Suppression of natural killer cell activity by high-dose narcotic anesthesia in rats

Anesthesia and cancer recurrence: a narrative review

Cancer is a leading cause of death worldwide. With the increasingly aging population, the number of emerging cancer cases is expected to increase markedly in the foreseeable future. Surgical resection with adjuvant therapy is the best available option for the potential cure of many solid tumors; thus, approximately 80% of patients with cancer undergo at least one surgical procedure during their disease. Agents used in general anesthesia can modulate cytokine release, transcription factors, and/or oncogenes. This can affect host immunity and the capability of cancer cells to survive and migrate, not only during surgery but for up to several weeks after surgery. However, it remains unknown whether exposure to anesthetic agents affects cancer recurrence or metastasis. This review explores the current literature to explain whether and how the choice of anesthetic and perioperative medication affect cancer surgery outcomes.

Lost in Translation: Failure of Preclinical Studies to Accurately Predict the Effect of Regional Analgesia on Cancer Recurrence

The major goal of translational research is to evaluate the efficacy and effectiveness of treatments and interventions that have emerged from exhaustive preclinical evidence. In 2007, a major clinical trial was started to investigate the impact of paravertebral analgesia on breast cancer recurrence. The trial was based on preclinical evidence demonstrating that spinal anesthesia suppressed metastatic dissemination by inhibiting surgical stress, boosting the immunological response, avoiding volatile anesthetics, and reducing opioid use. However, that trial and three more recent randomized trials with a total of 4,770 patients demonstrate that regional analgesia does not improve survival outcomes after breast, lung, and abdominal cancers. An obvious question is why there was an almost complete disconnect between the copious preclinical investigations suggesting benefit and robust clinical trials showing no benefit? The answer is complex but may result from preclinical research being mechanistically driven and based on reductionist models. Both basic scientists and clinical investigators underestimated the limitations of various preclinical models, leading to the apparently incorrect hypothesis that regional anesthesia reduces cancer recurrence. This article reviews factors that contributed to the discordance between the laboratory science, suggesting that regional analgesia might reduce cancer recurrence and clinical trials showing that it does not-and what can be learned from the disconnect.

Regional anesthesia might reduce recurrence and metastasis rates in adult patients with cancers after surgery: a meta-analysis

BACKGROUND

The influence of anesthesia techniques on cancer recurrence and metastasis following oncological surgery is a topic of growing interest. This meta-analysis investigates the potential effects of regional anesthesia (RA), either independently or combined with general anesthesia (GA), on these outcomes.

METHODS

We performed an extensive search across PubMed, Embase, and the Cochrane Library databases. The primary outcome was cancer recurrence, while the secondary outcomes were local recurrence and distant metastasis. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated by utilizing random-effects models. The Newcastle-Ottawa Scale (NOS) was used for quality assessment of observational studies, the Cochrane Risk of Bias Tool for Randomized Trials (Rob 2.0) was used for randomized controlled trials, and all the outcomes were assessed by using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE).

RESULTS

This study included 32 studies comprising 24,724 cancer patients. RA, either alone or in combination with GA, was significantly associated with reduced cancer recurrence compared to GA alone (OR = 0.82; 95% CI = 0.72 to 0.94; p < 0.01). This association remained significant for prostate cancer patients in subgroup analyses (OR = 0.71; 95% CI = 0.51 to 0.98; p = 0.04) and in the context of epidural anesthesia combined with GA. However, there were no significant associations noted for local recurrence or distant metastasis.

CONCLUSIONS

This meta-analysis provides evidence that RA, used alone or adjunctively with GA, is associated with a lower risk of cancer recurrence, particularly in patients with prostate cancer. However, no significant effects were observed on local recurrence or distant metastasis. Further prospective studies should be conducted to clarify this important issue.

Increased LPS-Induced Fever and Sickness Behavior in Adult Male and Female Rats Perinatally Exposed to Morphine

As a result of the current opioid crisis, the rate of children born exposed to opioids has skyrocketed. Later in life, these children have an increased risk for hospitalization and infection, raising concerns about potential immunocompromise, as is common with chronic opioid use. Opioids can act directly on immune cells or indirectly via the central nervous system to decrease immune system activity, leading to increased susceptibility, morbidity, and mortality to infection. However, it is currently unknown how perinatal opioid exposure (POE) alters immune function. Using a clinically relevant and translatable model of POE, we have investigated how baseline immune function and the reaction to an immune stimulator, lipopolysaccharide, is influenced by in utero opioid exposure in adult male and female rats. We report here that POE potentiates the febrile and neuroinflammatory response to lipopolysaccharide, likely as a consequence of suppressed immune function at baseline (including reduced antibody production). This suggests that POE increases susceptibility to infection by manipulating immune system development, consistent with the clinical literature. Investigation of the mechanisms whereby POE increases susceptibility to pathogens is critical for the development of potential interventions for immunosuppressed children exposed to opioids in utero.

A comparison of two techniques of postoperative analgesia: lignocaine-fentanyl intravenous infusion and ropivacaine-fentanyl epidural infusion in patients undergoing cytoreductive cancer surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC)-prospective randomized control study

BACKGROUND

Extensive surgical dissection, hemodynamic alterations associated with cytoreductive surgery (CRS), and hyperthermic intraperitoneal chemotherapy (HIPEC) make pain management challenging. We hypothesized that infusions of intravenous lignocaine and fentanyl provide comparable analgesia to epidural ropivacaine and fentanyl in these patients.

METHODS

Fifty patients scheduled to undergo CRS and HIPEC were enrolled in the study. The patients in group IV (Intravenous) received a bolus dose of 1.5 mg/kg lignocaine over 15 min, starting approximately 15 min before the surgical incision and fentanyl 0.5 mcg/kg, about 2 min before the surgical incision, following which patient received lignocaine infusion at 1 mg/kg/hr and fentanyl infusion at 0.5 mcg/kg/hr intraoperatively. Patients in group EPI (Epidural) received 6 mL of Ropivacaine 0.2% and fentanyl (2mcg/mL) approximately 15 min before surgical incision, followed by continuous infusion at the rate of 5 mL/hr. The procedure for induction and maintenance of anesthesia was standardized for both groups. In the postoperative period, the infusion of analgesics was reduced to half the intraoperative rates and continued for 24 h.

RESULTS

Demographic profile and clinical parameters were comparable between both groups (p > 0.05). There was no difference between the number of fentanyl doses given in the IV group [Langenbecks Arch Chir 373(3):189-196, 4, IQR (2-11)] and the EPI group [Reg Anesth Pain Med 35(4):370-376, 12, IQR (5-21)] in the postoperative period (p = 0.229). The need for intraoperative rescue analgesia was comparable among the groups (p = 0.882).

CONCLUSION

The two techniques, epidural (ropivacaine and fentanyl) and IV (lignocaine and fentanyl) infusions, provide comparable analgesia in patients undergoing CRS and HIPEC.

TRIAL REGISTRATION NUMBER

CTRI/2020/08/027052 dated 09/08/2020.

Immunosuppression by opioids: Mechanisms of action on innate and adaptive immunity

Opioids are excellent analgesics for the clinical treatment of various types of acute and chronic pain, particularly cancer-related pain. Nevertheless, it is well known that opioids have some nasty side effects, including immunosuppression, which is commonly overlooked. As a result, the incidence of opportunistic bacterial and viral infections increases in patients with long-term opioid use. Nowadays, there are no effective medications to alleviate opioid-induced immunosuppression. Understanding the underlying molecular mechanism of opioids in immunosuppression can enable researchers to devise effective therapeutic interventions. This review comprehensively summarized the exogenous opioids-induced immunosuppressive effects and their underlying mechanisms, the regulatory roles of endogenous opioids on the immune system, the potential link between opioid immunosuppressive effect and the function of the central nervous system (CNS), and the future perspectives in this field.

Anesthesia and cancer recurrence: an overview

Several perioperative factors are responsible for the dysregulation or suppression of the immune system with a possible impact on cancer cell growth and the development of new metastasis. These factors have the potential to directly suppress the immune system and activate hypothalamic-pituitary-adrenal axis and the sympathetic nervous system with a consequent further immunosuppressive effect.Anesthetics and analgesics used during the perioperative period may modulate the innate and adaptive immune system, inflammatory system, and angiogenesis, with a possible impact on cancer recurrence and long-term outcome. Even if the current data are controversial and contrasting, it is crucial to increase awareness about this topic among healthcare professionals for a future better and conscious choice of anesthetic techniques.In this article, we aimed to provide an overview regarding the relationship between anesthesia and cancer recurrence. We reviewed the effects of surgery, perioperative factors, and anesthetic agents on tumor cell survival and tumor recurrence.

Effect of opioids on cancer survival in patients with chronic pain: a propensity score-matched population-based cohort study

BACKGROUND

The impact of opioid analgesic use before cancer diagnosis on survival in patients with chronic pain is unclear. Therefore, we designed a propensity score-matched population-based cohort study to compare overall and cancer-related survival of patients with chronic pain who received long-term opioid analgesic treatment with that of those who did not receive such treatment.

METHODS

We included patients with chronic pain and categorised them into the following two groups according to their analgesic use: patients with cancer and chronic pain who were prescribed ≥180 defined daily doses of opioid analgesics per year >3 months before cancer diagnosis comprised the case group, and those who were prescribed <28 defined daily doses of opioid analgesics per year before cancer diagnosis comprised the control group. Patients in both groups were matched at a ratio of 1:5. The primary outcome was overall long-term survival.

RESULTS

The matching process yielded a final cohort of 1716 patients (286 and 1430 in the case and control groups, respectively) who were eligible for further analysis. The adjusted hazard ratio for overall survival in patients receiving long-term opioids was 3.53 (95% confidence interval: 3.03-4.11; P<0.001).

CONCLUSIONS

Long-term opioid analgesic use before cancer diagnosis might be associated with poor overall survival in patients with chronic pain compared with such patients who did not receive long-term opioid analgesics.

Opioids and Breast Cancer Recurrence: A Systematic Review

Breast cancer has the greatest epidemiological impact in women. Opioids represent the most prescribed analgesics, both in surgical time and in immediate postoperative period, as well as in chronic pain management as palliative care. We made a systematic review analyzing the literature's evidence about the safety of opioids in breast cancer treatment, focusing our attention on the link between opioid administration and increased relapses. The research has been conducted using the PubMed database. Preclinical studies, retrospective and prospective clinical studies, review articles and original articles were analyzed. In the literature, there are several preclinical in vitro and in vivo studies, suggesting a possible linkage between opioids administration and progression of cancer disease. Nevertheless, these results are not confirmed by clinical studies. The most recent evidence reassures the safety of opioids during surgical time as analgesic associated with anesthetics drugs, during postoperative period for optimal cancer-related pain management and in chronic use. Currently, there is controversial evidence suggesting a possible impact of opioids on breast cancer progression, but to date, it remains an unresolved issue. Although there is no conclusive evidence, we hope to arouse interest in the scientific community to always ensure the best standards of care for these patients.

Nonexperimental Xenobiotics: Unintended Consequences of Intentionally Administered Substances in Terrestrial Animal Models

Review of the use of nonexperimental xenobiotics in terrestrial animal models and the potential unintended consequences of these compounds, including drug-related side effects and adverse reactions.

Anesthetic Strategies in Oncological Surgery: Not Only a Simple Sleep, but Also Impact on Immunosuppression and Cancer Recurrence

Tumor recurrences or metastases remain a major hurdle in improving overall cancer survival. In the perioperative period, the balance between the ability of the cancer to seed and grow at the metastatic site and the ability of the patient to fight against the tumor (i.e. the host antitumor immunity) may determine the development of clinically evident metastases and influence the patient outcome. Up to 80% of oncological patients receive anesthesia and/or analgesia for diagnostic, therapeutic or palliative interventions. Therefore, anesthesiologists are asked to administer drugs such as opiates and volatile or intravenous anesthetics, which may determine different effects on immunomodulation and cancer recurrence. For instance, some studies suggest that intravenous drugs, such as propofol, may inhibit the host immunity to a lower extent as compared to volatile anesthetics. Similarly, some studies suggest that analgesia assured by local anesthetics may provide a reduction of cancer recurrence rate; whilst on the opposite side, opioids may exert negative consequences in patients undergoing cancer surgery, by interacting with the immune system response via the modulation of the hypothalamic-pituitary-adrenal axis and autonomic nervous system, or directly through the opioid receptors on the surface of immune cells. In this review, we summarize the main findings on the effects induced by different drugs on immunomodulation and cancer recurrence.

Suppression of Human Natural Killer Cells by Different Classes of Opioids

BACKGROUND

The use of regional and other opioid-sparing forms of anesthesia has been associated with a decrease in the recurrence of certain malignancies. Direct suppression of human natural killer cells by opioids has been postulated to explain this observation. However, the effect of different classes of opioids on suppression of natural killer cell cytotoxicity has not been systematically characterized.

METHODS

After confirming that freshly isolated natural killer cells from peripheral human blood express opioid receptors, cells were incubated with increasing concentrations of clinically used or receptor-specific opioid agonists. We also evaluated the effect of pretreatment with receptor-specific antagonists or naloxone. Treated natural killer cells were then coincubated with a carboxyfluorescein succinimidyl ester-labeled target tumor cell line, K562. Annexin V staining was used to compare the percent of tumor cell apoptosis in the presence of opioid-pretreated and untreated natural killer cells. Treated samples were compared to untreated samples using Kruskal-Wallis tests with a post hoc Dunn correction.

RESULTS

Morphine, methadone, buprenorphine, loperamide, [D-Ala2, N-MePhe4, Gly-ol]-enkephalin, and U-50488 significantly decreased natural killer cell cytotoxicity. When natural killer cells were pretreated with naloxone, cyprodime, and nor-binaltorphimine before exposure to morphine, there was no difference in natural killer cytotoxicity, compared to the amount observed by untreated natural killer cells. Fentanyl, O-desmethyltramadol, and [D-Pen2,D-Pen5] enkephalin did not change natural killer cell cytotoxicity compare to untreated natural killer cells.

CONCLUSIONS

Incubation of isolated natural killer cells with certain opioids causes a decrease in activity that is not observed after naloxone pretreatment. Suppression of natural killer cell cytotoxicity was observed with μ- and κ-receptor agonists but not δ-receptor agonists. These data suggest that the effect is mediated by μ- and κ-receptor agonism and that suppression is similar with many clinically used opioids.

Morphine decreases the function of primary human natural killer cells by both TLR4 and opioid receptor signaling

BACKGROUND

Opioids are commonly used to provide analgesia for cancer pain, and functional opioid receptors have been identified on natural killer (NK) cells, the lymphocytes responsible for surveillance and elimination of cancer cells. Opioids also bind to other lymphocyte receptors, such as Toll-like receptor (TLR)-4. Here, we characterized the effects of morphine on primary human NK cell cytotoxicity and mediator release, which occur through classical opioid receptor or TLR4 signaling.

METHODS

Purified primary human NK cells were pretreated with inhibitors of opioid receptors or TLR4 before being cultured with target tumor cell line K562 in the presence or absence of morphine. Apoptosis of K562 cells in each treatment condition was measured with an Annexin V flow cytometry-based assay and compared to that of K562 cells cultured with NK cells alone. Supernatant concentrations of 13 cytokines and cytotoxic mediators were measured with a multiplex bead-based flow cytometry assay.

RESULTS

Exposure of NK cells to morphine decreased their ability to induce apoptosis in K562 cells. Pretreating the NK cells with either naloxone, a mu- and kappa-opioid receptor antagonist, or TAK-242, a selective inhibitor of TLR4 signaling, prevented this effect. Paradoxically, morphine increased the concentration of interleukin-6, granzyme A, and granzyme B in cell supernatants. Pretreatment of NK cells with TAK-242 prevented the morphine-induced increase in interleukin-6, whereas pretreatment with naloxone inhibited the morphine-induced increase in granzymes A and B.

CONCLUSIONS

Both classical opioid receptors and TLR4 participate in morphine-induced suppression of NK cell cytotoxic activity. These studies have important implications for maintenance of immune function during management of cancer pain.

Opioids and the immune system - friend or foe

Systemically administered opioids are among the most powerful analgesics for treating severe pain. Several negative side effects (respiratory depression, addiction, nausea and confusion) and the risk of opioid-induced hyperalgesia accompany opioid administration. One other side effect is the potential of opioids to suppress the immune response and thereby to increase the vulnerability to infections. The link between opioids and immunosuppression has been investigated both in vitro and in vivo as well as in patients. However, the results are inconsistent: Exogenous opioids such as morphine and fentanyl have been found to impair the function of macrophages, natural killer cells and T-cells and to weaken the gut barrier in vitro and in animal studies. In epidemiological studies, high doses and the initiation of opioid therapy for non-malignant pain have been correlated with a higher risk of infectious diseases such as pneumonia. However clear randomized controlled studies are missing. Furthermore, immune cells including neutrophils, macrophages and T-cells have been shown to secrete endogenous opioid peptides, which then bind to peripheral opioid receptors to relieve inflammatory and neuropathic pain. In addition to cytokines, hormones and bacterial products, the release of opioid peptides is stimulated by the application of exogenous opioids. In summary, there is a reciprocal interaction between the immune system and endogenous as well as exogenous opioids. Further to the existing epidemiological studies, controlled clinical studies are needed in the future to elucidate the role of the opioid-immune system interaction in patients and to determine its clinical relevance.

LINKED ARTICLES

This article is part of a themed section on Emerging Areas of Opioid Pharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.14/issuetoc.

Dysfunctional Natural Killer Cells in the Aftermath of Cancer Surgery

The physiological changes that occur immediately following cancer surgeries initiate a chain of events that ultimately result in a short pro-, followed by a prolonged anti-, inflammatory period. Natural Killer (NK) cells are severely affected during this period in the recovering cancer patient. NK cells play a crucial role in anti-tumour immunity because of their innate ability to differentiate between malignant versus normal cells. Therefore, an opportunity arises in the aftermath of cancer surgery for residual cancer cells, including distant metastases, to gain a foothold in the absence of NK cell surveillance. Here, we describe the post-operative environment and how the release of sympathetic stress-related factors (e.g., cortisol, prostaglandins, catecholamines), anti-inflammatory cytokines (e.g., IL-6, TGF-β), and myeloid derived suppressor cells, mediate NK cell dysfunction. A snapshot of current and recently completed clinical trials specifically addressing NK cell dysfunction post-surgery is also discussed. In collecting and summarizing results from these different aspects of the surgical stress response, a comprehensive view of the NK cell suppressive effects of surgery is presented. Peri-operative therapies to mitigate NK cell suppression in the post-operative period could improve curative outcomes following cancer surgery.

Ultrasound-Assisted Thoracic Paravertebral Block Reduces Intraoperative Opioid Requirement and Improves Analgesia after Breast Cancer Surgery: A Randomized, Controlled, Single-Center Trial

OBJECTIVES

The contribution of ultrasound-assisted thoracic paravertebral block to postoperative analgesia remains unclear. We compared the effect of a combination of ultrasound assisted-thoracic paravertebral block and propofol general anesthesia with opioid and sevoflurane general anesthesia on volatile anesthetic, propofol and opioid consumption, and postoperative pain in patients having breast cancer surgery.

METHODS

Patients undergoing breast cancer surgery were randomly assigned to ultrasound-assisted paravertebral block with propofol general anesthesia (PPA group, n = 121) or fentanyl with sevoflurane general anesthesia (GA group, n = 126). Volatile anesthetic, propofol and opioid consumption, and postoperative pain intensity were compared between the groups using noninferiority and superiority tests.

RESULTS

Patients in the PPA group required less sevoflurane than those in the GA group (median [interquartile range] of 0 [0, 0] vs. 0.4 [0.3, 0.6] minimum alveolar concentration [MAC]-hours), less intraoperative fentanyl requirements (100 [50, 100] vs. 250 [200, 300]μg,), less intense postoperative pain (median visual analog scale score 2 [1, 3.5] vs. 3 [2, 4.5]), but more propofol (median 529 [424, 672] vs. 100 [100, 130] mg). Noninferiority was detected for all four outcomes; one-tailed superiority tests for each outcome were highly significant at P<0.001 in the expected directions.

CONCLUSIONS

The combination of propofol anesthesia with ultrasound-assisted paravertebral block reduces intraoperative volatile anesthetic and opioid requirements, and results in less post operative pain in patients undergoing breast cancer surgery.

TRIAL REGISTRATION

ClinicalTrial.gov NCT00418457.

Segmental thoracic spinal has advantages over general anesthesia for breast cancer surgery

BACKGROUND

Thoracic spinal anesthesia has been used for laparoscopic cholecystectomy and abdominal surgeries, but not in breast surgery. The present study compared this technique with general anesthesia in breast cancer surgeries.

MATERIALS AND METHODS

Forty patients were enrolled in this comparative study with inclusion criteria of ASA physical status I-III, primary breast cancer without known extension beyond the breast and axillary nodes, scheduled for unilateral mastectomy with axillary dissection. They were randomly divided into two groups. The thoracic spinal group (S) (n = 20) underwent segmental thoracic spinal anesthesia with bupivacaine and fentanyl at T5-T6 interspace, while the other group (n = 20) underwent general anesthesia (G). Intraoperative hemodynamic parameters, intraoperative complications, postoperative discharge time from post-anesthesia care unit (PACU), postoperative pain and analgesic consumption, postoperative adverse effects, and patient satisfaction with the anesthetic techniques were recorded.

RESULTS

Intraoperative hypertension (20%) was more frequent in group (G), while hypotension and bradycardia (15%) were more frequent in the segmental thoracic spinal (S) group. Postoperative nausea (30%) and vomiting (40%) during PACU stay were more frequent in the (G) group. Postoperative discharge time from PACU was shorter in the (S) group (124 ± 38 min) than in the (G) group (212 ± 46 min). The quality of postoperative analgesia and analgesic consumption was better in the (S) group. Patient satisfaction was similar in both groups.

CONCLUSIONS

Segmental thoracic spinal anesthesia has some advantages when compared with general anesthesia and can be considered as a sole anesthetic in breast cancer surgery with axillary lymph node clearance.

Comparison of combined general-epidural anesthesia with general anesthesia effects on survival and cancer recurrence: a meta-analysis of retrospective and prospective studies

OBJECTIVE

Animals underwent combined general-epidural anesthesia (EGA) is reported to have better long-time outcome than general anesthesia (GA). This study aimed to make overall evaluation of the association between these two anesthetic techniques and prognosis of cancer patients undergoing surgery.

METHODS

Related databases such as PubMed and EMbase were searched for eligible studies that evaluated the influence of EGA and GA on the prognosis of cancer patients undergoing surgery. Selected studies were evaluated according to the inclusion criteria by two reviewers respectively, followed by data extraction and quality assessment. The odds ratio (OR) with their 95% confidence intervals (CIs) were calculated to assess the influence strength of EGA and GA on prognosis of cancer patients.

RESULTS

A total of ten studies involving 3254 patients were included. The overall results demonstrated that there was no significant difference between EGA and GA group (OR = 0.88, 95% CI 0.73 to 1.06, P = 0.187) concerning postoperative recurrence and metastasis rate. In regard to the following two factors: cancer category and time of follow-up, subgroup analysis identified significant differences between EGA and GA in the group of patients with prostate cancer and the group with follow-up less than or equal to two years (OR = 0.66, 95% CI 0.46 to 0.95, P = 0.027; OR = 0.70, 95% CI 0.51 to 0.98, P = 0.035; respectively) concerning postoperative recurrence and metastasis rate. However, no significant difference was found in the group of patients with colorectal cancer (OR = 1.06, 95% CI 0.84-1.33, P = 0.62).

CONCLUSIONS

This meta-analysis showed that EGA might be associated with improvement in prognosis of patients with operable prostate cancer and the cancer patients with follow-up less than or equal to two years. However, no obvious relationship between the improvement in prognosis of colorectal cancer and EGA were detected, comparing to GA. Furthermore, all the results should be interpreted cautiously, as heterogeneous data were used for analyzing.

NK cells in the tumor microenvironment

The presence of natural killer (NK) cells in the tumor microenvironment correlates with outcome in a variety of cancers. However, the role of intratumoral NK cells is unclear. Preclinical studies have shown that, while NK cells efficiently kill circulating tumor cells of almost any origin, they seem to have very little effect against the same type of tumor cells when these have extravasated. The ability to kill extravasated tumor cells is, however, is dependent of the level of activation of the NK cells, as more recent published and unpublished studies, discussed below, have demonstrated that interleukin-2-activated NK cells are able to attack well-established solid tumors.

The effect of anesthetic technique on survival in human cancers: a meta-analysis of retrospective and prospective studies

Animal models have shown that regional anesthesia (combined with or without general anesthesia) would attenuate the surgical stress response by preserving immune function and result in better long-term outcome. In order to test the hypothesis that cancer patients who had surgery with epidural anesthesia (EA) would have better outcome (either overall survival [OS] or recurrence-free survival [RFS]) than those who were general anesthesia (GA), we performed this meta-analysis. By searching relevant literature, a total of 14 studies containing 18 sub-studies (seven in OS analysis and eleven in RFS analysis) were identified and meta-analyzed. Adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) were used to assess the strength of association. For OS, the random-effects model was used to analyze the data and demonstrated an OS benefit in favor of EA compared with GA alone (HR = 0.84, 95% CI 0.74–0.96, P = 0.013). The influence analysis showed the robustness of the results. Specifically, a significantly positive association between EA and improved OS was observed in colorectal cancer (HR = 0.65, 95% CI 0.43–0.99, P = 0.045). For RFS, the random-effects model was used to analyze the data and no significant relationship between RFS benefit and EA (HR = 0.88, 95% CI 0.64–1.22, P = 0.457) was detected. In conclusion, our meta-analysis suggests that epidural anesthesia and/or analgesia might be associated with improved overall survival in patients with operable cancer undergoing surgery (especially in colorectal cancer), but it does not support an association between epidural anesthesia and cancer control. Prospective studies are needed to determine whether the association between epidural use and survival is causative.

[Influence of anesthesia procedure on malignant tumor outcome]

Malignant tumors are the second major cause of death in Germany. The essential therapy of operable cancer is surgical removal of primary tumors combined with adjuvant therapy. However, several consequences of surgery may promote metastasis, such as shedding of tumor cells into the circulation, decrease in tumor-induced antiangiogenesis factors, excessive release of growth factors for wound healing and suppression of immunity induced by surgical stress. In the last decade it has become clear that cell-mediated immunity controls the development of metastasis. Various perioperative factors, such as surgical stress, certain anesthetic and analgesic drugs and pain can suppress the patients' immune system perioperatively. On the other hand, by modifications of the anesthesia technique (e.g. regional anesthesia) and perioperative management to minimize immunosuppression, anesthesiologists can play a considerable role for a better outcome in patients having malignant tumors. Sufficient clinical evidence is not yet available to prove or disprove the hypothesis that anesthesia practice can improve cancer prognosis. Despite difficulties in study design, several prospective randomized trials are currently running and the results are awaited to elucidate this topic.

Use of opioids or benzodiazepines and risk of pneumonia in older adults: a population-based case-control study

OBJECTIVES

To examine whether use of opioids or benzodiazepines is associated with risk of community-acquired pneumonia in older adults.

DESIGN

Population-based case-control study.

SETTING

An integrated healthcare delivery system.

PARTICIPANTS

Community-dwelling, immunocompetent adults aged 65 to 94 from 2000 to 2003. Presumptive pneumonia cases were identified from health plan automated data and validated through medical record review. Two controls were selected for each case with pneumonia, matched on age, sex, and calendar year.

MEASUREMENTS

Information about opioid and benzodiazepine use came from computerized pharmacy data. Information on covariates including comorbid illnesses and functional and cognitive status came from medical record review and electronic health data.

RESULTS

One thousand thirty-nine validated cases of pneumonia and 2,022 matched controls were identified. One hundred forty-four (13.9%) cases and 161 (8.0%) controls used prescription opioids (adjusted odds ratio (OR) = 1.38, 95% confidence interval (CI) = 1.08-1.76 vs nonuse). Risk was highest for opioids categorized as immunosuppressive based on immunological studies (OR = 1.88, 95% CI = 1.26-1.79 vs nonuse), whereas for nonimmunosuppressive opioids the OR was 1.23 (95% CI = 0.89-1.69). Risk was highest in the first 14 days of use (OR = 3.24, 95% CI = 1.64-6.39 vs nonuse). For long-acting opioids, the OR was 3.43 (95% CI = 1.44-8.21) versus nonuse, whereas for short-acting opioids, it was 1.27 (95% CI = 0.98-1.64). No greater risk was seen for current benzodiazepine use compared to nonuse (OR = 1.08, 95% CI = 0.80-1.47).

CONCLUSION

Use of opioids but not benzodiazepines was associated with pneumonia risk. The differences in risk seen for different opioid regimens warrant further study.

Anaesthetic technique may affect prognosis for ovarian serous adenocarcinoma: a retrospective analysis

BACKGROUND

Animal studies have shown that regional anaesthesia and analgesia may prevent or attenuate the surgical stress response by preserving immune function and result in better long-term outcome. We have tested the hypothesis that patients with ovarian serous adenocarcinoma who had surgery with epidural anaesthesia and analgesia would have better long-term outcome than those who were given general anaesthesia (GA) and i.v. opioid analgesia.

METHODS

A retrospective review of medical records identified 143 patients with ovarian serous adenocarcinoma who underwent surgery between January 1994 and October 2006 at the Sun Yat-sen University Cancer Center. Data in the analysis included age, anaesthesia-analgesia technique, ASA status, blood loss, transfusion, duration of surgery, status of preoperative cancer antigen 125, tumour size, International Federation of Gynecology and Obstetrics stage, histological grade, lymph node status, residual macroscopic tumour, and chemotherapy. Survival analysis was made with the main outcome measure of death.

RESULTS

The 3- and 5-yr overall survival rates were 78% and 61% in the patient group who received epidural anaesthesia and analgesia (Group E, n=106), and 58% and 49% in the patient group who received GA and i.v. opioid analgesia (Group G, n=37), respectively. After adjusting for the other variables, Group G had a hazard ratio of 1.214 (P=0.043) in a multivariable Cox regression model compared with Group E.

CONCLUSIONS

This retrospective analysis suggests that epidural anaesthesia and analgesia for ovarian serous adenocarcinoma surgery may reduce mortality during the initial years of follow-up.

Effect of anaesthetic technique and other perioperative factors on cancer recurrence

Surgical excision is the mainstay of treatment for potentially curable solid tumours. Metastatic disease is the most important cause of cancer-related death in these patients. The likelihood of tumour metastases depends on the balance between the metastatic potential of the tumour and the anti-metastatic host defences, of which cell-mediated immunity, and natural killer cell function in particular, is a critical component. It is increasingly recognized that anaesthetic technique and other perioperative factors have the potential to effect long-term outcome after cancer surgery. Surgery can inhibit important host defences and promote the development of metastases. Anaesthetic technique and drug choice can interact with the cellular immune system and effect long-term outcome. The potential effect of i.v. anaesthetics, volatile agents, local anaesthetic drugs, opiates, and non-steroidal anti-inflammatory drugs are reviewed here. There is particular interest at present in the effect of regional anaesthesia, which appears to be beneficial. Retrospective analyses have shown an outcome benefit for paravertebral analgesia for breast cancer surgery and epidural analgesia for prostatectomy. Blood transfusion, pain, stress, and hypothermia are other potentially important perioperative factors to consider.

The effect of perioperative intravenous lidocaine on postoperative pain and immune function

BACKGROUND

Surgery-associated tissue injury leads to nociception and inflammatory reaction, accompanied by increased production of proinflammatory cytokines. These cytokines can induce peripheral and central sensitization, leading to pain augmentation. Recently, a frequently used local anesthetic, lidocaine, was introduced as a part of a perioperative pain management technique. In addition to its analgesic effects, lidocaine has an antiinflammatory property, decreasing the upregulation of proinflammatory cytokines. We focused on the effects of preincisional and intraoperative IV lidocaine on pain intensity and immune reactivity in the postoperative period.

METHODS

Sixty-five female patients (ASA physical status I-II) scheduled for transabdominal hysterectomy were recruited to this randomized, placebo-controlled study. Thirty-two patients in the treatment group received IV lidocaine starting 20 min before surgery, whereas the control group (33 patients) received a matched saline infusion. Both groups received patient-controlled epidural analgesia during the postoperative period. Blood samples were collected before, 24, 48, and 72 h after surgery to measure ex vivo cytokine production of interleukin (IL)-1 receptor antagonist (IL-1ra) and IL-6, as well lymphocyte mitogenic response to phytohemagglutinin-M. A 10-cm visual analog scale was used to assess pain intensity at rest and after coughing.

RESULTS

Patients in the lidocaine + patient-controlled epidural analgesia group experienced less severe postoperative pain in the first 4 and 8 h after surgery (visual analog scale 4/3.7 at rest and 5.3/5 during coughing versus 4.5/4.2 and 6.1/5.3, respectively, in the placebo group). There was significantly less ex vivo production of IL-1ra and IL-6, whereas the lymphocyte proliferation response to phytohemagglutinin-M was better maintained than in the control group.

CONCLUSION

The present findings indicate that preoperative and intraoperative IV lidocaine improves immediate postoperative pain management and reduces surgery-induced immune alterations.

[Could anaesthesia, analgesia and sympathetic modulation affect neoplasic recurrence after surgery? A systematic review centred over the modulation of natural killer cells activity]

OBJECTIVE

The Natural Killer cells (NK) are an important part of non-specific cellular-mediated and antitumoral immunity. The goal of this review is to recapitulate data published over NK activity during the perioperative period and the influence of anaesthesia, analgesia and modulation of sympathetic system.

DATA SOURCES

Pubmed/Medline database.

STUDY SELECTION AND DATA EXTRACTION

Keywords-based selection, without limit of date: fundamental studies, randomized controlled trials and non-randomized comparative studies.

DATA SYNTHESIS

In human as in animal studies, an important correlation exists between NK activity and prognosis linked to the development of metastasis. The great depression of this cytotoxicity during the perioperative period could be able to compromise host defenses. The influence of anaesthetics and analgesics is important. The effects of the opioids, the agonists and the antagonists of the sympathetic nervous system, the prostaglandins, the NSAIDs, the ketamine, the hypnotics and the locoregional anaesthesia are systematically reviewed. The limits of experimental model presented are covered.

CONCLUSION

The effects of anaesthetic/analgesic drugs and techniques, the consequences of sympathomodulation on NK activity are numerous and sometimes opposite. It is important for the anaesthesiologist to keep in mind that the long term consequences of his techniques on the patients' outcome must be clarified.

Pain management: is opioid immunosuppression a clinical problem?

For more than 100 years, the use of opioid analgesic agents has been linked with modulation of the immune system in man. More recently, it has become apparent that both exogenous and endogenous opioids exert some effect upon the immune system but that this can be beneficial or deleterious depending on numerous variables. Of the strong opioid analgesics in current use, the majority are seen to cause immunosuppression in man. However, it still remains unclear whether this is clinically important in man although it would appear to be good practice to avoid such agents in patients already immunosuppressed by disease or pharmacotherapy. Powerful opioid analgesics without immunosuppressive properties can be selected and should be used in such situations and as these agents can offer additional benefits in addition to their non-immunosuppresive analgesia, it should be considered whether to use them at all times in preference to immunosuppressive opioids.

Immunologic effects of opioids in the presence or absence of pain

Opioids are acknowledged to suppress immune functions following both acute and chronic administration; however, there appear to be differences according to the schedule of administration as well as the state of the organism. For example, whereas a single dose of morphine in the absence of pain is well known to be immune suppressive, the biologic consequences of this suppression are largely unknown. Repeated and chronic opioid ingestion in the absence of pain appears to result in significant consequences including high infectious disease prevalence. On the other hand, in the presence of acute pain, there is evidence that opioid administration in analgesic doses is protective. Much less is known regarding the immune and disease implications related to chronic opioid treatment for chronic pain states.

Low-dose remifentanil infusion does not impair natural killer cell function in healthy volunteers

BACKGROUND

Mu opioid agonists suppress natural killer (NK) cell activity in animal models. Studies in human volunteers, however, have yielded conflicting results, with morphine suppressing and fentanyl increasing NK cell activity. This study evaluated the effect of a constant 8-h infusion of remifentanil on NK cell number and function in human volunteers.

METHODS

After IRB approval and informed consent was obtained, 10 healthy volunteers underwent an 11 pm to 7 am infusion of saline, and at least 1 week later an infusion of 0.02-0.04 microg x kg(-1) min(-1) remifentanil. Blood was collected at 7 am for measurement of NK cell cytotoxicity using a (51)Cr release assay and measurement of NK cell number using fluorescent flow cytometry.

RESULTS

Median and range of the total NK cell cytotoxicity (KU ml(-1)) was 745.0 (498.3-1483.6) on the control morning and 818.6 (238.5-1454.5) on the morning following the remifentanil infusion. Neither the number of NK cells ml(-1) (2.5 x 10(5) (1.4 x 10(5)-4.2 x 10(5)) vs 2.7 x 10(5) (1.1 x 10(5)-4.4 x 10(5))) nor the cytotoxicity per 1000 NK cells (KU 1000 NK cells(-1)) (3.0 (1.8-5.2) vs 2.9 (0.9-6.7)) changed between the control and remifentanil conditions.

CONCLUSIONS

An 8-h infusion of remifentanil did not affect NK cell activity in normal volunteers. This result differs from previous findings of morphine-induced NK cell activity suppression and fentanyl-induced NK cell activity enhancement in normal volunteers.

The effects of postoperative pain management on immune response to surgery

Surgery is associated with immune alterations, which are the combined result of tissue damage, anesthesia, postoperative pain, and psychological stress. In the present study, we compared the effects of several postoperative pain management techniques on postoperative immune function. Patients hospitalized for abdominal surgery were randomly assigned to one of three postoperative pain management techniques: opiates on demand (intermittent opiate regimen [IOR]), patient-controlled analgesia (PCA), and patient-controlled epidural analgesia (PCEA). Postoperative pain was assessed. Blood samples were collected before and 24, 48, and 72 h after surgery. Production of interleukin (IL)-1beta, IL-2, and IL-6, natural killer cell cytotoxicity, and lymphocyte mitogenic responses were assessed. Patients of the PCEA group exhibited lower pain scores in the first 24 h after surgery compared with patients of the IOR and PCA groups. Mitogenic responses were suppressed in all groups in the first 24 h, returned to preoperative values by 72 h in the PCEA group, but remained suppressed in the PCA group. Production of IL-1beta and IL-6 increased in the IOR and PCA groups, whereas it remained almost unchanged in the PCEA group. Patients receiving an epidural mixture of opiate and local anesthetics (PCEA group) exhibited reduced suppression of lymphocyte proliferation and attenuated proinflammatory cytokine response in the postoperative period.

Morphine-6beta-glucuronide modulates the expression of inducible nitric oxide synthase

The immunomodulatory effects of morphine are well established; however, suprisingly little is known about the immunomodulatory properties of the major metabolites of morphine. The present study tests the hypothesis that expression of inducible nitric oxide synthase (iNOS) is modulated by the administration of the morphine metabolite, morphine-6beta-glucuronide. The initial study using rats shows that morphine-6beta-glucuronide administration (0, 1.0, 3.163, 10 mg/kg s.c.) results in a pronounced reduction in lipopolysaccharide (LPS)-induced expression of iNOS (inducible nitricoxide synthease) in spleen, lung, and liver tissue as measured by western blotting. Morphine-6beta-glucuronide also produces a reduction in the level of plasma nitrite/nitrate, the more stable end-product of nitric oxide degradation. In a subsequent study, administration of the opioid receptor antagonist, naltrexone (0.1 mg/kg) prior to the injection of morphine-6beta-glucuronide (10 mg/kg) blocks the morphine-6beta-glucuronide induced reduction of iNOS expression and plasma nitrite/nitrite levels indicating that the effect is mediated via the opioid-receptor. This study provides the first evidence that morphine-6beta-glucuronide alters the expression of iNOS.

Opioid mediated effects on the immune system: sympathetic nervous system involvement

Opioids have been hypothesized to suppress parameters of immune function by acting within the central nervous system to increase the activity of the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Production of catecholamines and adrenocorticoids have been demonstrated to be responsible for many of the observed immunomodulatory effects which occur following opioid administration. In general, the sympathetic nervous system has been shown to play a role in regulating lymphocyte proliferation and natural killer cell activity as well as several other parameters of immune function. Here, we will focus primarily on the role of the sympathetic nervous system in modulating opioid induced immunosuppression. The role of the hypothalamic-pituitary adrenal axis is reviewed elsewhere in this issue.

Comparison of the time course of morphine's analgesic and immunologic effects

Morphine, an opioid analgesic commonly prescribed and abused, produces immune-altering effects. Whether morphine's antinociceptive and immunologic effects occur concurrently is unknown. Therefore, we investigated the time course of morphine's immunologic and antinociceptive effects. Rats were given a 15-mg/kg morphine injection (subcutaneously), and experimental assessments were taken at 30 min, 1 h, 2 h, 6 h, 12 h, and 24 h after treatment. Immune measures included natural killer (NK) cell activity, proliferation of splenic T and B lymphocytes, and cytokine production. Antinociception was assessed by using the tail withdrawal assay. Results show that morphine's immunomodulatory effects on NK cell activity begin within 30 min, continue for at least 12 h, and return to control values by 24 h. In contrast, proliferation of splenic T and B cells and interferon-gamma production are not altered within 30 min; maximal suppression occurs at 1 h, and recovery begins within 2 h. In all immune measures, therefore, maximal suppression is present at the 1-h time point, and recovery is complete within 24 h. Morphine induces antinociception 30 min to 2 h after drug administration; recovery is complete within 6 h. These results suggest the possibility that different mechanisms modulate morphine's immunologic and analgesic effects.

IMPLICATIONS

Acute morphine treatment in rats produces immune alterations and antinociception. Although there are slight differences in morphine's maximal immunological and antinociceptive effects, morphine suppresses immune status at time points concordant with its antinociceptive effects. These effects should be considered when administering morphine to patients whose systems are immunocompromised.

Mirfentanil antagonizes morphine-induced suppression of splenic NK activity in mice

Mirfentanil [N-(2-pyrazinyl)-N-(1-phenethyl-4-piperidinyl)-2-furamide] was studied for its antinociceptive and immunomodulatory effects in mice Mirfentanil (1.0-32.0 mg/kg) increased tail-flick latency to a thermal stimulus and this effect was antagonized (94 +/- 2%) by naltrexone (10.0 mg/kg). Unlike naltrexone, the delta opioid selective antagonist naltrindole (20.0 mg/kg) had no effect on mirfentanil-induced analgesia. In a dose-dependent fashion, the mu-selective antagonists beta-funaltrexamine (1.0-40.0 mg/kg) and naloxonazine (1.0-35.0 mg/kg) blocked mirfentanil (10.0 mg/kg)-induced analgesia up to 75% of the maximum analgesic effect. Norbinaltorphimine (10.0 mg/kg) partially blocked (35%) the maximum analgesic effect following mirfentanil (10.0 mg/kg) administration. Single doses of mirfentanil (0.1-32.0 mg/kg) had no effect on splenic NK activity. However, preadministration of mirfentanil (1.0-10.0 mg/kg) blocked morphine-induced suppression of splenic NK activity. Collectively, the results suggest that mirfentanil is a novel opioid that induces antinociception predominately through mu opioid receptors but, unlike morphine or fentanyl, does not suppress splenic NK activity.

Effects of anesthesia based on large versus small doses of fentanyl on natural killer cell cytotoxicity in the perioperative period

Surgical stress and general anesthesia suppress immune functions, including natural killer cell cytotoxicity (NKCC). This suppression could be attributable, at least in part, to opiates. We have previously shown that large-dose fentanyl administration suppressed NKCC in rats. The present study sought to compare the effects of two anesthetic protocols, based on large- (LDFA) versus small (SDFA)-dose fentanyl anesthesia on NKCC in the perioperative period. Forty patients were included in this study; half were assigned to each protocol of anesthesia. In each anesthetic group, half the patients were undergoing surgery for malignant diseases, and half for benign conditions. Blood samples were collected during the perioperative period. NKCC was assessed using the chromium release assay. Initially, both types of anesthesia similarly suppressed NKCC, with a peak effect 24 h after surgery. The two types of anesthesia, however, differed in the rate of recovery of NKCC suppression. By the second postoperative day, NKCC returned to control values in the SDFA patients, whereas NKCC was still significantly suppressed after LDFA. These results indicate that LDFA causes prolonged suppression of NK cell function. Whether this suppression might have a long-term impact on the overall outcome, especially in cancer patients, remains to be determined.

Exogenous and endogenous opioids as biological response modifiers

Narcotic opioid compounds are among the most widely prescribed drug interventions for individuals suffering pain. Among the unwarranted side effects of respiratory depression, constipation, and physical dependence are the immunosuppressive qualities, particularly those which affect cell-mediated immunity. The immunosuppressive characteristics of opioid narcotics (e.g., morphine) have recently come into focus with the advent of acquired immune deficiency syndrome (AIDS) and the putative causative agent, human immunodeficiency virus type 1 (HIV-1). Specifically, a vast reservoir of HIV-1-infected individuals exists among drug abusers. Moreover, experimental evidence would suggest narcotic opioids may increase viral load in infected individuals by modifying the cellular machinery of activated leukocytes. Likewise, investigators have shown that opioids modify tumor growth and development. In this review, a comparison between endogenous opioid peptides and exogenous opiates on cell-mediated immunity and its relationship to viral infection and tumors is described.

Prognostic value of anesthesia type for patients treated for cutaneous melanoma

BACKGROUND

General anesthesia has been reported to compromise several cell-mediated immune functions. Hence it is plausible that anesthesia could affect the postoperative outcome of cancer patients.

OBJECTIVE

To study the influence of the type of anesthesia on survival of 459 patients with localized cutaneous melanoma observed between 1980 and 1991.

METHODS

Crude survival proportions were calculated by the methods of Kaplan and Meier. Cox proportional hazards regression analysis was used to estimate the effect on death rates of the type of anesthesia.

RESULTS

The 5-year survival proportions were 81% for patients treated under local anesthesia, 71.9% for patients receiving halothane isoflurane or enflurane, and 88.4% for neuroleptanalgesia (P < .05). After multiple adjustment for other prognostic variables (tumor thickness, presence of ulceration, age, sex, cross-sectional profile), using patients treated under local anesthesia as a reference group, the relative risk for general anesthesia with volatile agents was 1.3 (95% CI, 0.84-2.10).

CONCLUSION

The type of anesthesia does not seem to affect the survival of patients with cutaneous melanoma, when other prognostic factors are considered.

Cellular mechanisms involved in morphine-mediated suppression of CTL activity

Based on a plethora of data from many laboratories, we have proposed the following mechanisms by which morphine alters immune homeostasis and immunocompetence in vivo (Fig. 2). Specifically, the administration of morphine subcutaneously via routing through blood interacts directly with opioid receptors on cells of the immune system or on receptors within the central nervous system. Although there is currently no evidence to support the direct involvement of morphine on lymphocyte opioid receptors, in vitro studies show the existence of functional, naloxone-sensitive opioid receptors (25). In addition, pharmacological and biochemical characterization of lymphocyte opioid receptors has been shown to be consistent in many instances, with the profile of neural-derived opioid receptors (25-27). Finally, recent molecular studies using oligonucleotide primers specific for the delta-class opioid receptor cloned from NG-108-15 cells (28) have been used in reverse transcription-polymerase chain reactions to generate a 400 bp product in SL which has 100% sequence homology with a published opioid receptor cloned from a brain library (35). However, future studies are necessary to establish the role of lymphocyte opioid receptors following the in vivo administration of opioids (e.g. fentanyl, methadone, and morphine). Since the administration of morphine subcutaneously appears to predominately interact with brain opioid receptors (3) located in the mesencephalon (5), other neuroendocrine systems become candidates for activation and subsequent direct modulation of immune function: (i) the HPA axis and (ii) the sympathetic nervous system (SNS).(ABSTRACT TRUNCATED AT 250 WORDS)

OHM3295: a fentanyl-related 4-heteroanilido piperidine with analgesic effects but not suppressive effects on splenic NK activity in mice

The immunoregulatory effects of fentanyl and a fentanyl-related compound, OHM3295, were studied in mice. Male CD1 mice treated with a range of fentanyl doses (0.1-1.0 mg/kg, subcutaneously) showed suppression of splenic natural killer (NK) activity following 0.25-0.50 mg/kg fentanyl dose but not higher (0.75-1.0 mg/kg) or lower (0.1 mg/kg) doses. Fentanyl (0.01-32.0 mg/kg) also induced dose-related analgesia as measured by an increase in tail flick latency; these analgesic effects were antagonized by naltrexone (1.0-10.0 mg/kg). Pretreatment with naltrexone (1.0-3.2 mg/kg) resulted in significant suppression of splenic NK activity following fentanyl (10.0-32.0 mg/kg) administration. In comparison to fentanyl, OHM3295 (3.2-25.0 mg/kg) augmented splenic NK activity in a naltrexone-reversible manner. Similar to fentanyl, OHM3295 (1.0-32.0 mg/kg) also induced a naltrexone-sensitive, dose-related analgesia as measured by an increase in tail flick latency. These results with OHM3295 demonstrate a novel profile of effects which includes naltrexone-sensitive analgesic effects in the absence of immunosuppressive effects. In addition, this is the first reported case in which a compound with opioid analgesic effects has been shown to potentiate natural killer cytolytic activity following in vivo administration.