X-Message-Number: 30854
Date: Fri, 11 Jul 2008 21:27:35 -0700 (PDT)
From: 
Subject: tea catechins may reduce vitrification solution toxicity

[Green tea catechins reduce membrane fluidity. DMSO toxicity is partly
mediated by increases in membrane fluidity. Therefore it is reasonable to
suppose that green tea catechins would reduce DMSO toxicity, and
consequently also reduce vitrification solution toxicity. A experiment to
test this hypothesis would seem to be indicated.]

Pharmacology. 1999 Jul;59(1):34-44.
Effects of green tea catechins on membrane fluidity.
    Tsuchiya H. Department of Dental Pharmacology, Asahi University School
of Dentistry, Hozumi, Gifu, Japan.
    Catechins originating from green tea have been used in plaque inhibition
for caries prevention and treatment for liver damage because of their
antibacterial activity against cariogenic bacteria and protective activity
on hepatic cells. The effects of catechins on membrane fluidity were studied
by a fluorescence polarization method using liposomes prepared with
dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine to assess
their pharmacological mechanism at micromol/l levels found in human body
fluids after clinical application. All eight catechins tested, ranging from
1 to 1,000 micromol/l, significantly reduced membrane fluidity in both
hydrophilic and hydrophobic regions of lipid bilayers. Catechin gallate
esters were superior in fluidity reduction to the corresponding nonesters.
The fluidity-reducing degree was different between the cis and trans forms,
suggesting the stereospecific activity of catechins. A reference antiplaque
agent, chlorhexidine, similarly reduced membrane fluidity at the
antibacterial concentration. (+)-Catechin (250 micromol/l) and
(-)-epigallocatechin gallate (2.5 micromol/l) significantly prevented the
membrane fluidization induced by hepatotoxic chloroform. These results
indicate that the reduction in membrane fluidity is responsible for the
antiplaque and hepatoprotective effects of green tea catechins.
PMID: 10352424

[Increased membrane fluidization may account for much of DMSO's toxicity.]

J Phys Chem B. 2007 Sep 6;111(35):10453-60. Epub 2007 Jul 28.
Modulating the structure and properties of cell membranes: the molecular
mechanism of action of dimethyl sulfoxide.
    Gurtovenko AA, Anwar J. Computational Laboratory, Institute of
Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire,
BD7 1DP, U.K.
    Dimethyl sulfoxide (DMSO) is a small amphiphilic molecule which is
widely employed in cell biology as an effective penetration enhancer, cell
fusogen, and cryoprotectant. Despite the vast number of experimental
studies, the molecular basis of its action on lipid membranes is still
obscure. A recent simulation study employing coarse-grained models has
suggested that DMSO induces pores in the membrane (Notman, R.; Noro, M.;
O'Malley, B.; Anwar, J. J. Am. Chem. Soc. 2006, 128, 13982-13983). We report
here the molecular mechanism for DMSO's interaction with phospholipid
membranes ascertained from atomic-scale molecular dynamics simulations. DMSO
is observed to exhibit three distinct modes of action, each over a different
concentration range. At low concentrations, DMSO induces membrane thinning
and increases fluidity of the membrane's hydrophobic core. At higher
concentrations, DMSO induces transient water pores into the membrane. At
still higher concentrations, individual lipid molecules are desorbed from
the membrane followed by disintegration of the bilayer structure. The study
provides further evidence that a key aspect of DMSO's mechanism of action is
pore formation, which explains the significant enhancement in permeability
of membranes to hydrophilic molecules by DMSO as well as DMSO's
cryoprotectant activity. The reduction in the rigidity and the general
disruption of the membrane induced by DMSO are considered to be
prerequisites for membrane fusion processes. The findings also indicate that
the choice of DMSO concentration for a given application is critical, as the
concentration defines the specific mode of the solvent's action. Knowledge
of the distinct modes of action of DMSO and associated concentration
dependency should enable optimization of current application protocols on a
rational basis and also promote new applications for DMSO.
PMID: 17661513

[Green tea catechins (polyphenols) also dramatically reduce chilling
damage.]

Cell Transplant. 2008;17(1-2):203-9.
Green tea polyphenols affect skin preservation in rats and improve the rate
of skin grafts.
    Kawazoe T, Kim H, Tsuji Y, Morimoto N, Hyon SH, Suzuki S. Department of
Plastic and Reconstructive Surgery, Postgraduate School of Medicine, Kyoto
University, Kyoto 606-8507, Japan.
    Green tea polyphenols have been recently reported to promote the
preservation of tissues, such as blood vessels, corneas, nerves, islet
cells, articular cartilage, and myocardium, at room temperature. These
findings indicate the possibility of a new method of tissue banking without
freezing. A main active ingredient of green tea, epigallocatechin-3-gallate
(EGCG), is a polyphenol that possesses antioxidant, antimicrobial,
antiproliferative, and free radical scavenging effects. This study examined
the effects of EGCG regarding skin preservation. Skin sample biopsy
specimens measuring 1 x 1 cm from GFP rats were held in sterile containers
with 50 ml preserving solution at 4 degrees C and 37 degrees C for up to
about 8 weeks. Periodically, some of the preserved skin specimens were
directly examined histologically and others were transplanted into nude
mice. Histological examinations of skin preserved at 4 degrees C revealed a
degeneration of the epidermal and dermal layers from 5 weeks in all groups.
In the groups preserved at 37 degrees C, degeneration and flakiness of the
epidermal layer were demonstrated starting at 2 weeks preservation
regardless of addition of EGCG. After 2-7 weeks of preservation the rat skin
grafted to nude mice in the EGCG groups stored at 4 degrees C showed
successful engraftment. However, grafts preserved at 4 degrees C without
EGCG and at 37 degrees C did not demonstrate GFP-positive keratinocyte or
fibroblasts. In conclusion, the present findings suggest the future clinical
usefulness of EGCG for skin preservation without freezing; however, the
mechanism by which EGCG promotes skin preservation still remains unclear.
PMID: 18468251

[Membrane fluidization may underlay toxicity of many cryoprotectants.]

Toxicol Appl Pharmacol. 1996 Oct;140(2):296-314.
An analysis of dimethylsulfoxide-induced action potential block: a
comparative study of DMSO and other aliphatic water soluble solutes.
    Larsen J, Gasser K, Hahin R. Northern Illinois University, Biological
Sciences Department, DeKalb 60115, USA.
    A series of water soluble aliphatic solutes were chosen for study. Fifty
percent effective doses (ED50) to block propagated compound action
potentials (AP's) were obtained by examining dose-response relations for
each solute. All solutes used were liquids at room temperature and are
typically used as solvents. The solutes studied were dimethylsulfoxide
(DMSO), dimethylformamide (DMF), dimethylacetamide, acetone, and
hexamethylphosphoramide (HMPA); the octanol/water partition coefficients for
these test substances form an ordered sequence that increased 40-fold from
DMSO to HMPA. AP's were recorded from desheathed frog sciatic nerves using
the sucrose-gap technique; test solutes were added to Ringer's solution and
applied externally to the nerve. ED50's for the solutes could be predicted
as a function of the molar volume (dV/dn), polarity (P), and the hydrogen
bond acceptor basicity (beta). Voltage-clamp experiments employing the
vaseline-gap technique on single muscle fibers showed that each solute
reduced Na+ current with little change in their kinetics at all voltages
studied. Experiments using DMSO or DMF showed that Na+ channel block alone
is insufficient to explain the respective ED50 values of AP block.
Experiments conducted using a chloride transport-sensitive membrane fluidity
assay, using rat pancreas secretory granules, suggested that each of the
solutes act to increase membrane fluidity at doses below and above ED50
values. Light microscopic observations of fixed thick sections of whole
nerves previously exposed to DMSO or DMF show structural changes; however,
ED50 values cannot be simply explained by osmotic alterations of nerve
structure. ED50's are likely to be produced by a combination of effects
including osmotically induced nerve structural changes, ion channel block,
and fluidity changes. The toxicity (lethal doses or toxic concentrations) of
each of these five solutes correlates well with the ED50 and could be
predicted as a function of dV/dn, P, and beta.
PMID: 8887446

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