Hypercholesterolaemia, signs of islet microangiopathy and altered angiogenesis precede onset of type 2 diabetes in the Goto-Kakizaki (GK) rat.

AIMS/HYPOTHESIS: The adult non-obese Goto-Kakizaki (GK) rat model of type 2 diabetes, particularly females, carries in addition to hyperglycaemia a genetic predisposition towards dyslipidaemia, including hypercholesterolaemia. As cholesterol-induced atherosclerosis may be programmed in utero, we looked for signs of perinatal lipid alterations and islet microangiopathy. We hypothesise that such alterations contribute towards defective pancreas/islet vascularisation that might, in turn, lead to decreased beta cell mass. Accordingly, we also evaluated islet inflammation and endothelial activation in both prediabetic and diabetic animals. METHODS: Blood, liver and pancreas were collected from embryonic day (E)21 fetuses, 7-day-old prediabetic neonates and 2.5-month-old diabetic GK rats and Wistar controls for analysis/quantification of: (1) systemic variables, particularly lipids; (2) cholesterol-linked hepatic enzyme mRNA expression and/or activity; (3) pancreas (fetuses) or collagenase-isolated islet (neonates/adults) gene expression using Oligo GEArray microarrays targeted at rat endothelium, cardiovascular disease biomarkers and angiogenesis, and/or RT-PCR; and (4) pancreas endothelial immunochemistry: nestin (fetuses) or von Willebrand factor (neonates). RESULTS: Systemic and hepatic cholesterol anomalies already exist in GK fetuses and neonates. Hyperglycaemic GK fetuses exhibit a similar percentage decrease in total pancreas and islet vascularisation and beta cell mass. Normoglycaemic GK neonates show systemic inflammation, signs of islet pre-microangiopathy, disturbed angiogenesis, collapsed vascularisation and altered pancreas development. Concomitantly, GK neonates exhibit elevated defence mechanisms. CONCLUSIONS/INTERPRETATION: These data suggest an autoinflammatory disease, triggered by in utero programming of cholesterol-induced islet microangiopathy interacting with chronic hyperglycaemia in GK rats. During the perinatal period, GK rats show also a marked deficient islet vascularisation in conjunction with decreased beta cell mass.

Type 2 diabetes - a matter of failing beta-cell neogenesis? Clues from the GK rat model.

Now that reduction in beta-cell mass has been clearly established in humans with type 2 diabetes mellitus (T2D), the debate focuses on the possible mechanisms responsible for decreased beta-cell number. Appropriate inbred rodent models are essential tools for this purpose. The information available from the Goto-Kakizaki (GK) rat, one of the best characterized animal models of spontaneous T2D, is reviewed in such a perspective. We propose that the defective beta-cell mass in the GK model reflects mostly a persistently decreased beta-cell neogenesis. The data discussed in this review are consistent with the notion that poor proliferation and/or survival of the endocrine precursor cells during GK foetal life will result in a decreased pool of endocrine precursors in the pancreas, and hence an impaired capacity of beta-cell neogenesis (either primary in the foetus or compensatory in the newborn and the adult). As we also demonstrated that beta-cell neogenesis can be pharmacologically reactivated in the GK model, our work supports, on a more prospective basis, the concept that facilitation of T2D treatment may be obtained through beta-cell mass expansion after stimulation of beta-cell regeneration/neogenesis in diabetic patients.

Defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly in the Goto-Kakizaki rat model of type 2 diabetes.

AIMS/HYPOTHESIS: The Goto-Kakizaki (GK) rat is a spontaneous model of type 2 diabetes. Defective beta cell mass detectable in late fetal age precedes the onset of hyperglycaemia. Our hypothesis was that an embryonic IGF production deficiency might be involved in beta cell mass anomaly in the diabetic GK rat. To test this, we evaluated during pancreatic organogenesis: (1) the beta cell development in GK rats on embryonic day (E) 13.5 and E18.5; (2) IGF2 and IGF1 receptor (IGF1R) pancreatic protein production on E13.5 and E18.5; (3) the in vitro development of GK pancreatic rudiment on E13.5; and (4) the in vitro effect of IGF2 addition on beta cell mass. MATERIALS AND METHODS: Beta cell quantitative analyses were determined by immunohistochemistry and morphometry. IGF2 and IGF1R pancreatic protein production was evaluated using western blot analyses. Dorsal pancreatic rudiments were dissected on E13.5, separated from surrounding mesenchyme and cultured for 7 days without or with recombinant IGF2. RESULTS: While beta cell mass was already decreased on E18.5, the differentiation of the first beta cells was in fact normal in E13.5 GK pancreas. Moreover, defective IGF2 and IGF1R protein production was detected in GK pancreatic rudiment as early as E13.5. The isolated GK pancreatic rudiment as maintained in vitro mimics the GK beta cell deficiency observed in vivo. This last approach enabled us to show that GK beta cells were fully responsive to IGF2 as far as their net growth is concerned. CONCLUSIONS/INTERPRETATION: In diabetic GK rat, defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly. IGF2 supplementation expands the pool of beta cells.

[Intestinal alterations and reduction of growth in prepuberal rats fed with soybean]. / Alteraciones intestinales y disminución del crecimiento en ratas prepúberes alimentadas con soja.

Weanling rats from the inbred lines alpha and beta were fed with a soybean-cereal mixture used for human consumption (AN). A group fed with laboratory rat chow was used as reference (AC). Growth and other nutritional parameters as well as intestinal morphohystometry were evaluated from 22 to 44 days of age. Growth rate and final weight were greater with AC in both lines of rats. The greater initial food conversion efficiency of AN diet, compared to AC, decreased rapidly with the progression of age, particularly in the beta strain. Nitrogen (N) and lipid fecal contents were significantly larger for AN in both lines. Apparent nitrogen digestibility, expressed as the difference between N intake and fecal N with respect to N intake was AC < AN (p < 0.01) for line alpha and AC > AN (p < 0.01) for line beta. The weight and the mucosal total width of the small intestine were AC > AN in both lines. AN produced a significant decrease of villi goblet cells in both strains (p < 0.005). Cecum weight was AC > AN (p < 0.01) for the beta strain. These results alert about uncontrolled consumption of soybean products without adequate inhibition of antinutritional factors, a potential risk for growing animal populations.

Alteraciones intestinales y disminución del crecimiento en ratas prepúberes alimentadas con soja. / [Intestinal alterations and reduction of growth in prepuberal rats fed with soybean]

Weanling rats from the inbred lines alpha and beta were fed with a soybean-cereal mixture used for human consumption (AN). A group fed with laboratory rat chow was used as reference (AC). Growth and other nutritional parameters as well as intestinal morphohystometry were evaluated from 22 to 44 days of age. Growth rate and final weight were greater with AC in both lines of rats. The greater initial food conversion efficiency of AN diet, compared to AC, decreased rapidly with the progression of age, particularly in the beta strain. Nitrogen (N) and lipid fecal contents were significantly larger for AN in both lines. Apparent nitrogen digestibility, expressed as the difference between N intake and fecal N with respect to N intake was AC < AN (p < 0.01) for line alpha and AC > AN (p < 0.01) for line beta. The weight and the mucosal total width of the small intestine were AC > AN in both lines. AN produced a significant decrease of villi goblet cells in both strains (p < 0.005). Cecum weight was AC > AN (p < 0.01) for the beta strain. These results alert about uncontrolled consumption of soybean products without adequate inhibition of antinutritional factors, a potential risk for growing animal populations.

Energy balance through age-related diurnal body weight variations in genetic obese and nonobese rats.

Indirect evidence of energy balance in laboratory rats is provided through the study of diurnal body weight variations in two inbred lines: obese beta and nonobese alpha, from birth to 200-300 days of age, with different feeding patterns from 25 to 75 days of age. Nocturnal weight gain (NWG) was the gain recorded after the dark phase, in direct relation to the acquisition of exogenous calories in excess of the current metabolic expenditure at nighttime. Daytime weight variation was either weight gain during lactation (DWG) or weight loss from weaning onwards (DWL), recorded after the light phase. DWL is in direct relation to daytime energy output, when metabolic expenditure exceeds the low rate of acquisition of exogenous calories. The correlation between averaged individual DWL and NWG absolute values was highly significant at every age studied. An increase in absolute DWL values with age was observed and at adulthood DWL was compensated for equivalent NWG. This increasing energy output with age during daytime, is most likely related to the maintenance of increasing biomass and consequently, to progressive reduced growth energy availability. The existence of energy homeostasis and ponderostat with set points genetically prescribed in adults, is suggested. Significant differences between lines found before adulthood give indirect evidence of higher fat accretion in the obese line in those periods of intense growth, known as the active phase of obesity.

[Chemical and nutritional assessment of a soybean and cereal mixture for adults]. / Evaluación química y nutricional de un alimento para adultos a base de soja y cereales.

Legume seeds and fibre rich plant foods usually improve aspects of human diabetes control as they are potential sources of "delayed release" carbohydrates. A regional bakery mixture of soybean and cereals, interesting for its palatability and high content in non starch polysaccharides was chemically and nutritionally evaluated. Comparisons were made with the usual commercial laboratory chow and with a cafeteria mixture. Each one of the three diets was offered ad libitum to adult rats of line IIMb/Fm beta (beta), affected by obesity, hypertriglyceridemia and glucose intolerance or diabetes. Treatments lasted three months and were performed on two groups of male rats: (a) From 100 days old growing significantly. (b) From 200 days old. Meals had similar carbohydrate and calorie contents but acid followed by enzymatica hydrolysis was required to free monosaccharides from the soybean mixture. Cafeteria mixture lacked in fibre, was rich in saturated fats and sodium, and it caused hyperphagia. Each group of rats showed similar food intakes in both ages although weight gain was significantly higher in the younger animals. In the latter, values of glycemic response showed no difference between diets. Cafeteria mixture caused significant hyperglycemia to the elder rats, while the soybean bakery mixture produced a remarkably lower glycemic response; in one case it was even lower than the one produced by the commercial chow. Differential response showed more clearly with age. The results of the feces analysis demonstrated an increased proportion of fecal water for the bakery mixture group, probably due to the amount of undigestible fibre, inducing beneficial effects on large bowel functionality.

Female reproductive profile in a fertile, genetically obese line of rats.

The female reproductive profile of a fertile genetically obese line of rats, named beta, is characterized. Hypophysis, ovaries, oviducts, and uteri weights do not differ from those of nonobese controls. Histological features in ovary, uterus, and vagina in beta line and alpha controls are similar, in agreement with classical descriptions in the subject. Vaginal opening, number of estrus, number of corpora lutea at ovulation time, and pregnancy patterns (i.e., ovary weight, number of corpora lutea, sites of implantation, and living fetuses, as well as productivity, fertility, litter size, and preweaning mortality) show no significant differences between obese and nonobese animals. From a reproductive standpoint, obese beta line would behave as nonobese. Up to now beta would represent the only fertile genetically obese line of rats, appearing as a profitable biological model to widen and deepen reproductive analysis on obesity.

[Peripuberal development of genetic obesity in beta rats. Daily changes in food intake, body weight, deep body temperature, triglyceridemia and glycemia]. / Desarrollo peripuberal de la obesidad genética en ratas beta (beta). Variaciones diarias de ingestión, peso, temperatura corporal profunda, trigliceridemia y glucemia.

The moderate quality of beta obesity and its relatively slow evolution make it potentially useful for defining the sequence of events that lead to the overt syndrome. Estimates of food intake, live body weight, deep body temperature, triglyceridemia and glycemia were obtained at several times during the day in beta genetically obese and alpha (alpha) control male rats at peripuberal age, in order to characterize the dynamic phase of this obesity and to attempt the definition of some previous proceedings that eventually produce the full obesity syndrome. Beta higher food intake in the light cycle preceded its whole day hyperphagia. Both genotypes showed the normal pattern of predominantly nocturnal feeding. A lower light phase's weight loss in beta preceded the overweight. Thus, beta rats were not significantly heavier than alpha until the end of the last period studied, when they were 75 days old. A defect in adaptive thermogenesis in beta genotype is suggested, as values on deep body temperature in relation to alpha were significantly lower at all times of day tested. Correlation coefficient value between daily net weight gain versus deep body temperature was: r = -0.601 (p less than 0.01), suggesting a diminished lipolytic stimulation in beta brown adipose tissue. A sustained hypertriglyceridemia in beta at every time of the day studied suggested its endogenous source. Differences in glycemia values were not statistically significant between genotypes, though apparently wider variations in beta could reflect a certain glycemic regulation lability in the obese genotype.

Desarrollo peripuberal de la obesidad genética en ratas beta (beta). Variaciones diarias de ingestión, peso, temperatura corporal profunda, trigliceridemia y glucemia. / [Peripuberal development of genetic obesity in beta rats. Daily changes in food intake, body weight, deep body temperature, triglyceridemia and glycemia]

The moderate quality of beta obesity and its relatively slow evolution make it potentially useful for defining the sequence of events that lead to the overt syndrome. Estimates of food intake, live body weight, deep body temperature, triglyceridemia and glycemia were obtained at several times during the day in beta genetically obese and alpha (alpha) control male rats at peripuberal age, in order to characterize the dynamic phase of this obesity and to attempt the definition of some previous proceedings that eventually produce the full obesity syndrome. Beta higher food intake in the light cycle preceded its whole day hyperphagia. Both genotypes showed the normal pattern of predominantly nocturnal feeding. A lower light phases weight loss in beta preceded the overweight. Thus, beta rats were not significantly heavier than alpha until the end of the last period studied, when they were 75 days old. A defect in adaptive thermogenesis in beta genotype is suggested, as values on deep body temperature in relation to alpha were significantly lower at all times of day tested. Correlation coefficient value between daily net weight gain versus deep body temperature was: r = -0.601 (p less than 0.01), suggesting a diminished lipolytic stimulation in beta brown adipose tissue. A sustained hypertriglyceridemia in beta at every time of the day studied suggested its endogenous source. Differences in glycemia values were not statistically significant between genotypes, though apparently wider variations in beta could reflect a certain glycemic regulation lability in the obese genotype.

Spontaneous hypertriglyceridemic obesity and hyperglycemia in an inbred line of rats.

A genetically mild obesity syndrome of pubertal onset in a highly inbred line of rats differentiated as beta (beta) has been described. It was discovered in both sexes fed a stock diet for rodents. Hyperphagia was not noticeable. Total fat content reached 31 percent of total body weight in mature males. Obesity was associated with normal plasma cholesterol values and hypertriglyceridemia. Fasting blood sugar levels at maturity were within the normal range for rats, but significantly higher than in lean alpha (alpha) controls. This syndrome developed into a mild glucose intolerance and glucosuria in older obese rats.