The fructans content, determined in the unfermented and symbiotic product, was found to be compatible with recommended daily intake of prebiotics (4-5 g/day) to stimulate the growth of Bifidobacterium
], while doses of 3 to 10 g/day promote reduction of blood pressure, have a beneficial effect on lipid metabolism, improve gastrointestinal health [42
] and provide hypoglycemic effect [43
]. Although a high content of fructans in the unfermented and symbiotic products was found, a hypoglycemic effect was not observed, but it may have been one of the factors that contributed to reducing the triglycerides in groups III and IV. In addition, some studies suggest that caffeic acid, chlorogenic acid (3-caffeoylquinic acid) and very probably other caffeic acid derivatives, such as 3,4-dicaffeoylquinic, 3,5-dicaffeoylquinic and 4,5-dicaffeoylquinic acids, are also the active principles related to the hypoglycemic effect of yacon leaves [44
The highest feed intake observed in the diabetic groups can be explained by the absence of circulating insulin, which causes a deficiency in glucose transport, leading to a deficiency of energy in the cells, resulting in increased feeding to compensate for that lack of energy [46
In addition, it can be explained by physiological processes related to the pathology, such as hyperglycemia, glycosuria, and polyuria, while the weight loss is due to the catabolic processes involved in diabetes mellitus [47
While in the non-diabetic group (group 1), the animals appeared, throughout the experiment, in good general condition, with normal appetite, progressive weight gain and maintenance of water intake, food intake and diuresis, the diabetic animals had a strong odor of urine and functional changes, such as polyuria and polydipsia. However, there were no significant changes of the coat or apathy, as described by Passos and Park [48
In the present study, the increased serum glucose levels in groups II, III and IV confirmed that the STZ was effective in inducing diabetes mellitus, values of around 120 mg/dL rising to nearly 500 mg/dL, a level correlated with severe experimental diabetes [49
In the blood tests used to check for induction reversal (T2), the highest blood glucose levels were recorded, thus confirming the absence of reversion. The rate of induction was 100%, since long-term diabetes mellitus was found in all animals, as observed by Rakieten et al. [50
], in rats and dogs, at the same doses of 50 mg STZ per kg body weight.
At T0, there was no statistical difference in glycemic level among the groups. After induction and until the end of the experiment, only group I (non-diabetic) maintained low values, by significantly differing from the other groups, which all had become diabetic.
Although a reduction in blood glucose occurred at the end of the experiment, it cannot be suggested that, thus revealed a tendency for diabetes to stabilize, owing to the presence of yacon and/or probiotic bacteria, since the animals in group II received only water and feed and showed the same reduction. Studies by Maffezzoli [51
] showed results similar to those in this study.
The organism itself tends to normalize high blood glucose levels by three main routes: stimulating glucose uptake by peripheral tissues (muscle and adipose tissue); altering the insulin metabolism (by reducing the degradation of insulin in the liver or stimulating insulin secretion) and, finally, by inhibiting the reabsorption of glucose by the kidneys, resulting in the elimination of glucose in the urine [52
The glycemic control observed in animal studies and early studies in humans has indicated that ingested fructooligosaccharides probably act to stimulate glucose utilization in peripheral tissues (muscle and adipose tissue) [52
The enzymes analyzed in this study are markers of liver injury; the observed increase in AST and ALT activity indicates an aggressive hepatocyte injury [53
] with regard to these enzymes, it was noted that there was no significant difference among the three diabetic groups, indicating again that the presence of yacon extract did not improve the condition of the liver of animals in groups III and IV.
A study by Baroni et al. [54
] evaluated the activity of AST and ALT in the plasma of diabetic and non-diabetic animals that received 10% hydroethanolic extract of yacon for 14 days. These researchers observed that the activity of these enzymes increased in diabetic rats but that, on administration of the extract, the enzyme activities of diabetic rats were close to those of control animals. One possible explanation is that the administration of the yacon extract may have decreased the hepatic lesions caused by the disease. However, these results were not confirmed in our study.
Regarding the lipid profile, it was observed that at the end of the experiment, triglycerides levels were lower in groups III and IV than in group II, although all these levels were higher than that observed in group I, indicating that both the unfermented and fermented products may have reduced this serum lipid in STZ-induced animals. Numerically, group IV had the lowest triglycerides, which may be related to the aqueous yacon extract [55
] and the probiotic one [56
] used in the synbiotic product.
Whereas diabetes results in increased lipolysis in adipose tissue, leading to higher blood levels of fatty acids, there is also a greater production of ketone bodies by the liver. However, the excess fatty acid captured by the liver is not fully oxidized to ketone bodies by ketogenesis. Thus, these excess fatty acids are directed to the synthesis of triglycerides, which is converted into VLDL. As VLDLs in excess are not be fully metabolized by lipoprotein lipase, a state of a hypertriglyceridemia would occur [57
As for total cholesterol, note that at the end of the experiment groups II, III and IV did not differ, although they were significantly different from group I. However, group IV again showed, numerically, the lowest value for this parameter, although not statistically different from the others; that may be an indicative of a tendency, in agreement with the results observed by Rossi et al. [58
], which showed that E. faecium
CRL 183 was able to reduce total cholesterol levels by 18.4% in hyperlipidemic rabbits.
A variety of past in vitro experiments and in vivo trials have provided evidence to support the roles of probiotics in lowering serum cholesterol and improving lipid profiles.
Several mechanisms of cholesterol reduction by probiotics via control of cholesterol metabolism have been proposed. One such mechanism is the removal of cholesterol by assimilation. The assimilation of cholesterol by probiotics in the small intestine could reduce serum cholesterol by reducing the absorption of cholesterol in the intestines [59
]. Probiotics must be viable and growing, in order to be able to remove or assimilate cholesterol [60
]. Other researchers have suggested that the incorporation of cholesterol into cell membranes could be another mechanism used to reduce cholesterol in media, or that it involves the ability of certain probiotics to deconjugate bile acids enzymatically [61
Regarding HDL-C at the end of the experiment (T3), group IV (symbiotic) differed from the other groups, with the highest value for this parameter, which may be due to the presence of E. faecium
CRL 183. This ability of E. faecium
CRL 183 to promotion increase in HDL-C has been observed in a study by Rossi et al. [58
], where the authors showed an increase of this fraction by 17.8%.
In comparison to the results of Khamisy [62
], who administered a suspension of Bifidobacterium
and Lactobacillus acidophilus
, separately or in combination to diabetic albino rats, the presented results were more satisfactory in terms of the increase in HDL-C in group IV, which received the symbiotic product; this is an important condition in reducing the risk of onset of coronary heart disease in diabetics.
In another study conducted by Manzoni et al. [17
], concerning the beneficial effects on rat serum lipid effects of soy yogurt fermented with E. faecium
CRL 183, only HDL levels were changed positively, by showing a 46% increase.
Research indicates that the hypocholesterolemic action of probiotics may be enhanced by the use of a prebiotic [63
]. The effects of probiotic combinations and certain prebiotics i.e. symbiotic on blood lipids were investigated by Kiebling et al. [64
] and Greany et al. [65
]. One study reported that the ingestion of yogurt fermented with L. acidophilus
145 and B. longum
913 plus 1% oligofructose [64
] raised the level of HDL-C, while another, which tested the combination L. acidophilus
DDS-1, B. longum
UABL-14 and fructooligosaccharides, found no effect [65
Regarding the fraction nHDL-C, no statistical difference was observed among the 4 groups during the experimental period.