Cranial irradiation of female rats causes dose-dependent and age-dependent activation or inhibition of pubertal development

Effects of chronic γ-irradiation on growth and sexual maturation of the Tohoku hynobiid salamander, Hynobius lichenatus

There are still considerable gaps in knowledge regarding the biological effects of chronic ionising radiation exposure in amphibians. To fill these gaps, Tohoku hynobiid salamanders, Hynobius lichenatus (Amphibia, Caudata), were chronically irradiated with ¹³⁷Cs γ-rays from embryonic to adult stages over 1954 days, and the effects on their growth and sexual maturation were examined under laboratory conditions. Irradiation at a dose rate of 33 μGy h^-1 had some stimulatory effects on growth (body weight increase) of H. lichenatus, while growth was temporarily or permanently suppressed at 150 or 510 μGy h^-1, respectively. On day 1802, secondary sexual characteristics (a tubercle at the anterior angle of the cloacal vent for males and ovisac development for females) were observed in 91% of the salamanders irradiated at 33 μGy h^-1, and in a similar percentage of non-irradiated controls. At 150 and 510 μGy h^-1, secondary sexual characteristics were not observed in any individuals. These results suggest that the derived consideration reference level (DCRL) of the International Commission on Radiological Protection (ICRP) for Reference Frog, i.e. 40-400 μGy h^-1, is applicable for the protection of H. lichenatus, and that growth and sexual maturation of this salamander may not have been adversely affected even in the most severely contaminated area in Fukushima, where the highest dose rate to salamanders was estimated to be 50 μGy h^-1. However, observations in the contaminated area are required to confirm this conclusion, considering the possible confounding factors which may make this salamander more sensitive to radiation in the natural environment than under laboratory conditions.

Radiations and female fertility

Hundreds of thousands of young women are diagnosed with cancer each year, and due to recent advances in screening programs, diagnostic methods and treatment options, survival rates have significantly improved. Radiation therapy plays an important role in cancer treatment and in some cases it constitutes the first therapy proposed to the patient. However, ionizing radiations have a gonadotoxic action with long-term effects that include ovarian insufficiency, pubertal arrest and subsequent infertility. Cranial irradiation may lead to disruption of the hypothalamic-pituitary-gonadal axis, with consequent dysregulation of the normal hormonal secretion. The uterus might be damaged by radiotherapy, as well. In fact, exposure to radiation during childhood leads to altered uterine vascularization, decreased uterine volume and elasticity, myometrial fibrosis and necrosis, endometrial atrophy and insufficiency. As radiations have a relevant impact on reproductive potential, fertility preservation procedures should be carried out before and/or during anticancer treatments. Fertility preservation strategies have been employed for some years now and have recently been diversified thanks to advances in reproductive biology. Aim of this paper is to give an overview of the various effects of radiotherapy on female reproductive function and to describe the current fertility preservation options.

Olfactory Memory Impairment Differs by Sex in a Rodent Model of Pediatric Radiotherapy

Although an effective treatment for pediatric brain tumors, cranial radiation therapy (CRT) damages surrounding healthy tissue, thereby disrupting brain development. Animal models of pediatric CRT have primarily relied on visual tasks to assess cognitive impairment. Moreover, there has been a lack of sex comparisons as most research on the cognitive effects of pediatric CRT does not include females. Therefore, we utilized olfaction, an ethologically relevant sensory modality, to assess cognitive impairment in an animal model of CRT that included both male and female mice. Specifically, we used the novel odor recognition (NOdorR) task with social odors to test recognition memory, a cognitive parameter that has been associated with olfactory neurogenesis, a form of cellular plasticity damaged by CRT. In addition to odor recognition memory, olfactory ability or discrimination of non-social and social odors were assessed both acutely and 3 months after CRT. Magnetic resonance imaging (MRI) and histology were performed after behavioral testing to assess long-term damage by CRT. Long-term but not acute radiation-induced impairment in odor recognition memory was observed, consistent with delayed onset of cognitive impairment in human patients. Males showed greater exploration of social odors than females, but general exploration was not affected by irradiation. However, irradiated males had impaired odor recognition memory in adulthood, compared to non-irradiated males (or simply male controls). Female olfactory recognition memory, in contrast, was dependent on estrus stage. CRT damage was demonstrated by (1) histological evaluation of olfactory neurogenesis, which suggested a reduction in CRT versus control, and (2) imaging analyses which showed that the majority of brain regions were reduced in volume by CRT. Specifically, two regions involved in social odor processing (amygdala and piriform cortex) were damaged by cranial irradiation in males but not females, paralleling olfactory recognition findings.

Radiation-Induced Growth Retardation and Microstructural and Metabolite Abnormalities in the Hippocampus

Cranial radiotherapy (CRT) increases survival in pediatric brain-tumor patients but can cause deleterious effects. This study evaluates the acute and long-term impact of CRT delivered during childhood/adolescence on the brain and body using a rodent model. Rats received CRT, either 4 Gy fractions × 5 d (fractionated) or a cumulative dose of 20 Gy (single dose) at 28 d of age. Animals were euthanized 1 d, 5 d, or 3.5 mo after CRT. The 3.5 mo group was imaged prior to euthanasia. At 3.5 mo, we observed significant growth retardation in irradiated animals, versus controls, and the effects of single dose on brain and body weights were more severe than fractionated. Acutely single dose significantly reduced body weight but increased brain weight, whereas fractionation significantly reduced brain but not body weights, versus controls. CRT suppressed cell proliferation in the hippocampal subgranular zone acutely. Fractional anisotropy (FA) in the fimbria was significantly lower in the single dose versus controls. Hippocampal metabolite levels were significantly altered in the single dose animals, reflecting a heightened state of inflammation that was absent in the fractionated. Our findings indicate that despite the differences in severity between the doses they both demonstrated an effect on cell proliferation and growth retardation, important factors in pediatric CRT.

Radiation-induced hypopituitarism

PURPOSE OF REVIEW

Progressive and irreversible neuro-endocrine dysfunction following radiation-induced damage to the hypothalamic-pituitary (h-p) axis is the most common complication in cancer survivors with a history of cranial radiotherapy involving the h-p axis and in patients with a history of conventional or stereotactic pituitary radiotherapy for pituitary tumours. This review examines the controversy about the site and pathophysiology of radiation damage while providing an epidemiological perspective on the frequency and pattern of radiation-induced hypopituitarism.

RECENT FINDINGS

Contrary to the previously held belief that h-p axis irradiation with doses less than 40 Gy result in a predominant hypothalamic damage with time-dependent secondary pituitary atrophy, recent evidence in survivors of nonpituitary brain tumours suggests that cranial radiation causes direct pituitary damage with compensatory increase in hypothalamic release activity. Sparing the hypothalamus from significant irradiation with sterteotactic radiotherapy for pituitary tumours does not appear to reduce the long-term risk of hypopituitarism.

SUMMARY

Radiation-induced h-p dysfunction may occur in up to 80% of patients followed long term and is often associated with an adverse impact on growth, body image, skeletal health, fertility, sexual function and physical and psychological health. A detailed understanding of pathophysiological and epidemiological aspects of radiation-induced h-p axis dysfunction is important to provide targeted and reliable long-term surveillance to those at risk so that timely diagnosis and hormone-replacement therapy can be provided.

Interaction between ionizing radiation and estrogen: what we are missing?

Following complexity as a new approach in science of 21st century biomonitoring of biological effects caused by ionizing radiation received an option of a new dimension. Insight in biological response of mammals to ionizing radiation exposure by integration of genome, non-genome and distant organ bystander effects will significantly change evaluation of health risk and preventive measures. Impact of estrogen on carcinogenesis caused by occupational or accidental exposure to ionizing radiation additionally enables biodosimetry to recognize vulnerable subpopulations according to gender and age. Estrogen, as a potent molecule involved in number of biological pathways during development and adulthood, shows close interaction with pathological processes launched by overexposure to ionizing radiation which should be included in future research and radiation protection.

Abnormal timing of menarche in survivors of central nervous system tumors: A report from the Childhood Cancer Survivor Study

BACKGROUND

Children who receive high-dose radiotherapy to the hypothalamic-pituitary (H-P) axis may be at risk for both early and late puberty. To the authors' knowledge, data regarding the risk of altered timing of menarche after higher dose radiotherapy (RT), as used in the treatment of central nervous system (CNS) tumors, are limited.

METHODS

The authors evaluated 235 female survivors of CNS tumors, diagnosed between 1970 and 1986, and >1000 sibling controls who were participants in the Childhood Cancer Survivor Study, and provided self-reported data concerning age at menarche.

RESULTS

Survivors of CNS tumors were more likely to have onset of menarche before age 10 years compared with their siblings (11.9% vs 1.0%) (odds ratio [OR], 14.1; 95% confidence interval [95% CI], 7.0-30.9). Of the 138 survivors who received RT to the H-P axis, 20 (14.5%) had onset of menarche before age 10 years, compared with 4.3% of those who did not receive RT (OR, 3.8; 95% CI, 1.2-16.5). Age <or=4 years at the time of diagnosis was associated with an increased risk (OR, 4.0; 95% CI, 1.7-10.0) of early menarche. In addition, survivors of CNS tumors were more likely than siblings to have onset of menarche after age 16 years (10.6% vs 1.9%) (OR, 6.6; 95% CI, 3.4-11.4). Doses of RT to the H-P axis >50 gray OR, 9.0; 95% CI, 2.3-59.5) and spinal RT conferred an increased risk of late menarche, as did older age (>10 years) at the time of diagnosis (OR, 3.0; 95% CI, 1.3-7.0).

CONCLUSIONS

Survivors of CNS tumors are at a significantly increased risk of both early and late menarche associated with RT exposure and age at treatment.

Hypopituitarism following radiotherapy

Deficiencies in anterior pituitary hormones secretion ranging from subtle to complete occur following radiation damage to the hypothalamic-pituitary (h-p) axis, the severity and frequency of which correlate with the total radiation dose delivered to the h-p axis and the length of follow up. Selective radiosensitivity of the neuroendocrine axes, with the GH axis being the most vulnerable, accounts for the high frequency of GH deficiency, which usually occurs in isolation following irradiation of the h-p axis with doses less than 30 Gy. With higher radiation doses (30-50 Gy), however, the frequency of GH insufficiency substantially increases and can be as high as 50-100%. Compensatory hyperstimulation of a partially damaged h-p axis may restore normality of spontaneous GH secretion in the context of reduced but normal stimulated responses; at its extreme, endogenous hyperstimulation may limit further stimulation by insulin-induced hypoglycaemia resulting in subnormal GH responses despite normality of spontaneous GH secretion in adults. In children, failure of the hyperstimulated partially damaged h-p axis to meet the increased demands for GH during growth and puberty may explain what has previously been described as radiation-induced GH neurosecretory dysfunction and, unlike in adults, the ITT remains the gold standard for assessing h-p functional reserve. Thyroid-stimulating hormone (TSH) and ACTH deficiency occur after intensive irradiation only (>50 Gy) with a long-term cumulative frequency of 3-6%. Abnormalities in gonadotrophin secretion are dose-dependent; precocious puberty can occur after radiation dose less than 30 Gy in girls only, and in both sexes equally with a radiation dose of 30-50 Gy. Gonadotrophin deficiency occurs infrequently and is usually a long-term complication following a minimum radiation dose of 30 Gy. Hyperprolactinemia, due to hypothalamic damage leading to reduced dopamine release, has been described in both sexes and all ages but is mostly seen in young women after intensive irradiation and is usually subclinical. A much higher incidence of gonadotrophin, ACTH and TSH deficiencies (30-60% after 10 years) occur after more intensive irradiation (>60 Gy) used for nasopharyngeal carcinomas and tumors of the skull base, and following conventional irradiation (30-50 Gy) for pituitary tumors. The frequency of hypopituitarism following stereotactic radiotherapy for pituitary tumors is mostly seen after long-term follow up and is similar to that following conventional irradiation. Radiation-induced anterior pituitary hormone deficiencies are irreversible and progressive. Regular testing is mandatory to ensure timely diagnosis and early hormone replacement therapy.

Late structural alterations of cerebral white matter in long-term survivors of childhood leukemia

PURPOSE

To look for the presence and age-dependence of late structural alterations of otherwise normal-appearing cerebral gray and white matter after radiation and chemotherapy in adult survivors of acute lymphoblastic leukemia (ALL) during childhood.

MATERIALS AND METHODS

In a group of 13 adult survivors 17-37 years old, who had been treated by total brain radiation (18-24 Gy) and chemotherapy 16-28 years ago, prospective MR examinations including diffusion tensor imaging (DTI) were performed. Evaluation included volumetry, calculation of mean diffusivity (MD) and fractional anisotropy (FA), and comparison of results to an age-matched control group.

RESULTS

DTI showed significantly reduced FA values in the temporal lobes (difference of 0.069 units, P < 0.001), hippocampi (difference of 0.033 units, P < 0.001), and thalami (difference of 0.046 units, P = 0.001), which were accompanied by significant white matter volume loss (difference of 92 cm(3), P < 0.001). Significant elevations of MD were limited to the temporal white matter (difference of 42 x 10(-6) mm(2)/s, P = 0.005). Global and frontal white matter MD correlated negatively to increasing age of the survivors (P < 0.01).

CONCLUSION

With regard to structural white matter alterations, adult long-term survivors of childhood ALL, who had received total brain radiation and chemotherapy, apparently show the same overall age dependence as controls. Follow-up studies are needed for confirmation.

The ultraviolet filter benzophenone 2 interferes with the thyroid hormone axis in rats and is a potent in vitro inhibitor of human recombinant thyroid peroxidase

Endocrine disrupting chemicals (EDCs), either plant constituents or contaminants deriving from industrial products, may interfere with the thyroid hormone (TH) axis. Here, we examined whether selected EDCs inhibit the key reactions of TH biosynthesis catalyzed by thyroid peroxidase (TPO). We used a novel in vitro assay based on human recombinant TPO (hrTPO) stably transfected into the human follicular thyroid carcinoma cell line FTC-238. F21388 (synthetic flavonoid), bisphenol A (building block for polycarbonates), and the UV filter benzophenone 2 (BP2) inhibited hrTPO. BP2 is contained in numerous cosmetics of daily use and may be in regular contact with human skin. Half-maximal inhibition in the guaiacol assay occurred at 450 nmol/liter BP2, a concentration 20- and 200-fold lower than those required in case of the TPO-inhibiting antithyroid drugs methimazole and propylthiouracil, respectively. BP2 at 300 nmol/liter combined with the TPO substrate H(2)O(2) (10 mumol/liter) inactivated hrTPO; this was, however, prevented by micromolar amounts of iodide. BP2 did not inhibit iodide uptake into FRTL-5 cells. In BP2-treated rats (333 and 1000 mg/kg body weight), serum total T(4) was significantly decreased and serum thyrotropin was significantly increased. TPO activities in the thyroids of treated animals were unchanged, a finding also described for methimazole and propylthiouracil. Thus, EDCs, most potently BP2, may disturb TH homeostasis by inhibiting or inactivating TPO, effects that are even more pronounced in the absence of iodide. This new challenge for endocrine regulation must be considered in the context of a still prevailing iodide deficiency in many parts of the world.

Gene expression changes in the rodent hippocampus following whole brain irradiation

Therapeutic cranial irradiation may result in debilitating cognitive impairments. In human patients these deficits are age and radiation dose-dependent and are attributed to a diminished capability to learn and memorize new tasks and information. Because of the known involvement of the hippocampus in memory consolidation, it is important to identify irradiation-induced changes including alterations in gene expression in this structure. Whole brain irradiation doses of 0, 0.3, 3, 10, or 30 Gray (Gy) were administered to 3-month-old rats in a single session. Twenty-four hours following cranial irradiation, hippocampi were processed for oligonucleotide microarrays analysis. Metallothioneins (MT)-I and -II, heat shock protein (Hsp-27), glial fibrillary acidic protein alpha (GFAP), and c-Fos genes were altered significantly across the various doses of irradiation. A pathway analysis shows that these genes were centered around the immediate early gene myc and tumor suppressor gene (TP53). Our results identified important genes and possible pathways that are altered in the hippocampus in the acute phase following cranial irradiation, and implicate gene pathways important for both learning and memory and apoptosis.

Pituitary deficiency after brain radiation therapy

Brain radiotherapy is a frequent and overlooked cause of pituitary deficiency in adults which may alter patients' health and quality of life. Hormonal consequences have been better studied in children. The onset of hormonal deficiencies depends on the dose delivered to the pituitary-hypothalamic region while their incidence and severity depends on dose fractionating and follow-up duration. Somatotrophic function is the first affected, 90% of patients being GH deficient 10 years after radiotherapy. Other anterior pituitary functions are affected later and less frequently. While initial damage occurs in the hypothalamus, accounting for mild hyperprolactinemia in 30-50% of cases, diabetes insipidus is never observed. Direct pituitary deficiency may occur later. Responses to ACTH or GHRH-arginine tests may be normal for several years though an ACTH and/or GH deficiency has been demonstrated by an insulin tolerance test, which is considered as the gold standard. When the cranio-spinal area--including the neck--has been irradiated, primary thyroid deficiency might occur. Repeated cervical ultrasonographic follow-up is mandatory to exclude radiation-induced thyroid cancer. The gonadotrophic function might be altered after small doses of irradiation causing precocious puberty, while at higher doses delayed puberty or true gonadotrophic deficiencies are more often observed. Combined radio- and chemotherapy might result in mixed central and peripheral deficiencies that might be difficult to diagnose. When radiotherapy is performed in adulthood, GH deficiency is less common, although the sequence of hormonal deficiencies is similar to that observed in children. Prospective longitudinal studies are required to determine the time course and sequence of onset of each deficiency, in order to tailor the monitoring of these patients to their specific needs.

Sensitivity of anterior pituitary hormones to irradiation

Cranial irradiation is used in the management of a diverse group of intracranial pathologies. However, if any part of the hypothalamic-pituitary axis is included in the radiation field, there is a risk of developing neuroendocrine dysfunction. Growth hormone is the most radiosensitive of the anterior pituitary hormones, followed by the gonadotropins, adrenocorticotropic hormone and thyroid-stimulating hormone. A number of factors determine both the occurrence and severity of hypothalamic-pituitary dysfunction, including: the dose of radiation received by the hypothalamic-pituitary axis (determined by a number of factors including total dose and fractionation schedule and ultimately expressed as the biological effective dose); length of time since cranial irradiation; age of the patient at the time of cranial irradiation; type of radiotherapy administered; and the different inherent radiosensitivities of the anterior pituitary hormones. These neuroendocrine abnormalities usually develop a number of years after the initial insult and, therefore, patients who have received cranial irradiation should receive annual endocrine assessments. The establishment of endocrine late-effect clinics for the survivors of childhood cancers have gone some way to addressing this problem; however, other groups of patients, particularly those receiving cranial irradiation in adult life, may not have systematic endocrine assessment.

Pathophysiology of radiation-induced growth hormone deficiency: efficacy and safety of GH replacement

Radiation-induced growth hormone deficiency (GHD) is primarily due to hypothalamic damage. GH secretion by the pituitary may be affected either secondary to some degree of quantitative deprivation of hypothalamic input or, if the radiation dose is high enough, by direct pituitary damage. As a consequence, the neurosecretory profile of GH secretion in an irradiated patient remains pulsatile and qualitatively intact. The frequency of pulse generation is unaffected, but the amplitude of the GH pulses is markedly reduced. Over the last 25 years, the final heights achieved by children receiving GH replacement for radiation-induced GHD have improved; these improvements are attributable to refinements in GH dosing schedules, increased use of GnRH analogues for radiation-induced precocious puberty, and a reduced time interval between completion of irradiation and initiation of GH therapy. When retested at the completion of growth, 80-90% of these teenagers are likely to prove severely GH deficient and, therefore, will potentially benefit from GH replacement in adult life. Such long-term GH treatment in patients treated previously for a brain tumor means that critical and continuous surveillance must be devoted to the risk of tumor recurrence and the possibility of second neoplasms.

Hypopituitarism as a consequence of brain tumours and radiotherapy

Radiation-induced damage to the hypothalamic-pituitary (h-p) axis is associated with a wide spectrum of subtle and frank abnormalities in anterior pituitary hormones secretion. The frequency, rapidity of onset and the severity of these abnormalities correlate with the total radiation dose delivered to the h-p axis, as well as the fraction size, younger age at irradiation, prior pituitary compromise by tumour and/or surgery and the length of follow up. Whilst, the hypothalamus is the primary site of radiation-induced damage, secondary pituitary atrophy evolves with time due to impaired secretion of hypothalamic trophic factors and/or time-dependent direct radiation-induced damage. Selective radiosensitivity in the neuroendocrine axes with the GH axis being the most vulnerable to radiation damage accounts for the high frequency of GH deficiency, which usually occurs in isolation following irradiation of the h-p axis with doses less than 30 Gy. With higher radiation doses (30-50 Gy), however, the frequency of GH insufficiency substantially increases and can be as high as 50-100%, and TSH and ACTH deficiency start to occur with a long-term cumulative frequency of 3-6%. Abnormalities in gonadotrophin secretion are dose-dependent; precocious puberty can occur after radiation dose less than 30 Gy in girls only, and in both sexes equally with a radiation dose of 30-50 Gy. Gonadotrophin deficiency occurs infrequently and is usually a long-term complication following a minimum radiation dose of 30 Gy. Hyperprolactinemia, due to hypothalamic damage leading to reduced dopamine release, has been described in both sexes and all ages but is mostly seen in young women after intensive irradiation and is usually subclinical. A much higher incidence of gonadotrophin, ACTH and TSH deficiencies (30-60% after 10 years) occur after more intensive irradiation (>70 Gy) used for nasopharyngeal carcinomas and tumours of the skull base and following conventional irradiation (30-50 Gy) for pituitary tumours. Radiation-induced anterior pituitary hormone deficiencies are irreversible and progressive. Regular testing is mandatory to ensure timely diagnosis and early hormone replacement therapy to improve linear growth and prevent short stature in children cured from cancer, and in adults preserve sexual function, prevent ill health and osteoporosis and improve the quality of life.

Endocrine active compounds affect thyrotropin and thyroid hormone levels in serum as well as endpoints of thyroid hormone action in liver, heart and kidney

To assess interference with endocrine regulation of the thyroid axis, rats (female, ovariectomised) were treated for 12 weeks with the suspected endocrine active compounds (EAC) or endocrine disrupters (ED) 4-nonylphenol (NP), octyl-methoxycinnamate (OMC) and 4-methylbenzylidene-camphor (4-MBC) as well as 17beta-estradiol (E2) and 5alpha-androstane-3beta,17beta-diol (Adiol) on the background of a soy-free or soy-containing diet, and endpoints relevant for regulation via the thyroid axis were measured. Thyrotropin (TSH) and thyroid hormone (T4, T3) serum levels were altered, but not in a way consistent with known mechanisms of feedback regulation of the thyroid axis. In the liver, malic enzyme (ME) activity was significantly increased by E2 and Adiol, slightly by OMC and MBC and decreased by soy, whereas type I 5'-deiodinase (5'DI) was decreased by all treatments. This may be due rather to the estrogenic effect of the ED, as there is no obvious correlation with T4 or T3 serum levels. None of the substances inhibited thyroid peroxidase (TPO) in vitro, except for NP. In general, several endocrine active compounds disrupt the endocrine feedback regulation of the thyroid axis. However, there was no uniform, obvious pattern in the effects of those ED tested, but each compound elicited its own spectrum of alterations, arguing for multiple targets of interference with the complex network of thyroid hormone action and metabolism.

Reduction of gamma-aminobutyric acid-ergic neurotransmission as a putative mechanism of radiation induced activation of the gonadotropin releasing-hormone-pulse generator leading to precocious puberty in female rats

Brain irradiation in prepubertal children with malignomas can cause precocious puberty. A selective cranial cobalt (Co(60))-irradiation technique has been developed in rats. In two experiments early juvenile (13-15 days old) female rats received a single dose of 5 Gy or sham irradiation. At pubertal age (post-natal days 33-34) irradiated rats had higher serum estradiol and luteinizing hormone levels. In experiment 1 irradiated rats had higher gonadotropin releasing-hormone (GnRH) mRNA levels in the preoptic area compared to controls (P<0.05). In experiment 2 the release rates of gamma-aminobutyric acid (GABA) in vitro from preoptic mediobasal hypothalamic areas of irradiated rats were significantly reduced after stimulation with the GABA(A) receptor agonist muscimol (maximum values 4607+/-804 vs. 7399+/-1048 pM in controls, mean+/-SEM, P<0.05). Radiation induced central precocious puberty might be caused by damage to inhibitory GABAergic neurons leading to premature activation of the GnRH-pulse generator.