De schildklierfunctie bij patiënten met seleniumdeficiëntie vertoont een hoge vrije T4 tot T3-ratio

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Lid geworden op: 08 nov 2014, 17:53

De schildklierfunctie bij patiënten met seleniumdeficiëntie vertoont een hoge vrije T4 tot T3-ratio

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De schildklierfunctie bij patiënten met seleniumdeficiëntie vertoont een hoge vrije T4 tot T3-ratio

Ryohei Kobayashi / Mari Hasegawa / Chiharu Kawaguchi / Naoko Ishikawa
. allen > Afdeling Kindergeneeskunde, Todaiji Ryoiku Hospital for Children, Nara, Japan


Abstract
Selenium, een van de essentiële sporenelementen, is in vivo aanwezig in de vorm van selenoproteïnen.
Iodothyronine dejodinase, een selenoproteïne, is betrokken bij de activering en inactivering van schildklierhormoon.

Daarom kunnen patiënten met seleniumtekort veranderingen in de schildklierhormoonspiegels vertonen als gevolg van remming van de omzetting van T4 naar T3; deze veronderstelling staat echter nog ter discussie.

In de huidige studie hebben we retrospectief de schildklierfunctie onderzocht bij 22 patiënten met seleniumtekort. De niveaus van het schildklierstimulerend hormoon (TSH) en vrij T4 (FT4) waren verhoogd bij respectievelijk 3 (14%) en 5 (23%) patiënten, en de niveaus van vrij T3 (FT3) waren verlaagd bij 6 (27%) patiënten.

De FT4 / FT3-ratio was significant hoger bij patiënten met seleniumtekort dan in de controlegroep. Er bleek een positieve correlatie te bestaan tussen de verlaagde seleniumspiegels en de FT4 / FT3-ratio, wat erop duidt dat patiënten met een ernstig seleniumtekort ook abnormale schildklierhormoonspiegels vertoonden.

Bovendien, toen selenium werd aangevuld bij zeven patiënten met abnormale schildklierhormoonspiegels, werden de TSH-, FT4- en FT4 / FT3-ratio significant verlaagd en de FT3-spiegel verhoogd.

Gezamenlijk zouden patiënten met seleniumtekort de kenmerken kunnen vertonen van niet alleen een lage FT3 maar ook een hoge FT4 en FT4 / FT3 ratio. wanneer selenium werd aangevuld bij zeven patiënten met abnormale schildklierhormoonspiegels, werden de TSH-, FT4- en FT4 / FT3-ratio significant verlaagd en de FT3-spiegel verhoogd

Table 1A
Characteristics of clinical and laboratory findings in selenium-deficient patients with abnormal thyroid hormone levels

Table 1B.
Characteristics of clinical and laboratory findings in selenium-deficient patients with normal thyroid hormone levels Case Age (yr.) Sex Underlying disease Diet

Fig. 1.
Relationship between decreased selenium concentration and free T4 (FT4)/ free T3 (FT3) ratio in patients with selenium deficiency. The relationship between the severity of selenium deficiency and the FT4/FT3 ratio was analyzed. The severity of selenium deficiency was assessed by comparing the decrease rate with the lower limits of the standard serum selenium levels for each age group. The decrease rate was calculated as follows: (1 − serum selenium level/lower limit of the standard serum selenium level for that age group) × 100 (%). Spearman correlation coefficient was used to evaluate the relationship, and p < 0.05 was defined as statistically significant.

Fig. 2.
Comparison of thyroid hormone levels between the abnormal thyroid group in selenium-deficient patients and normal controls. Serum thyroid stimulating hormone (TSH), free T4 (FT4), and free T3 (FT3) levels as well as FT4/FT3 ratio of the abnormal thyroid group in patients with selenium deficiency were compared with those of the control group. The Mann-Whitney U-test was used for between-group comparisons. The median values are depicted within the boxes. The boxes end at the 25th and 75th percentiles, and the whiskers extend to the farthest points. Statistically significant differences were defined as p < 0.05. N.S., not significant.

Fig. 3.
Changes in serum selenium and thyroid hormone levels following selenium supplementation in abnormal thyroid group of selenium-deficient patients. (A): Selenium levels were compared before and after selenium supplementation. (B): Serum thyroid stimulating hormone (TSH), free T4 (FT4), and free T3 (FT3) levels, and FT4/FT3 ratio were compared before and after selenium supplementation. The Wilcoxon rank-sum test was used to compare the changes. Statistically significant differences are defined as p < 0.05. Pre, Presupplementation; Post, Postsupplementation.



Een klein gedeelte uit het artikel;
In the present study, the increase in TSH was mild (5–9 µU/mL) despite low FT3 levels. T4 is synthesized in the thyroid, whereas bulk daily T3 production occurs in various extrathyroidal tissues via 5’ deiodination catalyzed by DIO1 and DIO2 (9). In contrast, certain studies have reported that the selenium concentration and DIO activity in selenium-deficient patients differ across various tissues (9, 27). Selenium is retained in the brain, pituitary gland, and thyroid even when selenium intake is insufficient, whereas selenium content in plasma, liver, and skeletal muscle rapidly decreases, that is, in case of selenium deficiency in blood, the selenium concentration and DIO activity is maintained in the cerebrum, pituitary gland, and thyroid gland.

Therefore, since the conversion from T4 to T3 in the pituitary gland was maintained, a negative feedback effect was diminished, presumably resulting in the mild increase of TSH despite the low FT3 level. Thus, individual differences may occur between selenium intake/serum concentration and the appearance of selenium deficiency-associated symptoms, including abnormal thyroid hormone status. Differences in the absorption efficiency of selenium and the degree of DIO activity in each organ may also be influenced.

The limitations of this study are as follows:
(i)the small number of cases,
(ii) standard values of thyroid function differed between the two participating facilities,
(iii) patients with epilepsy were included in both groups, and it could be denied that antiepileptic drugs might have affected thyroid function,
and (iv) cases without intake of iodine and selenium may affect thyroid function.

To solve the problem of standard values, age and facility were matched between both groups, as described in the Methods.
As selenium was supplemented and iodine was not, and no switch in antiepileptic drugs was observed, changes in the thyroid function due to increased selenium concentrations alone could be examined.
As only few studies have assessed the effect of selenium supplementation on thyroid function in Japanese population, the present study could prove valuable. Increasing the number of cases and adding iodine assessments could provide a more detailed and accurate assessment of the selenium effects on thyroid function


Conclusion
Some cases of selenium deficiency could exhibit abnormal thyroid hormone levels, which present with the characteristics of high FT4 and high FT4/FT3 ratio as well as low FT3 (which is already a diagnostic criterion).
Moreover, we need to consider selenium deficiency when encountering unique thyroid hormone status such as those in clinical practice.

Conflict of interests: The authors declare no conflicts of interest.


Volledig artikel:
https://www.jstage.jst.go.jp/article/cp ... f/-char/en


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