Gifu University of Medical Science

Two novel resveratrol dimers, vaticanols O (1) and P (2), were isolated from the bark and stem wood of Vatica albiramis (Dipterocarpaceae), a genus rich in highly oligomerized stilbenoids. Along with seven known constituents, their structures were elucidated by comprehensive spectroscopic analyses, including 1D and 2D NMR, HR-ESI-MS, and ECD measurements. Compound 1 possesses a rare fused ring skeleton comprising a 1,2-dihydrobenzo[1, 2-b:4,3-b'] difuran unit, while 2 features a 6,10b-dihydro-1H-anthra[1, 9-bc] furan skeleton with an additional C₁ unit. Absolute configurations were assigned from NOESY correlations and electronic circular dichroism (ECD) data, supported by molecular modeling. Importantly, both dimers can be generated from ( -)-(E)-ε-viniferin under UV irradiation, as verified by LC-ESI-QTOF-MS, providing experimental support for plausible non-enzymatic biosynthetic pathways. These UV-induced transformations, monitored by LC-ESI-QTOF-MS, represent the first report of photo-triggered structural diversification of ( -)-(E)-ε-viniferin.

Hydroquinone is widely used for its hypopigmenting effects in treating hyperpigmentation disorders. However, its topical application has been linked to adverse effects, notably exogenous ochronosis, raising concerns about its safety and mechanisms of action.

To elucidate the metabolic pathway of hydroquinone in human melanocytes and to clarify the role of tyrosinase in the development of exogenous ochronosis.

We conducted an in vitro investigation using human tyrosinase to analyse the metabolism of hydroquinone. The study involved assessing the oxidation of hydroquinone in the presence of L-DOPA and L-cysteine, measuring the production of dopaquinone and its subsequent derivatives, including 2-S-cysteinyl–hydroquinone (Cys-HQ) and hydroquinone–pheomelanin (HQ-PM).

Our findings demonstrate that human tyrosinase effectively oxidizes hydroquinone primarily via dopaquinone, with L-cysteine facilitating the formation of Cys-HQ. Further oxidation of Cys-HQ leads to the production of HQ-PM. Notably, the results indicate that tyrosinase activity is crucial for the induction of exogenous ochronosis by hydroquinone. Additionally, while high-molecular-weight hydroquinone derivatives may remain within melanosomes, low-molecular-weight metabolites can penetrate the dermis, potentially triggering the polymerization of ochronotic particles similar to those seen in exogenous ochronosis.

Tyrosinase plays a significant role in hydroquinone-induced exogenous ochronosis, suggesting that hydroquinone acts as a ‘pseudo’ substrate for this enzyme. The findings highlight the importance of using tyrosinase inhibitors to reduce the risk of exogenous ochronosis, while cautioning against other melanogenesis inhibitors that may have similar side effects.

Localized vibration (LV) can enhance or replace stretching to increase flexibility. However, its effects on muscle flexibility remain unclear.

This study examines the immediate effects of short-duration LV training using a whole-body vibration device and conventional static stretching (SS) on lower limb flexibility in healthy individuals. This was achieved using muscle ultrasound (MUS), including three-dimensional shear wave elastography (3D-SWE).

This study employed a same-subject, repeated-measures design within a randomized crossover trial. Fourteen healthy participants were recruited and randomly assigned to receive either 1 min of LV to the bilateral crural muscles at 30 Hz and 3-mm amplitude or conventional SS. Each intervention was administered randomly on different days, with at least a one-day washout period. Each intervention was followed by a stand-and-reach test, and the medial and lateral heads of the gastrocnemius and soleus were examined using 3D-SWE and Doppler MUS. Each muscle was assigned a separate power Doppler subjective score (range, 0-3), and the power Doppler index (PDI) was calculated as the sum of the scores of all three muscles.

Both LV and SS resulted in decreased stand and reach test performance. However, the reduction was significantly lower with LV than SS. The PDI after LV was significantly higher than before LV (P < 0.01). Furthermore, SWE values at the medial/lateral head of the gastrocnemius was significantly lower after LV administration (P < 0.05), indicating a change in muscle elasticity.

SWE and Doppler MUS may be valuable for assessing muscle condition.