Liquid chromatography-tandem mass spectrometry method for the quantification of a potent H3 receptor antagonist conessine in serum and its application to pharmacokinetic studies

Conessine, a steroidal alkaloid obtained from the bark and seeds of the plant species of Apocynaceae family, elicits a histamine antagonistic action, selectively for the H₃ histaminergic receptors. This alkaloid is used mainly for the treatment of dysentery and helminthic disorders. For the quantification of conessine in serum, a liquid chromatography-tandem mass spectrometry method was developed. Chromatographic separation was achieved on a Zorbax SB-CN column (100 × 4.6 mm, 3.5 µm), and a mobile phase consisting of 90% methanol in aqueous ammonium acetate buffer (pH 3.5) with 0.1% (v/v) formic acid at an isocratic flow rate of 0.6 ml/min at 40℃ provides efficiency in separation. A volume of 40 µl was injected each time and the run time for each sample was 5 min. Phenacetin (internal standard) was added to 50 µl of serum sample prior to liquid-liquid extraction using 3% isopropanol in n-hexane. The detection was performed on a 5500 QTRAP mass spectrometer by multiple reaction monitoring mode via electrospray ionization source. The multiple reaction monitoring of conessine and IS was m/ z 357.4 to m/ z 312.1 and m/ z 180.1 to m/ z 138.1, respectively. The method that showed selectivity and linearity in the range of 1-200 ng/ml was validated in terms of sensitivity, accuracy, precision and stability. The detection and quantitation limits were recognized at 0.1 and 1 ng/ml, respectively. The intra- and inter-day precision and accuracy fulfils the acceptance criteria. Applying the method to the pharmacokinetic studies in rats, conessine showed a peak serum concentration at 2 h post oral dose with a good bioavailability of 71.28 ± 4.65%.

Histamine and Histaminergic Receptors in Colorectal Cancer: From Basic Science to Evidence-based Medicine

BACKGROUND

Histamine is an imidazolic compound performing a crucial function in the pathogenesis of inflammation. Several studies have also emphasized its pro-carcinogenic effect in colorectal cancer (CRC).

OBJECT

In fact, increased histamine levels have been observed in CRC and a decreased catabolism of this molecule is typical of colorectal adenomas. Additional data have demonstrated that CRC is characterized by an altered balance of histamine receptors (HRs); in fact, HR1 and HR4 are down-regulated in CRC, while HR2 is overexpressed.

METHOD

Based on this evidence, we reviewed several studies investigating the role of HR2 antagonists (HR2A), such as cimetidine in CRC.

RESULTS

From a clinical point of view, HR2A may prolong the survival rates of patients with CRC, and a recent meta-analysis seems to confirm this finding. From a biological perspective, it has been demonstrated that HR2A could have a beneficial effect on CRC for many reasons: i) promotion of peri-tumoral lymphocyte growth and improvement of immune response against the tumor, ii) suppression of adhesion molecules which might favor metastasis, iii) anti-angiogenetic activity (reduction of VEGF), iv) increased production of some cytokines which may counteract tumor growth, such as tumor necrosis factor (TNF) alpha, interleukin (IL)-10 and IL-15. On the contrary, HR1 antagonists did not demonstrate any beneficial effect on CRC. Therefore, it is presumable that histamine could be a relevant player in the development of CRC, but its effect might be mediated by an imperfect homeostasis of its receptors.

CONCLUSION

In this scenario, HR2A could inhibit carcinogenesis whereas HR2 might act as a pro-carcinogenetic, while HR1 and HR4, being suppressed in CRC, may antagonize neoplastic development.