The fallacy of enzymatic hydrolysis for the determination of bioactive curcumin in plasma samples as an indication of bioavailability: a comparative study

Abstract

BackgroundNumerous health benefits have been demonstrated for curcumin which is extracted from turmeric (Curcuma longa L). However, due to its poor absorption in the free form in the gastrointestinal tract and rapid biotransformation, various formulations have been developed to enhance its bioavailability. Previous studies indicate that the free form of curcumin is more bioactive than its conjugated counterparts in target tissues. Most curcumin pharmacokinetics studies in humans designed to assess its absorption and bioavailability have measured and reported total (free plus conjugated) curcumin, but not free, bioactive curcumin in the plasma because enzymatic hydrolysis was employed prior to its extraction and analysis. Therefore, the bioavailability of free curcumin cannot be determined.MethodsEight human subjects (4 male, 4 female) consumed a single dose of 400 mg curcumin in an enhanced absorption formulation, and blood samples were collected over 6 h. Plasma was treated either with or without glucuronidase/sulfatase prior to extraction. Curcumin and its major metabolites were analyzed using HPLC-tandem mass spectrometry. In addition, the literature was searched for pharmacokinetic studies involving curcumin using PubMed and Google Scholar, and the reported bioavailability data were compared based on whether hydrolysis of plasma samples was used prior to sample analysis.ResultsHydrolysis of blood plasma samples prior to extraction and reporting the results as “curcumin” obscures the amount of free, bioactive curcumin and total curcuminoids as compared to non-hydrolyzed samples. As a consequence, the data and biological effects reported by most pharmacokinetic studies are not a clear indication of enhanced plasma levels of free bioactive curcumin due to product formulations, leading to a misrepresentation of the results of the studies and the products when enzymatic hydrolysis is employed.ConclusionsWhen enzymatic hydrolysis is employed as is the case with most studies involving curcumin products, the amount of free bioactive curcumin is unknown and cannot be determined. Therefore, extreme caution is warranted in interpreting published analytical results from biological samples involving ingestion of curcumin-containing products.Trial registrationClinicalTrails.gov, trial identifying number NCT04103788, September 24, 2019. Retrospectively registered.

Highly Bioavailable Forms of Curcumin and Promising Avenues for Curcumin-Based Research and Application: A Review

“…Due to large variations in administration, analytical techniques, dosage and other parameters, the AUCs and C MAX data are not directly comparable across studies and formulations. However, when data from various pharmacokinetic studies are compared by normalizing the results based on AUC/mg and CMAX/mg of ingested curcumin, meaningful comparisons can be made [15,19,51,52], and clearly indicate that micro-and nano-formulations Pharmacokinetic studies in human have administered curcumin with and without DMC and BDMC. However, few human studies have assessed DMC and BDMC, even when they were quantified (total but not free) following enzymatic hydrolysis of the conjugated forms [24][25][26][27]35].…”

“…Due to large variations in administration, analytical techniques, dosage and other parameters, the AUCs and C MAX data are not directly comparable across studies and formulations. However, when data from various pharmacokinetic studies are compared by normalizing the results based on AUC/mg and C MAX /mg of ingested curcumin, meaningful comparisons can be made [15,19,51,52], and clearly indicate that micro-and nano-formulations provide greatly enhanced bioavailability as compared to products that offer increased solubility [15,19].…”

“…A major issue is the fact that with few exceptions [15,19,36], most pharmacokinetic studies have hydrolyzed plasma samples prior to analysis, resulting in the determination of total and not just free curcumin [51,52]. Enzymatically hydrolyzing plasma with glucuronidase/sulfatase to free curcumin from its conjugates as opposed to measuring free curcumin in non-hydrolyzed plasma samples results in determining total curcumin and not free, bioactive curcumin.…”

“…Enzymatically hydrolyzing plasma with glucuronidase/sulfatase to free curcumin from its conjugates as opposed to measuring free curcumin in non-hydrolyzed plasma samples results in determining total curcumin and not free, bioactive curcumin. Thus, reporting total curcumin from hydrolyzed plasma samples provides greatly exaggerated and misleading results [51,52]. As a consequence, it is difficult to provide meaningful comparisons of curcumin absorption and bioavailability between products, unless direct comparative studies are conducted.…”

Piper nigrum based diet had a chemopreventive antineoplastic effect potentiated by Curcuma longa in C57BL/6 mice

“…Curcumin when consumed orally undergoes rapid conjugation in the small bowel, undergoing rapid excretion in the urine and feces. Various approaches have been used to overcome curcumin poor absorption, rapid metabolism and poor bioavailability, including micelles and liposomes formulations or by interaction with macromolecules such as gelatin, and various polysaccharides [21].…”