By Davis W. Lamson, MS, ND
Tahoma Clinic (Tukwila,Washington)

Abstract
Piperine, isolated from black pepper, has a published record of many beneficial medical uses. Some fall into the area of complementary oncology. Yet in spite of defining publications, this agent seems largely ignored by that field. The present text is intended as a primer on piperine in complementary oncology, designed for the complementary practitioner and divided into subject categories to assist in better utilization of this agent.

Introduction

The appearance of a new natural agent for use in complementary oncology is rare. Piperine, isolated from black pepper, seems bypassed in this regard (Figure 1). Possibly the major awareness of piperine with respect to oncology occurred with the report in 1998 that it greatly increased the absorption of curcumin.¹ The mechanism seems general for increased absorption of almost any substance and has been demonstrated for several agents, with many in humans. Discussion is included below.

A 2020 review and others earlier outline various biological effects of piperine, demonstrating a broadness of beneficial medicinal effects and well worth reading by the general physician.^2-5 Two previous reviews on piperine and cancer are available.^6,7 The present summary is limited to discussing attributes of piperine useful in oncology practice from a different view. It should be considered more of a primer developed to assist consideration of piperine use in complementary oncology rather than as an exhaustive survey. Information here is divided into the following categories.

• Safety of piperine
• Absorption and bioavailability of piperine
• Metabolism of piperine
• Piperine effect on P-glycoprotein and CYP3A4
• Potential incompatibility of piperine with high dose intravenous ascorbate
• Piperine and cancer stem cells
• Effect of piperine on radiotherapy
• Piperine and DNA
• Direct action of piperine on cancer
• Piperine as accessory to chemotherapy
• Piperine oral dosing
  

Safety of Piperine

Piperine is included in the FDA GRAS list (Generally Recognized as Safe) for inclusion in food.⁸ For a more quantitative estimate of safety, the results of a 1999 rat study are illustrative. Chemical toxicity is known to reduce glutathione and protein thiol groups, and cause cell injury. Piperine administered orally (5-20 mg/kg body weight) resulted in increased glutathione level, with no alteration of protein thiols. Glutathione reductase activity was not altered. The authors interpreted this as piperine having a protective role against cellular oxidation.

Using the usual conversion equation from rat to human, this corresponds for humans to 0.81 to 3.24 mg/kg or 40.5 mg to 162 mg of piperine for a 50 kg person.¹⁰ That seems more than the average person might find comfortable on the stomach.

Absorption and Bioavailability of Piperine

Although piperine is lipophilic with low water solubility, it is rapidly absorbed across the small intestine boundary. It is suggested to alter membrane dynamics and permeability and induce proteins associated with cytoskeletal function thereby increasing small intestine absorptive surface. Piperine was shown to extend the length of rat intestine villi over a period of two hours, returning to usual by three hours.¹¹ (For that reason piperine is being studied at this clinic as a means of increasing nutritional absorption in persons with refractory celiac disease.)

There may be an additional factor regarding piperine enhancement of curcumin and possibly other molecules. A recent report states that curcumin and piperine interact to form a π—π intermolecular complex, which enhances the bioavailability of curcumin by inhibition of glucuronidation of curcumin in the liver. Whether that result is due to piperine reduction of CYP3A4 was not discussed.¹²

Because of research on piperine as a general bioenhancer, it should be remembered that this may include any prescription drug. Thus, possible overdose of prescription medication needs to be kept in mind.

Metabolism of Piperine

Administration of piperine by gavage to rats at a dose of 30 mg (170 mg/kg) resulted in approximately 97% absorption. Three per cent of the dose was excreted as piperine in the feces and not detectable in urine. It was shown that piperine did not undergo any metabolic change during absorption.

Only traces of piperine (less than 0.15%) were detected in serum, kidney and spleen from 30 min to 24 h. The increased excretion of conjugated uronic acids, conjugated sulphates, and phenols indicated that scission of the methylenedioxy group of piperine, glucuronidation, and sulphation appear to be the major steps in the disposition of piperine in the rat.¹³

In a second study, oral administration of piperine (170 mg/kg) to rats examined metabolites in bile and urine. Four metabolites of piperine (piperonylic acid, piperonyl alcohol, piperonal and vanillic acid) were identified in the free form in 0-96-hour urine. Only piperic acid was detected in 0-6-hour bile.¹⁴

Piperine Effect on P-glycoprotein and CYP3A4

P-glycoprotein is a drug transporter that effluxes drugs from cells, including chemotherapeutic drugs, and is implicated in the development of resistance of cancer cells to chemotherapeutic drugs. The enzyme CYP3A4 contributes greatly to first-pass elimination of many drugs. Piperine inhibits both the drug transporter P-glycoprotein and the major drug-metabolizing enzyme CYP3A4. Results are from rodents, human cell studies and some human studies.^15-17

Potential Incompatibility of Piperine with High Dose Intravenous Ascorbate

A number of publications report on the antioxidant effect of piperine. One reported that piperine scavenged hydrogen peroxide, superoxide, and hydroxyl radical generated by the copper-ascorbate system. It seems a reasonable assumption that oral piperine could greatly decrease the hydrogen peroxide-dependent oxidative effect of high dose ascorbic acid administered as cancer therapy on the same day.¹⁸ There is in vivo demonstration of this effect when glutathione is included in high-dose intravenous ascorbate.¹⁹

Piperine and Cancer Stem Cells

Cancer stem cells (CSCs) are involved in recurrent hepatocellular carcinoma and there is a lack of effective treatment targeting these. CD44+ and CD133+ CSCs are greatly expressed in HepG2 cells. Piperine is known to be effective against metastasis and was found here to be active against CD44+/ CD133+ CSCs, causing cell cycle arrest at G1/G0 phase.

TGF-β activated epithelial-mesenchymal transition (EMT) has been involved in the invasion and metastasis of HepG2 cells in hepatocellular carcinoma. Piperine inhibited TGF-β, but was unable to restore the level of Vimentin (mesenchymal marker) and SNAIL (EMT-inducing transcription factor). This study was said to indicate that piperine could be an effective treatment strategy for recurrent hepatocarcinogenesis.²⁰

To determine whether curcumin and piperine were able to modulate self-renewal of normal and malignant breast stem cells, the effects of these compounds were examined on mammosphere formation, on expression of the breast stem cell marker aldehyde dehydrogenase (ALDH), and on Wnt signaling. Curcumin and piperine each inhibited mammosphere formation, serial passaging and percent of ALDH+ cells, by 50% at 5 μM and completely at 10 μM concentration in normal and malignant breast cells. There was no toxicity to differentiated cells. Wnt signaling was inhibited by both curcumin and piperine by 50% at 5 μM and completely at 10μM.²¹

Effect of Piperine on Radiotherapy

Piperine was examined for radio-sensitizing the colorectal adenocarcinoma cell line HT-29. Pretreatment at 12.5 and 25 μg/mL concentrations was followed by exposed to γ-radiation (1.25 Gy). Combination treatment arrested cells at G2/M phase nearly 2.8-fold higher than radiation alone, inducing apoptosis through mitochondria-dependent pathway. Piperine was suggested for radio-sensitization in colon cancer.²²

The expression of estrogen receptor beta (Erβ) was increased in the cells treated with piperine. Activation of ERβ, a nuclear hormone transcription factor promoting tumor suppression represents a novel clinical advance towards management and prevention of cancers. References are included on the benefit of ERβ in prostate, ovarian and lung cancer cells.^23-25

Piperine and DNA

Piperine showed specificity for G-quadruplex DNA over double stranded DNA, with highest affinity for G-quadruplex structure formed at the c-myc promoter region. In-vitrostudies show that piperine causes apoptosis-mediated cell death that further emphasizes the potential of this natural product as a promising candidate for targeting G-quadruplex structure and act as a potent anti-cancer agent.²⁶

Direct Action of Piperine on Cancer

Most of the citations of direct action of piperine on cancer are in vitro studies with few in vivo. Précis of effects on the four most common cancers are included. No reports on piperine with lymphoma or pancreatic cancer were found. The one report of piperine with leukemia cells is omitted as editors have found it of doubtful veracity.

Prostate cancer. Piperine inhibited proliferation of LNCaP, PC-3, 22RV1 and DU-145 prostate cancer cells in a dose dependent manner and induced apoptosis in hormone dependent LNCaP cells. An additional technique showed that apoptosis resulted in caspase activation in LNCaP and PC-3 cells. Piperine resulted in activation of caspase-3 and cleavage of PARP-1 proteins in LNCaP, PC-3 and DU-145 cells and disrupted androgen receptor expression in LNCaP cells. There was significant reduction of Prostate Specific Antigen (PSA) levels following piperine treatment in LNCaP cells.

NF-kB and STAT-3 transcription factors play a role in angiogenesis and invasion of prostate cancer cells. Treatment of LNCaP, PC-3 and DU-145 cells with piperine resulted in reduced expression of phosphorylated STAT-3 and NF-kB. Piperine also reduced cell migration of LNCaP and PC-3 cells and reduced the androgen-dependent and -independent tumor growth in a mouse model xeno-transplanted with prostate cancer cells. All this would seem a strong recommendation for a trial of piperine for human prostate cancer.²⁷

Treatment with piperine blocked Voltage gated K+ channels in both androgen sensitive (LNCaP) and insensitive (PC-3) prostate cancer cells and produced concentration-dependent induction of G1 phase cell cycle arrest and apoptosis.²⁸

Piperine markedly repressed cell proliferation and migration, and induced apoptosis in metastatic DU145 prostate cancer cells. Piperine reduced the expression of Akt, MMP-9 and mTOR, suggesting they participate in regulating cell migration.²⁹

The growth inhibitory effects of piperine on human prostate cancer was examined on DU145, PC-3 and LNCaP cells. Piperine gave dose-dependent inhibition of proliferation of these cell lines with cell cycle arrest at G0/G1. The level of p21Cip1 and p27Kip1 was increased dose-dependently by piperine in both LNCaP and DU145, but not in PC-3 cells, in line with more robust cell cycle arrest in the former two cell lines than the latter. Although piperine induced low levels of apoptosis, it promoted autophagy as evidenced by the increased level of LC3B-II and the formation of LC3B puncta in LNCaP and PC-3 cells.³⁰

Breast cancer. The effect of piperine was investigated on the growth and motility of triple-negative breast cancer (TNBC) cells. Piperine inhibited the in vitro growth of TNBC cells, as well as hormone-dependent breast cancer cells, without affecting normal mammary epithelial cell growth. Piperine decreased the percentage of TNBC cells in the G2 phase of the cell cycle. In addition, G1- and G2-associated protein expression was decreased and p21Waf1/Cip1 expression was increased in piperine-treated TNBC cells. Piperine inhibited survival-promoting Akt activation in TNBC cells and caused caspase-dependent apoptosis via the mitochondrial pathway. Combined treatment with piperine and γ radiation was more cytotoxic for TNBC cells than γ radiation alone. The in vitro migration of piperine-treated TNBC cells was impaired and expression of matrix metalloproteinase-2 and -9 mRNA was decreased, suggesting an antimetastatic effect by piperine. Intra-tumoral administration of piperine inhibited the growth of TNBC xenografts in immune-deficient mice.³¹

The mechanisms by which piperine exerts antitumor effects in HER2-overexpressing breast cancer cells was investigated. Piperine strongly inhibited proliferation and induced apoptosis through caspase-3 activation and PARP cleavage. HER2 gene expression was inhibited at the transcriptional level. Blockade of extracellular signal-regulated kinase (ERK)1/2 signaling significantly reduced sterol regulatory element-binding protein-1 and fatty acid synthase  expression. Piperine strongly suppressed epidermal growth factor-induced MMP-9 expression through inhibition of Activator protein-1 and NF-kB activation by interfering with ERK1/2, p38 MAPK, and Akt signaling pathways resulting in reduced migration. Piperine pretreatment enhanced sensitization to paclitaxel killing in HER2-overexpressing breast cancer cells.³²

Lung cancer. Mice with benzo(a)pyrene induced lung carcinogenesis were used to evaluate the effect of piperine on the mitochondrial tricarboxylic acid cycle and phase I and glutathione-metabolizing enzymes. Lung cancer bearing mice had a decrease in activities of mitochondrial enzymes with increased NADPH-cytochrome reductase, CYP450 and CYPb5 – along with lower activities of glutathione-metabolizing enzymes and G6PD. Piperine supplementation to tumor-induced animals lowered the phase-I enzymes with a rise in glutathione-metabolizing enzymes, which indicated an anti-tumor and anti-cancer effect along with a role in mitochondrial energy production.³³

Piperine suppressed benzo(a)pyrene (B(a)p) induced lung cancer in mice. Altered levels of total protein and protein bound carbohydrate components were observed in serum, lung and liver tissues of tumor bearing mice. Dietary piperine (50 mg/kg body weight) to B(a)p animals decreased the total protein and protein bound carbohydrate levels of lung cancer bearing animals during initiation and post-initiation phases. Data suggest that piperine furnishes chemoprevention by modulating protein bound carbohydrate levels, which are indicators of tumorigenesis.³⁴

Colon cancer. The effect of piperine was investigated on the growth of HRT-18 human rectal adenocarcinoma cells. Piperine inhibited metabolic activity and cell cycle progression of HRT-18 cells in a dose- and time-dependent fashion, suggesting a cytostatic and/or cytotoxic effect. HRT-18 cells died by apoptosis. The cells showed increased production of reactive oxygen species, indicating that cytotoxicity was mediated at least in part by reactive oxygen species.³⁵

Piperine as Accessory to Chemotherapy

Piperine anticancer effects were examined against resistant human ovarian cancer cells, using the drug-sensitive ovarian cancer cell line W1 and its sublines resistant to paclitaxel (PAC) and topotecan (TOP). Piperine increases the cytotoxic effect of PAC and TOP in drug-resistant cells. An increase in receptor-type tyrosine-protein phosphatase kappa expression correlated with decreased phosphotyrosine level after piperine treatment and downregulation of P-glycoprotein and breast cancer resistant protein expression. There was a decrease in COL3A1 and TGFBI gene expression in investigated cell lines and increased COL3A1 expression in media from W1PR2 cells. Expression of Ki67 protein and cell proliferation rate decreased after piperine treatment. Piperine markedly inhibited W1TR cell migration. The authors stated that piperine can be considered a potential anticancer agent, increasing chemotherapy effectiveness in cancer patients.³⁶

Docetaxel (DTX) is widely used for metastatic castration resistant prostate cancer, but efficacy is often compromised by drug resistance from low intracellular concentrations. Piperine (PIP) can enhance the bioavailability of other drugs via inhibition of CYPs and P-glycoprotein (P-gp) activities. Mice implanted with taxane-resistant human prostate cancer cells were administrated with saline as well as PIP and DTX separately and in combination. Compared with DTX alone, DTX-PIP combination significantly inhibited the tumor growth (114% vs. 217%) with corresponding higher intra-tumor DTX concentrations. DTX metabolism was much decreased from in mouse liver microsomes. DTX accumulation in MDCK-MDR1 cells was enhanced in the presence of PIP. PIP inhibited P-gp as well as CYP1B1 gene expression and induced a significant gene expression change relating to inflammatory response, angiogenesis, cell proliferation, or cell migration.³⁷

Piperine and mitomycin-C (MMC) co-treatment resulted in a dose-dependent suppression of cell proliferation in cervical cancer cells resistant to MMC and in mice xenograft models. Decreasing of phosphorylated-signal transducer and activator of transcription (p-STAT3) was linked to the suppression of p65 by PP and MMC combination treatment. PP potentiated the effects of MMC on apoptosis induction, which was dependent on Bcl-2 inhibition. Pro-apoptotic proteins of Bax and Bid were up-regulated, accompanied with caspase cleavage. In mice xenograft models, the combined therapy inhibited tumor growth compared to the separate PP or MMC mono-therapy groups.³⁸

Piperine Oral Dosing

From its origin as pepper extract, it seems best that piperine not be placed on an empty stomach. Trials at this clinic showed that 20 mg with a meal produced no obvious gastric irritation. The agent is mostly available as the product Bioperine in thin tablets of 10 mg. Step-wise escalation from 10 mg with a meal daily to 20 mg at meals two or three times daily was quite acceptable. If there were gastric difficulty at that level, it might be indicative of sub-optimal condition of the stomach lining and deserved separate attention.

Summary

The subjects covered above are not exhaustive but seem adequate to illustrate that piperine really is a neglected molecule for oncology use. There are few if any other agents that demonstrate enhanced absorption of other molecules, ability to concentrate agents in cancer cells, reduce invasion and metastasis by effect on cancer stem cells, enhance radiation and chemotherapy, interact with cancer cell DNA to cause apoptosis, and have a multiplicity of actions against cancer cells of many types—all with a great degree of safety.

Obviously, many more in vivo studies and eventually human ones are needed before mainstream oncology will give it a look. That’s unlikely as there is no great profit to be made from a pepper extract. However, its very inexpensiveness and safety may foster investigation to find if tolerable doses can be effective in complementary oncology.

It is hoped that careful physicians will survey the existing literature on piperine and use its attributes for the benefit of their patients.