Lower-Limb Exoskeletons Appeal to Both Clinicians and Older Adults, Especially for Fall Prevention and Joint Pain Reduction.

Exoskeletons are a burgeoning technology with many possible applications to improve human life; focusing the effort of exoskeleton research and development on the most important features is essential for facilitating adoption and maximizing positive societal impact. To identify important focus areas for exoskeleton research and development, we conducted a survey with 154 potential users (older adults) and another survey with 152 clinicians. The surveys were conducted online and to ensure a consistent concept of an exoskeleton across respondents, an image of a hip exoskeleton was shown during exoskeleton-related prompts. The survey responses indicate that both older adults and clinicians are open to using exoskeletons, fall prevention and joint pain reduction are especially important features, and users are likely to wear an exoskeleton in the scenarios when it has the greatest opportunity to help prevent a fall. These findings can help inform future exoskeleton research and guide the development of devices that are accepted, used, and provide meaningful benefit to users.

Time From Authorization by the US Food and Drug Administration to Medicare Coverage for Novel Technologies.

Importance: A wide variety of novel medical diagnostics and devices are determined safe and effective by the US Food and Drug Administration (FDA) each year, but to our knowledge the literature lacks evidence documenting how long it takes to establish new Medicare coverage for these technologies. Objective: To measure time from FDA authorization to at least nominal Medicare coverage for technologies requiring a new reimbursement pathway. Design, Setting, and Participants: In this cross-sectional study, public databases were used to associate each technology to billing codes, determine the effective date of each code and Medicare coverage decisions, and stratify by the maturity of the Medicare coverage. At least nominal coverage was defined as achievement of explicit coverage milestones through a national coverage determination, local coverage determinations by Medicare administrative contractors, or by implicit coverage aligned to a new billing code. Characterization by product type (acute treatment, chronic or ongoing treatment, diagnostic assay, and diagnostic device), manufacturer size, and evidence level were assessed for association with coverage achievement. The study included new product applications authorized by the FDA through the premarket approval pathway, the de novo pathway, or with breakthrough designation in the 510(k) pathway from January 1, 2016, to December 31, 2019. Data analysis took place between May 1, 2022, and December 31, 2022. Main Outcome Measurement: Time from FDA authorization to the first coverage milestone. Results: Among 281 identified technologies in the total sample, 64 (23%) were deemed novel technologies based on the absence of coverage determinations and/or the use of temporary or miscellaneous billing codes. Twenty-eight of 64 technologies (44%) successfully achieved explicit or implicit coverage following FDA authorization. The median time to at least nominal coverage for the analysis cohort was 5.7 years (90% CI, 4.4-NA years). Analysis of time-to-coverage data highlighted company size (log-rank P<.001) and product type (log-rank P = .01) as significant covariates associated with coverage achievement. No association was observed for technologies with level 1 evidence at FDA authorization and subsequent coverage milestone achievement (log-rank P = .40). Conclusions and Relevance: In this cross-sectional study of 64 novel technologies, only 28 (44%) achieved coverage milestones over the study timeline. The several-year period observed to establish at least nominal coverage suggests existing coverage processes may affect timely reimbursement of new technologies.

Characterization of structural determinants of granzyme B reveals potent mediators of extended substrate specificity.

Granzymes are trypsin-like serine proteases mediating apoptotic cell death that are composed of two genetically distinct subfamilies: granzyme A-like proteases resemble trypsin in their active site architecture, while granzyme B-like proteases are quite distinct. Granzyme B prefers substrates containing P4 to P1 amino acids Ile/Val, Glu/Met/Gln, Pro/Xaa, and aspartic acid N-terminal to the proteolytic cleavage. By investigating the narrow extended specificity of the granzyme B-like proteases the mediators of their unique specificity are being defined. The foci of this study were the structural determinants Ile99, Tyr174, Arg192, and Asn218. Even modest mutations of these residues resulted in unique extended specificity profiles as determined using combinatorial substrate libraries and individual fluorogenic substrates. As with other serine proteases, Ile99 completely defines and predicts P2 specificity, primarily through the binding constant Km. Asn218 variants have minor effects alone but in combination with mutations at Arg192 and Ile99 alter P2 through P4 extended specificity. For each variant, the activity on its cognate substrate was equal to that of granzyme B for the same substrate. Thus, mutations at these determinants change extended selectivity preferentially over catalytic power. Additionally Asn218 variants result in increased activity on the wild type substrate, while the N218A/I99A variant disrupts the additivity between P2 and P4 specificity. This defines Asn218 not only as a determinant of specificity but also as a structural component required for P2 and P4 independence. This study confirms four determinants of granzyme B extended substrate specificity that constitute a canon applicable to the study of the remaining family members.

Albumin is a substrate of human chymase. Prediction by combinatorial peptide screening and development of a selective inhibitor based on the albumin cleavage site.

Human chymase is a chymotryptic serine peptidase stored and secreted by mast cells. Compared with other chymotryptic enzymes, such as cathepsin G and chymotrypsin, it is much more slowly inhibited by serum serpins. Although chymase hydrolyzes several peptides and proteins in vitro, its target repertoire is limited compared with chymotrypsin because of selective interactions in an extended substrate-binding site. The best-known natural substrate, angiotensin I, is cleaved to generate vasoactive angiotensin II. Selectivity of angiotensin cleavage depends in major part on interactions involving substrate residues on the carboxyl-terminal (P1'-P2') side of the cleaved bond. To identify new targets based on interactions with residues on the aminoterminal (P4-P1) side of the site of hydrolysis, we profiled substrate preferences of recombinant human chymase using a combinatorial, fluorogenic peptide substrate library. Data base queries using the peptide (Arg-Glu-Thr-Tyr-X) generated from the most preferred amino acid at each subsite identify albumin as the sole, soluble, human extracellular protein containing this sequence. We validate the prediction that this site is chymase-susceptible by showing that chymase hydrolyzes albumin uniquely at the predicted location, with the resulting fragments remaining disulfide-linked. The site of hydrolysis is highly conserved in vertebrate albumins and is near predicted sites of metal cation binding, but nicking by chymase does not alter binding of Cu2+ or Zn2+. A synthetic peptidic inhibitor, diphenyl N alpha-benzoxycarbonyl-l-Arg-Glu-Thr-PheP-phosphonate, was designed from the preferred P4-P1 substrate sequence. This inhibitor is highly potent (IC50 3.8 nM) and 2,700- and 1,300-fold selective for chymase over cathepsin G and chymotrypsin, respectively. In summary, these findings reveal albumin to be a substrate for chymase and identify a potentially useful new chymase inhibitor.