The role of lactic acid bacteria in colon cancer prevention: mechanistic considerations

Colorectal cancer is one of the most important causes of cancer morbidity and mortality in Western countries. While a myriad of healthful effects have been attributed to the probiotic lactic acid bacteria, perhaps the most controversial remains that of anticancer activity. It should be pointed out already at this point that there is no direct experimental evidence for cancer suppression in humans as a result of consumption of lactic cultures in fermented or unfermented dairy products. However, there is a wealth of indirect evidence, based largely on laboratory studies, in the literature. The precise mechanisms by which lactic acid bacteria may inhibit colon cancer are presently unknown. However, such mechanisms might include: enhancing the host's immune response; binding and degrading potential carcinogens; quantitative and/or qualitative alterations in the intestinal microflora incriminated in producing putative carcinogen(s) and promoters (e.g. bile acid-degrading bacteria); producing antitumorigenic or antimutagenic compounds in the colon; alteration of the metabolic activities of intestinal microflora; alteration of physicochemical conditions in the colon; effects on physiology of the host. These potential mechanisms are discussed in the present paper.     

Lactic acid translocation: terminal step in glycolysis by Streptococcus faecalis

Streptococcus faecalis obtains metabolic energy chiefly from the conversion of glucose to lactic acid; the present experiments deal with the mechanism of lactic acid translocation across the cytoplasmic membrane. Efflux of [(14)C]lactate from preloaded cells was accelerated by raising the external pH, and also by the ionophores nigericin and valinomycin. These results suggest that lactate leaves the cell by an electroneutral process, presumably as lactic acid. Further evidence was obtained by studying the entry of [(14)C]lactate into nonmetabolizing cells. It appears that the membrane is essentially impermeable to the lactate anion, but allows passage of lactic acid. The most persuasive evidence is that, upon establishment of a pH gradient such that the cytoplasm was alkaline, l-[(14)C]lactate accumulated in the cells against the concentration gradient. Accumulation was transient, and dissipated in parallel with the collapse of the pH gradient. The concentration gradient attained at the peak was a function of the pH difference. Ionophores which are known to collapse a pH gradient, such as nigericin and valinomycin, abolished accumulation of l-lactate. We infer that lactic acid translocation, whether into the cells or outward, is an electroneutral process and for that reason the distribution of lactic acid across the membrane is a function of the pH of cytoplasm and medium. The specificity of translocation and its kinetic parameters suggest that it is mediated by a carrier of low specificity.     

Targeting acidity in cancer and diabetes

While cancer is commonly described as “a disease of the genes”, it is also a disease of metabolism. Indeed, carcinogenesis and malignancy are highly associated with metabolic re-programming, and there is clinical evidence that interrupting a cancer's metabolic program can improve patients' outcomes. Notably, many of the metabolic adaptations observed in cancer are similar to the same perturbations observed in diabetic patients. For example, metformin is commonly used to reduce hyperglycemia in diabetic patients, and has been demonstrated to reduce cancer incidence. Treatment with PI3K inhibitors can induce hyperinsulinemia, which can blunt therapeutic efficacy if unchecked. While commonalities between metabolism in cancer and diabetes have been extensively reviewed, here we examine a less explored and emergent convergence between diabetic and cancer metabolism: the generation of lactic acid and subsequent acidification of the surrounding microenvironment. Extracellular lactic acidosis is integral in disease manifestation and is a negative prognostic in both disease states. In tumors, this results in important sequela for cancer progression including increased invasion and metastasis, as well as inhibition of immune surveillance. In diabetes, acidosis impacts the ability of insulin to bind to its receptor, leading to peripheral resistance and an exacerbation of symptoms. Thus, acidosis may be a relevant therapeutic target, and we describe three approaches for targeting: buffers, nanomedicine, and proton pump inhibitors.     

Cytokine immunotherapy of cancer with controlled release biodegradable microspheres in a human tumor xenograft/SCID mouse model

 A novel biodegradable poly(lactic acid) microsphere formulation was evaluated for in vivo cytokine immunotherapy of cancer in a human tumor xenograft/severe combined immunodeficiency (SCID) mouse model. Co-injection of interleukin-2 (IL-2)-loaded microspheres with tumor cells into a subcutaneous site resulted in the complete suppression of tumor engraftment in 80% of animals. In contrast, bovine-serum-albumin(BSA)-loaded particles or bolus injections of poly(ethylene glycol)/IL-2 were ineffective in preventing tumor growth. The antitumor effect of IL-2 released by the microspheres was shown to be mediated by the mouse natural killer cells. This is the first evidence that the rejection of human tumor xenografts can be provoked by the sustained in vivo delivery of IL-2 from biodegradable microspheres. The use of poly(lactic acid) microspheres to deliver cytokines to the tumor environment could provide a safer and simpler alternative to gene therapy protocols in the treatment of cancer. Received: 9 September 1997 / Accepted: 30 October 1997     

Metformin is also effective on lactic acidosis-exposed melanoma cells switched to oxidative phosphorylation

Low extracellular pH promotes in melanoma cells a malignant phenotype characterized by an epithelial-to-mesenchymal transition (EMT) program, endowed with mesenchymal markers, high invasiveness and pro-metastatic property. Here, we demonstrate that melanoma cells exposed to an acidic extracellular microenvironment, 6.7±0.1, shift to an oxidative phosphorylation (Oxphos) metabolism. Metformin, a biguanide commonly used for type 2 diabetes, inhibited the most relevant features of acid-induced phenotype, including EMT and Oxphos. When we tested effects of lactic acidosis, to verify whether sodium lactate might have additional effects on acidic melanoma cells, we found that EMT and Oxphos also characterized lactic acid-treated cells. An increased level of motility was the only gained property of lactic acidic-exposed melanoma cells. Metformin treatment inhibited both EMT markers and Oxphos and, when its concentration raised to 10 mM, it induced a striking inhibition of proliferation and colony formation of acidic melanoma cells, both grown in protons enriched medium or lactic acidosis. Thus, our study provides the first evidence that metformin may target either proton or lactic acidosis-exposed melanoma cells inhibiting EMT and Oxphox metabolism. These findings disclose a new potential rationale of metformin addition to advanced melanoma therapy, e.g. targeting acidic cell subpopulation.     

Mitochondria: Role of citrulline and arginine supplementation in MELAS syndrome

Mitochondria are found in all nucleated human cells and generate most of the cellular energy. Mitochondrial disorders result from dysfunctional mitochondria that are unable to generate sufficient ATP to meet the energy needs of various organs. Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a frequent maternally inherited mitochondrial disorder. There is growing evidence that nitric oxide (NO) deficiency occurs in MELAS syndrome and results in impaired blood perfusion that contributes significantly to several complications including stroke-like episodes, myopathy, and lactic acidosis. Both arginine and citrulline act as NO precursors and their administration results in increased NO production and hence can potentially have therapeutic utility in MELAS syndrome. Citrulline raises NO production to a greater extent than arginine, therefore, citrulline may have a better therapeutic effect. Controlled studies assessing the effects of arginine or citrulline supplementation on different clinical aspects of MELAS syndrome are needed.     

Extract of Lactobacillus plantarum strain 06CC2 induces JNK/p38 MAPK pathway-mediated apoptosis through endoplasmic reticulum stress in Caco2 colorectal cancer cells

Colorectal cancer is a multi-factorial disease involving genetic, environmental and lifestyle risk factors. In recent years, many changes in the bacterial composition of the intestinal microflora have been reported in colorectal cancer, suggesting the involvement of the intestinal microflora in the development and progression of colorectal cancer. Along with these reports, research on lactic acid bacteria that have a beneficial effect on the human body for the purpose of improving the intestinal environment and treating intestinal diseases has advanced. Among these studies, biogenics (defined as a component derived from lactic acid bacteria that acts directly on diseases regardless of the state of intestinal microflora) is a recent concept derived from the work on probiotics. Based on this concept, it is important to evaluate the effectiveness of various components derived from lactic acid bacteria in the treatment to diseases from and apply them in prevention and treatment. In this study, we investigated the antitumor effect of an extract obtained from Lactobacillus plantarum strain 06CC2 on colorectal cancer cells. In in vitro experiments, the extract derived from Lactobacillus plantarum 06CC2 significantly suppressed the proliferation of Caco2 colorectal cancer cells in comparison to control and non-cancer cells. Furthermore, we found that endoplasmic reticulum stress and the JNK/p38 MAPK signaling system are involved in the induction of apoptosis. These findings indicate the direct antitumor effect of the Lactobacillus plantarum 06CC2 extract on Caco2 colorectal cancer cells, and that this extract may have potential application as a biogenics.     

Tissue specific defect of complex I of the mitochondrial respiratory chain

Deficiency of complex I is one of the most commonly reported defects of the mitochondrial respiratory chain in man. Clinical evidence of tissue specific expression of complex I deficiency has not previously been confirmed biochemically. We report here slow oxidation of NAD+-linked substrates, low activity of complex I and low amounts of immunoreactive complex I peptides in skeletal muscle mitochondria from a patient with muscle weakness and lactic acidosis. In liver mitochondria complex I activity was normal and all the immunoreactive subunits of complex I were present in normal amounts.     

Health and nutritional benefits from lactic acid bacteria

Abstract There are several potential health or nutritional benefits possible from some species of lactic acid bacteria. Among these are: improved nutritional value of food, control of intestinal infections, improved digestion of lactose, control of some types of cancer, and control of serum cholesterol levels. Some potential benefits may result from growth and action of the bacteria during the manufacture of cultured foods. Some may result from growth and action of certain species of the lactic acid bacteria in the intestinal tract following ingestion of foods containing them. In selecting a culture to produce a specific benefit it is necessary to consider not only the wide variation among species of the lactic acid bacteria but also that among strains within a given species. With the possible exception of improving lactose utilization by persons who are lactose maldigestors, no specific health or nutritional claims can yet be made for the lactic acid bacteria.     

Health and nutritional benefits from lactic acid bacteria

There are several potential health or nutritional benefits possible from some species of lactic acid bacteria. Among these are: improved nutritional value of food, control of intestinal infections, improved digestion of lactose, control of some types of cancer, and control of serum cholesterol levels. Some potential benefits may result from growth and action of the bacteria during the manufacture of cultured foods. Some may result from growth and action of certain species of the lactic acid bacteria in the intestinal tract following ingestion of foods containing them. In selecting a culture to produce a specific benefit it is necessary to consider not only the wide variation among species of the lactic acid bacteria but also that among strains within a given species. With the possible exception of improving lactose utilization by persons who are lactose maldigestors, no specific health or nutritional claims can yet be made for the lactic acid bacteria.     

On-line estimation of lactic acid concentration by conductivity measurement in fermentation broth

On-line estimation of lactic acid concentration in fermentation broth is very feasible with conductivity probe directly in fermenter. This paper shows that lactic acid is the most influent parameter of medium on the conductivity measurements. The precision and longevity of conductivity probe are excellent in normal conditions of lactic acid production by fermentation process.     

Microbes versus microbes: immune signals generated by probiotic lactobacilli and their role in protection against microbial pathogens

Probiotic lactic acid bacteria can signal the immune system through innate cell surface pattern recognition receptors or via direct lymphoid cell activation. In some cases, this action has been shown to be sufficient to modulate local- and systemic-level in vivo immune responses. Practical applications of probiotics include their use in anti-tumour and anti-allergy immunotherapy, but there is also increasing evidence that some probiotics can stimulate a protective immune response sufficiently to enhance resistance to microbial pathogens. This review outlines the experimental and clinical evidence for enhanced anti-microbial immune protection by probiotic lactic acid bacteria, focussing on those studies where a correlative or suggestive link has been shown between immune modulation and enhanced protection.     

miR-148a通过靶向调节己糖激酶2基因抑制乳腺癌细胞糖酵解和细胞增殖能力

为了探讨miR-148a及己糖激酶2（hexokinase 2,HK2）基因对人乳腺癌细胞糖酵解代谢途径的影响和可能机制,利用实时荧光定量PCR（real-time fluorescent quantitative PCR,qRT-PCR）检测多种乳腺癌细胞系中miR-148a的表达量,从中筛选miR-148a表达量相对较低的乳腺癌细胞系作为研究对象。再通过观察miR-148a表达量的变化对乳腺癌细胞葡萄糖摄取量、乳酸生成量和细胞增殖指标的影响,以探究miR-148a对乳腺癌细胞糖代谢能力的影响。随后,通过TargetScan在线数据库预测miR-148a和HK2基因的靶向关系,再通过双荧光素酶报告实验、Western免疫印迹以及基因回复实验进行验证,以进一步明确miR-148a和HK2在乳腺癌细胞的糖酵解代谢途径中的作用机制。通过qRT-PCR发现miR-148a在多种乳腺癌细胞系表达降低,尤其是在乳腺癌细胞系MDA-MB231中表达量显著降低（P<0.000 1）。过表达miR-148a使MDA-MB231细胞的葡萄糖摄取量、乳酸生成量、细胞增殖指标均显著下降（P<0.01）;而抑制miR-148a表达使MDA-MB231细胞葡萄糖摄取量、乳酸生成量、细胞增殖指标均显著上升（P<0.01）。通过TargetScan在线数据库预测得出,miR-148a与HK2基因3′非编码区（3′-untranslated region,3′-UTR）具有部分结合位点;而双荧光素酶报告实验发现miR-148a与野生型HK2基因的3′-UTR荧光素酶报告载体结合,不与突变型HK2基因的3′-UTR结合。Western免疫印迹检测结果表明,过表达miR-148a使MDA-MB231细胞中HK2蛋白表达量显著下降（P＜0.000 1）,而抑制miR-148a表达则促进HK2蛋白表达量显著上升（P<0.05）。基因回复实验显示,过表达HK2基因使MDA-MB231乳腺癌细胞的葡萄糖摄取量、乳酸生成量、细胞增殖指标显著上升（P＜0.01）;将过表达miR-148a载体与过表达HK2载体共转染MDA-MB231细胞,miR-148a逆转了HK2所致的葡萄糖摄取量增加和乳酸生成量上升,并抑制细胞增殖。因此,研究提示,miR-148a可通过靶向抑制HK2基因表达而抑制乳腺癌细胞MDA-MB231糖酵解代谢和细胞增殖。     

The p53 tumour suppressor gene: a model for molecular epidemiology of human cancer

The gene encoding the tumour suppressor protein p53 is one of the most commonly mutated genes in human cancers. Analysis of the mutational events that target the p53 gene has revealed evidence for both exogenous and endogenous mutational mechanisms. For example, the p53 mutational spectrum reveals evidence for a direct causal effect of ultraviolet radiation in skin cancer, of aflatoxin B1 in liver cancer and of tobacco smoke in lung cancer. This novel field, molecular epidemiology of human cancer risk, has added a new dimension to classical associative epidemiology by providing a direct link between human cancer and carcinogen exposure.     

Batch and continuous production of lactic acid from salt whey using free and immobilized cultures of lactobacilli

Salt whey permeate was used as a substrate for lactic acid production by different strains of homofermentative lactobacilli. An isolate from Egyptian Cheddar cheese proved to be the most effective lactic acid producer. The salt whey permeate was optimized by addition of yeast extract and minerals to enable exponential growth of organisms. The lactic acid productivity of free and immobilized cells was compared and fermentation conditions were improved. Continuous lactic acid fermentation from salt whey permeate with cells immobilized in agarose beads was successfully carried out in a chemostat with a steady lactic acid concentration of 33.4 mg/ml.