Differential effects of nicotine and tobacco smoke condensate on human annulus fibrosus cell metabolism

Bioenergetic dysfunction in the pathogenesis of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a frequent cause of low back pain and is the most common cause of disability. Treatments for symptomatic IVD degeneration, including conservative treatments such as analgesics, physical therapy, anti-inflammatories and surgeries, are aimed at alleviating neurological symptoms. However, there are no effective treatments to prevent or delay IVD degeneration. Previous studies have identified risk factors for IVD degeneration such as aging, inflammation, genetic factors, mechanical overload, nutrient deprivation and smoking, but metabolic dysfunction has not been highlighted. IVDs are the largest avascular structures in the human body and determine the hypoxic and glycolytic features of nucleus pulposus (NP) cells. Accumulating evidence has demonstrated that intracellular metabolic dysfunction is associated with IVD degeneration, but a comprehensive review is lacking. Here, by reviewing the physiological features of IVDs, pathological processes and metabolic changes associated with IVD degeneration and the functions of metabolic genes in IVDs, we highlight that glycolytic pathway and intact mitochondrial function are essential for IVD homeostasis. In degenerated NPs, glycolysis and mitochondrial function are downregulated. Boosting glycolysis such as HIF1α overexpression protects against IVD degeneration. Moreover, the correlations between metabolic diseases such as diabetes, obesity and IVD degeneration and their underlying molecular mechanisms are discussed. Hyperglycemia in diabetic diseases leads to cell senescence, the senescence-associated phenotype (SASP), apoptosis and catabolism of extracellualr matrix in IVDs. Correcting the global metabolic disorders such as insulin or GLP-1 receptor agonist administration is beneficial for diabetes associated IVD degeneration. Overall, we summarized the recent progress of investigations on metabolic contributions to IVD degeneration and provide a new perspective that correcting metabolic dysfunction may be beneficial for treating IVD degeneration.

A new perspective on intervertebral disc calcification-from bench to bedside

Disc degeneration primarily contributes to chronic low back and neck pain. Consequently, there is an urgent need to understand the spectrum of disc degeneration phenotypes such as fibrosis, ectopic calcification, herniation, or mixed phenotypes. Amongst these phenotypes, disc calcification is the least studied. Ectopic calcification, by definition, is the pathological mineralization of soft tissues, widely studied in the context of conditions that afflict vasculature, skin, and cartilage. Clinically, disc calcification is associated with poor surgical outcomes and back pain refractory to conservative treatment. It is frequently seen as a consequence of disc aging and progressive degeneration but exhibits unique molecular and morphological characteristics: hypertrophic chondrocyte-like cell differentiation; TNAP, ENPP1, and ANK upregulation; cell death; altered Pi and PPi homeostasis; and local inflammation. Recent studies in mouse models have provided a better understanding of the mechanisms underlying this phenotype. It is essential to recognize that the presentation and nature of mineralization differ between AF, NP, and EP compartments. Moreover, the combination of anatomic location, genetics, and environmental stressors, such as aging or trauma, govern the predisposition to calcification. Lastly, the systemic regulation of calcium and Pi metabolism is less important than the local activity of PPi modulated by the ANK-ENPP1 axis, along with disc cell death and differentiation status. While there is limited understanding of this phenotype, understanding the molecular pathways governing local intervertebral disc calcification may lead to developing disease-modifying drugs and better clinical management of degeneration-related pathologies.

Achilles' Heel-The Significance of Maintaining Microenvironmental Homeostasis in the Nucleus Pulposus for Intervertebral Discs

The dysregulation of intracellular and extracellular environments as well as the aberrant expression of ion channels on the cell membrane are intricately linked to a diverse array of degenerative disorders, including intervertebral disc degeneration. This condition is a significant contributor to low back pain, which poses a substantial burden on both personal quality of life and societal economics. Changes in the number and function of ion channels can disrupt the water and ion balance both inside and outside cells, thereby impacting the physiological functions of tissues and organs. Therefore, maintaining ion homeostasis and stable expression of ion channels within the cellular microenvironment may prove beneficial in the treatment of disc degeneration. Aquaporin (AQP), calcium ion channels, and acid-sensitive ion channels (ASIC) play crucial roles in regulating water, calcium ions, and hydrogen ions levels. These channels have significant effects on physiological and pathological processes such as cellular aging, inflammatory response, stromal decomposition, endoplasmic reticulum stress, and accumulation of cell metabolites. Additionally, Piezo 1, transient receptor potential vanilloid type 4 (TRPV4), tension response enhancer binding protein (TonEBP), potassium ions, zinc ions, and tungsten all play a role in the process of intervertebral disc degeneration. This review endeavors to elucidate alterations in the microenvironment of the nucleus pulposus during intervertebral disc degeneration (IVDD), with a view to offer novel insights and approaches for exploring therapeutic interventions against disc degeneration.

The Impact of Smoking Cessation Therapy on Lumbar Fusion Outcomes

OBJECTIVE

While there are several reports on the impact of smoking tobacco on spinal fusion outcomes, there is minimal literature on the influence of modern smoking cessation therapies on such outcomes. Our study explores the outcomes of single-level lumbar fusion surgery in active smokers and in smokers undergoing recent cessation therapy.

METHODS

MARINER30, an all-payer claims database, was utilized to identify patients undergoing single-level lumbar fusions between 2010 and 2019. The primary outcomes were the rates of any complication, symptomatic pseudarthrosis, need for revision surgery, and all-cause readmission within 30 and 90 days.

RESULTS

The exact matched population analyzed in this study contained 31,935 patients undergoing single-level lumbar fusion with 10,645 (33%) in each of the following groups: (1) active smokers; (2) patients on smoking cessation therapy; and (3) those without any smoking history. Patients undergoing smoking cessation therapy have reduced odds of developing any complication following surgery (odds ratio 0.86, 95% confidence interval 0.80-0.93) when compared with actively smoking patients. Nonsmokers and patients on cessation therapy had a significantly lower rate of any complication compared with the smoking group (9.5% vs. 17% vs. 19%, respectively).

CONCLUSIONS

When compared with active smoking, preoperative smoking cessation therapy within 90 days of surgery decreases the likelihood of all-cause postoperative complications. However, there were no between-group differences in the likelihood of pseudarthrosis, revision surgery, or readmission within 90 days.

Platelet-Derived Biomaterials Inhibit Nicotine-Induced Intervertebral Disc Degeneration Through Regulating IGF-1/AKT/IRS-1 Signaling Axis

Apart from aging process, adult intervertebral disc (IVD) undergoes various degenerative processes. However, the nicotine has not been well identified as a contributing etiology. According to a few studies, nicotine ingestion through smoking, air or clothing may significantly accumulate in active as well as passive smokers. Since nicotine has been demonstrated to adversely impact various physiological processes, such as sympathetic nervous system, leading to impaired vasculature and cellular apoptosis, we aimed to investigate whether nicotine could induce IVD degeneration. In particular, we evaluated dose-dependent impact of nicotine in vitro to simulate its chronic accumulation, which was later treated by platelet-derived biomaterials (PDB). Further, during in vivo studies, mice were subcutaneously administered with nicotine to examine IVD-associated pathologic changes. The results revealed that nicotine could significantly reduce chondrocytes and chondrogenic indicators (Sox, Col II and aggrecan). Mice with nicotine treatment also exhibited malformed IVD structure with decreased Col II as well as proteoglycans, which was significantly increased after PDB administration for 4 weeks. Mechanistically, PDB significantly restored the levels of IGF-1 signaling proteins, particularly pIGF-1 R, pAKT, and IRS-1, modulating ECM synthesis by chondrocytes. Conclusively, the PDB impart reparative and tissue regenerative processes by inhibiting nicotine-initiated IVD degeneration, through regulating IGF-1/AKT/IRS-1 signaling axis.

Canine models of spine disorders

Neck and low back pain are common among the adult human population and impose large social and economic burdens on health care and quality of life. Spine-related disorders are also significant health concerns for canine companions with etiopathogeneses, clinical presentations, and diagnostic and therapeutic options that are very similar to their human counterparts. Historically, induced and spontaneous pathology in laboratory rodents, dogs, sheep, goats, pigs, and nonhuman primates have been used for study of human spine disorders. While each of these can serve as useful preclinical models, they all have inherent limitations. Spontaneously occurring spine disorders in dogs provide highly translatable data that overcome many of the limitations of other models and have the added benefit of contributing to veterinary healthcare as well. For this scoping review, peer-reviewed manuscripts were selected from PubMed and Google Scholar searches using keywords: "intervertebral disc," "intervertebral disc degeneration," "biomarkers," "histopathology," "canine," and "mechanism." Additional keywords such as "injury," "induced model," and "nucleus degeneration" were used to further narrow inclusion. The objectives of this review were to (a) outline similarities in key features of spine disorders between dogs and humans; (b) describe relevant canine models; and (c) highlight the applicability of these models for advancing translational research and clinical application for mechanisms of disease, diagnosis, prognosis, prevention, and treatment, with a focus on intervertebral disc degeneration. Best current evidence suggests that dogs share important anatomical, physiological, histological, and molecular components of spinal disorders in humans, such that induced and spontaneous canine models can be very effective for translational research. Taken together, the peer-reviewed literature supports numerous advantages for use of canine models for study of disorders of the spine when the potential limitations and challenges are addressed.

Relationship of lumbar disc degeneration with hemoglobin value and smoking

BACKGROUND/OBJECTIVE

Although a number of studies report an important effect of smoking on disc degeneration and herniation, others did not identify such a relationship. The purpose of this study was to assess the relationship of lumbar disc degeneration with hemoglobin value and smoking.

METHODS

The study included 200 adult patients who presented to the neurosurgery polyclinic with a complaint of back pain. Smoking habits were classified as "smoking for more than 10 years", "smoking for less than 10 years", and "not smoking". Lumbar disc degeneration was classified on modified Pfirrmann score according to lumbar MR images. Degeneration level was compared according to smoking group on Kruskal-Wallis test. The relationship between hemoglobin value and disc degeneration according to smoking group was assessed on the Spearman correlation coefficient.

RESULTS

Disc degeneration values were significantly different between groups in L5-S1, L4-L5 and L3-L4 (P=0.018, P=0.012, P=0.038). Degeneration levels in L5-S1 in those who did not smoke were significantly lower than in those who smoked for both less and more than 10 years (P=0.048, P=0.022). No significant differences were found in degeneration level between those who smoked for more versus less than 10 years. For L3-L4 degeneration, there was a significant relationship with hemoglobin value in the group that did not smoke and in the group that smoked for more than 10 years (r=-0.395; P=0.009, r=0.329; P=0.018).

CONCLUSION

This study found that, when risk factors such as systemic disease, heavy working conditions, obesity, trauma and family history were excluded, smoking increased lumbar disc degeneration. In addition, chronic smoking was found to increase hemoglobin values.

Detection of apoptosis and matrical degeneration within the intervertebral discs of rats due to passive cigarette smoking

Although low-back pain is considered to be associated with cigarette smoking, the influence of cigarette smoking on the intervertebral discs (IVD) has not been confirmed. We established a rat model of passive cigarette smoking-induced IVD degeneration, and investigated the cytohistological changes in the IVD and the accompanying changes in gene expression. IVD from rats exposed to 8 weeks of passive cigarette smoking were stained with Elastica van Gieson, and exhibited marked destruction of the supportive structure of the reticular matrix in the nucleus pulposus (NP). Positive signals on safranin O, alcian blue, type II collagen and aggrecan staining were decreased in the destroyed structure. Safranin O and type II collagen signals were also decreased in the cartilage end-plate (CEP) after 4- and 8-weeks of cigarette smoking. In the CEP, the potential for apoptosis was increased significantly, as demonstrated by staining for single-strand DNA. However, there were no signs of apoptosis in the NP or annulus fibrosus cells. Based on these findings, we hypothesized that passive cigarette smoking-induced stress stimuli first affect the CEP through blood flow due to the histological proximity, thereby stimulating chondrocyte apoptosis and reduction of the extracellular matrix (ECM). This leads to reduction of the ECM in the NP, destroying the NP matrix, which can then progress to IVD degeneration.

Electronic cigarette liquid exposure induces flavor-dependent osteotoxicity and increases expression of a key bone marker, collagen type I

Electronic cigarettes (e-cigarettes) are nicotine delivery devices advertised as a healthier alternative to conventional tobacco products, but their rapid rise in popularity outpaces research on potential health consequences. As conventional tobacco use is a risk factor for osteoporosis, this study examines whether exposure to electronic liquid (e-liquid) used in e-cigarettes affects bone-forming osteoblasts. Human MG-63 and Saos-2 osteoblast-like cells were treated for 48 hours with 0.004%-4.0% dilutions of commercially available e-liquids of various flavors with or without nicotine. Changes in cell viability and key osteoblast markers, runt-related transcription factor 2 and Col1a1, were assessed. With all e-liquids tested, cell viability decreased in a dose-dependent manner, which was least pronounced in flavorless e-liquids, most pronounced in cinnamon-flavored e-liquids and occurred independently of nicotine. Col1a1, but not runt-related transcription factor 2, mRNA expression was upregulated in response to coffee-flavored and fruit-flavored e-liquids. Cells treated with a non-cytotoxic concentration of fruit-flavored Mango Blast e-liquid with or without nicotine showed significantly increased collagen type I protein expression compared to culture medium only. We conclude that the degree of osteotoxicity is flavor-dependent and occurs independently of nicotine and that flavored e-liquids reveal collagen type I as a potential target in osteoblasts. This study elucidates potential consequences of e-cigarette use in bone.

Effect of compliant layers within piezoelectric composites on power generation providing electrical stimulation in low frequency applications

For patients that use tobacco or have diabetes, bone healing after orthopedic procedures is challenging. Direct current electrical stimulation has shown success clinically to significantly improve bone healing in these difficult-to-fuse populations. Energy harvesting with piezoelectric material has gained popularity in the last decade, but is challenging at low frequencies due to material properties that limit total power generation at these frequencies. Stacked generators have been used to increase power generation at lower voltage levels but have not been widely explored as a load-bearing biomaterial to provide DC stimulation. To match structural compliance levels and increase efficiency of power generation at low frequencies, the effect of compliant layers between piezoelectric discs was investigated. Compliant Layer Adaptive Composite Stacks (CLACS) were manufactured using five PZT discs connected electrically in parallel and stacked mechanically in series with a layer of low modulus epoxy between each disc. The stacks were encapsulated, keeping PZT and overall volume constant. Each stack was electromechanically tested by varying load, frequency, and resistance. As compliant layer thickness increased, power generation increased significantly across all loads, frequencies, and resistances measured. As expected, increase in frequency significantly increased power output for all groups. Similarly, an increase applied peak-to-peak mechanical load also significantly increased power output. The novel use of CLACS for power generation under load and frequencies experienced by typical orthopedic implants could provide an effective method to harvest energy and provide power without the use of a battery in multiple low frequency applications.

A retrospective study: Does cigarette smoking induce cervical disc degeneration?

OBJECTIVE

To investigate cigarette smoking's relevance with cervical disc degeneration.

METHODS

We randomly selected 320 patients who came to our spine disease department outpatient clinic with chief complaint of neck-shoulder pain during June 2014-June 2016. According to the detailed smoking history, these patients were divided into 3 different groups, which were active smoker group (AS), passive smoking group (PS) and never-smoker group (NS). Each patient's Miyazaki's magnetic resonance imaging (MRI) classification of cervical disc degeneration was analyzed based on their cervical MRI films. In addition, VAS scores were applied to evaluate the degree of patients' neck-shoulder pain. With the help of statistical techniques, relevance between cigarette smoking, cervical disc degeneration and neck-shoulder pain were analyzed.

RESULTS

In the NS group, the overall Miyazaki score, especially for C2/3, C3/4, C5,6 segments, are superior to those in the PS group, in addition, the Miyazaki scores for C1/2 - C6/7 segments in NS group beat the same segments in AS group with statistical significance (P < 0.05). In the AS and PS group, discs from C4/5 to C5/6 segments which score IV and V on Miyazaki classification account for a larger proportion than those discs from C1/2 to C3/4 segments with statistical significance (P < 0.05). In the AS group, male cases have larger proportion of Miyazaki level IV and V discs than female with statistical significance (P < 0.05). While in the AS and PS group, Miyazaki scores of patients whose smoking history ranges from 5 to 10 years are superior to those with smoking history longer than 10 years, with statistical significance (P < 0.05). In addition, VAS scores also vary among the three groups, in which, VAS scores in AS group are higher than those in the NS group.

CONCLUSION

Smoking could accelerate the process of cervical disc degeneration, presenting with more severe neck-shoulder pain on the patients. In addition, the impact of smoking on the lower cervical discs is greater than the upper cervical discs.

The Effect of Smoking on Spinal Fusion

BACKGROUND

Spinal fusion surgery is performed about half a million times per year in the United States and millions more worldwide. It is an effective method for reducing pain, increasing stability, and correcting deformity in patients with various spinal conditions. In addition to being a well-established risk factor for a variety of medical conditions, smoking has deleterious effects on the bone healing of spinal fusions. This review aims to specifically analyze the ways in which smoking affects the outcomes of spinal fusion and to explore ways in which these negative consequences can be avoided.

PURPOSE

This article provides a complete understanding of the ways smoking affects spinal fusion from a biochemical and clinical perspective. Recommendations are also provided for ways in which surgeons can limit patient exposure to the most serious negative outcomes associated with cigarette smoking.

STUDY DESIGN/SETTING

This study was a retrospective literature review done using the NCBI database. The research was compiled at NYU Hospital for Joint Diseases and the NYU Center for Musculoskeletal Care.

METHODS

A comprehensive literature review was done spanning research on a variety of subjects related to smoking and spinal fusion surgery. The biochemistry of smoking and fusion healing were examined in great detail. In addition, both in vivo animal studies and human clinical studies were evaluated to explore fusion success related to the effects of smoking and its biochemical factors on spinal fusion surgery.

RESULTS

Smoking significantly increases the risk of pseudoarthrosis for patients undergoing both lumbar and cervical fusions. In addition to nonunion, smoking also increases the risk of other perioperative complications such as infection, adjacent-segment pathology, and dysphagia. Treatment options are available that can be explored to reduce the risk of smoking-related morbidity, such as nicotine replacement therapy and use of bone morphogenetic proteins (BMPs).

CONCLUSIONS

It has been clearly demonstrated from both a biochemical and clinical perspective that smoking increases the rate of perioperative complications for patients undergoing spinal fusion surgery, particularly pseudoarthosis. It has also been shown that there are certain approaches that can reduce the risk of morbidity. The most important recommendation is smoking cessation for four weeks after surgery. In addition, patients may be treated with certain surgical techniques, including the use of BMPs, to reduce the risk of pseudoarthrosis. Lastly, nicotine replacement therapy is an area of continued interest in relation to spinal fusion outcomes and more research needs to be done to determine its efficacy moving forward.

ADAMTS5 Deficiency Protects Mice From Chronic Tobacco Smoking-induced Intervertebral Disc Degeneration

STUDY DESIGN

ADAMTS5-deficient and wild type (WT) mice were chronically exposed to tobacco smoke to investigate effects on intervertebral disc degeneration (IDD).

OBJECTIVE

The aim of this study was to demonstrate a role for ADAMTS5 in mediating tobacco smoking-induced IDD.

SUMMARY OF BACKGROUND DATA

We previously demonstrated that chronic tobacco smoking causes IDD in mice because, in part, of proteolytic destruction of disc aggrecan. However, it was unknown which matrix proteinase(s) drive these detrimental effects.

METHODS

Three-month-old WT (C57BL/6) and ADAMTS5 mice were chronically exposed to tobacco smoke (four cigarettes/day, 5 day/week for 6 months). ADAMTS-mediated cleavage of disc aggrecan was analyzed by Western blot. Disc total glycosaminoglycan (GAG) content was assessed by dimethyl methylene blue assay and safranin O/fast green histology. Vertebral osteoporosity was measured by microcomputed tomography. Human nucleus pulposus (hNP) cell cultures were also exposed directly to tobacco smoke extract (TSE), a condensate containing the water-soluble compounds inhaled by smokers, to measure ADAMTS5 expression and ADAMTS-mediated cleavage of aggrecan. Activation of nuclear factor (NF)-κB, a family of transcription factors essential for modulating the cellular response to stress, was measured by immunofluorescence assay.

RESULTS

Genetic depletion of ADAMTS5 prevented vertebral bone loss, substantially reduced loss of disc GAG content, and completely obviated ADAMTS-mediated proteolysis of disc aggrecan within its interglobular domain (IGD) in mice following exposure to tobacco smoke. hNP cell cultures exposed to TSE also resulted in upregulation of ADAMTS5 protein expression and a concomitant increase in ADAMTS-mediated cleavage within aggrecan IGD. Activation of NF-κB, known to be required for ADAMTS5 gene expression, was observed in both TSE-treated hNP cell cultures and disc tissue of tobacco smoke-exposed mice.

CONCLUSION

The findings demonstrate that ADAMTS5 is the primary aggrecanase mediating smoking-induced disc aggrecanolysis and IDD. Mouse models of chronic tobacco smoking are important and useful for probing the mechanisms of disc aggrecan catabolism and IDD.

LEVEL OF EVIDENCE

N/A.

The Clinical Correlations between Diabetes, Cigarette Smoking and Obesity on Intervertebral Degenerative Disc Disease of the Lumbar Spine

Study Design

Retrospective analysis of a nationwide private insurance database. Chi-square analysis and linear regression models were utilized for outcome measures.

Purpose

The purpose of this study was to investigate any relationship between lumbar degenerative disc disease, diabetes, obesity and smoking tobacco.

Overview of Literature

Diabetes, obesity, and smoking tobacco are comorbid conditions known to individually have effect on degenerative disc disease. Most studies have only been on a small populous scale. No study has yet to investigate the combination of these conditions within a large patient cohort nor have they reviewed the combination of these conditions on degenerative disc disease.

Methods

A retrospective analysis of insurance billing codes within the nationwide Humana insurance database was performed, using PearlDiver software (PearlDiver, Inc., Fort Wayne, IN, USA), to identify trends among patients diagnosed with lumbar disc degenerative disease with and without the associated comorbidities of obesity, diabetes, and/or smoking tobacco. Patients billed for a comorbidity diagnosis on the same patient record as the lumbar disc degenerative disease diagnosis were compared over time to patients billed for lumbar disc degenerative disease without a comorbidity. There were no sources of funding for this manuscript and no conflicts of interest.

Results

The total number and prevalence of patients (per 10,000) within the database diagnosed with lumbar disc degenerative disease increased by 241.4% and 130.3%, respectively. The subsets of patients within this population who were concurrently diagnosed with either obesity, diabetes, tobacco use, or a combination thereof, was significantly higher than patients diagnosed with lumbar disc degenerative disease alone (p <0.05 for all). The number of patients diagnosed with lumbar disc degenerative disease and smoking rose significantly more than patients diagnosed with lumbar disc degenerative disease and either diabetes or obesity (p <0.05). The number of patients diagnosed with lumbar disc degenerative disease, smoking and obesity rose significantly more than the number of patients diagnosed with lumbar disc degenerative disease and any other comorbidity alone or combination of comorbidities (p <0.05).

Conclusions

Diabetes, obesity and cigarette smoking each are significantly associated with an increased diagnosis of lumbar degenerative disc disease. The combination of smoking and obesity had a synergistic effect on increased rates of lumbar degenerative disc disease. Patient education and preventative care is a vital goal in prevention of degenerative disc disease within the general population.

An ultrastructural study of chondroptosis: programmed cell death in degenerative intervertebral discs in vivo

Apoptosis has been regarded to mediate intervertebral disc degeneration (IDD); however, the basic question of how the apoptotic bodies are cleared in the avascular intervertebral disc without phagocytes, which are essential to apoptosis, remains to be elucidated. Our goals were to investigate the ultrastructure of nucleus pulposus (NP) cells undergoing chondroptosis, a variant of apoptotic cell death, in a rabbit annular needle-puncture model of IDD. Experimental IDD was induced by puncturing discs with a 16-G needle in New Zealand rabbits. At 4 and 12 weeks after puncture, progressive degeneration was demonstrated by X-ray, magnetic resonance imaging and histological staining. TUNEL staining suggested a significant increase in the apoptosis index in the degenerated NP. However, the percentage of apoptotic cells with the classic ultrastructure morphology was much less than that with chondroptotic ultrastructure morphology under transmission electron microscopy (TEM). The chondroptotic cells from the early to late stage were visualized under TEM. In addition, the percentage of chondroptotic cells was significantly enhanced in the degenerated NP. Furthermore, 'paralyzed' cells were found in the herniated tissue. Western blotting revealed an increase in caspase3 expression in the degenerated NP. The expression of the Golgi protein (58K) was increased by the fourth week after puncture but decreased later. These findings indicate that chondroptosis is a major type of programmed cell death in the degenerated rabbit NP that may be related to the progressive development of IDD.

Acidification changes affect the inflammasome in human nucleus pulposus cells

BACKGROUND

Interleukin (IL)-1β is involved in the pathology of intervertebral disc degeneration. Under normal conditions, IL-1β is present in cells in an inactive form (pro-IL-1β). However, under pathological conditions, pro-IL-1β is turned into its active form (IL-1β) by the inflammasome, a multi-protein complex of the innate immune response that activates caspase-1. Under conditions of degeneration, the disc experiences an environment of increased acidification. However, the implications of acidification on the innate immune response remain poorly explored.

METHODS

Here we have studied how pH changes in human nucleus pulposus cells affect inflammasome activation by immunoblot analysis of protein lysates obtained from nucleus pulposus cells that were exposed to different pH levels in culture.

RESULTS

In this study, we have found that in nucleus pulposus cells, with increased acidification, there was a decrease in inflammasome activation consistent with lower levels of active IL-1β. However, this effect at a pH of 6.5, the lowest pH level tested, was abrogated when cells were treated with IL-1β.

CONCLUSIONS

Taken together, these findings suggest that the inflammatory response through IL-1β experienced by the human disc is not initiated in nucleus pulposus cells when the stimulus is acidification.

Effects of Tobacco Smoking on the Degeneration of the Intervertebral Disc: A Finite Element Study

Tobacco smoking is associated with numerous pathological conditions. Compelling experimental evidence associates smoking to the degeneration of the intervertebral disc (IVD). In particular, it has been shown that nicotine down-regulates both the proliferation rate and glycosaminoglycan (GAG) biosynthesis of disc cells. Moreover, tobacco smoking causes the constriction of the vascular network surrounding the IVD, thus reducing the exchange of nutrients and anabolic agents from the blood vessels to the disc. It has been hypothesized that both nicotine presence in the IVD and the reduced solute exchange are responsible for the degeneration of the disc due to tobacco smoking, but their effects on tissue homeostasis have never been quantified. In this study, a previously presented computational model describing the homeostasis of the IVD was deployed to investigate the effects of impaired solute supply and nicotine-mediated down-regulation of cell proliferation and biosynthetic activity on the health of the disc. We found that the nicotine-mediated down-regulation of cell anabolism mostly affected the GAG concentration at the cartilage endplate, reducing it up to 65% of the value attained in normal physiological conditions. In contrast, the reduction of solutes exchange between blood vessels and disc tissue mostly affected the nucleus pulposus, whose cell density and GAG levels were reduced up to 50% of their normal physiological levels. The effectiveness of quitting smoking on the regeneration of a degenerated IVD was also investigated, and showed to have limited benefit on the health of the disc. A cell-based therapy in conjunction with smoke cessation provided significant improvements in disc health, suggesting that, besides quitting smoking, additional treatments should be implemented in the attempt to recover the health of an IVD degenerated by tobacco smoking.

Molecular basis of intervertebral disc degeneration and herniations: what are the important translational questions?

BACKGROUND

Intervertebral disc degeneration is a common condition with few inexpensive and effective modes of treatment, but current investigations seek to clarify the underlying process and offer new treatment options. It will be important for physicians to understand the molecular basis for the pathology and how it translates to developing clinical treatments for disc degeneration. In this review, we sought to summarize for clinicians what is known about the molecular processes that causes disc degeneration.

RESULTS

A healthy disc requires maintenance of a homeostatic environment, and when disrupted, a catabolic cascade of events occurs on a molecular level resulting in upregulation of proinflammatory cytokines, increased degradative enzymes, and a loss of matrix proteins. This promotes degenerative changes and occasional neurovascular ingrowth potentially contributing to the development of pain. Research demonstrates the molecular changes underlying the harmful effects of aging, smoking, and obesity seen clinically while demonstrating the variable influence of exercise. Finally, oral medications, supplements, biologic treatments, gene therapy, and stem cells hold great promise but require cautious application until their safety profiles are better outlined.

CONCLUSIONS

Intervertebral disc degeneration occurs where there is a loss of homeostatic balance with a predominantly catabolic metabolic profile. A basic understanding of the molecular changes occurring in the degenerating disc is important for practicing clinicians because it may help them to inform patients to alter lifestyle choices, identify beneficial or harmful supplements, or offer new biologic, genetic, or stem cell therapies.

Responses and adaptations of intervertebral disc cells to microenvironmental stress: a possible central role of autophagy in the adaptive mechanism

Intervertebral discs comprise the largest avascular cartilaginous organ in the body, and its nutrient condition can be impaired by degeneration, aging and even metabolic disease. The unique microenvironment brings special stresses to various disc cell types, including nucleus pulposus cells, notochordal cells, annulus fibrosus cells and endplate chondrocytes. These cells experience nutrient starvation, acidic stress, hypoxic stress, hyperglycemic stress, osmotic stress and mechanical stress. Understanding the detailed responses and complex adaptive mechanisms of disc cells to various stresses might provide some clues to guide therapy for disc degeneration. By reviewing the published literatures describing disc cells under different hostile microenvironments, we conclude that these cells exhibit different responses to microenvironmental stresses with different mechanisms. Moreover, the interaction and combination of these stresses create a complex environment that synergistically increase or decrease influences on disc cells, compared with the effects of a single stress. Interestingly, most of these stresses activate autophagy, a self-protective mechanism by which dysfunctional protein and organelles are degraded. It is becoming clear that autophagy facilitates the cellular adaptation to stresses and might play a central role in regulating the adaptation of disc cells under stress. Therefore, autophagy modulation might be a potential therapeutic method to treat disc degeneration.

Transcript levels of major interleukins in relation to the clinicopathological profile of patients with tuberculous intervertebral discs and healthy controls

Objectives

The purpose of the present study was to simultaneously examine the transcript levels of a large number of interleukins (ILs; IL-9, IL-10, IL-12, IL-13, IL-16, IL-17, IL-18, IL-26, and IL-27) and investigate their correlation with the clinicopathological profiles of patients with tuberculous intervertebral discs.

Methods

Clinical data were collected from 150 patients participating in the study from January 2013 to December 2013. mRNA expression levels in 70 tuberculous, 70 herniated, and 10 control intervertebral disc specimens were determined by real-time polymerase chain reaction.

Results

IL-10, IL-16, IL-17, IL-18, and IL-27 displayed stronger expression in tuberculous spinal disc tissue than in normal intervertebral disc tissue (P<0.05). Our results illustrated multiple correlations among IL-10, IL-16, IL-17, IL-18, and IL-27 mRNA expression in tuberculous samples. Smoking habits were found to have a positive correlation with IL-17 transcript levels and a negative correlation with IL-10 transcript levels (P<0.05). Pain intensity, symptom duration, C-reactive protein levels, and the erythrocyte sedimentation rate exhibited multiple correlations with the transcript levels of several ILs (P<0.05).

Conclusions

The experimental data imply a double-sided effect on the activity of ILs in tuberculous spinal intervertebral discs, suggesting that they may be involved in intervertebral discs destruction. Our findings also suggest that smoking may affect the intervertebral discs destruction process of spinal tuberculosis. However, further studies are necessary to elucidate the exact role of ILs in the intervertebral discs destruction process of spinal tuberculosis.

Cigarette smoking and musculoskeletal disorders

Cigarette smoking has deleterious effects on the musculo-skeletal system. The loss of bone mineral content and increased incidence of fractures are the best known negative consequences. The pathogenesis is complex, due to direct toxic effects on osteoblasts/osteoclasts activity of nicotine, and indirect actions on sex and adrenocortical hormones, vitamin D, intestinal calcium absorption, vessels and oxygen supply. Smoking may favour the onset or aggravate the progression of rheumatoid arthritis and back pain. Negative influences have been observed on muscle and on tendons. Moreover, smoking habit is associated to a number of short term post-operative complications and higher resource consumption. Smoking cessation is highly advisable with positive effects on the bone metabolism on the long term. More positive and immediate results can be obtained in patients submitted to orthopedic surgery: the healing process is improved, the frequency of complications is reduced, and the length of hospital stay is shortened.

Biologically based therapy for the intervertebral disk: who is the patient?

The intervertebral disk (IVD) is a fascinating and resilient tissue compartment given the myriad of functions that it performs as well as its unique anatomy. The IVD must tolerate immense loads, protect the spinal cord, and contribute considerable flexibility and strength to the spinal column. In addition, as a consequence of its anatomical and physiological configuration, a unique characteristic of the IVD is that it also provides a barrier to metastatic disease. However, when injured and/or the subject of significant degenerative change, the IVD can be the source of substantial pain and disability. Considerable efforts have been made over the past several decades with respect to regenerating or at least modulating degenerative changes affecting the IVD through the use of many biological agents such as growth factors, hydrogels, and the use of plant sterols and even spices common to Ayurvedic medicine. More recently stem/progenitor and autologous chondrocytes have been used mostly in animal models of disk disease but also a few trials involving humans. At the end of the day if biological therapies are to offer benefit to the patient, the outcomes must be improved function and/or less pain and also must be improvements upon measures that are already in clinical practice. Here some of the challenges posed by the degenerative IVD and a summary of some of the regenerative attempts both in vitro and in vivo are discussed within the context of the vital question: "Who is the patient?"

Body mass index is associated with lumbar disc degeneration in young Finnish males: subsample of Northern Finland birth cohort study 1986

BACKGROUND

The role of environmental factors in lumbar intervertebral disc degeneration (DD) in young adults is largely unknown. Therefore, we investigated whether body mass index (BMI), smoking, and physical activity are associated with lumbar DD among young adults.

METHODS

The Oulu Back Study (OBS) is a subpopulation of the 1986 Northern Finland Birth Cohort (NFBC 1986) and it originally included 2,969 children. The OBS subjects received a postal questionnaire, and those who responded (N = 1,987) were invited to the physical examination. The participants (N = 874) were invited to lumbar MRI study. A total of 558 young adults (325 females and 233 males) underwent MRI that used a 1.5-T scanner at the mean age of 21. Each lumbar intervertebral disc was graded as normal (0), mildly (1), moderately (2), or severely (3) degenerated. We calculated a sum score of the lumbar DD, and analyzed the associations between environmental risk factors (smoking, physical activity and weight-related factors assessed at 16 and 19 years) and DD using ordinal logistic regression, the results being expressed as cumulative odds ratios (COR). All analyses were stratified by gender.

RESULTS

Of the 558 subjects, 256 (46%) had no DD, 117 (21%) had sum score of one, 93 (17%) sum score of two, and 92 (17%) sum score of three or higher. In the multivariate ordinal logistic regression model, BMI at 16 years (highest vs. lowest quartile) was associated with DD sum score among males (COR 2.35; 95% CI 1.19-4.65) but not among females (COR 1.29; 95% CI 0.72-2.32). Smoking of at least four pack-years was associated with DD among males, but not among females (COR 2.41; 95% CI 0.99-5.86 and 1.59; 95% 0.67-3.76, respectively). Self-reported physical activity was not associated with DD.

CONCLUSIONS

High BMI at 16 years was associated with lumbar DD at 21 years among young males but not among females. High pack-years of smoking showed a comparable association in males, while physical activity had no association with DD in either gender. These results suggest that environmental factors are associated with DD among young males.

Expression and regulation of metalloproteinases and their inhibitors in intervertebral disc aging and degeneration

BACKGROUND CONTEXT

Destruction of extracellular matrix (ECM) leads to intervertebral disc degeneration (IDD), which underlies many spine-related disorders. Matrix metalloproteinases (MMPs), and disintegrins and metalloproteinases with thrombospondin motifs (ADAMTSs) are believed to be the major proteolytic enzymes responsible for ECM degradation in the intervertebral disc (IVD).

PURPOSE

To summarize the current literature on gene expression and regulation of MMPs, ADAMTSs, and tissue inhibitors of metalloproteinases (TIMPs) in IVD aging and IDD.

METHODS

A comprehensive literature review of gene expression of MMP, ADAMTS, and TIMP in human IDD and reported studies on regulatory factors controlling their expressions and activities in both human and animal model systems.

RESULTS

Upregulation of specific MMPs (MMP-1, -2, -3, -7, -8, -10, and -13) and ADAMTS (ADAMTS-1, -4, and -15) were reported in human degenerated IVDs. However, it is still unclear from conflicting published studies whether the expression of ADAMTS-5, the predominant aggrecanase, is increased with IDD. Tissue inhibitors of metalloproteinase-3 is downregulated, whereas TIMP-1 is upregulated in human degenerated IVDs relative to nondegenerated IVDs. Numerous studies indicate that the expression levels of MMP and ADAMTS are modulated by a combination of many factors, including mechanical, inflammatory, and oxidative stress, some of which are mediated in part through the p38 mitogen-activated protein kinase pathway. Genetic predisposition also plays an important role in determining gene expression of MMP-1, -2, -3, and -9.

CONCLUSIONS

Upregulation of MMP and ADAMTS expression and enzymatic activity is implicated in disc ECM destruction, leading to the development of IDD. Future IDD therapeutics depends on identifying specific MMPs and ADAMTSs whose dysregulation result in pathological proteolysis of disc ECM.

Smoking Cessation Related to Improved Patient-Reported Pain Scores Following Spinal Care

BACKGROUND

Smoking is associated with low back pain, intervertebral disc disease, inferior patient outcomes following surgical interventions, and increased rates of postoperative complications. The purpose of the present study was to examine the effect of smoking and smoking cessation on pain and disability in patients with painful spinal disorders.

METHODS

We examined a prospectively maintained database of records for 5333 patients with axial or radicular pain from a spinal disorder with regard to smoking history and the patient assessment of pain on four visual analog scales during the course of care. Confounding factors, including secondary gain, sex, age, and body mass index, were also examined. The mean duration of follow-up was eight months. Multivariate statistical analysis was performed with variables including smoking status, secondary gain status, sex, depression, and age as predictors of pain and disability.

RESULTS

Compared with patients who had never smoked, patients who were current smokers reported significantly greater pain in all visual analog scale pain ratings (p < 0.001). The mean improvement in reported pain over the course of care was significantly different between nonsmokers and current smokers (p <0.001). Compared with patients who had continued to smoke, those who had quit smoking during the course of care reported significantly greater improvement in pain in visual analog scale pain ratings for worst (p = 0.013), current (p < 0.05), and average weekly pain (p = 0.024). The mean improvement in the visual analog scale pain ratings was clinically important in patients in all three groups of nonsmokers. As a group, those who had continued smoking during treatment had no clinically important improvement in reported pain.

CONCLUSIONS

Given a strong association between improved patient-reported pain and smoking cessation, this study supports the need for smoking cessation programs for patients with a painful spinal disorder.

Five-year adjacent-level degenerative changes in patients with single-level disease treated using lumbar total disc replacement with ProDisc-L versus circumferential fusion

OBJECT

The authors report the 5-year results for radiographically demonstrated adjacent-level degenerative changes from a prospective multicenter study in which patients were randomized to either total disc replacement (TDR) or circumferential fusion for single-level lumbar degenerative disc disease (DDD).

METHODS

Two hundred thirty-six patients with single-level lumbar DDD were enrolled and randomly assigned to 2 treatment groups: 161 patients in the TDR group were treated using the ProDisc-L (Synthes Spine, Inc.), and 75 patients were treated with circumferential fusion. Radiographic follow-up data 5 years after treatment were available for 123 TDR patients and 43 fusion patients. To characterize adjacent-level degeneration (ALD), radiologists at an independent facility read the radiographic films. Adjacent-level degeneration was characterized by a composite score including disc height loss, endplate sclerosis, osteophytes, and spondylolisthesis. At 5 years, changes in ALD (ΔALDs) compared with the preoperative assessment were reported.

RESULTS

Changes in ALD at 5 years were observed in 9.2% of TDR patients and 28.6% of fusion patients (p = 0.004). Among the patients without adjacent-level disease preoperatively, new findings of ALD at 5 years posttreatment were apparent in only 6.7% of TDR patients and 23.8% of fusion patients (p = 0.008). Adjacent-level surgery leading to secondary surgery was reported for 1.9% of TDR patients and 4.0% of fusion patients (p = 0.6819). The TDR patients had a mean preoperative index-level range of motion ([ROM] of 7.3°) that decreased slightly (to 6.0°) at 5 years after treatment (p = 0.0198). Neither treatment group had significant changes in either ROM or translation at the superior adjacent level at 5 years posttreatment compared with baseline.

CONCLUSIONS

At 5 years after the index surgery, ProDisc-L maintained ROM and was associated with a significantly lower rate of ΔALDs than in the patients treated with circumferential fusion. In fact, the fusion patients were greater than 3 times more likely to experience ΔALDs than were the TDR patients. Clinical trial registration no.: NCT00295009.

Spine degeneration in a murine model of chronic human tobacco smokers

OBJECTIVE

To investigate the mechanisms by which chronic tobacco smoking promotes intervertebral disc degeneration (IDD) and vertebral degeneration in mice.

METHODS

Three month old C57BL/6 mice were exposed to tobacco smoke by direct inhalation (4 cigarettes/day, 5 days/week for 6 months) to model long-term smoking in humans. Total disc proteoglycan (PG) content [1,9-dimethylmethylene blue (DMMB) assay], aggrecan proteolysis (immunobloting analysis), and cellular senescence (p16INK4a immunohistochemistry) were analyzed. PG and collagen syntheses ((35)S-sulfate and (3)H-proline incorporation, respectively) were measured using disc organotypic culture. Vertebral osteoporosity was measured by micro-computed tomography.

RESULTS

Disc PG content of smoke-exposed mice was 63% of unexposed control, while new PG and collagen syntheses were 59% and 41% of those of untreated mice, respectively. Exposure to tobacco smoke dramatically increased metalloproteinase-mediated proteolysis of disc aggrecan within its interglobular domain (IGD). Cellular senescence was elevated two-fold in discs of smoke-exposed mice. Smoke exposure increased vertebral endplate porosity, which closely correlates with IDD in humans.

CONCLUSIONS

These findings further support tobacco smoke as a contributor to spinal degeneration. Furthermore, the data provide a novel mechanistic insight, indicating that smoking-induced IDD is a result of both reduced PG synthesis and increased degradation of a key disc extracellular matrix protein, aggrecan. Cleavage of aggrecan IGD is extremely detrimental as this results in the loss of the entire glycosaminoglycan-attachment region of aggrecan, which is vital for attracting water necessary to counteract compressive forces. Our results suggest identification and inhibition of specific metalloproteinases responsible for smoke-induced aggrecanolysis as a potential therapeutic strategy to treat IDD.