A rat bioassay for measuring the comparative availability of carbohydrates and its application to legume foods, pure carbohydrates and polyols

Multigeneration Reproduction Study of Lactitol in Rats

Lactitol is a disaccharide sugar alcohol (polyol) which holds promise as a reduced calorie, noncariogenic sugar substitute. In a multigeneration reproduction study, lactitol was fed to Wistar-derived Cpb:WU rats of both sexes throughout three successive generations at dietary concentrations of 0, 2, 5, and 10%. A comparison group receiving a diet with 20% lactose was included during the F., generation. The initial mating comprised 20 male and 40 female rats per group. For subsequent matings, 10 males and 20 females were used. In each generation, two litters were reared until they were at least 3 weeks old. Fertility was uniformly high in all treatment groups throughout the study and the feeding of lactitol was not associated with any adverse effects on fertility and reproductive performance. However, growth rates and survival were slightly decreased in pups of the 10% lactitol group, except in F3 litters where no effect of lactitol on survival was seen. In the 20% lactose group of the F, generation, a similar growth retardation and decreased survival was seen. The second litter of third-generation rats (F3b) was subjected to gross and histopathological examination 4 weeks after weaning. F3b rats fed 5 or 10% lactitol showed cecal enlargement which was not associated with any morphological alterations and which is commonly seen in rodents fed polyols or slowly digestible carbohydrates. In some F3b males of all dosage groups, an opaque appearance of the liver cell cytoplasm was noted. However, this effect was not dose related and was not accompanied by any other hepatic changes in the lactitol groups. Since this phenomenon was not seen in older rats or after chronic administration of lactitol, it was considered to be a transient manifestation of an altered metabolism in young rats. All other histopathological findings were equally distributed between control and test animals, or occurred in one or a few rats only. It is concluded that lactitol administered in the diet to three successive generations of rats at levels up to 10%, has no adverse effects on reproductive performance in either sex. The slight developmental delay which occurred in some generations, has been observed earlier with other polyols and may be attributed to the poor digestibility of these compounds.

Biochemical perspectives of xylitol extracted from indigenous agricultural by-product mung bean (Vigna radiata) hulls in a rat model

BACKGROUND

The production of xylitol from lignocellulosic material is of great interest around the world. It can be used as bulk sweetener and its possible lower energy value has increased acceptance for discerning consumers. Xylitol was produced from indigenous agricultural by-product (mung bean hulls) through Candida tropicalis fermentation. Further, xylitol incorporation at different concentrations (0, 100 and 200 g kg⁻¹) was carried out with the purpose of appraising the suitability and claimed health benefits of this dietetic ingredient in food products. Asserted biochemical perspectives of the xylitol intake were evaluated through biological studies for normal and streptozotocin-induced diabetic rats.

RESULTS

The addition of xylitol significantly affected feed intake, weight gain, liver and cecum weight in both normal and diabetic rats. The biochemical profile of serum was improved with xylitol incorporation in the diet. Serum glucose, cholesterol and triglycerides levels were decreased depending on xylitol intake level.

CONCLUSION

The results of the present study demonstrated that mung bean hulls have high potential as a new feedstock for xylitol production. In addressing the current concerns of obesity and diabetes, xylitol extracted from such agricultural waste should be considered in diet-based therapies for weight loss programmes.

Similarity of hydrolyzing activity of human and rat small intestinal disaccharidases

BACKGROUND

The purpose of this study was to clarify whether it is possible to extrapolate results from studies of the hydrolyzing activity of disaccharidases from rats to humans.

MATERIALS AND METHODS

We measured disaccharidase activity in humans and rats using identical preparation and assay methods, and investigated the similarity in hydrolyzing activity. Small intestinal samples without malignancy were donated by five patients who had undergone bladder tumor surgery, and homogenates were prepared to measure disaccharidase activity. Adult rat homogenates were prepared using small intestine.

RESULTS

Maltase activity was the highest among the five disaccharidases, followed by sucrase and then palatinase in humans and rats. Trehalase activity was slightly lower than that of palatinase in humans and was similar to that of sucrase in rats. Lactase activity was the lowest in humans, but was similar to that of palatinase in rats. Thus, the hydrolyzing activity of five disaccharidases was generally similar in humans and rats. The relative activity of sucrose and palatinase versus maltase was generally similar between humans and rats. The ratio of rat to human hydrolyzing activity of maltase, sucrase, and palatinase was 1.9-3.1, but this was not a significant difference. Leaf extract from Morus alba strongly inhibited the activity of maltase, sucrase, and palatinase, but not trehalase and lactase, and the degree of inhibition was similar in humans and rats. L-arabinose mildly inhibited sucrase activity, but hardly inhibited the activity of maltase, palatinase, trehalase and lactase in humans and rats. The digestibility of 1-kestose, galactosylsucrose, and panose by small intestinal enzymes was very similar between humans and rats.

CONCLUSION

These results demonstrate that the digestibility of newly developed saccharide materials evaluated by rat small intestinal enzymes can substitute for evaluation using human enzymes.

High-Fat diet enhances accumulation of hexachlorobenzene in rat dams and delays its transfer from rat dams to suckling pups through milk

Effect of diets on the distribution and transfer of hexachlorobenzene (HCB) from dams to fetuses and suckling pups was investigated. In pregnant rats, the amount of HCB accumulated in fat tissues of the high-fat diet group was higher than that of the control diet group (P < 0.05). The amounts of HCB in fetuses of the high-fat and control diet groups were estimated to be about 0.28 and 0.12% of the dam's total intake during pregnancy, respectively. In both groups, a large proportion of HCB in dams disappeared during lactation period and was transferred to their pups through the milk. In the pups of the high-fat diet group, the amount of HCB in stomach contents was lower immediately after birth and decreased slowly compared with that in the control diet group during lactation. These results showed that a high-fat diet reduced the speed of the transfer of HCB from the dams to their suckling pups through milk.

Nutritional and physiological consequences of tumour glycolysis

A frequent characteristic of many malignant tumours is an increase in anaerobic glycolysis, that is the conversion of glucose to lactate, when compared to normal tissues. The causes of this intensification involve changes in enzyme and glucose transporter levels, shifts of the isoenzyme patterns in the cancer cells to those similar to foetal tissues and a breakdown in the normal control mechanisms, most notably the Pasteur effect. The host must adapt, with a corresponding increase in gluconeogenesis. This change, along with other adaptations made by the host, eventually results in the syndrome known as cancer cachexia, which is characterized by anorexia and depletion and redistribution of the host energy stores. In some ways many malignant tumours behave much like parasites, drawing upon the host for nutrients such as glucose and returning waste products such as lactate to the host for recycling or disposal. This cycling of glucose and lactate between host and tumour has been the target for a number of proposed and tested treatments, with regard to the possible inhibition of tumour growth and/or possible prevention of some or all of the cachectic effects. Some of these suggested treatments have reached the point of clinical testing and show promise for continued research.

The long-term effect of dietary administration of refined sugars and sugar alcohols on plasma biochemistry, urine biochemistry and tissue histology in mice given a limited degree of dietary self-selection

A prototype animal feeding model is described in which mice were meal-fed a balanced diet but were given free access to water (controls) or 20% (w/v) solutions of glucose, sucrose, fructose, xylitol or sorbitol. Under these conditions it was found that the provision of an alternative energy source, in the form of a refined carbohydrate, produced marked effects on total energy intake, mouse cube (i.e. balanced energy) intake and body weight. There were also changes in the metabolic states of the animals as assessed by serum levels of glucose, urea and cholesterol, plasma levels of lactate and D-3-hydroxybutyrate, and urinary excretion of urea and oxalate. Histological examinations of tissue indicated that the sucrose-fed mice had a tendency to suffer from acute congestion of the lungs and liver steatosis. Given a limited degree of dietary self-selection it appears that mice are more likely to be at risk of excessive food consumption and obesity when given glucose- or sucrose-containing diets than they are when fructose-, xylitol- or sorbitol-containing diets are given.

Bioavailability of glucose from Palatinit

For the sake of metabolic insight into the fate of the sugar substitute Palatinit, its two components D-glucosyl-alpha (1 leads to 1)-D-mannitol and D-glucosyl-alpha (1 leads to 6)-D-glucitol [D-glucosyl-alpha-(1 leads to 6)-D-sorbitol] were assayed for glucose bioavailability by the procedure of Karimzadegan et al. using ketotic rats. With conversion rates into glucose of 6 and 20%, respectively, for free mannitol and glucitol (sorbitol), 39% for glucosylmannitol and 42% for glucosylglucitol, the metabolic glucose pool of the rat does not receive the full carbohydrate complement of these compounds. The preformed glucose moiety of the glucosylhexitols is bioavailable by 36 and 32%, respectively, from glucosylmannitol and glucosylglucitol, with 50% as theoretical maximum. Less than theoretical bioavailability of glucose from Palatinit is ascribed to microbial attack in the hindgut. The data on rats are held valid also for other species demonstrating carbohydrate fermentation in the caecum and/or colon. Differences between D-glucosyl-alpha (1 leads to 1)-D-mannitol and D-glucosyl-alpha (1 leads to 6)-D-glucitol are caused by a differential delay of glucose absorption in the small intestine, also exerted by D-glucitol. The deep metabolic insight offered by the glucose bioavailability assay into the fate of carbohydrates includes the mammal-microbial symbiosis in the large bowel. Since a rather complete survey of the metabolic consequences after their intake can be obtained, the assay system should be generally applied in assessments of food safety also of other sugar substitutes.