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<front>
<journal-meta>
<journal-id journal-id-type="nlm-ta">Explor Drug Sci</journal-id>
<journal-id journal-id-type="publisher-id">EDS</journal-id>
<journal-title-group>
<journal-title>Exploration of Drug Science</journal-title>
</journal-title-group>
<issn pub-type="epub">2836-7677</issn>
<publisher>
<publisher-name>Open Exploration Publishing</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.37349/eds.2024.00040</article-id>
<article-id pub-id-type="manuscript">100840</article-id>
<article-categories>
<subj-group>
<subject>Perspective</subject>
</subj-group>
</article-categories>
<title-group>
<article-title>Clinical studies with drugs and biologics aimed at slowing or reversing normal aging processes—emerging results and future perspectives</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<contrib-id contrib-id-type="orcid">https://orcid.org/0000-0001-6209-926X</contrib-id>
<name>
<surname>Garay</surname>
<given-names>Ricardo P.</given-names>
</name>
<role content-type="https://credit.niso.org/contributor-roles/conceptualization/">Conceptualization</role>
<role content-type="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing—review &amp; editing</role>
<xref ref-type="aff" rid="I1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="I2">
<sup>2</sup>
</xref>
<xref ref-type="corresp" rid="cor1">
<sup>*</sup>
</xref>
</contrib>
<contrib contrib-type="editor">
<name>
<surname>Sabatier</surname>
<given-names>Jean-Marc</given-names>
</name>
<role>Academic Editor</role>
<aff>Aix-Marseille University, France</aff>
</contrib>
</contrib-group>
<aff id="I1">
<sup>1</sup>Department of Pharmacology and Therapeutics, Craven Center, 91360 Villemoisson-sur-Orge, France</aff>
<aff id="I2">
<sup>2</sup>Department of Life Sciences, Centre National de la Recherche Scientifique, 75016 Paris, France</aff>
<author-notes>
<corresp id="cor1">
<sup>*</sup>
<bold>Correspondence:</bold> Ricardo P. Garay, Department of Pharmacology and Therapeutics, Craven Center, 46bis, rue Galliéni, 91360 Villemoisson-sur-Orge, France. <email>ricardo.garay@orange.fr</email></corresp>
</author-notes>
<pub-date pub-type="ppub">
<year>2024</year>
</pub-date>
<pub-date pub-type="epub">
<day>10</day>
<month>04</month>
<year>2024</year>
</pub-date>
<volume>2</volume>
<issue>2</issue>
<fpage>144</fpage>
<lpage>153</lpage>
<history>
<date date-type="received">
<day>03</day>
<month>08</month>
<year>2023</year>
</date>
<date date-type="accepted">
<day>05</day>
<month>01</month>
<year>2024</year>
</date>
</history>
<permissions>
<copyright-statement>© The Author(s) 2024.</copyright-statement>
<license xlink:href="https://creativecommons.org/licenses/by/4.0/">
<license-p>This is an Open Access article licensed under a Creative Commons Attribution 4.0 International License (<ext-link ext-link-type="uri" xlink:href="https://creativecommons.org/licenses/by/4.0/">https://creativecommons.org/licenses/by/4.0/</ext-link>), which permits unrestricted use, sharing, adaptation, distribution and reproduction in any medium or format, for any purpose, even commercially, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.</license-p>
</license>
</permissions>
<abstract>
<p>Five families of investigational products are in clinical investigation to slow or reverse normal aging processes [longevity candidates, mesenchymal stem cells, senolytics drugs, sirtuin activators, and nicotinamide adenine dinucleotide (NAD)<sup>+</sup> precursors]. The longevity candidates, vitamin D and metformin, appear to significantly reduce all-cause mortality and prolong life expectancy. This should be confirmed by interventional studies. The mesenchymal stem cell family is the most advanced in clinical trial development [phase 2b randomized controlled trial (RCT)]. An allogeneic bone marrow stem cell preparation (Lomecel-B) reduced locomotor frailty in older people. The improvement in locomotion was modest. In the future, attempts could be made to improve potency through a precondition or genetic modification of naive bone marrow stem cells. Autologous adipose stem cell-assisted fat grafting increased graft survival, facial volume, and skin quality. The association of the senolytic drugs dasatinib and quercetin was well tolerated, with low brain penetration of dasatinib and undetectable levels of quercetin. The sirtuin-1 activator resveratrol (combined with physical exercise) improved physical function in older adults with physical limitations. The NAD<sup>+</sup> precursor nicotinamide riboside improved physical exercise performance. In conclusion, Lomecel-B is the most advanced agent in clinical trial development for normal aging processes (phase 2b for locomotion frailty), followed by resveratrol and nicotinamide riboside.</p>
</abstract>
<kwd-group>
<kwd>Aging</kwd>
<kwd>clinical trials</kwd>
<kwd>frailty</kwd>
<kwd>longevity</kwd>
<kwd>rejuvenation</kwd>
<kwd>senolytics</kwd>
<kwd>stem cells</kwd>
<kwd>vitamin D</kwd>
</kwd-group>
</article-meta>
</front>
<body>
<sec id="s1">
<title>Introduction</title>
<p id="p-1">Aging is characterized by a slow loss of organ function, reducing vitality, resilience, and healthy life expectancy. The International Conference on Frailty and Sarcopenia Research (ICFSR) clinical practice guidelines (CPGs) specify that there is no specific medical or biological treatment for these normal conditions of aging. The ICFSR does not recommend any of the non-specific pharmacological treatments currently available (only therapeutic interventions based on exercise and nutritional supplements are recommended) [<xref ref-type="bibr" rid="B1">1</xref>].</p>
<p id="p-2">A substantial effort is currently deployed to find specific drugs and biologics intended to slow or reverse normal aging processes. Currently, several literature reviews are available that identify and analyze clinical studies with the following specific families of compounds (<xref ref-type="table" rid="t1">Table 1</xref>): (i) longevity candidates [<xref ref-type="bibr" rid="B2">2</xref>, <xref ref-type="bibr" rid="B3">3</xref>], (ii) mesenchymal stem cells [<xref ref-type="bibr" rid="B4">4</xref>–<xref ref-type="bibr" rid="B6">6</xref>], (iii) senolytics drugs [<xref ref-type="bibr" rid="B7">7</xref>–<xref ref-type="bibr" rid="B9">9</xref>], (iv) sirtuin activators [<xref ref-type="bibr" rid="B10">10</xref>–<xref ref-type="bibr" rid="B13">13</xref>], and (v) nicotinamide adenine dinucleotide (NAD)<sup>+</sup> precursors [<xref ref-type="bibr" rid="B14">14</xref>–<xref ref-type="bibr" rid="B18">18</xref>].</p>
<table-wrap id="t1">
<label>Table 1</label>
<caption>
<p>Drugs and biologics that have shown positive results in clinical research to slow or reverse normal aging processes</p>
</caption>
<table frame="hsides" rules="groups">
<thead>
<tr>
<th>
<bold>Family</bold>
</th>
<th>
<bold>Indication</bold>
</th>
<th>
<bold>Leading agent</bold>
</th>
<th>
<bold>Study type</bold>
</th>
<th>
<bold>Reference</bold>
</th>
</tr>
</thead>
<tbody>
<tr>
<td rowspan="2">Longevity candidates</td>
<td rowspan="2">Longevity</td>
<td>Vitamin D</td>
<td>Observational</td>
<td>[<xref ref-type="bibr" rid="B34">34</xref>, <xref ref-type="bibr" rid="B36">36</xref>]</td>
</tr>
<tr>
<td>Metformin</td>
<td>Observational</td>
<td>[<xref ref-type="bibr" rid="B40">40</xref>]</td>
</tr>
<tr>
<td rowspan="2">Mesenchymal stem cells</td>
<td>Locomotion frailty</td>
<td>Lomecel-B</td>
<td>RCT (phase 2)</td>
<td>[<xref ref-type="bibr" rid="B47">47</xref>]</td>
</tr>
<tr>
<td>Facial rejuvenation</td>
<td>SVF</td>
<td>RCT</td>
<td>[<xref ref-type="bibr" rid="B54">54</xref>]</td>
</tr>
<tr>
<td>Senolytics drugs</td>
<td>Cognitive decline</td>
<td>D + Q</td>
<td>OL (phase 1)</td>
<td>[<xref ref-type="bibr" rid="B58">58</xref>]</td>
</tr>
<tr>
<td>Sirtuin activators</td>
<td>Aging frailty</td>
<td>Resveratrol</td>
<td>RCT (phase 2)</td>
<td>[<xref ref-type="bibr" rid="B61">61</xref>]</td>
</tr>
<tr>
<td>NAD<sup>+</sup> precursors</td>
<td>Physical performance</td>
<td>NRS</td>
<td>RCT</td>
<td>[<xref ref-type="bibr" rid="B65">65</xref>]</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>SVF: stromal vascular fraction; D + Q: dasatinib and quercetin; NRS: nicotinamide riboside supplements; OL: open-label</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p id="p-3">An overview of emerging results and future perspectives from clinical studies conducted with the five compound families mentioned above is presented here. Preclinical data and details about ongoing clinical trials (without results) can be found in the literature reviews cited above [<xref ref-type="bibr" rid="B2">2</xref>–<xref ref-type="bibr" rid="B12">12</xref>, <xref ref-type="bibr" rid="B14">14</xref>, <xref ref-type="bibr" rid="B15">15</xref>]. The reader interested in pharmacological mechanisms and biomarkers can consult the reviews by Nielsen et al. [<xref ref-type="bibr" rid="B16">16</xref>], Tchkonia et al. [<xref ref-type="bibr" rid="B19">19</xref>], Moskalev et al. [<xref ref-type="bibr" rid="B20">20</xref>], and Fraser et al. [<xref ref-type="bibr" rid="B21">21</xref>].</p>
</sec>
<sec id="s2">
<title>Longevity candidates</title>
<p id="p-4">Twenty years ago, the National Institute on Aging (NIA, USA) launched an Intervention Testing Program (ITP) dedicated to identifying longevity candidates in a genetically heterogeneous mouse model (candidates are evaluated in three independent laboratories) [<xref ref-type="bibr" rid="B22">22</xref>]. The ITP has identified two longevity drug candidates, the immunosuppressant rapamycin [<xref ref-type="bibr" rid="B23">23</xref>] and the antidiabetic acarbose [<xref ref-type="bibr" rid="B24">24</xref>] that are currently under clinical investigation [<xref ref-type="bibr" rid="B3">3</xref>]. Vitamin D and the antidiabetic drug metformin have been identified in other animal models and are also under clinical investigation [<xref ref-type="bibr" rid="B3">3</xref>, <xref ref-type="bibr" rid="B25">25</xref>].</p>
<p id="p-5">The mechanism by which these longevity candidates prolong animal lifespan is unclear. Rapamycin is a [mammalian target of rapamycin (mTOR)] kinase inhibitor, which possesses immunosuppressive and antiproliferative properties [<xref ref-type="bibr" rid="B25">25</xref>]. Ehninger et al. [<xref ref-type="bibr" rid="B26">26</xref>] have suggested that rapamycin extends lifespan in mice by suppressing cancerogenesis. Acarbose is an inhibitor of alpha-glucosidases, a class of intestinal enzymes necessary to digest carbohydrates [<xref ref-type="bibr" rid="B27">27</xref>]. Acarbose exerts anti-inflammatory effects on human monocytic THP-1 cells [<xref ref-type="bibr" rid="B28">28</xref>], and Sadagurski et al. [<xref ref-type="bibr" rid="B29">29</xref>] suggested that acarbose may prolong lifespan in mice by inhibiting age-related hypothalamic inflammation. Metformin appears to exert antiaging actions via multiple mechanisms, including nutrient sensing, DNA repair, oxidative stress, telomere attrition, inflammation, cellular senescence, stem cell decline, and autophagy [<xref ref-type="bibr" rid="B30">30</xref>]. Finally, vitamin D is a gene expression modifier (acting on more than 200 genes) and has pleiotropic biological actions [<xref ref-type="bibr" rid="B31">31</xref>].</p>
<sec id="t2-1">
<title>Emerging results with vitamin D</title>
<p id="p-6">Vitamin D is mainly synthesized in skin exposed to sunlight, and strong sunlight at equatorial latitudes leads to high mean serum concentrations of 25-hydroxy vitamin D [25(OH)D = around 115 nmol/L] [<xref ref-type="bibr" rid="B32">32</xref>]. On the contrary, low levels of 25(OH)D (&lt; 50 nmol/L) have been found in a considerable proportion of individuals from temperate countries, 40% in Europe and 24% in the USA [<xref ref-type="bibr" rid="B33">33</xref>]. In China, the prevalence of vitamin D deficiency in older adults was 68.4% (in 2014) [<xref ref-type="bibr" rid="B34">34</xref>, <xref ref-type="bibr" rid="B35">35</xref>].</p>
<p id="p-7">A recent observational and Mendelian analysis in middle-aged European persons [<xref ref-type="bibr" rid="B36">36</xref>] suggested a causal relationship between low levels of 25(OH)D (&lt; 40 nmol/L) and all-cause mortality. In China, all-cause mortality was significantly higher in subjects with low vitamin D status, and the change from vitamin D deficiency to no deficiency was associated with a lower risk of all‐cause mortality [<xref ref-type="bibr" rid="B34">34</xref>].</p>
</sec>
<sec id="t2-2">
<title>Emerging results with metformin</title>
<p id="p-8">Kulkarni et al. [<xref ref-type="bibr" rid="B37">37</xref>] conducted a phase 4, crossover design RCT (<ext-link xlink:href="https://clinicaltrials.gov/" ext-link-type="uri">ClinicalTrials.gov</ext-link> identifier: NCT02432287) to investigate the effect of metformin on metabolic and nonmetabolic regulation pathways in skeletal muscle and subcutaneous adipose tissue from 14 older adults (around 70 years old). Participants received oral metformin (1,700 mg/day) or placebo for 6 weeks. Metformin was found to significantly modify gene expression (RNA sequencing) in biopsies from skeletal muscle (647 genes) and subcutaneous adipose tissue (146 genes) [<xref ref-type="bibr" rid="B37">37</xref>]. These transcriptomic changes included several well-known anti-aging genes from the GenAge database [<xref ref-type="bibr" rid="B37">37</xref>, <xref ref-type="bibr" rid="B38">38</xref>]. In addition, a Mendelian randomization study using UK Biobank data [<xref ref-type="bibr" rid="B39">39</xref>] showed that metformin use was associated with younger phenotypic age.</p>
<p id="p-9">Campbell et al. [<xref ref-type="bibr" rid="B40">40</xref>] reviewed observational studies comparing all-cause mortality in patients with diabetes taking metformin with non-diabetics, or with diabetics receiving non-metformin therapies. The results suggested that metformin reduces all-cause mortality independently of its antidiabetic effect [<xref ref-type="bibr" rid="B40">40</xref>].</p>
<p id="p-10">Several clinical trials have been conducted with metformin for aging-related diseases, but they are outside the scope of this article for a recent review, see [<xref ref-type="bibr" rid="B41">41</xref>].</p>
</sec>
<sec id="t2-3">
<title>Perspectives of clinical research with longevity candidates</title>
<p id="p-11">All-cause mortality is a marker of longevity [<xref ref-type="bibr" rid="B3">3</xref>]. The above results from observational studies suggest that vitamin D supplementation [in persons with low 25(OH)D serum levels] [<xref ref-type="bibr" rid="B34">34</xref>, <xref ref-type="bibr" rid="B36">36</xref>] as well as metformin [<xref ref-type="bibr" rid="B40">40</xref>] can significantly reduce all-cause mortality and prolong life expectancy (<xref ref-type="table" rid="t1">Table 1</xref>). This prolongevity efficacy should be confirmed by interventional studies.</p>
<p id="p-12">A phase 3 clinical trial with metformin [Targeting Aging with Metformin (TAME)] was planned to assess the time to new onset of a composite outcome including cardiovascular events, cancer, dementia, and mortality [<xref ref-type="bibr" rid="B42">42</xref>, <xref ref-type="bibr" rid="B43">43</xref>]. TAME plans to include 3,000 participants, aged 65–79 years, at 14 centers across the US. In 2015, TAME started a discussion with the Food and Drug Administration (FDA, USA), but to this day it is not included in the ClinicalTrials.gov database.</p>
<p id="p-13">According to Barzilai et al. [<xref ref-type="bibr" rid="B43">43</xref>], the goal of TAME was to demonstrate “that metformin modulates aging and its diseases, beyond an isolated impact on diabetes”. According to Glossmann and Lutz [<xref ref-type="bibr" rid="B44">44</xref>]: “The acronym chosen and the intention behind it – namely, that aging is a ‘disorder’ that can be treated like any other disease – was a clear provocation.”.</p>
<p id="p-14">It is interesting to mention that two other longevity candidates (rapamycin and acarbose) are currently in clinical trials, but the results have not yet been reported to ClinicalTrials.gov [<xref ref-type="bibr" rid="B3">3</xref>].</p>
</sec>
</sec>
<sec id="s3">
<title>Mesenchymal stem cell preparations</title>
<p id="p-15">Mesenchymal stem cell preparations and multipotential stromal cells were in development for locomotion frailty and facial skin aging [<xref ref-type="bibr" rid="B4">4</xref>].</p>
<sec id="t3-1">
<title>Positive results on locomotion frailty</title>
<p id="p-16">Physical frailty in the elderly is characterized by reduced locomotor activity [<xref ref-type="bibr" rid="B1">1</xref>], and locomotion frailty is associated with an increased risk of falls, disability, and hospitalization [<xref ref-type="bibr" rid="B45">45</xref>].</p>
<p id="p-17">Lomecel-B (Longeveron, USA) is an allogeneic bone marrow stem cell preparation expanded in culture [<xref ref-type="bibr" rid="B46">46</xref>]. The [allogeneiC human mesenchymal stem cells in patients with aging fRAilTy via intravenoUS delivery (CRATUS)] trial [<xref ref-type="bibr" rid="B46">46</xref>, <xref ref-type="bibr" rid="B47">47</xref>] included: (i) a phase 1 safety study in 15 frail aging patients followed for 1 month [<xref ref-type="bibr" rid="B46">46</xref>], and (ii) a phase 2 RCT [<xref ref-type="bibr" rid="B47">47</xref>] investigating the efficacy of intravenous Lomecel-B to reduce physical frailty in 30 elderly subjects with mild to moderate locomotion frailty (treatment period: 6 months). The phase 1 study showed that Lomecel-B was safe and immunologically tolerated [<xref ref-type="bibr" rid="B46">46</xref>]. Participants in the phase 2 RCT [<xref ref-type="bibr" rid="B47">47</xref>] received 100 million cells (<italic>n</italic> = 10), 200 million cells (<italic>n</italic> = 10), or placebo (<italic>n</italic> = 10). The 6-min walk distance (6-MWD) increased significantly in the 100 m group (from 345.9 m to 410.5 m, mean values at baseline and 6 months, respectively). Immunotolerability was acceptable. Tumor necrosis factor (TNF)-alpha levels decreased significantly.</p>
<p id="p-18">Lomecel-B is a candidate for further development in phase 3 trials.</p>
</sec>
<sec id="t3-2">
<title>Perspectives of clinical research with stem cell preparations for physical frailty</title>
<p id="p-19">Locomotion frailty improvement with intravenous Lomecel-B was modest [<xref ref-type="bibr" rid="B48">48</xref>]. Preconditioning of naive bone marrow stem cells (with growth factors, drugs, or other agents), as well as genetic modification, can improve their therapeutic efficacy [<xref ref-type="bibr" rid="B49">49</xref>]. On the other hand, intravenous administration risks trapping the stem cells in the lungs [<xref ref-type="bibr" rid="B50">50</xref>]. In such a case, (smaller) exosomes may be an option to increase efficacy.</p>
<p id="p-20">Several other phase 1 and 2 clinical trials with stem cell preparations are currently underway [<xref ref-type="bibr" rid="B4">4</xref>]. In particular, a clinical trial (NCT04314011) using an allogeneic preparation of umbilical cord-derived stem cells was recently completed, but the results have not yet been reported to ClinicalTrials.gov.</p>
<p id="p-21">The use of allogeneic stem cell preparations may limit its clinical application. Predictive markers of graft rejection are being developed [<xref ref-type="bibr" rid="B51">51</xref>], markers that could help identify patients at risk of tissue rejection before administering stem cells.</p>
</sec>
<sec id="t3-3">
<title>Positive results on facial skin aging</title>
<p id="p-22">Facial skin aging is due to natural causes, as well as extrinsic factors (especially sun exposure: photoaging). The [stromal vascular fraction (SVF)] is a preparation of human adipose stem cells obtained by liposuction, followed by collagenase digestion and centrifugation [<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B52">52</xref>, <xref ref-type="bibr" rid="B53">53</xref>]. Yin et al. [<xref ref-type="bibr" rid="B54">54</xref>] conducted an RCT to investigate autologous SVF-assisted fat grafting for facial rejuvenation. Fifty patients were randomly assigned into two groups: an intervention group (<italic>n</italic> = 25) and a control group (<italic>n</italic> = 25, fat grafting only). SVF-assisted autologous fat grafting increased graft survival, facial volume, and skin quality (<xref ref-type="table" rid="t1">Table 1</xref>).</p>
</sec>
<sec id="t3-4">
<title>Perspectives of clinical research with stem cell preparations for facial rejuvenation</title>
<p id="p-23">Several clinical trials for facial skin aging are currently underway in Egypt, Indonesia, Cuba, Iran, and Malaysia [<xref ref-type="bibr" rid="B4">4</xref>]. Autologous SVF preparations are regulated as biological products by the FDA (USA) because they require mechanical processing [<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B41">41</xref>], and very numerous clinical trials with autologous SVF preparations for facial rejuvenation [<xref ref-type="bibr" rid="B53">53</xref>] are not registered on ClinicalTrials.gov. This was not the case with the study of Yin et al. [<xref ref-type="bibr" rid="B54">54</xref>], which was registered in <ext-link xlink:href="https://clinicaltrials.gov/" ext-link-type="uri">ClinicalTrials.gov</ext-link> (NCT02923219) as well as other clinical trials conducted in Egypt (NCT03928444) and Indonesia (NCT05508191) [<xref ref-type="bibr" rid="B4">4</xref>]. Results from trials NCT03928444 and NCT05508191 have not yet been posted to ClinicalTrials.gov. The application of similar RCT protocols could pave the way for autologous SVF preparations (in the USA) to be registered on ClinicalTrials.gov and comply with FDA regulations.</p>
</sec>
</sec>
<sec id="s4">
<title>Senolytic drugs</title>
<p id="p-24">Cellular senescence stops the proliferation of damaged or dysfunctional cells [<xref ref-type="bibr" rid="B7">7</xref>]. Aging is associated with the accumulation of senescent cells in various tissues and organs. In 2011, the group of Baker et al. [<xref ref-type="bibr" rid="B55">55</xref>] showed that killing senescent cells using a transgenic suicide gene is beneficial in preventing or delaying tissue dysfunction and prolonging lifespan in mouse models. Subsequently, the same group reported the discovery of senolytic agents in animal models: (i) the combination of D + Q in 2015 [<xref ref-type="bibr" rid="B56">56</xref>], and (ii) fisetin in 2017 [<xref ref-type="bibr" rid="B57">57</xref>].</p>
<sec id="t4-1">
<title>Results</title>
<p id="p-25">Gonzales et al. [<xref ref-type="bibr" rid="B58">58</xref>] recently reported the results of a 12 week, phase 1 clinical trial investigating the safety and cerebrospinal fluid (CSF) penetrance of D + Q in 5 participants (aged 70 years to 82 years) with early-stage symptomatic Alzheimer’s disease (<xref ref-type="table" rid="t1">Table 1</xref>). D + Q (100 mg and 1,000 mg respectively) were orally given for two days, followed by a treatment interruption of 13 days to 15 days, for a total of 6 cycles. Treatment was well tolerated and was not discontinued prematurely [<xref ref-type="bibr" rid="B58">58</xref>]. Low levels of dasatinib were detected in the CSF of 4 participants. Quercetin was not detectable in the CSF.</p>
</sec>
<sec id="t4-2">
<title>Perspectives</title>
<p id="p-26">Several senolytics, including D + Q and fisetin, are in development for cognitive decline [<xref ref-type="bibr" rid="B59">59</xref>], aging frailty, and skeletal health in normal postmenopausal women [<xref ref-type="bibr" rid="B7">7</xref>]. A clear advantage of some senolytics (quercetin, fisetin) is that they are natural products [<xref ref-type="bibr" rid="B60">60</xref>], but it seems too early to draw conclusions about clinical research with senolytic agents.</p>
</sec>
</sec>
<sec id="s5">
<title>Sirtuin activators</title>
<p id="p-27">Human sirtuins are a family of 7 signaling NAD<sup>+</sup>-dependent protein deacetylases that are involved in metabolic regulation, resistance to stress, and cellular processes, including aging and cell death [<xref ref-type="bibr" rid="B10">10</xref>, <xref ref-type="bibr" rid="B11">11</xref>]. The natural polyphenol resveratrol is a powerful activator of sirtuin-1 (SIRT1) [<xref ref-type="bibr" rid="B12">12</xref>, <xref ref-type="bibr" rid="B13">13</xref>]. Curcumin (another natural polyphenol) is a non-specific activator/upregulator of sirtuins (mainly influencing SIRT1 and SIRT3) [<xref ref-type="bibr" rid="B13">13</xref>].</p>
<sec id="t5-1">
<title>Positive results</title>
<p id="p-28">Harper et al. [<xref ref-type="bibr" rid="B61">61</xref>] have recently conducted a pilot clinical trial showing that resveratrol and exercise combined improve aging frailty (<xref ref-type="table" rid="t1">Table 1</xref>).</p>
</sec>
<sec id="t5-2">
<title>Perspectives</title>
<p id="p-29">The positive results of the pilot trial by Harper et al. [<xref ref-type="bibr" rid="B61">61</xref>] deserve confirmation in larger-scale trials.</p>
</sec>
</sec>
<sec id="s6">
<title>NAD<sup>+</sup> precursors</title>
<p id="p-30">A large body of evidence clearly shows that aging is associated with a reduction in cellular NAD<sup>+</sup> levels [<xref ref-type="bibr" rid="B14">14</xref>–<xref ref-type="bibr" rid="B18">18</xref>]. In particular, Mouchiroud et al. [<xref ref-type="bibr" rid="B62">62</xref>] found that NAD<sup>+</sup> levels are reduced in aged worms (the nematode <italic>Caenorhabditis elegans</italic>) and aged mice and that decreasing NAD<sup>+</sup> levels reduced worm lifespan. Zhu et al. [<xref ref-type="bibr" rid="B63">63</xref>] reported a decrease in intracellular NAD<sup>+</sup> levels in the healthy aged human brain <italic>in vivo</italic>. Massudi et al. [<xref ref-type="bibr" rid="B64">64</xref>] found a strong negative correlation between age and NAD<sup>+</sup> levels in human pelvic skin samples.</p>
<p id="p-31">Barker et al. [<xref ref-type="bibr" rid="B14">14</xref>] published a systematic review of 26 trials that investigated the effect of NAD<sup>+</sup> precursors on physical frailty outcomes. Only four of these trials enrolled participants with a mean age of 60 years or more [<xref ref-type="bibr" rid="B14">14</xref>]. Of these, only two trials included healthy participants. Dolopikou et al. [<xref ref-type="bibr" rid="B65">65</xref>] found that NRS significantly improved exercise performance (isometric peak torque and fatigue index) in the elderly. Martens et al. [<xref ref-type="bibr" rid="B66">66</xref>] reported that NRS elevates NAD<sup>+</sup> levels in circulating peripheral blood mononuclear cells of healthy middle-aged and older adults.</p>
</sec>
<sec id="s7">
<title>Concluding remarks</title>
<p id="p-32">Clinical research with drugs and biologics intended to slow or reverse normal aging processes has only recently begun [<xref ref-type="bibr" rid="B2">2</xref>–<xref ref-type="bibr" rid="B18">18</xref>]. Positive results are beginning to emerge from the very numerous clinical trials (and observational studies) launched worldwide (<xref ref-type="table" rid="t1">Table 1</xref>).</p>
<p id="p-33">Research highlights and perspectives:</p>
<p id="p-34">
<list list-type="simple">
<list-item>
<label>(1)</label>
<p>Vitamin D and metformin are leaders in the clinical development of longevity candidates (<xref ref-type="table" rid="t1">Table 1</xref>). Observational studies strongly suggested that these compounds can significantly reduce all-cause mortality (and prolong life expectancy) (<xref ref-type="table" rid="t1">Table 1</xref>). This prolongevity efficacy should be confirmed by interventional studies.</p>
</list-item>
<list-item>
<label>(2)</label>
<p>Intravenous Lomecel-B (a mesenchymal stem cell preparation) showed efficacy in reducing locomotor frailty in older people. However, the frailty improvement was modest. Preconditioning and/or genetic modification of naive mesenchymal stem cells can improve their therapeutic efficacy. The use of allogeneic stem cell preparations may limit its clinical application. Predictive markers of graft rejection are being developed, markers that could help identify patients at risk of tissue rejection before administering stem cells.</p>
</list-item>
<list-item>
<label>(3)</label>
<p>An RCT on facial rejuvenation [<xref ref-type="bibr" rid="B54">54</xref>] was registered on <ext-link xlink:href="https://clinicaltrials.gov/" ext-link-type="uri">ClinicalTrials.gov</ext-link> (NCT02923219) and showed that an autologous fat graft enriched with human adipose tissue stem cells improves graft survival, facial volume, and skin quality. The application of a similar RCT protocol could pave the way for autologous SVF preparations to be registered on ClinicalTrials.gov and comply with FDA regulations.</p>
</list-item>
<list-item>
<label>(4)</label>
<p>Senolytic drugs (including D + Q and fisetin), the SIRT1 activator resveratrol, and the NAD<sup>+</sup> precursor nicotinamide riboside (NR) are being developed to slow normal aging processes, but it seems too early to draw conclusions about the current clinical research with these compounds.</p>
</list-item>
</list>
</p>
</sec>
</body>
<back>
<glossary>
<title>Abbreviations</title>
<def-list>
<def-item>
<term>25(OH)D</term>
<def>
<p>25-hydroxy vitamin D</p>
</def>
</def-item>
<def-item>
<term>CSF</term>
<def>
<p>cerebrospinal fluid</p>
</def>
</def-item>
<def-item>
<term>D + Q</term>
<def>
<p>dasatinib and quercetin</p>
</def>
</def-item>
<def-item>
<term>FDA</term>
<def>
<p>Food and Drug Administration</p>
</def>
</def-item>
<def-item>
<term>NAD</term>
<def>
<p>nicotinamide adenine dinucleotide</p>
</def>
</def-item>
<def-item>
<term>NRS</term>
<def>
<p>nicotinamide riboside supplements</p>
</def>
</def-item>
<def-item>
<term>RCT</term>
<def>
<p>randomized controlled trial</p>
</def>
</def-item>
<def-item>
<term>SIRT1</term>
<def>
<p>sirtuin-1</p>
</def>
</def-item>
<def-item>
<term>SVF</term>
<def>
<p>stromal vascular fraction</p>
</def>
</def-item>
<def-item>
<term>TAME</term>
<def>
<p>Targeting Aging with Metformin</p>
</def>
</def-item>
</def-list>
</glossary>
<sec id="s8">
<title>Declarations</title>
<sec>
<title>Author contributions</title>
<p>RPG: Conceptualization, Writing—review &amp; editing.</p>
</sec>
<sec sec-type="COI-statement">
<title>Conflicts of interest</title>
<p>The author declares that he has no conflicts of interest.</p>
</sec>
<sec>
<title>Ethical approval</title>
<p>Not applicable.</p>
</sec>
<sec>
<title>Consent to participate</title>
<p>Not applicable.</p>
</sec>
<sec>
<title>Consent to publication</title>
<p>Not applicable.</p>
</sec>
<sec sec-type="data-availability">
<title>Availability of data and materials</title>
<p>Not applicable.</p>
</sec>
<sec>
<title>Funding</title>
<p>Not applicable.</p>
</sec>
<sec>
<title>Copyright</title>
<p>© The Author(s) 2024.</p>
</sec>
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