 respectively. These differences did not achieve statistical significance. It is concluded that diabetes alters the molecular anatomy of the tight junctions in cerebral tissue by altering the content of select structural proteins.