The Merits and the Pitfalls of Low Carbohydrate Diet: A Concise Review

Low carbohydrate diets (LCD) may help body weight loss and glycemic control in diabetes but their long-term consequences are not known. The aim of this review is to highlight the contrast between the potential benefits of short term LCD and the adverse health effects of long-term consumption of LCD. LCD can enhance weight loss in the short term although its effect is small and not sustainable. In people with diabetes and insulin resistance, LCD is helpful in achieving glycemic control. However, there are untoward side effects especially when carbohydrates are severely restricted (< 50 gm a day) to induce ketosis. The latter curbs appetite but also may cause nausea, fatigue water and electrolyte losses and limits exercise capacity. In addition, observational studies suggest that low carbohydrate diets (< 40% energy form carbohydrates) as well as very high carbohydrate diets (> 70% energy from carbohydrate) are associated with increased mortality. The available scientific evidence supports the current dietary recommendations to replace highly processed carbohydrates with unprocessed carbohydrates as well as limiting added sugars in the diet.

Academic advancement of clinician educators: why is it so difficult?

The role of clinician educators (CEs) in institutions and medical centres continues to be vital without any doubt. Although there has been more than a century since Sir William Osler established the role of the CE and the tradition by encouraging bed-side teaching, there is still a lack of consensus on the attributes that define a 'clinician-educator'. The concept of a superior clinician who is also a dedicated teacher seems to fit the description of a CE but most often seems insufficient to support the CE's academic advancement.

The effect of healthcare provider education on diabetes management of hospitalised patients

BACKGROUND

The importance of optimising blood glucose (BG) control in hospitalised patients is widely accepted. To determine whether focused education of physicians and nurses would result in measurable changes in glycaemic control, the effect of a diabetes-focused educational programme on point of care (POC) BG measures was monitored.

METHODS

This programme included 2 h symposium and 2 h interactive session. The POC BG measures were determined at 2-month period prior to implementing the programme and the ensuing 7 months after. Outcome parameters included the mean BG values, the incidence of hyperglycaemia (BG > 180 mg/dl) and hypoglycaemia (BG < 60 mg/dl). The outcome parameters were analysed by comparing the Internal Medicine (target service) to other such as Neurology and Surgical Trauma where no programme was offered.

RESULTS

On Internal Medicine, the mean BG decreased soon after implementing the programme and stayed lower than the baseline values over 7 months. The changes were significant at the third, fourth, seventh and the ninth month of the study. Hyperglycaemia decreased significantly (p < 0.05) on the third, fourth, seventh and eighth month, while hypoglycaemia increased following the education programmes. On Neurology and Surgical Trauma, the mean BG values were significantly higher, and hypoglycaemia was significantly lower during the same time frame.

CONCLUSIONS

Implementing an educational programme for healthcare providers had significant effects on the lowering of mean BG values and the incidence of hyperglycaemia, but increased the risk of hypoglycaemia. The merits of such programmes need to be tested before their widespread implementation.

The incidence of Hashimoto's disease in nodular goitre: the concordance in serological and cytological findings

OBJECTIVE

To determine the incidence of Hashimoto's disease in nodular goitre and to ascertain the degree of the concordance between serological and cytological findings.

METHODS

We retrospectively reviewed data from 188 patients who underwent a fine needle aspiration biopsy of the thyroid for uninodular or multinodular goitre with a documented serological level of antithyroid peroxidase (TPO) antibodies. AntiTPO antibodies were measured by immunochemiluminescent assay (Quest Diagnostics, Madison, NJ, USA).

RESULTS

The study cohort consisted of 170 female and 18 male patients with a mean (+/- SD) age of 47.8 +/- 14.9 years. AntiTPO antibodies were positive in 74 (39.36%) of the individuals and negative in 114 (60.63%). The cytodiagnoses were as follows: 5 (2.6%) cancerous, 18 (9.5%) suspicious, 12 (6.3%) inadequate, 92 (48.9%) benign and 61 (32.4%) consistent with chronic lymphocytic thyroiditis (CLT). For further analysis, we excluded all inadequate specimens. Based on the final sample of 176 patients, the sensitivity and specificity of antiTPO antibody test to detect CLT in nodular goitre were estimated to be 76.38% and 94.23% respectively. The prevalence of CLT in nodular goitre based on cytological criteria was (35.46%) compared with (31.97%) goitre based on positive antiTPO titres only.

CONCLUSION

There is a high degree of concordance between serological and cytological findings of CLT in people with nodular goitres. The high prevalence of CLT in nodular goitre justifies the use of antiTPO antibodies as part of the workup in this population.

Diagnosis and management of hyponatraemia in hospitalised patients

Hyponatraemia is a commonly encountered electrolyte abnormality in hospitalised patients and is associated with significant morbidity and mortality. The fact that most cases of hyponatraemia are the result of water imbalance rather than sodium imbalance underscores the role of antidiuretic hormone (ADH) in the pathophysiology. Hyponatraemia can be classified according to the measured plasma osmolality as isotonic, hypertonic or hypotonic. Hyponatraemia with a normal plasma osmolality usually indicates pseudohyponatraemia, while hyponatraemia because of a high plasma osmolality is typically caused by hyperglycaemia. After excluding isotonic and hypertonic causes, hypotonic hyponatraemia is further classified according to the volume status of the patient as hypovolaemic, hypervolaemic or euvolaemic. Hypovolaemic hyponatraemia is accompanied by extracellular fluid (ECF) volume deficit, while hypervolaemic hyponatraemia manifests with ECF volume expansion. The syndrome of inappropriate ADH (SIADH) should be suspected in any patient with euvolaemic hyponatraemia with a urine osmolality above 100 mOsm/kg and urine sodium concentration above 40 mEq/l. In the management of any hyponatraemia regardless of the patient's volume status, it is advised to restrict free water and hypotonic fluid intake. Hypertonic saline and vasopressin antagonists can be used to correct symptomatic hyponatraemia. The rate of correction is dependent upon the duration, degree of hyponatraemia and the presence or absence of symptoms. Symptomatic acute hyponatraemia (< 48 h) is a medical emergency requiring rapid correction to prevent the worsening of brain oedema. In asymptomatic patients with chronic hyponatraemia (> 48 h or unknown duration), fluid restriction and close monitoring alone are sufficient, while a slow correction by 0.5 mEq/l/h may be attempted in symptomatic patients. Excessive rapid correction should be avoided in both acute and chronic hyponatraemia, because it can lead to irreversible neurological complications including central osmotic demyelination.

Clinical utility of anion gap in deciphering acid-base disorders

The anion gap (AG) measurement is a very useful tool in the evaluation of patients with acid-base disorders. Once metabolic acidosis is identified, AG will provide the important first step in the differential diagnosis of disorders that either increase the AG and those that leave the AG unchanged. Delta gap is the comparison between change (delta) in the AG and the change (delta) in bicarbonate (HCO(3)(-)). Delta ratio, defined as delta AG:delta HCO(3)(-) is usually 1:1 in patients with an uncomplicated high AG acidosis. A value below 1:1 suggests a combined high and normal AG acidosis. A value above 2:1 suggests a combined metabolic alkalosis and a high AG acidosis. Urine AG (unmeasured anions-unmeasured cations) is an indirect estimate of the urine NH(4)(+) excretion. It is typically negative in patients with normal AG metabolic acidosis secondary to diarrhoea. Utilisation of AG calculations helps clinicians in identifying and treating acid-base disorders.

Low serum high-density lipoprotein cholesterol in obese subjects with normal serum triglycerides: the role of insulin resistance and inflammatory cytokines

BACKGROUND

The cause of obesity-related low HDLc in the absence of hypertriglyceridemia is not known.

SUBJECTS & METHODS

A total of 32 subjects with a body mass index (BMI)(kg/m(2)) greater than 30 and normal serum triglycerides (<150 mg/dl) were identified.

RESULTS

People with low HDLc (n = 16) compared to those with normal HDLc (n = 16) had higher BMI (37.53 +/- 4.54 vs. 33.99 +/- 3.65 kg/m(2), p < 0.021), higher body fat weight (42.59 +/- 9.51 vs. 34.76 +/- 8.7 kg, p < 0.023), and higher insulin resistance index (3.75 +/- 2.51 vs. 1.95 +/- 1.10, p < 0.013). Seven subjects with low HDLc and none of those with normal HDLc, had elevated serum tumor necrosis factor alpha and/or interleukin-6 (p < 0.010).

CONCLUSIONS

Low HDLc levels can occur in obesity independently of elevated serum triglycerides and may be secondary to elevated serum levels of inflammatory cytokines.

Glyburide/metformin combination product is safe and efficacious in patients with type 2 diabetes failing sulphonylurea therapy

AIM

To compare the efficacy, safety and tolerability of a fixed combination glyburide/metformin preparation with those of glyburide or metformin alone in patients with type 2 diabetes inadequately controlled by sulphonylurea, diet and exercise.

METHODS

In this 16-week, randomized, double-blind, parallel group study, 639 patients with inadequate glycaemic control on at least half-maximal dose of sulphonylurea were randomly assigned to: glyburide 10 mg b.i.d. (n = 164); metformin 500 mg (n = 153); glyburide/metformin 2.5 mg/500 mg (n = 160); or glyburide/metformin 5 mg/500 mg (n = 162). Titration was allowed to maximum doses of 2000 mg for metformin or 10 mg/2000 mg and 20 mg/2000 mg for glyburide/metformin 2.5 mg/500 mg and 5 mg/500 mg respectively. The primary outcome measure was HbA1c level after 16 weeks; secondary end-points included fasting and 2-h post-prandial plasma glucose. Adverse events (AEs) were recorded and summarized by treatment group.

RESULTS

Both strengths of glyburide/metformin equally reduced mean HbA1c by 1.7% more than did glyburide alone (p < 0.001), and by 1.9% more than did metformin alone (p < 0.001). Final mean fasting plasma glucose concentrations were also lower in both glyburide/metformin groups than in the glyburide (-2.8 mmol/l, -51.3 mg/dl; p < 0.001) and metformin groups (-3.6 mmol/l, -64.2 mg/dl; p < 0.001). Safety and tolerability were similar across all treatment groups, except for a higher incidence of gastrointestinal AEs in the metformin monotherapy group, and more patients reporting mild or moderate symptoms of hypoglycaemia while taking glyburide/metformin.

CONCLUSIONS

Both glyburide/metformin tablet strengths produced, with equal efficacy, significantly better glycaemic control than monotherapy with either agent. These data also confirm that glycaemic efficacy does not require maximal sulphonylurea doses in combination with metformin.

Regulation of apoA1 gene expression with acidosis: requirement for a transcriptional repressor

Serum apolipoprotein A(1) (apoA(1)) concentration is inversely correlated with the risk of premature atherosclerosis. Serum apoA(1) concentrations are regulated, in part, at the transcriptional level. ApoA(1) mRNA is synthesized primarily in the liver and small intestine, under the direction of a number of signaling molecules and tissue-specific regulatory elements. Previously, we demonstrated that extracellular acidosis suppresses apoA(1) mRNA levels at the level of transcription. Here we demonstrate that intracellular acidosis, in the absence of extracellular pH changes, represses apoA(1) promoter activity. Repression occurs through a pH responsive element (pH-RE) located within the apoA(1) gene promoter. Acidosis increases the specific DNA binding activity of a putative repressor protein within the immediate 5'-flanking region of the apoA(1) gene. The cis-element that binds the putative repressor protein contains a negative thyroid hormone response element (nTRE) located 3' and adjacent to the apoA(1) TATA box. Mutation of the nTRE/pH-RE abrogates protein binding and alters the activity of reporter genes controlled by this element. Repression by acidosis did not require de novo mRNA and protein synthesis. Inhibition of tyrosine kinase activity and diacylglycerol-stimulated protein kinase C (PKC) signaling pathways with tyrophostin A47 and phorbol myristate acetate, respectively, did not affect the repression of apoA(1) promoter activity with acidosis. These results suggest that transcriptional repression of the apoA(1) gene by alterations in ambient pH is associated with enhanced DNA binding activity of a repressor protein, through a mechanism which appears to be independent of de novo mRNA and protein synthesis, tyrosine kinase activity, or PKC activation.

Malondialdehyde modification of proteins in vitro is enhanced in the presence of acetaldehyde

To test the hypothesis that the cardioprotective effect of alcohol is related to the inhibition of malondialdehyde (MDA) modification of proteins by acetaldehyde (AA), we studied the effect of AA on MDA modification of bovine serum albumin (BSA) in vitro. BSA was incubated simultaneously with a fixed concentration of MDA (70 mM) and different concentrations of AA (120, 60, 30, 10, or 0 mM) for 24 h at 37 degrees C. The MDA-modified or AA-modified BSA was quantitated with immunoblotting by using specific anti-MDA and specific anti-AA protein antisera, respectively. In another set of experiments, BSA was incubated sequentially, first with different concentrations of AA and then with 70 mM of MDA. In both incubation protocols, the presence of AA and AA modification of BSA enhanced MDA binding. These in vitro observations suggest that the putative cardioprotective effects of alcohol or wine cannot be ascribed to AA-mediated reduction in MDA protein formation, a possible biochemical pathway of accelerated atherosclerosis.

Role of repeated fine-needle aspiration of thyroid nodules with benign cytologic features

OBJECTIVE

To determine the role of repeated fine-needle aspiration (FNA) biopsy in the evaluation of thyroid nodules initially classified as benign.

METHODS

We retrospectively reviewed data on 235 patients with clinically palpable thyroid nodules who underwent a repeated FNA biopsy after an initially benign diagnosis. All the nodules were evaluated and biopsies were obtained by the same endocrinologist. Cytodiagnoses were divided into four major categories: inadequate, benign, suspicious, or malignant.

RESULTS

The study cohort consisted of 211 female and 24 male patients with a mean age of 47.1 years. The repeated FNA cytodiagnoses were as follows: 204 (86.8%) remained benign and 19 (8.1%), 11 (4.7%), and 1 (0.4%) became inadequate, suspicious, and malignant, respectively. All patients with benign or inadequate cytologic results on repeated FNA who underwent thyroid surgical resection had benign histologic findings (N = 23). The mean follow-up period between the initial and the last benign FNA cytodiagnosis in the 186 patients without surgical intervention was 1,078 days (2.95 years). Nine of 11 patients with suspicious cytologic results underwent a thyroid surgical procedure, which revealed a benign lesion in 7 and malignant disease in 2 (18%). The other two patients with suspicious cytologic findings had a 13-year clinical follow-up without any clinical evidence of a thyroid malignant lesion. The only patient with malignant cytologic findings on repeated FNA (a 76-year-old woman) refused surgical treatment and was lost to follow-up.

CONCLUSION

Although the yield of finding a malignant lesion on repeated FNA biopsy in the follow-up of a presumably benign thyroid nodule may be low, rebiopsy reduces the rate of false-negative diagnosis from an average of 5.2% to <1.3%.

Obesity: a rational target for managing diabetes mellitus

Obesity is a growing public health problem worldwide. It is a particularly common problem among individuals with type 2 diabetes mellitus. The magnitude of obesity, the central location of fat, and a history of weight gain are independent risks for developing diabetes mellitus. Potential factors implicated in the pathogenesis of diabetes mellitus in obese patients include increased plasma free fatty acid concentrations, increased production of cytokines, increased leptin levels, and increased levels of a recently discovered protein called resistin. Epidemiological and interventional studies suggest that even modest loss of body weight, either by changes in lifestyle or pharmacological means is associated with significant amelioration of insulin resistance and improvement in diabetes mellitus control. Treatment of obesity is an important therapeutic goal in the management of patients with type 2 diabetes mellitus.

Troglitazone stimulates acetyl-CoA carboxylase activity through a post-translational mechanism

Troglitazone, a thiazolidinedione, is known to act as an insulin sensitizer. The various effects of the drug include stimulation of glucose utilization and inhibition of gluconeogenesis and fatty acid oxidation. We studied the effect of troglitazone treatment on rat liver acetyl-CoA carboxylase (ACC), the key enzyme that catalyzes the formation of malonyl-CoA, the rate-limiting step in the synthesis of long chain fatty acids. Treatment of rats with troglitazone for 18 days resulted in more than 200% increase in the activity of hepatic acetyl-CoA carboxylase (1.01+/-0.14 and 2.33+/-0.28 mU/mg supernatant protein for control and troglitazone-treated rats, respectively) (p<0.001). The expression of acetyl-CoA carboxylase mRNA, as studied by RNAse protection assay, was not significantly different between the two groups of animals. The ACC from control and troglitazone-treated groups was purified by avidin-affinity chromatography. The purified enzyme migrated as a major protein band (Mr 262,000) on SDS-polyacrylamide gels. Troglitazone treatment was associated with increased citrate sensitivity of ACC. The specific activity of the purified preparation in troglitazone-treated rats was increased by 67% (2.5 vs. 1.5 U/mg). Quantitation of alkali-labile phosphate content of the purified preparation revealed 5.66+/-0.17 and 6.29+/-0.13 mol Pi/mol subunit of 262 Kda for control and troglitazone-treated rats, respectively (P<0.01). The subtle increase in phosphate content does not explain the observed activation of the enzyme. It is possible that additional mechanisms such as troglitazone related rearrangement of the occupancy of select phosphate binding sites or altered binding of the biotin cofactor may also contribute to the observed activation of ACC.

Induction of the apolipoprotein AI gene by fasting: a relationship with ketosis but not with ketone bodies

Apolipoprotein AI (apoAI) expression is inversely related to the incidence of atherosclerosis. ApoAI expression is also influenced by the nutritional state and diabetes. We used both cell culture and animal models to examine the effect of fasting and ketoacidosis on apoAI gene expression. Two days of food deprivation in rats increased hepatic and intestinal apoAI mRNA by 2.6- and 2.3-fold, respectively (P < .05). The absolute concentration of plasma apoAI did not change. However, the plasma apoAI concentration relative to the plasma concentration of serum proteins was increased 23% (P < .05). In fasting rats, there was a significant positive correlation between the serum beta-hydroxybutyrate concentration and hepatic or intestinal apoAI mRNA level. Despite this correlation, changes in apoAI mRNA are probably not mediated by ketone bodies, since neither hepatic nor intestinal apoAI mRNA levels were altered in rats maintained on a ketogenic diet for 10 days or treated with isobutyramide, an orally active ketone analog. In addition, the activity of the rat apoAI promoter was not altered in Hep G2 cells treated with isobutyramide or fatty acids or exposed to hypoglycemic conditions, while dexamethasone increased promoter activity 1.9-fold (P < .05). These data indicate that metabolic changes other than ketone bodies, such as an increase in plasma glucocorticoids, may account for starvation-induced expression of apoAI.

Age-related changes in rat hepatic acetyl-coenzyme A carboxylase

Acetyl-CoA carboxylase (ACC) catalyzes the rate-limiting step in the synthesis of long-chain fatty acids. Since aging influences adiposity, we studied the activity of ACC and its mRNA content in livers of 4-, 12-, and 24-month-old male Fischer 344 rats. The mean (+/- SEM) activity of ACC (mU/mg protein) in liver homogenates from 4-month-old rats was 1.01 +/- 0.14. There was an 80% increase in activity (1.83 +/- 0.27) in 12-month-old rats (P < 0.01). However, there was significantly less activity (0.46 +/- 0.06) in livers of 24-month-old rats (P < 0.001). The total activity of ACC (per g liver) followed the same trend. The enzyme from all age groups was purified by avidin-affinity chromatography. The purified preparation migrated as a major protein band (M(r) 262,000) on sodium dodecyl sulfate (SDS)-polyacrylamide gels. The specific activity of the purified preparation was 1.5, 1.8, and 1.8 U/mg for 4-, 12-, and 24-month-old rats, respectively. The alkali-labile phosphate content was 5.66 +/- 0.17, 5.64 +/- 0.21, and 6.21 +/- 0.35 mols P(i)/mole subunit for 4-, 12-, and 24-month-old rats, respectively. These age-related differences were not significant. The hepatic ACC mRNA measured by ribonuclease protection assay when corrected for G3PDH mRNA was significantly reduced in 24-month-old rats (0.24 +/- 0.03) compared with 12-month-old (0.58 +/- 0.04) or 4-month-old rats (0.43 +/- 0.007) P < 0.01. In summary: (i) Aging in rats is associated with significant changes in ACC activity; (ii) the purified ACC preparations from the three age groups had similar specific activity and similar phosphate content; and (iii) the changes in ACC mRNA content of the liver paralleled the changes in total enzyme activity when 12-month-old rats were compared with 24-month-old rats whereas the increase in ACC activity in 12-month-old rats compared with 4-month-old rats could not be ascribed to changes in hepatic mRNA levels. These results indicate that the age-related changes in hepatic ACC occur at a post-translational level during early years of aging and at a pretranslational level at late states of senescence. These changes may contribute to the age-related alterations in body adiposity.

Effect of select antioxidants on malondialdehyde modification of proteins

To determine whether commonly used antioxidants alter malondialdehyde (MDA) modification of proteins, a known mechanism of free radical-related tissue injury, we studied the effect of adding 1 mg/mL of pycnogenol, 5 mM of alpha-tocopherol, 5 mM of ascorbate, and 0.2 mg/mL of an ethanol equivalent of red and white wine on MDA-protein content of endothelial cells in culture. The addition of pycnogenol but not of the other antioxidants was associated with significant reduction in MDA-protein content compared with controls (0.521 +/- 0.041 in arbritrary units versus 1.011 +/- 0.021, P < 0. 001). To determine whether the observed effect occurs distal to MDA generation, the effect of these antioxidants on the modification of bovine serum albumin with MDA generated in a cell-free system was studied. In this cell-free assay, pycnogenol but not the other antioxidants reduced MDA-BSA generation by approximately 50%. It is concluded that pycnogenol may reduce MDA modification of proteins at a step distal to MDA generation. This may be an additional mechanism of protective effects of pycnogenol against oxidative stress.

Hyperinsulinemic hypoglycemia associated with possible hypopituitarism in a patient with acquired immunodeficiency syndrome

OBJECTIVE

To describe endocrine dysfunctions associated with human immunodeficiency virus (HIV) infection.

METHODS

We present a case report, discuss the laboratory findings, and suggest potential contributing factors in this complex milieu.

RESULTS

A 44-year-old man infected with HIV was admitted with loss of consciousness after a grand mal seizure and was found to have a prolonged course of hypoglycemia in conjunction with increased serum levels of insulin and C peptide. Iatrogenic hypoglycemia was excluded by laboratory evaluations. Hypothalamic-pituitary dysfunction was suspected because the serum growth hormone and cortisol concentrations during hypoglycemia were low. Radiologic evaluation of the brain revealed no structural abnormalities involving the hypothalamic-pituitary area. A normal cortisol response to adrenocorticotropic hormone stimulation (cosyntropin, 250 mg) was documented on two occasions. The cause of the severe hypoglycemic episode and the possible hypothalamic-pituitary-adrenal axis dysfunction in this patient is unknown.

CONCLUSION

Despite the complexity of endocrine disorders in HIV-infected patients, the course of the disease in this patient underscores the possibility that some of the endocrinologic changes may be reversible.

Age-related changes in plasma leptin binding activity in rats: A comparison of a simple acid-ethanol precipitation technique with column chromatography

A novel assay for measuring the free leptin fraction was developed and validated against a chromatographic technique. The assay used acid-ethanol extraction (AEE) for separation of bound/free leptin moieties. The interassay coefficient of variation was 3.9%. The specificity for leptin binding was confirmed by incubation with 1 microg of unlabeled rat leptin that effectively competed with radiolabeled leptin whereas human growth hormone and interleukin-6 were ineffective in competing with radiolabeled leptin binding. Scatchard analysis of competitive binding experiments with rat plasma demonstrated a linear relationship with a binding affinity of 0.3-0.6 x 109 M-1. This novel assay was used to determine if age-related insensitivity to leptin action is secondary to altered serum leptin binding. Rats at various age groups were studied for changes in body adiposity and serum total and free leptin concentrations. Serum free leptin concentrations (ng/ml mean +/- SEM) were significantly increased in 24-month-old rats (5.56 +/- 0. 21) compared with 18-month-old rats (4.76 +/- 0.17) (P < 0.01) despite similar body weight and adiposity of the two age groups. The increase in plasma free leptin concentrations in 12-month-old rats (3.86 +/- 0.28) and 6-month-old rats (2.05 +/- 0.06) relative to 3-month-old rats (1.37 +/- 0.06) (P < 0.001) was out of proportion to the increase in body adiposity in aging rats. It is concluded that aging in rats is associated with relative insensitivity to leptin. This change cannot be attributed to increased plasma binding or to a reduction in the leptin free fraction.

Effects of ketoacidosis on rat apolipoprotein A1 gene expression: a link with acidosis but not with ketones

To determine if ketoacidosis contributes to reduced apolipoprotein A1 (apoA1) expression in insulin-deficient diabetic rats, we examined the regulation of apoA1 gene expression in response to changes in ambient pH or ketone body concentrations. Hepatic apoAI mRNA levels were reduced 42% in diabetic rats relative to nondiabetic controls (means+/-s.d.; 321.8+/-43.7 vs 438.7+/-58.8 arbitrary units; P<0.03). Neither endogenous apoA1 mRNA nor transcriptional activity of the rat apoA1 gene promoter (from -474 to -7) were altered by sodium butyrate or isobutyramide (0.3 mM to 10 mM) in Hep G2 or Caco-2 cells. Rat hepatic and intestinal apoA1 mRNA levels, and plasma apoA1 concentration, were not altered 24 h after isobutyramide administration (500 mg/kg by gavage). When the effect of altering ambient pH within a wide range commonly encountered in vivo was studied, acidosis (pH 6.7), relative to alkalosis (pH 7.9), decreased apoAI mRNA levels relative to glyceraldehyde-3-phosphate dehydrogenase mRNA by 47% in Hep G2 cells (P<0.025) and by 24% in Caco-2 cells (P<0.017). Acidosis did not alter cytomegalo virus (CMV)-beta-galactosidase activity, or the activity of the simian virus (SV40) early-region promoter, in either cell line transfected with the respective constructs. The lowering of ambient pH was associated with a graded reduction in apoAI promoter activity. At pH 6.7, apoAI promoter activity was reduced by 75% compared with promoter activity at pH 7.9. These observations indicate that acidosis, but not ketosis, contributes to the reduction in apoA1 expression during diabetic ketoacidosis by down-regulating apoAI promoter activity.

Efficacy and safety of sibutramine in obese white and African American patients with hypertension: a 1-year, double-blind, placebo-controlled, multicenter trial

BACKGROUND

Obesity is a highly prevalent medical condition and is commonly accompanied by hypertension. This study assessed the efficacy and safety of treatment with sibutramine hydrochloride for promoting and maintaining weight loss in obese patients with controlled hypertension, including a subset analysis of African American patients.

PATIENTS AND METHODS

Obese patients with a body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters) between 27 and 40 and a history of hypertension controlled with a calcium channel blocker (with or without concomitant thiazide diuretic treatment) were randomized to receive sibutramine (n = 150) or placebo (n = 74) with minimal behavioral intervention for 52 weeks. African Americans constituted 36% of enrolled patients. Efficacy assessments were body weight and related parameters (BMI and waist and hip circumferences), metabolic parameters (serum levels of triglycerides, high-density lipoprotein cholesterol [HDL-C], low-density lipoprotein cholesterol [LDL-C], total cholesterol, glucose, and uric acid), and quality-of-life measures. Safety assessments included recording of blood pressure, pulse rate, adverse events, and reasons for discontinuation.

RESULTS

For patients receiving sibutramine, weight loss occurred during the first 6 months of the trial and was maintained to the end of the 12-month treatment period. Among patients receiving sibutramine, 40.1% lost 5% or more of body weight (5% responders) and 13.4% lost 10% or more of body weight (10% responders) compared with 8.7% and 4.3% of patients in the placebo group, respectively (P<.05). Changes in body weight were similar among African Americans and whites. Sibutramine-induced weight loss was associated with significant improvements in serum levels of triglycerides, HDL-C, glucose, and uric acid. Waist circumference and quality-of-life measures also improved significantly in patients receiving sibutramine. Sibutramine-treated patients had small but statistically significant mean increases in diastolic blood pressure (2.0 mm Hg) and pulse rate (4.9 beats/min) compared with placebo-treated patients (-1.3 mm Hg and 0.0 beats/min; P<.05); these changes were similar among African Americans and whites. Most adverse events were mild to moderate in severity and transient. The most common adverse event resulting in discontinuation among patients receiving sibutramine was hypertension (5.3% of patients receiving sibutramine vs 1.4% of patients receiving placebo).

CONCLUSIONS

In obese patients with controlled hypertension, sibutramine was an effective and well-tolerated treatment for weight loss and maintenance. Sibutramine-induced weight loss resulted in improvements in serum levels of triglycerides, HDL-C, uric acid, and glucose, and in waist circumference and quality-of-life measures. Blood pressure and heart rate increased by a small amount. Efficacy and safety profiles for sibutramine among African American and white obese patients with controlled hypertension were similar.

A rational approach to drug therapy of type 2 diabetes mellitus

Several new pharmacological agents have recently been developed to optimise the management of type 2 (non-insulin-dependent) diabetes mellitus. The aim of this article is to briefly review the various therapeutic agents available for management of patients with type 2 diabetes mellitus and to suggest a potential approach to drug selection. There are three general therapeutic modalities relevant to diabetes care. The first modality is lifestyle adjustments aimed at improving endogenous insulin sensitivity or insulin effect. This can be achieved by increased physical activity and bodyweight reduction with diet and behavioural modification, and the use of pharmacological agents or surgery. This first modality is not discussed in depth in this article. The second modality involves increasing insulin availability by the administration of exogenous insulin, insulin analogues, sulphonylureas and the new insulin secretagogue, repaglinide. The most frequently encountered adverse effect of these agents is hypoglycaemia. Bodyweight gain can also be a concern, especially in patients who are obese. The association between hyperinsulinaemia and premature atherosclerosis is still a debatable question. The third modality consists of agents such as biguanides and thiazolidinediones which enhance insulin sensitivity, or agents that decrease insulin requirements like the alpha-glucosidase inhibitors. Type 2 diabetes mellitus is a heterogeneous disease with multiple underlying pathophysiological processes. Therapy should be individualised based on the degree of hyperglycaemia, hyperinsulinaemia or insulin deficiency. In addition, several factors have to be considered when prescribing a specific therapeutic agent. These factors include efficacy, safety, affordability and ease of administration.

Monosaccharide-enriched diets cause hyperleptinemia without hypophagia

To determine the effect of monosaccharide-enriched diets on plasma leptin and food consumption, body weight, food intake, and serum glucose, insulin, and leptin concentrations were measured in rats maintained on a 10-d course of 60% glucose or 60% fructose diet. The serum leptin concentration in rats fed a high-glucose diet (7.60 +/- 0.6 ng/mL) or a high-fructose diet (5.12 +/- 0.8 ng/mL) was significantly increased compared with that in control rats (2.45 +/- 0.10 ng/mL; P < 0.001). To ascertain that the observed effect was related to hyperinsulinemia, a group of rats were infused with exogenous insulin or rendered insulin resistent with a high-fat diet. When hyperinsulinemia was induced with exogenous infusion, the serum leptin was increased (5.56 +/- 0.23 ng/mL; P < 0.001). High-fat feeding was associated with increased serum leptin (12.1 +/- 1.4 ng/mL) and insulin levels. The increased serum leptin concentration was not associated with decreased food intake. We conclude that monosaccharide-enriched diets, probably through hyperinsulinemia or relative or absolute insulin resistance, cause hyperleptinemia, which does not appear to change feeding behavior.

Serum leptin response to endogenous hyperinsulinemia in aging rats

To determine if aging is associated with altered serum leptin response to diet-induced changes in endogenous hyperinsulinemia, male Fisher 344 (F344) rats at different age groups were studied while on regular rat chow and following 10 days of experimental diets consisting of 60% of the weight as fructose or glucose. The serum leptin concentration (ng/ml) gradually increased from basal levels of 2.5+/-0.1 at age of 4 months to 3.7+/-0.1, 6.9+/-0.9, 9. 4+/-0.3 and 8.9+/-1.1 at 6, 12, 18 and 24 months of age, respectively (P<0.001). Hyperinsulinemia associated with 60% fructose diet was associated with increased serum leptin levels in 4, 12, and 24 month old rats to 5.1+/-0.8, 6.7+/-1.2, and 8.6+/-1.1, respectively (P<0.001). Feeding 60% glucose diet also was associated with increased serum leptin levels in 4, 12 and 24 month old rats to 7.6+/-0.6, 7.2+/-0.7, and 9.1+/-1.1, respectively (P<0.001). Restricting dietary intake to 60% of the calories consumed by control rats for 10 days resulted in a decrease in serum leptin to 1.0+/-0.02 in 4 month old rats and 2.5+/-0.4 in 24 month old rats (P<0.01). It is concluded that aging in F344 rats is associated with increased serum leptin concentrations. However, diet-related hyperinsulinemic effect on leptin is blunted in aging rats although leptin response to caloric restriction is maintained. The inability of aging rats to mount hyperleptinemic response to dietary changes may contribute to the age-related increase in adiposity.

Effect of amitriptyline on the messenger RNA of thyroid hormone-responsive genes in rat cerebral tissue

To determine the molecular mechanisms of the potentiating effect of thyroid hormones (TH) on the therapeutic efficacy of tricyclic antidepressants (TCA), the expression of two known TH-responsive mRNAs was measured in control rats and rats treated with triiodothyronine (T3, 10 microg/100 g for 10 days), amitriptyline (10 mg/kg for 10 days), or combined T3 and amitriptyline. Northern blot analysis was carried out to measure the cerebral tissue content of a novel translational repressor (NAT-1) and another thyroid hormone-responsive (THR) mRNA. Rats treated with the combination of T3 and amitriptyline had significantly higher NAT-1 expression (2691.1+/-134.1 arbitrary units) than rats treated with T3 only (1688.5+/-77.8) or with amitriptyline only (1452.5+/-87.5) or the untreated control rats (731.3+/-23.0), P<0.01. Amitriptyline treatment did not alter the expression of THR mRNA or THR protein in either control or T3-treated rats. It is concluded that alterations in the expression of selective T3 responsive genes in cerebral tissue could be a mechanism of the known T3 potentiation of the therapeutic efficacy of TCA.

Dose-response profile of acarbose in older subjects with type 2 diabetes

OBJECTIVE

To examine the dose-response relationship of acarbose, an alpha-glucosidase inhibitor, in older subjects with type 2 diabetes.

RESEARCH DESIGN

Fourteen subjects with type 2 diabetes who were over 65 years old were studied. Five subjects had been treated with diet alone and 9 were receiving a sulfonylurea. The subjects underwent a meal tolerance test in the presence of varying doses of acarbose (0, 25, 50, and 100 mg) on 4 occasions, each 1 week apart. The test meal was chosen to include food items commonly consumed during breakfast in the United States. The 483-kcal meal consisted of 51% of calories in the form of carbohydrates, 14% protein, and 35% fat. The serum glucose, insulin, and triglyceride levels were measured at 0, 1, and 2 hours after the meal.

RESULTS

The postprandial hyperglycemic response to the test meal was significantly reduced with 25 mg of acarbose compared with baseline values. Increasing doses of acarbose to 50 or 100 mg had no significant additional ameliorating effects on postprandial hyperglycemia. Postprandial insulin or triglyceride levels were not significantly altered with single dose acarbose treatment.

CONCLUSIONS

It is concluded that the acute efficacy of acarbose is near maximal at 25 mg when the meal size does not exceed 483 kcal and contains only 61 gm of carbohydrates.

Implications of the UK prospective diabetes study: questions answered and issues remaining

The UK Prospective Diabetes Study (UKPDS) provides the first conclusive proof for the importance of intensifying diabetes control in individuals with type 2 diabetes mellitus. However, reduction in cardiovascular disease risk with intensive therapy was modest and did not reach statistical significance. Metformin therapy in obese individuals with type 2 diabetes mellitus was associated with reduced cardiovascular death. These observations should be re-evaluated to determine whether various therapeutic agents available for treatment of type 2 diabetes mellitus have different effects on cardiovascular complications of diabetes. The addition of alpha-glucosidase inhibitor, acarbose, improved glycaemic control irrespective of concomitant therapy for diabetes, although compliance with this agent was poor. The tight blood pressure control study embedded in UKPDS reaffirms the importance of lowering the blood pressure below 150/85 to reduce microvascular and macrovascular complications of diabetes.

Design and baseline characteristics for the aminoguanidine Clinical Trial in Overt Type 2 Diabetic Nephropathy (ACTION II)

Advanced glycosylation endproduct (AGE) formation has been implicated in the development and progression of nephropathy in type 2 diabetes mellitus. In diabetic animals, aminoguanidine inhibits AGE-mediated cross-linking of proteins in vascular and renal tissue and slows the progression of renal disease. ACTION II is a randomized, double-blind, placebo-controlled trial comparing two dose levels of aminoguanidine with placebo on the progression of nephropathy in 599 type 2 diabetic patients with renal disease from 84 centers in the United States and Canada. The primary endpoint is time to doubling of serum creatinine concentration. Secondary endpoints include the effect of aminoguanidine on time to all-cause mortality, end-stage renal disease (ESRD), cardiovascular morbidity and mortality, rate of change in indices of renal function (iothalamate, Cockcroft and Gault [C&G] calculated creatinine and measured creatinine clearances), proteinuria, retinopathy, circulating and urinary AGE levels, and estimation of the relationship between plasma aminoguanidine concentrations and primary and secondary efficacy endpoints and adverse events. Progression of macrovascular disease was monitored and fundus photography performed. Type 2 diabetic patients aged 30 to 70 years were eligible for the trial if their blood pressure was < or =180 mm Hg systolic and < or =120 mm Hg diastolic, serum creatinine concentration > or =1.0 mg/dL (in women) or > or =1.2 mg/dL (in men), C&G clearance > or =40 mL/min, and proteinuria > or =500 mg/d with diabetic retinopathy or diabetic nephropathy on renal biopsy. Recruitment began in July 1995 and terminated in December 1996. The trial randomized a total of 599 subjects. At baseline, the mean (standard deviation [SD]) age was 58 (7.7) years, diabetes duration 16.5 (7.5) years, body mass index 32 kg/m2 (10-90% range 2642), arterial blood pressure 105 (12) mm Hg, C-peptide concentration 2.55 (1.71) ng/mL, serum glucose concentration 201 (89) mg/dL, hemoglobin A1c 8.7% (1.6), serum creatinine concentration 1.6 (0.5) mg/dL, iothalamate clearance 52 (25) mL/min/1.73 m2, proteinuria 4.1 (4.2) g/d, triglycerides 259 (214) mg/dL, and LDL cholesterol 144 (40) mg/dL. Patients are 72% male, 68% white, 16% black, and 16% Asian American and Native American. At baseline, 76% were receiving concomitant angiotensin-converting enzyme (ACE) inhibitors and 43% lipid-lowering agents. Follow-up in ACTION II was scheduled to continue through December 1998, so that follow-up was to be 2 years after the date of randomization of the final enrolled patient. The trial in fact ended in March 1998. This trial will contribute to our understanding of the natural history of type 2 diabetes mellitus-associated nephropathy and determine whether aminoguanidine will slow the progression of established diabetic renal disease.

Age-related changes in the thyroid hormone effects on malondialdehyde-modified proteins in the rat heart

To determine the age-related changes in thyroid hormone (TH) effects on malondialdehyde (MDA)-modified proteins in cardiac tissue, rats at 4, 12, and 25 months of age were studied. Hyperthyroidism was induced with daily injection of L-triiodothyronine (15 microg/100 g) intraperitoneally for 10 days. Hypothyroidism was induced with 0. 025% methimazole in the drinking water for 4 weeks. MDA proteins were measured with immunoblots using a specific anti-MDA antiserum. MDA was measured as thiobarbituric acid reactive substance. Hypothyroidism in 4-month-old rats was associated with significant reduction in MDA proteins compared to euthyroid rats (13.4 +/- 5.9% vs. 99.8 +/- 10.4% of controls P < 0.001). Hyperthyroidism did not result in a significant change of MDA proteins. In aged rats, neither hypothyroidism nor hyperthyroidism was associated with significant changes in cardiac MDA proteins. The changes in MDA proteins did not correlate with cardiac MDA concentrations. In young rats, the MDA concentrations (nmol/mg) were significantly reduced in hypothyroidism (2.71 +/- 0.21) and were increased in hyperthyroidism (8.19 +/- 0.78) compared to euthyroid values (5.06 +/- 0.71) P < 0. 01. In aged rats, cardiac MDA content was significantly increased during both hyperthyroidism and hypothyroidism. We conclude that alterations in MDA protein content is yet another potential biochemical effect of TH in cardiac tissue. This particular effect is significantly blunted with age.

Age-related changes in thyroid hormone effects on glucose transporter isoforms of rat heart

To determine the age-related changes in thyroid hormone (TH) effects on cardiac glucose transporter one (GLUT-1) and four (GLUT-4) isoforms, male Fischer 344 rats at 4, 12, and 25 months of age were studied at euthyroid, hyperthyroid and hypothyroid conditions. Hyperthyroidism was induced with daily intraperitoneal injections of triiodothyronine (15 microg/100 gm) for 10 days. Hypothyroidism was achieved with 0.025% methimazole in the drinking water for 4 weeks. Immunoblot analysis indicated that at euthyroid basal conditions GLUT-1 protein was not significantly altered with age while GLUT-4 protein was significantly reduced in 25 month old rats (82.0 +/- 28.8% of a 4 month old rat p <0.01). In 4 months old rats, GLUT-1 was increased in both hypothyroidism (432.5 +/- 208.7% of age-matched euthyroid control) and to a lesser extent in hyperthyroidism (242.0 +/- 93.3% of control) p<0.01. In 25 month old rats, hyperthyroidism was also associated with increased GLUT-1 mass (190.8 +/- 117.6% of age-matched euthyroid control) p<0.01. Hypothyroidism in this age group was not associated with significant change in GLUT-1 protein. The cardiac GLUT-4 protein was increased during both hypothyroidism and hyperthyroidism. The changes of GLUT-4 in aged rats were similar to those found in young rats. It is concluded that TH effect on GLUT-1 expression in the heart is altered with age while TH effects on GLUT-4 are age independent.

Malondialdehyde binding of rat cerebral proteins is reduced in experimental hypothyroidism

To determine the effect of thyroid hormones (TH) on cerebral tissue malondialdehyde (MDA) content and accumulation of MDA-bound proteins, hyperthyroid rats and hypothyroid rats were compared to euthyroid controls. Hyperthyroidism was induced by daily injection of l-3,5, 3'-triiodothyronine (15 ug (100 g)-1) intraperitoneally daily for 10 days. Hypothyroidism was induced with 0.025% methimazole in the drinking water for 4 weeks. Immunoblot analysis of cerebral and plasma proteins was carried out using a specific anti-MDA-protein antiserum. MDA was measured as thiobarbituric acid reactive substance. Hypothyroidism was associated with significant reduction in MDA-proteins of plasma (59.3+/-9.5% vs. 99.8+/-23.0% of control p<0.05) and cerebral tissue (17.6+/-19.9% vs. 100.2+/-29.0% of control p<0.001). Hyperthyroidism did not significantly alter MDA-protein distribution. These changes did not correlate with cerebral tissue or plasma MDA concentration. It is concluded that hypothyroidism in rats is associated with significant decrease in MDA-bound proteins. This may have some clinical and biological implications.

The age-related changes in lipogenic enzymes: the role of dietary factors and thyroid hormone responsiveness

To determine whether resistance to insulin or to thyroid hormones rather than an inherent defect in enzyme activity expression account for the age-related changes in lipogenic enzymes, the activities of malic enzymes (ME), fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G-6PD) and 6-phosphogluconate dehydrogenase (6-PGD) were assayed in hepatic, retroperitoneal fat and epididymal fat cytosol of male Fischer 344 rats at 3.5, 12 and 25 months of age. The rats were maintained on either regular rat chow with 62% of calories as complex carbohydrates or were given either high glucose or fructose diet with 65.7% of calories provided by glucose or fructose respectively. Additional groups of young and aged rats were treated with L-triiodothyronine (T3) (15 microg/100 g body weight) for 10 days. Treatment with T3 resulted in higher levels of hepatic ME activity regardless of the diet consumed or the age of the rats. T3 had no consistent effect on FAS, G-6PD or 6-PGD activities. ME response to T3 in young rats was significantly greater than that found in aged rats regardless of diet. The age-related decrease in basal hepatic ME activity was not apparent in rats maintained on the high glucose or the high fructose diets, yet the T3 responsiveness of ME in rats maintained on these diets was not normalized. In adipose tissue, with the exception of the age-related changes in basal activity of the lipogenic enzymes, neither T3 nor the feeding of the test diets had any consistent effects. Since insulin resistance induced by high fructose feeding did not reduce hepatic lipogenic enzymes, it is unlikely that the age-related increase in insulin resistance explains the reduced lipogenic enzyme activity in aged rats. However, resistance to thyroid hormone action found in aged rats may partly account for the reduced hepatic lipogenic enzyme activity.

Glucotoxicity: potential mechanisms

Plasma concentration of glucose is found within a relatively narrow range of values for most animal species, yet it has little correlation with maximum lifespan; however, hyperglycemia in most animals is associated with premature death. This article presents evidence for hyperglycemia-induced tissue toxicity and discusses potential mechanisms of glucotoxicity and implications for the aging organism.

Drug therapy of postprandial hyperglycaemia

It is widely accepted that the most challenging goal in the management of patients with diabetes mellitus is to achieve blood glucose levels as close to normal as possible. In general, normalising postprandial blood glucose levels is more difficult than normalising fasting hyperglycaemia. In addition, some epidemiological studies suggest that postprandial hyperglycaemia (PPHG) or hyperinsulinaemia are independent risk factors for the development of macrovascular complications of diabetes mellitus. Recently, several drugs with differing pharmacodynamic profiles have been developed which target PPHG. These include insulin lispro, amylin analogues, alpha-glucosidase inhibitors and meglitinide analogues. Insulin lispro has a more rapid onset of action and shorter duration of efficacy compared with regular human insulin. In clinical trials, the use of insulin lispro was associated with improved control of PPHG and a reduced incidence of hypoglycaemic episodes. Repaglinide, a meglitinide analogue, is a short-acting insulinotropic agent which. when given before meals, stimulates endogenous insulin secretions and lowers postprandial hyperglycaemic excursions. Both insulin lispro and repaglinide are associated with postprandial hyperinsulinaemia. In contrast, amylin analogues reduce PPHG by slowing gastric emptying and delivery of nutrients to the absorbing surface of the gut. Alpha-Glucosidase inhibitors such as acarbose, miglitol and voglibose also reduce PPHG primarily by interfering with the carbohydrate-digesting enzymes and delaying glucose absorption. With the availability of agents which preferentially reduce postprandial blood glucose excursions, it is now possible to achieve glycaemic goals in a larger proportion of individuals with diabetes mellitus.

Novel translational repressor (NAT-1) expression is modified by thyroid state and age in brain and liver

The technique of reverse transcriptase-polymerase chain reaction differential display was used to identify thyroid hormone (TH) responsive mRNAs in the adult rat cerebral tissue. A partial cDNA (0.76 kb) was cloned and sequenced. Comparison of the sequence to the GenBank data base showed almost 100% homology to mouse translational repressor (NAT-1) mRNA 3'-end. In a northern blot analysis this cDNA hybridized with a mRNA whose expression in hyperthyroid rat cerebral tissue was approximately 6-fold higher than in euthyroid rats. The time course studies showed a rapid induction of this mRNA within 3 h following thyroxine administration. This mRNA is widely expressed in various tissues, and in hepatic tissue it is also TH responsive. To determine if TH responsiveness of this mRNA persists during aging, 25-month-old aged rats were studied and the results were compared with those of 4-month-old rats. Unlike young mature rats, the TH responsiveness of NAT-1 mRNA in both the cerebral and hepatic tissue of aged rats was blunted. It is concluded that cerebral tissue in aging rats beyond the developmental stages, like the hepatic tissue, is associated with altered TH responsiveness.

Effects of glucose and insulin on rat apolipoprotein A-I gene expression

We have examined the regulation of apolipoprotein A-I (apoA-I) gene expression in response to glucose and insulin. In Hep G2 cells, endogenous apoA-I mRNA was suppressed by one-half or induced 2-fold following 48 h of exposure to high concentrations of glucose (22.4 mM) or insulin (100 microunits/ml), respectively, compared with control. Transcriptional activity of the rat apoA-I promoter (-474 to -7) in Hep G2 cells paralleled endogenous mRNA expression, and this activity was dependent on the dose of glucose or insulin. Deletional analysis showed that a 50-base pair fragment spanning -425 to -376 of the promoter mediated the effects of both insulin and glucose. Within this DNA fragment there is a motif (-411 to -404) that is homologous to a previously identified insulin response core element (IRCE). Mutation of this motif abolished not only the induction of the promoter by insulin but also abrogated its suppression by glucose. Electrophoretic mobility shift assay analysis of nuclear extracts from Hep G2 cells revealed IRCE binding activity that formed a duplex with radiolabeled probe. The IRCE binding activity correlated with insulin induction of apoA-I expression. In summary, our data show that glucose decreases and insulin increases apoA-I promoter activity. This effect appears to be mediated by a single cis-acting element.

Age-related changes in thyroid hormone responsive protein (THRP) expression in cerebral tissue of rats

To determine if aging in rats is associated with insensitivity of cerebral tissue to thyroid hormones (TH), the expression of a TH responsive protein or (THRP) in cerebral tissue was studied in male Fischer rats at 4, 12 and 24 months of age during euthyroid, hypothyroid and hyperthyroid states. The basal levels of THRP mRNA was significantly increased in 24-month-old and in 12-month-old rats while THRP mass measured by Western blots was decreased compared to 4-month-old rats. Compared to euthyroid rats, hyperthyroidism in 4-month-old rats was associated with 5.1-fold increase in THRP mRNA and 3.7-fold increase in protein content while in hyperthyroid aged rats, the increase of THRP mRNA was only 1.6-fold and the increase in the protein was 2.4-fold. Hypothyroidism did not significantly alter THRP or its mRNA in either young or aged rats. It is concluded that aging in rats is associated with reduced cerebral tissue responsiveness to thyroid hormones.

Chronic treatment of African-American type 2 diabetic patients with alpha-glucosidase inhibition

OBJECTIVE

To evaluate the long-term efficacy, safety, and tolerability of the alpha-glucosidase inhibitor miglitol in the treatment of African-American patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 345 African-American type 2 diabetic patients (mean age 55.6 years, BMI 31.9 kg/m2, duration of diabetes 4.9 years, baseline HbA1C 8.7%) treated with either diet alone or sulfonylurea were randomized to 1 year of double-blind treatment with either placebo (n = 117) or miglitol (n = 228) at doses of 50 or 100 mg t.i.d., titrated based on tolerability. The primary efficacy criterion was change from baseline in HbA1C at the 6-month visit. Secondarily efficacy parameters included changes from baseline in plasma glucose and serum insulin (both fasting and 120 min after a standardized test meal), fasting lipids, and urinary albumin-to-creatinine ratio. Safety and tolerability evaluations were primarily based on reporting of adverse events and symptoms and on periodic laboratory analyses.

RESULTS

Miglitol treatment was associated with a mean placebo-subtracted reduction in HbA1C from baseline of 1.19% at 6 months. Fasting and 120-min postprandial plasma glucose levels were reduced in parallel to HbA1C, in association with miglitol treatment. Significant reductions versus placebo in 120-min postprandial insulin levels, in LDL cholesterol, and in fasting triglycerides, were also seen in the miglitol group at individual study time points. Softer, more frequent stools and flatulence were significantly more common in the miglitol group. Urinary tract infections, hematuria, and herpes simplex infections were significantly more common in the placebo group.

CONCLUSIONS

Miglitol treatment appears to be at least as efficacious in the African-American type 2 population as in the U.S. type 2 population at large, with comparable tolerability. alpha-Glucosidase treatment may be an important therapeutic option in these patients in view of their greater risk for microvascular complications and the accumulating body of evidence that better glucose control reduces the risk of these complications.

The effect of metabolic acidosis and alkalosis on the H+-ATPase of rat cerebral microvessels

To determine the role of the proton translocating adenosine triphosphatase (H+-ATPase) of the blood-brain barrier, the density of the 31 Kd subunit of the vacuolar type H+-ATPase was quantitated in isolated rat cerebral microvessels with immunoblotting techniques. To establish the tissue specificity of the findings, synaptosomal membranes were also studied. Metabolic acidosis was induced with 1.5% ammonium chloride in drinking water for five days. Metabolic alkalosis was induced with 2.35% NaHCO3 in drinking water and daily injections of 10 mg/Kg furosemide intraperitoneally for 5 days. The quantity of the 31 Kd subunit (in arbitrary units) in cerebral microvessels was significantly increased in acidosis (3.98 +/- 0.45) (p<0.05) and was significantly decreased in metabolic alkalosis (0.49 +/- 0.16) (p<0.00) compared to controls (1.77 +/- 0.73). In synaptosomal membranes, metabolic alkalosis was associated with significant decrease in the quantity of the 31 Kd subunit-H+-ATPase (0.62 +/- 0.12 vs 0.92 +/- 0.01) p<0.05. The increase in the 31 Kd subunit in synaptosomal membranes with acidosis did not reach statistical significance. It is concluded that the quantity of vacuolar H+-ATPase in the blood-brain barrier is modulated by blood H+ or HCO3- content. These changes may be relevant to the physiology of the acid-base balance in the central nervous system.

Testosterone pharmacokinetics after application of an investigational transdermal system in hypogonadal men

This open-label, randomized, placebo lead-in, three-treatment crossover study in 19 hypogonadal men (27-82 years of age) evaluated dose proportionality of serum testosterone concentrations with application of one or two investigational transdermal testosterone systems for application to the arm or torso. Testosterone in vivo kinetics profiles were determined using DeMonS, a recently developed numerical deconvolution method that estimates drug absorption at different time intervals and/or drug disposition model parameters. After application of the investigational transdermal systems, the mean serum testosterone, dihydrotestosterone, estradiol, and free testosterone concentrations were elevated to normal levels. Treatment allowed approximation of the normal circadian pattern of endogenous testosterone secretion, and the increase in serum testosterone concentrations was proportional to the surface area of systems applied. The investigational transdermal system provided effective testosterone replacement therapy as judged by pharmacokinetic parameters.

Age-related changes in glucose transporter-one mRNA structure and function

To determine the molecular mechanisms of age-related changes in the expression of glucose transporter 1 (GLUT-1) mRNA in cerebral tissue, male Fischer 344 rats at 4, 12, and 24 months of age were studied. The GLUT-1 mRNA in cerebral tissue was not significantly different among the various age groups. The in vitro translatability of GLUT-1 mRNA of 24-month-old rats (0.867 +/- 0.066 arbitrary units) was significantly lower than that in 4-month-old (1.403 +/- 0.153) P < 0.01 or 12-month-old rats (1.387 +/- 0.122) P < 0.01. The poly (A) tail length of GLUT-1 mRNA decreased from 200-350 nt in 4-month-old rats to only 50-100 nt in 24-month-old rats. Twelve-month-old rats also showed reduced poly (A) tail lengths. The poly (A) tail of G3PDH mRNA was not altered with age. The changes in GLUT-1 mRNA translatability did not correlate with GLUT-1 content in total cerebral tissue homogenate or in isolated cerebral microvessels, suggesting that GLUT-1 protein turnover is altered with age. It is concluded that aging is associated with significant changes in the structure and function of GLUT-1 mRNA.

Vitamin supplementation therapy in the elderly

Vitamin supplementation in large dosages is increasingly common in the older population. Often, such supplementation is used in an attempt to improve an individual's health status. There have been claims that the effects of vitamins halt the normal aging process or prevent and cure disease. However, several recent studies have failed to demonstrate the efficacy of vitamin supplementation in preventing several types of cancer. In moderate dosages, supplementation with vitamin E (tocopherols) shows promise as a lipid antioxidant, and may reduce the risk of coronary heart disease. However, before vitamin E becomes an accepted medical therapy, further long term studies must be undertaken to examine the safety and efficacy of such therapy. An adequate intake of vitamins should be ensured by adherence to a well balanced diet. However, the elderly are prone to circumstances that may prevent them from eating a balanced diet. In addition, there are several age-related medical conditions that may predispose individuals to dietary and vitamin deficiencies. To prevent vitamin deficiency diseases and their associated morbidity, modest vitamin supplementation may be necessary. However, supplementation should be reserved for individuals with documented deficiency or who are at risk of developing such deficiencies, especially those who are homebound or institutionalised. Vitamins taken in large dosages should be considered as drugs. These medicines, which are obtainable over-the-counter, should be carefully regulated to prevent toxicity.

Pathophysiology of central nervous system complications in diabetes mellitus

It is now generally accepted that diabetes can alter central nervous system (CNS) function. Even in the absence of overt cerebrovascular accidents or repeated hypoglycemic reactions, uncontrolled hyperglycemia is associated with cognitive changes. These changes are documented both in patients with diabetes as well as in animal models of experimental diabetes. The cognitive impairment can be ameliorated with optimization of blood glucose control. The potential causes of CNS dysfunction in diabetes can be broadly categorized as either vascular causes including changes in the blood-brain barrier and metabolic changes. The latter causes include repeated hypoglycemic episodes, hyperglycemia, hyperosmolality, acidosis, ketosis, neuroendocrine or neurochemical changes. The other contributory causes of CNS dysfunction in diabetes include the presence of hypertension, uremia, peripheral and autonomic neuropathy and multiple drug use.

Cloning and characterization of a complementary DNA for a thyroid hormone-responsive protein in mature rat cerebral tissue

A gene responsive to thyroid hormone (TH) has been identified in the adult rat brain cerebral tissue. A cDNA probe differentially expressed in euthyroid, hypothyroid and hyperthyroid rat cerebral tissue, generated by reverse transcriptase-PCR differential display of mRNA, was used to screen the rat brain cDNA library. A 3.4 kb positive clone hybridized in Northern blots with a 3.8 kb mRNA that proved to be TH responsive (THR). The remaining coding sequence and a part of the 5' untranslated region of this cDNA were obtained by 5' rapid amplification of cDNA ends. The deduced amino acid sequence revealed that THR protein (THRP), a 68 kDa moiety, has 83% sequence similarity with c-Abl interactor protein (Abi-2), which is a substrate for tyrosine kinase activity of c-Abl. The extensive similarity between the two proteins suggests a potential role for THRP as a substrate for c-Abl. Northern analysis showed that the expression of THR mRNA in hyperthyroid rats is 6-fold that in euthyroid rats. There is also a 4-6-fold increase in the concentration of THRP, as analysed by Western analysis. Owing to the extensive similarity between rat THRP and human Abi-2, a polyclonal anti- (human Abi-2) antibody was successfully used for Western analysis of proteins from the rat tissues. The observed increase in both the mRNA and the protein did not decline after beta-adrenergic system blockade with propranolol, suggesting that the action of TH on the expression of this gene is not mediated through the beta-adrenergic system. Immunohistochemical studies revealed that neuronal cells were particularly rich in THRP. Both THR mRNA and THRP are rapidly induced in vivo after intravenous administration of thyroxine. Tissue distribution studies indicated that the cerebral tissue was particularly enriched with THR mRNA and 68 kDa THRP. A cDNA clone for a THR gene could provide a useful tool to study the molecular mechanisms of TH effects on cerebral tissue in adult animals.

Apolipoprotein A1 expression in young and aged rats is modulated by dietary carbohydrates

To determine if dietary carbohydrates modulate apolipoprotein A1 (ApoA1) expression, plasma ApoA1 protein and hepatic ApoA1 mRNA levels were measured in young and aged rats maintained on a high-fructose (60% of diet weight consisting of fructose), or high-glucose (60% glucose) diet or fed regular rat chow for 10 days. Aged rats on regular chow had significantly higher plasma ApoA1 concentrations and hepatic ApoA1 mRNA than young rats maintained on this diet. Plasma ApoA1 and hepatic ApoA1 mRNA levels in young rats or aged rats maintained on the 60% fructose diet were significantly higher than in rats within the same age group maintained on regular rat chow (P < .01). Similar induction of ApoA1 protein and mRNA was found in rats maintained on the 60% glucose diet (P < .01). It is concluded that ApoA1 expression in rats is modulated by factors related to the nature of dietary carbohydrates rather than insulin resistance associated with high-fructose feeding.

GLUT-1 expression in the cerebra of patients with Alzheimer's disease

To investigate the molecular basis of reduced GLUT-1 concentration of the blood-brain barrier in patients with Alzheimer's disease (AD), the GLUT-1 mass, mRNA content, and structure were studied in eight patients with AD and seven age-matched controls. The results indicate that the 55-kDa GLUT-1 is significantly reduced in AD without a significant change in GLUT-1 mRNA concentrations. Because in some animal models changes in GLUT-1 expression is associated with changes in GLUT-1 mRNA structure, the length of the poly(A) tail of the GLUT-1 mRNA was estimated with a reverse transcription-polymerase chain reaction technique. The length of poly(A) tail of GLUT-1 mRNA in AD subjects was not significantly different from the controls. It is concluded that the AD-related change in GLUT-1 expression is not the result of altered poly(A) length of GLUT-1 mRNA.

Age-related changes in the blood-brain barrier

Aging of the cerebral microcirculation results in significant alteration in the blood-brain barrier (BBB). The barrier function appears to remain intact in older animals, although it may be more susceptible to disruption by external factors (hypertension) and drugs (haloperidol). While overall transport processes do not change with age, aging animals and humans have altered BBB function of select carrier mediated transport systems including the transport of choline, glucose, butyrate and triiodothyronine. These age-related changes are the result of either alteration in the carrier molecules or the physiochemical properties of the cerebral microvessels. At the present time, it is not known whether changes in the BBB contribute to the age-related neurodegenerative diseases or are merely epiphenomena of aging.

Shortening of poly (A) tail of glucose transporter--one mRNA in experimental diabetes mellitus

To determine the molecular mechanisms of diabetes-related changes in the expression of GLUT-1 in cerebral tissue, streptozotocin-induced diabetic rats and vehicle injected controls were studied after 4 weeks of diabetes. The GLUT-1 mass in cerebral microvessels was reduced in diabetic rats by approximately 38% (P < 0.01). The GLUT-1 concentration in insulin-treated diabetic group was not significantly different from controls. The GLUT-1 mRNA content of cerebral tissue in diabetic rats (0.064 +/- 0.007) was significantly reduced compared to control rats (0.122 +/- 0.011) or insulin-treated diabetic rats (0.122 +/- 0.015) P < 0.01. The in vitro translation of GLUT-1 mRNA of diabetic rats (0.793 +/- 0.047 arbitrary units) was also significantly lower than that in control rats (1.403 +/- 0.153) P < 0.01 or insulin-treated diabetic rats. (1.124 +/- 0.083) P < 0.01. These changes occurred in asssociation with a reduction in poly (A) tail length of GLUT-1 mRNA which decreased from a control value of 200-350 nt to only 50-100 nt in diabetic rats. Shortening of poly (A) tail of mRNAs is a novel mechanism of diabetes-related changes in the expression of specific genes which are regulated at a translational level.

Central nervous system complications of diabetes mellitus--a perspective from the blood-brain barrier

A host of diabetes-related changes in the central nervous system (CNS) has been recognized. The underlying causes of these changes are multiple. An important contributor to the changes in the CNS is the blood-brain barrier (BBB). Diabetes is associated with changes in both the barrier and transport functions of the cerebral microvessels. Structural changes in cerebral microvessels may account for some of the observed changes. Additional mechanisms include alterations in hemodynamic variables such as arteriovenous shunting, changes in biophysical properties and biochemical compositions of the endothelial cells including changes in lipid fluidity and composition, and alterations of neurotransmitter activity in the cerebral microvessels, notably altered beta adrenergic neurotransmission. These observations indicate that the CNS is not immune against the microangiopathic complications commonly found in various tissues of diabetic animals.

Thyroid hormone-induced GLUT-1 expression in rat cerebral tissue: effect of age

To determine if thyroid hormone (TH) modulates the expression of cerebral glucose transporter one (GLUT-1) and whether there are age-related differences in TH effect, young male Fischer 344 rats (6 months old) and aged rats (26 months old) were studied at euthyroid, hyperthyroid and hypothyroid conditions. Immunoblot analysis indicated that 55 kDa GLUT-1 mass was decreased in hypothyroid young rats (174 +/- 15 arbitrary units) and hyperthyroid rats (144 +/- 22) compared to euthyroid young rats (395 +/- 57) P < 0.01. Jr. aged rats the 55 kDa GLUT-1 mass was significantly increased in hyperthyroidism (392 +/- 49) compared to euthyroid aged rats (237 +/- 27) P < 0.05. The 45 kDa isoform of GLUT-1 in rat cerebral tissue did not significantly change with age or thyroidal state. The changes in 55 kDa GLUT-1 mass did not correlate with the changes of GLUT-1 mRNA content. It is concluded that alterations in cerebral GLUT-1 content in response to altered thyroid state are age-specific.

Age-related changes in the responsiveness of apolipoprotein A1 to thyroid hormone

To determine the age-related changes in the effect of thyroid hormone on apolipoprotein A1 (ApoA1) gene expression, male Fischer 344 rats at 4 (young) and 26 (aged) mo of age were studied. Hyperthyroidism was induced with daily intraperitoneal injections of 3,5,3'-triiodothyronine (15 micrograms/100 g body wt) for 10 days. Hypothyroidism was induced with 0.025% methimazole in drinking water for 4 wk. Hyperthyroidism was associated with increased serum ApoA1 levels in young rats [7.52 +/- 0.41 vs. 3.67 +/- 0.30 optical density (OD); P < 0.01]. The increase in aged rats (6.5 +/- 0.87 vs. 5.14 +/- 0.09 OD) did not reach statistical significance. Hypothyroidism was not associated with significant changes in serum ApoA1 levels in either young or aged rats. Hyperthyroidism was associated with a 2.5-fold increase in ApoA1 mRNA in young rats and a 1.7-fold increase in aged rats. Hypothyroidism was associated with a 3.6-fold reduction in ApoA1 mRNA in young rats, but there was no significant change in aged hypothyroid rats. Mobility shift assays indicated that the binding of transacting factors to ApoA1 promoter increased in hyperthyroid young rats but not in hyperthyroid aged rats. It is concluded that aging in rats is associated with reduced ApoA1 responsiveness to thyroid hormones. This altered responsiveness could partly be the result of changes in the binding activity of nuclear factors to the ApoA1 promoter.