Diabetes in Africans. Part 2: Ketosis-prone atypical diabetes mellitus

Diabetes is increasing with ageing and changes in lifestyle in populations of African ancestry as described in the first part of this review. Apart from classical type 1 and Type 2 diabetes, atypical presentations are observed in these populations, especially "tropical" and "ketosis-prone" atypical diabetes. Ketosis-prone atypical diabetes that has been classified by ADA as idiopathic Type 1 diabetes or Type 1b is the most common atypical form. It is characterised by an acute initial presentation with severe hyperglycaemia and ketosis, as classical Type 1 diabetes. In the subsequent clinical course after initiation of insulin therapy, prolonged remission is often possible with cessation of insulin therapy and maintenance of appropriate metabolic control. Metabolic studies showed a markedly blunted insulin secretory response to glucose, partially reversible with the improvement of blood glucose control. Variable levels of insulin resistance are observed, especially in obese patients. Pancreatic B-cell autoimmunity is an exceptional finding. Association with type 1 susceptibility HLA alleles is variable. The molecular mechanisms underlining the insulin secretory dysfunction are still to be understood and may involve gluco-lipotoxicity processes, glucagon dysregulation, effect of stress, or may be genetically determined. The present review summarises the available clinical and metabolic features and suggests some pathogenetic hypotheses and principles of management for the ketosis-prone atypical diabetes of the Africans.

Diabetes in Africans. Part 1: epidemiology and clinical specificities

The prevalence of diabetes in African communities is increasing with ageing of the population and lifestyle changes associated with rapid urbanisation and westernisation. Traditional rural communities still have very low prevalence, at most 1-2%, except in some specific high-risk groups, whereas 1-13% or more adults in urban communities have diabetes. Type 2 diabetes is the predominant form (70-90%), the rest being represented by typical type 1 patients and patients with atypical presentations that require more pathophysiological insight. Due to the high urban growth rate, dietary changes, reduction in physical activity, and increasing obesity, it is estimated that the prevalence of diabetes is due to triple within the next 25 years. In addition, long-term complications occur early in the course of diabetes and concern a high proportion of patients, probably higher than in other ethnic groups, and that could be partly explained by uncontrolled hypertension, poor metabolic control and possible ethnic predisposition. The combination of the rising prevalence of diabetes and the high rate of long-term complications in Africans will lead to a drastic increase of the burden of diabetes on health systems of African countries. The design and implementation of appropriate strategy for early diagnosis and treatment, and population-based primary prevention of diabetes in these high-risk populations is therefore a public health priority.

Effect of satiation on brain activity in obese and lean women

OBJECTIVE

To investigate the response of the brains of women to the ingestion of a meal.

RESEARCH METHODS AND PROCEDURES

We used measures of regional cerebral blood flow (rCBF), a marker of neuronal activity, by positron emission tomography to describe the functional anatomy of satiation, i.e., the response to a liquid meal in the context of extreme hunger (36-hour fast) in 10 lean (BMI < or = 25 kg/m(2); 32 +/- 10 years old, 61 +/- 7 kg; mean +/- SD) and 12 obese (BMI > or = 35 kg/m(2); 30 +/- 7 years old, 110 +/- 14 kg) women.

RESULTS

In lean and obese women, satiation produced significant increases in rCBF in the vicinity of the prefrontal cortex (p < 0.005). Satiation also produced significant decreases in rCBF in several regions including the thalamus, insular cortex, parahippocampal gyrus, temporal cortex, and cerebellum (in lean and obese women), and hypothalamus, cingulate, nucleus accumbens, and amygdala (in obese women only; all p < 0.005). Compared with lean women, obese women had significantly greater increases in rCBF in the ventral prefrontal cortex and had significantly greater decreases in the paralimbic areas and in areas of the frontal and temporal cortex.

DISCUSSION

This study indicates that satiation elicits differential brain responses in obese and lean women. It also lends additional support to the hypothesis that the paralimbic areas participate in a central orexigenic network modulated by the prefrontal cortex through feedback loops.

Exercise training-induced triglyceride lowering negatively correlates with DHEA levels in men with type 2 diabetes

OBJECTIVE

To investigate the effect of an exercise training program on lipid profile in correlation with DHEA level and body weight and body composition in type 2 diabetic men.

DESIGN

Longitudinal, controlled clinical intervention study with exercise training consisting of an 8 week supervised program of aerobic exercise (75% VO(2) peak, 45 min), twice a week and intermittent exercise, once a week, on a bicycle ergometer.

SUBJECTS

Sixteen men (age 45.4+/-7.2 y (mean+/-s.d.), HbA1c 8.15+/-1.7%, body mass index (BMI) 29.6+/-4.6 kg/m(2)) were randomly divided into two groups: trained group (n=8) and control group (n=8).

MEASUREMENTS

Lipid, apo- and lipoprotein and DHEA concentrations. Cross-sectional areas of subcutaneous and visceral adipose tissue and mid-thigh muscle by magnetic resonance imaging.

RESULTS

Training decreased visceral (153.25+/-38.55 vs 84.20+/-21.30 cm(2), P<0.001), subcutaneous (241.55+/-49.55 vs 198.00+/-39.99 cm(2), P<0.001) adipose tissue area and triglyceride levels (2.59+/-1.90 vs 1.79+/-1.08 nmol/l, P<0.05) and increased mid-thigh muscle cross-sectional area (148.30+/-36.10 vs 184.35+/-35.85 cm(2), P<0.001), and DHEA levels (11.00+/-3.10 vs 14.25+/-4.10 nmol/l, P<0.05) with no modification in body weight. Changes in triglycerides were negatively correlated with changes in DHEA (r=-0.81, P=0.03). This correlation was independent of changes in abdominal fat distribution.

CONCLUSION

Training decreases abdominal fat depots, improves muscular mass and affects favourably triglyceride and DHEA levels. Changes in triglycerides and DHEA were inversely related.

Low acute insulin secretory responses in adult offspring of people with early onset type 2 diabetes

The offspring of Pima Indians with early onset type 2 diabetes are at high risk for developing diabetes at an early age. This risk is greater among those whose mothers were diabetic during pregnancy. To define the metabolic abnormalities predisposing individuals in these high-risk groups to diabetes, we conducted a series of studies to measure insulin secretion and insulin action in healthy adult Pima Indians. In 104 normal glucose-tolerant subjects, acute insulin secretory response (AIR) to a 25-g intravenous glucose challenge correlated with the age at onset of diabetes in the mother (r = 0.23, P = 0.03) and, in multiple regression analyses, the age at onset of diabetes in the father (P = 0.02), after adjusting for maternal age at onset and after allowing for an interaction between these terms. In contrast, insulin action (hyperinsulinemic glucose clamp) did not correlate with the age at onset of diabetes in the parents. To determine whether early onset diabetes in the parents affected insulin secretion in the offspring across a range of glucose concentrations, responses to a stepped glucose infusion were measured in 23 subjects. Insulin secretion rates were lower in individuals whose mothers had developed diabetes before 35 years of age (n = 8) compared with those whose parents remained nondiabetic until at least 49 years of age (n = 15) (average insulin secretory rates: geometric mean [95% CI] 369 [209-652] vs. 571 [418-780] pmol/min, P = 0.007). Finally, the AIR was lower in individuals whose mothers were diabetic during pregnancy (n = 8) than in those whose mothers developed diabetes at an early age but after the birth of the subject (n = 41) (740 [510-1,310] vs. 1,255 [1,045-1,505] pmol/l, P < 0.02). Thus, insulin secretion is lower in normal glucose tolerant offspring of people with early onset type 2 diabetes. This impairment may be worsened by exposure to a diabetic environment in utero.

[Physical exercise and insulin sensitivity]

Physical exercise is known to be essential in the treatment of type 2 diabetes. An increased glucose uptake is evidenced during acute muscular exercise, over the post-exercise period, and following physical training. In this paper, we review metabolic and molecular aspects of physical exercise. We emphasize on the non-insulin dependent glucose transport induced by muscular contraction, which involves AMP-activated protein kinase. The discovery of this pathway is likely to open new therapeutic targets for type 2 diabetes.

Differential brain responses to satiation in obese and lean men

Knowledge of how the brain contributes to the regulation of food intake in humans is limited. We used positron emission tomography and measures of regional cerebral blood flow (rCBF) (a marker of neuronal activity) to describe the functional anatomy of satiation (i.e., the response to a liquid meal) in the context of extreme hunger (36-h fast) in 11 obese (BMI > or =35 kg/m2, age 27+/-5 years, weight 115+/-11 kg, 38+/-7% body fat; mean +/- SD) and 11 lean (BMI < or =25 kg/m2, age 35+/-8 years, weight 73+/-9 kg, 19+/-6% body fat) men. As in lean men, satiation in obese men produced significant increases in rCBF in the vicinity of the ventromedial and dorsolateral prefrontal cortex and significant decreases in rCBF in the vicinity of the limbic/paralimbic areas (i.e., hippocampal formation, temporal pole), striatum (i.e., caudate, putamen), precuneus, and cerebellum. However, rCBF increases in the prefrontal cortex were significantly greater in obese men than in lean men (P < 0.005). rCBF decreases in limbic/paralimbic areas, temporal and occipital cortex, and cerebellum were also significantly greater in obese men than in lean men (P < 0.005), whereas rCBF decreases in the hypothalamus and thalamus were attenuated in obese men compared with lean men (P < 0.05). This study raises the possibility that the brain responses to a meal in the prefrontal areas (which may be involved in the inhibition of inappropriate response tendencies) and limbic/paralimbic areas (commonly associated with the regulation of emotion) may be different in obese and lean men. Additional studies are required to investigate how these differential responses are related to the pathophysiology of obesity.

Regions of the human brain affected during a liquid-meal taste perception in the fasting state: a positron emission tomography study

BACKGROUND

The sensation of taste provides reinforcement for eating and is of possible relevance to the clinical problem of obesity.

OBJECTIVE

Positron emission tomography (PET) was used to explore regions of the brain that were preferentially affected during the taste perception of a liquid meal by 11 right-handed, lean men in the fasting state.

DESIGN

After subjects had fasted for 36 h, 2 measurements of regional cerebral blood flow (rCBF) obtained immediately after subjects retained and swallowed 2 mL of a flavored liquid meal (the taste condition) were compared with 2 measurements of rCBF obtained immediately after subjects retained and swallowed 2 mL of water (the baseline condition).

RESULTS

Compared with the baseline condition, taste was associated with increased rCBF (P < 0.005) in the left dorsolateral prefrontal cortex and superior temporal gyrus; the right ventrolateral prefrontal cortex, supramarginal gyrus, and anterior thalamus; and bilaterally in the hippocampal formation, posterior cingulate, midbrain, occipital cortex, and cerebellum. Taste was also associated with decreased rCBF (P < 0.005) in the right dorsolateral prefrontal cortex, superior temporal gyrus, and supplementary motor area, and bilaterally in the medial prefrontal cortex and inferior parietal lobule.

CONCLUSIONS

This exploratory study provides additional evidence that the temporal cortex, thalamus, cingulate cortex, caudate, and hippocampal formation are preferentially affected by taste stimulation. The asymmetric pattern of activity in the dorsolateral prefrontal cortex and superior temporal gyrus may contribute to the taste perception of a liquid meal perceived as pleasant. Additional studies are required to determine how these regions are affected in patients with obesity or anorexia.

Neuroanatomical correlates of hunger and satiation in humans using positron emission tomography

The central role of the hypothalamus in the origination and/or processing of feeding-related stimuli may be modulated by the activity of other functional areas of the brain including the insular cortex (involved in enteroceptive monitoring) and the prefrontal cortex (involved in the inhibition of inappropriate response tendencies). Regional cerebral blood flow (rCBF), a marker of neuronal activity, was measured in 11 healthy, normal-weight men by using positron emission tomography in a state of hunger (after 36-h fast) and a state of satiation (after a liquid meal). Hunger was associated with significantly increased rCBF in the vicinity of the hypothalamus and insular cortex and in additional paralimbic and limbic areas (orbitofrontal cortex, anterior cingulate cortex, and parahippocampal and hippocampal formation), thalamus, caudate, precuneus, putamen, and cerebellum. Satiation was associated with increased rCBF in the vicinity of the ventromedial prefrontal cortex, dorsolateral prefrontal cortex, and inferior parietal lobule. Changes in plasma insulin concentrations in response to the meal were negatively correlated with changes in rCBF in the insular and orbitofrontal cortex. Changes in plasma free fatty acid concentrations in response to the meal were negatively correlated with changes in rCBF in the anterior cingulate and positively correlated with changes in rCBF in the dorsolateral prefrontal cortex. In conclusion, these findings raise the possibility that several regions of the brain participate in the regulation of hunger and satiation and that insulin and free fatty acids may be metabolic modulators of postprandial brain neuronal events. Although exploratory, the present study provides a foundation for investigating the human brain regions and cognitive operations that respond to nutritional stimuli.

Development of beta 3-adrenoceptor agonists for the treatment of obesity and diabetes--an update

Beta 3-adrenoceptor (beta 3-AR) agonists were found to have remarkable anti-obesity and anti-diabetic effects in rodents shortly after their discovery in the early 1980s. Despite these promising qualities, several pharmaceutical problems and theoretical concerns have slowed the development of these products as therapeutic agents in humans during the last 15 years. To date, the pharmaceutical industry has not been successful in developing a beta 3-AR agonist for use in the treatment of human obesity and type 2 diabetes. Pharmaceutical problems in this area concern important differences between rodent and human beta 3-AR and the difficulty in finding a compound with sufficient bioavailability that is a highly selective and full agonist at the human receptor. Some of these problems seem to have been solved with the cloning of the human beta 3-AR, which has made it possible to develop novel compounds directly and specifically against the human receptor. However, several theoretical concerns still remain. These include the major question as to whether the number of biologically active beta 3-ARs in adult humans is sufficient to produce relevant metabolic effects and, if so, whether their long-term stimulation is safe and free of unwarranted side effects. In addition, the mechanisms of action of beta 3-AR agonists remain poorly understood. Recent studies using CL 316,243, a highly selective beta 3-adrenergic compound, have provided new insights into the potential mechanisms of action of these drugs in rodents as well as the first evidence that treatment with a highly selective beta 3-AR agonist exerts relevant metabolic effects in humans. It appears that chronic beta 3-adrenergic stimulation in white adipose tissue increases the expression of newly discovered mitochondrial uncoupling proteins (UCP 2 and 3) and a "reawakening" of dormant brown adipocytes. In addition, beta 3-ARs may be present in skeletal muscle where ectopic expression of UCP-1 has been reported. If these findings are confirmed, tissues other than brown fat may play an important role in mediating beta 3-adrenergic effects on thermogenesis and substrate oxidation. In humans, treatment with CL 316,243 for 8 weeks, in spite of limited bioavailability, induced marked plasma concentration-dependent increases in insulin sensitivity, lipolysis, and fat oxidation in lean volunteers, without causing beta 1-, or beta 2-mediated side effects. These results clearly indicate that favourable metabolic effects can be achieved by selective beta 3-AR stimulation in humans. The compounds of the next generation currently emerging from preclinical development are full agonists at the human beta 3-AR. These agents have demonstrated promising results in non-human primates. It will be interesting to see whether their efficacy in clinical trials is superior to that achieved with previous (rodent) beta 3-AR agonists and, if so, whether their effects will eventually translate into weight loss and improved metabolic control that could facilitate their use as effective drugs for the treatment of obesity and Type 2 diabetes in humans.

Metabolic predictors of weight gain

Human obesity is the result of both environmental and genetic factors. In this manuscript, we briefly review the metabolic factors predicting body weight gain in Pima Indians, a population prone to obesity. The metabolic predictors of weight gain are: 1) a low metabolic rate, 2) low levels of physical activity, 3) low rates of fat oxidation, 4) insulin sensitivity, 5) low sympathetic nervous system activity, and 6) low plasma leptin concentrations. In contrast, obesity is associated with high metabolic rate, high fat oxidation, low insulin sensitivity and high plasma leptin concentration. This observation emphasizes the need to conduct prospective studies to obtain a better understanding of the etiology of obesity. In addition, genetic studies will help to identify new pathways involved in the pathophysiology of obesity.

Visceral adipose tissue is not increased in Pima Indians compared with equally obese Caucasians and is not related to insulin action or secretion

Pima Indians are insulin resistant and hyperinsulinaemic compared with Caucasians. We investigated whether abdominal fat distribution was different between Pimas and Caucasians and whether differences in the amount of visceral fat explained metabolic differences between the groups. Total body fat (absorptiometry) and abdominal fat distribution at L4-L5 (magnetic resonance imaging) were compared in 20 Pima Indians (10 men/10 women) and 20 age-, sex- and BMI-matched Caucasians. Insulin action was measured as glucose disposal during a two-step hyperinsulinaemic-euglycaemic glucose clamp and insulin secretion was assessed in response to oral and intravenous glucose tolerance tests. By design, percent body fat was similar in Pimas and Caucasians. Abdominal visceral and subcutaneous adipose tissue areas were also similar in the two groups (151+/-16 vs 139+/-15 cm2 and 489+/-61 vs 441+/-7 cm2 respectively). Plasma insulin concentrations were higher in Pimas than Caucasians in the fasting state (27+/-6 vs 11+/-2 mU/ml; p < 0.01) and after a 75-g oral glucose load (area under the curve 19975+/-2626 vs 9293+/-1847 mU x l(-1) x 180 min(-1); p < 0.005). Glucose disposal was lower in Pimas than Caucasians during both steps of the clamp and negatively correlated (after adjustment for percent body fat and sex) with visceral adipose tissue in Caucasians (partial r = -0.51, p = 0.03), but not in Pima Indians (r = -0.03, p = 0.92). Insulin secretion was not related to visceral fat independently of percent body fat in either group. We conclude that a relative increase in visceral fat does not explain insulin resistance and hyperinsulinaemia in Pima Indians.

Evaluation of abdominal fat distribution in noninsulin-dependent diabetes mellitus: relationship to insulin resistance

Accumulation of visceral adipose tissue is associated with metabolic complications such as noninsulin-dependent diabetes mellitus. The aim of this study was to evaluate the effect of abdominal adipose tissue on insulin sensitivity in subjects with noninsulin-dependent diabetes mellitus (NIDDM). Areas of abdominal fat were calculated from axial magnetic resonance images obtained at the level of the umbilicus in 21 men with NIDDM [age, 45.6 +/- 8.3 (+/-SD) yr; body mass index, 29.3 +/- 4.5 kg/m(-2); total body fat (skinfold thickness), 26.8 +/- 5.4%; waist to hip ratio, 0.97 +/- 0.07; duration of diabetes, 59 +/- 47 months; hemoglobin A1c, 8.1 +/- 1.5%]. Insulin sensitivity was evaluated by an insulin tolerance test. The areas of deep abdominal fat and sc abdominal fat were, respectively, 135.3 +/- 55.1 and 211.8 +/- 99.1 cm2. The blood glucose disappearance rate was 2.11 +/- 0.87%/min and was negatively related to deep abdominal fat (r = 0.72; P = 0.0025). In contrast, areas of sc abdominal fat, total body fat, body mass index, and waist to hip ratio were not related to the blood glucose disappearance rate. Plasma triglyceride concentrations averaged 1.8 +/- 0.8 mmol/L and were positively related to deep abdominal fat (r = 0.69; P = 0.0018). We conclude that insulin sensitivity is strongly related to visceral adipose tissue accumulation in NIDDM.

[Insulin sensitivity and hepatic glucose production: nycthemeral variations]

Glucose tolerance is subject to circadian variations and has been found to be better in the morning or afternoon. An increase in plasma glucose and insulin concentrations has recently been observed between 5 and 9 a.m. These physiological changes correspond to an increase in insulin requirements in patients with insulin-dependent diabetes mellitus (the "dawn phenomenon"). In patients with non-insulin-dependent diabetes mellitus, the circadian rhythm of insulin secretion is suppressed. Studies of insulin sensitivity during a hyperinsulinaemic hyperglycaemic clamp (a supraphysiological experimental condition) indicated that: i) insulin-induced glucose utilization is decreased in the morning according to a circadian rhythm; ii) this change results from an increase in hepatic glucose production but not from a decrease in glucose uptake; and iii) a circadian rhythm is also observed for plasma free fatty acids and cortisol concentrations, which could account in part for the circadian changes in insulin sensitivity. Recognition of these circadian changes has implications for the treatment of non-insulin-dependent diabetes mellitus.

Glucose turnover in humans in the basal state and after intravenous glucose: a comparison of two models

This study investigated the ability of two models to represent glucose kinetics in the basal steady state and during an intravenous glucose tolerance test (IVGTT). Six young nonobese male subjects were studied after an overnight fast. Two bolus injections of [U-13C]glucose were given 150 min apart, the first without and the second together with concomitant injection of unlabeled glucose. [3-3H]glucose was constantly infused throughout the study and served to provide an independent means for evaluation of system responses. A linear time-invariant three-compartmental model and the two-compartment time-variant model proposed by Caumo and Cobelli were used to interpret measured time courses of [U-13C]glucose and to reconstruct endogenous glucose production and glucose removal. The ability of the two models to describe the glucose tracer time course was comparable. Simulation studies showed that the two-compartmental time-variant system better predicted measured [3-3H]glucose concentration profiles than did the three-compartmental time-invariant model. However, endogenous glucose production and the integral of excess glucose removal over basal during the IVGTT derived from the two models were almost identical.

Mobilization of visceral adipose tissue related to the improvement in insulin sensitivity in response to physical training in NIDDM. Effects of branched-chain amino acid supplements

OBJECTIVE

To evaluate the effects of an intense physical training program on abdominal fat distribution, glycemic control, and insulin sensitivity in patients with NIDDM and to determine whether branched-chain amino acid (BCAA) supplements influence these effects.

RESEARCH DESIGN AND METHODS

Twenty-four patients (ages 45 +/- 2 [mean +/- SE] years, BMI 30.2 +/- 0.9 kg/m2, HbA1c 7.9 +/- 0.3%) were randomly assigned to four groups: training plus BCAA supplement (n = 6), training plus placebo (n = 6), sedentary plus BCAA supplement (n = 6), and sedentary plus placebo (n = 6). Physical training consisted of a supervised 45-min cycling exercise at 75% of their oxygen uptake peak (VO2 peak) two times per week and an intermittent exercise one time per week for 2 months.

RESULTS

Patients who exercised increased their VO2 peak by 41% and their insulin sensitivity by 46%. Physical training significantly decreased abdominal fat evaluated by magnetic resonance imaging (umbilicus), with a greater loss of visceral adipose tissue (VAT) (48%) in comparison with the loss of subcutaneous adipose tissue (18%), but did not significantly affect body weight. The change in visceral abdominal fat was associated with the improvement in insulin sensitivity (r = 0.84, P = 0.001). BCAA supplementation had no effect on abdominal fat and glucose metabolism.

CONCLUSIONS

Physical training resulted in an improvement in insulin sensitivity with concomitant loss of VAT and should be included in the treatment program for patients with NIDDM.

Influence of simulated altitude on the performance of five blood glucose meters

OBJECTIVE

To determine the reliability of five blood glucose meters (BGMs) at various simulated altitudes using a hypobaric chamber.

RESEARCH DESIGN AND METHODS

Blood glucose levels (ranged from 1.5 to 26.3 mmol/l, according to the reference method) were measured in 18 venous blood samples by each BGM at 200, 1,000, and every 500 m up to 4,000 m in a hypobaric chamber, where temperature and humidity were held constant.

RESULTS

Four BGMs underestimated and one overestimated blood glucose concentration while barometric pressure decreased. The average percent error varied in relation to simulated altitude from 0.26 +/- 4.8% (SD) at 200 m to -28.9 +/- 4.5% at 4,000 m (Glucometer 3; P < 0.05), from 28.4 +/- 5.7 to 49.3 +/- 5.9% (Accu-Chek Easy; P < 0.05), from -10.5 +/- 2.6 to 19.8 +/- 4.3% (Tracer, P < 0.05), from -5.5 +/- 2.6 to -11.2 +/- 3.0% (Reflolux; NS), and from 17.8 +/- 4.3 to 14.8 +/- 3.6% (One Touch; NS). The most accurate seemed to be the Reflolux, except for high blood glucose levels at simulated high altitudes. The One Touch II showed a good agreement, whatever the barometric pressure and the range of blood glucose concentrations. The highest underestimation was seen with the Glucometer 3.

CONCLUSIONS

Except for the Accu-Chek Easy, low barometric pressure underestimated the BGM results in comparison with measurements taken at simulated low altitudes. The lack of accuracy and consistency of performance > 2,000 m should be known by diabetic patients practicing sports activities, such as trekking or skiing at high altitudes.