Studies in fetal wound healing: I. A factor in fetal serum that stimulates deposition of hyaluronic acid

Primary anastomosis as a valid alternative for extremely low birth weight infants with spontaneous intestinal perforation

The aim was to assess the results of primary anastomosis (PA) compared to enterostomy (ES) in infants with spontaneous intestinal perforation (SIP) and a weight below 1000 g. Between 2014 and 2016, enterostomy was routinely carried out on extremely low birth weight (ELBW) patients with SIP. From 2016 until 2019, all patients underwent anastomosis without stoma formation. We compared outcome and complications in both groups. Forty-two patients with a median gestational age of 24.3 weeks and a birth weight of 640 g with SIP were included. Thirty patients underwent PA; ES was performed in 12 patients. Overall in-hospital mortality was 11.9% (PA: 13.3%, ES: 8.3%). Reoperations due to complications became necessary in 10/30 patients with PA and 4/12 patients with ES. Length of stay was 110.5 days in the PA group and 124 days in the ES group. Median weight at discharge was higher in the PA group (PA: 2258 g, ES: 1880 g, p = .036).Conclusion: Primary anastomosis is a feasible treatment option for SIP in infants < 1000 g and may have a positive impact on weight gain and length of hospitalization. However, further studies on selection criteria for PA are necessary. What is Known: • Enterostomy (ES) and primary anastomosis (PA) are feasible treatment options in preterm infants with spontaneous intestinal perforation (SIP). • Stomal complications or failure to thrive due to poor food utilization can pose significant problems. What is New: • Primary anastomosis in case of SIP is equal to enterostomy in terms of mortality and revision rate; however, length of stay and weight gain can be presumably positively influenced. • Primary anastomosis is a valid treatment option even for patients weighing less than 1000 g.

Inflammation as an orchestrator of cutaneous scar formation: a review of the literature

Inflammation is a key phase in the cutaneous wound repair process. The activation of inflammatory cells is critical for preventing infection in contaminated wounds and results in the release of an array of mediators, some of which stimulate the activity of keratinocytes, endothelial cells, and fibroblasts to aid in the repair process. However, there is an abundance of data suggesting that the strength of the inflammatory response early in the healing process correlates directly with the amount of scar tissue that will eventually form. This review will summarize the literature related to inflammation and cutaneous scar formation, highlight recent discoveries, and discuss potential treatment modalities that target inflammation to minimize scarring.

The Dynamics of the Skin's Immune System

The skin is a complex organ that has devised numerous strategies, such as physical, chemical, and microbiological barriers, to protect the host from external insults. In addition, the skin contains an intricate network of immune cells resident to the tissue, crucial for host defense as well as tissue homeostasis. In the event of an insult, the skin-resident immune cells are crucial not only for prevention of infection but also for tissue reconstruction. Deregulation of immune responses often leads to impaired healing and poor tissue restoration and function. In this review, we will discuss the defensive components of the skin and focus on the function of skin-resident immune cells in homeostasis and their role in wound healing.

Peritoneal drainage in pneumoperitoneum in extremely low birth weight infants

The aim was to determine if peritoneal drainage (PD) is a suitable treatment for pneumoperitoneum in extremely low birth weight (ELBW) infants. A retrospective chart review of 42 ELBW infants with pneumoperitoneum at the University Hospital of Cologne between November 2014 and April 2017 was performed. Forty-two infants with a median birth weight of 645 g (interquartile range (IQR) 550, 806) and a median gestational age of 24.3 weeks (IQR 23.2, 25.6) were treated for pneumoperitoneum. Twenty-six (62%) received PD, and in ten (38%), the drain could be removed without further intervention. Infants in the PD group were of significantly lower birth weight (622g vs. 750 g), age (4.5 vs. 10.0 days), and weight at diagnosis (538 vs. 778 g). The mortality in the PD group was 15% at 90 days of life, but no patient deceased in the primary laparotomy group.

CONCLUSION

We suggest PD with close evaluation of drainage and clinical course as an alternative treatment for pneumoperitoneum in ELBW infants allowing bridging the vulnerable first days of life until these infants are in a more stable condition. Despite not reaching statistical significance in our series, PD showed the trend towards higher mortality. What is known: • Pneumoperitoneum is traditionally treated with laparotomy, but placement of peritoneal drainage (PD) is a valuable treatment option. • Previous randomized controlled trials have shown no significant differences in mortality for PD versus laparotomy. What is new: • In our cohort, 38% of the infants with PD could be saved from secondary laparotomy, but in the PD group there was a trend towards higher mortality. • PD allows bridging the vulnerable first days of life until ELBW infants are in a more stable condition for possible laparotomy.

Scarless wound healing: Transitioning from fetal research to regenerative healing

Since the discovery of scarless fetal skin wound healing, research in the field has expanded significantly with the hopes of advancing the finding to adult human patients. There are several differences between fetal and adult skin that have been exploited to facilitate scarless healing in adults including growth factors, cytokines, and extracellular matrix substitutes. However, no one therapy, pathway, or cell subtype is sufficient to support scarless wound healing in adult skin. More recently, products that contain or mimic fetal and adult uninjured dermis were introduced to the wound healing market with promising clinical outcomes. Through our review of the major experimental targets of fetal wound healing, we hope to encourage research in areas that may have a significant clinical impact. Additionally, we will investigate therapies currently in clinical use and evaluate whether they represent a legitimate advance in regenerative medicine or a vulnerary agent. WIREs Dev Biol 2018, 7:e309. doi: 10.1002/wdev.309 This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Plant Development > Cell Growth and Differentiation Adult Stem Cells, Tissue Renewal, and Regeneration > Environmental Control of Stem Cells.

Hyaluronic Acid and Periodontitis

Hyaluronic acid (HA; synonyms- Hyaluronan, Hyaluronate) is a glycosaminoglycan found in the connective tissue of vertebrates. It is the most abundant glycosaminoglycan of higher molecular weight in the extracellular matrix of soft periodontal tissues. The use of HA in the treatment of inflammatory process is established in medical areas such as orthopedics, dermatology and ophthalmology. In the field of dentistry, it has shown anti-inflammatory and anti-bacterial effects in gingivitis and periodontitis therapy. Due to its tissue healing properties, it could be used as an adjunct to mechanical therapy in the treatment of periodontitis.

Identifying Novel Targets for Treatment of Liver Fibrosis: What Can We Learn from Injured Tissues which Heal Without a Scar?

The liver is unique in that it is able to regenerate. This regeneration occurs without formation of a scar in the case of non-iterative hepatic injury. However, when the liver is exposed to chronic liver injury, the purely regenerative process fails and excessive extracellular matrix proteins are deposited in place of normal liver parenchyma. While much has been discovered in the past three decades, insights into fibrotic mechanisms have not yet lead to effective therapies; liver transplant remains the only cure for advanced liver disease. In an effort to broaden the collection of possible therapeutic targets, this review will compare and contrast the liver wound healing response to that found in two types of wound healing: scarless wound healing of fetal skin and oral mucosa and scar-forming wound healing found in adult skin. This review will examine wound healing in the liver and the skin in relation to the role of humoral and cellular factors, as well as the extracellular matrix, in this process. While several therapeutic targets are similar between fibrotic liver and adult skin wound healing, others are unique and represent novel areas for hepatic anti-fibrotic research. In particular, investigations into the role of hyaluronan in liver fibrosis and fibrosis resolution are warranted.

Effect of amniotic fluid on the in vitro culture of human corneal endothelial cells

The present study was designed to evaluate the effects of human amniotic fluid (HAF) on the growth of human corneal endothelial cells (HCECs) and to establish an in vitro method for expanding HCECs. HCECs were cultured in DMEM-F12 supplemented with 20% fetal bovine serum (FBS). Confluent monolayer cultures were trypsinized and passaged using either FBS- or HAF-containing media. Cell proliferation and cell death ELISA assays were performed to determine the effect of HAF on cell growth and viability. The identity of the cells cultured in 20% HAF was determined using immunocytochemistry (ICC) and real-time reverse transcription polymerase chain reaction (RT-PCR) techniques to evaluate the expression of factors that are characteristic of HCECs, including Ki-67, Vimentin, Na+/K+-ATPase and ZO-1. HCEC primary cultures were successfully established using 20% HAF-containing medium, and these cultures demonstrated rapid cell proliferation according to the cell proliferation and death ELISA assay results. The ICC and real time RT-PCR results indicated that there was a higher expression of Na+/K+-ATPase and ZO-1 in the 20% HAF cell cultures compared with the control (20% FBS) (P < 0.05). The 20% HAF-containing medium exhibited a greater stimulatory effect on HCEC growth and could represent a potential enriched supplement for HCEC regeneration studies.

Decellularized allogeneic and xenogeneic tissue as a bioscaffold for regenerative medicine: factors that influence the host response

Biologic scaffold materials composed of mammalian extracellular matrix (ECM) are prepared by decellularization of source tissues harvested from either humans (allogeneic) or a variety of other (xenogeneic) species. These matrix scaffold materials are commonly regulated and used as surgical mesh materials for applications such as ventral hernia repair, musculotendinous tissue reconstruction, dura mater replacement, reconstructive breast surgery, pelvic floor reconstruction, and the treatment of cutaneous ulcers, among others. The clinical results for these applications vary widely for reasons which include characteristics of the source tissue, methods and efficacy of tissue decellularization, and methods of processing/manufacturing. However, the primary determinant of success or failure in the clinical setting is the response of the host to these implanted biologic scaffold materials. It is logical to question why any non-self biologic material, particularly a xenogeneic material, would not elicit an early and aggressive adverse immune response. The present manuscript briefly describes the known mechanisms by which these biologic scaffold materials can facilitate a constructive remodeling response, the known causative factors of an adverse response, and provides a general discussion of the role of the macrophage in determining outcome.

Hyaluronic Acid: a boon in periodontal therapy

Hyaluronic acid is a naturally occurring linear polysaccharide of the extracellular matrix of connective tissue, synovial fluid, and other tissues. Its use in the treatment of the inflammatory process is established in medical areas such as orthopedics, dermatology, and ophthalmology. The Pubmed/Medline database was searched for keywords “Hyaluronic acid and periodontal disease” and “Hyaluronic acid and gingivitis” which resulted in 89 and 22 articles respectively. Only highly relevant articles from electronic and manual search in English literature were selected for the present review article. In the field of dentistry, hyaluronic acid has shown anti-inflammatory and anti-bacterial effects in the treatment of periodontal diseases. Due to its tissue healing properties, it could be used as an adjunct to mechanical therapy in the treatment of periodontitis. Further studies are required to determine the clinical efficacy of hyaluronic acid in healing of periodontal lesion. The aim of the present review, article is to discuss the role of hyaluronic acid in periodontal therapy.

Wound Healing: An Overview

Understanding wound healing today involves much more than simply stating that there are three phases: inflammation, proliferation, and maturation. Wound healing is a complex series of reactions and interactions among cells and "mediators." Each year, new mediators are discovered and our understanding of inflammatory mediators and cellular interactions grows. This article will attempt to provide a concise overview on wound healing and wound management.

Reduction of neural adhesions by biodegradable autocrosslinked hyaluronic acid gel after injury of peripheral nerves: an experimental study

OBJECT

Adhesion formation is a serious problem in peripheral nerve surgery, frequently causing dysfunction and pain. The authors aimed to develop an objective biomechanical method of quantifying nerve adhesions and to use this technique for the evaluation of the efficacy of an autocrosslinked hyaluronic acid (HA) gel as an antiadhesion therapy.

METHODS

Thirty-three female Wistar rats underwent dissection, crush injury, or transection plus repair of the sciatic nerve. The nerves were or were not treated with the HA gel. Six weeks after surgery, the adhesions formed were assessed by measuring the peak force required to break the adhesions over a standardized area. Results of biomechanical measurements demonstrated that the peak force significantly increased as the severity of the injury increased. After using the HA gel to treat the nerve, the peak force was significantly reduced in rats with any of the three types of injuries; peak force decreased by 26% in the animals in the dissection group, 29% in the crush injury group, and 38% in the transection and repair group, compared with the untreated animals.

CONCLUSIONS

The biomechanical method described is an objective, quantitative technique for the assessment of nerve adherence to surrounding tissue. It will be a valuable tool in future studies on antiadhesion therapies. Furthermore, HA gel significantly reduces nerve adhesions after different types of nerve injuries.

[Effect of the hyaluronic acid on tracheal healing. A canine experimental mode]

Several drugs have been used to modulate of the tracheal healing process in order to prevent tracheal stenosis. Hyaluronic acid (HA) is a modulator of the fibrogenesis. In this work we evaluate the effect in order the application of hyaluronic acid has on tracheal healing, after cervical tracheoplasty in dogs. A cervical tracheal resection and tracheoplasty was performed in 12 dogs and they were treated following surgery as follows: Group I (n = 6) Topical application of normal saline solution (0.9%) on the anastomosis site. Group II Topical application of hyaluronic acid on the trachea anastomosed. The animals were evaluated clinical, radiological and tracheoscopically during 4 weeks and were submitted to euthanasia. Macroscopic and microscopic examinations of the tracheal anastomotic healing were evaluated. Biochemical collagen quantification by the Woessner method was performed to evaluate the collagen development at the anastomotic site. All the animals survived the surgical procedure and the study time. No animal presented differences in clinical evaluation. Radiological and endoscopical findings both two showed more development of the tracheal stenosis in-group than in group II. The tracheoscopy and macroscopic studies showed major inflammation and development of fibrotic tissue with a firm consistency in the healing of the group I than in group II. Microscopic examination in group I showed severe fibrosis and inflammatory reaction. The group II presented deposits of a thin and organized collagen fibers and minimal inflammatory reaction. Biochemical collagen concentration was larger in-group I, however significantly. We conclude that the hyaluronic acid applied after cervical tracheoplasty in dogs reduces postsurgical tracheal stenosis and inflammation, as well as improve the quality of the tracheal healing.

Hyaluronic acid prevents peripheral nerve adhesion

The purpose of this study was to clarify the effectiveness of hyaluronic acid (HA) in the prevention of scar formation after neurolysis using a rabbit model. In the first stage, the left sciatic nerve was exposed and elevated along a 3 cm section. Then, the surface of the neural bed was coagulated using a bipolar coagulator. Finally, the sciatic nerve was replaced and fixed to the neural bed with 8/0 nylon sutures, and the wound was closed. In the second stage, the adherent sciatic nerve was re-exposed after 6 weeks. In the neurolysis group, a simple neurolysis was performed. In the HA group, the neurolysis was performed in a surgical field coated with HA from the beginning to the end of the operation. In the steroid group, methyl prednisolone acetate was infiltrated at the end of the neurolysis. In the third stage, electrophysiological, histological and biomechanical measurements were taken 6 weeks after the second stage. While there was no significant difference between the HA and the steroid groups, the electrophysiological functions of the HA and steroid groups were significantly better than that of the neurolysis group. Histology showed that the formation of intraneural and extraneural scar tissue was lowest in the HA group, followed by the steroid and neurolysis groups. The tensile strength required to strip the sciatic nerve from the neural bed of the HA group was significantly less than that of the neurolysis group. However, there was no significant difference between the steroid and neurolysis groups. In conclusion, HA effectively reduced scar formation after neurolysis.

The effect of hyaluronan on bone and soft tissue and immune response in wound healing

BACKGROUND

The aims of this study were to investigate the anti-inflammatory effect and the effect on bone regeneration of hyaluronan in surgical and non-surgical groups.

METHODS

In each of 15 individuals, 2 teeth with defects of similar character and magnitude in the upper or lower jaw were chosen. There were at least 2 teeth between the test and the control sites. In the surgical group, a bioabsorbable membrane was used for both test and control sites, and hyaluronan was placed in the intrabony pocket of the test site. In the non-surgical group, the periodontal pockets were scaled and hyaluronan was administered 3 times with an interval of 1 week in the test pockets. Alveolar bone height and bone healing patterns were analyzed using digital intraoral radiographs. Measurements of bone height were performed in the original digital black-and-white radiographs to obtain quantitative data on bone gain or loss. Bone healing patterns were studied with color-coded radiographs, using specially designed software in a personal computer with subsequent combinations of radiographs. Gingival crevicular fluid immunoglobulin (Ig)G, C3, and prostaglandin E2 (PGE2) responses; periodontal probing depth; bleeding on probing; and the presence of plaque were studied to evaluate the anti-inflammatory effect. Data were obtained at baseline before treatment, and at 2 weeks, and 1, 3, 6, and 12 months after treatment.

RESULTS

For the surgical treatments, bone height was increased in the test group treated with hyaluronan (mean value 2.2%, corresponding to an average increase of approximately 0.5 mm) and reduced in the control group (mean value -1.8%, corresponding to an average decrease of approximately - 0.4 mm) (P<0.05) after 12 months. For the non-surgical treatments, bone height was reduced by a mean value of -1.1% (corresponding to an average decrease of approximately -0.25 mm) in the test group treated with hyaluronan and -3.3% (corresponding to an average decrease of approximately -0.75 mm) in the control group after 12 months (N.S.). According to the digital color-coded radiographs, the test sites in the surgical and non-surgical groups showed apposition of bone minerals. Immune responses showed no differences during the 12 months studied for the surgical and non-surgical sites. Mean periodontal probing depths were reduced between 2.5 mm and 4.1 mm in the surgical and non-surgical groups.

CONCLUSIONS

The observed difference in bone height between test and control sites in the surgical group after 12 months was less than 1 mm, which was only detectable on radiographs. No statistical difference was found on radiographs in the non-surgical group, where a decrease in bone height was found for both groups after scaling. Probing depth reduction after the surgical treatment, as well as after scaling and root planing, was as expected. Hyaluronan in contact with bone and soft tissues had no influence on the immune system in this study. Further studies are needed to determine the extent to which hyaluronan can lead to clinically significant healing of periodontal lesions.

Hyaluronic acid induces tumour necrosis factor-alpha production by human macrophages in vitro

Foetal wounds heal with minimal or no scar formation. High levels of hyaluronic acid (HA) have been implicated as a contributory factor. Macrophages are essential for normal wound healing, a role facilitated by secretion of an array of cytokines. Of these, tumour necrosis factor alpha (TNF-alpha) has been shown to reduce wound collagen levels and thus scarring. This study examines the ability of HA to stimulate TNF-alpha production by human macrophages. The human U937 myelomonocytic cell line was differentiated into DU937 adherent macrophages. DU937 monolayers were exposed to HA at concentrations of 0.1, 1, 10 and 100 micrograms/ml. Conditioned media from HA-exposed monolayers were assayed for TNF-alpha activity using a standard L929 fibroblast bioassay. TNF-alpha activities of HA-exposed DU937 culture supernatants were compared to those of controls and expressed as % cytotoxicity. Exposure of macrophages to HA at concentrations of 10 micrograms/ml and 100 micrograms/ml significantly stimulated TNF-alpha production, as demonstrated by % cytotoxicities expressed as median (interquartile range) of 33.5 (29-34.5)% (P = 0.03) and 77.5 (67-85)% (P = 0.029) respectively (Mann-Whitney U test). This effect was specifically associated with TNF-alpha generated during HA exposure, as these cytotoxic effects could be abolished by addition of anti-TNF-alpha antibody, reducing cytotoxicity to 9 (6.5-13.5)% and 8.5 (6-12)% respectively. These observations indicate that HA stimulates TNF-alpha production by human macrophages. TNF-alpha is known to downregulate fibroblastic collagen synthesis within experimental wounds. We suggest that the high levels of HA within foetal wounds may play a part in limiting fibroplasia, and thereby limit scarring, via an upregulation of TNF-alpha production from wound macrophages.

Fetal and postnatal sera differentially modulate human dermal fibroblast phenotypic and functional features in vitro

Fetal wounds heal without scar formation, fibrosis, or contracture. Compared with adult wounds, they are characterized by major differences in the extracellular matrix and the absence of myofibroblastic cells. The reasons for these differences are not well known and determination of factors affecting the absence of scarring in the fetus may lead to strategies for controlling adult pathological scarring. In the present study, we have assessed the effects of serum on the behavior of normal human dermal fibroblasts. Using an in vitro approach, we investigated the effects of fetal and adult serum on cell properties such as growth rate, collagen synthesis, gelatinase activities, and differentiation to myofibroblasts using biochemical, morphological, and ultrastructural parameters. We studied the induction of alpha-smooth muscle (alpha-SM) actin in fibroblasts, and its correlation with increased collagen gel contraction by the cells. Our results showed that, compared with FBS (fetal bovine serum), postnatal calf serum (PCS) decreased mitogenic activity and collagenase synthesis but not collagen synthesis. Furthermore, cells cultured with PCS differentiated to myofibroblasts with an increase in cell diameter, number of stress fibers, alpha-SM actin expression, and collagen gel contraction. To characterize the molecules involved in this differentiation process, the amount of transforming growth factor beta (TGFbeta) in FBS and PCS was determined and the effect of neutralizing anti-TGFbeta antibody was evaluated. It was determined that FBS contained more TGFbeta than PCS, but that essentially all the TGFbeta was latent in both sera. However, results obtained with anti-TGFbeta antibody show that active TGFbeta is present when human dermal fibroblasts are cultured with medium containing PCS. These results suggest that, in the presence of PCS but not FBS, the cells either produce active TGFbeta or an enzyme that is able to activate latent serum TGFbeta. Alternatively, sera may contain two different forms of latent TGFbeta, the PCS form being activated by the dermal fibroblast cells. A similar mechanism may be involved, at least in part, in skin wound healing and may underlie the appearance of myofibroblasts in postnatal wounds.

Subpopulations of fetal-like gingival fibroblasts: characterisation and potential significance for wound healing and the progression of periodontal disease

Wound healing in the adult is commonly compromised by excessive scar formation. In contrast, fetal wound healing is a regenerative process characterised by the conspicuous absence of scarring. Available evidence suggests that phenotypic differences between fetal and adult fibroblasts are important determinants of these distinct modes of tissue repair. In this context, a number of groups (including our own) have documented differences between fetal and adult fibroblasts with respect to such potentially relevant characteristics as migratory activity, motogenic response to cytokines and the synthesis of motility factors, cytokines and matrix macromolecules. The oral mucosa appears to be a privileged site in the adult in that it continues to display a fetal-like mode of wound healing. Data are presented in this review indicating that a subpopulation of gingival fibroblasts expresses several 'fetal-like' phenotypic characteristics. These observations are discussed in terms of both the continued expression of a fetal-like mode of wound healing in the oral mucosa and the possible differential involvement of distinct fibroblast subpopulations in the progression of periodontal disease.

Acceleration of granulation tissue ingrowth by hyaluronic acid in artificial skin

Hyaluronic acid (HA), which is known to play an important role in wound healing, was incorporated in an artificial skin material and studied for its potential to create a wound bed which would support a skin graft. Collagen sponge based artificial skin was soaked in 0.3% HA in phosphate buffered saline and grafted onto skin defects in rats. Control grafts were soaked in normal saline solution. HA incorporated implants and control implants were simultaneously grafted onto wounds made on either side of the spine. To examine the effect of HA incorporation, the percentage area of cellular tuft infiltration and the number of capillaries present in the graft matrix were evaluated at 7 and 14 days after the operation. At postoperative day 7, there was a statistically significant difference in the number of capillaries in the matrix of the experimental versus the control implants. There was no difference in the percentage area of cellular tuft infiltration. At postoperative day 14, all implants exhibited better ingrowth of granulation tissue than at day 7. The differences between the experimental and control implants were statistically significant with respect to both the percentage area of cellular tuft infiltration and the number of capillaries. It is therefore concluded that in artificial skin HA incorporation accelerates the ingrowth of granulation tissue, making a more suitable graft bed.

Glycosaminoglycan composition of uninjured skin and of scar tissue in fetal, newborn and adult sheep

Few details are available on the heterogeneity of glycosaminoglycans (GAGs) in healing fetal wound tissue. We used a sensitive assay for hexosamines to examine changes occurring in the development of normal sheep skin and of wound healing tissue in PVA sponges inserted subcutaneously at different stages of gestation. It was assumed that glucosamine was derived mainly from hyaluronan and galactosamine mainly from dermatan sulphate and chondroitin sulphate. Hexosamine-containing tissue infiltrating the sponges was deposited more rapidly in the first week than in the second week. Three days after wounding, approximately 70% of the total GAGs in wound tissue was hyaluronan. The proportion of hyaluronan then fell progressively and by the 14th day contributed 57% to the total GAGs. In uninjured skin the contribution of hyaluronan to the total GAGs fell progressively with increasing fetal maturity, the level being 70% at 75 days gestation, but only 35-40% in newborn or adult skin. At no stage of development was there a sudden change in GAG composition suggestive of a transition from regeneration to scar formation. It is concluded that hyaluronan may play an important role in the biochemical sequence leading to collagen fibrillogenesis and mature scar formation.

Hyaluronic acid. A review of its pharmacology and use as a surgical aid in ophthalmology, and its therapeutic potential in joint disease and wound healing

Hyaluronic acid is a naturally occurring polysaccharide with distinct physicochemical properties which underlie its application as a viscoelastic tool in ophthalmological surgery. In cataract surgery the role of hyaluronic acid in facilitating procedures and protecting the corneal endothelium is well established. Some benefit has also been gained with the use of hyaluronic acid in penetrating keratoplasty, trabeculectomy, retinal reattachment and trauma surgery, although its efficacy in these indications is less well-defined in the published literature. In addition to its lubricating and cushioning properties, demonstration of some in vitro anti-inflammatory activity and a possible disease-modifying effect for hyaluronic acid in animals has prompted its investigation as a treatment in osteoarthritis and, to a much lesser extent, in rheumatoid arthritis. Hyaluronic acid 20 mg, as weekly intra-articular injections for 3 to 7 weeks, improved knee pain and joint motion in patients with osteoarthritis. Although this occurred to a greater degree than with placebo in most comparisons, the effects of hyaluronic acid was similar to those of placebo in the largest trial. In the few available comparisons with other agents, hyaluronic acid appeared equivalent to methylprednisolone 40 mg (for 3 weeks) and to a single injection of triamcinolone 40 mg. Hyaluronic acid was distinguished from other therapies by providing a sustained effect after treatment discontinuation. Together with its very good tolerability profile, these properties justify further study of hyaluronic acid in patients with osteoarthritis. Some limited evidence of improvement in patients with rheumatoid arthritis, and a possible healing effect of hyaluronic acid on tympanic membrane perforations, represent additional areas of interest for future investigation. In summary, hyaluronic acid is a well-established adjunct to cataract surgery and may prove to be a promising option in the treatment of patients with osteoarthritis. Its very good tolerability provides further impetus for examination of its potential role in an extended scope of arthritic and ophthalmological indications, and in wound healing.

Wound healing in the fetal period: the resistance of the scar to rupture

Wound healing in the fetal period is fundamentally different from that of the adult. In order to better understand this difference, we have studied wound healing in three types of wounds which are the most common in surgical practice, and have paid special attention to tensile strength in the scar. A sutured wound, a nonsutured wound, and an electrocautery burn were performed on a group of 30 rabbit fetuses with a gestational age of 23 days. Seven days later, the resulting scars were examined using histological, mechanical, and biochemical studies. The results were compared with those obtained in a group of 30 newborn rabbits and in a group of 30 adult rabbits who had had the same type of wounds performed on them. The body weight of operated fetuses was smaller than their control siblings. The sutured wound in the fetuses showed a more perfect macroscopic repair than in older subjects. However, the nonsutured wounds and the burns of the fetal group did not close. In the fetuses, the tensile strength of the sutured wound was 20% of the tensile strength of healthy skin. A similar relationship occurred in the group of adult rabbits. In the sutured wound of the fetal group, the synthesis of collagen was significantly less than in the adult group. The ratio between hydroxyproline (HYP) concentration in the sutured wound and HYP concentration in healthy skin was also significantly less in the fetal group than in the adult group.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyaluronate metabolism undergoes an ontogenic transition during fetal development: implications for scar-free wound healing

Wound healing in the fetus occurs by a different process from that in the adult. Instead of healing with scar formation, fetal cutaneous wounds heal by regeneration that results in complete restoration of normal skin architecture. The mechanisms responsible for this remarkable phenomenon involve factors in the fetal environment and properties intrinsic to fetal cells. Hyaluronic acid (HA) is a major component of the fetal extracellular matrix (ECM) and is believed to play an important role in this process. In this study, HA and HA-stimulating activity (HASA) in fetal and adult wound fluid were examined using sensitive, newly developed assays. In an ovine model, higher levels of HA and HASA were observed in fetal as compared with adult wound fluid. This difference was most prominent in wound fluid from fetal lambs at 75 and 100 days gestation (term = 145 days); these samples contained persistently elevated HA and HASA levels for up to 2 weeks after wounding (HA peak levels 145 micrograms/mL and 110 micrograms/mL, respectively). In contrast, wound fluid from 120-day-gestation fetuses had significantly lower levels (P < .001) that were transient and similar to that in the adult (HA peak levels 70 micrograms/mL and 10 micrograms/mL, respectively). These observations confirm an ontogenic transition in wound HA metabolism from a fetal to an adult-like phenotype. Levels of HASA as a function of time after wounding correlated with levels of HA, suggesting a role for HASA in controlling HA deposition during tissue repair. Two patterns of HASA and HA synthesis were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in nonhuman primate (M. nemestrina) lung proteoglycans during normal development and acute hyaline membrane disease

Proteoglycans (PGs) and lung hyaluronan (HA) are important components of the lung matrix both during normal development and in response to injury. We combined morphologic and biochemical techniques to study changes in PG and HA in a developmental series of Macaca nemestrina lungs ranging from 62% gestation to 3 mo post-term (n = 16), in adult lungs (n = 6), and from prematurely delivered, mechanically ventilated monkeys with hyaline membrane disease (HMD) (n = 7). Three groups of cuprolinic blue-positive (CuB) precipitates, identified by size, location, and susceptibility to enzyme digestion were found in lungs from all animals. Immature alveolar interstitium is characterized by loosely woven collagen bundles and an abundance of large (100 to 200 nm) stained filaments representing chondroitin sulfate proteoglycans (CSPGs). As maturation proceeds, the interstitial matrix appears increasingly organized, with large collagen bundles associated with 20 nm CuB-stained deposits (dermatan sulfate proteoglycans, DSPGs), and fewer large CSPGs. Fetal alveolar basement membrane contains CuB-stained heparin sulfate proteoglycans (HSPGs) (10 nm) scattered throughout. Lung matrix from animals with HMD appeared to have a disruption of the collagen-DSPG relationship, in addition to an enrichment in large CSPG. Complementary biochemical analysis of lung PGs and HA was done. Minced lung parenchyma was cultured with [3H]-glucosamine and [35S]-sulfate for 24 h; PGs and HA were extracted and analyzed. While PG synthesis during development tended to be highest at 80% gestation, animals with HMD showed greatly increased synthesis, approximately 2.5-fold higher than comparable fetal animals. In the developmental series, [3H]-glucosamine incorporation into HA was maximal at term, falling abruptly thereafter. HMD animals, however, showed a 2.3-fold increase over controls in net HA synthesis. Extracted PGs were separated according to buoyant density by dissociative cesium chloride density gradient ultracentrifugation. Two peaks of 35S-labeled PGs were separated from each density gradient fraction by chromatography on Sepharose CL-4B. A large CSPG was the principal PG eluting in the voiding volume, while the second broad peak (K(av) = 0.42) contained a mixed population of CSPG, DSPG, and HSPGs, the proportions of which varied with age. Both ultrastructural and biochemical analyses indicate that production of a large, high buoyant density CSPG predominates in fetal lung tissue, and diminishes with developmental age. Synthesis of large CSPG is greatly increased in lung explants from prematurely delivered animals with HMD.(ABSTRACT TRUNCATED AT 400 WORDS)

Extracellular matrix contraction by fibroblasts: peptide promoters and second messengers

Cells contracting connective tissue matrices generate tractional forces in tissues. Studies of fibroblast contraction, using collagen gels in an in vitro model, demonstrate that it involves the actin cytoskeleton, specific extracellular matrix receptors and requires stimulation by exogenous promoters. Fibroblast contraction is stimulated by factors released by platelets and potentially secreted within the contracting tissue. Endothelial cells secrete a potent promoter of fibroblast contraction which has been identified as endothelin 1. The pathway through which fibroblast contraction is stimulated appears to require activation of protein kinase C. Tumor cells can also secrete endothelin. These mechanisms may be relevant to tumor progression.

Hyaluronic acid in a cardiac myxoma: a biochemical and histological analysis

Cardiac myxoma is the most common primary tumor of the heart. This tumor has a gelatinous stroma that is thought to be composed of glycosaminoglycans, the classical acid mucopolysaccharide ground substance. We examined both biochemically and histologically the hyaluronic acid in a case of cardiac myxoma using a newly developed hyaluronic acid-binding protein probe. We observed that hyaluronic acid was localized in the amorphous stroma and occurred at levels 30 times that found in normal atrial septum.

Animal models for the study of fetal tissue repair

Recent experimental and clinical evidence suggests that the fetus responds to injury in a fashion fundamentally different from that of the adult. Acute inflammation is almost always absent, hyaluronic acid is a prominent component of the wound matrix, and collagen is deposited in a scarless manner. Using a variety of animal models and techniques, numerous investigators have begun to analyze the constituents of the fetal wound healing process in an attempt to understand the control mechanisms that endow the fetus with unique healing abilities. Since scarring and fibrosis dominate some diseases in almost every medical specialty, the ultimate clinical aim is to delineate the biological principles of fetal wound healing and then apply them to modulate adult wound healing problems.

Midgestational excisional fetal lamb wounds contract in utero

Clinical observations and experimental data suggest that fetal wound healing is very different from adult wound healing. An understanding of the biology of scarless fetal wound healing has tremendous clinical potential for modulating postnatal wound problems. In this study, the fetal lamb model was used to assess excisional fetal skin wound contraction in utero. Full-thickness 9-mm punch biopsy wounds were created on fetal lambs at 100 days' gestation (term, 145 days). Half of the wounds remained exposed to amniotic fluid, whereas the other half were covered by a silastic patch to exclude amniotic fluid. Wounds were harvested 3, 7, or 14 days later and wound areas were calculated. Exposure to amniotic fluid retarded wound contraction significantly at 3 days, but by 14 days all wounds had completely contracted and reepithelialized. Myofibroblasts are an important cellular element of wound contraction. The presence of wound myofibroblasts was documented by both transmission electronmicroscopy and immunocytochemistry with antimuscle actin antibody. It is concluded that fetal lamb wounds contract in utero and exposure to amniotic fluid appears to retard fetal skin wound contraction only during the early healing process.

Low-fat, high-carbohydrate diets improve wound healing and increase protein levels in surgically stressed rats

The specific effects of omega 3 and omega 6 polyunsaturated fatty acids on wound healing, nutrition status, or immune function are controversial. Therefore, we investigated the effects of fatty acid supplementation on wound healing and nitrogen retention in a surgically stressed rat model. Male Sprague-Dawley rats (weighing 250 g) were placed into three isocaloric, isonitrogenous feeding groups (controls [standard Vivonex]; 30% safflower oil [omega 6]; or 30% fish oil [omega 3]) for 8 days prior to receiving subcutaneous vascular graft wound cylinders in their dorsal midline. Nitrogen balance was monitored daily. Wounds healed for 10 days, animals were then euthanized, serum was drawn, and wound cylinders were harvested for analyses. The low-fat, high-carbohydrate control group had higher serum albumin levels at 10 days than either fatty acid-supplemented group (3.5 +/- 0.4 g/dL v 2.9 +/- 0.3 g/dL and 2.7 +/- 0.2 g/dL, omega 3 and omega 6, respectively; both P less than .05) and had better nitrogen balance (8.6 +/- 0.8 mg N/d v -2.6 +/- 0.9 mg N/d and 0.8 +/- 1.2 mg N/d, omega 3 and omega 6, respectively; both P less than .05). They also had better healed wounds at 10 days (450 +/- 290 micrograms 5-hydroxyproline [OHP]/cm of wound cylinder v 150 +/- 40 micrograms OHP/cm and 145 +/- 90 micrograms OHP/cm, omega 3 and omega 6, respectively). Surgically stressed rats had higher protein levels, better nitrogen balance, and improved wound healing when fed a diet high in carbohydrates and low in fat.

Studies in fetal wound healing. V. A prolonged presence of hyaluronic acid characterizes fetal wound fluid

Midgestation fetal wound healing is characterized by healing without fibrosis or scar formation. The mechanisms that underlie this remarkable process are mediated in part through a fetal wound extracellular matrix rich in hyaluronic acid. In this study a newly developed assay was used to determine the hyaluronic acid levels in fetal and adult wound fluid. Adult wound fluid had a rapid increase in hyaluronic acid, which peaked at 3 days and decreased to 0 by 7 days. In contrast levels of hyaluronic acid in fetal wound fluid increased rapidly and remained significantly elevated for 3 weeks. This prolonged presence of hyaluronic acid in the matrix of fetal wounds creates a 'permissive' wound environment that promotes fetal fibroblast movement and proliferation and inhibits cytodifferentiation. Such a matrix environment promotes healing by regeneration rather than by scarring. This observation has therapeutic implications. The prolonged application of hyaluronic acid or hyaluronate protein complexes to wounds in children or adults may modulate healing in a manner that makes the wounds more fetal-like.

Fetal wound healing: an in vitro explant model

The ability of fetal skin wounds to heal without scar formation is remarkable. The mechanisms that endow the fetus with this unique healing ability remain unknown. We have developed an in vitro explant model using fetal sheep skin to investigate fetal wound healing. This model eliminates the complex systemic mechanisms that modulate in vivo wound healing. We demonstrated that using an enriched medium, midgestation fetal sheep skin explants following wounding reepithelialized within 4 days. By 7 days after wounding the confluent epidermis was thicker, but the dermal wound remained open. This model demonstrates that it is possible to achieve conditions in culture that maintain tissue viability and support reepithelialization. This model may allow us to resolve some of the individual components that participate in the process of scarless fetal skin healing.

A rabbit model for fetal cleft lip repair

Recent clinical and experimental data indicate that fetal wound healing occurs without the accompanying inflammation and scar formation typical of postnatal wounds. The lack of scar tissue may have significant implications for craniomaxillofacial surgery. This report documents the development of a model for fetal cleft lip repair in rabbits. The survival rate for the first 47 fetuses was 76.6%.

Studies in fetal wound healing, VII. Fetal wound healing may be modulated by hyaluronic acid stimulating activity in amniotic fluid

Fetal wound healing occurs rapidly and without inflammation, fibrosis, or scar formation. It is a process fundamentally different from adult wound healing. The mechanisms that underlie such unique healing properties are unknown. However, hyaluronic acid, a glycosaminoglycan component of the extracellular matrix, is prominent throughout the course of fetal wound healing, and is thought to play a major role in the healing process. Amniotic fluid contains high levels of hyaluronic acid. Amniotic fluid also contains a number of potent growth factors that are critical for fetal development. In this report, a new factor in amniotic fluid that stimulates deposition of hyaluronic acid is described. This activity is measured in an in vitro assay system in which cultured fibrosarcoma cells are used as indicator cells. Amniotic fluid thus provides two separate mechanisms for the deposition of hyaluronic acid. One is by exogenous application directly onto fetal skin wounds; the second is by providing a factor to increase the production of hyaluronic acid endogenously, by stimulating cells around the wound site. The resulting hyaluronic acid-rich area may support the ability of the fetal wound to heal with its unique properties.

Studies in fetal wound healing. IV. Hyaluronic acid-stimulating activity distinguishes fetal wound fluid from adult wound fluid

Recent clinical and experimental evidence suggests that the fetus responds to injury in a fashion fundamentally different from that of the adult. Our initial experience with human open fetal surgery reinforces experimental observations that the fetal wounds heal without the scarring, inflammation, and contraction that often accompany adult wounds. In this study we examine fetal wound fluid in an attempt to elucidate the control mechanisms that endow the fetus with unique healing properties. The extracellular matrix of fetal wounds is rich in hyaluronic acid, a glycosaminoglycan found in high concentrations whenever there is tissue proliferation, regeneration, and repair. We establish that wound fluid from the fetus contains high levels of hyaluronic acid-stimulating activity that may underlie the elevated deposition of hyaluronic acid in the fetal wound matrix. In contrast there was no hyaluronic acid-stimulating activity present in adult wound fluid. Hyaluronic acid, in turn, fosters an extracellular environment permissive for cell motility and proliferation that may account for the unique properties observed in fetal wound healing.

Studies in fetal wound healing: II. A fetal environment accelerates fibroblast migration in vitro

We have used an in vitro model of wound healing using scratches made in a confluent monolayer of fibroblasts. The effects of fetal calf and postnatal calf serum on the migration of fibroblasts were compared. Differences between fetal and calf serum-incubated fibroblasts grown on coverslips were observed within 15 minutes of exposure. Cells in fetal serum began to change both shape and orientation and to move into the trough created by the scratch. The fibroblasts incubated in fetal calf serum completely filled in the trough within 16 hours while those incubated in calf serum did not do so even after 24 hours. We estimate that, at any point, there was a 50% lag time in the migration of the fibroblasts in the presence of postnatal calf serum. This difference in migration and filling was not a function of mitogenesis; the mitogenicity of the two sera were comparable. The results suggest that fibroblast migration in vitro is accelerated by the fetal serum. A similar mechanism may occur in vivo and may underlie the ability of the fetal wound to heal more rapidly.