Although kombucha tea is popular around the world as a beneficial medicinal health-promoting drink, its beneficial and/or adverse effects on human health have not been scientifically determined yet. No previous study has, for instance, so far reported on the systematic investigation and evaluation of the antidiabetic activity of kombucha. To the authors’ knowledge, the present work is the first attempt to investigate the protective effects of kombucha on diabetes and its complications on the functions of the liver, kidney, and pancreas.
Several of the enzymes secreted by the pancreas, namely α-amylase and lipase, are known to break down dietary polysaccharides and lipids into monosaccharides and free fatty acids, which represent some of the major nutrients needed to maintain human health [36
]. Although most of the research so far conducted on diabetes has focused on dyslipidemia as a major risk factor for cardiac, cerebral, and renal complications, several studies have recently showed an impairment of pancreatic exocrine function in type 1 and type 2 diabetes. The analysis of serum/plasma pancreatic enzymes was suggested to provide additional informative parameters for the assessment of the chronicity and progress of the illness as well as of the response to therapy [38
The findings of the present study showed that the administration of kombucha to surviving diabetic rats significantly reduced pancreatic α-amylase activity, which plays a key role in the digestion of carbohydrates. This was indicative of lowered levels of absorbable glucose being formed from the digestion of carbohydrate and leading to reduced levels of blood glucose. The inhibition of pancreatic α-amylase activity in the human digestive tract represents one of the therapeutic approaches commonly used for the control and prevention of postprandial hyperglycemia in non-insulin-dependent diabetic patients through reducing the uptake of glucose released by those enzymes from starch [42
To produce kombucha, black tea ingredients and sucrose undergo progressive modifications due to the action of the tea fungus. Several metabolites can be identified in the fermented beverage, including acetic, lactic, gluconic and glucuronic acids, ethanol, glycerol and polyphenols [20
]. Most of the properties of kombucha are attributed to the polyphenolic composition of the beverage. Tea polyphenolics were previously reported to inhibit and reduce α-amylase activity in the in the saliva and intestines of rats, respectively, which, in turn, were described to lower the hydrolysis of starch to glucose and to reduce the assimilation of glucose [47
The present study also showed that the administration of kumbucha to surviving diabetic rats reduced pancreatic lipase activity, a decrease that is responsible for the hydrolysis of non-absorbable dietary triglycerides into absorbable monoglycerides and free fatty acids, which, in turn, leads to the decrease of plasma cholesterol and TG level [48
]. This represents one of the therapeutic approaches commonly used for the control and prevention of dyslipidemia. Polyphenols were reported to inhibit pancreatic lipase in vitro
. Previous data suggested that the presence of galloyl moieties within polyphenol chemical structures was required for the enhancement of pancreatic lipase inhibition [51
Alloxan is a specific toxin that destroys the pancreatic β-cells, provoking a state of primary deficiency in insulin without affecting other types of islets. The diabetic effect of alloxan is due to an excess in the production of reactive oxygen species (ROS). This excess leads to toxicity in pancreatic cells, which, in turn, reduces the synthesis and release of insulin while concurrently affecting other organs, such as liver [52
]. Increased lipid peroxidation products and decreased plasma or tissue concentrations of superoxide dismutase, catalase, and glutathione have been well documented in the literature on alloxan-induced diabetes [30
Chronic hyperglycemia and dyslipidemia are associated with a variety of metabolic disorders in human and animal diabetic patients [54
], causing oxidative stress, depleting the activity of the antioxidative defense system, and resulting in elevated levels of ROS [30
]. Oxidative environments might cause the damage of cells and tissues in the liver and kidney [5
], which is observed in the increased levels of AST, ALT, and GGT activities (indices of liver dysfunction) and of urea and creatinine (indices of kidney dysfunction). As far as the present study is concerned, the findings showed that kombucha proved remarkably efficient in the decrease of the liver and kidney dysfunction indices in surviving diabetic rats, namely the AST, ALT, and GGT activities and the urea and creatinine levels. This supplement could, therefore, be considered as a potential strong candidate for future industrial application as a therapeutic agent against liver and kidney toxicity.
Several recent studies have provided ample support for the strong candidacy of kombucha for application as an antioxidant agent for the alleviation of oxidative stress and free radicals as well as the enhancement of enzymatic defenses. Bhattacharya et al.
have, for instance, showed that murine hepatocytes treated with KT prevented the disruption of mitochondrial membrane potential and blocked the activation of mitochondria-dependent apoptotic signaling pathways, thus displaying a significant reduction of tertiary butyl hydroperoxide-induced ROS generation and a considerable attenuation of malonaldehyde levels [20
]. The inhibition of radical species could, therefore, be one of the mechanisms involved in the efficient hepatoprotective and curative properties of KT. These findings are, in fact, in good agreement with the results previously reported by Murugesan et al.
showing that KT has the potential to revert the CCl4
-induced hepatotoxicity back through the production of antioxidant molecules during fermentation [17
]. The presence of glucaric acid and its derivatives, as potent detoxifying agents, could also be considered as another reason for the hepatoprotective effects of KT [19
Furthermore, Gharib et al.
showed that, owing to its antioxidant potential, KT can ameliorate trichloroethylene-induced kidney damage by preventing lipid peroxidation and ROS species formation [16
]. The nephroprotective effects kombucha were also attributed to organic acids (e.g. acetic and glucuronic acids) which are known to facilitate the detoxification process through conjugation with toxins, which they then solubilise and eliminate from the body [56
Kombucha polyphenols may, therefore, prevent the damage and death of pancreatic β-cells, and/or stimulate the regeneration of this type of cells in diabetic rats. Coskun et al.
have reported that the administration of polyphenols, such as quercetin and epicatechin, to surviving diabetic rats protects the architecture of pancreatic β-cells, preserves the secretion of insulin, and stimulates the regeneration of this type of cells [57
]. The administration of an antioxidant-rich beverage, such as kombucha, to diabetic rats would, therefore, presumably decrease the ROS-mediated toxicity in pancreatic β-cells [35
]. The ability of kombucha to reduce the blood glucose level could also be attributed to its ability to modulate the immune system [18
], leading to the decrease of β-cell damages. It is worth noting that the findings indicated that the curative effects achieved with the administration of KT were more pronounced than those reported for BT, which could presumably be attributed to the large amounts of polyphenols and flavonoids present in KT as compared to black tea [20
]. In fact, further studies on the mechanisms and modes of action of kombucha are needed to fully appreciate its values and limitations.