Antiviral and anti-proliferative in vitro activities of piperamides from black pepper

The dried unripe fruits of Piper nigrum L. (black pepper) are known in almost every cuisine worldwide and are often referred to as “king of spices”. Moreover, P. nigrum is described to be endowed with health beneficial and disease preventing properties, like e.g. anti-inflammatory, antiviral, antipyretic, immune and bioavailability enhancing qualities [1]. Its main alkaloid piperine (1) has been confirmed to be mainly responsible for the medicinal value and pungency [2]. In this work, ten piperamides (Fig. 1) were isolated from a combined methanol/dichloromethane extract (PNE) of black pepper fruits, and investigated for (i) their antiviral properties against three viruses related to upper respiratory tract infections, and (ii) their anti-proliferative activity in vascular smooth muscle cells (VSMCs), which is a key element in the prevention of restenosis. Concerning the antiviral effect, the extract of P. nigrum was found to inhibit coxsackie virus type B3 (CVB3) with an IC₅₀ of 10.6 µg/mL in a cytopathic effect inhibition assay [3]. It showed no activity against further two investigated viruses, i.e. human rhinovirus type 2 (HRV2), and influenza virus type A (HK68). Out of the ten isolates, 6, 7, and 9 showed moderate activity against CVB3 with IC₅₀s between 10.0 – 28.7µM, but also distinct cytotoxicity in HeLa cells. Interestingly, although PNE was not tested positive against HRV2, 1 inhibited this virus with moderate activity (IC₅₀ of 29.9µM) without noteworthy cytotoxicity. Besides the detected antiviral effects, we found 1 to inhibit the proliferation of VSMCs with an IC₅₀ of 21.6µM in a resazurin conversion assay. Investigation of the other isolated constituents revealed pipertipine (10) to be even more potent with an IC₅₀ of 3.4µM [4]. This could be confirmed with a second assay, the 5-bromo-2'-deoxyuridine (BrdU) incorporation immunoassay. With these findings we add some insight into the pharmacological potential behind the famous reputation of black pepper.

Fig. 1: Chemical structures of piperamides (1-10) isolated from P. nigrum fruits.

Acknowledgements: CEM is grateful for her position funded by the Austrian Science Fund (FWF): P24587.

Keywords: Piper nigrum, piperine, anti-viral, inhibition of vascular smooth muscle cell proliferation.

References:

[1] Meghwal M, Goshwami T. Chemical composition, nutritional, medicinal and functional properties of black pepper: A review. Open Access Sci Rep. 2012; 1:1 – 5.

[2] Vasavirama K, Upender M. Piperine: a valuable alkaloid from piper species. Int J Pharm Pharm Sci. 2014: 6:34 – 38

[3] Mair, CE, Grienke U, Draschl, C, Kramer, C, Richter, M, von Grafenstein S, Kirchmair J, Liedl KR, Schmidtke M, Rollinger JM. Linking ethnopharmacology with phenotypic and virtual screening for the identification of antiviral agents from natural sources. Planta Med 2014: 80: WS17.

[4] Mair CE, Liu R, Atanasov AG, Wimmer L, Nemetz-Fiedler D, Sider N, Heiss EH, Mihovilovic MD, Dirsch VM, Rollinger JM. Piperine congeners as inhibitors of vascular smooth muscle cell proliferation. Planta Med 2015; 81: 1065 – 1074