Time- and Dose-Dependent Effects of Hyaluronidase on the Degradation of Different Hyaluronan-Based Fillers In Vitro

Retrobulbar Hyaluronidase in Hyaluronic Acid-Induced Ocular Vascular Occlusion: Efficacy, Challenges, and Implications for Clinical Practice

INTRODUCTION

Ophthalmic vascular occlusion due to hyaluronic acid (OVOH) is a rare but devastating complication of cosmetic filler injections, often resulting in severe vision loss.

MATERIALS

The methodology involved a systematic search across PubMed, NCBI, Google Scholar, and Cochrane to investigate factors influencing central retinal artery occlusion (CRAO) caused by fillers. Searches focused on "eye vascular anatomy," "ocular physiology in response to ischemia," "components AND hyaluronic acid AND inflammation," "recovery from blindness associated with fillers," "retrobulbar technique," and "hyaluronidase degradation AND fillers." This review examines the pathophysiology, clinical presentation, and management of OVOH by synthesizing findings from case reports, clinical studies, and experimental research. It elucidates retinal vascular anatomy, HA embolization mechanisms, and treatment efficacy, highlighting the critical importance of timely intervention.

RESULTS

OVOH typically presents with rapid vision loss within minutes of HA injection, often accompanied by severe ocular pain. The primary treatment, hyaluronidase (HYAL), is most effective when administered early, although retrobulbar HYAL shows limited overall success. Factors such as ischemia duration and the presence of cilioretinal arteries significantly influence retinal survival and recovery. The review discusses the complexities of retinal hypoxia and the implications of various intervention strategies.

CONCLUSION

Timely intervention is crucial for managing OVOH. Although retrobulbar HYAL remains a key treatment option, its effectiveness varies and necessitates optimization. Early and accurate diagnosis is essential, underscoring the need for further research to refine treatment strategies and improve outcomes for patients with retinal vascular occlusions.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Elevated fluid and glycosaminoglycan content in the Achilles tendon contribute to higher intratendinous pressures: Implications for Achilles tendinopathy

BACKGROUND

Tendinopathy alters the compositional properties of the Achilles tendon by increasing fluid and glycosaminoglycan content. It has been speculated that these changes may affect intratendinous pressure, but the extent of this relationship remains unclear. Therefore, we aimed to investigate the impact of elevated fluid and glycosaminoglycan content on Achilles tendon intratendinous pressure and to determine whether hyaluronidase (HYAL) therapy can intervene in this potential relationship.

METHODS

Twenty paired fresh-frozen cadaveric Achilles tendons were mounted in a tensile-testing machine and loaded up to 5% strain. Intratendinous resting (at 0% strain) and dynamic pressure (at 5% strain) were assessed using the microcapillary infusion technique. First, intratendinous pressure was measured under native conditions before and after infusion of 2 mL physiological saline. Next, 80 mg of glycosaminoglycans were administered bilaterally to the paired tendons. The right tendons were additionally treated with 1500 units of HYAL. Finally, both groups were retested, and the glycosaminoglycan content was analyzed.

RESULTS

It was found that both elevated fluid and glycosaminoglycan content resulted in higher intratendinous resting and dynamic pressures (p < 0.001). HYAL treatment induced a 2.3-fold reduction in glycosaminoglycan content (p = 0.002) and restored intratendinous pressures.

CONCLUSION

The results of this study demonstrated that elevated fluid and glycosaminoglycan content in Achilles tendinopathy contribute to increased intratendinous resting and dynamic pressures, which can be explained by the associated increased volume and reduced permeability of the tendon matrix, respectively. HYAL degrades glycosaminoglycans sufficiently to lower intratendinous pressures and may, therefore, serve as a promising treatment.

Spontaneous and induced degradation of dermal fillers: A review

Dermal fillers are among the most versatile tools in esthetic medicine. A broad range of temporary, semipermanent, and permanent filler products are on the market. We performed a narrative review on spontaneous and induced degradation of dermal fillers in vitro and in vivo. Hyaluronic acid-based fillers are the most frequently used temporary fillers. The products differ in their hyaluronic acid content, cross-linking, and rheological parameters. Endogenous hyaluronidase and reactive oxygen species are responsible for the spontaneous degradation of these fillers. Hyaluronidase digests the filler material by cleavage of the β-1,4 glycosidic linkage between N-acetylglucosamine and D-glucuronic acid. The enzyme can be used for treatment of medical and cosmetic adverse events due to hyaluronic acid-based filler. Higher hyaluronidase content and higher degree of cross-linking are major factors contributing to filler persistence over time. Semipermanent fillers are poly-(D), l-lactic acid and calcium hydroxylapatite. These filler types are decomposed by hydrolysis and osteoclastic enzymes. They usually persist up to 2 years, in single patients even more than 5 years. Sodium thiosulfate can stimulate degradation of calcium hydroxylapatite, but it is slow acting and not effective in case of emergency. Permanent fillers may show some kind of modification in situ, but spontaneous or induced degradation has not been documented. Once implanted the permanent fillers remain lifelong. Intralesional laser treatment supports the removal of permanent filler material as an alternative to surgery. Besides biocompatibility and toxicity, filler materials should also be assessed for degradation to improve patient safety.

Comparison of Hyaluronidase-Mediated Degradation Kinetics of Commercially Available Hyaluronic Acid Fillers In Vitro

BACKGROUND

The ability to degrade hyaluronic acid (HA)-based fillers with hyaluronidase allows for better management of adverse effects and reversal of suboptimal treatment outcomes.

OBJECTIVES

The aim of this study was to compare the enzymatic degradation kinetics of 16 commercially available HA-based fillers, representing 6 manufacturing technologies.

METHODS

In this nonclinical study, a recently developed in vitro multidose hyaluronidase administration protocol was used to induce degradation of HA-based fillers, enabling real-time evaluation of viscoelastic properties under near-static conditions. Each filler was exposed to repeated doses of hyaluronidase at intervals of 5 minutes to reach the degradation threshold of G' ≤ 30 Pa.

RESULTS

Noticeable differences in degradation characteristics were observed based on the design and technology of different filler classes. Vycross fillers were the most difficult to degrade and the Cohesive Polydensified Matrix filler was the least difficult to degrade. Preserved Network Technology products demonstrated proportional increases in gel degradation time and enzyme volume required for degradation across the individual resilient hyaluronic acid (RHA) products and indication categories. No obvious relationship was observed between gel degradation characteristics and the individual parameters of HA concentration, HA chain length, or the degree of modification of each filler when analyzed separately; however, a general correlation was identified with certain physicochemical properties.

CONCLUSIONS

Manufacturing technology was the most important factor influencing the reversibility of an HA product. An understanding of the differential degradation profiles of commercially available fillers will allow clinicians to select products that offer a higher margin of safety due to their preferential reversibility.

LEVEL OF EVIDENCE: 4

Use of Minimal Amounts of Hyaluronidase in the Ultrasound-Guided Treatment of Acute Vascular Occlusion by Hyaluronic Acid: A Preliminary Report

Background

Complications from hyaluronic acid (HA) fillers are increasingly frequent, given the very high number of treatments performed every day worldwide. They are routinely treated with high doses of hyaluronidase, which can cause significant local and general unwanted effects.

Objectives

The aim of our work is to demonstrate that when the origin of the complication is precisely identified and treated under ultrasound guidance, a few hyaluronidase units are enough to treat it effectively.

Methods

Five young female patients came to our observation for vascular lesions from injection of HA fillers performed in the immediately preceding days, in 4 cases, and a few weeks earlier in the fifth case. All lesions were accurately identified by ultrasound and treated with hyaluronidase.

Results

The 4 promptly treated patients fully recovered with a hyaluronidase dose of 87 ± 44 IU (range, 30-150 IU). The fifth patient, treated later, markedly improved regarding clinical picture and symptoms. No early or late side effects have been reported from this hyaluronidase dosage.

Conclusions

Our data confirm that if the lesion at the origin of the skin damage is precisely localized with ultrasound examination and treated under ultrasound guidance, a few units of hyaluronidase, injected directly into the HA accumulation, effectively resolve the skin damage. At the doses we used, which were much lower than those usually recommended, hyaluronidase proved to be not only effective but also free of any side effects.

Level of Evidence 5