The present study was designed to investigate whether the dietary polyphenols curcumin and piperine influence the self-renewal of normal and malignant breast stem cells. Currently available breast cancer preventives typically only reduce the incidence of hormonally driven cancer. According to the cancer stem cell hypothesis, malignancies arise in stem and/or progenitor cells through the dysregulation or acquisition of self-renewal, offering another potential pathway to reduce malignancy. The study examined the effects of curcumin (found in turmeric) and piperine (found in black pepper) on mammosphere formation, expression of the breast stem cell marker aldehyde dehydrogenase, and Wnt signaling. Wnt proteins are signaling molecules that regulate certain cell-to-cell interactions such as embryogenesis. Both curcumin and piperine were found to inhibit mammosphere formation, serial passaging, and percent of aldehyde dehydrogenase+ cells by approximately 50% at 5 μM and entirely at 10 μM concentration in both normal and malignant breast cells. No effect on cellular differentiation was observed. Curcumin and piperine both inhibited Wnt signaling by 50% at 5 μM and entirely at 10 μM. Curcumin and piperine both separately and in combination were found to reduce breast stem cell self-renewal but not to cause toxicity to differentiated cells. In fact, piperine enhanced the effects of curcumin. In other words, they decreased the number of stem cells while having no effect on normal differentiated breast cells. The authors conclude that these compounds could be potential cancer preventive agents.

The current review summarizes the physiological effects of black pepper, its extracts, and its major active component, piperine. Dietary piperine significantly reduces gastrointestinal food transit time by favorably stimulating the digestive enzymes of the pancreas. In vitro studies have shown that piperine protects against oxidative damage. The most remarkable attribute of piperine is its inhibitory influence on enzymatic drug biotransforming reactions in the liver. Piperine has been shown to strongly inhibit hepatic and intestinal aryl hydrocarbon hydroxylase and UDP-glucuronyl transferase, thereby enhancing the bioavailability of a number of therapeutic drugs and phytochemicals. Although previously there were several controversial reports published regarding black pepper's safety as a food additive, more recent animal studies have established the safety of black pepper and piperine. In addition to having been found non-genotoxic, piperine has in fact been found to possess anti-mutagenic and anti-tumor properties.

The current study measured the concentration of polyphenols in black and white peppercorns and investigated the radical scavenging activities of hydrolyzed and nonhydrolyzed pepper extracts. As part of normal metabolic processes, our bodies produce reactive oxygen species capable of damaging DNA and cells, as well as contributing to chronic disease, all through oxidization. This process can be weakened or perhaps reversed by diets containing spices with the ability to scavenge reactive oxygen species. In the study, the hydrolyzed and nonhydrolyzed extracts of black pepper were found to contain significantly more polyphenols than those of white pepper. The hydrolyzed extract contained significantly more polyphenols compared with the nonhydrolyzed extract for both of the peppercorns. The free radical and reactive oxygen species scavenging activities of each of the extracts were shown to be dose-dependent, with the black pepper extracts being the most powerful. The authors conclude that peppercorns, especially black pepper, have nutritional importance as antioxidants and free radical scavengers.

The present study was designed to investigate the effects of red chilli (Capsicum annum L.), cumin (Cuminum cyminum L.), and black pepper (Piper nigrum L.) on carcinogen-induced colon cancer in rats. Colon cancer was induced by injection of 15 doses of 1,2-dimethylhydrazine (DMH) at one-week intervals. The rats continued to be fed with a standard pellet diet, and supplemented throughout the remaining experimental period with one of the following (mixed in the diet): red chilli (0.015% (wt/wt); cumin seeds (1.25% (wt/wt); or black pepper ( 0.5% (wt/wt). After 32 weeks, the incidence and number of tumors in the colon were found to be significantly higher in the rats administered DMH and/or red chillis, compared to those administered DMH and cumin or black pepper. No tumors were found in the control animals that did not receive DMH. The levels of fecal bile acids and neutral sterols in 24-hour fecal samples were significantly lower in the DMH plus chilli group, whereas the excretion of fecal bile acids and neutral sterols was significantly higher in the DMH plus cumin and DMH plus black pepper groups. The authors conclude that chilli supplementation promotes colon carcinogenesis, whereas cumin or black pepper suppresses colon carcinogenesis in the presence of the procarcinogen 1,2-dimethylhydrazine.

The present study examined the protective role of piperine during experimental lung carcinogenesis. Piperine is a pure, pungent alkaloid found in black and long peppers (piper nigrum and piper longum). In the study, the activities of detoxifying enzymes such as quinone reductase (QR), glutathione transferase (GST), and UDP-glucuronosyl transferase (UDP-GT) were found to be attenuated, while the hydrogen peroxide level was increased, in lung cancer-bearing animals. Supplementation with piperine was found to enhance the detoxification enzymes and reduce DNA damage, as determined by single cell electrophoresis. In addition, DNA-Protein cross links (found to be high in lung cancer bearing animals) were also modulated as a result of supplementation with piperine. The authors conclude that the results help explain the ability of piperine to prevent cancer.