Platelet-rich plasma (PRP) is the fraction of autologous plasma that contains a supraphysiological concentration of platelets, which are an important reservoir of growth factors. PRP is today one of the treatments of choice in regenerative medicine in both humans and animals. The aim of this study was to assess the existing literature on the possible influence of the patient’s physiological factors on different PRP characteristics, like platelet concentration, quantity of obtained plasma, quantity and types of growth factors (GFs) in human and veterinary medicines. In addition, a secondary aim was to compare protocols used to prepare PRP in these studies. In a total of 34 studies evaluated, the use of different protocols for the preparation and characterization of PRP and certain physiological factors such as age, sex and body condition substantially modify the characteristics of PRP in both human and veterinary medicine. Therefore, it is essential to standardize PRP collection protocols and define study groups based on physiological factors like sex, age, body mass index, fertility status and analyzed GFs to ensure reliable data and derive precise, informative conclusions.

Osteoarthritis (OA) is the most prevalent degenerative joint disease in both humans and companion animals, causing progressive cartilage destruction for which no curative treatment currently exists. Plasma rich in growth factors (PRGF) has shown chondroprotective effects in veterinary and preclinical models, but its efficacy is limited by the viscosity of synovial fluid and rapid degradation of growth factors within the joint. This study aimed to evaluate the effect of intra-articular co-administration of PRGF and urease-powered enzymatic nanobots on serum biomarkers of inflammation, oxidative stress, and cartilage metabolism in a rabbit (Oryctolagus cuniculus) full-depth chondral defect model (approval code: CEEA 2023-VSC-PEA-0242). Forty-one New Zealand White rabbits were allocated to a Control group (PRGF alone; n = 9 evaluable) or a Nanobots group (PRGF + nanobots; n = 24 evaluable). Twelve serum biomarkers were measured at baseline and days 28, 56, and 84. The Nanobots group showed markedly elevated serum hyaluronic acid at all timepoints (p < 0.006), significantly lower type II collagen cleavage neoepitope at day 28 (p = 0.018), persistently lower ferric reducing ability of plasma (p < 0.003), and higher C-reactive protein at days 56 and 84 (p < 0.035). These results provide preliminary in vivo evidence that urease-powered nanobots produce a distinct biomarker profile when combined with PRGF in a rabbit chondral defect model, with potential translational relevance for veterinary orthopedic therapy.

Platelet-rich plasma (PRP) exhibits substantial inter-individual variability, yet the physiological factors influencing its composition remain poorly defined. Most studies evaluate PRP as a homogeneous product, potentially masking associations between donor-related characteristics and platelet parameters. This study aimed to determine how key physiological factors influence whole blood (WB) and PRP indices and to assess their relationship with platelet enrichment. Ninety-seven client-owned dogs were categorized according to sex, age, body condition score (BCS), fertility status, and activity level. PRP samples were stratified according to platelet enrichment (Q1 < 1.5×, Q2 1.5–2.5×, Q3 > 2.5×), which served as a descriptive framework for characterizing PRP heterogeneity. WB and PRP indices were analyzed using univariate methods and multivariable models, including linear regression to identify predictors of platelet enrichment and ordinal logistic regression as a complementary approach. Physiological factors were associated with variability in platelet morphological and compositional indices. Among the variables evaluated, BCS was the only physiological factor consistently associated with platelet enrichment across multivariable analyses. Higher BCS was associated with increased platelet enrichment and a higher probability of belonging to higher hematological enrichment tiers. Age was negatively associated with platelet enrichment in the multivariable linear regression model, but this association was not retained in the ordinal regression analysis. In contrast, sex, fertility status, and activity level showed no independent associations with platelet enrichment after adjustment for potential confounders. Correlation analyses revealed strong clustering among concentration-related indices [platelet count (PLT), plateletcrit (PCT), and large platelets (LARGEPLT)] and a consistent internal organization of platelet parameters within both WB and PRP. These findings indicate that platelet enrichment is primarily determined by preparation-related factors, whereas physiological factors contribute mainly to inter-individual variability in platelet structural characteristics. Among the physiological factors evaluated, BCS appeared to be the most relevant source of biological variability in platelet enrichment. Platelet enrichment and platelet structural phenotype therefore represent related but distinct dimensions of PRP characterization. Future studies incorporating functional and biochemical markers are needed to determine the biological significance of the structural variability described here.

Progesterone (P4) exerts important vascular and immunomodulatory effects that influence platelet (PLT) activation and serotonin (5-HT) handling across mammalian species; nevertheless, its role in modulating PLT physiology during diestrus in mares remains poorly defined. This study hypothesized that physiological variations in luteal activity during diestrus are associated with changes in PLT activation and 5-HT-related parameters. The first objective was to determine whether changes in circulating P4 during diestrus are associated with alterations in PLT aggregation, circulating 5-HT, and PLT morphological indices in healthy mares; the second objective was to identify a diestrus day providing consistent physiological conditions for assessing PLT-related biomarkers. Twenty clinically healthy Spanish Purebred mares aged 4–9 years old were monitored. Blood samples were collected on days 5, 14, and 16 post-ovulation, with luteal status confirmed by ultrasonography. P4 concentrations were determined using a solid-phase I-125 radioimmunoassay (RIA), 5-HT concentrations were quantified using a competitive enzyme immunoassay, and PLT indices were measured using an ADVIA 2120i hematology analyzer. Data were compared using appropriate parametric or non-parametric tests after assessing distribution, and correlations were analyzed using rank-based correlation analysis, using Pearson or Spearman coefficients according to variable distribution. P4 concentrations were higher on days 14 and 16 compared with day 5 (p < 0.05), with no significant differences between days 14 and 16. Platelet aggregates (AGREG) showed the greatest variation, with significantly higher values on day 14 compared with day 5 (p < 0.05). In contrast, circulating 5-HT and all PLT morphological indices (PLT count, PCT, MPV, PLCR, PDW, PCDW, MPM, and PMDW) remained unchanged across diestrus. PLT aggregation showed a strong positive association with circulating P4 concentrations (r = 0.88, p < 0.05), whereas no meaningful correlations were observed between 5-HT and AGREG or between 5-HT and PLT morphological parameters. Internal correlations among PLT indices followed expected biological patterns, confirming the stability of structural PLT traits over short physiological intervals. These findings demonstrate that during diestrus, PLT activation—but not PLT morphology or circulating 5-HT—varies in parallel with P4 in mares. Day 14, corresponding to mid-diestrus, characterized by high luteal activity, represents an informative time point for assessing PLT activation and related biomarkers, providing a framework for standardizing sampling protocols for PLT-derived products in equine reproductive medicine.