Low dose EGCG treatment beginning in adolescence does not improve cognitive impairment in a Down syndrome mouse model

Down syndrome (DS) or Trisomy 21 causes intellectual disabilities in humans and the Ts65Dn DS mouse model is deficient in learning and memory tasks. DYRK1A is triplicated in DS and Ts65Dn mice. Ts65Dn mice were given up to ~ 20 mg/kg/day epigallocatechin-3-gallate (EGCG), a Dyrk1a inhibitor, or water beginning on postnatal day 24 and continuing for three or seven weeks, and were tested on a series of behavioral and learning tasks, including a novel balance beam test. Ts65Dn as compared to control mice exhibited higher locomotor activity, impaired novel object recognition, impaired balance beam and decreased spatial learning and memory. Neither EGCG treatment improved performance of the Ts65Dn mice on these tasks. Ts65Dn mice had a non-significant increase in Dyrk1a activity in the hippocampus and cerebellum. Given the translational value of the Ts65Dn mouse model, further studies will be needed to identify the EGCG doses (and mechanisms) that may improve cognitive function

Reactivity of Damaged Pyrimidines: DNA Cleavage via Hemiaminal Formation at the C4 Positions of the Saturated Thymine of Spore Photoproduct and Dihydrouridine

Described here are mechanistic details of the chemical reactivities of two modified/saturated pyrimidine residues that represent naturally occurring forms of DNA damage: 5-thyminyl-5,6-dihydrothymine, commonly referred to as the “spore photoproduct” (SP), and 5,6-dihydro-2′-deoxyuridine (dHdU), formed via ionizing radiation damage to cytosine under anoxic conditions and also serving as a general model of saturated pyrimidine residues. It is shown that due to the loss of the pyrimidine C5–C6 double bond and consequent loss of ring aromaticity, the C4 position of both these saturated pyrimidines is prone to the formation of a hemiaminal intermediate via water addition. Water addition is facilitated by basic conditions; however, it also occurs at physiological pH at a slower rate. The hemiaminal species so-formed subsequently converts to a ring-opened hydrolysis product through cleavage of the pyrimidine N3–C4 bond. Further decomposition of this ring-opened product above physiological pH leads to DNA strand break formation. Taken together, these results suggest that once the aromaticity of a pyrimidine residue is lost, the C4 position becomes a “hot spot” for the formation of a tetrahedral intermediate, the decay of which triggers a cascade of elimination reactions that can under certain conditions convert a simple nucleobase modification into a DNA strand break

Differential effects of Epigallocatechin-3-gallate containing supplements on correcting skeletal defects in a Down syndrome mouse model

SCOPE: Down syndrome (DS), caused by trisomy of human chromosome 21 (Hsa21), is characterized by a spectrum of phenotypes including skeletal abnormalities. The Ts65Dn DS mouse model exhibits similar skeletal phenotypes as humans with DS. DYRK1A, a kinase encoded on Hsa21, has been linked to deficiencies in bone homeostasis in DS mice and individuals with DS. Treatment with Epigallocatechin-3-gallate (EGCG), a known inhibitor of Dyrk1a, improves some skeletal abnormalities associated with DS in mice. EGCG supplements are widely available but the effectiveness of different EGCG-containing supplements has not been well studied. METHODS AND RESULTS: Six commercially available supplements containing EGCG were analyzed, and two of these supplements were compared with pure EGCG for their impact on skeletal deficits in a DS mouse model. The results demonstrate differential effects of commercial supplements on correcting skeletal abnormalities in Ts65Dn mice. Different EGCG-containing supplements display differences in degradation, polyphenol content, and effects on trisomic bone. CONCLUSION: This work suggests that the dose of EGCG and composition of EGCG-containing supplements may be important in correcting skeletal deficits associated with DS. Careful analyses of these parameters may lead to a better understanding of how to improve skeletal and other deficits that impair individuals with DS

Epigallocatechin-3-gallate (EGCG) consumption in the Ts65Dn model of Down syndrome fails to improve behavioral deficits and is detrimental to skeletal phenotypes

Down syndrome (DS) is caused by three copies of human chromosome 21 (Hsa21) and results in phenotypes including intellectual disability and skeletal deficits. Ts65Dn mice have three copies of ~ 50% of the genes homologous to Hsa21 and display phenotypes associated with DS, including cognitive deficits and skeletal abnormalities. DYRK1A is found in three copies in humans with Trisomy 21 and in Ts65Dn mice, and is involved in a number of critical pathways including neurological development and osteoclastogenesis. Epigallocatechin-3-gallate (EGCG), the main polyphenol in green tea, inhibits Dyrk1a activity. We have previously shown that EGCG treatment (~ 10 mg/kg/day) improves skeletal abnormalities in Ts65Dn mice, yet the same dose, as well as ~ 20 mg/kg/day did not rescue deficits in the Morris water maze spatial learning task (MWM), novel object recognition (NOR) or balance beam task (BB). In contrast, a recent study reported that an EGCG-containing supplement with a dose of 2–3 mg per day (~ 40–60 mg/kg/day) improved hippocampal-dependent task deficits in Ts65Dn mice. The current study investigated if an EGCG dosage similar to that study would yield similar improvements in either cognitive or skeletal deficits. Ts65Dn mice and euploid littermates were given EGCG [0.4 mg/mL] or a water control, with treatments yielding average daily intakes of ~ 50 mg/kg/day EGCG, and tested on the multivariate concentric square field (MCSF)—which assesses activity, exploratory behavior, risk assessment, risk taking, and shelter seeking—and NOR, BB, and MWM. EGCG treatment failed to improve cognitive deficits; EGCG also produced several detrimental effects on skeleton in both genotypes. In a refined HPLC-based assay, its first application in Ts65Dn mice, EGCG treatment significantly reduced kinase activity in femora but not in the cerebral cortex, cerebellum, or hippocampus. Counter to expectation, 9-week-old Ts65Dn mice exhibited a decrease in Dyrk1a protein levels in Western blot analysis in the cerebellum. The lack of beneficial therapeutic behavioral effects and potentially detrimental skeletal effects of EGCG found in Ts65Dn mice emphasize the importance of identifying dosages of EGCG that reliably improve DS phenotypes and linking those effects to actions of EGCG (or EGCG-containing supplements) in specific targets in brain and bone