Lipid metabolism is an important aspect for the production of energy and the maintenance of health of human beings. Breakdown of lipids is intricately associated with the carbohydrate metabolism and oxidation of fatty acid. Initially the lipid is hydrolyzed into long chain fatty acids and glycerol within the cytoplasm. However, there are several factors that may influence the ability of the lipid metabolism activity of the human system. A deviation from the balanced breakdown of these ingredients of diet may result in various side effects and often chronic health disorders. Since, the probiotics has beneficial effects on the gut microflora thereby modulating metabolism, its role in mediating the desired end to the fat intake has been contemplated.
Prevalent Knowledge About Probiotics in Lipid Metabolism:
In the early 70s, Mann and his group noticed that the Maasai tribes of Africa showed reduced plasma lipid levels since they were on a high intake of fermented milk. Other studies proved that the inclusion of Lactobacillus strains within the fermented food products lead to low lipid levels. This lipid reducing ability of the probiotics has come into prominence after it was discovered that they possess bile salt hydrolyzing capability. Once this information was established a number of in vivo and in vitro studies were carried out to screen for probiotics with lipid reducing properties. There are available data for the beneficial effects of soy milk in the regulation of lipid levels. An improvement in the lipid profile of the individuals under probiotic and isoflavones supplementation was observed.
The probiotics have been implicated in a number of ways to maintain low-lipid content within the recipients.
Modulation of Lipid Regulating Hormones:
The hormones like adiponectin, osteocalcin and leptin have got varying roles to play in the metabolism of lipid. Previous literature reports suggest that the obese population have been diagnosed with low adiponectin and osteocalcin levels and significant high levels of leptin. The role of leptin in the regulation and control of food intake and the subsequent expenditure of energy is now well accepted throughout the scientific community. In addition, it has also been demonstrated that the hypothalamus dictates the leptin in such functions. On the other hand, adiponectin increases the triglyceride content and fatty acids that are associated with sensitivity to insulin. Osteocalcin activity could be altered by leptin which could impact the synthesis of adiponectin. There are very recent reports available that suggest that various probiotic strains could modulate these genes thereby regulating lipid metabolism.
Interaction of Probiotics With Receptors:
There are a number of receptors present that can modulate the expression and activity of gene involved in lipid import and export as well as its metabolism. Infact many of them have been targeted to control lipid breakdown modules. Recent studies indicate that the administration of probiotics can interfere with the downstream signalling of the receptors like Toll-like receptors (TLRs), G protein coupled receptors (GPRs), nuclear receptors, etc. But whether there is any association between these signalling pathways could not be clearly deciphered as yet.
Control of The Gut Microbiota:
The gut microbiota when evaluated have given insights for the presence a significant number of gut microbial flora with bile salt hydrolyzing abilities which suggest that they might as well possess lipid down-regulating potential. Therefore, while considering the effect of microbes on lipid metabolism, the entire population needs to be taken into account. The past few years have seen tremendous advancement to that effect. The microbial diversity of the human gut is tremendous with an estimated 1000 different species leaving aside the number of different strains available. The importance of the maintenance of a proper Firmicute-Bacteroidetes number in the control of lipid metabolism is now well established and beyond doubt. The probiotic strains could manipulate and maintain the right balance of Firmicute-Bacteroidetes so as to keep reduced levels of lipid. Therefore, the probiotics can curb the lipopolysaccharide associated gut microbial population. There are other microbes which can positively influence the lipid metabolism with increased accumulation of fat within the host body. There are possibilities that the probiotic bacteria can control the growth and activity of such microorganisms. The introduction of prebiotics that can selectively give advantage to the probiotics can be added to the diet. As a result the probiotic strains would thrive at the expense of the unwanted microbes thereby maintaining low lipid content within the recipient.
Other Mechanisms to Explore:
Within the last few years several other mechanisms by which probiotics can potentially control metabolism of lipids have been proposed. The research group led by Khedara has demonstrated that reduced nitric oxide levels could result in the decrease of fatty acid oxidation and as a result higher accumulation of lipids. Some of the strains of probiotics could stimulate the synthesis of nitric oxide through the induction of nitric oxide synthase thereby resulting in enhanced lipid metabolism. The work of Tanida et al. shows that the L. paracasei strain has the capacity to amplify lipolysis of adipose tissue via the enhancement of autonomic nervous system. The probiotics could even exert its beneficial lipid reducing act in the liver. Probiotics could increase the expression of the Angiopoietin-4 gene leading to reduced storage of fat within the adipose tissues.
The administration of probiotics results in the relative abundance of KRT10 and ElF4A that can show betterment in the integrity of the gut with a reduced influx of lipopolysaccharide. The formation of micelles formed by the bile salts play an important role in the absorption and metabolism of lipids. The probiotics result in the release of acids through the bile salt deconjugation and prevent micelle formation. The probiotics can also release HMG CoA which results in blockade of the activity of HMG CoA reductase which is associated with the synthesis of certain groups of lipids being the limiting enzyme in the process. The probiotics can even reduce lipid absorption through binding.
The probiotics can render its influence on lipid metabolism by modulating a number of factors. Therefore, the application of probiotics in the regulation of lipid metabolism and the maintenance of homeostasis is an important avenue to explore under the present scheme of things.