The Detection of Xylazine in Tijuana, Mexico: Triangulating Drug Checking and Clinical Urine Testing Data.

Introduction: Xylazine is a veterinary anesthetic increasingly present alongside illicit fentanyl in the US and Canada, presenting novel health risks. Although xylazine remains less common in the Western US, Mexican border cities serve as key trafficking hubs and may have higher prevalence of novel substances, but surveillance has been limited. Methods: We examined deidentified records from the Prevencasa harm reduction clinic in Tijuana, describing urine and paraphernalia testing from patients reporting using illicit opioids within 24 hr. Xylazine (two types), fentanyl, opiate, methamphetamine, amphetamine, benzodiazepine, and nitazene test strips were used to test urine and paraphernalia samples. Paraphernalia samples were also analyzed with mass spectrometry. Results: The study consisted of 23 participants that provided both urine and paraphernalia samples. Of the participants studied, 100 %, 91.3 %, and 69.6 % reported using China White/fentanyl, methamphetamine, and tar heroin, respectively. The mean age was 41.7 years, 95.7 % were male, 65.2 % were unhoused, and 30.4 % had skin wounds at the time of sample collection.Xylazine positivity in urine, for the two types used, was 82.6 % and 65.2 %. For paraphernalia testing, the xylazine positivity was 65.2 % and 47.8 %. Confirmatory testing of paraphernalia samples by mass spectrometry indicated a 52.2 % xylazine positivity. This testing also revealed positivity rates for fentanyl (73.9 %), fluorofentanyl (30.4 %), tramadol (30.4 %), and lidocaine (30.4 %).The mass spectrometry results suggest lidocaine triggered n = 3 and n = 0 false positives among the xylazine test strip types. A total of n = 0 and n = 1 false negatives were also observed. Discussion: Xylazine is present on the U.S.-Mexico border, requiring public health intervention. High lidocaine positivity complicates the clinical detection of xylazine via testing strips. Xylazine was found to be more prevalent in urine than in paraphernalia samples. Confirmatory urine studies are needed to better understand possible complications of using test strips for toxicological testing.

The introduction of fentanyl on the US-Mexico border: An ethnographic account triangulated with drug checking data from Tijuana.

BACKGROUND: Illicitly-manufactured fentanyls (fentanyl) have changed the risk environment of people who use drugs (PWUD). In California and many western US states, the opioid overdose rate spiked from 2016 to 2021, driven largely by fentanyl. Mexican border cities act as transit through-points for the illicit drug supply and similar evolving health risks are likely to be present. Nevertheless, due to data gaps in surveillance infrastructure, little is known about fentanyl prevalence in Mexico. METHODS: We employ intensive ethnographic participant-observation among PWUD, as well as key informants including harm reduction professionals, EMTs, and physicians on the front lines in Tijuana, Mexico. We triangulate interview data and direct observations of consumption practices with n=652 immunoassay-based fentanyl tests of drug paraphernalia from mobile harm reduction clinics in various points throughout the city. RESULTS: PWUD informants described a sharp increase in the psychoactive potency and availability of powder heroin-referred to as "china white"-and concomitant increases in frequency of overdose, soft tissue infection, and polysubstance methamphetamine use. Fentanyl positivity was found among 52.8% (95%CI: 48.9-56.6%) of syringes collected at harm reduction spaces, and varied strongly across sites, from 2.7% (0.0-5.7%) to 76.5% (68.2-84.7%), implying strong market heterogeneity. Controlling for location of collection, syringe-based fentanyl positivity increased by 21.7% (10.1-42.3%) during eight months of testing. Key informants confirm numerous increased public health risks from fentanyl and describe the absence of a systematic or evidence-based governmental response; naloxone remains difficult to access and recent austerity measures have cut funding for harm reduction in Mexico. CONCLUSIONS: Fentanyl, linked to powder heroin, is changing the risk environment of PWUD on the US-Mexico border. Improved surveillance is needed to track the evolving street drug supply in Mexico and related health impacts for vulnerable populations. Structural factors limiting access to naloxone, harm reduction, substance use treatment, and healthcare, and minimal overdose surveillance, must be improved to provide an effective systemic response.

Fentanyl is used in Mexico's northern border: current challenges for drug health policies.

BACKGROUND AND AIMS: Results from a recent study among 750 heroin users in three Mexico's northern border cities revealed an increase in white powder availability (also known as China white) and preference for this product among heroin users, as well as a general perception of increased overdose cases among this population. Here, we questioned whether those findings reflect an increased presence of heroin laced with fentanyl, which is associated with greater risks of overdose but that, until now, has not been described in Mexico. DESIGN: We tested fentanyl using highly sensitive test strips in syringe plungers, metal cookers and drug wrappings associated with heroin use. SETTING: Three injection sites in Tijuana, Baja California, México. PARTICIPANTS: Eighty-nine heroin users who interchanged paraphernalia for new syringes. MEASUREMENTS: We tested 59 residues of 'pure' white powder. The rest were white powder with black tar (n = 5) or white powder with crystal meth (n = 9), black tar with crystal meth (n = 1), black tar only (n = 13) and crystal meth only (n = 2). FINDINGS: Users believed that they consumed either white powder heroin, white powder heroin with crystal meth, white powder with black tar heroin or black tar heroin only. Analyses revealed that 93% (n = 55) of the 'pure' white powder samples had fentanyl. All (n = 9) the white powder samples mixed with crystal meth and 40% (n = 2) of the white powder with black tar were also laced with fentanyl. CONCLUSIONS: In a sample of 89 heroin users in Mexico, most white powder heroin users were unknowingly exposed to fentanyl, with fentanyl detected in 93% of white powder samples.

Development of chemotactic smart scaffold for use in tissue regeneration.

BACKGROUND: Regenerative medicine aims to obviate the need for autologous grafting through the use of bioengineered constructs that combine stem cells, growth factors, and biocompatible vehicles. Human mesenchymal stem cells and vascular endothelial growth factor (VEGF) have both shown promise for use in this context, the former because of their pluripotent capacity and the latter because of its chemotactic activity. The authors harnessed the regenerative potential of human mesenchymal stem cells and VEGF to develop a chemotactic scaffold for use in tissue engineering. METHODS: Human mesenchymal stem cells were transduced with human VEGF via lentivirus particles to secrete VEGF. The chemotactic activity of the VEGF-transduced stem cells was evaluated via a trans-well assay. Migration through semipermeable membranes was significantly greater in chambers filled with medium conditioned by VEGF-transduced cells. VEGF-transduced cells were then seeded on apatite-coated poly(lactic-co-glycolic acid) scaffolds, thereby creating the Smart Scaffold. To determine in vivo angiogenesis, the Smart Scaffolds were implanted into subcutaneous pockets in the backs of nude mice. RESULTS: Significantly larger numbers of capillaries were observed in the Smart Scaffold compared with control implants on immunohistologic studies. For the chemotactic in vivo study, human mesenchymal stem cells tagged with a fluorescent dye (1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide) were injected intravenously via tail vein after the subcutaneous implantation of the Smart Scaffolds. In vivo fluorescent imaging revealed that fluorescent dye-tagged human mesenchymal stem cells successfully accumulated within the Smart Scaffolds. CONCLUSION: These observations suggest that VEGF may play a vital role in the design of clinically relevant tissue regeneration graft substitutes through its angiogenic effects and ability to chemoattract mesenchymal stem cells.

Supporting the minority physician pipeline: providing global health experiences to undergraduate students in the United States-Mexico border region.

BACKGROUND: The sizeable US Latino population calls for increasing the pipeline of minority and bilingual physicians who can provide culturally competent care. Currently, only 5.5% of US providers are Hispanic/Latino, compared with 16% of the US population (i.e., >50.5 million persons). By 2060, it is predicted that about one-third of all US residents will be of Latino ethnicity. ACTIVITIES AND OUTCOMES: This article describes the Health Frontiers in Tijuana Undergraduate Internship Program (HFiT-UIP), a new quarterly undergraduate internship program based at a US-Mexico binational student-run free clinic and sponsored by the University of California, San Diego School of Medicine and the Universidad Autónoma de Baja California in Tijuana, Mexico. The HFiT-UIP provides learning opportunities for students and underrepresented minorities interested in medical careers, specifically Latino health. DISCUSSION: The HFiT-UIP might serve as a model for other educational partnerships across the US-Mexico border region and may help minority and other undergraduates seeking academic and community-based enrichment experiences. The HFiT-UIP can also support students' desires to learn about Latino, border, and global health within resource-limited settings.

A bioengineered peripheral nerve construct using aligned peptide amphiphile nanofibers.

Peripheral nerve injuries can result in lifelong disability. Primary coaptation is the treatment of choice when the gap between transected nerve ends is short. Long nerve gaps seen in more complex injuries often require autologous nerve grafts or nerve conduits implemented into the repair. Nerve grafts, however, cause morbidity and functional loss at donor sites, which are limited in number. Nerve conduits, in turn, lack an internal scaffold to support and guide axonal regeneration, resulting in decreased efficacy over longer nerve gap lengths. By comparison, peptide amphiphiles (PAs) are molecules that can self-assemble into nanofibers, which can be aligned to mimic the native architecture of peripheral nerve. As such, they represent a potential substrate for use in a bioengineered nerve graft substitute. To examine this, we cultured Schwann cells with bioactive PAs (RGDS-PA, IKVAV-PA) to determine their ability to attach to and proliferate within the biomaterial. Next, we devised a PA construct for use in a peripheral nerve critical sized defect model. Rat sciatic nerve defects were created and reconstructed with autologous nerve, PLGA conduits filled with various forms of aligned PAs, or left unrepaired. Motor and sensory recovery were determined and compared among groups. Our results demonstrate that Schwann cells are able to adhere to and proliferate in aligned PA gels, with greater efficacy in bioactive PAs compared to the backbone-PA alone. In vivo testing revealed recovery of motor and sensory function in animals treated with conduit/PA constructs comparable to animals treated with autologous nerve grafts. Functional recovery in conduit/PA and autologous graft groups was significantly faster than in animals treated with empty PLGA conduits. Histological examinations also demonstrated increased axonal and Schwann cell regeneration within the reconstructed nerve gap in animals treated with conduit/PA constructs. These results indicate that PA nanofibers may represent a promising biomaterial for use in bioengineered peripheral nerve repair.