The Role of Recombinant Parathormone derivative in Bone healing. Making the Unfavorable, Favorable-A Systematic Review

Wound Healing is one of the most complex biological processes that occur throughout the life of humans. Immediately after an Injury, there is a coordinated response of various cellular and intracellular pathways to restore homeostasis.1 Unlike invertebrates like salamanders, which are capable of regenerating their limb or missing appendages,2 We Humans do not possess any such magical capabilities. Our System needs a programmed and well-orchestrated healing cascade in order to repair itself.


INTRODUCTION
Wound Healing is one of the most complex biological processes that occur throughout the life of humans. Immediately after an Injury, there is a coordinated response of various cellular and intracellular pathways to restore homeostasis. 1 Unlike invertebrates like salamanders, which are capable of regenerating their limb or missing appendages, 2 We Humans do not possess any such magical capabilities. Our System needs a programmed and well-orchestrated healing cascade in order to repair itself.
Poor Healing after trauma, surgery or a chronic disease condition affects millions worldwide. When this is the case for Healthy individuals, the prognosis for those who are systemically compromised is even poor. In addition to this, in this fast paced world, fractures have become very common, be it from a fall or an RTA or due to any chronic condition. An impaired fracture healing leads to delayed union, non-union and other defects, which may lead to further complication, thus affecting the quality of life of the patients. 3 Numerous grafting techniques and regenerative materials have been studied and investigated for effective regeneration. But, they take have been at the back seat because of the complexities and complications involved by their usage.
Unraveling the mysteries and key mechanisms involved in wound healing has led the researchers towards a different approach of using recombinant therapies to facilitate an effective healing process. Thus, identifying better and novel strategies to prevent complications as well as accelerate healing have become a necessity. One such approach is the use of Recombinant Parathyroid hormone.
Parathyroid Hormone is an 84 amino acid polypeptide that is responsible for calcium Homeostasis in our body. Studies have suggested that the N-terminal fragment of the PTH molecule encompassing amino acids 1-34 and called PTH (1-34) is the principal constituent responsible for Biological activity. 4,5 The effect of this fragment on bone formation process, initially recognized in 1930s has been brought to the forefront only recently after studies proved that Osteoblasts that are responsible for bone formation express the PTH receptors while Osteoclasts do not. Teriparatide is a recombinant form of these 34 amino-terminal residues that is manufactured using a genetically modified strain of Escherichia coli and has a molecular mass of 4117.8 daltons. 6 It is currently used as subcutaneous injection for osteoporotic patients. Apart from this recognized application, there is growing evidence suggesting its potential to accelerate healing of fractures as well. It is said to increase the bone mineral density. Although the exact mechanism remains unknown, it is said to increase osteoblastogenesis, reduced osteoblast apoptosis, activate growth factors such as IGF-1 and TGF-beta in the immediate bone marrow environment. Andreassen et al. in 1999 showed that intermittent administration of PTH  at 60 and 200 microgram doses produced increases in callus volume of 42% and 72% respectively. 7 In the same year, Holzer et al. found similar results of increased callus volume in histological sections after daily PTH (1-34) administration in rats. 8 Komatsubara et al. in 2004 showed that intermittent teriparatide at 30 microgram per kg before and after osteotomy accelerated the fracture healing process in rats up to 12 week osteotomy. 9 In 2010 Mognetti et al. noted that 40 microgram per kg per day of teriparatide accelerated callus formation. 10 Alkhiary et al. showed that beneficial effects from teriparatide is not just limited to the periods during which treatment is given but also continues after. In his study, he found that there was a sustained anabolic effect throughout the remodeling phase. 11 Studies have shown that teriparatide proved to be useful in situations where sub-optimal fracture repair mechanisms are expected like smoking, diabetes, patients under corticosteroid treatment, metabolic bone diseases, oestrogen deficiency etc. Nozaka et al. in 2008 examined the effects of Teriparatide in ovariectomized rats and found that the drug reduced bone resorption parameters. 12 The effects of teriparatide on humans have also been reported earlier.
Chintamaneni et al. in 2010 reported a case of a 67-year-old male who had sustained a fracture of the body of the sternum as a result of a motor vehicle accident, which subsequently failed to heal resulting in a painful atrophic non-union. This patient was then administered 20 microgram teriparatide per day and showed significant healing in a short period of 3 months. 13 There were few other case reports by Rubery and Bukata et al. where teriparatide showed benefits in Bone healing in type III odontoid fractures in osteoporotic women. 14 In animal experiments and case reports they have proved to be beneficial. However, in clinical studies their results are in conflict. Evidence based evaluation of the potential role of teriparatide in bone healing is limited. This provides an impetus for the present systematic review. This systematic review aims to assess the Literature evidence for the role of teriparatide in bone regeneration and healing in terms of clinical, radiographic, histologic parameters and Biochemical markers in patients with fractures and patients with osteoporosis. Article selection:

Search results
The title and abstract of the entries yielded from the initial electronic database searches were read. After this initial filter, the full-text versions of the studies that could be potentially included in this review were read and a final selection of articles was done after applying the eligibility criteria.  Placebo-17 (27) Teriparatide-6(11)

Results of literature selection process
The initial search yielded 219 entries in PubMed database, Google scholar and Cochrane library. Excluding all animal studies, case series, case reports, systematic review and duplicate studies, 20 articles were human clinical trials. Out of this, the total of 15 articles were selected after reviewing the titles and abstracts. 2 articles were excluded after full-text review. A final selection of 13 articles, were made ( Figure 1).

RESULTS
The selected 13 studies compared teriparatide to either placebo or another anti-resorptive drug. Out of the 13, 8 studies were done to evaluate the improvement and healing of bone in Osteoporotic patients whereas 5 studies were done on improvement in fracture healing (Figures 2 and 3). The studies evaluated outcome parameters such as Clinical and Radiological improvement, Biomarkers of Bone resorption and formation and Safety.6 studies assessed clinical parameters, 12 studies assessed radiological parameters,7 studies assessed biomarkers, 11 studies assessed safety parameters by means of occurrence of any adverse effects ( Figure 3). All the 8 studies done on osteoporotic patients showed a good improvement. Of the 5 studies on fracture healing (Figure 4), only 2 studies showed beneficial effects while the other 3 did not show any benefits ( Figure 5).

DISCUSSION
This Systematic review provides a summary of the clinical evidence for the efficacy of teriparatide for treating individuals with Osteoporosis as well as for healing of fractures. The 13 selected trials used teriparatide injections to treat fractures as well as Osteoporosis.       osteoporotic patients and Nikolaos K Kanakaris et al. in healing of hip fracture in elderly. All the 8 studies done on osteoporotic patients were effective whereas out of 5 studies in healing of fractures, 2 were beneficial whereas 3 were non beneficial. This could mean that Teriparatide may be a potential viable therapy for the treatment of osteoporosis, however, it lacked the effectiveness for healing fractures. None of the studies reported any serious side effects associated with the use of teriparatide. The most common side effects that the patients experienced were nausea, Gastrointestinal disturbances, occasional headaches.
6 of the 8 studies done in Osteoporotic individuals evaluated biomarkers such as ,CTX-1(serum C-telopeptide of type 1 collagen),BSAP(Bone specific Alkaline phosphatase),urine N-telopeptide of type I collagen, bone NTX (N telopeptides corrected for creatinine),P1NP(serum N-terminal propeptide of type 1 collagen),BSAP,osteocalcin and found significant differences. 1 study evaluated only clinical parameter and found significant reduction in pain relief scores whereas 7 of the studies evaluated radiological improvements and observed a significant improvement in Bone mineral Density.
In fracture healing, Bhandari et al. 15 , Kanakaris et al. 16 and Johansson et al. 17 did not find any significant improvement with the usage of teriparatide. Mohit Bhandari et al. studied whether teriparatide 20 microgram injection could improve femoral neck fracture healing and found that there was no significant difference between the groups in radiographic evidence of healing, further they also found that there were no differences in patients who required revision surgeries to potentiate healing. Thus, Teriparatide did not decrease the risk of revision surgery or improve fracture healing. Similarly, Johansson et al. and kanakaris in their study did not observe an improvement in clinical parameters such as Level of Pain or the DASH score in treated patients when compared to the control group.
2 of the authors, Per Aspenberg et al. and Almirol et al., in their study found significant improvements in teriparatide treated group in healing of fractures. Per Aspenberg et al. in their study assessing efficacy of 20 microgram and 40 microgram teriparatide for treating distal radial fractures observed a significant difference between the placebo group and teriparatide group in clinical parameters -PRWE score as well as improvement in grip strength in patients treated with Teriparatide. 18 The time to radiographic healing was shortened in the teriparatide group when compared to placebo group. However, time to radiographic healing was not statistically significant. Similar results were obtained by Almirol et al. who evaluated the effects of teriparatide versus placebo to treat lower extremity stress fractures and observed a significant improvement in Tibial cortical Area and thickness in patients treated with teriparatide. They also assessed biomarkers such as serum ALP, serum P1NP, serum osteocalcin, serum CTX, urine NTX. However, significant differences were observed only in serum P1NP and serum osteocalcin. 19 In osteoporotic individuals, all studies showed beneficial results. Some had very significant improvements compared to others.Neer et al. in his study observed that women with postmenopausal osteoporosis showed reduction in risk of new vertebral(RR 0.35,95% CI 0.22-0.55) and non vertebral fracture (RR 0.47, 95% CI 0.25-0.88) fracture after treatment with teriparatide 20 microgram compared with placebo for a median of 21 months. 20 The Study by Miyauchi et al. supported the concept of "Anabolic Window" with teriparatide therapy, which was characterized by a rapid and an early increase in P1NP-markers of Bone formation followed by an associated increase in markers of bone resorption.  [21][22][23][24][25] The exact cellular mechanisms that is responsible for the anabolic impact of teriparatide on bone is not fully known. Dobnig and Turner stated that intermittently administered parathormone enhances bone formation by possibly increasing the number of osteoblasts and their activity. In their study they found that after infusion of thymidine to label all cells progressing through mitosis during treatment, it was found that almost all osteoblasts induced by parathormone were unlabeled in 16 month old rats. 5 Based on this, they postulated that the increased number of osteoblasts seen is due to the activation of resting bone lining cells to become mature osteoblasts. Similar results were obtained by other researchers like Li et al., Watson et al.. 26,27 This view was further supported by Leaffer et al. who found ultra structural evidence consistent with thee previous studies. 28 Jilka et al. stated that intermittent parathormone could also postpone osteoblast apoptosis. The mitogenic effect may be mediated by induction of potent mitogens for osteoprogenitor cells such as Transforming growth factor β (TGF β) and Insulin like growth factor-1 (IGF-1). 29 This hypothesis was further substantiated by experiments by Watson et al.
Okazaki et al. postulated that teriparatide acted in an autocrine and paracrine fashion and thereby improved callus formation and played a huge role in regulating chrondrocyte differentiation. 30 In addition, Nakazawa et al. in their study showed that PTH had an additional effect on mesenchymal (chondroprogenitor) cells by stimulating their proliferation and increasing their recruitment into the chondrocyte lineage. As a result, a higher proportion of progenitor cells achieved full osteoblast differentiation. 31 Thus, the present review was undertaken to evaluate the efficacy of teriparatide in bone healing. Our aim was to search for the best possible evidence available with respect to teriparatide in bone regeneration and healing in different clinical scenarios and compile them together in a systematic manner to provide more clarity regarding the usage of teriparatide. Invitro studies are also being done at present for bone regeneration in rabbit and rats for their potential use in periodontal and other dentoalveolar conditions. Quality assessment of the 13 selected randomized control trials were carried out. Criteria like Selection bias, Performance bias, detection bias, attrition bias, reporting bias was taken into consideration. Out of the 5 studies done in healing of fractures, 2 studies showed high risk of bias, 2 studies showed moderate risk of bias and 1 study showed low risk of bias. Out of the 8 studies on osteoporosis, 4 studies showed low risk of bias, 2 studies showed moderate risk of bias and 2 studies showed a high risk of bias ( Figure 6).
Based on this systematic review, Teriparatide seemed to be beneficial to treat osteoporosis. However, human trials in fractures have yielded conflicting results. The main limitation of this systematic review is that the unpublished data were not included. There is wide heterogeneity with respect to the study population and therefore the possibility of a meta analysis is ruled out. Some studies have favored the use of teriparatide while others have not found any benefits. More high quality clinical trials following similar comparison protocol is essential in order to analyze the efficiency by means of a meta analysis.

CONCLUSION
Teriparatide could have beneficial effects in bone healing in osteoporotic patients. However, the results are inconclusive whether they have beneficial effects in treating fractures. More Homogenous Randomized control trials are required to ascertain whether teriparatide could improve bone healing.

CONFLICTS OF INTEREST
None.