Jennifer Luke
School of Biological Sciences,
University of Surrey, Guildford, UK
Department of Obstetrics and Gynaecology, The Royal London
Hospital
Original Paper
Caries Res 2991;35:125-128
Key Words
Calcium, Distribution, Fluoride, Human pineal gland, Hydroxyapatite, Pineal
concretions
Abstract
The purpose was to discover whether fluoride (F) accumulates in the aged human
pineal gland. The aims were to determine (a) F-concentrations of the pineal
gland (wet), corresponding muscle (wet) and bone (ash); (b)
calcium-concentration of the pineal. Pineal, muscle and bone were dissected from
11 aged cadavers and assayed for F using the HMDS-facilitated diffusion, F-ionspecific
electrode method. Pineal calcium was determined using atomic absorption
spectroscopy. Pineal and muscle contained 297±257 and 0.5±0.4 mg F/kg wet
weight, respectively; bone contained 2,037±1,095 mg F/kg ash weight. The pineal
contained 16,000±11,070 mg Ca/kg wet weight. There was a positive correlation
between pineal F and pineal Ca (r = 0.73, p<0.02) but no correlation between
pineal F and bone F. By old age, the pineal gland has readily accumulated F and
its F/Ca ratio is higher than bone.
The pineal gland is a small organ situated near the centre of the brain. It is
intimately related to the third ventricle. It is composed of pinealocytes and
neuroglial cells amongst which ramifies a rich network of capillaries and
postganglionic nerve fibres. The pineal gland is a mineralizing tissue. Its
calcified concretions range from a few micrometres to several millimetres in
diameter. The larger ones are identifiable on skull X-rays, cranial CT and MRI
scans. The concretions are composed of hydroxyapatite (HA) [Angervall et al.,
1958; Earle, 1965; Mabie and Wallace, 1974; Galliani et al., 1990; Bocchi and
Valdre, 1993] whose chemical composition, morphology, and unit cell dimensions
are similar to HA in bone and teeth [Mabie and Wallace, 1974; Bocchi and Valdre,
1993]. The pineal (calcified and uncalcified) has a high trace element content
(zinc, iron, manganese, magnesium, strontium and copper) in humans [Krstic,
1976; Michotte et al., 1977] and in rats [Humbert and Pévet, 1991, 1996].
Michotte et al. [1977] suggested that, within the pineal, there are areas which
are heavily loaded with calcium and which attract trace elements, even though
these calcium-rich areas are not yet identifiable as concretions. Calcium is
distributed throughout the pinealocytes: in the mitochondria, Golgi apparatus,
cytoplasm, and nucleus [Krstic, 1976, 1995; Welsh, 1984; Pizarro et al., 1989,
Lewczuk et al., 1994].
Fluoride does not accumulate in brain. Of all tissues, brain has the lowest
fluoride concentration [Jenkins, 1991; Whitford, 1996; Ekstrand, 1996]. It is
generally agreed that the blood-brain barrier restricts the passage of fluoride
into the central nervous system. The human pineal gland is outside the
blood-brain barrier [Arendt, 1995]. It is one of a few unique regions in the
brain (all midline structures bordering the third and fourth ventricles) where
the blood-brain barrier is weak. Cells in these regions require direct and
unimpeded contact with blood [Rapoport, 1976]. Therefore, pinealocytes have free
access to fluoride in the bloodstream. This fact, coupled with the presence of
HA, suggest that the pineal gland may sequester fluoride from the bloodstream.
The purpose of this study was to discover whether fluoride accumulates in the
aged pineal gland. Its objectives were to determine (a) the fluoride
concentrations of the pineal gland (wet), corresponding muscle (wet) and bone
(ash); (b) the pineal concentrations of calcium and HA.
Materials and Methods
The pineal glands and corresponding bone and muscle samples were dissected from
I I aged cadavers (7 females and 4 males) in the Anatomy Department, UCL. The
mean age was 82 years (range 70-100).
Preparation of the Samples
The pineal glands were blotted dry with tissue paper, weighed to the nearest
milligram, homogenized in I ml double-distilled water using an agate pestle and
mortar and sonicated for 10 min. Each pineal was divided into two portions that
were analysed separately. Muscle samples weighing about 100 mg were treated
likewise. Bone samples were cleaned of any adherent soft tissue with a razor
blade, dried overnight at 110'C in an oven, and ashed (in porcelain crucibles
with no fixatives) at 550-600°C in a muffle furnace for 8 h. Bone ash was
pulverized into a fine powder using an agate pestle and mortar. Bone solutions
were made by dissolving known weights of bone ash in 3 ml 2 M HC104.
Bone solutions were analysed for fluoride in replicates of six and the mean
fluoride concentrations in bone were calculated.
Determination of the Fluoride Concentrations
The homogenized pineal, homogenized muscle and bone solutions were assayed for
fluoride using the HMDS-facilitated diffusion, F-ion-specific electrode method
originally described by Taves [19681 and modified by Whitford and Reynolds
[1979]. The protocol was further modified for use with the pineal glands. The
concentration and volume of the base trap were increased to 0.5 M NaOH
and 100 µl, respectively; the strength of the acetate buffer was increased to 50
µl 2 M acetic acid and the volume of the analysed solution was adjusted
to 150 µl with double-distilled water. Diffusion time for pineal and muscle was
3 days; for bone 18 h.
Standards: pineal: 1,000, 2,500 and 5,000 nmol F; muscle: 5, 50 and 500 nmol F;
bone: 10, 50, 100 and 500 nmol F.
Determination of the Concentration of Total Calcium in the Human Pineal Gland
The acid digests, which remained in the Petri dishes following the separation of
fluoride from the pineal glands, were wet-acid ashed to decompose the organic
component. The acid digests were placed in clean glass tubes and I ml conc. HN03
was added. The tubes were heated slowly to 50°C and maintained at 50°C for 30
min in a fume cupboard. The procedure was repeated using I ml 60% HC104.
Two millilitre of double-distilled water was added to each tube and the volumes
were measured. Calcium concentration was determined using atomic absorption
spectroscopy.
Statistical Methods
Results were expressed as means ± SD. Differences between the groups were tested
for significance using unpaired Student's t-test. Differences were regarded as
statistically significant when p<0.05.
Pearson's correlation coefficient was used to test association between pineal
fluoride and pineal calcium; and pineal fluoride and bone fluoride.
Fig. 1. The relationship between the calcium and fluoride
contents of ten aged human pineal glands.
Results
The aged pineal gland weighed 112±52 mg (56-198 mg). Pineal had a significantly
higher F concentration than muscle: 297 ± 257 (14-875) vs. 0.5 ± 0.4 (0.2-1.5)
mg F/kg wet weight (p<0.001). Bone contained 2,037± 1,095 (838-3,711) mg F/kg
ash weight. The mean coefficient of variation between the replicates of F
contents of bone solutions was 2.5 ± 1. 1 %. There was no correlation between
pineal F and bone F. The pineal gland contained 16,000±11,070 (4,600-37,250) mg
Ca/kg wet weight. Pineal fluoride and pineal calcium were directly correlated: r
= 0.73, p < 0.02, n = 10, slope= 0.02 (fig. 1). Assuming stoichiometric HA, the
pineal contained an estimated 40,000 ± 27,700 mg HA/kg wet weight (11,600-93,200
mg HA/kg). The estimated F concentration of pineal HA was 9,000 ± 7,800 mg/kg
(650-21,800 mg/kg). Figure 2 shows that the F/calcium ratio was higher in pineal
HA than in corresponding bone HA.
Discussion
This study has added new knowledge on the fate and distribution of fluoride in
the body. It has shown for the first time that fluoride readily accumulates in
the human pineal gland although there was considerable inter-individual
variation (14-875 mg F/kg). By old age, the average pineal gland contains about
the same amount of fluoride as teeth (300 mg F/kg) since dentine and whole
enamel contain 300 and 100 mg F/kg, respectively [Newbrun, 1986]. Unlike brain
capillaries, pineal capillaries allow the free passage of fluoride through the
endothelium. If there had been a bloodbrain barrier in the pineal, it would have
prevented the passage of fluoride into the pinealocytes and the pineal fluoride
content would have been similar to or lower than muscle. This was obviously not
the case: the fluoride concentration of the pineal was significantly higher
(p<0.001) than muscle. The high fluoride levels in the pineal are presumably due
to the large surface area of the HA crystallites both intra- and extracellularly.
In addition, the pineal has a profuse blood flow and high capillary density;
pineal blood flow (4 ml/min/g) is second only to the kidney [Arendt, 19951.
The extent of pineal calcification also varied between individuals: ranging from
4,600 to 37,250 mg Ca/kg wet weight. One of the aged pineals had very little
precipitation. This supports the age independence of pineal calcification and
agrees with previous studies [Cooper, 1932; Arieti, 1954; Tapp and Huxley, 197
1; Hasegawa et aL, 1987; Galliani et al., 1990]. The estimated fluoride
concentration of pineal HA was 9,000 ± 7,800 mg/kg. The F/Ca ratio was higher in
pineal HA than in corresponding bone (fig. 2). The extremely high level of
substitution in the crystal structure of pineal HA by fluoride illustrates the
readiness with which fluoride replaces the hydroxyl ion in the HA crystal. By
old age, pineal HA has a higher fluoride content than other biological apatites.
Unlike pineal concentrations of magnesium, manganese, zinc and copper, which,
although very high, were generally within the limits found in bone and teeth [Michotte
et al., 1977].
Fig. 2. A comparison of the F/Ca ratio in aged pineal HA and
corresponding bone ash (µg F/100 µg calcium). Calcium content of bone determined
stoichiometrically.
There was no corTelation between pineal fluoride and bone fluoride. Therefore,
unlike bone, pineal fluoride concentrations are not indicators of long-term
fluoride exposure and body burden. Pineal fluoride, however, was significantly
correlated with pineal calcium.
The methodology used in this project was accurate because the F values obtained
for bone and muscle agreed with literature values. For example, the mean
fluoride concentration of bone from elderly subjects was 2,000 mg/kg ash weight
which agrees with previous studies using bone from subjects of a similar age [Ebie
et al., 1992; Charen et al., 1979; Zipkin et al., 1958]. In this study, muscle
contained 0.5 mg F/kg wet weight, a typical fluoride concentration for soft
tissue [WHO, 1984]. The pineal and bone were treated differently during sample
preparation (the pineal was wet-acid ashed, bone was dry ashed) which may
somewhat obscure a direct comparison of the fluoride contents of pineal HA and
bone. However, it is unlikely that there would be a significant analytical
error.
In conclusion, this study presented evidence that fluoride readily accumulates
in the aged pineal. Fluoride may also accumulate in a child's pineal because
significant amounts of calcification have been demonstrated in the pineals from
young children [Cooper, 1932; Wurtman, 1968; Kerényi and Sarkar, 1968; Tapp and
Huxley, 197 1; Doskocil, 1984]. In fact, calcification of the developing enamel
organs and the pineal gland occur concurrently. If fluoride does accumulate in
the child's pineal (this needs verification), the pinealocytes will be exposed
to relatively high local concentrations of fluoride. This could affect pineal
metabolism in much the same way that high local concentrations of fluoride in
the developing enamel organ affect ameloblast function. Research is presently
underway to discover whether fluoride affects pineal physiology during
childhood: specifically pineal synthesis of melatonin.
Acknowledgements
I acknowledge the Anatomy Deptartment, UCL, for providing the pineal glands;
Prof. Gary Whitford, Medical College of Georgia, USA, and Gordon Hartman,
University of Surrey, for their assistance with the fluoride analysis; Nicholas
Porter, The Royal Surrey County Hospital, Guildford, for help with the
determination of pineal-calcium concentrations. The Colt Foundation, The Heinz
and Anna Kroch Foundation and The New Moorgate Trust funded the research.
References
Copyright © 2001 S. Karger AG, Basel
http://www.icnr.com/articles/fluoride-deposition.html