Turmeric rhizome is the yellow-orange colored cousin of ginger. Ayurveda, the ancient but still-practiced native healing system of India, dates turmeric's medicinal use to as early as 2500 BC.^[1] These nearly 5000 year old texts have founded the renown of turmeric today, both in describing its varied therapeutic benefits as well as the need for preparation in maximizing its healing potential. Modern science has revealed that the inherent obstacles, overcome anecdotally through formulation, lie in the low-bioavailability profile of the spice's pigment actives, curcuminoids.^[2]

The curcuminoids in turmeric are a collective of individual compounds with very similar structures. The 3 major actives are curcumin, demethoxycurcumin (DMC), and bisdemethoxycurcumin (BDMC). Tetrahydrocurcumin (THC), one of the primary metabolites of curcumin converted in human intestine and liver via enzymatic reduction.^[3,4] Curcuminoids have been studied for their various therapeutic applications which include anti-oxidant, anti-inflammatory, anti-thrombotic, immune stimulatory, cognitive enhancement and anti-cancer activity.^[5] Curcumin's anti-inflammatory activity, as demonstrated through scientific studies, is shown to occur by suppressing cyclooxygenase-2, lipoxygenase and inducible nitric oxide synthase via down-regulation of nuclear factor kappa B and other cytokines involved in pro-inflammatory signaling pathways.^[5–7] Curcuminoids also display antithrombotic effects, with experiments identifying thromboxane synthesis and arachidonic acid-induced platelet aggregation interferences as probable mechanisms in its inhibitory activity on platelet-activating factor.^[8]

Despite curcuminoids diversity of bioactivity, low bioavailability still presents a formidable challenge to realizing its full potential in humans. Formulation strategy, as a compensatory mechanism, has been aimed at one of at least 3 known targets of low-curcuminoid bioavailability: absorption, biotransformation and/or systemic elimination.^[9] While not exhaustive, the pharmacokinetic data that does exist for curcuminoids evidences differences in measurable plasma concentrations between diseased and healthy subjects. It also confirms that even high-doses of pure or nearly-pure actives cannot wholly counter the need for formulation as a way to overcome bioavailability constraints. In the first phase 1 clinical trial to evaluate the pharmacokinetics of purified curcumin (99.3%), patients with high-risk or pre-malignant lesions presented with negligible serum levels of curcumin despite receiving doses of 4000 mg/d.^[9,10] While patient compliance became an issue at 8 g/d, no treatment related toxicity was found at the max dose of 12 g/d. Contrastingly, a similar dose-escalation pharmacokinetic pilot study evaluating curcuminoids in a healthy population revealed that it took even higher doses than identified in the pre-malignancy population, 10,000 and 12,000 mg of curcumin respectively, to achieve measurable plasma levels.^[11]

As purification and high dose strategies have not successfully proven benefit over formulation, novel preparations with varying levels of success in increasing curcuminoids bioavailability have continued to evolve. Combining curcumin with piperine, for instance has increased the bioavailability in rats and human subjects by 150% and 2000%, respectively.^[12] Other formulations including emulsions, essential oils complexes and liposomes, reduced particle size through micronization and nanocrystals, or the addition of whey protein, cyclodextrin, and/or surfactants have shown enhanced-bioavailability benefits.^[13] Notwithstanding the ingenuity, criticisms have surfaced that question the use and necessity of synthetic adjuncts in some of these formulas, the ratio of formulation ingredients to active material, and/or the limited safety data that exists on these additives or manufacturing processes.^[14]

This study purposes to establish the bioavailability advantages of CURCUGEN, a patent-pending curcuminoid formulation, 98.5% derived from turmeric and 50% concentrated in curcuminoids, over a standard reference curcuminoid product, also known as a 95% extract of curcuminoids (or, C-95) in a healthy population. Increased dispersion is a known mechanism of enhancing bioavailability.^[15] Turmeric-native polar-resins, which are uniquely co-extracted with the curcuminoids, drive the dispersion characteristics of CURCUGEN and position it for improved absorption kinetics. Of the 98.5% of CURCUGEN turmeric base, 2 notable turmeric-native compounds, including 1.5% of turmeric essential oils and turmeric polysaccharides exist and are posited to complement the formulation's dispersion properties and enhance its bioavailability.^[16] As CURCUGEN is not highly purified from the semi-solid oleoresin state wherein curcuminoids, resins and essential oils naturally cohabitate, the curcuminoid analogues: curcumin, DMC and BDMC reflect a uniquely-preserved “food-state” ratio, as characterized exclusively in the turmeric rhizome in its dry-powdered form.^[17] The micronized, pharmaceutical/food-grade anti-caking ingredient, silicon dioxide contributes to the formulation's free-flow properties and rounds out the remaining 1.5% of its total composition. Silicon dioxide, trademarked as Aerosil 200 Pharma was sourced from Evonik Industries., India.

Differences in the ratios of major curcuminoid analogues have been proposed as a factor of influence in curcuminoid pharmacokinetics. Research that has investigated the structural differences between the curcuminoids has associated significant clinical^[18–22] and pharmacokinetic value to BDMC as the most soluble and stable of the analogues.^[23] One study established BDMC as 7× more stable than curcumin, with a duration of stability 3-folds greater than curcumin.^[23] It was the conclusion of that study that BDMC's stabilizing role plausibly helps curcumin metabolites arrive to “the right place at the right time”^[23] contributing kinetically to curcumin's bioactivity. The concentration of BDMC, as compared to curcumin in dried turmeric rhizome is starkly different from the ratio of BDMC to Curcumin found in C-95.^[17] Likewise, CURCUGEN, in its ability to preserve the ratio of this “food-state” delivers from 2 to 7× more BDMC (weight-to-weight basis) than C-95 extracts or the various formulations that derive from it.

Beyond formulation differences, curcuminoid analytical practices – which are foundational to the measurement of plasma curcuminoids concentrations and the bioavailability claims that result, have been described as “scantily detailed and outdated”.^[14,24] The best practices of bioavailability study design have been described as being inclusive of an established and standardized HPLC method that analyzes for Curcumin, DMC, BDMC, and THC; having a minimum sampling duration of 12 hours post intake with regular testing intervals; and utilizing sufficient quantities of C-95, as an edible, highly purified (i.e., 95%) curcuminoids extract and reference standard to establish measurable baseline blood plasma concentration for the comparison of the test formulation (e.g., CURCUGEN).

Our study utilized a method of determining plasma curcuminoid concentration by LC/MS/MS analysis as previously reported.^[25,26] Analytical methods were developed and validated to best appropriate our samples and study goals of including free curcumin, total curcumin, total DMC, total BDMC and total THC in our evaluations. Of importance, this study appropriated LC-MS-MS as a measurement tool over HPLC, given its resiliency. Described as being less affected by potential matrix interference, LC/MS/MS has been regarded as the ideal method for analyzing curcuminoids.^[24] Our study exceeded the minimal sampling duration of 12 hours, with a 24-hour design and dosed curcuminoids in both treatment and reference groups at 2 g, as this was the minimum curcuminoids dose found to have achieved consistently measurable plasma levels in previous studies.^[14,27]