Date Published: March 28, 2013
Publisher: BioMed Central
Author(s): Wolfgang W Quitschke, Nicole Steinhauff, Jean Rooney.
Curcuminoids may improve pathological conditions associated with Alzheimer’s disease. However, their therapeutic potential is limited by their exceedingly low bioavailability after oral administration. A method to deliver solubilized curcuminoids by injection was evaluated in Alzheimer transgenic mice.
Amyloid protein precursor (APP)SWE, PS1dE9 mice were intravenously or subcutaneously injected at weekly intervals between the ages of 4 and 12 months with serum- or cyclodextrin-solubilized curcuminoids to assess their potential for plaque prevention. Alternatively, mice between the ages of 11 and 12 months were intravenously injected with cyclodextrin-solubilized curcuminoids at biweekly intervals to evaluate their ability to eliminate existing plaques. Plasma and brain levels of curcuminoids and their metabolites were also determined after subcutaneous and intravenous injection.
Weekly long-term injections did not result in a significant plaque load reduction. However, intravenous injection of cyclodextrin-solubilized curcuminoids at higher curcuminoid concentrations and at a biweekly frequency between the ages of 11 and 12 months reduced the plaque load to approximately 70% of the control value. After intravenous injection, plasma levels of 100 μM curcuminoids and brain levels of 47 nmol/g could initially be achieved that declined to essentially undetectable levels within 20 minutes. The primary curcuminoid metabolites in plasma were the conjugates of glucuronide or sulfate and hexahydrocurcuminoids as reduction products. In the brain, both hexahydrocurcuminoids and octahydrocurcuminoids were detected as major metabolites. After subcutaneous injection, maximal curcuminoid plasma levels of 23 μM and brain levels of 8 nmol/g were observed at 30 minutes after injection and curcuminoids remained detectable for 2 to 3 h.
Curcuminoids are rapidly metabolized after injection and their effect on reducing plaque load associated with Alzheimer’s disease may be dependent on the frequency of administration.
Curcumin is a yellow pigment extracted from the spice and coloring agent turmeric, where it occurs in amounts of 2 to 8% . Commercial curcumin preparations typically contain a mixture of polyphenols, collectively referred to as curcuminoids. In addition to the primary component curcumin (CUR, 65 to 80%), they also contain smaller amounts of the co-extracted congeners demethoxycurcumin (DMC, 15 to 25%) and bisdemethoxycurcumin (BDMC, 5 to 15%) [2-4].
The oral administration of curcumin to humans, mice and rats has resulted in plasma levels typically not exceeding 1 μM concentrations and similarly low tissue levels (for recent reviews and references therein see: [26-28,44]). Alternatively, curcumin has been delivered to mice or rats by intraperitoneal (i.p) injection at dosages of 6 to 100 mg/kg body weight [15,45-47]. For this purpose, curcumin was either dissolved in DMSO [45-47] or in NaOH followed by neutralization . In those studies, peak curcumin plasma concentrations were within the range of approximately 3.5 to 25 μM and brain levels approximately 1 to 2 nmol/g. After i.v. injection in rats of 10 mg/kg curcumin solubilized in a cocktail containing DMA/PEG/dextrose, initial plasma concentrations of approximately 27 μM were reported . Similar results were reported in another study in which curcumin had been solubilized in glycerol formal and i.v. injected at a dosage of 40 mg/kg . By comparison, in the present study mice were i.v. injected with 0.1 ml of 24 mM curcuminoids solubilized in 10% HP-γ-CD. This represents a total dose of 0.84 mg or approximately 33 mg/kg curcuminoids. Under these conditions, initial curcuminoid plasma concentrations of about 100 μM were attainable. Adjusted for the total dose applied, these concentrations are similar to those observed for the rat , but they resulted in transient brain concentrations of approximately 47 nmol/g (Figure 4), which were higher than those reported in any other study. Similarly, a four-fold higher curcuminoid dose (approximately 134 mg/kg) administered by s.c. injection yielded maximal plasma concentrations of approximately 23 μM and brain levels of approximately 8 nmol/g. Although these amounts are lower than those achieved by i.v. injection, the parental curcuminoids were released gradually from the injection site and they persisted longer in both plasma and brain (Figure 5). These levels are also higher than those typically observed after i.p. injection (see above). However, in one study curcumin was administered at a much lower dose (3 mg/kg) and this yielded relatively high brain levels of approximately 3.2 nmol/g at four hours after intramuscular injection .
This study was undertaken to examine the feasibility of using an injectable form of curcuminoids to modulate the formation of amyloid plaques in brains of Alzheimer transgenic mice. This was based on the premise that relatively low concentrations of curcumin suffice to eliminate or reverse amyloid fibril formation in vitro. Furthermore, a number of studies have reported a reduction in plaque load following long-term (four to nine months) oral uptake of curcumin in similar transgenic mouse models. Despite low plasma levels, the plaque load was reduced to 48 to 69% of control values [9,15-17]. However, including curcumin in the diet represents chronic exposure to low levels of curcumin. In this study, the amount of curcuminoids injected was relatively high, yielding a significant rapid distribution into both plasma and tissues. Nevertheless, the high rate of metabolism rendered these levels short-lived. In effect, the long-term intermittent exposure at intervals of once/week had no discernable influence on plaque formation, although at four-fold higher dosage and with a frequency of twice/week for one month, a reduction in plaque load to about 70% of control values was observed. Indeed, similar plaque load reductions were reported in the same strain of mice after daily tail vein injections for seven days using only 7.5 mg/kg curcumin . It is, therefore, conceivable that inhibition of plaque formation and plaque resolution depends on a more frequent administration of curcuminoids. Since frequent long-term tail vein injections in mice are problematic, these could be augmented or substituted with better tolerated subcutaneous injections in future studies. These modes of administration could also be complemented with formulations for improved oral uptake. For example, preliminary studies with HP-γ-CD-solubilized curcuminoids in drinking water yielded consistent plasma concentrations in the range of 0.5 to 1 μM (not shown). Therefore, combining the oral uptake of curcuminoids via both food and drinking water with injection protocols may result in more effective procedures for plaque prevention and elimination.
AD: Alzheimer’s disease; APP: amyloid protein precursor; BDMC: bisdemethoxycurcumin; CUR: curcumin; DMA, N: N-dimethylacetamide; DMC: demethoxycurcumin; DMEM: Dulbecco’s Minimal Essential Medium; DMSO: dimethyl sulfoxide; FCS: fetal calf serum; HP-γ-CD: 2-hydroxypropyl-γ-cyclodextrin; i.v.: intravenous; PBS: phosphate-buffered saline; PEG: polyethylene glycol; s.c.: subcutaneous
The authors declare that they have no competing interests.
All authors contributed to the manuscript. WQ devised the protocols and performed the biochemical experiments. NS and JR carried out all animal related procedures. All authors read and approved the final manuscript.