Brick Tea Research Articles

Analysis of F, Al, Mn, Zn, Fe, Cu, Ca and Mg concentrations in brick teas from main producing areas in China

Analysis of F, Al, Mn, Zn, Fe, Cu, Ca and Mg concentrations in brick teas from main producing areas in China

The characteristics of dissolution of fluoride and aluminum from brick tea

Four experiments have been done on the influence of times of infusion, temperature, time and ratio of tea to water on the dissolving characteristics of fluoride and aluminum in brick tea. According to the results, the behaviors of F and Al which found their way into tea liquor were analyzed and the conclusions have been drawn: the dissolution of F and Al is not synchronous and after the elements find their way into tea liquor respectively, they will be reset to form complexes of F and Al.

Two Stable, Conducting Conformations of the Selectivity Filter in Shaker K+ Channels

We have examined the voltage dependence of external TEA block of Shaker K+ channels over a range of internal K+ concentrations from 2 to 135 mM. We found that the concentration dependence of external TEA block in low internal K+ solutions could not be described by a single TEA binding affinity. The deviation from a single TEA binding isotherm was increased at more depolarized membrane voltages. The data were well described by a two-component binding scheme representing two, relatively stable populations of conducting channels that differ in their affinity for external TEA. The relative proportion of these two populations was not much affected by membrane voltage but did depend on the internal K+ concentration. Low internal K+ promoted an increase in the fraction of channels with a low TEA affinity. The voltage dependence of the apparent high-affinity TEA binding constant depended on the internal K+ concentration, becoming almost voltage independent in 5 mM. The K+ sensitivity of these low- and high-affinity TEA states suggests that they may represent one- and two-ion occupancy states of the selectivity filter, consistent with recent crystallographic results from the bacterial KcsA K+ channel. We therefore analyzed these data in terms of such a model and found a large (almost 14-fold) difference between the intrinsic TEA affinity of the one-ion and two-ion modes. According to this analysis, the single ion in the one-ion mode (at 0 mV) prefers the inner end of the selectivity filter twofold more than the outer end. This distribution does not change with internal K+. The two ions in the two-ion mode prefer to occupy the inner end of the selectivity filter at low K+, but high internal K+ promotes increased occupancy of the outer sites. Our analysis further suggests that the four K+ sites in the selectivity filter are spaced between 20 and 25% of the membrane electric field.

External TEA block of shaker K+ channels is coupled to the movement of K+ ions within the selectivity filter.

Recent molecular dynamic simulations and electrostatic calculations suggested that the external TEA binding site in K+ channels is outside the membrane electric field. However, it has been known for some time that external TEA block of Shaker K+ channels is voltage dependent. To reconcile these two results, we reexamined the voltage dependence of block of Shaker K+ channels by external TEA. We found that the voltage dependence of TEA block all but disappeared in solutions in which K+ ions were replaced by Rb+. These and other results with various concentrations of internal K+ and Rb+ ions suggest that the external TEA binding site is not within the membrane electric field and that the voltage dependence of TEA block in K+ solutions arises through a coupling with the movement of K+ ions through part of the membrane electric field. Our results suggest that external TEA block is coupled to two opposing voltage-dependent movements of K+ ions in the pore: (a) an inward shift of the average position of ions in the selectivity filter equivalent to a single ion moving ∼37% into the pore from the external surface; and (b) a movement of internal K+ ions into a vestibule binding site located ∼13% into the membrane electric field measured from the internal surface. The minimal voltage dependence of external TEA block in Rb+ solutions results from a minimal occupancy of the vestibule site by Rb+ ions and because the energy profile of the selectivity filter favors a more inward distribution of Rb+ occupancy.

Fluoride and aluminium concentrations of tea plants and tea products from Sichuan Province, PR China

Some Tibetans in Sichuan Province in southwestern China have been suffering from fluorosis, due to drinking and eating tea with high fluoride (F) and aluminium (Al) contents. Tea plants, soils of tea plantations and tea products from Yaan, Gaoxian and Yibin Cities in Sichuan Province were investigated to evaluate the factors affecting F and Al contents in tea products. The F and Al concentrations of four commercial brands of brick teas were significantly higher than those of 11 brands of green teas. Chemical analysis indicated that total and available F and Al concentrations in tea plantation soils in Yaan and Gaoxian were within the normal range compared with acid soils in South China and tea soils in Fujian Province. Edaphic conditions did not contribute to the high F and Al concentrations in brick tea. Analysis of raw materials of brick tea indicated that old leaves were the major contributors to the high F and Al contents contained in brick tea. There were also great variations among different tea varieties in accumulating F and Al, and concentrations of F and Al in tea variety of Qianmei 303 were about 2–3-fold higher than the other three varieties. Selection of appropriate varieties would be important to lower F and Al contents in tea products.

Prevention and control of brick-tea type fluorosis—a 3-year observation in Dangxiong, Tibet

To evaluate the effects of preventing and controlling brick-tea type fluorosis, we carried out a 3-year field observation and assayed the total daily fluoride intake, urinary and serum fluoride level, and dental fluorosis prevalence and index in a boarding school in Dangxiong, Tibet, in students aged 8–15. We replaced the traditional brick tea with low-fluoride brick tea (LFBT). Reduction in the traditional brick-tea consumption decreased the total daily fluoride intake among the children, which still remained within the level of chronic intoxication but at a safe level. The study suggests that the LFBT is effective in the prevention and control of endemics of brick tea type fluorosis, although further improvement of the LFBT is required.

Brick tea fluoride as a main source of adult fluorosis

An epidemiological survey was conducted in Naqu County, Tibet in September 2001 to investigate the manifestations of fluorosis in adults caused by the habitual consumption of brick tea. Profiles were obtained for the total daily fluoride intake, environmental fluoride levels and average urinary fluoride concentration, and a physical examination and a skeletal radiographic study were conducted. One hundred and eleven 30–78-year-old adults were enrolled. It was found that the fluoride level of water sources in Naqu County was 0.10±0.03 mg/l; no evidence of fluoride air pollution was found, but the brick tea water processed foods—zamba and buttered tea—had fluoride contents of 4.52±0.74 mg/kg and 3.21±0.65 mg/l, respectively. The adult daily fluoride intake reached 12 mg, of which 99% originated from the brick tea-containing foods. The positive rate of clinical symptoms by physical examination was 89%; furthermore, 42 of the 111 subjects were diagnosed by X-ray. The positive examination rate was 83%. Although the osteosclerosis-type skeletal fluorosis (overall increased bone matrix density) affected 74%, arthropathy and arthritis affected a significant number of the patients, resulting in functional disability. The results suggest that this brick tea-type fluorosis had even more severe adverse effects on human health compared with both the water-type and coal combustion-type fluorosis that occurred in other areas of China.

Aluminium and fluoride contents of tea, with emphasis on brick tea and their health implications

Tea plant takes up a large quantity of aluminium (Al) and fluoride (F) from acidic soils. It has been known that fluorosis can be developed for people who consume a large quantity of tea made from brick tea, a low quality tea consisting mainly of old tea leaves in China. In addition, it has been claimed that Alzheimer's disease (AD) is linked with the Al content in the human brain. Therefore, the high Al content in tea, especially brick tea is also a concern. This article reviews the basis background on tea including classification, growth conditions, types of tea leaves and their production, and processing of tea. Special emphasis is made on the transfer of Al and F from soil to tea plant and then to tea liquor. Health implications of drinking a large quantity of tea liquor especially those made from brick tea are discussed. Recommendations are suggested to reduce the uptake of these two elements by tea plant, and lower their contents in tea products.

Anomalous Effects of External TEA on Permeation and Gating of the A-Type Potassium Current in H. aspersa Neuronal Somata

The model proposed for external TEA block of Shaker K+ channels predicts a proportional relationship between TEA sensitivity and calculated electrical distance derived from measurements of voltage dependence of TEA block. In the present study, we examined this relationship for the A-type K+ current (IA) of Helix aspersa in neuronal somata using the whole-cell patch-clamp technique. External TEA inhibited IA with strong voltage dependence, such that the TEA dissociation constant was increased at depolarized test potentials. The half-inhibition constant (V0.5) for TEA block was approximately 21 mM at 0 mV, and V0.5 increased to approximately 67 mM at 50 mV. The calculated electrical distance for TEA block suggested that TEA traversed 65% of the way into the membrane electrical field. TEA also caused significant shifts in the voltage-dependence of A-type K+ channel gating. For example, at TEA concentrations below that required to fully suppress delayed outward currents, TEA caused depolarizing shifts in the voltage-dependence of A-type channel activation, steady-state inactivation, time for removal of inactivation, and slowed channel activation kinetics. Taken together, these observations suggest that TEA biased the local field potential near voltage-sensing domains of A-type K+ channels, causing the transmembrane electrical field to be relatively hyperpolarized in the presence of TEA. In summary, the calculated electrical distance of TEA block of A-type K+ channels in H. aspersa neurons is unprecedented among other K+ channels. This raises concerns about the conventional interpretation of this value. Furthermore, the voltage-dependent properties of IA are modified by TEA at concentrations previously used to isolate delayed rectifier potassium channels (IKDR) selectively. This lack of specificity has important implications for recent, as well as future studies of IA in H. aspersa and possibly other snail neurons.

PCDD/PCDF, chlorinated pesticides and PAH in Chinese teas

Four samples of Chinese tea (two green teas, and two brick teas) were analyzed for their concentrations of polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans (PCDD/PCDF), chlorinated pesticides and PAH. The infusions prepared from these teas were also analyzed for PCDD/PCDF. The levels of DDT and its metabolites in tea leaves were within the safety limit of 0.2 mg/kg. Rather high levels of total PAH were obtained in brick tea (1048–1162 mg/kg), when compared with green tea (497–517 mg/kg). In terms of PCDD/PCDF, the concentrations of green tea and brick tea differed by a factor of 16, while the concentrations of all infusions were within a factor of 2. The dioxin concentrations in green tea leaves can be explained through uptake of atmospheric PCDD/PCDF. The higher concentrations in the brick tea leaves are due the longer exposure time, and to certain extent, the use of old leaves, branches and roots when making the tea, and additional components such as soil particulates through contamination. Certain Chinese populations drinking a large amount of brick tea (>3 l per day) indicated that individuals of these populations consume more tea than Europeans or North Americans result in a comparably higher intake of PCDD/PCDF. Tea consumption can attribute to up to 10% of the TDI recommended by WHO (only PCDD/PCDF considered, no PCB analyzed).

Processing procedures of brick tea and their influence on fluorine content

China is the only country that produces brick tea, and more than 90% of the brick tea is consumed in the western minority nationality regions of China. The high fluorine content of brick tea is possibly associated with the special processing procedures, but no investigation has been conducted in this field. To explore the characteristic features of brick tea manufacturing and the alterations in fluorine content during the processing procedures, we performed a field survey involving two brick tea factories and the nearby tea plantations. For the fluorine contents of the initial, intermediate and final processing products, altogether eight types of specimens were collected and determined by using the ion-selective electrode standard curve technique. It was found that the raw material tea leaf for brick tea processing was old, coarse and not the tender delicate tea leaf used for ordinary green or black tea processing. For the fluorine content of the raw material tea leaf, the intermediate and the final products showed that the fresh raw leaf contained a fluorine content as high as 489.31–512.68 mg/kg. During one fermentation-like processing procedure, the fluorine content rose by 4.67% and 1.88% in the specimens from the two factories, respectively, which revealed no statistical significance ( P>0.5). These results suggest that the high fluorine content in brick tea might be due to the high content in the raw material and not related with the processing procedures.

Prevention of brick tea fluorosis in rats with low-fluoride brick tea on laboratory observation

To test whether low-fluoride brick tea can prevent the occurrence of fluorosis, rats had access only to a specially prepared low-fluoride brick tea for 1 year. The daily fluoride intake, fluoride metabolism, tissue distribution and development of tooth fluorosis were observed at 4-monthly intervals, at the end of months 4, 8 and 12, respectively. Rats drinking ordinary brick tea (F − 503.5 mg/kg) served as control. The daily intake of fluoride in the ordinary brick tea group was 0.3 mg, and this group developed dental fluorosis characterized as brown and white horizontal marks at the end of month 8, and white chalky dental fluorosis developed at the end of month 12. The total incidence was 75%. In contrast, the daily fluoride intake of the low-fluoride brick tea (F − 210 mg/kg) group was 0.19 mg, and this group did not develop any signs of dental fluorosis. Fluoride distribution was mainly retained in the bone tissue, and about half of the absorbed fluoride was excreted via urine and feces. The results suggest that this low-fluoride brick tea did not induce fluorosis in rats and can be used as an effective control measure for humans.

Affinity and Location of an Internal K+ Ion Binding Site in Shaker K Channels

We have examined the interaction between TEA and K+ ions in the pore of Shaker potassium channels. We found that the ability of external TEA to antagonize block of Shaker channels by internal TEA depended on internal K+ ions. In contrast, this antagonism was independent of external K+ concentrations between 0.2 and 40 mM. The external TEA antagonism of internal TEA block increased linearly with the concentration of internal K+ ions. In addition, block by external TEA was significantly enhanced by increases in the internal K+ concentration. These results suggested that external TEA ions do not directly antagonize internal TEA, but rather promote increased occupancy of an internal K+ site by inhibiting the emptying of that site to the external side of the pore. We found this mechanism to be quantitatively consistent with the results and revealed an intrinsic affinity of the site for K+ ions near 65 mM located approximately 7% into the membrane electric field from the internal end of the pore. We also found that the voltage dependence of block by internal TEA was influenced by internal K+ ions. The TEA site (at 0 internal K+) appeared to sense approximately 5% of the field from the internal end of the pore (essentially colocalized with the internal K+ site). These results lead to a refined picture of the number and location of ion binding sites at the inner end of the pore in Shaker K channels.

Differential Expression of KCNQ2 Splice Variants: Implications to M Current Function during Neuronal Development

The KCNQ family of K(+) channels has been implicated in several cardiac and neurological disease pathologies. KCNQ2 (Q2) is a brain-derived gene, which in association with KCNQ3 (Q3) has been shown to provide a molecular basis for the neuronal M current. We have cloned a long (Q2L) and a short (Q2S) splice variant of the human KCNQ2 gene; these variants differ in their C-terminal tail. Northern blot analysis reveals that Q2L is preferentially expressed in differentiated neurons, whereas the Q2S transcript is prominent in fetal brain, undifferentiated neuroblastoma cells, and brain tumors. Q2L, transfected into mammalian cells, produces a slowly activating, noninactivating voltage-gated K(+) current that is blocked potently by tetraethylammonium (TEA; IC(50), 0.14 mm). Q2S on the other hand produces no measurable potassium currents. Cotransfection of Q2S with either Q2L, Q3, or Q2L/Q3 heteromultimers results in attenuation of K(+) current, the suppression being most profound for Q3. Inclusion of Q2S in the heteromultimer also positively shifts the voltage dependence of current activation and alters affinity for the TEA block, suggesting that under these conditions, some Q2S subunits incorporate into functional channels on the plasma membrane. In view of the crucial role of M currents in modulating neuronal excitability, our findings provide important insight into the functional consequences of differential expression of KCNQ2 splice variants: dampened potassium conductances in the developing brain could shape firing repertoires to provide cues for proliferation rather than differentiation.

Varied Ecological Environment and Fluorosis in Tibetan Children in the Nature Reserve of Mount Qomolangma

To determine the extent of brick tea consumption fluorosis in children living at elevations of 2000 and 4300 m, 519 children aged 8–15 years living in Xiege'er Town at 4300 m and Zhangmu Town at 2000 m were examined for dental fluorosis, their urinary fluoride concentration was determined, their dietary structure investigated, and the fluoride concentrations of various foods, freshwaters, soils, and fuels determined. Fifteen Tibetan families living in these two areas of the nature reserve of Mount Qomolangma were studied according to UNEP, FAO, and WHO guidelines for the study of dietary intake of chemical contaminants, Horowitz's classification and examination of dental fluorosis, and Dean's dental fluorosis index. The results demonstrated that dental fluorosis in Tibetan children living at an elevation of 2000 m was significantly lower than that of children at 4300 m (P<0.01). Higher elevation can worsen the extent of fluorosis, leading to retention of fluoride in tissues as a result of hypoxia, but fluorosis can also be associated with the deterioration of the ecological environment at high elevation and a low-level economy. Beverages and foods mixed with brick tea water are responsible for the dental fluorosis in the children.

ACCUMULATION OF FLUORIDE AND ALUMINIUM RELATED TO DIFFERENT VARIETIES OF TEA PLANT

Samples of young shoot, mature leaf, twig, root, and litter were taken from four recently bred varieties Zhe-nong 113, Zhe-nong 121, Zi-sun, and Bi-feng grown at two tea plantations located at Zhejiang and Jiangsu Provinces. The results showed that the concentrations of F and Al in tea plants were significantly different among the four varieties. It is therefore possible that F and Al concentrations in tea products can be reduced through variety selection. The results also revealed that old leaves would be the major contribution to the high levels of F and Al in brick tea since it is produced mainly for old leaves. Therefore, in order to eliminate the hazard of over-exposure to F and Al derived from tea, younger shoot should be used for making tea products while mature leaves should be avoided.

Changes in Ca, Cu, Fe, Mg, and Zn contents in mouse brain tissues after prolonged oral ingestion of brick tea liquor containing a high level of Al.

A study was conducted to analyze the regional distribution of Ca, Cu, Fe, Mg, and Zn contents in brain tissues after animals were given liquor of brick tea that contained a high Al content. In 25 normal adult male mice given either water or 0.9% NaCl for 1 mo or 2 mo, the metal concentrations in the serum, liver, frontal cortex, hippocampus, cerebellum, and brain stem were comparable (p > 0.05). When the drinking water was replaced by a 1% brick tea liquor, which contained a high Al content, serum Al concentration was increased significantly 1 mo after the onset of the experiment and remained high at the end of the second month. The level of Al was also elevated in both the cortex and hippocampus at 1 mo after replacing tea for drinking water. In addition to Al, there were a significant increase in hippocampal Zn and a decrease in Cu contents. There was no change in tissue Mg or Fe contents, but there was a significant increase in Ca content in every brain region studied. It was suggested that the increase in Ca might be the result of the effect of other components in tea. Unlike the brain, there was no change in the concentration of any of the metals, including Al, in the liver, which further demonstrated that the changes observed in the brain was specific. The results of the present study confirmed that Al, when given orally in the form of tea, could be absorbed into the bloodstream. The absorbed Al could accumulate in selected brain regions. The presence of Al might also change the tissue content of endogenous trace metals.

Cloning and functional expression of rKCNQ2 K + channel from rat brain

By homologue cloning, we have isolated a cDNA encoding a voltage-gated K + channel, rKCNQ2, from a rat brain cDNA library using RACE. The open reading frame of the translated protein comprises 852 amino acids with 6 transmembrane segments and a pore motif between S5 and S6. rKCNQ2 shares 96% amino acid identity with human KCNQ2 in which mutations cause a form of epilepsy known as benign familial neonatal convulsions (BFNC). Northern blotting with a rKCNQ2-specific probe revealed a robust single band of 8.6-kb transcript expressed in brain not in other tissues. Functional expression of rKCNQ2 in an HEK 293 cell line by whole-cell current recording and in Xenopus oocytes by two-electrode voltage clamp showed outward K + selective currents that displayed delayed rectifier-type kinetics. The G– V curve, fitted with a Boltzmann function, showed voltage dependence of activation with a threshold of activation approximately −60 mV. The rKCNQ2 currents were sensitive to TEA block with a Ki of 0.1 mM. In addition, rKCNQ2 currents were down-regulated upon exposure of cells to either a broad-spectrum tyrosine kinase inhibitor genistein or a Src-like tyrosine kinase inhibitor herbimycin A. Our findings add a rodent member to the KCNQ channel subfamily, providing new information of the channel modulation, and will facilitate generation of rodent models of epilepsy.

Environmental Fluoride Content in Tibet

As the first report of the environmental fluoride level in Tibet, the determination by the fluoride ion-selective electrode method of fluoride concentration in water, soil, fuel, grains, food, vegetables, and tea was made for the Tibetan people living on various land types with various ecological characteristics. The average level of fluoride concentration in water in Tibet was 0.06 mg/L; the level of dissolved fluoride in the soil was 0.45 mg/kg; the fluoride concentration in main fuels was 0.10 mg/kg; the levels in main grains, food, and vegetables were 0.06–0.33 mg/kg; those in buttered tea and Zanba mixed with brick tea were 3.09–3.61 mg/kg; and water-dissolved fluoride concentrations in the brick tea produced in Sichuan Province and Yunan Province were 533.89–617.32 mg/kg. Tibet is the prevailing area of brick tea fluorosis.

Ion-Ion interactions at the selectivity filter. Evidence from K(+)-dependent modulation of tetraethylammonium efficacy in Kv2.1 potassium channels.

In the Kv2.1 potassium channel, binding of K(+) to a high-affinity site associated with the selectivity filter modulates channel sensitivity to external TEA. In channels carrying Na(+) current, K(+) interacts with the TEA modulation site at concentrations </=30 microM. In this paper, we further characterized the TEA modulation site and examined how varying K(+) occupancy of the pore influenced the interaction of K(+) with this site. In the presence of high internal and external [K(+)], TEA blocked 100% of current with an IC(50) of 1.9 +/- 0.2 mM. In the absence of a substitute permeating ion, such as Na(+), reducing access of K(+) to the pore resulted in a reduction of TEA efficacy, but produced little or no change in TEA potency (under conditions in which maximal block by TEA was just 32%, the IC(50) for block was 2.0 +/- 0.6 mM). The all-or-none nature of TEA block (channels were either completely sensitive or completely insensitive), indicated that one selectivity filter binding site must be occupied for TEA sensitivity, and that one selectivity filter binding site is not involved in modulating TEA sensitivity. At three different levels of K(+) occupancy, achieved by manipulating access of internal K(+) to the pore, elevation of external [K(+)] shifted channels from a TEA-insensitive to -sensitive state with an EC(50) of approximately 10 mM. Combined with previous results, these data demonstrate that the TEA modulation site has a high affinity for K(+) when only one K(+) is in the pore and a low affinity for K(+) when the pore is already occupied by K(+). These results indicate that ion-ion interactions occur at the selectivity filter. These results also suggest that the selectivity filter is the site of at least one low affinity modulatory effect of external K(+), and that the selectivity filter K(+) binding sites are not functionally interchangeable.