Effect of melatonin suppression on scoliosis development in chickens by either constant light or surgical pinealectomy

The role of pineal gland volume in the development of scoliosis

PURPOSE

Adolescent idiopathic scoliosis (AIS) is believed to be caused by genetic, neurological, osseous growth anomalies, histological variables including muscle fiber percentage and core structure changes, metabolic and hormonal dysfunction, vestibular dysfunction, and platelet microarchitecture. The objective of this study was to contribute to the determination of the cause of AIS by analyzing the changes in pineal gland volume in AIS cases.

METHODS

Study (AIS) and control group were each comprised of 26 patients who met the inclusion requirements. Scoliosis radiograph and MRI of the pineal glands were used for radiological examinations. The distribution of age, gender, Risser grading for skeletal radiological development, and sexual maturation according to Tanner categorization were uniform and statistically insignificant between groups.

RESULTS

When the pineal gland volumes of the cases were evaluated according to age, the AIS group was found to have significantly reduced pineal gland volumes in all age groups. The pineal gland volume was found to be 38.1% lower in the AIS group compared to the control group (p˂0.001). In the AIS group, patients aged 13 years had the lowest pineal gland volume (77.2 ± 13.86 mm³), while patients aged 15 years had the highest volume (97.9 ± 16.47 mm³).

CONCLUSION

Changes in pineal gland volume support the role of the pineal gland in the etiopathogenesis of AIS.

Reactivation of Vertebral Growth Plate Function in Vertebral Body Tethering in an Animal Model

Flexible spine tethering is a relatively novel fusionless surgical technique that aims to correct scoliosis based on growth modulation due to the pressure exerted on the vertebral body epiphyseal growth plate. The correction occurs in two phases: immediate intraoperative and postoperative with growth. The aim of this study was to evaluate the reactivation of vertebral growth plate function after applying corrective forces. The rat tail model was used. Asymmetric compression and distraction of caudal growth plates were performed using a modified external fixation apparatus. Radiological and histopathological data were analysed. After three weeks of correction, the activity of the structures increased across the entire growth plate width, and the plate was thickened. The height of the hypertrophic layer and chondrocytes on the concave side doubled in height. The height of chondrocytes and the cartilage thickness on the concave and central sides after the correction did not differ statistically significantly from the control group. Initiation of the correction of scoliosis in the growing spine, with relief of the pressure on the growth plate, allows the return of the physiological activity of the growth cartilage and restoration of the deformed vertebral body.

Zebrafish: an important model for understanding scoliosis

Scoliosis is a common spinal deformity that considerably affects the physical and psychological health of patients. Studies have shown that genetic factors play an important role in scoliosis. However, its etiopathogenesis remain unclear, partially because of the genetic heterogeneity of scoliosis and the lack of appropriate model systems. Recently, the development of efficient gene editing methods and high-throughput sequencing technology has made it possible to explore the underlying pathological mechanisms of scoliosis. Owing to their susceptibility for developing scoliosis and high genetic homology with human, zebrafish are increasingly being used as a model for scoliosis in developmental biology, genetics, and clinical medicine. Here, we summarize the recent advances in scoliosis research on zebrafish and discuss the prospects of using zebrafish as a scoliosis model.

Current insights into the aetiology of adolescent idiopathic scoliosis

Scoliosis occurs in about 0.2-0.6% of the general population. In the majority of cases the cause of this entity remains mostly unidentified. The search for the causes covers almost all aspects of its possible origin. We collected and systematised the contemporary theories and concepts concerning the aetiology of adolescent idiopathic scoliosis. Genetic and hereditary factors are commonly accepted as possible causes; however, the identification of the single gene responsible for the development of this condition seems impossible, which suggests multifactorial mechanism of its formation. Dysfunctions of the nervous system are recognised risks related to the development of scoliosis, but they are classified as belonging to a separate aetiological category. Scoliosis develops at the quickest rate during the child's growth spurt, which prompted the research on the role of the growth hormone in scoliosis aetiology. Melatonin is another hormone that is studied as a possible factor involved in development of this entity. In cases of progressive scoliosis, increased activity of calmodulin-a protein that regulates the levels of calcium ions-has been observed. The scientists have characterised numerous qualitative and quantitative changes in the composition of the tissue of intervertebral discs, spinal ligaments and paraspinal muscles. Some of the theories, explaining the nature of this entity, presented in this review seem to have only a purely theoretical value; their proliferation only confirms the fact that the actual nature of this condition has not been unveiled yet, and suggests its multifactorial aetiology.

Understanding the role of the immune system in adolescent idiopathic scoliosis: Immunometabolic CONnections to Scoliosis (ICONS) study protocol

INTRODUCTION

Adolescent idiopathic scoliosis (AIS) affects up to 3% of children around the world. There is limited knowledge of AIS aetiopathogenesis, and this evidence is needed to develop new management strategies. Paraspinal muscle in AIS demonstrates evidence of differential fibrosis based on curve sidedness. Fibrosis is the hallmark of macrophage-driven inflammation and tissue remodelling, yet the mechanisms of fibrosis in paraspinal muscle in AIS are poorly understood.

OBJECTIVES

The primary objective of this study is to determine the influence of curve sidedness on paraspinal muscle inflammation. Secondary objectives include defining the mechanisms of macrophage homing to muscle, and determining muscle-macrophage crosstalk in muscle fibrosis in AIS.

METHODS AND ANALYSIS

This is a cross-sectional study conducted in a tertiary paediatric centre in Hamilton, Ontario, Canada. We will recruit boys and girls, 10-17 years of age, who are having surgery to correct AIS. We will exclude children who have an active infection or are on immunosuppressive therapies within 2 weeks of surgery, smokers and pregnant girls. Paraspinal muscle biopsies will be obtained at the start of surgery. Also, blood and urine samples will be collected from participants, who will fill questionnaires about their lifestyle. Anthropometric measures will also be collected including height, weight, waist and hip circumferences.

ETHICS AND DISSEMINATION

This study has received ethics authorisation by the institutional review board. This work will be published in peer-reviewed journals and will be presented in oral and poster formats at scientific meetings.

DISCUSSION

This study will explore the mechanisms of paraspinal muscle inflammation, remodelling and fibrosis in AIS. This will help identify pathways and molecules as potential therapeutic targets to treat and prevent AIS. It may also yield markers that predict scoliosis progression and response to treatment in these children.

A review of pinealectomy-induced melatonin-deficient animal models for the study of etiopathogenesis of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a common orthopedic disorder of unknown etiology and pathogenesis. Melatonin and melatonin pathway dysfunction has been widely suspected to play an important role in the pathogenesis. Many different types of animal models have been developed to induce experimental scoliosis mimicking the pathoanatomical features of idiopathic scoliosis in human. The scoliosis deformity was believed to be induced by pinealectomy and mediated through the resulting melatonin-deficiency. However, the lack of upright mechanical spinal loading and inherent rotational instability of the curvature render the similarity of these models to the human counterparts questionable. Different concerns have been raised challenging the scientific validity and limitations of each model. The objectives of this review follow the logical need to re-examine and compare the relevance and appropriateness of each of the animal models that have been used for studying the etiopathogenesis of adolescent idiopathic scoliosis in human in the past 15 to 20 years.

Understanding the Basis of Genetic Studies: Adolescent Idiopathic Scoliosis as an Example

STUDY DESIGN

A review of the general concepts of genetics studies with specific reference to adolescent idiopathic scoliosis (AIS).

OBJECTIVES

To equip the average spine surgeon with the vocabulary and understanding needed to understand the genetics of scoliosis and the approaches used to identify risk genes.

SUMMARY OF BACKGROUND DATA

Adolescent idiopathic scoliosis is a multifactorial disease. Increasing evidence from families and monozygotic twins suggests the involvement of genetic factors. An estimation of heritability also indicates a strong influence of genetics on the disease. Increasing focus has been placed on identifying genes and genetic variants associated with AIS.

REVIEW

This is a review of genes and genetic variations, the phenotype definition of AIS in genetics studies, concepts and approaches to identifying associated genes, and the evaluation of results. Different types of genetic variations are present in the genome. These variations may modulate the expression or function of protein products, which in turn alter individuals' susceptibility to disease. Identifying the variants related to AIS requires an objective and clearly defined phenotype, among which the Cobb angle is commonly used. The phenotype helps classify subjects into cases and controls. By selecting candidate genes of growth factors and hormonal receptors, which are speculated to be involved in the mechanism of disease, the variants within these genes were compared between cases and controls to identify any differences. Another approach was to use large families and inspect the co-segregation of variants and phenotypes. Recently, arrays covering the variants of the whole genome were developed and assist in high-throughput screening for associated genes.

CONCLUSIONS

Genetic factors have an important role in AIS. Deciphering the genes and genetic variants associated with AIS can improve our understanding of the mechanisms of the disease, as well as assist in designing treatment methods and preventive measures.

Experimental animal models in scoliosis research: a review of the literature

BACKGROUND CONTEXT

Many animal species and an overwhelming variety of procedures that produce an experimental scoliosis have been reported in the literature. However, varying results have been reported on identical procedures in different animal species. Furthermore, the relevance of experimental animal models for the understanding of human idiopathic scoliosis remains questionable.

PURPOSE

To give an overview of the procedures that have been performed in animals in an attempt to induce experimental scoliosis and discuss the characteristics and significance of various animal models.

STUDY DESIGN

Extensive review of the literature on experimental animal models in scoliosis research.

METHODS

MEDLINE electronic database was searched, focusing on parameters concerning experimental scoliosis in animal models. The search was limited to the English, French, and German languages.

RESULTS

The chicken appeared to be the most frequently used experimental animal followed by the rabbit and rat. Additionally, scoliosis has been induced in primates, goats, sheep, pigs, cows, dogs, and frogs. Procedures widely varied from systemic to local procedures.

CONCLUSIONS

Although it has been possible to induce scoliosis-like deformities in many animals through various ways, this always required drastic surgical or systemic interventions, thus making the relation to human idiopathic scoliosis unclear. The basic drawback of all used models remains that no animal resembles the upright biomechanical spinal loading condition of man, with its inherent rotational instability of certain spinal segments. The fundamental question remains what the significance of these animal models is to the understanding of human idiopathic scoliosis.

The role of melatonin in the pathogenesis of adolescent idiopathic scoliosis (AIS)

The cause of adolescent idiopathic scoliosis (AIS) in humans remains obscure and probably multifactorial. At present, there is no proven method or test available to identify children or adolescent at risk of developing AIS or identify which of the affected individuals are at risk of progression. Reported associations are linked in pathogenesis rather than etiologic factors. Melatonin may play a role in the pathogenesis of scoliosis (neuroendocrine hypothesis), but at present, the data available cannot clearly show the role of melatonin in producing scoliosis in humans. The data regarding human melatonin levels are mixed at best, and the melatonin deficiency as a causative factor in the etiology of scoliosis cannot be supported. It will be an important issue of future research to investigate the role of melatonin in human biology, the clinical efficacy, and safety of melatonin under different pathological situations. Research is needed to better define the role of all factors in AIS development.

Scientific basis for the potential use of melatonin in bone diseases: osteoporosis and adolescent idiopathic scoliosis

The objective of this paper was to analyze the data supporting the possible role of melatonin on bone metabolism and its repercussion in the etiology and treatment of bone pathologies such as the osteoporosis and the adolescent idiopathic scoliosis (AIS). Melatonin may prevent bone degradation and promote bone formation through mechanisms involving both melatonin receptor-mediated and receptor-independent actions. The three principal mechanisms of melatonin effects on bone function could be: (a) the promotion of the osteoblast differentiation and activity; (b) an increase in the osteoprotegerin expression by osteoblasts, thereby preventing the differentiation of osteoclasts; (c) scavenging of free radicals generated by osteoclast activity and responsible for bone resorption. A variety of in vitro and in vivo experimental studies, although with some controversial results, point toward a possible role of melatonin deficits in the etiology of osteoporosis and AIS and open a new field related to the possible therapeutic use of melatonin in these bone diseases.

Pinealectomy in the chicken: a good model of scoliosis?

The phenomenon of spinal deformity in the pinealectomized chicken has led researchers to postulate a disturbance of melatonin activity as a potential cause of adolescent idiopathic scoliosis (AIS). More recently, structural differences between curves seen in this model and those seen in scoliosis have been highlighted suggesting the deformities observed are not as similar as first thought. We examined melatonin levels, and the radiological and histological characteristics of scoliosis after pinealectomy in chickens. They underwent pinealectomy (P) at 2 days of age, sham surgery (S) or served as controls (C). Mean melatonin levels were 32.9 pmol/L (P), 175 pmol/L (S) and 227.3 pmol/L (C). Scoliosis developed in 75% of chickens after pinealectomy and 38% after a sham procedure. Nineteen percent of unoperated controls also developed scoliosis. A lower melatonin level was associated with the development of scoliosis (p < or = 0.001), but exceptions were seen with levels up to 265 pmol/L observed in one case. Most of the curves occurring spontaneously and after sham surgery and almost half after pinealectomy were short angular curves: distinct from those resembling idiopathic scoliosis. These occur over one or two segments and are characterized by marked apical wedging, frequently associated with subluxation or dislocation. The intervertebral joint in the chicken is more like a synovial joint histologically than an intervertebral disc. This study highlights important differences between the chicken and the human, and between their respective spinal deformities. Caution is advised when drawing conclusions regarding the pathogenesis of AIS from this model.

The pathogenesis of adolescent idiopathic scoliosis: review of the literature

STUDY DESIGN

Review of the literature on the pathogenesis of adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To discuss the different theories that have appeared on this subject.

SUMMARY OF BACKGROUND DATA

The pathogenesis of AIS, a condition exclusive to humans, has been the subject of many studies. Over the years, practically every structure of the body has been mentioned in the pathogenesis of AIS; however, the cause of this spinal deformity remains little understood. The pathogenesis of this condition is termed multifactorial.

METHODS

PubMed and Google Scholar electronic databases were searched focused on parameters concerning the pathogenesis of adolescent idiopathic scoliosis. The search was limited to the English language.

RESULTS

No single causative factor for the development of idiopathic scoliosis has been identified, it is thus termed multifactorial. AIS is a complex genetic disorder. The fully erect posture, which is unique to humans, seems to be a prerequisite for the development of AIS.

CONCLUSION

Although any or all of the mentioned factors in this review may play a certain role in the initiation and progression of AIS at a certain stage, the presented material suggests that in the observed deformation, genetics, and the unique mechanics of the fully upright human spine play a decisive role.

Adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) affects 1-3% of children in the at-risk population of those aged 10-16 years. The aetiopathogensis of this disorder remains unknown, with misinformation about its natural history. Non-surgical treatments are aimed to reduce the number of operations by preventing curve progression. Although bracing and physiotherapy are common treatments in much of the world, their effectiveness has never been rigorously assessed. Technological advances have much improved the ability of surgeons to safely correct the deformity while maintaining sagittal and coronal balance. However, we do not have long-term results of these changing surgical treatments. Much has yet to be learned about the general health, quality of life, and self-image of both treated and untreated patients with AIS.

Idiopathic scoliosis and pineal lesions in Australian children

PURPOSE

To determine whether treatment of pineal lesions in children is associated with development of idiopathic scoliosis.

METHODS

38 boys and 10 girls with pineal lesions were identified. Their mean age at presentation was 10 years. The pineal pathology varied from cysts and epidermoid to teratoma, germinoma, pineocytoma, and glioblastoma. Treatment ranged from biopsy/extirpation to radiotherapy.

RESULTS

12 patients died. No scoliosis was found in any females or any of the deceased. Two boys had scoliosis: one had a 12-degree right upper thoracic curve with 32-degree kyphosis and the other had a 60-degree right thoracolumbar idiopathic curve, requiring a 2-stage arthrodesis.

CONCLUSION

Pineal ablation is not related to the development of idiopathic scoliosis in humans.

Are animal models useful for studying human disc disorders/degeneration?

Intervertebral disc (IVD) degeneration is an often investigated pathophysiological condition because of its implication in causing low back pain. As human material for such studies is difficult to obtain because of ethical and government regulatory restriction, animal tissue, organs and in vivo models have often been used for this purpose. However, there are many differences in cell population, tissue composition, disc and spine anatomy, development, physiology and mechanical properties, between animal species and human. Both naturally occurring and induced degenerative changes may differ significantly from those seen in humans. This paper reviews the many animal models developed for the study of IVD degeneration aetiopathogenesis and treatments thereof. In particular, the limitations and relevance of these models to the human condition are examined, and some general consensus guidelines are presented. Although animal models are invaluable to increase our understanding of disc biology, because of the differences between species, care must be taken when used to study human disc degeneration and much more effort is needed to facilitate research on human disc material.

Recent advances in the aetiology of adolescent idiopathic scoliosis

The aetiology of adolescent idiopathic scoliosis (AIS) is still unknown despite many years of research effort. Theories on AIS's aetiology have included mechanical, hormonal, metabolic, neuromuscular, growth, and genetic abnormalities. Amongst these, some factors may be epiphenomena rather than the cause itself. Other factors may even contribute to curve progression, rather than curve initiation. Current views maintain that AIS is a multifactorial disease with genetic predisposing factors [Lowe et al. in J Bone Joint Surg [Am] 82:1157-1168, 2000]. With improvements in diagnostic methods, imaging and genomics, there has been considerable recent work on aetiology. This review aims to bring readers up-to-date with the latest developments in scoliosis research.

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited

OBJECTIVE

The objectives of this white paper are to review and summarize the basic science literature relevant to spinal fixation (subluxation) and spinal adjusting procedures and to make specific recommendations for future research.

METHODS

PubMed, CINAHL, ICL, OSTMED, and MANTIS databases were searched by a multidisciplinary team for reports of basic science research (since 1995) related to spinal fixation (subluxation) and spinal adjusting (spinal manipulation). In addition, hand searches of the reference sections of studies judged to be important by the authors were also obtained. Each author used key words they determined to be most important to their field in designing their individual search strategy. Both animal and human studies were included in the literature searches, summaries, and recommendations for future research produced in this project.

DISCUSSION

The following topic areas were identified: anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system. A relevant summary of each topic area and specific recommendations for future research in each area were the primary objectives of this project.

CONCLUSIONS

The summaries of the literature for the 6 topic sections (anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system) indicated that a significant body of basic science research evaluating chiropractic spinal adjusting has been completed and published since the 1997 basic science white paper. Much more basic science research in these fields needs to be accomplished, and the recommendations at the end of each topic section should help researchers, funding agencies, and other decision makers develop specific research priorities.

Changes in melatonin receptors in relation to the development of scoliosis in pinealectomized chickens

STUDY DESIGN

The 2[125I]iodomelatonin binding assay was used to investigate the involvement of melatonin receptors in the development of scoliosis in pinealectomized chickens.

OBJECTIVE

To compare the binding properties of melatonin receptors in the thoracic spinal cord between pinealectomized chickens that had scoliosis develop and those that did not.

SUMMARY OF BACKGROUND DATA

Surgical pinealectomy in young chickens induced scoliosis with a reported incidence of 50% to 100%. The factors regulating the development of scoliosis in this animal model are unclear. Melatonin receptors have been shown in the spinal cord of chickens, but their functions are still unknown. This study addresses the question as to whether spinal cord melatonin receptors are related to the pathogenesis of scoliosis in pinealectomized chickens.

METHOD

Control and pinealectomized chickens were kept under controlled lighting conditions and monitored for scoliosis development. At 9-11 weeks after pinealectomy, thoracic spinal cords were removed for 2[125I]iodomelatonin binding assay, and blood was collected for serum melatonin assay at either the middle of the light period or middle of the dark period.

RESULTS

Pinealectomy in young chickens produced: (1) loss of diurnal variations in serum melatonin levels, (2) 50% incidence of scoliosis, and (3) attenuation in the diurnal variations in the receptor affinity to melatonin. No differences were detected in the serum melatonin levels or binding of spinal cord melatonin receptors between the pinealectomized chickens that had scoliosis develop and those that did not.

CONCLUSION

Changes are detected in melatonin receptor binding after pinealectomy. However, these changes cannot account for the reason why scoliosis develops in some chickens after pinealectomy, while it does not in others. Neither low melatonin serum level nor changes in spinal cord melatonin binding can be a sole etiologic factor in the pathogenesis of scoliosis in pinealectomized chickens.

Unilateral enucleation affects the laterality but not the incidence of scoliosis in pinealectomized chicken

STUDY DESIGN

Randomized prospective study using an experimental scoliosis model in a pinealectomized chicken.

OBJECTIVE

To investigate the effect of the side of visual impairment on the incidence and laterality of the curves on a pinealectomized chicken model.

SUMMARY OF BACKGROUND DATA

Visual impairment has been shown to increase the incidence of idiopathic-like scoliosis in human subjects when compared to the incidence of the general population. However, an association between the laterality of the visual impairment and incidence or laterality of scoliosis has not been established.

METHODS

A total of 60 newly hatched white leghorn chicks was divided equally into 3 study groups of no visual impairment (n = 20) (group 1), left-sided blindness by enucleation (n = 20) (group 2), and right-sided blindness (n = 20) (group 3). Pinealectomies and enucleations were performed on the second day after hatching. Anteroposterior radiographs were obtained at the 5th and 10th weeks, and the incidence, side, and magnitude of the resulting scoliotic curves were recorded.

RESULTS

The pinealectomy model yielded a general scoliosis incidence of 60%. The occurrence of scoliosis was not different among the groups (65%, 55%, 60%, respectively, P = 0.812). The incidences at the 5th and 10th weeks were both 40%, as a result of the death of 6 chickens between the 5th and 10th weeks, as well as the appearance or disappearance of curves during this time, again not different among the groups. However, the laterality of the curves was significantly different (P = 0.045). The visually impaired groups tended to have left thoracic curves as frequently as the right thoracic curves (7 right and 4 left in group 2, and 7 right and 6 left in group 3), whereas in group 1, the thoracic curves were predominantly right sided (12 right and 1 left). The average magnitude of the curves was 30.47 degrees +/- 19.32 degrees , not significantly different among the groups (27.6 degrees +/- 16.7 degrees , 23.7 degrees +/- 21.5 degrees , 39.8 degrees +/- 17.7 degrees , respectively, P = 0.109).

CONCLUSIONS

Unilateral visual impairment does not have a significant effect on the overall incidence and magnitude of scoliosis in the pinealectomized chicken. It does affect the laterality of the curves though, visually impaired subjects having a significantly higher likelihood of left thoracic curves, regardless of the side of blindness. It may be worthwhile to see if such an association is present in human beings as well.

The effect of pinealectomy on scoliosis development in young nonhuman primates

STUDY DESIGN

Prospective study on pinealectomy in primates.

OBJECTIVE

To evaluate whether pinealectomy in a bipedal nonhuman primate model will result in the development of scoliosis.

SUMMARY OF BACKGROUND DATA

Pinealectomy in newborn chickens consistently resulted in scoliosis development. Published data suggest that the surgical removal of the pineal, loss of melatonin secretion, and a bipedal posture are important elements in the development of scoliosis in lower animal models.

METHOD

There were 18 rhesus monkeys between 8 and 11 months old that underwent pineal excision. All monkeys were kept in a regulated 12-hour light-dark cycle. Monthly radiographs assessed scoliosis development. Completeness of pineal excision was assessed by measurement of a major metabolite of melatonin in the urine, 6-sulfatoxymelatonin, using an enzyme-linked immunosorbent assay assessed.

RESULTS

Mean follow-up was 28 months (range 10-41). Seven monkeys died prematurely, and 11 survived to date; the data from those that died could still be used, although follow-up was shortened. At the latest follow-up or death, scoliosis did not develop in any of the monkeys. Urinary 6-sulfatoxymelatonin measurements revealed 3 patterns. Group 1 consisted of 10 monkeys, which showed definite evidence of complete pineal excision. Group 2 consisted of an uncertain group of 2 monkeys in which the nighttime melatonin level is slightly high. Group 3 consisted of 6 monkeys that had incomplete pineal excision or ectopic melatonin production.

CONCLUSIONS

To our knowledge, this is the first report of pinealectomy in nonhuman primates. Of the 18 monkeys, 10 had a loss of melatonin secretion, for a mean of 29 months after surgery. Because none of the monkeys had scoliosis develop, this study strongly suggests that the possible etiologic factors producing idiopathic scoliosis in lower animals are different from primates, and findings in lower animals cannot necessarily be extrapolated to human beings.

Role of melatonin in neurodegenerative diseases

The pineal product melatonin has remarkable antioxidant properties. It scavenges hydroxyl, carbonate and various organic radicals, peroxynitrite and other reactive nitrogen species. Melatonyl radicals formed by scavenging combine with and, thereby, detoxify superoxide anions in processes terminating the radical reaction chains. Melatonin also enhances the antioxidant potential of the cell by stimulating the synthesis of antioxidant enzymes like superoxide dismutase, glutathione peroxidase and glutathione reductase, and by augmenting glutathione levels. The decline in melatonin production in aged individuals has been suggested as one of the primary contributing factors for the development of age-associated neurodegenerative diseases, e.g., Alzheimer's disease. Melatonin has been shown to be effective in arresting neurodegenerative phenomena seen in experimental models of Alzheimer's disease, Parkinsonism and ischemic stroke. Melatonin preserves mitochondrial homeostasis, reduces free radical generation, e.g., by enhancing mitochondrial glutathione levels, and safeguards proton potential and ATP synthesis by stimulating complex I and IV activities. Therapeutic trials with melatonin have been effective in slowing the progression of Alzheimer's disease but not of Parkinson's disease. Melatonin's efficacy in combating free radical damage in the brain suggests that it may be a valuable therapeutic agent in the treatment of cerebral edema after traumatic brain injury.