Effect of oral zinc administration on prolactin and thymulin circulating levels in patients with chronic renal failure

Existing knowledge on Zn status biomarkers (1963-2021) with a particular focus on FADS1 and FADS2 diagnostic performance and recommendations for further research

The role of Zn in human health was discovered 60 years ago, and despite remarkable research efforts, a sufficiently sensitive and specific biomarker of Zn status is still lacking. Plasma/serum Zn, currently the best available and most accepted population Zn status indicator, responds well to severe Zn deficiency, yet, mild to moderate Zn deficiency states usually remain unrecognized. Identifying early-stage Zn deficiency requires additional robust markers of Zn status. This paper discusses the sensitivity, specificity, and responsiveness of plasma Zn concentrations to Zn interventions. It describes the biochemical and dietary basis for the causal association between Zn and fatty acid desaturases activity, FADS1 and FADS2, based on data collected through studies performed in animals and/or humans. The influence of potential confounders and covariates on the observed relationships is considered. Additional potential Zn biomarkers are discussed and suggestions for further research in this area are provided.

Prolactin and Other Pituitary Disorders in Kidney Disease

Prolactin levels are increased in chronic kidney disease (CKD) as a result of reduced clearance and increased secretion. Hyperprolactinemia manifests as galactorrhea and hypogonadism. Treatment of hyperprolactinemia should focus on improving bothersome galactorrhea or hypogonadism by using dopamine agonists and/or replacement of sex hormone(s). Changes in the hypothalamic-pituitary-adrenal axis in CKD are characterized by increases in adrenocorticotropic hormone (ACTH) and cortisol levels, largely preserved circadian rhythms of ACTH and cortisol, and a normal response of cortisol to ACTH, metyrapone, and insulin-induced hypoglycemia. However, the hypothalamic-pituitary-adrenal axis is less inhibited by 1 mg dexamethasone but retains normal suppression by higher-dose dexamethasone. Diagnosis of adrenal insufficiency in CKD patients, as in normal subjects, usually is made by finding a subnormal cortisol response to ACTH. The mainstay of treatment of adrenal insufficiency is to replace glucocorticoid hormone. Cushing's disease in CKD is difficult to diagnose and relies on the dexamethasone suppression test and the midnight salivary cortisol test because the 24-hour urine free cortisol test is not useful because it is increased already in CKD. Treatment of Cushing's disease involves surgery, complemented by radiation and/or medical therapy if necessary. Growth hormone levels are increased and insulin-like growth factor 1 levels are normal in patients with CKD. In a normal patient with CKD, as in one with acromegaly, there can be a paradoxic increase in growth hormone after an oral glucose load. Therefore, diagnosis of acromegaly in renal insufficiency is challenging. The treatment of choice for acromegaly is surgery, although data for medical treatment for acromegaly in CKD are rare. In patients with renal impairment, arginine vasopressin levels are increased as a result of decreased clearance, and there also is impairment of arginine vasopressin signaling in renal tubules. Diabetes insipidus can be masked in advanced kidney disease until kidney transplantation. Diagnosis of the syndrome of inappropriate antidiuretic hormone is similar in mild or moderate kidney disease as in normal subjects, but is challenging in patients with advanced kidney disease owing to the impairment in urine dilution.

Rats with metabolic syndrome resist the protective effects of N-acetyl l-cystein against impaired spermatogenesis induced by high-phosphorus/zinc-free diet

Consumption of relatively high amounts of processed food can result in abnormal nutritional status, such as zinc deficiency or phosphorus excess. Moreover, hyperphosphatemia and hypozincemia are found in some patients with diabetic nephropathy and metabolic syndrome. The present study investigated the effects of high-phosphorus/zinc-free diet on the reproductive function of spontaneously hypertensive rats/NDmcr-cp (SHR/cp), a model of the metabolic syndrome. We also investigated the effects of antioxidant, N-acetyl-l-cysteine (NAC), on testicular dysfunction under such conditions. Male SHR/cp and control rats (Wistar Kyoto rats, WKY) were divided into three groups; rats fed control diet (P 0.3%, w/w; Zn 0.2%, w/w), high-phosphorus and zinc-deficient diet (P 1.2%, w/w; Zn 0.0%, w/w) with vehicle, or high-phosphorus and zinc-deficient diet with NAC (1.5mg/g/day) for 12 weeks (n=6 or 8 rats/group). The weights of testis and epididymis were significantly reduced by high-phosphate/zinc-free diet in both SHR/cp and WKY. The same diet significantly reduced caudal epididymal sperm count and motility and induced histopathological changes in the testis in both strains. Treatment with NAC provided significant protection against the toxic effects of the diet on testicular function in WKY, but not in SHR/cp. The lack of the protective effects of NAC on impaired spermatogenesis in SHR/cp could be due to the more pronounced state of oxidative stress observed in these rats compared with WKY.

Trace elements in hemodialysis patients: a systematic review and meta-analysis

BACKGROUND

Hemodialysis patients are at risk for deficiency of essential trace elements and excess of toxic trace elements, both of which can affect health. We conducted a systematic review to summarize existing literature on trace element status in hemodialysis patients.

METHODS

All studies which reported relevant data for chronic hemodialysis patients and a healthy control population were eligible, regardless of language or publication status. We included studies which measured at least one of the following elements in whole blood, serum, or plasma: antimony, arsenic, boron, cadmium, chromium, cobalt, copper, fluorine, iodine, lead, manganese, mercury, molybdenum, nickel, selenium, tellurium, thallium, vanadium, and zinc. We calculated differences between hemodialysis patients and controls using the differences in mean trace element level, divided by the pooled standard deviation.

RESULTS

We identified 128 eligible studies. Available data suggested that levels of cadmium, chromium, copper, lead, and vanadium were higher and that levels of selenium, zinc and manganese were lower in hemodialysis patients, compared with controls. Pooled standard mean differences exceeded 0.8 standard deviation units (a large difference) higher than controls for cadmium, chromium, vanadium, and lower than controls for selenium, zinc, and manganese. No studies reported data on antimony, iodine, tellurium, and thallium concentrations.

CONCLUSION

Average blood levels of biologically important trace elements were substantially different in hemodialysis patients, compared with healthy controls. Since both deficiency and excess of trace elements are potentially harmful yet amenable to therapy, the hypothesis that trace element status influences the risk of adverse clinical outcomes is worthy of investigation.

Relationships among plasma zinc, plasma prolactin, milk transfer, and milk zinc in lactating women

The objective was to analyze interrelationships among plasma zinc (PZ), plasma prolactin (PRL), milk transfer, and milk zinc from a longitudinal study of lactating women with a range of zinc intakes. Sixteen of 26 women received a 15 mg/d zinc supplement, resulting in a significant increase in total zinc intake compared with nonsupplemented participants (P<.001). No significant differences in key variables were observed between the zinc-supplemented and non-zinc-supplemented women; data were thus combined. An inverse trend between PRL and PZ was observed at 0.5 (r=-.36, P=.08) and 7 months (r=-.38, P=.06). Correlations between PRL at 0.5 months and at 3, 5, and 7 months were significant (r>.50, P<.01). PRL concentrations and milk transfer were positively correlated at 5 (r=.67, P<.001) and 7 months (r=.53, P<.01), consistent with PRL role in lactation maintenance. Studies including zinc-deficient lactating women are required to clarify the interrelationships between zinc status and PRL secretion.

Plasticity of neuroendocrine-thymus interactions during aging

Thymic regrowth and reactivation of thymic endocrine activity may be achieved even in old animals by different endocrinological or nutritional manipulations such as, (a) intrathymic transplantation of pineal gland or treatment with melatonin, (b) implantation of a growth hormone (GH) secreting tumor cell line or treatment with exogenous GH, (c) castration or treatment with exogenous luteinizing hormone-releasing hormone (LH-RH), (d) treatment with exogenous thyroxine or triiodothyronine, and (e) nutritional interventions such as arginine or zinc supplementation. These data strongly suggest that thymic, involution is a phenomenon secondary to age-related alterations in neuroendocrine-thymus interactions and that it is the disruption of such interactions in old age that is responsible for age-associated dysfunction. With regard to the mechanisms involved in hormone-induced thymic reconstitution, it is at present, difficult to draw any definitive conclusions. The effect of GH, thyroid hormones, and LH-RH may be due to the presence on thymic epithelial cells supposed to produce thymic peptides, of the specific hormone receptors. Melatonin or other pineal factors may also act through specific receptors, but experimental evidence is still lacking. The role of zinc, whose turnover is usually reduced in old age, is diverse. The effects range from the reactivation of zinc-dependent enzymes, required for both cell proliferation and apoptosis, to the reactivation of thymulin, a zinc-dependent thymic hormone. The role of zinc may even be more crucial. According to recent preliminary data obtained both in animal and human studies, it appears that the above reported endocrinological manipulations capable of restoring thymic activity in old age, may act also by normalizing the altered zinc pool.

A case-control study on selenium, zinc, and copper in plasma and hair of subjects affected by breast and lung cancer

The purpose of our study was to investigate the relationship between plasma and hair levels of Se, Zn, and Cu, and cancer. We selected a total of 66 patients affected by either breast (38) or lung (28) cancer. They entered into the study at the onset of disease, and before any chemical or radiotherapy. Controls were randomly selected among healthy people and were matched for sex, age, smoking habits, and residence. In the group of breast cancer, a significant decrease in hair Se was found compared to controls (p < 0.01), whereas plasma Se was only slightly decreased. No difference between cases and controls was detected in both hair and plasma levels of Zn and Cu. Subjects who developed lung cancer were significantly lower in hair Zn (p < 0.05) and Cu (p < 0.01) than controls, whereas there was no difference with regard to Se. In addition, plasma Cu of these patients was increased as compared to controls.

Reversibility of the thymic involution and of age-related peripheral immune dysfunctions by zinc supplementation in old mice

With advanced ageing the zinc pool undergoes progressive reduction as shown by the low zinc plasma levels and the negative crude zinc balance, both in humans and in rodents. It has been suggested that such zinc deficiency might be involved in many age-related immunological dysfunctions, including thymic failure. The relevance of zinc for good functioning of the entire immune system is, at present, well documented. In particular, zinc is required to confer biological activity to one of the best-known thymic peptides, thymulin, which is responsible for cell-mediated immunity. In deep zinc deficiencies, in humans and other animals, the low thymulin levels are due not to a primary failure of the thymus, but to a reduced peripheral saturation of thymic hormones by zinc ions. In aged mice both a reduced peripheral saturation of the hormone and a decreased production by the thymus were present. Oral zinc supplementation in old mice (22 months old) for 1 month induced a complete recovery of crude zinc balance from negative (-1.82) to positive values (+1.47), similar to those of young animals (+1.67). A full recovery of thymic functions with a regrowth of the organ and a partial restoration of the peripheral immune efficiency, as measured by mitogen responsiveness (PHA and ConA) and natural killer cell (NK) activity, were observed after zinc supplementation. These findings clearly pin-point for relevance of zinc for immune efficiency and suggest that the age-related thymic involution and peripheral immunological dysfunctions are not intrinsic and irreversible events but are largely dependent on the altered zinc pool.

Endocrine interaction between zinc and prolactin. An interpretative review

Zinc plays a very important role in animal and human metabolism. Nowadays, it is one of the most extensively studied trace element, since its sphere of action has been demonstrated to be very broad. From the biochemical standpoint, it controls more than 300 different enzymes, many of them involved with intermediary metabolism, DNA and RNA synthesis, gene expression, and immunocompetence. It also plays a significant role in hormonal homeostasis, since it can interact with almost all hormones. Zn2+ is closely related to the thyroid and steroid hormones, insulin, parathormone, and pituitary hormones, particularly prolactin (PRL). Zn2+ can inhibit PRL secretion within a range of physiologically and pharmacologically relevant concentrations. This property has raised the possibility of clinical applications of zinc. In this article, we review the literature on the subject in an attempt to provide a comprehensible general view.

Zinc, human diseases and aging

Zinc is one of the most important trace elements in the body for many biological functions; it is required as a catalytic component for more than 200 enzymes, and as a structural constituent of many proteins, hormones, neuropeptides, hormone receptors, and probably polynucleotides. Due to its role in cell division and differentiation, programmed cell death, gene transcription, biomembrane functioning and obviously many enzymatic activities, zinc is considered a major element in assuring the correct functioning of an organism, from the very first embryonic stages to the last periods of life. This biological role together with the many factors that modulate zinc turnover explains on one hand, the variety of clinical and laboratory signs resulting from its reduced bioavailability, and on the other, the high number of human pathologies characterized by alterations in the zinc pool. As zinc supplementation is efficacious in most of these conditions, it is regarded more as an oriented therapeutical support, than a simple dietary integrator. Furthermore, the relevance of zinc status to many age-associated diseases and, according to experimental studies, the aging itself of the major homeostatic mechanisms of the body, i.e., the nervous, neuroendocrine and immune systems, places zinc in a pivotal position in the economy of the aging organism.

Biomarkers of aging in the neuroendocrine-immune domain. Time for a new theory of aging?

A common and generally accepted assumption is that with advancing age, the thymus undergoes progressive and irreversible involution. This is considered the main cause for the age-related deterioration of various immune functions and, ultimately, for the increased incidence of infectious, neoplastic, and automimmune diseases in old age. This assumption is no longer tenable because of several clear-cut demonstrations that age-related thymic involution is not an intrinsic and irreversible phenomenon. Various neuroendocrine or nutritional manipulations can to induce a regrowth of the thymus, even when applied in old age. This thymic reconstitution is followed by a consistent recovery of peripheral immune functions. These data strongly support the idea that thymic involution is a phenomenon secondary to age-related alterations in neuroendocrine-thymus interactions and that it is the disruption of such interactions in old age that is responsible for most of the age-associated dysfunctions. On the basis of this experimental and clinical evidence and as an alternative to purely immune or neuroendocrine theories of aging, a neuroendocrine-immune hypothesis is proposed. Further work is required to determine if the age-related disruption of neuroendocrine-immune interactions occurs because of progressive accumulation of stressor-dependent consequences at the level of one or the other system or if it may depend on a single common cause.

Zinc and bromocriptine long-term administration in patients with prolactinomas: effects on prolactin and thymulin circulating levels

Several studies have demonstrated zinc (Zn), prolactin (PRL) and thymulin (Zn-FTS) interplay: Zn inhibits, in a dose related manner, PRL release from lactotropes in vitro and stimulates thymulin synthesis in vivo both in humans and in animals. PRL receptors are present on thymic epithelial cells (TEC); PRL stimulates TEC trophism and activity. Little is known about the influence of PRL on Zn metabolism, though in prolactinomas we found reduced Zn and thymulin circulating levels. For this reason, we evaluated PRL, Zn, bioactive thymulin (Zn-FTS) and total thymulin (T-FTS: Zn-bound plus Zn-unbound form) serum levels in 58 patients with prolactinomas (PRL: 253 +/- 263 micrograms/L), Zn (82 +/- 23 micrograms/dl), Zn-FTS (2.2 +/- 0.20 log2(-1] and T-FTS (3.7 +/- 0.25 log2(-1] were significantly lower (p less than .01) than those found in age matched controls. Zn-unbound bioinactive thymulin form (FTS) levels were in the normal range. Bromocriptine administration (Brc) (2.5-5 mg p.o., b.i.d. for 9 months) to 20 patients with microprolactinomas lowered serum PRL levels (10.5 +/- 6.2 micrograms/L) and significantly increased (p less than .01) Zn (118.6 +/- 14.7 micrograms/dl), Zn-FTS (3.96 +/- 0.7 log2(-1)) and T-FTS (4.66 +/- 0.7 log2(1)) circulating levels. ZnSO4 administration (400 mg p.o. daily for 3 months) to 6 patients with microprolactinomas, significantly increased (p less than .01) Zn (136 +/- 18 micrograms/dl), Zn-FTS (4.5 +/- 0.5 log2(-1)) and T-FTS (5.6 +/- 0.9 log2(-1)) levels, while caused only a slight decrease in serum PRL concentrations (from 95 +/- 8 to 75 +/- 9 micrograms/L; p: NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Survey of thymic hormone effects on physical and immunological parameters in C57BL/6NNia mice of different ages

Immunosenescence occurs with aging, which is seen in decline in response to mitogens PHA, ConA, decline in cell-mediated immunity, increase in anemia, and increase in autoimmune antibodies to erythrocytes and DNA. These studies compared FTS, TP5, TM4, and TF5 in C57BL/6NNia mice. Mice aged 4, 26, 52, 78 and 104 wk were treated with various hormones 5x/wk for 3 wk and monitored for hormonal effects on weight; hematocrit; peripheral blood, spleen, and thymic cell numbers; spleen and peripheral blood cell mitogen responses to PHA, ConA, LPS; IgM hemolysin autoantibody; and cell-mediated cytotoxicity to P815 allogenic cells. Hormone treatments altered mitogen responses, enhanced IgM hemolysin autoantibody production, and modulated cell-mediated immune responses. The effects were not consistent for every hormone. There was a tendency for enhancement in younger mice and suppression in older animals. Treatment with FTS showed the greatest changes in either enhancing or suppressing the different parameters measured. The hormonal effects appeared to be age specific in that certain activities were altered for certain age groups but not in others. Hormone treatment did not restore any immune parameters in old mice to the level of young animals. In general, the different hormones did not consistently produce the same effects in C57BL/6NNia mice of different age groups. Even though all animals received from National Institutes on Aging (NIA) animal models program were held under strictly controlled conditions, intrinsic variations between cohorts of different ages are difficult to control. Cohorts of aging animals tested at different times might be intrinsically different. This inherent variability in the cohorts could affect the range of activity, specificity and reproducibility of hormone effects in vivo. Most importantly, it should be emphasized that cross-sectional data identifies age differences rather than age changes. There is no assurance that age changes in any individual or in all subpopulations follow this pattern. In our studies only healthy animals were used. Old, sick, or tumor-bearing animals were culled out prior to being sent to us. Therefore, the 78- and 104-wk-old mice represent selected healthy cohorts. The age changes that take place can be answered only from repeated measurements made in the same individual over time.

Thymic endocrine activity in children with idiopathic growth-hormone deficiency

Experimental and clinical evidences suggest that thymic endocrine function is modulated by the neuroendocrine network and in particular by growth hormone. The plasma of thymulin has been found reduced in congenital hypopituitarism and increased in acromegalic conditions when compared with the values observed in age-matched controls. In the present paper we have investigated in congenital GH-deficient children the effect of one year therapy with GH on the plasma level of thymulin, IGF-1 and plasma zinc; this last parameter has been checked because zinc is required for thymulin activity and modulates IGF-1 production. The basal thymulin and IGF-1 values are lower in GH deficient children than age-matched controls whereas zinc levels show a slight reduction. GH therapy induces a significant increment both of thymulin and IGF-1 levels and a slight increase of plasma zinc. A positive correlation has been found between zinc values and thymulin activity but not between GH and thymulin. Whether the recovery of thymulin production in GH deficient children by GH therapy is mediated by IGF-1 or by bioavailability of zinc ions remains to be established.

[Effect of zinc substitution on lymphocyte subsets and cellular immune function in hemodialysis patients]

Infection is a major cause of morbidity and mortality in patients undergoing hemodialysis for end stage renal disease. Low plasma zinc levels have been associated with immunodepression in these patients. In a randomized, placebo controlled double-blind cross over study, plasma zinc levels, delayed hypersensivity to 7 Antigens (Merieux-Multitest), absolute lymphocyte counts, T- and B-lymphocytes, suppressor-T and helper T-cells and natural killer cells were studied in 25 hemodialysis patients before, during and after intravenous zinc supplementation for 8 weeks. The hemodialysis patients had significantly lower predialysis plasma zinc concentrations compared to 76 healthy controls (74 +/- 12 vs. 126 +/- 28 mcg/dl, p less than 0.001). The plasma zinc concentrations increased to the normal range during the treatment period. Lymphocyte subtype analysis showed a significant decrease of suppressor-T cells and an increase of the helper-T/suppressor-T ratio (2.09 +/- 0.26 vs. 3.18 +/- 0.48, p less than 0.05) after zinc supplementation. Delayed hypersensivity to intradermal antigens increased significantly only after zinc treatment (2.0 +/- 0.7 vs. 5.8 +/- 1.7, p less than 0.05), not after placebo. The changes were reversible after finishing the zinc treatment. It is concluded, that plasma zinc levels are reduced in hemodialysis patients and that the substitution of zinc restores some of the depressed immune functions in these patients.

Control of prolactin secretion

1. Prolactin is a 21,500 Dalton single-chain polypeptide hormone but may occur in 50 kDa and 150 kDa molecular variants. 2. These large PRL variants may be secreted predominantly; this condition is termed "macroprolactinemia". It is characterized by high immunological and normal biological serum levels of prolactin, and lack of clinical symptoms of hyperprolactinemia. 3. The information on PRL is encoded on chromosome 6. Transcription can be enhanced and suppressed by a variety of hormonal factors. 4. PRL is secreted in a pulsatile fashion; it displays a circadian rhythm (with a maximum during sleep) and is stimulated by some amino acids. PRL also responds to mechanical stimulation of the breast. 5. PRL rises during pregnancy, and maintainance of hyperprolactinemia (and, thereby, physiological infertility) is dependent on the frequency and duration of breast feedings. 6. Hypothalamic regulation of prolactin mainly involves tonic inhibition via portal dopamine. The physiological importance of various stimulating factors present in the hypothalamus is still incompletely understood. In particular, there is still no place for TRH in PRL physiology. 7. PRL is released in response to stress; this response may be mediated by opioids. The low-estrogen, low-gonadotropin amenorrhea of endurance-training women is not mediated by prolactin, however. 8. Estrogens stimulate PRL gene transcription via at least two independent mechanisms. There are many clinical examples of this estrogen effect on prolactin serum levels, and also on the growth of prolactinomas. 9. Mild hyperprolactinemia remains an enigma which cannot satisfactorily be resolved by biochemical or radiological testing. The border between "normal" and "elevated" prolactin is ill-defined. The possibility of macroprolactinemia complicates this matter even further. 10. The number of drugs which suppress prolactin by acting on pituitary D2 receptors, and which are useful in the treatment of hyperprolactinemia, continues to increase. In the field of ergot alkaloids, parenteral application appears to be a logical solution to the problem of the high first-pass effect; in addition, this form of treatment is frequently better tolerated than the oral route. 11. Prolactinoma development is presently being studied employing molecular biological techniques; the question of whether tumorigenesis can be attributed to specific defects of gene regulation remains to be answered.

Prolactin, thymulin and zinc in chronic hemodialysis: effect of renal transplant

The interrelationships between PRL, thymulin and Zn, were studied in 25 patients with chronic renal failure (CRF) undergoing kidney transplantation and immunosuppressed with cyclosporine A (CsA). The possible role of serum PRL levels in predicting allograft rejection was also investigated. Before the kidney transplant serum PRL levels were significantly higher than in normals (mean +/- SE, 28.3 +/- 7.1 vs 7.5 +/- 0.6 micrograms/l, p less than 0.001) and their response to TRH (200 micrograms iv) was impaired (mean delta % at peak, 45.4 +/- 9.5 vs + 641 +/- 47.5, p less than 0.001). After kidney transplantation a dramatic decrease in serum PRL concentrations was observed in all patients, followed by a slight upward trend in the following two weeks, while TRH test administered on 3rd, 7th and 14th day, induced a progressive increase in serum PRL responses (delta % at peak, 201 +/- 43.3, 220 +/- 37.1 and 305 +/- 15.5, respectively). No difference in serum PRL patterns was observed between patients with (8 cases) and without (17 cases) clinical features and kidney fine needle biopsies suggestive of rejection. Basal serum Zn levels of patients with CRF (18.1 +/- 0.6 mumol/l) were similar to those observed in normals (17.7 +/- 0.2 mumol/l) and without any correlation with serum PRL levels. A decrement in serum Zn was recorded during CsA infusion and on the first day after the surgery, followed by a slight and slow upward trend. Basal serum thymulin titers were low [2.92 +/- 0.18 (1/log2)], were further reduced after CsA infusion [1.68 +/- 0.15 (1/log2)] and returned to the pretransplant levels in the two weeks after grafting.(ABSTRACT TRUNCATED AT 250 WORDS)